Hydraulic damper with a hydraulic compression stop assembly

The present invention relates to a hydraulic damper comprising a main tube; a main piston assembly; a base valve assembly; and a hydraulic compression stop assembly comprising an insert fixed on the base valve assembly, and an additional piston assembly apt to be introduced inside the first inner chamber of the insert at the end of the damper compression stroke to generate additional damping force. Said additional piston assembly comprises a piston rod extender fixed to the piston assembly or the piston rod at the side of the compression chamber, and a tenon fixed to said piston rod extender and radially displaceable with regard thereto, wherein said tenon is terminated with a first entry surface having diameter monotonically diminishing towards the compression end of said tenon, while the insert is provided with a second entry surface having diameter monotonically increasing towards the rebound end of the insert.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 202110399636.8, filed on Apr. 14, 2021, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a hydraulic damper, in particular a motor vehicle suspension damper, comprising a main tube filled with working liquid; a main piston assembly disposed slidably inside the main tube along an axis, attached to a piston rod led outside the hydraulic damper through a sealed piston rod guide, dividing the main tube into a rebound chamber and a compression chamber, to control the flow of working liquid passing between the rebound chamber and the compression chamber; a base valve assembly located at the end of the compression chamber to control the flow of working liquid passing between the compression chamber and an additional compensation chamber; and a hydraulic compression stop assembly (HCS) located in the compression chamber and comprising an insert fixed on the base valve assembly, configured to allow the flow of fluid between the insert and the main tube through the base valve assembly, and provided with a first inner chamber, and an additional piston assembly displaceable along with the main piston assembly and apt to be introduced inside the first inner chamber of the insert at the end of the damper compression stroke to generate additional damping force.

BACKGROUND OF THE INVENTION

A hydraulic damper of this kind is disclosed, for example in the patent publication EP3499084. In order to improve durability of the HCS assembly at high velocities of the piston rod that high velocities may occur e.g. while a vehicle wheel hits an obstacle and induce a rapid increase of the pressure within the insert, which pressure may crack the insert or destroy other components of the HCS assembly, it comprises a second compression chamber located at least partially inside of the additional piston assembly, wherein a displaceable partition is disposed between the first and the second compression chamber.

Publication EP3244090 discloses a HCS assembly comprising an additional plastic piston snaplocked over the piston rod in an annular recess of the rod and capable of rotational and axial displacement within the limits of this snapping recess. The additional piston is provided with a number of preferably equiangularly spaced radially internal channels, and a number of preferably equiangularly spaced radially external channels, each having a cross-sectional surface in a plane perpendicular to the piston rod axis that decreases along the additional piston length and is the largest at its face distal to the main piston assembly.

It has been the object of the present invention to provide a hydraulic damper with a HCS assembly, which would be cost efficient and simple in manufacture and assembly, which would endure high pressures within the insert, and provide versatile tuning properties for shaping the additional damping force as a function of the tenon position within the insert, such that this additional damping force characteristic would be substantially monotonic and devoid of any undesirable peaks even at high velocities of the piston rod.

Yet another object of the present invention has been to provide a damper with a HCS assembly that would not require substantial modifications of the remaining components of a damper and might be employed as an add-on device in existing damper designs.

SUMMARY OF THE INVENTION

Therefore, a damper of the kind mentioned in the outset, according to the present invention is characterised in that said additional piston assembly comprises a piston rod extender fixed to the piston assembly or the piston rod at the side of the compression chamber, and a tenon fixed to said piston rod extender and radially displaceable with regard to said piston rod extender, wherein said tenon is terminated with a first entry surface having diameter monotonically diminishing towards the compression end of said tenon, while the insert is provided with a second entry surface having diameter monotonically increasing towards the rebound end of the insert.

This provides axial guidance of the tenon and smooth activation of the HCS assembly. Misaligned tenon shall always be displaced the axis due to the cooperation of the second entry surface of the insert and the first entry surface of the tenon and peak forces that may occur at the entry of the tenon into the insert are eliminated, even at high speeds of the tenon, when high level of the additional damping force is required.

Preferably said tenon has a substantially tubular shape and is provided with an internal annular recess defining an internal opening, wherein said additional piston assembly further comprises a mounting member provided with shank having diameter smaller than the diameter of said internal opening and fixed inside the piston rod extender along the axis, so that the internal annular recess of the tenon is disposed between the piston rod extender and a head of said mounting member.

This provides simplicity of the hydraulic compression stop assembly.

