Abstract:
The invention concerns a cylinder head arrangement for a piston compressor, with a cylinder block, in which a compression chamber is formed, which is delimited on one side by a valve plate that is clamped between the cylinder block and a cylinder head cover. In order to provide a cylinder head arrangement that has a high degree of tightness and can be manufactured in a cost-effective manner, the valve plate ( 6 ) has on at least one side at least one bead ( 40 ) projecting from the valve plate surface ( 21 ) concerned.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Applicant hereby claims foreign priority benefits under U.S.C. §119 from German Patent Application No. 10 2006 008 867.0 filed on Feb. 21, 2006, the contents of which are incorporated by reference herein. 
       FIELD OF THE INVENTION 
       [0002]    The invention concerns a cylinder head arrangement for a piston compressor, with a cylinder block, in which a compression chamber is formed, which is delimited on one side by a valve plate that is clamped between the cylinder block and a cylinder head cover. 
       BACKGROUND OF THE INVENTION 
       [0003]    From the German patent document DE 199 15 918 C2 is known a compressor, in which the end faces of the cylinder head, the top and bottom sides of the valve plate, as well as the sealing face of the cylinder head cover are made to be plane. The individual components are joined by means of screw bolts using flat gaskets as intermediate layers. The known compressor could, for example, be a refrigerant compressor. During operation, conditions may occur in refrigerant compressors, in which the discharge side pressure under the cylinder head cover increases heavily. This can, for example be caused by restrictions or even blocking of pipes or by decreased heat dissipation at a condenser of a corresponding refrigeration system. In order to avoid leakages or damage of sealing gaskets in such cases, the components must be held together by large tightening forces. On the one hand, this places heavy demands on the mounting process and the material properties of the bolts. On the other hand deformations of the cylinder may occur, as the bolts are screwed into the cylinder head in the immediate vicinity of the cylinder. This increases the risk of leakages through the piston-cylinder gap, which again reduces the efficiency of the compressor. 
         [0004]    As the tightening bolts are located in the edges of the substantially rectangular cylinder head, an increased pressure in the compression chamber may cause a sagging of a centre area of the valve plate away from the compression chamber. This reduces the compression surface and the surface pressure, which may cause failure of the gasket. To prevent this problem, the sealing surface of the cylinder head cover may have a slightly convex shape, so that the central area of the cover sealing surface is pressed harder against the valve plate. A deflection of the valve plate in the direction of the cylinder caused by this prestressing can be compensated by a somewhat thicker gasket between the valve plate and the cylinder block. This will also cause a slight increase of the dead volume of the compressor. Further, the manufacturing of a cover with a convex sealing surface is expensive. 
         [0005]    It is possible to provide the convex sealing surface of such a cylinder head cover with a circumferential bead to increase the surface pressure in the first gasket and to equalise possible manufacturing tolerances. However, this will still require large tightening forces of the mounting bolts to ensure a sufficient sealing by the second gasket between the cylinder block and the valve plate. Usually, cylinder head covers for refrigerant compressors are made as aluminium castings. A bead in such a component can, however, easily be damaged during handling in the assembly process, as the material is relatively soft. 
       SUMMARY OF THE INVENTION 
       [0006]    The task of the invention is to provide a cylinder head arrangement according to the preamble of claim  1 , which has a high degree of tightness and can be manufactured in a cost effective manner. 
         [0007]    With a cylinder head arrangement for a piston compressor, with a cylinder block, in which a compression chamber is formed, which is delimited on one side by a valve plate that is clamped between the cylinder block and a cylinder head cover this task is solved in that on at least one side the valve plate has at least one bead projecting from the valve plate surface concerned. This bead will substantially increase the surface pressure on the valve plate. Thus, also with high pressures a reliable sealing can also be ensured with relatively small tightening forces. Further, an expensive grinding of the valve plate surface concerned can be avoided. 
         [0008]    A preferred embodiment of the cylinder head arrangement is characterised in that the bead extends along a closed line. The bead does not have to be completely closed. It could also be effective when being interrupted by small openings. However, it could be advantageous for the bead to be completely closed. 
         [0009]    A further preferred embodiment of the cylinder head arrangement is characterised in that both sides of the valve plate have a bead projecting from the corresponding valve plate surface, the beads extending along a substantially closed line. This, for example, offers the advantage that an increased surface pressure is generated in both gaskets. Further, cylinder head covers with a plane sealing surface can be used. 
         [0010]    A further preferred embodiment of the cylinder head arrangement is characterised in that the valve plate is made as a sintered part. Manufacturing by sintering gives the advantage that the shaping of the valve plate with the bead or the beads is made relatively simply already when pressing the unsintered valve plate workpiece and a subsequent grinding of the valve plate can be avoided. Preferably, the valve plate is made of sinter metal. 
         [0011]    A further preferred embodiment of the cylinder head arrangement is characterised in that at least on one side, particularly on both sides, the valve plate has at least one, particularly several spacer pieces. The spacer pieces serve the purpose of preventing a caking of the pressed, unsintered valve plate workpieces during the sintering process, during which several plates are stacked. 
         [0012]    A further preferred embodiment of the cylinder head arrangement is characterised in that the spacer piece(s) project(s) somewhat more from the corresponding valve plate surface in question than the related bead. A slightly higher spacer piece compared to the bead will reliably prevent a caking of the valve plates during the sintering. In case the spacer pieces are located in the area of gaskets or beads, it is advantageous to provide recesses in the bead or the gasket to adopt the spacer piece. Alternatively, the spacer pieces can be deformed in the area of the beads or gaskets after the sintering, so that their height is smaller than the height of the beads. 
         [0013]    A further preferred embodiment of the cylinder head arrangement is characterised in that several through-holes are made in the valve plate. The through-holes have different functions, and for example serve the purpose of passing a medium into the compression chamber or out of the compression chamber. Further, the through-holes can serve as insertion holes for positioning or fixing elements. 
         [0014]    A further preferred embodiment of the cylinder head arrangement is characterised in that a valve seat of a suction valve and a valve seat of a discharge valve are impressed in the valve plate. Preferably, both the suction valve and the discharge valve are fixed to the valve plate. 
         [0015]    A further preferred embodiment of the cylinder head arrangement is characterised in that a gasket is located between the valve plate and the cylinder block and between the valve plate and the cylinder head cover, respectively. With very small working efforts, the combination of bead and gasket will provide a high degree of tightness. 
         [0016]    A further preferred embodiment of the cylinder head arrangement is characterised in that the extension of the bead perpendicularly to the belonging valve plate surface is smaller than the thickness of the gasket concerned. This prevents an unwanted cutting of the gasket. 
         [0017]    A further preferred embodiment of the cylinder head arrangement is characterised in that the extension of the bead perpendicularly to the belonging valve plate surface is 5 to 75%, particularly 25 to 50% of the thickness of the gasket concerned. In connection with the invention concerned, these values have proved to be particularly advantageous. 
         [0018]    A further preferred embodiment of the cylinder head arrangement is characterised in that on the valve plate surface facing the cylinder block the bead surrounds a projection of the opening of the compressing chamber on this valve plate surface. This prevents an unwanted escape between the valve plate and the cylinder block of medium from the compressing chamber. 
         [0019]    A further preferred embodiment of the cylinder head arrangement is characterised in that on the valve plate surface facing the cylinder block the bead surrounds at least one suction opening and at least one discharge opening. The openings belong to through-holes which permit passage of the medium into the compressing chamber and out of the compressing chamber. 
         [0020]    A further preferred embodiment of the cylinder head arrangement is characterised in that on the valve plate surface facing the cylinder head cover the bead surrounds a projection of the opening of a discharge chamber on this valve plate surface. This will prevent an unwanted escape between the valve plate and the cylinder head cover of medium from the discharge chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Further advantages, characteristics and details of the invention occur from the following description, in which an embodiment is described in detail with reference to the drawings, showing: 
           [0022]      FIG. 1  is a cylinder head arrangement with a valve plate in cross-section; 
           [0023]      FIG. 2  is a top view of the valve plate in  FIG. 1 ; 
           [0024]      FIG. 3  is a bottom view of the valve plate in  FIG. 1 ; 
           [0025]      FIG. 4  is a section along the line IV-IV in  FIG. 3 ; 
           [0026]      FIG. 5  is an enlarged view of a section V of  FIG. 4 ; and 
           [0027]      FIG. 6 to 9  are different embodiments of the beads in cross-section. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]      FIG. 1  shows a cross-section of a piston compressor cylinder head  1  in a refrigerating machine. The cylinder head  1  is fixed on a cylinder block  2  by means of screw bolts (not shown). The cylinder block  2  has a cylinder bore  3 , which is also called compression chamber. In a manner known per se, the cylinder bore serves the purpose of adopting a piston (not shown) of the piston compressor. 
         [0029]    The cylinder head  1  comprises a cylinder head cover  5  and a valve plate  6 . Between the cylinder head cover  5  and the valve plate  6  is located a first gasket  8 . Between the valve plate  6  and the cylinder block  2  is located a second gasket  9 . In the cylinder head cover  5  a discharge chamber  10  is formed, which is connected to the compression chamber  3  in the cylinder block  2  via at least one through-hole in the valve plate  6 . 
         [0030]    The  FIGS. 2 and 3  show a top view and a bottom view of the valve plate of  FIG. 1 . The valve plate  6  comprises a square basic body  20  of sintered metal. The basic body  20  has a square basal surface, which is rounded at the edges. The valve plate bottom side seen in  FIG. 2  and facing the compression chamber  3  has the number  21 . The valve plate upper side seen in  FIG. 3  and facing away from the compression chamber  3  has the number  22 . In the corner areas of the valve plate  6  four through-holes  24  to  27  are made, which are used to pass through fixing bolts. 
         [0031]    In  FIG. 2  a dashed circle  30  shows a projection of the cylinder bore ( 3  in  FIG. 1 ) on the valve plate bottom side  21 . Due to the circular shape of the projection  30 , it is also called a circle. Inside the circle  30  are made a suction through-hole  31  and a discharge through-hole  32 . These two through-holes  31  and  32  permit the passage of refrigerant sucked into the compression chamber ( 3  in  FIG. 1 ) and compressed. 
         [0032]    In a manner known per se, the suction through-hole  31  can be closed by a suction valve that opens when sucking refrigerant into the compression chamber. In a manner also known per se, the pressure through-hole  32  can be closed by a discharge valve that connects the compression chamber ( 3  in  FIG. 1 ) to the discharge chamber ( 10  in  FIG. 1 ) after a working stroke of the piston (not shown) of the piston compressor. 
         [0033]    Radially outside the circle  30 , between the two through-holes  24  and  27 , two additional through-holes  34  and  35  are made. These two through-holes  34  and  35  serve the purpose of adopting fixing pins of the suction valve. The suction through-hole  31 , the pressure through-hole  32  and the two through-holes  34  and  35  are surrounded by a closed bead  40 . 
         [0034]    The bead  40  projects from the valve plate bottom side  21  and substantially has the shape of the arch of a circle  41  that surrounds the circle  30 . In the area of the two through-holes  34  and  35  the bead  40  expands radially outwards, so that also the two through-holes  34  and  35  are surrounded by the bead  40 . In the area of the two through-holes  34  and  35 , the bead  40  substantially has the shape of an oblong hole  42 . The oblong hole  42  is made up of two arcs of a circle, whose one end is connected to one end of the arc of the circle  41 , the other ends being connected to each other by means of a straight line. In the cross-section, for example, the bead  40  has the form of a circle segment. However, the bead  40  can also have a substantially triangular cross-section with a rounded tip or a trapezoidal cross-section. 
         [0035]    Outside the bead  40 , six additional through-holes  44  to  49  are made in the valve plate. The through-holes  44  and  45  permit the passage of compressed refrigerant from the discharge chamber  10  and are therefore also surrounded by closed beads  51 ,  52 . The through-holes  46  and  47  serve the purpose of fixing the discharge valve. The through-holes  48  and  49  serve the purpose of adopting positioning pins for a suction arrangement. 
