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

Transmission 725.017 in model 222 

Function requirements for transmission control, general 

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

Transmission control, general 

The function of the fully integrated transmission control unit consists of the evaluation of various input signals (relevant for the transmission function). Depending on this, the electromechanical hydraulic valves (solenoids) are actuated, which in turn determine the transmission ratio of the automatic transmission (gear selection) 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 drive authorization system enable is sent by the electronic ignition lock control unit (N73) over the chassis FlexRay (Flex E), powertrain control unit (N127) and the drive train CAN (CAN C1) to the fully integrated transmission control unit.

The fully integrated transmission control unit actuates the following components electronically:

• 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)
• Engine clutch solenoid K0 (Y3/8y21)

The following signals are processed by the fully integrated transmission control unit:

• Pressure sensor (Y3/8b5)
• Turbine wheel rpm sensor (Y3/8n1)
• Internal transmission rpm sensor (Y3/8n2)
• Output shaft rpm sensor (Y3/8n3)
• Transmission oil temperature sensor (Y3/8s2)
• Park pawl position sensor (Y3/8s4)
• Electronic ignition switch control unit

Transmission control function sequence 

The function sequence is described in the following steps:

• Function sequence for engine clutch (K0) 
• Function sequence for basic shift program 
• Function sequence for electronic and hydraulic transmission control 
• Function sequence for kickdown 
• Function sequence for limp-home mode 

Function sequence for engine clutch (K0) 

Further function requirements for control of engine clutch are:

• Circuit 15 ON
• Combustion engine ON or electric transmission oil pump ON

The engine clutch serves to decouple the combustion engine in electric mode. In addition, the combustion engine can be started using the electric machine (A79/1) via the engine separator clutch, which reduces loss of power in the drive train in all operating modes in which the combustion engine is decoupled.

Control pressure is applied to the engine clutch K0 by the engine clutch solenoid K0, which is actuated by the fully integrated transmission control unit. This acts on the piston of the engine clutch and opens it.

Function sequence for basic shift program 

The basic shift program includes upshift and downshift characteristics for all 9 gears, designed for:

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

The driver operates the DYNAMIC SELECT switch (A40/9s19) (with code 448 (Touchpad)) or the DYNAMIC SELECT switch (N72s19) (with code 446 (Touchpad only)) to select the required drive program and receives operation feedback in the instrument cluster (A1) as well as in the Audio/COMAND display (A40/8). The head unit (A26/17) generates the signal for displaying the audio/COMAND display, and sends it over a high-speed video link (HSVL).

The signal from the DYNAMIC SELECT switch (with code 448 (Touchpad)) is read in by the Audio/COMAND control panel (A40/9). The Audio/COMAND control panel sends the signal via the telematics CAN (CAN A), the head unit, the user interface CAN (CAN HMI), the electronic ignition lock control unit (N73) and the suspension FlexRay (Flex E) to the Electronic Stability Program control unit (N30/4). The Electronic Stability Program control unit puts the information for the chosen transmission mode on the chassis FlexRay. The powertrain control unit receives this information and transmits it via the powertrain CAN to the fully integrated transmission control unit.

The signal from the DYNAMIC SELECT switch (with code 446 (Touchpad only)) is read in by the lower control panel (N72). The lower control panel sends the signal via the LCP LIN (LIN A3), the touchpad (A105), the telematics CAN, the head unit, the user interface CAN, the electronic ignition lock control unit and the suspension FlexRay to the Electronic stability Program control unit. The Electronic Stability Program control unit puts the information for the chosen transmission mode on the chassis FlexRay. The powertrain control unit receives this information and transmits it via the powertrain CAN to the fully integrated transmission control unit.

In vehicles with code 550 (Trailer hitch), the trailer recognition control unit (N28/1) sends the trailer recognition status to the fully integrated transmission control unit via the interior CAN (CAN B), the electronic ignition lock control unit, the suspension FlexRay, the powertrain control unit and the powertrain CAN.

