Patent GB-722994-A (GB)
Title: A hydraulic damper with a desired damping effect for each phase of the oscillation to be damped
IPC: F16F9/18
Filed: 1950-12-28
Abstract: 722,994. Hydraulic dampers. GIRARD, A. A. L. Dec. 28, 1950 [Jan. 13, 1950; April 12, 1950], No. 31464/50. Class 108 (3). The invention relates to a hydraulic damper comprising one or two pistons defining in a reservoir chamber, two pressure chambers, and at least one intermediate chamber. According to the invention, each pressure chamber communicates with an intermediate chamber by a narrow groove having a curvilinear base so that its cross-section varies according to the position of the piston, the intermediate chamber or chambers communicating with the pressure chambers via non-return valves. The grooves may be formed on a surface of the reservoir along which the pistons slide. They may be formed in an element fixed rigidly in or adjustably with respect to, the reservoir, the element passing through an opening in the piston or pistons. The grooves may be formed on an element fixed to the piston or pistons and co-operating with an opening in a partition integral with the reservoir. In the constructions shown in Fig. 3a, pistons C, D are both rigidly connected to an operating head 7 and work in respective cylinders A1, A2 to define the working pressure chambers X, Y. The spaces remaining in the two cylinders are connected by a duct 14 and together form the intermediate chamber Z. Damping is provided by passages 1 to 4 of variable cross-section formed in rods 10, 11 rigid with the cylinders A1, A2. These passages may be formed in the walls of the respective cylinders. In a modification, Fig. 3b (not shown) the passages 1, 4 are formed in the rod 6 of the piston D, and the flow between chambers X and Z is damped (instead of flow between either side of the piston D). The duct 14 in this case extends coaxially within the piston rod 6. In a further modification, Figs. 1 to 2c (not shown), the head 7 is given an oscillatory movement by an operating lever so that the movement of the pistons occurs in opposite directions. The pistons may be biased by coiled springs. In a further alternative, Figs. 4 to 4b (not shown), the cylinder A2 is of greater diameter than, and disposed concentrically to, the cylinder A1, the piston C being of annular form. In this construction, air may be compressed in the space above the liquid in chamber Z. In the construction of Fig. 15 the pistons C, D operate in a common cylinder A to define pressure chambers X, Y and an intermediate chamber Z. The pistons C, D have ports which co-operate with variablesection damping passages 1 to 4 formed in a fixed rod 33. The passages 1 to 4 may, however, be formed in the wall of the cylinder A. The rod 33 may be movable axially relative to the cylinder A instead of being fixed thereto (Fig. 10, not shown). The chambers X, Y may be connected by a duct, the damping action of which may be varied by the setting of one or a pair of tapered screws, Figs. 6, 7 (not shown). This duct may be of fixed cross-section, however, and provided at each end with non-return valves O, P. The duct may be connected at an intermediate point with the chamber Z. Each piston C, D may be provided with spring-loaded safety valves, Fig. 8 (not shown). The safety valves may be spring-loaded ball valves which are disposed concentrically within spring-loaded, disc-type, replenishing valves, Figs. 19 to 21 (not shown). The safety valves may, however, be provided in respective ducts connecting the chambers X and Y, Fig. 9 (not shown). In the form in which the rod 33 is axially movable, a tapered recess in the rod may co-operate with a port leading from the chamber X into an external passage which is connected with the chamber Y, Fig. 11 (not shown). Thus, axial adjustment of the rod 33 to vary the action of the passages 1 to 4 also varies the restriction to flow through the external passage. A tapered recess and co-operating port, may be formed at each end of the external passage which at its central point may be connected with the intermediate chamber Z, Fig. 12 (not shown). In addition, the rod 33 may be rotatable about its axis in order to vary the area of the port leading to the external passage without altering the axial setting of the passages 1 to 4, Fig. 13 (not shown). In the construction shown in Fig. 17a, a single piston B and co-operating cylinder A1 define the working pressure chambers X, Y. The intermediate chamber Z is formed by an outer concentric chamber A. Flow between chambers X, Y takes place through variablesection passages 2, 3 in a rod 115 and a valvecontrolled piston port 110. Flow between chambers Y, Z occurs (for the opposite direction of piston movement) through passages 1, 4. The port 110 may be replaced by a port 113 in the piston rod so that flow occurs between the chambers X and Z, instead of X and Y. In a modification, the rod 115 may be rigid with the piston B and slidably mounted in the head of the cylinder A1, which is then spaced from the end of