Control method for an internal combustion engine and control device for an internal combustion engine

Abstract

To suppress a flame failure of an internal combustion engine due to response delay of supercharging pressure.SOLUTION: An internal combustion engine at the time of compression self-ignition combustion is controlled to pass through: a first process for increasing only an engine speed toward an operation point to achieve target output when increasing the target output in a supercharging region; a second process for increasing intake pressure and an engine speed; and a third process for increasing only intake pressure toward the operation point to achieve the target output. In the second process, the engine speed is increased to the engine speed at which the target output is achieved. In the third process, the intake pressure is increased to the intake pressure with which the target output is achieved. That is, in the internal combustion engine at the time of compression self-ignition combustion, an upper limit of the engine speed is set according to actual intake pressure in a transition period in which the target output is increased in a supercharging region, and the engine speed is controlled not to exceed the upper limit.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] For example, Patent Document 1 discloses a technique for setting a target boost pressure based on combustion chamber temperature, engine rotational speed, and torque in a self-ignition internal combustion engine, and controlling the rotational speed of a supercharging means so as to achieve the target boost pressure. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-285997 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, Patent Document 1 is based on the premise that the supercharging means is a mechanical supercharger or a supercharger driven by an electric motor, and does not take into consideration the response delay of the boost pressure caused by the supercharging means.

[0005] For example, in an internal combustion engine that performs compression self-ignition combustion and includes a supercharger that causes a response delay in boost pressure, when increasing the target output of the internal combustion engine in a supercharged state, the response delay of the boost pressure occurs, whereby the engine rotational speed of the internal combustion engine increases before the boost pressure rises, and there is a risk that compression self-ignition combustion cannot be performed and misfire occurs.

[0006] That is, in an internal combustion engine that performs compression self-ignition combustion and includes a supercharger that causes a response delay in boost pressure, there is room for further improvement when performing control that takes into consideration the response delay of the boost pressure. [Means for Solving the Problem]

[0007] The internal combustion engine of the present invention performs compression autoignition combustion, and in the supercharging region where a turbocharger is used, during the transient period when the target output of the internal combustion engine is increased, in accordance with the actual boost pressure The misfire limit of an internal combustion engine Set the upper limit of the engine speed of the internal combustion engine. The above upper limit increases as the actual boost pressure increases, and during the above transient, the control proceeds through the following steps: a first process in which the engine speed is increased only to the misfire limit of the internal combustion engine toward the operating point where the actual boost pressure is kept constant and the target output is achieved; a second process in which, after the first process, both the engine speed and the actual boost pressure increase in line with the misfire limit of the internal combustion engine, and the engine speed reaches the engine speed of the target output; and a third process in which, after the second process, only the actual boost pressure increases, and the actual boost pressure reaches the boost pressure of the target output. The engine speed of the internal combustion engine is controlled so as not to exceed the above upper limit. [Effects of the Invention]

[0008] According to the present invention, an internal combustion engine can suppress misfires caused by a delay in the response of boost pressure. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram illustrating the general outline of a vehicle drive system to which the present invention is applied. [Figure 2] A schematic diagram illustrating the system configuration of an internal combustion engine. [Figure 3] A schematic diagram illustrating the operating range of an internal combustion engine during compression autoignition combustion. [Figure 4] An explanatory diagram showing an example of changes in engine speed and intake pressure during the transient period when increasing the target output of an internal combustion engine. [Figure 5] A timing chart showing the changes in the operating state of an internal combustion engine during the transient period when increasing the target output of the internal combustion engine. [Figure 6] This diagram illustrates an example of changes in engine speed and intake pressure when the compression ratio of an internal combustion engine is increased during a transient period of increasing the target output of the internal combustion engine. [Figure 7] A timing chart showing the changes in the operating state of an internal combustion engine when the compression ratio of the internal combustion engine is increased during the transient period of increasing the target output of the internal combustion engine. [Figure 8] A flowchart illustrating the control flow of a motor generator. [Figure 9] A flowchart illustrating the control flow of a variable compression ratio actuator. [Figure 10] A schematic diagram illustrating the control flow of an internal combustion engine according to the present invention. MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] FIG. 1 is a schematic explanatory diagram schematically showing the outline of a drive system of a vehicle 1 to which the present invention is applied. The vehicle 1 includes a drive unit 3 that drives drive wheels 2, and a power generation unit 4 that generates electric power for driving the drive wheels 2.

[0012] The drive unit 3 includes a drive motor 5 as a second electric motor that rotationally drives the drive wheels 2, a first gear train 6 and a differential gear 7 that transmit the driving force of the drive motor 5 to the drive wheels 2. Electric power is supplied to the drive motor 5 from a battery 8 charged with the electric power generated by the power generation unit 4 or the like.

[0013] The power generation unit 4 includes a motor generator 9 as a first electric motor that generates electric power to be supplied to the drive motor 5, an internal combustion engine 10 that drives the motor generator 9 to generate power, and a second gear train 11 that transmits the rotation of the internal combustion engine 10 to the motor generator 9.

[0014] The vehicle 1 travels by driving the drive motor 5 with electric power from the motor generator 9 driven by the internal combustion engine 10 and electric power from the battery 8, and is a so-called series hybrid vehicle that does not directly use the internal combustion engine 10 as a driving source. That is, the internal combustion engine 10 is dedicated to power generation.

