BMW 3

Airbag Tests

Increased Safety
The first airbag tests in the new BMW 3 Series were carried out in Munich at the beginning of 2003. The objective was to integrate the passenger airbag module into the dashboard. BMW chose the airbag laboratory at Bertrandt’s subsidiary in Munich to run the tests. The laboratory has already carried out airbag tests on a wide variety of cars.

 

Prototype components enable testing at an early stage

Bertrandt was first contacted by BMW with regards to the 3 Series passenger airbag project in 2002. At that time, BMW requested pressure tests data for a previous model. BMW incorporated the data into the calculation and simulation processes as part of the functional development process. This resulted in the production of prototype components that enabled for initial tests to be carried out in spring 2003. The results of these tests were incorporated into the development process that speeded up the process of integrating the airbag module into the dashboard.


Integrating all partners makes for faster progress
The BMW 3 Series dashboard is not produced by a supplier but by the BMW factory in Landshut on the basis of the work of the research centre. Only the components, for example the airbag module, covers and air vents, are thirdparty products.


The development and testing of the individual components ran smoothly, and the first project milestones, such as connecting the airbag cover to the dashboard insert, were soon achieved. In various additional stages, the Bertrandt engineers were able to test the functioning and positioning of components such as the cup holder, covers and fresh air inlets. The companies that supplied the individual system components were on site for the testing so that any necessary changes could be implemented quickly.

 

New unfolding sequences based on out-of-position tests
By means of the latest high-speed video technology, the project then focused on the unfolding sequence of the airbag and on the times of opening. At speeds of up to 9 000 frames per second, even the fastest events, which are not perceptible to the human eye, can be clearly displayed and carefully analysed. The conclusion drawn from out-ofposition tests carried out by the airbag manufacturer was that a change in the way the airbag material was folded could give a passenger sitting in an unfavourable position a far greater level of protection. For this reason, the airbag manufacturer provided a range of different airbag folding sequences for the test. This enabled the possibility to identify the sequence that met the demands for airbag integrity and the requirements of the out-of-position tests. After a successful release test was carried out for the relevant BMW department, the project was completed.

 

Together on the move in future

This project has given the airbag laboratory’s Vehicle Safety Competence Centre additional experience in functional development. BMW and Bertrandt are already cooperating on new products in the vehicle safety field in which the out-of-position concept plays a more important role.

 

An airbag cover with an invisible split line opening in the new BMW 3 Series (high-speed video recording at 9 000 frames/ second).

Improved Performance
This project has given the airbag laboratory’s Vehicle Safety Competence Centre additional experience in functional development. BMW and Bertrandt are already cooperating on new products in the vehicle safety field in which the out-of-position concept plays a more important role.

Concept
The initial investigations into the system of the new BMW 3 Series began in October 2001 on the basis of the previous model. During the unfiltered air intake, air is induced by twin inlets above the BMW double-kidney grille and subsequently transported towards the air filter. Studies were carried out and designs produced for the required components, the demoulding concepts, the mounting concept and the seal between the air induction and the engine compartment, to prevent hot air from being induced. In collaboration with Mahle, several variants were developed and evaluated.

Another important issue was the connection between the engine compartment and the front bulkhead. The initial assumption was that the route to the engine compartment would go across the bulkhead. The subsequent evolution stages of the bulkhead resulted in the creation of an interface. This meant that the air induction had to consist of at least two components.

A convoluted rubber gaiter was utilised as decoupling module between the unfiltered air induction and the air filter. As both the air conveyance and the filter are mounted onto the bodywork, there was no need to balance out their movements relative to one another. The convoluted rubber gaiter makes assembly easier and is used to compensate for tolerances. In the original design, the convoluted rubber gaiter was attached to the plastic components using latches. However, after the trial phase, Mahle decided to weld the convoluted rubber gaiter to the air conveyance, which eliminated one of the interfaces.

A convoluted rubber gaiter was utilised as decoupling module between the unfiltered air induction and the air filter. As both the air conveyance and the filter are mounted onto the bodywork, there was no need to balance out their movements relative to one another. The convoluted rubber gaiter makes assembly easier and is used to compensate for tolerances. In the original design, the convoluted rubber gaiter was attached to the plastic components using latches. However, after the trial phase, Mahle decided to weld the convoluted rubber gaiter to the air conveyance, which eliminated one of the interfaces.

The convoluted rubber gaiter for filtered air forms the connection between the air filter and the throttle valve and is the last component in the air induction system. In addition to transporting the air, its main task is to accommodate the relative movements of the engine (throttle valve) and the air filter. As a result of its complex shape the convoluted rubber gaiter for filtered air is also blow-moulded.

 

 

 

 

 

 

 

The Development Process

The total volume of the clearance: unfiltered-air intake system, air filter and clean air boot.

Air conduction system
Under the guidance of the Mahle computing department, several proposals for the flow geometry of the air induction system were produced. In addition, the cross-sections of the system were optimised to prevent a break-up of the airflow. The aim of these measures was to reduce the pressure loss as much as possible throughout the air induction system, as this has a direct impact on engine performance.

Under the guidance of the Mahle computing department, several proposals for the flow geometry of the air induction system were produced. In addition, the cross-sections of the system were optimised to prevent a break-up of the airflow.

The aim of these measures was to reduce the pressure loss as much as possible throughout the air induction system, as this has a direct impact on engine performance.

Casing and lid
The primary consideration in the design of the air filter casing and lid was to achieve as much volume as possible in the specified environment. Another important factor was the structure-borne noise. Bertrandt worked closely with the Mahle computing department in this area. This enabled noise reduction measures to be incorporated into the models at an early stage, including ribbing and embossing of smooth surfaces. However, this remained a critical issue right through to the start of production. In particular in the case of components where the design is critical, the appearance and the function must be in harmony. This resulted in the lid of the casing being reinforced in order to prevent the gleaming through of the ribbing due to sink marks.

 

Convoluted rubber gaiter for filtered air
One might think that this convoluted rubber gaiter would be the simplest component to develop, but this is not entirely the case. Because of the constantly changing environment, a new route for the convoluted rubber gaiter was needed. For this reason, the position of the convolutions had to be changed. In order to ensure the required level of flexibility (20 mm in both directions), a minimum number of convolutions were required. The convoluted rubber gaiter is mounted on the throttle valve in advance. This means that it is already fitted when the engine is mounted in the bodywork and is therefore "in the way".

For this reason, the convoluted rubber gaiter is divided in two. The shorter, more rigid part is mounted onto the throttle valve and the flexible part is then fitted onto the air filter. Acoustic factors also played a part here. The convoluted rubber gaiter for filtered air is the ideal component to accommodate resonators that filter out unwanted frequencies in the air induction system. A resonator is used in the new BMW 3 Series that was developed in collaboration with Mahle’s acoustics engineers.

Conclusion
One of the main features of the project was the mutual trust and openness displayed by both partners. This formed the basis for the successful collaboration between the two companies. The creation of the 3D data for the production tools in spring 2004 marked the end of a very interesting and wide-ranging project for Bertrandt. However, Mahle and Bertrandt also worked together on another 3 Series project: the parallel development of an air filter for the US market. Other versions of the engine will follow in future.