When we see the advertising that the different brands make of your car in the means of communication, we can observe that, on a technical level, will often show a series of figures relating to speed, consumption, acceleration,… in short, a few cold numbers that in addition to a high percentage of the drivers may not be able to match ever. However, there is a data physical yes enjoy all of the conductors, which are rarely advertised and that not many years ago if you gave a certain importance: the torque.
Not too long ago, when cars had not yet suffered the escalation of current power, it is presumed the reprís of the car as his ability to gain speed. This statement popular, although the interpretation of what is the reprís is correct, for to understand what is the engine torque falls short of, or rather inaccurate
What is the torque?
The torque motor, also known as torque, is a physical magnitude that measures the moment of force to be applied to a shaft that rotates on itself to a certain speed. Applied to the world of the automotive and explained in a way that everyone can understand can be defined as the force required for the engine crankshaft rotate and, hence, is capable of transmitting said movement to the rest of the mechanical elements necessary to move the vehicle.
And here is where we see the first difference between the fact and the custom; when we refer to torque in order to express the capacity of acceleration that has a vehicle we’re really not defining what it is in itself the motor torque, we’re just describing one of its applications. This is so because the torque of a motor measured the power needed for the engine to turn a certain number of laps but do not have in mind the power supplementary to be applied to modify the angular velocity of the shaft or crankshaft.
A little bit of physics
To explain what is the torque fleeing from physical principles I will explain the function of the crankshaft and the forces on it act.
A combustion engine generates energy in the cylinders. Within these chambers produces the explosion of the fuel mixture-air and is the energy released by this explosion which generates a linear movement to push the piston in the opposite direction to the cylinder head of the engine. The pistons of the various cylinders are attached to the crankshaft by the connecting rods and it is right at the junction of these with the crankshaft which transforms the linear movement in rotational motion.
it is Worth to name at this point, the exceptional construction of the rotary motors, in which the chambers in a circular of the “cylinder” directly surround a central shaft that rotates on itself moved by the explosions produced in the chambers, so that in this case is generated directly by the rotational motion. In any case, the physical principles that act in regard to the engine torque are the same. Even without entering into a study excessively, to simplify the idea of transformation of energy, one could say that the block rotating produce torque instead of power. You can not make a truth of the faith in this sense because neither the cameras nor the rotor of the rotary motors are exactly circular and the ignition of the fuel occurs in a portion of the camera, unlike the engine with cylinders conventional in that the mixture fuel-air occupies the entire volume.
Returning to the explanation of physical, the force that makes the piston on the crankshaft is not constant during the expansion process. This is because inside of each cylinder, the maximum value of power is generated at the time of ignition of the fuel. And these moments of maximum power involve also moments of maximum torque. The delay between the time at which it generates maximum power in the cylinder, and applies the maximum on the crankshaft the engine is not an easily calculable. This is because the pistons do not make a movement purely linear, but that, because of the crankshaft the engine is not totally straight, perform a move that board to the linear effect of the piston with the circular bearing of the connecting rod. However these moment of maximum power and maximum torque have a great importance in what refers to the perception of the smoothness in the operation of the engine.
the more cylinders the vehicle, more times per minute there will be that moment of maximum force and more homogeneous will be the perception of the driver on the smooth operation of the engine. This is because in an engine of 2 cylinders, there will be a moment of maximum strength with each 360 ° rotation of the crankshaft, in a three-cylinder engine will happen every 240 º, in one of six each 120°, and so on. Clear that this should be interpreted as pure theory, because today’s manufacturers struggle in that their engines are as smooth as possible in what relates to its operation.
This factor also influences the fact that idling the engine to generate more vibrations and which are also more noticeable: at 1,000 revolutions per minute there are half of times of maximum force to 2,000 rpm. For example, starting from an idle average of 850 revolutions per minute, a three-cylinder engine will generate less than ten moments of force to the second, while a block of six cylinders will generate almost twenty. If we take into account that the ‘normal’ human, with a force intermittent continuous application, better recognized the larger intervals to a tenth of a second than the lower ones, here is the explanation banal by which the public recognizes the vibrations of the engines of two-or three-cylinder: because the interval between the moments of maximum out-is superior to a tenth of a second.
What is the torque delivery of your engine?
In many publications on the world of motor it is usual to measure the torque that “delivery” as the engine of a vehicle. It is affirmation, by definition, is not correct in as much we understand that the pair is a applied force and not a resultant force. However, also by the physical principle of action-reaction, when on a shaft that rotates about itself applies a moment of force, it automatically generates a moment of force of the same intensity and direction but opposite sense to the original (Newton’s third law).
