Hydraulic System

Location of Components
(1) Double-pump drive. (2) Cooling and test manifold. (3) Propel pump. (4) Shift valve. (5) Speed range shift switch. (6) Propel level. (7) Propel filter. (8) Front gear reducer. (9) Axle assembly. (10) Rear propel motor.

Introduction

The propel system hydraulics allow the operator to drive the machine in a forward or reverse direction. The operator uses the speed range shift switch (5) to set the speed range in either high or low. He then uses the propel lever (6) to control the machine's direction and speed.

The propel system also provides the primary service brake function normally used to stop the machine. When the propel lever is set in the STOP position, the pump is in a zero output condition. This blocks oil flow through front gear reducer (8) and rear propel motor (10), stopping the machine.

The front gear reducer (8) provides propulsion to the drum. The rear propel motor (10) provides propulsion to the rear wheels through axle assembly (9).

The front gear reducer (8) and rear propel motor (10) are part of two closed-loop hydraulic circuits. Each propel loop is powered by one section of the propel pump (3). The propel pump is mounted to a double-pump drive (1), which is driven by the machine engine.

The front section of the propel pump (closest to double-pump drive) provides pressure to the front gear reducer (8), driving the drum. The rear section of the propel pump provides pressure to the rear propel motor (10), driving the rear wheels.

Propel Pump (3).

The propel pump (3) is a tandem, variable-displacement piston pump which provides minimum pressure to the system when the machine is not moving. When not operating, the pressure of the oil in the propel system will be 1655 to 2140 kPa (250 to 310 psi).

Propel Lever (6).

Speed Range Shift Switch (5).

The operator controls the propel system using the speed range shift switch (5) and the propel lever (6). When the operator moves the speed range shift switch to HIGH or LOW, shift valve (4) sets the displacement of the front gear reducer (8) and the rear propel motor (10). This determines the speed range of the machine. By moving the propel lever forward or backward, the operator sets the displacement of the propel pump. This determines the direction and speed of the machine.

Propel Filter (7).

A propel filter assembly (7) is used to ensure the cleanliness of fresh hydraulic oil entering the system. The filter has a three micron replaceable element, and is equipped with a 172 kPa (25 psi) bypass valve. A pressure switch in the filter is connected to a lamp on the operator's console. This lamp alerts the operator if the element becomes clogged.

Cooling and Test Manifold (2)

A portion of the hot oil in the two closed-loops is continually routed through the cooling and test manifold (2). The manifold ports this oil to the hydraulic oil tank. This permits fresh oil to enter the system regularly, keeping the components from overheating.

Test Ports

The cooling and test manifold has eight test ports which are used to check hydraulic pressure of the machine systems.

Double-Pump Drive

Double-Pump Drive
(1) Coupling. (2) Output gear. (3) Housing. (4) Input gear. (5) Drive shaft. (6) Drive plate.

The double-pump drive provides a mechanical connection between the propel pump and the engine. The double-pump drive has a 1:1 gear ratio, so the pump is always driven at engine rpm.

Reference: The double-pump drive also connects the vibratory pump to the engine. See Vibratory Systems Operation Testing and Adjusting, Form No. KEBR2360.

Drive plate (6) is installed into the engine flywheel, and the housing (3) is installed on the engine flywheel housing. Drive shaft (5) is splined at both ends. It is installed into the drive plate (6) at one end, and into the input gear (4) at the other end. The teeth of the input gear mesh with teeth of the output gear (2). Coupling (1) has internal and external splines, and provides the final connection to the propel pump.

When the engine is operating, the flywheel transfers torque through drive shaft and input gear, to the output gear. Output gear is connected to the propel pump through coupling, turning propel pump shaft at engine rpm.

Pump Components

Propel Pump in Off Position
(1) Displacement control valve. (2) Outlet to rear propel motor for forward operation (3) Check/relief valve. (4) Charge oil outlet. (5) Charge oil inlet. (6) Check/relief valve. (7) Shift oil outlet. (8) Outlet to front gear reducer for forward operation. (9) Charge relief valve. (10) Displacement control valve. (11) Servo-piston. (12) Swashplate. (13) Rotating group. (14) Chamber. (15) Chamber. (16) Outlet to rear propel motor for reverse operation. (17) Check/relief valve. (18) Case drain outlet. (19) Supply oil inlet. (20) Charge pump. (21) Check/relief valve. (22) Outlet to front gear reducer for reverse operation. (23) Chamber. (24) Chamber. (25) Rotating group. (26) Swashplate. (27) Servo-piston.

The propel pump contains the following components:

* Charge pump (20). The charge pump is driven off the main pump shaft. It provides charge pressure to the drum propel loop, and the wheel propel loop. Charge pressure is also used to shift the front gear reducer and rear propel motor to high speed range.

* Charge relief valve (9). Maintains charge pressure in the system at 1655 to 2140 kPa (250 to 310 psi). This relief valve allows unneeded charge oil to flow through the pump case (for cooling), to the hydraulic oil tank.

* Displacement control valve (1) and (10). These valves are controlled by the operator with the propel lever. As each displacement control valve is moved off center, it directs charge oil to the servo-piston, setting the displacement of the pump.

* Servo-piston (11) and (27). These are opposed double-acting pistons, which are spring-loaded to hold the swashplate in the center/stop position when the propel system is off. When the operator moves the propel lever, the displacement control valves send charge oil to one side or the other of each servo-piston, tilting the swashplates.

* Swashplate (12) and (26). The swashplates are mounted in cradle bearings, and are mechanically connected to the servo-pistons. When the servo-pistons move, the swashplates tilt. This sets the displacement of the pump.

* Rotating group (13) and (25). Consists of the pump input shaft and an attached piston block with seven pistons. The input shaft is connected to the double-pump drive, and rotates at engine rpm. When the swashplates are tilted, each pump section produces an output of high-pressure oil.

