POWER TRAIN COMPONENTS
3. Controlled current output driver: The ECM will energize the solenoid with 1.25 amps for approximately one half second and then decrease the level to 0.8 amps for the
duration of the on time. The initial higher amperage gives the actuator rapid response and the decreased level is sufficient to hold the solenoid in the correct position. An added benefit is an increase in the life of the solenoid.
The Power Train ECM controls the transmission speed and directional clutches. The Power Train ECM interprets signals from the shift lever to signal the transmission to perform the following options: Upshift, Downshift, Forward Neutral, and Reverse.
The Power Train ECM communicates through the CAT Data Link. The CAT Data Link allows high speed proprietary serial communications over a twisted pair of wires. The CAT Data Link allows different systems on the machine to communicate with each other and also with service tools such as Caterpillar Electronic Technician (ET).
The Power Train ECM has built-in diagnostic capabilities. As the Power Train ECM detects fault conditions in the power train system, it logs the faults in memory and displays them on the Caterpillar Monitoring System.
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Power Train Electrical System
This illustration shows the input components which provide power or signals to the Power Train ECM.
Power Train ECM Inputs:
Shift lever (Forward, Neutral, Reverse, and Gear): Combines control of the transmission shifting to a single input device. The shift lever can be pushed forward, backward, or placed in the middle position for machine direction. The lever is rotated in order to change the speeds of the transmission. This is the standard control for shifting that comes with the Hand Metering Unit (HMU) steering.
Direction switch (Forward, Neutral, Reverse, Upshift, and Downshift): Combines control of the transmission shifting with a single input device. The 3 position switch controls direction and the 2 thumb-switches controls upshift and downshift. This is the control for shifting that comes with the Command Control Steering (CCS).
Key start switch: Provides a signal to the Power Train ECM when the operator wants to start the engine. The direction switch/shift lever must be in the NEUTRAL position before the Power Train ECM will permit engine starting.
Transmission Output Speed Sensor 1 and 2
Power Train ECM Pedal Position Sensor Shift Lever
Auto / Manual Speed Selector Switch (CCS Option)
Primary Steering Pressure Switch Secondary Steering
Pressure Switch Torque Converter Output Speed Sensor
Ride Control Switch
Location Code 2 (Ground) +24 Battery Voltage
Location Code Enable (Ground) Auto / Manual Speed
Selector Switch (HMU)
Variable shift control selector switch: The variable shift control switch is an input of the Power Train ECM. The switch allows the selection of a range of shifting points in the Power Train ECM for each speed. The switch has three inputs to the power train ECM.
Transmission output speed sensors: These sensors measure the transmission output speed in the range of 25 to 3000 rpm. By looking at the difference in phase in between these 2 sensors, direction can be derived.
Torque converter output speed sensors 1 and 2: Measures the torque converter speed in the range of 25 to 3000 rpm.
Auto/manual speed selector switch (HMU): Signals the Power Train ECM which shift mode the operator wants to operate on a standard machine. The operator can select between manual shifting or automatic shifting in the range of gears 4 to 2 or in the range of gears 4 to 1.
Maximum gear, if lower gear than 4 is desired, will be determined by the shift lever position.
Auto/manual speed selector switch (CCS option): Signals the Power Train ECM which shift mode the operator wants to operate on a machine with the optional Command Control Steering.
The operator can select between manual shifting and automatic shifting with maximum gear of 4, 3, or 2 and also a 4 to 1 range shifting mode.
Primary steering pressure switch: Sends a signals the Power Train ECM if the primary steering system loses steering oil flow.
Secondary steering pressure switch: It tells the ECM if the secondary steering pump is correctly building up pressure. When the pump is running and we still do not see pressure a warning indicator is lit. It is mostly used as feedback for the start-up test and the manual switch test to ensure that the system is working properly.
Left pedal position sensor: Signals the position of the torque converter pedal to the Power Train ECM. The position of the pedal is being used to downshift the transmission and
neutralize the transmission during operation. Both the downshift and neutralization function of the pedal can be disabled and hence the pedal would function as a brake pedal only.
