Parking pawl

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Interior of an automatic transmission, showing the toothed locking wheel and the pawl below it Pawl brake engaged.png
Interior of an automatic transmission, showing the toothed locking wheel and the pawl below it

A parking pawl is a device fitted to a motor vehicle's automatic transmission in order for it to lock up the transmission. It is engaged when the transmission shift lever selector is placed in the Park position, which is always the first position (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)) through SAE J915, [1] and in most other vehicles worldwide.

Motor vehicle self-propelled wheeled vehicle

A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-propelled vehicle, commonly wheeled, that does not operate on rails and is used for the transportation of people or cargo.

Automatic transmission type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves

An automatic transmission, also called auto, self-shifting transmission, n-speed automatic, or AT, is a type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually. Like other transmission systems on vehicles, it allows an internal combustion engine, best suited to run at a relatively high rotational speed, to provide a range of speed and torque outputs necessary for vehicular travel. The number of forward gear ratios is often expressed for manual transmissions as well.

Gear stick

A gear stick, gear lever, gearshift or shifter is a metal lever attached to the shift assembly in a manual transmission-equipped automobile and is used to change gears. In an automatic transmission-equipped vehicle, a similar device is known as a gear selector. A gear stick will normally be used to change gear whilst depressing the clutch pedal with the left foot to disengage the engine from the drivetrain and wheels. Automatic transmission vehicles, semi-automatic transmissions, and those with continuously variable transmission gearboxes do not require a clutch pedal.

Contents

Design and operation

The parking pawl locks the transmission's output shaft to the transmission casing by engaging a pawl (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. [2]

Pawl

A pawl is a mechanical component that engages with another component to prevent movement in one direction, or prevent movement altogether. It is a type of latch. It consists of a spring-loaded solid part that is pivoted at one end and engages the other component at a steep angle at the other end. Pawls are often tapered, being wide at the pivoting end and narrow at the engaging end.

Applicable standards

Recommendations

Most vehicle manufacturers [3] and auto mechanics [4] 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. Constant use of only the parking pawl, especially when parking on a steep incline, means that driveline 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.

Automotive industry Organizations involved with motor vehicles

The automotive industry is a wide range of companies and organizations involved in the design, development, manufacturing, marketing, and selling of motor vehicles. It is one of the world's largest economic sectors by revenue. The automotive industry does not include industries dedicated to the maintenance of automobiles following delivery to the end-user, such as automobile repair shops and motor fuel filling stations.

Parking brake secondary automotive braking system

In road vehicles, the parking brake, also called hand brake, emergency brake, or e-brake, is used to keep the vehicle stationary and in many cases also perform an emergency stop. Parking brakes on older vehicles often consist of a cable connected to two wheel brakes at one end and the other end to a pulling mechanism which is operated with the driver's hand or foot. The mechanism may be a hand-operated lever, at floor level beside the driver, or a straight pull handle located near the steering column, or a (foot-operated) pedal located beside the drivers leg. In most automobiles the parking brake operates only on the rear wheels, which have reduced traction while braking. Some automobiles have the parking brake operate on the front wheels, for example most Citroens manufactured since the end of World War II, and the early models of the Saab 900.

Powertrain system that powers a vehicle; main components that generate power, deliver it to the road surface, water, air;includes the engine, transmission, drive shafts, differentials, and the final drive

In a motor vehicle, the powertrain or powerplant comprises the main components that generate power and deliver it to the road surface, water, or air. This includes the engine, transmission, drive shafts, differentials, and the final drive. More recently in hybrid powertrains the battery, the electric motor and the control algorithm are also seen as elements of the powertrain.

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

Related Research Articles

Clutch machine element for rigid, elastic, movable or releasable connection of two shafts

A clutch is a mechanical device which engages and disengages power transmission especially from driving shaft to driven shaft.

Double clutching is a method of shifting gears used primarily for vehicles with an unsynchronized manual transmission, such as commercial trucks and specialty vehicles. While double clutching is not necessary in a vehicle that has a synchronized manual transmission, the technique can be advantageous for smoothly downshifting in order to accelerate, and when done correctly it prevents wear on the "synchros" which normally equalize transmission input and output speeds to allow downshifting.

Transmission (mechanics) machine in a power transmission system for controlled application of the power;gearbox,uses gears/gear trains to provide speed,torque conversions from a rotating power source to another device;reduces the higher engine speed to the slower wheel speed

A transmission is a machine in a power transmission system, which provides controlled application of the power. Often the term transmission refers simply to the gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device.

