JP3340912B2 - Fuel injection amount control device for starting internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection amount control at the start of an internal combustion engine, and more particularly to a technique for controlling a fuel injection amount by estimating a shortage of fuel pressure at the start by a high-pressure fuel pump or the like.

[0002]

2. Description of the Related Art In recent years, in a spark ignition type engine such as a gasoline engine, research has been conducted on a system in which an injection hole of a fuel injection valve is installed facing a combustion chamber and fuel is directly injected into the combustion chamber by the fuel injection valve. According to the spark ignition type direct injection internal combustion engine, as compared with a premixed type spark ignition engine having a fuel injection valve at an intake port, deterioration of transient operation characteristics due to fuel transport delay and emission composition There is an advantage that the deterioration of can be suppressed.

[0003] In this type of engine, a high-pressure fuel pump is provided in the middle of a fuel supply passage as a method of increasing the fuel injection pressure in order to enhance the atomization effect of the fuel (Japanese Patent Application Laid-Open No. Hei 5 (1993) -107).
-321783 etc.).

[0004]

By the way, in the high-pressure fuel pump of the internal combustion engine, the fuel pressure does not increase to the pressure adjusted by the pressure regulator at the time of starting. Insufficient injection volume. For this reason, it has been considered to control the fuel injection amount by detecting the fuel pressure with a fuel pressure sensor and correcting the injection time (pulse width) of the fuel injection valve with the fuel pressure.

However, the region where the fuel pressure at the time of starting is low is a region where the accuracy of the fuel pressure sensor is originally poor, so that there is a problem that the accuracy cannot be obtained by correcting the fuel injection amount based on the detection value of the fuel pressure sensor. . The present invention has been made in view of such a conventional problem, and has as its object to improve the fuel injection amount control accuracy by accurately estimating the fuel pressure at the time of starting.

[0006] In this end, the invention according to claim 1, the fuel discharged from the fuel pump is supplied to the fuel injection valve via the fuel piping, an internal combustion engine for fuel injection into the engine from the fuel injection valve, fuel pipe A means for detecting the fuel pressure inside
When the engine is started, the fuel pressure in the fuel pipe is calculated from the remaining fuel pressure in the fuel pipe before the rotation of the fuel pump, the cumulative number of rotations of the fuel pump, the rotation speed of the fuel pump, and the fuel injection valve. And the fuel consumption is estimated by a model formula using the parameters as parameters, and the fuel injection amount at the time of starting is controlled based on the estimated fuel pressure.

(Operation / Effect) In this way, the fuel pressure rise characteristic after the fuel pump starts operating at the time of starting is predicted by a model formula using various state quantities of the fuel system as parameters, and the fuel piping The fuel pressure in the fuel cell can be accurately estimated, and the fuel injection amount at the time of starting can be controlled with high accuracy based on the estimated fuel pressure.

The invention according to claim 2 is provided with means for detecting the fuel pressure in the fuel pipe, and when the fuel pressure is higher than a predetermined value, the detected fuel pressure is expressed by the model formula. The present invention is characterized in that the model formula is modified in comparison with the estimated fuel pressure. (Operation / Effect) Since the accuracy of the detected value of the fuel pressure is obtained when the fuel pressure is high, the detected value is compared with the estimated value of the model formula to correct the model formula so that the model formula is used. The fuel pressure at the time of starting can be estimated with higher accuracy, and the highly accurate estimation can be maintained even with the lapse of time.

[0009]

Further, the invention according to claim 3 is characterized in that the fuel system includes a fuel pressure adjusting means for regulating the fuel pressure in the fuel pipe to a predetermined value or less. (Action /
Effect) When the rotation speed of the fuel pump increases and the discharge capacity becomes sufficient, the increase in the fuel pressure is regulated to a predetermined value by the fuel pressure adjusting means, and the fuel is injected by the fuel injection time (pulse width) based on the predetermined pressure. Control of the injection amount can be performed.

According to a fourth aspect of the present invention, in the fuel pump according to the first aspect of the present invention, the fuel pump increases and discharges fuel discharged from a low-pressure fuel pump that discharges fuel at a pressure lower than the discharge pressure of the fuel pump. The pressurized fuel is provided so as to be directly injected into a combustion chamber of the engine.

(Operation / Effect) As described above, in an engine that includes a low-pressure fuel pump and a high-pressure fuel pump and directly injects fuel into the combustion chamber, the discharge pressure of the high-pressure fuel pump during starting is insufficient. By applying to the system,
The effect of improving the fuel injection amount control accuracy at the time of starting is great.

FIG. 1 shows the configuration and functions of the invention according to the first to fourth aspects.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows an overall system configuration according to an embodiment of the present invention. In FIG. 2, an engine 1 has an electromagnetic fuel injection valve 2 arranged with its injection hole facing the combustion chamber 3, and suctioned into the combustion chamber 3 via an intake port 4 and an intake valve 5. This is a spark-ignition direct-injection engine in which fuel is injected from the fuel injection valve 2 to form air-fuel mixture, and the air-fuel mixture is ignited by spark ignition by a spark plug 6.

