阅读说明：本技术 操作内燃机的方法 (Method for operating an internal combustion engine ) 是由 B·珀蒂让 F·玛松 J·阿斯佩尔迈尔 于 2019-07-25 设计创作，主要内容包括：本发明公开了一种用于操作内燃机的方法,所述内燃机包括用于将燃料注入燃烧室中的可控喷油器,所述喷油器与储油器连通并且通过所述储油器而被供以燃料,所述方法包括以下步骤：基于第一压力测量确定所述储油器中的压力的第一压力值；基于在所述第一压力测量之后进行的第二压力测量确定所述储油器中的压力的第一压力值；以及根据所述第一压力值和所述第二压力值确定喷油器打开持续时间。(The present invention discloses a method for operating an internal combustion engine comprising a controllable injector for injecting fuel into a combustion chamber, said injector communicating with a reservoir and being supplied with fuel through said reservoir, said method comprising the steps of: determining a first pressure value of the pressure in the oil reservoir based on the first pressure measurement; determining a first pressure value of the pressure in the oil reservoir based on a second pressure measurement taken after the first pressure measurement; and determining the opening duration of the fuel injector according to the first pressure value and the second pressure value.)

1. A method for operating an internal combustion engine including a controllable fuel injector for injecting fuel into a combustion chamber, the fuel injector being in communication with a reservoir through which the fuel injector is fueled, the method comprising the steps of:

-determining a first pressure value of the pressure in the oil reservoir based on the first pressure measurement;

-determining a first pressure value of the pressure in the oil reservoir based on a second pressure measurement taken after the first pressure measurement; and

-determining a duration of opening of the injector as a function of said first and second pressure values.

2. A method according to claim 1, in which the first pressure measurement is taken before the injector is opened and/or the second pressure measurement is taken after the injector has been opened.

3. Method according to claim 1 or 2, wherein the first pressure value and the second pressure value are determined by different evaluation methods, wherein preferably the second evaluation method for determining the second pressure value is run faster than the first evaluation method for determining the first pressure value.

4. The method of claim 3, wherein at least one of the following method steps is performed for determining the first pressure value, while the at least one step is not required for determining the second pressure value:

-correcting the pressure measurement value with respect to changes in the supply voltage and/or temperature;

-down-sampling;

-digital filtering.

5. A method according to any one of the foregoing claims, in which a first injector opening duration is first determined on the basis of said first pressure value, and said first injector opening duration is corrected on the basis of said second pressure value when said second pressure value is available.

6. The method according to claim 5, wherein the correction of the first injector opening duration is dependent on a desired injection quantity and/or pressure in the oil reservoir and/or is effected by means of a characteristic map which is dependent on the desired injection quantity and/or pressure in the oil reservoir.

7. Method according to claim 6, wherein, for correcting the first injector opening duration, a correction value is read from a characteristic map, wherein the correction value is read based on the first pressure value before determining the second pressure value, and wherein the correction value is adjusted, in particular scaled, based on the second pressure value after reading the correction value.

8. Method according to any one of the preceding claims, wherein the injector opening duration, and in particular the first injector opening duration, is determined and corrected as a function of a pressure difference between the second pressure value and a third pressure value, preferably determined by applying the same evaluation method.

9. The method of claim 8, wherein the third pressure value is determined based on the first pressure measurement and/or based on a third pressure measurement, wherein the third pressure measurement is preferably performed immediately after and/or before the first pressure measurement, the determination of the first pressure value preferably being performed immediately after the determination of the third pressure value.

10. Method according to any one of the preceding claims, wherein the second pressure measurement and/or the determination of the second pressure value is/are carried out at a predetermined fixedly determined time relative to the time when the injector is open, wherein this time is predetermined fixedly determined, in particular independently of a term injection quantity, or wherein the second pressure measurement and/or the determination of the second pressure value is carried out at a time which is variable relative to the time when the injector is open, in particular in dependence on an expected injection quantity for a respective opening operation of the injector.

11. A method according to any one of the foregoing claims, in which the combustion engine comprises a common reservoir for a plurality of injectors assigned to different combustion chambers, and/or in which the combustion engine comprises a plurality of injectors, the injector opening duration being determined individually for each injector.

12. The method according to any of the preceding claims, wherein the internal combustion engine comprises a pump for generating a variable target pressure in the oil reservoir, wherein the target pressure and a desired injection quantity are specified based on engine operating parameters and/or user input, wherein the injector on-duration is determined according to the desired injection quantity.

13. An engine control software comprising commands for performing the method according to any one of claims 1-12.

14. An internal combustion engine comprising a controllable injector for injecting fuel into a combustion chamber and further comprising a reservoir, the injector communicating with the reservoir and being supplied with fuel through the reservoir, the internal combustion engine further comprising a pressure sensor for measuring the pressure in the reservoir, the internal combustion engine comprising an engine control unit programmed to perform the steps of:

-determining a first pressure value of the pressure in the oil reservoir based on the first pressure measurement;

-determining a first pressure value of the pressure in the oil reservoir based on a second pressure measurement taken after the first pressure measurement; and

-determining a duration of opening of the injector as a function of said first and second pressure values.

15. An internal combustion engine according to claim 14, wherein the engine control unit is programmed to perform the method according to any one of claims 1-12.

Technical Field

The present invention relates to a method of operating an internal combustion engine comprising a controllable fuel injector for injecting fuel into a combustion chamber, the fuel injector being in communication with a fuel reservoir and being supplied with fuel through the fuel reservoir, wherein the fuel reservoir may in particular be an accumulator.

Background

In the case of a method in which the injection quantity is dependent on the pressure in the reservoir and the injector opening duration, pressure changes in the reservoir can thus lead to an undesirable deviation of the actual injection quantity from the target injection quantity if the injector opening duration remains unchanged.

Thus, DE 10332213 a1 proposes continuously monitoring the pressure in the oil reservoir during the injection and performing an integration by means of a varying injection rate based on the pressure estimate. Then, once the integrated fuel injection amount reaches the target fuel injection amount, the injector is closed. Although the procedure proposed in DE 10332213 a1 theoretically achieves a particularly precise control of the injected fuel quantity, it fails in reality because the conventional engine control units cannot perform the algorithmic operation proposed in DE 10332213 a1 at the required speed, due to the real-time requirements to be met by the system.

Disclosure of Invention

It is therefore an object of the present invention to provide a method for controlling a fuel injector that takes into account the real-time requirements to be met by such a system.

