![Handbrake lever](https://upload.wikimedia.org/wikipedia/commons/7/7c/Handbrake_lever.JPG)
In road vehicles, the parking brake, also known as a handbrake or emergency brake (e-brake), is a mechanism used to keep the vehicle securely motionless when parked. Parking
brake
A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.
Background ...
s often consist of a
cable
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
connected to two wheel brakes, which is then connected to a pulling mechanism. In most vehicles, the parking brake operates only on the rear wheels, which have reduced traction while braking. The mechanism may be a hand-operated
lever
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or ''fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is div ...
, a straight pull handle located near the steering column or a foot-operated
pedal
A pedal (from the Latin '' pes'' ''pedis'', "foot") is a lever designed to be operated by foot and may refer to:
Computers and other equipment
* Footmouse, a foot-operated computer mouse
* In medical transcription, a pedal is used to control p ...
located with the other pedals.
Overview
While most automatic transmission vehicles have parking brakes, it is often not engaged by American drivers when parking. However, it is recommended to use it, as the
parking pawl
A parking pawl is a device fitted to a motor vehicle's automatic transmission that locks up the transmission when the transmission shift lever selector is placed in the Park position. "Park" is the first position of the lever (topmost on a column ...
in the gearbox could fail due to stress or another vehicle striking the car, causing the car to roll. In
manual transmission
A manual transmission (MT), also known as manual gearbox, standard transmission (in Canada, the United Kingdom, and the United States), or stick shift (in the United States), is a multi-speed motor vehicle transmission (mechanics), transmission ...
vehicles, the parking brake can be engaged to help keep the vehicle stationary.
When parking on an uphill gradient, it is recommended that the front wheels face away from the
curb
A curb (North American English), or kerb (Commonwealth English except Canada; see spelling differences), is the edge where a raised sidewalk or road median/central reservation meets a street or other roadway.
History
Although curbs have ...
. This would prevent the car from rolling into the roadway by using the curb to block the front passenger tire in the event of a parking brake failure. Similarly, on a downhill gradient, the front wheels should face the curb for the same reason, and the wheels should face to the right on an uncurbed road regardless of orientation. In a manual transmission, leaving the car in first gear (or in reverse if pointing downhill) is also advised, as the
engine
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...
will prevent the car from rolling if the parking brake fails.
The parking brake in most vehicles is still completely mechanical. Traditionally engaged by pulling a lever, the cables manually engage part of the car's braking system, usually the rear disk or drum brakes. The mechanical nature allows the driver to apply the brake even if the main
hydraulic brake
A hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically containing glycol ethers or diethylene glycol, to transfer pressure from the controlling mechanism to the braking mechanism.
History
During 1904, Frederick ...
system fails.
Pictograph
A pictogram, also called a pictogramme, pictograph, or simply picto, and in computer usage an icon, is a graphic symbol that conveys its meaning through its pictorial resemblance to a physical object. Pictographs are often used in writing and gr ...
symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
s and/or lights may be used to indicate the location of a parking brake, its application or release.
Other uses
In manual and automatic transmission vehicles, the parking brake can also be used for various driving situations which require the vehicle to be momentarily stopped. For example, the brake can be engaged when moving off an uphill slope, as this allows the driver to hold the accelerator and
clutch pedals steady without the vehicle rolling backwards. Other common situations is when the vehicle is stopped at a
traffic light
Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order to control flows of traf ...
, a
pedestrian crossing
A pedestrian crossing (or crosswalk in American English) is a place designated for pedestrians to cross a road, street or avenue. The term "pedestrian crossing" is also used in the Vienna and Geneva Conventions, both of which pertain to road sig ...
, or simply waiting to turn in front of oncoming traffic. The parking brake would ensure the car is secure, should another vehicle come into physical contact from behind, causing the car to jolt forward. It is not recommended to use the parking brake when the vehicle is in-motion, unless there is a problem with the main brakes, as this can lock the back wheels and cause a skid. This is known as a
handbrake turn
The handbrake turn (also known as the bootlegger's turn) is a driving technique used to deliberately slide a car sideways, either for the purpose of quickly negotiating a very tight bend, or for turning around well within the vehicle's own turning ...
