Patent Publication Number: US-2013247861-A1

Title: Exhaust gas recirculation valve

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-068841 filed on Mar. 26, 2012, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exhaust gas recirculation valve, which is capable of switching between fluid passages, and whereby an exhaust gas of an internal combustion engine is recirculated from an exhaust system to an intake system. 
     2. Description of the Related Art 
     Heretofore, an exhaust gas recirculation valve has been used, for example, for eliminating harmful components that are discharged from an internal combustion engine. Such an exhaust gas recirculation valve has functions to communicate between the intake system and the exhaust system of the internal combustion engine for recirculating the exhaust gas, which has been discharged from the internal combustion engine, to an intake system, in order to reduce harmful components such as NOx or the like contained in the exhaust gas. 
     In Japanese Laid-Open Patent Publication No. 2010-236686, the present applicant has proposed a fluid passage valve, which is disposed in an exhaust gas recirculation passage connected between an intake passage and an exhaust passage of an internal combustion engine. The fluid passage valve includes a main body, which is connected to the exhaust gas recirculation passage, and having a spherical shaped ball valve, which is arranged rotatably in the interior of the main body. In addition, by rotating the ball valve, which is connected through a shaft to a rotary drive source, through a predetermined angle, a state of communication is switched between an exhaust gas inlet port and an exhaust gas outlet port that are formed in the main body, whereby a flow through state of the exhaust gas into the exhaust gas recirculation passage is controlled. 
     SUMMARY OF THE INVENTION 
     A general object of the present invention is to provide an exhaust gas recirculation valve, which is capable of realizing a more linear flow rate characteristic of the exhaust gas, together with enabling an increase in the flow rate of the exhaust gas. 
     The present invention is an exhaust gas recirculation valve including a body having a fluid passage through which an exhaust gas flows, a valve arranged in the fluid passage that switches a flow through state of the exhaust gas, at least a portion of an outer peripheral surface of the valve being spherically shaped, a seat member having a seat section, which is disposed in the fluid passage on an upstream side from the valve and on which the valve is seated, and a shaft connected to the valve and which rotates the valve, wherein a percentage of an eccentricity amount between a center of curvature of the valve when the valve is completely closed and an axis of the shaft along a direction of flow of the exhaust gas with respect to a diameter of an inlet port formed in the body and into which the exhaust gas flows is 5.5% or greater. 
     According to the present invention, in an exhaust gas recirculation valve having such a valve, in which at least a portion of an outer peripheral surface of the valve is spherically shaped, by setting the eccentric distance (offset distance) between the center of curvature of the outer peripheral surface and the axial center of the shaft such that the percentage thereof with respect to the diameter of the exhaust gas inlet port of the body into which the exhaust gas flows is 5.5% or greater, the flow rate characteristic of the exhaust gas that flows through the fluid passage can be made more linear, while also enabling the flow rate of the exhaust gas to be increased. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view shown partially in cross section of an exhaust gas recirculation valve according to an embodiment of the present invention; 
         FIG. 2  is a cross sectional view taken along line II-II of  FIG. 1 ; 
         FIG. 3  is a characteristic line diagram showing a relationship between an eccentric distance between an axis of a shaft and an axis of the valve along a direction of flow of the exhaust gas, and the flow rate of an exhaust gas when the valve is completely open, in the exhaust gas recirculation valve of  FIG. 1 ; 
         FIG. 4A  is a characteristic line diagram with respect to the exhaust gas recirculation valve of  FIG. 1 , showing a relationship between the eccentric distance of the shaft and the exhaust gas flow rate when the valve is completely open, for a case in which the diameter of a gas inlet port is small; and 
         FIG. 4B  is a characteristic line diagram with respect to the exhaust gas recirculation valve of  FIG. 1 , showing a relationship between the eccentric distance of the shaft and the exhaust gas flow rate when the valve is completely open, for a case in which the diameter of a gas inlet port is large. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIGS. 1 and 2 , an exhaust gas recirculation valve  10  includes a main body (body)  12 , a valve  14  disposed rotatably in the interior of the main body  12 , a valve seat (seat member)  16  with which an outer peripheral surface of the valve  14  is in abutment (contact), and a drive force transmission mechanism  18  disposed in an upper portion of the main body  12  and which imparts a rotary drive force to the valve  14 . 
     The main body  12  is formed from a metallic material, for example. On the lower side of the main body  12 , there are provided a gas inlet port (inlet port)  20  to which the exhaust gas is supplied, and a gas outlet port  22  disposed on an opposite side from the gas inlet port  20  through which the exhaust gas is directed out and circulated to an internal combustion engine (not shown). In the main body  12 , the gas inlet port  20  and the gas outlet port  22  are disposed substantially on a straight line. Further, a communication chamber (fluid passage)  24  is formed in the main body  12  between the gas inlet port  20  and the gas outlet port  22 , and the substantially disk-shaped valve  14  is arranged rotatably in the interior of the communication chamber  24 . 
