How do electric cars and hybrids work?

HOW DO ELECTRIC CARS and HYBRIDS WORK?

Prepared: Hamdi TOSUN

Source: Explainthatstuff

Sr. Wire Harness Design / Electrical System Design

/hamditosun

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Contents

• Electric cars

• What is an electric car?

• Hybrid cars

• How does a plug-in hybrid work?

• Hydrogen fuel-cell cars

• Key components of an electric car

• Electric motor

• Batteries

• Advantages and disadvantages of electric cars

• A brief history of electric cars

HAMDİ TOSUN Sr. Wire Harness Design / Electrical System

Design Engineer

Electric cars

Electric cars use older technology than gasoline cars and, in their late-19th-century infancy, looked set to rule the world. The first electric car was built in 1834 and by 1900 some 38 percent of all cars were electric But oil was cheap and abundant and, in many ways, offered a better method of powering fast cars over long distances. Henry Ford's mass-production of affordable gas-powered cars soon put paid to electric dreams. Fortunately, as people finally woke up to the environmental and economic drawbacks of petroleum in the late 20th century, technology turned full circle and cars powered by the zap of electricity started to return to our streets. But is it really inevitable that all cars will go electric? How long will it take? Before we can consider that question, it helps to ask something much more fundamental: how exactly do electric cars work? What's so good about them anyway and what are the drawbacks? Can you really go to work powered by a few buzzing electrons? Let's take a closer look!


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Design Engineer

What is an electric car?

Electric cars are child's-play; I know that, for a fact, because I built my first one at the age of eight. Now, admittedly, it wasn't a Tesla Roadster or a Chevrolet Volt, but it had all the key features of any electric car. It was a toy I'd made with a construction set using a battery, electric motor, four little rubber-tired wheels, and a simple transmission built from ready-made gears. Real electric cars aren't much more than this, though building one is certainly more of a technical challenge than snapping together a toy.


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What is an electric car?

All cars gas, electric, hydrogen, or using any other "fuel" are essentially energy conversion devices: they turn potential (stored) energy into kinetic (movement) energy. In a conventional car, the energy is stored in chemical form, locked inside the gas you've pumped in your tank; you release it through a chemical reaction happening inside the engine in which the hydrocarbon molecules in gasoline burn with oxygen in the air to release heat, which pushes the pistons that turn the wheels. Electric cars also use stored chemical energy, though they release it electrochemically, without any kind of combustion, as electrons ping from their slowly discharging batteries; there's no burning of fuel, no air pollution spewing from the tailpipe, and no emissions of any kind are produced by the car itself.


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Design Engineer

2016

Hybrid cars

So.... electric car or gasoline? Both have their advantages; both have their drawbacks. That's why many of the electric cars on the road today are actually hybrids that incorporate both technologies side by side: they have a smaller than usual gasoline engine suited to nippy highway driving and an electric motor for all that stopping and starting in the city.


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Hybrid cars

Hybrids come in various different flavors. In parallel hybrids, the engine and the motor both send power to the wheels; in series hybrids, only the motor powers the wheels, while the engine simply drives the motor like a generator, recharging the batteries. Full hybrids have powerful enough electric motors and batteries to drive the engine independently, while in mild hybrids, the motor is too puny to power the car by itself and simply assists the engine (or allows it to switch off when the car is idle in traffic). Ordinary hybrids charge up their batteries using power from the engine and energy recovered from the regenerative brakes (which we'll come onto in a moment); plugin hybrids can also be "refueled" from a charging station or domestic power supply, have much bigger batteries, and can be driven by the motor and batteries alone, so work more like conventional electric cars.


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Hybrid cars

Whatever the coupling of engine and motor, the basic idea is to combine the best of both worlds to boost fuel economy. The big drawback of a hybrid is that its around 20–30 percent more expensive than a comparable gasoline model. It's likely to be 10 percent heavier (despite is lighter engine, it has an electric motor, batteries, regenerative brakes, and all the rest) and have more sluggish performance. But hybrids score far better on both safety and fuel economy than gasoline cars, which makes them popular with eco-conscious families who prize their green credentials


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How does a plug-in hybrid work?

