JP2008157104A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve drivability in an internal combustion engine by restraining the occurrence of a torque level difference in air fuel ratio change and by reducing control time. <P>SOLUTION: A turbosupercharger 45 compressing and supplying intake air to a combustion chamber 18 is provided, and a combustion mode can be switched from a non-supercharged stoichiometric combustion mode to a supercharged lean combustion mode by an ECU 55 in accordance with an engine operation state. The ECU 55 retards ignition timing when the combustion mode is switched from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, and sets a delay quantity of the ignition timing so that an actual supercharging pressure approaches a target supercharging pressure after switching the combustion mode, and the ignition timing is advanced, and the actual supercharging pressure is set to be the target supercharging pressure in switching of the combustion mode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine capable of switching an operating state between a non-supercharged stoichiometric combustion mode and a supercharged lean combustion mode.

  In a general in-cylinder injection type engine, a lean combustion mode capable of realizing homogeneous combustion at a lean air-fuel ratio and a stoichiometric combustion mode capable of realizing homogeneous combustion at a theoretical (stoichiometric) air-fuel ratio can be switched. In this case, for example, the control device has a combustion mode map based on the engine speed and the engine load, and performs switching control between the lean combustion mode and the stoichiometric combustion mode according to the engine operating state.

  In such an engine capable of switching the combustion mode, when switching between the lean air-fuel ratio and the stoichiometric air-fuel ratio according to the operating state, the generated torque differs if the air-fuel ratio is greatly changed. There is a problem that a large torque step occurs when the air-fuel ratio is switched, and drivability deteriorates.

  Therefore, conventionally, control for retarding the ignition timing is executed in order to prevent a torque step generated when the air-fuel ratio is changed. For example, when the stoichiometric combustion mode is switched to the lean combustion mode, the control device controls the stoichiometric air-fuel ratio during the switching control, and changes from stoichiometric to lean after the switching control. That is, when a command for switching from the stoichiometric combustion mode to the lean combustion mode is issued in accordance with the engine operating state, the throttle opening is increased to increase the intake air amount and the fuel injection amount. At this time, by retarding the ignition timing, an increase in the generated torque is suppressed, and after a predetermined period of time, the ignition timing is advanced to an ignition timing according to the operating state, and the fuel injection amount is reduced. By doing so, it changes from stoichiometric to lean.

  In addition, there exists what was described in following patent document 1 as such an internal combustion engine.

Japanese Patent Laid-Open No. 08-114166

  However, when the turbocharger is mounted on the internal combustion engine and the combustion mode is switched between the non-supercharged stoichiometric combustion mode and the supercharged lean combustion mode, the boost pressure becomes higher than necessary due to the increase in exhaust energy. Thus, a torque step occurs at the end of the air-fuel ratio switching control, and drivability deteriorates. That is, when switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, the exhaust gas temperature rises due to the retard of the ignition timing, and the actual supercharging pressure rises above the target supercharging pressure by the turbocharger. Since the boost pressure becomes higher than necessary, the torque increases, and the increased torque needs to be reduced at the end of the air-fuel ratio switching control, so that the control time becomes longer or a torque step occurs here. The problem that will get worse.

  The present invention is for solving such a problem, and provides an internal combustion engine that suppresses the generation of a torque step when the air-fuel ratio is changed and shortens the control time to improve drivability. With the goal.

  In order to solve the above-described problems and achieve the object, an internal combustion engine of the present invention includes a supercharger capable of compressing intake air and supplying the compressed air to a combustion chamber, and a supercharging pressure detecting means for detecting a supercharging pressure. The air-fuel ratio changing means capable of changing the air-fuel ratio, the ignition timing changing means capable of changing the ignition timing, and the ignition timing changing means when the air-fuel ratio changing means changes the stoichiometric air-fuel ratio to the lean air-fuel ratio. In the internal combustion engine having a control means for retarding the ignition timing, the control means detects the supercharging pressure detection means when retarding the ignition timing in order to change from the stoichiometric air-fuel ratio to the lean air-fuel ratio. Set the retard amount of the ignition timing so that the boost pressure approaches the target boost pressure after changing the air-fuel ratio, advance the ignition timing when changing the air-fuel ratio, and set the boost pressure to the target boost pressure It is characterized by.

  In the internal combustion engine of the present invention, when the ignition timing is retarded in order to change from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the supercharging pressure is maintained at a constant value while maintaining the throttle opening at a constant value. A retard amount of the ignition timing is set so as to approach the pressure, the ignition timing is advanced when the air-fuel ratio is changed, and the throttle opening is increased to set the supercharging pressure to the target supercharging pressure.

  In the internal combustion engine of the present invention, when the ignition timing is retarded to change from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the throttle opening is increased so that the supercharging pressure approaches the target supercharging pressure after the air-fuel ratio change. The ignition timing is retarded, the ignition timing is advanced when the air-fuel ratio is changed, and the throttle opening is increased to set the boost pressure to the target boost pressure.

  In the internal combustion engine of the present invention, when the control means changes from the stoichiometric air-fuel ratio to the lean air-fuel ratio, during the air-fuel ratio change control, the ignition timing is retarded while maintaining the stoichiometric air-fuel ratio, and after changing the air-fuel ratio, It is characterized by changing to an air-fuel ratio and advancing the ignition timing and setting the ignition timing to MBT.

  According to the internal combustion engine of the present invention, when the ignition timing is retarded to change from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the ignition timing is delayed so that the supercharging pressure approaches the target supercharging pressure after the air-fuel ratio change. When the air-fuel ratio is changed, the ignition timing is advanced and the supercharging pressure is set to the target supercharging pressure. The generation of a step can be suppressed, and the control time can be shortened. As a result, drivability can be improved.

  Embodiments of an internal combustion engine according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this Example.

  1 is a schematic configuration diagram of an in-line four-cylinder engine that represents an internal combustion engine according to Embodiment 1 of the present invention, FIG. 2 is a mode map that represents a combustion mode in the in-line four-cylinder engine of Embodiment 1, and FIG. FIG. 4 is a time chart showing the engine operating state when the combustion mode is switched in the in-line four-cylinder engine of the first embodiment.

  In this embodiment, an in-line four-cylinder in-cylinder engine is applied as the internal combustion engine. In this in-line four-cylinder engine, as shown in FIG. 1, a cylinder head 12 is fastened on a cylinder block 11, and pistons 14 are fitted to a plurality of cylinder bores 13 formed on the cylinder block 11 so as to be movable up and down. Match. A crankcase 15 is fastened to the lower part of the cylinder block 11, and a crankshaft 16 is rotatably supported in the crankcase 15. Each piston 14 is connected to the crankshaft 16 via a connecting rod 17. Has been.

  The combustion chamber 18 is constituted by the wall surface of the cylinder bore 13 in the cylinder block 11, the lower surface of the cylinder head 12, and the top surface of the piston 14, and the combustion chamber 18 has a high central portion at the upper portion (lower surface of the cylinder head 12). It has a pent roof shape that is slanted. An intake port 19 and an exhaust port 20 are formed on the upper portion of the combustion chamber 18, that is, the lower surface of the cylinder head 12, and the intake valve 19 and the exhaust valve 20 are opposed to the intake port 19 and the exhaust port 20. The lower end portions of 22 are respectively positioned. The intake valve 21 and the exhaust valve 22 are supported by the cylinder head 12 so as to be movable in the axial direction, and are urged and supported in a direction (upward in FIG. 1) for closing the intake port 19 and the exhaust port 20. ing. An intake camshaft 23 and an exhaust camshaft 24 are rotatably supported on the cylinder head 12, and the intake cam 25 and the exhaust cam 26 are in contact with upper ends of the intake valve 21 and the exhaust valve 22.

  Although not shown, an endless timing chain is wound around the crankshaft sprocket fixed to the crankshaft 16 and the camshaft shaft sprockets fixed to the intake camshaft 23 and the exhaust camshaft 24, respectively. The crankshaft 16, the intake camshaft 23, and the exhaust camshaft 24 can be interlocked.

  Accordingly, when the intake camshaft 23 and the exhaust camshaft 24 rotate in synchronization with the crankshaft 16, the intake cam 25 and the exhaust cam 26 move up and down the intake valve 21 and the exhaust valve 22 at a predetermined timing. 19 and the exhaust port 20 can be opened and closed so that the intake port 19 and the combustion chamber 18 can communicate with the combustion chamber 18 and the exhaust port 20, respectively. In this case, the intake camshaft 23 and the exhaust camshaft 24 are set to rotate once (360 degrees) while the crankshaft 16 rotates twice (720 degrees). Therefore, the engine 10 executes the four strokes of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke while the crankshaft 16 rotates twice. At this time, the intake camshaft 23 and the exhaust camshaft 24 are set to one. It will rotate.

