FR2723624A1 - Pressurised hydraulic damper for vehicle suspensions - Google Patents

Abstract

The damper consists of a cylindrical tube (1) containing a damping liquid and in which slides a piston (2). A blanking off piece (3) is fixed in relation to the interior wall of the cylinder and also serves as a guide for the piston rod (4) in its axial movement. The blanking piece contains a sealing joint (13a,13b) held in a sandwich between a plug (11) and a bottoming stop (12). It is characterised that the stop (12) contains a body in the form of a disc provided with a rectangular shaped circular throat (14) to receive a circlip (15). This circlip contained in this throat, also cooperates with a similar internal throat (18) in the cylinder so that due to the spring effect of the circlip it holds in position axially the stop element (12) in the cylinder (1).

Description

Pressurized hydraulic shock absorber provided with an axially immobilized trigger stop element.

 The present invention relates to a pressurized hydraulic shock absorber commonly used in the construction of vehicles making it possible in particular to ensure passenger comfort despite variations in the surface condition of the roads.

 Pressurized hydraulic shock absorbers generally comprise a cylindrical tube containing a damping liquid and in which slides a piston which separates the cylindrical tube into two hydraulic compartments. One end of the cylindrical tube has a bottom in which a pressurized gas is enclosed which is sealed from one of the hydraulic compartments by a cylindrical diaphragm sliding along the inner walls of the cylindrical tube. The open end of the cylindrical tube is enclosed by a closure device which is immobilized relative to the interior walls of the tube by means of circlips. The closure device has a central passage for guiding the piston rod in its axial translation movements relative to the cylindrical tube.

 The closure device comprises three essential elements: a guide plug, a trigger stop element and a seal sandwiched between the plug and the trigger stop element. The immobilization of the closure device relative to the inner walls of the cylindrical tube is carried out by means of two circlips engaged in two annular grooves in the inner walls of the cylindrical tube serving as an axial stop on the one hand to prevent movement of the plug towards outside the tube, and on the other hand to prevent the trigger stop element from moving towards the inside of the hydraulic compartments of the cylindrical tube.

 The inventor has found that for pressurized hydraulic shock absorbers which function satisfactorily under normal conditions of use, the leaks of the damping liquid from the interior of the cylindrical tube towards the exterior at the level of the closure device appear. when the relaxation efforts of the shock absorbers have become significant. In addition, under extreme conditions of use, noises appear during the operation of pressurized hydraulic shock absorbers.

 In seeking a solution to this problem, the inventor has discovered that the cause lies in the seal which performs two functions simultaneously: the sealing of the closure device, and the transmission of mechanical forces between the element of the expansion stop and the plug during the expansion phase of the shock absorber. The fact that the detent stop element is only axially limited in one direction by a circlip results in its axial displacement against the seal during the detent relaxation phase. This axial movement compresses the seal which is made of rubber against the plug and creates an elastic deformation of the seal, in particular by a radial withdrawal of the latter towards the annular space (expansion volume) available between the expansion stop element and cap. The peripheral edge of the seal is no longer in perfect contact with the interior walls of the cylindrical tube and the damping oil can then pass through the gap thus creating between the peripheral edge of the seal and the inner walls of the cylindrical tube. When the shock absorber is released after the expansion phase, the damping oil trapped between the deformed peripheral edge of the seal and the inner walls of the cylindrical tube can also pass through the peripheral gap between the seal and the tube. cylindrical by an oil wedge phenomenon (local overpressure of trapped oil).

 In order to remedy the drawbacks of the conventional pressurized hydraulic shock absorbers indicated above, the present invention provides a particularly simple and effective solution which consists in attributing only to the seal its primary function which is sealing and eliminating its conventional secondary function for transmitting mechanical forces during the expansion phase of the shock absorber. To do this, the invention proposes to completely immobilize the axial movement of the trigger stop element during the operation of the damper. Thus, during the expansion phase of the damper, the seal no longer undergoes an axial crushing force coming from the part of the relaxation stop element which is immobilized relative to the internal walls of the cylindrical tube. .

 This also eliminates the noisy phenomenon due to the offset movements of the piston rod and the radial clearance between the inner walls of the cylindrical tube and the rebound stop element during the rebound phase of the shock absorber (lateral accelerations of the trigger stop element relative to the cross section of the cylindrical tube thus create mechanical shocks against the internal walls of the cylindrical tube). The complete immobilization of the trigger stop element in the cylindrical tube creates a damping by a film of damping liquid between the trigger stop element and the inner walls of the cylindrical tube and therefore eliminates the risk of noisy shocks .