Parking brake pressure switch: Provides a signal to the Power Train ECM when the pressure is adequate to release the parking brake.
Ride control switch (ON/OFF/AUTO): Signals the Power Train ECM which mode the operator wants to operate. The operator should never operate in ON mode since this is the service mode.
Transmission neutralizer disable switch: Provides an input to the Power Train ECM that will disable the the left pedal neutralization of the transmission.
Transmission oil temperature sensor: Provides an input to the Power Train ECM with the temperature of the transmission oil.
ECM to downshift the transmission. This switch is only used on a HMU steering machine.
Engine speed: The Power Train ECM receives the engine speed over the CAN Data Link from the Engine ECM.
Location code enable (grounded): The location code enable is a grounded input signal to the Power Train ECM that enables the location code detection feature to become active. J1-32 pin on the Power Train ECM connector is connected.
Location code 2 (grounded) : The location code pin number 2 is a grounded input signal that establishes the ECM is dedicated to the Power Train operation. J1-27 pin on the Power Train ECM connector is connected.
+24 Volts: Unswitched power supplied to the Power Train ECM from the battery.
Engine Start Switch and Diagnostic Service Tool Connector
The engine start switch (1) signals the Power Train ECM that the operator wants to start the engine. The ECM determines if the transmission directional switch (not shown) is in the NEUTRAL position. When the directional switch is in the NEUTRAL position and the key start switch (1) is turned to the START position, the ECM energizes the starter relay.
The diagnostic service tool connector (2) for a laptop computer using Caterpillar Electronic Technician (ET) are on the front panel on the right side.
A laptop computer with ET can be used for: calibrating, checking and clearing fault codes, and monitoring system inputs and outputs for troubleshooting the transmission system.
Also shown are the the hazard switch (3), and the 12 Volt adapter socket (4).
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Transmission Shift Lever
This is a picture of the standard type of transmission shift lever control group (arrow) that is found on the 966H/972H Wheel Loaders. This control group is found on machines with conventional (HMU) steering systems.
The shift lever is mounted on the left side of the steering column. The operator moves the shift lever forward to travel in the FORWARD direction or toward the rear to travel in the
REVERSE direction.
FIRST through FOURTH speeds are selected by rotating the shift lever.
When the transmission is in the Manual Mode, the Transmission ECM allows the shift lever to control the transmission. The Transmission ECM shifts the transmission to the exact gear and direction shown on the shift lever.
When the transmission is in the Automatic Mode, the shift lever selection is the maximum gear the transmission will obtain. The Power Train ECM will automatically select the correct speed clutches (SECOND, THIRD, or FOURTH) based on the engine and transmission output speeds.
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Transmission Shift Control
This illustration shows the transmission shift control for the optional Command Control Steering (CCS).
The directional control switch (1), and the upshift/downshift switch (2) are mounted on the left side of the half moon shaped steering wheel.
The directional control switch is a three-position switch with which the operator selects either FORWARD (toggle forward), NEUTRAL (center position), or REVERSE (toggle backward) directions. The switch position the operator selects closes (grounds) that contact while the remaining two contacts stay open. Closing a switch contact sends a signal to the Power Train ECM indicating the direction selected by the operator.
The upshift switch/downshift switch are identical in construction and operation. When the operator wants to manually shift to a higher or lower gear, the upshift switch or downshift switch is pressed. Each switch has two input connections at the Power Train ECM. When the switches are not activated, one connection is closed (grounded) and the other connection is open. When the operator pushes the upshift or downshift switch, the selected switch
momentarily reverses connections to signal the Power Train ECM to change the desired speed.
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This illustration shows the location of the ride control ON/OFF/AUTO switch (1). The ride control switch has three positions. In the center position, ride control is disabled. In the UP position (as shown) the ride control switch is in the AUTO position. With the switch in AUTO, the ride control system will be enabled when the machine is traveling at least 9.5 km/h (6.0 mph). The SERVICE position (as shown on the switch) is used for service to the ride control system.
