JPH09256893A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid deterioration of the control accuracy of the air-fuel ratio by the fuel pressure fluctuation caused by the delay in the response of the fuel pressure control when the fuel injection pulse duration is changed. SOLUTION: The change ΔTi of the injection pulse duration Ti is operated (S2). The basic target fuel pressure PBA is corrected based on the coefficient C set according to the engine speed correlated to the discharge of a fuel pump to be driven by an engine and the change ΔTi, and the final target fuel pressure PS (PS=PBA+C×ΔTi) is set (S3). The actual fuel pressure P detected by the fuel pressure sensor is compared with the target fuel pressure PS, and the return quantity of the return fuel is adjusted (S4-S6) in the direction in which the fuel pressure P is brought close to the target fuel pressure PS.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to a technique for compensating a response delay of fuel pressure control with respect to a sudden change in injection pulse width.

[0002]

2. Description of the Related Art Conventionally, a fuel injection valve for injecting fuel directly into a combustion chamber of an engine is provided, and fuel is injected in the latter stage of a compression stroke in order to suppress the dispersion of the fuel and supply the fuel near the spark plug. A direct injection type (cylinder injection type) gasoline engine is known (see Japanese Patent Laid-Open No. 30420/1985).

[0003]

By the way, in the above direct injection type gasoline engine, in order to inject fuel directly into the combustion chamber in the compression stroke, high pressure fuel is injected into the fuel injection valve as compared with the case of intake port injection. Need to supply. Therefore, the direct-injection gasoline engine has a characteristic that the injection amount per unit time is large and the required fuel flow rate changes largely due to the change of the injection pulse width.

Therefore, for example, when the injection pulse width sharply increases during acceleration, the fuel pressure falls below the target pressure as shown in FIG. Since the injection amount decreases, the desired fuel amount corresponding to the injection pulse width cannot be injected, and the air-fuel ratio may become lean.

The present invention has been made in view of the above problems, and it is possible to prevent the pressure of the fuel supplied to the fuel injection valve from fluctuating due to the response delay of the fuel pressure adjustment during the transient operation, and to control the air-fuel ratio. The purpose is to improve accuracy.

[0006]

Therefore, in the invention according to claim 1, while supplying fuel of a predetermined pressure to the fuel injection valve, the fuel injection is performed based on the injection pulse width calculated according to the engine operating condition. In a fuel injection control device for an internal combustion engine configured to intermittently open a valve, the fuel injection control device predicts a change in fuel pressure due to a change in the injection pulse width and suppresses the change in fuel pressure. The pressure of the fuel supplied to the valve is configured to be corrected in advance.

According to this structure, when a change in the fuel pressure is predicted due to a change in the injection pulse width, the injection pulse is corrected by making a correction in advance of the change in the fuel pressure before the fuel pressure actually changes. Suppresses fuel pressure fluctuations due to width changes. The invention according to claim 2 is configured as shown in FIG. In FIG. 1, the injection control means intermittently drives the fuel injection valve to open based on the injection pulse width calculated according to the engine operating conditions.

Further, the fuel pressure detecting means detects the pressure of the fuel supplied to the fuel injection valve, and the fuel pressure feedback control means makes the fuel pressure detected by the fuel pressure detecting means close to the target pressure. Feedback control the pressure. On the other hand, the fuel pressure change predicting means predicts the change amount of the fuel pressure due to the change of the injection pulse width, and the target pressure correcting means corrects the target pressure according to the change amount predicted by the fuel pressure change predicting means.

According to this structure, the feedback control is performed so that the actual fuel pressure approaches the target pressure, but when it is predicted that the fuel pressure will change with the change of the injection pulse width, such change is suppressed. The target pressure is corrected in advance in a possible direction to prevent the fuel pressure from varying due to the response delay of the fuel pressure feedback control.

According to the third aspect of the present invention, the fuel pressure change predicting means calculates the change amount of the injection pulse width as a value correlated with the predicted change amount of the fuel pressure. According to such a configuration, when the change in the injection pulse width is large, it is estimated that the fuel pressure fluctuation will be larger, so that the change in the fuel pressure generated by the change in the injection pulse width can be reliably predicted.

According to another aspect of the present invention, the fuel pressure change predicting means calculates the change amount of the signal that causes the change of the injection pulse width as a value correlated with the predicted change amount of the fuel pressure. And According to such a configuration, it is possible to execute the fuel pressure correction in consideration of the change in the injection pulse width in advance before the change in the injection pulse width is detected, and it is possible to further advance the fuel pressure control.

