JP5088282B2 - Direct-injection spark ignition internal combustion engine - Google Patents

Description

  The present invention relates to a direct-injection spark ignition internal combustion engine, and more particularly to fuel injection control at the time of engine start.

In Patent Document 1, in a direct injection spark ignition internal combustion engine, at the time of stratified combustion in which fuel is injected in a compression stroke, the fuel injection is divided into a plurality of times, and the fuel that has been divided and injected is injected first On the other hand, the fuel injected thereafter is injected so as to overlap in the vicinity of the spark plug. That is, of the divided fuels, the previously injected fuel forms an air-fuel mixture in a region determined by the injection characteristics of the fuel injection valve, the injection direction, the influence of gas flow in the combustion chamber, and the like. The fuel injected after this injection has a flow along the injection direction due to the influence of the previous injection, so that the fuel injected later forms a spray of the same form. Then, it proceeds through the combustion chamber at a higher speed than the previously injected fuel. Therefore, the fuel injected later is made to catch up with the previously injected fuel so as to overlap, thereby forming an air-fuel mixture with an appropriate concentration degree at that position. However, when the engine is cold, the engine wall surface temperature is low and the adverse effect on the combustion performance due to the fuel wall surface adhesion is large, so split injection is prohibited and single injection is performed only once.
JP 2002-115593 A

  If the split injection is prohibited at the time of starting the engine and only one injection is performed as in the technique described in Patent Document 1, the concentration (homogeneity) of the stratified mixture decreases and the combustion stability decreases. Moreover, since the penetration of fuel spray is stronger in single injection than in split injection, the amount of adhesion to the wall surface may increase.

  However, at the time of starting the engine, as shown in FIG. 7, the fuel pressure Fp and the boost pressure are suddenly increased as the engine speed Ne is rapidly increased. Therefore, as shown in FIG. If the body lift amount (static flow rate) is constant H0, the engine speed Ne increases at the first explosion (for example, about 200 rpm), to a low speed (for example, about 500 rpm) and to a medium speed (for example, about 700 rpm). Along with this, the pulse width of each injection IT1, IT2 of divided injection, that is, the injection time τ1, τ2, becomes shorter in time, and the injection interval between the injection start timing of the previous injection IT1 and the injection start timing of the subsequent injection IT2. τ12 becomes shorter in time. For this reason, for example, in the state immediately after the start of the start at an engine speed of around 200 rpm, such as at the time of the first explosion, the injection interval τ12 becomes longer in time, and the diffusion of fuel injected at the initial stage of the previous injection IT1 proceeds. As described above, the fuel injected later cannot catch up with the previously injected fuel and overlap therewith, so that there is a possibility that good stratified combustion cannot be realized.

  In this specification, “time” and “time” mean an absolute time (second, minute, etc.) rather than a relative period with respect to the engine speed (rotation speed).

  The present invention has been made in view of such a problem, and an object thereof is to stably perform stratified combustion using split injection even when the engine is started.

  A direct-injection spark ignition internal combustion engine according to the present invention includes a fuel injection valve and an ignition plug in a combustion chamber, and has a control unit that controls operations of the fuel injection valve and the ignition plug. Then, at the time of engine start, this control unit performs stratified combustion by performing fuel injection immediately before the ignition timing, and also divides the fuel injection into a plurality of times so that the injection start timing of the previous injection and the subsequent injection The operation of the fuel injection valve is controlled so that the injection interval from the injection start timing is maintained at a constant time.

  According to the present invention, when the engine is started, the injection interval in the divided injection is made constant in time, so that the concentration (homogeneity) of the air-fuel mixture in stratified combustion is maintained at a high level, and at the time of engine start. The combustion stability can be improved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a direct injection spark ignition internal combustion engine according to an embodiment of the present invention. In this internal combustion engine, a pent roof type combustion chamber 4 is formed by a cylinder head 1, a cylinder bore 2, and a piston 3, and a fuel injection valve 5 is disposed downward in the center of the upper part thereof. The fuel injection valve 5 is an outward valve as shown in FIG. 2, and a fuel passage 51 is formed along the axis at the tip of the fuel injection valve body 50, and a tapered opening is formed at the lower end of the fuel passage 51. An opening 52 is formed. A rod portion 53 is fitted to the fuel passage 51 so as to be movable in the passage direction. A poppet type valve element 54 is provided at the tip of the rod portion 53, and a poppet type valve element 54 is provided in the tapered opening 52. The taper surfaces are opposite. Accordingly, when the valve body 54 is lifted downward, an outward annular jet port 55 is formed between the tapered opening 52 and the tapered surface of the valve body 54, and fuel is injected from the jet port 55. The fuel spray has a hollow conical shape.

  The spark plug 6 is disposed obliquely at a position eccentric from the upper center of the combustion chamber 4, and is thereby disposed to ignite the outer edge of the hollow conical fuel spray injected from the fuel injection valve 5. Yes. More specifically, a part of the outer edge of the hollow conical fuel spray injected from the fuel injection valve 5 is swelled (swelled) by shearing with the surrounding air. Are arranged to be.

  An engine control unit (ECU) 7 serving as a control unit includes signals such as the engine speed Ne detected by the engine speed sensor, the fuel pressure detected by the fuel pressure sensor, that is, the fuel pressure Pf, and the water temperature Tw detected by the water temperature sensor. Is entered. The fuel pressure Pf is, for example, the pressure in the high-pressure fuel rail that supplies high-pressure fuel to each fuel injection valve 5. The ECU 7 controls the operation of the fuel injection valve 5 and the spark plug 6 based on these signals. In particular, for the fuel injection valve 5, the fuel injection timing, that is, the injection start timing, the injection end timing, and the injection width (injection time) are controlled by energization control to the solenoid that drives the rod portion 53 provided with the valve element 54. In addition, the lift amount of the valve element 54 corresponding to the static flow rate can be adjusted and controlled.

  The operation mode (combustion mode) of the internal combustion engine includes a homogeneous operation mode and a stratified operation mode. In the homogeneous operation mode, fuel injection of the fuel injection valve 5 is performed in the intake stroke, and a homogeneous air-fuel mixture is formed in the entire combustion chamber 4 by the ignition timing by the spark plug 6, so that the stoichiometric air-fuel ratio or lean Homogeneous combustion is performed at an air-fuel ratio (A / F = 20 to 30).

  On the other hand, in the stratified operation mode, the fuel injection of the fuel injection valve 5 is performed in the compression stroke, and the stratified mixture is formed in a part of the combustion chamber 4 (the central portion of the combustion chamber 4 that can be ignited by the spark plug 6). By forming an air mass, stratified combustion is performed at a very lean air-fuel ratio (A / F = 30 to 40) as a whole.

  By the way, when stratified combustion is performed at the time of engine start-up, in other words, when starting with stratified combustion to reduce the amount of HC emissions at the start and immediately after start-up, not only stratifying the air-fuel mixture, It is necessary to make it compact. Therefore, when the engine is started, fuel injection for stratified combustion is divided into a plurality of times using the characteristics of the outward valve. And this division | segmentation injection (multistage injection) is set as the structure which performs subsequent injection at the timing at which the fuel spray injected later is drawn into the fuel spray injected previously.

  The stratified combustion by the divided injection using the characteristics of such an outward valve will be described with reference to FIG. In the case of a single injection (when the required injection amount is injected at a time), as shown in FIG. 3A, the penetration is large, and the inside of the hollow conical spray has a large space. On the other hand, in the case of divided injection (when the required injection amount is divided into two injections; in the case of two injections), it is as follows.

  As shown in FIG. 3 (b-1), in the first injection of the second injection, the amount of injection per injection is reduced as compared to the case of a single injection, so the penetration is reduced. Therefore, the spread is also reduced. In other words, the fuel spray of the outward valve has a low penetration in the first place, but by dividing the injection amount, the momentum is further reduced and the spray stays near the spray point. And the negative pressure area | region by the flow velocity of injection generate | occur | produces behind the spray of the 1st injection. As shown in FIG. 3B-2, the second injection of the second injection is performed toward the negative pressure region behind the spray of the first injection. Therefore, since the spray of the second injection is attracted by negative pressure, the flow velocity is higher than that of the spray of the first injection, catching up with the spray of the first injection, and the spray of the second injection entering the spray of the first injection. In other words, the rear end of the spray has a negative pressure, and normally ambient air flows in. However, by performing the second injection there, the second spray is drawn into the first spray. It is.

  Thus, finally, as shown in FIG. 3 (b-3), the spray of the second injection enters the spray of the first injection, and diffusion prevention and improvement in uniformity are expected. Moreover, vaporization is also accelerated | stimulated by the collision with the surrounding air at the time of drawing.

  In this way, when stratified combustion is performed at the time of engine start-up, the fuel is injected in a plurality of times, thereby not only increasing the concentration level but also suppressing fuel spray penetration, and a compact and homogeneous stratified mixture. The flame propagation stability and combustion speed can be shortened, combustion stability can be improved, and the amount of gas quench due to diffusion can be reduced.

  In this embodiment, when the engine is started, stratified combustion is performed by performing fuel injection during the compression stroke immediately before the ignition timing as described above, and the fuel injection is divided into a plurality of times as shown in FIG. Then, the operation of the fuel injection valve 5 is controlled so that the injection interval τ12 between the injection start timing of the previous injection IT1 and the injection start timing of the subsequent injection IT2 is maintained at a constant time. That is, when the engine is started, the lift amount of the valve body is decreased from H1 to H2 and H3 in accordance with the increase in the engine speed Ne so as to keep the injection interval τ12 at a constant time.

  Furthermore, when starting the engine, in addition to the above-described injection interval τ12, each of the injection widths (pulse width / injection time) τ1, τ2 of each fuel injection IT1, IT2 and the injection pause time τr between both injections are initially set. Control is performed to maintain a certain period of time during the start-up transition period from the start to the completion of start-up, including during explosion, low speed, and medium speed.

  As an example of the specific setting of the lift amount in the start-up injection control at the time of starting the engine, an example using the required pulse width (injection time) Ti calculated and set in the normal injection control after the start will be described. This will be described with reference to FIG. Note that the required fuel injection amount during engine startup is constant. The required pulse width Ti in the normal injection control is large between the pulse width Ti1 corrected by the fuel pressure and the water temperature with respect to the input value from the air flow meter, and the pulse width Ti2 obtained from the table value of the fuel pressure / water temperature / engine speed. Select the direction. FIG. 5A shows an example of a fuel pressure table, and this table is set in consideration of an increase in static flow rate according to the fuel pressure and pulse width as shown in FIGS. 5B and 5C. The engine speed table is set in consideration of the decrease in charging efficiency as the engine speed increases, and the water temperature table is set in consideration of wall flow fuel and charging efficiency changes due to changes in water temperature. Is done.

  Using the required pulse width Ti in such normal injection control, the required lift amount H of the valve body 54 of the fuel injection valve 5 in the starting injection control is set. Specifically, since the pulse width (injection time) at the time of starting the engine is a constant value τ (= τ1 + τ2), the pulse width Ti at the reference lift amount H0 in the normal injection control and the actual value at the time of starting the engine A pulse width ratio Ti / τ with a set pulse width τ (= τ1 + τ2) is obtained, and a required lift amount H is obtained based on the pulse width ratio Ti / τ. Specifically, as shown in FIG. 5D, since the injection amount increases as the lift amount (injector lift amount) increases, the pulse width ratio increases as shown in FIG. 5E. The lift amount H is set so as to become smaller.

  The setting of the lift amount at the time of starting the engine is not limited to this, and the lift amount may be reduced more simply as the engine speed (or fuel pressure) increases.

  FIG. 6 is a flowchart schematically showing the flow of fuel injection control. In step S1, various signals representing the engine operating state such as the engine speed Ne, the fuel pressure Pf, and the water temperature Tw are read. In step S2, it is determined whether the engine rotational speed Ne is less than a predetermined start completion rotational speed N1 (for example, 700 to 800 rpm), that is, whether the engine starts from the start to the completion of the engine start (starting transition period). .

  If the engine speed Ne is less than the start completion speed N1, the process proceeds to step S3, and it is determined whether the fuel pressure Fp exceeds a determination value P1 at which the engine can be started. When the fuel pressure Fp exceeds the determination value P1, the process proceeds to step S4, and the above-described injection control at the time of engine start is performed.

  On the other hand, if the engine speed Ne exceeds the start completion speed N1, the process proceeds from step S2 to step S5, and the injection control after the start is performed. Since this post-startup injection control is not the main part of the present case, it will be briefly described. For example, in normal control after warm-up, homogeneous combustion and stratified combustion are performed according to operating conditions (mainly engine speed and load). Is switched, that is, stratified combustion is performed in a low rotation / low load region, and homogeneous combustion is performed in a high rotation / high load region.

  Further, during the warm-up operation immediately after starting, for example, the ignition timing is retarded to TDC or later together with the ignition timing, and the expansion stroke injection is performed. In this case, since the piston is moving downward, the air-fuel mixture is more easily diffused than the compression stroke injection, and the generation timing of the negative pressure at the rear end of the spray due to the previous injection is also earlier, so the divided injection By making the injection interval shorter than the injection interval in the compression stroke injection at the time of starting the engine described above, the air-fuel mixture is likely to diffuse because the piston is moving downward during the expansion stroke injection. Nevertheless, the concentration of the air-fuel mixture can be maintained at a high level, and in response to the earlier generation of negative pressure at the rear end of the spray due to the earlier injection, the effect of being able to perform the post-injection at an appropriate time is effective. can get.

  As described above, in this embodiment, at the time of engine start, stratified combustion is performed by performing fuel injection during the compression stroke immediately before the ignition timing, and the fuel injection is divided into a plurality of times, and the previous injection IT1 Since the operation of the fuel injection valve 5 is controlled so that the injection interval τ12 between the injection start timing and the injection start timing of the subsequent injection IT2 is kept constant over the engine start transition period, the initial interval of the previous injection IT1 Diffusion of fuel injected into the engine does not progress excessively, and good combustion is achieved by maintaining the concentration and homogeneity of the stratified mixture by split injection at a high level from the start to the end of the engine start. In addition, the amount of gas quenching at the time of engine start can be reduced to reduce the amount of HC emissions.

  Further, as the fuel injection valve 5, an outward valve that is provided downward in the center of the upper portion of the combustion chamber 4 and that forms a hollow conical fuel spray by an outward annular jet outlet 55 is used. The fuel spray from the low-penetration outward valve 5 is further reduced to a lower penetration by split injection in the first place by direct ignition at the outer edge of the hollow conical fuel spray. (Homogeneity) can be further increased, and fuel spray can be ignited and burned without reaching the piston crown surface or cylinder wall surface, thereby reducing the amount of HC emissions at the time of engine start.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, in the above embodiment, the number of divided injections is set to two. However, if possible, the number of divided injections may be divided into three or more to further suppress penetration, thereby improving the homogeneity of the stratified mixture. .

  Furthermore, by changing / controlling the ratio / ratio of the injection amount (pulse width) between the previous injection and the subsequent injection in accordance with the change in the in-cylinder pressure due to the variable valve mechanism or the like at the time of starting the engine, the spray penetration can be controlled. It is also possible to make it appropriate according to the in-cylinder pressure change.

1 is a configuration diagram showing a direct injection spark ignition internal combustion engine according to an embodiment of the present invention. Explanatory drawing which shows a fuel injection valve (outward valve). Explanatory drawing of division | segmentation injection. The timing chart which shows the starting injection control at the time of engine starting which concerns on a present Example. The flowchart which shows simply the flow of the fuel-injection control of a present Example. Explanatory drawing which concerns on the example of 1 setting of the valve body of the fuel injection valve of a present Example. The graph which shows the change of engine speed and fuel pressure at the time of engine starting. Explanatory drawing which shows the fuel-injection control at the time of engine starting which concerns on a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cylinder head 2 ... Cylinder bore 3 ... Piston 4 ... Combustion chamber 5 ... Fuel injection valve 6 ... Spark plug 7 ... ECU (control part)
DESCRIPTION OF SYMBOLS 50 ... Fuel-injection-valve main body 51 ... Fuel channel 52 ... Tapered opening part 53 ... Rod part 54 ... Valve body 55 ... Injection hole

Claims (3)

In a direct-injection spark ignition internal combustion engine having a fuel injection valve and a spark plug in the combustion chamber,
A control unit for controlling the operation of the fuel injection valve and the spark plug;
The fuel injection valve is an outward valve that is provided downward in the upper center of the combustion chamber, and forms a hollow conical fuel spray from a jet port between the opening and the valve body,
The controller may, at the time of engine starting, with to perform stratified combustion by performing fuel injection immediately before the ignition timing, the fuel injection is divided into a plurality of times, the start of the injection tip of the injection start timing and the later injection of the injection A direct-injection spark-ignition internal combustion engine characterized in that the lift amount of the valve body is reduced in accordance with an increase in engine speed so as to keep the injection interval with the time constant. 2. The direct injection spark ignition internal combustion engine according to claim 1 , wherein the spark plug is arranged to ignite an outer edge of the hollow conical fuel spray. 3. The direct injection spark ignition type according to claim 1, wherein the control unit controls the operation of the fuel injection valve so that an injection time of each fuel injection becomes constant when the engine is started. 4. Internal combustion engine.

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