US3672398A

US3672398A - Accumulator for absorbing a pulsation of pump pressure

Info

Publication number: US3672398A
Authority: US
Inventors: Ken Ichiryu; Mitsuaki Takenoshita
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1969-07-23
Filing date: 1970-07-15
Publication date: 1972-06-27
Anticipated expiration: 1989-06-27
Also published as: GB1313615A; DE2036199A1; CH512012A; JPS521126B1; FR2055443A5

Abstract

An accumulator to be provided in a conduit leading from a pump for absorbing a pulsation of pump pressure, which is so constructed that the ratio of the diameter of the accumulator neck da to the diameter of the conduit dp is not smaller than 0.5, i.e. da/dp > OR = 0.5 and the ratio of the length of the neck dL to the diameter of the conduit dp is not larger than 0.5, i.e. dL/dp < OR = 0.5.

Description

United States Patent Ichiryu et al. June 27, 1972 1541 ACCUMULATOR FOR ABSORBING A [56] References Cited PULSATION OF PUMP PRESSURE UNITED STATES PATENTS [72' hwcmnm. Km khhyu Hitachi; a 3,065,766 11/1962 Wenzl... ..138/30 Takwushna Kmsuta' both fj p 2,290,337 7/1942 Knauth ....138/30 7 3,211,348 10/1965 Green... 138/30 X 1 1 Assigneer Hitachi -1 y Japan 1,922,656 8/1933 Berdon ..138/26 [22] Filed: July 1970 Primary Examiner-Henry T. Klinksiel: [21] App1.No.: 55,147 Attorney-Craig, Antonelli, Stewart and Hill 57 ABSTRACT [30] Foreign Application Priority Data J 4 57687 An accumulator to be provided in a conduit leading from a July 23, 1969 Japan ..4 7 pump for absorbing a pulsation of p p pressure which is so constructed that the ratio of the diameter of the accumulator [52] US. Cl ..l37/586, 138/26 neck da to the diameter of the conduit dp is not smaller than 1 1 55/04 0.5, i.e. da/dp 0.5 and the ratio ofthe length ofthe neck dL 58 Field ofSearch ..138/26, 30; 137/568 to the diameter the conduit dp is not larger than 05 M dL/dp 0.

5 Claims, 9 Drawing Figures PATENTEnJum m2 SHEET 10F 3 H6. PR/Of? ART F/G 2 PR/Of? ART B EH33 mmbmmmmm 95x33 km Rags FREQUENCY INVENTORS KEN \u-HRYU mo MH'SUAKI TAKENOSMTA BY CW3, Ann-mm, S Qumr-I: L H-ill ATTORNEYS PATENTEDJum m2 3, 572,398

sum 20F 3 F/GI 7 INVENTORS KEN \CHIRYU AND MITSUAKI TAKENOSH TA Carols, HnRanelln', Stewart PH-i ATTORNEYS ACCUMULATOR FOR ABSORBING A PULSATION OF PUMP PRESSURE The present invention relates to an accumulator for absorbing a pulsation of pump pressure.

The object of the present invention is to provide an accumurepresented by the formula,

lator of the type described which is most effective for absorbing a pulsation of pump pressure.

It is well known to use an accumulator for absorbing a pulsation of pump pressure, but in practice, it is extremely difficult to absorb the pulsation effectively. In the case of hydraulic pumps, such as gear pumps, vane pumps and piston pumps, in particular, which operate with a pulsating pressure of several hundreds cycles, a veryfew cases have met with success in absorbing the pulsation.

This is mainly because'prior art accumulators have been designed based on a wrong idea that the concept of pressure accumulating or shock absorbing accumulators can be applied as such to the absorption of a' high frequency pulsation of pump pressure. Namely, the prior art accumulators, the capacities of which are in the range from several tens cubic centimeters to several tens liters, have been constructed as shown in FIG. 1, with a view to protecting a rubber bag as well as to increasing r of the neck 6 is small by reason of the check valve 3 and a valve seat therefor.

