Operation Of The All Wheel Drive System At Low Speeds
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| Illustration 1 | g00274365 |
All wheel drive control in MANUAL or AUTOMATIC Transmission control in first speed forward, second speed forward, third speed forward or fourth speed forward (1) All wheel drive accumulator (right side) (2) All wheel drive piston motor (right side) (3) Displacement solenoid (4) All wheel drive control valve (5) Drive solenoid (6) Charge solenoid (7) Check valve (8) Flushing and cooling control valve (9) Hydraulic oil cooler (10) Pump oil pressure (11) All wheel drive piston pump (12) Crossover relief valve (13) Check valve (14) All wheel drive accumulator (left side) (15) All wheel drive piston motor (left side) (16) Flow divider and combiner valve (17) Relief valve (18) Drive spool (19) Charge spool (20) Low pressure oil (21) Return line to all wheel drive gear pump (22) Charge pressure sequence valve (23) Purge pressure sequence valve (24) Shuttle spool (25) Low pressure oil (26) Pump pressure solenoid (27) All wheel drive pressure sensor (28) All wheel drive filter (29) All wheel drive gear pump (30) Hydraulic and steering pump (31) Check valve (AA) Pump oil pressure (BB) Low pressure oil (CC) Cooling oil (DD) Charge oil (EE) Hydraulic tank pressure | |
This example is low speed and high torque.
When the all wheel drive control is in the ON position (MANUAL or AUTOMATIC ), hydraulic and steering pump (30) will drive all wheel drive gear pump (29) . All wheel drive gear pump (29) will supply charge oil through all wheel drive filter (28) . Then, the charge oil flows into the all wheel drive system.
Charge oil is supplied to all wheel drive piston pump (11) . Pump pressure solenoid (26) will move to position (H) when the transmission electronic control module sends a signal for a forward gear to the all wheel drive electronic control module. When All wheel drive piston pump (11) receives an electrical signal from the all wheel drive electronic control module, the swashplate in all wheel drive piston pump (11) will change angles. The amount of change to the swashplate angle will determine the amount of flow and pump oil pressure (10) that is generated. High oil pressure now fills pump oil pressure (10) . This holds check valve (13) closed. Charge oil passes through check valve (31) . This keeps the low pressure side of the main circuit filled with oil.
There are two crossover relief valves (12) in all wheel drive piston pump (11) . Crossover relief valves (12) are not adjustable. The crossover relief valves are set at 41300 kPa (6000 psi). If the pressure in the all wheel drive system reaches that point, the crossover relief valves will open. This will allow the high oil pressure to pass.
High pressure oil from the all wheel drive piston pump enters flushing and cooling control valve (8) . The high pressure oil shifts shuttle spool (24) to position (A) . The shuttle spool will block the high oil pressure from passing through purge pressure sequence valve (23) . This will force the oil to flow to all wheel drive control valve (4) . Pump pressure solenoid (26) is activated. Signals that are received from all wheel drive pressure sensor (27) are used by the all wheel drive electronic control module to control the all wheel drive piston pump. This will maintain the desired pressure for the all wheel drive system.
Shuttle spool (24) will block the flow of charge oil from flushing and cooling control valve (8) . Charge oil will flow to charge pressure sequence valve (22) . When the charge pressure in the all wheel drive system increases beyond 3000 kPa (435 psi), charge pressure sequence valve (22) will open. This allows the oil to flow to hydraulic oil cooler (9) and back to the hydraulic oil tank.
Low oil pressure (25) is equal to the charge pressure. Low oil pressure (25) passes through shuttle spool (24) to purge pressure sequence valve (23) . Purge pressure sequence valve (23) regulates the low pressure at 2000 kPa (290 psi). Then, excess oil passes through hydraulic oil cooler (9) and back to the hydraulic oil tank.
As the oil leaves the all wheel drive system through the hydraulic oil cooler or the cooler bypass, makeup flow is introduced by check valve (31) on the low pressure side of the drive loop.
High oil pressure is sent to all wheel drive control valve (4) . Charge solenoid (6) is activated. This allows charge oil to pass through check valve (7) . Then, charge spool (19) shifts to position (F) . This allows high oil pressure to pass through charge spool (19) . Drive solenoid (5) is activated. This allows the charge oil to pass through drive spool (18) . The charge oil will shift drive spool (18) to position (D) . Charge spool (19) shifts approximately 0.75 seconds before drive spool (18) shifts. This allows the charge pressure to fill the lines prior to the high pressure oil from the all wheel drive piston pump. This allows high oil pressure to pass through drive spool (18) . The high pressure oil passes a single cartridge in the crossover relief valve (17) . This protects the forward side and reverse side of the drive loop. If the pressure exceeds 37900 kPa (5500 psi) the relief valve opens. Then, high oil pressure passes to all wheel drive piston motor (15) and all wheel drive piston motor (2) . This high oil pressure drives the all wheel drive piston motor. If the transmission modulator pedal is depressed, drive solenoid (5) is deactivated. This allows the all wheel drive piston motor to coast. When the transmission is in low gears, displacement solenoid (3) that is in all wheel drive control valve (4) is not activated. This blocks the charge oil from passing to all wheel drive piston motor (2) and to all wheel drive piston motor (15) . Drain oil can pass through displacement solenoid (3) and back to the hydraulic oil tank.
