Abstract:
For locking against rotation a piston on a piston rod, the piston having a peripheral groove and at least one radial through-hole to be positioned over a notch, a locking clip with a first straight end part and a curved part has a first end part extending through the radial hole in the piston and a part of the curved part of the locking clip rests in the peripheral groove when in a piston-locking position.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a device for locking a piston onto a piston rod, for example for a hydraulic or pneumatic cylinder. The invention also concerns a locking clip and a piston intended to be locked onto a piston rod by the locking clip. 
     There are a number of known solutions to how a piston can be locked onto a piston rod for a hydraulic or pneumatic cylinder. 
     DESCRIPTION OF THE RELATED ART 
     A known example is when the piston is threaded onto the end of the piston rod after which a hole is bored radially through the piston and the piston rod. Subsequently, a locking means in the shape of a cylindrical pin is pressed into the hole, whereby relative rotation between the piston and the piston rod is prevented. 
     In another known example a two-piece piston is used where both parts of the piston are threaded onto a piston rod. The outer part is provided with a number of axially directed screws which are screwed against the other part so that an axially directed force occurs in the threaded joint between the piston rod and the piston parts. In this way a firm locking of the piston parts onto the piston rod is achieved. 
     When changing the packing in a cylinder end through which the piston rod passes, the piston, because of the design of the piston rod, must be dismantled from the piston rod. In big cylinders this dismantling must sometimes be performed in uncomfortable circumstances, e.g. in the field, wherefore a complicated locking device which consists of a number of small parts is unsatisfactory. 
     Large forces and load changes act between the piston and the piston rod. Because of the elasticity of the material of the piston and the piston rod, the large forces can produce a relative movement between the piston and the piston rod in the axial direction. If the locking means of the locking device then takes up the whole of the force which acts between the piston and the piston rod, the locking device will be destroyed because of fatigue. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to produce a cheaper, better and more secure device for locking against rotation a piston onto a piston rod, which device consists of only a small number of components. 
     A further object is to achieve a device for locking a piston onto a piston rod, which device permits assembly and disassembly with simple tools and manipulations. 
     Yet another object is to achieve a device for locking a piston onto a piston rod which device is designed to cope with large forces and load changes. 
     These objects are achieved through the piston being equipped with at least one radial through-hole which is intended to be positioned over a groove in the piston rod and by a locking clip, which comprises a first straight end part and a curved part, being intended to have its first end part extend through the radial hole in the piston and into the groove in the piston rod, in addition to which the piston is provided with a peripheral groove in which a part of the curved part of the locking clip is intended to rest in a piston-locking position. 
     Owing to the curved part of the locking clip describes an arc which is less than 180°a simple mounting of the locking clip on the piston and the piston rod is made possible. 
     The piston comprises a circular body with an axial through-hole for the introduction of a piston rod and a circumferential groove which is in the same radial plane on the piston as the radial hole. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described below in more detail by means of an embodiment with reference to the appended drawings, in which: 
     FIG. 1 shows an end view of a piston which is mounted on a piston rod and fastened by means of a first embodiment of a locking clip according to the invention; 
     FIG. 2 shows a lateral view of the device in FIG. 1; and 
     FIG. 3 shows a lateral view of a second embodiment of the locking clip according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 show a piston 1 which is equipped with a threaded, axial through-hole 3 and which is screwed onto a threaded part of a piston rod 5. In order to prevent the piston 1 from loosening, i.e. unscrewing, from the piston rod 5, a first end part 7 of a locking clip 10 is introduced into a radial through-hole 15 in the piston 1. The first end part 7 of the locking clip 10 is straight and extends through the radial hole 15 in the piston 1 and into one of three notches 20 which are formed in the piston rod 5. The notches 20 are preferably shaped like elongated grooves which extend in the axial direction in an end part 25 of the piston rod 5. 
     The notches 20 are evenly distributed around the periphery of the end part 25 in order to cooperate and coincide with the radially directed hole 15 in the piston in a desired position between the piston and the piston rod. Owing to the notches 20 being shaped as axially directed longitudinal grooves, the first end part 7 of the locking clip 10 will not take up any forces in the axial direction, but only in the rotational direction. 
