New sequential transmission
Shifting gears even faster with the seven-speed SMG gearbox
The concept of a high-revving engine only proves successful if the engine is combined with a transmission that matches the prodigious performance and translates the torque made available by the engine into optimum forward thrust by means of a short overall transmission ratio.
The seven-speed sequential M gearbox (SMG) is exactly what is needed to ideally transfer the power of the V10 engine to the drive train and finally to the wheels. With this gearbox, BMW M is the one and only manufacturer world-wide to market a seven-speed sequential gearbox with drivelogic function. Nonetheless, the new seven-speed gearbox is by no means an extended six-speed transmission. Instead, it is a completely novel gearbox, which has been designed exclusively for use in the new M5. Even more highly perfected than the previous six-speed transmission, the seven-speed SMG gearbox enables extremely fast manual gear changes as well as comfortable cruising thanks to the automated gearshift mode.
The new transmission is technically designed to handle a torque of up to 550 Newton metres and engine speeds of up to 8,500 rpm. This gives the transmission sufficient reserves to ensure reliable operation throughout the new M5’s entire lifecycle, which is further enhanced by a separate oil cooling system for the high-performance engine.
Even closer speed gaps than with the six-speed gearbox.
Compared to a six-speed gearbox, seven gear steps offer even more reduced engine speed and torque gaps when changing gears. As forward thrust is closely related to high engine speeds, these reduced gaps assist the new M5 in achieving awesome acceleration.
The SMG transmission stands for sublime shifting pleasure.
It goes without saying that the new seven-speed SMG gearbox offers all the advantages inherent in a sequential gearbox concept: gears are changed using the gearshift lever on the centre console or the paddles on the steering wheel. The driver does not have to press down the clutch and gear changes are possible even with the throttle foot flat on the floor. As opposed to an automatic transmission, the SMG transmission does not require an energy-consuming and performance-impairing torque converter.
As a matter of principle, all gears of the SMG transmission are shifted electro-hydraulically. The SMG gearbox features shift-by-wire technology, which has its origins in aerospace synergism and by which gears are changed in the fraction of a second without a mechanical link. In contrast to previous six-speed SMG transmission, the new M5’s SMG hydraulic unit and the actuators have been integrated into the transmission housing. If a gear change request is made, the control unit actuates the respective magnetic valves which control the overall system’s hydraulics. As a next step, the hydraulic oil with a high operating pressure of up to 90 bar flows swiftly via a magnetic valve into the clutch master cylinder to open the clutch. Then, using solenoid valves in the hydraulic unit, four hydraulic cylinders in the actuator are switched, which carry out the actual shifting process by means of four separate gearshift rods. When shifting down, the engine double-declutches automatically.
The new SMG boosts speed by 20 percent.
The previous second-generation SMG transmission was already rapid-shifting, and, to top it all, the new, third SMG generation accelerates the process of shifting gears by another 20 percent: for a gearbox of this kind, the shift speed is unrivalled and the advantages for the M5 driver are as follows: gear changes are extremely smooth and effected at a speed even the most experienced driver could not attain, thus making the inevitable power flow interruptions when changing gears hardly noticeable. The M5 delivers an almost jerk-free performance when accelerating from a standstill to its top speed. The driver gets much enjoyment out of shifting gears as SMG elicits a true “Formula 1 feeling”.
Changing gears with an SMG gearbox also makes a valuable contribution to traffic safety: as shifting always involves the same level of speed and precision and is therefore absolutely reproducible, the driver does not have to concentrate that much on the process, meaning that the SMG gearbox promotes precise, safe and relaxed driving.
Drivelogic: the driver determines the SMG’s gear change characteristics.
Thanks to the SMG’s drivelogic function, the driver can choose from eleven gear change options, which enable him to adapt the SMG’s characteristics to his very own style of motoring. These programs differ from each other in the pre-selected gear change time: the higher the selected program, the engine speed and torque, the shorter the shift times.
Six of the eleven gear shift options can be pre-selected in the sequential manual gearbox mode (S mode), the spectrum ranging from balanced dynamic to very sporty. With the gearbox in the S mode, the driver always shifts gears manually, and the transmission does not at any time intervene in the shifting process.
Launch Control: moving up to maximum speed with full performance.
With the gearbox in S mode, the driver can profit from the Launch Control function, which is a complement to the purist, sporty S6 driving program. The Launch Control function enables “rookie racing drivers” to make a perfect standing start in order to maximise the initial acceleration. This function requires the prior deactivation of DSC.
The aim of the Launch Control function is to relieve the driver of shifting gears, giving him more freedom to concentrate on his actual job of driving. When the car is stationary, the only thing the driver has to do is to flip the selector lever forward and keep it in that position. If he now fully depresses the accelerator pedal, the engine is automatically set to its optimum starting speed. If the driver releases the selector lever, the M5 is accelerated with the ideal amount of slip, provided the driver keeps the accelerator pedal fully depressed. The driver does not have to change gears until the M5 reaches its peak speed – the SMG gearbox with drivelogic automatically shifts through the seven gears and changes from one gear to the next gear shortly before maximum engine speed is attained.
As is the case with all driving programs, a telltale in the cockpit informs the driver of the gear currently in mesh.
Automatic gearbox – one that can hold its own even on the race track.
Five of the eleven gear shift options of the Drivelogic function are available in the so-called automated D mode. If this mode is activated, gears are changed automatically, depending on the driving program selected, the driving situation, the speed and the position of the accelerator pedal. With the D1 driving program selected, for example, the gearbox sets off in second gear and ensures particularly delicate and smooth engagement of the clutch, this being of great help in wintry conditions.
Although having opted for automatic gearchanging, the driver can influence the process by, for example, releasing the accelerator pedal slowly, thus determining, also in D mode, the time when the gearbox shifts up. In turn, by depressing the accelerator pedal all the way down to the floor, he is able to effect fast downchanges. In S as well as in D mode, the gearbox automatically shifts down to the first gear as soon as the car is slowed to a halt. All the driver has to do to set the car in motion again is to step on the gas pedal.
Special functions for increased safety and comfort.
The seven-speed SMG gearbox in the M5 not only helps the driver to squeeze the most out of the engine’s prodigious performance but also offers a host of safety features. In critical situations, when shifting down on a slippery road for example, the gearbox opens the clutch in a split second in order to prevent the car from suddenly swerving out of control as a result of excessive drag torque at the driven wheels.
A further practical SMG feature is the so-called climbing assistant, which has up to now been featured exclusively in the M3 and allows for hill starts with virtually no roll-back. This effect is achieved by brake system intervention and can be taken advantage of in the sequential as well as the automated mode, irrespective of the direction of travel. The function is activated by applying the foot brake. As soon as the driver releases the brake pedal, the M5 is able to set off without rolling back in an uncontrolled manner.
The intelligent transmission on steep gradients.
The so-called hill detection adjusts the shift points on gradients and descents. This prevents gear hunting when driving uphill. When going downhill, the hill detection holds the lower gears for longer in order to make effective use of the engine’s braking power. In addition, with the gearbox in D mode, gear selection is adjusted to the steepness of the gradient.
These functions are only possible because the SMG control unit and the engine management system in the M5 closely communicate with each other via a particularly powerful CAN data bus, which connects the MS S65 engine management system with the SMG control unit, which is linked up to twelve redundant SMG sensors. In this way, the SMG control unit receives from the MS S65 the relevant data on the accelerator position, wheel and engine speeds, temperatures, steering angle and key memory. Moreover, the SMG and DSC directly communicate with one another.