Spring seat fixing structure for a hydraulic shock absorber

In a spring seat fixing structure of a hydraulic shock absorber (10), a proximal end side of a cap (44) is provided with a small diameter force-fit portion (71) which is fixedly forced into a small outer diameter portion (51) of a damper tube (11), and a distal end side of the cap (44) is provided with a large diameter force-fit portion (73) which is fixedly forced into a large outer diameter portion (52) of the damper tube (11).

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a spring seat fixing structure for a
 hydraulic shock absorber.
 2. Description of the Related Art
 Conventionally, a hydraulic shock absorber having a damper tube and a
 suspension spring has been proposed as disclosed in Examined Utility Model
 Publication (Kokoku) No. 55-12608. The hydraulic shock absorber is
 constructed in a manner that a cap is fixedly forced (pressed in) into a
 periphery of a shaft seal part of the damper tube, and a spring seat for
 the suspension spring is located on an outer periphery on a distal end
 side of the cap.
 In the aforesaid hydraulic shock absorber, in the case of providing a
 suspension spring having a desired length along an axial direction around
 the damper tube, a spring seat for the suspension spring must be located
 on a distal end side separated from the shaft seal part of the damper tube
 in the axial direction. Further, in order to retain the spring seat onto
 the damper tube without a misalignment, it is preferable that the cap is
 fixedly forced into the damper tube up to a location nearest to a spring
 seat mounting portion on the distal end side of the cap. Therefore, the
 cap needs to be fixedly forced into the damper tube by a considerably long
 range up to a location nearest to the spring seat mounting portion
 considerably separated from the shaft seal part of the damper tube in the
 axial direction.
 However, in the aforesaid prior art, an outer diameter of the damper tube
 is formed in a straight line. In the case where a considerably long
 portion from a proximal end side to the distal end side of the cap is used
 as a force-fit portion, in a process for fixedly forcing a force-fit
 portion on the distal end side of the cap into an outer diameter portion
 of the damper tube, a long portion of the damper tube is used as a
 force-fit surface. For this reason, it is difficult to force the cap into
 the damper tube.
 SUMMARY OF THE INVENTION
 An object of the present invention is to provide a spring seat mounting
 portion in a cap which is fixedly forced into a periphery of a shaft seal
 part of a damper tube, and to stably provide a spring seat without
 misalignment when mounting the spring seat onto a distal end side of the
 cap separated from the shaft seal part of the damper tube in the axial
 direction, and thus, to readily force the cap into the damper tube.
 To achieve the above object, the present invention provides a spring seat
 fixing structure for a hydraulic shock absorber which has a damper tube
 and a suspension spring, and is constructed in a manner such that a cap is
 fixedly forced into a periphery of a shaft seal part of the damper tube,
 and an outer periphery on a distal end portion of the cap is provided with
 a spring seat, wherein the damper tube has a small outer diameter portion
 around the shaft seal part and a large outer diameter portion on a side
 separated from the shaft seal part in an axial direction. A proximal end
 side of the cap is provided with a small diameter force-fit portion which
 is fixedly forced into the small outer diameter portion of the damper
 tube, and a distal end side of the cap is provided with a large diameter
 force-fit portion which is fixedly forced into the large outer diameter
 portion of the damper tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 As shown in FIG. 1, hydraulic shock absorber 10 is a single tube separate
 pressure type, and has a damper tube 11, a piston rod 12 and a suspension
 spring 13. A lower spring seat 14 is mounted to an outer periphery of the
 damper tube 11 as described later in detail. An upper spring seat 16 is
 mounted to the piston rod 12. The suspension spring 13 is stretched
 between the lower spring seat 14 and the upper spring seat 16.
 The hydraulic shock absorber 10 includes an axle side mounting part 18 at a
 lower portion of the damper tube 11, and a vehicle body side mounting part
 19 at the upper spring seat 16 mounted to the piston rod 12. The
 suspension spring 13 absorbs an impact from a road surface, and then, a
 damper included in the damper tube 11 damps a vibration by elongation and
 compression of the suspension spring 13.