* Check/relief valves (3) (17) (6) and (21). The check part of each valve directs charge oil to the rotating group to be used in the closed-loop system. The relief part of each valve protects the system during operation. If system pressure exceeds 30 000 kPa (4350 psi), high-pressure oil flows through the relief valve to the low-pressure side of the pump.

Pump Operation

Propel Pump in Off Position
(1) Displacement control valve. (2) Outlet to rear propel motor for forward operation (3) Check/relief valve. (4) Charge oil outlet. (5) Charge oil inlet. (6) Check/relief valve. (7) Shift oil outlet. (8) Outlet to front gear reducer for forward operation. (9) Charge relief valve. (10) Displacement control valve. (11) Servo-piston. (12) Swashplate. (13) Rotating group. (14) Chamber. (15) Chamber. (16) Outlet to rear propel motor for reverse operation. (17) Check/relief valve. (18) Case drain outlet. (19) Supply oil inlet. (20) Charge pump. (21) Check/relief valve. (22) Outlet to front gear reducer for reverse operation. (23) Chamber. (24) Chamber. (25) Rotating group. (26) Swashplate. (27) Servo-piston.

System Off

Charge pump (20) draws hydraulic oil from the tank into the pump through supply oil inlet (19). The charge pump puts the oil under charge pressure, and ports this oil out of the pump through charge oil outlet (4). Charge oil goes through the propel filter assembly, and re-enters the pump through charge oil inlet (5).

Because the propel lever (on operator's console) is in the STOP position, displacement control valves (1) and (10) are in the neutral position. This blocks charge oil to servo-pistons (11) and (27). The spring-loaded servo-pistons hold swashplates (12) and (26) in the center/stop positions. Although rotating groups (13) and (25) are rotated by the double-pump drive, no high-pressure oil output is generated.

When swashplates (12) and (26) are in the center/stop position, the pump blocks the flow of oil to the front gear reducer and the rear propel motor. This provides primary service braking, stopping the machine or holding it in position.

Charge oil opens the check part of all four check/relief valves (3) (17) (6) and (21). This applies pressure to the rotating groups at chambers (14) (15) (23) and (24). Charge pressure also exits the pump through outlets (2) (16) (8) and (22). Charge pressure is applied to both ports of the rear propel motor, both ports of the front gear reducer, and four ports of the cooling and test manifold.

Because charge pressure is the same at all ports, oil is blocked at the rear propel motor, front gear reducer, and cooling and test manifold. This results in "no flow" through the propel loops except for a small amount of case drain flow through the rear propel motor and front gear reducer.

Charge oil also exits the pump through shift oil outlet (7), and is routed to the shift valve. This oil is used to set the speed range of the machine.

The charge relief valve (9) maintains charge pressure at 1655 to 2140 kPa (250 to 310 psi). Charge oil opens the relief valve, flows through the pump case, and exits the pump through case drain outlet (18). This case drain oil is then routed through the rear propel motor to the hydraulic oil tank.

It is important to note that charge pressure is present at all four rotating group chambers (14) (15) and (23) (24). This means that charge oil is available at any time to create high-pressure output oil when the operator moves the propel lever off center.

System On - Forward

Propel Pump in Forward Position
(1) Displacement control valve. (2) Outlet to rear propel motor for forward operation (3) Check/relief valve. (4) Charge oil outlet. (5) Charge oil inlet. (6) Check/relief valve. (7) Shift oil outlet. (8) Outlet to front gear reducer for forward operation. (9) Charge relief valve. (10) Displacement control valve. (11) Servo-piston. (12) Swashplate. (13) Rotating group. (14) Chamber. (15) Chamber. (16) Outlet to rear propel motor for reverse operation. (17) Check/relief valve. (18) Case drain outlet. (19) Supply oil inlet. (20) Charge pump. (21) Check/relief valve. (22) Outlet to front gear reducer for reverse operation. (23) Chamber. (24) Chamber. (25) Rotating group. (26) Swashplate. (27) Servo-piston.

When the operator moves the propel lever to the FORWARD position, displacement control valves (1) and (10) shift from the neutral position as shown. Filtered charge oil enters the pump at charge oil inlet (5). Charge oil flows through the displacement control valves to servo-pistons (11) and (27), causing swashplates (12) and (26) to tilt.

Swashplate angle is determined by how far the propel lever is moved off center. Due to normal operating force changes, the swashplates tend to drift from the set position. Drift is sensed by the feedback linkage connecting the swashplates to the displacement control valves. This activates the displacement control valves, supplying pressure to the servo-pistons and maintaining the swashplates in the set position.

As soon as the swashplates are tilted, the rotating groups take in charge oil at chambers (15) and (24). High-pressure output oil is created at chamber (14) and (23). The passages connected to chambers (15) and (24) become the low-pressure side of the pump. The passages connected to chambers (14) and (23) become the high-pressure side of the pump.

High-pressure output oil closes the check part of check/relief valves (3) and (6). The check part of check/relief valves (17) and (21) remain open so that incoming charge oil is added to the low-pressure side of the pump.

High-pressure oil from the rear section of pump exits through outlet (2), and is routed to the rear propel motor. High-pressure oil from the front section of pump exits through outlet (8), and is routed to the front gear reducer. These high-pressure oil flows cause rear propel motor and front gear reducer to rotate, driving the machine in a forward direction.

Hydraulic oil leaving the rear propel motor and front gear reducer is routed to the low-pressure side of the pump through outlets (16) and (22). Most of this oil is taken up by the rotating groups at chambers (15) and (24), and is reused in the closed-loops.

