JP5943147B2 - Control device and control method for internal combustion engine - Google Patents

Description

  The present invention relates to a control device and control method for an internal combustion engine having a variable compression ratio mechanism that changes a mechanical compression ratio, and more particularly, to a compression ratio in an internal combustion engine that increases the amount of fuel for protecting a protection target component in an exhaust system. Regarding control.

  Various types of variable compression ratio mechanisms for changing the mechanical compression ratio of an internal combustion engine have been known. For example, the applicants have proposed a number of variable compression ratio mechanisms in which the piston top dead center position is displaced up and down by changing the link geometry of a multi-link piston crank mechanism. A variable compression ratio mechanism is also known in which the mechanical compression ratio is similarly changed by displacing the cylinder position up and down with respect to the center position of the crankshaft.

  In such a variable compression ratio mechanism, it is basically desirable that the compression ratio be as high as possible within a range that does not cause abnormal combustion such as knocking. Therefore, as a general trend of the target compression ratio, a low load In the region, the compression ratio is high, but the higher the load, the lower the compression ratio. For example, in Patent Document 1, a target compression ratio of a variable compression ratio mechanism is set with reference to a compression ratio map in which an optimal target compression ratio is assigned in advance using the load and rotation speed (rotation speed) of the internal combustion engine as parameters. Is disclosed.

  On the other hand, in Patent Document 2, in order to avoid the excessively high temperature of the parts to be protected such as the exhaust pipe and any parts around it, the temperature rise due to the exhaust temperature of these parts to be protected is estimated, and the allowable temperature It is disclosed to increase the amount of fuel for lowering the exhaust temperature when exceeding the above.

  Furthermore, in Patent Document 3, in an internal combustion engine having a variable compression ratio mechanism, when the catalyst temperature is equal to or higher than a predetermined temperature, the engine load is shifted from a high load to a low load in order to protect the exhaust purification catalyst. In such a transition, a technology is disclosed in which the compression ratio is limited to a certain upper limit value or less.

  As described above, the target compression ratio in the variable compression ratio mechanism is basically limited by knocking. However, in order to protect the protection target parts in the exhaust system, the fuel increase is performed as in Patent Document 2. In this case, knocking is less likely to occur due to an increase in fuel, and the compression ratio can be further increased. If the compression ratio is increased, the exhaust temperature decreases, which is advantageous in protecting the parts to be protected in the exhaust system.

  In Patent Documents 1 and 2, no consideration is given to the relationship between the fuel increase and the compression ratio, and there is still room for improvement.

  In addition, Patent Document 3 restricts the compression ratio at the time of shifting to a low load to a certain upper limit value in recognition that unburned HC flowing into the exhaust purification catalyst increases as the mechanical compression ratio increases. No relationship between the fuel increase and the compression ratio is disclosed.

JP 2004-92639 A JP 2008-51092 A JP 2012-31839 A

The present invention is a control device for an internal combustion engine including a variable compression ratio mechanism for changing a mechanical compression ratio,
Means for setting a target compression ratio of the variable compression ratio mechanism based on the load and rotation speed of the internal combustion engine;
Fuel increasing means for increasing the fuel to protect the parts to be protected in the exhaust system;
Correction means for correcting the target compression ratio to the high compression ratio side when fuel increase is performed by the fuel increase means;
It has.

  That is, in the present invention, when the parts to be protected in the exhaust system (including parts directly in contact with the exhaust and surrounding parts indirectly receiving the exhaust heat) become excessively high, Fuel increase is executed to lower the exhaust temperature. While the fuel increase is being executed in this way, at the same time, the compression ratio by the variable compression ratio mechanism is corrected to the high compression ratio side. In other words, the compression ratio is controlled to be higher than when the fuel increase is not performed under the same load and rotation speed.

  The mechanical compression ratio of the internal combustion engine is preferably as high as possible from the viewpoint of thermal efficiency, but is limited by knocking. Therefore, a general tendency of the target compression ratio is that the higher the load, the lower the compression ratio. It becomes. However, when the fuel is increased, the mixture cooling action due to the latent heat of vaporization of the fuel increases, so that knocking is less likely to occur than when the fuel is not increased, and operation with a higher mechanical compression ratio is possible. It is. And, by setting the high compression ratio, the thermal efficiency is increased and the exhaust temperature is lowered, so that the amount of fuel increase necessary to prevent overheating of the protection target component is reduced as compared with the case where the fuel increase is simply performed. . Therefore, as a result, it is possible to reduce fuel consumption.

