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Flapper System
The Vane Air Flow Meter (VAFM), was one of the first airflow sensors in use and has been largely phased out of new car production. In a vane, or as it’s commonly called, “flapper-style” air flow meter, intake air flow exerts force against the surface area of a measuring plate, which is deflected in proportion to the volume of air flow meeting the plate. Movement of the measuring plate is transferred through a shaft to a slider on a potentiometer resistor, which produces a variable voltage signal proportional to the air intake volume. Once air volume, expressed as force exerted over a surface area, is measured, air mass is calculated in conjunction with an air temperature sensor.
Another mechanical-type AFM is the plunger type, which uses a sliding sprung cone-shaped plunger, rather than flap, to measure airflow, deduced from its position on a calibrated scale. Due to the mechanical nature of measurement, vane and plunger type meters are largely impervious to the effects of contaminants, but less accurate than other AFM/MAF types.
Hot Wire
Unlike air flow meters, hot wire or hot film mass air flow sensors directly measure air mass, as the convective qualities of air are affected by factors like temperature, humidity and density. Hot wire sensors create an analog signal and hot film sensors a digital frequency signal.
Most common hot-wire MAF sensors use a platinum wire or filament heated to a prescribed, maintained temperature above ambient, located centrally in the incoming air stream. These sensors function on the electrical principle that resistance increases with temperature. As intake air moves past the wire or film, the cooling effect causes a measurable drop in resistance, and thus lower voltage is required to maintain the prescribed temperature. The hot-wire MAF control unit is sent a reference voltage of 5V, and returns around .4V to.5V at idle and from 4.5V to 5V at full throttle. Based on a fixed data set, an accurate assumption of air mass is made.
Readings can stray from the target values as a result of contamination of the wire and for the sake of accuracy, an additional input from an integrated intake temperature sensor is sometimes used. Many hot wire MAFs incorporate a burn off cycle when the ignition is switched off, heating the element to over 1800-degrees F to clear it of contamination. Hot wire sensors are the most physically delicate and easily contaminated of all the air flow and mass sensors.
Errm.........I did cheat a bit with this answer (good old Google !) although I did understand my flapper system...honest
The Vane Air Flow Meter (VAFM), was one of the first airflow sensors in use and has been largely phased out of new car production. In a vane, or as it’s commonly called, “flapper-style” air flow meter, intake air flow exerts force against the surface area of a measuring plate, which is deflected in proportion to the volume of air flow meeting the plate. Movement of the measuring plate is transferred through a shaft to a slider on a potentiometer resistor, which produces a variable voltage signal proportional to the air intake volume. Once air volume, expressed as force exerted over a surface area, is measured, air mass is calculated in conjunction with an air temperature sensor.
Another mechanical-type AFM is the plunger type, which uses a sliding sprung cone-shaped plunger, rather than flap, to measure airflow, deduced from its position on a calibrated scale. Due to the mechanical nature of measurement, vane and plunger type meters are largely impervious to the effects of contaminants, but less accurate than other AFM/MAF types.
Hot Wire
Unlike air flow meters, hot wire or hot film mass air flow sensors directly measure air mass, as the convective qualities of air are affected by factors like temperature, humidity and density. Hot wire sensors create an analog signal and hot film sensors a digital frequency signal.
Most common hot-wire MAF sensors use a platinum wire or filament heated to a prescribed, maintained temperature above ambient, located centrally in the incoming air stream. These sensors function on the electrical principle that resistance increases with temperature. As intake air moves past the wire or film, the cooling effect causes a measurable drop in resistance, and thus lower voltage is required to maintain the prescribed temperature. The hot-wire MAF control unit is sent a reference voltage of 5V, and returns around .4V to.5V at idle and from 4.5V to 5V at full throttle. Based on a fixed data set, an accurate assumption of air mass is made.
Readings can stray from the target values as a result of contamination of the wire and for the sake of accuracy, an additional input from an integrated intake temperature sensor is sometimes used. Many hot wire MAFs incorporate a burn off cycle when the ignition is switched off, heating the element to over 1800-degrees F to clear it of contamination. Hot wire sensors are the most physically delicate and easily contaminated of all the air flow and mass sensors.
Errm.........I did cheat a bit with this answer (good old Google !) although I did understand my flapper system...honest
Flapper = airflow meter uses a swinging 'flap' that pivots further, the more air is being sucked into the engine.
Hotwire = the airflow meter is just a straight-through bore, but there's a length of wire passing through the middle that is heated. In a separate chamber is another wire similarly heated, but the one in the bore gets cooled by the rushing air, so the device works out how much extra current is needd to keep it heated to the same temperature as the 'sheltered' one and uses that as a measure of how much air is flowing in.
Yours has a flapper
Hotwire = the airflow meter is just a straight-through bore, but there's a length of wire passing through the middle that is heated. In a separate chamber is another wire similarly heated, but the one in the bore gets cooled by the rushing air, so the device works out how much extra current is needd to keep it heated to the same temperature as the 'sheltered' one and uses that as a measure of how much air is flowing in.
Yours has a flapper
me too, either can have my 
Just going back to the technical angle.....
