Abstract:
A hydraulic servo device includes: a servo piston configured to move in an axial direction with respect to a device main body; and a stroke sensor configured to detect an amount of movement of the servo piston with respect to the device main body. The hydraulic servo device is configured to change a supply flow rate of exhaust gas to a turbine of a turbocharger by moving the servo piston according to applied hydraulic pressure. A cooling water channel through which cooling water is to be supplied is provided at a part between the turbocharger and the stroke sensor.

Description:
FIELD 
       [0001]    The present invention relates to a hydraulic servo device and a turbocharger. 
       BACKGROUND 
       [0002]    Some turbochargers are provided with a hydraulic servo device. The hydraulic servo device includes a servo piston that is movably disposed to a device main body, and a stroke sensor for detecting the amount of movement of the servo piston with respect to the device main body, and functions to change the area of an exhaust passage of the turbocharger by the movement of the servo piston. The stroke sensor includes a moving element that is provided to the servo piston, and a stator that is provided to the device main body, and detects the amount of movement of the servo piston with respect to the device main body by detecting movement of the moving element by the stator. According to a turbocharger provided with this type of hydraulic servo device, the supply flow rate of exhaust gas to a turbine is changed by changing the area of the exhaust passage. Accordingly, for example, in a low revolution area of an engine, the supply flow rate of exhaust gas to the turbine may be increased by reducing the area of the passage, and the rotation energy of the turbine is increased, and the charging performance of a compressor may be increased (for example, see Patent Literature 1). 
       CITATION LIST 
     Patent Literature 
       [0003]    Patent Literature 1: Japanese Patent Application Laid-open No. 2010-59844 
       SUMMARY 
     Technical Problem 
       [0004]    To constantly achieve optimal charging performance at the turbocharger provided with the hydraulic servo device as described above, accurate control of the position of the servo piston becomes a key issue. However, the turbocharger through which exhaust gas passes is continuously maintained at a high temperature during operation of the engine, and thus, the temperature of the stroke sensor also becomes high, thereby possibly affecting the output result. 
         [0005]    Therefore, according to the disclosure of Patent Literature 1, the problem described above is solved by causing oil to circulate in a chamber, of the device main body, where the moving element is accommodated. However, a turbocharger that is applied to an engine with a large displacement generates a great amount of heat. Accordingly, a hydraulic servo device that can reduce the influence of heat on the stroke sensor even when provided to a turbocharger that is applied to an engine with a large displacement is desired. 
         [0006]    In view of the above circumstances, the present invention has its object to provide a hydraulic servo device that can reduce the influence of heat on a stroke sensor, and a turbocharger. 
       Solution to Problem 
       [0007]    To achieve the object, a hydraulic servo device according to the present invention includes: a servo piston configured to move in an axial direction with respect to a device main body; and a stroke sensor configured to detect an amount of movement of the servo piston with respect to the device main body, the hydraulic servo device is configured to change a supply flow rate of exhaust gas to a turbine of a turbocharger by moving the servo piston according to applied hydraulic pressure, and a cooling water channel through which cooling water is to be supplied is provided at a part between the turbocharger and the stroke sensor. 
         [0008]    Moreover, the above-described hydraulic servo device according to the present invention includes a heat shield portion at a part surrounding the stroke sensor, and the heat shield portion includes the cooling water channel. 
         [0009]    Moreover, in the above-described hydraulic servo device according to the present invention, the cooling water channel includes a plate-shaped space that is provided inside a thick portion of the heat shield portion. 
         [0010]    Moreover, in the above-described hydraulic servo device according to the present invention, the stroke sensor includes: a moving element that is provided at one end portion of the servo piston; and a stator that is disposed to the device main body, at a part around the moving element, and that is configured to detect a change in a position of the moving element with respect to the device main body, and the device main body is provided with the cooling water channel at a sensor holding portion that holds the stator, at a connection part to the turbocharger. 
         [0011]    Moreover, in the above-described hydraulic servo device according to the present invention, the stroke sensor includes: a moving element that is provided at one end portion of the servo piston; and a stator that is disposed to the device main body, at a part around the moving element, and that is configured to detect a change in a position of the moving element with respect to the device main body, and the device main body is provided with the cooling water channel at a sensor holding portion that holds the stator, at a connection part to the turbocharger, and a heat shield portion including the cooling water channel inside a thick portion, the heat shield portion being provided in a manner covering a surrounding of the stroke sensor, where the cooling water channel of the device main body and the cooling water channel of the heat shield portion are connected with each other. 
