JP2009264150A - Control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of catalyst deterioration diagnosis as compared with the prior art.
A control device (2) of the present invention includes a compression ratio control unit and a catalyst diagnosis unit (201). The compression ratio control unit (201) controls the compression ratio of the engine (1) according to the operating state. The catalyst diagnosis unit (201) acquires the maximum oxygen storage amount in the catalyst (161) based on the output of the gas sensor (178b), and based on the acquired value of the maximum oxygen storage amount and the reference value, the catalyst ( 161) is determined. When the acquired value of the maximum oxygen storage amount when the compression ratio is the first value is lower than the reference value, the control device (2) reduces the compression ratio below the first value and again increases the maximum oxygen storage amount. Try to get.
[Selection] Figure 1

Description

  The present invention relates to an engine configured to be able to change a compression ratio, a catalyst interposed in a passage of exhaust gas discharged from the engine, and a downstream side in the flow direction of exhaust gas from the catalyst in the passage. The present invention relates to a control device that is applied to a system including a gas sensor configured to generate an output corresponding to the concentration of a specific component in exhaust gas that is interposed and passes through the catalyst.

  In this type of system (for example, an automobile), a catalyst is interposed in the exhaust passage in order to purify the exhaust gas. This catalyst deteriorates due to harmful components (lead, sulfur, etc.) in the fuel. When this catalyst deteriorates, the exhaust gas purification rate deteriorates and exhaust emission increases. Therefore, various devices for determining the deterioration of the catalyst have been proposed in the past (see, for example, JP-A-5-133264, JP-A-2004-28029, JP-A-2006-57461, etc.). ).

  As this type of catalyst, so-called three-way catalysts are widely used. This three-way catalyst has a function called an oxygen storage function or an oxygen storage function. This oxygen storage function has the following two features: (1) When the air-fuel ratio of the fuel mixture is lean, NOx is taken away from nitrogen oxide (NOx) in the exhaust gas. And (2) when the air-fuel ratio of the fuel mixture is rich, the stored oxygen is converted into unburned components (HC) in the exhaust gas. , CO, etc.) for oxidation.

  Therefore, the larger the maximum value of the amount of oxygen that can be stored by the three-way catalyst (hereinafter referred to as “oxygen storage amount”), the higher the purification capacity of the three-way catalyst. That is, the deterioration state of the three-way catalyst can be determined by the above-mentioned maximum value (hereinafter referred to as “maximum oxygen storage amount”).

  Therefore, the catalyst deterioration degree detection device disclosed in JP-A-5-133264 and the like is configured as follows: a first air-fuel ratio sensor is disposed upstream of the three-way catalyst in the exhaust passage. ing. A second air-fuel ratio sensor is disposed downstream of the three-way catalyst in the exhaust passage. In such an apparatus configuration, the above-described three-way catalyst deterioration state determination (maximum oxygen storage amount calculation) is performed as follows.

First, the air-fuel ratio of the fuel mixture supplied into the engine cylinder is set to a predetermined lean air-fuel ratio for a predetermined time. Thereby, oxygen is occluded by the three-way catalyst up to the limit of the occlusion capacity. Thereafter, the air-fuel ratio of the fuel mixture is forcibly changed to a predetermined rich air-fuel ratio. Then, the air-fuel ratio detected by the second air-fuel ratio sensor changes to the rich side after being maintained at the theoretical air-fuel ratio for a certain time Δt. Based on the difference Δ (A / F) between the theoretical air-fuel ratio and the rich air-fuel ratio at this time, Δt, and the intake air amount, the maximum oxygen storage amount is obtained.
JP-A-5-133264 Japanese Patent Laid-Open No. 2004-28029 JP 2005-69129 A JP 2006-57461 A JP 2007-85300 A

  Conventionally, an engine (variable compression ratio engine) configured to be able to change the compression ratio is known (see, for example, JP-A-2005-69129 and JP-A-2007-85300). In this variable compression ratio engine, when the compression ratio is changed, the exhaust temperature changes.

  When the exhaust temperature changes, the exhaust gas purification function of the catalyst also changes (see, for example, FIG. 4 of JP-A-2007-85300). This is because the catalyst temperature also changes due to the change in the exhaust temperature. Specifically, the maximum oxygen storage amount increases as the temperature of the three-way catalyst increases.

  Therefore, if the catalyst deterioration determination is made immediately based on the acquired value of the maximum oxygen storage amount without considering the compression ratio setting state and the catalyst temperature at the time of acquiring the maximum oxygen storage amount, the determination accuracy becomes poor (for example, originally In the case of a catalyst that has not yet deteriorated abnormally). The present invention has been made to cope with such a problem. That is, an object of the present invention is to improve the accuracy of the catalyst deterioration diagnosis as compared with the prior art.

  The control device of the present invention is applied to a system including an engine, a catalyst, and a gas sensor. The engine to which the present invention is applied is configured to be able to change the compression ratio. Here, the “compression ratio” includes “mechanical compression ratio” and “actual compression ratio” as described below. The present invention is not limited to a case where the mechanical compression ratio can be changed, and can be applied to a case where the actual compression ratio can be widely changed.

  The mechanical compression ratio is a value obtained by dividing the sum of the gap volume (combustion chamber volume at the piston top dead center) and the piston stroke volume by the gap volume, and is also referred to as a nominal compression ratio or a geometric compression ratio. The mechanical compression ratio can be changed, for example, by relatively moving a crankcase in which the crankshaft is rotatably supported and a cylinder block having a cylinder head fixed to the upper end portion along the central axis of the cylinder. . Alternatively, the mechanical compression ratio can be changed by changing the bending state of the connecting rod when the connecting rod (member connecting the piston and the crankshaft) is configured to be bent.

  The actual compression ratio is an effective compression ratio with respect to intake air, and is typically a value obtained by dividing the combustion chamber volume at the start of compression of intake air by the combustion chamber volume at the end of compression. This actual compression ratio can naturally be changed in accordance with the change in the mechanical compression ratio as described above. The actual compression ratio can be changed by changing the operation timing of the intake valve and the exhaust valve together with the change of the mechanical compression ratio or instead of the change of the mechanical compression ratio.

