938H Wheel Loader and IT38H Integrated Toolcarrier Power Train Caterpillar

Autoshift Control

Illustration 1	g01420183
Left side dash panel (1) Autoshift switch (2) MANUAL position

Illustration 2	g01420184
Right Side of the Cab (3) Transmission downshift switch

Illustration 3	g01420185
(4) Transmission direction and speed control lever

In order for the transmission to shift automatically, the autoshift switch (1) must be in one of the two AUTO positions and the left brake pedal must be fully released. The power train electronic control module (ECM) shifts the transmission automatically. 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 in order to regulate transmission shifts. The power train ECM does not allow upshifts to a speed that is higher than the speed that is selected with transmission direction and speed control lever (4). An automatic downshift from second speed to first speed occurs only if the autoshift switch (1) is in the "1-4" position.

When transmission downshift switch (3) is depressed, the transmission downshift switch signals the power train ECM to downshift the transmission by one speed. Pressing and holding the transmission downshift switch signals the power train ECM to continue to downshift the transmission as the machine speed decreases. The power train ECM delays resuming automatic upshifts for five seconds after the transmission downshift switch is released. Automatic upshifts are enabled if transmission direction and speed control lever (4) is moved from the current direction and the left brake pedal is not depressed. The automatic upshifts are enabled by either of the following:

• Moving the transmission direction and moving the speed control lever

• The five second delay

When the key start switch is turned from the OFF position to the ON position, the power train ECM is activated. When the power train ECM is first activated all the modulating valves (transmission clutch) are de-energized regardless of the position of transmission direction and speed control lever (4). The power train ECM then determines if the transmission direction and speed control lever is in the NEUTRAL position. The power train ECM disables the transmission if the NEUTRAL position is NOT selected. If the NEUTRAL position is NOT selected, the transmission direction and speed control lever must be returned to the NEUTRAL position before a direction can be selected. The power train ECM activates the start relay and the power train ECM allows the engine to start if the transmission direction and speed control lever is in the NEUTRAL position. The power train ECM allows the initial selected speed to be changed if the transmission direction and speed control lever is in the NEUTRAL position.

Note: Transmission direction and speed control lever (4) must be in the NEUTRAL position when the key start switch is turned to the START position. If the transmission direction and speed control lever is not in the NEUTRAL position, the start relay will not be activated when the key start switch is turned.

ReferenceFor more information on the neutral start function, refer to the Service Manual module Systems Operation, "Power Train Electronic Control System" for the machine that is being serviced.

ReferenceFor more information on the transmission direction and speed control lever and the key start switch, refer to the Service Manual module Systems Operation, "Switches" for the machine that is being serviced.

ReferenceFor more information on the power train electronic control module (ECM), refer to the Service Manual module Systems Operation, "Electronic Control Module (Power Train)" for the machine that is being serviced.

Variable Shift Control

Illustration 4	g01420217
Messenger in the "Settings" mode

The variable shift control uses the engine speed in order to provide optional autoshift points. The power train electronic control module (ECM) uses the Messenger setting and the engine speed in order to determine the autoshift points for the transmission.

Illustration 5	g01423642
"Economy" mode

Illustration 6	g01423645
"Mid Range" mode

Illustration 7	g01423646
"Power" mode

The Messenger has three inputs to the power train electronic control module (ECM). The Messenger allows the operator to select a range of operation for the system.

The Messenger has three modes:

• "Econcomy" mode

• "Mid Range" mode

• "Power" mode

The "Econcomy" mode allows the power train ECM to determine shift points at a lower engine speed. Each of the remaining modes increase the shift speeds. The "Power" mode forces the transmission to shift at a higher rpm than the "Mid Range" mode.

Refer to the System Operation, RENR3065, "Monitoring System" for more information on the Messenger operation.

Integrated Braking System

Illustration 8	g01420227
Block Diagram of the Integrated Braking System (1) Power train electronic control module (ECM) (2) CAT Data Link (3) Transmission direction and speed control lever (4) Transmission downshift switch (5) Indicator for the transmission neutralizer (6) Engine speed sensor (7) Torque converter output speed sensor (8) Transmission output speed sensor (9) Left pedal position sensor (10) 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. The Integrated Braking System does not change the transmission direction. The Integrated Braking System neutralizes the transmission if the following conditions are met:

• First speed is engaged or second speed is engaged.

• The transmission neutralizer is enabled.

• The left brake pedal is depressed past the transmission neutralization point.

Illustration 9	g01420229
(11) Calibrated initial brake pressure point (12) Transmission neutralization point (13) Maximum pedal travel (14) Stop light limit switch (15) Left brake pedal position sensor (A) Left brake pedal deadband (B) Downshifting with no service brakes applied. (C) Downshifting with service brakes applied.

