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| Illustration 1 | g03610456 |
Attachment pump | |
The attachment pump is located on the right side of the machine. The doors on the right-rear side of the machine provide access to this component.
The attachment pump is a piston pump with a variable displacement. Pump rotation is counterclockwise. The pump contains an integral charge pump. The charge pump is a gerotor type pump. The attachment pump provides oil flow to the motor or motors of common attachments.
This document only deals with the operation of the attachment pump (hydrostatic work tool pump). Refer to the following publications for the system operation of the work tool system (rotary ax and the mulcher):
- System Operation, UENR0345, "Rotary Ax (Brush Cutter)"
- System Operation, UENR1684, "Mulching Head (Landscape Grinder)"
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| Illustration 2 | g03610583 |
Location of components on the Attachment (Work tool) Pump (1) Forward attachment solenoid (2) Reverse pressure limiter (3) Forward pressure port "MB" (4) Control neutral adjustment (5) Reverse attachment solenoid (6) Forward pressure limiter (7) Servo gauge port "M5" (8) Reverse high-pressure relief valve (9) Port "F" (to charge filter) (10) Port "E" (from charge filter) (11) Pressure port "A" (12) Servo gauge port "M4" (13) Forward high-pressure relief valve (14) Charge relief valve (15) Charge pressure port "M3" (16) Charge inlet port "S" (17) Reverse pressure port "MA" (18) Pressure port "B" | |
The attachment pump is controlled by an electronic displacement control (EDC). The EDC has two proportional solenoids. When the machine electronic control system determines that the attachment should be rotating forward, the MD3 prompts the XA2 module in the cab to send a pulse-width modulated signal to forward attachment solenoid (1). The forward attachment solenoid controls the oil flow from port "B" of the attachment pump.
When the machine electronic control system determines that the attachment should be rotating in reverse, the MD3 prompts the XA2 module in the cab to send a pulse-width modulated signal to reverse attachment solenoid (5). The reverse attachment solenoid controls the oil flow from port "A" of the attachment pump.
Note: The attachment pump is functionally similar to the propulsion pump. The terms forward and reverse are used to describe the rotation of the attachment pump and attachments.
The attachment pump is equipped with two pressure limiter valves; one for forward operation (6) and one for reverse operation (2). The pressure limiter valves in this type of pump destroke the pump when the pressure reaches the setting of the valve. In the attachment hydraulic system, the pressure limiters are set to open when the pressure differential between the low-pressure loop and the high-pressure loop reaches 37,370 ± 345 kPa (5420 ± 50 psi). The pressure limiter valve is a slow-acting valve.
The attachment pump is equipped with two high-pressure relief valves (8) and (13). These valves contain a relief section and a makeup section. The relief section of these valves limits the pressure in the attachment hydraulic circuit. These valves are set approximately 8000 kPa (1160 psi) higher than the pressure limiter setting. The makeup section of the valves allows charge oil to flow into the low-pressure circuit in order to replenish the oil lost to internal leakage. The relief section of the makeup and relief valve is a fast-acting valve.
Note: The high-pressure relief valves (8) and (13) also can act as bypass valves. When both of the high-pressure relief valve cartridges are loosened three turns, the forward and the reverse sides of the pump are connected.
The pump housing is equipped with a charge relief valve (14). The charge relief valve is set to open when the pressure differential between the charge system and the case drain is 2412 kPa (350 psi).
Several ports are located in the housing of the attachment pump. Each of these ports is identified by a letter or an alpha-numeric designation which is cast into the housing next to the port. The function of each port used in the attachment system is as follows.
Port "B" (18) is the high-pressure port when forward attachment solenoid is energized. On the attachment pump, supply oil flows out port "B" when the attachment is operating in forward.
Port "A" (11) is the high-pressure port when the reverse attachment solenoid is energized. On the attachment pump, supply oil flows out port "A" when the attachment is operating in reverse.
Port "MA" (12) registers pressure in the reverse circuit, and port "MB" (3) registers pressure in the forward circuit. A hose connects each of these ports to a remote pressure tap. Port "M3" registers pressure in the charge circuit. A hose also connects port "M3" to the attachment pump charge filter.
Port "S" (16) is the suction port for the charge pump. The charge pump draws oil directly from the hydraulic oil tank.
Other important ports on the attachment pump include port "M4" (12) and port "M5" (7). The pressure on either side of the servo piston can be measured at these ports. Port "M4" is located at the end of the servo piston on the side of the pump nearest to the forward attachment solenoid. Port "M5" is located at the end of the servo piston on the side of the pump nearest to the reverse attachment solenoid. Port "M4" is pressurized when the attachment is operating in forward. Port "M5" is pressurized when the attachment is operating in reverse.
