First, there is the question of the strength of the magnetic field. Engineers and technicians use a term called flux to describe what they imagine a magnetic field to look like in their minds. Magnetic lines of force come out of one pole and go around a bend and in through another pole, and like the isobars on a weather map that indicate the strength of the wind, the stronger the magnetic field, the more and denser the lines of force. When a wire passes through a strong magnetic field, the many lines of magnetic force "cut" the wire, resulting in an induced electric potential.
Since you can use more than one line of magnetic force to "cut" the wire, it is also possible to use more than one wire at the same time to pass through the magnetic field, the wire will be made into a multicartridge coil will increase the induced potential and the total current. A typical alternator has a stator winding with three coils spaced 120° apart from each other. When the rotor rotates, the magnetic field generated by the rotor "cuts" the coils, resulting in three pulses of voltage, timed to be 120° out of phase with each other. For a less fluctuating current, it is better to have more pulses per revolution of the rotor, because this means that the average voltage is higher.
Another way to increase the output of an alternator is to increase the number of magnets. A typical Lundell claw-pole rotor has a coil in the center and six or seven poles on each side. The finger teeth on the claw poles mesh together so that each claw pole separated from the other is connected to a different end of the coil. When current is passed through the coil, a magnetic field is created that is guided around the coil by the claw poles. If you count around the rotor, you will find *** there are 12 or 14 pairs of north and south poles, and each pole represents another magnet, the resulting flux will be on the stator winding "cut".
The time factor is also important. When the "cut", the faster the magnetic lines or wires move, the higher the output potential. Therefore, the alternator and harmonic balancer pulleys should be carefully sized so that the alternator rotates at two to three times the engine speed, which ensures that the alternator maintains good performance even when the engine is idle.
As mentioned earlier, when an electric current is passed through a wire, a magnetic field is created, the strength of which is proportional to the amount of current. The voltage regulator controls the output of the alternator by detecting the battery voltage and regulating the current through the rotor. Therefore, increasing or decreasing the current to the rotor changes the strength of the interaction between the electromagnet and the stator coil, and one of the major advantages of Lundell's claw-pole rotor is that as soon as the current to the magnetic field or the rotor coil is cut off, the output (voltage) goes to zero.
In fact, alternators have some performance limitations, and for a number of practical reasons, the maximum output of an alternator is limited to about 200A of current or 3000W of power. While this may seem like a lot of current, you only have to look at today's cars to realize that more current is really needed, especially at idle.
As mentioned earlier, the faster the magnetic poles run, the more induced current is generated. On the opposite side of the coin, the generator's output is lowest when the engine is idling or the car is running at low speed. Not coincidentally, this is precisely when there may be the greatest demand for current. To illustrate: imagine that you are preparing to park a modern car on a snowy night. The engine is working around idle, the lights, air compressor and rear defogger are on, the windshield wipers are working, but more power is still needed to feed the electronic power steering system. With all the available power from the generator tied up, the only source left to power the power steering is the battery itself. When the driver turns off the engine, the battery is undercharged, which is undesirable because the battery's operating life is shortened by prolonged undercharging.
Today's alternator designs suffer from poor efficiency, with a typical Lundell claw-pole rotor generator being only about 50% efficient. This means that it takes about 6000W of power to drive the alternator, and the output is only 200A of current (3000W of power). The bad news is that the lost power is then converted into heat that accumulates in the alternator, and with the engine compartment temperatures already high, the heat must be dissipated.
So how do you make an alternator more efficient, produce more power, and generate less heat? It is also particularly important that at relatively low generator speeds, the higher the output, the better. Here's how manufacturers of alternators do this.
The first step is to find out why the efficiency is low. Just take a look at a claw-pole rotor and you'll see that it's not worth the trouble. A shaft, a pair of claw poles, a coil pack, and a collector ring are enough to make up the entire rotor. The problem is that this design is leaky, not all the flux is used to "cut" the coils to maximize current output, and some of it leaks out to no avail.
One solution is to use a Hybrid rotor. While a normal rotor has nothing between the claw poles, a Hybrid rotor has a permanent magnet between the claw poles. Magnetic flux comes out of the magnet into the melon pole and returns to the magnet through the rotor mandrel and the claw pole on the other side of the magnet. With the permanent magnet filling the gap between the claw poles, the flux generated by the rotor windings doesn't leak away. This forces more flux from the rotor into the stator windings, thus increasing the output efficiency of the alternator.
