A Four-Speed Internal-Underdrive Transmission 270018
ALTHOUGH the enormous demand for automobiles has been met with continual improvement in performance, economy, comfort, and appearance of the vehicle, the development of the transmission has lagged badly for more than a decade. Car-ability has been handicapped by the limitations of the three-ratio gearbox. Notwithstanding that the added car-flexibility, economy and smoothness that result from increasing the number of ratios between the engine and the axle have long been appreciated by engineers, the short-comings of conventional four-speed transmissions, friction drives and two-speed rear-axles having double ring-gears and pinions are many, and the first cost and lack of over-all efficiency of the gasoline-electric drive have prevented their greater use in passenger-car and truck service. The reasons for the failure of the present four-speed transmissions to give satisfaction are cited, and stress is laid on the need of reducing the maximum engine-speed while at the same time maintaining or improving the over-all car-ability.
A description is then given of a four-speed transmission by which the gasoline consumption, as indicated by road tests, is said to show a saving of approximately 20 per cent. The assembly consists essentially of a three-speed gearbox on the forward end of which is housed an internal-gear unit that provides a reduction of approximately 1.4 to 1.0 for the third-speed ratio. Shifting from third to fourth or from fourth to third is accomplished by a hollow metal-clutch, the tooth arrangement of which allows the maximum angular-motion of 40 deg. between the mating parts. The shift can, therefore, be made with ease regardless of the car speed. It is pointed out that this is of prime importance if the advantage of an additional ratio is to be realized. Tables and curves show the comparative performance of passenger-cars and trucks equipped with the four-speed internal-underdrive transmission and with the three-speed gearbox.
The conclusion is reached that, if no other advantage existed, the gasoline economy effected by the use of an additional gear-ratio would justify the expenditure of effort required to develop a successful product.