AFM(Air Flow Meter) , MAP(Manifold Absolute Pressure) & MAF(Mass Air Flow)(

[Jellybean]

Was reading up about AFM(Air Flow Meter) , MAP(Manifold Absolute Pressure) & MAF(Mass Air Flow)

 

From what I can see , reading here and on the web

 

Supra TT Jspec uses a MAP setup

Supra TT UK/USDM use a MAF ; not too sure if it is different for VVTI or Non VVTI? Hotwire sensor I presume?

RB26 uses a AFM

 

Looking on Wikipedia

 

MAF -- When a MAF is used in conjunction with an oxygen sensor, the engine's air/fuel ratio can be controlled very accurately. The MAF sensor provides the open-loop predicted air flow information (the measured air flow) to the ECU, and the oxygen sensor provides closed-loop feedback in order to make minor corrections to the predicted air mass (Hot wire sensor or Vane meter sensor typically used)

 

MAP-- A manifold absolute pressure sensor (MAP) is one of the sensors used in an internal combustion engine's electronic control system. Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel metering for optimum combustion. MAP sensor data can be converted to air mass data using the speed-density method. Engine speed (RPM) and air temperature are also necessary to complete the speed-density calculation

 

AFM-- An air flow meter is used in some automobiles to measure the quantity of air going into the internal combustion engine. All modern electronically controlled diesel engines use air flow meter,[citation needed] as it is the only possible means of determining the air intake for them. In the case of a petrol engine, the electronic control unit (ECU) then calculates how much fuel is needed to inject into the cylinder ports. In the diesel engine, the ECU meters the fuel through the injectors into the engines cylinders during the compression stroke.

 

Stoichiometry -- One thing I keep see coming up again and again is Stoichiometry; I presume this is in reference to the EGT reading

Gas stoichiometry deals with reactions involving gases, where the gases are at a known temperature, pressure, and volume, and can be assumed to be ideal gasses.

 

 

Few Questions

• Why are there so many different methods/Sensors to measure AFR; why do all car manufactures not have a standardised method?
  
• Why did Toyota use 2 different setups between UK/ USDM and JSPEC ? Where they just showing off? Ha ha
  
• Is this why a UK Supra requires 2 Oxygen sensors? One is part of the closed loop system to work with the MAF sensor, why does it need 2 O2 Sensors?
  
• Is the Closed loop system and Open loop system only applicable to an MAF and O2 sensor setup?
  

[David Reid]

There is also MAF & MAP is currently used by most prestige sports cars manufactuers in order to meet emissions and get best fuel ecomomy, performance and drivability..

 

The basic advantages/dissadavantage:-

 

MAF:- Very accurate steady state, disadvantage is slow to read in transients and expensive

MAP:- Cheap, very fast reading in transinets, disadvantage hard to model accurate flow from it steeady state

 

MAP & MAF = Best of both worlds

 

The reason for these systems is basically emissions, Toytota probably found they could not meet Euro emmisions based on MAP so moved to MAF. The reason not to fit MAF to japanese cars is probably cost if they could meet emissions without.

[Tricky-Ricky]

AFM and MFA are the same animal,but there are several different methods of accomplishing it.

Stoichiometry, is basically measurement og the unburnt fuel content of the combustion process, and is measured by a lambda sensor, narrowband being just a glorified switch, and wideband, which can deliver an accurate measurement of the precise fuel air mixture=AFR.

[Kris H]

I think Stoichiometric refers to the ideal Air/Fuel Ratio of 14.7:1 ??

[David Reid]

Bassically you are trying to control to your target Lambda value, at idle and in emiisions areas this will be 14.7, or leaner on DI. towards wide open throttle it will be whaterver is optimum for maximum performance.

 

It is not true that a narrow band Lambda sesnor is a switch, as per its name it is very accurate over a narrow Lambda band arround 14.7. It its not unusaual to have both narrow and wide band Lambda sensors fitted as wideband (again given away by the name) is good over a wideband but not as accurate as the narrow band arround 14.7.

 

This technology is now 20 years out of date and all modern cars use a model based system to model airflow into the ports from MAF and MAP inputs and considering the flow dynamics of the intake manifold. Target AFR is then mapped against engine speed and requested load, and you work back from your modelled airflow to give a fuel amount to acheive your target AFR. Ontop of this you have a Lambda controller which adds an adapted value to your base calculated fuelling amount.

 

It very complex stuff and the systems I use polynomial curves to define sufaces rather than traditional 3-D maps as 3-d maps arent accurate enough or too costly in ROM RAM to have large enough with sufficient resolution.

Edited August 20, 2010 by David Reid (see edit history)

[Tricky-Ricky]

Narrow band lambda is seen by an ECU as a switch, so as soon as a voltage of more than 0.45v = Stoic, is seen the ECU just adjusts the injector pulse width to run more fuel, if less than 0.45v it removes fuel, the ECU has no idea just what the actual AFR value is outside of 0.45v=14.7 AFR.

[David Reid]

Narrow band lambda is seen by an ECU as a switch, so as soon as a voltage of more than 0.45v = Stoic, is seen the ECU just adjusts the injector pulse width to run more fuel, if less than 0.45v it removes fuel, the ECU has no idea just what the actual AFR value is outside of 0.45v=14.7 AFR.

 

I am not sure which narrow band you have been working with or if it was broken, but most operate 0.2 to 0.8v. Think about it its there to allow the ECU to achevie 14.7 AFR, if everytime it went slightly out side this it turned off it wouldn't work as a control device as the ECU would not now how far past 14.7 the fuelling was and you would end up with a constantly oscilating AFR.