[0015] For example, when the remaining battery level (charge amount) of the battery 8 decreases, the vehicle 1 drives the internal combustion engine 10 to charge the battery 8, and the motor generator 9 generates electric power.

[0016] The drive motor 5 is a direct driving source of the vehicle 1, and is driven by, for example, alternating-current power from the battery 8. The drive motor 5 also functions as a generator during deceleration of the vehicle 1.

[0017] The motor generator 9 converts rotational energy generated in the internal combustion engine 10 into electrical energy, for example, to charge the battery 8. The motor generator 9 also functions as an electric motor that drives the internal combustion engine 10, enabling motoring of the internal combustion engine 10. The motor generator 9 may function as a starter motor for the internal combustion engine 10. It should be noted that the electric power generated by the motor generator 9 may be directly supplied to the driving motor 5 instead of being charged to the battery 8, depending on the operating conditions.

[0018] Figure 2 is an explanatory diagram schematically showing the system configuration of the internal combustion engine 10. The internal combustion engine 10 includes a cylinder block 12 provided with a plurality of cylinders 12a, a cylinder head 13 fixed to the upper side of the cylinder block 12, and an oil pan 14 fixed to the lower side of the cylinder block 12. Note that this figure only depicts the cylinder 12a of one cylinder, and in actuality, a plurality of cylinders 12a are arranged in a single row along the cylinder row direction.

[0019] A piston 15 is slidably disposed in each cylinder 12a, and a combustion chamber is formed above each piston 15 between the piston 15 and the lower surface of the pent-roof type cylinder head 13. An intake passage (intake port) 17 is connected to each combustion chamber via an intake valve 16, an exhaust passage (exhaust port) 19 is connected via an exhaust valve 18, and an ignition plug 20 for spark-igniting an air-fuel mixture is provided at the center of the top in the combustion chamber.

[0020] The internal combustion engine 10 is also provided with a turbocharger 21 serving as a supercharger that is driven by exhaust energy to supercharge intake air. The turbocharger 21 includes a turbine 22 provided in the exhaust passage 19 and driven by exhaust gas, and a compressor 23 provided in the intake passage 17 and configured to supercharge intake air. The turbine 22 and the compressor 23 are arranged coaxially.

[0021] The boost pressure of the internal combustion engine 10 is controllable according to the operating conditions. Specifically, the boost pressure is controllable by controlling the opening degree of the exhaust bypass valve 25 provided in the bypass passage 24. The bypass passage 24 is capable of bypassing a portion of the exhaust from the upstream side of the turbine 22 to the downstream side of the turbine 22, and is connected to the exhaust passage 19.

[0022] The intake passage 17 is equipped with, in order from the upstream side, an air filter 26 for collecting foreign matter in the intake air, an air flow meter 27 for detecting the intake air volume, a compressor 23, an electronically controlled throttle valve 28 for adjusting the intake air volume, a water-cooled intercooler 29 for cooling the supercharged air, and a fuel injector 30 for injecting fuel into the intake port.

[0023] In the exhaust passage 19, catalysts 31a and 31b, such as a three-way catalytic converter, are arranged in series, and a muffler 32 for sound silencing is provided downstream of these catalysts 31a and 31b.

[0024] Furthermore, a variable compression ratio mechanism (variable compression ratio mechanism) 40 utilizing a double-link piston-crank mechanism is provided as a variable compression ratio means that can change the engine compression ratio (hereinafter also simply referred to as "compression ratio") of the internal combustion engine 10. This variable compression ratio mechanism 40 is publicly known, as described in, for example, Japanese Patent Publication No. 4415464, so to briefly explain it, it has a lower link 41 that is rotatably mounted on the crank pin 34 of the crankshaft 33, an upper link 42 that connects the lower link 41 and the piston 15, and a control link 43 with one end connected to the lower link 41, the other end of which is rotatably mounted on an eccentric shaft portion that is eccentrically provided on the control shaft 44.Therefore, by changing the rotational position of the control shaft 44 with a variable compression ratio actuator 45 such as a motor, the posture of the lower link 41 changes via the control link 43, and thereby the compression ratio can be changed along with a change in the piston stroke characteristics.

[0025] The ECU (Engine Control Unit) 50 has the function of storing and executing various control processes, and based on the engine operating state detected or estimated from various sensors, it outputs control signals to the fuel injector 30, spark plug 20, throttle valve 28, exhaust bypass valve 25, and variable compression ratio actuator 45, etc., to control the fuel injection amount and timing, ignition timing, throttle opening (intake air amount), boost pressure, and compression ratio.

[0026] The EUC50 receives signals from various sensors, including an engine speed sensor 51 that detects the engine speed of the internal combustion engine 10, a coolant temperature sensor 52 that detects the coolant temperature as the engine temperature, an in-cylinder pressure sensor 53 that detects the pressure inside the combustion chamber, an intake pressure sensor 54 that detects the intake pressure downstream of the intercooler 29, a battery charge level sensor 55 that detects the charge level of the battery 8, an accelerator pedal sensor 56 that detects the amount the accelerator pedal is depressed, and an actual compression ratio detection sensor 57 that detects the actual compression ratio value (actual compression ratio) of the internal combustion engine 10, which is variably controlled by the variable compression ratio mechanism 40 of the internal combustion engine 10.

