If a conventional vehicle decelerates, a large part of the kinetic energy is converted to heat by the friction brake and emitted into the environment without being used.

Hybrid and electric vehicles can recuperate some of the kinetic energy. When braking in a hybrid or electric vehicle, the electric motor switches to generator mode. The wheels transfer kinetic energy via the drivetrain to the generator. The generator turns in a similar way to a bicycle light generator transforming part of the kinetic energy into electrical energy, which is then stored in a high-voltage battery. At the same time, generator resistance produced from the electricity created, slows the vehicle. When more braking torque is required than the generator alone can provide, additional braking is accomplished by friction brakes. The electrical energy stored in the vehicle’s high-voltage battery is available to the electric motor to be used for driving off or accelerating.

In many cases, the generator's braking power is sufficient to slow the vehicle as desired by the driver. The friction brake is used less often, for example, for very rapid deceleration, at very low speeds and when stationary.

Regenerative braking contributes toward increasing the range of electrical vehicles. It helps to save fuel in hybrid vehicles and to reduce emissions of CO2 and pollutants, particularly in urban traffic situations involving frequent braking and acceleration. In addition, using the generator for braking also reduces brake wear and the build-up of brake dust.

For vacuum-based regenerative braking systems, the conventional braking system is supplemented with a pedal-travel sensor for the brake pedal as well as a vacuum pump as an alternative. Intelligent modifications allow for the vehicle's brake control system to be used for regenerative braking.

ESP® with Regenerative Braking Control

The entry-level version of vacuum-based regenerative braking systems complies with low recuperation requirements and is suitable for hybrid vehicles with low electrical output. To enable regenerative braking, the vehicle's brake control system is enhanced with special software.

ESP® hev for front axle/rear axle brake circuit distribution

ESP® hev enables purely generative deceleration of up to 0.2g. This ensures it completely covers the deceleration cycles within the New European Driving Cycle (NEDC).

The system decouples the rear axle braking circuit from the brake pedal each time braking takes place, regardless of whether the vehicle is decelerated using a generative or hydraulic process. The system continuously conceals the braking torque on the rear axle without disruptive transitions in deceleration. The pedal feel is solely dependent on the front axle braking circuit and is similar to the feel the driver is used to in conventional vehicles. Decoupling of the rear axle allows the pedal feel and the design of the braking system to be more flexible in configuration.

Vacuum-independent regenerative braking systems fulfill the highest level of recuperation requirements. These systems are particularly suited to vehicles driven for long periods of time or continuously without the combustion engine. They inherently do not have an adequate vacuum pressure source, e.g. plug-in hybrids or electric cars.

HAS hev

The HAS hev vacuum-independent regenerative braking system enables purely generative deceleration of up to 0.3g. This ensures it completely covers the deceleration cycles within the New European Driving Cycle (NEDC).

The system can be used for all braking circuit configurations and drive concepts. Regardless of whether the vehicle is decelerated using a generator or friction brake, HAS hev provides the driver with a consistent pedal feel and a constant pedal position at all times as the system features a pedal feel simulator. The transition from generative to hydraulic braking is concealed with minimum noise and no disruptive transitions in deceleration. The brake torque is distributed hydraulically on both axles.