A hybrid car is like two cars in one: it has a conventional gasoline (petrol) engine for fast freeway driving and an electric motor for more economic, pollution-free travel (or idling). In different designs, the wheels are driven by the engine, the motor, or both together.


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Hydrogen fuel-cell cars

Cars powered by fuel cells are also electric, though they use tanks of hydrogen to generate electricity and power an electric motor instead of banks of batteries. You can read more about them in our separate article on fuel cell cars.


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Key components of an electric car

Gas-powered cars and electric ones have a great deal in common and the key differences are the stored energy they use (gasoline versus electricity), the machine they use to convert it into kinetic energy (an engine or an electric motor), and the way the stored energy powers that machine (through a gearbox and transmission, in the case of an ordinary car, but often more directly in an electric car). Let's examine the two key components of electric cars the motor and the batteries in a bit more detail and compare them with what we have in a conventional car.


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Electric motor

Motors are quite different from gasoline engines—and not just in the fuel they burn. An engine needs to spin round relatively quickly to work efficiently (usually thousands of times a minute), but a car's wheels seldom need to go anything like that fast. The power an engine can produce at any given moment may be very different from what the driver needs. For example, if you're moving off from a cold start, or a traffic signal, you need the engine to produce a great deal of force (torque as it's called) at a relatively low speed, whereas if you're overtaking on a speedy highway, you'll need the opposite: more speed and less torque.


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Electric motor

Instant torque

There's not a great deal you can do to control the output from a car engine because it's a chemical machine, driven by an essentially simple chemical reaction between fuel and oxygen that produces useful mechanical power. In that respect, an internal combustion engine is just like the external combustion engine you'll find on something like a steam engine. If you want more power, you need to burn more fuel more quickly a basic law of physics called the law of conservation of energy tells us that which is why operating a car's accelerator is informally called "stepping on the gas": burning gas faster makes more power and ultimately delivers more speed. Apart from the accelerator (supplying more or less fuel), the other two key controls of a conventional car engine are the gears (transforming the power coming from the engine so the wheels turn quickly with low force or slowly with high force) and the clutch (briefly engaging or disengaging the engine's power from the gearbox altogether). And we need the gears and the clutch because of basic limitations in how an engine works as a machine that enjoys spinning around thousands of times a minute, however fast you're driving (the engine keeps turning, burning fuel and costing money, even if you're stopped at a traffic signal).


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Electric motor

The motor in an electric car is very different: up to a point, it has no "preference" whether it spins fast or slow—it's pretty good at delivering the same torque at any moderate speed. If you had an electric train set when you were young, you probably controlled the engine with a transformer that had a dial you could turn up or down. Starting off, you'd have the dial turned down low to make the train move slowly (by feeding a relatively small electric current to the motor inside it); you could go faster simply by turning up the current to make the motor spin more quickly. There's no clutch in a toy train and (usually) no gearbox either: the electric motor drives the train wheels directly, and does so equally well whether the train is going fast or slow.


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Electric motor

Transmission

In theory, an electric motor can drive a full-sized electric car just as simply as a toy train, without the clumsy old gearbox and transmission you'd use in a conventional gasoline engined car. In practice, electric cars are clearly more complex. Toys are small and move fairly slowly, while real cars are much bigger and go faster. When a real car corners, its two outside wheels are traveling around a curve of bigger radius than its two inside wheels but in exactly the same time, which means they have to spin slightly faster. (The same is true of toy cars, but the effect is too small to notice.) That's why real cars need complex transmissions with speed-adjusting gears called differentials that allow one pair of wheels to go at a slightly different speed faster on the outside of a curve, slower on the inside than the other.


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Electric motor

The same happens in an electric car when it goes around a corner, and that rules out any kind of simple transmission. One solution is to have a front-located electric motor driving the same kind of transmission as an ordinary gasoline car, using a driveshaft and differential in the usual way. Another is to do away with the driveshaft and have a motor, gearbox, and differential unit between two of the wheels and driving them both. A third option is to have two front or rear motors, each driving one wheel independently. The final option is to use two or four hub motors,which are motors built into the wheels themselves. That raises a different technical issue: how to build a motor that's lightweight, compact, and still powerful enough to drive a car.