FIG. 2 exemplifies a small sized accumulator which has been called noise damper and used for the purpose of protecting the needle of a pressure gauge or the like. In FIG. 2, numeral l designates a rubber bag, 2 a-bomb, 3" a rigid plate bonded to the rubber bag to protect the latter by contacting with a seat portion 4' of the inside surface of the bomb, and 5' r a port connected with a main conduit. The effective inner diameter of a neck 6 is usually small.

It has been provided both theoretically and experimentally that it is almost impossible to lessen a high frequency pulsation of pump pressure by either one of such prior art constructions.

Now, this will be explained theoretically. FIG. 3 isa view schematically showing the conduit arrangement of a pump, in which an accumulator is incorporated to absorb a pulsation of.

pump pressure and thereby to prevent a vibration and noise of g the conduit. In the illustration, numeral 11 designates the the accumulator becomes small and similarlythe intended pump, 12 a main conduit, 13 a neck of the accumulator, 14 a bomb of the accumulator, 15 a rubber bag of the accumulator, 16 a sealed gas chamber of the accumulator, 17 a throttle and 18 a tank. The throttle 17 is depicted in the sense that the hydraulic line performs a work.

For absorbing a high frequency pulsation of pump pressure by an accumulator, two conditions must be satisfied, i.e. (l) the natural frequency of the accumulator system must be close to a main component of pulsating pressure and (2) the pulsation attenuation band must be wide so as to damp two or three components of pulsating pressure, since the frequency of pulsation of pump pressure is usually wide. In the case of l the mass M which governs the natural frequency of the accumulator is represented, in terms of the dimensions of the neck, approximately by the following formula,

M=pSdL (I) wherein p is the density of oil, S is the cross-sectional area of the neck and dL is the effective length of the neck. The spring constant K of the accumulator, in terms of the dimensions of the neck, is represented by the formula,

K 'y.P.S /v (2) wherein is the polytropic number of the sealed gas, P is the inherent mean pressure and v is the volume of the gas at a pressure I.

Therefore, the natural frequency fn of the accumulator is P small, if the values of Pand p are constant.

The amount of pulsating pressure damped by the accumulator is shown in FIG. 4. As seen, the damping band appears on each side of the natural frequency fn of the accumulator. The

area. of thedamping band can be expressed by the ratio of a comer frequency f at which the pulsating pressure is damped I by 3 dB, to the natural frequency fn, i.e. (f /L). The frequency f is represented theoretically by the formula,

. f l/21r ('y.P. S,,)/(p.C.v) (4) wherein S, is the cross-sectional area of the conduit and C is the velocity of the fluid.

wherein a is S/dLv.

Namely, the width of the damping region can be increased by making the value of f small when the value of j}, is constant or, in other words, under the condition that the value of a is constant; and by making the value of Sp/S small when the value within the radical sign of Formula (5) is constant. Thus,

it will be seen that it is effective to increase the cross-sectional I 1 area of the neck.

From the above result, it is concluded that, in order to satisfy the conditions l) and (2) set forth above, it is necessa-" ry (l) to increase the cross-sectional areaof the neck and to decrease the length L ofthe same, and (2) to make the capacity of the accumulator as large as possible to increasethe width of the damping band. I

It has been confirmed through experiment that the best result can be obtained when da/dp E 0.5 and further dL/dp s 0.5 wherein da is the diameter of the accumulator neck, dp is the diameter of the conduit and d1. is the length of the accumulator neck. 7 1

When da/dp 0.5, the secondary and .higher pulsating pressure cannot be absorbed, aswill be apparent from the line 6f da/dp.= 0.4 in FIG. 8, and hencethe intended effect cannot be produced, while when dL/dp 0.5, the natural frequency of effect cannot be achieved.

