Bearings, in automotive applications, are rolling type elements that allow relative motion between two parts. Bearings are also used to provide radial and axial support.
Bearings consist of inner and outer races, balls, or rollers, and cages. The inner and outer races are rings with grooves that accommodate the balls fit to permit rotation. Cages are used to keep the balls separate and evenly spaced in the races, which ensures smooth movement with consistent torque, provides minimal friction and wear, and prevents jamming.
Bearings are subject to very high rotation speeds, so it is critical that they are designed with reliable, durable components, in order to minimize noise and vibration.
There are many types of bearings, each used for different purposes. In automotive applications, some of the most frequently used are ball bearings and tapered roller bearings:
- ball bearing - ball bearing units are very sensitive to torque loads, and great care must be taken when mounting them. The contact between the ball and the races occurs over a very small surface area, which allows the bearings to spin smoothly. If the bearing is overloaded, the excess pressure will deform the balls, causing bearing drag and uneven rotation, and can lead to bearing failure. Meeting proper torque specifications and using torque wrenches are essential to the proper mounting of a bearing.
- tapered roller bearings - tapered roller bearings can support large radial and axial loads. Pairs of tapered roller bearings are used in vehicles where they must cope simultaneously with large vertical (radial) and horizontal (axial) forces. In many applications, tapered roller bearings are used in back-to-back pairs so that axial forces can be supported equally in either direction. With a higher load-carrying capacity, roller bearings are ideal for non-driven front-wheel and rear-wheel applications.
Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers support the load, allowing the device to spin smoothly.
The bearings on a wheel end have to deal with two kinds of loading, radial and thrust (axial). The radial load comes from the weight of the car; the thrust load comes from the cornering forces when you go around a turn.