The Central Scientific Research Automobile and Automotive Engines Institute, abbreviated as NAMI, was established in the Soviet Union in 1920 as a research institute. Foreign cars and engines were tested and their strengths and weaknesses evaluated, lessons being incorporated into the Soviet auto industry. In 1947, NAMI conducted an evaluation of two Tatra T87s. Unlike the rudimentary testing performed by Vauxhall of a captured Tatra T87 staff car in 1946, NAMI tested put both cars through extensive road and bench tests in city and country driving scenarios. In their final wrap up, the testers were not particularly impressed with the Tatra, especially its handling due to the rear engine placement. Poor build quality was also called out, which seems ironic given the common misconception of the generally poor quality of Soviet products. Nevertheless, the NAMI testers made a number of recommendations for improvements to the Tatra T87 which were passed on to the Czech authorities. By the time the testing was complete however, production of the Tatra T87 had ceased in favour of the smaller, better balanced T600 Tatraplan.
This is my English translation, performed with help from Google Translate. I have adjusted some phrasing for readability in English. I have skipped several tables and graphs and focused mainly on the analysis pages.
PREFACE:
This report presents the results of testing of the Tatra-87 model 1948, mainly in terms of its aerodynamics, fuel consumption, stability, cross-country ability and comfort. Special attention is paid to the features connected with the rear location of the engine on this vehicle, such as the weight distribution on the axles, body layout, etc., as well as its aerodynamics and fuel economy.
Tests have shown good aerodynamic and economic qualities of the car. Fuel consumption can be reduced by 15-20% without compromising the vehicles aerodynamics by eliminating assembly defects and changing the carburetor adjustment.
The unusual arrangement of the drive unit for this class of vehicle (i.e., rear engine placement) improves the use of space, driver visibility, streamlining, fuel economy and insulates the passengers from engine noise, but the large weight of the power unit leads to unsatisfactory stability.
The vehicle is equipped with a drive unit of an outdated design, which is why, in particular, the smoothness of the ride and ease of control of the vehicle are inadequate.
The car's cross-country ability is average.
TABLE OF CONTENTS
Introduction Pg 1
Description of the car Pg 3
Technical specifications Pg 7
Speed and performance
1. Maximum speed Pg 16
2. Acceleration Pg 17
3. Running and braking Pg 19
Fuel consumption
1. Adjusting the carburetor Pg 19
2. Road economic characteristics Pg 20
3. Fuel consumption in urban conditions Pg 32
4. Operating fuel consumption Pg 35
5. Conclusions Pg 38.
Vehicle stability
1. Determination of roll and roll angles Pg 39
2. Detection of the roll axis position Pg 42.
3. Distribution of overturning moment Pg 44
4. Conclusions Pg 46
Suspension tests
1. Suspension design Pg 49n
2. Test results Pg 53
3. Conclusions Pg 54
Body testing
1. Layout Pg 57
2. Ambition Pg 57
3. Composition of the car shape Pg 58
4. Streamlining Pg 59
Design and manufacturing flaws of the car Pg 62
Notes on driving and service Pg 63
Comments on the vehicle's cross-country ability Pg 65
Conclusions. Pg 65
INTRODUCTION
The tests of the Tatra-87 automobile, conducted in 1948-49 in the Department of Automobile Scientific Research Laboratories and the Department of Automobile Testing of NAMI, pursued, basically, two goals:
1/ Study and compilation of data for the design of cars with a rear engine.
2/ Determination of dynamic and economic qualities and assessment of the quality of the car as a whole.
In this [first] section of the work, the greatest attention was paid to the following issues: weight distribution along the axles, stability, aerodynamics (especially in terms of the effect of air resistance on the body), suspension comfort; use of the vehicle for its intended purpose (i.e., for passengers, ease of boarding, visibility, temperature in various areas of the interior of the body). All these issues directly relate to the rear engine location on the Tatra-87 vehicle. In addition, the automotive laboratory department conducted engine start-up tests in a winter laboratory in order to test the engine's starting performance under these conditions. 1/ See the report: "Test for starting a carburettor engine" Air-cooled Tatra-87, 1949.
The work of the second section was intertwined with the work of the first. The evaluation of the qualities of the car as a whole was of particular interest to us, since the Tatra-87 was a post-war product of Czechoslovakia, a friendly state to the Soviet Union, and as a certain number of cars of this type are operated in the USSR. It was desirable to identify the possibilities of improving the car and to give recommendations on its correct use. This, in particular, applied to fuel consumption, noise reduction, and the car's cross-country ability, as well as to the shortcomings of the body trim, as well as the car's control technology.
The tests were carried out on two cars manufactured in 1948 with factory numbers being chassis 173090, engine 222801 for the first car, and chassis No. 73114, engine 222825 for the second car.
The driving part of the test was carried out under operational conditions for the first vehicle during the period January - July 1949, and for the second vehicle in October 1948 - August 1949.
The total kilometers of the vehicles under their various driving conditions are given in Table 1.
The vehicle load during driving tests varied between 1-5 people, and during special tests to determine economy and aerodynamic qualities, at full load, corresponding to the weight of 5 people (375 kg). The vehicle was serviced according to the manufacturer's instructions.
Description of the car
The Tatra-87 car (fig. 1-8) belongs to the middle class of cars in terms of capacity, basic dimensions, aerodynamics, power and engine displacement, but differs from all known cars of this class in its layout: its power unit is located at the rear (this scheme is more widespread in small cars). The rear location of the engine predetermined the design solutions of a number of elements of the car, mainly from the point of view of the improvement of weight distribution along the axles. The engine is made relatively small (V-shaped) and light (utilizing air cooling and castings from light alloy). The seats in the body are shifted somewhat forward, and the rear seat is shifted forward so much that the distance for the knees of a seated rear passenger is extremely reduced. Under the cover of the front "false hood" there is a spare wheel, fuel tank, batteries, oil radiator, and tools. Without the need to artificially redistribute the weight along the axles it would be more expedient to place the battery, tank and oil radiator closer to the engine.
Despite all these measures, the car has a clearly unfavorable weight distribution along the axles (no more than 39% on the front and more than 61% on the rear wheels). Thus, the advantages of the rear engine location (the absence of a drive shaft through the body, noise and heat from the engine, good forward visibility, low center of gravity, compact power unit) are to some extent devalued in the layout of the Tatra car by unsatisfactory stability.
The engine (Fig. 9-13) is a 4-stroke, 8-cylinder, with a double-row arrangement of cylinders set at an angle of 90°. Cylinders are cast separately. Pistons are made of light alloy. The crankshaft rests on 5 bearings. The valves are overhead, controlled by camshafts (one for each row of cylinders) and rocker arms. The camshafts are driven from the crankshaft by a double roller chain passing through an oil bath in a closed box. The valve seats have seats made of tool steel.
The engine is cooled by air, with two turbofans, one for each row of cylinders. The fans are located in casings under each row of cylinders. The fans are driven by V-belts from the crankshaft pulley (left fan) and from an additional pulley (right fan).
The fuel tank is located in front under the false hood (Fig. 14), has a reserve compartment, a drain cock and a three-way cock. The cock control buttons are located under the instrument panel. Fuel is supplied by a diaphragm pump driven by the camshaft of the right cylinder bank. There are two radiators. The carburetor and air cleaners are located in the box above the engine.
The ignition system is 12 volt. The distributor breaker is located with the fuel pump and is driven by the camshaft of the right cylinder bank. A centrifugal ignition timing regulator is built into the breaker.
Clutch - single-disc dry, sub-centrifugal type.
The gearbox has 4 gears, of which the 3rd and 4th have helical gears of constant engagement and synchronizers. The gearbox does not have a direct drive. The gearbox control is mechanical.
The clutch, gearbox and final drive housing is connected to the engine housing by 8 studs. The power unit is installed in the body of the load-bearing body on three rubber supports.
The rear axle is split. The half-axle gears roll over the main gear pinions without losing engagement with them. Thus, there are no cardan joints in the transmission; the weight of the unsprung parts of the rear axle is reduced to a minimum; the swinging half-axles have the maximum possible length from the vehicle axle to the wheel (due to this, the change in track when the wheels swing is small, while in a design with cardan joints the half-axle is comparatively short).
The front wheel suspension is independent, on two transverse sub-elliptical leaf springs (Fig. 15). The front axle roll is missing. The springs are secured with clamps to the platforms of the load-bearing body beam. There are hydraulic telescopic shock absorbers. The wheels are lubricated on tapered roller bearings.
The steering column is located on the left. The steering mechanism acts on a transverse toothed rack. The split transverse steering rod is located in front.
The rear wheel suspension is on two semi-cantilever quarter-elliptical springs, mounted on the fork of the backbone beam of the supporting body and resting on rubber cushions on the axle shafts. There are hydraulic shock absorbers.
The pushing forces from the drive axle and the body are absorbed by the axle stockings and swinging forks.
The foot brake is hydraulic and acts on all four wheels. The hand brake acts by means of cables on the rear wheel pads. The reservoir for the hydraulic brake fluid is located on the left on the front shield (under the false hood). There, on the right, is the central chassis lubrication reservoir. Under the false hood is a spare wheel and there is a small space for luggage or for a second spare wheel. The main luggage space is in the body, behind the rear seats.
The supporting element is the body, the base of which is reinforced by a ridge beam with a fork at the rear end and a box for attaching the front springs. Special console brackets serve to support two side supports of the power unit. The body is all-steel, welded.
The body is a 4-5 seat four door limousine, without a partition between front and rear and a sliding roof (option). The front seats are adjustable and have folding backs, which allow you to adjust the seating position. Fastening the front springs. serve to support two side supports of the power unit.
The body differs from the usual one in its streamlined shape and design. In particular, the rear wings of the Tatra 87 are absent. In the rear part of the body sidewalls there are protruding air intake ducts and fans. A stabilizer rises above the "tail" of the car. In the lower part of the body sidewall, under the doors, there are recesses for the jack support.
The rear wheels of the car are covered on the sides with shields.
The electrical system, in addition to the ignition devices, includes (see diagram, Fig. 16 above): two batteries located in the front under the false hood; a starter with a capacity of 1.4 hp; a generator with a capacity of 150 watts driven by a V-shaped belt from a pulley on the front end of the camshaft of the left row of cylinders; two headlights, a spotlight, two signals, a turn signal lamp, a lamp for lighting the instrument panel, two rear lights and a brake light; a cigarette lighter, a double windshield wiper. The fuse box is located on the left under the instrument panel.
On the instrument panel (Fig. 17-18) is a speedometer, clock, fuel and oil level lamps, temperature indicators, indicator lights: generator operation (red), engine lubrication system oil pressure (red) and turn signal (orange) switch; turn signal handle; ashtray and cigarette lighter; buttons: choke, windshield wipers, instrument panel lighting, second signal and spotlight; ignition switch; starter button.
Under the instrument panel there is a petrol tap, a fan and heating switch handle, two buttons for the three-way fuel tank valve, a clock winder and a central oil lubrication pump pusher.
The levers and pedals are arranged in the usual order. The positions of the gearshift lever are standard for a four-speed gearbox.
There are slits under the windshield for vortex-free ventilation and for blowing on the glass to prevent it from fogging up.
TECHNICAL CHARACTERISTICS
Main dimensions and weight
Dimensions
Length - 4820 mm
Width – 1665 mm
Base load height - 1558 mm
Base – 2850 mm Front track with load - 1252 mm
Rear track with load - 1224 mm
Rolling radius of front wheels without load - 348.7 mm
Rolling radius of front wheels with load - 344.5 mm
Rolling radius of rear wheels without load - 343.6 mm
Rolling radius of rear wheels with load - 340.5 mm
Front overhang (along the bumper) - 697 mm
Rear overhang (along the bumper) - 1273 mm
Approach angle (with load) front - 30.5 degrees
Approach angle (with load) rear – 17.5 degrees
Minimum turning radius front
Outer wheel to the left - 6.80 m.
Outer wheel to the right - 6.88 m.
Minimum overall dimensions, radii.
External (along the front wing) to the left 7.18 m, to the right 7.26 m
Internal (along the rear wing) to the left 4.77 m, to the right 4.95 m
Weight distribution by axles (with full fuel, spare wheel and tool).
No load With a load of 5 people (375 kg)
Front wheels 560 kg – 37.8% 725 kg – 38.7%
rear wheels 940 kg – 62.7% 1150 kg – 61.3%
Total weight - 1875 kg
The car's tare weight according to the company (without refueling) - 1370 kg.
Operational data
Highest car speed - 148 km/h.
Fuel consumption on the highway at a speed of 70 km / h. - 10 litres /100 km.X
Fuel consumption in urban conditions 14.5 Litres /100 km.X
X = fuel consumption data obtained after changing the adjustment of the carburetor.
Clearances (lowest points) of the car
No Load With load
Front bumper (middle) 328 mm 307 mm
Front spring axle 248 mm 226 mm
Lower part of the body
(at the central pillar) 263 mm 249 mm
Rear axle housing 238 mm 220 mm
Shock absorber bracket
Right rear 216 mm 208 mm
Shock absorber bracket
Left rear 214 mm 205 mm
Crankcase 265 mm 245 mm
End of exhaust pipe 360 mm 347 mm
Rear bumper (middle) 403 mm 394 mm
Engine
Type - carburetor, 4-stroke, air-cooled
Number and arrangement of cylinders - 8, V-shape, air-cooled
Cylinder diameter - 75 mm
Piston stroke - 84 mm
Working volume - 2.958 litre
Compression ratio – 5,6
Maximum engine power at 3500 rpm (according to the company) - 75 hp
Maximum torque - 15,3 KTM
Power-train suspension - At the track points on rubber pads.
Cylinders - Individual cylinders, equipped with cooling fins, are attached to the crankcase with anchor bolts.
Crankcase – Light alloy
Cylinder heads – S dark ribbed, individual for each cylinder, made of light alloy with steel valve seats.
Poria material – aluminum alloy
Number of piston rings: Compression - 2, oil-return - 1.
Crankshaft - On five supports with four connecting rod journals.
Connecting rods – with a split lower head, located in pairs in a row on each crank pin
Gas distribution - Valve arrangement: overhead, inclined two-way, one intake and one exhaust valve per cylinder
Camshafts – two, one for each bank of cylinders, are located above he cylinder heads, driven from the crankshaft via a double chain located in the oil pan.
Valve drive – through the rocker arms
Gas pipeline - Double-sided, a casing is attached to the right exhaust pipe, designed to heat the air in the body.
Lubrication system – combined (pressure and splash) lubrication. Pressure lubrication lubricates the crankshaft and camshaft bearings, valve rocker arms, and valve stems. The remaining parts are lubricated by splash lubrication.
Oil pump – geared
Oil pressure control – green lamp (on the dashboard), the lamp lights up when there is pressure in the oil line.
Oil temperature – thermometer
Oil filters – A mesh filter in the crankcase and a coarse plate filter in the line running from the engine to the oil cooler. The filter plate are connected by a drive to the clutch pedal and rotates at a certain angle with each press of the pedal.
Oil radiator – tubular with cooling plates, mounted at the front of the car.
Air purifier – dry with two grids located in a cylindrical tube, the air cleaner has two slide valves, which, when turned in cold weather, such the air heated by the engine.
Carburetor – Solex type with a falling pot with an accelerator pump and a starting device.
Fuel pump – diaphragm, driven by the right camshaft
Fuel tank – it is located in the front part of the vehicle and has a reserve compartment and a drain cock.
Cooling – air, two turbofans, one for each row of cylinders
Fan drive – V-belts from the crankshaft pulley (left fan) and from the additional pulley (right fan)
Ignition – battery
Transmission
Clutch – single-disc, dry, semi-centrifugal
Clutch housing – common with the gearbox housing and the main gear housing, it is cast from an aluminum alloy and is attached to the engine housing with 8 studs
Gear box – three-way, four speed, 3rd and 4th gears with helical teeth (there is a synchronizer for 3rd and 4th gears) and in constant engagement
Gear ratios:
1st gear – 4.70
2nd gear – 2.95
3rd gear – 1.56
4th gear – 1.04
Reverse – 5.92
Gearbox control – mechanical shift lever and rod
Rear Axle:
Main gear type – two pairs of bevel gears with spiral teeth, separately for each axle shaft.
