JPH1047189A - Fuel supply device for internal combustion engine and control method therefor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize a stable fuel pressure control in a fuel supply device that controls the current of a fuel pump by suppressing the influence of the fuel pump over time. SOLUTION: The process proceeds to step 107 only when the integrated operation time exceeds 500 hours and the vehicle is in a steady running state, reads the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor, and determines whether the air-fuel ratio is richer than the target air-fuel ratio in the subsequent step 108. Determine whether it is lean. In the case of rich, the duty ratio Duty (%) for determining the control current value of the fuel pump is offset by C in the fuel pressure decreasing direction (step 109), the fuel injection amount is reduced, and the air-fuel ratio is changed from rich to stoichiometric. to correct. In the case of lean, the duty ratio Duty is offset by C in the fuel pressure increasing direction (step 110),
The air-fuel ratio is corrected from lean to stoichiometric by increasing the fuel injection amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel supply apparatus for an internal combustion engine and a control method for controlling the pressure of fuel supplied from a fuel pump to a fuel injection valve by controlling a drive motor of a fuel pump. It is about.

[0002]

2. Description of the Related Art Conventionally, this type of fuel supply device is provided with a fuel pressure sensor for detecting the pressure of fuel in a fuel pipe (hereinafter referred to as "fuel pressure"), and makes the fuel pressure equal to a target fuel pressure based on the detection result. In many cases, the drive voltage of the fuel pump (voltage applied to the drive motor) is feedback-controlled.
However, such a voltage control method requires a fuel pressure sensor, and thus has a disadvantage of increasing costs.

[0003]

Therefore, it has been considered to adopt a current control method for controlling the fuel pressure by controlling the current value supplied to the drive motor of the fuel pump. In this current control method, since the fuel pressure can be controlled to a constant value by the control current value (in other words, the fuel pressure is determined by the control current value), an inexpensive fuel pressure control system that does not require fuel pressure feedback control using a fuel pressure sensor can be realized. There are advantages.

However, if the characteristics of the fuel pump change over time, the relationship between the control current value and the fuel pressure (ie, the fuel pressure control characteristic) shifts. Therefore, even with the same control current value,
The actual fuel pressure deviates from the original target fuel pressure as the fuel pump changes over time. Such a shift in fuel pressure causes a shift in the fuel injection amount of the fuel injection valve, and eventually causes a shift in the air-fuel ratio.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and accordingly, has as its object to meet the demand for cost reduction by employing a current control method, and to reduce the influence of the aging of the fuel pump over time. It is an object of the present invention to provide a fuel supply device for an internal combustion engine and a control method thereof, which can realize suppressed and stable fuel pressure control.

[0006]

When the fuel pressure deviates from the original target fuel pressure due to the temporal change of the fuel pump, the fuel injection valve is controlled on the assumption that the fuel pressure is controlled to the target fuel pressure. The fuel injection amount shifts, and as a result, the air-fuel ratio of the exhaust gas shifts to rich or lean.

Attention is paid to the relationship between the deviation of the fuel pressure control characteristic due to the temporal change of the fuel pump and the deviation of the air-fuel ratio of the exhaust gas, and the fuel supply apparatus for an internal combustion engine and the control thereof according to claims 1 and 6 of the present invention. In the method, when controlling a current value supplied to a DC motor that drives a fuel pump, information about an air-fuel ratio of exhaust gas discharged from an internal combustion engine is detected by air-fuel ratio information detecting means, and fuel is detected based on the detected value. The control current value of the DC motor of the pump is corrected by the control means.

In this manner, by detecting the deviation of the air-fuel ratio of the exhaust gas, the deviation of the fuel pressure control characteristic due to the temporal change of the fuel pump is indirectly detected, and the direct current of the fuel pump is determined based on the detected value. By correcting the control current value of the motor, it is possible to perform fuel pressure control in which a shift in fuel pressure control characteristics due to a change over time of the fuel pump is corrected. This makes it possible to realize stable fuel pressure control that suppresses the influence of changes over time of the fuel pump. Moreover, the air-fuel ratio information detecting means for detecting the air-fuel ratio information of the exhaust gas may use an existing air-fuel ratio sensor, oxygen sensor, etc., which has been conventionally used for the air-fuel ratio feedback control of the internal combustion engine. There is no need to provide a sensor. In addition, in the present invention, since the fuel pressure is controlled by the current control method, an inexpensive fuel pressure control system can be realized without requiring a fuel pressure sensor.

