As technologically advanced as today's sportbikes are, it's interesting to note that while even the most basic and bottom-rung econobox automobile comes standard with an anti-lock brake system, none of this seemingly basic safety technology has made its way to the supersport market. Of course, it could be said that ABS (anti-lock brake system) has barely made inroads into the motorcycle market in general, much less sportbikes. But with many sport-touring and standard motorcycles now being offered with ABS as an option, why hasn't it been even attempted with a supersport bike?
The two biggest reasons have been performance and weight. A sportbike is lighter, nimbler, smaller, and more powerful than your average motorcycle, and as such demands a more tactile approach to riding it. This is especially true when it comes to slowing all that performance; today's braking systems are highly-developed designs that are engineered not only to bleed off all that speed as quickly as possible, but also to provide the rider with maximum control over that deceleration via feedback and modulation. Any interference in that line of communication degrades the riding experience, and most ABS systems' threshold up to this point have been too low to avoid the disconnection that would inevitably occur on a supersport machine. And then there is the added weight of all the additional componentry and hydraulic fluid, of which there is very little room for on the compact and pared-to-the-bones build of a sportbike.
Leave it to Honda, then, to tackle the seemingly impossible task of engineering an ABS system specifically for supersport models that doesn't intrude upon their personality or performance.
Combined ABS--Brake-By-Wire
We covered some of the primary aspects of Honda's new Combined ABS in a previous issue ("Honda Unveils Brake-By-Wire ABS for Sportbikes", Late Braking, September '08), but now that we've managed to get a CBR600RR C-ABS model for test (the C-ABS is also available as an option on the CBR1000RR), there are a ton of important details on the system that have come to light.
The biggest difference between conventional ABS and Honda's Combined ABS is that the Honda system is a true "brake-by-wire" design, meaning the brakes are electronically controlled--and that includes normal operation, when the ABS isn't triggered. Conventional ABS uses hydraulic pressure generated by the brake master cylinders from the rider pulling on the front brake lever/pushing on the rear brake pedal and redistributes it via a pressure control valve and/or pump to vary the hydraulic force at the point of wheel lockup. This often causes a loss of feedback at the lever (with many ABS, the lever feel becomes mushy and soft) due to the hydraulic pressure being rerouted through the various components when the system is activated.
These are the main components...
These are the main components of the Combined ABS: the two valve units on upper left and upper right measure the hydraulic pressure generated by the rider through the conventional brake master cylinders, and send data to the electronic control module in the center, which interprets the data and sends commands to the power units on lower left and lower right to apply pressure to each brake.
In order to make room for...
In order to make room for the C-ABS rear brake power unit located underneath the tailsection, Honda had to add a remote reservoir to the rear shock.
Both the standard and C-ABS...
Both the standard and C-ABS bike receive this lower fairing extension for '09 that completely covers up the engine. Its main purpose is to hide the C-ABS components that are mounted behind the engine.
Instead of using hydraulic pressure generated by master cylinders in the usual manner, the Combined ABS produces hydraulic pressure using an electric power unit for each wheel. The power unit consists of a DC stepper motor that spins a gear-driven ball screw (basically a screw riding in ball bearings that allows it to spin smoothly and quickly) attached to the hydraulic piston. These are controlled by an electronic control module (separate from the engine's ECU) that interprets data provided by valve units--again, one for each wheel--that measure the amount of pressure the rider exerts on the brake lever/pedal. The ECM tells the power units exactly how much hydraulic pressure to generate based on the data from the valve units; because the ECM is capable of hundreds of calculations and commands every second and the power units are able to adjust the hydraulic pressure just as quickly, there is no need for an inline pressure control valve as with a conventional ABS. This also eliminates the pulsing at the lever common with standard systems.
If the rider isn't controlling the brakes with hydraulic pressure, then won't the feel at the lever be non-existent? Another innovative idea in Honda's system called the "stroke simulator" handles that aspect. In order to simulate the brake feel in both normal and ABS operating modes, two rubber cushions of differing density in each valve unit provide increasing amounts of resistance as the lever/pedal stroke increases. This is designed to offer a familiar sensation to the rider that is claimed to be nearly identical to those generated by traditional hydraulic brakes.