Auto Service World
Feature   November 1, 2008   by Auto Service World

Wheel Bearing Evolution

Knowledge Building: For the Counterperson; This illustration of a wheel hub bearing assembly from a 2003 Lincoln Navigator shows an integrated ABS tone wheel and sensor unit, two of the more key developments in wheel end technology.

With a design life that can often take them beyond the useful life of a vehicle, wheel bearings are not always top of mind among counterpeople — until a customer calls, that is, and they are reminded of how much has changed.

While one might be hard pressed to find a technician who remembers having to repack wheel bearings on a car, thinking back not all that many years ago, wheel bearings were cheap, easy to replace (which was good because it happened often), and not subject to all that much parts proliferation.

Percentage margins were pretty reasonable, too, even if they didn’t translate into much in the way of dollars per unit.

Then things started to get interesting as automakers and bearing manufacturers started developing bearing assemblies that integrated more and more functionality, and left less and less up to the technician.

Going back though, the original, simple bearing units (now referred to as Generation 1, or Gen 1) were just that: simply a bearing, using tapered roller or ball bearings. Pressed into a housing and lubricated “for life,” they provided a step up from the unsealed assemblies that required an annual, or semi-annual, grease application.

Gen 2 bearings, as a genuine hub assembly, were the first real step up. Again using ball bearings or tapered roller bearings, these units feature an integral wheel flange. The compact design enables the bearing to be easily fitted to a spindle or axle. The bearing units have preset internal clearance, are greased for life, and have integrated seals.

Two variations are available: one for driven-wheel applications in which the inner rings rotate and the outer ring does not, while for undriven wheels, where the unit supports the brake disc and wheel, the outer ring rotates while the inner rings are held in place.

There are also some Gen 2.1 assemblies, which are said to combine the economy of the Gen 1 design with the advantages of preset clearances as in an integrated hub unit, but using a snap ring to hold the bearing’s outer ring in place.

Gen 3 bearings bring the integration concept to a whole new level. With flanges for the brake disc, wheel, and steering knuckle, the technology allows for the highest possible running accuracy. They were developed as a response to the need to integrate a lower friction design, since fuel economy is on the minds of every automaker, as well as to house the wheel speed sensors (though Gen 2 units can also integrate ABS sensors).

One can surmise that this approach is the result of recognizing the downside of having ABS sensors and tone rings exposed to the elements, and the maintenance issues that have resulted.

A few variations to this approach have developed, however. While the original ABS setup used the Hall-effect sensors to detect the tone wheel’s rotation — a so-called “passive” approach — some sensors have become equipped with internal chips that allow them to detect extremely low wheel speeds.

Some of these “active sensors” have a bias magnet built in, and those that do use a conventional tone wheel. Active sensors without a bias magnet use a multipolar magnetized encoder, of which there are two types: axial and radial.

The advantage of this approach is that they can be integrated into smaller packaging.

Regardless of the specific applications, wheel bearing replacement has become a more costly venture for the car owner, as a result of both labour and parts cost factors.

While most jobbers certainly understand the need to provide quality parts to their customers, and can appreciate the need to be competitive from a price standpoint, on a number of occasions the issue of pricing has been raised in regards to bearings. This has generally been found to be the result of applying a standard margin to wheel bearings across an entire line.

In some cases, this has put jobbers in the embarrassing position of being out of step with their competition, which may have applied a lower percentage to the higher-priced units, focusing on dollar margin.

Which is only to say that it is important to ensure that your pricing matrix is providing the appropriate value to your customers, while still returning the necessary profitability to continue to provide the service they require.

While most passenger car applications use roller bearing units, heavier vehicles often require the additional stability provided by tapered roller bearings.

The downside of that approach is a higher rolling resistance, with consequent penalties in fuel mileage.

One bearing manufacturer says it may have a solution. FAG says its four-row angular contact ball bearing provides improved fuel usage figures worth taking note of.

Its four-row angular contact ball bearings — so-called “twin tandem” bearings — which replace the conventional tapered roller

bearings inside a vehicle’s wheel hub assembly are particularly suited for use in SUVs, light trucks, and delivery vans. Replacing tapered roller bearings with the twin tandem bearings on both axles can reduce fuel consumption by up to 1.5% in everyday driving, says the company, adding that this represents an important contribution toward improving fuel economy and reducing emissions.

In a twin tandem bearing, each of the rows of tapered rollers is replaced by two ball rows. This means that a double- row tapered roller bearing becomes a four-row ball bearing. Replacing the tapered rollers’ contact line with the balls’ contact points eliminates rib friction and reduces bearing friction by approximately 50%. This also means that the twin tandem bearing has a lower operating temperature, which significantly increases the service life of the bearings’ lubricants. Compared with the tapered roller bearing, cornering stiffness is also increased.

The company says that these bearings could be integrated into existing vehicle designs. The new wheel-hub assembly has been engineered to make replacement simple and straightforward, without having to change the existing installation space. All types of sensors (e. g., ABS) can be accommodated. Compared with conventional tapered roller-bearing hub units, installation inside the vehicle’s hub assembly remains unchanged.

In absolute terms, the savings put forth by the company are significant.

A vehicle driven 15,000 km per year generates 300 g of CO2 per kilometre. The twin tandem bearing will help reduce CO2 emissions by up to 67.5 kg over a year of driving. For a typical light truck travelling 15,000 km per year, fuel consumption drops by 1.5%, or 40 litres per year.

While that savings to the consumer of about $40 in fuel bills may seem relatively insignificant, when taken as a whole, the impact adds up. The company says that, globally, the bearing could be used in as many as seven million vehicles being produced annually. Projecting savings across this volume of vehicles results in a potential savings of as much as 280 million litres of fuel, and half a million tons of CO2.

All from a wheel bearing.

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