Gear ratio:
Final drive – 3.15
Half shafts – unloaded, swinging with stockinged axle shafts
Front wheel suspension – independent on two transverse springs
Rear wheel suspension - independent on two quarter springs located at an angle
Type and number of shock absorbers – four hydraulic, telescopic
Wheel type – disc, steel
Rim type and size – deep 4.50E x 16
Tire size – 6.50 x 16
Tire pressure:
Front wheels – 1.2 kg/cm2
Rear wheels – 1.8-2 kg/cm2
Brake type – shoe
Number of brakes – 4
Brake location – on all wheels
Foot brake – hydraulic
Handbrake – mechanical, affect only the rear wheel brake pads
Steering gear type – worm and helical rack
Transverse steering rod – split
Lubrication system:
Chassis – central
Central lubrication oil – motor
Body
Load-bearing, steel, 5-seater, 4-doors, closed without front partition, with a sliding roof, front and rear hoods
Capacity data
Fuel tank – 55 litres of which 10 litres are reserve
Engine lubrication system – 9 litres
Gearbox housing and final drive – 5 litre
Hydraulic brake circuit – 0.5 litre
Central lubrication system – 0.5 litre
Installation and Adjustment data
Clearance between rocker arm and valve step (for all valves on a cold engine) – 0.15 mm
Interrupter contact gap – 0.40 mm
The gap between the spark plug electrodes – 0.5 mm
Initial ignition setting – 5 degrees before TDC
Free travel of the clutch pedal – 40-50 mm
Front wheel alignment – 0.3 mm
Front wheel tilt and vertical – 1 degree 30’
Forward tilt of the kingpins – 4 degrees
Electrical equipment and devices
Wiring system – single-wire, minus connected to the ground
Rated voltage in:
Wiring – 12 volts
Batteries – 2 x 6 volt batteries connected in series, capacity 75 amps
Generator – a four-pole, 12-volt, 150-watt Scintilla “SA” motor with a fan. Drive: V-belt from an additional pulley on the left camshaft. Right-hand rotation on the drive side, gear ratio 1.29. Number of brushes: 4, box-type brush holders. Weight: 10 kg.
Relay regulator – Scintilla “Khra” four-stage, located on the body partition, weight 0.370 kg.
Starter – 12-volt, 1.5 hp. Scintilla, four-pole, series type with a friction clutch located inside the armature shaft. Left-hand rotation, gear ratio 11.33, weight 12 kg.
Starter switch – Electromagnetic, remote, button on the instrument panel
Distributor – Scythilla with two breakers and one square cam
Operating procedure – 1 – 2 – 7 – 8 - 6 – 3 – 4 – 5
Cylinder arrangement – 1 3 5 7 > Flywheel side
2 4 6 8
Ignition coil – Scintilla, 12 volts
Glow plugs – disassemblable, diameter 14 mm
Ignition switch – combined with the central light switch, it has two longitudinal positions and three rotational positions. The ignition is turned on only with the second longitudinal push of the key
Battery charging control – the control lamp on the instrument panel (red)
Headlights – two; has high beam, low beam lamps, two filament with a power of 32432 watts and headlight lamps at 5 watts each
Spotlight – one has a single filament lamp 32 watts
spotlight switch – separate works only when the high beam is on
Taillights – two, each lantern has a filament lamp 5 watts
Brake-lights – two, each lantern has filament lamp 15 watts
Stop light switch - hydraulic
License plate light - equipped with two single filament 13 watt lamps
Direction indications – electromagnetic, semaphore, each semaphore is equipped with a 2 watt lamp
Turn signal switch – independent, works when the ignition is on
Instrument panel warning lights – battery, 2 watts each, two of them illuminate the fuel gauge and oil temperature gauge; two illuminate the speedometer and clock
Ceiling lamp – one 5 watt
Ceiling light switch – independent, in the lamp housing
Signals – two vibration-type alarms operate when the ignition is on. One of the alarms can be turned off using a dedicated switch.
Alarm button – on the steering wheel
Fuses – 12 – 15 amperes each
Cigarette lighter – electrical, on the instrument panel
Wiper – electric, dual
Wiper switch – independent, works when the ignition is on
Fuel gauge – electric, turns on when the ignition is turned on
Oil temperature gauge – remote thermometer
Speedometer – combined in one device with an indicator of the distance traveled
PERFORMANCE.
Note: dynamic tests were carried out by engineer G.A. Krestovnikov at the 42nd kilometre of the Moscow – Minsk highway in the summer of 1949. Three series of experiments were carried out, namely:
1. Determination of the performance of vehicle No. 73090 with factory carburetor adjustment.
2. Determination of the performance of vehicle No. 73090 with modified carburetor adjustment (description of the modification is in the “fuel consumption” section).
3. Determination of the performance of vehicle No. 733224 with factory carburetor adjustment.
Each of the above consisted of the following experiments:
1. Determining the maximum speed of the vehicle.
2. Determining the vehicle’s responsiveness when accelerating in 1st gear from standstill.
3. Determining the vehicle’s responsiveness during acceleration in 1st, 2nd, 3rd and 4th gears from established initial speeds equal to 5, 6, 10 and 15 km/h, respectively.
4. Determining the vehicle’s responsiveness when accelerating from a standstill with gear shifting.
5. Determining the distance and time it takes to travel from an initial speed of 50 km/h.
In addition, the braking distance of vehicle No. 73090 from an initial speed of 30 km/h was determined.
All experiments were carried out with a vehicle load of 5 people.
The air temperature during the tests was +13 +24 C
Test 1. Maximum speed
The maximum speed was determined by the time it took the vehicle to travel a measured kilometre from a standing start. The preliminary acceleration time was 2.5 km. The resulting maximum speeds are presented in Table 2.
Highest Car Speeds
Car 73090 KM/Sec Speed Highest Speed
Factory carb. from Moscow 24.4 147.5 148.15
To Moscow 24.2 148.8 148.15
Changed carb. from Moscow 24.5 146.9 145.45
To Moscow 25.0 144.0 145.45
Car 73114 KM/Sec Speed Highest Speed
Factory carb. from Moscow 24.8 145.2 142.8
To Moscow 24.8 145.2 142.8
Changed carb. from Moscow 24.2 142.9 142.8
To Moscow 26.1 137.9 142.8
From Table 2 it can be seen that:
1. The obtained maximum speed of both vehicles is higher than that indicated in the factory instructions; long-term maximum speed (135 km/h) and lower than that indicated there, short-term (160 km/h).
2. The obtained for car No. 73090 with the changed carburetor adjustments is practically no different from that obtained for the same car with the factory carburetor adjustment.
Test 2. Acceleration
Acceleration was determined by measuring the time it took the vehicle to travel a measured kilometre from a standing start, as well as using a self-recording “distance-time-speed” device. The acceleration results are presented in Table 3 and Figs. 19-31.
Table 3
Accelerating a car from a standstill
Car 73090 Time Speed Average Speed
Factory carb. from Moscow 41.9 85.9 84.9
To Moscow 42.9 83.9 84.9
Changed carb. from Moscow 42.2 85.3 84.8
To Moscow 42.7 84.3 84.8
Car 73114 KM/Sec Speed Highest Speed
Factory From Moscow 44.0 81.9 82.3
To Moscow 43.0 83.7 82.3
Changed from Moscow 44.0 81.9 82.3
To Moscow 44.0 81.9 82.3
From the table and graphs provided it is clear that:
The acceleration of both Tatra-87 vehicles is almost the same.
The acceleration of car No. 73090, obtained with the modified carburetor adjustment, is almost the same as that obtained with the factory carburetor adjustment.
The car has high performance, however, this is achieved with the help of the 4-speed gearbox, and the lowest stable speeds in each gear are relatively fast..
In urban conditions, you have to resort to frequent gear shifting or prolonged driving in 2-3 gears (of which 2nd gear is noisy).
Thus the vehicle’s high-performance dynamics can be effectively and conveniently utilized when driving on the highway, when overtaking, and on uncongested roadways. It should be noted that the dimensions of the driven clutch disc linings clearly do not correspond to the vehicle’s dynamic characteristics (the outer disc diameter is 229 mm). The clutch is prone to slippage and premature wear, compared to a typical vehicle's clutch wear.
Test 3. Running and braking
The test speed of both vehicles was 50 km/h. The distance traveled was measured using a distance-time-speed device. In Fig. 32-33 it is evident that the distance and time taken by vehicle 73114 from the specified initial speed are somewhat greater than the same figures for vehicle No. 73090, which can be explained by the installation of lugged tires on the latter. Car No. 73090 was braked from an initial speed of 30 km/h. The braking distance from this speed was 8.5 meters.
Fuel Consumption.
(Fuel economy tests were carried out by E.N. Shuvalov and N.A. Grechkina).
Adjusting the carburetor
Fuel economy tests were conducted on the highway at various speeds (road fuel economy characteristics were measured in urban conditions). In addition, daily fuel consumption was recorded during the driving tests (by topping up the tank to full capacity).
The vehicle’s load corresponded to the weight of 5 people (375 kg). B-70 gasoline (first grade) was used as fuel. Tests of car No. 73090 were carried out with two carburetors (original carburetor No. 4791602 and new No. 4791638), and car No. 73114 – only with its original carburetor No. 4791574. The carburetor adjustment during testing involved:
1. Eliminating the incorrect throttle positioning;
2. By changing the diameter of the idle jets (the diameter of the calibrated hole is 0.30 mm, instead of 0.55 mm).
The Tatra vehicle is equipped with a twin Solex inverted carburetor model 30 AAUR 70 (Fig. 34-36)
During testing, it was discovered that vehicles with factory-adjusted carburetors exhibited increased fuel consumption, reaching 20-22 litres/100 km in urban conditions. Furthermore, the engines idled erratically and it was impossible to achieve satisfactory performance using the adjusting screws.