Low oil pressure passes out of all wheel drive piston motor (15) and all wheel drive piston motor (2) and back through all wheel drive control valve (4) . These two lines are connected in all wheel drive control valve (4) through flow divider and combiner valve (16) . This keeps an even amount of oil pressure to all wheel drive piston motor (2) and all wheel drive piston motor (15) if there is a loss of traction in either wheel.
There is an all wheel drive accumulator (14) in the drain line for all wheel drive piston motor (15) and an all wheel drive accumulator (1) in the drain line for all wheel drive piston motor (2) . These accumulators absorb any high pressure spikes in the case drains of all wheel drive piston motor (2) and of all wheel drive piston motor (15) .
All Wheel Drive System In The OFF Position
With the all wheel drive control in the OFF position, hydraulic and steering pump (30) will drive all wheel drive gear pump (29) . All wheel drive gear pump (29) will supply purge oil to wheel drive filter (28) . Then, the purge oil flows into the all wheel drive system.
With the all wheel drive system OFF, there are two ways for the charge oil to enter flushing and cooling control valve (8) . The first means is straight from all wheel drive gear pump (29) to charge pressure sequence valve (22) or purge pressure sequence valve (23) . The second means is from all wheel drive gear pump (29) to the makeup relief valves in the all wheel drive piston pump. With equal pressure on each end of shuttle spool (24) , the spool is held in position (B) . This allows the charge oil to pass through purge pressure sequence valve (23) . The excess charge flow will pass out of flushing and cooling control valve (8) through hydraulic oil cooler (9) and back to the hydraulic oil tank. Pump pressure solenoid (26) is not activated.
All wheel drive control valve (2) has three solenoid valves:
- Displacement solenoid (3)
- Drive solenoid (5)
- Charge solenoid (6)
When the all wheel drive system is off, all three solenoids are not activated. Because charge solenoid (6) is not activated, there is no oil flow to charge spool (19) . Spring pressure will hold charge spool in position (G) . In this position, the forward side of the drive loop and the reverse side of the drive loop are connected together. This prevents the all wheel drive piston pump from building drive pressure.
The All Wheel Drive System ON And Coasting
When the engine is on and the all wheel drive control is in MANUAL position or AUTOMATIC position, hydraulic and steering pump (30) will drive all wheel drive gear pump (29) . All wheel drive gear pump (29) will supply charge oil through all wheel drive filter (28) . Then, the charge oil flows into the all wheel drive system.
Charge oil enters flushing and cooling control valve (8) with equal pressure on each end of shuttle spool (24) . The spool is held in position (B) . This will allow the charge oil to flow through purge pressure sequence valve (23) , hydraulic oil cooler (9) and the hydraulic oil tank. Pump pressure solenoid (26) is activated once the transmission Electronic Control Module (ECM) sends a valid code over the data link.
All wheel drive control valve (4) has three solenoid valves:
- Displacement solenoid (3)
- Drive solenoid (5)
- Charge solenoid (6)
When Charge solenoid (6) is activated, charge oil will shift charge spool (19) to position (F) . Charge oil passes through charge spool (19) . Then, the charge oil flows to all wheel drive piston motor (15) and all wheel drive piston motor (2) . There is charge pressure to the all wheel drive piston motors but not drive pressure. With charge pressure at the all wheel drive piston motor, the pistons in the all wheel drive piston motor will contact the cam ring. Drive solenoid (5) and displacement solenoid (3) are not activated.
Operation Of The All Wheel Drive System At High Speed
This example is high speed and reduced torque.
With the all wheel drive control in the ON position (MANUAL or AUTOMATIC ), hydraulic and steering pump (30) will drive all wheel drive gear pump (29) . All wheel drive gear pump (29) will supply charge oil through all wheel drive filter (28) . Then, the charge oil flows into the all wheel drive system.
Charge oil is supplied to all wheel drive piston pump (11) . When all wheel drive piston pump (11) receives an electrical signal from the all wheel drive electronic control module, the swashplate in all wheel drive piston pump (11) will change angles. The amount of the angle of the swashplate determines the amount of flow that is generated in pump oil pressure (10) . Pump oil pressure (10) will hold check valve (13) closed. This allows charge oil to pass through check valve (31) . This keeps the low pressure side of the main circuit filled with oil.
There are two nonadjustable pressure relief valves (12) in the all wheel drive piston pump (11) . The pressure relief valves are set at 41300 kPa (6000 psi). If pressure in the all wheel drive system reaches that point, the pressure relief valves will open. This will allow the high oil pressure to pass.
High pressure oil enters flushing and cooling control valve (8) . The high pressure oil shifts shuttle spool (24) to position (A) . This blocks the high oil pressure from passing through purge pressure sequence valve (23) . This forces the high pressure oil to flow to all wheel drive control valve (4) . The signals from pump pressure sensor (27) are used by the all wheel drive electronic control module in order to control the all wheel drive piston pump. This will maintain the desired pressure for the all wheel drive system.
