Monotube damper

Abstract: A monotube damper includes a cylindrical tube (12) with a piston (20) sealingly and slidably carried within the cylindrical tube. The piston separates the cylindrical tube into extension (32) and compression (30) chambers. A piston rod (26) is connected to the piston assembly. A rod guide assembly (25) surrounds the piston rod and includes a lower annular leg with a hub (53) and an upper annular skirt (54). A lower bushing (72) supports the piston rod and is carried by the hub. An upper bushing (70) is spaced away from the lower bushing and supports the piston rod.

Description: Technical Field The present invention relates to a monotube damper, as disclosed in GB-A-691477 and the preamble of claim 1. Background of the Invention Monotube gas charged dampers are conventionally known wherein a piston with a connected piston rod is slidably contained in a fluid filled tube with a separate piston called a gas cup slidably carried in the tube on the opposite side of the piston from the rod. The gas cup separates a compressible gas charge from the fluid. It has been found that monotube gas charged dampers exhibit desirable performance characteristics when used in some suspension assemblies. However, the use of gas charged monotube dampers has been limited to only certain suspension assemblies among those where such use is desirable. For example, when a damper is used in a front wheel drive vehicle, it is generally carried above the axle and below the hood or fender line. This limits the overall length of the damper. For viability, the travel length of a damper must be acceptably long as determined by the vehicle's suspension requirements. With known monotube gas charged dampers, the gas charge and gas cup introduce an undesirable amount of inactive length to the assembly, thereby reducing active travel length of the damper. This creates difficulties in packaging the damper within the suspension and in some cases, precludes the use of a monotube gas charged damper. A further complicating factor in providing an acceptable travel length arises due to increased load carrying requirements placed on dampers. To sufficiently carry higher loads, a damper's structural rod is of an increased diameter. Therefore, the amount of oil displaced when the rod enters the tube during compression is greater. Displacement of more fluid necessitates greater volumetric compensation needs, requires greater linear movement of the gas cup and necessarily increases the overall length of the damper assembly. Summary of the Invention It is an aspect of the present invention to provide a monotube damper according to the Features of claim 1. The rod guide body and the piston body are provided as stampings with a shape that permits them to mate together in an overlapping fashion as the damper approaches full extension. Therefore, the active travel length of the suspension damper is maximized. In addition, the rod guide utilizes a pair of independent bushings to maximize the lateral support provided to the piston rod which has increased extendability. Preferably, the rod seal is included as two individual components on opposite sides of the outer bushing in order to provide a more secure sealing arrangement for the damper. The rod guide is also preferably designed to be self-aligning during closure of the top end of the cylinder tube. A conventional means is provided to introduce a gas charge into the cylinder tube between its bottom closed end and the inserted gas cup. The gas cup is preferably designed in a fashion to additionally mate with the piston assembly in an overlapping fashion. Brief Description of the Drawings Figure 1 is a cross sectional view of a suspension damper. Figure 2 is a fragmentary cross sectional view of the rod guide and piston assemblies of the suspension damper of Figure 1 shown in a full extension position. Figure 3 is a fragmentary cross sectional view of the suspension damper of Figure 1 shown in a full compression position. Description of the Preferred Embodiment Referring to the drawings, illustrated in Figure 1 is a suspension damper 10 of the monotube gas charged shock type. Damper 10 includes an elongated outer cylindrical tube 12 which is closed at its lower end 14. A piston assembly 20 is mounted for reciprocal movement within the tube 12. Piston assembly 20 includes a stamped steel piston body 21 which carries a band of low friction material 22 sealingly and slidably engaging the inner wall 15 of cylindrical tube 12. Piston assembly 20 hydraulically separates the tube 12 into two expansible and contractible working chambers designated as compression chamber 30 and extension chamber 32. The upper end 16 of tube 12 is formed to securely carry a rod guide assembly 25. A piston rod 26 is securely connected to the piston assembly 20 and extends through extension chamber 32 and rod guide assembly 25 exiting the tube 12. Piston rod 26 includes an annular shoulder 28 that carries a generally cylindrical dust tube assembly 29 that extends down over the tube 12. The upper end 34 of piston rod 26 includes an attachment fitting 35 which is provided for attachment to the body of a vehicle (not illustrated). The lower end 14 of