Lotus ‘Safe and Sound’ hybrid makes presence heard, if not felt

Hybrid cars such as the Toyota Prius and Honda Civic Hybrid could endanger lives of pedestrians and cyclists due to creeping up on them silently. Lotus Engineering has the ‘Safe and Sound’ answer.

At slower speeds, and when switching fully to their electric motors, such cars are undetectable to the naked ear, making them troublesome for partially sighted or blind people.

With this pressing safety issue praying on the minds of Lotus Engineering, the automotive research consultancy arm of Lotus has come up with what it thinks is a solution that will appease both pedestrians and cyclists. The simulation of a real engine sound to attract the attentions of those who might otherwise escape its environmentally best intentions.

Drawing on technologies it’s developed in the past, Lotus Engineering has channelled all this good into the confines of a Toyota Prius and slapped a ‘Safe and Sound’ adhesive across its panels and declared it Lotus Engineering’s official ‘Safe and Sound’ demonstrator model.

Recreating the aurally-appreciative growl of a combustion engine, every one is left in no doubt that something potentially dangerous is nearby at the exact juncture the hybrid vehicle chooses to cut its conventional power source and run on its electric motor.

Without crossing into the realms of a non-engineer's worst nightmare, this is essentially how the ‘Safe and Sound’ works.

• A road speed signal is taken from the vehicle to synthesize the engine sound, whilst a waterproof loudspeaker system is located adjacent allowing the sound to emanate from the vehicles front end.

• 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 behavior of a conventional engine was monitored so as to instantly recognize the pitch and frequency of sound identifiable by its distance and speed.

• 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.

• 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 power train 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.