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

TRANSMISSION 722.930 up to 5/31/11, 722.931 as of 6/1/11 in MODEL 212.0/2 

Function requirements for shift mechanism in general for vehicles up to facelift 13 

• Circuit 87 ON
• Circuit 61 ON
• Engine speed, from ME-SFI [ME] control unit (N3/10)
• Transmission not in limp-home mode
• Chassis CAN (CAN E) signals

General shift operation for vehicles up to facelift 13 

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 intelligent servo module for DIRECT SELECT (A80) passes the selector lever positions "P", "R", "N", "D" on to the fully integrated transmission control unit via the chassis CAN taking various information into consideration.

The intelligent servo module for DIRECT SELECT changes the position of the selection range lever, which is forwarded mechanically to the selection range sensor (Y3/8s1). The shift range is displayed in the instrument cluster (A1). 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.

For vehicles as of facelift 13 the current chassis CAN will be replaced by the chassis CAN 1 (CAN E1). A chassis CAN 2 (CAN E2) is used between the instrument cluster and the front SAM control unit with fuse and relay module (N10/1).

Function sequence for shift operation 

The function sequence is subdivided into the following steps:

• Function sequence for shifting up and down 
• Function sequence for 1 to 2 shift 

Function sequence for shifting up and down In transmission modes Sport "S", Sport Plus "S+" and Comfort "C", 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):

For vehicles up to facelift 13 

• Pressing the downshift steering wheel gearshift button once activates the gear limitation function or triggers the downshift function which, if the engine speed permits, causes the transmission to shift down to the gear that is one gear below the gear currently engaged.
• Pressing and holding down the downshift steering wheel gearshift button selects the "shift to optimum gear" function. The gear that allows optimum acceleration of the vehicle is selected.
• Pressing the upshift steering wheel gearshift button once with gear limitation selected increases gearshift limitation by one gear (e.g. from 3rd gear to 4th gear).
• Pressing the upshift steering wheel gearshift button once with gear range "D" selected sends an upshift request to the fully integrated transmission control (VGS). The latter then shifts up according to the driving situation. Pressing and holding down the upshift steering wheel gearshift button cancels the gear limitation function completely (gearshift to "D").
• In comparison to transmission mode "S" and "S+", transmission mode "C" has a shorter shift range (shifting at low engine speed) and therefore a lower drive torque when starting off in a forward or reverse direction. This enables a gentler start-off as the gears are not driven to the limit.
• With transmission mode Manual "M", the individual gears "1", "2", "3", "4", "5", "6", "7" can be shifted directly using the downshift steering wheel gearshift button and upshift steering wheel gearshift button.
• The reverse gear, park position and neutral position can only be engaged via the DIRECT SELECT INTERFACE (N150).

The gear limitation is replaced by the function "Short-term M mode". Short-term mode M is a temporary program that is activated when the steering wheel gearshift buttons or the DIRECT SELECT INTERFACE 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 a minimum speed being dropped below (e.g. stopping), where lateral acceleration is detected by the yaw rate sensor for lateral and longitudinal acceleration (B24/15) 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 prematurely cancel the short-term mode M through specific actions, e.g. if the driver operates and holds the upshift steering wheel gearshift button or the DIRECT SELECT INTERFACE 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.

The transmission mode Manual "M" is no longer active if the status of circuit 15 changes. The last selected transmission mode is then always used to start off ("S", "S+" or "C").

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 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 multi-disk brake B1 being increased and, if necessary, engine torque being reduced via the ME-SFI [ME] 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.