Power band - AbsoluteAstronomy.com

The power band of an engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

or electric motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

refers to the range of operating speeds under which an the engine or motor is able to operate efficiently. While engines and motors have a large range of operating speeds, the power band is usually a much smaller range of engine speed, only half or less of the total engine speed range (electric motors are an exception - see Electric Motors below).

Specifically, power band is defined by the range from peak torque to peak horsepower (or sometimes to redline). For example: combustion engines typically generate maximum torque

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

at perhaps 2500 RPM. The peak horsepower

Horsepower

Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...

might be 5000 RPM. Such an engine would have a power band of 2500 to 5000 RPM, in which the engine would be very efficient.

Applications

Since engines produce the highest power over a relatively narrow range of speeds, a power-splitting device such as a clutch

Clutch

A clutch is a mechanical device which provides for the transmission of power from one component to another...

or torque converter

Torque converter

In modern usage, a torque converter is generally a type of hydrodynamic fluid coupling that is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load...

is required to efficiently achieve a wide range of speeds.

A transmission

Transmission (mechanics)

A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...

with a selection of different gear ratios is designed to make satisfactory power and torque available over the full range of road speeds. The goal of a transmission is essentially to keep the engine operating in its powerband.

By careful gear selection, an engine can be operated in its power band, throughout all vehicle speeds. Such use prevents the engine from labouring at low RPMs or exceeding recommended operating speeds.

Gasoline Engines

A modern, well designed and engineered fuel injected

Fuel injection

Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....

, computer controlled

Electronic control unit

In automotive electronics, electronic control unit is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle....

, multivalve (and optionally variable-valve timing

Variable valve timing

In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...

equipped) gasoline engine using good fuel can achieve remarkable flexibility, with a near-flat torque output from 1500 to 6000 RPM, allowing easy cruising and forgiving low-speed road manners. However, achieving maximum horsepower for strong acceleration or high road speed still requires high RPM, as power is the product of torque multiplied by speed of rotation (analogous to force x speed). Though the literal power band covers most of the operating RPM range, particularly in 1st gear (as there is no lower gear to shift down to, and no powerless "flat spot" much above a medium jogging pace), the effective band whilst on the move changes in each gear, becoming the range spanned at the upper end by either the limiter, or a point roughly located between peak power and the redline/rev limiter where power drops off, and at the lower end whatever engine speed changing up from that point in the next lower gear lands you at.

Diesel Engines

A typical small diesel has a narrower band, generating peak torque at lower rpm (often 1500-2000 RPM) but also with a sharper fall-off below this, and reaching peak power around 3500-4500 RPM, again rapidly losing strength above this speed. Turbo diesel engines can display this characteristic very markedly as it combines with the turbo lag (narrowed, exaggerated power band) intrinsic to most turbocharged engines. Therefore the manufacturer's (or purchaser's/modifier's) choice of gearing, and appropriate use of the available ratios, is even more crucial to make best use of the available power and avoid being "bogged down" in flat spots.

Electric Motors