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What is an EV?
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|12/02/2013 07:00 AM|
|To those who think texting and driving is somehow OK....|
Some claim this ad is sensationalist and violent, and shouldn't be shown to children. If anything I think it understates the accident itself because people who are cossetted in their 'safe' cars seem to have lost sight of the fact that accidents DO happen. They think that texting and general cellphone use whilst driving is OK because they think that they can multitask. They're wrong. Until this message gets across to people, and until the police and local authorities actually start penalising people for doing it, ads like this are the best shot of trying to get people to understand.
Yes, it's a re-post, but it's been 4 years since I posted it last, and given the sheer idiocy of drivers with their cellphones nowadays, I thought it was worth bringing up again.
EV = Electric Vehicle. An EV is not a hybrid, it's a vehicle powered entirely by electricity either via a motor-generator, a fuel cell, or a battery pack. Historically, GM first proved that a fully-electric car could be a success with their EV1, a car which ultimately was killed off by short-sightedness and political lobbying. (See the film Who Killed The Electric Car for the torrid history of that vehicle.
Ah yes. I've heard of EVs then - the Chevy Volt, right?
Sort of, but not really. The Chevy Volt was supposed to be the world's first mass-produced, family-friendly, everyman electric vehicle. It looked like it would happen too; the original idea behind the Volt was fantastic. It's a battery-powered vehicle that can get a decent commuter range on pure battery power. At night you plug it in to recharge it, and if you start to run short on juice during the daytime, a small onboard petrol engine could spin up a generator to provide recharging capability to the batteries on-the-fly. If you stayed within the electric range, the petrol engine would never come on. This is how Chevy promoted the Volt up until October 2010 when it transpired that a tiny design change had been made which turned the Volt from an EV into a petrol-electric hybrid instead. Up until that point, GM had been promoting the mantra that there was "no mechanism in the Volt to drive the wheels even if the engineers wanted to" source). It was when Motor Trend first test drove a production Volt that they discovered that the petrol engine could and did drive the wheels. Whilst there is no direct mechanical link (like a driveshaft) between the Volt's gas engine and the wheels, above 70mph a linkage is accomplished by meshing the power output of the engine with the power output of one of the motor-generators through the plantary gearset. Just like a Prius. No matter which way you cut it, the gas engine can now directly contribute to driving the transmission. That means it's not an EV, it's a hybrid (although GM like to call it a Range-Extended EV or ER-EV for short).
(Motor Trend Explains the Volt's Powertrain)
(Motor Trend Explains the Volt's Powertrain)
Picture credit: Chevrolet
After the Volt, the next most likely name you'll have heard of for an EV is Tesla Motors. These guys were the first manufacturers to build a pure EV that wasn't some joyless science experiment. Instead they took some novel design approaches to the motor, transmission and batteries and shoehorned the lot into a Lotus Elise body, creating a 2-seat roadster that people were already familiar with and making it fun to drive. It's important to note here that Tesla did not take a Lotus Elise and convert it to be an EV, but built their own chassis and EV system and put an Elise body on top.
The Roadster was, by all accounts, an amazing car to drive with sports-car handling and if you drove it with a light foot, a 250 mile range. The Roadster was a boutique car though - not manufactured in large numbers and the cost was prohibitive for the average buyer. To combat that, Tesla next vehicle was/is the the Model S - a 4 seat family sedan which they hope will be what the Chevy Volt should have been - a fully electric family car for the masses. Prices are steep but not intergalactic (base price in 2013 is around $57,000).
Picture credits: Tesla Motors
Electric motors are all torque
There is a pronounced difference in the driving experience when you step into an EV for the first time. There is typically no gearbox or transmission. Electric motors differ greatly from internal combustion engines in the way they deliver power and torque, and for the most part, you have full torque from the instant you mash the accelerator pedal until the motor overheats. It's like an instant "go" pedal - there's no hanging about waiting for the engine to get up to speed, no changing gears, nothing. Unless you've driven an EV it's very difficult to explain what it feels like, but the best way is this: imagine your car in first gear with your foot flat to the floor. Now imagine that acceleration all the way up to the top speed of the car without any interruption. But then accompanied by an electrical buzz that sounds like a swarm of bees on crack.
