JP2024056157A - Control method and control device for internal combustion engine - Google Patents

Abstract

An object of the present invention is to suppress misfires in an internal combustion engine caused by delayed response of supercharging pressure.
[Solution] An internal combustion engine during compression autoignition combustion is controlled to go through a first process of increasing only the engine speed toward an operating point that realizes the target output when increasing a target output in a supercharging region, a second process of increasing the intake pressure and the engine speed, and a third process of increasing only the intake pressure toward an operating point that realizes the target output. The second process increases the engine speed to the engine speed at which the target output is realized. The third process increases the intake pressure to the intake pressure at which the target output is realized. In other words, an internal combustion engine during compression autoignition combustion sets an upper limit value for the engine speed according to the actual intake pressure during a transient period in which the target output is increased in the supercharging region, and controls the engine speed so as not to exceed this upper limit value.
[Selected Figure] Figure 4

Description

The present invention relates to a method for controlling an internal combustion engine and a control device for an internal combustion engine.

For example, Patent Document 1 discloses a technology for a self-ignition internal combustion engine in which a target boost pressure is set based on the combustion chamber temperature, engine speed, and torque, and the speed of the boost means is controlled to achieve this target boost pressure.

JP 2004-285997 A

However, Patent Document 1 assumes that the supercharging means is a mechanical supercharger or a supercharger driven by an electric motor, and does not take into account the response delay of the supercharging pressure caused by the supercharging means.

For example, in an internal combustion engine that performs compression autoignition combustion and is equipped with a turbocharger that causes a response delay in the boost pressure, when the target output of the internal combustion engine is increased while the engine is being supercharged, a response delay in the boost pressure occurs, causing the engine speed of the internal combustion engine to increase before the boost pressure increases, which may result in a misfire and failure to perform compression autoignition combustion.

In other words, in internal combustion engines that use compression ignition combustion and are equipped with a turbocharger that causes a response delay in the boost pressure, further improvements can be expected in controlling the engine to take into account the response delay in the boost pressure.

The internal combustion engine of the present invention performs compression autoignition combustion, and during the transient period in which the target output of the internal combustion engine is increased in the supercharging region in which supercharging is performed by a turbocharger, an upper limit value for the engine speed of the internal combustion engine is set according to the actual supercharging pressure, and the engine speed of the internal combustion engine is controlled so as not to exceed the upper limit value.

According to the present invention, the internal combustion engine can suppress misfires caused by delayed response of the boost pressure.

1 is an explanatory diagram that illustrates a schematic overview of a drive system of a vehicle to which the present invention is applied; FIG. 1 is an explanatory diagram illustrating a system configuration of an internal combustion engine. FIG. 2 is an explanatory diagram that illustrates a schematic diagram of an operating region of an internal combustion engine during compression autoignition combustion. FIG. 4 is an explanatory diagram showing an example of changes in engine speed and intake pressure during a transition when the target output of the internal combustion engine is increased. 4 is a timing chart showing a change in the operating state of the internal combustion engine during a transition when a target output of the internal combustion engine is increased; FIG. 4 is an explanatory diagram showing an example of changes in engine speed and intake pressure when the compression ratio of the internal combustion engine is increased during a transition period in which the target output of the internal combustion engine is increased; 5 is a timing chart showing a change in the operating state of an internal combustion engine in which the compression ratio of the internal combustion engine is increased during a transitional period in which the target output of the internal combustion engine is increased. 4 is a flowchart showing a control flow of a motor generator. 4 is a flowchart showing a control flow of the variable compression ratio actuator. FIG. 2 is an explanatory diagram showing a schematic flow of control of the internal combustion engine according to the present invention.

Below, one embodiment of the present invention will be described in detail with reference to the drawings.

Figure 1 is an explanatory diagram that shows a schematic overview of the drive system of a vehicle 1 to which the present invention is applied. The vehicle 1 has a drive unit 3 that drives drive wheels 2, and a power generation unit 4 that generates electricity to drive the drive wheels 2.

