Patent Publication Number: US-11028855-B2

Title: Method of manufacturing supercharger

Description:
TECHNICAL FIELD 
     The present invention relates to a method of manufacturing a supercharger including a compressor having an impeller configured to rotate according to the rotational force of a turbine to compress air. 
     BACKGROUND ART 
     In a turbocharger (supercharger), a turbine rotationally drives according to exhaust gas of an engine, and an impeller of a centrifugal compressor rotates according to the rotational force of the turbine. Compressed air compressed by the centrifugal compressor is fed into the engine. 
     In the centrifugal compressor of the turbocharger, on an inner surface side of a housing, a clearance gap is provided between the housing and the impeller. This can prevent contact between the housing and the impeller that is caused by the influence of heat expansion and vibration in operations, and component tolerance. 
     On the other hand, by narrowing the clearance gap between the housing and the impeller, the performance of the turbocharger can be enhanced. For this reason, a member that is easily abraded even if the impeller comes into contact with the member (hereinafter, also referred to as an “abradable material”) is provided on a housing inner surface in some cases. The following PTL 1 discloses that an abradable coating layer made of synthetic resin is formed on an inner periphery of a housing that faces an impeller. 
     An abradable layer narrows a clearance gap between the housing and the impeller. The performance can be thereby enhanced while reliability is assured because the impeller is not damaged even if the impeller comes into contact with the abradable layer. 
     CITATION LIST 
     Patent Literature 
     {PTL 1} 
     Japanese Unexamined Utility Model Application, Publication No. Hei 3-52398 
     {PTL 2} 
     The Publication of Japanese Patent No. 3639846 
     {PTL 3} 
     Japanese Unexamined Patent Application, Publication No. 2010-796 
     SUMMARY OF INVENTION 
     Technical Problem 
     The aforementioned PTL 2 discloses a method of attaching a synthetic-resin slide member to a housing by adhesion. Nevertheless, productivity degrades because a process of manufacturing the synthetic-resin slide member and an adhesion process are additionally required, and the number of components increases. In addition, it is necessary to separately manufacture the synthetic-resin slide members according to the shape of the housing or the impeller, so that the number of types of components also increases. 
     The aforementioned PTL 3 discloses a method of closely adhering a molding die to the inner surface side of a housing, and injecting synthetic resin into a space between the housing and the molding die. Using this method, a slide member is formed on the inner surface side of the housing through injection molding. Nevertheless, productivity is bad because it is necessary to change the molding die according to the shape of the housing or an impeller. 
     Furthermore, the aforementioned PTL 1 discloses a method of forming the abradable coating layer on the inner periphery of the housing by spraying synthetic resin onto the inner periphery of the housing by means of thermal spraying. Nevertheless, in the case of thermal spraying and spray coating, it is difficult to confine an application region. In addition, it is also difficult to adjust a coating thickness. Thus, masking of regions surrounding the application region, and post-processing or finishing for adjusting a coating thickness are generally required, which degrades productivity. 
     The present invention has been contrived in view of such circumstances, and the object of the present invention is to provide a method of manufacturing a supercharger that can promptly and easily form an abradable layer in the supercharger. 
     Solution to Problem 
     For solving the aforementioned problems, a method of manufacturing a supercharger according to the present invention employs the following solutions. 
     More specifically, a method of manufacturing a supercharger according to the present invention is a method of manufacturing a supercharger including a turbine configured to rotationally drive, and a compressor having an impeller configured to rotate according to rotational force of the turbine and a housing configured to store the impeller, and the method includes a process of applying coating of an abradable material which is to form an abradable layer when being solidified, only to a predetermined range on either one of surfaces of the impeller and the housing via which the impeller and the housing face. 
     With this configuration, because the coating of the abradable material is applied onto the surface of the impeller or the surface of the housing, it is unnecessary to additionally manufacture an abradable material as a component, and to perform changeover according to the shape of the impeller or the housing. In addition, in the coating application, adjustment of a coating thickness is generally easy, so that the post-processing and the finishing become unnecessary. 