  The catalyst is interposed in an exhaust gas passage exhausted from the engine, and is configured to purify the exhaust gas. The gas sensor is interposed downstream of the catalyst in the passage in the flow direction of the exhaust gas. This gas sensor is configured to generate an output corresponding to the concentration (for example, oxygen concentration) of a specific component in the exhaust gas that has passed through the catalyst (this gas sensor generates an output corresponding to the air-fuel ratio of the fuel mixture). Therefore, it may be referred to as an “air-fuel ratio sensor”).

  The present control device includes a compression ratio control unit and a catalyst diagnosis unit. The compression ratio control unit controls the compression ratio of the engine according to the operating state. The catalyst diagnosis unit acquires the maximum oxygen storage amount in the catalyst based on the output of the gas sensor, and the state (deterioration state) of the catalyst based on the acquired value of the maximum oxygen storage amount and a predetermined reference value. It comes to judge.

  A feature of the present invention is that when the acquired value at the compression ratio is lower than the reference value, the maximum oxygen storage amount is acquired again by reducing the compression ratio below the first value. That is, the control device (the compression ratio control unit and the catalyst diagnosis unit) is configured to try. The compression ratio control unit may control the compression ratio to be constant during acquisition of the maximum oxygen storage amount by the catalyst diagnosis unit.

  In such a configuration, first, the maximum oxygen storage amount at which the compression ratio is the first value is acquired. When the acquired value is lower than the reference value, an attempt is made to reacquire the maximum oxygen storage amount by reducing the compression ratio below the first value. Specifically, the compression ratio control unit sets the compression ratio to a second value lower than the first value when the compression ratio is the first value and the acquired value is lower than the reference value. Try to set.

  In addition, when the compression ratio is lowered by the compression ratio control unit, that is, the compression ratio cannot be changed from the first value to the second value (for example, the first value can be changed in the compression ratio). When it is at or near the lowest value in the range, the occurrence of an abnormality (due to deterioration) of the catalyst can be determined.

  When the first value is higher than the lowest value in the changeable range, and the compression ratio is set to the second value by the compression ratio control unit, the catalyst diagnosis unit has a compression ratio of The state of the catalyst is determined based on the acquired value after being set to the second value by the compression ratio control unit. That is, for example, the catalyst diagnosis unit determines the state of the catalyst based on the acquired value in the second value. Alternatively, for example, the catalyst diagnosis unit determines the state of the catalyst based on the acquired value in the first value and the acquired value in the second value.

  As described above, according to the present invention, even if the acquired value of the maximum oxygen storage amount when the compression ratio is the first value is lower than the reference value, the abnormality determination of the catalyst is not immediately performed. Instead, the acquisition of the maximum oxygen storage amount is attempted again by reducing the compression ratio below the first value. Thereby, the determination of the state of the catalyst, that is, the deterioration diagnosis of the catalyst can be performed with higher accuracy than before. Specifically, for example, the erroneous determination of deterioration for the catalyst that should not be determined for deterioration can be favorably avoided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the present invention (an embodiment that the applicant considers best at the time of filing of the present application) will be described with reference to the drawings.

  In addition, the description about the following embodiment is specific to the extent possible, merely an example of the embodiment of the present invention in order to satisfy the description requirement (description requirement / practicability requirement) of the specification required by law. It is only what is described in. Therefore, as will be described later, it is quite natural that the present invention is not limited to the specific configurations of the embodiments described below. Modifications to the embodiments are listed together at the end, as insertions during the description of the embodiment impede understanding of the description of the consistent embodiment.

<Overall system configuration>
FIG. 1 is a schematic configuration diagram showing an overall configuration of a system S (vehicle) to which the present invention is applied, including an in-line multiple cylinder engine 1 and a control device 2 according to an embodiment of the present invention. . FIG. 1 is a cross-sectional view of the engine 1 taken along a plane orthogonal to the cylinder arrangement direction.

  In the present embodiment, the engine 1 is configured to be able to change the mechanical compression ratio between about 10: 1 to about 16: 1, as will be described later. In addition, the control device 2 of the present embodiment is configured to control the operation of the engine 1, determine the state of each part, and appropriately display the determination result to the driver.

<Engine and surrounding configuration>
The engine 1 includes a cylinder block 11, a cylinder head 12, a crankcase 13, and a variable compression ratio mechanism 14. An intake passage 15 and an exhaust passage 16 are connected to the engine 1.

<< Engine block >>
The cylinder block 11 is formed with a cylinder bore 111 that is a substantially cylindrical through hole. A piston 112 is accommodated inside the cylinder bore 111 so as to be capable of reciprocating along a cylinder center axis CCA as a center axis of the cylinder bore 111.

  A cylinder head 12 is joined to the upper end of the cylinder block 11, that is, the end of the cylinder block 11 on the top dead center side of the piston 112. The cylinder head 12 is fixed to the above-described upper end portion by a bolt (not shown) or the like so as not to move relative to the cylinder block 11.

  In the lower end portion of the cylinder head 12, a plurality of concave portions are provided at positions corresponding to the upper end portions of the cylinder bores 111. That is, the space inside the cylinder bore 111 on the cylinder head 12 side (upper side in the figure) with respect to the top surface of the piston 112 in a state where the cylinder head 12 is joined and fixed to the cylinder block 11 and the inside of the above-described recess ( A combustion chamber CC is formed by the space on the lower side in the drawing. An intake port 121 and an exhaust port 122 are formed in the cylinder head 12 so as to communicate with the combustion chamber CC.

  The cylinder head 12 includes an intake valve 123, an exhaust valve 124, a variable intake valve timing device 125, a variable exhaust valve timing device 126, and an injector 127.

  The intake valve 123 is a valve for controlling the communication state between the intake port 121 and the combustion chamber CC. The exhaust valve 124 is a valve for controlling the communication state between the exhaust port 122 and the combustion chamber CC. The variable intake valve timing device 125 and the variable exhaust valve timing device 126 are configured to change the opening / closing timing of the intake valve 123 and the exhaust valve 124. Since the specific configurations of the variable intake valve timing device 125 and the variable exhaust valve timing device 126 are well known, description thereof will be omitted.

  The injector 127 is configured so that fuel to be supplied into the combustion chamber CC can be injected into the intake port 121.

  A crankshaft 131 is disposed in the crankcase 13 in parallel with the cylinder arrangement direction. The crankshaft 131 is rotatably supported. The crankshaft 131 is connected to the piston 112 via a connecting rod 132 so as to be rotationally driven based on reciprocal movement along the cylinder central axis CCA of the piston 112.

