The Knowledge Bank at The Ohio State University

Ohio State Engineer

Title: Fluid Drives --- Something New in Automobiles

Creators: Segna, F. Robert

Issue Date: 1940-02

Publisher: Ohio State University, College of Engineering

Citation: Ohio State Engineer, vol. 23, no. 3 (February, 1940), 10-16.

URI: http://hdl.handle.net/1811/35675

FLUID DRIVES-SomdBy ROBERT F. SEGNA

Many industries in our modern civilization are todayfacing their "last great frontier". Science and humanknowledge have made such great advancements in thelast few decades that almost all the major imperfec-tions have been eliminated from our mechanical equip-ment.

Engineers are of the opinion that the United StatesAutomotive Industry is now facing its last great revo-lutionary change. The struggle of transmissions is themost active sector on this, industry's most competitivefront.

When this dream comes true, the motorist will drivein an automotive Utopia. He will only have to stepinto his car and press the starter. The engine will

turn over comfortably. He steps on the acceleratorand the car glides away like flowing oil. The carpicks up speed without "feathering" the clutch, or"pumping" the gear stick, and without his doing morethan pressing the accelerator, the car hits a steady clip.A traffic light brings him up as his foot presses thebrake and the engine throttles down to a waiting purr.

The Hydraulic Transmission, which now occupiesthe liveliest portion of the experimental departmentsin the large designing offices of the industry, threatensto run the present conventional mechanical slidinggear shifts into obsolescence. The chief reason forthe optimism about this new arrangement is primarilybecause it offers complete automatic transmission witha unit less complicated than exists in the present system.

The Chrysler Fluid Fly-

wheel and its position in

the power transmission

system.

The conventional clutchand transmission can beseen behind the fluid

unit.

Upper right shows thedissembled parts of the

unit.

Page 10

ing New in AutomobilesThe transmission is the very heart of the internal

combustion engine. A gasoline engine has a congenitalweakness when throttled down which is an inability toexert enough torque through the drive shaft to over-come the inertia of the car. Consequently the trans-mission must do the job of adjusting the torque of theengine to the required torque of the wheels.

This adjustment of the engine speed, which is high,to mesh with the stronger twist on the driving shaftis called the multiplying torque. So far, the U. S.

gasoline engine has no feasible device to adjust thejob automatically and with top efficiency.

Panhard and Levassor devised the mechanical slid-ing-gear device, that turns almost all the automobiles,about fifty years ago. The system is very crude butas Panhard explained when he presented it, "It works."Several gear wheels step up the torque from the engineand change it into a slower, stronger twist on the pro-peller shaft. A clutch or torque switch allows for themanual engagement of the different gears. The gaps

Page 11

The Grapefruit idea ofthe Hydraulic Trans-

mission.

1. One-half filled withwater . . .

2. . . . spins and centri-fugal f o r c e sends

water upward and out-ward . . .

3. . . . striking vanes of

second half and driv-

ing it nearly as fast as

the first.

between the fixed speed ranges of the respective gearsproduces wasted power and gasoline. If it is not runproperly, this system can be much abused and this isexactly the way it is treated by many drivers. Jerkytransmission of the torsional vibrations and shocksare very noticeable on our cars today.

Manufacturers have cut gears with microscopic pre-cision, worked out synchronizers, constant mesh andhelical gears to overcome this undesirable feature, butit still presists. Many experimental projects in thelaboratories have been tested and patents issued onbelt transmission, friction disks, grooved wheels,rollers, chain drives, ratchet designs, centrifugal forcedevices and many other ideas that flooded the patentoffices.

The only arrangement that has approached theanswer to smooth starting in the mass production as-sembly lines is the planetary-type transmission of theModel T Fords. In the Borg-Warner overdrive andother advanced forms, the planetary transmission iscoming back in more improved style. The 1937 Olds-mobile had a four speed semi-automatic planetarytransmission in which gears are shifted at variousspeeds by oil pressure. Hudson also used the electro-vacuum shift developed by Bendix.

These systems only exhibit the well-known propen-sity of accessory mechanisms for getting out of order.This feature alone proves unpopular among motoristsbecause so few repair men understand the complexarrangements and immediate repairs are often impos-sible.

The Hydraulic Transmission affords the simplestanswer to the many complications of the other nu-merous systems. It allows engines to operate in theirefficient range although the device does not multiplythe engine's torque. The transmission of powerthrough fluid instead of through the usual mechanicalassembly features this system of conveyance.