[0027] The actual compression ratio detection sensor 57 consists of, for example, a rotary potentiometer or rotary encoder that detects the rotation angle of the control shaft 44 or the rotation angle of the output shaft of the variable compression ratio actuator 45. Alternatively, the actual compression ratio may be detected without using a sensor by determining the amount of rotation of the electric motor from the command signal to the electric motor constituting the variable compression ratio actuator 45, and then determining the rotation angle of the control shaft 44 from this amount of rotation.

[0028] The ECU50 controls the switching between spark ignition combustion (SI combustion) and compression-induced autoignition combustion (HCCI combustion).

[0029] Furthermore, when the internal combustion engine 10 is undergoing compression autoignition combustion, the ECU 50, during the transient period in which the turbocharger 21 provides supercharging to increase the target output of the internal combustion engine 10, takes into account the response delay of the intake pressure and sets an upper limit for the engine speed of the internal combustion engine 10 according to the actual intake pressure (actual supercharging pressure), which is the intake pressure (supercharging pressure) at that time, and controls the engine speed of the internal combustion engine 10 so as not to exceed this upper limit.

[0030] Figure 3 is a schematic diagram illustrating the operating region R of the internal combustion engine 10 during compression autoignition combustion. The dashed characteristic line P in Figure 3 shows the relationship between the engine speed (target speed) and intake pressure (target boost pressure) set by the ECU 50 for the target output of the internal combustion engine 10. In other words, the ECU 50 controls the internal combustion engine 10 at the operating point on the characteristic line P for the target output of the internal combustion engine 10. Note that the operating region without supercharging within the operating region R during compression autoignition combustion is only the lower left portion of the operating region R shown as a triangle.

[0031] The operating region R is the operating region in which the internal combustion engine 10 can operate stably without knocking or misfire (failure to ignite) during compression autoignition combustion, and is the region enclosed by line segments r1, r2, and r3 in Figure 3. Line segment r1 represents the knocking limit of the internal combustion engine 10 during compression autoignition combustion. Line segment r2 represents the misfire limit of the internal combustion engine 10 during compression autoignition combustion. Line segment r3 represents the lower limit of the engine speed of the internal combustion engine 10 during compression autoignition combustion. The higher limit of the engine speed of the internal combustion engine 10 during compression autoignition combustion is the engine speed at the intersection of line segments r1 and r2.

[0032] The characteristic curve P is a predetermined line segment set within the operating region R. For example, it is the line segment connecting the midpoint of line segment r3 to the intersection of line segments r1 and r2. In other words, the characteristic curve P is located at the center of the operating region R.

[0033] Furthermore, when the operating range of the internal combustion engine 10 during compression autoignition combustion is in the supercharged range, the ECU 50 sets the intake pressure (target boost pressure) and engine speed on the characteristic curve P as the target intake pressure and target engine speed (target engine speed), respectively, for the target output of the internal combustion engine 10. In other words, when the operating range of the internal combustion engine 10 during compression autoignition combustion is in the supercharged range, the ECU 50 sets the engine speed and intake pressure located on the characteristic curve P as the target operating point corresponding to the target output of the internal combustion engine 10.

[0034] Therefore, when the operating region of the internal combustion engine 10 during compression autoignition combustion is in the supercharging region, the operating point corresponding to the target output of the internal combustion engine 10 is limited by the upper and lower limits of the intake pressure according to the engine speed, as shown by the double-ended arrow Y1, and by the upper and lower limits of the engine speed according to the intake pressure, as shown by the double-ended arrow Y2, as shown by the double-ended arrow Y2.

[0035] Furthermore, when the operating range of the internal combustion engine 10 during compression autoignition combustion is in the supercharging range, the ECU 50 controls the engine speed and intake pressure (supercharging pressure) as shown in Figure 4 during the transient when the target output of the internal combustion engine 10 increases and the operating point within the operating range R changes from A to D.

[0036] Figure 4 is an explanatory diagram showing an example of changes in engine speed and intake pressure during a transient period when increasing the target output of the internal combustion engine 10.

[0037] In Figure 4, operating point A is the operating point before the target output increases. In Figure 4, operating point B is the operating point where the engine speed is increased to the misfire limit within the operating region R, while keeping the intake pressure constant from operating point A. In Figure 4, operating point C is the operating point where, during the transient, the engine speed within the operating region R reaches the target engine speed corresponding to the target output, along with the misfire limit. At operating point C, the intake pressure has not reached the target intake pressure corresponding to the target output. In Figure 4, operating point D is the operating point corresponding to the target output.

[0038] During compression autoignition combustion, the internal combustion engine 10 is controlled so that the operating point changes in the order A→B→C→D during the transient period when increasing the target output to operating point D while operating at operating point A, as shown by the dashed characteristic line Q1 in Figure 4.

