HYDROSTATIC TRANSMISSION CONTROL SYSTEM

摘要

HYDROSTATIC TRANSMISSION CONTROL SYSTEM An improved hydrostatic transmission control system includes two pilot valves which are selectively operable to perform the dual functions of (1) effecting actuation of a main control valve from a neutral position to either one of two actuated positions to port fluid to vary the displacement of the hydrostatic transmission and (2) effecting a change in the rate at which fluid is ported and the displacement of the hydrostatic transmission is varied. When the displacement of the hydrostatic transmission is to be increased, a first one of the pilot valves is actuated to effect operation of the main control valve from the neutral position to a first actuated position in which fluid is ported to a swashplate motor to effect an increase in the displacement of the hydrostatic transmission. If a relatively large increase is to be made in the displacement of the hydrostatic transmission, the second pilot valve is also actuated to increase the rate of fluid flow between the main control valve and the swashplate motor. When the displacement of the hydrostatic transmission is to be decreased, the second pilot valve is actuated to effect operation of the main control valve from the neutral position to a second actuated position in which fluid is ported to the swashplate motor to effect a decrease in the displacement of the hydrostatic transmission. If a relatively large reduction is to be made in the displacement of the hydrostatic transmission, the first pilot valve is also actuated to increase the rate at which fluid is conducted between the main control valve and the swashplate motor. A control circuit for effecting operation of the two pilot valves to either increase or decrease the displacement of the hydrostatic transmission in response to a command signal includes a time delay circuit to effect sequential operation of the two pilot valves when a relatively large change is to be made in the displacement of the hydrostatic transmission.