Expansible chamber devices – Cylinder detail – Cylinder or liner retained in casing by casing closure or...
Patent
1995-06-27
1998-03-03
Nguyen, Hoang
Expansible chamber devices
Cylinder detail
Cylinder or liner retained in casing by casing closure or...
29523, F01B 1102
Patent
active
057223122
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for mounting a cylinder sleeve in a base member, in which the cylinder sleeve is inserted in the base member and the outer diameter of the inserted cylinder sleeve is enlarged at one end, and to a hydraulic machine with a base member in which at least one cylinder sleeve is arranged in a cylinder bore.
Hydraulic machines which convert pressure and movement into one another by means of pistons moving back and forth in cylinders have long been known. In order to keep the wear and tear in such machines to a minimum, it is usual to let the pistons run not directly in bores formed in the base member, but to insert in the base member cylinder sleeves or bushings in which the pistons can move. In this manner, it is possible to use suitable combinations of material for the piston and cylinder sleeve without having to make the entire base member from the generally more expensive material of the cylinder sleeve. The material of the base member can then be selected to take into account other side constraints, such as strength.
The problem of having to match cylinder sleeves or bushings to the pistons is also found with other hydraulic elements and devices, for example, in hydraulic valves.
To be able to fix cylinder sleeves in the base member, it is known (DE-AS 12 67 985) to fix the cylinder sleeve first of all by means of a press fit in a cylinder bore in the base member. Here, the cylinder sleeve has a collar which is pressed into an annular groove of substantially rectangular cross-section in the inner wall of the cylinder bore. To produce the collar, the cylinder sleeve has at one end an enlargement of its material which projects inwards. After pressing the cylinder sleeve into the cylinder bore, a mandrel is pressed into the liner so that the collar is expanded, with the result that the collar engaging in the annular groove is formed on the outside of the cylinder sleeve.
The prerequisite for such a procedure is that the material of the cylinder sleeves allows such a deformation without the cylinder sleeve being damaged. This is generally the case only with metals. But even with metals, this procedure can lead to embrittlement with the consequences of premature wear or even failure of the machine. A number of materials which, together with the material of the piston, have inherently suitable running properties for the application therefore have to be ruled out because a reliable mounting of the cylinder sleeve in the base member cannot be guaranteed.
SUMMARY OF THE INVENTION
The problem underlying the invention is therefore to enable cylinder sleeves made of other materials to be mounted also.
This problem is solved in a method of the kind mentioned in the introduction in that the cylinder sleeve is heated before its outer diameter is enlarged.
Heating the liner means that in many cases the material is more readily deformable. Embrittlement, such as occurs in many cases in the known cold-forming method, can in this case be reliably counteracted. Cylinder sleeves of materials that are not deformable in the cold state but would break, can now be expanded by such a heating process. This is the case in particular with many plastics materials. The mounting method according to the invention now enables material combinations of piston and cylinder sleeve to be used that work satisfactorily even when the hydraulic fluid has only a reduced lubricating capacity.
Preferably, the cylinder sleeve is heated only at the end to be expanded. This saves energy. Moreover, the material structure is affected by the temperature increase only at the end to be expanded. The cylinder sleeve remains otherwise unchanged. Faults such as those that could occur in the material structure of the cylinder sleeve as a result of a temporary temperature increase are thereby largely avoided. In the region of the end to be expanded, on the other hand, such a change does not matter since processing or deformation is effected here anyway by the expansion.
The cylinder sleeve is prefer
REFERENCES:
patent: 325692 (1885-09-01), Parker
patent: 1587967 (1926-06-01), Limont
patent: 1696229 (1928-12-01), Fantz
patent: 5083363 (1992-01-01), Ransom et al.
patent: 5496656 (1996-03-01), Waggoner
Danfoss A/S
Nguyen Hoang
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