JP2010025080A - Failure determination system of variable compression-ratio mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a failure determination system of a variable compression ratio mechanism by which, at the determination of whether an operation failure occurs or not in the variable compression ratio mechanism, malfunctions such as deterioration in output performance, fuel economy, and the deterioration of exhaust emission are restrained. <P>SOLUTION: During an idling operation of an internal combustion engine, compression ratio forced-variation control is executed by which a compression ratio ε is varied in accordance with the transition of a desired compression ratio εtf for failure determination set for the failure determination of the variable compression ratio mechanism to obtain a maximum value Pcumax and a minimum value Pcumin of a cylinder pressure Pcu at the end of compression (S103), whether the variation range of a calculated maximum cylinder pressure ΔPcuw is not higher than ΔBw or not is determined (S104, S105), and if the variation range of the maximum cylinder pressure ΔPcuw is not higher than ΔBw, it is determined that an operation failure occurs in the variable compression ratio mechanism 9 (S106). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a failure determination device for a variable compression ratio mechanism applied to an internal combustion engine.

  In an internal combustion engine equipped with a variable compression ratio mechanism capable of changing the compression ratio of the internal combustion engine, the compression ratio of the internal combustion engine is set so as to improve the output performance, the fuel consumption, the exhaust emission, and the like. It is controlled according to the state.

However, if the variable compression ratio mechanism does not operate normally for some reason, the compression ratio of the internal combustion engine cannot be controlled according to the operating state. As a result, there is a possibility that drivability deteriorates due to a decrease in output performance or exhaust emission deteriorates. Therefore, a failure determination device that determines whether or not the variable compression ratio mechanism has failed has been developed (see, for example, Patent Document 1).
Japanese Utility Model Publication No. 1-88039 JP 2004-218522 A

  As this type of failure determination device, it is necessary to forcibly change the compression ratio of the internal combustion engine in order to detect the occurrence of a failure in the variable compression ratio mechanism. However, it is rare that the compression ratio that is forcibly changed when determining the failure of the variable compression ratio mechanism is adapted to the operating state of the internal combustion engine. For this reason, it is difficult to avoid a decrease in output performance, a deterioration in fuel consumption, a deterioration in exhaust emission, etc. at the time of the failure determination as a contradiction when the failure determination of the variable compression ratio mechanism is performed with priority.

  Therefore, the present invention has been made in view of the above circumstances, and its purpose is to reduce output performance, fuel consumption, exhaust emission when determining whether or not the variable compression ratio mechanism is malfunctioning. It is an object of the present invention to provide a failure determination device for a variable compression ratio mechanism that can suppress the occurrence of problems such as these.

In order to achieve the above object, a failure determination apparatus for a variable compression ratio mechanism according to the present invention employs the following means.
That is, a variable compression ratio mechanism that can change the mechanical compression ratio of the internal combustion engine according to the operating state;
A command for issuing an operation command to the variable compression ratio mechanism in order to change the mechanical compression ratio in accordance with the transition of the target compression ratio set for determining the failure of the variable compression ratio mechanism during idle operation of the internal combustion engine. Means,
Obtaining means for obtaining a value of a predetermined driven parameter that changes due to the variable compression ratio mechanism changing the mechanical compression ratio based on the operation command;
The variable when the maximum change width, which is the difference between the maximum value and the minimum value of the driven parameter acquired by the acquisition means, is equal to or less than a predetermined reference change width set according to the transition of the target compression ratio. Determining means for determining that the compression ratio mechanism is malfunctioning.

In the above configuration, when determining whether or not a failure has occurred in the variable compression ratio mechanism, the variable compression ratio mechanism is forcibly operated in accordance with an operation command issued by the command means. In other words, the mechanical compression ratio when the failure determination for the variable compression ratio mechanism is not performed is controlled so as to match the operation state of the internal combustion engine, whereas when the failure determination is performed, regardless of the operation state, To match the target compression ratio set in

  The driven parameter in the above configuration is a parameter that changes following the operation of the variable compression ratio mechanism based on the command means, and is a parameter that changes in correlation with the actual change in the mechanical compression ratio. In the present invention, paying attention to the correlation between the mechanical compression ratio and the driven parameter, whether or not the variable compression ratio mechanism has failed based on the change in the driven parameter acquired when the variable compression ratio mechanism is forcibly operated. Judgment is made.

  When an operation failure occurs in the variable compression ratio mechanism, the mechanical compression ratio cannot be changed in accordance with the transition of the target compression ratio. In this case, the maximum change width of the driven parameter acquired by the acquisition unit is smaller than that in the case where no operation failure has occurred in the variable compression ratio mechanism. In the present invention, when the maximum change width of the driven parameter is equal to or less than the predetermined reference change width, it is determined that the variable compression ratio mechanism is malfunctioning.

  This reference change width is set according to the transition of the target compression ratio. This is because if the transition of the target compression ratio is different, the method of proper transition of the driven parameter is different. The reference change width in the present invention is a threshold value for determining whether or not an operation failure has occurred in the variable compression ratio mechanism, and it is assumed that the actual mechanical compression ratio is normally changed in accordance with the transition of the target compression ratio. It may be set lower than the maximum change width of the driven parameter that can be obtained.

  In the present invention, the difference between the maximum value and the minimum value of the target compression ratio among the transitions of the target compression ratio set for determining the failure of the variable compression ratio mechanism (that is, the fluctuation range of the target compression ratio). The reference change width may be set to be a larger value as the value is larger. Thus, when the operation command is issued by the command means, the reference change width can be set to a more appropriate value even if the transition of the target compression ratio is set in various patterns.

  When executing the failure determination of the variable compression ratio mechanism, it is necessary to forcibly change the mechanical compression ratio regardless of the operation state. On the other hand, in the present invention, the failure determination of the variable compression ratio mechanism can be performed during the idling operation of the internal combustion engine, so that the output performance, the fuel consumption, and the exhaust emission are deteriorated during the failure determination. Can be suppressed. That is, according to the present invention, it is possible to determine the failure of the variable compression ratio mechanism while reliably avoiding the occurrence of these problems. In addition, during the idling operation of the internal combustion engine, since the operation state such as the load and the rotational speed is not changed and is stable, the reliability of the driven parameter with respect to the acquired value can be improved. Therefore, by performing failure determination of the variable compression ratio mechanism during idle operation of the internal combustion engine, the determination can be performed stably and accurately.

  In addition, according to the above configuration, since the failure determination of the variable compression ratio mechanism is performed based on the magnitude relationship between the maximum change width, which is the difference between the maximum value and the minimum value of the driven parameter, and the reference change width, Even if an error occurs in the actual acquired value with respect to the value of, the influence of the error on the failure determination can be made as small as possible. This is because it is difficult for the acquisition means to acquire the value of the driven parameter without including any error. Therefore, according to this structure, the precision concerning the failure determination of a variable compression ratio mechanism can be improved.

  Incidentally, as the mechanical compression ratio of the internal combustion engine increases, the in-cylinder pressure at a specific time in the combustion cycle increases. The specific time includes in-cylinder pressure in the compression stroke (for example, compression end in-cylinder pressure at the compression top dead center), in-cylinder pressure in the expansion stroke, and the like. Therefore, the present invention further includes an in-cylinder pressure sensor for detecting the in-cylinder pressure of the internal combustion engine, and the driven parameter is detected by the in-cylinder pressure sensor when the variable compression ratio mechanism is operating based on the operation command. In-cylinder pressure may be used.

  Since the operating state is stable during the idling operation of the internal combustion engine, when the variable compression ratio mechanism is forcibly operated, the in-cylinder pressure changes so as to follow the actual change in the mechanical compression ratio. Therefore, by acquiring the in-cylinder pressure when the operation command is issued from the command means, and comparing the maximum variation width of the in-cylinder pressure based on this with the reference variation width, the failure determination of the variable compression mechanism is accurately performed. Can be done well. In this configuration, various timings can be adopted as the detection timing of the in-cylinder pressure by the in-cylinder pressure sensor as long as it is common for each combustion cycle. Here, it is the in-cylinder pressure in the compression stroke and the expansion stroke that the influence due to the change in the mechanical compression ratio appears remarkably. Therefore, the in-cylinder pressure at these timings may be detected by the in-cylinder pressure sensor.

  The failure determination device for a variable compression ratio mechanism according to the present invention includes an idle speed control valve (hereinafter referred to as “ISC valve”) and an engine speed during idling operation by controlling the opening of the ISC valve. Idle speed control means (hereinafter referred to as “ISC means”) for maintaining the target idle speed may be further provided. This target idle speed is a target value of the engine speed during idling, and may be set to a higher speed side as the load from an air conditioner, an alternator, or the like is higher.

