Instrumentation • Electronics
wheel turns an encoder connected to a computer to steer the wheels, just as most throttles do nowadays instead of using a mechanical link between the accelerator pedal and a butterfly valve in the throttle.” Armstrong holds that improved
vehicle fuel economy has also been achieved by electronic means in other vehicle constituent parts, like suspension yaw and pitch control or stability control by modulating the braking and acceleration of different wheels when cornering for example. In electric vehicles, the power
drive usually runs on a high voltage battery of cells connected in series to produce a PWM output of 400-700V, whereas everything else typically runs off a conventional 12V battery. Higher voltage produces the same power at lower current in order to reduce cable size to save on cost and weight. From a product liability point
Association (MIRA), they will often exceed these requirements with additional tests devised in house. “The standards call for testing of
surges, voltage dips and interruptions, particularly for to grid where you need to make sure you are not putting harmonics into the network,” Wayland clarifies. “When an electric vehicle is charging, there must also be no radio interference, so it depends on how well the PWM inverter is suppressed, the shielding techniques used and how much engineering has been put into it all. “We are talking of high current
“EMC shielding is costly and adds unnecessary weight.”
Keith Armstrong, Principal,
of view, there is a legal requirement for auto makers to apply stringent tests according to ISO 11451 Part 2 and CISPR 12 and 25 specifications, but according to Carl Wayland, EMC technical and quality manager at the Motor Industries Research
Cherry Clough Consultants
at high voltage, so what gives off EMC emissions is given by the change in voltage, or dv/dt, in a signal to drive a motor. You need expensive test equipment like receivers, signal generators, amplifiers and transient generators to replicate high voltage transients which occur in the environment and surges to simulate electrical strikes, as well as voltage dips and variations on power mains.
“These tests are generally performed in an anechoic chamber kitted out with network analysers, scalar analysers and other diagnostic equipment for monitoring the vehicles under
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.
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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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