JP2012107601A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine capable of contributing to improvement of various kinds of performance such as output performance, fuel economy performance and exhaust performance by improving combustion with a simple constitution and at low cost to reduce load to a post-treatment system.SOLUTION: This internal combustion engine 1 controls at least one of an excess air ratio, an EGR rate and a residual gas rate so that an oxygen molar fraction of intake air (new air (outside air) and EGR gas, etc.) led to the inside of a combustion chamber 5 is a target oxygen molar fraction. The excess air ratio is controlled by changing intake charging efficiency by controlling valve opening and closing characteristics by a variable valve mechanism (VVA mechanism 200).

Description

  The present invention relates to an internal combustion engine control technique that can improve output performance, fuel consumption performance, exhaust performance, and the like of an internal combustion engine (engine) equipped with an EGR system.

  Purifying the exhaust from the internal combustion engine to suppress the spread of air pollution is an important issue. As one of the systems (apparatus) for this purpose, a part of the exhaust is recirculated into the combustion chamber and recombusted. A so-called EGR (Exhaust Gas Recirculation) system is known for reducing the combustion temperature and reducing the concentration (exhaust amount) of nitrogen oxides (hereinafter referred to as NOx) in exhaust gas (patent) Reference 1 etc.).

  However, by increasing the flow rate of exhaust gas (EGR gas) recirculated into the combustion chamber and increasing the EGR rate (EGR gas amount / (new air amount + EGR gas amount) × 100 (%)), the amount of NOx emissions is further increased. If we try to reduce it, soot emissions tend to increase.

  That is, NOx emissions and PM containing soot (particulate matter: particulate matter = mainly black smoke (soot), unburned fuel and sour component called SOF, light oil fuel called sulphate The amount of emissions of the components generated from the sulfur content therein and other solid substances) is in a so-called trade-off relationship.

  For this reason, conventionally, in order to improve the mixing of injected fuel and air, for example, a fuel injection valve with a small nozzle diameter and high pressure injection are used together to improve the soot discharge amount (soot discharge concentration). Searching for a point where both NOx emission and soot emission can be achieved while trying.

JP 2008-101544 A

  However, since there is a limit to such high-pressure injection, the burden on an aftertreatment system including a diesel particulate filter and various catalysts (selective reduction type NOx catalyst, etc.) is increasing. However, it is difficult to reduce costs.

  The present invention has been made in view of such circumstances, and can contribute to improvement of various performances such as output performance, fuel consumption performance, and exhaust performance by improving combustion while having a simple and low-cost configuration. An object of the present invention is to provide an internal combustion engine that can reduce the burden on the aftertreatment system.

Therefore, the internal combustion engine according to the present invention is
At least one of the excess air ratio, EGR ratio, and residual gas ratio is controlled so that the oxygen mole fraction of the intake air (fresh air (outside air), EGR gas, etc.) guided into the combustion chamber becomes the target oxygen mole fraction. It is characterized by that.

  The present invention can be characterized in that control is performed to increase the swirl ratio at light loads.

  In the present invention, the excess air ratio can be controlled by changing the intake charging efficiency by controlling the valve opening / closing characteristics by a variable valve mechanism.

  According to the present invention, although it is a simple and low-cost configuration, it can contribute to improvement of various performances such as output performance, fuel consumption performance, and exhaust performance by improving combustion, and thus a burden on the post-processing system. It is possible to provide an internal combustion engine that can reduce the above.

1 is a schematic overall configuration diagram schematically showing an overall configuration of an internal combustion engine according to an embodiment of the present invention. It is a figure for demonstrating the control for implement | achieving the target oxygen mole fraction at the time of the transition of the internal combustion engine which concerns on embodiment same as the above. It is a partial enlarged view of the combustion chamber vicinity for demonstrating the directive port and helical port of an internal combustion engine which concern on embodiment same as the above. It is a figure for demonstrating control of a swirl ratio in the case of the two-stage lift of the intake valve of the internal combustion engine which concerns on embodiment same as the above. It is a figure which shows the relationship between the oxygen mole fraction according to the excess air ratio (lambda), and soot discharge. It is a figure which shows the relationship between the compression top dead center in-cylinder gas temperature according to an EGR rate, and soot discharge amount. It is a figure which shows the relationship between the oxygen mole fraction according to excess air ratio (lambda) and the compression top dead center in-cylinder gas temperature, and a soot discharge amount.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. The present invention is not limited to the embodiments described below.

  The control for improving the combustion of the internal combustion engine according to the embodiment of the present invention is based on the following idea.

The inventors of the present invention are as follows at the 20th internal combustion engine symposium on September 1, 2009 (literature number 20090082, literature title “A Study on the Soot Model in Current Diesel Combustion”, Authors Arisa Kudo and Dai Nakajima). It is announced about such knowledge.

  Here, although the outline is described, when the EGR rate is increased (when the EGR amount is increased) in the same excess air ratio state, the oxygen molar concentration in the cylinder increases because oxygen is contained in the EGR gas. Therefore, it seems that reduction of soot emissions can be expected, but in actual engine experiments, soot emissions tend to deteriorate.

Here, the oxygen molar fraction of the in-cylinder gas is expressed using the excess air ratio, the EGR ratio, and the residual gas ratio.
Oxygen mole fraction≈0.21 × (1-eol) (1)
eol = ((e + r) / (1 + r)) / λ
e: EGR ratio (EGR rate)
r: Residual ratio (residual gas rate)
λ: Excess air ratio (excess air ratio)

From the above equation (1), it is understood that when the EGR rate is increased with respect to the excess air ratio, the in-cylinder oxygen mole fraction decreases.
Therefore, even if the equivalence ratio of the air-fuel mixture immediately before ignition is the same in the jet of fuel injected into the cylinder (in the cylinder, the combustion chamber), the higher the EGR rate with respect to the excess air ratio, It can be seen that the proportion of the inert gas increases and the increase in gas temperature due to combustion decreases.

  In addition, it has been experimentally confirmed that if the excess air ratio is kept constant and the EGR rate is increased, the amount of soot emission increases. As described above, this is because the introduction of EGR gas causes the in-cylinder oxygen concentration to increase. This shows that the soot emission deteriorates even if becomes higher.

  However, as shown in FIG. 5, it was confirmed that the soot discharge amount has a characteristic that it protrudes upward with respect to the oxygen mole fraction. Further, it was confirmed that the soot discharge tends to decrease as the excess air ratio increases even at the same oxygen mole fraction.

  Further, as shown in FIG. 6, it was confirmed that when the EGR rate is low, there is a temperature region in which the soot discharge amount decreases as the compression top dead center gas temperature (combustion chamber average gas temperature) is increased. .

  Further, as shown in FIG. 7, when the excess air ratio is 1.4, the excess air ratio is within the range of the oxygen mole fraction where the soot emission tends to monotonously increase with respect to the oxygen mole fraction. By setting the compression top dead center gas temperature to 2.0 and 1100 K, the soot discharge tends to gradually decrease with respect to the oxygen mole fraction.

  Therefore, in an internal combustion engine equipped with an EGR system and executing EGR, for example, target performance (output performance, fuel consumption performance, exhaust performance (NOx emissions, soot), etc., depending on operating conditions (rotation speed, load, engine temperature, etc.). The target oxygen mole fraction that can achieve the target emissions molar fraction is controlled, and the excess air ratio, EGR ratio, residual gas ratio, etc. are controlled to achieve the target oxygen mole fraction. Is effective in effectively achieving the target performance.

  For this reason, in the present embodiment, a performance experiment or the like of the internal combustion engine is performed, and the target performance (output performance, fuel consumption performance, exhaust performance (in accordance with the rotational speed of the internal combustion engine, load, engine temperature, etc.)) ( NOx emissions, soot emissions, particulate emissions, etc.) are obtained, and a target oxygen mole fraction setting map according to the operating state is created. Is stored, and control is performed so that the actual oxygen mole fraction becomes the target oxygen mole fraction.

  For this reason, in this embodiment, as will be described later, an oxygen concentration sensor capable of acquiring the oxygen concentration is provided, for example, in the exhaust passage in order to acquire the actual oxygen mole fraction of the internal combustion engine. Note that an oxygen concentration sensor may be provided in the intake passage after the EGR gas has merged.

  Furthermore, in the internal combustion engine according to the present embodiment, in order to achieve the target molar fraction, the intake charge efficiency (excess air ratio), residual gas ratio, The EGR rate can be variably controlled. For example, the intake charge efficiency (excess air ratio) and the residual gas ratio can be controlled by a VVA mechanism which will be described later, and the EGR ratio can be controlled by an EGR system.

  More specifically, as shown in FIG. 1, outside air (fresh air) is sucked into the internal combustion engine 1 according to the present embodiment through an air cleaner or the like (not shown). After being guided to a compressor (impeller) 3A of the supercharger 3 through a compressor and compressed to a predetermined level, it is cooled to a predetermined level via an intercooler 4 interposed in the intake passage 2 and is combusted. It comes to be guided in.

  Then, the gas after combustion discharged from the combustion chamber 5 is guided to an exhaust passage (exhaust manifold portion) 6 through an exhaust port (not shown) that faces the combustion chamber 5 and is then supercharged. After supplying rotational energy to the exhaust turbine 3B of the machine 3, a predetermined process is performed in an exhaust treatment device (not shown) (an oxidation catalyst, a NOx reduction catalyst, a diesel particulate filter, etc.) disposed downstream of the exhaust passage 6. Purified and discharged into the atmosphere.

  Further, in the present embodiment, part of the gas after combustion (that is, exhaust gas) is led again to the combustion chamber 5 together with intake air (fresh air), thereby reducing the combustion temperature and reducing NOx. An apparatus 100 is provided.

  The EGR device (system) 100 according to the present embodiment includes, for example, an EGR passage (exhaust gas recirculation passage) 101 that communicates with an exhaust passage (exhaust manifold portion) 6, and the EGR passage 101 includes the EGR passage 101. An EGR cooler 110 for intercooling the exhaust gas (EGR gas: recirculation exhaust gas) flowing through the passage 101 is provided.

  An EGR valve 120 is interposed in the vicinity of the connection portion between the EGR passage 101 and the intake passage 2, and in a predetermined operation state, a part of the exhaust flowing through the exhaust passage 6 is partially opened by EGR gas. As described above, while being cooled by the EGR cooler 110, it is guided to the intake passage 2 of the internal combustion engine 1.

  As for the control of the EGR rate, for example, a performance experiment of the internal combustion engine or the like is performed, and the target NOx emission amount or the like is achieved according to the operating state (rotational speed, load, engine temperature, etc. of the internal combustion engine). A target EGR rate that can be obtained is acquired in advance, and the opening degree of the EGR valve 120 of the EGR device 100 is controlled in accordance with this.

  Furthermore, the internal combustion engine 1 according to the present embodiment is provided with a VVA (Variable Valve Actuation) mechanism 200 as a valve operating mechanism for driving an intake valve (and / or an exhaust valve) provided facing the combustion chamber 5. The opening / closing characteristics such as the opening / closing timing and the lift amount of the intake valve (and / or the exhaust valve) can be variably controlled.

  Note that, according to the VVA mechanism 200, for example, the opening / closing timing of the intake valve (and / or the exhaust valve), the lift amount, and the like are controlled according to the generation state of the in-cylinder negative pressure, the intake pulsation, and the like. It is possible to effectively increase the intake charging efficiency in a wide range of operation from high speeds to light loads to high loads.

  In the internal combustion engine 1 having such a configuration, in the present embodiment, in order to achieve the target oxygen mole fraction set according to the operating state (load, rotation speed, engine temperature, etc.), the internal combustion engine As basic information for calculating (acquiring) the actual oxygen mole fraction of intake air (new air + EGR gas) introduced into one combustion chamber 5, intake air (new air) introduced into the combustion chamber 5 of the internal combustion engine 1 + EGR gas) is acquired, and an oxygen concentration sensor 300 for which detection data is used for this purpose is disposed in the exhaust passage.

  In the present embodiment, the case where the oxygen concentration sensor 300 is disposed in the exhaust passage is illustrated from the viewpoint of the availability and durability of the oxygen concentration sensor 300, but the present invention is not limited to this. The oxygen concentration sensor 300 may be arranged in the intake passage 2 after the operation.

  An ECU (not shown) that controls the internal combustion engine 1 acquires a cooling water temperature (engine temperature) based on a signal from a water temperature sensor, and acquires an engine rotation speed based on a signal from a crank angle sensor or the like. At the same time, the crank angle position and the like can be acquired as necessary.

  In addition, the operation amount (acceleration request level) of the driver's accelerator pedal is input to the ECU, and the ECU sets the fuel injection supply amount of the internal combustion engine 1 based on the driver's acceleration request level and the actual fuel. The actual load information of the internal combustion engine 1 can be acquired based on the valve opening signal of the injection valve.

  Further, a signal from a cam angle sensor or the like is input to the ECU as information necessary for controlling the valve opening / closing characteristics of the VVA mechanism 200.

In the internal combustion engine 1 according to the present embodiment having such a configuration, the following control is performed.
That is, as shown in FIG. 2, in the internal combustion engine 1, when the accelerator pedal is depressed from a relatively light load operation state to a relatively high load operation state (uphill starting) When the internal combustion engine 1 is controlled by the rotational speed and the fuel injection amount (fuel injection amount) as in the past, the actual control can follow the change degree (transient characteristics) of the operating state well. Therefore, it is easy to become a combustion state in which oxygen is insufficient, and there is a possibility that the amount of soot emission increases.

  Conversely, when shifting from a relatively high load operation state to a relatively light load operation state with a reduced accelerator pedal stroke (such as when climbing is completed), the rotational speed and fuel injection amount (fuel) When the internal combustion engine 1 is controlled by the input amount), the actual control cannot satisfactorily follow the degree of change in the operating state (transient characteristics), and the combustion state with a lot of oxygen tends to occur, and the NOx emission amount increases. There was a fear.

  In the present embodiment, the ECU acquires the actual oxygen mole fraction based on the detection result of the oxygen sensor 300 and controls the VVA mechanism 200 so that the target oxygen mole concentration is obtained. Yes.

  As shown in the lower part of FIG. 2, the ECU uses a point A where the in-cylinder negative pressure is generated and intake pulsation, etc., to maximize the intake charge efficiency and Pmax (maximum in-cylinder) at full load. The intake valve opening timing B capable of achieving the target oxygen mole fraction is set between the point C for preventing the pressure) from exceeding a predetermined level. In addition, when the point A and the point C become the same time, the point C is set as the valve opening time B of the intake valve.

  Thus, during transient operation (not limited to the above case, including the case where the load does not change and the rotational speed changes, and the case where the rotational speed does not change and the load changes), the actual oxygen mole fraction Since the VVA mechanism 200 is controlled so that the target oxygen mole fraction can be achieved, the increase in the NOx emission amount and the deterioration of the soot emission amount during transient operation can be suppressed. it can.

  Therefore, according to the present embodiment, since the system already provided in the internal combustion engine 1 is effectively used, combustion improvement can be achieved without causing a complicated configuration and an increase in cost. Accordingly, it is possible to provide an internal combustion engine that can promote improvement in various performances such as output performance, fuel consumption performance, exhaust performance, and, in turn, can reduce the burden on the aftertreatment system.

  The technique for controlling the oxygen mole fraction is not limited to the technique by controlling the intake valve opening / closing characteristics as described above to control the intake charge efficiency (excess air ratio), for example, VVA. It is also possible to control the oxygen mole fraction as desired by controlling the residual gas ratio by controlling the opening / closing characteristics of the exhaust valve by the mechanism 200.

  Further, for example, by controlling the opening degree of the EGR valve 120 of the EGR device (system) 100 (by performing increase / decrease correction with respect to the target opening degree corresponding to the target EGR rate), the EGR rate is controlled to control oxygen. It is also possible to control the molar fraction as desired.

  Furthermore, in the internal combustion engine 1 according to the present embodiment, as shown in FIG. 3, it is possible to employ a configuration in which two intake ports for introducing intake air into the combustion chamber 5 are provided in each cylinder.

  Of the two intake ports, the directive port 211 is formed by a relatively straight intake passage, and introduces the intake air straight and downward in the state of low ventilation resistance toward the lower side of the combustion chamber 5. It is formed in the cylinder head so that it can.

  On the other hand, the helical port 212 is formed with a predetermined bend as seen from a direction substantially orthogonal to the plane of FIG. 3 and can introduce intake air while providing a swirling component (swirl component) in the circumferential direction of the combustion chamber 5. It is formed in the cylinder head.

  For example, when the oxygen mole fraction is small (eol = ((e + r) / (1 + r)) / λ is large), the soot discharge tends to increase. In such a case, the helical port Control is performed to increase the swirl ratio by increasing the lift amount of the intake valve on the 212 side and reduce the soot discharge amount.

  On the other hand, when the oxygen mole fraction is large (eol = ((e + r) / (1 + r)) / λ is small), the soot discharge tends to be low. In such a case (soot discharge) In the case where there is a small amount), control is performed such that the swirl ratio is suppressed and the NOx emission amount is reduced by increasing the lift amount of the intake valve on the direct port 211 side.

  Further, as shown in FIG. 4, when the lift of the intake valve is controlled in two stages, it is possible to configure the time until the shift from the low lift to the high lift is controlled for each port.

  Since the in-cylinder negative pressure approaches positive pressure by shifting the intake valve on the direct port 211 side to a high lift before the intake valve on the helical port 212 side, the amount of air flowing in from the helical port 212 side Therefore, the swirl ratio can be reduced.

  Conversely, the intake valve on the helical port 212 side is shifted to a higher lift before the intake valve on the direct port 211 side, so that air can flow from the helical port 212 side in a state where the negative pressure in the cylinder is large. Therefore, the swirl ratio can be increased.

  As described above, according to the present embodiment, the swirl ratio is controlled in accordance with the oxygen mole fraction, which further contributes to improvements in output performance, fuel consumption performance, exhaust performance, and the like of the internal combustion engine. be able to.

  Further, in the internal combustion engine 1 that performs diesel combustion, in the light load region (operation region where the fuel injection amount is small), the fuel injection amount is small and the spray momentum is small. Therefore, it is not possible to perform good combustion.

  In such a light load operation region, for example, by using the VVA mechanism 200, the amount of intake air (fresh air (outside air) + EGR gas) introduced into the cylinder is increased as much as possible to increase the in-cylinder density. Therefore, it is possible to improve the combustion and reduce the soot emission.

  In addition, if the swirl ratio can be increased in such a light load region, the shortage of the spray momentum can be compensated, and the atmosphere around the fuel spray can be well taken into the burning part, and the combustion can be reduced. Improvements can be made and soot emissions can be reduced.

  For this reason, in the internal combustion engine 1 according to the present embodiment, the VVA mechanism 200 is controlled so as to increase the swirl ratio in the light load region.

  In order to increase the swirl ratio, in the same way as described above, the lift amount of the intake valve on the helical port 212 side is increased from the lift amount of the intake valve on the direct port 211 side. This can be achieved by shifting the intake valve on the helical port 212 side to a high lift.

  By the way, since the excess air ratio is large in the light load region, the oxygen mole fraction has a large value, whereas in the high load region, the excess oxygen ratio becomes small, so the oxygen mole fraction tends to be small. By controlling the swirl ratio according to the fraction, it is possible to contribute to improvements in the output performance, fuel consumption performance, exhaust performance, etc. of the internal combustion engine.

  For example, in a region where the oxygen mole fraction is large (light load region), control is performed to increase the swirl ratio to improve combustion and reduce soot emissions, while the oxygen mole fraction is small. In (high load area), the swirl ratio is reduced, for example, the direct port 211 is mainly used to increase the intake air amount (filling efficiency) by reducing the airflow resistance, and to suppress the spray interference due to over swirl etc. It is possible to perform such control.

  As described above, according to the present embodiment, the swirl ratio is controlled according to the oxygen mole fraction set according to the operating state (load, rotation speed, etc.). This can contribute to improvements in output performance, fuel consumption performance, exhaust performance, etc.

  By the way, as an internal combustion engine according to the present invention, a diesel engine is applicable, but is not limited to this, and can be applied to a combustion engine that performs diesel combustion using alcohol or other substances as a fuel. It is not limited to either a formula or a stationary formula.

  The VVA mechanism 200 is not particularly limited, and may employ a variable valve control mechanism of a type that switches a cam or moves a cam relative to a mechanism that drives a valve by an actuator. it can.

  Furthermore, the control of the swirl ratio is not limited to that by the drive control of the intake valve by the VVA mechanism 200. For example, a swirl control system that controls the inflow of intake air to the helical port 212 by a butterfly valve is used. It is also possible.

  Further, the present invention is not limited to an internal combustion engine having an exhaust turbine supercharger (turbocharger), but may be a turbocharger (such as a pressure wave type) using other exhaust or mechanically driven. The present invention can be applied to a supercharger or the like, or to a so-called naturally aspirated internal combustion engine that does not include such a supercharger.

  Further, an aftertreatment system such as a catalyst device or a particulate filter can be interposed in the exhaust passage.

  The embodiment described above is merely an example for explaining the present invention, and various modifications can be made without departing from the gist of the present invention.

1 Internal combustion engine 2 Intake passage 3 Exhaust supercharger (turbocharger)
5 Combustion chamber (cylinder, in cylinder)
100 EGR device 120 EGR valve 200 VVA mechanism (equivalent to variable valve mechanism)
211 Directional port 212 Helical port 300 Oxygen concentration sensor

Claims (3)

  An internal combustion engine that controls at least one of an excess air ratio, an EGR ratio, and a residual gas ratio so that an oxygen mole fraction of intake air led into a combustion chamber becomes a target oxygen mole fraction.   2. The internal combustion engine according to claim 1, wherein control for increasing the swirl ratio is performed at light load. 3. The internal combustion engine according to claim 1, wherein the excess air ratio is controlled by changing the intake charging efficiency by controlling the valve opening / closing characteristics by a variable valve mechanism.

Images