Active Noise Control with Colin Peachey of Lotus Engineering
Automotive IQ spoke with Colin Peachey, Group Chief Engineer Controls and Electrical, Lotus Engineering, UK in a three part interview series. Part 2 focuses on the opportunities made available with active noise control.
"You could theoretically have a whole bank of different sounds or you could download sounds like phone ringtones. You could even make your own!"
You have already given us a wonderful history of the technology but how specifically does active noise control relate to CO2 reduction?
C.P.: A couple of things from the conventional approach just to give you a bit of background: The first thing is many engines, have balance shafts in them. In order to counteract the noise and vibration that an engine inherently makes these shafts that basically spin around at the bottom of the engine that effectively smooth out the vibrations. Such shafts are an alternative to active noise but these shafts have a significant cost, they also have a significant weight, they also have a power requirement to run them. So, for example, quite a lot of the American muscle car series start with a road car and the first thing they do when they convert it to a race car is that they take out the balance shafts because they straight away get an extra 5 percent power out of it.
If we can delete engine balance shafts we typically will get a straight 2 or 3 per cent benefit to the CO2 figure straight away. If you replace them with active noise then that is a straight benefit.
The other thing that manufacturers are also employing is cylinder deactivation.
Imagine you've got a car with a V8 engine that can provide you with 400 horse power. For most of the time and definitely for the tests determining your CO2 levels for taxation, you've got so much power in reserve that you simply don't need half of that engine. So cylinder deactivation is effectively switching off half of the engine. Some manufacturers call it "Displacement on Demand." It has been applied in production mainly on larger engines (12 cylinders down to six or eight down to four).
A constant speed cruising the most efficient way of operating is by switching half the engine off. When you start to look at published papers and how engineers have investigated doing this for four cylinder engines switching down to two or six down to three, there is a problem: If you've got a six cylinder engine and you switch half of it off, it simply doesn't sound like a six cylinder engine anymore.
Generally, the range of speed and load the customer will accept cylinder deactivation is limited by issues such as the noise and vibration performance, because as soon as the difference in sound becomes noticeable generally the customer finds it unacceptable. When we switch off half the engine, what we find is that the characteristic frequencies that the engine produces are fundamentally changed. Some of the noise content will go up and some of the noise content will go down. Overall it would typically be noisier. The advantage of engine order cancellation is I can take away the new increased noises that I don't want and I can use my sound synthesis to put back in some of the noises that might be missing. Although I've switched to driving on just half of the engine I can now use this active technology to redress the sound balance to make it sound as if it is still running on eight. The idea is that the operational window for running half the engine has now increased. That could give for example, another 5 to 10 per cent CO2 benefit by being able to use my big engine in half-size mode a lot more of the time.
Do you see a sound app market developing around this technology?
C.P.: You could theoretically have a whole bank of different sounds or you could download sounds like phone ringtones. You could even make your own!
People are developing apps now that will do some of this in a very basic way. They're the sort of areas where a conventional car can also benefit. For example, we worked on a replacement for a six cylinder gasoline engine with a four cylinder turbo engine which would give the same power and the same performance as the larger engine. It was much lighter, the engine was 20 per cent cheaper and there was a 20 per cent CO2 reduction by using the four cylinder turbo compared to the original V6. The only negative aspect was that it didn't sound right!
Again one of the things we would do would be to actually to use the sound creation to enhance the engine sound to make it sound more like a premium product. Interestingly, the customer didn’t ask if we could make the four cylinder sound like a six cylinder because they didn't want to mislead the customer. Our target was to simply enhance the four to make it sound like a nice, powerful four-cylinder engine.
Some of those things do start to cross over into the world of EV and hybrids. For example, getting more specific, let’s look at how we can use road noise cancellation to save weight. If we can save weight, we know every percent of weight saved is a direct savings on our CO2. Weight is a key driver, particularly on an EV and a hybrid. On an EV every kilogram you carry around on the car actually has to be powered from a battery with finite capacity, so taking weight out gives you extra performance and extra range, which is one of the key things that people are working toward. Getting the weight out is quite important.
With quite a lot of the hybrids, there are several ways of doing things. Some of them have a range extender engine (a smaller internal combustion engine with perhaps two or three cylinders that primarily acts to power a generator to supplement the battery). Generally these engines are designed for maximum efficiency not refinement. So you can imagine an expensive, luxury car with a two or three cylinder engine in it would not be consistent with the image and the brand and the pricing of the product from the customer expectation.
The other key thing about these engines is because they are running as a generator; they're not directly linked to the road wheels and are set to run at their most efficient point which is probably a fixed speed at high load. One of the things about a conventional engine is when you drive it, and use your right foot to control the vehicle speed is that engine sound is part of your audio cue as to what you're actually doing. It gives you feedback. It tells you how fast you're going. It gives you a level of control.
Anyone driving a stick-shift, for example.
C.P.: Yes. But if you consider an engine linked to a generator that is just running at a constant note in the background that isn't really related to what you're doing with your right foot, and particularly a hybrid where at some points it will come on, some points it won't be operating, depending upon the state of the battery and how you're trying to drive it. It’s good for occasional use. It's a small, compact engine, it's probably quite noisy and unrefined so how do we manage it? It’s not efficient to simply throw all the typical NVH material at it, and balance shafts are an additional energy drain. With a small two or three cylinder engine running at high specific loads creating high levels of order related noise so engine noise cancellation to actually reduce the impact of when the engine kicks in and out is quite a major benefit.
