AUTOMATIC TRANSMISSION 5A-57
POWER FLOW - DRIVE 4 (OVERDRIVE)
In Drive 4 (Overdrive), transmission drive is via the input shaft to the forward clutch cylinder. The elements of the transmission function as follows :
The C1 clutch is applied to drive the planet carrier clockwise.
The B1 band is applied to hold the reverse sun gear stationary.
As the planet carrier tuns, the long pinion ‘walks ’ around the stationary reverse sun gear and rotates around its
axis driving the internal ring gear and output shaft in a clockwise or forward direction at a speed faster than the input shaft i.e. in overdrive ratio.
The forward sun gear is also driven faster than the input shaft and overruns the 3-4 OWC.
The C2 clutch is engaged to reduce the speed differential across the 3-4 OWC.
Control
To maintain this arrangement in the steady state solenoids and valves are activated as follows: Solenoid S1 is switched On. S2 is switched Off.
With S1 switched On the 3-4 shift valve is held in the fourth gear position by line 500 pressure on the small end
of the valve.
With S2 switched Off the 2-3 shift valve is held in the fourth gear position by line 500 pressure on the large end of the valve.
The 1-2 shift valve is held in the fourth gear position by S2 oil pressure.
2nd oil (line pressure) from the 1-2 shift valve is directed to the band apply regulator valve, and to the 2-3 shift
valve.
The band apply regulator valve supplies 2nd oil (regulated to line pressure multiplied by the valve ratio) to the
band apply feed (BAF) circuit.
Band apply feed oil is directed to: - the outer apply area of the front servo- the inner apply area of the front servo piston via the 3-4 shift valve
- the 1-2 shift valve to provide an exhaust port when the transmission is shifted to first gear
2nd oil at the 2-3 shift valve is directed to the 3rd oil circuit.
3rd oil from the 2-3 shift valve is directed to the clutch apply regulator valve, and to the 4-3 Sequence Valve.
The clutch apply regulator valve supplies oil (regulated to line 500 pressure multiplied by the valve ratio) to the
clutch apply feed (CAF) circuit.
The CAF oil is directed to:- the C1 clutch- the C1 bias valve- the 4-3 sequence valve
Drive oil (line pressure) from the manual valve engages the C2 clutch
Refer to figure 5.8 and table 5.9.
Table 5.9 - Engaged Elements - Drive 4 (Overdrive)
Gear State
Drive 4 (Overdrive) C1
X C2
X C3
- C4
- B1
X B2
- 1-2
OWC - 3-4
OWC X LU
CLUTCH -
ELEMENTS ENGAGED
