Abstract:
A pressure accumulator includes an accumulator housing ( 2 ) in which a movable separating element ( 30 ) fluid-tightly separates a gas chamber ( 16 ) filled with a working gas from a fluid chamber ( 28 ). A monitoring device ( 50, 54 ) supplies an optical signal in the event of a malfunction affecting the sealing effect of the separating element ( 30 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a pressure accumulator having an accumulator housing. A movable separating element separates a gas chamber filled with a working gas from a fluid chamber in a fluid-tight manner in the accumulator housing. 
     BACKGROUND OF THE INVENTION 
     Hydro-pneumatic accumulators of this type are prior art. They are widely used in fluid systems and hydraulic systems, for example, as a pulsation dampers for smoothing pressure fluctuations or for storing hydraulic energy. The publication EP 1 709 334 B1, for example, discloses a pressure accumulator of this type in the form of a bellows accumulator, which is provided, in particular, as a pulsation damper. Crucial for the functionality of such accumulators is that the separating element forms an absolute separation between the working chambers, gas side and fluid side, and maintains this separation during operation. A defect appearing on the separating element, whether it is a folding bellow or a membrane, which defect results in the transfer of fluid to the gas side and, therefore in the reduction of the gas volume, results in the progressive reduction of the damping effect in the case of pulsation dampers or in the loss of storage capacity in the case of energy stores. 
     Movable separating elements in the form of folding bellows or elastomer membranes are subjected to high mechanical stresses during operation. The risk then exists of a rupture during operation. During operation of pressure accumulators, detecting such a disruption quickly and timely enough to be able replace the accumulator before a malfunction or a failure of an affected associated system occurs is difficult. 
     SUMMARY OF THE INVENTION 
     In view of this problem, an object of the invention is to provide an improved pressure accumulator, which ensures an enhanced operating reliability in connection with a fluid system or hydraulic system to which it is allocated. 
     According to the invention, the object is basically achieved by a pressure accumulator having, as an essential feature of the invention, a monitoring device, which supplies a visually detectable signal in the event of a disruption that adversely affects the sealing effect of the separating element. This monitoring device provides the advantageous possibility of carrying out the functional capability of the pressure accumulator during continuous operation, i.e., without having to remove the pressure accumulator from the system and subjecting it to external functional testing. Thus, the removal of an affected pressure accumulator from the system is required only if the occurrence of a disruption is signaled. The defective pressure accumulator can therefore be replaced before a more serious operational disruption or operational failure of the allocated system occurs, so that an improved operating reliability may be achieved. 
     The invention is particularly advantageously provided in the case of a pressure accumulator, which has a folding bellows as a separating element, in particular, in the form of a metal bellows. Folding bellows, in particular, metal bellows are preferably used in pulsation dampers, where high mechanical alternating stresses occur on the bellows during operation, in particular, at the folds. A corresponding risk of a defect occurring exists. Thus, the possibility of monitoring provided by the invention proves to be particularly advantageously. 
     The monitoring device may particularly advantageously include a viewing window on the wall of the housing, through which an indicator is preferably observable. The indicator is connected to the gas chamber. The visual properties of the indicator noticeably change when wetted with fluid. Because a transfer of fluid to the gas side is detectable by observing an indicator through the viewing window, it allows functional monitoring to be carried out during continuous operation in a particularly easy and reliable manner. 
     An indicator that changes its color when wetted can be particularly advantageously provided. 
     In advantageous exemplary embodiments, a sample quantity of glass-fiber wool is provided as an indicator. That wool is white in the non-wetted state and becomes visually noticeably discolored in various ways when wetted with fluids of various types. During an operation with a fluid in the form of hydraulic oil, a potential leak is detectable by a relatively dark discoloration of the glass-fiber wool. When using the pressure accumulator in fuel systems, a wetting by diesel oil, on the other hand, results in a lighter discoloration. For example, gasoline or ethylene glycol results in a yellower or orange-colored discoloration, i.e., in discolorations that differ clearly noticeably from the white initial state of the glass-fiber wool. 
     In advantageous exemplary embodiments, the glass-fiber wool is disposed in a bore passing through the wall of the housing into the gas chamber. 
     The bore may be closed on the housing outer side by a threaded insert, which includes a pressure-resistant viewing window. In a particularly advantageous manner, the glass-fiber wool is disposed in the bore between threaded insert including the viewing window and a screen body located at the inner end of the bore. An observation just through the viewing window or sight glass can suffice for an operator or maintenance person to be able to detect damage to the separating element, even without an indicator. 
     In a particularly advantageous manner, the bore is designed as a continuous threaded bore, to the inner end of which a threaded ring, which forms the holder for the screen body, may be screw-fastened. This arrangement results in a particularly simple structural design for the monitoring device. 
