torque car driving theory
The advancement of the vehicle must depend on the torque exerted by the engine. The so-called torque is called torque in physics.
The concept of torque has been explained from the lever principle in elementary school. It is defined as the force in the vertical direction multiplied by the distance from the center of rotation. The metric unit is Newton-meter (N-m). After dividing by the acceleration of gravity of 9.8m/sec2, the unit can be Converted into kilograms-meters (kg-m) familiar to Chinese people. The imperial unit is pound-feet (lb-ft), which is more common in American car catalogs. To convert to metric, just divide the lb-ft number by 7.22.
The calculation method of the driving force of the car:
Dividing the torque by the wheel radius can be seen from the engine horsepower-torque output curve. It can be found that there is a relative torque value at each speed. How to convert these values into the actual force to push the car? The answer is simple, divide by a length to get force data. For example, a 1.6-liter engine can exert a maximum torque of about 15.0kg-m. At this time, if a 185/60R14 size tire is directly connected with a radius of about 41 cm, the propulsion force exerted by the wheel is 15 cm. /0.41=36.6 kilograms of force (in fact, kilograms are not a unit of force, but a unit of weight, which must be multiplied by the acceleration of gravity 9.8m/sec2 is the standard unit of force is Newton).
How does 36 kilograms of force push a metric ton of vehicle weight? Moreover, the engine speed of thousands of revolutions is unlikely to be exactly the tire speed. By connecting and matching gears of different sizes, the speed of rotation can be reduced and the torque can be amplified at the same time. Since the circumference ratio of the gear is the radius ratio, when the power is transmitted from the pinion to the large gear, the ratio of the speed reduction and the multiple of the torque amplification are exactly equal to the ratio of the number of teeth of the two gears, which is the so-called gear ratio.
for example
The big gear is driven by the pinion, assuming that the number of teeth of the pinion is 15 and the number of teeth of the large gear is 45.
When the pinion rotates at 3000rpm and the torque is 20kg-m, the speed transmitted to the big gear is reduced by 1/3 and becomes 1000rpm; but the torque is tripled and becomes 60kg-m. This is the basic principle that engine torque via the gearbox reduces revs and amplifies torque.
In a car, the torque is amplified twice from the engine output to the tires. The first time is caused by the gear action of the gearbox, and the second time is caused by the final gear ratio (or final drive ratio). The total torque magnification is simply the transmission gear ratio multiplied by the final gear ratio. For example, the gear ratio of the first gear of the sixth-generation Ximei manual is 3.250, the final gear ratio is 4.058, and the maximum torque of the engine is 14.6kgm/5500rpm, so we can calculate that the maximum torque of the first gear is 14.6× after amplification 3.250×4.058=192.55kgm, which is 13 times larger than the original engine. At this time, divide it by the tire radius of about 0.41m to obtain a thrust of about 470 kg. However, the above value is not the actual thrust. After all, there must be wear loss in the process of mechanical transmission, so the factor of mechanical efficiency must be taken into account.
When it comes to mechanical efficiency, every time a gear is transmitted, there will be a power loss. The mechanical efficiency of the manual transmission is about 95%, and the automatic transmission is worse, about 88%, and the universal joint of the drive shaft. The efficiency is about 98%, and you can see how much the actual thrust is left. Overall, the driving force of the car can be calculated by the following formula: Torque × Gear Ratio × Final Gear Ratio × Mechanical Efficiency Driving Force = ———————————————————— Tires Radius (in meters) Horsepower is not actually a force, but a unit of power, which is defined as the amount of work that can be done per unit time. Power is calculated from torque, and the calculation formula is quite simple: power (W)=2π×torque (N-m)×speed (rpm)/60, after simplifying the calculation, it becomes: power (kW)=torque (N-m)×speed (rpm)/9549, please refer to the block article for detailed derivation. However, how to convert the power kW into the common horsepower. Imperial or Metric? 1PS=735W; 1hp=746W
horsepower definition
Imperial horsepower (hp) is defined as: a horse pulling a 200-pound (lb) object 165 feet (ft) in one minute, multiplied to equal 33,000 ft-lb/min; while metric horsepower (PS ) is defined as a horse pulling a 75 kg object 60 meters in one minute, which is multiplied to 4500 kg-m/min. After unit conversion, (1lb=0.454kg; 1ft=30.48cm), it was found that 1hp=4566kg-m/min, which is slightly different from the metric 1PS=4500kg-m, and if the power W (1W=1Nm/sec=9.8 kgm/sec) to convert, you can get 1hp=746W; 1PS=735W two different results. The difference between 1PS and 1hp is only 1.5%, which is 1.5 hp per 100 horsepower, which is not a big difference. The horsepower of a general RV is mostly below 200 horsepower, and the difference between the two is only about 3 horsepower due to the difference in definition. Let’s increase the SAE standard data by 1.5%! However, there are also some differences between the various test standards of SAE, JIS, DIN, and EEC, and the units cannot really be equated. However, in the case of not much difference, PS or hp can be regarded as almost equal.
formula conversion
Substitute the above-mentioned conversion method of horsepower and power into the conversion formula of power and torque, and convert the unit of torque to the familiar kg-m, the following results can be obtained: British horsepower hp = torque (kg-m) × engine speed (rpm)/727 Metric horsepower PS = torque (kg-m) × engine speed (rpm) / 716 From the perspective of horsepower hp = torque × speed / 727, if the engine speed can be increased, and the torque remains unchanged, it can be increased horsepower. For example, if the speed can be increased from 6000rpm to 8000rpm, which is equivalent to an increase of 33%, but the torque at 8000rpm is reduced by 10% due to the limitation of the camshaft, the horsepower can still be increased by 19.7%, which explains why the modification of computers nowadays It can greatly increase the horsepower after the oil cut is removed.
If at the same speed, increase 20 horsepower, how much thrust can be increased? When the maximum torque point is exerted at 5000rpm, the formula is slightly changed, and it can be found that the increased torque=20hp×727/5000rpm=2.9kgm. Then substitute this result into the formula of the driving force of the car, which is also calculated by the first gear of Ximei, 2.9×3.250×4.058/0.41=93 kg. For a one-ton body, the impact does not seem to be very big; in addition, if there is a difference of 5 horsepower, the thrust will only increase by 23 kilograms. It can be seen that the difference of 5 horsepower is not much difference at all.
High horsepower determines true performance
In the end, a high-horsepower car runs faster, or a high-torque car runs faster?
It can be known from the formula that the reason for the high horsepower is that the high torque value is still maintained at high speed, that is to say, to have high horsepower, not only the torque at low speed is better, but also the torque at high speed must continue to be maintained, which means that torque and horsepower The debate is superfluous at all. As long as high horsepower can be achieved, in addition to indicating that the torque in each speed region is large, it also represents the superiority of material technology, and the material and weight of the piston, intake and exhaust valves will be strengthened and lightened. Quantification, in order to increase the engine speed.
