EMC In the Motor Industry

The European EMC framework directive 89/336/EEC now requires that all electrical and electronic products offered for sale in the European Community conform with its requirements, and be 'CE' marked, unless they are covered by a separate product specific directive. One example of such a product specific directive is the automotive industry.

The large semi-anechoic EMC chamber at the Motor Industry Research Association

The Automotive Industry

In the case of a computer interfering with a radio, it may be fairly easy to relocate one of the items, but if a motor vehicle suffers an engine stall each time it is driven past a television transmitter, it may be impossible to avoid the problem, and therefore the immunity requirements are much higher. With the increasing use of electronics in even the most basic motor car, and the trend towards safety critical applications like anti lock brakes, the requirement for a high level of immunity is paramount.

Furthermore, motor vehicles have been the subjected of EMC legislation for nearly 40 years. The requirement was introduced in the late 1950s to protect domestic radio and television sets from RF emissions generated by ignition systems. This test forms part of the Type Approval process which all new vehicles must go through - a range of 44 tests including exhaust emissions, crash protection, lighting and so on.

The Automotive Directive

Because of the existing Type Approval test, which was well known and understood by the automotive industry, the obvious way forward was to expand this requirement to cover the new aspects of EMC. The amending EMC Directive was created by a European group of motor vehicle manufacturers and unlike the framework directive, includes all the technical information required to test.

Article 2.2 of the generic Directive states "insofar as protection requirements specified in this Directive are harmonised, in the case of certain apparatus, by specific Directives, this Directive shall not apply or shall cease to apply with regard to such apparatus..." This means that once the Automotive Directive came into force, motor vehicles and components fitted to motor vehicles, were completely exempt from the generic Directive. The 'CE' mark is not applicable, since the Type Approval process results in an 'e' mark for a product or whole vehicle. This has important implications for some automotive products.

The Automotive Directive applies to whole vehicles and also vehicle components, and must be witnessed by the appropriate Type Approval Authority (in the UK this is the Vehicle Certification Agency - an Executive Agency with the Department of Transport). Once the test has been completed successfully, a certificate is issued which becomes a part of the vehicle type approval.

There are 3 areas - broadband emissions predominantly generated by the ignition system of petrol engines, narrowband emissions generated by harmonics of microprocessor clock oscillators, and immunity to externally radiated EM fields.

There are two ways in which a vehicle can be approved - the whole vehicle, together with all its available components can be tested, or components can be tested individually on the bench, and approved in their own right. This option is important where there may be a range of alternative components available, for example a series of audio systems. It would be time consuming and expensive to repeat the whole vehicle test for each alternative radio which was available, so by approving a range of radios on their own, it is possible to include all of these in the vehicle type approval.

Test Details

The existing requirement for broadband emissions from the ignition system is carried out on an open area site, and measures the interference at a distance of 10m, and an antenna height of 3m, with the engine running. A second emissions test has now been added, measured in exactly the same way, to cover narrowband emissions from the electronic control units on the vehicle. In this case the engine is not running, but the ignition is switched on.

For immunity, the requirement is to demonstrate that the basic safety of the vehicle will not be compromised by radio transmissions. This implies that the only components which need to pass the immunity requirements are those which may affect the direct control of the vehicle, such as cruise control, anti lock brakes and steering, but also the lighting, since this may cause confusion to others. Convenience features such as interior lamp timers or electronic air conditioning control are not covered.

The immunity test is carried out in a large (usually semi anechoec) The immunity test is carried out in a large (usually semi anechoec) chamber, with the vehicle on a chassis dynamometer running under road load simulation - this is required to confirm the engine control systems under realistic conditions. The test limit is 30 V/m which is much higher than the limit for most domestic or light industrial equipment due to the environmental conditions already described.

Some systems, such as anti lock brakes, pose a particular problem for testing, and a number of different methods have been devised for their actuation. Some test houses have developed computer simulations where the wheel speed sensors are connected to a test fixture simulating the signals. Others have produced complex mechanical systems to control the wheel speeds directly during the test.

Due to the field strengths being generated, it is essential that the test is carried out, and monitored under remote control. For the legislative test only those systems which have a safety function need to be considered, but most manufacturers will monitor all of the systems on the vehicle for their own quality reasons. This can be quite time consuming to set up because of the number of systems which may need to be monitored.

As a minimum, there needs to be a video camera monitoring he instrument panel, and at least one monitoring the exterior of the vehicle, to observe the lighting system during the test. A range of fibre optics may be used to confirm correct operation of other systems, and there needs to be some way of maintaining the vehicle speed at a constant level, and of monitoring that speed.

Application

One of the difficulties with the automotive industry is the time scale for new product development. The cost of developing a new car is so high that the lifespan must be as long as possible, often more than 10 years - a "new" car, which is visually different to an existing model is often virtually the same under the skin. This means that the Type Approval of the vehicle is sometimes carried across from one model to another, and therefore it may be difficult to comply with the new EMC requirements.

For this reason, the new Directive applies to new vehicle types introduced onto the market after 1.1.96. Existing vehicles which have been type approved without EMC testing can continue to be sold until 1.10.2002 after which all vehicles must comply.

Problems

The application of the EMC directive to these products has been the subject of much discussion between the vehicle manufacturers, the component suppliers, and the Government. The difficulty lies with the component manufacturer not knowing where his products will be fitted. It is quite normal for car audio products to be fitted to boats, and in this instance the automotive Directive would not apply, and the product would be expected to conform to the generic Directive.

This gives rise to a problem with the markings. The generic Directive will result in the now familiar 'CE' mark, whereas the automotive Directive, being type approval, results in an 'e' mark. The current legal interpretation is that it will be illegal to fit parts carrying the 'CE' mark to a motor vehicle. It is hoped that this interpretation will be ignored provided the parts carry the 'e' mark, as otherwise it will become very difficult for the audio industry to supply the same product both inside and outside the motor industry.

Special Cases

One of the issues which must be defined is what is a motor vehicle? Do we include a milk float, and what about a bulldozer? The definition of a motor vehicle is itself the subject of a European Directive, but a basic definition is included in the automotive directive as: "Any motor vehicle intended for use on the road, being complete or incomplete, having at least 4 wheels and a maximum design speed exceeding 25 kph, and its trailers, with the exception of vehicles which run on rails and of agricultural and forestry tractors and all mobile machinery."

Summary