HYDROSPATIAL STORAGE

Description

[0001] The invention relates to a hydraulic accumulator with an accumulator housing which is closed at least on one free end face with a cover part which can be fixed along a threaded section in the accumulator housing.

[0002] DE 10 2018 005 204 A1 discloses a generic hydraulic accumulator, in particular in the form of a piston accumulator, having an accumulator housing and a separating element arranged therein, in particular in the form of a piston, which separates a fluid side from a gas side, wherein at least the gas side can be inspected by means of a sight glass in a cover part of the hydraulic accumulator, which is designed to be fixable in the accumulator housing along a threaded section, in particular to be screwed in and out.

[0003] In the known solution, the threaded section consists of an internal thread in the accumulator housing and a matching external thread in the cover section. Such hydropneumatic piston accumulators, even with very large diameters, are closed via the threaded section using so-called compact covers as cover parts at the free, open ends. In this way, very solid cover parts are screwed into the piston accumulator tube, which forms the accumulator housing in the form of a cylindrical shell. The rigidity of the cylindrical shell of the accumulator housing is orders of magnitude lower than that of the compact cover part. In the event of fatigue failure, the fracture occurs in almost all cases on the first thread turn behind a thread undercut in the cylindrical shell of the accumulator housing.The fact that stress increases that can lead to fracture actually exist in this area can be proven in the form of so-called FEM analyses.

[0004] The magnitude of the stress increase depends heavily on the thread modulation and the associated notch effect. Furthermore, tests have shown that significant scatter can occur in the test results. Even when the tubular accumulator housings and the compact cover parts are each made from the same material batches, these "chaotic" scatters occur. The cause is the smallest differences in the threads, which are caused by different geometries of the manufacturing tools, even if these are within the permissible tool tolerances. This leads to wear or small chipping on the tools, which indirectly lead to fatigue fractures in the threads of the machined thread section.

[0005] The metric standard threads or ISO threads used to date, with at least a trapezoidal profile for the respective internal thread, which is incorporated in the accumulator housing, create a correspondingly sensitive thread to notch effects and, in particular, when high pressures or rapid pressure changes occur in the accumulator housing, fatigue fractures occur during operation and thus lead to failure of the hydraulic accumulator as a whole.

[0006] Although it has already been proposed for hydropneumatic pressure accumulator solutions or hydraulic accumulators to fold the cylindrical ends of the accumulator housing onto the corresponding cover part using a flanging process, avoiding the use of fixing threads, and to permanently fill the resulting fillet weld between the folded edge of the accumulator housing and the top of the cover part with a weld seam to secure the cover part to the accumulator housing, this solution alone (DE 10 2014 010 006 A1) can only be removed by destructive means, meaning that such hydraulic accumulators must be replaced with new ones in the event of failure, and opening the accumulator housing, particularly for maintenance purposes or to replace the separating piston, is fundamentally impossible. In this respect, preference should be given to hydraulic accumulator solutions that have cover parts that can be screwed in and out of an accumulator housing.

[0007] Further hydraulic accumulators are described in JP H01-224509 A, EP 1 564 413 A1 and DE 37 12 671 A1.

[0008] DIN 405-1: 1997-11, DE 38 40 731 C2 and US 3 433 117 A concern threads.

[0009] Based on this prior art, the invention is based on the object of further improving the hydraulic accumulator mentioned at the outset in such a way that fatigue fractures are avoided even when the hydraulic accumulator is subjected to correspondingly high pressure stress.

[0010] A hydraulic accumulator having the features of patent claim 1 in its entirety solves this problem.

[0011] Due to the fact that, according to the characterizing part of patent claim 1, an internal thread in the form of a round thread is present as part of the thread section on the side of the storage housing, the individual thread flanks of which enclose a flank angle of 60° with one another in a fictitious extension and the fact that the radius of the rounding in the head-side area of ​​the round thread is larger than the radius in the foot-side area of ​​the round thread, large defined radii are realized in the thread crest as the head-side thread area and the thread root as the foot-side thread area, so that the mentioned notch effect for the internal thread of the storage housing is significantly reduced and unwanted fatigue fractures are avoided.