The drive unit 3 has a drive motor 5 as a second electric motor that drives and rotates the drive wheels 2, and 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. The drive motor 5 is supplied with power from a battery 8 that is charged with electricity generated by the power generation unit 4, etc.

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

The vehicle 1 runs by driving the drive motor 5 with power from the motor generator 9 driven by the internal combustion engine 10 and power from the battery 8, and is a so-called series hybrid vehicle in which the internal combustion engine 10 is not directly used as a drive source. In other words, the internal combustion engine 10 is used exclusively for generating electricity.

For example, when the remaining battery charge (charge level) of the battery 8 becomes low, the vehicle 1 drives the internal combustion engine 10 to generate electricity using the motor generator 9 in order to charge the battery 8.

The drive motor 5 is the direct drive source for the vehicle 1, and is driven by AC power from the battery 8, for example. The drive motor 5 also functions as a generator when the vehicle 1 decelerates.

The motor generator 9 converts the 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, making it possible to motor the internal combustion engine 10. The motor generator 9 may also function as a starter motor for the internal combustion engine 10. Note that the electric power generated by the motor generator 9 may be supplied directly to the drive motor 5, for example, instead of being charged to the battery 8, depending on the operating state.

Figure 2 is an explanatory diagram that shows a schematic diagram of the system configuration of an internal combustion engine 10. The internal combustion engine 10 has a cylinder block 12 in which multiple cylinders 12a are provided, 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 in this diagram, only one cylinder 12a is drawn, and in reality, multiple cylinders 12a are arranged in a row in the cylinder row direction.

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

The internal combustion engine 10 is also provided with a turbocharger 21 that is driven by exhaust energy to supercharge the intake air. The turbocharger 21 has a turbine 22 that is provided in the exhaust passage 19 and driven by the exhaust, and a compressor 23 that is provided in the intake passage 17 and supercharges the intake air (intake air). The turbine 22 and compressor 23 are arranged coaxially.

The boost pressure of the internal combustion engine 10 can be controlled according to the operating conditions. Specifically, the boost pressure can be controlled by controlling the opening of an exhaust bypass valve 25 provided in the bypass passage 24. The bypass passage 24 allows a portion of the exhaust gas to be bypassed from the upstream side of the turbine 22 to the downstream side of the turbine 22, and is connected to the exhaust passage 19.

In the intake passage 17, from the upstream side, there are provided an air filter 26 that collects foreign matter in the intake air, an air flow meter 27 that detects the intake air volume, a compressor 23, an electronically controlled throttle valve 28 that adjusts the intake air volume, a water-cooled intercooler 29 that cools the supercharged air, and a fuel injection valve 30 that injects fuel into the intake port.

Catalysts 31a and 31b, such as three-way catalysts, are arranged in series in the exhaust passage 19, and a muffler 32 for silencing noise is provided downstream of these catalysts 31a and 31b.

Furthermore, a variable compression ratio mechanism (compression ratio variable mechanism) 40 using a multi-link piston-crank mechanism is provided as a variable compression ratio means capable of changing 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, for example as described in Japanese Patent No. 4415464, and in brief, it has a lower link 41 rotatably attached to the crank pin 34 of the crankshaft 33, an upper link 42 connecting the lower link 41 and the piston 15, and a control link 43 one end of which is connected to the lower link 41, and the other end of this control link 43 is rotatably attached to an eccentric shaft portion provided eccentrically on a control shaft 44. Therefore, by changing the rotational position of the control shaft 44 by a variable compression ratio actuator 45 such as a motor, the posture of the lower link 41 changes via the control link 43, and the compression ratio can be changed with a change in the piston stroke characteristics.

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

As the various sensors mentioned above, the EUC 50 receives signals from 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 amount sensor 55 that detects the charge amount of the battery 8, an accelerator pedal sensor 56 that detects the amount of depression of the accelerator pedal, and an actual compression ratio detection sensor 57 that detects the actual compression ratio value (actual compression ratio) of the internal combustion engine 10 that is variably controlled by the variable compression ratio mechanism 40 of the internal combustion engine 10.

