Hytrel jounce bumper hits European Roads

The jounce bumper is part of a vehicle’s shock-absorber system and designed to absorb impact and dampen noise, vibration, and harshness (NVH) by preventing the metal shock absorber spring from fully compacting during shock impacts due to potholes, curb and objects in the road. It also offers an additional spring function to improve vehicle behaviour when negotiating smaller holes on the road surface and cobblestones or during quick direction changes or sudden braking. Up to now these parts are usually made of polyurethane foam. Within the cooperation an alternative model has been developed using DuPont’s thermoplastic polyester elastomer Hytrel instead of polyurethane.

The new design eliminates the need for metal or reinforced polyamide saturation cups and acetal or rubber rings normally used to increase energy absorption and can integrates dust protection. Patrick Cazuc, Automotive Director Europe, DuPont Performance Polymers, said: “Materials are critical in component design and the best results happen when the three primary phases in product development – design, materials and processing – converge.”

DuPont modified Hytrel to deliver better mechanical performance, particularly under high strain conditions, a good shape recovery, a good balance between stiffness and low-temperature properties, thermal stability resulting in low moulding variation and good processing capabilities. It also takes advantage of a blow-moulding process that uses an Ossberger machine, which can tightly control the thickness profile, facilitating optimum energy-absorbing properties with a maximum compression ratio.

An additional advantage of the new solution is weight reduction. Patrick Cazuc confirmed in an interview with TPE Magazine at a pre K press briefing held in June in Geneva that the new part is lighter than the traditional solution with polyurethane.

Non-linear Finite Element Analysis (FEA) and Expert System software are used to develop designs that can be tailored to an OEM's specific force displacement curve requirements. This software is able to model plastic deformation, large deformation, nonlinear material behaviour and processing limitations to create the optimum thickness profile. Rapid prototyping of mould tools and laboratory testing is available at the DuPont European Technical Centre in Geneva, Switzerland. Ceram, an independent French automotive dynamic analysis road center, can provide vehicle road tests to help optimise the jounce bumper performance.

Road tests

The jounce bumper has been tested by several professional test drivers. Some of whom have reported a higher comfort and steering feedback with a reduction of the front axis roll angle. In addition, several OEMs have also tested the new design on a variety of vehicles over tens of thousands of kilometres without any behavioural issues. The tests have proven that the new design delivers similar performance to polyurethane, but with lower part damage. Indeed, after traversing 3,000 km of cobble stoned roads the jounce bumper made of Hytrel exhibited less than 3 % permanent deformation far below the industry target of 10 %.

The part will be featured at DuPont’s stand at K 2013 in hall 06, stand C43.