Electric engineering 06 February 2013
As increasing numbers of LCVs and PSVs are equipped with hybrid and electric powertrains, engineers and technicians need updating not only on the technologies, but also the maintenance and safety issues. John Challen and Brian Tinham report
Hybrid and electric vehicles (EVs) are fast becoming more familiar sights on our roads, so it's obvious that fleet and workshop managers, as well as their technicians, need a proper grounding in good and safe practices and procedures. Less obvious, perhaps, is the point that workers in the emergency services, and even drivers (professional or otherwise), also need to be made properly aware of the risks these machines can present to the unwary. And for each group, there is the complication that powertrain systems, batteries, motors and ancillaries are still evolving – meaning that standards and best practices are moving feasts.
Eliot Smith, an independent training provider at Pro-Moto Automotive Training Solutions, based in Aldershot, is good value here. Formerly a technical training co-ordinator with Honda (home to a wealth of experience on alternative drives for passenger cars), Smith later headed the team writing national training qualifications for technicians working on electric and hybrid vehicles, published in 2011. He now develops and runs courses for manufacturers, colleges and associations, aimed at everything from full technician certification to raising awareness of the risks for people using or coming into contact with these vehicles.
"There are several grades of qualifications for IMI [Institute of the Motor Industry] members," explains Smith. "The first is an awareness qualification for those who use electric and hybrid vehicles in their line of work – such as delivery drivers and professional drivers." Courses primarily cover awareness of hazards in the event of an accident or a system fault. Delegates get a Level One certificate.
"The second qualification is hazard management – developed for the emergency services," continues Smith. "If a hybrid or electric car or LCV is involved in an accident, the ambulance, police and fire crews – but also vehicle recovery operators – need to be aware of the hazards involved in handling and moving these vehicles." This course is all about explaining the types of hazards, and identifying potential risks. It leads to a Level Two qualification.
Then there are two further certification grades, designed for technicians covering respectively routine maintenance or repair of hybrids and EVs – the latter necessarily including removal and replacement of high-voltage components. Both of these are Level Three qualifications.
"If something goes wrong, technicians need an in-depth awareness of the technologies. They also need to know how to establish where the fault might lie, bearing in mind that there are engine management units but also HV systems, and different equipment for diagnostics. Most importantly, though, they need to be aware of the risks," states Smith.
"So for Level Two And Three qualifications, we essentially identify how hybrid and electric vehicles work and the kinds of voltages they operate at," he continues. "Beyond that, we also explain some of the less obvious risks – not just the electrical hazards, but also mechanical and the possibility of combustion."
Smith gives the example of the potential for damaged or ageing batteries to become unstable. At the most basic level, he also warns that batteries are likely to be fully charged, and hence dangerous, even if a vehicle is switched off. "Most manufactures follow standard shutdown procedures, but capacitors can retain very high charges for some time, and batteries always have significant potential across them – so there are very real and present dangers," warns Smith.
"If technicians are working on the HV side of a vehicle, it's because there's a fault," he observes. "And, unlike with internal combustion engines, you can't hear, smell or see a problem with the electrics until it's too late... Remember, these batteries deal in dc [direct current] and capacitors can discharge very quickly and at very high voltages. It only takes 50 milli Farads to kill you."
As a result, in large part, certified training and qualifications relate to taking common sense precautions – using the correct PPE (personal protective equipment) and ensuring that operatives are protected throughout repair and maintenance operations. However, they also cover the importance of checking that no HV hazards are left on a vehicle that might cause a problem for its users.
Most important, says Smith, the courses look at the risks associated with electric motors themselves. "All hybrids, even fuel cell types, use electric motors and these are very powerful. They can accelerate very quickly and deliver very high torque, even at low speeds. They also use powerful rare earth magnets, so, for example, if a technician has a pace maker, they can seriously affect him or her."
But perfectly healthy people can get hurt, too. "I know of one guy who lost the tops of his fingers... And bear in mind that electric motors can also become HV generators, if they're turned over. There won't be any warning."
Smith adds that similar caution is required around stop-start systems. "If an engine is switched on, but not running, it can spring back to life by itself, and very fast. So when technicians are working on vehicles with these systems, they need to be aware. They need to restrict access and make sure that appropriate signage is in place. That's especially the case if they're testing and running up an engine. It can restart even from a low battery charge. Several parameters can affect what happens, even humidity in the cab."
What's more, there are fire hazards around EV batteries. "Li-Ion cells can be dangerous – as seen when an electric bike spontaneously combusted at Donnington Park not that long ago," he warns. "They get very hot and produce hydrogen. It's very easy to be blaze around engines – until something goes wrong. The fact is that, with EVs, if something goes wrong, or there's an accident, then the risks go up exponentially... It's like anything: if you're aware than you can minimise the dangers. If you're not, then you have no idea of the risks you're exposing yourself and others to."
Potentially groundbreaking work on electric and hybrid batteries is being carried out at Millbrook Proving Ground, aimed at improving their vibration resistance, and so reducing repair and warranty issues for operators and manufacturers alike.
"We were asked by a customer for some consultancy on how best to test EV batteries for vibration durability," explains Jim Hooper, senior engineer in Millbrook's component test laboratory. "We did some background research, and found little published data for electric vehicles."
Closer inspection uncovered some standards and an ECE regulation on the horizon that will make vibration testing a legal requirement for EVs. "But the data was derived from ICE [internal combustion engine] products, which have very different vibration characteristics," states Hooper. He also reveals that, in some cases, data had been taken from consumer electronics studies, aimed at abuse testing. Using this as a baseline might well lead to over-engineered batteries, he says, with all that means in terms of cost and weight.
Millbrook's solution has been to borrow some electric vehicles and evaluate the battery packs, comparing their behaviour against ICE-powered vehicle equivalents. "We found that even in an EV battery pack, there is some powertrain-induced vibration," he says. "We also found some high energy vibration spikes above 300Hz on some of the vehicles' batteries.
"This is an area we are still researching, but we believe it is associated with the different battery cooling strategies." Other possibilities include the power electronics and electric motors.
The next step will be to determine the most effective vibration isolation methods. And it's not just about the motor and battery mountings. "The cooling strategy also has an effect on the vibration durability of the [battery] pack," explains Hooper, who says that results will be made public in due course.
John Challen and Brian Tinham
Millbrook Proving Ground Ltd
Society of Operations Engineers
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