Control method for internal combustion engine and control apparatus therefor

Abstract

To correct supercharge pressure considering the durability of a supercharger.SOLUTION: In an internal combustion engine 1, boost pressure is controlled in accordance with an engine revolution speed of the internal combustion engine 1 and atmospheric pressure. A control unit 31 calculates given basic target boost pressure in accordance with an operating state of the internal combustion engine 1. Then, the control unit 31 corrects the basic target boost pressure by using a pressure correction factor being a boost pressure correction amount that is set so as to change in accordance with the atmospheric pressure and the engine revolution speed of the internal combustion engine 1, thus calculating final target boost pressure. The pressure correction factor is calculated from a given pressure correction factor map by using the engine revolution speed and the atmospheric pressure. The final target boost pressure is calculated for example multiplying the given basic target boost pressure and the pressure correction factor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control method for an internal combustion engine and a control device for an internal combustion engine. [Background technology]

[0002] For example, Patent Document 1 discloses a technology for suppressing a decrease in engine output during driving at high altitudes by controlling a basic duty ratio control value based on engine speed and engine intake pressure based on a corrected duty ratio value corrected by an atmospheric pressure correction value set for each of multiple ranges of atmospheric pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Publication No. 2005-98220 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, the engine speed of the internal combustion engine is not taken into consideration when correcting the supercharging pressure. Therefore, in Patent Document 1, the supercharging pressure cannot be reduced or increased according to the engine speed of the internal combustion engine by correcting the supercharging pressure.

[0005] That is, there is room for further improvement in the internal combustion engine in terms of correcting the supercharging pressure. [Means for solving the problem]

[0006] The internal combustion engine of the present invention calculates a basic target boost pressure in accordance with an operating state, corrects the basic target boost pressure using a predetermined boost pressure correction amount to calculate a final target boost pressure, and controls a booster of the internal combustion engine so as to achieve the final target boost pressure. The boost pressure correction amount is set to change in accordance with atmospheric pressure and engine speed of the internal combustion engine. Effect of the Invention

[0007] By correcting the boost pressure according to the atmospheric pressure and engine speed, the internal combustion engine can output torque at any altitude, at the same level as at low altitudes or up to the potential limit of the internal combustion engine, and even at higher altitudes (lower atmospheric pressure), torque reduction can be kept to a minimum. [Brief description of the drawings]

[0008] [Figure 1] 1 is an explanatory diagram that illustrates a schematic overview of a system configuration of an internal combustion engine to which the present invention is applied; [Diagram 2] 3 is a timing chart relating to the control of the supercharging pressure of the internal combustion engine according to the present invention. [Diagram 3] 4 is a characteristic diagram showing torque characteristics of an internal combustion engine during WOT. [Figure 4] 4 is a characteristic diagram showing torque characteristics of an internal combustion engine during WOT. [Diagram 5] 4 is a characteristic diagram showing torque characteristics of an internal combustion engine during WOT. [Figure 6] A characteristic diagram showing the turbine efficiency of a turbocharger. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0010] FIG. 1 is an explanatory diagram that shows a schematic system configuration of an internal combustion engine 1 to which the present invention is applied.

[0011] The internal combustion engine 1 is a so-called reciprocating type internal combustion engine that converts the reciprocating linear motion of a piston 2 into the rotational motion of a crankshaft 3 and extracts the rotational motion as power.

[0012] The internal combustion engine 1 has an intake passage 4 and an exhaust passage 5. The intake passage 4 is connected to a combustion chamber 7 via an intake valve 6. The exhaust passage 5 is connected to the combustion chamber 7 via an exhaust valve 8.

[0013] The internal combustion engine 1 has a fuel injection valve 9 that directly injects fuel into the combustion chamber 7. The fuel injected from the fuel injection valve 9 is ignited by an ignition plug 10 in the combustion chamber 7. Note that the internal combustion engine 1 may also be one that injects fuel into the intake port of each cylinder.

[0014] The intake passage 4 is provided with an air cleaner 11 that collects foreign matter in the intake air, an air flow meter 12 that detects the amount of intake air, and an electric throttle valve 13 whose opening is controlled by a control signal from a control unit 31, which will be described later.

