The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2004-286054, filed on Sep. 30, 2004. The subject matter of this priority document is incorporated by reference herein.
1. Field of the Invention
The present invention relates to an air-fuel ratio sensor mounting structure for mounting the sensor to an exhaust system component of a motorcycle, and to an exhaust subassembly incorporating the sensor. More particularly, the present invention relates to a mounting structure for affixing an air-fuel ratio sensor to an exhaust pipe in a motorcycle, and to a related exhaust subassembly including the sensor, the mounting structure, and the exhaust pipe.
2. Background Art
It is well known to employ an oxygen sensor in a motorcycle exhaust system as a control device, so as to improve the catalytic efficiency thereof. In a motorcycle having a multi-cylinder engine, such an oxygen sensor is typically mounted on a manifold of exhaust pipes at a position upstream of a catalytic converter and spaced apart from the engine on the rear lower side thereof. The catalytic converter is used for exhaust purification, for example, and may comprise a three-way catalyst. In a motorcycle having a single-cylinder engine, such an oxygen sensor is located in an empty space, the space selected such that the sensor does not interfere with the engine body. This position improves the maintainability of the sensor and protects the sensor.
Related to this mounting structure, there has been proposed an invention entitled “Air-Fuel Ratio Control Device for Internal Combustion Engine” (Japanese Patent Laid-open No. 59-74360). In Japanese Patent Laid-open No. 59-74360, a catalyst for exhaust purification is provided in an exhaust pipe of an internal combustion engine for a vehicle, and an exhaust gas sensor is mounted upstream of the catalyst. The composition of an exhaust gas to be supplied to the catalyst is detected by the exhaust gas sensor, and the air-fuel ratio of an air-fuel mixture to be taken into the engine is controlled according to a detection signal output from the exhaust gas sensor. According to the description in Japanese Patent Laid-open No. 59-74360, feedback control of such an air-fuel ratio is performed by a known air-fuel ratio control device so that the composition of the exhaust gas is optimized, allowing best purification of the exhaust gas by the catalyst. Further, Japanese Patent Laid-open No. 59-74360 also discloses that an oxygen sensor for detecting the concentration of oxygen in an exhaust gas is generally used as the exhaust gas sensor.
Further, according to the description in an invention entitled “Exhaust Gas Sensor Device in Motorcycle” (Japanese Patent Laid-open No. 2000-335467), an exhaust gas sensor for detecting the concentration of oxygen or the like in an exhaust gas discharged from an engine mounted on a motorcycle may be mounted on an upper wall of an exhaust pipe at a position on the front side of a right projecting portion of a crankcase and on the outer side of a right side surface of a cylinder block.
In both of the references cited above, an oxygen sensor is used as the exhaust gas sensor. This kind of oxygen sensor determines whether the air-fuel ratio is rich or lean with respect to a stoichiometric air-fuel ratio in a narrow region near the stoichiometric air-fuel ratio, but it is not suitable for linear detection of the oxygen concentration over a wide range of values.
Also in a motorcycle, it is desirable to detect the air-fuel ratio in a wide region by using an air-fuel ratio sensor in place of the oxygen sensor mentioned above. In other words, the oxygen sensor merely detects the presence or absence of oxygen in an exhaust gas as mentioned above, whereas the air-fuel ratio sensor can linearly detect the oxygen concentration in an exhaust gas over a wide range by using an element whose output voltage changes in proportion to the oxygen concentration.
Accordingly, the air-fuel ratio sensor is fixed to an exhaust pipe in a motorcycle. However, there is a possibility that water may gather in the exhaust pipe, for example, in driving an engine mounted in the motorcycle. Water gathered in the exhaust pipe may have an adverse effect on the operation of the air-fuel ratio sensor.
Further, it will be necessary to arrange the air-fuel ratio sensor on the exhaust pipe in consideration of a banked operation of the motorcycle, experienced during tight turning thereof. In particular, the air-fuel ratio sensor must be arranged to avoid interference with the surface of the ground when the motorcycle is sharply banked during a turn.
Accordingly, it is an object of the present invention to provide a mounting structure for an air-fuel ratio sensor in a motorcycle which can eliminate the influence of water gathered in the exhaust pipe upon the air-fuel ratio sensor, can eliminate the sensor interference with the surface of the ground during banked operation, and can improve the mountability of the air-fuel ratio sensor to the exhaust pipe, that is, the ease and durability of mounting of the air-fuel ratio sensor.
According to the present invention, there is provided a mounting structure for an air-fuel ratio sensor in a motorcycle, in which the air-fuel ratio sensor is mounted on an exhaust pipe so as to be pointed upwardly toward the central lateral plane of the motorcycle, as viewed in front elevation of the motorcycle. Preferably, the air-fuel ratio sensor is inclined upward by an angle of 10° or more, with respect to a horizontal line passing through the center of the exhaust pipe in its cross section.
