Hydraulic damper with a hydraulic stop arrangement

A hydraulic damper including a tube defining a chamber. The tube has a main section and a narrowed section. A main piston assembly is disposed in the main section and connected to a piston rod. A resisting mechanism is fixed to the piston rod. A secondary piston is moveable into the narrowed section. An inner surface of the secondary piston defines at least one radially internal channel. The piston rod defines an annular recess. The secondary piston includes a locking mechanism axially slideable within the annular recess. The secondary piston is axially moveable between a hydraulic stop engagement stroke wherein the secondary piston engages the resisting mechanism and restricts the flow of fluid through the radially internal channel, and a hydraulic stop disengagement stroke wherein the secondary piston is spaced from the resisting mechanism and allows the flow of fluid through radially internal channel.

TECHNICAL FIELD

The invention relates to a hydraulic damper for a vehicle. More particularly, the invention relates to a hydraulic damper for a vehicle including a main piston assembly and a secondary piston assembly providing a hydraulic stop arrangement.

BACKGROUND OF THE INVENTION

It is known in the art for hydraulic dampers to include a main piston assembly in a main section of a tube of the damper, and a secondary piston assembly in a narrowed section of the tube. The secondary piston assembly forms a so called hydraulic stop arrangement that generates additional damping force over a predefined end section of an operating range of piston rod travel. Exemplary dampers provided with such a hydraulic stop arrangements are disclosed in U.S. Pat. No. 3,447,644 and European Patent Application Publication Nos. EP 2 302 252 and EP 2 952 775.

Such hydraulic stop arrangements provide dissipation of energy at the end of the stroke and enable the generation of an additional damping force depending mainly on the position of the piston rod. They also provide a progressive increase of damping force in dependence of the rod displacement.

Nonetheless many of these constructions are complicated in terms of design, assembly process and/or labor consumption.

Therefore it is an object of the present invention to provide a hydraulic damper with a hydraulic stop arrangement that has a simple and cost efficient construction, has very few components, and is easy to assemble and requires only minor modifications of the other components of an existing damper assembly to be implemented thereon.

SUMMARY OF THE INVENTION

According to an aspect of the disclosure, a hydraulic damper is provided for a motor vehicle. The hydraulic damper includes a tube extending along an axis and defining a chamber for holding a fluid. The tube has a main section having a first diameter and a narrowed section having a second diameter being smaller than the first diameter. A main piston assembly is disposed in the main section of the tube and is axially slideable within the main section of the tube to generate a damping force. A piston rod is attached to the main piston assembly and extends axially outside of the tube. A resisting mechanism is disposed about and fixed to the piston rod. A secondary piston is disposed about the piston rod on the axially opposite side of the resisting mechanism as the main piston assembly and has an external diameter substantially corresponding to the second diameter of the narrowed section of the tube and is axially displaceable with the main piston assembly and moveable into the narrowed section of the tube to generate an additional damping force. The secondary piston defines a radially inner surface engaging the piston rod and a radially outer surface opposite the radially inner surface. The radially inner surface defines at least one radially internal channel extending axially. The piston rod defines an annular recess at least partially in axial alignment with the secondary piston. The secondary piston includes at least one locking mechanism positioned in the annular recess of the piston rod and axially slideable within the annular recess. The secondary piston is axially moveable between a hydraulic stop engagement stroke and a hydraulic stop disengagement stroke, wherein the secondary piston axially engages the resisting mechanism and restricts the flow of working fluid through the at least one radially internal channel during the hydraulic stop engagement stroke, and wherein the secondary piston is axially spaced from the resisting mechanism and defines an annular channel between the piston rod and the secondary piston allowing the flow of working fluid through the at least one radially internal channel during the hydraulic stop disengagement stroke.

The secondary piston requires very few components, thus significantly decreasing manufacturing costs and providing a simple assembly process of the hydraulic damper. Moreover, no significant modifications of the piston rod are required to utilize the secondary piston, and thus the secondary piston may be employed in a variety of existing dampers. In particular, the annular recesses of the piston rod may be formed by simple machining of the rod.

