JP2012052483A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine that is superior in responsibility when output torque is decreased.SOLUTION: The internal combustion engine includes: a variable compression ratio mechanism in which a volume of a combustion chamber is formed so as to be variable; and an exhaust treatment device which is arranged on an engine exhaust passage. In the exhaust treatment device, an allowable temperature which is a reference whether deterioration occurs is predetermined. An amount of a temperature increase is evaluated in advance when the internal combustion engine performs the control of increasing temperature of the exhaust treatment device with a change of an operation state if torque outputted from the internal combustion engine is decreased. If a temperature in which the amount of a temperature increases is added to the temperature of the exhaust treatment device detected when the torque outputted from the internal combustion engine is decreased is higher than the allowable temperature, the internal combustion engine performs the control of decreasing a compression ratio by the variable compression ratio mechanism.

Description

  The present invention relates to an internal combustion engine.

  In an internal combustion engine, fuel and air are supplied to a combustion chamber, and the fuel burns in the combustion chamber to output a driving force. The internal combustion engine is operated in accordance with the required driving force. When the internal combustion engine is disposed in an automobile, for example, the required torque is detected from the depression amount of the accelerator pedal. Depending on the required torque, the opening degree of the throttle valve and the like are adjusted, and the amount of air and the amount of fuel supplied to the combustion chamber are adjusted.

  In an internal combustion engine, ignition is performed in a compressed state of a mixture of air and fuel. It is known that the compression ratio of an internal combustion engine affects the output torque and fuel consumption. By increasing the compression ratio, the output torque can be increased or the fuel consumption can be reduced. On the other hand, it is known that if the compression ratio is too high, abnormal combustion such as knocking phenomenon occurs. In the prior art, an internal combustion engine capable of changing the compression ratio during an operation period is known.

  Japanese Patent Laid-Open No. 2005-155507 discloses a control device for an internal combustion engine that sets a target compression ratio and sets a target throttle opening in accordance with the accelerator opening. The control device for the internal combustion engine calculates a required torque reduction amount according to the accelerator opening. It is disclosed that one of the target compression ratio and the target throttle opening is corrected to the decrease side in accordance with the required torque decrease amount.

JP-A-2005-155507

  The required torque increases or decreases during operation of the internal combustion engine. When the required torque decreases, for example, the throttle valve opening is controlled to decrease, and the torque output from the internal combustion engine decreases.

  During operation of the internal combustion engine, it may be preferable that the response of the torque output with respect to the required torque is high. In particular, there is a case where it is desired to rapidly reduce the output torque. For example, when the internal combustion engine is disposed in an automobile, the acceleration may be suddenly stopped during the acceleration period. There is a case where the amount of depression of the accelerator pedal is drastically reduced during a period in which the accelerator pedal is depressed deeply. Or you may take your foot off the accelerator pedal.

  In such a case, even if the throttle valve opening is controlled to be small, a response delay occurs, and a predetermined time is required until the torque output from the internal combustion engine decreases. In such a case, the torque that is output suddenly is reduced by performing fuel cut control that stops the supply of fuel from the fuel injection valve or by performing control that retards the ignition timing in the combustion chamber. Can be made.

  On the other hand, an exhaust treatment device for purifying exhaust gas is disposed in the engine exhaust passage of the internal combustion engine. For example, an oxidation catalyst may be disposed in the engine exhaust passage. The exhaust treatment device preferably has an allowable temperature during the operation period, and the operation is preferably continued within the allowable temperature range. Deterioration may occur if the temperature of the exhaust treatment device exceeds the allowable temperature during the operation period.

  If the fuel cut control is performed when the required torque of the internal combustion engine is reduced, excess air gas is supplied to the exhaust treatment device. At this time, the oxidation reaction of unburned fuel remaining in the oxidation catalyst may be promoted. For example, afterburning of a rich field occurs. As a result, the temperature of the exhaust treatment device increases. Or if the control which retards the ignition timing in a combustion chamber is performed, the temperature of the exhaust gas which flows out from a combustion chamber will rise. Since the temperature of the exhaust gas flowing into the exhaust treatment device rises, the temperature of the exhaust treatment device rises.

  When the exhaust treatment device is in the vicinity of the allowable temperature, if the fuel cut control or the control for retarding the ignition timing is performed, there arises a problem that the temperature of the exhaust treatment device increases and exceeds the allowable temperature. Therefore, in the conventional internal combustion engine, for example, control for reducing the opening of the throttle valve has been limited. As a result, there is a problem that it is difficult to reduce the torque output in a short time.

  An object of the present invention is to provide an internal combustion engine that is excellent in responsiveness when the output torque is reduced.

  An internal combustion engine of the present invention includes a compression ratio variable mechanism that changes a compression ratio, and an exhaust treatment device that is disposed in an engine exhaust passage. The compression ratio variable mechanism is formed so that the volume of the combustion chamber is variable. In the exhaust treatment apparatus, an allowable temperature that serves as a reference for whether or not deterioration occurs is determined in advance. When the torque output from the internal combustion engine is reduced, the amount of increase in temperature when the control is performed to increase the temperature of the exhaust treatment device in accordance with the change in the operating state. When the temperature of the exhaust treatment device is detected when the torque output from the internal combustion engine should be reduced, and the temperature obtained by adding the temperature increase amount to the detected temperature of the exhaust treatment device is higher than the allowable temperature, the variable compression ratio mechanism Control to reduce the compression ratio is performed.

