The valve body contains six solenoid valves:
- three PWM solenoid valves (pulse width modulation solenoid valves,
- two shift solenoid (on/off) valves,
- one main regulating valve (variable force solenoid).
The individual clutches and bands are supplied pressure from the PWM solenoid valves and the shift solenoid (on/off) valves and thus the gears are shifted.
The PWM solenoid valves allow direct actuation of the clutches and bands to ensure extremely smooth gear shifting through precise pressure regulation.
The shift solenoid (on/off) valves switch the hydraulic path to the clutches and bands, reducing the number of required modulating valves.
The main regulating valve (variable force solenoid) ensures that sufficient hydraulic pressure is available in all operating conditions.
PWM solenoid valves 1-3
PWM solenoid valves 1, 2 and 3 control the pressure to the bands and clutches.
Shift solenoid (on/off) valves 1 and 2
The shift solenoid (on/off) valves switch the different oil passages in the valve body to direct the pressure to the individual clutches and bands.
The use of the shift solenoid valves are needed for direct actuation of the individual clutches and bands.
Main regulating valve
The main regulating valve (variable force solenoid) controls the required main line pressure for the individual transmission ranges.
The main line pressure is controlled dependent on the current engine load.
----------------------------------------------------------------------------------------------------
Electronic synchronous shift control (ESSC)
Control of shift operations
During a shift operation certain elements are released while others are actuated. Ideally this process takes place simultaneously (synchronously) to avoid jerky gear shifting.
The time for the shift operation should remain within the time limits provided.
When the shift operation is controlled conventionally, the pressure build up and reduction at the shift elements are set and defined for ideal conditions (synchronous shifting).
As there is no way of influencing the control in the event of different levels of wear in the shift elements, when the transmission has been used for a fairly high mileage it is possible that the pressure build up and reduction may no longer be synchronous.
The result or premature pressure reduction at the element to be switched off is an unwanted rise in the turbine shaft speed as the element to be switched on cannot transmit the input torque.
The result of delayed pressure reduction at the element to be switched off is an unwanted decrease in the turbine shaft speed as both shift elements transmit the input torque. In the process the torque is transmitted to the transmission housing through internal locking.
In both cases a **** will be felt during the shift operation.
In addition, wear in the shift elements leads to a lengthening of the shift operation. Therefore, shifting takes longer when the transmission has accumulated a higher mileage.
Control of shift operations with ESSC
In the 4F27E automatic transmission electronic synchronous shift control (ESSC) is used.
ESSC monitors the shift operations and is able to adapt to the wear in the shift elements over the life of the transmission.
This is possible since the shift elements are actuated by modulating valves.
The system monitors the shift time whether the shift operation is synchronous.
If the PCM detects a deviation from the stored values for the shift time and synchronization of the shift operation, the pressure build up or reduction is adapted accordingly.
Throttle position (TP) sensor
The TP sensor is located on the throttle body.
It supplies the PCM with information about the position of the throttle plate.
It also detects the speed of actuation of the throttle plate.
The PCM uses the signals for the following functions among other things:
- to determine the shift timing,
- to control the main line pressure,
- to control the torque converter lock-up clutch,
- for kickdown.
In case of absence of the TP signal the engine control uses the signals of the MAF and IAT sensors as a substitute signal. The main line pressure is increased and hard shifts may occur.
Mass air flow (MAF) and intake air temperature (IAT) sensor
The MAF sensor is located between the air cleaner housing and the air intake hose leading to the throttle housing.
The IAT sensor is incorporated in the housing of the MAF sensor.
The MAF sensor in conjunction with the IAT sensor provides the PCM with the primary load signal.
The PCM uses the signals for the following functions among other things:
- to control the shift operations,
- to control the main line pressure.
If the MAF sensor fails, the signal of the TP sensor is used as a substitute.
Crankshaft position (CKP) Sensor
The CKP sensor is located on the engine/transmission flange.
The CKP sensor is an inductive sensor which provides the PCM with information about the engine speed and position of the crankshaft.
The signal is used for the following functions among other things:
- to control the torque converter lock-up clutch,
- to check the torque converter slip,
- to control the main line pressure.
No substitute signal is available for the CKP sensor. If the signal is not present, the engine stops.
Turbine shaft speed (TSS) sensor
The TSS sensor is located in the transmission housing over the transmission input shaft.
The TSS sensor is an inductive sensor which senses the speed of rotation of the transmission input shaft.
The signal is used for the following functions:
- to control the shift operations,
- to control the torque converter clutch,
- to check the torque converter slip.
If the TSS sensor fails, the signal of the output shaft speed (OSS) sensor is used as a substitute signal.
×