According to the fifth aspect of the present invention, the signal that causes the change of the injection pulse width is the request signal for the engine output torque. According to such a configuration, when it is required to change the engine output torque due to a change in the air-fuel ratio and / or the intake air amount, for example, a torque increase or torque for alleviating a shift shock in an automatic transmission combined with the engine. When the air-fuel ratio is changed or the intake air amount is changed by a down request signal or a torque down request signal associated with traction control that avoids slipping of the drive wheels, the injection pulse is output according to the torque request signal. Since the width changes, it is possible to execute the fuel pressure correction in consideration of the change in the injection pulse width in advance.

The request signal for the engine output torque is as follows:
In addition to the signals for alleviating the shift shock and for avoiding the slip, an air-fuel ratio enrichment request signal for ensuring acceleration performance, an accelerator operation signal, etc. are included. In a sixth aspect of the invention, the signal that causes the change of the injection pulse width is the detection signal of the throttle valve opening of the engine.

According to such a configuration, the intake air amount of the engine is adjusted by the throttle valve, and the injection pulse width is determined according to the intake air amount. Therefore, the change in the injection pulse width is preempted and the fuel pressure correction is executed. It becomes possible. In the invention according to claim 7, the fuel pump for supplying the fuel to the fuel injection valve is an engine-driven pump, and the fuel pressure change predicting means has a larger fuel pressure change amount as the engine rotation speed is lower. As a result, the change amount is predicted.

According to this structure, even if the amount of change in the injection pulse width is the same, if the engine speed is low and the discharge amount of the fuel pump is small, the fuel pressure will change more greatly than during high speed rotation. The change in fuel pressure due to the change in injection pulse width can be accurately predicted.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.
Description will be given based on the attached drawings. In FIG. 2 showing the system configuration of the fuel system, a fuel injection valve 1 is provided facing each combustion chamber of an internal combustion engine (not shown). In the present embodiment, a case of a direct injection type (cylinder injection type) gasoline engine equipped with the fuel injection valve 1 facing each combustion chamber will be described, but the present invention is not limited to this. Also applicable to intake port injection type gasoline engine.

The fuel injection valve 1 is an electromagnetic solenoid type fuel injection valve in which a solenoid is energized to open the valve, and energization is stopped to close the valve.
At 0, the engine is driven by receiving an injection pulse signal having a pulse width set according to the engine operating condition and opening the valve at a preset injection timing during the compression stroke for a time corresponding to the pulse width, for example. Fuel, which is pressure-fed from the high-pressure fuel pump 2 through the high-pressure fuel pipe 4 and is adjusted to a predetermined high pressure by the high-pressure side pressure regulator 3, is intermittently injected and supplied into the engine combustion chamber.

Although only one fuel injection valve 1 is shown in FIG. 2, it is assumed that a plurality of fuel injection valves 1 facing each combustion chamber are connected to the high-pressure fuel pipe 4, respectively. The high-pressure fuel pipe 4 includes the high-pressure side pressure regulator 3 for adjusting the fuel pressure in the high-pressure fuel pipe 4 to a desired value, and the fuel in the high-pressure fuel pipe 4 so that the fuel pressure does not become too high. The fuel, which is communicated with the safety valve 5 for restricting the pressure but becomes surplus due to these pressure regulating operations, returns to the fuel tank 10 via the fuel return pipe 7 provided with the low pressure side pressure regulator 9. It is supposed to be.

Here, the low pressure side pressure regulator 9 is a mechanical pressure regulator that opens and closes the opening toward the fuel return pipe 7 depending on the balance between the set load and the fuel pressure by the elastic body. 3 is composed of an electronic pressure regulator that controls the flow of fuel to the fuel return pipe 7 side by an electromagnetic opening / closing valve that opens / closes in response to a control signal from the control unit 20 as described later.

In the high-pressure fuel pump 2, the fuel sucked up from the fuel tank 10 by the electric feed pump 11 is passed through a low-pressure fuel supply pipe 6 in which a check valve, a fuel filter and the like (not shown) are interposed. Is controlled to a predetermined feed pressure and supplied. The adjustment of the feed pressure is performed by the low-pressure side pressure regulator 9 which communicates with the low-pressure fuel supply pipe 6 via a bypass pipe 8.

