JPH07310577A - Fuel supply control device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Purpose] The objective is to improve exhaust emission by optimally setting the first fuel supply amount and the second fuel supply amount. [Structure] The intake air amount Q, the engine rotation speed N, and the engine cooling water temperature TWN are called in (S1). The required fuel injection amount TP is calculated (S2). From TP and N, the first fuel injection timing (I / T1) and the second fuel injection timing (I
/ T2) is called in (S3). Second fuel injection ratio TR
Call TR2 according to the TWN from the table of No. 2 (S
4). HR2 corresponding to N and TP is called from the map of the second fuel injection ratio correction constant HR2 (S5). The second fuel injection amount TP2 is calculated (S6). The first fuel injection amount TP1 is calculated as the difference between TP and TP2 (S
7). By such fuel injection control, the first fuel injection amount and the second fuel injection amount can be optimized depending on the operating state and temperature state of the engine, and exhaust emission is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel supply control device for an internal combustion engine, and more particularly to a technique for improving exhaust emission.

[0002]

2. Description of the Related Art A conventional fuel injection control technique for an internal combustion engine is shown in FIG. That is, in the control unit 25, the intake air amount Q is calculated from the detection signal output from the air flow meter 22, and the crank angle sensor 23
Based on the detection signal output from the
Are calculated respectively. The control unit 25 calculates the required fuel injection amount TP from the calculated intake air amount Q and the engine rotation speed N, and based on the reference pulse signal calculated from the crank angle signal output from the crank angle sensor 23, The fuel injection valve 26 is controlled to inject fuel at the required fuel injection timing.

The above-mentioned fuel injection timing is defined as fuel injection timing, and the same definition will be applied in the following description. In the conventional fuel injection control technique (conventional example 1), the fuel is injected well before the intake stroke in order to promote vaporization of the fuel (FIG. 22).
(See (A)).

However, if the fuel is injected well before the intake stroke in this way, the responsiveness of fuel injection deteriorates when the engine operating state changes (during transition). That is, if the operating conditions deteriorate immediately after the fuel is injected, the response will be delayed by one cycle. Therefore, conventionally, Japanese Patent Laid-Open No. 63-9653
As disclosed in Japanese Patent Laid-Open Publication No. JP-A-2003-264, there is one that injects fuel in a plurality of times in one cycle.

That is, in this technique (conventional example 2), the fuel is injected in two times, for example, and a part of the required fuel injection amount is injected into the compression stroke of the engine (first injection).
However, by injecting the rest (second injection) when the intake valve is open, both fuel vaporization promotion and responsiveness are made compatible (see FIG. 22 (B)).

[0006]

However, in such a conventional fuel injection control technique, the first and second fuel injection amounts are calculated without considering the temperature condition of the engine. As a result, there is a problem that exhaust emission is deteriorated. That is, FIG. 4 shows the characteristic of the HC emission amount with respect to the I / T (fuel injection timing) at the time of engine cold (cooling), and at the time of engine cold, the intake valve is open because the vaporization of fuel is poor. When fuel is injected at times, the amount of HC emission significantly increases.

Therefore, in the conventional fuel injection control technique, the HC emission amount remarkably increases because the second fuel injection timing is set even when the engine is cold, when the intake valve is open. Further, FIG. 5 shows the characteristic of the HC emission amount with respect to the I / T when the engine is hot (warm up).
Since the fuel is easily vaporized, even if the fuel is injected while the intake valve is open, the HC emission amount does not increase.

On the other hand, FIG. 3 shows the characteristics of the intake port wall flow rate of fuel with respect to I / T. When fuel is injected while the intake valve is open, the fuel easily enters the cylinder and the intake port Since the amount of fuel taken up by the part wall is small, the fuel wall flow rate is small. However, in the conventional fuel injection control technique, the first fuel injection timing is set during the compression stroke even when the engine is hot, so that the wall flow rate at the intake port increases and the air-fuel ratio (A / The fluctuation of F) becomes large and the exhaust emission deteriorates.

In view of the above-mentioned conventional problems, the present invention sets the first fuel supply amount and the second fuel supply amount optimally in accordance with the temperature condition of the engine, thereby It is an object of the present invention to reduce the amount of hydrogen emission and to reduce the fluctuation of the air-fuel ratio during a transition to improve the exhaust emission.

