Valve Block and Solenoid Valves
The gearbox uses nine solenoid valves located on the valve block. The solenoid valves are energised/de-energised by the EAT ECU to control the gearbox fluid flow around the gearbox to supply clutches, brakes and brake band (gear change scheduling), fluid to the torque converter, lubrication and cooling.
Each solenoid valve is controlled separately by the EAT ECU. All nine solenoid valves can be classified into two types by their operating mode. Three of them are duty solenoid valves and the remaining six are on-off solenoid valves.
Each solenoid valve consists of an internal coil and needle valve. A voltage is passed through the coil of the solenoid to actuate the needle valve. The needle valve opens and closes the fluid pressure circuits. On-off solenoid valves close the fluid pressure circuits in response to current flow.
Duty solenoid valves repeatedly turn on and off in 50 Hz cycles. This opens and closes the fluid circuits allowing a higher level of control on the circuits. For example, smooth operation of the lock-up clutch in the torque converter to eliminate harsh engagement/ disengagement.
All of the solenoid valves are supplied with battery voltage and an earth path by the EAT ECU.
On/Off Solenoid Valves
The on/off solenoid valves are:
- Shift solenoid valve A
- Shift solenoid valve B
- Shift solenoid valve C
- Low clutch timing solenoid valve
- Reduction timing solenoid valve
- 2-4 brake timing solenoid valve.
The EAT ECU switches the on/off solenoid valves to open and close in response to vehicle speed and throttle opening.
Shift solenoid valves A, B and C are used to engage the different gear ratios within the gearbox. The position of these solenoid valves at any one time determines the gear selected.
The reduction timing solenoid valve, low clutch timing solenoid valve and 2-4 timing solenoid valve are used by the
EAT ECU to control the timing of the gear shift changes.
These solenoid valves carry out three main functions:
- Shift timing control: For some shifts these three solenoid valves are used to assist line pressure control or 2-4 brake pressure control.
- Line pressure cut back: When the gearbox takes up the drive there should be a high line pressure present. The EAT ECU controls the low clutch timing solenoid valve which is related to the vehicle speed in order to switch the fluid circuit of the line pressure to on or off therefore controlling cut back.
- Reverse inhibition: If the vehicle exceeds 6 mph (10 km/h) and Reverse (R) is selected, the EAT ECU switches the low clutch timing solenoid valve on. This drains the gearbox fluid from the reverse clutch, therefore the clutch will be unable to engage.
Duty Solenoid Valves
The duty solenoid valves are:
- Lock-up duty solenoid valve
- Line pressure duty solenoid valve
- 2-4 duty brake solenoid valve.
The lock-up duty solenoid valve is used by the EAT ECU to control the lock-up of the torque converter depending upon the vehicle speed and throttle position.
The EAT ECU will actuate the lock-up solenoid valve, which operates the lock-up control valve to direct fluid to either lock or unlock the torque converter.
The line pressure duty solenoid valve and 2-4 duty brake solenoid valve are used by the EAT ECU to control fluid line pressure in the gearbox.
The EAT ECU calculates the line pressure by using the engine speed, vehicle speed and throttle angle. The EAT ECU then actuates the solenoid valves accordingly to achieve the required line pressure.
The solenoid valves can fail in the following ways:
- Open circuit
- Short circuit to 12 or 5 volts
- Short circuit to earth.
In the event of a solenoid valve failure any of the following symptoms may be observed:
- Gearbox selects fourth gear only (shift solenoid valve failure)
- Gearbox will not upshift to fourth gear (timing solenoid valve failure)
- Increased fuel consumption and emissions (lock-up solenoid valve failure)
- Gear shifts will have no torque reduction therefore gear changes will be very harsh (line pressure duty solenoid valve failure)
- No pressure control will occur therefore gear changes from fifth gear will be very harsh (2-4 brake duty solenoid valve failure).
The gearbox uses nine solenoid valves located on the valve block. The solenoid valves are energised/de-energised by the EAT ECU to control the gearbox fluid flow around the gearbox to supply clutches, brakes and brake band (gear change scheduling), fluid to the torque converter, lubrication and cooling.
Each solenoid valve is controlled separately by the EAT ECU. All nine solenoid valves can be classified into two types by their operating mode. Three of them are duty solenoid valves and the remaining six are on-off solenoid valves.
Each solenoid valve consists of an internal coil and needle valve. A voltage is passed through the coil of the solenoid to actuate the needle valve. The needle valve opens and closes the fluid pressure circuits. On-off solenoid valves close the fluid pressure circuits in response to current flow.
Duty solenoid valves repeatedly turn on and off in 50 Hz cycles. This opens and closes the fluid circuits allowing a higher level of control on the circuits. For example, smooth operation of the lock-up clutch in the torque converter to eliminate harsh engagement/ disengagement.
All of the solenoid valves are supplied with battery voltage and an earth path by the EAT ECU.
On/Off Solenoid Valves
The on/off solenoid valves are:
- Shift solenoid valve A
- Shift solenoid valve B
- Shift solenoid valve C
- Low clutch timing solenoid valve
- Reduction timing solenoid valve
- 2-4 brake timing solenoid valve.
The EAT ECU switches the on/off solenoid valves to open and close in response to vehicle speed and throttle opening.
Shift solenoid valves A, B and C are used to engage the different gear ratios within the gearbox. The position of these solenoid valves at any one time determines the gear selected.
The reduction timing solenoid valve, low clutch timing solenoid valve and 2-4 timing solenoid valve are used by the
EAT ECU to control the timing of the gear shift changes.
These solenoid valves carry out three main functions:
- Shift timing control: For some shifts these three solenoid valves are used to assist line pressure control or 2-4 brake pressure control.
- Line pressure cut back: When the gearbox takes up the drive there should be a high line pressure present. The EAT ECU controls the low clutch timing solenoid valve which is related to the vehicle speed in order to switch the fluid circuit of the line pressure to on or off therefore controlling cut back.
- Reverse inhibition: If the vehicle exceeds 6 mph (10 km/h) and Reverse (R) is selected, the EAT ECU switches the low clutch timing solenoid valve on. This drains the gearbox fluid from the reverse clutch, therefore the clutch will be unable to engage.
Duty Solenoid Valves
The duty solenoid valves are:
- Lock-up duty solenoid valve
- Line pressure duty solenoid valve
- 2-4 duty brake solenoid valve.
The lock-up duty solenoid valve is used by the EAT ECU to control the lock-up of the torque converter depending upon the vehicle speed and throttle position.
The EAT ECU will actuate the lock-up solenoid valve, which operates the lock-up control valve to direct fluid to either lock or unlock the torque converter.
The line pressure duty solenoid valve and 2-4 duty brake solenoid valve are used by the EAT ECU to control fluid line pressure in the gearbox.
The EAT ECU calculates the line pressure by using the engine speed, vehicle speed and throttle angle. The EAT ECU then actuates the solenoid valves accordingly to achieve the required line pressure.
The solenoid valves can fail in the following ways:
- Open circuit
- Short circuit to 12 or 5 volts
- Short circuit to earth.
In the event of a solenoid valve failure any of the following symptoms may be observed:
- Gearbox selects fourth gear only (shift solenoid valve failure)
- Gearbox will not upshift to fourth gear (timing solenoid valve failure)
- Increased fuel consumption and emissions (lock-up solenoid valve failure)
- Gear shifts will have no torque reduction therefore gear changes will be very harsh (line pressure duty solenoid valve failure)
- No pressure control will occur therefore gear changes from fifth gear will be very harsh (2-4 brake duty solenoid valve failure).
