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The SBC system was introduced on the R230 SL-class, which went on sale in Europe in October 2001. In a hydraulic brake system, the driver applies force by a mechanical link from the pedal to the master brake cylinder.
In turn the master brake cylinder develops hydraulic pressure in the wheels. In contrast, the electro-hydraulic brake SBC provides the brakes with a brake fluid supply from the hydraulic high-pressure reservoir, which is sufficient for several braking events. A piston pump driven by an electric motor supplies a controlled brake fluid pressure between 140 and 160 Bar in the gas diaphragm reservoir. When the driver presses the brake pedal – or when ESP intervenes to stabilize the vehicle – the SBC control unit calculates the desired target brake pressures on each individual wheel.
Through the use of independent pressure modulators the system regulates the hydraulic pressure at each wheel. These four pressure modulators consist of one inlet and one outlet valve, controlled by electronic output stages. The system employs a travel sensor and a pressure sensor at the pedal to measure the speed and force of the driver’s command.
The control unit processes this information and generates the control signals for the wheel pressure modulators. Normally, the master brake cylinder is detached from the brake circuit. A pedal travel simulator creates normal pedal feedback.
If ESP intervenes, the high-pressure reservoir supplies the required brake pressure quickly and precisely to selected wheels, without any driver involvement. With fine-grained control of pressure at each wheel, SBC offers a unique platform in which to implement skid protection and traction control compared to cf. Moreover, the system offers innovative functions to reduce the driver’s workload. These include Traffic Jam Assist, which brakes the vehicle automatically in stop-and-go traffic once the driver takes his or her foot off the accelerator.
The Soft-Stop function – another first – assists with smooth stopping in town traffic. In case of computer failure, SBC reverts to a hydraulic master cylinder, but driver effort and stopping distance is reported to increase.
In case of pump failure the high-pressure reservoir is capable of retaining enough pressure to stop the vehicle electronically. Information on other types of failure remain an open question.