Upon inspection of these carburetors, it was established that the throttle valves in the mixing chambers were positioned incorrectly defined as per the factory assembly, i.e., both the lower and upper outlet openings of the idle system, with the valves fully closed, were located under the valves in the vacuum zone (Fig. 30 position 1). This position of the throttle valves, when the engine was idling and the vehicle moving at low speeds (with the throttle closed) caused excessive enrichment of the working mixture, unstable engine operation and higher fuel consumption.
After correcting the defect (Fig. 37, position 2), some improvement in engine performance was noted, but stable idle operation could not be achieved. The working mixture still remained over-rich.
To lean out the fuel mixture and improve the carburetors responsiveness at idle, the idle jets were replaced. The factory jets, with calibrated holes measuring 0.55 mm, were replaced with jets measuring 0.30 mm. With this modified carburetor adjustment, the engine now idled satisfactorily and did not experience any dips when pressing to full throttle.
Highway fuel economy characteristics
The vehicle’s performance was measured by driving 10-kilometer directions. Fuel consumption was determined by weighing a graduated tank before and after the drive. The following speed limits were adopted for the tests:
30-40 60-80 and 100 km/h
Table 4 and Fig. 38 show the test data for vehicle No. 73090 with its own carburetor No. 4791602 and with factory idle jets (calibrated hole diameter 0.55 mm, but with a modified throttle valve position. With this carburetor adjustment, fuel consumption at a speed of 30 km/h was 12.95 litre/100 km, and consumption values at other speeds (from 40 to 100 km/h) did not exceed 12 litres/100 km (i.e., the consumption value specified by the company).
The results of the test with modified idle jets / jet diameter 0.30 mm together with 0.55 are shown in Table 5 and Fig. 39. From these data it is evident that replacing the idle jets resulted in a significant reduction in fuel consumption at lower speeds; thus at a speed of 30 km/h, consumption became equal to 8.13 litre/100 km. A slight increase in fuel consumption at a speed of 100 km/h is explained by the influence of the wind during the test (see Fig. 40 for a comparison of characteristics).
Table 4
Fuel consumption of vehicle No. 72090 when driving on the highway at various speed modes.
Test date: July 7 1949
The car’s mileage is 15,764 km
Test location Minsk highway between the 45th and 55th kilometre
Fuel grade – Gasoline B70, specific gravity 0.732 at 20 C
Carburetor #4791602 with factory idle jets and a changed throttle position
The weather is clear, the air temperature is +22 degrees Celsius
Table 5
Fuel consumption of vehicle No. 73090 when driving on the highway at various speeds.
Test date July 2, 1949
Vehicle mileage 14,634 km
Test location Minsk highway between the 45th to 55th kilometer
Fuel grade – gasoline B70. Specific gravity 0.732 at 20 C
Carburetor No. 4791602 with replaced idle jets stroke 0.30 mm instead of 0.55 mm and a changed position of the throttle valve Weather – cloudy, windy, air temperature +18 degrees Celsius.
After the vehicle had covered 23,000 km, repeat fuel economy control tests were conducted. The data obtained, presented in Tables 6 and 7 and in Figs. 41 and 42, showed that with identical carburetor adjustments, the fuel economy characteristics remained the same, but the consumption values increased slightly with increasing vehicle mileage.
In parallel with our own carburetor, fuel efficiency tests were also carried out with another, new carburetor No. 4791638. The adjustment changes to this carburetor consisted only of replacing the idle jets (the position of the throttle valves on this carburetor was correct).
The test results for vehicle No. 73090: with carburetor 4791638 with factory and modified settings are shown in Tables 8 and 9 and in Figs. 43 and 44, and their comparison with each other is shown in Fig. 45.
From the obtained data it follows that with the factory adjustment of the carburetor, the change in fuel consumption in the speed range from 30 to 100 km/h occurs within the range from 10.07 to 12.27 litres per 100 km.
The most economical driving mode corresponds to a speed of 70-80 km/h.v
After replacing the idle jets with a smaller calibrated section diameter (0.30 mm instead of 0.55 mm), the range of fuel consumption values became from 8.03 t0 11.41 litre / 100 km, and the economical speed of the car was 30 km/h.
Table 6
Fuel consumption of the car No. 73090 when driving on the highway at various speeds.
Test date October 13, 1949
The car’s mileage is 23,178 km
Test location: Minsk highway, 45th – 50th km.
Fuel grade: gasoline B-70. Specific gravity: 0.732.
Carburetor No. 4791602 with factory idle jets and a changed throttle position.
The weather is clear, air temperature +8 +10 degrees Celsius
Table 10
Fuel consumption of vehicle No. 73114 when driving on the highway at different speeds.
Test date May 25, 1949
Vehicle mileage: 7,818 km
Test location: Minsk highway 45 km – 55 km
Carburetor No. 4791574 factory adjustment
Fuel grade: gasoline B-70, specific gravity 0.74 at 20 degrees Celsius
The weather is clear. The air temperature is 25C
Table 11
Fuel consumption of vehicle No. 73114 when driving on the road at different speeds.
Test date June 1, 1949
The car’s mileage is 8,564 km.
Test location: Minsk highway, 45 km – 55 km.
Table 12
Fuel consumption litres / 100 km of vehicle No. 73114 when driving on the highway at various speeds.
Test date: June 3, 1949
The car’s mileage is 8,900 km
Test location: Minsk highway, 45-55 km
Fuel grade: gasoline B-70. Specific gravity: 0.74 at 20 degrees Celcius
Carburetor No. 4791574, adjustment modified.
The weather is clear. Air temperature is +25C
Test 3. Fuel consumption in urban conditions
Measurements were taken while driving along a designated radial-ring route within the Garden Ring. The test route was approximately 47 km long.
The characteristic driving conditions during the trips, the following was recorded: the number of gear changes and the time spent in each gear, the number of stops, and the amount of braking. Tables 13-14 present the values of these parameters (converted to 100 km), the average speed per trip (average operating speed), the average net speed (average technical speed), and fuel consumption.
The movement indicators given in the tables are on average the composition for one km:
Stops – 1.1
Braking – 1.8
Inclusions (P-E) – 1.4
Gear changes (O-I) – 1.9
The time spent stopping at traffic lights accounts for 14.4% of the total travel time.
The average operating speed was 26 km/h
The average technical speed was 22.2 km/h
The travel time in gears was:
In 1st gear 2.2%
In 2nd gear 10.3%
In 3rd gear 20.5%
In 4th gear 67.0%
From the given average values of the driving indicators, it follows that the route on which the cars were tested for fuel efficiency was intense.
Fuel consumption on this route was:
For vehicle No. 73090:
With carburetor No. 479160, factory adjustment 21.5 litres/100 km and 14.5 litres/100 km with modified carburetor adjustment.
With carburetor No. 4791638, factory adjustment 16.8 litres/100 km.
For vehicle No. 73114
With carburetor No. 4791574 factory adjustment 22.8 litres /100km / modified 13.2 litres /100 km.
Test 4. Operating fuel consumption
In addition to individual measurements to determine fuel consumption when driving on the highway and in urban conditions, throughout the entire period of running tests, operational fuel consumption was recorded.
5. Conclusions
Incorrect throttle valve positioning, which occurred in carburetors #4791602 and 4791574, resulted in increased fuel consumption at low speeds. When driving on the highway at 30 km/h, consumption reached 16 litres/100 km, and in urban conditions, up to 20-22 litres/100 km.
With the correct throttle position and factory idle jets, the car has good fuel economy on the highway and poor fuel economy in urban conditions. The most fuel-efficient driving mode (with a consumption of 10 litres/100 km) corresponds to a speed 70-80 km/h. In urban conditions, these settings result in a consumption of 16-18 litres/100 km.
To improve fuel economy in urban driving conditions, in addition to adjusting the throttle position, it is recommended to reduce the diameter of the idle jets. Increasing the main jet diameter from 0.55 mm to 0.80 mm significantly improves fuel economy when driving at highway speeds. When driving on the highway at a speed of 30 km/h, fuel economy decreases from 16-18 litres/100 km to 13-14 litres/100 km.
At the same time, when the carburetor adjustment is changed, the engine’s idle performance improves and the vehicles dynamic qualities remain virtually unchanged (see the dynamics section).
General conclusion on fuel efficiency
The 1948 Tatra-87, with the appropriate carburetor adjustment, offers excellent fuel economy both on the highway and in urban conditions.
