JP2019152114A - Control device for engine - Google Patents

Abstract

To suppress the worsening of emission performance during engine cold operation.SOLUTION: A control device for an engine includes an electric supercharger 53, an exhaust emission control catalyst 61, means for detecting/estimating the active state of the exhaust emission control catalyst 61, compression ratio regulation means (an intake valve drive mechanism 30) for changing the effective compression ratio of an engine body 10, and a PCM 100 for controlling the operation of an engine 1. When the non-active state of the exhaust emission control catalyst 61 is detected/estimated, the PCM 100 allows the operation of the electric supercharger 53 for a predetermined period after starting the engine 1 and uses the compression ratio regulation means to make the effective compression ratio lower than that right after the predetermined period elapses.SELECTED DRAWING: Figure 9

Description

  The technology disclosed herein belongs to a technical field related to an engine control device.

  Conventionally, an engine in which an electric supercharger is disposed in an intake passage is known.

  For example, Patent Document 1 discloses an electric supercharger that is disposed in an intake passage and supercharges intake air, a current probe that detects a drive current of the electric supercharger, and an electric supercharger that is driven when the engine is started. An engine abnormality detection device is disclosed that includes a drive control unit that controls the abnormality of the engine based on the drive current of the electric supercharger detected by a current probe when the engine is started.

  Patent Document 1 discloses that a catalyst (exhaust gas purification catalyst) for purifying harmful substances in the exhaust gas is disposed in the exhaust passage.

JP 2008-106636 A

  By the way, in recent years, the compression ratio of the engine body has been increased from the viewpoint of improving fuel consumption. However, according to studies by the present inventors, it has been found that when the effective compression ratio of the engine body is high, unburned HC is easily discharged when the engine is cold, and the emission performance is likely to deteriorate.

  That is, when the effective compression ratio of the engine body is high, the in-cylinder temperature at the compression top dead center of the piston is increased, and the combustion pressure and the combustion temperature are increased. For this reason, the temperature difference between the gas temperature and the engine body increases, and heat is easily released from the exhaust gas to the engine body. This increases the cooling loss, lowers the temperature of the exhaust gas, and takes time to activate the exhaust purification catalyst. As a result, harmful substances in the exhaust gas are discharged to the outside of the vehicle without being purified, and the emission performance is deteriorated. In addition, when the effective compression ratio of the engine body is high, the fuel supplied into the cylinder easily enters a gap (hereinafter referred to as a clevis portion) between the piston and the cylinder in the vicinity of the top of the piston. . Since the flame at the time of combustion hardly reaches the clevis part, the fuel that has entered the clevis part does not burn but tends to remain as unburned HC. Since the unburned HC is discharged together with the exhaust gas in the exhaust stroke, if the exhaust purification catalyst is in an inactive state, it is discharged as it is outside the vehicle. This also deteriorates the emission performance. Therefore, there is room for improvement from the viewpoint of suppressing the deterioration of the emission performance when the engine is cold.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to suppress deterioration in emission performance when the engine is cold.

  In order to solve the above problems, the technology disclosed herein is directed to an engine control device in which an electric supercharger is disposed in an intake passage, and a cylinder that can communicate with the intake passage by opening and closing an intake valve. An engine body having a piston, a piston fitted in the cylinder, an exhaust purification catalyst provided in an exhaust passage for exhausting exhaust gas from the cylinder, and an active state of the exhaust purification catalyst is detected or estimated Means for changing the effective compression ratio of the engine body, and control means for controlling the operation of the engine. The control means detects or estimates an inactive state of the exhaust purification catalyst. When the engine is started, the electric supercharger is operated for a predetermined period from the start of the engine, and the effective pressure is increased by the compression ratio adjusting means compared to immediately after the predetermined period has elapsed. Is configured to reduce the ratio was assumed that.

  According to this configuration, if the effective compression ratio of the engine body is reduced, the in-cylinder temperature when the piston is at the compression top dead center is lowered, and the combustion pressure and the combustion temperature are lowered. The conduction is reduced. Thereby, the cooling loss is reduced, the temperature of the exhaust gas can be kept relatively high, and the exhaust purification catalyst can be activated early. As a result, unburned HC is hardly released to the outside of the vehicle, and deterioration of emission performance is suppressed. Further, when the effective compression ratio of the engine body is reduced, it becomes difficult to enter a gap (hereinafter referred to as a clevis portion) between the piston and the cylinder in the vicinity of the top of the piston. Thereby, the amount of unburned HC in the exhaust gas is reduced as compared with the case where the effective compression ratio of the engine body is high. For this reason, the deterioration of the emission performance when the engine is cold can be suppressed.

  On the other hand, if the effective compression ratio is relatively small, misfire may occur. On the other hand, in the technique disclosed here, the electric supercharger is operated after the engine body is started. Since the pressure in the intake passage can be increased by operating the electric supercharger, the pump loss is reduced. As a result, it is possible to secure the amount of intake air supplied into the cylinder, suppress misfire, and obtain sufficient engine output. As a result, the operating state of the engine is appropriately maintained, and it is possible to suppress a decrease in the exhaust amount and a decrease in the engine speed due to misfire, and the early activation of the exhaust purification catalyst can be performed efficiently.

  Accordingly, it is possible to suppress the deterioration of the emission performance after the engine cold start.

  Furthermore, after the predetermined period has elapsed, the heat conduction from the cylinder to the engine body can be increased by increasing the effective compression ratio of the engine body. Thereby, warming-up promotion of an engine main body can also be aimed at.

  In one embodiment of the engine control apparatus, the predetermined period is a period until the exhaust purification catalyst changes from an inactive state to an active state.

  According to this configuration, the effective compression ratio of the engine body is kept small until the exhaust purification catalyst is activated. Thereby, in the period before the exhaust purification catalyst is activated, the amount of unburned HC contained in the exhaust gas can be reduced. For this reason, even when the exhaust purification catalyst is not sufficiently activated, the amount of unburned HC released to the outside of the vehicle can be reduced, and the deterioration of the emission performance when the engine is cold is more effectively prevented. Can be suppressed. Further, since the exhaust gas having a high temperature is supplied to the exhaust purification catalyst until the exhaust purification catalyst is activated, the period itself from the inactive state to the active state can be shortened as much as possible. . This also makes it possible to more effectively suppress the deterioration of the emission performance when the engine is cold.