 In the hydraulic shock absorber 10, a working fluid is filled in the damper
 tube 11, and a piston 21 is arranged so as to be slidable. The piston 21
 partitions an interior of the damper tube 11 so as to form a rod side
 chamber 22A which is filled with a working fluid and receives the piston
 rod 12, and a piston side chamber 22B which is filled with a working fluid
 and does not receive the piston rod 12.
 As described above, the hydraulic shock absorber 10 is a single tube
 separate pressure type. A free piston 23 is slidably located in the damper
 tube 11, and the damper tube 11 is partitioned into a pressure gas chamber
 24 and a reservoir chamber 25 by means of the free piston 23. A free
 piston stopper 26 is fastened and fixed between the reservoir chamber 25
 and the piston side chamber 22B. The piston side chamber 22B and the
 reservoir chamber 25 communicate with each other via an orifice 27 of the
 stopper 26. The reservoir chamber 25 compensates a working fluid
 corresponding to a volumetric change by the piston rod 12 which advances
 into or retreats from the damper tube 11 during a compression stroke and
 an elongation stroke of the hydraulic shock absorber 10.
 In the hydraulic shock absorber 10, a valve stopper 28, a piston 21 and a
 valve stopper 29 are fixed onto an insert end of the piston rod 12 into
 the damper tube 11 by means of a nut 30. The piston 12 having an
 elongation side damping valve 31A and a compression damping valve 32A,
 includes an elongation side channel 31 which is capable of connecting the
 rod side chamber 22A and the piston side chamber 22B, and a compression
 side channel 32 which is capable of connecting the rod side chamber 22A
 and the piston side chamber 22B. By doing so, in an elongation stroke of
 the hydraulic shock absorber 10, the working fluid of the rod side chamber
 22A passes through the elongation side channel 31 of the piston 21, and
 then elastically deforms the elongation side damping valve 31A so as to
 generate an elongation side damping force, and thus, flows into the piston
 side chamber 22B. On the other hand, in a compression stroke of the
 hydraulic shock absorber 10, the working fluid of the rod side chamber 22B
 passes through the compression side channel 32 of the piston 21, and then
 elastically deforms the elongation side damping valve 32A so as to
 generate a compression side damping force, and thus, flows into the piston
 side chamber 22A
 In the hydraulic shock absorber 10, a rod guide 34 is fastened and fixed at
 one end of a shaft seal part 33 of the damper tube 11, and the piston rod
 12 penetrates through the rod guide 34 so as to be supported thereto. The
 shaft seal part 33 includes an oil seal 35. Further, the shaft seal part
 33 is subjected to bending (fastening) so as to retain an end plate 36
 located outside of the oil seal 35 (see FIG. 3).
 In the hydraulic shock absorber 10, pads 38A and 38B are positioned on an
 outermost end portion of the piston rod 12 by means of a joint collar 37,
 and mounting buffers 15A and 15B are interposed between pads 38A and 38B.
 A mounting nut 39 is screwed onto an upper end portion of the piston rod
 12 in order to hold the aforesaid vehicle body side mounting part 19
 between the mounting buffers 15A and 15B, and thus, the upper end portion
 of the piston rod 12 is elastically mounted to the vehicle body side
 mounting part 19. Also, the vehicle body side mounting part 19 is provided
 with the aforesaid upper spring seat 16.
 In the hydraulic shock absorber 10, a cover 42 is fixed at the outer end
 portion of the piston rod 12 and between a pad stopper 41 for supporting
 the pad 38B to the piston rod 12 and the pad 38B. The cover 42 extends up
 to the upper end portion of the damper tube 11, and is arranged so as to
 surround a rubber bumper 43, which is backed up by the pad stopper 41
 around the piston rod 12.