Charge oil enters flushing and cooling control valve (8) and the charge oil is blocked by shuttle spool (24) . Charge oil also passes to the charge pressure sequence valve (22) . When charge pressure in the all wheel drive system increases beyond 3000 kPa (435 psi), the charge pressure sequence valve opens. This allows charge oil to enter hydraulic oil cooler (9) and the hydraulic oil tank.
Low oil pressure (25) passes through shuttle spool (24) to purge pressure sequence valve (23) . When low oil pressure (25) exceeds 2000 kPa (290 psi), purge pressure sequence valve (23) opens. This oil will allow the purge oil to enter hydraulic oil cooler (9) and the hydraulic oil tank.
High oil pressure is sent to all wheel drive control valve (4) . Charge solenoid (6) is activated. This allows charge oil to pass through check valve (7) in order to shift charge spool (19) to position (F) . This allows high oil pressure to pass through charge spool (19) . Drive solenoid (5) is activated. This allows charge oil to shift drive spool (18) to position (D) . Charge spool (19) shifts approximately 0.75 seconds before drive spool (18) shifts. This allows the charge pressure to fill the lines with the high pressure oil from the all wheel drive piston pump. This allows high oil pressure to pass through drive spool (18) . The high oil pressure will flow past crossover relief valve (17) . If the pressure exceeds 37900 kPa (5500 psi) the relief valve opens. Then, high oil pressure passes to all wheel drive piston motor (15) and all wheel drive piston motor (2) . This high pressure oil drives the all wheel drive piston motors. Drive solenoid (5) is deactivated when the transmission modulator pedal is depressed. This allows the all wheel drive piston motor to coast.
Displacement solenoid (3) in all wheel drive control valve (4) is activated. This allows the charge oil to pass to all wheel drive piston motor (2) and all wheel drive piston motor (15) . This will change the displacement of the all wheel drive piston motor. This allows all wheel drive piston pump (11) to maintain flow at higher speeds.
Low oil pressure passes out of all wheel drive piston motor (15) and all wheel drive piston motor (2) and back through all wheel drive control valve (4) . These two lines are connected in all wheel drive control valve (4) through the flow divider and combiner valve (16) . This keeps an even amount of oil pressure to all wheel drive piston motor (2) and all wheel drive piston motor (15) , if there is a loss of traction in either wheel.
There is an all wheel drive accumulator (14) in the drain line for all wheel drive piston motor (15) and an all wheel drive accumulator (1) in the drain line for all wheel drive piston motor (2) . These accumulators absorb any high pressure spikes in the case drains of all wheel drive piston motor (2) and all wheel drive piston motor (15) .
Operation Of The All Wheel Drive System In Freewheel
With the all wheel drive control in the ON position (MANUAL or AUTOMATIC ), hydraulic and steering pump (30) will drive all wheel drive gear pump (29) . All wheel drive gear pump (29) will supply charge oil through all wheel drive filter (28) . Then, the charge oil flows into the all wheel drive system.
Purge oil enters flushing and cooling control valve (8) . The Purge oil exerts pressure on each end of shuttle spool (24) . The spool remains centered in position (B) . This allows the charge oil to flow through purge pressure sequence valve (23) , through hydraulic oil cooler (9) and to the hydraulic oil tank. Pump pressure solenoid (26) will be activated when the machine is in a forward gear.
The all wheel drive control valve (4) has three solenoid valves:
- Charge solenoid (6)
- Drive solenoid (5)
- Displacement solenoid (3)
Charge solenoid (6) is not activated. Charge solenoid (6) connects the end of charge spool (19) to the hydraulic oil tank. The spring force keeps the charge spool in position (G) . Drive solenoid (5) is not activated. Drive solenoid (5) connects the end of drive spool (18) to the hydraulic oil tank. The spring force keeps the drive spool in position (E) . This connects the all wheel drive piston motor lines together. The all wheel drive piston motor lines drain through charge spool (19) . Displacement solenoid (3) is activated. The charge oil provides a signal to all wheel drive piston motor (15) and all wheel drive piston motor (2) .
With charge spool (19) in position (G) , all wheel drive piston motor (2) and all wheel drive piston motor (15) are connected to return line (21) . Return line (21) is connected to all wheel drive gear pump (29) . Oil flows from the sides of all wheel drive piston motor (2) and all wheel drive piston motor (15) . There is a slight suction in the return line to all wheel drive gear pump (29) . The return line returns to all wheel drive gear pump (29) . This slight suction keeps the motor pistons retracted.
Operation Of The All Wheel Drive System In Reverse
Forward operation and reverse operation of the all wheel drive system are identical. All wheel drive piston pump (11) , all wheel drive piston motor (15) and all wheel drive piston motor (2) turn in the opposite direction.
First speed reverse, second speed reverse and third speed reverse are low speed and high torque. Fourth speed reverse and fifth speed reverse are high speed and reduced torque. Sixth speed reverse allows the front wheels to freewheel.