  In the above configuration, the engine torque changes when the mechanical compression ratio is actually changed by an operation command from the command means. Then, since the engine speed during idling varies, the ISC means adjusts the opening of the ISC valve so that the engine speed is maintained at the target idle speed. Here, since the change amount of the engine torque correlates with the actual change amount of the mechanical compression ratio, the change amount of the opening of the ISC valve correlates with the actual change amount of the mechanical compression ratio. Therefore, the driven parameter in the present invention may be the opening of the ISC valve controlled by the ISC means when the variable compression ratio mechanism is operating based on the operation command. That is, the degree of opening of the ISC valve when the operation command is issued from the command means is acquired, and the maximum change width of the opening of the ISC valve is compared with the reference change width, thereby accurately determining the failure determination of the variable compression mechanism. Can be done well.

  As described above, the failure determination of the variable compression ratio mechanism in the present invention is performed during the idling operation of the internal combustion engine. For this reason, it is necessary to forcibly change the mechanical compression ratio in accordance with the transition of the target compression ratio within a limited time during the idling operation of the internal combustion engine, and quickly acquire the maximum change width of the driven parameter. .

  Here, the timing at which the acquisition unit acquires the value of the driven parameter may be performed based on the combustion cycle of the internal combustion engine. It is considered that the value of the driven parameter acquired in one combustion cycle does not change unless it shifts to the next combustion cycle at the earliest. Therefore, the acquisition frequency of the follower parameter by the acquisition means is preferably set based on the combustion cycle.

  Here, the time required for one combustion cycle becomes shorter as the engine speed during idling is higher. Therefore, considering the relationship between the number of acquisitions of the value of the follower parameter that can be acquired by the acquisition means and the target idle speed during idle operation in a certain time, the higher the target idle speed, the higher the acquisition number. Can be increased. Conversely, as the target idle speed is lower, the number of acquisitions of the driven parameter in the predetermined time is reduced.

Therefore, the command means of the present invention may set the amount of change in the target compression ratio for each combustion cycle of the internal combustion engine based on the engine speed during idle operation. According to this, when the number of acquisition of the driven parameter cannot be secured so much as when the engine speed during idling is low, the change amount of the machine target compression ratio for each combustion cycle is increased (increased). Thus, the operation for determining the failure of the variable compression ratio mechanism can be completed quickly. Therefore, the maximum change width of the driven parameter can be reliably acquired during the idling operation of the internal combustion engine. Therefore, the failure determination of the variable compression ratio mechanism can be reliably performed during the idling operation of the internal combustion engine.

  In addition, when the number of acquisitions of the driven parameter can be sufficiently ensured, such as when the engine speed during idling is high, the amount of change in the target compression ratio for each combustion cycle can be made smaller (smaller) to make it finer. Follow parameters can be acquired with a simple pitch. As a result, the maximum change width of the driven parameter can be acquired with higher accuracy, and the accuracy of determining the failure of the variable compression ratio mechanism can be improved.

  The command means may set the amount of change in the target compression ratio for each combustion cycle of the internal combustion engine as a large value when the engine speed during idling is low compared to when the engine speed is high. The command means may set the amount of change in the target compression ratio for each combustion cycle of the internal combustion engine as a larger value as the engine speed during idling is lower. According to this, the change amount of the mechanical compression ratio for each combustion cycle can be set as a more appropriate value according to the engine speed during idling. Therefore, it is possible to more appropriately achieve both the reliable determination of the failure of the variable compression ratio mechanism during idle operation and the improvement of the determination accuracy.

  By the way, even when the variable compression ratio mechanism is not malfunctioning, a responsiveness abnormality may occur. The response abnormality is an actual change speed of the mechanical compression ratio (hereinafter referred to as “actual change speed”) when the change speed of the mechanical compression ratio requested by the operation command from the command means is relatively high. It can be considered as a phenomenon that cannot be increased to the speed that is achieved. If such a responsive abnormality occurs in the variable compression ratio mechanism, it becomes difficult to change the mechanical compression ratio to its target value by a desired time.

  Therefore, in the present invention, the transition of the target compression ratio is a predetermined reverse V-shaped transition pattern that reverses from the rising state to the falling state with the maximum value of the target compression ratio as a boundary, and the minimum value of the target compression ratio. When the command means is formed to include at least one of the predetermined V-shaped transition patterns that reverse from the descending state to the ascending state, the command means changes the speed at which the target compression ratio changes (hereinafter referred to as “target change”). Two types of operation commands that differ only in “speed” may be issued to the variable compression ratio mechanism.

  Here, if responsiveness abnormality does not occur in the variable compression ratio mechanism, the actual change speed of the mechanical compression ratio when the variable compression ratio mechanism is operated substantially matches the target change speed. Since the only difference in the transition of the respective target compression ratios is the target change speed, the fluctuation ranges of the target compression ratios in both are equal. Therefore, in this case, the maximum change width (hereinafter referred to as “maximum change width at low speed change”) acquired when an operation command having a lower target change speed is issued and the target change speed are set high. There is almost no difference from the maximum change width acquired when the other operation command is issued (hereinafter referred to as “maximum change width at high speed change”). That is, the maximum change width at the time of high speed change is not excessively smaller than the maximum change width at the time of low speed change.

However, if a responsiveness abnormality occurs in the variable compression ratio mechanism, the actual change speed of the mechanical compression ratio when the variable compression ratio mechanism is activated is excessively lower than the target change speed. Here, since the transition of the target compression ratio is formed to include at least one of the inverted V-shaped transition pattern and the V-shaped transition pattern, when the responsiveness abnormality occurs as described above, the target compression ratio transition is slow. The maximum change width at the time of high-speed change becomes excessively smaller than the maximum change width at the time of change. This is because when the transition of the target compression ratio includes an inverted V-shaped transition pattern, the variable compression ratio mechanism is in an elevated state before the actual mechanical compression ratio rises to the maximum value of the target compression ratio. This is because it is reversed to the lowered state. Also, when the transition of the target compression ratio includes a V-shaped transition pattern, the variable compression ratio mechanism increases the mechanical compression ratio in the lowered state before the actual mechanical compression ratio decreases to the minimum value of the target compression ratio. This is because the state is reversed.

  Therefore, the determination means in the present invention is the difference between the maximum change widths acquired by the acquisition means when each operation command is issued (that is, the difference between the maximum change width at the low speed change and the maximum change width at the high speed change). Based on the above, it may be determined whether or not a responsive abnormality has occurred in the variable compression ratio mechanism. According to this, based on the difference in the maximum change width obtained when the variable compression ratio mechanism is operated based on two types of operation commands that differ only in the target change speed, the presence or absence of responsiveness abnormality in the mechanism is suitable. Can be judged.

  Further, the determination means in the present invention is such that the difference in the maximum change width is larger than a predetermined reference difference that is set according to the difference in the speed at which the target compression ratio changes (target change speed) in each operation command. It may be determined that a responsiveness abnormality has occurred in the variable compression ratio mechanism. This predetermined reference difference can be obtained in advance by experiments or the like in order to determine the presence or absence of responsiveness abnormality in the variable compression ratio mechanism.

  Here, when responsiveness abnormality occurs in the variable compression ratio mechanism, the difference in the maximum change width between the two becomes larger when the difference in the target change speed is larger than when the difference in the target change speed is small. On the other hand, according to this configuration, the predetermined reference difference can be set according to the difference in the target change speed, so that a reasonable judgment is made as to whether or not a responsiveness abnormality has occurred in the variable compression ratio mechanism. be able to. In the present invention, the predetermined reference difference may be set as a larger value as the difference in target change speed is larger. This is because when the responsiveness abnormality occurs in the variable compression ratio mechanism, the difference in the maximum change width increases as the difference in the target change speed increases.

  Further, the determination means according to the present invention is such that the maximum change width acquired when an operation command with a lower speed at which the target compression ratio changes is greater than the reference change width is obtained, and the target compression ratio is When the maximum change width acquired when an operation command with a higher speed of change is issued is equal to or less than the reference change amount, it is determined that the variable compression ratio mechanism has a responsive abnormality rather than an operation failure. Good.

  Here, the two types of target change speeds may be obtained in advance through experiments or the like. In particular, for the higher target change speed of the two types, if the variable compression ratio mechanism is in a state where no responsiveness abnormality has occurred, the maximum change width will surely be greater than the reference change width, resulting in a responsiveness abnormality. If it is in such a state, it is preferable to set the speed so that the maximum change width is surely equal to or less than the reference change width.