  In the engine control apparatus, the compression ratio adjusting means is an intake valve drive mechanism capable of adjusting a closing timing of the intake valve, and the controlling means determines the closing timing of the intake valve after the predetermined period. You may comprise so that the said effective compression ratio may be made small by making it slow compared with immediately after.

  According to this configuration, by relatively delaying the opening timing of the intake valve, a part of the intake air returns to the intake passage in the compression stroke, so that the effective compression ratio of the engine body can be reduced. If the effective compression ratio of the engine body can be reduced, the cooling loss can be reduced as described above, so that the emission performance can be prevented from deteriorating when the engine is cold.

  Moreover, if the opening timing of the intake valve is relatively delayed and the electric supercharger is operated, the pump loss is reduced by the electric supercharger, and the amount of intake air supplied into the cylinder is secured. Can do. For this reason, even if the intake valve opening timing is relatively delayed, sufficient engine output can be obtained. Thereby, the driving | running state of an engine can be maintained appropriately. As a result, it is possible to appropriately exert the effect of preventing the deterioration of the emission performance when the engine is cold.

  As described above, according to the technique disclosed herein, the cooling loss can be reduced by reducing the effective compression ratio of the engine body. Further, the risk of misfire caused by reducing the effective compression ratio of the engine body can be avoided by operating the electric supercharger. Thereby, activation of the exhaust purification catalyst can be promoted. Furthermore, the amount of unburned HC in the exhaust gas can be reduced by reducing the effective compression ratio of the engine body. Therefore, deterioration of the emission performance when the engine is cold can be suppressed.

It is the schematic which shows the engine controlled by the control apparatus which concerns on exemplary embodiment. It is sectional drawing which shows the structure of an engine main body. It is an enlarged view which shows the periphery of the contact part of the side wall and piston of an engine main body. It is a block diagram which shows the control system of an engine. It is a performance curve graph which shows the characteristic of the compressor and electric motor of an electric supercharger. It is a figure which shows an example of the opening / closing pattern of an intake valve and an exhaust valve. It is a graph which shows the relationship between stroke volume and cylinder pressure. It is a flowchart which shows the processing operation of PCM. It is a timing chart which shows the operating state of each apparatus at the time of the cold start of an engine.

  Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

  FIG. 1 shows an engine 1 controlled by the control device according to the present embodiment. The engine 1 is an engine mounted on a vehicle such as an automobile. The engine body 10 of the engine 1 is an in-line four-cylinder gasoline engine in which four cylinders 11 are arranged in series, and fuel whose main component is gasoline is supplied to each cylinder 11.

  As shown in FIG. 2, the engine body 10 includes a cylinder block 12 provided with a plurality of cylinders 11 (only one is shown in FIG. 2), and a cylinder head 13 disposed on the cylinder block 12. And an oil pan 14 which is disposed below the cylinder block 12 and stores lubricating oil. A piston 15 is fitted into each cylinder 11 of the engine body 10 so as to be reciprocally slidable. The piston 15, the cylinder block 12, and the cylinder head 13 define a combustion chamber 16 (see FIG. 2). The piston 15 is connected to the crankshaft 18 via a connecting rod 17 in the cylinder block 12. The shape of the combustion chamber 16 is not limited to the shape shown in the figure. For example, the shape of the top surface of the piston 15 and the shape of the ceiling of the combustion chamber 16 can be changed as appropriate.

  As shown in FIGS. 2 and 3, a plurality of piston rings 15 a are fitted into the piston 15, and the combustion chamber 16 is defined by the piston rings 15 a being in close contact with the inner peripheral surface of the cylinder 11. ing. The piston ring 15 a closest to the cylinder head 13 among the plurality of piston rings 15 a is located on the side opposite to the cylinder head 13 than the top surface of the piston 15. For this reason, as shown in FIG. 3, a clevis portion 16 a is formed between the piston 15 and the cylinder 11 in the vicinity of the top of the piston 15.

  As shown in FIG. 2, an intake port 19 and an exhaust port 20 are formed in the cylinder head 13 for each cylinder 11. The intake port 19 and the exhaust port 20 are respectively provided with an intake valve 21 and an exhaust valve 22 that open and close the opening on the combustion chamber 16 side.

  Each intake valve 21 is opened and closed by an intake valve drive mechanism 30, and each exhaust valve 22 is opened and closed by an exhaust valve drive mechanism 40. The intake valve drive mechanism 30 and the exhaust valve drive mechanism 40 have an intake camshaft 31 and an exhaust camshaft 41, respectively. The camshafts 31 and 41 are connected to the crankshaft 18 via a power transmission mechanism such as a chain / sprocket mechanism (not shown). As a result, the camshafts 31 and 41 rotate in conjunction with the rotation of the crankshaft 18.

  The intake valve drive mechanism 30 and the exhaust valve drive mechanism 40 are configured to include an electric S-VT (Sequential-Valve Timing) that makes the valve timing and / or the valve lift variable. Each electric S-VT is attached to the end portions of the intake camshaft 31 and the exhaust camshaft 41, as shown in FIG. Each electric S-VT is configured to continuously change the rotational phases of the intake camshaft 31 and the exhaust camshaft 41 within a predetermined angle range. Since the electric S-VT can adopt a known configuration, detailed description of the configuration is omitted. Note that a hydraulic S-VT may be adopted instead of the electric S-VT. As will be described in detail later, in the present embodiment, the intake valve drive mechanism 30 constitutes a compression ratio adjusting means for adjusting the effective compression ratio of the engine body 10.

  For each cylinder 11, an injector 23 (fuel injection valve) that directly injects fuel into the cylinder 11 is attached to the cylinder head 13. As shown in FIG. 2, the injector 23 is disposed so that its nozzle hole faces the combustion chamber 16 from one side of the cylinder head 13 (in this embodiment, the intake side). The injector 23 directly injects an amount of fuel into the combustion chamber 16 at an injection timing set according to the operating state of the engine 1 and according to the operating state of the engine 1.

