Torque Physics
In physics, torque is the magnitude of the moment, which is equal to the product of the force and the force arm. The international unit is Newton meter Nm. In addition, we can also see torque units such as kgm and lb-ft. Since G=mg, when g=9.8 At this time, 1kg=9.8N, so 1kgm=9.8Nm, and the pound-feet lb-ft is the imperial torque unit, 1lb=0.4536kg; 1ft=0.3048m, you can calculate 1lb-ft=0.13826kgm. In people's daily expressions, torque is often referred to as torsion (in physics, these are two different concepts). Now let's take an example: the torque of the 8th generation Civic1.8 is 173.5Nm@4300rpm, which means that the output torque of the engine at 4300 rpm is 173.5Nm. How can the power of 173.5N make a car of more than 1 ton run? ? In fact, the torque issued by the engine has to be amplified (at the cost of reducing the speed at the same time), which depends on the gearbox, final transmission and tires. The torque released by the engine first goes through the gearbox for "adjustable" torque amplification (or shrinks when the ratio is over), and then is transmitted to the final transmission (tail teeth) for further amplification (while the speed is further reduced), and finally passes through the tires. Release the driving force. For example, if the gear ratio of the 1st gear of a car (the gear ratio of the gears, which is essentially the radius ratio of the gears) is 3, the tail teeth are 4, the tire radius is 0.3 meters, and the original torque is 200Nm, the final torque on the axle becomes 200 ×3×4=2400Nm (set the transmission efficiency as 100%) After dividing by the tire radius of 0.3 meters, the friction part between the tire and the ground has a driving force of 2400Nm/0.3m=8000N, which is enough to drive the car. When it comes to mechanical efficiency, every time a gear is transmitted, there will be a power loss. The mechanical efficiency of the manual gearbox is about 95%, and the automatic gearbox is worse, about 88%, and the universal joint of the drive shaft is about 88%. Efficiency is about 98%. On the whole, the driving force of the car can be calculated by the following formula: Formula Torque × Gear Ratio × Final Gear Ratio × Mechanical Efficiency Driving Force = ———————————————————— Tire radius (unit: meters)
Summary: 1kgm=9.8Nm1lb-ft=0.13826kgm1lb-ft=1.355Nm Under the condition of a certain displacement, the cylinder with small cylinder diameter and long stroke pays more attention to the exertion of torque, and the rotation speed will not be too high, which is suitable for cylinders requiring large loads. vehicle. The cylinder with a large bore and a short stroke pays more attention to the output of power, and the speed is usually higher, which is suitable for fast-running vehicles. Simply put: power is proportional to torque x speed.
Calculation Why can the power of the engine be calculated from the torque? Power P = work W ÷ time t work W = force F × distance s So, P = F × s/t = F × speed v where v is the linear speed, and in the engine, the linear speed of the crankshaft = the angular speed of the crankshaft ω × crankshaft radius r, substitute into the above formula to get: power P = force F × radius r × angular velocity ω; and force F × radius r = torque, we can get: power P = torque × angular velocity ω, so the power of the engine can be determined from torque and speed The unit of angular velocity calculated in radians/second, in radian system, a π represents 180 degrees
