Velocity air meter

Velocity air meter

A Velocity air meter measures the force of air rushing into an engine against a spring-loaded door in an air tunnel. A linear potentiometer rotated along with the hinge of the air door measures the angle of the opening and sends an electrical signal to the engine control unit (ECU) that changes as the door opens more or less. The ECU can deduce airflow into the engine based on this value after making certain corrections. The problem is that the force against the door is a function of two variables - weight of the air and speed of the air - and the ECU cannot distinguish , for a given door angle, whether the air is less dense but traveling faster or whether the air is denser but traveling more slowly. Therefore air velociy must be corrected for air density (temperature and barometric pressure) in order to reflect air mass (actual number of air molecules entering the engine per unit of time).


Velocity air meters from Bosch have been commonly used on systems such as older Bosch L-Jetronic and as a part of many factory systems, though they now have mostly been superseded by mass airflow sensors which have many advantages and are less damaging to engine volumetric efficiency (VE). Velocity air meters can be rather restrictive, particularly when engines have been modified for significantly greater airflow than stock (e.g. by fitting turbochargers or superchargers). Velocity air meters have the additional disadvantage that, once the door is fully open, there is no way for the sensor to measure further increases in airflow.

Because they can be restrictive and because they rapidly run out of measurement upside on the high-end of airflow, VAF meters are virtually never used with aftermarket electronic fuel injection (EFI). They are often replaced on factory systems with speed-density or MAF conversions. Some programmable engine management systems like Motec's can be configured to access VAF as engine loading information.


With L-Jetronic type airflow meter, adjustment is accomplished by tightening the spring tension. One notch is approximately equal to a 2 percent change in fuel mixture. For example, if you change to 20 percent larger injectors, you should tighen the spring by 10 notches. Verify fuel mixture by checking with a wideband meter to verify that AFR's (air/fuel ratios) are correct under wide-open throttle and adjust if necessary.


This type of airflow sensor was used mostly on European imports equipped with Bosch L-Jetronic fuel injection, Japanese imports equipped with Nippondenso multi-port electronic fuel injection, and Ford vehicles equipped with Bosch multi-port EFI (EscortLynx, Turbo Thunderbird, Mustang with 2.3 liter turbo engines, and Ford Probe with the 2.2 liter engine) [Motorbooks WORKSHOP "HOW TO TUNE AND MODIFY ENGINE MANAGEMET SYSTEMS" BY Jeff Hartman] .


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Air flow bench — An air flow bench is a device used for testing the internal aerodynamic qualities of an engine component and is related to the more familiar wind tunnel. Used primarily for testing the intake and exhaust ports of cylinder heads of internal… …   Wikipedia

  • Ultrasonic flow meter — A ultrasonic flow meter measures the velocity of a liquid or gas through a pipe using acoustic sensors. This has some advantages over other measurement techniques. The results are slightly affected by temperature, density or conductivity.… …   Wikipedia

  • Gas meter — A gas meter is used to measure the volume of fuel gases such as natural gas and propane. Gas meters are used at residential, commercial, and industrial buildings that consumes fuel gas supplied by a gas utility. Gases are more difficult to… …   Wikipedia

  • Clear Air Turbulence — Die Clear Air Turbulence (abgekürzt CAT) bzw. Reinluftturbulenz oder Klarsichtturbulenz bezeichnet Luftturbulenzen in Bereichen ohne sichtbare Wolkenphänomene. Sie führen zu einer ungewollten Höhenänderung eines Flugzeugs und werden von… …   Deutsch Wikipedia

  • Clear Air Turbulences — Die Clear Air Turbulence (abgekürzt CAT, wörtlich „Turbulenz in klarer Luft“, umgangssprachlich „Luftloch“ – dann aber als Sammelbegriff für alle möglichen Turbulenzen) bezeichnet Luftturbulenzen in großen Höhen. Sie treten während des Fluges auf …   Deutsch Wikipedia

  • Current meter — Current Cur rent, n. [Cf. F. courant. See {Current}, a. ] [1913 Webster] 1. A flowing or passing; onward motion. Hence: A body of fluid moving continuously in a certain direction; a stream; esp., the swiftest part of it; as, a current of water or …   The Collaborative International Dictionary of English

  • Flow measurement — is the quantification of bulk fluid movement. Flow can be measured in a variety of ways. Positive displacement flow meters acumulate a fixed volume of fluid and then count the number of times the volume is filled to measure flow. Other flow… …   Wikipedia

  • Conveyor system — Conveyor redirects here. For other uses, see Conveyor (disambiguation). This article is about conveyor systems. For information on conveyor belts, see conveyor belts. For information on overhead conveyors, see overhead conveyors. An overhead… …   Wikipedia

  • Internal combustion engine — The internal combustion engine is an engine in which the combustion of a fuel (normally a fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine, the expansion of the high temperature and high …   Wikipedia

  • APS amphibious rifle — APS APS underwater rifle with 5.66 mm cartridge Type Underwater Assault rifle …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”