  A spark plug 24 for burning fuel injected into the cylinder 11 is attached to the cylinder head 13 for each cylinder 11. As shown in FIG. 2, the spark plug 24 is disposed so that the electrode 24 a faces the combustion chamber 16 from the ceiling of the combustion chamber 16. The spark plug 24 receives a control signal from the PCM 100, which will be described later, and energizes the electrode 24a so as to generate a spark at a desired ignition timing.

  The geometric compression ratio of the engine body 10 is set high for the purpose of improving the theoretical thermal efficiency. Specifically, the geometric compression ratio of the engine body 10 is 14 or more. The geometric compression ratio may be 18, for example. The geometric compression ratio may be set as appropriate in the range of 14 to 20.

  As shown in FIG. 1, an intake passage 50 is connected to one side surface of the engine body 10 so as to communicate with the intake port 19 of each cylinder 11. On the other hand, the other side of the engine body 10 is connected to the exhaust port 20 of each cylinder 11 and is connected to an exhaust passage 60 for discharging burned gas (that is, exhaust gas) from each cylinder 11. Yes. Therefore, each cylinder 11 is a cylinder 11 that can communicate with the intake passage 50 and the exhaust passage 60 by the intake valve 21 and the exhaust valve 22.

  An air cleaner 51 that filters intake air is disposed at the upstream end of the intake passage 50. On the other hand, a surge tank 52 is disposed in the vicinity of the downstream side of the intake passage 50. The intake passage 50 on the downstream side of the surge tank 52 is an independent intake passage that branches for each cylinder 11, and the downstream end of each independent intake passage is connected to the intake port 19 of each cylinder 11.

  Between the air cleaner 51 and the surge tank 52 in the intake passage 50, an electric supercharger 53 and a throttle valve 54 are disposed in order from the upstream side to the downstream side.

  The intake passage 50 is provided with an intake bypass passage 55 that bypasses the electric supercharger 53. The intake bypass passage 55 has an upstream end connected to a passage between the air cleaner 51 and the electric supercharger 53 in the intake passage 50, and a downstream end connected to the electric supercharger 53 and the throttle valve in the intake passage 50. 54 is connected to the passage between the two. As a result, the intake bypass passage 55 communicates the passage upstream of the electric supercharger 53 and the passage downstream of the electric supercharger 53 in the intake passage 50. An intake bypass valve 56 for adjusting the amount of air flowing to the intake bypass passage 55 is disposed in the intake bypass passage 55. By adjusting the opening degree of the intake bypass valve 56, the ratio between the intake air amount supercharged by the electric supercharger 53 and the intake air amount passing through the intake bypass passage 55 is changed stepwise or continuously. Will be able to. As will be described in detail later, the intake bypass passage 55 causes a portion of the intake air supercharged by the electric supercharger 53 to flow back to a passage upstream of the electric supercharger 53 in the intake passage 50 to be introduced into the intake passage. It may become a circulation passage for circulating in 50.

  The electric supercharger 53 includes a compressor 53a provided in the intake passage 50, and an electric motor 53b that drives the compressor 53a. By driving the electric motor 53b, the compressor 53a is rotationally driven, and the intake air is supercharged. The supercharging pressure capability of the electric supercharger 53 (that is, the supercharging pressure by the electric supercharger 53) is changed by changing the driving force of the electric motor 53b. The electric motor 53b is driven by electric power stored in a battery 25 described later or electric power generated by a motor generator 70 described later. The magnitude of the driving force of the electric motor 53b is changed depending on the magnitude of the electric power supplied to the electric motor 53b. The electric motor 53b is composed of a relatively small motor, and power consumption during operation is smaller than that of a motor generator 70 described later.

  The throttle valve 54 corresponds to a flow rate adjustment valve that adjusts the amount of intake air supplied to the cylinder 11. The opening degree of the throttle valve 54 is changed based on a control signal from the PCM 100 described later.

  The upstream portion of the exhaust passage 60 is constituted by an exhaust manifold having an independent exhaust passage branched for each cylinder 11 and connected to the outer end of the exhaust port 20 and a collecting portion where the independent exhaust passages gather. ing.

  An exhaust purification catalyst 61 is disposed downstream of the exhaust manifold in the exhaust passage 60. The exhaust purification catalyst 61 is a so-called three-way catalyst, and purifies NOx, CO, unburned HC and the like contained in the exhaust gas. The exhaust purification catalyst 61 exhibits a purification action appropriately at a temperature equal to or higher than a predetermined activation temperature.

  As shown in FIG. 1, the engine 1 of the present embodiment is provided with a motor generator 70. A motor shaft 71 of the motor generator 70 is connected to a first pulley 72, and the first pulley 72 is connected to a second pulley 73 via a belt 74. The second pulley 73 is connected to the crankshaft 18 of the engine body 10. Thus, when the motor generator 70 is driven to rotate, the rotational force of the motor generator 70 is transmitted to the crankshaft 18 via the first pulley 72, the belt 74, and the second pulley 73, so that the crankshaft 18 rotates. To do.

  The motor generator 70 functions as a starter motor that rotates the engine 1 when the engine 1 (strictly, the engine body 10) is started. When the engine 1 is started, the motor generator 70 is rotationally driven by electric power stored in a battery 25 described later. Since the motor generator 70 has to generate a rotational force enough to rotate the crankshaft 18, the motor generator 70 is configured by a motor larger than the electric motor 53b described above. In the following description, “rotating the crankshaft 18 of the engine body 10” may be simply expressed as “rotating the engine 1”.

  After the engine 1 is started, the motor generator 70 functions as a generator that generates power based on the engine output from the engine body 10. The electric power generated by the motor generator 70 is stored in a battery 25 (to be described later) and supplied to the electric motor 53b of the electric supercharger 53 and the like.

  As shown in FIG. 1, the engine 1 of the present embodiment is provided with a battery 25 in which electric power for operating the electric supercharger 53, the motor generator 70, and the like is stored. The battery 25 stores, for example, the electric power generated by the motor generator 70 as described above. The battery 25 supplies power to the electric supercharger 53, the motor generator 70, and the like based on a control signal from the PCM 100 described later. The battery 25 is a 48V battery, for example.

