When it comes to environmental performance, in order to amply meet the basic performance requirements of a Sports bike as well as the challenging environmental performance targets we had set ourselves, a variety of technologies were introduced in all areas of the power unit.
Compared with SOHC, DOHC gave us free rein to choose the shape of the combustion chamber, the shape of the ports and the layout angle of the valves, and also make the valves more lightweight, so we went with DOHC. While DOHC naturally improved performance, it was also a factor in making the end-product more attractive as a Sports bike.
For the valves, by deploying a roller rocker arm extremely compactly, we were able to realize small cylinder heads with low friction valve drives. By choosing shim-type valve tappet adjustment we were able to lighten the weight of the rocker arm, which meant we could set a lower valve-spring load and so reduce friction.
Also, by using a silent cam chain (SV Chain) with which the surface of the pins is treated with vanadium, we were able to both reduce friction and increase protection against dust.
Roller Rocker Arm
Silent Cam Chain
For the piston, we chose the same φ67 bore size as employed on the CBR600RR. We also optimized the balance between piston rigidity and strength and made maximum use of CAE technology to make the piston thoroughly light weight.
We also worked to reduce friction by adding Striations on the piston skirt, and by combining the AB1* process used on the CBR600RR for the piston pin/connecting rod.
Piston, Connecting Rod
Striations on the Piston Skirt
For the crankcase, in order to keep cylinder irregularity to a minimum we used centrifugal-casted thin-walled sleeves and as in the CBR600RR, made the crankcase more compact and lightweight by making the bore interval 7mm.
Also, through measures such as eliminating partitions in the 180° phase crankcase transmission chamber, we reduced the pumping losses that occur during piston oscillation.
For the oil pump, we used the internal relief structure used in the CBR1000RR and as well as reducing friction, improved aeration performance and simplified the shape of the oil pan.
As well as building an AI system into the cylinder heads, we also put an O2 sensor and catalyzer inside the exhaust pipe to meet the EURO 4 exhaust gas regulations and achieve our own higher environmental targets.
In order to meet regulatory requirements in Thailand and California, we have also used an evaporative emission control system (a device that inhibits the emission of fuel evaporative emissions) that satisfies the Level 6 emission gas regulations in Thailand. This is a power unit that truly respects the environment.