Lotus Engineering has developed technologies to synthesize external sound on electric and hybrid vehicles to counteract the growing concern these `quiet' vehicles pose to pedestrians and cyclists. A simulation of the sound of a real engine is used on the `Safe & Sound' technology demonstration vehicle, making it instantly recognizable that the vehicle is in motion.
Electric and hybrid vehicles, a favorite among the environmentally conscientious, have recently come in for criticism from blind and partially sighted people because the almost silent operation of hybrid vehicles at slower speed when running on electric power means blind and partially sighted pedestrians may be at risk when they cannot hear these quiet vehicles approaching.
Mike Kimberley, Chief Executive Officer of Group Lotus plc said "The increased acceptance of 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 legislators introduce minimum noise requirements for vehicles to encourage the adoption of technologies, such as ours, to increase pedestrian safety."
Clive Wood, Transport Policy Officer at The Guide Dogs for the Blind Association said: "Blind and partially sighted people use the noise of oncoming traffic as a cue for when it is safe to cross a road " if a `quiet' hybrid electric vehicle is approaching, they will no longer have this cue and are immediately put at risk.
The Lotus `Safe & Sound' Hybrid technology demonstrator uses a standard Toyota Prius, one of the highest volume 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 hybrid vehicle, without the potential risk to pedestrians and cyclists.
The solution that Lotus has devised is a novel reapplication and development of its Sound Synthesis technology. This is a part of the Lotus suite of patented active noise technologies, which comprise three main systems: Active Road Noise Cancellation, Engine Order Cancellation and Sound Synthesis.
To synthesize 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 synthesized sound projects a realistic engine sound in front of the vehicle. The technology was designed around the behavior of a conventional engine, using an existing engine sound to make it instantly recognizable, with the pitch and frequency helping to identify vehicle distance and speed. When the hybrid's gasoline 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 analyzed to establish the characteristic frequencies at different engine speeds. These frequencies are then entered into the synthesis controller, which outputs the sound through an amplifier and the loudspeakers.
We can only hope that the future of this technology means we can customize how our silent hybrids might sound in the future, maybe giving you the choice of high-revving racecar or deeper V8 engine sounds!
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