EP0286644B1 - Process for electronic determination of the quantity of fuel of an internal combustion engine - Google Patents

Abstract

Process for obtaining filtered output signals of an electronic control device in an internal combustion engine. The basic output signals obtained from various operating parameters are fed to filter systems, the filter characteristics of which can be varied as a function of the operating parameters of the internal combustion engine. The dynamic processes are taken into account by the fact that the filtering characteristics of the filters used can be varied as a function of the first differential functions of the signal from the position indicator of the throttle. Another possibility is to provide, for the choice of filtering characteristics, a multi-dimensional characteristic diagram which is a function of the operating parameters. It is also planned to form around the basic signals calculated an insensitivity region which the filtered signal should not go beyond. If it does, the filtering characteristic is modified in such a way that the filtered signal again returns to the insensitivity region.

Description

State of the art

As a result of increasing legal requirements for the maximum permissible pollutant content of the exhaust gas of internal combustion engines, but also with a view to improving the driving comfort of motor vehicles, electronic control devices for controlling the various machine parameters are being used with increasing frequency. It is known, for example, to calculate the fuel requirement electronically from the intake air quantity or air mass or the pressure in the intake pipe and the rotational speed, and then to control an injection device with a corresponding control signal. In full-load operation, however, the suction strokes of the machine sometimes cause such large pulsations in the air quantity mass signal and thus in the load signal, which may be in the form of an injection time or a quantity of fuel, that this results in disturbing fluctuations in the mixture composition which lead to increased pollutant emissions. When the internal combustion engine is idling and especially when the engine is running at idle speed, the phase shift between air quantity or speed detection, injection timing and delivered torque is also often noticeable. There are instabilities in the idle mode of the internal combustion engine and jerky phenomena in the push mode.

From DE-OS-24 55 482 an arrangement for obtaining signals is known, from which control signals for the fuel metering are generated in an electronic control unit. The signals of the engine speed and the sucked-in air mass which serve as input signals to the control device are fed to a smoothing device with a low-pass character in order to dampen any AC voltage components which may arise as a result of unintended influences. Since the characteristic of the smoothing device remains fixed, i.e. the changing conditions of the machine is not adapted, the arrangement does not always work quite satisfactorily. Above all, sudden load changes result in filter-related delays in fuel metering.

US-A-4. 436 072 discloses a so-called gear-dependent smoothness control. For this purpose, the quotient speed to driving speed is formed and stipulated that only a certain speed variation (Ni - Ni -1) is permitted for each gear stage. The control intervention takes place in a corresponding fuel metering or ignition with the aim of preventing torque fluctuations which are disturbing for the driver in the form of jerking of the vehicle. The teaching of US Pat. No. 4,436,072 is limited to an evaluation of the speed signal.

FR-A-21 63 241 (corresponds to DE-A-22 43 037) is concerned with an acceleration enrichment based on a change signal of the intake air quantity. Depending on the size of the air volume, a different RC element is activated with the result of an acceleration enrichment dependent on the air flow rate.

A further acceleration enrichment is shown in EP-A-106 366. There, depending on the size of a change in the throttle valve and, inter alia, the water temperature, an additional amount of fuel is determined, which is then metered in the sense of an acceleration enrichment.

Finally, EP-A-54 112 shows an "electronically controlled fuel metering system for an internal combustion engine" which includes devices for damping bucking. For this purpose, various mean values are formed in advance on the basis of a current basic metering signal and the desired metering signal is then determined as a function of the operating parameters. For example, depending on the speed-load range, averaging or progressive approximation to the current load value can occur.

It has now been shown that the known systems are unable to deliver an optimal result. It is therefore the object of the invention to provide a method which fulfills the requirements of a modern internal combustion engine control as comprehensively as possible.

The object of the invention is to provide a method with which this disruptive effect of filter devices can be reduced, if not completely eliminated. This problem is solved by the method with the features of the main claim.