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Electric motor

Artwork: Transmissions: How does power get from the motor to the wheels? Four example arrangements of the electric motor (green), gearbox (orange), differential (scarlet), driveshafts (light blue), and hub motors (red) in an electric car.

1) In this arrangement, the electric motor powers the car much like a traditional engine through a gearbox and driveshaft.

2) A central motor powers both wheels through one or two gearboxes.

3) Two separate motors power two wheels through separate gearboxes.

4) Hub motors power two (or sometimes all four) wheels with no other gearboxes, driveshafts, or other transmission parts.


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Batteries

Every car is an electric car inasmuch it uses a battery to get the engine spinning when you first start off. Historically, cars were the pioneers of rechargeable batteries. Long before we had laptops and cellphones, windup torches and all the rest, back when most of us routinely used batteries one minute and threw them away the next, cars were demonstrating the possibility of using batteries over and over again. The only trouble was, car engines used big and heavy lead-acid batteries that weren't good enough to power vehicles at high speeds, over long distances, for long periods of time.


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Batteries

Today's electric cars mostly use lithium-ion batteries, exactly the same technology you'll find in your laptop or ebook reader. They're relatively light, fairly good at storing useful amounts of power for their weight, last several years and hundreds of charges, and perform reasonably well at the varied range of temperatures most car drivers routinely encounter round the world (though not always that well in the extremes you can find even in hotter and colder US states). That doesn't mean they're perfect. The main problem with car batteries is that they still can't carry as much energy as gasoline per unit of mass; in other words, they have a lower energy density. Lithium-ion batteries are likely to remain the popular choice for electric cars for the foreseeable future, though alternatives such as nickel metal hydride (NiMH), which are safer and cheaper, and other lithium-based technologies (including lithium-nickel-manganese-cobalt, lithium-phosphate, lithium-manganese, and lithium-cobalt) are also waiting in the wings. Supercapacitors (also called ultracapacitors) are another promising alternative. A bit like a cross between batteries and capacitors, they offer much faster charging times.


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Advantages and disadvantages of electric cars

What's good?

Emissions

At first sight, electric cars are green cars: sometimes they're even referred to as ZEVs (zero-emission vehicles) and the official fueleconomy.gov website actually quotes zero grams of CO2 emissions per mile for most electric cars. Now while it's true that the car itself makes no pollution and produces no CO2 emissions in the place where you drive it, it's also misleading: unless your electricity comes from a wind turbine or a solar panel, some emissions are still produced in the process of electricity generation in a distant power plant somewhere). Even with that qualification, electric cars are no worse than the greenest fossil fueled cars and that comparison will only get more favorable as electricity generation becomes greener.


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How much better are electric cars? This chart compares mpge (mpg equivalent) or mpg ratings for 18 cars with 2015 specifications: six electrics (green), six hybrids (yellow), and six gasoline cars (red).


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Performance

Even in performance, electric cars sometimes outclass gasoline ones. As we've already seen, electric motors can produce high torque even at low speeds, which means they can accelerate more quickly than gasoline cars that don't produce their peak torque until they reach relatively high engine speeds. They're also quieter and smoother. As Tesla have demonstrated, there's no reason whatsoever why electric motors and batteries once thought of as dull, worthy, and rather plodding can't power racy, exciting sports cars. A Tesla Model S can accelerate from 0–60mph (100km/h) in just 3.9 seconds, comparable to a high-performance gasoline powered BMW M5

Size is no obstacle for electric power either. Diesel-electric trains (in which diesel engines power electric motors that provide the traction) have been around for years. In November 2014, truck manufacturer BelAZ announced a super powerful new 500 tonne diesel electric mining truck in which four giant AC motors are powered by two 16 cylinder diesel engines.


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Maintenance

Maintenance is also less of a chore, because electric cars are generally simpler than gasoline ones. According to a 2012 report by the Institute of Automobile Economics, electric vehicles cost about a third less to maintain than equivalent gas or diesel cars. Why? An electric motor is an inherently simpler bit of kit than a gasoline engine with far fewer moving parts to wear out; if it uses no transmission or gearbox, that makes the entire car simpler still. Even the brakes last longer, since regenerative braking means you need to use the conventional (frictional) brake pads much less than in an ordinary car. On the other hand, some of the technology used in electric cars is relatively untested, which means it could be more prone to early failure even if it is, paradoxically, simpler and theoretically more reliable in the long run.


