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Power cut: EV makers focus on post-crash performance

Despite the slow start that many high profile battery electric vehicles have made in terms of sales, there is widespread agreement that new cars will increasingly use some form of powertrain electrification. Bringing live electricity into a vehicle, be it battery electric, plug-in hybrid or fuel cell, adds complexity to the safety features designed and developed for that vehicle. Nevertheless, in late 2012, the Volvo V60 Plug-in Hybrid scored five stars in its Euro NCAP test; in the US, the 2013 Ford Focus Electric recently scored five stars in its NHTSA NCAP test.

In 2012, Thatcham research in the UK became the eighth Euro NCAP-accredited test lab. Megatrends spoke to Andrew Hooker, Future Vehicles Engineer at Thatcham Research, about the safety aspects of electric vehicles

What are the fundamental differences between electric vehicle (EV) and internal combustion engine (ICE) car safety?

EV powercutThe core difference between EV and ICE safety is that we have familiarity with ICE technology developed over many years, yet for many, EV is new and unfamiliar. The vehicle manufacturers and the other technology providers are naturally striving to develop the most efficient EV that today’s technology constraints will allow; yet as soon as that vehicle is launched, it is released on consumers, service and repair industries, and emergency services largely unfamiliar with it. EVs were keenly promoted in the early 20th century, but in reality, since marketing of the Mitsubishi i-MiEV and the Nissan Leaf began, Thatcham has managed a surge of concern from many sectors within and outside of the industry.

How do the safety requirements differ between different forms of electrified powertrain, for example, between battery electric vehicles (BEVs), hybrid EVs (HEVs), plug-in hybrid EVs (PHEVs) and fuel cell EVs (FCEVs)?

With HEVs and PHEVs, the lack of knowledge is compounded, because to the untrained it appears to be an ICE vehicle. OEMs have done well with the safety protocols for EVs with automatic cut-out of the high voltage system governed by the SRS [safety restraint system]. Yet this does not account for every emergency scenario. We know from our collaboration with the emergency services regarding casualty extraction that they often require the electrical system to be active for moving electric seats to a position where a driver with spinal injuries can be safely extracted.

With an ICE vehicle, the fuel cut-out reduces the risk from fuel system fire, but leaves the electrical system operating. With an EV, there are a number of components that still present a risk, even after the high voltage system which powers the engine has been ‘locked out’. Capacitors still hold charge, the magnets in the motor rotor mean it can move and align itself, and the battery itself remains susceptible to temperature.

Should EVs undergo different safety tests from ICEs?

No, at Thatcham we do not as yet believe this is necessary. We have the very successful Euro NCAP programme that is far more than just a test of the vehicle structure, with aspects such as pedestrian safety and ADAS [advanced driver assistance systems] technologies being assessed. A well known incident in the US, in which NHTSA crash tested an EV which subsequently caught fire, did exactly what it should have done: it identified an issue, albeit in less than ideal circumstances.

What can be done to ensure the safety of EVs not only in crash situations, but also post-crash, where often small garages and warehousing may be involved in the storage or repair of the vehicle?

EV powerThe solution is greater dissemination of EV knowledge through accurate specific data and training. The media has commented on the slow take up of EVs, yet in the UK alone there are 50,000 Honda and Toyota HEVs already on the road in addition to battery EVs. At Thatcham we’re proud to have been central to this up-skilling, as being non franchise-specific we’ve been able to provide knowledge and training across the industry to many sectors and are continuing to do so. Vehicle recovery specialists, emergency services, and even HM Customs and Excise have received training and equipped themselves with the tools and necessary PPE [personal protective equipment].

Incidents involving laptop batteries or the NHTSA incident we referred to have led to questions about the safety of lithium-ion (Li-ion) batteries, yet they remain the battery of choice for the majority of EVs. What is the view among safety experts of the Li-ion battery versus other energy storage solutions?

Li-ion battery technology is the choice for the majority of EVs because of its energy density. That is only logical as the manufacturers need range performance to make EVs a practical alternative to ICEs. Yes, there have been incidents with Li-ion batteries, but put this into perspective with volume: according to Cisco Systems, by the end of 2013 there will be more smartphones than people on earth. That’s a lot of Li-ion batteries, and comparatively few incidents. Vehicle engineers have learned how to safely package fuel tanks, SRS airbags and LPG, and we are already seeing developments in battery handling.

What is the procedure for post-crash EV batteries?

There is no set procedure for batteries post-crash. Actions depend on the incident. If the vehicle is flood damaged or otherwise badly damaged enough to be deemed a total loss, it will probably go to a salvage specialist intact. The better salvage companies have handling procedures.

The exception really is Renault, with its battery lease scheme, where most aspects are covered by Renault, including battery shipment costs to France.