According to another aspect of the disclosure, the radially outer surface of the secondary piston defines a plurality of radially external channels that each extend axially. Accordingly, no channels formed in the narrowed section of a damper tube are required to decrease an abrupt increase of an additional damping force generated in the phase of an entry of the secondary piston into the narrowed section.

According to another aspect of the disclosure, a cross-sectional surface of the radially external channels of the secondary piston in a plane perpendicular to the axis is the largest at its face opposite the resisting mechanism and decreases along the axial length of the secondary piston. Accordingly, the damping force generated by the secondary piston while it engages the narrowed section increases smoothly and progressively.

According to another aspect of the disclosure, a plurality of radially internal bridges extending axially are defined between the radially internal channels, each of the axially extending bridges terminates axially at one of the hooks, and the secondary piston defines a chamber about the hooks.

According to another aspect of the disclosure, each of the hooks includes a flat surface extending perpendicularly to the axis, and a conical surface extending at an angle relative to the flat surface. Such a shaping of the hooks facilitates positioning the secondary piston over the piston rod during assembling the damper. More particularly, the conical surfaces of the hooks may yield allowing for simple drawing of the piston down over the rod until the front flat surfaces of the hooks engage the annular recess of the piston rod.

According to another aspect of the disclosure, an end of the secondary piston defines a convex guiding surface, thus decreasing possible mechanical stresses affecting the damper components during an engagement stroke.

According to another aspect of the disclosure, the secondary piston is of a plastic material. Accordingly, it may therefore be manufactured with high cost efficiency, such as by utilizing a molding technique like injection molding.

According to another aspect of the disclosure, the resisting mechanism is a retaining ring that is fixed in the annular recess of the piston rod. Such a ring makes assembly of the secondary piston very simple.

According to another aspect of the disclosure, at least one spring is disposed in the narrowed section of the tube for axially engaging the secondary piston to generate an additional damping force. According to yet a further aspect of the disclosure, at least one bumper is positioned in the narrowed section of the tube for axially engaging the secondary piston to generate an additional damping force. The spring and/or bumper provide the generation of an additional damping force at the end of an engagement stroke, thus further improving the tunability of the hydraulic stop of the present invention.

According to another aspect of the disclosure, the tube extends axially between a compression end and a rebound end, and the narrowed section is located at the rebound end of the tube.

According to another aspect of the disclosure, the damper assembly is a twin-tube damper.

According to an aspect of the disclosure, the at least one axial slot is defined in the narrowed section of the tube. Accordingly, a smooth and adjustable increase of damping force is provided while the secondary piston assembly enters the narrowed section of the tube.

The damper assembly according to the present invention may easily be configured to generate additional damping forces, both for compression and rebound strokes enabling for wide range tuning of force gains, wherein the performance of the arrangement may depend both on the piston position as well as on the piston velocity.

DESCRIPTION OF THE ENABLING EMBODIMENT

Reference numerals to functionally equivalent elements remain the same on all figures of the drawing, wherein where appropriate they are supplemented with additional suffixes (a-d) to differentiate elements of the same functionality but different construction.

FIG. 1presents an embodiment of a twin-tube damper1aaccording to the present invention that may be employed in a typical motor vehicle suspension during a rebound stroke. The damper1acomprises an external tube2and a main tube3, each extending along an axis and filled with viscous working fluid. A movable main piston assembly4is disposed in the main tube3and is attached to a piston rod5led outside the damper1athrough a sealed piston rod guide6. The damper1ais also provided with a base valve assembly7fixed at the 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 rod guide6and the main piston assembly4) and a compression chamber12(between the main piston assembly4and the base valve assembly7). An additional compensation chamber13is located at the other side of the base valve assembly7.

The main piston assembly4is provided with compression and rebound valve assemblies42,41to control the flow of working fluid passing between the rebound chamber11and the compression chamber12while the main piston assembly4is in motion. Also, the base valve assembly7is provided with rebound and compression valve assemblies71,72to control the flow of working fluid passing between the additional compensation chamber13and the compression chamber12, respectively, during rebound and compression stroke of the damper1a. Valve assemblies41,42and71,72provide design parameters that may be used to shape desired characteristic of the damper1a.

