SHAFT GP-DRIVE 2098849 - Caterpillar

Charge Pump
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Charge pumpThe charge pump is a gerotor pump that is located at the rear of the piston pump. The charge pump provides oil for the hydrostatic system at start-up. Charge oil is also makeup oil that is used for lubrication and cooling of the pump and the motor.The charge oil is used by the speed sensing valve to provide signal oil to the pump and the motor controls. Charge oil that is not used by the hydrostatic system flows into the pilot system.Charge Relief Valve
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Location of the charge relief valve
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Charge relief valveThe charge relief valve limits the pressure of the charge oil that does not flow through the speed sensing valve. The charge relief valve controls the pressure in the low pressure side of the hydrostatic loop. The charge relief valve also controls the maximum pressure for the pilot system. The charge relief valve is set at 3200 kPa (460 psi).Speed Sensing Valve
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Location of the speed sensing valve
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Speed sensing valveThe speed sensing valve detects the change in the oil flow of the charge pump as the engine speed changes. The orifice in the speed sensing valve creates a pressure differential which is a proportional amount to the engine speed. This signal oil is used to control the pump and the motor.The signal oil from the speed sensing valve flows to the Forward/Neutral/Reverse valve on the pump and to the displacement control valve on the motor. All oil that is not used by the speed sensing valve flows to the remainder of the charge oil circuit and flows to the pilot system.An orifice in the passage after the speed sensing valve allows the master cylinder valve to function correctly. The orifice also allows the POR valve to function correctly. If the orifice is not installed, the speed sensing valve will compensate for the loss of the flow of signal oil through the master cylinder. The loss of flow would prevent the pump from destroking and the motor from upstroking in order to help the braking of the machine. If the orifice is not installed, the POR valve will not correctly limit the maximum pressure of the drive loop.Crossover Relief Valves
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Crossover relief valvesThere are two crossover relief valves. There is one crossover relief valve for each side of the hydrostatic circuit. The crossover relief valves limit spikes of high pressure. The relief valves are not capable of passing a large amount of oil. The maximum pressure for each direction of the closed circuit is limited to 48200 kPa (6990 psi) by the crossover relief valves. The maximum pressure is determined by the combination of the spring in the crossover relief valve and the amount of charge pressure. The oil from each valve flows into the charge oil circuit.There is also a makeup valve in each relief valve. The makeup valve allows the charge oil to flow to the low pressure side of the hydrostatic circuit. This makeup oil replenishes the oil that is