789D Off-Highway Truck
POWER TRAIN
• Identify main power train components.
INTRODUCTION
The power train on the 789D truck is similar to the 789C truck. The Rear Axle Lubrication System (RAXL) has been updated on the 789D.
Power flows from the engine to the rear wheels through the power train. The main components in the power train are:
* Torque converter (1) •
* Drive shaft (2) •
* Transfer gears (3) •
* Transmission (4) •
* Differential (5) •
* Final drives (6) •
The RAXL oil filter (7) is also visible in this image.
Explain torque converter hydraulic system oil flow.
TORQUECONVERTERHYDRAULIC SYSTEM
This schematic shows the oil flow from the torque converter pump (5) through the torque converter hydraulic system on the 789D truck.
The scavenge pump section (1) pulls oil through the scavenge screen (6) from the torque converter housing and sends the oil to the hydraulic tank.
The charging pump section (2) sends oil through the torque converter charging filter (7) to the torque converter inlet relief valve (8) and to the torque converter. Oil flows from the torque converter to the outlet relief valve (9) and through the converter outlet screen (10) to the front brake oil cooler (11) and to the front brakes.
The parking brake release pump section (3) sends oil through the parking brake release filter (12) to the parking brake release valve (13) and to the following components:
* Torque converter lockup clutch valve (14)
* Hydraulic Automatic Retarder Control (HARC) valve (15)
* Traction Control System (TCS) valve (16)
* Hoist valve (17)
Most of the oil flows through the parking brake release valve and the front brake oil cooler to the front brakes. The brake cooling pump section (4) of the torque converter pump sends oil through the rear brake oil coolers (18) and to the rear brakes.
Identify torque converter components
In converter drive, the torque converter multiplies engine torque to the transmission. At higher ground speeds, a lockup clutch engages to provide direct drive. The NEUTRAL and REVERSE ranges are converter drive only. FIRST SPEED is converter drive at low ground speed and direct drive at high ground speed. SECOND through SIXTH SPEEDS are direct drive only. The torque converter is in converter drive between each shift (during clutch engagement) to provide smooth shifts.
The torque converter inlet relief valve (1) limits the maximum pressure of the supply oil to the torque converter. The torque converter inlet relief pressure can be checked by removing a plug on the inlet relief valve and installing a pressure tap. Normally, the inlet relief valve pressure will be slightly higher than the outlet relief valve pressure.
Oil flows through the inlet relief valve and enters the torque converter. Some of the oil will leak through the torque converter to the bottom of the housing to be scavenged. Most of the oil in the torque converter is used to provide a fluid coupling and flows through the torque converter outlet relief valve (2).
The outlet relief valve maintains a minimum pressure inside the torque converter to keep the torque converter full of oil and prevent cavitation. The outlet relief valve pressure can be measured at the tap (3) on the outlet relief valve.
Also mounted to the back of the torque converter housing is the lockup clutch valve (4) and the torque converter pump (5).
Identify torque converter outlet temperature sensor
A torque converter outlet temperature sensor (arrow) provides an input signal to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends the signal to VIMS, which informs the operator of the torque converter outlet temperature.
Identify torque converter pump components.
* Torque converter scavenge (1)
* Torque converter charging (2)
* Parking brake release (3)
* Rear brake oil cooling (4)
Excess oil that accumulates in the bottom of the torque converter is scavenged by the first section of the pump through a screen behind the access cover (5) and returned to the hydraulic tank.
Explain operation of torque converter in Converter Drive.
This sectional view shows a torque converter in CONVERTER DRIVE. The lockup clutch (1) is not engaged. During operation, the rotating housing and impeller (2) rotate faster than the turbine (3). The stator (4) remains stationary and multiplies the torque transfer between the impeller and the turbine. The output shaft (5) rotates slower than the engine crankshaft, but with increased torque.
Explain operation of torque converter in Direct Drive.
In DIRECT DRIVE, the lockup clutch (1) is engaged by hydraulic pressure and locks the turbine (3) to the impeller (2). The housing, impeller, turbine, and output shaft (5) then rotate as a unit at engine rpm. The stator (4), which is mounted on a freewheel assembly (6), is driven by the force of the oil in the housing and will freewheel at approximately the same rpm.