The actual compression ratio detection sensor 57 is composed of, for example, a rotary potentiometer or a 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. The actual compression ratio may be detected without using a sensor by determining the amount of rotation of the electric motor that constitutes the variable compression ratio actuator 45 from a command signal to the electric motor, and then determining the rotation angle of the control shaft 44 from this amount of rotation.

The ECU 50 controls the switching between spark ignition combustion (SI combustion) and self-ignition combustion (HCCI combustion).

In addition, when the internal combustion engine 10 is in a compressed self-ignition combustion state and in a transient state in which the target output of the internal combustion engine 10 is increased in the supercharging region (supercharging operation region) in which supercharging is performed by the turbocharger 21, the ECU 50 takes into account the response delay of the intake pressure and sets an upper limit value for the engine speed of the internal combustion engine 10 according to the actual intake pressure (actual supercharging pressure), which is the intake pressure at that time (supercharging pressure at that time), and controls the engine speed of the internal combustion engine 10 so that it does not exceed this upper limit value.

Figure 3 is an explanatory diagram that shows a schematic diagram of the operating region R of the internal combustion engine 10 during compression autoignition combustion. The characteristic line P shown by a dashed line in Figure 3 indicates the relationship between the engine speed (target speed) and the intake pressure (target boost pressure) set by the ECU 50 with respect to the target output of the internal combustion engine 10. In other words, the ECU 50 controls the internal combustion engine 10 at an operating point on the characteristic line P with respect to the target output of the internal combustion engine 10. Note that the operating region R during compression autoignition combustion without boost is only the lower left part of the operating region R shown by a triangle.

The operating region R is an operating region in which the internal combustion engine 10 can operate stably without knocking or misfire (not self-igniting) during compression autoignition combustion, and is the region surrounded by lines r1, r2, and r3 in FIG. 3. Line r1 represents the knocking limit of the internal combustion engine 10 during compression autoignition combustion. Line r2 represents the misfire limit of the internal combustion engine 10 during compression autoignition combustion. Line r3 represents the low-speed limit of the engine speed of the internal combustion engine 10 during compression autoignition combustion. The high-speed limit of the engine speed of the internal combustion engine 10 during compression autoignition combustion is the speed at the intersection of lines r1 and r2.

The characteristic line P is a predetermined line segment set within the operating region R, for example, a line segment connecting the midpoint of the line segment r3 and the intersection of the line segments r1 and r2. In other words, the characteristic line P is located in the center of the operating region R.

Then, when the operating region of the internal combustion engine 10 during compression autoignition combustion is in the supercharging region, the ECU 50 sets the intake pressure and engine speed on the characteristic line P as the target intake pressure (target supercharging pressure) and the target engine speed (target speed), respectively, for the target output of the internal combustion engine 10. In other words, when the operating region of the internal combustion engine 10 during compression autoignition combustion is in the supercharging region, the ECU 50 sets the engine speed and intake pressure located on the characteristic line P as the target operating point corresponding to the target output of the internal combustion engine 10.

Therefore, when the operating range of the internal combustion engine 10 during compression autoignition combustion is in the supercharging range, the operating point corresponding to the target output of the internal combustion engine 10 is such that the upper and lower limits of the intake pressure are limited by line segments r1 and r2 according to the engine speed, as shown by the double-ended arrow Y1, and the upper and lower limits of the engine speed are limited by line segments r2 and r3 according to the intake pressure, as shown by the double-ended arrow Y2.

In addition, when the operating region of the internal combustion engine 10 during compression autoignition combustion is in the supercharging region, the ECU 50 controls the engine speed and intake pressure (supercharging pressure) as shown in FIG. 4 during a transition in which the target output of the internal combustion engine 10 increases and the operating point within the operating region R changes from A to D.