 Thanks to the invention, the relaxation stop element alone ensures the mechanical stresses during the expansion phase of the shock absorber at the end of the stroke, which allows the seal to fully ensure its sealing function and thus eliminating leaks of the damping liquid at the peripheral edge of the seal. It is also possible to adjust the level of preload necessary on the gasket, since it is possible to adjust the level of axial stop of the plug relative to the element of relaxation stop axially immobilized.

 According to the invention, a pressurized hydraulic shock absorber is produced which comprises a cylindrical tube containing a damping liquid and in which slides a piston, a closure device immobilized relative to the internal walls of the cylindrical tube and serving as a guide for the rod. of the piston in its axial translational movement. The closure device includes a seal sandwiched between a plug and an expansion stop member. The detent stop element comprises a body in the form of a disc comprising a peripheral groove of rectangular section, and a circlip housed in a mobile manner radially in the peripheral groove. The circlip can disappear radially and completely in the peripheral groove of the disc. The cylindrical tube has on its inner walls at least one inner circular groove which can receive the circlip which, pressed by its elasticity at the bottom of the inner groove of the tube has a part projecting radially inwards to cooperate with the peripheral groove of the disc. , so as to axially immobilize the rebound stop element in the cylindrical tube.

 The plug of the closure device can be limited in its movement by a one-way axial stop, for example by means of a conventional circlip. In this case, it is preferable to make a second inner circular groove of the tube to receive the stopper retaining ring with a special profile. The profile of this second groove has a frustoconical ramp from the bottom of the second inner groove to the cylindrical inner walls of the tube on the side near the first inner groove. This characteristic is important when it is desired to simplify the mounting of the closure device in the cylindrical tube as will be developed in the following description.

 In a variant of the invention, the peripheral groove of the disc is deep enough to receive an elastic annular seal at the bottom, which deforms radially when the circlip disappears radially in the peripheral groove of the disc and tends to expel radially towards the outside the circlip, which makes it possible to eliminate the risks of jamming of the circlips in the peripheral groove of the disc during assembly of the obturation device and to exert a pressing force by this annular seal on the circlips in its groove when this this is subject to axial stresses in expansion.

The invention will be better understood and other advantages will appear in the detailed description of some embodiments taken by way of non-limiting example and illustrated by the appended drawings, in which
FIG. 1 is a partial view in axial section of a pressurized hydraulic shock absorber according to a first embodiment of the invention,
FIGS. 2 to 5 represent the steps for mounting the device for closing the damper according to FIG. 1,
FIG. 6 is a partial view in axial section of a pressurized hydraulic shock absorber according to a second embodiment of the invention,
FIGS. 7 to 10 show partial sections of the relaxation stop elements according to the third, fourth, fifth and sixth embodiments of the invention,
FIGS. 1a and 1b schematically illustrate the trigger stop element according to the seventh embodiment of the invention,
FIG. 12 represents a section of the trigger stop element according to an eighth embodiment of the invention,
Figures 13 to 17 show some other alternative embodiments of the pressurized hydraulic damper according to the invention.

 As illustrated in FIG. 1, the pressurized monotube hydraulic damper comprises a cylindrical tube 1 containing a damping liquid separated into two hydraulic compartments A and B by a piston 2 which slides axially in the tube 1. The bottom not shown of the tube 1 contains a gaseous volume under pressure separated from the second compartment B by a sliding diaphragm, not shown, in a manner known per se. The upper end of the tube 1 is closed by a closure device 3 which is immobilized axially with respect to the internal walls of the tube 1 and serves as a guide for the axial translational movement for the rod 4 of the piston 2.

 The piston 2 comprises a piston body 5 in the form of a disc provided with a plurality of axial perforations 6 establishing communication between the two hydraulic compartments A and B of the damper. A washer or circular plate 7 is mounted around a shoulder 8 of the piston rod 4 and supports a cup 9 in which there is an annular elastic stop 10 surrounding the piston rod 4.

 The closure device 3 comprises a plug 11 at its upper part, a detent stop element 12 at its lower part and a seal in the middle composed of a static seal in the form of a washer 13a and a dynamic seal. 13b surrounding the piston rod 4. The detent stop element 12 can be made of steel, aluminum, metal alloys or plastic etc.

and has a body in the form of a disc provided with a peripheral groove 14 of substantially rectangular or other section which cooperates with a circlip 15 partially housed in an inner groove of the tube 1, which immobilizes the disc 12 axially relative to the tube 1. The plug 1 1 also has an axial stop, but only in the upward direction by means of a circlip 16 which cooperates with a second inner groove of the tube 1.

