JP2019070329A - Control device of internal combustion engine - Google Patents

Abstract

To generate stable diffusion combustion.SOLUTION: A fuel injection valve (9) is arranged in the center of a combustion chamber (4), an ignition plug (10) is arranged around the combustion chamber (4) which is apart from the fuel injection valve (9) by a half or a longer distance of a cylinder bore radius, and fuel injection is performed into the combustion chamber (4) from the fuel injection valve (9) a plurality of times during one cycle. After generating a flame by igniting a spray generated by first fuel injection by the ignition plug (10), a spray generated by second fuel injection is injected into the flame, and diffused and combusted. When an in-cylinder temperature at the second fuel injection is lower than a stable diffusion combustion temperature, an actual compression ratio is raised.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine.

  A spark plug is disposed in the vicinity of the fuel injection valve to ignite fuel injected from the fuel injection valve disposed at the central portion of the combustion chamber by the spray guide method, and fuel is injected from the fuel injection valve into the combustion chamber during one cycle. After performing injection twice and igniting the spray by the first fuel injection with the spark plug to generate a flame, the spray by the second fuel injection is injected into this flame to diffuse and burn, thereby stabilizing An internal combustion engine that ensures lean combustion is known (see, for example, Patent Document 1). As described above, when performing lean combustion, the amount of fuel injected from the fuel injection valve is small, and the penetration power of the injected fuel is low, so the injected fuel is vaporized and diffused in a short time after injection, It becomes a flammable mixture. Therefore, even if the spark plug is disposed close to the fuel injection valve, that is, even if the distance between the fuel injection valve and the spark plug is shortened, the injected fuel is sufficiently vaporized when the injected fuel reaches the spark plug. The mixture is diffused and has a combustible mixture, so that the injected fuel ignited by the spark plug can be burned well.

JP 2007-278257 A

  However, if the air-fuel ratio of the mixture to be combusted is reduced, for example, if the air-fuel ratio of the mixture to be combusted to perform exhaust gas purification using a three-way catalyst is made the stoichiometric air-fuel ratio, the injected fuel from the fuel injection valve The quantity increases and the penetration of injected fuel increases. Therefore, as in the above-described internal combustion engine, if the distance between the fuel injection valve and the spark plug is short, the injected fuel can not be sufficiently vaporized and diffused until the injected fuel reaches the spark plug, and the spark plug The mixture around it becomes rich. As a result, the amount of unburned components generated when the injected fuel is ignited and burned by the spark plug increases, and there is a problem that the combustion efficiency decreases due to the low air utilization at this time. Furthermore, in this internal combustion engine, there is a problem that diffusion combustion can not be performed when the in-cylinder temperature decreases.

  In order to solve the above problems, according to the present invention, the fuel injection valve and the spark plug are disposed in the combustion chamber, and fuel injection is performed a plurality of times from the fuel injection valve into the combustion chamber in one cycle. In a control device of an internal combustion engine in which a spray by a fuel injection is ignited by a spark plug to generate a flame, and then a spray by a second or subsequent fuel injection is injected into the flame to diffuse and burn the fuel injection valve. The spark plug is disposed at the center of the combustion chamber and at the periphery of the combustion chamber at a distance of 1/2 or more of the cylinder bore radius from the fuel injection valve, and the in-cylinder temperature during the second and subsequent fuel injections is stable diffusion combustion If the temperature is lower than the temperature, a control device for an internal combustion engine is provided to increase the actual compression ratio.

  Even if the air-fuel ratio of the mixture to be burned is reduced, the injected fuel reaches the spark plug by arranging the spark plug at the periphery of the combustion chamber at a distance of 1/2 or more of the cylinder bore radius from the fuel injection valve. Around that time, the injected fuel is sufficiently vaporized and diffused to form a combustible mixture. Therefore, the injected fuel can be well burned when ignited by the spark plug. Furthermore, when the in-cylinder temperature at the time of fuel injection for the second and subsequent times is less than the stable diffusion combustion temperature, the in-cylinder temperature can be raised by raising the actual compression ratio, whereby stable diffusion combustion can be performed.

FIG. 1 is a longitudinal sectional view of an internal combustion engine, and (B) is a side sectional view of (A). FIG. 2 is a view when the combustion chamber is viewed from below. FIG. 3 is a diagram showing the injection timing and the ignition timing. FIG. 4 is a view showing a combustion confirmation area. FIG. 5 is a view showing a combustible region. FIG. 6 is a view showing an opening period of the intake valve. FIG. 7 is a view showing a diffusion combustion area and a flame propagation combustion area. FIG. 8 is a flowchart for performing operation control of the engine.

  FIG. 1 shows a longitudinal sectional view of an internal combustion engine using gasoline, and FIG. 2 shows a view from below of the combustion chamber of the internal combustion engine shown in FIG. In addition, in FIG. 1, a figure (B) shows side surface sectional drawing of a figure (A). 1 and 2, 1 is a cylinder block, 2 is a cylinder head mounted on a cylinder block 1, 3 is a piston reciprocating in the cylinder block 1, 4 is formed between a cylinder head 2 and a piston 3 A combustion chamber 5, an intake valve 5, an intake port 6, an exhaust valve 7, and an exhaust port 8, respectively.

  As shown in FIGS. 1 and 2, the fuel injection valve 9 is disposed at the center of the combustion chamber 4, in the example shown in FIGS. 1 and 2, at the center of the upper wall of the combustion chamber 4. As shown in A) and FIG. 2A, the fuel spray F1 is injected radially from the fuel injection valve 9 toward the periphery of the combustion chamber 4. On the other hand, as shown in FIG. 1 (A) and FIGS. 2 (A) and 2 (B), a spark plug 10 is disposed around the combustion chamber 4. In the example shown in FIG. 1 (A) and FIGS. 2 (A) and 2 (B), a pair of spark plugs 10 are disposed at the periphery of the combustion chamber 4 opposite to the cylinder bore central axis. As shown in FIGS. 1A and 2A, these spark plugs 10 are disposed so as to be located in the fuel spray F1 when fuel is injected from the fuel injection valve 9.

  As shown in FIG. 1B, the intake air flows into the intake port 6 through the intake air amount detector 11 and is then supplied into the combustion chamber 4 through the intake valve 5. In the embodiment according to the present invention, a pressure sensor for detecting the pressure in the combustion chamber 4 is provided. This pressure sensor, as shown in FIG. 1A, comprises a pressure sensor 12 attached to the fuel injection valve 9, for example consisting of a piezoelectric element, and the output signal of this pressure sensor 12 comprises a digital computer It is input to the electronic control unit 13. In addition, although not shown in the figure, an atmospheric temperature detection sensor for detecting an atmospheric temperature, an atmospheric pressure detection sensor for detecting an atmospheric pressure, and a rotational speed detection sensor for detecting an engine rotational speed are provided. The output signals of the atmospheric temperature detection sensor, the atmospheric pressure detection sensor, and the rotation speed detection sensor are input to the electronic control unit 13.

  On the other hand, as shown in FIG. 1B, the intake valve 5 is controlled to open and close by a camshaft 14 provided with an intake valve drive cam, and this camshaft 14 advances the intake valve drive cam or It is connected to a variable valve timing mechanism 15 capable of movement control to the retard side. In the embodiment according to the present invention, the variable valve timing mechanism 15 controls the closing timing of the intake valve 5 to the advance side or the retard side.

  Next, with reference to FIG. 3, the injection timing and the ignition timing in the embodiment of the present invention will be described. In FIG. 3, the horizontal axis indicates the crank angle, and TDC on the horizontal axis indicates the compression top dead center. Referring to FIG. 3, in the embodiment according to the present invention, the preinjection is performed before the compression top dead center TDC, and the fuel spray of this preinjection is indicated by F1 in FIGS. 1 (A) and 2 (A). There is. As shown in FIGS. 1A and 2A, when the fuel spray F1 of this preinjection reaches the spark plug 10, the fuel spray F1 of this preinjection is ignited by the spark plug 10. The ignition timing of this pre-injection fuel spray F1 is shown in FIG. 3, and as shown in FIG. 3, the pre-injection fuel spray F1 is ignited before the compression top dead center TDC. In this case, the ignition timing of the fuel spray F1 of the preliminary injection is controlled by the injection timing of the preliminary injection. Therefore, a spark plug whose ignition timing can be controlled can be used as the spark plug 10, but It is also possible to use a heater such as a glow plug, which does not require the control of the ignition timing.

  When the fuel spray F1 of the preinjection is ignited, a flame is generated, and the generation area of the flame at the beginning of ignition is indicated by SF in FIG. 2 (B). Then, the flame generation area SF gradually spreads toward the center of the combustion chamber 4. Next, as shown in FIG. 3, the main injection is performed near the compression top dead center TDC, and the fuel spray of the main injection is indicated by F2 in FIG. 2 (B). The main injection is injected into the flame being generated, and when the fuel spray F2 of the main injection is fed into the flame, it is sequentially diffused and burned as indicated by SD in FIG. 2 (B). . Diffusion combustion is a gentle combustion that is rate-limited by the evaporation rate of the fuel from the fuel droplets, and therefore does not cause knocking when diffusion combustion is performed. In the embodiment of the present invention, the amount of fuel for the preliminary injection and the amount of fuel for the main injection are set as the amount of fuel necessary to make the air-fuel ratio of the mixture burned in the combustion chamber 4 the theoretical air-fuel ratio There is.

  If the distance between the fuel injection valve 9 and the spark plug 10 is short, the fuel can not be sufficiently vaporized and diffused until the fuel spray F1 of the preinjection reaches the spark plug 10, and the mixture around the spark plug 10 My heart is overwhelmed. As a result, the amount of unburned components generated when the pre-injection fuel is ignited and burned by the spark plug 10 increases, and the air utilization rate at this time decreases, resulting in a decrease in combustion efficiency. On the other hand, when the distance between the fuel injection valve 9 and the spark plug 10 is increased, the fuel is sufficiently vaporized and diffused by the time the fuel spray F1 of the preliminary injection reaches the spark plug 10, and the combustible mixture air It has become. Therefore, when the fuel spray F1 of the preinjection is ignited by the spark plug 10, it can be well burned.

  FIG. 4 shows that the distance X of the spark plug 10 from the fuel injection valve 9 disposed on the cylinder bore central axis O and that the fuel spray F1 of the preinjection is well burned when ignited by the spark plug 10 The experimental results showing the relationship with the determined combustion confirmation area are shown. From the experimental results shown in FIG. 4, when the distance X between the fuel injection valve 9 and the spark plug 10 is 1/2 or more of the cylinder bore radius, that is, a combustion chamber separated from the fuel injection valve 9 by 1/2 or more of the cylinder bore radius. If the spark plug 10 is arranged at the periphery of 4, it is understood that the fuel spray F1 of the preinjection can be well burned when ignited by the spark plug 10. Therefore, in the embodiment of the present invention, the spark plug 10 is disposed at the periphery of the combustion chamber 4 which is separated from the fuel injection valve 9 by 1/2 or more of the cylinder bore radius.

  On the other hand, even if the fuel spray F1 of the preinjection is well burned, if the temperature in the combustion chamber 4 when the main injection is injected is low, stable diffusion combustion of the main injection fuel is not performed, and the fuel injection is stable. In order to perform the diffusion combustion of the main injection fuel, it is necessary that the temperature in the combustion chamber 4 at the time of injection of the main injection fuel be somewhat high. FIG. 5 shows the experimental results showing the relationship between the temperature in the combustion chamber 4 at the compression top dead center TDC (hereinafter referred to as TDC temperature) and the combustible area where stable diffusion combustion of the main injection fuel can be performed. It shows. It can be understood from FIG. 5 that stable diffusion combustion of the main injection fuel can be performed if the TDC temperature is equal to or higher than TK. In the embodiment of the present invention, the lower limit temperature TK of the TDC temperature capable of performing the stable diffusion combustion of the main injection fuel is referred to as a stable diffusion combustion temperature. In the embodiment shown in FIG. 5, this stable diffusion combustion temperature TK is 1100K. Therefore, in the embodiment of the present invention, when the main injection fuel is to be diffused and burned, when the TDC temperature is the stable diffusion combustion temperature TK, that is, 1100 K or less, the TDC temperature is stably diffused combustion by increasing the actual compression ratio. The temperature Tk is to be exceeded.

  That is, in the present invention, the fuel injection valve 9 and the spark plug 10 are disposed in the combustion chamber 4 and fuel injection is performed a plurality of times from the fuel injection valve 9 into the combustion chamber 4 in one cycle. The control device for an internal combustion engine according to an internal combustion engine in which a spray by the second fuel injection is injected into this flame for diffusion combustion after the spray by the spark is generated by the spark plug 10 to generate a flame. Is disposed at the central portion of the combustion chamber 4, and the spark plug 10 is disposed at the periphery of the combustion chamber 4 separated from the fuel injection valve 9 by a half or more of the cylinder bore radius. When the temperature is less than the stable diffusion combustion temperature TK, the actual compression ratio is increased.

  Next, a method of increasing the actual compression ratio will be briefly described with reference to FIG. In the embodiment of the present invention, the actual compression ratio is increased by controlling the closing timing of the intake valve 5 by the variable valve timing mechanism 15. FIGS. 6A and 6B show the opening period of the intake valve 5, and BDC and TDC indicate compression bottom dead center and compression top dead center, respectively. Further, in FIGS. 6A and 6B, arrows indicate the opening period of the intake valve 5, and IC and IC ‘indicate the closing timing of the intake valve 5. Further, FIG. 6 (A) shows a case where an Atkinson cycle for controlling the amount of intake air into the combustion chamber 4 by controlling the closing timing of the intake valve 5 is adopted, and FIG. The figure shows the case where a mirror cycle for controlling the amount of intake air into the combustion chamber 4 by controlling the closing timing of the intake valve 5 is employed.

  In FIG. 6A, the solid line indicates the reference opening period of the intake valve 5 determined from the operating state of the engine, and IC indicates the reference closing timing of the intake valve 5. When the actual compression ratio is to be increased when the Atkinson cycle is adopted, the intake valve drive cam of the camshaft 14 is moved to the advance side by the variable valve timing mechanism 15, and as a result, FIG. The closing timing IC 'of the intake valve 5 is advanced as indicated by the broken line in FIG. When the closing timing IC ‘of the intake valve 5 is advanced, the actual compression ratio is increased, and the TDC temperature is raised. On the other hand, also in FIG. 6B, the solid line indicates the reference valve-opening period of the intake valve 5 determined from the operating state of the engine, and IC indicates the reference valve-closing timing of the intake valve 5. When the actual compression ratio is to be increased when the Miller cycle is employed, the variable valve timing mechanism 15 moves the intake valve drive cam of the camshaft 14 to the retard side, as a result, as shown in FIG. The closing timing IC 'of the intake valve 5 is retarded as indicated by the broken line in FIG. When the closing timing IC ‘of the intake valve 5 is retarded, the actual compression ratio is increased, and the TDC temperature is increased.

  FIG. 7 shows the relationship between the flame propagation combustion area, the diffusion combustion area, the engine speed, and the output torque of the engine. In the example shown in FIG. 7, when the fuel injection amount is large and the output torque of the engine is high, a diffusion combustion area is set. In this diffusion combustion area, as shown in FIG. 3, the preliminary injection and the main injection are performed. The main fuel spray F2 is diffused and burned. On the other hand, in the example shown in FIG. 7, when the fuel injection amount is small and the output torque of the engine is low, the flame propagation combustion area is reached. In this flame propagation combustion area, all fuel is injected from the fuel injection valve 9 before compression top dead center TDC. Is injected, and the flame generated by the ignition action of the spark plug 10 causes the entire fuel to be flame propagated and burned.

  Next, an engine operation control routine will be described with reference to FIG. This routine is executed by interruption every fixed time. As described above, a spark plug capable of controlling the ignition timing can be used as the ignition plug 10, and a heating element such as a glow plug which does not require management of the ignition timing can also be used. Hereinafter, an operation control routine of the engine will be described by taking a spark plug capable of controlling the ignition timing as the spark plug 10 as an example. Further, an operation control routine of the engine will be described by taking, as an example, a case in which an Atkinson cycle for controlling the amount of intake air into the combustion chamber 4 by controlling the closing timing of the intake valve 5 is employed.

  Referring to FIG. 8, first, at step 20, it is judged if the operating condition of the engine is in the diffusion combustion zone shown in FIG. When it is determined that the operating state of the engine is not in the diffusion combustion zone shown in FIG. 7, that is, when the operating state of the engine is determined to be the flame propagation combustion zone shown in FIG. Propagation combustion is performed. That is, in step 21, the reference closing timing of the intake valve 5 corresponding to the operating state of the engine stored in advance in the ROM of the electronic control unit 13 is read, and the closing timing of the intake valve 5 is the reference closing. It is considered time. Next, at step 22, the total injection fuel amount, the injection timing and the ignition timing according to the operating state of the engine prestored in the ROM of the electronic control unit 13 are read, and according to these values Fuel injection control and ignition control of the spark plug 10 are performed. At this time, all the fuel injected from the fuel injection valve 9 is subjected to flame propagation combustion by the flame generated by the ignition action of the spark plug 10.