     For example, the coating of the abradable material is applied onto an inner peripheral surface of the housing (a surface facing a tip portion of a blade of the impeller, or a surface facing an outer peripheral surface on an end plate side of the impeller), the tip portion of the blade of the impeller, or the outer peripheral surface on the end plate side of the impeller. 
     In the aforementioned invention, coating of the abradable material is applied only to the predetermined range without applying masking. 
     With this configuration, because the coating of the abradable material is applied only to the predetermined range without applying masking, productivity can be enhanced. In addition, because the coating is applied without performing masking, the abradable material wetly spreads on the surface of the impeller or the housing. This consequently causes a state in which no level difference is generated at an end portion of the abradable layer, unlike a case of applying masking. Thus, the separation of airflow on the surface of the impeller or the housing can be suppressed, and efficiency degradation of the supercharger can also be suppressed. 
     In the aforementioned invention, coating of the abradable material is applied using a constant amount discharge nozzle, a brush, or a pad. 
     With this configuration, the coating of the abradable material is applied in a state in which the abradable material is brought close to the surface of the impeller or the housing, or pressed against the surface of the impeller or the housing. It is therefore easy to form the abradable layer only in the predetermined range without applying masking. 
     In the aforementioned invention, a process of forming a protruding portion or a recess portion on the surface of the impeller or the housing at a boundary of a region in which the abradable layer is to be formed, before the process of applying coating of the abradable material is further included. 
     With this configuration, by the protruding portion or the recess portion being formed on the surface of the impeller or the housing, it becomes difficult for the abradable material to spread excessively, and the abradable layer is surely applied to the predetermined range. When the protruding portion or the recess portion is formed, the protruding portion or the recess portion desirably has such a height or a depth that a flow of air is not disturbed, and preferably has such a shape that the abradable layer and the impeller or the housing are smoothly connected. 
     In the aforementioned invention, a process of increasing a roughness degree in an outside region of a region in which the abradable layer is to be formed, to be rougher than a roughness degree in the region in which the abradable layer is to be formed, before the process of applying coating of the abradable material is further included. 
     With this configuration, by the roughness degree getting higher in the outside region of the region in which the abradable layer is to be formed, it becomes difficult for the abradable material to spread excessively, and the abradable layer is surely applied to the predetermined range. 
     In the aforementioned invention, the abradable material contains synthetic resin and fine particles having a self-lubricating property. 
     With this configuration, because the slidability of the abradable layer is assured, frictional resistance caused when the impeller comes into contact therewith can be reduced, and damages to the impeller can be prevented. 
     In the aforementioned invention, coating of the abradable material is applied so that a density becomes lower on a surface side of the abradable layer than a density on a side of the impeller or a side of the housing, when the abradable material is solidified. 
     With this configuration, because strength becomes lower on the surface side of the abradable layer, the abradable material becomes easily-abradable when the impeller comes into contact therewith, and damages to the impeller can be prevented. 
     Advantageous Effects of Invention 
     According to the present invention, an abradable layer can be promptly and easily formed in a supercharger. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a vertical cross-sectional view illustrating a supercharger according to a first embodiment of the present invention. 
         FIG. 2  is a vertical cross-sectional view illustrating a housing of a compressor of the supercharger according to the first embodiment of the present invention. 
         FIG. 3  is a vertical cross-sectional view illustrating an abradable layer formed on a housing inner surface of the supercharger according to the first embodiment of the present invention, and illustrates a state immediately after coating application. 
         FIG. 4  is a vertical cross-sectional view illustrating the abradable layer formed on the housing inner surface of the supercharger according to the first embodiment of the present invention, and illustrates a state in which time has elapsed from the coating application. 
         FIG. 5  is a perspective view illustrating a three-axis robot and a constant amount discharge nozzle. 
         FIG. 6  is a schematic view illustrating a pad and a container in pad printing. 
         FIG. 7  is a schematic view illustrating the housing of the supercharger and the pad in the pad printing. 
         FIG. 8  is a vertical cross-sectional view illustrating the abradable layer and a protruding portion according to the first embodiment of the present invention. 
         FIG. 9  is a vertical cross-sectional view illustrating the abradable layer and a recess portion according to the first embodiment of the present invention. 
