Power plants – Pressure fluid source and motor – Having leakage collecting structure
Patent
1993-11-18
1995-11-28
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Having leakage collecting structure
92 82, 92 86, F16D 3102
Patent
active
054697042
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a hydraulic drive apparatus as set forth in the preamble of claim 1.
Such a hydraulic drive apparatus is known from DE 3026877A1. In DE 3026877A1 a hydraulic cylinder is disclosed having a piston rod which extends to through the cylinder head and is sealed by means of two seals. The primary seal which is located closer to the working or operating chamber of the piston is a ring which consists of a metal or another material having a stable shape, for instance a plastic material having the respective characteristics. Said primary seal is wear resistant but not free of leackage. For that reason between the primary seal and the secondary seal an annular collecting groove is provided for the leakage oil which is not held back by the primary seal; said leakage oil can be drained from said annular collecting groove by means of a leakage oil conduit extending from said annular collecting groove. Thus, the secondary seal is not subjected to the system pressure and load holding pressure, respectively. As a consequence, the wear of the secondary seal is small. The constant loss of leakage oil is a disadvantage of said known hydraulic drive apparatus, because said loss of leakage oil does not permit to maintain a load at a certain location or position in case the pump is switched off. In such a situation, the piston would slowly move away from its position and, as a consequence, also the load would change its position.
The problem underlying the present invention is to further develop a hydraulic drive apparatus having the features of the preamble of claim 1 in such a manner that the cylinder will maintain its position even if the pump is switched off.
This problem is solved for a hydraulic drive apparatus with the features of the preamble of claim 1 by providing that the leakage oil conduit is subjected to the load holding pressure by switching a valve. Thus, for a hydraulic drive apparatus of the invention there exists the possibility to stop the drainage of leakage oil via the leakage oil conduit by switching said valve; thus, if the pump is switched off, the piston and the piston rod of the cylinder no longer move due to the action of the load. The load holding pressure, which acts, when the piston rod is stationary, in the leakage oil conduit and in a possibly existent leakage oil collection space between the primary seal and the secondary seal, also acts upon the secondary seal. The secondary seal is strongly urged or pressed against the sealing surfaces of the piston rod and the cylinder head and also seals, free of leakage, with respect to the high load holding pressure. The strong or firm application or abutment at the stationary piston rod does, however, not lead to wear of the secodary seal which would jeopardize the life span of the cylinder. In case, the piston of the cylinder is moved then the leakage oil can be connected with the tank via the valve, so that the secondary seal is not subjected to the system pressure and applies at the sealing surfaces with a smaller tension (force), a tension which is, however, sufficient to provide for a leakage free sealing effect for the passage of the piston rod through the cylinder head, said tension being, however, also so small that the movement of the piston rod will lead only to a small wear of the secondary seal.
Preferred embodiments of the hydraulic drive apparatus of the invention can be gathered from the dependent claims.
The valve, which can be switched, so as to subject the leakage oil conduit to the load holding pressure is of a particularly simple design if the leakage oil conduit can be blocked by switching the valve in accordance with claim 2. Then, the load holding pressure in front of the secondary seal builds up along the piston rod. In case the pressure build-up should occur quickly, then it appears to be desirable that the leakage oil conduit is connectable via the valve to the pressure chamber of the cylinder at the piston rod side in accordance with claim 3.
So as to provide for movement of the piston of a cylinder in o
REFERENCES:
patent: 2761425 (1956-09-01), Bertsch et al.
patent: 2988058 (1961-06-01), Warnecke
patent: 4084668 (1978-04-01), Rybicki
patent: 4667472 (1987-05-01), Clay et al.
Die Passende Antwort, (Brochure of the Merkel Company-no date available).
Lopez F. Daniel
Mannesmann Rexroth GmbH
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