Few motorcycle manufacturers have developed automatic transmissions in recent years. Even fewer currently have one equipped on a production bike. That’s why BMW Motorrad stands to join an exclusive class with the introduction of its Automated Shift Assistant (ASA).
In its fully automated ‘D’ mode, ASA automatically shifts gears based on the current ride mode, engine speed, throttle position, and lean angle. Users don’t have to relinquish all gearbox duties to the system, however. The manual ‘M’ mode allows riders to change gears with the gearshift lever alone (similar to using a quickshifter). That’s ASA in a nutshell, but how does it work and how is it different from Honda’s Dual-Clutch Transmission? Let’s find out.
Under the surface
Just like a manual transmission, ASA employs a hydraulically connected master cylinder and slave cylinder to control the clutch, but instead of the rider operating a hand lever, an electromechanical actuator automatically regulates the clutch slip, engagement, and disengagement. That allows BMW to eliminate clutch levers altogether on ASA models. That’s just one part of the process, though.
Automated clutch and gear actuation means users can start and stop without the use of a clutch lever, allowing BMW to eliminate them from ASA models. When the engine control unit (ECU) determines that conditions necessitate an upshift or downshift, another electronically controlled actuator bypasses the gearshift lever and triggers a gear change. The process is only slightly different in ‘M’ mode. Whereas ‘D’ mode synchronizes the clutch and shift actuators, manual mode forces the system to adapt to the rider’s inputs.
When the user engages the gearshift lever, sensors monitoring the transmission input shaft and clutch position send data to the transmission control unit (TCU), which is also connected to the ECU. If a rider-initiated shift occurs within the desired gear’s acceptable rev range, the gear change is completed directly. If it’s initiated outside those parameters, ASA smooths the transition. Even in manual mode, the system steps in if the rider misses a downshift, automatically completing the gear change in order to prevent the engine from stalling when the revs drop too low for a given gear.
The German marque describes the new system as a “technical evolution” of its Shift Assistant Pro quickshifter. Note the clutch master cylinder mounted at the engine’s rear.
The German marque claims that each shift is “fast, precise, rev- and load-adapted” in both automatic and manual modes. From long-distance touring to off-roading, from steep hill starts to two-up riding, BMW cites several instances where automatic transmissions benefit riders. Of course, beginners also come to mind, but as of now, the brand only plans to feature ASA on boxer engines (famously big-bored). Unfortunately, it hasn’t specified which models will receive the automatic gearbox nor when an ASA-outfitted model will reach dealers.
Same difference?
BMW’s Automated Shift Assistant shares the same objectives with Honda’s Dual-Clutch Transmission (DCT) but both systems accomplish those ends by very different means. While ASA utilizes one clutch pack, DCT features two. One pack engages odd-numbered gears (1, 3, and 5) while the other corresponds to even-numbered gears (2, 4, and 6). The two operate alternately, which smooths out gear transitions. For instance, when the DCT determines that a shift from third to fourth gear is necessary, it actuates fourth gear before making the change. It only releases third gear after it fully engages fourth gear, resulting in a seamless shift.
American Honda currently offers Dual-Clutch Transmission on Rebel 1100, Africa Twin, Gold Wing, and NC750X variants.
So, what are the drawbacks, then? Well, because DCT systems require two clutch packs, they’re often bulkier and heavier than fully manual transmissions. On the other hand, DCT models often offer manual shifting via grip-mounted switch/paddle shifters. With ASA representing a clear alternative to DCT, it will be interesting to see how Beemer buffs, and the motorcycling public at large, receive BMW’s automatic transmission.