D4, D6K2 and D6K Track-Type Tractor Systems Power Train System Caterpillar




Illustration 1	g03722276
(1) Speed sensor (2) Piston motor (Left) (3) Motor displacement control (4) Passage (5) Hydraulic pressure sensor connector (6) Hydraulic pressure sensor connector (7) Line (8) Line (9) Proportional solenoid valve (10) Passage (11) Passage (12) Actuator piston (13) Passage (14) Passage (15) Proportional solenoid valve (16) Passage (17) Actuator piston (18) Line (19) Line (20) Piston pump (Left) (21) Hydraulic pressure sensor connector (22) Connector (23) Connector (24) Line (25) Hydraulic pressure sensor connector (26) Piston pump (Right) (27) Motor displacement control (28) Speed sensor (29) Piston motor (Right) (30) Hydraulic temperature sensor (31) Electronic Control Module (ECM) (32) Hystat joystick base

The hystat joystick base (32) sends a signal from an operator request to be in the NEUTRAL position. The ECM (31) interprets the two signals and ECM (31) determines that the joystick is in the NEUTRAL position. As a result, ECM (31) sends signals to the piston pumps and to the piston motors.

ECM (31) sends the following signals to piston motor (2) and to piston motor (29).

A signal with less than initialization current is sent to the motor displacement control (3).
A signal with less than initialization current is sent to the motor displacement control (27).

ECM (31) sends the following signals to proportional solenoid valve (9) of piston pump (26).

A signal with a solenoid duty cycle of less than initialization current is sent to the reverse solenoid of proportional solenoid valve (9).
A signal with a solenoid duty cycle of less than initialization current is sent to the forward solenoid of proportional solenoid valve (9).

ECM (31) sends the following signals to proportional solenoid valve (15) of piston pump (20).

A signal with a solenoid duty cycle of less than initialization current is sent to the reverse solenoid of proportional solenoid valve (15).
A signal with a solenoid duty cycle of less than initialization current is sent to the forward solenoid of the proportional solenoid valve (15).

As a result of the signals to the solenoids of the piston motors, the piston motors remain at the maximum displacements. As a result of the signals to the solenoids of piston pump (20), pilot oil flows to proportional solenoid valve (15). The oil flows through the proportional solenoid valve (15) to passage (14) to the pump case drain. Since the pressure in passage (16) is equal to the pressure in passage (13), the springs on each side of actuator piston (12) centers actuator piston (12) and the swashplate for piston pump (20) remains at zero angle. As a result of the signals to the solenoids of piston pump (26), pilot oil flows to proportional solenoid valve (9). The oil flows through proportional solenoid valve (9) to passage (4) to the pump case drain. Since the pressure in passage (11) is equal to the pressure in passage (10), the springs on each side of actuator piston (17) centers actuator piston (17) and the swashplate for piston pump (26) remains at zero angle. Since the piston pumps are at zero angle, both loops of the hydrostatic system are in a hydraulic lock and the machine does not move.

The ECM (31) receives feedback from speed sensors (28) and (1) on track speed, and sensors (25), (21), (6), and (5).

Forward Travel

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Illustration 2	g03730837
(1) Speed sensor (2) Piston motor (Left) (3) Motor displacement control (4) Passage (5) Hydraulic pressure sensor connector (6) Hydraulic pressure sensor connector (7) Line (8) Line (9) Proportional solenoid valve (10) Passage (11) Passage (12) Actuator piston (13) Passage (14) Passage (15) Proportional solenoid valve (16) Passage (17) Actuator piston (18) Line (19) Line (20) Piston pump (Left) (21) Hydraulic pressure sensor connector (22) Connector (23) Connector (24) Line (25) Hydraulic pressure sensor connector (26) Piston pump (Right) (27) Motor displacement control (28) Speed sensor (29) Piston motor (Right) (30) Hydraulic temperature sensor (31) Electronic Control Module (ECM) (32) Hystat joystick base

The hystat joystick base (32) sends a signal from an operator request to be in the FORWARD position. ECM (31) interprets the two signals and ECM (31) determines that the joystick is in the FORWARD position. As a result, ECM (31) sends signals to the piston pumps and to the piston motors.

ECM (31) sends the following signals to piston motor (2) and to piston motor (29).

A variable signal with a solenoid duty cycle above initialization current is sent to the motor displacement control (3).
A variable signal with a solenoid duty cycle above initialization current is sent to the motor displacement control (27).

ECM (31) sends the following signals to proportional solenoid valve (9) of piston pump (26).

A variable signal with a solenoid duty cycle of less than initialization current is sent to the reverse solenoid of proportional solenoid valve (9).
A variable signal with a solenoid duty cycle above initialization current is sent through to the forward solenoid of proportional solenoid valve (9).

ECM (31) sends the following signals to proportional solenoid valve (15) of piston pump (20).

