The valve units measure the...
The valve units measure the hydraulic pressure exerted by the rider via the conventional brake master cylinders, and relay the information to the ECM, which tells the power units how much braking power to provide. The stroke simulator comprises two rubber cushions of differing density to replicate the resistive feel and feedback of a conventional brake system. When the engine is off or if there is a failure in the C-ABS, solenoid valves 2 and 3 close, isolating the system away from the brake system and allowing normal actuation of the brakes in the conventional manner.
Because there is a separate system for the front and rear wheel controlled by the ECM, Honda was able to incorporate its Linked Braking System philosophy--where actuating either brake also actuates the other (although using the rear brake does not automatically engage the front brake unless wheel lockup is detected; more on that later)--into the Combined ABS (hence the "combined" prefix). Instead of being constricted to a fixed ratio of front/rear brake power distribution as with the LBS, however, the Combined ABS is able to continuously and infinitely vary the braking power to each wheel, allowing the system to adapt to the CBR's more demanding handling characteristics and hopefully making the system much more transparent than its predecessor.
The Combined ABS precisely...
The Combined ABS precisely and quickly controls hydraulic pressure using two electrohydraulic power units, one for each wheel. Based on data provided by the valve units, the ECM tells each of these power units exactly how much hydraulic pressure to provide and when. The electric stepper motor on the left spins the gear-driven ball screw that moves the modulator piston, precisely controlling braking force as often as hundreds of times per second.
"And what if the Combined ABS system should suddenly develop an internal failure of some sort," question the luddites, "or if you move the bike when it is off? Would you have no brakes at all?" The elegant design of the Combined ABS also includes the fact that it is built in line with the standard brake system. The valve units that send data to the ECM measure hydraulic pressure generated by the rider operating the standard master cylinders via brake lever/pedal; a solenoid valve connects the two systems. When the engine is off or there is an electronic failure, the valve is open, allowing the rider to operate the brakes by the master cylinders in the conventional manner. Once the engine is running and the bike begins traveling over 3 mph, the valve closes and hydraulic pressure control is then turned over to the Combined ABS' components.
Oh, Right, There's The Bike, Too
Lost in all the hoopla of the Combined ABS is that the CBR600RR received some minor updates for '09. New crossover balance tubes on the exhaust header pipes and a muffler valve similar to the unit on the CBR1000RR, along with a new shot-peening process in the intake ports, are claimed to boost midrange power. The front brake calipers are the same monoblock design used on the bigger CBR (400 grams lighter) and the bodywork has been slightly revised, with the lower portion of the engine now covered with a fairing to hide the Combined ABS components mounted behind the engine. And amazingly enough, Honda finally updated the turn signals; the previous units were basically the same as those used on the original CBR600F Hurricane of '87.
So How's It Ride?
Needless to say, we were a bit skeptical of the Combined ABS' ability to simulate a conventional brake system's feel at the lever, and we decided to take the standard '09 CBR600RR along for comparison purposes. Our testing ran the gamut of city traffic, highway drone, canyon carving, and even some closed circuit scratching (although the standard CBR wasn't available during that time).
Interestingly, Honda apparently decided not to promote C-ABS on the 600RR, as there are no logos or insignia anywhere on the bike. In fact, the C-ABS model looks identical to the standard model, and the only way you can tell the two apart (other than the sensor rings that are barely visible from the right side) is the gold-colored monoblock front brake calipers of the C-ABS version.
Pushing the C-ABS bike around with the engine off, and the brakes feel like any conventional system, which they should since you're actuating them in the standard fashion. Turn the ignition key on, and both bikes' dashes go through the same startup exercise, with the stepper motor on the tach running the needle to its full range and back, and the digital speedometer curiously running backwards from 180 mph to 0 mph in about two seconds. A small yellow ABS warning light on the lower left of the dash remains lit until you ease out the clutch and roll past 3 mph, which is basically anywhere with the clutch disengaged and the bike in motion.
Puttering along in city traffic, we were pleasantly surprised to find that the C-ABS brakes' feel is indeed nearly identical to a conventional brake system. Everything from lightly brushing the brakes while negotiating a tight space to moderate use while pulling up to stop or slowing to avoid a lane-encroaching automobile revealed no weird mushiness or numbness, with some "virtual" feedback actually being felt through the lever when you modulated the braking pressure at the lever in various situations. In fact, the response and feel is so seamless that there is no way anyone would be able to tell that they were riding the C-ABS bike.