Control system for hydrostatic transmission

Abstract

Hydrostatic transmissions are commonly employed in the drive train of earthmoving and industrial vehicles. It is difficult to stop some such vehicles at a precise location on a slope due to the presence of a delay valve included in the controls for delaying application of a friction brake until the vehicle has been stopped by the hydrostatic transmission. In the present control system, a manual control valve (74) is moved to a first operative position and a hand control lever (25) is manipulated in combination therewith to reduce the displacement of a variable displacement pump (12) to establish a minimum drive condition sufficient to hold the vehicle motionless. Thereafter the manual control valve (74) can be moved to a second operative position to apply a friction brake (18) while the transmission maintains the vehicle motionless. In order to start the vehicle from the stopped position on a slope without unwanted roll, the transmission is either maintained at the minimum drive condition while the vehicle is stopped or the control lever (25) is manipulated to reestablish the minimum drive condition such that when the friction brake (18 ) is released by returning the control valve (74) to the first operative position, no undesired vehicle motion will occur. Normal vehicle motion may then resume by further manipulation of the control lever (25) and/or the manual control valve (74).

Dependencies are inferred from the claim text.