Sensotronic Brake Control

Sensotronic Brake Control (SBC) is an electro-hydraulic brake system, where the wheel brake cylinders on a vehicle are operated through a servomechanism.

The SBC system developed by Daimler and Bosch was introduced on the R230 SL-class, which went on sale in Europe in October 2001.

Mechanics
The SBC operates the brakes using a brake fluid supply from a hydraulic high-pressure reservoir. A piston pump driven by an electric motor supplies a controlled brake fluid pressure at range between 140 bar and 160 bar in the gas diaphragm reservoir.

When the brakes are applied, the SBC control unit will calculate the desired target brake pressures on each individual wheel. The system uses four independent pressure modulators to regulate a hydraulic pressure at each wheel. The 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. 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.

Advantages and disadvantages
With fine-grained control of pressure at each wheel, SBC allows for the implementation of traditional stability control methods, such as Anti-lock braking system (ABS) and Electronic Stability Program (ESP). The system offers electronically controlled functions intended to reduce the driver's workload. Traffic Jam Assist brakes the vehicle automatically in stop-and-go traffic once the driver takes his or her foot off the accelerator. The Soft-Stop function assists with smooth stopping in town traffic by reducing braking pressure.

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.

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 to US customers dated August 2018, a warranty addendum was sent extending coverage for 25 years and unlimited miles on the following SBC components:
 * Hydraulic control unit
 * Hydraulic Pump
 * Pressure Reservoir
 * Brake Operating Unit
 * Front and Rear wheel speed sensors
 * Brake lamp switch
 * Yaw Rate Sensor

Sensotronic Brake Control applications

 * 2003–2006 E-Class (W211)
 * SLR
 * Maybach
 * 2003–2006 Mercedes-Benz CLS-Class (W219)
 * 2001–2011 SL-Class

Other production electro-hydraulic brake systems

 * Toyota Prius (Introduced in 1997; uses an ehb system from Advics)
 * Toyota Estima Hybrid (Introduced in 2001 in Japan)
 * Ford Escape Hybrid (Introduced in 2003)
 * Acura NSX, 2nd generation (Introduced in 2015)
 * Audi e-tron (Introduced in 2018)