793D Off-Highway Truck Power Train: Selector and Pressure Control Valve (Transmission)

TORQUE CONVERTER DRIVE Selector and pressure control valve in NEUTRAL with a running engine (AA) Pressure of the oil from the pump for transmission charging in torque converter drive (BB) Pilot pressure in torque converter drive (1) Passage to the upshift solenoid, downshift solenoid, and lockup clutch solenoid (2) Passage for pilot oil from the lockup clutch solenoid (3) Passage from the pump for transmission charging (4) Passage for pilot oil to Station "D" on the pressure control valve (5) Rotary selector spool (6) Selector and pressure control valve (7) Neutralizer valve (8) Drain passage (9) Shuttle spool (10) Chamber (11) Metering point for the priority reducing valve in torque converter drive (12) Chamber (13) Passage to the clutch supply rail in the pressure control valve (14) Priority reduction valve (15) Spring for the dual stage relief valve (16) Dual stage relief valve (17) Two springs for the priority reducing valve (18) Chamber (19) Cam for the rotary selector spool (20) Passage from Station "D" on the pressure control valve (21) Passage to the clutch supply rail in the pressure control valve(22) Passage to the torque converter inlet relief valve

DIRECT DRIVE Selector and pressure control valve in NEUTRAL with a running engine (DD) Pressure of the oil from the pump for transmission charging and the oil in the pilot oil passage in direct drive (EE) Pressure in the clutch supply rail at the No. 3 clutch in direct drive (FF) Pressure from Station "D" (1) Passage to the upshift solenoid, downshift solenoid, and lockup clutch solenoid (2) Passage for pilot oil from the lockup clutch solenoid (3) Passage from the pump for transmission charging (4) Passage for pilot oil to Station "D" on the pressure control valve (5) Rotary selector spool (6) Selector and pressure control valve (7) Neutralizer valve (8) Drain passage (9) Shuttle spool (10) Chamber (11) Chamber (13) Passage to the clutch supply rail in the pressure control valve (14) Priority reduction valve (15) Spring for the dual stage relief valve (16) Two springs for the priority reducing valve (17) Dual stage relief valve (18) Chamber (19) Cam for the rotary selector spool (20) Passage from Station "D" on the pressure control valve (21) Passage to the clutch supply rail in the pressure control valve (22) Passage to the torque converter inlet relief valve(23) Metering point for the priority reducing valve in direct drive

The selector and pressure control valve controls the flow of oil that goes to the pressure control valve. The selector and pressure control valve consists of five valves. The following chart provides the basic function of each valve.

Table 1

Operation of the Components in the Selector and Pressure Control Valve
Valve	Function
Priority reduction valve (14)	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 (14) is shimmed in order to set the pressure of the oil in the segments for the transmission charge pump and the 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 pump for transmission charging in direct drive.
Neutralizer valve (7)	When the transmission is not in NEUTRAL and the engine is started, this valve stops the flow of pilot oil to rotary selector spool (5).
Shuttle valve (9)	This valve allows the pilot oil that is flowing to Station D to drain quickly to the hydraulic tank when Station "D" is released.
Rotary selector spool (5)	The rotary selector spool directs the pilot oil to the appropriate clutch stations for each speed of the transmission.
Dual stage relief valve (17)	In torque converter drive, the dual stage relief valve controls the segments of oil for the transmission charge pump section and for the clutch supply rail. 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 (16) 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.

Priority Reduction Valve

At selector and pressure control valve (6), the oil in passage (1) from the transmission charge pump section flows to two locations. Some of the oil flows through passage (2) to the upshift solenoid, to the downshift solenoid, and to the lockup clutch solenoid. The remainder of the pump oil flows to priority reduction valve (14). The oil flows through an orifice in the priority reduction valve. This oil opens a check valve. The oil then flows to the upper end of priority reduction valve (14). As the oil pressure increases, the oil moves the priority reduction valve downward against the force of two springs (16). The spool for the priority reduction valve will shift to metering point (11) in torque converter drive and to metering point (23) in direct drive.

Torque Converter Drive

Priority reduction valve (14) shifts to metering point (11). In torque converter drive, the oil that is flowing from priority reducing valve (14) to neutralizer valve (7) is controlled by the priority reduction valve. When neutralizer valve (7) is moved downward, the oil flows into chamber (10) of rotary selector spool (5). Chamber (10) has a screen that filters the oil. This oil is able to flow to the pressure control valve. This pressure oil is the pilot oil that controls the movement of the selector pistons in the pressure control valve.

The oil in passage (1) from the transmission charge pump section flows around the spool for priority reduction valve (14) to dual stage relief valve (17). In torque converter drive, dual stage relief valve (17) controls the maximum pressure in passages (1), (2), (13), and (21). Some of the oil from passage (13) flows through passage (21) to the clutch supply rail in the pressure control valve. This oil is used to fill the clutches in the transmission.

Direct Drive

Now, priority reduction valve (14) shifts to metering point (23). This occurs as a result of the action of Station "D" on the dual stage relief valve. The oil that is flowing from passage (1) flows around the spool for priority reducing valve (14) to neutralizer valve (7). When neutralizer valve (7) is moved downward, the oil flows into chamber (10) of rotary selector spool (5). Chamber (10) has a screen that filters the oil. This oil is able to flow through the open ports in rotary selector spool (5) to the appropriate clutch stations in the pressure control valve. This pressure oil is the pilot oil that controls the movement of the selector pistons in the pressure control valve. In direct drive, the oil in passage (1) from the transmission charge pump section and the oil that flows to rotary selector spool (5) is controlled by priority reducing valve (14) .