It will be obvious from the foregoing description that the prior art accumulators of the types shown in FIGS. 1 and 2 are FIG. 3 is a schematic view illustrating the manner in which the accumulator is used;

FIG. 4 is a diagram showing a theoretical curve of damping by the accumulator;

FIG. 5 is a side view showing in section an embodiment of the accumulator according to the present invention;

FIG. 6 is a front elevational view 'of the protective metal screen;

FIG. 7 is a side view showing in section another embodiment of the accumulator according to the invention;

FIG. 8 is a diagram illustrating in comparison the pulsating pressure absorbing results in a gear pump when no accumulator was used, when the prior art accumulator of FIG. 2 was used and when the accumulator, of this invention is used,

respectively; and

FIG. 9 is a cross-sectional view showing the construction of the rubber bag effectively used in the present invention.

Referring to FIGS. 5 and 7, numeral 20 designates a coupling-like segment of a pressure fluid conduit and a neck 21 of an accumulator is formed integrally therewith. By forming the neck 21 as a part of the conduit segment 20, the handling of the accumulator becomes extremely simple, and in addition, a fluid leakage which would otherwise occur at the a joint of the neck and the conduit, can be completely avoided. Numeral 22 designates a flange formed around the top end of the nee}: 21,'and 23 designates a flexible rubber bag having a U-shaped cross-section and disposed in the interior cavity A of the neck 21. The rubber bag 23 has a flange 24 formed at the means of bolts 28. Thereafter, a high pressure gas is sealed in the rubber bag 23 through the gas inlet hole 26. Numeral 29 designates a metal screen secured to the lower portion of the neck 21 as by welding, so as to be located on the underside of the rubber bag 23. As shown in FIG. 6, the metal screen 29 is composed of warps a and wefts b. Thismetal screen 29 serves to prevent rupture of the rubber bag 23 due to excessive exhigher components of pulsating preSsure though slightly effective against the primary component of the same. As contrasted, the accumulator according to the invention has an effect of damping the primary component of pulsating pressure by about dB and the secondary and tertiary components of the same by about 10 dB.

FIG. 9 shows the constructions of a rubber bag effectively used in the present invention. As shown, the wall thickness of the rubber bag is made smallest at 'the crest portion 41 of the outwardly bulged peripheral wall thereof and is progressively increased both upwardly and downwardly therefrom. Byemployin such structure, it is possible to decrease the rigidity of he ru r bag as a whole and to decrease the, stress developed in the rubber. It is also possible to make sufficiently large the wall thickness at the flange portion 42 and the portion 44 .where the metal plate 43 isattached to the rubber bag 40. A

life test conducted on the rubber bag of such construction has proved that the rubber bag is useful for a sufliciently long period.

It is to be understood that the rubber bag may be made from a rubber material having a tire cord incorporated therein, and

the use of such rubberimaterial is highly effective in preventing an excessive expansion of the rubber bag at the time of pansion and also to increase the undersurface area of the rubber bag 23 or the area S of the neck. Numeral 30 designates external threads formed on each end of the conduit segment 20 for connection with a pressure fluid conduit, e.g. the conduit 12 shown in FIG. 3. In the embodiment described above, the ratio of the neck diameter da to the diameter of the conduit tip is l, i.e. da/dp l.

FIG. 7 shows another embodiment of the present invention, in which same numerals as those used in FIG. 5 indicate same parts. Numeral 31 designates a neck. of an accumulator formed integrally with a conduit segment 20. The inside peripheral surface of the neck 31 is recessed as at 32 and an annular seat 33 isformed below the recess32. Numeral 34 designates a rubber bag disposed in the internal cavity A of the neck 31. The peripheral wall of the rubber bag 34 isbulged outwardly in a shape complementary to the shape of the-recess 32, and a metal plate 35 is secured to the undersurface of the rubber bag 34 by an adhesive. The metal plate 35 has the same functions as the metal screen 29 in the preceding embodiment, by contacting the seat 33.

