OVERDRIVE GEAR
MODIFIED DESIGN IN AMERICA Most motorists are by now familiar with that excellent fitting found on many cars today, the overdrive gear. Tests have shown that when it is engaged, fuel consumption is reduced by a gratifying margin, while the quieter running of the comparatively slowly revolving engine is distinctly pleasant to driver and passengers. In most cases, overdrive is engaged by easing the accelerator back at about 45 miles an hour, and it will stay in engagement until the speed drops to about 30 m.p.h., when it automatically disengages itself, and the normal top gear ratio is resumed. There is one small fault in the overdrive There are occasions when the car is hill-climbing with the overdrive in use, and the greater power of the normal ratio is required. That involves slowing the car down to 30 m.p.h. or thereabouts, so that the overdrive will drop out of engagement. But that in turn often means a road speed so low that the engine cannot pick up its revolutions again, and the car either struggles to the top or a change to second has to be made. If it were possible to disengage the overdrive at any speed, that trouble would not arise. The manufacturers of one of the bestknown overdrive gears, according to an American report, have recently modified the design so that by pressing the accelerator pedal a little beyond the normal full throttle position, the overdrive can be disengaged. This is quite a good arrangement, because any driver wishing to change down to normal top would already have the throttle wide open. It is unlikely that he would want to resume the normal drive when cruising with a small throttle opening on level country unless he suddenly required better acceleration, when again the downward movement of the accelerator is a perfectly natural one.
The mechanism, which has been de-
vised to obtain the desired result, is a simple arrangement of an electric solenoid, and the extra pressure on the accelerator closes the operating switch.
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Bibliographic details
Southland Times, Issue 23794, 17 April 1939, Page 4
Word Count
339OVERDRIVE GEAR Southland Times, Issue 23794, 17 April 1939, Page 4
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