JP6699272B2 - Engine and control method thereof - Google Patents

Description

  The present invention relates to an engine that operates by switching an air-fuel ratio between a plurality of air-fuel ratios and a control method thereof.

  An engine that operates by switching the air-fuel ratio between a plurality of air-fuel ratios is already known from patent documents and the like. While the engine is operating, when changing to an air-fuel ratio that is relatively higher than the currently set air-fuel ratio, specifically, when changing from the stoichiometric air-fuel ratio to the lean air-fuel ratio, while suppressing fluctuations in engine torque. The air-fuel ratio may be changed by increasing the intake air amount. In this case, there is the following problem due to the delay in the change of the intake air amount. An aerodynamic response delay is inherent in the change in the intake air amount. Therefore, if the switching is executed immediately without waiting for the change in the intake air amount, the fuel injection amount becomes insufficient by the amount corresponding to the shortage of the intake air amount, and the required engine torque cannot be obtained. That is, it deteriorates drivability. As a measure for solving such a torque shock problem, it is possible to switch the air-fuel ratio after waiting for a change in the intake air amount (Patent Document 1).

JP, 2015-086780, A

  However, if the air-fuel ratio is switched after waiting for a change in the intake air amount, it naturally takes time to switch the air-fuel ratio accordingly. With the recent demand for reduction of exhaust gas and improvement of fuel efficiency, development of an engine that operates at an air-fuel ratio higher than before is underway.In such an extremely lean combustion engine, the intake air is changed when the air-fuel ratio is switched. The air amount must be changed significantly, and there is a concern that the time required for switching the air-fuel ratio will be prolonged due to the response delay of the intake air amount.

  Therefore, an object of the present invention is to quickly achieve air-fuel ratio switching while suppressing torque shock.

  The present invention, in one form, provides a method for controlling an engine.

An engine control method according to an aspect of the present invention is a method of operating an engine by switching between a first air-fuel ratio and a second air-fuel ratio higher than the first air-fuel ratio, and the engine is operated according to an operating state of the engine. Select the air-fuel ratio to operate. Then, at the time of switching from the first air-fuel ratio to the second air-fuel ratio or from the second air-fuel ratio to the first air-fuel ratio, the engine control amount related to the intake air amount in a steady state corresponding to the air-fuel ratio after switching An air amount correction control for increasing or decreasing the engine control amount based on the intake air amount is executed.

  According to the present invention, by operating the air-fuel ratio by switching between the first air-fuel ratio and the second air-fuel ratio, both the drivability of the vehicle and the fuel efficiency are achieved, and the air amount correction is performed when the air-fuel ratio is switched. Through the control, the response of the intake air amount at the time of switching can be corrected. Therefore, it is possible to quickly change the actual intake air amount toward the target air amount after switching, thereby shortening the time required for switching, and suppressing the torque shock and quickly switching the air-fuel ratio. Can be achieved.

FIG. 1 is an overall configuration diagram of an engine according to a first embodiment of the present invention. FIG. 2 is a schematic diagram showing the tendency of the engine operating region map. FIG. 3 is a timing chart showing the behavior of the vehicle by the air amount control according to the first embodiment of the present invention. FIG. 4 is a timing chart showing the specific contents of the air amount control. FIG. 5 is a timing chart showing the specific contents of the air amount control. FIG. 6 is a flowchart showing a basic flow of the air amount control according to the first embodiment of the present invention. FIG. 7 is a flowchart showing the flow of the air amount correction process of the air amount control. FIG. 8 is an explanatory diagram showing an example of setting valve timing by the air amount correction process. FIG. 9 is an overall configuration diagram of an engine according to a modification of the first embodiment of the present invention. FIG. 10 is a timing chart showing the specific contents of the air amount control according to the modified embodiment. FIG. 11 is a timing chart showing the behavior of the vehicle by the air amount control according to the second embodiment of the present invention. FIG. 12 is a timing chart showing the specific contents of the air amount control. FIG. 13 is a timing chart showing the behavior of the vehicle by the air amount control according to the third embodiment of the present invention. FIG. 14 is a timing chart showing the specific contents of the air amount control. FIG. 15 is a timing chart showing the specific contents of the air amount control.

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

(Explanation of overall structure)
FIG. 1 shows the overall configuration of an engine 1 according to the first embodiment of the present invention.

  In FIG. 1, thick lines indicate passages through which gas (air or exhaust) flows, and dotted lines indicate paths through which signals are transmitted.

  In the present embodiment, the engine 1 is an internal combustion engine (gasoline engine) that uses gasoline as fuel, and has a plurality of cylinders #1 to #4.

  An air cleaner 12 is attached to an intake portion of the intake passage 11 of the engine 1, and foreign matter such as dust in the sucked air is removed by the air cleaner 12. A compressor unit 131 of a turbocharger 13 is provided in the intake passage 11, and intake air is compressed by the turbocharger 13 and then supplied to a main body E of the engine 1 via a manifold unit 111.

  In this embodiment, the intercooler 14 is installed on the downstream side of the compressor unit 131, and the intercooler 14 cools the air compressed by the turbocharger 13. An intake throttle valve 15 is installed on the upstream side of the collector portion, that is, on the downstream side of the intercooler 14 in the present embodiment, and the flow rate of intake air (intake air amount) supplied to the engine body E by the intake throttle valve 15. Is controlled. A passage that bypasses the compressor portion 131 is formed in the turbocharger 13, and a blow-off valve 13a is interposed in this passage. When the intake throttle valve 15 is closed, the blow-off valve 13a is driven to open, whereby the excessive boost pressure generated on the downstream side of the compressor section 131 is released on the upstream side of the compressor section 131.