<<< Variable compression ratio mechanism >>>
The variable compression ratio mechanism 14 in the engine 1 of the present embodiment moves the joined body of the cylinder block 11 and the cylinder head 12 relative to each other along the cylinder center axis CCA with respect to the crankcase 13 so that the clearance volume is increased. By changing, the mechanical compression ratio can be changed within the above range.

  The variable compression ratio mechanism 14 has the same configuration as that described in Japanese Patent Application Laid-Open Nos. 2003-206871 and 2007-85300. Therefore, in this specification, detailed description of this mechanism will be omitted, and only an outline will be described.

  That is, the variable compression ratio mechanism 14 includes a connection mechanism 141 and a drive mechanism 142. The coupling mechanism 141 is configured to couple the cylinder block 11 and the crankcase 13 so as to be movable relative to each other along the cylinder center axis CCA. The drive mechanism 142 includes a motor, a gear mechanism, and the like, and is configured to move the cylinder block 11 and the crankcase 13 relative to each other along the cylinder center axis CCA.

<< Intake and exhaust passage >>
An intake passage 15 including an intake manifold, a surge tank, and the like is connected to the intake port 121. A throttle valve 151 is interposed in the intake passage 15. The throttle valve 151 is configured to be rotationally driven by a throttle valve actuator 152 formed of a DC motor.

  An exhaust passage 16 including an exhaust manifold is connected to the exhaust port 122. The exhaust passage 16 is a passage for exhaust gas discharged from the combustion chamber CC via the exhaust port 122. A catalytic converter 161 is interposed in the exhaust passage 16. The catalytic converter 161 includes a three-way catalyst having an oxygen storage function therein, and is configured to purify HC, CO, and NOx in the exhaust gas.

<< Various sensors >>
The system S includes a cooling water temperature sensor 171, a crank position sensor 172, an intake cam position sensor 173, an exhaust cam position sensor 174, an air flow meter 175, an intake air temperature sensor 176, a throttle position sensor 177, an upstream air-fuel ratio sensor 178a, and a downstream side. Various sensors such as an air-fuel ratio sensor 178b and an accelerator opening sensor 179 are provided.

  The coolant temperature sensor 171 is attached to the cylinder block 11 in the engine 1. The coolant temperature sensor 171 is configured to output a signal corresponding to the coolant temperature Tw in the cylinder block 11.

  The crank position sensor 172 is attached to the crankcase 13 in the engine 1. The crank position sensor 172 is configured to output a waveform signal having a pulse corresponding to the rotation angle of the crankshaft 131. Specifically, the crank position sensor 172 outputs a signal having a narrow pulse every time the crankshaft 131 rotates 10 ° and a signal having a wide pulse every time the crankshaft 131 rotates 360 °. It is configured. That is, the crank position sensor 172 is configured to output a signal corresponding to the engine speed Ne.

  The intake cam position sensor 173 and the exhaust cam position sensor 174 are attached to the cylinder head 12 in the engine 1. The intake cam position sensor 173 outputs a waveform signal having a pulse corresponding to the rotation angle of an intake cam shaft (not shown) for reciprocating the intake valve 123 (included in the variable intake valve timing device 125). It is configured. Similarly, the exhaust cam position sensor 174 is configured to output a waveform signal having a pulse corresponding to a rotation angle of an exhaust camshaft (not shown).

  The air flow meter 175, the intake air temperature sensor 176, and the throttle position sensor 177 are attached to the intake passage 15. The air flow meter 175 is configured to output a signal corresponding to an intake air flow rate Ga that is a mass flow rate of intake air flowing through the intake passage 15. The intake air temperature sensor 176 is configured to output a signal corresponding to the temperature of the intake air. The throttle position sensor 177 is configured to output a signal corresponding to the rotational phase of the throttle valve 151 (throttle valve opening TA).

  The upstream air-fuel ratio sensor 178 a and the downstream air-fuel ratio sensor 178 b are attached to the exhaust passage 16. The upstream air-fuel ratio sensor 178a is disposed upstream of the catalytic converter 161 in the exhaust gas flow direction. The downstream air-fuel ratio sensor 178b is disposed downstream of the catalytic converter 161 in the exhaust gas flow direction.

  FIG. 2A is a graph showing output characteristics of the upstream air-fuel ratio sensor 178a shown in FIG. FIG. 2B is a graph showing output characteristics of the downstream air-fuel ratio sensor 178b shown in FIG. As shown in FIG. 2A, the upstream air-fuel ratio sensor 178a is an all-region type air-fuel ratio sensor having a relatively linear output characteristic in a wide air-fuel ratio range. Specifically, the upstream air-fuel ratio sensor 178a is composed of a limiting current type oxygen concentration sensor.

  As shown in FIG. 2B, the downstream air-fuel ratio sensor 178b corresponding to the gas sensor of the present invention is substantially constant on the rich side and the lean side from the stoichiometric air-fuel ratio, but suddenly changes before and after the stoichiometric air-fuel ratio. This is an air-fuel ratio sensor having output characteristics. Specifically, the downstream air-fuel ratio sensor 178b is composed of a solid electrolyte type zirconia oxygen sensor.

  Referring to FIG. 1 again, the accelerator opening sensor 179 is configured to output a signal corresponding to the operation amount Accp of the accelerator pedal 181 operated by the driver. Further, an alarm device 182 is provided at a position that is easily visible by the driver. The alarm device 182 includes a warning indicator light.

<Control device>
The control device 2 according to the present embodiment includes a CPU 201, a ROM 202, a RAM 203, a backup RAM 204, an interface 205, and a bus 206. The CPU 201, ROM 202, RAM 203, backup RAM 204, and interface 205 are connected to each other via a bus 206.

  The ROM 202 stores in advance a routine (program) executed by the CPU 201, tables (lookup tables, maps), parameters, and the like that are referred to when the routine is executed. The RAM 203 is configured to temporarily store data as necessary when the CPU 201 executes a routine. The backup RAM 204 is configured so that data is stored when the CPU 201 executes a routine with the power turned on, and the stored data can be retained even after the power is shut off.

