The present invention relates generally to a flow-control passive valve for controlling the flow of a fluid between a high-pressure upstream space and a low-pressure downstream space.

The flow-control passive valve of the present invention has been conceived in view of its application in a damping-adjustable shock-absorber, intended for instance to be used in an active or semi-active suspension system for a motor vehicle, and reference to such an application will be made in the following description. It is however clear that such a specific application is to be intended as not limiting the scope of protection of the present application.

Damping-adjustable shock-absorbers, which are able to change their damping characteristics under control of an electronic control unit to modify the behaviour of the vehicle suspension system depending for instance on the road conditions and/or on the vehicle driving conditions, are nowadays more and more often used, particularly in the automotive field.

With reference to Figure 1 of the attached drawings, a damping-adjustable shock-absorber according to a known embodiment is generally indicated 10 and basically comprises:

a pressure tube 12 enclosing a pressure chamber 14 filled with a damping fluid, typically oil;

a plunger 16 which is slidably mounted inside the pressure chamber 14 of the pressure tube 12 and divides it into a lower pressure chamber 14a and an upper pressure chamber 14b;

a rod 18 which carries at an end thereof the plunger 16 and projects on the opposite side from the pressure tube 12;

an outer tube 20;

an intermediate tube 22 which is fitted onto the pressure tube 12 and encloses a bypass chamber 24 which communicates with the upper pressure chamber 14b through communication holes 26 provided in the pressure tube 12; and

a flow-control active valve 28, typically a solenoid valve, which is connected to the intermediate tube 22 and is arranged to control the flow of the damping fluid between the pressure chamber 14 and the by-pass chamber 24.

Figure 2 of the attached drawings shows a typical pressure- flow rate characteristic curve of the damping-adjustable shock-absorber according to the prior art illustrated in Figure 1, with different values of the driving current of the flow-control solenoid valve. As can be seen, the pressure-flow rate characteristic curves have each a first ascending section (low flow rate values), the gradient of which increases along with the driving current of the solenoid valve, and a second section (high flow rate values), which is also ascending, the gradient of which is lower than that of the first section. It would be preferable to obtain pressure-flow rate characteristic curves having a first ascending section and a constant, if not even descending, second section, adjacent to the first one.

An example of a desired pressure-flow rate characteristic curve is shown in Figure 3 of the attached drawings, where a indicates the gradient of the first ascending section, in particular a substantially linearly ascending section, of the curve (from a flow rate value equal to zero to a flow rate value indicated Q*) and p* indicates the constant value of the pressure starting from the flow rate value Q*. Nowadays, in order to obtain an operation of the shock-absorber which is as closest as possible to the ideal one represented by the pressure- flow rate characteristic curve of Figure 3, the flow control solenoid valve can be operated with suitable driving logics. It is thus possible to obtain a second section of the pressure- flow rate characteristic curve which has a lower gradient than that of the first section, but which is still typically ascending instead of constant.

It is an object of the present invention to allow to obtain a pressure-flow rate characteristic curve in which a first ascending section is immediately followed by a second constant section, as in the characteristic curve shown in Figure 3, or even by a second descending section.

This and other objects are fully achieved according to the invention by virtue of a flow- control passive valve having the features defined in the appended independent claim 1. Advantageous embodiments of the invention are set forth in the dependent claims, the content of which is to be intended as integral and integrating part of the following description. In particular, the present invention relates to a damping-adjustable shock-absorber, particularly for an active or semi-active suspension system for a motor vehicle, comprising a flow-control passive valve as defined in the appended claims.

The features and advantages of the present invention will result more clearly from the following detailed description, given purely by way of non-limiting example with reference to the appended drawings, in which:

Figure 1 shows an axial section view of a damping-adjustable shock-absorber according to the prior art;

Figure 2 shows an example of a pressure-flow rate characteristic curve of the damping-adjustable shock-absorber of Figure 1 ;

Figure 3 shows an example of a desired pressure-flow rate characteristic curve of a damping-adjustable shock-absorber;

Figure 4 is an axial section view on an enlarged scale which shows a flow-control passive valve according to a preferred embodiment of the present invention, interposed between the intermediate tube and the flow-control active valve of a damping-adjustable shock-absorber of the same type as the one shown in Figure 1;

Figure 5 is an axial section view on a further enlarged scale which shows a detail of the flow-control passive valve of Figure 4; and

Figure 6 is an exploded view of the flow-control passive valve of Figure 4.

