GB2494743A

GB2494743A - A damping device of a hydraulic assembly

Info

Publication number: GB2494743A
Application number: GB1211884.0A
Authority: GB
Inventors: Reiner Fellmeth; Oliver Gaertner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2011-09-13
Filing date: 2012-07-03
Publication date: 2013-03-20
Also published as: DE102011082585A1; FR2979960A1; DE102011082585B4; GB201211884D0

Abstract

A damping device 10 for damping the flow of a fluid 14 in a hydraulic assembly 12 is provided. The damping device 10 has a gas-filled damper chamber 32 and a damper membrane 30. The damper membrane 30 separates the flowing fluid 14 off from the damper chamber 32 and the damper chamber 32 is formed with a porous material 36.

Description

a hydraulic assembly

Prior art

The invention relates to a damping device of a hydraulic assembly for damping the flow of a fluid, having a gas-filled damper chamber and a damper membrane which separates the flowing fluid off from the damper chamber. Furthermoe, the invention relates *to a use of such a damping device on a hydraulic piston pump of a vehicle braking system.

In hydraulic assemblies or hydraulic units, in particular of vehicle braking systems, for example with antilock braking system (ASS) and electronic: stability programme (ESP), piston pumps are employed for conveying pressure media. The pressure media used are fluids, in particular liquids, such as for example brake liquid. Typical piston pumps comprise at least a pump element having a preferably cylindrical pump housing and a piston movable in and out situated therein. The piston serves, on the one hand, for sucking in and, on the other hand, for compressing the pressure medium. Furthermore, situated on the pump housing are in each case one or more inlet and outlet -valves for the pressure medium, which serve for controlling the pressure medium flow durin the piston-generated intake phase and subsequent compression phase. The inlet and outlet valves are typically formed as spring-loaded ball valves, that is to say with a ball as valve closing member, an associated valve seat and a spring as return means.

In the case of the individual inlet valve, the suction produced by an outward piston movement causeshe valve closing member to be lifted off from its associated valve seat in accordance with the suctiob, so that the fluid can flow in. During the inflow process, the valve closing member oscillates largely'. . in accordance with the suction differences produced in the fluid flow by the inflow. During a subsequent opposite inward piston movement, firstly pressure is produced on the fluid by the piston, and this, on the one hand, presses the valve closing member of the inlet valve against the valve seat of the latter and closes the inlet valve. On the other hand, the fluid is forced in the direction of the individual outlet valve. This gives rise to a fluid flow which lifts the valve closing member of the outlet valve off from the associated valve seat, sd that the fluid can flow out. During the outflow process, the valve closin member oscillates largely in accordance with the pressure differences produced in. the fluid flow by the outflow.

Overall, therfore, the abrupt chang between. suction and pressure causes strong conveying flow pulsations, which lead to strong pressure pulsations and mechanical oscillations.

In order to minimise such pressure pulsations or pressure differences, in known pump elements damping devices, such as for example pump darnpihg elements, are employed. Conventional pump damping elements have a space filled with gas, in particular with air, and a membrane which separates the flowing fluid off froth the gas-filled space. The gas-filled space is positioned behind the membrane in the flow direction of the fluid.. If the fluid flows past the valve closing member lifted off from the valve seat and strikes the membrane, then the membrane is deformed. This deformation causes the gas in the space located behind the membrane in the flow direction of the fluid to be compressed. A complete compression of the gas is not possible since with increasing compression the interactions of the compressed gas particles among one anothe increase and thus the backpressure and the temperatu±e of the gas rise.

Disclosure of the invention

According to the invention, a damping device of a hydraulic assethbly for damping the flow of a fluid is provided, having a gas-filled damper chamber and a damper membrane which separates the flowing fluid off from the damper chamber and in which the damper chamber is formed with a porous material.

The gas-filled damper chamber here is arranged after the damper membrane in the flow direction of the fluid. When the fluid flows, in accordance with the pressure or suction caused by the piston movement, against the valve closing member, the valve closing member is lifted off from the associated valve seat. In the process, the valve closing member. is pressed against the return spring and the fluid flows past the valve closing member.

