Patent Application
20110038739
1. Field of the Invention
The subject invention relates to swash plate axial piston pumps including condition responsive control of pump displacement.
2. Description of the Prior Art
In such pumps, the relative locations of the swash rotation axis, swash central axis of the swash device, and the plane containing the connection pivot points between the pistons and the swash device affect the performance characteristics of the pump such as maintaining clearance between the pistons and the valve plate and bias of the swash device to rotate to a higher or lower angle position. To increase the displacement of such a pump, the prior art typically employed three strategies: adding more pistons, increasing the diameter of the pistons, or increasing the diameter of the swash device to increase the stroke length of each piston. Each of these strategies necessarily increases the size and/or complexity to the pump, and therefore added cost or weight.
An example of an swash plate axial piston pump including condition responsive control of pump displacement is disclosed in U.S. Pat. No. 5,644,968 to Kimura. The '968 patent discloses a housing that has a piston block disposed therein which defines a plurality of piston bores. A piston is disposed and translational in each of the piston bores. A swash device defines a swash bore about a swash central axis and defines a swash rotation axis for rotation thereabout. A pivotal connection pivotally connects each of the pistons to the swash device for rotation about a connection pivot point during relative movement between the swash device and piston. The connection pivot points are aligned in a plane. A shaft is supported by the housing and passes through the swash bore and defines a shaft central axis. A hinge assembly pivotally supports the swash device about a hinge axis disposed on the opposite side of the plane from the piston block and is movable radially relative to the shaft central axis during relative movement of the swash device along the shaft. The swash rotation axis is offset from the plane away from the hinge axis and radially offset from the swash center axis away from the hinge axis to limit the clearance between the pistons and a valve plate disposed on the opposite side of the pistons from the swash device.
U.S. Pat. No. 5,253,576 to Bethke discloses a pump having a plurality of pistons and a swash device defining a swash center axis and a swash rotation axis. A pivotal connection connects each of the pistons to the swash device for rotation about a connection pivot point during relative movement between the swash device and the piston. The connection pivot points are aligned on a plane. A hinge assembly pivotally supports the swash device and is disposed on the opposite side of the plane from the piston block. The swash rotation axis is offset from the plane toward the hinge assembly and radially offset from the swash center axis toward the hinge assembly to bias the swash device to a higher angle position.
Contrary to such prior art, the subject invention provides a new relationship wherein the swash rotation axis is offset from the plane away from the hinge axis and is radially offset from the swash center axis toward the hinge axis.
The present invention repositions the reaction forces that the swash device experiences from the relative pushing and pulling on the swash device by the pistons. Accordingly, the upstroking of the pistons is greatly improved, especially at low speeds when the inertia of the swash device is less significant. As a result, the pump has a higher effective output than a similar pump of the same number of pistons, same piston diameter, and same swash device diameter.
Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, the invention comprises a pump or compressor, as shown generally at
A cylinder or piston block 34 coaxial with the housing 20 defines a plurality of cylinder or piston bores 36. Each of the piston bores 36 define a piston bore axis CP and each of the piston bore axes CP are parallel to each other. The piston block 34 is disposed within the housing 20 and has an outside diameter 38 engaging the inside diameter 22 of the housing 20. The piston block 34 has a rear surface 40 adjacent to and coplanar with the rear opening 26 and a front surface 42 that is opposite the rear surface 40. The front surface 42 of the piston block 34 and the front housing cover 28 define an internal crank chamber 44 therebetween. The piston block 34 defines a shaft bore 46 along the main central axis CM. A rear bearing 48 or guide is disposed in the shaft bore 46.
A piston 50 is disposed and translational in each of the piston bores 36 along the piston bore axis CP. Each of the pistons 50 has a bore end 52 disposed in the piston bore 36, and a crank end 54 opposite the bore end 52 and exposed to the crank chamber 44. Each of the crank ends 54 are C-shaped and define a rear socket 56 that is concave and faces away from the piston block 34 and a front socket 58 opposite the rear socket 56 that is concave and faces the piston block 34.
A swash device 60 is disposed in the crank chamber 44 and includes a journal 62 that defines a swash bore 64 about a swash central axis CSW and defines a swash rotation axis CR for rotation thereabout. The swash device 60 includes a swash plate 66 supported by the journal 62 and having a front face 68 facing away from the piston block 34 and a rear face 70 parallel and opposite the front face 68 and facing toward the piston block 34.
