What is Rack and Pinion?- Definition and Application

What is Rack and Pinion?

A rack and pinion is a type of linear actuator that comprises a circular gear (the pinion) engaging a linear gear (the rack), which operates to translate rotational motion into linear motion. A rack and pinion drive can use both straight and helical gears.

Driving the pinion into rotation causes the rack to be driven linearly. Driving the rack linearly will cause the pinion to be driven into a rotation.

Helical gears are preferred due to their quieter operation and higher load-bearing capacity. The maximum force that can be transmitted in a rack and pinion mechanism is determined by the tooth pitch and the size of the pinion.

For example, in a rack railway, the rotation of a pinion mounted on a locomotive or railroad car engages a rack between the rails and helps move the train up a steep incline.

There is a base rack for every pair of conjugate involute profiles. This base rack is the profile of the conjugate gear with an infinite pitch radius. A generation rack is a rack outline used to indicate tooth details and dimensions for the construction of a generation tool, such as a hob or gear mill.

What Are Signs My Rack and Pinion Is Failing?

The rack and pinion, also known as the steering rack, is an assembly in your vehicle that allows your wheels to rotate from side to side when you turn your steering wheel. The rack and pinion got it’s from the type of gears used in the assembly.

A small pinion gear is connected to the steering wheel that connects with a long rack gear. Connected to both ends of the rack is a tie rod that connects the steering arm on the spindle. When you turn your steering wheel, it pushes the rack right or left.

The rack and pinion make it easier to turn your wheels and converts the rotating motion of your steering into the linear motion need to turn your wheels. So, what are signs that your rack and pinion is failing?

There are a few key signs that can help you identify issues with your rack and pinion. The first identifier is a power steering fluid leak. Your rack and pinion lie at the bottom of your car, so a steering fluid leak may not always be the rack and pinion, but it’s definitely worth looking into.

Steering fluid is powered hydraulically so you won’t lose fluid unless there is a leak somewhere in the system. Steering fluid has a burning oil smell and is typically pink or red in color. Look for these signifiers near your engine to spot any potential issues.

A steering wheel that is hard to turn, or very tight could be a sign that you’re having problems with your rack and pinion. If your gearbox builds up heat, or loses hydraulic pressure from lack of steering fluid, this can be another indicator.

Like other failing automotive parts, excess heat and lack of lubrication over time can cause you to hear a grinding noise while turning left or right. If you hear, see, or feel any of these symptoms, reach out to a trusted ASE certified mechanic for a diagnostic or inspection.

Application of rack and pinion

A rack and pinion are commonly found in the steering mechanism of cars or other wheeled, steered vehicles. Rack and pinion provide less mechanical advantage than other mechanisms such as recirculating ball, but less backlash and greater feedback, or steering “feel”.

Here are just a few of the common modern applications that regularly utilize rack and pinion gearsets:

  • Car steering: The system works by converting a revolving motion into linear motion. Most cars, small trucks, and SUVs come equipped with a rack and pinion system, rather than the recirculating ball steering found in larger trucks, larger SUVs, and other heavy-duty vehicles.
  • Railways: Rack railways are mountain railways that use a rack built into the center of the track and a pinion on their locomotives. This allows them to work on steep gradients, up to 45 degrees, as opposed to conventional railways which rely on friction alone for locomotion. Additionally, the rack and pinion addition provides these trains with controlled brakes and reduces the effects of snow or ice on the rails.
  • Stairlifts: Virtually all stairlifts contain a rack and pinion gear, with the gear allowing for upward movement in similar ways as above.
  • Actuators: Actuators are machines that move various components, such as a pipeline transport system. In such a system, a rack and pinion gear help control the valves that the system requires for basic functioning.