Both the fluid and optionally the return spring and/or the valve closing member itself press against the damper membrane here and deform the latter. The deformation of the dathper membrane causes a compression of the gas in the adjoining damper chamber. The damper chamber includes walls which bound the gas f1o and thus additionally contribute to the. compression of the gas. In the compressioh of the gas, some of the kinetic energy of the fluid and ome of the deformation enery of the damper membrane, which has in turn already absorbed some of the kinetic energy of the valve closing member, is stored. A backpressure of the gas is built up, which on a subsequent expansion of the gas is reduced again, partly releasing the stored energy again. With this process, the damping effect of conventional damping devics is also largely realised. . . . . According to the invention, the damper chamber is formed with a porous material. The pnrous material has pore walls which at least partly, surround the pores or hollow spaces. If the individual pore is completely surrounded by the pore walls, then it is a closed pore which is not connected to the other pores.

Particularly preferably, for the most part the porous material has open pores which are characterised in that the individual *pcre is not completely surrounded by. pore walls. As a result, these open pores are connected to One another and to the environment and fluid, in particular gas, can penetrate.

According to the invention, with this porous material,, an the one hand, a statid and/or stabilising effect is achieved and at the' same time a larder volume for absorbing compressible gas, in particular air, is created in the damper chamber.

Given the same stability and same space requirement of the components compared with conventional damping devices, the larger volume can on the one hand provide'more compressible gas for the same pressure conditions. If more compressible gas is present, the damper membrane is deflected further and thus the valve closing member is lifted off further. Advantageously, greater fluid delivery rates are thus made possible.

On the other hand, particularly advantageously less constructional space is taken up for the damper chamber if a largely equal'volume of compressible gas is used, since in the porous material itself space is already created for the compressible gas. Moreover, a lightweight compcnent is created with the damper chamber made of porous material.

Advantageously, an improved damping effect is additionally achieved, since, on entry of the, gas into the porous material and on compression of the gas in the porous material, additional energy has to be' expended due to,frictional losses' at the material, , in particular at the pore wails., This energy',, expenditure contributes to the damping and thus increases the damping effect. The same applies on exit of the gas from the porous material as the piston moves in the opposite direction.

Particularly preferably, the damper chamber is formed with a first section which is free from material and a second section which is connected in a gas-conducting manner thereto and is filled with porous material. In this case, the first. section which is free from material is situated behind the damper membrane in the flow direction of the fluid, preferably directly adjoining the damper membrane, and the second section which is filled with porous material is situated after the first section in the same direction. Owing to the fact that the first section of the damper chamber is free from material or empty and in particular filled with gas, a largely free deflection of the damper thembr.ane is ensured. The deflection is only limited by the deformability of the damper membrane itself and by the backpressure which builds up owing to the compression of the gas. This backpressure of the gas is firstly reduced, since the qas flows or is pressed into the second section adjoining the first section and connected in a gas-conducting manner thereto.

The second section is formed with porous material, thereby creating with iLs interconnected pores or hollow spaces an additional volume for the absorption of the gas and the associated reduction of the backpressure. The reduced backpressure of the gas enables a further deflection of the damper membrane until the original backpressure of the gas is reached. This means that the damper membrane can be deflected further and preferably optionally the complete space of the first secticn is thus available as a compression space.

Advantageously, this enables higher delivery rates per unit of time. . . Preferably, the spatial extent of the first section and of the second section is designed such that the damper membrane after deflection largely rests in a supporting manner on the porous material of the second section. The.darnping backpressure is thus exerted on the damper membrane not only by the gas, but also by the, porous material. Pdvantagecusly, higher pressures or suctions can thus be produced by the piston and hence the fluid, and press against the damper membrane without the risk of damaging the damper membrane. In contrast thereto, this risk is present in conventional damping elements without such a support.

