JPH07217478A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To restrain a knock without causing any deterioration in fuel consumption, upon occurrence thereof in the fuel injection control device of an internal combustion engine. CONSTITUTION:This fuel injection control control device of an internal combustion engine is equipped with a fuel injection valve 6 at the side of an intake valve 2 on the peripheral surface of the upper section of a cylinder, so as to conically inject fuel toward the crown of a piston 7 nearing the end of intake stroke. Also, the device begins to inject a necessary amount of fuel on optimum timing after intermediate intake stroke. Regarding this control device, a part of the required fuel amount is injected in advance at the early stage of intake stroke, when a knock takes place.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for suppressing knocking, particularly in a cylinder injection type spark ignition engine which always performs uniform combustion.

[0002]

2. Description of the Related Art The temperature of a cylinder head above a cylinder is maintained higher on the exhaust valve side than on the intake valve side cooled by intake air. The temperature of the air-fuel mixture at the time of ignition also shows a similar tendency due to the heat of this cylinder head.At the time of ignition, the hot air-fuel mixture on the exhaust valve side ignites and burns to expand, and the air-fuel mixture on the intake valve side is compressed and rises in temperature. To do. If this rising temperature does not reach the ignition temperature, the flame is propagated to the air-fuel mixture on the intake valve side to achieve good combustion, but when it reaches the ignition temperature, the air-fuel mixture on the intake valve side ignites spontaneously and knocks. Occur.

Japanese Unexamined Patent Publication (Kokai) No. 4-183951 discloses a cylinder injection type spark ignition engine which always performs stratified combustion.
When knocking occurs, the ignition timing is retarded and the fuel injection timing in the compression stroke is retarded. This is to suppress ignition of the air-fuel mixture on the intake valve side, that is, knocking, by retarding the ignition timing when knocking occurs, thereby lowering the air-fuel mixture pressure at the time of ignition and lowering the air-fuel mixture temperature. is there.

[0004]

The ignition timing retard is, of course, effective for suppressing knocking in a direct injection spark ignition engine that always performs uniform combustion, but combustion is started after compression top dead center, That is, the equal volume of combustion is lowered, so the output is reduced, and in order to obtain a desired output, it is necessary to increase the amount of fuel, which deteriorates fuel efficiency.

Therefore, an object of the present invention is to provide a fuel injection control device capable of suppressing knocking without deteriorating fuel consumption in a cylinder injection type spark ignition engine which always performs uniform combustion.

[0006]

A fuel injection control device for a cylinder injection type spark ignition engine according to the present invention is arranged on the intake valve side around the upper part of a cylinder and conically forms fuel on the piston top surface at the end of the intake stroke. In a fuel injection control device for a cylinder injection type spark ignition engine, which is equipped with a fuel injection valve for injecting toward, and starts injection of a required fuel amount from an optimum timing after the middle of the intake stroke,
When knocking occurs, a part of the required fuel amount is injected in advance in the early stage of the intake stroke.

[0007]

The above-described fuel injection control device for a cylinder injection type spark ignition engine is arranged on the intake valve side around the upper part of the cylinder and injects fuel conically toward the top surface of the piston at the end of the intake stroke. In normal times, the injection of the required fuel amount is started from the optimum timing after the middle of the intake stroke so that the injected fuel does not adhere much to the piston top surface, and when knocking occurs, a portion of the required fuel amount is The fuel is injected in advance at the beginning of the intake stroke, and this fuel is positively collided with the intake valve side of the piston top surface.

[0008]

1 is a schematic longitudinal sectional view of a cylinder injection type spark ignition engine to which a fuel injection control device according to the present invention is attached, and FIG. 2 is a schematic plan view thereof. In these drawings, reference numeral 1 denotes an ignition plug located substantially in the center of the upper portion of the cylinder, around which two intake valves 2 and exhaust valves 3 adjacent to each other are provided.
Are arranged. Reference numeral 4 is two intake passages communicating with the inside of the cylinder via the intake valve 2, and 5 is two exhaust passages communicating with the inside of the cylinder via the exhaust valve 3.

Reference numeral 6 denotes a fuel injection valve for directly injecting fuel into the cylinder, which is mounted on the intake valve 2 side around the upper part of the cylinder. Reference numeral 7 is a piston, and a shallow recess 7a is formed on the top surface thereof.
Are formed.

The in-cylinder injection type spark ignition engine of the present embodiment always performs uniform combustion capable of obtaining high output,
Therefore, the fuel injection valve 6 atomizes the fuel in a conical shape and injects it, and the injection direction is directed to the top surface of the piston 7 at the intake bottom dead center. By setting the fuel injection direction in this manner, the injected fuel does not directly adhere to the inner wall of the cylinder at any piston 7 position and adheres to the recess 7a of the piston 7 as shown in FIG. Even if the fuel flowing flows, it does not reach the inner wall of the cylinder. This prevents the fuel adhering to the inner wall of the cylinder from being taken up by the lubricating oil film and discharged as unburned fuel.

The fuel injection control by the fuel injection valve 6 is shown in FIG.
It is performed according to the flowchart shown in. This flowchart is executed every predetermined time or every predetermined crank angle. First, in step 101, for example,
The intake air weight Ga is measured by an air flow meter (not shown) provided upstream of the throttle valve (not shown) in the intake passage 1, and in step 102, the intake air weight Ga ′ to each cylinder is the desired air-fuel ratio A. The required fuel injection amount Qf is calculated by dividing by / F. Next, at step 103, the engine speed Ne is detected by the rotation sensor, and the routine proceeds to step 104.

In step 104, for example, a knocking sensor (not shown) mounted on the outer wall of the cylinder and detecting knocking by sound or vibration determines whether knocking has occurred in at least one cylinder. . When this determination is affirmative, that is, when knocking occurs, the routine proceeds to step 105, where it is determined whether the flag F is 1. This flag F is reset to 0 when the engine is stopped, and this determination is initially denied and the routine proceeds to step 106.

At step 106, the flag F is set to 1, and the routine proceeds to step 107, where the preliminary fuel injection amount Q1 is set to the minimum fuel injection amount Qmin, and the routine proceeds to step 114. The minimum fuel injection amount Qmin is the minimum injectable fuel injection amount that is determined by the characteristics of the fuel injection valve 6. Flag F
Is reset to 0 in step 113 when the preliminary fuel injection amount Q1 is set to 0 in step 112 described later, that is, 1 as long as the preliminary fuel injection is executed.
Is maintained at. In step 114, the crank angle range necessary to inject the preliminary fuel injection amount Q1 is calculated in consideration of the injection period Tinj1 of the preliminary fuel injection, that is, the engine speed Ne, and in step 115, the predetermined crank angle immediately after the start of the intake stroke. The injection start timing SOI1 of the preliminary fuel injection fixed at the angle θ1 is added with the injection period Tinj1 to end the injection EO of the preliminary fuel injection.
I1 is calculated.

Next, at step 116, the main fuel injection amount Q2 is calculated by subtracting the preliminary fuel injection amount G1 from the required fuel injection amount Gf, and at step 117, the injection period Tinj2 of the main fuel injection, that is, the engine speed Ne. Considering this, the crank angle range required to inject the main fuel injection amount Q2 is calculated. Next, at step 118, it is judged if the difference between the predetermined crank angle θ2 in the first half of the intake stroke and the injection end timing EOI1 of the preliminary fuel injection is the interval I (Ne) or more. The interval I (Ne) is the minimum time during which the fuel injection valve 6 can normally receive the next valve opening command after receiving the valve closing command in the crank angle range based on the current engine speed Ne. When the preliminary fuel injection amount Q1 is the minimum fuel injection amount Qmin, this judgment is affirmed even if the engine speed Ne is high, and the main fuel injection can be performed from the predetermined crank angle θ2. At 119, the injection start timing SOI2 of the main fuel injection
In the normal combustion, the injected fuel is
The injection port of the fuel injection valve 6 and the top surface of the piston 7 are provided in order to prevent a large amount of the fuel from adhering to the top surface and be discharged as unburned fuel and to advance the injection end timing as early as possible in order to form a uniform mixture. Is set to the optimum crank angle θ2 in the first half of the middle of the intake stroke, and step 12
Go to 1.

In step 121, the injection start timing S
The injection period T calculated in step 117 for OI2
inj2 is added and injection end timing EOI2 of main fuel injection
Is calculated.

Therefore, as shown by the solid line in FIG. 4, the fuel injection immediately after the knocking occurs is the preliminary fuel injection with the minimum fuel injection amount Qmin at the beginning of the intake stroke of the required fuel injection amount Gf. The remainder is injected as the main fuel from the crank angle θ2 in the first half of the middle stage of the intake stroke.

As described above, knocking occurs when the temperature rise due to the compression of the air-fuel mixture on the intake valve side due to the expansion of the air-fuel mixture on the exhaust valve side due to the ignition and combustion exceeds the ignition temperature. According to the fuel injection control of the present embodiment, as described above, at the beginning of knocking, the preliminary fuel injection with the minimum fuel injection amount Qmin is executed at the beginning of the intake stroke, and the fuel injected at this time is Since the distance from the injection port of the fuel injection valve 5 to the top surface of the piston 7 is small, it collides with the top surface of the piston 7 with a large penetrating force and adheres to the intake valve 2 side of the top surface of the piston 7 and at the same time as the cylinder above the cylinder. It bounces to the intake valve 2 side of the head and adheres there. These adhering fuels take heat from the top surface of the piston 7 and the intake valve side of the cylinder head above the cylinder to be vaporized, so that these parts are cooled and even if the air-fuel mixture on the intake valve side is compressed immediately after ignition. It becomes difficult for the temperature to exceed the ignition temperature, and knocking can be suppressed.

If the preliminary fuel injection amount Q1 is the minimum fuel injection amount Qmin and the knocking continues because the top face of the piston 7 and the intake valve side of the cylinder head above the cylinder cannot be sufficiently cooled, the determination in step 105 is as follows. Since the flag F has already been set to 1, the determination is affirmative and the routine proceeds to step 108, where the preliminary fuel injection amount Q1 is increased by a predetermined amount Δq from the previous amount (initially the minimum fuel injection amount Qmin), and the processing after step 114 is executed. Done. Each time this flow is repeated, the preliminary fuel injection amount Q1 is increased by a predetermined amount Δq,
If the determination in step 118 is negative, the routine proceeds to step 120, where the injection start timing SOI2 of the main fuel injection is the end of injection of the preliminary fuel injection to enable this fuel injection, as indicated by the alternate long and short dash line in FIG. The crank angle is delayed from the timing EOI1 by the interval I (Ne), the routine proceeds to step 121, where the injection end timing EOI2 is determined.

The solid line and the alternate long and short dash line in FIG. 4 show the case of the same engine speed and the same required fuel injection amount, and thus the injection of the main fuel injection as the preliminary fuel injection amount Q1 increases. Even if the start timing SOI2 is delayed, the main fuel injection amount Q2 is reduced accordingly, so that the injection end timing EOI2 is not delayed and there is no disadvantage in forming a homogeneous mixture. If knocking does not occur due to the preliminary fuel injection, the determination at step 104 is denied and the routine proceeds to step 109. As at step 105, it is determined whether or not the flag F is 1, and this determination is affirmative and the routine proceeds to step 110. move on.

In step 110, the preliminary fuel injection amount Q1 is reduced by a predetermined amount Δq from the previous amount, and in step 111, it is judged whether or not the current preliminary fuel injection amount Q1 is less than the minimum fuel injection amount Qmin. Initially,
This determination is denied and the processing from step 114 onward is executed. As described above, since the minimum preliminary fuel injection amount Q1 required for suppressing knocking is selected, all the fuel injected at this time and adhering to the top surface of the piston 7 and the cylinder head is vaporized at the time of ignition and remains liquid. Exhaust emissions are not deteriorated by being discharged as unburned fuel. If the determination in step 111 is affirmed while repeating the above-described flow, it is practically impossible to inject less than the minimum fuel injection amount Qmin, so the routine proceeds to step 112, where the preliminary fuel injection amount Q1 is 0. Then, in step 113, the flag F is reset to 0, and the processing of step 114 and subsequent steps is executed. At this time, in step 114, the injection period T of the preliminary fuel injection
Since inj1 is in the 0 ° crank angle range, the injection end timing EOI1 of the preliminary fuel injection calculated in step 115 is the same as the injection start timing θ1, no preliminary fuel injection is performed, and the determination in step 118 is naturally affirmative. Then, the main fuel injection is performed at the required fuel injection amount Qf with the fuel injection start timing SOI2 being θ2.

When knocking does not occur even if the preliminary fuel injection is not performed, the determination in step 109 is denied and the routine proceeds to step 112, where the preliminary fuel injection amount Q1 is set to 0.
At the same time, the flag F is maintained at 0 in step 113, the processes of step 114 and the subsequent steps are executed, and the main fuel injection with the required fuel injection amount Qf is performed as described above.

In the present embodiment, the start timing SOI1 of the preliminary fuel injection is fixed to the predetermined crank angle θ1 at the beginning of the intake stroke, but it may be advanced to the intake top dead center side as the preliminary fuel injection amount Q1 increases. It is possible to make it variable, so that even if the preliminary fuel injection amount Q1 increases to some extent, there is an opportunity to inject the main fuel injection from the predetermined crank angle θ2 in the first half of the middle of the intake stroke in consideration of the engine speed Ne. Increased by that amount, injection end timing EOI2 of main fuel injection
Becomes faster, which is advantageous for forming a uniform mixture.

[0023]

As described above, according to the fuel injection control device for a cylinder injection type spark ignition engine of the present invention, the fuel is conically arranged on the intake valve side around the upper part of the cylinder and the fuel is conically shaped at the piston top at the end of the intake stroke. It is equipped with a fuel injection valve that injects toward the surface, and normally, in order to prevent the injected fuel from adhering too much to the top surface of the piston, injection of the required amount of fuel is started from the optimum timing after the middle of the intake stroke, causing knocking. Sometimes, a portion of the required fuel quantity is injected in advance in the early stage of the intake stroke, and this fuel is positively collided with the intake valve side of the piston top surface to adhere to the intake valve side of the piston top surface, and the cylinder of the cylinder head Even if the air-fuel mixture on the intake valve side is compressed by combustion expansion of the air-fuel mixture on the exhaust valve side, the temperature rises to the ignition temperature by making it bounce back to the upper intake valve side and adhering to it, cooling them by the heat of vaporization of the fuel. To do Is prevented, it is possible to suppress the knocking. At this time, it is not necessary to delay the ignition timing, and since combustion can be performed with a high degree of equality, it is unnecessary to increase the amount of fuel for improving the output, and it is possible to prevent deterioration of fuel efficiency.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a direct injection spark ignition engine to which a fuel injection control device according to the present invention is attached.

FIG. 2 is a schematic plan view of FIG.

FIG. 3 is a flowchart for fuel injection control.

FIG. 4 is a diagram showing fuel injection in a specific engine operating state.

[Explanation of symbols]

 1 ... Spark plug 2 ... Intake valve 3 ... Exhaust valve 4 ... Intake passage 5 ... Exhaust passage 6 ... Fuel injection valve 7 ... Piston

Claims (1)

[Claims] 1. A fuel injection valve, which is arranged on the intake valve side around the upper part of a cylinder and injects fuel conically toward the top surface of the piston at the end of the intake stroke, is equipped with a required fuel from the optimum timing after the middle of the intake stroke. In a fuel injection control device for a cylinder injection type spark ignition engine that starts injection of an amount of fuel, a cylinder injection type spark ignition engine characterized in that when knocking occurs, a part of the required fuel quantity is injected in advance in the early stage of the intake stroke. Fuel injection control device.