  In the above-described invention, in order to reduce the torque output from the internal combustion engine, the exhaust gas processing apparatus when the operating state is changed by performing the control for retarding the ignition timing in the combustion chamber or the control for increasing the combustion air-fuel ratio. When the estimated temperature of the exhaust treatment device is higher than the allowable temperature, the compression ratio can be controlled to be reduced by the variable compression ratio mechanism.

  In the above-described invention, when control for reducing the compression ratio is to be performed by the compression ratio variable mechanism, the temperature of the exhaust treatment device after the reduction of the compression ratio is estimated, and the estimated temperature of the exhaust treatment device is determined in advance. When the temperature is lower than the determined temperature, at least one of control for retarding the ignition timing and control for increasing the combustion air-fuel ratio can be performed.

  In the above-described invention, when the torque output from the internal combustion engine is reduced, the control unit has a plurality of controls for increasing the temperature of the exhaust treatment device in accordance with the change in the operation state, It is preferable to calculate the temperature obtained by adding the temperature increase amount to the temperature of the exhaust treatment device using the largest temperature increase amount.

  ADVANTAGE OF THE INVENTION According to this invention, the internal combustion engine excellent in the responsiveness when reducing the output torque can be provided.

1 is a schematic view of an internal combustion engine in an embodiment. It is a general | schematic disassembled perspective view of the compression ratio variable mechanism in embodiment. It is a schematic sectional drawing of the part of a cylinder block and a crankcase when the internal combustion engine in embodiment is a high compression ratio. It is a schematic sectional drawing of the part of a cylinder block and a crankcase when the internal combustion engine in embodiment is a low compression ratio. It is a flowchart of the 1st operation control in an embodiment. It is a time chart of the 1st operation control in an embodiment. It is a time chart of the operation control of the comparative example in embodiment. It is a flowchart of the 2nd operation control in an embodiment. It is a time chart of the 2nd operation control in an embodiment.

  The internal combustion engine in the embodiment will be described with reference to FIGS. In the present embodiment, an internal combustion engine disposed in a vehicle will be described as an example.

  FIG. 1 is a schematic view of an internal combustion engine in the present embodiment. The internal combustion engine in the present embodiment is a spark ignition type. The internal combustion engine includes an engine body 1. The engine body 1 includes a cylinder block 2 and a cylinder head 4. A piston 3 is disposed inside the cylinder block 2. The piston 3 reciprocates inside the cylinder block 2. In the present invention, the space in the cylinder surrounded by the crown surface of the piston and the cylinder head when the piston reaches compression top dead center is referred to as a combustion chamber.

  The combustion chamber 5 is formed for each cylinder. An engine intake passage and an engine exhaust passage are connected to the combustion chamber 5. The engine intake passage is a passage for supplying air or a mixture of fuel and air to the combustion chamber 5. The engine exhaust passage is a passage for discharging exhaust gas generated by the combustion of fuel from the combustion chamber 5.

  An intake port 7 and an exhaust port 9 are formed in the cylinder head 4. The intake valve 6 is disposed at the end of the intake port 7 and is configured to be able to open and close the engine intake passage communicating with the combustion chamber 5. The exhaust valve 8 is disposed at the end of the exhaust port 9 and is configured to be able to open and close the engine exhaust passage communicating with the combustion chamber 5. A spark plug 10 as an ignition device is fixed to the cylinder head 4. The spark plug 10 is formed to ignite fuel in the combustion chamber 5.

  The internal combustion engine in the present embodiment includes a fuel injection valve 11 for supplying fuel to the combustion chamber 5. The fuel injection valve 11 in the present embodiment is arranged so as to inject fuel into the intake port 7. The fuel injection valve 11 is not limited to this configuration, and may be arranged so that fuel can be supplied to the combustion chamber 5. For example, the fuel injection valve may be arranged to inject fuel directly into the combustion chamber.

  The fuel injection valve 11 is connected to the fuel tank 28 via an electronically controlled fuel pump 29 with variable discharge amount. The fuel stored in the fuel tank 28 is supplied to the fuel injection valve 11 by the fuel pump 29.

  The intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake branch pipe 13. The surge tank 14 is connected to an air cleaner (not shown) via an intake duct 15 and an air flow meter 16. An air flow meter 16 that detects the amount of intake air is connected to the intake duct 15. A throttle valve 18 driven by a step motor 17 is disposed inside the intake duct 15. On the other hand, the exhaust port 9 of each cylinder is connected to a corresponding exhaust branch pipe 19. The exhaust branch pipe 19 is connected to the exhaust treatment device 21. The exhaust treatment device 21 in the present embodiment includes an oxidation catalyst 20. The exhaust treatment device 21 is connected to the exhaust pipe 22.

  The internal combustion engine in the present embodiment includes an electronic control unit 31. The electronic control unit 31 in the present embodiment includes a digital computer. The electronic control unit 31 includes a RAM (random access memory) 33, a ROM (read only memory) 34, a CPU (microprocessor) 35, an input port 36 and an output port 37 which are connected to each other via a bidirectional bus 32. .

