Daewoo Korando. Manual - part 248

AUTOMATIC TRANSMISSION  5A-35

2-3 Shift Valve

The 2-3 shift valve (refer to figure 3.12) is a two position valve. It is used on all 2-3 and 3-2 gearshifts.

The switching of this valve is achieved by S2 which is located at the end of the valve spool.

When in the (1,2) position, second gear oil from the 1-2 shift valve is prevented from entering the third gear circuit.
When the valve is moved to the (3,4) position, oil from the second gear circuit is routed to the third gear circuit and the
transmission changes to third gear.

Figure 3.12 - 2-3 Shift Valve

3-4 Shift Valve

The 3-4 shift valve (refer to figure 3,13) is a two position valve. It is used for all 3-4 and 4-3 gearshifts.

The switching of this valve is achieved by S1 which is located at the end of the valve spool.

During a 3-4 gearshift the 3-4 shift valve:

l

Exhausts the front band release circuit (B 1R) thereby allowing the application of the front band (B1).

l

Connects the inner apply area of the front servo (B 1AI) to the band apply feed circuit (BAF) thus allowing
greater apply forces to the front band.

l

Exhausts the overrun clutch circuit (OC) which allows the C4 clutch to disengage.

During a 4-3 gearshift, the C4 clutch is engaged and the front band (B1) is released. These actions are sequenced
by the 4-3 sequence valve (described below).

The 3-4 shift valve also switches during 1-2 and 2-1 gearshifts (see 1-2 shift valve above) where its function is to
apply the overrun clutch (C4) in second gear but to release it in first gear. Note that the C4 clutch is applied in Manual
1 by virtue of the manual valve and the 1-2 shift valve (as described in the 1-2 shift valve section).

Figure 3.13 - 3-4 Shift Valve

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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