953C Track-Type Loader Power Train Caterpillar

Power Train Oil System

Usage:

953C BBX

Drive Loops

The hydrostatic drive system is a variable speed hydraulic transmission.

The drive pumps are designed to provide varied rates of flow through the hydraulic lines to the drive motors. This allows the tracks to be driven at different speeds.

The pressure in the drive loop is determined by the load on the drive motors. If this load increases, the pressure in the drive loop increases.

Leakage in the drive pumps and motors is necessary in order to provide lubrication and cooling for the internal components.

Refer to Power Train Schematic, RENR5644 for additional information on the power train oil system.

Drive Pumps

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Illustration 1	g01140051
(1) Drive pump (2) Pump control valve (3) Barrel assembly (4) Spring (5) Actuator (6) Swashplate (7) Charge pump (8) Piston (9) Input shaft

The left and right drive pumps (1) are variable displacement piston pumps that have bidirectional flow. The drive pumps are driven from the front side of the pump drive in a counterclockwise rotation. The drive pumps use power from the engine in order to turn input shaft (9) .

Input shaft (9) turns barrel assembly (3) , nine pistons (8) , and a coupling.

When signal oil is sent to one end of the actuator piston, swashplate (6) tilts. The tilted swashplate causes the pistons (8) to move in and out of the barrel assembly (3) . The movement of the pistons causes oil to flow from the outlet port.

The swashplate regulates the flow and direction of the oil to the drive motor.

When the angle of the swashplate is increased, the flow rate of oil to the drive motor is increased. The increased flow results in an increase in machine speed. A decrease in the angle of the swashplate results in a decrease in the flow rate, which reduces the machine speed.

Reverse flow is accomplished by tilting the swashplate in the opposite direction. The swashplate angle, which varies from 17.5 degrees to negative 17.5 degrees, is changed by actuator (5) that is actuated by pump control valve (2) . The steering valves in the ECM manifold control the shifting of the pump control valve. The steering valves are controlled by the power train ECM which receives signals from the operator controls.

The output from the drive pumps is directed to the drive motors. This results in both the FORWARD movement and the REVERSE movement of the machine.

Drive Motors

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Illustration 2	g01189653
(10) Drive motor (11) Drive plate (12) Barrel assembly (13) Port plate (14) Flushing relief valve (15) Flushing shuttle valve (16) Actuator Group (17) Pistons (18) Output shaft

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Illustration 3	g00984399
Location (7) Drive motors

The operation of the drive motors is opposite from the drive pumps. High pressure oil enters the inlet port. This forces pistons (14) away from port plate (10) . The reciprocating of the pistons becomes rotary motion as the pistons turn barrel (9) . This is due to the angle between the barrel and drive plate (8) . The rotary motion is sent as mechanical power to the final drive gears.

The direction of rotation of the drive motors determines the direction of travel of the machine. The speed of the drive motor determines the speed of the track.

Oil flow through the drive motors can be in either direction. A change to the direction of oil flow changes the direction of rotation of barrel assembly (9) , piston assemblies (14) , drive plate (8) , and output shaft (15) .

The displacement of a motor is dependent on the angle of the barrel. The angle of the barrel is regulated by the motor control valve, which senses the output pressures from the steering valves within the ECM manifold. A resolver valve in the ECM manifold responds to the highest output pressure of the steering valves in the corresponding loop. The resolver sends this signal to the motor control valve. The motor control valve responds to this signal by allowing charge pressure oil to act on the actuator piston for the drive motor, which changes the motor displacement.

As the angle of the barrel decreases, the output speed increases. When the angle of the port plate increases, the output speed decreases.

Flushing Shuttle Valve

A flushing shuttle valve is located inside each motor. This allows a continuous flow of oil from the low pressure side of the drive loop to enter the motor case. This flushing flow removes contaminants that enter the drive loops or the contaminants that are created within the drive loops.

The flushing flow also removes hot oil that can be generated in the drive loop.

When the direction/speed control lever is in the NEUTRAL position, the flushing shuttle valve is in the center position because the forward and reverse sides of the drive loops are equally pressurized.

Case drain oil for the drive motor and the pumps comes from three main locations:

The leakage flow from the rotating groups
The flushing flow from the flushing shuttle valve
The flow of the drain oil from the steering valves in the ECM manifold

These flows combine and the flow is directed to the case drain filter. This flow removes any contaminants in the drive loop.

Steering Valves

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Illustration 4	g01092783
(AA) Mechanical connection (BB) Cutaway section (CC) Surface color (DD) No pressure (EE) Pneumatic pressure (FF) Activated components (GG) Tank pressure (HH) Lubricating oil (JJ) High pressure (KK) First pressure reduction (LL) Second pressure reduction (MM) Third pressure reduction (NN) Secondary source pressure (PP) Charge pressure or pilot pressure (QQ) Reduced charge pressure or pilot pressure (RR) Second reduction of charge pressure or pilot pressure (SS) Trapped oil

Note: Refer to Illustration 4 for information on the color codes that are used in the following illustrations.

Two-Stage TEHC Valves For Total Electronic Hystat Control

Five two-stage Total Electronic Hystat Control valves (TEHC valves) are mounted in the ECM manifold. Four of the valves are used in order to control the speed of the machine and the direction of the machine. One of the valves is used in order to control the flow of oil to the other four valves. This valve is the override valve. When the machine is in PARK position or in NEUTRAL position, a signal is not sent to the override valve. When the direction/speed control lever is moved in the FORWARD direction or in the REVERSE direction, the ECM sends maximum current to the solenoid of the override valve. This causes the valve to open fully.

