MECHATRONIC Valve Block

The Mechatronic valve block is located in the bottom of the transmission and is covered by the fluid pan. The valve block houses the TCM, electrical actuators, speed sensors, control valves and the hydraulic impulse storage which provide all electro-hydraulic control for all transmission functions. The Mechatronic valve block comprises the following components:

• TCM
• Seven pressure regulator solenoids
• Two park lock solenoids
• Twenty one hydraulic spool valves
• Temperature sensor
• Turbine speed sensor
• Output shaft speed sensor
• Hydraulic impulse storage.

Valve Block Components 

Electronic Pressure Regulator Solenoids (EPRS) 

Seven EPRS are located in the valve block. The solenoids are controlled by PWM signals from the TCM. The solenoids convert the electrical signals into hydraulic control pressure proportional to the signal to actuate the spool valves for precise transmission operation.

Solenoids EPRS A, B, D, E and WK supply a higher control pressure as the signal amperage increases and can be identified by an orange connector cap. The TCM operates the solenoids using PWM signals.

The TCM monitors engine load and clutch slip and varies the solenoid duty cycle accordingly. The solenoids have a 12 V operating voltage and a pressure range of 0 - 4.7 bar (0 - 68 lbf.in² ).

Solenoids EPRS C and SYS supply a lower control pressure as the signal amperage increases and can be identified by a gray connector cap. The TCM monitors engine load and clutch slip and varies the solenoid duty cycle accordingly. The solenoids have a 12 V operating voltage and a pressure range of 4.7 - 0 bar (68 - 0 lbf.in² ).

The resistance of the solenoid coil winding for EPRS solenoids is 5.05 Ohms at 20 °C (68 °F).

Control Solenoid (MV 1) 

A shift control solenoid MV1 (Magnetic Valve 1) is located in the valve block. The solenoid is controlled by the TCM and converts electrical signals into hydraulic control signals to control clutch application.

The shift control solenoid is an open/closed, on/off solenoid which is controlled by the TCM switching the solenoid to earth. The TCM also supplies power to the solenoid. The TCM energises the solenoid in a programmed sequence for clutch application for gear ratio changes and shift control.

The resistance of the solenoid coil winding for solenoid is between 10 to 11 Ohms at 20 °C (68 °F).

Control Solenoid (MV 2) 

A control solenoid MV 2 (Magnetic Valve 2) is located in the valve block. The solenoid is controlled by the TCM and converts electrical signals into hydraulic control signals to control the electronic park lock function

The control solenoid is an on/off solenoid which is controlled by the TCM by switching the solenoid to earth.

When the park position is deselected, control solenoid MV2 resets the parking lock valve in the Mechatronic valve block. This is achieved by the TCM providing the ground for the solenoid which is energized, releasing the claws from retaining the park lock piston. Main fluid pressure acting on the parking lock piston, pushes the piston back to release the lock.

When the park position is selected, control solenoid MV2 is deenergized. The fluid pressure at the parking lock cylinder piston is vented and the mechanical interlock of the piston is opened. A pre-tensioned torsion spring at the park lock disc pulls the piston into the "park" position where the piston engages with the control solenoid claws and is locked in the park position. An emergency release wire cable can be used to release the parking lock manually if an electrical failure occurs.

The resistance of the solenoid coil winding for solenoid is 25 Ohms at 20 °C (68 °F).

When the neutral "N" position is selected and the engine is turned off, the fluid pressure at the park lock cylinder piston is released. The current supply to the control solenoid MV2 remains. The park lock cylinder piston is still held in the unlocked position by the spring force acting on the park lock disc, preventing the park lock plate from engaging the parking lock. This allows the vehicle to be moved when the engine is not running for a short time. Should the battery voltage fall below the level required to maintain the solenoid in the energized condition, the park lock will be engaged.

Hydraulic Impulse Storage 

The DW12C engine features ECO stop/start technology. Following an ECO stop, the vehicle must be able to restart and drive away within a very short period of time, less than 400ms from the point of the engine starting. The transmission must also be able to react in this time. When the engine is not running the ATF pump is not operating and fluid pressure decays to zero and the brake and clutch elements unlock. When the engine is re-started, the transmission ATF pump requires approximately 800ms to provide the fluid volume and pressure required to engage the shift elements. The hydraulic impulse storage system overcomes this by providing fluid pressure quickly to the shift elements during the engine start process within the engine start time parameter.

Hydraulic Impulse Storage - Sectional View 

The hydraulic impulse storage system comprises a cylindrical accumulator which contains an electro-mechanical locking unit, a spring actuated piston and a one-way restrictor. The accumulator is located at the rear of the Mechatronic valve block and is secured in position with 3 screws and sealed into a port in the transmission casing with an O ring seal.

The electro-mechanical locking unit comprises a low-current solenoid, a spring loaded keeper incorporating a magnetic core and a number of balls. The keeper has a detent into which the balls locate during filling of the hydraulic impulse storage when the engine is running and the ATF pump is producing pressure

The one-way restrictor is located in the inlet/outlet port of the accumulator. The restrictor provides a controlled charging of the hydraulic impulse storage, to allow a small volume flow of ATF. This ensures that the operation of the transmission shift elements are not compromised but a sudden drop in ATF pressure. The restrictor allows a charging time for the hydraulic impulse storage of approximately 5 seconds. When discharge is required, the restrictor allows full flow from the cylinder.

The filling process for the hydraulic impulse storage has several steps:

• When the engine is running and the ATF pump is producing pressure, the one-way restrictor allows a controlled flow of ATF which acts on the piston.
• The ATF pressure moves the piston into the accumulator cylinder. A locking ring on the piston passes over the balls which are at this point located in the keeper detent.
• As the piston continues to move, a spring in the center of the keeper moves the locking cylinder and the magnetic core towards the solenoid windings and into the final fully charged position. The energized solenoid holds the magnetic core and the balls are lifted from the detent by the movement of the keeper, locking the piston in the charged position. The hydraulic impulse storage is now electro-mechanically locked and ready for an engine stop to occur.
• When the engine is stopped, the ATF pump also stops and ATF pressure is decayed, The pressure acting on the piston is also decayed and the piston moves to be held in the locked position by the balls. The energy required for hydraulic filling during engine start is now stored in the tensioned piston spring. The solenoid remains energized to hold the keeper in position and the balls out of the detent to lock the piston.

Charging 

Charged 

Engine start process: 

• When the engine is restarted, the solenoid holding current is removed, which starts the unlocking process.
• The magnetic core is released and the keeper is moved towards the piston under spring pressure. The balls fall into the detent in the keeper, releasing the piston.
• The piston is moved under spring pressure, pushing out the volume of ATF. The one-way restrictor opens fully to allow unrestricted flow of ATF from the accumulator cylinder into the transmission housing. The process is completed between 300 and 350 ms.
• Once the engine is started, the ATF pump produces flow and pressure to provide seamless transmission shift element engagement as soon as the engine is started.

Discharging