  In the engine 1 shown in the present embodiment, an EGR passage for returning the exhaust gas flowing through the exhaust passage 60 to the intake passage 50 is not provided. However, the present disclosure does not exclude application to an engine having an EGR passage.

  The engine 1 configured as described above is controlled by a powertrain control module (hereinafter referred to as PCM) 100 as shown in FIG. The PCM 100 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. As shown in FIG. 3, the PCM 100 includes a water temperature sensor SW1 for detecting the temperature of engine cooling water, a supercharging pressure sensor SW2 for detecting the supercharging pressure by the electric supercharger 53, and an intake air temperature sensor SW3 for detecting the intake air temperature. An exhaust temperature sensor SW4 for detecting the exhaust temperature, a crank angle sensor SW5 for detecting the rotation angle of the crankshaft 18, and an accelerator opening sensor SW6 for detecting the accelerator opening corresponding to the operation amount of the accelerator pedal (not shown) of the vehicle. , And a detection signal from the catalyst temperature sensor SW7 for detecting the temperature of the exhaust purification catalyst 61 is input. The PCM 100 receives a signal from the ignition switch SW8.

  The PCM 100 calculates the engine speed and engine speed of the engine 1 from the detection result of the crank angle sensor SW5, and calculates the engine load from the detection result of the accelerator opening sensor SW6.

  When the engine water temperature detected by the water temperature sensor SW1 is lower than the first predetermined temperature Tc, the PCM 100 determines that the temperature in the cylinder 11 is low and the engine 1 is in a cold state (engine cold state). To do. Further, the PCM 100 estimates that the exhaust purification catalyst 61 is in an active state when the engine water temperature detected by the water temperature sensor SW1 is equal to or higher than the first predetermined temperature Tc. That is, since the exhaust purification catalyst 61 is likely to be warmed compared to the engine coolant, if the engine water temperature is high, it can be estimated that the exhaust purification catalyst 61 is naturally warmed up and is in an active state. Thus, the water temperature sensor SW1 and the PCM 100 constitute a means for estimating the active state of the exhaust purification catalyst 61. In the present embodiment, the first predetermined temperature Tc is set to 40 ° C., for example.

  Further, the PCM 100 determines whether or not the exhaust purification catalyst 61 is in an active state based on the temperature of the exhaust purification catalyst 61 detected by the catalyst temperature sensor SW7. Specifically, the PCM 100 determines that the exhaust purification catalyst is in an active state when the temperature of the exhaust purification catalyst 61 is equal to or higher than the activation temperature Ta. That is, the PCM 100 and the catalyst temperature sensor SW7 correspond to means for detecting the active state of the exhaust purification catalyst 61. In the present embodiment, the activation temperature Ta is set to 300 ° C., for example, but can be appropriately changed according to the type of the exhaust purification catalyst. Further, even in the same exhaust purification catalyst as in the present embodiment, the activation temperature Ta may be set as a temperature lower than 300 ° C. (eg 290 ° C.) or higher (eg 310 ° C.) as the activation temperature Ta. . The catalyst temperature sensor SW7 itself may detect the active state of the exhaust purification catalyst 61 based on the detected temperature. In this case, the catalyst temperature sensor SW7 constitutes a means for detecting the active state of the exhaust purification catalyst 61.

  The PCM 100, based on the input signal, the injector 23, the battery 25, the intake valve drive mechanism 30, the exhaust valve drive mechanism 40, the electric supercharger 53 (strictly, the electric motor 53b of the electric supercharger 53), the throttle Control signals are output to the actuator of the valve 54, the actuator of the intake bypass valve 56, and the motor generator 70.

  The PCM 100 realizes the fuel injection amount and the injection start timing corresponding to the engine load (the required torque to the engine 1) by controlling the operation of the injector 23. The engine load increases as the accelerator opening increases and as the external load of the motor generator 70 as a generator increases. The fuel injection amount is set so as to increase as the engine load increases.

(Outline of electric turbocharger control)
Next, control of the electric supercharger 53 by the PCM 100 will be described. In FIG. 5, the performance curve showing the characteristic of the electric supercharger 53 is shown. The upper diagram of FIG. 5 is a performance curve graph showing the characteristics of the compressor 53a of the electric supercharger 53, and the vertical axis represents the pressure ratio of the electric supercharger 53 (that is, the ratio of the upstream pressure to the downstream pressure). The horizontal axis is the discharge flow rate. In the upper diagram of FIG. 5, a curve LL represents a rotation limit line, a straight line SL represents a surge line, and a straight line CL represents a choke line. A region surrounded by these lines is a region where the electric supercharger 53 can be operated. The operation efficiency of the electric supercharger 53 increases as the position is closer to the center of this region.

  Since the electric supercharger 53 is used for the purpose of adjusting the amount of fresh air introduced into the cylinder 11, the engine cooling water is located in a region away from the rotation limit line as shown by a mesh in the upper diagram of FIG. 5. Depending on the water temperature and the engine speed, the engine is operated at an appropriate speed. That is, the electric supercharger 53 is operated in a partial state far away from the limit rotational speed.

  The lower diagram of FIG. 5 illustrates the characteristics of the electric motor 53b of the electric supercharger 53. The vertical axis represents the torque of the electric motor 53b, and the horizontal axis represents the rotation speed of the electric motor 53b. The one-dot chain line in the lower diagram of FIG. 5 indicates a line with equal power consumption. The power consumption increases as it goes to the upper right of the diagram, and the power consumption decreases as it goes to the lower left. The electric supercharger 53 is operated in the region indicated by the mesh in the upper diagram of FIG. 5. At this time, the electric motor 53 b operates in the region indicated by the mesh in the lower diagram of FIG. 5. The electric power consumption of the electric motor 53b is relatively low, and the efficiency of the electric motor 53b is relatively high. The state in which the electric motor 53b is operating at a torque lower than the maximum torque may be referred to as operating in the partial state of the electric supercharger 53. As described above, although the electric supercharger 53 is always rotating during operation of the engine body 10, it is possible to reduce power consumption by operating the electric supercharger 53 in a partial state. .

(Control at engine start)
Here, in order to improve the emission performance when the engine is cold, the amount of unburned HC discharged to the outside of the vehicle is reduced from when the engine 1 is started until the exhaust purification catalyst 61 is activated. This is very important. In order to suppress the discharge amount of unburned HC to the outside of the vehicle, it is necessary to activate the exhaust purification catalyst 61 at an early stage. In order to activate the exhaust purification catalyst 61 at an early stage, it is required to supply exhaust gas having a temperature as high as possible to the exhaust purification catalyst 61. As a method for increasing the temperature of the exhaust gas, it is possible to suppress the cooling loss.

  On the other hand, when the effective compression ratio of the engine body 10 is high, the cooling loss may increase. That is, the cooling loss can be defined by the following equation.

Cooling loss = thermal conductivity x heat transfer area x (gas temperature-section screen temperature)
In the above formula, the thermal conductivity depends on the material of the engine body 10. The transmission area is a contact area between the gas in the cylinder 11 and the inner peripheral surface of the cylinder 11. The gas temperature is the temperature of the gas in the cylinder, and the temperature on the section screen is the temperature of the inner peripheral surface of the cylinder 11 in contact with the gas in the cylinder 11. When the effective compression ratio is high, the in-cylinder temperature at the compression top dead center (TDC) of the piston 15 is increased, and the combustion pressure and the combustion temperature are increased. For this reason, the temperature difference between the temperature of the exhaust gas and the inner peripheral surface of the cylinder 11 increases, and heat is easily released from the exhaust gas to the engine body 10. This increases the cooling loss. In general, the higher the temperature of a metal, the higher the thermal conductivity. For this reason, if the in-cylinder temperature at the compression top dead center (TDC) of the piston 15 is high, the thermal conductivity of the inner peripheral surface of the cylinder 11 increases immediately before the combustion of the fuel. For this reason, the cooling loss is further increased.

  As the cooling loss increases, the temperature of the exhaust gas discharged decreases. When the temperature of the exhaust gas is lowered, it takes time to activate the exhaust purification catalyst 61. As a result, harmful substances including unburned HC in the exhaust gas are discharged to the outside of the vehicle without being purified, and the emission performance is deteriorated.

  Further, when the effective compression ratio of the engine body 10 is high, the amount of unburned HC in the exhaust gas may be increased. That is, when the effective compression ratio is high, the fuel supplied into the cylinder 11 easily enters the clevis portion 16 a of the combustion chamber 16. Since the flame at the time of combustion does not easily reach the clevis portion 16a (that is, the clevis portion 16a is likely to become a quench zone), the fuel that has entered the clevis portion 16a is likely to remain as unburned HC without burning. Since the unburned HC is discharged together with the exhaust gas in the exhaust stroke, the unburned HC in the exhaust gas increases.

  As described above, when the effective compression ratio of the engine body 10 is high, it takes time to activate the exhaust purification catalyst 61 and the unburned HC in the exhaust gas increases when the engine 1 is cold started. The emission performance may be deteriorated. On the other hand, when the effective compression ratio of the engine body 10 is high, the thermal efficiency of the engine 1 is increased, which is preferable from the viewpoint of fuel consumption. Therefore, in this embodiment, the PCM 100 adjusts the effective compression ratio of the engine body 10 and activates the electric supercharger 53 when the exhaust purification catalyst 61 is in an inactive state when the engine 1 is cold started. By doing so, the deterioration of the emission performance is suppressed.

  Specifically, in the present embodiment, when the inactive state of the exhaust purification catalyst 61 is estimated, the PCM 100 operates the electric supercharger 53 for a predetermined period t1 after the engine 1 is started, The effective compression ratio is made smaller than immediately after the predetermined period t1. More specifically, the PCM 100 reduces the effective compression ratio by performing a so-called Miller cycle, in which the intake valve drive mechanism 30 causes the closing timing of the intake valve 21 to be delayed compared to immediately after the predetermined period t1 has elapsed. To do. In the present embodiment, the PCM 100 estimates that the exhaust purification catalyst 61 is in an inactive state when the detected temperature of the engine water temperature sensor SW1 is lower than the first predetermined temperature Tc. In the present embodiment, the predetermined period t1 is a period until the exhaust purification catalyst 61 changes from the inactive state to the active state, that is, a period until the detected temperature of the catalyst temperature sensor SW7 becomes equal to or higher than the activation temperature Ta. Is set. In the following description, the control for delaying the valve closing timing of the intake valve 21 as compared with the time immediately after the predetermined period t1 is referred to as mirror cycle control. In this embodiment, the closing timing of the intake valve 21 is defined at the time of 0.3 mm lift. The closing timing of the intake valve 21 may be defined at 1 mm.

  The mirror cycle control will be described with reference to FIG. FIG. 6 is a graph showing the opening / closing timing of the intake valve 21 and the exhaust valve 22. 6 shows an example of the opening / closing timing of the intake and exhaust valves 21 and 22 after the activation of the exhaust purification catalyst 61, and the lower figure of FIG. 6 shows the intake and exhaust valves 21 and 22 before the activation of the exhaust purification catalyst 61. An example of opening and closing time is shown.

  As shown in the upper diagram of FIG. 6, in this embodiment, after the exhaust purification catalyst 61 is activated, the intake valve 21 is basically opened immediately before the compression top dead center (TDC), Closed immediately after the dead center (BDC) (for example, about 30 ° after the compression bottom dead center). This is to ensure that intake air flows into the cylinder 11 while the piston 15 is descending, and to take in as much intake air as possible into the cylinder 11 using the inertia of intake air flowing into the cylinder 11. is there. On the other hand, at the time of the mirror cycle control, as shown in the lower diagram of FIG. 6, the closing timing of the intake valve 21 is retarded, and the intake valve 21 is opened after the compression top dead center, Close after compression bottom dead center. More specifically, in this embodiment, the valve closing timing of the intake valve 21 is retarded by about 60 ° during the mirror cycle control. Thus, by retarding the closing timing of the intake valve 21, the intake valve 21 is opened during the compression stroke, and a part of the intake air supplied into the cylinder 11 is taken into the intake port 19. Pushed back. Thereby, an effective compression ratio becomes small and the said effective compression ratio can be made small.