         [0036]    Further,  FIG. 2  shows that the through-hole  44  is surrounded by a circular bead  51 . Also the through holes  45  and  46  are surrounded by a common bead  52 . Further, the through-hole  47  is surrounded by a bead  53 . Additionally, several spacer pieces  61  to  66  project from the valve plate bottom side  21 , said spacer pieces extending perpendicularly upwards to the drawing level. Each spacer piece  62 ,  63 ,  65  and  66  is located in the vicinity of one of the through-holes  27 ,  26 ,  25 ,  24 . The two spacer pieces  61  and  64  are located approximately in the centre of the valve plate  6 . The height of the spacer pieces  61  to  66  is somewhat larger than the height of the beads  40 ,  51  to  53 . Thus, during manufacturing of the valve plates a baking of several valve plate workpieces during the sintering process is prevented. 
         [0037]      FIG. 3  shows that a closed bead  50  is provided on the valve plate upper side  22 . Within the bead  50 , which has the same cross-section as the bead  40  in  FIG. 1 , the through-holes  32 ,  34 ,  35 ,  44 ,  45 ,  46  and  47  are located. However, also different cross-sections and heights can be used for the different beads of the valve plate. Outside the bead  50  the through-holes  24  to  27 ,  48 ,  49  and  31  are located. The bead  50  is substantially U-shaped, circle-arc shaped concavities being formed in the area of the through-holes  24  to  27 . 
         [0038]    Making the beads  40  and  50  on the valve plate  6  generates an increased surface pressure in the corresponding sealing surface. The increased surface pressure in the contact area between bead  40 ,  50  and gasket  9 ,  8  ensures a reliable sealing also with high pressures. At the same time, the tightening forces required for a safe tightening of the cylinder head  5  and the valve plate  6  on the cylinder block  2  can be reduced. Further, the manufacturing of the valve plate is simplified, as a plane grinding of the valve plate can be avoided. 
         [0039]    Preferably, the valve plate is manufactured by sintering of a sinter metal, merely the valve seats for the suction and discharge valves having to be impressed. In any case, the beads  40 ,  50  ensure that in spite of manufacturing tolerances an all-round and sufficient sealing pressure will be maintained. Further, as mentioned above, the tightening forces required for fixing the valve plate  6  can be reduced, that is, the fixing bolts used do not have to be tightened so much. This will reduce the shape defects of the cylinder and leakages through the cylinder-piston gap, which will have a positive effect on the efficiency of the compressor. 
         [0040]    According to a further essential aspect of the invention, the height of the bead, that is, the extension of the bead  40 ,  50  is smaller than the thickness of the belonging gasket  9 ,  8 . Thus, an unwanted cutting of the gasket by the bead is avoided. Preferably, the height of the bead is 5 to 75% of the gasket thickness, particularly preferred is 25 to 50% of the gasket thickness. 
         [0041]    Further,  FIG. 3  shows that also on the valve plate upper side  22  several spacer pieces  71  to  75  are provided. The spacer pieces  71 ,  72  and  74 ,  75  are located within the bead  50 . The spacer piece  73  is located outside the bead  50 . The height of the spacer pieces  71  to  75  is slightly larger than the height of the bead  50 . 
         [0042]      FIG. 4  shows a section along the line IV-IV in  FIG. 3 . The sectional view makes it clear that the spacer pieces  64  to  66  and  71  to  73  project more from the belonging valve plate surface than the beads, which have no reference numbers in the sectional view. 
         [0043]      FIG. 5  shows an enlarged section V of  FIG. 4 . The enlarged section shows that in the cross-section the bead  40  has the shape of a circle segment. 
         [0044]      FIG. 6  suggests that in the cross-section the beads  40  ( 51  to  53  in  FIG. 2 and 50  in  FIG. 3 ) can also have the shape of a rectangle  81  with rounded edges. 
         [0045]      FIG. 7  suggests that in the cross-section the beads can also have the shape of an ellipse section  82 . 
         [0046]      FIG. 8  suggests that in the cross-section the beads can also have the shape of an isosceles trapezoid  83 . 
         [0047]      FIG. 9  suggests that in the cross-section the beads can also have the shape of a triangle  84 . 
         [0048]    While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present invention.