973D Track-Type Loader Power Train Hydraulic Block Caterpillar


Hydraulic Block
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973D Track-Type Loader Power Train [KENR6524]
POWER TRAIN
COOLER GP
973D Track-Type Loader Power Train Hydraulic Block

The following features are controlled through the hydraulic block:

  • Oil cooler bypass

  • Brake solenoid valve

  • Override solenoid valve




Illustration 1g01949618

(1) Inlet from the right charge pump

(2) Outlet to the hydraulic tank

(4) Pilot oil outlet to the hydrostatic pumps

(5) Location of the parking brake solenoid valve

(6) Passages to the parking brakes

(8) Inlet from the case drain of the left hydrostatic pump

(10) Inlet from the case drain of the left hydrostatic motor

(13) Plug assembly for the hydraulic oil flow to the cooler

(14) Plug assembly for the hydraulic oil flow

(17) Spring

(18) Spring




Illustration 2g01949628

(2) Outlet to the hydraulic tank

(3) Location of the Override solenoid valve

(5) Location of the parking brake solenoid valve

(6) Passages to the parking brakes

(9) Inlet from the case drain of the right hydrostatic pump

(11) Outlet to the hydraulic oil cooler

(12) Inlet from the hydraulic oil cooler

(13) Plug assembly for the hydraulic oil flow to the cooler

(14) Plug assembly for the hydraulic oil flow

(19) Inlet from the case drain of the right hydrostatic motor

The hydraulic block is used to distribute all the return oil from the case drains of the pumps and motors in the power train system. The system is divided into four systems. The components are the oil cooler system, the brake system, the drive system, and the hydraulic tank.

The oil cooler bypass valve maintains the hydraulic oil at the optimum operating temperature. For SAE 10W hydraulic oil, the oil cooler bypass valve maintains an operating temperature of 60 °C (140 °F). The oil flows from case drains of the pumps and motors to either the oil cooler or the hydraulic tank. When the machine is started the oil temperature is cool and the case drain pressure is high. The poppets and springs are the oil cooler bypass valves. The force of springs (17) and (18) and the poppets move downward in order to open the oil flow. The components will not be able to overcome the pressure of the return oil and the oil cooler bypass valve will open. Most of the return oil flows through port (2) to the hydraulic tank.

When the temperature of the oil is very high, the viscosity of the return oil is very low. The flow resistance to the hydraulic oil cooler is low. Thus, the pressure of the return oil from the case drain is low.

As a result of the low pressure of the return oil, the oil will flow through ports (8) and (9). The low pressure oil will not overcome the force of spring (17) and (18). The oil will flow through the port (11) to the oil cooler. The oil will return from the cooler, through port (12) and flow back to the tank.

The brake system is controlled by the parking brake solenoid valve. The solenoid valve is located at port (5). When the machine is started the solenoid valve is in a energized position. Releasing the spring is accomplished by pilot oil. The spring-applied brake is released when pilot oil flows to the brake housing from port (6) .

As the machine is turned off the solenoid valve will become de-energized. This allows the pilot oil to be released. The brake pack is engaged as the pilot oil is released. This engages the parking brakes on the machine. This will lock the brakes in the engaged position.

As the pilot oil enters the hydraulic block through port (1) the flow of pilot oil into port (3) controls a override solenoid valve. When the override solenoid has no current, the valve is in the closed position, closing off the supply oil and allowing the oil from the pump control valve to drain to the tank through port (2). When the override solenoid is active, supply oil is provided through port (1) to the pump control valves through port (4) and the tank port on the valve to port (2) is closed. At the same time pilot oil is also flowing through port (5) in order to release the brakes for forward movement.

As the pilot oil enters the hydraulic block through port (1) a limited amount of oil flows through an orifice in the block. The oil then enters both hydrostatic motor bearing ports in order to cool the bearings.

The flow of the return oil from ports (1), (8), (9), (6) and (4) is routed to the hydraulic tank by port (2).

Information System:

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