A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (i.e., by the use of a throttle). The term throttle has come to refer, informally and incorrectly, to any mechanism by which the power or speed of an engine is regulated.
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Internal combustion engines
In a petrol (gasoline) internal combustion engine, the throttle is a valve that directly regulates the amount of air entering the engine, indirectly controlling the fuel burned on each cycle due to the fuel-injector or carburetor maintaining a relatively constant fuel/air ratio. In a motor vehicle the control used by the driver to regulate power is sometimes called the throttle pedal or accelerator.
The throttle is typically a butterfly valve. In a fuel-injected engine, the throttle valve is housed in the throttle body. In a carbureted engine, it is found in the carburetor.
When a throttle is wide open, the intake manifold is usually at ambient atmospheric pressure. When the throttle is partially closed, a manifold vacuum develops as the intake drops below ambient pressure.
Usually the throttle valve is mechanically linked with the throttle pedal or lever. In vehicles with electronic throttle control, the throttle valve is electronically controlled, which allows the ECU greater possibilities in reducing air emissions.
Because diesel engines use compression ignition, they do not need to control air volumes or mixture (indeed this would be undesirable). Thus they lack a butterfly valve in the intake tract, and do not have a throttle (although recent developments in Exhaust Gas Recirculation have introduced throttle-style designs1). They instead regulate engine power by directly controlling the quantity of fuel injected into the cylinder just before top dead centre (TDC) of the compression stroke.
Environmental aspects
Regulation of the throttle is also a mechanism for controlling engine exhaust emissions. In many modern internal combustion engines an electronic throttle is used, eliminating the older accelerator cable.2
Throttle application via the accelerator pedal also results in increased sound emission from the engine. At lower operating speeds this component of vehicle noise is prominent, contrasted with higher operating speeds, for which aerodynamic and tire noise are more significant.3
Other engines
Most engines have some kind of throttle control, though the particular way that power is regulated is often different.
Liquid rockets are throttled by controlling the pumps which send liquid fuel and oxidizer to the combustion chamber. Solid rockets are more difficult to throttle, but some may have mechanisms for this.
In a jet engine, engine output is also directly controlled by changing the amount of fuel flowing into the combustion chamber, usually with an autothrottle. In some instances, a "throttle" is known as a "thrust lever" (as in most Boeing aircraft.) This is chiefly due to the fact that a standard "throttle" is associated with internal combustion engnes.4
Computing
Analogously, Intel CPUs feature a "self throttle mechanism" to prevent them from overheating while still maintaining functionality. This serves as a fail-safe system. The CPU consumes more power under workload, but uses significantly less power when idle. The more power it consumes the more heat it produces. When its heatsink or associated cooling fan has failed or is inadequate to dissipate the heat generated by the CPU, the CPU temperature will increase past a predefined threshold. If this happens, the throttle function interrupts the running processes, forcing the CPU turn into idle state and/or by other means limit the workload, and therefore decreases its power consumption allowing it to cool down. The computer system may experience reduced performance as a result, but may still be fully functional.5 AMD also have some mobile processors possess similar ability but most desktop products do not. Most CPUs have a shut off temperature, by design higher then the "throttle temperature", as the last protection. Should both fail, overheating of the CPU could cause the computer to malfunction and could result in hardware damage.
Self throttle mechanism of a CPU is not to be confused with energy efficiency technologies, such as Intel's SpeedStep and AMD's Cool'n'Quiet and PowerNow!, which serves a different purpose. In contrast, self throttle is activated only when the CPU is under heavy workload and starts to overheat, while energy efficiency feature instead intended to reduce CPU power consumption when there are little or no workload. In addition, the self throttle mechanism is inside the CPU core for extra reliability and protection that works independently, while energy efficiency technologies are application controlled that would not execute without software support. 67
References
- ^ http://delphi.com/manufacturers/cv/powertrain/mvrv/
- ^ Victor Albert Walter Hillier and Peter Coombes, ‘'Hillier's Fundamentals of Motor Vehicle Technology'‘, 2004, 544 pages ISBN 0748703179
- ^ C..Michael Hogan, Analysis of Highway Noise, Journal of Water, Air, & Soil Pollution, Vol. 2, No. 3, Biomedical and Life Sciences and Earth and Environmental Science Issue, pages 387-392, Sept., 1973, Springer Verlag, Netherlands ISSN 0049-6979
- ^ http://www.avweb.com/news/ceocockpit/ceo_of_the_cockpit_84_terms_of_up_gearment_198161-1.html
- ^ http://www.heatsink-guide.com/maxtemp.htm
- ^ http://www.intel.com/support/processors/sb/CS-028855.htm
- ^ http://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_9485_9487%5E10272,00.html
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