         [0012]    Moreover, in the above-described hydraulic servo device according to the present invention, the stroke sensor includes: a moving element that is provided at one end portion of the servo piston; and a stator that is disposed to the device main body, at a part around the moving element, and that is configured to detect a change in a position of the moving element with respect to the device main body, and the heat shield portion covers a part surrounding the stator and a part at an extension of an axis of the servo piston, and includes the cooling water channel at at least the part surrounding the stator. 
         [0013]    Moreover, a turbocharger according to the present invention includes: a center housing between a compressor housing accommodating a compressor and the turbine housing, a shaft to which the compressor and the turbine are attached is rotatably supported at the center housing by a bearing, and a housing cooling water channel whose part surrounding the bearing is to be supplied with cooling water is provided, and the hydraulic servo device is attached to the center housing in a state where the cooling water channel is connected to the housing cooling water channel. 
       Advantageous Effects of Invention 
       [0014]    According to the present invention, a cooling water channel to which cooling water is to be supplied is provided around a stroke sensor, at a part between the stroke sensor and a turbocharger, and thus, the entire stroke sensor is cooled, and even in the case of application to an engine with a great displacement, the influence of heat may be reduced. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a perspective view illustrating an external appearance of a turbocharger to which a hydraulic servo device which is an embodiment of the present invention is applied. 
           [0016]      FIG. 2  is a cross-sectional plan view of the turbocharger and the hydraulic servo device illustrated in  FIG. 1 . 
           [0017]      FIG. 3  is a cross-sectional side view of the turbocharger illustrated in  FIG. 1 . 
           [0018]      FIG. 4  is a cut-away view, seen from left, of main portions of the hydraulic servo device applied to the turbocharger illustrated in  FIG. 1 . 
           [0019]      FIG. 5  is a cut-away view, seen from a rear side, of main portions of the hydraulic servo device illustrated in  FIG. 4 . 
           [0020]      FIG. 6  is a rear cross-sectional perspective view of a heat shield portion of the hydraulic servo device illustrated in  FIG. 3 , seen from a rear wall side. 
           [0021]      FIG. 7  is a side cross-sectional perspective view of the heat shield portion of the hydraulic servo device illustrated in  FIG. 3 , seen from the rear wall side. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0022]    Hereinafter, a preferred embodiment of a hydraulic servo device according to the present invention will be described in detail with reference to  FIGS. 1 to 7  appended. Arrows X, Y and Z in the drawings indicate the same directions. In the following, for the sake of convenience, description may be given taking the arrow X as the front in the front-back direction (opposite is the rear), the arrow Y as the left in the left-right direction (opposite is the right), and the arrow Z as the top in the top-down direction (the opposite is the down). 
         [0023]      FIGS. 1 and 2  illustrate a turbocharger to which a hydraulic servo device which is an embodiment of the present invention is applied. A turbocharger  1  illustrated here is assumed to be mounted on an engine with a large displacement (for example, a diesel engine with a displacement of at least 23,000 cc), and includes a center housing  4  between a turbine housing  2  that accommodates a turbine  2   a  and a compressor housing  3  that accommodates a compressor  3   a.  As illustrated in  FIG. 3 , the center housing  4  rotatably supports a shaft  6  by a bearing  5 . Although not illustrated, the shaft  6  has the turbine  2   a  attached to one end portion and the compressor  3   a  attached to the other end portion. A housing cooling water channel  4   a  is provided at a part, of the center housing  4 , around the bearing  5 . The housing cooling water channel  4   a  is a watertight space having a water intake port  4   b  at a lower end portion, and a water discharge port  4   c  at an upper end portion. The housing cooling water channel  4   a  has a water supply pipe L 1  connected to the water intake port  4   b,  and a water discharge pipe L 2  connected to the water discharge port  4   c.  The water supply pipe L 1  connects to a discharge port of a water pump that is driven by an engine not illustrated, and the water discharge pipe L 2  connects to an inlet of a radiator (not illustrated). That is, when the water pump is driven by the engine, cooling water is supplied and circulated through the housing cooling water channel  4   a  of the center housing  4 . With the turbocharger  1  according to which cooling water is supplied and circulated through the housing cooling water channel  4   a  of the center housing  4 , lubricating oil is not exposed to high temperature, and the bearing  5  and the shaft  6  are constantly lubricated by the lubricating oil, and thus, seizure and abnormal wear do not occur between the bearing  5  and the shaft  6 . 
