CP-563E, CP-573E, CS-563E, CS-573E and CS-583E Vibratory Soil Compactors Propel System Piston Pump (Axle Propel and Drum Propel) Caterpillar


Piston Pump (Axle Propel and Drum Propel)
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1.1. Location and Function
2.1. Components of the Axle and Drum Propel Pumps
3.2. Servo Piston
4.2. Pressure Override Valve (POR)
5.2. Charge Relief Valve
6.2. Combination Valves
7.3. High Pressure Relief Valve
8.3. Makeup Check Valve
9.3. Bypass Valve (Towing)
10.2. Directional Control Valve
11.2. Neutral Start Control
12.2. Axle Interlock Valve
13.1. Oil Flow for the Propel and Axle Pumps
14.2. Propel Lever in FORWARD Position and Propel Range Switch in SLOW SPEED Position
15.2. Propel Lever in NEUTRAL Position

Location and Function




Illustration 1g00942353

Axle propel pump (A) is located on the machine, as shown. The axle propel pump provides oil for the axle propel motor.

Drum propel pump (B) is located on the machine, as shown. The drum propel pump provides oil for the drum propel motor.

Components of the Axle and Drum Propel Pumps




Illustration 2g00942053

Propel Pump

(1) Drive shaft

(2) Bearing housing

(3) Swashplate

(4) Piston

(5) Spring washers

(6) Case

(7) Barrel assembly

(8) Shims

(9) Inlet/outlet port

(10) Inlet/outlet port

(11) Port plate

(12) Directional control valve

(13) Servo piston

(14) Cup

The axle and drum propel pumps are mounted to the rear of the engine. The charge pressure for the propel system is supplied by the steering pump. When the engine is running, drive shaft (1) and barrel assembly (7) are rotating. There are nine pistons (4) in the barrel assembly. Port plate (11) and swashplate (3) are fastened to case (6). The port plate and the swashplate do not rotate. Spring washers (5) keep a force on the barrel assembly in order to make a high pressure seal between the barrel assembly and the port plate. When the barrel assembly is rotating, each piston (4) follows the angle of the swashplate. If the swashplate angle is at zero, the pistons do not move in and out of the barrel assembly and there is no oil flow.

The position of the swashplate is controlled by manual directional control valve (12) and servo piston (13). Movement of the propel control lever moves the directional control valve. The directional control valve routes charge oil into the servo piston. The servo piston controls the direction and the angle of the swashplate.

The steering pump maintains charge oil in the propel pumps in order to keep the barrel assembly full of oil. The charge oil lubricates the pump components. The internal loss of oil due to leakage is replenished by the charge oil. The charge oil is also used in order to release the brakes and the charge oil will provide the shift valve with oil.

Oil flows from the propel pumps to the propel motors and back to the propel pumps by way of inlet/outlet ports (9) and (10). The position of the swashplate determines the direction of flow. The output flow is the high pressure side of the closed loop circuit.

Servo Piston




Illustration 3g00942187

The Location of the Servo Pistons on the Axle and Drum Propel Pumps

(13) Servo piston (axle propel pump)

(C) Servo piston (drum propel pump)




Illustration 4g00942135

Servo Piston

(15) Springs

(16) Slot for feedback lever

(17) Servo piston

(18) Slot for swashplate control

Oil from the control valve goes to either the right or the left end of servo piston (17). The servo piston also receives a mechanical input from the feedback lever that is connected to slot (16) .

The swashplate control is attached to the servo piston in slot (18). When the servo piston moves, the lever moves the swashplate to the angle that corresponds to the position of the servo piston.

When the control pressure is relieved by the POR valve, springs (15) move servo piston (17) toward the centered position. This reduces the angle of the swashplate in the pump which causes the pump output to be reduced.

Pressure Override Valve (POR)




Illustration 5g00942172

Pressure Override Relief Valve

(19) Adjustment screw

(20) Locknut

(21) Spring

(22) Passage

(23) Valve

(24) Passage

(25) Piston

(26) Chamber

(27) Passage

(28) Shuttle

(29) Passage

The POR valve is located in the propel pump. The POR valve limits the maximum pressure on both sides of the propel loop. This valve limits the output pressure that is supplied by the pump. When the valve opens, control oil drains from the control pressure side of the servo piston in the propel pump. As this charge pressure is drained, the centering springs in the servo piston move the swashplate toward the minimum pump output at the pressure setting of the POR valve. As a result, the system pressure will be maintained and the pump flow will be reduced.