This object is achieved by the method briefly described below. The preferred embodiments of the present invention are merely exemplary.

The invention comprises a method for operating an internal combustion engine comprising a controllable injector for injecting fuel into a combustion chamber, which injector is in communication with a reservoir and is supplied with fuel through the reservoir, the method comprising the steps of:

-determining a first pressure value of the pressure in the oil reservoir based on the first pressure measurement;

-determining a second pressure value of the pressure in the oil reservoir based on a second pressure measurement performed after the first pressure measurement; and

-determining a duration of opening of the injector as a function of the first pressure value and the second pressure value.

Due to this action the first pressure measurement is performed relatively early. Thereby, the first pressure value may also be obtained relatively early, and the first pressure value may be used for time consuming subsequent steps of the method and/or may be determined with high accuracy. However, by subsequently determining the second pressure value, a high accuracy will be achieved with respect to the change of pressure in the oil reservoir that occurs after the first pressure measurement.

The injector opening duration may be determined in several substeps, which may not necessarily need to be performed only after the second pressure value is determined. Instead, at least one substep for determining the injector on-duration is carried out based on the first pressure value before the second pressure value is available.

According to a possible embodiment of the invention, the method further comprises the steps of:

-specifying a desired injection quantity.

The injector opening duration is determined from the first and second pressure values and the desired injection quantity. In particular, the injector opening duration is determined as a function of the first and second pressure values, so that a desired injection quantity is achieved.

According to a possible embodiment of the invention, the method further comprises the steps of:

-controlling the injector based on a previously determined injector opening duration.

In particular, the previously determined injector on-duration may be used to specify the time at which the injector is closed.

According to a possible embodiment of the invention, the first pressure measurement is performed before the injector is opened. This provides sufficient calculation time for an accurate evaluation of the pressure sensor signal for determining the first pressure value.

According to a possible embodiment of the invention, the second pressure measurement is performed after the fuel injector has been opened. This means that the current pressure value determined during the injector opening duration, and thus during the injection process, will be available in the form of the second pressure value. It follows that if the pressure in the oil reservoir changes between the first pressure measurement and the start of the injection process or during the injection process, this pressure change will also be taken into account.

The first pressure value and the second pressure value are generated by signal evaluation based on the respective sensor signals.

According to a possible embodiment of the invention, the first pressure value and the second pressure value are determined by different evaluation methods. In particular, this allows different requirements to be taken into account for the task runtime.

Preferably, the second evaluation method for determining the second pressure value is run faster than the first evaluation method for determining the first pressure value, i.e. the second evaluation method has a shorter task run time and will therefore run faster on the motor control unit.

According to a possible embodiment of the invention, at least one of the following method steps is performed to determine the first pressure value, whereas the determination of the second pressure value does not require the at least one step:

-correcting the pressure measurement value with respect to changes in the supply voltage and/or temperature;

-down-sampling;

-digital filtering.

Alternatively or additionally, a second pressure value may be determined on the motor control unit with a higher priority than the determination of the first pressure value.

According to a possible embodiment of the invention, the duration of opening of the first injector is first determined according to the first pressure value, and when the second pressure value is available, the duration of opening of the first injector is corrected according to the second pressure value.

This means that the determination of the second pressure value may even be made later, since the injector opening duration does not have to be determined when the second pressure value is available, but will be sufficient to correct the first injector opening duration that has been determined temporarily.

Therefore, preferably, the first injector opening duration is determined before determining the second pressure value and/or before performing the second pressure measurement.

According to a possible embodiment of the invention, the correction of the injector opening duration depends on the desired injection quantity and/or the pressure in the reservoir. In particular, the correction of the opening duration of the first injector may incorporate a desired injection quantity and/or pressure in addition to the second pressure value and/or the pressure difference between the second pressure value and the third pressure value.

According to a possible embodiment of the invention, the determination of the correction value is made in a plurality of steps, at least one step being already performed before the second pressure value and/or the pressure difference between the second pressure value and the third pressure value is available.

According to a possible embodiment of the invention, the correction of the opening duration of the first injector is carried out by means of a characteristic map which depends on the desired injection quantity and/or the pressure in the reservoir. The characteristic map can be stored in the engine control unit, for example, in tabular form and/or in formulaic relationship.

Preferably, the correction value is read from a map for correcting the opening duration of the first injector based on the first pressure value. This is advantageous to some extent, since the correction value can already be determined as soon as the first pressure value is available, and thus the correction value can be determined at a relatively early moment.

In particular, a correction value may be read based on the first pressure value before the second pressure value has been determined.

Preferably, the correction value may be adjusted based on the second pressure value after the correction value has been read. This adjustment is achieved in particular by scaling the correction value with the second pressure value and/or the pressure difference between the second pressure value and the third pressure value.

The correction value stored in the characteristic map can, for example, correspond to the pressure difference predetermined in a fixed manner and can be adjusted if the pressure difference which is present between the second pressure value and the third pressure value and which is actually determined by the second pressure value deviates from the pressure difference predetermined in a fixed manner.

However, according to an alternative embodiment of the invention, the second pressure value and/or the pressure difference before the second pressure value and the third pressure value is used to correct the first pressure value.

In this case, the injector opening duration is preferably determined based on the corrected pressure value.

According to a possible embodiment of the invention, the injector opening duration is determined as a function of the pressure difference between the second pressure value and the third pressure value. This pressure difference allows taking into account the change in pressure occurring in the reservoir between the first pressure measurement and the second pressure measurement.

In particular, the correction of the opening duration of the first injector as described above may depend on the pressure difference between the second pressure value and the third pressure value.

According to a possible embodiment of the invention, the first pressure value itself may be used as the third pressure value. However, this would be disadvantageous if different evaluation methods were used to determine the first and second pressure values. Thus, the third pressure value is preferably determined separately from the first pressure value.

According to a possible embodiment of the invention, the second pressure value and the third pressure value are determined by applying the same evaluation method. Thus, any systematic error that occurs in determining the pressure values will likewise be a part of both pressure values. This will result in a compensation or a small overcompensation or a small undercompensation when a pressure difference is formed.

Preferably, the third pressure value is determined using an evaluation method having a shorter task run time than the evaluation method used for determining the first pressure value.

Preferably, the pressure difference is related to a change in pressure in the reservoir between the first pressure measurement and the second pressure measurement. For this purpose, the third pressure value is preferably determined on the basis of the first pressure measurement or a third pressure measurement, which is carried out immediately after the first pressure measurement in time.

According to a first variant, the third pressure value may be determined based on the first pressure measurement. If the first pressure measurement is used to determine the third pressure value, an optimal time correspondence between the first pressure value and the third pressure value will be obtained. However, in this case, the additional calculation time required for the evaluation requires that the first pressure measurement has to be performed earlier, and this is disadvantageous with respect to accuracy.

According to a second variant, the third pressure value may thus be determined based on a third pressure measurement (i.e. a pressure measurement performed in addition to the first and second pressure measurements).

The third pressure measurement may be performed after the first pressure measurement. However, in this case, the additional calculation time required for the evaluation requires that the first pressure measurement has to be performed earlier, and this will be disadvantageous with respect to accuracy.

Thus, the third pressure value is preferably determined based on a third pressure measurement, where the third pressure measurement is performed before the first pressure measurement.

Preferably, the first force value is determined immediately after the third force value is determined. As a result, the time offset between the first pressure measurement and the third pressure measurement remains relatively small.

According to a possible first variant of the invention, the second pressure measurement and/or the determination of the second pressure measurement is/are carried out at a fixedly predetermined time relative to the opening time of the injector.

In particular, the time can be fixedly predefined independently of the desired injection quantity, and therefore may not differ between different injection events. This has the advantage of being particularly simple and reliable to implement.

In this case, the instant will preferably be determined such that: with the shortest possible opening duration, the final value of the injector opening duration will just be available for closing the injector at the appropriate time.

According to a second variant of the invention, the second pressure measurement and/or the determination of the second pressure value is carried out at a time variable with respect to the opening time of the injector. This means that in many cases the second pressure measurement can be made even later.

In particular, the time can be determined according to the desired injection quantity for the respective opening operation of the injector.

It follows that, if, for example, the quantity of injected fuel provided for the second injection event is greater than the quantity of injected fuel provided for the first injection event (which would lead to a longer duration of injection of the injector), the second pressure measurement and/or the determination of the second pressure value would be carried out at a later time than in the case of the first injection event with respect to the opening time of the injector.

The method according to the invention is preferably used for an internal combustion engine which comprises a common oil reservoir for a plurality of injectors which are assigned to different combustion chambers, in particular in an internal combustion engine having a common rail injection system.

According to a possible embodiment of the invention, the method is used for an internal combustion engine comprising a plurality of injectors, the injector opening duration being determined individually for each injector.

According to a possible embodiment of the invention, the internal combustion engine comprises a pump for generating a variable target pressure in the oil reservoir, the target pressure and the desired injection quantity being specified on the basis of engine operating parameters and/or user inputs.

In this case, in particular, a change in the target pressure and/or the operation of the pump may cause a significant change in the pressure in the reservoir, which, however, is difficult to coordinate with the operation of the fuel injector. The method according to the invention, however, allows a reliable and accurate control of the injection quantity.

Preferably, the injector opening duration is determined according to the desired injection quantity.

In particular, the first injector opening duration may be determined based on the desired injection quantity and the first pressure value. The correction by the second pressure value will then increase the accuracy of the actually injected fuel quantity.

In addition to the method according to the invention, the invention also comprises engine control software comprising instructions for carrying out a method of the type described hereinbefore. In particular, the engine control software is programmed to automatically perform the method according to the invention when run on the engine control unit.

The present invention also includes an internal combustion engine comprising: a controllable fuel injector for injecting fuel into the combustion chamber; and a reservoir with which an injector communicates and through which the injector is supplied with fuel; and the engine further comprises a pressure sensor for measuring the pressure in the oil reservoir. The internal combustion engine includes an engine control unit programmed to perform the steps of:

-determining a first pressure value of the pressure in the oil reservoir based on the first pressure measurement;

-determining a second pressure value of the pressure in the oil reservoir based on a second pressure measurement performed after the first pressure measurement; and

-determining a duration of opening of the injector as a function of the first pressure value and the second pressure value.

According to a preferred embodiment, the engine control unit is programmed to perform the following steps:

-determining a first pressure value of the pressure in the reservoir based on the first pressure measurement, and determining a first injector opening duration as a function of the first pressure value; and

-determining a second pressure value of the pressure in the reservoir based on the second pressure measurement, and correcting the first injector opening duration in accordance with the second pressure value.

Preferably, the engine control unit communicates with at least one pressure sensor for measuring the pressure in the oil reservoir and evaluates the signal of the pressure sensor.

Additionally, the engine control unit preferably communicates with and controls the fuel injector. In so doing, the engine control unit controls the timing of the opening and closing of the injector, in particular according to the injector opening duration corrected as disclosed in the present invention.

The method according to the invention preferably runs automatically on the engine control unit.

Preferably, the engine control unit is programmed such that it performs the method according to the invention as described above.

The engine control unit preferably includes a microprocessor and a non-volatile memory area in which engine control software is stored. The engine control software is executed by the microprocessor. The engine control unit communicates with the sensor and evaluates the signal of the sensor and controls the actuators of the engine, in particular the injectors of the engine.

The internal combustion engine according to the invention may be a four-stroke engine. The four-stroke engine operates according to the otto process and/or the diesel process.

The internal combustion engine according to the invention may be an off-road engine. In particular, the internal combustion engine according to the invention can be used for driving a mobile working machine.

The invention therefore also comprises a mobile working machine with an internal combustion engine of the type described above.

However, it is also conceivable to use the internal combustion engine according to the invention in stationary applications, for example for driving an electric generator, as it is conceivable to use the internal combustion engine in any other application.

Drawings

The invention will now be described in more detail with reference to embodiments and the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of an internal combustion engine according to the present disclosure;

FIG. 2 illustrates a graph showing injector current versus time during a fuel injection event for different injector on-time durations (TOC);

FIG. 3 shows a graph illustrating injector current and injection rate as a function of time during an injection event and an exemplary pressure curve in an accumulator;

fig. 4 shows a diagram which also shows the injector current and the injection rate as a function of time during the injection process and an exemplary pressure curve in the pressure accumulator, and in which the relevant times a to I according to the invention are depicted.

Fig. 5 shows a block diagram of a first embodiment of the method according to the invention;

FIG. 6 shows a detailed block diagram of an embodiment of the method according to the invention as shown in FIG. 5;

FIG. 7 shows a graph illustrating a characteristic map for determining a first injector on-duration based on pressure and a desired injection quantity;

fig. 8 shows a diagram illustrating a characteristic diagram for determining a correction value as a function of the pressure and the desired injection quantity;

fig. 9 shows a block diagram of a second embodiment of the method according to the invention;

fig. 10 shows two graphs which show, for a first test cycle, the deviation between the desired fuel injection quantity and the actual fuel injection quantity, the upper graph showing the operation according to the method of the prior art, and the lower graph showing the operation according to the method disclosed by the invention; and

fig. 11 shows two graphs which show the deviation between the desired fuel injection quantity and the actual fuel injection quantity for a second test cycle, the upper graph showing the operation according to the method of the prior art, and the lower graph showing the operation according to the method disclosed by the invention.

Detailed Description

Fig. 1 shows an embodiment of an internal combustion engine 1 according to the invention. The internal combustion engine includes a plurality of injectors for injecting fuel into combustion chambers B ₁To B _nFuel injector I in ₁To I _n. The injectors communicate with a common accumulator 3, which supplies each injector with fuel. The present embodiment is therefore a common rail injection system. Therefore, the accumulator will also be referred to as a rail (fuel rail) hereinafter. However, the method according to the invention can also be used for other injection systems, in particular also in the case in which the pressure accumulator supplies fuel to only one injector. The accumulator serves for temporarily storing fuel, which supplies one or more injectors with fuel and, because of its appearance as a reservoir.

The pressure in the pressure accumulator 3 is measured by a pressure sensor 4. In addition, a high-pressure pump 5 is provided, which generates a target pressure in the accumulator 3. The high-pressure pump supplies fuel through a volume control valve 6 and pumps the fuel into the accumulator 3. The accumulator 3 is connected to the tank via a pressure control valve 7 and a return line. The pressure control valve 7 operates as a relief valve and opens when the target pressure has been reached.

The signal of the pressure sensor 4 is evaluated by the engine control unit 8. Engine control unit controlled fuel injector I ₁To I _nA high pressure pump 5 and valves 6 and 7. In addition, the engine control system receives values from other sensors 9 as input signals, in particular crankshaft position and camshaft position, and user inputs, such as desired engine speed.

Referring to fig. 2 and 3, fuel injector I will first be shown ₁To I _nThe injection rate or quantity and the control of the pressure in the accumulator 3.

During the injection process, whether it is a main injection, a pilot injection or a post injection, it is not possible to directly monitor whether the target quantity of fuel to be injected meets specifications. Therefore, it is impossible to adjust the injection rate on a single cycle basis, and the control is also inaccurate. The observation of the target fuel injection quantity can only be achieved over the entire range encompassing a plurality of ignition processes.

The rail pressure is determined by an engine operating strategy implemented in the engine control unit. However, the direct physical effect on rail pressure exerted by engine speed and engine torque is small. The pressure increase in the rail is decoupled from the injection process. The capacity of the rail far exceeds the maximum fuel injection amount during the fuel injection process. Thus, the rail pressure remains reasonably constant (even during the injection event), provided of course that the engine operating strategy anticipates that the rail pressure will remain constant during the observation period.

In the common rail system according to fig. 1, which is considered for explaining the invention, the amount of fuel supplied during the injection process can be specified by the rail pressure and the injection duration, i.e. the time period during which the injectors are open. In transient operation of the internal combustion engine, i.e. in the case of strong speed and torque changes occurring for short periods of time, the rail pressure can be adapted to the new operating point provided by the engine operating strategy only with a certain time delay, whereas the injection duration can be adapted quickly to the new operating situation.

For example, if the rail pressure is still significantly lower than its new target value at the time of a sudden load change acting on the combustion engine, the expected total fuel quantity for the injection event occurring at that moment can be provided by increasing the injection duration, i.e. by extending the period of time during which the injector is open.

Furthermore, the starting point of the injection process, i.e. the time at which the injector is opened or the crank angle, can be specified. The starting point of the injection is advantageously specified according to the respective operating situation, is of importance for operating the internal combustion engine as optimally as possible, and is a central aspect of the injection strategy within the engine software.

In the ideal and greatly simplified case, in which the rail pressure value is precisely known and is neither locally changed nor changed over time during the injection, the injection duration can be precisely adjusted and in this way a precise target injection quantity can be achieved. In fact, there are many factors that affect the actual amount of fuel injected. The following requirements are also provided without any requirements for comprehensiveness:

a) fuel discharge from open injectors results in increased pressure.

b) During the injection process, it may happen that the high-pressure pump feeds fuel to the rail.

c) The sensing range of the pressure sensor is spatially separated from the blind hole inside the injector nozzle. In addition to the stationary housing (which is not present in an operating internal combustion engine), the operating time (travel time) between the pressure sensor and the injector occurs in the fuel system, thus generating different instantaneous pressure values.

d) The pump is pulsed.

e) The rapid opening and closing of the fuel injector causes pressure fluctuations.

f) The actual start of injection and the end of injection have a certain time delay for the control of the injector.

g) Ageing of fuel injectors

h) Temperature dependence of fuel density.

Studies of the extent of these lesions have shown that: the time overlap that may occur between the injection of fuel and the supply of fuel by the high-pressure pump leads to a relatively large deviation between the target and the actual quantity of injection. These overlaps are not duplicable. The time profile (time diagram) of the rail pressure will differ according to load variations. Depending on the operating conditions of the internal combustion engine, the engine operating strategy will specify different start points for injection with respect to crank angle. However, even at the stationary operating point of the internal combustion engine, there is in most cases no synchronous operation between the high-pressure pump and the injection.

Although the duration of energization of the injector is well defined by the engine operating strategy, this predetermination is based on input values that are no longer valid during actuation of the actuator. As the dynamics required of internal combustion engines increase, the compensation potential that can be utilized by the invention will increase.

The invention thus serves to follow the target injection quantity for each individual injection event more precisely. The time periods (in the microsecond range) considered in this regard will be explained in more detail on the basis of fig. 2 to 4.

Fig. 3 shows a simplified and idealized injection sequence based on the time curve of rail pressure bar, injector current a and injection rate mg/ms. At the start of the observation period (the start is set to time t equal to 0 for simplicity), the injector current I is equal to 0A, and therefore the injection rate is 0. The rail pressure of 1000bar (bar) initially present is increased by the high-pressure pump supplying fuel. This fuel supply is started slightly less than one millisecond after the start of the observation. When the rail pressure approaches 1200 bar, the performance of the high pressure pump will be reduced or shut down, and therefore the rail pressure will temporarily maintain this value. At a time slightly below 3 milliseconds, the injector is energized. Thus, with some delay, fuel will begin to flow through the nozzle spray holes. When injector current is no longer present, the injector closing process begins and fuel flow ceases. During the fuel supply, the rail pressure is reduced from the initial 1200 bar to 1000 bar. The sequence of steps described above begins immediately after the rail pressure has decreased to that value and the injectors have just been closed, with the next injector being activated according to the engine firing sequence.

The values specified in the chart and in the text and the resulting values are orders of magnitude larger than the values based only on the actual system. For example, the indicated time is directly dependent on crankshaft speed and may vary multiple times depending on operating conditions. The time curve shown is simplified and idealized to provide the simplest possible interpretation.

Fig. 2 shows three time curves of the injector current. This is a simplified illustration for clarity. With respect to the time dimension of injector power-on, the edge steepness depicted is less than what actually occurs. If the current threshold is exceeded, the injector will open. If the current is below the threshold, the injector will close. With respect to the graph, the switching on of the three currents occurs at the same point on the abscissa. It can be seen that the injector current is switched off after different switch-on durations (TOC 2< TOC 1< TOC 3). TOC means current time. This refers to the duration of time that the injector is energized during injection. In a simplified and idealized case, the TOC value corresponds to the fuel injection time and is therefore equivalent to the injector opening duration within the framework of the invention explained herein. The TOC value is closely related to the fuel injection time due to the response time of the actual system; this also applies to the rising edge of the injector current at the start of injection and the falling edge of the injector current at the end of injection resulting in a value of 0.

In the case of rail pressure of equal height in all three cases (p 1-p 2-p 3), the maximum amount of fuel is supplied to the combustion chamber during the injection with the longest injector current (i.e. the three relevant TOC values reach their maximum). Likewise, at higher rail pressures p, the injector current may be turned off after a correspondingly shorter duration, thereby achieving reproducibility of the injected fuel quantity. At lower rail pressures, of course, TOC can be increased in order to again allow reproducibility of the injected fuel quantity.

Thus, the diagram in fig. 2 may illustrate the following three scenarios.

Case 1: for the upcoming injection event, rail pressure p1 is at a target value specified by the engine operating strategy. The target value for the on-time of the injector current having the magnitude TOC 1 is generated by the engine operating strategy.

Case 2: the rail pressure is above its target value. To ensure that a predetermined total amount of fuel will be supplied to the combustion chamber during the upcoming injection, the injectors will have to be energized for a short period of time (TOC 2< TOC 1).

Case 3: the rail pressure is below its target value. To ensure that a predetermined total amount of fuel will be supplied to the combustion chamber during the upcoming injection, the injectors will be energized for a longer period of time (TOC 3< TOC 1).

It can be seen that the deviation between the target value and the actual value of the rail pressure can in principle be compensated by adjusting the energization duration, so that the target quantity of supplied fuel intended for the injection process can be met. It goes without saying that the value of the duration of the energization must be known before the earliest possible end of the energization, otherwise the injectors will not close in time if the rail pressure target value has been significantly exceeded, and, as a result, an excessive amount of fuel will inevitably be injected.

Before using the function of determining injector on-duration and TOC, the engine operating strategy, as disclosed herein with respect to the corresponding next injection event, depends on certain state variables (e.g., engine speed) having specified injection angles with respect to crankshaft and camshaft angular positions 0 ° to 720 °. In order to determine the injection duration by means of the engine operating strategy, the actual value of the rail pressure is required as a relevant input variable, i.e. as a digital signal, which is processed on the basis of the raw signals of the sensors.

In order to achieve a reliable agreement between the actually existing physical rail pressure and the digital measurement, a signal processing comprising various individual steps is required.

Several milliseconds may have elapsed before a reliable rail pressure value meeting the requirements is available for the engine operating strategy. The speed-torque operating point of an internal combustion engine has a significant effect on the time at which the rail pressure value must be available for the engine operating strategy. Preferably, the moment of use of this value is provided exactly, the calculation of the end of injection having been completed exactly at the moment at which the end of injection required for observing the shortest duration of the injection period to be considered can still be achieved.

FIG. 4 shows a detail of the curve shown in FIG. 3 during a period when the injector is energized and fuel is thus being fed through the injection orifices. The time instants identified by letters are to be understood as qualitative indications and are used to explain the sequence of process steps in the following.

Since the total fuel quantity of the impending injection and the start of the injection is already specified by the engine control software, the rail pressure value must be available for the injection at the latest at a defined time a. As will be seen below, it is advantageous to set time a to the last possible time. Depending on the respective common rail system, the time point a will be specified differently, but it is always within a time interval within the switch-on time range of the injector energizing B.

Based on this rail pressure value available at time A, the duration of injector energization, TOC, and thus the closing time of the injector energization is determined. The latter is time I in the graph. The time marked H in the graph is the earliest injector-on close time to be considered. In order to ensure that the injector current can be closed in time, time a must not be too late when the relevant conditions prevail (particularly high rail pressures exist and particularly small amounts of fuel need to be provided for the immediately following, upcoming injection). (e.g., such influencing factors exist in the case of an impending pre-injection followed by a main injection with high fuel demand).

The change in rail pressure that occurs during injection, which in the diagram used to illustrate the process drops from approximately 1200 bar to 1000bar, is a significant disadvantage because the calculated moment at which the injector current will close and the calculated moment at which the injector current is closed in the prior art system are based on incorrect specifications in the final analysis, which is why the actual quantity of fuel injected in the given example is less than the target quantity. Likewise, during the injection event, in the event that the high-pressure pump supplies fuel to the rail during an ongoing fuel injection event, the actual amount of fuel injected may be higher than the target amount.

Although the high-pressure pump is driven directly by the internal combustion engine via the power take-off, the factor of the transmission ratio (actually the fixed transmission ratio) is a factor which represents a relatively large double common multiple, because, on the one hand, the high-pressure pump should not be operated at unnecessarily high speeds in order to limit the friction losses and the wear resulting therefrom. On the other hand, the transmission ratio must be sufficiently high so that the high-pressure pump can have a sufficiently high fuel delivery rate at any crankshaft speed. (based on a four-stroke engine, because of its widespread use.) if the transmission ratio is, for example, 1:7, the cycle duration of the value pair (angular position of the crankshaft and angular position of the high-pressure pump) would be 34 revolutions in the case of a 4-stroke engine. Due to the long period duration of the value pairs of the angular positions, the fuel injection quantity cannot easily be homogenized even in the case of a stationary operating internal combustion engine, by means of the parameters implemented fixedly in the engine control software.

In dynamic applications, it is not possible in any case to homogenize the injection quantity by means of a parameter, since in this case the deviation between the target value and the actual value of the rail pressure is not only dependent on the value pair of the above-mentioned angular position, but is also influenced by a constantly changing target injection quantity. In addition, the angular position at which injection begins is affected by the corresponding speed-torque operating point of the internal combustion engine. Furthermore, for efficiency reasons, the delivery rate of the high-pressure pump can be variably adjusted in relation to the speed. In short, there is no periodicity in a dynamically operating internal combustion engine due to changes in rail pressure during continuous injection.

Thus, it can be broadly stated that the calculation of the injector energization duration is based on incorrect specifications, which are the reason for missing the target amount of fuel injection. As already mentioned, the delivery rate of the high-pressure pump is adjustable, but this only allows adaptation to a set of a plurality of injection events, without readjusting the rail pressure of the individual injection immediately following.

The present invention thus provides a compensation method that can be added to an engine operating strategy in the form of additional software and that makes use of existing sensors and actuators such that the deviation between the target value and the actual value of the injection quantity for a single injection is reduced.

When the compensation method according to the invention is used as a supplement to the control of the injection system corresponding to the prior art, the processed rail pressure value must already be the first pressure value at an earlier instant a, unlike in the case of the prior art system, because some additional software functions, which will be explained below, must be performed before the injector current is switched off.

According to the prior art, the final calculation of the injector current cut-off time is performed based on the rail pressure value available at time a.

However, according to the present invention, according to the first embodiment, the first temporary injector opening duration, and thus the temporary time for turning off the injector current, is calculated based on the first rail pressure value available at time a. This value must be available at time C (see fig. 4). However, according to the second embodiment, only the first rail pressure value is determined at time a, without first determining the injector on-duration.

At a precisely defined time D, a processed, updated second rail pressure value must be available. With regard to the processing of the second rail pressure value, the short task running time is given a much higher priority than the accuracy of the absolute value, except in the case of rail pressure values available at the first moment a. At the instant E, the difference dp between the two read-in rail pressure values can be obtained. At time F, a correction value calculated from the existing data can be obtained.

At time G, a well-specified closing time of the injector current may be obtained.

For the sake of clarity, it should again be pointed out that, according to the first embodiment described in detail below, the second rail pressure value determined at the instant D is not used as a basis for fully recalculating the injector opening duration and therefore the injector current closing time, but as a basis for calculating a correction value for determining the second final injector opening duration and therefore the final closing time I by taking into account the previously calculated first injector opening duration and therefore the previously calculated temporary closing time.

However, according to the second embodiment, the second pressure value available at time D is used to correct the first pressure value, and then the injector opening duration is calculated from the corrected pressure value.

The processing of the first track pressure value available at the instant a is mainly aimed at a high accuracy, i.e. the highest possible correspondence between the physical track pressure actually present and the digital value determined therefrom, whereas the duration of the signal processing is of secondary importance. As for the second track pressure value available at time D, the speed of signal processing is more important.

It has turned out that the omission of certain processing steps for the signal processing of the processed first rail pressure value to be transmitted to the engine control software at the time a leads to a significantly higher change of the actual fuel injection quantity relative to the target quantity, although the signal sampling period associated therewith can occur in a later time period and the measured value acquisition period is therefore closer to the injection period. However, as far as the second rail pressure value to be transmitted to the engine control software for calculating the correction value K at the time D is concerned, it has turned out that the targeted omission of certain processing steps of the signal processing and thus possibly later signal sampling leads to a correction value K, the use of which reduces the deviation between the actual fuel injection quantity and the target fuel injection quantity.

The following lists a sequential sequence of preferred processing steps performed for signal processing for the first rail pressure value available at time a:

sensor signal sampling (sample and hold);

analog-to-digital conversion;

reading digital input variables into the software;

correcting the pressure signal due to a deviation between a target value and an actual value of the sensor supply voltage;

averaging;

additional digital filtering; and

down-sampling.

However, in the signal processing of the second rail pressure value available at the time D, the following processing steps are preferably omitted:

correcting the pressure signal due to a deviation between a target value and an actual value of the sensor supply voltage;

additional digital filtering; and

down-sampling.

However, other processing steps may be performed in the same manner as the first force value.

To allow the advantage of faster signal evaluation to be exploited, the signal sampling period must be done in a later period; ideally, this is done approximately during the time period when the digital second rail pressure value is still just allowed to be available at time D.

According to a preferred embodiment, for calculating the track pressure value difference dp required for determining the correction value K, not the first track pressure value, which has previously been processed with a particularly great effort and is available at the instant a, but a third track pressure value, which is determined by a similar and preferably identical process to the process on which the second track pressure value read-in at the instant D is based.

During the common signal sampling, two values, i.e., the first and third rail pressures, that quantify the rail pressure before the start of injection may be determined. On the one hand, this would be advantageous, since two digital values would be obtained that would differ only in signal processing mode, as required. On the other hand, in this case, the signal sampling must be performed earlier before the task running time required for additional signal processing.

The basically existing possibility of separating the signal samples (by their to be quantified rail pressure values before injection) and performing the third rail pressure value by a fast process after two signal samples is disadvantageous.

The remaining possibility of separating the signal samples (by which the rail pressure values are to be quantified before injection) and determining the third rail pressure value already by a fast process before the start of the signal samples for generating the first rail pressure value (the processing of which requires a great effort) has the advantage that: the time interval between the last-mentioned signal sampling and the injection does not increase further.

An advantage of this preferred embodiment would be that the calculated pressure difference dp is based on two pressure values, which are mainly subject to the same disturbance. As a result, there is a higher agreement between the difference in the physically present rail pressure and the digital value calculated for calculating the correction value K.

A simple example is the thermally induced drift of the supply voltage of the pressure sensor. In order to determine an accurate absolute value, it would be useful to compensate for such disturbances or to perform corrective calculations on the damage caused by such disturbances. For pressure differences, if both pressure values are subject to such disturbances, the damage will be much smaller than if a correction calculation were performed on only one of the two pressure values.

