Introduction

Reference: For Specifications with illustrations, refer to the Specifications for the CB-534 Propulsion System, Form No. KENR2420. If the Specifications in Form No. KENR2420 are not the same as listed in the Systems Operation and the Testing And Adjusting, look at the print date on the back cover of each book. Use the Specifications listed in the book with the latest date.

Propulsion System

General Information

Propulsion Circuit Schematic
(1) Hydraulic tank. (2) Hydraulic filter. (3) Front drum hydraulic motor. (4) Propulsion control lever. (5) Solenoid valve for brake system and propulsion control lever pilot circuit. (6) Motor displacement changeover solenoid valve. (7) Rear drum hydraulic motor. (8) Propulsion pump group.

The propulsion system is a hydrostatic system. The main components of the system are hydraulic tank (1), hydraulic filter (2), propulsion pump group (8), front and rear hydraulic motors (3) and (7), propulsion control lever (4), solenoid valve (5) and hydraulic motor displacement changeover solenoid valve (6).

Hydraulic Tank And Filter Location
(1) Hydraulic tank. (2) Hydraulic filter. (9) Pressure drop indicator.

Hydraulic filter (2) is installed horizontally in hydraulic tank (1). Oil for the propulsion, vibration, steering and brake circuits passes through this filter.

Hydraulic Filter Group
(10) Filter cartridge. (11) By-pass spring. (12) Cartridge face.

All the return line oil enters the tank. All of the oil goes through filter cartridge (10), before going to the different circuits.

When filter cartridge (10) is plugged or when the oil is cold, there is a pressure build-up inside the cartridge. This pressure goes against the walls of the filter and the base of the cartridge. Spring (11), set at 100 kPa (15 psi) is compressed, moving the cartridge along with it. The oil will then flow around the end of cartridge face (12), down the outside of the cartridge, and out to the pumps.

Pressure drop indicator (9) is mounted on the filter output line. A pressure drop is caused between the filter and pump when cartridge (10) becomes plugged. This drop in pressure acts on the membrane of pressure drop indicator (9). An electric circuit opens which in turn lights up a warning lamp on the dashboard.

Pressure drop indicator (9) is set at 30 kPa (4.5 psi). Its setting is less than the filter by-pass valve. If the warning light comes on, the filter cartridge must be replaced immediately. Otherwise, the by-pass valve will open and oil will flow from the tank into the different circuits without being filtered.

Pump Group
(8) Propulsion pump section. (13) Vibration pump section.

A dual circuit pump is used for both propulsion and vibration functions. Both sections of the pump are for closed circuit operation. They are independent to one another and are of the axial piston swashplate design.

Propulsion pump section (8) has variable displacement. Vibration pump section (13) is also the variable displacement type, but is used as a fixed displacement pump.

In addition to this dual pump group, there is a small gear type pump installed directly on the engine. It is used for the steering function of the machine. All of the engine output (horsepower) of the compactor is used to turn these pumps.

Propulsion Pump

Dual Pump Group
(1) Vibration pump. (2) Splitter box. (3) Propulsion pump.

Propulsion pump (3), which is part of the dual pump group, is installed at the rear of the engine. It is driven through splitter box (2). The rpm of the propulsion pump is identical to vibration pump (1). The rpm of each pump under load is approximately 1.47 times the engine rpm. Any change in engine rpm will automatically and simultaneously change the rpm of the pumps.

Propulsion Pump
(4) Closed circuit loop line port. (5) Portplate. (6) Hydraulic regulator. (7) Direction control valve. (8) Cup. (9) Shims. (10) Main case. (11) Drive shaft. (12) Charge pump. (13) Passage. (14) Closed circuit loop line port. (15) Head. (16) O-ring. (17) Piston (one of nine). (18) Cylinder barrel. (19) Spring washer. (20) Swashplate. (21) Bearing housing.

Each charge pump (12) has an independent gravity-fed oil supply line from the hydraulic tank. When the engine is running, drive shaft (11), cylinder barrel (18) and charge pump (12) drive gears turn. There are nine cylinders and pistons in the barrel assembly. The remainder of the components of the pump are fastened to or are held by the pump housing.

Swashplate And Barrel Assemblies
(17) Piston. (18) Cylinder barrel. (19) Spring washer. (20) Swashplate.

In the position shown, swashplate (20) could be at any angle between maximum and minimum. Shaft (11) turns cylinder barrel (18). Each piston (17) follows the angle of swashplate (20). As the pistons follow the angle of the swashplate, they move in and out of the cylinders in the barrel. As the piston moves out of the cylinder, oil is supplied behind it. This oil is delivered under pressure from charge pump (12) through passage (13).

Oil that is pushed ahead of the piston goes through outlet passages of portplate (5) and leaves the pump through loop line ports (4) and (14). Portplate (5) and cylinder barrel (18) valve surfaces are spherical in shape. Inlet oil is sealed from outlet oil by a metal-to-metal seal between the spherical faces of the portplate and cylinder barrel. On the other face of the portplate, the seal is made with the face of head (15). O-ring (16) seals head (15) from main case (10). Since outlet pressures can be as high as 42 000 kPa (7000 psi), the sealing faces must be made with precision. No damage is permissible. Protection must be given to these faces during disassembly and assembly.

Spring washers (19) and shims (9) are held in place on swashplate (20) by cup (8). The compression of the springs is the force which holds the face of cylinder barrel (18) against portplate (5) and head (15).

Spring Assembly
(8) Cup. (9) Shims. (18) Cylinder barrel. (19) Spring washer.

The length of piston stroke is changed when swashplate (20) is turned around its axis. At vertical (neutral) position, the piston stroke and oil delivery is zero. At maximum inclination of ± 15°, the piston stroke is at its maximum.

Charge And Main Line Relief Valves

Charge And Main Line Relief Valves
(22) Charge pump circuit relief valve. (23) Main line relief valve. (24) Main line relief valve.

Charge Relief Valve

Charge pump oil delivers cooled filtered oil from the tank to the variable displacement pump. It is also used for various other tasks. These include hydraulic piloting of hydraulic regulator (6), piloting direction control solenoid valve (7), releasing the parking brakes, piloting the motor displacement changeover spool and compensating for internal oil leakage inside the closed circuit loop lines. Both pilot and loop circuit return line pressure is limited to 2200 kPa (320 psi) by relief valve (22).

Charge Pump Circuit Relief Valve
(25) Adjustment screw. (26) Locknut. (27) Spring. (28) Valve. (29) Outlet passage to tank. (30) Inlet passage.

Oil from charge pump (12) enters the valve through inlet passage (3). When circuit oil pressure is less than the relief valve setting, the force of spring (27) keeps valve (28) closed. When the oil pressure reaches the relief valve setting, valve (28) will move and allow oil to flow through outlet passage (29) into the tank return line.

Main Line Relief Valves
(31) Passage. (32) Valve surface. (33) Valve surface. (34) Pressure relief valve section. (35) Spring. (36) Nut. (37) Valve surface. (38) Dump valve section. (39) Passage. (40) Spring. (41) Passage. (A) Passage. (B) Passage.

The maximum working pressure of each loop line of the closed circuit is limited to 42 000 kPa (7000 psi) by two relief valves. There is one for each loop line. These valves are the indirect-acting type. They limit the main circuit pressure to specified values which can be changed by adjusting the valve setting. Each indirect-acting valve group is made up from two valves. They are pressure relief valve section (34) and dump valve section (38).

Oil from the propulsion pump enters the valve group through passage (A). Oil passes through passage (31), in the center of dump valve (38), and into the chamber that contains spring (40). The oil pressure acts against pressure relief valve (34). The force of spring (35) keeps valve (34) closed until oil pressure in the loop line reaches relief pressure. Dump valve (38) also remains closed. The oil pressure acts on both dump valve surfaces (33) and (37). Surface (33) is larger than surface (37). The force exerted on this surface (33) is therefore greater. The combination of this force plus the force of valve spring (35) will keep dump valve (38) closed. When the oil pressure reaches the relief valve setting, relief valve (34) will open. Oil, which is in the chamber that contains spring (40), passes around relief valve (34). Oil then flows through passage (41) and into the return line of the loop circuit.

When there is a drop in oil pressure in the chamber of spring (40), only the force of spring (40) is acting against dump valve (38). The force acting on the opposite face of the valve is greater. Therefore the valve will open. Delivery line oil from inlet passage (A) can now go through passage (39) into the return line of the closed circuit.

This valve group also has a secondary function. It acts as a check valve for the charge pump circuit. When the propulsion control lever is in neutral, only the charge pump is delivering oil. Charge pump oil can only enter the loop lines of the closed circuit by passing through dump valve section (38) of the main relief valve. Charge circuit relief valve limits the line pressure to 2200 kPa (320 psi). Pressure oil arriving at passage (B), acts on dump valve surface (32). The force acting on this surface is greater than the force exerted by spring (40). Dump valve (38) opens. Charge pump oil passes around valve (38), into passage (A), and into the loop lines of closed circuit.

When the propulsion control lever is moved either to the forward or reverse travel mode, the relief valves on the pump delivery and the return lines will be closed. Dump valve section (38) of the relief valve on the return line of the circuit will continue its secondary function. It will open and allow charge pump oil into the return line to compensate for oil loss through internal leakage.

Hydraulic Regulator And Direction Control Valve

Hydraulic Regulator And Direction Control Valve Location
(6) Hydraulic regulator. (7) Direction control valve.

Swashplate movement and inclination angle is controlled by hydraulic regulator (6) and direction control valve (7). Both valves are activated by oil pressure from the charge pump circuit.

Movement of the propulsion control valve will allow oil to pilot direction control valve (7). The pressure oil will move the valve spool allowing oil to pass across it out into one of the pilot lines to hydraulic regulator (6).

Direction Control Valve
(42) Port. (43) Tension spring arms. (44) Tension spring. (45) Stop. (46) Spool. (47) Port. (48) Spool control arm. (49) Tension spring arm pivot. (50) Feedback lever.

As soon as pressure oil arrives at port (42) or (47) it will cause spool (46) to move. Arm (43) opposite to the port which receives pressure oil, will be forced open by spool control arm (48). Spring (44) will then be under tension. This tension is proportional to the pressure found in the line which pilots the spool. Pressure oil passes across the spool of the direction control valve into chamber (52) of the hydraulic regulator, causing piston (51) to move. Piston movement is regulated by the signal sent through feed-back lever (50) from tension spring (44) and arms (43).

Hydraulic Regulator
(51) Piston. (52) Piston chamber.

When piston (51) moves, it draws feed-back lever (50) along with it. Movement of the feed-back lever will cause the following:

a. Stop (45) causes a follow-through pivoting action of tension spring arms (43) in the opposite direction to the movement of piston (51). The spring tension which was originally determined by the initial opening of one of the spring arms is maintained.

b. Spool control arm (48) will also move as feedback lever (50) moves. As control arm (48) moves, it draws spool (46) back towards its neutral position.

Regulator Block And Propulsion Control Lever

Regulator Block And Propulsion Control Lever
(1) Propulsion control lever. (2) Stop control. (3) Rotary selector.

Modulation of the oil flow from the propulsion pump to the two hydraulic drive motors is controlled by propulsion control lever (1) and rotary selector (3). They are a part of regulator block (4). Oil from the charge pump circuit is used for the hydraulic piloting functions of these controls.

Regulator Block And Propulsion Control Lever Schematic
(3) Rotary selector. (4) Regulator block. (5) Reducing valve. (6) Reducing valve. (7) Propulsion control valve. (8) Restrictor orifices. (9) Check valve. (10) Check valve. (11) Tank return line. (12) Output line port. (13) Output line port. (14) Inlet port.

Oil from the charge pump arrives at inlet port (14) of propulsion control valve (7) at 2200 kPa (320 psi). It passes through control valve (7) into regulator block (4). It then flows behind the two pressure reducing valves (5) and (6). When the control lever of the propulsion control valve is in neutral (middle position), pilot oil is blocked at the two reducing valves. Movement of control lever (1) forward or backward allows pressure oil to flow through one of the two reducing valves.

Pressure reducing valves (5) and (6) reduce the inlet pressure to an output line pressure proportional to lever movement of control valve (7). Minimum outlet pressure from reducing valves is 500 kPa (72 psi). Maximum pressure is 1900 kPa (275 psi).

The outlet line oil from reducing valves (5) and (6) passes through 1.0 mm (.04 in) restrictor orifices (8). These orifices slow down the flow which has been determined by the propulsion control valve. The machine reacts by starting or stopping in a smooth progressive manner.

After passing through one or another of restrictor orifices (8), the oil leaves regulator block (4) by either port (12) or (13). Oil flows towards the direction control valve mounted on the propulsion pump.

Rotary selector (3) of regulator block (4) controls the output line oil pressure at ports (12) and (13). When rotary selector (3) is in the closed position (turned fully in a clockwise direction), the oil pressure will be at a maximum of 1900 kPa (275 psi). When fully turned in a counterclockwise direction, the selector will be fully open. In the open position, oil will cause check valve (10) to close on the tank return line and open on the feed line passage. Oil will then pass through rotary selector (3). Check valve (9), which is set at 450 kPa (66 psi), will open. The oil now returns to the tank through port (12).

A minimum pressure of 450 kPa (66 psi) will be found in the output line to the direction control valve mounted on the propulsion pump. Low output pressure through port (12) or (13) will give minimum inclination of the pump's swashplate. This will cause low pump delivery rate resulting in low travel speed. Higher output pressures from these ports will increase the angle of the swashplate. This will cause higher pump delivery rate and higher travel speeds.

Solenoid Valves

Solenoid Valves Location
(1) Propulsion motor, displacement changeover control solenoid valve. (2) Parking brake and propulsion control lever solenoid valve.

Charge pump oil arrives at two solenoid valves mounted just under the main suction filter. Valve (2) is used to control the brake release circuit and at the same time, pilot the propulsion control lever. Valve (1) is used to control the displacement changeover of the rear propulsion motor.

Stop Control And Propulsion Control Lever
(3) Propulsion control lever. (4) Stop control. (5) Travel speed range selector switch.

When stop control (4) is pushed down, electrical flow to solenoid valves (1) and (2) is stopped.

Solenoid Valve
(6) Spring. (7) Spool valve. (8) Solenoid. (A) Inlet line port. (B) Outlet line port.

NOTE: Both solenoid valves are explained below. The above drawing is used for both of them. The internal components of the solenoid valves are identical.

The operation of the solenoid valve for the parking brake and propulsion lever is as follows. When solenoid (8) is not energized, spring (6) will push spool valve (7) so that the flow of oil between inlet port (A) and outlet port (B) is stopped. Oil from the charge pump circuit flowing to inlet port (A) of the solenoid valve will be blocked. The pilot lines to the brakes and the propulsion control valve are connected directly to the tank return port. The pressure will drop in the pilot lines and then the multi-disc brake will be applied by spring force. At the same time, the swashplate of the propulsion pump will automatically return to neutral.

As soon as stop control valve (4) is pulled up, solenoid (8) will become energized. This causes spool (7) to move, which allows oil to pass across the spool from port (A) into port (B) and out into the parking brake pilot lines. The 2200 kPa (320 psi) pressure oil overcomes the force of the spring and releases the brakes.

The operation of the solenoid valve for the displacement (speed range) changeover of the rear propulsion motor is as follows. The displacement changeover solenoid is activated by travel speed range selector switch (5). At low travel speed range selection, solenoid (8) is not energized. Spring (6) will push spool valve (7) so that the passage of oil between inlet port (A) and outlet port (B) is stopped. Oil from the charge pump circuit flowing to inlet port (A) of solenoid valve will be blocked. The pilot line to propulsion motor displacement changeover spool valve will be connected directly to the tank return port. The pressure will drop in the pilot line. Spring force will position the changeover spool in the LARGE displacement position.

Movement of switch (5) to the high travel speed position will energize solenoid (8). This moves spool valve (7) allowing oil to pass across the spool from port (A) into port (B) and out into the motor displacement changeover pilot line. The 2200 kPa (320 psi) pressure oil overcomes the force of the spring and positions the changeover spool in the SMALL motor displacement. When stop control (4) is pulled up, solenoid (8) will become energized. This causes spool (7) to move, allowing oil to pass across the spool. This machine is now in the slow travel speed range (high displacement).

Propulsion Motor

Propulsion Motor
(1) Valve group. (2) Brake group. (3) Transmission case. (4) Drum flange. (5) Motor group. (6) Hub. (A) Port. (B) Port.

A slow speed hydraulic motor is mounted on each drum of the compactor. Hub (6) supports the motor and drum assembly to the side frames. Transmission case (3) is bolted directly onto drum flange (4). This gives a direct final drive.

The major sections of the propulsion motor are:

(1) Valve group. The valve group controls the motor. The valve group receives oil from passages in hub (6) and directs it towards motor group (5). There are two types of motors. They are single or dual displacement. A dual displacement motor can operate in either large or small displacement depending on the position of the displacement changeover spool which is part of valve group (1).

(2) Brake group. Transmission (3) case is braked mechanically by a multi-disc brake group. The brake is applied by spring force and released by hydraulic oil.

(3) Transmission Case. The mechanical energy of motor group (5) is transmitted to the external transmission case. This provides a direct final drive to the drums of the compactor.

(5) Motor group. The motor group receives oil from valve group (1). The motor group converts the pressurized oil into mechanical energy in the form of torque and speed.

(6) Hub assembly. All the hydraulic circuit hoses for the closed circuit, displacement changeover spool, brake release and motor case drain are connected to the hub section of the motor. Passages inside the hub shaft direct oil to the different components of the motor.

Motor Operation

Oil Distribution (Shown With Motor In Clockwise Rotation)
(1) Hub shaft. (2) Distributor housing. (3) External distributor. (4) Screws. (5) Internal distributor. (6) Sealing rings. (7) Displacement changeover spool. (A) Supply or return passage. (B) Supply or return passage. (T) Internal leakage tank return line passage. (Y) Motor displacement changeover spool pilot line passage. (X) Brake release pilot line passage.

Oil distribution is done by two parts:

1. Internal distributor (5) which remains stationary and is mounted to shaft (1) by four screws (4).

2. External distributor (3) which rotates and is mounted to distributor housing (2). Rings (6) ensure sealing between the internal and external distributors. Motor displacement is changed by means of spool (7).

Slow Speed Range

Clockwise Motor Rotation

Oil coming from the propulsion pump enters hydraulic motor through port (A). It then passes through the passage in shaft (1) towards internal distributor (5). Displacement changeover spool (7) is not piloted. External distributor (3) is supplied with oil through passages (C) and (D).

