Patent GB-718707-A (GB)
Abstract: 718,707. Dynamometers. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 10, 1952 [July 10, 1951], No. 16327/51. Class 106 (2). [Also in Groups XXIX and XXXVIII] A thrust measuring appliance comprises a hydraulic cylinder and piston arrangement, without packed joints, adapted to balance the thrust or part of the thrust, means for maintaining the cylinder and piston in relative rotation without a radial load between the cylinder and piston being thereby imparted and means automatically set in action by any small relative axial movement of the cylinder and piston from a null position to cause the thrust applying means to be returned to and constantly he'd close to the null position, the connections to the cy'inder being such that substantially no radial loads between cylinder and piston are imparted by the liquid. As shown in Fig. 1 the cylinder 2 is movable on a stationary piston 1, the piston 1 having an upper groove 10 connected to a continuously driven pump 17 and a lower groove 11 connected to a sump 19. In the null position both grooves, as shown, are covered by the cylinder 2. If the load, applied for example by a dynamometer beam 4, increases, the cylinder 2 is forced downwards to uncover the groove 10. Liquid is then forced into an upper chamber 12 in the cylinder 2 until the pressure is sufficient to raise the cylinder 2 to its original position when the groove 10 will again be covered. If the load applied by the beam 4 decreases, the cylinder 2 will rise and a groove 14 therein connected to the chamber 12 will register with the groove 11 in the piston. Liquid in the chamber 12 will then escape through the groove 11 to the sump 19 thereby lowering the cylinder 2 until it has returned to its null position when the groove 11 will again be closed by the cylinder. A pressure gauge 23 or a manometer 24 connected to the chamber 12 by a pipe 22 will thus give a measure of the thrust applied to the cylinder 2. The pump 17 draws from the sump 19 To provide for conditions when the cylinder is at or above null position, a pipe 20 connects the delivery side of the pump to the sump via a loaded relief valve 21. The cylinder 2 is rotated relatively to the piston 1 Juring the operation of the apparitus either electrically or mechanically. The thrust applying means preferably engages the cylinder or piston, as the case may be, through a all or like bearing roller 28. In the modification shown in Fig. 2 fluid is supplied under pressure through a pipe 37 to a space above a piston 35 in a loaded cylinder 34 to maintain the cylinder 34 in a floating condition on the piston 35, the movements of the cylinder 34 in response to variations in load, causing corresponding displacements in a disc 49 between opposed inductances 51 and 52. The resultant effect on the inductances actuates an electronic amplifier and power pack the output of which through a variable speed and direction device actuates a pump plunger or the like displaceab!e element by which the pressure of a liquid applied to the chamber above the cylinder through a pipe 37 is varied to maintain the cylinder in a null position. The said pressure is again a measure of the thrust applied to the apparatus. Fig. 7 shows an arrangement in which the cylinder 88 is stationary and the piston 89 is movable, the piston being rotated relatively to the cylinder by a belt pulley 96. An inlet 111 from the pump leads into the chamber 107, a connection 112 from a pressure gauge or manometer leads into the chamber 109, and an exhaust connection 113 to the sump leads from the chamber 114. If the reaction of the piston to the load is too low, the piston descends to admit pressure fluid from chamber 107 to chamber 109 and urge the piston upwards. If the reaction is too high the piston rises, alloving pressure fluid from the chamber 109 to escape through a duct 108 in the piston to the chamber 106 and thus to the chamber 114 and the exhaust connection 113, thus allowing the piston to sink. Addition of a jockey arm.-The load range of the piston and cylinder device can be increased by balancing part of the load by jockey weight running on a jockey, arm. Such an arrangement is indicated in Fig. 6 wherein a horizontal jockey arm 66 extends equally on either side of the axis of a dynamometer 5. A. jockey weight.67 is controlled by a feed screw 69 driven by a reversible electric motor 71. The electric motor 71 may be operated by the previously mentioned amplifier and power pack 68 controlled by a metal disc 49 on the cylinder 34 moving between the ends of aligned inductances 51, 52. A remote Indicator 83 may .be actuated by a repeater motor 72 to indicate on a dial the torque of the jockey weight. Another indicator 84 may be actuated by the pressure in the piston and cylinder arrangement to indicate the load taken thereby. Fig. 6 illustrates the use of an accumulator instead of the previously mentioned pump to supply fluid under pressure to the piston and cylinder. The cylinder and piston of the hydraulic accumu'ator are maintained in relative rotation during operation. Apparatus used for controlling the pressure of a liquid.-To maintain a liquid under constant pressure, a cylinder-piston unit such as is shown in Fig. 1 or Fig. 7 is coupled to a weigh-beam. The jockey weight on the weigh-beam will then be adjusted to the required position and the pipe connection 22 or 37 then provides the constant pressure supply provided the pump is adequate. To vary the pressure of a liquid in a predetermined manner the jockey weight on the weighbeam is moved in a manner producing the required liquid pressure variation.