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

Operating point A in FIG. 4 is the operating point before the target output is increased. Operating point B in FIG. 4 is the operating point where the engine speed is increased to the misfire limit within operating region R from operating point A while keeping the intake pressure constant. Operating point C in FIG. 4 is the operating point where the engine speed becomes the target engine speed corresponding to the target output in line with the misfire limit within operating region R during a transient state. At operating point C, the intake pressure has not reached the target intake pressure corresponding to the target output. Operating point D in FIG. 4 is the operating point corresponding to the target output.

During compression autoignition combustion, the internal combustion engine 10 is controlled so that the operating point changes in the order of A → B → C → D during a transitional period in which the target output is increased to operating point D while operating at operating point A, as shown by the dashed characteristic line Q1 in Figure 4.

In other words, when increasing the target output in the supercharging region, the internal combustion engine 10 during compression autoignition combustion is controlled to go through a first process of increasing only the engine speed toward an operating point that realizes the target output, a second process of increasing the intake pressure (supercharging pressure) and the engine speed, and a third process of increasing only the intake pressure (supercharging pressure) toward an operating point that realizes the target output. 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 realized. The third process is performed immediately after the second process, and increases the intake pressure (supercharging pressure) to the intake pressure (supercharging pressure) at which the target output is realized.

In other words, when the internal combustion engine 10 is in a state where it is performing compressed self-ignition combustion and the target output is being increased in the supercharging region, an upper limit for the engine speed is set according to the actual intake pressure (actual supercharging pressure), and the engine speed is controlled so as not to exceed this upper limit.

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

When the internal combustion engine 10 is in a transient state where the target output is increased in the supercharging region, a response delay occurs in the intake pressure.

Therefore, during a transient period in which the target output is increased in the supercharging region, the internal combustion engine 10 increases (increases) the engine speed prior to the increase in intake pressure. Therefore, during a transient period in which the target output is increased in the supercharging region, the internal combustion engine 10 first changes the operating point from operating point A to operating point B, which is the misfire limit while keeping the intake pressure constant (first process). In other words, during a transient period in which the target output is increased to operating point D while operating at operating point A, in the first process in which the operating point changes from operating point A to operating point B, only the engine speed increases toward the operating point that realizes the target output.

Next, the internal combustion engine 10 changes the operating point along the misfire limit as the intake pressure increases to operating point C where the engine speed becomes the target engine speed (second process). In other words, during the transient period in which the target output is increased to operating point D while operating at operating point A, in the second process in which 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 realizes the target output.

Next, the internal combustion engine 10 changes the operating point to operating point D where the intake pressure becomes the target intake pressure (target boost pressure) (third process). In other words, during the transient period in which the target output is increased to operating point D while operating at operating point A, in the third process in which the operating point changes from operating point C to operating point D, only the intake pressure (boost pressure) increases and the intake pressure (boost pressure) reaches the target intake pressure (target boost pressure) that realizes the target output.

Here, in the process from operating point A to operating point C on characteristic line Q1, the engine speed of internal combustion engine 10 is limited by the upper limit of the engine speed of internal combustion engine 10, which is set according to the intake pressure (boost pressure) at that time.

Figure 5 is a timing chart showing the change in the operating state of the internal combustion engine 10 during a transient period in which the target output of the internal combustion engine 10 is increased.

Time t1 is the timing 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 timing when the operating point of the internal combustion engine 10 reaches operating point B. Time t3 is the timing when the operating point of the internal combustion engine 10 reaches operating point C. Time t4 is the timing 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.

The period from time t1 to time t2 corresponds to a 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 a 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 a third process in which only the intake pressure (boost pressure) of the internal combustion engine 10 increases.

In this way, during the compression autoignition combustion, the internal combustion engine 10 sets an upper limit for the engine speed of the internal combustion engine 10 according to the actual intake pressure (actual boost pressure) during the transient period in which the target output of the internal combustion engine 10 is increased in the supercharging region in which supercharging is performed by the turbocharger 21, and the engine speed of the internal combustion engine 10 is controlled so as not to exceed this upper limit.

As a result, the internal combustion engine 10 can suppress misfires caused by delayed response of the intake pressure (boost pressure) (delayed response of the turbocharger 21).