  Further, the valve mechanism of the engine 10 is a variable valve timing-intelligent (VVT) mechanism 27 or 28 that controls the intake valve 21 and the exhaust valve 22 at an optimal opening / closing timing according to the operating state. It has become. The intake / exhaust variable valve mechanisms 27 and 28 are configured by providing VVT controllers 29 and 30 at the shaft end portions of the intake camshaft 23 and the exhaust camshaft 24, respectively, The phases of the camshafts 23 and 24 with respect to the cam sprocket are changed by acting on advance and retard chambers (not shown) of the VVT controllers 29 and 30, and the opening and closing timings of the intake valve 21 and the exhaust valve 22 are advanced or retarded. Is something that can be done. In this case, the intake / exhaust variable valve operating mechanisms 27, 28 advance or retard the opening / closing timing while keeping the operating angle (opening period) of the intake valve 21 and the exhaust valve 22 constant. In addition, the intake camshaft 23 and the exhaust camshaft 24 are provided with cam position sensors 33 and 34 for detecting the rotational phase thereof.

  A surge tank 36 is connected to the intake port 19 via an intake manifold 35, and an intake pipe 37 is connected to the surge tank 36. An air cleaner 38 is attached to an air intake port of the intake pipe 37. . An electronic throttle device 40 having a throttle valve 39 is provided on the downstream side of the air cleaner 38.

  An exhaust pipe 42 is connected to the exhaust port 20 via an exhaust manifold 41, and a three-way catalyst 43 and a NOx occlusion reduction type catalyst 44 for purifying harmful substances contained in the exhaust gas are connected to the exhaust pipe 42. Is installed. The three-way catalyst 43 simultaneously purifies HC, CO, and NOx contained in the exhaust gas by an oxidation-reduction reaction when the air-fuel ratio (exhaust air-fuel ratio) is stoichiometric. The NOx occlusion reduction type catalyst 44 is in a rich combustion region or stoichiometric combustion region where the NOx contained in the exhaust gas is temporarily stored when the air-fuel ratio (exhaust air-fuel ratio) is lean, and the oxygen concentration in the exhaust gas is reduced. Sometimes, the stored NOx is released and NOx is reduced by the added fuel as a reducing agent.

  The engine is provided with a turbocharger 45 that turns the turbine by the energy of the exhaust gas and pushes air into the combustion chamber by a compressor directly connected thereto. The turbocharger 45 is configured such that a compressor 46 provided in an intake pipe 37 and a turbine 47 provided in an exhaust pipe 42 are integrally connected by a connecting shaft 48. The intake pipe 37 on the downstream side of the compressor 46 in the turbocharger 45 is provided with an intercooler 49 that cools the intake air that has been compressed by the compressor 46 and has risen in temperature.

  The cylinder head 12 is provided with an injector 50 that directly injects fuel into the combustion chamber 18. The injector 50 is located on the intake port 19 side and is inclined at a predetermined angle from the horizontal upper end. . An injector 50 attached to each cylinder is connected to a delivery pipe 51, and a high-pressure fuel pump 53 is connected to the delivery pipe 51 via a high-pressure fuel supply pipe 52 so that fuel of a predetermined pressure can be supplied. . The cylinder head 12 is provided with a spark plug 54 that is located above the combustion chamber 18 and ignites the air-fuel mixture.

  The vehicle is equipped with an electronic control unit (ECU) 55 that can control the fuel injection timing of the injector 50, the ignition timing of the spark plug 54, and the like. The fuel injection amount, injection timing, ignition timing, and the like are determined based on engine operating conditions such as temperature, supercharging pressure, throttle opening, accelerator opening, engine speed, and coolant temperature. That is, an airflow sensor 56 and an intake air temperature sensor 57 are mounted on the upstream side of the intake pipe 37, and the measured intake air amount and intake air temperature are output to the ECU 55. Further, a supercharging pressure sensor 58 is attached to the surge tank 36, and the measured supercharging pressure is output to the ECU 55. The electronic throttle device 40 is provided with a throttle position sensor 59, and the accelerator pedal is provided with an accelerator position sensor 60, which outputs the current throttle opening and accelerator opening to the ECU 55. Further, the crankshaft 16 is provided with a crank angle sensor 61, which outputs the detected crank angle to the ECU 55. The ECU 55 determines the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke in each cylinder based on the crank angle. Calculate the engine speed. Further, the cylinder block 11 is provided with a water temperature sensor 62 and outputs the detected engine cooling water temperature to the ECU 55.

  An air-fuel ratio (A / F) sensor 63 is provided upstream of the three-way catalyst 43 in the exhaust pipe 42. The A / F sensor 63 detects the exhaust air / fuel ratio of the exhaust gas exhausted from the combustion chamber 18 through the exhaust port 20 and the exhaust manifold 41 to the exhaust pipe 42, and outputs the detected exhaust air / fuel ratio to the ECU 55. The ECU 55 corrects the fuel injection amount by feeding back the exhaust air-fuel ratio detected by the A / F sensor 63 and comparing it with the target air-fuel ratio set according to the engine operating state.

  The ECU 55 can control the intake / exhaust variable valve mechanisms 27 and 28 based on the engine operating state. That is, when the temperature is low, the engine is started, the engine is idle, or the load is light, the exhaust gas blows back to the intake port 19 or the combustion chamber 18 by eliminating the overlap between the exhaust valve 22 closing timing and the intake valve 21 opening timing. Reduce the amount to enable stable combustion and improved fuel efficiency. Further, at the time of medium load, by increasing the overlap, the internal EGR rate is increased to improve the exhaust gas purification efficiency, and the pumping loss is reduced to improve the fuel consumption. Further, at the time of high-load low-medium rotation, the closing timing of the intake valve 21 is advanced, thereby reducing the amount of intake air that blows back to the intake port 19 and improving the volume efficiency. At the time of high load and high rotation, the closing timing of the intake valve 21 is retarded in accordance with the rotation speed, so that the timing is adjusted to the inertial force of the intake air and the volume efficiency is improved.

By the way, in the direct four-cylinder engine of this embodiment, the ECU 55 can realize a lean combustion mode capable of realizing homogeneous combustion at a lean air-fuel ratio according to the engine operating state and homogeneous combustion at a theoretical (stoichiometric) air-fuel ratio. The stoichiometric combustion mode can be switched. In this case, as shown in FIG. 2, the ECU 55 has a combustion mode map based on the engine speed and the engine load (air amount), and the lean combustion mode and the stoichiometric combustion mode are determined using this combustion mode map. Is controlled. In this case, when the combustion mode of the engine is switched from the stoichiometric combustion mode to the lean combustion mode, a switching boundary line L ₁ from the stoichiometric combustion mode to the lean combustion mode indicated by a solid line in FIG. 2 is set, and this switching boundary line A switching control start boundary line L ₂ is set outside L ₁ , that is, on the stoichiometric combustion mode side.

  When the ECU 55 performs switching control between the lean combustion mode and the stoichiometric combustion mode using the combustion mode map, the ECU 55 performs control with the stoichiometric air-fuel ratio during the switching control, and changes the air-fuel ratio after the switching control. That is, when switching from the stoichiometric combustion mode to the lean combustion mode, an increase in torque generated by retarding the ignition timing is suppressed, and the stoichiometric air-fuel ratio is maintained by changing the air amount and changing the fuel amount. After completion of the switching control after a predetermined period of time, the ignition timing is advanced to change to the ignition timing according to the operating state, and the air amount and the fuel amount are changed to change from the stoichiometric air fuel ratio to the lean air fuel ratio. ing.

  However, when the engine is equipped with a turbocharger, when the combustion mode is switched from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, the boost pressure becomes higher than necessary due to an increase in exhaust energy, and the A torque step occurs at the end of the switching control of the fuel ratio, and the control time becomes longer due to the need to reduce the supercharging pressure, and drivability deteriorates.

  Therefore, in the internal combustion engine of the first embodiment, when the ECU 55 changes the non-supercharged stoichiometric combustion mode (stoichiometric air-fuel ratio) to the supercharged lean combustion mode (lean air-fuel ratio) and retards the ignition timing, The retard amount of the ignition timing is set so that the boost pressure detected by the pressure sensor 58 approaches the target boost pressure after the combustion mode (air / fuel ratio) change, and the ignition timing is advanced in the combustion mode (air / fuel ratio). At the same time, the supercharging pressure is set to the target supercharging pressure. In this embodiment, the supercharging pressure sensor 58 is applied as a supercharging pressure detecting means for detecting the supercharging pressure, an air-fuel ratio changing means capable of changing the air-fuel ratio, an ignition timing changing means capable of changing the ignition timing, The ECU 55 is applied as a control means for retarding the ignition timing by the ignition timing changing means when the stoichiometric air-fuel ratio is changed from the stoichiometric air-fuel ratio by the air-fuel ratio changing means.

  In this case, the ECU 55 sets a target supercharging pressure in accordance with the engine operating state, and this target supercharging pressure is determined from a required supercharging pressure set based on the engine operating state (for example, accelerator opening). The quantitative value is set low.

  Further, the ECU 55 changes the supercharging pressure from the non-supercharging stoichiometric combustion mode to the supercharging lean combustion mode so that the supercharging pressure approaches the target supercharging pressure after the change of the air-fuel ratio while maintaining the throttle opening degree of 3965 at a constant value. The retard amount of the ignition timing is set to the ignition timing, the ignition timing is advanced when the combustion mode (air-fuel ratio) is changed, and the throttle opening is increased to set the boost pressure to the target boost pressure. .

  In this case, when changing from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, the ignition timing is retarded while maintaining the stoichiometric air-fuel ratio during the combustion mode change control, and the lean air-fuel ratio is changed after the combustion mode is changed. The ignition timing is advanced and the ignition timing is set to MBT.

  Here, in the in-line four-cylinder engine of this embodiment described above, the combustion mode switching control will be specifically described based on the flowchart of FIG.

In the in-line four-cylinder engine of this embodiment, as shown in FIG. 3, it is determined in step S11 whether there is a request for switching from the non-supercharging stoichiometric combustion mode to the supercharging lean combustion mode based on the engine operating state. judge. Specifically, based on the engine speed and the engine load (amount of air), when changing from the non-supercharged stoichiometric combustion mode to the lean combustion mode side determines whether exceeds the switching control start boundary line L _2. If it is determined that there is no request for switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, the ECU 55 executes normal ignition timing retardation control in step S17.

On the other hand, in step S11, When the ECU55 is, there is a request for switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, that is, it is determined that exceeds the switching control start boundary L _2, in step S12, The actual boost pressure is detected by the boost pressure sensor 58, and the lean target boost pressure is calculated based on the engine operating state. In this case, the lean target boost pressure is calculated by subtracting a predetermined value set in advance from the lean required boost pressure calculated based on the accelerator opening detected by the accelerator position sensor 60. When switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, during this switching control, the ignition timing is retarded to suppress an increase in torque, and the turbocharger 45 is increased by increasing the exhaust temperature. Operates and the supercharging pressure increases (the amount of air increases), so that the stoichiometric air-fuel ratio is maintained.

In step S13, the ECU 55 executes ignition timing retard control, and in step S14, the ECU 55 determines whether or not a switching signal from the non-supercharging stoichiometric combustion mode to the supercharging lean combustion mode is input. To do. Specifically, based on the engine speed and the engine load (amount of air), when changing from the non-supercharged stoichiometric combustion mode to the lean combustion mode side determines whether exceeds the switching換境boundary line L _1. Here, when it is determined not to exceed the switching換境boundary line L ₁ repeats the processing in steps S13 and S14. Then, at step S14, if it is determined that exceeds the switching換境boundary line L _1, in step S15, advances the ignition timing. Thereafter, in step S16, the throttle opening is corrected in accordance with the lean target boost pressure, and the combustion mode switching control is terminated.

  Here, in the in-line four-cylinder engine of the present embodiment, a change in the engine operation state accompanying the combustion mode switching control will be specifically described based on the time chart of FIG.

In the in-line four-cylinder engine of this embodiment, as shown in FIG. 4, at time t ₁ , a switching request from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, that is, a switching control start boundary line L ₂ is set. If exceeded, the ignition timing is gradually retarded. Then, the amount of heat of the exhaust gas is increased by this ignition timing, the exhaust gas temperature is increased, and the turbocharger 45 is operated. Therefore, the turbine rotation speed is increased, the actual supercharging pressure is increased, and the intake air amount is increased. However, the fuel injection amount is increased in order to maintain the stoichiometric air-fuel ratio.

Then, at time t _2, no switching signal is input from the supercharged stoichiometric combustion mode to the supercharged lean combustion mode, that is, exceeds the switching換境boundary line L _1, after retarding the ignition timing to a predetermined value, the ignition Advance the timing and set the ignition timing according to the engine operating condition. At this time, in order to change from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the throttle opening is increased to the target throttle opening corresponding to the engine operating state, and the fuel injection amount is decreased. Then, at time t _3, the combustion mode switching control from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode is completed.

  As described above, in the internal combustion engine of the first embodiment, the turbocharger 45 capable of compressing the intake air and supplying the compressed air to the combustion chamber 18 is provided in the in-line four-cylinder engine, and the ECU 55 responds to the engine operating state. The combustion mode can be switched from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, and the ECU 55 retards the ignition timing when switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode. Set the retard amount of the ignition timing so that the supply pressure approaches the target boost pressure after changing the combustion mode, advance the ignition timing when changing the combustion mode, and set the actual boost pressure to the target boost pressure I have to.

  Therefore, when switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, retarding the ignition timing can suppress an increase in torque more than necessary, and the actual supercharging pressure is changed after the combustion mode is changed. By setting the retard amount of the ignition timing so as to approach the target boost pressure, it is possible to suppress an increase in the boost pressure and torque more than necessary due to the retard of the ignition timing. By suppressing the occurrence of torque steps, drivability can be improved. Further, when the turbo mode is switched to the combustion mode, the turbocharger 45 is operated, whereby the supercharging pressure is increased and the air amount is increased, so that the switching control time can be shortened.

  In this case, the target boost pressure is set to a predetermined amount lower than the required boost pressure set based on the operating state such as the accelerator opening, and the increase of the boost pressure more than necessary due to the retard of the ignition timing, An increase in torque can be appropriately suppressed.

  In the internal combustion engine of the first embodiment, the ECU 55 maintains the throttle opening at a constant value when retarding the ignition timing in order to switch from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode. The retard amount of the ignition timing is set so that the boost pressure approaches the target boost pressure after the air-fuel ratio change. Accordingly, it is possible to appropriately suppress an increase in supercharging pressure and an increase in torque due to the retard of the ignition timing.

  In the internal combustion engine of the first embodiment, when switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, the ECU 55 retards the ignition timing while maintaining the stoichiometric air-fuel ratio during the combustion mode change control, After changing the air-fuel ratio, the air-fuel ratio is changed to a lean air-fuel ratio, the ignition timing is advanced, and the ignition timing is set to MBT. Therefore, the air-fuel ratio after switching of the combustion mode can be appropriately changed to a desired lean air-fuel ratio.

  FIG. 5 is a flowchart showing combustion mode switching control in an in-line four-cylinder engine representing an internal combustion engine according to Embodiment 2 of the present invention. FIG. 6 is an engine operating state at the time of combustion mode switching in the in-line four-cylinder engine of Embodiment 1. It is a time chart showing. The overall configuration of the internal combustion engine of the present embodiment is substantially the same as that of the first embodiment described above, and will be described with reference to FIGS. 1 and 2 and members having the same functions as those described in the present embodiment. Are denoted by the same reference numerals, and redundant description is omitted.

  In the in-line four-cylinder in-cylinder injection engine as the internal combustion engine of the present embodiment, as shown in FIGS. When the ignition timing is retarded by changing to the lean air-fuel ratio, the ignition timing is retarded so that the supercharging pressure detected by the supercharging pressure sensor 58 approaches the target supercharging pressure after the change of the combustion mode (air-fuel ratio). The amount is set, the ignition timing is advanced in the combustion mode (air-fuel ratio), and the supercharging pressure is set to the target supercharging pressure.

