Instrumentation • Electronics
connection methods in parallel, which may be programmed at the foundry or at the assembly stage by the auto maker,” reveals Coenen. “Welded steel parts are becoming less common today and are being replaced by carbon fibre parts fastened with epoxy, as in the aerospace industry for example, where the wings of an Airbus are glued to the body. This makes them more transparent to electromagnetic interference. “The bus interfaces and
supply voltages are already defined so whatever is done in silicon is up to the IC manufacturer. I work with three of them and depending on the foundry, and in most cases they are mixed signal devices, of which the major part is digital nowadays. I carry out circuit simulations and 3D electromagnetic solving for them but the topology used by auto makers in the wiring harness is undefined, so you can
only simulate up to the device terminals. “With earlier designs you had 12V solenoids to open and close fuel injection valves, but with PWM this can be anything from 60V to 100V to speed up the actuation for better fuel efficiency. Therefore the harness carries many more signals nowadays than in the past with internal combustion engines and needs more validation with respect to electromagnetic interference.” Coenen discloses that the
“EMC shielding is costly and adds unnecessary weight.”
Keith Armstrong, Principal,
Cherry Clough Consultants
Vauxhall Ampera for example has 30kg of cable shielding. Electric vehicle charging stations may output power at 100kW in order to reduce charging time to around ten minutes, which in itself is twice as long as petrol refuelling, whereas domestic charging from mains may take anything from six to ten hours. German auto makers have
recently founded a work council for development and testing of electric vehicles, tabling an
Renault’s EMC test chamber R
enault’s EMC unit at Aubevoye in France was built in 2006 to keep
pace with the use of electronics in vehicle safety systems, such as ABS and emergency brake assist, ESP (Electronic Stability Programme) and airbags, as well as hands-free kits and satellite navigation.
The goals are to ensure the immunity of vehicles to electromagnetic interference from external sources, to control electromagnetic emissions from vehicles and to measure the radiation performance of radio aerials. A team of 30 researchers, engineers and technicians is involved in EMC/RF activities. A vehicle in traffic is constantly exposed
to electromagnetic fields from sources such as mobile phone transmissions, broadcasting transmitters and radar equipment. Regardless of the power or frequency of the field, it must not interfere in any way with the operation of the vehicle.
The EMC engineers use the immunity test cage to measure the resistance to interference of the vehicle and its equipment with the aid of four antennas that expose the vehicle to electromagnetic radiation over a wide range of powers and frequencies. The 1,800 square metre building houses three Faraday chambers grouped around a remote control room, with each room designed to be impervious to electromagnetic interference from external sources. The radio frequency test
chamber is dedicated to testing the radiation performance of radio aerials. Incorporating a 12-metre diameter arch comprised of 132 high-frequency and low-frequency sensors, the chamber enables 3D radiation diagrams to be produced in two hours compared with about two days for 2D patterns. In the immunity test chamber, the electromagnetic resistance of the vehicle is tested under extreme conditions. Placed on a roller test bed simulating actual running conditions, the vehicle is exposed to electromagnetic fields from antennas generating over 100 V/m at frequencies from 100 kHz to 3 GHz. European regulations specify a resistance of 30 V/m, which is much higher than the values encountered in the traffic environment. Conversely, the quietness (emissions) test chamber enables the electromagnetic emissions from the vehicle and its electronic equipment to be measured while excluding external radiation. ●
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