23 01 03 (002)

Sequential manual transmission (SMG), based on GS6-37BZ


The idea of a Sequential Manual Gearbox (SMG) originates in motor racing and has now been adapted for volume production road vehicles.

Specifically, SMG means that in contrast to conventional manual gearboxes, the clutch control and gear changes are automated. An electrohydraulic control system handles the functions that are otherwise performed by the driver shifting with the clutch pedal, gear lever and accelerator pedal.

The Sequential Manual Gearbox SMG makes possible

  • Sequential manual gear change = manual mode

    The gears are engaged sequentially by pressing the tip switch ”+/-”. Rapid repeated action of this 'tip switch' enables individual gear ratios to be skipped.

    Gear changes (shifts) are performed

    • using the shift lever in the centre console
    • using 2 shift paddles on the steering wheel.

    The gears can be engaged manually at any vehicle speed and/or with the accelerator pedal in any desired position. The shift pulse is transmitted electrically to the SMG control unit. With this gearshift method (”shift‐by‐wire”) there are no mechanical linkages between the gear lever or shift paddles and the transmission.

  • Automatic function = cruise mode

    In automatic function, the gear shifts are controlled and adapted automatically in accordance with characteristic curves and the driving situation. [System overview ...]

To differentiate from the SSG sequential transmission (C-SMG) used until now in the E46, based on the 5-speed manual gearbox (C transmission), the new SMRG introduces the following changes:

  • The SMG GS6S37BZ (H-SMG) based on the 6-speed manual gearbox GS6-37BZ (H transmission).
  • The attachment positions of the hydraulic components and the sensors on the transmission housing have changed.
  • For the high pressure lines on the hydraulic unit, flexible lines with snap fasteners are used.
  • The electromechanical reversing light switch has been dropped and replaced by a relay in the electronics box.
  • The forced upshift and the kickdown downshift are dispensed with in manual mode. Exception: When using the launch control (race start function), the forced upshift is retained to support the driver.
  • The FDC driving dynamics control system can also be engaged in automatic function (SPORT button).

The SMGs offer the following major advantages when compared to conventional manual gearboxes:

  • No longer any need for the clutch pedal because the engagement and disengagement process runs automatically
  • Shift options - choice of 3 shift modes:
    • Sequential, manual shifts using gearshift lever and shift paddles
    • Driving dynamics control (FDC) using SPORT button: A more sporty driving style through intervention in the steering, engine and electronic transmission control (in manual mode and in Cruise mode = automatic mode)
    • Automatic function = cruise mode
  • Short and precise gear shifts, no shift errors possible (gear changes in up to 0.15 seconds)
  • Active safety and comfort: due to the shift paddles on the steering wheel, hands can remain on the steering wheel when changing gear.

Launch date: The SMG will be offered as optional equipment (SA 206).

Model Engine Planned introduction date
E46 M54B25 M54B30 03/03 worldwide, except for USA, CAN, OFF
Brief component description

The SMG system consists of the following components:

  • Gearshift lever with gearshift bracket and gearshift lever cover

    The gearshift lever makes it possible to change gear sequentially using 'tip' action. The gearshift lever has 6 positions: 3 spring-loaded engaged positions for neutral ”N”, reverse gear ”R” and manual mode (symbol ”-” between Neutral and Cruise mode) as well as 3 non-engaged positions which are only 'tipped' (”+”, ”-”, ”C” (Cruise mode = automatic function). To detect the gear lever positions, the gearshift bracket is equipped with 7 Hall effect sensors. The shift lever interlock (Shiftlock) is also installed on the gearshift bracket.

    The gearshift lever cover houses the illuminated gearshift lever position indicator and the SPORT button for engaging the Driving Dynamics Control (DDC). [more ...]

  • Steering wheel with rocker switches

    The steering wheel with shift paddle enables manual gear changes to be made without taking your hands off the steering wheel. By pulling one or both shift paddles, an upshift takes place. By pressing them, the transmission performs a downshift. [more ...]