[0039] In other words, when the internal combustion engine 10 undergoes compression autoignition combustion, it is controlled to increase the target output in the supercharged region by going through a first process of increasing only the engine speed toward the operating point where the target output is achieved, a second process of increasing both the intake pressure (supercharge pressure) and the engine speed, and a third process of increasing only the intake pressure (supercharge pressure) toward the operating point where the target output is achieved. The second process is performed immediately after the first process and increases the engine speed to the engine speed at which the target output is achieved. The third process is performed immediately after the second process and increases the intake pressure (supercharge pressure) to the intake pressure (supercharge pressure) at which the target output is achieved.

[0040] In other words, during compression autoignition combustion, the internal combustion engine 10 sets an upper limit for engine speed according to the actual intake pressure (actual boost pressure) during the transient period when increasing the target output in the supercharging region, and controls the engine speed so as not to exceed this upper limit.

[0041] The upper limit of engine speed corresponding to the actual intake pressure (actual boost pressure) is the engine speed on the line segment r2 in Figures 3 and 4.

[0042] In the internal combustion engine 10, during the transient period when increasing the target output in the supercharging region, a response delay occurs in the intake pressure.

[0043] Therefore, in the transient period when the internal combustion engine 10 increases the target output in the supercharging region, it increases the engine speed prior to the increase in intake pressure. For this reason, in the transient period when the internal combustion engine 10 increases the target output in the supercharging region, it first changes the operating point from operating point A to operating point B, where the intake pressure is constant and the misfire limit is reached (first process). In other words, in the transient period when the target output is increased to operating point D while operating at operating point A, in the first process when the operating point changes from operating point A to operating point B, only the engine speed increases towards the operating point that achieves the target output.

[0044] Next, the internal combustion engine 10 changes its operating point along the misfire limit as the intake pressure increases, up to operating point C where the engine speed reaches the target engine speed (second process). In other words, during the transient period when the target output is increased to operating point D while operating at operating point A, in the second process when the operating point changes from operating point B to operating point C, both the engine speed and intake pressure increase, and the engine speed reaches the target engine speed that achieves the target output.

[0045] Next, the internal combustion engine 10 changes its operating point to an operating point D where the intake pressure reaches the target intake pressure (target boost pressure) (third process). In other words, during the transient period when the target output is increased from operating point A to operating point D, in the third process where the operating point changes from operating point C to operating point D, only the intake pressure (boost pressure) increases until the intake pressure (boost pressure) reaches the target intake pressure (target boost pressure) that realizes the target output.

[0046] Here, in the characteristic curve Q1, the process from operating point A to operating point C is characterized by a state in which the engine speed of the internal combustion engine 10 is limited by the upper limit of the engine speed of the internal combustion engine 10, which is set according to the intake pressure (supercharge pressure) at that time.

[0047] Figure 5 is a timing chart showing the changes in the operating state of the internal combustion engine 10 during the transient period when increasing the target output of the internal combustion engine 10.

[0048] Time t1 is the moment when the target output of the internal combustion engine 10 increases and the internal combustion engine 10 is at operating point A. Time t2 is the moment when the operating point of the internal combustion engine 10 reaches operating point B. Time t3 is the moment when the operating point of the internal combustion engine 10 reaches operating point C. Time t4 is the moment when the operating point of the internal combustion engine 10 reaches operating point D and the output of the internal combustion engine 10 reaches the target output.

[0049] The period from time t1 to time t2 corresponds to the first process in which only the engine speed of the internal combustion engine 10 increases. The period from time t2 to time t3 corresponds to the second process in which both the engine speed and intake pressure of the internal combustion engine 10 increase. The period from time t3 to time t4 corresponds to the third process in which only the intake pressure (supercharge pressure) of the internal combustion engine 10 increases.

[0050] Thus, during compression autoignition combustion, the internal combustion engine 10, in the supercharging region where the turbocharger 21 provides supercharging, sets an upper limit for the engine speed of the internal combustion engine 10 in accordance with the actual intake pressure (actual boost pressure) during the transient period in which the target output of the internal combustion engine 10 is increased, and controls the engine speed of the internal combustion engine 10 so as not to exceed this upper limit.

[0051] Therefore, the internal combustion engine 10 can suppress misfires caused by a delay in the response of the intake pressure (boost pressure) (a delay in the response of the turbocharger 21).

[0052] Furthermore, during compression autoignition combustion, the internal combustion engine 10 uses a motor generator 9 to control the engine speed of the internal combustion engine 10 so that it does not exceed the upper limit of the engine speed of the internal combustion engine 10, which is set according to the actual intake pressure (actual boost pressure), during the transient period in the supercharging region where the turbocharger 21 is performing supercharging, thereby increasing the target output of the internal combustion engine 10. As a result, the internal combustion engine 10 can control its engine speed while suppressing the impact on the drivability of the vehicle 1 on which it is installed.

[0053] Furthermore, during compression autoignition combustion, the internal combustion engine 10 may perform a high compression ratio correction during the transient period when the target output is increased in the supercharging region where the turbocharger 21 provides supercharging, thereby raising the compression ratio of the internal combustion engine 10 to the high compression ratio side by a predetermined high compression ratio correction amount. An upper limit of the engine speed may be set according to the actual intake pressure (actual supercharging pressure) and the actual compression ratio, and the engine speed may be controlled so as not to exceed this upper limit.

