Due to the almost silent operation of hybrid and electric vehicles running on electric power at slow speeds, blind and partially sighted pedestrians may be at risk while crossing roads or walking through parking lots since they cannot hear the vehicles as they approach.
Lotus Engineering, a name most commonly associated with lightweight sports cars, has announced that it has developed a system to synthesize external sound on electric and hybrid vehicles to make them more audible to pedestrians and cyclists. A simulation of a real engine sound is used on Lotus' Safe & Sound Hybrid technology demonstrator vehicle, making it instantly recognizable that the vehicle is in motion.
The demonstration vehicle is a Toyota Prius equipped to demonstrate the sound synthesis application. The solution Lotus has devised is a reapplication and development of its Sound Synthesis technology, a suite of technologies originally designed to reduce the amount of cabin noise in a conventional motor vehicle by using active sound cancellation.
An artificial engine sound is played through a waterproof loudspeaker in the car's nose, compensating for the lack of engine noise emitted by the vehicle when running on an electric motor. Because it's just a speaker, Lotus can make any sound they want, but they've stuck to using an existing engine sound that makes the vehicle instantly recognizable, with the pitch and frequency helping to identify its distance and speed. Front-facing speakers mean that once the vehicle has passed, the sound is no longer heard.
In electric-only vehicles, the system is always on, but for hybrids the system only operates when the vehicle is using electric power. If the hybrid's engine starts operating--either at higher speeds, higher throttle demands, or lower battery levels--the control system automatically stops the external synthesis. It is all completely automatic and, according to Lotus, the driver hears almost none of the additional sound.