D6K Track-Type Tractor Electrohydraulic Power Train Caterpillar

Switches

Switches provide an open signal, a ground signal, or a +battery signal to the inputs of the ECM. Switches are open or closed.

• When a switch is open, no signal is provided to the corresponding input of the ECM. This "no signal" condition is also called "floating".

• When a switch is closed, a ground signal or a +battery signal is provided to the corresponding input of the ECM.

Brake Pedal and Deceleration Pedal (Limit Switch)

Illustration 1	g01339845

The switch is a limit switch that is mounted on the pedal assembly of the brake. The pedal provides an input to the ECM that controls the braking of the transmission and the control of the parking brake solenoid. When the pedal is fully depressed past the detent, the switch is closed indicating that the operator is requesting the application of the parking brake.

Switch (Parking Brake)

The parking brake switch has a normally open contact and a normally closed contact. The contacts provide switch to ground inputs to the ECM in order to indicate the position of the switch. When the ECM determines that the parking brake switch has been engaged and the machine is in motion, the ECM will fully upstroke the motors and the ECM will fully destroke the pumps. Then, the ECM will apply the parking brake. The following table provides the switch operation for the parking brake switch.

Start Switch (Key)

Illustration 2	g00785945

The keyswitch is an input to the ECM. Power is supplied to the ECM from connector contact J1-1. Power is supplied when the keyswitch is in the START position or when the keyswitch is in the RUN position.

The key start switch is switched to the battery. The input is active when the keyswitch is in the START position. When the input is active, the input will control the start relay. The switch connects to connector contact J2-1. The switch tells the ECM that the operator wants to start the engine. The switch closes to the + battery when the switch is in the START position.

Recall Speed

Illustration 3	g01339851

The switch has a normally open contact that connects to the ECM at contact J1-42. The switch has a normally closed contact that connects to the ECM at contact J1-41. The contacts provide switch to ground inputs to the ECM in order to indicate the position of the switch. When the switch is pressed and held for more than 3 seconds, the forward and the reverse speeds are saved. The preset speeds are recalled if the speeds have been saved. Press the switch and release the switch within 3 seconds in order to recall the speed. The following table is the switch operation.

Horn

Illustration 4	g01339852

This switch activates the horn.

Sensors

Sensors provide information to the ECM about the intent of the operator or changing conditions. The sensor signal changes proportionally to the changing of operator input or changing conditions. The following types of sensor signals are used by the hydrostatic transmission control.

Frequency - The sensor produces a signal and the frequency (Hz) varies as the condition changes.

Pulse width modulated - The sensor produces a signal. The duty cycle of the signal varies as the condition changes. The frequency of this signal is constant.

Analog - The ECM measures the voltage that is associated to a specific condition of the control.

Thumb Switch

Illustration 5	g01339854

The ECM increases the desired speed of the machine when the thumb switch is moved toward the operator. The ECM decreases the desired speed of the machine when the thumb switch is moved away from the operator.

Hystat Joystick

Illustration 6	g01338124

The electrohydraulic control system has a two axis joystick as the operator interface. The joystick is used in order to supply direction and steering commands. The longitudinal displacement of the joystick will control the forward and the reverse direction of the machine. The lateral displacement of the joystick will provide the steering control. The steering sensor of the joystick (1) provides a 500 Hz PWM signal and the joystick F/N/R sensor (2) provides a 500 Hz PWM signal. The signal is proportional to the joystick sensor position for each axis. The range of the sensor in the longitudinal axis is nominal at 27% at the full forward position to 3% at the full reverse position. The range of the sensor in the lateral axis is nominal at 3% at the full left position to 7% at the full right position.

Speed Sensor (Engine)

Illustration 7	g00288428
Speed Sensor (Engine)

The engine speed sensor is an input to the ECM. The sensor tells the ECM the speed of the engine. The engine sensor produces a signal. The frequency of the sensor signal will vary as the engine speed changes. The signal frequency is one pulse per tooth on the flywheel. The ECM uses information from the engine speed sensor and the position sensor for the decelerator pedal in order to perform the underspeed function.

Speed Sensors

Speed Sensor (Left Track)

Speed Sensor (Right Track)

Illustration 8	g00787531

A track speed sensor is integrated into the output stage of the hydrostatic drive motors. The sensor provides two square wave signals that are 90 degrees out-of-phase and the frequency remains proportional to motor speed while the amplitude remains constant. These signals are used in order to calculate both the track speed and the direction of rotation. The sensors require a regulated 8 volt power supply.

Pedal Position Sensors

Brake Pedal and Deceleration Pedal

Illustration 9	g00904530

The position sensors inform the ECM of the position of the pedal that is controlled by the operator. The position sensor outputs a pulse width modulated signal. The duty cycle of the signal will vary in proportion to the position of the pedal. These PWM signals are inputs to the ECM. The ECM uses the signals in order to determine the position of the pedal. The frequency of this signal is constant at approximately 500 Hz. The ECM provides an 10 volt supply to the sensor.

The position sensor for the pedal continuously informs the ECM of the position of the pedal. The ECM uses the duty cycle of the signal in order to determine the position of the pedal. The ECM uses the position of the pedal in order to control the braking of the transmission. The ECM also uses the position of the pedal to control the engine deceleration if the parameter is configured. See Systems Operation Section, KENR5148, "Configuration Parameters" for more information.

If the pedal is pressed past a specific point, the ECM will apply the parking brake. The duty cycle of the sensor decreases as the pedal is depressed.

Travel Pressure Sensor

Illustration 10	g01339834

This sensor is an analog sensor that informs the ECM of the hydrostatic oil pressure within the drive loop of the hydrostatic transmission. The ECM measures a voltage that is associated to the pressure in the drive loop. This information is used in order to maintain an optimal pressure in the drive loop during machine operation.