Patent Publication Number: US-2012035829-A1

Title: Control device for internal combustion engine

Description:
TECHNICAL FIELD  
     The present invention relates to a control device for an internal combustion engine. 
     BACKGROUND ART  
     There is a cooling unit for cooling exhaust gases of an internal combustion engine. There is the cooling unit which is provided between an exhaust port and an exhaust manifold or which is provided around the exhaust manifold (See Patent Document 1). The exhaust gases are cooled with coolant water flowing through the cooling unit. 
     PRIOR ART DOCUMENT  
     Patent Document  
     [Patent Document 1] Japanese Patent Application Publication No. 63-208607. 
     SUMMARY OF THE INVENTION  
     Problems to be Solved by the Invention  
     Such a cooling unit is arranged on a path through which a coolant flows. The coolant is circulated through the path by a pump. Also, such a cooling unit stores a part of the heat quantity of the exhaust gas. When the internal combustion engine is stopped, the pump is stopped and then the coolant is not circulated. For this reason, the heat quantity stored in the cooling unit is transmitted to the coolant, and then the coolant might boil. 
     It is an object of the present invention to provide a control device of an internal combustion engine suppressing boiling of a coolant. 
     Means for Solving the Problems  
     The above object is achieved by a control device for an internal combustion engine, the control device including: a cooling unit arranged on a path where a coolant is circulated, and cooling an exhaust gas of the internal combustion engine with the coolant flowing through the cooling unit; a pump circulating the coolant; an estimation portion estimating a heat quantity of the exhaust gas, and a control portion deciding whether or not to operate the pump after an ignition switch is detected to be OFF, in response to the estimated heat quantity of the exhaust gas. With these arrangements, for example, in even cases where the heat quantity of the exhaust is high and the ignition switch is detected to be OFF, the pump is operated to circulate the coolant, thereby preventing boiling of the coolant caused by the heat quantity stored in the cooling unit. 
     Effects of the Invention  
     According to the present invention, there is provided a control device of an internal combustion engine suppressing boiling of a coolant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is an explanatory view of a control device for an internal combustion engine; 
         FIG. 2  is a view of a path of a coolant; 
         FIG. 3  is a flowchart of an example of a control performed by an ECU; 
         FIG. 4A  is a map for calculating an exhaust gas temperature, and  FIG. 4B  is a map for calculating an idling period; 
         FIG. 5  is a timing chart to explain the control performed by the ECU; 
         FIG. 6  is a timing chart to explain the control performed by the ECU; 
         FIG. 7  is a view of a path of the coolant in the cooling device for the internal combustion engine according to a second embodiment; 
         FIG. 8  is a flowchart of an example of the control performed by the ECU; 
         FIG. 9  is an explanatory view of a path of the coolant in the cooling device for the internal combustion engine according to a third embodiment; and 
         FIG. 10  is a flowchart of an example of the control performed by the ECU. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION  
     Embodiments will be described below with reference to the drawings. 
     First Embodiment  
       FIG. 1  is an explanatory view of a control device for an internal combustion engine. An engine  10  has a pair of banks  12 L and  12 R. The banks  12 L and  12 R are arranged obliquely to each other. The engine  10  is a so-called V-type engine. The bank  12 L has a cylinder group including three cylinders  14 L. Likewise, the bank  12 R has cylinders  14 R. 
     Also, the bank  12 L is provided with fuel injection valves  15 L injecting fuel directly into the cylinders  14 L. Likewise, the bank  12 R is provided with fuel injection valves  15 R injecting fuel directly into the cylinders  14 R. An intake path  4 L and an exhaust manifold  5 L are connected to the bank  12 L. An intake path  4 R and an exhaust manifold  5 R are connected to the bank  12 R. The intake paths  4 L and  4 R are jointed to each other at their upstream sides. The jointed portion is provided with a throttle valve  6  for adjusting intake air quantity and an airflow meter for detecting the intake air quantity. 
     Catalysts  20 L and  20 R are provided at the lower ends of the exhaust manifolds  5 L and  5 R, respectively. The catalysts  20 L and  20 R clean the exhaust gases exhausted from the cylinders of the banks  12 L and  12 R, respectively. Air-fuel ratio sensors  9 L and  9 R are attached to the exhaust manifolds  5 L and  5 R, respectively. 