  The engine body E is formed with four cylinders #1 to #4. In the present embodiment, the fuel can be individually supplied to each cylinder, and a fuel injector (not shown) is provided for each cylinder. The fuel injector is embedded in the cylinder head of the engine body E so that fuel can be injected toward the port of each cylinder. As the fuel injector, a type that directly injects fuel into the cylinder may be adopted. Further, a spark plug (not shown) is installed in the cylinder head for each cylinder, and the spark plug ignites a mixture gas having a predetermined air-fuel ratio formed in the cylinder.

  In the exhaust passage 21 of the engine 1, a turbine section 132 of the turbocharger 13 is provided downstream of the manifold section 211. The turbine unit 132 is driven by the exhaust energy, and the rotary motion of the turbine unit 132 is transmitted to the compressor unit 131, whereby the turbocharger 13 functions. A passage that bypasses the turbine portion 132 is formed in the turbocharger 13, and a waste gate valve 13b is interposed in this passage. By driving the waste gate valve 13b to open, a part of the exhaust gas bypasses the turbine portion 132, and an excessive increase in boost pressure is suppressed.

  The catalytic converter 22 is installed on the downstream side of the turbine section 132. The catalytic converter 22 has a built-in exhaust gas purification catalyst that purifies nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC) that are harmful components in the exhaust gas. In this embodiment, a three-way catalyst 221 and a NOx trap catalyst 222 are provided as the exhaust purification catalyst. The NOx trap catalyst 222 traps NOx in the exhaust during combustion with a lean air-fuel ratio, and purifies the exhaust. NOx trapped in the NOx trap catalyst 222 can be desorbed from the catalyst and reduced by temporarily reducing the air-fuel ratio below the theoretical air-fuel ratio and increasing the unburned fuel component in the exhaust gas. Is. By such an operation, the NOx trap catalyst 222 can be regenerated.

  Further, the exhaust passage 21 on the downstream side of the catalytic converter 22 and the intake passage 11 on the upstream side of the compressor section 131 of the turbocharger 13 are connected via an EGR pipe 23, and a part of the exhaust gas in which harmful components are purified is partially exhausted. , To the intake passage 11 through the EGR pipe 23. An EGR valve 24 is installed in the EGR pipe 23, and the opening area of the EGR pipe 23 is changed by the ERG valve 24, and the flow rate of exhaust gas recirculated through the EGR pipe 23 is adjusted. The recirculated exhaust gas is mixed with the intake air and is again distributed to the cylinders #1 to #4. The remaining exhaust gas is discharged into the atmosphere through a muffler (not shown).

  The operation of the engine 1 is controlled by the electronic control unit 101. The electronic control unit 101 receives the detection signals of the accelerator sensor 201, the rotation speed sensor 202, and the cooling water temperature sensor 203, and also the detection signals of the air flow meter 204, the intake pressure sensor 205, the air-fuel ratio sensor 206, and the like. It The accelerator sensor 201 detects the amount of operation of the accelerator pedal by the driver. The rotation speed sensor 202 detects the rotation speed of the engine 1. A crank angle sensor can be used as the rotation speed sensor 202. The cooling water temperature sensor 203 detects the temperature of the engine cooling water. The temperature of the engine lubricating oil may be used instead of the temperature of the engine cooling water. The air flow meter 204 detects the intake air amount. The intake pressure sensor 205 detects the pressure in the intake passage 11 on the downstream side of the compressor section 131 of the turbocharger 13. The air-fuel ratio sensor 206 detects the air-fuel ratio of exhaust gas. The electronic control unit 101 sets the fuel injection amount, the ignition timing, etc. based on signals from various sensors, and sets the opening degrees of the intake throttle valve 15 and the EGR valve 24 to control the operation of the engine 1. To do.

  In this embodiment, variable valve operating devices 31 and 32 are used for the intake valve and the exhaust valve (not shown), and the valve timings of the intake valve and the exhaust valve are changeable. The variable valve operating devices 31, 32 may be of a mechanically driven type or an electromagnetically driven type. As a mechanical variable valve operating device, a so-called VTC system configured to change the valve timing by changing the phase of the camshaft with respect to the crankshaft, as well as the operating angle and lift amount of the intake valve are continuously changed. There is a VVEL system which is practically used. An example of the electromagnetic variable valve operating device is an electromagnetically driven valve operating device that uses a solenoid as a drive source.

  The electronic control unit 101 constitutes a “combustion control device”, and the accelerator sensor 201 and the rotation speed sensor 202 constitute a “state detection device”.

(Outline of engine control)
The contents of the control executed by the electronic control unit 101 will be described.

  In the present embodiment, the engine 1 has a plurality of operating regions and operates by switching the air-fuel ratio for each region.

  FIG. 2 shows an operating region map created in advance for the engine 1, and map data having such a tendency is stored in the electronic control unit 101 in advance. In the present embodiment, the electronic control unit 101 includes a storage unit that stores the map data of the tendency.

  Specifically, the operating region of the engine 1 is a region on the low rotation speed and low load side (indicated by “λ2” in FIG. 2 and hereinafter referred to as “λ2 region”) and other regions (λ1 in FIG. , And hereinafter referred to as “λ1 region”). In the latter λ1 region, the target value of the air-fuel ratio when the engine 1 is operated in a steady state (hereinafter referred to as “the steady-state target air-fuel ratio”) is set to the theoretical air-fuel ratio, and in the former λ2 region, the steady-state target of the engine 1 is set. The lean air-fuel ratio is set so that the air-fuel ratio is higher than the stoichiometric air-fuel ratio. In this embodiment, as the lean air-fuel ratio, an air-fuel ratio in the range of 24 to 29, which is approximately 2 in terms of excess air ratio conversion (=air-fuel ratio/theoretical air-fuel ratio), is adopted. This lean air-fuel ratio corresponds to the "second air-fuel ratio".

