Abstract:
In a V-type engine in which first and second banks arranged in a V-shape are provided continuously to a crankcase, and in which a carburetor is placed at a valley between the first and second banks, the carburetor is placed spaced from the first and second banks. Further, the carburetor is connected to intake ports of the first and second banks via first and second intake pipes, respectively, and first and second heat shield plates each made of synthetic resin are attached to side faces of the respective first and second banks, the side faces facing the carburetor, each of the first and second heat shield plates covering a corresponding one of the side faces and defining a cooling air passage between the heat shield plate and the side face. Accordingly, it is possible to surely prevent heat from the banks from affecting the carburetor in order to prevent percolation in the carburetor even in the case where the engine stops its operation in a high-temperature state.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention claims priority under 35 USC §119 based on Japanese patent application No. 2008-146531 filed Jun. 4, 2008. The subject matter of this priority document is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improvement of a V-type engine in which first and second banks arranged in a V-shape are provided continuously to a crankcase, and in which a carburetor is placed at a valley between the first and second banks, the carburetor communicating with intake ports of the respective banks. 
     2. Description of the Related Art 
     Immediately after such a V-type engine stops its operation, cooling air stops flowing. Consequently, heat of the banks easily stays in a valley between the first and second banks, which can cause percolation in a carburetor placed in the valley. The percolation makes it difficult for the V-type engine to restart in a high-temperature state. To this regard, the following conventional measure is known. Specifically, an insulator is provided at a joint part between each of the banks and the carburetor, and a heat shield flange is integrally formed on the insulator in such a manner as to extend vertically, thereby the heat between the bank and the carburetor is shielded (see, for example, Japanese Patent Application Laid-open No. 58-53640). 
     However, in the above conventional measure, the carburetor is joined to the banks with the relatively-thin insulators in between, and such thin insulators have a limited heat shield capability. Accordingly, when the V-type engine in a high-temperature state stops its operation, the heat from the banks might be conducted to the carburetor through the insulators to cause percolation. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of such circumstances, and has an objective of providing a V-type engine that can have excellent restartability in a high-temperature state by surely preventing heat from banks from affecting a carburetor in order to prevent percolation in the carburetor even in the case where the engine stops its operation in a high-temperature state. 
     In order to achieve the above object, according to a first feature of the present invention, there is provided a V-type engine in which first and second banks arranged in a V-shape are provided continuously to a crankcase, and in which a carburetor is placed at a valley between the first and second banks, the carburetor communicating with intake ports of the respective banks, wherein the carburetor is placed spaced from the first and second banks and connected to the intake ports of the first and second banks via first and second intake pipes, respectively, and first and second heat shield plates each made of synthetic resin are attached to side faces of the respective first and second banks, the side faces facing the carburetor, each of the first and second heat shield plates covering a corresponding one of the side faces and defining a cooling air passage between the heat shield plate and the corresponding side face. 
     According to the first feature of the present invention, the first and second heat shield plates each define the cooling air passage between the heat shield plate and the corresponding side face of the first and second banks B 1  and B 2 , and cooling air is guided into the cooling air passage while the V-type engine is in operation. Thereby, the banks can be cooled. When the V-type engine in a high-temperature state stops its operation, the first and second heat shield plates interposed between the corresponding first and second banks and the carburetor shield the carburetor from radiation heat from the banks. Furthermore, the carburetor is placed at the valley between the first and second banks while being spaced from the banks, and connected to the banks with the intake pipes, respectively. Accordingly, heat radiation effects of the intake pipes allow less heat to be conducted from the banks to the carburetor. The carburetor can thus be prevented from heating up. Accordingly, percolation in the carburetor can be prevented, and this can contribute to improvement of the restartability of the engine in a high-temperature state. 
     As described, the first and second heat shield plates play two functions: guidance of cooling air to the surrounding of the first and second banks while the V-type engine E is in operation; and shielding of the carburetor from radiation heat from the banks when the V-type engine E stops its operation. This can contribute to simplification of the structure around the V-type engine. 
     Further, according to a second feature of the present invention, in addition to the first feature, the first and second heat shield plates attached to the respective side faces of the first and second banks are integrally connected to each other by a bottom plate covering a bottom face of the valley, whereby the first and second heat shield plates and the bottom plate form a single component. 
     According to the second feature of the present invention, the first and second heat shield plates are integrally connected to each other by the bottom plate to form the single component. Since the single component is integrally formed, not only can the heat shield plates be manufactured at once, this synthetic resin member can be attached to the V-type engine easily and speedily. 
     Further, according to a third feature of the present invention, in addition to the second feature, a holding part for holding a linear member is integrally formed to the single component. 
     According to the third feature of the present invention, the holding part holding the linear member is integrally formed to the single component. Accordingly, a holding member dedicated to the linear member does not need to be attached to the V-type engine. This can contribute to reduction in the number of components. 