, which is often performed in
street racing
Street racing is typically an unsanctioned and illegal form of auto racing that occurs on a public road. Racing in the streets is considered an ancient hazard, as horse racing occurred on streets for centuries, and street racing in automobiles is ...
and off-road
rally racing
Rally or rallye may refer to:
Gatherings
* Demonstration (political), a political rally, a political demonstration of support or protest, march, or parade
* Pep rally
A pep rally or pep assembly is a gathering of people, typically students ...
to initiate rear wheel
drift
Drift or Drifts may refer to:
Geography
* Drift or ford (crossing) of a river
* Drift, Kentucky, unincorporated community in the United States
* In Cornwall, England:
** Drift, Cornwall, village
** Drift Reservoir, associated with the village
...
.
In the event of hydraulic brake failure, the parking brake can be used to slow a vehicle. In such cases, the lever should be slowly engaged to prevent locking up the wheels and reduce speed.
Parking brake variations
![B02 Parking brake indication](https://upload.wikimedia.org/wikipedia/commons/f/f2/B02_Parking_brake_indication.svg)
The position of the parking brake differs between vehicle models and manufacturers. However, a universal feature is either one or two of the warning lights which appear on the dashboard when the parking brake is engaged.
![B01 Brake failure](https://upload.wikimedia.org/wikipedia/commons/d/d8/B01_Brake_failure.svg)
Center or stick lever
The most common placement of the parking brake is in the
center console of the vehicle, in between the driver and front passenger seats. Operating the brake is performed by pulling the lever up (which is connected to a
ratchet
Ratchet may refer to:
Devices
* Ratchet (device), a mechanical device that allows movement in only one direction
* Ratchet, metonomic name for a socket wrench incorporating a ratcheting device
* Ratchet (instrument), a music instrument and a ...
) until there is tension. To disengage the brake, the button is held while simultaneously pulling the lever up to disengage the ratchet and then pushed all the way down with the button still held. In older vehicle models, a stick lever may be used instead which is located under the
instrument panel.
Pedal or pull handle
Some vehicles have the parking brake operated by a small foot pedal, located by the other pedals. Depressing the foot pedal would engage the brake and pressing it again will release it. A pull handle variation also exists; by pulling or releasing the handle, this engages and releases the parking brake, respectively. Many vehicles have a combination of the two; a pedal to engage the brake and a handle to release it.
Electronic
A recent development is the electronic parking brake, also known as an electric park brake. Introduced to the mainstream market in 2001, it was first used in the 2001
BMW 7 Series (E65)
The fourth generation of the BMW 7 Series consists of the BMW E65 and BMW E66 luxury cars. The E65/E66 was produced from 2001 to 2008 and is often collectively referred to as the E65. The E65 replaced the E38 7 Series and was produced with petro ...
. Two variations are available: In the more-traditional "cable-pulling" type, an electric motor simply pulls the parking brake cable on the push or pull of a button rather than a mechanical lever or pedal in the cabin.
A more complex unit (first seen on the 2003
Audi A8
The Audi A8 is a full-size luxury sedan manufactured and marketed by the German automaker Audi since 1994. Succeeding the Audi V8, and now in its fourth generation, the A8 has been offered with both front- or permanent all-wheel drive—and in s ...
) uses a computer-controlled motor attached to each of the two rear brake calipers referred to as the Motor on Caliper (MoC) system.
Many car manufacturers such as Jaguar, Land Rover, BMW, Renault, Subaru and Volkswagen sell models whereby the parking brake automatically engages when the vehicle is stopped and is released when the gas pedal is pressed, eliminating the need for the driver to operate a button. An extension of this system, known as hill-hold or hill-assist, prevents the vehicle from rolling back when moving-off on an uphill gradient.
Types of brakes
In vehicles with rear
disc brake
A disc brake is a type of brake that uses the calipers to squeeze pairs of pads against a disc or a "rotor" to create friction. This action slows the rotation of a shaft, such as a vehicle axle, either to reduce its rotational speed or to hol ...
s, the parking brake either actuates the disc calipers (with much less force) or a small drum brake housed within the hub assembly (the inner circumference of the disc is often used instead of a separate drum). This secondary drum parking brake is often referred to as a banksia brake. It is usually used in conjunction with rear disc brakes employing multi-piston calipers, as mechanically actuating these calipers is more difficult than single piston calipers.
Another less common setup for rear discs is the use of a separate, smaller, cable actuated caliper (such as the Wilwood MC4), which is used exclusively for the parking brake. This is sometimes used as an alternative to a separate drum parking brake when multi-piston main calipers are used.
