Hydraulic suspension damper with a spring valve assembly

A hydraulic damper (2) includes at least one spring valve assembly (28b, 28c) having a body (231, 261) provided with through flow channels (282), at least one deflectable disc (281) covering these through flow channels (282), and a supporting member (285, 285c) fixed to an axial member for clamping the at least one disc (281) at the inner circumferential part thereof. A spring seat (283b, 283c) is disposed around the supporting member (285, 285c) and abuts the at least one deflectable disc (281) in at least one radial position (2831, 2832) at the outer circumferential part thereof. A spring (284) is preloaded between the spring seat (283b, 283c) and the supporting member (285, 2851c). The spring seat (283b, 283c) includes at least one axial projection (2833b, 2833c) perimetrically engaging the at least one disc (281), and a circular gap (286) is provided between the spring seat (283b, 283c) and the supporting member (285, 2851c).

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of PCT International Application Serial No. PCT/CN2013/078807 filed on Jul. 4, 2013 and entitled a “Hydraulic Suspension Damper with a Spring Valve Assembly”, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a hydraulic damper, in particular a motor vehicle suspension damper, comprising a tube filed with working liquid inside of which a slidable piston body attached to a piston rod led outside the damper is disposed, wherein the flow of the working liquid is controlled within said tube during the rebound and the compression stroke of the piston body by at least one spring valve assembly provided with an axial member and rebound and compression valves surrounding the axial member. Said at least one spring valve assembly comprisesa body provided with through flow channels,at least one deflectable disc covering these through flow channels,a supporting member fixed to said axial member,a spring seat disposed around said supporting member and abutting said at least one disc in at least one radial position at the outer circumferential part thereof, anda spring preloaded between the spring seat and the supporting member.

BACKGROUND OF THE INVENTION

Valve assembly of this kind, where the spring seat is disposed slidably around the supporting member, is known from the state of art (cf. for example Polish patent applications P. 358597, P. 358598, P. 358599 and European patent applications EP 1925845 A1, EP 2233775). For its efficient operation it is absolutely essential to ensure substantially frictionless sliding (axial) movement of the spring seat with respect to the supporting member.

Various factors contribute to this problem including eccentricity and radial dimensional tolerances of particular elements of the valve assembly, possible buckling of the spring and distribution of the axial pressure exerted by the spring over the perimeter of the spring seat.

Influence of friction on operation of a valve assembly of this kind may be observed by measuring the force reaction of a damper in dependence to the velocity of the piston rod (a force to velocity characteristic). As it appears a substantial hysteresis occurs.

In other words forces measured while the piston rod accelerates to trigger opening of the spring valve assembly and deflection of discs are higher than forces measured while the piston rod decelerates to close the spring valve assembly and discs move to their neutral position. A difference exists therefore between damping forces generated by the damper for the same velocity of the piston rod but measured during its acceleration or deceleration and it is desirable to limit this difference as much as possible in order to improve the damper performance, repeatability coefficient and also the comfort for the passengers of the vehicle.

Patent specification GB 699896 discloses a hydraulic shock absorber, where a spring seat has a form of an abutment ring having an outwardly extending flange which rests upon the outer deflectable disc adjacent its outer edge. The outer deflectable disc is provided with an orifice covered by the inner deflectable disc and a clearance exists between the abutment ring and a cylindrical member that allows fluid communication through said orifice between the flow channels and the chamber of the shock absorber once the discs are deflected.

Patent specification U.S. Pat. No. 4,096,928 discloses a valve assembly for a shock absorber, where a spring seat has a form of a valve cage having a cylindrical portion surrounding the resilient valve disc for a centered guiding thereof. The cylindrical portion has an edge face which serves as an abutment for cooperating with the closing disc.

It has been the object of the present invention to provide a hydraulic damper having an improved sensitivity of operation in a result of minimizing the friction between cooperating elements of the valve assembly.

Another object of the present invention is to provide a hydraulic damper that would enable to achieve comparable working characteristic of all dampers in the line production within a large range of dimensional tolerances of the damper components in order to minimize the production specific losses, decrease the costs of production and increase the result repeatability coefficient.

SUMMARY OF THE INVENTION

In order to accomplish the aforementioned and other objects, in a damper of the kind mentioned in the outset, according to the present invention the spring seat of said at least one spring valve assembly comprises at least one axial projection perimetrically engaging said at least one disc and a circular gap is provided between said spring seat and said supporting member.

Such a construction enables for centering of the spring seat only with relation to the upper deflectable disc of the spring valve assembly, so that no guidance of the seat is required for its axial movement and no sliding problems occur.

