Along with many characteristics of the machine, the power and torque of the engine occupy a special place. Despite the interest in these parameters, for an ordinary car enthusiast, when choosing a car, they are never decisive. He is much more concerned about the brand, model, equipment, type and fuel consumption, cost. Even color is usually more important than horses and Newtons. Nevertheless, for many this topic is interesting at least in a theoretical aspect. The task of this material on a ABS is to explain in simple terms what power and torque are, how they fundamentally differ, and what they affect in practice.
The power of the mechanism began to be measured long before the advent of cars - in 1789. It was called by the term "horsepower", and was intended to show the superiority of steam engines over real live horses. We calculated it empirically - by watching the horses. There were several ways, but the most understandable is the following. In practice, it was found that one healthy horse could pull a load weighing 75 kg for a long time at a constant speed of 1 m/s. Substituting the obtained values into the fundamental formula from physics, we calculated that the power of one horse is 735.5 watts.
Horsepower has remained a unit of power to this day. The official unit is the watt (W). Both units were conceived and calculated by James Watt, who distinguished himself by many achievements, including the invention of the steam engine, which came to replace horses.
The power of an internal combustion engine indicates how much and what kind of work the unit can perform per unit of time. It depends on the volume, manufacturability, type and other criteria. Engine power is highly dependent on rpm. The higher they are, the more fuel is burned in the combustion chambers, the more energy is released, the more work the engine can do, and the higher its power.
In the characteristics of cars, the maximum power is always indicated. It is expressed in two units at once - kW and hp. (kilowatts and horsepower). These two units are interrelated, such as the meter and foot (100 cm and 30 cm). It was said above that 1 hp - this is 735.5 W (or 0.736 kW). Accordingly, 1 kW is 1.36 hp.
What is the maximum power? The maximum speed that the car can develop. For acceleration dynamics. Power affects fuel consumption, since the more we burn it, the more useful work the engine can do.
How can power be increased? To do this, you need to "force" the engine to burn more fuel in the same unit of time. And not just burn, but do it effectively. To achieve this, several methods are used. For example, it is possible to increase the volume of the engine by increasing the volume of the combustion chamber (the larger the piston diameter, the higher the volume) or by increasing their number. You can also supply more air-fuel mixture to the combustion chamber per duty cycle. This is done using turbines and other methods.
Torque is closely related to power. To find out the power of a particular motor, the torque is first measured. Like power, torque is highly dependent on engine speed, but in a slightly different way.
First, let's find out what the concept is - torque. For clarity, let's take a tightened bolt that we need to unscrew. To do this, we need to apply a certain force to it in such a way as to make it rotate. If we try to unscrew the bolt with our bare hands, we will not succeed. Little strength. To solve the problem, you can call the hero, who has more strength in his hands. And you can take the key, which is nothing more than a lever that increases our strength according to the law of Archimedes.
Torque is the force applied in this case to the body that must be rotated. In an internal combustion engine, this force, on the contrary, is released. On the crankshaft. And it is used to rotate the driving wheels of the car. The greater this force, the better the engine will be able to overcome the forces that resist the rotation of the wheel. There are a lot of these forces - friction, rolling, car mass, slope and even headwind.
There is one more thing you need to know about torque. If the power grows steadily from idle to cutoff, then the torque first increases, stabilizes, and closer to maximum speed begins to decline. This happens due to increasing losses due to friction, heating, and so on.
Both parameters are usually displayed on the same graph as two curves. As a rule, the power curve constantly and steadily goes up, and stabilizes in the cutoff region. The torque curve jumps sharply at first, then stays at the same level in the medium speed range, and starts to decline closer to the cutoff.
Torque is measured in Newton meters (Nm), and in theory can be calculated if power is known. To do this, multiply the power in kW by a factor of 9549 and divide the result by the number of revolutions of the crankshaft per minute.
Although in practice the opposite is true. The car is placed on a stand that creates resistance to the wheels. The engine overcomes this resistance, and what force it applied for this is measured by instruments. Next is the matter of technology. The resulting torque is multiplied by a factor of 9549 and by revolutions per minute. It turns out kilowatts of power, which are easy to convert into horsepower more familiar to the people.
What is more important in practice?
If all engines had the same design and principle of operation, then this question would never have arisen. There would be a stable direct relationship, the same for all cars - the more torque, the more power is needed to create it. However, in practice, everything is much more complicated.
One engine with a maximum power of 180 hp produces 240 N*m of torque, and the other is more powerful (200 hp), but it produces only 200 N*m of torque. Which of these engines is the best?
To answer such questions, we must first decide why we need an engine. So, if we want to accelerate the car to maximum speed, then we need one with a more powerful engine. If we need to accelerate as intensively as possible, then for these tasks we need a more traction motor, that is, which has more torque. This is an oversimplified explanation that ignores many factors. But that's exactly how it works.
Power and torque, like bare numbers, don't make one car better, faster, more dynamic than another. The following factors must also be taken into account:
- The mass of the car - the lighter the car, the faster it will accelerate and will be able to accelerate to a higher maximum speed. There are even such concepts as horsepower or newton meters per kilogram. For example, a motorcycle weighing 300 kg and with a 300 hp engine it will easily disappear over the horizon if you chase it in a car with an engine of the same power, but weighing under 2 tons.
- Transmission - the gearbox has a significant impact on the maximum speed and dynamics of the car. The type of transmission - mechanics, automatic, CVT - also largely affect these indicators.
- Road grip - sometimes affects the dynamics of the car to a greater extent than power and torque. If there is no normal grip, then the lion's share of the engine's work will be spent on the useless friction of the tires on the surface.
- Wheel diameter - even this affects the dynamics of the car. The principle is the following. The larger the diameter of the wheels (driving), the higher the maximum speed and worse acceleration. And vice versa.
There are several dozen such factors, and all of them, to one degree or another, will affect the dynamics and maximum speed of the car. Some will even be more significant than the power and torque of the engine.
For an ordinary car enthusiast, it is important to learn that a car engine is most efficient and economical when it is running at maximum torque. For gasoline engines, this range is between 1500 and 3000 rpm. Diesels are slightly lower. It is in these ranges that you need to keep the speed while driving, and then the fuel consumption will be minimal, and the dynamics margin will be maximum.