[0054] In other words, when the internal combustion engine 10 is undergoing compression autoignition combustion, the ECU 50 may increase the compression ratio using the variable compression ratio mechanism 40 during the transient period in which the turbocharger 21 provides supercharging to increase the target output of the internal combustion engine 10, and set an upper limit for the engine speed of the internal combustion engine 10 according to the actual intake pressure (actual boost pressure) and the actual compression ratio, and control the engine speed of the internal combustion engine 10 so as not to exceed this upper limit.

[0055] Figure 6 is an explanatory diagram showing an example of changes in engine speed and intake pressure when the compression ratio of the internal combustion engine 10 is increased during the transient period of increasing the target output of the internal combustion engine 10.

[0056] In the operating region R (the triangular region shown by the solid line in Figure 6) during compression autoignition combustion, as the compression ratio of the internal combustion engine 10 is increased, the operating region Rp (the triangular region shown by the dashed line in Figure 6) shifts parallel to the side where the overall intake pressure is lower, as shown by the operating region Rp (the triangular region shown by the dashed line in Figure 6). In other words, when the compression ratio of the internal combustion engine 10 performing compression autoignition combustion is increased during the transient period when the target output of the internal combustion engine 10 is increased, the operating region R of the internal combustion engine 10 shifts to the side where the intake pressure is lower as the compression ratio increases.

[0057] The operating region Rp is the operating region in which the internal combustion engine 10 can operate stably without knocking or misfire (failure to self-ignite) during compression autoignition combustion, with the compression ratio higher than that in the operating region R by a predetermined high-compression ratio correction amount. This region is enclosed by line segments r1', r2', and r3' in Figure 6. Line segment r1' represents the knocking limit of the internal combustion engine 10 during compression autoignition combustion. Line segment r2' represents the misfire limit of the internal combustion engine 10 during compression autoignition combustion. Line segment r3' indicates the lower limit of the engine speed of the internal combustion engine 10 during compression autoignition combustion. The higher limit of the engine speed of the internal combustion engine 10 during compression autoignition combustion is the rotational speed at the intersection of line segments r1' and r2'. Line segments r1', r2', and r3' correspond to line segments r1, r2, and r3 of the operating region R, respectively.

[0058] The amount of parallel shift in the operating region Rp increases as the compression ratio of the internal combustion engine 10 increases (the larger the high compression ratio correction amount).

[0059] In Figure 6, operating point A is the operating point before the target output increases. In Figure 6, operating point B' is the operating point where the engine speed is increased to the misfire limit within the operating region Rp, while keeping the intake pressure constant from operating point A. In Figure 4, operating point C' is the operating point where, during the transient, the engine speed within the operating region Rp reaches the target engine speed corresponding to the target output, along with the misfire limit. At operating point C', the intake pressure has not reached the target intake pressure corresponding to the target output. In Figure 4, operating point D is the operating point corresponding to the target output.

[0060] During compression autoignition combustion, when the internal combustion engine 10 is operating at operating point A and the target output is increased to operating point D, increasing the compression ratio will cause the operating point to change in the order A → B' → C' → D, as shown by the characteristic curve Q2, which is shown as a thick dashed line in Figure 6.

[0061] In other words, when the internal combustion engine 10 undergoes compression autoignition combustion, it is controlled to go through the first, second, and third processes described above, even when increasing the compression ratio to increase the target output in the supercharging region.

[0062] In other words, during compression autoignition combustion, the internal combustion engine 10, in the transient period when increasing the target output and compression ratio in the supercharging region, sets an upper limit for the engine speed according to the actual intake pressure (actual boost pressure) and the actual compression ratio, and controls the engine speed so as not to exceed this upper limit.

[0063] In the transient state when the internal combustion engine 10 increases both the target output and the compression ratio in the supercharging region, it increases the engine speed prior to the rise in intake pressure. In the transient state when the internal combustion engine 10 increases both the target output and the compression ratio in the supercharging region, it changes its operating point from operating point A to operating point B', which is the misfire limit in the operating region Rp, while keeping the intake pressure constant (first process). In other words, in the transient state when the target output is increased to operating point D and the compression ratio is increased while operating at operating point A, in the first process when the operating point changes from operating point A to operating point B', only the engine speed increases towards the operating point that achieves the target output. Furthermore, by increasing the compression ratio, the drivable region of the internal combustion engine 10 changes from operating region R to operating region Rp, which increases (expands) the upper limit of the engine speed corresponding to the actual supercharging pressure and actual compression ratio.

[0064] Next, the internal combustion engine 10 changes its operating point to the target engine speed C', which is the point at which the engine speed reaches the target engine speed, in line with the misfire limit in the operating region Rp as the intake pressure increases (second process). In other words, during the transient period when the target output is increased to the operating point D and the compression ratio is increased while operating at operating point A, in the second process when the operating point changes from operating point B' to operating point C', both the engine speed and intake pressure increase, and the engine speed reaches the target engine speed at which the target output is achieved.

[0065] Next, the internal combustion engine 10 changes its operating point to the operating point D where the intake pressure reaches the target intake pressure (target boost pressure) (third process). In other words, during the transient period when the target output is increased to the operating point D while operating at operating point A, in the third process when the operating point changes from operating point C' to operating point D, only the intake pressure (boost pressure) increases until the intake pressure (boost pressure) reaches the target intake pressure (target boost pressure) that realizes the target output. During the transient period when the internal combustion engine 10 increases the target output to the operating point D while operating at operating point A, once the engine speed reaches the target speed that realizes the target output, the compression ratio, which had been increased by the high compression ratio correction amount, is returned to the original compression ratio.

