JPH01277633A - Fuel injection control method and its device - Google Patents

Abstract

PURPOSE:To permit the control accuracy to be enhanced, by eliminating dispersion of an air-fuel ratio control due to fluctuation of the atmospheric pressure by adding a change of exhaust efficiency, obtained from a measured value of the atmospheric pressure, to an operation expression of the opening time of a fuel injection valve as the correction amount. CONSTITUTION:An absolute pressure sensor 4 detects an intake negative pressure while the atmospheric pressure under a predetermined condition to be output to a control unit 12. Thus obtaining a change of exhaust efficiency of an engine 1 from fluctuation of the atmospheric pressure, this change of exhaust efficiency is added to an operation expression of the opening time of a fuel injection valve 4 as the correction amount. In this way, a basic fuel injection amount, obtained from measured values of an intake pipe internal pressure from the absolute pressure sensor 4 and of an engine speed from an engine speed sensor 7, is corrected by the amount corresponding to the change of exhaust efficiency by the atmospheric pressure fluctuation in its turn to the change of intake efficiency. As a result, the dispersion of air-fuel ratio, being based on the atmospheric pressure fluctuation, is eliminated, and the air-fuel ratio control accuracy can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection control system for an engine, and in particular to a D-Jetro system (Druck) that controls the amount of fuel injection based on the pressure inside the intake pipe of the engine and the engine speed. M
The present invention relates to a fuel injection control method and device for the engine Masser 5yste+++).

[Conventional technology]

In recent years, in the field of fuel supply for automobile engines, electronic fuel injection control systems have become popular in place of carburetor one-way systems.

This electronic fuel injection control system includes the D-Jetro type (intake negative pressure sensing type injection system), the L-Jetro type (air flow rate sensing type injection system), etc.

Among these, the D-JETRO type normally measures the engine intake pipe pressure and engine speed, and based on these measurements, calculates the fuel injection amount (fuel injection valve opening time) according to the engine load. The output of the fuel injection valve is controlled based on the calculated value.

A conventional example of such a JETRO-type fuel injection control system is, for example, "Electronic Controlled Gasoline Injection" (Publisher: Sankaido, July 5, 1988) in the Automotive Engineering Series.
There is one described on pages 126 to 132 of the Japanese publication).

[Problem to be solved by the invention]

In the D-JETRO type fuel injection control system, the density of air taken into the engine can be detected through measurement of intake pipe pressure (negative pressure) using an absolute pressure sensor. Therefore, cars are in low-lying areas.

Even if the atmospheric pressure level (air density) changes as the vehicle travels through various locations such as highlands, the intake pipe internal pressure is always taken as absolute pressure, so the intake air density is automatically corrected.

Therefore, it is possible to determine the flow rate and mass of the intake pipe based on the output value of the absolute pressure sensor, and determine the fuel injection amount suitable for this.

By the way, this is perfect for correcting the intake air density, but when considering the intake efficiency of the engine.

The following considerations also need to be made regarding the influence of exhaust back pressure, that is, the pressure on the engine exhaust side.

The intake efficiency of an engine is usually expressed by the relationship between the negative pressure in the engine's intake pipe and the pressure in the cylinder, while the exhaust efficiency is also expressed by the relationship between the pressure in the engine cylinder and the pressure in the exhaust pipe.

Furthermore, the intake efficiency and exhaust efficiency of the engine are closely related in that as the exhaust efficiency increases, the amount of residual exhaust gas in the cylinder decreases, and as a result, the engine intake rate increases.

Also, exhaust efficiency is affected by atmospheric pressure. That is, the lower the atmospheric pressure (the higher the altitude), the greater the difference between the cylinder internal pressure and the exhaust pipe internal pressure, so the exhaust efficiency increases (so-called exhaust gas blowing becomes better). As a result, engine intake efficiency also increases. Therefore, in order to perform proper air-fuel ratio control without variations, it is desirable to capture changes in exhaust efficiency and even intake efficiency due to fluctuations in atmospheric pressure, and to control the fuel injection amount by taking this change into consideration. However, in the past, sufficient consideration has not been given to this point.

