Equations for power and torque relationship

Power, Torque and RPM Calculations - RACELOGIC Support Centre {\displaystyle {\begin{aligned}{\text{power}}&={\text{torque}}\cdot 2\pi \cdot {\text{ rotational speed}}\cdot {\frac {{\text{ft}}\cdot {\text{lbf}}}{\text{min}}}\cdot {\frac. VBOX Test Suite and VBOX Tools Software have the ability to calculate BHP at the wheels using any Racelogic VBOX Data Logger that can record speed Power, Torque and RPM Calculations To calculate kW enter the following equation. This means that torque that is causing the angular speed to increase is doing work and the generated power may be calculated as: Mathematically, the equation.

If you increase the load at some point motor stops this is called stall. When it occurs the torque is at maximum and it is called stall torque. While it is hard to measure stall torque without special tools you can find this value by plotting speed-torque graph. You need to take at least two measurements with different loads to find the stall torque. How accurate is the torque calculation? While voltage, current and speed could be accurately measured, efficiency of the motor may not be correct.

It depends on the accuracy of your assembly, sensor position, friction, alignment of the motor and generator axles etc. If you want to get meaningful numbers you might use a second generator kit as explained in Torque and Efficiency Calculation section. Speed, torque, power and efficiency of the motors are not constant values. Usually the manufacturer provides the following data in a table like this one sample data from one of the motors used in generator kit: Also the manufacturers usually provide power curves for the motor at nominal voltage: These curves are generated by plotting motor speed, consumed current, and efficiency as functions of the motor torque.

Sometimes there might be also a curve representing mechanical output power. As you can see from the graph speed and current are linear functions of torque so you might need only two measurements to draw these graphs. Efficiency and power will need more data. While it is technically better to follow the same format and create similar curves for your motor it is not absolutely necessary for a good science project.

AND, in reality, the car with the lighter 2-liter engine will likely weigh less than the big V8-powered car, so will be a better race car for several reasons. Measuring Power A dynamometer determines the POWER an engine produces by applying a load to the engine output shaft by means of a water brake, a generator, an eddy-current absorber, or any other controllable device capable of absorbing power.

Then it applies various factors air temperature, barometric pressure, relative humidity in order to correct the observed power to the value it would have been if it had been measured at standard atmospheric conditions, called corrected power.

Calculations

Power to Drive a Pump In the course of working with lots of different engine projects, we often hear the suggestion that engine power can be increased by the use of a "better" oil pump. Implicit in that suggestion is the belief that a "better" oil pump has higher pumping efficiency, and can, therefore, deliver the required flow at the required pressure while consuming less power from the crankshaft to do so. While that is technically true, the magnitude of the improvement number is surprisingly small. How much power does it take to drive a pump delivering a known flow at a known pressure? We have already shown that power is work per unit time, and we will stick with good old American units for the time being foot-pounds per minute and inch-pounds per minute. Since flow is more freqently given in gallons per minute, and since it is well known that there are cubic inches in a gallon, then: Since, as explained above, 1 HP is 33, foot-pounds of work per minute, multiplying that number by 12 produces the number of inch-pounds of work per minute in one HPDividingby gives the units-conversion factor of Therefore, the simple equation is: When the equation is modified to include pump efficiency, it becomes: So suppose your all-aluminum V8 engine requires 10 GPM at 50 psi.

The oil pump will have been sized to maintain some preferred level of oil pressure at idle when the engine and oil are hot, so the pump will have far more capacity than is required to maintain the 10 GPM at 50 psi at operating speed. That's what the "relief" valve does: It is actually pumping roughly 50 GPM 10 of which goes through the engine, and the remaining 40 goes through the relief valve at 50 psi. The power to drive that pressure pump stage is: That pump at the same flow and pressure will consume: General Observations In order to design an engine for a particular application, it is helpful to plot out the optimal power curve for that specific application, then from that design information, determine the torque curve which is required to produce the desired power curve.

By evaluating the torque requirements against realistic BMEP values you can determine the reasonableness of the target power curve.

Power and Torque: Understanding the Relationship Between the Two, by EPI Inc.

Typically, the torque peak will occur at a substantially lower RPM than the power peak. For a race engine, it is often beneficial within the boundary conditions of the application to operate the engine well beyond the power peak, in order to produce the maximum average power within a required RPM band. However, for an engine which operates in a relatively narrow RPM band, such as an aircraft engine, it is generally a requirement that the engine produce maximum power at the maximum RPM.

That requires the torque peak to be fairly close to the maximum RPM. For an aircraft engine, you typically design the torque curve to peak at the normal cruise setting and stay flat up to maximum RPM.

That positioning of the torque curve would allow the engine to produce significantly more power if it could operate at a higher RPM, but the goal is to optimize the performance within the operating range.

Power, Torque and RPM Calculations

An example of that concept is shown Figure 3 below. The three dashed lines represent three different torque curves, each having exactly the same shape and torque values, but with the peak torque values located at different RPM values. The solid lines show the power produced by the torque curves of the same color. Again, moving the same torque curve to the right another RPM blue, lb-ft torque peak at RPM causes the power to peak at about HP at RPM Using the black curves as an example, note that the engine produces HP at both and RPM, which means the engine can do the same amount of work per unit time power at as it can at The RPM band within which the engine produces its peak torque is limited.

You can tailor an engine to have a high peak torque with a very narrow band, or a lower peak torque value over a wider band.

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