Figure 4-15 is a series of drawings that illustrateshow the universal joint is used in the operationof this pump.First, a rocker arm is installed on a horizontalshaft. (See fig. 4-15, view A.) The arm is joinedto the shaft by a pin so that it can be swung backand forth, as indicated in view B. Next, a ring isplaced around the shaft and secured to the rockerarm so the ring can turn from left to right asshown in view C. This provides two rotarymotions in different planes at the same time andin varying proportions as may be desired. Therocker arm can swing back and forth in one arc,and the ring can simultaneously move from leftFigure 4-15.–Relationship of the universal joint in operationof the axial piston pump.to right in another arc, in a plane at right anglesto the plane in which the rocker arm turns.Next, a tilting plate is added to the assembly.The tilting plate is placed at a slant to the axisof the shaft, as depicted in figure 4-15, view D.The rocker arm is then slanted at the same angleas the tilting plate, so that it lies parallel to thetilting plate. The ring is also parallel to, and incontact with, the tilting plate. The position of thering in relation to the rocker arm is unchangedfrom that shown in figure 4-15, view C.Figure 4-15, view E, shows the assembly afterthe shaft, still in a horizontal position, has beenrotated a quarter turn. The rocker arm is still inthe same position as the tilting plate and is nowperpendicular to the axis of the shaft. The ringhas turned on the rocker pins, so that it haschanged its position in relation to the rocker arm,but it remains parallel to, and in contact with, thetilting plate.View F of figure 4-15 shows the assembly afterthe shaft has been rotated another quarter turn.The parts are now in the same position as shownin view D, but with the ends of the rocker armreversed. The ring still bears against the tiltingplate.As the shaft continues to rotate, the rockerarm and the ring turn about their pivots, with eachchanging its relation to the other and with the ringalways bearing on the plate.Figure 4-15, view G, shows a wheel added tothe assembly. The wheel is placed upright andfixed to the shaft, so that it rotates with the shaft.In addition, two rods, A and B, are looselyconnected to the tilting ring and extend throughtwo holes standing opposite each other in the fixedwheel. As the shaft is rotated, the fixed wheelturns perpendicular to the shaft at all times. Thetilting ring rotates with the shaft and alwaysremains tilted, since it remains in contact with thetilting plate. Referring to view G, the distancealong rod A, from the tilting ring to the fixedwheel, is greater than the distance along rod B.As the assembly is rotated, however, the distancealong rod A decreases as its point of attachmentto the tilting ring moves closer to the fixed wheel,while the distance along rod B increases. Thesechanges continue until after a half revolution, atwhich time the initial positions of the rods havebeen reversed. After another half revolution, thetwo rods will again be in their original positions.As the assembly rotates, the rods move in andout through the holes in the fixed wheel. This isthe way the axial piston pump works. To get apumping action, place pistons at the ends of the4-13
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