Like many other mechanical devices that are beingintroduced today, the Hydraulic Transmission is notnew. It was devised by Dr. Foittinger at Hamburg,Germany, in 1905, to act as an oil cushion againstpowerful thrusts of Diesels that were cracking thecrude gears of the early days.

Some engineers explain that he received his ideafrom two grapefruit halves that were served to himfor breakfast one morning. Others claim it occurredwhen he accidentally faced two electric fans together,one running and one not. They could both be correctbecause his original device resembles two grapefruithalves, and he used light oil about the consistency ofkerosene for his fluid medium instead of air.

What he really achieved was a centrifugal pumpwhich moves oil in a continuous circuit. It starts fromthe center of the driver and is swirled to the periphery,then to the periphery and center of the driven vane.All the energy and power is thus transmitted througha liquid medium.

Foettinger discovered that it worked best at con-stant speed. To secure multiplication of power neces-sary to move the car up a steep hill or out of mud,he hitched a flywheel to a conventional geared trans-mission and shifted for the extra power as needed.Later, he disepnsed with this by arranging several setsof vanes in the driven half of the device, interposingsets of "stator", or non-whirling, vanes between themafter the manner of a multistage steam turbine. Hecalled this arrangement the "hydraulic torque con-verter".

It received its first commercial use in England inthe Daimler Car and Leyland Bus, and has been usedextensively in Europe and Canada since 1930.

Why the automotive industry in the United Stateshas been holding it up involves a complexity of eco-nomic obstacles, efficiency equations, consumer un-certainty and plain engineering intractability. Strippedof its technicalities, it all means that the Americanengineer has been watching European efforts at inter-posing the cushioning and shock absorbing effect ofa liquid connection between engine and the wheels,and have decided that the "bugs" are sufficientlyin control for volume production. They have finallypersuaded the American automobile manufacturersthat now may be the time to give American driversthe greater driving ease that comes as an additionalliquid-drive dividend.

Page 12 THE OHIO STATE ENGINEER

In our country, the two types originally devised byFoettinger are used by the different factions in theindustry. Chrysler and A. C. F. are using modifiedforms of the flywheel-gear-box combination while theYellow Coach Company sticks to the torque converter:.

Chrysler's development has been led by their chieftransmission engineer, Carl Neracher, who has spentsome twenty-five years as a specialist with automobiles.Although the principle is relatively simple, the me-chanical arrangement has presented a fistful of toughengineering and production problems. The composi-tion of the wheels and housing of the transmission wasthe first problem that was encountered. The Englishmodels used cast aluminum but it cracked under thepowerful LJ. S. engines and was rather expensive formass production. Forgings were out of reason for

the modern assembly line. The metallurgists triedmany mixtures for the castings, but none proved suc-cessful.

Finally they had to use stamped steel welded unitswhich were able to stand 9,000 revolutions a minuteand since this is beyond the present day auto speeds,it was the only satisfactory method available. Itproved difficult to work with at first because each finhad to be spot welded, totalling 138 welds on eachunit. Recent strides in the spot welding techniquefinally have enabled the industry to perform this jobin an efficient production manner.

They have now speeded up the assembly productionuntil they can now turn out 500 units a day and 5,000with more tooling equipment. Last year, Chryslerintroduced "Fluid Drive" on their Custom Imperials

February, 1940The Yellow Coach Torque Converter.

Page 13

(#2,600 to #2,800) and optional at #150 extra on theregular Imperials (#1,250 to #1,500).

The manufacturers must be sure of the project be-fore laying out from #4,000,000 to #6,000,000 fortooling to make this great change. About 2,000 ofthese Chryslers are now on the road. The Chryslerengineers have already discovered that it allows forthe use of a lighter transmission which means less costand wear on the transmission.

So far the consumer reaction has been encouragingbecause it is a tangible experience. The oil pocket(requiring one-half pint of oil per year) damps tor-sional vibrations and shocks so that the difference indriving quality is promptly apparent. As a result, thecar gets off with satin smoothness from any start.Deceleration slows the car with pneumatic ease. Extragear shifting is only necessary on steep grades or inreverse. There is definitely no stalling at traffic lightsand other quick stops. The getaway is made by open-ing the throttle wide and the automatic overdrive maybe engaged when sufficient speed is reached. A lowgear for a burst of speed may thus be obtained bydepressing the accelerator to the floorboard.

