Revolutionising Riding

Interview with Dual Clutch Transmission Chief Engineer Mr. Dai Arai 

Dai Arai joined Honda in 1999 and has been a driving force behind Honda’s unique Dual Clutch Transmission for ten years.  

This Q&A gives an insight into his background, his life in motorcycling and in Honda, and the challenges faced over a decade of developing DCT for bikes. 

On ten years with DCT… 

What is the origin of DCT? 

Before my time at Honda, there were other automatic transmissions such as the ‘Hondamatic’ gearbox in the 1970s which relied on a torque converter, and the Human Friendly Transmission on the DN01.  

So before the VFR1200F came with the first DCT, the idea of making an automatic transmission was around for many years.     

The big difference with DCT is that it involves much less losses than the previous systems, so it gives a much more direct and sporty feeling.      

What was the hardest problem to solve? 

Everything on the development of the very first DCT for the VFR1200F was a real struggle.  

No-one had ever done it before, so it was so difficult from both the hardware and software point of view. It was really the first time transmission engineers had been involved in electronic controls. 

With the hardware, we had to develop a crankshaft case that could be used for both DCT and manual transmission engines, to allow us to prepare MT and DCT variants in the same frame. So we used two mainshafts with one inside the other to keep the package compact. Giving that small package the required strength and durability was a big challenge.  

There was also the challenge of reducing the noise of the gear shift. Because the gear mechanism itself is the same as a manual bike, the DCT makes the exact same ‘pre-engagement’ noise from the gear dogs as on a manual shift. For some riders, hearing this shifting sound in automatic modes without the normal ‘manual’ inputs into a gear change could sound strange, so reducing that sound was a big extra challenge.   

On the software side, programming the gear shift schedules for this new kind of technology was a real challenge. No-one had attempted to make such a system, and it takes thousands of hours to come up with the right programmes for the shift schedules.    

What do you think had been the biggest single improvement throughout the decade of DCT? 

It’s not possible to pinpoint one particular change as most important. That’s because the system has been evolved consistently over the decade, with different changes being introduced that not only improved DCT itself, but also made it bring out more and more the different riding characteristics required of each different model.  

One of the first big steps was the automatic return to Automatic mode if you used the manual triggers as an override to select a gear. It’s a lot of programming to make the return to automatic as intuitive as possible, because you have to calculate the riding situation and therefore the rider’s intention – was it a downshift coming into a tight corner, a downshift to overtake on a straight road, etc. It’s not just a question of returning the system to Automatic after a certain number of seconds.    

Later, we refined the way that the throttle ‘blip’s on the downshift to accurately match the revs and make those shifts really smooth. These changes involved a lot of synchronization with the PGM-FI fuel injection controls. 

We also introduced the ‘Adaptive Clutch Capability Control’ which uses the electronic control of the DCT system to ‘slip’ the clutch a little when the throttle position is changed initially from a fully closed or fully opened position. That really helped smooth out the bike behaviour.  

On the other hand, the ‘G’ switch introduced on the CRF1000L Africa Twin and later the X-ADV reduces the amount of clutch slip to give a more direct feeling for rear wheel traction. Especially off-road, this can allow riders to do controlled slides.    

We’ve also linked the system with riding modes thanks to Throttle by Wire on the Gold Wing, which also helps to shorten the shifting time.  

And on the latest CRF1100L Africa Twin, linking with the IMU really helps refine the gear shift timing through corners, as the IMU gives definitive information about lean angle. 

So the system has developed continuously, and will continue to do so. That’s one of its great advantages – it can be continuously improved.  

How would you personally describe the benefits of DCT?  

The biggest thing for me is how much brain ‘bandwidth’ it frees up to use on what is most enjoyable about riding – cornering, looking for the right lines, timing your braking and acceleration.  

The other things is that it is both easy and direct. ‘Easy’ meaning no need to use a clutch in slow traffic, no chance of stalling, no bashing helmets with a pillion. ‘Direct’ being the speed of the gear change, the ability to use the triggers, and, as I mentioned, to concentrate purely on your riding.  

What would you like to see as the next application for DCT?　  

Personally, I’d love to see DCT on our Dakar Rally bike. That kind of riding – where fatigue is possible, and concentration so important – means the system has a big benefit.  

Off-road, people are often surprised at how much DCT can help them – working a clutch lever standing up is not so easy, and uses up a lot of energy and concentration. Also, of course, with DCT the rider cannot stall in difficult situations.  

What would your message be to riders who don’t think DCT is for them? 

Please give it a try. It may take a short time to become used to it, but it really opens up new possibilities in your riding. 　 

What projects have you worked on at Honda?  

Most of the DCT bikes since the first VFR1200F. Work on the quickshifter for the Fireblade. And several ATV and Side-by-Side models.