A pivotal connection 72 pivotally connects each of the pistons 50 to the swash device 60 for rotation about a connection pivot point 74 during relative movement between said swash device 60 and said piston 50. The connection pivot points 74 are aligned in a plane P. The plane P is parallel to the front and rear faces 68, 70 of the swash plate 66 and bisects the swash plate 66 midway between the front face 68 and the rear face 70 of the swash plate 66.
Each of the pivotal connections 72 include shoes 76, 78 being hemispherical in shape and having a flat surface 80 which is flat, and a convex surface 82 opposite the flat surface 80. The convex surfaces 82 are convex and shaped complementary to the sockets 56, 58. Each of the pivotal connections 72 has a front shoe 76 and the flat surface 80 of the front shoe 76 is disposed and slidable on the front face 68 of the swash plate 66. The convex surface 82 of the front shoe 76 is disposed on and slidable on the front socket 58 of the piston 50. Each of the pivotal connections 72 has a rear shoe 78 opposite the front shoe 76. The flat surface 80 of each of the rear shoes 78 is disposed and slidable on the rear face 70 of the swash plate 66 and the convex surface 82 is disposed and slidable on the rear socket 56 of the piston 50.
A bar or shaft 84 defines a shaft central axis CSH and is coaxial with the main central axis CM. The shaft 84 has a rear end 86 which extends through the shaft opening 30 and the crank chamber 44. The rear bearing 48 rotatably supports the rear end 86 of the shaft 84. The shaft 84 has a front end 88 opposite the rear end 86. The front bearing 32 rotatably supports the shaft 84 between the front end 88 and the rear end 86. A pulley 90 is fixed to the front end 88 of the shaft 84 and is used to rotate the shaft 84. A ring 92 is fixed to and about the shaft 84 adjacent the front face 68 of the piston block 34.
A connector joint 94 is rotatably connected to the swash device 60 about the swash rotation axis CR. The connector joint 94 includes a sleeve 96 or slide disposed within the swash bore 64 and about and translational along the shaft 84. The swash rotation axis CR extends through the sleeve 96 and travels with the sleeve 96 as it translates along the shaft 84. The sleeve 96 defines a first sleeve hole 98 and a second sleeve hole 100. The sleeve holes 98, 100 are coaxial to each other and extend transversely to the shaft 84. The journal 62 defines a first and second journal rotation hole 102, 104 and the journal rotation holes 102, 104 are coaxial to each other and to the sleeve holes 98, 100 and define the swash rotation axis CR of the swash device 60 about the sleeve 96.
The connector joint 94 includes a first journal rotation pin 106 which extends through the first sleeve hole 98 and the first journal rotation hole 102 and rotatably connects the journal 62 to the sleeve 96 about the swash rotation axis CR. A second journal rotation pin 108 extends through the second sleeve hole 100 and the second journal rotation hole 104 and rotatably connects the journal 62 to the sleeve 96 about the swash rotation axis CR.
A hinge assembly 110 pivotally supports the swash device 60 about a hinge axis CHI disposed on the opposite side of the plane P from the piston block 34. The hinge axis CHI is movable radially relative to the shaft central axis CSH during relative movement of the sleeve 96 along the shaft 84. The hinge assembly 110 includes the journal 62 defining a pair of parallel and offset journal ears 112. Each ear extends radially outward from the journal 62 and is circumferentially aligned with one of the sleeve holes 98, 100. Each of the journal ears 112 define a journal lever hole 114 extending transversely to the shaft 84 and parallel to the swash rotation axis CR and axially offset from the swash rotation axis CR. Each journal lever hole 114 is coaxial to each other journal lever hole 114 and the journal lever holes 114 define the hinge axis CHI.
The hinge assembly 110 includes a rotor 116 disposed in the crank chamber 44 and fixed to the shaft 84 adjacent the front bearing 32. The hinge assembly 110 includes a pair of hinge links 118 rotatably connected to the swash device 60 about the hinge axis CHI and rotatably connected to the rotor 116 about a static axis CST which is fixed relative to the shaft 84. The rotor 116 defines a pair of parallel and offset rotor ears 120 extending radially outward from the rotor 116 toward the journal ears 112. Each rotor ear 120 is circumferentially aligned with one journal ear 112. Each of the rotor ears 120 defines a rotor hole 122 extending parallel to the swash rotation axis CR and axially offset from the sleeve holes 98, 100. Each rotor hole 122 is coaxial to each other rotor hole 122 and define the static axis CST.