         FIG. 10  is a vertical cross-sectional view illustrating a protruding portion according to the first embodiment of the present invention. 
         FIG. 11  is a vertical cross-sectional view illustrating the abradable layer and a protruding portion according to the first embodiment of the present invention. 
         FIG. 12  is a vertical cross-sectional view illustrating the abradable layer according to the first embodiment of the present invention. 
         FIG. 13  is a vertical cross-sectional view illustrating an impeller of a supercharger according to a second embodiment of the present invention. 
         FIG. 14  is a partially-enlarged vertical cross-sectional view illustrating an impeller and a housing of a supercharger according to a third embodiment of the present invention. 
         FIG. 15  is a vertical cross-sectional view illustrating an abradable layer formed on a housing inner surface of a conventional supercharger, and illustrates a state in which a masking tape is peeled off. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A turbocharger (supercharger) according to a first embodiment of the present invention will be described below using  FIG. 1 . 
     A turbocharger  1  includes a turbine  2 , a compressor  3 , and a rotation shaft  4  coupled to the turbine  2  and the compressor  3 . The turbine  2  rotationally drives according to exhaust gas from an engine, and an impeller  11  of the compressor  3  rotates according to the rotational force of the turbine  2 . Air compressed by the compressor  3  is supplied to the engine. 
     The turbine  2  is disposed on one end side of the rotation shaft  4 , and includes an impeller  6 , a housing  5 , and the like. 
     The impeller  6  includes a blade  7 , and is coupled to the rotation shaft  4  to rotate around a shaft line. 
     The housing  5  covers the impeller  6  from the outside, and a scroll passage  8  communicating the inside and the outside of the housing  5  is formed therein. The scroll passage  8  extends from an end portion (a leading edge portion  7   a ) on the outside in a radial direction of the blade  7 , outward in the radial direction, and is formed into a ring shape around the shaft line of the rotation shaft  4 . The exhaust gas is introduced into the impeller  6  from the scroll passage  8  to rotate the impeller  6  and the rotation shaft  4 . 
     A discharge port  9  opening on one end side of the shaft line of the rotation shaft  4  is formed in the housing  5 . Exhaust gas having passed through the blade  7  is discharged to the outside of the housing  5  through the discharge port  9 . 
     The compressor  3  is a centrifugal compressor, for example, and is disposed on the other end side of the rotation shaft  4 , and includes the impeller  11 , a housing  10 , and the like. 
     The impeller  11  includes a blade  12 , and is coupled to the rotation shaft  4  to rotate around the shaft line. 
     The housing  10  covers the impeller  11  from the outside. A suction port  13  opening on the other end side of the shaft line of the rotation shaft  4  is formed in the housing  10 . Air is introduced into the impeller  11  from the outside through the suction port  13 . The rotational force of the impeller  6  of the turbine  2  is transmitted to the impeller  11  via the rotation shaft  4 , so that the impeller  11  rotates. Air introduced from the outside is compressed by passing through the impeller  11 . 
     A compressor passage  14  communicating the inside and the outside of the housing  10  is formed in the housing  10 , and the compressor passage  14  extends from an end portion (a trailing edge portion  12   b ) on the outside in a radial direction of the blade  12 , outward in the radial direction, and is formed into a ring shape around the shaft line of the rotation shaft  4 . Air compressed in the impeller  11  is introduced into the compressor passage  14  and is discharged to the outside of the housing  10 . 
     A bearing housing  15  is disposed between the turbine  2  and the compressor  3  to couple the turbine  2  and the compressor  3 . The bearing housing  15  covers the rotation shaft  4  from the outside. A bearing  16  is provided in the bearing housing  15 , and the bearing  16  supports the rotation shaft  4  so as to be rotatable with respect to the bearing housing  15 . 
     In addition, depending on the configuration of the turbocharger  1 , in some cases, the bearing housing  15  is disposed so that an inner peripheral surface of the bearing housing  15  faces the impeller  11 . 
