GB1600081A

GB1600081A - Piston/cylinder assemblies

Info

Publication number: GB1600081A
Application number: GB11576/78A
Authority: GB
Original assignee: Festo Maschinenfabrik Gottlieb Stoll Firma
Current assignee: Festo Maschinenfabrik Gottlieb Stoll Firma
Priority date: 1977-04-27
Filing date: 1978-03-23
Publication date: 1981-10-14
Also published as: FR2389019B1; CH633864A5; DE2718639C2; IT1093921B; FR2389019A1; DE2718639A1; SE7804755L; IT7821661A0; ES469171A1

Abstract

In a pneumatic or hydraulic, single-acting piston/cylinder unit, a return spring (27) is provided between the piston (17) and the cylinder (12) closed off at one side by a cylinder lid (13). As viewed in cross-section, the piston (17) and the cylinder (12) form an elongated and narrow rectangle, and the return spring (27) is a corresponding helical spring wound in a square profile. This results in a narrow, slim construction which is especially suitable for fitting in precision mechanical equipment on account of the small space requirement and is distinguished by a large guiding surface and precise guidance. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO PISTON/CYLINDER ASSEMBLIES (71) We FEsTo-MAscHINENFAsRIK GOTTLIEB STOLL, a Company organised under the laws of the Federal Republic of Germany of Ulmer Strasse 48, 73 Esslingen/N, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with improvements in or relating to piston/cylinder assemblies.

Widely used piston/cylinder assemblies of this type to which pneumatic or hydraulic pressure is admitted preferably to one side of the piston, with a return spring being provided between the piston and the cylinder, have a circular or annular cross-section and comprise a circular coil spring which, in the absence of pressure medium, forces the ton to return into its original position. Piston/cylinder units of this type are often found to be too large, or rather to take up too much of the installation space, to be used with precision mechanics, or rather to be mounted on appliances such as sewing machines, where small and even minute components have to be arranged in a highly space-saving manner.With assemblies which substantially consist of flat levers, wheels, riggings and the like, a circular cylinder takes up too much room in so far as the free space between the round and the square parts cannot be profitably utilised.

It is therefore an object of the invention to provide a piston/cylinder assembly which may be mounted in a space saving manner, especially in precision-mechanical appliances, machines, or the like.

According to the present invention there is provided a piston/cylinder assembly, comprising a piston and a cylinder each having an elongate, substantially rectangular cross section, the piston being hollow with an open end facing an end face of the cylinder and a helical tension spring with the piston extending between an internal face of the piston and the end face of the cylinder, the spring having a substantially rectangular coil cross section.

An embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawing in which: Fig. 1 is a longitudinal section in a schematic presentation through a piston/cylinder assembly according to the invention; and Fig. 2 is a transverse section along the line II-II in Fig. 1.

A piston/cylinder assembly 11 as shown in the drawing is designed for admittance of pneumatic or hydraulic pressure from one side and serves essentially for assembly with precision-mechanical instruments, apparatus, machines or the like such as, for example, sewing machines, the aim being to adapt the new assembly to the dimensions of the existing units in a space saving manner where there is practically no space lost between the piston/cylinder assembly 11 and the other mechanical components such as levers, riggings, discs, wheels and the like.

The piston/cylinder assembly 11 is of an oblong cross-section, that is to say its external periphery forms an elongate, rectangle.

A cylinder 12 is made of a rectangular, hollow section cut to the required length and having the required external dimensions; it is closed at one end by a rectangular cover 13. This cylinder cover 13 comprises a bore 14 which opens into a delivery connection for the pressure medium (not illustrated).

A piston 17 is defined by a hollow, rectangular section cut to length and closed on one side by a piston head 18. The dimensions of the hollow rectangular section of the piston are such that it may be inserted into the rectangular hollow section which forms the cylinder 12, leaving a narrow, uniformly continuous gap 19 between the two parts. The lengths of the piston and cylinder may be equal or different. The piston 17 and the cylinder 12, being of U-shaped longitudinal section, are in fact hood- or pot-shaped. In this design the piston is formed by an integral structure element which also functions the the piston rod.

The piston 17, whose open end 21 is pushed into the open end of the cylinder 12, has a large guiding surface because of its rectangular overall form and is therefore anchored against angular displacements and is very accurately controlled. In a region towards its front, that is to say in a zone adjacent to the open end section 21, which is always located inside the cylinder 12, the piston 17 is provided with a continuous sealing striP 22 which extends around an outer circumference 23 of the piston 17 to which it is vulcanised, forming a seal against an inner surface 24 of the cylinder 12.

A variable pressure-chamber 26 is defined by the piston 17 and the cylinder 12, and locates therein a tension spring 27 which, though having the form of a coil spring, differs from the conventional coil springs by having a substantially rectangular coil cross-section. The external dimensions of this spring 27 substantially correspond to the internal dimensions of the piston 17 and therefore having a large guiding surface the spring 27 is held inside the piston 17 in a closely fitting manner, and torsional movements are prevented. One end of the spring 27, which acts as a return spring, is supported against an internal face of the piston head 18 and its other end is fixed in a suitable manner to a cylinder end face defined by the cylinder cover 13.It is apparent that the head 18 and the cover 13 must be pressure-tightly fitted to the piston 17 and cylinder 12 respectively. It is for example even possible for the piston or the cylinder to be manufactured as an integral, deepdrawn unit.

As hereinbefore described all parts of the piston/cylinder assembly 11 have rectangular, elongate, external dimensions and substantially fit into each other without creating unnecessary play. The restoring, or rather return-spring 27 enables the piston/cylinder unit 11 to be designed as an extremely slim, that is to say, flat element. When the piston/cylinder assembly is built for example into a sewing machine, the piston head 18 may conveniently carry a blade to cut the thread, which is not shown in the drawing, and which would be operated with the aid of the assembly 11 when pressure medium is omitted.

A rectangular piston/cylinder of this kind is ideally suited for the installation conditions of precision-mechanical assemblies, because the piston/cylinder unit may be mounted immediately at the side of, and parallel with, the existing riggings and leverage systems, without creating free spaces which would be difficult to fill. Since the return spring has a substantially rectangular coil cross-section it is possible for the piston/cylinder components to be built into extremely flat assemblies, much flatter than could be achieved when incorporating a coil spring of cylindrical cross-section. The guiding surfaces taking part in the design are large and include the advantage of precision control; this ensures that none of the various parts may be distortionally displaced relative to the other parts.In particular, the return spring, held from all sides in positive surface contact, provides constant spring conditions. Another advantage is that given identical space requirements, the force of the new assembly is about 2,4 times as great as that of a cylindrical unit. In other words, savings of about 140% of the base area can be made when designing an assembly for the same force output.

This arrangement of the piston and cylinder creates a large pressure chamber and enables the stroke to be correspondingly high. The piston and/or cylinder may be manufactured in a simple manner from commercially available rectangular sections cut to the required lengths and subsequently assembled with the piston head or cylinder cover as required. Since there is only one cylinder cover which has to be provided with a discharge connection for the pressure medium, manufacture is simple and there are no sealing problems to be considered.

WHAT WE CLAIM IS: 1. A piston/cylinder assembly, comprising a piston and a cylinder each having an elongate, substantially rectangular crosssection, the piston being hollow with an open end fang an end face of the cylinder, and a helical tension spring within the piston extending between an intended face of the piston and the end face of the cylinder, the spring having a substantially rectangular coil cross-section.

2. A piston/cylinder assembly according to Claim 1 wherein the piston is formed by an integral element which also functions as a piston rod.

3. A piston/cylinder assembly according to Claim 1 or 2, wherein a continuous seal is provided between, and fixed to one of, the piston and the cylinder.

4. A piston/cylinder assembly according to Claim 3 wherein the continuous seal is vulcanised on to the piston at a location within the cylinder.

5. A piston/cylinder assembly according to any of the preceding Claims, wherein the spring is fixed to the end face of the cylinder and/or the internal face of the piston.

6. A piston/cylinder assembly according to any of the preceding Claims wherein one or each of the cylinder and the piston is defined by a rectangular section cut to length, with respectively a head cover adjoining the end face of the cylinder or/and a head of the piston adjoining the internal face being fitted thereto.

7. A piston/cylinder assembly according

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The piston 17, whose open end 21 is pushed into the open end of the cylinder 12, has a large guiding surface because of its rectangular overall form and is therefore anchored against angular displacements and is very accurately controlled. In a region towards its front, that is to say in a zone adjacent to the open end section 21, which is always located inside the cylinder 12, the piston 17 is provided with a continuous sealing striP 22 which extends around an outer circumference 23 of the piston 17 to which it is vulcanised, forming a seal against an inner surface 24 of the cylinder 12. A variable pressure-chamber 26 is defined by the piston 17 and the cylinder 12, and locates therein a tension spring 27 which, though having the form of a coil spring, differs from the conventional coil springs by having a substantially rectangular coil cross-section. The external dimensions of this spring 27 substantially correspond to the internal dimensions of the piston 17 and therefore having a large guiding surface the spring 27 is held inside the piston 17 in a closely fitting manner, and torsional movements are prevented. One end of the spring 27, which acts as a return spring, is supported against an internal face of the piston head 18 and its other end is fixed in a suitable manner to a cylinder end face defined by the cylinder cover 13.It is apparent that the head 18 and the cover 13 must be pressure-tightly fitted to the piston 17 and cylinder 12 respectively. It is for example even possible for the piston or the cylinder to be manufactured as an integral, deepdrawn unit. As hereinbefore described all parts of the piston/cylinder assembly 11 have rectangular, elongate, external dimensions and substantially fit into each other without creating unnecessary play. The restoring, or rather return-spring 27 enables the piston/cylinder unit 11 to be designed as an extremely slim, that is to say, flat element. When the piston/cylinder assembly is built for example into a sewing machine, the piston head 18 may conveniently carry a blade to cut the thread, which is not shown in the drawing, and which would be operated with the aid of the assembly 11 when pressure medium is omitted. A rectangular piston/cylinder of this kind is ideally suited for the installation conditions of precision-mechanical assemblies, because the piston/cylinder unit may be mounted immediately at the side of, and parallel with, the existing riggings and leverage systems, without creating free spaces which would be difficult to fill. Since the return spring has a substantially rectangular coil cross-section it is possible for the piston/cylinder components to be built into extremely flat assemblies, much flatter than could be achieved when incorporating a coil spring of cylindrical cross-section. The guiding surfaces taking part in the design are large and include the advantage of precision control; this ensures that none of the various parts may be distortionally displaced relative to the other parts.In particular, the return spring, held from all sides in positive surface contact, provides constant spring conditions. Another advantage is that given identical space requirements, the force of the new assembly is about 2,4 times as great as that of a cylindrical unit. In other words, savings of about 140% of the base area can be made when designing an assembly for the same force output. This arrangement of the piston and cylinder creates a large pressure chamber and enables the stroke to be correspondingly high. The piston and/or cylinder may be manufactured in a simple manner from commercially available rectangular sections cut to the required lengths and subsequently assembled with the piston head or cylinder cover as required. Since there is only one cylinder cover which has to be provided with a discharge connection for the pressure medium, manufacture is simple and there are no sealing problems to be considered. WHAT WE CLAIM IS:

1. A piston/cylinder assembly, comprising a piston and a cylinder each having an elongate, substantially rectangular crosssection, the piston being hollow with an open end fang an end face of the cylinder, and a helical tension spring within the piston extending between an intended face of the piston and the end face of the cylinder, the spring having a substantially rectangular coil cross-section.

7. A piston/cylinder assembly according

to any of the preceding claims, wherein the cylinder incorporates a delivery connection for pressure medium.

8. A piston/cylinder assembly substantially as hereinbefore described with reference to the accompanying drawing.