VEHICLE STABILITY
1. Determination of roll and roll angles.
Since rear-engine vehicles had not previously been tested for stability, the Tatra-87 vehicle was tested according to an expanded program. The methodology for testing stability can be found in the book by Ya. M. Pevzner “Testing the Stability of a Car” and in the test reports for the Moskovich and Pobeda cars. Stability tests were carried out by engineer A.M. Gorelik (laboratory stability and suspension of the OANIL, head of laboratory – candidate of technical services Ya. M. Pevzner).
Accepted designations:
Wheel turning angle - Theta (theta symbol) denotes the theoretical angle of rotation of the wheels in the absence of slip, and d(a) is the actual angle of rotation wheels
S/B S/A - slip angle of the rear and front wheels, respectively
2 – vehicle roll angle
??? – specific lateral load
G/a g/R - lateral force acting on the car (in this case a centrifugal force)
Va – vehicle speed in m/sec
R – the radius of the circle on which the tests take place
g – 9.81 m/sec
G – vehicle weight
GG – load on the rear or front axle, respectively.
RR – pressure in the rear or front tires, respectively.
Fig. 47 shows the test results for the recommended water tire pressure (P = 1.2 kg/cm2; P= 2.0 kg/cm2). The dots mark the results of stability tests (curve 8) with a load of 5 people. The crosses, with a load of 2 people. The rear wheel slip angle (curve 8) and the roll angle (curve 2) were measured only for a load of 5 people.
The dotted lines are constructed directly based on the test results, the solid lines take into account the zero offset (for the curve and dotted line coincides with the solid line).
The curves theta3 for loads of 2 and 5 people coincide, since with a significant total weight of the car, the weight distribution along the axles with a load of 2 and 5 people remains almost unchanged / respectively.
GA: in 0.65 and GA: Go 0.639
According to the diagram, the car has very little understeer and at a specific lateral load on 12:Go = 0.4 the value of B reaches only 1/40/
Typically, in modern passenger cars (ZIS-110, “Moskvich”, the magnitude of understeer at 7: Go = 0.4 reaches 1.5-2 degrees. The value of the rear wheel slip angle at B is satisfactory. 2: Ga = 0.4/. This value is satisfactory. It is approximately 5-6 B.
The bank angle is JGa 10.4 is about 5 degrees.
This roll angle is insignificant. Let us remember that the car does not have a transverse…
The small roll angle is explained by the use of a rear suspension with swinging half-axles, which, in combination with any front independent suspension, ensures small role angles of the car.
Figs. 48-50 show the test results for a normal load (5 people), but with different tire pressures. Fig. 48 corresponds to the case where the pressure of the front tires is increased to 2 kg/cm3, and the pressure in the rear tires is normal B = 2 kg/cm3. As expected, with an increase in the pressure in the front tires (i.e., with an increase in the coefficient of resistance to slip of the front axle (the slip angle of the front wheel decreases, and the car already has excessive turning d/a).
When the pressure in the front and rear tires decreases to 1.5 kg/cm, the excess steering increases slightly.
A pressure Pn = 2 kg/cm3 and B – 1.5kg/cm, the magnitude rotation 2 2 increases further. The curvilinear portion of the dependence in this begins ….. (equation with result = 0.22)v
In Fig. 51 the test results of tests to determine the influence of the vehicle suspension design and layout on its stability. The tests were conducted at the same tire pressure (P = 2.0 kg/cm3) and at the same axle loads (Ga = G8 = 1000 kg). To obtain the same axle load, a spare wheel was placed in the front trunk instead of the spare wheel
The load was placed on the vehicle. The equality of the load on the front and rear axles was checked on the scales.
If the suspension design had no effect on vehicle stability, then under these test conditions its stability characteristics would be neutral. In reality, the vehicle exhibits understeer, transitioning to oversteer. Understeer is explained by the fact that during roll, the front wheel tilt is greater than the rear wheel tilt. The transition from understeer to oversteer is explained by the influence of traction and the fact that the vertical load moment of the rear axle is significantly greater than that of the front axle.
This experiment demonstrates the significant influence of suspension kinematics and the ratio of front and rear suspension angular stiffness on vehicle stability. It should be noted that the theoretical possibility of transitioning from understeer to oversteer has long been known. This is the first time such a transition has been experimentally observed during testing at NAMI.
Fig. 53 shows the results of the stability test at P = 2 kg/cm3: GA = 816 kg and G = 1000 kg, 1 GA: Go = 0.445. This test was conducted to determine the influence of the position of the centre of gravity of the car on stability. In this experiment, the position of the centre of gravity is average between the position of the centre of gravity in the tests shown in Fig. 48 (Ga Ga = 0.39) and the tests shown in Fig. 52 (G: Go = 0.5).
Fig. 47 shows a summary diagram of the test results on the effect of load redistribution along the vehicle axles on stability. The total weight of the car during these experiments was approximately the same. The tire pressure is also the same P – 2 kg/cm3. As expected, the vehicle stability is better at Ga Ga = 0.5. Under normal loads of 2-5 people, Ga: GB = 0.39; in this case, vehicle stability deteriorates significantly.
As is known, the critical speed is determined from the expressions (the influence of these factors on stability covered in detail in the work of Ya. M. Pevzner “The Theory of Automobile Stability, Mashgiz, 1946).
GA: in 0.65 and GA: Go 0.639
According to the diagram, the car has very little understate and at a specific lateral load of 12:Go = 0.4 the value of B reaches only 1/40.
Typically, in the modern passenger cars (ZIS-110, “Moskvich”, the magnitude of understeer at 7: Go = 0.4 reaches 1.5 – 2 degrees.
The value of the rear wheel slip angle at B is satisfactory. 2: Ga = 0.4/. This value is satisfactory. It is approximately 5-6 degrees B.
The bank angle at JGa 10.4 is about 5 degrees.
This roll angle is explained by the use of a rear suspension with swinging half-axles, which, in combination with any front independent suspension, ensures small roll angles of the car.
Figs. 48-50 show the test results for a normal load (5 people), but with different tire pressures. Fig. 48 corresponds to the case where the pressure in the front tires is increased to 2 kg/cm3, and the pressure in the rear tires is normal B = 2kg/cm3. As expected, with an increase in the pressure of the front tires (ie, with an increase in the coefficient of resistance to slip of the front axle) the slip angle of the front wheels decreases, and the car already has excessive turning.
When the pressure in the front and rear tires decreases to 1.5kg/cm3, the excess steering increases slightly.
At pressure P = 2kg/cm3 and of B = 1.5 kg/cm3, the magnitude of rotation 2/2 increases further. The curvilinear portion of the dependence in this case begins already…. Formula
In Fig. 51 the test results for a load of 5 people and different pressures are summarized in one diagram.
Fig. 50 shows the results of the tests to determine the influence of the vehicle suspension design and layout on its [the car’s] stability. The tests were conducted at the same tire pressure (P = 2kg/cm3) and at the same axle load (Ga = G8 = 1000kg). To obtain the same axle load, the spare wheel was placed in the front trunk instead of the spare wheel [space? This is an odd sentence as the two spare wheels were normally placed under the hood as a counterweight]. Where the car [formula] can therefore be easily calculated for each case using the test diagrams provided.
In table 17 (below), the columns are left blank in cases where tests were not carried out, and the columns are crossed out for which the critical speed does not exist, since the car has insufficient turning [ratio?]
Table 17
Critical speed of the car km/h
As the table shows, if the tire pressure is incorrectly selected the critical speed of the Tatra-87 vehicle can drop to 63 km/h.
2.2 Definition of the position of the roll axes
As is known, for the front suspension of the Tatra-87 type, when rolling, the change in th angle of inclination of the wheels and the road plane is equal to the angle of roll (if gaps and deformations are not taken into account).
To verify the correctness of this position, and to determine the influence of gaps and deformations, the following experiment was conducted (fig. 55). A bar was fixed to the wheel journal hook, perpendicular to the plane of the wheel. A straight line was painted on the bar in white.
>X See the NAMI report “Study of the influence of the kinematic design of the suspension on the stability of the car when turning.” No. 3635 for 1918.
A camera was mounted on the car body approximately 1.5 metres from the bar. The bar was photographed while the car was moving in a circle at low speed (ie, at a slight bank angle); then the speed was increased (and consequently the bank angle increased), and th bar was photographed again for the same frame.
Since the body shifts slightly relative to the wheel as the roll angle increases, two white lines appear in the photograph. These lines are parallel, meaning deformations and clearances do not significantly affect the inclination of the wheel plane relative to the body. This experiment also confirms the assumption that for this type of suspension, the change in the wheel inclination is equal to the roll angle.
Fig. 55a shows the results of photography with a change in the bank angle of approximately 2 degrees. In Fig. 55b the bank angle changed by approximately 4 degrees.
As is known, the distribution of the overturning moment between the wheels, the angle of the body roll and the inclination of the wheels during roll depend on the position of the roll axis.
