A DEVICE AND METHOD FOR FIXING A PISTON OR A PISTON ROD ATTACHMENT TO A PISTON ROD

Abstract: The invention relates to a device for fixing a piston (1), or a piston rod attachment, to a piston rod (5), one of the piston (1) and the piston rod (5) having a hole (2) running in its axial direction, and the other of these having a portion designed for being received by the hole (2) for connection of the piston (1) and the piston rod (5). The device comprises an elongate locking means (10), at least one first opening (8a, 8b) in the piston and at least one second opening (9) in the piston rod (5), which openings (8a, 8b, 9) in the piston rod (5), which openings (8a, 8b, 9) extend in a different direction from said axial direction and are designed for receiving the locking means (10) for the purpose of bringing about said fixing. The elongate locking means (10) has a greater extent in its transverse direction, along at least a part of said means, than the extent of at least one of said openings (8a, 8b, 9) in its transverse direction, along at least a part thereof, for form locking between the locking means (10) and the opening. The invention also relates to a method for said fixing.

Description: A device and method for fixing a piston or a piston rod attachment to a piston rod FIELD OF THE INVENTION The present invention relates to a device for fixing a piston or a piston rod attachment to a piston rod, one of the piston or the piston rod attachment and the piston rod having a hole running in its axial direction and the other of these comprising a portion designed for being received by the hole for connection of the piston or the piston rod attachment and the piston rod, the device comprising an elongate locking means, at least one first opening in the piston or the piston rod attachment and at least one second opening in the piston rod, which openings extend in a different direction from said axial direction and are designed for receiving the locking means for the purpose of bringing about said fixing. The invention can, for example, be applied to both a hydraulic and a pneumatic cylinder. The invention also relates to a method for said fixing. PRIOR ART The specification US 6,032,569 describes a device for fixing a piston to a piston rod. The piston is provided with a threaded axial through-hole intended for receiving a corresponding externally threaded portion of the piston rod. The piston is also provided with a portion of reduced diameter, through which said hole extends. This narrower portion is provided with a number of radial through-openings, which open into a groove extending in the circumferential direction. The piston rod is, close to its end, provided with a number of axially running grooves. For fixing the piston on the piston rod, the piston rod is screwed into the piston in such a manner that one of the openings coincides with one of the axial grooves. The device also comprises a locking clamp which is in principle C- shaped. One end portion of the clamp projects from one end of the C shape essentially in the direction toward the other end of the clamp. The locking clamp also has such resilient properties that the ends of the clamp can be positioned at different spacings relative to each other. When the piston has been screwed to the intended location on the piston rod, the locking clamp is clamped firmly in such a manner that said end portion of the clamp passes through the opening in the narrower portion of the piston and down into the groove of the piston rod. The clamp is thus clamped firmly in the groove running in the circumferential direction around the portion of reduced diameter. In this way, the piston is fixed rotationally relative to the piston rod. SUMMARY OF THE INVENTION A first object of the invention is to produce a construction which is simple and cost-effective in production terms for fixing a piston or a piston rod attachment to a piston rod. This object is achieved by virtue of the elongate locking means has a greater extent in its transverse direction, along at least a part of said means, than the extent of at least one of said openings in its transverse direction, along at least a part thereof, for form locking between the locking means and the opening. Only a simple tool, for example a hammer, is needed for putting the locking means in place. With this type of construction, a strong fixing device, which it is possible to assemble rapidly and easily, is obtained at a low production cost. According to a preferred embodiment, the piston or the piston rod attachment is provided with said hole, which is at least partly threaded, and the piston rod is provided with said portion intended for being received in the hole of the piston, which portion comprises a threading corresponding to the threading of the hole. This connection type is reliable and cost-effective from the point of view of manufacture. According to another preferred embodiment, the first opening has a longitudinal extent at least essentially at right angles to the axial direction of the piston or the piston rod attachment and is also open in the axial direction thereof. In other words, the first opening consists of a slot or a groove and is therefore open in the axial direction of the piston or the piston rod attachment. Such an opening can be produced in a number of different ways, inter alia by casting or by milling, which allows scope for simplified and thus cost- effective manufacture. According