The high-pressure and low-pressure side of each propel loop is connected to the cooling and test manifold. This allows some used oil to return to the hydraulic oil tank. As hot oil leaves the system, fresh charge oil flows through the check part of check/relief valves (17) and (21) to chambers (15) and (24) for use in the two propel loops.

Charge relief valve (9) maintains oil in the low-pressure side of the pump at 1655 to 2140 kPa (250 to 310 psi). Fresh charge oil not needed by the system, passes through the charge relief valve. This oil exits the pump through case drain outlet (18) and is routed through the rear propel motor to the hydraulic oil tank.

Check/Relief Valves (3) and (6) in Relief Position
(28) Low-pressure side. (29) High-pressure side.

The relief part of check/relief valves (3) and (6) monitor the high-pressure sides of the two propel loops. If system pressure in either loop exceeds 30 000 kPa (4350 psi), the appropriate relief valve opens, passing oil to the low-pressure side of the pump.

System On - Reverse

Propel Pump in Reverse Position
(1) Displacement control valve. (2) Outlet to rear propel motor for forward operation (3) Check/relief valve. (4) Charge oil outlet. (5) Charge oil inlet. (6) Check/relief valve. (7) Shift oil outlet. (8) Outlet to front gear reducer for forward operation. (9) Charge relief valve. (10) Displacement control valve. (11) Servo-piston. (12) Swashplate. (13) Rotating group. (14) Chamber. (15) Chamber. (16) Outlet to rear propel motor for reverse operation. (17) Check/relief valve. (18) Case drain outlet. (19) Supply oil inlet. (20) Charge pump. (21) Check/relief valve. (22) Outlet to front gear reducer for reverse operation. (23) Chamber. (24) Chamber. (25) Rotating group. (26) Swashplate. (27) Servo-piston.

Propel pump operation for reverse is similar to that for forward operation. However, the high-pressure and low-pressure sides of the pump are switched around. Filtered charge oil enters the pump through charge oil inlet (5) and encounters displacement control valves (1) and (10).

When the operator moves the propel lever to the REVERSE position, the displacement control valves shift as shown. Charge oil is routed through the displacement control valves to servo-pistons (11) and (27). This tilts swashplates (12) and (26) in the opposite direction from forward operation.

The rotating groups take in charge oil at chambers (14) and (23), creating high-pressure output oil at chambers (15) and (24). High-pressure oil closes the check part of check/relief valves (17) and (21). The check part of check/relief valves (3) and (6) remain open. This creates the high-pressure and the low-pressure sides of the pump.

High-pressure oil from the rear section of pump exits through outlet (16), and is routed to the rear propel motor. High-pressure oil from the front section of pump exits through outlet (22), and is routed to the front gear reducer. This causes the rear propel motor and front gear reducer to rotate, driving the machine in the reverse direction.

Hydraulic oil leaving the rear propel motor and the front gear reducer is routed to the low-pressure side of the pump through outlets (2) and (8). Most of this oil is taken up by the rotating groups at chambers (14) and (23), and is reused in the two propel loops.

The high-pressure and low-pressure side of each propel loop is connected to the cooling and test manifold. This allows some used oil to return to the hydraulic oil tank. As hot oil leaves the system, fresh charge oil flows through the check part of check/relief valves (3) and (6) to chambers (14) and (23) for use in the two propel loops.

Charge relief valve (9) maintains oil in the low-pressure side of the pump at 1655 to 2140 kPa (250 to 310 psi). Fresh charge oil not needed by the system, passes through the charge relief valve. This oil exits the pump through case drain outlet (18) and is routed through the rear propel motor to the hydraulic oil tank.

Check/Relief Valves (17) and (21) in Relief Position
(28) Low-pressure side. (29) High-pressure side.

The relief part of check/relief valves (17) and (21) monitor the high-pressure sides of the two propel loops. If system pressure in either loop exceeds 30 000 kPa (4350 psi), the appropriate relief valve opens, passing oil to the low-pressure side of the pump.

Filter

Propel Filter
(1) Inlet port. (2) Bypass valve. (3) Pressure switch. (4) Outlet port. (5) Element.

Before being used in the two propel loops charge oil passes through the propel filter. During normal operation, charge oil comes from the propel pump, enters the filter at inlet port (1), and passes through the element (5). The element traps any debris that is in the oil. Oil then exits the filter through outlet port (4), and is routed back to the propel pump where it is used in the propel system.

If the element becomes clogged with debris, the restriction to the flow of oil causes a pressure increase outside the element. If the pressure differential across the element reaches 172 kPa (25 psi), the pressure of the oil causes bypass valve (2) to shift. Charge oil passes directly through the bypass valve and exits the filter through outlet port (4). When the oil does not go through the element, the debris in the oil will cause damage to the components in the propel system.

Pressure inside and outside the element is also applied to a pressure switch (3). If the element becomes clogged so that pressure differential across the element reaches 172 kPa (25 psi), the pressure switch closes. This lights a lamp on the operator's console, alerting the operator that filter has reached the "bypass" condition.

Correct maintenance must be used to make sure that filter element (5) does not become clogged, stopping the flow of clean oil to the propel system.

NOTE: It is normal for the filter indicator lamp to light when starting the engine, particularly during cold weather. As the hydraulic oil warms up, the lamp should go off, unless the element is clogged.

Front Gear Reducer

Front Gear Reducer
(1) Planetary gear reducer. (2) Variable-displacement motor.

The front gear reducer contains a variable-displacement hydraulic motor (2) and a double-reduction planetary gear reducer (1). When the machine operates in forward or reverse, the front gear reducer receives high-pressure hydraulic oil from the front section of the propel pump. The variable-displacement motor (2) changes the hydraulic force into mechanical torque. This torque is sent through the planetary gear reducer (1), driving the drum in a forward or reverse direction.