cylinder A. The piston rod 112 of piston B is then entirely solid, and flow from chamber X takes place directly to the chamber Z through the passages 2, 3. In the construction shown in Fig. 22, the chamber X is formed between the upper face of a piston D and its cylinder 56, and the chamber Y is formed in the annular space beneath the lower face of the outer annular portion C of the piston D. The piston D is carried by a hollow piston rod 59 which is rigid at its outer end with a tube 62 connected with the piston portion C. One intermediate chamber W is formed beneath the piston D, and another intermediate chamber Z is formed within the tube 62. The chambers W and Z are connected by way of a conduit 58, ports 61 in a plug 63, and ports 64 in the piston rod 59. The chamber X is connected directly with the chamber Z through the variable cross-section passages 1, 4. However, on the occurrence of excess pressure in the chamber X, liquid passes through ports 69 in the piston rod 59, through vertically-disposed ports 71 in the plug 63 and lifts a ball valve 68 leading to the chamber Z. A controlled flow to chamber Z may also take place via an adjustable valve 74 and a tube 75. The chambers Y and Z are connected by the passages 2, 3, but a safety valve 66 provides for flow to chamber W, and a controlled flow to chamber W is provided via a valve 77. Annular replenishing flap-valves O, P are provided respectively for the chambers X, Y. In the construction shown in Figs. 24a and 24b (Fig. 24b is a downward continuation of Fig. 24a), a piston B defines working pressure chambers X, Y within a cylinder A. An intermediate chamber Z is formed partly by an annular space between the rod 112 of the piston B and an outer cylinder 119, rigid with the outer end of the piston rod 112. The remainder of chamber Z is formed by an annular space between the cylinder A and a concentrically disposed outer cylinder 117 rigid with the cylinder A. The two parts of the chamber Z are in communication, but baffles 144 are provided to limit splashing of liquid into the upper part. On compression, liquid flowing from the chamber X to the chamber Y is metered by the action of passages 2, 3 formed in a rod 115 rigid with the cylinder A. The flow proceeds via piston passages 128, 129 and a flap valve 116. An additional flow path is provided via a port 137 leading to the hollow interior of the rod 115. The rod 115 leads to the interior of a tube 121 disposed concentrically within the piston rod 112 of the piston B. The liquid then passes through an externally-adjustable valve 131 to the annular space 123 between the tube 121 and the piston rod 112, and from thence to the chamber Y via a port 136. In the event of excess pressure in the chamber X, liquid passes directly to the chamber Z via a ball valve 147. On extension, flow between the chambers Y and Z is metered by passages 1, 4 co-operating with the gland 142 of the piston rod 112. Additional' flow from the chamber Y may also occur via the port 136, annular space 123, adjustable valve 131 and port 137 to the chamber X. Excess pressure is relieved by a ball valve 139 leading to the chamber Z. Air is compressed above the liquid in the chamber Z. In the construction shown in Fig. 25, integral rotary vanes C, D operated within a casing A by an arm 82, define working pressure chambers X, Y separated by a fixed partition 83 and an intermediate chamber Z. Variable cross-section damping passages 1, 4 and 2, 3 formed in a ring 87, co-operate with the vanes C and D to meter the flow from chamber Y to chamber Z and chamber X to chamber Z respectively. A similar passage 92 in the ring 87 connects the chambers X, Y directly. The ring is rotatable relative to the casing A by the action of a pin (not shown) which is eccentrically mounted on an externally-adjustable stem mounted in the casing A. The chambers X, Y are also connected by a duct 91, the restriction of which may be adjusted by means of a valve 109. Respective spring-loaded ball valves are mounted in passages 89a, 90a, and provide for relief of excess pressure in the chambers X and Y. Valves O, P provide for replenishment of the chambers X, Y from the chamber Z. In a modification of this construction, Fig. 5 (not shown), the passages 1-4 are formed in the inner periphery of the casing A. In a further modification, Figs. 29 to 32 (not shown), a single moving vane co-operates with a pair of fixed partitions. The passages 1 to 4 are formed in the periphery of the boss of the vane and co-operate with the radially-innermost surfaces of the partitions. The two excess-pressure valves are disposed in the respective partitions, and are connected between the intermediate chamber and the respective pressure chamber. The duct 91 is disposed in the body of the vane and is controlled by a screw coaxially mounted in the boss. In any of the above-described constructions, the areas of pairs of pistons or vanes may be unequal. Single damping passages, safety valves, or non-return valves may be replaced by a plurality of such passages or