[0010]

Therefore, according to the invention described in claim 1, as shown in FIG. 1, the engine operating condition detecting means for detecting the operating condition of the engine and the engine temperature detecting the temperature condition of the engine. 1 depending on the state detecting means and the engine operating state
The required fuel supply amount determining means for determining the required fuel supply amount per cycle and the fuel supply frequency per cycle are set to 2
Fuel supply timing determining means for respectively determining two fuel supply timings according to the operating state of the engine, and a second fuel supply amount according to the operating state and temperature state of the engine. The second fuel supply amount determining means and the first fuel supply amount determining means for determining the first fuel supply amount from the difference between the required fuel supply amount and the second fuel supply amount are included.

According to a second aspect of the present invention, the fuel supply timing determining means determines the fuel supply timing immediately after the intake valve is closed as the first fuel supply timing, and the second fuel supply timing when the intake valve is open. The configuration will be decided. According to a third aspect of the present invention, the fuel supply timing determination means is determined by fixing the fuel supply start timing in the first fuel supply timing and fixing the fuel supply end timing in the second fuel supply timing. The configuration.

According to a fourth aspect of the present invention, means for determining whether or not the required fuel supply amount has changed immediately after the first fuel supply and before the second fuel supply is performed, and a determination result by the determination means. When the required fuel supply amount changes based on the above, the second fuel supply amount is determined based on the difference between the latest required fuel supply amount and the first fuel supply amount. And a quantity determining means.

[0013]

In the invention described in claim 1, the fuel supply amounts of the first and second times can be optimized, and for example, unburned hydrocarbons can be reduced when the engine temperature is low. When the temperature condition of the engine is high, the total amount of hydrocarbon emissions can be reduced, and these can improve exhaust emission.

According to the second aspect of the present invention, a part of the required fuel injection amount is injected in the compression stroke of the engine, and the rest is injected when the intake valve is open. It is possible to achieve both sex. Claim 3
In the invention described above, vaporization of the fuel can be promoted in the first fuel supply, and in the second fuel supply, the injected fuel can be reliably put into the cylinder just before the end of the fuel injection.

In the fourth aspect of the invention, when the required fuel injection amount increases, the fuel does not run short and the responsiveness during transient operation of the engine can be secured.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. In FIG. 2, an air flow meter 1 for detecting an intake air amount Q introduced through an air cleaner 18 into an intake passage 17 of an internal combustion engine (hereinafter referred to as an engine) 11.
2, a throttle valve 19 that controls the intake air amount Q in association with the accelerator pedal is provided, and an electromagnetic fuel injection valve 16 as fuel supply means is provided for each cylinder in the downstream manifold portion.

In addition, a distributor (not shown)
The crank angle sensor 13 is built-in, and the crank unit angle signal output from the crank angle sensor 13 in synchronization with the engine rotation is counted for a certain period of time, or the cycle of the crank reference angle signal is measured to determine the engine rotation. The speed N is detected. Further, a water temperature sensor 14 for detecting the cooling water temperature TWN of the engine 11 is provided as a means for detecting the temperature state of the engine 11.

The control unit 15 includes a CPU and an R
OM, and an air flow meter 12 for the CPU.
A detection signal of the intake air amount Q output from the crank angle sensor 13, a detection signal of the rotation speed N output from the crank angle sensor 13, and a detection signal of the water temperature TWN output from the water temperature sensor 14 are input to the fuel injection valve 16. Is output. The ROM
Stores various kinds of data necessary for the calculation of the CPU.

The fuel injection valve 16 is opened and driven by an injection pulse signal from the control unit 15 to inject and supply fuel. That is, a basic fuel injection pulse width TP (a required fuel injection amount described later) corresponding to a variable indicating a basic operating condition (for example, the intake air amount Q and the engine rotation speed N) is TP = k · Q / N (k: Constant), and this T
By correcting P with the correction amount Coef based on other operating variables, the air-fuel ratio feedback correction coefficient α calculated from the deviation between the actual air-fuel ratio and the target air-fuel ratio, and the voltage correction coefficient Ts, the fuel injection pulse width Ti is reduced. It is calculated according to the following formula.

Ti = TP × Coef × α + Ts Fuel is supplied from the fuel injection valve 16 at an I / T (fuel injection timing) calculated by the control unit 15 based on the crank reference angle signal output from the crank angle sensor 13. Is jetted. Here, in one embodiment of the invention described in claim 1, the control unit 15 has a function as a required fuel supply amount determining means for determining a required fuel supply amount per cycle according to an engine operating state, and one cycle. When the number of times of fuel supply per hit is two, the function as a fuel supply timing determining means for determining two fuel supply timings according to the engine operating state, and the function depending on the operating state and temperature state of the engine A function as a second fuel supply amount determining means for determining a second fuel supply amount, and a first fuel for determining a first fuel supply amount from a difference between the required fuel supply amount and the second fuel supply amount. The software is equipped with a function as a supply amount determining means.

Next, the operation will be described. As shown in FIG. 3, when the fuel is injected when the intake valve is open, the wall flow in the intake port portion becomes smaller. But,
As shown in FIG. 4, when all required fuel is injected in the intake stroke when the engine temperature is not too high, H
C increases. This is because the vaporization of fuel does not proceed and unburned HC increases.

On the other hand, as shown in FIG. 5, when the engine temperature is sufficiently high, HC does not increase even if all the fuel is injected while the intake valve is open. It is advantageous to inject when the intake valve is decreasing, where That is, when the intake port wall flow is small, the fuel flowing through the wall of the intake port and flowing into the cylinder is reduced, and the fuel in the wall flow state not involved in combustion in the cylinder is also reduced. Further, when the intake port wall flow is small, the A / F fluctuation during the transition is also reduced, which is advantageous for the exhaust emission.

When the fuel is injected when the intake valve is open as described above, the unburned HC does not increase even if the fuel is injected when the intake valve is open. The amount of fuel varies depending on the temperature condition of the engine. . FIG. 6 shows the fuel amount at which HC does not deteriorate in each engine temperature state. The higher the engine cooling water temperature as the engine temperature, the more easily the fuel is vaporized, so that the amount of fuel that can be injected when the intake valve is open increases.

Here, an outline of the fuel injection control of the invention according to claim 1 will be described. FIG. 7 shows an example of this fuel injection control. The first fuel injection (immediately after the intake valve is closed, that is, during the compression stroke) and the second fuel injection (when the intake valve is open) at each engine cooling water temperature are shown. The example of fuel injection is shown. First, in the embodiment of the invention described in claim 1, the fuel injection control is as follows.

When the engine cooling water temperature is low, fuel cannot be injected when the intake valve is opened for the second time, and therefore a large amount of fuel is injected for the first time. On the other hand, when the engine cooling water temperature is high, the fuel vaporizes well, and therefore a large amount of fuel is injected when the intake valve is opened for the second time.
In addition, in the first fuel injection, the fuel vaporization is promoted in the first time, and it is desired to inject the fuel at the earliest possible timing. Therefore, the fuel injection start timing of the first fuel injection timing is fixed.

That is, when the fuel injection end timing is fixed, when the required fuel injection amount increases and the fuel injection pulse width becomes longer, a part of the fuel injected at the start of fuel injection remains in the cylinder. It is used in the previous cycle and the A / F error becomes large (see FIG. 8). Further, if the fuel injection timing is set in consideration of the maximum fuel injection pulse width, the fuel injection timing will be on the retard side, which is disadvantageous when considering vaporization of fuel.

Therefore, it is preferable to fix the fuel injection start timing in the first fuel injection timing as described above. Further, in the second fuel injection, the fuel injection end timing of the fuel injection timing is fixed. That is, if the fuel injection start timing of the second fuel injection timing is fixed and controlled, and if the fuel injection pulse width becomes long as described above, a portion of the injected fuel will be in the cylinder just before the end of fuel injection. May not enter.

Therefore, it is preferable to fix the fuel injection end timing of the second fuel injection timing as described above. When the influence of engine operating conditions is taken into consideration, the higher the engine speed, the shorter the time per unit crank angle, so it is difficult to vaporize,
The second fuel injection ratio is reduced. Further, when the engine load becomes high, the turbulence of the air becomes large, so that the fuel is easily vaporized, and the second fuel injection amount becomes large. Therefore, as shown in FIG. 9, the fuel injection ratio of the second time increases as the load increases and the rotation speed decreases.

Next, according to the flow chart of FIG.
A state of fuel injection control (determination of fuel injection timing and determination of fuel injection amount) according to the embodiment of the invention described in claim 1 by the control unit 15 will be described. First, in step 1 (abbreviated as S1 in the figure, the same applies hereinafter), the intake air amount Q, the engine rotation speed N, the engine cooling water temperature TWN.
, Respectively.

Next, in step 2, the required fuel injection amount TP is calculated by the following formula. TP = k · Q / N (k is a constant) In step 3, the first fuel injection timing (I / T1) and the second fuel injection timing (I / T2) are calculated from the required fuel injection amount TP and the engine speed N. Are called from the maps shown in FIGS. 11 and 12, respectively. These maps are calculated in advance based on the required fuel injection amount TP and the engine rotation speed N (I /
T1) and (I / T2) are allocated and stored in the ROM of the control unit 9.

Here, when the engine speed becomes high,
Since the time per crank unit angle CA becomes shorter, I /
T must advance. Also, the engine load (T
When P) becomes smaller, the flow velocity of air becomes faster, and it takes time for the fuel to enter the cylinder. Therefore, the I / T must be advanced. Next, in Step 4, in FIG.
TR2 corresponding to the engine cooling water temperature TWN is called from the table of the second fuel injection ratio TR2 shown in FIG. This table is based on the engine cooling water temperature TWN in advance.
R2 is allocated and stored in the ROM of the control unit 15.

In step 5, HR2 corresponding to the engine speed N and the required fuel injection amount TP is called from the map of the second fuel injection ratio correction constant HR2 shown in FIG. In this map, HR2 is assigned in advance based on the engine speed N and the required fuel injection amount TP.
It is stored in the ROM of the control unit 15.

In step 6, the second fuel injection amount TP
2 is calculated by the following formula. TP2 = TP · TR2 · HR2 Finally, in step 7, the first fuel injection amount T
P1 is calculated as the difference between TP and TP2 (TP1 = TP-
TP2). According to the fuel injection control described above, the fuel injection amount of the first time (compression stroke) and the fuel injection amount of the second time (when the intake valve is open) are optimized depending on the operating state and temperature state of the engine 11. And as a result of this,
Exhaust emissions are improved.

That is, when the engine cooling water temperature is low, as shown in FIG. 15, the uninjected H
C can be reduced, and total HC emission can be reduced (see FIG. 16). Further, when the engine cooling water temperature is high, as shown in FIG. 17, by increasing the fuel injection amount when the intake valve is open and decreasing the fuel injection amount during the compression stroke as compared with the conventional fuel injection control. The wall flow in the intake port section can be reduced, and the HC generation due to the wall flow in the cylinder section can be reduced to reduce the total HC discharge amount (see FIG. 18).

Next, an embodiment of the invention described in claim 4 will be described. In this embodiment, fuel injection control corresponding to the transient operation of the engine is performed. In the embodiment of the invention described in claim 1 shown in the flow chart of FIG. 10, when the engine operating condition changes before the first fuel injection, the first and second fuels are based on the latest required fuel injection amount. Fuel injection is performed by calculating the injection ratio.

However, when the operating conditions change after the first fuel injection is completed, for example, when the required fuel injection amount is increased as shown in FIG. 19, the ideal second fuel injection with less HC is performed. If the fuel injection amount is to be protected, the fuel becomes insufficient and the responsiveness during transient operation of the engine deteriorates. Therefore, in this embodiment, in order to prioritize the improvement of responsiveness during transient operation of the engine, at the time of the second fuel injection, the required fuel injection amount after the change of the engine operating condition is set to 1
The fuel injection amount is subtracted from the actual fuel injection amount for the second time.

By such fuel injection control, when the required fuel injection amount increases, the fuel does not run short, and the responsiveness during transient operation of the engine can be secured. Next, the manner of fuel injection control (determination of fuel injection timing and determination of fuel injection amount) according to the embodiment of the invention described in claim 4 by the control unit 15 will be described with reference to the flowchart of FIG.

Steps 11 to 17 are the same as steps 1 to 7 in the flowchart of FIG. Then, in step 18, it is determined whether or not the first fuel injection has ended. If not completed, the process returns to step 11 to always obtain the latest required fuel injection amount TP. When the first fuel injection is completed, the routine proceeds to step 19, where the current intake air amount Q and the current engine speed N are called in before the second fuel injection is performed. In step 20, the required fuel injection amount TPA is calculated [TPA = k · Q
/ N (k is a constant)]. In step 21, the change (| TP-TPA |) in the required fuel injection amount is checked. That is, | TP
-TPA | is compared with the reference value α (= 0.1 ms), and T
If the difference between P and TPA exceeds the reference value α (| T
P-TPA |> α), the routine proceeds to step 22, and the second fuel injection amount TP2 is newly obtained from TP2 = TPA-TP1. In step 21, if the difference between TP and TPA is less than or equal to the reference value α, (| TP-TPA | ≦
α) The process is ended without newly obtaining the fuel injection amount TP2 for the second time.

[0039]

As described above, according to the first aspect of the invention, when the number of times of fuel supply per cycle is two, the first time and the second time depending on the operating condition and temperature condition of the engine. Since the fuel supply amount of the engine is determined, it is possible to optimize the fuel supply amount of the first and second times. For example, when the engine temperature is low, unburned hydrocarbons can be reduced. When the temperature condition of the engine is high, the total amount of hydrocarbon emissions can be reduced, and these can improve exhaust emission.