Identify components on right side of truck, in front of hydraulic tank
Oil flows from the torque converter charging section of the pump to the torque
converter charging filter (1) located on the right side of the truck in front of the hydraulic tank (2). An oil filter bypass switch (3) is located on the torque converter charging filter. The oil filter bypass switch provides an input signal to the VIMS, which informs the operator if the filter is restricted.
Identify torque converter outlet screen and outlet screen bypass switch
Identify parking brake release oil filter and release filter bypass switch
tank. Oil flows from the parking brake release section of the torque converter pump to the parking brake release filter. A parking brake release filter bypass switch (2) is located on the parking brake release filter. The bypass switch provides an input signal to the Brake ECM. The Brake ECM sends a signal to VIMS, which informs the operator if the parking brake release filter is restricted.
Identify torque converter lockup clutch components.
Oil from the parking brake release section of the torque converter pump supplies oil to the torque converter lockup clutch valve through the inlet port (1). When the lockup clutch solenoid (located on the transmission housing) is energized by the Transmission/Chassis ECM, transmission pump supply oil (signal oil) enters the lockup valve through the signal oil hose (2). The signal oil pressure is approximately 1725 kPa (250 psi). The signal oil causes the lockup valve to start the modulation process for torque converter lockup. The lockup clutch valve then supplies oil to
ENGAGE the lockup clutch in the torque converter. Torque converter lockup clutch pressure can be measured at the tap (3). Torque converter lockup clutch pressure should be approximately 2135 ± 70 kPa (310 ± 10 psi) at 1300 rpm or higher. Do not check the torque converter lockup clutch pressure below 1300 rpm.
Explain operation of torque converter lockup clutch valve in Direct Drive.
Shown is a sectional view of the torque converter lockup clutch valve in DIRECT DRIVE. Supply oil from the parking brake release pump (1) is used to provide lockup clutch oil.
First, supply pressure is reduced to provide pilot pressure to the relay valve (2). Supply oil to the lockup reducing valve (3) flows through cross-drilled orifices in the spool, past a check valve, and enters the slug chamber. The check valve dampens spool movement and reduces the possibility of valve chatter and pressure fluctuation.
Oil pressure moves the slug in the right end of the spool to the right and the spool moves to the left against the spring force. The slug reduces the effective area on which the oil pressure can push. Because of the reduced effective area, a smaller, more sensitive spring can be used. Pilot pressure will be equal to the force of the spring on the left end of the spool. The spring force can be adjusted with shims. Pilot pressure is approximately 1725 ± 70 kPa (250 ± 10 psi).
When the lockup solenoid (4) is energized, the transmission charge pump (5) oil or signal oil (6) is directed to the relay valve. Before moving the selector piston (7), the pilot oil moves a shuttle valve (8) to the right, which closes the lower left drain passage and opens the check valve. Oil then flows to the selector piston inside the lockup clutch modulation valve (10). Moving the selector piston blocks the upper drain passage, the load piston springs are compressed, and oil flows to the lockup clutch (11).
When the solenoid is energized, supply oil from the parking brake release pump is reduced to provide the lockup clutch pressure. Lockup clutch pressure depends mainly on the force of the load piston valve springs. When the solenoid is energized, pilot oil moves the selector piston down against a stop. When the load piston (9) that compresses the springs is at the top against the selector piston, lockup clutch pressure is at its lowest controlled value.
This value is called “primary pressure.” As the load piston moves down, lockup clutch pressure increases gradually until the load piston stops. Maximum lockup clutch pressure is then reached. The gradual increase in pressure, which depends on how fast the load piston moves, is called “modulation.” The speed of the load piston movement depends on how fast the oil can flow to the area above the load piston. The load piston orifice meters the flow of oil to the load piston chamber and determines the modulation time. Primary pressure is adjusted with shims in the load piston. Final lockup clutch pressure is not adjustable.
If the primary pressure is correct and final lockup clutch pressure is incorrect, the load piston should be checked to make sure that it moves freely in the selector piston. If the load piston moves freely, the load piston springs should be replaced.
Explain transmission hydraulic system oil flow
Shown is the oil flow in the transmission hydraulic system.
