966G Wheel Loader and 972G Wheel Loader Power Train Caterpillar

Illustration 1	g00774660
Block Diagram of the Integrated Braking System (1) Power train electronic control module (ECM). (2) CAT Data Link. (3) Transmission direction and speed control (conventional steering). (4) Transmission direction and speed control (command control steering). (5) Transmission downshift switch (conventional steering). (6) Five-position transmission auto/manual switch (command control steering). (7) Three-position transmission auto/manual switch (conventional steering). (8) Engine speed sensor. (9) Transmission neutralizer on/off indicator. (10) Torque converter output speed sensor. (11) Transmission neutralizer override switch. (12) Transmission output speed sensor. (13) Left pedal position sensor. (14) Transmission output speed sensor.

The Integrated Braking System enables the operator to downshift the transmission by depressing the left brake pedal. Downshifting the transmission reduces the ground speed of the machine before the brakes are actually applied. The Integrated Braking System only changes the transmission speed. Integrated Braking System does not change the transmission direction. The Integrated Braking System neutralizes the transmission if first speed or second speed is engaged, the transmission neutralizer is enabled and the left brake pedal is depressed past the transmission neutralization point.

Illustration 2	g00774838
Left brake pedal (15) Calibrated Initial Brake Pressure Point. (16) Calibrated neutralization point. (17) Maximum pedal travel. (18) Stop light limit switch. (19) Left brake pedal position sensor. (A) Left brake pedal deadband. (B) Initial mode. (C) Normal mode.

Illustration 3	g00774922
Transmission Autoshift Switch (Conventional Steering)

Illustration 4	g00774924
Transmission Autoshift Switch (Command Control Steering)

The Integrated Braking System uses the following inputs in order to downshift the transmission.

• Left Brake Pedal Position

• Position of the Transmission Auto/Manual Switch

• Actual Transmission Speed

• Calibrated Initial Brake Pressure Point

• Torque Converter Output Speed

• Transmission Output Speed

• Engine Speed

The Integrated Braking System is enabled in all of the positions of the transmission auto/manual switch if the following conditions are met.

• Left brake pedal position sensor has been calibrated.

• Engine speed is below 2425 RPM.

• The left brake pedal is depressed beyond left brake pedal deadband (A) .

• The torque converter output speed sensor, transmission output speed sensors or left brake pedal position sensor do not show any diagnostic codes.

Initial Mode and Normal Mode

The Integrated Braking System is in initial mode (B) when the operator depresses the left brake pedal between left brake pedal deadband (A) and calibrated initial brake pressure point (15). The Integrated Braking System is in normal mode (C) when the operator depresses the left brake pedal between calibrated initial brake pressure point (15) and the point of maximum pedal travel (17) .

The Integrated Braking System performs the functions that follow when the operator depresses the left brake pedal in initial mode or normal mode.

If the transmission is in third speed or fourth speed, the transmission will downshift one speed at a time until second speed is reached. The transmission will downshift regardless of the position of the transmission auto/manual switch. Each downshift will occur when the transmission output speed decreases to the shift point for the current transmission speed.

The transmission will downshift from second speed to first speed if the transmission auto/manual switch is in the AUTO 1-4 position. The transmission will downshift when the transmission output speed decreases to the 2-1 shift point for initial mode or for normal mode. If the transmission auto/manual switch is in the AUTO 1-4 position, the transmission will downshift from second speed to first speed when the transmission output speed decreases to the 2-1 shift point for initial mode or normal mode.

Illustration 5	g00774949
Transmission Downshift Switch (Conventional Steering)

Illustration 6	g00774950
Transmission Downshift Switch (Command Control Steering)

If the transmission auto/manual switch is not in the AUTO 1-4 position, the transmission will not downshift from second speed to first speed unless the operator depresses the transmission downshift switch. The operator may need to depress the transmission downshift switch twice. The ground speed of the machine determines if the transmission downshift switch is depressed one time or two times.

Illustration 7	g00774968
Transmission Direction and Speed Control (Conventional Steering)

After the operator releases the left brake pedal and the left brake pedal returns beyond left brake pedal deadband (A), the events that follow occur.

• If the transmission auto/manual switch is in the MANUAL position, the Integrated Braking System shuts off. The power train ECM upshifts the transmission sequentially to the speed that is selected by the transmission direction and speed control. This occurs only in machines that are equipped with conventional steering.

• If the transmission auto/manual switch is in the MANUAL position, the Integrated Braking System shuts off. The transmission remains in the speed that was engaged. This occurs only in machines that are equipped with command control steering.