In addition, during the compression autoignition combustion, the internal combustion engine 10 uses the 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 set according to the actual intake pressure (actual boost pressure) during the transient period in which the target output of the internal combustion engine 10 is increased in the supercharging region where supercharging is performed by the turbocharger 21. Therefore, the internal combustion engine 10 can control the engine speed while suppressing the impact on the drivability of the vehicle 1 in which the internal combustion engine 10 is installed.

Furthermore, during compression autoignition combustion, the internal combustion engine 10 may perform a high compression ratio correction to increase the compression ratio of the internal combustion engine 10 to the high compression ratio side by a predetermined high compression ratio correction amount during a transient period in which the target output is increased in the supercharging region where supercharging is performed by the turbocharger 21, and may set an upper limit value for the engine speed according to the actual intake pressure (actual supercharging pressure) and the actual compression ratio, and control the engine speed so as not to exceed this upper limit value.

In other words, when the internal combustion engine 10 is in a compressed self-ignition combustion state and in a transient state in which the target output of the internal combustion engine 10 is increased in the supercharging region (supercharging operation region) in which supercharging is performed by the turbocharger 21, the ECU 50 may increase the compression ratio using the variable compression ratio mechanism 40, set an upper limit value for the engine speed of the internal combustion engine 10 according to the actual intake pressure (actual supercharging pressure) and the actual compression ratio, and control the engine speed of the internal combustion engine 10 so that it does not exceed this upper limit value.

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 a transient period in which the target output of the internal combustion engine 10 is increased.

When the compression ratio of the internal combustion engine 10 is increased, the operating region R during compression autoignition combustion (the triangular region shown by the solid line in FIG. 6) moves in parallel overall toward the side where the intake pressure is lower, as shown in the operating region Rp (the triangular region shown by the dashed line in FIG. 6) shown by the dashed line in FIG. 6. In other words, when the compression ratio of the internal combustion engine 10 performing compression autoignition combustion is increased during a transient period in which the target output of the internal combustion engine 10 is increased, the operating region R of the internal combustion engine 10 moves toward the side where the intake pressure is lower as the compression ratio increases.

The operating region Rp is an operating region in which the internal combustion engine 10 can operate stably without knocking or misfire (not self-igniting) during compression autoignition combustion, with the compression ratio being higher than that during the operating region R by a predetermined high compression ratio correction amount, and is the region surrounded by lines r1', r2', and r3' in FIG. 6. Line r1' represents the knocking limit of the internal combustion engine 10 during compression autoignition combustion. Line r2' represents the misfire limit of the internal combustion engine 10 during compression autoignition combustion. Line r3' represents the low-speed limit of the engine speed of the internal combustion engine 10 during compression autoignition combustion. The high-speed limit of the engine speed of the internal combustion engine 10 during compression autoignition combustion is the speed at the intersection of line r1' and line r2'. Line segments r1', r2', and r3' correspond to line segments r1, r2, and r3 in the operating region R, respectively.

The higher the compression ratio of the internal combustion engine 10 (the larger the high compression ratio correction amount), the greater the parallel shift of the operating region Rp from the operating region R.

Operating point A in FIG. 6 is the operating point before the target output is increased. Operating point B' in FIG. 6 is the operating point where the engine speed is increased to the misfire limit within the operating region Rp from operating point A while keeping the intake pressure constant. Operating point C' in FIG. 4 is the operating point where the engine speed becomes the target engine speed corresponding to the target output in line with the misfire limit within the operating region Rp during a transient state. At operating point C', the intake pressure has not reached the target intake pressure corresponding to the target output. Operating point D in FIG. 4 is the operating point corresponding to the target output.

During compression autoignition combustion, when the compression ratio is increased during a transient period in which the target output is increased to operating point D while operating at operating point A, the internal combustion engine 10 is controlled so that the operating point changes in the order of A → B' → C' → D, as shown by the thick dashed characteristic line Q2 in Figure 6.