[0015] The air flow meter 12 is disposed upstream of the throttle valve 13. The air flow meter 12 has a built-in temperature sensor and is capable of detecting the intake air temperature at the intake port. The air cleaner 11 is disposed upstream of the air flow meter 12.

[0016] An upstream catalyst 14 and a downstream catalyst 15 are provided in the exhaust passage 5. The upstream catalyst 14 and the downstream catalyst 15 are exhaust purification catalysts made of, for example, a three-way catalyst. In addition, an A / F sensor 16 is disposed in the exhaust passage 5 on the upstream side (inlet side) of the upstream catalyst 14. The A / F sensor 16 is, for example, a so-called wide-range air-fuel ratio sensor having an approximately linear output characteristic according to the air-fuel ratio.

[0017] The internal combustion engine 1 also has an exhaust turbine type supercharger (turbocharger) 17 that includes a compressor 18 provided in the intake passage 4 and an exhaust turbine 19 provided in the exhaust passage 5, which are coaxially arranged. The compressor 18 is disposed upstream of the throttle valve 13 and downstream of the air flow meter 12. The exhaust turbine 19 is disposed upstream of the upstream catalyst 14.

[0018] A recirculation passage 20 is connected to the intake passage 4. In the recirculation passage 20, an electric recirculation valve 21 capable of releasing the supercharging pressure from the downstream side of the compressor 18 to the upstream side of the compressor 18 is disposed.

[0019] Further, an intercooler 22 is provided in the intake passage 4 downstream of the compressor 18 to cool the intake air compressed (pressurized) by the compressor 18, thereby improving the charging efficiency.

[0020] An exhaust bypass passage 23 that bypasses the exhaust turbine 19 and connects the upstream side and downstream side of the exhaust turbine 19 is connected to the exhaust passage 5. An electric wastegate valve 24 that controls the exhaust flow rate in the exhaust bypass passage 23 is arranged in the exhaust bypass passage 23. The wastegate valve 24 is capable of bypassing a portion of the exhaust gas guided to the exhaust turbine 19 to the downstream side of the exhaust turbine 19, and is capable of controlling the boost pressure of the internal combustion engine 1.

[0021] 1 denotes a collector portion of the intake passage 4. If the internal combustion engine 1 is a multi-cylinder internal combustion engine, the intake passage 4 is branched downstream of the collector portion 29 as an intake manifold for each cylinder.

[0022] The control unit 31 is a well-known digital computer equipped with a CPU, ROM, RAM, and an input / output interface. Detection signals from various sensors, such as the air flow meter 12, the A / F sensor 16, the crank angle sensor 32, the accelerator opening sensor 33, the boost pressure sensor 34, and the atmospheric pressure sensor 35, are input to the control unit 31.

[0023] The crank angle sensor 32 detects the crank angle of the crankshaft 3 and is capable of detecting the engine speed of the internal combustion engine 1 .

[0024] The accelerator opening sensor 33 detects the amount of depression of the accelerator pedal (accelerator opening) operated by the driver.

[0025] The supercharging pressure sensor 34 detects the supercharging pressure, which is the intake pressure supercharged by the supercharger 17. The supercharging pressure sensor 34 is attached to the intake passage 4 so as to be able to detect the intake pressure at a position between the intercooler 22 and the throttle valve 13, for example.

[0026] The atmospheric pressure sensor 35 detects the atmospheric pressure. The atmospheric pressure sensor 35 is attached to the intake passage 4 so as to detect the intake pressure on the upstream side of the compressor 18, for example.

[0027] The control unit 31 controls the opening and closing of the throttle valve 13, the recirculation valve 21, and the wastegate valve 24 based on detection signals from various sensors.

[0028] Here, when the supercharging pressure is corrected using only the atmospheric pressure, as the supercharging pressure increases, for example, the rotation speed (turbo rotation speed), temperature, and pressure of the parts related to the supercharger 17 increase. Therefore, when the supercharging pressure is corrected using only the atmospheric pressure, it is necessary to limit the correction amount of the supercharging pressure to a value that takes into consideration the functionality assurance, and there is a risk that the internal combustion engine 1 will not be able to demonstrate its original potential.

[0029] Therefore, in the internal combustion engine 1 of this embodiment, the supercharging pressure is corrected in accordance with the engine speed of the internal combustion engine 1 and the atmospheric pressure.