The graph here gives you a theoretical comparison. The orange plot represents an electric motor torque curve and the blue plot represents an electric motor power curve. By comparison, the black plot shows a high performance internal combustion engine torque curve. From this you can see the full torque from zero of the electric motor as well as the linear power delivery. It's also interesting to note that most decent petrol engines are spent by about 8000rpm whereas a half-decent EV motor can go up to 15000rpm or so.
EV Range and Infrastructure
The major drawback to a fully electric vehicle is that when you run out of juice, you can't simply walk to the nearest petrol station. When the battery is dead, it's dead, and the range is highly dependent on multiple factors. Driven correctly, a Tesla Roadster can (and does) return about 200 miles on a charge. Driven with a lead foot, it can be as little as 60. Weather affects EVs too - cold days mean less juice not only because of the inherent design issues of batteries, but because as a driver you'll typically want to run the heater at the same time. Same goes for very hot days - turn on the electric air conditioning and your range can drop in half.
Is it really that bleak?
That depends. If you're a horsepower-driven petrolhead, then yes, it really is that bleak. If you're a little more reasonable, things aren't so bad. For example if your daily commute is less than 100 miles each way, an EV is the ideal car. If your workplace is forward-thinking enough to provide charging posts for some of the parking spots, things look even better because you can leave your car charging whilst you work. The problem comes when you start talking about long journeys and road trips. No EV is going to give you a 500 or 1000 mile range like a petrol or diesel car can. And internal combustion engines are simple to get going again - pull in to a petrol station, spend 3 minutes filling up and you're on your way. EVs do not have the luxury of that sort of infrastructure yet - it's not like you can pull in somewhere and juice your car. Granted there are more charging posts than there were, but time becomes the issue then. A slow charge for an EV battery pack is typically 8 hours. A quick charge with the correct equipment is 2 hours - better but it's still not 3 minutes. Until battery technology can overcome the charging issue, EVs will be stuck in the commuter market and realistically that's no bad thing. Less pollution in crowded cities can only be good for everyone.
EV charging stations are not yet a common sight in most places and as such, there's no accepted way of informing drivers where they are. There is an open source road sign being proposed in Europe by a Dutch group, but at the moment it is still just a public domain proposal and has not yet been officially sanctioned. EVINFRA are also proposing standard charging bay layouts and couplers in an attempt to prevent VHS vs. BETAMAX or BluRay vs. DVD-HD type standards battles that do nothing other than set back the technology and confuse consumers.
One possible solution to the slow recharge issue would require all manufacturers to homologate on a common battery pack design and access. Given the history of commonality between different vehicles, I think we all know this would be difficult if not impossible to achieve but the benefits of doing it would be huge. Why? Imagine the battery pack isn't bolted into the car permanently, but that it is removable. Future charging stations wouldn't have charging posts, but would have a way of pulling the depleted battery pack out of your car and replacing it with a fully-charged one. Your depleted pack is then charged 'offline' by the facility and is then put into someone else's car when they come in for a 'fill up'. In essence, you own your car, but not the battery pack - it becomes like petrol - a commodity your vehicle uses but you don't own it. A good-sized EV battery pack is hefty - it weighs a couple of hundred kilos at least and it's not something you could just whip out on your own. The charging station would need to have automated equipment to do it for you which is why there would need to be a common standard for battery pack design, location and access.
One company that pioneered a lot of infrastructure technology is Better Place, based out of Palo Alto, California. They brought electric taxis to California as well as a planned $1bn charging post infrastructure. They worked on swappable battery packs (the video below shows an example) and flirted with foreign markets in Europe, Asia, Australia and Israel. Sadly this is all past tense though as Better Place went bankrupt early in 2013.