Oil Flow In Distributors, Clockwise Rotation, Slow Speed Range
(3) External distributor. (5) Internal distributor. (7) Displacement changeover spool. (A) Supply or return passage. (B) Supply or return passage. (C) Passages. (D) Passages. (E) Passages.

When motor displacement spool (7) is in the position shown, six passages (C) and (D) have high pressure oil passing through them. This high pressure oil flows to the cylinder block. Six passages (E) have return oil from the cylinder block.

Counterclockwise Motor Rotation

High pressure oil coming from the propulsion pump enters hydraulic motor through port (B). It flows through internal distributor (5) and enters external distributor (3) at passages (E). Passages (C) and (D), which were formerly supplied with high pressure oil, now have return oil passing through them. Since the supply has been reversed, the hydraulic motor turns in the opposite (counterclockwise) direction.

Oil Flow In Distributors, Counterclockwise Rotation, Slow Speed Range
(3) External distributor. (5) Internal distributor. (7) Displacement changeover spool. (A) Supply or return passage. (B) Supply or return passage. (C) Passages. (D) Passages. (E) Passages.

Motor Case Drive

Motor Case Drive
(3) External distributor. (5) Internal distributor. (8) Cylinder block. (9) Drive disc. (10) Hub flange. (11) Motor case. (12) Cam. (13) Pistons.

As pistons (13) move on the cam surface, cam (12) will rotate. Motor case (11) will also rotate. Since hub flange (10) is driven by the case, the machine will now move. Drive disc (9) is pinned to both the motor case and external distributor (3). This causes the external distributor to rotate with the motor case. As the external distributor rotates, the pistons in cylinder block (8) move the oil in the supply and return lines of the closed circuit.

Hydrostatic Compensation

Motor Case Drive
(3) External distributor. (5) Internal distributor. (6) Sealing rings. (8) Cylinder block. (14) Springs.

When the motor is not supplied with high pressure oil, external distributor (3) is held against cylinder block (8) by springs (14).

When high pressure oil is sent through one or more of the passages in internal distributor (5), the pressure is felt by external distributor (3) at the surfaces between sealing rings (6). The pressure at these surfaces will push the external distributor against the cylinder block. The higher the pressure in the passages, the more force is applied to the external distributor. The sealing system keeps internal leakage to a minimum.

Cylinder Block, Clockwise Rotation

External distributor (3) has twelve equally spaced oil passages (C), (D) and (E). These twelve passages allow pressure oil or return line oil to be fed to and from the different piston chambers. Cylinder block (8) has ten equally spaced openings (F). Each opening is connected to a chamber of one of the pistons.

Oil Flow In Cylinder Block, Clockwise Rotation
(3) External distributor. (5) Internal distributor. (8) Cylinder block. (12) Cam. (13) Pistons. (C) Passage. (D) Passage. (E) Passage. (F) Passage.

Six passages (C) and (D), of external distributor (3), are supplied with high pressure oil. Only four of these passages are connected with four passages (F) of cylinder block (8). The other two passages are located between two of the passage openings in cylinder block (8) and are temporarily sealed.

The same applies to six return line passages (E). Of ten passages (F) of cylinder block (8), two are located between high and low pressure passage openings in external distributor (3), and are therefore sealed off.

Oil Flow From Cylinder Block To Pistons, Clockwise Rotation
(3) External distributor. (5) Internal distributor. (7) Displacement changeover spool. (8) Cylinder block. (11) Motor case. (12) Cam. (13) Pistons. (C) Passage. (D) Passage. (E) Passage.

At slow speed range, the motor will always have:

a. Four pistons (13) supplied with high pressure oil. The action of these pistons with cam (12) provide the motor torque.

b. Four pistons connected with the return line of the loop circuit.

c. Two pistons in neutral.

The number of pistons in contact with high pressure oil determines the direction of rotation of the motor. When the oil flow is reversed, the motor is also reversed. All of the motor components work the same as with clockwise motor rotation. Pistons (13), which were supplied with high pressure oil, are now connected to the return line. The pistons which were open to the return line for clockwise motor rotation are now under high pressure. The reverse action of the pistons on cam (12) causes motor case (11) to turn counterclockwise.

High Speed Range

Clockwise Motor Rotation

Oil Flow In Distributors, Clockwise Rotation, High Speed Range
(3) External distributor. (5) Internal distributor. (7) Displacement changeover spool. (A) Supply or return passage. (B) Supply or return passage. (C) Passage. (D) Passage. (E) Passage. (Y) Displacement changeover spool pilot line passage.

High speed range is obtained by piloting spool (7) through passage (Y) with charge pump circuit oil. The high speed range isolates passages (C) from (D) and (E). Passages (D) and (E) are now connected.

