Motorcars.in

Hand Brake or Parking Brake  |  Discussion forums Glossary of motoring terms

 

Hand Brake (also known as the emergency brake, e-brake, park brake, or parking brake) is a supplementary system that can be used if the vehicle's primary brake system (usually hydraulic brakes) has a failure. Automobile e-brakes usually consist of a cable (usually adjustable for length) directly connected to the brake mechanism on one end and to some type of lever that can be actuated by the driver on the other end. The lever is traditionally and more commonly a hand-operated system (hence the hand brake name), the most common configuration being a handle on the floor between the driver and front passenger, and less commonly being a handle bar located on the lower portion of the dashboard somewhere close to the steering wheel column. Alternatively, the lever can also be foot-operated, in form of a pedal in the foot well in front of the driver, located to the far left apart from the other pedals.

However, the most common use for an automobile emergency brake is to keep the vehicle motionless when it is parked, thus the alternative name, parking brake. Car emergency brakes have a ratchet locking mechanism that will keep them engaged until a release button is pressed. On vehicles with automatic transmissions, this is usually used in concert with a parking pawl in the transmission. Automotive safety experts recommend the use of both systems to immobilize a parked car, though many individuals use only the "Park" position on the automatic transmission and not the parking brake. Also, manual transmission cars are recommended to be left in in their lowest gear (usually either first or reverse) when parked, especially when parked on an incline. It should be noted, however, that increasing vehicle moving resistance may increase damage in the event of a crash - less momentum can be gained through the car rolling and hence more energy is transferred to the disfigurement of the crashed vehicles.

Types of Brakes

While both hand-operated systems and foot-operated system serve for parking brakes, the hand-operated systems are more useful in other situations. Hand-operated brake can be used for assistance in starting on steep inclines in manual transmission cars, which is more difficult with the foot-operated parking brake. In addition, with the centrally placed handle (but not the dashboard-mounted type handle), the brake can be easily activated either by the driver or passenger (if the driver were to become unconscious, for instance) in case of an emergency. The centrally placed handle is also preferred for initiating handbrake turns, as the release button can be held down to prevent the brake from latching; this is very difficult with the foot pedal operated configuration.

Foot pedal parking brake is traditionally mostly found in American cars, since many American cars came with front-row bench seats, making a central handle impossible. Whereas, non-American cars predominantly came with front bucket seats, and so they were equipped with a lever between the seats. Non-American cars, when equipped with front bench seat, usually had the dashboard-mounted handle.

School buses which are equipped with a hydraulic brake system will have a hand brake lever to the left of the driver near the floor. It is operated by pushing the lever down with one's hand to apply the brake, and pushing it upwards to release it. However, this has been known to cause severe back problems in drivers who do this regularly, and many choose to push it up with their feet.

A parking brake cable which is unused for a long period of time may rust and seize, so that the brake will not be able to be actuated when it is eventually desired to do so. Conversely, in cold climates, a parking brake which is applied when there is some amount of water in the cable housing or in the mechanism may freeze when left for several hours, particularly overnight when temperatures drop, immobilizing the car when it is desired to restart it. It is recommended for this reason that when conditions are such as to make this a possibility, the parking brake be only partially applied, as it is relatively easy to break free of the ice by pulling the lever or pressing the pedal further, then releasing the brake, whereas the return/release spring does not have enough strength to do so by itself and there is no way to aid it in the release direction.

Historically, some cars with automatic transmissions were fitted with automatically releasing parking brakes. The parking brake would be released if the gear selector was placed in a forward or reverse gear. This automatic release system was eventually discontinued as a safety hazard, since there would be no protection against accidentally knocking the transmission into gear. Worse still, many North American-market Ford Motor Company cars from the late 1960s had a flaw in which, when the steering-column mounted shifter's bearings wore, the car could jump into reverse from park on its own. This and automatically releasing parking brakes were a deadly combination.

In cars with rear drum brakes, the emergency brake typically uses the same mechanism. In cars with rear disc brakes, the emergency brake most often actuates the same system, but sometimes (in the Mazda RX-5 and its twin the Cosmo, for instance) actuates a small drum brake housed within the hub assembly.

A number of production vehicles have been made with a separate drum brake on the transmission tailshaft. This has an advantage of being completely independent of other braking systems. As long as the drive train is intact (propeller shaft, differential, and axle shafts) this is effective. It is however, particularly dangerous when used in combination with a bumper jack at the rear of the vehicle if wheel block wedges are not used; jacking one rear wheel up will allow the differential to operate and the vehicle can roll off of the jack. This can be particularly dangerous if the wheel has been removed.

New System: Electric Parking Brake

A recent variation is the electric parking brake. First installed in the 2003 Lincoln LS, electric brakes have since appeared in a number of vehicles, including the Audi A6 and A8, BMW 7 Series, Jaguar S-Type and XJ, and the 2006 Volkswagen Passat.

Two variations are available: In the more-primitive 'cable-pulling' type, an electric motor simply pulls the emergency brake cable rather than a mechanical handle in the cabin. A more advanced unit uses a computer-controlled motor attached to the brake caliper to activate it.

It is expected that these systems will incorporate other features in the future. BMW already has a system where the emergency brake initiates when the car stops and then goes off as soon as the gas pedal is pressed preventing the car from drifting. The vehicle operator can easily turn off the system.
 






Above text originally from wikipedia.org  This text is available under GPL.

Free Java Guide      Birding in India      Haryana Online      North India Online

Motorcars.in
Copyright motorcars.in 2006-2009