  When controlling the operation of the engine 1, the electronic control unit 101 determines the operating state of the engine 1 based on the detection signals of the accelerator sensor 201 and the rotation speed sensor 202. Then, with reference to the tendency map data shown in FIG. 2, the region (λ1 region or λ2 region) to which the operating state of the engine 1 belongs is determined, and the operating air-fuel ratio of the engine 1 (steady target air (Fuel ratio) is switched, and the intake air amount is controlled to a target air amount according to the operating air-fuel ratio.

  Further, the electronic control unit 101 monitors the amount of NOx trapped in the NOx trap catalyst 222, and temporarily reduces the air-fuel ratio below the stoichiometric air-fuel ratio when the NOx trap amount reaches the allowable limit amount. Perform a rich spike operation. The air-fuel ratio lower than the stoichiometric air-fuel ratio corresponds to the “first air-fuel ratio” according to this embodiment.

(Explanation of air volume control)
Hereinafter, the overall operation of the air amount control (hereinafter, simply referred to as “air amount control”) according to the present embodiment will be described with reference to a timing chart, and then the control flow will be described with reference to a flowchart.

  In this embodiment, it is assumed that the operation amount of the accelerator pedal does not change and the air-fuel ratio is switched based on the regeneration request of the NOx trap catalyst 222. Specifically, the operating state of the engine 1 is in the λ2 region (for example, point A shown in FIG. 2), there is no transition of the operating region before and after the switching of the air-fuel ratio, and the regeneration request of the NOx trap catalyst 222 is met. The air-fuel ratio is temporarily set to an air-fuel ratio lower than the stoichiometric air-fuel ratio, and thereafter, the lean air-fuel ratio is switched to the original lean air-fuel ratio again by the judgment of the end of regeneration. Through this series of rich spike operations, the engine speed and the vehicle speed are maintained constant. The regeneration request for the NOx trap catalyst 222 is generated by the electronic control unit 101. The electronic control unit 101 determines whether or not the NOx trapped in the NOx trap catalyst 222 has reached the permissible limit amount based on the accumulated value of the engine speed from the previous regeneration and the like, and the permissible limit amount. Is reached, a regeneration request is generated and the air-fuel ratio is made lower than the stoichiometric air-fuel ratio. Further, the electronic control unit 101 calculates the elapsed time from when the air-fuel ratio is made lower than the stoichiometric air-fuel ratio, makes a judgment of the end of regeneration when the time reaches a predetermined time, and determines the lean air-fuel ratio based on the original lean air-fuel ratio. Switch to air-fuel ratio.

  3 to 5 are timing charts showing the content of the air amount control according to the present embodiment.

  FIG. 3 shows the behavior that appears in the vehicle due to the air amount control. As shown in the figure, the vehicle speed, the accelerator opening, and the engine speed do not substantially change, and the operating range does not change, but at time t6, the engine torque slightly changes. This torque shock is accompanied by switching to the lean air-fuel ratio after the end of regeneration. In the present embodiment, the air-fuel ratio is set to approximately 2 in terms of excess air ratio in the λ2 region. Combustion at such a high air-fuel ratio improves the combustion efficiency, and as a result, the fuel injection amount required to generate the same engine torque is small. This is to reduce the amount slightly.

  FIG. 4 shows the specific content of the air amount control when the air-fuel ratio is switched to the original lean air-fuel ratio after the regeneration of the NOx trap catalyst 222 is completed.

  When it is determined that the NOx trapped in the NOx trap catalyst 222 has reached the allowable limit amount (time t1), a regeneration request for the NOx trap catalyst 222 is generated, and the lean burn permission condition is changed from established to unestablished. Along with this, the rich spike operation is started by switching the air-fuel ratio from the lean air-fuel ratio to an air-fuel ratio lower than the stoichiometric air-fuel ratio. By the rich spike operation, the air-fuel ratio is set to a lower air-fuel ratio than the stoichiometric air-fuel ratio (time t2), the unburned fuel component in the exhaust gas increases, and it functions as a reducing agent, so that the NOx trap catalyst NOx desorbed from 222 and NOx in the exhaust gas are reduced. Then, when the elapsed time after the air-fuel ratio is lowered below the stoichiometric air-fuel ratio reaches a predetermined time, it is judged that the regeneration is completed (time t3), and the lean burn permission condition is changed to be satisfied.

  When the regeneration of the NOx trap catalyst 222 is judged to be finished, the control for switching the air-fuel ratio to the original lean air-fuel ratio is started. In the present embodiment, when the air-fuel ratio is switched, an air amount correction request is generated, and until the request is canceled (time t3 to t8), the lean air-fuel ratio after switching the engine control amount related to the intake air amount or the intake pressure is changed. A control for increasing the control amount based on the target intake pressure according to (steady target air-fuel ratio) (hereinafter referred to as "air amount correction control") is executed. The air amount correction control corrects the responsiveness of the supercharging pressure when switching the air-fuel ratio, and thus the responsiveness of the intake air amount, as compared with the case where this is not executed.

  In this embodiment, the rotation speed (supercharger rotation speed) Nchg of the turbocharger 13 is adopted as the "engine control amount related to the intake air amount". The target value of intake pressure (hereinafter referred to as “corrected target intake pressure”) Pmd during switching is increased to be larger than the target intake pressure (hereinafter referred to as “steady target intake pressure”) Ptrg according to the lean air-fuel ratio after switching. The rotational speed Nchg (Nchga) of the turbocharger 13 at the time is controlled so as to realize the corrected target intake pressure Pmd. As a result, the intake pressure Pinta at the time of switching is made higher than the intake pressure Pintb when the rotational speed of the turbocharger 13 is controlled based on the steady target intake pressure Ptrg after switching.

  With the generation of the air amount correction request, the air amount correction control is started (time t3). By the air amount correction control, the intake pressure Pinta is rapidly increased as compared with the case where this is not executed (intake pressure Pintb), and the response of the intake air amount is corrected. Then, the intake pressure Pinta is monitored, and when it is detected that the intake pressure Pinta has reached the predetermined pressure Pdtm (time t5), the air-fuel ratio is switched to the lean air-fuel ratio, and the fuel injection amount is slightly decreased accordingly (time t6). Therefore, in the present embodiment, after the lean combustion permission condition is satisfied and the control for switching the air-fuel ratio is started (time t3), there is a time delay DLY until the actual switching of the air-fuel ratio is achieved (time 6). To do. As described above, the decrease in the fuel injection amount causes a slight fluctuation in the engine torque (Fig. 4). The predetermined pressure Pdtm is lower than the steady state target intake pressure Ptrg after switching and is set to a pressure obtained by multiplying the steady state target intake pressure Ptrg by a predetermined coefficient smaller than 1.

  The intake pressure Pinta is continuously monitored, and when it is detected that the steady-state target intake pressure Ptrg after switching is exceeded (time t7), the target intake pressure is changed from the corrected target intake pressure Pmd to the steady target intake pressure Ptrg, The rotation speed Nchg of the turbocharger 13 is controlled so that the steady target intake pressure Ptrg is achieved. Then, when it is detected that the intake pressure Pinta has reached the steady-state target intake pressure Ptrg after the switching (time t8), the air amount correction request is released, the air amount correction control is terminated, and the normal control is performed.

  FIG. 5 shows a specific method for correcting the response of the boost pressure.

  In this embodiment, the rotational speed of the turbine section 132 of the turbocharger 13 is increased in order to correct the response of the boost pressure. As a result, the rotation speed of the compressor unit 131 connected to the turbine unit 132 is increased, and the rotation speed Nchg (Nchga) of the turbocharger 13 is controlled based on the steady target intake pressure Ptrg after switching. Also raises.

  In the present embodiment, in the rich spike operation, the waste gate valve 13b is opened to reduce the supercharging pressure more than in the λ2 region, and the ignition timing is set to the ignition timing that maximizes the engine torque. Then, with the generation of the air amount correction request (time t3), the opening degree of the waste gate valve 13b is decreased to increase the flow rate of the exhaust gas flowing on the wheels of the turbine section 132, and the ignition timing is retarded. Increase exhaust temperature. As a result, the rotation speed of the turbine unit 132 is increased. Then, along with the change to the lean air-fuel ratio (time t6), the ignition timing is changed to an ignition timing suitable for combustion at the lean air-fuel ratio, and the change to the steady target intake pressure Ptrg after the change (time t7). By increasing the opening of the wastegate valve 13b by a predetermined opening, the rotation speed of the turbine section 132 is reduced.

  6 and 7 are flowcharts showing the flow of the air amount control according to this embodiment.

  In the present embodiment, the electronic control unit 101 has a timer function and executes air amount control at a predetermined cycle.

  FIG. 6 shows the overall flow of air amount control.

  In S101, the operating region of the engine 1 is determined. The map data of the tendency shown in FIG. 2 is used for the determination of the operating region. The electronic control unit 101 determines which region on the map the operating state (torque and rotational speed) of the engine 1 calculated based on the detection signals of the accelerator sensor 201 and the rotational speed sensor 202 is. If it is in the λ1 region, the process proceeds to S104, and if it is in the λ2 region, the process proceeds to S102.

  In S102, it is determined whether the lean burn permission condition is satisfied. The lean burn permission condition basically holds when the operating state of the engine 1 is in the λ2 region, but even when it is in the λ2 region, the air-fuel ratio is temporarily higher than the theoretical air-fuel ratio due to the rich spike operation. Is set to be low (time t1 to t3). If the lean burn permission condition is satisfied, the process proceeds to S103, and if not, the process proceeds to S104.

  In S103, a target air amount suitable for combustion with a lean air-fuel ratio is set.

  In S104, a target air amount suitable for combustion at the stoichiometric air-fuel ratio is set.

  Here, in the present embodiment, a rich spike operation for reducing the air-fuel ratio below the stoichiometric air-fuel ratio is executed when the NOx trap catalyst 222 is regenerated. In this case, the target air amount set by the process of S104 is a target air amount suitable for combustion at an air-fuel ratio lower than the stoichiometric air-fuel ratio.

  In S105, it is determined whether there is an air amount correction request. If there is an air amount correction request, the process proceeds to S106, and if there is no air amount correction request, the process proceeds to S107.

  In S106, air amount correction control is executed.

  In S107, normal control is executed. In the normal control, the electronic control unit 101 controls the intake air amount to the target air amount set in S103 or S104.

  FIG. 7 shows the specific contents of the air amount correction control.

  In S201, the intake pressure Pint is read. The intake pressure Pint is calculated based on the detection signal of the intake pressure sensor 205.

  In S202, it is determined whether the target intake pressure switching flag Fswc is 0. The target intake pressure switching flag Fswc is set to 0 by initialization at the time of engine start, and as described above, when the intake pressure Pinta at the time of switching the air-fuel ratio reaches the steady target intake pressure Ptrg after switching ( It is switched to 1 at time t7). If the target intake pressure switching flag Fscw is 0, the process proceeds to S203, and if it is 1, the process proceeds to S208.

  In S203, the target intake pressure is set to the corrected target intake pressure Pmd. As a result, the rotational speed Nchg of the turbocharger 13 is controlled so as to achieve the corrected target intake pressure Pmd (Nchga), the responsiveness of the supercharging pressure at the time of switching is enhanced, and the intake air amount is rapidly increased.

  In S204, it is determined whether the intake pressure Pinta has reached the air-fuel ratio switching determination pressure Pdtm. If the air-fuel ratio switching determination value Pdtm has been reached, the process proceeds to S205, and if not, the control of this routine ends.

  In S205, switching of the air-fuel ratio is executed.

  In S206, it is determined whether or not the intake pressure Pinta has reached the steady-state target intake pressure Ptrg after switching. If the steady-state target intake pressure Ptrg has been reached, the process proceeds to S207, and if not, the control of this routine ends.

  In S207, the target intake pressure switching flag Fswc is switched to 1.

  In S208, the target intake pressure is set to the steady target intake pressure Ptrg after switching. As a result, the rotational speed Nchg (Nchga) of the turbocharger 13 is controlled so as to achieve the steady target intake pressure Ptrg, and the intake pressure Pinta converges to the steady target intake pressure Ptrg.

  In S209, it is determined whether or not the intake pressure Pinta has reached the post-switching steady-state target intake pressure Ptrg (in the present embodiment, after it has exceeded the steady-state target intake pressure Ptrg, has been reduced to Ptrg again). If the steady-state target intake pressure Ptrg has been reached, the process proceeds to S210, and if not, the control of this routine ends.

  In S210, the air amount correction request is canceled. As a result, the air amount correction control is ended and the normal control is performed.

  In S211, the target intake pressure switching flag Fswc is set to 0.

  The above is the contents of the air amount control (including the air amount correction control at the time of switching), and the effects obtained by this embodiment will be summarized below.

(Explanation of effects)
First, the air-fuel ratio when operating the engine 1 is switched between a plurality of air-fuel ratios, and the air-fuel ratio is set to a higher air-fuel ratio than the theoretical air-fuel ratio in the low rotation speed and low load side region (λ2 region). However, in the other region (λ1 region), the stoichiometric air-fuel ratio is set. As a result, the drivability of the vehicle can be secured by combustion at the stoichiometric air-fuel ratio in the λ1 region, and the fuel consumption amount can be reduced by combustion at the lean air-fuel ratio in the λ2 region.

  Secondly, at the time of switching the air-fuel ratio, the response of the intake air amount at the time of switching is improved through the air amount correction control that positively increases or decreases the engine control amount related to the intake air amount (in this embodiment, intake pressure). I decided to correct it. As a result, it is possible to quickly change the actual intake air amount toward the target air amount corresponding to the air-fuel ratio after switching (steady target air-fuel ratio), and thus to shorten the time (DLY) required for switching. Become. Therefore, it is possible to quickly achieve the switching of the air-fuel ratio while suppressing the torque shock.

  Thirdly, the target value of the intake pressure at the time of switching is set to the corrected target intake pressure Pmd higher than the steady target intake pressure Ptrg after the switching, and the engine control amount is set based on this corrected target intake pressure Pmd. I decided. As a result, the intake pressure Pinta (in other words, the supercharging pressure) can be positively increased or decreased, and the intake air amount can be quickly changed.

  Fourthly, the rotational speed Nchg of the turbocharger 13 is adopted as the engine control amount, and the response of the supercharging pressure is corrected by the air amount correction control to correct the intake air amount in the engine 1 performing supercharging. It can be easily realized. Then, at the time of switching to a relatively high air-fuel ratio, for example, when switching to a lean air-fuel ratio at the time of ending the rich spike operation, the rotation speed of the turbine section 132 of the turbocharger 13 is increased to increase the boost pressure. The responsiveness can be easily corrected.

  Fifthly, after the change of the fuel injection amount toward the target injection amount after the switching (in other words, the actual switching of the air-fuel ratio) is started, the air amount correction control is started, and then the intake pressure Pinta is changed to the steady target after the switching. The process is executed when a predetermined pressure (air-fuel ratio switching determination pressure) Pdtm lower than the intake pressure Ptrg is reached. As a result, the fuel injection amount can be changed in a state where the intake air amount approaches the target air amount after switching, so that the torque shock can be further suppressed and the NOx emission itself can be suppressed. it can.

(Explanation of Modification)
In the above description, in order to correct the responsiveness of the supercharging pressure at the time of switching, the exhaust temperature is raised by retarding the ignition timing, and the rotational speed of the turbine portion 132 of the turbocharger 13 is increased by increasing the exhaust energy. I decided. In addition to the above, in order to raise the exhaust temperature, an overlap period is set between the intake valve and the exhaust valve by changing the valve timing, and the scavenging effect increases the exhaust efficiency of combustion gas and Secondary air may be supplied to cause recombustion of unburned fuel components in the exhaust passage.

  FIG. 8 shows the operation when the valve timing is changed. As shown in FIG. 8B, the intake valve opening timing IVO is moved to the advance side and the exhaust valve closing timing EVC is moved to the retard side with respect to the normal time (FIG. 8A). , Valve overlap period OVL is formed.

  Further, in order to correct the responsiveness of the supercharging pressure, in addition to increasing the rotational speed of the turbocharger 13 itself, a second supercharger 51 is provided in addition to the turbocharger 13, and the second supercharger 51 is provided when switching the air-fuel ratio. The supercharger 51 may be operated.

  FIG. 9 shows the overall configuration of the engine 1 ′ when the second supercharger 51 is used. The compressor section 511 of the second supercharger 51 is installed in the intake passage 11, and the intake air is configured to be supercharged in multiple stages by the turbocharger 13 and the second supercharger 51. Here, the second supercharger 51 has a drive source other than the exhaust turbine, and is, for example, a mechanical drive type or an electric type supercharger. In the present embodiment, the second supercharger 51 is an electric supercharger, includes an electric motor 512 as a drive source, and the compressor unit 511 is driven by the power of the electric motor 512. In the case of the mechanical drive supercharger, the power of the crankshaft of the engine 1'is transmitted to the compressor section 511.

  FIG. 10 specifically shows the content of the air amount control in the case of the second supercharger 51.

  The difference from the above-described air amount control (FIGS. 4 and 5) will be mainly described. When the NOx trap catalyst 222 is judged to be finished with regeneration (time t3), an air amount correction request is generated and released. Until (time t3 to t8), the air amount correction control is executed. The air amount correction control corrects the responsiveness of the boost pressure when switching the air-fuel ratio, and thus the responsiveness of the intake air amount.

  In the air amount correction control, a corrected target intake pressure Pmd higher than the switched steady target intake pressure Ptrg is set, and the second supercharger 51 is operated in addition to the turbocharger 13. Then, by controlling the respective rotation speeds Nchg1 and Nchg2 of the turbocharger 13 and the second supercharger 51 so as to realize the corrected target intake pressure Pmd, the intake pressure Pinta at the time of switching is changed to only the turbocharger 13. The intake pressure Pintb is made higher than the intake pressure Ptb.

  The intake pressure Pinta is monitored, and when it is detected that it exceeds the steady state target intake pressure Ptrg after switching (time t7), the second supercharger 51 is stopped, and the rotation speed Nchg1 of the turbocharger 13 is kept constant. The control is performed so as to realize the target intake pressure Ptrg. Then, when it is detected that the intake pressure Pinta has reached the steady target intake pressure Ptrg (time t8), the air amount correction request is canceled and the normal control is performed.

  In this way, the second supercharger 51 is provided as the supercharger in addition to the turbocharger 13, and the second supercharger 51 is operated when switching to a relatively high air-fuel ratio, so that only the turbocharger 13 is used. The intake air amount can be corrected by increasing or decreasing the intake pressure Pinta as compared with the case.

  Here, by adopting a supercharger having a drive source other than the exhaust turbine as the second supercharger 51, the shortage of the supercharging pressure formed only by the turbocharger 13 is compensated with high accuracy, and the intake pressure Pinta is reduced. It can be increased or decreased precisely.

  The second supercharger 51 may be an air-driven supercharger that uses an exhaust turbine as a drive source. For example, by adopting an impeller having a smaller diameter or a lower inertia than the turbocharger 13 in the compressor portion of the second supercharger 51, high responsiveness similar to that of an electric or mechanical drive type supercharger can be obtained. As a result, the intake pressure Pinta can be increased or decreased.

(Description of other embodiments)
In the above description, the case where the switching of the air-fuel ratio occurs with the return from the rich spike operation without depending on the shift of the operating region has been described. The present invention is not limited to this, and can also be applied to the case where the switching of the air-fuel ratio is due to the shift of the operating region. Therefore, hereinafter, a case will be described in which the operating region shifts between the λ1 region and the λ2 region by slightly releasing or slightly depressing the accelerator pedal during traveling at a constant speed. In the following description, the theoretical air-fuel ratio set in the λ1 region corresponds to the “first air-fuel ratio”.

  11 and 12 are timing charts showing the details of the air amount control according to the second embodiment of the present invention.

  In the present embodiment, by returning the accelerator pedal by a small amount during constant traveling at a relatively low speed, the operating region of the engine 1 is changed from the λ1 region (for example, the point B1 in FIG. 2) to the λ2 region (for example, in FIG. 2). It is assumed that the point B2) is changed to.

  FIG. 11 shows the behavior of the present embodiment that appears in the vehicle due to the accelerator operation.

  In the present embodiment, unlike the first embodiment, the engine speed does not substantially change, but the accelerator pedal is returned by a small amount (time t3), and as a result, the engine torque decreases. , The vehicle is slightly decelerating (time t6).

  FIG. 12 shows the specific content of the air amount control when switching the air-fuel ratio from the stoichiometric air-fuel ratio in the λ1 region to the lean air-fuel ratio in the λ2 region.

  When the operating region of the engine 1 shifts from the λ1 region to the λ2 region by returning the accelerator pedal (time t3), an air amount correction request is generated and control for switching the air-fuel ratio to the lean air-fuel ratio is started. In this embodiment, the engine speed Nchg of the turbocharger 13 is adopted as the "engine control amount related to the intake air amount" as in the first embodiment, and the corrected target intake pressure Ptrg higher than the steady target intake pressure Ptrg after switching is adopted. By setting Pamd, the response of the boost pressure is corrected. Specifically, the rotational speed Nchg (Nchga) of the turbocharger 13 at the time of switching is controlled so as to achieve the corrected target intake pressure Pmd, so that the intake pressure Pinta at the time of switching is set to the rotational speed of the turbocharger 13. The intake pressure Pintb is made higher than the intake pressure Pintb when the control is performed based on the steady target intake pressure Ptrg after switching. Then, when it is detected that the intake pressure Pinta reaches the air-fuel ratio switching determination pressure Pdtm (time t5), the air-fuel ratio is switched to reduce the fuel injection amount to the target injection amount after switching. Further, when it is detected that the intake pressure Pinta exceeds the target intake pressure Ptrg (time t7), the target intake pressure is changed from the corrected target intake pressure Pmd to the switched steady target intake pressure Ptrg, and the steady target intake pressure Ptrg is changed. The rotation speed Nchg (Nchga) of the turbocharger 13 is controlled so as to realize Ptrg. After that, when it is detected that the intake pressure Pinta has reached the steady target intake pressure Ptrg (time t8), the air amount correction request is canceled, the air amount correction control is terminated, and the normal control is performed.

  The means for increasing the rotation speed Nchg of the turbocharger 13 may be the same as in the first embodiment, and the opening of the waste gate valve 13b is decreased to reduce the flow rate of exhaust gas flowing on the wheels of the turbine section 132. The temperature of the exhaust gas may be increased by increasing the ignition timing or retarding the ignition timing. Further, in addition to increasing the rotation speed of the turbocharger 13 itself, a second supercharger may be provided and operated when switching the air-fuel ratio.

  13 to 15 are timing charts showing the details of the air amount control according to the third embodiment of the present invention.

  In the present embodiment, it is assumed that the operating region of the engine 1 shifts from the λ2 region (point B2) to the λ1 region (point B1) by depressing the accelerator pedal by a very small amount during constant traveling at a relatively low speed.

  FIG. 13 shows the behavior of the present embodiment that appears in the vehicle by the accelerator operation.

  In the present embodiment, the accelerator pedal is slightly depressed (time t3). As a result, although the engine speed does not substantially change, the engine torque is increased and the vehicle is slightly accelerated (time t6).