High pressure oil enters distributor (5) from passage (A). The internal distributor sends the oil to three passages (C) in external distributor (3). Passages (C) direct the high pressure oil to the cylinder block. Return oil from the cylinder block flows through nine passages (D) and (E). The oil then goes into the return line of the loop circuit through passage (B).

Counterclockwise Motor Rotation

Oil Flow In Distributors, Counterclockwise Rotation, High Speed Range
(3) External distributor. (5) Internal distributor. (7) Displacement changeover spool. (A) Supply or return passage. (B) Supply or return passage. (C) Passage. (D) Passage. (E) Passage. (Y) Displacement changeover spool pilot line passage.

Passages (C), which previously supplied high pressure oil to the cylinder block, now become the return lines. The return oil flows from passages (C) into the internal distributor and leaves through passage (A). Passages (D) and (E) are supplied with high pressure oil. The high pressure oil is sent to the cylinder block. The flow has been reversed, causing the hydraulic motor to turn in the opposite direction.

Cylinder Block, Clockwise Rotation

Oil Flow In Cylinder Block, Clockwise Rotation
(3) External distributor. (8) Cylinder block. (C) Passage. (D) Passage. (E) Passage. (F) Passage.

Of twelve passages (C), (D) and (E) inside external distributor (3), three will have high pressure oil passing through them. Nine will have return oil. Of three passages (C) under high pressure, two are connected with two passages (F) in cylinder block (8). The third passage is temporarily sealed off in a neutral position. Of nine passages (D) and (E) under low pressure, six are connected with three passages (F) in cylinder block (8). The other three are located between the other cylinder block passages.

Of the ten passages in the cylinder block, two are located between passages in distributor (3) and are therefore sealed off in neutral. Two passages are connected with the high pressure oil delivery line. Six passages are connected with the low pressure return line.

Oil Flow From Cylinder Block To Pistons, Clockwise Rotation
(3) External distributor. (5) Internal distributor. (7) Displacement changeover spool. (8) Cylinder block. (11) Motor case. (12) Cam. (13) Pistons. (C) Passage. (D) Passage. (E) Passage.

Cylinder Block, Counterclockwise Rotation

Oil Flow in Cylinder Block, Counterclockwise Rotation
(3) External distributor. (8) Cylinder block. (C) Passage. (D) Passage. (E) Passage. (F) Passage.

Of twelve passages (C), (D) and (E) inside external distributor (3), nine will have high pressure oil passing through them. Three will have return oil. Of nine high pressure passages (D) and (E), six are connected with six passages (F) in cylinder block (8). The other three are positioned between passages in the cylinder block and are temporarily sealed off in a neutral position.

Of the ten passages in the cylinder block, two are located between passages in distributor (3) and are therefore temporarily sealed off in neutral. Six passages are connected with the high pressure oil delivery line. Two are connected with the low pressure return line. Of the six pistons which receive high pressure oil, there are four whose actions cancel each other out. This is due to their opposed action.

Oil Flow From Cylinder Block To Pistons, Counterclockwise Rotation
(3) External distributor. (5) Internal distributor. (7) Displacement changeover spool. (8) Cylinder block. (11) Motor case. (12) Cam. (13) Pistons. (C) Passage. (D) Passage. (E) Passage.

At high speed range and counterclockwise rotation, the motor will always have:

a. Six pistons (13) supplied with high pressure oil. Since four of the pistons work against each other, only two are effective. The action of these two pistons with cam (12) provide the motor torque.

b. Two pistons connected with the return line of the loop circuit.

c. Two pistons in neutral.

Pistons And Cam

Motor Startup Phase
(3) External distributor. (8) Cylinder block. (12) Cam. (13) Piston. (14) Roller.

Pressure oil enters external distributor (3) through a passage which sends the oil to cylinder block (8). Oil from distributor (3) passes into the cavity of piston (13). The piston pushes roller (14) against cam (12). This is the startup phase of the motor.

Full Force Phase
(3) External distributor. (8) Cylinder block. (12) Cam. (13) Piston. (14) Roller.

The pressure which acts on piston (13) causes roller (14) to roll on the face of cam (12). This will drive the cam and motor case in the direction shown by the arrow. Distributor (3) also rotates along with the cam and motor case. This means that the supply passage moves from a partial connection with piston (13) to a full one. This is the full force phase.

Bottom Neutral Phase
(3) External distributor. (8) Cylinder block. (12) Cam. (13) Piston. (14) Roller. (15) Piston.

When roller (14) goes to bottom of the cam, the inlet port of piston (13) will be located between the distributor passages. Since there is no connection between the two passages, the piston no longer drives the cam and motor case.

Piston (15) takes over the role as the driving piston. This allows piston (13) to move up the cam face. The cam and motor case will continue turning. This is the bottom neutral phase.