     An abradable layer  20  (refer to  FIG. 2 ) is formed in a portion on the inner peripheral surface of the housing  10  of the compressor  3  that faces a side edge portion  12   a  of the blade  12 . The abradable layer  20  is made of a material that is easily abraded even if the impeller  11  comes into contact with the material (hereinafter, referred to as an “abradable material”), and is formed so as to narrow a clearance gap between the housing  10  and the blade  12  of the impeller  11 . The formation of the abradable layer  20  narrows the clearance gap between the housing  10  and the impeller  11 . As a result, the performance of the turbocharger  1  can be enhanced, and reliability can be assured because the impeller  11  is not damaged even if the impeller  11  comes into contact with the abradable layer  20 . 
     The abradable material is a material which is to form the abradable layer  20  when being solidified, and is synthetic resin, for example. Epoxy resin, polyamide, polyimide, and the like can be applied as synthetic resin. In addition, as the abradable material, synthetic resin may contain fine particles having a self-lubricating property that are dispersed at a content rate of 5 wt % to 50 wt %. The fine particles have a grain size of 5 μm to 50 μm, and examples of the fine particles include molybdenum disulfide, polytetrafluoroethylene (PTFE), hexagonal boron nitride (hBN), graphite, and the like. 
     By the fine particles having a self-lubricating property being dispersed in the abradable material, the slidability of the solidified abradable layer  20  can be assured. As a result, frictional resistance caused when the impeller  11  comes into contact with the abradable layer  20  can be reduced, and damages to the impeller  11  can be prevented. 
     In addition, the abradable layer  20  may have such a structure that a resin density becomes lower on a surface side of the abradable layer  20  than that on a surface adhering to the housing  10  being a base material. With this structure, the abradable layer  20  tightly adheres to the housing  10  on the surface adhering to the housing  10 , whereas the strength of the abradable layer  20  becomes lower on the surface side of the abradable layer  20 . Thus, the abradable layer  20  becomes easily-abradable when the impeller  11  comes into contact with the abradable layer  20 , and damages to the impeller  11  can be prevented. 
     As a method of lowering the resin density on the surface side of the abradable layer  20 , the following methods are conceivable. 
     (1) No air bubble is contained on the surface side adhering to the housing  10 , whereas air bubbles are contained on the surface side of the abradable layer  20 . A layer containing air bubbles is thereby formed on the surface side of the abradable layer  20 , and the resin density on the surface side of the abradable layer  20  can be lowered. 
     (2) An asperity surface having a relatively-high surface roughness degree is formed on the surface of the abradable layer  20 . Similarly to the case of (1), the resin density on the surface side of the abradable layer  20  can be thereby lowered. 
     (3) A content rate of fine particles on the surface side of the abradable layer  20  is made higher than that on the surface side adhering to the housing  10 . Accordingly, a larger number of fine particles are contained on the surface side of the abradable layer  20 , and the resin density on the surface side of the abradable layer  20  can be lowered. More specifically, by dispersing, in the abradable material, fine particles with a density lower than that of synthetic resin serving as a base material, the fine particles are suspended on the surface side before the abradable material is solidified, and then, the fine particles are fixed on the surface side when the abradable material is solidified. Examples of the fine particles include molybdenum disulfide, PTFE, hBN, graphite, hollow floating fine particles, and the like. 
     For lowering the resin density on the surface side of the abradable layer  20 , the aforementioned (1) to (3) methods may be implemented using the same synthetic resin, or may be implemented as a multilayered structure including two or more layers using different types of synthetic resin or different compositions. For example, synthetic resin or a composition having high density and high adhesiveness is employed on the surface side adhering to the housing  10 , whereas synthetic resin or a composition having high abradability is employed on the surface side of the abradable layer  20 . 
     A method of applying the abradable layer  20  according to the present embodiment will be described below. 
     The abradable layer  20  is formed by applying coating of the abradable material only to a predetermined range on the inner peripheral surface of the housing  10 , without applying masking. In addition, because this is coating application, a coating thickness can be adjusted in the application, so that post-processing or finishing for adjusting a coating thickness is not performed. 
     Because the coating of the abradable material is applied onto the surface of the housing  10 , it is unnecessary to additionally manufacture an abradable material as a component, and to perform changeover according to the shape of the impeller  11  or the housing  10 . In addition, because the coating application can be performed in the same productive facilities regardless of the shape of the impeller  11  or the housing  10 , productivity is high. 