Reference: The front gear reducer also contains a spring-applied, hydraulically-released brake. This is used as the machine's secondary/parking brake. See Secondary/Parking Brake Systems Operation Testing and Adjusting, Form No. KEBR2375.

Operation of the variable-displacement motor (2) and the planetary gear reducer (1) are explained in the following sections. The variable-displacement motor (2) has four operating modes:

* Forward - LOW speed range

* Reverse - LOW speed range

* Forward - HIGH speed range

* Reverse - HIGH speed range

The planetary gear reducer (1) operates the same way in forward and reverse operation.

Variable-Displacement Motor Operation

Variable Displacement Motor in LOW Speed Range
(1) Swing frame. (2) Swashplate. (3) Pistons. (4) Output shaft. (5) Cylinder block. (6) Chamber. (7) Chamber. (8) Inlet port for forward operation. (9) Inlet port for reverse operation. (10) Check ball. (11) Piston. (12) Chamber. (13) Shift oil inlet. (14) Lever. (15) Spring. (16) Spool. (17) Case drain port.

Forward - LOW Speed Range

High-pressure oil from the front section of propel pump enters front gear reducer at port (8). Oil is routed to chamber (6) in cylinder block (5), and to left side of check ball (10). High-pressure oil moves check ball cavity to the right. Oil flows through check ball to left side of piston (11), moving piston to the right. Spring (15) holds spool (16) in position shown. Spool (16) blocks oil from entering chamber (12).

Piston (11) is attached to swing frame (1) through lever (14). When piston moves to the right, lever holds swing frame and swashplate (2) in position shown.

This is the maximum displacement of the motor. This means that for a given input of high-pressure oil, output shaft (4) turns relatively slowly, but with a high torque.

High-pressure oil from port (8) enters cylinder block (5) at chamber (6), causing pistons (3) to stroke outward. As pistons stroke, they push against swashplate (2). This causes pistons (3), cylinder block (5), and output shaft (4) to rotate.

Swashplate (2) is tilted so that as the unit rotates, the pistons become fully extended, then retract into the cylinder block. As pistons retract, they push low-pressure oil through chamber (7). Low-pressure oil exits front gear reducer at port (9).

Output shaft (4) transfers power from variable-displacement motor to planetary gear reducer.

Reverse - LOW Speed Range

Variable Displacement Motor in LOW Speed Range
(1) Swing frame. (2) Swashplate. (3) Pistons. (4) Output shaft. (5) Cylinder block. (6) Chamber. (7) Chamber. (8) Inlet port for forward operation. (9) Inlet port for reverse operation. (10) Check ball. (11) Piston. (12) Chamber. (13) Shift oil inlet. (14) Lever. (15) Spring. (16) Spool. (17) Case drain port.

High-pressure oil from front section of propel pump enters front gear reducer at port (9). Oil is routed to chamber (7), and to right side of check ball (10). Check ball moves to the left. Oil flows through check ball cavity to left side of piston (11). Piston moves to the right. Spring (15) holds spool (16) in position shown. Spool (16) blocks oil from chamber (12).

Piston (11) is attached to swing frame (1) through lever (14). When piston moves to the right, lever holds swing frame and swashplate (2) in position shown. This is the maximum displacement of the motor. This means that for a given input of high-pressure oil, output shaft (4) turns relatively slowly, but with a high torque.

High pressure oil from port (9) enters cylinder block (5) at chamber (7), causing pistons (3) to stroke outward. As pistons stroke, they push against swashplate (2). This causes pistons (3), cylinder block (5), and output shaft (4) to rotate. Rotation is in the opposite direction from forward operation.

Swashplate (2) is tilted so that as the unit rotates, the pistons become fully extended, then retract into the cylinder block. As pistons retract, they push low-pressure oil through chamber (6). Low-pressure exits front gear reducer at port (8).

Output shaft (4) transfers power from variable-displacement motor to planetary gear reducer.

Forward and Reverse - HIGH Speed Range

Variable Displacement Motor in HIGH Speed Range
(1) Swing frame. (2) Swashplate. (3) Pistons. (4) Output shaft. (5) Cylinder block. (6) Chamber. (7) Chamber. (8) Inlet port for forward operation. (9) Inlet port for reverse operation. (10) Check ball. (11) Piston. (12) Chamber. (13) Shift oil inlet. (14) Lever. (15) Spring. (16) Spool. (17) Case drain port.

Variable-displacement motor operation in HIGH speed range is similar to operation in LOW speed range in both forward and reverse. The only difference is that the displacement of the motor is set differently. This increases the output speed of the front gear reducer, driving the drum faster.

Hydraulic oil from the shift valve enters the front gear reducer at inlet (13). This oil is routed to right side of spool (16). Spool moves to the left, compressing spring (15).

High-pressure oil enters the front gear reducer at port (8) or (9). This oil is ported through check ball cavity to chamber (12). Oil flows through chamber (12) to right side of piston (11). Pressure at right side of piston overcomes pressure at left side of piston (right side of piston has a larger area). Piston moves to the left.

When piston (11) moves to the left, lever (14) pushes swing frame (1) and swashplate (2) to the position shown. This is the minimum displacement of the motor. This means that for a given input of high-pressure oil, output shaft (4) turns faster, but with less torque than when in low speed range.

Output shaft transfers power from variable-displacement motor to planetary gear reducer.

Planetary Gear Reducer Operation

Planetary Gear Reducer Components
(1) Planetary gears (three). (2) Planet gears (four). (3) Carrier hub shafts. (4) Output housing. (5) Variable-displacement motor. (6) Sun shaft. (7) Sun gear. (8) Carrier hub.

Sun shaft (6) is connected to motor output shaft by splines at one end. The other end of sun shaft engages large teeth of three planetary gears (1). Small teeth of planetary gears engage short teeth of sun gear (7). Sun gear fits over center part of sun shaft (6), but is not connected to sun shaft.

