Sensotronic Brake Control

Sensotronic Brake Control (SBC) 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.[1]

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. [2]

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(ABS) and Electronic Stability Program (ESP), 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.[3] 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.[4]

Sensotronic Brake Control applications

  • 2003-2006 E-Class
  • SLR
  • Maybach
  • 2003-2006 CLS-Class
  • 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)

References

  1. “Mercedes’ luxury transformer”. NZ Herald. 2001-08-11. Retrieved 2009-07-31.
  2. “Sensotronic Brake Control: System Information”. Bayhas.com. Retrieved 2017-03-25.
  3. “Mercedes cancels by-wire brake system; decision a blow to technology’s future: AutoWeek Magazine”. Autoweek.com. 2005-01-02. Retrieved 2009-06-01.
  4. “Mercedes cancels by-wire brake system; decision a blow to technology’s future: AutoWeek Magazine”. Autoweek.com. 2005-01-02. Retrieved 2009-06-01.
Brake fluid Brake fluid is a type of hydraulic fluid used in hydraulic brake and hydraulic clutch applications in automobiles, motorcycles, light trucks, and some bicycles. It is used to transfer force into pressure, and to amplify braking force. It works because liquids are not appreciably compressible. Most brake fluids used today are glycol-ether based, but mineral oil (Citroën/Rolls-Royce liquide hydraulique minéral (LHM)) and silicone-based (DOT 5) fluids are also available. Brake fluids must meet certain requirements as defined by various standards set by organizations such as the SAE, or local government equivalents. For example, most brake fluid sold in North America is classified by the US Department of Transportation (DOT) under its own ratings such as "DOT 3" and "DOT 4". Their classifications broadly reflect the concerns addressed by the SAE's specifications, but with local details - Alaska and the Azores for example, have different normal temperature and humidity ranges to consi...
Air brake (road vehicle) An air brake or, more formally, a compressed air brake system, is a type of friction brake for vehicles in which compressed airpressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle. Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers, in addition to their use in railroad trains. George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on March 5, 1872. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake. In the early 20th century, after its advantages were proven in railway use, it was adopted by manufacturers of trucks and heavy road vehicles. Truck air actuated disc brake. Design and function Air brake systems are typically used on heavy trucks and buses. The system consists...
Engine braking Engine braking occurs when the retarding forces within an engine are used to slow a vehicle down, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes. The term is often confused with several other types of braking, most notably compression-release braking or "jake braking" which uses a different mechanism. Traffic regulations in a large number of countries require trucks to always drive with an engaged gear, which in turn provides a certain amount of engine braking (viscous losses to the engine oil and air pumped through the engine and friction losses to the cylinder walls and bearings) when no accelerator pedal is applied. Type Gasoline engines The term "engine braking" refers to the braking effect that occurs in gasoline engines when the accelerator pedal is released. This results in the throttle valve that controls intake airflow closing and the air flow through the intake becoming greatly restricted (but not cut off complet...
Electric friction brake An electric friction brake, often referred to as just electric brake or electric trailer brake is a brake controlled by an electric current and can be seen on medium duty trailers like caravans/RVs and consumer-grade car trailers. It is related to the electromagnetic track brake used in railways which also use electric current to directly control the brake force. Mechanical principle This describes the electrically controlled drum brake principles.   The brake is built with the brake shield (1) as a base that contains the mechanism. The brake shield is mounted on an axle/spindle using the holes in the centre. The brake shoes (3) are the items performing the braking by pressing outwards at the drum that covers all the innards. The brake shoes are held in place by reactor springs (2) and an adjuster (7) spring. There are also some minor clips not pictured to keep the brake shoes in place. Braking starts with applying a current proportional to the desired brake f...
Electric park brake Electric park brakes (EPB) are used on passenger vehicles to hold the vehicle stationary on grades and flat roads. This was accomplished traditionally using a manual parking brake. With electric park brakes, the driver activates the holding mechanism with a button and the brake pads are then electrically applied onto the rear brakes. This is accomplished by an electronic control unit (ECU) and an actuator mechanism. There are two mechanisms that are currently in production: 1. Cable puller systems and 2. Caliper integrated systems. EPB systems can be considered a subset of Brake-by-wire technology. First installed in the 2002 BMW 7 Series (E65), electric park brakes have since appeared in a number of vehicles. Electric park brake in the center console in a Volkswagen Touran Functionality Apart from performing the basic vehicle holding function required of park brakes, the EPB systems provide other functions like automatic release of the park brakes when the driver presses the...