     In addition, unlike conventional thermal spraying and spray coating, the coating application can form the abradable layer  20  only in the predetermined range without applying masking. This can enhance productivity. Furthermore, in the coating application, adjustment of a coating thickness can be easily performed, so that the post-processing and the finishing become unnecessary. As a result, mass productivity becomes high, and the application can be performed inexpensively. 
     Furthermore, because the coating is applied without performing masking, the abradable layer  20  obtained immediately after the coating application is in a state as illustrated in  FIG. 3 , and the abradable material wetly spreads on the surface of the housing  10  as time elapses. When masking is applied, after the abradable material is solidified to some extent, a masking tape  38  or the like is peeled off as illustrated in  FIG. 15 . This generates a level difference at an end portion of an abradable layer  26 . In contrast, unlike the case of applying masking, the present embodiment can cause a state in which no level difference is generated at an end portion of the abradable layer  20  as illustrated in  FIG. 4 . Thus, the separation of airflow on the surface of the housing  10  can be suppressed, and efficiency degradation of the supercharger can also be suppressed. 
     As a method of applying coating of the abradable material, as illustrated in  FIG. 5 , there is a method of using a constant amount discharge nozzle  32  of which the position is controlled by a three-axis robot  30  in three-axis directions. In addition, the housing  10  to which the abradable material is applied is not illustrated in  FIG. 5 . The constant amount discharge nozzle  32  is provided in the three-axis robot  30 , and the constant amount discharge nozzle  32  is supplied with the abradable material from a tank  34 . An amount of the abradable material discharged from the constant amount discharge nozzle  32  is adjusted by adjusting the pressure of air supplied from a controller  36 . 
     With this configuration, the coating of the abradable material is applied in a state in which the abradable material is brought close to the surface of the housing  10 . Thus, the abradable layer  20  can be formed only in the predetermined range without applying masking. In addition, a device that performs the position control of the constant amount discharge nozzle  32  is not limited to the three-axis robot  30 , and another device such as a robot that can perform position control only in two-axis directions may be used. 
     In addition, a tool used in the coating application performed on the surface of the housing  10  is not limited to the constant amount discharge nozzle, and a brush may be used. Also in this case, position control is performed by the three-axis robot  30  or the like. The brush is installed in place of the aforementioned constant amount discharge nozzle  32 . With this configuration, the coating of the abradable material is applied in a state in which the abradable material is pressed against the surface of the housing  10 . Thus, the abradable layer  20  can be formed only in the predetermined range without applying masking. 
     Furthermore, as illustrated in  FIGS. 6 and 7 , the coating application performed on the surface of the housing  10  may be performed by pad printing. A generally-performed method can be applied to the pad printing. More specifically, after an abradable material  44  stored in a container  42  is adhered to a silicone pad  40  as illustrated in  FIG. 6 , the pad  40  is brought into contact with the housing  10  as illustrated in  FIG. 7 . The coating of the abradable material  44  is thereby applied onto the inner surface of the housing  10 . Also in this case, the coating of the abradable material is applied in a state in which the abradable material is pressed against the surface of the housing  10 . Thus, the abradable layer  20  can be formed only in the predetermined range without applying masking. 
     Before the coating of the abradable material is applied onto the surface of the housing  10 , as illustrated in  FIG. 8 or 9 , a protrusion (protruding portion  21 ) or a recess (recess portion  23 ) may be formed on the surface of the housing  10  at a boundary of a region in which the abradable layer  20  is to be formed. By the protruding portion  21  or the recess portion  23  being formed on the surface of the housing  10 , it becomes difficult for the abradable material to spread excessively, so that the abradable layer  20  is surely applied to the predetermined range. The protruding portion  21  or the recess portion  23  has such a height or a depth that a flow of air is not disturbed, and the performance of the turbocharger  1  is not affected. It is desirable that the protruding portion  21  be a minute protrusion lower than the height of the abradable layer  20 . 