  According to this configuration, it is possible to suitably detect whether or not there is a responsive abnormality in addition to an operation failure in the variable compression ratio mechanism.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  According to the present invention, there is provided a variable compression ratio mechanism that can suppress the occurrence of problems such as a decrease in output performance, deterioration in fuel consumption, and deterioration in exhaust emission when determining whether or not the variable compression ratio mechanism is malfunctioning. A failure determination device can be provided.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

<Example 1>
A first embodiment for carrying out the present invention will be described. FIG. 1 is a diagram showing a schematic configuration of a variable compression ratio internal combustion engine (hereinafter simply referred to as “internal combustion engine”) 1 in which the compression ratio is variable in the present embodiment. In the present embodiment, in order to display the internal combustion engine 1 in a concise manner, some components are not shown.

  An intake pipe 19 is connected to the combustion chamber in the cylinder 2 via an intake port 18 provided in the cylinder head 10. Inflow of intake air into the cylinder 2 is controlled by an intake valve 5. The opening and closing of the intake valve 5 is controlled by the rotational drive of the intake side cam. The intake pipe 19 is provided with a throttle valve 7 that can change the cross-sectional area of the intake air flowing through the intake pipe 19. An exhaust pipe 21 is connected via an exhaust port 20 provided in the cylinder head 10. Exhaust exhaust to the outside of the cylinder 2 is controlled by an exhaust valve 6. The opening and closing of the exhaust valve 6 is controlled by the rotational drive of the exhaust side cam.

  Further, a fuel injection valve 17 that injects fuel into the intake air flowing through the intake port 18 is attached to the intake port 18. A spark plug 16 that ignites the air-fuel mixture in the cylinder 2 and an in-cylinder pressure sensor 24 that detects in-cylinder pressure are provided at the top of the cylinder 2. The piston 15 is connected to the crankshaft 13 via a connecting rod 14. As a result, the crankshaft 13 rotates as the piston 15 reciprocates. A crank position sensor 25 that detects a rotation angle (crank angle) of the crankshaft 13 is disposed in the vicinity of the crankshaft 13.

  The internal combustion engine 1 is provided with an electronic control unit (hereinafter referred to as “ECU”) 30 for controlling the internal combustion engine 1. The ECU 30 includes a CPU, a ROM, a RAM, and the like that store various programs and maps to be described later, and controls the operating conditions of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's request. Unit.

  The ECU 30 is electrically connected to an accelerator opening sensor 22 that outputs an electrical signal corresponding to the amount of depression of the accelerator pedal (accelerator opening). The ECU 30 receives a signal corresponding to the accelerator opening, and calculates the engine load and the like required for the internal combustion engine 1. A crank position sensor 23 is electrically connected to the ECU 30. The ECU 30 receives a signal corresponding to the crank angle of the internal combustion engine 1, so that the engine speed of the internal combustion engine 1, the vehicle speed of the vehicle on which the internal combustion engine 1 is mounted, etc. from the engine speed and gear ratio, etc. Is calculated. The in-cylinder pressure sensor 24 is also electrically connected to the ECU 30, and an output signal is input to the ECU 30. The ECU 30 is electrically connected to a throttle valve 7, a fuel injection valve 17, and a spark plug 16, and these are controlled by the ECU 30.

Further, the internal combustion engine 1 in the present embodiment is provided with a variable compression ratio mechanism 9. The variable compression ratio mechanism 9 moves the cylinder block 3 relative to the crankcase 4 in the axial direction of the cylinder 2 to change the mechanical compression ratio of the internal combustion engine 1 (hereinafter simply referred to as “compression ratio”). The That is, the variable compression ratio mechanism 9 includes the cylinder block 3, the cylinder head 10, and the piston 15 by moving the cylinder head 10 together with the cylinder block 3 relative to the crankcase 4 in the axial direction of the cylinder 2. The volume of the combustion chamber is changed, and as a result, the compression ratio of the internal combustion engine 1 is variably controlled. For example, when the cylinder block 3 moves relative to the direction away from the crankcase 4, the combustion chamber volume increases and the compression ratio decreases. Conversely, when the cylinder block 3 moves relative to the crankcase 4, the combustion chamber volume decreases and the compression ratio increases (increases).

  Here, the detailed configuration of the variable compression ratio mechanism 9 will be described. The variable compression ratio mechanism 9 includes a shaft portion 9a, a cam portion 9b having a circular cam profile fixed to the shaft portion 9a while being eccentric with respect to the central axis of the shaft portion 9a, a cam portion 9b, A movable bearing portion 9c having the same outer shape and rotatable with respect to the shaft portion 9a and mounted in an eccentric state like the cam portion 9b, a worm wheel 9d provided concentrically with the shaft portion 9a, and a worm wheel A worm 9e that meshes with 9d and a motor 9f that rotationally drives the worm 9e.

  The cam portion 9 b is installed in a storage hole provided in the cylinder block 3, and the movable bearing portion 9 c is installed in a storage hole provided in the crankcase 4. The motor 9f is fixed to the cylinder block 3 and moves integrally with the cylinder block 3. Here, the driving force from the motor 9f is transmitted to the shaft portion 9a via the worm 9e and the worm wheel 9d. Then, the cam block 9b and the movable bearing portion 9c in an eccentric state are driven, whereby the cylinder block 3 is moved relative to the crankcase 4 in the axial direction of the cylinder 2.

  Here, the motor 9 f constituting the variable compression ratio mechanism 9 is electrically connected to the ECU 30. Then, the motor 9 f is driven by a command from the ECU 30, and the compression ratio ε of the internal combustion engine 1 is changed by the variable compression ratio mechanism 9. Specifically, the variable compression ratio mechanism 9 is operated so that the compression ratio ε matches the target value set according to the operating state (engine load and engine speed) of the internal combustion engine 1. Thereby, the improvement of the output performance, the improvement of fuel consumption, the improvement of exhaust emission, etc. during the operation of the internal combustion engine 1 are achieved.

  However, the variable compression ratio mechanism 9 may not operate normally for some reason. In this case, not only the above-mentioned items cannot be realized but also causes various problems. For example, when the operation is continued at a compression ratio ε not suitable for the operation state of the internal combustion engine 1, especially when operating in a high rotation range, a large engine vibration is caused by torque fluctuation, or the engine is damaged by knocking. There is a risk of doing.

  Therefore, in this embodiment, in order to avoid the above problem, a process for determining whether or not an operation failure has occurred in the variable compression ratio mechanism 9 (hereinafter referred to as a “variable mechanism failure determination process”) is being performed. Is executed by the ECU 30.

  In the variable mechanism failure determination process, the ECU 30 determines the compression ratio in accordance with the transition of a target compression ratio (hereinafter referred to as “failure determination target compression ratio”) εtf that is preset for failure determination of the variable compression ratio mechanism 9. An operation command is issued to the variable compression ratio mechanism 9 in order to change ε, and control for forcibly changing the compression ratio ε (hereinafter referred to as “compression ratio forced change control”) is performed.

  In the compression ratio forced change control, when the compression ratio ε changes due to the operation of the variable compression ratio mechanism 9, the in-cylinder pressure (hereinafter referred to as “compression end in-cylinder pressure”) Pcu at the compression top dead center in each combustion cycle changes. To do. There is a correlation between the compression ratio ε of the internal combustion engine 1 and the compression end in-cylinder pressure Pcu. Therefore, the ECU 30 continuously monitors the compression end in-cylinder pressure Pcu based on the output signal of the in-cylinder pressure sensor 24 when executing the compression ratio forced change control. Then, it is determined whether or not the variable compression ratio mechanism 9 has failed based on the change in the compression end in-cylinder pressure Pcu. The timing at which the piston 15 reaches the compression top dead center in each combustion cycle can be detected based on an output signal of a cam angle sensor (not shown). During the execution of the compression ratio forced change control, the injection timing of the fuel injection valve 17, the ignition timing of the spark plug 16, and the opening of the throttle valve 7 are maintained constant.

  As described above, the compression ratio ε when the variable mechanism failure determination process is not performed (hereinafter referred to as “normal operation”) is controlled so as to match the operating state of the internal combustion engine 1. On the other hand, in the compression ratio forced change control, the compression ratio ε is changed in accordance with the transition of the failure determination target compression ratio εtf regardless of the operation state. Therefore, in this embodiment, the variable mechanism failure determination process is performed during the idling operation of the internal combustion engine 1. If the engine is in idle operation, the required output to the internal combustion engine 1 is not changed by the driver, and there is no problem even if the compression ratio ε is forcibly changed in accordance with the transition of the failure determination target compression ratio εtf. Because. In this embodiment, the compression end in-cylinder pressure Pcu corresponds to a predetermined driven parameter in the present invention.

  The detailed contents of the variable mechanism failure determination process executed by the ECU 30 will be described with reference to FIGS. FIG. 2 is a time chart showing a transition of the failure determination target compression ratio εtf and a transition of the compression end in-cylinder pressure Pcu in the variable mechanism failure determination processing in the present embodiment. The upper row represents the transition of the failure determination target compression ratio εtf, and the lower row represents the transition of the compression end in-cylinder pressure Pcu. The time ts on the horizontal axis represents the start time of the compression ratio forced change control, and the time tf represents the end time of the compression ratio forced change control. The end of the compression ratio forced change control is a time when the forced change of the compression ratio ε is completed in accordance with the transition of the failure determination target compression ratio εtf. The sign εid in the transition of the failure determination target compression ratio εtf is a compression ratio at the start of the compression ratio forced change control (hereinafter referred to as “reference compression ratio”). This reference compression ratio εid is set in advance as a value suitable for idle operation.

  As shown in the figure, the transition of the failure determination target compression ratio εtf is an inverted V shape that reverses from the rising state to the falling state at the maximum value εtfu (time t1, t3) of the failure determination target compression ratio εtf. A transition pattern and a V-shaped transition pattern that reverses from a descending state to an ascending state with a minimum value εtfl (time t2) as a boundary are formed in combination. The maximum value εtfu is a target value on the high compression ratio side by the first specified value Δε1 with respect to the reference compression ratio εid. Further, the minimum value εtfl is a target value on the low compression ratio side by a second specified value Δε2 with respect to the reference compression ratio εid. The first specified value Δε1 and the second specified value Δε2 are set in advance for the variable mechanism failure determination process.

  The transition of the compression end in-cylinder pressure Pcu will be described. The solid line is changed in accordance with the transition of the failure determination target compression ratio εtf when the variable compression ratio mechanism 9 has no operating failure, that is, the actual compression ratio ε. The transition of the compression end in-cylinder pressure Pcu is shown. For example, the operation failure is that the cam portion 9b and the movable bearing portion 9c in the variable compression ratio mechanism 9 are fixed, or the cam portion 9b and the movable bearing portion 9c are driven only within a limited range. Thus, it can be understood that the compression ratio ε cannot be changed as the target compression ratio εtf changes.

  When an operation failure occurs in the variable compression ratio mechanism 9, the compression end in-cylinder pressure Pcu changes as shown by the broken line in FIG. When the operation failure has occurred in the variable compression ratio mechanism 9, the change in the compression end in-cylinder pressure Pcu becomes smaller than that in the case where no operation failure has occurred. In the variable mechanism failure determination process of the present embodiment, the difference between the maximum value Pcumax and the minimum value Pcumin in the compression end in-cylinder pressure Pcu when the compression ratio forced change control is performed (hereinafter referred to as “maximum in-cylinder pressure change width”) ΔPcuw When the maximum in-cylinder pressure change width ΔPcuw is equal to or less than the reference change width ΔBw, it is determined that an operation failure has occurred in the variable compression ratio mechanism 9.

  The reference change width ΔBw is a threshold value for determining whether or not an operation failure has occurred in the variable compression ratio mechanism 9, and the actual compression ratio ε is normally adjusted in accordance with the transition of the failure determination target compression ratio εtf. If it is changed, it is set lower than the maximum in-cylinder pressure change width ΔPuw obtained.

  The reference change width ΔBw is set according to the transition of the failure determination target compression ratio εtf. This is because if the transition of the failure determination target compression ratio εtf is different, the proper transition of the compression end in-cylinder pressure Pcu is also different. More specifically, in this embodiment, the difference between the maximum value and the minimum value of the failure determination target compression ratio εtf set in FIG. 2 (also referred to as the fluctuation range of the failure determination target compression ratio εtf). The larger the value is, the larger the reference change width ΔBw is set. This is because, if there is no operation failure in the variable compression ratio mechanism 9, the variation range of the compression end in-cylinder pressure Pcu that changes with the variation range of the failure determination target compression ratio εtf increases. Thus, by setting the reference change width ΔBw in relation to the fluctuation range of the failure determination target compression ratio εtf, the compression ratio forced change control is performed in accordance with the transition of the failure determination target compression ratio εtf of various patterns. Even when the above is performed, the reference change width ΔBw is set to an appropriate value. In this embodiment, the maximum in-cylinder pressure change width ΔPuw corresponds to the maximum change width in the present invention.

  FIG. 3 is a flowchart illustrating a control routine according to the variable mechanism failure determination process of the present embodiment. This control routine is a routine stored in advance in the ROM of the ECU 30. Further, this routine is periodically executed by the ECU 30. When this routine is executed, it is determined in step S101 whether or not the internal combustion engine 1 is idling. If it is determined that the internal combustion engine 1 is idling, it is determined that the condition for performing the variable mechanism failure determination process is satisfied, and the process proceeds to step S102. Otherwise, the present routine is temporarily exited. .

  In step S102, it is determined whether or not the failure determination completion flag is OFF. If it is determined in this step that the failure determination completion flag is OFF, it is determined that variable mechanism failure determination processing should be performed, and the process proceeds to step S103. Otherwise, this routine is temporarily exited.

  In step S103, an operation command is issued from the ECU 30 to the variable compression ratio mechanism 9 in order to execute the compression ratio forced change control. With this operation command, the variable compression ratio 9 is operated so that the compression ratio ε is changed in accordance with the transition of the failure determination target compression ratio εtf shown in FIG. In this embodiment, the ECU 30 that executes the processing of this step corresponds to the command means in the present invention.

  In this step, when the compression ratio forced change control is executed, the maximum value Pcumax and the minimum value Pcumin of the compression end in-cylinder pressure Pcu are acquired. Specifically, the ECU 30 detects the compression end in-cylinder pressure Pcu for each combustion cycle based on the output signal of the in-cylinder pressure sensor 24. In this routine, if the value of the compression end in-cylinder pressure Pcu detected by the ECU 30 is the maximum detected in the current compression ratio forced change control, the value is updated as the maximum value Pcumax. If the value of the compression end in-cylinder pressure Pcu detected by the ECU 30 is the minimum detected in the current compression ratio forced change control, the value is updated as the minimum value Pcumin. Thereby, acquisition of the maximum value Pcumax and the minimum value Pcumin of the compression end cylinder internal pressure is acquired in this step. When the process in this step is completed, the process proceeds to step S104.

  In step S104, the minimum value Pcumin is subtracted from the maximum value Pcumax acquired in step S103 to calculate the maximum in-cylinder pressure change width ΔPcuw. In this embodiment, the ECU 30 that executes the processes of steps S103 and S104 corresponds to the acquisition means in the present invention.

In step S105, it is determined whether or not the maximum in-cylinder pressure change width ΔPcuw is equal to or smaller than the reference change width ΔBw. If an affirmative determination (ΔPcuw ≦ ΔBw) is made in this step (represented by a broken line in FIG. 2), it is determined that an operation failure has occurred in the variable compression ratio mechanism 9, and the process proceeds to step S106. On the other hand, if a negative determination is made (ΔPcuw> ΔBw) (represented by a solid line in FIG. 2), it is determined that the variable compression ratio mechanism 9 is not operating normally and is operating normally, and the step The process proceeds to S107. In the present embodiment, the ECU 30 that executes the process of step S105 corresponds to the determination means in the present invention.

  In step S106, after the failure flag of the variable compression ratio mechanism 9 is turned ON, the process proceeds to step S108. In step S107, after the failure flag of the variable compression ratio mechanism 9 is turned OFF, the process proceeds to step S108. When the failure flag is turned on, the driver is informed that the variable compression ratio mechanism 9 has failed. For example, it is possible to employ a technique in which an indicator is attached to the cab of the vehicle and the failure lamp of the variable compression ratio mechanism 9 is turned on when the failure flag is ON. In step S108, after the failure determination completion flag is turned ON, this routine is once ended.

  As described above, in this embodiment, since the variable mechanism failure determination process is performed during the idling operation of the internal combustion engine 1, the output performance, the fuel consumption, the exhaust emission, and the like are deteriorated during the execution of the process. You can avoid that.

  Further, when determining the failure of the variable compression ratio mechanism 9, since it is based on the magnitude of the maximum in-cylinder pressure variation ΔPcuw that is the difference between the maximum value Pcumax and the minimum value Pcumin in the compression end in-cylinder pressure Pcu, the in-cylinder pressure sensor Even if the detected value of the compression end in-cylinder pressure Pcu by 24 includes some errors, the influence on the determination accuracy with respect to the operation failure of the variable compression ratio mechanism 9 can be minimized. Accordingly, it is possible to improve the accuracy of the failure determination of the variable compression ratio mechanism 9.

  In the embodiment, the compression end in-cylinder pressure Pcu is adopted as a driven parameter that changes with a change in the compression ratio ε, and the failure determination of the variable compression ratio mechanism 9 is performed based on the change in the compression end in-cylinder pressure Pcu. However, the failure determination can be performed based on a change in the in-cylinder pressure (for example, the in-cylinder pressure in the expansion stroke in each combustion cycle) at other timings.

<Example 2>
Next, a second embodiment for carrying out the present invention will be described. FIG. 4 is a diagram showing a schematic configuration of the internal combustion engine 1 in the present embodiment. The internal combustion engine 1 of the present embodiment has an idle speed control function for maintaining the engine speed NEi (hereinafter referred to as “idle speed”) NEi during idling of the internal combustion engine 1 at the target idle speed NEit that is the target value. Have The target idle speed NEit is determined based on the magnitude of a load by an air conditioner or an alternator (not shown) during idle operation, and is set to a higher speed side as the load is higher.

  As shown, the intake pipe 19 is provided with a bypass pipe 26 that bypasses the throttle valve 7. The bypass pipe 26 is provided with an idle speed control valve (hereinafter referred to as “ISC valve”) 27 capable of adjusting the cross-sectional area of the intake air flowing through the bypass pipe 26 by changing its opening degree. . The ISC valve 27 is connected to the ECU 30 via an electrical wiring, and the opening degree (hereinafter referred to as “ISC opening degree”) ISCA of the ISC valve 27 is controlled by the ECU 30. In the present embodiment, the idle speed control function is realized by the ECU 30 performing feedback control of the ISC opening degree ISCA so that the idle speed NEi during the idling operation is maintained at the target idle speed NEit. In this embodiment, the ECU 30 that performs feedback control of the ISC opening degree ISCA corresponds to the idle speed control means in the present invention. The internal combustion engine 1 according to this embodiment is different from the first embodiment in that the in-cylinder pressure sensor 24 is not provided.

  Also in the variable mechanism failure determination process in the present embodiment, the compression ratio forced change control is executed by a command from the ECU 30 as in the first embodiment. When the compression ratio ε changes, the thermal efficiency of the internal combustion engine 1 changes. Therefore, when the compression ratio ε changes in the compression ratio forced change control, the engine torque changes and the idle speed NEi changes. On the other hand, the ECU 30 feedback-controls the ISC opening ISCA so as to maintain the idle rotation speed NEi at the target idle rotation speed NEit while maintaining the opening of the throttle valve 7 in the closed state. That is, the ISC opening ISCA changes due to the variable compression ratio mechanism 9 changing the compression ratio ε. Therefore, in this embodiment, the failure determination of the variable compression ratio mechanism 9 is performed based on the change in the ISC opening ISCA, not the change in the compression end in-cylinder pressure Pcu at the time of executing the compression ratio forced change control. In this embodiment, the ISC opening ISCA that is controlled to maintain the idle speed NEi at the target idle speed NEit corresponds to the predetermined driven parameter in the present invention.

  FIG. 5 is a time chart showing the transition of the failure determination target compression ratio εtf and the transition of the ISC opening ISCA in the variable mechanism failure determination processing in the present embodiment. The upper row represents the transition of the failure determination target compression ratio εtf, and the lower row represents the transition of the ISC opening ISCA. Note that the same reference numerals as those in FIG. 2 are synonymous with those in FIG.

  The lower solid line is the transition of the ISC opening degree ISCA when there is no operation failure in the variable compression ratio mechanism 9. When the actual compression ratio ε increases in accordance with the transition of the failure determination target compression ratio εtf, the ISC opening ISCA is controlled in the closing direction. As a result, when the intake air amount decreases, the increase in the idle speed NEi is suppressed, and the idle speed NEi is maintained in the vicinity of the target idle speed NEit. On the other hand, when the actual compression ratio ε decreases in accordance with the transition of the failure determination target compression ratio εtf, the ISC opening ISCA is controlled in the opening direction. As a result, the decrease in the idle speed NEi is suppressed by increasing the intake air amount, and the idle speed NEi is maintained in the vicinity of the target idle speed NEit.

  However, as indicated by the broken line in the figure, when the operation failure occurs in the variable compression ratio mechanism 9, the ISC opening degree ISCA is compared with the case where no operation failure occurs (solid line in the figure). Less change. Therefore, in this embodiment, the difference (hereinafter referred to as “maximum ISC opening change width”) ΔISCAw between the maximum value ISCAmax and the minimum value ISCAmin in the ISC opening ISCA when the compression ratio forced change control is performed is obtained. Then, when the maximum ISC opening change width ΔISCAw is equal to or smaller than the second reference change width ΔBw2, it is determined that an operation failure has occurred in the variable compression ratio mechanism 9.

  The second reference change width ΔBw2 is a threshold value for determining whether an operation failure has occurred in the variable compression ratio mechanism 9, and the actual compression ratio ε is normal in accordance with the transition of the failure determination target compression ratio εtf. Is set to a value lower than the maximum ISC opening change width ΔISCAw. The second reference change width ΔBw2 is set according to the transition of the failure determination target compression ratio εtf, similarly to the reference change width ΔBw in the first embodiment. In this embodiment, the maximum ISC opening change width ΔISCAw corresponds to the maximum change width in the present invention. Further, the second reference change width ΔBw2 corresponds to the reference change width in the present invention.

  FIG. 6 is a flowchart showing a control routine according to the variable mechanism failure determination process of the present embodiment. This control routine is a routine stored in advance in the ROM of the ECU 30. Further, this routine is periodically executed by the ECU 30. In this routine, the processing steps with the same reference numerals as those in FIG. 3 have the same processing contents, and thus the description of those steps is omitted.

In this routine, in step S203, EC is executed to execute the compression ratio forced change control.
An operation command is issued from U30 to the variable compression ratio mechanism 9. By this operation command, the variable compression ratio 9 is operated so that the compression ratio ε changes in accordance with the forced change pattern shown in FIG. In this embodiment, the ECU 30 that executes the processing of this step corresponds to the command means in the present invention.

  Further, in this step, when executing the compression ratio forced change control, the maximum value ISCAmax and the minimum value ISCAmin in the ISC opening ISCA are acquired. Specifically, the ECU 30 stores a control signal for controlling the ISC opening ISCA so as to maintain the idle rotation speed NE at the target idle rotation speed NEit, so that the maximum value ISCAmax of the ISC opening ISCA and The minimum value ISCAmin is acquired. When the process of this step is completed, the process proceeds to step S204.

  In step S204, the minimum value ISCAmin is subtracted from the maximum value ISCAmax acquired in step S203 to calculate the maximum ISC opening change width ΔISCAw. In the present embodiment, the ECU 30 that executes the processing of steps S203 and 204 corresponds to the acquisition means in the present invention.

  In step S205, it is determined whether or not the maximum ISC opening change width ΔISCAw is equal to or smaller than the second reference change width ΔBw2. If an affirmative determination (ΔISCAw ≦ ΔBw2) is made in this step (represented by a broken line in FIG. 5), it is determined that an operation failure has occurred in the variable compression ratio mechanism 9, and the process proceeds to step S106. On the other hand, if a negative determination (ΔISCAw> ΔBw2) is made (represented by a solid line in FIG. 5), it is determined that the variable compression ratio mechanism 9 is not operating normally and is operating normally. The process proceeds to S107. In this embodiment, the ECU 30 that executes the process of step S205 corresponds to the determination means in the present invention.

  As described above, in the variable mechanism failure determination process of the present embodiment, attention is paid to the relationship between the change in the ISC opening ISCA and the change in the compression ratio ε when the compression ratio forced change control is executed. And failure determination of the variable compression ratio mechanism 9 can be accurately performed based on the change in the ISC opening ISCA. Further, in the present embodiment, it is not necessary to install the in-cylinder pressure sensor 24, so that the cost can be reduced, and simplification and simplification of the control content related to the failure determination can be realized.

  The transition of the failure determination target compression ratio εtf shown in FIGS. 2 and 5 is merely an example, and various other patterns may be employed. The transition of the failure determination target compression ratio εtf as the simplest pattern is, for example, a pattern in which the failure determination target compression ratio εtf is increased from the reference compression ratio εid to the maximum value εtfu (for example, time t0 to t1 in FIGS. 2 and 5). Or a pattern in which the failure determination target compression ratio εtf is lowered from the reference compression ratio εid to the minimum value εtfl may be employed. However, as shown in FIGS. 2 and 5, the maximum value εtfu of the failure determination target compression ratio is higher than the reference compression ratio εid, and the minimum value εtfl is lower than the reference compression ratio εid. It is preferable that By doing so, even if an operation failure occurs only in either the increasing direction or the decreasing direction of the compression ratio ε in the variable compression ratio mechanism 9, the failure can be reliably detected.

<Example 3>
Next, a third embodiment for carrying out the present invention will be described. The basic configuration of the internal combustion engine 1 in the present embodiment is the same as that in the first embodiment, and the description thereof is omitted. The variable mechanism failure determination process in this embodiment is characterized in that the control is properly completed within the reference time ΔTMb after the compression ratio forced change control is started. This is because the time during which the idling operation is continued in the internal combustion engine 1 is limited, and it is necessary to reliably determine the failure of the variable compression ratio mechanism 9 during the idling operation. The proper completion of the compression ratio forced change control means that the variable compression ratio ε is changed so as to change the compression ratio ε in accordance with the transition of the failure determination target compression ratio εtf set in advance for failure determination of the variable compression ratio mechanism 9. This means that the operation of the mechanism 9 is performed to the end.

The reference time ΔTMb is a target value for the time required for executing the compression ratio forced change control, and is determined in advance. In this embodiment, the average idle operation duration of the internal combustion engine 1 is obtained, and the reference time ΔTMb is set as a time further shortened by a predetermined time. Thus, by suppressing the time required for the compression ratio forced change control to be within the reference time ΔTMb, reliable execution of the failure determination of the variable compression ratio mechanism 9 during the idling operation is guaranteed. The length of the reference time ΔTMb can be changed as appropriate, but may be set to about 30 (sec), for example.

  As in the first embodiment, the ECU 30 detects the compression end in-cylinder pressure Pcu that changes due to the execution of the compression ratio forced change control based on the output signal of the in-cylinder pressure sensor 24 for each combustion cycle. Here, the number of combustion cycles within the above-described reference time ΔTMb increases as the idling speed NEi of the internal combustion engine 1 increases, and the number of combustion cycles decreases as the idling speed NEi decreases. That is, the higher the idling speed NEi of the internal combustion engine 1, the more times the ECU 30 can acquire the compression end in-cylinder pressure Pcu within the reference time ΔTMb, and the lower the idling speed NEi, the more the compression end in-cylinder pressure within the reference time ΔTMb. The number of times that Pcu can be acquired is reduced.

  Therefore, in this embodiment, when the compression ratio ε is changed in accordance with the transition of the failure determination target compression ratio εtf by executing the compression ratio forced change control, the change amount of the failure determination target compression ratio εtf in each combustion cycle. (Hereinafter referred to as “compression ratio target increment Δεcy”) is changed in accordance with the idle speed NEi.

  FIG. 7 is an explanatory diagram for explaining the compression ratio target increment Δεcy according to the idle speed NEi in the present embodiment. The upper stage shows the transition of the target compression ratio εtf when the idle speed NEi is high and the compression ratio target increment is Δεcy1 (illustrated by L1). Further, the middle stage (illustrated by L2) and the lower stage (illustrated by L3) show the transition of the target compression ratio εtf when the idling speed NEi is low (in this figure, the idling speed NEi at L2 and L3 is equal).

  Symbols Δt1 and Δt2 shown in the figure are required times for each combustion cycle. As described above, in L1, since the idle speed NEi is higher than in L2 and L3, the required time Δt1 for each combustion cycle is shorter than Δt2. Further, the compression ratio target increment in L2 is Δεcy1 common to L1, and the compression ratio target increment in L3 is set to Δεcy2 which is larger than Δεcy1. The symbols εid, εtfu, εtfl, Δε1, and Δε2 are synonymous with those in FIG. Further, in the transition of the failure determination target compression ratio εtf, the total change amounts Σεcy of the target compression ratios in L1 to L3 are all set equal (Σεcy = (Δε1 + Δε2) × 2).

  In L1 in this figure, the time required for executing the compression ratio forced change control is substantially equal to the reference time ΔTMb described above. Hereinafter, L2 and L3 are compared with reference to L1. First, when comparing L1 and L2, the required time for each combustion cycle in L2 is equal (Δεcy1) for both compression ratio target increments Δεcy, despite being longer than the required time in L1 (Δt2> Δt1). . In this case, since the total change amount Σεcy of the target compression ratio in L1 and L2 is equal, the time required for the compression ratio forced change control over L2 exceeds the reference time ΔTMb.

Therefore, in this embodiment, as indicated by L3, when the idle speed NEi is low, the compression ratio target increment Δεcy is increased (Δεcy2) compared to when the idle speed NEi is high. > Δεcy1). Thus, by increasing the compression ratio target increment Δεcy, the required time for the compression ratio forced change control can be kept within the reference time ΔTMb even if the required time for each combustion cycle in L3 is longer than L1. it can.

  In the present embodiment, the compression ratio target increment Δεcy is further increased as the idle speed NEi at the time of executing the compression ratio forced change control is lower. Therefore, even if the idle speed NEi changes depending on the use state of the air conditioner, etc., the compression ratio target increment Δεcy can be set to an appropriate value according to the situation. Therefore, the time required for the compression ratio forced change control can be suppressed within the reference time ΔTMb without depending on the idle speed NEi. Therefore, the failure determination of the variable compression ratio mechanism 9 can be reliably performed while the idling operation of the internal combustion engine 1 is continued.

Here, a method of calculating the compression ratio target increment Δεcy corresponding to the idle speed NEi will be described. In this embodiment, when a variable mechanism failure determination process execution request is issued to the variable compression ratio mechanism 9, for example, when an affirmative determination is made in step S102 in FIG. The amount Δεcy is calculated. Specifically, the ECU 30 detects the current idle speed NEi based on the output signal of the crank position sensor 25. Then, based on the idle speed NEi and the reference time ΔTMb, the number of combustion cycles (hereinafter referred to as “reference combustion cycle number”) Ncy within the reference time ΔTMb is calculated. This reference combustion cycle number Ncy can be calculated by the following equation, for example.
Ncy = NE / (2 × 60) × ΔTMb
However, unit of NE: rpm, unit of ΔTMb: sec

  Then, the compression ratio target increment Δεcy is calculated by dividing the total change amount Σεcy of the target compression ratio by the reference combustion cycle number Ncy. For example, in FIG. 7, the total change amount Σεc of the target compression ratio can be calculated as (Δε1 + Δε2) × 2. In calculating the reference combustion cycle number Ncy, the value of the target idle speed NEit may be adopted instead of the current idle speed NEi.

<Example 4>
Next, a fourth embodiment for carrying out the present invention will be described. The basic configuration of the internal combustion engine 1 in the present embodiment is the same as that in the first embodiment, and the description thereof is omitted. In the variable mechanism failure determination processing according to Examples 1 to 3, the presence or absence of an operation failure of the variable compression ratio mechanism 9 was determined. However, even when such an operational failure has not occurred, there may be a responsive abnormality. Here, the responsiveness abnormality of the variable compression ratio mechanism 9 refers to the actual change speed of the compression ratio when the change speed of the compression ratio required when the variable compression ratio mechanism 9 changes the compression ratio ε is high to some extent. This can be understood as a phenomenon in which Vεr (hereinafter referred to as “actual change speed”) cannot be increased to the required speed. As a situation where this responsiveness abnormality occurs, there can be exemplified a situation where a malfunction occurs in the motor 9f, the worm 9e rotated by the motor 9f, etc., and the actual change speed Vεr cannot be increased so much.

  When such a responsive abnormality occurs in the variable compression ratio mechanism 9, the compression ratio ε cannot be changed to the target value by a desired time. Therefore, in the variable mechanism failure determination process of the present embodiment, it is also determined whether or not there is an abnormality in the responsiveness of the variable compression ratio mechanism 9 during the idling operation of the internal combustion engine 1.

The basic part of the variable mechanism failure determination process in the present embodiment is common to the first embodiment or the second embodiment. That is, the compression ratio forced change control is executed during the idling operation of the internal combustion engine 1, and the compression ratio ε in accordance with the transition of the failure determination target compression ratio εtf preset for failure determination of the variable compression ratio mechanism 9. The variable compression ratio mechanism 9 is actuated to change. Then, the ECU 30 acquires the maximum in-cylinder pressure change width ΔPcuw from the change in the compression end in-cylinder pressure Pcu at the time of execution of the compression ratio forced change control.

