Door modules with innovative carrier materials help to meet stricter crash test guidelines while saving weight and costs.

As of 2023, the Insurance Institute for Highway Safety (IIHS) is raising the criteria for its side impact tests. Vehicle flanks will then have to withstand over 80 percent more energy than before. Against this background, car manufacturers are not only examining the design of their bodies but also their door structures. Although the interior of the door plays only a minor role in the crash, door modules used there enable new approaches to the test procedure.

Pre-tested systems for uncomplicated assembly processes

The door module principle is well established in the automotive industry: The most important functional components of the vehicle door are combined into one system on a carrier plate. In the conventional construction of side doors, many individual components must first be assembled on a door assembly line. With the modular construction method, however, the manufacturer receives the system as a pre-tested unit from the supplier. It can be inserted into the door frame with just a few hand movements. The more functions of the door are integrated on the module, the less additional work has to be carried out until the side door is attached to the body. Various equipment variants are already implemented at the supplier and, if required, are made available just-in-sequence, which means in line with the customer’s production cycle.

Door modules in a side crash

Even with the adapted IIHS system, the criteria for lateral barrier impact remain unchanged – intrusion depth and occupant exposure. The key factor for the test result is the structural integrity of the body. Inside the door, only the hinges, the lock as well as the sill cover and the side impact beam are relevant. The interior area of the door, in which the module is located, only plays a minor role. Therefore, the decision for or against the modular design has only minimal effects on the test result of the vehicle. In the future, however, vehicles will have to be able to withstand crash loads at a higher level in the event of a side impact. According to the announcements of the IIHS, mass and impact velocity of the barrier will increase. The energy input will change from 290 kN to 530 kN. Vehicle manufacturers have to react to the increased requirements with adjustments to the vehicle body. Door modules can support OEMs in this task. The possibilities are particularly promising when using carrier plates made of continuous glass reinforced thermoplastics, so-called organo sheets.

Weight reduction with functional advantages

Organo sheet is an innovative lightweight construction material. It consists of continuous glass fibers embedded in a thermoplastic matrix. When the material is heated, it acquires a soft consistency and can be pressed into the desired shape. At the same time, reinforcements and functional elements made of plastic are attached by back-injection. This process is carried out in a conventional injection molding machine using appropriate tools.

Brose has been manufacturing door modules made of organo sheet in large series since 2018. Compared to conventional plastic door systems made of PP-LGF30, this results in a weight advantage of 45 percent or up to two kilograms per vehicle – and with better crash behavior. The carrier made of glass-fiber-reinforced plastic can absorb many times more energy. In addition, much more stable connections to the body are possible, as holes are made during the forming process to protect the fibers. It stands to reason that the advantages of organic sheet should be exploited when dealing with the new crash requirements. On the one hand, the kilos saved can at least partially offset the additional weight from necessary reinforcements in the body. On the other hand, it is worth taking a closer look at the possibilities of functional integration, for example of crash elements. So-called pads and pushers can be integrated directly into the unit carrier or as a mounting part on the door system. This does not result in any new assembly steps on the manufacturer’s line, as the complete module is placed in the door with a single action.

Evolution to a structural module

Further areas of application emerge when the system limits of the door modules are extended so that they also take over static structural tasks in the door. In the future, the door body shell can be designed in such a way that it only achieves its full rigidity in combination with this so-called structural module. As a result, it will not only be possible to significantly enlarge the cut-out in the inner part of the door, but also to omit components such as metallic reinforcements, crash pads or pushers. Their function is then assumed by the structural module. In addition to the extra weight loss of more than one kilogram per door, this procedure also brings significant cost advantages for the manufacturer: in addition to the components, the corresponding tools and joining processes are no longer required.

The extended structural modules have already been fully validated at Brose. The new approach enables weight savings of up to eight kilograms per vehicle compared to a conventional door design. It is important to note that this innovative approach requires the vehicle manufacturer to involve the supplier in the development process at an early stage. After all, the simulations required to design the body can only be carried out with the aid of precise data on the structural module and its connection to the door. Although this coordination may seem unusual at present, it is the only way to achieve the greatest possible advantages in terms of crash behavior and weight – and at lower cost.

Authors:

Dr. Marcus Klopp, Director Advanced Development Door Modules Brose

Michael Thienel, Expert Door Concepts Advanced Development Door Modules Brose

Eike Ritthaler, Project Engineer Advanced Development Door Modules Brose