By the way, it is needless to say that the change with time of the fuel pump need not be considered in a new vehicle having a small integrated traveling distance. In addition, in a new vehicle, the operation of the internal combustion engine system is not stabilized unless a certain amount of break-in operation is performed, and the air-fuel ratio of the exhaust gas is likely to vary. Therefore, the deviation of the air-fuel ratio at the time of a new vehicle is not due to the change over time of the fuel pump, but mainly due to the variation in the operation of the internal combustion engine system at the time of a new vehicle. Then, on the contrary, the fuel pressure control characteristics may be deteriorated.

Therefore, it is preferable that the correction of the control current value is started after the accumulated traveling distance of the vehicle exceeds a predetermined distance. With this configuration, it is possible to perform appropriate correction when the control current value needs to be corrected without being affected by the variation in the operation of the internal combustion engine system when the vehicle is new.

Alternatively, the correction of the control current value may be started after the integrated operation time of the vehicle exceeds a predetermined time. With this, it is possible to perform appropriate correction when the control current value needs to be corrected without being affected by the variation in the operation of the internal combustion engine system when the vehicle is new.

Further, when the operating state of the internal combustion engine is in a transient state, that is, during acceleration / deceleration, the air-fuel ratio of the exhaust gas tends to shift even if the fuel pump has not deteriorated over time. Therefore, if the control current value is corrected based on the air-fuel ratio information at the time of the transient operation, the fuel pressure control characteristics may be rather deteriorated. On the other hand, when the operating state of the vehicle is in a steady state, the air-fuel ratio of the exhaust gas is relatively stable, and the influence of the fuel pressure deviation due to the deterioration over time of the fuel pump appears on the air-fuel ratio of the exhaust gas.

Therefore, it is preferable that the control current value is corrected during a period in which the operating state of the vehicle is in a steady state. In this way, the correction control of the control current value is not affected by the deviation of the air-fuel ratio during the transient operation. Value correction can be performed.

It is preferable that the correction characteristic of the control current value has an offset in the opposite direction depending on whether the air-fuel ratio detected by the air-fuel ratio information detecting means is lean or rich. For example, when the air-fuel ratio is lean, if the correction characteristic of the control current value is offset in the fuel pressure increase direction, the fuel injection amount is increased by the fuel pressure increase, and the air-fuel ratio is changed from lean to stoichiometric (λ = 1). Can be corrected. Further, when the air-fuel ratio is rich, if the correction characteristic of the control current value is offset in the fuel pressure lowering direction, the fuel injection amount is reduced by the fuel pressure lowering, and the air-fuel ratio can be corrected from the rich to the stoichiometric direction.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment (1) of the present invention will be described below with reference to FIGS. A fuel pump 12 is provided in the fuel tank 11, and a filter 13 is attached to a suction port of the fuel pump 12. The fuel pump 12 includes a DC motor (not shown) as a drive source. The fuel discharged from the fuel pump 12 is
The fuel is sent to the delivery pipe 18 through the route of the fuel pipe 15 → the fuel filter 16 → the fuel pipe 17.
The fuel is injected into each cylinder from the fuel injection valve 19 of each cylinder attached to the cylinder 8. The fuel piping system supplies excess fuel from the delivery pipe 18 to the fuel tank 11 to simplify the configuration.
The return-less piping configuration eliminates the return piping.

An electronic control unit (hereinafter, referred to as "ECU") 20 for performing overall control of an internal combustion engine (hereinafter, referred to as "engine") is mainly composed of a microcomputer and reads signals output from various sensors 21 to 25. . Here, the engine speed sensor 21 outputs a pulse signal (engine speed signal) Ne having a frequency corresponding to the engine speed, and the water temperature sensor 22 detects the engine coolant temperature. The air-fuel ratio sensor 23 is attached to an exhaust pipe (not shown) of the engine and outputs a voltage signal that changes linearly according to the air-fuel ratio of the exhaust gas. Play a role. The vehicle speed sensor 24 detects the vehicle speed and outputs an integrated operation time counter 25.
Accumulates the vehicle driving time up to the present.