     A cooling unit  40 L is provided between an exhaust port (not illustrated) of the bank  12 L and the exhaust manifold  5 L. Likewise, a cooling unit  40 R is provided between an exhaust port (not illustrated) of the bank  12 R and the exhaust manifold  5 R. 
     The cooling units  40 L and  40 R are configured such that the coolant flows around pipes of the exhaust manifolds  5 L and  5 R respectively. The cooling units  40 L and  40 R will be described later in detail. 
     The opening degree of the throttle valve  6  is individually controlled for each of the banks  12 L and  12 R by electronic Control Units (ECUs)  7 L and  7 R, respectively. Also, the fuel quantities injected from the fuel injection valves  15 L and  15 R are individually controlled by the ECUs  7 L and  7 R, respectively. The ECUs  7 L and  7 R can cut fuel injected from the fuel injection valves  15 L and  15 R. The ECUs  7 L and  7 R correspond to an estimation portion, and a control portion, as will be described later in detail. The ECUs  7 L and  7 R can communicate to each other via a telecommunication line  8 . In order to control operations of the banks for which the ECUs  7 L and  7 R are responsible, the ECUs  7 L and  7 R exchange information via the telecommunication  8  to refer to information on an operating state of each bank. 
     Also, the air-fuel ratio sensors  9 L and  9 R output detection signals according to the air-fuel ratio of the exhaust gas to the ECUs  7 L and  7 R respectively. The ECUs  7 L and  7 R control each of the fuel injection quantities injected into the cylinders  14 L and  14 R based on the output signals from the air-fuel ratio sensors  9 L and  9 R respectively, so as to control the air-fuel ratio to be feed back. Such a control for feeding back the air-fuel ratio is to control the fuel injection quantity or the like such that the detected air-fuel ratio of the exhaust gas is identical to a target air-fuel ratio. 
     A water temperature sensor  52  outputs detection signals according to a temperature of the coolant, as will be described later, to the ECR  7 L. Additionally, the water temperature sensor  52  is arranged at an arbitrary position on the path through which the coolant is circulated. An ignition switch  30  outputs an ON signal or an OFF signal to the ECU  7 L. 
       FIG. 2  is a view of a path of the coolant. As illustrated in  FIG. 2 , a radiator  72 , an inlet  74 , a pump  76 , and the like are arranged on the path of the coolant. A primary path  82  circulates the coolant through the inlet  74 , the pump  76 , the engine  10 , and the radiator  72 , in this order. The primary path  82  circulates the coolant to the radiator  72  from a rear joint portion  19  of the engine  10 . A supporting path  88  circulates the coolant through the inlet  74 , the pump  76 , the engine  10 , the cooling units  40 L and  40 R, and a V bank pipe  60 , in this order. The supporting path  88  diverges from the rear joint portion  19 , and includes divergence paths  86 L and  86 R which circulate the coolant through the cooling units  40 L and  40 R respectively. 
     The pump  76  is a mechanical pump which operates in conjunction with the revolution of the engine  10 . The coolant flows from the inlet  74  to the engine  10 . The coolant flows into a block side water jacket  11 w of the engine  10  at first, and then flows into head side water jackets  12 Lw and  12 Rw. The coolants discharged from the head side water jackets  12 Lw and  12 Rw join together at the rear joint portion  19 . The primary path  82  and the supporting path  88  are connected to the rear joint portion  19 . The coolant flowing through the primary path  82  flows from the rear joint portion  19  to the radiator  72 , and radiates heat in the radiator  72 . 
     The cooling unit  40 L is arranged on the divergence path  86 L. The coolant flows through the cooling unit  40 L. The coolant flows through the cooling unit  40 L, thereby reducing a temperature of the exhaust gas exhausted from the cylinders  14 L of the bank  12 L. Likewise, these arrangements are applicable to the divergence path  86 R and the cooling unit  40 R. 
       FIG. 3  is a flowchart of an example of a control performed by the ECUs  7 L and  7 R. The ECUs  7 L and  7 R detect a coolant temperature based on the outputs from the water temperature sensor  52  (step S 1 ). Additionally, the coolant temperature may be estimated by a known method without depending on the outputs from the water temperature sensor  52 . 
     Next, the ECUs  7 L and  7 R calculate an exhaust gas temperature and an exhaust gas quantity (step S 2 ). For example, the exhaust gas temperature is calculated based on a map illustrated in  FIG. 4A .  FIG. 4A  is a map for calculating the exhaust gas temperature, and is stored beforehand in the ECUs  7 L and  7 R. As illustrated in  FIG. 4A , the vertical axis indicates the revolution number of the engine  10 , and the horizontal axis indicates the load of the engine  10 . The exhaust gas temperature is calculated to be higher as the revolution number and the load of the engine  10  are higher. 
     Also, the exhaust gas quantity (g/sec) is calculated based on the intake air quantity detected by the outputs from the airflow meter  18  and the air-fuel ratio detected by the outputs from the air-fuel ratio sensors  9 L and  9 R. 
     Next, the ECUs  7 L and  7 R estimate the heat quantity P of the exhaust gas (step S 3 ). Specifically, this is estimated by the following formula. 
         P=M×Cp ×( Tex−Tair )   (1)
 
     M stands for exhaust gas quantity, Cp stands for specific heat of exhaust gas, Tex stands for exhaust gas temperature, and Tair stands for outside air temperature. The heat quantity P is calculated by substituting the exhaust gas quantity and the exhaust gas temperature calculated in step S 2  into M and Tex respectively. Also, an outside air temperature may be detected by a known sensor, or estimated or calculated by a well-known method. 
     Next, the ECUs  7 L and  7 R decide whether or not the coolant temperature is higher than a decision value D 1  (step S 4 ). When the coolant temperature is higher than the decision value D 1 , the ECUs  7 L and  7 R decide whether or not the heat quantity of the exhaust gas is higher than a decision value D 2  (step S 5 ). Herein, the heat quantity of the exhaust gas is one calculated in step S 3 . When the heat quantity is higher than the decision value D 2 , the ECUs  7 L and  7 R set a previous first counter value T 1  added with 1 as a current first counter value T 1  (step S 6 ). The first counter value T 1  is a value used for measuring a period while the heat quantity of the exhaust gas is higher than the decision value D 2 . 
     Next, the ECUs  7 L and  7 R decide whether the first counter value T 1  is higher than a decision value D 3  (step S 7 ). When the first counter value T 1  is higher than the decision value D 3 , the ECUs  7 L and  7 R turn ON a flag for performing the idling after the ignition switch  30  is detected to be OFF (step S 8 ). The reason why the idling is performed after OFF of the ignition switch is detected is as follows. The pump is operated by performing the idling for a given period even after the ignition switch  30  is OFF so as to prevent boiling of the coolant caused by the heat quantities stored in the cooling units  40 L and  40 R. 
     Next, the ECUs  7 L and  7 R calculate an idling period (step S 9 ). Specifically, the ECUs  7 L and  7 R calculate an idling period corresponding to the first counter value T 1  as illustrated in  FIG. 4B .  FIG. 4B  is a map for calculating the idling period. As for the map illustrated in  FIG. 4B , the vertical axis indicates the idling period, and the horizontal axis indicates the first counter value T 1 . As illustrated in  FIG. 4B , the idling period is set to be longer as the first counter value T 1  is larger. This is because the heat quantities stored in the cooling units  40 L and  40 R seem to be higher as the first counter value T 1  is higher. For example, when the first counter values T 1  are 1000, 2000, 3000, and 4000, the idling period is set to be 30, 60, 90, and 120 (sec), respectively. The first counter value T 1  corresponds to a period while the heat quantity of the exhaust gas is higher than the decision value D 2 . Thus, the idling period is set in response to the period while the heat quantity of the exhaust gas is higher than the decision value D 2 . That is, the operating period of the pump  76  is set in response to the period while the heat quantity of the exhaust gas is higher than the decision value D 2 . 
     Next, the ECUs  7 L and  7 R decide whether or not an OFF signal is detected from the ignition switch  30  (step S 10 ). When a negative decision is made, the ECUs  7 L and  7 R perform step S 1  again. When the ECUs  7 L and  7 R detect an OFF signal from the ignition switch  30 , the ECUs  7 L and  7 R perform the idling (step S 11 ). The idling is performed, so the pump  76  is operated in conjunction with the engine  10 . Thus, even if the ignition switch  30  is turned OFF, the pump  76  is operated for a given period, and then the coolant circulates through the path. This prevents boiling of the coolant caused by the influence of the heat quantities stored in the cooling units  40 L and  40 R. 
