Sound EV safety solutions from Lotus and Harman

  • 09-Nov-2009 05:28 EST
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Noise mapping (left) of the HALOsonic warning system compared with that of a standard car.

For decades, OEMs and their major suppliers have been striving to reduce the external and internal noise levels of vehicles. But with the advent of electric propulsion, that need is being inverted in the name of safety.

In the U.S., Japan, and now Europe, there are growing concerns about “stealthy” electrically propelled cars that may cause a hazard to pedestrians (particularly the blind and partially sighted) and pedal-cyclists.

U.S. Senators John Kerry (D-MA) and Arlen Specter (R-PA) have introduced legislation that addresses the concerns about pedestrians; in Japan, the government is considering the situation with the aid of experts; and in the U.K., Lord Low of Dalston has tabled a question to the government, asking what assessment it has made of the danger the technology poses to pedestrian and cyclists.

Because of this growing concern and the looming likelihood of legislation for minimum vehicle noise, Lotus Engineering and audio specialists Harman International formed a partnership to develop an external sound system to warn of the approach of an electric vehicle. They are also working on the simulation of interior sound, regarded as a necessary cue to help the blind more easily achieve an awareness of the progress of a journey and their whereabouts.

The first deployment will be in an external synthesized sound system on a commercial vehicle using Lotus and Harman’s umbrella brand name HALOsonic (HArman and LOtus sonic). Initially the system will be produced in limited numbers. Harman has the exclusive rights to all Lotus’ active noise technologies for the OEM market, and those technologies are being integrated and packaged into the next generation of audio systems, stated the companies.

Called ESS (Electronic Sound Synthesis), the external application involves the use of one or two loudspeakers projecting simulated engine sound forward in a controlled band. When the vehicle reverses, it emits a “beeping” sound.

Particularly important is that an engine idle sound is produced immediately when electric power is switched on and the park-brake released; a specific potential danger is a silent vehicle suddenly moving.

The projected sound ahead of the car does not have to be that of an internal-combustion engine, said Lotus NVH engineer Andy Mackay. “It is possible to create any type of engine sound or almost any other noise that a manufacturer might regard as a warning device, including those that could identify a vehicle’s brand.”

But such freedom to create “aural badges” could result in a discordant cacophony of sound on the roads that would make legislation essential.

Lotus and Harman have installed External Electronic Sound Synthesis (EESS) on a Toyota Prius hybrid as a demonstration vehicle. These sounds include flat-six, flat-four, V8, V8 supercharged, and V12 engines, projected ahead of the car in a controlled band, and could be mapped against accelerator opening as well as—at present—vehicle speed.

But the development EESS also includes what the companies describe as “spaceship” noise. There are two variations: one fairly subdued and the other that would not shame a Star Wars X-wing starfighter. The external sounds can be separately transmitted in the cabin.

Moving through this repertoire on British roads proved entertaining for those inside and outside the Toyota.

It may also be possible with a production system for a driver to select specific sounds, said Tony Harberman, Director of Sales for Harman/Becker Automotive Systems. “Some manufacturers are conservative about this and want authentically replicated mechanical IC (internal combustion) noise, even including fuel injector sound. But others ask if we can produce a sound like a Star Trek-like ‘whoosh’! That is certainly a ‘can do’ for us.”

If integrated within an audio system, the cost of such a system would probably add about 20% to its standard cost—typically, more than a pair of foglights, rather less than a pair of heated seats. An OEM might consider it as part of a “fun pack,” giving a worthy, practical, and probably dull vehicle a very interesting sound identity.

But it is likely that only the sound of an IC engine would meet any legislation for external sound. That of a regular IC engine—diesel or gasoline—is certainly expected to be the preferred vehicle approach warning of blind people.

John Welsman, Transport Policy Officer for the U.K.’s Guide Dogs for the Blind Association, said: “Any artificial sound generated by an electric vehicle has to be consistent and immediately identifiable. It is possible to judge speed by engine sound, and we would want that sound to vary according to the size of the vehicle to identify a large SUV or a small sedan.” A guide dog also needs a sound cue, he added; the dog might show insufficient awareness of an electric vehicle without it.

Harberman said that academic research in the U.S. had shown that a vehicle with conventional IC engine could be aurally identified when it was almost three times further away from the listener than an electric vehicle.

Welsman would also want electric vehicles to have synthesized engine sound audible in the cabin. The sound of an engine under load when climbing a hill, on the overrun, on a downgrade, or ticking over when stationary could all make a subconscious, psychological difference, allowing blind people to identify with the environment outside the car and to be more in touch with others on board, so “participating” in the journey.

Interior sound would also reassure the driver, particularly on the overrun when the accustomed braking effect would be negligible and the sound of a slowing engine absent and also when making turns in heavy traffic.

Lotus and Harman are also working on road noise cancellation (RNC) and engine order cancellation (EOC) for IC engines, including those in hybrids.

Although active noise cancellation was first demonstrated (by Lotus among others) a couple of decades ago and was briefly incorporated in the Nissan Bluebird in 1992 (Japan only), it is only now that processor capability and costs have reached a level at which the technology can be regarded as wholly viable. The systems are particularly apposite for premium models but may quickly cascade to cheaper vehicles.

For RNC operation, up to 250 Hz global cancellation could be achieved at all occupant positions. “For example, a client had a bad 40-Hz boom on an SUV that had defied two years of remedial attempts; we solved it in two weeks,” said Mackay.

Lotus and Harman are developing systems to provide rapid transient response and co-related predictive capability.

“EOC benefits include avoidance of exhaust boom at various rpm and allow a different automatic transmission strategy to be implemented to help reduce engine CO2 emissions but still maintain required NVH levels,” said Mackay. “And it could also extend cylinder de-activation range while achieving a weight saving of up to 10% over the use of conventional NVH material throughout a vehicle.”

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