Patent Publication Number: US-2023140241-A1

Title: Spool valve

Description:
TECHNICAL FIELD 
     The present disclosure relates to a spool valve for shifting a spool by an electric motor. 
     BACKGROUND ART 
     Spool valves have been known as one type of flow control valves for use in hydraulic circuits. In such a spool valve, a spool is slidably located in a slide hole of a housing, and the flow rate of a fluid flowing between passages formed in the housing is controlled by the position of the spool. 
     In one type of spool valve, the spool is shifted by pilot pressure, and in another type of spool valve, the spool is shifted by an electric motor. For example, Patent Literature 1 discloses a spool valve that includes a linear motion mechanism between an electric motor and a spool. The linear motion mechanism converts rotational motion into linear motion. Specifically, in the spool valve, the spool is coupled to a piston; a nut is fixed to the piston; and a screw shaft screwed with the nut is rotated by the electric motor. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: WO 2019/138945 A1 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the spool valve disclosed by Patent Literature 1, in a case where the diameter of the spool is large, a force that the spool receives from the fluid flowing between the passages is great (this force is often called “flow force”). Therefore, in this case, a high-power electric motor is necessary for precise control of the position of the spool. This causes an increase in cost as well as an increase in the size of the spool valve. 
     In view of the above, an object of the present disclosure is to provide a spool valve that makes it possible to precisely control the position of the spool even in a case where the electric motor is a low-power motor. 
     Solution to Problem 
     In order to solve the above-described problems, a spool valve according to the present disclosure includes: a first housing including passages and a slide hole; a spool slidably located in the slide hole; a second housing that forms a servo chamber that is coaxial with the slide hole; a sleeve slidably located in the servo chamber, the sleeve dividing the servo chamber into a first pressure chamber and a second pressure chamber, the first pressure chamber being adjacent to the first housing, the second pressure chamber being away from the first housing, the sleeve being coupled to the spool in the first pressure chamber; a piston slidably fitted in the sleeve and extending from inside the sleeve beyond the second pressure chamber; a nut fixed to the piston; a screw shaft screwed with the nut; and an electric motor that rotates the screw shaft. The second housing includes a drain port and an input port that is to be connected to a pressure source of a hydraulic fluid. The first pressure chamber communicates with the input port. In a balanced state where a force that is applied to the sleeve by the hydraulic fluid in the first pressure chamber, and a force that is applied to the sleeve by the hydraulic fluid in the second pressure chamber, are balanced, the second pressure chamber is blocked from the input port and the drain port by the piston. From the balanced state, when the piston shifts in a direction toward the spool, the second pressure chamber comes into communication with the input port. From the balanced state, when the piston shifts in a direction away from the spool, the second pressure chamber comes into communication with the drain port. 
     According to the above configuration, from the balanced state, when the piston is shifted by the electric motor in the direction toward the spool, the second pressure chamber comes into communication with the input port. Consequently, the pressure in the second pressure chamber increases, and the sleeve also shifts in the direction toward the spool. However, when the sleeve shifts beyond the position where the balanced state is achieved, the second pressure chamber comes into communication with the drain port, and consequently, the pressure in the second pressure chamber decreases. Due to this function, the sleeve comes to a stop again at the position where the balanced state is achieved. That is, the sleeve shifts in a manner to follow the shifting of the piston. The same applies to a case where, from the balanced state, the piston is shifted by the electric motor in the direction away from the spool. 
     Meanwhile, in a case where the piston does not shift, the balanced state is maintained. That is, the second pressure chamber is blocked from the input port and the drain port by the piston. Therefore, even when the spool receives a force from the fluid flowing between the passages of the first housing, due to the incompressibility of the hydraulic fluid in the second pressure chamber, the sleeve does not shift. 
     As described above, in the present disclosure, since the force that the spool receives from the fluid flowing between the passages does not affect the electric motor, even in a case where the electric motor is a low-power motor, the position of the spool can be controlled precisely. 
     Advantageous Effects of Invention 
     The present disclosure makes it possible to precisely control the position of the spool even in a case where the electric motor is a low-power motor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a sectional view showing an entire spool valve according to one embodiment of the present disclosure. 
         FIG.  2    is a sectional view of a part of the spool valve of  FIG.  1   . 
         FIG.  3    is an enlarged view of an essential part of  FIG.  2   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG.  1    shows a spool valve  1  according to one embodiment of the present disclosure. In the present embodiment, the spool valve  1  is a three-position valve including three ports  2   a  to  2   c . Alternatively, the spool valve  1  may be a two-position valve. The number of ports of the spool valve  1  may be changed as necessary. 
