NEWS, RESEARCHES, INVENTIONS
RUBRIC MATERIALS PREPARED ALEXEY SPARROW-SHOES, ANATOLY FOMIN
SEVEN TIMES INCLUDED
Sports cars are becoming more powerful and faster, but the gear shifting process is not very modernizable. It’s easier with racing cars - boxes without synchronizers with manual or automatic switching have been working there for a long time. But for road cars, their characteristics are unacceptable - gear changes are too tough. Yes, and it’s better to get underway with a slip - metal-ceramic racing clutches of “tenderness” do not like.
An experienced driver in an ordinary car is capable of shifting gears in 0.3–0.4 s, in the ideal case (and without concern for the mechanism) - in 0.15–0.2 s. Faster is impossible - it’s not even a matter of human abilities, but the physics of the process itself: synchronizers simply do not have time. At a time when "charged" versions of production cars are gaining "a hundred from a place" in five seconds, tenths become more than significant.
Not surprisingly, for the new BMW M5 with an engine capacity of over 500 liters. with. developed a special gearbox. The seven-speed SMG Mk III Drivelogic unit features a uniquely short switching time of 0.065 s. This is three times faster than the result of the rider. What is the secret to this achievement?
In the design, at first glance, everything is simple. The seven-speed gearbox of a traditional two-shaft hydraulically-driven electronically controlled gearbox is paired with a dual-disc clutch. Two discs can reduce inertia and cope with a torque of up to 550 N.m with a modest diameter. BMW experts attribute the box to the third generation SMG (Sequential M Getriebe). The first made its debut with the past BMW M3 and received conflicting ratings from demanding drivers - I did not like “thoughtfulness”, although it switched gears no worse than a trained athlete. The second generation proved to be much better, but it was still far from ideal. Unlike its predecessors, the new unit was originally designed exclusively for the "machine."
The system does not have a mechanical connection between the controls and actuators, this allows to reduce the response time. Pressing the lever on the steering wheel or moving the selector on the transmission tunnel - and the switching process is started. The control unit sends a signal to the solenoid valves, and the hydraulic actuator with a pressure of 9 MPa does its job: squeezes the clutch, selects the gear, moves the synchronizers, releases the clutch. The engine automatically adjusts to this process, although the driver does not release the gas pedal - its control system is connected to the gearbox controller by a high-speed data bus. Switching “down” is more difficult: automation does not forget about “double squeeze” and “gas rebate”. What modern drivers have not remembered for a long time.