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We explain abbreviations in the automotive industry

psooya 8052 6
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  • #1
    Level 38  
    Due to repeated queries about WOT, CL, OL, AFR etc. I decided to explain some of the most needed abbreviations with a small description of the action necessary when working with LPG.
    A request to moderators for hanging in the LPG department as an announcement and adding explanations as well as giving a meaningful title to the thread. Here we go:
    WOT - Wide Open Throttle - a pedal in the floor and pull to the episodes
    AFR - Air to Fuel Ratio - air to fuel ratio. Typical for work in CL is 14.7: 1 Kg air / Kg fuel (gasoline) and it is a stoichiometric mixture. For gaseous fuel, the stoichiometric ratio is slightly different and amounts to 15.5: 1. To standardize these values, you can use the lambda coefficient of 1 means a stoichiometric mixture, so you don't have to know the correct AFR for different fuels. In OL the most optimal is 12.8 and it is found in the range of 14.7 to ~ 10. Not found in gasoline and gas systems AFR greater than 14.7 because, despite the greatest economy, it generates a temperature increase. Any AFR that deviates from 14.7: 1 causes a significant reduction in exhaust emissions.
    Most importantly, because I wrote that a different AFR is for gasoline and another for gas giving a stoichiometric mixture someone could get lost why it is said about 14.7 for lpg. Well, this is due to the measuring instrument which is the AFR probe, which is scaled by default for gasoline and so it would be common to give the same ratio of 14.7: 1 for gas and for petrol, because this is what the instrument indicates regardless of the fuel we are driving. It is often possible to change the meter settings and scale it to lpg where lambda = 1 is for 15.5 afr but it is not practical when adjusting the lpg installation. It is easier to set up installations obtaining the exact same values for both fuels than when switching, compare them additionally by calculating.
    Lambda coefficient - often confused with the lambda probe is nothing but a different interpretation of AFR. ? = 1.00 for gasoline means AFR = 14.7: 1 for 15.5: 1 gas 1.15 * 14.7 = 16.9
    OL - Open Loop - operation of the injection system in which the lambda probe indications are omitted and the fuel dose is generated from a rigid PB map in the PB set. Often safe mode is a transition in OL. The OL mode is designed to increase the engine power by a few% in a nutshell due to the lower AFR, reduce the combustion temperature, protect the engine from defects in the fuel system
    CL - reverse operation to OL, i.e. the controller reading the voltage from the lambda probe corrects the composition of the mixture to maintain a strictly set AFR 14.7: 1

    Please develop the topic, however, abbreviations of the names of components such as MAF, MAP, APP, TPS seem to be unnecessary here because Google can easily find the answer. Alternatively, please contact a moderator.
    best regards
  • #2
    Level 43  
    I can't find it, but there was a published description of the OBD standard somewhere, if someone found it, it would be worth putting - understanding the principle of fuel dosage I consider as the basis for diagnostics / repair / adjustment of LPG installations, even if people from the forum would lead "by the hand".
    The topic is worth hooking up, the more that so far, even referring to mpi engines or even diesel, such terms as "choke" are used. Like everyone knows what is going on and many unknowingly mix the concepts of carburetor and injection, not to mention the distinction between types of injection systems.
  • #4
    Level 38  
    EGT - Exhaust gas temperature - the exhaust temperature is the most important here in the combustion chamber
    We will briefly describe fuel trim in "new" cars, or how the computer dose and how to learn a new dose. Unfortunately, what the car manufacturer is teaching and deleting adaptations and interpretation of corrections is different, but here I will give general principles to outline the topic.
    Available parameters are:
    Fuel dose map - rigid, unmodifiable table with fuel doses as a function of engine load sensors like MAF / MAP / TPS - original map established at the car production stage
    STFT - Short Term Fuel Trim - short-term correction of the fuel dose whose task is to constantly correct the mixture to obtain the stoichiometric ratio based on the lambda probe
    LTFT - Long Term Fuel Trim - long-term correction of the fuel dose which task is to remember dose corrections when it significantly deviates from the original map. At the moment when the STFT corrections come out of the range, e.g. +/- 10%, there is a change in the LTFT correction, e.g. by a value outside the range, and the STFT correction oscillates within its given range again. This correction changes when the gas system is incorrectly adjusted and can lead to problems with starting the vehicle and other interesting anomalies such as emergency operation on the PB. Developing this concept, I will add that controllers can have multi-level long corrections and the controller uses the one that corresponds to the given engine load area.
    Loop condition : CL / OL - Here we have other curiosities, in most cases the corrections work as above, while in OL on WOT I encountered 2 cases:
    1. STFT = 0 and LTFT = 0 and the controller uses only the original fuel dose map - it is a safe and comfortable situation for LPG fueled engines, but does not take into account the wear of the PB injection system.
    2 STFT = 0 and LTFT = x and the controller uses the correction value added to the original map - here there may be a case of damage to the engine having LPG at PB operation because it may turn out that the gasoline mixture will be too lean, which will increase EGT