How to calculate the motor torque – Load motor
The motor torque can be measured but its calculation is extremely complicated and almost impossible for mortals so that it is easier to leave it to professionals to be able to handle modern machines and computer programs are very complex, although to the naked eye we only see a bank of rollers. As is clear from its definition, in a combustion engine the pair is a variable that depends on the power generated in the chambers of the cylinders and of the number of revolutions at which it is spinning the engine at the particular moment so that it could calculate its value from the formula P = T · ω where P is the power expressed in wattios or watts, T is the torque expressed in Newton meter and ω is the rotation speed of the radial is expressed in radians per second.
however, there are other factors that affect the theoretical values that could be obtained of the direct application of the formula as, for example, friction internal to the engine. These frictions internal to make you a part of the power obtained by the motor is not usable externally, but that is “lost” in the process of movement of the motor, usually in the form of heat. Remember that the energy can neither be created nor be created nor destroyed, only transformed.
There are also external factors which can impact on the power generated by an engine, even in the face of situations that internally might be comparable. For example, the same engine turning at a constant speed of 2,000 revolutions per minute, will generate more power when driving on a flat road that descends a slope. Despite the fact that the number of revolutions is constant, and therefore also the angular velocity of the crankshaft, the different value of the power generated in each moment also results in a different value of the torque applied on the crankshaft.
Many of you wonder how can this be and explanation is very simple. As we all know, the movement is generated by the ignition of the stoichiometric mixture fuel-to-air in the chambers of the cylinders and if it requires less power, the solution is to inject a mixture poor in fuel, and more rich in air. This is the reason also why the computers in our cars is marked by a consumption instant less or even zero when we leave a port.
All of these parameters that modify the operation and the theoretical results of a mechanical receive the name of load engine, which canfinirse as the amount of torque that should produce an engine in order to overcome the resistances that oppose themselves to its movement.
As we have seen the load motor depends on both internal causes of the engine, as may be the friction of the various moving parts, such as external agents such as may be the friction of the tires, or the aerodynamics of the car. I have put these two examples are totally external to what is the mechanics of the vehicle because in both cases generate forces opposed to and continuously variable with the movement of the vehicle, which also has repercussions on the value of the load motor will be a parameter also continuously variable.
The load on the engine affects us also in the driving of it is very clear that all the drivers know how to appreciate. If we continue with the same example of a vehicle traveling at a constant speed and to a regime of revolutions constant, too, why in a stretch uphill to the car, it’s harder to gain speed on a stretch downward? As for the variation of the load motor.
Entering again in a theoretical world, when a car travels a constant speed on a flat road has two external forces that oppose its motion: the aerodynamic drag and the friction. When the vehicle starts to move by a stretch upward, if we keep the speed constant, we can consider that the aerodynamic force opposing the motion is maintained, but the friction is modified in the sense that it is a gravitational force, and at the time that the vehicle begins to ascend, there will be a part of the friction “pull” of the car backwards.
If we want to spin already very thin, can’t get in game also the kinetic energy and the potential energy. The kinetic energy depends on the mass and the speed of the vehicle and the potential of the mass and the height. As the height increases, by the principle of conservation of energy, the kinetic energy is transformed into potential energy.
In this case road ascending, by summing the set of external forces that oppose the movement, we can affirm that the load on the engine increases and therefore, the amount of torque “usable” of the engine descends, is to be seen a number of situations:
- If we want to maintain the constant turning of the engine we must demand more power by squeezing more strongly on the throttle to inject a mixture more rich in fuel in the chambers of the cylinders.
- If the inclination of the road increases can reach the point in time at which the vehicle begins to to lose speed. This is because the load motor (forces opposed to the movement) is greater than the torque able to be generated in the motor (positive forces in the movement).
- To stay constant power and torque, and increase the load motor, there will be less power available to increase the speed of the vehicle because the acceleration is proportional to the force applied: if there is less power there is less power of acceleration.
The engine torque and the gearbox
however, physics is also able to modify the behavior of bodies subjected to various forces, and in the case of the crankshaft of the engine of our car, we can affirm that it is able to send the torque that it receives from the cylinder to other parts of the vehicle, as may be the gearbox.
The torque comes from the engine to the change in the form of rotational movement through the primary axis. It is for this reason that when a manufacturer speaks of his catalogue of changes it is always about limitations of torque and not power. Inside the case of changes takes place transformation of torque into tangential force and again in par. How?
