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

Transmission 722.9 05 in model 166 as of model year 2016 

Transmission 722.9 05 in model 292 

Function requirements for Transmission control, general 

Transmission control, general 

To check the function requirements, the fully integrated Transmission control unit reads in the following signal over the drive train CAN (CAN C):

To check the function requirements, the intelligent servo module for DIRECT SELECT (A80) reads in the following signal over the drive train CAN:

The following control solenoid valves are actuated by the fully integrated Transmission control unit:

The following signals are processed by the fully integrated Transmission control unit:

The Transmission control system electronically actuates the control solenoid valves. 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 control solenoid valves are actuated that then determine the Transmission ratio (gear selection), the working pressure and the torque converter lockup. To run the shift function, the ME-SFI [ME] control unit requires information from the Transmission control. To do so, the fully integrated Transmission control unit sends the status of the Transmission control over the drive train CAN to the ME-SFI [ME] control unit. The ME-SFI [ME] control unit sends the status of the engine management to the fully integrated Transmission control unit.

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 Transmission mode control (N72/4s1), which is located in the area of the center console in the Transmission mode control panel (N72/4). The button status is sent via the center console switch LIN (LIN B12), the SAM control unit (N10), the interior CAN (CAN B), the electronic ignition lock control unit, chassis CAN 1, the ME-SFI [ME] control unit and the drive train CAN to the fully integrated Transmission control unit.

The Transmission mode "M" button (N72s37), which is located in the lower control panel control unit (N72), can be used to select the Transmission mode "M". The button status is sent via the center console switch LIN, the SAM control unit, the interior CAN, the electronic ignition lock control unit, chassis CAN 1, the ME-SFI [ME] control unit and the drive train CAN to the fully integrated Transmission control unit.

In the manual ("M") Transmission mode, the individual gears "1", "2", "3", "4", "5", "6", "7" can be directly selected using the steering wheel downshift and upshift buttons.

IMPORTANT The fully integrated Transmission control unit sends the Transmission mode status over drive train CAN to the ME-SFI [ME] control unit and onward over chassis CAN 1 and chassis CAN 2 (CAN E2) with the electronic ignition lock control unit interface to the instrument cluster (A1). The selected Transmission mode is shown to the driver on the multifunction display (A1p13) in the instrument cluster.

In vehicles with CODE 550 (Trailer hitch), the trailer recognition control unit (N28/1) transmits the trailer recognition status to the fully integrated Transmission control unit over the interior CAN, the electronic ignition lock control unit, chassis CAN 1, the ME-SFI [ME] control unit and the drive train CAN.

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:

The Electronic Stability Program control unit (N30/4) receives the wheel speed signal and uses it to calculate the vehicle speed. This routes the signal for vehicle speed over chassis CAN 1 to the ME-SFI [ME] control unit. The ME-SFI [ME] control unit routes the signal over the drive train CAN to the fully integrated Transmission control unit and to the intelligent servo module for DIRECT SELECT.

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 is supplied to the hydraulic elements, such as hydrodynamic torque converter, shift elements and hydraulic Transmission control, via an oil pump connected to the torque converter or the electric oil pump (M42) (on model 166) or electric auxiliary oil pump (M42) (on model 292). 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 any impermissible 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 gear oil auxiliary pump control unit (N89). The ME-SFI [ME] control unit sends the request over the drive train CAN to the Transmission oil auxiliary pump control unit. This actuates the electric auxiliary oil pump to meet requirements and forwards the status of the electric auxiliary oil pump to the ME-SFI [ME] control unit again.

Function sequence for kickdown 

The driver's wish for maximum acceleration is met by the kickdown function. The kickdown function is activated as from a pedal travel of > 90 %. The "kick-down" signal is received by the ME-SFI [ME] control unit 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 

In order to ensure safe driving and to prevent damage to the transmission, the fully integrated Transmission control unit switches to limp-home mode in the event of critical faults. The fault is stored with the assigned fault code in the fault memory and forwarded to the ME-SFI [ME] control unit over the drive train CAN. The ME-SFI [ME] control unit sends an indicator lamp request over chassis CAN 1 and chassis CAN 2 with the electronic ignition lock control unit interface to the instrument cluster. The instrument cluster activates the engine diagnosis indicator lamp (A1e58).

If the signals are implausible, the Transmission control system is only partially operational and switches to the programmed emergency performance map. Using the DIRECT SELECT lever (S16/13), the driver can engage the desired gear ranges "P", "R", "N", "D". 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. The selector lever positions "P", "R", "N", "D" are sent by the DIRECT SELECT lever over the steering column tube module control unit (N80) over chassis CAN 1 to the ME-SFI [ME] control unit. This sends the information to the drive train CAN. The intelligent servo module for DIRECT SELECT routes the selector lever positions to the fully integrated Transmission control unit taking various information into consideration. The intelligent servo module for DIRECT SELECT changes the position of the selection range lever which is passed on mechanically to the selection range sensor.

IMPORTANT The faults are stored in the fault memory. These can be read out using Xentry Diagnostics. The status of the Transmission control diagnosis is sent to the diagnostic connector (X11/4) by the fully integrated Transmission control unit via the drive train CAN, ME-SFI [ME] control unit, chassis CAN 1, electronic ignition lock control unit, and diagnostic CAN (CAN D).

IMPORTANTShort-term M program 

The short-term M mode is a temporary mode that is activated when the steering wheel gearshift buttons 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 undershooting a minimum speed (e.g. stopping), upon recognition of a lateral acceleration or if the vehicle is in a deceleration phase. If none of the stated criteria are active anymore, the short-term M mode remains active for a specified period of time. After this remaining time has elapsed, a switch is made back to the initial shift program. In addition, the driver is shown a recommended shift operation in the instrument cluster. This is part of the gearshift recommendation that is also integrated. The driver can prematurely cancel the short-term M mode through specific actions, e.g. if he/she presses and holds the steering wheel upshift button in the "positive" direction (+), if the gear range changes or if he/she changes the Transmission mode. If one of these preconditions is met, a switch is made back to the initial shift program.

IMPORTANT Shifts, which could result in non-permissible high or low engine speeds, are not performed.

  Electrical function schematic, fully integrated Transmission control   PE27.19-P-2061-97NBC
  Overview of system components for automatic Transmission (AT)   GF27.10-P-9992ANN
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