Anti-lock braking systems are used in motor vehicles, including some motorcycles and motor scooters, to prevent vehicle wheels from locking against rotation when excessive braking force is applied to an individual wheel brake. Such systems control the brake fluid pressure applied to a wheel brake in a manner which maximizes the braking force yet allows the wheel to predominantly roll, rather than slide, across a road surface. A typical anti-lock braking system includes a number of wheel speed sensors, an electronic control unit (“ECU”) which monitors the wheel speed sensors to detect and respond to wheel lockup, and a motorized hydraulic control unit (“HCU”) which may be actuated by the ECU in response to wheel lockup to reduce and ultimately modulate the brake fluid pressure that is delivered to the affected wheel brake.
Anti-lock braking systems used in automobiles such as passenger cars and light trucks are conventionally designed as multiple channel units where the ECU and HCU are integrated to form an electro-hydraulic control unit (“ECHU”). The integration of the ECU and HCU permits constituent elements such as valve solenoids to be surface mounted on the ECU control circuit to reduce the complexity of assembly, while the provision of multiple channels permits the pumping elements servicing each channel to be driven by a common, suitably specified motor. The predominant method of providing multiple channels in an EHCU employs pairs of opposed piston pumps driven by a single cam or eccentric mounted on a motor shaft, so that the opposed piston pumps and common HCU motor are oriented perpendicular to each other within the overall device.
Anti-lock braking systems used on motorcycles and motor scooters are typically adapted from the multi-channel, integrated designs described above due to economies of scale. However while such systems can provide the braking performance required in these vehicles, their designs do not efficiently adapt to the spatial constraints and opportunities present in these vehicle framing systems. Accordingly, there is a need for a hydraulic modulator unit that is adapted for use with motorcycles, motor scooters, and other such vehicles having a generally open, comparatively planar frames.