Abstract: 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.

Abstract: A turning control system for a hydro-mechanical transmission of a vehicle including a mechanical transmission having a plurality of speed range change-over clutches, a pair of output shafts connected to the mechanical transmission, and pairs of hydraulic pumps and motors, each motor being operatively connected to the mechanical transmission. A turning of the vehicle is effected by changing displacement volume of one of the hydraulic pumps relative to the other pump to thereby change number of revolutions of one output shaft relative to the other output shaft. The turning control system includes a plurality of fluid pressure detection switches for detecting one of speed range change-over clutches currently engaged, a pair of motor speed detectors for detecting hydraulic motor speeds, an engine speed detector for detecting engine speed and a steering angle detector for detecting steering angle.

Abstract: An engine speed control 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 control system includes a throttle position detector for detecting throttling position of an engine and generating a throttle position signal. This signal is fed into an engine speed setter where target engine speeds corresponding to the throttle positions are stored. The engine speed setter then sends out a target engine speed signal. An engine speed detector is provided for detecting an actual engine speed and sending out an actual engine speed signal. This actual engine speed signal is compared with the target engine speed signal in a comparator and an engine speed difference signal is generated from the comparator.