EP0372113B1 - Method of controlling the amount of fuel supplied to an internal-combustion engine - Google Patents

Description

The invention relates to a method for determining the amount of fuel to be supplied to an internal combustion engine during dynamic transitional operation, according to the preamble of claim 1.

Such a method is described in US 4,424,568. The measured value of the intake pressure is corrected by a computer factor during dynamic transition processes such as acceleration or deceleration. This computer factor takes into account that during the time required to calculate the quantity of fuel to be supplied, the intake pressure has changed compared to the measured value. The fuel quantities thus determined for the transitional operation of the internal combustion engine result in an improved transient behavior.

The object of the invention is to further improve the transition behavior by correcting the falsifying influence of other factors on the measured intake pressure.

The solution according to the invention is characterized in claim 1. Advantageous developments of the invention can be found in the subclaims.

The invention is based on the consideration that the influences of various ambient pressures and temperatures must first be compensated for an accurate correction of the measured intake pressure. If one assumes a certain throttle valve angle and a certain speed in stationary operation, different intake pressures result for different ambient pressures and temperatures.

The solution according to the invention therefore uses support maps in which, depending on the throttle valve angle and the speed a certain ambient pressure and a certain ambient temperature, the values for the suction pressure are stored. At least four such characteristic maps are used. Two of them apply to the same first ambient pressure, but for two different ambient temperatures. The other two apply to the same second ambient pressure and the two different ambient temperatures.

These support maps are determined experimentally and stored in the computer unit that executes the pressure corrector.

From the two characteristic diagrams for the same first ambient pressure, two base values for the pressure are now read out in accordance with the values for the degree of opening of the throttle valve and the speed that are currently determined for each working cycle of the internal combustion engine. These two base values apply to the ambient temperature for which the respective base map was determined. In order to obtain a pressure value for the prevailing ambient temperature, a linear approximation is carried out. It is assumed that the prevailing ambient temperature corresponds to an intake air temperature, which is recorded via a temperature sensor.

A support part ratio is calculated that relates the intake air temperature value to the values of the two ambient temperatures for which the two support maps apply. With this support part ratio, a support high value is then determined from the two support values for the pressure. In relation to the two support values, this high support value behaves like the intake air temperature value in relation to the two ambient temperatures.

The support high value therefore represents a temperature-compensated value for the intake pressure valid for the determined first ambient pressure.

The same procedure is carried out with the other two maps, which are valid for the same second ambient pressure and the two ambient temperatures. This then results in a support low value, which represents a temperature-compensated value for the intake pressure valid for the second ambient pressure.

Instead of the two support maps used for the two ambient pressures, more can also be used. In the case of temperature compensation, a support high value or support low value is calculated from the respective two support values, linear relationships being assumed. This is inevitably an approximation, which can be improved by using additional support maps and thus linearization in sections. The support part ratio is then advantageously calculated based on those two support maps, between whose ambient temperatures the intake air temperature lies and which come closest to the intake air temperature.

In a similar manner, additional support maps can also be used for further ambient pressures. Then the respective two base values for the calculation of the support high value or support low value are preferably taken from those support characteristic maps between whose ambient pressures the measured value of the suction pressure lies and which comes closest to it.

The value of the intake pressure measured in the stationary operation of the internal combustion engine is now somewhere between the high support value and the low support value. A partial ratio is calculated for this position, which relates the size of this measured intake pressure to the high support value and the low support value.

If the internal combustion engine is now accelerated or decelerated from stationary operation, the values for the degree of opening of the throttle valve and / or the speed change accordingly. With each work cycle is then with these new A new support high value and support low value are calculated from the four support maps. Since the measured values for the intake pressure are too imprecise in the present dynamic operation of the internal combustion engine, they are corrected with a compensated intake pressure valid for the new operating state, which is calculated from the new values for the support high and low support value and the partial ratio. This compensated suction pressure in dynamic operation, based on the new support high value and support low value, behaves like the measured suction pressure in stationary operation to the support high value and support low value valid there.

One concludes from static to dynamic operation by assuming that this partial ratio remains the same for the currently valid intake pressure in dynamic operation compared to stationary operation.

The measured intake pressure is now corrected to a dynamic intake pressure with the aid of the compensated intake pressure by adding the difference between the compensated intake pressure and the measured intake pressure divided by a time constant. This time constant takes into account the time delay between the measured intake pressure and the dynamic intake pressure actually present in the intake manifold.

Finally, a computer factor is added to the dynamic intake pressure value. The computing factor takes into account the computing time for performing the correction calculation. A corrected pressure value determined in this way is then the value which, together with the rotational speed, determines the quantity of fuel to be supplied in each case.

Figur 1

ein grob vereinfachtes Blockschaltbild einer Einrichtung zur Durchführung des Verfahrens,

Figur 2

vier Stützkennfelder, von denen die Korrekturrechnung ausgeht und

Figur 3

ein Druckzeitdiagramm zur Erläuterung der Zeitverzögerung der Druckwerte während eines dynamischen Betriebs.

The method is explained in more detail with reference to the figures. Show:

Figure 1

a roughly simplified block diagram of a device for performing the method,

Figure 2

four support maps from which the correction calculation is based and

Figure 3

a pressure timing diagram to explain the time delay of the pressure values during dynamic operation.

FIG. 1 shows a block diagram of a device which is used to supply the internal combustion engine with the required amount of fuel. 1 denotes a microcomputer to which the values for a speed n, an opening degree α of the throttle valve, an intake air temperature TAL and a measured intake pressure pm are supplied as input signals. The microcomputer 1 uses this to calculate the required fuel quantity for each work cycle of the internal combustion engine using various characteristic maps. It then issues a corresponding command to an injection system 2, which comprises all the components necessary for the process, such as a metering device, injection valves, etc.

In Figure 2, four support maps are indicated, which are stored in the microcomputer 1. These characteristic support maps form the basis for the calculation of a corrected intake pressure value pkorr during dynamic transitional operation based on a measured intake pressure value pm during stationary operation of the internal combustion engine.

The support maps each contain pressure values as a function of the opening degree α of the throttle valve and the speed n of the internal combustion engine. They have been determined experimentally and apply to various environmental conditions. The two support maps shown on the right apply to a high ambient pressure PUH of 970 mbar, one for a high ambient temperature TUH of + 50 ° C and the other for a low ambient temperature TUL of -20 ° C. Accordingly, the two support maps shown on the left apply to one low ambient pressure PUL of 1040 mbar, one again for the high ambient temperature TUH and the other for the low ambient temperature TUL.

The support maps are stored in the microcomputer 1 as memory areas, the values for α and n each representing the addresses for the memory cells with the associated pressure value.

A steady-state operating state of the internal combustion engine is now assumed with an opening degree α 0 of the throttle valve and a speed n0. With these values, a support value psa to psd for the pressure is read from each of the support maps. In order to illustrate the following calculation method, these four basic values are transferred to a straight line in FIG. 2, the values increasing from left to right.

A support part ratio λ s, which characterizes the size of the intake air temperature value TAL in relation to the high and low ambient temperature TUH and TUL, is determined according to the equation

und damit

$\text{psH = psa - λ s x (psa - psb).}$

The support part ratio λ s is used to calculate a temperature-compensated support high value psH from the two support values psa and psb valid for the high ambient pressure PUH. Accordingly, it is

and thus

$\text{psH = psa - λ sx (psa - psb).}$

In the same way, a support low value psL is calculated from the two support values psc and psd, valid for the low ambient pressure PUL

$\text{psL = psc - λ sx (psc - psd).}$

The calculated quantities for this support high value psh and support low value psL are also entered in FIG. 2 on the pressure number line. The measured intake pressure value pm is also shown. A partial ratio λ for this measured intake pressure pm with respect to the support high value psH and support low value psL then results in

All of these values calculated so far remain the same as long as the steady-state operating state (α0, n0) persists. It is now assumed that, starting from this stationary operating state, the internal combustion engine is accelerated from an opening degree α0 to an opening degree α 1 by opening the throttle valve.

During each work cycle, the above-described method is then carried out for the currently detected values of the degree of opening α and the speed n until a new support high value psH and support low value psL are determined.

und damit

$\text{pk = psH1 - λ x (psH1 - psL1).}$

A compensated intake pressure value pk then results with the partial ratio λ calculated during stationary operation. Is accordingly

and thus

$\text{pk = psH1 - λ x (psH1 - psL1).}$

τ ist dabei eine experimentell ermittelte Zeitkonstante, die die Totzeiten der Luftmassen im Ansaugtrakt berücksichtigt. Sie berücksichtigt also den Zeitverzug zwischen dem gemessenen Ansaugdruck pm und dem im Saugrohr wirklich vorhandenen dynamischen Ansaugdruck pdyn.This compensated intake pressure pk is now used to correct the values of the measured intake pressure pm during dynamic transitional operation. A dynamic intake pressure pdyn results from the relationship

τ is an experimentally determined time constant that takes into account the dead times of the air masses in the intake tract. It therefore takes into account the time delay between the measured intake pressure pm and the dynamic intake pressure pdyn actually present in the intake manifold.

The different curves of the measured intake pressure pm and the dynamic intake pressure pdyn actually present in the intake manifold during the dynamic transitional operation Opening the throttle valve from α 0 to α 1 is shown in FIG. 3 in a pressure-time diagram.