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 depending on:

• Vehicle speed
• Selected gear range at DIRECT SELECT lever (S16/13)
• Accelerator pedal position
• Transmission mode selection
• Selected gear, for short-term M mode
• Signals on the drive train CAN
• Torque of electrical machine
• Charge level of high-voltage battery (A100g1)

The vehicle speed is calculated using the wheel speed signals.

The calculated vehicle speed is sent by the instrument cluster via the user interface CAN, the electronic ignition lock control unit, the suspension FlexRay, the powertrain control unit and the powertrain CAN to the fully integrated transmission control unit.

The charge level of the high-voltage battery and the status of the electric machine are sent by the power electronics control unit (N129/1) and the battery management system control unit (N82/2) via the hybrid CAN (CAN L), the powertrain control unit and the powertrain CAN to the ME-SFI control unit (N3/10).

Messages and displays in instrument cluster 

Information about the selected gear, the gear range or the transmission mode is made available on the drive train CAN by the fully integrated transmission control unit. The powertrain control unit receives and forwards it via chassis FlexRay with the electronic ignition lock interface via the user interface CAN to the instrument cluster. This then actuates the relevant display via the following signals:

Instrument cluster 

• Gear indicator, actuation
• Transmission mode display, actuation

Function sequence for electronic and hydraulic transmission control 

While the electronic transmission control is responsible for gear selection and adaptation of pressures to the torque to be transmitted, power supply control for the automatic transmission is performed by the hydraulic elements of the fully integrated transmission control controller unit. The oil supply for the hydraulic elements (hydrodynamic torque converter, shift elements, hydraulic transmission control) is provided through an oil pump (primary pump) connected to the drive shaft and/or over the electrical auxiliary oil pump. The transmission control system allows for precise adaptation of the pressure 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 shift range can be changed while driving in the forward gears. The transmission control system prevents any impermissible high engine speeds with a downshift lockout device.

Furthermore, the transmission control offers the advantage of flexible adaptation to various vehicle versions.

The electrical auxiliary oil pump ensures the oil supply of the hydraulic system when the combustion engine is switched off. It also supports the primary pump in the combustion engine's lower speed range. The ME-SFI control unit sends the "Electric auxiliary oil pump ON" request to the fully integrated transmission control unit. The electrical auxiliary oil pump is actuated directly over the fully integrated transmission control unit. The fully integrated transmission control unit sends the status of the electrical auxiliary oil pump back to the ME-SFI control unit.

Function sequence for kickdown 

The driver's wish for maximum acceleration is met by the kickdown function.

The kickdown function is activated from a pedal travel of > 90 % at the accelerator pedal.

The "Kick-down" signal is sent by the ME-SFI control unit, which forwards the status of the engine management via drive train CAN to the fully integrated transmission control unit.

Based on this information the fully integrated transmission control unit actuates the solenoid valves so that upshifts and downshifts take place at an increased engine speed in order to achieve maximum performance.

The forced downshift into the next lower gear is performed when transmission temperatures are too high and vehicle speed is too low.

Function sequence for limp-home mode 

In case of a defect in one of the solenoids, the corresponding gear is blocked. 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 fault codes are stored in the fault memory. These can be read out using Xentry Diagnostics. The diagnosis status of the transmission control is received by the diagnostic connector (X11/4) from the fully integrated transmission control unit over the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the diagnostic CAN (CAN D).

Short-term M program 

The short-term M mode is a temporary mode that is activated when the steering wheel gearshift buttons 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 undershooting a minimum speed (e.g. stopping), upon recognition of a lateral acceleration or if the vehicle is in deceleration mode. If none of the stated criteria are active anymore, the short-term M mode remains active for a specified period of time. After this remaining time has elapsed, a switch is made back to the initial shift program. In addition, the driver is shown a recommended shift operation in the instrument cluster. This is part of the gearshift recommendation that is also integrated. The driver can prematurely cancel the short-term M program through specific actions, e.g. by pressing and holding the steering wheel upshift button (S111/1) in the "positive" direction (+), by changing the gear range or by changing the transmission mode. If one of these preconditions is met, a switch is made back to the initial shift program.

Shifts, which could result in non-permissible high or low engine speeds, are not performed.

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