JP2010053828A - Control unit of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control unit of an internal combustion engine, improving the controllability of torque in a small torque range while maintaining the performance of the internal combustion engine as a whole. <P>SOLUTION: When reduction of torque is requested, the torque is reduced by advancing opening timing of an exhaust valve if catalyst temperature is less than a predetermined temperature and torque is reduced by combination of enriching an air-fuel ratio and retarding ignition timing if the catalyst temperature is equal to or higher than the predetermined temperature. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an internal combustion engine control device, and more particularly, to an internal combustion engine control device having a plurality of torque adjusting elements.

In an internal combustion engine, there are a plurality of elements for adjusting the torque. The throttle valve opening is the main torque adjusting element, and the valve timing, ignition timing, air-fuel ratio, etc. of the intake and exhaust valves are also included in the torque adjusting element. A control device for controlling an internal combustion engine, particularly a control device for controlling an internal combustion engine by so-called torque demand control, responds to a torque request to the internal combustion engine by appropriately operating the plurality of torque adjusting elements. For example, in the technique disclosed in Japanese Patent Application Laid-Open No. 8-121204, when there is a torque reduction request, the valve timing of the intake / exhaust valve is set to a position where the output decreases in the full load region, and the residual in the partial load region. The gas content is set to decrease.
JP-A-8-121204 JP 2002-188491 A Japanese Patent Laid-Open No. 4-252838

  By the way, in many of the torque adjusting elements of the internal combustion engine, the operation affects the output of the internal combustion engine other than the torque, for example, exhaust temperature, exhaust emission, and the like. For this reason, if the torque adjustment element is operated based only on the torque request, the performance of the internal combustion engine as a whole may be degraded. This is true even when there is a demand for torque reduction. In particular, since the torque controllability itself is difficult in a small torque region such as before and after the fuel cut, the torque adjustment element used according to the torque reduction request maintains the performance of the entire internal combustion engine. However, it is required that high torque controllability can be obtained even in a small torque region.

  The present invention has been made to solve the above-described problems, and provides a control device for an internal combustion engine that improves the controllability of torque in a small torque region while maintaining the performance of the internal combustion engine as a whole. With the goal.

In order to achieve the above object, a first invention provides a control device for an internal combustion engine,
Torque request acquisition means for acquiring a torque request to the internal combustion engine;
Catalyst temperature acquisition means for acquiring the temperature of the exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine;
First torque reduction means for reducing torque by an advance angle of the opening timing of the exhaust valve;
A second torque reduction means for reducing torque by a combination of enrichment of air-fuel ratio and ignition timing retardation;
When the acquired torque request includes a torque reduction request, at least one of the first torque reduction unit and the second torque reduction unit is selected according to the acquired catalyst temperature, and the selected torque reduction is performed. Control means for controlling the torque by operating the means;
It is characterized by having.

According to a second invention, in the first invention,
The first torque reducing means is characterized in that the ignition timing is retarded together with the advance timing of the exhaust valve opening timing.

According to a third invention, in the first or second invention,
When the acquired catalyst temperature is lower than a predetermined lower limit temperature, the control means operates the first torque reducing means to control the torque.

A fourth invention is any one of the first to third inventions,
The control means controls the torque by operating the second torque reduction means when the acquired catalyst temperature is higher than a predetermined upper limit temperature.

According to a fifth invention, in the first or second invention,
The control means controls the torque by operating the first torque reduction means when the acquired catalyst temperature is in a low temperature range, and the second control means when the acquired catalyst temperature is in a high temperature range. The torque reduction means is operated to control the torque, and when the obtained catalyst temperature is in the middle temperature range between the low temperature range and the high temperature range, the first torque reduction means and the second torque The torque is controlled by operating both of the reduction means.