  According to the present invention, by increasing the compression ratio in conjunction with the increase in fuel for protecting parts in the exhaust system, the thermal efficiency can be improved, and the fuel consumption can be reduced while reliably protecting the parts from the exhaust heat. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows one Example of this invention. The block diagram about the exhaust system protection control of this embodiment. The flowchart which shows the control of this Example. It is a timing chart for demonstrating the effect | action of this Example, and is a timing chart which shows the example when an exhaust manifold temperature exceeds a threshold value. The timing chart which shows an example when both exhaust manifold temperature and sensor part temperature exceed each threshold value. The timing chart which shows the example where correction | amendment of the compression ratio was prohibited based on load.

  FIG. 1 is an explanatory diagram showing a system configuration of an internal combustion engine 1 including a control device according to the present invention.

  The internal combustion engine 1 includes a known variable compression ratio mechanism 2 in which the piston top dead center position is displaced up and down by changing the link geometry of the multi-link type piston crank mechanism, and changing the link geometry, that is, mechanical compression. In order to change the ratio, a variable compression ratio actuator 3 composed of, for example, an electric motor is provided. The variable compression ratio actuator 3 also functions as a sensor that detects an actual mechanical compression ratio (actual compression ratio rCR) at the same time. The internal combustion engine 1 has a spark plug 4 in the center of the combustion chamber and a fuel injection valve 5 that injects fuel toward the intake port. Although the illustrated example has a so-called port injection type configuration, the present invention can also be applied to a direct injection type internal combustion engine that injects fuel into the combustion chamber.

  An exhaust temperature sensor 8 for measuring the exhaust temperature is attached to the exhaust manifold 7 of the internal combustion engine 1.

  Further, as operating conditions of the internal combustion engine 1, an accelerator pedal sensor 9 for detecting the opening degree of the accelerator pedal (required load tT) operated by the driver, and the rotational speed (rotational speed) Ne of the internal combustion engine 1 are detected. A rotation speed sensor 10 is provided. The detection signals of these sensors are input to the engine control unit 11, and the injection amount and injection timing of the fuel injection valve 5, the ignition timing of the spark plug 4 and the like are controlled based on these detection signals. The variable compression ratio actuator 3 of the variable compression ratio mechanism 2 is driven so as to achieve a target compression ratio.

  FIG. 2 shows a control block diagram of the exhaust system protection control realized by the engine control unit 11. The basic target compression ratio calculation unit 21 is based on the required load tT detected by the accelerator pedal sensor 9 and the engine speed Ne detected by the rotational speed sensor 6, that is, the basic value of the mechanical compression ratio, that is, the basic target. The compression ratio btCR is calculated. Similarly, the basic target air-fuel ratio calculation unit 22 calculates the basic target air-fuel ratio btAF based on the required load tT and the engine speed Ne. The basic target air-fuel ratio btAF is a value equivalent to the stoichiometric air-fuel ratio, except for some operating regions such as a high load region.

  The component temperature calculation unit 23 calculates the exhaust manifold temperature Tem and the exhaust temperature sensor unit temperature Tes as the temperatures of the components to be protected from the exhaust temperature Texh detected by the exhaust temperature sensor 8. The exhaust manifold temperature Tem indicating the temperature of the exhaust manifold 7 rises later than the exhaust temperature Texh because the heat capacity of the exhaust manifold 7 is larger than that of the exhaust temperature sensor 8 itself as described in Patent Document 2 and the like. To do. Further, the sensor portion temperature Tes corresponds to the temperature of a portion of the exhaust temperature sensor 8 such as a harness portion connected to the engine control unit 11 and is not directly exposed to the exhaust, so that the component temperature rises with respect to the rise of the exhaust temperature Texh. Is an example of a part to be protected that is milder than the exhaust manifold 7 but has a low heat-resistant temperature. Of course, harnesses, vehicle body parts, and the like that are close to other exhaust systems can be targeted as protection target parts.

  The target air-fuel ratio correction unit 24 corrects the basic target air-fuel ratio btAF output from the basic target air-fuel ratio calculation unit 22 when the exhaust manifold temperature Tem and the exhaust temperature sensor unit temperature Tes are high (that is, the fuel increase amount). The target air-fuel ratio tAF is calculated by using the actual compression ratio rCR output from the variable compression ratio actuator 3 in addition to the exhaust manifold temperature Tem and sensor unit temperature Tes. Based on the target air-fuel ratio tAF, the fuel injection amount calculation unit 25 calculates the fuel injection amount Qf of the fuel injection valve 5.

