SHOCK ABSORBER WITH A HYDRO-MECHANICAL STOP

Abstract: A shock absorber (10) has a rebound stop assembly (22). The rebound stop assembly (22) rests upon a shoulder (30) fixed to a piston rod (16). The rebound stop assembly (22) includes an elastomeric ring (24) interposed between two collars (26 and 28) forming an annular chamber (74) therebetween. At the end of the rebound stroke of piston rod (16), the rebound stop assembly (22) is axially compressed between the shoulder (30) of piston rod (16) and the rod guide (18) until the elastomeric ring (24) deforms to abut the inner wall (64) of the working cylinder. As the elastomeric ring deforms, the annular chamber decreases in volume. A restrictive passage (71) allows a restrictive flow of fluid therefrom. An additional chamber (70) is formed which is in restrictive fluid communication through the passage (71) with section (68) of rebound chamber (20). Further compression of the stop assembly (22) decreases the volume of both chambers (70 and 74), and causes restrictive fluid flow out therefrom through the passage (71) into the section (68) of rebound chamber (20). The compression of the elastomeric ring and the restrictive fluid flow provides additional damping at the end of the rebound stroke.

Description: SHOCK ABSORBER WITH A HYDRO-MECHANICAL STOP Technical Field This invention relates to a stop for a shoc absorber and , more par ticularly, to a hydraulic assi ste rebound stop. Background Disclosure Information Often shock absorbers are designed such that th damping rate of the shock absorber becomes higher at th extreme ends of the rebound and compression strokes . Th additional damping is desired to prevent an abrupt hal t t the piston stroke and to prevent j arr ing metal-to-meta contact between the various par ts in the shock absorber . variety of mechanisms have been devised .to render a highe damping rate at the two extremes. Spring s and elastomer i jounce bumpers have been incor porated internally as well a externally of the working cylinder . In addition , secondar pistons have been used which become operative only at the extreme ends of the piston stroke . All previous mechanism added to the cost of the shock absorber . It is desired to have a hydro-mechanical stop which effectively dampens the end of a piston stroke while being economical to manufacture and assemble . Summary of the Invention In accordance with the invention, "a shock absorber has a working cylinder wi th a piston slideably received therein attached to a piston rod which ex tends through a rod guide at one end of the cylinder . A hydro-mechanical stop is coaxially mounted about the pi ston rod between the piston and the rod guide . The hydro-mechanical stop includes a tubular resiliently flexible ring mounted about the piston rod. The flexible ring has an outer annular -ψπλEJC OMPI v. W VVIUPOU wall having a diameter smaller than the diameter of the inner wall of the working cylinder. The ring rests on a shoulder fixed to the piston rod such that at the end of a rebound stroke of the piston rod, the ring is axially compressed between the shoulder and the rod guide. The ring is sufficiently flexible such that upon axial compression of a predetermined amount, the outer annular wall enlarges until it abuts the inner wall of the working cylinder to form with said cylinder and said rod guide a substantially closed hydraulic chamber. Upon further compression of the flexible ring, hydraulic fluid is forced from the hydraulic chamber through a restrictive passage to provide additional damping. Preferably, collars are mounted at opposite axial ends of the flexible ring. It is desirable that each collar has an axial extending cylinder section with a central aperture therethrough large enough to receive the piston rod and to provide an annular space therebetween. The cylindrical section has an outer wall with a diameter sized such that the cylindrical section is pressed fit within an axial end of the flexible ring. In addition, each collar has a radially extending flange. Each flange has an axially inner facing surface which abuts an axial end of the flexible ring. The outer surface of one of the radially extending flanges has a plurality of circumfer- entially spaced protrusions which are abuttable with the rod guide. The outer surface of the other radially extend¬ ing flange has a plurality of protrusions which abut the shoulder fixed to the piston rod. Two sections of the restrictive passage are formed by spaces between the protru¬ sions. Another section is formed by the annular space about the piston rod. One end of the passage communicates with the hydraulic chamber. The other end communicates with a lower portion of a rebound chamber in the working cylinder. In broader terms, a tubular resilient flexible OM ring is mounted about the piston rod. The ring has an annular wall with a diameter intermediate the diameter of the inner wall of the working cylinder and the diameter