Design and development of a control algorithm for an Anti-lock Braking System (ABS) for e-bikes

This thesis project was realized in collaboration with RAICAM Driveline S.r.l., Mondovì (Italy). E-bikers, like pedestrians, motorcyclists, cyclists, and users of mopeds are classified as Vulnerable Road Users (VRU). VRU are traffic members for whom there are no mechanical means of protection and account for about 45% of the fatalities on European Union (EU) roads. Electric bicycles, due to the available electrical energy provided by the battery pack and the similar structure to motorcycles, give the possibility of implementing active systems to improve cyclist’s safety and to protect other road users, such as an anti-lock braking system (ABS). Therefore, this thesis project is focused on the development of a control algorithm for an ABS specifically designed for e-bikes. An anti-lock braking system (ABS) is an active safety system that prevents wheel locking in emergency braking situation. It reduces the braking distance, increasing the steerability, avoiding the rear wheel from lifting and the consequent rollover, thus increasing the comfort and safety of the rider and other road users. A control algorithm based on wheel slip measurements, acceleration and on the front wheel caliper pressure was implemented in Simulink® with a model-based approach. The vehicle speed, used to calculate the wheel slip, was estimated. The controller is able to modulate the pressure within the brake line regardless of the lever force and brings the wheel slip into a range that ensures optimal braking performance. The correct detection of the road surface between tarmac and gravel, which is not known a priori, differentiates the ABS behaviour under these two conditions. The generated code was tested by using a test bike equipped with the Hydraulic Control Unit of a commercial e-bike ABS and the hardware and software architecture developed by RAICAM Driveline S.r.l. Straight line braking tests were performed on different surfaces and weather conditions in order to evaluate its performances. From the field test acquisitions, it was possible to verify the effectiveness of the controller results showing the ability to decrease the stopping distance and avoiding rollover.