Patent Application
20060000204
1. Field of the Invention
The present invention relates to a multicylinder internal combustion engine, and more particularly to a multicylinder internal combustion engine in which an exhaust gas sensor for determining the exhaust air-fuel ratio is provided in an exhaust system.
2. Description of the Related Art
As one of exhaust emission control devices which purify exhaust gas in an internal combustion engine, catalysts are provided in an exhaust passage of the engine. The air-fuel ratio of exhaust gas flowing into the catalysts must be controlled to an approximately stoichiometric ratio so that the catalysts can offer satisfactory performance. A multicylinder internal combustion engine adapted to attain such an object has been disclosed in Unexamined Japanese Patent Publication No. 11-280458, for example. In this multicylinder internal combustion engine, exhaust gas sensors such as an O2 sensor are disposed in the vicinity of the inlets of the catalysts so that the air-fuel ratio of the internal combustion engine can be controlled based on the exhaust air-fuel ratio of determined by the exhaust gas sensors. It should be noted that the catalysts are provided in respective one of a pair of exhaust passages located upstream of a junction thereof, and a common exhaust gas sensor is provided in a communication passage that brings the exhaust passages in the vicinity of the inlets of the catalysts into communication with each other.
In the case where the exhaust gas sensors are provided in the vicinity of the inlets of the catalysts as is the case with the above internal combustion engine, an exhaust system with a certain degree of volume exists upstream of the exhaust gas sensors. Thus, determination of the air-fuel ratio by the exhaust gas sensors has a delay corresponding to a delay in exhaust gas transmission which occurs due to the volume of the exhaust system. Also, in the case where the air-fuel ratio of the internal combustion engine is controlled based on the exhaust air-fuel ratio determined by the exhaust gas sensors, fluctuation in air-fuel ratio (self-excited fluctuation in air-fuel ratio) necessarily occurs due to the delay in the determination of exhaust air-fuel ratio. If there is a long delay in the determination of exhaust air-fuel ratio, the amplitude of fluctuation in the air-fuel ratio of air-fuel mixture supplied to the internal combustion engine is increased. As a result, fuel economy is likely to deteriorate due to an increase in the amplitude of fluctuation to the rich side, and also, combustion is likely to deteriorate due to an increase in the amplitude of fluctuation to the lean side.
The delay in the determination of exhaust air-fuel ratio can be eliminated by, for example, attaching exhaust gas sensors to respective exhaust ports of the internal combustion engine to reduce the volume of the exhaust system located upstream of the exhaust gas sensors. In this case, however, it is necessary to provide the exhaust gas sensors for the respective exhaust ports if the internal combustion engine is a multicylinder type, and hence another problem that manufacturing costs increase arises.
An aspect of the present invention is a multicylinder internal combustion engine including a plurality of cylinders, comprising: exhaust passages connected to exhaust ports of the respective cylinders; a catalyst provided in the exhaust passages, for purifying exhaust gas; exhaust communication passages in communication with at least two of the exhaust ports; and an exhaust gas sensor provided in the exhaust communication passages, wherein the distance from the exhaust ports to the exhaust gas sensor is shorter than the distance from the exhaust ports to the upstream inlet of the catalyst.
The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein:
A description will hereunder be given of a multicylinder internal combustion engine according to a first embodiment of the present invention.
A flange 7 of an exhaust pipe 6 (exhaust passage) is connected to the downstream flange 5 of the exhaust manifold 1 by bolts, not shown. The upstream side of the exhaust pipe 6 connected to the flange 7 is bifurcated to be in communication with the respective exhaust passage junctions 4 of the exhaust manifold 1. The downstream sides of the exhaust pipe 6 join together at an exhaust passage junction 8 and connected to a catalyst 9. Further, the exhaust pipe 6 is extended to the rear of a vehicle via a muffler, not shown. Therefore, when the internal combustion engine is operating, exhaust gases emitted from the exhaust ports 10 sequentially join together while being guided in the exhaust manifold 1 and the exhaust pipe 6, and then emitted to the outside via the catalyst 9 and the muffler.