Manual transmission type of transmission used in motor vehicle applications

A manual transmission, also known as a manual gearbox, a standard transmission or colloquially in some countries as a stick shift, is a type of transmission used in motor vehicle applications. It uses a driver-operated clutch, usually engaged and disengaged by a foot pedal or hand lever, for regulating torque transfer from the engine to the transmission; and a gear selector that can be operated by hand or foot.

Freewheel

In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An overdrive is sometimes mistakenly called a freewheel, but is otherwise unrelated.

Transfer case

A transfer case is a part of the drivetrain of four-wheel-drive, all-wheel-drive, and other multiple powered axle vehicles. The transfer case transfers power from the transmission to the front and rear axles by means of drive shafts. It also synchronizes the difference between the rotation of the front and rear wheels, and may contain one or more sets of low range gears for off-road use.

A semi-automatic transmission is an automobile transmission that combines manual transmission and automatic transmission.

Hydramatic

Hydramatic is an automatic transmission developed by both General Motors' Cadillac and Oldsmobile divisions. Introduced in 1939 for the 1940 model year vehicles, the Hydramatic was the first mass-produced fully automatic transmission developed for passenger automobile use.

Ford-O-Matic was the first automatic transmission widely used by Ford Motor Company. It was designed by the Warner Gear division of Borg Warner Corporation and introduced in 1951 model year cars. In contrast to Detroit Gear Division's three band automatic originally designed for Studebaker which became superseded by this unit, a variation of Warner Gear's three-speed unit named Ford-O-Matic continued to evolve later into Cruise-O-Matic named transmissions in 1958 and finally the FMX named transmissions in 1968. This line continued in production until 1980, when the AOD was introduced. Like Ford, variations of this same Borg Warner design were used by other automobile manufacturers as well, such as AMC, International Harvester, Studebaker, Volvo and Jaguar, each of them having the necessary unique adaptations required for the individual applications.

Preselector gearbox

A preselector or self-changing gearbox is a type of manual gearbox used on a variety of vehicles, most commonly in the 1930s. The defining characteristic of a preselector gearbox is that the manual shift lever is used to "pre-select" the next gear to be used, then a separate control is used to engage this in one single operation, without needing to work a manual clutch.

The AXOD was a 4-speed automatic transaxle for transverse front wheel drive automobiles from the Ford Motor Company. It was introduced in the 1986 Ford Taurus/Mercury Sable. The AXOD and its successors are built in Ford's Van Dyke Transmission plant in Sterling Heights, Michigan. Production of the final member of the family, the 4F50N, ended in November 2006.

Clutch control refers to the act of controlling the speed of a vehicle with a manual transmission by partially engaging the clutch plate, using the clutch pedal instead of the accelerator pedal. The purpose of a clutch is in part to allow such control; in particular, a clutch provides transfer of torque between shafts spinning at different speeds. In the extreme, clutch control is used in performance driving, such as starting from a dead stop with the engine producing maximum torque at high RPM.

The following outline is provided as an overview of and topical guide to automobiles:

A non-synchronous transmission is a form of transmission based on gears that do not use synchronizing mechanisms. They are found primarily in various types of agricultural and commercial vehicles. Because the gear boxes are engineered without "cone and collar" synchronizing technology, the non-synchronous transmission type requires an understanding of gear range, torque, engine power, range selector, multi-functional clutch, and shifter functions. Engineered to pull tremendous loads, often equal to or exceeding 40 tons, some vehicles may also use a combination of transmissions for different mechanisms. An example would be a power take-off.

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 traditional mechanical system which involves linkages between the gear shifter and the transmission. The main components of a park by wire system include the driver interface which could be a lever, switch or knob as designed by the OEM (input), an electronic control unit to host the control system and actuators which are capable of driving the parking pawl into and out of the locking position with the parking gear of the transmission.

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.

References

  1. http://standards.sae.org/j915_196507/
  2. Jeyakumaran, Jeku; Zhang, Nong (2008). "Dynamic Analysis of an Automatic Transmission Parking Mechanism". University of Adelaide, Australia.(subscription required)
  3. "Chevy Cruze Owner's Manual" Archived 2013-12-20 at the Wayback Machine .. Chevrolet.com.
  4. "Driver's Ed Guru - Always set the parking brake". DriverSEdGuru.com