Flapper (Vane) meters measure air flow, and they are attached to a variable resistor to give a voltage between 0 and 5 (on the digital systems anyway). I know from EEC-IV studies that this value than has to be adjusted and recalculated to get true air MASS, to get the actual real number for the 14.6:1 ratio fuel to inject. The EEC_IV first recalcs. the value against air temperature, and then for air pressure, as both of these affect the force which pushes the actual flap (vane).
(NB. Air pressure can be treated as a constant in UK, so not all systems have a pressure sensor, but this is not true in USA, where some cities are quite high up. Denver for example is 5000ft (?ish) above sea level)
A lot of people don't realise flappers are affected by air pressure as well as temp...
As stated above, The hot wire systems use a heated resistance wire, and the air flow cools the wire, so the boxes measure how much current they have to feed the wire to keep it at a constant temperature (by its resistance value).
This neatly bypassses all that tedious mucking about with temperature and pressure, as it yields the air mass figure directly, and it's also 'solid state', no moving parts, so technically more reliable.
Happy to bore you all rigid with more techie stuff - just ask !!
Flapper (Vane) meters measure air flow, and they are attached to a variable resistor to give a voltage between 0 and 5 (on the digital systems anyway). I know from EEC-IV studies that this value than has to be adjusted and recalculated to get true air MASS, to get the actual real number for the 14.6:1 ratio fuel to inject. The EEC_IV first recalcs. the value against air temperature, and then for air pressure, as both of these affect the force which pushes the actual flap (vane).
(NB. Air pressure can be treated as a constant in UK, so not all systems have a pressure sensor, but this is not true in USA, where some cities are quite high up. Denver for example is 5000ft (?ish) above sea level)
A lot of people don't realise flappers are affected by air pressure as well as temp...
As stated above, The hot wire systems use a heated resistance wire, and the air flow cools the wire, so the boxes measure how much current they have to feed the wire to keep it at a constant temperature (by its resistance value).
This neatly bypassses all that tedious mucking about with temperature and pressure, as it yields the air mass figure directly, and it's also 'solid state', no moving parts, so technically more reliable.
Happy to bore you all rigid with more techie stuff - just ask !!
Edited by RCK974X on Thursday 18th October 22:04
RCK, my dad used to own a 1959 Mercedes 300D pillarless limousine. It had various levers under the dash, the purpose of which he never determined through twiddling whilst driving along.
Some years later I found a book with extensive info. on the car and it transpired the levers were to compensate for air temperature and pressure differences - pretty high-tech for the 50s! Admittedly still requiring driver input rather than self-adjusting but still nice of Mercedes to think of it.
Some years later I found a book with extensive info. on the car and it transpired the levers were to compensate for air temperature and pressure differences - pretty high-tech for the 50s! Admittedly still requiring driver input rather than self-adjusting but still nice of Mercedes to think of it.
Wow, I didn't know Mercs even had such a system...just shows how much we all DON'T know....
I'm guessing a 300D would be a diesel ...?
So very advanced indeed for 50's technology.
AND whilst I'm here....
There are other airflow systems too - like the Karmann Vortex (I think that's spelled right..) which measures turbulence somehow and returns an air flow factor from that.
With modern digital systems some use 'Speed-Density' formula, which only needs manifold pressure sensor, throttle position, and rpm, and derives air mass from that. Pretty complex and apparently has to modelled for each individual engine design, but it's quite common...
I'm guessing a 300D would be a diesel ...?
So very advanced indeed for 50's technology.
AND whilst I'm here....
There are other airflow systems too - like the Karmann Vortex (I think that's spelled right..) which measures turbulence somehow and returns an air flow factor from that.
With modern digital systems some use 'Speed-Density' formula, which only needs manifold pressure sensor, throttle position, and rpm, and derives air mass from that. Pretty complex and apparently has to modelled for each individual engine design, but it's quite common...
Edited by RCK974X on Friday 19th October 23:21
RCK974X said:
Wow, I didn't know Mercs even had such a system...just shows how much we all DON'T know....
I'm guessing a 300D would be a diesel ...?
So very advanced indeed for 50's technology.
Nope, 3L staight-six petrol, I should have said 300d with a small d I'm guessing a 300D would be a diesel ...?
So very advanced indeed for 50's technology.
http://en.wikipedia.org/wiki/Mercedes-Benz_Type_30...
My old man's was a powder blue colour, it had been a lease car used by the Earl of Norfolk or Duke of Whitstable or some such, I forget... it was 10 years old when dad bought it in '69, long before the term 'classic car' had been invented. He wanted a big old Yank tank but there weren't too many around so he bought the Merc instead (for £350). It was only some 35 years after he got rid of it that we found more info on it through the internet: Mercedes only built about 1200 of them and at one stage they were fetching £48000 at auction. He swapped it for a Mk 4 Zephyr
Wedg1e said:
Nope, 3L staight-six petrol, I should have said 300d with a small d
http://en.wikipedia.org/wiki/Mercedes-Benz_Type_30...
Wow - Wikipedia article is impressive, comparing it to a Roller.... Banghead indeed !!http://en.wikipedia.org/wiki/Mercedes-Benz_Type_30...
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