Transmission Control, Function - GF27.60-P-2002RFH

Transmission 724.2 in model 205, 253 

Function requirements 

• Terminal 15 ON
• Function test of fully integrated transmission control unit (Y3/8n4) carried out

The electronic ignition lock control unit (N73) transmits the status of circuit 15 via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the fully integrated transmission control unit (Y3/8n4).

Transmission control 

The transmission control includes the electronic recording of all influencing factors and the electrohydraulic actuation of the relevant actuators in the automatic transmission by the fully integrated transmission control unit.

The fully integrated transmission control unit evaluates the signals of the following components:

• Wet clutch oil pressure sensor (Y3/8b1)
• D/R oil pressure switch 1 (Y3/8b3)
• D/R 2 oil pressure switch (Y3/8b4)
• Turbine wheel RPM sensor (Y3/8n1)
• Rpm sensor for internal input speed (Y3/8n2)
• Output shaft RPM sensor (Y3/8n3)
• Transmission oil temperature sensor (Y3/8s2)
• Park pawl position sensor (Y3/8s4)

The fully integrated transmission control unit also communicates over the drive train CAN with the powertrain control unit and is therefore connected to the vehicle electronics.

The fully integrated transmission control unit also evaluates the following variables for transmission control:

• Engine management information and requests (from the CDI control unit (N3/9) (diesel engine) or the ME-SFI [ME] control unit (N3/10) (gasoline engine))
• Information about the driving condition, driving style (e.g. wheel speed, status of service brake) (from the Electronic Stability Program control unit (N30/4))
• Driver requests (e.g. transmission mode selection) (from the steering column tube module control unit (N80) and from the lower control panel (N72/4))

  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 reads in the signals of the DIRECT SELECT lever directly and transmits these via the chassis FlexRay, powertrain control unit and the drive train CAN to the fully integrated transmission control unit. Various transmission modes can be selected 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). The left lower control panel reads in the status of the relevant switch directly and transmits this via 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 (CAN HMI), the electronic ignition lock control unit, the periphery CAN (CAN PER), the powertrain control unit and the drive train CAN to the fully integrated transmission control unit.

Depending on all of this information, the fully integrated transmission control unit actuates the following transmission control actuators:

• Electric auxiliary oil pump (M42)
• Park pawl lift solenoid (Y3/8l1)
• Working pressure control solenoid valve (Y3/8y1)
• K1 clutch control solenoid valve (Y3/8y2)
• K2 clutch control solenoid valve (Y3/8y3)
• K3 clutch control solenoid valve (Y3/8y4)
• B1 multidisk brake control solenoid valve (Y3/8y5)
• B2 multidisk brake control solenoid valve (Y3/8y6)
• B3 multidisk brake control solenoid valve (Y3/8y7)
• Wet clutch control solenoid valve (Y3/8y9)
• D/R switchover valve (Y3/8y10)
• Park pawl switchover valve (Y3/8y 11)

When doing this, the transmission ratio (gear selection), the gear ranges ("P" or "not P", "R" and "D"), the working pressure and the wet clutch control are defined.

While the electronic transmission control is responsible for gear selection and the adaptation of pressures to the torque to be transferred, the automatic transmission's power supply is controlled through the hydraulic elements in the fully integrated transmission controller unit (Y3/8). The oil is supplied for the hydraulic elements (wet clutch, shift elements, hydraulic transmission control) over an oil pump connected to the transmission input shaft or over the electric auxiliary oil pump. The transmission control system allows for precise adaptation of pressures to the respective operating conditions and to the engine output or output of the electric machine during the shift phase, which results in a significant increase in shift quality. It is possible to reach the engine RPM limit in the individual gears using full throttle and kickdown. The transmission control system prevents impermissible high engine speeds with a downshift lockout function. Furthermore, the transmission control system offers the advantage of a flexible adaptation to various vehicle and engine versions.

Using the two switchover valves (D/R switchover valve and park pawl switchover valve) installed on the fully integrated transmission controller unit, gear range selection is carried out electrohydraulically and there is no need for an intelligent servo module.

Various transmission control activities are displayed on the instrument cluster (A1). To do so, the fully integrated transmission control unit sends corresponding requests over the drive CAN, powertrain control unit, peripherals CAN, electronic ignition lock control unit and the user interface CAN to the instrument cluster. The instrument cluster then actuates the multifunction display (A1p13) or the engine diagnosis indicator lamp (A1e58).

The fully integrated transmission control unit also transmits the status of the transmission control via the drive train CAN to the CDI control unit or the ME-SFI [ME] control unit.

Kickdown 

The driver's wish for maximum acceleration is met by the kickdown function. If the accelerator pedal is almost fully depressed (pedal travel more than 90 %), the kickdown function is activated. The CDI control unit or the ME-SFI [ME] control unit reads in the signals from the accelerator pedal sensor (B37) directly, and transmits the "kick-down" request via the drive train CAN to the fully integrated transmission control unit.

Limp-home mode 

In the case of implausible signals the transmission control is only operational to a limited extent and shifts into the programmed limp-home mode characteristic map. The fault is stored with the assigned fault code in the fault memory. Due to integration of the DIRECT SELECT shift components (D/R switchover valve and park pawl switchover valve) in the fully integrated transmission control controller unit, the hydraulic limp-home function no longer functions if the fully integrated transmission control unit malfunctions. If the hydraulic control system fails, e.g. due to interruption of the power supply of the fully integrated transmission control unit, the park pawl is engaged by means of actuation of the park pawl lift solenoid by the electronic ignition lock control unit via the AUX power supply line. It is only possible to release the park pawl hydraulically via the park pawl switchover valve.

Up to 16 faults are stored in the fault memory. These can be read out with the diagnostic tester.

	Electrical function schematic, fully integrated transmission control		PE27.19-P-2061-97FBH
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