US 3871032 A
An artificial ankle joint with an articulate connection between the foot part and the lower leg part of an artificial leg. A damping device comprising at least two hydraulic cylinders connected by conduits and each provided with a piston is hinged to the foot part and the lower leg part, respectively. The pistons have hollow chambers filled with storage oil and pressure-balancing channels lead to the upper end of the hollow chambers.
Description (OCR text may contain errors)
United States Patent [1 1 Karas 1 Mar. 18, 1975 ARTIFICIAL HYDRAULIC ANKLE JOINT Primary ExaminerRonald L. Frinks 75 I W If K V A t mentor 0 gang aras lenna' us nd Attorney, Agent, or Firm-Stemberg and Blake  Assignee: Forschungsinstitut fur Orthopadie-Technik, Vienna, Ausma 57 ABSTRACT  Filed: Apr. 4, 1974 An artificial ankle joint with an articulate connection  Appl 458049 between the foot part and the lower leg part of an artificial leg. A damping device comprising at least two  Foreign Application Priority Data hydraulic cylinders connected by conduits and each Mar. 8, 1974 Austria 1928/74 Provided with a Piston is hinged to the foot and the lower leg part, respectively. The pistons have hol- 521 U.S.Cl. 3/1.2, 3/30 10W chambers filled Wlth Storage 011 and Pressure-  CL A6 U00 A6lf H04 A6 H08 balancing channels lead to the upper end of the hol-  Field of Search 3/12, 30-35 10W Chambers- Between the pressure chambers of the hydraulic cylin-  References Cited der and the hollow chamber of the piston 21 snifting UNITED STATES PATENTS valve is provided which sucks hydraulic liquid from 2.470.480 5/1949 F H 3/l.2 the hollow iston chamber. 2.657.393 ll/l953 Hz ilir 3/l.2 p
FOREIGN PATENTS OR APPLlCATlONS 5 Claims, 2 Drawing Figures 818328 l0/l95l Germany 3/l.2
PATENTEU 3.8711132 sum 2 OF 2 FIG? . ARTIFICIAL HYDRAULIC ANKLE JOINT The present invention relates to an artificial ankle joint with an articulate connection between the foot part and the lower leg part of an artificial leg and provided with a damping device hinged, on the one hand, to the foot part and, on the other hand, to the lower leg part, which device comprises two or more hydraulic cylinders connected by connection conduits and each cylinder being provided with a piston.
Known artificial ankle joints of this kind have the disadvantage that on account of the high pressures occurring in the pressure chambers of the hydraulic cylinders, problems as to the tightness arise, which lead to the gradual loss of hydraulic liquid. Consequently after a short time there is a play between the moveable parts, which impairs the usability of the prosthesis. A further problem in known artificial ankle joints is the connection of the foot part with the lower leg part, which has hitherto been achieved by connecting-rod joints, which however take up much space, are heavy and technically complicated.
Other problems of known artificial ankle joints result from the temperature dependence of the hydraulic medium, as the viscosity properties vary strongly with the temperature.
The invention aims at avoiding the above mentioned difficulties and disadvantages and sets the task of providing an artificial ankle joint, in which the hydraulic medium is automatically replenished; in which the connection between the lower leg part and the foot part is achieved in a technically simple and reliable manner and which is widely independent from temperature fluctuations.
The aims of the invention in an artificial ankle joint of the above described type are achieved in that the pistons are hollow, the hollow chambers are filled with storage oil and pressure-balancing channels being in contact with the surrounding atmosphere lead to the upper end of the hollow chambers, wherein a springloaded snifting valve is provided between the pressure chamber of the hydraulic cylinder, respectively the hollow chamber of the piston, preferably in the bottom part of the latter.
Preferably the lower leg part is provided with two rollers of equal diameter, arranged symmetrically in relation to the joint, which rollers are connected by a tension spring with the pistons of two equally dimensioned hydraulic cylinders arranged parallel, each piston being held in contact with the rollers by the tension springs.
Suitably the pistons are supported by means of a tappet on the rollers, the tappets having roll-off surface acting against the roller surfaces.
According to a preferred embodiment of the invention throttle valves with obstacles for ensuring a permanently turbulent flow are installed in the connection conduits of the hydraulic cylinders.
The subject of the invention will now be described in more detail by way ofexample with reference to the accompanying drawings.
FIG. I is a vertical section through the artificial ankle joint and FIG. 2 is a section along line "-11 of FIG. 1.