[0066] Here, in the characteristic curve Q2, the process from operating point A to operating point C' represents a state where the engine speed of the internal combustion engine 10 is limited by an upper limit of the engine speed of the internal combustion engine 10, which is set according to the intake pressure (supercharge pressure) and actual compression ratio at that time.

[0067] Furthermore, the high compression ratio correction amount is set so that the intake pressure (supercharge pressure) does not exceed a predetermined intake pressure upper limit (supercharge pressure upper limit) so that misfires do not occur in the third process. In other words, the high compression ratio correction amount is set so that the intake pressure (supercharge pressure) is always located within at least one of the operating region R or operating region Rp in the third process. More specifically, the high compression ratio correction amount is set so that the intake pressure force on the line segment r2 representing the misfire limit in the operating region R when the engine speed of the internal combustion engine 10 is the target speed at which the target output is achieved is less than or equal to the intake pressure on the line segment r1' representing the knocking limit in the operating region Rp when the engine speed of the internal combustion engine 10 is the target speed at which the target output is achieved. In other words, the high compression ratio correction amount is set such that, when the engine speed of the internal combustion engine 10 is the target speed at which the target output is achieved, an operating region is formed between the line segment r2 representing the misfire limit in the operating region R and the line segment r1' representing the knocking limit in the operating region Rp, in which the internal combustion engine 10 can operate stably without knocking or misfires.

[0068] Therefore, the internal combustion engine 10 can suppress accidental misfires when returning to its original high compression ratio during transient periods.

[0069] Furthermore, the high compression ratio correction amount is set so that the engine speed does not exceed a predetermined upper limit of engine speed, in order to prevent knocking in the first process. In other words, the high compression ratio correction amount is set so that the engine speed in the first process is always located within at least one of the operating region R or operating region Rp. More specifically, the high compression ratio correction amount is set so that the engine speed on the line segment r2 representing the misfire limit in the operating region R at the intake pressure (supercharge pressure) before the intake pressure (supercharge pressure) of the internal combustion engine 10 starts to rise is equal to or greater than the engine speed on the line segment r1' representing the knocking limit in the operating region Rp at the intake pressure (supercharge pressure) before the intake pressure (supercharge pressure) of the internal combustion engine 10 starts to rise. In other words, the high compression ratio correction amount is set such that, at the intake pressure (supercharge pressure) of the internal combustion engine 10 before the intake pressure (supercharge pressure) begins to rise, an operating region is formed between the line segment r2 representing the misfire limit in operating region R and the line segment r1' representing the knocking limit in operating region Rp, in which the internal combustion engine 10 can operate stably without knocking or misfires.

[0070] Therefore, the internal combustion engine 10 can suppress accidental knocking when increasing the compression ratio during transient periods.

[0071] Figure 7 is a timing chart showing the changes in the operating state of the internal combustion engine 10 when the compression ratio of the internal combustion engine 10 is increased during the transient period of increasing the target output of the internal combustion engine 10. The dashed line in Figure 7 shows, for comparison, the changes in the operating state of the internal combustion engine 10 when the compression ratio is not increased during the transient period of increasing the target output of the internal combustion engine 10. In other words, the dashed line in Figure 7 shows the changes in the operating state of the internal combustion engine 10 in Figure 5 described above.

[0072] Time t1 is the moment when the target output of the internal combustion engine 10 increases and the internal combustion engine 10 is at operating point A. The internal combustion engine 10 increases its compression ratio at time t1. Time t2' is the moment when the operating point of the internal combustion engine 10 reaches operating point B'. Time t3' is the moment when the operating point of the internal combustion engine 10 reaches operating point C'. The internal combustion engine 10 returns to its original compression ratio at time t3. Time t4' is the moment when the operating point of the internal combustion engine 10 reaches operating point D and the output of the internal combustion engine 10 reaches its target output.

[0073] The period from time t1 to time t2' corresponds to the first process in which only the engine speed of the internal combustion engine 10 increases. The period from time t2' to time t3' corresponds to the second process in which both the engine speed and intake pressure of the internal combustion engine 10 increase. The period from time t3' to time t4' corresponds to the third process in which only the intake pressure (supercharge pressure) of the internal combustion engine 10 increases.

[0074] Time t2 is the moment when the operating point of the internal combustion engine 10 reaches operating point B, assuming the compression ratio is not increased during the transient. Time t3 is the moment when the operating point of the internal combustion engine 10 reaches operating point C, assuming the compression ratio is not increased during the transient. Time t4 is the moment when the operating point of the internal combustion engine 10 reaches operating point D, assuming the compression ratio is not increased during the transient.

[0075] Thus, in the internal combustion engine 10 during compression autoignition combustion, the response delay of the intake pressure (boost pressure) can be reduced by increasing the compression ratio during the transient period when the target output of the internal combustion engine 10 is increased in the supercharging region where the turbocharger 21 performs supercharging. In other words, as shown by the solid line in Figure 7, increasing the compression ratio makes it possible to raise the intake pressure (boost pressure) to the target intake pressure (boost pressure) earlier.