     Specifically, the spool valve  1  includes a first housing  2  and a spool  3 . The first housing  2  includes the ports  2   a  to  2   c  on its outer surface. The spool  3  is held by the first housing  2 . The spool valve  1  further includes a second housing  4 , a casing  73 , and an electric motor  74 , which are coaxial with the spool  3 . The second housing  4  is mounted to the first housing  2 , and the electric motor  74  is mounted to the second housing  4  via the casing  73 . 
     The first housing  2  includes a slide hole  21  therein. The spool  3  is slidably located in the slide hole  21 . The first housing  2  further includes three passages  22  to  24 , which extend from the slide hole  21  to the ports  2   a  to  2   c , respectively. The number of passages in the first housing  2  may be changed as necessary in accordance with the number of ports. 
     The spool  3  includes two annular grooves  31  and  32 . Hereinafter, for the sake of convenience of the description, one side in the axial direction of the spool  3  (the right side in  FIG.  1   ) is referred to as the right side, and the other side in the axial direction of the spool  3  (the left side in  FIG.  1   ) is referred to as the left side. When the spool  3  is at a neutral position thereof, the spool  3  blocks the passage  22  from both of the passages  23  and  24 . When the spool  3  shifts from the neutral position toward the right side, the passage  22  comes into communication with the passage  23  via the annular groove  31 . When the spool  3  shifts from the neutral position toward the left side, the passage  22  comes into communication with the passage  24  via the annular groove  32 . 
     In the present embodiment, when the spool  3  is at the neutral position, the left end of the spool  3  protrudes from the first housing  2 . However, the length of the spool  3  may be changed as necessary. When the spool  3  is at the neutral position, the left end of the spool  3  may be accommodated within the first housing  2 . In the present embodiment, the diameter of the left end of the spool  3  is less than the diameter of the slide hole  21 . Alternatively, the diameter of the left end of the spool  3  may be the same as the diameter of the slide hole  21 . Further alternatively, the diameter of the left end of the spool  3  may be larger than the diameter of the slide hole  21 , so long as within the movable range of the spool  3 , the left end of the spool  3  does not interfere with the first housing  2 . 
     As shown in  FIG.  2   , the second housing  4  forms a servo chamber  41 , which is coaxial with the slide hole  21  of the first housing  2 . Specifically, the second housing  4  includes a deep bottomed hole whose center line coincides with the center line of the slide hole  21 . The bottomed hole, by being covered by the first housing  2  and the spool  3 , forms the servo chamber  41 . 
     A sleeve  5  is slidably located in the servo chamber  41 . Specifically, the sleeve  5  divides the servo chamber  41  into a first pressure chamber  42  and a second pressure chamber  43 . The first pressure chamber  42  is adjacent to the first housing  2 . The second pressure chamber  43  is away from the first housing  2 . The sleeve  5  includes a tubular portion and a sealing portion. The tubular portion surrounds an internal space of the sleeve  5 . The sealing portion seals the internal space of the sleeve  5  from the right side. That is, the internal space of the sleeve  5  is open only toward the left side. 
     In the first pressure chamber  42 , the sleeve  5  is coupled to the spool  3 . In the present embodiment, the right end of the sleeve  5  and the left end of the spool  3  are coupled to each other by a universal joint. Specifically, the spool  3  includes a groove  35  at its left end. A ball  15  is held in the groove  35 . The sleeve  5  includes a plate-shaped protrusion  45  at its right end. The plate-shaped protrusion  45  is located in the groove  35 . The protrusion  45  includes a hole that is fitted to the ball  15 . 
     Conversely to the present embodiment, the sleeve  5  may include, at its right end, the groove  35  in which the ball  15  is held, and the spool  3  may include, at its left end, the protrusion  45  located in the groove  35 . Alternatively, the right end of the sleeve  5  and the left end of the spool  3  may be coupled to each other by a joint different from a universal joint (e.g., a ball joint or spherical joint). 
     A piston  6  extends from inside the sleeve  5  toward the left side beyond the second pressure chamber  43 . The piston  6  is slidably fitted in the sleeve  5 . The piston  6  penetrates a part of the second housing  4 , the part being positioned on the left side of the second pressure chamber  43 . A left side portion of the piston  6 , the left side portion being positioned outside the second housing  4 , is accommodated in the casing  73 . 