     In pressure accumulators having a cylindrical housing that includes a housing cover at one end forming an axial housing closure, advantageously the bore of the monitoring device can be designed to be in the housing cover. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the drawings, discloses a preferred embodiment of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings that form a part of this disclosure: 
         FIG. 1  is a side view in section of a pressure accumulator according to an exemplary embodiment of the invention; 
         FIG. 2  is a side view in section of the threaded insert of the exemplary embodiment of the pressure accumulator, including a viewing window, drawn on a larger scale as compared to  FIG. 1 ; 
         FIG. 3  is a side view in section of a threaded ring with screen body of the pressure accumulator, drawn on a larger scale as compared to  FIG. 1 ; and 
         FIG. 4  is a perspective view of the threaded ring of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The exemplary embodiment of a pressure accumulator in the form of a metal bellows accumulator is depicted in the drawing, in particular for a use in hydraulic systems and fuel facilities, to dampen and to smooth pressure surges in the operating medium. In the area of fuel systems, the operating medium includes, in particular, diesel fuel, gasoline or the like. A pressure accumulator could also be used in conjunction with electrohydraulic brake systems, for example, in automotive construction. The pressure accumulator depicted has an accumulator housing  2 , having a substantially circular cylindrical, pot-shaped main section  6 , defining a longitudinal axis  4 . One end of the main section  6  has a housing cover  8  as a housing closure, which is connectable to the main section  6  by the folding of its end edge  10  onto a diagonal surface  12  of the cover  8 . An O-ring  14  forms the seal. The folded over end edge  12  may be connected to the housing cover  8  by an additional weld (not depicted). A filling connection (also not depicted) for introducing a working gas, such as N 2 , into a working chamber on the gas side, which is identified in  FIG. 1  as gas chamber  16 , may also be provided in the housing cover  8 . 
     The main section  6  of the accumulator housing  2  includes a base  18  at the end opposite the cover  8 . A fluid connection on the base  18  has a cylindrical connecting element  20  coaxial to the longitudinal axis  4 . The base includes two fluid connections  22 ,  24 , which open into a common entrance chamber  26 , which leads to the fluid side  28  in the housing  2 . In the present exemplary embodiment, a metal bellows  30 , which, as in the aforementioned pressure accumulator disclosed EP 1 709 334 B1, is tightly connected by welding at its one end  32  to an inner annular extension  34  of the cover  8 , and is provided as a separating element between the gas chamber  16  and the fluid chamber  28 . The metal bellows  30  surrounds the outer side of a circular cylindrical, inner pot body  36 , which is open at the end facing the housing base  18 . The other bellows end  40  is tightly connected by welding to the open edge  38  of the pot body  36 . 
     To form the monitoring device, which signals a transfer of fluid from the fluid chamber  28  to the gas chamber  16  resulting from a bellows rupture, a continuous threaded bore  44  is formed in the housing cover  8  in the present exemplary embodiment, displaced laterally relative to the longitudinal axis  4 . The outer end of the threaded bore  44  is tightly sealed by a threaded insert  46 . A threaded ring  48  may be screwed into the inner end of the threaded bore  44 . The outer threaded insert  46  is formed by a screwed sight glass, which includes a viewing window  50  made of a pressure-resistant glass. In the present example, a screw sight glass, available commercially under the name “Metaglas”, which includes a viewing window  50  made of borosilicate glass, is provided by Herberts Industrieglas, Gewerbeschulstr. 72, D-42289 Wuppertal, Germany. The threaded ring  48 , which is screwed into the threaded bore  44  at the inner end thereof, supports a screen body  52 . The screen body forms a support for a glass-fiber wool  54 , provided as an indicator, which is located between the screen body  52  and the viewing window  50  of the threaded insert  46 . 
     As shown most clearly in  FIGS. 3 and 4 , the screen body  52  has the shape of a hemispherical cupola, made of a metallic structural webbing, in the present example, having a mesh size of 0.1 mm. A support webbing  56 , also metallic, having a mesh size of 0.83 mm with a wire thickness of 0.22 mm, extends over the outer side of the structural webbing. 
     The glass-fiber wool  54 , which is white in its unwetted original state, becomes discolored when wetted with fluid that passes from the fluid chamber  28  to the gas chamber  16  in the case of a defect in the separating element, in the present case, a bellows rupture. In the case of fluids, such as hydraulic oil or diesel fuel, the result is a strong dark coloration of the glass-fiber wool  54  observable via the viewing window  50 . Other fluids, depending on their color, result in different discolorations of the indicator, for example, in lighter discolorations in the case of gasolines and the like. In any case, the wetting of the glass-fiber wool  54  functioning as the indicator is clearly detectable through the viewing window  50 . Instead of the glass-fiber wool  54 , other substances can be provided as an indicator, which noticeably alter their optical property when wetted with the fluids in question in a visually noticeable manner, in particular, become discolored. The original state of the unwetted indicator need not necessarily be white. 
     A simplified exemplary embodiment is described above, in which visual changes to the indicator are immediately noticeable visually by observation through the viewing window  50 . The invention may be used with equal advantage if relevant pressure accumulators are installed in such a way that a direct eye contact for visual observation of the viewing window  50  is not possible. In such cases, an optical sensor device of a known type may be provided, for example, including a light source that illuminates the indicator through the viewing window  50 . Any substance, which, when wetted, changes its optical property or reflectivity in a manner detectable by a sensor device, may be considered. As stated previously, color changes need not start with white as the original state. They may also involve monochrome changes in reflectivity. 
     The viewing window  50  may also be glued into the housing part  46 , which is designed as a threaded insert. As another possibility, a pressure-tight press fit may be produced between the viewing body  50  and the housing part  46 . This may take place via suitable fitting-in operations. However, producing a type of friction locking connection between viewing window  50  and associated housing part  46  is particularly preferred. As part of such a frictional locking connection, a physical and/or chemical pressure-resistant connection may form between the adjoining wall portions of viewing window  50  and housing part  46 . As a further alternative solution, the housing part  46  and the viewing window  50  can be produced as a single piece, in particular, to form the housing part  46  completely from a transparent material, in particular, a pressure-resistant glass material. 
     While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the claims.