  • SPORT button for dynamic driving control FDC

    Dynamic Driving Control (FDC) is activated with the SPORT button: Gearshift times are shortened and the shift characteristics are made more sporty. The engine responds more swiftly to changes in the position of the accelerator pedal.

    When the engine starts, the Dynamic Driving Control (DDC) function is always disabled. [more ...]

  • Hydraulic unit with sensors

    With the help of the hydraulic unit and the sensors, the clutch process and the gear changes are performed automatically. [more ...]

    • Shift/selection angle actuator

      The shift/selection angle actuator moves the gearshift shaft along its axis and rotates the gearshift shaft during gate changes. [more ...]

    • Shift travel sensor and selector angle sensor

      The current transmission position is identified by the shift travel sensor and selector angle sensor: The shift travel sensor records the forward and backward movement of the gearshift shaft in each of its shift gates.

      The selector angle sensor detects the rotational movement of the gearshift shaft and therefore also the change in shift gate. [more ...]

    • Pressure accumulator

      The pressure accumulator is installed on the lower left of the gearbox and ensures that the oil pressure is always sufficient for the gear shifts. A piston subdivides the pressure accumulator into 2 chambers. One chamber is filled with approx. 27 bar nitrogen at -25°C. The second chamber takes in the oil emerging from the hydraulic pump. It has a storage volume of approx. 285 cm3.

    • Pressure sensor

      The pressure sensor is directly installed on the valve block and reports prevailing oil pressure to the SMG control unit. The hydraulic pump is switched on or off as required.

    • Clutch actuator with clutch release travel sensor

      The clutch actuator performs clutch engagement and disengagement. The release travel of the clutch is detected by the clutch release travel sensor. [more ...]

    • Hydraulic pump

      The hydraulic pump with electric motor develops a system pressure of up to 55 bar and is activated by the SMG control unit.

    • Sensor for transmission input speed

      The sensor records the transmission input speed and compares it to the engine speed. This comparison enables the SMG control unit, to decide the level of closing speed at which power flow between engine and transmission can be established via the clutch.

    • Expansion tank

      The expansion tank ensures that there is always sufficient hydraulic fluid for the system. Moreover, oil in the expansion tank can expand. To check the oil-level, there is a maximum and a minimum mark on the expansion tank. For pre-filtering the oil a filter is integrated in the expansion tank.

    • Valve block

      The valve block houses the solenoid valves, the pressure sensor, the pressure accumulator, a non-return valve and a fine filter.

    • Solenoid valves

      The valve block contains a total of 4 solenoid valves. 3 solenoid valves control the clutch actuator and the shift actuator for shift movement.

      1 solenoid valve controls the selector angle brake (S-Cam = sleeve with s-shaped contour) and the shift/selector angle actuator used to perform gate changes. The solenoid valve also acts as a pressure relief valve for the hydraulic system.

      The solenoid valves are only energise during clutch operation and gear changes.

  • SMG control unit

    The SMG control unit is the one familiar from the E46, i.e. the GS30. The SMG control unit calculates the activation signals for the solenoid valves for clutch operations and gear changes from these sensor signals. In addition, the SMG control unit provides information to various control units, e.g. for adaptation of engine speed, for program display and for display of gear lever position. [more ...]

  • Relay for the reversing light

    The signal for the selector lever position of reverse gear is directed to the SMS control unit by the shift travel sensor and the selector angle sensor. The SMG control unit generates the signal for the relay. The relay for the reversing light is located in the end cover of the electronics box.

  • Transmission

    The SMG is based on the 6-speed manual gearbox GS6-37BZ. The gearbox housing has been modified and houses the hydraulic unit with the actuators for clutch operations and gear changes as well as additional sensors. The gear detent and selector detent on the gearshift shaft have been adapted. The transmission layout and the clutch remain unchanged.

  • Instrument panel display

    The selected drive positions and driving programs and the symbol for operate in the emergency program are depicted in 3 segments on the instrument panel. [more ...]

