What is the torque : Torque is the force that causes the object to rotate. The torque of the engine is the torque that the engine outputs from the crankshaft end. It is inversely proportional to the engine speed under the condition of fixed power. The faster the speed, the smaller the torque, and vice versa, it reflects the load capacity of the car within a certain range.
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Torque and power are one of the main indexes of a car engine. It is reflected in the performance of the car, including acceleration, climbing ability and suspension. Its exact definition is: the reciprocating motion of the piston in the cylinder, the reciprocating one has a certain work, its unit is Newton. The work done at each unit distance is torque. This is the case. Torque is an important criterion for measuring the quality of a car engine. The torque of a car is proportional to the power of the engine. For a popular example, for example, when a person's body is in motion, power is like the durability of the body, and torque is the explosive power of the body. For a family car, the greater the torque, the better the acceleration; for off-road vehicles, the greater the torque, the greater the degree of climb; for trucks, the greater the torque, the greater the weight of the car. In the case of the same displacement, the higher the torque, the better the engine. When you drive, you will feel that the car is free to do whatever you want. If you want to accelerate, you can speed up. Now I have an important data for evaluating a car, which is the acceleration time of the car at 0-100 km / h. This acceleration time depends on the torque of the car engine. In general, the highest index of torque can be achieved at a speed of 2000-4000/min, which means that the engine of the car is better and the power is good. Some cars reach the highest index of the car's torque at around 5,000/min, which means that "power" is not the director of the car.
Torque is the magnitude of the torque in physics, equal to the product of the force and the arm. The international unit is the Nm of the cow. In addition, we can also see the torque unit such as kgm and lb-ft. Since G=mg, when g=9.8 At the time, 1kg = 9.8N, so 1kgm = 9.8Nm, and the pound lb-ft is the English torque unit, 1lb = 0.4536kg; 1ft = 0.3048m, can calculate 1lb-ft = 0.113826kgm. In people's daily expressions, torque is often referred to as torque (this is two different concepts in physics). Now let's take an example: The torque of the 8th generation Civic 1.8 is 173.5Nm@4300rpm, which means that the output torque of the engine is 173.5Nm at 4300 rpm. How can the strength of 173.5N make more than 1 ton of cars run? In fact, the torque emitted by the engine has to be amplified (the cost is to reduce the speed at the same time). This depends on the gearbox, final transmission and tires. The torque released by the engine is first amplified by the gearbox (or reduced in the super-shift) and then transmitted to the final transmission (the tail) for further amplification (while the speed is further reduced), and finally through the tire Release the driving force. For example, if the 1st gear ratio of a car (the gear ratio of the gear is essentially the ratio of the radius of the gear) is 3, the tail tooth is 4, the tire radius is 0.3 m, and the original torque is 200 Nm, then the torque in the axle becomes 200. ×3×4=2400 Nm (with transmission efficiency of 100%) After the tire radius is 0.3 m, the friction between the tire and the ground has a driving force of 2400 Nm/0.3 m=8000 N, which is enough to drive the car.
When it comes to mechanical efficiency, every time a gear is transmitted, a power loss will occur. The mechanical efficiency of the manual transmission is about 95%. The self-displacement gearbox is miserable, about 88% left, and the universal joint of the transmission shaft. The efficiency is about 98%. Overall, the driving force of a car can be calculated by the following formula:
Torque × transmission gear ratio × final gear ratio × mechanical efficiency driving force = ————————————————————
Tire radius (unit: meter)
Summary: 1kgm=9.8Nm 1lb-ft=0.13826kgm 1lb-ft=1.355Nm
In general, in the case of a certain displacement, the cylinder diameter is small, and the cylinder with a long stroke pays more attention to the torque, and the rotation speed is not too high, and is suitable for a vehicle that requires a large load. The cylinders with large bore diameter and short stroke are more focused on power output, and the rotational speed is usually higher, which is suitable for fast running vehicles. Simply put: power is proportional to torque × speed
Add one more point: Why is the power of the engine calculated from the torque?
We know that power P = work W ÷ time t work W = force F × distance s Therefore, P = F × s / t = F × speed v
Here v is the linear velocity, and in the engine, the linear velocity of the crankshaft = the angular velocity of the crankshaft ω × the crankshaft radius r, substituted into the above formula: power P = force F × radius r × angular velocity ω; and force F × radius r = Torque
It is concluded that the power P = torque × angular velocity ω, so the power of the engine can be calculated from the torque and the rotational speed.
The unit of angular velocity is radians/second. In the arc system, a unit representing 180 degrees, "torque" and "power" are important indicators for characterizing the dynamic performance of the engine.
The torque that the engine outputs to the outside through the flywheel is called the effective torque, expressed in Te, in units of N·m. The effective torque is balanced with the resistance torque externally applied to the crankshaft of the engine. The power that the engine outputs to the outside through the flywheel is called efficient, expressed in Pe, in kW. It is equal to the product of the effective torque and the angular velocity of the crankshaft.
