JP5049924B2 - Control method for internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine control method including an exhaust gas recirculation device that recirculates exhaust gas to a downstream side of a throttle valve of an intake system, and a variable valve mechanism that changes opening / closing timing of at least one of the intake valve and the exhaust valve. About.

  Conventionally, in order to improve the fuel consumption of the internal combustion engine, an exhaust gas recirculation passage for recirculating exhaust gas downstream of the intake system throttle valve and an exhaust gas recirculation control valve for adjusting the flow rate of the exhaust gas recirculation passage are provided, It is widely known to perform exhaust gas recirculation control (hereinafter referred to as external EGR control) that controls the opening degree of the exhaust gas recirculation control valve using the load factor of the internal combustion engine as a parameter.

  Also, variable valve timing that changes the opening / closing timing of at least one of the intake valve and the exhaust valve in order to improve the fuel efficiency of the internal combustion engine in the low load range and to obtain high output from the internal combustion engine in the high load range. It is also widely known to perform exhaust gas recirculation control (hereinafter referred to as internal EGR control) through variable valve timing control that includes a mechanism and introduces fresh air into the combustion chamber while leaving exhaust in the combustion chamber of the internal combustion engine. It has been.

Conventionally, the opening degree of the exhaust gas recirculation control valve and the opening / closing timing by the variable valve timing mechanism are respectively determined based on the load factor of the internal combustion engine, and when the load factor is less than a predetermined value, external EGR control is performed. A control method is considered in which internal EGR control is performed when the load factor is equal to or greater than a predetermined value (see, for example, Patent Document 1).
JP 2003-328839 A

  By the way, if the external EGR control and the internal EGR control are selectively performed according to the load factor of the internal combustion engine as in the control method described in Patent Document 1, the following problems may occur.

  That is, when the load factor exceeds a predetermined value, it becomes difficult to improve fuel efficiency by performing external EGR control. Therefore, the process shifts to internal EGR control, and in a region where the load factor becomes high, combustion is performed to obtain high output. It is conceivable to increase the amount of fresh air introduced into the room. However, immediately after this transition, by performing internal EGR control, the amount of fresh air introduced into the combustion chamber is reduced, and the load factor is reduced. When the load factor falls below a predetermined value, the exhaust gas recirculation control for opening the exhaust gas recirculation control valve is started, and the internal EGR control is stopped. When the internal EGR control is stopped, the amount of fresh air introduced into the combustion chamber increases again, and the load factor exceeds a predetermined value. Therefore, the external EGR control is stopped, the internal EGR control is restarted, and the load The rate drops again. That is, by performing internal EGR control in the region where the load factor of the internal combustion engine is in the vicinity of the predetermined value, the load factor rises and falls in the region in the vicinity of the predetermined value, and hunting occurs, making it difficult to smoothly shift to the internal EGR control. Can be a malfunction.

  An object of the present invention is to solve such a problem, that is, to enable a smooth transition from external EGR control to internal EGR control as the engine load factor increases.

  That is, the control method for an internal combustion engine according to the present invention provides an exhaust gas recirculation line for recirculating exhaust gas downstream from the throttle valve of the intake system, and the exhaust gas recirculation line in order to solve the problems described above. In an internal combustion engine comprising an exhaust gas recirculation device having an exhaust gas recirculation control valve for adjusting the flow rate of the exhaust gas, and a variable valve timing mechanism for changing the opening / closing timing of at least one of the intake valve and the exhaust valve, the exhaust gas recirculation control valve And the opening / closing timing by the variable valve timing mechanism are set according to the load factor of the internal combustion engine, and the exhaust gas recirculation control for controlling the opening of the exhaust gas recirculation control valve of the exhaust gas recirculation device is performed. Performing exhaust gas recirculation control for controlling the opening degree of the exhaust gas recirculation control valve in the first load region where improvement of A control method for an internal combustion engine that performs exhaust gas recirculation control through open / close timing control by a variable valve timing mechanism in a second load region on a higher load side than the first load region, and detects an opening of a throttle valve When the detected opening of the throttle valve is less than a predetermined threshold, exhaust gas recirculation control is performed to control the opening of the exhaust gas recirculation control valve. In the case described above, exhaust gas recirculation control is performed through opening / closing timing control by a variable valve timing mechanism.

  If this is the case, an operation to increase the opening of the throttle valve to obtain a high output is performed, and when the opening of the throttle valve exceeds a predetermined threshold, the actual engine load factor Regardless, it is possible to smoothly shift to exhaust gas recirculation control through open / close timing control by a variable valve timing mechanism for obtaining high output from the internal combustion engine.

  In order to solve the above problems, in order to further improve the fuel consumption, it is desirable that the predetermined value be increased as the rotational speed is increased. This is because, when the rotational speed is high, performing exhaust gas recirculation control that opens the exhaust gas recirculation control valve is effective in further improving fuel efficiency even in a region where the load factor is higher.

  When the control method for an internal combustion engine according to the present invention is employed, the opening / closing timing by the variable valve timing mechanism when the throttle valve opening is equal to or greater than a predetermined threshold value to obtain a high output, regardless of the actual engine load factor. It is possible to shift to exhaust gas recirculation control through control. Therefore, when an operation for increasing the opening degree is performed on the throttle valve in order to increase the output, when shifting to the exhaust gas recirculation control via the opening / closing timing control by the variable valve timing mechanism in order to obtain a high output. Furthermore, hunting associated with changes in the engine load factor can be eliminated, and this transition can be made smooth.

  Hereinafter, an embodiment of the present invention will be described.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

An engine 100 schematically showing the configuration of one cylinder in FIG. 1 is a three-cylinder for an automobile. The intake system 1 of the engine 100 is provided with a throttle valve 11 that opens and closes in response to an accelerator pedal (not shown), and a resin-made intake manifold 12 is disposed downstream of the throttle valve 11. The intake manifold 12 includes a surge tank 13 and a manifold portion 14 extending from the surge tank 13 to the intake port of each cylinder. A fuel injection valve 3 is further provided in the vicinity of the end of the intake manifold 12 on the cylinder head 22 side, and this fuel injection valve 3 is controlled by the electronic control unit 4. The intake air is drawn into the cylinder 2 from the intake manifold 12 through the intake valve 21. Further, in the exhaust system 5, an O ₂ sensor 51 for measuring the oxygen concentration in the exhaust gas discharged from the combustion chamber 23 through the exhaust valve 24 is disposed in a pipe line leading to a muffler (not shown). The three-way catalyst 52 is attached at a position upstream. The engine 100 further includes a variable valve timing mechanism (hereinafter referred to as VVT9) for changing the opening / closing timing of the intake valve 21. This VVT 9 has a configuration similar to that of a known variable valve timing mechanism of this type. That is, the VVT 9 uses a so-called swing cylinder mechanism, and includes a rotor (not shown) fixed to the intake camshaft 91, a housing (not shown) fitted to the rotor, and a housing with respect to the rotor. An oil control valve 92, which is an electromagnetic four-way switching control valve for rotation, and a pair of gears 94, 95, one of which is fixed to the housing and the other is fixed to the intake camshaft 91 so as to mesh with each other.

  The direction and amount of hydraulic oil flowing into and out of the housing in response to the opening / closing timing signal p from the electronic control unit 4 is controlled by the oil control valve 92 to change the relative angle of the housing with respect to the rotor, and the exhaust camshaft 93 An arbitrary rotation phase difference is generated between the intake camshaft 91 and the intake camshaft 91 to variably control the valve timing. That is, the opening / closing timing of the exhaust valve 24 and the opening / closing timing of the intake valve 21 are changed by constantly changing the opening / closing timing of the intake valve 21 while the exhaust valve 24 is always opened / closed with respect to the rotation of the crankshaft (not shown). Relative phase difference can be freely changed within a predetermined angle range. A cam sensor 97 for outputting a crank angle signal and a cylinder discrimination signal is attached to one end of the exhaust camshaft 93, and 240 ° CA (crank) is attached to one end of the intake camshaft 91. A timing sensor 96 that outputs an intake cam signal each time it rotates is attached.

  In this embodiment, an exhaust gas recirculation device (hereinafter referred to as an EGR device) 6 for mixing exhaust gas with fresh air flowing into the intake manifold 12 via the throttle valve 11 is provided with an intake system 1 and an exhaust system. 5 is provided so as to communicate with 5. That is, the EGR device 6 includes an exhaust gas recirculation pipe (hereinafter referred to as an EGR pipe 61) in which the intake system 1 and the exhaust system 5 are selectively communicated, and an EGR pipe 61 provided in the EGR pipe 61. An exhaust gas recirculation control valve (hereinafter referred to as an EGR valve 62) that controls the amount of exhaust gas (EGR gas) that passes through or recirculates the passage 61 is configured. The EGR valve 62 is controlled by the electronic control device 4 that constitutes a part of the EGR device 6.

The electronic control device 4 is mainly configured by a microcomputer system including a central processing unit 41, a storage device 42, an input interface 43, and an output interface 44. The central processing unit 41 controls the operation of the engine 100 by executing a program described later stored in the storage device 42. Information necessary for controlling the operation of the engine 100 is input to the central processing unit 41 via the input interface 43, and the central processing unit 41 sends a control signal to the fuel via the output interface 44. It is output to the injection valve 3 and the EGR valve 62. Specifically, the input interface 43 includes an air flow rate signal a output from the air flow meter 71 for detecting the air flow rate F flowing into the intake manifold 12 and a rotation speed sensor 72 for detecting the engine speed Ne. The output rotation speed signal b, the vehicle speed signal c output from the vehicle speed sensor 73 for detecting the vehicle speed, the IDL signal d output from the idle switch 74 for detecting the open / closed state of the throttle valve 11, the throttle valve 11 An opening degree signal e output from the throttle opening degree sensor 75 for detecting the opening degree of the engine, that is, the throttle opening degree θ, a water temperature signal f output from the water temperature sensor 76 for detecting the cooling water temperature of the engine 100, A voltage signal h output from the O ₂ sensor 51 is input. On the other hand, from the output interface 44, the ignition signal m for the spark plug 8, the fuel injection signal n for the fuel injection valve 3, the valve opening / closing signal o for the EGR valve 62, and the oil control valve 92 for VVT9. An opening / closing timing signal p or the like is output.

  The storage device 42 of the electronic control unit 4 uses the air flow rate signal a output from the air flow meter 71 and the rotation speed signal b output from the rotation speed sensor 72 as main information, and depends on the operating state of the engine 100. The basic injection time is corrected with various correction factors that are determined to determine the opening time of the fuel injection valve 3, that is, the final energization time of the injector, and the fuel injection valve 3 is controlled according to the determined energization time in accordance with the engine load. A fuel injection amount control program for injecting fuel from the fuel injection valve 3 to the intake system 1 is incorporated.

  In addition, the storage device 42 determines the ignition timing of the spark plug 8 in accordance with the operating condition, and performs an ignition timing control program for performing control to instruct the spark plug 8 to output the ignition signal m. Is also built-in.

  Further, when the load factor is in the first load region where the fuel efficiency can be improved by performing the external EGR control, the air flow rate F corresponding to the air flow rate signal a is stored in the storage device 42 as a parameter. An external EGR control program for determining the amount of exhaust gas to be mixed with fresh air, that is, for determining the opening degree of the EGR valve 62 is also incorporated. The external EGR control program outputs an EGR valve opening / closing signal o to the EGR valve 62 based on the determined opening degree of the EGR valve 62 so as to correspond to the determined opening degree. Exhaust gas recirculation control (hereinafter referred to as external EGR) for controlling the opening degree of the EGR valve 62 is performed.

  The storage device 42 stores the opening / closing timing of the intake valve 21 using the air flow rate F corresponding to the air flow rate signal a as a parameter in the second load region where the load factor is higher than the first load region. A VVT control program for determining and outputting the opening / closing timing signal p to the VVT 9, more specifically, the oil control valve 92 is also incorporated. The control of the opening / closing timing of the intake valve 21 via the VVT 9 by this VVT control program advances the opening / closing timing of the intake valve 21 to improve fuel consumption, and fresh air is left in the combustion chamber 23 with exhaust remaining. Is introduced into the combustion chamber 23. In other words, this control is exhaust gas recirculation control (hereinafter referred to as internal EGR control) through opening / closing timing control by the VVT 9.

