CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

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 12L and 12R. The banks 12L and 12R are arranged obliquely to each other. The engine 10 is a so-called V-type engine. The bank 12L has a cylinder group including three cylinders 14L. Likewise, the bank 12R has cylinders 14R.

Also, the bank 12L is provided with fuel injection valves 15L injecting fuel directly into the cylinders 14L. Likewise, the bank 12R is provided with fuel injection valves 15R injecting fuel directly into the cylinders 14R. An intake path 4L and an exhaust manifold 5L are connected to the bank 12L. An intake path 4R and an exhaust manifold 5R are connected to the bank 12R. The intake paths 4L and 4R 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 20L and 20R are provided at the lower ends of the exhaust manifolds 5L and 5R, respectively. The catalysts 20L and 20R clean the exhaust gases exhausted from the cylinders of the banks 12L and 12R, respectively. Air-fuel ratio sensors 9L and 9R are attached to the exhaust manifolds 5L and 5R, respectively.

A cooling unit 40L is provided between an exhaust port (not illustrated) of the bank 12L and the exhaust manifold 5L. Likewise, a cooling unit 40R is provided between an exhaust port (not illustrated) of the bank 12R and the exhaust manifold 5R.

The cooling units 40L and 40R are configured such that the coolant flows around pipes of the exhaust manifolds 5L and 5R respectively. The cooling units 40L and 40R will be described later in detail.

The opening degree of the throttle valve 6 is individually controlled for each of the banks 12L and 12R by electronic Control Units (ECUs) 7L and 7R, respectively. Also, the fuel quantities injected from the fuel injection valves 15L and 15R are individually controlled by the ECUs 7L and 7R, respectively. The ECUs 7L and 7R can cut fuel injected from the fuel injection valves 15L and 15R. The ECUs 7L and 7R correspond to an estimation portion, and a control portion, as will be described later in detail. The ECUs 7L and 7R can communicate to each other via a telecommunication line 8. In order to control operations of the banks for which the ECUs 7L and 7R are responsible, the ECUs 7L and 7R exchange information via the telecommunication 8 to refer to information on an operating state of each bank.

Also, the air-fuel ratio sensors 9L and 9R output detection signals according to the air-fuel ratio of the exhaust gas to the ECUs 7L and 7R respectively. The ECUs 7L and 7R control each of the fuel injection quantities injected into the cylinders 14L and 14R based on the output signals from the air-fuel ratio sensors 9L and 9R 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 7L. 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 7L.

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 40L and 40R, and a V bank pipe 60, in this order. The supporting path 88 diverges from the rear joint portion 19, and includes divergence paths 86L and 86R which circulate the coolant through the cooling units 40L and 40R 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 11w of the engine 10 at first, and then flows into head side water jackets 12Lw and 12Rw. The coolants discharged from the head side water jackets 12Lw and 12Rw 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 40L is arranged on the divergence path 86L. The coolant flows through the cooling unit 40L. The coolant flows through the cooling unit 40L, thereby reducing a temperature of the exhaust gas exhausted from the cylinders 14L of the bank 12L. Likewise, these arrangements are applicable to the divergence path 86R and the cooling unit 40R.

FIG. 3 is a flowchart of an example of a control performed by the ECUs 7L and 7R. The ECUs 7L and 7R detect a coolant temperature based on the outputs from the water temperature sensor 52 (step S1). 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 7L and 7R calculate an exhaust gas temperature and an exhaust gas quantity (step S2). 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 7L and 7R. 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 9L and 9R.

Next, the ECUs 7L and 7R estimate the heat quantity P of the exhaust gas (step S3). 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 S2 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 7L and 7R decide whether or not the coolant temperature is higher than a decision value D1 (step S4). When the coolant temperature is higher than the decision value D1, the ECUs 7L and 7R decide whether or not the heat quantity of the exhaust gas is higher than a decision value D2 (step S5). Herein, the heat quantity of the exhaust gas is one calculated in step S3. When the heat quantity is higher than the decision value D2, the ECUs 7L and 7R set a previous first counter value T1 added with 1 as a current first counter value T1 (step S6). The first counter value T1 is a value used for measuring a period while the heat quantity of the exhaust gas is higher than the decision value D2.

Next, the ECUs 7L and 7R decide whether the first counter value T1 is higher than a decision value D3 (step S7). When the first counter value T1 is higher than the decision value D3, the ECUs 7L and 7R turn ON a flag for performing the idling after the ignition switch 30 is detected to be OFF (step S8). 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 40L and 40R.