The effective power of the engine can be measured by the bench test method, that is, the effective torque and the crank angular velocity are measured by the dynamometer, and then the effective power of the engine can be calculated by the following formula.
Pe=Te·(2âˆÂ·n/60)/1000=Te·n/9550(kW)
Where: Te - effective torque, N · mn - engine speed, r / min
The maximum value of the effective torque is called the maximum torque, and the maximum value of the effective power is called the maximum power.
When introducing a certain model in a newspaper, the torque and power in its technical parameters are usually the maximum torque and the maximum power. The power indicated on the engine nameplate and the corresponding speed are called rated power and rated speed. The rated power is generally less than the maximum power. According to the requirements of the vehicle engine reliability test method, the automobile engine should be able to operate continuously under rated conditions. - 1000h.
As for the meaning of torque and power, the popular point is that the torque is better than the 100-meter runner at the starting point, ready to go, ready to rush forward to the moment of the impulse; and power is to maintain this strength can run faster and faster, The ability to run to the finish line. By increasing the displacement of the engine, Te and Pe can be increased. In order to increase the engine displacement, the number of cylinders can be increased (for example, three cylinders to four cylinders), or the volume of a unit cylinder can be increased (for example, the cylinder inner diameter is increased).
Second, a correct understanding of the "torque" and "power" relationship of the engine
To put it simply: the torque of the engine is the amount of oil and gas that can be sucked in by the cylinder. This inspiratory volume will increase with the increase of the throttle opening and the gradual increase of the engine speed, but it will not always become larger. Going up, at a certain speed, it will reach the peak, which is the maximum torque that people usually say. When the engine speed rises again, it will gradually drop. This is the characteristic of the internal combustion engine such as gasoline engine, and it is also the most unsatisfactory place. The power is equal to the torque multiplied by the speed, which is the amount of oil that the engine can draw in per unit of time. Therefore, when the engine speed gradually rises to the maximum torque point, the amount of oil sucked in each breath and the number of inhalations per unit time are increasing, so the power is always rising; when the speed exceeds the maximum torque point, although every breath is sucked in The amount of oil and gas is reduced, but since the decrease is small and the number of inhalation is increasing, it is increased until the maximum power point; when the speed exceeds the maximum power point, the amount of oil and gas absorbed by each breath is greater than the increase of the number of inhalation. The amplitude, so the power starts to decrease.
Third, how to compare the advantages and disadvantages or enhancement of different engines
The engine dynamics indicators Te and Pe required by the car are obtained at a certain rotational speed. Different cars have different requirements for use, and the speed is different (for example, the speed of the truck and the car is different), the corresponding engine speed is different, so the engine of different purposes, even when the effective power is equal. The speeds corresponding to them are also different. In other words, the engines with the same power do not meet the requirements of all models. They must also look at the corresponding speeds while considering the power and torque, so that the engine can be fully seen. Whether the power performance indicators Te and Pe meet the requirements.
The two dynamic indicators of Te and Pe cannot be directly used to evaluate the pros and cons of the different displacement engines, that is, the engine with high power and torque is better or the degree of reinforcement is higher, but it depends on the unit cylinder work. The power and torque emitted by the volume.
TL and PL are the torque and power that represent the working volume of a unit cylinder. Using these two indicators can compare the strengths and weaknesses or enhancements of different engines.
Range of automotive engines TL and PL:
Gasoline engine: TL=600kPa-1000kPa PL=22kW/L—55kw/L
Diesel engine: TL=600kPa-900kPa PL=11kW/L—26kw/L
Under rated conditions, the power emitted by the engine per liter of cylinder working volume is called the rising power.
PL=Pe/(Vh·i)(kw/L) where: Vh——cylinder working volume (L) i——number of cylinders
The utilization rate of the cylinder working volume of the power meter, the larger the PL, the greater the power generated by the working volume of the unit cylinder. When the engine power is constant, the larger the PL, the smaller the engine and the smaller the material quality.
There are four main ways to increase the power:
(1) Increasing the amount of inflation Fuel combustion requires air, and it is more difficult for air to enter the cylinder than fuel. The use of supercharging technology or improved ventilation processes (such as reduced intake resistance) can increase the amount of inflation.
(2) Improve the quality of the mixed gas and the quality of the combustion. Under a certain amount of air, the air and the oil are uniformly mixed, the combustion is sufficient, and the heat supply per unit of the cylinder volume is increased.
(3) Improve the mechanical efficiency of the engine to reduce the mechanical loss to increase the output of the effective power. Reducing mechanical losses is mainly to reduce the friction loss of each friction pair, and secondly to reduce the power consumption and pumping loss of the auxiliary mechanism.
(4) Appropriately increasing the rotational speed mainly increases the frequency of work (or inflation), that is, increases the amount of inflation per unit time. However, in addition to the mechanical strength, the increase in the engine speed, the increase in the amount of charge per cycle, the increase in mechanical losses, and the difficulty in organizing the combustion process, that is, the increase in the number of revolutions will cause Pe to decrease. Therefore, the increase in the number of revolutions is also moderate.
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