The three-section transmission pump (4) is mounted on the rear of the pump drive, which is located inside the right frame rail near the torque converter. The three sections are:
* Transmission scavenge (1)
* Transmission lube (2)
* Transmission charging (3)
• The transmission scavenge section pulls oil through the magnetic screens (5) located at the bottom of the transmission.
The scavenged oil from the transmission is sent to the transmission tank. Oil flows from the charging section of the transmission pump to the transmission charging filter (6). Oil flows from the transmission charging filter to the transmission control valve located on top of the transmission. Transmission charging oil flows from the transmission control valve and joins with the oil from the transmission lube section of the transmission pump.
Oil flows from the lube section of the transmission pump to the transmission lube filter (7). Oil from the transmission lube filter and the transmission control valve flows through the transmission oil cooler (8). Oil flows from the transmission oil cooler to the transfer gears (9) and the transmission to cool and lubricate the internal components.
Identify transmission hydraulic system components.
Power flows from the torque converter (1) through a drive shaft (not shown) to the transfer gears (2). The transfer gears are splined to the transmission input shaft. The transmission (3) is located between the transfer gears and the differential.
The Individual Clutch Modulation (ICM) transmission is electronically controlled and hydraulically operated the same as the 789C truck. The transmission is a power shift planetary design which contains six hydraulically engaged clutches. The transmission provides six FORWARD speeds and one REVERSE speed.
The main components in the transmission hydraulic system are:
* Three-section transmission pump (4)
* Transmission charging oil filter (5)
* Transmission lube oil filter (6)
* Magnetic scavenge screen (7)
Identify transmission charging filter and oil filter bypass switch.
Oil flows from the charging section of the transmission pump to the transmission charging oil filter (1). The transmission charging filter is now mounted to a bracket that is attached to the frame near the bottom of the left hoist cylinder.
Oil flows from the transmission charging filter to the transmission control valve located on top of the transmission. An oil filter bypass switch (2) is located on the transmission charging oil filter. The oil filter bypass switch provides input to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends signals to the VIMS, which informs the operator if the filter is restricted.
Identify transmission lube filter outside frame behind right front tire
Oil flows from the lube section of the transmission pump to the transmission lube filter (1) located on the outside of the frame behind the right front tire.
Oil flows from the transmission lube filter through the transmission oil cooler to the transfer gears. Transmission lube oil flows through the transfer gears and the
transmission to cool and lubricate the internal components. The oil filter bypass switch (2) provides input to the Transmission/Chassis ECM. The Transmission/Chassis ECM sends signals to the VIMS, which informs the operator if the filter is restricted. Transmission oil samples can be taken at the S•O•S port (3).
Identify transmission oil cooler and transmission oil cooler bypass valve
The transmission oil cooler (1) is located on the inside of the right frame rail next to
the engine. Oil flows from the transmission lube filter and the transmission control valve through the transmission oil cooler bypass valve (2) to the transmission oil cooler. The bypass valve for the transmission oil cooler permits oil flow to the system during cold starts when the oil is thick or if the cooler is restricted. Oil flows from the transmission oil cooler to the transfer gears and the transmission to cool and lubricate the internal components.
Identify transmission components
Oil flows from the transmission oil cooler to the transfer gears through a lube oil inlet hose (1). Transmission lube oil flows through the transfer gears and the transmission to cool and lubricate the internal components.
The transmission lube pressure relief valve is in the transmission case near the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission lube circuit. Transmission lube oil pressure can be measured at the lube oil port (2).
At HIGH IDLE, the transmission lube pressure should be approximately 140 to 205 kPa (20 to 30 psi). At LOW IDLE, the transmission lube pressure should be a minimum of 4 kPa (.6 psi).
The transmission oil temperature sensor (3) is now located on the right side of the output transfer gear. The transmission oil temperature sensor sends a signal to the Transmission/Chassis ECM indicating transmission oil temperature. The Transmission/Chassis ECM sends a signal to the VIMS, which displays the transmission oil temperature.
Identify components on right side of transmission hydraulic control valve
The transmission charging pump supplies oil to the transmission hydraulic control valve and the shift solenoids through the inlet port (1). Excess transmission charging oil either drops to the bottom of the housing to be scavenged or flows to the transmission oil cooler through the outlet hose (2).
