EP0054112A2 - Control method and electronically controlled metering system for an internal-combustion motor - Google Patents

Abstract

An electronically controlled fuel metering system for an internal combustion engine is proposed, which includes devices for damping bucking. The signals generated are: ti (k) as the current load value, tiM as the current averaged load value, ti (k-1) + Δti / 2 as a special load value for use at transition to overrun mode, and tiM + ΔtiM / 2 for successive approximation of the Average value of current load values with slow acceleration processes and flat load decreases. A computer-controlled implementation is possible according to a specified flow chart for the formation and selection of these individual values, and a block diagram of an electronically controlled fuel metering system constructed with discrete components is also given.

Description

State of the art

The invention relates to an electronically controlled fuel metering system for an internal combustion engine according to the preamble of the main claim. It is known to avoid torque jumps and thus undesirable jerking of the internal combustion engine to monitor the individual metering signals and to limit changes in these metering signals. This takes place in the known system in that an upper and a lower limit value for the next following metering signal is formed on the basis of a certain metering signal and, if the changes are too great, these limit values come into effect.

It has now been shown that this known "anti-jerk" system does not always work satisfactorily, since the change limitation must be switched off in transitional operations such as acceleration and overrun and inaccuracies arise especially when these areas occur.

Advantages of the invention

With the electronically controlled fuel metering system according to the invention with the features of the main claim, an anti-jerk system is obtained which achieves good results with regard to driving behavior and exhaust gas composition even in critical operating conditions. In particular, it is advantageous to choose different limits for different operating states, so that individual requirements can be taken into account very precisely.

drawing

An embodiment of the invention is shown in the drawing and described and explained in more detail below. 1 shows a speed-load diagram with indication of a jerk-sensitive area, FIG. 2 shows various examples of the mode of operation of the system under different operating conditions, FIG. 3 shows a flow diagram in connection with a computer-controlled implementation of the invention, FIG. 4 shows a block diagram as an example of a hardware solution, and Fig. 5 shows a detail on the subject of Fig. h.

Description of the embodiment

The exemplary embodiment relates to an electrically controlled fuel metering system in an internal combustion engine with spark ignition, the fuel being metered in via pulse-controlled injection valves.

Jerking is a driving operation in which the vehicle is braked and accelerated again by cyclical torque fluctuations. The reason lies in the type of load recording. The load signal ti is proportional the air flow in the intake pipe and thus proportional to the output signal of the air flow meter and inversely proportional to the speed. When jerking, an approximately constant air volume signal can be assumed, while the speed fluctuates around an average value. With a constant output voltage of the air volume measuring device, a decrease in speed causes the mixture to enrich, while increasing speed leads to leaning.

If you are now in the design of a fuel metering system in a λ range in which the torque is proportional to the λ value, then increasing speed causes the mixture to become leaner and thereby also a, under certain circumstances, a very strong decrease in torque, which in turn leads to a increased speed drop leads. According to the mathematical relationship of the load signal ti ≈ Q / n, this decrease in speed produces an enrichment of the mixture and thus an increase in torque, which is equivalent to an acceleration. The consequence of this is again an increase in speed and the whole process starts again.

Coupled with an appropriately vibrating system (engine - clutch - gearbox - cardan shaft - rear axle - tires), this leads to "jerky driving". This process can be stimulated e.g. by a single too high load signal ti or by a bump or the like, which stimulates a rapid change in speed.

With regard to the aforementioned oscillatory system as such, there are different areas with different tendency to jerk in the load-speed characteristic diagram of an internal combustion engine.

Such a map is shown in FIG. 1 and different areas for different countermeasures are drawn in this map, as well as a particularly critical area in which bucking due to the design of Engine and vehicle is particularly critical.

You can dampen jerky phenomena by making the whole mixture richer. With regard to economical consumption and good exhaust gas, however, this method is not generally applicable. In the case of the embodiment, on the other hand, averaging of the individual metering signals is preferably carried out in the area prone to jerking, a special regulation being affected in transition areas.

2 shows various diagrams of the mode of operation of the exemplary embodiment in different operating states. 2a shows a quite restless load signal (ti) whose individual values are averaged in a compensating sense.

2b shows the signal behavior in a typical acceleration process, namely when the load signal rises sharply and exceeds certain change threshold values. The situation with a slow load increase is shown in FIG. C. Initially, the averaging is effective due to the fact that a certain change in the load signal has not yet been reached. Ultimately, this averaging would lead to an ever greater gap between actual and averaged values, so that an approximation of these two different values must be ensured.