     A nut  71  is fixed to the left side portion of the piston  6 . To be more specific, the piston  6  includes a holding hole  65  in its left side portion. The holding hole  65  is positioned on the center line of the piston  6 , and is open toward the left side. The nut  71  is located in the holding hole  65 . An unshown guide mechanism guides the piston  6  such that the piston  6  is shiftable only in the left-right direction (i.e., the piston  6  is prevented from rotating). 
     A screw shaft  72  is screwed with the nut  71 . The screw shaft  72  is rotated by the aforementioned electric motor  74 . Specifically, when the electric motor  74  rotates the screw shaft  72  in one direction, the piston  6  to which the nut  71  is fixed shifts toward the right side, whereas when the electric motor  74  rotates the screw shaft  72  in the opposite direction, the piston  6  to which the nut  71  is fixed shifts toward the left side. Since the sleeve  5  shifts in a manner to follow the shifting of the piston  6 , the spool  3  coupled to the piston  6  also shifts in the same direction and by the same amount as the piston  6 . This will be described below in detail. 
     As shown in  FIG.  3   , the present embodiment includes a mechanism between the casing  73  and the left side portion of the piston  6 . The mechanism serves to keep the spool  3  at the neutral position when the electric motor  74  is not supplied with electric power. The mechanism includes: a coil spring  81 , within which the nut  71  is positioned; and a first spring receiver  82  and a second spring receiver  83 , which support both ends of the coil spring  81 , respectively. 
     The coil spring  81  applies an urging force to the piston  6  to keep the spool  3  at the neutral position. Each of the first spring receiver  82  and the second spring receiver  83  is ring-shaped and slidably fitted to the left side portion of the piston  6 . 
     The piston  6  includes a flange  66  at its left end. The flange  66  contacts the first spring receiver  82 . At a position that is away from the flange  66  toward the right side, a stopper  67 , which contacts the second spring receiver  83 , is mounted to the piston  6 . 
     On the inner side surface of the tubular casing  73 , a first stepped portion  84  is located at a position corresponding to the flange  66 , and a second stepped portion  85  is located at a position corresponding to the stopper  67 . 
     With the above-described structure, when the electric motor  74  is not supplied with electric power, the urging force of the coil spring  81  causes the first spring receiver  82  to contact both the flange  66  and the first stepped portion  84 , and causes the second spring receiver  83  to contact both the stopper  67  and the second stepped portion  85 . Consequently, the spool  3  is kept at the neutral position. 
     From a state where the spool  3  is at the neutral position, when the piston  6  shifts toward the right side, the first spring receiver  82  is pushed by the flange  66  to become spaced apart from the first stepped portion  84 , and also, the stopper  67  becomes spaced apart from the second spring receiver  83 . On the other hand, from the state where the spool  3  is at the neutral position, when the piston  6  shifts toward the left side, the flange  66  becomes spaced apart from the first spring receiver  82 , and also, the second spring receiver  83  is pushed by the stopper  67  to become spaced apart from the second stepped portion  85 . 
     Next, the second housing  4  and the internal structure thereof are described in more detail with reference to  FIG.  2   . 
     The second housing  4  includes an input port  4   a  and a drain port  4   b  on its outer surface. The input port  4   a  is to be connected to a pressure source  11  of a hydraulic fluid (e.g., a hydraulic pump). The drain port  4   b  is connected to, for example, a tank  12 , which stores the hydraulic fluid. For example, in a case where a fluid flowing between the passages  22  to  24  of the first housing  2  is oil, the hydraulic fluid supplied from the pressure source  11  to the input port  4   a  may be the same oil as the oil flowing between the passages  22  to  24 . 
     The second housing  4  includes a first passage  44 , which extends from the input port  4   a  to the first pressure chamber  42 . That is, the first pressure chamber  42  communicates with the input port  4   a  via the first passage  44 . 
     At the bottom (the right side) of the internal space of the sleeve  5 , there is a drain chamber  53 , which faces the right end surface of the piston  6 . The sleeve  5  includes side holes  54  and  55 , which extend radially outward from the drain chamber  53 . 
     The second housing  4  includes an annular groove  46  on the inner peripheral surface of the servo chamber  41 . The annular groove  46  is located at a position corresponding to the side holes  54  and  55 . The second housing  4  further includes a second passage  47 , which extends from the bottom of the annular groove  46  to the drain port  4   b.    
     The piston  6  includes a longitudinal hole  63 , which extends along the center line of the piston  6 . The longitudinal hole  63  allows the drain chamber  53  and the above-described holding hole  65  to communicate with each other. 
     The piston  6  further includes, on its outer peripheral surface, a first annular groove  61  and a second annular groove  62 . The second annular groove  62  is positioned on the right side relative to the first annular groove  61 . Accordingly, there is a land  60  between the first annular groove  61  and the second annular groove  62 . 