The transmission neutralization disable switch (2) is used to disable the neutralization of the left brake pedal. Pressing the upper section of the switch will activate the override. When the neutralization is enabled, the left brake pedal will not neutralize the transmission, but will function as a service brake only. The normal, default position of the switch is the lower (released) position
The heated mirror switch (3) enables the heated mirror relay that is located behind the operator seat below the Power Train ECM.
If the machine is equipped with the optional secondary steering, there will be a secondary steering test switch (4) mounted in the blocked position on the panel. When the switch is depressed it feeds a ground signal to a relay and also to a switch input on the Power Train ECM. The relay turns on the secondary steering pump and motor, which supplies flow for the steering system.
The Power Train ECM is monitoring the pressure of the secondary steering hydraulic lines.
This action ensures the pressure has increased to an acceptable level while the pump is running.
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If the switch is depressed and the pressure is not increased to the acceptable level within 3 seconds, the secondary steering warning indicator will be illuminated to indicate that the pump is not functioning properly.
The 966H and 972H Wheel Loaders are equipped with a variable shift control switch (1). The variable shift control uses the engine speed in order to provide optional autoshift points. The Power Train (ECM) uses the position of the variable shift control switch and the engine speed to determine the autoshift points for the transmission. The variable shift control switch has three inputs to the Power Train Electronic Control Module (ECM).
The Auto/manual gear selector switch (2) sends a signal to the Power Train ECM to control shifting mode in auto. The Power Train (ECM) shifts the transmission automatically. To regulate transmission shifts, the Power Train ECM evaluates the input that is sent from the engine speed sensor, the transmission speed sensors, the torque converter output speed sensor, and the left brake pedal position sensor. The automatic mode of operation is represented by two numbers that are separated by a dash. The first number indicates the speed of the transmission when the transmission is placed into gear. The second number indicates the highest speed of the transmission when the machine is traveling.
For example, place the autoshift control switch into the 2-4 position. The machine will automatically shift into second gear when the transmission is placed into gear. The transmission will automatically upshift into fourth gear as the machine accelerates.
The Power Train ECM does not allow an upshift to a speed that is higher than the speed that is selected with the transmission direction and speed control lever. An automatic downshift from second speed to first speed occurs only if the autoshift switch is in the 1-4 position.
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This illustration shows the panel with the optional Command Control Steering. The
Auto/Manual gear selector switch sends a signal to the Power Train ECM to control shifting mode in auto. In the MANUAL position, the operator is responsible for upshifting and
downshift the transmission. The Power Train ECM automatically shifts the transmission if the autoshift switch is in one of the four AUTO positions and the left brake pedal must be released.
To regulate transmission shifts, the Power Train ECM evaluates the inputs that are sent from the engine speed sensor, the transmission speed sensors, the torque converter output speed sensor, and the left brake pedal position sensor.
When the machine is operating in "AUTO" mode, the transmission speed selector switch can be used in order to downshift the transmission. This switch is normally used to downshift from second speed to first speed in order to load a bucket. The transmission will remain in the downshifted gear for three seconds after the switch is released. Then, automatic shifting will resume. If the transmission is downshifted to first speed, the machine remains there until there is a direction change or a manual upshift.
For example, place the autoshift switch into position "3." The machine will automatically shift into second gear when the transmission is placed into gear. The transmission will automatically upshift into third speed when the machine accelerates. An automatic downshift from second speed to first speed occurs only if the autoshift switch is in the 1-4 position.
The Power Train ECM does not allow an automatic upshift to a speed that is higher than the speed that is selected with the auto/manual switch. The autoshift switch is used to select the top speed for the transmission when the transmission is in the AUTO mode. There are four modes of automatic operation: 4 position, 3 position, 2 position and 1-4 position.
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The Power Train ECM receives inputs from three speed sensors on the transmission. The sensors are:
- No. 1 output speed sensor (1) - No. 2 output speed sensor (2).
- Torque converter output speed sensor (3)
The output speed sensors (1 and 2) are positioned out of phase with each other. The Power Train ECM uses the phasing of the input data to determine the direction of rotation of the intermediate and output gears. The torque converter output speed sensor measures torque converter output speed in the range of 25 to 3000 rpm.