  Further, the target compression ratio correction unit 26 corrects the basic target compression ratio btCR output from the basic target compression ratio calculation unit 21 toward the high compression ratio side when performing fuel increase. Based on the target air-fuel ratio tAF and the actual compression ratio rCR, the corrected target compression ratio tCR is calculated. The variable compression ratio actuator 3 is driven according to the corrected target compression ratio tCR.

  FIG. 3 is a flowchart showing a flow of the control process in the engine control unit 11. In step 1, the required load tT, the engine speed Ne, the exhaust temperature Texh, and the actual compression ratio rCR are read.

  In step 2, the basic target air-fuel ratio btAF and the basic target compression ratio btCR corresponding to the required load tT and the engine speed Ne at that time are obtained by referring to the predetermined air-fuel ratio map and the predetermined compression ratio map. Each of the air-fuel ratio map and the compression ratio map is obtained by assigning optimal values of the air-fuel ratio and the mechanical compression ratio in advance using the required load and the engine speed as parameters. Note that, as described above, the basic target air-fuel ratio btAF is a value corresponding to the theoretical air-fuel ratio, except for some operating regions such as a high load region. In addition, the basic target compression ratio btCR has the highest compression ratio in the low load region, and tends to be lower as the load is higher in consideration of occurrence of knocking.

  In step 3, based on the exhaust temperature Texh detected by the exhaust temperature sensor 8, the exhaust manifold temperature Tem and the sensor unit temperature Tes, which are the temperatures of the parts to be protected, are calculated. The calculation of the exhaust manifold temperature Tem and the sensor unit temperature Tes is, for example, a method in which a time constant of each temperature change with respect to the exhaust temperature Texh is experimentally obtained in advance and calculated using this time constant, or the exhaust Known methods such as a method of estimating from the heat capacity of each part such as the manifold 7 and the amount of heat transfer can be used.

  In step 4, it is determined whether or not the exhaust manifold temperature Tem is higher than a predetermined threshold (Tem threshold). In general, the threshold value may be a fixed value, but may be a value variably set in consideration of some other factor. If the exhaust manifold temperature Tem is higher than the threshold value, the process proceeds to step 5 to calculate an air-fuel ratio correction value (exhaust manifold protection correction value) necessary to protect the exhaust manifold 7 from overheating. For calculating the air-fuel ratio correction value, for example, the relationship between the air-fuel ratio and the exhaust gas temperature obtained experimentally is used. On the other hand, if the exhaust manifold temperature Tem is equal to or lower than the threshold value, the routine proceeds to step 6 where the air-fuel ratio correction value is set to zero.

  Next, in step 7, it is determined whether or not the sensor temperature Tes that rises later than the exhaust manifold temperature Tem is higher than a predetermined threshold (Tes threshold). The threshold for the sensor unit temperature Tes (Tes threshold) is a temperature lower than the threshold for the exhaust manifold temperature Tem (Tem threshold). That is, the allowable temperature of the harness portion of the exhaust temperature sensor 8 indicated by the sensor temperature Tes is lower than that of the exhaust manifold 7. In general, the threshold value may be a fixed value, but may be a value variably set in consideration of some other factor. If the sensor temperature Tes is higher than the threshold value, the process proceeds to step 8 to calculate an air-fuel ratio correction value (exhaust temperature sensor protection correction value) necessary for protecting the harness portion of the exhaust temperature sensor 8 from overheating. For calculation of the air-fuel ratio correction value, as in step 5, for example, the relationship between the air-fuel ratio experimentally obtained and the exhaust temperature is used. On the other hand, if the sensor temperature Tes is equal to or lower than the threshold value, the process proceeds to step 9 where the air-fuel ratio correction value is set to zero.

  After obtaining the two air-fuel ratio correction values as described above, in step 10, the larger one of the two air-fuel ratio correction values (that is, the one with the larger fuel increase) is selected, and the actual compression ratio is selected. The target air-fuel ratio tAF is calculated by correcting the basic target air-fuel ratio btAF while taking rCR into consideration. That is, when the mechanical compression ratio is increased, the thermal efficiency is improved and the exhaust temperature is lowered. Therefore, the target air-fuel ratio tAF after the fuel increase is set in consideration of the influence of the compression ratio. Here, the change amount of the exhaust temperature with respect to the actual compression ratio rCR and the air-fuel ratio correction value is experimentally obtained in advance, and the target air-fuel ratio tAF is calculated. As described above, knocking is unlikely to occur under the condition where fuel increase is being performed, and a high compression ratio can be achieved. In step 11, the target air-fuel ratio tAF determined in step 10 and the target at that time are set. The final target compression ratio tCR is calculated from the actual compression ratio rCR, which is the basis for calculating the air-fuel ratio tAF, and the basic target compression ratio btCR corresponding to the required load tT and the engine speed Ne.

