Hand brake

In cars, the hand brake (also known as the emergency brake, e-brake, park brake, slide stick or parking brake) is a latching brake usually used to keep the car stationary. 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 or between the driver and his or her door. Alternatively, the lever can be located to the left of the driver or foot-operated, in the form of a pedal in the foot well in front of the driver, located to the far left apart from the other pedals.

Although sometimes known as an emergency brake, using it in any emergency where the footbrake is still operational is likely to badly upset the brake balance of the car and vastly increase the likelihood of loss of control of the vehicle, for example by initiating a rear-wheel skid. Additionally, the stopping force provided by using the handbrake instead of or in addition to the footbrake is usually small and would not significantly aid in stopping the vehicle, again because it usually operates on the rear wheels which suffer reduced traction compared to the fronts while braking. The emergency brake is instead intended for use in case of mechanical failure where the regular footbrake is inoperable or compromised, hopefully with opportunity to apply the brake in a controlled manner to bring the vehicle to a safe, if gentle halt before seeking service assistance. Modern brake systems are typically very reliable and engineered with failsafe (e.g. dual-circuit hydraulics) and failure-warning (e.g. low brake fluid sensor) systems, meaning the handbrake is no longer often called on for its original purpose.

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, and the use of two systems is required by law in some jurisdictions, yet 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 their lowest gear (usually either first or reverse) when parked, especially when parked on an incline.

A "Hand Brake Machine" however is not used for cars but is a manually operated device that uses leverage to bend sheet metal.

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. On the other hand, the location close to the driver's door greatly increases the possibility of stopping an unoccupied rolling car. The floor handle in either location 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, but not a left-side handle, impossible. Whereas, non-American cars predominantly came with front bucket seats, and so they were often equipped with a lever between the seats. Non-American cars, when equipped with front bench seat, usually had the dashboard-mounted handle, although this was also found in some American cars.

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 regularlyFact|date=August 2008, 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. Also, 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.

Some cars with automatic transmissions are fitted with automatically releasing parking brakes. Later models require the foot brake to be depressed before the car's transmission can be moved from park. When reverse or drive is selected, the parking brake automatically releases. Earlier models would release the parking brake when the gear selector was placed in a forward or reverse gear without requiring any input on the brake pedal at all. These earlier automatic release systems were 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 by 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 cable usually actuates these drums mechanically with much less force than is available through the hydraulic system. In cars with rear disc brakes, the emergency brake either actuates the disc calipers (again, with much less force) or 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.

Large vehicles

Large vehicles are usually fitted with power operated or power assisted handbrakes.Power assisted handbrakes are usually found on large vans as well as some older heavy vehicles. These operate in the same way as a conventional handbrake, but pulling the lever will operate a valve that allows air or hydraulic pressure or vacuum into a cylinder which applies force to the brake shoes and makes applying the handbrake easier. When releasing the handbrake, the same mechanism also provides assistance to the driver in disengaging the ratchet. Particularly on commercial vehicles with air operated brakes, this has the added benefit of making it much harder or even impossible to release the parking brake when insufficient air pressure is available to operate the brakes. A reservoir or accumulator is usually provided so a limited amount of power assistance is available with the engine off.Power operated handbrakes are fitted to heavy commercial vehicles with air brakes, such as trucks and buses. These usually are spring applied, with air pressure being used to hold the brake off and powerful springs holding the brakes on. In most cases, a small lever in the cab is connected to a valve which can admit air to the parking brake cylinders to release the parking brake, or release the air to apply the brake. On some modern vehicles the valve is operated electrically from a lever or button in the cab. The system is failsafe since if air pressure is lost the springs will apply the brakes. Also, the system prevents the parking brake being released if their is insufficient air pressure to apply the foot brake. A disadvantage to this system is that if a vehicle requires towing and can not provide its own air supply, an external supply must be provided to allow the parking brake to be released, or the brake shoes must be manually wound off against the springs.

New system: electric parking brake

A recent variation is the electric parking brake. First installed in the 2001 Renault Vel Satis, electric brakes have since appeared in a number of vehicles, including the Audi A6 and A8, the2002 BMW 7 Series, Lincoln LS, Jaguar S-Type, XF and XJ, Renault Scénic, Espace and Laguna II.phase II 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, Renault and VW already have 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 rolling. The vehicle operator can easily turn off the system.

Jacking

It is important to know which wheels are providing the braking action when lifting the car with a jack. Typically the rear wheels are the ones that are stopped with parking brakes. The Saab 99s, Pre-Facelift 900's, the Citroen Xantia and most early Subarus applied the handbrake force to the front wheels, which makes them notable exceptions. If one lifts the braking wheels off the ground then the car can move and fall off the jack. This is why makers recommend that jacking be conducted on level ground and with the wheels that are not being raised chocked.

ee also

* Handbrake turn

References

* [http://www.familycar.com/brakes.htm#Parking%20Brakes "A Short Course on Brakes: Parking"]
* [http://www.wisegeek.com/is-a-parking-brake-the-same-as-an-emergency-brake.htm"Is a Parking Brake the Same as an Emergency Brake?"]