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

Transmission 725.0 (except 725.017) in model 205 

Function requirements, general 

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

The electronic ignition lock control unit (N73) sends the status of circuit 15 over the suspension FlexRay (Flex E), powertrain control unit (N127) and the drive CAN (CAN C1) to the fully integrated transmission control unit.

Transmission control, general 

The fully integrated transmission control unit evaluates all the input factors relevant for the transmission function. Depending on this, the fully integrated transmission control unit actuates the electromechanical hydraulic valves (solenoids). These in turn determine the transmission ratio of the automatic transmission (gear selection), drive ranges ("P", "N", "R", "D") and the working pressure. The solenoids are positioned on the fully integrated transmission control controller unit (Y3/8). This then realizes the hydraulic functionality.

The electronic ignition lock control unit transmits the release from the drive authorization system via the suspension FlexRay, powertrain control unit and drive CAN to the fully integrated transmission control unit.

The DIRECT SELECT lever (S16/13) located on the right on the steering column tube module control unit (N80) can be used to select drive ranges "P", "R", "N" and "D". The steering column tube module control unit reads in the DIRECT SELECT lever signals directly and sends them over the chassis FlexRay, powertrain control unit and the drive train CAN to the fully integrated transmission control unit.

The fully integrated transmission control unit processes the signals for the following components:

• Pressure sensor (Y3/8b5)
• 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 actuates the following assembly parts directly:

• Electric auxiliary oil pump (M42)
• Park pawl lift solenoid (Y3/8l1)
• Lubrication pressure solenoid (Y3/8y12)

• K81 clutch control solenoid (Y3/8y13)
• K38 clutch control solenoid (Y3/8y14)
• K27 clutch control solenoid (Y3/8y15)
• B08 multidisk brake control solenoid (Y3/8y16)
• B05 multidisk brake control solenoid (Y3/8y17)
• B06 multidisk brake control solenoid (Y3/8y18)
• Working pressure solenoid (Y3/8y19)
• Torque converter lockup clutch solenoid (Y3/8y20)

The fully integrated transmission control unit and the CDI control unit (N3/9) (diesel engine) or the ME-SFI [ME] control unit (N3/10) (gasoline engine) also exchange the following data over the drive CAN:

• Status of engine management
• Request and status of electric auxiliary oil pump
• Status of transmission control
• Request to display messages in instrument cluster (A1)

Messages and displays in instrument cluster 

The fully integrated transmission control unit sends the requests to display messages over the drive CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and the user interface CAN (CAN HMI) to the instrument cluster.

The transmission control includes the following functions:

• Basic shift program 
• Electronic and hydraulic transmission control 
• Kickdown 
• Limp-home mode 

Basic shift program 

The basic shift program includes upshift and downshift characteristics for all nine gears, designed for:

• Empty vehicle
• Operating temperature
• Smooth road
• Sea level

The DYNAMIC SELECT switch (N72/4s11) in the left lower control panel (N72/4) enables the driver to select various drive programs. The basic shifting program is influenced accordingly.

The left lower control panel sends the status of the DYNAMIC SELECT switch over the LCP-LIN (LIN A3), Audio/COMAND control panel (A40/9) (except code 446 (Touchpad only) or touchpad (A105) (with code 446 (Touchpad only)), telematics CAN (CAN A), head unit (A26/17), user interface CAN, electronic ignition lock control unit and the suspension FlexRay to the Electronic Stability Program control unit (N30/4). The Electronic Stability Program control unit transmits information on the selected drive program via the suspension FlexRay, powertrain control unit and drive CAN to the fully integrated transmission control unit. The driver receives operation feedback in the instrument cluster. For vehicles with code 550 (Trailer hitch), the trailer recognition control unit (N28/1) transmits the trailer recognition status via interior CAN (CAN B), electronic ignition lock control unit, suspension FlexRay, powertrain control unit and drive CAN to the fully integrated transmission control unit.

The shift programs are adapted by offsetting the characteristics, depending on:

• Load condition of vehicle
• Change in driving resistance
• Accelerator pedal movement

The fully integrated transmission control unit monitors and shifts (gear) depending on:

• Vehicle speed
• Selected gear range at DIRECT SELECT lever (S16/13)
• Accelerator pedal position
• Drive program selection
• Selected gear in short term M program

The vehicle speed is calculated using the wheel speed signals. The Electronic Stability Program control unit sends the vehicle speed over the suspension FlexRay, powertrain control unit and drive CAN to the fully integrated transmission control unit.

The powertrain control unit transmits information on the accelerator pedal position via the drive CAN to the fully integrated transmission control unit.

Messages and displays in instrument cluster 

The fully integrated transmission control unit sends the information on the selected gear, drive range or the drive program over the drive CAN, powertrain control unit, suspension FlexRay, electronic ignition lock and the user interface CAN to the instrument cluster. This then controls the corresponding displays.

Electronic and hydraulic transmission control 

The electronic transmission control makes the gear selection and adapts the pressures to the torque being transferred. The power supply control of the automatic transmission is regulated by hydraulic elements in the fully integrated transmission control controller unit. The oil supply for the hydraulic elements (hydrodynamic torque converter, shift elements, hydraulic transmission control) is provided via an oil pump (primary pump) connected to the drive shaft or via the electrical auxiliary oil pump. During the shifting phase, the transmission control enables a precise adaptation of the pressure to be made to the respective operating states and the engine output. This results in a significant improvement in shift quality. It is possible to reach the engine RPM limit in the individual gears using full throttle and kickdown. The shift range can be changed while driving in the forward gears. The transmission control system uses a downshift lockout device to prevent any non-permissible high engine speeds.

Furthermore, the transmission control allows flexible adaptation to various vehicle versions.

When the engine is switched of, the electric auxiliary oil pump maintains the oil supply of the hydraulic system. The electric auxiliary oil pump also supports the primary pump in the engine's lower RPM range. The CDI control unit (N3/9) (diesel engine) or the ME-SFI [ME] control unit (N3/10) (gasoline engine) sends the "Electric auxiliary oil pump ON" request over the drive CAN to the fully integrated transmission control unit. The fully integrated transmission control unit actuates the electric auxiliary oil pump directly and sends the actuation status over the drive 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. The kickdown function is activated as from a pedal travel of more than 90 %. The powertrain control unit reads in the kickdown signal from the accelerator pedal sensor (B37) directly and sends it over the drive CAN to the fully integrated transmission control unit. The fully integrated transmission control unit uses this information to regulate the solenoids so that the upshifts and downshifts occur at a higher engine speed. This enables maximum performance to be achieved. The forced downshift to the next lower gear is performed when transmission temperatures are too high and vehicle speed is too low.

Limp-home mode 

In the event of a defective solenoid, the corresponding gear is then locked. This gear can no longer be selected. The driver can engage the desired gear ranges "P", "R", "N" or "D" using the DIRECT SELECT lever. The driver can choose been forward and reverse travel, engage the park pawl or, when in neutral, interrupt the power flow between torque converter and automatic transmission.

The corresponding fault codes are then filed in the fault memory of the fully integrated transmission control unit. These can be read out with a diagnostic tester.

	Electrical function schematic, fully integrated transmission control		PE27.19-P-2061-97FBC
	Overview of system components for automatic transmission (AT)		GF27.10-P-9992ANG