The torque converter lockup clutch solenoid (3) is energized by the Transmission/ Chassis ECM when DIRECT DRIVE (lockup clutch ENGAGED) is required. Transmission charge pump supply (signal) oil flows through the small hose (4) to the lockup clutch control valve. The lockup clutch control valve then engages the lockup clutch.
The transmission charging pressure relief valve is part of the transmission hydraulic control valve. The relief valve limits the maximum pressure in the transmission charging circuit. Transmission charging pressure can be measured at the tap (5).
Identify transmission hydraulic control valve above the transmission case
Shown is the Individual Clutch Modulation (ICM) transmission hydraulic control valve. Transmission clutch pressures are measured at the pressure taps (1).
The transmission hydraulic control valve contains a priority valve. The priority valve controls the pressure that is directed to the selector pistons in each of the clutch stations. The transmission priority valve pressure is 1720 kPa (250 psi).
The transmission lube pressure relief valve (2) limits the maximum pressure in the transmission lube circuit.
The “D” Station (3) is used to control the dual stage relief valve setting for the clutch supply pressure. In DIRECT DRIVE, the pressure measured at the tap for station “D” will be approximately 1380 kPa (200 psi). This valve station is adjusted to obtain the correct transmission charge pressure in DIRECT DRIVE.
At LOW IDLE in TORQUE CONVERTER DRIVE, transmission charging pressure should be approximately 2515 kPa (365 psi) minimum. At HIGH IDLE in TORQUE CONVERTER DRIVE, transmission charging pressure should be approximately 3175 kPa (460 psi) maximum.
During torque converter lockup (DIRECT DRIVE), clutch supply pressure is reduced to extend the life of the transmission clutch seals. At 1300 rpm in DIRECT DRIVE, the clutch supply pressure should be approximately 2020 + 240 - 100 kPa (293 + 35 - 15 psi). The corresponding transmission charge pressure is reduced to approximately 2100 ± 100 kPa (305 ± 15 psi).
Transmission electronic control system input and output components.
TRANSMISSIONELECTRONIC CONTROLSYSTEM
This illustration shows the input and output components in the transmission electronic control system. The transmission electronic control system determines the desired transmission gear and energizes solenoids to shift the transmission up or down as required based on information from both the operator and the machine.
The Transmission/Chassis ECM (1) is located in the rear cab compartment and receives input signals from various input components. Based on the input information, the Transmission/Chassis ECM determines whether the transmission should upshift, downshift, engage the lockup clutch, or limit the transmission gear. These actions are accomplished by sending signals to various output components such as the upshift, downshift, and lockup solenoids.
The following input components have been added to the 789D Transmission/Chassis ECM:
* Transmission Input Speed Sensor (5)
* Transmission Oil Level Sensor (18)
* An additional Transmission Output Speed Sensor (4)
The Transmission/Chassis ECM also provides the service technician with enhanced diagnostic capabilities through the use of onboard memory, which stores diagnostic codes for retrieval at the time of service.
The Transmission/Chassis ECM, the Engine ECM, the Brake ECM, and the VIMS all communicate through the Cat Data Link. Communication between the electronic controls allows the sensors of each system to be shared. Many additional benefits are provided, such as Controlled Throttle Shifting (CTS). CTS occurs when the Transmission/Chassis ECM signals the Engine ECM to reduce or increase engine fuel during a shift to lower stress to the power train.
The Transmission/Chassis ECM is also used to control the following:
* Hoist system .
* Automatic lubrication system .
* Neutral-start function • Back-up alarm .
* Optional machine lockout function .
* Engine idle shutdown function .
Identify shift console lever switch
The shift lever (also referred to as the “Cane” or “Gear Selector”) switch (1) is located inside the cab in the shift console and provides input signals to the Transmission/ Chassis ECM. The shift lever switch controls the desired top gear selected by the operator. The shift lever switch inputs consist of six wires. Five of the six wires provide codes to the Transmission/Chassis ECM. Each code is unique for each position of the shift lever switch. Each shift lever switch position results in two of the five wires sending a ground signal to the Transmission/Chassis ECM.