Preferably said spring seat comprises one axial projection or alternatively a number of axial projections distributed, preferably equiangularly, over the outer perimeter thereof.

Preferably axially outer diameter of said at least one axial projection is larger than its axially inner diameter to ensure axial guidance of the spring seat over said at least one disc during assembly of the hydraulic damper.

Preferably said at least one valve assembly is a part of a piston valve assembly.

Alternatively or additionally (in case of a twin-tube damper) said at least one valve assembly may form a part of a base valve assembly.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1schematically illustrates a fragment of an exemplary vehicle suspension1attached to a vehicle chassis11by means of a top mount12and a number of screws13disposed on the periphery of the upper surface of the top mount12. The top mount12is connected to a coil spring14and a rod21of a mono- or twin-tube hydraulic damper2. Inside a tube of the damper2a piston assembly attached to the rod21led outside the tube is slidably disposed. At the other end the damper tube is connected to the steering knuckle15or a swing arm supporting the vehicle wheel.

A hydraulic damper2shown in part inFIG. 2is an example of a twin-tube damper that may be employed in a vehicle suspension1presented inFIG. 1. It comprises a movable piston assembly23making a sliding fit with the inner surface221of the tube22and dividing the tube22into a rebound chamber24(above the piston assembly) and a compression chamber25(below the piston assembly).

At one end the piston rod21passes through and is secured to the piston assembly23. The other end of the piston rod21is led axially outside the damper2through a sealed rod guide (not shown). At the compression end, the tube22is closed by a base valve assembly26.

Valve assemblies27and28bof the piston assembly23control the flow of working liquid passing between the rebound chamber24and the compression chamber25while the piston is in movement. Similarly, valve assemblies29and28ccontrol the flow of working liquid passing between the compression chamber25and an additional compensation chamber30located between the tube22and the second outer tube32of the damper.

Valve assembly28bof the piston assembly23has been illustrated inFIG. 4in comparison to the valve assembly28aknown from the state of art illustrated inFIG. 3. Above and below, reference numerals of elements performing the same or similar functions remain the same, wherein suffixes (b-c) have been added to distinguish particular embodiments of the invention, where appropriate.

As shown, axial member in a form of partially threaded projection211of the piston rod21supports the compression valve assembly27, a piston body231and the rebound valve assembly28b.

The compression valve assembly27comprises a number of discs271deflectably covering the compression through channels (not shown) in the piston body23. Similarly, the stack of deflectable discs281covers the rebound through channels282in the piston body231. All elements of the piston assembly23are clamped at the inner circumferential portions thereof by a supporting member in a form of a shoulder nut285screwed on the external thread provided on a part of the projection211with a predetermined torque. Supporting member285clamps at least one disc271of the valve assembly27at the inner circumferential part thereof.

Deflectable discs281are additionally preloaded by a spring284compressed between the shoulder of the nut285and a spring seat283aor283bdisposed to displace along the longitudinal axis of the damper2in order to angularly equalize possible variations in axial pressure of the spring over its perimeter transferred to the top disc281surface. Furthermore, each spring seat283aand283bis provided with two circumferential projections2831and2832to control deflection of the discs under the pressure of the working liquid flowing through the channels282during rebound stroke of the damper2.

Number, shape, diameter and thickness of discs281, number and diameter of the channels282and preload of the spring284, among others, constitute the parameters that are used to adjust damping forces.

As shown the spring seat283aknown from the state of art is disposed to slide over the surface of the shoulder nut285and in its sliding movement is guided by the surface of the shoulder nut285. Therefore this sliding movement is prone to dry friction that is influenced by various factors, such as possible buckling of the spring that generates bending moment over the spring seat283aso it may grind over the surface of the shoulder nut285. Dimensional tolerance of the particular elements of the assembly also influences the operation of a valve assembly after it is manufactured.

If for example a nominal diameter of the supporting member285is d1and nominal diameter of the spring seat283ais d2then to ensure the sliding movement between any pair of these components taken out of the production batch:
d1/2+Δd1/2<d2/2−Δd2/2
where Δd1and Δd2are respectively upper deviation of the supporting member285diameter and lower deviation of the spring seat283adiameter. From the inequality above it follows that a gap will usually exist between the spring seat283aand the shoulder nut285at least in some angular areas due to mutual eccentricity of these elements. This gap will obviously negatively influence sliding between these elements.

Contact between the spring seat283aand the shoulder nut285is obviously necessary for the sliding guidance of the spring seat283aover the shoulder nut285but at the same time, due to the unpredictable (inevitable axial shift of these elements) locations of these areas of contact and the contact itself, aforementioned friction problems occur.

