Abstract:
A hydraulic motor comprises a body and a piston able to slide in a reciprocating movement in a cylindrical housing of the body. A chamber (C 1,  C 2 ) is formed on each side of the piston and hydraulic switching means are provided for feeding and evacuating the respective chambers (C 1,  C 2 ), these switching means being able to adopt two stable positions. Control means (H) having elastic means for abruptly bringing about changes in the position of the switching means are included. There are triggering means ( 13, 15 ) able, at the end of the stroke of the piston ( 9 ), to bring about the change in position of the switching means (G). The piston ( 9 ) has a closed cross section and the switching means (G) are arranged in the body ( 1 ) of the machine, redially on the outside of the cylindrical housing ( 7 ) in which the piston ( 9 ) slides.

Description:
FIELD OF THE INVENTION 
   The invention relates to a hydraulic machine of the kind comprising:
         a body;   a piston able to slide in a reciprocating movement in a cylindrical housing of the body, a chamber being formed on each side of the piston;   hydraulic switching means for feeding and evacuating the respective chambers, these switching means being able to adopt two stable positions;   control means for an abrupt change in the position of the switching means, comprising elastic means;   and triggering means able, at the end of the stroke of the piston, to bring about the change in position of the switching means.       

   BRIEF DESCRIPTION OF THE INVENTION 
   The invention relates more particularly, although not exclusively, to hydraulic motors. However, the invention could apply to other machines, such as hydraulic pumps. 
   A hydraulic motor of this kind equipping a metering device for injecting an additive into a main liquid, which is under enough pressure to actuate the motor, is known, for example from FR-2 789 445 or U.S. Pat. No. 4,756,329. 
   These hydraulic machines, particularly the motors, are satisfactory. However, they are relatively bulky, their size being greater than twice the stroke of the piston, in the direction in which the piston moves. 
   A first object of the invention is to afford a hydraulic machine of the kind in question whose bulk, particularly in the direction of travel of the piston, is smaller. 
   Another object is to improve the sealing of the switching means and prevent the position of the piston from having an influence on these switching means. 
   Another object of the invention is to provide a hydraulic machine of a simple structure able to clearly define the strokes of the piston, particularly in order to provide precise metering in the case of a motor coupled to a metering device. 
   According to the invention, a hydraulic machine, particularly a hydraulic motor, of the kind defined hereinabove, is characterized in that:
         the piston is a simple, piston, having a closed cross section;   and the switching means are arranged in the body of the machine, radially on the outside of the cylindrical housing in which the piston slides.       

   Ducts are provided in the body in order to feed and evacuate liquid to and from chambers connected with the switching means. 
   Advantageously, the body of the machine comprises, on the inside, an exchangeable cylindrical liner defining the cylindrical housing for the piston. This cylindrical liner may be made of a different, more wear-resistant, material than that of the body. 
   The body of the machine can be cylindrical and have a first geometric axis, and the cylindrical housing for the piston has a second geometric axis parallel to the first but offset radially. 
   The switching means can comprise two valves comprising seats situated in the body, or in a piece that is fixed relative to the body, one valve letting liquid in and the other valve letting it out. 
   The valves are preferably housed in the part of the body situated, with respect to the geometric axis of the body, on the opposite side to the geometric axis of the housing for the piston. 
   Each valve may comprise a cylindrical passage open at each axial end to communicate with one of the chambers delimited by the piston. Each passage is equipped with a seat at each of its ends, and a plunger able to move axially in the passage is able, depending on its position, to close one of the ends of the passage by pressing against the corresponding seat. 
   As a preference, the geometric axes of the passages of the two valves are parallel to one another and parallel to the direction of travel of the piston. The passages may be adjacent to one another, separated by a wall. 
   Each plunger may comprise, toward each end, a bulge advantageously equipped with a seal able to press against a corresponding seat, and the region situated more or less mid-way along the passage communicates with an inlet or outlet duct opening to the outside. This duct may have an axis at right angles to that of the valve passage and intersect this passage. 