Long teeth of sun gear (7) engage four planet gears (2). Planet gears (2) are held inside output housing (4), and rotate on carrier hub shafts (3). Carrier hub (8) is secured to front yoke of machine and does not rotate.

Power from the motor output shaft turns the sun shaft (6). Sun shaft turns three planetary gears (1). This provides the first speed reduction and torque increase. Small teeth of planetary gears (1) turn sun gear in the same direction as sun shaft (6), but at a slower speed.

Sun gear turns four planet gears (2). Since carrier hub (8) is held stationary by front frame, output housing (4) moves around the planet gears. This provides the second speed reduction and torque increase.

Output housing (4) is secured to the vibratory drum. The vibratory drum rotates in the same direction and speed as output housing.

Rear Propel Motor Operation

Rear Propel Motor in LOW Speed Range
(1) Inlet for reverse operation. (2) Chamber. (3) Case drain inlet. (4) Spring. (5) Stop. (6) Output shaft. (7) Servo-piston. (8) Inlet for forward operation. (9) Chamber. (10) Piston block. (11) Case drain outlet. (12) Swashplate. (13) Shift oil inlet.

Forward - LOW Speed Range

The rear propel motor is a variable-displacement, bi-rotational, piston-type motor. When the machine propels, the motor receives high-pressure oil from the rear section of the propel pump. The motor changes this hydraulic force into mechanical torque, and transmits this torque through the axle assembly to the rear wheels.

Servo-piston (7) is mechanically connected to swashplate (12). Spring (4) holds servo-piston in position shown. This tilts swashplate as illustrated. This is the maximum displacement of the motor. This means that for a given input of high-pressure oil, output shaft (6) turns relatively slowly, but with a high torque.

High-pressure oil enters motor at inlet (8). Oil is routed to chamber (9) in piston block (10). Oil enters piston block, causing pistons to stroke outward. As pistons stroke, they push against swashplate (12). This causes pistons, piston block (10), and output shaft (6) to rotate.

Swashplate (12) is tilted so that as the unit rotates, the pistons become fully extended, then retract into the piston block. As pistons retract, they push low-pressure oil through chamber (2). Low-pressure oil exits motor at inlet (1).

Output shaft (6) transfers power from rear propel motor to axle assembly.

Case drain oil from propel pump enters motor at case drain inlet (3). Case drain oil from motor adds to this flow. All case drain oil exits motor at case drain outlet (11), and is routed through the vibratory pump to the hydraulic oil tank.

Reverse - LOW Speed Range

Rear Propel Motor in LOW Speed Range
(1) Inlet for reverse operation. (2) Chamber. (3) Case drain inlet. (4) Spring. (5) Stop. (6) Output shaft. (7) Servo-piston. (8) Inlet for forward operation. (9) Chamber. (10) Piston block. (11) Case drain outlet. (12) Swashplate. (13) Shift oil inlet.

Reverse operation in LOW speed range is similar to forward operation. Spring (4) holds servo-piston (7) and swashplate (12) in the maximum displacement position.

High-pressure oil enters motor at inlet (1). Oil is routed to chamber (2) in piston block (10). Oil enters piston block, causing pistons to stroke outward. As pistons stroke, they push against swashplate (12). This causes pistons, piston block (10), and output shaft (6) to rotate. Rotation is in the opposite direction from forward operation.

Swashplate (12) is tilted so that as the unit rotates, the pistons become fully extended, then retract into the piston block. As pistons retract, they push low-pressure oil through chamber (9). Low-pressure oil exits motor at inlet (8).

Output shaft (6) transfers power from rear propel motor to axle assembly.

Case drain oil from propel pump enters motor at case drain inlet (3). Case drain oil from motor adds to this flow. All case drain oil exits motor at case drain outlet (11), and is routed through the vibratory pump to the hydraulic oil tank.

Forward and Reverse - HIGH Speed Range

Rear Propel Motor in HIGH Speed Range
(1) Inlet for reverse operation. (2) Chamber. (3) Case drain inlet. (4) Spring. (5) Stop. (6) Output shaft. (7) Servo-piston. (8) Inlet for forward operation. (9) Chamber. (10) Piston block. (11) Case drain outlet. (12) Swashplate. (13) Shift oil inlet.

Rear propel motor operation in HIGH speed range is similar to operation in LOW speed range in both forward and reverse. The only difference is that the displacement of the motor is set differently. This increases the output speed of the motor, driving the rear wheels faster.

Hydraulic oil from the shift valve enters the rear propel motor at inlet (13). This oil is routed to the bottom of servo-piston (7). Oil moves servo-piston against stop (5), compressing spring (4). This tilts swashplate (12) to position shown. This is the minimum displacement of the motor. This means that for a given input of high-pressure oil, output shaft (6) turns faster, but with less torque then when in low speed range.

High-pressure oil enters motor at inlet (8) or (1). Oil is routed to piston block (10), causing pistons to stroke. Pistons, piston block, and output shaft rotate in the forward or reverse direction. Output shaft (6) transfers power from rear propel motor to axle assembly.

Axle Assembly

Axle Assembly
(1) Wheel end assembly. (2) Carrier. (3) Wheel end assembly. (4) End reduction case.

The axle assembly receives power from the rear propel motor. Axle components provide speed reductions and torque increases, then transmit power to the rear wheels, driving the machine.

End reduction case (4) receives power from the rear propel motor. The end reduction case provides a speed reduction and torque increase, and sends this power to the carrier (2).

Carrier (2) provides the second speed reduction and torque increase. Carrier contains a no-spin differential. The carrier sends power through the no-spin differential to the wheel end assemblies (1) and (3).

The rear wheels are attached to the two wheel end assemblies (1) and (3). The wheel end assemblies provide the final speed reduction and torque increase, driving the wheels and propelling the machine.

