EP0359791A1

EP0359791A1 - Process and system for adjusting the lambda value.

Info

Publication number: EP0359791A1
Application number: EP89902627A
Authority: EP
Inventors: Martin Klenk; Ernst Linder; Winfried Moser
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1988-03-16
Filing date: 1989-02-23
Publication date: 1990-03-28
Anticipated expiration: 2009-02-23
Also published as: EP0359791B1; US5014668A; DE3808696A1; KR900700740A; JPH02503460A; DE58900795D1; JP3048587B2; WO1989008777A1; KR0137222B1

Abstract

Procédé et système pour le réglage de la valeur lambda du mélange air-carburant à injecter dans un moteur à combustion interne, réglant le papillon des gaz de manière à obtenir un mélange pauvre à sous charge réduite et un mélange stoechiométrique (lambda = 1) sous charge élevée.Method and system for adjusting the lambda value of the air-fuel mixture to be injected into an internal combustion engine, adjusting the throttle valve so as to obtain a lean mixture at reduced load and a stoichiometric mixture (lambda = 1) high load.

Description

Method and system for setting the lambda value

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 a setting system are known from DE-C2-33 41 720. The system has an adjusting means which, depending on the respective value of an accelerator pedal position signal supplied to it, outputs an adjusting signal to a throttle valve actuator for adjusting the amount of air to be supplied to the internal combustion engine in such a way that below a position threshold value 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.

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 5. Advantageous further developments and refinements are the subject of the dependent claims.

The method and the setting system according to the invention differ from the prior art in that for values of the accelerator pedal position signal above the position threshold value, at least during steady-state operation, adjustment signals are output such 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 equipped with a catalytic converter, low pollutant values are thus achieved even in the upper load range. In the independent claims 1 and 5, 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 period 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 development, the adjusting means has a transition means which, when changing from an adjusting signal for the 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 which are common today and which often work with microcomputers, it is advantageous to implement all the functional means by means of 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 operation 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

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

Fig. 1 is a functional diagram of a setting system shown as a block diagram;

2a and 2b correlated via the accelerator pedal position

Diagrams 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 waveforms 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 adjustable by a throttle valve actuator 11 and an injection valve 13 in an intake port. There is a lambda probe 14 in the exhaust pipe arranged. The setting 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 adjustment means 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 actually required injection time 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. Based on 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, on the other hand the sol value switch 25 is switched upwards, so that a setpoint value from the Lambda setpoint ROM 15 is supplied to it depending on the throttle valve position and the speed is regulated to the read setpoint instead of. The read setpoint leads to a lambda value greater than 1, that is to say a lean control.

1, the throttle valve is not adjustable directly 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 issues. 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 also shown in dash-dot lines in the lower load range and is designated by SA ', while the part lying in the upper load range is drawn in solid lines and is designated by 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 sub-branches ML or ML 'and the throttle valve angle as sub-branches MA or MA' in FIGS. 2a and 2b, respectively. 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 case is indicated by 1.4 in FIG. 2a. If the value of the accelerator pedal position signal FPS is increased further, 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 initially operated in a stationary manner with an accelerator pedal position signal FPS of 50%. This value lies in the lower load range, so that values U _ML and U _SL on the respective lean branches ML and MA are used as a basis both for the lambda value and for the throttle valve angle. Now suddenly at a time tß, 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 within a period of time which corresponds to two computing cycles of the setting system implemented by a microcomputer. With each ignition process, or with a certain phase shift with respect 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 start of a computing cycle. This cycle has the number "1" in FIGS. 2 and 3. At the beginning of the second computing 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 is required. 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 into the lower load range. In the case of transient operation, special control conditions often apply, z. B. it has long been customary to make an acceleration enrichment that is curtailed. Depending on the internal combustion engine in each case, it can be disadvantageous to superimpose functions for the changeover from lean operation to stoichiometric operation or vice versa to the control functions for transient operation. The microprocessor therefore checks for four cycles from time t _B1 , namely for cycles "3", "4", "5" and "6", whether the fluctuation J. FPS of the accelerator pedal position signal FPS over the four cycles is a predetermined fluctuation range dFPSU falls below. If this has been established, 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 from the adjustment signal ROM 21, but the throttle valve angle α _S for stoichiometric operation is dependent 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 for reading lambda equal to 1 is read out and the control means 15 also controls Using this fixed setpoint.