     Between the communication chamber  24  and the gas inlet port  20 , an installation opening  26  is formed, which is expanded in diameter with respect to the gas inlet port  20 . The valve seat  16 , which slides on the outer peripheral surface of the valve  14 , is disposed in the installation opening  26 . The valve seat  16 , for example, is formed from a metallic material, and is equipped with a communication hole  28  that penetrates therethrough in an axial direction (the direction of arrows A 1  and A 2 ), and a tapered seat section  30 , which gradually expands in diameter from the interior of the communication hole  28 . In the installation opening  26 , the communication hole  28  is arranged on the side of the gas inlet port  20  of the main body  12  (in the direction of the arrow A 2 ), whereas the seat section  30  is arranged on the side of the communication chamber  24  (in the direction of the arrow A 1 ). In addition, the gas inlet port  20  and the communication chamber  24  are placed in communication through the communication hole  28  of the valve seat  16 . 
     Further, the valve seat  16  is movably disposed in the installation opening  26  both in an axial direction (the direction of arrows A 1  and A 2 ) and in a radial direction. A spring  34  is interposed between the valve seat  16  and a ring-shaped stopper  32  provided on the communication chamber  24  side of the installation opening  26 . The valve seat  16  is urged by the spring  34  toward the side of the gas inlet port  20  (in the direction of the arrow A 2 ). 
     On the other hand, as shown in  FIG. 1 , in a substantially central portion of the main body  12 , a shaft hole  36  is formed, which penetrates in a vertical upward direction from the communication chamber  24 . A later-described shaft  38  of the drive force transmission mechanism  18  is inserted through the shaft hole  36 . 
     The valve  14  comprises a substantially disk-shaped main body portion  40  having a hemispherical shaped outer peripheral surface, and an axial portion  42 , which projects in the axial direction (the direction of the arrow A 2 ) from an end of the main body portion  40  and is connected to the shaft  38 . 
     The drive force transmission mechanism  18  includes the shaft  38 , which is connected to the valve  14 , a valve gear  44  connected to an upper end of the shaft.  38 , and a drive source  46  connected to an upper part of the main body  12  and which drives the shaft  38  rotatably through the valve gear  44 . 
     The upper end of the shaft  38  is inserted through a substantially central portion of the valve gear  44 , and the shaft  38  is fixed to the valve gear  44  by tightening a nut  48  thereon. In addition, the shaft  38  is rotatably supported by a pair of bearings  50   a,    50   b,  which are mounted in the main body  12  respectively above and below the valve  14 . 
     Further, as shown in  FIG. 2 , the axis B 1  of the shaft  38  is connected so as to be positioned eccentrically (i.e., offset) with respect to an axis B 2  through which the center of curvature of the outer peripheral surface on the valve  14  when the valve  14  is completely closed passes. More specifically, the axis B 1  is set to be parallel with the axis B 2  of the valve  14 , and is separated therefrom by a predetermined distance. 
     For this reason, the valve  14  is arranged within the communication chamber  24  so as to be rotatable (swingable) about the axis B 1 , which is set at a position eccentric (offset) from the axis B 2 . 
     The axis B 1  of the shaft  38  is arranged so as to be eccentric with respect to the axis B 2  of the valve  14  by a predetermined distance (eccentric distance L) toward the downstream side (in the direction of the arrow A 1 ) along the direction of flow of the exhaust gas. 
     More specifically, the percentage of the eccentric distance L with respect to the diameter D of the gas inlet port  20  in the main body  12  is set to be equal to or greater than 5.5% (L/D×100≧5.5). Stated otherwise, the value obtained by dividing the eccentric distance L by the diameter D is equal to or greater than 0.055. 
     The drive source  46  is constituted, for example, from a stepping motor or a rotary actuator, which is driven rotatably by supply of electric current thereto. By transmitting the rotary drive force of the drive source  46  to the shaft  38  via the valve gear  44 , the valve  14 , which is connected to the shaft  38 , is moved or actuated rotatably about the axis B 1 . 
     The exhaust gas recirculation valve  10  according to the embodiment of the present invention is constructed basically as described above. Next, operations and advantages thereof shall be explained. A valve-closed state, as shown in  FIGS. 1 and 2 , will be described as an initial position, in which the outer peripheral surface of the valve  14  is seated on the seat section  30  of the valve seat  16 , and communication between the gas inlet port  20  and the gas outlet port  22  is blocked. 
     From the initial position, which is the valve-closed state as described above, by driving the drive source  46  of the drive force transmission mechanism  18 , a rotary drive force of the drive source  46  is transmitted to the shaft  38  through the valve gear  44 . The shaft  38  rotates the valve  14 , which is connected to the shaft  38 , counterclockwise a predetermined angle about the axis B 1 , which is located at a position eccentric (offset) from the axis B 2 . Consequently, the valve  14  is displaced in a direction to gradually separate away from the valve seat  16 . 
