Electric and hybrid vehicles, a favourite choice of the environmentally conscientious have recently come in for criticism from blind and partially sighted people. Due to the almost silent operation of hybrid vehicles at slower speed when running on electric power, the independent travel of the blind and partially sighted may be put at risk as they cannot hear these quiet vehicles as they approach, making crossing a road or walking through a car park hazardous.
Mike Kimberley, Chief Executive Officer of Group Lotus plc said "The increased acceptance of greener vehicles such as hybrid and electric vehicles is to be encouraged; they have an important role in improving fuel economy and reducing emissions. Our advanced external sound synthesis technology increases pedestrian safety, while retaining the car's environmental benefits. We hope that legislators introduce minimum noise requirements for vehicles to encourage the adoption of technologies, such as ours, which will ultimately increase pedestrian safety"
The Lotus 'Safe & Sound' Hybrid technology demonstrator uses a standard Toyota Prius, one of the highest volume and most advanced hybrid vehicles to demonstrate the sound synthesis application and compensate for the lack of engine noise emitted by the vehicle when running on an electric motor. What has resulted is the same environmentally conscious hybrid vehicle, without the potential risk to pedestrians and cyclists.
To synthesise the engine sound, a road speed signal is taken from the vehicle and a waterproof loudspeaker system is positioned adjacent to the radiator allowing the sound to emanate from the front of the vehicle. Once the vehicle has passed, the sound is not heard. When the car is operating on the electric motor only, throttle and speed dependent synthesised sound projects a realistic engine sound in front of the vehicle. The technology was designed around the behaviour of a conventional engine, using an existing engine sound which makes it instantly recognisable with the pitch and frequency helping to identify vehicle distance and speed. If the hybrid's engine starts operating, at higher speeds or throttle demands or lower battery levels, the control system automatically stops the external synthesis. When the powertrain control system switches the car back to running on the electric motor only, the synthesis controller instantaneously sets the system running again. It is all completely automatic and the driver hears almost none of the additional sound.
In order to generate the engine sound, recordings of a suitable donor engine were made and analysed to establish the characteristic frequencies at different engine speeds. These frequencies are then entered into the synthesis controller in the form of a 'voice' which outputs the sound through an amplifier and out through the loudspeakers.