Differences between an electric motor and a heat engine
Content
What are the fundamental differences between a heat engine and an electric motor? Because if the connoisseur finds the question fairly straightforward, most newbies will probably have questions about this ... However, we will not be limited to just watching the engine, but we will also quickly study the transmission to better understand the philosophy. these two types of technologies.
See also: Why do electric cars accelerate better?
Basic concepts
First of all, I would like to remind you that engine power and torque values are, in the end, only fragmented data. Indeed, to say that two engines with a capacity of 200 hp. and 400 Nm of torque are identical, actually not true… 200 hp and 400 Nm are only the maximum power offered by these two engines, and not the full data. In order to compare these two engines in detail, the power/torque curves of each need to be compared. Because even if these motors have the same characteristics, namely the same power and torque peaks, they will have different slew curves. So the torque curve of one of the two engines will be on average higher than the other and therefore it will be slightly more efficient despite the fact that they looked identical on paper... the diesel engine is overall more impressive than the gasoline engine of the same power, although I admit that the example given here is not perfect (the maximum torque will necessarily be very different, even if the power of both engines is the same).
Read also: Difference Between Torque and Power
Components and operation of electric and heat motors
Electric motor
Let's start with the simplest thing, the electric motor works thanks to the electromagnetic force, namely the "force of magnets" for those who do not fully understand the concept. In fact, you have already been able to experience the fact that love can create force on another magnet when they are connected together, and indeed, the electric motor uses this latter to move.
Although the principle remains the same, there are three types of electric motors: a DC motor, a synchronous AC motor (a rotor that spins at the same speed as the current supplied to the coils), and asynchronous AC (a spinning rotor slightly slower current sent). Thus, there are also brushed and brushless motors, depending on whether the rotor induces juice (if I move a magnet next to it, even without contact, the juice appears in the material) or is transmitted (in which case I need to physically inject the juice into the reel and so I create a connector that allows the rotor to move: a brush that rubs and lets juice through like a train is connected to the electrical cables from above using levers called a pantograph).
Thus, an electric motor consists of a very small number of parts: a "rotating rotor" that rotates in a stator. One induces an electromagnetic force when a current is directed to it, and the other reacts to this force and therefore begins to rotate. If I do not inject more current, the magnetic force will no longer disappear and therefore nothing else will move.
Finally, it is supplied with electricity, alternating current (the juice goes back and forth) or continuous (rather alternating current in most cases). And if an electric motor can develop 600 hp, for example, it can develop 400 hp. only if it does not receive enough energy ... A battery that is too weak can, for example, restrict the engine's operation and it will potentially not work. able to develop all his power.
See also: how the motor of an electric car works
Heat engine
A heat engine uses thermodynamic reactions. Basically, it uses the expansion of heated (one might even say, flammable) gases to rotate mechanical parts. The mixture of fuel and oxidizer is locked in the chamber, everything burns, and this causes a very strong expansion and therefore a lot of pressure (the same principle for firecrackers on July 14). This expansion is used to rotate the crankshaft by sealing the cylinders (compression).
See also: work of a heat engine
Electric motor transmission VS heat engine
As you undoubtedly know, electric motors can run at very high speeds. Thus, this characteristic convinced the engineers to abandon the gearbox (there is still a reduction, or rather a reduction, and therefore a report), which in the process reduces the cost and complexity of the car (and therefore reliability). Note, however, that the following should bring a second report for reasons of efficiency and motor heating, this also applies to the Taycan.
Therefore, there is a significant gain here, as the heat engine will waste time shifting gears with the added bonus of reduced torque.
Thus, in recovery, this is also an advantage, because we are always in electric mode on a good record, since there is only one. On a thermal machine, it will be necessary to find the most suitable mechanically and let the gearbox do it automatically (kick-down to improve performance), and that wastes time.
To summarize, we can say that the electric motor has one power / torque curve when accelerating, while the heat engine will have several (depending on the number of gears), jumping from one to the other thanks to the gearbox.
Electric motor power VS heat engine
Thermal and electrical devices not only differ greatly in transmission, but also do not have the same methods of transmitting power and torque.
The electric motor has a much wider range because it can pick up very high speeds while maintaining very high torque and power. Thus, its torque curve starts at the top and only goes down. The power curve rises very quickly and then gradually decreases as you climb to the point.
ENGINE THERMAL CURVE
Here is the curve of a classical heat engine. Usually, the most torque and power are around the middle of the rev range (they are interrelated, see the link at the beginning of the article). On a turbocharged engine, this occurs towards the middle, and on a naturally aspirated engine, towards the top of the tachometer.
ELECTRIC MOTOR CURVE
A heat engine has a completely different curve, with maximum torque and power developed in a small part of the rev range. And so we will have a gearbox to use this power/torque peak throughout the ramp up phase. The rotational speed (maximum speed) is limited by the fact that we are dealing with rather heavy moving metal parts and wanting the motor frequency too high endangers the parts which can then spin (more speed increases friction) and therefore the heat that can make parts “softer” due to slight “melting”). Therefore, we have a petrol switch (ignition limit) and a limited injection frequency on diesels.
Roughly speaking, a heat engine has a top speed of less than 8000 rpm, while an electric motor can easily reach 16 rpm with good levels of torque and power throughout this range. The heat engine has high power and torque only in a small engine speed range.
One final difference: if we get to the end of the electrical curves, we will notice that they suddenly fall. This limit is related to the AC frequency associated with the number of motor poles. This means that when you reach the maximum speed, you will not be able to exceed it, as the motor creates resistance. If we exceed this speed, we will have a powerful engine brake that will get in your way.
One comment
Pele
Thank you