[0030] More specifically, the control unit 31 calculates a predetermined basic target supercharging pressure according to the operating state of the internal combustion engine 1. Next, the control unit 31 corrects the basic target supercharging pressure using a pressure correction coefficient, which is a supercharging pressure correction amount set to change according to the atmospheric pressure and the engine speed of the internal combustion engine 1, to calculate a final target supercharging pressure. The pressure correction coefficient is calculated from a predetermined pressure correction coefficient map using the engine speed and atmospheric pressure of the internal combustion engine 1. The pressure correction coefficient map is a map to which pressure correction coefficients associated with the atmospheric pressure and the engine speed are assigned. The final target supercharging pressure is calculated, for example, by multiplying the basic target supercharging pressure by the pressure correction coefficient. Then, the control unit 31 controls the supercharger 17 so as to achieve the final target supercharging pressure. In other words, the control unit 31 corresponds to a basic target supercharging pressure calculation unit that calculates the basic target supercharging pressure, a supercharging pressure correction amount calculation unit that calculates the supercharging pressure correction amount, a final target supercharging pressure calculation unit that calculates the final target supercharging pressure, and a control unit that controls the supercharger 17 so as to achieve the final target supercharging pressure.

[0031] The internal combustion engine 1 of the embodiment described above is able to output torque at the same level as at low altitudes or up to the potential limit of the internal combustion engine 1 at any altitude by correcting the boost pressure in accordance with the atmospheric pressure and engine speed, and is able to minimize torque reduction in high altitude environments (where atmospheric pressure is low).

[0032] FIG. 2 is a timing chart relating to the control of the supercharging pressure of the internal combustion engine 1 according to the present invention.

[0033] The atmospheric pressure shown by the solid line in Figure 2 indicates the value when the altitude is moderate, somewhat higher than "0 m." The atmospheric pressure shown by the dashed line in Figure 2 indicates the value when the altitude is "0 m."

[0034] The pressure correction coefficient indicated by the solid line in Fig. 2 indicates a value when the altitude is a moderate height that is somewhat higher than "0 m." When the altitude is a moderate height that is somewhat higher than "0 m," the pressure correction coefficient is set to a value greater than "1" and to decrease as the engine speed increases, for example.

[0035] The pressure correction coefficient is set to a value of "1" or greater when the atmospheric pressure becomes lower than the atmospheric pressure at an altitude of "0 m", that is, when the altitude becomes higher than "0 m".

[0036] The pressure correction coefficient indicated by the dashed line in Figure 2 indicates the case where the altitude is "0m." When the altitude is "0m," there is no need to take into account the decrease in air density, so the pressure correction coefficient is "1" regardless of the engine speed.

[0037] 2, the pressure correction coefficient indicated by the thin solid line shows a comparative example in which the correction of the boost pressure is performed in an ON / OFF manner at a predetermined engine speed (predetermined engine speed threshold) at a moderate altitude that is somewhat higher than "0 m." The pressure correction coefficient of the comparative example shown by the thin solid line becomes "1" when the engine speed becomes higher than the predetermined engine speed.

[0038] The boost pressure indicated by the solid line in Fig. 2 indicates the boost pressure during WOT (wide open throttle) when the present invention is applied at a moderate altitude that is somewhat higher than "0 m." In other words, the boost pressure indicated by the solid line in Fig. 2 is the boost pressure corrected using the pressure correction coefficient indicated by the solid line in Fig. 2.

[0039] The boost pressure indicated by the dashed line in FIG. 2 indicates the boost pressure during WOT (wide open throttle) when the altitude is "0 m."

[0040] The boost pressure indicated by the thin solid line in Fig. 2 indicates the boost pressure during WOT (wide open throttle) of a comparative example in which the boost pressure correction is performed on and off at a predetermined engine speed at a moderate altitude somewhat higher than "0 m." In other words, the boost pressure indicated by the thin solid line in Fig. 2 is the boost pressure corrected using the pressure correction coefficient indicated by the thin solid line in Fig. 2.

[0041] By applying the present invention to control the boost pressure, as shown in FIG. 2, even when the atmospheric pressure is low (the altitude is high), the boost pressure during WOT (wide open throttle) can be made close to the boost pressure during WOT (wide open throttle) when the atmospheric pressure is high and the altitude is "0 m."