  In addition, in this embodiment, the air flow rate F is used as a parameter indicating the engine load factor, and the opening degree of the EGR valve 62 and the opening / closing timing of the intake valve 21 are set in advance so that the fuel efficiency is best. Specifically, in a predetermined area of the storage device 42, the opening degree of the EGR valve 62 and the advance amount of the opening / closing timing of the intake valve 21 are shown in FIG. As shown schematically in FIG. 6, the EGR valve opening map and the opening / closing timing advance amount map are respectively stored. In FIG. 3, the horizontal axis represents the air flow rate F (load factor in the figure), and the vertical axis represents the exhaust gas recirculation amount corresponding to the opening degree of the EGR valve 62 and the advance amount of the opening / closing timing of the intake valve 21. (EGR amount in the figure) is shown. In FIG. 3, the exhaust gas recirculation amount corresponding to the opening degree of the EGR valve 62 is indicated by a solid line a, and the exhaust gas recirculation amount corresponding to the advance amount of the opening / closing timing of the intake valve 21 is indicated by a broken line b.

  The storage device 42 detects the opening θ of the throttle valve 11, and when the detected opening θ of the throttle valve 11 is less than a predetermined threshold T, the load factor is in the first load region. External EGR control is performed on the assumption that the throttle valve 22 is present. On the other hand, if the detected opening θ of the throttle valve 22 is equal to or greater than a predetermined threshold T, the internal EGR is regarded as being in the second load region. An EGR control selection program for performing control is also incorporated. This EGR control selection program is executed, for example, every predetermined time only when the air flow rate F is equal to or higher than the lower limit of the first load region. Here, the threshold value T is determined so that the threshold value T becomes larger as the engine speed Ne becomes higher, with the engine speed Ne as a parameter in the present embodiment. The threshold value T is experimentally obtained in advance as the opening degree θ of the throttle valve 11 when the air flow rate F becomes the upper limit of the first load region for each rotation speed Ne. Further, this threshold value T is set to a different value when the opening degree θ of the throttle valve 11 increases and when the opening degree θ of the throttle valve 11 decreases. The threshold value T when the opening degree θ of the throttle valve 11 decreases is increased. Set to value. Then, a threshold value T for a typical engine speed Ne when the opening degree θ of the throttle valve 11 increases and decreases is stored as a threshold map in a predetermined area of the storage device 42 in the electronic control unit 4.

  Hereinafter, the procedure of processing performed by the electronic control unit 4 based on the EGR control selection program, the external EGR control program, and the VVT control program will be described with reference to FIG. 2 which is a flowchart.

  First, in step S1, the throttle opening degree sensor 75 detects the opening degree θ of the throttle valve 11 (throttle opening degree θ in the figure). Next, the process proceeds to step S2.

  In step S2, the previously detected opening degree θ of the throttle valve 11 is compared with the currently detected opening degree θ of the throttle valve 11. If the opening degree θ of the throttle valve 11 has increased, the value of the acceleration state flag A 1 and when the opening degree θ of the throttle valve 11 is decreasing, 0 is substituted for the value of the acceleration state flag A. Then, the opening θ of the throttle valve 11 detected this time is stored in a predetermined area of the storage device 42. Next, the process proceeds to step S3.

  In step S3, the engine speed Ne is detected. Next, the process proceeds to step S4.

  In step S4, the threshold value T is determined with reference to the threshold map using the values of the engine speed Ne and the acceleration state flag A as parameters. Thereafter, the process proceeds to step S5. Here, the actual threshold value T is determined by interpolation calculation using the engine speed Ne as a parameter.

  In step S5, it is determined whether the opening degree θ of the throttle valve 11 detected in step S1 is less than the threshold value T. When it is determined that the opening θ of the throttle valve 11 is less than the threshold value T, the process proceeds to step S6. On the other hand, if it is determined that the opening θ of the throttle valve 11 is equal to or greater than the threshold value T, the process proceeds to step S7.