One ends of respective pipe-shaped exhaust communication passages 11 are connected to the respective branches 3 of the exhaust manifold 1 in the vicinity of areas where the branches 3 are welded to the upstream flange 2. The other ends of the respective exhaust communication passages 11 are connected to a sensor fixing base 12 to join together at one point. An exhaust gas sensor 13 is fixed to the sensor fixing base 12; the exhaust gas sensor 13 and the exhaust communication passages 11 are in communication with each other within the sensor fixing base 12. It should be noted that the exhaust gas sensor 13 may be implemented by any of an 02 sensor, air-fuel ratio sensor, NOx sensor, and so forth. Also, it should be noted that the exhaust communication passages 11 may be connected to exhaust ports, not shown, not to the exhaust manifold 1.
The exhaust gas sensor 13 is electrically connected to an ECU (Electronic Control Unit) aboard the vehicle; the output from the exhaust gas sensor 13 is input to the ECU. The ECU provides air-fuel ratio control requiring small fluctuation in air-fuel ratio for the internal combustion engine based on the exhaust air-fuel ratio determined by the exhaust gas sensor 13, such as air-fuel ratio feedback control and inflammability limit control.
The exhaust communication passages 11 are extended upward from the respective branches 3 and bent at about 90 degrees to reach the sensor fixing base 12 located between the second cylinder #2 and the third cylinder #3. Thus, the exhaust communication passages 11 as a whole are located just above the exhaust manifold 1. Because of this layout, the distance A1 along the exhaust communication passages 11 from the exhaust ports 10 to the exhaust gas sensor 13 can be kept to the minimum necessary. Thus, although the exhaust communication passages 11 differ in length according to the cylinders, the distance A1 of even the longer exhaust communication passage 11 for the first cylinder #1 or fourth cylinder #4 is considerably shorter than the distance A2 from the exhaust ports 10 to the upstream inlet of the catalyst 9.
In the multicylinder internal combustion engine according to the present embodiment constructed as described above, the exhaust air-fuel ratio is determined by the exhaust-gas sensor 13 as described below.
When the internal combustion engine is operating, exhaust gases are sequentially emitted from the exhaust ports 10 in the order of ignition, i.e. the exhaust ports 10 of the cylinders #1, #3, #4, and #2 in this order and flow in the branches 3 of the exhaust manifold 1. Part of the exhaust gases in the branches 3 are taken into the exhaust communication passages 11. The exhaust gases that have been taken into the exhaust communication passages 3 reach the exhaust gas sensor 13 via the exhaust communication passages 11 mainly because of a gas diffusing action. The exhaust gas sensor 13 sequentially detects the air-fuel ratio of exhaust gases from the respective cylinders, which are supplied via the exhaust communication passages 11. Because the distance A1 from the exhaust ports 10 to the exhaust gas sensor 13 is very short as mentioned above, the delay in the transmission of exhaust gases emitted from the exhaust ports 10 to the exhaust gas sensor 13 can be suppressed to the minimum. Therefore, as compared with a conventional layout in which the exhaust gas sensor 13 is attached to the upstream inlet of the catalyst 9, more responsive determination of the exhaust air-fuel ratio can be realized.
As a result, the air-fuel ratio control carried out by the ECU based on the determined air-fuel ratio can be made more responsive, which makes it possible to solve the problem that exhaust gas components are emitted without being properly purified by the catalyst. This prevents deterioration of purifying performance. Also, the responsive air-fuel ratio control can realize high-speed self-excited fluctuation in which fluctuation in air-fuel ratio is small. This prevents fuel economy from being deteriorated by an increase in the amplitude of fluctuation to the rich side and prevents combustion from being deteriorated due to an increase in the amplitude of fluctuation to the lean side. Further, as shown in the characteristic diagram of
On the other hand, exhaust gases emitted from the respective cylinders are led to the common exhaust gas sensor 13 via the exhaust communication passages 11 so as to detect the air-fuel ratio. For this reason, as compared with e.g. the case where exhaust gas sensors 13 are provided in exhaust ports of respective cylinders, the required number of exhaust gas sensors 13 can be reduced, which makes it possible to reduce manufacturing costs for the internal combustion engine.
Further, as is apparent from
By the way, in the case where the high-speed self-excited fluctuation of the air-fuel ratio is carried out as mentioned above, the purifying efficiency at the COP can be improved, but the so-called window width of air-fuel ratio tends to be reduced due to a decrease in fluctuation period as shown in
Also, to prevent emission of HC when the air-fuel ratio falls outside the window, an appropriate delay time is set for determination of the air-fuel ratio by the exhaust gas sensor 13 so as to extend the period of high-speed self-excited fluctuation on purpose. Even in this case, since the period of high-speed self-excited fluctuation can be arbitrarily set, the period of self-excited fluctuation can be reduced to the minimum possible level while the emission of HC is prevented. Therefore, more responsive determination of the air-fuel ratio can be realized as compared with conventional self-excited fluctuation of the air-fuel ratio.
