CX28, CX31 and CX35 On-Highway Transmissions Power Train Electronic Control System Caterpillar

Auto Neutral Function

The auto neutral function is used to neutralize the transmission when an external attachment is activated. This function can be programmed to automatically shift back out of neutral if conditions warrant or it may require the operator to reselect his direction again. There are a set of programmable parameters to activate the auto neutral functionality and tailor it to the application.

The auto neutral function parameter will essentially disable the whole feature if programmed to OFF. The auto neutral inputs will not affect the transmission if this feature is programmed to OFF. The second parameter, auto neutral switch type, defines the switch inputs used for the auto neutral function. The switch can be a single input SWC input, single input SWB, or a dual input SWC input.

The following is the input for the single switch to common:

The following is the input for the switch to battery.

Direction Shift Inhibit Function

Direction Shift Inhibit is implemented via J1939 for use with on-highway truck engines. The directional shift management function is used to reduce driveline stress during directional shifts. The Transmission ECU sends a signal to the engine ECU during directional shifts. This signal is used in order to reduce torque during a shift. Cycle the keyswitch in order to activate the feature after the paramter has been selected.

If the direction inhibit function is programmed to OFF, it means the direction inhibit function is disabled. If the parameter is programmed to REV, the direction inhibit is enabled. When a shift to REVERSE is attempted the transmission is locked to NEUTRAL. Locked to NEUTRAL means that the operator must select NEUTRAL on the shift selector before attempting another shift to REVERSE. The shifter display will show "RN". If the parameter is programmed to FOR, the direction inhibit is enabled. When a shift to a forward gear is attempted the transmission is locked to NEUTRAL. Locked to NEUTRAL means that the operator must select NEUTRAL on the shift selector before attempting another shift to a forward gear. The shifter display will show the maximum forward gear available and an N "**N". If the switch is programmed to FORWARD and REVERSE, then the direction inhibit will not allow any shift to a forward gear or reverse. Once the direction has been attained, then the input does not affect the direction selection. When the direction inhibit is enabled by the switch, the switch is in the open position. Once a directional shift has been prohibited, you must select Neutral with the shifter, put the switch in the closed position, and then reselect the desired gear. The transmission will not allow a shift to gear until this has been completed.

Note: If the switch is opened and the direction inhibit is enabled while the transmissin is in gear, the transmission will remain in the active gear. Once the transmission is shifted in to Neutral by selecting "N" on the shifter, any attempt to shift in to a gear that is selected for inhibit will be prohibited.

The function is configurable using the Cat ET service tool. The direction inhibit switch type parameter is used to specify whether a single switch SWC type input or one of the SWB type inputs is used.

Driveline PTO Mode

The Driveline Power Take-Out (PTO) feature allows the transmission to provide mechanical power through the transmission output shaft for non-propulsion purposes. The Driveline PTO feature is used to provide mechanical power to non-propulsion vehicle components, such as pumps or generators. The feature provides modified gear selection, torque converter lockup clutch engagement, and a configurable output shaft brake feature. This customer parameter is used to enable the feature, and program which transmission gear will be used during Driveline PTO operation. The Driveline PTO feature requires the following switch inputs:

• Park Brake

• DPTO Request

• DPTO Latch Enable

Driveline PTO Mode Enable Gear Configuration - The DPTO Mode Enabled Gear Configuration parameter provides the ability to choose the desired gear for DPTO operation. When the feature is programmed to Disabled, the feature will not function.

Driveline PTO Latching Engine Speed - Some applications require the Driveline PTO (DPTO) mode to be disengaged solely based on the engine speed value. This provides a robust system, which once the DPTO is engaged, will continue to function during vehicle electrical faults. A customer parameter is provided to set the engine speed that will "latch" the DPTO mode. Caution should be used in implementing a Driveline PTO Latching speed, in that the only method of neutralizing the transmission is to reduce the engine speed to less than the programmed parameter value. Interrupting electrical power to the transmission, selecting NEUTRAL from the shift selector interface, changing the status of the Driveline PTO switch input to the transmission control, or releasing the parking brake will not ensure the transmission will select a neutral gear.

