Abstract:
An hydraulic pressure reservoir having at least one pressure chamber with a fluid connection to a hydraulic circuit. The pressure chamber is formed between a movable partition member carried in a housing and having a pressure limiting valve, and a fixed partition. The movable partition member is in the form of a diaphragm spring.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a hydraulic pressure reservoir having at least one pressure chamber with a fluid connection to a hydraulic circuit, and that is arranged between a movable partition positioned in a housing and a fixed partition, and that includes a pressure limiting valve.  
         [0003]     2. Description of the Related Art  
         [0004]     Hydraulic circuits are employed in many applications, for example to trigger control pulses or also to produce an actuating force by actuating a piston/cylinder unit.  
         [0005]     An automatically operated clutch can be operated by means of a hydraulic actuator, for example, or such a hydraulic circuit can also be employed to adjust the transmission ratio between the two pairs of conical disks of a belt-driven conical-pulley transmission. When such an actuating force has to be built up very quickly, the start-up process of an electric motor of an electrically-powered hydraulic pump can result in the start-up time needed for the start-up process of the electric motor being too long. It is therefore necessary to hold a certain volume of pressure fluid in reserve at a predetermined pressure, so that the required actuating force can be built up in the required time with the pressure fluid.  
         [0006]     Hydraulic pressure reservoirs in the form of a membrane reservoir, for example, can be employed to keep that volume of pressure fluid ready at the predetermined pressure level. The membrane reservoir, however, has the disadvantage that, on the one hand, the membrane is not completely pressure-tight, and, on the other hand, it is subject to fatigue effects, so that the life span required of the pressure reservoir cannot be met with the membrane reservoir.  
         [0007]     A further possibility of such a pressure reservoir is a piston pressure tank with a helical spring, with which the desired quantity of pressure fluid can be stored at the predetermined pressure level. Such a piston pressure tank has a pressure piston that is axially movable in a cylinder, whereby the pressure fluid can be kept at the desired pressure level. However, as the pressure rises, the problems of the seal between the pressure piston and the cylinder wall also increase, so that it is necessary to produce the fit between the pressure piston and the cylinder with high precision, which results in high production costs. Furthermore, the piston pressure tanks require that tipping or tilting of the piston in the cylinder bore must be prevented, so that the piston must include a certain guide length in order to be able to seal well.  
         [0008]     The same problem also arises with a piston pressure tank acting against gas pressure, where the helical spring has merely been replaced by a gas reservoir.  
         [0009]     In that regard, an object of the present invention is to provide a hydraulic pressure reservoir that can be manufactured economically, that also eliminates the problem of the pressure chamber leaking, and, additionally, that has little wear after many load change cycles and thus is distinguished by a long life span.  
       SUMMARY OF THE INVENTION  
       [0010]     To achieve that object, the present invention provides a hydraulic pressure reservoir having at least one pressure chamber in fluid connection with a hydraulic circuit. The pressure chamber is formed between a movable partition arranged in a housing and a fixed partition, and it includes a pressure limiting valve. The movable partition is in the form of a diaphragm spring.  
         [0011]     Employing the diaphragm spring as the movable partition solves the problem of membrane leakage in a membrane pressure reservoir. The formation of a pressure piston with a certain length to avoid the problem of the piston tipping in a cylinder bore is also eliminated. Furthermore, the pressure reservoir equipped with the diaphragm spring is pressure-tight even when the fluid stored in the pressure chamber is at a very high pressure, because a configuration is possible in which the diaphragm spring is continuously pressed harder against the sealing elements as the internal pressure in the pressure chamber rises, or a configuration in which the sealing elements are pressed continuously harder against the diaphragm spring as the interior pressure rises. In that way a completely fluid-tight pressure chamber can be achieved, and also nothing changes structurally even after many load change cycles of the diaphragm spring, which serves as the movable partition of the pressure chamber.  
         [0012]     In accordance with the invention, it is also possible for the diaphragm spring to include a diaphragm spring body in the form of a ring disk, with a center opening that is closed by means of an inner cover that closes the pressure chamber off from the outside. That configuration makes it possible to use a known diaphragm spring, where only its center opening has to be closed by the inner cover. An arrangement is possible in which the inner cover is pressed against the body of the diaphragm spring, with a sealing element interposed in the form of an elastomeric body, for example, so that a defined pressure force can be built up between the inner cover and the body of the diaphragm spring in the region of the sealing element.  
         [0013]     In order to prevent an internal pressure that exceeds a predetermined pressure level in the pressure chamber, a pressure limiting valve that opens at a predetermined threshold pressure is provided in the pressure chamber, and in accordance with a further embodiment of the invention, it can be positioned in a throughbore in the inner cover.  