  Here, if the effective compression ratio is reduced, the amount of intake air supplied into the cylinder 11 is reduced, and misfire may occur. On the other hand, in the present embodiment, the electric supercharger 53 is operated during the mirror cycle control after the engine body 10 is started. By operating the electric supercharger 53, the pump loss is reduced and the intake air amount to be supplied into the cylinder 11 can be secured. For this reason, even if the valve opening timing of the intake valve 21 is delayed relatively, misfire can be suppressed and sufficient engine output can be obtained. Thereby, the driving | running state of the engine 1 can be maintained appropriately.

  Thus, by adjusting the effective compression ratio of the engine body 10 and operating the electric supercharger 53, the cooling loss is reduced and the exhaust gas having a relatively high temperature is supplied to the exhaust purification catalyst 61. Can do. This will be described with reference to FIG.

  FIG. 7 shows the relationship between the stroke volume per one cycle from the intake stroke to the exhaust stroke of the engine body 1 and the in-cylinder pressure. A broken line in FIG. 7 indicates a case where the closing timing of the intake valve 21 is a normal closing timing (opening / closing timing as shown in FIG. 6A) and the electric supercharger 53 is not operated (hereinafter, during normal control). The solid line in FIG. 7 shows the case where the closing timing of the intake valve 21 is the closing timing at the time of the mirror cycle control and the electric supercharger 53 is operated. The position where the stroke volume becomes the smallest corresponds to the compression top dead center of the piston 15, and the position where the stroke volume becomes the largest corresponds to the compression bottom dead center of the piston 15.

  During the normal control, a negative pressure that overcomes the negative pressure in the intake passage 50 in the intake stroke is generated in the cylinder 11 to draw in the intake air, so that the in-cylinder pressure is lower than that in the exhaust stroke. Next, the in-cylinder pressure increases in the compression stroke, the in-cylinder pressure increases at a time during combustion in the combustion stroke, and the in-cylinder pressure decreases as the piston 15 descends. In the exhaust stroke, the in-cylinder pressure is approximately the same as the atmospheric pressure. On the other hand, in the case of the present embodiment, since the supercharging pressure generated by the electric supercharger 53 is used in the intake stroke, intake air can be supplied into the cylinder 11 with a higher in-cylinder pressure than during the exhaust stroke. . Next, in the compression stroke, since the intake valve 21 is opened by the mirror cycle control, the intake air is pushed back to the intake port 19. For this reason, the in-cylinder pressure remains substantially constant while the intake valve 21 is open even during the compression stroke. Then, after the intake valve 21 is closed, the in-cylinder pressure increases. Then, the in-cylinder pressure suddenly increases during the combustion stroke, and the in-cylinder pressure decreases due to the lowering of the piston 15, and becomes substantially the same as the atmospheric pressure during the exhaust stroke.

  When the mirror cycle control is being performed, the effective compression ratio is reduced, so that the cylinder pressure at the compression top dead center of the piston 15 is lower than that during the normal control, as shown in FIG. As described above, the cylinder pressure at the compression top dead center of the piston 15 is lowered, and the cylinder pressure and the cylinder temperature during combustion are also lowered. Further, since the in-cylinder pressure at the compression top dead center of the piston 15 is lowered, the in-cylinder temperature is lowered, and the thermal conductivity of the inner peripheral surface of the cylinder 11 immediately before combustion is lowered. As described above, the temperature difference between the gas temperature in the cylinder 11 and the inner peripheral surface of the cylinder 11 is reduced, and the thermal conductivity of the inner peripheral surface of the cylinder 11 is reduced. Heat conduction to 10 is reduced and cooling loss is reduced. By reducing the cooling loss, the in-cylinder pressure in the later stage of the combustion stroke becomes higher during the mirror cycle control than during the normal control. When the in-cylinder pressure increases, the in-cylinder temperature (that is, the exhaust gas temperature) naturally increases.

  Thus, if the cooling loss is reduced, the temperature of the exhaust gas in the later stage of the combustion stroke can be kept relatively high, and the exhaust purification catalyst 61 can be activated early. As a result, the amount of unburned HC discharged to the outside of the vehicle between the start of the engine 1 and the activation of the exhaust purification catalyst 61 can be reduced, and the deterioration of the emission performance can be suppressed. it can.

  Further, when the effective compression ratio of the engine body 10 is reduced by the Miller cycle control and the in-cylinder pressure in the compression stroke is reduced, the fuel supplied into the cylinder 11 is less likely to enter the clevis portion 16a of the combustion chamber 16. Become. That is, when the in-cylinder pressure is high, part of the fuel supplied into the cylinder 11 is pressed toward the clevis portion 16a, and the fuel easily enters the clevis portion 16a. On the other hand, when the in-cylinder pressure is lowered, the pressure toward the clevis portion 16a also decreases, so that the fuel is less likely to enter the clevis portion 16a. If the fuel becomes difficult to enter the clevis portion 16a, the amount of unburned HC in the exhaust gas decreases. As a result, deterioration of emission performance can be suppressed.

  Therefore, when the engine 1 is cold-started, the effective compression ratio of the engine body 10 is reduced, and the electric supercharger 53 is operated to suppress the deterioration of the emission performance.

  Furthermore, by operating the electric supercharger 53 during the mirror cycle control, as shown in FIG. 7, not only the pump loss can be reduced but also the energy can be recovered. That is, at the time of the normal control, the piston 15 has to do work for generating a negative pressure in the cylinder 11, and a pump loss occurs as shown by a mesh portion in a dotted line in FIG. On the other hand, when the electric supercharger 53 is operated, not only the work of the piston 15 is reduced, but also the energy in the cylinder 11 can be recovered as shown in the mesh portion in FIG. it can.

  In this embodiment, after the predetermined time has elapsed, that is, after the exhaust purification catalyst 61 is activated, the mirror cycle control is stopped and the valve closing timing of the intake valve 21 is advanced. . Thus, heat is actively transmitted from the exhaust gas in the cylinder 11 to the engine body 10 to warm up the engine body 10. If the engine body 10 can be warmed up at an early stage, the combustion stability is improved at an early stage, so that the fuel consumption can be improved.