Illustration 10	g01420231
(16) Autoshift switch

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

• "Integrated Braking System Manual Mode Enable Status" in the power train ECM

• Left Brake Pedal Position

• Position of the Autoshift Switch

• Actual Transmission Speed

• Calibrated Initial Brake Pressure Point

• Torque Converter Output Speed

• Transmission Output Speed

• Engine Speed

Note: The input from the "Integrated Braking System Manual Mode Enable Status" is used only in the manual shifting mode. The Integrated Braking System is always enabled in the autoshift mode.

The Integrated Braking System is enabled if the following conditions are met:

• The "Integrated Braking System Manual Mode Enable Status" must be set to "Enable".

• The position sensor for the left brake pedal 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, and the position sensor for the left brake pedal do not show any diagnostic codes.

Note: The "Integrated Braking System Manual Mode Enable Status" only needs to be set to "Enable" in the manual shifting mode. The Integrated Braking System is always enabled in the autoshift mode.

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 (11). The Integrated Braking System is in normal mode (C) when the operator depresses the left brake pedal between calibrated initial brake pressure point (11) and the point of maximum pedal travel (13) .

The Integrated Braking System performs the following functions 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 autoshift 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 autoshift 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.

Illustration 11	g01420244
Transmission Downshift Switch

If the autoshift 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.

Depress the switch one time if the ground speed is below the "AUTO 2-1" ground speed.

Depress the switch two times if the ground speed is above the "AUTO 2-1" ground speed.

Illustration 12	g01420252
Transmission Direction and Speed Control Lever

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 autoshift 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 autoshift 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 autoshift switch is in any of the AUTO positions, the Integrated Braking System shuts off. The transmission resumes automatic 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, the Integrated Braking System signals the power train ECM to downshift the transmission speed. The 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: The Integrated Braking System is disabled if the left brake pedal is released beyond left brake pedal deadband (A). After the 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 Messenger is the only input to the transmission neutralizer control. The transmission neutralizer control will be enabled when the machine is started. The indicator for the transmission neutralizer is not illuminated when the transmission neutralizer control is enabled.

The transmission neutralizer control is alternately enabled or disabled when the momentary transmission neutralizer override switch is depressed. The transmission neutralizer 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, engaged transmission speed, transmission neutralization setpoint, status of the transmission neutralizer control and ground speed of the machine.

The following conditions must be met in order for the transmission to be neutralized:

• First speed must be engaged for transmission mode "AUTO 1-4".

• Second speed must be engaged for all positions of the transmission speed switch except "AUTO1-4".

• The left brake pedal must be depressed beyond the transmission neutralization setpoint (12).

• The transmission neutralizer control must be enabled.

The transmission engages after neutralization if the left brake pedal is released and the left brake pedal travels at least four 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 control is disabled.

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

Change the Status of the IBS in ET

Illustration 13	g01420256
(21) Diagnostic Connector (ET)

1. Connect ET to diagnostic connector (21) .

2. Turn the engine start switch key to the ON position, but do not start the engine.

Show/hide table



Illustration 14	g01420258

3. Start the ET software and select "Transmission" under the heading "Select an ECM".

Show/hide table



Illustration 15	g01420261

4. Select the "Configuration Tool" icon.

Show/hide table



Illustration 16	g01420264

5. Under the heading "Available ECM(s)" and "Transmission", select "Axle and Brake Parameters". Then, select "Integrated Braking System Manual Mode Enable Status", as shown. Click on the "Change" button in the bottom left of the screen.

Show/hide table



Illustration 17	g01420272

6. Select "Enable" or "Disable" from the menu.

When "IBS Manual Disable" is configured and the transmission control is in the "Manual" position, the transmission will not downshift when the left brake pedal is depressed. The transmission will be neutralized when the left brake pedal is depressed to transmission neutralization setpoint (12). The transmission will engage when the left brake pedal is released 4 degrees. The transmission will be neutralized if the left pedal is depressed 2 degrees. The transmission is engaged and the transmission remains in current speed gear when the pedal is fully released.

Note: The IBS will still function in the autoshift mode.

ReferenceFor more information on changing the transmission neutralization setpoint, refer to Testing and Adjusting, "Position Sensor (Left Brake Pedal) (Electronic Technician) - Calibrate" for the machine that is being serviced.

Ground Speed Limiter

The ground speed limiter is an optional function that is enabled by a programmable parameter via the Caterpillar Electronic Technician (ET). The ground speed limiter can only be enabled or disabled in ET with a factory password. The software for the ground speed limiter provides a means of setting the maximum ground speed for a machine that is operating on a level surface. The ground speed limiter will attempt to limit the machine to a maximum speed of 20 km/h (12.5 mph).

The software for the speed limiter uses the following inputs to control the ground speed of the machine: engine speed, machine acceleration and ground speed. If a speed sensor fails the ground speed limiter defaults to the engine speeds in table 2.

Note: The software for the speed limiter will not prevent a machine from exceeding the speed limit during downhill travel.