 In the hydraulic shock absorber 10, a proximal end portion of a bump
 stopper cap 44 is fixedly forced into a periphery of the aforesaid shaft
 seal part 33 of the damper tube 11, and the aforesaid lower spring seat 14
 is provided at an outer periphery on the distal end side of the cap 44. A
 proximal surface of the cap 44 is provided with a rubber bumper abutting
 plate 45. When the hydraulic shock absorber 10 is compressed to the
 maximum, the aforesaid rubber bumper 43 is abutted against the abutting
 plate 45, and then, is compressively deformed so as to restrict the
 maximum compression stroke. The aforesaid cover 42 restricts an expansive
 deformation of the rubber bumper 43 by its compression during the maximum
 compression, and thus, sets a spring characteristic when the hydraulic
 shock absorber 10 is compressed to the maximum.
 In the hydraulic shock absorber 10, a rebound rubber 47 backed up and
 supported onto a rebound stopper 46 is provided at a periphery of the
 piston rod 12 situated in the rod side chamber 22A of the damper tube 11.
 When the hydraulic shock absorber 10 is elongated to the maximum, the
 rebound rubber 47 is abutted against the aforesaid rod guide 34 so as to
 restrict the maximum elongation stroke.
 As described above, in the hydraulic shock absorber 10, in the case where
 the spring seat 14 for the suspension spring 13 is provided on the outer
 periphery of the damper tube 11, the bump stopper cap 44 is fixedly forced
 around the shaft seal part 33 of the damper tube 11, and the spring seat
 14 is provided on the outer periphery on the distal end side of the cap
 44. The following is a detailed description on a fixing structure of the
 spring seat 14.
 As shown in FIG. 3 and FIG. 4, in the hydraulic shock absorber 10, the
 damper tube 11 has the following outer diameter portions, that is, a small
 outer diameter portion 51 (a range shown by a length A1) around the shaft
 seal part 33, and a large outer diameter portion 52 (a range shown by a
 length A2 excluding the length Al from the entire length of damper tube 11
 in this embodiment) on a side separated from the shaft seal part 33 in the
 axial direction. The small outer diameter portion 51 is made smaller than
 the large outer diameter portion 52 by being subjected to cutting or
 drawing or the like.
 Further, in the hydraulic shock absorber 10, as shown in FIG. 3 and FIG.
 5A, the cap 44 has the following inner diameter portions enlarged
 successively from the proximal end side to the distal end side, that is, a
 small inner diameter portion 61 (a range shown by a length B1), a large
 inner diameter portion 62 (a range shown by a length B2), a first enlarged
 diameter portion 63 (a range shown by a length B3), and a second enlarged
 diameter portion 64 (a range shown by a length B4). Also, a predetermined
 taper portion is formed at each boundary portion of the small inner
 diameter portion 61, large inner diameter portion 62, first enlarged
 diameter portion 63 and second enlarged diameter portion 64, which are
 adjacent to each other.
 Further, the hydraulic shock absorber 10 has a small diameter force-fit
 portion 71 formed in a manner that the small inner diameter portion 61 on
 the proximal end side of the cap 44 is fixedly forced into the small outer
 diameter portion 51 of the damper tube 11, a non-force fit portion 72
 which is a part of the large inner diameter portion 62 of the cap 44 and
 is a portion corresponding to the small outer diameter portion 51 of the
 damper tube 11, and a large diameter force-fit portion 73 formed in a
 manner that the other part of the large inner diameter portion 62 of the
 cap 44 is fixedly forced into the large outer diameter portion 52 of the
 damper tube 11.
 Furthermore, the hydraulic shock absorber 10 has a spring seat mounting
 portion 74 formed in a manner that the first enlarged diameter portion 63
 on the proximal end portion counter to the large diameter force-fit
 portion 73 of the cap 44 is enlarged more than the large outer diameter
 portion 52 of the damper tube 11. The spring seat 14 is fixedly forced
 into a periphery on the distal end of the spring seat mounting portion 74.
 Also, in the cap 44, the second enlarged diameter portion 64 extending
 from the first enlarged diameter portion 63 functions as a seat retainer
 portion 75 which is additionally included in the spring seat mounting
 portion 74.
 Moreover, the proximal end surface of the cap 44 is formed with an air vent
 hole 44A when the rubber bumper 43 is abutted against the abutting plate
 45 (see FIG. 5A and FIG. 5B).
 The hydraulic shock absorber 10 obtains a sub-assembled state such that the
 spring seat 14 is fixedly forced into the spring seat mounting portion 74
 so as to prevent it from coming off from the seat retainer portion 75 of
 the cap 44. Thereafter, the cap 44 is forced from the small outer diameter
 portion 51 around the shaft seal part 33 of the damper tube 11 toward the
 large outer diameter portion 52 so that the small diameter force-fit
 portion 71 of the cap 44 is fixed onto the small outer diameter portion 51
 of the damper tube 11 and the outer diameter force-fit portion 73 of the
 cap 44 is fixed onto the large outer diameter portion 52 of the damper
 tube 11. At this time, the outer diameter force-fit portion 73 of the cap
 44 is loosely inserted without resistance until the distal end portion of
 the large inner diameter portion 62 passes through the small outer
 diameter portion 51 having a length A1 of the damper tube 11. Thereafter,
 the outer diameter force-fit portion 73 of the cap 44 is scarcely started
 to be forced before reaching the large outer diameter portion 52 of the
 damper tube 11, so that the force-fit margin can be shortened. Further, a
 forced range of the cap 44 with respect to the damper tube 11, that is,
 the total length (B1+B2) of the small inner diameter portion 61 and the
 large inner diameter portion 62 is set longer in order to stably support
 the long suspension spring 13 without causing misalignment. In such a
 case, the force-fit margin in the small diameter force-fit portion 71 and
 the large diameter force-fit portion 73 of the cap 44 can be also
 shortened because the non-force fit portion 72 exists.
 Therefore, the following effects (operations) are obtained according to
 this embodiment.
 (1) The cap 44, which is fixedly forced around the shaft seal part 33 of
 the damper tube 11, is provided with the spring seat mounting portion 74,
 and the spring seat 14 is provided on the distal end side separated from
 the shaft seal part 33 of the damper tube 11 in the axial direction. In
 this case, the small diameter force-fit portion 71 on the proximal end
 side of the cap 44 is fixedly forced into the small outer diameter portion
 51 of the damper tube 11 while the large diameter force-fit portion 73 on
 the distal end side of the cap 44 is fixedly forced into the large outer
 diameter portion 52 of the damper tube 11. Therefore, in the case of
 providing the spring seat 14 on the distal end side of the cap 44, the
 large diameter force-fit portion 73 on the distal end side of the cap 44
 is fixedly forced into the damper tube 11, so that the spring seat 14 can
 be stably retained without misalignment. Further, the large diameter
 force-fit portion 73 on the distal end side of the cap 44 is loosely
 inserted into the small outer diameter portion 51 around the shaft seal
 part 33 of the damper tube 11, and then, is scarcely started to be forced
 before reaching the large outer diameter portion 52 thereof. Thus, the
 force-fit margin is short, and it is possible to readily force the cap
 into the damper tube.
 (2) The cap 44 has the non-force fit portion 72 between the small diameter
 force-fit portion 71 and the large diameter force-fit portion 73. The
 suspension spring 13 is long; and for this reason, the large diameter
 force-fit portion 73, where the spring seat mounting portion 74 of the cap
 44 is located, is fixedly forced at a position which is a relatively large
 distance from the shaft seal part 33 of the damper tube 11. In this case,
 therefore, a force-fit margin of the large diameter force-fit portion 73
 is further shortened by a length corresponding to the non-force fit
 portion 72, and is shortened more than the force-fit margin of the small
 diameter force-fit portion 71, and thus, it is possible to readily force
 the cap into the damper tube.