Driveline PTO Torque Converter Lockup Clutch Engagement Speed - The transmission torque converter clutch may be engaged during DPTO operation, to increase the efficiency of the overall vehicle system. The torque converter lockup clutch may remain disengaged to provide a compliant element in the DPTO system if required. The transmission once the initial DPTO range is attained, will engage the torque converter lockup clutch when the PTO LUC Engagement Speed is exceeded, after a short (- 1 second) delay time is reached. Once engaged, the torque converter lockup clutch will disengage when the engine speed is 200 rpm less than the programmed speed, or if the engine falls below low idle speed.

Driveline PTO Inertia Brake - The Driveline PTO feature includes a mode where, if the NEUTRAL is selected while the parking brake is set and the driveline PTO Engagement request switch is ON, the transmission will apply an internal brake to stop the output shaft speed rotation if the engine, and transmission output shaft speeds are initially less than 1000 rpm.

Driveline PTO Engaged Input - This input indicates that the DPTO driven equipment is mechanically engaged to the transmission output shaft. This input, in conjunction with the Driveline PTO Request input, results in the transmission selecting the gear indicated in the Driveline PTO Mode Enabled Gear Configuration parameter when the operator selects the drive range ("D" button) on the operator shifter interface.

DPTO and Parking Brake Interaction - The Driveline PTO functionality requires the parking brake operation so it should be programmed to ON and the wiring to the parking brake pressure switch circuit installed. The programmed state ON w/Neutralize means that the parking brake will be read, but it will also neutralize the transmission when it is set. The transmission is put in NEUTRAL if the output speed is below the programmed value, the shift selector is not in NEUTRAL, and the parking brake input is set. The transmission is held in NEUTRAL until the operator shifts to NEUTRAL and then back to a range. The transmission will remain in gear until the operator shifts into NEUTRAL or releases then re-applies the parking brake.

Lockup Clutch Function

The lockup clutch controls the direct drive electrically. When the ECU activates the lockup solenoid the lockup clutch in the torque converter mechanically connects the torque converter input shaft to the torque converter output shaft. This mechanically connects the transmission to the engine.

The ECU keeps the lockup clutch engaged as much as possible during normal operation. When the transmission shifts the lockup solenoid is deactivated for easier shifting. The vehicle is in torque converter drive when the lockup solenoid is deactivated.

The transmission's reverse gear and the transmission's neutral gear are torque converter drive. First gear is torque converter drive. The second gear is torque converter drive on the low end and direct drive on the high end. The third gear and all other forward transmission gears are direct drive. Direct drive means that the transmission output shaft is mechanically connected to the input shaft.

First Gear and Torque Converter Lock Up Function

Some vehicle operations require that the torque converter's lock up clutch be engaged when the transmission is in the first gear forward. A typical operation example would be operation on a steep down hill grade that requires engine retarding at slow vehicle speeds. Another example includes preventing transmission oil temperature increases when operating for extended periods of thime while in the first gear forward in torque converter drive. The torque converter's lock up clutch will engage when first gear is the programmed maximum desired gear and the engine speed is more than 1400 rpm. The lock up clutch will disengage when the engine speed is below 1400 rpm.

The maximum desired gear of the vehicle is controlled by the operator by using the down arrow button on the shift pad to the first gear position. The maximum desired gear can also be controled by moving the shift lever to the first gear position.

Note: If the operating conditions require the transmission to upshift to the second gear, the lock up clutch will disengage in order to prevent an engine over speed event.

Neutral To Gear Inhibit Function

The neutral to gear inhibit function provides the ability for inhibiting shifts out of NEUTRAL due to external equipment of the vehicle in operation. This function requires a switch input and programmable parameters through the service tool. If this function is enabled via the programmable parameter, then the function must be integrated in the vehicle wiring. This input can be used in order to prevent unwanted shifts out of neutral when external equipment is operating or other vehicle functions such as a seat switch. Cycle the keyswitch in order to activate the feature after the paramter has been selected.

If the neutral to gear inhibit function is programmed to OFF, it means the direction inhibit function is disabled. If the parameter is programmed to REV, the direction inhibit is enabled. When a shift to REVERSE is attempted the transmission is locked to NEUTRAL. Locked to NEUTRAL means that the operator must select NEUTRAL on the shift selector before attempting another shift to REVERSE. The shifter display will show "RN". If the parameter is programmed to FOR, the direction inhibit is enabled. When a shift to a forward gear is attempted the transmission is locked to NEUTRAL. Locked to NEUTRAL means that the operator must select NEUTRAL on the shift selector before attempting another shift to a forward gear. The shifter display will show the maximum forward gear available and an N "**N". If the switch is programmed to FORWARD and REVERSE, then the neutral to gear inhibit will not allow any shift to a forward gear or reverse. Once the shift has been attained, the input does not affect the gear selection. When the neutral to gear inhibit is enabled by the switch, the switch is in the open position. Once a shift has been prohibited, you must select Neutral with the shifter, put the switch in the closed position, and then reselect the desired gear. The transmission will not allow a shift to gear until this has been completed.