         [0024]    Furthermore, as illustrated in  FIG. 2 , a hydraulic servo device  10  is attached to a front surface  4   d  of the center housing  4 . As illustrated in  FIG. 4 , the hydraulic servo device  10  is provided with a servo piston  12  and a stroke sensor  13  at a device main body  11 . The servo piston  12  is movably disposed in a cylinder bore  11   b  provided at a base portion  11   a  of the device main body  11 . Although not illustrated, a movable member  15  (see  FIG. 2 ) of the turbocharger  1  is linked to the servo piston  12  by a link mechanism. The movable member  15  operates according to the amount of movement of the servo piston  12 , and changes the opening area of an exhaust passage  2   b  that is provided to the turbine housing  2 . As is clear from  FIG. 4 , a sensor holding portion  11   c  having a substantially rectangular outer shape is provided to the device main body  11 , at an upper end portion of the cylinder bore  11   b  of the base portion  11   a.  The sensor holding portion  11   c  includes a stopper portion  11   d  to be fitted with the cylinder bore  11   b.  The servo piston  12  reaches a stroke end when abutting against the stopper portion  11   d  of the sensor holding portion  11   c.    
         [0025]    The stroke sensor  13  is for detecting the amount of movement of the servo piston  12  with respect to the device main body  11 . In the present embodiment, the stroke sensor  13  is formed by attaching a moving element  13 A at an upper end portion of the servo piston  12 , and disposing a stator  13 B at the device main body  11 , at a position including the movement range of the moving element  13 A. The moving element  13 A is formed as a permanent magnet rod, and is disposed at an extension of an axis of the servo piston  12  with respective axes coinciding with each other. The stator  13 B includes a magnetic field detection member, such as a hall IC, and is disposed between an outer cylindrical portion lie and an inner cylindrical portion  11   g  that are provided in a manner surrounding the moving element  13 A. The stator  13 B detects the magnetic field at the time of the moving element  13 A moving in the top-down direction according to the operation of the servo piston  12 , and outputs a detection signal through a signal cable  13 C extending outside the outer cylindrical portion lie. The outer cylindrical portion lie and the inner cylindrical portion  11   g  where the stator  13 B is disposed each have a shape of a bottomed circular cylinder, and are attached to the sensor holding portion  11   c  by having an outer circumferential surface at an open end fitted in a fitting hole  11   f  provided to the sensor holding portion  11   c.  The inner cylindrical portion  11   g  is fitted inside the outer cylindrical portion lie, and shuts off the stator  13 B from oil that is supplied to around the moving element  13 A. 
         [0026]    As illustrated in  FIGS. 4 to 7 , a heat shield portion  20  is provided to the device main body  11 , at a part around the stroke sensor  13 . In the present embodiment, the heat shield portion  20  including a rear wall portion  21 , a top wall portion  22 , and two side wall portions  23  is provided. The rear wall portion  21  is a cuboid part extending upward along the axis of the servo piston  12  from a rear edge part which is adjacent to the front surface  4   d  (see  FIG. 2 ) of the center housing  4  at an upper surface  11   c   1  of the sensor holding portion  11   c.  The top wall portion  22  is a cuboid part protruding forward from an upper end portion of the rear wall portion  21 . The top wall portion  22  is a cuboid part extending in a manner covering the entire upper surface of the sensor holding portion  11   c,  including the outer cylindrical portion lie. The two side wall portions  23  are provided from left and right edge parts of the upper surface  11   c   1  of the sensor holding portion  11   c,  so as to block an opening between the sensor holding portion  11   c  and the top wall portion  22 . 
