The value of OEM designed and validated automotive bearings for the aftermarket


Traditionally the global independent aftermarket for automotive repair parts is flooded with a wide range of more or less validated parts from a vast range of suppliers.

In many cases, the parts are not more than dimensional copies made from random materials by non-certified companies. On the other side of the spectrum we see parts that are virtually the same as the original parts validated by the carmakers as OEM (Original Equipment Manufacturing) and OES (Original Equipment Service) parts, but then supplied to the independent aftermarket as well.

The unique added value of OEM validated parts for the users, compared to ‘re-engineered’ or ‘copied’ parts is very often misunderstood or at least misjudged.

This paper intends to explain the background of the OEM validation process that is used by carmakers in cooperation with their selected suppliers to make sure that the parts are optimized for their specific application, from a cost, performance, quality and appearance point of view.

Designing, developing and validating a new component for a new car model
When a carmaker starts the development of a new car model it will typically ask a selected number of key suppliers to quote on the project. The project consists of the design and validation phase and, after SOP (Start of Production), the production phase.

After nomination of the supplier the development of the part is started which should finally result in the full validation, just before SOP. This trajectory is often called ‘from nomination until SOP’ and can take 2-4 years depending on the carmaker.

The design and development of a car component for a new application is an iterative process, where car maker and supplier engineers and manufacturing experts work closely together to improve the design in a step-by-step fashion.

If we take the example of the development of a new wheel bearing, during the process the parts are tested by the supplier in in-house bench tests, like: accelerated life tests, thermal shock tests, fatigue life tests, muddy water tests, desert sand test (the ‘Arizona dust test’ is notorious due to its penetrant particles, testing sealing and contamination design tolerance to the extreme), temperature cycle tests and corrosion tests.

In parallel the carmaker will test the wheel bearing in prototype cars used for in-house bench tests, test track tests and field tests like winter tests (extreme cold) and summer tests (extreme heat).

This whole validation process will lead to a fully optimized part, which will be suitable to perform its duty alongside the surrounding parts during the specified life (typically at least 240,000 km on a modern car). As all carmakers know, a careful validation is critical for the performance of the car in the field and early recalls are costly and detrimental to the image, something to be avoided at all times.

Case studies
As can be seen from these short case studies (all from the bearing industry), the interdisciplinary cooperation of engineers from both supplier as well as carmaker is essential to create optimised products for the specific application conditions that are expected in daily operation.

Clearly, from these case studies it can be understood that design ‘copies’ can lead to serious damage.

Case 1: Optimised chamfer on TRB for transmissionAfter testing a new transmission it appeared that an adjacent gear was insufficiently supported and showed too much deflection, ultimately leading to early failure. After analyzing together with the supplier, the solution was found in reducing the chamfer radius of the TRB cone side face, compared to the ‘catalogue design’ standard, resulting in sufficient contact/support area for the gear. In the repair market, often standard/catalogue design products are offered for repair, leading to problems in the repaired transmission in operation and ultimately leading to early failure. Using OEM validated parts is the only way to be assured of having the best ‘custom made’ and officially tested and validated parts for repair.

Case 2: Tensioner pulley with optimized mass/inertiaDuring the development of a new bearing pulley for an auxiliary belt tensioner it was recognized that the material and weight of the pulley is key for optimal operation of the whole belt system. To optimize the life of both the pulley as well as the whole belt system, it is essential that the components are not only optimized to attain the specified life, but are also optimized to minimize vibrations and resonance effects in the complete belt system. Typically PA66 or phenolic resin and a very specific pulley design are developed, by the engineers of both the supplier and carmaker, to reach the required specifications. What we can often see in the aftermarket are ‘copied’ parts that are made of different materials, even solid steel, which may result in early failure of the pulley and its surrounding parts.

Case 3: Wheel bearing with optimized sealing system

When a new wheel bearing is developed for a specific car model one of the challenges is to optimize the life of the bearing, by using an optimized sealing system to keep contamination out and the lubricating grease inside, while minimizing the friction to help improve fuel efficiency and CO2 emission. Both engineers from the supplier and the carmaker work closely together to test the seal in house and in the field, under all possible operational conditions, to make sure that all required specifications are met. Copied wheel bearings that we find in the aftermarket often lack the design sophistication that is required for an optimal performance, leading to early failure in the field.

Summary of case studies 
In the case of the tensioner pulley, the importance of proper plastic pulley design and the corresponding inertia of the system is demonstrated to avoid vibrations and resonance effects that would lead to early failure of the auxiliary or timing belt system. In the case of the taper roller bearing design for a transmission shaft, the critical chamfer of the TRB cup side face is described which should provide the optimal adjacent gear support, to avoid early failure. In the case of the seal for the wheel bearing hub unit, it is clearly explained that using wrong/imitation products can easily lead to early failure due to intrusion of contamination and/or bleeding out of lubricant.

Designing and developing a suitable automotive part is a meticulous multidisciplinary process involving both engineers and experts from the supplier as well as from the carmaker.

Copying the design for the aftermarket is not only about applying the same nominal dimensions, it is also about tolerances, material properties, surface treatment and proper mating parts. Therefore using OEM validated parts is the best warranty that they will perform according to the specifications required to assure the proper long lasting performance in the field.

Koyo bearings
Koyo Bearings, a division of JTEKT Corporation, is a major developer and supplier of automotive bearings to the global automotive industry OEMs and aftermarket. The large range of OEM validated parts that are offered to the aftermarket are actually the same parts, from the same production processes as the ones that are originally supplied to the carmaker (as OEM parts) or the carmaker dealer network (as OES parts). The only difference is the marking and the special individual packing for distribution to the independent aftermarket.

Should you be interested to learn more, please do not hesitate to contact: Edward Korver or Jaap ten Kate.