In other words, the internal combustion engine 10 during compression autoignition combustion is controlled to go through the first, second, and third steps described above, even when the compression ratio is increased to increase the target output in the supercharging region.

In other words, during the transitional period when the internal combustion engine 10 is in the compressed autoignition combustion mode and the target output is increased in the supercharging region while the compression ratio is increased, an upper limit for the engine speed is set according to the actual intake pressure (actual supercharging pressure) and the actual compression ratio, and the engine speed is controlled so as not to exceed this upper limit.

During a transient period in which the internal combustion engine 10 increases the target output and the compression ratio in the supercharging region, the engine speed increases (increases) prior to the increase in intake pressure. During a transient period in which the internal combustion engine 10 increases the target output and the compression ratio in the supercharging region, the engine changes the operating point from operating point A to operating point B', which is the misfire limit of the operating region Rp while keeping the intake pressure constant (first process). In other words, during a transient period in which the target output is increased to operating point D while operating at operating point A and the compression ratio is increased, in the first process in which the operating point changes from operating point A to operating point B', only the engine speed increases toward the operating point that realizes the target output. In addition, by increasing the compression ratio, the internal combustion engine 10 changes the operable region from the operating region R to the operating region Rp, thereby increasing (expanding) the upper limit value of the engine speed according to the actual supercharging pressure and the actual compression ratio.

Next, as the intake pressure increases, the internal combustion engine 10 changes the operating point to operating point C' where the engine speed becomes the target engine speed, in line with the misfire limit of the operating range Rp (second process). In other words, during a transitional period in which the target output is increased to operating point D while operating at operating point A and the compression ratio is increased, in the second process in which 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 realizes the target output.

Next, the internal combustion engine 10 changes the operating point to operating point D where the intake pressure becomes the target intake pressure (target boost pressure) (third process). That is, during a transient period in which the target output is increased to operating point D and the compression ratio is increased while operating at operating point A, in the third process in which the operating point changes from operating point C' to operating point D, only the intake pressure (boost pressure) increases and the intake pressure (boost pressure) reaches the target intake pressure (target boost pressure) that realizes the target output. During a transient period in which the target output is increased to operating point D and the compression ratio is increased while operating at operating point A, when the engine speed reaches the target speed that realizes the target output, the compression ratio that was increased by the high compression ratio correction amount is returned to the original compression ratio.

Here, in the process from operating point A to operating point C' on characteristic line Q2, the engine speed of internal combustion engine 10 is limited by the upper limit of the engine speed of internal combustion engine 10, which is set according to the intake pressure (boost pressure) and actual compression ratio at that time.

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

As a result, the internal combustion engine 10 can prevent accidental misfires when returning to a compression ratio that was increased during a transient period.

In addition, the high compression ratio correction amount is set so that the engine speed does not exceed a predetermined engine speed upper limit value so that knocking does not occur 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 range R or the operating range Rp. Furthermore, the high compression ratio correction amount is set so that the engine speed on the line segment r2 representing the misfire limit of the operating range R at the intake pressure (boost pressure) before the intake pressure (boost pressure) of the internal combustion engine 10 begins to rise is equal to or greater than the engine speed on the line segment r1' representing the knocking limit of the operating range Rp at the intake pressure (boost pressure) before the intake pressure (boost pressure) of the internal combustion engine 10 begins to rise. In other words, the high compression ratio correction amount is set so that an operating region is formed between the line segment r2 representing the misfire limit of the operating region R and the line segment r1' representing the knocking limit of the operating region Rp, when the intake pressure (boost pressure) of the internal combustion engine 10 is at a pressure before it starts to rise, allowing the internal combustion engine 10 to operate stably without knocking or misfire.

As a result, the internal combustion engine 10 can prevent accidental knocking when the compression ratio is increased during a transient state.

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

Time t1 is the timing 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 the compression ratio at time t1. Time t2' is the timing when the operating point of the internal combustion engine 10 reaches operating point B'. Time t3' is the timing when the operating point of the internal combustion engine 10 reaches operating point C'. The internal combustion engine 10 returns the compression ratio that was increased at time t3 to its original state. Time t4' is the timing 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.