Although in the present embodiment, the exhaust communication passages 11 of the respective cylinders join together at one point and connected to the single exhaust gas sensor 13, the present invention is not limited to this, but the layout of the exhaust communication passages 11 and the number of exhaust gas sensors 13 may be changed insofar as a smaller number of exhaust gas sensors 13 than the number of cylinders can be provided and the exhaust communication passages 11 of the respective cylinders can be connected to any of the exhaust gas sensors 13. Therefore, for example, the exhaust communication passages 11 of respective three cylinders may be connected to a single exhaust gas sensor 13, or the exhaust communication passages 11 of respective two cylinders may be connected to a single exhaust gas sensor 13.
By the way, in the present embodiment, exhaust gases are transferred in the exhaust communication passages 11 by the gas diffusing action as mentioned above. For this reason, exhaust gases tend to not so smoothly exchanged in the exhaust communication passages 11. Therefore, a description will now be given of second to fifth embodiments of the present invention, in which a gas exchange facilitating means for facilitating gas exchange in the exhaust communication passages 11. It should be noted that the basic arrangements (such as the distances Al and A2) of the second to fifth embodiments are the same as the arrangement of the first embodiment, and the second to fifth embodiments differ from the first embodiment in that the above-mentioned gas exchange is facilitated. Thus, elements and parts corresponding to those of the first embodiment are denoted by the same reference numerals, and therefore the above-mentioned difference will be intensively explained below with duplicate description omitted.
In the vicinity of the exhaust valve 22 in the exhaust port 10, exhaust gas from a combustion chamber 23 is emitted diagonally upward along an exhaust gas flow line LI indicated by the arrow in
As a result, as compared with the first embodiment in which exhaust gas is transferred mainly by the gas diffusing action, exhaust gases in the respective cylinders can be smoothly transferred to the exhaust gas sensor 13 via the exhaust communication passages 11 to thereby facilitate gas exchange in the exhaust communication passages 11. Therefore, determination of the air-fuel ratio by the exhaust gas sensor 13 can be made more responsive as compared with the first embodiment.
It should be noted that the connected state of the exhaust communication passages 11 is not limited to the present embodiment, but the exhaust communication passage 11 may be connected to the exhaust manifold 1 as shown in
While exhaust pressure (positive pressure) acts on the branches 3 to which the exhaust communication passages 11 are connected, intake pressure (negative pressure) acts on the intake manifold 32 to which the intake communication passage 31 is connected. For this reason, there is a difference in pressure before and after the exhaust gas sensor 13. Thus, exhaust gases in the exhaust communication passages 11 flow into the low-pressure intake communication passage 31 via the exhaust gas sensor 13. As a result, exhaust gases in the respective cylinders are smoothly transferred to the exhaust gas sensor 13 via the exhaust communication passages 11, so that gas exchange in the exhaust communication passages 11 can be facilitated.
By the way, to prevent the intake communication passage 31 from being obstructed by the flow of exhaust gas, the intake communication passage 31 must have a certain degree of cross-sectional area. Therefore, a larger amount of exhaust gas than the amount of exhaust gas required for facilitating gas exchange tends to flow back into the intake manifold 32 via the intake communication passage 31. Thus, in the case where the EGR (Exhaust Gas Recirculation) amount is increased to the limit of inflammability or its vicinity in EGR control so as to reduce NOx, exhaust gas flowing back into the intake manifold 32 via the intake communication passage 31 may cause deterioration of combustion. To address this problem, as indicated by the broken line in
As compared with the branches 3 of the exhaust manifold 1 to which the exhaust communication passages 11 are connected, in an area downstream of the catalyst 9 to which the exhaust downstream communication passage 41 is connected, the exhaust pressure is decreased due to the venturi action, etc. of the catalyst 9, and hence there is a difference in pressure before and after the exhaust gas sensor 13. Therefore, exhaust gases in the exhaust communication passages 11 flow into the low-pressure exhaust downstream communication passage 41 via the exhaust gas sensor 13. As a result, exhaust gases in the respective cylinders are smoothly transferred to the exhaust gas sensor 13 via the exhaust communication passages 11, so that gas exchange in the exhaust communication passages 11 can be facilitated.
