Sensotronic Brake Control is an electro-hydraulic brake system developed by Daimler and Bosch. The SBC system was introduced on the R230 SL-class, which went on sale in Europe in October 2001.
How it works
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.
Advantages and disadvantages
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. Anti-lock braking system and Electronic Stability Program, respectively. 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.
Industry recognition
In 2001 the μ-Club, an association of international experts in the field of brake technology, honored Robert Bosch and Daimler Chrysler for the development of the electrohydraulic brake SBC.
Problems
In May 2004, Mercedes recalled 680,000 vehicles equipped with the system; in March 2005 a total of 1.3 million vehicles were recalled. In 2006 high-volume models such as the E-class returned to conventional hydraulic brake systems. Low-volume luxury models such as the SL, the Maybach and the SLR continued to use SBC due to the prohibitive cost of redesign. In a letter - only to US customers - dated August 2018 a warranty addendum was sent extending coverage for 25 years and unlimited miles on the following SBC components.
