does not mean that it does not exist. This statement, of course, can apply to many aspects but this time it will apply to electromagnetic waves. Their action is generally not directly visible. Nevertheless, all forms of wave interaction with devices have been encountered by all of us. The first example is storms and lightning. Sometimes a near storm causes TV viewing to be interrupted by signal fades or strange artifacts in the picture. The same is true of radio. Here, however, reception problems are less in the form of crackles. Many older users with a Safari radio in their Fiat 126p found out about an impending storm just by listening to the broadcast. And they were not meteorological announcements at all…. In the first of two articles, we will discuss what role electromagnetic interference plays in the automotive industry.
This is an issue that has existed for a long time but has not been regulated from the beginning. This was due to the fact that electromagnetic interference at the beginning of automotive development was associated with spark ignition. And in fact, for many years they were not a problem. At this point it is worth distinguishing that the car can be a source but also a receiver of interference. Initially, very many of the systems the vehicle had on board were electromechanical designs. Such as ignition apparatuses, relayed alternator controllers, etc. These systems emitted a lot of interference that did not affect other vehicles but began to be a nuisance to radio listeners.
And it is the production of interference that disturbs (is perceived) that has become one of the most important reasons for the slant of various organizations on this topic. It was because of them that the first step was, for example, the introduction of metal braided ignition cables or candle pipes as shielding. This allowed a significant reduction in the generated interference. Similarly, manufacturers have begun to add in the car’s so called “”in-vehicle”. anti-interference capacitor (also called ignition coil capacitor, ignition apparatus). This was another important step in the fight against interference. It was often the failure of this capacitor that caused the radio listener to hear a distinctive crackling sound on the radio. And outside the window he could see a flashing motorcycle whose owner was unfortunately unaware of anything. From his point of view, the proper functioning of the components of the ignition system was correct. This was due to the fact that the capacitance of this capacitor was decreasing and the engine was working properly. Unfortunately, in practice, the street’s residents were the first to learn of the failure.
This is the slogan that many people have probably encountered. More under the acronym EMC (Electromagnetic compatibility). If anyone has had a chance to read the manual of any electronic device (especially radio equipment, as users of a smartphone or Wi-Fi router) there is often information in the specifications about meeting a standard related to this issue. In general, this term refers to the ability of a given device to operate in a particular electromagnetic environment , but also not to emit an electromagnetic field that interferes with the correct operation of other devices operating in that environment. For the automotive industry, two standards are particularly important: EN55012 / EN55025.
Today, it is standard that electronics must now pass many tests, including those specifically related to EMC. Manufacturers must meet standards but on the other hand strive to ensure that the solutions they use to meet them are cost-optimized. The very process of electromagnetic compatibility testing of electric, hybrid or internal combustion vehicles is performed by examining the electromagnetic interference of individual components. But it is also necessary to obtain the data you need by examining the entire product of the car. While products that are specific components of subassemblies are easier to test, the entire vehicle requires special facilities for this testing.
As a rule, EMC tests are performed in so-called. Reflection-free chamber. This electromagnetic compatibility test room has walls, ceiling and floor isolated from external electromagnetic fields. The finishing materials used, which absorb electromagnetic waves, give immunity to the influence of the outside world on the circuits under test. Making such a chamber for a large object such as a car, additionally requiring air supply and exhaust is expensive. Not to mention all the control and measurement equipment necessary for use during these tests.
Research costs are of great importance, which is why many design paths are supported by special software at the design stage. This is additionally important because the elaborate electronics of modern cars make it more difficult to achieve electromagnetic compatibility.
Simulation-based design systems have another important feature. They allow you to catch problems that may arise when all the components are integrated into the system. And this has a not inconsiderable impact on costs because fixing problems at the prototyping stage is much cheaper than at the production stage.
Examples of methods to eliminate interference are numerous. Following the principle that it is better not to do something than to protect yourself from it later, you have to start at the source. One of the best methods is shielding. It involves separating the device from the outside world with a layer of metal – e.g. foil, metal casing, fittings, etc. Unfortunately, it has several drawbacks. It is expensive because of the cost of the material used and the increase in weight it causes. With that said, the higher the frequency you want to eliminate, the thinner the materials used can be. Therefore, cheaper methods are used. An example is, for example, the use of inductive elements that have the ability to “stop” electromagnetic interference at the source.
Removal of the “common-mode” coil in the motor circuit of the controller/setter:
It is precisely because of the resistance to electromagnetic interference that special data buses are designed for the automotive industry. A good example of this is CAN which works on the principle of a symmetrical signal. A disturbance that enters the harness with the signal will cause a voltage disturbance that will be equal in each wire. But their difference will remain at a level that the bus controller can correctly interpret.
Generalizing the subject of disturbance generation, it can be said that greater current and faster change in its intensity cause greater electromagnetic interference. Both in terms of intensity and frequency range. In the case of electric vehicles, virtually all components have electric power. Power systems are particularly important in this case because the functions they perform involve delivering large currents with rapid changes. This is especially true for motor power circuits and braking energy recovery.
Security and the systems that follow make electromagnetic compatibility important because many sensors become RF emitters. Any radars and the microwaves they use must operate so as not to interfere with other vehicles on the road. It can be said that inside the car, a person is in a sense separated from external electromagnetic fields. However, because the body is not uniform and has, for example, a fair share of glass in the surface, it is to some extent permeable to waves. If this were not the case then not even smartphones would work inside.
Recently, many automakers have decided to remove the AM receiver from electric vehicles. In Poland, after the gradual dismantling of medium- and long-wave transmitters, the lack of such a receiver is not a problem. However, there are places where AM radio is important because of its range. There are more than 4,000 broadcasters in the U.S. with more than 80 million monthly listeners. It is important to remember that wireless Internet is not available everywhere, and there is no substitute for streaming-only reception and the use of the so-called “ wireless Internet “. internet radio. In the aforementioned United States, the radio station additionally plays an important informational role in large agricultural areas. It was the National Association of Agricultural Broadcasters that strongly protested the removal of AM receivers from vehicles.
Even such obvious equipment as power windows and mirrors can be that source of interference that prevents the use of analog AM radio. But they are used casually and securing them is doable. Unfortunately, shielding the drive train of an electric car is much more difficult and costly. As the manufacturers additionally argue, additional means of enabling AM radio would result in increased weight. And the resulting reduction in coverage….
Other disruptions and their impact on daily life and motoring will appear in Part 2 of the article.
DeltaTech Electronics to polski producent i ekspert w branży automotive, który na bazie ponad 25 lat doświadczenia wyznacza trendy w innowacyjnej diagnostyce samochodowej.
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