  According to the first invention, as means for reducing the torque, the first torque reducing means for reducing the torque by the advance angle of the opening timing of the exhaust valve, the richness of the air-fuel ratio, and the retard of the ignition timing, The second torque reducing means for reducing the torque by combining the two can be used. Both the first torque reducing means and the second torque reducing means are not only excellent in torque controllability in a small torque region, but the first torque reducing means has an effect of increasing the exhaust temperature. The torque reducing means 2 has the effect of lowering the exhaust temperature. As is well known, the exhaust temperature affects the purification performance of the exhaust purification catalyst. Therefore, according to the first aspect of the present invention, by appropriately selecting and operating the first and second torque reducing means according to the catalyst temperature, high torque control can be performed while maintaining the purification performance of the exhaust purification catalyst high. To meet the demand for torque reduction.

  According to the second aspect of the present invention, the ignition timing is retarded together with the advance timing of the exhaust valve opening timing, so that a higher torque reduction effect and an exhaust temperature increase effect can be obtained.

  According to the third aspect of the invention, when the catalyst temperature is lower than the lower limit temperature, the exhaust valve opening timing is advanced to increase the exhaust temperature while reducing the torque, thereby increasing the catalyst temperature early. Can do.

  According to the fourth aspect of the invention, when the catalyst temperature is higher than the upper limit temperature, the exhaust gas purification catalyst is reduced by reducing the exhaust temperature while reducing the torque by combining the enrichment of the air-fuel ratio and the retardation of the ignition timing. Can be prevented from overheating.

  According to the fifth aspect, when the catalyst temperature is in the low temperature range, the exhaust temperature can be increased by the advance angle of the opening timing of the exhaust valve, and thereby the catalyst temperature can be raised early. On the contrary, when the catalyst temperature is in the high temperature range, the exhaust gas temperature can be lowered by a combination of the rich air-fuel ratio and the ignition timing retardation, thereby preventing the exhaust purification catalyst from overheating. When the catalyst temperature is in the middle temperature range, the torque reduction method by advancement of the exhaust valve opening timing and the torque reduction method by combination of enrichment of the air-fuel ratio and retardation of the ignition timing should be used in combination. Thus, the exhaust temperature can be maintained in a suitable range while reducing the torque as required.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of a control device for an internal combustion engine as an embodiment of the present invention. The internal combustion engine according to the present embodiment is a spark ignition type internal combustion engine, and at least a throttle valve 2, an exhaust valve timing variable device (hereinafter referred to as exhaust VVT) 4, an ignition device 6, and an actuator for adjusting the torque thereof. A fuel injection device 8 is provided. These actuators 2, 4, 6, and 8 operate based on instructions from the torque control unit 10 of the control device. The torque controller 10 instructs the throttle valve opening (TA) for the throttle valve 2, instructs the exhaust valve opening timing (EVO) for the exhaust VVT4, and ignites the ignition device 6. The time (SA) is instructed, and the air-fuel ratio (A / F) is instructed to the fuel injection device 8.

  The torque request acquired by the torque request acquisition unit 12 is supplied to the torque control unit 10. The torque request acquisition unit 12 calculates the torque requested by the driver based on the accelerator pedal operation amount. The torque control unit 10 appropriately controls the operations of the actuators 2, 4, 6, and 8 according to instructions according to the content of the torque request in order to realize the supplied torque request. That is, the control device of the present embodiment is configured as a control device that controls the internal combustion engine by so-called torque demand control.

  Further, the temperature of the exhaust purification catalyst acquired by the catalyst temperature acquisition unit 14 is also supplied to the torque control unit 10. There is no limitation on the method for obtaining the catalyst temperature by the catalyst temperature obtaining unit 14. The temperature of the exhaust purification catalyst (catalyst bed temperature) may be directly measured, or may be calculated from the temperature of the exhaust gas passing through the exhaust purification catalyst. Alternatively, the catalyst temperature may be estimated using a physical model or statistical model of the exhaust system of the internal combustion engine. As will be described later, the torque control unit 10 uses the supplied catalyst temperature as information for torque control.