In the following, a survey of the qualitative recording moments of the individual method steps will be given again:

a: availability of the processed first rail pressure value (priority of accuracy of absolute value);

b: starting the energization of the oil injector;

c: availability at a temporarily specified time of injector current shut-off;

d: availability of a processed second track pressure value (priority for short task run time to allow delayed signal sampling);

e: availability of a pressure difference dp;

f: availability of the correction value K;

g: availability at relevant times for injector current shut-off;

h: the earliest possible moment at which the injector current can be actually turned off according to relevant specifications; and

i: the injector current defined at time G is turned off.

Fig. 5 shows an abstract block diagram of a first exemplary embodiment of the invention in relation to the preferred specific embodiment described above.

The function for determining the TOC value first receives a target amount of fuel for a subsequent injection from the engine control strategy in box 11 and determines a first pressure value of the rail pressure by complex signal processing in box 12. In block 13, a first TOC value is calculated using the relevant input variable for the target fuel quantity of the subsequent injection and the exact first value of the rail pressure as close as possible in time before the start of the injection.

In the case of the method according to the invention, the first TOC determined in this way is only a temporarily specified value. The second TOC value actually used to energize the injectors is specified in accordance with the invention by another function, hereinafter referred to as the correction function 17. The correction function 17 generates a correction value, in particular in the form of a correction factor, by means of which the first TOC value in the block 18 is corrected in order to provide a final second TOC value.

The correction function 17 exhibits a dependency on a second pressure value of the rail pressure measurement 14, which is executed again later, i.e. updated, the rail pressure measurement 14 preferably being executed partially before the injection.

In this embodiment, this re-executed rail pressure measurement 14 has no effect on the temporarily calculated first TOC value, but exerts its effect on the finally specified second TOC value via the correction function 17. Therefore, the entire injection determination portion of the engine control software need not be executed with the updated second rail pressure value.

The second pressure value is introduced into the correction function 17 in the form of a pressure difference dp. For this purpose, a third pressure value is determined in block 15 just before the instant a at which the first pressure value is determined, which third pressure value is processed in the same way as the second pressure value. In block 16, a pressure differential between the second pressure value and the third pressure value is formed and communicated to the correction function 17.

In this embodiment, the correction function 17 also exhibits a dependency on the first rail pressure value, which is of decisive importance for specifying the temporary first TOC value. In addition, the correction function may depend on the target fuel amount that has been specified for the subsequent injection.

In order to allow the updated second rail pressure measurement to be carried out as late as possible, i.e. as close as possible to the earliest possible closing time of the injector current, the processing of the resulting updated second rail pressure value must (as already explained in detail) have as low a task running time as possible and the correction function must be configured such that the sum of its processing and the calculated task running time of the correction is as short as possible. (this expression using the deliberately chosen term "task run time" implies that the required maximum computation time is as short as possible).

Fig. 6 shows the flowchart already shown in fig. 5, supplemented with a possible implementation of the correction function 17 optimized with respect to the task runtime. Accordingly, with respect to other functions and blocks, reference is first made to the above description of fig. 5.

In this embodiment, the TOC value associated with the power-on is determined in block 18 by multiplying the previously calculated temporary first TOC value by the correction value determined by the correction function. Thus, correction value 1 corresponds to no change.

The correction function 17 has a situation discrimination 20. The decision criterion depends on the updated second rail pressure value available at time D. The situation discrimination 20 can therefore only be solved relatively late.

The feature maps K1, K2 are stored in all two paths of case differentiation. The two input variables of both characteristic maps are the first rail pressure value available at time a and already measured relatively early, and a target value for the injection quantity of the following fuel injection, which is available even earlier. Thus, before the instant D at which the second pressure value is available, the characteristic maps K1 and K2 are read out in blocks 23 and 24, respectively.

For calculating the correction factor, only the initial value of one of the two characteristic maps 21, 22 is required in the final analysis. Since both maps are read out beforehand, the second rail pressure measurement acquisition (i.e. the corresponding signal sample for providing the updated second rail pressure value) may be delayed for a duration corresponding to the task run time for reading out the characteristic map.

Of course, the principle can also be applied to cases where case discrimination includes more than two cases or where case discrimination is not performed. It goes without saying that this principle can also be applied if calculation rules or the like have to be processed instead of the feature map.

Characterized by the following strategies: when determining the correction factor, part of the calculation procedure has been performed before the updated second value of the rail pressure is available.

In the present embodiment, this is achieved by reading values from the maps K1, K2 based on the first pressure value and the target fuel injection amount.

Then, the correction coefficient is determined by the interpolation functions 23, 24, and the interpolation functions 23, 24 adjust the values read from the respective characteristic maps in accordance with the pressure difference dp. In the present embodiment, the value read from the characteristic map corresponds to the given value p of the pressure difference dp _k1Or p _k2And now, in particular by interpolation, to the pressure difference actually determined by the second pressure value and the third pressure value.

Interpolation will now be explained based on the following example, which is described under the assumption that dp ≧ 0. In the example assumed, the target value for the upcoming injection is 150mg, at which time the first rail pressure value available at time A is pb. The synthesis initial value of the correction map K1 is preferably determined before the instant of time D and has a value of 1.6 in the given example.

Assuming that the third pressure value and the second track pressure value available at the time of time a and time D are equal, i.e., dp is 0, the initial value of the correction matrix is not considered. The initial value of block 23, i.e. the correction value, then has the value 1.

Assuming that the variable dp reaches or exceeds a specified threshold p _k1A correction value of 1.6 is obtained. If the threshold is exceeded, the values read from the profile will be used as correction values without extrapolation.

Assume that the value of the variable dp is between 0 and the threshold p _k1Then a linear interpolation between the value 1 and the correction map initial value 1.6 is performed. For example, if the variable dp is equal to the threshold p _k110% of the total linear interpolation would yield a value of 1.06. In the study of this example, the temporarily specified TOC value was multiplied by a factor of 1.06.

Threshold value p _k1、p _k2Stored in a parameter set of the engine control unit.

FIG. 7 shows an exemplary fuel injector map, commonly referred to as a fingerprint, of a type that may be used to calculate the TOC value in block 13. The curves shown in the figures show the isobaric lines. The latter refers to the total amount of fuel supplied to the combustion chamber of the engine during the injection. From the perspective of the engine control unit, the calculated target amount of the immediately following injection determines the ISO mass line. Once the rail pressure value is available, the desired TOC value can be obtained. For each fuel injector, the engine control unit includes a set of parameters that include fingerprint features to specify the TOC value when the input variables are known.