[0012] In a particularly advantageous manner, an external thread in the form of a round thread is provided as a further part of the threaded section on the cover part side, the individual thread flanks of which, in a fictitious extension, enclose a flank angle of 60° with each other, and the radius of the rounding in the base area is smaller than the radius in the head area of ​​the external thread. Thus, within the threaded sections, the thread flanks of the internal and external threads are in contact with each other, with the adjacent thread roundings maintaining a radial distance from each other.In this way, the fatigue and fracture strength of the external thread of the cover part is also increased and the aforementioned interaction of the round threads from the internal thread of the accumulator housing to the external thread of the cover part leads to hydraulic accumulator solutions, such as piston accumulator solutions, with a very long service life, even if the respective hydraulic accumulator design is exposed to high pressure loads and pressure cycling stresses during operation.

[0013] Advantageous embodiments of the hydraulic accumulator according to the invention are the subject of the subclaims.

[0014] In the following, the solution according to the invention is explained in more detail using an exemplary embodiment according to the drawing. In this diagram, not to scale, the Fig. 1 shows a longitudinal section through the essential components of a hydraulic accumulator, in particular in the form of a piston accumulator, but without a separating piston illustration; Fig. 2 shows a partial longitudinal section through an internal thread of the accumulator housing according to the invention with parts of a standard thread according to the prior art; Fig. 3 shows a partial longitudinal section through an external thread of the cover part according to the invention with parts of a standard thread according to the prior art; and Fig. 4 shows the internal and external threads interacting along a thread section according to the Fig. 2 or 3.

[0015] The Fig. 1 The hydraulic accumulator, shown in a horizontal position, has an accumulator housing 10 that forms a closed, cylindrical hollow body shell. At each of its free, opposing end faces 12, the accumulator housing 10 is closed with a cover part 14 that is designed as a solid, compact cover. The two identically designed cover parts 14 close off an interior space 16 in the accumulator housing 10 from the environment. A separating element (not shown in detail) is arranged in the interior space 16, for example in the form of a separating piston that is movably guided along the inner wall of the accumulator housing 10. Such hydraulic accumulator arrangements are state of the art and are shown, for example, in DE 10 2018 005 204 A1.

[0016] The separating element (not shown in detail), particularly in the form of a separating piston, regularly separates a gas side from a liquid side within the accumulator housing 10. This arrangement is also conventional, so it will not be discussed in more detail here. With regard to this design, however, both cover parts 14 have an inner channel 18, with which the hydraulic accumulator can be connected to a fluid circuit (not shown in detail), such as a hydraulic circuit, and can also be filled with a compressible working gas, such as nitrogen gas, via this inner channel 18. After being filled with the working gas accordingly, the inner channel 18 is then tightly closed to the outside, for example by means of a plug or the like.

[0017] The respective cover part 14 is fixed in the storage housing 10 via a threaded section 20. Along one free end side of the cover part 14, on its upper side, diametrically opposed to the longitudinal axis 22 of the storage housing 10, screw-in bores 24 are provided, which serve as an engagement point for an operating tool (not shown in detail) for screwing the respective cover part 14 into and out of the storage housing 10. The wall of the storage housing 10 is relatively thin compared to the very thick wall thickness of the respective compact cover part 14 used, which is designed as a cylindrical solid component and whose outer diameter is adapted to the inner diameter of the storage housing 10 along the threaded section 20.

[0018] As in particular the Fig. 2 shows, as part of the thread section 20 on the side of the storage housing 10, there is a round thread 26 designed as an internal thread 25, the individual thread flanks 28 of which enclose a flank angle α of 60° with each other in a fictitious extension. As can be further seen from the Fig. 2 The radius is R 2 of the rounding in the head area 30 larger than the radius R 1 in the foot-side area 32 of the round thread 26. For comparison, next to the round thread 26 in the Fig. 2 A metric standard thread 34 in a trapezoidal shape, as is state of the art, is used to secure cover parts 14 in the associated storage housing 10. Like the round thread, the standard thread has a pitch P of 2 mm. Other pitches P are available if required. In this case, a metric internal thread M210 x 2 is used.