In direct drive, the dual stage relief valve operates at a lower pressure than torque converter drive. The oil that is flowing through passage (13) is controlled by dual stage relief valve (17). Some of the oil from passage (13) flows through passage (21) to the clutch supply rail in the pressure control valve. This oil is used to fill the clutches in the transmission. Some of the oil from passage (13) also flows to rotary selector spool (5). This oil activates neutralizer valve (7). When the rotary selector spool is in the NEUTRAL-1 position, oil from passage (1) is able to flow to chamber (10). This causes neutralizer valve (7) to move downward. Pilot oil is now able to flow to chamber (10) of rotary selector spool (5) .

Neutralizer Valve

Neutralizer valve (7) will not allow movement of the machine if the engine is started and the rotary selector spool (5) is not in the NEUTRAL-1 position.

When the engine is started and the transmission is in NEUTRAL-1, pressure oil from passage (13) flows to rotary selector spool (5). The pressure oil then flows to chamber (11). The pressure in chamber (1) moves neutralizer valve (7) downward against the force of the spring. This allows pilot oil to go around the neutralizer valve to chamber (10) of the rotary selector spool. The clutches can be engaged in the transmission.

As neutralizer valve (7) moves downward, pilot oil is able to flow through an orifice in the neutralizer valve to the upper end of the neutralizer valve. Neutralizer valve (7) is now held in the position shown by the pressure of the pilot oil.

When rotary selector spool (5) is moved from the NEUTRAL-1 position, pressure oil from passage (13) cannot go to chamber (11). Chamber (11) is now open to chamber (18) because of the position of rotary selector spool (5) .

When the rotary selector spool is not in NEUTRAL-1 and the engine is started, the position of rotary selector spool (5) stops the flow of pump oil to chamber (11). Neutralizer valve (7) will not move downward in order to provide oil to chamber (10). No oil can flow to the selector pistons of the pressure control valve. The clutches in the transmission will not engage.

Rotary Selector Spool

Rotary selector spool (5) determines the selector pistons in the pressure control valve that receive pilot oil and the selector pistons that are drained. Orifices in the rotary selector spool provide the correct sequence in order for the proper clutches to engage. The rotary actuator is mechanically connected to the upper end of rotary selector spool (5). The rotary actuator is hydraulically controlled by the upshift solenoid and the downshift solenoid. When the rotary actuator turns, rotary selector spool (5) turns. The transmission gear switch is also connected to the upper end of the spool. Cam (19) is fastened to the lower end of the spool. Two spring assemblies are in contact with cam (19) in order to hold the spool correctly in each speed position.

Chamber (10) of rotary selector spool (5) contains pilot oil. The position of the spool will send this pilot oil through the passages to the pressure control valve. The oil flows to a selector piston. This causes the selector piston to move. This will cause a clutch to engage in the transmission. Chamber (10) has a screen which stops foreign material from entering the pressure control valve.

The clutches of the transmission that are disengaged return any pressure oil that is in the selector pistons to chamber (18). Chamber (18) allows the oil to go to the transmission case reservoir.

In NEUTRAL-1 position, rotary selector spool (5) sends pump oil to chamber (11) in order to move neutralizer valve (7). In the other speed positions, chamber (11) is blocked from pump oil and open to chamber (18) .

Dual Stage Relief Valve

Torque Converter Drive

Dual stage relief valve (17) controls the pressure of the pump for transmission charging in torque converter drive. Pump oil comes from passage (1) to the dual stage relief valve (17). The oil flows through an orifice in the dual stage relief valve (17). This opens a poppet valve. Oil fills the chamber between the poppet and the slug. As the pressure increases, the oil moves the dual stage relief valve (17) against the force of the spring. When the pressure of the oil reaches the relief pressure, the dual stage relief valve (17) moves upward so that oil can flow out of passage (22) to the torque converter inlet relief valve.

The pressure setting of dual stage relief valve (17) during torque converter drive can be changed by the removal or the addition of shims inside the spool of the dual stage relief valve.

Direct Drive

In direct drive, the action of Station "D" on the dual stage relief valve lowers the pressure in the clutch supply rail. Oil from the pump for transmission charging flows to Station "D". When Station "D" is activated, pressure (FF) flows under the dual stage relief valve. This pressure reduces the pressure setting of the dual stage relief valve. Metered oil from the priority reducing valve flows from passage (1) to the dual stage relief valve (17). The oil flows through an orifice in the dual stage relief valve (17). This opens a poppet valve. Oil fills the chamber between the poppet and the slug. As the pressure increases, the oil moves the relief valve upward against the force of the spring (16) .

At the same time, the lockup clutch solenoid sends pilot oil to passage (3). This oil pressure causes the ball that is inside shuttle valve (9) to move downward. This blocks drain passage (8) and pilot oil is sent to passage (4). This pilot oil travels through passage (4) to Station D of the pressure control valve. Oil pressure (FF) from station D of the pressure control valve flows through passage (20) to the slug chamber at the lower end of dual stage relief valve (17). When the pressure of the oil reaches the relief pressure, dual stage relief valve (17) moves up. Oil is then able to flow out of passage (22) to the torque converter inlet relief valve. The relief pressure of the dual stage relief valve (17) is lower during direct drive.

The lower pressure setting in direct drive provides only enough pressure for the prevention of clutch slippage. This lengthens the life of the large rotating clutch seal rings.

Refer to the Power Train Testing and Adjusting, "Transmission Hydraulic Control (Pressure Pack) - Test and Adjust" for the proper procedure to adjust the pressures in the transmission hydraulic control.

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793D Off-Highway Truck Power Train: Selector and Pressure Control Valve (Transmission) 2013-01-02T21:10:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown