1. Field of the Invention
The present invention relates to an engine oxygen concentration sensor mounting structure in which an oxygen concentration sensor is mounted in an exhaust pipe connected to an outlet of a collector exhaust manifold of an engine.
2. Description of the Related Art
Conventionally known is a technique of detecting the oxygen concentration of an exhaust gas from an engine by an oxygen concentration sensor and controlling the amount of fuel injected into the engine based on the detected oxygen concentration. In a conventional multicylinder engine, an oxygen concentration sensor is generally provided in a collector exhaust pipe connected to the downstream side of a combined part of an exhaust manifold. In this case, it is known that equalizing the lengths of a plurality of exhaust single pipes forming the exhaust manifold can balance the contribution levels of the exhaust gases discharged from each of the combustion chambers, thereby enhancing the accuracy in detecting the oxygen concentration.
In a multicylinder engine in which the crankshaft is placed widthwise in the lateral direction in an engine compartment, it is comparatively easy to equalize the lengths of a plurality of exhaust single pipes. However, in a multicylinder engine in which the crankshaft is placed lengthwise in the longitudinal direction, an exhaust single pipe extending to a combustion chamber on the front side of the vehicle body inevitably becomes long, and an exhaust single pipe extending to a combustion chamber on the rear side of the vehicle body inevitably becomes short. As a result, when an oxygen concentration sensor is provided in a collector exhaust pipe connected to the downstream side of the combined part of an exhaust manifold, variations are produced in the levels contributed to the oxygen concentration by the exhaust gases discharged from the combustion chambers, leading to a problem of degradation of the accuracy in detection of the oxygen concentration.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to ensure accurate detection by an oxygen concentration sensor provided in an exhaust pipe on the downstream side of an exhaust manifold even when the lengths of a plurality of exhaust single pipes thereof are nonuniform.
In order to accomplish the above-mentioned object, in accordance with a first aspect of the present invention, there is proposed an engine oxygen concentration sensor mounting structure in which an oxygen concentration sensor is mounted in a collector exhaust pipe connected to an outlet of an exhaust manifold of an engine, wherein the oxygen concentration sensor is mounted in the curved collector exhaust pipe extending to the outlet of the exhaust manifold, which has a plurality of exhaust single pipes, and when a straight line is drawn from a detection part of the oxygen concentration sensor positioned within the collector exhaust pipe so as to be parallel to a section of a centerline of the collector exhaust pipe closest to the detection part, the straight line passes outside the outlet of the exhaust manifold.
In accordance with this arrangement, because the oxygen concentration sensor is mounted in the curved collector exhaust pipe extending to the outlet of the exhaust manifold and, when a straight line is drawn from the detection part of the oxygen concentration sensor so as to be parallel to the section of the centerline of the collector exhaust pipe closest to the detection part, this straight line passes outside the outlet of the exhaust manifold, the exhaust gases discharged from the exhaust manifold can be adequately mixed within the curved collector exhaust pipe, thus compensating for differences in the lengths of the plurality of exhaust single pipes and thereby ensuring accurate detection by the oxygen concentration sensor. The adequate mixing of the exhaust gases within the collector exhaust pipe can be achieved by the exhaust gases impinging on the inner wall of the curved exhaust pipe and being diffused, where the inner wall faces the outlet of the exhaust manifold.
Furthermore, in accordance with a second aspect of the present invention, there is proposed an engine oxygen concentration sensor mounting structure wherein the oxygen concentration sensor is mounted on the inside of the curve of the collector exhaust pipe.
In accordance with this arrangement, because the oxygen concentration sensor is mounted on the inside of the curve of the collector exhaust pipe, the oxygen concentration sensor can be placed by effectively utilizing the dead space formed by the curve in the collector exhaust pipe, thereby enhancing space efficiency. Moreover, it is possible to secure working space for the oxygen concentration sensor to be installed and removed, thereby enhancing ease of maintenance.
Moreover, in accordance with a third aspect of the present invention, there is proposed an engine oxygen concentration sensor mounting structure wherein the engine is mounted in a vehicle, and the oxygen concentration sensor is disposed on the front side of the collector exhaust pipe.
In accordance with this arrangement, because the oxygen concentration sensor is disposed on the front side of the collector exhaust pipe, the oxygen concentration sensor can be cooled by the passage of air as the vehicle travels, thereby enhancing durability.