By the way, at the time of cold-start, unburned gas generated due to an increase in the amount of fuel is emitted via the exhaust downstream communication passage 41 while bypassing the catalyst 9. To address this problem, a switching valve 42, which is the same as the switching valve 33 of the third embodiment, may be provided in the exhaust downstream communication passage 41 as indicated by the broken line in
It should be noted that the exhaust downstream communication passage 41 should not necessarily be connected to the downstream side of the catalyst 9, but may be connected to the upstream side of the catalyst 9. In this case, if the exhaust downstream communication passage 41 is connected to the downstream side of the existing venturi provided in the exhaust pipe 6 or another venturi for causing a difference in pressure, the same venturi effect as the effect obtained by the above catalyst 9 can be obtained to facilitate gas exchange.
Therefore, exhaust gas having passed through the exhaust gas sensor 13 is let into the cooling space 51 via the exhaust downstream communication passage 41 to change in volume (volume decrease) due to temperature decrease. With this change in volume, exhaust gas in the exhaust downstream communication passage 41 and upstream of the cooling space 51 is transferred into the cooling space 51, and exhaust gas in the exhaust communication passage 11 is transferred into the exhaust downstream communication passage 41 via the exhaust gas sensor 13. As a result, as compared with the fourth embodiment in which the cooling space 51 is omitted, gas exchange in the exhaust communication passages 11 can be further facilitated.
Here, to efficiently facilitate gas exchange in the exhaust communication passages 11 by means of the cooling space 51, it is preferred that substantially all of exhaust gases in the exhaust communication passages 11 are transferred to the exhaust downstream communication passage 41 as the volume of exhaust gas changes in the cooling space 51. To this end, at least one of the volume of the cooling space 51, the volume of the exhaust communication passages 11, and the rate of temperature decrease in the cooling space 51 is set so that a change in the volume of exhaust gas in the cooling space 51 and the volume of the exhaust communication passages 11 can be substantially equal.
It should be noted that the cooling space 51 should not necessarily be independently provided in the exhaust downstream communication passage 41, but it may be arranged such that the exhaust downstream communication passage 41 or a cooling system such as a fin or a cooling water channel provided in part of the exhaust downstream communication passage 41 functions as the cooling space 51.
Further, although in the present embodiment, the cooling space 51 is provided in the exhaust downstream communication passage 41, the cooling space 51 may be provided in the intake communication passage 31 of the above described third embodiment. In this case as well, the cooling space 51 can achieve the same effects as described above to further facilitate gas exchange.
This completes the description of the second to fifth embodiments relating to the gas exchange facilitating means, but other embodiments can be envisaged and will now be sequentially described.
A multicylinder internal combustion engine according to a sixth embodiment of the present invention differs from the multicylinder internal combustion engine according to the first embodiment, in which the exhaust communication passages 11 are provided outside the exhaust manifold 1, in that the exhaust manifold communication passages 11 are incorporated in the exhaust manifold 1.
Each of the head-side spacer member 61 and the manifold-side spacer member 62 is in the form of a plate similar in shape to the upstream side flange 2 (see
The sensor fixing base 12, which is circular, is welded to a surface of the manifold-side spacer member 62 on the manifold side such that the sensor fixing base 12 is located at a slightly upper position between the port communication hole 65 of the second cylinder #2 and the port communication hole 65 of the third cylinder #3. An exhaust gas sensor-fixing screw hole 67 is formed at the center of the sensor fixing base 12, and an insertion hole 68 is formed in the manifold side spacer member 62 in a manner corresponding to the screw hole 67. An end of a bent passage 69 is opened in a surface of the head-side spacer member 61 on the manifold side in a manner corresponding to the insertion hole 68 of the manifold-side spacer member 62. The bent passage 69 is bent upward at a substantially right angle; the other end of the bent passage 69 is opened at the upper edge of the head-side spacer 61 via a screw hole 70.
The exhaust gas sensor 13 is engaged with and fastened in the screw hole 67 of the sensor fixing base 12. A detector 13a of the exhaust gas sensor 13 is located in the bent passage 69 as well as the insertion hole 68, and has an end thereof extended to substantially the innermost part of a horizontal section in the bent passage 69. On the other hand, an end of the intake communication passage 31 according to the above described third embodiment or the exhaust downstream communication passage 41 according to the fourth embodiment is connected to the screw hole 70 of the head-side spacer member 61. Therefore, the screw hole 70 is in communication with the intake manifold 32 of the internal combustion engine via the communication passage 31 or the downstream side of the catalyst 9 in the exhaust pipe 6 via the communication passages 41.