  The air flow meter 16 generates an output voltage proportional to the amount of intake air taken into the combustion chamber 5. This output voltage is input to the input port 36 via the corresponding AD converter 38. A load sensor 41 is connected to the accelerator pedal 40. The load sensor 41 generates an output voltage proportional to the depression amount of the accelerator pedal 40. This output voltage is input to the input port 36 via the corresponding AD converter 38.

  The crank angle sensor 42 generates an output pulse each time the crankshaft rotates, for example, a predetermined angle, and this output pulse is input to the input port 36. The engine speed can be detected from the output of the crank angle sensor 42. Further, the crank angle can be detected from the output of the crank angle sensor 42. In the engine exhaust passage, a temperature sensor 43 as a temperature detector that detects the temperature of the exhaust treatment device 21 is disposed downstream of the exhaust treatment device 21. The output of the temperature sensor 43 is input to the input port 36 via the corresponding AD converter 38.

  The output port 37 of the electronic control unit 31 is connected to the fuel injection valve 11 and the spark plug 10 via the corresponding drive circuits 39. The electronic control unit 31 in the present embodiment is formed to perform fuel injection control and ignition control. That is, the fuel injection timing and the fuel injection amount are controlled by the electronic control unit 31. Further, the ignition timing of the spark plug 10 is controlled by the electronic control unit 31. The output port 37 is connected to a step motor 17 and a fuel pump 29 that drive the throttle valve 18 via a corresponding drive circuit 39. These devices are controlled by the electronic control unit 31.

  The intake valve 6 is formed to open and close as the intake cam 51 rotates. The exhaust valve 8 is formed to open and close as the exhaust cam 52 rotates. The internal combustion engine in the present embodiment includes a variable valve mechanism. The variable valve mechanism includes a variable valve timing device 53 that changes the opening / closing timing of the intake valve 6. The variable valve timing device 53 in the present embodiment is connected to the rotation shaft of the intake cam 51. The variable valve timing device 53 is controlled by the electronic control unit 31.

  The internal combustion engine in the present embodiment includes a variable compression ratio mechanism. The compression ratio of the internal combustion engine is determined depending on the volume of the combustion chamber and the like. The internal combustion engine in the present embodiment is formed such that the compression ratio is changed by changing the volume of the combustion chamber. The compression ratio of the internal combustion engine is expressed by (compression ratio) = (combustion chamber volume + piston stroke volume when the intake valve is closed) / (combustion chamber volume).

  FIG. 2 is an exploded perspective view of the compression ratio variable mechanism of the internal combustion engine in the present embodiment. FIG. 3 is a first schematic cross-sectional view of the combustion chamber portion of the internal combustion engine. FIG. 3 is a schematic view when the internal combustion engine has a high compression ratio.

  2 and 3, a plurality of protrusions 80 are formed below the side walls on both sides of the cylinder block 2. The protrusion 80 is formed with a cam insertion hole 81 having a circular cross section. A plurality of protrusions 82 are formed on the upper wall of the crankcase 79. The protrusion 82 is formed with a cam insertion hole 83 having a circular cross-sectional shape. The protrusion 82 of the crankcase 79 is fitted between the protrusions 80 of the cylinder block 2.

  The compression ratio variable mechanism in the present embodiment includes a pair of camshafts 84 and 85. A circular cam 86 that is rotatably inserted into the cam insertion hole 81 is fixed to each of the cam shafts 84 and 85. These circular cams 86 are formed coaxially with the rotation shafts of the cam shafts 84 and 85.

  On the other hand, as shown in FIG. 3, eccentric shafts 87 arranged eccentrically with respect to the rotation shafts of the respective cam shafts 84 and 85 extend between the circular cams 86. A circular cam 88 is eccentrically attached to the eccentric shaft 87 so as to be rotatable. The circular cam 88 is disposed between the circular cams 86. These circular cams 88 are rotatably supported in the corresponding cam insertion holes 83.

  The compression ratio variable mechanism includes a motor 89. Two worm gears 91 and 92 having spiral directions opposite to each other are attached to the rotating shaft 90 of the motor 89. Gears 93 and 94 are fixed to the end portions of the camshafts 84 and 85, respectively. The gears 93 and 94 are arranged so that the worm gears 19 and 92 and the gears 93 and 94 mesh with each other. When the motor 89 rotates the rotating shaft 90, the camshafts 84 and 85 can be rotated in directions opposite to each other.

  Referring to FIG. 3, when the circular cams 86 fixed on the camshafts 84 and 85 are rotated in opposite directions as indicated by arrows 96, the eccentric shaft 87 moves toward the lower end. The circular cam 88 rotates in the opposite direction to the circular cam 86 as indicated by an arrow 97 in the cam insertion hole 83.

  FIG. 4 shows a second schematic cross-sectional view of the combustion chamber portion of the internal combustion engine in the present embodiment. FIG. 4 is a schematic view when the internal combustion engine has a low compression ratio. As shown in FIG. 4, when the eccentric shaft 87 moves to the lower end, the central axis of the circular cam 88 moves below the eccentric shaft 87. Referring to FIGS. 3 and 4, the relative position between crankcase 79 and cylinder block 2 is determined by the distance between the central axis of circular cam 86 and the central axis of circular cam 88. The cylinder block 2 moves away from the crankcase 79 as the distance between the central axis of the circular cam 86 and the central axis of the circular cam 88 increases. As the cylinder block 2 moves away from the crankcase 79 as indicated by an arrow 98, the volume of the combustion chamber 5 when the piston 3 reaches the compression top dead center increases.