The ECU 20 includes an engine speed sensor 2
1. Calculate ignition timing, fuel injection amount, target fuel pressure, etc. based on output signals of various sensors that detect the engine operating state such as a water temperature sensor 22 and an air-fuel ratio sensor 23, and drive the fuel injection valve 19 of each cylinder. At the same time, the constant current control circuit 26 for driving the DC motor of the fuel pump 12 is controlled.

As shown in FIG. 2, the constant current control circuit 26 uses a battery 27 mounted on a vehicle as a power source,
A control signal (duty signal indicating a target fuel pressure) input from U20 is shaped by an input processing circuit 28, which is converted into a target current value by a target current value conversion circuit 29, and a duty ratio is set by a duty ratio setting circuit 30. The ratio Duty is set, and the drive circuit 31 is driven by the duty ratio to drive the DC motor of the fuel pump 12 by the PWM method, and the control current value actually flowing to the DC motor is detected by the current detection circuit 32 to detect the control current. Feedback control is performed so that the control current value matches the target current value.
The target current value is corrected by the current correction circuit 34 based on the drive voltage detected in step 3. The engine control circuit 20
May be used as the control signal instead of the duty signal.

The ECU 20 executes a fuel pressure control routine shown in FIG. 3 to function as a control means for performing a fuel pressure control in which a deviation of the fuel pressure control characteristic due to a temporal change of the fuel pump 12 is corrected. The fuel pressure control routine of FIG. 3 is executed by interruption processing at predetermined time intervals or at predetermined crank angle intervals after an ignition switch (not shown) is turned on. When the processing of this routine is started, first, in step 101, the integrated operation time up to the present time integrated by the integrated operation time counter 25 is read, and in the following step 102, it is determined whether the integrated operation time has exceeded 500 hours, for example. Is determined, and 500
If the time has not elapsed, the routine proceeds to step 103, where the injection pulse width (injection time of the fuel injection valve 19) Ti is calculated by the following equation, and this routine ends.

Ti = Tp × Fc + Tv (1) Here, Tp is a basic injection pulse width, which is obtained from a map of an engine speed and an intake manifold. Tv
Is the invalid injection pulse width determined by the battery voltage. Fc is various correction coefficients, which are obtained by the following equations.

Fc = g (FET, FAD, F0, FL, FH, FIS) (2) FET: correction coefficient related to engine temperature FAD: correction coefficient during acceleration / deceleration operation F0: feedback correction to stoichiometric air-fuel ratio Coefficient FL: Correction coefficient by learning control FH: Correction coefficient at high load / high speed operation FIS: Idle stabilization correction coefficient

Thereafter, when the accumulated operation time exceeds 500 hours, the routine proceeds from step 102 to step 104, where the injection pulse width Ti is calculated. Also in this case, the injection pulse width Ti is calculated by the above equation (1). In this case, the air-fuel ratio feedback correction and the learning control are stopped, the feedback correction coefficient F0 is set to 0, and the correction coefficient FL by the learning control is The value when the accumulated operation time reaches 500 hours is used. This is because the air-fuel ratio is corrected by a fuel pressure correction described later.

Then, in the next step 105, the vehicle speed and the engine speed (vehicle running state) output from the vehicle speed sensor 24 and the engine speed sensor 21 are read, and in a succeeding step 106, it is determined whether or not the vehicle is running normally. . When the vehicle is not traveling in a steady state, that is, during a transient operation, the air-fuel ratio of the exhaust gas tends to shift even if the fuel pump 12 has not deteriorated over time. Therefore, if the control current value of the fuel pump 12 is corrected based on the air-fuel ratio during the transient operation, the fuel pressure control characteristics may be rather deteriorated. In consideration of this point, when the vehicle is not traveling normally, the routine ends without performing the processing after step 107.

On the other hand, during steady running, step 1
From step 06, the process proceeds to step 107, in which the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor 23 is read, and in step 108, it is determined whether the air-fuel ratio is richer or leaner than the target air-fuel ratio. If it is rich, the process proceeds to step 109, where the duty ratio Duty for determining the control current value of the fuel pump 12 is set.
(%) Is corrected by the following equation.

Duty = m × Pt−C (3) where m is the target fuel pressure and the duty ratio Du shown in FIG.
The slope of a straight line that determines the relationship with ty, Pt is the target fuel pressure, C
Is an offset. When the air-fuel ratio is rich, the duty ratio Duty is offset by C in the fuel pressure decreasing direction (minus direction on the vertical axis in FIG. 4) according to the above equation (3), so that the fuel injection amount decreases due to the fuel pressure decrease. , The air-fuel ratio is corrected from rich to stoichiometric (λ = 1).

