793D Off-Highway Truck Power Train: Transmission Hydraulic Control

This schematic shows the transmission hydraulic control in torque converter drive in the NEUTRAL position. (L) Pressure tap for the transmission charge pump section (AA) Pressure of the transmission charge pump section in torque converter drive (BB) Pilot pressure in torque converter drive (CC) Pressure at clutch (3) in torque converter drive (1) No. 1 clutch (2) No. 2 clutch (3) No. 3 clutch (4) No. 4 clutch (5) No. 5 clutch (6) No. 6 clutch (7) Lockup clutch solenoid (8) Downshift solenoid (9) Upshift solenoid (10) Rotary actuator (11) Pressure control valve (12) Passage to the torque converter lockup clutch and synchronizing valve (13) Modulation reduction valves for Stations "A", "B", "C", "E", "F", and "G" (14) Supply passage from the transmission charge pump section (15) Neutralizer valve (16) Rotary selector spool (17) Metering point for the priority reducing valve in torque converter drive (18) Shims for the priority reducing valve (19) Priority reducing valve (20) Dual stage relief valve (21) Shims for the dual stage relief valve (22) Clutch supply rail (23) Passage to the torque converter inlet relief valve (24) Selector and pressure control valve (25) Shims for Station "D"(26) Modulation reduction valve for Station "D"

This schematic shows the transmission hydraulic control in direct drive in the NEUTRAL position. (C) Pressure tap for the No. 3 clutch at Station "C" (L) Pressure tap for the transmission charge pump section (DD) Pressure of the transmission charge pump section in direct drive (EE) Pressure in the clutch supply rail at the No. 3 clutch in direct drive (FF) Pressure from Station "D" (1) No. 1 clutch (2) No. 2 clutch (3) No. 3 clutch (4) No. 4 clutch (5) No. 5 clutch (6) No. 6 clutch (7) Lockup clutch solenoid (8) Downshift solenoid (9) Upshift solenoid (10) Rotary actuator (11) Pressure control valve (12) Passage to the torque converter lockup clutch and synchronizing valve (13) Modulation reduction valves for Stations "A", "B", "C", "E", "F", and "G" (14) Supply passage from the transmission charge pump section (15) Neutralizer valve (16) Rotary selector spool (18) Shims for the priority reducing valve (19) Priority reducing valve (20) Dual stage relief valve (21) Shims for the dual stage relief valve (22) Clutch supply rail (23) Passage to the torque converter inlet relief valve (24) Selector and pressure control valve (25) Shims for Station "D" (26) Modulation reduction valve for Station "D"(27) Metering point for the priority reducing valve in direct drive

To describe the operation of this system, there are four different segments of oil that need to be defined. Each segment of oil has a change in pressure when the machine goes from torque converter drive to direct drive. These pressures (AA), (BB), (CC), (DD), (EE), and (FF) are shown in Illustration 1 and Illustration 2.

• Oil from the transmission charge pump

Oil from the transmission charge pump flows through passage (14). This segment of oil flows to priority reducing valve (19), lockup solenoid (7), downshift solenoid (8), and upshift solenoid (9) .

• Pilot oil

The segment of pilot oil is the oil that flows from priority reducing valve (19) through neutralizer valve (15) to rotary selector spool (16). Rotary selector spool (16) directs the pilot oil to the various clutch stations on pressure control valve (11) .

• Oil in the clutch supply rail

Oil in the passages from priority reduction valve (19) to clutch supply rail (22) is another segment of oil. This segment of oil is supply oil for all of the modulation reduction valves in each station on pressure control valve (11) .

• Clutch oil

Another segment is the oil that flows past the modulation reduction valves in all seven stations in the pressure control valve. This oil in Stations "A", "B", "C", "E", "F", and "G" flows to the transmission clutches. In Station "D", this segment of oil flows under dual stage relief valve (20).