 In general, during the operation of the shock absorber, when the vehicle is traveling on a bump, the corresponding wheel lifts by compressing the shock absorber associated with the wheel. The movement is transmitted to the piston rod 4 and results in a depression of the piston 2 in the tube 1, which reduces the volume of the second compartment B in favor of the first compartment A. If the compression is rapid and its value exceeds the limit of the forces admitted by the shock absorber, a cavitation phenomenon is created in which the pressure of the damping oil in the vicinity of the trigger stop element 12 in the compartment A tends towards zero. The force created on the closure device 3 by the pressure difference between the atmospheric pressure exerted on the plug 11 and the low cavitation pressure is quite low. The circlip 15 does not undergo a significant force and easily keeps the relaxation stop element 12 stationary. Under these conditions, it is not necessary to immobilize the plug 11 axially in its downward movement as it is proposed for the detent stop element 12 (cooperation between the peripheral groove 14 and the immobilization circlips 15).

In the shock absorber expansion phase, the piston 2 rises, reducing the volume of compartment A in favor of the compartment
B. At the end of the stroke, the rod 4 pulls on the piston which transmits the relaxation force to the relaxation stop element 12 by means of the elastic stop 10 which is crushed against the stop element of trigger 12.

The expansion force thus transmitted to the expansion stop element 12 is distributed circumferentially in the cylindrical tube 1 via the peripheral groove 14 of the element 12 and the circlip 15 which cooperates with the corresponding internal groove of the tube 1. The detent stop element 12 does not move axially or very slightly relative to the tube 1 and does not therefore crush the static seal 13a against the plug 1 1 (as was the current shock absorbers).

 Figures 2 to 5 illustrate in more detail the part of the invention related to the shutter device as described above.

According to the invention, the assembly of the closure device 3 can take place in the following manner.

 First, a mounting tube 17 is placed on the upper end of the cylindrical tube 1, the internal diameter of which is substantially identical to the internal diameter of the cylindrical tube 1 of the damper. In the mounting tube 17 is introduced the detent stop element 12 with the circlip 15 which disappears completely in the peripheral groove 14 (Figure 2). The cylindrical tube 1 of the shock absorber has a first inner groove 18 for receiving the circlip 15 associated with the relaxation stop element 12, and a second inner groove 19 for cooperating with the circlips 16 associated with the plug 11. The second groove inner 19 has the particularity of presenting a frustoconical ramp 19a from the bottom of the groove 19 towards the inner walls of the cylindrical tube 1 on the side of the first inner groove 18.

 The detent stop element 12 slides around the piston rod 4 from the interior walls of the mounting tube 17 to the interior walls of the cylindrical tube 1 of the damper until the peripheral groove 14 is opposite of the second inner groove 19 of the tube. The circlip 15 then extends radially outwardly by elasticity to enter the bottom of the second internal groove 19 (FIG. 3).

 If the axial force exerted on the trigger stop element 12 is sufficiently great, the circlip 15 will be forced to go up the frustoconical ramp 1 9a of the second internal groove 19 to finally enter again the peripheral groove 14 of the stop and detent element 12 to continue the mounting operation (FIG. 4).

 The downward movement of the stop and detent element 12 continues until the peripheral groove 14 is opposite the first internal groove 18. The circlip 15 then extends again radially to be housed at the bottom of the inner groove 18 by its elasticity. The internal groove 18 is shallow and leaves a part of the circlip 15 projecting radially towards the inside of the tube 1, which constitutes an axial stop for the trigger stop element 12 in the two axial directions thanks to its peripheral groove 14. After mounting the detent stop element 12, one can mount all the seals 13a, 13b and the plug 1 1 of the closure device 3 and then mount the circlip 16 constituting an axial stop for the upward movement of the plug 1 1 as is the case in the conventional closure device (Figure 5).

 To improve the characteristics of the shutter device 3, it is preferable to create a rebound volume filled with damping oil between the seals 13a, 13b and the element and rebound stopper 12. As illustrated in Figures 2 to 5, it is possible to provide an annular depression 1 2a on the upper face of the trigger stop member 12 or on the lower face of the static seal 13a, (configuration not shown), to constitute an expansion volume at the static seal 13a. Radial grooves 12b are in communication with the annular expansion volume 12a and the internal opening 12c surrounding with radial clearance the rod 4 of the piston. Thus a permanent communication is created between the hydraulic compartment A and the expansion volume 12a. It is also possible to put the annular trigger volume 12a and the compartment A into direct communication by means of one or more direct passages 12d passing through the thickness of the trigger stop element 12.