  In step S6, external EGR control is performed. More specifically, the opening degree of the EGR valve 62 is determined based on the load factor using the air flow rate F as a parameter, and the valve opening / closing signal o corresponding to the determined opening degree is output to the EGR valve 62. And this control is once complete | finished. More specifically, the opening degree of the EGR valve 62 is determined by performing interpolation calculation with reference to an EGR valve opening degree map using the air flow rate F as a parameter.

  In step S7, internal EGR control is performed. More specifically, the advance angle amount of the opening / closing timing of the intake valve 21 is determined based on the load factor, and the opening / closing timing signal p corresponding to the determined advance angle amount is supplied to the VVT 9, more specifically, the oil control valve 92. Output. And this control is once complete | finished. More specifically, the advance amount of the opening / closing timing of the intake valve 21 is determined by performing interpolation calculation with reference to the opening / closing timing advance amount map using the air flow rate F as a parameter.

  Here, before and after shifting from the first load region to the second load region, that is, by increasing the opening θ of the throttle valve 11 to perform acceleration, the opening θ shifts from less than the threshold T to more than the threshold T. In the period before and after, the control actually performed by the VVT control program and the EGR valve control program will be described.

  In the period when the opening degree θ of the throttle valve 11 is less than the threshold value T, the control of the steps S1, S2, S3, S4, S5, and S6 is sequentially performed. That is, the opening / closing timing of the intake valve 21 is a normal opening / closing timing, and the EGR valve 62 is opened at a predetermined rate, and external EGR control for introducing EGR gas from the exhaust system 5 to the intake system 1 via the EGR pipe 61 is performed. .

  On the other hand, during the period when the opening degree θ of the throttle valve 11 is equal to or greater than the threshold value T, the control of the steps S1, S2, S3, S4, S5, and S7 is sequentially performed. That is, the EGR valve 62 is completely closed, and internal EGR control is performed to advance the opening / closing timing of the intake valve 21 by the VVT 9. At that time, in the time zone immediately after the opening degree θ of the throttle valve 11 becomes equal to or higher than the threshold value T, the air flow rate F becomes equal to or higher than the threshold value T by performing the internal EGR control. Although it temporarily decreases compared with the air flow rate F just before, in step S4, the selection of whether to perform the internal EGR control or the external EGR control is not the air flow rate F but the opening θ of the throttle valve 11. Therefore, the internal EGR control is continuously performed.

  In particular, when the opening degree θ of the throttle valve 11 is the maximum value θmax, that is, when the throttle valve 11 is fully open, the opening / closing timing of the intake valve 21 is determined by the piston 25 in order to introduce fresh air into the combustion chamber 23 to the maximum extent. Control is performed with a normal opening / closing timing that opens when the piston reaches near the top dead center and closes when the piston 25 reaches near the bottom dead center.

  That is, as shown in FIG. 4, the load factor and the exhaust gas recirculation amount (EGR amount in the figure) during this period are obtained when the opening degree θ of the throttle valve 11 is less than the threshold T, that is, FIG. Since the external EGR control is performed in the region on the left side of t1, the EGR valve opening map is referred to and changes along a in FIG. Then, when the opening θ of the throttle valve 11 becomes equal to or greater than the threshold T, that is, at t1 in FIG. 4, the external EGR control is stopped regardless of the opening of the EGR valve 62 on the EGR valve opening map, and the exhaust The amount of gas reflux once decreases toward zero. Thereafter, since the internal EGR control is performed, the opening / closing timing advance amount map is referred to, and the load factor and the exhaust gas recirculation amount change along b in FIG. Therefore, the load factor and the exhaust gas recirculation amount change along the solid line in FIG.

  The internal EGR control is performed in the third load region on the lower load side than the lower limit of the first load region.

  According to the control method of the engine 100 according to the present embodiment, as described above, the throttle valve 11 is operated to increase the opening degree θ so as to obtain a high output. When the threshold value T is exceeded, the process shifts to the internal EGR control regardless of the actual load factor, that is, the air flow rate F. Compared with the mode in which the external EGR control and the internal EGR are selected based on the actual air flow rate F. Thus, it is possible to smoothly shift from the external EGR control for improving fuel efficiency to the internal EGR control for obtaining high output.