  The interface 205 includes a coolant temperature sensor 171, a crank position sensor 172, an intake cam position sensor 173, an exhaust cam position sensor 174, an air flow meter 175, an intake air temperature sensor 176, a throttle position sensor 177, an upstream air-fuel ratio sensor 178a, and a downstream air It is electrically connected to various sensors such as a fuel ratio sensor 178b and an accelerator opening sensor 179, and is configured so that signals from these sensors can be transmitted to the CPU 201.

  The interface 205 is electrically connected to operating parts such as a variable intake valve timing device 125, a variable exhaust valve timing device 126, an injector 127, a drive mechanism 142, an alarm device 182 and the like. The CPU 201 is configured to transmit an operation signal for causing the CPU 201 to these operation units.

  That is, the control device 2 receives signals from the above-described various sensors via the interface 205 and sends the above-described operation signals to each operation unit based on the calculation result of the CPU 201 corresponding to the signals. It is configured as follows.

  In the present embodiment, the control device 2 (CPU 201) that controls the drive mechanism 142 for setting the relative movement state of the cylinder block 11 and the cylinder head 12 and the crankcase 13 by the variable compression ratio mechanism 14 is used. A compression ratio control unit (compression ratio control means) is configured. In addition, the catalyst diagnosis unit (catalyst diagnosis means) of the present invention is configured by the control device 2 (CPU 201) that diagnoses the deterioration state of the catalytic converter 161 based on the output of the downstream air-fuel ratio sensor 178b as described later. .

<Overview of operation>
In the system S of the present embodiment, the control device 2 performs the following processing.

<< Air-fuel ratio control >>
A target air-fuel ratio is set based on the throttle valve opening and the like. This target air-fuel ratio is normally set to the stoichiometric air-fuel ratio. On the other hand, at the time of acceleration or the like, the target air-fuel ratio can be set to a value slightly shifted from the stoichiometric air-fuel ratio to the rich side or lean side as necessary.

  Further, a deterioration state diagnosis (catalyst OBD: OBD is an abbreviation for on-board diagnosis) of the catalytic converter 161 is performed under a predetermined operation state during steady operation. In this case, the target air-fuel ratio is controlled to change in a rectangular wave between a value shifted from the stoichiometric air-fuel ratio to the rich side and a value shifted from the stoichiometric air-fuel ratio to the lean side (air-fuel ratio active). control).

  Based on the target air-fuel ratio set as described above, the intake air flow rate, and the like, the basic value (basic fuel injection amount) of the fuel amount injected from the injector 127 is acquired.

  If the predetermined feedback control condition is not satisfied, such as when the upstream air-fuel ratio sensor 178a and the downstream air-fuel ratio sensor 178b are not sufficiently warmed up immediately after the engine 1 is started, the engine is opened based on the basic fuel injection amount. Loop control is performed (in this open loop control, learning control based on a learning correction coefficient can be performed).

  When the feedback control condition is satisfied, the basic fuel injection amount is feedback-corrected based on the outputs from the upstream air-fuel ratio sensor 178a and the downstream air-fuel ratio sensor 178b, so that the actual fuel injection amount from the injector 127 is obtained. (Command fuel injection amount) is acquired. Further, based on the outputs from the upstream air-fuel ratio sensor 178a and the downstream air-fuel ratio sensor 178b, air-fuel ratio learning for acquiring the learning correction coefficient in the above-described open loop control is performed.

<< Catalyst OBD >>
The maximum oxygen storage amount Cmax of the catalytic converter 161 is acquired by the above-described air-fuel ratio active control. Whether or not the deterioration abnormality of the catalytic converter 161 has occurred is determined based on whether or not the acquired value of the maximum oxygen storage amount Cmax is equal to or greater than a predetermined reference value Cmax_r. That is,
Cmax <Cmax_r
In this case, it is determined that a deterioration abnormality of the catalytic converter 161 has occurred, and a catalyst abnormality process (notification to the driver via the alarm device 182) is performed.

  However, the characteristics of the catalytic converter 161 differ depending on the temperature and the degree of deterioration. FIG. 3 is a graph showing temperature characteristics of the catalytic converter 161 shown in FIG.

  As shown in FIG. 3, when the catalytic converter 161 is new (see (1) in the figure), the oxygen storage amount is large even if the catalyst temperature is relatively low. In this case, the degree of increase in the oxygen storage amount with respect to the increase in the catalyst temperature (the slope of the characteristic line in the figure) is very small (flat) in the region above the predetermined activation temperature (see the dashed line in the figure). close).

  As the catalytic converter 161 gradually deteriorates with use, the oxygen storage amount decreases and the relationship between the catalyst temperature and the oxygen storage amount gradually approaches linear (see (2) to (5) in the figure). .

  Here, when the deterioration level of the catalyst is medium (see (2) to (3) in the figure), the oxygen storage amount is a required level (corresponding to the reference value Cmax_r) by increasing the catalyst temperature to a predetermined activation temperature. : Refer to the two-dot chain line in the figure). Further, in this case, the degree of increase in the oxygen storage amount with respect to the increase in the catalyst temperature (the slope of the characteristic line in the figure) gradually increases as the deterioration of the catalyst proceeds.

  On the other hand, when the deterioration level of the catalyst becomes high (see (4) to (5) in the figure), even if the catalyst temperature rises to a predetermined activation temperature, the oxygen storage amount may not reach the required level. In this case, the degree of increase in the oxygen storage amount with respect to the increase in the catalyst temperature (the slope of the characteristic line in the figure) gradually decreases as the deterioration of the catalyst proceeds. When the catalytic converter 161 is deteriorated to an extent unsuitable for use, the oxygen occlusion amount does not reach a necessary level even if the catalyst temperature is increased within a range in which the temperature can be increased (see (5) in the figure).

  Further, when the compression ratio is lowered, the exhaust temperature rises and the catalyst temperature rises. On the other hand, when the compression ratio is increased, the exhaust temperature decreases and the catalyst temperature decreases.

Based on the above relationship, in the present embodiment, Cmax <Cmax_r in a certain mechanical compression ratio setting state.
In this case, an attempt is made to reacquire the maximum oxygen storage amount Cmax by lowering the mechanical compression ratio.

<< Compression ratio control >>
The mechanical compression ratio is controlled based on the operating state of the engine 1 such as a warm-up state or a load state.

