Technology: Vibracoustic decoupling prevents unwanted steering wheel vibrations

Darmstadt, Germany – Vibracoustic GmbH has developed an innovative steering column bushing to address unwanted vibrations in the steering wheel.

The product is optimised towards reducing vibrations in comparison to conventional hardy disc decouplers while being is lighter, more compact, said the supplier of automotive NVH (noise, vibration and harshness) systems in a release 12 Nov.

According to Vibracoustic, conventional hardy disc decoupler has been the product of choice for engineers when it comes to isolating torsional vibrations. It can transfer great torque and has good isolating characteristics but comes with downsides. 

However, due to its radial construction, the outer diameter is big, which takes up a lot of design space, which in areas like the steering column, can negatively affect the legroom of the driver. 

Furthermore, being built by a combination of different cord packages for the torsional vibrations in both directions, the cords become softer over time, decreasing the direct steering behavior. 

To provide even better isolating characteristics and to overcome the downsides of conventional hardy discs, Vibracoustic engineers developed a compact steering column bushing which provides “significantly more” design space, as the radius is only around half of that of a hardy disc. 

The design furthermore features an elastomer layer around the aluminum core, providing high isolation in push and pull direction (low axial stiffness), i.e. towards or away from the driver. 

The bushing offers the “radial stiffness” needed to provide a direct steering feel and secure optimised handling of the vehicle. 

“The whole bushing is highly robust and durable, and the decrease in stiffness is as low as 10% over lifetime,” the company statement explained.

While neither a hardy disc nor a cardan joint can resist coning, the Vibracoustic steering column bushing is claimed to prevent buckling of the steering column due to its high conical stiffness, given its compact construction.

To strike the balance between these contradicting demands, the Vibracoustic engineers integrated a radial progression into the component, which can be tuned by the geometry of the elastomer around the aluminum core. 

If the steering force reaches a specific level, the coupling stiffens up and transmits the full force to the steering column, turning the wheels in the needed direction. 

If the driver, for instance, steers towards a curb, the steering feel first needs to be soft, in case the curb was just touched by fault. However, if the car goes over the curb the steering becomes stiff to deliver the driver’s intended maneuver.   

“This progressive behavior can be precisely tuned by the elastomer geometry – something which is not possible with other conventional solutions,” said Vibracoustic.

The good “tunability” of the elastomer geometry is achievable since its outside geometry is fully accessible during vulcanisation. Thus, the outer elastomer geometry is only limited by mould constraints. 

After vulcanisation, two plastic outer shells are welded together by ultrasonic vibrations, once the outer shells are laid over the core and the elastomer layer. Here, a stopper system is integrally formed to easily tune the progression behaviour.