Oil from the high pressure side of the closed loop circuit enters the POR valve at passage (27) or (29). This is dependent on the side of the closed loop circuit that has the higher pressure. Shuttle (28) moves up if the high pressure is in passage (29). The shuttle moves down if the high pressure is in passage (27). This sends the high pressure oil to chamber (26) .

When the pressure setting of the POR valve is reached, the pressure moves piston (25) and valve (23) against spring (21). This opens passage (22). As a result, the control oil goes through passage (24) and to the case drain. When the charge oil goes to the case drain, the centering springs shift the servo piston and the angle of the swashplate is reduced.

Valve (23) serves two purposes. The valve modulates in order to maintain the system pressure at the setting of the POR valve until the load is reduced. The valve maintains the control pressure so that the angle of the swashplate is large enough in order to compensate for system leakage.

Reference: The POR valve can be adjusted. See Specifications, Systems Operation/Testing and Adjusting, "Relief Valve (Pressure Override) - Test and Adjust" for the correct adjustment procedure.

Charge Relief Valve




Illustration 6g00942204

(30) Charge pressure relief valve (axle propel pump)

(D) Charge pressure relief valve (drum propel pump)

The axle and drum propel pumps have a charge relief valve. Charge relief valve (30) and charge pressure relief valve (D) is located in the pump housings. When the charge relief valve opens, excess oil is directed back to the pump case.

Reference: See Specifications, Systems Operation/Testing and Adjusting, "Relief Valve (Charge) - Test and Adjust" for the correct adjustment procedure.

Combination Valves




Illustration 7g00942213

(31) Reverse combination valve (axle propel pump)

(32) Forward combination valve (axle propel pump)

(E) Reverse combination valve (drum propel pump)

(F) Forward combination valve (drum propel pump)

The two sets of combination valves for each pump are designed to provide the following three functions:

  • High pressure relief valve

  • Makeup check valve

  • Bypass valve (towing)

This valve limits the main circuit pressure to specified values which can be changed by adjusting the valve setting.

Reference: See Specifications, Systems Operation/Testing and Adjusting, "Relief Valve (Main) - Test and Adjust" for the correct adjustment procedure.

High Pressure Relief Valve




Illustration 8g00942228

Combination Valve

(33) Cap

(34) Stud

(35) Locknut

(36) Spring

(37) Collar

(38) Spring

(39) Spindle

(40) Passage

(41) Poppet

(42) Seat

(43) Seat

(44) Passage

The high pressure relief valve functions in order to protect the circuit from high pressure spikes. The valve also protects against damage to the circuit components if the POR valve malfunctions. Oil from the high pressure side of the closed loop circuit enters the valve at passages (40) and (44). Spring (38) forces spindle (39) against seat (43). The oil pressure acts against the force of spring (38). When the circuit pressure reaches the high pressure relief setting, spindle (39) is lifted off seat (43). This movement instantly dumps high pressure oil into the low pressure side of the closed loop circuit.

Makeup Check Valve




Illustration 9g00942243

Combination Valve

(33) Cap

(34) Stud

(35) Locknut

(36) Spring

(37) Collar

(38) Spring

(39) Spindle

(40) Passage

(41) Poppet

(42) Seat

(43) Seat

(44) Passage

The combination valve has a second function. The valve acts as a makeup valve for the closed loop circuit. When the pressure in passages (40) and (44) (low pressure side of the closed loop circuit) drops below the charge pressure, charge oil fills the closed loop circuit. Charge oil pressure on poppet (41) compresses spring (36). Poppet (41) is lifted off seat (42). Oil from the charge pressure circuit flows into the low pressure side of the closed loop circuit.

Bypass Valve (Towing)




Illustration 10g00942251

Combination Valve

(33) Cap

(34) Stud

(35) Locknut

(36) Spring

(37) Collar

(38) Spring

(39) Spindle

(40) Passage

(41) Poppet

(42) Seat

(43) Seat

(44) Passage

The combination valve has a third function. The valve allows the machine to be towed. To tow the machine, loosen locknut (35) and turn stud (34) clockwise until the stud makes contact with the top of collar (37). Spring (36) is compressed. Then turn stud (34) until the top of the stud is flush with locknut (35). Spindle (39) moves downward and the oil flows across seat (43). This action allows the oil to pass from one side of the closed loop circuit to the other side.