  Specifically, during the warm-up operation, the compression ratio is set to the low compression ratio side for early warm-up of the main body of the engine 1 and the catalytic converter 161. When the operating state of the engine 1 reaches the normal range after warming up (during city driving or high-speed cruise), the compression ratio is set to the high compression ratio side. Thereby, thermal efficiency becomes high and fuel consumption improves. On the other hand, the compression ratio is set to the low compression ratio side in a high output range (during rapid acceleration or running uphill). Thereby, knocking is suppressed.

  For this reason, the mechanical compression ratio is set to the low compression ratio side according to the driver's request (operation of the accelerator pedal 181 etc.) when driving in a high output range such as sudden acceleration or climbing is required. The mechanical compression ratio is set as high as possible on the high compression ratio side.

  However, if the compression ratio changes during the execution of the catalyst OBD, as described above, the temperature of the catalytic converter 161 fluctuates, and thus the oxygen storage amount also changes. Therefore, the mechanical compression ratio is kept constant during acquisition of the maximum oxygen storage amount Cmax in the catalyst OBD. Thereby, the maximum oxygen storage amount Cmax is obtained with high accuracy, and the accuracy of the catalyst OBD is improved.

Furthermore, in this embodiment, when the catalyst OBD is executed in a state where a certain mechanical compression ratio is set,
Cmax <Cmax_r
In this case, the control device 2 tries to lower the mechanical compression ratio in order to reacquire the maximum oxygen storage amount Cmax.

<Details of operation>
Next, a specific example of the catalyst OBD operation by the control device 2 of the present embodiment shown in FIG. 1 will be described.

  In this specific example, the mechanical compression ratio of the engine 1 after completion of the warm-up operation is determined in a plurality of stages (preferably 3 to 3) according to predetermined engine parameters such as the engine speed Ne and the load factor KL and a predetermined map. 5 stages, for example, 10: 1/12: 1/14: 1/16: 1).

  After the warm-up operation is completed, the compression ratio is set to the high compression ratio side when the operating state of the engine 1 reaches the normal range, and then other catalyst OBD conditions (the vehicle speed is a predetermined speed or more and the intake air flow rate is a predetermined amount or less) , Etc.) is first established, the catalyst OBD is started.

  When the maximum oxygen storage amount Cmax acquired at the compression ratio at the start of the catalyst OBD is equal to or greater than the reference value Cmax_r, the catalyst OBD is completed. On the other hand, when the maximum oxygen storage amount Cmax is lower than the reference value Cmax_r, the compression ratio is lowered by one step, and the maximum oxygen storage amount Cmax is acquired again. Then, the final deterioration state determination of the catalytic converter 161 is made based on the maximum oxygen storage amount Cmax acquired for the second time.

  Hereinafter, the operation of this example will be described using a flowchart. In the following flowchart and the description thereof, “step” is abbreviated as “S”.

  The CPU 201 executes the catalyst OBD routine 400 shown in FIG. 4 at every predetermined timing. When this routine 400 is started, first, in S410, it is determined whether or not the maximum oxygen storage amount Cmax_a at the high compression ratio side compression ratio (εa: first value) has been acquired. When the maximum oxygen storage amount Cmax_a has not been acquired (S410 = No), the process proceeds to S420, the acquisition process of the maximum oxygen storage amount Cmax_a is started (or the startup state is continued), and this routine is temporarily ended.

  Here, FIG. 5 is a graph showing how the maximum oxygen storage amount Cmax is obtained in the catalyst OBD. In FIG. 5, (i) is a graph showing the air-fuel ratio change during the execution of the catalyst OBD. (Ii) is a graph showing the oxygen storage amount OSA of the catalytic converter 161 that changes corresponding to the air-fuel ratio change shown in (i). (Iii) is a graph showing the output Voxs of the downstream air-fuel ratio sensor 178b corresponding to the change in the air-fuel ratio shown in (i) and the change in the oxygen storage amount OSA shown in (ii).

  First, as shown in FIG. 5 (i), from the catalyst OBD start time t1, the air-fuel ratio is set to be leaner by ΔA / F than the stoichiometric air-fuel ratio (stoich). Then, a lean air-fuel ratio exhaust gas flows into the catalytic converter 161. Therefore, as shown in FIG. 5 (ii), the oxygen storage amount OSA of the catalytic converter 161 gradually increases and reaches the peak value Cmax2 at time t2.

  When the oxygen storage amount OSA of the catalytic converter 161 reaches the peak value Cmax2, the catalytic converter 161 can no longer store oxygen. Therefore, from time t2, exhaust gas containing oxygen (exhaust gas having a lean air-fuel ratio) starts to flow out downstream of the catalytic converter 161. For this reason, as shown in (iii) of FIG. 5, the output Voxs of the downstream air-fuel ratio sensor 178b changes to a value that is greatly displaced to the lean side from the stoichiometric air-fuel ratio.

  When it is determined at time t2 that the output Voxs of the downstream air-fuel ratio sensor 178b has changed to a value that is greatly displaced to the lean side from the stoichiometric air-fuel ratio, as shown in FIG. The air-fuel ratio is set richer by ΔA / F than the stoichiometric air-fuel ratio. Then, rich air-fuel ratio exhaust gas flows into the catalytic converter 161. At this time, the oxygen stored in the catalytic converter 161 is consumed for the oxidation of the inflowing unburned HC and CO. Accordingly, as shown in FIG. 5 (ii), the oxygen storage amount OSA of the catalytic converter 161 gradually decreases from Cmax2, and the oxygen storage amount of the catalytic converter 161 becomes “0” at time t3.

  When the oxygen storage amount OSA of the catalytic converter 161 becomes 0, the catalytic converter 161 can no longer oxidize unburned HC and CO. Therefore, at time t3, the rich air-fuel ratio gas starts to flow out downstream of the catalytic converter 161. Therefore, as shown in (iii) of FIG. 5, the output Voxs of the downstream air-fuel ratio sensor 178b changes from a value indicating lean to a value indicating rich.

  When it is determined at time t3 that the output of the downstream side air-fuel ratio sensor 178b has changed from a value indicating lean to a value indicating rich, as shown in (i) of FIG. The fuel ratio is set to be leaner by ΔA / F than the stoichiometric air-fuel ratio. As a result, as shown in FIG. 5 (ii), the oxygen storage amount OSA of the catalytic converter 161 continues to increase from “0” and reaches the peak value Cmax4 at time t4. Then, as described above, at time t4, the output Voxs of the downstream air-fuel ratio sensor 178b changes from a value indicating rich to a value indicating lean. When the change in the output Voxs of the downstream air-fuel ratio sensor 178b as described above at time t4 is determined, the catalyst OBD is terminated and the air-fuel ratio control is returned to the normal control.