   Advantageously, the plungers of the valves are coupled to a valve cage able to move parallel to the direction of the axes of the valve passages. This valve cage may be arranged in a housing of the body situated on the opposite side of the valves to a cover that closes the body. The valve cage may occupy two stable positions. 
   The control means for an abrupt change in the position of the switching means and of the valve cage are advantageously formed by a rocker device directed overall at right angles to the direction of travel of the piston. The rocker may comprise a link rod articulated, at its end furthest from the valve cage, to a pin borne by the body of the machine, and a rotary arm articulated to the same pin, this arm being longer than the link rod and bearing, at its end furthest from the articulation pin, a striker able to move in a window of the valve cage; a leaf spring in the shape of an arc of a curve is compressed between two pins secured respectively to the link rod and to the arm. The two stable positions of the rocker correspond to two configurations whereby the link rod is on one or other side of the arm. 
   A plug forming an end stop is mounted such that it can be turned in the housing of the body underneath the valve cage and, in a given angular position, allows the valve cage to be halted more or less mid-way through its travel so as to provide a bypass function. 
   A valve with a preloaded spring is advantageously arranged between the inlet and the outlet so as to open should the pressure drop increase. 
   The invention also relates to a metering device equipped with a hydraulic motor constituting a machine as defined hereinabove, characterized in that it comprises an injection device comprising a cylindrical metering body fixed to the body of the motor, coaxial with the housing for the piston of the motor, and a piston plunger coupled to the piston and sliding in the metering body. 
   Apart from the provisions set out hereinabove, the invention consists in a certain number of other provisions which will be dealt with more explicitly hereinbelow with reference to an exemplary embodiment described in detail with reference to the attached drawings, but which is not in any way limiting. In these drawings: 

   
     BRIEF DESCRIPTION OF THE FIGURES. 
       FIG. 1  is a vertical elevation of a metering device with hydraulic motor according to the invention; 
       FIG. 2  is a section on II—II of  FIG. 1 , the piston being in a bottom position and the switching means in the position that causes the piston to rise again; 
       FIG. 3  shows, in a similar way to  FIG. 2 , the piston in a top position, with the switching means in the other stable position causing its descent; 
       FIG. 4  is a horizontal section on IV—IV of  FIG. 2 ; 
       FIG. 5  is a vertical section on V—V of  FIG. 2 ; 
       FIG. 6  is a vertical section on VI—VI of  FIG. 3 ; 
       FIG. 7  is a vertical part section on VII—VII of  FIG. 2 ; 
       FIG. 8  is a cross section of a sealing ring for the piston, and 
       FIG. 9  is a vertical section of an alternative form of embodiment, the section being taken along the line of the geometric axes of the inlet and outlet ports. 
   

   The drawings, particularly  FIGS. 1 and 2 , show a metering device D comprising a hydraulic motor M of cylindrical overall shape, and an injection device I fixed under the motor. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The motor M comprises an essentially cylindrical body  1  with a circular cross section of vertical geometric axis A—A. The body  1  is closed, at the top, by a cover  2  screwed onto an external screw thread of the upper end of the body  1 . The cover  2  is equipped at its center with a vent button  3  comprising a threaded hole into which the end of a screw  4  is screwed. The plug  3  is covered with a deformable boot made of flexible material. The screw  4  passes through a hole made in the cover  2  and the screw head lies inside the cover. An O-ring seal  5  is provided around the screw  4  inside the cover  2  to be pressed in a sealed fashion by the screw head against the cover. A compression spring  6  is arranged on the outside of the cover  2  between the button  5  and the cover. The spring  6  pushes back the button  3  and presses the seal  5  against the cover. Pressure on the button  3  allows the screw  4  to be pushed in and the device vented to atmosphere by air or fluid passing between the screw and the wall of the hole in the cover. 