To determine the position of this axis, it is sufficient to find the positions of its two points – the instantaneous centres of rotation. The instantaneous centres of rotation lie in the longitudinal plane of symmetry of the vehicle, when determining the instantaneous centres of rotation, plane-parallel motion is considered.
Strips are attached to the front and rear bumpers using special clamps (Fig. 56). They are secured so that a straight while line drawn on the strip lies in the plane of longitudinal symmetry of the vehicle. During the experiment, the position of this line is photographed in one frame at slight roll angles. To tilt the vehicle, a massive horizontal bar is attached transversely between the front and rear seats. Vertical forces of equal magnitude but opposite directions are applied to the ends of the bar, which creates the heeling moment.
It is known that is the centre of rotation lines on a line, the positions of which are fixed during the movement of the body, then the centre will be at the point of intersection of these positions of the line.
Therefore, in our case, the centre of rotation lies at the intersection point of the white line images in the photograph. Fig. 56 shows a front view (Fig. 56a) and rear view (Fig. 56b) of the Tatra-87 vehicle.
Fig 56a shows the white line is applied to the position of the bar, photographed at a bank equal to zero. The position of the while line when banking to the right (1) and its position when banked to the left (2) are also recorded in this photograph. The intersections of lines 1 and 2 (points A Od and Ov) represent the instantaneous centre of rotation.
The pin on pillar 3 marks the road level for the front view, and the centre of the rear wheels for the rear view. The bar is marked with transverse divisions. The division value is 10 mm. The distance from the position marked by the pillar to the instantaneous centre of rotation can be determined directly from the photograph.
Fig. 56b shows a side view of the Tatra-87. Line Ot-O is the roll axis. Points Od and Ov mark the position of the body’s centre of gravity. A B are the roll centres.
3. Distribtion of overturning moment
The setup diagram for determining the distribution of the overturning moment is shown in Fig. 57.
The centrifugal force is reproduced by cable, via:
1. One end of the cable is attached to the tensioning device
2. The other end is secured with a special device at the centre of gravity of the body.
3. The force acting on the vehicle is measured by dynamometer 3.
4. To measure vertical loads, each wheel is mounted on hydraulic scales (ladometers).
Since hydraulic scales do not operate under horizontal loads, to eliminate horizonal loads, rotary circles (5) and clamps (6) are placed between the hydraulic scales and the wheel.
Fig. 58 shows the results of the experiment on the distribution of the overturning moment, with a load of 5 people. The ordinate axis shows the change in vertical loads on the wheels. For odd photographs, the intersection point of the line is determined by enlarging the negative using a projection apparatus.
The abscissa axis shows the ratio of the lateral force to the mean weight of the vehicle L: Ga/X is the arithmetic mean of the load increments on the left and right wheels. As can be seen from the diagram, the redistribution of vertical reactions on the rear wheels of the vehicle DAV is significantly greater than on the front DHAA.
The dotted lines show the values of the quantities DHA and DHV obtained by theoretical calculations using the formulas proposed in report of the Laboratory of Stability and Suspension from 1948
Where B=track.
6=the height of the roll centre of the front or rear suspension.
Lateral force acting on the front or rear axle.
M is the movement of elastic forces of the front and rear suspension.
As we can see, the theoretical calculation matches the experimental data with reasonable accuracy. However, the calculation using the previously existing method yields a significant error, as per Chudakov E.A. "The influence of tangential elasticity of wheels on the lateral stability of a car", Moscow-Leningrad, 1949..
Fig. 59 shows the dependence of the wheel camber angle on the experiment is to examine the specific lateral force Iz:Ga. The purpose of effect of tire pressure on wheel camber. All studies of wheel camber as a function of vehicle roll do not consider the influence of the minimum. Therefore, for a suspension like the Tatra-87 rear suspension, the wheel camber angle is independent of the roll angle and is equal to zero. In reality, as the experiment shows, with a roll angle of approximately 50 degrees, the rear wheel camber is approximately 20 degrees. To study vehicle stability, it is important to know the difference between the front and rear wheel camber angles. Ignoring the tire effect, this difference will be approximately5 degrees; with the tire effect, the difference is approximately 38 degrees. Thus, in this case, the error in the calculation without considering the tire effect is approximately 40%.
X / see footnote to art. 42
4. Conclusions
With a load of 2-5 people and the factory-recommended tire pressure (P=1.2 kg/cm3; P3 = 2.0 kg/cm3) the Tatra 87 vehicle has an insignificant amount of understeer (with a specific lateral load I: G2 = 0.4; dn-dp= ¼). Therefore, the stability characteristics of the Tatra 87 vehicle, even with strict adherence to tire pressure, cannot be considered as meeting modern requirements.
At Ud:Ga=0.3-:-0.35, an intensive increase in the difference (br-ba) is desirable, since this improves stability during various turns at significant speeds. The characteristics of of the Tatra-87 vehicle do not provide such an increase, due to the favourable distribution of the overturning moment between the axles.
2) Under operating conditions, it is impossible to precisely maintain to company’s recommended pressure ration for the front and rear tires. Therefore, the stability of the Tatra-87 vehicle under operating conditions, even on dry roads, may be unsatisfactory, which was observedin some cases when driving uphill with a full load.
3) The moment of vertical loads on the front wheels is approximately half the moment on the rear wheels (Mn:M3=0.5). Such a distribution of the overtuning moment is unfavourable for reasons of vehicle stability. Refer to Ya. M. Pevzner. Theory of vehicle stability, Moscow, 1947.
When designing a vehicle with a similar kinematic suspension scheme, an increase in the moment of vertical loads on the front wheels can be achieved by increasing the angular rigidity of the front suspension and slightly increasing the position of the roll centre (due to greater bending of the front springs).
An increase in Mi:M3 at Jz:Ga > 0.3 can be obtained by appropriately arranging the front suspension buffers.
4) The centre of the gravity of the Tatra-87 vehicle is significantly closer to the rear axle 0.61 = 0.39: H. Ga:Ga GB:Ga
SUSPENSION TESTS
And road tests of the suspension consisted of the following:
Laboratory tests.
a. Determination of wheel loads (vehicle wheel alignment) without passengers, with passengers and determination of the position of the centre of gravity by length and height.
b. Calibration of front and rear suspensions.
c. Recording the damping curves of the body and wheels vibrations on a test stand.
Passenger experience
These tests were carried out by engineer A.V. Vorobyov, Laboratory of Stability and Suspension of the OANIL.
Recording of vertical accelerations perceived by front and rear seat passengers while driving the car on a cobblestone road at different speeds and with different tire pressures.
1. Suspension design
The front suspension is independent, with two transverse leaf springs, one on top of the other, the ends of the springs connected by a pair of struts. Each leaf spring is additionally surrounded by a second leaf spring, apparently to prevent an accident in the event of a spring breakage.
Two hydraulic telescopic shock absorbers are installed to dampen vibrations. A stabilizer and travel stops (buffers) are missing.
The rear suspension is independent; the elastic elements are quarter leaf springs, installed at an angle of approximately 22 degrees to the longitudinal axis of the car.
The spring eye is embedded in a specially shaped shackle hanging on the axle shaft liner pin. The spring operates only in bending. The wheel, together the axle shaft, initially moves in a transverse-vertical plane relative to the centre, located near the vehicle’s final drive.
The system features a variable track and variable wheel alignment. Two hydraulic telescopic shock absorbers are installed to dampen vibrations.
There is no stabilizer; downward wheel travel is limited by a buffer, a rigid rubber plate to a special bracket. The clearance from the buffer to the wheel sock on a loaded vehicle is 60 mm.
2. Test results
Looking at Table 18, the following can be established:
Distribution of loads across vehicle axles
Column 1 -1 driver at 150 kg.
Column 2 - 1 driver and load of 375 kg
Column 3 - 1 driver and 4 passengers
Kg on the front wheels 560 650 730
Kg on the rear wheels 940 1000 1145
Kg total weight 1500 1650 1875
Distribution ratio % 37.3 / 62.7 39.4 / 60.6 38.9 / 61.1
Centre location
Front axle weight (mm) 1790
From road level (mm) 597
Without passengers and with 5 passengers (including the driver) for the Tatra 87 vehicle, the weight on the rear wheels is 62.7% and 61.1% of the total load, respectively.
This weight distribution is explained by the engine’s location behind the rear axle of the vehicle. The presence of passengers only slightly evens out the weight distribution between the axles (by only 1.6%). Such weight distribution is not found in passenger cars with a front-engine location.
It’s worth noting that the centre of gravity is low. The rear seat, along the length of the car, is located close to the centre of gravity.
Calibration of the front suspension (excluding tires shows that its rigidity (K) is constant throughout the entire measured length of suspension deformation and is equal to 8.2 kg/mm (Fig. 60).