By executing the rectangular wave air-fuel ratio control (active control) as described above, the maximum oxygen storage amount Cmax of the catalytic converter 161 is obtained by the following equation. In the following formula, the value “0.23” is the weight ratio of oxygen contained in the atmosphere. mfr is the total amount of the fuel injection amount Fi within a predetermined time (calculation cycle tsample).
ΔO2 = 0.23 · mfr · ΔA / F
Cmax2 = ΣΔO2 (section t = t2 to t3)
Cmax4 = ΣΔO2 (section t = t3 to t4)
Cmax = (Cmax2 + Cmax4) / 2

  As shown in this equation, the total injection amount mfr within a predetermined time tsample in the interval t = t2 to t3 is multiplied by the deviation ΔA / F of the air / fuel ratio A / F from the theoretical air / fuel ratio. Then, the air shortage amount at the predetermined time tsample is obtained, and the oxygen storage amount change amount (occlusion oxygen consumption) ΔO2 at the predetermined time tsample is obtained by multiplying the air shortage amount by the weight ratio of oxygen. It is done. Then, by accumulating the oxygen storage amount change amount ΔO2 from time t2 to time t3, the oxygen consumption amount from the state where the catalytic converter 161 stores oxygen to the maximum consumed state, that is, the peak value. Cmax2 is estimated and calculated. Similarly, in the section t = t3 to t4, the oxygen storage amount from the state where the catalytic converter 161 consumes all the oxygen to the state where the oxygen is stored to the maximum is obtained by accumulating the oxygen storage amount change ΔO2. That is, the peak value Cmax4 is estimated and calculated.

When the in-cylinder intake air amount Mc is constant during the catalyst OBD (that is, the intake air flow rate Ga is constant), the above equation can be simplified as follows.
Cmax2 = 0.23 · mfr · ΔA / F · (t3−t2)
Cmax4 = 0.23 · mfr · ΔA / F · (t4−t3)
Cmax = (Cmax2 + Cmax4) / 2

  Referring to FIG. 4 again, when the maximum oxygen storage amount Cmax_a has been acquired (S410 = Yes), the process proceeds to S430, and it is determined whether or not the maximum oxygen storage amount Cmax_a is lower than the reference value Cmax_r. When the maximum oxygen storage amount Cmax_a is equal to or greater than the reference value Cmax_r (S430 = No), the process proceeds to S440, the normal process is performed, and this routine is temporarily ended.

  When the maximum oxygen storage amount Cmax_a is lower than the reference value Cmax_r (S430 = No), the process proceeds to S450, and the maximum oxygen storage amount Cmax_b at the low compression ratio side compression ratio (εb: second value) has been acquired. It is determined whether or not there is. If the maximum oxygen storage amount Cmax_b has not been acquired (S450 = No), the process proceeds to S460, the acquisition process of the maximum oxygen storage amount Cmax_b is started (or the startup state is continued), and this routine is temporarily ended.

  When the maximum oxygen storage amount Cmax_b has been acquired (S450 = Yes), the process proceeds to S470, and it is determined whether or not the maximum oxygen storage amount Cmax_b is lower than the reference value Cmax_r. When the maximum oxygen storage amount Cmax_b is equal to or greater than the reference value Cmax_r (S470 = No), the process proceeds to S440 and the normal process is performed. On the other hand, when the maximum oxygen storage amount Cmax_b is lower than the reference value Cmax_r (S470 = Yes), the process proceeds to S490, and the process when the catalyst is abnormal is performed. Thereafter, this routine is temporarily terminated.

  As described above, in this specific example, after the engine 1 is warmed up, the maximum oxygen storage amount Cmax_a is first acquired when the operating state reaches the normal range and becomes the high compression ratio side. When catalyst deterioration is suspected by this acquired value, the compression ratio is set to the low compression ratio side and the catalyst temperature is raised, and then the maximum oxygen storage amount Cmax_b is acquired again. Based on the re-acquired value, catalyst deterioration diagnosis is performed. That is, the catalyst deterioration state determination is performed at the higher value of the maximum oxygen storage amount Cmax.

  Thus, in this specific example, the catalyst OBD is executed while the compression ratio is set as high as possible. Further, in this specific example, when the state of the catalytic converter 161 is not yet to be deteriorated yet (see (4) in FIG. 3), the first maximum oxygen storage amount Cmax that tends to be low in the catalyst temperature. Rather than being determined immediately based on the value at the time of acquisition, normality determination can be made based on the value at the time of acquisition of the second maximum oxygen storage amount Cmax. Therefore, according to this example, the accuracy of the catalyst OBD is improved while maintaining good fuel efficiency.

  In this specific example, the mechanical compression ratio of the engine 1 after the end of the warm-up operation is finely divided in units of 0.5: 1 based on predetermined engine parameters such as the engine speed Ne and the load factor KL and a predetermined map. Is set.

  When the predetermined catalyst OBD condition is first established after the warm-up operation is completed, the catalyst OBD is started (in this case, unlike the first specific example described above, the catalyst OBD is started on the low compression ratio side). Can be).

  In this specific example, when the maximum oxygen storage amount Cmax acquired at the compression ratio at the start of the catalyst OBD is lower than the reference value Cmax_r, the maximum oxygen storage amount Cmax is reduced when the compression ratio is lowered by one step. An acquisition is attempted. Based on the first and second maximum oxygen storage amounts Cmax, the final deterioration state determination of the catalytic converter 161 is performed.

  Hereinafter, the operation of this example will be described using a flowchart. The CPU 201 executes the catalyst OBD routine 600 shown in FIG. 6 at every predetermined timing. The processing of S610 to S660 in this routine 600 is the same as S410 to S460 in the flowchart of FIG. Further, the processing of S680 and S690 in this routine 600 is the same as S480 and S490 in the flowchart of FIG. Therefore, only the characteristic part of this routine 600 will be described below.

  If the first maximum oxygen storage amount Cmax_a is lower than the reference value Cmax_r and the second maximum oxygen storage amount Cmax_b has been acquired (S650 = Yes), the process proceeds from S672 to S676.