   A cylindrical housing  7  of axis B-B parallel to the axis A—A but radially offset is delimited by an exchangeable cylindrical liner  8  held removably in the body  1 . 
   The liner  8  may be made of a different, more wear-resistant, material than that of the body  1 . For example, the body  1  is made of PVC, while the liner  8  is made of glass or HDPE (high density polyethylene). Of course, the liner  8  could be made of the same material as the body  1 , for example PVC, as the case may be. 
   A piston  9  is able to slide with a reciprocating movement in the direction of the axis B, inside the housing  7 . This piston  9  is a simple, piston, which has a closed cross section  10  devoid of any opening. The piston  9  forms a kind of slightly frustoconical disk, the concave side of which faces toward the cover  2 . The peripheral edge of the piston  9  comprises an annular groove  11  in which a sealing ring  12  is housed, this ring being depicted in detail in  FIG. 8 . The piston  9  is generally made of a plastic, for example polypropylene or polyethylene. 
   The ring  12  comprises an outer ring section  12   a  made of a material with a low coefficient of friction, for example PTFE (polytetrafluoroethylene), having a concave interior surface in which an inner ring section  12   b , for example toric, is housed, this being made of a material that is not so hard, particularly of an elastomeric material, the cross section of which is compressed. The ring section  12   b  exerts radial thrust outward on the ring section  12   a  to press it against the wall of the housing  7 . 
   The bottom end of the stroke and the top end of the stroke of the piston  9  are determined respectively by end stops e 1 , e 2  which have a determined fixed position with respect to the body  1 . The bottom end stop e 1  may be formed by a shoulder provided directly on the body, while the top end stop e 2  may consist of a flange projecting downward under the cover  2 . 
   Two chambers C 1 , C 2  are formed in the body  1  on each side of the piston, below and above the piston  9  respectively. 
   The piston  9  comprises, at its center, a coaxial cylindrical sleeve  13  closed at the cover  2  end and open at the opposite end. The upper end of the rod  14  of a piston plunger  15  is fixed in the sleeve  13 , particularly by screwing. The piston plunger  15  can slide in a tubular element  16  of the injection device I, fixed in a sealed manner under the lower part of the body  1 , coaxial with the liner  8 . The piston plunger  15  comprises an annular groove fitted with a piston plunger seal  17  designed to allow liquid to pass when the piston plunger  15  descends, and to prevent any passage of liquid as the piston plunger  15  ascends. 
   The lower end of the tubular element  16  is equipped with a screw-on splined coupling  18  with a valve  19  comprising a slot  19   a  at its middle. The valve  19  opens as the piston plunger  15  ascends (intake phase) and closes as the piston  15  descends (delivery or injection phase). A pipe, not depicted, which dips down into a container containing a liquid additive to be injected into the main liquid is connected to the coupling  18 . This main liquid is formed for example of water under sufficient pressure, which operates the motor M. 
   Hydraulic switching means G ( FIGS. 4–6 ) allow liquid to be fed to and evacuated from the chambers C 1  and C 2 . 
   The switching means G are arranged in the body  1  radially on the outside of the cylindrical housing  7  and of the liner  8 . The means G are housed in a region of the body  1  situated, with respect to the axis A, on the opposite side to the axis B. To make it easier to house the means G, the body  1  may comprise, in this region, a bulge  20  forming a portion of a cylinder, the generatrices of which are at right angles to the axis A. 
   The switching means G comprise two valves Va, Vs, for letting the liquid in and out respectively, depicted schematically by arrows. 
   The seats  21   a ,  22   a  and  21   s ,  22   s  of the valves Va and Vs are situated on the body  1  or on a piece that is fixed with respect to the body. 
   Each valve comprises a cylindrical passage  23   a ,  23   s  provided in the body  1 , the axis of which is parallel to the axis A of the body and which open, at their upper axial ends, into a space K situated radially on the outside of the wall  8 . The space K communicates, at its top, with the chamber C 2 . At its lower axial end, each passage  23   a ,  23   s  opens into a housing L communicating with the chamber C 1 . The passages  23   a ,  23   s  are separated from one another by a median wall  24  of the body  1 . 