     The piston rod 5 has a threaded portion 30 which is adjacent to the end part 25 which has the notches 20. The threaded position 30 is intended to cooperate with the thread in the axial hole 3 in the piston 1. Being adjacent to the threaded portion 30 is a region which comprises a shoulder surface 35 which is intended to cooperate with a corresponding shoulder surface 40 on the piston 1. This co-operation occurs during the mounting of the piston 1 on the piston rod 5, when the piston 1 is screwed onto the piston rod 5 so far that the shoulder surfaces 35, 40 about each other. Subsequently, the piston 1 is unscrewed backwards so that the radial hole 15 in the piston 1 coincides with the first reached groove in the piston rod 5 that it meets. 
     As well as the first straight end part 7, the locking clip 10 also comprises a curved part 45 which is intended to cooperate with a circumferential groove 50 in the periphery of the piston. The locking clip 10 preferably has a circular cross-section with a radius which can correspond with the cross-sectional radius of the circumferential groove 50. The curved part 45 of the locking clip 10 can comprise one or more bent parts. In the embodiment according to claim 1, the locking clip 10 has a first, a second and a third bend 55, 60 resp. 65. In the locked position of the locking clip, parts of the first and second bends 55 resp. 60 are outside the circumferential groove 50. This permits dismantling of the locking clip 10 by a dismantling tool, e.g. a screw-driver, being introduced into a free space 66 between the locking clip 10 and the piston 1. The tool is introduced until it comes into contact with a first circumferential shoulder 70 (FIG. 2), whereafter the locking clip 10 is prized out of the circumferential groove 50 by leverage. When the locking clip 10 has partially been prized out of the circumferential groove 50, it may become necessary to change the purchase chase of the tool, whereby it is placed against a second circumferential shoulder surface face 75 on the piston 1, after which the disassembly can be completed. 
     The first, second and third bent parts 55, 60 resp. 65 have respectively a first, a second and a third bending radius. The second bending radius is greater than the third bending radius, and the third bending radius is greater than the first bending radius. According to the embodiment in FIG. 1, it is only the third bent part 65 which is in contact with the circumferential groove 50. It is, however, conceivable that also the second bent part 60 can be in contact at least partially with the circumferential groove 50. 
     The locking clip 10 has essentially a C-shape with an angle α of less than 180°. 
     FIG. 3 shows an alternative embodiment of a locking clip 10&#39; according to the invention. The locking clip 10&#39; comprises, as well as a first straight end part 7, a curved part 45 and a second straight end part 80. The curved part 45 comprises a first, a second and a third bent part 55, 60 resp. 65 with respectively a first, a second and a third bending radius, wherein the first bent part 55 is adjacent to the first end part 7, the third bent part 65 is adjacent to the second end part 80 and the second bent part 60 is arranged between the first and third bent parts 55 and 65. 
     The second bending radius is greater than the third bending radius, and the third bending radius is greater than the first bending radius. The first end part 7 has a first end surface 85 and the second end part 80 has a second end surface 90, wherein the normal of the respective end surfaces 85, 90 cut each other at a point. The locking clip 10&#39; has essentially a C-shape which describes an angle β of less than 180°. 
     During assembly of the locking clip 10, 10&#39;, the first straight end part 7 is introduced into the radially directed hole 15 in the piston 1 and into one of the notches 20 in the piston rod 5, with the clip lying essentially coincident with an axial plane through the centre line of the radial hole 15, whereafter the locking clip 10, 10&#39; is swung around the centre axis of the radial hole 15. This is only possible in the case that the curved shape of the locking clip 10, 10&#39; is less than 180°. By applying a mounting tool, e.g. a screwdriver, between the locking clip 10, 10&#39; and the circumferential groove 50 in the piston 1, the locking clip 10, 10&#39; can be prized into the circumferential groove 50. 
     The locking clip 10, 10&#39; is preferably manufactured from spring steel but also other materials are conceivable, such as stainless steel, aluminium or polymer materials. The cross section of the locking clip 10, 10&#39; is preferably round. Another cross-section is also conceivable. 
     The above embodiments concern a locking clip for locking a piston onto a piston rod. It is also conceivable to lock two or more randomly shaped bodies in relation to each other by means of a locking clip according to the invention. Such bodies could for example be formed of an internally threaded ring element on an externally threaded pin or spindle, such as a screw and nut.