to another preferred embodiment, the piston or the piston rod attachment comprises a portion of reduced diameter projecting in its axial direction, and the first opening extends through this portion. The piston or the piston rod attachment also comprises at least one set of two of said first openings, which extend through the body of the projecting portion, and the longitudinal direction of which extends along an at least essentially straight line. Opportunities are thus afforded for fixing the locking means at two points on the piston or the piston rod attachment, which provides increased functional reliability. According to another preferred embodiment, at least one of the piston or the piston rod attachment and the piston rod comprises a shoulder intended for interaction with a portion of corresponding design of the other of the piston or the piston rod attachment and the piston rod for the purpose of limiting the axial movement of the piston rod relative to the piston or the piston rod attachment. By virtue of, during connection of the piston or the piston rod attachment and the piston rod, first bringing these together so that said shoulder is brought into contact, and then moving the piston or the piston rod attachment relative to the piston rod in another direction so that the shoulder no longer makes contact and in this position making said first and second openings coincide and inserting the locking means into these openings, the axial forces which arise when the piston works in the cylinder will be taken up by the threads of the piston and/or the piston rod attachment and the piston rod and not by the locking means. This reduces the risk of fatigue damage. Another object of the invention is to bring about a method for fixing a piston or a piston rod attachment to a piston rod, which allows simplified mounting in relation to the known art. A further object of the invention is to bring about a method for fixing a piston or a piston rod attachment to a piston rod, which affords opportunities for cost-effective manufacture of the parts necessary for fixing. These objects are achieved by a method according to Claim 13. Further advantages and advantageous embodiments of the invention emerge from the description below and the remaining patent claims . BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in greater detail below, with reference to the embodiment shown in the accompanying drawings . Figure 1 shows a partly cut-away perspective view of the device according to the invention for fixing a piston to a piston rod in the unfixed state. Figure 2 shows a partly cut-away perspective view of the device according to the invention for fixing a piston rod attachment to a piston rod in the unfixed state. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION Figure 1 illustrates a piston 1 with a through-hole 2 in the axial direction. The hole 2 is provided with a threaded portion 3 intended for receiving a corresponding threaded portion 4 of a piston rod 5. The piston 1 is provided with a shoulder 6, and the piston rod 5 is provided with a corresponding shoulder 7, the purpose of which shoulders is to limit the axial movement of the piston rod relative to the piston during connection of these. The piston 1 is also provided with two sets of two first openings 8a, 8b, which openings extend essentially at right angles to the axial direction 12 of the piston and are open in the axial direction of the piston 1. The two openings 8a, 8b in each of the sets have a longitudinal direction which extends along an at least essentially straight line. The piston rod 5 is provided with a second opening 9 which extends essentially at right angles to the axial direction 12 of the piston rod and is a through-opening. Figure 1 also shows a cylindrical locking means 10 which, as described below, is intended to be fitted after the piston 1 has been connected to the piston rod 5. An essentially cylindrical design of the locking means 10 makes possible simple and cost-effective production. In order to make form locking possible, the locking means 10 has a slightly greater diameter than the second opening 9. As the second opening 9 is a through-opening, removal of the locking means 10 is facilitated, which is an advantage during, for example, maintenance work. With the second opening in the piston rod being a through-opening, a locking means of a length roughly corresponding to the reduced diameter of the projecting portion of the piston can be used. Owing to the fact that the length of the locking means corresponds roughly to the reduced diameter of the piston, centering of the locking means in the radial direction of the piston is not critical as there is no risk of said locking means wearing against the inner surfaces of the cylinder on account of slight miscentering. For the sake of completeness, a cylinder 11, in which the piston 1 is intended to perform its work, is also shown in Figure 1. The piston 1 comprises a portion 13 of reduced diameter projecting in its axial direction, to which portion the first openings 8a, 8b are assigned. The hole 2 also extends through this portion of reduced diameter. Machining of that of the surface of the piston 1 which comes into contact with the inner surface of the cylinder 11 during work is thus avoided. There is no risk, moreover, that the locking means 10 will wear against the inner surfaces of the cylinder on account of a slight miscentering of the locking means 10 in the radial direction of the piston. The method for fixing the piston 1 to the piston rod 5 is performed by these first being interconnected via a relative movement in said axial direction 12, their threaded portions 3, 4 interacting with one another. To be precise, the piston rod 5 is screwed into the piston 1 until the shoulders 6, 7 are brought into contact with one another. The piston 1 and the piston rod 5 are then moved away from one another via an opposite relative movement until one of the sets of the first openings 8a or 8b coincides with the second opening 9, after which the locking means 10 is brought down into said first and second openings 8a, 9 or 8b, 9. The piston 1 and the piston rod 5 are then fixed and thus prevented from moving axially or rotating relative to one another. The component parts 1, 5, 10 required for performing the method can be manufactured in a cost- effective manner, and no form of finishing is therefore necessary. This makes the method rapid and simple. As described above, use is made of only one of the two sets of the first openings 8a, 8b when the piston 1 is fixed to the piston rod 5. A sealing position (not shown) between the piston 1 and the piston rod 5 requires a certain axial positioning tolerance. A number of sets of openings 8a, 8b leads to greater accuracy in axial positioning. No torque tightening is required either. It lies within the scope of the following patent claims of course that the piston 1 be provided with a different number of said sets of openings 8a, 8b. Three and four sets are mentioned here by way of example . Figure 2 illustrates a piston rod attachment 101, here in the form of a piston rod lug with a through-hole 115 for receiving a pivot pin or the like. The piston rod attachment 101 comprises a hole 102 running in its axial direction. The hole 102 has a bottom and is provided with a threaded portion 103 intended for receiving a corresponding threaded portion 104 of the piston rod 5. The piston" rod attachment 101 is provided with a shoulder 106, and the piston rod 5 is provided with a corresponding shoulder 107, the purpose of which shoulders is to limit the axial movement of the piston rod relative to the piston rod attachment 101 during connection of these. The shoulder 106 of the piston rod attachment 101 is provided in said hole 102. The piston rod attachment 101 is also provided with two sets of two first openings 108a, 108b, which openings extend essentially at right angles to the axial direction 112 of the piston rod attachment 101 and are open in the axial direction thereof. The two openings 108a, 108b in each of the sets have a longitudinal direction which extends along an at least essentially straight line. The piston rod 5 is provided with a second opening 109 which extends essentially at right angles to the axial direction 112 of the piston rod and is a through-opening. In order to make form locking possible, the locking means 10 has a slightly greater diameter than the second opening 109. As the second opening 109 is a through-opening, removal of the locking means 10 is facilitated, which is an advantage during, for example, maintenance work. The piston rod attachment 101 comprises a portion 113 of reduced diameter projecting in its axial direction, to which portion the first openings 108a, 108b are assigned. The hole 102 also extends through this portion of reduced diameter. The method for fixing the piston rod attachment 101 to the piston rod 5 is performed in a similar manner to that described above for connection of the piston 1 to the piston rod 5. This is therefore carried out by these first being interconnected via a relative movement in said axial direction 112, their threaded portions 103, 104 interacting with one another. To be precise, the piston rod 5 is screwed into the piston rod attachment 101 until the shoulders 106, 107 are brought into contact with one another. The piston rod attachment 101 and the piston rod 5 are then moved away from one another via an opposite relative movement until one of the sets of the first openings 108a or 108b coincides with the second opening 9, after which the locking means 10 is brought down into said first and second openings 108a, 109 or 108b, 109. The piston rod attachment 101 and the piston rod 5 are then fixed and thus prevented from moving axially or rotating relative to one another. The component parts 101, 5, 10 required for performing the method can be manufactured in a cost-effective manner, and no form of finishing is therefore necessary. This makes the method rapid and simple. As described above, use is made of only one of the two sets of the first openings 108a, 108b when the piston rod attachment 1 is fixed to the piston rod 5. A sealing position (not shown) between the piston rod attachment 101 and the piston rod 5 requires a certain axial positioning tolerance. A number of sets of openings 108a, 108b leads to greater accuracy in axial positioning. No torque tightening is required either. It lies within the scope of the following patent claims of course that the piston rod attachment 101 be provided with a different number of said sets of openings 108a, 108b. Three and four sets are mentioned here by way of example. The embodiment described is to be regarded as only a preferred example, and a number of further variants and modifications are possible within the scope of the following patent claims. For example, the shoulder 6; 106 can consist of the outer delimiting surface of the piston 1, or the piston rod attachment 101, in the axial direction, which faces the piston rod 5. Furthermore, the openings 8a, 8b; 108a, 108b in the piston 1 or, respectively, the piston rod attachment 101 can consist of holes in its wall, which means that they are no longer open in the axial direction of the piston. As far as the locking means 10 is concerned, it does not necessarily have to be cylindrical or be of the length illustrated in Figures 1 and 2. Other shapes, such as a polygonal cross-sectional shape, are also possible. As mentioned above, the form locking is not tied to the opening 9; 109. In other words, the first opening 8; 108 and/or the second opening 9; 109 can be adapted for form locking, or an interference fit as it is sometimes known, of the locking means 10. It is also possible to conceive of using two or more locking means . The locking means 10 can also, for example, have a conical shape, be cambered (that is to say comprise a bulging portion) , or comprise an indentation or a notch. The indented portion in such an indented locking means is intended to be compressed slightly during fitting and to exert pressure outwardly in the radial direction against the wall of the opening. The locking means 10 can also be referred to as a dowel or locking pin. Likewise, the invention is not limited to the openings 8a, 8b, 9; 108a, 108b, 109 having a circular or part- circular cross-sectional shape either, but they can have, for example, a polygonal cross-sectional shape. One or more of them can also have a rounded shape in its or their longitudinal direction. One or more of the openings can also have the shape of a cone or a truncated cone. According to another alternative, the hole 2 in the piston 1 does not have to be a through-hole but instead comprise a bottom. In such an alternative, the shoulders 6, 7 can consist of, for example, the end surface of the piston rod 5 and said bottom in the hole 2. According to a further alternative, it is possible to conceive of a reversed construction relative to Figure 1 and/or 2, where the piston rod 5, instead of the piston 1 or, respectively, the piston rod attachment 101, is provided with a hole 2; 102 intended for receiving a projecting portion of the piston 1 or the piston rod attachment 101. The threaded portion 3, 4; 103, 104 of the piston 1, or the piston rod attachment 101, and, respectively, the piston rod 5, is preferably roll-pressed and consists of what is known as a rolled thread. The screwed joint can thus take up great axial loads, the value and direction of which change frequently. The solution according to the invention is not, however, limited to such a rolled thread, but also includes other threads, such as a cut thread. In the embodiment shown in Figure 1, the threading of the hole 2 is assigned to that area of the hole 2 which extends through the projecting portion 13 of the piston. According to an alternative embodiment, the threading is assigned to an inner area of the hole and thus not to that part of the hole 2 which extends through the projecting portion 13.

Claims: PATENT CLAIMS 1. A device for fixing a piston (1) or a piston rod attachment (101) to a piston rod (5) , one of the piston (1) or the piston rod attachment (101) and the piston rod (5) having a hole (2, 102) running in its axial direction and the other of these having a portion designed for being received by the hole (2, 102) for connection of the piston (1) or the piston rod attachment (101) and the piston rod (5) , the device comprising an elongate locking means (10), at least one first opening (8a, 8b; 108a, 108b) in the piston or the piston rod attachment and at least one second opening (9; 109) in the piston rod (5) , which openings (8a, 8b, 9; 108a, 108b, 109) extend in a different direction from said axial direction and are designed for receiving the locking means (10) for the purpose of bringing about said fixing, characterized in that the elongate locking means (10) has a greater extent in its transverse direction, along at least a part of said means, than the extent of at least one of said openings (8a, 8b, 9; 108a, 108b, 109) in its transverse direction, along at least a part thereof, for form locking between the locking means (10) and the opening. 2. The device as claimed in claim 1, characterized in that the piston (1) or the piston rod attachment (101) is provided with said hole (2; 102) , which is at least partly threaded, and the piston rod (5) is provided with said portion intended for being received in the hole (2; 102) of the piston, which portion comprises a threading (4; 104) corresponding to the threading (3; 103) of the hole. 3. The device as claimed in claim 1 or 2, characterized in that the first opening (8a, 8b; 108a, 108b) has a longitudinal extent at least essentially at right angles to the axial direction of the piston (1) or the piston rod attachment (101) , and in that it is also open in the axial direction thereof. 4. The device as claimed in any one of claims 1-3, characterized in that the piston (1) or the piston rod attachment (101) comprises a portion (13; 113) of reduced diameter projecting in its axial direction, and in that the first opening (8a, 8b; 108a, 108b) extends through this portion. 5. The device as claimed in claims 2 and 4, characterized in that said threaded hole (2; 102) of the piston (1) or the piston rod attachment (101) extends at least partly through said projecting portion. 