Cylinder-and-piston arrangement and method of manufacturing the same
BACKGROUND OF THE INVENTION 
     The present invention relates to a cylinder-and-piston arrangement in which a piston slidably arranged in a cylinder has a piston rod projecting with one end through an opening in an end wall of the cylinder and in which a fork-shaped member is connected by welding to the projecting end of the piston rod. 
     In a known arrangement of this type, the fork-shaped member is a forged part which is provided at its bottom with a blind bore into which a portion of reduced diameter of the piston rod extends. The piston rod and the fork-shaped member are thus arranged along a common axis. The piston rod and the fork-shaped member are further connected by an annular weld seam extending circumferentially of the piston rod. This known construction has the disadvantage that it is relatively expensive, especially since the fork-shaped member is a forged part and the weld seam requires additional welding material. 
     A cylinder-and-piston arrangement is further known in which the cylinder comprises a central tubular section and two opposite cylinder heads connected to the tubular section of the cylinder by friction welding. Connecting nipples for feeding pressure medium to opposite sides of the piston into the cylinder are also connected by friction welding to the tubular section of the cylinder. For connecting the fork-shaped member to the free end of the piston rod, the latter is provided at its free end with an external screw thread engaging an internal screw thread in the fork-shaped member, or the fork-shaped member is connected by means of a snap ring to the piston rod. The fork-shaped member itself is formed by machining the various faces thereof. This construction is likewise relatively expensive and can be produced only by time-consuming machining operations. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a cylinder-and-piston arrangement of the aforementioned kind which avoids the disadvantages of such cylinder-and-piston arrangements known in the art, as well as a method of manufacturing such a cylinder-and-piston arrangement which is simpler and less expensive than such methods known in the art. 
     This is obtained according to the present invention in that the fork-shaped member is constituted by a bent flat strip of steel and connected to the projecting end of the piston rod by a friction weld. This will result in a cylinder-and-piston arrangement which can be constructed in a very simple, inexpensive manner in which the fork-shaped member is simply bent from a flat steel strip and fixedly connected to the end of the piston rod by a friction weld. Expensive machined parts and additional welding material are avoided in the construction according to the present invention and time-consuming additional manufacturing and finishing steps become unnecessary. In addition, since the full cross section of the piston rod is fixedly connected by the friction weld to the fork-shaped member, greater forces can be transmitted between the fork-shaped member and the piston rod than can be transmitted in arrangements in which the piston rod is connected to the fork-shaped member by an annular weld seam. 
     An especially advantageous construction is derived when the fork-shaped member is provided in its curved bottom part with a planar circular welding face produced by material deforming technique, that is without a cutting or material removing operation. The fork-shaped member in this construction can have two leg portions which are relatively closely arranged to each other, even though a relatively thick, flat strip may be used for its production. 
     The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a partial, partially sectioned side view of the cylinder-and-piston arrangement according to the present invention; 
     FIG. 2 is a partial, partially sectioned top view of the fork-shaped member and part of the piston rod; 
     FIG. 3 is a longitudinal cross section through the fork-shaped member; 
     FIG. 4 is a transverse cross section through the fork-shaped member; and 
     FIG. 5 is a bottom view of the fork-shaped member, in which in FIGS. 3 - 5 the fork-shaped member is shown before its connection to the piston rod. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 partially illustrates a hydraulic cylinder 10 in which a piston P is arranged and in which the cylinder head 11 is provided with a connection 12 for feeding pressure fluid into and out from the cylinder. A piston rod 13 projects in a usually sealed manner, not shown in the drawing, beyond the cylinder head 11 and a piston P is fixedly connected, in any known manner, to the inner end of the piston rod 13. The piston rod 13 carries at its end 14, projecting beyond the cylinder head 11, a fork-shaped member 15 connected by a friction weld, as will be described later on in detail, to the end 14 of the piston rod. The fork-shaped member 15 has two parallel legs 17 and 18 which are connected to each other by a curved bottom part 19 and which is provided in its legs with two coaxial bores 16. The fork-shaped member 15 is bent from a strip of flat steel. In its bottom part 19 there is provided a planar circular welding face 21 which is surrounded by a rim 22 having an inner conical surface. 
     This rim 22 will assure that during the friction welding, a friction welding bead 23, forming on the free end of the piston rod, will curl against the circumferential surface of the latter in the region of the free end so that finishing of the friction weld at its peripheral region 24 becomes unnecessary. The piston rod 13 itself has at its free end 14 a planar welding face 25 of a diameter which is smaller or equal to the diameter of the welding face 21 at the bottom part 19 of the fork-shaped member. 
     The above-described construction is produced in the following manner: 
     A flat strip of steel is bent into fork shape and during such bending, or immediately thereafter, the planar welding face 21 at the bottom part 19 of the fork-shaped member is formed by material deforming technique, that is by a pressing or a hammering operation without removing material from the fork-shaped member. This formation of the welding space 21 may be carried out while the fork-shaped member is in cold or in hot condition and, due to a suitable shape of the forming member, there will be formed a rim 22 of conical inner surface about the planar circular welding face 21. In this way it is possible to form the welding face 21 planar and of relatively large diameter, even if the legs 17 and 18 of the fork-shaped member are relatively close to each other and the bottom portion 19 thereof is extensively curved. The piston rod 13 with its planar welding face 25, or the fork-shaped member with its planar welding face 21 is then rotated at high speed about its axis and the two parts are pressed against each other with considerable force. Due to the relative movement of one of the aforementioned members through a predetermined time, the necessary heat for welding the two members to each other is thus produced, so that, after the rotating member is arrested while the two members are pressed with considerable force against each other, the piston rod is connected by a friction weld over its whole cross section with the fork-shaped member. The thereby resulting friction weld bead 23 on the piston rod will curl against the peripheral surface of the end 14 of the latter so that a finishing operation at the portion 24 of the friction weld will not be necessary. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of cylinder-and-piston arrangements, differing from the types described above. 
     While the invention has been illustrated and described as embodied in a cylinder-and-piston arrangement, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.