D8T STEERING PUMP - SIDE VIEW
IMPLEMENT HYDRAULIC SYSTEM
The implement hydraulic system for the D8T contains the following components:
- a load sensing, pressure compensated, variable displacement piston pump;
- electro hydraulic implement control valves (pilot operated/solenoid controlled), a pilot manifold, and a pilot filter, all combined in one assembly and located in the notch of the fuel tank;
- electronic implement controls with an A4 Implement ECM;
- filters for steering charge circuit oil, case drain oil, and pilot supply oil; and - an oil-to-air hydraulic oil cooler mounted behind the radiator cores;
The differential steering system and the hydraulic demand fan system are both connected to the implement system and all three systems use the same hydraulic oil. However, the steering system is controlled by the Power Train ECM and the fan system is controlled by the Engine ECM. These steering and fan systems are explained in other sections of this module.
The status of all sensors and solenoids may be viewed through the Advisor panel (Implement System Status screens) or through Cat ET.
Hydraulic
104
The hydraulic tank (1) is mounted on top of the right fender, just ahead of the right rollover support post. The hydraulic tank serves as a reservoir that provides oil for the operation of the implements, the hydraulic demand fan, and the steering pump. Components and service points for the hydraulic tank shown in the above illustration are:
2. vacuum breaker
3. hydraulic case drain filter access (one, 6-micron filter) 4. hydraulic oil fill tube and locking cap
5. hydraulic oil temperature sensor 6. implement return oil line
7. case drain return line (from case drain manifold)
8 main hydraulic oil line to suction manifold (for all hydraulic pumps)
Not visible above is the pilot oil return line. It connects to the front side of the hydraulic tank, next to the hydraulic oil temperature sensor.
A fluid level sight glass, which can be viewed from the right side of the machine, is located on the right side of the tank and is visible from the ground.
2 3
1
7
8 5
6 4
105
The implement pump (1) for the D8T is a load sensing, pressure compensated, variable
displacement piston pump. It is mounted to the upper, right rear corner of the flywheel housing.
Mounted to the top of the implement pump is the main suction manifold (2), which supplies hydraulic oil to all of the hydraulic pumps in the hydraulic system. Additional components shown above are:
3. pressure compensator adjustment screw 4. flow compensator adjustment screw
5. signal line from the resolver network of the implement control valve stack
6. cold oil relief valve (not visible above, and on the opposite side of the manifold, is the line from the steering charge pump discharge to the cold oil relief valve)
7. main suction line connection to hydraulic tank 8. hydraulic demand fan pump supply line (suction) 9. steering charge pump supply line (suction) 10. implement pump case drain line
11. return oil line from the hydraulic oil cooler/fan motor 4 3
5 6
11
2 1
Implement pump pressure settings are:
- Low pressure standby for the implement hydraulic pump should be set to approximately 2860 ± 760 kPa (410 ± 110 psi).
- Margin pressure for the implement pump should be set to approximately 2100 ± 172 kPa (305 ± 25 psi).
- High pressure cutoff for the implement pump is approximately 24000 ± 520 kPa (3480 ± 75 psi).
The main relief valve and the charging valve are installed in the inlet manifold. The main relief valve protects the system from pressure spikes over 27600 kPa (4000 psi). The charging valve restricts return flow to the tank that helps prevent cavitation in the cylinders.
106
The implement valve stack and pilot manifold are located in the notch of the fuel tank, under a protective cover (removed in the above illustration). The implement control valve stack
assembly consists of two parallel valve sections (four if the machine is equipped with a ripper or a winch).
At the left side of the assembly is the inlet manifold (1). The inlet manifold contains the pump discharge (HA) pressure test port (2) and the pump signal (HB) pressure test port (3).
Either end of each implement control valve contains a control solenoid (9) and a pilot pressure test port (4) for testing pilot pressure at that end of the valve.
The pilot manifold (7) is located at the right end of the assembly, bolted to the valve stack end cover (6). The pilot manifold contains the accumulator (5) and the pilot oil filter (8). The accumulator allows the operation of the implements for a short time when the engine is off. The pilot oil filter ensures that clean oil is sent to the solenoid controlled implement pilot valves.
Implement pump supply oil enters the inlet manifold at the left end of the inlet manifold (not visible, above). Return oil from the implement control valves is directed back to the hydraulic oil tank from the outlet, through the hard tube (10) at the bottom of the manifold.
1 2
7
8 9
10
107
The illustration above shows the valve stack and pilot manifold assembly, as viewed from the front of the fuel tank. The charging valve (1) and the main relief valve (2) are contained in the inlet manifold.
The charging valve (1) restricts the cylinder return oil flow to the tank. This valve keeps oil pressure in the cylinder return oil passage of the implement control valves and is used with the makeup valves to prevent cavitation in the cylinders. A typical function when the charging valve assists the makeup valve and the quick-drop valve for the lift cylinders is when the dozer control lever is moved to the full lower position (quick-drop) and the dozer is lowered rapidly.
Opening pressure for the charging valve is approximately 1050 kPa (150 psi), at 190 ± 4 L/min (50 ± 1 gpm).
The main relief valve (2) is set at approximately 27600 kPa (4000 psi), at 38 ± 4 L/min (10 ± 1 gpm). This setting is approximately 3585 kPa (520 psi) higher than the pressure compensator (cutoff) valve. The primary purpose of the main relief valve is to eliminate
pressure spikes in the system. If the system is in a stall condition, the pressure cutoff valve will cause the implement pump to destroke toward a minimum angle.
2
1 4 3
6 5
7
8
9
5. ripper lift valve 6. ripper tip valve
The pilot relief valve (7) is installed in the front side of the pilot manifold.
