Automatic speed range change-over system for a hydro-mechanical transmission

摘要

An automatic speed range change-over system for a hydro-mechanical transmission of a vehicle including a mechanical transmission having a plurality of speed range change-over clutches and pairs of hydraulic pumps and motors, each motor being operatively connected to the mechanical transmission. The speed range change-over system includes an engine speed detector, a pair of motor speed detectors and a plurality of fluid pressure detection switches for selectively detecting a currently engaged clutch. Signals from the engine speed detector, motor speed detectors and fluid pressure detection switches are fed into an arithmetic unit where relative number of revolutions between the clutch elements of another clutch adjacent to the clutch currently engaged is calculated based upon those signals and a relative number of revolutions signal is sent out therefrom. The relative number of revolutions signal is fed into a comparator and is compared with a predetermined value stored therein. The comparator sends out a signal only when the relative number of revolutions becomes less than the predetermined value. The signal from the comparator is fed into a speed range change-over signal generator for generating a signal thereby directing pressurized fluid into the adjacent clutch to be engaged so as to engage the same. Upon engagement of the adjacent clutch, the fluid pressure detection switch sends out a signal to thereby disengage the clutch currently engaged.