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.
According to ABB, the Torductor is capable of measuring changes in torque from individual combustions in the engine and can be used to smooth gearshifts or even smooth power over a bumpy section of pavement. With a torque sensor providing actual torque feedback to the EMS, it would be possible to modulate the engine’s output to an exact torque value based on the rider’s input, for perfectly linear throttle response in addition to better traction and wheelie control. The Torductor used on the Honda MotoGP bikes works using magnetoelastic materials, which generate a magnetic flux around a rotating shaft — the transmission output shaft in this case. The magnetic flux changes depending on the actual torque in the shaft, and can be converted to an electronic signal proportional to the torque. As a slight digression, it’s notable that the Torductor (or any other torque sensor) also measures back-torque under deceleration, and could be used to help modulate engine braking entering a turn.
A mid-season rule change last year in World Superbike allowed the addition of ride-by-wire throttle to bikes not equipped as such from the factory, effectively allowing the use of torque-by-wire. Jonathan Rea immediately won his first outing on a CBR1000RR equipped as such, showing the system’s effectiveness. No doubt Yamaha, Honda and other manufacturers producing bikes with ride-by-wire throttles have incorporated at least some torque-by-wire into the bikes’ ECUs already. My only question now is, with the twistgrip even more disconnected from the actual butterflies, can we even call it a throttle? sr
With throttle butterflies controlled by electronics becoming more common, it’s possible to change things so that torque output…is more directly related to throttle position.