The Power Train ECM has no direct feed back information to determine if clutch engagement and disengagement is completed. The Power Train ECM uses the speed sensor information, including the engine speed sensor data, to measure expected clutch slippage and planetary speeds to ensure the transmission is shifting according to the application program stored in the ECM memory.
The speed sensor information is also used by the Power Train ECM to set and adjust transmission shift points.
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Transmission Oil Temperature Sensor
The transmission oil temperature sensor (arrow) is a two-wire passive temperature sensor that is located on the left side of the machine. The sensor is an input to the Power Train ECM. The oil temperature sensor information is used to adjust transmission clutch fill times.
The transmission oil temperature sensor information is also sent by the Power Train ECM to the Caterpillar Monitoring System over the Cat Data Link.
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Left Brake Pedal Position Sensor
The left brake pedal position sensor (arrow) is located in the cab as part of the left brake pedal.
The position sensor (left brake pedal) sends an input to the Power Train ECM. The sensor continuously generates a 500 Hz PWM signal. The duty cycle varies in proportion to the position of the left brake pedal position sensor. The left pedal position sends a change in the input signal to the Power Train ECM. The ECM measures the duty cycle in order to determine the position of the pedal for downshifting the transmission and neutralizing the clutches.
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Implement Pod Downshift Switch And Remote F-N-R Switch
The downshift switch (1) is located on the implement pod. If the machine is equipped with a joystick, the downshift switch will be located on the joystick handle.
When the Power Train ECM is operating in the Manual Mode, depressing the downshift switch will cause a downshift from SECOND speed to FIRST speed. In the Manual mode, the
downshift switch will not shift from FOURTH to THIRD speed or from THIRD to SECOND speed. The transmission will remain in FIRST speed until one of the following conditions occurs:
1. A directional shift is made.
2. The shift lever is moved to NEUTRAL before selecting a speed.
3. The shift lever is turned to FIRST speed and then to another speed.
When operating in the Automatic mode, depressing the downshift switch causes the Transmission ECM to downshift the transmission at a higher than normal ground speed.
Pressing and immediately releasing the downshift switch causes the Transmission ECM to immediately downshift the transmission one speed range. A downshift will occur only if the machine speed and engine speed will not result in an engine overspeed.
Automatic shifting is disabled for five seconds after the downshift switch is pressed. After five seconds, automatic shifting, based on speed sensor inputs, is reactivated.
NOTE: The remote F-N-R switch (2) is only installed on the machines that are equipped with the standard HMU steering.
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Parking Brake Pressure Switch
The parking brake pressure switch (1) is a normally closed switch with the parking brake engaged. When the parking brake is engaged, the parking brake indicator light (3) will be illuminated. When the parking brake knob is pushed to the IN position, the parking brake valve (2) will direct oil pressure to the parking brake release cylinder. The parking brake pressure switch will open, turning the parking brake indicator light OFF. Then, the Power Train ECM will receive a signal that the parking brake is disengaged.
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Based on the input signals, the Power Train ECM energizes the appropriate transmission control modulating valve for speed and directional clutch engagement. The Power Train ECM also energizes the starter relay when starting the machine and the back-up alarm when the operator selects a reverse gear.
The Cat Data Link connects the Power Train ECM to the other machine ECMs. The Cat Data Link also connects the ECM to the Caterpillar Monitoring System and electronic service tools such as Caterpillar Electronic Technician (ET).
Power Train ECM Outputs:
Engine start relay: The Power Train ECM energizes the key start relay when the appropriate conditions are met to start the engine. Controls the current between the key start switch and the starter relay.
Transmission oil filter bypass indicator LED: The Power Train ECM illuminates the indicator LED when the oil is bypassing the transmission filter.
Low fuel level warning indicator LED: The Power Train ECM illuminates the indicator LED when the fuel level in the tank is below 10% of total fuel tank volume as read by the fuel level sensor (input to EMS-III communicated over Cat Data Link).
Clutch 3
Power Train ECM Cat Data Link
OUTPUT COMPONENTS
Clutch 6 1st Speed Solenoid
Clutch 6 1st Speed Solenoid