Axial Piston PumpsIn axial piston pumps of the in-line type,where the cylinders and the drive shaft are parallel(fig. 4-13), the reciprocating motion is created bya cam plate, also known as a wobble plate, tiltingplate, or swash plate. This plate lies in a planethat cuts across the center line of the drive shaftand cylinder barrel and does not rotate. In afixed-displacement pump, the cam plate will berigidly mounted in a position so that it intersectsthe center line of the cylinder barrel at an angleapproximately 25 degrees from perpendicular.Variable-delivery axial piston pumps are designedso that the angle that the cam plate makes witha perpendicular to the center line of the cylinderbarrel may be varied from zero to 20 or 25 degreesto one or both sides. One end of each piston rodis held in contact with the cam plate as the cylinderblock and piston assembly rotates with the driveshaft. This causes the pistons to reciprocate withinthe cyIinders. The length of the piston stroke isproportional to the angle that the cam plate is setfrom perpendicular to the center line of thecylinder barrel.A variation of axial piston pump is thebent-axis type shown in figure 4-14. This type doesnot have a tilting cam plate as the in-line pumpdoes. Instead, the cylinder block axis is variedfrom the drive shaft axis. The ends of theFigure 4-14.—Bent-axis axial piston pump.connecting rods are retained in sockets on a discthat turns with the drive shaft. The cylinder blockis turned with the drive shaft by a universal jointassembly at the intersection of the drive shaft andthe cylinder block shaft. In order to vary the pumpdisplacement, the cylinder block and valve plateare mounted in a yoke and the entire assemblyis swung in an are around a pair of mountingpintles attached to the pump housing.The pumping action of the axial piston pumpis made possible by a universal joint or link.Figure 4-13.—In-line axial piston pump.4-12
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