ZF 6HP26 Operation

ZF 6HP26 Transmission System
The transmission unit uses planetary gears, with hydraulic-electronic control. The valve body and transmission control module form a composite element that is installed as a single unit in the transmission fluid pan. The TCM uses a newly developed shift strategy known as adaptive shift strategy.

Engine power reaches the transmission via a hydrodynamic torque converter with integral converter lock-up clutch. The six forward gears and one reverse gear are obtained from a single-web planetary gear set followed by a double planetary gear set. Known as Lepelletier-type gear sets. Theses gears make it possible to obtain 6 forward speeds.

Gear selection is achieved by controlling the flow of automatic transmission fluid to operate various internal clutches. The TCM controls the electrical components for gear-selection shift pressure and torque converter slip-control. In the event of a system malfunction the TCM provides failure mode effect management, to maintain maximum functional operation of the transmission, with minimum reduction in vehicle and occupant safety. In the event of loss of transmission control through electrical power failure, the basic transmission function: Park, Reverse, Neutral and Drive are retained by the hydraulic system. The transmission will operate in limp-home mode; 3rd or 5th gear fixed, dependant upon gear selection at the time of the malfunction.

Combining the transmission control module and valve body into one unit provides the following advantages:
- Minimum tolerances, as the TCM is directly connected to the solenoids.
- Better coordination of gear shifts.
- Increased refinements.
- Optimised shift quality.
- Good reliability, since the number of plug connections and interfaces are reduced.

The TCM controls the operation of the transmission by processing signal such as:
- Transmission input and output speed.
- Throttle pedal position.
- Engine torque and speed.
- Transmission fluid temperature.
- Brake pedal status.
- Engine oil temperature.
- Engine coolant temperature.
- Wheel speed, etc

Using the above signals and stored information the TCM calculates the correct gear and torque converter lock-up clutch setting and the optimum pressure settings for gear shift and lock-up clutch control.

Five pressure regulators and one solenoid valve are used to direct transmission-fluid flow. Select internal clutches and control the fluid pressure at the clutch for gear control. A separate pressure regulator is used exclusively for torque converter clutch control. The TCM monitors input and output signals to confirm correct system operation. If a malfunction does occur the TCM reverts to a default state and informs the driver of a problem via the instrument cluster.