If the switch is opened and the neutral to gear inhibit is enabled while the transmissin is in gear, the transmission will remain in the active gear. Once the transmission is shifted in to Neutral by selecting "N" on the shifter, any attempt to shift in to a gear that is selected for inhibit will be prohibited.

Top Gear Function

This feature is defaulted to "ON", but can be configured to either "ON" or "OFF" using Cat ET. This function limits the maximum ground speed of the vehicle. The ECU prevents upshifting to any gear that is greater than top gear. The value for top gear is stored in the ECU. The value of the top gear is programmable by the service personnel. The value of the top gear is programmed at the factory to the maximum top gear for the particular vehicle model.

Note: The Cat ET service tool can be used to program the top gear function. Use the configuration screen in the Cat ET service tool in order to change the top gear setting.

The range of numbers for the CX28 are listed below.

Factory setting ... 6

Range ... 3 to 6

The range of numbers for the CX31 are listed below.

Factory setting ... 6

Range ... 3 to 6

The range of numbers for the CX35 are listed below.

Factory setting ... 8

Range ... 1 to 8

Alternate Maximum Gear Function

This function allows for customization of the maximum gear in the alternate shift schedules. The default setting is Disabled. Any available gear may be selected as the maximum gear.The shift selector reflects the programmed value on the left of the gear display when the alternate shift schedule is active. The transmission will limit operation to the programmed gear unless an upshift is required in order to prevent an engine over speed event.

Rapid Downshift Function

The ECU does not allow a turnaround shift until a short time after a shift occurs. A turnaround shift is an opposite shift from the previous shift. For example, a downshift is prevented for a short time after an upshift and an upshift is prevented for a short time after a downshift. The turnaround feature allows the conditions to stabilize before an opposite shift. The delay prevents hunting between gears.

Elevated Downshift Function

This function improves retarding performance by elevating the upshift and the downshift points. When the retarder on the service brake is engaged, the ECU raises the shift points.

When the engine retarder is on, the upshift and downshift points are raised because the retarder systems are more effective at higher engine speeds.

Transmission PTO Control Selection

The transmission PTO feature controls the PTO enable output driver at J2-6. The PTO enable driver is used to control an OEM supplied control system that is connected to the transmission's auxiliary output shaft. This output is capable of driving 2 Amps and will be turned ON when all of the programmed conditions have been met.

This function requires a SWC input, an Output Driver, and a set of programmable parameters that are controlled by the service tool. The PTO Control function reads an operator PTO switch input in order to direct it to turn on the PTO driver.

Each system has specific operational conditions that must be met. The operational conditions are set by accessing the programmable parameters with the service tool.

The following items are available for tailoring the PTO operation for a specific vehicle:

PTO Mode Enable - The PTO mode enable parameter must be programmed to enabled before any of the other parameters will be in effect.

PTO Mode Neutral Restriction - The PTO neutral restriction parameter is used to restrict the PTO operation to NEUTRAL. The PTO "ON/OFF" switch status will be ignored when the transmission is not in NEUTRAL.

PTO Mode Gear Limit - The PTO mode gear limit parameter is used to limit the maximum gear that the PTO enable output may be energized. When programmed to FIRST gear, then the PTO enable output may be energized when in NEUTRAL, REVERSE, or FIRST gear. The PTO operation will be blocked the transmission is in SECOND gear or a higher gear.

PTO Mode Maximum Engine Speed for Engagement - The PTO enable output can be restricted from energizing at too high of an engine RPM.

PTO Mode Maximum Engine Speed for Operation - This feature limits the PTO operation to below the programmed engine RPM. When the engine rises above the programmed limit the PTO enable output will de-energize.

PTO Mode Maximum Engine Speed for Engagement - This feature is used in order to prevent the PTO enable output from energizing above the programmed RPM.

