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

(1) Drain passage (seven) (2) Passage to the No. 2 clutch (3) Drain passages (4) Passage to the No. 4 clutch (5) Pilot oil passage (seven) (6) Passage to the No. 1 clutch (7) Drain passage (seven) (8) Passage to the No. 3 clutch (9) Passage to the No. 5 clutch (10) Selector piston (seven) (11) Load piston (seven) (12) Modulation reduction valve (seven) (13) Passage to the No. 6 clutch (14) Passage to the dual stage relief valve in the selector and pressure control valve (15) Passage from the transmission charging pump section (A) Identification of load piston body (B) Identification of load piston body (C) Identification of load piston body (D) Identification of load piston body (E) Identification of load piston body (F) Identification of load piston body (G) Identification of load piston body(H) This load piston body is not used.

The pressure control valve has seven modulation reduction valves (12). There is one modulation reduction valve for each clutch in the transmission. There is one modulation reduction valve at station D which controls the relief valve pressure setting in the selector and pressure control valve. Each modulation reduction valve acts separately. This is known as Individual Clutch Modulation (ICM). The modulation reduction valves control the amount of pressure that will be used for clutch engagement and for the release of the clutch. The modulation reduction valves also determine the duration of clutch engagement.

Each load piston body has an identification letter for the purposes of disassembly and assembly. Pilot passages (5) are connected to passages from the rotary selector spool of the selector and pressure control valve. Pump oil from the selector and pressure control valve is in passage (15). Drain passages (3) are connected to the transmission case reservoir.

Pilot passage (5) for station D is connected to the shuttle valve in the selector and pressure control valve. When pilot oil from the lockup clutch solenoid is sent through pilot passage (5), the pilot oil pushes selector piston (10), load piston (11), and modulation reduction valve (12) to the right. Pump oil flows from passage (15) to passage (14). Passage (14) sends pump oil to the bottom of the dual stage relief valve in the selector and pressure control valve. This lowers the setting of the dual stage relief valve. Station D does not have a modulating orifice or a decay orifice.

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.

All of the modulation reduction valves operate in a similar way, so only the basic operation is provided.

The Beginning of a Shift and the Clutch is Filling

Modulation reduction valve at the beginning of a shift (1) Drain passage (2) Passage for pump oil (3) Passage to clutch (4) Drain passage (5) Springs (6) Load piston (7) Passage in the selector piston (8) Selector piston (9) Pilot passage (10) Spring (11) Modulation reduction valve (12) Ball check valve (13) Load piston orifice (14) Load piston plug (15) Decay orifice (16) Drain passage (17) Selector piston plug(18) Load piston body

When a shift is started, pilot passage (9) receives pilot oil at the correct sequence from the rotary selector spool. Selector piston (8) and load piston (6) move against the force of springs (5). Modulation reduction valve (11) moves against the force of spring (10). Passage (3) is blocked to drain passage (4). Passage (3) is open to passage (2). The pump oil now fills the clutch.

At the same time, oil flows through load piston orifice (13) and passage (7). This oil goes between selector piston (8) and load piston (6) .

Completed Shift with an Engaged Clutch

Modulation reduction valve at the end of a shift (1) Drain passage (2) Passage for pump oil (3) Passage to clutch (4) Drain passage (5) Springs (6) Load piston (7) Passage in the selector piston (8) Selector piston (9) Pilot passage (10) Spring (11) Modulation reduction valve (12) Ball check valve (13) Load piston orifice (14) Load piston plug (15) Decay orifice (16) Drain passage (17) Selector piston plug(18) Load piston body

After the clutch is full of oil, the pressure of the pump oil in the selected clutch increases. This causes load piston (6) to move against the force of springs (5). Clutch oil flows through an orifice in the modulation reduction valve (11). Ball check valve (12) opens and oil flows into the slug chamber at the left end of the modulation reduction valve.

This oil pressure works against the pressure at the end of load piston (6). The pressure increases until load piston (6) is moved fully to the left against the stop. The pressure in the clutch is now at the maximum. Modulation reduction valve (11) moves to the right and to the left in order to maintain a constant pressure in passage (3) .

Two factors control the amount of time that is necessary for the pressure in the clutch to achieve the maximum amount. The two factors are the size of load piston orifice (13) and the force of springs (5). The force of springs (5) can be changed by the removal of shims in load piston (6) or by the addition of shims in load piston (6) .

Shift with a Released Clutch

Modulation reduction valve with a disengaged clutch (1) Drain passage (2) Passage for pump oil (3) Passage to clutch (4) Drain passage (5) Springs (6) Load piston (7) Passage in the selector piston (8) Selector piston (9) Pilot passage (10) Spring (11) Modulation reduction valve (12) Ball check valve (13) Load piston orifice (14) Load piston plug (15) Decay orifice (16) Drain passage (17) Selector piston plug(18) Load piston body

When a clutch is disengaged, pilot passage (9) is open in order to drain through the rotary selector spool. The force of springs (5) moves selector piston (8) fully to the right against load piston body (18). Passage (7) is now aligned with drain passage (16). The force of springs (5) moves load piston (6) fully to the right against selector piston (8) .

Modulation reduction valve (11) is moved fully to the right by the force of spring (10). In this position, pump oil in passage (2) cannot flow into passage (3). Passage (3) is open to drain passage (4) and the pressure in the clutch is released. Decay orifice (15) in drain passage (16) controls the amount of time that is necessary for the clutch pressure to release. The No. 6 clutch does not have a decay orifice.

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793D Off-Highway Truck Power Train: Pressure Control Valve (Transmission) 2013-01-02T21:11:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown