JPH06317230A - Method and equipment for controlling fuel injection system - Google Patents

Abstract

PURPOSE: To reduce injection quantity dispersion by a pilot injection by temporally modulating a pilot injection driving period by prescribed frequency and amplitude and improving detection sensitivity from dead time to the pilot injection driving period. CONSTITUTION: Prescribed quantity of fuel is supplied from a fuel pump 30 to an engine 10. Various kinds of sensors 40 detect a measured value 15 featuring an operating state of the engine 10 and supply this value 15 to a control device 20. The control device 20 calculates a driving pulse 35 to be supplied to a fuel pump 30 based on the measured value 15 and other variables to parameters 25, fixes fuel quantity to be injected by a driving period and performs a pilot injection before an originally main injection. A pilot injection driving period ASDV is increased from the starting of a small value in which an injection is not performed till a detection that an injection is performed based on an output signal U of the sensors 40 and is temporally modulated by prescribed frequency and amplitude. Therefore, sensitivity for detecting dead time t01 , t02 can be improved and injection quantity dispersion can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for controlling a fuel injection system, and more particularly to determining the amount of fuel to be injected by at least one electrically actuatable valve, in which case it is predetermined. The present invention relates to a fuel injection system capable of detecting the dead time of the fuel injection system under the above operating conditions, and more particularly to a method and an apparatus for controlling a high pressure fuel pump.

[0002]

2. Description of the Related Art A method of this kind for controlling a fuel injection system is known from DE-OS 3929747 (US-A50).
70836).

The publication describes a method of controlling a fuel injection system for a high-pressure fuel pump in which the amount of fuel to be injected into the internal combustion engine is determined by at least one solenoid valve. The solenoid valve is driven so that first injection (first-stage injection) is performed first, and then main injection is performed.

Due to manufacturing errors and aging, the amount of fuel injected into each cylinder of the internal combustion engine varies. Due to this variation, different amounts of fuel are supplied to the internal combustion engine when injection is performed in advance with the same drive signal.

Since the preliminary injection amount is extremely small, if the drive signals are the same, the preliminary injection may not be performed or a considerably large amount of the preliminary injection may be performed. This eliminates the advantages of prior injection with respect to combustion noise. That is, enhanced combustion noise is generated, or soot emission is significantly increased. Since the variation between individual cylinders is quite large, it is possible that correct pre-injection is performed in some cylinders, whereas pre-injection is not performed in other cylinders, or a considerably large amount of pre-injection is performed. Occur.

In order to compensate for this variation, in the prior art, the drive pulse period of the solenoid valve at which the injection is started just before the predetermined operating condition is required. Based on that, an adjustment signal of the drive pulse for performing the preliminary injection is formed and stored. In order to detect the drive pulse at which the injection has just begun, the duration of the drive pulse is increased starting from the drive pulse in which the previous injection is not performed until the detection signal detects that the previous injection has been performed.

This method has the disadvantage that the signal examined changes very little in the transition from the state in which the injection is not performed to the state in which the injection is performed. This makes it very difficult to determine from which period of the drive pulse the injection should take place.

[0008]

The object of the present invention is to eliminate the above-mentioned conventional drawbacks, and it is possible to reduce the variation in the amount of fuel injected and improve the sensitivity for detecting dead time. Another object of the present invention is to provide a method and apparatus for controlling a fuel injection system.

[0009]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention defines the amount of fuel to be injected by at least one electrically actuatable valve, in which case the fuel injection is performed in a predetermined operating condition. In a fuel injection system in which system dead time is detected, particularly in a method of controlling a high-pressure fuel pump, a drive period of injection prior to detecting dead time is temporally modulated with a predetermined frequency and amplitude,
A configuration is adopted in which starting from a small value at which the preliminary injection is not performed, and increasing until it is detected that the preliminary injection is performed based on the output signal of the sensor.

Further, according to the present invention, there is provided a fuel injection system having at least one valve which is electrically operable to define an amount of fuel to be injected, and means for detecting a dead time of the fuel injection system under a predetermined operating condition, In particular, in the control device for the high-pressure fuel pump, in order to detect the dead time, the driving period of the injection is temporally modulated with a predetermined frequency and amplitude,
A configuration is also provided in which means is provided for starting from a small value at which the preliminary injection is not performed and increasing it until it is detected that the preliminary injection is performed based on the output signal of the sensor.

[0011]

In such a structure, the driving period of the preliminary injection is started from a small value at which the preliminary injection is not performed until the fact that the preliminary injection is performed is detected based on the output signal of the sensor. At this time, since the driving period of the preliminary injection is temporally modulated with a predetermined frequency and amplitude, it is possible to improve the sensitivity for detecting the dead time, and thus the variation of the injection amount due to the preliminary injection can be improved. Can be reduced.

In the preferred embodiment, a cylinder pressure sensor,
The output signals of the solid-state transmission sound sensor, the acceleration sensor, the acoustic probe in the engine compartment, the engine torque sensor or the rotation speed sensor are evaluated or examined, and the preceding injection is detected thereby.

In this case, when the signal appears at the output of the filter means to which the output signal of the sensor is supplied, it is detected that the pre-injection is performed. A bandpass filter whose lower cutoff frequency is considerably higher than the engine speed is used as the filter means. A bandpass filter whose center frequency corresponds to the modulation frequency is used as the filter means.

The drive period of the preceding injection is temporally modulated as described above, and its modulation frequency is set according to the engine speed.

In a preferred embodiment of the present invention, an adjustment signal for a drive pulse for performing injection is formed and stored based on the determined dead time. This adjustment signal is obtained once at the end of engine manufacture or at predetermined intervals.

[0016]

The present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 shows a block diagram of a main part of an apparatus for injecting fuel into an internal combustion engine. A predetermined amount of fuel is supplied to the internal combustion engine 10 from a fuel (injection) pump 30. Various sensors 40 detect a measured value 15 which characterizes the operating state of the internal combustion engine and supplies it to the control unit 20. The controller 20 calculates the drive pulse 35 supplied to the fuel pump 30 based on the measured value 15 and another variable or parameter 25.

The internal combustion engine 10 is preferably a self-ignition internal combustion engine (diesel engine). In particular, the fuel pump 30 has an electrically actuatable valve. The start and end of fuel injection can be controlled by driving the valve. As an electrically actuable valve, for example, a valve actuated by piezoelectric or magnetostriction can be used. Hereinafter, this electrically actuable valve is referred to as a solenoid valve.

The controller 20 calculates the amount of fuel to be injected into the internal combustion engine in a known manner. This calculation is carried out in accordance with various measured values 15, such as, for example, the engine speed, the engine temperature, the actual start of injection, as well as other parameters 25 which characterize the operating conditions of the internal combustion engine or vehicle. Other parameters are, for example, accelerator pedal position or ambient air pressure.

The controller 20 then converts the desired amount of fuel into drive pulses. This drive pulse is applied to the fuel pump 30.
Is supplied to a member that determines the injection amount of. For example, a solenoid valve is used as a member that determines the injection amount, and this solenoid valve is configured to determine the fuel amount to be injected depending on the opening period or the closing period of the solenoid valve.

In the solenoid valve, a predetermined pressure is formed in the pump unit chamber after the solenoid valve is closed at the feeding stage of the pump unit, and when the pressure exceeds a predetermined pressure value, injection is automatically performed. It is located in the high pressure fuel pump. After the solenoid valve is opened, the pressure in the unit chamber drops and the injection ends. By closing the solenoid valve for a short time and then opening it during the feeding stage of the pump unit, it is possible to perform the injection prior to the original main injection.

Preferably, for each cylinder, a separate high pressure fuel pump is provided with a solenoid valve defining the amount of fuel to be injected. Alternatively, it is also possible to provide one high-pressure fuel pump with solenoid valves which supply fuel to all cylinders one after the other.

It is known that a small amount of fuel injected into the cylinder for a short period before the original main injection significantly improves the noise characteristics of the engine. This injection is called prior injection (previous injection) or pilot injection.

The reason why the engine noise characteristics are improved is
The pressure rise that occurs during ignition in the cylinder is to level out a very steep pressure rise that causes noise such as when nailing a diesel engine.

The pre-injection amount required for the pre-injection, which is remarkably smaller than that of the main injection, cannot be detected by measuring technology.
Alternatively, it is not possible to measure sufficiently accurately due to various disturbance amounts that cannot be processed.

In electromagnetic valve controlled or piezoelectric controlled injection systems, in which the pressure buildup of the fuel is controlled by an electrically drivable electromagnetic or piezoelectric actuator and consequently the opening of the electromagnetic valve is pressure controlled, for example, The disturbance amount is a dead time t01 from the start of the electric control signal to the opening of the injection valve needle and a dead time t02 from the end of the electric control signal to the closing of the injection valve needle.

These quantities are shown in FIG. Figure 2
The drive signal U relating to the injection having the preceding injection and the main injection is shown in FIG. Prior injection is the period ASDV
Have. FIG. 2B shows the transition of the pressure P in the injection nozzle. The stroke H of the injection valve needle is shown in FIG. These signals are illustrated with respect to time t or with respect to crank angle (degrees).

The dead time (delay time) t01 elapses from the drive time point A at which the drive signal U changes from a low signal level to a high signal level to the time point SBI at which the injection needle moves. A dead time t02 elapses between the drive end time point B and the end of injection when the injection valve needle returns to the initial position.

After the driving time point A, a predetermined pressure is formed in the injection nozzle as time passes. This rise is a dead time t
It takes place during 01. When the pressure reaches a predetermined value, the injection valve needle is lifted and injection is started.

After the drive end time point B when the drive signal U drops to zero again, the fuel pressure in the injection nozzle decreases with the passage of time. At the same time, the injection valve needle returns to the initial position again.

Fuel injection is performed during the period when the injection valve needle moves from its inoperative position. The following equation holds for the injection period ti of the preliminary injection.

Ti = ASDV- (t01-t02) Bracketed (t01-t02) indicates the effective dead time. This is called dead time below. This value fluctuates between individual cylinders, and this fluctuation is based on the tolerance of the fuel injection system (apparatus) that is composed of the injection valve, the injection pipe and the solenoid valve. Furthermore, this value changes as the operating time elapses. Therefore, it is necessary to obtain this dead time extremely accurately.

Both dead times may be longer than the original injection time ti, especially in the case of prior injection. Therefore,
This small percentage change in the dead time results in a large percentage change in the injection time and thus the fuel quantity injected. The dead time depends on the viscosity of the fuel or the electrically actuated tolerance actuators, which is particularly related to the nozzle opening pressure or temperature, which is related to the product, or it varies with the operating time.

An object of the present invention is to determine the dead time continuously or at predetermined time intervals as accurately as possible. As a result, the amount of fuel that is previously injected can be measured more accurately.

FIG. 3 shows the waveform of the pressure P in the cylinder and the stroke NH of the solenoid valve needle with respect to time or crank angle. The solid line shows the characteristics without prior injection, and the dotted line shows the curve with prior injection. As is apparent from FIG. 3, the steep pressure rise of the cylinder pressure after the ignition of the fuel is flattened by the preceding injection.

FIG. 4 shows the frequency spectrum of the pressure curve. fN is the frequency of camshaft rotation. fK
Is the frequency of crankshaft rotation, 3fN is the triple frequency of camshaft rotation, and 2fK is the double frequency of crankshaft rotation. The solid line shows the envelope of the frequency spectrum when there is no preceding injection. What is indicated by the dotted line is the characteristic when there is prior injection. As is clear from the figure, the amplitude of the high frequency component is reduced by the preliminary injection. It is possible to detect that the injection has been performed based on the fact that the high frequency amplitude of the pressure signal is reduced in this way.

The following processing is performed to obtain the dead time.

Starting from a short drive period ASDV in which no injection is performed, the drive period is continuously increased.

At the same time, the driving period is amplitude-modulated with an extremely small amplitude. The drive period is preferably modulated with an amplitude corresponding to a crank angle of 0.1 degree. The modulation frequency fM per cylinder is obtained on the basis of the formula: fM = 0.5 * N / 60 * X where N is the number of crankshaft revolutions per minute and X is preferably the value 1/2, 1 / 3, 1/4, 1/5, 1/6, ... 1 / K
(K is a natural number greater than 2) is a coefficient that can take. This equation preferably applies for a 4-cycle engine.