This scheme can increase the original efficiency by 20% from 50%. Thus an alternator with a total efficiency of 60% would only need to use 5000W of power, or about 4474W, to produce as much output as the original, with the side benefit that less than 1000W of heat would have to be dissipated.
The second step in alternator improvement would necessarily be to put water jackets around the alternator and connect it to the engine cooling system. This is very beneficial. Since it is the water jacket that really does the cooling, there is no need to force the alternator into a stream of cold air into the engine compartment. And the water jacket reduces the rate at which the alternator warms up or cools down, which contributes to the durability of the alternator. This is because sharp temperature changes are detrimental to materials that expand and contract at different rates, and the use of a water jacket eliminates this concern.
Water jackets naturally have other advantages. For example, Visteon claims in its literature that its alternator can transfer nearly 1,250W of lost heat to the cooling system, which ends up in the vehicle's defrost and heaters, where it is used to help clean the windshield and heat the passenger compartment. So, the coolant and engine can warm up and get warmer faster, and the catalytic converters can fire faster, which greatly reduces emissions during cold starts.
If a 20% increase in efficiency does so much, why not go for even higher efficiency nick? That's the key technology behind the new alternator developed by Ecoair, which will go into production later this year, primarily in emergency vehicles, where a lot of power is needed to operate flashing lights, automotive medical equipment, etc. Ecoair's basic concept can be used in all vehicles, including dual-powered vehicles, and the generator is also theoretically suitable for use in all vehicles. The basic concept of Ecoair can be applied to all vehicles, including dual-powered ones, and the generator is also theoretically applicable to the 42V electronic system that will be introduced in 2003.
Ecoair's generator, in one of its designs, actually has a rotor consisting of two separate parts mounted side-by-side on a rotor mandrel, one of which is fitted with permanent magnets to form the 12 poles, while the magnets and the surrounding metal are inherently magnetic and do not depend on the rotor current; the other half of the rotor assembly is a winded coil, with the coils and poles shod with a certain assembly relationship.
The Ecoair alternator has three separate modes of operation. At low speeds, the permanent magnet portion of the rotor induces current in the stator, and during starting operation, both the permanent magnet and the winding coil produce maximum flux, and the generator produces maximum output. Therefore electromagnets always pose the problem that how do you cut off the current or reduce the flux to lower the power output if necessary? To solve this problem, a third mode is used to operate the Ecoair alternator, this mode is called "compensation" (buck) type, here is how it works.
When the output current exceeds the demand of the electronic system, the current through the rotor coil is first reduced to zero. If the output current is still too high, the direction of the rotor coil current is switched. When the current is reversed, the winding coils cancel each other out by producing magnetism opposite to that of the permanent magnets. In this way, by controlling the polarity and the amount of current in the rotor coil section, it is possible to reduce the output of the alternator to zero - the same technique is used in an automatic fail-safe circuit.
Although the rotor is constructed in two parts and its internal design is intricate, it offers some unexpected benefits. For starter motors, the compound design allows for 80% high efficiency. This means that only 3,750W or slightly less than 3,730W of power is required to obtain an output current of 200 amps (3,000 watts). At the same time, because the power and heat losses of the drive generator are reduced, the generator can be made smaller in size and lighter in weight for a given output power, and so on. In addition, in a conventional alternator, the diameter size must be similar to the distance between the front and rear, while Ecoair's hybrid alternator can have a longer form like the old alternator. Because it is not always possible to infinitely expand the diameter of the alternator, given the limited radial space available for the auxiliary drive belt to form, increasing its effective length is a good way to increase output, and also helps to increase drive belt torque and engine capacity.
The alternator is also attractive because of its fuel economy, especially when idling or operating at low speeds. Bosch has empirically determined that for every 5 percent increase in alternator efficiency, fuel economy improves by about 1 percent. And DaimlerChrysler has conducted comparative tests. Comparative tests conducted by DaimlerChrysler show that when Ecoair's alternator and driveline gearbox*** are operating at idle, fuel economy improves by 5.8% when the input remains constant and the output power increases by 13.4%.
The importance of the alternator and charging system in any design problem cannot be underestimated. Components like electrically driven water pumps, engine oil pumps, power steering and brakes with fuel-saving features would be available now if it weren't for the limitations of available electricity. But perhaps all it takes is a high-efficiency, high-power, 42V alternator to build a solid bridge to the other side.