         [0027]    As illustrated in  FIG. 5 , cooling water channels  30  and  31  are provided, respectively, to the heat shield portion  20  and the sensor holding portion  11   c  described above. As illustrated in  FIG. 4 , the cooling water channels  30  of the heat shield portion  20  are spaces provided inside thick portions of the rear wall portion  21  and the top wall portion  22 , and are plate-shaped and are linked to each other inside the thick portions. The cooling water channel  30  of the top wall portion  22  is open to the outside through a water discharge channel  32  opened at an upper surface. A suction port of the water pump is connected to the water discharge channel  32  through a water discharge passage not illustrated. The cooling water channel  31  of the sensor holding portion  11   c  is a circular columnar space, and extends along a flat plane orthogonal to the axis of the moving element  13 A, at a part between the center housing  4  and the moving element  13 A. As illustrated in  FIG. 5 , both end portions of the cooling water channel  31  of the sensor holding portion  11   c  communicate with the cooling water channel  30  of the rear wall portion  21  through connecting water channels  33 , and moreover, as illustrated in  FIG. 2 , the cooling water channel  31  is connected to the housing cooling water channel  4   a  through a connecting water channel  34  provided to the base portion  11   a  of the device main body  11  and a connecting water channel  4   e  of the center housing  4 . 
         [0028]    According to the turbocharger  1  configured in the above manner, when the engine is operated, cooling water supplied to the housing cooling water channel  4   a  of the center housing  4  is supplied to the cooling water channel  31  of the sensor holding portion  11   c  through the connecting water channel  34 , and is further supplied to the cooling water channels  30  of the heat shield portion  20  through the connecting water channels  33 . Accordingly, even in the case of application to an engine with a large displacement, transfer of heat from the center housing  4  of the turbocharger  1  to the stator  13 B of the stroke sensor  13  is suppressed by the action of cooling water passing through the cooling water channel  31  of the sensor holding portion  11   c.  Also, radiation of heat from the turbocharger  1  to the stator  13 B of the stroke sensor  13  is suppressed by the action of the heat shield portion  20  where cooling water is supplied to the cooling water channel  30  on the inside. As a result, because the influence of heat is reduced, the stroke sensor  13  is enabled to accurately detect and output the amount of movement of the servo piston  12 . That is, according to the turbocharger  1  described above, the area of opening of the exhaust passage may be accurately controlled based on the amount of movement of the servo piston  12  output from the stroke sensor  13 , and optimal charging performance may be constantly achieved. 
         [0029]    Additionally, in the embodiment described above, the cooling water channels  30  provided to the heat shield portion  20  and the cooling water channel  31  provided to the sensor holding portion  11   c  are serially connected, and cooling water passing through the cooling water channel  31  of the sensor holding portion  11   c  is supplied to the cooling water channels  30  of the heat shield portion  20 , but the present invention is not limited to such a case. For example, the cooling water channel  30  may be provided only to the heat shield portion  20 , or cooling water may be separately supplied to the cooling water channels  30  of the heat shield portion  20  and the cooling water channel  31  of the sensor holding portion  11   c.    
         [0030]    Also, in the embodiment described above, the cooling water channels  30  of the heat shield portion  20  are connected to the housing cooling water channel  4   a,  and cooling water passing through the housing cooling water channel  4   a  is supplied to the cooling water channels  30  of the heat shield portion  20 , but the cooling water channels  30  of the heat shield portion  20  do not necessarily have to be connected to the housing cooling water channel  4   a . Additionally, in the case where the cooling water channels  30  of the heat shield portion  20  are connected to the housing cooling water channel  4   a,  it is also possible to supply, to the housing cooling water channel  4   a,  cooling water which has passed through the cooling water channels  30  of the heat shield portion  20 . 
         [0031]    Furthermore, in the embodiment described above, the cooling water channels  30  are provided to the rear wall portion  21  and the top wall portion  22  of the heat shield portion  20 , but the cooling water channel  30  may alternatively be provided only to the rear wall portion  21  of the heat shield portion  20 . Moreover, if a cooling water channel is provided also to the side wall portion  23  of the heat shield portion  20 , it is possible to reduce the influence of heat from the turbocharger  1 . 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Turbocharger 
           2  Turbine Housing 
           2 A Turbine 
           3  Compressor Housing 
           3 A Compressor 
           4  Center Housing 
           4 A Housing Cooling Water Channel 
           5  Bearing 
           6  Shaft 
           10  Hydraulic Servo Device 
           11  Device Main Body 
           11 C Sensor Holding Portion 
           12  Servo Piston 
           13  Stroke Sensor 
           13 A Moving Element 
           13 B Stator 
           20  Heat Shield Portion 
           30  Cooling Water Channel 
           31  Cooling Water Channel