PTO Maximum Engine Speed for Operation - This feature is used to limit the PTO operation to below the programmed transmission output shaft speed. When the output shaft speed rises above the programmed limit, the PTO enable output will be de-energized.

Shifter Selection Function

The ability to have two shift selectors is desired for some applications. This function requires a SWC input to the ECU sensor common and some programmable parameters.

Note: The SWC must return to pin J2-22 for sensor common at the ECU. A chassis ground connection for the SWC is incorrect.

When the shift selector input has a closed circuit, then the shift selector input switches to the second shift selector. The switch will only occur if both shift selectors are selecting NEUTRAL, the transmission is in NEUTRAL, and the output speed is zero. The display of the inactive shift selector is blank if it is a push button shift selector. If any of the conditions are not met, then the shift selector input will not switch until all the conditions are met.

The secondary shifter parameter is used to designate whether or not a secondary shifter is installed. When the paramter is programmed to "Not Installed", the transmission will ignore the switch input at contact J2-35. The the parameter is programmed to "J1939", the transmission will respond to the secondary shifter when the circuit is closed at contact J2-35.

Note: When the secondary shifter is installed, the display will show the active gear selection of the transmission.

Economy Shift Mode

This function is a SWC input or switch via the Mode switch on the shift selector. The economy mode is used to lower the full throttle shift points. This mode is typically used for lightly loaded vehicles in urban environments. OFF means the input is disabled. On means the input is enabled. If the SWC input has a closed circuit, then the transmission control has the economy mode active. When the "MODE" button is used to activate the feature, the "MODE" button LED will be enabled. The LED will remain enabled as long as the feature is active.

Hold Input Function

This function requires a SWC input and a programmable parameter through the service tool. When the hold input is set, the transmission will attempt to hold the current gear. The transmission will only upshift at the engine over speed point. Normal downshifting is allowed as the vehicle slows down. As the transmission downshifts, the hold continues which means that the transmission will stay in the downshifted gear unless the engine over speed point allows it to upshift again.

OFF means the input is disabled. ON means the input and function are enabled. The hold input can be a SWC input or the Mode Button on the shift selector. The hold input button is a momentary switch when used with a SWC input.

If the transmission is in a forward range and the "MODE" button is pressed and released, the hold function is active and the current selected gear is the gear to attempt to hold. If the operator presses and releases the "MODE" button again, then the function is disabled. If a different range is selected, the hold function is disabled. Selecting a different range can be done by choosing NEUTRAL or by pushing the up or down buttons on the shift selector.

Quick Gear Limit

The Quick Gear Limit feature is used to limit the transmission gear selection to a customer-specified level, when OEM installed inputs to the transmission control indicate gear-limited transmission operation is desired. The Quick Gear Limit Feature utilizes an OEM installed switch circuit or shift selector MODE switch activation to indicate that the transmission will not upshift beyond 1^st gear. This feature can be used to effectively limit vehicle speed during vehicle maneuvering or stop-and-go driving during refuse applications. Further, the reverse range may be inhibited during Quick Gear Limiting if desired. The Quick Gear Limit feature only inhibits upshifts past 1^st gear. If the transmission is above 2^nd gear, the transmission will continue to operate normally until 2^nd gear is attained, at which time upshift will normally be inhibited. Vehicle operation conditions sufficient to over speed the engine in 1^st gear will result in an engine-protection upshift to higher gears.

Quick Gear Limit Function Customer Parameter Programming -

Programming as shown enables the Quick Gear Limit function:

Quick Gear Limit Switch Customer Parameter Programming - The quick Gear Limit switch may be programmed to any one of 4 inputs. Three switch to battery positive, and one switch to sensor common inputs are available.

Quick Gear Limit Input-Switch to Battery - The Quick Gear Limit Input may be configured as a switch-to-battery input, using any of the 3 switch-to-battery inputs available on the transmission control.

Quick Gear Limit Input-Switch to Common - The Quick Gear Limit Input is configured as a switch to common.

Quick Gear Limit Logic - The Quick Gear Limit feature only limits the transmission-selected gear to 1^st forward, or 1^st forward and 1^st reverse. If the transmission is in 3^rd or higher gear when the Quick Gear Limit Switch is ON, the transmission will not take any actions to effect the shift points. IF the transmission is in 2^nd gear or lower, the transmission will inhibit upshifts until the Quick Gear Limit switch is OFF.