Everyone knows that if you want big power fast there is only one logical way to go, forced induction. What is not discussed as often are the potential drawbacks of a blown engine in terms of maintenance and everyday rideability. One look at the old Turbo bikes of the 80's will show you just how many compromises had to be made in order to make those bikes saleable.
But this is 2014, while many of the extra maintenance requirements will still persist some of the rideability issues can be sorted out technologically.
So where do we start? Well lets start with maintenance for one, complexity is always more unreliable than simple, complex is at the mercy of its weakest point. Ostensibly this would make a roots type charger the favourite, simple design with few moving parts and spins tons of boost at low RPM's. However in a motorcycle application roots may not be the best bet, they tend to run much hotter and their boost tapers off towards the top end of the rev range. For a free revving inline 4 that will likely spend most its time above 10K RPM this may not be the best use of boost.
Luckily Kawasaki's patents seem to indicate that they will be going with a centrifugal blower, which is far more efficient through the rev range and runs significantly cooler than a roots, which is key on a motorcycle where packaging issues come into conflict with the need for a larger intercooler.
Now before we get giddy there are issues with a centrifugal blower as well, namely it delivers boost in direct proportion to the rise in RPM's which means that with a single ratio driven blower the power curve is extremely sharp leading to an almost unrideable experience. There's a reason why most blown bikes are drag specials, forced induction bikes prove tricky to ride off corners because of the modulating power curve.
Thankfully Kawasaki has also considered this. The patent filings would seem to indicate a two speed drive which would allow the crank driven blower to remain in a fairly constant range through the rev range making boost and power delivery more predictable. Even better would be the continuously variable drive mentioned in the same patent application, which would keep the impellers top speed at a constant through the rev range leaving you with a flat and ideal torque curve.
Multi speed superchargers are nothing new to KHI, Kawasaki was building multi speed supercharged fighter jet engines during WWII to combat the effects of diminishing atmospheric pressure on performance. Of course barring an expensive continuously variable drive the power can be mitigated through electronic aids, the ideal setup from a cost efficiency standpoint IMO is a 2 speed drive coupled with Kawasakis already excellent S-KRTC system as seen on the ZX-10R.Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings which are used only for the purpose of illustration, those skilled in the art will readily conceive numerous changes and modifications within the framework of obviousness upon the reading of the specification herein presented of the present invention. By way of example, the supercharged air SA, the temperature of which is increased in the supercharger 38, may be cooled by an intercooler and/or the supercharger 38 may be driven by means of a train of gears, not by means of the endless chain 51.
This is Kawasaki's most recently published patent (Apr 29, 2014; Publication Number US8707931 B2) for an Engine Super Charging Device.
An engine supercharging device includes are a supercharger (38) for pressurizing air introduced in an engine (E), an air cleaner (36) for purifying an ambient air, a purified air supply passage (56) for supplying a purified air (CA) from the air cleaner (36) towards the supercharger (38), a supercharged air passage (62) for supplying the supercharged air (SA) from the supercharger (38) towards an air intake passage (60) of the engine (E), and a relief valve (68) for adjusting an air pressure within the supercharged air passage (62). The relief valve (68) has a discharge port portion (68 b) which is accommodated within the air cleaner (36). The engine (E) has a plurality of engine cylinders, and a downstream portion of the supercharged air passage (62) is defined by an intake air chamber (54) for supplying the sucked air to respective air intake passages (60) of the plural engine cylinders.