In the wedge brake , also electronically controlled brake wedge (English Electronic Wedge Brake, abbreviation EWB), called a small pushes electric motor a brake pad with a wedge-shaped back profile between brake shoes and the brake disc . Just like a drum brake , it does not contain a brake cylinder and part of the contact pressure (braking force) between the lining and the disc is obtained from the movement of the disc. As a result, these two brakes theoretically only need approx. 10% of the energy of a comparable, usually hydraulically actuated disc brake. Due to the fact that the coefficient of friction between the brake lining and the brake disc is not constant due to surface pressure and temperature, the advantage in practice is significantly lower. In addition, an additional mechanism for lining wear adjustment must be implemented, which greatly increases the complexity of the system.
Further advantages are faster response, the elimination of the hydraulic system and the conventional handbrake . The wedge brake is a brake-by-wire system. In 2006, Siemens VDO announced that it would go into series production in cars until 2010. As part of the Siemens-Continental merger in 2008, series use was questioned. The work has meanwhile been stopped.
The conventional wedge brake (not electronically controlled) has the disadvantage that the wheel locks quickly and the brake (depending on the mechanical design) can only be released when the vehicle is stationary. That is why it was only used to lock the wheels of horse-drawn carriages . The coachman rams a wedge between the wheel and the wheel arch. This wedge brake has a long bracket in order to be able to use the leverage effect in addition to self-reinforcement. Only then can the driver effect the necessary delay.