EVs are not a pollution-free green nirvana
The Green brigade get all foamy at the mouth over EVs because of the perception that they are pollution-free. Locally, they are - ie directly around the vehicle itself, there is no pollution generated by the vehicle. But globally, they are not. You have to charge an electric vehicle, which means you have to use electricity. Electricity generation happens at power plants, which produce pollution. So an EV is a displaced polluter, which isn't a bad thing. There's a far higher chance of being able to figure out how to clean up the source of electricity generation than there is of trying to clean up millions of individual cars.
The true nirvana
Of course the dream here would be to use renewable energy like wind or solar power to provide the electricity to charge electric vehicles. At that point, the only pollution involved would be during the manufacture of the vehicles themselves. In daily use, they would effectively be fully zero-emission vehicles.
EV Battery pack technology
Currently most electric vehicles use either nickel metal hydride (NiMH) or lithium-ion (Li-ion) batteries providing a DC voltage up to 500v, and a power rating of anything from 18 to 50 kilowatt-hours. This is why you need a charging station or a special kit to rapid-charge an EV battery. A typical household electrical supply simply isn't capable of providing the amount of power required to perform a quick-charge.
Li-ion batteries are now preferred because, configured correctly, they can weigh less than half of what a similar capacity NiMH battery pack weighs. Tesla's current generation battery pack crams so much power into such a small footprint that they currently have the highest energy density in the industry, and one pack could run a small house for 2 days on a single charge.
Tesla's battery packs are unique in that they use thousands of 18650 form factor cells that are 18mm in diameter by 65mm in length. If you dismantled the battery pack, the cells look like AA batteries. Tesla claim that this form factor increases battery life and is more efficient for heat transfer.
The Chevy Volt, by comparison, uses a more traditional system of interleaved vertical plates packed together into modules, several of which are stacked to form the entire battery pack - a T-shaped unit that sits behind the rear seats and protrudes down the centre of the car where a traditional transmission tunnel would be.
Picture credit: Tesla Motors
Service disconnect switches
To paraphrase Spiderman, With great voltage comes great opportunity for frying yourself. For first-responders attending the scene of an accident and for home mechanics alike, the terms Manual Disconnect Switch (MDS) and Service Disconnect Switch (SDS) will become very important. All EVs (and most Hybrids for that matter) have an easily-identifiable switch that can be pulled, pushed, or thrown to disconnect the high voltage battery from all the vehicle's other electrical systems. Fortunately the industry seems to have standardised on bright orange for the high voltage components - both wiring and the disconnect switches. The MDS/SDS is normally located on the battery pack itself.
Here's an interesting idea : never service your car. With internal combustion you know where that will get you. But on a fully electric vehicle, what needs regular maintenance? Only the consumable items. Check the brake pads and discs, and the tyres. That's about it. Transmission fluid needs looking at every 60,000 miles or so but there's no oil to change, no oil or air filters, no spark plugs. There might still be coolant to check - EVs typically use radiators and coolant to keep the operating temperature of the battery packs down, but other than that, the whole concept of regular servicing becomes really skewed when you start talking about electric vehicles.
Generating electricity in the car itself: Extended Range EVs, or ER-EVs
A pure plug-in EV is simply a motor and a rack of batteries. A Hybrid is a combination of electric motor and internal combustion engine both of which can drive the wheels. Until infrastructure and technology comes along to solve the battery charging issue, the immediate solution is ER-EVs - extended-range electric vehicles. ER-EVs are essentially EVs but with an onboard mechanism of generating more electricity on the go. Generating electricity as you drive isn't a new idea, there are several methods of doing it right now, and these are used in various combinations to help range-boost electric vehicles.
