Automotive Exterior

Self Lubricating Bearings For Automotive Exterior Designs

Bearings for automotive doors and closures

The exterior of a car has numerous opening and closures that rely on bearings that can withstand high load, high usage and tight tolerances.

In vehicles bearings are used in every pivot point and for every type of exterior hinge; forged stamped and profile door hinges, trunk hinges, door handles or sliding door mechanisms (the list could go on). What unites all these hinges is the combined requirement of performance longevity and functionality.

Across the whole vehicle new developments are constantly being introduced to improve the experience for the driver and passenger(s). For the car exterior, powered doors are starting to become the norm which introduces a new requirement of torque overload protection.

Existing challenges

The existing challenges of corrosion, weight reduction, paint defects and minimizing NVH continue to present themselves. The growth of electric cars has accelerated or re-prioritized some of these challenges and automotive suppliers, like Saint-Gobain Bearings, are continuously developing new products and materials to overcome these challenges. A good example here is the charger cap on electric vehicles (EV’s). Depending on their range EV’s generally need to be charged more regularly that combustion engines need refueling. The charger cap hinge will have to withstand more open/close cycles throughout the lifetime of the vehicle, the impact of this will need to be factored in by EV engineers and may influence the choice of hinge material or type.

Corrosion

Corrosion can occur for a number of reasons: galvanic or contact corrosion, movement and environmental exposure to name a few influencing factors.

OEM’s are unrelenting in their demands to reduce corrosion. Red rust is the primary focus but the prevention of white rust is also a concern. The continual exposure to everyday dirt, debris and the weather all have an impact on the life span of hinge systems.

Industry standard tests have been introduced to tackle corrosion and demonstrate high corrosion resistance. At a component level, which includes a single bearing, the Salt Spray test (ISO 9227) is one standard. Depending on the hinge type and position this test can last for 720 hours or more proving the hinge’s resistance to corrosion.

To prevent galvanic corrosion components need to be designed to work together. The mating components of the hinge system; the shaft, housing, bearing and type of plating (bronze and graphite are known drivers of galvanic corrosion when in contact with (coated) steel) will need to be harmonized to achieve optimum performance and reduce contact corrosion. The other cause of corrosion is movement. Pivot points are known to have the weakest resistance. This is due to the permanent movement and unavoidable gaps between the components in the hinge system. Here, the choice of bearing and bearing materials can play a huge role in the prevention of corrosion.

Weight Reduction

It’s simple maths – the heavier a vehicle the more power it consumes. Lightweight design is an important factor for any car manufacturer and crucial for efficiency. If cars consume less power they will be more environmentally friendly. Car manufacturers have to meet sustainability targets and customer expectations. An environmentally friendly car is a marketing advantage but it is only achieved through engineering solutions.

Bearings from Saint-Gobain offer weight saving and design freedom. With a full bandwidth of differential material solutions and load capabilities the hinge material and also the design can be adapted with high degrees of freedom. Using advanced materials for hinge components, overall weight can be brought down significantly, whilst not compromising on robustness or performance.

Paint defects

Paint defects are caused when paint debris sticks to the surface of the car. Paint defects are a particular problem around pivot points when the bearing is fully conductive. A fully conductive bearing allows each layer of the e-coating process to adhere to all of the hinge’s components. When the hinge or pivot point is moved by robots during the next stage of the painting process, previous paint layers flake off.

Figure 1: Paint bridge caused by fully conductive bearing

A NORGLIDE^® Bearing is made from non-conductive material with added conductivity notches. The notches allow the electric charge to pass through the hinge during the e-coating process but prevents the paint from sticking to the where paint is not required as an example the bush. This prevents build-up of the various layers of paint and reduces/eliminates paint flake, reducing rework during the e-coating process. Explored in more detail, the blog How NORGLIDE^® Bearings reduce e-coating paint defects, explains the challenges of paint defects.

Figure 2: Reduction of paint on pivot point using a non-conductive bearing with notches

Noise and Vibration (N.V.H.)

Noise can be unpleasant and irritating for vehicle drivers and passengers. Unexpected noise, for example, an abrasive sound when opening or closing the driver’s door, can give the impression of poor performance or quality, impacting the users experience and perception of the brand.

The choice of assembly process could result in unwanted high torque at the pivot points and over-tightening can lead to unfavorable loads on the system. Both of these issues result in noise and vibrations that can be easily reduced or removed by using the right bearings and selecting the right materials. Introducing a thick PTFE-compound layer on the bearing softens the movement improving the feel for the user and eliminating some NVH issues. A precise fit assembly process removes free play in the hinges preventing vibration and rattling noises. NVH tests on door hinges can be carried out at our own semi-anechoic chamber to help and identify areas of improvement.

