773E and 775E Off-Highway Truck Hydraulic System: Hoist Control, Position Sensor (Hoist Control) & Electronic Control (Body Down or Up Switch)

Hoist Control

(1) RAISE position (2) HOLD position (3) FLOAT position(4) LOWER position

The hoist control is located to the left of the operator's seat. The hoist control has four positions: RAISE, HOLD, FLOAT and LOWER. The machine should normally be operated with the hoist control in the FLOAT position.

The hoist control is connected to the hoist control position sensor. The hoist control position sensor sends electrical signals to the Power Train Electronic Control Module (Power Train ECM). See the hydraulic system System Operation, "Position Sensor (Hoist Control)" for additional information.

When the hoist control is released a spring will move the hoist control from the RAISE position to the HOLD position or from the LOWER position to the FLOAT position.

Position Sensor (Hoist Control)

Location of the hoist control position sensor

The hoist control position sensor is located on the left side of the operator's seat. The hoist control position sensor is a Pulse Width Modulation position sensor. The hoist control postion sensor sends duty cycle signals to the Power Train Electronic Control Module (Power Train ECM).

The Power Train ECM uses these signals to energize the appropriate hoist proportioning solenoid on the hoist control valve. The hoist proportioning solenoid will move the spool in the hoist control valve. This will cause oil to be sent to the hoist cylinders in order to move the dump body.

The signal from the hoist control position sensor is also used to neutralize the transmission. The Power Train ECM will allow only a forward speed position or the NEUTRAL position when the hoist control position sensor is in the RAISE position. The Power Train ECM will not allow a shift to the REVERSE position until the hoist control position sensor has been moved from the RAISE position and the transmission shift lever is in the NEUTRAL position.

Note: If the machine is in REVERSE and the hoist position sensor is in the RAISE position the Power Train ECM will shift the transmission to NEUTRAL. The machine will remain in NEUTRAL until the hoist control is moved into the HOLD or the FLOAT position and the transmission control has been cycled through NEUTRAL.

Electronic Control (Body Down or Up Switch)

(1) Magnet assembly(2) Body down or up switch

The body down or up switch (2) is located on a bracket on the rear frame. The magnet assembly (1) is connected to the dump body. When the dump body is raised, body down or up switch (2) sends a signal to the Power Train Electronic Control Module (Power Train ECM). The signal indicates that the dump body is in the UP position. When the dump body is lowered the magnet assembly (1) will pass in front of body down or up switch (2) and a signal will be sent to the Power Train ECM. This signal indicates that the dump body is DOWN. The adjustment of the body down or up switch (2) is very important. Refer to the Hydraulic System Testing and Adjusting, "Electronic Control (Body Down or Up Switch) - Adjust" for the proper adjustment procedure.

Body down or up switch (2) is used to limit the top gear while the dump 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 dump 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 or THIRD gear.

The signal from body down or up switch (2) is also used to control the SNUB position of the hoist control valve. The Power Train ECM will signal the hoist proportioning solenids to move the hoist control valve to the SNUB position when the dump body that is being lowered nears the frame. The speed in FLOAT is reduced in the SNUB position in order to prevent the dump body from contacting the frame too hard.

The signal from the body down or up switch (2) is used to provide warnings to the operator when the truck is moving with the dump body UP.

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773E and 775E Off-Highway Truck Hydraulic System: Hoist Control, Position Sensor (Hoist Control) & Electronic Control (Body Down or Up Switch) 2013-01-10T18:55:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown