What is a suspension strut bearing?

From absorbing road impact to facilitating movement, the suspension strut and the bearing provide vehicle users with a smooth ride.

The suspension strut plays a pivotal role in how the car handles. This simple yet hugely important part can have an enormous impact on how end users, both drivers and passengers, perceive the ride quality of the car and consequently the overall quality of the vehicle.

The suspension strut consists of the suspension spring coil and damper and it connects the axle to the car body. When the vehicle is traveling the coil compresses and extends absorbing the impact from road, the damper controls the movement by limiting the spring oscillation. To facilitate this process, the coil needs to pivot and rotate, it is the suspension strut bearing that enables this movement against the static top mount.

Because of its role the suspension strut bearing has a number of demands placed upon it. If the top mount bearing has a too high friction this can lead to stick-slip behaviour: showing itself as jerky movements and vibrations for those traveling in the vehicle. From a performance perspective a low but constant friction (or torque) is needed, allowing the system to move with no stick-slip or juddering. It is also used to transmit the suspension loads to the chassis: this has to be accommodated in the bearing design.

The suspension strut sub-system is reliant upon the suspension strut bearing to offer a smooth ride over the lifetime of the vehicle. 

 

Traditional suspension strut bearings

Currently, the majority of suspension strut bearings are either ball bearings, made from steel, or sliding bearings made from plastic. Although sliding bearings are becoming increasingly popular due to their adaptability, ball bearings still account for over 80% of the market. Here we take a closer look at their advantages and disadvantages.

In summary, ball bearings provide superior torque performance whereas sliding bearings offer a better packing and weight solution. Yet, no matter what solution an engineer picks a compromise is made.

Performance considerations of suspension strut bearings

Force, temperature, corrosion, NVH and more can all impact the performance of the strut bearing. This can be broken down further as each criterion can have multiple sources impacting performance. On top of this each criterion can effect each other; this adds complexity to the performance requirements of the strut bearing. For example, the force applied to the strut bearing can come from multiple sources; in a sports car the lateral forces are increased adding additional radial load on the strut bearing. At the same time the trend for e-mobility will see higher dynamics acting on the suspension, but the expectation of the consumer still remains the same: a greater ride comfort. This changes the requirements of the suspension system.

The available packaging space in the suspension strut system is important for delivering a smooth ride. In order to maximise road dynamics and ride comfort, the travel of the strut needs to be maximised for the given packaging space. Some strut bearings eat away at this important space; the thicker the bearing, the more compromise has to be made on handling and comfort.

Lifetime performance or wear is another big consideration and is one of the top 5 challenges faced by the industry. Over their lifetime ball bearings suffer from both corrosion and brinelling that can lead to knocking, clunking noises and stiff steering which can increase the risk of alignment issues. 

All are unwanted outcomes that will influence the end user’s experience and perceptions of performance and therefore the brand.

What changes are being introduced that will impact the suspension strut bearing?

The ever growing demands to increase the use of electric vehicles (EV’s) and the longer-term move towards autonomous driving are adding new demands to suspension systems and the suspension strut bearing. As engines become quieter and internal cabin noise is no longer masked by the internal combustion engine (ICE) NVH is receiving much more attention. Components will need to reduce NVH and this will become an increasingly important aspect during selection. Currently ball bearings offer no NVH damping.

The acceleration of sustainability programmes could impact regulatory requirements with the potential use of some materials or lubricants to be restricted. Another dynamic is light weighting, a topic that has been propelling change for a number of years. It is well known that to improve the range for EV’s and reduce CO₂ vehicles need to be lighter; this means each single component in a vehicle needs to be lighter and smaller.

The current challenges of the industry

Back in 2016 the team at Saint-Gobain Mobility started to research the automotive suspension strut market. The aim was to find out more about the products on offer and if they fulfilled the needs of the automotive manufacturers (the OEM’s and tier 1 suppliers). 

What began with a review of the market, took the team to multiple shows, customer visits and led to a number of interviews with key customers. The outcome of the review revealed what was demanded from the suspensions strut bearing was well understood but existing solutions were not delivering on all aspects, as has been detailed above.

Is the industry happy with the options available? Answer: not entirely. Across each customer interview, conversation and industry event five points came up again and again. The current options do already capture these but not altogether, in summary there isn’t one solution that delivers and as a result there is opportunity to develop a more robust solution. Collating the results, the top five issues were:

• Cost efficiency: When comparing to ball bearings, as these can often be in multiples of euros.
• Lightweight and downsizing: Especially around the thickness of the parts as this gives more travel stroke for the coil and the damper, directly affecting the ride comfort.
• Issues with lifetime performance: When comparing to ball bearings that can suffer from corrosion and brinelling effect. 
• NVH damping: When evaluating the properties of ball bearings there are no damping features and can generate noise and vibration from brinelling and wear. 
• Torque performance: While ball bearings offer excellent nominal torque levels, they can suffer at colder temperatures and current sliding bearing offerings have very high torque levels. 

So what’s the solution that can overcome the issues that have been presented and is enough to convince the OEM’s and tier 1’s to implement.

Presenting the NORGLIDE^® suspension strut sub-system

Introducing a new component, sub-system or even complete system presents challenges for the OEM’s – R&D needs to be conducted, cost analysis and due diligence needs to be proven. Any solution has to offer on multiple levels for it to be considered. 

Having understood the challenges, outlined the performance requirements and spoken to numerous experts and customers from across the globe what is required of the suspension strut bearing is clear. 

Work began on developing the NORGLIDE^® suspension strut bearing in 2018 with the creation of prototypes for testing. The design needed to be unique; not only to be new and innovative but it would also allow the team to develop a bearing that would stand up to the demands of the industry.

Our engineers combined plastic with PTFE-containing NORGLIDE^® material to a high-performing suspension strut bearing; saving space and weight and offering consistent torque control with NVH dampening. On-going testing helped to refine the design and allow the engineers to understand the inputs (load, temperature, torque) that would impact performance. This helps when creating the suspension strut bearing for your system as each one is tailor made. Our approach is to develop solutions engineer to engineer.

Our NORGLIDE^® suspension strut bearing is presented in more detail on the application page that provides more information into the performance characteristics and test results.

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