  On the other hand, when it is determined in step 20 that the operating state of the engine is in the diffusion combustion area shown in FIG. 7, the process proceeds to step 23, and the pressure in the combustion chamber 4 at the compression top dead center TDC from the output signal of (TDC in-cylinder pressure) is calculated. Next, at step 24, the intake air amount detected by the intake air amount detector 11, the atmospheric pressure detected by the atmospheric pressure detection sensor, the atmospheric temperature detected by the atmospheric temperature detection sensor, the rotational speed detection sensor The amount (g) of intake air charged into the combustion chamber 4 is calculated from the engine speed. Next, at step 25, for example, using the equation of state (PV = nRT), the temperature in the combustion chamber 4 at the compression top dead center TDC, that is, the TDC temperature is calculated. That is, the in-cylinder pressure P at the compression top dead center TDC calculated from the output signal of the pressure sensor 12, the combustion chamber volume V, the intake air amount (g) filled in the combustion chamber 4 and the weight of air (g / g The TDC temperature T is calculated from the number of moles n calculated from mol) and the gas constant R. In this case, the TDC temperature calculated in this manner can be corrected by the amount of residual gas remaining in the cylinder during the intake stroke.

  Next, at step 26, it is judged if the TDC temperature is higher than the stable diffusion combustion temperature TK (FIG. 5). When the TDC temperature is lower than the stable diffusion combustion temperature TK, the process proceeds to step 27, the valve closing timing of the intake valve 5 is advanced by one degree by the variable valve timing mechanism 15, and then the process proceeds to step 22. At this time, a flame propagation combustion zone is performed. Thereafter, the closing timing of the intake valve 5 continues to be advanced by one degree until it is determined in step 26 that the TDC temperature is higher than the stable diffusion combustion temperature TK. Next, when it is determined in step 26 that the TDC temperature is higher than the stable diffusion combustion temperature TK, it is determined that stable diffusion combustion can be performed, and the process proceeds to step 28.

  In step 28, it is judged if the TDC temperature is the stable diffusion combustion temperature TK + α, that is, if the TDC temperature is excessively higher than the stable diffusion combustion temperature TK. If it is determined that the TDC temperature is lower than the stable diffusion combustion temperature TK + α, the process proceeds to step 30. In step 30, the amount of fuel for preliminary injection, the injection timing, and the ignition timing according to the operating state of the engine stored in advance in the ROM of the electronic control unit 13 are read, and preliminary values from the fuel injection valve 9 are read according to these values. Fuel injection control of injection and ignition control of the spark plug 10 are performed. At this time, a flame is generated by the ignition action of the spark plug 10. Next, at step 31, the fuel amount and injection timing of the main injection according to the operating state of the engine stored in advance in the ROM of the electronic control unit 13 are read, and the main injection from the fuel injection valve 9 is performed according to these values. Fuel injection control is performed. At this time, the main injection fuel is injected into the generated flame, and stable diffusion combustion is performed.

  On the other hand, when it is determined that the TDC temperature has become higher than the stable diffusion combustion temperature TK + α, the routine proceeds to step 29, where the variable valve timing mechanism 15 retards the closing timing of the intake valve 5 by one degree. Next, the process proceeds to step 30. The determination of whether the TDC temperature exceeds the stable diffusion combustion temperature TK performed in step 26 is made by detecting the change in angular velocity of the crankshaft from the output signal of the rotation number detection sensor, that is, the crank angle sensor. It can also be judged. That is, immediately before the compression top dead center TDC, the in-cylinder temperature rises, thereby increasing the in-cylinder pressure and reducing the angular velocity of the crankshaft. In this case, if the increase amount of the in-cylinder temperature is large, the decrease amount of the angular velocity of the crankshaft becomes large. Therefore, when the reduction amount of the angular velocity of the crankshaft immediately before the compression top dead center TDC exceeds a predetermined value, it can be determined that the TDC temperature exceeds the stable diffusion combustion temperature TK.

4 combustion chamber 5 intake valve 7 exhaust valve 9 fuel injection valve 13 electronic control unit

Claims (1)

  A fuel injection valve and an ignition plug are disposed in the combustion chamber, fuel injection is performed a plurality of times from the fuel injection valve into the combustion chamber in one cycle, and the spray by the first fuel injection is ignited by the ignition plug to generate a flame. Then, in the control device for an internal combustion engine in which the spray by the second and subsequent fuel injections is injected into the flame for diffusion combustion, the fuel injection valve is disposed at the central portion of the combustion chamber, and the fuel injection is performed. If the spark plug is placed at the periphery of the combustion chamber at a distance of 1/2 or more of the cylinder bore radius from the valve and the in-cylinder temperature at the time of fuel injection for the second and subsequent times is less than the stable diffusion combustion temperature Control system for internal combustion engines to raise.