Note: The brakes must be released prior to towing the machine.

Directional Control Valve




Illustration 11g00942260

Directional Control Valve

(45) Lever

(46) Spool

(47) Passage (charge oil)

(48) Control valve body

(49) Feedback lever

The propel lever delivers a mechanical input to lever (45). The input determines the amount of rotation of spool (46). The output of the propel pump is proportional from 0 to 100 percent. This is based on the amount of control oil that is allowed to flow from passage (47) through spool (46) and into the servo piston. Control oil flows through passage (47) to spool (46). The oil is then sent to either the right end of the servo piston or left end of the servo piston. The control oil pressure shifts the servo piston, and a mechanical signal is sent to the swashplate. This upstrokes the propel pump.

Neutral Start Control




Illustration 12g00942266

Location of Neutral Start Switch on Axle Propel Pump

(50) Neutral start switch




Illustration 13g00942282

Neutral Start Switch

(51) Spool

(52) Electrical switch

(53) Neutral start switch pin

When spool (51) is centered properly, neutral start switch pin (53) will rest between the spool and electrical switch (52). The electrical contact for the starter relay will not be broken. If spool (51) is shifted from neutral, neutral start switch pin (53) will be pushed outward. This will cause the contact inside electrical switch (52) to open. When this happens the electrical continuity of the start circuit will be broken and the machine will be prevented from starting.

Axle Interlock Valve




Illustration 14g00942290

(54) Axle interlock valve (axle propel pump)

(G) Axle interlock valve (drum propel pump)

Axle interlock valve (54) and drum interlock valve (G) prevents the pump swashplate from moving out of neutral when the parking brake is applied.

The interlock valves have a solenoid on one end in order to move the valve spool. There is a spring on the other end in order to position the valve spool when the solenoid is not energized.

When the parking brake switch is in the ON position, the solenoid for the interlock valve is not energized. In this position, the interlock valve shifts and the directional control valve is open to the hydraulic oil tank. When the directional control valve is open to the hydraulic tank, the servo piston shifts to the neutral position. This causes the swashplate to move to the neutral position.

When the parking brake switch is in the OFF position, the solenoid for the axle interlock valve is energized. In this position, the interlock valve shifts and the charge oil flows to the directional control valve. When the charge oil becomes available for the directional control valve, any movement of the propel lever causes the servo piston to shift the swashplate.

Oil Flow for the Propel and Axle Pumps

Propel Lever in FORWARD Position and Propel Range Switch in SLOW SPEED Position




Illustration 15g00943816

Axle or Drum Propel Pump

(1) Drive shaft

(3) Swashplate

(4) Piston

(7) Barrel assembly

(11) Port plate

(12) Directional control valve

(13) Servo piston

(17) Servo piston

(23) Spool

(25) Piston

(30) Charge relief valve

(31) Reverse combination valve

(32) Forward combination valve

(49) Feedback lever

(50) Neutral start switch

(55) Slipper feet

(56) POR valve

(57) Reverse port

(58) Orifice

(59) Shuttle valve

(60) Forward port

(AA) System pressure

(AB) Charge pressure

(AC) Sump

(AD) Activated components

(AE) First pressure reduction

The propel lever is in FORWARD position and the propel range switch is in LOW SPEED position in Illustration 15.

Charge oil is sent from the steering motor through the charge filter. Charge pressure oil acts on forward makeup check valve and the reverse makeup check valve. If the pressure in the closed loop circuit falls below the pressure setting, the appropriate makeup check valve will open. This will allow charge pressure oil to flow into the closed loop circuit.

Note: The makeup check valves are part of the combination valves.

The reverse balance line and the forward balance line modulates large pressure differences by allowing oil to transfer between the axle propel circuit and the drum propel circuit.

The position of the swashplate is controlled by manual directional control valve (12) and servo piston (13). Movement of the propel control lever moves the directional control valve. The directional control valve routes charge oil into the servo piston. The servo piston controls the direction and the angle of the swashplate.