Preferably said tenon is provided with a number of, preferably equiangularly spaced, axially extending grooves, each having a cross-sectional surface that diminishes along the length of the groove towards the main piston assembly.

This provides smooth built-up and tunability of the damping force. Thanks to placing the grooves on the tenon, deep grooves can be made right at the first entry surface. On the other hand the insert devoid of the grooves features an improved durability and simplified construction.

Preferably said tenon is provided with a second inner chamber facing the first inner chamber of the insert.

This enables for a radial deflection of said tenon into said second inner chamber and thus improves axial guidance of the tenon.

Preferably said tenon is provided with at least one axially extending channel fluidly communicating said second inner chamber of said tenon with the compression chamber.

This also provides smooth built-up and tunability of the damping force.

Preferably said tenon is made of plastic.

This improves its deflection.

Preferably said insert is made of metal and is press-fitted to a metal fixing member fixed to the base valve assembly, wherein an inner cylindrical surface of said insert and an external wall of said fixing member define said inner chamber.

Alternatively preferably said insert is fixed to a fixing member fixed to the base valve assembly, wherein an inner cylindrical surface and a bottom surface of said insert define said first inner chamber.

Preferably said first entry surface of said tenon and/or said second entry surface of said insert is/are conical.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG.1schematically illustrates a fragment of an exemplary vehicle suspension comprising a damper1of the present invention attached to a vehicle chassis101by means of a top mount102and a number of screws103disposed on the periphery of the upper surface of the top mount102. The top mount102is connected to a coil spring104and a piston rod5of the damper1. The tube2of the damper1is connected to the steering knuckle105supporting the vehicle wheel106.

FIG.2presents an embodiment of a twin-tube damper1according to the present invention. The damper1comprises an external tube2and a main tube3filled with viscous working liquid inside of which a movable piston assembly4attached to a piston rod5led outside the damper1through a sealed piston rod guide6is disposed. The damper1is also provided with a base valve assembly7fixed at the other end of the main tube3. The piston assembly4makes a sliding fit with the inner surface of the main tube3and divides the tube3into a rebound chamber11(between the piston assembly4and the piston rod guide6) and a compression chamber12(between the piston assembly4and the base valve assembly7). An additional compensation chamber13is located at the other side of the base valve assembly7.

The piston assembly4is provided with compression42and rebound41valve assemblies to control the flow of working liquid passing between the rebound chamber11and the compression chamber12while the piston assembly4is in motion along an axis A. Also the base valve assembly7is provided with rebound71and compression72valve assemblies to control the flow of working liquid passing between the additional compensation chamber13and the compression chamber12, respectively, during rebound and compression stroke of the damper1. As it is well known to those skilled in the art, the valve assemblies41,42and71,72provide design parameters that may be used to shape desired characteristic of the twin-tube damper1.

The damper1is further provided with a hydraulic compression stop assembly8alocated in the compression chamber12to generate an additional damping force at the end of the compression stroke e.g. in order to avoid abrupt stop of the piston assembly4. Main components of the compression stop assembly8aare an insert81aand an additional piston assembly83a. In this embodiment the insert81ais fixed to the base valve assembly7by means of a sintered steel fixing member82apress-fitted to the base valve assembly7and to the main tube3. The insert81ahas a simple cylindrical shape and is made of metal by cold drawn method. The insert81ais also press-fitted to the fixing member82a. The insert81ais provided with an inner cylindrical surface811that, along with an external wall821of the fixing member82a, define a first inner chamber84. The insert81ahas a radially external wall812distanced from the inner wall of the main tube3, allowing the flow of fluid from the compression chamber12to the additional compensation chamber13(and in the opposite direction) between the insert81aand the main tube3through a number of flow passages822in the fixing member82aand the base valve assembly7.

The reference numerals corresponding to the same functional elements remain the same throughout the description with suffixes (a, b, c) added, where appropriate to distinguish particular embodiments of the hydraulic compression stop assembly8a,8b,8c.

The additional piston assembly83ais displaceable along with the piston assembly4and comprises a piston rod extender832, a tenon831aand a mounting member833. In this embodiment the piston rod extender832is fixed to the piston rod5at the side of the compression chamber12. In other embodiments it could be fixed to the piston assembly4.