Idling at the traffic light at about 350 revolutionsper minute there is insufficient slosh of oil to set therunner wheel moving. This means that the slip is100%. Immediate acceleration snaps the motor upto 1200 revolutions per minute (about 25 m.p.h.) andreduces the slip to 6% and finally 0.5% as speed ispicked up. The slip is then due to the power lost infriction. Again when the car is brought to a stop inhigh gear the action is reversed.

Some engineers argue that this arrangement cutsdown efficiency because the fluid coupling is a gasconsumer. They also claim that the high selectivityof the torque at which it operates most efficiently withconstant slip characteristics makes ideal operation rare.Small slip, they say, prevails only on the level roadand not under most driving conditions.

Chrysler engineers answer by declaring that the sliploss is counteracted by the loss from the increase inmotor speed and gas consumption in low gears underthe difficult driving conditions for the mechanicalgear, and actual test proves that the difference in econ-omy losses is negligible.

Smoothness in the ride and the consequent decreasein wear and repair costs more than compensate thisloss in operation efficiency. Actual test proves thatthe life of all parts are increased 60% by "FluidDrive". The elimination of the clutch is also veryimportant and the safety factors such as theskidless traction on icy roads renders more advantagesto the system. Regardless, the arrangement needs someform of transmission to multiply power, and as a re-sult, the flywheel-gear-box has been added.

In their buses, A. C. F. mounts the engine underthe floor with the flywheel and three-speed transmis-sion directly attached. A new pneumatic control de-veloped by Westinghouse and Bendix consisting of asmall lever under the steering wheel is the only thingnecessary for the power "shift". The accelerator mustbe released but this momentary slowing of the engine

permits the gears to change automatically withoutshock or jerk.

The Yellow Bus offers a more complete approachto the entire problem of multiple torque. Only asmall handlever for forward drive instead of thenumerous gears is necessary in their arrangement, andno clutch or gear shift is used, only the brake andaccelerator. This set-up is more difficult to under-stand than to drive.

The motor turns a centrifugal pump wheel throwingthe fluid against a set of runner blades. So far it isthe same as Chrysler's. But the cycle does not finishhere. The liquid passes through these blades, is de-flected by a fixed set of blades in the housing andis directed to another set of blades on the runner.Whereupon it drops to the center axis and recirculatesto the pump.

In the "Fluid Drive", the power of the motor notabsorbed by the runner is lost in friction until con-stant speed of both is reached. In the turbine type,the power not absorbed in the first set, is utilized bythe second set instead of being wasted as slip, and theunused power in the second set is absorbed in a thirdset. The fixed blades which the fluid bounces fromare reaction points at which power is redirected. Thefinal result of this system is a larger part of the torquefrom the faster engine being absorbed in the trans-mission. It has the effect of a torque multiplyinggear box.

The tendency of the first set of blades is to catchup with the speed of the impeller, just as with therunner in the fluid coupling. As the first set gathersspeed, the second and third series get less and lessload until the one to one ratio is approached betweenthe impeller and runner, and from then on it is op-erating the same as "Fluid Drive".

Colonel George Green, the Vice President of theYellow Coach Company, is leading their developmentof the "Hydraulic Drive". He has been designingbuses since 1902. The Company is working in col-laboration with the Spicer Manufacturing Companyof Toledo, Ohio, under Swedish patents and it hascost #150,000 to develop so far. The torque converterhas a tendency of high efficiency at low speeds againstthe fluid drive high efficiency at high speeds. So,Yellow developed an ingenious automatic roller thatnow switches the engine from the turbine to directdrive at high speeds.

Actual tests show a 5 % loss in gasoline operatingeconomy of the "Hydraulic Drive", but they also showa 30% gain in Diesel operating economy.

"Hydraulic Drive" removes some of the strain onthe bus driver and offers more riding comfort to thepassenger. Since the bus driver must make change,collect fares, issue transfers, open and shut doors andwatch traffic, any relief in driving is a help in humandriving efficiency.

The torque converter is expensive because it is al-most a hand made job, and will cost #500 extra ontrucks and buses until production is stepped up.Naturally the new process involves more cost at the

Page 14 THE OHIO STATE ENGINEER

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start and a little loss in transmission economy. An- feel that he has a sense of control over the gears,other question puzzling to the engineers, is, "Just how The answer to this problem will soon be in theautomatic should the gear be?" motorists-hands. You and I must decide whether we

Again, some engineers think hydraulic drive is want this new improvement that engineers are offer-coming too late because the mechanical shift is so well ing to us or whether we shall cling to the old ineffi-established today. Psychologically, the driver likes to cient mechanical transmission.

Page 16 THE OHIO STATE ENGINEER