[0019] Fig. 3 now relates to an external thread 35 as part of the thread section 20 on the cover part 14, again in the form of a round thread 36, whose individual thread flanks 38 enclose a flank angle β of 60° with each other in a fictitious extension. The radius R 1 ′ the rounding in the foot area 40 is smaller than the radius R 2 ′ in the head-side area 42 of the external thread 35.

[0020] Also in the Fig. 3 a previously used metric standard thread 44 is again shown, which encloses the round thread 36 of the external thread 35 as an envelope and which, with the corresponding pitch P, is connected to the standard thread 34 according to the Fig. 2 Here, too, the pitch for the round thread 36 is 2 mm as shown in the illustration according to the Fig. 2 . In the Fig. 4 The interaction of the internal thread 25 of the storage housing 10 with the external thread 35 of the cover part 14 is now shown, wherein the adjacent thread flanks 28, 38 are paired together in contact with each other. Furthermore, the foot-side and head-side curves are kept at a radial distance from each other, wherein a curve R 2 , R 2 ′ with a larger radius always a rounding R 1 ′ , R 1 with a smaller radius, so that the respective rounding with the larger radius can support the smaller rounding via the thread flanks 28, 38 and accordingly notch effects are reliably avoided even when the hydraulic accumulator is subjected to high stress in the thread root.

[0021] The following formulas for the foot-side rounding result: R 1 , R 1 ′ = 1 6 H and for the head-side rounding R 2 , R 2 ′ = 1 5 P with H = 3 2 P and with P as the pitch of the round thread.

[0022] In this case, the pitch is 2 mm, resulting in a value of H of 1.73 mm. The curves R 1 , R 1 ′ have a radius of 0.289 mm and the head-side radii R 2 , R 2 ′ are 0.4 mm. The nominal diameter in the area of ​​thread section 20 for the hydraulic accumulator is given as 210 mm as an example. Other values ​​are conceivable, all of which depend on the choice of pitch for the round thread 26 or 36.

[0023] As can be seen from the Fig. 2 The fictitious extensions of two adjacent thread flanks 28 of the internal thread 25 of the storage housing 10 end in an acute angle, the angle vertex 46 of which is at a distance from the base-side rounding 32 at the deepest point A F = 1 6 H respectively a distance of 0.29, which corresponds to the radius R 1 , R 1 ′ corresponds.

[0024] Furthermore, the fictitious extensions of two adjacent thread flanks 28 end in another acute angle, the further base-side angle vertex 48 of which leads to a secant 50, which runs along the free head side of the standard thread with the same pitch P of 2 mm as the pitch determined for the round thread 26 of the internal thread 25, and passes through the head-side rounding 30 of the internal thread 25, with a distance A K = 1 4 H , which corresponds to a value of approximately 0.43 mm. As already explained, both threads of thread section 20 are designed with a nominal diameter that corresponds approximately to 100 times the pitch P of the respective round threads 26, 36 and, based on a pitch P of 2 mm, here has a value of 210 mm.

[0025] As can be seen in particular from the Fig. 1The threaded section 20 runs along a free end region of the storage housing 10, in which the wall thickness of the storage housing 10 is reduced such that the threaded section 20 comes to lie within a fictitious extension of the remaining cylindrical inner wall region 52 of the storage housing 10.

[0026] For an effective relief of the threaded section 20, it is further provided that at its opposite ends it opens into an annular recess 54, 56 which is delimited by wall parts of the storage housing 10 and the cover part 14.

[0027] The inventive solution creates a thread for securing cover parts 14 in accumulator housings 10 of hydraulic accumulator solutions that is insensitive to notches and their negative impact on fatigue strength. Characteristic of the new thread are the large, defined radii in the thread crest and thread root with mutual flank support in the transition area, effectively reducing notch effects. The trapezoidal standard threads otherwise used form thread pairs with an extremely stiff "screw" versus an extremely thin-walled "nut," which frequently leads to fatigue fractures due to notch effects in the aforementioned application area.Also atypical compared to such standard thread forms is the use of so-called fine threads with smaller pitches in hydropneumatic accumulators, which increase fatigue strength and thus ensure long-term operation of the hydraulic accumulator, even under high pressure loads. This has no equivalent in the state of the art.

Claims

1. Hydraulic accumulator having an accumulator housing (10) which is closed at least on a free end face (12) by a cover part (14) which can be fixed in the accumulator housing (10) via a threaded section (20), wherein, as part of the threaded section (20) on the accumulator housing (10), an internal thread (25) in the form of a round thread (26) is present, the individual thread flanks (28) of which together enclose, in a notional extension, a flank angle (α) of 60°, and in that the radius (R2) of the rounding is larger in the crest-side region (30) of the round thread (26) than the radius (R1) in the root-side region (32) of the round thread (26).

2. Hydraulic accumulator according to claim 1, characterised in that as a further part of the threaded section (20) on the cover part (14), an external thread (35) in the form of a round thread (36) is present, the individual thread flanks (38) of which together enclose, in a notional extension, a flank angle (β) of 60°, and in that the radius ( R 1 ′ ) of the rounding is smaller in the root-side region (40) than the radius ( R 2 ′ ) in the crest-side region (42) of the external thread.

3. Hydraulic accumulator according to claim 1 or 2, characterised in that, according to the following formulae, the root-side rounding (R1, R 1 ′ ) of the internal (25) and the external thread (35) where R1, R 1 ′ = 1 6 H and the crest-side rounding (R2, R 2 ′ ) of the internal (25) and external thread (35) whereR2, R 2 ′ = 1 5 P, where H = 3 2 P and where P is the pitch of the round thread (26, 36).

4. Hydraulic accumulator according to Claim 3, characterised in that the notional extensions of two adjacent thread flanks (28) of the internal thread (25) of the accumulator housing (10) terminate in an acute angle, the angular apex (46) of which is at a distance A F = 1 6 H from the root-side rounding (32) at the lowest point.

5. Hydraulic accumulator according to one of the preceding claims 3 or 4, characterised in that the notional extensions of two adjacent thread flanks (28) terminate in a further acute angle, the angular apex (48) of which extends at a distance A K = 1 4 H from a secant (50), which runs along the free crest side of a standard thread with the same pitch as the pitch determined for the round thread (26) of the internal thread (25) and passes through the crest-side rounding (30) of the internal thread (25).

6. Hydraulic accumulator according to one of the preceding claims, if dependent on claim 2, characterised in that the internal thread and the external thread are designed in such a manner that the nominal diameter of the threaded section (20) is approximately one hundred times the pitch P of the respective round thread (26, 36).

7. Hydraulic accumulator according to one of the preceding claims, if dependent on claim 2, characterised in that the notional contour of a metric ISO standard thread corresponding to the round thread (36) of the cover part (14) envelops the round thread (36) of the external thread (35).

8. Hydraulic accumulator according to one of the preceding claims, if dependent on claim 2, characterised in that within the threaded section (20) the thread flanks (28, 38) of the internal (25) and external threads (35) are in contact with each other and the thread turns R2, R 1 ′ ; R1, R 2 ′ adjacent to each other are spaced apart from each other.

9. Hydraulic accumulator according to one of the preceding claims, characterised in that the threaded section (20) extends along a free end region of the accumulator housing (10) in which the wall thickness of the accumulator housing (10) is reduced in such a manner that the threaded section (20) comes to lie within a notional extension of the other cylindrical inner wall region (52) of the accumulator housing (10).

10. Hydraulic accumulator according to one of the preceding claims, if dependent on claim 2, characterised in that the threaded section (20), consisting of an internal (25) and an external thread (35), opens at its opposing ends in each case into an annular recess (54, 56) which is formed by wall parts of the accumulator housing (10) and the cover part (14).