Advantages of the invention

The method with the features of the main claim has the advantage over the known prior art that a filter with variable characteristics is used. In addition, it is not the input signals of the control device that are filtered, but rather the output signals calculated from these. Another advantage can be seen in the fact that in stationary or quasi-stationary operation of the internal combustion engine, the filter characteristic is taken from an at least two-dimensional map, as a result of which the filter effect can be matched to the operating range of the engine.

Further advantages of the invention result from the measures specified in the subclaims and from the description below.

drawing

1 shows the system representation of an electronic control unit with input and output signals, FIG. 2 shows the dependency of the filter characteristic on the first derivative da _oK / dt of the throttle valve position sensor _signal , FIG. 3 shows a two-dimensional map, divided into areas with different filter characteristics, 4 shows a block diagram of a device with the properties according to FIG. 2, FIG. 5 shows an example of an insensitivity range around an output signal, FIG. 6 shows a flow diagram for determining the filter characteristic from a characteristic diagram and FIG. 7 shows a flow diagram for determining the filter characteristic from da _ok / dt .

Description of the embodiments

In FIG. 1, 10 denotes an electronic control device to which a series of input variables are fed. With 11 is the signal of a throttle valve position sensor, with 12 the signal of an air mass sensor (in the following air mass and air quantity are used interchangeably, since it is known to the person skilled in the art to calculate the air mass from the air quantity), which is a hot wire air mass sensor, a sensor working according to the damper principle or can be a pressure sensor. A speed signal n is supplied via input 13, and 14 is used to denote further signals, such as, for example, engine temperature, fuel temperature, knock signal and lambda sensor signal. A signal _VFZ proportional to the speed of the vehicle reaches the control unit via 15.

In control unit 10, a multiplicity of output signals are calculated and generated from the input signals. 16 denotes an output for control signals from fuel injection valves, 17 denotes an output for ignition pulses, and 18 denotes the outputs for further signals.

In the diagram according to FIG. 2, the time derivative of the throttle valve position sensor signal da _{Dr / dt is} plotted on the abscissa and the filter characteristic is plotted on the ordinate. Around the zero point 20 there is an insensitivity region 21, to which a filter characteristic 22 is assigned. This range is followed by a variable filter characteristic 23 for positive values of da _OK / dt, and a constant filter characteristic 24 for negative values of a _OK / dt. The following results from FIG. 2 for the operation of the internal combustion engine:

In the event of slight fluctuations in the throttle valve position, such as occur, for example, in full load operation, the throttle valve position transmitter signal remains within the insensitivity range 21. The fuel metering signal is filtered by a strongly damping filter. In most cases, the fuel metering signal corresponds to an injection time, which is then also filtered accordingly. The disruptive suction stroke effects are eliminated by the filtering. If the throttle valve suddenly opens (positive since _ok / dt), damping of the fuel _{metering signal} is no longer desirable, since this would inevitably lead to damping of the acceleration. In this case, therefore, a filter characteristic 23 which is dependent on da _oK / dt is selected. FIG. 2 shows at 23 a piece-wise linear dependency of the filter characteristic on da _DK / dt, however any dependency can be realized here. Optimal solutions have to be determined experimentally from case to case. For sudden closing of the throttle valve, corresponding to a negative value of da _oK / dt, a filter characteristic 24 becomes smaller in its value than the value at 22 and greater than that selected at 23. The characteristics described at the beginning can be compensated for by such a characteristic. The double arrows marked with 25 indicate that the filter characteristics can also depend on operating parameters of the internal combustion engine, such as the engine temperature.

• Je nach Betreibszustand wird aus dem Kennfeld die für diesen Zustand günstigste Filtereinwirkung ermittelt, mit der das Lastsignal, das die Grundeinspritzzeit darstellt, gefiltert wird.

FIG. 3 shows an implementation in the event that there is no - a comparative example throttle position transmitter. The engine speed n is plotted on the abscissa, and a load signal (such as, for example, basic injection duration, pressure in the intake manifold, intake air mass flow in relation to speed, fuel quantity) is plotted on the ordinate. Other parameters are conceivable. If you divide each of the axes into five areas, a sufficiently fine network is inherited for the selection of operating mode-dependent filter characteristics. 30 corresponds to full load, 32 to partial load and 31 to idling. The process then works as follows:

• Depending on the operating state, the most favorable filter effect for this state is determined from the characteristic diagram, with which the load signal, which represents the basic injection time, is filtered.