[0042] Time t1 in Fig. 2 is the timing when the engine speed starts to increase. Time t2 in Fig. 2 is the timing when the engine speed reaches a predetermined speed threshold. Time t3 in Fig. 2 is the timing when the pressure correction coefficient in the comparative example becomes "1" and the correction of the supercharging pressure in the comparative example ends. Time t4 in Fig. 2 is the timing when the increase in the engine speed ends.

[0043] 3 to 5 are characteristic diagrams showing the torque characteristics of the internal combustion engine 1 at WOT (wide open throttle), where FIG. 3 shows the case where the altitude is low (atmospheric pressure is high), FIG. 4 shows the case where the altitude is medium (atmospheric pressure is medium), and FIG. 5 shows the case where the altitude is high (atmospheric pressure is low).

[0044] In addition, in Figures 3 to 5, the characteristic lines shown by solid lines are characteristic lines of the torque of the internal combustion engine 1 obtained when the supercharging pressure is corrected using the pressure correction coefficient. In Figures 3 to 5, the characteristic lines shown by dashed lines are characteristic lines of the torque of the internal combustion engine 1 when the altitude is "0 m" at which supercharging pressure correction is not necessary. In Figures 3 to 5, the characteristic lines shown by dashed lines are characteristic lines of the torque of the internal combustion engine 1 when supercharging pressure correction using the pressure correction coefficient is not performed.

[0045] 3 to 5, in the internal combustion engine 1 of the present invention, when the internal combustion engine 1 is in a predetermined low rotation speed region, the torque is suppressed as a result of the correction of the supercharging pressure, and surging of the supercharger 17 is avoided. That is, in the present invention, the pressure correction coefficient is set so that when the engine speed of the internal combustion engine 1 is in a predetermined low rotation speed region, the turbo rotation speed of the supercharger 17 (e.g., the rotation speed of the exhaust turbine 19) is suppressed so that surging of the supercharger 17 can be avoided. In other words, the pressure correction coefficient is set so that when the engine speed of the internal combustion engine 1 is in a predetermined low rotation speed region, the supercharging pressure is suppressed in consideration of the durability of the supercharger 17.

[0046] Also, as shown in Figs. 3 to 5, in the internal combustion engine of the present invention, when the internal combustion engine 1 is in a predetermined high rotation speed region, the torque is suppressed as a result of the correction of the supercharging pressure, and the over-rotation of the supercharger 17 is avoided. That is, in the present invention, the pressure correction coefficient is set so that when the engine speed of the internal combustion engine 1 is in a predetermined high rotation speed region, the turbo rotation speed of the supercharger 17 (for example, the rotation speed of the exhaust turbine 19) does not exceed a predetermined upper limit rotation speed (limit rotation speed). That is, the pressure correction coefficient is set so that when the engine speed of the internal combustion engine 1 is in a predetermined high rotation speed region, the turbo rotation speed of the supercharger 17 (for example, the rotation speed of the exhaust turbine 19) is suppressed so as not to exceed the rotation speed limit of the supercharger 17. In other words, the pressure correction coefficient is set so that when the engine speed of the internal combustion engine 1 is in a predetermined high rotation speed region, the supercharging pressure is suppressed in consideration of the durability of the supercharger 17.

[0047] In the case of a medium altitude in Fig. 4, the predetermined high speed region is a speed region lower than the maximum engine speed, and in this region the pressure correction coefficient cannot be made sufficiently large, making it impossible to realize maximum torque comparable to that at low altitudes, but in the vicinity of the maximum engine speed, which is higher than the predetermined high speed region, the restriction by the turbo speed becomes looser, making it possible to realize maximum torque comparable to that at low altitudes. Also, in the case of a high altitude in Fig. 5, the restriction by the turbo speed becomes strictest in the engine speed region slightly lower than the maximum engine speed, and the drop in maximum torque from the maximum torque at low altitudes becomes large.

[0048] Fig. 6 is a characteristic diagram showing the turbine efficiency of the turbocharger 17. The vertical axis in Fig. 6 represents, for example, the ratio of the pressure on the upstream side (inlet side) and the downstream side (outlet side) of the exhaust turbine 19 of the turbocharger 17. The horizontal axis in Fig. 6 represents, for example, the flow rate of exhaust gas passing through the exhaust turbine 19 of the turbocharger 17.