Preferably', the first section and the second section are each disc-shaped and the two sections adjoin one another with their end faces. Through such' a design, the sections and thus the damper chamber fit particularly well into the spatial extent of conventional, preferably, cylindrical, pump. elements. Moreover, a disc-shaped first material-free section, affords freedom of movement for a film membrane in, particular. The end-face boundary of the two section's forms a large transitional area for an entry and exit of the gas into and from the porous material, resulting in a quick gas exchange and pressure equalisation between the two sections.

Particularly preferably, the' first section is' surrounded by a ring-shaped sealing element. This sealing element or sealing ring seals the first section off at the latter's circumference from the fluid as pressure. medium. The ring-shaped design of the sealing element enables a simple, arrangement n a, blind bore while, simultaneously sealing the, first section. and advan'tagepusly the adjacent secnd section. Preferably, the adjacent damper membrane is simultaneously sealed off in addition. .. . . In a particularly preferred manner, the sealing element is formed in one piece with the damper membrane. The function of sealing off the first section, and optionally the second section, and the function of the damper membrane are thus combined in only one component, whereby on the one hand a high stability is achieved and on the other hand thi component can be produced advantageously simply by means of injection moulding or vulcanisation.

Preferably, a danping device is provided, in which the porous material is arranged in a cover of the hydraulic assembly.

Through such a design, the cover performs a dual function. The cover closes the hydraulic assembly, in particular an inlet or outlet valve and serves sirnultaneouèly at least partly as the second section of the damping device according tothe inention.

Space in the installation space is saved in a component by this dual function. Furthermore, owing to the fact that the cover is often advantageously of large-area design, a large area is provided for the entry and optionally exit of the gas into the porous material. A quick gas e<change and pressure equalisation between the gas-filled first section and the second section with porous material is ensured.

In a further advantageous development, the porous material extends through the cover from the inner side of the cover up to the outer side thereof. As a result, a gas-conducting connection exists through the cover, whereby advantageously a pxessure equalisation up to the outer side is possible. -If the pressure at the inner side is greater than the pressure at the outer side, a gas-conducting. connection from the inside, towards the outside is created. The gas flows outwards. If the pressure at the outer side is greater than at the innef side, the gas flows from the outside towards the inside. A pressure équalisation is

S

largely always ensured. Simultaneously, a damping effect is achieved by means of the flow friction of the gas through the porous material or medium. A backpressure of the gas through compression is achieved here largely only to the extent that the pore walls of the, porous material hinder the gas flowing throuh.

Furthermore, an advantageous damping device is provided, in which the entire cover is formed froth porous material. The cover -10 is produced very, simply from only one maLerial in one process, which saves time and costs. At the same time, the aforementioned effects and advantages of a cover with dual function and/or of a cover whose porous material extends through the cover are achieved.

Preferably, the porous material is formed with a sintered material. The sintered material is produced in a sintering process. To this end, granular or pulver-ulent materials are mixed, then brought into a shape, particularly advantageously already -into the desired shape, in particular a cover shape, and pressed together. Subsequent heating to a temperature below the melting point causes the sintCred material to agglomerate, that is t2 say be compacted and hardened, at high temperatures-. This results in a component already in the desired shape and with a specific proportion of pores or hollow spaces which ensure the.

permeability for the porous material. This-means that advantageously only one production process has to be carried out here, which saves costs. Particularly preferably, the sintered material is a sintered metal. Despite their pordsity, sintered metals are particularly stable and therefore advantageously suitable for use at high resures. Moreover, sintered metals are already produced in large series especially in the automotive -industry, so-' that adahtagdouSly existing manufacturing processes can be largely utilised with appropriate adaptation.

* In summary, according to the invention, with the use of porous material a novel damping device can be provided for a hydraulic assembly for damping the flow of a fluid. Advantageously, the damping device according to the invention is particularly lightweight, takes up little constructional space and can be produced cost-effectively and with a neutral design. Moreover, the complete utilisation of the compression space, only filled with gas. for deflecting the damper membrane is possible, since.

the gas is pressed into the pores of the porous material and compressed. Furthermore, higher pressures than in conventional damping elements can be Lealised with the fluid if the damper * 15 membrane is supported on the porous material.