The high-pressure fuel pipe 4 is provided with a fuel pressure sensor 12 (fuel pressure detecting means) for detecting the fuel pressure P in the high-pressure fuel pipe 4. And this fuel pressure sensor 12
Is inputted to the control unit 20. The control unit 20 controls the high pressure side pressure so that the fuel supply pressure to the fuel injection valve 1 detected by the fuel pressure sensor 12 approaches the target pressure. The open / close control signal sent to the electromagnetic open / close valve forming the regulator 3 is feedback-controlled (fuel pressure feedback control means).

The control unit 20 is a CP
It is composed of a microcomputer including U, ROM, RAM, an A / D converter, an input / output interface, etc., receives input signals from various sensors, and outputs to the fuel injection valve 1 by arithmetic processing based on these signals. The pulse width of the ejection pulse signal to be output is determined. The various sensors include, in addition to the fuel pressure sensor 12 described above, an air flow meter 21 for detecting the intake air flow rate Q of the engine, a reference angle signal REF for each reference angle position, and a unit angle signal for each 1 ° or 2 °. A crank angle sensor 22 that outputs POS, a water temperature sensor 23 that detects the cooling water temperature of the engine, and the like are provided.

The engine speed Ne is calculated in the control unit 20 based on the detection signal from the crank angle sensor 22. Control unit 20
The CPU of the microcomputer built into the
According to the above program, the injection pulse width T based on the intake air flow rate Q, the engine rotation speed Ne, the cooling water temperature Tw, etc.
i is calculated, and an injection pulse signal having the injection pulse width Ti is output to the fuel injection valve 1 at a predetermined injection timing synchronized with the engine rotation (injection control means).

Here, the state of the fuel pressure control by the control unit 20 will be described in detail with reference to the flowchart of FIG. The functions as the fuel pressure feedback control means, the fuel pressure change prediction means, and the target pressure correction means are provided in software by the control unit 20 as shown in the flowchart of FIG.

In the flow chart of FIG. 3, first, in step 1 (denoted by S1 in the figure; the same applies hereinafter), the most recently calculated injection pulse width Ti is read. In the next step 2, the injection pulse width Ti _OLD read in step 1 during the previous execution of this routine is subtracted from the latest injection pulse width Ti read in this time in step 1,
A change amount ΔTi of the injection pulse width Ti is calculated.

In step 3, a value obtained by adding a correction amount corresponding to the change amount ΔTi to the basic target fuel pressure P _BA is set as the final target fuel pressure P _S. Specifically, the final target fuel pressure P _S is calculated as P _S = P _BA + C × ΔTi. Incidentally, C (> 0) is a coefficient for converting the variation amount ΔTi of the injection pulse width Ti into a fuel pressure correction value.

If the target pressure P _S is set as described above, when the injection pulse width Ti increases and changes,
Variation ΔTi is more basic target fuel pressure P _BA Gayori greatly increase modified when large, conversely, the injection pulse width Ti during reduction change of the amount of change ΔTi enough when the absolute value is larger basic target fuel pressure P _BA Gayori It will be reduced and corrected. The required fuel flow rate increases when the injection pulse width Ti changes, but in the fuel pressure feedback control using the fuel pressure sensor 12, a response delay occurs because the return fuel amount is controlled after the fuel pressure decreases. . Therefore,
When the injection pulse width is increasing and the fuel pressure decrease is predicted due to the delay of the feedback control, the above C ×
By increasing the target fuel pressure P _S in advance by using ΔTi as a predicted value of the fuel pressure decrease, it is possible to suppress the decrease of the fuel pressure due to the increase change of the injection pulse width.

Similarly, when the injection pulse width Ti decreases, an increase change in the fuel pressure due to a response delay in feedback control is suppressed by reducing the target pressure in advance. The coefficient C may be a fixed value,
As shown in FIG. 4, when the engine rotation speed Ne at which the discharge amount of the high-pressure fuel pump 2 driven by the engine decreases, becomes lower,
The coefficient C may be set larger. That is, even if the change amount of the injection pulse width is the same, if the engine rotation speed is low and the discharge amount of the fuel pump is small, the fuel pressure changes more greatly than at the time of high rotation with a large discharge amount. By setting the coefficient C to be larger as the engine speed Ne is lower, the target pressure can be corrected and set according to the difference in the fuel pressure change due to the difference in the discharge amount.

In step 3, the target pressure P is set as described above.
_{When S} is set, in step 4, the detection result by the fuel pressure sensor 12 is compared with the target pressure P _S. If the actual fuel pressure is higher than the target, the process proceeds to step 5 to increase the return fuel amount by increasing the control signal to increase the opening degree of the electromagnetic on-off valve that constitutes the high pressure side pressure regulator 3. Change.

