Siemens VDO plans series production of the wedge brake this decade
By Mike Hanlon
September 13, 2005
September 14, 2005 At the 61st IAA Motor Show in Frankfurt Siemens VDO Automotive is exhibiting future braking technology with the electronic wedge brake, which will enable brake-by-wire production before the end of this decade. The modern wedge brake offers considerable safety and comfort advantages over the hydraulic brake. Future driver assistance systems will not only monitor the current traffic situation, but actively assist the driver in emergencies. Autonomous intervention in vehicle dynamics will increasingly help keep the vehicle under control, even in difficult operating situations. A rapid and intelligent braking system is one of the foundations for advancing the next generation of driver assistance systems. Siemens VDO sees its electronic wedge brake (EWB) brake-by-wire technology as the answer to future vehicle chassis safety, weight, reliability and space requirements.
Siemens VDO's EWB is based on innovative technology developed by eStop, a firm which was acquired by the company in early 2005, and its control-related foundations originate from German Aviation and Aerospace Center applications. During the braking operation a brake pad attached to a wedge is pressed between the brake caliper and the brake disk. As the wheel turns the wedge effect is automatically intensified. This allows any level of braking power with a minimum of intricacy.
Vehicles employing the electronic wedge brake solution will have an intelligent wheel-braking module fitted on each wheel. The module consists of the brake pad, the wedge attached to the wedge-bearing mechanism, the mechanical power transmission between the two electric motors and a sensor system for monitoring movement and force. The sensors measure current wheel speed approximately one hundred times per second and braking forces and wedge position to a high degree of accuracy and resolution.
When the driver engages the brake pedal, the EWB system electronically transmits the activation signal to the interconnected brake modules. When the brake activation signal is received, electric motors actuate a wedge-bearing mechanism consisting of several rollers to move the wedge into the required position according to the sensor feedback values. This causes the brake pad to be pressed against the brake disk. Based on the principle of self-energization, the braking effect builds up very rapidly and the intelligent control prevents any danger of the wedge blocking. This principle of "unstable" control structures was taken from high safety-critical systems for aviation and aerospace applications and adapted for automotive purposes.
The EWB eliminates the need for components such as hydraulic pipes, brake cylinders, brake boosters or antilock braking control units. This lowers overall weight and makes for greater reliability for improved safety, with reduced servicing requirements. By doing away with the hydraulic braking system, it also helps to reduce the vehicle's environmental impact.
Finally, the EWB is not only for braking while the vehicle is moving, but also can be used as an automatic parking brake. This allows vehicle designers to do away with the traditional hand-pulled brake, while helping prevent the vehicle of the future against rolling away when parked. The mechanical decoupling of the brake pedal and the brake also can be used to reduce the often misunderstood pulsing of the brake pedal when ABS is in use, or to eliminate it altogether if desired. In the event of a collision, the mechanical decoupling of the brake pedal and the brake also makes for greater occupant protection in the foot area.
The use of the traditional 12-volt vehicle electrical system opens up new design potential for the automobile manufacturer, as the hydraulic-free wedge brake takes up less space both in the engine compartment and in the chassis. At the same time, it reduces assembly times on the production line and the number of components required for the brake. The electronic brake system also can be adapted more easily and faster to new types of vehicle helping to save time and development costs.
For Siemens VDO, the electronic wedge brake is another area of application in the development and production of x-by-wire technologies, which have been part of the company's day-to-day business for more than 20 years. The electronic accelerator pedal is now a standard feature on millions of vehicles. Today, any modern car with an electronically controlled fuel injection system already uses the mechanical pressure exerted by the driver on the accelerator pedal to electronically transmit the driver's input to the electronic engine control unit. In the future, electronics will replace other mechanical and hydraulic systems, thereby reducing costs, enabling new functions and increasing reliability.