  FIG. 14 shows the specific content of the air amount control when the air-fuel ratio is switched from the lean air-fuel ratio in the λ2 region to the stoichiometric air-fuel ratio in the λ1 region.

  When the operating region of the engine 1 shifts from the λ2 region to the λ1 region by depressing the accelerator pedal (time t3), control for switching the air-fuel ratio to the stoichiometric air-fuel ratio is started. In this embodiment, when switching to a relatively low air-fuel ratio, an air amount correction request is generated as in the first embodiment, and is related to the intake air amount until the request is released (time t3 to t8). The air amount correction control is executed to reduce the engine control amount below the control amount based on the steady target intake pressure Ptrg according to the air-fuel ratio after switching (steady target air-fuel ratio).

  In the present embodiment, the rotational speed Nchg of the turbocharger 13 is adopted as the "engine control amount related to the intake air amount", but the corrected target intake pressure Pmd which is the target intake pressure at the time of switching is set to the steady target intake after switching. Decrease below atmospheric pressure Ptrg. Then, by controlling the rotation speed Nchg (Nchga) of the turbocharger 13 at the time of switching so as to realize the corrected target intake pressure Pmd, the intake pressure Pinta at the time of switching is changed to the value after the rotation speed of the turbocharger 13 is switched. The intake pressure Pintb is made lower than the intake pressure Pintb when controlled based on the steady target intake pressure Ptrg.

  Then, the intake pressure Pinta is monitored, and when it is detected that the intake pressure Pinta has reached the air-fuel ratio switching determination pressure Pdtm (time t5), the air-fuel ratio is switched to the target injection amount after the switching. Up to. In the present embodiment, the air-fuel ratio switching determination pressure Pdtm is set to a pressure that is higher than the switched steady target intake pressure Ptrg and that is obtained by multiplying the steady target intake pressure Ptrg by a predetermined coefficient greater than 1.

  The intake pressure Pinta is continuously monitored, and when it is detected that the steady-state target intake pressure Ptrg after switching is reached (time t7), the target intake pressure is changed from the corrected target intake pressure Pmd to the steady target intake pressure Ptrg, The rotational speed Nchg (Nchga) of the turbocharger 13 is controlled so as to achieve the steady target intake pressure Ptrg. In the present embodiment, the intake pressure Pinta smoothly converges to the steady target intake pressure Ptrg after switching, and the air amount correction request is canceled at the same time as the change to the steady target intake pressure Ptrg (time t8), and the normal control is performed. Transition.

  FIG. 15 shows a specific method for correcting the response of the boost pressure.

  In this embodiment, the rotational speed Nchg of the turbocharger 13 is reduced in order to correct the response of the boost pressure.

  Specifically, when the air amount correction request is generated (time t3), the opening degree of the waste gate valve 13b is increased and the flow rate of the exhaust gas flowing on the wheels of the turbine unit 132 is decreased, so that the turbine unit 132 is cooled. The rotation speed is reduced and the rotation speed Nchg (Nchga) of the turbocharger 13 is reduced. Then, along with switching to the stoichiometric air-fuel ratio (time t6), the ignition timing is changed to ignition timing suitable for combustion at the stoichiometric air-fuel ratio, and also to switching to the steady target intake pressure Ptrg after switching (time t7). The opening degree of the waste gate valve 13b is decreased by a predetermined opening degree. The ignition timing suitable for combustion at the stoichiometric air-fuel ratio is generally the ignition timing that maximizes the engine torque, and this is also adopted in this embodiment.

  In this way, when the air-fuel ratio is switched, by executing the air amount correction control that actively reduces the engine control amount related to the intake air amount, the target air amount corresponding to the air-fuel ratio (steady target air-fuel ratio) after switching is executed. It is possible to rapidly change the actual intake air amount toward the amount, shorten the time (DLY) required for switching, and quickly achieve switching of the air-fuel ratio. According to the present embodiment, at the time of switching to a relatively low air-fuel ratio, the target value of the intake pressure at the time of switching is set to the corrected target intake pressure Pmd lower than the steady target intake pressure Ptrg after switching, and the turbocharger is set. The engine speed Nchg (Nchga) of 13 is set based on this corrected target intake pressure Pmd. As a result, the rotational speed Nchg (Nchga) of the turbocharger 13 can be positively reduced, the intake pressure Pinta can be reduced, and the intake air amount can be quickly changed.

  The response of the supercharging pressure can be corrected by reducing the rotational speed of the turbocharger 13 and also by decreasing the flow rate of air passing through the intake throttle valve 15. Specifically, by opening the blow-off valve 13a in response to the air amount correction request, and recirculating a part of the air supercharged by the turbocharger 13 to the upstream side of the compressor unit 131 via the blow-off valve 13a, The flow rate of the intake air that passes through the intake throttle valve 15 and is supplied to the combustion chamber can be reduced. The response of the boost pressure can be corrected by closing the intake throttle valve 15. FIG. 15 shows a change in the opening degree of the intake throttle valve 15 by closing the intake throttle valve 15 by a chain double-dashed line. In this way, the intake throttle valve 15 is closed by the start of the air amount correction control, the intake pressure Pinta is reduced, and when the steady target intake pressure Ptrg after switching is reached (time t7), it is opened by a predetermined opening degree.

  In the above description, the turbocharger 13 is operated to perform supercharging in at least the λ2 region of the operating region of the engine 1. However, the present invention is not limited to such a supercharged engine, but can be applied to a naturally aspirated engine that does not perform supercharging for the purpose of operating at a steady target air-fuel ratio. In this case, an intake air compressor is provided in the intake passage 11, and the intake air compressor is operated intermittently. Specifically, when the intake air compressor is switched to a relatively high air-fuel ratio, the intake air compressor is temporarily operated. The responsiveness of the quantity can be corrected.

  Some of the concepts derived from the above description are listed below.

