This invention relates generally to a hydraulic end of stroke stop for use on a hydraulic shock absorber for vehicle suspension, such as of the mono-tube or twin-tube type. More specifically, this invention relates to a hydraulic stop operating during the extension movement of the shock absorber.

Traditionally, a hydraulic shock absorber for a vehicle suspension has a first end of stroke buffer, which is arranged within the shock absorber and is configured to act during the extension stroke of the shock absorber, and a second end of stroke buffer, which is arranged outside the shock absorber and is configured to act during the compression stroke of the shock absorber.

End of stroke buffers may be of an elastic or hydraulic type.

Elastic end of stroke buffers are made of high-stiffness elastic material (e.g., polyurethane) and their function is to ensure that when the end of stroke position of the shock absorber is reached, whether during the extension or compression phase, there are elastic shocks between the surfaces that come into contact, thus preventing these shocks from occurring between metallic surfaces. Therefore, elastic end of stroke buffers behave like springs that act parallel to the mechanical spring (mainspring) of the suspension at the end of stroke positions and have a much higher stiffness than the mechanical spring of the suspension. However, elastic end of stroke buffers do not act at any intermediate point of the shock absorber stroke.

Elastic end of stroke buffers have, among others, the following disadvantage. During a violent impact on the buffers, in extension or compression, caused for example by the presence of obstacles (potholes or bumps) on the road, the kinetic energy of the suspension is transformed into elastic deformation energy of the concerned buffer. The elastic energy stored by the buffer is completely (or nearly) released in the next phase of motion reversal. Therefore, after the impact, the suspension continues to oscillate without its motion being sufficiently damped, and these oscillations result in a worsening of the contact conditions between the road and the tire, and therefore a worsening of the vehicle’s grip on the road.

To overcome the aforesaid disadvantage of elastic buffers, hydraulic stops are known to be used, either alone or in combination with elastic buffers.

Hydraulic stops are dissipating devices which, when an end of stroke position is reached and depending on the speed of movement of the shock absorber, allow the kinetic energy of the suspension to be dissipated hydraulically, namely by forcing a certain volume of oil contained in the shock absorber to laminate through appropriately calibrated passages. In this way, the energy produced as a result of an impact is hydraulically dissipated and is not returned to the suspension in the subsequent reversal of motion. The oscillations of the suspension are thus dampened, resulting in improved grip conditions between the road and the tire and therefore an improvement of the vehicle’s grip on the road.

In addition, because the hydraulic stops act in parallel with their respective elastic buffers, part of the energy generated by the impact is hydraulically absorbed, and thus the size of the elastic buffers and their supports may be reduced.

Finally, while elastic buffers react only as a function of the deformation to which they are subjected, the action of hydraulic stops is proportional to the speed with which the shock absorber rod reaches the end of stroke position. Therefore hydraulic stops allow for a much more progressive handling of the impacts that occur when the shock absorber reaches its end of stroke positions, resulting in reduced noise.

Hydraulic stops are typically used as rebound end of stroke devices, wherein the automotive hydraulic stop comprises a cup-shaped body, which is adapted to be attached within the rebound chamber of the shock absorber, and a piston, which is adapted to be attached to the stem of the shock absorber. The piston is capable of sliding along a cylindrical side wall of the cup-shaped body. Said wall expediently has a series of channels to allow oil to escape when the piston is pushed toward the cup-shaped body during the extension stroke of the shock absorber, and thus compresses the oil contained in a working chamber of the cupshaped body. In a buffer thus constructed, the piston motion, and therefore of the shock absorber rod motion, is therefore damped during the shock absorber extension stroke, due to the leaking of oil from the cup-shaped body through channels provided in the cylindrical side wall of said body. These channels have a decreasing section in the direction of the extension stroke of the shock absorber in such a way that, as the piston moves toward the inside of the cupshaped body, the damping effect produced by the device increases.

The object of this invention is to provide a hydraulic buffer operating in extension for a hydraulic shock absorber of a vehicle suspension, which combines strength, low inertia and optimal friction coefficients at the interface between the piston and the cup-shaped body.

A further object of this invention is to provide a hydraulic buffer that may be manufactured in a simple and economical manner.

These and other objects are fully achieved according to the invention by a hydraulic stop having the features defined in the appended claims.

In summary, the invention is based on the idea of making parts of the piston (namely, the cylindrical body and/or the sealing ring, as defined below) and/or the cup-shaped body of plastic material, whereby these parts may be shaped in such a way as to improve the mechanical and structural properties of the device. This permits the device to be lighter from a structural point of view and simplifies the manufacturing.

Advantageous embodiments of the invention are specified in the dependent claims, the content of which is to be understood as an integral and integrating part of the following description.

Brief description of the drawings The functional and structural features of some preferred embodiments of a shock absorber with hydraulic rebound buffer according to the invention will now be described. Reference is made to the appended drawings, wherein:

- Fig. 1 is an axial sectional view of a shock absorber comprising a rebound stop, according to one embodiment of the invention;

- Fig. 2 is an axial sectional view of a hydraulic rebound stop incorporated in a shock absorber, according to one embodiment of the invention;

- Fig. 3 is a longitudinal sectional exploded view of a hydraulic rebound stop, according to one embodiment of the invention;

- Fig. 4A and 4B are two perspective views of a piston for a hydraulic stop according to one embodiment of the invention, during an extension stroke of the shock absorber, and during a compression stroke of the shock absorber, respectively;

- Fig. 5A and 5B are respectively a side and perspective view from below of a piston for a hydraulic stop according to one embodiment of the invention; and

- Fig. 6 A and 6B are, respectively, a side and top perspective view of a piston for a hydraulic stop according to a further embodiment of the invention.

Detailed description

Before describing a plurality of embodiments of the invention in detail, it should be clarified that the invention is not limited in its application to the construction details and configuration of the components presented in the following description or illustrated in the drawings. The invention may assume other embodiments and be implemented or constructed in practice in different ways. It should also be understood that the phraseology and terminology have a descriptive purpose and should not be construed as limiting.

Referring by way of example to Fig. 1 , a hydraulic shock absorber 10, particularly for vehicle suspension, comprises a cylindrical tube 14, a rod 18, which is arranged coaxially to the cylindrical tube 14 and partially protrudes therefrom, and a primary piston 20, which is attached to a first end of the rod 18 and is slidably mounted in the cylindrical tube 14 so as to divide the inner volume of the cylindrical tube 14 into an extension chamber 22 and a compression chamber 24. The hydraulic shock absorber 10 further comprises a hydraulic stop 30, which is arranged in the extension chamber 22 and is adapted to operate during the extension stroke of the shock absorber 10 to hydraulically dissipate kinetic energy as the shock absorber 10 approaches an extended end of stroke position.

The hydraulic stop 30 comprises a cup-shaped body 32 mounted in the extension chamber 24 of the shock absorber 10, coaxially thereto, and an auxiliary piston 34 mounted to said first end of the rod 18 of the shock absorber 10, coaxially thereto, below the primary piston 20 of the shock absorber.

The cup-shaped body 32, in turn, comprises a side wall 36 that defines, together with the auxiliary piston 34 of the hydraulic stop 30, a working chamber 52, which expediently coincides with the end section of the extension chamber 24. Said working chamber 52 is therefore contained within the inner volume of the cup-shaped body 32 and is configured so that a damping fluid from the shock absorber 10 is compressed by the auxiliary piston 34 of the hydraulic stop 30 during the extension stroke of the shock absorber 10.

The auxiliary piston 34 comprises a cylindrical body 50, which is attached to the rod 18 of the shock absorber 10 and has an outer diameter smaller than the inner diameter of the side wall 36 of the cup-shaped body 32, a sealing ring 54, which is axially mounted slidable about the cylindrical body 50 and is adapted to seal against the inner surface of the side wall 36 of the cup-shaped body 32, and a first and a second annular abutment element 56, 58, which are axially constrained to the cylindrical body 50 and are configured to axially restrict, in either direction, the axial sliding movement of the seal ring 54 along the cylindrical body 50. Expediently, the first annular abutment element 56 (i.e., the axially lower abutment for the sealing ring 54, as illustrated by way of example in Fig. 3 and 4B) is formed by the upper surface of a ring integrally forming part of the cylindrical body 50.

The sealing ring 54, the first abutment element 56, and the second abutment element 58 are configured whereby, when the sealing ring 54 runs along the inner surface of the side wall 36 of the cup-shaped body 32 during the extension stroke of the shock absorber 10, the sealing ring 54 is in abutment against the first abutment element 56 and no damping fluid is allowed to pass from one side of the sealing ring 54 to the other, and during the compression stroke of the shock absorber 10, the sealing ring 54 is in abutment against the second abutment element 58 and damping fluid is allowed to pass from one side of the sealing ring 54 to the other.

The cylindrical body 50 and the sealing ring 54 are made of a plastic material, and the auxiliary piston 34 further comprises an annular body 60 made of a metallic material, adapted to form a support surface or axial abutment to the cylindrical body 50.

In effect, the annular body 60 is coupled to the cylindrical body 50 on the auxiliary piston side 34 axially opposite to the side facing the working chamber 52. The auxiliary piston 34 is thus configured whereby, when the cylindrical body 50 reaches the extended end of stroke position of the hydraulic shock absorber 10, the annular body 60 forms an axial abutment for said cylindrical body 50, preventing it from sliding along the rod 18 in the opposite direction, and axially locking the auxiliary piston 34 on the rod 18. For this purpose, the cupshaped body 32 is preferably provided with a shoulder 38, radially projecting inwardly from the cup-shaped body 32 and adapted to form an abutment against which the auxiliary piston 34 will rest when the hydraulic shock absorber 10 is in an extended end of stroke position (as exemplified in Fig. 2).