  Furthermore, in this embodiment, after the warm-up of the engine body 10 is completed, the PCM 100 puts the engine 1 into an idle operation state, retards the valve closing timing of the intake valve 21, and performs the mirror cycle control again. Execute. Thereby, in the state after the warm-up of the engine body 10 is completed, the operation efficiency of the engine 1 is increased while suppressing abnormal combustion such as knocking. Thereafter, when the accelerator pedal is depressed by the driver of the vehicle, the PCM 100 advances the valve closing timing of the intake valve 21. This is because the engine is operated with an engine load corresponding to the accelerator opening.

  Next, processing operations from the start of the engine 1 by the PCM 100 to the warming up of the engine body 10 will be described based on the flowchart of FIG. The processing operation of the PCM 100 is executed every time the engine 1 is requested to start. Note that the control shown in FIG. 8 is a control in the case where the engine 1 is started from a state where the engine 1 is stopped in a state where the closing timing of the intake valve 21 is retarded.

  In the first step S101, the PCM 100 reads signals from various sensors, and in the next step S102, the PCM 100 determines whether or not the engine water temperature is lower than the first predetermined temperature Tc. When the determination in step S102 is NO, it is estimated that the exhaust purification catalyst 61 is in an active state, and the process proceeds to step S115. On the other hand, when the determination in step S102 is YES, the exhaust purification catalyst 61 is in an inactive state. And the process proceeds to step S103.

  In the next step S103, the PCM 100 drives the motor generator 70 as a starter motor.

  In step S104, the PCM 100 advances the closing timing of the intake valve 21, and in the next step S105, the PCM 100 starts fuel injection.

  In the next step S106, the PCM 100 determines whether or not the instantaneous engine rotation speed is equal to or higher than a predetermined rotation speed. When the determination in step S106 is NO, the process returns to step S105, while when the determination in step S106 is YES, the process proceeds to step S107.

  In step S107, the PCM 100 retards the closing timing of the intake valve 21 to execute the mirror cycle control, and in the next step S108, the PCM 100 drives the electric supercharger 53.

  In step S109, the PCM 100 determines whether or not the catalyst temperature is equal to or higher than the activation temperature Ta. When the determination in step S109 is NO, the process returns to step S108, while when the determination in step S109 is YES, the process proceeds to step S110.

  In the next step S110, the PCM 100 places the electric supercharger 53 in the idle rotation state.

  In the subsequent step S111, the PCM 100 advances the valve closing timing of the intake valve 21 in order to warm up the engine body 10.

  In the next step S112, the PCM 100 determines whether or not the engine water temperature has become equal to or higher than the second predetermined temperature Tw. When the determination in step S112 is NO, it is determined that the warming up of the engine body 10 is not completed, and the process returns to step S111. On the other hand, when the determination in step S112 is YES, the warming up of the engine body 10 is completed. And the process proceeds to step S113. In the present embodiment, the second predetermined temperature Tw is set to 80 ° C., for example.

  In step S113, the PCM 100 retards the closing timing of the intake valve 21.

  In the next step S114, the engine 1 is put into an idle operation state. At this time, the PCM 100 controls the fuel injection amount and the like, thereby reducing the rotational speed of the engine 1 (strictly, the engine body 10) and putting the engine 1 in an idle operation state. After step S114, the PCM 100 ends the process.

  On the other hand, in step S115 which proceeds when the determination in step S102 is NO, the motor generator 70 as a starter motor is driven, and in the next step S116, the PCM 100 starts fuel injection.

  In step S117, the PCM 100 determines whether or not the instantaneous engine speed has become equal to or higher than a predetermined speed. When the determination in step S117 is NO, the process returns to step S116, while when the determination in step S117 is YES, the process proceeds to step S118.

  In step S118, the PCM 100 places the engine 1 in an idle operation state. At this time, the PCM 100 controls the fuel injection amount and the like to lower the rotational speed of the engine 1 and put the engine 1 in an idle operation state. After step S118, the PCM 100 ends the process.

  The operation of each device under the control of the PCM 100 will be described with reference to the time chart of FIG. Here, a description will be given from when the engine 1 is stopped to when the engine 1 is started until the engine 1 is in an idle operation state.

  In the initial state, it is assumed that the opening / closing timing of the intake valve 21 is retarded. From this initial state, when the ignition switch SW8 is turned on and a start request is made, the opening / closing timing of the intake valve 21 is advanced and the motor generator 70 as a starter motor is driven. After the motor generator 70 as a starter motor is driven, fuel is not injected until a predetermined time t2 has elapsed. For this reason, after the motor generator 70 as a starter motor is driven, the engine rotation speed becomes substantially constant during the predetermined time t2.

  After a certain time t2 has elapsed since the motor generator 70 as the starter motor is driven, fuel is supplied. As a result, the fuel burns in the cylinder 11 to which the fuel is supplied, and the engine speed increases. Thereafter, when the instantaneous engine rotation speed becomes equal to or higher than a predetermined rotation speed (here, the instantaneous rotation speed is set to a speed of 800 to 900 rpm) and the complete explosion of the engine 1 is confirmed, the starter motor is The motor generator 70 is stopped. When the fuel burns in the cylinder 11, the exhaust gas is sent to the exhaust purification catalyst 61, and the temperature of the exhaust purification catalyst 61 begins to rise.

  After the complete explosion of the engine 1 is confirmed, the opening / closing timing of the intake valve 21 is retarded and the electric supercharger 53 is driven to warm up the exhaust purification catalyst 61 early. As a result, exhaust gas having a high temperature is supplied to the exhaust purification catalyst 61, and the temperature of the exhaust purification catalyst 61 rises. While the warming-up of the exhaust purification catalyst 61 is being promoted (that is, during the predetermined period t1), the PCM 100 causes the fuel injection valve 23 (fuel injection amount and injection timing) and the like so that the engine speed becomes substantially constant. To control.