If the air-fuel ratio is lean, the process proceeds from step 108 to step 110, where the duty ratio Duty (%) for determining the control current value is corrected by the following equation. Duty = m × Pt + C (4)

That is, when the air-fuel ratio is lean, the duty ratio Duty is offset by C in the fuel pressure increasing direction (positive direction on the vertical axis in FIG. 4) according to the above equation (4). The injection amount increases, and the air-fuel ratio is corrected from lean to stoichiometric.

By executing the above-described fuel pressure control routine shown in FIG. 3, it is possible to perform fuel pressure control in which the deviation of the fuel pressure control characteristics due to the temporal change of the fuel pump 12 is corrected, and the influence of the temporal change of the fuel pump 12 is suppressed. Stable fuel pressure control can be realized. In addition, the air-fuel ratio information detecting means for detecting the air-fuel ratio information of the exhaust gas may use the existing air-fuel ratio sensor 23 conventionally used for the air-fuel ratio feedback control of the engine. There is no. In addition, in the above embodiment (1), since the fuel pressure control is performed by the current control method, a fuel pressure sensor is not required, and an inexpensive fuel pressure control system can be realized.

Further, in the above-mentioned embodiment (1), the correction of the control current value (Duty) is started after the integrated operation time of the vehicle exceeds a predetermined time (500 hours). In this case, an appropriate correction can be performed when the control current value needs to be corrected without being affected by the variation in the operation. In other words, when a new vehicle is used, the operation of the engine system will not be stable without a certain amount of break-in operation, and the air-fuel ratio of the exhaust gas tends to fluctuate. Therefore, the correction of the control current value must be started after the operation of the engine system is stabilized. If this is the case, it is possible to appropriately correct the deviation of the fuel pressure control characteristics due to the temporal change of the fuel pump. Note that the time for starting the correction of the control current value (Duty) is not limited to 500 hours, and may be changed as appropriate.

In the embodiment (1), since the control current value is corrected during steady running, the correction control of the control current value is not affected by the deviation of the air-fuel ratio at the time of transient operation. An appropriate correction of the control current value can be performed at the time of steady running in which the influence of the deterioration over time of the pump appears in the air-fuel ratio of the exhaust gas.

Next, the fuel pressure control in the embodiment (2) of the present invention will be described with reference to FIG. The fuel pressure control routine of FIG. 5 is executed by interruption processing at predetermined time intervals or at predetermined crank angle intervals after an ignition switch (not shown) is turned on. When the processing of this routine is started, first, in step 201, the accumulated mileage to date accumulated by the accumulated odometer (not shown) is read, and the cooling water temperature,
Read the increase after startup, warm-up, and battery voltage. Thereafter, in step 202, the accumulated traveling distance is, for example, 10 km.
Is determined. Here, the accumulated mileage 10
km is an integrated traveling distance at which correction of the control current value (Duty) is started, and is not limited to 10 km, and may be changed as appropriate. If the accumulated mileage is 1
If it does not exceed 0 km, proceed to step 203,
The injection pulse width Ti is calculated by the above-described equations (1) and (2), and this routine ends.

Thereafter, when the accumulated traveling distance exceeds 10 km, the routine proceeds from step 202 to step 204, where the injection pulse width Ti is calculated. Various correction coefficients Fc used for calculating the injection pulse width Ti are obtained by the following equations. Fc = g (FET, FAD, F0 / 2, FL / 2, FH, FIS) (2 ′)

In this embodiment (2), the correction of the air-fuel ratio is performed by both the correction of the fuel pressure and the correction of the injection pulse, which will be described later.
In addition, the correction coefficient FL by the learning control is halved, and is reflected on various correction coefficients Fc. Needless to say, the correction of the air-fuel ratio may be performed only by the fuel pressure correction as in the above-described embodiment (1).

Then, in the next step 205, the vehicle speed and the engine speed (vehicle running state) are read, and in the following step 206, it is determined whether or not the vehicle is traveling in a steady state. This routine is terminated without performing.