The present invention has been made in view of the above points, and its purpose is to eliminate variations in air-fuel ratio control and to eliminate variations in air-fuel ratio control even if changes occur in engine exhaust efficiency and even intake efficiency due to changes in atmospheric pressure. An object of the present invention is to provide a fuel injection control method and device that can improve fuel ratio control accuracy.

[Means to solve the problem]

The above purpose is to measure the intake pipe internal pressure, engine speed, etc., and based on these measured values, calculate the opening time of the fuel injection valve so that the amount of fuel injection corresponds to the engine load. In this method of controlling fuel injection using calculated values, the pressure inside the engine's intake pipe is detected and measured as absolute pressure, and atmospheric pressure is also measured, and changes in engine exhaust efficiency are detected from the measured atmospheric pressure. This is achieved by adding this change in exhaust efficiency as a correction to the arithmetic expression for determining the valve opening time of the fuel injection valve, and performing fuel injection control.

Further, a device that embodies such a fuel injection control method is configured as follows.

That is, means for measuring intake pipe pressure, engine speed, etc., and means for calculating the opening time of the fuel injection valve based on these measured values so that the amount of fuel injection corresponds to the engine load. and a means for controlling the output of the fuel injection valve based on this calculated value, a means for measuring atmospheric pressure and a means for detecting changes in engine exhaust efficiency from the measured value of one atmospheric pressure, means for adding the change in efficiency as a correction to an arithmetic expression for determining the opening time of the fuel injection valve.

(Function) According to the fuel control method or device having such a configuration, the pressure inside the engine's intake pipe is measured using an absolute pressure sensor as in the past, so even if there are fluctuations in atmospheric pressure,
The density of the inspired air is detected with automatic correction. Furthermore, changes in engine exhaust efficiency are determined from changes in atmospheric pressure (measured atmospheric pressure), and this change in exhaust efficiency (change in atmospheric pressure) is added as a correction to the equation for calculating the opening time of the fuel injection valve. . In this way, the basic fuel injection amount (the opening time of the fuel injection valve) is corrected by the amount corresponding to the change in exhaust efficiency (and thus the change in intake efficiency of the engine) due to the change in atmospheric pressure. As a result, it is possible to eliminate variations in the air-fuel ratio due to atmospheric pressure fluctuations and further improve the air-fuel ratio control accuracy.

Note that for the correction added as a change in exhaust efficiency, it is sufficient to use the atmospheric pressure change value determined by atmospheric pressure measurement.The calculation formula for calculating the valve opening time of the fuel injection valve can be calculated based on, for example, the intake pipe pressure, engine filling, etc. The basic fuel injection amount is calculated using efficiency correction coefficients etc. as parameters, and this basic fuel injection amount is converted into the valve opening time of the fuel injection valve. Therefore, the correction amount due to the change in exhaust efficiency can be added as follows: The calculation may be performed by adding directly to the fuel injection valve opening time, which is the calculated value of the calculation formula, or by adding it to numerical values such as engine filling efficiency, intake pipe pressure, etc., which are calculation elements.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. FIG. 1 is a system diagram of a D-Jetro type fuel injection device to which the present invention is applied.

In FIG. 1, 1 is an engine, 2 is an intake pipe, 3 is a throttle valve, 4 is an absolute pressure sensor for detecting the pressure inside the intake pipe, 5 is a throttle sensor for detecting the opening degree of the throttle valve 3, and 6 is a throttle valve.
7 is an electromagnetic fuel injection valve, and 7 is a rotary pickup built into the power distribution device. The rotational pickup 7 detects the rotational speed of the engine.

8 is a water temperature sensor that detects the temperature of engine cooling water, 9 is an exhaust sensor, 10 is a fuel pump, 11 is a fuel tank, 1
2 is a control unit.

The control unit 12 is composed of a microcomputer, and includes absolute pressure sensors 4. Various sensor signals such as the throttle sensor 59 rotation pickup 7, water temperature sensor 8, exhaust sensor 9, etc. are input, and based on these signals, various calculations related to the engine condition are performed to control the fuel injection valve 9. Sends an output signal from the fuel pump 10, etc.

Next, fuel injection control, which is the gist of this embodiment, will be explained.

