Variable valve methods have gotten extra frequent on bikes and BMW’s ShiftCam stands out for being a intelligent and comparatively easy answer among the many present designs. It’s already in use on the R 1250 boxer twins and the S 1000 RR’s inline-four. Subsequent goal within the BMW line? A brand new patent utility reveals that BMW’s G-series single-cylinder vary together with the G 310 R and G 310 GS are prone to get the expertise.
How BMW ShiftCam Works
The ShiftCam system does precisely what its identify suggests. It shifts the inlet camshaft to deliver certainly one of two doable cam profiles into contact with the inlet valves, altering not solely the cam timing but additionally the valve carry. The profit is that the engine can have a conservative cam profile for low revs, with much less carry (how extensive the valve is opened) to extend the gasoline velocity into the combustion chamber, growing torque at low revs. The low-rpm cam lobe additionally has much less timing advance and length, decreasing overlap (the interval when the inlet valves open earlier than the exhaust valves have closed). Meaning there’s much less time for unburned consumption cost to flee into the exhaust, enhancing effectivity and decreasing emissions.
At increased revs, when the valves are opening and shutting quicker, that low-lift, short-duration cam profile can’t get sufficient air-fuel combination into the combustion chamber within the transient window when the valve is open, so a extra aggressive cam profile is introduced into play by sliding the camshaft laterally. This profile has rather more valve carry and length (how lengthy the valve is open for), letting extra air and gasoline into the cylinder to extend peak energy and most torque. As a result of the engine is revving increased, the valve timing may also be superior, opening the inlet valve earlier and growing overlap and there nonetheless gained’t be sufficient time for the unburned gasoline to flee into the exhaust, so emissions and effectivity stay good.
Different Kinds of Variable Valve Timing and Carry
The precept is identical as different cam-switching VVT methods, essentially the most well-known being the Honda VTEC setup used on the VFR800 first in 2002 and on its vehicles for greater than 30 years, however BMW’s technique of attaining the impact—by sliding the camshaft to swap lobes—is in contrast to different manufacturers’ options and distinctive in motorcycling. It’s achieved by having a slidable camshaft (on the R 1250, the S 1000 model has a slidable sleeve over a splined central part of the camshaft). The motion is managed by solenoids that push pins right into a spiral groove machined into the camshaft. When a pin is engaged, the spiral makes the shaft transfer to at least one facet. The spiral groove means the cam lobes will swap over when the consumption valve is closed, so there’s no likelihood of a mechanical conflict of making an attempt to vary the timing throughout an inlet stroke.
Different VVT methods such because the one used on Ducatis use oil strain in chambers to differ the cam place versus the pushed sprocket. Ducati has actuators (managed by solenoid valves and oil strain) on consumption and exhaust cams for extra timing flexibility, however carry is just not diverse.
What’s Totally different About ShiftCam for the New Singles
Whereas the general thought is identical because the ShiftCam system within the newest R 1250 and S 1000 engines, the single-cylinder within the new patent is extra compact. It’s made smaller by becoming the solenoid actuator between the 2 consumption valves—it’s a four-valve engine—so the camshaft doesn’t must be any longer than a traditional design. Placing the actuator within the center does imply the spark plug must be fitted at an angle, and since the entire camshaft slides, there’s a further loafer gear connecting the consumption and exhaust cams, somewhat than having a direct chain drive from the crankshaft to the camshafts.
The patent particularly says that the brand new engine is a single-cylinder. In the meanwhile, BMW’s solely singles are the G 310 vary, made in India by TVS on BMW’s behalf and together with the G 310 GS, G 310 R, and G 310 RR, and the C 400 scooters manufactured in China by Loncin. The patent may relate to any of these bikes, with the G-series fashions being a extra probably goal, or it could possibly be a sign that BMW is creating a wholly new single-cylinder engine, maybe a bigger, higher-performance one to plug the hole between the G 310 bikes and the F-series parallel twins.