Correspondingly, FIGS. 2d and e show the conditions in the event of a transition to overrun mode and in the case of slow load decrease.

It is essential that the individual driving conditions are recognized, evaluated accordingly and subsequently the correct conclusions are drawn in the sense of a jerk countermeasure.

With regard to increasingly common fuel metering systems with computer controls, FIG. 3 shows a flow chart for a computer-controlled solution of the fuel metering system according to the invention.

3, at the beginning 10 individual areas are initialized in a block. Counters reset memory contents deleted, etc. The following is then performed tsignalen formation of a difference of successive _Las in block 11, which in turn follows a double query in 12 and 13. FIG. The query in block 12 is used. _Be acceleration detection and if it is given, then the newest value is taken as the new load value (14), forwarded and processed accordingly.

The second query in FIG. 13 concerns the thrust detection. If there is a transition to overrun mode, then either this newest value is switched through or, with a view to a smooth transition, an adapted new value according to the formula

tineu = ti (k-1) + Δti / 2

chosen. This alternative option is characterized by solid and dashed lines.

In the present exemplary embodiment, the averaging takes place over the last maximum of eight load values. It takes place on the basis of the values stored in a shift register, with the shift register being loaded with the latest value in so-called push-through operation in stationary operation, while the oldest is lost. The push mode control serves a counter to determine the ranking of the individual memory values. In the flowchart according to FIG. 3, a query for the maximum counter reading is denoted by 16 and a subtraction point for the last load value during stationary operation is denoted by 17. The control of the shift register is characterized by a block 18, the latest load value occupying the shift register location Z1 after 19.

The respective load values are summed in block 20. The subsequent division for averaging takes place in block 21. Since the deviation of the latest value from the mean is also processed, a corresponding calculation is provided in block 22.

The next interrogation unit 23 is used for the area classification. Two interrogation units 24 and 25 follow, with which slow load decreases and slow load increases in the sense of FIGS. 2c and e are recorded. As long as the thresholds shown there have not yet been reached, the latest basic injection quantity value corresponds to the averaged load signal. Otherwise there is a progressive approximation to the respective load value according to the formula

tineu = tiM + ΔtiM / 2

to wear over block 26. This also applies in the event that a special area is recognized via the area detection stage 23 and the change in this special area exceeds a certain threshold value (27). If the new basic injection value is the averaged value, block 28, then the serial number Z is continuously increased by one until an end value N is reached (30) and then jumped back to the starting point A. If, on the other hand, a signal deviating from the mean value is generated as the new basic injection value, a new mean value formation and a new writing of values into the shift register take place in accordance with the specifications in a block 29.

With the aid of the program flow shown in FIG. 3 as a flow chart, various limit values for the basic injection signal are thus generated and queried, which come into play depending on the cases shown in FIG. 2. What is essential is the continuous averaging during stationary operation, the behavior in the respective transitional operations such as acceleration and thrust, whereby the driver's wishes come into play immediately in order to achieve the best possible acceleration, while a shallower drop is chosen to achieve a smooth transition in overrun operation can be. In addition, slow acceleration processes and load decreases are recognized and appropriate signal processing is carried out.

• - ti neu = ti (k) für Beschleunigungsfälle und gegebenenfalls für den Schubbetrieb.
• - ti neu = ti (k-1) + Δti/2 für einen weichen Übergang in den Schubbetrieb.
• - ti neu = tiM als gemittelten Wert im stationären Fahrbetrieb, und
• - ti neu = tiM + ΔtiM/2 zur sukzessiven Annäherung des Mittelwertsignals an das Lastsignal im Falle langsamer Beschleunigungsvorgänge und flacher Lastabschwächungen.

There are four different options for the new basic injection value:

• - ti new = ti (k) for acceleration cases and possibly for overrun.
• - ti new = ti (k-1) + Δti / 2 for a smooth transition to overrun.
• - ti new = tiM as averaged value in stationary driving, and
• - ti new = tiM + ΔtiM / 2 for successive approximation of the mean value signal to the load signal in the case of slow acceleration processes and flat load weakening.

An example of a hardware implementation is shown in FIG. 4. For the sake of a better overview, the individual blocks of FIG. 4 are provided with the reference numbers known from FIG. 3 if they match, although the blocks of the flowchart basically represent pure arithmetic operations. while those of Fig. 4 mark circuit arrangements for realizing the special function.