The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent from an explanation of a preferred embodiment that will be described in detail below by reference to the attached drawings.
Referring to
As shown in
Formed on the mounting face 13a of the cylinder head 13 are at least two (two in the embodiment) stud bolts 26 and a plurality of (five in the embodiment) threaded holes 13b. Formed on the outer periphery of the mounting flange 21 of the exhaust manifold 17 are a reinforcing rib 21a projecting outward (in a direction away from the cylinder head 13), two notches 21b corresponding to the two stud bolts 26, and five through holes 21c corresponding to the five threaded holes 13b. The two notches 21b are provided on opposite ends, in the longitudinal direction, of a lower part of the mounting flange 21 and open downward, and there are breaks in the reinforcing rib 21a in these parts.
The mounting flange 21 is thus secured to the cylinder head 13 by means of two nuts 27 screwed onto the two stud bolts 26 and five bolts 28 running through the through holes 21c of the mounting flange 21 and screwed into the threaded holes 13b in the mounting face 13a with a gasket 29 (see
Four outwardly projecting annular reinforcing ribs 21d are formed on the mounting flange 21 of the exhaust manifold 17 at positions corresponding to the exhaust ports 22a to 22d of the cylinder head 13. Four annular parts 24a on the inner end of the first cover half 24 are fitted into the inner circumferences of the four reinforcing ribs 21d. Further, the upstream ends of the four exhaust single pipes 23a to 23d are fitted into the inner circumferences of the annular parts 24a, and joined together as a unit by welds 30 (see FIG. 5). The four exhaust single pipes 23a to 23d are merged at their downstream ends to form a combined part 31, and the combined part 31 is joined by a weld 32 (see
The second cover half 25 covers the face of the exhaust manifold 17 on the front side frame F side and is detachably fixed to the first cover half 24 by three bolts 34, 35 and 36. The three bolts 34, 35 and 36 run through three through holes 25a, 25b, and 25c, respectively, of the second cover half 25 and through the through holes 24b of the first cover half 24, and are screwed into weld nuts 37, 38, and 39, respectively, on the inner surface of the first cover half 24 (see FIG. 6). A semi-cylindrical part 25d formed on the outer end of the second cover half 25 encloses the upstream end of the collector exhaust pipe 19 in cooperation with the semi-cylindrical part 24c of the first cover half 24 in a state in which the second cover half 25 and the first cover half 24 are joined together. The first cover half 24 and the second cover half 25 have apertures 24d and 25e, respectively, and one of the five bolts 28 securing the mounting flange 21 to the cylinder head 13 is attached and detached through the apertures 24d and 25e.
As is clear from
When installing the exhaust manifold 17 on the engine E mounted in the vehicle body, because the front side frame F is positioned in the proximity of the side of the cylinder head 13, the exhaust manifold 17 cannot be installed by moving it in a direction perpendicular to the mounting face 13a of the cylinder head 13. In the present embodiment, the exhaust manifold 17 is firstly moved from the rear to the front so as to be inserted between the cylinder head 13 and the front side frame F, and then moved downward so that the mounting flange 21 of the exhaust manifold 17 moves along the mounting face 13a of the cylinder head 13 (see arrows A in FIGS. 1 and 4). In this way, the two notches 21b opening downward in the mounting flange 21 engage with the two stud bolts 26 of the cylinder head 13, thereby provisionally fixing the exhaust manifold 17 to the cylinder head 13. In this state, screwing the nuts 27 onto the two stud bolts 26, running the five bolts 28 through the through holes 21c of the mounting flange 21, and screwing them into the threaded holes 13b of the cylinder head 13 can secure the exhaust manifold 17 to the cylinder head 13.
Because the exhaust manifold 17 can thus be secured to the cylinder head 13 by moving it in a direction along the mounting face 13a of the cylinder head 13 without moving it in a direction perpendicular to the mounting flange 13a, the exhaust manifold 17 can be installed on the cylinder head 13 without interfering with the front side frame F. Furthermore, because the exhaust manifold 17 can be provisionally fixed to the cylinder head 13 by engaging the notches 21b of the mounting flange 21 with the stud bolts 26 of the cylinder head 13, the subsequent operation of screwing the nuts 27 onto the bolts 28 can be carried out easily.