The following sections provide additional information on the end reduction case, carrier, no-spin differential, and wheel end assemblies.

End Reduction Case

End Reduction Case
(1) Case. (2) Input gear. (3) Cover. (4) Output gear.

The end reduction case provides a mechanical connection between the rear propel motor and the carrier. The end reduction case also provides a gear reduction, so the output rpm is less than the input rpm from the rear propel motor.

Rear propel motor is mounted to cover (3). The splined output shaft of the rear propel motor meshes with the internal splines of input gear (2). The teeth of the input gear mesh with the teeth of output gear (4). Case (1) is mounted directly to the carrier. Output gear (4) has internal splines which provide the connection to the carrier pinion shaft.

When the propel motor is operating, input gear (2) transfers power to output gear (4). The output gear is larger than the input gear, providing a reduction in output rpm to the carrier.

Carrier

Carrier
(1) Ring gear. (2) Case. (3) Pinion shaft. (4) No-spin f differential.

The carrier receives power from the end reduction case, and provides a speed reduction and a torque increase. The carrier transfers this power through a no-spin differential to the wheel end assemblies.

Pinion shaft (3) is connected by splines to the output gear in end reduction case. The beveled teeth of the pinion shaft are engaged with ring gear (1). Ring gear is secured to case (2). The no-spin differential assembly (4) is held inside case (2) by the spider part of the differential.

Power from the end reduction case turns pinion shaft (3). The pinion shaft causes ring gear (1) to rotate at a slower speed than the pinion shaft. The ring gear causes the attached case (2) and no-spin differential (4) to rotate at the same speed as the ring gear. The no-spin differential provides power to the two wheel end assemblies

No-Spin Differential

No-Spin Differential (Assembled)
(1) Side gear. (2) Driven clutch. (3) Spring. (4) Holdout ring. (5) Holdout ring. (6) Spring. (7) Driven clutch. (8) Side gear. (9) Spring retainer. (10) Spring retainer. (11) Center cam. (12) Snap ring. (13) Spider.

The no-spin differential allows the axle to send different torques to each rear wheel. When the speeds of the wheels are the same, the no-spin differential can send the same amount of torque to each wheel. When the speeds of the wheels are different (when the machine is turning) the no-spin differential sends the torque to the wheel that turns slower. If one wheel loses traction on ice or mud, both wheels turn at the same speed, but the spinning wheel will have less torque.

No-Spin Differential (Left Side Disassembled)
(1) Side gear. (2) Driven clutch. (3) Spring. (4) Holdout ring. (9) Spring retainer. (11) Center cam. (12) Snap ring. (13) Spider.

The no-spin differential is the same on one side of the spider as it is on the other side. The no-spin has two springs (3) and (6), two side gears (1) and (8), two driven clutches (2) and (7), two holdout rings (4) and (5), one center cam (11), one snap ring (12), and one spider (13).

Spider (13) is fastened to the carrier case and turns at the speed of the ring gear. The spider has clutch teeth on both sides. Spider also has one long tooth called the spider key (15). Center cam (11) fits inside spider and is held in position by snap ring (12). Center cam is turned by spider key (15) which fits inside notch (14).

Spider and Center Cam
(11) Center cam. (13) Spider. (14) Notch in center cam. (15) Spider key.

Driven clutches (2) and (7) are identical. Each driven clutch has a cam (17) which is part of the clutch. The teeth on the cam engage with the teeth of center cam (11). The teeth of the driven clutch engage with the clutch teeth on spider (13).

Clutch and Holdout Ring
(2) Driven clutch. (4) Holdout ring. (16) Notch in holdout ring. (17) Cam.

The holdout ring (4) sits in the driven clutch, in the groove between the teeth of the driven clutch and the teeth of the cam. The teeth of the holdout ring engage with the notches in the center cam. Notch (16) in the holdout ring engages with spider key (15). The spider key controls the movement of the holdout ring in relation to the spider. There is no connection between the holdout ring and the driven clutch except friction.

Springs (3) and (6) fit between the side gears and springs retainers (9) and (10). The outside splines of the spring retainers are connected to the inside splines of the driven clutches. The force of the springs hold the driven clutches against spider (13) and the side gears against the differential case.

The outside splines of side gears (1) and (8) are connected to the inside splines of driven clutches (2) and (7). The inside splines of the side gears are connected to the axle shafts of the wheel end assemblies.

Operation of No-Spin Differential

Straight Operation

Straight Operation
(1) Side gear. (2) Driven clutch. (7) Driven clutch. (8) Side gear. (13) Spider. (18) Teeth of the spider. (19) Teeth of the driven clutches.

When the machine drives straight forward (or backward) on solid ground, both wheels provide tractive effort in moving the machine. Teeth (18) on both sides of the spider (13) are fully engaged with teeth (19) of driven clutches (2) and (7). The teeth of cams (17) engage with teeth of center cam (11).

In this fully engaged condition, spider (13) turns both driven clutches and side gears at the same speed as the ring gear. The two side gears provide power to the axle shafts of the wheel end assemblies.

Operation While Turning

Operation While Turning
(1) Side gear. (2) Driven clutch. (7) Driven clutch. (8) Side gear. (13) Spider.

When the machine enters into a turn, the travel of the outside wheel is further than the travel of the inside wheel. The traction of the road forces the outside wheel to turn faster than the speed of the ring gear. This movement of one wheel turning faster than the other wheel starts the "clutch action" of the no-spin differential.

The faster wheel causes side gear (1), and driven clutch (2) to turn faster than the ring gear. The teeth of center cam (11) work like ramps and the teeth of cam (17) move up the teeth of center cam (11).