The hinge links 118 are disposed in the crank chamber 44 and each define an front hinge hole 124 and a rear hinge hole 126. A rear hinge pin 128 is disposed through the rear hinge holes 126 and the journal lever holes 114 thereby rotatably connecting the hinge links 118 and the journal 62 about the hinge axis CHI. A front hinge pin 130 is disposed through the front hinge holes 124 and the rotor holes 122 thereby rotatably connecting the hinge links 118 and the rotor 116 about the static axis CST.
A front bias spring 132 is disposed about the shaft 84 and extends between the rotor 116 and the sleeve 96. A rear bias spring 134 is disposed about the shaft 84 and extends between the sleeve 96 and the piston block 34.
A disc-like valve plate 136 having a diameter as least as great as the outside diameter 38 of the piston block 34 is fixed to the rear surface 40 of the piston block 34. Each piston 50 and the valve plate 136 define a piston chamber 138 therebetween. A head cover or rear housing cover 140 is disposed over the valve plate 136. The rear housing cover 140 and the valve plate 136 define a discharge chamber 142 and a suction chamber 144 therebetween. The valve plate 136 defines a plurality of suction orifices 146 and discharge orifices 148. One suction orifice 146 is disposed between the suction chamber 144 and each piston chamber 138. One discharge orifice 148 is disposed between the discharge chamber 142 and each piston chamber 138. A flow control valve 150 is disposed in each of the orifices 146, 148.
The rear housing cover 140 defines an outlet valve opening 152 adjacent the discharge chamber 142, and an outlet valve 154 is disposed in the outlet valve opening 152. The rear housing cover 140 defines an inlet valve opening 156 adjacent the suction chamber 144, and an inlet valve 158 is disposed in the inlet valve opening 156. A crank pressure control valve 160 is disposed in the rear housing cover 140 adjacent to both the suction chamber 144 and the discharge chamber 142. The rear housing cover 140 defines a suction control channel 162 between the suction chamber 144 and the crank pressure control valve 160. The rear housing cover 140 defines a discharge control channel 164 between the discharge chamber 142 and the crank pressure control valve 160. The piston block 34, the valve plate 136, and the rear housing cover 140 define a pressure control channel 166 between the crank chamber 44 and the crank pressure control valve 160.
Each of the pistons 50 is in a top dead center position as the piston 50 alternates from approaching the valve plate 136 to retreating from said valve plate 136 and in a bottom dead center position as the piston 50 alternates from retreating from the valve plate 136 to approaching the valve plate 136. Each of the pistons 50 has a variable stroke length being the distance between the top dead center position and the top dead center position. The plane P and the shaft central axis CSH define a plane tilt angle θ. The angle θ decreases as the plane P approaches perpendicular with the shaft central axis CSH and the plane tilt angle θ increases in the opposite direction.
The swash rotation axis CR of the swash device 60 is offset from the plane P away from the hinge axis CHI and is radially offset from the swash center axis CSW in a direction toward the hinge axis CHI.
Accordingly, the pulley 90, shaft 84, rotor 116, sleeve 96, journal 62, and swash plate 66 rotate together about the main central axis CM as the shoes 76, 78 slide across the faces 68, 70 of the swash plate 66 and the pistons 50 reciprocate between top dead center position and bottom dead center. A working fluid disposed in the crank chamber 44 exerts crank pressure on each piston 50 and a working fluid disposed in each piston chamber 138 exerts piston pressure on each piston 50.
In response to the average of piston chamber 138 pressures increasing in relation to crank pressure the pistons 50 collectively push the swash plate 66 and the sleeve 96 along the shaft 84 toward the front housing cover 28 and thereby increasing the tilt angle θ of the plane P which increases the stroke length of the pistons 50. In response to the average of the piston chamber 138 pressures increasing in comparison to the crank chamber 44 pressure the pistons 50 collectively pull the swash plate 66 and the sleeve 96 along the shaft 84 toward the piston block 34 and thereby decreasing the plane tilt angle θ and decreasing the stroke length of the pistons 50.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