of the piston rod . The ring is interposed between an abutment fixed to the wor king cylinder and a shoulder fixed to the piston rod such that at the end of a piston stroke , the shoulder and the abutment axially compress the ring until its annular wall deforms and abuts one of the piston rod and the cyl inder . A hydraulic fluid chamber is formed in par t by the deformed annular wall . Hydraulic fluid is con¬ tained in the hydraulic fluid chamber . Further compression of the ring forces the hydraulic fluid out through a restr ictive passageway from the hydraulic fl uid chamber to provide addi tional damping at the end of the piston stroke . Brief Description of the Drawings Reference now will be made to the accompanying drawing s in which : Figure 1 is a fr agmentary side elevational and partially segmented view of a shock absorber di sclosing a rebound stop in accordance wi th the invention ; Figure 2 is a view similar to F ig ure 1 showing the rebound stop in par tial compr ession ; Figure 3 is a view similar to Figure 2 showing the rebound stop in full compression ; Figure 4 is a plan view of a collar shown in Figures 1 through 3 ; " Fig ure 5 is a cross-sectional view taken along the lines V-V in Figure 4; Figure 6 is a cross- sectional view of the elasto- mer ic ring shown in Fig ures 1 through 3 ; Figure 7 is a plan view of the elastomeric ring ; Fig ure 8 is a cross-sectional view of the rebound stop assembly shown in Figures ^ 1 through 3. Detailed Description of the Preferred Embodiment ' Referring to Figure 1, a shock absorber 10 has a working cylinder 12 with a piston 14 slideably mounted therein. The piston 14 is conventional in construction '5 with valved restrictive passageways 15. A piston rod 16 is connected to the piston 14. A- rod guide 18 is fixedly mounted at the end of the working cylinder 12. A jounce chamber 19 is defined below the piston 14. A rebound chamber 20 is defined within the cylinder 12 about the 0 piston rod 16 and bounded by the piston 14 and rod guide 18. In addition, a rebound stop assembly 22 is mounted within the working cylinder 12 about the piston rod 16. . The presently preferred embodiment of the rebound stop assembly 22 described below is the subject of a 5 co-pending improvement patent application filed on the same day as the present application jointly by Mr. James Peter Nagy and the present inventor, Mr. Jack Wayne Mourray, and entitled A HYDRO-MECHANICAL STOP HAVING A RESTRICTIVE PASSAGE. 0 The rebound stop assembly 22, as shown in Figure 8, includes a tubular elastomeric ring 24 and two collars 26 and 28 which are pressed fit within the elastomeric ring 24. The rebound stop assembly 22 is mounted on top of a shoulder 30 shown in Figure 1. The shoulder 30 is fixed, 5 at least in the axial direction, to the piston rod 16. The elastomeric ring 24, as shown in more detail in Figures 6 and 7, has an annular outer wall 32 of varying diameter with the midsection 34 having the largest diameter and the ends 36 having the smallest diameter. The inner 0 wall 40 defines a central opening 38. The inner wall 40 also has a varying diameter with its largest diameter at midsection 42. The collars 26 and 28 are identical in structure; therefore, reference now will only be made to collar 26 shown in Figures 4 and 5. The collar 26 has an axiall extending portion 44 and a radially extending shoulder 46. The axially extending portion 44 has an inner wall 4 forming a central opening 49 sized to receive a piston ro 16 and to provide an annular gap 50 as shown in Figure 1. The axial extending portion 44 has an outer wall 52 whic is sized to be pressed fit within the opening 38 at end 36 of the elastomeric ring 24. The inner wall 48 and outer wall 52 define the inner and outer diameter of an annular axial end 54. The radially extending shoulder 46 defines the second end 56 of collar 26. The end 56 has a pluralit of circular protrusions 58 circumferentially spaced abou the collar. Each protrusion 58 has a flat end surface.60. Each shoulder 46 also has an axial inner facing surface 62 which extends radially outwardly from annular wall 52. As shown in Figure 8, collars 26 and 28 have their axial portions pressed fitted within the opening * 38 at the opposite ends 36 of ring 24. The inner facing surface 62 of shoulder 46 of each collar abuts a respective end 36 of the ring 24. Referring back to Figure 1, the assembly 22 is mounted about the piston rod 16 seated on shoulder 30 within the rebound chamber 20. More specifically, the protrusions 58 of collar 28 rest on shoulder 30. The assembly 22 slides through the rebound chamber 20 as the piston 14 correspondingly slides within the cylinder 12. The midsection 34 has a diameter substantially smaller than the inner wall 64 of cylinder 12, thereby forming a substan¬ tially large annular gap 66 between lower section 68 and upper section 70 of the rebound chamber 20. The restric¬ tion between the sections 68 and 70 through gap 66 