Technical:
Energy is work. It can be several things - heat, mass in motion, or (mass raised to a height - kinetic energy) stored energy. Energy can be stored in a chemical form - gasoline can be burned to make heat, for example, or turn an engine to make motion (and heat). Battery chemicals can store energy as electriciy. and so on…
Basically a hybrid “micro-manages” your energy expenditures. Most city driving is stop-and-go. When you accelerate, that takes extra energy. To roll, there’s a certain amount of wind and rolling resistance, which takes energy to overcome (to maintain your speed). When you brake, you convert the energy of the moving vehicle to something else - heat or (in a hybrid) electricity.
My hybrid Camry uses the electric motor and the gas motor to move the vehicle. the electric motor can assist especially in acceleration - this means the gas motor can be significantly smaller than in a regular car this size.
The gas motor kicks in to also charge the batteries when they get low. More often than not, in straight and level driving, my gas motor is also running.
What the salesman was getting at was that the car’s energy of motion (momentum, sort of) can be turned into electricity when you hit the brake. (Brake too hard and conventional brakes kick in too, since the car assumes you really really need to stop in a hurry and those brakes can stop a car much better). Braking engages a generator. The electricity generated is energy subtracted from the car’s momentum, and added to the battery.
When you accelerate, you can reuse this energy. Essentially, I find I get highway gas mileage in city driving.
There are newer versions of Toyotas and others that are also plug-in. One item I read said that Toyota helps ensure the life of heir batteries by keeping them around 85% charged; apparently the quickest way to kill a battery is repeated deep discharges and recharges. Not sure how this compares in Prius version, and what happens with the plug-in version.
I guess it’s vaguely possible in a fairy-tale sense for the engine’s recharging function to also use wasted energy - heat, sound, what have you. Is there a method other than a steam turbine that can turn heat into energy?
Photovoltaic cells, like solar cells. They can derive electricity from infrared light. Also Stirling engines. But I think the problem has always been the relatively low temperature and intermittent heating for powering heat engines and steam engines. I don’t know how efficient the photovoltaic cells are, but some reports show promise. They may be too expensive to be practical though.
Any method of converting heat energy to other forms must inherently take advantage of what’s called a “cold reservoir”, and the maximum possible efficiency for the conversion depends on the ratio of temperatures of the hot and cold reservoirs. The coldest cold reservoir a car has available is the ambient environment, which is around 300 kelvins. The heat that we’re trying to recover from brake pads or whatever is perhaps a hundred kelvins higher. That means that, no matter how you try to harness that energy, you’re guaranteed to waste at least 3/4 of it, and in practice, you may end up wasting considerably more than that (especially since getting close to the theoretical maximum efficiency is a really slow process).
You guys have it all wrong. The optimal process would be to use the gas engine to power a fan which would spin the blades of a wind turbine which would light a lamp which would feed a solar panel which then would recharge the car’s battery. That way, we would be using wind energy and solar energy.
I expect Obama to call me shortly, begging me to take my rightful place as Secretary of Energy.
For electricity, there are thermoelectric devices: Thermoelectric generator - Wikipedia They can also work in reverse, and use electricity to pump heat (e.g. a small refrigerator). Space probes use such devices as energy sources.
You forgot to generate hydrogen, everyone knows hydrogen makes things more efficient, and greener.
The Seebeck effect describes a situation in which two dissimilar types of metal are arranged to form a circuit that has two junctions between the two types of metal. If the two junctions are held at different temperatures, a voltage develops between them, and current can be made to flow in the circuit.
NASA uses this phenomenon in radioisotope thermoelectric generators that power spacecraft: a hunk of plutonium generates heat through radioactivity, and that heat is used to by the TEG to produce electrical power. It’s very reliable since there are no moving parts, but it’s not very efficient. Theoretically you could use this to somehow convert heat in the brake rotors (or engine coolant or exhaust) into usable electrical power, but the cost and weight penalty are hard to justify.
Edit: ninja’d by AaronX.
