793D Off-Highway Truck Power Train: Position Sensor (Truck Body), Speed Sensor (Transmission), Solenoid Valve (Upshift and Downshift) & Solenoid Valve (Lockup Clutch)

1.-Position Sensor (Truck Body)

(1) Rod(2) Truck body position sensor

Truck body position sensor (2) is located on the left rear frame near the pivot pin for the truck body. The rod (1) is connected between the truck body position sensor (2) and the truck body. When the truck body is raised, rod (1) rotates truck body position sensor (2). This rotation changes the Pulse Width Modulated signal that is sent to the Power Train Electronic Control Module (Power Train ECM). The adjustment of the rod between the sensor and the truck body is very important. The length of the rod should be 360.0 ± 3.0 mm (14.17 ± 0.12 inch) from the center of both rod ends.

After rod (1) has been adjusted, the Power Train ECM will perform a calibration. The truck body position sensor (2) is calibrated by the Power Train ECM when all of the following conditions exist:

• The engine is running for one minute with no ground speed.
• The hoist control is in the FLOAT position.
• The signal from the truck body position sensor is 6 degrees different from the previous calibration.
• The duty cycle output must be less than 20 percent.

Truck body position sensor (2) is used to limit the top gear while the truck body is up. The Power Train ECM comes from the factory with the top gear value that is set to FIRST gear. The transmission will not shift past FIRST gear until the truck body is down. The top gear value is programmable by utilizing the Electronic Control Analyzer Programmer (ECAP) or the Electronic Technician (ET). The top gear value can be changed to SECOND gear, THIRD gear, or FOURTH gear.

The signal from truck body position sensor (2) is also used to control the SNUB position of the hoist control valve. The Power Train ECM will signal the hoist proportioning solenoids to move the hoist control valve to the SNUB position as the lowering truck body nears the frame. The speed in FLOAT is reduced in the SNUB position in order to prevent the truck body from contacting the frame too hard.

The signal from the truck body position sensor (2) provides warnings to the operator when the truck is moving with the truck body UP.

2.-Speed Sensor (Transmission)

(1) Location of the transmission speed sensors

(1) Transmission speed sensors(2) Gear

There are two speed sensors (1) for the transmission. Each transmission speed sensor (1) receives power from the Power Train Electronic Control Module (Power Train ECM). Transmission speed sensor (1) uses this current and power in order to send a signal to the Power Train ECM. Gear (2) for transmission speed sensors (1) has 30 teeth. Gear (2) for transmission speed sensors (1) is connected to the transmission output shaft.

The speed of the gear teeth will determine the signals that are sent by transmission speed sensors (1) to the Power Train ECM. This informs the Power Train ECM of the ground speed of the machine. This information and the information from the shift lever switch allow the transmission to automatically shift while the ground speed changes. The transmission will automatically shift until the information from the transmission gear switch signals the Power Train ECM to stop automatic shifts.

Usually, the transmission will not shift into a higher speed than the speed that is selected on the transmission control. During overspeed conditions, the transmission will upshift by one gear or the transmission will unlock the torque converter.

When the signals from transmission speed sensors (1) indicate a downshift, the Power Train ECM will automatically downshift.

3.-Solenoid Valve (Upshift and Downshift)

Transmission hydraulic control (1) Upshift solenoid (2) Downshift solenoid(3) Lockup solenoid

The solenoids receive an electrical signal from the Power Train Electronic Control Module (Power Train ECM). The solenoids supply hydraulic oil pressure for mechanical work. When upshift solenoid (1) and downshift solenoid (2) are activated, the solenoids allow hydraulic oil to flow to the rotary actuator. The hydraulic oil pressure turns the rotary actuator until upshift solenoid (1) or downshift solenoid (2) stops the hydraulic flow. The Power Train ECM keeps the solenoid activated until the correct signal is received from the transmission gear switch. The rotary actuator is connected to the rotary selector spool. The transmission gear switch is connected to the rotary actuator by a flexible coupling.

When the rotary selector spool is in the correct position, the Power Train ECM stops the current flow to the solenoid. The solenoid stops the oil pressure that is going to the rotary actuator. The rotation of the rotary selector spool stops. This sequence occurs for every upshift of the transmission or downshift of the transmission except in NEUTRAL. In the NEUTRAL position, the Power Train ECM will keep downshift solenoid (2) activated after the shift is complete.

4.-Solenoid Valve (Lockup Clutch)

Transmission hydraulic control (1) Upshift solenoid (2) Downshift solenoid(3) Lockup clutch solenoid

For the speed positions that require direct drive, lockup solenoid (3) must be activated after upshift solenoid (1) or downshift solenoid (2) is deactivated. The position of the transmission gear switch and the ground speed signal from the transmission speed sensor are used to determine the correct time in order to activate lockup clutch solenoid (3) .

Pump oil from the transmission charging pump section sends oil to the lockup clutch and synchronizing valve. This pump oil goes through the pressure reduction valve in the lockup clutch and synchronizing valve. The pressure reduction valve allows some of the pump oil to flow past the spool and into the pilot oil line. The pilot oil flows to the relay valve in the lockup clutch and synchronizing valve.

Lockup clutch solenoid (3) sends signal oil to the relay valve in the lockup clutch and synchronizing valve. This allows the pilot oil to flow past the relay valve. The oil then flows to the modulation reduction valve in the lockup clutch and synchronizing valve. The modulation reduction valve allows pump oil to flow to the lockup clutch. The lockup clutch will stay in direct drive until the signal pressure is removed by lockup clutch solenoid (3). When signal pressure is removed the spool in the relay valve blocks the pilot oil.

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793D Off-Highway Truck Power Train: Position Sensor (Truck Body), Speed Sensor (Transmission), Solenoid Valve (Upshift and Downshift) & Solenoid Valve (Lockup Clutch) 2013-01-01T17:09:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown