JP2007177792A - Internal combustion engine equipped with compression ratio change mechanism and method for controlling internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To operate an internal combustion engine while avoiding the occurrence of knocking when compression ratio is in a high compression ratio condition and is fixed. <P>SOLUTION: In this internal combustion engine provided with a mechanism for changing compression ratio, driving timing of a suction and exhaust valve is changed into the direction in which temperature of suction air compressed in a combustion chamber is reduced when detecting that compression ratio is in a high compression ratio condition and is fixed. Alternatively, suction air temperature and cooling water temperature may be reduced or speed reduction ratio of a shifting gear unit may be switched to a larger value to increase operation rotation speed of the internal combustion engine. Thus, knocking does not occur easily, and an operation while avoiding the occurrence of knocking is performed even when compression ratio is in the high compression ratio condition and is fixed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for changing the compression ratio of an internal combustion engine, and more particularly to a technique for appropriately operating an internal combustion engine even when a function for changing the compression ratio fails.

  The internal combustion engine has an excellent characteristic of being able to output relatively large power despite being small in size, so it can be used as a power source for various transportation engines such as automobiles, ships, airplanes, or as a power source for various stationary devices. As widely used. These internal combustion engines have an operating principle of combusting an air-fuel mixture compressed in a combustion chamber, converting the combustion pressure generated at this time into mechanical work, and taking it out as power.

  In such an internal combustion engine, a technique has been proposed in which the compression ratio of the air-fuel mixture can be changed according to operating conditions in order to achieve both improvement in conversion efficiency (thermal efficiency) into mechanical work and increase in maximum output. . If the compression ratio is changed according to the operating conditions, setting a low compression ratio under high load conditions will ensure a sufficient maximum output, while setting a high compression ratio under low and medium load conditions will improve thermal efficiency. It becomes possible. In general, the higher the compression ratio, the more likely abnormal combustion called knocking tends to occur. Therefore, an internal combustion engine that can change the compression ratio operates while changing the ignition timing as the compression ratio changes. Has been. That is, under operating conditions where the compression ratio is set to a high compression ratio, the ignition timing is usually set to be retarded as compared with operating conditions set to a low compression ratio.

  In this way, in an internal combustion engine that is operated while changing the compression ratio and ignition timing according to the operating conditions, if a failure occurs in the mechanism for changing the compression ratio, and it is stuck in a high compression ratio state In this case, only the ignition timing is changed according to the change of the operating condition. Therefore, knocking may occur depending on the operating conditions. In consideration of these points, the following technique has been proposed (Patent Document 1).

  The proposed technology is designed to avoid knocking by stopping supercharging when the compression ratio is fixed at a high compression ratio in an internal combustion engine that can change the compression ratio and also perform supercharging. It is.

Japanese Utility Model Publication No. 1-93340

  However, when the compression ratio is fixed in a high compression ratio state, knocking is likely to occur, not only in an internal combustion engine that performs supercharging, but can generally occur in an internal combustion engine that can change the compression ratio. . Therefore, in all internal combustion engines that can change the compression ratio regardless of whether or not supercharging is performed, the development of a technology that can reliably prevent the occurrence of knocking when the compression ratio is fixed in a high compression ratio state. It has been requested.

  The present invention has been made to solve such problems in the prior art, and in an internal combustion engine capable of changing the compression ratio, even when the compression ratio is fixed in a high compression ratio state, occurrence of knocking is reliably avoided. However, an object is to provide a technique capable of operating an internal combustion engine.

In order to solve at least a part of the problems described above, the first internal combustion engine of the present invention employs the following configuration. That is,
An internal combustion engine that outputs power by compressing intake air sucked from an intake valve and combusting it with fuel,
An intake valve driving means for driving the intake valve, comprising a characteristic changing mechanism capable of changing the valve opening characteristic of the intake valve;
A compression ratio changing mechanism capable of changing a compression ratio as an index representing the degree of compression of the intake air at least between a high compression ratio state and a low compression ratio state;
A high compression ratio fixation detecting means for detecting a failure state where the compression ratio changing mechanism is fixed in the high compression ratio state;
And a characteristic control means for performing control to change the valve opening characteristic of the intake valve in a direction to lower the temperature of the intake air compressed in the combustion chamber when the failure state is detected. And

The first control method of the present invention corresponding to the internal combustion engine is as follows.
An internal combustion engine capable of changing the compression ratio representing the degree of compression of the intake air sucked into the combustion chamber via the intake valve into at least a high compression ratio state and a low compression ratio state, and compressing the intake air and burning it together with fuel An engine control method,
Detecting that the compression ratio is a failure state that cannot be switched from the high compression ratio state,
The gist is to change the valve opening characteristic of the intake valve in a direction to lower the temperature of the intake air compressed in the combustion chamber when the failure state is detected.

  In the first internal combustion engine and the first control method of the present invention, when the compression ratio becomes a non-switchable state from the high compression ratio state, the temperature of the intake air compressed in the combustion chamber decreases. Change and control the opening characteristics of the intake valve in the direction. Generally, if the temperature of the intake air compressed in the combustion chamber decreases, abnormal combustion called knocking tends to be difficult to occur. Therefore, if the temperature at which the intake air is compressed is lowered in this way, even when a failure such as the compression ratio changing mechanism sticking in a high compression ratio state occurs, it is possible to avoid the occurrence of knocking. . The valve opening characteristics that can be changed in such control include valve opening start timing, valve opening completion timing, valve closing start timing, valve closing completion timing, valve opening speed, valve closing speed, and lift amount at valve opening. Can think of at least one of

  In such an internal combustion engine, the valve opening characteristics of the intake valve are changed so that the actual compression ratio, which is the compression ratio obtained by the volume of the combustion chamber at the start of compression of intake air and the volume of the combustion chamber at the end of compression, becomes smaller. It is good also as controlling. For example, the actual compression ratio can be reduced by greatly increasing the closing timing of the intake valve or by greatly delaying the closing timing.

  If the actual compression ratio is reduced, the temperature rise due to the compression of the intake air in the combustion chamber is reduced. For this reason, even when the compression ratio cannot be switched from the high compression ratio state, the occurrence of knocking can be suppressed.

  Or, in the direction from the compression top dead center to the intake bottom dead center during the intake stroke, the valve opening characteristics of the intake valve, such as the timing of the on-off valve and the on-off valve speed, are shortened. It is good also as controlling.

  If the intake valve is closed during the period from the compression top dead center to the intake bottom dead center during the intake stroke, the gas in the combustion chamber (such as air or air-fuel mixture) expands adiabatically and falls in temperature. Absorbs heat from the wall. Since the heat absorbed in this way is originally discharged from the internal combustion engine by cooling water or the like, the fact that such heat is absorbed by the air in the combustion chamber is the same as warming the intake air. As a result, knocking is more likely to occur. In other words, if a failure state is detected such that the compression ratio change mechanism is stuck in a high compression ratio state, if the valve opening characteristic is controlled in a direction to shorten the valve closing period of the intake valve during the intake stroke, knocking will occur. Can be suppressed.

  Alternatively, when a failure state in which the compression ratio changing mechanism is stuck in a high compression ratio state is detected, the residual amount of the combustion gas generated by the combustion of the air-fuel mixture in the combustion chamber decreases. In addition, the valve opening characteristic of at least one of the intake valve and the exhaust valve may be changed and controlled.

  Since the combustion gas is at a high temperature, if the combustion gas remains, the intake air that has flowed into the combustion chamber is heated by the combustion gas and the temperature rises, and knocking easily occurs accordingly. Therefore, if the amount of combustion gas remaining in the combustion chamber is reduced by controlling the valve opening characteristics of at least one of the intake valve and the exhaust valve, for example, the on-off valve timing, the temperature rise of the intake air is suppressed. In other words, knocking can be avoided even in a failure state in which the compression ratio changing mechanism is stuck in a high compression ratio state.

  Here, the residual amount of the combustion gas in the combustion chamber is such that the opening characteristic of at least one of the intake valve and the exhaust valve, such as an on-off valve, is shortened so that the period during which the intake valve and the exhaust valve are simultaneously opened is shortened. By changing and controlling the time, it can be easily reduced.

  Alternatively, if at least one of the operation of driving the exhaust valve for a short time during the intake stroke or the drive of the intake valve for a short time during the exhaust stroke is performed, by suppressing such an operation, However, it is possible to reliably reduce the residual amount of combustion gas.

In order to solve at least a part of the problems described above, the second internal combustion engine of the present invention employs the following configuration. That is, the second internal combustion engine of the present invention is an internal combustion engine that outputs power by compressing intake air sucked from an intake passage via an intake valve in a combustion chamber and combusting it with fuel,
A compression ratio changing mechanism capable of changing a compression ratio as an index representing the degree of compression of the intake air at least between a high compression ratio state and a low compression ratio state;
High compression ratio fixation detecting means for detecting a failure state where the compression ratio changing mechanism is fixed in the high compression ratio state;
And a control means for performing a predetermined control for lowering the temperature of the intake air sucked from the intake passage when the failure state is detected.

The second control method of the present invention corresponding to the internal combustion engine is as follows.
In a control method for an internal combustion engine, the compression ratio representing the degree of compression of intake air sucked into the combustion chamber can be changed at least between a high compression ratio state and a low compression ratio state, and the intake air is compressed and burned together with fuel. There,
Detecting that the compression ratio is a failure state that cannot be switched from the high compression ratio state,
When the failure state is detected, the gist is to perform a predetermined control for reducing the temperature of the intake air sucked from the intake passage.

  In the second internal combustion engine and the second control method of the present invention, when the compression ratio cannot be switched from the high compression ratio state, the predetermined control for lowering the temperature of the intake air flowing into the combustion chamber is performed. It is also good to do. If the temperature of the air flowing in from the intake passage decreases, the temperature after compression also decreases accordingly. As a result, it is possible to avoid the occurrence of knocking due to a failure state in which the compression ratio cannot be switched from the high compression ratio state.

  Here, when a part of the combustion gas is recirculated from the exhaust passage into the intake passage, the air flowing into the combustion chamber is heated by the recirculated combustion gas. Therefore, the temperature of the air flowing into the combustion chamber can be lowered only by suppressing the recirculation amount of the combustion gas.

  Alternatively, when the intake air is heated in the intake passage, the temperature of the air flowing into the combustion chamber can be easily reduced by suppressing the heating.

  Further, the internal combustion engine includes a first fuel injection valve that injects fuel into the intake passage and a second fuel injection valve that injects fuel into the combustion chamber. When the fuel is supplied by driving the valve, the following may be performed. That is, when a failure state is detected such that the compression ratio changing mechanism is stuck in a high compression ratio state, fuel is supplied in a state where the drive ratio of the second fuel injection valve to the first fuel injection valve is increased. It's also good.

  The fuel injected from the first fuel injection valve into the intake passage flows into the combustion chamber while gradually evaporating after almost all the fuel has once adhered to the inner surface of the intake passage. In contrast, some of the fuel injected from the second fuel injection valve into the combustion chamber adheres to the wall surface of the combustion chamber, but most of the fuel is vaporized in the combustion chamber without adhering to the wall surface, and the mixture is Form. In the latter case, most of the heat of vaporization absorbed when the fuel is vaporized is supplied from the air in the combustion chamber. On the other hand, in the former case, the air is supplied from the wall surface of the intake passage. Since the intake passage is warmed by the heat from the combustion chamber, after all, when fuel is injected into the intake passage, the vaporization heat of the fuel is supplied from the combustion chamber. As described above, since the heat supplied from the combustion chamber is originally discharged from the internal combustion engine by cooling water or the like, the fuel vaporized by such heat flows into the combustion chamber. It is almost equivalent to warming the intake air. In other words, when fuel is injected into the combustion chamber, it is almost equivalent to cooling the intake air by the heat of vaporization of the fuel. For this reason, if the compression ratio changing mechanism becomes in a failure state such as being stuck in a high compression ratio state, if the ratio of the fuel supplied from the second fuel injection valve is increased, the air flowing into the combustion chamber is reduced. The occurrence of knocking can be suppressed by the same effect as that of cooling.

In order to solve at least a part of the problems described above, the third internal combustion engine of the present invention employs the following configuration. That is, the third internal combustion engine of the present invention is
An internal combustion engine that outputs power by compressing an air-fuel mixture in a combustion chamber and burning the compressed air-fuel mixture,
A compression ratio changing mechanism capable of changing a compression ratio, which is an index representing the degree of compression of the air-fuel mixture, into at least a high compression ratio state and a low compression ratio state;
High compression ratio fixation detecting means for detecting a failure state where the compression ratio changing mechanism is fixed in the high compression ratio state;
And a combustion chamber temperature lowering means for lowering the wall surface temperature of the combustion chamber when the failure state is detected.

The third control method of the present invention corresponding to the internal combustion engine is as follows.
In a control method for an internal combustion engine, the compression ratio representing the degree of compression of intake air sucked into the combustion chamber can be changed at least between a high compression ratio state and a low compression ratio state, and the intake air is compressed and burned together with fuel. There,
Detecting that the compression ratio is a failure state that cannot be switched from the high compression ratio state,
The gist is to perform control to lower the wall surface temperature of the combustion chamber when the failure state is detected.

  In the third internal combustion engine and the third control method of the present invention, when the compression ratio becomes a failure state that cannot be switched from the high compression ratio state, control is performed to lower the wall surface temperature of the combustion chamber.

  Knocking is thought to occur because the air-fuel mixture is compressed near the combustion chamber wall surface and self-ignites, and if the temperature of the combustion chamber wall surface is lowered, the air-fuel mixture near the wall surface is cooled and knocking occurs. It is considered possible to suppress this. Therefore, even when the compression ratio changing mechanism is in a failure state in which the compression ratio changing mechanism is fixed in a high compression ratio state, it is possible to avoid the occurrence of knocking.

  Here, the wall surface temperature of the combustion chamber can be easily reduced by setting the temperature of the cooling water to be low, and hence the occurrence of knocking can be easily avoided.

  Some internal combustion engines set the cooling water temperature higher when the internal combustion engine is in a predetermined operating condition in order to improve thermal efficiency. If the cooling water temperature is raised, the viscosity of the lubricating oil is lowered, so that the friction loss is reduced, and as a result, the thermal efficiency can be improved. However, increasing the coolant temperature tends to be disadvantageous to knocking, that is, knocking is likely to occur. Therefore, in a failure state in which the compression ratio changing mechanism is stuck in the high compression ratio state, it is possible to avoid the occurrence of knocking if the high water temperature control is suppressed.

In order to solve at least a part of the problems described above, the fourth internal combustion engine of the present invention employs the following configuration. That is, the fourth internal combustion engine of the present invention is
An internal combustion engine that compresses a mixture of air and fuel in a combustion chamber and outputs power generated when the mixture is combusted from an output shaft,
Power transmission means for transmitting the power output from the internal combustion engine to a drive shaft that drives the load of the internal combustion engine while reducing the rotational speed of the output shaft at a predetermined ratio;
A compression ratio changing mechanism capable of changing a compression ratio as an index representing the degree of compression of the air-fuel mixture at least between a high compression ratio state and a low compression ratio state;
High compression ratio fixation detecting means for detecting a failure state where the compression ratio changing mechanism is fixed in the high compression ratio state;
A reduction ratio control means for controlling the operation of the power transmission means in a direction in which a reduction ratio as a ratio of a rotational speed of the output shaft to the drive shaft is increased when the failure state is detected; The gist.

Further, the fourth control method of the present invention corresponding to the internal combustion engine is as follows.
The compression ratio representing the degree of compression of the intake air sucked into the combustion chamber can be changed at least between a high compression ratio state and a low compression ratio state, and the intake air is compressed and combusted with fuel, and the power generated by the combustion Is a control method for an internal combustion engine that outputs power from a power shaft,
Detecting that the compression ratio is a failure state that cannot be switched from the high compression ratio state,
While transmitting the power output from the internal combustion engine to the drive shaft that drives the load of the internal combustion engine while reducing the rotational speed of the output shaft at a predetermined ratio,
When the failure state is detected, the gist is to perform control so that the reduction ratio, which is the ratio of the rotation speed of the output shaft to the drive shaft, is increased.

  In the fourth internal combustion engine and the fourth control method of the present invention, when the compression ratio is changed from the high compression ratio state to a failure state that does not require switching, the reduction ratio setting is changed to a large value. I do.

  If the reduction ratio setting is changed to a large value, the internal combustion engine is operated at a higher rotational speed if the rotational speed of the drive shaft is constant. As the rotational speed increases, the time for inhaling air into the combustion chamber is shortened accordingly, so the amount of intake air sucked into the combustion chamber in each intake stroke decreases, and as a result, the occurrence of knocking is suppressed. Will be. For this reason, when the compression ratio changing mechanism is fixed in a high compression ratio state, it is possible to avoid the occurrence of knocking by changing the setting of the reduction ratio to a large value.

In order to more clearly describe the operation and effect of the present invention, examples of the present invention will be described in the following order.
A. Device configuration:
B. Engine control:
C. Variation:
C-1. First modification:
C-2. Second modification:
C-3. Third modification:
C-4. Fourth modification:

A. Device configuration:
FIG. 1 is an explanatory diagram conceptually showing the configuration of the engine 10 of this embodiment provided with a variable compression ratio mechanism. As shown in the figure, the engine 10 is roughly composed of a cylinder head 20, a cylinder block ASSY 30, a main moving ASSY 40, an intake passage 50, an exhaust passage 58, an EGR passage 70, an engine control unit (hereinafter referred to as “engine control unit”). ECU) 60 and the like.

  The cylinder block ASSY 30 includes an upper block 31 to which the cylinder head 20 is attached and a lower block 32 in which the main moving ASSY 40 is accommodated. Further, an actuator 33 is provided between the upper block 31 and the lower block 32, and by driving the actuator 33, the upper block 31 can be moved in the vertical direction with respect to the lower block 32. ing. A cylindrical cylinder 34 is formed inside the upper block 31, and the outer surface of the cylinder 34 is cooled by cooling water. The temperature of the cooling water can be detected by a water temperature sensor 64 provided in the upper block 31.

  The main moving assembly 40 includes a piston 41 provided inside the cylinder 34, a crankshaft 43 that rotates inside the lower block 32, a connecting rod 42 that connects the piston 41 to the crankshaft 43, and the like. The piston 41, the connecting rod 42, and the crankshaft 43 constitute a so-called crank mechanism. As the crankshaft 43 rotates, the piston 41 slides up and down in the cylinder 34 as the crankshaft 43 rotates. As a result, the crankshaft 43 rotates in the lower block 32.

  When the cylinder head 20 is attached to the cylinder block ASSY 30, a combustion chamber is formed in a portion surrounded by the lower surface side (side contacting the upper block 31) of the cylinder head 20, the cylinder 34 and the piston 41. Accordingly, if the upper block 31 is moved upward using the actuator 33, the cylinder head 20 is also moved upward in accordance with this, and the volume in the combustion chamber increases, so that the compression ratio can be lowered. Conversely, if the cylinder head 20 is moved downward together with the upper block 31, the volume in the combustion chamber can be reduced and the compression ratio can be increased.

  The compression ratio can be detected using a compression ratio sensor 63 provided in the lower block 32. In this embodiment, a stroke sensor is used as the compression ratio sensor 63, and the compression ratio is detected by detecting the relative position of the upper block 31 with respect to the lower block 32. Of course, the compression ratio is not limited to such a method, and can be detected by other methods. For example, a pressure sensor may be provided in the cylinder head 20 and the compression ratio may be detected based on the pressure in the combustion chamber.

  The cylinder head 20 is formed with an intake port 23 for taking air into the combustion chamber and an exhaust port 24 for discharging exhaust gas from the combustion chamber. The intake valve 21 is provided, and the exhaust valve 22 is provided at a portion where the exhaust port 24 opens into the combustion chamber. The intake valve 21 and the exhaust valve 22 are driven by electric actuators 73 and 74, respectively. The electric actuators 73 and 74 are configured by laminating a plurality of electrostrictive elements such as piezo elements, and deform at an extremely high speed according to the applied voltage. Under the control of the ECU 60, by applying a driving voltage to the electric actuators 73 and 74 at an appropriate timing in accordance with the movement of the piston to open and close the intake valve 21 and the exhaust valve 22, air is sucked into the combustion chamber, or Exhaust gas can be discharged from the combustion chamber. The cylinder head 20 is also provided with a spark plug 27 for sparking and igniting the air-fuel mixture formed in the combustion chamber.

  An intake passage 50 for guiding outside air to the cylinder head 20 is connected to the intake port 23 of the cylinder head 20, and an air cleaner 51 is provided at the upstream end of the intake passage 50. The engine 10 of this embodiment is a so-called four-cylinder engine and includes four combustion chambers. The intake passages 50 of the respective combustion chambers are joined by a surge tank 54. The air sucked into the combustion chamber is removed of foreign matters such as dust by the air cleaner 51, and then distributed to the intake passage 50 of each combustion chamber by the surge tank 54 and flows into each combustion chamber via the intake port 23. To do. An intake heater 56 is provided in the intake passage 50 branched from the surge tank 54 for each combustion chamber. When the engine 10 is not warmed, the intake heater 56 is energized under the control of the ECU 60. The air sucked into each combustion chamber can be warmed.

  A throttle valve 52 is provided in the intake passage 50 upstream of the surge tank 54, and the amount of air flowing into the combustion chamber is controlled by controlling the opening degree of the throttle valve 52 using the electric actuator 53. be able to. The flow rate of air passing through the throttle valve 52 can be measured by the air flow sensor 57. Each combustion chamber is provided with two fuel injection valves 26 and 55. The fuel injection valve 26 provided in the cylinder head 20 directly injects fuel into the combustion chamber, and the fuel injection valve 55 provided in the intake passage 50 injects fuel from each intake passage 50 toward the intake port 23. Spray. The fuel injected from the fuel injection valve 26 or the fuel injection valve 55 in this way is vaporized in each combustion chamber, and forms a mixture of fuel and air in the combustion chamber.

  An exhaust passage 58 is connected to the exhaust port 24 of each combustion chamber, and the exhaust gas discharged from the combustion chamber is guided to the outside by the exhaust passage 58 and released. Further, the exhaust passage 58 and the intake passage 50 are connected by an EGR passage 70, and a part of the exhaust gas flowing through the exhaust passage 58 is recirculated into the intake passage 50 through the EGR passage 70 and sucked. It flows into the combustion chamber together with air. An EGR valve 72 is provided in the middle of the EGR passage 70. By adjusting the opening degree of the EGR valve, the flow rate of the recirculated exhaust gas (EGR gas) can be controlled.

  The ECU 60 is a microcomputer in which a ROM, a RAM, an input / output circuit, and the like are connected to each other via a bus with a central processing unit (hereinafter referred to as CPU) as a center. The ECU 60 reads necessary information from a crank angle sensor 61 provided on the crankshaft 43, an accelerator opening sensor 62 built in the accelerator pedal, an air flow sensor 57, and the like, and the electric actuators 73 and 74, a fuel injection valve, etc. 26, 55, the spark plug 27, etc. are driven at an appropriate timing to burn the air-fuel mixture in the combustion chamber to generate power. The driving of the electric actuator 53 is controlled to adjust the intake air amount, the actuator 33 is driven to switch the compression ratio, and the energization amount of the intake heater 56 is controlled based on the output of the water temperature sensor 64. The process is also controlled by the ECU 60.

  In the engine 10 having the above-described configuration, it is possible that a failure occurs in the mechanism for switching the compression ratio including the actuator 33, and the engine 10 is stuck in a high compression ratio state. As described above, abnormal combustion called knocking tends to occur more easily as the compression ratio becomes higher, and when knocking occurs, specific noise that gives the driver a feeling of strangeness is generated. For this reason, if the engine 10 is operated while being fixed in a high compression ratio state, the driver may feel uncomfortable due to the occurrence of knocking. In order to avoid such a situation, the engine 10 performs the following engine control.

B. Engine control:
FIG. 2 is a flowchart showing a flow for controlling the operation of the engine 10 in this embodiment. Hereinafter, it demonstrates according to a flowchart.

  When starting the engine control routine, the ECU 60 first detects the engine operating conditions (step S100). As operating conditions, engine speed Ne, accelerator opening θac, cooling water temperature, and the like are detected. The engine speed Ne can be calculated from the output of the crank angle sensor 61, the accelerator opening degree θac can be detected by using the accelerator opening degree sensor 62, and the coolant temperature can be detected by the water temperature sensor 64.

  Next, a process of setting the compression ratio according to the operating condition of the engine 10 is performed (step S102). In the ROM of the ECU 60, an appropriate compression ratio corresponding to the operating conditions is stored in advance in the form of a map having the engine speed Ne and the accelerator opening θac as parameters. FIG. 3 is an explanatory diagram conceptually showing a state in which an appropriate compression ratio is stored in the form of a map in the ROM. In step S102, by referring to such a map, after reading the compression ratio appropriately set according to the operating conditions, the actuator 33 is driven to set the compression ratio of the engine 10.

  The ECU 60 detects the compression ratio following the setting of the compression ratio (step S104). As described with reference to FIG. 1, the lower block 32 of the engine 10 is provided with the compression ratio sensor 63, and the ECU 60 can detect the compression ratio based on the output of this sensor.

  Subsequently, by comparing the compression ratio set in step S102 with the compression ratio detected in step S104, it is confirmed that the mechanism for changing the compression ratio is not fixed in the high compression ratio state (step S106). ). In other words, when the set compression ratio is a low compression ratio and the detected compression ratio is a high compression ratio, it is determined that the mechanism for changing the compression ratio is stuck in the high compression ratio state. can do. If it is determined that such sticking has not occurred (step S106: no), the operation mode is set to the normal operation mode (step S108), and it is determined that the sticking is in a high compression ratio state. (Step S106: yes), the knock avoidance mode is set (step S110). As will be described in detail later, in the engine control of the present embodiment, by performing the subsequent control according to the operation mode set in this way, even when the compression ratio changing mechanism is stuck in the high compression ratio state, the occurrence of knocking is avoided. It is possible to do.

  When the operation mode is set in this way, intake air heating control is started (step S112). This is control for promoting warm-up of the engine by heating the intake air using the intake heater 56 provided in the intake passage 50 when the engine 10 is not warmed, such as immediately after startup. If the intake air is heated, vaporization of the fuel is promoted, so that the air-fuel mixture can be stably burned even when the engine is not warm. In addition, if the intake air is heated, the compression start temperature of the air-fuel mixture becomes higher. From this point, combustion of the air-fuel mixture is promoted and the engine can be warmed up quickly.

  In step S112, the engine warm-up state is determined based on the coolant temperature detected by the water temperature sensor 64, and a process for controlling the energization amount of the intake heater according to the engine warm-up state is performed. In the ROM of the ECU 60, the energization amount with respect to the cooling water temperature is stored in the form of a map. FIG. 4 is an explanatory diagram conceptually showing such a map. A solid line in the figure indicates a map that is referred to when the vehicle is operating in the normal operation mode, and a broken line in the figure indicates a map that is referred to when the vehicle is operated in the knock avoidance mode. As shown in the figure, during operation in the knock avoidance mode, even when the coolant temperature is low, the energization amount is greatly suppressed compared to the normal operation state even when the intake heater is not energized or energized. As described above, since the compression start temperature of the air-fuel mixture increases when the intake air is heated, there is a concern that knocking may occur when the engine 10 is fixed in a high compression ratio state. Therefore, in such a case, it is possible to avoid the occurrence of knocking by prohibiting or suppressing heating by the intake heater.

  The ECU 60 performs EGR control following the intake air heating control (step S114). The EGR control refers to control for returning a part of the exhaust gas flowing in the exhaust passage 58 into the combustion chamber. If a part of the exhaust gas is recirculated by performing the EGR control, the concentration of nitrogen oxide called NOx contained in the exhaust gas can be lowered. If the exhaust gas recirculation amount (EGR gas amount) is too large, the air-fuel mixture will not be stably combusted. For this reason, the EGR gas amount has an optimum value corresponding to the operating conditions, and the EGR valve 72 has an optimum value for the opening degree. In step S114, a process for setting the opening degree of the EGR valve 72 to an optimum opening degree according to the operating condition of the engine 10 is performed. Specifically, in the ROM of the ECU 60, as shown in FIG. 5, the optimum opening degree of the EGR valve 72 corresponding to the operating condition is in the form of a map using the engine speed and the accelerator opening as parameters. The opening degree of the EGR valve 72 is set to an optimum opening degree by referring to the map.

  Here, as shown in FIG. 5, in the ECU 60, a map that is referred to during operation in the normal operation mode and a map that is referred to during operation in the knock avoidance mode are stored as different maps. . The map in the knock avoidance mode is set so that the opening degree close to that in the map in the normal operation mode or the EGR valve 72 is fully closed depending on the operation conditions. That is, during the operation in the knock avoidance mode, the EGR valve opening degree is closed and the operation is performed in a slight manner as compared with the operation in the normal operation mode. Thus, in the knock avoidance mode, if the opening of the EGR valve is set to be closed, the occurrence of knocking can be avoided for the same reason as when the intake air heating control is suppressed. That is, since the exhaust gas has a higher temperature than the intake air, when a part of the exhaust gas is recirculated to the intake passage 50, the intake air is heated by the high-temperature exhaust gas, and the compression start temperature of the mixture becomes high. Become. Therefore, when stuck in a high compression ratio state, the compression start temperature of the air-fuel mixture can be suppressed and knocking can be avoided by setting the opening of the EGR valve to be closed. It becomes.

  Following EGR control, drive control of the intake and exhaust valves is performed (step S116). In this control, the electric actuators 73 and 74 are driven at an appropriate timing to open and close the intake valve 21 and the exhaust valve 22 at an appropriate timing in accordance with the rotation of the crankshaft 43. FIG. 6 is an explanatory diagram showing the timing for opening and closing the intake valve 132 and the exhaust valve 134 in accordance with the rotation of the crankshaft 43, and FIG. 6 (a) shows the opening and closing in the normal operation mode. FIG. 6B shows the opening / closing timing in the knock avoidance mode. In the figure, TDC indicates the position where the piston is fully raised, that is, the timing at the top dead center, and BDC indicates the position where the piston is fully lowered, that is, the bottom dead center. The timing at the point is shown. In FIG. 6, the white arrow indicates the period during which the intake valve 21 is open, and the arrow with fine hatching indicates the period during which the exhaust valve 22 is open. Note that the asterisk represents the timing at which a spark is blown from the spark plug 27 and the air-fuel mixture is ignited. In step S116, the intake valve 21 and the exhaust valve 22 are driven at the timing shown in FIG. 6A in the normal operation mode, and shown in FIG. 6B in the knock avoidance mode. Control to drive the electric actuators 73 and 74 is performed so as to be driven at the timing. In this embodiment, the drive timing of the intake valve 21 and the exhaust valve 22 is realized by changing the drive timing of the electric actuators 73 and 74. However, the operation timing of the intake and exhaust valves 21 and 22 is determined by the cam phase. You may implement | achieve by using the mechanism to adjust and controlling the phase of a cam with a hydraulic actuator etc. It is not always necessary to be able to adjust the opening / closing valve timings of both the intake and exhaust valves 21 and 22, and any configuration that can adjust the opening timing or closing timing of either one can be adopted.

  Here, as shown in FIG. 6, the opening / closing timing in the knock avoidance mode is largely different from the opening / closing timing in the normal operation mode in the following two points. First, in the normal operation mode shown in FIG. 6 (a), there is an overlap period (a period in which the intake valve 21 and the exhaust valve 22 are simultaneously open near TDC). In the knock avoidance mode shown in FIG. 6B, no overlap period is provided. Secondly, in the normal operation mode, the intake valve 21 closes near the BDC, whereas in the knock avoidance mode, the intake valve 21 closes at a timing when the BDC is significantly exceeded. Even if the compression ratio change mechanism is stuck in a high compression ratio state, if the knock avoidance mode is set, if the intake and exhaust valves are opened and closed at such timing, the occurrence of knocking can be avoided for the following reasons. Can do.

  First, in the overlap period, the exhaust valve 22 and the intake valve 21 are both open, so that the exhaust gas flows back into the intake passage 50 due to the pressure difference between the exhaust passage 58 and the intake passage 50. The exhaust gas flowing backward in this way flows into the combustion chamber together with the intake air in the subsequent intake stroke, so that it becomes the same as recirculating a part of the exhaust gas after all. Thus, the phenomenon in which the exhaust gas recirculates through the combustion chamber is called internal EGR. On the other hand, recirculation of exhaust gas from the exhaust passage 58 to the intake passage 50 via the EGR passage 70 provided outside the combustion chamber may be referred to as external EGR. The internal EGR also increases the temperature of the air-fuel mixture in the same manner as the above-mentioned external EGR, and thus acts in a disadvantageous direction against the occurrence of knocking. Therefore, if the overlap period is shortened or the overlap period is abolished as illustrated in FIG. 6B, the occurrence of knocking is avoided even when the compression ratio changing mechanism is fixed in a high compression ratio state. It becomes possible.

  Further, while the intake valve 21 is open, even if the piston 41 rises, the air-fuel mixture escapes from the combustion chamber into the intake passage, so that the air-fuel mixture is not actually compressed. That is, even if the piston 41 starts to rise after passing the BDC, the compression of the air-fuel mixture is actually started in the combustion chamber after the intake valve 21 is closed. For this reason, even when the compression ratio changing mechanism is fixed in a high compression ratio state, it is possible to avoid the occurrence of knocking if the valve closing timing of the intake valve 21 is delayed more than BDC.

  Although the description has been given here assuming that the closing timing of the intake valve 21 is delayed from the BDC, the same effect can be obtained by advancing the closing timing from the BDC. That is, if the intake valve 21 is closed while the piston 41 is descending, the pressure in the combustion chamber decreases as the piston 41 is lowered (as the volume in the combustion chamber increases) between the closing time and BDC. To do. When the piston 41 starts to rise, the pressure recovers as the volume in the combustion chamber decreases. When the piston 41 reaches the same volume as when the intake valve 21 is closed, the pressure returns to the pressure before the decrease. That is, even if the piston 41 is raised, the pressure in the combustion chamber only recovers until the volume becomes the same as the volume in the combustion chamber when the intake valve 21 is closed, and the actual mixture is Compression will be initiated by a subsequent piston lift. From this, when the compression ratio changing mechanism is fixed in a high compression ratio state, it is possible to avoid the occurrence of knocking by making the closing timing of the intake valve 21 significantly earlier than the BDC.

  The ECU 60 starts fuel injection control following the intake / exhaust drive control (step S118). As described with reference to FIG. 1, the engine 10 is provided with the fuel injection valve 26 that can inject fuel directly into the combustion chamber and the fuel injection valve 55 that injects fuel into the intake passage 50. If the fuel is directly injected into the combustion chamber, the fuel spray is unevenly distributed in the combustion chamber to form a portion with a high fuel concentration (low air-fuel ratio) and a portion with a low fuel concentration (high air-fuel ratio). . If an air-fuel mixture having an appropriate air-fuel ratio distribution is formed in the combustion chamber, the overall fuel amount can be saved and the thermal efficiency of the engine can be improved. The method of directly injecting fuel into the combustion chamber is sometimes called in-cylinder injection.

  On the other hand, if fuel is injected into the intake passage, the injected fuel is sucked into the combustion chamber while being mixed with air while being vaporized here, so that a uniform air-fuel mixture in which fuel and air are sufficiently mixed is burned. Can be formed indoors. When a high output is required, it is desirable to form a uniform mixture in this way. The method of injecting fuel into the intake passage is sometimes called port injection.

  The engine 10 employs an appropriate fuel injection system in accordance with operating conditions so that an air-fuel mixture can be appropriately formed by taking advantage of such in-cylinder injection or port injection characteristics. In the ROM of the ECU 60, an appropriate fuel injection method is stored in the form of a map according to the engine operating conditions. FIG. 7 is an explanatory diagram conceptually showing such a map. As shown in the figure, the ROM stores a map for the normal operation mode and a map for the knock avoidance mode, and each map is referred to according to the set mode. The map referred to in the normal operation mode is set to perform port injection when the engine speed is high or the accelerator opening is high, and to perform in-cylinder injection under other operating conditions. In this way, sufficient output can be ensured by performing port injection at high rotation and high load, and engine thermal efficiency can be improved by performing in-cylinder injection at low rotation and low load. On the other hand, in the knock avoidance mode, the ratio of in-cylinder injection is increased. In the illustration of FIG. 7, the knock avoidance mode is set to perform in-cylinder injection in the entire operation region, but it is sufficient if the ratio of in-cylinder injection is higher than in the normal operation mode, for example, It is possible to extend the in-cylinder injection region or inject a part of the fuel into the cylinder during port injection. Thus, the occurrence of knocking can be suppressed by increasing the ratio of in-cylinder injection. Hereinafter, this reason will be briefly described.

  When fuel is injected into the intake passage (port injection), the fuel temporarily adheres to the inner surface of the intake passage and then flows into the combustion chamber while gradually evaporating. During the vaporization, the fuel absorbs vaporization heat for vaporization from the wall surface of the intake passage. In contrast, when fuel is injected into the combustion chamber (in-cylinder injection), some fuel adheres to the wall surface in the combustion chamber, but most of the fuel is vaporized in the combustion chamber without adhering to the wall surface. To form a mixture. The heat of vaporization at this time is absorbed from the air flowing into the combustion chamber and the combustion gas remaining without being discharged from the combustion chamber. In other words, in the port injection, the heat of vaporization taken from the wall surface of the intake passage flows into the combustion chamber together with the vaporized fuel, whereas in the case of in-cylinder injection, it is vaporized in the combustion chamber without touching the wall surface. Heat does not flow into the combustion chamber. For this reason, when in-cylinder injection is performed, the temperature of the air-fuel mixture in the combustion chamber becomes lower than in the case of port injection. This can be considered simply because, when in-cylinder injection is performed, the fuel vaporizes in the combustion chamber, so that the air-fuel mixture temperature is lowered by the amount that the air is cooled by the heat of vaporization. Knocking can also be thought of as a phenomenon in which the air-fuel mixture self-ignites due to the rise in temperature when the air-fuel mixture is compressed, so if the in-cylinder injection is performed to lower the air-fuel mixture temperature, the occurrence of knocking can be suppressed. Is possible.

  In step S118 of FIG. 2, an appropriate fuel injection method corresponding to the operating conditions is selected by referring to the map shown in FIG. Then, after calculating the fuel injection amount based on the intake air amount detected by the air flow sensor 57, the fuel injection valve 55 or the fuel injection valve 26 is driven according to the selected injection method. By doing so, an air-fuel mixture having an appropriate air-fuel ratio is formed in the combustion chamber.

  The ECU 60 performs ignition control following the fuel injection control (step S120). In the ignition control, a process of igniting the air-fuel mixture compressed in the combustion chamber is performed by blowing a spark from the spark plug 27 at an appropriate timing according to the operating conditions. An appropriate ignition timing is stored in advance in the form of a map in the ROM in the ECU 60 in accordance with the engine operating conditions. FIG. 8 is an explanatory diagram illustrating such a map. In the ignition control, the ECU 60 reads the ignition timing corresponding to the operating condition by referring to such a map, and then performs a process of flying a spark from the spark plug 27 at an appropriate timing. As a result, the air-fuel mixture burns in the combustion chamber and the pressure in the combustion chamber rises, and this pressure is converted into mechanical work by the crank mechanism and output to the outside as power.

  Next, the ECU 60 determines whether or not the driver has instructed to stop the engine 10 (step S122), and if it is determined that the driver has instructed to stop the engine 10 (step S122). S122: yes), the engine control routine shown in FIG. 2 is terminated. Conversely, when it is not instructed to stop the engine 10 (step S122: no), the process returns to step S100 and the above-described series of processing is repeated.

  As described above, the engine 10 of the present embodiment detects whether or not the mechanism for changing the compression ratio is fixed in the high compression ratio state, and when the mechanism is fixed in the high compression ratio state, Control is performed in the knock avoidance mode. In the knock avoidance mode, intake air heating control and EGR control are suppressed as compared with the normal operation mode. In addition, the opening and closing timings of the intake and exhaust valves are also controlled so that the overlap period is shortened and the internal EGR is reduced, and the closing timing of the intake valves is changed in a direction away from the BDC to reduce the actual compression ratio. Is done. In addition, the fuel injection method is also changed so that the ratio of in-cylinder injection increases. Each of these changes has an effect of suppressing the occurrence of knocking. Therefore, even when the compression ratio of the engine 10 is fixed in a high compression ratio state, the occurrence of knocking is controlled by controlling the engine in the knock avoidance mode. Can be avoided. These controls may be performed in combination of two or more controls as described above, but may be performed independently.

C. Variation:
Various modifications exist in the above-described embodiment. Hereinafter, these modified examples will be briefly described.

C-1. First modification:
In the knock avoidance mode, the opening / closing timing of the intake valve 21 may be changed as follows. That is, in the knock avoidance mode, it may be set to a timing at which the period during which the intake valve 21 is closed during the piston lowering of the intake stroke is shorter than in the normal operation mode.

  FIG. 9 is an explanatory diagram showing the opening / closing timing of the intake valve in the first modified example. 9A shows the opening / closing timing of the intake valve 21 in the normal operation mode, and FIG. 9B shows the opening / closing timing in the knock avoidance mode. In the normal operation mode shown in FIG. 9A, the intake valve 21 is opened after the piston 41 is slightly lowered from the TDC, and is further closed before the piston 41 reaches the BDC. Therefore, during the period indicated by the broken line in FIG. 9A, the intake valve 21 is closed even though the piston 41 is lowered. In this way, when the piston 41 descends while the intake valve 21 is closed, the air or residual gas in the combustion chamber expands adiabatically and removes heat from the wall surface of the combustion chamber, so that it is just like warming the air in the combustion chamber. As a result, knocking is likely to occur. On the other hand, when the intake valve 21 is opened and closed at the timing shown in FIG. 9B, the valve is opened near the TDC and closed near the BDC, and the piston 41 remains closed. The descent period is greatly shortened and knocking is less likely to occur. Therefore, in the knock avoidance mode, the occurrence of knocking can be avoided by changing the opening / closing timing of the intake valve 21 from the one shown in FIG. 9A to the one shown in FIG. 9B. It becomes possible to do.

  In the illustration of FIG. 9A, the state where the piston 41 descends while the intake valve 21 is closed occurs at two timings near TDC and BDC. In the illustration of FIG. 9B, At any timing, such a state is suppressed. However, the period during which the piston 41 descends while the intake valve 21 is closed may be shortened as a whole, and the opening / closing timing of the intake valve 21 is not limited to the example shown in FIG.

C-2. Second modification:
In the above-described embodiment, in the knock avoidance mode, the internal EGR is reduced by shortening the overlap period in which the intake valve 21 and the exhaust valve 22 are simultaneously opened in the vicinity of the intake TDC. However, in order to carry out internal EGR more aggressively in some engines, the exhaust valve is opened for a short period during the intake stroke, or the intake valve is opened for a short period during the exhaust stroke. There is something to do. In such an engine, in the knock avoidance mode, the intake / exhaust valve may be driven as follows.

  FIG. 10 is an explanatory view showing the movement of the valve for positively performing the internal EGR. FIG. 10 shows how the valve lift changes with the crank angle. The solid line shows the movement of the intake valve 21 and the broken line shows the movement of the exhaust valve 22. FIG. 10A shows a case where the intake valve 21 is opened during the exhaust stroke, and FIG. 10B shows a case where the exhaust valve 22 is opened during the intake stroke. For example, the case of FIG. 10A will be described. In the exhaust stroke, the exhaust valve 22 is lifted to exhaust the exhaust gas in the combustion chamber to the exhaust passage 58. At this time, if the intake valve 21 is opened only for a short period, the exhaust gas flows backward from the combustion chamber to the intake passage 50. The exhaust gas flowing backward in this way is sucked into the combustion chamber as EGR gas in the next intake stroke.

  In the case of FIG. 10B, the intake valve 21 is lifted during the intake stroke, and air flows into the combustion chamber from the intake passage 50. At this time, if the exhaust valve 22 is opened for a short period of time, the exhaust gas in the exhaust passage 58 is pushed by the back pressure, passes through the combustion chamber, and flows back into the intake passage 50. In the subsequent intake stroke, the exhaust gas flowing backward in this way flows into the combustion chamber as EGR gas.

  As shown in FIG. 10, if the exhaust valve is opened only for a short period during the intake stroke, or if the intake valve is opened only for a short period during the exhaust stroke, the internal EGR can be actively performed. In an engine that performs such control, in the knock avoidance mode, the opening amount of the exhaust valve during the intake stroke may be suppressed, or the opening amount of the intake valve during the exhaust stroke may be suppressed. . Here, suppressing the valve opening amount includes not only reducing the lift amount and shortening the valve opening period but also pausing the valve opening itself. If the valve opening amount is suppressed in this way, the internal EGR amount is reduced, so that occurrence of knocking can be avoided.

C-3. Third modification:
In the knock avoidance mode, the occurrence of knocking may be suppressed by controlling the cooling water temperature. Hereinafter, such a third modification will be described.

  FIG. 11 is an explanatory view conceptually showing the structure of a mechanism (cooling system) that controls the cooling water temperature when the engine 10 is viewed from the upper surface side (from the upper side of the cylinder head 20). The engine 10 is a so-called four-cylinder engine, and four cylinders 34 are provided. “# 1”, “# 2”, “# 3”, and “# 4” shown in the figure represent these four cylinders. The cooling system of the engine 10 has a water pump 80 that pumps cooling water to cool the cylinder 34 and the combustion chamber, a radiator 82 that radiates heat from the high-temperature cooling water, and the cylinder 34 and the combustion chamber. A cooling passage 84 for guiding the cooling water to the radiator 82, a recirculation passage 86 for returning the cooling water exiting the radiator 82 to the water pump 80, and a bypass passage for bypassing the radiator 82 when heat dissipation of the cooling water is unnecessary 88, a switching valve 90 for switching the bypass passage 88 under the control of the ECU 60, and the like.

  The ECU 60 can control the cooling water temperature by controlling the switching valve 90 while observing the output of the water temperature sensor 64 provided in the upper block 31. Hereinafter, this control will be described with reference to FIG.

  FIG. 11A shows a state where the engine 10 is operated while the cooling water is dissipating heat with the radiator 82. The arrows indicated by solid lines in the figure represent the flow of cooling water. When the cooling water is guided to the radiator 82, the switching valve 90 is switched to the “open” state under the control of the ECU 60. The cooling water is pumped by the water pump 80 to cool the inside of the engine, is guided to the radiator 82 via the cooling passage 84, passes through the reflux passage 86 and the switching valve 90, and is pumped again to the inside of the engine by the water pump 80. The

  When the cooling water temperature is not so high and the radiator 82 does not need to dissipate heat, the ECU 60 switches the switching valve to the “closed” state. Thus, the cooling water is supplied to the water pump 80 not from the reflux passage 86 but from the bypass passage 88. That is, the cooling water that has passed through the engine is supplied to the water pump 80 through the bypass passage 88 and flows by bypassing the radiator 82. If the engine is operated while bypassing the radiator 82 in this way, the cooling water temperature gradually increases. When the cooling water temperature rises, if the switching valve 90 is opened again so that the cooling water passes through the radiator 82, the cooling water temperature gradually decreases.

  As is apparent from the above description, the cooling water temperature of the engine 10 can be controlled to an arbitrary temperature by switching the switching valve 90 while detecting the cooling water temperature with the water temperature sensor 64. When the engine is operated at a relatively low load, if the cooling water temperature is controlled to be higher, the friction loss that lowers the viscosity of the lubricating oil decreases, so it is possible to improve the thermal efficiency of the engine. is there.

  In general, knocking is considered to be strongly influenced by the wall surface temperature of the combustion chamber. This is because the phenomenon in which the air-fuel mixture is compressed near the wall surface of the combustion chamber and self-ignited is a phenomenon called knocking, and it is considered that knocking is difficult to occur because the self-ignition is suppressed when the wall surface temperature is lowered. . For this reason, in the engine that can control the cooling water temperature, in the knock avoidance mode, if the cooling water temperature is controlled to a lower value, or the cooling water temperature is set to a higher value in order to improve thermal efficiency. If this is suppressed, occurrence of knocking can be avoided.

C-4. Fourth modification:
Alternatively, in the knock avoidance mode, the occurrence of knocking may be suppressed by switching the transmission (transmission) setting to a direction in which the reduction ratio is increased. Hereinafter, such a fourth modification will be described.

  FIG. 12 is an explanatory diagram conceptually showing a state in which the transmission 100 is connected to the engine 10. The transmission 100 receives power from the crankshaft 43 of the engine 10 and outputs it from a drive shaft 143 connected to a load. At this time, the rotational speed of the crankshaft 43 is shifted to a rotational speed corresponding to the reduction ratio of the transmission 100 and output from the drive shaft 143. Here, the reduction ratio is defined by a value obtained by dividing the rotational speed of the crankshaft 43 by the rotational speed of the drive shaft 143. Note that the transmission 100 shown in FIG. 12 is a so-called continuously variable transmission that can continuously change the reduction ratio, but of course, it may be a transmission that can be changed in stages to a plurality of reduction ratios. .

  Generally, if the speed reduction ratio is increased, the rotational speed of the engine 10 is increased, and if the rotational speed is increased, the time for sucking air into the combustion chamber is shortened, so that the intake air amount is reduced. Since knocking is a phenomenon in which the air-fuel mixture is compressed and self-ignited, knocking is less likely to occur if the amount of intake air decreases. Therefore, in the engine 10 of the fourth modified example, the reduction ratio of the transmission 100 may be switched to a large value in the knock avoidance mode. In this way, even when the compression ratio is fixed in a high compression ratio state, it is possible to effectively suppress the occurrence of knocking.

  Although various embodiments have been described above, the present invention is not limited to the above-described embodiments, and can be implemented in various modes without departing from the scope of the invention. For example, in the above embodiment, the timing of the opening / closing valve of the intake valve or the exhaust valve is changed and controlled. However, it is also possible to control the compression ratio by adjusting the lift amount of the intake valve or the exhaust valve. . Alternatively, the valve opening and closing speeds can be controlled.

It is explanatory drawing which showed notionally the structure of the engine of the present Example provided with the compression ratio variable mechanism. It is the flowchart which showed the flow which controls operation | movement of an engine in a present Example. It is explanatory drawing which represented notably that a suitable compression ratio was memorize | stored in the format of the map in ROM. It is explanatory drawing which showed notionally the map in which the energization amount of the intake heater was set according to the cooling water temperature. It is explanatory drawing which showed notionally the map in which the opening degree like an EGR valve was set according to the driving | running condition. It is explanatory drawing which showed the timing which opens and closes an intake valve and an exhaust valve according to rotation of a crankshaft. It is explanatory drawing which showed notionally the map in which the fuel injection system was set according to the driving | running condition. It is explanatory drawing which showed notionally the map in which the ignition timing was set according to the driving | running condition. It is explanatory drawing which showed the opening / closing timing of the intake valve in a 1st modification. It is explanatory drawing which showed the motion of the valve | bulb for performing internal EGR positively. It is explanatory drawing which showed notionally the structure for controlling a cooling water temperature. It is explanatory drawing which showed notionally the mode that the transmission was connected to the engine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Engine 20 ... Cylinder head 21 ... Intake valve 22 ... Exhaust valve 23 ... Intake port 24 ... Exhaust port 26 ... Fuel injection valve 27 ... Spark plug 30 ... Cylinder block ASSY
31 ... Upper block 32 ... Lower block 33 ... Actuator 34 ... Cylinder 40 ... Main moving ASSY
DESCRIPTION OF SYMBOLS 41 ... Piston 42 ... Connecting rod 43 ... Crankshaft 50 ... Intake passage 51 ... Air cleaner 52 ... Throttle valve 53 ... Electric actuator 54 ... Surge tank 55 ... Fuel injection valve 56 ... Intake heater 57 ... Air flow sensor 58 ... Exhaust passage 61 ... Crank Angle sensor 62 ... Accelerator opening sensor 63 ... Compression ratio sensor 64 ... Water temperature sensor 73 ... Electric actuator 74 ... Electric actuator 80 ... Water pump 82 ... Radiator 84 ... Cooling passage 86 ... Reflux passage 88 ... Bypass passage 90 ... Switch valve 100 ... Transmission 132 ... Intake valve 134 ... Exhaust valve 143 ... Drive shaft

Claims (20)

An internal combustion engine that outputs power by compressing intake air sucked from an intake valve and combusting it with fuel,
An intake valve driving means for driving the intake valve, comprising a characteristic changing mechanism capable of changing the valve opening characteristic of the intake valve;
A compression ratio changing mechanism capable of changing a compression ratio as an index representing the degree of compression of the intake air at least between a high compression ratio state and a low compression ratio state;
A high compression ratio fixation detecting means for detecting a failure state where the compression ratio changing mechanism is fixed in the high compression ratio state;
An internal combustion engine comprising: characteristic control means for performing control to change a valve opening characteristic of the intake valve in a direction to lower the temperature of intake air compressed in the combustion chamber when the failure state is detected. The internal combustion engine according to claim 1,
The changeable valve opening characteristic is at least one of valve opening start timing, valve opening completion timing, valve closing start timing, valve closing completion timing, valve opening speed, valve closing speed, and lift amount at the time of valve opening. An internal combustion engine. The internal combustion engine according to claim 1,
When the failure state is detected, the characteristic control means has a small actual compression ratio, which is the compression ratio obtained from the combustion chamber volume at the start of compression of the intake air and the combustion chamber volume at the end of compression. An internal combustion engine which is a means for performing control to change the valve closing characteristic of the intake valve in the direction as follows. The internal combustion engine according to claim 1,
In the direction where the period during which the intake valve is closed in the period from the compression top dead center to the intake bottom dead center during the intake stroke when the failure state is detected, An internal combustion engine which is means for performing control to change the valve opening characteristic of the intake valve. The internal combustion engine according to claim 1,
An exhaust valve for discharging combustion gas generated by the combustion from the combustion chamber;
A characteristic changing mechanism capable of changing a valve opening characteristic of the exhaust valve, and an exhaust valve driving means for driving the exhaust valve,
In addition to the control of the valve opening characteristic of the intake valve, or in place of the control of the valve opening characteristic of the intake valve, the characteristic control means is configured to reduce the combustion gas remaining in the combustion chamber. An internal combustion engine which is means for performing control to change the valve opening characteristic of the exhaust valve. An internal combustion engine according to claim 5,
The characteristic control means is a means for performing control to change a valve opening characteristic of at least one of the intake valve and the exhaust valve so that a period during which the intake valve and the exhaust valve are simultaneously opened decreases. Is an internal combustion engine. An internal combustion engine according to claim 5,
Combustion gas that causes the combustion gas to remain in the combustion chamber by performing at least one of the operation of driving the exhaust valve during the intake stroke of the internal combustion engine or driving the intake valve during the exhaust stroke. With residual means,
The internal combustion engine, wherein the characteristic control means is means for suppressing the operation of the combustion gas remaining means when the failure state is detected. An internal combustion engine that outputs power by compressing intake air sucked from an intake passage via an intake valve in a combustion chamber and burning it together with fuel,
A compression ratio changing mechanism capable of changing a compression ratio as an index representing the degree of compression of the intake air at least between a high compression ratio state and a low compression ratio state;
High compression ratio fixation detecting means for detecting a failure state where the compression ratio changing mechanism is fixed in the high compression ratio state;
An internal combustion engine comprising: control means for performing predetermined control for reducing the temperature of the intake air sucked from the intake passage when the failure state is detected. An internal combustion engine according to claim 8,
An exhaust passage for discharging combustion gas generated by the combustion;
Combustion gas recirculation means for recirculating a part of the combustion gas discharged from the exhaust passage into the intake passage;
The control means is an internal combustion engine which is means for suppressing a recirculation amount of the combustion gas recirculated into the intake passage when the failure state is detected. An internal combustion engine according to claim 8,
An intake air heating means for heating the intake air in the intake passage;
The internal combustion engine, wherein the control means is means for suppressing heating of the intake air when the failure state is detected. An internal combustion engine according to claim 8,
A first fuel injection valve for injecting fuel into the intake passage;
A second fuel injection valve for injecting fuel into the combustion chamber;
An operating condition detecting means for detecting an operating condition of the internal combustion engine;
Fuel injection valve driving means for driving the first fuel injection valve and the second fuel injection valve in accordance with the detected operating condition;
The control means is an internal combustion engine which is means for increasing a drive ratio of the second fuel injection valve to the first fuel injection valve when the failure state is detected. An internal combustion engine that outputs power by compressing a mixture of air and fuel in a combustion chamber and burning the compressed mixture.
A compression ratio changing mechanism capable of changing a compression ratio as an index representing the degree of compression of the air-fuel mixture at least between a high compression ratio state and a low compression ratio state;
High compression ratio fixation detecting means for detecting a failure state where the compression ratio changing mechanism is fixed in the high compression ratio state;
An internal combustion engine comprising: combustion chamber temperature lowering means for lowering a wall surface temperature of the combustion chamber when the failure state is detected. An internal combustion engine according to claim 12,
A cooling water temperature setting means for setting the temperature of the cooling water supplied to the combustion chamber;
The combustion chamber temperature lowering means is an internal combustion engine that is a means for lowering the setting of the cooling water temperature when the failure state is detected. An internal combustion engine according to claim 12,
Cooling water temperature setting means for setting the temperature of the cooling water supplied to the combustion chamber;
An operating condition detecting means for detecting an operating condition of the internal combustion engine;
A high water temperature control means for performing a high water temperature control for controlling the internal combustion engine by setting the setting of the cooling water temperature high when the detected operation condition is a predetermined operation condition;
The combustion chamber temperature lowering means is an internal combustion engine which is means for suppressing the high water temperature control when the failure state is detected. An internal combustion engine that compresses a mixture of air and fuel in a combustion chamber and outputs power generated when the mixture is combusted from an output shaft,
Power transmission means for transmitting the power output from the internal combustion engine to a drive shaft that drives the load of the internal combustion engine while reducing the rotational speed of the output shaft at a predetermined ratio;
A compression ratio changing mechanism capable of changing a compression ratio as an index representing the degree of compression of the air-fuel mixture at least between a high compression ratio state and a low compression ratio state;
High compression ratio fixation detecting means for detecting a failure state where the compression ratio changing mechanism is fixed in the high compression ratio state;
An internal combustion engine comprising: a reduction ratio control means for controlling the operation of the power transmission means in a direction in which a reduction ratio as a ratio of a rotation speed of the output shaft to the drive shaft is increased when the failure state is detected. . An internal combustion engine capable of changing the compression ratio representing the degree of compression of the intake air sucked into the combustion chamber via the intake valve into at least a high compression ratio state and a low compression ratio state, and compressing the intake air and burning it together with fuel An engine control method,
Detecting that the compression ratio is a failure state that cannot be switched from the high compression ratio state,
A control method for an internal combustion engine, wherein when the failure state is detected, the valve opening characteristic of the intake valve is changed in a direction to lower the temperature of intake air compressed in the combustion chamber. A control method for an internal combustion engine according to claim 16,
When the failure state is detected, in addition to the change in the valve opening characteristic of the intake valve or in place of the change in the valve opening characteristic of the intake valve, an exhaust valve that exhausts the burned combustion gas A method of controlling an internal combustion engine that changes valve opening characteristics. In a control method for an internal combustion engine, the compression ratio representing the degree of compression of intake air sucked into the combustion chamber can be changed at least between a high compression ratio state and a low compression ratio state, and the intake air is compressed and burned together with fuel. There,
Detecting that the compression ratio is a failure state that cannot be switched from the high compression ratio state,
A control method for an internal combustion engine that performs a predetermined control in which a temperature of intake air sucked from the intake passage is lowered when the failure state is detected. In a control method for an internal combustion engine, the compression ratio representing the degree of compression of intake air sucked into the combustion chamber can be changed at least between a high compression ratio state and a low compression ratio state, and the intake air is compressed and burned together with fuel. There,
Detecting that the compression ratio is a failure state that cannot be switched from the high compression ratio state,
A control method for an internal combustion engine that performs control to lower a wall surface temperature of the combustion chamber when the failure state is detected. The compression ratio representing the degree of compression of the intake air sucked into the combustion chamber can be changed at least between a high compression ratio state and a low compression ratio state, and the intake air is compressed and combusted with fuel, and the power generated by the combustion Is a control method for an internal combustion engine that outputs power from a power shaft,
Detecting that the compression ratio is a failure state that cannot be switched from the high compression ratio state,
While transmitting the power output from the internal combustion engine to the drive shaft that drives the load of the internal combustion engine while reducing the rotational speed of the output shaft at a predetermined ratio,
A control method for an internal combustion engine, wherein when the failure state is detected, control is performed in a direction in which a reduction ratio, which is a ratio of a rotational speed of the output shaft to the drive shaft, increases.

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