    You can leave the formula for the final composition of the mixture:
    Fuel feed from the original map + LTFT + STFT = current fuel injection time. So as STFT on gas increases it means that the mixture is too lean and LTFT correction may occur or is updated. Someone will accuse me of it. Yes, there are cars where increasing corrections do not mean a poorer dose but a richer one and then we are talking about inverted corrections.
    All the information above is only illustrative to outline what is happening there but each case must be approached individually.
    I did not mention deleting these values. Well, we have two ways:
    1. Disconnect the clamp for a few minutes
    2. Delete with diagnostic interface.
    Sometimesboth methods work and sometimes only one, unfortunately once I was sent the car back to the Authorized Service Center and there on downloading new software.
    I did not mention cars with two fuel banks or engines such as V where one side has a separate exhaust, collector, catalyst and lambda probe as well as the other side its equipment and as a result it looks like two independent engines with one shaft. Then we have to pay attention to both banks when tuning LPG.
    So when we regulate the installation for OBD corrections, we bring the fuel dose to the value where STFT and LTFT work in the same range as on PB.
  • #5
    Level 43  
    VVT - Variable Camshaft Timing , the name may vary depending on the manufacturer (VTEC - Honda, CVVT - Kia, VVT-i - Toyota, VANOS - BMW and others) - a system that allows changing the angle of opening / closing the valve. By default, the camshaft drive is rigidly connected to the crankshaft, so that the piston movement will always be accompanied by the same valve movement phase. In a VVT engine, the camshaft / shaft drive is expanded with a special system (the so-called variable-phase wheel), which allows a slight acceleration and deceleration of the valve phase during engine operation.

    MIL indicator - otherwise called "check engine", usually a yellow lamp with the engine symbol. This is a warning lamp informing the driver that the engine control is not able to maintain optimal exhaust composition.
    In general - the MIL indicator will light up permanently in the event that the engine controller for some reason, for a certain period of time or a certain number of engine cycles, will not be able to use the specified exhaust composition or will register the appropriate number of errors of monitored components. The indicator light will turn off automatically if the errors that caused it do not appear for a specified number of engine cycles. The error will be saved to the controller so that the diagnostician can later view the logs. The indicator may also flash regularly while the engine is running - flashing means that further driving may damage the catalytic converter. There can be many reasons, however, in cars with LPG installation, its ignition (of course, if there were no problems before installing the installation) usually means incorrectly selected or incorrectly adjusted gas installation. The engine controller while driving, based on the data from the sensors makes corrections STFT and LTFT. However, if, despite changes in fuel dosage, the controller is not able to maintain the correct composition of exhaust gases, a check engine will be displayed and depending mainly on the make and generation of the car (the OBD standard is one, but its implementations in different cars are different) the controller may switch to OL or completely custom loop state.
    Example: used injectors and reducer. Symptom - too lean mixture around the reducer activation temperature (in this case it was 40 ° C), too rich mixture just after releasing the gas pedal, too lean mixture at higher load, smothering at WOT. The result - running over corrections resulting in flooding the engine when its temperature was about 40 ° C (difficult to start with a cloud of blue smoke in summer and after the engine has not fully cooled). The second effect - the MIL indicator lights and the lambda probe disconnection (on the interface the reading does not oscillate), in the frozen frames two lambda probe errors (lean mixture, value out of range), while STFT and LTFT seemed to work normally. After clearing errors and turning off the MIL indicator with the same errors returned, sometimes after a dozen or so kilometers. After deleting the adaptation, the engine work is armageddon before collecting corrections.
    An example of a flashing MIL: acceleration on a damaged ignition system (one cylinder was almost inoperative, especially on LPG).
  • #6
    Level 29  
    Jako uzupełnienie:
    VVT - Variable Valve Timing
    MIL - Malfunction Indicator Lamp
  • #7
    Level 38  
    WBO - Wide-Band Oxygen sensor - broadband lambda probe - AFR measurement in a wide spectrum
    NBO - Narrow-Band Oxygen - narrowband lambda probe - AFR measurement for stoichiometric mix composition