  In the present embodiment, as torque control executed by the torque control unit 10, torque control in a small torque region is prepared separately from normal torque control. The small torque region here refers to a torque region that cannot be realized only by adjusting the throttle valve opening, for example, and that cannot be realized by a combination of the throttle valve opening and the retard of the ignition timing. In such a small torque region, as described later, the exhaust valve opening timing, or the ignition timing and the air-fuel ratio are used as torque adjusting elements. On the other hand, the normal torque control is a torque control mainly composed of the throttle valve 2 and the ignition device 6, and the throttle valve opening and the ignition timing are mainly used as torque adjusting elements.

  In the present embodiment, two methods described below can be selected as a torque control method in the small torque region.

  First, a method for controlling torque according to the opening timing of the exhaust valve will be described. FIG. 2 is a diagram showing the relationship between the opening timing of the exhaust valve and each output parameter of the internal combustion engine. As shown in FIG. 2, the torque of the internal combustion engine decreases as the exhaust valve opening timing is advanced. This is because the work of the combustion gas in the cylinder is not converted into the shaft torque because the exhaust valve opens during the expansion stroke. As a result, the exhaust temperature rises as much as the torque decreases. In addition, the amount of NOx generated in the expansion stroke is reduced by the amount that the exhaust valve opens quickly, and as a result, NOx discharged from the internal combustion engine is reduced.

  According to the advance angle of the opening timing of the exhaust valve, in addition to being able to greatly reduce the torque of the internal combustion engine, as a secondary effect, the exhaust temperature can be raised, and the NOx emission amount can be reduced. Can be reduced. Further regarding the controllability of torque, the torque control based on the opening timing of the exhaust valve is advantageous in that the torque can be controlled after ignition by the ignition device 6. According to this, since a stable combustion state can be ensured, torque controllability can be ensured even in the extremely small torque region.

  Note that the presence or absence of overlap shown in FIG. 2 indicates the presence or absence of valve overlap between the exhaust valve and the intake valve. By operating the exhaust VVT 4, the closing timing is also changed in conjunction with the opening timing of the exhaust valve. When the closing timing of the exhaust valve is retarded, the opening period eventually overlaps with the intake valve. When the valve overlap occurs, the torque, the exhaust temperature, and the NOx emission amount change according to the period. As shown in FIG. 2, torque can be reduced by valve overlap, but the torque controllability including the torque reduction effect is better at the opening timing of the exhaust valve.

  Next, a method of controlling torque by combining the enrichment of the air-fuel ratio and the retardation of the ignition timing will be described. FIG. 3 is a graph showing the relationship between the air-fuel ratio (A / F) and the ignition timing-torque characteristics. As shown in FIG. 3, when compared at the same ignition timing, the torque also increases by enriching the air-fuel ratio. However, enriching the air-fuel ratio has the effect of stabilizing the combustion state and increasing the combustion limit. Therefore, by enriching the air-fuel ratio, it becomes possible to retard the ignition timing much more than in the case of stoichiometry, and as a result, the torque can be further reduced as shown in FIG.

  According to the combination of the enrichment of the air-fuel ratio and the retard of the ignition timing, the torque of the internal combustion engine can be greatly reduced, and the controllability of torque in the small torque region can be ensured. Further, according to the enrichment of the air-fuel ratio, the exhaust temperature can be lowered as a secondary effect. FIG. 4 is a graph showing the relationship between the air-fuel ratio and the catalyst temperature. When the air-fuel ratio is enriched, the proportion of unburned fuel increases, and the exhaust temperature decreases due to the effect of the latent heat of vaporization.

  As described above, it is possible to obtain high torque controllability in a small torque region by either the method by the advance timing of the exhaust valve opening timing or the method by the combination of the richness of the air-fuel ratio and the retard of the ignition timing. Can do. The former method has the effect of increasing the exhaust temperature, while the latter method has the effect of decreasing the exhaust temperature. That is, regarding the influence on the exhaust temperature, the opposite effect can be obtained between the former and the latter.