On the other hand, when the actual fuel pressure is lower than the target, the routine proceeds to step 6, where the opening degree of the electromagnetic on-off valve which constitutes the high pressure side pressure regulator 3 is further reduced in order to reduce the return fuel amount. To change the control signal. By the way, in the above, in order to suppress the fluctuation of the fuel pressure caused by the change of the injection pulse width, the target pressure is corrected and set in advance according to the change amount of the injection pulse width. If the target pressure is corrected by predicting the change in the fuel pressure based on the signal that becomes, it becomes possible to correct the fuel pressure without delay.

For example, in an engine having a structure in which the intake air flow rate is adjusted by a throttle valve provided in the intake system, the intake air flow rate changes due to a change in the opening of the throttle valve, and the injection pulse width changes accordingly. Then, the fuel pressure fluctuates. Therefore, by correcting the target pressure in advance according to the change in the throttle valve opening, it is possible to effectively suppress the fuel pressure fluctuation caused by the change in the injection pulse width.

Specifically, as shown in the flowchart of FIG. 5, the throttle valve opening TVO detected by a throttle sensor (not shown) is read (step 11), and the change amount ΔTVO of the opening TVO is calculated as the fuel pressure. It is calculated as a value correlated with the amount of change (step 12). Then, in step 12, as in step 3, the target pressure P _S is corrected and set according to the opening change amount ΔTVO (P _S =
P _BA + C × ΔTVO). That is, when the opening of the throttle valve is increasing and changing, the basic target fuel pressure P _BA is increased and corrected, and when the opening of the throttle valve is decreasing and changing, the basic target fuel pressure P _BA is decreased and corrected, The target pressure P _S is corrected so as to suppress the fuel pressure fluctuation due to the change of the injection pulse width due to the change of the throttle valve opening.

The fuel pressure sensor 1 is set to the target pressure P _S.
The feedback control is performed on the opening degree of the electromagnetic on-off valve that constitutes the high pressure side pressure regulator 3 so that the actual fuel pressure detected in 2 approaches.
6). In addition to the throttle valve opening, a signal for requesting engine output torque may be used as a signal that causes the injection pulse width to change.

The engine output torque request signal is associated with, for example, a torque up or torque down request signal for alleviating a shift shock in an automatic transmission combined with an engine, and a traction control for avoiding a slip of a driving wheel. When the air-fuel ratio or the intake air amount is changed according to the torque request signal such as a torque down request signal, the injection pulse width changes after the request signal changes (output). Since the fuel pressure fluctuates, the fuel pressure can be corrected without delay as compared with the case where the target pressure is set from the change amount of the injection pulse width Ti.

The flowchart of FIG. 6 shows the control for setting the target pressure in accordance with the torque request signal, and like the embodiment of the configuration for correcting and setting the target pressure using ΔTi and ΔTVO described above, First, the torque request signal Tr is read (step 21), and the torque request signal T is read.
A change amount ΔTr of r is calculated (step 22). here,
When the target air-fuel ratio, the throttle amount of the intake air flow rate (throttle valve opening control amount), and the like are specified according to the torque request signal Tr, the torque request is made for the specified target air-fuel ratio and throttle amount. It is preferable that the change amount ΔTr is used as the signal Tr and calculated as the change amount of the target air-fuel ratio or the throttle amount.

Further, the target output torque is set according to the accelerator opening, and the target throttle valve opening is set so that the target torque can be obtained, and the throttle valve is set to the actuator so that the target opening is reached. In an engine configured to control opening and closing with, the accelerator opening signal can be regarded as a torque request signal. When the change amount ΔTr of the torque request signal Tr is calculated as described above, the change amount ΔTr
Target pressure P _S (P _S = P _BA + C × ΔTr) according to Tr
Is corrected and set (step 23). Here, for example, when there is a change in the torque request signal in the direction of making the target air-fuel ratio smaller (richer), the change in the torque request signal causes an increase change in the injection pulse width. Therefore, when the target pressure P _S is set to be increased, and when there is a change in the torque request signal in the direction of increasing the intake throttle amount (reducing the air amount),
Since the change of the torque request signal causes the decrease of the injection pulse width, the target pressure P _S may be set to be decreased.

