Horsepower (hp) is a non-system unit of measurement of power. Currently, it has officially been phased out in Russia (the standard SI unit for expressing power is the watt), but still continues to be widely used in the auto industry as an indicator of engine power.
In 1789, Scottish engineer and inventor James Watt coined the term "horsepower" to indicate how many horses his steam engines could do.
You should know that horsepower is not the maximum, but the average indicator of the power a horse can maintain for a long time. For a short time, the average horse can develop a power of about 1000 kg * m / s, that is, the power of one horse is 13.3 horsepower.
Basic units of engine power and their designation
1. Horsepower (735.49875 W). Denoted as: hp (this is netto engine power, measured using engine auxiliary units, such as muffler, generator), bhp (this is gross engine power, measured without the use of additional units).
You can also find other designations: PS (German), CV (French), pk (Nid.).
In English-speaking countries, horsepower is still more often equated to 745.6999 W, which is approximately equal to 1.014 European horsepower.
2. Watt
Since the description of the watt is beyond the scope of this article, we will not touch on it here.
Physical quantities
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How is horsepower calculated?
Horsepower is a conventional and ambiguous unit of measurement of power.
In Russia and almost all European countries, horsepower is defined as 75 kg*m/s (metric horsepower), that is, as the power sufficient to lift a load weighing 75 kg to a height of 1 meter in 1 second. In this case, 1 liter. With. is exactly 735.49875 watts.
The maximum power that a horse can develop is usually called boiler horsepower. You can easily calculate your maximum power. To do this, you need to measure the time t during which you run up the stairs of height h and substitute it into the formula: m*h/t, where m is the mass of your body.
To determine engine power, special stands are used, more about this is written below.
What it is
Not everyone knows why engine power is measured in horsepower. There's actually quite an interesting story here.
Many will be interested to know where this unit of measurement came from and why it’s all about horses. A lot of this has to do with marketing their time. Thanks to him, we currently measure the power of power units in horsepower. Now it’s worth telling why this happened.
Such a unit of measurement as LS was introduced back in the 18th century by James Watt. It is in his honor that another unit is named, that is, Watt.
Back in the 70s of the 18th century, he created the first steam engine, which significantly surpassed in its technical parameters the steam installation invented by Newcomen. At the same time, Watt did not know how to sell his development better and more profitably. One of his arguments was the fact that his engine needed 75% less fuel to operate.
Initially, the sale was carried out according to a somewhat unusual scheme. Customers who bought an engine gave away a third of the money they saved on fuel. But those times were a period when horses dominated the world of transport. As a result, few people were interested in steam engines.
As a result, Watt decided that it was necessary to compare his engine not with another steam unit, but with animals. As a result, his sales scheme was canceled and James tried slightly different sales tactics. He wanted to convince people to buy his engine.
This is how the unit of measurement that we all know today as horsepower was invented. This decision was made due to the fact that the client intuitively understood what was at stake when comparing the capabilities of a steam plant and a workhorse. In fact, it was a clever marketing ploy. But Watt supported his words with appropriate calculations.
He took an average workhorse as a basis and calculated how much energy it was capable of producing. No one knows exactly what experiments his calculations were based on. But it was found that in 60 seconds of work a horse produces approximately 45 thousand joules. And this corresponded to one horsepower.
In reality, the results turned out to be somewhat overestimated. Rare horses could work in this mode for a whole day. But realizing that the capabilities of animals were overestimated, Watt became convinced of the higher productivity of his development. This is exactly what he began to actively tell potential buyers about.
The story is unusual and quite interesting. But the fact is that such a cunning marketing move ultimately turned into a kind of revolution. Watt's engine played a huge role in the further development of the industry, and its advertising horsepower became a standard unit of measurement.
How is engine power measured?
Engine power is measured mainly to assess the effectiveness of tuning.
To determine engine power, there is only one accurate way: remove it from the car and install it on a special stand. Removing and installing an engine is a rather labor-intensive and expensive process that only automakers and serious racing teams can do.
For a less accurate measurement of power, dynamometer power stands are used (such as in the photo), which allow you to take readings “from the wheels”. The result can be influenced by: tire pressure, their grip properties, tire temperature (during measurement the tread gets very hot) and even the degree of attraction of the car with safety lines.
Measuring technique
The warmed-up car starts in first gear, accelerates to 40–50 km/h, after which the last gear is engaged, the gas pedal is pressed all the way and acceleration simulation begins. Upon reaching maximum speed (from the moment the power drop begins, visible on the monitor), neutral gear is engaged.
The measurement result is displayed in the form of a graph that shows the dependence of power on engine speed (blue curve - in horsepower).
Effect of horsepower and engine torque
During the combustion of the fuel mixture, the engine produces a certain amount of energy, which is power. This force is converted into torque, which pushes the car's wheels through a complex mechanical system. First, the energy goes to the crankshaft, then goes to the gearbox and through the drive axle it goes to the wheels. As a result of complex energy transfer, the car moves.
Torque - directly affects the movement of the car, converting energy into driving force, forcing the vehicle to move forward.
Additionally, torque is expressed as the motor force multiplied by the application arm. For example, when the fuel mixture detonates inside the cylinder, a certain pressure is created. This pressure is transmitted through the crank mechanism of the crankshaft and causes it to rotate faster.
On a note! Torque is the totality of the entire engine power, which is transmitted to the rotation of the shafts and gearbox through a gear system. The higher the indicator, the faster the car will accelerate.
Torque is measured in newton meters (Nm). This characteristic directly affects the implementation of the total motor power in real conditions. Therefore, the optimal motor power is always measured at maximum speed. In this case, horsepower will not matter without torque, since it is this that makes the car accelerate.