The other three wires remain open (ungrounded). The pair of grounded wires is unique for each shift lever position. The sixth wire is the “Ground Verify” wire, which is normally grounded. The Ground Verify wire is used to verify that the shift lever switch is connected to the Transmission/Chassis ECM. The Ground Verify wire allows the Transmission/Chassis ECM to distinguish between loss of the shift lever switch signals and a condition in which the shift lever switch is between detent positions.
To view the shift lever switch positions or diagnose problems with the switch, use the VIMS message center module or the status screen of Cat ET and observe the “Gear Lever” status. As the shift lever is moved through the detent positions, the Gear Lever status should display the corresponding lever position shown on the shift console.
The position of the shift lever can be changed to obtain better alignment with the gear position numbers on the shift console by loosening the three nuts (2) and rotating the lever. The position of the shift lever switch is also adjustable by moving the switch in the slot (3).
Identify transmission shift components.
The transmission gear switch (1) provides input signals to the Transmission/Chassis ECM. The transmission gear switch inputs (also referred to as the “actual gear inputs”) consist of six wires. Five of the six wires provide codes to the Transmission/ Chassis ECM. Each code is unique for each position of the transmission gear switch. Each transmission gear switch position results in two of the five wires sending a ground signal to the Transmission/Chassis ECM. The other three wires remain open (ungrounded). The pair of grounded wires is unique for each gear position.
The sixth wire is the “Ground Verify” wire, which is normally grounded. The Ground Verify wire is used to verify that the transmission gear switch is connected to the Transmission/Chassis ECM. The Ground Verify wire allows the Transmission/ Chassis ECM to distinguish between loss of the transmission gear switch signals and a condition in which the transmission gear switch is between gear detent positions.
Earlier transmission gear switches use a wiper contact assembly that does not require a power supply to Pin 4 of the switch. Current transmission gear switches are Hall-Effect type switches. A power supply is required to power the switch. A small magnet passes over the Hall cells, which then provide a noncontact position switching capability. The Hall-Effect type switch uses the same 24 volt power supply used to power the Transmission/Chassis ECM.
The solenoid outputs provide +Battery voltage to the upshift solenoid (2), the downshift solenoid (3), or the lockup clutch solenoid (4) based on the input information from the operator and the machine. The solenoids are energized until the transmission actual gear switch signals the Transmission/Chassis ECM that a new gear position has been reached.
identify speed sensors
These images show the speed sensors that provide input to the Transmission/ Chassis ECM to control several truck functions.
The engine speed sensor (1) is located on top of the flywheel housing. The engine speed signal is used for Transmission Output Speed (TOS) ratification and lockup clutch shift time.
The transmission input speed sensor (2), located on top of the output transfer gear housing, has replaced the torque converter output speed sensor but provides the same function. The transmission input speed sensor sends a signal to the Transmission/ Chassis ECM indicating torque converter output speed. The Transmission/Chassis ECM uses the engine speed signal and the transmission input speed sensor signal to calculate torque converter lockup clutch shift time.
There are now two Transmission Output Speed (TOS) sensors (not visible) on the 789D. The TOS sensors are located on the front of the transfer gears behind a cover (3). A small shaft runs from the speed sensors location through the entire length of the transmission and engages the transmission output shaft.
The transmission speed sensor signal serves many purposes. Some of the purposes are:
* Transmission shift time calculation .
* Ground speed and direction indications.
* Traction Control System (TCS) top speed limit.
* Truck Production Management System (TPMS) distance calculations .
* Machine speed input to VIMS to determine some warning categories.
Identify transmission oil level sensor and transmission tank.
A transmission oil level sensor (1) is now located on the back of the transmission
tank (2). The transmission oil level sensor sends a signal to the Transmission/ Chassis ECM indicating transmission oil level. The Transmission/Chassis ECM sends a signal to the VIMS, which displays the transmission oil level.
Identify components in compartment behind cab.
The service/retarder brake pressure switch (1) is located in the compartment behind the cab. The switch is normally closed and opens when service/retarder brake air pressure is present. The switch has three functions for the Transmission/Chassis ECM:
* Signals the Transmission/Chassis ECM to use elevated shift points, which provides increased engine speed during downhill retarding for increased oil flow to the brake cooling circuit.
* Cancels Control Throttle Shifting (CTS).
* Signals the Transmission/Chassis ECM to override the anti-hunt timer.