With this arrangement, the concentration of oxygen in an exhaust gas is accurately detected by the air-fuel ratio sensor substantially without being influenced by water gathered in the exhaust pipe, thereby improving detection accuracy. Furthermore, the air-fuel ratio sensor mounted on the exhaust pipe so as to extend upward does not interfere with the surface of the ground, during banked operation of the vehicle. In addition, the air-fuel ratio sensor is easily and firmly mounted on the exhaust pipe, that is, the mountability of the air-fuel ratio sensor is improved.
For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following drawings and description, like numbers refer to like parts. The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent from the detailed description of the embodiment of the invention presented below in conjunction with the attached drawings.
A selected illustrative embodiment of the mounting structure of the air-fuel ratio sensor in the motorcycle according to the present invention will now be described in some detail, with reference to
The positional relation between the front wheel 12 and each exhaust pipe 32 is shown in
As shown in
The air-fuel ratio sensor 34 includes a main sensor body 39, which is disposed outside of the exhaust pipe 32 in an installed configuration of the sensor, and a central hexagonal boss portion 41 which is fixedly attached to the main sensor body 39. The hexagonal boss portion 41 enables a mechanic or assembler to grasp the sensor with a tool (not shown) in order to install the sensor in, or remove it from the exhaust pipe 32. The air-fuel ratio sensor 34 also includes a cylindrical end cap 42 formed with a plurality of exhaust gas-introducing holes 40 extending therethrough, as shown. These exhaust gas-introducing holes 40 are composed of two groups spaced apart from each other in the axial direction of the cylindrical end cap 42. The holes 40 within each group are spaced apart from each other in the circumferential direction of the cylindrical end cap 42. A tip portion of the cylindrical end cap 42, having these two groups of holes 40 therein, is disposed within and exposed to the environment on the inside of the exhaust pipe 32. A base portion of the cylindrical end cap 42 is formed with an external thread 44 formed thereon, for engaging an internal thread formed on the inner surface of the nut 38. Accordingly, the air-fuel ratio sensor 34 is fixed to the exhaust pipe 32 by engaging the external thread 44 of the cylindrical end cap 42 of the sensor 34 with the internal thread of the nut 38 fixed to the hole 37 of the exhaust pipe 32. The air-fuel ratio sensor 34 itself could be one of a number of commercially available air-fuel sensors, so the detailed description of the internal structure thereof will be omitted herein.
As will be apparent from
The holes 40 formed at the tip portion of the cylindrical end cap 42 of the air-fuel ratio sensor 32 are exposed to the ambient environment inside of the exhaust pipe 32, so that exhaust gas in the exhaust pipe 32 is introduced into the cylindrical end cap 42 via the holes 40. The air-fuel ratio sensor 34 thereby detects the concentration of oxygen in the exhaust gas. It is sufficient that at least a part of the holes 40 should be exposed to the environment inside of the exhaust pipe 32, in order to attain the purpose of the air-fuel ratio sensor 34.
In this case, the air-fuel ratio sensor 34 is preferably located at a position immediately upstream of the corresponding catalytic converter 33, as shown in
According to this illustrative embodiment, the air-fuel ratio sensor 34 is mounted on each exhaust pipe 32 of the motorcycle 10 with the main sensor body 39 oriented so as to be inclined upward by an angle of 10° or more with respect to the horizontal line H, passing through the center of the exhaust pipe 32 in its cross section, and be pointed inwardly toward the central lateral plane of the motorcycle 10, as viewed in front elevation of the motorcycle 10 (i.e., as viewed from the vantage point of
With the arrangement that the air-fuel ratio sensor 34 is inclined upward by an angle of 10° or more as mentioned above, the air-fuel ratio sensor 34 is not significantly influenced by water which may accumulate in the corresponding exhaust pipe 32, so that the oxygen concentration is detected with higher accuracy. Furthermore, since the air-fuel ratio sensor 34 is located above the horizontal line H of the corresponding exhaust pipe 32, the air-fuel ratio sensor 34 is mounted easily and firmly. In addition, even when the motorcycle l is banked during operation, the surface of the ground does not interfere with the air-fuel ratio sensor 34.
Accordingly, the motorcycle 10 is easily driven, and the flexibility of design or layout in the motorcycle 10 is further increased.
While a working example of the present invention has been described above, the present invention is not limited to the working example described above, but various design alterations may be carried out without departing from the present invention as set forth in the claims.
Number | Date | Country | Kind |
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2004-286054 | Sep 2004 | JP | national |
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Number | Date | Country | |
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20060065041 A1 | Mar 2006 | US |