     Various methods can be applied to the formation of the protruding portion  21 . For example, the protruding portion  21  may be formed by coating application as illustrated in  FIG. 10 . In this process, by using a quick-drying material as a coating material of the protruding portion  21 , the process can be promptly shifted to the application of the abradable layer  20 . In addition, the same material as the abradable material may be used as the coating material of the protruding portion  21 . It accordingly becomes unnecessary to prepare a material different from that used in the formation of the abradable layer  20 , and compatibility in the abradable layer  20  becomes higher. This can prevent detachment and the like. 
     As the shape of the protruding portion  21 , a vertical cross-sectional shape may be a semicircular shape, or a vertical cross-sectional shape may have a gently-inclined surface as in a protruding portion  25  illustrated in  FIG. 11 . By forming the shape of the protruding portion  25  into a shape smoothly connected to the surface of the housing  10  on an upstream side of a flow of air on the abradable layer  20 , the protruding portion  25  can be prevented from disturbing the flow of air. 
     In addition, as illustrated in  FIG. 12 , before the coating of the abradable material is applied onto the surface of the housing  10 , processing may be performed so as to roughen a roughness degree in an outside region  10 B of a region  10 A in which the abradable layer  20  is to be formed, to be rougher than a roughness degree in the region  10 A in which the abradable layer  20  is to be formed. With this configuration, by the roughness degree getting higher in the outside region  10 B of the region  10 A in which the abradable layer  20  is to be formed, it becomes difficult for the abradable material to spread excessively, so that the abradable layer  20  is surely applied to the predetermined range. 
     Second Embodiment 
     Next, a turbocharger according to a second embodiment of the present invention will be described. In the aforementioned first embodiment, the description has been given of a case in which the abradable layer  20  is formed in the predetermined range on the inner peripheral surface of the housing  10  of the compressor  3 . Nevertheless, the present invention is not limited to this example. In the present embodiment, as illustrated in  FIG. 13 , an abradable layer  22  is formed in a side edge portion  12   a  of a blade  12  of an impeller  11  of a compressor  3 . 
     In the following description, the detailed descriptions of components described in the first embodiment will be omitted. 
     In the present embodiment, the abradable layer  22  is formed in the side edge portion  12   a  of the blade  12 , which is a portion facing the inner peripheral surface of a housing  10  of the compressor  3 . 
     The abradable layer  22  is made of an abradable material similar to that in the first embodiment, and is formed so as to narrow a clearance gap between the housing  10  and the blade  12  of the impeller  11 . The formation of the abradable layer  22  narrows the clearance gap between the housing  10  and the impeller  11 . As a result, the performance of a turbocharger  1  can be enhanced, and reliability can be assured because the impeller  11  is not damaged even if the impeller  11  comes into contact with the abradable layer  22 . 
     The abradable layer  22  is formed by applying coating of the abradable material only to a predetermined range at a tip of the blade  12 . When the coating of the abradable material is solidified, the abradable layer  22  is formed in the predetermined range. In addition, because this is coating application, a coating thickness can be adjusted in the application, so that post-processing or finishing for adjusting a coating thickness is not performed. 
     As a method of applying coating of the abradable material, similarly to the first embodiment, there are a method of using a constant amount discharge nozzle or a brush of which the position is controlled by a three-axis robot  30  in three-axis directions, and a method of using pad printing. In addition, a method of applying the abradable material is not limited to the coating application, and the abradable material may be applied by spray coating. Nevertheless, in this case, masking is performed on the outside of the predetermined range so that the abradable material is applied to the predetermined range. 
     An area in which the abradable material is applied to the side edge portion  12   a  of the blade  12  of the impeller  11  is smaller than an area in which the abradable material is applied to the inner peripheral surface of the housing  10 . Thus, by applying the abradable material not to the housing  10  but to the impeller  11 , a used amount of the abradable material can be reduced to a small amount, and the application of the abradable material becomes inexpensive. In addition, a volume of the impeller  11  is smaller than that of the housing  10 . Thus, when synthetic resin of the abradable material is thermoset resin, and rises in temperature when being cured, a temperature rise speed of the impeller  11  becomes higher than that of the housing  10 . This can shorten an application time, and can reduce facility costs. 