Discharge Phase
(3) External distributor. (8) Cylinder block. (12) Cam. (13) Piston. (14) Roller.

When piston (13) moves up the cam face, the piston cavity is connected with the return line passage of distributor (3). This the discharge phase.

Startup And Bottom Neutral Phase
(3) External distributor. (8) Cylinder block. (12) Cam. (13) Piston. (14) Roller. (15) Piston.

As roller (14) of piston (13) continues moving up the cam face, the connection between the piston cavity and distributor (3) return passage gradually closes. Piston (15) is now at the bottom neutral phase.

Top Neutral Phase
(3) External distributor. (8) Cylinder block. (12) Cam. (13) Piston. (14) Roller.

When roller (14) of piston (13) is at the top of cam (12), the port of the piston will be located between two distributor passages. Since there is no connection between the two ports, piston (13) is neutralized. This position is the top neutral phase.

As soon as the roller passes the top of the cam and starts to move down the opposite face, the piston cavity will be connected with a new pressure oil passage in distributor (3). This will give a new motor startup phase, and a new cycle will start for the piston.

Propulsion System Circuit Diagrams

Neutral Position

Propulsion System Circuit In Neutral Position With Stop Control On
(1) Hydraulic oil cooler. (2) Suction line filter. (3) Hydraulic tank. (4) Charge pump circuit. (5) Displacement changeover solenoid valve for rear propulsion motor. (6) Pilot line. (7) Parking brake and regulator block solenoid valve. (8) Direction control valve. (9) Suction line. (10) Variable displacement pump. (11) Charge pump. (12) Propulsion control lever. (13) Regulator block. (14) Displacement changeover pilot line. (15) Tank return line. (16) Closed circuit loop line. (17) Front motor brake. (18) Front hydraulic motor. (19) Rear hydraulic motor. (20) Rear motor brake. (21) Main loop line relief valve. (22) Charge pump circuit relief valve. (23) Main loop line relief valve. (24) Hydraulic regulator. (25) Closed circuit loop line.

Stop Control On

As soon as the engine is started, both charge pump (11) and variable displacement pump (10) turn. Oil which is drawn into the charge pump from hydraulic tank (3) passes through filter (2) before entering the pump through suction line (9). Solenoid valve (7), which controls the brake and pilot line functions to regulator block (13) and propulsion control lever (12), is not energized. Since the stop control on the dashboard is pushed down, the electric circuit to the valve is isolated.

Charge pump oil in line (4) is blocked at solenoid valve (7). Parking brake and regulator block pilot line (6) is not under pressure. Parking brakes (17) and (20) will be applied by spring force. Movement of regulator block (13) or propulsion control lever (12) will not have any effect on direction control valve (8). It remains in neutral. Hydraulic regulator (24) will also be in neutral, keeping the pump's swashplate at an angle of zero (neutral position). In this position there is no flow of oil from variable displacement pump (10).

Charge pump oil is limited by relief valve (22) to 2200 kPa (320 psi). The oil enters into the loop lines through the check valve of main relief valves (21) and (23). When charge line relief valve (22) opens, this oil along with internal leakage oil from pump (10), is returned to tank (3). The oil is returned to the tank in line (15). Before entering the tank the oil passes through hydraulic oil cooler (1).

Charge line pressure oil is used to pilot the displacement changeover spool of the rear hydraulic motor. Electric solenoid valve (5) controls this function. When the valve is not energized, charge line oil from line (4) is blocked at valve (5). The rear motor is in large displacement (low travel speed range). Moving the speed range selector switch on the dashboard to the high travel speed range will energize solenoid valve (5) and allow oil to flow through the valve from line (4) to pilot line (14). The motor is now in small displacement (high speed range).

Stop Control Off

Propulsion System Circuit In Neutral Position With Stop Control Off
(4) Charge pump circuit. (6) Pilot line. (7) Parking brake and regulator block solenoid valve. (12) Propulsion control lever. (13) Regulator block. (17) Front motor brake. (20) Rear motor brake.

As soon as the stop control on the dashboard is pulled up, solenoid valve (7) becomes energized. The valve spool moves from position (A) to position (B). Oil now flows across the spool valve from charge pump circuit line (4) into pilot line (6).

The pressure oil will release both parking brakes (17) and (20). At the same time, oil will flow through regulator block (13) to propulsion control lever (12). With the lever in the neutral travel position, the oil will remain blocked at the two spool valves inside the control lever unit.

Charge pump oil passes through the rest of the circuit the same way as the explanation given in Neutral Position With Stop Control On.

