993K Wheel Loader Power Train Caterpillar

Transmission Clutch

The machine's transmission is controlled by a computer through the use of five solenoids. The five solenoids activate different speed and direction clutches. The following table illustrates the relationship between the desired speed, direction of the transmission, and the energized solenoid valve for each gear:

The clutch solenoid valves are On/Off solenoids that are driven by the outputs of the Power train ECM. The Power Train ECM commands the signal to both the direction and speed solenoid valves during a shift. The hydraulic controls within the transmission engage the speed clutch prior to the direction clutch.

Transmission Shift

Manual shift

The manual shift mode allows the operator to use the inputs on the STIC steering control. The inputs select the speed range and the direction of travel. The selections are made regardless of the engine speed and transmission speed. When the upshift or the downshift switch is pressed, the Power Train ECM will select the next speed range. The next speed is selected when the switch is depressed. Holding a switch in the depressed position will not disable the other switch. The downshift switch is disabled when the transmission is in the first gear. The upshift switch is disabled when the transmission is in the third gear. The top gear can be set by changing the parameter for the top programmable gear.

Inhibit Downshifting

This feature protects the transmission from hazardous downshifts. A downshift is not allowed when the speed of the transmission is above the allowable limit for downshifting into a gear. The following table identifies the speed limits:

This feature is used to identify transmission input or transmission output speeds that are unacceptable in order to allow a transmission downshift to occur. The transmission input speed is not checked for shifts from the second gear forward to the first gear forward. Also, the transmission input speed is not checked for shifts from the second gear reverse to the first gear reverse. The feature also monitors the brake accumulator pressure. The feature is disabled if the brake accumulator pressure is low or lost. The status of the feature is available over the Cat Data Link.

Note: The gear display flashes for five seconds after a downshift is inhibited. The gear flashes in order to inform the operator that the downshift was not performed.

Quickshift

This feature aids the operator during a loading operation. The feature is enabled by using the switch that is located on the console. The feature automatically shifts the transmission to the second gear in the reverse direction when the operator selects a shift from the first gear in the forward direction to the reverse direction. The downshift switch must be used to shift to first gear when the machine enters the pile again.

Parking Brake Interlock

The interlock prevents the machine from accidental movement. The feature also prevents the operator from accidentally driving through the parking brake. The transmission will not shift to first gear forward or first gear reverse when the parking brake is engaged. The ECM shifts the transmission to the Neutral position when the transmission is in a gear and the parking brake is set. The transmission will not shift to a gear when the parking brake is released. The transmission must first be shifted to Neutral in order to shift to a gear.

Driving through the Parking Brake

This feature provides the capability to shift to first gear when the parking brake is engaged. The parking brake is engaged and the plunger that is in the cab pops out if the pressure for releasing the parking brake is not available. The operator can drive through the parking brake for a short distance. Hold the parking brake switch that is located in the cab in the OFF position. The switch contains a spring in order to resist this effort. This switch will automatically move to the ON position when the switch is released. Move the direction switch in the forward position or the reverse position. Do not release the parking brake switch. The transmission will shift to the respective gear. See table 3 for more information.

Programmable Top Gear

This feature allows the service tool to set the maximum transmission gear that is allowed for each direction. The Cat ET or the Advisor can be used to set the top gear.

Steering and Transmission Interlock

This feature neutralizes the transmission. This lockout switch is located in the cab. The transmission is neutralized and the STIC control is physically locked when the switch is in the lock position. The transmission is enabled when the switch is in the unlocked position. Direction shifts out of Neutral are inhibited when the switch is in the locked position. The transmission shifts to Neutral when the switch is placed in the locked position and the transmission is in a forward or reverse gear. The transmission will not shift to a gear when the switch is released. The transmission must shift to Neutral and the switch must be placed in the unlocked position before the transmission is allowed to shift gears.

Ground Level Transmission Lockout

The feature neutralizes the transmission. This lockout switch is located at the service center near the bumper. The STIC control is not physically locked when the switch is in the lock position. This allows the machine to be steered. The transmission is enabled when the switch is in the unlocked position. Direction shifts out of Neutral are inhibited when the switch is in the locked position. The transmission shifts to Neutral when the switch is placed in the locked position and the transmission is in a forward or reverse gear. The transmission will not shift to a gear when the switch is released. The transmission must shift to Neutral and the switch must be placed in the unlocked position before the transmission is allowed to shift gears. The indicator for the transmission lockout is illuminated when the switch is placed in the locked position. The indicator turns off when the switch is placed in the unlocked position. The engine shuts down when the keyswitch that is located in the cab is turned off and the lockout switch is in the locked position. The main relay will remain energized. The machine can be started once the engine speed has been below 400 rpm for more than three seconds.