The period from time t1 to time t2' corresponds to a 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 a 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 a third process in which only the intake pressure (boost pressure) of the internal combustion engine 10 increases.

Time t2 is the timing when the operating point of the internal combustion engine 10 reaches operating point B when the compression ratio is not increased during a transient state. Time t3 is the timing when the operating point of the internal combustion engine 10 reaches operating point C when the compression ratio is not increased during a transient state. Time t4 is the timing when the operating point of the internal combustion engine 10 reaches operating point D when the compression ratio is not increased during a transient state.

In this way, the internal combustion engine 10 during compression autoignition combustion can reduce the response delay of the intake pressure (boost pressure) by increasing the compression ratio during a transient period in which the target output of the internal combustion engine 10 is increased in the supercharging region where supercharging is performed by the turbocharger 21. In other words, as shown by the solid line in Figure 7, by increasing the compression ratio, it is possible to quickly raise the intake pressure (boost pressure) to the target intake pressure (boost pressure).

Figure 8 is a flow chart showing the flow of control of the motor generator 9 in the above-mentioned embodiment. It is a schematic explanatory diagram.

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.

In step S2, the target output when the internal combustion engine 10 is in the supercharging region during compression ignition combustion is calculated based on the output signals from the battery charge sensor 55 and the accelerator pedal sensor 56. That is, the target output is calculated according to the accelerator pedal opening and the battery charge.

In step S3, a first target engine speed is calculated, which is the engine speed that realizes the calculated target output. The first target engine speed is stored in advance in a ROM or the like in the ECU 50 in association with the target output, and the corresponding value is read out according to the calculated target output.

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, which is set according to the intake pressure (boost pressure) at that time.

In step S5, the first target speed is compared with the upper limit of the engine speed set according to the intake pressure (boost pressure). If in step S5 the first target speed is greater than the upper limit of the engine speed set according to the intake pressure (boost pressure), the process proceeds to step S6. If in step S5 the first target speed is equal to or less than the upper limit of the engine speed set according to the intake pressure (boost pressure), the process proceeds to step S7. Note that the first target speed is corrected so that it becomes higher (larger) as the compression ratio of the internal combustion engine 10 becomes higher.

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

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

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

Figure 9 is a flow chart showing the flow of control of the variable compression ratio actuator 45 in the above-mentioned embodiment. It is a schematic explanatory diagram.

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.

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

In step S13, a target compression ratio that realizes the calculated target output is calculated. The target compression ratio is stored in advance in a ROM or the like in the ECU 50 in association with the target output, and the corresponding value is read out according to the calculated target output.

In step S14, the target output is compared with the current output of the internal combustion engine 10. If in step S14 the target output is greater than the current output of the internal combustion engine 10, the process proceeds to step S15. If in step S14 the target output is equal to or less than the current output of the internal combustion engine 10, the process proceeds to step S16. In step S14, it is determined whether or not the internal combustion engine 10 is in a transient state in which the target output is to be increased.

In step S15, a high compression ratio correction is performed on 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.

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

Figure 10 is an explanatory diagram showing a schematic diagram of the control flow of the internal combustion engine 10 in the above-mentioned embodiment.

The ECU 50 has a target output calculation unit S21, a first target rotation speed calculation unit S22, a second target rotation 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.

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 rotation speed calculation unit S22 calculates a first target rotation speed that realizes the calculated target output. The second target rotation speed calculation unit S23 calculates an upper limit of the engine rotation speed that is the misfire limit from the current intake pressure (boost pressure) detected by the intake pressure sensor 54, and if the first target rotation speed is greater than this upper limit, calculates the upper limit as the second target rotation speed, and if the first target rotation speed is equal to or less than this upper limit, calculates the first target rotation speed as the second target rotation speed.