The tenon831ais made of plastic and has a substantially cylindrical shape with an internal annular recess8311defining an internal opening8315. In this embodiment the mounting member has a form of a bolt833aprovided with torque applying means8332in a form of a hex key socket and screwed inside the piston rod extender832along the axis A. The internal annular recess8311of the tenon831ais disposed between an axially external wall8321of the piston rod extender832and a head8331of the mounting bolt833a. The diameter of the mounting bolt833ashank is smaller than the diameter of the internal opening8315of the tenon831a, so that the tenon831ais to a certain extent radially displaceable with regard to the piston rod extender832.

The external diameter of the tenon831asubstantially corresponds to the diameter of the inner cylindrical surface811of the insert81a, wherein the tenon831ais terminated with a first entry surface8316ahaving diameter monotonically diminishing towards the compression end of the tenon831a. In this embodiment the first entry surface8316aof the tenon831ais conical. The insert81a, on the other hand, is provided with a second entry surface813ahaving diameter monotonically increasing towards the rebound end of the insert81a. In this embodiment the second entry surface813aof the insert81ais also conical.

In this embodiment the tenon831ais provided with a second inner chamber8313defined behind the head8331of the mounting bolt833a. An axially extending channel8312fluidly communicates the second inner chamber8313with the compression chamber12.

Radially external surface of the tenon831ais provided with four equiangularly spaced axially extending grooves8314, each having a cross-sectional surface that diminishes along its length towards the main piston assembly4. The axially extending channel8312is axially aligned with one of the grooves8314.

As the tenon831aenters the first inner chamber84of the insert81aat the end of the compression stroke additional damping force is generated, as shall be explained below.

As shown inFIG.3a, when the first entry surface8316aof the tenon831acontacts the second entry surface813aof the insert81aa reaction force, illustrated with an arrow in an enlarged fragment of the drawing, pushes the misaligned tenon831atowards the axis A. This provides a smooth activation of the hydraulic compression stop assembly8a. At the further stage of the stroke, shown inFIG.3b, the tenon831amakes a sliding fit with the insert81aand the working liquid may flow out of the first inner chamber84to the compression chamber12, as illustrated with dashed arrows, through the axially extending channel8312and through the grooves8314. Diminishing cross-sectional surface of the grooves8314provides a smooth built-up of the damping force. Grooves8314begin at the first entry surface8316a(cf. alsoFIG.4).

Another embodiment of a compression stop assembly8bshown inFIG.4is provided with a tenon831bdevoid of the axially extending channels8312. As the tenon831bmakes a sliding fit with the insert81bthe working liquid may flow out of the first inner chamber84to the compression chamber12, as illustrated with dashed arrows, solely through three equiangularly spaced axially extending grooves8314having a cross-sectional surfaces that diminish along their lengths towards the main piston assembly4. The lengths of the grooves8314are differentiated to fine tune the built up of the damping force. A first entry surface8316bof the tenon831band a second entry surface813bof the insert81bare substantially parabolic.

Yet another embodiment of a hydraulic compression stop assembly8cis shown inFIGS.5aand5b. Here an insert81cis made of metal and its inner cylindrical surface811, along with bottom surface814define a first inner chamber84. At its closed end the insert81cis provided with a circumferential locking yoke815extending annularly about a half of the perimeter of the insert81cand embracing a head823of a sintered steel fixing member82cthat is press-fitted to the base valve assembly7and to the main tube (not shown). The fixing member82cis also provided with a number of equiangularly spaced axial channels822(cf.FIG.5a) enabling fluid communication between the compression chamber12and the additional compensation chamber13through the base valve assembly7during the compression and the rebound stroke of the damper1.

In this embodiment a tenon831cof an additional piston assembly83cis provided with an elongated second inner chamber8313extending over its entire length, so that an internal annular recess8311defining an internal opening8315defines the end wall of the tenon831cdistal from the insert81. A first entry surface8316cof the tenon831cand a second entry surface813cof the insert81care conical with the aperture smaller than in the embodiment8a.

Furthermore a mounting member has a form of a plastic snap-fit member833chaving a hoop-strain annular projection8333engaging annular recess8322provided behind an internal opening8323of a piston rod extender832.

As the tenon831cmakes a sliding fit with the insert81cthe working liquid may flow out of the first inner chamber84cand the second inner chamber8313to the compression chamber12, as illustrated with dashed arrows, solely through an axial channel8312fluidly communicating a second inner chamber8313of the tenon831cwith the compression chamber12, as well as through an axially extending groove8314having a cross-sectional surface that diminishes along its length towards the main piston assembly4and is aligned with the axially extending channel8312.

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.

LIST OF REFERENCE NUMERALS