Hydraulic Shift Control Unit

Hydraulic Shift Control Unit

The Hydraulic Shift Control Unit (Mechatronik unit) is a combination of hydraulic and electronic control (TCM) modules, which is located in the transmission, in the oil sump.

This technical principle has the following advantages:

• Minimum tolerances
• Better coordination of gear shifts
• Increased refinement
• Optimised shift quality
• Good reliability, since the number of plug connections and interfaces is reduced

Electrostatic Discharge (ESD)

Caution
When working with the transmission control module (TCM) and main control valve body, all suitable safety precautions must be taken to protect the component against electrostatic discharge (ESD). Failure to follow these instructions may result in component damage.

Make sure all possible safety precautions are taken to protect the TCM and main control valve body unit against ESD.

Personal Wrist-Band Earthing

Earthing (grounding) by means of a wrist band or strap is the most reliable method of diverting electrostatic charges away from working personnel, and should therefore be used wherever possible, particularly if the person concerned is working while seated. The wrist band earthing (grounding) device consists of a bracelet closely attached to the wrist and a spiral earthing (grounding) cable connecting it to the earthing (grounding) contact point. This system must include a quick-release device so that the wrist can be released in the event of danger.

Shoes and Foot Earthing Straps

Electrically conductive shoes should be worn by persons who mainly work standing up or either standing or sitting in ESD protection zones, particularly if wrist band earthing (grounding) is impracticable. The standard calls for ESD shoes to record values between 0 and 35 Megga-ohms (MOhm) resistance. However, for antistatic working shoes resistance values between 0.1 and 1000 MOhm are called for, and a through-conducting resistance for protective shoes of 0.1 to 100 MOhm. A lower limit value of not less than 0.1 MOhm must be maintained on account of the contact voltage risk. For this reason the minimum value has been set contrary to the standard at the higher figure of 0.75 MOhm.

Transmission Control Module (TCM)

The transmission control module (TCM) and its input / output network control the following transmission operations:

• Shift timing
• Line pressure (shift feel)
• Torque converter clutch

The TCM processes signals from the transmission, the engine and the vehicle.

From the signal inputs and the memorised data the control program computes the correct gear and converter lock-up clutch setting and the optimum pressure settings for gear shift and lock-up clutch control.

By means of special output-side modules (power output stages, current regulator circuits), the TCM controls the solenoid valves and pressure regulators and thus influences the hydraulics of the automatic transmission. In addition, the amount and duration of engine interventions are supplied to the engine management by way of the CAN bus.

F1
Caution
Disconnection of other control modules and / or the vehicle battery, may introduce fault codes (DTCs). Following rectification and reconnection, ensure that no induced codes exist in the TCM memory.

Caution
Disconnection of other control modules and / or the vehicle battery, will cause shift adaptations to be lost; this may be apparent by slight shift quality degradation. Shift quality adaptations are made to compensate for changing transmission characteristics over time. Following reconnection, a period of adaptation will be required as the TCM re-learns the transmissions operating characteristics.

Controller Area Network (CAN) Interface

For the TCM to be able to perform shift point and shift quality management a number of external signals are required. For shift point management alone the TCM requires output speed sensor, throttle pedal position, brake pedal status and virtual gear selector position. The controller area network (CAN) bus is used to share information between control modules. The TCM obtains most of its required data over the CAN bus from the electronic engine controls, EMS, Driver inputs and ABS, Instruments pack and diagnostic tools.