The exhaust gas of the engine 1 is discharged from the fuel chamber 3 through an exhaust valve 7 and an exhaust port 8, and is discharged to the atmosphere through an exhaust purification catalyst and a muffler (not shown). The fuel in the fuel tank 9 is discharged at a relatively low pressure by the first fuel pump 10 and filtered by a filter 12 interposed in a low-pressure fuel passage 11A. The fuel adjusted to a constant low pressure by the low-pressure regulator 13 provided by-passing the fuel passage 11B is sent to the high-pressure second fuel pump 14.

The high-pressure second fuel pump 14 is driven directly by a crankshaft or a camshaft of the engine 1 or indirectly via a gear or a belt, and pressurizes and discharges the low-pressure fuel to a high pressure. . The fuel discharged from the second pump 14 is
The fuel pressure is adjusted to a constant high pressure by a high pressure regulator 16 provided in the high pressure side fuel passage 15 in a bypass manner. And
Control unit with built-in microcomputer
The fuel injection valve 2 is controlled to open according to a pulse signal having a predetermined width corresponding to the engine operating state sent from the fuel injection chamber 17 at a predetermined injection timing.
Inject into and supply.

The control unit 17 is used for detecting the engine rotational speed for controlling the fuel injection.
Various sensors such as a crank angle sensor 18 also for detecting the rotation speed of the second fuel pump 14, an air flow meter 19 for detecting the intake air flow rate, and a fuel pressure sensor 20 for detecting the fuel pressure in the high-pressure side fuel passage 15 Is input.

Here, the control unit 17 controls the pulse width of the injection pulse signal, and starts the output of the injection pulse signal, that is, the fuel injection valve 2.
Controls the fuel injection period. In such a system configuration, the routine for estimating the fuel pressure in the high-pressure side fuel passage discharged from the high-pressure second fuel pump at the time of engine start by using a model formula and controlling the fuel injection amount is shown in FIG. 3 will be described.

In step 1, the fuel pressure Pss detected by the fuel pressure sensor 20 and the crank angle sensor
The engine speed Ne calculated by the signal from the engine 18, that is, the engine speed Np of the second fuel pump 14 driven by the engine is read. In step 2, the detected fuel pressure P
ss is compared with an upper limit fuel pressure Pmax regulated by the high-pressure regulator 16.

When the detected fuel pressure Pss is equal to the upper limit fuel pressure Pma
When it is determined that the value is smaller than the value obtained by subtracting the predetermined value α from x, the routine proceeds to step 3, where the detected engine speed Ne is detected.
It is determined whether (rotational speed Np of the second fuel pump 14) is 0, that is, before starting. When it is determined that the engine rotation speed Ne before starting is 0, the routine proceeds to step 4. In step 4, and sets the fuel pressure Pss detected in the step 1 as the initial residual fuel pressure Ps _0.

If it is determined in step 3 that the engine has been started, or if the residual fuel pressure Ps ₀ is set in step 4, the process proceeds to step 5. In step 5, the cumulative number of rotations ΔNp since the second fuel pump 14 started rotating is calculated. This is a value corresponding to the total amount of fuel discharged from the fuel pump 14.

In step 6, the cumulative number of rotations ΣNp
Is retrieved from the map according to the first fuel pressure coefficient Pa. In step 7, the second fuel pressure coefficient Pb corresponding to the rotational speed of the second fuel pump 14, that is, the engine rotational speed Ne is determined.
From the map. In step 8, the fuel injection valve 6
From the fuel pressure Pc. This is obtained based on the amount of fuel consumed by the injection from the fuel injection valve 6 per hour and the fuel pipe volume.

In step 9, the fuel pressure MPs in the high-pressure fuel passage 15 is estimated by the following model formula based on the above values. In _{MPs = Ps 0 + Pa × Pb} -Pc step 10, the detected fuel pressure Pss as compared to high pressure of a predetermined value Psh, determines whether or not it is high enough to modify the model formula.

When it is determined that the fuel pressure Pss is equal to or higher than the predetermined value Psh, the process proceeds to step 11, and then to step 12, and when it is determined that the fuel pressure Pss is lower than the predetermined value Psh, the process proceeds directly to step S12.
Proceed to 12. In step 11, the correction coefficient k is obtained by performing a weighted average calculation on the ratio between the detected fuel pressure Pss and the estimated fuel pressure MPs in the model equation as in the following equation. The correction coefficient k is stored in the backup memory, and the stored value is used as an initial value at the start of the next operation.

K = a · k _old + b · Pss / MPs
(a + b = 1; a, b> 0) In step 12, a corrected pressure Ps obtained by correcting the estimated value MPs of the fuel pressure by the following equation is calculated using the correction coefficient k. Ps = k × MPs In step 13, the fuel injection amount at the start is calculated by the following equation.

T _IS = Te × (Pmax / Ps) ^1/2 + Ts Note that Te is an effective injection pulse width when the fuel is injected at the upper limit fuel pressure Pmax regulated by the high-pressure regulator.
Ts is an invalid injection pulse width corresponding to the battery voltage.
In step 2, the detected fuel pressure Pss is set to the upper limit fuel pressure P
If it is determined that it is equal to or greater than the value obtained by subtracting the predetermined value α from max,
Since the fuel pressure has risen sufficiently, it is determined that the detection accuracy of the fuel pressure sensor 20 can be obtained, and the routine proceeds to step 14, where the detected fuel pressure Pss is set as the pressure Ps for correcting the fuel injection amount.

Next, the correction of the model formula based on the detected value of the fuel pressure by the fuel pressure sensor 20 will be described. Since the fuel pressure sensor generally has a full-scale error (offset error), the error increases as the pressure decreases, as shown in FIG. For example, an error of ± 3% at a pressure value of 5 MPa regulated by the high-pressure regulator 16 results in an error of ± 30% at a low pressure of 0.3 MPa regulated by the low-pressure regulator 13 immediately after starting or the like.

The discharge pressure of a high-pressure pump such as a direct injection engine can reach an upper limit pressure (5 to 8 M) determined by a pressure regulator when the pump rotation speed becomes sufficiently high (300 to 500 rpm or more).
Pa), the fuel pressure is determined with high accuracy by the pressure regulator. However, as described above, the fuel pressure does not rise to the upper limit pressure of the pressure regulator at the start of rotation at the time of starting, etc. If an attempt is made to use the values, the accuracy is not obtained because of the influence of the above error. Further, if a fuel pressure sensor that can obtain high accuracy even at a low pressure is used, the cost increases.

Therefore, the fuel pressure at low rotation is estimated by a model formula determined by the physical characteristics of the pump.
However, since the pump itself also has an error (including endurance change) from the model formula, the correction coefficient k is calculated using the detection value at high pressure at which high accuracy can be obtained even with a low-cost fuel pressure sensor.
To correct. As described above, according to the present embodiment, the fuel pressure is accurately estimated using the fuel system model formula at the start when the discharge pressure of the fuel pump is insufficient and the fuel injection amount control at the start is performed with high accuracy. In addition, since the model formula is modified based on the detection value of the fuel pressure sensor at the time of high pressure at which the detection accuracy of the fuel pressure can be obtained, the fuel injection amount control according to the model formula at the time of the start is performed. Can always be maintained with high accuracy,
As a result, the starting performance (starting time) and the exhaust purification performance at the time of starting can be improved.

Also, since it is not necessary to use a high-precision fuel pressure sensor that can obtain accuracy even at a low pressure,
Cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

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

FIG. 3 is a flowchart showing a fuel injection amount control routine at the time of start of the embodiment.

FIG. 4 is a diagram showing an error characteristic of a fuel pressure sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Fuel injection valve 3 Combustion chamber 10 1st fuel pump 14 2nd fuel pump 17 Control unit 18 Crank angle sensor 20 Fuel pressure sensor

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI G01L 7/00 G01L 7/00 D (72) Inventor Masayuki Yasuoka 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. 56) References JP-A-7-63412 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/00-45/00 F02M 37/00-37/18 G01L 7 / 00

Claims (4)

(57) [Claims] An internal combustion engine in which fuel discharged from a fuel pump is supplied to a fuel injection valve through a fuel pipe and fuel is injected from the fuel injection valve into the engine, the fuel pressure in the fuel pipe is increased.
Means for detecting the fuel pressure in the fuel pipe at the start of the engine, the remaining fuel pressure in the fuel pipe before the rotation of the fuel pump, the cumulative number of rotations of the fuel pump,
The rotational speed of the fuel pump and the fuel pressure consumed from the fuel injection valve are estimated by a model formula using parameters as parameters, and the fuel injection amount at the time of starting is controlled based on the estimated fuel pressure. A starting fuel injection amount control device for an internal combustion engine. And means for detecting a fuel pressure in the fuel pipe, and comparing the detected fuel pressure with a fuel pressure estimated by the model formula in a state where the fuel pressure is higher than a predetermined value. 2. The starting fuel injection amount control device according to claim 1, wherein the model formula is modified. 3. The internal combustion engine according to claim 1 , wherein said fuel system includes a fuel pressure adjusting means for regulating a fuel pressure in a fuel pipe to a predetermined value or less. When fuel injection amount control device. 4. The fuel pump according to claim 1, wherein said fuel pump pressurizes and discharges fuel discharged from a low-pressure fuel pump which discharges fuel at a pressure lower than a discharge pressure of said fuel pump. The fuel injection amount control device for starting an internal combustion engine according to any one of claims 1 to 3 , wherein the fuel injection amount control device is provided so as to be directly injected into a combustion chamber.