The intake air amount of the engine 1 is controlled by a throttle valve 3,
A negative pressure PMM in the intake pipe 2 is determined. This intake negative pressure P
MM is detected by the intake pressure sensor 4, but since this intake pressure sensor 4 is an absolute pressure detection type sensor,
The intake negative pressure PMM is detected as an absolute pressure PM, and this is input to the control unit 12.

On the other hand, the rotational speed of the engine is detected by a rotation pickup 7 provided in the power distributor, and is input to the control unit 12.

In the control unit 12, based on the absolute pressure PM and the engine speed signal, the injection pulse width (opening time of the fuel injection valve) determines the amount of fuel to be injected, as described later.
is calculated, and an injection pulse is output, for example, once per rotation, and the fuel injection valve 6 provided in each cylinder is opened. The fuel injection valve 6 injects fuel pumped from the fuel tank 11 by the fuel pump 10 into the intake port 2a of the engine.

FIG. 2 shows the fuel injection control system shown in FIG. 1 as an input/output of the control unit 12. For example, 5ENS1 corresponds to an intake pressure sensor, 5ENS2 corresponds to a rotation sensor, and 5ENS3 corresponds to a throttle sensor. On the other hand, the output signal is shown on the right side of the figure, for example, 4
In the case of a cylinder, there are four injectors Inj,
These valves are opened in order according to the timing of intake air of the engine.

Here, calculation of the fuel injection pulse width (valve opening time) required for fuel injection control is performed, for example, as follows.

That is, when the control unit 12 inputs the measured value of the intake pipe internal pressure from the intake pressure sensor 4 and the measured value of the engine rotation speed from the rotation sensor 7, the control unit 12 inputs the measured value of the intake pipe internal pressure,
The basic fuel injection amount is determined using parameters such as engine filling efficiency correction coefficient and the like, which are influenced by the engine speed, and this basic fuel injection amount is converted into the output pulse width (valve opening time) of the fuel injection valve.

If this is expressed as a formula, it becomes Tp=P This is the intake temperature correction coefficient.

In this equation, the intake pipe negative pressure PM is the absolute pressure PM which is not affected by atmospheric pressure or other influences, as shown in Figure 3 (Figure 3 shows the output characteristics of the intake pressure sensor 4).
Detected as . Therefore, even if the atmospheric pressure changes, the engine intake air amount (mass flow rate) automatically includes density correction, and there is no need to correct this part.

On the other hand, changes in atmospheric pressure change the engine's exhaust efficiency and, by extension, its intake efficiency. That is, the intake efficiency of an engine is generally expressed by the relationship between the negative pressure in the engine's intake pipe and the pressure in the cylinder, while the exhaust efficiency is expressed by the relationship between the pressure in the cylinder of the engine and the pressure in the exhaust pipe.

Furthermore, the intake efficiency and exhaust efficiency of the engine are closely related in that as the exhaust efficiency increases, the amount of residual exhaust gas in the cylinder decreases, and as a result, the engine intake efficiency substantially increases. In other words, the actual intake efficiency of the engine can be said to be the formal intake efficiency expressed by the relationship between the engine's intake pipe negative pressure and the pressure inside the cylinder, plus the exhaust efficiency. When the atmospheric pressure changes, the difference between the engine cylinder pressure and the exhaust pipe pressure (exhaust back pressure) changes, so the exhaust efficiency also changes.For example, the higher you go to higher altitudes, the thinner the air density becomes. However, since the atmospheric pressure level decreases, the difference between the cylinder internal pressure and the exhaust pipe internal pressure increases, increasing exhaust efficiency. As a result, the engine's intake efficiency also increases. FIG. 4 shows the relationship between atmospheric pressure and engine intake efficiency at this time.

No consideration (correction) should be taken for such changes in intake efficiency.
If the fuel injection control amount is controlled based on equation (1) without the above, variations will occur in the air-fuel ratio control. For example, as shown in Figure 4, if fuel injection control is performed as before even if the intake efficiency changes due to fluctuations in atmospheric pressure, the air-fuel ratio will change at low atmospheric pressure as shown in Figure 5. On the lean side, where atmospheric pressure is high, the air-fuel ratio tends to shift to the rich side.

Therefore, in this embodiment, in order to cope with such a situation, fuel injection control is performed by adding a change in exhaust efficiency based on a change in atmospheric pressure to equation (1) as a correction amount.

FIG. 6 is a flowchart showing a concept for correcting this. Basically, the atmospheric pressure Pa is detected in advance, and then correction is performed according to any one of (1), (2), and (2) in FIG.

Here, prior to the explanation of FIG. 6, the method for detecting the atmospheric pressure Pa, which is the premise of this, will be explained based on the flowchart of FIG. 7.

In this embodiment, the atmospheric pressure Pa is measured in the following manner using the absolute pressure sensor 4 that detects the pressure inside the intake pipe, without using a dedicated atmospheric pressure sensor.

The first measuring method is St in the flowchart.

S2. As shown in Ss and S4, atmospheric pressure is first measured based on the absolute pressure sensor output value when a predetermined period of time has elapsed with the key switch on and the starter switch off. That is, from the time when the key switch is turned on until the starter switch is turned on, the engine is in a non-operating state and the inside of the intake pipe is at the atmospheric pressure level, so the atmospheric pressure at this time is read from the output value of the absolute pressure sensor. Note that if you operate the switch without a pause between turning on the key switch and turning off the starter switch, there will be insufficient reading time and the atmospheric pressure measurement will lack accuracy.In this case, use the first measurement method to measure the atmospheric pressure. Not performed. In other words, the first measurement method considers the reading time and uses the absolute pressure sensor output value when a predetermined period of time (about several seconds) has elapsed with the key switch on and the starter switch off as a condition for atmospheric pressure measurement. do.

If the first measurement method is not performed, that is, if less than a predetermined elapsed time from key switch-on to starter switch-off is performed, the second measurement method is performed.

The second measurement method is a routine shown in Sze Sa' t St, in which the engine speed is in a low engine speed range below a predetermined value (engine speed x predetermined value).

The absolute pressure sensor output value when the throttle opening is more than a predetermined value (throttle opening>predetermined value) is taken as atmospheric pressure.Such a state is 1. For example, when accelerating immediately after starting the engine, etc., in this case. The throttle valve is fully open when the engine is running at low speed, and there is almost no intake negative pressure in the engine, so the P detected under this condition is
M can be taken into the control unit 12 as atmospheric pressure. FIG. 8 is a graph showing the atmospheric pressure level in the intake pipe due to the relationship between the engine speed and the throttle opening, and the area above the solid line X is the atmospheric pressure level. As shown in the figure, with respect to engine speed,
The throttle opening that should reach the atmospheric pressure level is also proportional.

Next, fuel injection amount correction will be explained based on the flowcharts shown in FIGS.

In the case of (3), when atmospheric pressure Pa is detected, it is searched in a pre-stored table to compensate for the intake pipe internal pressure Δ.
P, and in addition to the intake pipe pressure PM', PM'
Substituting PM found by +ΔP into equation (1),
The pulse width Tp of the fuel injection valve is calculated. Here, ΔP,
corresponds to changes in exhaust efficiency affected by atmospheric pressure fluctuations, and P
M' is the intake pipe internal pressure before correction. As a result, each time a correction is made on the exhaust side as well, taking into account changes in atmospheric pressure. Note that, as described above, the density correction based on fluctuations in the atmospheric pressure on the intake side is automatically performed by measuring the intake pipe pressure as an absolute pressure.

In the case of ■, is there a shadow of exhaust back pressure instead of ■? (Change in exhaust efficiency) as a way to cancel.

A method of directly adding the correction value ΔTp to the basic injection amount (in other words, the opening time of the fuel injection valve) Tp (T p = T p '
+ΔTp), and Tp' is the basic injection amount before correction.

Δ'rp is a basic injection amount correction value, and this ΔTp corresponds to changes in exhaust efficiency that are affected by atmospheric pressure fluctuations.

In the case of ■, instead of ■ and ■, the method is to add a correction to the engine's charging efficiency η (η = η' + Δη), where η' is the charging efficiency before correction, Δη is the charging efficiency correction value, and this Δη is Corresponds to changes in exhaust efficiency due to atmospheric pressure fluctuations.

Therefore, in any of the cases of ■, ■, and ■ in Fig. 6, it is possible to absorb variations in the air-fuel ratio caused by changes in engine exhaust efficiency and engine intake efficiency caused by changes in atmospheric pressure. The air-fuel ratio control accuracy of the fuel injection system can be improved.

Furthermore, according to this embodiment, changes in atmospheric pressure are detected using an intake pressure sensor (absolute pressure sensor) without using a dedicated atmospheric pressure sensor, which reduces the number of parts and reduces costs. obtain.

〔Effect of the invention〕

As described above, according to the present invention, even if there is a change in engine exhaust efficiency and even intake efficiency due to a change in atmospheric pressure, the fuel injection amount is corrected in response to this change, thereby reducing variations in air-fuel ratio control. By eliminating this, it is possible to improve the accuracy of air-fuel ratio control.

[Brief explanation of the drawing]

Figures 1 and 2 are system configuration diagrams of the D-JETRO fuel injection system to which the present invention is applied, Figure 3 is a characteristic diagram showing the relationship between intake pipe pressure and output, and Figure 4 is a diagram showing the relationship between atmospheric pressure and output. A characteristic diagram showing the relationship with engine intake efficiency, FIG. 5 is an explanatory diagram showing the fluctuation state of the air-fuel ratio affected by atmospheric pressure, and FIGS. 6 and 7 show specific examples of the fuel injection control method of the present invention. The flowchart shown in FIG. 8 is a diagram showing the relationship between the engine speed and the throttle opening when the inside of the intake pipe becomes atmospheric pressure. 1... Engine, 2... Intake pipe, 3... Throttle valve,
4... Intake pressure sensor (combined atmospheric pressure sensor), 6...
Fuel injection valve, 12... Control unit (calculating means, output control means, correction means), PM... Intake pipe pressure, Tp... Fuel injection valve opening time, Ri... Engine filling efficiency, ΔP JΔTp, Δη... Corresponds to changes in exhaust efficiency.

Claims (1)

[Claims] 1. Measure the intake pipe pressure, engine speed, etc., and adjust the opening time of the fuel injection valve based on these measured values so that the amount of fuel injection corresponds to the engine load. In this method, the pressure inside the engine's intake pipe is measured by detecting the absolute pressure, and the atmospheric pressure is also measured, and the exhaust efficiency of the engine is calculated from the measured atmospheric pressure. A fuel injection control method characterized in that the change in exhaust efficiency is detected and the change in exhaust efficiency is added as a correction to an arithmetic expression for determining the opening time of a fuel injection valve to perform fuel injection control. 2. The fuel injection control method according to claim 1, wherein the correction amount corresponding to the change in exhaust efficiency is directly added to the valve opening time of the fuel injection valve, which is the calculated value of the calculation formula. 3. In the first aspect, the calculation formula for determining the valve opening time of the fuel injection valve calculates the basic fuel injection amount using intake pipe internal pressure, engine filling efficiency, etc. as calculation elements, and calculates the basic fuel injection amount by calculating the basic fuel injection amount. A fuel injection control method in which the correction amount corresponding to the change in the exhaust efficiency is added to the engine charging efficiency in the arithmetic expression. 4. In the first claim, the calculation formula for determining the valve opening time of the fuel injection valve calculates the basic fuel injection amount using intake pipe internal pressure, engine filling efficiency, etc. as calculation elements, and calculates the basic fuel injection amount by calculating the basic fuel injection amount. The fuel injection control method is performed by converting the valve opening time into the valve opening time, and the correction corresponding to the change in the exhaust efficiency is added to the intake pipe internal pressure in the arithmetic expression. 5. In any one of claims 1 to 4, the means for measuring the atmospheric pressure is an absolute pressure sensor that detects the pressure inside the intake pipe without using a dedicated atmospheric pressure sensor, and the key Based on the absolute pressure sensor output value when a predetermined period of time has elapsed from switch on to starter switch off, or when the throttle opening is above a predetermined value in a low rotation speed range where the engine speed is below a predetermined value. A fuel injection control method that measures atmospheric pressure based on the value. 6. Means for measuring intake pipe pressure, engine speed, etc., and means for calculating the opening time of the fuel injection valve based on these measured values so that the amount of fuel injection corresponds to the engine load. and a means for controlling the output of the fuel injection valve based on this calculated value. 1. A fuel injection control device comprising means for adding a change in efficiency as a correction to an arithmetic expression for determining a valve opening time of a fuel injection valve.