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What's bad?

Batteries

Electric motors and batteries are the two main points of difference between conventional and electric cars. Where motors are well understood and highly reliable, giant battery packs remain the Achilles heel of electric cars. Despite its environmental and economic drawbacks, kilo for kilo, a tank of gasoline can carry far more energy than a bunch of batteries (see chart below)—and that will remain the case for the foreseeable future. You can completely refuel a gas-powered car in a couple of minutes (as long as it takes to fill up your tank) and drive several hundred kilometers on the energy you've pumped in without stopping. But electric cars can take anything from half-an-hour to a whole night to recharge ("fill up") and, even then, probably won't get you further than a couple of hundred kilometers before the batteries run flat. Where a gas tank is a relatively compact thing that sits neatly out of sight, the batteries in an electric car are expensive (about a quarter of the cost of a Tesla, which still works out at around $20,000), bulky, heavy, and take up room you might use for other things.

HAMDİ TOSUN

Sr. Wire Harness Design / Electrical System Design Engineer


Why we still drive gasoline cars in a nutshell. Kilo for kilo, gasoline can carry far more energy than batteries. Hydrogen is a much better energy carrier, but there are significant problems in making and storing it. Coal scores highly too, but it's dirty and impractical: steam cars disappeared long ago!


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A brief history of electric cars

• 1800: Italian Alessandro Volta invents the battery (a primitive stack of zinc and silver discs separated by cardboard soaked in saltwater).

• 1821: English chemist Michael Faraday shows how electricity and magnetism can work together to make a force—the basic scientific principle of the electric motor.

• 1829: American electricity pioneer Joseph Henry develops a practical motor, though it's still far from a viable machine.

• 1834: Thomas Davenport develops a viable electric motor and goes on to develop the first battery-powered electric car running on a track. Unlike in modern electric cars, the batteries are not rechargeable.

• 1837: Robert Davidson of Scotland develops a battery powered car and later (in 1842) an electric train that whizzes along the Edinburgh to Glasgow Railway at a breathtaking 6km/h (4mph).

• 1859: Frenchman Gaston Planté invents the lead-acid battery, made from nine cells connected in parallel, and demonstrates it to the French Academy of Sciences the following year.


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• 1859: Electricity pioneer and prolific US inventor Thomas Edison develops an electric car.

• 1881: Siemens constructs the first permanent electric railroad in Lichterfelde, Germany.

• 1885: Leo Daft uses an electric motor to power a commuter train to 50km/h (30mph) in New York City.

• 1890: William Morrison develops the first successful American electric car. It can manage a respectable 23km/h (14mph).

• 1900: German Ferdinand Porsche develops the world's first hybrid, hub-motor electric car (the Lohner-Porsche).

• 1908: Henry Ford gives his wife Clara a Detroit Electric car as a present after she complains she couldn't start a gasoline car with a hand crank. Later, he buys another one for his friend Thomas Edison as a Christmas present.

• 1910s–1960s: Ironically, despite Ford's enthusiasm, his development of cheap, mass-produced gasoline cars pushes electric car technology to one side.

• 1940s–1970s: Electric vehicles are used for little more than powering delivery vehicles, such as "milk floats" (widely used to deliver dairy products door-to-door in the UK before supermarkets take over).


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• 1971: Apollo 15 astronauts David Scott and James Irwin drive the electric Lunar Roving Vehicle on the Moon for the first time.

• 1976: US Congress passes the Electric and Hybrid Vehicle Research, Development, and Demonstration Act to encourage the production of electric cars.

• 1990: The California Air Resources Board spurs the development of electric cars with its zero-emission vehicle program.

• 1996: General Motors begins leasing its pioneering and futuristic looking EV1. Later, the cars are controversially taken back by GM and crushed.

• 1997: Toyota launches the Prius in Japan—and it soon becomes the world's best-selling hybrid.

• 2008: The first Tesla Roadster electric car is shipped to customers.

• 2013: Toyota announces it has sold over 5 million hybrids worldwide, including 2 million in the United States alone.


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How do electric cars and hybrids work?

Engineering

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