Rapid upshifting and downshifting is always allowed. The anti-hunt timer prevents a rapid upshift-downshift sequence or a rapid downshift-upshift sequence (transmission hunting). The timer is active during normal operation. It is overridden when either the service/retarder or parking/secondary brakes are engaged.
A diagnostic code is stored if the Transmission/Chassis ECM does not receive a closed (ground) signal from the switch within seven hours of operation time or an open signal from the switch within two hours of operation time.
The parking/secondary brake pressure switch (2) is in the parking/secondary brake air pressure line. The normally open switch is closed when air pressure is present. The purpose of the switch is to signal the Transmission/Chassis ECM when the parking/secondary brakes are ENGAGED.
Since the parking/secondary brakes are spring engaged and pressure released, the parking/secondary brake switch is closed when the brakes are RELEASED and opens when the brakes are ENGAGED. This signal is used to override the anti-hunt timer for rapid downshifting and is used to sense when the machine is parked. A diagnostic code is stored if the Transmission/Chassis ECM does not receive a closed (ground) signal from the switch within seven hours of operation time or an open signal from the switch within one hour of operation time.
Identify body position sensor and position sensor arm.
The body position sensor (1) is located on the frame near the left body pivot pin. A rod assembly is connected to the end of the position sensor arm (2). When the body is raised, the rod rotates the sensor, which changes the Pulse Width Modulated (PWM) signal that is sent to the Transmission/Chassis ECM. The adjustment of the rod between the sensor and the body is very important.
After the rod has been adjusted, a calibration should be performed. The body position sensor is calibrated by the Transmission/Chassis ECM when the following conditions occur:
* Engine is running .
* Hoist output is in FLOAT or LOWER .
* No ground speed is present for one minute.
* Body position sensor duty cycle output is stable for 23 seconds (body is down) .
* Body position is different than previous calibration .
* Duty cycle output from the sensor is between 3% and 30%.
Use the VIMS display to view the body position. When the body is down, the VIMS should display zero degrees. If the position is greater than zero degrees, the sensor rod may have to be adjusted.
The body position signal is used for several purposes.
* Body up gear limiting.
* Hoist snubbing .
* Signals a new load count (after 10 seconds in RAISE position) .
* Lights the body up dash lamp .
* Allows the VIMS to provide body up warnings .
The body position sensor signal is used to limit the top gear into which the transmission will shift when the body is UP. The body up gear limit value is programmable from
FIRST to THIRD gear using Cat ET. The Transmission/Chassis ECM comes from the factory with this value set to FIRST gear. When driving away from a dump site, the transmission will not shift past the programmed gear until the body is down. If the transmission is already above the limit gear when the body goes up, no limiting action will take place.
The body position sensor signal is also used to control the SNUB position of the hoist control valve. When the body is being lowered, the Transmission/Chassis ECM signals the hoist LOWER solenoid to move the hoist valve spool to the SNUB position. In the SNUB position, the body float speed is reduced to prevent the body from making hard contact with the frame. The body position sensor signal is used to provide warnings to the operator when the truck is moving with the body UP. The faster the ground speed, the more serious the warning.
Identify raxl system components.
REARAXLELUBRICATION(RAXL) SYSTEM
The 789D truck will be equipped with a new Rear Axle Lubrication (RAXL) system. The pump for the new RAXL has been removed from inside the banjo and installed on the outside of the differential oil housing. The truck does not need to be moving to provide flow, so the oil can be controlled according to the current conditions. The oil is filtered while lubricating the rear axle and final drives.
This image shows the main components in the RAXL system. The RAXL motor drive pump (1) is mounted to the steering pump (2). The RAXL motor drive pump pulls oil from the steering oil tank and sends the oil to the RAXL motor (3) to drive the motor. The RAXL motor drives the RAXL pump (4). The RAXL pump pulls oil from the
differential and sends the oil through the RAXL oil filter (5) and RAXL manifold (6) to the differential and final drives.
Identify optional raxl oil cooler and fan inside rear frame above rear axle housing
The RAXL system may be equipped an optional RAXL oil cooler (1) and cooling fan. The oil cooler and fan are mounted to the frame above the rear axle housing. The cooling fan is driven by an electric motor (2), which is controlled by the Brake ECM.