As shown inFIG. 4the spring seat283bof the present invention is centered in relation to the top disc281by perimetrically engaging the seat283bby means of an axial projection2833b. In this embodiment, the seat285bis provided with one projection2833bextending over the whole perimeter of the seat283b(cf.FIG. 5) and abutting the perimetric edge of the top disc281.

As shown outer diameter of the axial projection2833bis slightly larger than its axially inner diameter, do that the seat285bsimply draws over the top disc281during assembly of the piston assembly23.

A circular gap286is provided between the inner surface of the sleeve-like part of the seat283band the external surface of the shoulder nut285. In a result, the seat283bis guided solely by means of the top disc281in such a manner that the seat283bdoes not contact the shoulder nut285at all during its axial movement. The sleeve-like part of the seat283bserves only for positioning (centering) the spring284relative to the seat283band for guiding the spring284. In other words the gap286serves to avoid contact of the seat283band the shoulder nut285and is not an obstacle for the axial movement of these two components that is required in the assembly28aknown from the state of art (cf.FIG. 3).

FIG. 6presents an alternative embodiment of the spring seat283cprovided with six axial projections2833cequiangularly distributed over the outer perimeter of the seat283c. The seat283cmay be successfully employed in the valve assembly28bin place of the seat283bofFIG. 5.

FIG. 7presents a detailed view of the base valve assembly26of the hydraulic damper2shown in part inFIG. 2. Axial partially threaded projection311of a bolt31of the base valve assembly26supports the compression valve assembly28cand the rebound valve assembly29on a body261of the base valve assembly26. The deflectable discs of the valve assemblies28cand29are clamped on the projection311at the inner circumferential portions thereof by a nut285cscrewed on the external thread provided on part of the projection311with a predetermined torque. Deflectable discs of the compression valve assembly28care preloaded by a spring284compressed between a supporting member2851cand the spring seat283cofFIG. 6. The supporting member in a form of a clamp nut2851cis clamped on the nut285cforming at least one indent in at least one circular undercut of the nut285c.

Similarly as in the rebound valve assembly28bofFIG. 4, between the inner surface of the sleeve-like part of the seat283cand the outer surface of the external surface of the nut285ca circular gap is provided, wherein the seat283cis centered in relation to the disc of the valve assembly28cby means of the axial projections2833cperimetrically engaging the disc.

As the seat283cis not guided by the nut285c, it may be substantially shortened to a length sufficient only for reliable catching the uppermost one or two coils of the spring284thus enabling for appropriate positioning of the spring284relative to the seat283c. In comparison with the embodiment ofFIG. 4, such a construction is less sensitive to possible axial distortions of the seat283c. In order to compensate shortening of the spring seat283c, the supporting member2851cis provided with a lengthened section guiding the spring284and providing an improved stabilization and guidance for the lower section of the spring284.

In order to measure the influence of valve assembly of the present invention on the damper performance the inventors conducted the following experiment.

Eight springs have been used of various deflection angle defined as an angle between bottom and top surfaces of the spring so that a perfect spring would have a zero angle. Springs1-3were three different but typical springs used in valve assemblies of this kind; springs4-8were additionally deformed in order to artificially increase this naturally present deflection angle. Three spring seats have been used: two spring seats according to the present invention (Spring seat No.1, cf.283bonFIG. 4andFIG. 5and Spring seat No.2cf.283conFIG. 6) and a standard spring seat (Spring seat No.3, cf.283aonFIG. 3).

Springs and seats were mounted on a piston assembly of a twin-tube damper as shown inFIG. 2wherein each spring was tested with each spring seat so that 24 experiments have been performed.

Testing procedure involved measuring damping force as a piston rod velocity input sinusoidal function and subsequently determining the maximum measured difference D (“force gap”) during rebound stroke between damping forces observed for the same velocity value during acceleration and deceleration of the piston rod.

Results of the testing procedure are listed in Table 1 and illustrated inFIGS. 8, 9showing a force to velocity characteristic observed for a standard spring seat283ashown onFIG. 3.

As shown, the valve assembly with a spring seat of the present invention allowed on average for 77% (Spring seat No.1) and 82% reduction (Spring seat No.2) of the measured “force gap” with respect to the typical spring seat known from the prior art.

The above embodiments of the present invention are merely exemplary. The figures are not necessarily to scale, and some features may be exaggerated or minimized. These and other factors however should not be considered as limiting the spirit of the invention, the intended scope of protection of which is indicated in appended claims.