Hudson automobiles used an unusual hybrid hydraulic-mechanical dual-brake system which operated the rear brakes through the otherwise conventional mechanical parking brake system when a failure of the hydraulic system allowed the pedal to travel beyond its normal limit.
A number of production vehicles, light and medium duty trucks, and motor homes have been made with a separate drum brake on the driveline; called a
transmission brake
A transmission brake or driveline parking brake is an inboard vehicle brake that is applied to the drivetrain rather than to the wheels.
Historically, some early cars used transmission brakes as the normal driving brake and often had wheel brake ...
. This has an advantage of being completely independent of other braking systems. This is effective when there are multiple driving axles, all driven wheels are braked at once.
A
line lock
A line lock is a device that allows the front brakes to lock independently of the rear brakes via a switch. The device is an electric solenoid that controls a valve which allows the brakes to be controlled individually. This allows the front brak ...
is a temporary parking brake that makes use of the vehicles standard hydraulic brakes. They are often used for off road conditions or when stopping on steep grades is required. By trapping hydraulic pressure in the brake lines, all four wheels can be locked.
Large vehicles
Large vehicles are usually fitted with power operated or power assisted parking brakes. Power assisted parking brakes are usually found on large vans as well as some older heavy vehicles. These operate in the same way as a conventional parking brakes, but pulling the lever operates a valve that allows air or hydraulic pressure or vacuum into a cylinder which applies force to the brake shoes and makes applying the parking brake easier. When releasing the parking brake, 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 parking brakes are fitted to heavy commercial vehicles with air brakes, such as trucks and buses. These are usually 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 relatively safe since if air pressure is lost the springs will apply the brakes. Also, the system prevents the parking brake being released if there is insufficient air pressure to apply the foot brake. A disadvantage to this system is that if a vehicle requires towing and cannot 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.
Railroad hand brakes
Virtually all
railroad
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
rolling stock
The term rolling stock in the rail transport industry refers to railway vehicles, including both powered and unpowered vehicles: for example, locomotives, freight and passenger cars (or coaches), and non-revenue cars. Passenger vehicles can b ...
is equipped with manually operated mechanical hand brake devices that set and release the brakes. Most of these involve a chain linked to the brake rigging, most often at the brake cylinder, that when tightened pull the piston out against the releasing springs, thus applying the brakes on the car (if there is only one brake cylinder per car) or
bogie
A bogie ( ) (in some senses called a truck in North American English) is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transp ...
(if there is more than one cylinder per car). Newer locomotives have electric systems that simply place an electric motor in place of the chain winding mechanism. This brake acts independently of the action of the
automatic air brakes, which function collectively when coupled in a
train
In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and Passenger train, transport people or Rail freight transport, freight. Trains are typically pul ...
and are under the control of the locomotive driver / engineer.
Manual hand brakes serve to keep a piece of rolling stock stationary after it has been spotted in a rail yard or at a customer for unloading or loading. They are also used to secure a parked train from inadvertent movement, especially while unmanned.
Before the development of
locomotive-actuated train braking systems in the late 19th century, designated railroad employees known as
brakemen would move about the tops of cars, setting hand brakes in an effort to stop the train in a timely manner. This process was imprecise and extremely dangerous. Many brakemen lost life and limb as a result of falling from a moving train, icy and wet conditions often adding to the hazards involved in negotiating the top of a swaying
boxcar
A boxcar is the North American ( AAR) term for a railroad car that is enclosed and generally used to carry freight. The boxcar, while not the simplest freight car design, is considered one of the most versatile since it can carry most ...
. In the U.S., an 1893 federal law, the
Railroad Safety Appliance Act, required automatic brakes on all railroads, effective in 1900.
[United States. Act of Mar. 2, 1893, , recodified, as amended, .]
See also
*
Handbrake turn
The handbrake turn (also known as the bootlegger's turn) is a driving technique used to deliberately slide a car sideways, either for the purpose of quickly negotiating a very tight bend, or for turning around well within the vehicle's own turning ...
*
Johnson bar (vehicle)
A Johnson bar is a hand lever with several distinct positions and a positive latch to hold the lever in the selected position. The latch is typically activated with a spring-loaded squeeze handle on the lever so that only one hand is needed to rel ...
Notes
External links
* Family Car Parts
"A Short Course on Brakes: Parking."
{{Railway brakes
Vehicle braking technologies