  On the other hand, in the variable mechanism failure determination processing according to the present embodiment, the speed at which the failure determination target compression ratio εtf changes, that is, the amount of change in the failure determination target compression ratio εtf per unit time (hereinafter referred to as “target change speed”). ) Two types of operation commands that differ only in Vεtf are issued to the variable compression ratio mechanism 9. Note that these two types of operation commands are not issued simultaneously from the ECU 30, and any order may be used first.

  Here, the transition of the failure determination target compression ratio εtf applied to the operation command with the lower target change speed Vεtf is referred to as a “low speed change pattern”, and the target compression for failure determination applied to the operation command with the higher target change speed Vεtf is used. The transition of the ratio εtf is referred to as a “high-speed change pattern”. FIG. 8 is a time chart showing the transition of the failure determination target compression ratio εtf and the transition of the compression end in-cylinder pressure Pcu in the variable mechanism failure determination processing in the present embodiment. (A) is a time chart in a low-speed change pattern. (B) is a time chart in a high-speed change pattern.

  In each figure, the solid line drawn in the upper row represents the transition of the failure determination target compression ratio εtf, and the broken line represents the transition of the actual compression ratio ε when the variable compression ratio mechanism 9 has a responsive abnormality. Note that the actual transition of the compression ratio ε substantially coincides with the solid line when no responsiveness abnormality has occurred in the variable compression ratio mechanism 9. Further, the solid line drawn in the lower stage represents the transition of the compression end cylinder pressure Pcu when the variable compression ratio mechanism 9 has no responsiveness abnormality, and the broken line represents the case where the variable compression ratio mechanism 9 has responsiveness abnormality. The transition of the compression end cylinder internal pressure Pcu at. Note that the same reference numerals as those in FIG. 2 are synonymous and will not be described.

  First, the transition of the failure determination target compression ratio εtf in each figure, that is, the low speed change pattern (a) and the high speed change pattern (b) will be described. As shown in the figure, both patterns are an inverted V-shaped transition pattern that reverses from the rising state to the falling state at the boundary of the maximum value εtfu of the failure determination target compression ratio εtf, and from the falling state at the boundary of the minimum value εtfl. It is formed in combination with a V-shaped transition pattern that reverses to the rising state.

  Here, in the low-speed change pattern in (a), an inverted V-shaped transition pattern is formed at time ta1 and ta3, and a V-shaped transition pattern is formed at time ta2. On the other hand, in the high-speed change pattern in (b), an inverted V-shaped transition pattern is formed at time tb1 and tb3, and a V-shaped transition pattern is formed at time tb2. Note that the only difference between the low speed change pattern and the high speed change pattern is the target change speed Vεtf of the target compression ratio for failure determination, and therefore the total change amount Σεcy of the target compression ratio in both is equal.

  Hereinafter, the influence of the difference in the target change speed Vεtf in the failure determination target compression ratio on the maximum in-cylinder pressure change width ΔPcuw will be described. First, a case where the compression ratio forced change control is performed in accordance with the low speed change pattern of (a) will be described. In the low speed change pattern, the target change speed Vεtf of the target compression ratio for failure determination is low. Therefore, even if responsiveness abnormality occurs in the variable compression ratio mechanism 9, the actual change speed Vεr can be substantially matched with the target change speed Vεtf. Therefore, when the compression ratio forced change control is performed in accordance with the low speed change pattern, the actual compression ratio ε is used for failure determination without causing a response delay even if the responsiveness abnormality occurs in the variable compression ratio mechanism 9. It is possible to follow the transition of the target compression ratio εtf.

As a result, as shown in the lower part of (a), the difference in presence or absence of responsiveness abnormality in the variable compression ratio mechanism 9 hardly affects the fluctuation range of the compression end in-cylinder pressure Pcu. Here, when the compression ratio forced change control is performed in accordance with the low speed change pattern, and the maximum in-cylinder pressure change width ΔPcuw when no responsiveness abnormality occurs is ΔPcuw1, and the responsiveness abnormality occurs The maximum in-cylinder pressure change width ΔPcuw is ΔPcuw2. Then, there is little or no difference between ΔPcuw1 and ΔPcuw2. In this figure, ΔPcuw2 is larger than the reference change width ΔBw.

  Next, the case where the compression ratio forced change control is performed in accordance with the high speed change pattern (b) will be described. Here, at the times tb1 and tb3, the failure determination target compression ratio εtf reverses from the rising state to the falling state at the boundary of the maximum value εtfu, so the rotation direction of the shaft portion 9a in the variable compression ratio mechanism 9 is switched. . Similarly, at time tb2, the failure determination target compression ratio εtf is reversed from the lowered state to the raised state at the minimum value εtfl, so that the rotation direction of the shaft portion 9a in the variable compression ratio mechanism 9 is switched.

  Here, if the responsiveness abnormality does not occur in the variable compression ratio mechanism 9, even if the target change speed Vεtf of the target compression ratio for failure determination is high, the actual change speed Vεr can be substantially matched with the target change speed Vεtf. Accordingly, in this case, there is almost no difference in the maximum in-cylinder pressure change width ΔPcuw between the high speed change pattern and the low speed change pattern. If the maximum in-cylinder pressure change width ΔPcuw3 is ΔPcuw3 when the compression ratio forced change control is performed in accordance with the high-speed change pattern and no responsiveness abnormality occurs, this ΔPcuw3 is substantially equal to the above-described ΔPcuw1. Or, it is not excessively smaller than at least ΔPcuw1.

  On the other hand, when responsiveness abnormality occurs in the variable compression ratio mechanism 9, if the target change speed Vεtf is set high as in the high-speed change pattern, the actual change speed Vεr can be increased to the target change speed Vεtf. Can not. Therefore, the actual compression ratio ε cannot be increased to the maximum value εtfu by the time tb1 and tb3. In addition, the actual compression ratio ε cannot be reduced to the minimum value εtfl by time tb2.

  As a result, even if the total change amount Σεcy of the target compression ratio in the high-speed change pattern and the low-speed change pattern is equal, the maximum in-cylinder pressure change width when the compression ratio forced change control is performed according to the high-speed change pattern. ΔPcuw will decrease. Accordingly, in the case where the compression ratio forced change control is performed in accordance with the high-speed change pattern and the maximum in-cylinder pressure change width ΔPcuw when the responsiveness abnormality occurs is ΔPcuw4, this ΔPcuw4 is compared with the above-described ΔPcuw2. And become too small. In this figure, ΔPcuw4 is lower than the reference change width ΔBw.

  In this embodiment, when the compression ratio forcible change control is executed based on two types of operation commands that differ only in the target change speed Vεtf, if the responsiveness abnormality does not occur in the variable compression ratio mechanism 9, each compression ratio forcing It was noted that the difference in the maximum in-cylinder pressure change width ΔPcuw acquired in the change control is small, and that the difference in the maximum in-cylinder pressure change width ΔPcuw is large if the responsiveness abnormality occurs. Then, based on the difference between the respective maximum in-cylinder pressure change widths ΔPcuw, it is determined whether or not a responsive abnormality has occurred in the variable compression ratio mechanism 9. Hereinafter, the control content executed by the ECU 30 for determining whether or not the responsiveness abnormality has occurred in the variable compression ratio mechanism 9 will be described.

[First control]
First, the first control in the present embodiment will be described. In this first control, the ECU 30 executes the compression ratio forced change control in accordance with the low speed change pattern and the high speed change pattern, and the low speed change change width ΔPcuwl, which is the maximum in-cylinder pressure change width ΔPcuw, and the high speed change change. The width ΔPcuwh is acquired. Here, the magnitude relationship between the two is that, as described above, the change width ΔPcuwh at the time of high speed change is equal to or less than the change width ΔPcuwl at the time of low speed change.

  In this control, if the difference between the change width ΔPcuwl at the time of low speed change and the change width ΔPcuwh at the time of high speed change (hereinafter referred to as “maximum in-cylinder pressure change width difference ΔPcuwd”) is small, a response abnormality occurs in the variable compression ratio mechanism 9. If the maximum in-cylinder pressure change width difference ΔPcuwd is large, it is determined that a responsiveness abnormality has occurred. Specifically, when the maximum in-cylinder pressure change width difference ΔPcuwd is larger than a preset reference difference ΔPcuwdb, it is determined that a responsiveness abnormality has occurred. This reference difference ΔPcuwdb can be experimentally obtained in advance for determination of responsiveness abnormality in the variable compression ratio mechanism 9.

