Traditionally the bearing used in suspension struts was the ball bearing and it is still the predominant choice today. The alternative sliding bearing is becoming more widely available and accepted. However, neither solution is perfect and a compromise is being made. Understanding what industry experts want from a suspension strut top mount bearing, the changes that are being introduced and future ambitions are central to developing a solution to remove compromise. The blog ‘what is a suspension strut’ presents the results of market research and expert interviews on this subject. It was this market review that led to the development of the NORGLIDE® suspension strut bearing.
NORGLIDE® suspension strut top mount bearing - Custom designed, based on customer requirements, it’s made using plastics and our unique NORGLIDE® PTFE containing sliding pad technology that offers three key benefits:
Even over loads and temperatures.
Lower in system height and width (than ball bearings), giving flexibility in design (resulting in more room) with system cost savings vs. traditional solutions. NORGLIDE® technology can be designed into current system packaging, allowing for drop in/turn-key solutions.
The thick layer of PTFE eliminates rattling in the system and avoids stick-slip (as a source for creaking).
Essential for ride comfort
A suspension strut bearing (also known as a top mount bearing, top strut mount bearing, axial bearing or thrust bearing) is an essential part of the suspension system that influences the vehicle’s handling and ride comfort.
Why? First let’s explain the suspension strut. The suspension strut connects the axle to the car body and is simply made up of the suspension spring coil and damper. This complete system is called the Macpherson Strut.
As the vehicle travels over irregularities and curvatures in the road the suspension coil will absorb the impact of this unevenness, the damper controls the movement by limiting the spring oscillation. The suspension strut’s role is to isolate the NVH generated from the road and wheels to the car body, improving the driving experience and comfort for the vehicle’s driver and passengers.
The NORGLIDE® suspension strut bearing is supplied as a complete subsystem in line with customer expectations and to fulfil the needs of suspension system engineers. It is designed to fit the Macpherson strut.
The bearing is the main component of the suspension strut subsystem; it is the bearing that has to withstand the demands placed on the subsystem and meet performance requirements. To secure the operation of the bearing pads it makes sense to provide the full sub-assembly. The whole subsystem can be custom designed allowing for each individual function to be tailored to the vehicle’s needs with the added benefit of ease of assembly. There is the option to use the NORGLIDE® suspension strut bearing with or without grease. Where grease is added into the system a locking seal encapsulates the grease to prevent leakage.
Currently there are two main solutions available; roller bearings and sliding bearings. Both have their advantages and disadvantages (as described in our suspension strut blog) and when selecting either option, a compromise is being made on lifetime performance or temperature stability.
The NORGLIDE® suspension strut top mount bearing is a better solution when all design considerations are taken into account. It provides a more consistent performance over load, temperature and lifetime.
When looking at the torque performance of both solutions at ambient temperature over different loading conditions, there is a distinct difference between the two. Figure 1 compares a roller bearing design with four comparative sliding bearings. The roller bearings have a much lower torque performance, and although the sliding bearings offer cost savings, there is a big sacrifice in performance.
Figure 1: Torque performance against load
NORGLIDE® Bearings make a step change in performance on sliding bearing performance (roughly 3-4 times better). On the face of it, roller bearings seem, on a performance level, much better performing.
However, when temperature ranges are introduced, and in particular at low temperatures, roller bearings’ torque increases significantly (and this phenomenon can be witnessed across a range of ball bearing designs as shown in figure 2 below). When this is compared to the NORGLIDE® suspension strut top mount bearing the performance remains consistent over temperature ranges.
Figure 2: Torque performance against temperature
When comparing lifetime performance, a roller bearing at the ideal temperature will give a consistent performance. However, when reviewing the performance of sliding bearings on the market to the NORGLIDE® suspension strut bearing (Saint-Gobain) in figure 3 demonstrates the improvement in lifetime performance that NORGLIDE® offers; with a more consistent torque over different speeds.
Figure 3: Torque performance over lifetime at varying speeds
With NORGLIDE® strut mount bearings you can get consistently low torque performance over loads, temperature and lifetime.
Roller bearings suffer from two disadvantages: cost and size. Roller bearings are multiple times thicker than sliding bearings; both traditional and NORGLIDE® options. Weight is another consideration – for a comparable roller bearing you can save around 80% of the weight by using a NORGLIDE® strut bearing.
|Typical roller bearing
|NORGLIDE® suspension strut bearing
Over time wear through brinelling and corrosion can have an impact on ball bearings resulting in rattle noise. The unique design of the NORGLIDE® pads with a thick PTFE layer provides damping properties to reduce and even eliminate NVH. Zero clearance is an additional advantage created by the PTFE layer that makes up the NORGLIDE® suspension strut top mount bearing ensuring there is no chance of rattle or noise due to the clearance, even over the lifetime of the product, unlike with roller bearings. This is achieved by designing features that allow the parts to be clicked together and are in constant compression, whether loaded or unloaded.
Not only does the NORGLIDE® strut bearing offer low friction under loads and temperature for life, gives downsizing and light weighting benefits, helping to reduce NVH issues, our approach to development is to work engineer to engineer. This means we partner with you to deliver the best solution: