To those who haven't already read this, take some time to read it, very interesting stuff
The Second Generation Sequential M Gearbox with Drivelogic.
Since Ralf Schumacher’s successes at the WilliamsF1 BMW power-house interested drivers have known that changing gears in the international superclass of motor sport is no longer done through the by means of a shift lever but, instantaneously by operating so-called rocker switches on the steering wheel.
Whereas the driver of a conventional car moves his shift lever in a classic H-type gear shift pattern to select the desired gear, Ralf Schumacher and his Formula 1 competitors just briefly pull two butterfly-type rocker switches behind the steering wheel, the so-called "paddles" – pulling the right rocker switch causes the gearbox to shift up, pulling the left one will produce a downshift.
At the same time, the driver can keep his foot on the accelerator pedal: The most advanced engine electronics interrupt the engine’s tractive power for just milliseconds, the control unit effects the gear change electrohydraulically and opens and closes the clutch; the clutch pedal has disappeared.
The preliminary stage of this sophisticated system, which has long become a standard feature in Formula 1, was used by BMW in its successful race-tuned touring cars as long as about a decade ago. With this system, albeit with a central shifter, gear changes are carried out in a rank, i.e. sequentially, as in the case of a motorcycle: For up-shifting, the driver – without operating a clutch – just pulls the shift lever backwards, forward for downshifting. This system provides extremely short gear shift times on the one hand, and prevents possible shift errors on the other.
BMW is the first car maker to offer this type of gearbox.
In close collaboration with the companies of Getrag and Sachs, BMW M has transferred this motor sport experience into applications for every-day road use, and developed a new high-performance driveline concept which, in its second generation, is now arriving on the market as a "sequential M gearbox" (SMG II) in the M3.
It was as early as 1996 that BMW M, as the world’s first supplier of an all-automatic manual gearbox, took center stage and went on sale with the SMG exclusively in the M3. This system established itself very well and guaranteed that, with the M3 predecessor model, almost every other car featured this progressive driveline concept.
The second-generation SMG, which was significantly upgraded from the first variant, and is technically identical with the regular manual gearbox of the M3 with six forward speeds, is not only operated by means of a selector lever, as in the past, but also offers the driver two rocker switches on the steering wheel. The driver thus has the choice of how he wants to shift gears. It is, above all, shifting by means of the rocker switches that contributes to increased active safety, as the driver can keep his hands on the steering wheel at all times.
"Formula 1 feel" when shifting on the steering wheel.
This new SMG gearbox which combines both the option of sporty sequential shifting and the ease of automated shifting offers many benefits:
-- the driver can choose between two shift modes two shift modes at any time – the sequential ("S") mode or the automated ("A") mode
-- the "Drivelogic" function allows the driver to individually match the SMG’s shift characteristic to his preferred driving habits in eleven driving programs
-- when downshifting, the engine will automatically double-clutch
-- operating the clutch and consequently also the clutch pedal are therefore no longer necessary and, unlike an automatic gearbox, there is no energy-consuming and performance-degrading torque converter either
-- there is a markedly increased pleasure of shifting, as the SMG in the sequential mode can be up and downshifted instantaneously and thus produces a realistic "Formula 1 experience"
-- as compared with a manual gearbox, there are slightly better and, above all, fully reproducible ride performance values
-- the fact that the driver no longer needs to concentrate on gear changing with this gearbox makes for precise, safer and more relaxed motoring
-- with the sequential M gearbox, it is easier to benefit from the high power reserves of the M3 through selection of the optimum shift point with so-called "shift lights" (LEDs in the cockpit indicating the optimum shift point on the tachometer)
Shifting in record time.
The second generation of the SMG gearbox stands out owing to its even shorter tractive power interruption – the time required for the fastest shift operations is merely 80 milliseconds: Hardly anyone would be able to change gears manually within such a short period of time.
Furthermore, owing to Drivelogic, the M3 driver is able to manually match the shift dynamics to his individual driving habits in six different programs – ranging from a balanced dynamic program (S1) to a very sporty (program S5). Finally, the driver can also choose the S6 program when the DSC system (Dynamic Stability Control), which comes standard with the M3, is deactivated. In that case, the SMG will shift at gear change times matching the sporting performance of a true race car.
But the new sequential M gearbox also has many benefits in respect of safety functions:
In critical driving situations, such as when downshifting on slippery pavements, the clutch is released instantaneously. In the case of excessive engine drag torque, the car will not break away at the driving wheels. This will eliminate shift errors by the driver.
Finally, there is considerably improved ease of operation, because the sequential M gearbox, owing to the automated ("A") mode, generally makes for less stress and fatigue on the driver – on motor-ways and race circuits alike. Both in the sequential ("S") mode and in the "A" mode, the gearbox will automatically shift back into first gear when the vehicle stops; to move on, all its takes is to depress the accelerator pedal.
Active also in the automated mode.
In the "A" mode, the gearbox shifts automatically, depending upon the Drivelogic driving program selected, the driving situation, vehicle speed and position of the accelerator pedal. In driving program A1, for instance, the second gear is selected automatically for pulling away, the clutch is then particularly soft, which is a great advantage for instance in wintry road conditions.
If a gear-dependent minimum speed is exceeded, slow backing off the throttle can initiate upshifting which allows the driver to determine the upshift point even in the automated ("A") mode. The respective driving situation is, in that case, identified and factored in by sensors.
To accelerate hard, for instance in passing maneuvers, the driver can fully depress the throttle pedal, which causes rapid downshifting as a function of the respective shifting program selected.
The "shift center" of this new system is located in the MS S54 electronic engine management unit, which was developed by BMW M itself and operates in conjunction with the control unit of the sequential M gearbox. Both control units are interconnected via an extremely powerful data bus (SMG-CAN).