  In the variable compression ratio mechanism in the present embodiment, the volume of the combustion chamber is variably formed by moving the cylinder block relative to the crankcase. In FIG. 3, the piston 3 has reached the compression top dead center, and the volume of the combustion chamber 5 is reduced. In this state, the compression ratio increases. On the other hand, in FIG. 4, the piston 3 has reached the compression top dead center, and the volume of the combustion chamber 5 is increased. At this position, the compression ratio becomes small. Thus, the internal combustion engine in the present embodiment can change the compression ratio during the operation period.

  The variable compression ratio mechanism according to the present embodiment changes the compression ratio by moving the cylinder block relative to the crankcase. However, the present invention is not limited to this configuration, and any mechanism that can change the volume of the combustion chamber. This mechanism can be adopted. For example, a variable compression ratio mechanism in which the position of the compression top dead center of the piston can be changed can be employed.

  During the operation period of the internal combustion engine, the required torque increases or decreases. The torque to be output can be changed by changing the amount of air supplied to the combustion chamber of the internal combustion engine. For example, it is possible to perform control to reduce the amount of air supplied to the combustion chamber by reducing the opening of the throttle valve or delaying the timing of closing the intake valve by the variable valve timing device.

  By the way, during the operation period of the internal combustion engine, the output torque may be rapidly reduced. For example, the required torque may drop rapidly. When the internal combustion engine is disposed in an automobile, the driver may suddenly reduce the amount of depression of the accelerator pedal. For example, it may be necessary to decelerate suddenly during the acceleration period. Alternatively, when the wheel recovers the clipping force during the period when the vehicle wheel is slipping, the required torque is drastically decreased because the vehicle is accelerated rapidly. For example, the accelerator pedal may be depressed from a middle level to zero.

  In the control for reducing the amount of air supplied to the combustion chamber, a predetermined response delay occurs. For example, in the control for reducing the opening of the throttle valve, a response delay depending on the volume of the engine intake passage from the throttle valve to the combustion chamber occurs. When the throttle valve opening is reduced, it takes a certain amount of time for the pressure in the engine intake passage from the throttle valve to the combustion chamber to drop, making it difficult to reduce the amount of air supplied to the combustion chamber with high response. is there. For example, referring to FIG. 1, since the intake branch pipe 13 and the surge tank 14 function as a buffer tank, even if the opening of the throttle valve 18 is reduced, a predetermined time is required until the pressure in the engine intake passage decreases. Need time. For this reason, a predetermined time is required until the amount of air flowing into the combustion chamber decreases and the output torque decreases.

  When the torque output from the internal combustion engine is sharply reduced, fuel cut control for stopping the supply of fuel from the fuel injection valve can be performed. By performing the fuel cut control, the combustion of fuel in the combustion chamber can be stopped, so that the output torque can be rapidly reduced. Or control which retards the ignition timing in a combustion chamber can be performed. By performing control to retard the ignition timing, it is possible to delay the timing at which the combustion of fuel in the expansion stroke starts, and it is possible to rapidly reduce the output torque.

  However, when fuel cut control is performed, excess air exhaust flows into the exhaust treatment device. For example, if the exhaust treatment device has an oxidation function and further unburned fuel remains, the oxidation reaction of the unburned fuel is promoted by the excessive exhaust air flowing in. For this reason, the temperature of the exhaust treatment device rises. Further, when the control for retarding the ignition timing is performed, the amount of work on the piston is reduced, so that the temperature of the exhaust becomes high. The temperature of the exhaust gas flowing into the exhaust treatment device rises, and the temperature of the exhaust treatment device rises.

  In the exhaust treatment apparatus in the present embodiment, the upper limit allowable temperature during the operation period is determined in advance. As the allowable temperature, a temperature serving as a reference for determining whether or not the exhaust treatment apparatus is deteriorated when the exhaust treatment apparatus becomes high can be adopted. When the temperature of the exhaust treatment device is in the vicinity of the allowable temperature, the fuel cut control or the control for retarding the ignition timing causes a problem that the temperature of the exhaust treatment device rises and exceeds the allowable temperature. .

  In the internal combustion engine of the present embodiment, when the output torque is suddenly reduced, control is performed to reduce the compression ratio by the variable compression ratio mechanism.

FIG. 5 shows a flowchart of the first operation control in the present embodiment.
First, in step 101, a decrease in the required torque of the internal combustion engine is detected. With reference to FIG. 1, the required torque can be detected by, for example, a load sensor 41. Or you may detect reducing a torque in arbitrary control.

  Further, in step 101, it may be detected that the required torque has rapidly decreased. That is, it may be detected that the required torque has greatly decreased in a short time. For example, it may be detected that a predetermined amount of reduction in required torque has occurred during a predetermined time.

  Next, in step 102, the temperature of the exhaust treatment device is detected. In the present embodiment, the temperature of the oxidation catalyst 20 included in the exhaust treatment device 21 is detected. The temperature of the oxidation catalyst 20 can be detected by the temperature sensor 43.

