ETAS experimental platform inside a Schroff enclosure: functional, robust and mobile

Engine management systems, ABS systems, driver displays or body electronics: development platforms for these units are used in the laboratory and during the testing of vehicles. Apart from the user specific functionality, a robust enclosure that withstands extreme environmental conditions, played an important part during the conception of these systems.

ETAS GmbH with their headquarters in Stuttgart were established in 1994 as a subsidiary of Robert Bosch GmbH. As partner to the Automobile Industry ETAS provides solutions for the entire development processes of embedded systems. The systems consist of efficient hardware and software components, are modular, scalable and can be used on their own or as a combination.

The product range covers the total "V-model" development cycle of driver units in the automobile sector. Modelling and simulation systems, rapid prototyping systems, software engineering systems, measuring, calibration, validation and testing tools for direct measurements inside vehicles are offered by ETAS. There is a high demand for quality and safety for all these development tools, especially where related to safety critical systems like brakes or steering-by-wire applications. From these exacting demands not even hardware components like e.g. enclosures, are excluded.

More functionality, new design

During the development of the ES1000.3 (Picture 1), apart from improving the functionality (higher performance, remote handling via Ethernet-connection or one input connector, battery pack), the demands on the enclosure were re-defined. The ES1000.3 is used in laboratories and test areas, as well as during tests inside vehicles.

It has to withstand extreme environmental conditions, e.g. with so-called winter or summer testing (- 40 to + 70 °C). With regard to the EMC guide lines it had to be ensured that neither the functions of the vehicle nor those of the steering mechanism are affected by inward or outward radiation. For the mobile use of the vehicle it is most important for it to be mechanically stable and robust. This entails also the secure fixing of the installed VME64x interface boards. The latter ensure that the systems are impact and vibration proof during mobile operation. Further prerequisites for the use in a vehicle are compact measurements and ease of handling.

The output voltage of a vehicle battery can fluctuate considerably depending on environmental and load bearing conditions. At the same time the ES1000.3 in its final installation with various boards requires up to 100 VAC. This puts high demands on the power supply used, which for the ES1000.3 with a variable input voltage between 6 and 36 V guarantees the safe operation of the systems.

For the launch of this new generation a new design was created and by integrating the ETAS corporate colour the affiliation with the entire product range was portrayed.

Total change of internal assembly for the systems enclosure

The system case cardpac II from Schroff was used for this application. A die-cast AlZn front frame and Al side panels form the stable frame of this case. The adjustable strap handle ensures ease of transport for mobile use. The cooling concept of the cardpac case guarantee efficient heat dissipation. Ventilation grilles at the bottom of the front frame and ½ U free space at the top and bottom of the case dissipate the heat through natural convection. For the internal assembly the side panels have a 10 mm assembly grid.

In comparison to the case of the previous model the assembly and the size (3 U high, 360 mm deep) remained the same. The design was only accentuated by the ETAS corporate colours on the front frame. A further alteration to the outer assembly occurs through the optional integration of the battery pack, which for safety reasons provides a buffer zone for the board net during the testing of the vehicle. For the assembly the top cover which is being secured with knurled screws is removed and placed in the space available at the base. Now the installation which will receive the battery pack (mechanical and electrical connections) can be seen in the cover plate (Picture 2). The battery pack can be clipped into place and can be removed just as easily (Picture 3). The housing for the battery pack was also designed and manufactured by Schroff.

The internal assembly of the cardpac case was completely reworked in order to realise extended functionality. The assembly space for the ETAS boards and the driver of the power supply are situated in the front area. In the rear area of the enclosure the operating part can be assembled directly on to the backplane. Schroff not only delivers the enclosures for these applications, but also integrates components supplied by other manufacturers.

Electro-magnetic compatibility (EMC) and cooling

To fulfil the required EMC requirements the cardpac case in its standard version is already equipped with EMC shielding. The integration possibility of the battery pack made further EMC shielding in the top cover area necessary. Corresponding EMC measurements confirm optimal protection from inward and outward radiation. Apart from the robust, shock-proof case especially secured plug and screw connections ensure the equipment is not damaged and its functionality is not affected on rough terrain during active field service.

The cooling of the case was a particular challenge. The use of power PCs (with future capacities of 800 MHz to 1 GHz) creates a high loss in capacity, which in the form of heat has to be dissipated. Additionally potential ambient temperatures of +70 °C (summer testing) had to be taken into account. The cooling concept of the cardpac case already provides very efficient temperature regulation. A temperature sensor controls the fans that are installed in the rear panel. The air that is expelled from the heat exchanger integrated in the power supply is also sucked up by the fans on the rear.

Schroff supplies the pre-assembled case in a special packing to ETAS. Here in accordance with the requested customer applications the subracks are plugged into the system. After the functionality has been tested the systems are sent to the customer in the packing that has been supplied.