Instrumentation • Electronics
Fig. 2. The Vauxhall Ampera has 30kg of cable shielding to counter electromagnetic interference.
test. It can well over £3 million to fully kit out an EMC test chamber complete with ‘rolling road’ dynamometer and test equipment. “We currently have 11 test facilities at MIRA and do 15 to
20 shifts a day to keep up with technology and changing test requirements.”
Over-engineering
Wayland cautions against over-engineering in vehicle design without paying attention to the subsequent test regime this will incur. EMC can be modelled on a desktop computer but until the vehicle is actually in a chamber with RF being directed at it and RF being emitted from it, the position of units and modules means that millimetres can make a significant difference in terms of results. Auto makers therefore ensure that component suppliers test their subsystems at a high level. EMC design therefore needs to be integrated into
silicon, the first part of the vehicle supply chain. Mart Coenen, chief executive officer at EMCMCC in Eindhoven, The Netherlands, is involved with integrated circuit (IC) development, pre-qualification and characterisation for linking to various vehicle sensors like temperature, pressure and fuel flow. Between the ICs and their sensors, the interface may range from simple analogue to sophisticated digital fieldbus protocols. “Most sensors nowadays are provided with four 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 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
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