Parameter sets that may be used to describe such feature maps may be provided, for example, in the form of a table of values. The corresponding columns of this table of values have recorded therein the TOC support points for different fuel quantities and the fixedly maintained rail pressure values. For a fixedly held fuel quantity and for different rail pressure values, the TOC support points are recorded in the corresponding row.

The signatures used to determine the TOC values may also be used to calculate signatures K1 and K2, respectively, from which values are read to determine the correction coefficients. To this end, another set of parameters will be created, the support points of which are based on the same fuel quantity value. With respect to the rail pressure value, two support pointsThe same pressure difference as in the actual characteristic diagram still exists therebetween; however, in the second profile, the corresponding pressure entries (pressure entries) for all the support points are reduced by the corresponding same pressure value difference p _k2. Thus, in the second profile, the value of the TOC entry is higher at the corresponding same position.

These two profiles can be used to determine a correction map therefrom. The grid between the rail pressure value and the fuel quantity corresponds to the grid of the characteristic diagram of the TOC value. The grid is preferably not an equidistant grid. The reason for this is that the profile is non-linear and therefore, on the basis of skilled selection, a higher accuracy can be achieved while maintaining a certain number of support points.

In the calibration map, the respective support points refer to the fuel quantity and the rail pressure value, as shown in the characteristic map for determining TOC, which map has been explained first. In the calibration chart, the support point k (m) _i，p _j) The entries of (a) correspond to the respective quotient of the entries of the first-mentioned characteristic map, the so-called fingerprint map and the second characteristic map, wherein the TOC value at each supporting point is determined by a fixed pressure difference p _k2And (4) moving.

With respect to FIG. 6, the correction map K2 for exemplary purposes encompasses dp<0, i.e. the rail pressure drop starting from a first rail pressure value, which is used for determining the temporary TOC value and which must be available at the moment of time a, and an updated second rail pressure value, which must be available at the moment of time D. For the correction map K1 for covering another case, in the calculation of the support points, the dividend is the same as in the case of the correction map K2, but for the divisor, a characteristic map is used in which each entry corresponds to an increase by a constant pressure value difference p _k1TOC value of pressure value of (a).

Fig. 8 shows an exemplary representation of the correction map K2. Since the dividend and the divisor are both time variables, the initial value of the correction map is dimensionless.

In the first embodiment according to the present invention shown in fig. 5 to 8, the first injector opening duration is first determined based on the first pressure value, and then corrected based on the second pressure value.

However, the present invention is not limited to such an embodiment.

Fig. 9 shows, in block diagram form, a second embodiment of the invention in which the second pressure value is used not to correct the previously determined injector on-duration, but to correct the first pressure value. Only then is the injector on-duration determined based on the corrected pressure value.

Blocks 11, 12 and 14 to 16 correspond to the first embodiment shown in fig. 5, and reference is therefore made to the above explanation. They provide a first pressure value p (a, 1), an injection quantity m and a pressure difference dp.

In the case of the embodiment shown in fig. 9, a correction function is provided which passes through the pressure difference dp (i.e. p) between the second pressure value p (D, 0) and the third pressure value p (a, 0) _korrThe first pressure value p (a, 1) is corrected in block 30 for p (a, 1) + dp (p (D, 0) -p (a, 0)). As can be seen, in the present embodiment, the pressure difference itself forms a correction value and is added to the first pressure value.

Then, in block 31, the corrected pressure value p is passed _korrAnd target injection quantity m (i.e., TOC [ m, p ] _korr]) The final injector on-time TOC is read directly from the TOC map.

The invention enables the accuracy of the quantity of fuel actually injected to be considerably improved. In the following, this will be demonstrated by a series of measurements, which were established with the first embodiment of the invention.

In fig. 10, both graphs illustrate the operating behavior of the common rail system for a fuel injector in the case of a statically operated internal combustion engine, respectively. In order to measure the respective actual quantities of the individual fuel injectors with high precision, the series of measurements shown in the figure is not carried out in a burning internal combustion engine, but in a common rail system operating on a test stand, without fuel combustion taking place via the injection orifices. Environmental conditions associated with the common rail system were simulated on the test stand. In the test procedure of the graph, the rotation speed of the high-pressure pump was 1000 revolutions per minute, and the target fuel amount per injection event was 250 mg. The abscissa corresponds to the time and the number of injection events considered. The value of the actual injected fuel quantity is plotted along the ordinate.

In both test series, each injection event recorded in the diagram is triggered in a corresponding manner at the same crankshaft angle. The upper graph shows the actual value of fuel injection without the compensation method of the present invention. The lower graph shows the corresponding fuel quantities using the compensation method of the invention under otherwise identical test conditions.

When comparing the results of the two test series, it is particularly noteworthy that the compensation method according to the invention significantly prevents a particularly strong deviation from the target value. But in aggregate, the deviation is reduced by a factor of about 2 to 3.

In fig. 11, these two figures likewise show the operating behavior of the common rail system. The high-pressure pump is operated at 1000 revolutions per minute, and the target fuel quantity to be supplied per injection event is 200 mg. Unlike the previous diagram shown in fig. 10, an intentional variation of the start of injection is performed. The intentional variation of the start of the injection is slow in terms of the time interval between two injections. Thus, in the above figure, a systematic offset of the actual values can be seen, which is based on the measured value acquisition, without applying the compensation of the invention, since two piston strokes occur on the high-pressure pump used per revolution of its shaft. The test setup included six injectors and a piston stroke of the high pressure pump, with each injector being performed simultaneously. The graph shows the injection value of one of the six injectors. Thus, three high pressure pump shaft rotations occur between the two measurement points. With this arrangement, clearly identifiable reproducible disturbances can be imposed on the test setup by changing the start of injection. The present invention effectively attenuates this interference, as shown in the following figures.

In many applications in the field of mobile working machines, particularly high dynamic requirements are present. The diesel engines used in this field are classified as so-called off-road engines. The latter being subject to special exhaust gas regulations. Wherein the specified emission limit is based on a standardized test Cycle NRTC (non road Transient Cycle). The present invention can also be substantially improved in the field of exhaust gas generated by an engine by precisely controlling the amount of fuel injected.