In the case of steady running, the process proceeds to step 207, and after the warm-up is completed (cooling water temperature ≧ 80 ° C. and increase after starting =
0) and the battery voltage is normal (battery voltage ≧ 11.
5V), and if this condition is not satisfied, the vehicle operation state and the operation state of the fuel pump 12 are not stable, so this routine is terminated without performing the processing of step 208 and thereafter. I do.

Therefore, only after the warm-up is completed and when the battery voltage is normal, the routine proceeds to step 208, where the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor 23 is read. Or lean. If it is rich, the routine proceeds to step 210, where the duty ratio Duty (%) for determining the control current value of the fuel pump 12 is corrected by the following equation.

Duty = m × Pt−C ′ (3 ′) Here, C ′ is an offset, and the embodiment (1)
(C ′ = C /
2). This is because the air-fuel ratio is corrected by both the fuel pressure correction and the injection pulse correction. m is the slope of a straight line that determines the relationship between the target fuel pressure and the duty ratio Duty shown in FIG. 4, and Pt is the target fuel pressure.

If the air-fuel ratio is lean, the process proceeds from step 209 to step 211, where the duty ratio Duty (%) for determining the control current value is corrected by the following equation. Duty = m × Pt + C ′ (4 ′)

By performing the above processing, it is possible to perform fuel pressure control in which the deviation of the fuel pressure control characteristics due to the temporal change of the fuel pump 12 is corrected, and to realize stable fuel pressure control in which the influence of the temporal change of the fuel pump 12 is suppressed. be able to.

In each of the above embodiments, the air-fuel ratio information detecting means for detecting the air-fuel ratio of the exhaust gas is
Although the air-fuel ratio sensor 23 whose output voltage changes linearly according to the air-fuel ratio is used, an oxygen sensor whose output voltage is inverted depending on whether the air-fuel ratio is rich or lean may be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an entire system according to an embodiment (1) of the present invention;

FIG. 2 is a block diagram illustrating a configuration of a constant current control circuit.

FIG. 3 is a flowchart showing a flow of a process of a fuel pressure control routine according to the embodiment (1).

FIG. 4 is a diagram showing a relationship between a target fuel pressure and a duty ratio Duty.

FIG. 5 is a flowchart showing the flow of processing of a fuel pressure control routine according to the embodiment (2).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Fuel tank, 12 ... Fuel pump, 15, 17 ... Fuel piping, 18 ... Delivery pipe, 19 ... Fuel injection valve, 2
0: ECU (control means), 21: engine speed sensor, 22: water temperature sensor, 23: air-fuel ratio sensor (air-fuel ratio upper detecting means), 24: vehicle speed sensor, 25: integrated operation time counter, 26: constant current control circuit.

Claims (6)

[Claims] 1. A fuel supply device for an internal combustion engine, wherein a pressure of fuel supplied from a fuel pump to a fuel injection valve is controlled by controlling a current value supplied to a DC motor for driving a fuel pump. Air-fuel ratio information detection means for detecting information on the air-fuel ratio of exhaust gas discharged from the engine; control means for correcting a control current value of a DC motor of the fuel pump based on output information of the air-fuel ratio information detection means; A fuel supply device for an internal combustion engine, comprising: 2. The fuel supply device for an internal combustion engine according to claim 1, wherein the control means starts correcting the control current value after an accumulated traveling distance of the vehicle exceeds a predetermined distance. 3. The fuel supply device for an internal combustion engine according to claim 1, wherein the control means starts correcting the control current value after an integrated operation time of the vehicle exceeds a predetermined time. 4. The internal combustion engine according to claim 1, wherein the control unit corrects the control current value during a period when the driving state of the vehicle is in a steady state. Fuel supply device. 5. The correction characteristic of the control current value by the control means is provided with an offset in the opposite direction depending on whether the air-fuel ratio detected by the air-fuel ratio information detection means is lean or rich. The fuel supply device for an internal combustion engine according to any one of claims 1 to 4. 6. A control method for a fuel supply device for an internal combustion engine, which controls a pressure of fuel supplied from a fuel pump to a fuel injection valve by controlling a current value supplied to a DC motor for driving a fuel pump. A method for controlling a fuel supply device for an internal combustion engine, comprising detecting information relating to an air-fuel ratio of exhaust gas discharged from an engine, and correcting a control current value of a DC motor of the fuel pump based on the detected value.