Four grooves 71 that connect the port communication holes 65 and the insertion hole 68 to each other are formed on a surface of the manifold-side spacer member 62 on the head side. As shown in
Also, in the present embodiment, the distance A1 from the exhaust ports 10 to the exhaust gas sensor 13 can be reduced to the minimum possible level as is the case with the first embodiment. The distance A1 is considerably shorter than the distance A2 (see
Further, since the exhaust communication passages 11 are formed in the spacer members 61 and 62 which are interposed between the cylinder head 63 and the upstream side flange 2 of the exhaust manifold 1, radiation of exhaust gases flowing in the exhaust communication passages 11 can be suppressed. Therefore, it is possible to achieve another advantage that exhaust gases are supplied to the exhaust gas sensor 13 while being maintained at high temperatures, and thus inactivation of the exhaust gas sensor 13 is prevented and quick activation of the exhaust gas sensor 13 is realized.
It should be noted that the arrangement for suppressing the radiation of exhaust gases in the exhaust communication passages 11 should not be limited to the above described one. For example, in the first embodiment in which the exhaust communication passages 11 are provided outside the exhaust manifold 1, the exhaust communication passages 11 may be configured as double pipes, or may be covered with a heat-retaining material. In this case as well, the radiation of exhaust gases can be suppressed to obtain the same effects as in the present embodiment. Also, instead of suppressing the radiation of exhaust gases, the exhaust gas sensor 13 may be positively heated to prevent inactivation of the exhaust gas sensor 13 and realize quick activation thereof.
On the other hand, the constructions of the head-side spacer member 61 and the manifold-side spacer member 62 are not limited to the above described ones. A variation thereof will now be described.
Although in the sixth embodiment, the head-side spacer member 61 is formed with the bent passage to connect the exhaust gas sensor 13 to the intake communication passage 31 and the exhaust downstream communication passage 41, the intake communication passage 31 and the exhaust downstream communication passage 41 may be omitted as is the case with the first embodiment. In this case, the facilitation of gas exchange due to a difference in pressure cannot be expected, but the radiation of exhaust gas can be suppressed as is the case with the sixth embodiment.
In the sixth embodiment, the end of the detector 13a of the exhaust gas sensor 13 is located at substantially the innermost part of the horizontal section in the bent passage 69 as shown in
In the sixth embodiment, the exhaust gas sensor 13 and the intake communication passage 31 or the exhaust downstream communication passage 41 are in communication with each other via the bent passage 69 formed in the head-side spacer member 61. However, in place of the bent passage 69, a groove 72 may be formed in the manifold-side spacer member 62 as is the case with the exhaust communication passage 11. Specifically, as shown in
In the sixth embodiment, the head-side spacer member 61 and the manifold-side spacer member 62 are fabricated as members independent of the cylinder head 63 and the exhaust manifold 1, and the exhaust communication passage 11 and the exhaust gas sensor 13 are provided in the spacer members 61 and 62. However, either one or both of the spacer members 61 and 62 may be integrated with the cylinder head 63 and/or the exhaust manifold 1.
By the way, when the amount of gases exchanged in the exhaust communication passages 11 via the exhaust gas sensor 13 is not uniform, the effect of the air-fuel ratio of a specific cylinder on the output from the exhaust gas sensor 13 is increased or decreased, and hence the exhaust air-fuel ratio would not be correctly determined. Therefore, a description will now be given of a multicylinder internal combustion engine according to seventh and eighth embodiments of the present invention, which is adapted to make uniform the amount of gases exchanged in the exhaust communication passages 11.
As is the case with the sixth embodiment, four grooves 81 and 82 are formed on a surface of the manifold-side spacer member 62 on the head side. In the present embodiment, as compared with the grooves 81 for the first cylinders #1 and the fourth cylinder #4 far from the exhaust gas sensor 13, the grooves 82 for the second cylinders #2 and the third cylinder #3 near the exhaust gas sensor 13 are formed to be wider and larger in cross-sectional area although they have the same depth. Therefore, the volumes of all the exhaust communication passage 11 between the port communication holes 65 and the insertion hole 68 are substantially equal.
