Abstract
Regenerative braking applied to electric or hybrid vehicles enables access to brake torque from other devices that is usually lost to heat and noise during friction braking. The energy is recovered by an electrical system for use in traction drive or other devices via an E-machine or stored within inertia flywheels.
During coastdown or driver demanded braking on an electric or hybrid vehicle, brake blending or energy arbitration is normally required to maximise the energy recovered whilst ensuring the vehicle is not compromised within the limits of tyre vertical load and the vehicle stability limit.
Typical systems in the marketplace fitted on higher cost vehicles seek to maximise recovery and hence require complex brake blending algorithms and pedal feel simulation. This activity demands substantial resource during development, application to the vehicle and significant on-cost to the vehicle. The resultant increased time to market on a relatively small niche application is often difficult to justify for the Vehicle Manufacturer, contributing to slow adoption of hybrid technology. The application of complex blending solutions effectively excludes their adoption from city cars and B/C segment cars where brake regeneration can offer significant benefits to their typical duty cycles.
This paper identifies ideal vehicle architectures and real world duty cycles where a nonintegrated brake regeneration strategy could be applied at relatively low cost. This strategy largely negates the requirement for additional brake system complexity and vehicle application. The braking system efficiency, effect upon pedal feel and vehicle dynamics is considered for a typical B/C segment vehicle application.
The fuel consumption benefits are quantified for fuel consumption drive cycles and real world duty cycles for a generic B/C segment vehicle. Reduction in real world fuel consumption up to 10% can be achieved, although the influence of regenerative braking on fuel consumption is dependant upon its integration into the whole vehicle.
For a front wheel drive vehicle, the dynamic behaviour and refinement under the influence of regeneration can be made acceptable to the customer with the infrequent excursions into the unstable region mitigated by application of the Anti-lock braking and Electronic Stability Control system.
Keywords: Regenerative braking, Hybrid, electric vehicles, Low-Integration