If the battery is removed post-crash, for vehicle repair, it should be clearly labelled and identified, and stored somewhere dry at a suitable temperature. It should be remembered that although the battery lock-out or cut-off will have been performed, the battery will still be in whatever charged state it was in prior to this.

PSA and Bosch are jointly developing Hybrid Air, a hybrid solution which will enable the production of battery-free hybrid cars. Apart from the efficiency, cost and energy storage advantages that PSA has mentioned, could there be any safety advantages in removing entirely a Li-ion battery from a vehicle?

At Thatcham we are of course aware of Hybrid Air, but we’ll let PSA and Bosch, and others, mature the technology before we comment on this specifically. There are efficiency and energy storage issues to overcome too, not least of which will be the temperature changes induced by changes in air density. This will be an issue for the storage tank, and the mechanical pump and motor. And although very rare, a storage system is susceptible to failure too. Yes, we’d always advocate removal of any potentially harmful component from a vehicle, such as a Li-ion battery, but so far we have seen little evidence of unacceptable safety risk.

What is the best way to cool batteries – coolant or air?

There are advantages and disadvantages to both methods. Water cooling works well, but one notable incident in an American safety test was as a result of battery shorting in conjunction with a coolant leak. Air cooling is simpler, and more energy efficient. The proposed lithium-air batteries, as the name implies, are open to air so self-cool to a degree. But moisture content in the atmosphere is an issue that manufacturers have to overcome.

Hybrid powertrains add considerable weight to a vehicle, especially one which is also available with an ICE. What impact does this additional weight have on developing safety technology and safety testing for a vehicle?

There has been some, as yet unconfirmed, data from the US that the additional mass is resulting in a reduction in occupant injuries in HEVs and PHEVs, but the weight is not an issue with safety testing. At Thatcham we carry out assessments on the Volvo V60 Plug-in Hybrid, as we would on the V60 with an ICE, and it passes or fails. The manufacturer is aware of the additional mass and must engineer the vehicle to perform. In the case of the V60 Plug-in Hybrid, Volvo still achieved the five-star rating in the Euro NCAP assessment. That’s the advantage of a clear and transparent protocol like Euro NCAP; the vehicle manufacturers know what they’re working towards.

Volvo V60 crash test

In late 2012, the Volvo V60 Plug-in Hybrid scored five stars in its Euro NCAP test

From a pure safety perspective, what is the safest way of designing and manufacturing an EV?

The battery location that most manufacturers have chosen, namely deep and central within the structure, makes the most sense as it is away from harm in the majority of incidents. Toyota has located a compact Li-ion battery under the front centre console of the Prius+. The location of the high voltage cut-out device has been markedly better in some vehicles than in others. But of equal importance is that the EV, HEV or PHEV is recognisable as such, so that appropriate care is taken. The clear identification of high voltage cabling in orange has been well received, but we’d like manufacturers to ensure that thought is given in development to emergency rescue and repair, so that no cables are channelled around the exterior, close to panels that might need to be cut through. And lessons learned from the NHTSA Volt incident, regarding what happens in accidents when the vehicle is unlikely and unable to perform within its usual parameters, are vital.

Does the rising use of different materials for alternative powertrain cars, like carbon fibre, present any problems, challenges or opportunities to vehicle safety?

At Thatcham, we know and accept that OEMs can and will use different and new materials. As conventional ICE vehicle structures get stronger with increased inclusion of press-hardened steels in the body construction, this should translate into safer structures for the PHEV and BEV derivatives. Some OEMs are much better than others at building practical and economical ‘repairability’ into their designs. Obviously weight reduction, whether by CFRP [carbon fibre reinforced plastic] inclusion or by UHSS [ultra-high strength steel], can lead to smaller and less exposed battery packs. As some are looking at integrating the battery cells within the vehicle structure itself, we could see an opportunity for the engineering of battery behaviour following an impact within the impact force load paths. Many engineers feel steel is not a suitable housing for a high voltage battery, but it is a known material with predictable behaviour, so maybe body integration could be a good compromise.

Is there anything in particular that you are pushing for in terms of EV safety?

As discussed before, we accept that PHEVs and EVs are in development, and are here to stay. Clear and specific handling and repair information needs to be available. Whilst we respect the manufacturers’ needs for their own branded aftersales networks, we know that in reality, cars soon disseminate externally into the wider independent networks. Thatcham has been approached by, and is working with, some manufacturers so that we can train and educate industry sectors, and we are happy to collaborate on this with others.

Martin Kahl is the Editor of Automotive World

This article was first published in the Q1 2013 issue of Automotive World Megatrends Magazine. Follow this link to download the full issue