One thing common to many hybrid cars is the twin-pronged benefit of refinement and silence.
Just a brief drive in a hybrid is usually enough to confirm that, at low engine speeds at least, they don't produce a lot of noise. Even less when running in electric mode.
Still, there are always improvements to be made, and engineers at Bosch are looking into noise-cancellation techniques in order to reduce the noise hybrids make as the engine switches on.
As Wired reports, Automatic Noise Cancellation (ANC) is nothing new, and has been used for years to reduce noise in luxury cars.
But with fuel-saving techniques like cylinder deactivation, and with hybrid powertrains where the engine switches on and off, the noise generated can be more apparent due to a change in frequency of specially-designed engines.
Dr. Takeshi Abe, who worked on noise, vibration and harshness on the 2013 Ford Fusion Hybrid, explains that the unique firing order of the engine actually creates quite a boomy, unpleasant engine noise.
The Fusion Hybrid actually uses ANC--a technique that acoustically cancels out noises by generating an out-of-phase noise at the same frequency--to cancel this boomy noise.
That means the car can be made more efficient without sacrificing passenger comfort, and without loading the car with excessive levels of heavy sound-damping material. And efficient it is: The 2013 Fusion Hybrid manages 47 mpg combined.
Honda will also use the technology on its upcoming Accord Hybrid, but actually uses it on every variant of the 2013 Accord. Honda says the technology lowers the sound pressure level by about 3 decibels, in a range between 1,000 and 2,000 rpm where uneven engine pulses can create a harsh sound.
By actively cancelling noises produced by the engine, automakers can make their engines more efficient than ever before--and in the case of hybrid cars, make them even quieter...