  Here, paying attention to the relationship between the performance of the internal combustion engine and the exhaust temperature, the exhaust temperature greatly affects the purification performance of the exhaust purification catalyst. When the exhaust gas temperature is low, there is a possibility that sufficient exhaust gas purification performance cannot be obtained because the exhaust gas purification catalyst is not activated. On the other hand, when the exhaust gas temperature is high, the exhaust gas purification catalyst may be deteriorated due to overheating. The exhaust gas performance is a particularly important performance among various performances required for an internal combustion engine, and the purification performance of the exhaust purification catalyst greatly contributes to it. Therefore, it is important to obtain the torque control performance in the small torque region, but it is also important to prevent the exhaust purification performance from being lowered due to the change in the exhaust temperature. Desirably, it is desirable to improve not only torque control performance but also exhaust purification performance.

  Therefore, in the present embodiment, as described below, the torque control method in the small torque region is switched in accordance with the catalyst temperature acquired by the catalyst temperature acquisition unit 14. FIG. 5 is a flowchart showing a torque control routine executed by the torque control unit 10 in the embodiment of the present invention.

  In the first step S <b> 2 of the routine shown in FIG. 5, it is determined whether or not a torque reduction request is included in the torque request acquired by the torque request acquisition unit 12. The torque reduction request here cannot be realized by adjusting the throttle valve opening alone, but is required to reduce the torque to a torque range that cannot be realized by a combination of the throttle valve opening and the retarded ignition timing. It is. Such a torque reduction request is acquired, for example, immediately before execution of fuel cut or immediately after return from fuel cut.

  If there is no torque reduction request, the process proceeds to step S10. In step S10, normal torque control is performed using the throttle valve opening and the ignition timing as main torque adjusting elements.

  On the other hand, if there is a torque reduction request, the determination in step S4 is subsequently performed. In step S4, it is determined whether or not the catalyst temperature acquired by the catalyst temperature acquisition unit 14 is equal to or higher than a predetermined value.

  If the catalyst temperature is equal to or higher than the predetermined value, the process proceeds to step S6. In step S6, torque control is performed by a combination of rich air-fuel ratio and retarded ignition timing. Of course, in this case as well, the amount of intake air is controlled by the throttle valve 2, and the throttle valve opening is reduced as much as possible. That is, in this case as well, the control of the torque serving as the base is still the throttle valve opening, and torque control is performed by a combination of rich air-fuel ratio and retarded ignition timing in order to further reduce the torque.

  According to the torque control in step S6, high torque controllability can be obtained in the small torque region, and at the same time, the exhaust temperature can be lowered to prevent the exhaust purification catalyst from overheating. Further, immediately after returning from the fuel cut, the desorption of oxygen from the exhaust purification catalyst is promoted by the supply of unburned fuel, so that the NOx purification performance can be recovered early.

  If it is determined in step S4 that the catalyst temperature is lower than the predetermined value, the process proceeds to step S8. The situation where the catalyst temperature decreases is, for example, when the fuel cut is continued for a long time. At the time of return from the fuel cut for a long time, the torque control in step S8 is performed. The torque control performed in step S8 is torque control based on the advance angle of the exhaust valve opening timing. Of course, in this case as well, the amount of intake air is controlled by the throttle valve 2, and the throttle valve opening is reduced as much as possible. That is, in this case as well, the control of the torque serving as a base is still the throttle valve opening, and the torque control is performed by the advance angle of the opening timing of the exhaust valve in order to further reduce the torque.

  According to the torque control in step S6, high torque controllability can be obtained in the small torque region, and at the same time, the exhaust temperature can be increased to promote warming up of the exhaust purification catalyst. Further, NOx emission from the internal combustion engine when the activity of the exhaust purification catalyst is low can be suppressed.