The CAN bus networks eleven redundant SMG sensors. They constitute the key to many exclusive special functions of the SMG. For instance only one longitudinal "accelerometer" makes it possible to benefit from functions such as "climb assistant" or "slope identification". The gearbox control unit is capable of being fully diagnosed by any BMW franchised workshop.
Mode of operation of the sequential M gearbox
All gears are shifted electro-hydraulically; the control elements of the SMG in the M3 operate by wire, i.e. in lightning speed and safely without any mechanical connections as in aircraft and space vehicles.
When the system is in the automated ("A") mode when the vehicle is moving, the sequential M gearbox automatically shifts up and down in accordance with a program individually selected by the driver via the Drivelogic control function. When the shift lever is operated to change from the "A" to the "S" mode – which is possible any time when the vehicle is moving – the gears can be manually shifted up by pulling at the right rocker switch behind the steering wheel or by pushing the selector lever on the center console back towards the driver.
Moreover, the gearbox can be shifted down by pulling at the left rocker switch or by tipping the selector lever forward. Depending upon the driving program selected and the individual driving situation, the engine will automatically double-clutch like an experienced driver, so that the downshift operation can be faster and smoother.
Gears can be "skipped" as desired if the rocker switches or selector lever are operated repeatedly. However, these shift commands are carried out by the electronics only if it is possible within the wide rev band of the M3 engine. Over revving the engine in any driving situation is therefore excluded.
"Shift lights" indicate the optimum shift points.
An SMG display located on the instrument panel below the tachometer indicates to the driver the driving program currently activated and the position of the selector lever. Additionally, so-called shift lights in the tachometer, which light up consecutively, inform the driver that he is approaching the optimum shift speed, if in the sequential mode. Consistent with the instruments available in Formula 1 cockpits, the driver at the wheel of an M3 with SMG gearbox is thus able to make use of the maximum power of the engine for optimum pushing power. Since the sequential M gearbox by no means upshifts automatically – after all, the option of "active" manual shifting is to be retained deliberately.
The reverse gear is engaged, as with the manual gearbox, by moving the selector lever in the center forward and to the left. When the car is parked with a driving position engaged, it cannot roll.
An additional, practical function of the SMG, the so-called climbing assistant, permits pulling away on forward slopes almost without rolling back. It can be used both in the sequential and automatic mode, for forward and reverse travel. All the driver needs to do is to depress the service brake pedal with the car stationary and to pull the rocker switch on the steering wheel for a short period of time. When the service brake is released again, the M3 is ready to drive away within two seconds without first rolling away in an uncontrolled manner.
The acceleration assistant offers maximum possible acceleration.
When the driver has deactivated DSC and selected the S6 driving program, he can push the selector lever forward and keep it in that position when the car is stationary. If the driver now fully depresses the accelerator pedal, the optimum starting speed of the engine is automatically set. When the driver then releases the selector lever, the M3 accelerates with optimally controlled slip. This function is unique to the M3.
Starting of the engine is possible only if the service brake is depressed at the same time and the selector lever is in position "0" (idle). Furthermore, a so-called shift lock prevents unintentional activation of a driving position after starting the engine and without operating the service brake.
The complete system is controlled by solenoid valves.
The SMG control unit uses a redundant position sensor of the highest selection stage to identify the currently engaged gear.
If a shift operation is to be initiated, the control unit consecutively activates the appropriate solenoid valves which control the hydraulics of the complete system within several thousandths of a second.
The hydraulic fluid which is under a high system pressure (up to 85 bar), can then instantaneously flow into the clutch master cylinder via a solenoid valve, and the clutch, which is identical to that of a manual gearbox, is disengaged. In the next step, a maximum of three hydraulic cylinders in the shift actuator are activated via solenoid valves.
They carry out the shifting operation by precisely positioning the main selector shaft entering the gearbox in the appropriate shift slot and then shift the selector shaft forward or backwards in order to engage the desired gear. It makes no difference whether shift mode "A" or "S" has been selected.
In the event of failure of a processor in the gearbox control unit, a signal from the parallel processor is made available -- which ensures optimum operating safety at all times.
There is a large number of additional safety functions, such as against unintentional moving away with the driver’s door open, for instance when drivers swap seats. If this happens, a certain amount of time (approx. four seconds) will elapse. Should accelerator or brake pedal not be operated during that period of time, the gear is disengaged until the door is closed again and a new direction of travel has been chosen. When the engine hood is open, the car cannot be driven away either.
The M3 fitted with the SMG gearbox can be parked in positions "R" (reverse), "S","A" or "0" (with visual and audio warning signal); in these positions it is also possible to remove the ignition key.
SMG II with Drivelogic in brief
History:
In 1996, BMW M was the world’s first car maker to offer a fully automated manual gearbox.
Formula 1 feel:
Extremely fast and precise gear shifting within as little as 80 milliseconds, shifting on the steering wheel, "shift lights", acceleration assistant.
Individual adaptation to personal driving styles:
Drivelogic ("your personal gearbox") – eleven driving programs ranging from balanced dynamic to strictly sport.
Sequential shift mode:
Gear changing via rocker switches on the steering wheel or by operating a selector lever on the center console.
Automated shift mode:
System shifts automatically in accordance with the driving program selected and the functions logically combined in the Drivelogic function.
Special functions:
Slip recognition, climb assistant, "shift lights", acceleration assistant.
Active safety:
Hands on steering wheel, safe driving, shifting as a function of driving situations.
Passive safety:
Redundant sensors and signal processing similar to aerospace technology, protection system against improper operation.
Increased ease of operation: No clutch pedal, no shift errors.
SMG Press Release
) whereas BMW used a true sequential 'box with mechanical connection to the gears via gear lever, like a touring car.
Linear Mode