• If the transmission auto/manual switch is in any of the AUTO positions, the Integrated Braking System shuts off. The transmission auto shift control resumes control of speed shifts. This occurs in machines that are equipped with conventional steering or command control steering.

Safe Mode

The Integrated Braking System will enter safe mode if the engine speed exceeds 2550 RPM or torque converter output speed exceeds 3500 RPM.

If the Integrated Braking System enters safe mode, the Integrated Braking System will signal the power train ECM to upshift the transmission speed.

When the transmission output speed is less than the corresponding safe mode shift point, Integrated Braking System signals the power train ECM to downshift the transmission speed. Integrated Braking System will return to the initial mode or to the normal mode. The mode is dependent upon the position of the left brake pedal.

Note: Integrated Braking System is disabled if the left brake pedal is released beyond left brake pedal deadband (A). After Integrated Braking System is disabled, the power train ECM controls the transmission shifts according to the normal power train ECM shift logic.

Transmission Neutralizer

The transmission neutralizer override switch is the only input to the transmission neutralizer enable control. The transmission neutralizer enable control will be enabled when the machine is started. If the transmission neutralizer enable control is enabled, the transmission neutralizer on/off indicator is not illuminated.

The transmission neutralizer enable control is alternately enabled or disabled when the momentary transmission neutralizer override switch is depressed. The transmission neutralizer enable control is disabled if there are any diagnostic codes in the left brake pedal position sensor.

The transmission neutralizer control uses the inputs that follow: left brake pedal position, position of the transmission auto/manual switch, engaged transmission speed, calibrated neutralization point, status of the transmission neutralizer enable control and ground speed of the machine.

The transmission neutralizer control has two modes of operation, normal loading and truck loading. The mode of operation is determined by two factors, the type of transmission direction and speed control and the position of the transmission auto/manual switch. Refer to Table 1 that follows for the possible modes for the transmission neutralizer.

Normal Mode

If the machine is in normal mode, the following conditions must be met in order for the transmission to be neutralized.

• First speed or second speed must be engaged unless the transmission auto/manual switch is in the AUTO 1-4 position. If the transmission auto/manual switch is in the AUTO 1-4 position, first speed must be engaged.

• The left brake pedal must be depressed at least to calibrated neutralization point (16) or beyond the calibrated neutralization point.

• Ground speed of the machine must be less than 7.2 km/h (4.5 mph) if first speed is engaged. Ground speed of the machine must be less than 10.5 km/h (6.5 mph) if second speed is engaged.

• The transmission neutralizer enable control must be enabled.

Note: The transmission will be neutralized until the left brake pedal is released and the left brake pedal travels two degrees from the maximum depressed position. The maximum depressed position of the left brake pedal is stored by the transmission neutralizer enable control until the left brake pedal is fully released.

The transmission engages after neutralization if the left brake pedal is released and the left brake pedal travels up two degrees from the maximum depressed position. The transmission will be neutralized again if the left brake pedal is depressed to the maximum depressed position that was stored. If the operator depresses the left brake pedal past the current maximum depressed position, the new maximum depressed position is stored.

The transmission engages after neutralization if the transmission neutralizer enable control is disabled.

The transmission neutralizer enable control will shut off when the operator releases the left brake pedal to the fully released position. After the left brake pedal returns to the fully released position, the maximum depressed position is reset for the next neutralization.

Reference: For more information on calibrating the neutralization point, refer to Testing and Adjusting, "Position Sensor (Left Brake Pedal) - Calibrate" for the machine that is being serviced.

Truck Loading Mode

If the machine is in Truck Loading Mode, the following conditions must be met in order for the transmission to be neutralized.

• First speed or second speed must be engaged.

• The left brake pedal must be depressed to calibrated neutralization point (16) or beyond the calibrated neutralization point.

• Ground speed of the machine must be less than 7.2 km/h (4.5 mph) if first speed is engaged. Ground speed of the machine must be less than 10.5 km/h (6.5 mph) if second speed is engaged.

• The transmission neutralizer enable control must be enabled.

The transmission engages after neutralization if the left brake pedal is released and the left brake pedal travels at least two degrees upward from the maximum depressed position. The transmission will be neutralized again if the left brake pedal is depressed two degrees from the current left pedal position.

The transmission engages after neutralization if the transmission neutralizer enable control is disabled.

The transmission neutralizer override control is disabled if the left brake pedal travels two degrees past calibrated neutralization point (16) .

Reference: For more information on calibrating the neutralization point, refer to Testing and Adjusting, "Position Sensor (Left Brake Pedal) - Calibrate" for the machine that is being serviced.