     The above description, other objects, characteristics and advantages of the present invention will be clear from detailed descriptions which will be provided for the preferred embodiment referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a back view of a general-purpose V-type engine of the present invention; 
         FIG. 2  is a cross-sectional view taken along a line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a view seen from an arrow  3  in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along a line  4 - 4  in  FIG. 1 ; 
         FIG. 5  is a perspective view of a single member including first and second heat shield plates to be attached to the engine; 
         FIG. 6  is a view seen from an arrow  6  in  FIG. 5 ; and 
         FIG. 7  is a view seen from an arrow  7  in  FIG. 6 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be explained below with reference to  FIGS. 1 to 7 . 
     In  FIGS. 1 and 2 , a description will be given of an example in which the present invention is implemented to a general-purpose V-type two-cylinder engine E. The V-type engine E is formed of a crankcase  2  supporting a crankshaft  1 , and first and second banks B 1  and B 2 . The first and second banks B 1  and B 2  are continuously provided to the crankcase  2  at a top part, and are open in a V-shape having its center on a vertical plane P including an axis A of the crankshaft  1 . In the illustrated example, an included angle α between the first and second banks B 1  and B 2  is set to 90°. One end part of the crankshaft  1  protrudes frontward of the crankcase  2 , and a flywheel  3  and a cooling fan  4  are fixed to this end part. A fan cover  5  is attached to the crankcase  2 . By this fan cover  5 , the outside air taken in by the cooling fan  4  is guided, as cooling air, to the surrounding of each of the banks B 1  and B 2  and to the surrounding of a carburetor  14  which will be described later. The other end part of the crankshaft  1  protrudes rearward of the crankcase  2 , and serves as an output part. An engine installation flange  6  is integrally formed to the bottom part of the crankcase  2 . 
     The first and second banks B 1  and B 2  each include a single cylinder  7 . A piston  9  is fitted into the cylinder  7 , while being connected to the crankshaft  1  via a connecting rod  8 . Intake pipe attachment flanges  12  and  12  are formed on the head parts, at respective corner parts on the front side, which are opposite to each other, of the respective first and second banks B 1  and B 2 . Each intake port  13  opens to an end face of a corresponding one of the intake pipe attachment flanges  12  and  12 . First and second intake pipes  16   a  and  16   b  are attached to the intake pipe attachment flanges  12  and  12 , respectively. The carburetor  14  is placed at a center part of a valley  10  between the banks B 1  and B 2 . The first and second intake pipes  16   a  and  16   b  connect first and second intake paths  15   a  and  15   b  of the carburetor  14  to the intake ports  13  and  13  of the first and second banks B 1  and B 2 , respectively. Being placed at the center part of the valley  10 , the carburetor  14  is spaced from the banks B 1  and B 2  by an equal distance. 
     The first and second intake pipes  16   a  and  16   b  are joined, at their upstream ends, to a single large joint flange  17 , and thus connected to each other integrally. The carburetor  14  is joined, at its downstream end face, to the large joint flange  17  by bolts. Small joint flanges  18  and  18  are formed to the respective first and second intake pipes  16   a  and  16   b  at their downstream ends. These small joint flanges  18  and  18  are joined to the respective intake pipe attachment flanges  12  and  12  by bolts  19 . 
     As  FIG. 1  shows, the first and second intake paths  15   a  and  15   b  of the carburetor  14  are located on the left and on the right, respectively, with the vertical plane P in between. Butterfly throttle valves  20  and  20  close and open the respective first and second intake paths  15   a  and  15   b . Rotation of a common valve shaft  21  placed horizontally allows the open/close operation of the throttle valves  20  and  20 . Moreover, the carburetor  14  has, at its lower part, a float chamber  14   a  common to the first and second intake paths  15   a  and  15   b.    
     As  FIGS. 1 ,  3 , and  4  show, first and second heat shield plates  23   a  and  23   b  each made of synthetic resin are attached respectively to side faces of the first and second banks B 1  and B 2 , which face the carburetor  14 . Each of the first and second heat shield plates  23   a  and  23   b  covers the corresponding side face and defines a cooling air passage  22  between the heat shield plate and the side face. Many cooling fins  29 ,  29  are formed on an outer face of each of the banks B 1  and B 2  in such a manner as to face the corresponding cooling air passage  22 . 
     As  FIG. 4  clearly shows, front end parts of the respective first and second heat shield plates  23   a  and  23   b , that is, end parts at the cooling fan  4  side, are continuous with end parts of the fan cover  5  which are located at the downstream side of the cooling air. Further, a curved part  30  is formed at a rear end part of each of the first and second heat shield plates  23   a  and  23   b . The curved part  30  guilds cooling air from a corresponding one of the cooling air passage  22  and  22  to the back face side of the corresponding bank B 1  or B 2 . 
     As  FIGS. 1 and 3  to  7  show, the first and second heat shield plates  23   a  and  23   b  are integrally connected to each other by a bottom plate  24  which covers the bottom face of the valley  10 , and thereby the first and second heat shield plates and the bottom plate form an integrally-formed single component  25 . In the single component  25 , a single attachment boss  26  is formed in each of the first and second heat shield plates  23   a  and  23   b . Moreover, a screw boss  27  is formed in an outer face of each of the banks B 1  and B 2 . The single component  25  is attached to the V-type engine E by fixing a bolt  28  into each of the attachment bosses  26  and the corresponding screw boss  27  (see  FIG. 4 ). By making the first and second heat shield plates  23   a  and  23   b  the single component  25  in this way, the first and second heat shield plates  23   a  and  23   b  can be attached to the V-type engine E with a small number of bolts  28 . 