Table 1

Operation of Components in the Transmission Hydraulic Control
Component	Operation (Function)
Lockup solenoid (7)	This solenoid sends signal oil in order to activate the torque converter lockup clutch. This solenoid also activates Station "D" in direct drive in order to lower the pressure in clutch supply rail (22).
Downshift solenoid (8)	This solenoid controls the movement of rotary actuator (10) during downshifts.
Upshift solenoid (9)	This solenoid controls the movement of rotary actuator (10) during upshifts.
Rotary actuator (10)	This actuator controls movement of the rotary selector spool (16) in selector and pressure control valve (24).
Priority reduction valve (19)	In torque converter drive, priority reducing valve (19) controls the segment for pilot oil. In direct drive, the priority reducing valve controls the segments of oil for the transmission charge pump section and for the pilot oil. Priority reducing valve (19) is shimmed in order to set the pressure of the oil in the segments for the transmission charge pump and pilot oil in direct drive. The priority reducing valve is not shimmed in order to set the pilot oil pressure in torque converter drive. Pilot oil pressure in torque converter drive is a result of the setting of the pressure of the transmission charge pump section in direct drive.
Dual stage relief valve (20)	In torque converter drive, the dual stage relief valve controls the segments of oil for the transmission charge pump section and for clutch supply rail (22). In direct drive, the dual stage relief valve controls the segment of oil in the clutch supply rail only. In direct drive, the action of Station "D" on dual stage relief valve (20) lowers the pressure in the clutch supply rail. The dual stage relief valve is shimmed in torque converter drive in order to set the pressure of the oil in the segments for the pump and the clutch supply rail.
Station "D"	In torque converter drive, Station "D" is not activated. The action of Station "D" maintains the oil of clutch supply rail (22) at a reduced pressure in direct drive. Station "D" is shimmed in order to set the pressure of the clutch supply rail in direct drive.
Stations "A", "B", "C", "E", "F", and "G"	Each station is used to control a clutch in the transmission planetary.

Torque Converter Drive

In torque converter drive, the operation is very similar for all current ICM transmission hydraulic controls with a dual stage relief valve. Oil from the transmission charge pump section flows through passage (14). The oil pressure (AA) from the transmission charge pump section supplies priority reducing valve (19). In torque converter drive, the spool for priority reducing valve (19) is at metering point (17) and regulating the segment for pilot oil at a reduced pressure. Oil pressure from the transmission charge pump section in passage (14) is directed to the clutch supply rail (22). The segment of oil from the transmission charging pump and the segment of oil in clutch supply rail (22) are at the same oil pressure (AA). In torque converter drive, dual stage relief valve (20) is shimmed in order to control the pressure setting of these two segments of oil. At high idle in torque converter drive, the pressure of the oil in the clutch supply rail is higher than the pressure setting of Stations "A", "B", "C", "E", "F", and "G". Therefore, modulation reduction valves (13) in the clutch stations are controlling the pressure that is flowing to the engaged clutches.

Direct Drive

In direct drive, oil pressure (DD) from the transmission charge pump section flows through passage (14). Some of this oil flows through the lockup clutch solenoid (7) to Station "D". When Station "D" is activated, oil pressure (EE) in clutch supply rail (22) is reduced to oil pressure (FF) from Station "D" by modulation reduction valve (25) in Station "D". Oil pressure (FF) from Station "D" flows under dual stage relief valve (20). Oil pressure (FF) from Station "D" causes the pressure setting of the dual stage relief valve to be reduced. The oil pressure in the segment of oil for clutch supply rail (22) drops to the pressure setting of oil pressure (EE). When the pressure drops, priority reducing valve (19) shifts from metering point (17) to metering point (27). The segment of oil from the transmission charge pump section and the segment for pilot oil are at the same oil pressure. This only occurs in direct drive. Now, priority reducing valve (19) is shimmed in order to set the oil pressure from the transmission charge pump section. Oil pressure (DD) from the transmission charge pump section in passage (14) is directed into the segment for pilot oil to rotary selector spool (16). The rotary selector spool directs the pilot oil to the clutch stations.

In direct drive, the pressure of clutch supply rail (22) is less than or equal to the pressure settings of clutch stations "A", "B", "C", "E", "F", and "G". Therefore, modulation reduction valves (13) in these clutch stations are open, and the pressure of the clutch supply rail is equal to the clutch pressure. Now, the pressure of the clutch supply rail can be measured at pressure tap (C) for the No. 3 clutch in direct drive. The pressure of the clutch supply rail is a result of the action of Station "D" on the dual stage relief valve. The pressure of the clutch supply rail is set by adjusting the shims in Station "D" in direct drive.

Note: The ICM transmission hydraulic control on the 793D functions differently than most other ICM transmission hydraulic controls with a dual stage relief valve. A special procedure in the Power Train Testing and Adjusting, "Transmission Hydraulic Control (Pressure Pack) - Test and Adjust" describes the proper order for adjusting the pressures of the transmission charge pump section and the clutch supply rail in torque converter drive and direct drive. The oil that is flowing from the transmission charge pump section also supplies the torque converter lockup clutch. If the pump pressure is set too low in direct drive, the supply oil for the torque converter lockup clutch will be low. If the supply pressure to the torque converter lockup clutch is low, the lockup clutch will slip and a premature failure may occur.

If you need more information, You can visit:

http://www.cat.com

793D Off-Highway Truck Power Train: Transmission Hydraulic Control 2013-01-02T21:07:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown