JP5843012B2 - Control device and control method for internal combustion engine - Google Patents

Description

  The present invention relates to an in-cylinder direct injection internal combustion engine equipped with a turbocharger, and more particularly to a technique for improving torque using scavenging.

  In an in-cylinder direct injection internal combustion engine equipped with a turbocharger, the rotational speed of the exhaust turbine is increased by using the effect of scavenging air blown from the intake passage to the exhaust passage during the valve overlap period. A technique for improving torque by increasing filling efficiency is known.

  As a related technique, Patent Document 1 discloses that in a region where the engine torque is relatively low, the turbocharger is driven to perform a lean combustion operation to improve fuel efficiency, while in a region where the engine torque is relatively high, A technique for suppressing the occurrence of smoke and knocking by driving a turbocharger and performing a homogeneous combustion operation near the stoichiometric air-fuel ratio is described. Patent Document 2 describes a technique for suppressing the occurrence of early ignition and knocking by increasing the amount of scavenging and lowering the in-cylinder temperature when switching from 4-cycle operation to 2-cycle operation. Furthermore, Patent Document 3 describes that the fuel injection amount is reduced during steady running in a scavenged state.

JP 2007-146854 A JP 2004-204745 A JP 2007-247434 A

  In an in-cylinder direct injection internal combustion engine equipped with such a turbocharger, the fuel injection amount is increased from the theoretical air-fuel ratio during scavenging, that is, enriched, and combustion is performed in the exhaust passage upstream of the exhaust turbine. By performing this, the present applicant is considering increasing the work of the exhaust turbine and improving the torque by increasing the charging efficiency into the cylinder.

  However, if the fuel injection amount is simply enriched during scavenging, the combustion may not be performed well in the exhaust passage upstream of the exhaust turbine because the exhaust temperature is low. In this case, not only the desired torque improvement effect can be obtained, but also fuel consumption and exhaust performance are deteriorated.Furthermore, in the unlikely event that combustion occurs in the vicinity of the catalyst provided downstream of the exhaust turbine, There is a risk of excessive temperature rise of exhaust system parts including the catalyst.

  The present invention has been made in view of such circumstances. That is, the internal combustion engine according to the present invention supercharges intake air by driving a fuel injection valve that directly injects fuel into a cylinder and an intake compressor provided in the intake passage by an exhaust turbine provided in the exhaust passage. And a turbo-supercharger, and a valve overlap period variable means such as a variable valve mechanism capable of adjusting a valve overlap period in which both the intake valve and the exhaust valve are opened.

  The scavenging rate of the scavenging air that blows from the intake passage to the exhaust passage during the valve overlap period is estimated, and the exhaust temperature of the exhaust gas flowing in the exhaust passage upstream of the exhaust turbine is detected or estimated, When the rate and the exhaust temperature satisfy predetermined conditions, the fuel injection amount to be supplied into the cylinder is set so that combustion is performed in the exhaust passage upstream of the exhaust turbine.

  More specifically, when the scavenging rate is equal to or higher than a first predetermined value and the exhaust temperature is equal to or higher than a second predetermined value, the scavenging rate can be reliably burned in the exhaust passage upstream of the exhaust turbine. It is determined that the condition is satisfied, and the fuel injection amount supplied into the cylinder is enriched. As a result, combustion is performed in the exhaust passage upstream of the exhaust turbine, the work of the exhaust turbine is increased, and the engine torque can be improved by increasing the charging efficiency into the cylinder.

  In other words, unless the above condition is satisfied, the fuel injection amount for making combustion in the exhaust passage is not enriched, for example, the fuel injection amount so that the stoichiometric air-fuel ratio or the lean air-fuel ratio is obtained. By controlling this, it is possible to prevent the unburned fuel from flowing out to the exhaust side, to avoid a situation where combustion occurs downstream from the exhaust turbine, and to prevent excessive temperature rise of exhaust parts such as a catalyst. be able to.

  According to the present invention, only when each of the scavenging rate and the exhaust temperature satisfies a predetermined condition, the fuel injection amount to be supplied into the cylinder is appropriately set, so that the exhaust passage upstream of the exhaust turbine is set in the exhaust passage. The engine torque can be increased by increasing the work of the exhaust turbine and increasing the charging efficiency into the cylinder by performing combustion.

  In addition, by limiting the conditions for performing combustion in the exhaust passage upstream of the exhaust turbine by the scavenging rate and the exhaust temperature, it is possible to prevent inadvertent combustion in the exhaust passage downstream of the exhaust turbine. It is possible to avoid excessive heating of exhaust parts such as a catalyst.

The system block diagram which shows an example of the control apparatus of the internal combustion engine which concerns on this invention. Explanatory drawing which shows the relationship of the scavenging rate with respect to an engine speed and an engine load, and valve overlap amount (O / L amount). The flowchart which shows the flow of control which concerns on one Example of this invention. The functional block diagram which shows an example of the calculation process of valve overlap (O / L) amount.

  Hereinafter, the present invention will be described with reference to illustrated embodiments. FIG. 1 shows an example of a system configuration of an internal combustion engine according to the present invention. The internal combustion engine 1 is an in-cylinder direct injection type in-line four-cylinder gasoline internal combustion engine. Intake air is supplied to each cylinder 1 </ b> A of the four cylinders via the intake passage 2, and exhaust gas after combustion is discharged via the exhaust passage 3. A branch pipe-shaped intake manifold 4 having a plurality of intake branches connected to the intake ports of the respective cylinders 1A is provided on the downstream side of the intake collector 2A of the intake passages 2. A branch pipe-shaped exhaust manifold 8 having a plurality of exhaust branches connected to the exhaust port 1A is provided.

  In the intake passage 2 upstream of the intake collector 2A, in order from the upstream side, an air cleaner 7 that collects foreign matters such as dust in the intake air, and an air flow that measures the amount of fresh intake air passing through the intake passage 2 Meter 6, intake compressor 11 of turbocharger 10, electronically controlled throttle valve 5 for adjusting the amount of intake air flowing into cylinder 1 </ b> A of internal combustion engine 1, and intercooler 13 for cooling intake air And are provided.

  The turbocharger 10 supercharges intake air using exhaust energy, and an intake compressor 11 and an exhaust turbine 12 are coaxially connected via a shaft, and the exhaust turbine 12 is an internal combustion engine. When it is rotated by the exhaust energy of 1, the intake compressor 11 is rotationally driven to pump the intake air downstream.

  The recirculation passage 14 is a passage connecting the upstream portion and the downstream portion of the intake compressor 11 in the intake passage 2 and is opened and closed by a recirculation valve 15 provided in the middle. The recirculation valve 15 is opened when the differential pressure between the supercharging pressure and the pressure in the intake manifold 4 (hereinafter referred to as intake pipe pressure) becomes a predetermined value or more, as is generally known. To do. For example, the reaction force of the built-in spring is urged in the valve closing direction against the valve body provided inside, and the boost pressure acts in the valve opening direction of the valve body, while the intake pressure is applied in the valve closing direction. When the pipe pressure is applied and the differential pressure between the supercharging pressure and the intake pipe pressure exceeds the reaction force of the spring, the valve is opened. Thereby, when the throttle valve 5 is fully closed during traveling in the supercharging state, it is possible to prevent the supercharging pressure from being excessively increased. The differential pressure between the supercharging pressure and the intake pipe pressure when the recirculation valve 15 is opened can be set to an arbitrary value depending on the spring constant of the spring.

  An exhaust gas purification catalyst 9 is disposed in the exhaust passage 3 downstream of the exhaust turbine 12. As this exhaust catalyst 9, a three-way catalyst or the like is used. The exhaust bypass passage 16 is a passage connecting the upstream portion and the downstream portion of the exhaust turbine 12 in the exhaust passage 3, and the opening degree is adjusted by a wastegate valve 17 provided in the middle. The operation of the wastegate valve 17 is controlled by a control unit 25 which will be described later. When the supercharging pressure reaches a predetermined set value, the wastegate valve 17 is opened so that excess exhaust gas is directly discharged through the exhaust bypass passage 16. .

  The EGR passage 20 is a passage connecting the exhaust passage 3 downstream of the exhaust catalyst 9 and the intake passage 2 downstream of the air flow meter 6 and upstream of the intake compressor 11. The EGR passage 20 is provided with an EGR control valve 21 that adjusts an EGR amount that is the amount of exhaust gas recirculated to the intake passage 2, and an EGR cooler 22 that cools the exhaust gas flowing through the EGR passage 20. Is provided.

  Each cylinder 1A of the internal combustion engine 1 is provided with a fuel injection valve 40 that directly injects fuel into the cylinder 1A. Further, in this embodiment, as means capable of adjusting the valve overlap period in which both the exhaust valve and the intake valve are opened, in this embodiment, an intake valve timing changing mechanism (intake VTC) 41 capable of changing the valve timing of the intake valve, An exhaust valve timing changing mechanism (exhaust VTC) 42 capable of changing the valve timing of the exhaust valve is provided. These valve timing changing mechanisms 41 and 42 can simultaneously and continuously change the opening timing and closing timing of the intake valve or the exhaust valve by changing the rotational phase of the camshaft with respect to the crankshaft, as is well known. It is a thing. The mechanism that can adjust the valve overlap period is not limited to this, and any mechanism that can change at least one of the intake valve opening timing (IVO) and the exhaust valve closing timing (EVC) may be used. Other generally known variable valve mechanisms may be used, such as a lift operating angle changing mechanism that changes the lift amount and operating angle of the exhaust valve.

  The control unit 25 as a control unit has a function of storing and executing various engine control processes based on the engine operating state detected from various sensors. As the various sensors described above, the intake collector 2A of the intake passage 2 includes a pressure sensor 27 for detecting a boost pressure as a boost pressure, and a pressure sensor 27 for detecting a boost pressure as a boost pressure, and an intake collector 2A as an intake air temperature. An intake air temperature sensor 30 for detecting the temperature of the intake air, and an exhaust temperature sensor 28 for detecting the exhaust gas temperature upstream of the exhaust turbine 12 in the exhaust passage 3. A crank angle sensor 26 for detecting the engine rotation speed, an accelerator opening sensor 29 for detecting the opening of an accelerator pedal operated by the driver, and the like are provided.

  The control unit 25 controls the fuel injection amount and fuel injection timing by the fuel injection valve 40 as the various engine controls described above, and the valve timing (VTC conversion angle) of the intake and exhaust valves by the valve timing changing mechanisms 41 and 42. Further, ignition timing control or the like is performed by a spark plug (not shown) provided in the combustion chamber.

  The control unit 25 estimates the scavenging rate of the scavenging air blown from the intake passage 2 to the exhaust passage 3 based on the valve overlap period and the like. Here, the “scavenging rate” corresponds to the ratio of the scavenging amount blown from the intake passage 2 to the exhaust passage 3 during the valve overlap period with respect to the intake air amount sucked into the cylinder 1A. The “cylinder fresh air amount” corresponds to the amount of fresh air that is filled in the cylinder 1A and used for combustion. In this specification, the intake gas supplied to the cylinder 1A is referred to as “intake fresh air” or simply “new air” and does not contain exhaust gas EGR gas or the like, and includes EGR gas or the like. Things are called “intake air” or simply “air”.

  When the pressure in the intake manifold 4 is higher than the pressure in the exhaust manifold 8, the control unit 25 changes the valve timing so that the valve timing during which the valve overlap period during which the intake valve and the exhaust valve are open occurs. The mechanisms 41 and 42 are operated. This is because, during the valve overlap period, the fresh air flowing from the intake manifold 4 is blown out as it is to the exhaust manifold 8 as a scavenging gas, so that the rotational speed of the exhaust turbine 12 is increased and into the cylinder 1A. This is to increase the filling efficiency.

  Specifically, as shown in FIG. 2, the valve overlap amount (also referred to as “O / L amount” or “valve O / L amount”) as the valve overlap period increases on the low rotation high load side, It is set to be smaller on the high rotation and low load side. The scavenging rate also increases on the low rotation high load side and decreases on the high rotation low load side in proportion to the O / L amount.

  Further, in order to prevent the EGR gas from being scavenged, the EGR region Regr that applies EGR by opening the EGR control valve 21 is not subjected to the valve overlap amount, and the scavenging rate is 0. It is set in the scavenging region RsNo.

  FIG. 3 is a flowchart showing a control flow according to an embodiment of the present invention. In step S11, it is determined whether the required torque is equal to or greater than a predetermined value DD # corresponding to the output when the throttle is fully open (WOT). In step S12, it is determined whether or not the valve overlap period is given, that is, a predetermined scavenging region Rs (see FIG. 2) on the low-rotation and high-load side where scavenging can occur.

  In step S13, it is determined whether the valve overlap period, that is, the valve overlap amount (valve O / F amount) exceeds a predetermined value XX #. This is because, even in the scavenging region Rs, the scavenging rate varies depending on the valve O / L amount, so that the scavenging rate is reduced in advance, that is, the valve O / L amount is equal to or smaller than the predetermined value XX #. This is because it is excluded from the region where the enrichment is performed in order to improve the torque described later.

  FIG. 4 shows an example of the valve O / L amount calculation process stored and executed by the control unit 25. Reference numeral B13 is a control map showing a retard amount with respect to the exhaust top dead center of the exhaust valve closing timing retarded or advanced by the exhaust valve overlap changing mechanism (exhaust VTC) 42. It is mapped so as to be a positive value when it is retarded from the dead point. Reference numeral B14 is a control map showing an advance amount with respect to the exhaust top dead center of the intake valve opening timing retarded or advanced by the intake valve overlap changing mechanism (intake VTC) 41. It is mapped so as to be a positive value when it is advanced from the dead point.

  By referring to the exhaust VTC control map B13 based on the target load (B11) and the engine speed (B12), the retard amount of the exhaust valve closing timing with respect to the exhaust top dead center is calculated and the intake VTC is used. By referring to the control map B14, the advance amount of the intake valve opening timing with respect to the exhaust top dead center is calculated, and the valve O / L amount (B16) is obtained by adding both in the addition unit B15. it can.

  In this example, the valve O / L amount is obtained based on the target conversion angle (advance amount / retard amount) of the exhaust VTC or the intake VTC. However, the present invention is not limited to this, and for example, the rotation angle of the camshaft is detected. The actual valve O / L amount may be detected using the output of the sensor or the like.

  Referring to FIG. 3 again, in step S14, it is determined whether the supercharging pressure exceeds a predetermined value ZZ #. The supercharging pressure is detected by the pressure sensor 27 or estimated according to the engine operating state such as the engine speed and the load.

  If all the conditions of steps S11 to S14 are satisfied, the process proceeds to step S15, and the scavenging rate is estimated. The scavenging rate is estimated in consideration of the engine speed, the intake air temperature, etc. in addition to the valve O / L amount. For simplification, the determination process in step S13 or step S14 may be omitted.

  In step S16, it is determined whether or not the estimated scavenging rate exceeds a predetermined value SS # (for example, about 25%) that allows combustion in the exhaust passage 3 upstream of the exhaust turbine 12. In step S17, the exhaust temperature in the exhaust passage 3 upstream of the exhaust turbine 12 exceeds a predetermined value YY # (for example, about 700 degrees) that allows combustion in the exhaust passage 3 upstream of the exhaust turbine 12. It is determined whether or not. The exhaust temperature is directly detected by the exhaust temperature sensor 28 described above. However, the exhaust temperature sensor 28 may be omitted, and the exhaust temperature may be estimated based on the supercharging pressure (intake amount), the engine speed, the ignition timing, the fuel injection amount, the fuel injection timing, and the like.

  Only when the conditions of both step S16 and step S17 are satisfied, the process proceeds to step S18, and the in-cylinder rich due to the increase in the fuel injection amount is performed so that combustion is performed in the exhaust passage 3 upstream of the exhaust turbine 12. Allow For example, when the scavenging rate is 25%, if the oxygen concentration in the exhaust gas exceeds 5%, the combustion limit is exceeded and combustion is possible. Therefore, if the exhaust temperature in this state exceeds 700 ° C., which is the combustion temperature of CO, the possibility of combustion before the exhaust turbine 12 becomes sufficiently high, and combustion before the exhaust turbine 12 can be performed with high probability. Therefore, the in-cylinder enrichment described above is permitted. The amount of increase in the fuel injection amount at the time of in-cylinder enrichment is set according to the scavenging rate, and specifically, the fuel increase amount is set to increase as the scavenging rate increases.

  In this way, the fresh air due to scavenging and the unburned gas due to the increase in fuel are combusted on the upstream side of the exhaust turbine 12, thereby increasing the supercharging pressure, improving the charging efficiency, and improving the engine torque. Can do.

  Further, when the enrichment for improving the torque is performed in this way, the throttle valve 5 is fully opened, and the valve overlap amount is increased and the fuel injection amount is increased in accordance with the increase in the engine required load. By doing so, the engine load can be increased in accordance with the increase in the engine required load. Since the combustion in the exhaust turbine 12 is directly linked to the work amount of the exhaust turbine 12, the response speed of the turbocharger 10 is increased and the torque response is excellent.

  On the other hand, if any of the conditions in steps S11 to S14, S16, and S17 is not satisfied, enrichment for improving the torque in step S18 is not performed, and the stoichiometric or lean air / fuel ratio is stoichiometric or lean. The fuel injection amount is set to be on the side. Thus, unless the combustion in the exhaust passage 3 upstream of the exhaust turbine 12 is reliably performed, the fuel increase for combustion before the exhaust turbine is not performed. Thus, it is possible to reliably prevent inadvertent combustion in the exhaust passage 3 on the downstream side, and to reliably suppress excessive temperature rise of the exhaust parts including the exhaust catalyst 9.

  Although the present invention has been described based on the illustrated embodiments as described above, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the technical idea described in the claims. It goes without saying that it can be achieved.

Claims (2)

A fuel injection valve that directly injects fuel into the cylinder;
In a control device for an internal combustion engine comprising: a turbocharger that drives an intake compressor provided in an intake passage by an exhaust turbine provided in the exhaust passage to supercharge intake air;
A valve overlap period variable means capable of adjusting a valve overlap period in which both the intake valve and the exhaust valve are opened;
Scavenging rate estimating means for estimating a scavenging rate of scavenging air blown from the intake passage to the exhaust passage during the valve overlap period;
Exhaust temperature acquisition means for detecting or estimating the exhaust temperature of the exhaust flowing in the exhaust passage upstream of the exhaust turbine;
A fuel injection amount for setting a fuel injection amount to be supplied into the cylinder so that combustion is performed in an exhaust passage upstream of the exhaust turbine when the scavenging rate and the exhaust temperature satisfy predetermined conditions. Setting means;
A throttle valve provided in the intake passage for adjusting the amount of intake air;
I have a,
The fuel injection amount setting means opens the throttle valve fully when the scavenging rate exceeds a first predetermined value and the exhaust gas temperature exceeds a second predetermined value. A control apparatus for an internal combustion engine that enriches a fuel injection amount supplied into a cylinder by increasing the fuel injection amount while increasing the valve overlap period in response to an increase in required load . A fuel injection valve that directly injects fuel into the cylinder;
A turbocharger that supercharges intake air by driving an intake air compressor provided in the intake passage by an exhaust turbine provided in the exhaust passage;
A valve overlap period variable means capable of adjusting a valve overlap period in which both the intake valve and the exhaust valve are opened;
A throttle valve provided in the intake passage for adjusting the amount of intake air;
An internal combustion engine control method comprising:
Estimating the scavenging rate of scavenging air blown from the intake passage to the exhaust passage during the valve overlap period,
Detecting or estimating the exhaust temperature of the exhaust flowing in the exhaust passage upstream of the exhaust turbine,
When the scavenging rate and the exhaust temperature satisfy predetermined conditions, a fuel injection amount to be supplied into the cylinder is set so that combustion is performed in the exhaust passage upstream of the exhaust turbine ,
When the scavenging rate exceeds a first predetermined value and the exhaust temperature exceeds a second predetermined value, the throttle valve is fully opened, and according to an increase in engine demand load, A control method for an internal combustion engine, wherein the fuel injection amount supplied into the cylinder is enriched by increasing the fuel injection amount while increasing the valve overlap period .

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