  Further, since the threshold value T is increased as the engine speed Ne increases, external EGR control is performed even in a region where the load factor is higher when the engine speed Ne is high, thereby further improving fuel efficiency. be able to.

  The present invention is not limited to the embodiment described above.

  For example, in the internal EGR control, not only the opening / closing timing of the intake valve is advanced, but the opening / closing timing of the exhaust valve may be delayed, and the advancement timing of the intake valve's opening / closing timing and the opening / closing timing of the exhaust valve may be delayed. You may make it perform a corner simultaneously. That is, it is only necessary to determine the length of the overlap period between the time period for opening the exhaust valve and the time period for opening the intake valve, using the load factor as a parameter.

  Then, when shifting from the internal EGR control in the third load region to the external EGR control in the first load region, and vice versa, the determination when performing the reverse shift may also be made based on the opening of the throttle valve. Good. In this case, for example, the opening degree θ of the throttle valve 11 corresponding to the lower limit of the first load region is set in advance as a second threshold value TT smaller than the predetermined threshold value T, and the control in step S4 and the control in step S5 are performed. Is performed to determine whether the opening θ of the throttle valve 11 detected in step S1 is less than the second threshold value TT, and the opening θ of the throttle valve 11 is determined to be the predetermined threshold value T. If it is less than or equal to the second threshold value TT, the load factor is regarded as being in the first load region regardless of the actual air flow rate F, and the control in step S5, that is, the external EGR control is performed, and detected in step S1. If the opening θ of the throttle valve 11 is less than the second threshold value TT, it is assumed that the load factor is in the third load region regardless of the actual air flow rate F. The control or better to perform the internal EGR control.

  In addition, as a parameter indicating the load factor of the internal combustion engine, a parameter other than the air flow rate, for example, an intake pipe pressure may be used.

  In addition, various changes may be made without departing from the spirit of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows schematic structure of one Embodiment of this invention. The flowchart which shows the outline of the control procedure of the embodiment. The figure which shows roughly the EGR valve-opening degree map and opening-and-closing timing advance amount map in the embodiment. The figure which shows roughly the load factor at the time of performing control in the same embodiment, and exhaust gas recirculation amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Engine 1 ... Intake system 11 ... Throttle valve 21 ... Intake valve 24 ... Exhaust valve 4 ... Electronic control unit 6 ... EGR device (exhaust gas recirculation device)
61 ... EGR pipe (exhaust gas recirculation pipe)
62 ... EGR valve (exhaust gas recirculation control valve)
9 ... VVT (Variable valve timing mechanism)

Claims (2)

An exhaust gas recirculation device having an exhaust gas recirculation conduit for recirculating exhaust gas downstream from the throttle valve of the intake system and an exhaust gas recirculation control valve for adjusting a flow rate in the exhaust gas recirculation conduit; an intake valve and exhaust In an internal combustion engine comprising a variable valve timing mechanism that changes the opening / closing timing of at least one of the valves,
The opening degree of the exhaust gas recirculation control valve and the opening / closing timing by the variable valve timing mechanism are respectively set according to the load factor of the internal combustion engine,
The opening degree of the exhaust gas recirculation control valve is controlled in the first load region where the fuel consumption can be improved by performing the exhaust gas recirculation control for controlling the opening degree of the exhaust gas recirculation control valve of the exhaust gas recirculation apparatus. A control method for an internal combustion engine that performs exhaust gas recirculation control and performs exhaust gas recirculation control via open / close timing control by a variable valve timing mechanism in a second load region higher than the first load region,
Detect the throttle valve opening,
When the detected opening of the throttle valve is less than a predetermined threshold, exhaust gas recirculation control for controlling the opening of the exhaust gas recirculation control valve is performed,
A control method for an internal combustion engine, characterized in that exhaust gas recirculation control is performed through opening / closing timing control by a variable valve timing mechanism when the detected opening of the throttle valve is equal to or greater than a predetermined threshold value.   The control method for an internal combustion engine according to claim 1, wherein the predetermined threshold value is increased as the rotational speed increases.

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