Another possibility for executing the method results from FIG. The time t is plotted on the abscissa, and a basic injection duration t _{L is} plotted on the ordinate to represent the amount of fuel to be injected. The solid line marked with 40 represents the time course of the basic injection signal t _L , the dashed lines 41 indicate a range of insensitivity around 40. At time 43, there is a sudden load change, which results in a strongly kinking curve 40. The course of the filtered signal corresponding to curve 40 is designated by 42. At time 43, this curve follows curve 40 with continuously increasing deviation due to the damping effect of the filter, and intersects upper curve 41, which characterizes the insensitivity range. Leaving the insensitivity range leads to the switching of the filter characteristic, whereupon a signal curve corresponding to that with 44 marked curve results. If curve 44 undercuts the limitation of the insensitivity range at point 45, the system switches back to a more damping filter, from which the course identified by 46 results.

FIG. 5 shows a block diagram of the method in which all three previously mentioned methods for adapting the filter characteristic to the operating state of the internal combustion engine are contained. 51 is a differentiating device, to which the signal from the throttle valve position sensor is fed. 51 is connected to a device 53, the output signal of which is connected to the switch 54.

• Im dynamischen Betrieb, bei dem das Signal da_DK/dt eine bestimmte Schwelle überschreitet, bewirkt die Einrichtung 52 eine Schalterstellung des Schalters 54 so, daß der Ausgang der Einrichtung 53 mit der Filtereinrichtung 55 verbunden wird. Die Charakteristik von 55 wird dann entsprechend dem Signal von 53 eingestellt. Wird die in 52 vorgebbare Schwelle nicht überschritten, verbindet der Schalter 54 das Kennfeld 50 mit der Filtereinrichtung 55. In diesem stationären oder quasistationären Betrieb wird im Filter 55 eine Charakteristik nach Maßgabe des Kennfeldes eingestellt. Dem Filter 55 wird ein Kraftstoffmengengrundsignal, im Fall des Ausführungsbeispieles eine Grundeinspritzzeit t_L zugeführt. Am Ausgang des Filters steht dann das gefilterte Signal zur Verfügung. Im Fensterkomparator 56 wird geprüft, ob das gefilterte Ausgangssignal innerhalb oder außerhalb des um das Grundsignal liegenden Unempfindlichkeitsbereiches liegt.

At the same time, the output of 51 is connected to a threshold stage 52, which influences the positions of the switch 54. The switch 54 connects either the output of the device 53 or the output of the characteristic map 50 to a first filter device 55. The signals speed, basic injection time, vehicle speed and idling indicator are fed to the characteristic map 50. The basic injection time is also simultaneously fed to the first filter device 55, a window comparator 56 and a second filter device 57. Depending on the output signals of the first filter device 55 and the second filter device 57, the window comparator controls the position of the switch 58 to which it is connected via the operative connection 59. The switch 58 connects either the output of 55 or the output of 57 to amplification devices (not identified in any more detail), which then emit the signals for actuating control devices. The arrangement according to FIG. 5 works as follows:

• In dynamic operation, in which the signal da _DK / dt exceeds a certain threshold, the device 52 effects a switch position of the switch 54 so that the output of the device 53 is connected to the filter device 55. The characteristic of 55 is then adjusted according to the signal of 53. If the threshold which can be predetermined in 52 is not exceeded, the switch 54 connects the characteristic diagram 50 to the filter device 55. In this stationary or quasi-stationary operation, a characteristic is set in the filter 55 in accordance with the characteristic diagram. A basic fuel quantity signal, in the case of the exemplary embodiment a basic injection time t _{L, is} fed to the filter 55. The filtered signal is then available at the output of the filter. It is checked in the window comparator 56 whether the filtered output signal lies within or outside the insensitivity range around the basic signal.