The dan-ping device according to the invention is preferably used on a hydraulic piston pump of a vehicle braking system. The aforementioned advantages -have a particularly advantageous effect on such a piston pump. Above all, the small constructional space ad the low weight are desirable, in particular in motorcars, and thus contribute to fuel saving. The improved damping effect of the damping device according to the invention contributes to the creation of a low-vibration piston pump1 in which additionally an undesired audible vibration (NVH = Noise Vibration Harshness) is reduced. Furthermore, higher pressures than in conventional dampingelemerits can be realised with the fluid, in particular the brake liquid, and this may be of great advantage during the braking process. * Overall, an improvement in quality over conventional hydraulic piston pumps is thus achieved.

ParLicularly preferably, the porous material is not only permeable to gases, but also permeable to fluids. Fluids can then also be used as damping material.

Three exemplary embodiments of the solution according to the invention are explained: in more detaiY below with reference to the appended schematic drawings, in which: Fig. 1 shows a: longitudinal section of a first exemplary embodiment of a damping device according to the invention, Fig. 2 shows a longitudinal section of a second exemplary embodiment of a damping deviae according to the invention, and Fig. 3 shows a longitudinal section of a thitd exemplary embodiment of a damping device according -to the invention. -Figs. 1 to 3 each illustrate a damping device 10 of a partially illustrated cylindrical, hydraulic assembly 12 for damping the flow of a fluid 14, for example a brake liquid. In the present case, the hydraulic assembly 12 comprises a pump housing 16 having a piston (not illustrated specifically) mounted therein so as to be movable in and out, an inlet valve (not illustrated specifically) and an outlet valve 18. In the present case, the outlet valve 18 is configured as a -spring-loaded ball valve, having a ball as valve closing member 20, an associated valve seat 22 and a space-saving disc spring as return means 24. The return means 24 is held by a fastening element 26 which serves --simultaneously as outlet duct 28 for the fluid 14. Positioned after, the return means 24 in the flow direction of the fluid 14 is a damper membrane 30 and following that a gas-filled damper chamber 32. Thedamper membrane 30 is preferably disc-shaped and formed in one piece with a ring-shaped sealing element 34.

Together with the sealing element 34, the damper membrane 30 separates the fluid 14 off from the damper chamber 32. The damper chamber 32 is formed with porous material 36 which is arranged, in the present case, in a cover 38 of the hydraulic assembly 12. This cover 38 simultaneously forms the valve cover * of the outlet valve 18 and thus performs a dual function.

* The damper chamber 32 is surrounded by largely gas-impermeable walls 40 and formed with a first section 42 and a second section 44. The two sections 42 and 44 are each preferably disc-shaped (Figs. 1. to 2) and adjoin one another with.their end faces 46 and 48. The first section 42 is. arranged direotly after the damper membrane 30 in the flow direction of the fluid 14, is free from material and is filled with gas, in particular with air. The first section 42 is additionally surrounded preferably by a ring-shaped sealing element or sealing ring 34, which seals * the first section 42 off at the latter's circumference from the fluid 14 as pressure medium. In the present case, the ring- 20. shaped sealing element 34 is additionally formed in one piece with the disc-shaped damper membrane 30. Following the first section 42 in the flow direction of the fluid 14 is the second section 44, which is connected in a gas-conducting manner to the * first section 42 and filled with porous material 36. * 25

The porous material 36 has pore walls 50 at least partly Surrounding individual pores or hollow spaces 52 and 54. If the individual pore 52 is completely surrounded by the pore walls 50, then it is -closed pore 52. Preferably, however, for the most* part dpen pores 54 are present, in which the: individual pore 54 is only partly suirounded by the pore walls 50. A a result, the individual open pore 54 is connected in a gas-conducting manner to the other. opefl pores 54 and thus to the first material-free, gas-filled section 42. In the present case, the porous material 36 is a sintered material, in particular a sintered metal. Despite their porosity, sintered metals are particularly stable and therefore advantageously suitable for use at high pressures.