         [0014]     In accordance with the invention, the fixed partition can be provided in the form of a control plate having predetermined passageways to provide a fluid connection of the pressure chamber with the hydraulic circuit, and for a flange ring to be affixed on a flange surface of the control plate to releasably fix the diaphragm spring. Pressure fluid can be delivered into the pressure chamber and released again through the predetermined passageways in the control plate, so that the pressure chamber has a fluid connection with the hydraulic circuit through the control plate. It is possible to achieve functional integration through the fact that the control plate has a flange surface on which a flange ring can be affixed for releasable affixing of the diaphragm spring. To assemble the hydraulic pressure reservoir in accordance with the invention, the diaphragm spring therefore merely needs to be inserted, for example, into a recess provided in the control plate and then to be held against the flange surface of the control plate by means of the flange ring, with a sealing element interposed that seals the pressure chamber off from the outside.  
         [0015]     That arrangement also eliminates a problem that can be observed in pressure reservoirs, namely that as the internal pressure in the pressure chamber rises, a cover plate that closes off the pressure chamber from the outside becomes bowed toward the outside. The cover plate of the present invention is in the form of a flange ring, and the ring-disk-shaped diaphragm spring body that closes off the pressure chamber from the outside moves only slightly in relation to the fixed partition.  
         [0016]     That relative movement of the ring-disk-shaped diaphragm spring body relative to the fixed partition also results in a radial motion component of the region of the diaphragm spring body that lies radially toward the outside, because of the taper angle of the diaphragm spring.  
         [0017]     In order to prevent the region of the diaphragm spring that lies radially toward the outside, from producing a chip removing motion on the flange ring during that radial movement, the invention provides for the flange ring to include a U-shaped cross section on the side facing toward the pressure chamber, and for a wire ring to be located between the diaphragm spring and the U-shaped region, on which wire ring the region of the diaphragm spring that lies radially toward the outside can undergo a radial movement relative to the flange ring.  
         [0018]     The wire ring ensures that the diaphragm spring is able to undergo a sliding movement on the wire ring at its contact region lying radially to the outside, and that the latter is able to roll by a small amount on its contact surface, i.e., the region of the flange ring with the U-shaped cross section. Thus, by interposing the wire ring, a transition of the contact surface of the diaphragm spring lying radially toward the outside from a state of static friction to a state of dynamic friction on the flange ring, which would result in a chip-removing motion on the flange ring and thus to premature wear, is avoided. The result is that the pressure reservoir in accordance with the invention experiences little wear, even after many load change cycles, and hence is distinguished by a very long life span.  
         [0019]     In a similar way, a further embodiment of the invention provides that the inner cover at the region facing the diaphragm spring has a U-shaped cross section, and that a wire ring is positioned between the diaphragm spring and the U-shaped region, on which the region of the diaphragm spring lying radially toward the inside undergoes a radial movement relative to the inner cover. Here also, because of the wire ring, the problem of the wear of the inner cover and/or of the diaphragm spring body in the contact region between the diaphragm spring and the inner cover is avoided.  
         [0020]     As previously mentioned, sealing elements are provided between the pressure chamber and the outside, which can be positioned between the inner cover and the diaphragm spring and between the diaphragm spring and the control plate. The sealing elements, for example in the form of ring-shaped elastomeric elements, are therefore pressed against the inner cover and the diaphragm spring, as well as the control plate, by the internal pressure in the pressure chamber, and close off the pressure chamber hermetically from the outside with a fluid-tight seal.  
         [0021]     In accordance with a further embodiment of the invention, the pressure limiting valve previously described can include a valve body having a sealing surface facing and between the valve body and the inner cover, in particular a conical sealing surface, where the valve body can also include a throughbore to receive a shaft of a threaded bolt.  
         [0022]     The outer thread of the threaded bolt can be engaged with an inner thread in the throughbore of the valve body, so that the threaded bolt extends from the valve body and can be retained by means of a lock nut having a threaded blind bore. The shaft of the threaded bolt includes a bolt head that can engage a shoulder provided in the control plate to limit bolt outward movement. The retention by the nut on the outer thread of the threaded bolt provides a sealing surface between the valve body and the nut, which prevents the uncontrolled escape of pressure fluid from the pressure chamber into the surroundings.  