cylinder tube 12 also includes an attachment fitting 36 for connection to the wheel assembly of the vehicle (not illustrated). Therefore, in response to relative movement between the wheel assembly and the vehicle, the piston assembly 20 reciprocally moves within tube 12. The cylindrical tube 12 carries a supply of oil which provides a damping medium for the damper 10. During a compression stroke, as the piston assembly 20 slides downward in the tube 12, an increasing volumetric amount of the piston rod 26 enters the tube 12 through the rod guide assembly 25. Therefore, a means of accommodating this increased volume within the damper 10 must be provided. Accordingly, a compressible gas charge is carried within compensation chamber 38 which is separated from the compression chamber 30 by a reciprocal gas cup assembly 40. As the increasing amount of the piston rod 26 enters the tube 12 during a compression stroke of the damper 10, the gas within compensation chamber 38 is compressed as the gas cup assembly 40 slides downward in response to displacement of the noncompressible hydraulic fluid carried within compression chamber 30 and extension chamber 32. A conventional means of introducing a gas charge into the compensation chamber 38 is provided near the lower end 14 of tube 12. Referring to Figure 2, the piston assembly 20 and the rod guide assembly 25 are shown in greater detail with the damper 10 in its fully extended position. The piston body 21 includes a base 42 and an annular skirt 43 forming an annular cavity 44 that is open to the extension chamber 32. The base 42 includes an opening 45 that receives turned down section 46 of piston rod 26 and is secured thereon by a nut 47 which threadedly engages threaded section 48 of piston rod 26. A valve assembly 50 of the bidirectional monodisc type is carried about turned down section 46 of piston rod 26 within annular cavity 44 of piston assembly 20. The rod guide assembly 25 includes a stamped metal rod guide body 52 which includes a lower annular leg forming a hub 53. Hub 53 surrounds piston rod 26. An upper annular skirt 54 is offset outwardly in the upward direction and positioned against the upper end 16 of tube 12 between rolled groove 55 and annular leg 56. This results in a piloting effect from the alignment of piston rod 26 by the lower bushing 72 and upper bushing 70 minimizing internal friction in the damper 10. Closure of the damper 10 is achieved by simultaneously roll forming the radial groove 55 and forming over the upper end 16 by spinning or rolling the annular leg 56 substantially normal to the main portion of tube 12 and over the rod guide assembly 25. Formation of the radial groove 55 and the closure of the upper end 16 is critical and is therefore, conducted in the same machine resulting in aligned closure of the damper 10 and secure sealing thereof. A cavity 58 is formed about piston rod 26 near the upper end 16 of tube 12 between rod guide body 52 and annular leg 56 of tube 12. The cavity 58 carries a first seal assembly 60 and a second seal assembly 62 which are secured between annular leg 56 of tube 12 and ledge 51 of rod guide body 52. The outer seal assembly 60 includes an annular resilient seal element 61 which is carried by seal retainer 63 with a garter spring 65 biasing the seal element 61 against the piston rod 26. The inner seal assembly 62 includes a resilient seal element 67 which is carried by a seal retainer 68 and is biased against the piston rod 26 by a garter spring 69. Upper bushing 70 and lower bushing 72 are disposed in the rod guide assembly 25 in a spaced apart manner to provide an additional degree of lateral support to the piston rod 26 which maintains the piston rod 26 in an aligned orientation and assists in preventing the application of excessive lateral forces to the seal assemblies 60 and 62. The upper bushing 70 is carried against the piston rod 26 by the seal retainer 68. The lower bushing 72 is carried against the piston rod 26 by the hub 53 of rod guide body 52. By means of the downward extending annular leg carrying the hub 53 of the rod guide body 52 the lower bushing 72 is spaced a maximum practical distance from the upper bushing 70. An integral hydraulic rebound cutoff feature is carried by the piston assembly 20 and the rod guide assembly 25. The piston assembly 20 carries lower rebound cutoff element 76 which includes an annular base wall 77 captured between bearing washer 78 and valve assembly 50 and an upward extending cylindrical wall 79. The rod guide assembly 25 carries upper rebound cutoff element 80 which includes an annular base wall 81 fixed to rod guide body 52 and an downward extending cylindrical wall 82 which includes a flared-out end 83. The cylindrical wall 79 of lower rebound cutoff element 76 is matingly received within cylindrical wall 82 of upper rebound cutoff element 80 as the damper approaches a fully extended position. As this occurs, fluid trapped within cavity 85 is expelled through gap 86 between lower rebound cutoff element 76 and upper rebound cutoff element 80. Initially, the gap 86 is relatively large near the end 83 of upper rebound cutoff element 80 and as the lower rebound cutoff element 76 is