[0076] Figure 8 is a flowchart showing the control flow of the motor generator 9 in the embodiment described above. It is a schematic explanatory diagram.

[0077] In step S1, the sensor values ​​(output signals) of the intake pressure sensor 54, the battery charge level sensor 55, and the accelerator pedal sensor 56 are read.

[0078] In step S2, the target output is calculated based on the output signals from the battery charge sensor 55 and the accelerator pedal sensor 56, when the operating range of the internal combustion engine 10 during compression autoignition combustion is in the supercharged range. That is, the target output is calculated according to the accelerator pedal opening and the battery charge amount.

[0079] In step S3, a first target rotational speed is calculated, which is the engine rotational speed that achieves the calculated target output. The first target rotational speed is stored in advance in a ROM or similar location within the ECU 50, associated with the target output, and the corresponding value is read out according to the calculated target output.

[0080] In step S4, the upper limit of the engine speed of the internal combustion engine 10 is calculated based on the output signal of the intake pressure sensor 54. In other words, in step S4, the upper limit of the engine speed is calculated according to the intake pressure (boost pressure) at that time.

[0081] In step S5, the first target rotational speed is compared with the upper limit of the engine rotational speed set according to the intake pressure (supercharge pressure). If, in step S5, the first target rotational speed is greater than the upper limit of the engine rotational speed set according to the intake pressure (supercharge pressure), the process proceeds to step S6. If, in step S5, the first target rotational speed is less than or equal to the upper limit of the engine rotational speed set according to the intake pressure (supercharge pressure), the process proceeds to step S7. The first target rotational speed is adjusted to increase as the compression ratio of the internal combustion engine 10 increases.

[0082] In step S6, the upper limit of the engine speed is set as the second target rotational speed, according to the intake pressure (boost pressure).

[0083] In step S7, the first target rotation speed is set as the second target rotation speed.

[0084] In step S8, the motor generator 9 is controlled so that the engine speed of the internal combustion engine 10 reaches the second target speed.

[0085] Figure 9 is a flowchart showing the control flow of the variable compression ratio actuator 45 in the embodiment described above. It is a schematic explanatory diagram.

[0086] In step S11, the sensor values ​​(output signals) of the intake pressure sensor 54, the battery charge level sensor 55, and the accelerator pedal sensor 56 are read.

[0087] In step S12, the target output is calculated based on the output signals from the battery charge sensor 55 and the accelerator pedal sensor 56, when the operating range of the internal combustion engine 10 during compression autoignition combustion is in the supercharged range. That is, the target output is calculated according to the accelerator pedal opening and the battery charge amount.

[0088] In step S13, the target compression ratio, which is the compression ratio that achieves the calculated target output, is calculated. The target compression ratio is stored in advance in the ROM of the ECU 50, for example, in association with the target output, and the corresponding value is read out according to the calculated target output.

[0089] In step S14, the target output is compared with the current output of the internal combustion engine 10. If the target output is greater than the current output of the internal combustion engine 10 in step S14, the process proceeds to step S15. If the target output is less than or equal to the current output of the internal combustion engine 10 in step S14, the process proceeds to step S16. Step S14 determines whether or not it is a transient period in which the target output of the internal combustion engine 10 is being increased.

[0090] In step S15, a high compression ratio correction is applied to the target compression ratio calculated in step S13. The high compression ratio correction is a correction that adds a predetermined high compression ratio correction amount to the target compression ratio.

[0091] In step S16, the variable compression ratio actuator 45 is controlled so that the compression ratio of the internal combustion engine 10 reaches the target compression ratio.

[0092] Figure 10 is a schematic diagram illustrating the control flow of the internal combustion engine 10 in the embodiment described above.

[0093] The ECU50 includes a target output calculation unit S21, a first target rotational speed calculation unit S22, a second target rotational speed calculation unit S23, a first target boost pressure calculation unit S24, a second target boost pressure calculation unit S25, and a target compression ratio calculation unit S26.

[0094] The target output calculation unit S21 calculates the target output of the internal combustion engine 10 based on information from the battery charge sensor 55 and the accelerator pedal sensor 56. The first target rotational speed calculation unit S22 calculates the first target rotational speed that will achieve the calculated target output. The second target rotational speed calculation unit S23 calculates the upper limit of the engine rotational speed at which misfires will occur based on the current intake pressure (supercharge pressure) detected by the intake pressure sensor 54. If the first target rotational speed is greater than this upper limit, the upper limit is calculated as the second target rotational speed. If the first target rotational speed is less than or equal to this upper limit, the first target rotational speed is calculated as the second target rotational speed.

[0095] In other words, the second target rotational speed calculation unit S23 corresponds to an upper limit setting unit that sets an upper limit for the engine speed of the internal combustion engine 10 in accordance with the actual boost pressure during the transient period when the target output of the internal combustion engine 10 is increased in the supercharging region.

[0096] The motor generator 9 is controlled by the ECU 50 so that the engine speed of the internal combustion engine 10 reaches a second target speed. In other words, the ECU 50 is a control unit that controls the engine speed of the internal combustion engine 10 so as not to exceed the upper limit of the engine speed of the internal combustion engine 10 set according to the actual boost pressure.