  Next, in step 103, it is determined whether or not the fuel supply to the combustion chamber can be stopped. As described above, when the supply of fuel is stopped, exhaust gas with excess air is supplied to the oxidation catalyst 20, so that the temperature of the oxidation catalyst 20 rises. In the present embodiment, the temperature rise at this time is obtained in advance. The temperature increase amount is added to the detected temperature of the oxidation catalyst 20 to estimate the temperature of the oxidation catalyst 20 when the supply of fuel to the combustion chamber is stopped. In step 103, it is determined whether or not the temperature of the oxidation catalyst 20 when the supply of fuel to the combustion chamber is stopped is equal to or lower than an allowable temperature. When the temperature of the oxidation catalyst 20 when the fuel supply is stopped is equal to or lower than the allowable temperature, it is determined that the fuel supply can be stopped.

  In step 103, when the fuel supply to the combustion chamber is stopped, any method for determining whether or not the temperature of the exhaust treatment device is equal to or lower than the allowable temperature can be adopted. For example, the temperature increase amount of the exhaust treatment device may be obtained based on the state of the exhaust gas immediately before stopping the supply of fuel and the state of the exhaust gas after stopping the supply of fuel. When the estimated temperature of the exhaust treatment device is equal to or lower than the allowable temperature, it can be determined that the fuel supply can be stopped.

  If the fuel supply can be stopped in step 103, the routine proceeds to step 104. In step 104, the supply of fuel to the combustion chamber is stopped. In the present embodiment, fuel injection from the fuel injection valve 11 is stopped. With this control, the torque output from the internal combustion engine can be rapidly reduced.

  If it is determined in step 103 that the fuel supply cannot be stopped, the process proceeds to step 105. That is, when it is estimated that the temperature of the exhaust treatment device exceeds the allowable temperature when the supply of fuel to the combustion chamber is stopped, the routine proceeds to step 105.

  In step 105, it is determined whether or not the ignition timing can be retarded. As described above, when the ignition timing is retarded, the temperature of the exhaust treatment device increases. In the present embodiment, the temperature increase amount of the oxidation catalyst 20 when the ignition timing is retarded is obtained in advance. The temperature increase amount is added to the detected temperature of the oxidation catalyst 20 to estimate the temperature of the oxidation catalyst 20 when the ignition timing is retarded. In step 105, it is determined whether or not the temperature of the oxidation catalyst 20 when the ignition timing is retarded is equal to or lower than an allowable temperature. If the temperature of the oxidation catalyst 20 when the ignition timing is retarded is equal to or lower than the allowable temperature, it is determined that the ignition timing can be retarded. For example, a predetermined angle can be adopted as the retard amount of the ignition timing.

  In step 105, an arbitrary method for determining whether or not the temperature of the exhaust treatment device is equal to or lower than the allowable temperature when the ignition timing is retarded can be employed. For example, the temperature of the exhaust when the ignition timing is retarded can be estimated, and the amount of temperature increase can be obtained based on the estimated temperature of the exhaust. When the estimated temperature of the exhaust treatment device is equal to or lower than the allowable temperature, it can be determined that the ignition timing can be retarded.

  If it is determined in step 105 that the ignition timing can be retarded, the routine proceeds to step 106. In step 106, the ignition timing is retarded. With this control, the torque output from the internal combustion engine can be rapidly reduced. If it is determined at step 105 that the ignition timing cannot be retarded, the routine proceeds to step 107.

  In step 107, it is determined whether or not the compression ratio of the internal combustion engine can be reduced. In step 107, if the compression ratio of the internal combustion engine can be reduced, the routine proceeds to step 108. Alternatively, in step 107, it may be determined whether or not the compression ratio of the internal combustion engine is greater than a predetermined compression ratio determination value. If the compression ratio of the internal combustion engine is larger than a predetermined compression ratio determination value, the routine may proceed to step 108.

  In step 108, control for reducing the compression ratio is performed. For example, a predetermined reduction amount can be adopted as the reduction amount of the compression ratio. Or you may control so that a compression ratio may become the minimum. If it is determined in step 107 that the compression ratio cannot be reduced, the process proceeds to step 109.

  Referring to FIGS. 2 to 4, when the compression ratio is lowered, control is performed to move cylinder block 2 away from crankcase 79 by rotating motor 89. For example, as shown in FIG. 4, when the piston 3 reaches the compression top dead center, the compression ratio variable mechanism is controlled so that the volume of the combustion chamber 5 is increased.

  By reducing the compression ratio of the internal combustion engine, the temperature of the air-fuel mixture in the combustion chamber when the piston reaches the compression top dead center is lowered. Further, the temperature at which the fuel burns, that is, the combustion temperature decreases. Since the combustion temperature is lowered, the temperature of the exhaust gas flowing out from the combustion chamber is lowered. For this reason, it is possible to avoid an increase in the temperature of the exhaust treatment device. Further, when the compression ratio is lowered, the torque output from the internal combustion engine is lowered. Thus, by reducing the compression ratio, it is possible to reduce the output torque while avoiding an increase in the temperature of the exhaust treatment device disposed in the engine exhaust passage.

  Referring to FIG. 5, when the fuel supply is stopped in step 104, the process proceeds to step 109. Alternatively, when the ignition timing is retarded in step 106, the routine proceeds to step 109. Alternatively, when the compression ratio is decreased in step 108, the process proceeds to step 109.