In the following description only the flow-control passive valve interposed between the intermediate tube and the flow-control active valve of a damping-adjustable shock-absorber will be explained in detail. As far as the overall structure and operation of the shock- absorber are concerned, reference can be made to the explanation given in the introductory part of the description in connection with Figure 1.

In the following description and claims, the term "axial" indicates a direction coinciding with or parallel to the axis of the flow-control passive valve, while the terms "radial" or "transverse" indicate any direction perpendicular to that axis. With reference to Figure 4, where parts and elements identical or corresponding to those of Figure 1 have been given the same reference numerals, a damping-adjustable shock- absorber, particularly for motorcar suspensions, is generally indicated 10 and comprises a pressure tube 12 enclosing a pressure chamber 14 filled with damping fluid, typically oil, an outer tube 20, an intermediate tube 22 which is fitted onto the pressure tube 12 and encloses a by-pass chamber 24, and a flow-control active valve 28, made for instance as a solenoid valve, which is connected to the intermediate tube 22 and is arranged to control the flow of the damping fluid between the pressure chamber 14 and the by-pass chamber 24.

The flow-control active valve 28 (hereinafter simply indicated as active valve) is attached to the outer tube 20 so as to extend along an axis (indicated Y in Figures 1 and 4) substantially perpendicular to the axis (indicated X in Figures 1 and 4) of that tube, that is to say, to the axis of the shock-absorber. In particular, in the proposed embodiment the active valve 28 is screwed onto an internally threaded tubular mounting element 30 which is rigidly connected in turn to the outer tube 20, for instance by welding.

The shock-absorber 10 further comprises a flow-control passive valve, generally indicated 32. In the illustrated embodiment, the flow-control passive valve 32 (hereinafter simply indicated as passive valve) is axially interposed between the intermediate tube 22 and the active valve 28 so as to act in series with the active valve 28. However, different arrangements of the passive valve inside the shock-absorber are conceivable.

With reference to Figures 5 and 6 as well, the passive valve 32 basically comprises:

a valve body including a first cup-shaped valve body element 34 arranged on the side of the intermediate tube 22 and a second cup-shaped valve body element 36 arranged on the side of the active valve 28, wherein the first valve body element 34 integrally forms a bottom wall 38 facing the intermediate tube 22 and a cylindrical lateral wall 40, while the second valve body element 36 integrally forms a bottom wall 42 facing the active valve 28 and a cylindrical lateral wall 44, the bottom walls 38 and 42 defining along with the cylindrical lateral wall 40 of the first valve body element 34 a cylindrical chamber 46 having an axis substantially coinciding with the axis Y defined above;

a cup-shaped movable member 48 accommodated in the cylindrical chamber 46 of the valve body so as to slide in the direction of the axis Y of that chamber, the movable member 48 integrally forming a bottom wall 50 facing the bottom wall 38 of the first valve body element 34 and a cylindrical lateral wall 52 guided in the cylindrical lateral wall 40 of the first valve body element 34;

a cylindrical helical spring 54 axially interposed between the bottom wall 42 of the second valve body element 36 and the bottom wall 50 of the movable member 48 so as to apply on the movable member 48 a force tending to urge that member towards the bottom wall 38 of the first valve body element 34; and

a plurality of metering discs 56 interposed between the bottom wall 38 of the first valve body element 34 and the bottom wall 50 of the movable member 48.

In the illustrated embodiment, the two valve body elements 34 and 36 are secured to each other by engagement between an outer threading provided on the cylindrical lateral wall 40 of the first valve body element 34 and an inner threading provided on the cylindrical lateral wall 44 of the second valve body element 36. However, other ways to secure the two valve body elements 34 and 36 to each other may be envisaged.

A fitting 58 is axially interposed between the first valve body element 34 and the intermediate tube 22 and has an axial through hole 60 in fluid communication with the by-pass chamber 24 of the intermediate tube 22.

