World Superbike rules allowed...
World Superbike rules allowed ride-by-wire throttles for all bikes midway through last season, and it made a huge difference for the Castrol Honda team.
Ever since cables first connected twistgrips to carburetors, riders have been searching for better throttle response — the connection between input at the handlebar and power delivered to the rear wheel. Torque-by-wire throttle, an increasingly used buzzword that is likely to show up in new-model press material before too long, offers an interesting solution and may even change what we consider the throttle’s job to be.
When talking about response or feel, we are generally referring to how hard the bike is accelerating in relation to throttle position. If we open the throttle more, we want the bike to accelerate more; less throttle, less acceleration. If the motorcycle had a perfectly flat torque curve at every rpm and every throttle opening, the relationship between throttle opening and acceleration would be nicely linear. That is not the case, unfortunately. As you accelerate out of a corner, the amount of torque the engine generates at a given throttle opening changes as rpm scales through the torque curve’s peaks and valleys. In some cases the relationship is anything but linear, and it’s possible to even end up closing the throttle slightly on a corner exit while the engine climbs out of a dip in the powerband in order to keep torque constant.
With throttle butterflies controlled by electronics becoming more common, it’s possible to change things so that torque output — what we feel — is more directly related to throttle position. This is torque-by-wire throttle. As you exit a corner and open the twistgrip, torque goes up proportionately. Close the twistgrip, and torque goes down proportionately. There is an additional benefit in this scenario: Not only will response be improved, but also the engine can be tuned more for peak power rather than a smooth power curve — the electronics will hide any resulting peaks and valleys.
Torque-by-wire throttle can be accomplished in one of two ways. The first is by using an open-loop, map-style programming of the ECU, much as a manufacturer’s base fuel mapping is modified using a Power Commander or other fuel injection tool. Knowing the torque produced by the engine at any given combination of rpm and throttle position, an electronic butterfly’s programming can be modified to react accordingly, based on what the rider is asking for. The second is to use a closed-loop system, with a torque sensor providing feedback to the ECU just as an O2 sensor can be used for closed-loop fueling.
In 2008, Yamaha’s M1 included torque control as part of the EMS to “achieve more stable machine control.” By estimating wheelie and grip torque limits based on sensor inputs, calculating lean angle and tire traction capacity from those inputs, and knowing the actual engine torque, the EMS controlled the throttle action if necessary to apply optimum torque. Engine torque output may have been mapped into the EMS beforehand — an open-loop system — or measured directly using a sensor — a closed-loop system. According to Neil Spalding in his book MotoGP Technology, Honda has been using a Torductor, a torque-measuring device made by ABB, on its RC212V factory bikes since 2008. It’s likely that Yamaha has also been using a similar torque sensor. A Yamaha patent for traction control (“Advanced Traction Control,” Oct. ‘11) includes several modifications to the base system outlined in the patent, and one incorporates a “torque detection part” that provides real-time torque output to the ECU. Certainly all the manufacturers are using some form of torque-by-wire in their racing electronics.