  In this case, when retarding the ignition timing in order to change from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, the ECU 55 increases the throttle opening and changes the supercharging pressure to the combustion mode (air-fuel ratio). The retard amount of the ignition timing is set so that it approaches the target boost pressure of the engine, and when the combustion mode (air-fuel ratio) is changed, the ignition timing is advanced and the throttle opening is further increased to increase the boost pressure to the target boost pressure. It is set to.

  Here, in the in-line four-cylinder engine of the present embodiment described above, the combustion mode switching control will be specifically described based on the flowchart of FIG.

In the in-line four-cylinder engine of this embodiment, as shown in FIG. 5, it is determined in step S21 whether there is a request for switching from the non-supercharging stoichiometric combustion mode to the supercharging lean combustion mode based on the engine operating state. determined, specifically, when changing from the non-supercharged stoichiometric combustion mode to the lean combustion mode side determines whether exceeds the switching control start boundary line L _2. Here, if it is determined that there is no request for switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, the ECU 55 executes normal ignition timing retardation control in step S28.

On the other hand, in step S21, When the ECU55 is, there is a request for switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, that is, it is determined that exceeds the switching control start boundary L _2, in step S22, The actual boost pressure is detected by the boost pressure sensor 58, and the lean target boost pressure is calculated based on the engine operating state. When switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, during this switching control, the ignition timing is retarded to suppress an increase in torque, and the electronic throttle device 40 is controlled to control the throttle opening. As the exhaust gas temperature rises, the turbocharger 45 operates and the supercharging pressure rises (the air amount increases), so that the stoichiometric air-fuel ratio is maintained.

In step S23, the ECU 55 performs ignition timing retard control, and in step S24, the ECU 55 controls the electronic throttle device 40 to adjust, that is, increase the throttle opening. In step S25, the ECU 55 determines whether or not a switching signal for switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode is input. Specifically, based on the engine speed and the engine load (air amount), when changing from the non-supercharged stoichiometric combustion mode to the lean combustion mode side determines whether exceeds the switching換境boundary line L _1. Here, when it is determined not to exceed the switching換境boundary line L ₁ repeats the processing of step S23～S15. Then, at step S25, if it is determined that exceeds the switching換境boundary line L _1, in step S26, advances the ignition timing. Thereafter, in step S27, the throttle opening is corrected in accordance with the lean target supercharging pressure, and the combustion mode switching control is terminated.

  Here, in the in-line four-cylinder engine of this embodiment, the change in the engine operating state accompanying the combustion mode switching control will be specifically described based on the time chart of FIG.

In the in-line four-cylinder engine of this embodiment, as shown in FIG. 6, at time t ₁ , a switching request from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, that is, a switching control start boundary line L ₂ is set. If it exceeds, the throttle opening is gradually increased and the ignition timing is gradually retarded. Then, the amount of heat of the exhaust gas increases due to this ignition timing, the exhaust gas temperature rises, the turbocharger 45 operates, and the throttle opening increases, so the turbine speed increases. Although the actual supercharging pressure increases and the intake air amount increases, the fuel injection amount is increased in order to maintain the stoichiometric air-fuel ratio.

Then, at time t _2, no switching signal is input from the supercharged stoichiometric combustion mode to the supercharged lean combustion mode, that is, exceeds the switching換境boundary line L _1, after retarding the ignition timing to a predetermined value, the ignition Advance the timing and set the ignition timing according to the engine operating condition. At this time, in order to change from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the throttle opening is increased to the target throttle opening corresponding to the engine operating state, and the fuel injection amount is decreased. Then, at time t _4, the combustion mode switching control from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode is completed.

  Thus, in the internal combustion engine of the second embodiment, the turbocharger 45 capable of compressing the intake air and supplying it to the combustion chamber 18 in the in-line four-cylinder engine is provided, and the ECU 55 responds to the engine operating state. The combustion mode can be switched from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, and the ECU 55 increases the throttle opening and the ignition timing when switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode. Is set so that the actual boost pressure approaches the target boost pressure after changing the combustion mode, and the ignition timing is advanced when the combustion mode is changed and the throttle opening is further increased. Thus, the supercharging pressure is set to the target supercharging pressure.