Main section33of the tube3has a first diameter D1that in the example embodiment amounts to approximately 32 mm. As shown, the tube3has also a narrowed cylindrical section31of a smaller second diameter D2that in the example embodiment amounts to approximately 28 mm. This narrowed cylindrical section31extends through a conical section32into the main cylindrical section33of the tube.

A secondary piston assembly8is disposed over the piston rod5and is displaceable along with the main piston assembly4. The assembly8comprises only two components, namely a resisting mechanism81, which is shown in the example embodiment as a retaining ring81fixed in an annular recess51of the piston rod5, and an additional plastic secondary piston82snaplocked over the piston rod5in an annular recess52of the piston rod5and capable of rotational and axial displacement within the limits of this snapping recess52. The annular recess52is defined at least partially in axial alignment with the secondary piston assembly8. The secondary piston82is disposed on the axially opposite side of the resisting mechanism81as the main piston assembly4. The secondary piston82has a substantially tubular shape having a radially inner surface87having an internal diameter substantially corresponding to the diameter of the piston rod5and a radially outer surface89having an external diameter substantially corresponding to the diameter of the narrowed cylindrical section31of the tube3.

The radially outer surface89of the piston82is also provided with a number of equiangularly spaced radially external channels821extending axially and enabling for a tunable flow of working fluid from the narrowed section31to the rebound chamber11of the tube3and further through the rebound valve assembly41of the main piston assembly4during the rebound stroke as illustrated with a dashed arrow.

Such a shape of the main tube3and the secondary piston assembly8provide a hydraulic rebound stop for the damper1a. Functionality of such a hydraulic stop shall be explained later, in particular with reference toFIGS. 3 to 10.

FIG. 2presents another embodiment of a mono-tube damper1baccording to the present invention with a hydraulic compression stop of a construction similar to the one illustrated inFIG. 1during a rebound stroke. As shown inFIG. 2, a narrowed cylindrical section31of a damper tube3is located at the compression end of the tube3and an secondary piston assembly8is fixed to the damper piston rod5at the compression side of the main piston assembly4. As shown, the pressure of working fluid forced the secondary piston82to slide down in the annular snapping recess52away of the retaining ring81. Nonetheless, in an illustrated position, the secondary piston82is in the main section33of the tube3and working fluid flows through the rebound valve assembly41of the main piston assembly4and further down the compression chamber12freely around the secondary piston82as illustrated with dashed arrows.

In this embodiment, the conical section of the tube is separated with six equiangularly spaced axial slots321stamped from the outside of the tube3and separated with six axial bridges322. As a result, the conical section of the tube3comprises a semi-cylindrical section32bformed by six equiangularly spaced cylindrical sections of the bridges322, and a semi-conical section32aformed by six equiangularly spaced conical sections of the bridges322. Semi-cylindrical section32bprovides guidance for the secondary piston assembly8while retaining the slots321. Such a shaping also provides smooth built-up of the damping force between the main cylindrical section33and the narrowed cylindrical section31of the tube3and possible abrupt force peak is thus avoided.

A slidable diaphragm9separates the damper compression chamber12from an additional gas compensation chamber14. Furthermore, the tube comprises a cap34screwed on the end of the main tube3. A valve341is provided on the cap34, which provides for filling the gas compensation chamber14with gas after assembly of the damper.

Obviously, a damper according to the present invention may contain two hydraulic stops, each provided with an additional plastic piston, both at the compression and at the rebound side of the damper.

FIG. 3illustrates another embodiment of a twin-tube damper1cprovided with a hydraulic rebound stop comprising an additional spring83during a compression stroke. One end of the spring83is attached to the piston rod guide6and the spring83is capable of generating additional damping force after it is engaged by the front face of the secondary piston82at the end of the rebound stoke. Obviously, this force substantially linearly increases with the further increase of the rebound stroke travel.

As used above and below, the term “front” means the side of the secondary piston assembly8that engages the narrowed section31of the tube, while the term “rear” means the side of the secondary piston assembly8which is axially opposite the front side. Similarly the term “engagement stroke” denotes this stroke of the damper during which the secondary piston assembly may enter into the narrowed section31of the tube3, while the term “disengagement stroke” denotes the stroke opposite to the engagement stroke.