  Then, after confirming that the temperature of the exhaust purification catalyst 61 has become equal to or higher than the activation temperature Ta (immediately after the elapse of the predetermined period t1), the electric supercharger 53 is idle in order to promote warming up of the engine body 10. While being in the operating state, the opening / closing timing of the intake valve 21 is advanced. As a result, the effective compression ratio increases, and the in-cylinder temperature when the piston 15 is located at the compression top dead center in the compression stroke and the combustion temperature during combustion increase. As a result, the heat of the exhaust gas is easily transmitted to the engine body 10, and warming up of the engine body 10 is promoted.

  After the warm-up of the engine body 10 is completed (after the engine water temperature has become equal to or higher than the second predetermined temperature Tw), the engine speed is decreased and the engine is set to the idle operation state while retarding the opening / closing timing of the intake valve 21. . Note that the opening / closing timing of the intake valve 21 may be retarded after the engine speed is first reduced.

  Therefore, in the present embodiment, when the inactive state of the exhaust purification catalyst 61 is detected or estimated, the PCM 100 operates the electric supercharger 53 for a predetermined period t1 after the engine 1 is started and The valve drive mechanism 30 is configured to reduce the effective compression ratio of the engine body 10 compared to immediately after the predetermined period t1 has elapsed. Thereby, when the piston 15 is located at the compression top dead center in the compression step, the in-cylinder temperature can be lowered and the combustion temperature can be lowered, so that the cooling loss can be reduced. Further, the risk of misfire caused by reducing the effective compression ratio of the engine body 10 can be avoided by operating the electric supercharger 53. Thereby, early activation of the exhaust purification catalyst 61 can be promoted. Further, by reducing the effective compression ratio of the engine body 10, it is possible to suppress the fuel from entering the clevis portion 16a of the combustion chamber 16 and reduce the amount of unburned HC in the exhaust gas. Therefore, deterioration of the emission performance when the engine is cold can be suppressed.

  The technology disclosed herein is not limited to the above-described embodiment, and can be substituted without departing from the scope of the claims.

  For example, in the above-described embodiment, the effective compression ratio of the engine body 10 is reduced by executing the mirror cycle control for retarding the closing timing of the intake valve 21, but the present invention is not limited to this, and the intake valve 21 Advance the closing timing, reopen the closed intake valve 21 once in the compression stroke, open the exhaust valve 22, or open a dedicated valve provided separately, and open this dedicated valve. The effective compression ratio may be lowered by setting the compression stroke during the set period as a dead stroke.

  In the above-described embodiment, the PCM 100 estimates that the exhaust purification catalyst 61 is in an inactive state based on the detection result of the engine water temperature sensor SW1, but instead of or in addition to this, the PCM 100 The exhaust purification catalyst 61 may be detected to be in an inactive state based on the detection result of the catalyst temperature sensor SW7. When the engine water temperature is lower than the first predetermined temperature Tc and the catalyst temperature is equal to or higher than the activation temperature Ta, control for warming up the exhaust purification catalyst 61 (mirror cycle control and driving of the electric supercharger 53, FIG. 8). Steps S107 to S109) may be omitted and the engine 1 (strictly, the engine body 10) may be warmed up.

  Further, in the above-described embodiment, the valve closing timing of the intake valve 21 is advanced in order to warm up the engine body 10 after the catalyst temperature becomes equal to or higher than the activation temperature Ta. However, the intake valve 21 is closed when the catalyst temperature becomes a temperature slightly lower than the activation temperature Ta (for example, 290 ° C. when the activation temperature Ta is set to 300 ° C.). The valve timing may be advanced.

In the above-described embodiment, the exhaust purification catalyst 61 is detected based on the catalyst temperature. However, the present invention is not limited to this. For example, when the catalyst temperature sensor SW7 is not provided. Alternatively, the PCM 100 may determine that the exhaust purification catalyst 61 is activated when a preset reference time has elapsed since the start of the control for warming up the exhaust purification catalyst 61. In this case, the reference time corresponds to the predetermined period t1. Further, instead of the catalyst temperature sensor SW7, an O ₂ concentration sensor that detects the oxygen concentration in the passage immediately downstream of the exhaust purification catalyst 61 in the exhaust passage 60 is provided, and based on the detection result of the O ₂ concentration sensor, The PCM 100 may determine that the exhaust purification catalyst 61 has been activated.

  The above-described embodiments are merely examples, and the scope of the present disclosure should not be interpreted in a limited manner. The scope of the present disclosure is defined by the claims, and all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present disclosure.

  The technology disclosed herein is useful for accelerating the activation of the exhaust purification catalyst in an engine in which an electric supercharger is disposed in the intake passage.

1 Engine 10 Engine body 11 Cylinder 15 Piston 21 Intake valve 30 Intake valve drive mechanism (compression ratio adjusting means)
50 Intake passage 53 Electric supercharger 60 Exhaust passage 61 Exhaust purification catalyst 100 PCM (control means, means for detecting or estimating an activation state of the exhaust purification catalyst)
SW1 engine water temperature sensor (means for estimating the activation state of the exhaust purification catalyst)
SW7 catalyst temperature sensor (means for detecting the activation state of the exhaust purification catalyst)

Claims (3)

An engine control device in which an electric supercharger is disposed in an intake passage,
An engine body having a cylinder capable of communicating with the intake passage by opening and closing the intake valve;
A piston inserted into the cylinder;
An exhaust purification catalyst provided in an exhaust passage for exhausting exhaust gas from the cylinder;
Means for detecting or estimating the active state of the exhaust purification catalyst;
Compression ratio adjusting means for changing the effective compression ratio of the engine body;
Control means for controlling the operation of the engine,
When the inactive state of the exhaust purification catalyst is detected or estimated, the control means activates the electric supercharger for a predetermined period from the start of the engine, and the compression ratio adjustment means An engine control apparatus, wherein the effective compression ratio is made smaller than immediately after the predetermined period has elapsed. The engine control device according to claim 1,
The engine control apparatus according to claim 1, wherein the predetermined period is a period until the exhaust purification catalyst changes from an inactive state to an active state. The engine control device according to claim 1 or 2,
The compression ratio adjusting means is an intake valve drive mechanism capable of adjusting a closing timing of the intake valve;
The engine control apparatus, wherein the control means is configured to reduce the effective compression ratio by delaying the closing timing of the intake valve as compared with immediately after the predetermined period.

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