  By executing the routine described above, the torque control based on the advance angle of the exhaust valve opening timing and the torque control based on the combination of the rich air-fuel ratio and the retarded ignition timing are appropriately switched according to the catalyst temperature. be able to. Thereby, according to the control device of the present embodiment, it is possible to meet the torque reduction request with high torque controllability while maintaining high purification performance of the exhaust purification catalyst.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, as a torque control method when the catalyst temperature is less than a predetermined value, the ignition timing may be retarded together with the advance timing of the exhaust valve opening timing. By doing so, a higher torque reduction effect and an exhaust temperature increase effect can be obtained.

  Further, instead of switching the torque control method depending on whether the catalyst temperature is equal to or higher than a predetermined value, the torque control method may be switched for each temperature range by dividing the temperature range into three. In this case, when the catalyst temperature is in the high temperature range, torque control based on a combination of enrichment of the air-fuel ratio and retardation of the ignition timing is selected. When the catalyst temperature is in the low temperature range, torque control based on the advance angle of the exhaust valve opening timing or torque control based on the advance angle of the exhaust valve opening timing and the retard timing of the ignition timing is selected. When the catalyst temperature is in the middle temperature range between the low temperature range and the high temperature range, a combination of the torque reduction method by the advance timing of the exhaust valve opening timing, the richness of the air-fuel ratio and the retard timing of the ignition timing Torque control is performed in combination with the torque reduction method by. Thus, by switching the torque control method in three temperature ranges, it is possible to maintain the exhaust temperature within a suitable range while reducing the torque as required.

It is a block diagram which shows the structure of the control apparatus of the internal combustion engine as embodiment of this invention. It is a figure which shows the relationship between the opening timing of an exhaust valve, and each output parameter of an internal combustion engine. It is a figure which shows the relationship between an air fuel ratio and ignition timing-torque characteristic. It is a figure which shows the relationship between an air fuel ratio and catalyst temperature. It is a flowchart which shows the routine of the torque control performed in embodiment of this invention.

Explanation of symbols

2 Throttle valve 4 Exhaust VVT
6 Ignition device 8 Fuel injection device 10 Torque control unit 12 Torque request acquisition unit 14 Catalyst temperature acquisition unit

Claims (5)

In a control device for an internal combustion engine,
Torque request acquisition means for acquiring a torque request to the internal combustion engine;
Catalyst temperature acquisition means for acquiring the temperature of the exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine;
First torque reduction means for reducing torque by an advance angle of the opening timing of the exhaust valve;
A second torque reduction means for reducing torque by a combination of enrichment of air-fuel ratio and ignition timing retardation;
When the acquired torque request includes a torque reduction request, at least one of the first torque reduction unit and the second torque reduction unit is selected according to the acquired catalyst temperature, and the selected torque reduction is performed. Control means for controlling the torque by operating the means;
A control device for an internal combustion engine, comprising:   2. The control apparatus for an internal combustion engine according to claim 1, wherein the first torque reducing means also performs the retard of the ignition timing in addition to the advance of the opening timing of the exhaust valve.   3. The internal combustion engine according to claim 1, wherein the control means controls the torque by operating the first torque reduction means when the acquired catalyst temperature is lower than a predetermined lower limit temperature. Control device.   4. The control device according to claim 1, wherein when the acquired catalyst temperature is higher than a predetermined upper limit temperature, the control device controls the torque by operating the second torque reduction device. 5. The control apparatus for an internal combustion engine according to the item.   The control means controls the torque by operating the first torque reduction means when the acquired catalyst temperature is in a low temperature range, and the second control means when the acquired catalyst temperature is in a high temperature range. The torque reduction means is operated to control the torque, and when the obtained catalyst temperature is in the middle temperature range between the low temperature range and the high temperature range, the first torque reduction means and the second torque 3. The control apparatus for an internal combustion engine according to claim 1, wherein the torque is controlled by operating both of the reducing means.

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