     The sleeve  5  includes a first passage  51  and a second passage  52 . The first passage  51  allows the first pressure chamber  42  and the first annular groove  61  to communicate with each other. The second passage  52  allows the second pressure chamber  43  to communicate with the first annular groove  61  or the second annular groove  62 . The second passage  52  includes, on the inner peripheral surface of the sleeve  5 , a first opening  52   a  for the first annular groove  61  and a second opening  52   b  for the second annular groove  62 . 
     The distance from the left end of the first opening  52   a  to the right end of the second opening  52   b  is set to be equal to the width of the land  60  (i.e., the distance from the first annular groove  61  to the second annular groove  62 ). The piston  6  further includes side holes  64 , which extend from the bottom of the second annular groove  62  to the longitudinal hole  63 . 
     The external diameter of the sleeve  5  is set to be larger than the maximum diameter of the spool  3  in the slide hole  21 . Accordingly, a leftward force F 1  of the hydraulic fluid in the first pressure chamber  42  is applied to the sleeve  5 . In a case where the pressure in the first pressure chamber  42  is P 1 , the maximum diameter of the spool  3  in the slide hole  21  is Da, and the external diameter of the sleeve  5  is Db, the following equation holds true. 
         F 1= P 1×π×(( Db/ 2) 2 −( Da/ 2) 2 )
 
     Meanwhile, a rightward force F 2  of the hydraulic fluid in the second pressure chamber  43  is also applied to the sleeve  5 . In a case where the pressure in the second pressure chamber  43  is P 2 , the external diameter of the sleeve  5  is Db, and the diameter of the piston  6  is Dc, the following equation holds true. 
         F 2= P 1×π×(( Db/ 2) 2 −( Dc/ 2) 2 )
 
     In the configuration as described above, the pressure P 2  in the second pressure chamber  43  is adjusted such that the leftward force F 1  and the rightward force F 2 , which are applied to the sleeve  5 , are balanced (F 1 =F 2 ). In the balanced state, the sleeve  5  is at such a position that the first opening  52   a  and the second opening  52   b  of the second passage  52  are sealed by the land  60  of the piston  6 . Therefore, the second pressure chamber  43  is blocked from the input port  4   a  and the drain port  4   b  by the piston  6 . 
     From the balanced state, when the piston  6  is shifted by the electric motor  74  toward the right side (in a direction toward the spool  3 ), the second pressure chamber  43  comes into communication with the input port  4   a  via the second passage  52 , the first annular groove  61 , the first passage  51 , the first pressure chamber  42 , and the first passage  44 . Consequently, the pressure in the second pressure chamber  43  increases, and the sleeve  5  also shifts toward the right side. However, when the sleeve  5  shifts toward the right side beyond the position where the balanced state is achieved, the second pressure chamber  43  comes into communication with the drain port  4   b  via the second passage  52 , the second annular groove  62 , the side holes  64 , the longitudinal hole  63 , the drain chamber  53 , the side holes  54  and  55 , the annular groove  46 , and the second passage  47 . Consequently, the pressure in the second pressure chamber  43  decreases. Due to this function, the sleeve  5  comes to a stop again at the position where the balanced state is achieved. That is, the sleeve  5  shifts toward the right side in a manner to follow the rightward shifting of the piston  6 . 
     On the other hand, from the balanced state, when the piston  6  is shifted by the electric motor  74  toward the left side (in a direction away from the spool  3 ), the second pressure chamber  43  comes into communication with the drain port  4   b  via the second passage  52 , the second annular groove  62 , the side holes  64 , the longitudinal hole  63 , the drain chamber  53 , the side holes  54  and  55 , the annular groove  46 , and the second passage  47 . Consequently, the pressure in the second pressure chamber  43  decreases, and the sleeve  5  also shifts toward the left side. However, when the sleeve  5  shifts toward the left side beyond the position where the balanced state is achieved, the second pressure chamber  43  comes into communication with the input port  4   a  via the second passage  52 , the first annular groove  61 , the first passage  51 , the first pressure chamber  42 , and the first passage  44 . Consequently, the pressure in the second pressure chamber  43  increases. Due to this function, the sleeve  5  comes to a stop again at the position where the balanced state is achieved. That is, the sleeve  5  shifts toward the left side in a manner to follow the leftward shifting of the piston  6 . 