A further advantageous embodiment of the functional links in an adjustment system is in the execution. 1, the transition means 23 is present. This program stage leads to the fact that when the comparator means 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 was not carried out with one step, i.e. from one computing cycle to the other becomes. 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 subdivided 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

2a and 2b, the values U _SL and U _SA for the accelerator pedal position FPS to which the values U _ML and U _{MA also} belong are shown on the stoichiometric branches shown in broken lines in the lower load range . 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 operation to lean operation. Rather, values from the stoichiometric branch are still read out from the adjustment signal ROM 21, specifically from its part SA 'in lower load range. Only when the fluctuation ΔFPS of the accelerator pedal position signal has not exceeded the specified fluctuation range ΔFPSU again over four cycles, does switching take place at time tv2 up to time t _V3 the transition from the throttle valve angle α _S read out for the stoichiometric branch SA1 to the throttle valve angle α _M valid for the same value of the accelerator pedal position signal FPS 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 into 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 now want to switch from lean operation to stoichiometric operation, the throttle valve must go very far back be set so that their adjustment has any effect in reducing the air supply. 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 reason mentioned above, 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 affects the amount of air that can be sucked in, the accelerator pedal will not increase to any value Fuel supply and therefore no increased torque would come. I agree 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 internal combustion engine that is not regulated but only controlled.

It is again pointed out that the basic idea of the invention is to switch from lean operation to stoichiometric operation and vice versa when changing from the lower to the upper load range. This change is to 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 the transition is advantageously not carried out in a leap, but 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, which 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. These time spans can, however, be selected differently and in each case between 0 and a larger number of cycles, if the operation is carried out with the aid of a microcomputer, depending on e.g. 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 tent spans 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 span despite the increase in the cycles.

Claims

Expectations

1. Method for setting the lambda value of the air / fuel mixture to be supplied to an internal combustion engine, in which method a throttle valve actuator is adjusted depending on the respective value of an accelerator pedal position signal for setting the amount of air to be supplied to the internal combustion engine in such a way that below a position threshold value of the accelerator pedal Position signals, d. H. A lean air / fuel mixture is obtained in the lower load range, which means that values for the accelerator pedal position signal (FPS) are above the position threshold value (FPSU), ie. H. in the upper load range, at least during steady-state operation, the throttle valve is adjusted such that a stoichiometric mixture (lambda = 1) is essentially obtained.

2. The method according to claim 1, characterized in that the transition from lean operation GO to stoichiometric operation (α _S ) and vice versa is made dependent on the fact that the fluctuation (ΔFPS) of the accelerator pedal position signal (FPS) within a predetermined Time span falls below a predetermined fluctuation range (ΔFPSU).

3. The method according to any one of claims 1 or 2, characterized gekennzei chnet that the position threshold (FPSU) of the accelerator pedal position signal (FPS) is selected depending on the speed, preferably so that the threshold is approximately where the current speed, a further opening of the throttle valve no longer results in a significant further increase in the amount of air sucked in.

4. The method according to any one of claims 1-3, characterized i chnet that the adjustment of the throttle valve when the position threshold value (FPSU) is exceeded with speed-dependent variables.

5. Setting system for setting the lambda value of the air / fuel mixture to be supplied to an internal combustion engine

- An adjusting means which, depending on the respective value of an accelerator pedal position signal supplied to it, sends an adjusting signal to a throttle valve actuator for adjusting the amount of air to be supplied to the internal combustion engine in such a way that below a position threshold value of the accelerator pedal position signal, i. H. a lean air / fuel mixture is obtained in the lower load range, characterized in that

- The adjustment means (20) for values of the accelerator pedal position signal (FPS) above the position threshold (FPSU), ie in the upper load range, at least during stationary operation, outputs adjustment signals (α _S ) of such size that essentially a stoichiometric mixture (lambda = 1) is obtained.

6. Adjustment system according to claim 5, characterized in that the adjustment means (20) has a comparator means (22) which the over- of adjustment signals for lean operation (α _M ) to those for stoichiometric operation [α _S ) and vice versa makes it dependent on the fluctuation (ΔFPS) of the accelerator position signal (FPS) falling below a predefined fluctuation range (ΔFPSU) within a predefined period of time.

7. Adjustment system according to one of claims 5 or 6, characterized in that the adjusting means (20) has a transition means (23) which, during the transition from an adjustment signal for lean operation (α _M ) to one for stoichiometric operation (α _S ) or vice versa causes a gradual transition within a predetermined period of time.

8. Adjustment system according to one of claims 5-7, characterized in that the adjusting means (20) has an adjusting signal memory (21) which is addressable via values of the accelerator pedal position signal (FPS) for lean and stoichiometric operation

Set of calibration values (α _M or α _S ) is saved.

9. Adjustment system according to one of claims 5-8, characterized in that during those periods in which the adjusting means (20) outputs adjusting signals for stoichiometric operation (α _S ), the lambda value regulates to 1.

10. Adjustment system according to claim 9, characterized in that the control means (15) additionally during those periods in which the adjustment means (20) outputs adjustment signals for lean operation (α _M ), the lambda value depending on values of operating variables ( α _M , n) regulates the lean value.