In S672, the deviation ΔCmax of the maximum oxygen storage amount Cmax between the first time and the second time is calculated, and in the next S674, the rate of change s due to the temperature of the maximum oxygen storage amount Cmax between the first time and the second time is calculated. Is done. This rate of change s corresponds to the slope of the characteristic line in FIG. 3, and is calculated by the following equation.
s = ΔCmax / ΔT

  (ΔT is a difference in catalyst temperature between the compression ratio εa and the compression ratio εb, and is obtained based on εa, εb, other engine parameters, a map, and the like. In this specific example, (In order to improve diagnostic accuracy, the difference between the compression ratio εa and the compression ratio εb is set so that ΔT is 30 ° C. or higher.)

  Subsequently, the process proceeds to S676, and it is determined whether or not the rate of change s is smaller than a predetermined value sr. Specifically, at the stage where the catalyst deterioration has progressed to a considerable extent (S630 = Yes), as described above, the degree of increase in the oxygen storage amount with respect to the increase in the catalyst temperature gradually decreases as the catalyst deterioration progresses (FIG. (3) to (5) in 3). Therefore, when the rate of change s is equal to or greater than the predetermined value sr (S676 = No), the process proceeds to S680 and normal processing is performed. On the other hand, when the change rate s is smaller than the predetermined value sr (S676 = Yes), the process proceeds to S690, and the process when the catalyst is abnormal is performed.

  In this specific example, in addition to the operation and effect of the first specific example described above, the progress of catalyst deterioration can be accurately grasped based on the rate of change s. Further, in this specific example, even if both the first maximum oxygen storage amount Cmax_a and the second maximum oxygen storage amount Cmax_b are lower than the reference value Cmax_r, the catalytic converter that should not be determined for deterioration originally. With respect to the state 161 (the state between (4) and (5) in FIG. 3), normality can be determined based on the rate of change s. Therefore, according to this example, the accuracy of the catalyst OBD is further improved.

<Operations and effects according to the embodiment>
In the present embodiment, even when the first maximum oxygen storage amount Cmax_a is lower than the reference value Cmax_r, the processing at the time of catalyst abnormality is not performed immediately, but again after the compression ratio is lowered below εa. The maximum oxygen storage amount Cmax_b is tried. For this reason, even if the catalyst OBD is started in a state where the catalyst temperature is low, it is possible to satisfactorily avoid a deterioration erroneous determination for a catalyst state that should not be determined for deterioration.

  Therefore, according to this embodiment, the catalyst OBD can be executed with high accuracy. Further, according to the present embodiment, the catalyst OBD can be executed satisfactorily even if the execution conditions (catalyst OBD conditions) of the catalyst OBD are set widely in order to ensure the execution frequency of the catalyst OBD. That is, the catalyst OBD can be executed satisfactorily without performing extensive experiments and simulations that prepare a wide range of operating states and catalyst states (types and deterioration states). Therefore, accurate catalyst OBD can be performed with a simple apparatus configuration and processing.

<List of examples of modification>
Note that the above-described embodiment is merely an example of a specific configuration of the present invention that the applicant considered to be the best at the time of filing of the present application, as described above. It should not be limited at all by the embodiment. Therefore, it goes without saying that various modifications can be made to the specific configurations shown in the above-described embodiments within a range that does not change the essential part of the present invention.

  Hereinafter, some modifications will be exemplified. Here, in the following description of the modified example, components having the same configurations and functions as the components in the above-described embodiment are given the same name and the same reference numerals in the modified example. And And about description of the said component, description in the above-mentioned embodiment shall be suitably used in the range which is not inconsistent.

  However, it goes without saying that the modified examples are not limited to the following. The limited interpretation of the present invention based on the description of the above-described embodiment and the following modifications unfairly harms the interests of the applicant (especially rushing the application under the principle of prior application), but improperly imitates the imitator. It is good and not allowed.

  Further, it goes without saying that the configuration of the above-described embodiment and the configuration described in each of the following modifications can be applied in an appropriate combination within a technically consistent range.

  (1) The application target of the present invention is not limited to a vehicle. Further, the present invention can be applied to gasoline engines, diesel engines, methanol engines, bioethanol engines, and any other types of engines. The number of cylinders, cylinder arrangement system (series, V type, horizontally opposed), and fuel injection system (port injection, in-cylinder direct injection) are also not particularly limited.

  (2) The configuration of the engine 1 including the variable compression ratio mechanism 14 is not limited to that of the above-described embodiment. For example, even if the engine 1 is configured such that the connecting rod 132 has a multi-link structure and the mechanical compression ratio is changed by changing the bending state of the connecting rod 132, the present invention is good. Applies to

  (3) The compression ratio control in the above-described embodiment is mainly for the mechanical compression ratio. However, the present invention is not limited to this. For example, the present invention can be similarly applied to the actual compression ratio control by the variable intake valve timing device 125 and the variable exhaust valve timing device 126. Further, the actual compression ratio is changed in accordance with the operating state by combining the change of the mechanical compression ratio by the variable compression ratio mechanism 14 and the change of the valve timing by the variable intake valve timing device 125 and the variable exhaust valve timing device 126. Can also be done. The present invention can be applied to this case well.

  (4) The present invention is not limited to the specific processing contents described in the above specific examples. For example, the following modifications can be made.

In the first specific example, as a result of obtaining the second maximum oxygen storage amount Cmax,
Cmax <Cmax_r
In this case, the compression ratio may be lowered stepwise multiple times until the compression ratio reaches the minimum value εmin. That is, when the maximum oxygen storage amount Cmax_b is smaller than the reference value Cmax_r, the maximum oxygen storage amount Cmax_c may be acquired again after the compression ratio is lowered again. Then, even when the compression ratio is reduced to the minimum value εmin, if the acquired value of the maximum oxygen storage amount Cmax is lower than the reference value Cmax_r, the process when the catalytic converter 161 is abnormally deteriorated may be performed.

  In the first and second specific examples, when the first maximum oxygen storage amount Cmax_a is acquired, the set value of the mechanical compression ratio is at or near the minimum value εmin, and the maximum oxygen storage amount Cmax is reacquired. When the mechanical compression ratio cannot be reduced, the catalyst abnormality treatment may be performed as it is.

  FIG. 7 is a flowchart corresponding to this modification. Note that the processing of the first half (S710 to S750) in the catalyst OBD routine 700 of this variation is the same as S410 to S450 in the flowchart of FIG. 4 and S610 to S650 in the flowchart of FIG. Therefore, only the characteristic part of this routine 600 will be described below.