Moreover, not only can the exhaust manifold 17 be stably supported by the stud bolts 26 because the notches 21b open downward, but also the exhaust manifold 17 can be supported more stably because the notches 21b are formed on opposite ends of the mounting flange 21. Furthermore, because the stud bolts 26 and the threaded holes 13b are positioned so as to surround the outside of the annular parts 24a of the first cover half 24, which is welded integrally with the mounting flange 21 of the exhaust manifold 17, the nuts 27 and the bolts 28 can be screwed together without interference from the first cover half 24. Moreover, because the four exhaust single pipes 23a to 23d are completely covered from their inlets with the cover 18, it is possible to effectively prevent heat radiating from the exhaust gas and reduce the exhaust noise.
The exhaust manifold 17 can be detached by reversely following the above-mentioned installation procedure. Also in this case, it is possible to prevent the exhaust manifold 17 from interfering with the front side frame F.
Furthermore, because the reinforcing rib 21a provided on the outer periphery of the mounting flange 21 of the exhaust manifold 17 projects in a direction away from the cylinder head 13, the heat radiated in the vertical direction from the exhaust single pipes 23a to 23d through which high temperature exhaust gas flows, can be blocked by the reinforcing rib 21a, thereby enhancing the durability of the gaskets disposed between the cylinder block 12 and the cylinder head 13 and between the cylinder head 13 and the head cover 14. Moreover, because the reinforcing rib 21a extends to positions next to the notches 21b of the mounting flange 21, it is possible to minimize any reduction in rigidity of the mounting flange 21 caused by formation of the notches 21b.
Furthermore, although the part of the cover 18 covering the lower side and the side next to the vehicle body of the exhaust manifold 17 (that is, the second cover half 25) is easily corroded due to the attachment of water and mud, because the second cover half 25 is detachable from the first cover half 24, which is integral with the exhaust manifold 17, it is possible to exchange only the corroded second cover half 25, thereby economizing on maintenance costs.
Exhaust gases flow from the four exhaust single pipes 23a to 23d into the collector exhaust pipe 19 equipped with the oxygen concentration sensor 40 and, ideally, the exhaust gases discharged from the four exhaust ports 22a to 22d each should have a contribution level of 25% to the oxygen concentration. However, as shown in
In order to eliminate such a problem, it is necessary to make the exhaust gases flowing in from the four exhaust single pipes 23a to 23d impinge on the inner wall of the collector exhaust pipe 19 so as to adequately mix them before they act on the oxygen concentration sensor 40 by increasing the curvature of the collector exhaust pipe 19 and providing the oxygen concentration sensor 40 on the downstream side of the collector exhaust pipe 19. As hereinbefore described, the degree of curvature of the collector exhaust pipe 19 and the position where the oxygen concentration sensor 40 is mounted in order to satisfy the above-mentioned requirement are such that, when the straight line L is drawn from the detection part 40a at the extremity of the oxygen concentration sensor 40 so as to be parallel to the section of the centerline C of the collector exhaust pipe 19 closest to the detection part 40a, the straight line L is outside the confines of the outlet 17a on the downstream end of the exhaust manifold 17 (see FIG. 9). Satisfying this condition can bring the levels contributed to the oxygen concentration by the exhaust gases discharged from the four exhaust ports 22a to 22d close to 25% each, as shown in FIG. 10B.
Because the oxygen concentration sensor 40 is provided on the inside of the curve of the exhaust pipe 19, the oxygen concentration sensor 40 can be positioned by effectively utilizing the dead space on the inside of the curve of the collector exhaust pipe 19. Moreover, it is possible to ensure that there is space for a tool for attaching and removing the oxygen concentration sensor 40 to be operated, thereby enhancing the ease of maintenance. Furthermore, because the oxygen concentration sensor 40 is provided in the position on the front side of the collector exhaust pipe 19, the position being most efficiently exposed to the passage of air, the oxygen concentration sensor 40 can be effectively cooled, thereby enhancing its durability.
Although the present invention is explained in detail above, the present invention can be modified in a variety of ways without departing from the spirit and scope of the present invention.
For example, a V-type eight-cylinder engine E is illustrated in the embodiment, but the present invention can be applied to a V-type engine having a different number of cylinders or an in-line multicylinder engine.
Furthermore, the present invention is most effectively applied to an engine E that is mounted lengthwise in a vehicle, but it can also be applied to an engine other than a vehicle engine or an engine that is mounted widthwise in a vehicle.
Number | Date | Country | Kind |
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2001-211008 | Jul 2001 | JP | national |
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