     In addition, as a result of the outer peripheral surface of the valve  14  separating away from the seat section  30  of the valve seat  16 , a valve-open state is brought about, and the exhaust gas, which is supplied to the gas inlet port  20  through a gap between the outer peripheral surface and the seat section  30 , is introduced to the interior of the communication chamber  24 . By further rotation of the valve  14  under a driving action of the drive source  46 , the valve  14  is gradually separated away from the seat section  30 , whereby a fully valve-open state is brought about in which the valve  14  is rotated from the initial position, for example, by about 90°. 
     In the valve-open state, the exhaust gas supplied to the gas inlet port  20  flows through the communication hole  28  of the valve seat  16 , passes through the communication chamber  24 , and then flows to the gas outlet port  22 , whereupon the exhaust gas is supplied to a non-illustrated internal combustion engine. 
     Next, with reference to  FIGS. 3 ,  4 A and  4 B, explanations shall be given of the relationship between the diameter D of the gas inlet port  20  in the main body  12 , the eccentric distance L, and the flow rate at a time of full opening when the valve  14  is in a fully open state. 
       FIG. 3  is a characteristic line diagram showing a relationship between the eccentric distance L and the flow rate of the exhaust gas when the valve  14  is completely open, for a case in which the diameter D of the gas inlet port  20  is 18 mm.  FIG. 4A  is a characteristic line diagram showing a relationship between the eccentric distance L and the flow rate of the exhaust gas, for a case in which the diameter D of the gas inlet port  20  is 9 mm and thus is smaller in diameter than the aforementioned gas inlet port  20  of  FIG. 3 .  FIG. 4B  is a characteristic line diagram showing a relationship between the eccentric distance L and the flow rate of the exhaust gas, for a case in which the diameter D of the gas inlet port  20  is 27 mm and thus is larger in diameter than the aforementioned gas inlet port  20  of  FIG. 3 . 
     First, from the characteristic line diagram shown in  FIG. 3 , it can be understood that, from a condition in which the eccentric distance L is nonexistent (L=0) until the eccentric distance L reaches in the neighborhood of roughly 1 mm, the flow rate of the exhaust gas increases rapidly, and then as the eccentric distance L becomes equal to and exceeds 1 mm, the rise in the flow rate slows down or levels off. Stated otherwise, the rate of change at which the flow rate of the exhaust gas increases continues to rise and becomes greatest when the eccentric distance L reaches about 1 mm. More specifically, the flow rate characteristic undergoes a change in the vicinity of where the eccentric distance L is about 1 mm. 
     For this reason, since the increase in the flow rate of the exhaust gas continues to become larger until reaching an eccentric distance L at which the percentage (L/D×100) between the diameter D of the gas inlet port  20  and the eccentric distance L is roughly 5.5%, at least the percentage of the eccentric distance L with respect to the diameter D of the gas inlet port  20  should be set to 5.5% or greater. 
     Further, from the characteristic line diagram shown in  FIG. 4A , it can be understood that, from a condition in which the eccentric distance L is nonexistent (L=0) until the eccentric distance L reaches in the neighborhood of roughly 0.5 mm, the flow rate of the exhaust gas increases rapidly, and then as the eccentric distance L becomes equal to and exceeds 0.5 mm, the rise in the flow rate lessens and rises more slowly. More specifically, the flow rate characteristic undergoes a change in the vicinity of where the eccentric distance L is about 0.5 mm. In this case as well, the relationship between the eccentric distance L and the diameter D of the gas inlet port  20  is such that 0.5/9×100≈5.5%. 
     Furthermore, from the characteristic line diagram shown in  FIG. 4B , it can be understood that, from a condition in which the eccentric distance L is nonexistent (L=0) until the eccentric distance L reaches in the neighborhood of roughly 1.5 mm, the flow rate of the exhaust gas increases rapidly, and then as the eccentric distance L becomes equal to and exceeds 1.5 mm, the rise in the flow rate lessens and rises more slowly. More specifically, the flow rate characteristic undergoes a change in the vicinity of where the eccentric distance L is about 1.5 mm. In this case as well, the relationship between the eccentric distance L and the diameter D of the gas inlet port  20  is such that 1.5/27×100≈5.5%. 
     In the foregoing manner, according to the present embodiment, in an exhaust gas recirculation valve  10  in which the center of curvature (axis) B 2  of the valve  14  and the axis B 1  of the shaft  38  that rotates the valve  14  are eccentric, by setting the relationship between the diameter D of the gas inlet port  20 , which is formed in the main body  12  and through which the exhaust gas flows into the main body  12 , and the eccentric distance L between the center of curvature (axis) B 2  of the valve  14  and the axis B 1  of the shaft  38  along the flow direction of the exhaust gas, such that the eccentric distance L is 5.5% or greater than the diameter D, the flow rate characteristic of the exhaust gas can be made more linear, while the flow rate of the exhaust gas can also be increased. 
     The exhaust gas recirculation valve according to the present invention is not limited to the above-described embodiment, and it is a matter of course that various additional or modified structures could be adopted therein without deviating from the essential gist of the present invention.