The obtained rigidity is significant for a modern passenger car (exceeds the rigidity of of the front suspension of the GAZ No. M-20 car by 2-3 times).
The effective deflection (5) of the front suspension at full load is only 73 mm (for the GAZ M-20 vehicle, -5 =220 mm).
The rear suspension calibration (Fig. 61) indicates its high rigidity, and the presence of a non-elastic wheel downstop contributes to sharp impacts. When the wheel is lowered more than 60 mm, the suspension stiffness coefficient increases from 7 kg/mm to 100 kg/mm.
In Fig. 61 it is evident that the rear suspension has significant mechanical friction, giving P = +150 kg, which can be compared with the friction in the springs of some trucks, for example, GAZ-AA. In the GAZ-M-20 passenger car, the friction in the springs is P = +150 kg.
Small road irregularities that cause high-frequency forces that do not exceed the friction force are perceived harshly. High friction in the suspension supports significant loads, which are transmitted to the body as vibrations. The spring, however, experiences almost no deformation.
The static deflection of the rear suspension is 147 mm. The ratio of the static deflection of the front suspension to the static deflection of the rear is 0.46 for a vehicle without passengers, 0.5 for a vehicle with a load of 5 people, and the ratio of the average stiffness coefficients of the front and rear suspension is 1.17.
The recording of the vibration damping curves of the body and wheels was carried out on a “dropper” stand, where, when the car fell to a height of 65 mm, two curves were recorded (Figs. 62-63). The upper curve shows the vibrations of the body, and the lower curve the axle. The suspension was assessed based on these recordings using the following vibration indicators:
a) According to the natural frequency of vibrations of the body and wheels.
b) according to the degree of damping of body vibrations.
The tests are summarized to Tables 19 and 20.
Examination of curves and vibrations of the Tatra-87 car body shows:
1/ the damping of the main oscillations is strong,
2/ the natural frequency of oscillations is high and reaches 120 vibrations/min in the front and 130 vibrations.min in the rear. The obtained natural frequency of oscillations of the rear suspension significantly exceeds the calculated one, determined by the elasticity of the springs.
Table 19
Results of dropping the front of the car (front suspension)
Table 20
Results of dropping the rear of the car (rear suspension)
Designations:
H = height of fall of body and wheels;
K is the value of the first compression amplitude over the second compression amplitude
N is the frequency of body oscillations in the first period
N2
Z is the number of complete vibrations of the body before attenuation
Z2 is the number of
The estimated value, determined by the spring elasticity, should be attributed to excessive friction in the rear suspension springs, which, as previously noted, reaches +150 kg.
After the initial period of oscillation, low-amplitude oscillations occur, with both the sprung and unsprung masses moving at the same frequency and similar amplitudes. This indicates that the springs are completely deactivated at low oscillation amplitudes. To better understand the quality of the Tatra-87’s suspension, road tests were conducted on a medium-quality cobblestone road.
Using an optical accelerograph (Fig. 64), vertical accelerations perceived by a passenger in the front or rear seats were recorded.
The tests were carried out at speeds of 40 and 60 km/h with tire pressure (kg/cm):
1. recommended by the factory 1.2 in front 1.8 in the back.
2. increased pressure in 1.8 in front, 1.8 in the back.
The load in all cases of road tests was 4 people including the driver.
Fig. 65 shows the curves of vertical accelerations perceived by a passenger when driver a car with normal tire pressure. Looking at the acceleration curves, we see that the passenger feels two clearly expressed frequencies: 150-160 rpm and 1000-1400 rpm, depending on the vehicle’s speed. In addition, there is a third frequency of 650-750 rpm, which is not clearly expressed on the curve.
It was almost impossible to detect the natural frequency of the suspension oscillations of 107-120 rpm (obtained from the data of the ejector). A frequency of 650-750 rpm corresponds to vibrations of the unsprung part, and frequencies of 1000-1400 are vibrations from the engine; the first occurs at a vehicle speed of 40 km/h and the second at 60 km/h, which is transmitted to the passenger through the floor of the car.
c It was not possible to detect any effect of increasing the front tire pressure from 1.2 atm to 1.8 atm on ride comfort. The accelerations do not exceed 5.6 m/sec in the first frequency case, and 1.5 m/sec in the second and third frequency cases. In the back seat, the passenger feels acceleration (in magnitude) less than in the front seat.
3. Suspension
The independent suspension design on the Tatra-87 is simple and has a small number of joints, but it is difficult to make it soft, since the lateral forces are absorbed by the spring itself, which necessitates strengthening the spring.
High friction in the rear suspension quickly dampens oscillations preventing the car from pitching. Without this friction, pitching would be possible for this car, as it is determined by the stiffness ratio of the front and rear suspensions.
The placement of the seats close to the car’s centre of gravity also contributes to the least sensation of galloping, however, strong friction in the suspension increases the jolts from the road on potholes.
General conclusion: the car’s suspension is stiff and con only provide satisfactory comfort on good roads.
BODY TESTING
1. Layout
The body layout is shown in Fig. 66
Table 21 shows the main dimensions of the body layout and, for comparison, provides data on the measurements of the GAZ M-20 body of the latest version.
Table 21.
Main dimension of the GAZ M-20 and Tatra-87 layout
Parameters Model
Dimensions in mm, angles in degrees GAZ M-20 Tatra-87
From steering wheel to back 350 340
Driver’s seat depth 470 490
Driver’s seat height 370 390
Driver seat cushion width 1340 640+640 XXX
From steering wheel to seat cushion 130 125
From driver’s seat cushion to roof 980 980
From cushion to pedals (upper position) 510 580
From cushion to pedals (lower position) 480 510 XX
Seat pitch 920 850
From rear seat to driver’s seat back 300 265
Rear seat legroom 550 600
Rear seat height 390 390
From rear seat cushion to roof 910 910
Rear seat depth 500 500
Rear seat to rear axle 725 1050
Max width of rear seat 1420 1480
Min width of rear seat 1030 1480
Width of front door 830 830
Width of rear door 810 760
Passage width of front door 780 700
Passage width of rear door 730 660
Angle of rear seats 10 17
Angle between rear seat and back of the driver’s seat
96 95
Angle between the rear seat cushion and rear seat back
100 97
The main dimensions of the seats and interior space are sufficient for five passengers.
The car has a body with a capacity of 5955 mm. This value is typical for mid-class passenger cars with a four-door body. The front seats are separate and move horizontally. The driver’s position is not very comfortable, as the dimensions from the steering wheel to the cushion and backrest (in the middle position of the seat) are small, and the cushion and backrest are hard.
The rear seat width with the armrest folded down is sufficient for three passengers.
There are a number of things to note about the body layout. Both the front and rear seats are positioned as planned. The designer placed the left leg as close to the front axle as possible for the reasons noted in the introduction. As a result, the driver is forced to keep his left leg bent (when not pressing the clutch pedal), since the left front wheel housing and the pedal prevent him from fully extending his leg. Obviously, this shortcoming could be eliminated by installing an automatic or semi-automatic transmission (without a clutch pedal), which is already quite common on modern middle-class cars. The absence of such a transmission on the Tatra-87 (especially with a rear-mounted engine) once again demonstrates the insufficient perfection of this car’s mechanical mechanisms and their inadequacy.
The door opening is insufficient; the exit of the passenger and driver is difficult.
The distance between the rear seat cushion and the backrest of the front seat do not provide free seating for passengers, especially if the front seat is set to the rearmost position.
The roof’s rounded cross-section means that headroom above the rear seat cushion is only adequate in the middle section.
The trunks are poorly designed. Access to the rear trunk is difficult and its volume is small. Luggage cannot be stored under the false hood, as almost all the space is taken up by the fuel tank, spare tire and tools.
The device for folding the backrests of the front seats (Fig. 04) is simple and reliable.
The body has well-sealed door and window openings, almost completely eliminating dust penetration and providing good sound insulation. A casing enveloping the exhaust pipe and connected by pipes to openings in the body’s backbone beam is provided for heating. The openings can be closed with valves. This system does not provide the desired heating for the body in [Russian] winter conditions, especially since the lack of a front engine results in special cooling of the front part of the body. Furthermore, the engine heats up insignificantly in winter. The temperature in the body of the Tatra-87 was studied under …
The study materials will be part of a special report on the ventilation and heating of car bodies in general. The car body has a primitive device to prevent fogging and icing of the windshield, consisting of slots, pipes and a valve. Air enters the slots directly from the front of the car and, despite passing through an oil cooler, is not heated. Therefore, firstly, additional cooling of the car body is created, and secondly, during stops (even short ones, at intersections) the glass fogs up. The anti-fog device should be combined with a heating system.
2. Visibility
The visibility assessment and panoramic view shooting were carried out using the method adopted by NAMI.