   Each valve comprises a plunger  25   a ,  25   s  with two axially separated bulges respectively fitted with O-ring seals  26   a ,  26   s  and  27   a ,  27   s.    
   The seat  21   a  for the seal  26   a , provided at the bottom of the passage  23   a , is formed by a frustoconical surface diminishing in diameter toward the bottom and provided directly in the body  1 . The seat  22   a , provided at the upper part, is formed by a frustoconical surface diminishing in diameter toward the top. This seat  22   a  is situated at the lower end of a cylindrical component  28  comprising a lower part, the outside diameter of which is smaller than that of the upper part. A shoulder  29  is formed at the transition between the two outer surfaces. The lower part of the piece  28  is housed in a bore in the body  1 , coaxial with the passage  23   a . The shoulder  29  comes into axial abutment against the upper edge of the bore of the body  1 . The component  28  is kept in a fixed position by the bearing of the flange e 2  of the plug  2  against its upper edge. 
   The seats  21   s  and  22   s  consist of frustoconical surfaces provided directly on the body  1  and increasing in diameter from the passage downward and upward respectively. 
   The lower ends of the plungers  25   a ,  25   s  are fixed by screws  30   a ,  30   s  against the upper wall of a valve cage  31  formed of a more or less rectangular surround. The valve cage  31  comprises a window open on its two sides parallel to the plane passing through the axes of the plungers  25   a ,  25   s . The valve cage  31  is arranged in the housing L of the body  1  situated below the valves Va, Vs. The valve cage  31  is in contact with two opposing regions of the wall of the housing L, which guides the sliding of this valve cage. 
   The entry of liquid into the motor comprises an internally threaded hole Ta allowing a coupling to be fitted. The hole Ta is extended by a duct Ta 1  offset radially toward the outside and of smaller diameter than Ta. This duct Ta 1  intersects the passage  23   a  at right angles and communicates with it. 
   Similarly, a threaded hole Ts and a duct Ts 1  are provided for establishing a connection between the passage  23   s  and the outlet. The duct Ts 1  intersects the passage  23   s  at right angles. The wall  24  separates the inlet duct Ta 1  from the outlet duct Ts 1 . 
   According to the alternative form illustrated in  FIG. 9 , the duct Ta 1 , instead of being off-centered, is coaxial with the inlet hole Ta, and of the same diameter. The same is true of the outlet duct Ts 1  and the outlet hole Ts. Molding the body  1  out of plastic is easier in this alternative form. Advantageously, Ta, Ta 1 , Ts, Ts 1  are coaxial. 
   A rocker device H constitutes a control means for an abrupt change in the position of the valve cage  31  and of the switching means G. 
   The switching means G, in a first stable position illustrated in  FIG. 5  (corresponding to the top position of the valve cage  31 ), on the one hand allow liquid to enter the housing L and the chamber C 1  and, on the other hand, provide a connection between the chamber C 2  and the outlet. In this configuration, the plunger  25   a  bears via its seal  27   a  against the seat  22   a  and closes off the communication with the chamber C 2 . By contrast, the seal  26   a  is off the seat  21   a  and allows communication with the housing L and the chamber C 1 . As far as the other plunger  25   s  is concerned, the seal  27   s  is off the seat  22   s  and allows the passage  23   s  to communicate with the space K and the chamber C 2 . The seal  26   s  is pressed against the seat  21   s  and cuts off any communication between the passage  23   s  and the chamber C 1 . Fluid is let into the chamber C 1 , while the chamber C 2  is connected to the outlet. 
   A second stable position ( FIG. 6 ) corresponds to the bottom position of the valve cage  31 , with closure of the seat  21   a /opening of the seat  22   a , and closure of the seat  22   s /opening of the seat  25   s . In this configuration, the housing L and the chamber C 1  are connected to the outlet Ts, while the space K and the chamber C 2  are connected to the inlet Ta. 