In the case of a two-cycle engine, the formula fM = N / 60 * X holds.

In the case of X = 1/2, this means, for example, that the second preceding injection period ASDV in each case is increased by a time corresponding to a crank angle of 0.1 degree, and each of the other two cases.
This means that the second drive period is reduced by a crank angle of 0.1 degree. This is shown in FIG. 5 (a). Here, for example, the crank angle (KW) for prior injection
12.7 degrees and 12.9 degrees (° KW) are selected alternately.

The drive period in which the injection is performed just before is shown by a dotted line. As is clear from FIG. 5 (a),
The driving period is considerably lower than the driving period required for the preceding injection. Next, the average drive period ASDV is increased until the previous injection is performed.

In FIG. 5B, the average drive period ASD
V is just the amount of dead time required.
When the drive period is 0.1 degrees higher than the average drive period, the pre-injection is performed, and when it is lower than the average drive period, the pre-injection is not performed.

In FIG. 5C, the average driving period is selected so that the injection is performed prior to the reduction of the driving period. When driven as shown in FIGS. 5 (b) and 5 (c), preferably the high frequency components of the spectrum are accurately amplitude-modulated at the modulation frequency fM, as shown in FIG.
This means alternating between the various envelopes of the spectrum shown in FIG. 4 at the amplitude modulation frequency fM. When driven as shown in FIG. 5 (a), such modulation of the pressure signal P does not occur.

This modulation frequency fM is extracted from the pressure signal using a filter. This can be done quite easily. This is because the frequency fM is known. The average drive period ASDV is adjusted using a simple control circuit so that the modulation frequency fM is output. In that case, the average drive period ASDV corresponds to the dead time obtained.

A device for detecting the modulation frequency fM is illustrated in FIG. Reference numeral 600 indicates a cylinder pressure sensor. The output signal reaches the bandpass filter,
The output signal is supplied to the second bandpass filter 630 via the demodulator 620.

A high frequency component is extracted from the signal of the cylinder pressure sensor by using the first bandpass filter. First
The cutoff frequency of the bandpass filter is, for example, a frequency that is 5 to 100 times the crankshaft rotation fK.

The modulated signal is demodulated in the next demodulator. The second bandpass filter has a small bandwidth and its center frequency is at the modulation frequency fM. A signal is output to the output of the second bandpass filter only when the injection is performed in advance.

The cutoff frequency of the first bandpass filter shown in FIG. 6 is merely a standard value.
It should be regarded as an example value.

The above-mentioned device for detecting the modulation frequency fM can be realized as an analog circuit or as a program for a corresponding microprocessor.

Instead of the cylinder pressure sensor, it is also possible to use a solid transmission sound sensor (impact sound sensor), an engine acceleration sensor or an acoustic probe in the form of a microphone. In that case it is sufficient to have one sensor for all cylinders. For example, a knocking sensor is suitable as the solid-state transmission sound sensor.

In particular, it is effective to reduce the main injection amount by the actual or average preceding injection amount in order to keep the operating point of the engine constant.

The method will be briefly described with reference to the flowchart of FIG. It is identified in the first step 700 that the drive period correction value must then be determined.

In step 710, the average drive period ASDVM for the preliminary injection is set. This is chosen to be a value that ensures that prior injection does not occur. Next, in step 720, the drive period is amplitude-modulated.

In step 730, the sensor output signal is filtered. At decision step 740, the filtered signal is used to determine if a prior injection has occurred. Otherwise, in step 750 the average drive period ASDVM is increased by a small value (E). Then, the process returns to step 720 again.

If it is detected in step 740 that the injection is just performed, step 760 is performed.
In, the dead time is calculated based on the average drive period ASDVM.

Based on the dead time or the average drive period in which the injection is just performed, the adjustment signal of the drive pulse to be injected is formed and stored. This adjustment signal is preferably obtained once at the end of engine manufacture or at predetermined time intervals. For example, the dead time or the adjustment signal is obtained at the time of maintenance at a fixed time interval, at a predetermined mileage, or when a predetermined operating condition exists, for example, in an operating condition following the starting process. You can do it.

