From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Guide explaining the operation and economic advantages of the Chrysler automatic overdrive system.
| Identifier | ExFiles\Box 125\2\ scan0114 | |
| Date | 2nd November 1936 guessed | |
| PAGE 10 TOTAL PISTON TRAVEL IN CONVENTIONAL DRIVE CAR TRAVEL: 10 MILES EACH PISTON: 4 MILES PLUS 8 PISTONS: 32 MILES TOTAL PISTON TRAVEL IN OVERDRIVE CAR TRAVEL: 10 MILES EACH PISTON: 3 MILES PLUS 8 PISTONS: 24 MILES the overdrive which reduces the total piston travel to twenty-four miles plus for each ten miles of car travel or a reduction in piston travel equal to the entire distance travelled by the car. ADVANTAGES IN ECONOMY From what has already been said about the reduction in friction due to reduced engine speed, it is apparent that the overdrive also makes for increased economy of operation. There are a number of other considerations which are fully as important and which altogether mean a terrific cumulative saving in fuel and oil consumption. It is not generally realized that the greatest inherent loss in engine efficiency is due to operation under conditions which require only a fraction of the engine's power capacity. As we close the throttle of an engine running at a fixed speed in conventional drive, we not only do not decrease the friction losses, but we actually increase the parasitic work done by the engine due to the low vacuum under which the engine draws in the fuel mixture. Thus, at ordinary car speeds at which the actual power required to drive the car is very much less than the full throttle power of the engine, the parasitic losses become as great and even exceed the useful power. Another source of gain available with overdrive, lies in reduction of losses involved in such accessories as fan and muffler. These losses tend to increase roughly as the cube of the speed. If a fan consumes one horsepower at 2,000 revolutions per minute, • 10 • PAGE 3 HOW TO USE THE OVERDRIVE THE Chrysler automatic overdrive is a set of gears placed back of the regular transmission gears which will reduce the engine speed at high car speeds. They are engaged automatically when the driver takes his foot from the accelerator pedal at a speed of 45 miles per hour or over and they disengage automatically when the driver takes his foot off the accelerator pedal at speeds below 37 miles per hour. The car equipped with a Chrysler overdrive is driven exactly the same as the car you have been driving. There is nothing new to learn. In fact, the driver does not need to know that the car is equipped with an overdrive. If the driver wishes to accelerate quickly he simply keeps his foot on the accelerator until the car has reached the desired speed. The action of taking the foot from the accelerator pedal allows the overdrive to engage automatically. A lapse of time should be allowed before putting the foot on the accelerator again to allow the mechanism to engage. This time is about as long as the pause required in shifting gears. A very noticeable decrease in noise and a sense of eagerness of the car to increase in speed will be felt. But there is some loss in acceleration under these conditions. A word of warning at this time is in order. The car will attain higher speeds than the driver is aware of and may approach corners more rapidly than the driver realizes if an eye is not kept on the speedometer until the driver becomes accustomed to the new sensation and lack of consciousness of car speed. If it is desired to get high acceleration, to pass another car for instance, shift into second gear depressing the clutch pedal just as if there were no overdrive. After the acceleration has been complete shift back into high speed using the clutch as in a normal transmission. As the car speed is reduced either by hill climbing or on the part of the driver, the overdrive will be in operation to speeds lower than the engaging speed until the foot is taken off the • 3 • | ||