  Therefore, when switching from the non-supercharged stoichiometric combustion mode to the supercharged lean combustion mode, retarding the ignition timing can suppress an increase in torque more than necessary, and the actual supercharging pressure is changed after the combustion mode is changed. By setting the throttle opening and the retard amount of the ignition timing so as to approach the target boost pressure, it is possible to suppress an increase in the boost pressure and torque that are more than necessary due to the retard of the ignition timing, and combustion The drivability can be improved by suppressing the occurrence of a torque step during the mode change. Further, at the time of switching to the combustion mode, the throttle opening is increased and the turbocharger 45 is operated, whereby the supercharging pressure is increased and the air amount is increased, so that the switching control time can be further shortened. .

  In each of the above-described embodiments, the in-cylinder in-line four-cylinder engine is applied as the internal combustion engine. However, the engine type and the number of cylinders are not limited to those in the embodiment, and the port injection-type internal combustion engine. It may be.

  As described above, the internal combustion engine according to the present invention suppresses the occurrence of a torque step when the air-fuel ratio is changed and shortens the control time to improve drivability, and is useful for any internal combustion engine. is there.

1 is a schematic configuration diagram of an in-line four-cylinder engine that represents an internal combustion engine according to Embodiment 1 of the present invention. 3 is a mode map showing a combustion mode in the in-line four-cylinder engine of Embodiment 1. 2 is a flowchart showing combustion mode switching control in the in-line four-cylinder engine of Embodiment 1. 2 is a time chart showing an engine operating state at the time of combustion mode switching in the in-line four-cylinder engine of the first embodiment. It is a flowchart showing the combustion mode switching control in the inline 4 cylinder engine showing the internal combustion engine which concerns on Example 2 of this invention. 2 is a time chart showing an engine operating state at the time of combustion mode switching in the in-line four-cylinder engine of the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 18 Combustion chamber 19 Intake port 20 Exhaust port 21 Intake valve 22 Exhaust valve 37 Intake pipe 40 Electronic throttle device 42 Exhaust pipe 43 Three way catalyst 44 NOx occlusion reduction type catalyst 45 Turbocharger 50 Injector 54 Spark plug 55 Electronic control unit, ECU (control means, air-fuel ratio changing means, ignition timing changing means)
56 Air flow sensor (air quantity detection means)
58 Supercharging pressure sensor (Supercharging pressure detection means)
59 Throttle position sensor 60 Accelerator position sensor 61 Crank angle sensor

Claims (4)

  A supercharger capable of compressing intake air and supplying it to the combustion chamber; a supercharging pressure detecting means for detecting a supercharging pressure; an air-fuel ratio changing means capable of changing the air-fuel ratio; and an ignition timing capable of changing the ignition timing In the internal combustion engine comprising: a changing means; and a control means for retarding the ignition timing by the ignition timing changing means when the stoichiometric air-fuel ratio is changed from the stoichiometric air-fuel ratio by the air-fuel ratio changing means. When retarding the ignition timing in order to change from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the ignition timing is delayed so that the boost pressure detected by the boost pressure detecting means approaches the target boost pressure after the air-fuel ratio change. An internal combustion engine characterized in that an angular amount is set, an ignition timing is advanced when an air-fuel ratio is changed, and a supercharging pressure is set to a target supercharging pressure.   2. The internal combustion engine according to claim 1, wherein when the ignition timing is retarded in order to change from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the boost pressure is maintained after maintaining the throttle opening at a constant value. Set the retard amount of the ignition timing so as to approach the target boost pressure, advance the ignition timing when changing the air-fuel ratio, and increase the throttle opening to set the boost pressure to the target boost pressure An internal combustion engine.   2. The internal combustion engine according to claim 1, wherein when the ignition timing is retarded in order to change from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the throttle pressure is increased and the boost pressure becomes the target boost pressure after the air-fuel ratio change. The ignition timing is retarded so as to approach the engine, the ignition timing is advanced when the air-fuel ratio is changed, and the throttle opening is increased to set the boost pressure to the target boost pressure. .   4. The internal combustion engine according to claim 1, wherein when the control means changes from a stoichiometric air-fuel ratio to a lean air-fuel ratio, the ignition timing is maintained while the stoichiometric air-fuel ratio is maintained during the air-fuel ratio change control. The internal combustion engine is characterized in that, after changing the air-fuel ratio, the air-fuel ratio is changed to a lean air-fuel ratio, the ignition timing is advanced, and the ignition timing is set to MBT.

Images