  In the air amount correction control, the target value of the intake pressure at the time of switching is increased or decreased from the intake pressure in the steady state according to the air-fuel ratio after switching or the target intake pressure after switching, and the engine control amount of the intake pressure This is an engine control method that is set based on a target value.

  At the time of switching from the first air-fuel ratio to the second air-fuel ratio, the rotational speed of the exhaust turbine of the supercharger is made higher than the rotational speed based on the intake pressure in a steady state corresponding to the air-fuel ratio after switching. It is a control method.

  A first supercharger and a second supercharger are provided, and during operation at the second air-fuel ratio, only the first supercharger of the first and second superchargers is operated, and the second air-fuel ratio is changed to the second supercharger. This is a method of controlling the engine in which both the first and second superchargers are operated when switching to the air-fuel ratio.

  A method of controlling an engine, wherein the second supercharger is a supercharger having a drive source other than an exhaust turbine.

  A method of controlling an engine, wherein the second supercharger is a supercharger having higher responsiveness to the flow rate of exhaust gas than the first supercharger.

  At the time of switching from the second air-fuel ratio to the first air-fuel ratio, the rotational speed of the exhaust turbine of the supercharger is made lower than the rotational speed based on the intake pressure in the steady state corresponding to the air-fuel ratio after switching. It is a control method.

An intake throttle valve is provided in the intake passage on the downstream side of the compressor section of the supercharger,
A method for controlling an engine is to reduce the flow rate of air passing through the intake throttle valve when switching from the second air-fuel ratio to the first air-fuel ratio.

  It is a method of controlling an engine in which a change in the fuel injection amount toward the target injection amount after switching is executed in response to a change in the actual intake air amount after starting the air amount correction control.

  In addition, although the case where the rotation speed Nchg of the turbocharger 13 is adopted as the engine control amount related to the intake air amount has been described as an example, the “engine control amount” is not limited to this, and the supercharging pressure by the turbocharger 13, Any parameter may be used as long as it has a correlation, such as engine speed, exhaust flow rate, and exhaust temperature.

  Although the embodiments of the present invention have been described above, the present invention is not limited thereto, and various changes and modifications can be made within the scope of the matters described in the claims. There is no end.

1, 1'... Engine 11... Intake passage 111... Manifold part (intake manifold)
12... Air cleaner 13... Turbocharger (1st supercharger)
131... Compressor section (intake compressor)
132... Turbine part (exhaust turbine)
13a... Blow-off valve 13b... Waste gate valve 14... Intercooler 15... Intake throttle valve 21... Exhaust passage 211... Manifold part (exhaust manifold)
22... Catalytic converter 221... Three-way catalyst 222... NOx trap catalyst 23... EGR pipe 24... EGR valve 31... Intake side variable valve operating device 32... Exhaust side variable valve operating device 51... Second supercharger 511... Compressor section 522 Electric motor E Engine body #1 to #4 Cylinder 101 Electronic control unit (engine controller)
201... Accelerator sensor 202... Rotation speed sensor 203... Cooling water temperature sensor 204... Air flow meter 205... Intake pressure sensor 206... Air-fuel ratio sensor

Claims (6)

A method for controlling an engine, which is operated by switching between a first air-fuel ratio and a second air-fuel ratio higher than the first air-fuel ratio,
Select the air-fuel ratio for operating the engine according to the operating state of the engine,
At the time of switching from the first air-fuel ratio to the second air-fuel ratio, the engine control amount related to the intake air amount is made larger than the engine control amount based on the intake air amount in the steady state according to the switched air-fuel ratio. An engine control method for performing air amount correction control. A method for controlling an engine, which operates by switching between a first air-fuel ratio and a second air-fuel ratio higher than the first air-fuel ratio,
Select the air-fuel ratio to drive the engine according to the operating state of the engine,
At the start of switching from the second air-fuel ratio to the first air-fuel ratio, the engine control amount related to the intake air amount is set to the engine control amount related to the intake air amount at the start of the switching and the air-fuel ratio after switching. A control method for an engine, which executes air amount correction control for reducing the engine control amount based on the intake air amount in a steady state.   The engine control method according to claim 1, wherein the engine is operated by switching between the first air-fuel ratio and the second air-fuel ratio under the condition that the torque output from the engine is the same. I installed a supercharger,
The engine control method according to any one of claims 1 to 3, wherein the supercharging pressure is relatively increased during operation at the second air-fuel ratio as compared to during operation at the first air-fuel ratio. A state detection device that detects the operating state of the engine,
A combustion control device for controlling the combustion state of the engine,
The combustion control device,
A condition that the engine is operated at a first air-fuel ratio and a condition that the engine is operated at a second air-fuel ratio higher than the first air-fuel ratio are provided with a storage unit that is set according to an operating state of the engine;
Based on the operating state of the engine detected by the state detection device, select the air-fuel ratio for operating the engine by the storage unit,
At the time of switching from the first air-fuel ratio to the second air-fuel ratio, the engine control amount related to the intake air amount is made larger than the engine control amount based on the intake air amount in the steady state according to the switched air-fuel ratio. An engine that executes air amount correction control. A state detection device that detects the operating state of the engine,
A combustion control device for controlling the combustion state of the engine;
The combustion control device,
A condition that the engine is operated at a first air-fuel ratio and a condition that the engine is operated at a second air-fuel ratio higher than the first air-fuel ratio are provided with a storage unit that is set according to an operating state of the engine;
Based on the operating state of the engine detected by the state detection device, select the air-fuel ratio for operating the engine by the storage unit,
At the start of switching from the second air-fuel ratio to the first air-fuel ratio, the engine control amount related to the intake air amount is set to the engine control amount related to the intake air amount at the start of the switching and the air-fuel ratio after switching. An engine that executes air amount correction control for reducing the engine control amount based on the intake air amount in a steady state in accordance with the control amount.

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