     Meanwhile, in a case where the piston  6  does not shift, the balanced state is maintained. That is, the second pressure chamber  43  is blocked from the input port  4   a  and the drain port  4   b  by the piston  6 . Therefore, even when the spool  3  receives a force from the fluid flowing between the passages  22  to  24  of the first housing  2 , due to the incompressibility of the hydraulic fluid in the second pressure chamber  43 , the sleeve  5  does not shift. 
     As described above, in the present disclosure, since the force that the spool  3  receives from the fluid flowing between the passages  22  to  24  does not affect the electric motor  74 , even in a case where the electric motor  74  is a low-power motor, the position of the spool  3  can be controlled precisely. 
     (Variations) 
     The present disclosure is not limited to the above-described embodiment. Various modifications can be made without departing from the scope of the present disclosure. 
     For example, the coil spring  81  for keeping the spool  3  at the neutral position may be eliminated. However, in the case of including the coil spring  81  as in the above-described embodiment, regardless of whether or not the electric motor  74  is being supplied with electric power, the spool  3  can be kept at a constant position even when the force that the spool  3  receives from the fluid flowing between the passages  22  to  24  is great. In addition, in the case of including the coil spring  81 , the nut  71  is positioned within the coil spring  81 . Therefore, it is not necessary to increase the length of the entire spool valve  1  due to the inclusion of the coil spring  81 . 
     SUMMARY 
     A spool valve according to the present disclosure includes: a first housing including passages and a slide hole; a spool slidably located in the slide hole; a second housing that forms a servo chamber that is coaxial with the slide hole; a sleeve slidably located in the servo chamber, the sleeve dividing the servo chamber into a first pressure chamber and a second pressure chamber, the first pressure chamber being adjacent to the first housing, the second pressure chamber being away from the first housing, the sleeve being coupled to the spool in the first pressure chamber; a piston slidably fitted in the sleeve and extending from inside the sleeve beyond the second pressure chamber; a nut fixed to the piston; a screw shaft screwed with the nut; and an electric motor that rotates the screw shaft. The second housing includes a drain port and an input port that is to be connected to a pressure source of a hydraulic fluid. The first pressure chamber communicates with the input port. In a balanced state where a force that is applied to the sleeve by the hydraulic fluid in the first pressure chamber, and a force that is applied to the sleeve by the hydraulic fluid in the second pressure chamber, are balanced, the second pressure chamber is blocked from the input port and the drain port by the piston. From the balanced state, when the piston shifts in a direction toward the spool, the second pressure chamber comes into communication with the input port. From the balanced state, when the piston shifts in a direction away from the spool, the second pressure chamber comes into communication with the drain port. 
     According to the above configuration, from the balanced state, when the piston is shifted by the electric motor in the direction toward the spool, the second pressure chamber comes into communication with the input port. Consequently, the pressure in the second pressure chamber increases, and the sleeve also shifts in the direction toward the spool. However, when the sleeve shifts beyond the position where the balanced state is achieved, the second pressure chamber comes into communication with the drain port, and consequently, the pressure in the second pressure chamber decreases. Due to this function, the sleeve comes to a stop again at the position where the balanced state is achieved. That is, the sleeve shifts in a manner to follow the shifting of the piston. The same applies to a case where, from the balanced state, the piston is shifted by the electric motor in the direction away from the spool. 
     Meanwhile, in a case where the piston does not shift, the balanced state is maintained. That is, the second pressure chamber is blocked from the input port and the drain port by the piston. Therefore, even when the spool receives a force from the fluid flowing between the passages of the first housing, due to the incompressibility of the hydraulic fluid in the second pressure chamber, the sleeve does not shift. 
     As described above, in the present disclosure, since the force that the spool receives from the fluid flowing between the passages does not affect the electric motor, even in a case where the electric motor is a low-power motor, the position of the spool can be controlled precisely. 
     The above spool valve may further include a coil spring within which the nut is positioned, the coil spring applying an urging force to the piston to keep the spool at a neutral position thereof. According to this configuration, regardless of whether or not the electric motor is being supplied with electric power, the spool can be kept at a constant position even when the force that the spool receives from the fluid flowing between the passages is great. In addition, in the configuration including the coil spring, the nut is positioned within the coil spring. Therefore, it is not necessary to increase the length of the entire spool valve due to the inclusion of the coil spring. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  spool valve 
               11  pressure source 
               2  first housing 
               21  slide hole 
               22  to  24  passage 
               3  spool 
               4  second housing 
               4   a  input port 
               4   b  drain port 
               41  servo chamber 
               42  first pressure chamber 
               43  second pressure chamber 
               5  sleeve 
               6  piston 
               71  nut 
               72  screw shaft 
               74  electric motor 
               81  coil spring