In this article the automotive engineers at Robson Forensic provide an introduction to some of the vehicle safety concerns that are unique to hybrid/electric vehicles.
Hybrid/Electric Vehicle Safety
Hybrid/electric vehicles have been sold in the U.S. since 2000. In 2012 434,000 hybrid/electric vehicles including passenger cars, SUVs and pickup trucks were sold in U.S. These vehicles incorporate a variety of configurations to combine a conventional combustion engine with an electric motor paired with a rechargeable battery to deliver enhanced performance, superior fuel economy and ultra low emissions.
The vehicles are equipped with sophisticated transmissions, regenerative braking and multiple controllers combined with numerous sensors to provide functionality and a driving experience only slightly different from a conventionally powered vehicle.
In order to achieve a user-experience similar to what drivers are accustomed, hybrid/electric vehicles must respond to driver inputs in a predictable and reliable manner. Computers control the combustion engine, electric motor, and multiple driver aids, including traction and stability control. The sophisticated systems commonly include several computer processors and many sensors. Failure of these systems can result in unexpected and unreliable vehicle performance that may cause a crash.
Battery charging occurs during regenerative braking or during recharging for a “plug in” type hybrid vehicle. The recharging is computer controlled to prevent over charging and overheating that can cause an electric shock hazard or fire.
Computer Controlled Transmission
A sophisticated computer controlled transmission is required to combine power from the combustion engine and the electric motor. The power split may range from electric only, a combination of electric and combustion engine, or solely combustion engine. Failure of proper power delivery can result in unwanted or inadequate acceleration and may cause a crash.
The battery state of charge and operating temperature are continuously monitored. Excessive temperatures can lead to vehicle fires. Short circuits can lead to vehicle fire even after the vehicle is shut off.
The brakes may incorporate regenerative braking that recovers and stores electric energy. This may include the use of the electric motor as a generator in combination with conventional hydraulic brakes in order to slow the vehicle. The combining of the two systems is achieved with a sophisticated computer controlled system. Improper operation may cause inadequate braking and result in a crash.
Hybrid/electric vehicle must be designed and manufactured with additional crash safety features to protect the high energy battery pack and high voltage power electric circuits and components. Damage to these systems can cause electric shock and dangerous chemical exposure to occupants and emergency personnel.
Post Crash Safety
First responders must be trained to properly handle a damaged hybrid/electric vehicle. Vehicles are generally equipped with a master switch to de energize or isolate high voltage circuits that would pose a risk to emergency personnel.
Vehicle storage after a crash must be in an isolated location away from other vehicles and structures. For example, a damaged vehicle may have a slow coolant leak that can eventually cause a short circuit in the high voltage battery pack resulting in a vehicle fire.