In order to complete the circuit arrangement according to FIG. 4 in the sense of a fuel metering system, there is also a timing element 35 for generating the quotient of air throughput and speed based on signals from a speed sensor 36 and an air quantity measuring device 37. There is also a selection logic 38 for a desired switching of the individual variables depending on the individual driving conditions, and finally the valve winding of an injection valve 39 is indicated. In the signal line to this injection valve there are usually correction stages for at least the temperature and the battery voltage.

The individual structure is as follows. The output of the timing element 35, at which the latest ti (k) value is present, is inevitably coupled to all those stages which process or pass on the current basic injection value or load value. These are the selection logic 38, the difference formation stage 11 for successive load signals, a memory stage 40 for the respective previous load signal, a counter 30, which supplies the control signal for an adder 20 and the divider stage 21, and also a subtraction stage 22 for forming the difference between the current one Load value and the current mean value as well as a threshold level 23 for range inquiry.

On the output side, the subtraction stage 11 is coupled to two comparators 12 and 13 for recognizing the acceleration and the transition to overrun mode, the output signals of which in turn can be switched to two control inputs 41 and 42 of the selection logic 38. Furthermore, these comparators 12 and 13 supply reset signals for the adder stage 20. This is because the averaging in the special example according to FIG. 4 is to be stopped in each of these transitional operating states and corresponding addition values are to be deleted. The same reset signal is also received by the shift register 18 and the counter 30. The respective counter reading of the counter 30 controls the adder 20, the progression of the contents of the shift register 18 and the divider 21. The output of this divider 21 is an average of the basic injection time tiM, which in turn is as Input variable for the subtraction stage 22, the division and addition stage 26 and for the selection logic 38 is used.

A further division and subtraction stage 15 supplies a ti (k-1) + ti / 2 signal for a further input of the selection logic 38. The difference between the current load value and the current mean value is provided by the subtraction stage 22, which in turn provides the output signal to the divisions - And addition level 26 and a sign recognition level 42 passes on.

This is followed by two threshold switches 24 and 25 for querying thresholds in connection with slow acceleration processes and flat load decreases. Another control input 45 of the selection logic 38 receives output signals from the threshold switches 24, 25 and 27, the output signals of which likewise reset the adder 20 and the counter 30. The control stage 29 ensures that, depending on input signals at its three inputs 47, 48, 49, the latest load value tineu is written into the memory 40 for the previous load value as the newest value. The input 47 is connected to the control input 45 of the selection logic 38, the input 48 to the control input 41 and finally the input 49 to the control input 42. The control device 29 can be implemented by means of a triple-OR gate for the individual input variables.

In the selection logic 38 it must now be ensured that, depending on the operating state, the individually calculated quantity is switched through to the output as a new basic injection quantity value. FIG. 5 shows the required link, FIG. 5a again showing the diagram of the selection logic 38 with the individual data and value inputs, while FIG. 5b shows a logic table according to which the individual switches shown in FIG. 5a are to be closed . The first line of the table according to FIG. 5b shows the case of acceleration, the second line shows the signal output during the transition to overrun mode and lines 3 and 4 indicate different cases of more or less stationary operation. After the third line, the curve profiles dashed in FIGS. 2c and 2e are followed for the output signal.

Regardless of the particular implementation, whether computer-controlled or with a circuit arrangement constructed with discrete components, the fuel metering system described above is characterized in that it has very good driving behavior enabled in all operating conditions in all possible operating areas.

Claims (6)

1. Electronically controlled fuel metering system for an internal combustion engine with a metering signal generating stage for forming a basic metering signal, characterized in that preferably all four of the signals ti (k) (current load signal), tiM (average load signal), ti (k-1) + ati / 2 (special signal, preferably for a smooth transition to coasting operation) and tiM + ΔtiM / 2 (approximation signal to the current value) are formed, and at least the signals ti (k) and tiM are based on the additional metering signal generation, depending on the operating state. 2. Fuel metering system according to claim 1, characterized in that the averaging preferably starts again at the end of a transitional operation (acceleration and / or thrust). 3. Fuel metering system according to claim 1, characterized in that in the case of slow, continuous changes in the load signal, a progressive approximation to the current value takes place from a predetermined difference between the current load signal and the mean value. 4. Fuel metering system according to claim 3, characterized in that the progressive approximation takes place according to the formula tiM + ΔtiM / 2. 5. Device according to at least one of claims 1 to 4, characterized in that, depending on the speed-load range, averaging or a progressive approximation to the current load value (see Fig. 1). 6. Fuel metering system according to at least one of claims 1 to 5, characterized in that the averaging is preferably carried out over at most the last eight signal values.

Images