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Secrets of Suzuki’s VVT

Published: 06 January 2016

Updated: 06 January 2016

Cunning engineering gets round MotoGP variable valve timing rule – and it’s on the new GSX-R1000

Suzuki engineers have developed a variable valve timing set-up that skirts around the rules banning the systems in MotoGP, and the very same design will feature on the new GSX-R1000.

During the GSX-R’s unveiling at the Milan motorcycle show late last year, Suzuki announced that it ‘takes in technologies developed in MotoGP such as intake VVT’ – which raised some eyebrows since MotoGP rules specify that: ‘Variable valve timing and variable valve lift systems, driven by hydraulic and/or electric/electronic systems, are not permitted.’

The implication is that the GSX-RR MotoGP racer features a VVT system that circumvents that rule by using neither electronics nor hydraulics, and that the same design is used in the GSX-R1000. Now patent drawings have revealed how the Suzuki system works and how it’s legal in MotoGP.

Hydraulics are the norm

Most simple variable valve timing set-ups including the only two variable valve systems currently offered on large production bikes – Ducati’s DVT system and Kawasaki’s GTR1400 – are based on hydraulic cam phasers. These allow the camshaft to rotate a few degrees in relation to its drive sprocket, either advancing or retarding the valve timing in the process. Oil is forced into chambers inside the phaser to move and lock the camshaft into its advanced or retarded position. An electronic valve and control system directs the oil, making such set-ups fall foul of MotoGP regulations on both the ‘electronic’ and ‘hydraulic’ fronts.

Suzuki VVT system gets into the groove

Like most cam phasers, the Suzuki design splits the cam sprocket into two halves. One half carries the sprocket itself, the other attaches to the camshaft, and there’s scope for a few degrees of rotation between the two.

On Suzuki’s design, there are no hydraulics or electronics. Instead, radial grooves are machined onto the inner faces of the phaser’s halves, into which steel balls fit. Those balls move outwards under centrifugal force as revs increase.

The phasing happens because the grooves on the two surfaces don’t exactly line up; those on the sprocket side of the phaser are slightly curved while the camshaft-side ones are straight. As the balls move towards the outer edge, the fact that the grooves on one half are curved means it must rotate in relation to the other, retarding the valve timing.

A matter of control

But how does the engine control it without electronics? The trick is that the radial grooves get shallower towards the outer edge, so as the balls move outward they also need to force the two halves of the phaser apart. The camshaft half of the phaser is attached via a spline, so it can slide in and out while keeping the shaft turning, while a spring pushes the halves together.

At low revs the spring overcomes the centrifugal force acting on the steel balls, pushing them back towards the centre of the phaser so the timing is shifted to its ‘advanced’ position, boosting low-end torque and improving throttle response. As engine speeds increase, the centrifugal force pushes the balls outwards, retarding the timing and boosting peak power. While there’s no easily-tweakable electronics system to govern it, changing the tension on the spring will alter the revs that the timing changes at, allowing the system to be tuned, if required.

Future developments

While the GSX-R’s system is mechanical and works only on the intake camshaft, Suzuki have also patented an electronically-controlled version acting on both the intake and exhaust. Based on its 1000cc V-twin engine, the design uses two phasers on each bank, one for each camshaft, and features an electric system to alter the tension on the springs holding the halves of the phasers together. That gives it much more control over the changeover revs, although such a system wouldn’t be legal in MotoGP, it could be used in road applications.

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