Since the volumes of the respective exhaust communication passages 11 are substantially equal, pressure pulsations generated when exhaust gases flow in them uniformly affect the exhaust gases and hence the uniform amount of gases are exchanged in the exhaust communication passages 11. As a result, the exhaust air-fuel ratio can be accurately determined with the air-fuel ratios of the respective cylinders being uniformly reflected.
It should be noted that to adjust the cross-sectional areas of the respective exhaust communication passages 11, the depths of the grooves 81 and 82 may be varied instead of the width, or the widths and depths of the grooves 81 and 82 may be varied.
Here, there may be a case where resonance of pressure pulsations occurs depending on the lengths of the respective exhaust communication passages 11. In this case, the resonance of pressure pulsations changes the flow rate of exhaust gas to change the output from the exhaust gas sensor 13. Therefore, it is preferred that the lengths of the respective exhaust communication passages 11 are set to such values as to prevent the resonance of pressure pulsations in a regular rotational range of the internal combustion engine.
One ends of the four exhaust communication passages 11 are connected to the sensor fixing base 12 to which the exhaust gas sensor 13 is attached. The exhaust communication passages 11 are arranged at regular intervals of 90 degrees about the sensor fixing base 12 on a substantially horizontal plane. Although not illustrated, the other ends of the exhaust communication passages 11 are connected to the branches 3 of the exhaust manifold 1 for the respective cylinders. One end of the intake communication passage 31 of the third embodiment or the exhaust downstream communication passage 41 of the fourth embodiment is connected to the lower surface of the sensor fixing base 12, and the other end of the communication passage 31 or 41 is connected to the intake manifold 32 of the internal combustion engine or the downstream side of the catalyst 9 in the exhaust pipe 6.
Because the communication passages 11, 31, and 41 are arranged as described above, the exhaust communication passages 11 are located at substantially equal intervals about the intake communication passage 31 or the exhaust downstream communication passage 41. Therefore, exhaust gases from the exhaust communication passages 11 flow into the intake communication passage 31 or the exhaust downstream communication passage 41 via the exhaust gas sensor 13 under substantially the same conditions. Thus, the whole circumference of the detector 13a of the exhaust gas sensor 13 can be effectively used for detecting the air-fuel ratio to thereby improve responsiveness. Also, the problem that the effect of the air-fuel ratio of a specific cylinder is increased or decreased can be solved, so that the exhaust air-fuel ratio can be accurately determined with the air-fuel ratios of the respective cylinders being uniformly reflected.
By the way, in the case where the intake communication passage 31 is connected to the exhaust gas sensor 13 as in the third embodiment, the amount of exhaust gas flowing through the exhaust gas sensor 13 increases with an increase in the ratio of exhaust pressure to intake pressure. Then, at a time point the pressure ratio reaches a critical ratio, i.e. a critical state, the increase in the flow rate of exhaust gas is limited. If this critical state is caused to occur at the outlet or inlet of the exhaust gas sensor using the above phenomenon, various advantages can be obtained. A description will now be given of ninth and tenth embodiments of the present invention.
In the ninth embodiment, to reduce the effects of dependence on pressure on the exhaust gas sensor 13, the cross-sectional areas of the exhaust communication passage 11 and the intake communication passage 31 are set such that the critical state occurs at the outlet side of the exhaust gas sensor 13. Specifically, the total sum of the effective cross-sectional areas of the junctions of the exhaust communication passages 11 and the exhaust gas sensor 13 is set to be larger than the effective cross-sectional area of the junction of the intake communication passage 31 and the exhaust gas sensor 13.
On this occasion, the pressure of exhaust gas acts as exhaust pressure in an area upstream of the outlet side of the exhaust gas sensor 13 and acts as intake pressure in an area downstream of the outlet side of the exhaust gas sensor 13. Therefore, exhaust pressure closer to the atmosphere as compared with intake pressure acts on the exhaust gas sensor 13. In general, the exhaust gas sensor 13 has the property of changing detecting characteristics depending on the pressure of exhaust gas. For this reason, exhaust pressure closer to the atmosphere acts on the exhaust gas sensor 13, and therefore, the effects of dependence on pressure can be reduced to improve the accuracy in determination of the exhaust air-fuel ratio.