RAXL schematic
This schematic shows the oil flow in the rear axle lubrication system with the differential oil temperature warm or above 13°C (55°F).
Oil from the RAXL drive motor pump (1) flows to the RAXL motor and RAXL diverter solenoid (2). When the differential oil temperature is warm, the Brake ECM de-energizes the diverter solenoid and the oil from the RAXL drive motor pump rotates the RAXL motor (3). The RAXL motor drives the RAXL pumps (4), which send oil into the RAXL manifold (5) and through the RAXL oil filter (6).
Oil from the RAXL oil filter flows to the relief valve (7), the final drive bypass solenoid (8), the diverter valve (9), and to the differential (10). The orifice (11) regulates an equal amount of lube oil flow through the differential and the final drive (12). The relief valve limits pressure in the RAXL oil circuit. The final drive bypass solenoid controls the movement of the diverter valve.
When the Brake ECM de-energizes the final drive bypass solenoid, the diverter valve allows oil to flow to the final drives. When the Brake ECM energizes the final drive bypass solenoid, the diverter valve directs oil from the RAXL pump to the differential housing, but not to the final drives. The RAXL strategy prevents the final drives from receiving excessive amount of oil flow under certain temperature conditions. The tubes to the final drives and bevel gear contain orifices that balance the oil flow throughout each final drive.
If the machine is equipped with the auxiliary oil cooler (13), oil flows through the oil cooler before flowing to the differential, the final drive bypass solenoid, and the diverter valve. The plug (14) is installed only if the truck is equipped with the auxiliary oil cooler. NOTE: When the differential oil temperature is cold or below 13°C (55°F), the Brake ECM energizes the RAXL diverter solenoid, and the oil from the RAXL drive motor pump flows to the steering oil tank. The RAXL motor does not rotate and no oil is provided to the RAXL manifold. The Brake ECM also sends a message to the Transmission/Chassis ECM to limit transmission shifting.
Identify components inside right frame rail.
The RAXL motor drive pump (1) is a single section gear pump that is mounted to the front of the steering pump (2) inside the right frame rail. The pump pulls oil through the suction hose (3) and sends the oil through the supply hose (4) to the RAXL motor.
Identify raxl components
The RAXL motor (1) and RAXL pump (2) are mounted to a bracket which is attached to the front of the rear axle housing.
Oil from the RAXL motor drive pump flows to the RAXL motor through the motor inlet hose (3). Oil from the RAXL motor flows to the steering tank through the outlet port (4). The RAXL diverter solenoid (5) controls the oil flow to the RAXL pump. The RAXL pump pulls oil from the differential through a suction screen and the inlet hose (6) and provides the oil to the RAXL manifold (7) through the outlet hose (8).
From the RAXL manifold oil flows to the RAXL oil filter (9), the relief valve (10), and the final drive bypass solenoid (11).
The RAXL oil filter contains a S•O•S port (12) and an oil filter bypass switch (13). The bypass switch is normally closed and will indicate an open status to the Brake ECM when the oil filter is restricted.
The RAXL oil pressure sensor (14) sends a signal to the Brake ECM indicating RAXL oil pressure after the filter. The sensor data is also used by the Transmission/Chassis ECM for the transmission shifting control strategy.
Identify raxl components inside rear axle housing.
These images show the components that route the oil inside the rear axle.
The RAXL pump (1) pulls oil through the screen (2) and suction tube (3) in the rear axle housing.
Oil from the RAXL manifold flows into the differential through outlet hose (4) and through the hose (5), which is located on the front of the differential. Oil is ported through the differential case to the tubes (6) on the rear of the differential. The tubes lubricate the pinion gear and the bearings on each side of the carrier.
Oil from the relief valve (not visible), located on the RAXL manifold (7), is sent through a tube (10) back into the rear axle housing.
When the final drive bypass solenoid (8) is de-energized, oil from the RAXL manifold is sent to the final drives through final drive oil tubes (9).
Identify differential oil temperature sensor.
The differential oil temperature sensor (arrow) is located at the rear of the differential. The differential oil temperature sensor sends a signal to the Brake ECM indicating the oil temperature in the rear axle.