  Here, in order to improve the determination accuracy of the responsiveness abnormality in the variable compression ratio mechanism 9, the difference between the target change speed Vεtf (hereinafter referred to as “target change speed difference ΔVεtf”) between the low speed change pattern and the high speed change pattern is considered. Good. That is, when the responsiveness abnormality occurs in the variable compression ratio mechanism 9, it is considered that the maximum in-cylinder pressure change width difference ΔPcuwd becomes larger when the target change speed difference ΔVεtf is larger than when the target change speed difference ΔVεtf is small. Therefore, in this control, the magnitude of the reference difference ΔPcuwdb is set according to the target change speed difference ΔVεtf. More specifically, the reference difference ΔPcuwdb can be set to a larger value as the target change speed difference ΔVεtf is larger. According to this, the determination accuracy of the responsiveness abnormality in the variable compression ratio mechanism 9 can be improved. In this embodiment, the reference difference ΔPcuwdb corresponds to the predetermined reference difference in the present invention.

[Second control]
Next, the second control for determining whether or not the responsiveness abnormality has occurred in the variable compression ratio mechanism 9 will be described with reference to FIG. In this control, the change width ΔPcuwl at low speed change (corresponding to ΔPcuw2 in FIG. 8A) is larger than the reference change width ΔBw, and the change width ΔPcuwh at high speed change (in FIG. 8B). In the case where (corresponding to ΔPcuw4) is equal to or smaller than the reference change width ΔBw, it is determined that the variable compression ratio mechanism 9 is not malfunctioning but has a responsiveness abnormality.

  Note that the target change speed Vεtf in the low-speed change pattern and the target change speed Vεtf in the high-speed change pattern are obtained in advance through experiments or the like. In particular, the target change speed Vεtf in the high-speed change pattern is such that the change width ΔPcuwh at the time of high-speed change is surely larger than the reference change width ΔBw if the variable compression ratio mechanism 9 has no responsive abnormality, and the responsive abnormality is present. If it occurs, the optimum value may be obtained in relation to the reference change width ΔBw so that the change width ΔPcuwh at the time of high-speed change is surely equal to or less than the reference change width ΔBw.

  According to this control, when the compression ratio forced change control is executed in accordance with the low speed change pattern, the variable compression ratio mechanism 9 has the change width ΔPcuwl (ΔPcuw2) at the time of low speed change larger than the reference change width ΔBw. It can be determined that no operation failure has occurred. In this case, even when the compression ratio forced change control is executed in accordance with the high speed change pattern, if it can be confirmed that the change width ΔPcuwh (ΔPcuw4) during the high speed change is larger than the reference change width ΔBw, the variable compression ratio mechanism 9 It can be determined that no operational failure or responsiveness abnormality has occurred. On the other hand, when the change width ΔPcuwh at the time of high-speed change is equal to or less than the reference change width ΔBw, it can be determined that the responsiveness abnormality has occurred although no operation failure has occurred.

  In this embodiment, whether or not there is an abnormality in the responsiveness in the variable compression ratio mechanism 9 is determined based on the difference in the maximum in-cylinder pressure change width ΔPcuw when the compression ratio forced change control is executed based on the two types of operation commands. Although the example to do was demonstrated, the said determination can be performed based on the difference of largest ISC opening variation | change_quantity (DELTA) ISCAw.

Further, the transition of the failure determination target compression ratio εtf in the present embodiment is formed to include both the reverse V-shaped transition pattern and the V-shaped transition pattern described above, but includes only one of the patterns. It may be formed by.

1 is a diagram illustrating a schematic configuration of an internal combustion engine in Embodiment 1. FIG. 6 is a time chart showing a transition of a failure determination target compression ratio εtf and a transition of a compression end in-cylinder pressure Pcu in the variable mechanism failure determination processing in the first embodiment. 3 is a flowchart illustrating a control routine according to variable mechanism failure determination processing according to the first embodiment. FIG. 3 is a diagram illustrating a schematic configuration of an internal combustion engine in a second embodiment. 10 is a time chart showing a transition of a failure determination target compression ratio εtf and a transition of an ISC opening degree ISCA in a variable mechanism failure determination process in Embodiment 2. 6 is a flowchart illustrating a control routine according to variable mechanism failure determination processing according to the second embodiment. FIG. 10 is an explanatory diagram for explaining a compression ratio target increment Δεcy according to an idle speed NEi in the third embodiment. 10 is a time chart showing a transition of a failure determination target compression ratio εtf and a transition of a compression end in-cylinder pressure Pcu in a variable mechanism failure determination process according to a fourth embodiment. (A) is the figure which showed the compression end cylinder internal pressure Pcu in a low speed change pattern. (B) is the figure which showed transition of the compression end cylinder pressure Pcu in a high-speed change pattern.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Cylinder block 4 ... Crankcase 5 ... Cylinder head 7 ... Throttle valve 9 ... Variable compression ratio mechanism 15 ... Piston 17 ... Fuel injection valve 19 .. Intake pipe 21 .. Exhaust pipe 23 .. Crank position sensor 24 .. In-cylinder pressure sensor 26 .. Bypass pipe 27 .. ISC valve 30 .. ECU

Claims (8)

A variable compression ratio mechanism capable of changing the mechanical compression ratio of the internal combustion engine according to the operating state;
A command for issuing an operation command to the variable compression ratio mechanism in order to change the mechanical compression ratio in accordance with the transition of the target compression ratio set for determining the failure of the variable compression ratio mechanism during idle operation of the internal combustion engine. Means,
Obtaining means for obtaining a value of a predetermined driven parameter that changes due to the variable compression ratio mechanism changing the mechanical compression ratio based on the operation command;
The variable when the maximum change width, which is the difference between the maximum value and the minimum value of the driven parameter acquired by the acquisition means, is equal to or less than a predetermined reference change width set according to the transition of the target compression ratio. Determining means for determining that the compression ratio mechanism is malfunctioning;
A failure determination apparatus for a variable compression ratio mechanism, comprising:   2. The variable compression ratio mechanism according to claim 1, wherein the command unit sets a change amount of the target compression ratio for each combustion cycle of the internal combustion engine based on an engine speed during the idle operation. Failure determination device.   The command means sets the amount of change in the target compression ratio for each combustion cycle of the internal combustion engine as a larger value when the engine speed during the idling operation is low than when the engine speed is high. The failure determination device for a variable compression ratio mechanism according to claim 2. The transition of the target compression ratio is a predetermined reverse V-shaped transition pattern that reverses from the rising state to the falling state at the maximum value of the target compression ratio, and the rising state from the falling state at the minimum value of the target compression ratio When the command means is formed to include at least one of the predetermined V-shaped transition patterns that are reversed, the command means outputs two types of operation commands that differ only in the speed at which the target compression ratio changes. Take out to the variable compression ratio mechanism,
The determination means determines whether a responsiveness abnormality has occurred in the variable compression ratio mechanism based on the difference in the maximum change width acquired by the acquisition means when each operation command is issued. The failure determination device for a variable compression ratio mechanism according to any one of claims 1 to 3.   The determination means responds to the variable compression ratio mechanism when the difference in the maximum change width is larger than a predetermined reference difference set according to a difference in speed at which the target compression ratio changes in each operation command. The failure determination device for a variable compression ratio mechanism according to claim 4, wherein it is determined that a sexual abnormality has occurred.   The determination means is configured such that the maximum change width acquired when an operation command with a lower speed at which the target compression ratio changes is issued is greater than the reference change width, and the target compression is performed. When the maximum change width acquired when an operation command having a higher speed at which the ratio changes is issued is equal to or less than the reference change amount, the variable compression ratio mechanism has an responsive abnormality rather than an operation failure. The failure determination device for a variable compression ratio mechanism according to claim 4, wherein the failure determination device according to claim 4 is determined. A cylinder pressure sensor for detecting a cylinder pressure of the internal combustion engine;
The in-cylinder pressure detected by the in-cylinder pressure sensor when the variable compression ratio mechanism is operating based on the operation command, the driven parameter is any one of claims 1 to 6. The failure determination device of the variable compression ratio mechanism according to the item. An idle speed control valve, and an idle speed control means for maintaining the engine speed at the target idle speed by controlling the opening of the idle speed control valve,
2. The driven parameter is an opening degree of the idle speed control valve controlled by the idle speed control means when the variable compression ratio mechanism is operating based on the operation command. 7. The failure determination device for a variable compression ratio mechanism according to any one of items 1 to 6.

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