BMW ShiftCam single on the way
BMW's ShiftCam design is among the most advanced of all the motorcycle VVT setups, and patent applications have now been filed for a single-cylinder engine using the same technology.
The ShiftCam idea started life in the R1250 boxer engine and has already spread to the S1000RR's four-cylinder. Unlike rival VVT systems from Ducati, Kawasaki and Suzuki, which simply change the valve timing as revs rise, the ShiftCam setup physically switches between two completely different cam profiles.
That means BMW can use a 'soft' cam at low rpm, with relatively little valve lift, as well as a short duration and minimal overlap. That gives good low-down torque and reduces fuel consumption and emissions, but would strangle the engine at higher revs. The ShiftCam setup slides the whole camshaft sideways at a pre-determined point, bringing a much more aggressive cam lobe into contact with the intake valves. That lobe increases the lift, duration and overlap to maximise the amount of fuel and air that can get into the cylinder, ensuring the engine makes as much power as possible.
ShiftCam moves the camshaft by using a solenoid to insert a peg into a spiral groove on the camshaft. When engaged, the turning movement of the camshaft also moves it sideways, and the design means it can only switch lobes when the intake valves are closed and the cam lobes aren't applying pressure to them.
To move back to the low-rpm lobe, another solenoid and peg are engaged in a reversed version of the spiral groove, pulling the camshaft back again. In the S1000RR's four-cylinder engine, a slightly more complex version is needed to allow the lobes for different cylinders to be shifted separately.
Although a single-cylinder engine could use the same version of ShiftCam that's employed on each cylinder of the R1250 boxer twin, BMW's new patent shows a more compact version of the idea. The solenoids and the spiral grooves are positioned between the two intake valves, rather than at the end of the camshaft, to allow the engine to be narrower overall, and as a result the spark plug needs to be moved and mounted at an angle to make space for the ShiftCam actuators.
At the moment, BMW's single-cylinder models include the G310 range and the C400 scooter models. While either of these could be the target for the new single-cylinder ShiftCam system, there's also another possibility - perhaps a more likely one - that BMW is working on a larger-capacity single-cylinder engine for bikes to plug the gap between the 313 cc G310 models and the 853 cc F750 and F850 twins.
