Gear shift, function

GF27.60-P-2000AHN

Gear shift, function

22.2.13

TRANSMISSION

722.9 in MODEL 172

Function requirements for shift operation, general

 Circuit 87 (connected circuit 15) ON

 Circuit 61 (engine running)

 Engine speed from CDI control unit (N3/9) or ME-SFI [ME] control unit (N3/10)

 Transmission not in limp-home mode

 Drive train CAN (CAN C) signals

Shift operation, general

The fully integrated transmission control controller unit (Y3/8) converts the electrical signals coming from the fully integrated transmission control unit (Y3/8n4) into hydraulic signals.

The electronic selector lever module control unit (N15/5) passes on selector lever positions "P, R, N, D" to the fully integrated transmission control unit via the drive train CAN taking into account various pieces of information.

The electronic selector lever module control unit changes the position of the selector range lever, and this is transmitted mechanically to the selection range sensor (Y3/8s1).

Although the shift range can be changed in the forward gears while driving, the fully integrated transmission control unit prevents a shift operation if the engine speeds are too high or too low.

 Display of the selected gear range

The fully integrated transmission control unit sends the information on the position of the selector range lever over the drive train CAN to the CDI control unit or the ME-SFI [ME] control unit and it is then forwarded over the chassis CAN (CAN E) to the instrument cluster (A1), which shows the gear range engaged to the driver on the multifunction display (A1p13).

Function sequence for shift operation

The function sequence is described in the following steps:

 Function sequence for shifting up and down

 Function sequence of gearshift 1 to 2

Function sequence for shifting up and down

In the Sport ("S") and Economy "E" transmission modes (except code (990) AMG vehicles) or Controlled Efficiency "C" (with code (990) AMG vehicles), the driver can operate the selector lever (touch mode (+/-)) or the steering wheel downshift button (S110/1) or the steering wheel upshift button (S111/1) (with code (428) Steering wheel shift paddle) to select the following functions:

One press towards "-" activates the gear limitation or touchshift function (a downshift is made to the gear that lies exactly one below the currently selected one if the engine speed allows).

Pressing and holding towards "-" selects the "Shift to optimal gear" function (the gear which allows the best vehicle acceleration is selected).

One press toward "+" with the gear limitation function selected increases gearshift limitation by one gear (e.g. from 3 to 4).

One press toward direction "+" in gear range "D" sends an upshift request to the transmission (the transmission shifts up depending on the driving situation).

Pressing and holding toward "+" cancels the gear limitation function completely (gearshift to "D").

For the Economy "E" transmission mode (except code (990) AMG vehicles) or Controlled Efficiency "C" (with code (990) AMG vehicles) there is in contrast to the Sport ("S") transmission mode a shorter shifting range is available (shifting at low engine rpm) and therefore a lower drive torque when driving forward and when reversing.

This enables a gentler start-off as the gears are not driven to the limit.

For the Manual ("M") transmission mode with code 950 (Sport package), the individual gears "1, 2, 3, 4, 5, 6, 7" can be directly selected using the steering wheel downshift button and upshift button.

Reverse gear, park position and neutral can only be selected by way of the electronic selector lever module control unit.

 Manual transmission mode with code 950 (Sport package)

The Manual ("M") transmission mode with code 950 (Sport package) is no longer active after ignition is switched "OFF" "ON" using the ignition key (transmitter key (A8/1)) or using the KEYLESS-GO start-stop button (S2/3) (with code (889) Keyless Go). The transmission always starts in the last selected transmission mode.

 Display of selected transmission mode

The fully integrated transmission control unit sends the transmission mode status over the drive train CAN to the CDI control unit or the ME-SFI [ME] control unit and forwards it over the chassis CAN to the instrument cluster.

The selected transmission mode is indicated to the driver on the transmission mode display (A1p16) in the instrument cluster.

 The transmission mode "M" is only available with code 950 (Sport package). Vehicles without Sport package do not have transmission mode "M". On these vehicles, the transmission mode "M" is replaced by the "Short-term M mode".

Function sequence of gearshift 1 to 2

Multidisk brake B2, multidisk brake B3 and multidisk clutch K3 are engaged in 1st gear. When shifting from 1st gear to 2nd gear, multidisk brake B3 is disengaged and multidisk brake B1 is engaged.

The shift operation can be started by the fully integrated transmission control unit. In the process the multidisk brake B1 is filled with oil and the pressure in the multidisk brake B1 is continuously increased. Simultaneously the pressure in multidisk brake B3 is reduced.

This involves a flowing transition. When the 2nd gear torque is reached, the engine speed must be adapted to the 2nd gear level (elevation phase).

This speed adjustment is achieved by the pressure in the multidisk brake B1 being increased and, if necessary, engine torque being reduced via the CDI control unit or ME-SFI control unit.



A forced downshift occurs at excessively low rpm and a forced upshift occurs at an excessively high rpm.

When the vehicle is stationary the transmission automatically shifts into 1st gear. It is possible to start off both in 1st or 2nd gear.

 Display of engaged gear stage

The fully integrated transmission control unit sends the status of the currently engaged gear range over the drive train CAN to the CDI control unit or the ME-SFI [ME] control unit and forwards it over the chassis CAN to the instrument cluster.

The engaged gear step change is shown to the driver on the instrument cluster's gear indicator (A1p12).

 Introduction of short-term M mode, on vehicles as of AEJ 13/1
The gear limitation is replaced by the function "Short-term M mode". The short-term M program is a temporary program that is activated when the lever or the steering wheel gearshift buttons are operated. Pressing the plus (+) direction effects an upshift and pressing in the minus (-) direction effects a downshift, if these are 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 M mode remains active for a prescribed remaining time. After this remaining time expires, the initial shift mode is returned to. The driver can personally interrupt the short-term M mode prematurely with certain actions. If the driver presses the steering wheel upshift button or moves the lever towards "Plus" (+) and holds, changes gear range or when the driver changes the transmission mode. If one of these preconditions is met, a switch is made back to the initial shift program.

 In vehicles as of AEJ 13/1
As of modification year 13/1, a gearshift recommendation is also shown in the instrument cluster. This is part of the short-term M mode that is also integrated.

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