     Further, a holding part  34  is integrally formed to the single component  25  (i.e., in the illustrated example, one of the heat shield plates,  23   b ). The holding part  34  holds linear members  33  such as an electric wire for control of the V-type engine E, an operation cable, and a hose. 
     Referring back to  FIG. 1 , an opening exhaust port  31  is provided to a head part of each of the first and second banks B 1  and B 2 . The exhaust ports  31  are provided at the back faces of the respective banks B 1  and B 2 , which are opposite to the faces where the intake pipes  16   a  and  16   b  are provided. 
     Next, operations of this embodiment will be explained. 
     The first and second heat shield plates  23   a  and  23   b  made of synthetic resin are attached to the side faces of the first and second banks B 1  and B 2 , which face the carburetor  14 . Each of the first and second heat shield plates  23   a  and  23   b  covers the corresponding side face and defines a corresponding one of the cooling air passages  22  and  22  between the heat shield plate and the side face. The end parts of the first and second heat shield plates  23   a  and  23   b  at the cooling fan  4  side are continuous with the end parts of the fan cover  5  which are located at the downstream side of the cooling air. Accordingly, while the V-type engine E is in operation, cooling air taken in and sent under pressure by the cooling fan  4  that rotates with the crankshaft  1  is guided into the cooling air passages  22  and  22  around the respective banks B 1  and B 2 . Thereby, the banks B 1  and B 2  can be cooled. Especially because the many cooling fins  29 ,  29  of each of the banks B 1  and B 2  face a corresponding one of the cooling air passage  22  and  22 , the banks B 1  and B 2  can have improved cooling capability. Furthermore, part of the cooling air sent under pressure by the cooling fan  4  is also supplied to the carburetor  14  side, and cools the carburetor  14 . 
     Moreover, the curved part  30  at the rear end of each of the heat shield plates  23   a  and  23   b  bends the pathway of the cooling air flowing through a corresponding one of the cooling air passage  22  and  22  of the bank B 1  or B 2 , and the cooling air thereby travels to the back face side of the corresponding bank B 1  or B 2 . Accordingly, the back face side of the banks B 1  and B 2  can be cooled well. 
     When the V-type engine E stops its operation in a high-temperature state, the cooling fan  4  stops rotating, and consequently the cooling air stops flowing. Accordingly, the banks B 1  and B 2  dissipate heat peripherally. However, the carburetor  14  can be prevented from heating up because the heat shield plates  23   a  and  23   b  interposed between the corresponding bank B 1  or B 2  and the carburetor  14  shield the carburetor  14  from radiation heat from the banks B 1  and B 2 . 
     Furthermore, the carburetor  14  is placed at the center part of the valley  10  between the first and second banks B 1  and B 2  and is spaced from the banks B 1  and B 2 . The carburetor  14  is therefore connected to the banks B 1  and B 2  via the relatively-long intake pipes  16   a  and  16   b , respectively. Accordingly, heat radiation effects of the intake pipes  16   a  and  16   b  allow less heat to be conducted from the banks B 1  and B 2  to the carburetor  14 . The carburetor  14  can thus be prevented from heating up. Percolation in the carburetor  14  can be prevented in this way, and this can contribute to improvement of the restartability of the V-type engine E in a high-temperature state. 
     As described, the first and second heat shield plates  23   a  and  23   b  play two functions: guidance of cooling air to the surrounding of the first and second banks B 1  and B 2  while the V-type engine E is in operation; and shielding of the carburetor  14  from radiation heat from the banks B 1  and B 2  when the V-type engine E stops its operation. This can contribute to simplification of the structure around the V-type engine E. 
     In addition, the paired heat shield plates  23   a  and  23   b  are integrally connected to each other by the bottom plate  24  which covers the bottom face of the valley  10  between the first and second banks B 1  and B 2 , and thereby the first and second heat shield plates and the bottom plate form the single component  25 . Since the single component  25  is integrally formed, not only can the heat shield plates  23   a  and  23   b  be manufactured at once, the single component  25  can be attached to the V-type engine E with a small number of the bolts  28 . This can contribute to improvement of installation work efficiency. 
     Additionally, the holding part  34  is integrally formed to the single component  25  to hold the linear members  33  such as an electric wire for control of the V-type engine E, an operation cable, and a hose. Accordingly, the V-type engine E does not need to be installed with a holding member dedicated to the linear members  33 . This can contribute to reduction in the number of components. 
     The present invention is not limited to the above-mentioned embodiment and may be modified in a variety of ways as long as the modifications do not depart from its gist. As the carburetor  14 , independent first and second carburetors may be individually connected to the first and second intake pipes  16   a  and  16   b , respectively. The present invention can be applied to a general-purpose V-type engine of a vertical type in which the crankshaft is placed upright.