Further, it is possible to use an engine torque sensor or an engine speed sensor instead of the above-mentioned sensor. In that case, the main injection amount is not reduced, or is reduced by the average preceding injection amount.

Observing the engine speed or the engine torque, the engine torque or the engine speed is modulated at the time of driving shown in FIG. 5 (b) or FIG. 5 (c). At the time of driving as shown in FIG. 5A, the modulation of the torque or the rotational speed is not performed. The modulation frequency of the engine torque or engine speed signal can be detected by using a bandpass filter having the following frequency, that is, fM = 1/2 * N / 60 * X. The above formula holds for a 4-cycle engine.
In the case of a two-cycle engine, the following equation holds: fM = N / 60 * X If this modulation is detected in the speed signal or the torque signal, the drive period is greater than the dead time determined.

The dead time obtained using this method can also be used for correction of the drive period in the main injection.

[0061]

As is apparent from the above description, according to the present invention, the driving period of the preliminary injection is temporally modulated with the predetermined frequency and amplitude, so that the dead time or the preliminary injection is exactly performed. It is possible to improve the sensitivity for detecting the drive period, and thereby reduce the variation in the injection amount due to the previous injection.

[Brief description of drawings]

1 is a block diagram schematically illustrating an apparatus for carrying out the method of the present invention.

FIG. 2 is a diagram showing drive pulses, fuel pressure and stroke of an injection valve needle with respect to time.

FIG. 3 is a diagram showing cylinder pressure and needle stroke with respect to time.

FIG. 4 is a diagram showing a frequency spectrum of a cylinder pressure signal.

FIG. 5 is a waveform diagram showing various drive pulses.

FIG. 6 is a block circuit diagram showing details of a circuit for detecting a modulation frequency.

FIG. 7 is a flow chart illustrating the method of the present invention.

[Explanation of symbols]

 10 Internal Combustion Engine 20 Control Device 30 Fuel Pump 40 Sensor 600 Cylinder Pressure Sensor 610 Bandpass Filter 620 Decoder 630 Bandpass Filter

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Uwe Meienberg 70180 Stuttgart Farbenhenenstraße 9 (72) Inventor Klaus Scherbacher, Germany 71701 Schwieberdingen Helen Wiesenberg 6

Claims (9)

[Claims] 1. A fuel injection system, in particular a high-pressure fuel pump, in which the amount of fuel to be injected is defined by at least one electrically actuatable valve, in which the dead time of the fuel injection system is detected under predetermined operating conditions. In order to detect the dead time, the driving period of the preliminary injection is temporally modulated with a predetermined frequency and amplitude, starting from a small value at which the preliminary injection is not performed, and based on the output signal of the sensor. A method of controlling a fuel injection system, characterized in that it is increased until a prior injection is detected. 2. A cylinder pressure sensor, a solid-state transmission sound sensor,
Method according to claim 1, characterized in that the output signals of the acceleration sensor, the acoustic probe in the engine compartment, the engine torque sensor or the speed sensor are evaluated. 3. A method as claimed in claim 1 or 2, in which a prior injection is detected when a signal appears at the output of the filter means supplied with the output signal of the sensor. 4. The method according to claim 1, wherein the modulation frequency can be set according to the engine speed. 5. The method according to claim 1, wherein the filter means is a bandpass filter whose lower cutoff frequency is considerably higher than the engine speed. 6. The method according to claim 1, wherein a bandpass filter whose center frequency corresponds to the modulation frequency is used as the filter means. 7. The method according to claim 1, wherein an adjusting signal of a driving pulse for performing the injection is formed and stored based on the dead time. 8. The method according to claim 1, wherein the adjustment signal is obtained once at the end of engine production or at predetermined intervals. 9. A fuel injection system, in particular a high-pressure fuel pump, comprising at least one electrically actuatable valve for defining the amount of fuel to be injected and means for detecting the dead time of the fuel injection system under predetermined operating conditions. In order to detect the dead time, the control unit for the vehicle temporally modulates the drive period of the preliminary injection with a predetermined frequency and amplitude, starting from a small value at which the preliminary injection is not performed, and the preliminary injection is performed based on the output signal of the sensor. An apparatus for controlling a fuel injection system, characterized in that means are provided for increasing it until it is detected that it has been done.