When the target pressure is corrected and set in accordance with the ΔTr, the solenoid on-off valve constituting the high pressure side pressure regulator 3 is opened so that the actual fuel pressure detected by the fuel pressure sensor 12 approaches the target pressure P _S. Feedback control of the degree (step 24 to step 26). The above ΔT
Even in the configuration in which the target fuel pressure is corrected and set based on the amount of change in the signal that causes the injection pulse width to change, such as VO and ΔTr, the coefficient C is set to the engine speed Ne.
The high-pressure fuel pump 2 that is driven by the engine by changing it according to
It is preferable that the target pressure is corrected and set in accordance with the difference in fuel pressure fluctuation due to the difference in the discharge amount.

[0038]

As described above, according to the invention described in claim 1 or 2, when the change of the fuel pressure is predicted by the change of the injection pulse width, the pressure of the fuel supplied to the fuel injection valve is adjusted. Since the correction is performed in advance, it is possible to avoid the deterioration of the air-fuel ratio control accuracy caused by the fuel pressure fluctuation due to the response delay of the fuel pressure control.

According to the third aspect of the present invention, the fuel pressure can be properly corrected based on the correlation between the change amount of the injection pulse width and the fuel pressure change amount, and the fuel pressure fluctuation can be satisfactorily avoided. is there. According to the invention of any one of claims 4 to 6, before the change in the injection pulse width is detected,
It is possible to execute the fuel pressure correction in consideration of the change in the injection pulse width in advance, and it is possible to perform the fuel pressure correction without delay.

According to the invention described in claim 7, there is an effect that the fuel pressure can be accurately corrected in response to the difference in the fuel pressure fluctuation due to the difference in the discharge amount of the fuel pump.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of the invention according to claim 2.

FIG. 2 is a system configuration diagram of a fuel system according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a state of fuel pressure control in the same embodiment.

FIG. 4 is a diagram showing a characteristic of a coefficient C used for correcting a target fuel pressure in the embodiment.

FIG. 5 is a flowchart showing another embodiment of fuel pressure control.

FIG. 6 is a flowchart showing another embodiment of fuel pressure control.

FIG. 7 is a time chart for explaining conventional problems.

[Explanation of symbols]

 1 Fuel injection valve 2 High pressure fuel pump 3 High pressure side pressure regulator 4 High pressure fuel piping 5 Safety valve 6 Low pressure fuel supply piping 7 Fuel return piping 8 Bypass piping 9 Low pressure side pressure regulator 10 Fuel tank 11 Fuel pump 11 Fuel pressure sensor 20 Control unit 21 Airflow Meter 22 Crank angle sensor 23 Water temperature sensor

Claims (7)

[Claims] 1. An internal combustion engine configured to supply fuel of a predetermined pressure to a fuel injection valve, while intermittently driving the fuel injection valve to open based on an injection pulse width calculated according to engine operating conditions. In a fuel injection control device for an engine, predicting a change in fuel pressure due to a change in the injection pulse width, and correcting the pressure of fuel supplied to the fuel injection valve in advance so as to suppress the change in fuel pressure. And a fuel injection control device for an internal combustion engine. 2. An injection control means for intermittently driving a fuel injection valve to open based on an injection pulse width calculated according to engine operating conditions, and a fuel pressure detection for detecting a pressure of fuel supplied to the fuel injection valve. Means, fuel pressure feedback control means for feedback-controlling the fuel pressure so that the fuel pressure detected by the fuel pressure detection means approaches a target pressure, and fuel pressure for predicting the amount of change in the fuel pressure due to the change in the injection pulse width. A fuel injection control device for an internal combustion engine, comprising: a change prediction unit; and a target pressure correction unit that corrects the target pressure according to the amount of change predicted by the fuel pressure change prediction unit. 3. The fuel for an internal combustion engine according to claim 2, wherein the fuel pressure change predicting means calculates the change amount of the injection pulse width as a value correlated with the predicted change amount of the fuel pressure. Injection control device. 4. The fuel pressure change predicting means calculates a change amount of a signal which causes a change in the injection pulse width as a value correlated with a predicted change amount of the fuel pressure. A fuel injection control device for an internal combustion engine as described above. 5. The fuel injection control device for an internal combustion engine according to claim 4, wherein the signal that is a factor for changing the injection pulse width is a request signal for engine output torque. 6. The fuel injection control device for an internal combustion engine according to claim 4, wherein the signal which is a factor for changing the injection pulse width is a detection signal of a throttle valve opening of the engine. 7. A fuel pump for supplying fuel to said fuel injection valve is an engine-driven pump, and said fuel pressure change predicting means is such that the lower the engine speed, the greater the amount of change in fuel pressure. The fuel injection control device for an internal combustion engine according to any one of claims 2 to 6, wherein the change amount is predicted.