         [0023]     The threaded bolt described above can extend into a bore in the control plate, so that components of the pressure limiting valve are received in that bore. A further embodiment of the invention provides that a shoulder is formed in the bore, on which the head of the threaded bolt comes to rest in such a manner that if a predetermined threshold pressure in the pressure chamber is exceeded, the threaded bolt releases the contact of the valve body with the inner cover. Thereby an overrun of the threshold pressure within the pressure chamber is prevented, because the separation of the valve body from the inner cover as a result of the higher internal pressure allows pressure fluid to escape from the pressure chamber to the outside.  
         [0024]     The omnidirectional pressure that exists in the pressure chamber results in a pressure force acting on the fixed partition that is in the form of the control plate. To balance that pressure force, and furthermore to increase the volume of available pressure fluid, the invention provides that the hydraulic pressure reservoir has two pressure chambers, where two pressure reservoirs—as described above—with fixed partitions or control plates are adjacent to each other and with only one connection to the hydraulic circuit, are connected in such a manner that the pressure forces exerted on the respective partitions cancel each other out at the partition contact plane. That means that two hydraulic pressure reservoirs coupled together into one unit are connected with each other in such a way that the two fixed partitions come to rest against each other, and thus the pressure forces that prevail at the partition contact plane cancel each other out in accordance with the superposition principle.  
         [0025]     The fixed partitions identified above can be control plates having predetermined passageways. A further embodiment of the invention therefore provides for an intermediate plate to be placed between the fixed partitions, and which has bores to provide a fluid connection of predetermined passageways of the control plates, so that the pressure fluid in the two pressure chambers is connected with the hydraulic circuit through only one flange connection provided on a control plate, and the hydraulic fluid can reach both pressure chambers and can be released from them through that connection and the control plates, as well as the bores in the intermediate plate.  
         [0026]     In accordance with a further embodiment of the invention, the control plates are connected by means of threaded bolts that pass through the flange surfaces and flange rings. Through that arrangement bending of the control plates caused by internal pressure is prevented. The result of the threaded bolts passing through both control plates is that the number of threaded bolts does not increase compared to a hydraulic pressure reservoir having only one pressure chamber, because both diaphragm springs and both flange rings can be clamped against the respective control plates with the threaded bolts. Furthermore, that arrangement has the advantage that the control plates are not subjected to any bending load because the bolts are not supported against them, and it is also not necessary to place any stress grooves and costly inner threads in the control plates. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings in that:  
         [0028]      FIG. 1  is a top view of an embodiment of a pressure reservoir in accordance with the present invention;  
         [0029]      FIG. 2  is a cross-sectional view taken along the line A-A of  FIG. 1 ; and  
         [0030]      FIG. 3  is an enlarged, detailed view of the portion of  FIG. 2  shown within dashed lines  11 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     As can be clearly seen on the basis of  FIG. 1  of the drawing, hydraulic pressure reservoir  1  in accordance with the embodiment shown has a largely rectangular configuration with rounded corners, which is only one example of such a pressure reservoir.  
         [0032]     Through connection  2 , pressure reservoir  1  can be linked into a hydraulic circuit, so that the pressure fluid can be brought through connection  2  into pressure chambers  3 , which can be seen in more detail in  FIG. 2 , and can also be released from the pressure chambers through connection  2 .  FIG. 1  also shows a number of threaded bolts  4  spaced at equal intervals, with which the two fixed partitions in the form of control plates  7 ,  8  (the embodiment of the pressure reservoir shown in the drawing is an embodiment with two pressure chambers  3 ) can be bolted together through the flange rings  5 ,  6 .  
         [0033]     Connection  2  has a passageway  9  for supplying pressure chambers  3  with fluid. As can be seen in  FIG. 2 , passageway  9  leads into both pressure chambers  3  above through control plate  7  and through control plate  8 , respectively. The two pressure chambers  3  are axially bounded on one side by control plate  7  or control plate  8 , and on the other side by diaphragm springs  10  or  11 . A center opening  12  of each of diaphragm springs  10 ,  11  is closed by a respective inner cover  13 ,  14 , in each of which a pressure limiting valve  15 ,  16  is placed.  
         [0034]     An intermediate plate  8   a  can be positioned between the opposed faces of control plates  7 ,  8 . The intermediate plate has bores that are positioned to correspond with bores in control plates  7 ,  8  to provide a fluid connection between predetermined passageways of the adjacent control plates, so that the pressure fluid in the two pressure chambers  3  is connected with the hydraulic circuit through only one flange connection  2  provided on a control plate, and the hydraulic fluid can reach both pressure chambers and can be released from them through the control plate bores and through the bores in the intermediate plate to that one flange connection.  
         [0035]     The diaphragm spring  10  lies with its radially inwardly-lying region of the diaphragm spring body  17  against a wire ring  19  positioned in a U-shaped groove  18  (see  FIG. 3 ), so that radially inwardly-lying contact surface  20  of the diaphragm spring body  17  can undergo a radial displacement movement on wire ring  19 . As can be seen in more detail in  FIG. 3  of the drawing, positioned between inner cover  14  and diaphragm spring body  17  is a sealing element  21  in the form of an elastomeric seal having a circular cross section.  
         [0036]     In a similar manner, and referring again to  FIG. 2 , a wire ring  19   a  is positioned on the radially-outwardly-lying region of diaphragm spring  10 ,  11  in a U-shaped groove formed in flange ring  5 ,  6 , so that the radially-outwardly-lying region of diaphragm spring body  17  can undergo a radial displacement movement at that outer location.  
         [0037]     A sealing element  22  in the form of an elastomeric seal having a circular cross section seals off the pressure chambers  3  in the radially-outwardly-lying region. When a pressure fluid is introduced into pressure chambers  3  through connection  2  and placed under pressure, the result is an outward pressure against diaphragm springs  10 ,  11 , so that the latter undergo movement relative to control plates  7 ,  8  in the direction of the arrows C in  FIG. 2 . When the hydraulic fluid that is present under pressure in the pressure chambers is to be released, for example to quickly raise the operating pressure in the hydraulic circuit, connection  2  can be opened by means of a valve (not shown) and the pressure fluid in pressure chambers  3  can pressurize the hydraulic circuit. At the same time, diaphragm springs  10 ,  11  undergo a motion opposite to the direction shown by arrows C.  
         [0038]     By means of the threaded bolts  4  and the nuts  23 , the two control plates  7 ,  8  are pressed so firmly against each other that they are not subjected to bending loads as the pressure builds up in the pressure chambers  3 .  
         [0039]     The construction and functioning of the pressure limiting valve  16  (pressure limiting valve  15  is analogous in its construction and manner of operation) will now be explained on the basis of Detail II of  FIG. 2 , shown in enlarged form in  FIG. 3 .  
         [0040]     Pressure limiting valve  16  extends through a throughbore  24  in the inner cover  14 , and a valve body  25  is positioned in the region of throughbore  24 .  
         [0041]     Valve body  25  has a conically-shaped sealing surface  26 , that acts together with a correspondingly tapered surface of the inner cover  14  in the region of the throughbore  24 . Pressure limiting valve  16  includes a threaded bolt  28  positioned in a bore  27  of control plate  8 , valve body  25 , and a nut  29  having a blind bore, and is held in a closed position by means of a pressure spring  30  when the pressure chamber  3  is not under load, the pressure spring  30  being supported on a shoulder  31  formed in the bore  27  of control plate  8 . Between nut  29  and valve body  25  a sealing surface  32  is formed, through which pressure fluid cannot escape from the pressure chamber because screwing the nut  29  and the valve body  25  on the threads of the threaded bolt  28  between the top side of the valve body  25  and the underside of the nut  29  forms a sealing surface  32  that seals off the applied pressure force.  
         [0042]     If the pressure in pressure chamber  3  rises, diaphragm spring  11  undergoes movement in the direction of the arrow C (see  FIG. 2 ) and carries with it inner cover  14  and the pressure limiting valve  16 . If the pressure in pressure chamber  3  rises above a predetermined threshold value, further movement of diaphragm spring  11  results in the head  33  of threaded bolt  28  contacting the shoulder  31  of control plate  8 , which stops further outward movement of bolt  28 . Valve body  25  then remains stationary, and inner cover  14  moves out of sealing contact at sealing surface  26 . A gap opens and pressure fluid is able to escape via the throughbore  24  until the internal pressure in pressure chamber  3  has dropped far enough so that diaphragm spring  11  undergoes movement in a direction opposite to that indicated by arrow C as shown in  FIG. 2 , and the valve body  25 , which is subject to fluid pressure over its inner face  34  by the pressure fluid in pressure chamber  3 , again assumes a sealing contact with inner cover  14 .  
         [0043]     The hydraulic pressure reservoir in accordance with the invention is distinguished by the fact that the problem of a leaking membrane has been effectively eliminated, and a high number of load changes on the diaphragm springs  10 ,  11  does not result in leakage from pressure chamber  3 . Thus, expensive mechanical production steps, such as in the precise fitting and production of piston/cylinder units for piston pressure accumulators, are eliminated.  
         [0044]     With regard to features not explained in greater detail above, reference is made to the claims and the drawing.  
         [0045]     Although particular embodiments of the present invention include been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit of the present invention. It is therefore intended to encompass within the appended claims all such changes and modifications that fall within the scope of the present invention.