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.
Disc brake A disc brake is a type of brake that uses calipers to squeeze pairs of pads against a disc or "rotor" to create friction. This action retards the rotation of a shaft, such as a vehicleaxle, either to reduce its rotational speed or to hold it stationary. The energy of motion is converted into waste heat which must be dispersed. Hydraulically actuated disc brakes are the most commonly used form of brake for motor vehicles, but the principles of a disc brake are applicable to almost any rotating shaft. Design On automobiles, disc brakes are often located within the wheel A drilled motorcycle brake disc Development of disc-type brakes began in England in the 1890s. In 1902, the Lanchester Motor Company designed brakes that looked and operated in a similar way to a modern disc-brake system even though the disc was thin and a cable activated the brake pad.Other designs were not practical or widely available in cars for another 60 years. Successful...
Inboard brake An inboard braking system is an automobile technology wherein the disc brakes are mounted on the chassis of the vehicle, rather than directly on the wheel hubs. The main advantages are twofold: a reduction in the unsprung weight of the wheel hubs, as this no longer includes the brake discs and calipers; also, braking torque applies directly to the chassis, rather than being taken through the suspension arms. Inboard brakes are fitted to a driven axle of the car, as they require a drive shaft to link the wheel to the brake. Most have thus been used for rear-wheel drive cars, although four-wheel drive and some front-wheel drives have also used them. A rare few rear wheel drive racing cars (e.g., the Lotus 72) have also used inboard front discs, accepting the need to provide a drive shaft to gain the unsprung weight and braking torque advantages. McLaren M23 rear brakes Inboard brakes for early racing cars have rarely used drum brakes, although nearly all inboard brakes date from...
Brake wear indicator A Brake wear indicator is used to warn the user and/or owner of a vehicle that the brake pad is in need of replacement. The main area of use for this is on motor vehicles with more than three wheels. However brake wear indicators are also useful for brake pads in industrial applications, including wind turbines and cranes. This article refers to disc brakes as an example, but the principle is the same for other types of friction brakes. Types of indicators There are different types of wear indicators for brake pads: Ocular inspection: A cut is made in the pad material to the depth where it shall be replaced. Requires manual inspection of the pads. Mechanical: A metal plate is designed to scratch the brake disk causing a noise when the pad has worn down to the desired level. Electrical: A metal body is embedded in the pad material that comes in contact with the rotor when the desired wear level is reached. This will light an indicator in the instrument cluster. Positi...
Brake bleeding Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles. This is necessary because, while the brake fluid is an incompressible liquid, air bubbles are compressiblegas and their presence in the brake system greatly reduces the hydraulic pressure that can be developed within the system. The same methods used for bleeding are also used for purging, where the old fluid is replaced with new fluid, which is necessary maintenance. The process is performed by forcing clean, bubble-free brake fluid through the entire system, usually from the master cylinder(s) to the calipers of disc brakes (or the wheel cylinders of drum brakes), but in certain cases in the opposite direction. A brake bleed screw is normally mounted at the highest point on each cylinder or caliper. There are four main methods of bleeding: The pump and hold method, the brake pedal is pressed while one b...
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...