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Electric Vehicles

Gyuláné Vincze, Gergely György Balázs

Budapest University of Technology and Economics Department of Electric Power Engineering

Designing brake force in vehicles

Designing brake force in vehicles

In every vehicle, at least three independent brake systems must be used for security reasons:

  1. normal operation brake system,

  2. security brake system,

  3. arrester brake.

Arrester brake secures the vehicle in standing position without additional energy supply.

Normal operation brake in an electric vehicle is realized with controlling brake mode of the driving electric motor, almost without exception, despite of the fact that brake effect can only arise on driven wheels in case of vehicles running on wheels. (In case of levitated vehicles, brake mode of driving linear motor can affect along the whole length of the vehicle.) Brake mode of an electric drive can be lossy, or lossless, with regenerated energy. In modern vehicles, regeneration of braking energy plays an important role during design. Brake with loss (realized with resistance) is only used if regeneration cannot be used  because of some reason. In regeneration brake mode, brake force is limited by maximal regeneration brake power and maximal brake force, just like during traction mode (Figure 1.6).

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Figure 1-6. Tractive characteristic extended to brake mode

Novel electric vehicles are designed so that the whole energy can be regenerated, i.e. regenerated power equals to the used power during traction.

Energy saving that can be realized with regeneration is 5…35% of the input energy, depending on the road conditions and number of stops.

Security brake system is always mechanical and not electric. Hydraulic or pneumatic frictional brakes are used in vehicles with wheels and they are mounted on all wheels. In levitated vehicles, air resistance is increased to provide mechanical brake, this solution is called aerodynamic brake.

Normal mode and security brake systems are separated in most vehicles, and can be operated jointly or separately. Brake control is designed so that joint total brake force by normal mode and security brake should be  controllable, too, and brake force should be developed continuously, without steps.

Control of brake has several aims:

  1. to stop the vehicle securely,

  2. to set a comfort deceleration in time for the passengers,

  3. anti-blocking of the wheels, in case of vehicles with wheels.