The bottom wall 38 of the first valve body element 34 has, on its side facing the inside of the valve body, i.e. towards the cylindrical chamber 46, a first annular cavity 62 which is in fluid communication with the axial through hole 60 of the fitting 58, and via this latter with the intermediate tube 22, through a plurality of holes 64, or through a single annular opening, provided in the same bottom wall 38. A second annular cavity 66, of lower depth than that of the first annular cavity 62, is provided on the side of the bottom wall 38 facing the inside of the valve body. This second annular cavity 66 extends radially up to the inner surface of the cylindrical lateral wall 40 and is separated from the first annular cavity 62 by a first annular projection 68. A further cavity 70 of circular shape, also of lower depth than that of the first annular cavity 62, is provided in the centre of the side of the bottom wall 38 facing the inside of the valve body and is separated from the first annular cavity 62 by a second annular projection 72 extending in height up to the same level as the first annular projection 68.

The set of metering discs 56 stacked on each other is axially interposed in slidable way between the bottom wall 38 of the first valve body element 34 and the bottom wall 50 of the movable member 48 and, in the closed condition of the passive valve (which condition is illustrated in Figures 4-6), rests on the annular projections 68 and 72 of the bottom wall 38. The metering discs 56 have each a centre hole 74, the maximum radial size of which is smaller than the minimum radial size of the circular cavity 70 of the bottom wall 38. The centre hole 74 is preferably made as a circular hole of smaller radius than that of the circular cavity 70. At least one radial opening 76 (which can be seen only in Figure 6) extends from the centre hole 74 of the metering discs 56 (or better, at least of the bottom metering disc, i.e. the metering disc directly in contact, in the closed condition of the valve, with the annular projections 68 and 72) to allow, also in the closed condition of the passive valve, the damping fluid flowing from the intermediate tube 22 to the first annular cavity 62 of the bottom wall 38, in the manner described above, to flow towards the circular cavity 70 of the bottom wall 38 by-passing the second annular projection 72. Advantageously, the metering discs 56 have an outer diameter smaller than that of the cylindrical chamber 46 of the valve body so as to define with the inner surface of the cylindrical lateral wall 40 of that element a restrictor (that is to say, a passage having a reduced cross-section area) for the fluid flowing from the second annular cavity 66 to the cylindrical chamber 46.

In the bottom wall 50 of the movable member 48 a centre axial hole 78 is provided, whereby the cylindrical chamber 46 of the valve body is in fluid communication with the circular cavity 70 of the bottom wall 38 of the first valve body element 34 through that hole 78, as well as through the centre holes 74 of the metering discs 56. Moreover, in the cylindrical lateral wall 52 of the movable member 48 one or more openings 80 are provided which are made in such a manner that they put the second annular cavity 66 of the bottom wall 38 of the first valve body element 34 in fluid communication with the cylindrical chamber 46 of the valve body through the above-defined restrictor. The openings 80 thus have the function of allowing the fluid collecting in the second annular cavity 66 as a result of the upward movement of the movable member 48 to flow to the cylindrical cham- ber 46 of the valve body and from here to the active valve 28. The openings 80 may be radial openings made in the cylindrical lateral wall 52 of the movable member 38 or axial openings made in the bottom wall 50 of that member or again a combination of these two solutions, as in the illustrated embodiment.

Finally, the bottom wall 42 of the second valve body element 36 has a centre axial hole 82 in fluid communication with an inlet 84 of the active valve 28 to allow the fluid contained in the cylindrical chamber 46 of the valve body to flow towards that valve.

The operation of the passive valve 32 will be described now. In the closed condition of the valve, the movable member 48 is subjected to the elastic force of the spring 54, which tends to urge that member, along with the metering discs 56, against the bottom wall 38 of the first valve body element 34, i.e. to keep the valve closed, and to the force applied by the pressure pi of the fluid contained in the first annular cavity 62 of the bottom wall 38, which has a value close to that of the pressure P _H (high pressure) in the by-pass chamber 24 of the intermediate tube 22, the difference P _H - pi being due to the pressure drop through the holes 64. In such a condition, the radial opening (or the radial openings) 76 provided at least in the bottom metering disc 56 allows a minimum flow of fluid from the first annular cavity 62 to the cylindrical chamber 46 of the valve body, and from here to the active valve 28. The second annular cavity 66 is in fluid communication, through the restrictor defined between the radially outer edge of the metering discs 56 and the cylindrical lateral wall 40 of the first valve body element 34 and through the openings 80 provided in the movable member 48, with the cylindrical chamber 46 and hence with the active valve 28. The value P ₂ of the pressure in the second annular cavity 66 is therefore close to the value P _L of the pressure (low pressure) downstream of the passive valve 32.

