An ABS for a motor vehicle avoids excessive slipping between the tires and the road during braking, whereby the steering capacity and the lateral traction of the motor vehicle are maintained. An ABS four-channel system comprises two return pumps and two solenoid valves per wheel brake cylinder. Of the eight solenoid valves of the ABS for a car, four are usually open and the other four closed. When using the ABS during excessive slipping between the tires and the road, a line to the wheel brake cylinder of the wheel to be decelerated or the locking wheel is first blocked by a solenoid valve (that was previously open). If this is not sufficient to reduce the slipping or to release the locking wheel, the pressure is reduced by opening the other solenoid valve. At the same time, a return pump pumps brake fluid back into a line between the main brake cylinder and the solenoid valve. The excessive slipping is thereby reduced or the locking wheel can turn again, so a driver regains control of his vehicle.
An ESP in a motor vehicle takes care of the stability of the vehicle by targeted deceleration of individual wheels, for example during cornering. The ESP obtains the information required for this via sensors at the rims, an accelerator pedal sensor, an angle sensor on the steering wheel, and longitudinal, transverse and rotary acceleration sensors. The ESP in particular prevents instability of the vehicle during cornering, which can occur for example in the event of unadjusted speed, an unpredictable change in the surface of the road (wetness, slickness, dirt accumulation) or in the event of a suddenly necessary swerve. An ESP computer unit detects the ESP case with the aid of the data supplied by the sensors and controls a targeted braking operation.
The braking operations required for the ABS and the ESP are performed by a hydraulic controller which adjusts the requisite brake pressures at the caliper by means of solenoid valves. The hydraulic controller comprises a hydraulic device, also called a Hydraulic Control Unit (HCU), and a control device, also called an Electronic Control Unit (ECU). Valve units which open or close to control the brake fluid are located in the hydraulic device. The valve units are actuated by magnet coils which are located in the hydraulic controller.
In hydraulic controllers in the prior art, each magnet coil or each magnet coil yoke of the hydraulic controller is cast with a thermoplastic elastomer to achieve a requisite resilient pressing force of the magnet coil yoke in a direction of the hydraulic device. These cast thermoplastic elastomers also seal the magnet coil yoke from the hydraulic device. The process of casting each individual magnet coil yoke is time-consuming, complex and entails high costs.
Resilient elements made of a plastic material are also used in the prior art, which as separate, loose component parts, are used to provide a resilient force to the magnet coil yoke. Plastic resilient elements of this type can break and reduce the maximum operating temperature of the hydraulic controller as the plastic resilient elements soften at excessive temperatures and therefore diminish in resilient force. Assembly of the plastic resilient elements together with the magnet coil yoke is also time-consuming, and this in turn entails high production costs.
DE 198 33 498 A1 discloses a controller for a hydraulic brake which comprises an electronic control unit, flanged to a hydraulic unit, with coil units for solenoid valves. The coil units are fixed in the electronic control unit in this case between a base of the electronic control unit and a coil retention device located at free ends of the coils. Resilient mounting of the coil units takes place, on the one hand, via a resilient washer between the base of the electronic control unit and each coil unit and, on the other hand, via projections formed on the coil retention device and that are arranged mutually offset and so as to oppose one another, the projections providing, in collaboration with an outer side of the hydraulic unit, a second resilient force for the coil units.
Assembly of the coil units with the resilient washers and that of the coil retention device is complex. As a respective resilient force is provided at the two opposing free ends of the coil units, exact positioning of the coil unit in the assembled state of the electronic control unit on the hydraulic unit is not always ensured either.