The tenth embodiment of the present invention assumes a case where it is unnecessary to take measures to cope with dependence on pressure of the exhaust gas sensor 13 in the ninth embodiment, such as a case where the effect of dependence on pressure is small or a case where dependence on the pressure of gas is corrected. In the present embodiment, to make uniform the amount of exhaust gases flowing from the exhaust communication passages 11 into the exhaust gas sensor 13, the cross-sectional areas of the exhaust communication passages 11 and the intake communication passage 31 are set such that the critical status occurs at the inlet side of the exhaust gas sensor 13 contrary to the ninth embodiment. That is, the total sum of the effective cross-sectional areas of the junctions of the respective exhaust communication passages 11 and the exhaust gas sensor 13 is set to be smaller than the effective cross-sectional area of the junction of the intake communication passage 31 and the exhaust gas sensor 13. In the present embodiment, the effective cross-sectional areas of the junctions of the exhaust communication passages 11 are set to be equal.
Since the pressure reaches the critical state earlier at the inlet of the exhaust gas sensor 13 and the effective cross-sectional areas of the junctions of the respective exhaust communication passages 11 and the exhaust gas sensor 13 are set to be equal as mentioned above, the amounts of exhaust gases flowing from the respective exhaust communication passages 11 into the exhaust gas sensor 13 are substantially equal. As a result, the exhaust air-fuel ratio can be accurately determined with the air-fuel ratios of the respective cylinders being uniformly reflected.
Although the present invention has been described in some detail by way of illustration for purposes of clarity of understanding, embodiments of the present invention are not limited to the above described ones. For example, although in the above described embodiments, the internal combustion engine is implemented by the straight four-cylinder engine, the number and arrangement of cylinders are not limited to the above described embodiments but may be arbitrarily changed insofar as the internal combustion engine is a multicylinder type.
Also, the arrangements of the above described embodiments should not necessarily be practiced individually, but may be practiced in arbitrary combinations. For example, the arrangement of the second embodiment in which the inflow part 21 of the exhaust communication passages 11 is disposed at a sharp angle to the exhaust gas flow line L1 may be combined with the arrangement of the fifth embodiment in which the cooling space 51 is provided in the exhaust downstream communication passage 41.
Further, the intake communication passage 31 may be connected to an EGR downstream passage, not to the intake manifold 32.
Further, if a difference in pressure is such that gas exchange cannot be facilitated (for example, intake pipe negative pressure increases, upstream exhaust pressure increases, and downstream exhaust pressure increases), determination of the air-fuel ratio can be temporarily interrupted.
Also, it is preferred that the relationships between ventilation holes formed in a protective cover for the exhaust gas sensor 13 and communication holes of the respective exhaust communication passages 11 from which exhaust gas flows into the exhaust gas sensor 13 are made uniform between the cylinders so as to solve the problems described below. Specifically, if the flow rate of exhaust gas (gas to be checked) flowing into the exhaust gas sensor 13 is high, the amount of gas to be checked flowing into the detector 13a of the exhaust gas sensor 13 varies according to whether a large number of or small number of the ventilation holes are formed in projected areas of the communication holes, causing the problem that the effect of variation in the air-fuel ratio of the cylinders is increased. The present invention can solve this problem.
Further, although in the above described embodiments, the cross-sectional area is uniform in each of the exhaust communication passages 11, intake communication passage 31, and exhaust downstream communication passage 41, the present invention is not limited to this, but the cross-sectional area may be minimum at only a part of each passage. Since exhaust gas passes through each passage, the cross-sectional area varies in each passage due to adhesion of deposits or the like. For example in the case where the effective cross-sectional areas of the respective exhaust communication passages 11 of the respective cylinders are not uniform, there is a variation in determination of the air-fuel ratio of the cylinders. However, since deposits or the like are not uniformly adhered into each passage, if the cross-sectional area is set to be minimum at a part of each passage, the possibility that deposits are adhered to the minimum cross-sectional area can be lowered.
Therefore, it is possible to lower the possibility that the effective cross-sectional areas of the exhaust passages of the respective cylinders are not uniform. As a result, the accuracy in determination of the air-fuel ratio is less likely to be deteriorated due to variation in the detected air-fuel ratio of the cylinders.
Further, it may be arranged such that exhaust gases led from the exhaust communication passages are mixed in a space of the exhaust gas sensor 13, and the air-fuel ratio of the exhaust gases thus mixed is determined by the exhaust gas sensor 13. Also, the air-fuel ratios of the respective cylinders may be individually determined without mixing exhaust gases.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-198263 | Jul 2004 | JP | national |
