Clutchless snickers: KTM working on centrifugal clutch and auto shift for range of big twins

After decades of false starts, motorbikes with semi-automatic gearboxes are becoming ever more widely accepted into the mainstream.

Honda have now sold over 200,000 motorcycles across Europe equipped with their DCT system and now KTM are preparing to get in on the action with an automated version of their 1301cc LC8 V-twin.

The LC8 already powers KTM’s most touring-oriented bikes, the KTM 1290 Super Adventure S/R and KTM 1290 Super Duke GT, and the company have new versions of both under development for 2024 or 2025.

While the Honda Dual Clutch Transmission is complex and heavy, requiring electronic and hydraulic systems to operate and with no option to use the clutch and shifter in a completely conventional way, the KTM design is far more straightforward.

Rather like the SCS (Smart Clutch System) offered by MV Agusta, it uses a centrifugal clutch to connect the engine and transmission, engaging when revs rise much above idle to let you start and stop without using the clutch lever.

Once you are on the move, an up-and-down quickshifter and blipper system means gearshifts can be performed without disengaging the clutch. Not quite as silky as the seamless shifting that a dual-clutch transmission allows, but a solution with cost and weight benefits.

Locking on

KTM’s developments have emerged thanks to a patent application filed to solve a specific problem that comes with a centrifugal clutch. Because it defaults to a disengaged state, decoupling the engine from the transmission – the opposite of a normal, manual clutch – leaving the bike in gear won’t stop it from rolling if you park on a slope.

The solution used by MV Agusta and many scooter manufacturers is a separate parking brake, but KTM have developed an alternative in the form of a locking system inside the gearbox itself that prevents it from turning and thus stops the bike rolling away off its sidestand.

An L-shaped pawl inside the transmission pivots on the same rail that the shift forks attach to and can lock against the gear teeth to stop the transmission from turning. It’s controlled by the shift drum: for most of drum’s rotation the pawl is kept away from the gear teeth but when you select ‘Park’ the pawl engages, stopping the transmission from being able to turn.

As a safety measure, the pawl is shaped so it will bounce away from the gear teeth if the parking lock is accidentally engaged while the transmission is turning.

Although KTM’s system could, like MV Agusta’s, be used alongside a conventional, foot-operated manual shifter, the design is really intended to be used alongside an electric actuator (marked ‘27’ in the drawings) that moves the shift drum. It can be operated by the bike’s electronics, allowing the gearshifts to be made either via buttons on the bars or fully automatically.

Because the parking lock is controlled by the shift drum, there’s no way a rider can accidentally try to pull away without disengaging it. The pawl’s design means it’s impossible for the parking lock to remain engaged once a gear is selected.

Clutchless shifts in detail

Going contactless: A centrifugal clutch disengages the engine from the transmission when the revs drop to idle, so you can stop and pull away without using the clutch lever.

Parking up: The shorter arm of the L-shaped pawl rides on its own section of the shift drum, with a notch corresponding to the ‘Park’ position. It’s sprung, so when the shorter arm falls into the notch, the hook on the end of the long arm locks between two gear teeth.

Lock engaged: An alternate version of the system (shown in the CAD-style image), replaces the L-shaped arm with a straight one and uses a pin (labelled ‘18’) running in a groove (25) on the face of the shift drum to engage the parking lock.

Electric shifting: An electric motor (27) turns the shift drum and allows push-button or fully-auto shifts. The patent also says a simpler version could be made with a normal, foot-operated shifter.

V-twin power: The gearbox shown in KTM’s patent is based on the one used in all the company’s 1290 models, using the 1301cc V-twin, confirmed by part numbers visible on some of the components.