   The rocker H allows the valve cage  31 , and the plungers  25   a ,  25   s  of the valves, to be switched abruptly from the top position in  FIG. 5  to the bottom position in  FIG. 6 , and vice versa. The overall direction of the rocker H is more or less at right angles to the axis B—B of the housing  7 , that is to say to the direction of travel B—B of the piston  9 . 
   The rocker H comprises a link rod  32  comprising two parallel branches  32   a ,  32   b  between which the rod  14  of the piston plunger  15  passes. The end of the link rod  32  furthest from the valve cage  31  is articulated via a pin  33  at right angles to the plane passing through the axes A and B. The pin  33  is held in a housing in the body  1  by a clamp  34  held by a screw  35  inside the body  1 . The link rod  32  comprises, at each rear end of its branches, an upward projection  36   a ,  36   b  of more or less trapezoidal outline. The overall direction of the link rod  32  in the stable position of  FIG. 2  and  FIG. 5  is slightly inclined, from the pin  33  downward with respect to a plane at right angles to the axis B. 
   The rocker H also comprises an arm  37  formed of two branches  37   a ,  37   b  situated on each side of the branches  32   a ,  32   b  of the link rod  32 . The branches  37   a ,  37   b  are articulated to the pin  33 . The length of the branches  37   a ,  37   b  is greater than that of the link rod  32 . The branches  37   a ,  37   b  are cranked toward each other, in a region  38  beyond the free end of the link rod  32 , so that their separation decreases. The branches  37   a ,  37   b  at their end furthest from the pin  33  fit into the valve cage  31  and carry a pin  39  on which a striker  40  in the form of a circular ring is mounted. 
   As an alternative, the striker  40  may be included in the arm  37  to form just a single piece with this arm. 
   A leaf spring  41  in the shape of an arc of a curve is compressed between a pin  42  borne at the end of the link rod  32  facing toward the valve cage, and a pin  43  borne by the branches  37   a ,  37   b  of the arm  37  beyond the end of the link rod  32 . The spring  41  has its concave side facing downward and has a tendency to increase the angle of the stay formed between the link rod  32  and the arm  37 . The link rod  32  is thus kept pressed against the end wall of the body  1  while the striker  40  is kept pressed against the upper face of the opening of the valve cage  31 . 
   Another stable position of the rocker H is obtained when, starting from the position in  FIG. 2 , the pin  42  crosses the position of alignment with the pins  33  and  43  and passes over the pin  43 . The arm  37  is then pushed downward by the spring  41  and the striker  40  comes to press against the lower face of the opening of the valve cage  31 , while the link rod  32  is held in a position in which the projections  36   a ,  36   b  are in abutment against the internal wall of the body  1  (see  FIG. 3 ). 
   The abrupt change in position of the rocker from  FIG. 3  to  FIG. 2  is obtained at the bottom of the downstroke by action of the lower part of the sleeve  13  on the branches  32   a ,  32   b  which are pushed downward. 
   The reversal of position of the rocker from  FIG. 2  to  FIG. 3  occurs when the piston  9  reaches the end of its upstroke. The upper face of the piston plunger  15  pushes the link rod  32  upward and causes the change in configuration of the rocker H from  FIG. 2  to that of  FIG. 3 . 
   The lower part of the housing L is equipped with a plug  44  which, on its interior surface, has two diametrically opposed projections  44   a ,  44   b  equipped with a helical ramp  45 . This plug  44  is designed to occupy two angular positions one quarter of a turn apart. In the position illustrated in  FIG. 2 , the projections  44   a ,  44   b  are situated out of the path of the valve cage  31  which can move freely. 