[0049] The characteristic line shown by a solid line in FIG. 6 is the characteristic line of the turbine efficiency when the boost pressure is corrected using the pressure correction coefficient at high altitude. The characteristic line shown by a dashed line in FIG. 6 is the characteristic line of the turbine efficiency when the altitude is "0 m" at which the boost pressure correction is not necessary. The two-dot chain line in FIG. 6 indicates the usable limit line of the exhaust turbine 19 of the turbocharger 17 (the upper limit rotation speed of the exhaust turbine 19). The turbocharger 17 becomes more likely to break down when the turbine efficiency exceeds the two-dot chain line in FIG. 6. The three-dot chain line in FIG. 6 indicates the surging criteria of the turbocharger 17. The turbocharger 17 becomes more likely to break down when the turbine efficiency exceeds the three-dot chain line in FIG. 6.

[0050] In addition, when the turbocharger 17 is not corrected for the supercharging pressure at high altitude, the turbine efficiency has characteristics as shown by the dashed line in Fig. 6. In addition, the upper limit rotation speed of the exhaust turbine 19 is constant regardless of the atmospheric pressure, i.e., regardless of the altitude.

[0051] As shown in FIG. 6, the present invention can maximize turbine efficiency while avoiding surging of the turbocharger 17, without exceeding the upper limit rotation speed of the exhaust turbine 19.

[0052] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0053] For example, the turbocharger 17 may be a variable capacity type in which the exhaust turbine 19 is equipped with a variable nozzle.

[0054] The above-described embodiment relates to a control method for the internal combustion engine 1 and a control device for the internal combustion engine 1. [Explanation of symbols]

[0055] 1. Internal combustion engine 4…Intake passage 5...Exhaust passage 6...Intake valve 8...Exhaust valve 12...Air flow meter 13...Throttle valve 16...A / F sensor 17…Turbocharger 18…Compressor 19…Exhaust turbine 20…Recirculation passage 21...Recirculation valve 22…Intercooler 23...Exhaust bypass passage 24...Wastegate valve 31…Control unit 32...Crank angle sensor 33...Accelerator opening sensor 34…Boost pressure sensor 35...Atmospheric pressure sensor

Claims

1. Calculating a basic target boost pressure according to an operating state of the internal combustion engine; correcting the basic target supercharging pressure using a predetermined supercharging pressure correction amount to calculate a final target supercharging pressure; Controlling a supercharger of the internal combustion engine so as to achieve the final target supercharging pressure; A control method for an internal combustion engine, wherein the supercharging pressure correction amount is set to change in response to atmospheric pressure and engine speed of the internal combustion engine.

2. 2. The method for controlling an internal combustion engine according to claim 1, wherein the supercharging pressure correction amount is set in consideration of durability of the supercharger.

3. 3. The control method for an internal combustion engine according to claim 2, wherein the supercharging pressure correction amount is set so that, when the engine speed is in a predetermined low speed region, a turbo rotation speed of the supercharger is suppressed to avoid surging of the supercharger.

4. 3. The control method for an internal combustion engine according to claim 2, wherein the supercharging pressure correction amount is set so that, when the engine speed is in a predetermined high speed region, the turbo rotation speed of the supercharger is suppressed so as not to exceed a rotation speed limit of the supercharger.

5. 5. The method for controlling an internal combustion engine according to claim 4, wherein the predetermined high rotation speed region is a region where the rotation speed is lower than a maximum rotation speed of the engine.

6. A supercharger, a basic target boost pressure calculation unit that calculates a basic target boost pressure in accordance with an operating state of the internal combustion engine; a supercharging pressure correction amount calculation unit that calculates a supercharging pressure correction amount for correcting the basic target supercharging pressure; a final target supercharging pressure calculation unit that calculates a final target supercharging pressure by correcting the basic target supercharging pressure using the supercharging pressure correction amount; a control unit that controls the turbocharger so as to achieve the final target turbocharging pressure, 2. A control device for an internal combustion engine, wherein the supercharging pressure correction amount is set to change in accordance with atmospheric pressure and engine speed of the internal combustion engine.

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