If it lies within the insensitivity range, the connection 59 causes the switch 58 to be in a position which connects the output of 55 with reinforcing means which are not identified in any more detail. If it is determined in 56 that the filtered signal leaves the dead band, the switch 58 is connected to the output of a filter 57. Such a case occurs with large load changes. Filter 57, as can be seen in FIG. 4, takes effect at the point in time belonging to point 43. In the steady state, the filtering takes place in accordance with the map 50, in the dynamic state in accordance with the blocks 51 and 53. However, the blocks 55, 56 and 57 are effective both in the dynamic and in the stationary case.

FIG. 6 shows a flow chart for determining the filter characteristic from certain parameters of the internal combustion engine. The speed parameter is entered in 60, the load parameter in 61, and the filter characteristic corresponding to this parameter is determined in 62. In addition to the parameters speed and load, other machine parameters are also conceivable as input variables. The flow diagram according to FIG. 7 is based on the arrangement according to FIG. 5. In block 70, the first time derivative a _ok / dt is formed from the throttle valve position _{transmitter signal} . In block 71, a query is made as to whether the value of the differential quotient is greater or less than zero. If the differential quotient is greater than zero, the program branches to block 72, if it is less than zero it branches to block 73. In decision block 72 it is checked whether the differential quotient is greater than a positive constant. If it is greater than a positive constant, a filter characteristic is selected in 74 depending on the size of the differential quotient. If it is smaller than the positive constant, a filter constant C2 is selected in 75 in such a way that it is larger than the filter constant C1. If the differential quotient was less than or equal to zero in decision block 71, a check is made in decision block 73 as to whether the differential quotient is less than a certain lower bound. If it is smaller than a certain lower bound, a filter characteristic greater than C1 is determined in 76 depending on the size of the differential quotient. In the differential quotient larger than the lower bound, a filter characteristic of size C2 is determined in 77. From blocks 74, 75, 76 and 77 the program reaches the same point and is continued in 78. A filtered injection time t _{LF is} determined in 78 as a function of the basic injection time t _L and the filter characteristic determined in the course of the method. In decision block 79 it is checked whether the injection time calculated in 78 falls downwards or upwards from the insensitivity zone around the basic injection time t _L. If the insensitivity range is left, a changed filter characteristic is determined in block 80 from the filter characteristic that was previously valid. This filter characteristic generally results in a filter with less attenuation. A new injection time t _{LF is} formed from this filter characteristic in 81. If the time t _LF did not fall out of the insensitivity zone, the last determined value of this injection time is retained in 82 and fed to the amplifier means. The program jumps to the end of this program section from blocks 81 and 82.

The implementation of the method described can be carried out either in an analog or digital manner. Both the block diagram according to FIG. 4 and the flow diagrams can be set up using analog circuit technology as well as a digital program. Which implementation option the expert working in the field uses depends on the means available to him. In the case of analog circuitry, analog filters must be used; in the case of microprocessor-controlled systems, digital filter algorithms must be provided. A more precise description of one or the other implementation is beyond the scope of this description and can be assumed to be generally known.

Claims (5)

1. Process for acquiring filtered output signals, which are dependent on the operating parameters of an internal combustion engine, in an electronic control device for controlling the quantity of fuel to be fed to an internal combustion engine, a basic mixing signal being generated in dependence on engine speed and load, said basic mixing signal being subjected to a filtering with controllable filtering characteristic, and the filter characteristic being dependent on one of the variables

load change as the signal of the first chronological derivation of a throttle valve transmitter signal a_oK, a damping which is greater in relation to relatively large positive changes being provided in the region of the zero point of the change signal da_oK/dt between a negative and positive threshold,

driving speed signal

duration of the idling mode

the filtered signal leaves an insensitivity region.

2. Process according to Claim 1, characterized in that, with change signals derived from the throttle valve position which are smaller than a threshold, a filter with constant damping is used.

3. Process according to Claim 1, characterized in that, with change signals derived from the throttle valve position, the filter effect is reduced with increasing positive load change signal.

4. Process according to Claim 3, characterized in that the filter effect is reduced linearly.

5. Process according to Claim 1, characterized in that, with a filter characteristic which is dependent on the driving speed, the smallest damping is provided at driving speed zero.

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