During the pumping process in the hvdtaSlic assembly 12, as the piston moves out a suction or negative pressure arises in the interior of the pump housing 16, causing the fluid 14 to flow into the pump housing 16 via the inlet valve {not illustrated) The cutlet valve 18 i substantially fluid-tightly closed as the piston moves out. As the piston subsequently moves into the pump housing 16, the inlet valve is closed and the fluid 14 is forced in the direction of the outlet valve 18. In the process, the fluid 14 flows against the valve closing member 20 of the outlet valve 18, lifts this closing member 20 off from the associated valve seat 22 and presses the closing member 20 against the disc spring as return means 24. The fluid 14 flows past the valve closing member 20 into a hydraulic system (not illustrated specifically) to perform work. Both the fluid 14 and optionally the return means 24 eert pressure against the damper membrane during this outflow processand deform the damper membrane 30 in doing so. This deformation of the damper membrane 30 firstly causes a compression of th gas in the adjoining first-section 42. The gas is subsequently pressed into the open pores 54 of the second section 44 and compressed there. In the compression, some of the kinetic energy of the fluid 14 and some of the deformation energy of the damper membrane 30, which has in turn already absorbed some of the kinetic energy of the valve closing member 29, is stored. A backpressure of the gas is tuilt up, which has a damping effect on the deflection of the damper membrane 30 and thus on the flow of the fluid 14. On a subsequent expansion of the gas, this backpressure is reduced again and the stored energy partly released again. The damping effect i improved in the damping device 10 according to the invention, since, on entry of the gas into the porous material 36 and on compression of the gas in the porous material 36, additional energy has to be expended due to frictional losses at the pore walls 50. This energy expenditure contributes to the damping and thus increases the damping effect. The same applies on exit of the gas from the porous material 36 as the pisten moves in the opposite direction For the entry and exit of the gas into and from the porcus material 36, the endface boundary of the two sectIons 42 and 44 forms a large transitional area, resulting in a quick gas exchange and pressure equalisation between the two sections 42 and 44.

Furthermore, the open pores 54 form an additional space or more volume for the compressible gas; with the. result that more gas is available for compression. As a result, the damper membrane 30 is deflected further compared with known damping devices.

Preferably, optionally the complete space of the first section 42 is thus available as a compression space, advantageously enabling higher delivery rates per unit of time.

Alternatively, less constructional space is required compared with known damping devices, if a, largely equal volume df compressible gas i used, since in the porous material 36 with :the open pores 54 themselves space is already available for, the compressible gas. . 30, Preferably, the spatial extent of the first section 42 and of the second section 44 is designed such that the damper membrane afer deIdction largely rests in -a supporting manner on the porous material 36 of the second section 44. The damping backpressure is thus exerted on the damper membrane 30 not only by the gas, but also by the porous material 36. Advantageously, higher pressures can thus be produced by the piston and hence the fluid 14, and press against the damper membrane 30 without the risk of damaging the damper membrane 30.

In the second exemplary embodiment in Fig. 2, the porous material 36 extends through the cover 38 froth the inner *side 56 of the cover up to the outer side 58 thereof. As a result, a gas-conducting connection exists through the cover 38. If the pressure as the piston moves in is greater on the inner side 56 than on the outer side 58, a gas-conducting connection from the inside towards the outside is created, whereby advantageously a (optionally deliberately slow) pressure equalisation up to the outer side 58 is possible. If the pressure as the piston moves out is greater on the outer side 58 than on the inner side 56, the gas is conducted from the outside towards the inside.

Simultaneously, a damping effect is achieved by means of the flow friction of the gas through the porous material 36. A backpressure of the gas through compression is achieved here la±gely only to the extent that the pore walls 50 of the porous material 36 hinder the gas flowing through.

In the third exemplary embodiment in Fig. 3, the entire cover 38 is formed from porous material 36 which extends through the cover 38. To this end, the cover 38 is produced very simply from only one material in one process and preferably designed to be * only gas-permeable, that is to say impermeable to brake liquid.