Torque precision and control

Torque controls the position of the door in the frame and the hinge controls the torque. The hinge’s torque determines the fit of the door into the car body. Doors are fitted as an automated process completed by robots. To regulate this process all side doors have a predefined mounting position. If the hinge’s torque isn’t correct the side door cannot be fixed into position. Manually adjusting the hinge torque is an option, but should the hinge’s torque be extremely high (>4Nm) manual adjustment becomes difficult. The position of the hinge can also create problems and, like the hinge torque, it needs to sit within a predefined range. If the relative position of the hinge changes it cannot be properly tightened onto the car body.

For the vehicle driver and passengers, a door hinge’s torque will regulate the operation of the car’s doors and closures. A hinge’s torque, along with other parameters, directly influences the operational feel. If the torque is too high the effort to close the door might not feel as smooth as it should, and in extreme cases, the end user would have to use more force or slam the door closed, affecting the users experience.

Control of torque

To manage the torque variation of the hinge a decrease in the disparity of tolerance during press fit assembly is required. As an example, figure 3 shows a sizing pin with a sizing mandrel that is bigger than the inner diameter of the installed bearing. By pushing the pin through the bearing, the inner diameter of the bearing increases due to a certain percentage of plastic (permanent) deformability of the bearings structure.

Changing the material of the bearing can prevent deformability, compensate tolerances and decrease torque variation. Aluminum based materials offer good sizing capabilities when compared with DU-type or plastic alternatives. Both NORGLIDE^® SALC and SMALC materials with a stretched aluminum-cladded base metal and thick PTFE layer provide the sizing capabilities needed to compensate bearing wall thickness tolerances as well as housing diameter tolerances by choosing the right sizing pin.

Figure 3: Sizing pin in sizing mandrel

This results detailed below in a decrease in the tolerance field of max. vs min. press fit possibilities. The images in figure 4 show the worst case scenarios.

Sizing or calibration of the bush within the hinge assembly is important as this gives a consistent process within the hinge assembly that enhances the quality feel of the hinge for both the OEM and end user. Additionally, it significantly reduces / eliminates scrap and rework in production.

Figure 4: Theoretic worst case fit conditions in a typical bearing assembly

Managing torque, or protecting doors and closures from overload is another consideration. Systems such as a slip clutch, torque limiter or overload clutch are used to protect the hinge from damage. The RENCOL^® Tolerance Ring is a space-saving, in-line slip clutch giving a smooth consistent feel and protection for the hinge.

NORGLIDE^® Bearing solutions

On-going developments in bearing materials and technology can help solve some of the challenges for automotive hinges. Each NORGLIDE^® Bearing is designed for the individual project case and to satisfy performance requirements. The location,the loads on the bearing and the environment it needs to withstand are considered during the design phase and contribute to material selection. Recent developments in NORGLIDE^® technology optimizes the electrochemical potential of the bearing and facilitates the best fit solutions for typical hinge applications.

Corrosion resistance can be improved by selecting the right materials. NORGLIDE^® Bearings are available in a wide variety of materials; steel with a zinc coating, stainless steel, aluminum and aluminum cladded materials all provide high corrosion resistance. Selecting the right material to improve corrosion resistance will depend on the boundary conditions. Our engineers have the knowledge and experience to advise on choosing the right material for the right situation.

To overcome NVH issues the combination of advanced materials and a layer of PTFE along with a correctly designed fit can help to deliver noise-free performance. The optimized materials of NORGLIDE^® Bearings help reduce and absorb vibrations contributing to a smooth operational feel of any door or closure for the end user.

The picture shows a stamped door hinge with two bores (black part) that are not aligned. With the thick PTFE compound layer misalignment can be compensated and tolerances caused by misalignment are counteracted.

Overall NORGLIDE^® Bearings provide a great experience for the end-user. The high quality movement for the life of the door or closure improves the brand reputation of the vehicle and it is why NORGLIDE^® Bearings have a strong reputation and are recognized as a leader in the automotive market.

NORGLIDE^® Bearings can be used for all types of hinges, including:

Side door hinge (forged, stamped or profile version)
Trunk hinge (liftgate stamped hinge, liftgate forged hinge, gooseneck hinge)
Hood hinge (single pivot hinge, multibar hinge, multibar hinge with active passenger safety function)
Sliding door hinges (manual and powered)
Fuel cap/electric charger caps
Door handles
Hinges for convertibles, spoiler
Hinge systems for (powered) running board