Pawl

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A ratchet and pawl mechanism Trinquete no watermark.png
A ratchet and pawl mechanism
A parking pawl in an automatic transmission Pawl brake (English).png
A parking pawl in an automatic transmission

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 lever that engages a mating component at a steep enough angle to restrain it. Pawls are often tapered, being widened at their pivot for anchoring and narrow at their tip.

Applications

Anchor windlass
A pawl is used in an anchor windlass to prevent a free-spooling chain by grabbing and snubbing an individual link. Similar mechanisms include a Devil's claw, or a claw and dog.
Ratchet
A pawl is used in combination with a ratchet gear in socket wrenches, bicycle freehubs, winches, and many other applications. [1] [2]
Ladder
Dogs (in the form of pawls) are used on extension ladders to temporarily anchor their sections to one-another. [3]
Table saw
Pawls are used on table saws to prevent a workpiece being sawn from kicking back. [4]
Transmission
A parking pawl is a device in an automobile automatic transmission which prevents it from moving when the vehicle is parked . [5]
Revolvers
The hand (pawl) indexes the cylinder.

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In engineering, a dog is a tool or part of a tool, such as a pawl, that prevents or imparts movement through physical engagement. It may hold another object in place by blocking it, clamping it, or otherwise obstructing its movement. Or it may couple various parts together so that they move in unison – the primary example of this being a flexible drive to mate two shafts in order to transmit torque. Some devices use dog clutches to lock together two spinning components. In a manual transmission, the dog clutches, or "dogs" lock the selected gear to the shaft it rotates on. Unless the dog is engaged, the gear will simply freewheel on the shaft.

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.

References

  1. Nitaigour Premcahnd Mahalik, Mechatronics: Principles, Concepts and Applications, p. 271, Tata McGraw-Hill Education, 2003 ISBN   0070483744.
  2. Richard Krolak, Cruising World, "Servicing your winches", April 1990, pp. 107-108
  3. International Association of Fire Chiefs, Fundamentals of Fire Fighter Skills, p. 363, Jones & Bartlett Publishers, 2012 ISBN   1449666507.
  4. Table Saw Techniques: Use Your Saw Like a Pro, p. 12, Quarto Publishing Group USA, 2003 ISBN   1610602951.
  5. Keith Santini, Kirk Vangelder, Automotive Automatic Transmissions and Transaxles, p. 174, Jones & Bartlett Learning, 2017 ISBN   1284122034.