Edited August 20, 2010 by David Reid (see edit history)

[JODY T]

vvti used maf and map i believe

[Tricky-Ricky]

I am not sure which narrow band you have been working with or if it was broken, but most operate 0.2 to 0.8v. Think about it its there to allow the ECU to achevie 14.7 AFR, if everytime it went slightly out side this it turned off it wouldn't work as a control device as the ECU would not now how far past 14.7 the fuelling was and you would end up with a constantly oscilating AFR.

 

I was trying to simplify the explanation, in that 0.45v being stoic, ideal closed loop AFR, yes the ECU on seeing an increase/decrease either side of this threshold, dependant on the switch point of the ECU,like you say usually 0.2v and 0.8v being the trigger voltage for this.

The ECU will then add or decrease fuel to compensate, all it knows is that the fuelling is too rich or too weak, and not exactly what the AFR is, only the target, which was my point.

 

Every ECU i have ever seen that uses a narrowband lambda, fluctuates between rich and lean in a cycle of approximately once every two seconds, if its slower, it usually means they are going faulty, that how i have always tested them anyway.

[chrispot]

Few Questions

• Why are there so many different methods/Sensors to measure AFR; why do all car manufactures not have a standardised method?
  
• Why did Toyota use 2 different setups between UK/ USDM and JSPEC ? Where they just showing off? Ha ha
  
• Is this why a UK Supra requires 2 Oxygen sensors? One is part of the closed loop system to work with the MAF sensor, why does it need 2 O2 Sensors?
  
• Is the Closed loop system and Open loop system only applicable to an MAF and O2 sensor setup?
  

 

question 1 and 2 as david reid said

question 3 I think it is to check the efficiency of the cat, I presume that the second o2 sensor is after the cat?

question 4 no, closed loop is used in both map and maf setups.

closed loop is where the ecu is looking at the o2 sensor and adjusting the fuel trying to keep it at stoichiometric/ 14.7 to 1 afr, which is not the best for power. The car goes into open loop when starting and warming up and when at wot or at least 80% throttle. hope this helps, regards chris.

[Tricky-Ricky]

Few Questions

• Why are there so many different methods/Sensors to measure AFR; why do all car manufactures not have a standardised method?
  
• Why did Toyota use 2 different setups between UK/ USDM and JSPEC ? Where they just showing off? Ha ha
  
• Is this why a UK Supra requires 2 Oxygen sensors? One is part of the closed loop system to work with the MAF sensor, why does it need 2 O2 Sensors?
  
• Is the Closed loop system and Open loop system only applicable to an MAF and O2 sensor setup?
  

 

question 1 and 2 as david reid said

question 3 I think it is to check the efficiency of the cat, I presume that the second o2 sensor is after the cat?

question 4 no, closed loop is used in both map and maf setups.

closed loop is where the ecu is looking at the o2 sensor and adjusting the fuel trying to keep it at stoichiometric/ 14.7 to 1 afr, which is not the best for power. The car goes into open loop when starting and warming up and when at wot or at least 80% throttle. hope this helps, regards chris.

 

 

 

Just to confirm that yes the reason for two o2 sensors is down to monitoring the catalytic converter health, the second sensor returns a much slower response rate, IE pulse between rich and lean, which is then monitored by the ECU and compared with the std O2 sensor rate, once out of spec the ECU throws a CEL to tell you that the cat needs changing, so purely emissions based system.

[Chris Wilson]

May I ask what you do for a living David? I think you did once say you have something to do with OEM type ecu's? You obviously have an excellent knowledge of modern FI systems and their control I was wondering why Toyota use two cam position sensors on none vvti twin turbo Supra JZA80models? I can only conclude it was to get a synch signal in half the normal number of crank revolutions when starting and this small gain was enough to help meet cold start emission regulations, but I may well be quite wrong Can you tell me? Thanks.

[David Reid]

May I ask what you do for a living David? I think you did once say you have something to do with OEM type ecu's? You obviously have an excellent knowledge of modern FI systems and their control I was wondering why Toyota use two cam position sensors on none vvti twin turbo Supra JZA80models? I can only conclude it was to get a synch signal in half the normal number of crank revolutions when starting and this small gain was enough to help meet cold start emission regulations, but I may well be quite wrong Can you tell me? Thanks.

 

Hello Chris, I actually work for DENSO, with responsibility for OEM ECU strategy design but have also completed portions of calibration work for customers. I have worked for them for 10 years now and most of gasoline DI torque based control. Looking at emissions, performance, drivability and fuel ecomony, modern control is all about balancing those 4 especially with a premium customer.

 

I am now working on multi turbo (VNT+Bypass+active wastegate) diesel applications with two stages of EGR and DPF control with up to 8 fuel injections per cylinder and 250MPA fuel rail pressures which I find interesting.

 

I will ask the cam sensor engineer on Monday, but I would agree with you, assuming the rotors are 360 degrees out of phase, I expect toyota wanted as short crank time before firing on there premium product. I doubt there would be an emissions benefit as you wouldn't inject before the engine was synchronised. But it may have helped keep a small battery size for reduced cranking during cold start.

[Jellybean]

Rather than start a new thread , I see some of the new aftermarket ECU's to the market are using VE tuning

 

Do OEM manufacturers use Volumetric efficiency (VE)) or pulsewidth-based engine management systems

 

Is VE just propaganda to sell ECU's or are they taking on the latest OEM technology?