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Special sliders in the steering wheel accelerator ring for special vehicles

Fast and economical manufacture of complex special parts

  • What was needed: special sliders with complex geometries
  • Manufacturing method: laser sintering
  • Requirements: optimised sliding properties, self-lubricating, durable
  • Material: iglidur I3
  • Industry: automotive
  • Success for the customer: cost-effective, fast manufacture of small volumes. Durable components with dry operation.
Car drivers who cannot use their legs can now accelerate with their hands on the steering wheel thanks to the Darios digital accelerator ring. Developed by Kempf in Alsace, the elegant and unobtrusive accelerator ring ensures safe, comfortable driving and can be integrated into most automatic transmission vehicles. The challenge the engineers faced in adapting the accelerator ring to flattened steering wheels was getting the ring to slide around the corner. The solution took the form of special sliders made of the iglidur I3 3D printing polymer and earned the company the 2019 manus award for innovative polymer bearing solutions.
The iglidur I3 self-lubricating laser sintering polymer allows the igus 3D printing service to manufacture complex special parts within 24 hours. Parts printed with iglidur sliding polymers are remarkable for their great wear resistance and predictable service life.  

More about 3D printing at igus

The accelerator ring position is detected by two sensors and transmitted via a wire connection to a computer located under the side panel.  Each steering wheel model is measured with a 3D scanner in order to optimally integrate the mechanism, the sensors and a DARIOS printed circuit board. Source: Kempf


To manufacture accelerator rings for flattened steering wheels, the customer regularly needs special sliders that are joined together and slide "around the corner" on a metal ring. More than 200 elements are needed for each steering wheel. The only option for realising this movement is designing special sliders with a complex geometry involving numerous undercuts, as a result of which production with conventional manufacturing methods is not only difficult, but very expensive. As there is a 30-year guarantee on Kempf driving aids, the special sliders must be extremely durable and reliable. It is not possible to lubricate the components as they are permanently installed inside the leather sleeve of the accelerator ring.


The special sliders' complex structures and undercuts can be efficiently produced only with additive manufacturing. iglidur I3, a high-performance polymer with optimised sliding properties, gave Kempf the ideal material from which to print the delicate elements. Laser sintered within 24 hours, the special sliders require no lubrication or maintenance to move smoothly around the corner. Despite the high order quantity (more than 10,000 units per order), the special sliders' great complexity made 3D printing even more cost-effective than injection moulding.  

Kempf steering wheel with accelerator ring The Darios digital accelerator ring means that both hands can remain on the steering wheel. The driver can also steer and accelerate with one hand and operate the hand brake with the other hand. Source: Kempf

Driving with hands only: Darios, the digital accelerator ring on the steering wheel

 "The accelerator ring is the best product on the market in terms of quality. Its workmanship is superb and its reliability unabated. Up to now, I have driven a total of 785,000km without any technical problems. Yes, 785,000 kilometres, that is 19,625 times round the world. "
This is only one of the many enthusiastic customer references from Darios users. No wonder, after all, Kempf insists on the highest quality for its products and offers its customers a 30-year guarantee on all its driving aids.
KEMPF was established in 1955 by Hans Kempf, who had difficulty walking after suffering from polio. As an enthusiastic mechanic, he invented the accelerator ring in order to be able to drive with both hands on the steering wheel. By the time of his death in 2002, he had retrofitted more than 100,000 vehicles.
The hand-accelerator system developed by Kempf is the only one available on the market that adapts itself to the speed of the vehicle: at low speeds, the acceleration is gentle, progressive and economical, whereas at high speeds, the acceleration is dynamic in order to ensure safer driving and make it possible for the driver to perform fast overtaking manoeuvres precisely and easily. All the usual functions of the steering wheel such as adjustability, airbag and horn are retained. The pedals also continue to be capable of working – Darios can be deactivated by means of a switch so that other drivers can operate the vehicle in the usual manner.

Kempf steering wheel for disabled people. The accelerator ring can be installed in almost all cars with automatic transmission. It fits seamlessly and elegantly into the design of the interior. Source: Kempf

Precise acceleration thanks to freely moving sleeve

In order to accelerate, the ring is pressed in the direction of the steering wheel. Only a very small amount of force is needed for this (approximately 3 newtons). The stroke between idling and full acceleration is only approx. 18mm. When the steering wheel slides back to the straight-ahead position after a curve, the freely rotating sleeve enables precise acceleration when coming out of the curve, regardless of the position of the steering wheel. Both hands can remain on the steering wheel when Darios is being operated, whereby the accelerator ring can also be operated with only one hand in order to operate the hand brake with the other, for example.  
With its fine leather cover, the accelerator ring fits in harmoniously with the interior of vehicles and, on request, even the colour of the leather can be chosen. As many cars now have flat steering wheels, Darios 211 has been developed. This accelerator ring is flat but also has a freely rotating sleeve. But how can a flat ring be fitted with a sliding cover? 

3D printed components make it possible for the accelerator ring to have a flat design Many new vehicles have flat steering wheels. The accelerator ring therefore had to have a flat design for these vehicles and this presented the developers with some difficult technical problems. Source: Kempf

More than 200 special sliders made of iglidur I3 ensure frictionless sliding

The new trend of equipping vehicles with flat instead of round steering wheels presented the Kempf engineers with a big challenge. For a flat steering wheel, a flat accelerator ring as flattened as the steering wheel is necessary both for technical and aesthetic reasons. The unobtrusive device which seems to be a natural part of the vehicle is, in reality, full of numerous complex details. Equipping a round accelerator ring with a sliding sleeve is comparatively easy. Covering a flat accelerator ring with a sleeve that rotates as freely as a round one calls for a technically complex solution.  
The product developers of Kempf found this solution in collaboration with the igus 3D printing team. In the new Darios 211, the first flat accelerator ring in the world, additively manufactured components made of iglidur I3 polymer which has optimised sliding characteristics are used. The flat accelerator ring has more than two hundred such elements that are flexibly joined together. They form a sliding ring around the flat metal core of the accelerator ring and thus enable seamless sliding of the sleeve. For this especially innovative solution, the company Kempf received the bronze manus award at the Hannover Trade Show in 2019.

3D printed special sliders with complex geometries A Darios 211 accelerator ring contains more than 200 complex special sliders that enable frictionless sliding of the leather sleeve over the metal ring. Source: Kempf

Advantages of printed special sliders made of iglidur I3

The engineers decided to produce the complex special sliders in 3D printing, as the production in injection moulding was very complicated and therefore expensive due to numerous undercuts. Additive manufacturing imposes hardly any restrictions with regard to design rules and this makes the manufacture of components with complex geometries economical. As a result, there are also no tool costs.
One of the most important reasons for choosing iglidur I3 as the material for manufacture of the special sliders was the solid lubricants that the material contains. Maintenance of the components is therefore not necessary and their service life increases considerably as there is hardly any wear. iglidur I3 is an SLS powder that can be processed by all conventional laser sintering machines. The powder is melted with a laser layer after layer, thus enabling the precise reproduction of fine structures. Depending on the size of the component, several thousand pieces can be manufactured in a printing process lasting approximately 24 hours. The customer profits not only from the high cost savings but also from the unbeatably fast manufacturing and delivery time. A further special feature that only laser sintering enables in this form is the printing of packaging for the filigree parts in the same printing process. The costs of packaging and the work it involves are avoided and there is no risk that individual components will be lost or be damaged.
iglidur I3 is by far the most frequently used 3D printing polymer in the igus 3D printing service. In addition to its suitability for different sliding applications, it demonstrates its strengths as one of the best polymers on the market for .  

Further information on iglidur I3


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