As shown, the pressure of working fluid under the secondary piston82forces it to slide up in the annular snapping recess52away of the retaining ring81, thus forming an annular channel84of height H between the rear face of the secondary piston82and the front face of the retaining ring81. Therefore, working fluid flows freely from the rebound chamber11through this annular channel84and further through radially inner axial channels822(cf.FIG. 10) defined by the radially inner surface87of the secondary piston82to the narrowed section31of the tube3as illustrated with dashed arrows.

FIG. 4illustrates another embodiment of a twin-tube damper1dprovided with a hydraulic rebound stop8comprising an additional bumper85during a rebound stroke. The bumper85is attached to the piston rod guide6and is elastically deformable and thus capable of generating additional damping force after it is engaged by the front face of the secondary piston82at the end of the rebound stoke in order to protect the plastic secondary piston82from damaging.

Obviously, as shown inFIG. 2, in order to generate and adjust the characteristic of the additional damping force generation it is possible to employ both the radially external channels821of the piston82, as well as the axial slots321provided across the conical section32of the tube3. In this case however, rotation of the secondary piston82over the piston rod5should be blocked, e.g., by an axial recess of the piston rod5engaging appropriate protrusions of the secondary piston82(not shown in the drawing).

The embodiment of the secondary piston82shown inFIGS. 5 to 10is provided with five equiangularly spaced radially external channels821and five equiangularly spaced radially internal channels822.

In this embodiment the radially external channels821have a form of arched grooves and their cross-sectional surface in a plane perpendicular to the piston82axis progressively increases starting at a certain point along the piston82length toward the front side thereof, thus providing convenient tuning parameters for the secondary piston assembly8. When the secondary piston82enters the narrowed section31of the tube3this cross-sectional surface of the radially external channels821is the largest, providing substantially small restrictions for the flow of working fluid. As the secondary piston82enters further into the narrowed section31this cross-sectional surface diminishes and thus damping force becomes higher, up to the point when the flow of working fluid is possible only through a narrow annular slot between the outer surface of the secondary piston82now devoid of the radially external channels821and the inner surface of the narrowed section31. In this point, the flow restrictions and thus the damping force is obviously the highest.

The secondary piston82is also provided with a convex guiding surface823providing guidance for the piston82while entering the narrowed section31of the tube and compensating for its possible radial intolerances, as for the free sliding movement of the piston82over the piston rod5some annular gap between the piston82and the piston rod5must be provided.

In this embodiment the radially internal channels822also are formed as arched grooves, but their cross-sectional surface is substantially the same over their length and the channels822are delimited by radially internal bridges826.

At the rear side of the piston82the bridges826protrude into an internal chamber825and are terminated with at least one locking mechanism824capable of engaging the rod5in the annular snapping recess52of the rod5. In the example embodiment, the locking mechanism824includes a plurality of hooks824that are axially slideably within the annular recess52. Rear surfaces of the hooks824are substantially conical while the front surfaces are substantially perpendicular to the damper and the piston rod5axis. Such a shaping facilitates positioning the piston82over the piston rod5prior assembling the piston rod5inside the damper1. Rear conical surfaces of the hooks824may yield inside the internal chamber825allowing for simple drawing the piston82down over the piston rod5until the hooks824engage the recess52. Further sliding movement of the piston82down or during the engagement stroke is blocked by the retaining ring, while front surfaces of the hooks824perpendicular to the damper piston rod5axis prevents the piston82from sliding up during the hydraulic stop engagement stroke.

As shown inFIG. 1andFIG. 4during the engagement, in this case rebound, stroke of the damper, the secondary piston assembly8may enter the narrowed section31of the tube3through the conical section32. During this stroke, the retaining ring81pushes the secondary piston82and blocks the entrances of the radially internal channels822.

On the other hand, during the disengagement stroke shown inFIG. 2andFIG. 3, the pressure of working fluid pushes the secondary piston82away of the retaining ring81allowing for a substantially unrestricted flow of the fluid through thus formed annular channel84and the radially internal channels822.

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.