  That is, in the present embodiment, the target air-fuel ratio tAF corresponding to the actual compression ratio rCR is calculated in step 10 in advance, taking into account the relatively large response delay that is unavoidable of the variable compression ratio mechanism 2 including the mechanical mechanism. After that, by calculating the target compression ratio tCR in the next step 11, the mechanical compression ratio and the air-fuel ratio with respect to the required exhaust temperature are matched. Therefore, even if the target air-fuel ratio tAF changes stepwise as the fuel increase starts, the actual compression ratio rCR deviates from the target compression ratio tCR in the initial stage, and the actual compression ratio rCR is greatly different from the immediately preceding basic target compression ratio btCR. Therefore, in calculating the target air-fuel ratio tAF, the influence of the compression ratio (exhaust temperature decrease due to improved thermal efficiency) is not substantially taken into account, and the relative compression ratio until the actual compression ratio rCR converges to the target compression ratio tCR. A large fuel increase is made. Therefore, it is possible to avoid an increase in exhaust temperature due to a transient shortage of fuel increase.

  Next, the operation of the above embodiment will be described using the timing charts of FIGS.

  FIG. 4 shows a timing chart when the exhaust manifold temperature Tem exceeds the threshold value (Tem threshold value) due to the increase of the exhaust gas temperature Texh. The internal combustion engine 1 is operated with a constant load until time t1, and the load increases stepwise at time t1, so that the exhaust temperature Texh and the exhaust manifold temperature Tem start to increase. However, in this example, it is assumed that the load change is limited, and the basic target compression ratio btCR does not change. Since the exhaust manifold temperature Tem exceeds the threshold value (Tem threshold value) at time t2, the target air-fuel ratio tAF is shifted to the rich side, and at the same time, the target compression ratio tCR is corrected to the high compression ratio side. As the target air-fuel ratio tAF becomes richer, the exhaust temperature Texh decreases. However, since the actual compression ratio rCR has a slow response, the increase in the compression ratio does not affect the exhaust temperature at the time t2.

  From time t2 to time t3, the actual compression ratio rCR increases toward the target compression ratio tCR, and the exhaust temperature Texh further decreases accordingly. At time t3, the actual compression ratio rCR reaches the target compression ratio tCR, and accordingly, the target air-fuel ratio tAF after time t3 is shifted toward the lean side (approaching the theoretical air-fuel ratio) from time t2 to time t3. Is richer than the stoichiometric air-fuel ratio). In the above-described embodiment in which the target air-fuel ratio tAF is sequentially corrected based on the actual compression ratio rCR, actually, the target air-fuel ratio tAF gradually becomes lean between time t2 and t3. However, in the example of the figure, the target air-fuel ratio tAF changes stepwise.

  From time t3 to time t4, the exhaust manifold temperature Tem is maintained near the threshold value. Actually, it is desirable to further finely control the target air-fuel ratio tAF so that the exhaust manifold temperature Tem stays in the vicinity of the threshold value by feedback control or the like, but the description is omitted here.

  At time t4, the load on the internal combustion engine 1 decreases, and the exhaust temperature Texh starts to decrease. Therefore, the fuel increase is completed, and thereafter, the engine is operated at the normal target air-fuel ratio tAF and the target compression ratio tCR along the basic target air-fuel ratio btAF and the basic target compression ratio btCR. In the example of FIG. 4, the sensor temperature Tes that rises with a delay does not exceed the threshold value (Tes threshold value).

  Next, FIG. 5 shows a timing chart when both the exhaust manifold temperature Tem and the sensor unit temperature Tes exceed the respective threshold values. Up to time t3 is the same as the timing chart of FIG.

  There is no load change from time t3 to time t4, and the sensor temperature Tes continues to rise. And at time t4, sensor part temperature Tes exceeds a threshold (Tes threshold). Accordingly, the target air-fuel ratio tAF is further shifted to the rich side, and at the same time, the target compression ratio tCR is further corrected to the high compression ratio side. As the target air-fuel ratio tAF becomes richer, the exhaust temperature Texh decreases. However, as described above, even if the target compression ratio tCR changes stepwise, the actual compression ratio rCR has a relatively large response delay. Therefore, the actual compression ratio rCR is transiently deviated from the target compression ratio tCR. At time t4, there is no influence on the exhaust temperature Texh due to a further increase in the target compression ratio tCR.

