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(11) | EP 0 747 589 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Air fuel ratio control as a function of throttle position |
| (57) Air fuel ratio in an internal combustion engine is controlled as a function of throttle
position change and a proportional adder to improve response to acceleration tipins. |
[0001] This invention relates to controlling the operating conditions of an internal combustion engine using an electronic engine control module.
[0002] It is known to control the air fuel ratio of an internal combustion engine using an electronic engine control having inputs from various sensors. Such sensors can include, for example, the exhaust gas oxygen sensor, the mass air flow sensor, and the temperature sensor.
[0003] It is also known to adjust air fuel ratio. For example air to fuel ratio may be adjusted to be rich during engine operating conditions such as acceleration. Nevertheless, it would be desirable to improve engine operation in response to an acceleration condition. These are some of the problems this invention overcomes.
[0004] According to the present invention, there is provided a method of controlling air fuel ratio in an internal combustion engine having a throttle wherein air fuel ratio is controlled as a function of the rate of change of the throttle position of the internal combustion engine.
[0005] Further, according to the present invention, there is provided a method of controlling air fuel ratio in an internal combustion engine having a throttle including the steps of:
storing a minimum change required in throttle position to add fuel;
storing a lookup table of fuel compensation as a function of change in throttle position;
determining throttle position;
determining change in throttle position;
looking up the minimum change required in throttle position to add fuel;
determining if the change in throttle position is greater than the minimum change required in throttle position to add fuel;
if no, returning to the step of determining throttle position;
if yes, looking up the fuel compensation as a function of change in throttle position and determining the fuel mass required; and
returning to the step of determining if the change in throttle position is greater than the minimum change required in throttle position to add fuel.
[0006] This invention recognises utilising a throttle position sensor output and proportional control in an electronic engine control processor to more accurately and quickly predict tip in acceleration and control air to fuel ratio. That is, air to fuel ratio is more uniformly controlled and rich and lean air to fuel ratio excursions reduced. As a result, engine operation and customer satisfaction is improved.
[0007] The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Fig. 1 is a schematic block diagram of an engine and control system in accordance with an embodiment of this invention;
Fig. 2 is a graphic representation of characteristic traces versus time of throttle position, air charge, fuel pulsewidth, air fuel ratio;
Fig. 3 is a flow diagram of a control system in accordance with an embodiment of this invention; and
Fig. 4 is a graphical representation of fuel compensation for tip in as a function of change in throttle position angle per unit time.
[0008] Referring to Fig. 1, a powertrain for a vehicle includes an engine 10 which receives air through a intake duct 11 having therein a mass air flow sensor 12 and a throttle 13. Throttle 13 is connected to a position sensor 14, such as a Hall effect or a phased array optically encoded sensor, which produces a signal output applied to an electronic engine control module 15. Electronic engine control module 15 also receives an input from the output of mass air flow sensor 12. The output from electronic engine control module 15 is applied to a fuel injector 16 which controls the introduction of fuel into engine 10 from a fuel line 17.
[0009] Referring to Fig. 2, characteristic traces of throttle position, cylinder air charge, fuel mass (e.g. fuel injector pulsewidth), and air fuel ratio are shown with respect to time in response to a tip in or acceleration by the driver. The throttle position provides the most advanced information when the tip in occurs at time A. After point C intake air charge begins to increase in response to the change in throttle position. Fuel pulsewidth correction starts to occur at point B so that there is a time delay between point C and point B before the air fuel ratio is beginning to correct. Finally, the air fuel ratio versus time shows that there is a lean excursion starting at point C when air charge is increased but fuel is not increased.
[0010] Shown in dotted line on the air fuel ratio line is the improvement using information from the throttle position to control the air fuel ratio. Shown in dotted line on the fuel mass line is the corresponding change to the fuel mass in accordance with this invention. That is, the dotted change shown for fuel mass produces the improved control of air fuel ratio shown in dotted line. In particular, the magnitude of the lean excursion of the air fuel ratio at time B is reduced or eliminated as is the magnitude of a rich air fuel excursion after time B.
[0011] Referring to Fig. 3, logic flow for a method of throttle based fuel adder as a lean excursion eliminator begins at a start block 30. Logic flow goes to a block 31 wherein the throttle position (TPS) is calculated. Logic flow then goes to a block 32 where the minimum change required in throttle position to add fuel (MIN_DEL_TPS) is looked up from stored information . From block 32 logic flow goes to a decision block 33 where it is asked if the change in throttle position sensor output is greater than the minimum change set point of the throttle position per unit time (TPS greater than MIN_DEL_TPS).
[0012] If the answer is no, logic flows back to the input of block 31. If the answer is yes, logic flow goes from block 33 to a block 34 where there is a lookup function for fuel compensation for tip in as a function of throttle position and change in throttle position angle per unit time (TFC_TP = FNxxx(TPS, DEL_TPS). Logic flow then goes a block 35 wherein the fuel mass required is defined in terms of a proportional adder. In particular, the fuel mass required is defined as being equal to ((Cylinder air charge) (KAMREF)/((14.64) (LAMBSE))) - PCOMP + TFC_HR + TFC_TP. Wherein the terms are defined as:
Cylinder Air Charge-Quantity of air in the cylinder
KAMREF - Correction for historic air to fuel ratio performance of the engine
(adaptive keep alive memory)
LAMBSE - Fuel equivalence ratio
PCOMP - Factor for adjusting fuel mass when vapour canister purge is taking place
TFC_HR - Factor for adjusting fuel mass when engine transients are taking place
TFC_TP - Factor for adjusting fuel mass when throttle induced transients are taking place
[0013] Thus block 35 provides a proportional fuel adder and the throttle position fuel adder may be a function of throttle position change per unit of time. Logic flow from block 35 goes back to block 33.
[0014] Referring to Fig. 4, there is shown a graphical representation of fuel compensation for tip in as a function of change in throttle position angle per unit time. That is, the X-axis indicates the change in throttle position per unit time (DEL_TPS), and the Y-axis indicates the fuel compensation for tip in (TFC_TP). One line indicates the relationship between these parameters for small throttle angles, another for medium throttle angles, and another for large throttle angles. Thus the graphical representation shows the differing proportionalities of how much fuel is added as a function of throttle position.
establishing a calibrateable predetermined change in throttle position per unit time;
comparing the change in throttle position with respect to the calibrateable predetermined change in throttle position per unit time;
if the change is greater than the predetermined value adding fuel; and
if the change is not greater than the predetermined value repeating the comparison.
storing a minimum change required in throttle position to add fuel;
storing a lookup table of fuel compensation as a function of change in throttle position;
determining throttle position;
determining change in throttle position;
looking up the minimum change required in throttle position to add fuel;
determining if the change in throttle position is greater than the minimum change required in throttle position to add fuel;
if no, returning to the step of determining throttle position;
if yes, looking up the fuel compensation as a function of change in throttle position and determining the fuel mass required; and
returning to the step of determining if the change in throttle position is greater than the minimum change required in throttle position to add fuel.
defining the fuel mass required as being equal to ((Cylinder air charge) (KAMREF)/((14.64) (LAMBSE))) - PCOMP + TFC_HR + TFC_TP, wherein the terms are defined as:
Cylinder air charge-Quantity of air in the cylinder
KAMREF - Correction for historic air to fuel ratio performance of the engine (adaptive keep alive memory)
LAMBSE - fuel equivalence ratio
PCOMP - Factor for adjusting fuel mass when vapour canister purge is taking place
TFC_HR - Factor for adjusting fuel mass when engine transients are taking place
TFC_TP - Factor for adjusting fuel mass when throttle induced transients are taking place.