I can’t find info right now about the Prius or the Volt, but the Tesla Model S uses a “permanent magnet synchronous AC motor.” The idea is that the rotor is fitted with permanent magnets, so no electrical current has to be carried to/from the rotor, which means no losses or wear on a slipring connection (or the commutator you would find on a DC motor). Instead, they rely on AC current delivered to the motor’s field windings, with the AC frequency controlled by an inverter (an electrical device that converts DC to AC) so as to match up with the rotation of the motor. This is a very efficient system.
If you had a DC motor/generator, you’d have resistive losses at the contact between the brushes and commutator, you’d have mechanical wear on those same parts, and you’d probably also have to find a way to cope with plasma damage, since switching large DC currents (every time the commutator switches to a new winding loop) generates sparks that generate plasma. The Killacycle electric drag bike uses DC drive motors, and they struggle to deal with plasma-related damage during normal operation (this is separate from the occasional exploding battery or motor).
it’s kind of a blend between an AC induction motor and a DC brushless. The input to the motor is the same as a typical polyphase AC motor (three phase AC) but the rotor (IIRC) uses permanent magnets instead of squirrel-cage bars.
When you’re braking, the wheels are connected to a generator, which slows it down a lot. Turning a generator to generate electrical energy can give a LOT of braking. Not just “somewhat”.
Normally, braking is just throwing away energy (turning kinetic energy of motion into heat that blows away in the air). With a Prius, instead of throwing that energy away, we’re funneling it back into the battery.
It also has disc brakes as a backup, or whenever the amount of braking required exceeds the regen system’s maximum. My wife has a Prius, and when you apply the brakes, it doesn’t feel/respond quite the way good ol fashioned brakes do. If you pay attention, you can feel several different gradients as different braking systems kick in – at least, it feels that way to me. I bet it was a tricky bit of engineering to get as smooth and linear a response as possible. Fortunately, we learn pretty fast to adjust and after the first couple times don’t notice anything different. (We have to adjust to different brakes on different cars anyway, and many aren’t very linear.)
Any attempt to recover the energy lost to heat for normal braking would be very inefficient compared to the regenerator. It would suffer the usual problem with heat-driven systems, practically limited to a 30% or so efficiency, I believe. (Probably a lot less. That % is the ratio between the high and low temperatures involved, in absolute temperatures. If I understand it correctly. 30% is typical for things like steam engines.
To capture more wasted energy, it would be far better to simply beef up the regen system to the point where the disc brakes would only be used when at a standstill. (The regen doesn’t work when there’s no motion, so you’d slip, without a backup mechanical brake. Or you’d need to apply power.)
It’s a lot smoother. Since it’s using sinusoidal AC current to the stator windings, the stator field vector rotates smoothly and continuously. A brushless DC motor snaps the current to each pole on/off, resulting in perceptible torque pulses, particularly at low RPM.
I guess the difference lies in the inverter rather than the motor itself.
Here is an electric Mini Cooper that uses 4 wheel motors, captures more braking energy via utracaps (which can take a lot more juice at a time) and uses an ICE to recharge the battery when it starts to get low. They replaced the brakes completely with the wheel motors, which means really hard braking is done electrically. They say each wheel motor is 160hp, but I suspect they are using the standard for automotive engines, citing peak power rather than the electric motor standard of reporting continuous load power.
For a good idea of how regenerative braking works to slow the car and extract electricity, look at this video: Magnetic Brakes - YouTube The way the solid aluminium plate (nonmagnetic) slows at 2:22 is remarkable. Cars just take the electricity generated in the plate and store it in the battery.
That’s not how regenerative braking works. That’s an example of an eddy current brake, and while it does find use in many applications, it most definitely is not regenerative. The magnets produce eddy currents in the metal plate, and those eddy currents result in the production of heat; the energy collected by an eddy current brake can’t readily be harnessed and shoved into a battery. For that, you need an alternator (which produces AC power) or a generator (which produces DC power).