 (3) The spring seat mounting portion 74 of the cap 44 is enlarged in its
 diameter more than the outer diameter of the damper tube 11 so as not to
 contact the damper tube 11. Therefore, even if the inner diameter of the
 spring seat mounting portion 74 of the cap 44 is deformed by mounting the
 spring seat 14, the deformed portion of the spring seat mounting portion
 74 does not damage the damper tube 11, and there is no change
 (deformation) in the circular cross-sectional shape of the damper tube 11.
 Therefore, there would be no effect on the sliding motion of the piston 21
 and other pistons in the damper tube 11.
 (4) The spring seat mounting portion 74 of the cap 44 is additionally
 provided with the seat retainer portion 75 which is enlarged in its
 diameter more than the mounting inner diameter of the spring seat 14.
 Therefore, the spring seat 14 can be securely prevented from coming off
 from the spring seat mounting portion 74.
 In this embodiment, as shown in FIG. 6, the small diameter force-fit
 portion 71 and/or the large diameter force-fit portion 73 of the cap 44
 are/is provided with a plurality of protrusions 81 which extend in the
 axial direction along the circumferential direction of the inner diameter
 thereof. With the use of the protrusions 81, the cap 44 may be partially
 forced into the small outer diameter portion 51 and the large outer
 diameter portion 52 of the damper tube 11. The cap 44 is fixedly forced
 into the damper tube 11, not in surface contact but in point contact, so
 that a force-fit load can be reduced.
 As described above, the preferred embodiment of the present invention has
 been described with reference to the accompanying drawings. However,
 detailed construction of the present invention is not limited to the
 specific embodiment, and various changes and modifications are possible in
 design without departing from the sprit and scope of the present
 invention. For example, in the case of carrying out the present invention,
 the following modifications may be employed.
 (1) It is not essential that the cap should include the non-force fit
 portion between the small diameter force-fit portion and the large
 diameter force-fit portion.
 (2) Not only may the cap include two force-fit portions, that is, the small
 diameter force-fit portion and the large diameter force-fit portion with
 respect to the damper tube, but also the cap may include one or more
 intermediate diameter force-fit portions between the small diameter
 force-fit portion and the large diameter force-fit portion. In this case,
 the damper tube is provided with one or more intermediate outer diameter
 portions between the small outer diameter portion and the large outer
 diameter portion. At this time, the small diameter force-fit portion, one
 or more intermediate force-fit portions and the large diameter force-fit
 portion (the small outer diameter portion, the intermediate outer diameter
 portion and the large outer diameter portion) are successively enlarged in
 their force-fit diameter (outer diameter).
 (3) No limitation is set such that the spring seat is fixedly forced into
 the spring seat mounting portion of the cap, and the spring seat may be
 fixed thereto by other fixing means such as welding or the like. Further,
 the spring seat may be molded integrally with the cap.
 As is evident from the above description, according to the present
 invention, the cap, which is fixedly forced around the shaft seal part of
 the damper tube, is provided with the spring seat mounting portion, and
 the spring seat is provided on the distal end side separated from the
 shaft seal part of the damper tube in the axial direction. Therefore, the
 spring seat can be stably mounted onto the cap without misalignment, and
 it is possible to readily force the cap into the damper tube.
 While the preferred embodiments of the invention have been described in
 detail with reference to the drawings, they are by no means limitative,
 and various changes and modifications are possible without departing from
 the scope and spirit of the invention.
 Although the invention has been illustrated and described with respect to
 several exemplary embodiments thereof, it should be understood by those
 skilled in the art that the foregoing and various other changes, omissions
 and additions may be made to the present invention without departing from
 the spirit and scope thereof. Therefore, the present invention should not
 be understood as limited to the specific embodiment set out above but
 should be understood to include all possible embodiments which can be
 embodied within a scope encompassed by this description and equivalents
 thereof with respect to the features set out in the appended claims.