Identify raxl solenoid relay control.
raxl electrical System This image shows the location of the RAXL solenoid relay control (arrow). To access the relay control, remove the rear cover from the cab. The RAXL solenoid relay controls the RAXL diverter solenoid on the RAXL motor and the final drive bypass solenoid on the RAXL manifold.
Explain operation of rear axle lubrication electrical system
This illustration shows the electrical diagram for the rear axle lubrication system. The RAXL Solenoid Relay Control (1) contains two relays that transfer power to the Final Drive Bypass Solenoid (2) and the RAXL Diverter Solenoid (3) upon command of the Brake ECM (6).
The RAXL Final Drive Bypass Solenoid Feedback (4) and the RAXL Diverter Solenoid Feedback (5) are used to read the status of the voltage being applied to the final drive bypass solenoid and the RAXL diverter solenoid. The voltage status is needed because the solenoids are operated from open collector outputs driven by the relays. The Brake ECM cannot directly read the status of the relay output without feedback.
This illustration also shows the following RAXL system components that provide input to the Brake ECM:
* RAXL Oil Pressure Sensor (7)
* RAXL Oil Temperature Sensor (8)
* RAXL Oil Filter Bypass Switch (9)
Explain rear axle lubrication strategy
RAXLLubrication Strategy
The rear axle lubrication strategy has changed. Speed is no longer a factor in the RAXL logic and the Brake ECM will only use temperature to determine when to energize the RAXL diverter solenoid. The RAXL diverter solenoid will be ON (energized) and the RAXL pump will not produce flow when the axle oil temperature is below 56°C (133°F). The RAXL diverter solenoid will be OFF (de-energized) and the RAXL pump will produce flow when the axle oil temperature reaches 58°C (136°F).
The final drive bypass strategy has not changed. When the axle oil temperature reaches 58°C (136°F), the final drive bypass solenoid will be OFF (de- energized) and the lube oil will flow to the final drives. If the machine is traveling greater than 35 km/h (22 mph), the lube oil to the final drives is cycled ON and OFF. This cycling prevents filling the final drives due to the centrifugal force by keeping only a small amount of oil in the final drives.
A temperature gear limit is still used to limit the actual transmission gear to keep the machine from traveling at a high speed until the differential oil has warmed up enough for the lube system to be effective.
NOTE: If the RAXL cooling package is installed, the Brake ECM will energize the fan motor to rotate the cooling fan for five minutes when the RAXL oil temperature is above 85°C (185°F). The fan will stay on if the oil temperature stays above 85°C (185°F). When the RAXL oil temperature decreases below 80°C (176°F) and the fan has been running for more than five minutes, the fan will turn OFF.
Lab 1: Power Train Component Identification
Instructions: Identify the numbered components in the above illustration.
Lab 1: Power Train Component Identification (continued)
Instructions: Identify the numbered components in the above illustration.
Lab 1: Power Train Component Identification (continued)
Instructions: Identify the numbered components in the above illustration.
789D Off-Highway Trucks Power Train Post-Assessment
Instructions: Select the correct answer(s) for each question.
1. Which of the following has been updated in the 789D trucks?
a. Torque convertera.
b. Individual Clutch Modulation (ICM) transmissionb.
c. Parking brake release oil filterc.
d. [Rear Axle Lubrication (RAXL) system]d.
2. The torque converter outlet relief valve _______________.
a. ensures a constant oil pressure to the torque convertera.
b. maintains a constant maximum oil pressure inside the transmission charge filterb.
c. [maintains a constant minimum oil pressure inside the torque converter]c.
d. limits the maximum temperature inside the torque converterd.
3. Which of the following components limits the maximum transmission hydraulic pressure?
a. Pressure differential valvea.
b. Converter inlet relief valveb.
c. [Main relief valve]c.
d. Modulating relief valved.
4. Where is the transmission oil temperature sensor located?
a. [Output transfer gear]a.
b. Transmission oil filter baseb.
c. Torque converter sumpc.
d. Transmission control valved.
5. Which inputs will the Brake ECM use to determine when to energize the RAXL diverter solenoid?
a. Machine speeda.
b. Oil pressureb.
c. [Axle oil temperature]c.
d. Body position sensord.
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POWERTRAIN ON HAULTRUCK 789D
Reviewed by heri
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Reviewed by heri
on
12:06 AM
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