Further, the metal plate 35 obviates the disadvantage of the metal screen 29 that the rubber bag bulges through the individual meshes of the screen and tends to rupture when the meshes are coarse. The seat 33 has the advantage that the cumbersome operation required for mounting the metal screen 29 can be eliminated. The construction involving the seat 33 is employed only when the metal plate 35 is provided on the rubber bag. The ratio of the neck diameter da to the diameter of the conduit dp, in this embodiment, is l, i.e. da/dp 1.

FIG. 8 is a diagram showing the relationship between the frequency of pulsation and the amount of pulsating pressure damped, in the cases when no accumulator was used, when the conventional accumulator was used and when the accumulator of the present invention, shown in FIG. 5, was used. From the diagram, it will be clearly understood that the conventional accumulator is ineffective against the secondary and sealing a gas therein.

As described in detail herein, according to the present invention an accumulator can be obtained which is capable of highly effectively absorbing a pulsation of pump pressure, and hence the invention is of great industrial advantage.

What is claimed is: a

1. An accumulator for absorbing a pulsation of pump pressure comprising a cylindrical neck (21, 31) projecting outwardly from a conduit (20) connected to a pump, said neck defining a substantially cylindrical cavity (A) having a lower end directly opening to said conduit and an upper end closed with a cover (25), a substantially cylindrical rubber bag (23,

34) coaxially disposed in said cavity and sealingly secured at its upper end to said cover to form a gas containing chamber therein, and a gas inlet hole (26) provided on said cover for charging gas into said chamber, wherein the ratio of the inner diameterof said neck (cavity) da to the inner diameter of said conduit dp is not smaller than 0.5, i.e. da/dp z 0.5, and the v ratio of the length of said neck (cavity) dL to the inner diameter of said conduit dp is not larger than 0.5, i.e. dL/d 0.5.

2. An accumulator as defined in claim 1, further comprising a stopper consisting of a screen disposed at the lower portion of said cavity for restricting the expansion of said rubber bag, said stopper being formed to permit free communication of fluid between said cavity and said conduit.

3. An accumulator as defined in claim 1, wherein said rubber bag is provided with a metal plate 35 adhesively secured to the entire outer surface of the bottom wall of said a rubber bag and a' seat (33) being formed on the peripheral wall of saidcavity at the lower portion thereof to restrict the expansion of said rubber bag by contact with said metal plate.

4. An accumulator as defined in claim 1, wherein the peripheral wall of said rubber bag is outwardly bulged at the middle portion of the length thereof and the thickness of said peripheral wall is smallest at said middle portion and is progressively increased upwardly and downwardly therefrom.

5. An accumulator as defined in claim 2, wherein said screen is formed of a metal of large mesh.

Claims

1. An accumulator for absorbing a pulsation of pump pressure comprising a cylindrical neck (21, 31) projecting outwardly from a conduit (20) connected to a pump, said neck defining a substantially cylindrical cavity (A) having a lower end directly opening to said conduit and an upper end closed with a cover (25), a substantially cylindrical rubber bag (23, 34) coaxially disposed in said cavity and sealingly secured at its upper end to said cover to form a gas containing chamber therein, and a gas inlet hole (26) provided on said cover for charging gas into said chamber, wherein the ratio of the inner diameter of said neck (cavity) da to the inner diameter of said conduit dp is not smaller than 0.5, i.e. da/dp > OR = 0.5, and the ratio of the length of said neck (cavity) dL to the inner diameter of said conduit dp is not larger than 0.5, i.e. dL/dp < OR = 0.5.

3. An accumulator as defined in claim 1, wherein said rubber bag is provided with a metal plate (35) adhesively secured to the entire outer surface of the bottom wall of said rubber bag and a seat (33) being formed on the peripheral wall of said cavity at the lower portion thereof to restrict the expansion of said rubbEr bag by contact with said metal plate.