 In FIG. 6 is shown another alternative embodiment of the invention which differs from the mode illustrated in FIG. 5 in that the peripheral groove 14 of the trigger stop element 12 encloses at the bottom an elastic O-ring 20 which is elastically deformed when the circlip 15 is completely obliterated radially in the peripheral groove 14, so as to create a radial force which pushes the circlip 15 towards the outside of the peripheral groove 14. The presence of the elastic O-ring 20 can therefore be advantageous to avoid jamming or jamming of the circlip 15 in the peripheral groove 14 of the trigger stop element 12 during assembly of the closure device according to FIGS. 2 to 5. Likewise, the elastic O-ring 20 creates a force radial pressing the circlip 15 into the inner circular groove 18 of the tube 1 during shearing forces during the expansion phase of the damper.

 Obviously, this variant with the presence of an elastic O-ring 20 at the bottom of the peripheral groove 14 of the trigger stop element is applicable to all the variant embodiments of the present invention, in particular to those explicitly described in the present patent application.

 In FIG. 7 is illustrated a variant of the detent stop element 12 by which the communication of damping oil between the compartment A and the detent volume 12a is ensured by the radial grooves 12b and the central passage 12c.

 According to FIG. 8, the oil communication between compartment A and the expansion volume 1 2a is carried out by perforations 12d of the expansion stop element 12.

 According to the variant illustrated in FIG. 9, the communication between compartment A and the expansion volume 12a is ensured by means of an axial clearance 12e between the static seal 13a and the expansion stop element 12 as well as by means of the radial clearance between the central passage 12c and the rod 4 of the piston.

 According to the variant illustrated in FIG. 10, the communication between the detent volume 12a and the compartment A is ensured by means of the radial external grooves 12f and at the radial clearance 12g between the peripheral edge of the detent stop element 12 and the inner walls of the shock absorber tube 1. In this case, the section of the circlip 15 must be such that the radial clearance 12g does not deteriorate the mechanical blocking characteristics of the detent stop element 12 by the circlip 15.

Figures 11a and 1b illustrate another alternative embodiment of the trigger stop member 12 of the invention. The expansion volume 12a communicates with the hydraulic compartment
A of the shock absorber via the external slots 12h of the trigger stop element 12. This solution can be advantageous because it reduces the weight of the trigger stop element 12 without reducing its required mechanical characteristics . In addition, it is possible to provide a retaining ring 15 removable from the peripheral groove 14 for this variant which allows access to a tool to the retaining ring 15 by one of the external slots 12h.

 FIG. 12 illustrates another alternative embodiment of the invention by which an axial clearance 12e is provided between the static seal 13a and the expansion element 12 allowing the expansion volume 12a to enter into communication with the hydraulic compartment A of the damper on one side by the radial clearance between the central passage 12c of the trigger stop element 12 and the rod 4 of the piston, and on the other by the radial clearance 12g between the outer edge of the detent stop element 12 and the inner walls of the tube 1 of the shock absorber. The recommendations concerning the dimensions of the circlip 15 for the variant illustrated in FIG. 10 are applicable for this variant.

 Figures 13 to 17 show some other alternative embodiments of the invention which differ from the variant illustrated in Figure 1 only in terms of technical cooperation between the trigger stop member 12 and the piston 2 of the shock absorber . In the variant illustrated in FIG. 1, the lower surface of the detent stop element 12 has a peripheral notch 21 allowing the cup 9 to rise sufficiently high so that the elastic seal 10 can be crushed against the lower surface of the 'relaxation stop element 12 at the end of stroke of the piston 2 in the expansion phase of the shock absorber.

 It is possible to remove the cup 9 associated with the piston 2, in which case it is no longer necessary to provide the peripheral notch 21 on the lower face of the trigger stop element 12. This lower surface can be produced in the form a cup 22 oriented downwards in order to receive in a centered manner the elastic expansion joint 10 at the end of the travel of the expansion phase of the damper (FIG. 13) or else quite simply in the form of a flat surface 23 on which the elastic expansion joint 10 comes into abutment at the end of the piston stroke during the expansion phase of the shock absorber (FIG. 14).

 FIG. 15 illustrates another variant of the invention according to which the lower surface of the detent stop element 12 comprises a peripheral cylindrical skirt 24 extending downwards.

The elastic expansion joint 10 is crushed at the end of stroke of the piston 2 in the expansion phase of the damper against the lower surface of the expansion stop element 12, and in parallel, the circular plate 7 of the piston 2 enters coaxially in the annular space formed by the skirt 24 of the detent stop member 12, so as to trap a quantity of damping oil in the vicinity of the elastic detent seal 10, which creates a hydraulic brake effect at the piston at the end of travel in the expansion phase of the shock absorber.

 The variant illustrated in FIG. 16 does not include the elastic expansion joint 10 unlike the variant according to FIG. 15. The end of travel of the piston 2 in the expansion phase of the shock absorber is braked hydraulically and exclusively by means of the plate 7 of the piston which cooperates with the annular space delimited by the peripheral skirt 24 of the trigger stop element 12. The damping oil trapped between the upper surface of the plate 7 and the flat lower surface of the element of the relaxation stop 12 is laminated by the plate 7 and leaks towards the compartment A through the annular gap between the peripheral edge of the plate 7 and the cylindrical inner wall of the skirt 24.

 The variant illustrated in FIG. 17 differs from that illustrated in FIG. 16 only at the level of the plate 7 associated with the piston 2 of the shock absorber. The plate 7 has the same dimensions as above in order to be able to cooperate with the peripheral skirt 24 of the trigger stop element 12 in the manner just described.

The plate 7 comprises a plurality of axial perforations 25 distributed circumferentially and cooperating with an elastic tongue 26 on the upper surface to form a non-return valve. During the expansion phase of the shock absorber, there is no difference in operation compared to what has just been described. During the compression phase of the shock absorber, however, the non-return valves formed by the perforations 25 and the tabs 26 allow a faster passage of the damping oil from compartment B to compartment A, which makes it possible to reduce the phenomenon of cavitation under limiting conditions of compression, and thus improving the operation of the damper.

 In all the variants of the invention, it is possible to provide the circlip 15 of circular, rectangular or rectangular section with rounded edges according to the need for use.

Claims (7)

 1. Pressurized hydraulic shock absorber comprising a cylindrical tube (1) containing a damping liquid and in which slides a piston (2), a closure device (3) immobilized relative to the internal walls of the cylindrical tube and serving as a guide for the piston rod (4) in its axial translational movement, the closure device comprising a seal (13a, 13b) sandwiched between a plug (11) and a detent stop element (12), characterized in that the detent stop element (12) comprises a body in the form of a disc provided with a peripheral groove (14) of substantially rectangular section for receiving a circlip (15), the circlip being able to be erased radially and completely in said peripheral groove and capable of cooperating with an inner circular groove (18) of the cylindrical tube by being pressed by its elasticity at the bottom of said inner groove, so that the circlip protrudes radially inwardly to cooperate with said peripheral groove (14) in order to immobilize the rebound stop element (12) axially in the cylindrical tube (1).  2. Shock absorber according to claim 1, characterized in that the peripheral groove (14) of the trigger stop element (12) comprises at the bottom an annular elastic seal (20) which elastically deforms by the complete radial erasure of the circlips (15) in said peripheral groove and which exerts a radial force expelling the circlip towards the outside of said peripheral groove.  3. Shock absorber according to claim 1 or 2, characterized in that the cylindrical tube (1) comprises a second inner circular groove (19) intended to cooperate with a second circlip (16) to form an axial stop at the plug (11), the profile of said second internal groove having a frustoconical ramp (19a) from the bottom of said groove towards the internal walls of the cylindrical tube, so that during the mounting of the trigger stop element (12) in the tube cylindrical (1), the circlip (15) associated with the peripheral groove (14) of the trigger stop element can pass axially through the second inner groove (19) without being blocked in order to reach the level of the inner groove (18) associated with it.  4. Shock absorber according to one of claims 1 to 3, characterized in that between the seal (13a, 13b) and the trigger stop member (12) is created a trigger volume (12a) which is in permanent communication with a hydraulic compartment (A) of the shock absorber by means of passages (12b to 12h) through the trigger stop element or between the trigger stop element and the piston rod (4) or the inner walls of the cylindrical tube.  5. Shock absorber according to claim 4, characterized in that the detent stop element (12) comprises the external notches (12a) passing through its thickness and establishing direct communication between the detent volume (12a) and the hydraulic compartment ( A) adjacent.  6. Shock absorber according to one of the preceding claims, characterized in that the detent stop element (12) has on the lower surface a peripheral skirt (24) which can cooperate with a circular plate (7) of the piston to create a Hydraulic braking at the end of the piston stroke during the expansion phase of the shock absorber.  7. Shock absorber according to claim 6, characterized in that the circular plate (7) of the piston has axial perforations (25) and elastic tongues (26) to constitute non-return valves allowing the passage of the damping liquid through the circular plate during the compression phase of the shock absorber.