JP6148155B2 - Control system for compression ignition internal combustion engine - Google Patents

Description

  The present invention relates to a control system for a compression ignition type internal combustion engine.

  In a compression ignition type internal combustion engine such as a diesel engine, fuel is directly injected into compressed air in a cylinder from a fuel injection valve provided near the center of the cylinder. In order to improve the output of an internal combustion engine and to suppress smoke (soot) emission due to incomplete combustion, conventionally, it was injected using a swirl generated in a cavity (combustion chamber) formed at the top of the piston Techniques for effectively diffusing fuel spray are known.

  Here, for example, Patent Document 1 proposes a technique for adjusting the interval between sprays that are injected from each nozzle hole of the fuel injection valve and adjacent to each other in the swirl flow direction within a predetermined range that can suppress the occurrence of smoke. Has been. In this technique, the interval between fuel sprays is calculated from the wall surface collision time, which is the time until the injected spray collides with the wall surface of the cavity, the swirl downstream side surface position, and the swirl upstream side surface position. Then, the fuel injection conditions and the opening of the swirl control valve (SCV) are adjusted so that this interval falls within a predetermined range.

  By the way, when the injected fuel spray collides with the cavity wall surface, the heat of the flame generated in the vicinity of the wall surface is lost through the wall surface and the cooling loss increases, and the smoke increases due to the fuel spray being biased in the vicinity of the wall surface. There is a fear. Therefore, for example, in Patent Document 2, the number of multi-stage fuel injections is increased according to the injection amount so that the fuel spray does not reach the cavity wall surface in order to reduce cooling loss and smoke due to the fuel spray wall surface collision. Techniques to make it have been proposed.

JP 2013-160194 A JP 2012-229691 A

  By the way, in the technique described in Patent Document 1, in order to calculate the interval between the fuel sprays, a spray angle (a spread angle of the fuel spray) that changes according to the fuel injection pressure or the injection amount is used. The calculation method can be complicated. As a result, calculations for adjusting fuel injection conditions and SCV opening can be complicated. Further, the technique described in Patent Document 2 is not necessarily effective when the number of times of multistage injection is limited in terms of time, such as when the rotational speed of the internal combustion engine is high or when the fuel injection amount is large. .

  The present invention has been made in view of such a situation, and an object of the present invention is to reduce cooling loss by a simpler arithmetic process in a control system for a compression ignition internal combustion engine that controls a swirl ratio of a swirl in a cavity. It is an object of the present invention to provide a control system capable of reducing smoke while suppressing the above.

In order to solve the above-described problem, a control system for a compression ignition internal combustion engine according to the present invention includes a central portion of a cylinder that injects fuel from an injection hole toward an inner wall surface of a cavity formed at the top of a piston. A fuel injection valve provided in the vicinity, swirl control means for controlling a swirl ratio of a swirl generated in a combustion chamber including the cavity, and at a time when the temperature in the cylinder becomes highest during combustion of the injected fuel In a control system for a compression ignition type internal combustion engine, comprising a specifying means for specifying a certain maximum temperature time point, a distance from the nozzle hole to a position where the tip of the fuel spray is assumed to reach at the maximum temperature time point Is the distance from the nozzle hole to the opening edge of the cavity at the time of the maximum temperature, and the traveling direction of the tip of the spray from the nozzle hole On the cross section of the piston including the drawn line segment and the central axis of the piston, the line segment extends along the inner wall surface from the intersection point to the opening edge via the intersection point where the line segment intersects the inner wall surface. When the distance of the route is L2, the swirl control means controls the swirl ratio so that the value of L1 / L2 becomes 1.1.

  The fuel injection valve has a plurality of injection holes, and each injection hole injects fuel toward the inner wall surface of the cavity. Since the fuel is injected from the nozzle hole at a high pressure, the fuel is atomized and diffused into the cavity. The swirl control means is a means for controlling the swirl ratio of the swirl generated in the combustion chamber including the cavity (rotational angular velocity of the swirl with respect to the rotational angular velocity of the crankshaft). For example, a swirl control valve (SCV) is used. is there. Spray dispersion in the cavity is known to correlate with the swirl swirl ratio. Further, the specifying means specifies, for example, the crank angle at which the in-cylinder temperature becomes the highest during the combustion of the next injected fuel as the maximum temperature point from the history of the in-cylinder temperature one cycle before.

  Generally, when the fuel spray diffuses to the vicinity of the inner wall surface of the cavity, the cooling loss at which heat in the cylinder is lost through the inner wall surface increases. The amount of cooling loss is represented by the product of the heat transfer coefficient α determined by physical properties such as the gas flow velocity in the cavity and the temperature gradient ΔT between the gas in the cavity and the inner wall surface. For this reason, the cooling loss becomes particularly large in the combustion cycle of the internal combustion engine during a period of fuel combustion in which the temperature gradient ΔT increases as the in-cylinder temperature rises. Here, when the swirl exists in the cavity, both the heat transfer coefficient α and the temperature gradient ΔT can be changed by the swirl. Specifically, the heat transfer coefficient α tends to increase when the swirl ratio is large. This is because when the swirl ratio is large, the flow velocity of the gas increases, and the temperature boundary layer between the gas in the cylinder and the inner wall surface of the cavity becomes thin. On the other hand, the temperature gradient ΔT tends to decrease when the swirl ratio is large. This is because when the swirl ratio is large, diffusion of fuel spray in the cavity outer diameter direction is hindered, so that a relatively large amount of flame after ignition stays near the center of the cavity. This is because the temperature difference between the gas near the wall surface and the inner wall surface becomes small. Here, as a result of verification by the inventors of the present application, it has been found that during combustion of fuel in which the cooling loss increases, the cooling loss decreases as the swirl ratio increases. That is, during the combustion of the fuel whose in-cylinder temperature is high, the influence of the temperature gradient ΔT on the cooling loss becomes dominant. Therefore, in order to effectively reduce the cooling loss, it can be said that it is effective to increase the swirl ratio so that the fuel spray (flame after ignition) does not reach the inner wall surface. In particular, it can be said that it is most effective to increase the swirl ratio at the maximum temperature point, which is the point at which the temperature in the cylinder becomes the highest during fuel combustion.

  However, if the swirl ratio is excessively increased, the amount of smoke discharged may increase due to the fuel spray being excessively distributed near the center of the cavity. Here, an increase in smoke emission is not preferable from the viewpoint of emission regulations. Therefore, according to the control system of the present invention, the swirl ratio at the maximum temperature point is controlled so that the smoke discharge amount is further reduced on the premise of reducing the cooling loss.

By the way, in the control of the swirl ratio of the swirl generated in the combustion chamber including the cavity, the spray characteristics (spray reach distance and spray angle) of the fuel spray are generally used as control parameters. The spray characteristics can be calculated from the in-cylinder state such as the temperature, pressure, and density of the gas in the cylinder, and the injection conditions such as the fuel injection timing, the injection amount, and the injection pressure, but the processing can be complicated. . Therefore, according to the control system of the present invention, the swirl ratio is controlled without using the spray angle as a parameter.

  Specifically, in the swirl ratio control in the present invention, the swirl ratio is controlled using the distances L1 and L2 so that the value of L1 / L2 becomes 1.1. Here, the distance L1 is the distance from the nozzle hole to the position where the tip of the spray of fuel to be injected is supposed to reach at the above-mentioned maximum temperature point. This distance L1 (hereinafter also referred to as “reaching distance L1”) can be calculated from the in-cylinder state, the injection conditions, the swirl ratio (swirl speed), and the crank angle. Note that, depending on the injection conditions and the swirl ratio, the calculated reach distance L1 may be larger than the distance from the injection hole to the inner wall surface of the cavity. In this case, it is considered that the spray sprayed actually collides with the inner wall surface of the cavity and then diffuses. However, since the calculated reach distance L1 is a virtual value, in the swirl control in the present invention, Is used as is.

  Further, the distance L2 (hereinafter also referred to as “path distance L2”) is such that the spray that collides with the inner wall surface is further diffused along the inner wall surface in the direction of the piston top surface, so that the tip is opened at the maximum temperature. This can be regarded as the reaching distance of the tip when it is assumed that the edge has been reached. This path distance L2 can be calculated geometrically from the traveling direction of the tip of the spray, the shape of the inner wall surface (line profile) on the above-mentioned cross section, and the position of the piston at the crank angle at the maximum temperature. That is, in calculating the path distance L2, it is not necessary to consider the in-cylinder state and the injection conditions, so the calculation process is relatively simple.

  Then, when the value of L1 / L2 is calculated using the reach distance L1 and the elapsed distance L2 defined as described above, the diffusion state of the fuel spray in the cavity (for example, the spray is in the cavity) It is possible to grasp to some extent whether or not it has reached the opening edge. Here, in order to elucidate the more detailed relationship between the diffusion of the fuel spray and the smoke emission amount at the time of the above-mentioned maximum temperature, the inventor of the present application uses the value of L1 / L2 and the combustion of the fuel spray. As a result of verifying the relationship with the amount of smoke discharged, it was found that when the value of L1 / L2 is 1.1, the amount of smoke discharged is the lowest. Since there is a correlation between the swirl ratio and the fuel reach distance L1, the value of L1 / L2 can be adjusted by changing the swirl ratio. In particular, when the value of L1 / L2 is greater than 1.1, the swirl ratio may be increased to prevent the fuel spray from diffusing in the direction of the outer diameter of the cavity. Thus, the smoke discharge amount can be reduced by reducing the reach distance L1 and bringing the value of L1 / L2 closer to 1.1 while reducing the cooling loss. Therefore, if the swirl ratio is controlled so that the value of L1 / L2 at the time when the in-cylinder temperature becomes maximum is 1.1, it is possible to reduce smoke while suppressing cooling loss.

  As described above, according to the control system of the present invention, the swirl control means controls the swirl ratio so that the value of L1 / L2 becomes 1.1, so that the smoke discharge amount is reduced while suppressing the cooling loss. Is possible. The control of the swirl ratio uses the fuel spray reach distance L1 as a parameter, but does not use the fuel spray spray angle. Therefore, according to the control system according to the present invention, it is possible to control the swirl ratio by a simpler arithmetic process compared to the conventional control in which the spray angle needs to be calculated based on the fuel injection condition. become.

  According to the present invention, in a control system for a compression ignition internal combustion engine that controls the swirl ratio of the swirl in the cavity, smoke can be reduced while suppressing cooling loss by simpler arithmetic processing.

It is a figure which shows schematic structure of the compression ignition type internal combustion engine which concerns on an Example. It is a figure which shows schematic structure in the cylinder which concerns on an Example. It is a graph which shows transition of the cooling loss in a cylinder before and after compression top dead center. It is a flowchart which shows the routine of the swirl ratio control which concerns on an Example. It is a graph which shows the relationship between the value of L1 / L2, and a smoke discharge amount. It is a graph which shows the relationship between the value of L1 / L2, and a cooling loss. It is a flowchart which shows the other routine of swirl ratio control. It is a graph which shows the relationship between the spray angle and the amount of smoke discharged at the time of the highest in-cylinder temperature.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

[Example]
FIG. 1 is a diagram showing a schematic configuration of a compression ignition type internal combustion engine according to the present embodiment. An internal combustion engine 10 that is a compression ignition internal combustion engine is a diesel engine for a vehicle having a plurality of cylinders 11. A fuel injection valve 20 for injecting fuel into the combustion chamber is provided at the center of the cylinder 11. The fuel injection valve 20 is provided with a plurality of injection holes 21 for injecting fuel at the tip thereof, and fuel accumulated by a common rail (not shown) or the like is injected from the injection holes 21 at a high pressure (see FIG. 2). . In the cylinder 11, a piston 22 connected to a crankshaft (not shown) is provided, and a cavity 23 is formed at the top of the piston.

  An intake passage 13 is connected to the cylinder 11 via an intake port 12. The intake port 12 is provided with a swirl control valve (SCV) 14 for controlling a swirl ratio of a swirl (swirl flow around the cylinder axis of the cylinder 11) generated in the combustion chamber including the cavity 23. Specifically, the intake port 12 includes two systems, a normal port and a swirl port, and an SCV 14 including a butterfly valve capable of adjusting the opening is disposed in the normal port. The opening of the SCV 14 is adjusted by an actuator (not shown). As the opening of the SCV 14 increases, the amount of air sucked into the cylinder 11 from the normal port increases, so that the swirl generated by the intake air flowing from the swirl port is relatively weakened (the swirl ratio becomes small). Conversely, the smaller the opening of the SCV 14, the stronger the swirl (the swirl ratio increases).

  The intake passage 13 is provided with a throttle valve 15 for adjusting the flow rate of intake air taken into the cylinder 11 and an air flow meter 16 for detecting the flow rate. An exhaust passage 30 is connected to the cylinder 11 via an exhaust port. The exhaust passage 30 may be provided with various sensors, a catalyst having an oxidation function, a filter for collecting particulate matter (PM) in the exhaust, and the like.

The internal combustion engine 10 is also provided with an ECU 100 that is an electronic control unit for controlling the internal combustion engine 10. The ECU 100 is electrically connected to the SCV 14, the throttle valve 15, and the fuel injection valve 20, and these are controlled by the ECU 100. In addition, the ECU 100 receives an output signal from the electrically connected air flow meter 16. The ECU 100 is electrically connected to a crank position sensor 31 that detects the rotational position of the crankshaft of the internal combustion engine 10 and an accelerator opening sensor 32 that detects the opening of an accelerator pedal provided in the vehicle. Output signals from these are input to the ECU 100. The ECU 100 can grasp the operating state of the internal combustion engine 10 such as the engine load and the in-cylinder state of the cylinder 11 based on the input output signal. In this embodiment, the SCV 14 corresponds to the swirl control means in the present invention.

  Next, diffusion of fuel spray in the cylinder 11 will be described with reference to FIG. FIG. 2 is a diagram illustrating a schematic configuration in the cylinder 11 according to the embodiment. More specifically, FIG. 2 is a schematic diagram of the piston 22 including a line segment drawn from one nozzle hole 21 of the plurality of nozzle holes 21 in the traveling direction of the tip of the fuel spray F and the central axis C of the piston 22. It is a typical sectional view (hatching is omitted). FIG. 2 shows a state in the cylinder 11 at a time (maximum temperature time) when the temperature in the cylinder 11 (in-cylinder temperature) becomes highest during combustion of the fuel spray F being injected. .

  As shown in FIG. 2, the cavity 23 formed at the top of the piston 22 is a so-called toroidal cavity having a crown 24 raised at the center thereof. The cavity 23 together with the bottom surface of the cylinder head of the internal combustion engine 10 forms a combustion chamber in which fuel burns. An inner wall surface 25 is formed from the bottom of the cavity 23 toward an opening edge 27 formed on the top surface 26 of the piston 22. Since the cavity 23 has such a shape, a swirl around the cylinder axis C is suitably formed in the cavity 23 when intake air flows in from the intake port 12 while the intake valve (not shown) is opened. A squish along the inner wall surface 25 is also formed by the reciprocating motion of the piston 22 in the cylinder axis C direction.

  The fuel injection valve 20 provided at the center of the cylinder 11 injects high-pressure fuel from the injection hole 21 at a predetermined injection timing. The ECU 100 determines injection conditions such as fuel injection timing based on the operating state of the internal combustion engine 10. The injected fuel becomes a mist-like fuel spray F (hereinafter also simply referred to as “spray”) and diffuses into the cavity 23. Here, as shown in FIG. 2, the tip of the spray advances in the combustion chamber in the direction of the injection angle Φ. The installation position, the diameter, and the like of the injection hole 21 are determined in advance so that the tip of the injected spray proceeds toward the inner wall surface 25 at the injection angle Φ. Here, L1 shown in FIG. 2 indicates an arrival distance L1 that is a distance from the nozzle hole 21 to a position where the tip of the spray is assumed to arrive at the maximum temperature point. This reach distance L1 correlates with fuel injection conditions (injection timing, injection amount, injection pressure), in-cylinder state (in-cylinder density, in-cylinder pressure, in-cylinder temperature) and swirl ratio (or swirl speed). is there. Accordingly, the reach distance L1 can be calculated by appropriately detecting or calculating these physical quantities. L2 shown in FIG. 2 is the distance from the nozzle hole 21 to the opening edge 27 of the cavity 23 at the maximum temperature, and the line segment drawn from the nozzle hole 21 in the traveling direction of the tip of the spray is the inner wall surface. A route distance L2 (a distance indicated by a thick line in FIG. 2), which is a route distance extending along the inner wall surface 25 from the intersection point P to the point Q on the opening edge 27 via the intersection point P that intersects with 25. This path distance L2 can be calculated geometrically from the injection angle Φ, which is the traveling direction of the tip of the spray, the shape of the inner wall surface 25 (line profile), and the position of the piston 22 at the crank angle at the maximum temperature. . When the value of L1 / L2 is calculated using the reach distance L1 and the elapsed distance L2 defined as described above, it is possible to grasp to some extent the spray diffusion state in the cavity 23 based on the values. Become.

By the way, the heat in the combustion chamber (cavity 23) is reduced by the cooling loss through the inner wall surface of the combustion chamber. This cooling loss is generally represented by the product of a heat transfer coefficient α determined by gas property values such as flow velocity in the combustion chamber, and a temperature gradient ΔT between the in-cylinder gas and the inner wall surface. However, when a swirl is present in the cavity 23, both the heat transfer coefficient α and the temperature gradient ΔT are affected, resulting in a change in cooling loss. Hereinafter, the relationship between the cooling loss and the swirl will be described with reference to FIG. FIG. 3 is a graph showing the transition of the cooling loss in the cylinder 11 before and after the compression top dead center. FIG. 3 shows the transition during high load operation with a large amount of fuel injection. In FIG. 3, the horizontal axis indicates the crank angle before and after the compression top dead center (compression TDC), and the vertical axis indicates the amount of cooling loss (heat flux). Note that a graph G1 indicated by a solid line shows a change in cooling loss of spray sprayed when the swirl ratio is relatively small, and a graph G2 indicated by a one-dot chain line indicates when the swirl ratio is relatively large. The transition of the cooling loss of the spray sprayed is shown.

  As shown in FIG. 3, in the period before the spray ignition time T0, the cooling loss is larger when the swirl ratio is larger than when it is small. Here, before the ignition of the spray, since the temperature gradient ΔT between the in-cylinder temperature and the inner wall surface of the combustion chamber is relatively low, the influence of the heat transfer coefficient α on the cooling loss becomes dominant. When the swirl ratio is large, the heat transfer coefficient α increases as the temperature boundary layer between the in-cylinder gas and the inner wall surface 25 becomes thinner as the gas flow rate increases, resulting in an increase in cooling loss. To do.

  On the other hand, in the period after the ignition time T0, the cooling loss is smaller when the swirl ratio is larger than when it is small. As already described, during the period after ignition when the in-cylinder temperature is high (during fuel combustion), the influence of the temperature gradient ΔT on the cooling loss becomes dominant. When the swirl ratio is large, the temperature gradient ΔT is lowered by inhibiting the diffusion of the spray in the outer diameter direction of the cavity 23, and as a result, the cooling loss is reduced. That is, after the ignition of the spray, the influence of the decrease in the temperature gradient ΔT due to the increase in the swirl ratio is greater than the increase in the heat transfer coefficient α due to the increase in the swirl ratio.

  As shown in FIG. 3, the amount of cooling loss gradually decreases after reaching the maximum at the crank angle T1 at which the in-cylinder temperature is highest. At the crank angle T1, the difference between the cooling loss G1 when the swirl ratio is small and the cooling loss G2 when the swirl ratio is large is the largest. Therefore, in order to reduce the cooling loss, it can be said that it is effective to increase the swirl ratio at the time when the in-cylinder temperature becomes the highest and suppress the diffusion of the fuel spray (flame after ignition). Therefore, in the swirl ratio control according to the present embodiment, the swirl ratio at the crank angle T1 at which the in-cylinder temperature is highest is controlled.

  However, if the swirl ratio is excessively increased, the amount of smoke discharged may increase due to the spray being excessively distributed near the center of the cavity 23. Therefore, in the swirl control according to the present embodiment, the swirl ratio at the time of the maximum temperature is controlled so that the smoke discharge amount is further reduced on the premise of reducing the cooling loss. Hereinafter, a method for controlling a swirl ratio according to the present embodiment will be described with reference to the drawings.

  FIG. 4 is a flowchart showing a routine for controlling the swirl ratio performed by the ECU 100. This routine is executed by the ECU 100 at predetermined time intervals, for example.

  First, in step S101, the ECU 100 acquires the operating state of the internal combustion engine 10 and the fuel injection conditions during execution of this routine. Next, in step S102, the ECU 100 calculates the in-cylinder state of the cylinder 11 based on the operating state acquired in the previous step. Next, in step S103, the ECU 100 calculates the swirl speed in the cylinder 11. This swirl speed is calculated based on the swirl ratio at the time of execution of this routine, that is, the opening of the SCV 14 and the detected value of the air flow meter 16.

  Next, in step S104, the ECU 100 specifies a maximum temperature time point, which is a time point when the temperature in the cylinder 11 becomes the highest during combustion of fuel injected by the next fuel injection. The time point may be, for example, the crank angle at the time when the in-cylinder temperature becomes the highest in the previous combustion. Alternatively, it may be calculated based on the in-cylinder state in a plurality of past combustions, or a value corresponding to the operating state or in-cylinder state is read from a numerical map in which data obtained experimentally in advance is stored. But you can. Note that the ECU 100 that specifies the maximum temperature point in this step corresponds to the specifying means in the present invention.

  Next, in step S105, the ECU 100 calculates an arrival distance L1 of the fuel spray injected by the next fuel injection. This reach distance L1 is calculated based on each physical quantity acquired or calculated in the previous step. Similarly, in step S106, the ECU 100 calculates the path distance L2 of the fuel spray injected by the next fuel injection.

  Next, in step S107, the ECU 100 determines whether or not the value of L1 / L2 is equal to 1.1. Here, the relationship between the value of L1 / L2 and the smoke discharge amount will be described with reference to FIG. FIG. 5 is a graph showing the relationship between the value of L1 / L2 and the amount of smoke discharged at the time when the in-cylinder temperature is highest after ignition of the injected spray. In FIG. 5, the horizontal axis indicates the value of L1 / L2, and the vertical axis indicates the smoke discharge amount.

  As shown in FIG. 5, when the value of L1 / L2 is 1.1, the smoke discharge amount is the lowest. Therefore, if an affirmative determination is made in this step, the smoke discharge amount can be reduced while suppressing the cooling loss even if the swirl ratio is not adjusted during the execution of this routine. Therefore, the ECU 100 ends this routine without adjusting the swirl ratio. In the determination in this step, when a range including 1.1 is set and the value of L1 / L2 is within the range, the positive determination is made assuming that the value of L1 / L2 is approximately 1.1. You may be made to do.

  If a negative determination is made in step S107, the ECU 100 proceeds to step S108 and determines whether or not the value of L1 / L2 is greater than 1.1. Here, as shown in FIG. 5, when the value of L1 / L2 is larger than 1.1, that is, when the reach distance L1 is relatively long, the spray sprayed on the outer diameter side of the cavity 23 Due to the uneven distribution, the amount of smoke discharged becomes relatively large. In this case, the value of L1 / L2 can be brought close to 1.1 by increasing the swirl, ie, increasing the swirl ratio. Therefore, if an affirmative determination is made in this step, the ECU 100 proceeds to step S109 and adjusts the SCV 14 so that the swirl ratio becomes large. Then, ECU 100 executes the steps from step S103 again.

  On the other hand, as shown in FIG. 5, when the value of L1 / L2 is smaller than 1.1, that is, when the reach distance L1 is relatively short, near the center of the cavity 23 where the intake air is relatively small, Since the injected spray is unevenly distributed, the smoke discharge amount is relatively increased. In this case, the value of L1 / L2 can be brought close to 1.1 by weakening the swirl, that is, reducing the swirl ratio. Therefore, if a negative determination is made in step S108, the ECU 100 proceeds to step S110 and adjusts the SCV 14 so that the swirl ratio becomes small. Then, ECU 100 executes the steps from step S103 again.

  According to the control according to the present embodiment, since the swirl ratio of the SCV 14 is controlled by the ECU 100 so that the value of L1 / L2 becomes 1.1, it is possible to reduce the smoke discharge amount while suppressing the cooling loss. it can. In this control, although the spray reach distance L1 is used as a parameter, since the spray angle of the spray is not used, it is not necessary to calculate the spray angle according to the injection condition or the like. Therefore, according to the present embodiment, it is possible to reduce smoke while suppressing cooling loss by a simpler arithmetic process compared to conventional swirl ratio control.

[Other examples of swirl ratio control]
Unlike the above embodiment, in the swirl ratio control, if the injection angle is further used as a parameter and control is performed so that the value of L1 / L2 is less than 1, the arithmetic processing becomes complicated, but the cooling loss is reduced. It becomes possible to reduce more effectively. Hereinafter, an example of such swirl ratio control will be described.

  First, the relationship between the value of L1 / L2 and the cooling loss will be described with reference to FIG. FIG. 6 is a graph showing the relationship between the value of L1 / L2 and the cooling loss, where the horizontal axis shows the value of L1 / L2, and the vertical axis shows the amount of cooling loss.

  As shown in FIG. 6, the value of the cooling loss decreases as the value of L1 / L2 decreases, that is, as the spray spray does not diffuse and stays on the inner diameter side of the cavity 23. In particular, when the value of L1 / L2 is less than 1, that is, when the tip of the fuel spray does not reach the opening edge 27 of the cavity 23, the degree of reduction in cooling loss is large. Therefore, in order to more effectively reduce the cooling loss of the combustion heat, the value of L1 / L2 may be reduced to less than 1. As described above, if the swirl ratio is increased, the reach distance L1 can be shortened, so that the value of L1 / L2 can be reduced. However, if the swirl ratio is excessively increased, the spray tends to be biased near the center of the cylinder 11, so that the amount of smoke discharged may increase due to the overlap of the sprays injected from the adjacent injection holes 21. Therefore, in this control, the spray angle of the spray is further considered in order to suppress the overlap of sprays.

  Hereinafter, another example of the swirl ratio control will be described with reference to the drawings. FIG. 7 is a flowchart showing a routine of this control, which is performed by the ECU 100. This routine is executed by the ECU 100 at predetermined time intervals, for example. Note that the processing up to step S106 in this routine is the same as the routine shown in FIG.

  When the path distance L2 is calculated in step S106, the ECU 100 proceeds to step S207 and calculates the spray angle θ of the spray injected by the next fuel injection. The spray angle θ is calculated from a well-known arithmetic expression (for example, “Huan's expression”) based on each physical quantity acquired or calculated in the previous step. Or you may read the value according to the driving | running state and the in-cylinder state from the numerical map in which the data calculated | required experimentally beforehand are stored.

  Next, in step S208, the ECU 100 determines whether or not the value of L1 / L2 is less than 1. If an affirmative determination is made in this step, the smoke discharge amount can be reduced while further reducing the cooling loss even if the swirl ratio is not adjusted during execution of this routine. Therefore, the ECU 100 ends this routine without adjusting the swirl ratio.

  On the other hand, if a negative determination is made in step S208, the ECU 100 proceeds to step S209, and adjusts the swirl ratio in order to decrease the value of L1 / L2. In this step, the swirl ratio is basically increased. Next, in step S210, the ECU 100 recalculates the swirl speed and the spray characteristics (the reach distance L1, the path distance L2, and the spray angle θ) based on the increased swirl ratio. In step S211, the ECU 100 determines whether or not the spray angle θ acquired by recalculation is equal to 360 ° / the number of nozzle holes. Here, the relationship between the spray angle θ and the smoke discharge amount will be described with reference to FIG. FIG. 8 is a graph showing the relationship between the spray angle θ and the smoke discharge amount at the maximum temperature. The spray angle θ is a spread angle of the spray when the spray injected from the injection hole 21 is viewed from above the cylinder 11 as schematically shown in the lower right of FIG. In FIG. 8, the horizontal axis indicates the spray angle θ, and the vertical axis indicates the smoke discharge amount.

As shown in FIG. 8, as the spray angle θ becomes larger than 360 ° / the number of nozzle holes, the degree of overlap between the sprays injected from the adjacent nozzle holes 21 increases, so that a region where the spray concentration is high occurs. This increases smoke emissions. On the other hand, as the spray angle θ is smaller than 360 ° / the number of nozzle holes, the degree of overlap is reduced, but the concentration of each spray is relatively high, so that the smoke discharge amount is also increased. Therefore, when the spray angle θ is equal to 360 ° / the number of nozzle holes, the smoke discharge amount becomes the lowest. Therefore, if an affirmative determination is made in this step, it means that the smoke discharge amount can be reduced by using the swirl ratio increased in step S209. Therefore, the ECU 100 returns to step S208 and determines again whether or not the value of L1 / L2 is less than 1. In the determination in this step, a range including 360 ° / the number of injection holes may be set, and a positive determination may be made when the spray angle θ is within the range.

  On the other hand, if a negative determination is made in step S211, the ECU 100 returns to step S209 and adjusts the swirl ratio again. In this case, the swirl ratio is adjusted so that the spray angle θ approaches 360 ° / the number of nozzle holes.

  According to this control, the ECU 100 controls the swirl ratio of the SCV 14 so that the value of L1 / L2 is less than 1. Therefore, it is possible to more effectively reduce the cooling loss. In this control, the swirl ratio is controlled so that the spray angle θ is equal to 360 ° / the number of nozzle holes. Therefore, according to this control, smoke can be reduced while cooling loss is more effectively reduced.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11 Cylinder 20 Fuel injection valve 21 Injection hole 22 Piston 23 Cavity 100 ECU
L1 Distance L2 Route distance

Claims (1)

A fuel injection valve provided near the center of the cylinder for injecting fuel from the injection hole toward the inner wall surface of the cavity formed at the top of the piston;
Swirl control means for controlling the swirl ratio of the swirl generated in the combustion chamber including the cavity;
A specifying means for specifying a maximum temperature time point, which is a time point when the temperature in the cylinder becomes highest during combustion of the injected fuel;
In a control system for a compression ignition type internal combustion engine comprising:
The distance from the nozzle hole to the position where the tip of the fuel spray is assumed to reach at the maximum temperature point is L1,
The distance between the nozzle hole and the opening edge of the cavity at the highest temperature point, and includes a line segment drawn from the nozzle hole in the traveling direction of the tip of the spray and a central axis of the piston. On the cross-section, when the distance of the path extending along the inner wall surface from the intersection point to the opening edge through the intersection point where the line segment intersects the inner wall surface is L2,
The control system for the compression ignition type internal combustion engine, wherein the swirl control means controls the swirl ratio so that the value of L1 / L2 becomes 1.1.

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