This action causes driven clutch (2) to become disengaged with the spider. The driven clutch pulls holdout ring (4) out of the grooves in the center cam. The friction between the holdout ring and driven clutch turns the holdout ring until notch (16) in the holdout ring engages with spider key (15).

The holdout ring is now turned by the spider key at the speed of the ring gear. The teeth of the holdout ring are in a position so they can not engage the notches in the center cam. The driven clutch and cam moves around the holdout ring at a speed faster than the ring gear. The holdout ring keeps the driven clutch and cam from engaging with the center cam and spider. The driven clutch, cam, drive axle, and wheel now turn freely.

On the opposite side of the spider, driven clutch (7) and side gear (8) are fully engaged with the spider. The teeth of the spider send the drive force to this engaged driven clutch and side gear. This provides the driving force of the machine to the inside wheel.

When the turn is finished, the speed of the disengaged wheel slows to nearly the speed of the ring gear. The resistance of the ground to the wheel causes the torque on this wheel to be in a small reverse direction. This causes the driven clutch and cam to turn in a direction opposite the direction of the ring gear.

The friction between the holdout ring and the driven clutch causes the holdout ring to move in a direction opposite the direction of the ring gear. Notch (16) in the holdout ring moves away from spider key (15). When the teeth of the holdout ring are in a position to engage the notches in center cam (11), the force of the spring pushes the driven clutch and cam to the inside. The driven clutch pushes the holdout ring.

The holdout ring now engages the center cam and is turned at the speed of the ring gear. The teeth of cam (17) now engage the center cam and the teeth of the drive clutch engage the spider. At this time, both wheels are turned at the same speed.

Wheel End Assembly

Wheel End Assembly
(1) Spider. (2) Planetary shaft. (3) Ring gear. (4) Planetarygear. (5) Axle shaft. (6) Wheel hub. (7) Sun gear.

The two wheel end assemblies, one for each wheel, provide the final speed reduction and torque increase in the wheel propel system. Each wheel end assembly has the same components.

Axle shaft (5) is connected to the no-spin differential by splines at one end. The other end of axle shaft is connected by splines to sun gear (7). Sun gear is engaged with three planetary gears (4). Planetary gears are held inside ring gear (3), and are mounted to spider (1) with planetary shafts (2). Ring gear (3) is secured to the axle, and does not rotate. Spider (1) is secured to wheel hub (6). The rear wheel is mounted to the wheel hub.

Power from the differential turns axle shaft (5). The axle shaft turns sun gear (7). Sun gear turns planetary gears (4). Since ring gear (3) is held stationary to the axle, the planetary gears move around the inside of ring gear. The movement of the planetary gears causes spider (1) to turn. The spider turns wheel hub (6) and the attached rear wheel, in the same direction as sun gear (7), but at a slower speed.

Each wheel end assembly has its own oil supply. All components get lubrication as the gears move and oil is thrown about (splash lubrication).

Shift Valve

Shift Valve
(1) Working port. (2) Cartridge. (3) Inlet port. (4) Coil. (5) Tank port.

The shift valve is an electrically-operated two-position solenoid valve. The shift valve is used to shift the displacement of the front gear reducer motor and the rear propel motor, giving the machine a HIGH and a LOW speed range.

Inlet port (3) is connected to the shift oil outlet of the propel pump. Working port (1) is connected to the front gear reducer and the rear propel motor. Tank port (5) is connected to a return line leading to the hydraulic oil tank.

When the speed range shift switch (on instrument panel) is in LOW, coil (4) is de-energized. Hydraulic oil from the propel pump enters the shift valve at inlet port (3). This oil is under charge pressure, 1655 to 2140 kPa (250 to 310 psi). Hydraulic oil from port (3) is blocked at cartridge (2). Working port (1) is open to tank port (5), draining shift pressure from front gear reducer and rear propel motor to hydraulic oil tank. This causes front gear reducer motor and rear propel motor to remain in their normal LOW speed range.

When the operator moves the speed range shift switch to HIGH, coil (4) is energized. This moves a spool inside cartridge (2). Hydraulic oil from the propel pump enters the shift valve at inlet port (3). This oil is routed through cartridge (2), and exits the shift valve at working port (1). Oil is routed from working port to the front gear reducer motor and the rear propel motor, shifting their displacements to create the HIGH speed range.

Cooling and Test Manifold

Cooling and Test Manifold in Off Position
(1) Test port X7. (2) Orifice. (3) Test port X5. (4) Port E. (5) Port D. (6) Test port X8. (7) Orifice. (8) Test port X6. (9) Port F. (10) Chamber. (11) Right side of shuttle valve. (12) Relief valve. (13) Passage from vibratory part of manifold. (14) Port C. (15) Chamber. (16) Spring. (17) Left side of shuttle valve spool. (18) Shuttle valve spool. (19) Port T.

The cooling and test manifold is connected to the high-pressure side and the low-pressure side of the propel system, and the vibratory system. Its purpose is to remove hot, used hydraulic oil from the low-pressure side of the pump at a controlled rate. This allows fresh charge oil to enter the system regularly.

The propel part of the cooling and test manifold operates independently of the vibratory part (though they share a common return to the hydraulic oil tank).

Reference: Operation of the vibratory part of the cooling and test manifold is covered in Vibratory Systems Operation Testing and Adjusting, Form No. KEBR2360.

The propel part of the cooling and test manifold consists of a shuttle valve spool (18), a spring (16), and a relief valve (12). These parts are installed in an aluminum manifold. Port (4) and port (5) are connected to the drum propel loop. Port (14) and port (9) are connected to the wheel propel loop.

Test ports (3), (6), (1), and (8) have quick disconnect fittings. These test ports are used to measure the pressure at ports (4), (5), (14), and (9) respectively. Port (19) is connected to a return line which leads through an oil cooler and hydraulic return filter, to the hydraulic oil tank.

