Gear shift, function - GF27.60-P-2000AHO

TRANSMISSION 724.2 in MODEL 212 

Function requirements for shift operation, general 

• Status "Circuit 87 ON"
• Internal combustion engine running and/or electric machine (A79/1) ON
• Transmission not in limp-home mode
• Drive train CAN (CAN C) signals

Shift operation, general 

Use of the new fully integrated transmission control (VGS4 500), means that an additional mechanical or electronic gear range adjustment system is no longer required. All shift operations and gear stage changes are actuated electrohydraulically by the fully integrated transmission control.

The shift operations are initiated either fully automatically by the transmission control (to match each input signal or the current operating condition) or they can be influenced by the driver by operating the steering wheel downshift button (S110/1) or the steering wheel upshift button (S111/1).

Function sequence for shift operation 

The function sequence is subdivided into the following steps:

• Gear range change, function sequence 
• Function sequence for shifting up and down 
• Function sequence for 1 to 2 shift 

Function sequence for gear stage change for vehicles up to facelift 13 

Gear ranges "P", "R", "N", "D" are selected using the DIRECT SELECT lever (S16/13) located on the right of the steering column tube module. The gear stage change signal is read in by the steering column tube module control unit (N80), and sent over the chassis CAN (CAN E) and the drive train CAN by the interface CDI control unit (N3/9) or ME-SFI [ME] control unit (N3/10) to the fully integrated transmission control unit (Y3/8n4).

The fully integrated transmission control unit converts the electrical signals into hydraulic signals. Information on the currently engaged gear range sent by the fully integrated transmission control unit over the drive train CAN to the CDI control unit or to the ME-SFI [ME] control unit, and forwarded over the chassis CAN to the instrument cluster (A1).

The engaged gear range is shown to the driver on the instrument cluster's multifunction display (A1p13).

As of facelift 13 the current chassis CAN will be replaced by the chassis CAN 1 (CAN E1).

An additional chassis CAN 2 (CAN E2) is used between the instrument cluster and the front SAM control unit with fuse and relay module (N10/1). The ME-SFI [ME] control unit or the CDI control unit forms the interface between the drive train CAN and the chassis CAN 1. The interface between chassis CAN 1 and chassis CAN 2 is formed by the front SAM control unit with fuse and relay module.

Function sequence for shifting up and down 

In transmission modes Sport "S" and Economy "E", the driver can select the following functions by pressing the steering wheel downshift button and steering wheel upshift button:

Pressing the steering wheel downshift button once activates the gear limitation function (if the rpm of the combustion engine or the electric machine permits, the system shifts down to the gear that is one gear below the one currently used).

By pressing and holding the steering wheel downshift button, the function "Shift into optimum gear" is selected (the gear is selected which enables the best acceleration of the vehicle).

Pressing the steering wheel upshift button once with gear limitation selected increases gearshift limitation by one gear (e.g. from 3 to 4). Pressing the steering wheel upshift button once for gear range "D" sends a shift up request to the transmission (if possible, the transmission shifts into a higher gear, depending on the actual driving situation).

Pressing and holding down the upshift steering wheel gearshift button cancels the gear limitation function completely (gearshift to "D"). Compared to the Sport "S" transmission mode, the Economy "E" transmission mode has a shorter shift range (shifting at low rpm of the combustion engine or the electric machine) and therefore a lower drive torque is available when starting off forwards and starting off in reverse.

This enables a gentler start-off as the gears are not driven to the limit. Reverse gear, park position and neutral can only be shifted via the DIRECT SELECT lever.

Transmission mode selection "E" or "S" can be used to influence the thresholds for activating/deactivating the internal combustion engine for hybrid automotive operation. In transmission mode "S", the combustion engine is already activated at a lower accelerator pedal threshold in order to generate a faster acceleration.

Function sequence for 1 to 2 shift 

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. Here, the multidisk brake B1 is filled and the pressure in multidisk brake B1 is increased continuously. Simultaneously the pressure in multidisk brake B3 is reduced.

This involves a flowing transition. When the torque of 2nd gear is reached, the rpm of the combustion engine or the electric machine must be adapted to the level of 2nd gear (elevation phase).

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

In the hybrid or purely electric drive mode, a request for reducing the torque of the electric machine is also sent to the power electronics control unit (N129/1).

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.