AFM vs. MAF vs. MAP - Air flow SENSORS - HOW they WORK and how they DIFFER from each other

we all know that an engine needs to run at a certain air fuel ratio in order to run properly today we'll be exploring the different devices that measure the air coming into the engine and relay this important data to the ecu so that the ecu can inject the proper amount of fuel in order to obtain the desired air fuel ratio but before we get started i'll just take a literal minute of your time to tell you that today's video has been made possible by carly connected car so this thing here is a very nice car it's an and six-cylinder petrol with a nice amount of power and torque it's a joy to drive but it's also a modern car and modern cars are very complicated which is why when something goes wrong going from mechanic to mechanic and hearing different vague explanations of your problem often followed up by scary quotes can be very frustrating but carly can help you take back control of your car and fully understand what's happening with it at all times you simply plug it in into the obd port and connect it to your phone carly then translates the endless amount of data into valuable and easy to understand insights into your car's health maintenance and even some very nice and easy to access customization possibilities it's a simple and compact yet immensely powerful tool so if you want to take back control over your car check out the link in the video description so this big old clunky thing is an airflow meter or more specifically a vane type airflow meter it gets its name from the vein or flap that you can see inside you can most often find this thing on old fuel-injected cars from the 80s now some people also call this thing a math which means a mass airflow sensor but this is definitely not a math and as you'll be able to see in the rest of this video the afm or airflow meter works on a different principle to the math the vane air flow meter measures incoming air by relying on the drag force generated by the air the air pushes against the vein and opens it the more air pushes against it the more the vein will open the vein is connected to a variable resistor or a potentiometer in essence the potentiometer allows the voltage to enter it but exit only at the terminal that is proportional to the angle of the vein telling the engine's ecu how much the vane is open based on which the ecu determines the amount of air entering the engine and adjusts the quantity of fuel to be injected pretty much all vein airflow meters out there have a very similar outer shape the outer shape of the vein airflow meter is defined by the damping chamber and the compensation vein inside it unlike the main measuring vein the compensation vein doesn't measure anything it moves inside the damping chamber and absorbs the vibrations and sudden movements generated by rapid opening and causing of the throttle valve without the dampening chamber and the compensation vane the airflow meter would likely clatter when you suddenly open and close the throttle and would likely fail prematurely it's very important to understand that the goal of air flow measuring devices on an engine is to actually measure air mass as accurately as possible this is because a fuel-injected engine's air-fuel ratio is based on mass not volume now mass is the number of atoms or molecules within a substance it's the amount of matter within a substance volume is simply the physical space that number of atoms or molecules occupies this means that two equal volumes of air can actually have a different mass a different number of atoms or molecules within that same volume and this is why the air fuel ratio must be mass based an ideal perfect ecu is actually trying to match the number of air molecules with the appropriate number of fuel molecules of course this kind of accuracy is impossible with current technology but still we're going to be saying molecules of air today to better understand what's actually happening another reason why we can't base the air fuel ratio on volume is that air volume is determined by air density but air density changes with changing altitude and temperature and this means that accurately controlling the air fuel ratio based on volume would be impossible in changing ambient conditions as you can see the vane air flow meter doesn't really directly measure air mass it simply responds or reacts to the drag force of the incoming air and the drag force depends on both air velocity and air density but the vane air flow meter doesn't really know which of these two factors influence the opening of the vein more and this is why many vane air flow meters also incorporate an intake air temperature sensor within them by knowing the temperature which determines air density the ecu can make more accurate estimates of the incoming air mass and adjust the fuel injection accordingly but despite of this the vane airflow meter has many key drawbacks as you can see it has to react to the drag force of all of the air coming into the engine and this means that it actually restricts the airflow which in turn reduces the power output of the engine on top of this it's very important how the vane airflow meter is installed it must be installed in a dead horizontal position like this or this installing it in any position other than uh horizontal would actually impact the accuracy of this device because it would make the vein easier or harder to open and this would make the vein airflow meter actually useless this combined with the bulky size of the vein airflow meter means that it's pretty hard to find a suitable spot for this thing in an engine bay and this is why you really won't see a vane airflow meter in any car made in the last two decades or so now let's take a look at another device for measuring air for an engine but one that doesn't noticeably restrict the incoming intake air this one is called the karma vortex airflow mirror and it relies on