Safety implications of quiet electric and hybrid vehicles


Electric and hybrid cars are much more environmentally friendly when compared to their internal combustion counterparts. With Electric Vehicle sales rising, more attention is being given to both the advantages and disadvantages of owning such a vehicle.



One new characteristic of an electric vehicle is the quietness of the ride. This holds especially true when comparing the engine sounds while accelerating or slowing down, and when compared to vehicles with turbochargers. Due to the silent nature of their powertrain, electric and hybrid vehicles lack the (sonic) feedback on speed and rate of acceleration that drivers have become accustomed to. When Electric Vehicles are travelling at low speeds under 20 kmph, they can barely be heard. This makes it difficult for pedestrians who depend on auditory cues from vehicles to move near approaching traffic. To improve pedestrian safety around electric vehicles, governmental regulations worldwide are mandating deployment of pedestrian warning systems for electric and hybrid vehicles.


Making electric and hybrid vehicles safer with sound


An ideal solution to synthesize the engine sound would be able to analyze the guiding signals from the electric motor such as pedal position, RPM, and speed, indicate the engine status, help to generate engine harmonics and ultimately lend a natural characteristic to the targeted sound. It should enable automakers of electric or hybrid vehicles to project this specific electronically generated sound from speakers at the front and/or rear of the vehicle, giving an early warning to pedestrians that a car is approaching. 


Pedestrian safety and beyond


The lack of noise in HEVs [Hybrid Electric Vehicles] and EVs [Electric Vehicles] is particularly problematic for the elderly, children, cyclists, the blind and their guide dogs that are conditioned to listen for cars. The risks are even greater in areas that require slower speeds such as parking lots. Research in the US highlights that pedestrians are twice as likely to be hit by an EV or HEV compared to internal combustion (IC) engine car. Engine Sound Synthesis helps provide safety in urban environments reducing the greatest risk of a collision with pedestrians, especially with higher-risk groups as stated previously.


Compliance with safety regulations


In January 2010, President Obama signed the Pedestrian Safety Act (S. 841). Introduced by Senator John Kerry, the new US law directs National Highway Traffic Safety Administration (NHTSA) to determine "performance requirements for an alert sound that allows blind and other pedestrians to reasonably detect a nearby electric or hybrid vehicle operating at low speeds." The US may have been first but Europe and Japan, the country with the most hybrids, are working on their own legislation. By mid-2019, all newly developed HEVs and EVs in Europe should have minimum external sound criteria to meet when travelling using electric propulsion under 20 kmph. Depending on driving conditions, these vehicles will have to reach a minimum sound pressure in certain frequency bands to make them safer for pedestrians and cyclists when travelling at low speeds. The Japanese also released guidelines for external sound for quiet vehicles in 2010, stipulating that an 'engine like' sound must be produced by the vehicle.


Automaker branding


The sound of a car engine is an integral part of the experience behind the wheel as well and plays a crucial role in defining the DNA of the car. It becomes even more important to replicate the characteristic exhilarating engine sound when it comes to sporty Hybrid vehicles. HARMAN helps ensure that the sporty engine sound, befitting the brand DNA of the car, transitions seamlessly as the car’s electronic control unit (ECU) switches between IC engine and the electric motor, in its pursuit to reduce fuel consumption and CO2 emissions.


HARMAN enables OEMs to create custom-designed sounds, thereby helping them to define an OEM- specific car DNA. OEMs see the need to create a sound that reflects their brand DNA, and this could become a way to differentiate manufacturers. Traditionally, an external sound associated with a car has been limited to its engine noise. In the case of HEVs and EVs, Harman allows OEMs to design 'sound signatures' to differentiate their brand and even their models. Signature sounds could mean that pedestrians are able to distinguish a brand without even seeing the vehicle. In the future, a sound could become a real brand differentiator.


Providing Engine Sound Synthesis features in Electric and Hybrid vehicles is an important step forward in establishing a safer environment for consumers both inside and outside the vehicle. Harman has been helping OEMs since 2015 to comply with government regulations to help ensure pedestrian safety. HARMAN built solutions to create an electronic sound that is projected from external speakers at the front and/or rear of the electric vehicle to warn pedestrians of its approach.


Andrew Kork from CNET recently visited the HARMAN R&D facility in Novi, Michigan to check out its work in EV sound synthesis. Andrew Kork took a ride in Tesla Model S on which HARMAN applied its Sound Synthesis solution that works both inside and outside the vehicle: inside, it uses the car's own woofers; while outside, it relies on speakers tucked behind the bodywork. For more information about HARMAN Engine Sound Synthesis, check out his review here




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