D8T Track-Type Tractor Caterpillar

Illustration 1	g02103295
Typical Components for a Differential Steering System (1) Ring Gear (2) Sun Gear (3) Carrier (4) Outer Axle Shaft (5) Planetary Gears (6) Steering Motor (7) Sun Gear (8) Transmission Pinion (9) Bevel Gear (10) Stationary Ring Gear (11) Planetary Gears (12) Outer Axle Shaft (13) Sun Gear (14) Carrier (15) Inner Axle Shaft (16) Bevel Gear Shaft (17) Carrier (18) Planetary Gears (19) Ring Gear

Illustration 2	g02103333
Differential Steering System (1) Ring Gear (2) Sun Gear (3) Carrier (4) Outer Axle Shaft (5) Planetary Gears (6) Input from the Steering Motor (7) Sun Gear (8) Transmission Pinion (9) Bevel Gear (10) Stationary Ring Gear (11) Planetary Gears (12) Outer Axle Shaft (13) Sun Gear (14) Carrier (15) Inner Axle Shaft (16) Bevel Gear Shaft (17) Carrier (18) Planetary Gears (19) Ring Gear (20) Steering Differential (21) Bevel Gear Set (22) Planetary Gear Train

Steering differential (20) receives power from the following two components:

• Transmission

• Steering Motor

The transmission controls the speed and the direction of movement (FORWARD or REVERSE). The direction of rotation of the transmission pinion determines the direction of machine travel. The speed of the transmission pinion determines the speed of travel.

The steering motor increases the speed of one track and the motor decreases the speed of the other track in order to turn the machine. The direction of rotation of the steering motor determines the direction of the turn. The speed of the steering motor determines the tightness of the turn.

The following components are mechanically connected with the steering differential:

• Bevel gear set (21) of the transmission

• Planetary gear train (22)

• Brakes (not shown)

The components that are listed above are connected by the following components:

• Two outer axle shafts (4) and (12)

• Inner axle shaft (15)

• Bevel gear shaft (16)

Power is transmitted through the outer axle shafts to the final drives.

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Illustration 3	g06352426

Reference: For more information, refer to "Differential Steering System for D8T Track-Type Tractor" on Caterpillar Channel 1.

Transmission Power Flow

Illustration 4	g02103354
Differential Steering System (Straight Line Forward) (1) Ring Gear (2) Sun Gear (3) Carrier (4) Outer Axle Shaft (5) Planetary Gears (6) Input from the Steering Motor (7) Sun Gear (8) Transmission Pinion (9) Bevel Gear (10) Stationary Ring Gear (11) Planetary Gears (12) Outer Axle Shaft (13) Sun Gear (14) Carrier (15) Inner Axle Shaft (16) Bevel Gear Shaft (17) Carrier (18) Planetary Gears (19) Ring Gear

When the machine is moving in a straight line, only the transmission inputs power into the differential steering system. Input from the Steering motor (6) is in the HOLD position.

Power from the transmission flows through transmission pinion (8) to bevel gear (9).

Bevel gear (9) sends the power through bevel gear shaft (16) to carrier (17). Carrier (17) transfers power to planetary gears (18).

Some of the power goes through planetary gears (18) to ring gear (19). The rest of the power goes through the planetary gears to sun gear (7).

Ring gear (19) sends power through carrier (3) to outer axle shaft (4).

Sun gear (7) sends power through inner axle shaft (15) to sun gear (13). Sun gear (13), planetary gears (11), carrier (14) and stationary ring gear (10) multiply the power. The power is sent to outer axle shaft (12).

The power that is sent to the outer axles is equal. The direction of axle rotation is equal. The machine will move in a straight line. The speed of travel depends on the speed of rotation of transmission pinion (8). The direction of travel (FORWARD or BACKWARD) depends on the direction of rotation of transmission pinion (8).