Inside the gearbox there are a number of sprockets that transmit motion one to the other just by the gear teeth of each other. These gear rims, which make reference to the number of gears that you have the change, they are of a different size or “gear ratio”, that is why sometimes you can read that a change has x speeds or x relationships; it is the same thing. In any case, this difference in size of the crown wheel is the one that varies the input torque and output also by the physical principle of conservation of energy: When two wheels rotate together (theoretically) retain the energy, so that the product of the torque by the angular velocity should remain constant.
Explaining the basic foundation that has an impact on the pair, the rates more short-term gear of larger size than the gears longer and your logic physics is very easy to understand with an example because it is something that all drivers perceive and know to take advantage of, so we’re stuck with the same car traveling at 2.000 revolutions per minute, generating power and torque constants.
Circulating in first gear, the primary axis of entry is introducing torque in the change with a certain angular speed but is geared to the crown gear of larger size that will rotate at a speed lower than the input shaft. As the power is kept constant on the gear, to the descend of the angular speed of rotation increases the torque. On the contrary, if you ride your bike in the highest gear, with the crown gear even smaller than that of the primary shaft input, it will happen just the opposite: the crown of the highest gear will rotate at a higher speed and therefore will drop the output torque.
This variation in the torque to a theoretical evidence of both the effectiveness of the block as the load engine is the responsible of the different behaviour that can be observed from the car to gain speed. Because it is known that circulating a constant diet of revolutions, it is easier to increase the rotation speed of the engine in a lower gear than in a long while the power and torque generated in the engine is the same. The reason is that in a higher gear there is less torque to the drive wheels. The reason is that at the same revs, the tires will spin faster the higher the gear. That is why sometimes we might climb a ramp quite steep in first gear at 1500 revolutions per minute, and other times, driving in 5th or in 6th, the slightest slope causes us to shift down a gear so as not to lose speed-even if you move to a regime more speed.
Logically we are once more in a theoretical world because, in practice, as it increases the speed also increases the aerodynamic force that tends to slow the car, increase the energy losses for example, by the further warming of the tyres… In the end, a series of external agents that generate forces opposed to the motion, and that simply it is worth you sound a little to better understand the torque engine.
The torque in electric motors
as in The case of the rotary motors, the electric motors generate directly rotational motion and, therefore, torque instead of power understood as such. This is because the principle of operation of an electric motor is based on a basic principle of magnetism by which charges of equal sign repel and charges of opposite sign attract.
constructive basis of an electric motor, explained in broad outline, to be a cylinder magnet crossed by a rotor that rotates on itself thanks to the constant changes of load of the outer cylinder. The most basic example would be that of the compass: if you do not touch points to the magnetic north of the earth, but if you approach a magnet and we rotate with a circular motion around the compass, its needle will rotate on itself at the speed with which we’re moving the magnet.
There is a basic difference in what refers to the quality of the torque obtained: is almost constant. While in a heat engine the number of pair may vary according to the number of revolutions to rotate the block, in an electric motor the torque is almost constant. This is due to the principle of basic operation of this type of engines and the technology applied today.
As I have mentioned, the rotation of the rotor of an electric motor is due to the continuous polarization of the stator that becomes a small magnetic field capable of spinning the rotor by alternating you were of attraction and forces of repulsion, and it is at this point where the technical advances today allow that the gravitational forces generated in the rotor have a torque peak almost constant.
Torque power vs torque thermal
I commented that the couple is almost constant for an detail very particular, and that explains in some way the limitations of electric cars on motorways or dual carriageways but also its advantages in urban traffic. Unlike a thermal engine, the electric motors generate motor torque from the beginning of the rotation and keep it constant until you reach the level of power may, at which time the number of pair falls. For example, the BMW i3 offers the maximum power of 170cv and a maximum torque of 250Nm, but we will see how it is split:
- In the electric motor of the BMW i3 delivers a torque of 250Nm constant from almost 0 rpm of the engine up to approximately about 4,500 turns of the engine per minute.
- In this range of 0 to 4,500 revolutions per minute the power is increased from 0 to 170 hp (127kw).
- from 4,500 revolutions per minute as much torque as the power begin to decrease.
- To 8,000 revolutions per minute the motor of the BMW i3 offers about 150 horses or so and a torque of 125Nm.
What reading you can make of these figures? As in the case of the motor of the BMW i3 can say that equipped with a motor very cheerful up to 4,500 rpm, which makes this car to be very quick in accelerations at low speed. In fact, it reaches the 100km/h coming from standstill in just 7’3 seconds, which allows you to challenge you with the BMW 120i.
however, from 4,500 revolutions both power and torque start to decrease and adversely affect both the ability of acceleration as to the consumption, which may be doubled with respect to the figures approved. It is for this reason also that many electric cars have a “ECHO” that limits their maximum speed to 90 or 100 km/h, just when a car like the BMW 120i could get, to maintain a constant speed, fuel consumption very low.