  In step 109, control is performed to reduce the amount of air supplied to the combustion chamber. Referring to FIG. 1, in the present embodiment, control is performed to reduce the opening degree of throttle valve 18 by driving step motor 17. By reducing the opening of the throttle valve 18, the amount of air supplied to the combustion chamber 5 can be reduced, and the torque output from the internal combustion engine can be reduced. The internal combustion engine in the present embodiment can reduce the amount of air-fuel mixture supplied to the combustion chamber 5 by reducing the opening of the throttle valve 18.

  Control for reducing the amount of air supplied to the combustion chamber 5 is not limited to control for reducing the opening of the throttle valve, and arbitrary control that can reduce the amount of air supplied to the combustion chamber 5 can be performed. . For example, the variable valve mechanism can be controlled to delay the closing timing of the intake valve.

  In the internal combustion engine of the present embodiment, the temperature of the exhaust treatment device is detected, and the operating state is changed by performing control for retarding the ignition timing in the combustion chamber or control for reducing the amount of fuel supplied to the combustion chamber. In this case, the temperature of the exhaust treatment device is estimated. Control is performed to reduce the compression ratio when the estimated temperature of the exhaust treatment device becomes higher than the allowable temperature. With this control, it is possible to reduce the torque output in a short time while avoiding the exhaust treatment device from exceeding the allowable temperature.

  The control of the internal combustion engine is not limited to this mode, and the compression ratio may be lowered without determining whether the fuel supply can be stopped or the ignition timing can be retarded. Alternatively, in the first operation control of the present embodiment, the amount of air supplied to the combustion chamber is decreased after determining whether to stop supplying fuel, determining the retard of the ignition timing, or determining the compression ratio. However, the present invention is not limited to this mode, and the amount of air supplied to the combustion chamber may be reduced before each determination. Alternatively, the amount of air supplied to the combustion chamber may be reduced simultaneously with each determination.

  The control for increasing the temperature of the exhaust treatment device in accordance with a change in the operating state when the torque output from the internal combustion engine is reduced is not limited to stopping the supply of fuel or retarding the ignition timing. It is possible to employ a control for reducing an arbitrary torque accompanying the temperature increase. For example, control can be performed to increase the air-fuel ratio (combustion air-fuel ratio) when fuel burns in the combustion chamber. That is, the combustion air-fuel ratio can be controlled to the lean side. The fuel cut control is included in the control for increasing the combustion air-fuel ratio. By the control for increasing the combustion air-fuel ratio, a post-burning phenomenon occurs in the exhaust treatment device, the torque output from the internal combustion engine is reduced, and the temperature of the exhaust treatment device is raised.

  Further, when there are a plurality of controls in which the operation state for reducing the torque output from the internal combustion engine is changed, the largest temperature increase amount among the plurality of temperature increase amounts associated with the change in each operation state is used. Thus, it is preferable to calculate a temperature obtained by adding the temperature increase amount to the temperature of the exhaust treatment device. By this control, the minimum temperature of the exhaust treatment device that performs control to reduce the compression ratio by the compression ratio variable mechanism is lowered, and it is possible to more reliably suppress the temperature of the exhaust treatment device from exceeding the allowable temperature.

FIG. 6 shows a time chart of the first operational control in the present embodiment.
The required torque is rapidly decreased at time t1. In the first operation control, the case where the temperature of the exhaust treatment device is in the vicinity of the allowable temperature when the required torque is rapidly reduced is shown. That is, an operation example is shown in which it is impossible to stop the fuel supply to the combustion chamber and to retard the ignition timing. Control for reducing the compression ratio of the internal combustion engine is performed by detecting a decrease in the required torque.

  The compression ratio starts to decrease from time t1 and reaches the target value at time t2. The torque output from the internal combustion engine is drastically reduced from time t1 to time t2. Further, the temperature of the exhaust gas rapidly decreases from time t1 to time t2. Thus, by changing the compression ratio, the output torque can be drastically reduced and the temperature of the exhaust gas can be lowered. That is, the temperature rise of the exhaust treatment device can be avoided.

  Further, at time t1, control is performed to reduce the opening of the throttle valve. By reducing the opening of the throttle valve, the amount of intake air flowing into the combustion chamber gradually decreases. From time t2 to time t3, the output torque gradually decreases as the intake air amount gradually decreases. At time t3, the intake air amount reaches the target value and is substantially constant. Further, the output torque is substantially constant at time t3.

  In FIG. 7, the time chart of the operation control of the comparative example in this Embodiment is shown. In the operation control of the comparative example, when the torque output from the internal combustion engine is sharply reduced, only the control for reducing the amount of air supplied to the combustion chamber is performed.

  At the time t1, the required torque is rapidly decreased. At time t1, the opening of the throttle valve is reduced. However, the intake air amount does not decrease rapidly but gradually decreases from time t1 to time t2. For this reason, the torque output from the internal combustion engine also gradually decreases. Thus, the control for reducing the intake air amount has low responsiveness. Note that the temperature of the exhaust gas gradually decreases.

  Referring to FIG. 6, on the other hand, in the first operation control of the present embodiment, the torque output from the internal combustion engine can be sharply reduced by changing the compression ratio. That is, the torque output in a short time can be greatly reduced. Thus, the internal combustion engine of the present embodiment is excellent in output responsiveness to the required torque.

