Alternative Valve Operating Systems - Poppet Science

It's over a decade since BMW first prototyped the system, and it's not in production yet, suggesting even the Bavarian engine-meisters can't sort it yet. But when you consider the possibilities of electric valve operation, you can see why it might be worth working out the wrinkles. An ECU similar to a fuel injection computer could constantly vary the amount of lift for each valve, the time at when it opens and closes, and how long it stays open for. It could keep some valves closed like Honda's VTEC system, it could use the Valvetronic principles to get rid of throttle plates, and it could even selectively `switch off' cylinders to improve fuel economy while cruising. You could have different engine `modes' to give either superbike-level power and delivery, touring-bike flexibility and fuel economy, or soft power delivery for use in wet or icy conditions.

Air Valves
Another alternative high performance valve setup is pneumatic valves. These have been used on various MotoGP racebikes, including Honda and Yamaha's RCV and M1 racebikes. Pneumatic valves use compressed air to close the valves, while retaining the standard camshaft method of opening them. The advantage is, again, reduced chance of valve `float' over spring-closed valves. The compressed-air return springs can handle much higher rpm than steel springs and also reduce friction. The system needs a lot of intensive maintenance though, and isn't really suitable for a roadbike.

BMW Systems
If you believe some strong rumors doing the rounds, BMW is set to unveil some novel valve operation in its forthcoming S1000RR superbike. Nobody is sure exactly what yet, but the firm's car division has a range of technologies it uses. Perhaps the most interesting is its VANOS and Valvetronic systems. Essentially, the rocker arms that operate the valves are mounted on an eccentric shaft. A motor rotates this rocker shaft, and as it moves nearer or farther from the camshaft, the valves are opened more or less, and the timing of their opening and closing is also altered. In its ultimate development, the amount the valves open can be varied so much, it actually replaces the throttle valve in the engine intake. When the driver pushes the gas pedal, the Valvetronic system opens the valves more, allowing more mixture into the engine, much like opening a conventional throttle. When the driver lifts off the pedal, the ECU opens the valves much less, so less mixture gets into the engine, and the revs drop. It's a clever system, and while it would be much harder to work in a bike engine that revs to 16,000rpm than a car that revs to 7,000rpm, it doesn't seem impossible.