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Steering Yoke (Guide Bearing)

Automotive Chassis Steering Rack Guide Bushing PTFE NORGLIDE

The steering rack is a critical feature in all Automotive vehicles. The most common type of steering rack is one that incorporates a rack and pinion system that is driven by the steering wheel from the user. As the user turns the steering wheel the pinion drives the rack left and right, resulting in the wheels changing angle. Maintaining consistent contact between the rack and pinion gears is safety critical as disengagement of the gears would stop the driver having control over the direction of the vehicle.

Steering rack and pinion gear assembly bearing surface yoke and pre-loading springTo maintain a consistent engagement between the rack and pinion, a steering yoke (guide bearing) is employed. This device, in combination with a spring feature, is pressed onto the rack, pushing it against the pinion. The steering rack has to move through the steering yoke during steering operation meaning that friction at this interface significantly affects the steering feel. A low friction bearing will provide a smooth on-centre steering feel for the user, which should last for the lifetime of the vehicle.

NORGLIDE® steering yoke bearings are custom made to conform to the steering rack of any steering system. It is the unique laminate design that enables this innovation, as the thick PTFE layer allows low friction and smooth steering, drive after drive. 

Saint-Gobain engineers have designed the shape of the steering rack yoke laminate to allow for high rack conformity of the bearing (Figure 1). This results--compared to traditional design--in a higher contact area of the yoke onto the rack, reducing the pressure of the system, which leads to less wear over the lifetime of the vehicle. This is only achievable using our unique material due to the thick layer of PTFE used in NORGLIDE® Bearings (Figure 2). 

Figure 1: The offset between the steering yoke and the rack shaft is an order of magnitude less than competitor yokes. Here the NORGLIDE® steering yoke has an offset value of 0.03, compared to the competitor yoke with a 0.55 mm offset. This allows the NORGLIDE® steering yoke to be brought closer to the rack, ensuring more contact, resulting in reduced pressure and wear.

Automotive Steering Yoke Bearings with Low Friction and Smooth Steering (diagram)

 

Figure 2: Cross-section through the unique NORGLIDE® materials (left - SMTL, right - PRO) that will perform consistently throughout the lifetime of the part due to the thick PTFE layer.

NORGLIDE Steering Yoke (Fig 1) | Saint-Gobain
NORGLIDE Pro Bearings, Auto Steering Yoke (Fig 2) | Saint-Gobain

Smart Design Engineered Benefits for Steering YokesSmart Design Engineered Benefits for Steering Yokes

 

Durability tests are performed so the effect of wear on the performance can be discerned. The friction force of (a) the dynamic friction and (b) the static friction were measured where Fstatic= Fpeak- Fdynamic.

 

Smart Design Benefits for Steering Yoke, Durability (Friction) | Saint-Gobain 
Smart Design Benefits for Steering Yoke, Durability (Stick-Slip Friction) | Saint-Gobain 

 

 

Perfect Fit Engineered Benefits for Steering YokesPerfect Fit Engineered Benefits for Steering Yokes

 

The strength of the unique NORGLIDE® laminates offers improved dimple retention forces over competitor solutions. Here the maximum force required to completely shear the dimple from the yoke liner is shown for three samples of each material.

 

Noise Free Engineered Benefits for Steering YokesNoise Free Engineered Benefits for Steering Yokes

 

NORGLIDE® steering rack yokes exhibit much less wear in lifetime testing. High wear rates cause clearance in the system which can lead to gear teeth rattle at the rack and pinion interface. Speed: 66.7 mm/s, room temperature, 50 mm stroke, Multitemp AC-P grease, 180K cycles with 2.7 kN of force pressing the yoke onto the rack.

 

Long Life Engineered Benefits for Steering YokesLong Life Engineered Benefits for Steering Yokes

 

During the lifetime test, the coefficient of friction was measured to find out the effect of wear on performance. This test indicates the steering yokes ability to perform over the lifetime of the vehicle. As shown, NORGLIDE® steering yokes perform consistently throughout the test. Whereas the line-contact on the competitor yokes means a higher pressure, meaning increased wear into the porous Bronze matrix, resulting in increased friction of the steering system.