is significantly lower than the restriction through valved passages 15 in piston 14. The gap 66 consequently does not add any significant damping to the relative motion of the piston rod 16 and the cylinder 12 during normal vibrations. V ' I? In other words, the assembly 22 does not interfere with the normal damping characteristics of the shock absorber 10 during the normal stroke range. However, when the piston rod 16 approaches the end of its rebound stroke, the assembly 22 provides additional damping. The assembly 22 is moved upward through cylinder 12 until the protrusions 58 on collar 26 abut the rod guide 18. Further upward motion of the piston rod 16 causes shoulder 30 and rod guide 18 to axially compress the flexible ring 24. The deformation of the elastomeric ring 24 provides a certain amount of additional damping. The axial compression of ring 24 causes the outer diameter section 34 to enlarge- and abut the inner wall 64 of the cylinder as shown in Figure 2. Free fluid communication between section 68 of the rebound chamber 20 and section 70 is interrupted by the closure of gap 66. Sections 68 and 70 become two separate chambers. A restrictive passage 71 between chambers 68 and 70 is simultaneously formed. The upper portion 72 of the passage 71 is interposed between the upper surface 56 of collar 26 and the rod guide 18 between the circumferen- tially spaced protrusions 58. The annular gap 50 formed between the piston rod 16 and the inner wall 48 of collar 26 defines a second section of the passage 71. An annular chamber 74 formed between the collars 26 and 28 and between the piston rod 16 and the inner wall 40 of the flexible collar 24 defines a third section of the passage 71. The gap 50 between the inner wall 48 of collar 28 and the piston rod 16 defines a fourth section of the passage 72. A fifth section 75 of the passage is formed between the shoulder 30 and the outer surface 56 of the collar 28 between the spaced protrusions 58. Further upward movement of the piston rod 16 is damped by a highly restrictive fluid flow out from chambers 70 and 74 and the additional compression of elastomeric ring 24. The chamber 70 decreases in volume as the piston rod moves upwardly to compress the elastomeric ring 24. The fluid therein is forced through the restrictive passage 71 to chamber 68. In addition, the axial dimension of annular chamber 74 is shortened resulting in a decreased volume. The fluid within chamber 74 is also forced through the fourth and fifth sections of passage 71 to the chamber 68. The passage 71 allows a sufficient fluid flow from chamber 74 to prevent the hydraulic fluid therein from being excessively pressurized. Excessive pressure within chamber 74 may separate the flexible elastomeric ring 24 from its collars 26 and 28. In other words, the passage 72 provides a metered flow from both chambers 70 and 74. As the axial ends 54 of the collars come toward each other, a gap 75 therebetween narrows down. When the gap 75 becomes sufficiently narrow, it provides a restric¬ tion to the remainder of passage 71 from chamber 74. This restriction decreases the flow from chamber 74 further increasing the damping of the shock absorber.- The •decreased flow from chamber 74 occurs only after the elastomeric ring 24 is deformed to be sufficiently thick to withstand the buildup of pressure within chamber 74. If the rebound stroke is sufficiently strong to continue against the additional damping, the ends 54 of the collars 26 and 28 abut each other, as shown in Figure 3, and further axial compression of the elastomeric ring 24 is prevented. At this point, the piston rod 16 can no longer move upwardly. However, between the position as shown in Figure 1 and the position shown in Figure 3, the rebound stop assembly 22 provides high damping of the rebound stroke to soften any jarring impact which may otherwise occur " when the piston rod attains the position shown in Figure 3. Alternatively, the rebound stop assembly 22 may altogether prevent any jarring impact by totally damping the stroke before the piston rod attains the position shown in Figure 3. Passage 71 may be alernatively arranged. Alterna¬ tives can include axially extending notches cut into the midsection 34 of the elastomeric ring 24 such that when midsection 34 abuts the inner wall 64 of the cylinder 12, the notches will form a restrictive passage and restrict flow from chamber 70 to section 68. In this fashion, an easily manufactured rebound stop is possible which provides high damping capabilities as well as being economical to manufacture and easy to install on existing shock absorbers with minimal amount of modification. Variations and modifications of the present invention are possible without departing from its scope and spirit as defined by the appended claims. Industrial Applicability This invention has industrial applicability to shock absorbers and provides a damping system for the shock absorber at the end of a stroke.

Claims: CLAIMS The embodiments of the invention in which a exclusive property or privilege is claimed are defined a follows: 1. In a telescopic shock absorber including working cylinder, a piston slideably received within sai working cylinder and defining a boundary for a reboun chamber within said cylinder, a piston rod connected to said piston and extending through one end of said working cylinder, closure means for closing said one end of said cylinder and slideably mounting said piston rod, the improvement characterized by: a resiliently flexible ring mounted about said piston rod; said ring having an annular outer wall with a diameter smaller than the diameter of an inner wall of said working cylinder; said ring interposed between said closure means and a shoulder fixed to said piston rod such that, at the end of the rebound stroke of said piston rod, said shoulder and said closure means axially compress said ring; said ring being sufficiently flexible such that, when it is axially compressed, an annular portion of said outer wall enlarges to abut said inner wall of said working cylinder and forming with said cylinder and said closure means a hydraulic chamber; and restricting means for restricting hydraulic fluid flow from said hydraulic chamber upon further compression of said flexible ring. 2. A telescopic shock absorber as defined in claim 1 further characterized .by: said closure means at said end of said working ' cylinder comprising a rod guide radially extending inwardly from said inner wall of said working cylinder; said rod guide operably abutting said ring at the end of said rebound stroke; and said hydraulic chamber being formed by said inner wall of said cylinder, said rod guide, and said outer wall of said ring. 3. A telescopic shock absorber as defined in claim 2 further characterized by: two collars mounted at opposite axial ends of said flexible ring; each collar having an axial extending portion; each axial extending portion having an inner wall with a diameter sized to receive said piston rod and an outer wall with a diameter sized to be pressed fit within said flexible ring; each collar having a radially outwardly extending shoulder with an axially inner facing surface for abutting a respective axial end of said flexible ring; each collar having an axially outer facing end surface for abutting one of said shoulder and rod guide; and each axial extending portion having an axially inner end which abut each other after a predetermined amount of compression of said flexible ring to prevent further compression of said flexible ring. 4. In a telescopic shock absorber including a working cylinder, a piston slideably received within said working cylinder and defining a boundary for a rebound chamber within said cylinder, a piston rod connected to said piston and extending through one end of said working cylinder, closure means for closing said one end of said cylinder and slideably mounting said piston rod, the ( OM improvement characterized by: a resiliently flexible ring mounted about sai piston rod; said ring having an annular wall with a diamete intermediate with the diameter of an inner wall of sai working cylinder and the diameter of said piston rod; said , ring interposed between said closure mean and a shoulder fixed to said piston rod such that at the end of a rebound stroke of said piston rod said shoulder and said closure means axially compress said ring; said ring being sufficiently flexible such tha when it is axially compressed, the diameter of an annular portion of said annular wall changes dimensions to abut one of said piston rod and said cylinder; said ring, when said ring is axially compressed and said annular wall of said ring abuts one of said piston rod and said cylinder, forms with said respective cylinder or piston rod and said closure means a hydraulic chamber; and restricting means for restricting hydraulic fluid flow from said hydraulic chamber upon further compression of said flexible ring. 5. In a telescopic shock absorber including a working cylinder, a piston slidably received within said working cylinder and defining a boundary for a rebound chamber within said cylinder, a piston rod connected to said piston and extending through one end "of said working cylinder, the improvement characterized by: a resiliently flexible ring mounted about said piston rod; said ring having an annular wall with a diameter intermediate with the diameter of an inner wall of said working cylinder and the diameter of said piston rod; said ring interposed between an abutment fixed to said working cylinder and a shoulder fixed to said piston rod such that, at the end of a rebound stroke of sai ' piston rod, said shoulder and said abutment axiall compress said ring; said ring being sufficiently flexible such that, when it is axially compressed, the diameter of an annular portion of said annular wall changes dimensions to abut one of said piston rod and said cylinder; said ring, when said ring is axially compressed and said annular wall of said ring abuts one of said piston rod and said cylinder, forms with said respective cylinder or piston rod and said abutment a hydraulic chamber; and restricting means for restricting hydraulic fluid flow from said hydraulic chamber upon further compression of said flexible ring. OMPI

Inventors: MOURRAY JACK WAYNE, MOURRAY, JACK, WAYNE
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S.A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1982
Main classification: F16F9
IPC codes: F16F7, F16F9