Gear shift, function

Function requirements for shift operation, general

 Circuit 87 ON

 Circuit 61 (engine running)

 Engine speed from motor electronics control unit (N3/10)

 Transmission not in limp-home mode

 Engine compartment CAN (CAN-C) signals

Shift operation, general

The electric controller unit (Y3/6) converts the electrical signals coming from the ETC control unit (N15/3) into hydraulic signals.

-----------------------------------------------------------------------------------------

The electronic selector lever module control unit (N15/5) passes on the selector lever positions "P, R, N, D" to the ETC control unit, taking into account various information.

Via the steering wheel gear shifter MINUS (S110/1) and steering wheel gear shifter PLUS (S111/1) (with code 428 Steering wheel shift paddles) the shift range up to which the upshift of the transmission is possible is programmed. The shift range is displayed in the instrument cluster (A1).

The shift range can be changed in the forward gears while driving, but the ETC control unit prevents a shift at unacceptably high or low engine speeds.

-----------------------------------------------------------------------------------------

Shift operation, function sequence

The function sequence is subdivided into the following steps:

 Upshifting and downshifting

 1st gear shift

 Shift phase

 2nd gear shift

Upshifting and downshifting

In transmission modes Sport "S" and Comfort "C" the driver can select the following functions by operating the selector lever (touch-mode (+/-)) or steering wheel gear shifters MINUS and PLUS (with code 428 Steering wheel shift paddles):

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 "+" in gear range "D" sends an upshift request to the transmission (the transmission shifts up if the driving situation allows).

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

-----------------------------------------------------------------------------------------

In transmission mode Comfort "C" in comparison with the transmission mode Sport "S" a shorter shift range (shifting at low engine speed) and therefore a lower drive torque is available.

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

In transmission mode Manual "M" (except code 494 USA version) the individual gears "1, 2, 3, 4, 5" can be shifted directly via the steering wheel gear shifters MINUS and PLUS with (code 428 Steering wheel shift paddles).

Reverse gear, park position and neutral can only be engaged via the electronic selector lever module control unit.

 Manual transmission mode

Transmission mode Manual "M" is no longer active after ignition "OFF"  "ON". The transmission always starts in the last selected transmission mode. ("S" or "C").

1st gear shift

The end face of the 1 - 2 or 4 - 5 command valve is kept depressurized via the 1-2 und 4-5 shift solenoid valve. Working pressure is applied via the 1 - 2 or 4 - 5 holding pressure shift valve to the multidisk brake B1 The multidisk clutch K1 is unpressurized.



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. Starting off in 1st and 2nd gear is

possible due to the lack of excess force limitation.

P27.60-2747-76

Shown: shift position in 1st gear

0 Oil sump drain

21 Multidisk brake B1

24 Multidisk clutch K1

28a 1 - 2 or 4 - 5 holding pressure shift valve

29a 1 - 2 or 4 - 5 shift pressure shift valve

30a Overlap regulating valve
1 - 2 or 4 - 5

31a 1 - 2
or 4 - 5 command valve

p-A Working pressure

p-Mod Modulating pressure

p-S Shift pressure

p-SV Shift valve pressure

Y3/6y3 1-2 and 4-5 shift solenoid valve

Shift phase

Via the 1-2 and 4-5 shift solenoid valve the shift valve pressure is switched so that it acts on the end face of the 1 - 2 or 4 - 5 command valve. As a result the 1 - 2 or 4 - 5 command valve is moved and shift pressure, coming from the 1 - 2 or 4 - 5 shift pressure shift valve via the 1 - 2 or 4 - 5 command valve, is lead to the multidisk clutch K1. Overlap pressure is applied to the multidisk brake B1 at the same time from the 1 - 2 or 4 - 5 overlap regulating valve.

The pressure from the multidisk brake acting on the end face of the 1 - 2 or 4 - 5 shift pressure shift valve

B1 is superseded by the working pressure. The increasing shift pressure at the multidisk clutch K1 acts on the annular surface on the 1 - 2 or 4 - 5 overlap regulating valve and reduces the overlap pressure regulated by the 1 - 2 or 4 - 5 overlap regulating valve. At a corresponding pressure level at the 1 - 2 or 4 - 5 holding pressure shift valve this changes over.

P27.60-2748-76

Shown: shift phase

0 Oil sump drain

21 Multidisk brake B1

24 Multidisk clutch K1

28a 1 - 2 or 4 - 5 holding pressure shift valve

29a 1 - 2 or 4 - 5 shift pressure shift valve

30a Overlap regulating valve
1 - 2 bzw. 4 - 5

31a 1 - 2
or 4 - 5 command valve

p-A Working pressure

p-Mod Modulating pressure

p-S Shift pressure

p-SV Shift valve pressure

Y3/6y3 1-2 and 4-5 shift solenoid valve

2nd gear shift

Once the gear change is complete via the 1-2 and 4-5 shift solenoid valve the pressure on the end face of the 1 - 2 or 4 - 5 command valve is reduced and this is moved into the basic position. Working pressure now reaches the multidisk clutch via the 1 - 2 or 4 - 5 holding pressure shift valve and the 1 - 2 or 4 - 5 command valve K1.

The multidisk brake B1 is switched off (unpressurized). The spring in the shift pressure shift valve 1 - 2 or 4 - 5 shifts this into the basic position.

P27.60-2749-76

Shown: shift position in 2nd gear

0 Oil sump drain

21 Multidisk brake B1

24 Multidisk clutch K1

28a 1 - 2 or 4 - 5 holding pressure shift valve

29a 1 - 2 or 4 - 5 shift pressure shift valve

30a Overlap regulating valve
1 - 2 bzw. 4 - 5

31a 1 - 2
or 4 - 5 command valve

p-A Working pressure

p-Mod Modulating pressure

p-S Shift pressure

p-SV Shift valve pressure

Y3/6y3 1-2 and 4-5 shift solenoid valve