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Gear Shift, Function - GF27.60-P-2000RFH

Transmission 724.2 in model 205, 253 

Function requirements, general 

IMPORTANT The CDI control unit (N3/9) (diesel engine) or the ME-SFI [ME] control unit (N3/10) (gasoline engine) transmits the "Engine running" or "Drivetrain operational" signal via the drive train CAN (CAN C1) to the fully integrated transmission control unit (Y3/8n4).

Shift operation, general 

The fully integrated transmission control initiates all shift operations and gear range changes by means of electrohydraulic actuation. Gear ranges "P", "R", "N" and "D" are selected using the DIRECT SELECT lever (S16/13) located on the right of the steering column tube module. The steering column tube module control unit (N80) reads in the DIRECT SELECT lever switch positions directly and transmits them via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN to the fully integrated transmission control unit. The engaged gear and the selected gear range are displayed in the instrument cluster (A1). In order to do this, the fully integrated transmission control unit transmits Information about the selected gear and the engaged gear range via the drive train CAN, the powertrain control unit, the periphery CAN (CAN PER), the electronic ignition lock control unit (N73) and the user interface CAN (CAN HMI) to the instrument cluster. The instrument cluster then actuates the gear indicator (A1p12) or the transmission mode display (A1p16). In order to implement shifting procedures, the fully integrated transmission control unit continuously evaluates the signals of the following components:

The fully integrated transmission control unit for implementing shift operations for the following components:

The fully integrated transmission control unit communicates via the drive train CAN with the CDI control unit or the ME-SFI [ME] control unit. When doing this, the following information is exchanged:

The CDI control unit or the ME-SFI control unit communicates with the power electronics control unit (N129/1) via engine CAN (CAN C), powertrain control unit and hybrid CAN (CAN L). When doing this, the following information is exchanged:

The shift operation function sequence is subdivided into the following areas:

Basic shift program 

The basic shifting program includes upshift and downshift characteristic curves for all 7 gears under optimum operating conditions (e.g. vehicle unladen, smooth road).

Depending on the load condition of the vehicle, the air drag and rolling resistance (e.g. driving with a trailer (with code 550 (Trailer hitch))) and the acceleration requirement, this basic shifting program is modified by adjusting the shift characteristic curves.

The fully integrated transmission control unit then shifts depending on the vehicle speed, the gear range and the accelerator pedal position.

For this purpose, the Electronic Stability Program control unit (N30/4) transmits information about the wheel speeds via the chassis FlexRay, the powertrain control unit and the drive train CAN to the fully integrated transmission control unit. The steering column tube module control unit reads in the DIRECT SELECT lever switch positions directly and transmits these via the chassis FlexRay, powertrain control unit and the drive train CAN to the fully integrated transmission control unit. The CDI control unit or the ME-SFI [ME] control unit transmits information about the accelerator pedal position via the drive train CAN to the fully integrated transmission control unit.

IMPORTANT Undesired downshifts in the upper vehicle speed range are prevented if the accelerator is released slowly. Upshifting to the next gear is prevented if the accelerator is released quickly and only permitted again when the vehicle accelerates more slowly.

The basic shifting program can be modified by the driver by operating the AGILITY SELECT switch (N72/4s1) (up to model year 2016) or the DYNAMIC SELECT switch (N72/4s11) (as of model year 2016) in the left lower control panel (N72/4). The left lower control panel reads in the relevant status directly and sends this over 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, the electronic ignition lock control unit, the periphery CAN, the powertrain control unit and the drive train CAN to the fully integrated transmission control unit. The fully integrated transmission control unit then modifies the shift ranges.

Select shift range 

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.

IMPORTANT The thresholds for switching the internal combustion engine in and out during hybrid operation can be modified using transmission mode selection "E" and "S". In transmission mode "S", the combustion engine is already activated at a lower accelerator pedal threshold in order to generate a faster acceleration.

In Sport "S" and Economy "E" transmission modes, the driver can select the following functions by pressing the downshift steering wheel gearshift button (S110/1) and upshift steering wheel gearshift button (S111/1):

Activate gear limitation 

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).

Shift to optimum gear 

The function "Shift into optimum gear" is selected by pressing and holding the downshift steering wheel gearshift button. The gear that allows optimum vehicle acceleration is selected.

Increase gearshift limitation 

Pressing the steering wheel upshift button once with gear limitation selected increases gearshift limitation by one gear (e.g. from 3 to 4).

Cancel gear limitation 

Pressing and holding down the upshift steering wheel gearshift button cancels the gear limitation function completely (gearshift to "D").

The steering wheel electronics (N135) reads in the signals of steering wheel gearshift button directly and sends them to the fully integrated transmission control unit via steering LIN (LIN E1), steering column tube module control unit, chassis FlexRay, powertrain control unit and drive train CAN. This control unit converts the request into hydraulic signals which are executed by the respective regulating valve.

Shift (e.g. from 1st to 2nd gear) 

The B2 multidisk brake, the B3 multidisk brake and the K3 multidisk clutch are engaged in 1st gear. When shifting from 1st gear to 2nd gear, the B3 multidisk brake is disengaged and the B1 multidisk brake is engaged. The shift operation is 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 the B3 multidisk brake 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 (torque rise phase). This speed alignment is achieved because the pressure in the multidisk brake B1 is increased and, if necessary, the engine torque is reduced by the CDI control unit or the ME-SFI [ME] control unit. With hybrid operation or purely electric operation, the CDI control unit or the ME-SFI [ME] control unit also sends the request for torque reduction of the electric machine over the engine CAN, the powertrain control unit and the hybrid CAN (CAN L) to the power electronics control unit (/).

IMPORTANT If the RPM is too low, downshifting takes place. If the RPM is too high, upshifting takes place. If the vehicle is stationary, 1st gear is automatically selected. It is possible to start off both in 1st or 2nd gear.

IMPORTANTShort-term M program 

The short-term M mode is a temporary mode that is activated when the steering wheel gearshift buttons are operated. When one of the steering wheel gearshift buttons is operated, the transmission control switches up or down a gear, if it is allowed. If not, the current gear is maintained. After a specified time window, the short-term M mode is deactivated. The time window can be extended by undershooting a minimum speed (e.g. stopping), upon recognition of a lateral acceleration or if the vehicle is in overrun mode. After this time window has elapsed, a switch is made back to the initial shift program. The driver can prematurely end the short-term M program through specific actions, e.g. if he presses and holds the steering wheel upshift button, changes the drive range or changes the drive program. In this case, a switch is made to the initial shift program.

  Electrical function schematic for shift operation   PE27.19-P-2057-97FBH
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