The front visibility and rear visibility panoramas are shown in Fig. 68, and the projection of the front visibility panorama is shown in Fig. 69.
The window contours are well-designed relative to the driver’s seat, resulting in good forward visibility (visibility coefficient Ko=0.62%)
Rearward visibility through the side windows is good, but visibility through the rear window is completely unsatisfactory. The small area of the rear window is obscured by the hood vents, stabilizer, and hood supports. Visibility is also impaired by the double-glazed rear window[s].
3. Composition of the car shape
The car as an original appearance. The composition is well balanced (Fig. 30), despite the large volume of the rear section. This is explained by the correct proportions of the base, front and rear overhangs, front end, as well as the larger window area. The ratio of the base to the overall length of the car., the ratio of the front overhand to the rear are in the proportion of the “golden ratio.” The length of the front is equal to the length of the rear overhand. Comparatively large windows visually lighten the superstructure of the body. In general, the successful shape of the car is somewhat disrupted by the protruding visors of the air intake to the engine.
1/ See Proceedings of NAMI, Issue 52, 1948.
4. Streamlining
Undoubtedly, the car’s high top speed and excellent acceleration in 4th gear are a consequence of the streamlined body shape. To determine the drag coefficient, runs were made from 70 and 90 km/h (Figs. 34-39). The coefficient was calculated using the method described in the report “Aerodynamics of the Modern Passenger Car” (1947). The coefficient value was 0.02, i.e., somewhat greater than the values obtained in Kamm’s aerodynamic studies in Germany.
Substituting this value into the vehicle traction calculation equation gives accurate working balance results.
A so-called flow spectrum was also taken (Fig. 73). The spectrum shows that the bands on the side, near the windshield, and on the false hood oscillate insignificantly, while on the front fenders and above the rear of the body they oscillate quite noticeably. From this it can be concluded that the most positive smoothly tapering towards the rear end; the angular of glass of the windshield; the rear wheels covered with shields; a slight slope of the roof towards the rear end; and a smooth slope of the false hood.
The protruding front fenders and the strongly rounded shape of the hood (engine) have a negative impact on the streamlining of the car.
CAR DESIGN AND MANUFACTURING DEFICIENCIES
Throughout the entire testing period, the vehicle operated flawlessly. However, there were some negative phenomena, due to both design and technological reasons, namely:
1/ Engine knocking. The cause of the knocking is the timing chain links rubbing against the crankcase walls when the engine shifts to higher loads. Increasing the chain tension did not eliminate this problem. It can be completely eliminating by slightly enlarging the crankcase.
2/ Knocking noise in the rear shock absorbers. Eliminating the knocking noise proved to be quite difficult due to inconvenient access to the mechanisms. Access to the mechanisms generally requires labour-intensive work and removing the oil pan.
3/ The clutch lining dimensions are clearly inappropriate for the vehicle’s weight, engine power, and torque. The clutch wears out quickly and fails, even with careful use.
4/ Development of holes for the locks for fastening the rear wheel guards. Despite the extremely rare removal of the guards 12 times for lubrication and washing and 3 times for changing the tire, the edges of the hole were deformed and fastening the guards turned out to be difficult (Fig. 74)/
5/ Creaking noises in the front under the instrument panel. These creaking noises could not be eliminating.
6/ The hand brake cable slips off the roller when the foot and hand brakes are simultaneously applied. The cable can be easily reinstalled, but to eliminate the defect fully, it is necessary to install a limiter near the roller.
7/ Failure of the signals, windshield wipers, and turn signals. Externally mounted signals cause short circuits during rain. The issue was resolved by sealing the signal contacts with shellac, but to completely eliminate the problem, more reliable contact insulation is required, or better yet, the signals should be located under the false hood.
8/ Direction indicators sticking in their sockets.
9/ Noisy operation of the windshield wipers, insufficient coverage of the windshield surface, jamming of the brushes when they come into contact with the glass lining.
10/ Left turn signal bulb failure.
11/ Odd operation of the ceiling light switch.
12/ The clock is inaccurate / the clock runs fast.
13/ Inaccurate speedometer readings. The speedometer indicates a speed 3-6% higher than the actual speed. As the speed decreases, the speedometer needle lags.
14/ Significant increase in noise when opening the rear windows. All engine noise, especially fan noise, is clearly audible through the cooling system air intake vents.
15/ Poor wheel cover design. The covers are difficult to maintain, and the latches make cleaning difficult. Gaps in the covers allow water and dirt to penetrate, causing unpleasant noise in the covers after crossing the bow.
16/ The headlights can be adjusted normally due to their attachment to the fenders.
17/ Decorative trims (on the false hood and glove compartment door) are poorly secured. Self-loosening of the mounting screws leads to fasteners getting caught under the trims and being lost.
18/ The sliding part of the roof jammed.
19/ Destruction of coatings of nickel-plated parts/bumpers/caps/signal guards/rusting of parts (Fig. 45).
20/ Fading of upholstery around the windshield and in other areas.
21/ Squeaking noises in the window lifting mechanisms.
22/ Removing the screws that secure the door handles.
23/ The tread pattern of the tires causes significant noise.
24/ Destruction of the paintwork of the front license plate the factory plate on the rear right side of the body.
25/ Failure of the fuel level indicator.
26/ Crack on the rear left door window lift handle (Fig. 76).
Analyzing the above list of shortcomings, we come to the following conclusions:
1. The quality of some electrical equipment, units, devices and fittings of the vehicle is unsatisfactory.
2. Along with good sealing of the body, especially the door openings and the sliding part of the roof, insufficient attention has not been paid to the elimination and insulation from the passenger compartment of various noises, such as: creaking in the area of the front of the body and in the mechanisms for lifting the windows, knocking of the rear suspension, knocking of distribution chain, noise from water getting into the wheel caps, noisy gears and gear changes.
3. The design does not pay sufficient attention to the durability of the fittings and finishing parts (destruction of decorative coatings, unreliable fastening of decorative overlays, loosening of handle fastening screws, destruction of paint, fading of upholstery, etc).
CONCLUSION
The Tatra-87 mid-size passenger car with a rear-mounted engine and a five-seater closed body, model 1948, manufactured by the Czechoslovakian Tatra plant, is a modern design that attempts to depart from the conventional automobile layout. To a certain extent, these attempts have yielded positive results (utilization of vehicle space, visibility, streamlining, fuel consumption). However, the adopted vehicle layout, despite a relatively light engine, has resulted in the vehicle being inferior to modern vehicles of the same class in a number of parameters (stability, ease of control, cross-country ability). It is possible that, to properly address the needs of vehicles with a rear-mounted engine, a different overall vehicle layout and a more modern design of some components (gearbox, suspension) are required.
Brief conclusion on the qualities of the car:
a) The dynamics are quite satisfactory. The top speed is high, achieved mainly due to the streamlined shape of the body.
b) Stability is unsatisfactory, with strict adherence to different tire pressures on the front and rear wheels, especially on wet and slippery roads.
c) The body capacity is sufficient. Visibility is good forward, but unsatisfactory backward.
d) The ride smoothness is insufficient.
e) Insulation and ventilation of the body are good in summer, unsatisfactory in winter conditions.
f) The vehicle’s off-road performance is average. Driving on poor roads requires the driver to exercise extreme caution.
g) Fuel consumption is quite satisfactory with correct carburetor adjustment.
Brief conclusions on the design of the drive units:
a) The engine is reliable, does not overheat, requires little attention in maintenance; it starts easily in summer conditions; in winter conditions, the engine requires tightening.
b) The clutch is unreliable, requires extremely careful use and careful adjustment; it does not correspond to the engine power and torque.
c) The gearbox is imperfect and requires particularly skillful and frequent shifting.
d) The suspension is rigid, but the front and rear suspension are well chosen in terms of vehicle stability.
e) The steering wheel is light, but its tendency to over-steer leads to shocks during sharp turns.
f) The brakes are reliable.
g) The body is comfortable, has good appearance and low coefficient of air resistance; the trim parts, fitting and instruments are unsatisfactory [poor quality]; the trunk is small in volume and access is inconvenient.
General Conclusions
1/ The Tatra-87 vehicle in its current form requires significant modifications in terms of adapting it to various driving conditions (slippery roads, off-road), increasing reliability and simplifying control.
2/ The basic design of the car provides some increase in capacity, but the overload of the rear axle requires taking special measures to improve the stability of the car (increased pressure in the rear tires, suspension design).
3/ In order to take full advantage of the rear engine design, when placing seats within the base, you need to:
a/ significantly lighten the power unit;
b/ automate controls [i.e., use an automatic gear box];
c/ reduce the volume of the wheel housings [i.e., wheel arches];
d/ equip the car with a reliable heating system.
No comments:
Post a Comment