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| Illustration 3 | g03610679 |
Attachment pump cross section (19) EDC (20) Servo piston (21) Feedback link (22) Servo springs (23) Swashplate (24) Slipper pad (25) Input shaft (26) Rotating group (27) Piston (28) Charge pump | |
Engine rotation turns the pump input shaft, which then rotates the rotating group (26). The rotating group contains a piston (28) and barrel assembly. The pistons in the group rotate with the barrel assembly. The piston slipper pads (24) allow the pistons to follow the angle of swashplate (23). The rotating group only generates flow when the swashplate is not at zero angle.
When the XA2 module in the cab sends an output signal to one of the solenoids, the solenoid moves a spool. Spool movement directs oil into the chamber at one end of servo piston (20) (the high side) and opens the chamber at the other end of the servo piston (the low side) to the case drain. Under these conditions, the servo piston moves.
As servo piston (20) moves, the action of the control linkage causes the angle of swashplate (23) to change. As the swashplate moves, feedback link (21) tends to move the spool of the active solenoid back to neutral through an internal feedback spring. This action prevents the servo piston from tilting the swashplate too far by blocking the charge oil supply, once the tilt angle is equal to the input signal from the XA2 module in the cab.
Slipper pads (24) in each rotating group (26) follow the angle of swashplate (23). This action causes the pistons to move in and out of the barrel assembly as input shaft (25) rotates. As a piston moves out of the barrel assembly, oil in the low-pressure circuit is drawn into the piston chamber. As a piston moves into the barrel assembly, oil is forced out of the piston chamber and into the high-pressure circuit.
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| Illustration 4 | g03610684 |
Attachment pump pressure limiter valve: Top= Closed, Bottom= Open (29) To servo piston chamber (low side) (30) High-pressure oil (31) Poppet (32) Spring | |
High-pressure oil acts against one side of the poppet (31) in the pressure limiter valve. A spring acts against the other side of the poppet. When the pressure in the high-pressure circuit reaches 37,370 ± 345 kPa (5420 ± 50 psi), the force from the pressure moves the poppet against the force of spring (32). As the poppet moves, a passage opens. This opening purges high-pressure oil (30) into the low side of the servo piston.
The low side of the servo piston (29) is open to the pump case drain across the spool in the EDC. However, the passage across the spool in the EDC cannot purge all the oil entering the servo piston through the pressure limiter. Therefore, the pressure in the low side of the servo piston increases. Eventually the pressure in the low side of the servo piston becomes greater than the pressure in the high side of the servo piston. In this case, the servo piston moves the swashplate (23) to a lesser angle, and the flow from the pump decreases.
Decreased pump flow results in reduced pressure in the high-pressure circuit. When the pressure is less than 37,370 ± 345 kPa (5420 ± 50 psi), the pressure limiter valve closes. Eventually, the pressure limiter valve will reach equilibrium. At this point, the pressure limiter valve maintains the pressure in the high-pressure circuit at 37,370 ± 345 kPa (5420 ± 50 psi) until the pressure required to rotate the attachment decreases.
The pressure limiter valve is set to a lower pressure than the relief valve in the high-pressure relief valve. However, the pressure limiter valve does not react as fast as the relief valve in the high-pressure relief valve. Therefore, the relief valve purges the peak pressure in the system. The relief valve provides the pressure limiter valve time to react, and the pressure limiter eventually takes over the relief function. The lower setting of the pressure limiter allows the attachment circuit to work at high pressures with less heat generation.
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| Illustration 5 | g03610687 |
Attachment pump high-pressure relief valves: Top= Low-pressure operation, Bottom= High-pressure operation (33) Check valve (34) Spindle (35) Sleeve (36) Relief spring (37) Makeup spring | |
In the low-pressure side of the circuit, low-pressure oil acts against spindle (34) in conjunction with makeup spring (37). Relief spring (36) maintains contact between the spindle and check valve (33). Charge oil acts on the face of the check valve. The force from the charge oil is in opposition to the force from the low-pressure oil and the makeup spring.
Internal leakage causes the pressure in the low-pressure circuit to fall below charge pressure. In this case, charge oil forces check valve (33), spindle (34), and relief spring (36) to move as a unit against makeup spring (37). This movement opens a passage for charge oil to flow into the low-pressure circuit.
Pressure in the high-pressure circuit acts against the seat of sleeve (35) in the makeup and relief valve. If an external force causes the pressure in the high-pressure circuit to increase approximately 8000 kPa (1160 psi) above the setting of the pressure limiter valve, the oil acting against the seat of the sleeve compresses relief spring (36). This action moves spindle (34), and a passage is opened for oil in the high-pressure circuit to flow into the charge circuit.