Next, the ECUs 7L and 7R calculate an idling period (step S9). Specifically, the ECUs 7L and 7R calculate an idling period corresponding to the first counter value T1 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 T1. As illustrated in FIG. 4B, the idling period is set to be longer as the first counter value T1 is larger. This is because the heat quantities stored in the cooling units 40L and 40R seem to be higher as the first counter value T1 is higher. For example, when the first counter values T1 are 1000, 2000, 3000, and 4000, the idling period is set to be 30, 60, 90, and 120 (sec), respectively. The first counter value T1 corresponds to a period while the heat quantity of the exhaust gas is higher than the decision value D2. 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 D2. 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 D2.

Next, the ECUs 7L and 7R decide whether or not an OFF signal is detected from the ignition switch 30 (step S10). When a negative decision is made, the ECUs 7L and 7R perform step S1 again. When the ECUs 7L and 7R detect an OFF signal from the ignition switch 30, the ECUs 7L and 7R perform the idling (step S11). 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 40L and 40R.

When the coolant temperature is lower than the decision value D1 in step S4, the ECUs 7L and 7R turn off an idling performance flag (step S15). 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 D2 in step S5, the ECUs 7L and 7R decide whether or not the idling performance flag is ON (step S12). When a negative decision is made, the ECUs 7L and 7R perform step S15. When an affirmative decision is made, the ECUs 7L and 7R calculate a previous second counter value T2 added with 1 as a current second counter value T2 (step S13). The second counter value T2 is used for measuring a period while the heat quantity of the exhaust gas is lower than the decision value D1.

The ECUs 7L and 7R decide whether or not the second counter value T2 is higher than a decision value D4 (step S14). When the second counter value T2 is higher than the decision value D4, the ECUs 7L and 7R perform step S15. This is because the heat quantities stored in the cooling units 40R and 40L are estimated to be low in this case. When the second counter value T2 is lower than the decision value D2, the ECUs 7L and 7R turn ON the idling flag (step S8). This is because the heat quantities stored in the cooling units 40R and 40L are estimated to be still enough in this case. The second counter value T2 corresponds to the period while the heat quantity of the exhaust gas is lower than the decision value D2. 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 D2 and in response to the period while the estimated heat quantity of the exhaust gas is higher than the decision value D2. 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 D2 and to the period while the estimated heat quantity of the exhaust gas is higher than the decision value D2. 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 7L and 7R 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 40L and 40R.

Next, the control performed by the ECUs 7L and 7R will be described with reference to a timing chart. FIGS. 5 and 6 are timing charts to explain the control performed by the ECUs 7L and 7R. Additionally, FIGS. 5 and 6 illustrate the heat quantity P of the exhaust gas, the temperature Tc of the cooling units 40L and 40R, and the coolant temperature Tw. Further, the coolant temperature Tw indicates the temperature of the coolant around the cooling units 40L and 40R.

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 D2. When the ignition switch 30 is turned OFF in the state where the heat quantity P is higher than the decision value D2, the idling is performed in the engine 10. If the temperature Tc of the cooling units 40L and 40R 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 40L and 40R 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 40L and 40R.

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 40L and 40R is caused by the heat quantities stored in the cooling units 40L and 40R. 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 40L and 40R 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 D2 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 40L and 40R 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 76a is employed in the control device of the internal combustion engine according to the second embodiment. The pump 76a is an electric pump to operate based on instructions from the ECUs 7L and 7R. Thus, even after the engine 10 is stopped, the pump 76a operates based on instructions from the ECUs 7L and 7R.

Next, the control performed by the ECUs 7L and 7R will be described. FIG. 8 is a flowchart of an example of the control performed by the ECUs 7L and 7R. When the ECUs 7L and 7R perform steps S1 to S7, the ECUs 7L and 7R turn ON an execution flag for operating the pump 76a after the ignition switch 30 is detected to be OFF (step S8a). Next, an operation period of the pump 76a is calculated (step S9a). Additionally, the operation period of the pump 76a is calculated based on the first counter value T1, like the first embodiment. When the ignition switch 30 is detected to be OFF, the ECUs 7L and 7R stop the engine 10 and operate the pump 76a (step S11a).

In such a way, the pump 76a 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 40L and 40R. Additionally, when a negative decision is made in step S7 or an affirmative decision is made in step S14, the execution flag for operating the pump 76a is turned OFF after the ignition switch 30 is turned OFF (step S15a).

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 40L and 40R and connected in parallel with the primary path 82. Also, a control valve 78 is provided between the pump 76a 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 7L and 7R. Specifically, the control valve 78 can maintain its given opening degree in response to instructions from the ECUs 7L and 7R.

FIG. 10 is a flowchart of an example of the control performed by the ECUs 7L and 7R. When the ECUs 7L and 7R perform steps S1 to S10 and then the ignition switch 30 is detected to be OFF, the ECUs 7L and 7R operate the pump 76a (step S11a), and in addition, close the control valve 78 (step S11b). 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 40L and 40R. Hence, the cooling units 40L and 40R 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 40L and 40R. 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.

CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

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