     When the coolant temperature is lower than the decision value D 1  in step S 4 , the ECUs  7 L and  7 R turn off an idling performance flag (step S 15 ). This is because there is a little possibility that the coolant boils even after the ignition switch  30  is turned OFF in cases where the coolant temperature is low to some extent. 
     When the heat quantity of the exhaust gas is lower than the decision value D 2  in step S 5 , the ECUs  7 L and  7 R decide whether or not the idling performance flag is ON (step S 12 ). When a negative decision is made, the ECUs  7 L and  7 R perform step S 15 . When an affirmative decision is made, the ECUs  7 L and  7 R calculate a previous second counter value T 2  added with 1 as a current second counter value T 2  (step S 13 ). The second counter value T 2  is used for measuring a period while the heat quantity of the exhaust gas is lower than the decision value D 1 . 
     The ECUs  7 L and  7 R decide whether or not the second counter value T 2  is higher than a decision value D 4  (step S 14 ). When the second counter value T 2  is higher than the decision value D 4 , the ECUs  7 L and  7 R perform step S 15 . This is because the heat quantities stored in the cooling units  40 R and  40 L are estimated to be low in this case. When the second counter value T 2  is lower than the decision value D 2 , the ECUs  7 L and  7 R turn ON the idling flag (step S 8 ). This is because the heat quantities stored in the cooling units  40 R and  40 L are estimated to be still enough in this case. The second counter value T 2  corresponds to the period while the heat quantity of the exhaust gas is lower than the decision value D 2 . Thus, whether or not to perform the idling is decided in response to the period while the estimated heat quantity of the exhaust gas is lower than the decision value D 2  and in response to the period while the estimated heat quantity of the exhaust gas is higher than the decision value D 2 . That is, whether or not to operate the pump  76  is decided after the ignition switch  30  is turned OFF, in response to the period while the estimated heat quantity of the exhaust gas is lower than the decision value D 2  and to the period while the estimated heat quantity of the exhaust gas is higher than the decision value D 2 . This can decide whether or not to operate the pump  76 , in consideration of the driving state of the engine  10  before the ignition switch  30  is turned OFF. 
     As mentioned above, the ECUs  7 L and  7 R estimate the heat quantity of the exhaust gas, and decide whether or not to perform the idling after the ignition switch  30  is detected to be OFF in response to the estimated heat quantity. Therefore, when the heat quantity of the exhaust is high, the pump is operated after the ignition switch  30  is detected to be OFF, and then the coolant is circulated. It is thus possible to prevent boiling of the coolant caused by the heat quantities stored in the cooling units  40 L and  40 R. 
     Next, the control performed by the ECUs  7 L and  7 R will be described with reference to a timing chart.  FIGS. 5 and 6  are timing charts to explain the control performed by the ECUs  7 L and  7 R. Additionally,  FIGS. 5 and 6  illustrate the heat quantity P of the exhaust gas, the temperature Tc of the cooling units  40 L and  40 R, and the coolant temperature Tw. Further, the coolant temperature Tw indicates the temperature of the coolant around the cooling units  40 L and  40 R. 
       FIG. 5  is the timing chart in cases where the idling is performed after the ignition switch  30  is detected to be OFF. For example, when a vehicle runs up a slope and is continuously driven in the high-revolution and high-load state, the heat quantity P of the exhaust gas rises to be higher than the decision value D 2 . When the ignition switch  30  is turned OFF in the state where the heat quantity P is higher than the decision value D 2 , the idling is performed in the engine  10 . If the temperature Tc of the cooling units  40 L and  40 R is 200 degrees Celsius at the time when the ignition switch  30  is turned OFF, the heat quantity P of the exhaust gas is drastically decreased by performing the idling, and then the temperature Tc of the cooling units  40 L and  40 R is also gradually decreased from 200 degrees Celsius. Further, since the pump  76  is operated by performing the idling and the coolant is circulated through the path, the coolant temperature remains at about 90 degrees Celsius without being significantly changed before and after the ignition switch  30  is turned OFF. Such a manner can prevent boiling of the coolant caused by the heat quantities stored in the cooling units  40 L and  40 R. 
     It is supposed that the operation of the pump  76  is stopped when the ignition switch  30  is turned OFF. In this case, the pump  76  is stopped, and then the coolant is not circulated. Thus, there is a possibility that boiling of the coolant remained within or around the cooling units  40 L and  40 R is caused by the heat quantities stored in the cooling units  40 L and  40 R. However, in the present embodiment, the idling is performed for a given period even after the ignition switch  30  is turned OFF. Therefore, the coolant is circulated until the heat quantities stored in the cooling units  40 L and  40 R is reduced. This can prevent the coolant from boiling. 