Additional measured variables of the following components:

  • Brake light switch

    The signal from the brake light switch enters the SMG control unit in the same way. For safety purposes, the signal from the brake light switch is transmitted by the DME control unit (Digital Engine Electronics) via the PT-CAN (drive train CAN).

    The signal of the brake light switch is used for the following operations:

    • To unlock the shift lever interlock (Shiftlock)
    • For brake detection
    • To configure a gear during engine standstill
  • Starter lock and electronic immobiliser EWS

    The electronic immobiliser only enables the starter motor if the SMG control unit issues the release signal. Via the input on terminal 50, the SMG control unit identifies a wish to start the engine. The following conditions must be met for a start enable to take place:

    • Gear lever position N must be engaged ("N" must appear on the display on the instrument panel).
    • SMG control unit releases engine start, and the clutch opens.
System functions
The SMG comprises the following functions:
  • Engine start
  • Gear shift
  • Driving in Cruise mode ”C” (automatic function)
  • Launch control (racing start function)
  • See-sawing free, e.g. out of a snow drift
  • Vehicle at a standstill
  • Gear lever position in Neutral (N) and ignition OFF
  • Fault display, SMG warning light and emergency program

Engine start

To start the engine, gearshift lever and transmission must be in ”N” (Neutral). To ensure when the engine starts that there is enough system pressure to open the clutch, the SMG control unit is woken up by the basic module when the vehicle doors are unlocked remotely. Storage pressure is calculated. If storage pressure is too low, the hydraulic pump is activated once only. Once the system pressure has been reached, the hydraulic pump is switched off again by the SMG control unit. The "wake-up signal" activates the gear lever position display in the centre console. If after approx. 15 minutes, terminal 15 is not enabled, then the display of gear lever position is switched off again.

Gear shift

If in manual mode or in Cruise mode a gear shift is activated, the SMG control unit then activates the corresponding sequence of solenoid valves in the valve block. The pressurised hydraulic fluid flows into the clutch actuator and actuates the clutch. At the same time, the SMG control unit transmits information that a gear shift has been initiated and the request to reduce the engine torque to the DME control unit. In the next step, the shift/selector angle actuator is activated. The shift/selector angle actuator carries out the gear shift by simultaneously moving the gearshift shaft backwards and forwards and also rotating the gearshift shaft. This gear shift is supported when required by raising the engine speed (dipping the throttle). Once the gear has been engaged, the clutch closes automatically. The SMG control unit receives information about the precise clutch position from the clutch release travel sensor. After the shift operation, the current to the solenoid valve is switched off. The entire gear shift runs as a function of pedal sensor position, driving speed, engine speed, transmission speed and other factors (e.g. engine oil temperature).

Just before the vehicle comes to a standstill, the SMG switches to 1st gear and opens the clutch. The power transmission between engine and transmission is interrupted.

Gearshifts that would result in an excessively high or low engine speed are suppressed.

Driving in Cruise mode ”C” (automatic function)
  • Constant-speed driving

    Continuous changes in pedal sensor position (depressing then releasing the accelerator) are recorded in the SMG control unit. The control unit prevents the continuous change between neighbouring gears that this causes (back and forth/ [known as "hunting"], e.g. on a journey on the motorway at continuously changing vehicle speeds).

  • Upshift suppression

    The SMG control unit uses the pedal sensor on the accelerator pedal to detect fast closure of the throttle and activates the upshift suppression function. This prevents undesired / accidental upshifts (e.g. prior to braking) and the engine braking effect is retained.

  • Hill ascent

    The SMG control unit detects from data provided by the wheel speed sensors and the accelerator pedal value that the vehicle is driving uphill and prevents (e.g. by retaining the same engine speed but reducing pressure on the accelerator pedal) accidental upshifts and troublesome pendulum shifts.