[0097] The first target boost pressure calculation unit S24 calculates the first target boost pressure to achieve the calculated target output. The second target boost pressure calculation unit S25 calculates the upper limit of the intake pressure (boost pressure) that will cause knocking from the current engine speed (actual speed) detected by the engine speed sensor 51. If the first target boost pressure is greater than this upper limit, the upper limit is calculated as the second target boost pressure. If the first target boost pressure is less than or equal to this upper limit, the first target boost pressure is calculated as the second target boost pressure.

[0098] In other words, the second target boost pressure calculation unit S25 corresponds to a second upper limit setting unit that sets an upper limit for the intake pressure (boost pressure) of the internal combustion engine 10 according to the actual rotational speed during the transient period when the target output of the internal combustion engine 10 is increased in the supercharging region.

[0099] The turbocharger 21 is controlled by the ECU 50 so that the intake pressure (boost pressure) of the internal combustion engine 10 becomes a second target boost pressure. In other words, the ECU 50 corresponds to a second control unit that controls the turbocharger 21 so as not to exceed the upper limit of the intake pressure (boost pressure) of the internal combustion engine 10, which is set according to the actual rotational speed.

[0100] The target compression ratio calculation unit S26 calculates a target compression ratio that achieves the calculated target output.

[0101] The variable compression ratio actuator 45 is controlled by the ECU 50 so that the compression ratio of the internal combustion engine 10 becomes the target compression ratio.

[0102] Although specific embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0103] The above-described embodiment relates to a control method for an internal combustion engine and a control device for an internal combustion engine. [Explanation of Symbols]

[0104] 1…Vehicle 9…Motor Generator 10... Internal combustion engine 21... Turbocharger 30…Fuel injector 40... Variable compression ratio mechanism 45... Variable compression ratio actuator 50…ECU 51…Engine rotation speed sensor 52…Coolant temperature sensor 53…In-cylinder pressure sensor 54... Intake pressure sensor 55…Battery charge level sensor 56... Accelerator pedal sensor 57... Actual compression ratio detection sensor

Claims

1. A control method for an internal combustion engine that performs compression autoignition combustion, During the transient period when the target output of the internal combustion engine is increased in the supercharging range where turbocharging is performed, an upper limit is set for the engine speed of the internal combustion engine that becomes the misfire limit, corresponding to the actual boost pressure. This upper limit increases as the actual boost pressure increases. A control method for an internal combustion engine that controls the engine speed of the internal combustion engine so as not to exceed the above upper limit, by following the following steps during the above transient: a first step in which the engine speed is increased only to the misfire limit of the internal combustion engine toward an operating point where the actual boost pressure is kept constant and the target output is achieved; a second step in which, after the first step, both the engine speed and the actual boost pressure increase in line with the misfire limit of the internal combustion engine, and the engine speed reaches the engine speed of the target output; and a third step in which, after the second step, only the actual boost pressure increases, and the actual boost pressure reaches the boost pressure of the target output.

2. A method for controlling an internal combustion engine according to claim 1, using a motor generator that can be driven by the power of the internal combustion engine, to control the engine speed of the internal combustion engine so as not to exceed the above upper limit.

3. A control method for an internal combustion engine according to claim 2, wherein during the above transient period, a high compression ratio correction is performed using a variable compression ratio mechanism that can change the compression ratio of the internal combustion engine, so that the compression ratio is increased by a predetermined high compression ratio correction amount from the current compression ratio towards the high compression ratio side, and the above upper limit is corrected according to the actual compression ratio.

4. The above-mentioned high compression ratio correction is terminated when the engine speed of the internal combustion engine reaches the engine speed of the target output, according to the control method for an internal combustion engine as described in claim 3.

5. The control method for an internal combustion engine according to claim 4, wherein the high compression ratio correction amount is set so that the actual boost pressure does not exceed a predetermined boost pressure upper limit so that misfires do not occur in the third process.

6. The control method for an internal combustion engine according to claim 5, wherein the above-mentioned high compression ratio correction amount is set so that the engine speed does not exceed the above-mentioned upper limit so that knocking does not occur in the above-mentioned first process.

7. The control method for an internal combustion engine according to claim 5 or 6, wherein the internal combustion engine is dedicated to power generation for driving the motor generator described above.

8. A control device for an internal combustion engine that performs compression autoignition combustion, A turbocharger that supercharges an internal combustion engine, An upper limit setting unit sets an upper limit value for the engine speed of an internal combustion engine that becomes the misfire limit of the internal combustion engine in the transient period when increasing the target output of the internal combustion engine in the supercharging region, according to the actual supercharging pressure. During the above transient period, the system includes a control unit that controls the engine speed of the internal combustion engine to avoid exceeding the above upper limit by following three steps: a first step in which the engine speed is increased only to the misfire limit of the internal combustion engine toward the operating point where the target output is achieved while keeping the actual boost pressure constant; a second step in which, after the first step, both the engine speed and the actual boost pressure increase in line with the misfire limit of the internal combustion engine, and the engine speed reaches the engine speed of the target output; and a third step in which, after the second step, only the actual boost pressure increases, and the actual boost pressure reaches the boost pressure of the target output. The above upper limit is a control device for internal combustion engines that increases as the actual boost pressure increases.

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