Steering Power Flow

Illustration 5	g02103416
Differential Steering System (Sharp Left Turn) (1) Ring Gear (2) Sun Gear (3) Carrier (4) Outer Axle Shaft (5) Planetary Gears (6) Input from the Steering Motor (7) Sun Gear (8) Transmission Pinion (9) Bevel Gear (10) Stationary Ring Gear (11) Planetary Gears (12) Outer Axle Shaft (13) Sun Gear (14) Carrier (15) Inner Axle Shaft (16) Bevel Gear Shaft (17) Carrier (18) Planetary Gears (19) Ring Gear

When the machine is making a sharp turn, only the steering motor inputs power into the differential steering system. Transmission pinion (8) is in the NEUTRAL position.

Input from the Steering motor (6) sends power through ring gear (1) to planetary gears (5).

Power through planetary gears (5) goes in two directions. Some of the power goes through the planetary gears to sun gear (2). The rest of the power goes through carrier (3) to outer axle shaft (4).

Sun gear (2) sends power through inner axle shaft (15) to sun gear (13). Sun gear (13), planetary gears (11), carrier (14) and stationary ring gear (10) multiply the power. The power is sent to outer axle shaft (12).

Power to both outer axle shafts is equal but the direction of rotation is opposite. The machine rotates about the center of the machine. The direction of the turn depends on the direction of rotation of the steering motor.

Combined Transmission and Steering Power Flow

Illustration 6	g02103433
Differential Steering System (Gradual Left Turn) (1) Ring Gear (2) Sun Gear (3) Carrier (4) Outer Axle Shaft (5) Planetary Gears (6) Input from the Steering Motor (7) Sun Gear (8) Transmission Pinion (9) Bevel Gear (10) Stationary Ring Gear (11) Planetary Gears (12) Outer Axle Shaft (13) Sun Gear (14) Carrier (15) Inner Axle Shaft (16) Bevel Gear Shaft (17) Carrier (18) Planetary Gears (19) Ring Gear

When the machine makes a gradual turn, the machine is moving forward and turning at the same time. The power from the steering motor and the power from the transmission act together on the differential steering system.

The power from transmission pinion (8) follows the same path through the system. Refer to the “Transmission Power Flow” section.

The power from the steering motor input (6) flows differently through the system. The power does not flow in two directions. The steering power flows through the system to one outer axle or to the other outer axle.

When the machine makes a left turn, the rotation of input from the steering motor (6) and transmission pinion (8) are the same direction. Power from steering motor (6) flows to ring gear (1). Ring gear (1) transfers power through planetary gears (5) to sun gear (2).

Sun gear (2) sends the power through inner axle shaft (15) to sun gear (13). The combined power through the inner axle shaft that flows to sun gear (13) is multiplied by sun gear (13), planetary gears (11), carrier (14) and stationary ring gear (10). The power is sent to outer axle shaft (12). The power causes outer axle shaft (12) to increase in speed.

When one side of the differential speeds up, the other side of the differential slows down an equal amount. The increase in power causes the speed of the sun gears to increase. When the speed of sun gear (2) increases, the speed of ring gear (1) decreases. The decrease in speed of ring gear (1) causes carrier (3) to decrease in speed as well as the speed of outer axle shaft (4).

The resulting speed difference between outer axle shafts causes the machine to turn left.

When the machine makes a right turn, the rotation of steering motor (6) is opposite the rotation of transmission pinion (8). Power from steering motor (6) flows to ring gear (1). Ring gear (1) transfers power through planetary gears (5) to carrier (3).

The combined power goes through carrier (3) to outer axle shaft (4). The power causes outer axle shaft (4), carrier (3) and ring gear (1) to increase in speed.

When ring gear (1) increases in speed, this causes sun gear (2) to decrease in speed. The decrease in speed of sun gear (2) causes inner axle shaft (15), sun gear (13), carrier (14) and outer axle shaft (12) to decrease in speed also.

The resulting speed difference between the outer axle shafts causes the machine to turn to the right.

The amount of power to the axle shafts is controlled by the transmission. Also, the direction of rotation of the axle shafts is controlled by the transmission.

The amount of speed difference between the axle shafts and the direction of turn are controlled by the steering motor. The speed of the steering motor determines the tightness of the turn. A faster motor speed causes a sharper turn. The direction of rotation of the steering motor controls the direction of the turn.

Refer to Table 1 for the direction of rotation during the various operations.