further received within upper rebound cutoff element 80 the size of the gap 86 diminishes. A fluid back pressure created in cavity 85 hydraulically slows travel of the damper 10 as it approaches a full rebound condition. When the damper 10 reaches the full rebound condition, bearing washer 78 mechanically contacts hub 53 of rod guide body 52 positively limiting the extent of travel for the damper 10. The abruptness of this mechanical stop is softened by specifically tailoring the amount of gap provided between the lower rebound cutoff element 76 and the upper rebound cutoff element 80 which provides a hydraulic cushion. The end 83 of upper rebound cutoff element 80 is received within the annular skirt 43 of piston assembly 20 and the hub 53 of rod guide assembly 25 is received within the lower rebound cutoff element 76. By providing the mating overlap of the piston assembly 20 with the rod guide assembly 25 extension of the damper 10 is maximized. Referring to Figure 3, the damper 10 is illustrated in a full compression condition. The gas cup assembly 40 includes an annular groove 90 which carries a resilient seal 91 that contacts the inner wall 15 of tube 12 maintaining separation between the gas charge in compensation chamber 38 and the fluid carried in compression chamber 30. The gas cup assembly 40 also includes a cup element 92 which spans across the tube 12 and opens toward the compression chamber 30. The gas cup assembly 40 is designed to receive the lower end 23 of piston rod 26 within the cup element 92. The rim 93 of cup element 92 is engageable with the base 42 of piston assembly 20. The nut 47 is fully received within the cup element 92 so that the travel of the damper 10 in a compression direction is maximized. In accordance with the foregoing description, a damper 10 of the monotube gas charged shock type provides a greater degree of travel per unit length. In addition, a piston rod 26 of a relatively smaller diameter is made possible due to the lateral support provided by the spaced apart upper bushing 70 and lower bushing 72.

Claims: A monotube damper comprising: a cylindrical tube (12); a piston (20) sealingly and slidably carried within the cylindrical tube including an annular skirt (43) and a lower rebound cutoff element (76), the piston separating the cylindrical tube into extension (32) and compression (30) chambers; a piston rod (26) connected to the piston assembly and extending therefrom; and a rod guide assembly (25) surrounding the piston rod and including a lower annular leg with a hub (53) wherein when the damper is in a fully extended position the hub is received within the lower rebound cutoff element; characterised in that the rod guide assembly (25) further includes an upper rebound cutoff element (80), wherein when the damper is in a fully extended position the lower rebound cutoff element is received within the upper rebound cutoff element and the upper rebound cutoff element is received within the annular skirt of the piston assembly. A monotube damper according to claim 1 wherein when the damper is approaching the fully extended position a gap (86) exists between the upper rebound cutoff element and the lower rebound cutoff element through which fluid is allowed to flow, the gap reducing in size as the damper further approaches the fully extended position. A monotube damper according to claim 2 wherein the upper rebound cutoff element includes an annular configuration with a cylindrical wall (79) having a first diameter and having a flared out lower end (83), the lower end having a second diameter larger than the first diameter. A monotube damper according to claim 1 wherein the rod guide assembly includes a first bushing (70) and a second bushing (72) spaced apart from the first bushing wherein each bushing engages the piston rod and supplies lateral support to the piston rod. A monotube damper according to claim 1 wherein the piston has a body that includes a base (77) and together with the annular skirt forms an annular cavity (85) that is open to the extension chamber wherein the base is secured to the piston rod with a valve assembly (50) carried about the piston rod within annular cavity. A monotube damper according to claim 5 wherein the piston is secured to the piston rod such that a portion of the piston rod extends through the piston base and into the compression chamber and further comprising a gas cup (40) slidably and sealingly carried in the cylindrical tube separating a compensation chamber (38) off from the compression chamber. A monotube damper according to claim 6 wherein the gas cup includes a rim (93) and a cup element (92) that spans across the cylindrical tube and opens adjacent the compression chamber wherein the gas cup is capable of receiving the portion of the piston rod that extends through the piston base and into the compression chamber such that the piston base is engageable with the rim.

Inventors: CHEATHAM CLAUDE H, CLAUDE GEORGE THOMAS, PEES JAMES MITCHELL, WELLS JOEL RAY, CHEATHAM, CLAUDE H., CLAUDE, GEORGE THOMAS, PEES, JAMES MITCHELL, WELLS, JOEL RAY
Applicants: DELPHI TECH INC, DELPHI TECHNOLOGIES, INC.
Application year: 1997
Main classification: F16F9
IPC codes: F16F9