A variable signal with a solenoid duty cycle of less than initialization current is sent to the reverse solenoid of proportional solenoid valve (15).
A variable signal with a solenoid duty cycle above initialization current is sent to the forward solenoid of proportional solenoid valve (15).

The signals to the solenoids of the piston motors vary with the signals that are received from the travel speed switch of the joystick and the signals to the forward solenoids of the piston pumps vary with the signals that are received from the travel speed switch of the joystick. The signals determine the angle of the swashplates of the piston pumps and of the piston motors in order to achieve maximum machine performance.

As a result of the signals to the solenoids of piston pump (20), proportional solenoid valve (15) shifts to the left. Pilot oil flows through proportional solenoid valve (15) to passage (16). The oil flows from passage (16) into the chamber of actuator piston (12). The oil overcomes the force of the opposite spring and actuator piston (12) shifts to the left. As actuator piston (12) shifts to the left, oil flows from the chamber of actuator piston (12) to passage (13). The oil flows from passage (13) through proportional solenoid valve (15) through passage (14) to the pump case drain. As a result, the displacement of piston pump (20) increases.

As a result of the signals to the solenoids of piston pump (26), proportional solenoid valve (9) shifts to the left. Pilot oil flows through proportional solenoid valve (9) to passage (10). The oil flows from passage (10) into the chamber of actuator piston (17). The oil overcomes the force of the opposite spring and actuator piston (17) shifts to the left. As actuator piston (17) shifts to the left, oil flows from the chamber of actuator piston (17) to passage (11). The oil flows from passage (11) through proportional solenoid valve (9) through passage (4) to the pump case drain. As a result, the displacement of piston pump (26) increases.

Oil flows from piston pump (20) through line (7) to piston motor (2). Also, oil flows from piston pump (26) through line (19) to piston motor (29). As the oil flows through both piston motors, the piston motors rotate and the piston motors move the machine forward.

The ECM (31) receives feedback from speed sensors (28) and (1) on track speed, and sensors (25), (21), (6), and (5). These sensors help the ECM to determine the rate at which pressures are changing, and how fast the machine is moving. The sensors assist in the following operations:

ECM (31) adjusts the signals to the solenoids of the piston pumps and to the solenoids of the piston motors in order to prevent an overspeed condition.
ECM (31) adjusts the signals to the solenoids of the piston pumps and to the solenoids of the piston motors in order to prevent an underspeed condition or a stall condition.
ECM (31) ensures that the two piston motors are tracking in a straight line.

Reverse Travel

The operation of the reverse travel is similar to the operation of the forward travel.

Left Turn (Pivot Turn)

Note: The pivot turn is performed with no brake engagement.

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Illustration 3	g03730847
(1) Speed sensor (2) Piston motor (Left) (3) Motor displacement control (4) Passage (5) Hydraulic pressure sensor connector (6) Hydraulic pressure sensor connector (7) Line (8) Line (9) Proportional solenoid valve (10) Passage (11) Passage (12) Actuator piston (13) Passage (14) Passage (15) Proportional solenoid valve (16) Passage (17) Actuator piston (18) Line (19) Line (20) Piston pump (Left) (21) Hydraulic pressure sensor connector (22) Connector (23) Connector (24) Line (25) Hydraulic pressure sensor connector (26) Piston pump (Right) (27) Motor displacement control (28) Speed sensor (29) Piston motor (Right) (30) Hydraulic temperature sensor (31) Electronic Control Module (ECM) (32) Hystat joystick base

The hystat joystick base (32) sends a signal from an operator request to be in the FORWARD and PIVOT LEFT position. ECM (31) interprets the two signals and ECM (31) determines that the joystick is in the FORWARD position and in the PIVOT LEFT position. As a result, ECM (31) sends signals to the piston pumps and to the piston motors.

ECM (31) sends the following signals to piston motor (2) and to piston motor (29).

A signal with a solenoid duty cycle of less than initialization current is sent to motor displacement control (3).
A signal with a solenoid duty cycle above initialization current is sent to motor displacement control (27).

ECM (31) sends the following signals to proportional solenoid valve (9) of piston pump (26).

A signal with a solenoid duty cycle of less than initialization current is sent to the reverse solenoid of proportional solenoid valve (9).
A signal with a solenoid duty cycle above initialization current is sent to the forward solenoid of proportional solenoid valve (9).

ECM (31) sends the following signals to proportional solenoid valve (15) of piston pump (20).

A signal with a solenoid duty cycle of less than initialization current is sent to the reverse solenoid of proportional solenoid valve (15).
A signal with a solenoid duty cycle of less than initialization current is sent to the forward solenoid of proportional solenoid valve (15).

The signal to the solenoid of piston motor (29) vary with the signals that are received from the travel speed switch of the joystick and the signal to the forward solenoid of piston pump (26) vary with the signals that are received from the travel speed switch of the joystick . The signals determine the angle of the swashplates of piston pump (20) and of the piston motor (29) in order to achieve maximum machine performance.