Slipper feet (55) will follow the angle of swashplate (3). This will cause pistons (4) to move in and out of barrel assembly (7) as drive shaft (1) rotates. As the pistons move in, oil in the reverse circuit is drawn into the piston chamber. Rotation of the barrel assembly forces the oil in the piston chamber out of the forward port.

The system pressure in the forward circuit acts against the high pressure relief valve in forward combination valve (32). If the system pressure spikes above the setting for the high pressure relief valve in the POR valve, the system pressure oil will flow to the charge pressure side of the close loop circuit.

If the oil pressure in the reverse side of the closed loop circuit falls below charge pressure, charge pressure oil will open forward makeup check valve (69). This will allow charge pressure oil to flow to the reverse side of the close loop circuit. When the pressure in the reverse side of the circuit is above charge oil pressure, no charge oil will flow into the reverse side of the closed loop circuit.

Forward system pressure will act against one end of shuttle valve (59) in POR valve (56). Reverse circuit pressure will act against the other end of the shuttle valve. Because the forward system pressure is greater than the reverse circuit pressure, the shuttle valve will shift. This will allow the forward system pressure to act on piston (25). When the forward system pressure becomes greater than the pressure setting of the relief valve in the POR valve, the oil in the charge pressure circuit will flow to the pump case and to the hydraulic tank. The relief valve will close after the forward system pressure falls below the pressure setting of the relief valve in the POR valve.

When the pressure in the Charge pressure circuit is vented into the pump case, the pressure in the charge pressure circuit will decrease. Servo piston (13) will lessen the angle of swashplate (3). As a result, the angle of the swashplate will be reduced until the forward system pressure is reduced.

Propel Lever in NEUTRAL Position




Illustration 16g00943819

Axle Propel Pump

(1) Drive shaft

(3) Swashplate

(4) Piston

(7) Barrel assembly

(11) Port plate

(12) Directional control valve

(13) Servo piston

(17) Servo piston

(23) Spool

(25) Piston

(30) Charge relief valve

(31) Reverse combination valve

(32) Forward combination valve

(49) Feedback lever

(50) Neutral start switch

(55) Slipper feet

(56) POR valve

(57) Reverse port

(58) Orifice

(59) Shuttle valve

(60) Forward port

(AB) Charge pressure

(AC) Sump

(AD) Activated components

The propel lever is in NEUTRAL position in Illustration 16.

When the propel lever is in NEUTRAL position, charge pressure oil will be blocked by directional control valve (12). The oil that is acting against servo piston (13) will be open to the hydraulic tank. The centering springs in the piston will center the servo piston. As a result, the angle of the swashplate will be minimal. Pistons (4) will not move in and out in barrel assembly (7) as the pistons rotate. The axle propel pump will not produce oil flow. As a result, the propel motors will not turn.

The steering pump supplies the propel pumps with charge pressure oil. The charge pressure oil will continue to flow to the charge circuit in the propel pumps. If the pressure in the forward circuit or the reverse circuit falls below charge oil pressure, charge pressure oil will open either forward makeup check valve (69) or reverse makeup check valve (70). As a result, charge pressure oil will fill the appropriate circuit. This charge pressure oil will keep barrel assembly (7) full of oil. This oil will lubricate the pump components and will replenish the circuit with oil that is lost by internal leakage.

When the pressure in the forward circuit or the reverse circuit becomes greater then the pressure setting for charge relief valve (30), the excess oil will be vented to the pump case.

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AP-1000D, AP-1055D, AP-655C, BG-2255C, BG-2455D and BG-260D Asphalt Pavers MID 039 - CID 1705 - FMI 05
AP-1000D, AP-1055D, AP-655C, BG-2255C, BG-2455D and BG-260D Asphalt Pavers MID 039 - CID 1705 - FMI 06
AP-1000D, AP-1055D, AP-655C, BG-2255C, BG-2455D and BG-260D Asphalt Pavers MID 039 - CID 1706 - FMI 03
AP-1000D, AP-1055D, AP-655C, BG-2255C, BG-2455D and BG-260D Asphalt Pavers MID 039 - CID 1706 - FMI 05
AP-1000D, AP-1055D, AP-655C, BG-2255C, BG-2455D and BG-260D Asphalt Pavers MID 039 - CID 1706 - FMI 06
AP-1000D, AP-1055D, AP-655C, BG-2255C, BG-2455D and BG-260D Asphalt Pavers MID 039 - CID 1733 - FMI 03
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