EP0359791B1 - Process and system for adjusting the lambda value - Google Patents

Abstract

Process and system for adjusting the lambda value of the air/fuel mixture to be supplied to an internal combustion engine, whereby the throttle valve is adjusted so that lean operation is obtained in the lower load region, whereas stoichiometric operation (lambda = 1) is obtained in the upper load region.

Description

The invention relates to a method and a system for setting the lambda value of the air / fuel mixture to be supplied to an internal combustion engine during the transition from the lower load range to the upper load range.

State of the art

Such a method and such an adjustment system are known from DE-A-33 41 720. The system has an adjusting means which, depending on the respective value of an accelerator pedal position signal fed to it, outputs an adjusting signal to a throttle valve actuator in order to adjust the amount of air to be supplied to the internal combustion engine in such a way that below a position threshold of the accelerator pedal position signal, the limit between marked lower and upper load range, a lean air / fuel mixture is obtained. The system works in such a way that the throttle valve is fully opened shortly before the threshold value is reached. Once agreement between the threshold value and the value of the accelerator pedal position signal has been reached, the throttle valve is reset by a predetermined value which depends on the speed and the accelerator pedal position can. The resetting takes place to such an extent that a rich mixture is obtained in the upper load range, even if the throttle valve is opened again when the value of the accelerator pedal position signal increases further than the position threshold.

Operation with a lambda value of less than 1 in the upper load range results in increased pollutant emissions.
According to JP-A-61 123 735, λ <1 should be controlled for small throttle valve angles and λ = 1 for larger ones.
The invention is based on the object of specifying a method and a system for setting the lambda value of the air / fuel mixture to be supplied to an internal combustion engine during the transition from the lower load range to the upper load range and vice versa, which method or which system lead to low pollutant emissions.

Advantages of the invention

The invention is given for the method by the features of claim 1 and for the system by the features of claim 4. Advantageous further developments and refinements are the subject of the dependent claims.

The method and the setting system according to the invention differ, inter alia, from the prior art in that for values of the accelerator pedal position signal above the position threshold value, at least during stationary operation, adjustment signals are output in such a size that an essentially stoichiometric mixture is obtained. Lambda values greater than 1 are thus obtained in the lower load range, ie below the position threshold value of the accelerator pedal position signal, while the value Lambda is set to 1 in the upper load range. In an internal combustion engine that is equipped with a catalytic converter, low pollutant values are thus achieved even in the upper load range.

In the independent claims 1 and 4, the restriction "at least during steady-state operation" is mentioned with regard to the setting of the lambda value of 1. The reason for this restriction is that it is possible in the upper load range, as well as in the lower load range, for the accelerator pedal to be kept unchanged over longer periods of time, while it is equally possible for the accelerator to be decelerated without the range being closed leave. The former is called stationary operation, the latter is called transient operation. The period of time within which several engine revolutions take place is generally regarded as the time span within which no change in the accelerator pedal position is to take place so that one speaks of stationary operation. In the case of unsteady operation, the setting to lambda equal to 1 is expediently left because of the normally required smooth running properties.

In order to achieve smooth running, according to an advantageous further development, the adjustment means has a transition means which, when changing from an adjustment signal for lean operation to one for stoichiometric operation or vice versa, brings about a gradual transition within a predetermined period of time. This eliminates torque jumps that could occur if a sudden change from lean operation to stoichiometric operation were carried out.

In view of the motor electronics that are common today, which often work with microcomputers, it is advantageous to implement all functional means by the functions of such a microcomputer. Then it is also advantageous to use an adjustment signal memory which is addressable via values of the accelerator pedal position signal for lean and for stoichiometric operation Set of calibration values is saved. However, if very fast-working microcomputers are used, the adjustment values can also be calculated from the respective value of the accelerator pedal position signal using a mathematical relationship.

In order to achieve particularly low pollutant values, it is advantageous to regulate the lambda value, especially during stoichiometric operation.

drawing

• Fig. 1 ein als Blockschaltbild dargestelltes Funktionsdiagramm eines Einstellsystems;
• Fig. 2a und 2b über die Fahrpedalstellung korrelierte Diagramme betreffend die Abhängigkeit des Lambda-Wertes von der Fahrpedalstellung bzw. des Drosselklappenwinkels von der Fahrpedalstellung; und
• Fig. 3a, b und c zeitkorrelierte Signalverläufe von Fahrpedalstellung, Lambda-Wert und Drosselklappenwinkel für den Übergang vom unteren Lastbereich in den oberen Lastbereich und umgekehrt.

An embodiment of the invention is shown in the drawing and is explained in more detail in the following description. Show it:

• 1 is a functional diagram of a setting system shown as a block diagram;
• 2a and 2b diagrams correlated via the accelerator pedal position relating to the dependence of the lambda value on the accelerator pedal position or the throttle valve angle on the accelerator pedal position; and
• 3a, b and c time-correlated signal profiles of accelerator pedal position, lambda value and throttle valve angle for the transition from the lower load range to the upper load range and vice versa.

The functional sequence of an adjustment system shown in FIG. 1 is used on an internal combustion engine 10, which has a throttle valve 12 and an injection valve 13 that can be adjusted by a throttle valve actuator 11 in an intake port. There is a lambda probe 14 in the exhaust pipe arranged. The adjustment system includes a control means 15, a lambda setpoint ROM 16, a pilot control ROM 17, a subtraction means 18, a multiplication means 19 and, as a function means that is particularly important for the invention, an adjustment means 20. The latter has an adjustment signal ROM 21, a comparator means 22 and a transition means 23. The comparator 22 actuates two switches, namely an adjustment signal switch 24 and a setpoint switch 25. These switches are also usually implemented by parts of a program.

It is initially assumed that the throttle valve 12 is adjusted directly by the accelerator pedal and the setpoint switch 25 is switched to the lower position in which it gives a setpoint for regulation to lambda equal to 1 on the subtraction means 18, to which the voltage from the lambda Probe 14 is supplied as a setpoint. The control means 15 then outputs a control factor to the multiplication means 19, which is multiplied there by a pilot control value for the injection time, as a result of which the injection time actually required is obtained, which is fed to the injection valve 13. The pilot control value is read out from the pilot control value ROM 17 depending on the position of the throttle valve and the speed n. Under these assumptions, there is a conventional setting system that controls lambda equal to 1.

If it is still assumed that the position of the throttle valve 12 depends directly on the position of the accelerator pedal, the setpoint switch 25, on the other hand, is switched upwards, so that a setpoint from the Lambda setpoint ROM 16 is supplied to it depending on the throttle valve position and the speed , finds regulation on the read setpoint instead of. The setpoint value read out leads to a lambda value greater than 1, that is to say to lean regulation.

1, the throttle valve is not directly adjustable by the accelerator pedal, contrary to the assumption mentioned above, but the accelerator pedal position signal FPS is fed to the adjusting means 20, which processes this signal and then an adjusting signal to the throttle valve Actuator 11 outputs. The operation of the adjusting means 20 will now be explained in more detail with reference to FIG. 2.

In Fig. 2a, the horizontal line, which indicates that the lambda value remains constant at 1 over the entire range of the accelerator pedal position FPS from 0% to 100%, is between 0% and a position threshold value FPSU 70%, i. H. in the lower load range, dash-dotted as SL 'and then drawn as SL in the upper load range. In order to obtain the lambda value 1 for each accelerator pedal position FPS, the throttle valve angle α recorded over the accelerator pedal position FPS must have a profile as given by the lower curve in FIG. 2b. This curve for stoichiometric operation is shown in dash-dot lines in the lower load area and designated with SA ', while the part lying in the upper load area is drawn solid and designated with SA.

However, it is the case that the method or setting system according to the invention does not serve to carry out a stoichiometric setting in the entire range, but rather serves to ensure lean operation in the lower load range and stoichiometric operation in the upper load range. The curves corresponding to the curves for stoichiometric operation described above for lean operation lie for the lambda value as partial branches ML or ML 'and the throttle valve angle as partial branches MA or MA' in FIGS. 2a and 2b, respectively, above. In lean operation, the throttle valve already reaches the full opening angle of 90 ° at the FPSU position threshold of 70%. The lambda value achieved in this way is indicated by 1.4 in FIG. 2a. If the value of the accelerator pedal position signal FPS is further increased, this leads to an increased fuel supply and thus a decreasing lambda value, which is shown in FIG. 2a by the dash-dotted straight line denoted by ML '. The corresponding dash-dotted horizontal line, which in Fig. 2b indicates that the throttle valve angle α remains unchanged at 90 ° during lean operation, is denoted by MA '. Those curve parts in FIGS. 2a and 2b which lie in the partial load range during lean operation are shown in solid lines and are designated by ML and MA, respectively.

It is now assumed that the internal combustion engine 10 is first operated stationary with an accelerator pedal position signal FPS of 50%. This value lies in the lower load range, so that α values U _ML or U _SL on the respective lean branches ML or MA are taken as a basis both for the lambda value and for the throttle valve angle. Now suddenly at a time t _B , which is also shown in FIG. 3, the accelerator pedal is adjusted so far that an accelerator pedal position signal of 80%, corresponding to a value in the upper load range, is reached. It is assumed that the accelerator pedal is adjusted in a time period which corresponds to two computing cycles of the setting system implemented by a microcomputer. With each ignition process, or with a certain phase shift compared to each ignition process, a new computing cycle begins, so that at a speed of 3000 rpm in an internal combustion engine with 4 cylinders, the time between two cycle starts is approximately 30 ms.

It is further assumed that the point in time t _B at which the acceleration process begins coincides with the beginning of a computing cycle. This cycle has the number "1" in FIGS. 2 and 3. At the beginning of the second calculation cycle, the accelerator pedal position signal FPS is still in the lower load range, as a result of which the values marked "2" in FIGS. 2a and 2b are set on the respective lean-back rest ML for the lambda value and MA the throttle valve angle. At the beginning of the third cycle, that is to say after two completed cycles, as assumed, the accelerator pedal position signal at a time t _{B1 has reached} the final value of 80%, which is in the upper load range. In the upper load range, stoichiometric operation should be carried out. Stoichiometric operation in the upper load range with an accelerator pedal position signal FPS of 80% corresponds to the values shown in FIGS. 2a and 2b with O _SL and O _SA on the full loads SL and SA for lambda and the throttle valve angle. This jump to the values for stoichiometric operation can actually be carried out with suitable internal combustion engines which have hardly any torque jump. In order to achieve smooth running, however, even with internal combustion engines that are critical with regard to smooth running properties, the method is advantageously carried out as follows.

After the comparator 22 has determined at the beginning of the third computing cycle that the accelerator pedal position signal FPS is in the upper load range, it is still unclear whether the position now measured is the end position. There could be unsteady operation, in which the accelerator pedal is further adjusted, namely to larger or smaller values within the upper load range or even back to the lower load range. In the case of transient operation, special control conditions often apply, e.g. B. it has long been customary to make an acceleration enrichment that is curtailed. Depending on the internal combustion engine present in each case, it can be disadvantageous to superimpose functions for changing from lean operation to stoichiometric operation or vice versa to the control functions for unsteady operation. The microprocessor therefore checks for four cycles from time t _B1 , namely for cycles "3", "4", "5" and "6", whether the fluctuation ΔFPS of the accelerator pedal position signal FPS over the four cycles is a predetermined fluctuation range ΔFPSU falls below. If this is ascertained, as in the present example, the comparator means 22, ie in the usual case a comparative program step, outputs a switching signal to the adjustment signal switch 24 and the setpoint switch 25 for switching from lean operation to stoichiometric operation. The throttle valve angle α _M for lean operation is then no longer read out from the adjustment signal ROM 21, but throttle valve angle α _S for stoichiometric operation depending on the accelerator pedal position FPS and the speed n. The reason for the speed dependency is explained below. In addition, the lambda setpoint ROM 16 no longer reads setpoints for lean control as a function of the throttle valve angle α _M for lean operation and the rotational speed, but instead a fixed setpoint is obtained for achieving lambda equal to 1 and the control means 15 also controls Using this fixed setpoint.

The transition means 23 is present in the embodiment of FIG. 1 as a further advantageous embodiment of the function links in an adjustment system. This program stage leads to the fact that when the comparator 22 finally switches over from lean operation to stoichiometric operation at a time t _B2 the jump from the throttle valve angle marked with O _ML on the dash-dotted lean rest ML ′ to the throttle valve angle marked with O _SL for the same accelerator pedal position signal FPS on the stoichiometric branch SL is not carried out with one step, i.e. from one computing cycle to the other. Rather, the procedure is such that a jump from a throttle valve angle of 90 ° to one of approximately 60 °, as in the exemplary embodiment, is divided into four partial jumps in the computing cycles "7" - "10", e.g. B. in jumps to 75, 65, 62 and finally 60 °.

In addition to the values U _ML and U _MA on the lean branches for the lambda value and the throttle valve angle in FIGS. 2a and 2b, values U _SL and U _SA for the accelerator pedal position FPS are shown on the stoichiometric branches shown in dash-dot lines in the lower load range , which also includes the values U _ML and U _MA . It is assumed that the accelerator pedal is suddenly withdrawn from the position assumed in the acceleration process in the upper load range at a later time t _V (FIG. 3) to decelerate again to the original value in the lower load range. The function of the setting system described above is then repeated in a corresponding manner. At the beginning of the second calculation cycle (it is again assumed that the accelerator pedal is adjusted in a little less than two cycles) it is now determined by the comparator means 22 that an accelerator pedal position signal FPS less than the position threshold value FPSU has been reached, i.e. a value in the lower load range. However, this condition alone is not sufficient to switch from stoichiometric to lean operation. Rather, values from the stoichiometric branch are still read from the adjustment signal ROM 21, namely by its part SA 'in lower load range. Only when the fluctuation .DELTA.FPS of the accelerator pedal position signal has not exceeded the predetermined fluctuation range .DELTA.FPSU again over four cycles, does switching take place at time t _V2 . In this case, too, the jump with the switchover is not carried out in one step, but within four steps until time t _V3 the transition from the throttle valve angle α _S read out for the stoichiometric branch SA 'to that for the same value of the accelerator pedal position signal FPS applicable throttle valve angle α _M for lean operation on the branch MA.

It was mentioned above that not only one set of values for the relationship between the accelerator pedal position and the throttle valve angle α _M for lean operation or the throttle valve angle α _S for stoichiometric operation are stored in the adjustment signal ROM 21, but that several sets for different ones Speeds n are present, so that the respectively responsible throttle valve angle is read out depending on the signal of the comparator means 22, the value of the accelerator pedal position signal FPS and the speed n. The reason is as follows. If an internal combustion engine is operated at high load but at low speed, e.g. B. when driving uphill of the vehicle in which the internal combustion engine is mounted, and then the accelerator pedal is moved from a lower load position to an upper load position, this has the result that although more fuel is supplied because of the usual full load enrichment, but no more air is sucked in is because the amount of air that can be sucked in above a certain throttle valve position is no longer determined by the throttle valve position but by the speed of the engine. If you want to switch from lean operation to stoichiometric operation, the throttle valve must be set back very far so that their adjustment results in a reduction in the air supply at all. In contrast, at high speed, e.g. B. when driving downhill and then accelerating into the upper load range, a slight reduction in the throttle valve angle will lead to a reduction in the amount of air that can be drawn in. This shows that the relationship between the accelerator pedal position and the throttle valve angle is speed-dependent.

It has already been mentioned above that the values for the throttle valve angle can also be calculated from the respective value of the accelerator pedal position instead of from a table stored in an adjustment signal memory. The speed can accordingly be taken into account in such a calculation.

For the above-mentioned reason, namely that at low speeds the intake air quantity is no longer influenced by the position of the throttle valve even from a relatively low throttle valve angle, it is advantageous to design the position threshold value FPSU as a function of the speed. The threshold can e.g. B. at about 1200 rpm at about 27 °, at 2000 rpm at about 40 °, at 3000 rpm at about 60 ° and at 4000 rpm at about 70 °. The values to be used in the specific case, however, strongly depend on the throttle valve cross section and the volume of the internal combustion engine. If the position threshold FPSU were not shifted towards smaller throttle valve angles with decreasing speed, this would mean that from the value from which a further opening of the throttle valve no longer has an effect on the amount of air that can be sucked in, the accelerator pedal is not increased Fuel supply and therefore no increased torque would come. Exactly Such an increase in the fuel supply and the torque occurs, however, if a switch is made from lean operation to stoichiometric operation at the aforementioned threshold value.

The control means 15 is present in the configuration system according to the invention. However, an adjusting means with the properties described above can also be used on an uncontrolled, but only controlled, internal combustion engine.

It is again pointed out that the basic idea is to switch from lean operation to stoichiometric operation and vice versa when changing from the lower to the upper load range. This change must be made at least during stationary operation, i.e. H. when, after a certain period of time after the change from the lower to the upper load range or vice versa, it is established that there is no further major change in the accelerator pedal. Preferably, however, the transition from one operating mode to the other is made dependent on the condition that steady-state operation has occurred, and advantageously the transition is not carried out in leaps and bounds, but rather according to a regulation function from stored table values or according to a mathematical function.

It is pointed out that the term accelerator pedal is generally understood to mean a device for setting the torque desired by an operator. In a motor vehicle for the disabled, this can e.g. B. a lever to be adjusted by hand. Furthermore, it is pointed out that the term throttle valve is generally used as an adjusting element for the intake air quantity understand is. In this sense, the throttle valve can be an auxiliary flap that is adjusted with a secondary intake channel independently of the actual throttle valve that is directly coupled to the accelerator pedal.

The respective duration of four computing cycles corresponding to four engine cycles was specified as the time periods for determining whether stationary operation is present and for making the transition from lean to stoichiometric operation or vice versa. However, these time periods can be selected differently and each between 0 and a larger number of cycles, if the operation is carried out with the aid of a microcomputer, depending, for. B. from the desired smooth running behavior of a given internal combustion engine. For internal combustion engines with special behavior, it can also be advantageous to design the time periods as a function of the speed, in particular to use an increasing number of cycles with increasing speed, although this can lead to a shortening of the time period despite the increase in the cycles.

Claims (8)

1. Method for adjusting the lambda value of an air-fuel mixture which is to be supplied to an internal combustion engine, in which method a throttle flap actuator is adjusted in dependence on the respective value of a accelerator pedal position signal for adjusting the air volume to be supplied to the internal combustion engine in such a manner that a lean air/fuel mixture is obtained below a position threshold value of the accelerator pedal position signal, that is to say in the lower load range,
characterized in that for values of the accelerator pedal position signal (FPS) above the position threshold value (FPSU), that is to say in the upper load range, the throttle flap is adjusted, at least in steady-state operation, in such a manner that essentially a stoichiometric mixture (lambda = 1) is obtained and in that the transition from lean operation (α_M) to stoichiometric operation (α_S) and conversely is made dependent on the fact that the fluctuation (ΔFPS) of the accelerator pedal position signal (FPS) drops below a predetermined fluctuation range (ΔFPSU) within a predetermined time interval.

2. Method according to Claim 1, characterized in that the position threshold value (FPSU) of the accelerator pedal position signal (FPS) is selected to be dependent on rotation speed, preferably in such a manner that the threshold value is approximately located at the point where a further opening of the throttle flap no longer results in any significant further increase in the air volume taken in at the rotational speed existing in each case.

3. Method according to one of Claims 1 - 2, characterized in that the throttle flap is adjusted with rotational-speed-dependent values when the position threshold value (FPSU) is exceeded.

4. Adjusting system for adjusting the lambda value of the air/fuel mixture to be supplied to an internal combustion engine, comprising

- an adjusting means which outputs an adjusting signal to a throttle flap actuator in dependence on the respective value of a accelerator pedal position signal supplied to it, for adjusting the volume of air to be supplied to the internal combustion engine in such a manner that a lean air/fuel mixture is obtained below a position threshold value of the accelerator pedal position signal, that is to say in the lower load range,
characterized in that

- the adjusting means (20) outputs, at least during steady-state operation, adjusting signals (αs) of such a value that essentially a stoichiometric mixture (lambda = 1) is obtained for values of the accelerator pedal position signal (FPS) above the position threshold value (FPSU), that is to say in the upper load range and in that the adjusting means (20) exhibits a comparator means (22) which makes the transition from adjusting signals for lean operation (αm) to those for stoichiometric operation (αs) and conversely dependent on the fact that the fluctuation (ΔFPS) of the accelerator pedal position signal (FPS) drops below a predetermined fluctuation range (ΔFPSU) within a predetermined time interval.

5. Adjusting system according to Claim 4, characterized in that the adjusting means (20) exhibits a transition means (23) which effects a gradual transition within a predetermined time interval during the transition from an adjusting signal for lean operation (αm) to one for stoichiometric operation (αs) or conversely.

6. Adjusting system according to one of Claims 4, 5 characterized in that the adjusting means (20) exhibits an adjusting signal memory (21) which in each case stores a set of adjusting values (αm and αs, respectively) addressably via values of the accelerator pedal position signal (FPS) for lean and stoichiometric operation.

7. Adjusting system according to one of Claims 4 - 6, characterized in that during the time intervals in which the adjusting means (20) outputs adjusting signals for stoichiometric operation (αs) the lambda value is controlled to 1.

8. Adjusting system according to Claim 7, characterized in that the control means (15) additionally controls the lambda value to a lean value which is predetermined in dependence on values of operational variables (α_M, n) during the time intervals in which the adjusting means (20) outputs adjusting signals for lean operation (α_M).time interval in spite of the increase in cycles.

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