According to the second aspect of the present invention, the first fuel supply timing is determined immediately after the intake valve is closed, and the second fuel supply timing is determined when the intake valve is open. Therefore, by injecting a part of the required fuel injection amount in the compression stroke of the engine and injecting the rest in the intake stroke, both fuel vaporization promotion and responsiveness can be achieved.

According to the third aspect of the invention, the fuel supply start timing of the first fuel supply timing is fixed, and the fuel supply end timing of the second fuel supply timing is fixed. In the first fuel supply, the vaporization of the fuel can be promoted, and in the second fuel supply, the injected fuel can be surely put into the cylinder just before the end of the fuel injection.

According to the fourth aspect of the present invention, it is determined whether or not the required fuel supply amount has changed immediately after the first fuel supply and before the second fuel supply is performed, and the required fuel supply amount changes. In this case, the fuel supply amount for the second time is determined from the difference between the latest fuel supply amount for the request and the fuel supply amount for the first time. Therefore, when the required fuel injection amount increases, there is insufficient fuel. Without doing so, the responsiveness during transient operation of the engine can be secured.

[Brief description of drawings]

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

FIG. 2 is a system diagram of an embodiment of the above invention.

FIG. 3 is a characteristic diagram showing the relationship between fuel injection timing and wall flow rate.

FIG. 4 is a characteristic diagram showing a relationship between fuel injection timing and HC emission amount during engine cold.

FIG. 5 is a characteristic diagram showing the relationship between fuel injection timing and HC emission amount when the engine is hot.

FIG. 6 is a characteristic diagram showing a relationship between an engine cooling water temperature and a fuel injection amount during an intake stroke without HC deterioration.

FIG. 7 is a diagram showing the first and second fuel injection amounts at each engine cooling water temperature.

FIG. 8 is a diagram for explaining problems when the fuel injection end timing is fixed.

FIG. 9 is a diagram showing a second fuel injection amount ratio.

FIG. 10 is a flowchart for explaining the control contents of the embodiment of the above invention.

[Fig. 11] First fuel injection timing map

[Figure 12] Second fuel injection timing map

[Fig. 13] Table of second fuel injection ratio

[Fig. 14] Map of second fuel injection ratio correction constant

FIG. 15 is a comparison diagram of a fuel injection amount at the time of engine cold of the related art and the present invention.

FIG. 16 is a diagram illustrating the effect of the present invention.

FIG. 17 is a comparison diagram of fuel injection amounts when the engine is hot according to the related art and the present invention.

FIG. 18 is a diagram illustrating the effect of the present invention.

FIG. 19 is a diagram for explaining a fuel injection amount in the embodiment of the invention described in claim 4;

FIG. 20 is a flowchart for explaining the control contents of the embodiment of the invention described in claim 4.

FIG. 21 is a configuration diagram of a conventional fuel injection control technique for an internal combustion engine.

FIG. 22 is a diagram illustrating the content of conventional fuel injection control.

[Explanation of symbols]

 11 Engine 12 Air Flow Meter 13 Crank Angle Sensor 14 Water Temperature Sensor 15 Control Unit 16 Fuel Injection Valve

Claims (4)

[Claims] 1. An engine operating state detecting means for detecting an operating state of an engine, an engine temperature state detecting means for detecting a temperature state of the engine, and a required fuel supply amount per cycle depending on the engine operating state. A required fuel supply amount determining means, and a fuel supply timing determining means for determining two fuel supply timings each in accordance with an operating state of the engine, when the number of times of fuel supply per cycle is 2. Second fuel supply amount determining means for determining the second fuel supply amount according to the operating state and the temperature condition of the first fuel supply amount, and the first fuel supply amount from the difference between the required fuel supply amount and the second fuel supply amount. A fuel supply control device for an internal combustion engine, comprising: a first fuel supply amount determining means for determining. 2. The fuel supply timing determining means determines the fuel supply timing immediately after the intake valve is closed as the first fuel supply timing, and determines the fuel supply timing as the second fuel supply timing when the intake valve is open. A fuel supply control device for an internal combustion engine as described above. 3. The fuel supply timing determination means fixes the fuel supply start timing of the first fuel supply timing and fixes the fuel supply end timing of the second fuel supply timing. Item 3. A fuel supply control device for an internal combustion engine according to item 1 or 2. 4. Means for determining whether or not the required fuel supply amount has changed immediately after the first fuel supply and before the second fuel supply, and the required fuel based on the result of the determination by the determining means. When the supply amount changes, a second fuel supply amount determining means for changing the required fuel supply amount that determines the second fuel supply amount from the difference between the latest required fuel supply amount and the first fuel supply amount, The fuel supply control device for an internal combustion engine according to any one of claims 1 to 3, wherein the fuel supply control device includes an internal combustion engine.