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A parking pawl is a device fitted to a
"Driver's Ed Guru - Always set the parking brake"
DriverSEdGuru.com do not recommend using the transmission's parking pawl as the sole means of securing a parked vehicle, instead recommending it should only be engaged ''after'' first applying the vehicle's
Automatic transmission parking pawl for the 2004 Subaru Impreza
Design Requirements for Parking Pawl
Video of Parking Pawl in an automatic transmission
A parking pawl is a device fitted to a motor vehicle
A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-propelled land vehicle, commonly wheeled, that does not operate on rails (such as trains or trams) and is used for the transportation of people or cargo.
The ...
's automatic transmission
An automatic transmission (sometimes abbreviated to auto or AT) is a multi-speed transmission used in internal combustion engine-based motor vehicles that does not require any input from the driver to change forward gears under normal driving ...
that locks up the transmission
Transmission may refer to:
Medicine, science and technology
* Power transmission
** Electric power transmission
** Propulsion transmission, technology allowing controlled application of power
*** Automatic transmission
*** Manual 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 shift, frontmost on a floor shift) in all cars sold in the United States since 1965 (when the order was standardised by the ''Society of Automotive Engineers
SAE International, formerly named the Society of Automotive Engineers, is a United States-based, globally active professional association and standards developing organization for engineering professionals in various industries. SAE Internatio ...
'' (SAE)) through ''SAE J915'', and in most other vehicles worldwide.
Design and operation
The parking pawl locks the transmission's ''output shaft'' to the transmission casing by engaging a ''pawl
A pawl is a movable lever that engages a fixed component to either prevent movement in one direction or restrain it altogether. As such, it is a type of latch and can also be considered a type of dog. It typically consists of a spring-loaded ...
'' (a pin) that engages in a notched wheel on the shaft, stopping it (and thus the driven wheels) from rotating. The main components of a parking pawl mechanism are the parking gear, parking pawl, actuator rod, cam collar, cam plate, pivot pin, and parking pawl return spring. The mechanism assembly is designed so that the parking pawl tooth collides and overrides the parking gear teeth (ratchets) until a safe engagement speed for the vehicle is reached. Software controls are put in place to avoid this condition and engage the pawl only when the vehicle has come to a standstill.
Applicable standards
*FMVSS 114 – Theft Protection and Rollaway Prevention, Keyless Ignition Systems *SAE J2208 – Park Standard for Automatic Transmissions.Recommendations
Most vehicle manufacturers and auto mechanicsDriverSEdGuru.com do not recommend using the transmission's parking pawl as the sole means of securing a parked vehicle, instead recommending it should only be engaged ''after'' first applying the vehicle's
parking brake
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 brakes often consist of a cable connected to two wheel brakes, which i ...
. Constant use of only the parking pawl, especially when parking on a steep incline, means that driveline
A drivetrain (also frequently spelled as drive train or sometimes drive-train) is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the drivetrain is the components o ...
components, and transmission internals, are kept constantly under stress, and can cause wear and eventual failure of the parking pawl or transmission linkage. The pawl might also fail or break if the vehicle is pushed with sufficient force if the parking brake is not firmly engaged. Replacement can be an expensive operation since it not only requires removing the transmission from the vehicle, but it's usually the first component to be installed in the gearbox case during a complete rebuild.
It is highly inadvisable to use the parking pawl to stop a vehicle in motion. Modern parking pawls are connected to a safety mechanism that prevents the pawl from engaging unless the vehicle is stopped first. The pawl mechanism is generally not strong enough to stop a vehicle in motion if it engages at all. Under that much stress, the pawl may simply break off in the transmission, leading to costly repairs.
See also
* Electronic parking brake *Park by wire
A park by wire system engages the parking pawl of a transmission using electrical means. This can also be considered as part of a shift by wire system whose objective is to put the vehicle in Park, Reverse, Neutral and Drive modes without the tr ...
* 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 brak ...
External links
Automatic transmission parking pawl for the 2004 Subaru Impreza
Design Requirements for Parking Pawl
Video of Parking Pawl in an automatic transmission
References
{{DEFAULTSORT:Parking pawl Automotive transmission technologies Vehicle braking technologies