Pedal travel sensor offers wear-free operation, high safety

July 22, 2011 // By Christoph Hammerschmidt
Automotive Supplier Bosch has introduced a new pedal travel sensor for hybrid and electric vehicles. With its contactless design, the sensor offers wear-free measurement. Redundant output signals guarantee a high level of safety.

The PWG pedal travel sensor is Bosch's new sensor series for contactless pedal travel measurement. Travel sensors are a core component of electric brake pedals, which are required for regenerative braking systems in hybrid and electric vehicles. These pedals record the driver's desired level of braking, which the systems then implement electrically, hydraulically, or using a combination of the two. Features of the new sensor include contactless and thus entirely wear-free travel measurement using a magnetic field sensor as well as redundant signal recording. The compact design of the two sensor components (magnetic field sensor and magnetic circuit) means the sensor can be integrated cost-effectively into existing vehicle environments.

There are two designs which support a wide variety of configurations between them. The PWG12 has the sensor and the magnetic circuit fitted separately. This variant offers the greatest flexibility during installation and can be used, for instance, to measure the stroke of the brake rod. The PWG13 has the magnetic circuit already integrated. This variant can simply be applied mechanically, for instance for measuring the pedal angle. Both designs will shortly enter series production; prototypes are already available.

The measurement principle behind the Bosch pedal travel sensor is based on a Hall sensor that records the magnetic vector of a magnetic field. The magnetic field is generated using a magnetic circuit, which takes into account the design requirements of numerous braking systems and reports linear and rotational motion to the Hall sensor. Up to 45 millimeters of stroke (PWG12) or up to 55 degrees of rotation (PWG13) can be measured using the contactless process. Internal redundant signal recording and processing means the pedal travel sensor can provide the measured values at two separate outputs in the form of pulse-width-modulated signals. A control unit supplied with both these outputs can carry out constant plausibility checks on measured values by comparing the two, thus meeting the stringent safety requirements placed on electronically