Mechanical-hydraulic transmission gear system and method of controlling power transmission using the system

摘要

A mechanical-hydraulic transmission gear system for use in construction vehicles or construction equipment and a method of controlling power transmission using the system arranged such that when a prime mover is rotating at high speeds power transmission is effected only through a mechanical transmission gear to thereby reduce the power loss due to fluid pressure substantially to zero, whilst when the prime mover is rotating at low speeds power transmission is effected only through a hydraulic transmission gear so as to facilitate control of the speed of the vehicle and control of changing forward running over to reversing and vice versa. The mechanical-hydraulic transmission gear system comprises a hydraulic transmission gear (10) having a hydraulic pump (11) and a hydraulic motor (13); a mechanical transmission gear (30); change-over means (26) for changing forward running of the vehicle over to reversing and vice versa; a speed control means (27); a sensor means (22) for sensing the rotational speed of output shaft (14); and control means (20) for comparing the signals transmitted by the change-over means, the speed control means and the rotational speed sensor means so as to effect control of disconnection and connection of a clutch (31) mounted on an input shaft (2) of the mechanical transmission gear and control of discharge of fluid from the pump and the motor. The method of controlling power transmission using this system includes the steps of disconnecting the clutch of the mechanical transmission so as to transmit the power from the prime mover only through the hyraulic transmission gear to the output shaft when the rotational speed of the output shaft is lower than a predetermined value; and connecting the clutch of the mechanical transmission gear so as to transmit the power only through the mechanical transmission gear to the output shaft and minimizing the power required by the hydraulic transmission gear according to a command from the control means when the rotational speed of the output shaft is higher than the predetermined value. <IMAGE>