According to FIG. I the artificial ankle joint, comprises, according to the invention, two cylinders 2 and 3 borne in a common housing and having parallel axes, in which cylinders pistons 4 and 5 are guided. The pressure chambers of the cylinders are connected with each other by connection conduits 6, 7 (FIG.,2) which conduits are bored into the control block 8. which is flanged to the upper side of the housing. In the connection conduits 6, 7 throttle means are provided. The housing 1 is connected, on the one hand, with the foot part 10 via the joint 11 and, on the other hand, with the lower leg part 12 via the screw 13. The two axially parallel hydraulic pistons 4, 5 of equal size are provided with tappets 14, 15, which are supported by rollers or rolls 16, 17 respectively of equal diameter arranged symmetrically in relation to the axis of the joint 11. Tension springs 18, 19 which partly surround the rol lers, are secured to the pistons, so that the pistons are always kept in their lowest position and the bottom surface of the tappet is pressed against the peripheral surface of the rollers. Thus the bottom surfaces of the tappets roll off the peripheral surfaces of the rollers and a connecting-rod-type movement is imitated.
The pistons 4, 5 are hollow, the hollow chambers serving as storage containers for hydraulic liquid. They are filled with hydraulic liquid almost as far as the upper end (which is however not illustrated for the sake of better clarity). From these storage chambers hydraulic liquid is supplied, which is partly consumed during use in any hydraulic device for lubrication. For the purpose of supplementing the hydraulic liquid a pressure-balancing tube 20 is arranged in each piston, which tube is in contact with the surrounding atmosphere and reaches almost as far as the upper end of the chamber of the piston. At the front-side of the piston a snifting valve 21 is installed, which reaches close to the bottom of the piston. In the tube a valve body 26 is guided, on which a weak pressure spring 25 acts, which valve body is downwardly sealed off by seals 27. Into the upper end of the tube a worm screw 28 is inserted, by means of which the prestress of the spring may be altered.
When by the occurence of a leakage or on account of the normal loss of hydraulic liquid caused by the use of the prosthesis there is a play between the tappet and a roller, underpressure is caused in the cylinder and the missing quantity of liquid is sucked from the hollow piston chamber via the snifting valve.
At the given conditions, i.e., at the existing piston velocities and at a low quantity of hydraulic liquid being in flow very small Reynolds figures occur in the connection conduits of the hydraulic cylinders. This may lead to difficulties, as the viscosity properties of the hydraulic medium vary on account of the dependence on the temperature. In order to avoid this disadvantage, throttle valves are provided according to the invention in a particular manner in the connection conduits so as to guarantee a permanently turbulent flow. This is illustrated in more detail in FIG. 2.
Each connection conduit, respectively each overflow channel 6, 7 in the control block 8, contains a reflux valve 29 and a throttle valve 30, the flow direction in the two conduits being different. The throttle valves consist of an axially displaceable, sealed off piston slider 31 and the screwed-in valve body 32, whose ring channel 33 in connection with the bore 34 facilitates the radial inflow of the oil.
Obstacles are denoted with 35, which cause the formation of a turbulent flow. The reflux valves have the form of simple ball valves; they consist of the ball 36, the screwed-in valve body 37 and the adjustable, sealed off stroke limitation 38. The hydraulic medium is introduced through the bore 39.
As on account of the resulting high local flow velocities the creation of the necessary resistance in the throttles might lead to underpressures, to a degassing of the oil, to foam development and consequently to noise generation, it is suitable to create part of the damping resistance by means of throttle orifices inserted into the bores 34 and 39.
What I claim is:
1. An artificial ankle joint comprising a foot part and a lower leg part, an articulate connection arranged therebetween and a damping device hinged, on the one hand to the foot part and, on the other hand to the lower leg part, which damping device comprises at least two hydraulic cylinders with pressure chambers connection conduits connecting the hydraulic cylinders hollow pistons having a bottom part and an upper end and hollow chambers filled with storage oil pressure-balancing channels in contact with the surrounding atmosphere and guided as far as the upper end of the hollow chambers a spring-loaded shifting valve arranged between the pressure chamber of each hydraulic cylinder and the hollow chamber of each piston.
2. The artificial ankle joint set forth in claim 1, wherein the spring-loaded snifting valve is arranged in the bottom part of the piston.
3. The artificial ankle joint set forth in claim 1, wherein the lower leg part is provided with two rollers of equal diameter arranged symmetrically in relation to the articulate connection, which rollers are connected by means of a tension spring with the pistons of two equally dimensioned hydraulic cylinders arranged parallel, the pistons being held in contact with the rollers by means of the tension springs.
4. The artificial ankle joint set forth in claim 3, wherein the pistons are supported by means ofa tappet on the rollers the tappets having roll-off surfaces acting against the roller surfaces.
5. The artificial ankle joint set forth in claim 1, wherein in the connection conduits of the cylinders throttle valves with obstacles for ensuring a permanently turbulent flow are installed. 1: l