the property of all foots air in total of course to generate vortices as they encounter an obstacle in their flow the obstacle is usually in the shape of a triangular rod and in this case it's called a vortex generator now the frequency or the number of the vertices within a certain time frame is proportional to the intake air velocity the vortices are counted either by an ultrasonic signal or a metal foil which oscillates in response to the changes in pressure created by the vortices the oscillating foil obstructs an led which illuminates a photo transistor and the phototransistor grounds or opens a voltage signal to the ecu the end result is a voltage frequency signal which changes with the changing velocity of the air by knowing the air velocity and the volume of the space through which the air passes the ecu can make an estimation of the air mass by the way the word carmen in carmen vortex comes from the name theodore from carmen he was a hungarian engineer and foot dynamicist who is regarded as one of the most important aerodynamic jurisdictions of the 20th century now uh compared to the vane airflow meter the karman vortex airflow meter is actually much less common on cars you can usually find it on cars from the early 90s or so most notably the dsm trio a few lexus a few bmw vehicles and a bunch of mitsubishi's among others but despite being less restrictive than the vane airflow meter the karman vortex airflow meter still has drawback of not measuring air mass directly it actually measures air velocity and makes air mass estimates based on that but our next device doesn't do this it actually measures air mass directly meet the mass airflow sensor and already the name of this device tells us what it does it's actually sensing the air mass directly that's coming into the engine now we have two different kinds of mass airflow sensors the hot wire type and the hot film type but they both work in essentially the same way a map has a wire that sits in the incoming air stream constant voltage is applied to this thin wire heating it up hence the name hot wire the wire is usually made from a material that has a high temperature coefficient of resistance such as tungsten platinum platinum rhodium platinum iridium and so on a high temperature coefficient of resistance means that even minute changes in the temperature of the wire will change its electrical resistance basically the hotter the wire the higher its electrical resistance and ohm's law tells us that the electrical current flowing through a conductor such as a wire is inversely proportional to the voltage the higher the resistance the lower the current our voltage is constant which means only the changing resistance of the wire will determine how much current falls through it the incoming air mass or the actual number of molecules in the air mass cools our hot wire the more air mass the cooler the wire the core the wire the lower its resistance the lower its resistance the higher the current going through the wire the electronic circuit which is part of the sensor measures the current flowing through the wire and converts it into a calibrated signal for the ecu so that the ecu can match the mass of air with a mass of fuel because the maf directly measures air mass it's impossible to confuse it with a change in air density due to changing altitude or changing air temperature denser air is going to contain more air molecules which are going to cool down the wire in the math more which means that the math is always going to accurately respond to a change in altitude or air temperature in fact a mav sensor doesn't even need an air temperature sensor to work properly it can work by itself despite this many maf sensors also come together with an air temperature sensor which is required by some ecu's and it can also be used as a good secondary check to verify the operation of the maf sensor a hot film sensor takes things further than the hot wire because it's able to measure not just the actual air mass but also the direction and the pulsation or reversion of incoming ear mass this is great because sudden opening or closing of the throttle valve can cause all sorts of rapid changes and pulsations of the intake air the hot film airflow sensor can respond and compensate for this which means it helps the engine run better smoother and more efficiently in all conditions the hot film maf sensor senses air direction by having two air mass sensing elements next to each other they work the same way as the single hot wire but because there's two of them the integrated electrical circuit can see which element experiences changes in resistance first which means it can tell the direction of the air stream think of the hot wire and hot film maf sensors as buoys in the ocean the hot wire is the equivalent of one buoy and the hot film is the equivalent of two pulleys when an ocean wave passes by it raises the buoy and you can measure how big the wave is by measuring how much the buoy gets raised with two buoys you can not only tell how big the wave is you can also tell where it's coming from by watching which buoy gets raised first the hot film maf sensor works on a pretty similar basic principle so the mav sensor is better than our previous methods for measuring airflow because it directly measures air mass making it more accurate also it's better than the vane airflow meter for example because it only measures a small sample of the incoming air which means that it doesn't create any sort of restriction in the airflow but because it measures only a small sample of the incoming air it must make that sample representative and making this sample representative is the task of this thing this mesh here this is the rectifier and what it does is also it's also called a diffuser and what this does is that it equalizes or evenly and uniformly distributes the air throughout this entire tube and this means that the small sample of the air measured by the