A Comparison of Braking Behavior between an IC Engine and Pure Electric Vehicle in Los Angeles City Driving Conditions 2017-01-2518

The Los Angeles City Traffic Brake Test Schedule has been an established procedure used almost universally for generations by vehicle manufacturers to evaluate and validate braking systems for the attributes of NVH and brake wear behavior. The Los Angeles driving route, commonly known as the Los Angeles City Traffic Test (LACT), has long been considered an effective and “quasi” extreme set of real world driving conditions representative of the US passenger vehicle market and have been covered in other analysis including SAE Technical Paper 2002-01-2600 [1]

The performance of a vehicle, relative to braking, in LACT conditions is typically influenced by basic vehicle and brake system attributes including the ratios of vehicle mass to brake sizing attributes, friction material selection, and the acceleration, drag, and cooling behavior of the vehicle. The general character of the LACT Route and typical driving behavior establishes an energy input to the braking system that must be managed by the chosen set of brake components overlaid to a set of vehicle attributes. Brake system sizing has generally converged on typical sizing choices based on market forces and the typicality of vehicles in their associated segment. As a result, the general sizing of brakes systems tends to revert to a mean within a segment. Tradeoffs between, noise, wear, dust and other performance attributes are made with the selection of the friction material. Where, by example, a brake designer may tradeoff the attributes of higher dust, lower lining and rotor life in LACT for higher performance in extreme fade testing to achieve a desired market differentiation.

The need for the work presented is motivated by the relatively recent entry to the market of pure electric vehicles. Many of the Pure EV’s offer significant capability to employ regenerative braking, which allows the conversion of vehicle kinetic energy to electrical energy. Therefore, the potential exists to significantly affect the amount of energy input to a vehicle’s friction braking system. As the performance in a LACT is highly dependent on the energy input the brake system must manage, it is important to objectively understand how this may change with the contribution of regenerative braking. If it is determined that the energy input to the friction brake system is significantly different in pure EV’s, then the potential exists to design fundamental brake system attributes differently with the potential to realize an improved totality of associated metrics by altering many of the traditional tradeoff balances commonly constraining brake system designers.

This paper will provide an analysis by comparison between an exemplar IC engine based vehicle and a pure electric vehicle during a typical “day in Los Angeles”. The paper will provide an assessment of how regenerative braking influences the energy the brake system must manage, as well as any changes to the usage profile of the brake system in these driving conditions. Finally, this paper will offer some thoughts on how this could affect future design of brake systems of pure electric vehicles