   When the plug  44  is turned a quarter of a turn with respect to the position of  FIG. 2  or  3 , the valve cage  31  is halted more or less mid-way along its travel by the projections  44  as it descends from the top position illustrated in  FIG. 2 . If the valve cage  31  is in the bottom position, the ramps  45 , as the plug  44  is turned, lift the valve cage  31  into the intermediate position. The valve cage  31  therefore establishes a bypass between the inlet Ta and the outlet Ts of the motor in this intermediate position. This is effectively because none of the seats  21   a – 22   s  is closed. 
   A valve Q ( FIG. 9 ) with a preloaded spring Qr is advantageously arranged in an opening U in the wall  24 , between the inlet Ta, Ta 1  and the outlet Ts 1 , Ts of the motor. The valve Q, by opening, connects the inlet and the outlet directly, making it possible to spare the mechanisms, particularly those situated inside the body  1 , should the pressure drop suddenly rise. The head of the valve Q, in the closed position, is kept pressed in a sealed manner by the spring Qr against a seat on the wall  24  on the outlet side. On the inlet side, the spring Qr is compressed between the wall  24  and an end stop provided at the end of a valve stem. 
   Although the valve Q has been depicted only in the alternative form of  FIG. 9 , it is obvious that it could also be provided in the embodiments according to the other figures. 
   That being the case, the way in which the motor and the metering device work is as follows. 
   Let us consider a starting position corresponding to the one illustrated in  FIG. 2 . The piston  9  is at the end of its downstroke and the rocker H, which has just changed configuration, has raised the valve cage  31  and the plungers  23   a ,  23   s . The inlet Ta for pressurized liquid is connected to the lower chamber C 1  while the outlet Ts is connected to the chamber C 2 . 
   The liquid pressure is exerted on the underside of the piston  9  across its entire cross section and causes this piston to rise. The liquid in the chamber C 2  is delivered to the outlet. The piston plunger  15  ascends in the tubular element  16  and can draw an additive from a container connected to the coupling  18 . 
   At the end of the upstroke, the piston plunger  15  raises the link rod  32  and causes additional compression of the leaf spring  41 . When the pin  42  crosses the position of alignment with the pins  33  and  43 , the leaf spring  41  partially relaxes and causes an abrupt change in the configuration of the rocker. The arm  37  turns, in the clockwise direction according to the depiction of  FIG. 2 , about the pin  33  and the striker  40  strikes the lower wall of the valve cage  31  which abruptly moves into the bottom position as illustrated in  FIGS. 3 and 6 . 
   In this second position, the plungers  25   a ,  25   s  of the valves are in the bottom position. The chamber C 1  is placed in communication with the outlet, while the chamber C 2  is placed in communication with the inlet for pressurized liquid. 
   The liquid pressure is then exerted on the top side of the piston  9  across its entire cross section and causes it to descend. 
   The piston plunger  15  also descends, and this causes the valve  19  to close and the injection of the additive drawn in during the ascent. The passage of liquid is allowed by the seal  17 , as the piston plunger  15  descends, from the bottom side to the top side of this piston plunger. 
   In order to move into the bypass position, all that is required is for the plug  44  to be turned through a quarter of a turn. The plungers  25   a  and  25   s  then occupy an intermediate position allowing liquid to pass directly from the inlet Ta to the outlet Ts. 
   The invention makes it possible to use, on the ascent and on the descent, the entire stroke of the piston and its full diameter. This optimizes the compactness. 
   The rocker H is simple, reliable and compact. 
   As the valve seats are formed on the body, there is little or no seat deformation. The position of the piston has no influence on the valve plunger/seat pairing. The valve sealing is good at all flow rates. The fact of bringing the inlet/outlet valves closer together (these being separated simply by the wall  24 ) encourages compactness and, in the bypass position, liquid does not pass into the motor. 
   The liner  8 /ring  12  pairing allows the materials used to be modified easily to suit the application, for example according to the chemical products contained in the liquid and/or according to the temperature. The liner  8  can be changed quickly by unscrewing the cover  2 , extracting the liner  8  in a translational movement, and fitting a new liner.