math is actually representative of all the incoming air in this whole tube the karman vortex airflow meter also always has some sort of diffuser or rectifier because the carbon vortex ii only measures a small sample of the incoming air now other benefits of the maf sensor is that it's a lot more compact than both the vayne airflow meter and the carbon vortex and on top of this it's usually a lot less costly to replace the math than either the afm or the karma vortex one of the drawbacks of all maf sensors is that they're extremely sensitive to dirt debris or oil in the incoming air if any dirt or debris gets stuck on the hot wire or the hot film it's going to make the measurements uh by the math very inaccurate it's going to cause the engine to run poorly so a good way of ruining a good map sensor is to drive with a very dirty air filter or to use an aftermarket air filter that needs to be oiled and to oil it up excessively that's a sure way to ruin a good math and this is why this particular maf sensor has a very nice s-shaped curve and a deflecting bypass to try and separate the dirt and debris from the air that needs to be measured off our airflow measuring devices so far were located usually right after the air filter you're going to find the maf the afm as well as the carbon vortex in 99 of the cases right after the air filter but our last method for measuring air flow which is this thing the map sensor is different you're usually going to find this thing in the intake manifold and the name reveals it it's the manifold absolute pressure sensor and what it does is that it measures pressure in the intake manifold of the engine by measuring pressure the map sensor actually measures air density now air density tells us how tightly air molecules are packed into a certain volume our volume is the displacement of the intake manifold of the engine the denser the air the more air molecules are going to be packed into the intake manifold and the higher the pressure measured by the map sensor so by knowing the volume of the intake manifold and by measuring the pressure the map sensor can actually calculate air mass most map sensors measure pressure by relying on piezoelectricity which is the electrical charge that accumulates in certain materials when they're exposed to mechanical stress so basically when you press on them they generate a measurable electrical charge the more you press the more electrical charge there is to be measured air pressure acts on the piezoelectric material the more air pressure the more electrical charge you can measure now most modern map sensors actually use micro machined silicon pressure sensors aka silk chips in essence it's a tiny micro machined silicon membrane combined with a thin film of a piezoelectric material that seals away a chamber which either has vacuum or pre-calibrated pressure inside the changing air pressure inside the manifold will flex the silicone chip to different extents creating measurable changes in the current that accurately correspond to the changes in the air pressure inside the intake manifold so unlike the maf sensor the map sensor actually doesn't directly measure air mass it responds to changes in air density that being said it's still a superior airflow measuring device when compared for example to a vain airflow meter because density is directly influenced by changes in altitude and temperature a map sensor can always correctly compensate for changes in both temperature and altitude so in theory just like a map sensor a map sensor could work without an intake air temperature sensor but just like the map the map almost always comes together with an intake temperature sensor nowadays now a naturally aspirated petrol engine can function properly with just a map or just a math sensor that most naturally aspirated engines made in the last 10 or 20 years actually have both a map and a mav sensor and this is because both of these sensors together they can give you more insight into what's actually happening both before the intake manifold right after the air filter as well as inside the intake manifold itself more insight into what's happening means more power and more accuracy most forced induction turbocharged and supercharged engines have both a map and a math sensor and this is because uh the complex air movements generated by the turbocharger supercharger together with boost control and the rapid movements of the throttle valve can create extremely complex air reversions and pulsations and the ecu must be able to accurately compensate for this in order for the engine to run smoothly properly be efficient and make power and there you have the basic facts when it comes to airflow measurement inside a gasoline engine as you have seen map map carbon vortex and other sensors can definitely help a gasoline engine run at a correct air fuel ratio but they are not just useful for gasoline engines you can also find map and map sensors on diesel engines where they are used to verify the correct operation of the egr valve so yeah that's pretty much it for today i hope this video helps you better understand how all these different sensors work and how they play a key part in the performance efficiency and smoothness of your engine as always thanks a lot for watching i'll be seeing you soon with more fun and useful stuff on the d4a channel

Channel: driving 4 answers

Views: 349,120

Keywords: air flow meter, vane air flow meter, karman vortex air flow meter, karman vortex dsm, karman vortex bmw, karman vortex lexus, karman vortex street, MAF, maf sensor, maf cleaning, maf sensor how it works, mass air flow sensor, maf vs map sensor, manifold absolute pressure sensor, map sensor how it works, map sensor, maf sensor symptoms, maf sensor price, vane air flow sensor, flap air flow sensor, toyota air flow sensor, 4age air flow sensor, hot film maf, hot wire maf

Id: bxdwzlrRc8U

Length: 18min 43sec (1123 seconds)

Published: Sun Nov 15 2020