By the way, there is another advantage of very striking and interesting of the cars equipped with electric motors: shows less sensitive to a sporty driving or city traffic and the increase in the consumption of energy is not so pronounced as it would be in a vehicle with a heat engine equivalent. That’s because the offer you a couple so high and relatively constant, we can say that the engine has more easily to increase the speed of rotation of the motor or that demand less increase in torque to increase its rotation speed.
Few petrol vs torque diesel vs torque boost
In this section should not be extended much because of the differences between the torque obtained from a block powered by gasoline and the other fueled by diesel are due to the particular constructive characteristics each other and energy is released in the ignition of their respective fuels.
If we consider a classical read-out of these figures, understood as a comparison between blocks air fed by injection, or what has come to be more or less a jump to the 80, the blocks fed by diesel offer more torque and a lower regime compared to the block of gasoline, but in the eyes of today, their power levels could be even ridiculous.
In this regard we can remember the beginning of the article where I explain that the theoretical power of the vehicle is proportional to the torque and the angular velocity of rotation. A vehicle atmospheric petrol has a actual margin utilization approximately between 1,000 and 5,500 revolutions per minute and a diesel maximum torque of between 1,000 and 4,000 revolutions per minute. In the real world, the margin for practical use ranges between 2,000 and 4,000 revolutions per minute for the gasoline engines and between 1,500 and 3,000 turns for the mechanical powered by diesel fuel.
If we let constant one of the variables, for example the turning at 2,000 revolutions per minute, we will get a minor power in the diesel engine but at the same time we will offer more torque. Why is this? Because it is simple, the torque motor causes the linear movement of the pistons in accordance with the ignition of the fuel in the chambers of the cylinders and the power that is generated according to burn petrol or diesel is different. However, the explanation of mechanism is valid for both cases.
electronics and over-nutrition
today, this, which I just explained is for the memory of the more nostalgic. In fact many of you may have noticed that sometimes a manufacturer offers vehicles with the various figures of torque and power extracted from the same engine block. Or even a vehicle you have a “ECHO” able to modify those numbers by simply pressing a button as happens for example with the Fiat Panda Cross TwinAir: in the normal mode offers 90hp and 145Nm, and in the mode “ECO” is in 78cv and 100Nm.
This is due to the technical advances and mostly electronics applied to the world of automotive. To day of today already we are not surprised to hear about the drive phase for vehicles with cylinder head valve, diesel and petrol engines with the same compression ratio or even engine variable compression, but if there is something that has represented a giant step forward in regard to the figures of power and torque of a vehicle is the overfeeding.
Although its mechanical explanations can be very complicated, the basic foundation of the sobrealimentanción is very simple: increase the pressure within the chambers of the cylinder to increase the force generated in the ignition of the fuel, which causes the piston to descend with more force and, therefore, get more torque to the crankshaft.
As expected, its implementation mechanics are somewhat more complicated and requires so much to study in its correct location within the hood of a car, a few new collectors of input and output, of reinforcements, the specific pistons, connecting rods, crankshaft… but the basic principle is to increase the pressure within the chamber of the cylinder and this is what matters to relate it with the torque of a motor.
The supercharger can be driven directly by the rotation of the motor or by the pressure of the exhaust gases. Today, the electronics have also come to the overfeeding, and the new Audi SQ7 TDI has released the first turbo electric market and the results may not be more spectacular: 435cv constants between 3.750 and 5.000 revolutions per minute and 900Nm constants between 1,000 and 3.250 revolutions per minute.
Yesterday and today
Until not many years ago, only the experts knew that a car with the cylinders in square (bore = stroke) were the most balanced to drive, that if the race was less than the diameter would be a powerful car but with a number of pair modest and that if the race was superior to the diameter it would be just the opposite, more quiet and with more torque.
Today most of the engines belong to families of modular, which allows manufacturers to provide blocks of more or less cylinders and gasoline or diesel with relative ease and minimal changes, the variations in the engine torque and the power are given by the use and combination of different technical applications, and electronic that the manufacturer wants to use.
in spite of all this I have explained in this article, the reality trumps theory in all aspects. In the current market we can find six-cylinder engines with the power of one of eight, three-cylinder engines as smooth or more than others tetracilíndricos of similar ability or even diesel engines with the same compression ratio that a gasoline and is that today everything is possible.
main reason of this article was to explain understandable what is the torque, or torque, that ye may be able to recognize how it affects the daily driving and you realise that the power of a car, if it is not related to the engine torque, this value is not very indicative of the behavior of the same. I hope I have achieved that.