The other four valves are used in order to control the flow of the output of the drive pumps and the direction of the output of the drive pumps. The signal pressure that is output from the valves is sent to the pump control valves. The signal pressure is also sent to the control valves on motors. The ECM controls the signal pressure that is output from the valves by changing the signal current that is sent to the solenoids. There is a FORWARD valve and a REVERSE valve for the left side of the machine. Also, there is a FORWARD valve and a REVERSE valve for the right side of the machine.

Signal Off

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Illustration 5	g00984403
(16) Spring (17) Cross-drilled Holes (18) Drilled Passage (19) Valve Spool (20) Cartridge (Edge Filter) (21) Threads (22) Orifice (23) Drain Orifice (24) Pin (25) Solenoid (26) Ball (27) Slot in Threads (28) ECM Manifold (A) Flow from the Override Valve (B) Flow to the Pump and Motor Contol Valves (C) Flow to the Tank through the Case of the Pump

The valves are de-energized until signal current is sent from the ECM. When the machine is moved out of NEUTRAL, the override valve allows oil to flow through the ECM manifold to the control valves. The oil flows through hole (17) that is cross-drilled in spool (19) and into passage (18) that is drilled in the center of spool (19) . The oil flows from the center of spool (19) , through cartridge (edge filter) (20) , through orifice (22) , and into the chamber at the right end of spool (19) . Pin (24) is not being forced against ball (26) by solenoid (25) . Ball (26) is not restricting drain orifice (23) . The oil flows through drain orifice (23) and through slot (27) in threads (21) of the valve. The oil is directed through passage (C) to the tank through a pump case.

Signal Less Than the Maximum

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Illustration 6	g01092787
(16) Spring (19) Valve Spool (23) Drain Orifice (24) Pin (25) Solenoid (26) Ball (29) Spring Cavity (30) Armature (A) Flow from the Override Valve (B) Flow to the Pump and Motor Control Valves (C) Flow to the Tank through the Pump

When the direction/speed control lever is moved in order to demand more speed, the ECM sends more current to solenoid (25) . The current is proportional to the position of the direction/speed control lever. The signal pressure that is sent to the control valve through passage (B) is proportional to the signal current. The control valve causes the swashplate in the pump to move from the neutral position.

The signal current creates a magnetic force that moves armature (30) . This forces pin (24) against ball (26) . The force of pin (24) against ball (26) is proportional to the signal current that is sent from the ECM. Ball (26) begins to block the flow of the oil through drain orifice (23) . This restriction causes the pressure at the right end of spool (19) to increase. The pressure moves spool (19) to the left against the force of spring (16) .

The movement of spool (19) closes the passage between passage (B) to the control valve and passage (C) to the tank. The movement of spool (19) opens the passage between passage (A) from the override valve and passage (B) to the control valve. While the pressure increases in passage (B) to the control valve, the pressure increases in cavity (29) . This pressure and the force of spring (16) balance the pressure at the right end of spool (29) . This balance determines the position of spool (19) .

Maximum Signal

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Illustration 7	g00984405
(16) Spring (19) Valve Spool (23) Drain Orifice (24) Pin (25) Solenoid (26) Ball (A) Flow from the Override Valve (B) Flow to the Pump and Motor Control Valves (C) Flow to the Tank through the Pump

When the operator has selected maximum speed with the direction/speed control lever, the ECM sends maximum current to solenoid (25) . Pin (24) exerts more force on ball (26) . Ball (26) causes further restriction of the flow through drain orifice (23) to the tank. This causes pressure to increase on the right side of spool (19) . Spool (19) moves further to the left. More of flow (A) from the override valve is sent to passage (B) to the pump and motor control valves. This causes movement of the control valves in order to further move the swashplate in the pump and barrel in the motor. The maximum pressure to the control valve is reached at the left end of valve spool (19) . This pressure and the force of spring (16) cause spool (19) to move to the right. Spool (19) will stop moving when the force on left side of spool (19) equals the force on the right side of spool (19) .

This position maintains maximum available pressure in passage (B) to the control valve until the signal current from the ECM is reduced. The signal current is reduced under any of the following conditions.

A steering pedal is pressed.
The center pedal is pressed.
The direction/speed control lever is moved in order to reduce speed.
The ECM senses an engine underspeed event.

Demand Fan Cooling System

The demand fan cooling system is effective with the following machine BBX2000-UP.

The viscous fan drive is made of three main assemblies: input member, output member and control valve.

The input member is composed of the input shaft and the driving clutch plate.

The output member consists of the body assembly and a cover assembly. The clutch plate, the body, and the cover have complementary concentric lands and grooves. In order to assemble the clutch plate, the body, and the cover, go through the double bearing assembly. This will allow the output body to spin freely without contacting the input body. The resulting disconnected mesh of lands and grooves forms a "working chamber". Torque is transmitted from the input to the output in the working chamber via fluid shear forces through a medium of a highly viscous silicone fluid.

The control valve governs the amount of fluid flowing into the working chamber.

The fan speed is varied by controlling the amount of fluid in the working chamber. In order to control the fan clutch speed , the fan speed sensor is necessary. The fan speed sensor will control the electronic closed loop feedback . The ECM software controls the absolute fan speed. The fan speed is based on the use of various measured signals. Examples of the sending components are engine coolant temperature, inlet manifold air temperature, oil sump temperature and engine speed.

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