6. The device as claimed in claim 4 or 5, characterized in that the piston (1) or the piston rod attachment (101) comprises at least one set of two of said first openings (8a, 8b; 108a, 108b) , which extend through the body of the projecting portion, and the longitudinal direction of which extends along an at least essentially straight line. 7. The device as claimed in any one of claims 1-6, characterized in that the second opening (9; 109) is designed with a longitudinal direction at least essentially at right angles to the axial direction of the piston rod (5). 8. The device as claimed in any one of claims 1-7, characterized in that at least one of the piston (1) or the piston rod attachment (101) and the piston rod (5) comprises a shoulder (6, 7; 106, 107) intended for interaction with a portion (6, 7; 106, 107) of corresponding design of the other of the piston (1) or the piston rod attachment (101) and the piston rod (5) for the purpose of limiting the axial movement of the piston rod (5) relative to the piston (1) or the piston rod attachment (101) . 9. The device as claimed in any one of claims 1-8, characterized in that the locking means (10) has an at least essentially constant cross-sectional shape in its longitudinal direction. 10. The device as claimed in any one of claims 1-9, characterized in that the locking means (10) extends along an essentially straight line. 11. The device as claimed in any one of claims 1-10, characterized in that at least one of said openings (8a, 8b, 9; 108a, 108b, 109) has an at least essentially constant cross-sectional shape in its longitudinal direction. 12. The device as claimed in any one of claims 1-11, characterized in that the piston (1) is intended for a hydraulic cylinder (11) . 13. A method for fixing a piston (1) or a piston rod attachment (101) to a piston rod (5) , at least one first opening (8a, 8b; 108a, 108b) being formed in the piston (1) or the piston rod attachment (101) and at least one second opening (9; 109) being formed in the piston rod (5) in such a manner that their longitudinal directions differ from the axial direction of the piston (1) or the piston rod attachment (101) and, respectively, the piston rod (5) , the openings (8a, 8b, 9; 108a, 108b, 109) being designed for receiving an elongate locking means (10) for the purpose of bringing about said fixing, and the piston (1) or the piston rod attachment (101) being connected to the piston rod (5) via a relative movement between these in their axial direction, characterized in that the elongate locking means (10) has a greater extent in its transverse direction, along at least a part of said means, than the extent of at least one of said openings (8a, 8b, 9; 108a, 108b, 109) in its transverse direction, along at least a part thereof, and in that the locking means (10) is brought down into said openings for form locking between the locking means (10) and the opening after said relative movement. 14. The method as claimed in claim 13, characterized in that, during the relative movement, the piston (1) or the piston rod attachment (101) is moved relative to the piston rod (5) in a first direction until a shaped shoulder (6, 7; 106, 107) of at least one of the piston (1) or the piston rod attachment (101) and the piston rod (5) is brought into contact with a portion (6, 7; 106, 107) of corresponding design of the other of these, after which the locking means (10) is brought down into said openings (8a, 8b, 9; 108a, 108b, 109) . 15. The method as claimed in claim 14, characterized in that, after said shoulder (6, 7; 106, 107) has been brought into said contact, the piston (1) or the piston rod attachment (101) is moved relative to the piston rod (5) in a different direction, opposite to said first direction, until said openings (8a, 8b, 9; 108a, 108b, 109) coincide, after which the locking means (10) is brought down into said openings (8a, 8b, 9; 108a, 108b, 109) . 16. The method as claimed in any one of claims 13-15, characterized in that the first opening (8a, 8b; 108a, 108b) of the piston (1) or the piston rod attachment (101) is formed in such a manner that it has a longitudinal extent essentially at right angles to the axial direction of the piston (1) or the piston rod attachment (101) , and in that it is also open in the axial direction thereof. 17. The method as claimed in claim 16, characterized in that the piston (1) or the piston rod attachment (101) is formed with a portion of reduced diameter projecting in its axial direction, and in that the first opening (8a, 8b; 108a, 108b) is formed through this portion. 18. The method as claimed in claim 17, characterized in that at least one set of two of said first openings (8a, 8b; 108a, 108b) is formed through the body of the projecting portion in such a manner that their longitudinal direction extends along an at least essentially straight line. 19. The method as claimed in any one of claims 13-18, characterized in that the first and second openings (8a, 8b, 9; 108a, 108b, 109) are formed in the piston (1) or the piston rod attachment (101) and, respectively, the piston rod (5) before the piston (1) or the piston rod attachment (101) and the piston rod (5) are interconnected.

Inventors: SCHOELLIN JAN-OVE, SCHOELLIN, JAN-OVE
Applicants: SCHOELLIN JAN OVE, VOLVO WHEEL LOADERS AB, SCHOELLIN, JAN-OVE
Application year: 2001
Main classification: F16J1
IPC codes: F16J1