A parking brake is a brake that permanently blocks the wheels of a vehicle or an airplane . With it, the vehicle or airplane can be parked without it rolling away unintentionally. The parking brake of passenger cars is mostly operated as a cable brake with a hand or foot lever ( foot parking brake ), more recently also as an electrically operated parking brake . Cable pulls or servo-hydraulic systems are also used in aviation.
Prescribed requirements for a parking brake
The parking brake must be independent of the service brake . The mechanical parts located directly in front of the friction surfaces - in the case of spring-loaded brakes also the spring-loaded cylinders - can, however, be used together if they are strong enough. In Europe, the parking brake must at least act on all wheels on an axle . If the parking brake is also used as an auxiliary brake , it must make it possible to bring the vehicle to a stop if the service brake fails . The effect must be gradable. The auxiliary and parking brake can be combined in one device. The correct functioning of the parking brake in motor vehicles is checked on the brake test bench.
The parking brake in motorsport
In rally sport and autocross, the parking brake often has the additional task of bringing the vehicle into extreme drift angles (i.e. to oversteer) in order to avoid particularly tight or road-related difficult U and S curves laterally over the two outer wheels (which are at have no more traction during this process ). The property of the immediate locking of the braked rear wheels is used to make the car break away. This technique is called "side-turn" or "e-braking" . To make this process easier, rally and autocross vehicles usually have a particularly long parking brake lever that is almost vertical and close to the steering wheel.
Since a standard parking brake is usually only designed to be operated when the vehicle is stationary, its braking effect is too low for motorsport. Hydraulic parking brakes are therefore used, which use the brake circuit of the service brake to enable stable actuation while driving.
The electromechanical parking brake (EMF)
The electromechanical parking brake , also known as Electric Park Brake (EPB), replaces the conventional handbrake or foot-operated parking brake and is operated using a button on the dashboard or the center console. It works independently of the service brake so that in an emergency situation, emergency braking can be carried out to a standstill by pressing a button. It was first used in 2001 in the BMW 7-series (E65) .
At the same time, the automotive supplier Küster Automotive Control Systems GmbH based in Ehringshausen, Hesse, developed a system for Renault , abbreviated to AFB Frein de Parking Automatique , or EFB Electric Parking Brake , which premiered in the Renault Vel Satis and has since been used in other Renault models. The brake is applied both when the vehicle is stationary and the engine is stopped and automatically released when the vehicle is started; however, it can also be operated manually.
In addition to locking the vehicle and the emergency braking function, the electromechanical parking brake also enables the following additional functions:
- Auto Hold prevents the vehicle from rolling unintentionally by pressing a button once after the engine has started, for example when stopping at traffic lights by automatically applying the brakes or, in the case of Mercedes-Benz, by quickly "depressing" the brake pedal when the vehicle is stationary
- Hill Hold prevents the vehicle from rolling back when starting up an incline by automatically locking it
- Automatic parking brake function when the engine is switched off (e.g. on Jaguar , Citroën C5 and Lancia Thesis )
- Automatic hold-open function when the driver's door is opened and the engine is running (Lancia Thesis, Volkswagen Golf 7)
In any case, the brake is automatically released when moving off as soon as sufficient engine power is available to prevent the vehicle from rolling back.
When the engine is running, the braking processes are carried out hydraulically via the ESP pump or electromechanically, depending on the manufacturer . When changing the brake lining, the brake must first be opened using the respective button so that the brake caliper can be opened and the change can be carried out.
Additional security when parking
When parking a car with a manual transmission, not only should the parking brake be applied, but a gear should also be engaged, which further reduces the risk of rolling away. When going downhill, you should use the lowest possible gear or reverse gear - otherwise, insurance companies are not obliged to pay for damage to the car if the wrong gear or no gear was engaged. This also applies to the reverse case - i.e. if only one gear was engaged and the handbrake was not used. In cars with automatic transmissions, ideally you first apply the handbrake, move the selector lever to "N" (neutral = idle) and release the foot brake pedal so that the vehicle can "sit down" with the handbrake on - then you put the on the selector lever Parking lock ("P"), which cannot jam due to this sequence of procedures in such a way that a later release requires an uncomfortably high expenditure of force on the selector lever. Furthermore, in all cases when parking on sloping terrain, the front wheels should point away from the path or from the road to the curb so that the vehicle does not roll downhill in the event of a technical defect.
Additional function of the symbol
The symbol for the handbrake lights up on the one hand when the handbrake is applied, and on the other hand it lights up permanently if there are errors in the main brake system. In the simplest case, only the lid on the compensation tank for the brake fluid is not properly closed, since the sensor for the fluid level is often located here. Otherwise another fault has occurred in the braking system. Caution is advised here, as it is to be expected that the full braking force or no braking force at all will be available! The vehicle should be towed or, if it is unavoidable to continue driving, it should be driven immediately to the nearest workshop at low speed.
The parking brake, which can be operated from the vehicle or from the ground, is suitable for securing against escaping from parked railroad cars . It can be designed as an operable handwheel or as a spring-loaded brake and acts directly (mechanically) on the vehicle's brake pads .
See also section Mechanical brake in the article Brake (railway)
In order to secure the aircraft, a secondary control system, similar to a motor vehicle, causes the active braking system to apply the brakes. Depending on their size and age, these are cable pulls (smaller or older aircraft) or servo-hydraulic systems in which actuators apply the brakes.
In contrast to most motor vehicles, the parking brake of an aircraft is stronger than the drive and can therefore also be used to bring relatively slow-reacting engines to maximum thrust, without wasting valuable runway length by cautious taxiing. Due to the high forces, the high center of gravity of an aircraft and the abrupt roll-up, this type of take-off puts increased stress on the entire landing gear. In commercial aircraft, the pedal brake is used - if at all - for the run up , as it can be released more gently. In addition, it is also released before the starting power is reached.
- Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition. Friedr. Vieweg & Sohn Verlag, Wiesbaden 2003, ISBN 3-528-23876-3 .
- Hans-Hermann Braess, Ulrich Seiffert: Vieweg manual automotive technology. 2nd Edition. Friedrich Vieweg & Sohn Verlagsgesellschaft, Braunschweig / Wiesbaden 2001, ISBN 3-528-13114-4 .
- Bert Breuer, Karlheinz H. Bill (Ed.): Brake manual: Basics, components, systems, driving dynamics. 3. Edition. Vieweg & Teubner, 2006, ISBN 3-8348-0064-3 .
- ↑ K-Sport Germany: Hydraulic handbrake. Retrieved April 3, 2017 .
- ↑ Brake manual, chap. 14th