Reference: For information on the oil cooler and hydraulic return filter, see Steering System Operation Testing and Adjusting, Form No. KEBR2249.

Cooling and Test Manifold Operation

Cooling and Test Manifold in Off Position
(1) Test port X7. (2) Orifice. (3) Test port X5. (4) Port E. (5) Port D. (6) Test port X8. (7) Orifice. (8) Test port X6. (9) Port F. (10) Chamber. (11) Right side of shuttle valve. (12) Relief valve. (13) Passage from vibratory part of manifold. (14) Port C. (15) Chamber. (16) Spring. (17) Left side of shuttle valve spool. (18) Shuttle valve spool. (19) Port T.

System Off

When the propel system is off, there is no high-pressure output oil from either section of the tandem propel pump. Thus, there is no high-pressure and low-pressure side of the pump - only charge pressure.

Charge pressure from the drum propel loop enters the manifold at port (4) and port (5). Charge pressure from the wheel propel loop enters the manifold at port (14) and port (9).

Charge pressure from port (4) and port (14) is routed to the left side of shuttle valve spool (17), to chamber (15), to test port (3), and to test port (1).

Charge pressure from port (5) and port (9) is routed to the right side of shuttle valve spool (11), to chamber (10), to test port (6), and to test port (8).

Because the charge pressure is equal at both sides of the shuttle valve spool, spring (16) holds the shuttle valve spool (18) in the centered (closed) position. This blocks charge oil at chambers (15) and (10), preventing any oil flow through the manifold when the propel system is off.

System On - Forward

Cooling and Test Manifold in Forward Position
(1) Test port X7. (2) Orifice. (3) Test port X5. (4) Port E. (5) Port D. (6) Test port X8. (7) Orifice. (8) Test port X6. (9) Port F. (10) Chamber. (11) Right side of shuttle valve. (12) Relief valve. (13) Passage from vibratory part of manifold. (14) Port C. (15) Chamber. (16) Spring. (17) Left side of shuttle valve spool. (18) Shuttle valve spool. (19) Port T.

High-pressure oil from the wheel propel loop enters the manifold at port (14). This oil is routed to the left side of shuttle valve spool (17), to chamber (15), and to test port (1). High-pressure oil from the drum propel loop enters the manifold at port (4). This oil is routed directly to test port (3), and to orifice (2). Oil passes through orifice, and joins the high-pressure oil from port (14).

Low-pressure oil from the drum propel loop enters the manifold at port (5). This oil is routed to the right side of shuttle valve spool (11), to chamber (10), and to test port (6). Low-pressure oil from the wheel propel loop enters the manifold at port (9). This oil is routed directly to test port (8) and to orifice (7). Oil passes through orifice, and joins the low-pressure oil from port (5).

High-pressure oil from ports (14) and (4) overcomes force of spring (16) and low-pressure oil from ports (5) and (9). This causes shuttle valve spool (18) to shift to the right. High-pressure oil at chamber (15) is blocked. Low-pressure oil at chamber (10) flows through slots in shuttle valve spool to the relief valve (12). The low-pressure oil opens the relief valve, allowing a controlled amount of oil to exit the cooling and test manifold through port (19).

Note that low-pressure oil from port (5) is routed directly to chamber (10), but oil from port (9) must pass through orifice (7) first. This orifice restricts flow from port (9), allowing most flow through manifold to come from port (5). Thus, when the machine is traveling forward, most cooling oil comes from the drum propel loop.

Oil leaving the manifold passes through an oil cooler and a hydraulic return filter (both are part of the machine steer system). This return oil is then routed to the hydraulic oil tank.

System On - Reverse

Cooling and Test Manifold in Reverse Position
(1) Test port X7. (2) Orifice. (3) Test port X5. (4) Port E. (5) Port D. (6) Test port X8. (7) Orifice. (8) Test port X6. (9) Port F. (10) Chamber. (11) Right side of shuttle valve. (12) Relief valve. (13) Passage from vibratory part of manifold. (14) Port C. (15) Chamber. (16) Spring. (17) Left side of shuttle valve spool. (18) Shuttle valve spool. (19) Port T.

Cooling and test manifold operation for reverse is similar to that for forward operation, except the high-pressure and low-pressure sides of the propel pump are switched around.

High-pressure oil from the drum propel loop enters the manifold at port (5). This oil is routed to the right side of shuttle valve spool (11), to chamber (10), and to test port (6). High-pressure oil from the wheel propel loop enters the manifold at port (9). This oil is routed directly to test port (8), and to orifice (7). Oil passes through orifice, and joins the high-pressure oil from port (5).

Low-pressure oil from the wheel propel loop enters the manifold at port (14). This oil is routed to the left side of shuttle valve spool (17), to chamber (15), and to test port (1). Low-pressure oil from the drum propel loop enters the manifold at port (4). This oil is routed directly to test port (3), and to orifice (2). Oil passes through orifice, and joins the low-pressure oil from port (14).

High-pressure oil from ports (5) and (9) overcomes force of spring (16) and low-pressure oil from ports (14) and (4). This causes shuttle valve spool (18) to shift to the left. High-pressure oil at chamber (10) is blocked. Low-pressure oil at chamber (15) flows through slots in shuttle valve spool to the relief valve (12). The low-pressure oil opens the relief valve, allowing a controlled amount of oil to exit the cooling and test manifold through port (19).

Note that low-pressure oil from port (14) is routed directly to chamber (15), but oil from port (4) must pass through orifice (2) first. This orifice restricts flow from port (4), allowing most flow through manifold to come from port (14). Thus, when the machine is traveling in reverse, most cooling oil comes from the wheel propel loop.

Oil leaving the manifold passes through an oil cooler and a hydraulic return filter (both are part of the machine steer system). This return oil is then routed to the hydraulic oil tank.