  Between time t4 and time t5, the actual compression ratio rCR increases toward the target compression ratio tCR, and the exhaust temperature Texh further decreases accordingly. At time t5, the actual compression ratio rCR reaches the target compression ratio tCR, and accordingly, the target air-fuel ratio tAF is shifted to the lean side (approaching the theoretical air-fuel ratio). In the above-described embodiment in which the target air-fuel ratio tAF is sequentially corrected based on the actual compression ratio rCR, actually, the target air-fuel ratio tAF gradually becomes lean between time t4 and t5. However, in the example of the figure, the target air-fuel ratio tAF changes stepwise.

  As described above, in the example of the timing chart of FIG. 5, the fuel increase is performed in two stages in accordance with the two parts to be protected, but the target compression ratio tCR is corrected in a form corresponding to the total fuel increase. . Therefore, it is possible to more effectively obtain the improvement of the thermal efficiency and the reduction of the fuel consumption when the fuel is increased due to the decrease of the exhaust temperature.

  Next, FIG. 6 is a timing chart of an embodiment in which a high compression ratio at the time of fuel increase is prohibited in a high load range. Although not described in the flowchart of FIG. 3, in this embodiment, when the load at the time of fuel increase is equal to or greater than a predetermined threshold, the correction of the target compression ratio tCR accompanying the fuel increase is prohibited.

  In the example of FIG. 6, the load also increases at time t <b> 1. However, the load after the load change is higher than in the examples of FIGS. 4 and 5. The ratio is reduced (that is, the basic target compression ratio btCR is lowered). Thereafter, at time t2, the exhaust manifold temperature Tem exceeds the threshold value, and the fuel increase, that is, the target air-fuel ratio tAF shifts to the rich side. The ratio tCR is not increased in compression ratio. In this case, since the exhaust temperature lowering effect associated with the high compression ratio cannot be obtained, the fuel increase is given as a larger value.

  As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, A various change is possible. For example, in the above embodiment, a variable compression ratio mechanism using a multi-link type piston crank mechanism is used. However, the present invention is not limited to this type of variable compression ratio mechanism, but various types of variable compression ratio mechanisms. The present invention can be applied to an internal combustion engine having a mechanism. Further, in the above-described embodiment, when the actual compression ratio rCR deviates from the target compression ratio tCR, the target air-fuel ratio tAF is obtained based on the actual compression ratio rCR, thereby substantially adding an additional fuel amount. Although realized, an additional fuel increase may be separately provided during a transition period in which the actual compression ratio rCR is delayed from the target compression ratio tCR.

Claims (7)

A control device for an internal combustion engine including a variable compression ratio mechanism for changing a mechanical compression ratio,
Means for setting a target compression ratio of the variable compression ratio mechanism based on the load and rotation speed of the internal combustion engine;
Fuel increasing means for increasing the fuel to protect the parts to be protected in the exhaust system;
Correction means for correcting the target compression ratio to the high compression ratio side based on the fuel increase by the fuel increase means;
A control device for an internal combustion engine comprising:   The control device for an internal combustion engine according to claim 1, wherein the correction means increases the compression ratio correction amount as the degree of fuel increase increases.   3. The control device for an internal combustion engine according to claim 2, wherein the fuel increase means performs multi-stage fuel increase in response to a plurality of protection target parts sequentially reaching a protection required temperature.   4. The fuel increase means according to claim 1, wherein the fuel increase means sets a fuel increase necessary for protecting the protection target component in consideration of the compression ratio corrected to the high compression ratio side by the correction means. Control device for internal combustion engine.   5. The internal combustion engine according to claim 4, wherein the fuel increase means performs additional fuel increase during a transient period in which the target compression ratio corrected to the high compression ratio side by the correction means and the actual compression ratio deviate. Engine control device.   The control device for an internal combustion engine according to any one of claims 1 to 5, wherein correction of a compression ratio accompanying the fuel increase is not performed in a high load region that is equal to or higher than a predetermined load. In an internal combustion engine having a variable compression ratio mechanism for changing a mechanical compression ratio,
While setting the target compression ratio of the variable compression ratio mechanism based on the load and rotation speed of the internal combustion engine,
A control method for an internal combustion engine, wherein the target compression ratio is corrected to the high compression ratio side based on the fuel increase while the fuel increase is being performed to protect the parts to be protected in the exhaust system.

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