When the pressure pi of the fluid in the first annular cavity 62 is such as to overcome the elastic force of the spring 54, the movable member 48 moves away from the bottom wall 38, thereby allowing the metering discs 56 as well to move away from that wall. The fluid contained in the first annular cavity 62 can now flow towards the cylindrical chamber 46 not only directly through the passage defined between the bottom metering disc 56 and the second annular projection 72, but also indirectly through the second annular cavity 66, through the restrictor defined between the radially outer edge of the metering discs 56 and the cylindrical lateral wall 40 of the first valve body element 34 and through the openings 80 provided in the movable member 48. The pressure drop due to the restrictor defined between the bottom metering disc 56 and the first annular projection 68 causes the pressure p ₂ in the second annular cavity 66 to be lower than the pressure pi in the first annular cavity 62, the difference pi - p ₂ progressively decreasing up to zero as a result of an increase in the opening degree of the valve (upward movement of the movable member 48). Accordingly, the effective value of the area on which the pressure pi acts varies from a minimum value equal to the area of the first annular cavity 62 to a maximum value tending to the sum of the areas of the first and second annular cavities 62 and 66.

It has been experimentally seen that the use of a flow-control passive valve made in the way illustrated above in a damping-adjustable shock-absorber allows to obtain a pressure- flow rate characteristic curve of the shock-absorber with a second constant, if not even descending, section adjacent to a first ascending section.

The two fundamental parameters of the pressure-flow rate characteristic curve of the shock-absorber, that is to say, the gradient a of the first (substantially linearly) ascending section and the constant value p* (or the maximum value p*) of the second constant (or descending) section, can be adjusted independently of each other by suitably designing the components of the passive valve. In particular, the parameter a depends on the geometrical characteristics of the radial opening (or of the radial openings) 76 of the bottom metering disc 56 through which the first annular cavity 62 of the bottom wall 38 of the first valve body element 34 is in fluid communication with the cylindrical chamber 46 of the valve body, while the parameter p* depends on the preload of the spring 54 acting on the movable member 48.

As already stated above, even though the passive valve has been described herein in the specific case of its application to a damping-adjustable shock-absorber, it can be used in any other application requiring to control the flow of a fluid between an upstream space at a high pressure P _H and a downstream space at a low pressure P _L . In this connection, it can be said in general terms that the passive valve comprises a valve body inside which there are defined

a main space (in the present application the first annular cavity 62 of the shock- absorber 10) in fluid communication on the one side with the upstream space (in the present application the by-pass chamber 24 of the intermediate tube 22 of the shock-absorber 10) through a first fixed restrictor (in the present application the holes 64), and on the other side with the downstream space (in the present application the active valve 28 of the shock-absorber 10) both through a second fixed restrictor (in the present application the radial opening 76 in the bottom metering disc 56) and through a first variable restrictor (in the present application the passage between the bottom metering disc 56 and the second annular projection 72, the cross-section area of that passage depending on the upward movement of the movable member 48), and

a secondary space (in the present application the second annular cavity 66) in fluid communication on the one side with the main space through a second variable restrictor (in the present application the passage between the bottom metering disc 56 and the first annular projection 68, the cross-section area of that passage depending on the upward movement of the movable member 48) and on the other side with the downstream space through a third fixed restrictor (in the present application the passage between the radially outer edge of the metering discs 56 and the cylindrical lateral wall 40 of the first valve body element 34),

whereby the pressure pi in the main space is lower than the pressure P _H due to the pressure drop through the first fixed restrictor, while the pressure p ₂ in the secondary space varies between the pressure pi in the main space and the pressure P _L in the downstream space depending on the opening degree of the valve.

Naturally, the principle of the invention remaining unchanged, the embodiments and manufacturing details may be widely varied with respect to those described and illustrated purely by way of non- limiting example.