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CASE STUDY: LOTUS ENGINEERING
Author: Jamie Turner, Lotus Engineering
■ Electric and hybrid vehicles have been coming in for criticism recently from a group of consumers that don’t drive: the blind. The lack of noise from hybrid vehicles at slower speeds when running on electric power creates a hazard, according to blind and partially sighted people, who rely on their ears to determine whether it is safe to cross the road or walk through a parking lot.
It is not only the blind and partially sighted who experience greater risk: the problem has became evident to the engineers at Lotus Engineering, as the hybrid and electric vehicles the company develops for its long list of clients move slowly around its workshops. Even fully sighted people use audible cues to judge the proximity of moving vehicles. In response,
Lotus Engineering has developed a system to synthesize external sound from electric and hybrid vehicles to overcome what is seen as a growing problem facing pedestrians.
Similar concerns were expressed some years ago when almost silent electric trolley buses replaced trams in some
US cities, meaning that pedestrians, familiar with the noise of tram wheels on rails, would not notice the much quieter buses approaching. For the same reason, commercial vehicles in the UK have used external noise systems for some time. Buzzers, beepers, and synthesized voice systems are regularly heard when reversing
Hybrid and electric vehicles have been questioned in terms of safety – especially in urban environments to warn pedestrians. And now the issue is receiving attention from legislators.
In Washington DC, a bill is going through Congress to establish a minimum noise requirement for hybrid and electric vehicles. The EU is set to follow suit, with the
European Commission also reviewing proposed legislation.
This could make the need for added noise on hybrid and electric vehicles a legislated requirement for all vehicle manufacturers. And this is where
Lotus’s technologies come in.
External electronic sound synthesis is a part of the Lotus suite of patented active noise control (ANC) technologies, which comprises three main systems: electronic sound
The new Evora, but are Lotus engineers working an all-electric derivative? synthesis, road noise cancellation, and engine order cancellation. Each of these systems can be used individually or in combination.
Lotus began developing its
ANC technology – a method of canceling out one noise by generating an equal and opposite noise – more than 15 years ago. The major obstacle to wide-scale adoption at that time was that established solutions to intrusive noise issues were widely available in the form of conventional passive
NVH material or other more established engine technologies, such as balance shafts. The fact that these alternative solutions usually added mass to the vehicle or consumed more energy was not seen as important, and ANC, although feasible, never succeeded as a commercial product.
Over the past few years, however, things have changed.
The computing power required to run the ANC system is now
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CASE STUDY: LOTUS ENGINEERING
Some are calling for EVs to generate the same sound as IC-powered cars advantageous for more effi cient vehicles generally, the emergence of hybrid created new applications. Most
As well as NVH matters, Lotus
Engineering is also working on eco-friendly systems, such as this range-extender unit frequently present on a single chip in high-end audio systems at a fraction of the cost of 15 years ago. The need to save energy and reduce CO
2
levels means that the conventional approaches that sidelined
ANC are now less desirable.
Harman International, a manufacturer of premium in-car audio systems, has acquired the exclusive rights to develop the
Lotus ANC technologies for volume production.
This represents a major step toward making this technology to customers.
Although ANC is now viably vehicles has led to the reapplication of internal electronic sound synthesis to create external electronic sound as a means to enhance pedestrian safety. Amid growing claims that these almost silent vehicles present a danger to pedestrians and other road users such as cyclists, by generating an external warning sound of the right character, not only can these vehicles be made safer, but also the character of the brand identity can be enhanced.
Of course, hybrid and electric vehicles do make a sound in the form of road noise, but this noise is generally heard when the vehicle is travelling at speeds of more than 20mph. At slower speeds, they are very quiet. A recent study by the University of
California found that electric and hybrid vehicles had to be about 65% closer to a person than a car with a gasoline engine before the person could judge the direction of travel correctly.
Which also begs the question, what is a hybrid or electric vehicle supposed to sound like?
Interestingly, while road users ideally want a sound that is instantly recognizable as an approaching vehicle, manufacturers and owners of these vehicles want a distinct electric vehicle sound. This has led to a series of new sounds being generated that are
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CASE STUDY: LOTUS ENGINEERING futuristic enough to be distinguished from a conventional engine, but have enough similarities with existing engine sounds to be recognizable as an approaching vehicle. Careful positioning and design of the speaker ensure the sound is projected forward from the vehicle in a fairly tight beam
– exactly where it is needed as a warning to other road users – without generating undue extraneous noise.
As part of the agreement between Lotus Engineering and Harman International, a
Toyota Prius has been used as a technology showcase. Three out other, removing audibly unpleasant frequencies and adding external sound to increase pedestrian safety.
For engine input signals from the engine are fed into the sound signals, measured by microphones located in the cabin. The software algorithms of the controller then calculate what sound is needed to provide cancellation and the speakers of the in-car entertainment system are used to put this into the cabin. This process takes only a few hundredths of a second and is continuously repeated, seamlessly and instantaneously adapting to changes in speed or road condition.
The second system is internal electronic sound synthesis, the purpose of which is to enhance sound in the cabin. The control system uses the engine speed signal, a throttle position sensor
Emissions reduction and safety enhancement are key areas at Lotus
Based on a Proton Gen.2 with a 1.6-liter gasoline engine, the Lotus EVE technology demonstrator features a start/stop system, full parallel hybrid drive and a CVT unit be particularly useful to disguise the change in frequency during
to engine. This system also forms the basis of external electronic sound synthesis.
To synthesize the engine sound, a road speed signal is taken from the vehicle. The sound is transmitted through a waterproof loudspeaker system positioned behind the front grille. Sound can be synthesized from the rear of the vehicle in the same way, to give a warning when the vehicle is reversing.
When a car is operating on the electric motor only, throttle and speed-dependent synthesized sound projects an engine sound in front of the vehicle. 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 powertrain control system switches the car back to running on the electric motor only, the synthesis controller instantly reactivates the system. The process is completely automatic and the driver hears almost none of the additional sound.
To generate a realistic sound, recordings of a suitable donor engine are made and analyzed to establish the characteristic frequencies at various engine speeds. These frequencies are then entered into the synthesis controller in the form of a voice that outputs the sound via an amplifi er and the loudspeakers.
Alternatively, more futuristic sounds for electric vehicles can be created using sampled sounds and generated waveforms. As proven in the
Toyota Prius demonstrator, used together or individually, the ANC technologies offer numerous benefi ts.
With increasing use of common platforms shared between manufacturers, ANC offers a way to provide a premium high-end product from a mainstream donor platform with a high level of commonality, and to provide some level of brand differentiation through acoustics. In addition, the normal acoustic development between different body styles
(sedan, wagon, coupe) can all be reduced because the ANC system adapts to all vehicle types with minimal retuning.
So although the benefi ts and relevance of ANC are numerous, the agreement reached between
Lotus and Harman International is hugely signifi cant. For the fi rst time, through the combined expertise of Lotus and Harman, there is a defi ned route to production for the world’s car makers. It will not be long before these systems are improving the refi nement and safety of future vehicles. ETi
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