Also visible in illustration 107 is the "float pilot boost" line (8) and the external resolver (9), which is the last resolver in the signal resolver network. The "float pilot boost" strategy will be discussed later in this presentation.
108
The pilot manifold is mounted to the end cover (6) and is located at the right end of the valve stack.
The implement lockout solenoid (1) is ENERGIZED when the implement lockout switch is in the UNLOCKED position, allowing pilot oil to flow to the control valves and enabling
implement operation. When the lockout switch is in the LOCKED position, the solenoid is DE-ENERGIZED and pilot oil is prevented from flowing to the implement control valves. The implements will not move when the implement lockout switch is in the LOCKED position. The implement lockout solenoid (1) is also ENERGIZED when the engine is at low idle and the implement controls are in the HOLD position. Moving an implement control DE-ENERGIZES the implement lockout solenoid.
The pressure reducing valve (2) lowers the pressure of the implement pump supply oil to pilot supply pressure, which is approximately 3275 kPa (475 psi). The implement pump pressure sensor (3) senses the implement pump supply pressure as it enters the pilot manifold. The hydraulic pilot supply (HPS) pressure test port (4) may be used to check pilot pressure. The hydraulic pilot accumulator pressure (HPAP) may be tested at the lower test port (5).
Also located on the top of the pilot manifold (not visible above) are the accumulator check valve (at the left of the manifold) and the pilot filter bypass check valve (at the right of the manifold).
1 2
3 4
5
6
109
The pilot manifold is mounted to the end cover on the valve stack. It supplies pilot oil to the solenoid valves that are located on either end of each implement control valve. The pilot manifold is supplied with oil from the implement pump, through the inlet manifold, the valve stack, and then the end cover. The pilot manifold contains the implement pump pressure sensor, the pressure reducing valve, the Hydraulic Pilot Accumulator Pressure (HPAP) test port, and the Hydraulic Pilot Supply (HPS) pressure test port.
As the oil enters the pilot manifold, it passes through a screen before it reaches the pressure reducing valve. The pressure reducing valve is infinitely variable, and meters the oil to provide pilot oil pressure of approximately 3275 ± 172 kPa (475 ± 25 psi). After passing through the pressure reducing valve, this oil becomes pilot oil.
The pilot oil then passes through the pilot filter. From the pilot filter, the pilot oil then passes through the accumulator check valve, where it is available to the accumulator and the pilot relief valve.
Implement
Lockout Valve HPS
HPAP
Pressure Reducing Valve Screen
Implement Pump Pressure Sensor
Accumulator
Pilot Filter Bypass
Valve
Pilot Relief Valve
The pilot relief valve limits the pressure past the pressure reducing valve to approximately 6500 kPa (940 psi). In the event of pressure spikes in the pilot system, this valve opens to dissipate the excess pressure. The accumulator stores energy (pilot pressure) so that the implements may be lowered in a dead engine situation.
A check valve is positioned upstream of the accumulator which prevents back-flow in the system in case of low pressure conditions. The check valve also prevents the accumulator from discharging when the machine is shut down.
From the accumulator, the pilot oil then flows to the implement lockout valve. The implement lockout valve is solenoid operated and is ENERGIZED, when in the UNLOCKED condition.
The implement lockout valve is controlled by the implement lockout switch, located on the right console, in the operator compartment. When this valve is in the LOCKED condition, or
DE-ENERGIZED, the pilot oil is blocked and the implements cannot be moved with the implement controls.
When the implement lockout valve is in the UNLOCKED condition, the pilot oil exits the pilot manifold at the outlet and is directed through a passage in the end cover and then through the pilot oil passages in the valve stack. Each implement valve then directs the pilot oil to the solenoid valves located on either end of each implement control valve.
When the operator activates an implement, the appropriate solenoid valve directs the pilot oil into the pilot chamber of the valve. The pilot pressure then shifts the implement valve spool.
The hydraulic oil cooler (1) is an oil-to-air type cooler. It is mounted vertically behind the AMOCS radiator, on the right side of the radiator guard.
Return oil from the demand fan enters the cooler inlet (2) and is directed through the horizontal tube (3), toward the cooler outlet (4). When the oil is cold, the thermal bypass valve (5) remains open and the oil passes through the outlet and returns to the suction manifold. When the oil is warm, the bypass valve closes against the seat, forcing the oil upward through the cooling tubes (6) before returning to the outlet through the large vertical tube on the right side of the cooler (7). The cooled oil can then flow around the back side of the closed bypass valve to the outlet. Opening temperature for the thermal bypass valve is 62° - 65°C (143° - 149°F). When closed, the valve will open momentarily, in the event of pressure spikes in the system. Opening pressure for the bypass valve is 620 kPa (90 psi), at 71°C (159°F).
110
111 2
5
3
6
4 7
112
Implement System Operation
This schematic shows the components and conditions in the implement system with the engine started and all the implements in HOLD. Oil is drawn from the hydraulic tank by the load sensing variable displacement, piston-type implement pump. Supply oil is directed to the closed-center control valves by the pump. Return oil from the control valves and pump case drain oil are sent to the tank.
When a control lever is moved, oil from the implement control valve is directed to the double acting implement cylinders.
The signal network line is in series with each control valve and passes through each valve body.
The signal network terminates at the pump control valve. When an implement is activated, a signal is generated by the work port load. This signal is sent through the signal network. A resolver network inside the implement valves consists of a series of resolver valves which compare the signals from the implements and send the highest signal to the pump control valve.
The major components in this system are: the implement pump, the inlet manifold, the blade lift and tilt control valves, the ripper lift and ripper tip control valves, the pressure reducing valve, the solenoid controlled pilot valves, the implement cylinders, and the quick-drop valve.
Blade Lift