KIT-FENDER 1508316 - Caterpillar

The above listed machines are equipped with a hydrostatic transmission (variable displacement hydraulic pump and fixed displacement hydraulic motor).The hydrostatic transmission offers infinite control of speed and direction. The operator has complete control of the system with one lever for starting, stopping, forward or reverse motion.Control of the variable displacement, axial piston pump is the key to controlling the vehicle. Prime mover horsepower is transmitted to the pump. When the operator moves the control lever, the swashplate in the pump is tilted from neutral.When the variable pump swashplate is tilted, a positive stroke to the pistons is created. This, in turn, at any given input speed, produces a certain flow from the pump. This flow is transferred through high pressure lines to the motor. The ratio of the volume of flow from the pump to the displacement of the motor will determine the speed of the motor output shaft. Moving the control lever to the opposite side of neutral, the flow from the pump is reversed and the motor output shaft turns in the opposite direction. Speed of the output shaft is controlled by adjusting the displacement (flow) of the transmission. Load (working pressure) is determined by the external conditions, (grade, ground conditions, etc.) and this establishes the demand on the system.Pump and motors are contained in separate housings. All valves required for a closed loop circuit are included in either the pump or motor assemblies. A reservoir, filter, cooler and lines complete the circuit.A. Components (Figs. 1 and 2)
1. Charge Pump Circuit
a. Fluid flows from the reservoir through a filter to the inlet of the charge pump mounted on the main pump which is driven at pump shaft speed. The purpose of the charge pump is to provide a flow through the transmission for cooling purposes to supply fluid under pressure to maintain a positive pressure on the low pressure side of the main pump/motor circuit, to provide sufficient fluid under pressure for control purposes, and for internal leakage makeup.2. Main Pump and Motor Circuit
a. Fluid from the charge pump is directed to the low pressure side of the main circuit by means of one of two check valves. The second check valve is held closed by the fluid under high pressure on the other side of the main circuit.b. Fluid flows in the main circuit in a continuous closed loop. The quantity of fluid flow is determined by pump speed and displacement while direction of flow is determined by the swashplate angle from neutral.c. A manifold valve assembly, connected across the main circuit, includes elements essential to provide the proper operation of the transmission. The manifold valve contains two pilot operated high pressure relief valves which serve to prevent sustained abnormal pressure surges in either of the two main hydraulic lines by dumping fluid from the high pressure line to the low pressure line during rapid acceleration, abrupt braking and sudden application of load.d. Also provided in the manifold valve assembly is a shuttle valve and