     Next, a case where the idling is not performed will be described.  FIG. 6  is the timing chart in cases where the idling is not performed after the ignition switch  30  is detected to be OFF. As illustrated in  FIG. 6 , for example, in cases a vehicle is in a low-revolution and low-load driving state and the ignition switch  30  is turned OFF after the vehicle is in a high-revolution and high-load driving state, the heat quantity P of the exhaust gas has been already lower than the decision value D 2  by the low-revolution and low-load driving state. For this reason, the idling is not performed in such a state. This is because the heat quantity P of the exhaust gas is reduced and so the heat quantities stored in the cooling units  40 L and  40 R are estimated to be low. Thus, the idling is not performed in such a case. 
     Second Embodiment  
     Next, the control device for the internal combustion engine according to a second embodiment will be described.  FIG. 7  is a view of a path of the control device of the internal combustion engine of the second embodiment. A pump  76   a  is employed in the control device of the internal combustion engine according to the second embodiment. The pump  76   a  is an electric pump to operate based on instructions from the ECUs  7 L and  7 R. Thus, even after the engine  10  is stopped, the pump  76   a  operates based on instructions from the ECUs  7 L and  7 R. 
     Next, the control performed by the ECUs  7 L and  7 R will be described.  FIG. 8  is a flowchart of an example of the control performed by the ECUs  7 L and  7 R. When the ECUs  7 L and  7 R perform steps S 1  to S 7 , the ECUs  7 L and  7 R turn ON an execution flag for operating the pump  76   a  after the ignition switch  30  is detected to be OFF (step S 8 a). Next, an operation period of the pump  76   a  is calculated (step S 9 a). Additionally, the operation period of the pump  76   a  is calculated based on the first counter value T 1 , like the first embodiment. When the ignition switch  30  is detected to be OFF, the ECUs  7 L and  7 R stop the engine  10  and operate the pump  76   a  (step S 11 a). 
     In such a way, the pump  76   a  is operated for a given period after the ignition switch  30  is turned OFF, thereby preventing boiling of the coolant caused by the heat quantities stored in the cooling units  40 L and  40 R. Additionally, when a negative decision is made in step S 7  or an affirmative decision is made in step S 14 , the execution flag for operating the pump  76   a  is turned OFF after the ignition switch  30  is turned OFF (step S 15 a). 
     Third Embodiment  
     Next, the control device of the internal combustion engine according to a third embodiment will be described.  FIG. 9  is an explanatory view of the path of the coolant of the control unit of the internal combustion engine according to the third embodiment. As illustrated in  FIG. 9 , the path of the coolant includes: the primary path  82  passing through the engine  10 ; and a secondary path passing through the cooling units  40 L and  40 R and connected in parallel with the primary path  82 . Also, a control valve  78  is provided between the pump  76   a  and the engine  10  on the primary path  82 . The control valve  78  can control the flow rate of the coolant passing via the primary path  82  in response to instructions from the ECUs  7 L and  7 R. Specifically, the control valve  78  can maintain its given opening degree in response to instructions from the ECUs  7 L and  7 R. 
       FIG. 10  is a flowchart of an example of the control performed by the ECUs  7 L and  7 R. When the ECUs  7 L and  7 R perform steps S 1  to S 10  and then the ignition switch  30  is detected to be OFF, the ECUs  7 L and  7 R operate the pump  76   a  (step S 11 a), and in addition, close the control valve  78  (step S 11 b). Therefore, the coolant does not flow through the engine  10 , whereas the coolant flows through the secondary path  86 . This increases the flow rate of the coolant flowing through the cooling units  40 L and  40 R. Hence, the cooling units  40 L and  40 R are cooled for a short period with the large amount of the coolant flowing therehrough. It is thus possible to prevent boiling of the coolant caused by the heat quantities stored in the cooling units  40 L and  40 R. Further, the flow rate of the coolant flowing through the engine  10  may be suppressed by controlling the opening degree of the control valve  78  to be a given degree, instead of by fully closing the control valve  78 . 
     While the exemplary embodiments of the present invention have been illustrated in detail, the present invention is not limited to the above-mentioned embodiments, and other embodiments, variations and modifications may be made without departing from the scope of the present invention.