  • Driving downhill

    Via signals from the throttle valve potentiometer (load signal), from the wheel speed sensors (driving speed) and from the brake light switch (braking mode), the SMG control unit detects downhill driving. To retain and increase engine braking effect, the SMG control unit shifts down into the next lowest gear when driving speed increases.

  • Braking deceleration and automatic downshifting

    The SMG control unit uses the brake light switch, the wheel speed sensors and the accelerator pedal value to detect braking deceleration. To maintain the engine braking effect, the SMG control unit shifts down according to the driving speed. Here, a number of gears can be skipped. For renewed acceleration, the right gear is selected automatically.

  • Manual intervention by the drive in the automatic function

    If the drive actuates the gearshift lever or the shift paddles while in automatic function (Drive), the system automatically shifts into Manual mode. The automatic function then needs to be chosen again by the driver.

Launch control (racing start function)

Prerequisites for the launch control:

  • Roadway with good surface grip
  • Dynamic Stability Control DSC shut down (press and hold down the DSC button for more than 3 seconds)
  • SPORT button pressed

The launch control makes it possible for optimum acceleration at motor racing standards to be obtained straight from vehicle standstill. Normally, clutch engagement takes place at approx. 1300 rpm. With the launch control, speed increases to approx. 4000 rpm before the SMG system closes the clutch. For this, all the driver has to do is to depress the accelerator pedal quickly and completed (kickdown function). The forced upshift in Manual mode (only with the race start function) ensures that the engine does not reach any critical speeds. The race start function is disabled by reduction of the kickdown function via the position of the accelerator pedal, by a manual shift request, by switching off the driving dynamics control (DDC) function using the SPORT button or by activation of the DSC function.

See-sawing free, e.g. out of a snow drift

To see-saw free, e.g. out of a snow drift, move the gearshift lever rapidly from 1st gear position to ”R” (reverse) or vice versa. The gear shift must take place within 0.8 seconds otherwise the shift lever interlock (Shiftlock) is enabled.

Vehicle at a standstill

If the SMG control unit identifies that the vehicle is stationary from the pedal sensor on the accelerator pedal, the wheel speeds and the engine speed, regardless of driving program (Manual mode or Cruise mode), the clutch is opened and 1st gear is engaged.

With the engine running, whenever the driver's door is open, attention is drawn to any engaged drive position (warning signal 9 times in succession). Symbol N flashes (9 times) on the instrument panel. If neither pedals, shift paddles nor the gearshift lever is actuated, the gear is disengaged automatically about 2 seconds later.

Gear lever position in Neutral (N) and ignition OFF

If the gearshift lever is in Neutral position and the ignition is switched off, the 'N' symbol flashes in the transmission program display on the instrument panel. The standard acoustic sensor in the instrument panel issues a warning signal for approx. 9 seconds. The acoustic sensor is activated by the SMG control unit.

Fault display, SMG warning light and emergency program
  • The SMG warning light lights up and the warning signal sounds

    Whenever the SMG warning light lights up and a warning signal is issued, the driver is made aware of a fault in the SMG (e.g. failure of a sensor). Using substitute values, the fault is corrected in the SMG control electronics. The fault can have an impact on shift and driving quality.

  • Driving program ”C” is displayed, the SMG warning lamp lights up and a warning signal sounds

    The SMG is in its emergency program, i.e. restricted shift and driving quality, upshifts possible up to max. 3rd. gear, and max. driving speed is limited to approx. 80 km/h (50 mph).

  • Transmission fault ”F” is displayed, SMG warning lamp lights up and a warning signal sounds

    The driver's attention is drawn to the presence of a serious gearshift lever/transmission fault. The vehicle is no longer operational after a vehicle standstill.

Notes for Service department
The following notes for Service can be issued at this time:
  • General information: [more ...]
  • Diagnosis: ---
  • Encoding/programming: ---
  • Car & Key Memory ---
National-market version
  • US version

    The SPORT button (element of SA 224 Driving Dynamics Control) is only available with optional equipment M-sports suspension (SA 704) or SMG (SA 206).

Subject to change.
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