As a result of the signal to motor displacement control (3) of piston motor (2), piston motor (2) remains at the maximum displacement. As a result of the signals to the solenoids of proportional solenoid valve (15), pilot oil flows to proportional solenoid valve (15). The oil flows through proportional solenoid valve (15) to passage (14) to the pump case drain. Since the pressure in passage (13) is equal to the pressure in passage (16), the springs on each side of actuator piston (12) center actuator piston (12) and the swashplate for piston pump (20) remains at zero angle.

Since piston pump (20) is at zero angle, the left drive loop of the hydrostatic system is in a hydraulic lock and the left track does not move. As the oil flows through piston motor (29), the piston motor rotates and the right track moves forward. The machine turns to the left while the machine pivots on the left track.

ECM (31) adjusts the signals to the solenoids of piston pump (20) and to the solenoid of piston motor (29) in order to prevent an overspeed condition.
ECM (31) adjusts the signals to the solenoids of piston pump (20) and to the solenoid of piston motor (29) in order to prevent an underspeed condition or a stall condition.
ECM (31) ensures that the two piston motors are functioning properly during the turn.

Right Turn (Pivot Turn)

Note: The pivot turn is performed with no brake engagement.

The operation of the right turn (pivot turn) is similar to the operation of the left turn (pivot turn).

Left Turn (Counterrotate Turn)

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Illustration 4	g03730859
(1) Speed sensor (2) Piston motor (Left) (3) Motor displacement control (4) Passage (5) Hydraulic pressure sensor connector (6) Hydraulic pressure sensor connector (7) Line (8) Line (9) Proportional solenoid valve (10) Passage (11) Passage (12) Actuator piston (13) Passage (14) Passage (15) Proportional solenoid valve (16) Passage (17) Actuator piston (18) Line (19) Line (20) Piston pump (Left) (21) Hydraulic pressure sensor connector (22) Connector (23) Connector (24) Line (25) Hydraulic pressure sensor connector (26) Piston pump (Right) (27) Motor displacement control (28) Speed sensor (29) Piston motor (Right) (30) Hydraulic temperature sensor (31) Electronic Control Module (ECM) (32) Hystat joystick base

The hystat joystick base (32) sends a signal from an operator request to be in the FORWARD and COUNTERROTATE LEFT position. ECM (31) interprets the two signals and ECM (31) determines that the joystick is in the FORWARD position and in the COUNTERROTATE LEFT position. As a result, ECM (31) sends signals to the piston pumps and to the piston motors.

ECM (31) sends the following signals to piston motor (2) and to piston motor (29).

A signal with a solenoid duty cycle above initialization current is sent to motor displacement control (3).
A signal with a solenoid duty cycle above initialization current is sent to motor displacement control (27).

ECM (31) sends the following signals to proportional solenoid valve (9) of piston pump (26).

A signal with a solenoid duty cycle of less than initialization current is sent to the reverse solenoid of proportional solenoid valve (9).
A signal with a solenoid duty cycle above initialization current is sent to the forward solenoid of proportional solenoid valve (9).

ECM (31) sends the following signals to proportional solenoid valve (15) of piston pump (20).

A signal with a solenoid duty cycle above initialization current is sent to the reverse solenoid of proportional solenoid valve (15).
A signal with a solenoid duty cycle of less than initialization current is sent to the forward solenoid of proportional solenoid valve (15).

The signals to the solenoids of the piston motors vary with the signals that are received from the travel speed switch of the joystick and the signals to the solenoids of the piston pumps vary with the signals that are received from the travel speed switch of the joystick. The signals determine the angle of the swashplates of the piston pumps and of the piston motors in order to achieve maximum machine performance.

As a result of the signals to the solenoids of piston pump (20), proportional solenoid valve (15) shifts to the right. Pilot oil flows through proportional solenoid valve (15) to passage (13). The oil flows from passage (13) into the chamber of actuator piston (12). The oil overcomes the force of the opposite spring and actuator piston (12) shifts to the right. As actuator piston (12) shifts to the right, oil flows from the chamber of actuator piston (12) to passage (16). The oil flows from passage (16) through proportional solenoid valve (15) through passage (14) to the pump case drain. As a result, the displacement of piston pump (20) increases. Oil flows from piston pump (20) through passage (14) to piston motor (26).

As the oil flows through piston motor (2), piston motor (2) rotates and the left track rotates backward. As the oil flows through piston motor (29), piston motor (29) rotates and the right track rotates forward. As a result, the machine rotates counterclockwise through the center axis of the machine.

ECM (31) adjusts the signals to the solenoids of the piston pumps and to the solenoids of the piston motors in order to prevent an overspeed condition.
ECM (31) adjusts the signals to the solenoids of the piston pumps and to the solenoids of the piston motors in order to prevent an underspeed condition or a stall condition.
ECM (31) ensures that the two piston motors are rotating in opposite directions.
ECM (31) ensures that the two piston motors are rotating at the same speed.