Delphi Automotive’s air suspension module is one of the major features of the new Land Rover Range Rover, for which it was specially developed. Key to the success of the module is the world’s first automotive air spring damper strut with side load compensation. However, two of the four modules, situated at the front of the car near the engine, needed to have considerable heat resistance, so Delphi turned to DuPont in its quest for a suitable material. The solution was glass-reinforced Zytel HTN high-performance polyamide, a grade developed specifically for the application.
Material Properties and Design
Land Rover in Solihul, BMW in Munich, who were initially responsible for the development of the car, Delphi Automotive’s Luton and Paris offices, as well as DuPont specialists in the UK and France, worked together for more than two years to develop the pistons for the air spring damper strut. These are made of a new, specially-tailored 35% glass-reinforced grade of Zytel HTN, which combines very high-temperature resistance with excellent burst and compressive-pressure strength.
It was meeting the burst pressure requirement that was the most technically difficult part of the project. ‘After the initial testing, we offered a new toughened grade of Zytel HTN, which offered improved weldline strength compared with our first choice. This second grade had only become available during the course of the development programme of the air suspension sleeve, and resulted in the project’s success,’ said a DuPont spokesman.
Reasons for Selecting Zytel HTN
The injection moulded piston part of Zytel HTN provides triple functionality. Firstly, it acts as a guide on which the flexible, rubber air sleeve moves up and down with the suspension strokes. Secondly, the high performance polyamide parts efficiently seal the rubber air sleeve, which is crimped using a new manufacturing procedure developed by Delphi. Thirdly, its excellent surface finish provides a smooth surface for the internal o-rings to seal against the damper strut.
Operating Conditions and Materials Testing
In certain vehicle operations, the air spring module experiences extremely high pressure peaks under severe temperatures, ranging from -40°C to 100°C. Consequently the complete air spring and the piston made of Zytel HTN were tested to 65 bar burst pressure. In addition, each air spring module produced at Delphi Luton is leak tested at 10 bar air pressure.
According to Delphi Automotive, the newly developed 35% glass-reinforced grade of Zytel HTN was the material that best resisted three crucial factors - the high engine temperatures where the front two modules are positioned, the highly demanding burst pressure testing requirement and the crimping forces used to seal the rubber air sleeve. The previously used metal cast piston technology would have been too bulky, heavy and expensive to be incorporated on each of the Range Rover’s four wheels for an individual air suspension system. But happily for Range Rover drivers and DuPont, this is not the case with the plastic components.