  When the maximum oxygen storage amount Cmax_b has not been acquired (S750 = No), the process proceeds to S755, and it is determined whether Cmax_b can be acquired.

  Here, when the first maximum oxygen storage amount Cmax_a is acquired, the set value of the mechanical compression ratio is at or near the minimum value εmin, and the mechanical compression ratio decreases for reacquisition of the maximum oxygen storage amount Cmax. If not, the determination in S755 is “No”. In this case, after the process proceeds to S758 and the process at the time of catalyst abnormality is performed, this routine is once ended.

  On the other hand, when the mechanical compression ratio for reacquisition of the maximum oxygen storage amount Cmax can be reduced, the determination in S755 is “Yes”. In this case, the process proceeds from S760 onward, and the same process as the latter half of the first or second specific example described above is performed (therefore, the latter half of the routine 700 is not shown).

In the first and second specific examples, as a result of obtaining the first maximum oxygen storage amount Cmax_a,
Cmax_a <Cmax_r
In this case, the compression ratio may be lowered to the minimum value εmin all at once when acquiring the second maximum oxygen storage amount Cmax_b.

  The above examples can be combined. That is, in the first specific example, when the maximum oxygen storage amount Cmax_b is lower than the reference value Cmax_r (S470 = Yes), the rate of change s is obtained, and when the rate of change s is smaller than the predetermined value sr, the catalyst is abnormal. May be performed. The reference value Cmax_r in this case can be set higher than when the first specific example is implemented alone.

  -Even if the compression ratio is not controlled to be constant throughout the catalyst OBD execution period, it is only necessary that the compression ratio is controlled to be constant during acquisition of the maximum oxygen storage amount. Even when the maximum oxygen storage amount is being acquired, the compression ratio may be changed within a range that does not interfere with the acquisition. For example, there is no problem even if the compression ratio is slightly lowered during the acquisition of the maximum oxygen storage amount during slow acceleration.

  (5) Other modifications not specifically mentioned are also naturally included in the technical scope of the present invention within the scope not changing the essential part of the present invention. Furthermore, in each element constituting the means for solving the problems of the present invention, elements expressed functionally and functionally include the specific structures disclosed in the above-described embodiments and modifications, It includes any structure that can realize this action / function.

1 is a schematic configuration diagram illustrating an overall configuration of a system including an in-line multiple cylinder engine to which the present invention is applied and a control device according to an embodiment of the present invention. It is a graph which shows the output characteristic of the upstream air-fuel ratio sensor shown by FIG. It is a graph which shows the output characteristic of the downstream air-fuel-ratio sensor shown by FIG. It is a graph which shows the temperature characteristic of the catalytic converter shown by FIG. It is a flowchart which shows one specific example of operation | movement (catalyst OBD) of the control apparatus of this embodiment shown by FIG. FIG. 5 is a graph showing how the maximum oxygen storage amount Cmax is acquired in the catalyst OBD shown in FIG. 4. FIG. 6 is a flowchart showing another specific example of the operation (catalyst OBD) of the control device of the present embodiment shown in FIG. 1. 7 is a flowchart showing one modification of the operation (catalyst OBD) shown in FIG. 4 or FIG. 6.

Explanation of symbols

S ... System 1 ... Engine 11 ... Cylinder block 12 ... Cylinder head 13 ... Crankcase 14 ... Variable compression ratio mechanism 141 ... Connection mechanism 142 ... Drive mechanism 15 ... Intake passage 16 ... Exhaust passage 161 ... Catalytic converter 178b ... Downstream air-fuel ratio Sensor 182 ... Alarm device 2 ... Control device 201 ... CPU

Claims (6)

An engine configured to be able to change the compression ratio, a catalyst interposed in an exhaust gas passage exhausted from the engine, and a downstream side in the exhaust gas flow direction from the catalyst in the passage. A gas sensor configured to generate an output corresponding to the concentration of a specific component in the exhaust gas that has passed through the catalyst, and a control device,
A compression ratio control unit for controlling the compression ratio of the engine according to an operating state;
A catalyst diagnostic unit that acquires the maximum oxygen storage amount in the catalyst based on the output of the gas sensor, and determines the state of the catalyst based on the acquired value and the reference value of the maximum oxygen storage amount;
With
The compression ratio is lower than the reference value when the acquired value at the first value is lower than the first value, and the acquisition of the maximum oxygen storage amount is attempted again by reducing the compression ratio from the first value. Control device. The control device according to claim 1,
The catalyst diagnosis unit, when the compression ratio control unit cannot reduce the compression ratio, determines the occurrence of an abnormality of the catalyst. The control device according to claim 1 or 2,
The compression ratio control unit sets a compression ratio lower than the first value when the acquired value is lower than the reference value at the first value higher than the lowest value in the changeable range. Set to a value of
The control device characterized in that the catalyst diagnosis unit determines the state of the catalyst based on the acquired value after the compression ratio is set to the second value by the compression ratio control unit. An engine configured to be able to change the compression ratio, a catalyst interposed in an exhaust gas passage exhausted from the engine, and a downstream side in the exhaust gas flow direction from the catalyst in the passage. A gas sensor configured to generate an output corresponding to the concentration of a specific component in the exhaust gas that has passed through the catalyst, and a control device,
A compression ratio control unit for controlling the compression ratio of the engine according to an operating state;
A catalyst diagnostic unit that acquires the maximum oxygen storage amount in the catalyst based on the output of the gas sensor, and determines the state of the catalyst based on the acquired value and the reference value of the maximum oxygen storage amount;
With
The compression ratio control unit sets a compression ratio lower than the first value when the acquired value at the first value higher than the lowest value in the changeable range is lower than the reference value. Set to a value of
In this case, the catalyst diagnostic unit determines the state of the catalyst based on the acquired value after the compression ratio is set to the second value by the compression ratio control unit. Control device. The control device according to claim 3 or 4, wherein
The control device, wherein the catalyst diagnosis unit determines the state of the catalyst based on the acquired value in the first value and the second value. A control device according to any one of claims 1 to 5,
The engine control apparatus, wherein the compression ratio control unit controls the compression ratio so that the compression ratio becomes constant during the acquisition of the maximum oxygen storage amount by the catalyst diagnosis unit.

Images