  Alternatively, by performing the first operation control of the present embodiment, it is possible to avoid an increase in the size of the exhaust treatment device in order to increase the allowable temperature of the exhaust treatment device. That is, the heat capacity of the exhaust treatment device can be reduced. Alternatively, the exhaust treatment device can be reduced in size.

  Next, the second operation control in the present embodiment will be described. In the second operation control, when the required torque decreases and further fuel cut control and control for retarding the ignition timing are impossible, the compression ratio is reduced as in the first operation control. In the second operation control, control for retarding the ignition timing is performed in addition to control for reducing the compression ratio.

FIG. 8 is a flowchart of the second operational control in the present embodiment.
Steps 121 to 128 in the second operation control are the same as steps 101 to 108 in the first operation control (see FIG. 5). In step 128, if the compression ratio is lowered by the compression ratio variable mechanism, the process proceeds to step 129.

  In step 129, the temperature of the exhaust treatment device after the compression ratio is lowered is estimated. In the present embodiment, since the temperature of the exhaust treatment device corresponds to the temperature of the exhaust, the temperature of the exhaust when the compression ratio is reduced is estimated. The temperature of the exhaust treatment device is estimated based on the estimated temperature of the exhaust gas.

  In step 129, any control for estimating the temperature of the exhaust treatment device can be employed. For example, a temperature detector may be disposed in the engine exhaust passage to detect the temperature of the exhaust gas flowing out from the combustion chamber, and estimate the temperature of the exhaust treatment device based on the actual exhaust gas temperature. Alternatively, the combustion temperature of the fuel in the combustion chamber may be detected or estimated instead of the temperature of the exhaust gas.

  Next, in step 130, the retard amount of the ignition timing is derived from the temperature of the exhaust treatment device estimated in step 129. An angle capable of delaying the ignition timing is derived. For example, the retard amount of the ignition timing can be derived based on the difference between the temperature of the exhaust treatment device and the allowable temperature of the exhaust treatment device. The relationship between the temperature of the exhaust treatment device and the retard amount of the ignition timing can be stored in advance in the electronic control unit. By estimating the temperature of the exhaust treatment device, the retard amount of the ignition timing can be derived. Alternatively, a predetermined angle may be used as the retard amount of the ignition timing.

  Next, in step 131, control for retarding the ignition timing is performed based on the derived ignition timing.

  Next, in step 132, the amount of air supplied to the combustion chamber is decreased. Step 132 is the same as step 109 in the first operation control (see FIG. 5).

  By performing control to reduce the compression ratio, the temperature of the exhaust gas decreases. For this reason, the temperature of the exhaust treatment device disposed in the engine exhaust passage decreases. Since the temperature of the exhaust treatment device has a large margin with respect to the allowable temperature, the temperature of the exhaust can be increased. In the second operation control in the present embodiment, in addition to the control for reducing the compression ratio, the torque output in a shorter time can be reduced by retarding the ignition timing. In the second operation control, it is preferable to determine the retardation amount so that the temperature of the exhaust treatment device does not exceed the allowable temperature. For example, it is preferable to perform control to retard the ignition timing so that the temperature of the exhaust treatment device becomes substantially constant.

FIG. 9 shows a time chart of the second operational control in the present embodiment.
At the time t1, the required torque is rapidly decreased. The second operation control shown in FIG. 9 shows a case where the temperature of the exhaust treatment device is in the vicinity of the allowable temperature when there is a sudden decrease in the required torque. That is, an operation example is shown in which the supply of fuel to the combustion chamber is not stopped and the ignition timing cannot be retarded.

  The compression ratio is decreased from time t1 to time t2. In addition, the opening of the throttle valve is reduced. At this time, the temperature of the exhaust treatment device after the compression ratio is reduced is estimated, and the retard amount of the ignition timing is derived. In the example shown in FIG. 9, the ignition timing is retarded at time t1.

  By retarding the ignition timing, the output torque is drastically reduced from time t1 to time t2. In the time chart of torque and exhaust temperature output from the internal combustion engine of FIG. 9, a graph when the first operation control is performed is shown by a broken line. As can be seen from this graph, the output torque is greatly reduced in a short time by retarding the ignition timing in addition to the reduction in the compression ratio. Moreover, in the example of operation shown in FIG. 9, it turns out that the temperature of exhaust_gas | exhaustion is substantially constant. Thus, in the second operation control in the present embodiment, it is possible to reduce the torque that is output more rapidly while avoiding the exhaust treatment device from exceeding the allowable temperature.

  In the second operation control of the present embodiment, control for retarding the ignition timing is performed in addition to control for lowering the compression ratio. However, the present invention is not limited to this mode, and in addition to control for lowering the compression ratio. Thus, control for increasing the combustion air-fuel ratio may be performed. For example, you may perform control which stops supply of the fuel to a combustion chamber. In this case, the reduction amount of the fuel supplied to the combustion chamber can be derived from the estimated temperature of the exhaust treatment device.

  By the way, an internal combustion engine can be arrange | positioned at a hybrid drive device. The hybrid drive device is a drive device that generates power by combining an internal combustion engine and a drive motor. The hybrid drive device can be arranged in a vehicle such as an automobile.

