Electro-hydraulic brake
The electro-hydraulic brake , also known as SBC (Sensotronic Brake Control), is a wheel brake system in which the hydraulic pressure for the wheel brakes is regulated by an electrical signal . Compared to conventional, purely hydraulic braking systems, this enables better controllability of the braking power and thus a shorter braking distance depending on the situation.
functionality
With the electro-hydraulic brake, the driver's request is recorded electronically using sensor technology. A distance sensor determines the course of the pedal travel over time and from this the pedal speed and acceleration. In addition, the pressure curve in the control circuit is recorded by a pressure sensor. From this, the control unit derives the driver's request (partial braking, emergency braking, etc.) and calculates the required pressure for each wheel brake in the current driving situation. The control unit regulates a hydraulic unit that can build up an individual brake pressure for each wheel. Pressure sensors in each wheel line determine the actual pressure so that the target pressure can be adjusted individually for each wheel.
The pressure required to supply the brakes is generated by a high-pressure pump, which is supported by a pressure accumulator. The pressure accumulator holds enough energy in the form of a compressed gas to brake the vehicle at least once to a standstill, even if the pump fails. Often an electrical energy storage device with capacitors is also used, which can supply the system for a certain time even if the on-board voltage fails.
In contrast to the conventional braking system, with this system the driver no longer has any direct sensory contact with the wheel brakes. A simulator generates the well-known brake pedal feel, which in conventional brakes is caused as a counterforce by the hydraulic pressure of the brake fluid from the master brake cylinder to the wheel brakes. If the control system fails, a direct - but unreinforced - connection between the master cylinder and the wheel cylinders of the front axle is established via valves, just like with a conventional brake.
advantages
safety
The electrohydraulic brake enables shorter braking distances by taking advantage of the dynamic axle load shift (electronic chassis ) and faster brake response.
Another advantage is that there is no pulsating reaction on the pedal with ABS control . Studies have shown that drivers who are shocked by the pulsating brake pedal often reduce the braking force and thus waste braking distance. This behavior can be prevented by using electro-hydraulic brakes.
disadvantage
In contrast to conventional braking systems, the system is dependent on electrical energy. Errors in the energy supply can lead to brake failure. The brake goes into emergency mode. The vehicle can then practically no longer be used.
Depending on certain parameters such as the number of braking processes, frequency of brake fluid changes, etc., the vehicle software calculates that the SBC pump could be defective and switches the vehicle to emergency mode if the unit is not replaced (€ 2200 as of 2015). The user cannot see when the exchange is due. But this is particularly important for the used vehicle market.
There are devices to reset the display of the need for renewal. However, this procedure is not recommended, as it makes the operational reliability of the system incalculable.
In the case of electrohydraulic brake systems, the automatic pad application routine must be deactivated before replacing wearing parts such as brake discs and brake pads. If this is not done, the system can automatically build up pressure during assembly and seriously injure the fitter.
Comfort
In addition to increased traffic safety, comfort functions can be implemented with electrohydraulic braking systems that are more difficult or impossible with conventional brakes. Above all, the Mercedes-Benz system called Sensotronic Brake Control (SBC) has extensive additional functions:
As soon as precipitation is detected, the SBC applies the brake pads to the brake disc at regular intervals in order to remove the film of water adhering to them and to brake the disc dry. In addition, the SBC applies the brake pads to the disc when the driver suddenly takes off the accelerator, in order to achieve the best possible deceleration in the event of an emergency braking.
In addition, the SBC system has two functions called SBC Hold and SBC Stop . The function of the SBC-Hold is to secure the vehicle against rolling away when the vehicle is stationary and the engine is running (for example, waiting at a traffic light) and to significantly simplify starting up on hills. It is enough to press the brake pedal hard once. It is automatically deactivated when accelerating or pressing the brake again with the same pedal travel. SBC-Stop is a stop-and-go assistant that is activated using the cruise control switch and automatically takes over braking up to a speed of 60 km / h. This happens with a constant, relatively strong delay and without the involvement of further sensors. SBC-Stop was only available in the E-Class (211 series) for just under two model years and was then removed without replacement.
Furthermore, an electro-hydraulic brake in electric or hybrid vehicles, for example the Toyota Prius , enables kinetic energy to be converted into electrical energy, which is fed into the accumulator instead of converting it into useless heat via the brake discs. The brake discs only apply the brakes in the event of severe decelerations or at low speeds.
use
The first electro-hydraulic brake for vehicles was introduced by the Japanese company Advics (a subsidiary of Toyota) in the Toyota Estima Hybrid in spring 2001. It was only available in the Japanese market.
The first electro-hydraulic brake available worldwide was developed by Robert Bosch GmbH together with DaimlerChrysler and presented to the public in September 2001 at the IAA in Frankfurt. It is used as Sensotronic Brake Control in Mercedes-Benz vehicles of the type SL (R 230), SLR (R 199), in the E-Class (W 211 / S 211) , in the Mercedes CLS (C 219) and in the Maybach 57 and 62 (W 240 / V 240) in action. As a special feature, the Maybach uses two units, so that two redundant brake circuits are available.
Due to faults in the electrohydraulic brake system, Mercedes-Benz had to recall around 680,000 E- and SL-Class vehicles in May 2004. Further difficulties with the system, initially dubbed the super brake, led in 2005 to one of the largest product recalls in automobile history. Worldwide, around 1.3 million E, CLS and SL Class Mercedes had to go to the workshop. With the facelift in 2006, Mercedes turned away from the SBC for the E-Class and the CLS-Class and returned to the conventional braking system. In the SL (R230) and Maybach vehicles, however, SBC continued to be installed until the series was discontinued.
In 2000, Continental Teves presented a test vehicle with a comparable system in a modified VW Golf that had a braking distance of 30 m from 100 km / h. This corresponds to a braking deceleration of 12.86 m s −2 - at that time 38.5 m braking distance and 10.02 m s −2 braking deceleration were common. In the USA , an electro-hydraulic brake system from Continental Teves has been in series production in the Ford Escape Hybrid since 2003 .
Toyota further developed the first generation of its electro-hydraulic brake (ECB) and presented the ECB II for the 2003/2004 model change in the Toyota Prius II. This technology has proven itself in the Prius II and no failures have been reported so far.
The Toyota subsidiary Lexus also uses the electro-hydraulic brake from Advics in the CT 200h , RX 400h, GS 450h, LS 460 and LS 600h .
Launch
April 2001 : ECB from Advics in the Toyota Estima Hybrid (Japan)
September 2001: SBC from Bosch in the Mercedes-Benz SL 500
2003 : EMS from Continental Teves in the Ford Escape Hybrid (USA)
December 2003: ECB II from Advics in the Toyota Prius II
See also
literature
- Hans-Rolf Reichel: Electronic brake systems. From ABS to brake-by-wire . Expert publishing house. 2001. ISBN 3-8169-2010-1 .