Measuring and testing – With fluid pressure – Leakage
Patent
1991-03-18
1993-02-23
Williams, Hezron E.
Measuring and testing
With fluid pressure
Leakage
G01M 328
Patent
active
051879735
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of operating a hydraulic machine unit which is selectively connected to a tank or a pump via at least one conduit. The invention further relates to a hydraulic drive system, particularly for working machines used in underground mine operations, with a tank, a pump connected thereto and conduits leading to a machine unit for the supply and return of the hydraulic fluid, the conduits starting from a control device.
With hydraulic drive systems for working machines used in underground mine operations there is the problem that on the one hand damage to the associated hoses occurs relatively frequently because the hoses are subjected to external forces under the conditions which prevail underground and that on the other hand the damage to the hoses may only be detected and located with difficulty because the hoses are not visible or accessible or only with difficulty either in the vicinity of the working machine itself or as a consequence of the prevailing operational conditions.
If, for instance, the above problem is considered in the case of a so-called boom-type road header as a road header, the result is, in particular, a loading, which is absolutely typical for the conditions underground, of the machine units by the heap of debris which has been cut free and which reaches the partially exposed hoses and causes an external mechanical stressing of the hoses. Additionally, the hoses which are guided partially covered in or on the machine body are also involved since the boom-type road header also moves and operates in the heap of debris so that portions of the debris also reach the hoses guided in the vicinity of the machine.
Whilst hose breakages which occur may be relatively easily detected as a result of the hydraulic fluid which visibly escapes at high operational pressure in the drive system and above all may be located in accordance with its escape, there is a considerable problem in the detection of smaller leaks which can be scarcely detected and located as such even during operation of the machine. Thus such small leaks occur unnoticed even during idling of the drive unit or the machine during which an idling pressure in the hydraulic system of the order of, for instance, 3 bar can be assumed, also during working sequences at the machine as regards all units not involved therewith and thus not subjected to the operational pressure because a functional failure of the units in question does not occur. Such small leaks are thus frequently only presumed or detected as a result of establishing an above average "consumption" of hydraulic fluid and can only be cured during a stoppage of the machine.
The problem of leakage losses is however not limited to the working machines discussed above and used in underground mine operations but applies basically to all units driven with hydraulic fluid. In each case, leakage losses impair not only the efficiency of operation but also constitute an environmental load which should not be underestimated since the hydraulic fluids are to be regarded as aggressive pollutants.
It is thus the object of the invention to provide a hydraulic leak monitor with which even small leaks in the conduit system of the relevant working machine may be detected.
The solution of this object together with advantageous embodiments and features will be apparent from the content of the claims which precede this description.
The invention is based on the recognition that the stoppage times of the machine units in which they are switched off or are temporarily not acted on by the working pressure can be used to ensure the tightness of the conduits. For this purpose, a minimum pressure is set in the conduits which is at least at the level of the biassing pressure predetermined by the hydraulic system. This means that the conduit cannot discharge to the tank any further than to the predetermined minimum pressure. If, however, the pressure within the conduit sinks below the minimum pressure, this is an indication that a leak has occurred. Even slight leakages may t
REFERENCES:
patent: 4152925 (1979-05-01), Lindh
patent: 4608857 (1986-09-01), Mertens et al.
Francuz Josip
Kunze Hans-Jurgen
Kunze Silvia
Roskos Joseph W.
Williams Hezron E.
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