  For example, a hybrid vehicle can be driven by a drive motor when the torque required for the hybrid drive device is small. When the required torque is large, the engine can be operated using an internal combustion engine and a drive motor. Furthermore, when the hybrid vehicle decelerates, electricity can be generated by the drive motor and electricity can be stored in the storage battery.

  The hybrid drive device includes a storage battery that stores electricity. When the storage battery is repeatedly discharged and charged with a large current, the storage battery deteriorates or the possibility of failure increases. For this reason, it is preferable that the hybrid drive device controls electric power when discharging or charging the storage battery.

  Even in an internal combustion engine of a hybrid drive device, it may be preferable to reduce the torque that is suddenly output. For example, a hybrid vehicle equipped with a hybrid drive device may travel on a road surface where wheels such as water pools easily slip. When the vehicle travels on a road surface that easily slips during deceleration of the automobile, the wheels may lock. That is, the rotational speed of the wheel is rapidly reduced. At this time, the internal combustion engine may be over-rotated, and the drive motor may become a generator to generate power. A large amount of electricity is charged in the storage battery in a short time. That is, the current charged in the storage battery becomes large. In such a conventional internal combustion engine, for example, the ignition timing is retarded. However, as described above, there are cases where the exhaust treatment device exceeds the allowable temperature by retarding the ignition timing. By disposing the internal combustion engine of the present embodiment in the hybrid drive device, it is possible to rapidly reduce the output torque and to suppress the internal combustion engine from over-rotating. In addition, it is possible to avoid charging the storage battery with a large amount of electricity in a short time, and it is possible to suppress deterioration of the storage battery.

  Alternatively, the capacity of the storage battery can be increased in order to charge a large amount of electricity in a short time. However, in order to increase the capacity of the storage battery, the storage battery becomes large or heavy. In the hybrid drive device including the internal combustion engine of the present embodiment, it is possible to avoid an increase in the capacity of the storage battery. Or the capacity | capacitance (resistance of the current of an element or the tolerance of a voltage) of the component for discharging or charging electricity can be made small. Alternatively, when the regenerative brake is used, the capacity of the mechanical brake can be reduced in order to improve the effectiveness of the regenerative brake.

  In the internal combustion engine of the present embodiment, the example in which the exhaust treatment device includes the oxidation catalyst has been described. However, the present invention is not limited to this embodiment, and the internal combustion engine may include any exhaust treatment device having an oxidation function. it can. For example, the exhaust treatment device may include a three-way catalyst, a particulate filter, and the like.

  In the present embodiment, the internal combustion engine attached to the automobile has been described as an example. However, the present invention is not limited to this embodiment, and the present invention can be applied to any internal combustion engine. In each of the above-described controls, the order can be changed as appropriate.

  In the respective drawings described above, the same or corresponding parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. Further, the embodiments include changes in the form shown in the claims.

DESCRIPTION OF SYMBOLS 1 Engine body 2 Cylinder block 3 Piston 5 Combustion chamber 10 Spark plug 11 Fuel injection valve 18 Throttle valve 20 Oxidation catalyst 21 Catalytic converter 31 Electronic control unit 40 Accelerator pedal 41 Load sensor 43 Temperature sensor 79 Crankcase 84, 85 Camshaft 86 Circular shape Cam 87 Eccentric shaft 88 Circular cam 89 Motor 91, 92 Worm gear

Claims (4)

A variable compression ratio mechanism for changing the compression ratio;
An exhaust treatment device disposed in the engine exhaust passage,
The compression ratio variable mechanism has a variable combustion chamber volume,
In the exhaust treatment device, an allowable temperature that is a reference for whether or not deterioration occurs is determined in advance,
When the torque output from the internal combustion engine is reduced, the amount of temperature increase when control is performed to increase the temperature of the exhaust treatment device in accordance with the change in the operating state, is obtained in advance.
When the temperature of the exhaust treatment device is detected when the torque output from the internal combustion engine should be reduced, and the temperature obtained by adding the temperature increase amount to the detected temperature of the exhaust treatment device is higher than the allowable temperature, the variable compression ratio mechanism An internal combustion engine characterized by performing control to reduce the compression ratio.   In order to reduce the torque output from the internal combustion engine, control for retarding the ignition timing in the combustion chamber or control for increasing the combustion air-fuel ratio is performed to estimate the temperature of the exhaust treatment device when the operating state changes. 2. The internal combustion engine according to claim 1, wherein when the estimated temperature of the exhaust treatment device is higher than an allowable temperature, control is performed to reduce the compression ratio by a compression ratio variable mechanism.   When control for reducing the compression ratio is to be performed by the compression ratio variable mechanism, the temperature of the exhaust treatment device after the compression ratio is lowered is estimated, and the estimated temperature of the exhaust treatment device is less than a predetermined determination temperature. The internal combustion engine according to claim 1 or 2, wherein at least one of control for retarding the ignition timing and control for increasing the combustion air-fuel ratio is performed. A plurality of controls for increasing the temperature of the exhaust treatment device in accordance with a change in the operating state when the torque output from the internal combustion engine is reduced;
The temperature obtained by adding the temperature increase amount to the temperature of the exhaust treatment device is calculated using the largest temperature increase amount among the temperature increase amounts associated with the changes in the respective operation states. The internal combustion engine according to any one of the above.

Images