It should be understood that the acceleration dynamics of a car does not depend on the amount of horsepower, but on the amount of torque. Horsepower is only responsible for the “production” of a technical indicator!
Scale giving an approximate idea of the engine power range
To get an idea of the power range of the engines, please refer to the following figure:
- 0-100 l. With. — small cars;
- 100-200 l. With. - cars with medium power engines;
- 200-500 l. With. — sports cars;
- 500 l. With. and more - racing cars and supercars.
Torque
If expressed in the language of physics, the concept of torque is easy to understand if you know the principle of obtaining advantage from the use of a lever. Calculated by adding the forces applied to the lever (the weight of the load) to the length of the arm (lever), “Newton meters” show the potential amount of work performed. In the case of an internal combustion engine, the weight of the load is the force with which the piston moves back and forth after combustion of the fuel-air mixture. The length of the arm will be nothing more than the stroke of the piston (distance from TDC to BDC). Rotating force is created only during the power stroke.
How to determine the power of a car
You will need
- wattmeter, ammeter, voltmeter, screwdriver, knife, wires.
Instructions
The easiest way to determine the power is from the technical documentation supplied with the electrical appliance. The power of the device is indicated, as a rule, on the first pages of such documents. Open the manual (instructions) and find there words and expressions such as power, power consumption, average power, maximum power, etc. The number after them (the range indicated by two numbers separated by a dash) will be the power of the electrical appliance. After the number there should be a designation of the power unit: Watt (W), Kilowatt (kW), Milliwatt (mW) or its international designation - Watt, W, kW, mW, if the instructions are not in Russian.
If there are no instructions or other documentation for the electrical device, you can determine the power by reading the labels on the device. Just as in the case described above, focus on the words denoting power and the designations of power units.
If the device is relatively modern, then information about it is probably available on the Internet. Type the name and brand of your electrical appliance into the search engine. Most manufacturers of household and electronic appliances provide all the necessary information on their official websites. If you cannot find the necessary information (this often happens with old or homemade electrical appliances), measure the power using instruments. To do this, de-energize the electrical circuit by turning off the input circuit breaker or switch. Prepare an open circuit by disconnecting one of the power wires from the input device. Attach a piece of wire to this place, stripping the ends to the desired length. Prepare two pieces of wire of sufficient length. The length of the wires is selected based on the placement of electrical equipment and electrical measuring instruments.
Connect a wattmeter to the electrical circuit. Connect the current circuit to the prepared gap. Connect the voltage circuit using wires to the input device. Apply voltage by turning on the machine or switch. Using the indicator or scale of the wattmeter, determine the amount of power consumed.
If there is no wattmeter nearby, then you can get by with a multimeter or a couple of devices - an ammeter and a voltmeter. To do this, connect an ammeter or multimeter to a previously prepared electrical circuit break. If this is a multimeter, then switch it to current measurement mode. Turn on the circuit breaker or switch to apply voltage. Write down or remember the current readings on the indicator (scale). Turn off the voltage. Disconnect the ammeter (multimeter) and restore the circuit to its original state.
Apply voltage again. Take a voltmeter or set your multimeter to voltage mode. Measure the supply voltage by touching the probes of the device to the output contacts of the switching device. Remember or write down the measured voltage value. Then calculate the power consumption by multiplying the current value by the voltage value. If the voltage was measured in volts and the current in amperes, then the power would be in Watts (W).
If the electrical appliance is powered from a household power outlet, then the voltage can not be measured and taken equal to 220 Volts (V). If batteries with a known voltage are used for power supply, then voltage measurement also does not need to be performed.
Video on the topic
note
All operations with electrical equipment (except for measurements) should be carried out with the electrical circuit de-energized.
What does the torque shelf depend on?
According to the calculation formula Mkr = F x L, where F is the force and L is the arm length, the torque will depend on the combustion efficiency of the fuel-air mixture (F) and the piston stroke (L).
Since a car is a complex mechanism, engine torque is affected by a number of characteristics of other components and assemblies. The driving wheels of the car will receive maximum traction force only at the moment when the interaction of the mechanisms is optimal. The peak torque is achieved at such engine speeds when the combustion chamber is filled with the working mixture, combustion products are burned and exhaust gases are removed with minimal mechanical losses. For each engine, this parameter varies depending on the design features and the type of fuel used.
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Maximum speed:
A diesel engine is not a constant value, since this value depends on engine speed. To achieve maximum speed, the maximum strength of these parameters is necessary:
As an example, let's take a unit with a capacity of 150 horsepower. This internal combustion engine value can only be achieved at 6000 rpm.
When reaching 1500-3000 rpm, the number of “horses” decreases significantly. Therefore, to achieve maximum power, be sure to continuously press the accelerator pedal. The need to downshift to ensure efficient dynamics is explained by this.
To determine the power of the car, you need to make some calculations:
“Power is the energy generated by the engine, it is converted into torque on the output shaft of the internal combustion engine”
As a rule, progressive engines produce power in the amount of 5500-6500 rpm. As mentioned earlier, engine power is measured in horsepower. This means that most of the results need to be converted into kilowatts, for this there are special conversion calculators. (kW to hp)
For the simplest calculation of machine engine power, you need to determine or know the relationship between torque and revolutions. Engine torque is the product of force and the arm of the lever to which it is applied. Force is measured in Newtons, but lever arm is measured in meters - Nm.
To calculate torque from engine volume, there is a special formula:
P = Mkr * n/9549 [kW]
The essence of which:
- Mcr – engine torque (Nm),
- N – crankshaft speed (rpm),
- 9549 – coefficient so that the revolutions are substituted in rpm, and not in alpha cosines