How do you guys instill some of your own brand DNA into these types of engines or an EV/HEV?
C.P.: You haven't got the main engine noise that's a desirable sound; engine noise that's in synchronization with how you're driving that provides you with feedback and provides brand identity. It's quite important. I believe companies such as Harley Davidson or Porsche have almost got to the point where they are trying to take out a patent on their sound because it's such an intrinsic part of their brand. When you don't have that, but you've still got the road noise, the wind noise, you've still got the power steering pump and the air conditioning pump going in the background, you've taken away the one positive noise that you like and you're left with all the residual undesirable noises that you don't really want.
Here is a good experiment that I quite often do when I'm explaining this to people: if you're in a room and you're having a conversation, quite often people aren't aware of things like the air conditioning or their computer fans whirring in the background until you tell them to stop for a moment and listen, then they can hear all these other background office noises that your brain subconsciously filters out because your focus and attention is perhaps on what you're doing or the conversation that you're having.
It's a bit like that with a car. When you're driving, because the engine sound is so intrinsically linked to what you're doing, you tend to hear that and filter out the squeaks and rattles, the wind noise, the power steering pumps and all those other things. But when you take that engine noise away all of a sudden you're just left with this low level of mainly unpleasant or unwanted sounds that you don't really want. One of the key things on EVs that we believe to be beneficial is to use sound generation inside the car.
Firstly this can give you a level of brand identity and there's a big debate about whether or not the manufacturers will specify a single fixed sound supply a choice of sounds and the option to switch it off. I expect that if Harley Davidson ever made an electric bike, they would give it one Harley sound on that sounded like the sports exhaust and they wouldn't let anyone change it because that is such a fundamental part of their brand. But, because people have different preferences, other manufacturers might give you the choice of options. The other things we have found from similar discussions with manufacturers in Japan or America or Europe is that customer’s preferences for sounds are very different in different markets and cultures. I think it has something to do with the types of sounds that they find are pleasant in their music which provides a subconscious link to sounds that they emotionally respond to in a positive manner. For example different frequency ranges of different sounds affect people differently. Europeans tend like a lot of low frequency noise because that suggests power and sporty performance to them but to a Japanese customer that type of noise suggests unrefinement and bad design.
It opens up a whole different range of possibilities for the manufacturer, to customize for their different markets.
C.P.: Yes, particularly if you start talking about an EV. We've done projects for people where they've said: "I want my car to sound like an EV", and we say "Okay, so what does an electric car sound like from your perspective?" They then refer to films like "I Robot" or "Total Recall," with electric cars in them, and the sounds generated by the special effects people. It's normally somewhere between a jet engine and a force field, it is now the sound people expect an electric car to make.
If I played you the sound of a light sabre from Star Wars, you'd easily notice it was a light saber. But if I played you a Star Wars film clip with a different sound to the light sabre, you'd say: "That's just wrong, the light sabre doesn't sound like that."
It wouldn't feel right.
C.P.: No. There is no such thing as a light sabre, but you have within you a model, or impression, or idea, or an expectation about the sound and that's what it's like with electric cars. They say, an electric car theoretically could be really, really quiet but actually putting that into the movie doesn't sound right, so you want a whirring, humming force field type of sound so people think that's an electric car. We get faced with the challenge of trying to make it sound like the expectation of an electric car.
That must be really exciting from a research perspective.
C.P.: It definitely is. Up until recently, the noise your car made was a function of the design of what was the engine, what was the transmission, how was the body structure designed, what was the exhaust like? A lot of effort goes into the engineering of these components and systems to make the sound character right and all of a sudden it's not a function of engineering anymore. You can say, "I've now got a totally blank canvas for my sound." I can go to my marketing guys and ask, "What do you want this to sound like?"
The question remains whether manufacturers will let people actually adjust their car’s sound.
C.P.: That's right. I think the closest we've got is perhaps to have a quiet mode where you can listen to the radio so you don't have the sound generation. You might want something which is just a low level general background noise that gives the right sort of feeling and impression but at a more subconscious level. But then you might have a sport button which you press and then get extra acceleration performance and the suspension might go to sport but now the "engine sound" also goes to that mode as well. The car might then measure how you are driving it and give you the appropriate sound.
Something I guess you are not too far away from.
C.P.: No, it's quite feasible to do. We had a Lotus Elise, just a conventional engine, in which we put the sound generation and we made it sound like a V8. Then, without telling them, we took some of the car's marketing people out in the car and said: "What do you think of this?", and they were convinced that the engine was different. They thought it performed better. The feedback effect of engine sound creates such an overwhelming impression of what's happening.
One of the very first times I was out on the test track in the Tesla and the Tesla does not have this type of sound generation, I was driving around the test track and when I looked down I couldn't believe how fast I was going because I wasn't getting the audio feedback. The engine noise wasn't there and the electric motors were very quiet.
The conclusion of our interview series with Lotus Engineering’s Colin Peachey will focus on the safety and legislative aspects of noise optimization.