Regenerative braking. Similar to the same system in a hybrid vehicle, regenerative braking turns the electric motor into an electric generator when you slow down. The potential energy of the car traveling at speed is turned back into electricity to help recharge the batteries. Unless you're completely gullible, you understand the idea that a perpetual motion device is impossible, so you can't drive an EV up a hill then brake all the way down the other side to recover 100% of the charge you used in the climb. Regenerative braking boosts the range but can never fully recharge the batteries.
Internal combustion generators. If you've ever seen, heard or travelled on a train in the last few decades, you'll have experienced a diesel-electric engine at some point. These systems add a small internal combustion engine into the mix but rather than connecting it to the transmission (as in a hybrid), the engine is used solely for running a generator to recharge the onboard batteries. Imagine a golf cart with an emergency Honda power generator tied to the back of it and you get the picture. As mentioned at the top of the page, this is exactly what the Chevy Volt was supposed to be in its original design. The benefit of these systems is a hugely increased range because now you're not the battery's bitch any more - when it starts to run low, the engine recharges it. When the engine runs low on petrol or diesel, you fill the tank.
A good example of this particular type of technology was the Fisker Karma. It had two electric motors rated at a combined 402hp that drove the rear wheels, driven from a 600lb lithium-ion battery pack. Up front there was a 2 litre turbocharged petrol engine connected to a generator that came on when the battery range dropped to 15%. There was an onboard fuel tank that fed the petrol engine that, Fisker claimed, range-boosted the Fisker from a battery-only 50 miles up to 300 miles. And for good measure, Fisker added a roof full of solar panels to help recharge the battery pack too. Interestingly, the Karma did not produce enough power to run the electric motors at their full 400+hp unless the battery was full and the generator was running at the same time. In that case it was at the driver's command via a steering-wheel mounted switch that flicked it from 'Stealth' mode to 'Sport' mode.
Fisker ran into legal and financial troubles in 2013 and pretty much ceased trading facing financial meltdown and an inability to deliver cars to their customers.
Picture credits: Fisker Automotive
Hydrogen fuel cells. Ditch the battery pack completely and generate electricity on-the-fly with hydrogen fuel cells. I have a whole section on this over in the fuel & engine bible : Hydrogen fuel cells.
There will undoubtedly be improvements in battery technology for EVs but one of the biggest challenges right now still concerns the transmission. All current EVs have a tradition single motor coupled to a transmission which is used to drive the wheels. Volvo had a concept in 2007 called the ReCharge which was a diesel-electric hybrid, but had the noteable feature of wheel motors. This solves the transmission problem because instead of having one large motor, there are instead four smaller ones, one built into each wheel hub. This removes all the weight of the transmission and gives expanded possibilities for vehicle control. For example all-wheel-drive vehicles become very easy to build and control once you start using wheel motors. Rather than all that nonsense with limited-slip diffs, torque-sensing couplings, clutch packs, speed sensors, hydraulics etc, you simply have four wheel motors that can each be monitored for slip. If one is slipping, the electrical system simply reduces or cuts power to that motor.
In a similar fashion, stability control could be implemented the same way - rather than braking an errant wheel as we do today with ABS-coupled traction control, in a wheel motor solution, the wheel that needs to be brought into check could simply have the motor begin to act as a generator, inducing drag and slowing the wheel down like brakes do today. For that matter, 4-wheel regenerative braking would be a very efficient way of topping up battery charge on the move.
Picture credit: Volvo
Other EVs you need to become familiar with
As I mentioned at the top of this page, the Tesla Roadster and Model-S, and the Chevy Volt are the most common EVs you might know about, but there are others which are definitely worth paying attention to. The Nissan Leaf is a compact commuter vehicle, and Fiat now have the 500e. Smart have the electric drive Smart Car available too. In Europe, Renault and Peugeot are both bringing more EVs into their lineup, and globally Ford now have the Focus Electric available to everyone.
The big players are all gearing up for the electric revolution. - Audi's "e-tron" series of concept cars are just one example of a large manufacturer with big ideas.