In other words, the second target rotation speed calculation unit S23 corresponds to an upper limit setting unit that sets the upper limit of the engine rotation speed of the internal combustion engine 10 according to the actual boost pressure during a transient period in which the target output of the internal combustion engine 10 is increased in the boost region.

The motor generator 9 is controlled by the ECU 50 so that the engine speed of the internal combustion engine 10 becomes the second target speed. In other words, the ECU 50 corresponds to a control unit that controls 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 that is set according to the actual boost pressure.

The first target boost pressure calculation unit S24 calculates a first target boost pressure that realizes the calculated target output. The second target boost pressure calculation unit S25 calculates an upper limit value of the intake pressure (boost pressure) that is the knocking limit from the current engine speed (actual speed) detected by the engine speed sensor 51, and if the first target boost pressure is greater than this upper limit value, calculates the upper limit value as the second target boost pressure, and if the first target boost pressure is equal to or less than this upper limit value, calculates the first target boost pressure as the second target boost pressure.

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

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

The target compression ratio calculation unit S26 calculates the target compression ratio that achieves the calculated target output.

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.

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

The above-described embodiments relate to a method for controlling an internal combustion engine and a control device for an internal combustion engine.

Reference Signs List 1 vehicle 9 motor generator 10 internal combustion engine 21 turbocharger 30 fuel injection valve 40 variable compression ratio mechanism 45 variable compression ratio mechanism actuator 50 ECU
51: engine speed sensor 52: cooling water temperature sensor 53: cylinder pressure sensor 54: intake pressure sensor 55: battery charge amount sensor 56: accelerator pedal sensor 57: actual compression ratio detection sensor

Claims (8)

A method for controlling an internal combustion engine that performs compression ignition combustion, comprising:
A method for controlling an internal combustion engine, which sets an upper limit value for engine speed of the internal combustion engine according to an actual boost pressure during a transitional period in which a target output of the internal combustion engine is increased in a supercharging region in which supercharging is performed by a turbocharger, and controls the engine speed of the internal combustion engine so as not to exceed the upper limit value. The method for controlling an internal combustion engine according to claim 1, in which a motor generator that can be driven by the power of the internal combustion engine is used to control the engine speed of the internal combustion engine so as not to exceed the upper limit value. A method for controlling an internal combustion engine according to claim 2, in which a high compression ratio correction is performed to change the compression ratio from the current compression ratio to a higher compression ratio by a predetermined high compression ratio correction amount using a compression ratio variable mechanism capable of changing the compression ratio of the internal combustion engine during the above-mentioned transient period, and the upper limit value is corrected according to the actual compression ratio. The method for controlling an internal combustion engine according to claim 3, wherein the high compression ratio correction is terminated when the engine speed of the internal combustion engine reaches the engine speed of the target output. the internal combustion engine is controlled to undergo, during the above-mentioned transient state, a first process in which only the engine speed increases toward an operating point that realizes the target output, a second process in which both the engine speed and the supercharging pressure increase after the first process so that the engine speed reaches the engine speed of the target output, and a third process in which only the supercharging pressure increases after the second process so that the supercharging pressure reaches the supercharging pressure of the target output,
5. The method for controlling an internal combustion engine according to claim 4, wherein the high compression ratio correction amount is set so that the supercharging pressure does not exceed a predetermined upper limit value of the supercharging pressure in order to prevent misfire from occurring in the third process. The method for controlling an internal combustion engine according to claim 5, wherein the high compression ratio correction amount is set so that the engine speed does not exceed a predetermined upper limit of the engine speed in the first process to prevent knocking. The method for controlling an internal combustion engine according to claim 5 or 6, wherein the internal combustion engine is dedicated to generating electricity to drive the motor generator. A control device for an internal combustion engine that performs compression ignition combustion,
A turbocharger that supercharges an internal combustion engine;
an upper limit value setting unit that sets an upper limit value of an engine speed of the internal combustion engine in accordance with an actual supercharging pressure during a transitional period in which a target output of the internal combustion engine is increased in a supercharging region;
and a control unit that controls the engine speed of the internal combustion engine so that it does not exceed the upper limit value.

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