HYDRAULIC ASSEMBLY

Abstract: A hydraulic assembly (41) includes a group of hydraulic cylinders (30-33) connected in series. The group includes at least three consecutive cylinder sets or stages (I-IV), at least in every stage (II-IV), which follows after the first stage (I), in relation to one end of said group, two parallel hydraulic cylinders (31-33) being included, which are disposed outside the cylinders of a preceding stage. The piston rods (31A, 32A) of the as described consecutive hydraulic cylinder stages are alternatingly turned forwards towards one end of the group and backwards towards the other end respectively. Between at least two of the consecutive cylinder pairs is connected a clamp-shaped yoke (36) having connection elements (37), which connect the piston rods (31A) in the one of said cylinder pairs to the piston rods (32A) in the other one of said cylinder pairs.

Description: Hydraulic Assembly The Technical Field The present invention relates to a hydraulic assembly in¬ cluding a group of hydraulic cylinders connected in series. The Background of the Present Invention In hydraulic assemblies having a large total stroke length telescopic cylinders are conventionally used. The latter usually are single-acting. Consequently, in order to per¬ form reciprocating motions having a certain stroke length two cylinders are required, which for several reasons is a disadvantage, considering i.a. the costs. Also, telescopic cylinders usually do not work with the same speed in the various cylinder elements, which sometimes is a disadvan¬ tage, too. However, there are available so called same speed cylinders, but they are extremely expensive. E.g. EP 0056928, JP 57-178941 (Patent Abstract of Japan, Vol. 7, no. 24, p 189) , JP 58-1823324 (Patent Abstract of Japan, Vol. 8, No. 26, p 273) relate to methods of connecting two hydraulic cylinders to each other or hydraulic cylinder pairs after each other, so that they form a group of hyd- raulic cylinders connected in series. In this way the to¬ tal stroke length can be doubled. However, in case even larger stroke lengths of a hydraulic assembly are required, which assembly can be contracted to a much shorter total length, said known constructions do not offer any solution. A Brief Description of the Present Invention The object of the present invention is to produce a hydrau¬ lic assembly, which can be expanded to several times its length in its contraction phase, i.e. when the hydraulic rods are in their minus positions. Another object of the present invention is to be able to use hydraulic cylinders of standard design in order to attain cost savings. These and other objects can be achieved by having the group in¬ clude at least three consecutive cylinder sets or stages, in at least each stage, which follows the first stage in relation to one end of the group, two parallel!, hydraulic cylinders being included, which are disposed outside the cylinders in the preceding stage, by having the piston rods in the consecutive as described hydraulic cylinder stages alternatingly turned forward towards one end of the group and backwards towards the other end of the group respecti¬ vely, and by having connected between at least two of the consecutive cylinder pairs a clamp-shaped yoke having con¬ nection elements, which connect the piston rods of one of said cylinder pairs with the piston rods of the other one of said cylinder pairs. By means of a hydraulic assembly, constructed in this manner, very large stroke lengths can be achieved and at the same time a small length of the contracted hydraulic package. When the hydraulic package is compressed, i.e. when the pistons are in their minus positions, the cylinders and said yoke preferably form a dense hydraulic package, the connection elements of the yoke being disposed between the adjacent consecutive cylinders, which are connected to each other by means of the yoke, the cylinders abutting against sliding surfaces of said connection elements. The hydraulic assembly can be mounted on and slide on a plane surface, which normally is horizontal or inclined. Also, it is possible to place the assembly in a vertical position, but in this instance guides are used for the assembly on its two "plane sides", i.e. on mutual sides of a plane through the symmetry axes of the hydraulic cylinders. Additional characterizing features and advantages as to the present invention are stated in the subsequent patent claims and the following description of a preferred embodi¬ ment. A Brief Description of the Drawings In the following description of a preferred embodiment re¬ ference is made to the accompanying drawings, in which: Figure 1 is a top view of the hydraulic assembly in its contracted position; Figure 2 shows the same hydraulic assembly, on a smaller scale, when it is maximally expanded; and Figure 3 is a more diagrammatic view of a cross section of the hydraulic assembly along line III-III in Figure 1. A Description of a Preferred Embodiment Hydraulic assembly 41 includes, according to the preferred embodiment, four hydraulic cylinder stages, I, II, III and IV, connected in series. In each stage II-IV two cylinders 31,32 and 33 respectively, connected in parallell, are in¬ cluded, which have the same length and the same piston area, Hydraulic cylinder 30 of first stage I has the same length as the rest but suitably its piston area is twice as large. As an alternative this stage also includes two cylinders, connected in parallell and identical with the rest. Piston rod 30A of first stage I is fastened in the middle of a fixed transverse beam 13 in one end of the assembly. The outside of cylinder 30 is by means of plates 34 welded to the two hydraulic cylinders 31 of the second stage. Piston rods 31A of this second cylinder stage II are turned in the opposite direction in relation to said piston rods 30A and are fastened to a yoke 36. Yoke 36 is clamp-shaped and is provided with connection elements 37, which consist of box girders, one on each side outside said second hydrau¬ lic cylinders 31. Elements 37 connect front fastening plate 38 of yoke 36 (to which plate piston rods 31A are connec¬ ted) to two rear fastening plates 39, which extend trans- versely outwards and are connected to piston rods 32A, which belong to third hydraulic cylinders 32 of said third stage III. Connection elements 37 are on their surfaces provided with low friction coatings 40. Cylinders 31 and 32 abut and slide against these low friction coatings 40, when hydraulic assembly 41 is expanded. Finally, in this hyd¬ raulic assembly are included hydraulic cylinders 33 of fourth stage IV. In the same way as cylinders 30 and 31 were connected to each other by means of plates 34, cylin¬ ders 32 and 33 are welded to each other via plates 35. Cy- linders 33 are turned in the opposite direction in relation to cylinders 32. Piston rods 33A are connected to each oth¬ er by means of a transverse beam 21 on an element, not shown, which is to be moved on a plane support 10, which assembly 41 is mounted on. All of the hydraulic cylinders 30-33 are double-acting. From a hydraulic pump, not shown, a first hydraulic tube 43 leads to the plus chamber of one of the two additional hydraulic cylinders 31 and from there via a first and a se- cond hydraulic duct 45 to the plus chamber of the first hydraulic cylinder 30. From the plus chamber of first cy¬ linder 30 a second hydraulic tube 46 leads to the plus chamber of one of fourth hydraulic cylinders 33 and from there to third, fourth and fifth hydraulic ducts 47-49 to the plus chambers of the remaining hydraulic cylinders 32 and 33 respectively. In an analogous way third and fourth hydraulic tubes 50,51 and sixth to tenth hydraulic ducts 52-56 are connected to and connecting the minus chambers of the same hydraulic cylinders 30-33. The described assembly 41 functions and works as follows. It is presumed that the hydraulic pistons of all of cylin¬ ders 30-33, to start with, are in their minus positions, Figure 1, so that hydraulic assembly 41 is maximally cont- racted. When hydraulic oil is fed through first hydraulic tube 43, hydraulic rods 30A-33A are pushed outwards, so that the system of cylinders and piston rods increasingly is shaped as an equally sided pointed triangle, its point being po¬ sitioned in fixed beam 13 and its base being positioned in the movable beam 21. During the forward push movement cylin¬ ders 31 and 32 slide against low friction coatings 40 on connection elements 37 of yoke 36. This contact and sliding is important for the stiffness of the construction as well as the triangular force system, which has a stabilizing in¬ fluence and contributes to a prevention of the creation of a drawer effect, since the element, which is pushed along, is pushed along between two lateral walls. When assembly 41 is to be brought together again, hydraulic oil is fed in the same way as during the contraction stroke but in the present case to the plus chamber of cylinders 30-31 via connection tube 43. That element, which is con- nected to beam 21, is in this instance fed with a regular speed backwards towards the starting position.

Claims: Claims : 1. A hydraulic assembly including a group of hydraulic cylinders connected in series, c h a r a c t e r i z e d in that said group (41) includes at least three consecu¬ tive cylinder sets or stages I-IV, at least in every stage (II-III) , which follows after the first stage (I) in re¬ lation to one end of the group, two parallell hydraulic cylinders (31-33) being included, which are disposed out- side the cylinders of a preceding stage, that piston rods (31A,32A) of the as described consecutive hydraulic cylin¬ der stages are alternatingly turned forwards towards one end of said group and backwards towards the other end res¬ pectively and that between at least two of said consecutive cylinder pairs is connected a clamp-shaped yoke (36) having connection elements (37) , which connect the piston rods (31A) in one of said cylinder pairs to the piston rods (32A) in the other of said cylinder pairs. 2. An assembly according to claim 1, c h a r a c t e ¬ r i z e d in that the cylinders (30-33) and yoke (36) form a densely brought together hydraulic package (41) , when the pistons and the piston rods (30A-33A) are in their minus positions , i.e. are maximally pushed into the cylinders, connection elements (37) of the yoke be¬ ing disposed between the adjacent consecutive cylinders, which are connected to each other by means of the yoke and that the cylinders then abut against sliding surfaces (40) on said connection elements.

Inventors: BRUNER HASSE, PERSSON LARS-INGE, BRUNER, HASSE, PERSSON, LARS-INGE
Applicants: RIPPELTON NV, RIPPELTON N.V.
Application year: 1987
Main classification: F15B15
IPC codes: A01D90