Forward Drive Position

Propulsion System Circuit In Forward Drive
(1) Hydraulic oil cooler. (3) Hydraulic tank. (6) Pilot line. (8) Direction control valve. (10) Variable displacement pump. (12) Propulsion control lever. (13) Regulator block. (15) Tank return line. (16) Closed circuit loop line. (18) Front hydraulic motor. (19) Rear hydraulic motor. (21) Main loop line relief valve. (22) Charge pump circuit relief valve. (23) Main loop line relief valve. (24) Hydraulic regulator. (25) Closed circuit loop line. (26) Reducing valve. (27) Passage. (28) Flow restriction orifice. (29) Passage. (30) Tank return line. (31) Cooler bypass valve. (32) Direction control valve pilot line. (33) Closed circuit loop line. (34) Hydraulic regulator pilot line. (35) Output line. (36) Check valve. (37) Rotary selector. (38) Check valve. (39) Tank return line. (40) Tank return line.

With the engine running and the stop control pulled up, forward movement of the propulsion control lever will allow oil from pilot line (6) to pass through pressure reducing valve (26) of the propulsion control lever unit. The oil goes into passage (27). It then passes through restrictor (28) and leaves regulator block (13) through passage (35). This passage sends the oil into direction control valve pilot line (32). Check valve (36) also allows oil to flow to rotary selector (37) and at the same time blocks the passage of oil into passage (29).

Oil pressure in pilot line (32) is regulated by turning rotary selector (37) of regulator block (13). Movement of the spool section of direction control valve (8) is proportional to the oil pressure found in pilot line (32).

When rotary selector (37) is closed, maximum pressure will be found in line (32). This will correspond to maximum spool movement of valve (8). The spool is moved from position (D) to position (C). This will allow oil to pass across the spool valve from charge pump line passage (33) into regulator pilot line (34). The oil pressure moves hydraulic regulator (24) which in turn increases the angle of the swashplate of pump (10) to its maximum. Pump (10) will give maximum oil delivery. The oil circulates through the loop lines of the closed circuit. Pressure oil flows to propulsion motors (18) and (19) through loop line (16). Oil flow to the two motors is in parallel. Oil leaves the motors and returns to pump (10) along loop line (25). The check valve section of relief valve (21) will close when oil is pumped along loop line (16). The check valve section of relief valve (23) will open to allow oil from charge pump circuit to enter loop line. This will compensate for internal leakage within the different circuit components.

The delivery of oil from pump (10) is reduced by turning rotary selector (37) in a counterclockwise direction. The reduction in flow is proportional to the movement of the selector. Oil which passes through the rotary selector opens check valve (38) set at 500 kPa (72 psi). It is then routed back towards the tank through line (30). Allowing oil to flow back to the tank will reduce oil pressure in pilot line (32). The spool of direction control valve (8) will partially move. This will cause hydraulic regulator (24) to move towards its neutral position, bringing the swashplate of pump (10) along with it.

Main loop line relief valve (21) remains closed. If the pressure of the oil in the feed line reaches the same value as the setting of the valve, the valve will open and allow oil to flow into return line (25) of the closed circuit.

Oil from the cases of motors (18) and (19) is sent directly back to the tank through return lines (39) and (40). Oil from the case of pump (10), along with charge pump line oil which has passed through charge pump relief valve (22), is sent back to the tank through line (15). This oil passes through oil cooler (1) before entering tank (3). Cooler bypass valve (31) will open if the oil pressure in return line (15) becomes greater than 200 kPa (29 psi).

Reverse Drive Position

Propulsion System Circuit In Reverse Drive
(6) Pilot line. (8) Direction control valve. (10) Variable displacement pump. (12) Propulsion control lever. (16) Closed circuit loop line. (18) Front hydraulic motor. (19) Rear hydraulic motor. (21) Main loop line relief valve. (23) Main loop line relief valve. (25) Closed circuit loop line. (27) Passage. (28) Flow restriction orifice. (29) Passage. (33) Closed circuit loop line. (36) Check valve. (37) Rotary selector. (41) Direction control valve pilot line. (42) Hydraulic regulator pilot line. (43) Reducing valve.

When propulsion control lever (12) is moved to the reverse drive position, it will open pressure reducing valve (43). Oil will now flow from pilot line (6) into passage (29). It then passes through flow restrictor orifice (28) into direction control valve pilot line (41). Oil also flows through check valve (36) to rotary selector (37) and at the same time blocks the passage of oil into line (27). Oil in pilot line (41) moves the spool of direction control valve (8) from position (D) to position (E). This allows charge pump oil from passage (33) to flow through direction control valve (8) into regulator pilot line (42). The regulator moves, increasing the angle of the swashplate of pump (10). Oil is delivered into loop line (25) where it feeds motors (18) and (19) in parallel. Oil leaves the motors and returns to pump (10) through loop line (16).

The function of the check valve section of relief valves (21) and (23) are reversed. The check valve of valve (23) will close and the check valve of valve (21) will open. The flow of oil through the rest of the circuit is the same as explained in Forward Drive.