One concludes for the correction from static to dynamic operation by assuming that the partial ratio determined in static operation applies to this compensated suction pressure in dynamic operation.

Ein korrigierter Ansaugdruckwert pkorr berechnet sich dann aus

${\text{pkorr = pdyn}}_{\text{neu}}\text{+ RF.}$

Dieser korrigierte Ansaugdruckwert pkorr ist dann derjenige Wert, der zusammen mit dem Drehzahlwert n die bei jedem Arbeitstakt einzuspritzende Kraftstoffmenge bestimmt.This dynamic suction pressure pdyn must finally be corrected by a computer factor that takes into account the computing times of the microcomputer 1. This computer factor RF results from a pressure increase gradient multiplied by the delay time tv of the microcomputer 1. So

${\text{RF = (pdyn}}_{\text{New}}{\text{- pdyn}}_{\text{old}}\text{) x tv.}$

A corrected intake pressure value pkorr is then calculated

${\text{pkorr = pdyn}}_{\text{New}}\text{+ RF.}$

This corrected intake pressure value pkorr is then the value which, together with the speed value n, determines the fuel quantity to be injected with each work cycle.

The method described above is to be applied analogously for all dynamic transition processes, regardless of whether the internal combustion engine e.g. is accelerated or decelerated. In the second case, the pressure increase gradient corresponds to a pressure reduction gradient.

Claims (3)

1. Method for determining the quantity of fuel to be supplied to an internal combustion engine during a dynamic transitional mode, in which an intake pressure pm, a speed (n), an opening angle (α) of the throttle valve and an intake-air temperature (TAL) are measured for each cycle of the internal combustion engine,

   - starting from the intake-pressure value pm, a corrected intake-pressure value (pkorr) is determined which, together with the speed value (n), determines the quantity of fuel,

   characterised in that

   a) supporting characteristic maps are stored, each valid for one ambient pressure and one ambient temperature and containing supporting values for the pressure as a function of the speed (n) and the opening angle (α),

   b) for each cycle

   ba) a supporting division ratio is calculated which characterises the magnitude of the intake-air temperature value (TAL) in relation to the magnitudes of two ambient temperatures of two supporting characteristic maps valid for a first, identical ambient pressure, the supporting division ratio being calculated in relation to those two ambient temperatures, between which the intake-air temperature (TAL) lies, which come closest to it,

   bb) the currently determined values for the speed (n) and the opening angle (α) are each used to obtain a supporting value (psa to psd) from the two supporting characteristic maps for the first ambient pressure and two further supporting characteristic maps valid for a second ambient pressure and the two ambient temperatures, the first ambient pressure and the second ambient pressure used being those between which the measured intake pressure pm lies and which come closest to it,

   bc) a supporting high value (psH) is determined from the supporting division ratio and the two supporting values for the first ambient pressure,

   bd) a supporting low value (psL) is determined correspondingly from the two supporting values for the second ambient pressure,

   be) a division ratio is calculated which characterises the magnitude of the measured intake pressure pm in relation to the supporting high value (psH) and the supporting low value (psL),

   c) the steps mentioned under b) are repeated for each subsequent cycle,

   d) a compensated intake pressure pk is calculated from the division ratio and the respectively current supporting high value (psH) and supporting low value (psL), the division ratio used following a change in the throttle-valve position from a steady-state value (α0) to a value (α1) being that calculated in steady-state operation.

   e) using the compensated intake pressure pk, the respective currently measured intake pressure pm is corrected to give a dynamic intake pressure pdyn according to the relationship

   

   where τ is a time constant which takes into account the dead times of the air masses in the intake duct and

   f) the corrected intake pressure (pkorr) is obtained from the dynamic intake pressure pdyn plus a computer factor (RF) which takes into account a delay time (tv) due to the computing operations.
2. Method according to Claim 1, characterised in that four supporting characteristic maps are stored,

   - a first supporting value (pna) being obtained from a first characteristic map valid for a first, high ambient pressure (PUH) and a high ambient temperature (TUH),

   - a second supporting value (pnb) being obtained from a second characteristic map valid for the first, high ambient pressure (PUH) and a low ambient temperature (TUL),

   - a third supporting value (pnc) being obtained from a third characteristic map valid for a second, low ambient pressure (PUH) and the high ambient temperature (TUH),

   - a fourth supporting value (pnc) being obtained from a fourth characteristic map valid for the second, low ambient pressure (PUL) and the low ambient temperature (TUL).
3. Method according to Claim 1, characterised in that the computer factor (FR) is calculated from a pressure-rise gradient multiplied by a delay time (tv), i.e.
   
   ${\text{FR = (pdyn}}_{\text{new}}{\text{- pdyn}}_{\text{old}}\text{) x tv.}$

   

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