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Transmission Control, Function - GF27.60-P-2002AHE

TRANSMISSION 722.9 (except 722.930) in MODEL 205 

Function requirements for transmission control, general 

Transmission control, general 

The transmission control operates the actuators (control solenoid valves) electronically. The valves are located in the hydraulic valve body assembly. This realizes the hydraulic functionality and is part of the fully integrated transmission control controller unit (Y3/8).

The function of the fully integrated transmission control unit basically consists of the evaluation of various input signals relevant to the transmission function. Based on this, eight electromechanical hydraulic valves are actuated which determine the transmission ratio (gear selection), the working pressure and the torque converter lockup.

Transmission control function sequence 

The function sequence is described in the following steps:

Function sequence for basic shift program 

The basic shift program includes upshift and downshift characteristics for all 7 gears, designed for:

The basic shifting program can be influenced by the driver using the AGILITY SELECT switch (N72/4s1), which is located near the center console. The signal is read in via the lower control panel (N72/4). The lower control panel transmits the switch status via the LCP LIN (LIN A3), the Audio/COMAND control panel (A40/9), the telematics CAN (CAN A), the head unit (A26/17), the user interface CAN (CAN HMI) to the electronic ignition lock control unit (N73) and via the periphery CAN (CAN PER) to the powertrain control unit (N127). The powertrain control unit sends the button status over the drive train CAN (CAN C1) to the fully integrated transmission control unit.

The shift programs are adapted by offsetting the characteristics, depending on:

The fully integrated transmission control unit monitors and shifts depending on:

Slow accelerator release:

Rapid accelerator release:

Function sequence for electronic and hydraulic transmission control 

While the electronic transmission control system is responsible for gear selection and adaptation of pressures to the torque to be transmitted, power supply control for the transmission is performed by the hydraulic elements of the fully integrated transmission controller unit. The oil supply for the hydraulic elements, such as hydrodynamic torque converter, shift elements and hydraulic transmission control, is provided by an oil pump connected to the torque converter or through the electric auxiliary oil pump (M42).

The transmission control system makes possible a precise adaptation of pressures to the respective operating states and to the engine output during the gearshift phase, resulting in a significant improvement in shift quality.

It is possible to reach the engine RPM limit in the individual gears using full throttle and kickdown.

The transmission control system prevents impermissibly high engine speeds with a downshift lockout device. Furthermore, the transmission control system offers the advantage of a flexible adaptation to various vehicle and engine versions.

IMPORTANT

The electrical auxiliary oil pump ensures the oil supply of the hydraulic system when the internal combustion engine is switched off. It also supports the primary pump during coast down shifting in hot idling. This is actuated through the transmission oil auxiliary pump control unit (N89).

Function sequence for kickdown 

The driver's wish for maximum acceleration is met by the kickdown function.

The kickdown function is activated as of a pedal travel > 90 %. The "Kick-down" signal is received by the CDI control unit (N3/9) or the ME-SFI [ME] control unit (N3/10) and sent over the drive train CAN to the fully integrated transmission control unit.

Based on this information the fully integrated transmission control unit actuates the control solenoid valves so that upshifts and downshifts take place at an increased engine speed in order to achieve maximum performance.

Function sequence for limp-home mode 

If the signals are implausible, the transmission control system is only partially operational and switches to the programmed emergency performance map.

The driver can engage the desired gear range "P", "R", "N" or "D" using the DIRECT SELECT lever (S16/13).

The driver can choose been forward and reverse travel, engage the park pawl or, when in neutral, interrupt the power flow between torque converter and transmission.

IMPORTANT Short-term M program

The short-term M program is a temporary program that is activated when the steering wheel gearshift buttons or the DIRECT SELECT lever are operated. Pressing in the positive (+) direction triggers an upshift and pressing in the negative (-) direction triggers a downshift, insofar as this is permissible. If not, the current gear is maintained. After a specified time window, this function deactivates again automatically. The activated time can be extended by dropping below a minimum speed (e.g. stopping), when lateral acceleration is detected or when the vehicle is in a deceleration phase. If none of the stated criteria are active anymore, the M mode remains active for a prescribed remaining time. After this remaining time expires, the initial shift mode is returned to. The driver is also shown a recommended shift operation in the instrument cluster (A1). This is part of the gearshift recommendation that is also integrated. The driver can prematurely cancel the short-term M program through specific actions, e.g. if he/she operates and holds the upshift steering wheel gearshift button or the DIRECT SELECT lever in the "positive" direction, changes the gear range or changes the transmission mode. If one of these preconditions is met, a switch is made back to the initial shift program.

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