Override Powerup In A Gear

This feature provides a condition in order to power the transmission regardless of the position of the direction switch when the transmission is in Neutral. The direction switch must pass through neutral before the machine will start. The direction switch must pass through Neutral in order to shift to a gear.

Impeller Clutch

The impeller clutch is used in response to the pedal position for the torque converter and various operating conditions. The clutch is used to reduce speed in any direction to an acceptable level during directional shifts. The clutch is used to reduce the preset level of rimpull that is available from the power train. The clutch is used to increase clutch pressure during high speed direction shifts. The clutch is used to control the pressure under failure conditions.

Reducing Engine Speed

This feature reduces the loads on the drive train during a direction shift. The desired engine speed and the duration of the speed reduction is dependent on the current and requested gear. The duration begins at the start of a shift. The duration ends when the direction clutch locks up. The Power Train ECM sends a message to the Engine ECM in order to reduce the engine speed.

Lockup clutch (Attachment)

This feature is used in order to bypass the torque converter. Then, the feature directly couples the engine to the transmission. The lockup clutch is engaged during the following: enabled switch, transmission in third gear forward, transmission in third gear reverse and transmission input speed of 1500 rpm. The lockup clutch is disengaged when the input speed falls below 1350 rpm.

Ride control (Attachment)

This feature is used to make the ride of the machine smooth by using the weight of the lift arms and bucket. A three-position switch that is located in the cab is used in order to control this function. The ride control is disabled when the switch is in the OFF position. The ride control solenoid is always ON for purposes of service when the switch is in the ON position. The ride control is activated when the ground speed exceeds the programmed activation speed and the switch is in the AUTO position.

Note: The indicator light on the Advisor is illuminated when the switch is in the ON position or the AUTO position.

Autolube (Attachment)

This feature provides a way of automatically lubricating the machine during operation. The autolube charges the lubrication system periodically. Charging causes the injectors to fire. The injectors lubricate the pins on the machine. The feature also provides a means of manually lubricating the system through Advisor, Cat ET, or the manual lubrication switch.

Transmission Oil Level

This feature is used to warn the operator that the transmission oil level is low while the engine is running. See the Operation and Maintenance Manual, SEBU8076 for more information.

Transmission Pump Pressure

This feature provides data for the pressures of the transmission pump.

Powered Access (Attachment)

This feature is a powered lift platform that can raise personnel from the ground to the bumper level. The platform can also lower personnel from the level of the bumper to the ground. The platform can be raised from the ground level controls or from the controls in the lift. The switch is an input to the Power Train ECM. This feature drives a relay. The relay disables the powered access when the parking brake is disengaged or when the direction switch is not in Neutral.

Heated Mirror (Attachment)

This feature provides heat to the mirrors for five minutes. The switch will be turned on for five minutes when the momentary switch for the heated mirror is depressed. The time for heating the mirrors can not be configured. The timer is deactivated when the switch is pressed twice. The mirror will stop heating when the timer expires. Pressing the switch after this time will initiate the cycle for the heater and the timer.

Backup Alarm

The backup alarm sounds in order to alert all personnel that are near the machine that the operator intends to move the machine rearward. Two alarms are located on the machine.

Calculation of Ground Speed

This feature is used in order to calculate the ground speed of the machine. The ground speed is shown in MPH or in km/h.

Protection for the Air Conditioning Compressor

This feature provides protection to the compressor by monitoring various switch inputs and the system voltage. The operation of the compressor may be limited during situations that could damage the operating life of the compressor. The compressor clutch turns on when the HVAC blower switch is ON. The clutch is turned OFF if the system voltage drops below 22 volts or if the system voltage rises above 32 volts. The clutch will remain in a state for fifteen seconds before changing states. The two switch inputs are ignored during the fifteen second interval. The clutch will immediately respond to the switch inputs after the fifteen second interval has expired. This minimum period protects the clutch from damage that is caused by rapid cycling.

Synchronized System Clock

This feature provides a synchronized clock between all of the electronic control modules. The time is sent across the Cat Data Link. The system clock maintains the service hour meter readings between all of the electronic control modules. The system clock also defines the standard accumulation for time of service.

Synchronized Real Time Clock

This feature provides a synchronized clock between all of the electronic control modules. The date and the time zone is sent across the Cat Data Link from the VIMS. The Power Train ECM maintains a real time clock. The ECM requests the current date, time, and the time zone from the VIMS. The Power Train ECM then updates the maintained real time clock with the received information.