     Third Embodiment 
     Next, a turbocharger according to a third embodiment of the present invention will be described. In the aforementioned first embodiment, the description has been given of a case in which the abradable layer  20  is formed on a surface facing the blade  12 , in the inner peripheral surface of the housing  10  of the compressor  3 . Nevertheless, the present invention is not limited to this example. In the present embodiment, as illustrated in  FIG. 14 , an abradable layer  24  is formed on a surface facing an outer peripheral surface  17   a  of an end plate  17  of an impeller  11 , in the inner peripheral surface of a housing  10  of a compressor  3 . 
     In the following description, the detailed descriptions of components described in the first embodiment will be omitted. 
     In the present embodiment, the abradable layer  24  is formed on a surface, which is the inner peripheral surface of the housing  10  of the compressor  3 , and is a surface facing the outer peripheral surface  17   a  of the end plate  17  of the impeller  11 . 
     The abradable layer  24  is made of an abradable material similar to that in the first embodiment, and is formed so as to narrow a clearance gap between the housing  10  and the end plate  17  of the impeller  11 . The formation of the abradable layer  24  narrows the clearance gap between the housing  10  and the end plate  17  of the impeller  11 . As a result, the performance of a turbocharger  1  can be enhanced, and reliability can be assured because the impeller  11  is not damaged even if the impeller  11  comes into contact with the abradable layer  24 . 
     The abradable layer  24  is formed by applying coating of the abradable material only to a predetermined range on the surface facing the outer peripheral surface  17   a  of the end plate  17  of the impeller  11 , in the inner peripheral surface of the housing  10 . When the coating of the abradable material is solidified, the abradable layer  24  is formed in the predetermined range. In addition, because this is coating application, a coating thickness can be adjusted in the application, so that post-processing or finishing for adjusting a coating thickness is not performed. 
     As a method of applying the coating of the abradable material, similarly to the first embodiment, there are a method of using a constant amount discharge nozzle or a brush of which the position is controlled by a three-axis robot  30  in three-axis directions, and a method of using pad printing. In addition, a method of applying the abradable material is not limited to the coating application, and the abradable material may be applied by spray coating. Nevertheless, in this case, masking is performed on the outside of the predetermined range so that the abradable material is applied to the predetermined range. 
     An area in which the abradable material is applied to the surface facing the outer peripheral surface  17   a  of the end plate  17  of the impeller  11 , in the inner peripheral surface of the housing  10  is smaller than an area in which the abradable material is applied to the surface facing the blade  12 , in the inner peripheral surface of the housing  10 . Thus, by applying the abradable material to the surface facing the outer peripheral surface  17   a  of the end plate  17  of the impeller  11 , a used amount of the abradable material can be reduced to a small amount, and the application of the abradable material becomes inexpensive. 
     In addition, in the aforementioned embodiment, the description has been given of a case in which the abradable material is applied to the surface facing the outer peripheral surface  17   a  of the end plate  17  of the impeller  11 , in the inner peripheral surface of the housing  10 . Nevertheless, the present invention is not limited to this example. More specifically, when the impeller  11  and a bearing housing  15  face each other, an abradable layer may be formed on a surface facing the outer peripheral surface  17   a  of the end plate  17  of the impeller  11 , not in the inner peripheral surface of the housing  10  but in the inner peripheral surface of the bearing housing  15 . 
     In addition, an abradable layer may be formed not on the inner peripheral surface side of the housing  10  or the bearing housing  15 , but on the outer peripheral surface  17   a  of the end plate  17  of the impeller  11 . 
     Also in these cases, a clearance gap between the housing  10  and the end plate  17  of the impeller  11  becomes narrower. As a result, the performance of the turbocharger  1  can be enhanced, and reliability can be assured because the impeller  11  is not damaged even if the impeller  11  comes into contact with the abradable layer. 
     REFERENCE SIGNS LIST 
     
         
           1  turbocharger 
           2  turbine 
           3  compressor 
           4  rotation shaft 
           5  housing 
           6  impeller 
           7  blade 
           8  scroll passage 
           9  discharge port 
           10  housing 
           11  impeller 
           12  blade 
           13  suction port 
           14  compressor passage 
           15  bearing housing (housing) 
           16  bearing 
           17  end plate 
           20 ,  22 ,  24  abradable layer