The wheel bearings of a moving vehicle (car, truck, Railway Locomotive will have a complex set of forces with varying load conditions. If the object is moving in a straight line then the load will be purely radial and if the object is taking a turn then a combination of Radial and Axial loads will be there. In additional to this, the shock loads and vibrations due to various factors such as irregularities or poor conditions on the road (or railway way tracks for rail applications) will create shock load and vibrations. Also, there will be situation of high contamination like dust, salt, etc., and also the chances of water ingress in the bearing during the rainy season. not only this, the vehicle will run under different temperature conditions also like during the winter season or summer season.
Considering all the above factors, the bearings of vehicles have to be able to survive for reliability to avoid can kind of sudden failures, accidents, and also commercial warranty issues for OEMs. Also, vehicles (automobile and railway locomotives) are mass-produced so the assembly process of the bearing should be simple, fast, and reliable. It has been observed that more than 70% of the bearings fail due to poor fitment, poor lubrication, and/or contamination. In this article, we will discuss how the bearings used in modern Automobile and Railway Wheel Applications are different than the general machinery bearings and how the design of those bearings has evolved over the years for high speed, ease of assembly, and reliability factors.
Automobile Wheel Bearings
Earlier the Angular-contact ball bearings for automobile wheels were used to be individual bearings mounted in duplex sets. On assembly in the vehicle, these had to be adjusted to eliminate the bearing endplay. The same was true for tapered roller, and truck wheel bearing sets. To exclude contaminants from the bearings, external seals were required. The bearings were grease lubricated and, owing to the grease deterioration in this difficult application, needed to be regreased periodically. If this was not accomplished with care, inevitably contamination was introduced into the bearings and their longevity was substantially curtailed.
To overcome this situation, many bearings were provided as pre-adjusted, greased, and sealed for-life duplex sets. These units needed to be press-fitted into the wheel hubs. Further, To simplify the assembly for the automobile manufacturer and to minimize size, a flange was made integral with the outer ring of the bearing, thus, the unit could be bolted to studs on the wheel. Subsequently, a self-contained unit with a flange integral with each ring came into use; the unit can be bolted to the vehicle frame and the wheel for simple assembly. For heavier-duty, vehicles such as trucks, tapered roller bearings are used instead of ball bearings.
Further, with the advancement of electronics for automobiles, the compact, pre-adjusted, self-contained bearing unit is equipped with an integral speed sensor to provide a signal to the antilock braking system (ABS). Sensors are also placed in rolling bearings to measure the loading applied.