According to an embodiment (illustrated by way of example in Fig. 2), the rod 18 comprises a coupling seat having a profile complementary to an inner profile of the cylindrical body 50 and the annular body 60, whereby said cylindrical body 50 and annular body 60 are attached to the rod 18 by shape-coupling of their respective profiles.

Preferably, the rod 18 has two circumferential recesses at the axially outermost edges of the cylindrical body 50 and the annular body 60, said outermost edges being radially recessed toward the axis of the rod 18 whereby they abut within the respective circumferential recesses. Thus, an optimal shape-coupling of the auxiliary piston 34 to the piston rod 18 is achieved. The annular body 60 is in turn connected to the cylindrical body 50 by shape-coupling between at least one hook 62, projecting axially from the cylindrical body 50, and a prominence projecting radially from the annular body 60.

Said coupling may be achieved by configuring the hook 62 to engage with the prominence of the annular body 60 by surrounding it from the outside (as, for example, shown in Fig. 5A and 5B).

Alternatively (as, for example, shown in Fig. 6A and 6B), the prominence projecting radially from the annular body 60 may comprise at least one radial seat 64 configured as a groove into which the hook 64 is inserted and fixed.

According to an embodiment, the sealing ring 54 has an open annular shape.

According to a preferred embodiment, the cup-shaped body 32 is made of a plastic material.

According to a preferred embodiment, the plastic material from which the cylindrical body 50 and/or the sealing ring 54 and/or the cup-shaped body 32 is made is a composite material, reinforced with glass fibers or carbon fibers.

According to a preferred embodiment, the hydraulic shock absorber 10 is configured as a hydraulic shock absorber of the twin-tube type for a vehicle suspension. In such a configuration, the hydraulic shock absorber 10 comprises an outer cylindrical tube (coinciding with a body tube 15 of the hydraulic shock absorber 10), and an inner cylindrical tube (coinciding, in this embodiment, with the aforesaid cylindrical tube 14, against which the cup-shaped body 32 abuts radially). The inner cylindrical tube is coaxial to the outer cylindrical tube and defines therewith an annular chamber filled in an upper portion thereof with gas, and the stem 18 is arranged coaxially to the two cylindrical tubes and partially protrudes therefrom. The primary piston 20 is slidably mounted in the inner cylindrical tube and is attached to the lower end of the rod 18. The primary piston 20 separates the inner volume of the inner cylindrical tube 14 into an extension chamber and a compression chamber, within which the damping fluid (oil) is contained. According to one aspect of the invention (not illustrated), the hydraulic shock absorber 10 is configured as a hydraulic shock absorber of the single-tube type for a vehicle suspension, i.e., comprising only the outer cylindrical tube (coinciding with the body tube 15 of the hydraulic shock absorber 10, said body tube 15 in turn coinciding, in this embodiment, with said cylindrical tube 14, against which the cup-shaped body 32 abuts radially).

Preferably, axial channels 44 are provided on the inner surface of the side wall 36 of the cupshaped body 32, which extend parallel to a longitudinal axis (z) of the cup-shaped body 32 and are adapted to allow the damping fluid to flow axially out of the working chamber 52 when the auxiliary piston 34 flows through the working chamber 52 toward an extended end of stroke position of the shock absorber 10 (e.g., toward the shoulder 38 of the cup-shaped body 32).

Said axial channels 44 have a cross section, the area of which decreases continuously along the longitudinal axis (z) toward said extended end-of-travel position of the shock absorber 10.

According to the invention, the cup-shaped body 32 is made of a plastic material, and the entire outer surface of the side wall 36 of the cup-shaped body 32 is in direct contact with the cylindrical tube 14, said cylindrical tube 14 forming the outer cylindrical tube of the shock absorber 10. More precisely, it is intended that, given that the portion (axially) of the cup-shaped body 32 along which the auxiliary piston 34 is sliding, substantially the entire surface of the side wall 36, corresponding to said portion and facing the inner wall of the cylindrical tube 15, is in contact therewith.

Throughout this description and in the claims, terms, and expressions indicating positions and orientations, such as “longitudinal,” “transverse,” “vertical,” or “horizontal,” are to refer to the longitudinal axis (z) of the hydraulic shock absorber 10.

Various aspects and embodiments of a hydraulic shock absorber with a hydraulic rebound stop according to the invention have been described. It is understood that each embodiment may be combined with any other embodiment. Furthermore, the invention is not limited to the described embodiments, but may be varied within the scope defined by the appended claims.