Daewoo Musso. Manual - part 251

5A-36  AUTOMATIC TRANSMISSION

4-3 Sequence Valve

The 4-3 sequence valve (refer figure 3.14) is a two position spring loaded valve. It switches during 3-4 and 4-3
gearshifts although it performs no function during the 3-4 shift.

During the 4-3 shift the 4-3 sequence valve delays the connection of the clutch apply feed circuit (CAF) to the BIR
circuit until the BIR circuit has been fully pressurised by using the third gear circuit. This prevents objectionable
engine flare on completion of the 4-3 gearshift.

Figure 3.14 - 4-3 Sequence Valve

Figure 3.15 - Solenoid Supply Pressure Regulator Valve and Line Pressure Control Valve

Solenoid Supply Pressure Regulator Valve

The solenoid supply valve (refer figure 3.15) supplies a constant pressure to all solenoids (51 to 57). Line pressure
is used as the feed oil to this regulator and the output is termed line 500.

Line Pressure Boost Valve

Line pressure is controlled by 56, which acts as the line pressure boost valve (refer figure 3.15). When 56 pressure
is applied to the end of the PRV it is opposed by spring force and causes LOW line pressure for light throttle
application and cruising.

Heavy throttle application causes the normally open 56 to open (switch Off) thus closing line 500 and opening 56 to
exhaust. Removal of 56 pressure from the PRV results in HIGH line pressure.

AUTOMATIC TRANSMISSION  5A-37

Figure 3.16 - Clutch Apply Regulator Valve

Clutch Apply Regulator Valve

The clutch apply regulator valve (refer figure 3.16) is a fixed ratio valve. This valve provides a regulated pressure to
the C1 clutch and controls the rate of change of state of the clutch to give the desired shift quality.

This ratio is 2.25 : 1.

Third gear oil supplied to the valve is regulated to provide an output pressure (CAF) of 2.25 times the S5 signal
pressure when S3 is On. When S3 is Off the output pressure is 2.25 times the line 500 pressure.

Band Apply regulator Valve

The band apply regulator valve (refer figure 3.17) is a fixed ratio valve. It provides a regulated pressure to the front
servo, and controls the rate of change of state of the front band (B1) to give the desired shift quality.

This ratio is 1.4 : 1.

Second gear oil supplied to the valve is regulated to provide an output pressure (BAF) of 1.4 times the S5 signal
pressure when S4 is On. When S4 is Off the output pressure is 1.4 times the line 500 pressure.

Figure 3.17 - Band Apply Regulator Valve

5A-38  AUTOMATIC TRANSMISSION

Reverse Lockout Valve

The reverse lockout valve (refer figure 3.18) is a two position valve contained in the upper valve body. This valve
uses 51-52 pressure as a signal pressure and controls the application of the rear band (B2).

While the manual valve is in D,3,2, or 1 positions, drive oil is applied to the spring end of the valve, overriding any
signal pressures and holding the valve in the lockout position. This prevents the application of B2 in any of the
forward driving gears.

When the manual valve is in P, R or N positions, drive oil is exhausted and the reverse lockout valve may be toggled
by S1-S2 pressure.

B2 is applied in P, R, and N provided that the following conditions are satisfied:

1. In P or N, roadspeed     3 km/h.

2. In R, road speed    10 km/h.

3. Engine speed    1400 rpm.

4. For diesel vehicles, throttle    25%.

5. For gasoline vehicles, throttle    12%.

Under these conditions, the TCU switches solenoids S1 and S2 to Off. The reverse lockout valve toggles under the
influence of the S1-S2 pressure, to connect the line pressure to the B2 feed. Oil is fed to both the inner and outer
apply areas of the rear servo piston, applying B2.

If any of the above conditions are not satisfied, the TCU switches solenoids S1 and S2 to On. S1- S2 pressure is
exhausted and the valve is held in the lockout position by the spring. In this position, engagement of B2 is prohibited.

This feature protects the transmission from abuse by preventing the undesirable application of B2 at high speed, and
by providing a reverse lockout function.

Note that if the transmission is in failure mode, the rear band will be applied at all times in P, R and N.

Figure 3.18 - Reverse Lockout Valve

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AUTOMATIC TRANSMISSION  5A-39

Primary Regulator Valve

The primary regulator valve (PRV) (refer to figure 3.19) regulates the transmission line pressure (or pump output
pressure). This valve gives either high or low line pressure depending on whether S6 is switched Off or On, When S6
is switched On,S6 pressure is applied to the PRV moving it against spring pressure and opening the line pressure
circuit to the pump suction port resulting in reduced line pressure. Low line pressure is used during light throttle
applications and cruising. Heavy throttle will cause S6 to switch Off and thereby cause high line pressure.

This stepped line pressure control has no detrimental effect on shift feel because all shifting pressures are controlled
by separate band and clutch regulator valves, and the output of S5.

When reverse gear is selected, both the low and high line pressure values are boosted to guard against slippage.
This is achieved by applying reverse oil line pressure to the PRV to assist the spring load. The other end of the valve
contains ports for line pressure feedback and 56 pressure.

The PRV also regulates the supply of oil to the converter via the converter feed port. The cascade effect of the PRV
ensures the first priority of the valve is to maintain line pressure at very low engine speeds. When the engine speed
increases and the pump supplies an excess of oil the PRV moves to uncover the converter feed port thereby pressurising
the converter. If there is an excess of oil for the transmission’s needs then the PRV moves further to allow oil to return
to the suction port.

Figure 3.19 - Primary Regulator Valve