Hydraulic shock absorber with a rod guide having an annular doubled wall section

A hydraulic shock absorber is provided which includes generally a cylinder assembly to define working and reservoir chambers therewithin, a piston rod, a rod guide member which guides bounding and rebounding strokes of the piston rod, and an oil seal contacting with the piston rod to seal an opening of the cylinder assembly. The rod guide member includes outer and inner supporting sections. The inner supporting section also includes outer and inner wall sections which are coaxially arranged with a preselected interval therebetween. The outer wall section is spaced from an inner wall of the cylinder assembly to provide flexibility to the rod guide in cooperation with the inner wall section. The shock absorber further includes a reinforcement partly inserted into the oil seal to provide flexural rigidity to the outer supporting section of the rod guide and a communication path defined by a chambered surface formed on a peripheral surface of the reinforcement and a recessed portion formed in an edge portion of the first supporting section to fluidly connect the working and reservoir chambers.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates generally to a shock absorber for an 
automotive suspension system. More particularly, the invention relates to 
a hydraulic shock absorber which has an improved arrangement of a rod 
guide for guiding reciprocating motion of a piston rod. 
2. Background Art 
Japanese Utility Model First Publication No. 61-82141 discloses a hydraulic 
shock absorber which includes a rod guide having an opening in its center 
through which a piston rod is reciprocally displaced. A peripheral portion 
of the rod guide which retains the rod guide in a cylinder assembly of the 
shock absorber is provide with a thick wall having high rigidity. 
A rod guide for such a shock absorber is manufactured by powder molding, 
casting, or machining, resulting in increased weight and manufacturing 
costs. Additionally, the conventional rod guide has higher rigidity and 
thus when forces act on the piston rod from a lateral direction, pressure 
created at a contact point of the piston rod with the rod guide locally 
becomes great and causes friction between the members to be increased. 
This results in reduced durability. 
Japanese Utility Model First Publication No. 1-94639 discloses a 
double-cylindered hydraulic shock absorber. This shock absorber includes a 
rod guide which supports a piston rod so as to allow it to reciprocate. 
The rod guide has a liquid communication path for allowing liquid flow in 
a direction from the inner cylinder to the outer (reservoir) cylinder 
during a piston rebounding stroke. The liquid communication path is 
defined by cut-out portions in a supporting section of the rod guide, 
engaging with an inner wall of an outer cylinder, which is made of a metal 
plate. 
An edge of the outer cylinder is crimped so as to cover the supporting 
section of the rod guide to mount it in the outer cylinder such that a 
load caused by a bounding and/or rebounding motion of a vehicle body acts 
on the supporting section. The rigidity of the rod guide is insufficient 
against the load due to the cut-out portions for defining the 
communication path. Therefore, a technique for forming a liquid 
communication path hydraulically connecting between the inner cylinder and 
the reservoir chamber without reducing rigidity of the metallic supporting 
section of the rod guide has been sought by designers. 
SUMMARY OF THE INVENTION 
It is accordingly one object of the present invention to avoid the 
disadvantages of the prior art. 
It is another object of the invention to provide a light-weight shock 
absorber which is inexpensive to manufacture. 
It is a further object of the invention to provide a shock absorber which 
can unify pressure created on a contact area of a piston rod with a rod 
guide caused by exertion of lateral force on the piston rod to reduce 
local friction therebetween for improving durability. 
According to one aspect of the present invention, there is provided a shock 
absorber which comprises a cylinder assembly defining a working chamber in 
which a piston rod is disposed with a reservoir chamber, and a rod guide, 
provided in an opening of the cylinder assembly, guiding bounding and 
rebounding strokes of the piston rod, the rod guide including a first 
supporting section supporting the rod guide to the cylinder assembly and a 
second supporting section supporting the piston rod within the working 
chamber, the second supporting section including outer and inner wall 
sections, the outer wall section extending from the first supporting 
section, the inner wall section being spaced from the outer wall section 
to define a gap therebetween so as to provide a preselected degree of 
flexibility to the second supporting section. 
According to another aspect of the invention, there is provided a shock 
absorber which comprises a cylinder assembly having a circumferential edge 
portion at its end so as to define an opening, the cylinder assembly 
defining a working chamber in which a piston rod is disposed for bounding 
and rebounding strokes through the opening and a reservoir chamber, an oil 
seal disposed within the cylinder assembly to contact with the piston rod 
so as to seal the opening of the cylinder assembly, a rod guide plate 
member, provided in the cylinder assembly, guiding bounding and rebounding 
strokes of the piston rod, the rod guide including first and second 
supporting sections, the first supporting section supporting the oil seal 
and the second supporting section supporting the piston rod, and a 
reinforcement provided between the circumferential edge portion and the 
first supporting section of the rod guide to provide a preselected degree 
of rigidity to the first supporting section. 
According to a further aspect of the invention, there is provided a shock 
absorber which comprises a cylinder assembly having an opening at its end, 
the cylinder assembly including outer and inner cylinder sections to 
define a working chamber in the inner cylinder section filled with a 
hydraulic working fluid and a reservoir chamber between the outer and 
inner cylinder sections filled with the hydraulic working fluid and a 
pneumatic working fluid, a piston rod disposed within the inner cylinder 
section to reciprocate through the opening of the cylinder assembly, a rod 
guide member disposed within the cylinder assembly guiding bounding and 
rebounding strokes of the piston rod, the rod guide including first and 
second supporting sections, the first supporting section having a 
peripheral surface, engaging with an end portion of the cylinder assembly 
for supporting the rod guide, on which a chamfered surface is formed, the 
second supporting section supporting the piston rod, an oil seal 
contacting with the piston rod so as to seal the opening of the cylinder 
assembly, a supporting member engaging with the end portion of the 
cylinder assembly to support the oil seal, the supporting member having a 
groove in its edge portion which coincides with the chamfered surface of 
the first supporting section of the rod guide, and a communicating path 
defined by the chamfered surface of the rod guide and the groove of the 
supporting member to fluidly communicate between the working chamber and 
the reservoir chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings wherein like numbers refer to like parts in 
the several views, particularly to FIG. 1, a hydraulic shock absorber 
according to the present invention is shown. This shock absorber includes 
generally an inner cylinder 1, a piston 2, a rebound rubber 3, a piston 
rod 4, an outer cylinder 5, a bottom assembly 6, a rod guide 7, an upper 
working chamber A, a lower working chamber B, and a fluid reservoir 
chamber C. The reservoir chamber C is defined between the outer and inner 
cylinders 5 and 1 and filled with hydraulic fluid and pneumatic fluid. 
These arrangements are well known in the art and will not be described 
here in detail. 
Referring to FIG. 2, the rod guide 7 is shown. This rod guide is provided 
with a single square plate member pressed into a cylindrical member which 
includes an annular doubled section 74a and 74b folded inwardly to define 
a rod hole 71 through which the piston rod 4 slides. 
The rod guide 7 also includes an upper flange 72 which has a square 
configuration before pressing, as viewed from a plane. Each corner of the 
flange 72 contacts with an inner wall of the outer cylinder 5 so that a 
clearance is defined between the inner wall and a circumferential edge of 
the flange 72 to serve as a leaked oil path 72a. 
The rod guide 7 further includes a cylinder engaging section 73 below the 
flange 72. The cylinder engaging section 73 includes an annular wall 73a 
having a large diameter which tightly engages an inner wall of the 
cylinder 1 to support the rod guide thereto. 
A U-shaped rod supporting section 74 extending downwardly from the cylinder 
engaging section 73 or the annular wall 73a which is provided with an 
outer annular wall 74a smaller than the annular wall 73a in diameter, a 
supporting annular wall 74b for supporting the piston rod 4, and a bottom 
wall 74c connecting between the walls 74a and 74b. An annular chamber is 
defined between the outer annular wall 74a of the rod supporting section 
74 and the inner wall of the inner cylinder 1. 
A stopper 75 is provided below the bottom wall 74c which includes an outer 
wall 75a engaging with a circumferential surface of the outer annular wall 
74a so that a gap h is defined between the outer wall 75a and the inner 
wall of the inner cylinder 1. 
A guide bushing 9 is attached to an inner wall of the supporting annular 
wall 74b of the rod supporting section 74. A guide seal ring 8 is disposed 
below the guide bushing 9 to establish liquid-tight sealing between an 
inner periphery thereof and the piston rod 4 so as to restrict a liquid 
within the upper chamber A from leaking into a cavity 10 defined above the 
rod guide 7. The stopper 75 serves to prevent the guide seal ring 8 from 
being dislodged. 
An oil seal 11 is installed on an upper portion of the rod guide 7. This 
oil seal includes an annular reinforcement 11a which is attached to an 
inner surface of the outer cylinder 5 and a seal lip 11b which wraps an 
inside portion of the reinforcement 11a. The seal lip 11b has a check lip 
11c extending below the reinforcement 11a which engages with the flange 72 
of the rod guide 7 so as to establish a tight seal therebetween. The check 
lip 11c functions as a check valve to allow a liquid flowing into the 
cavity 10 from the upper chamber A through the guide bushing 9 to flow 
into the reservoir chamber C through the leaked oil path 72a, while 
preventing backflow. 
The flange 72 is stepped and includes an outer flat section 72b which is 
attached to an upper portion of the inner cylinder 1, an inner flat 
section 72c which contacts with the check lip 11c, and an intermediate 
wall 72d connecting therebetween. 
An upper end of the outer cylinder 5 is crimped so as to partly cover the 
oil seal 11 to provide internal residual stress to the oil seal 11 and the 
rod guide 7 for tightly fixing them. 
As previously mentioned, the rod guide 7 is formed with one square plate 
member by means of press bending, resulting in light weight and easy 
processing thus decreasing manufacturing costs. 
For assembling the rod guide 7, the cylinder engaging section 73 is first 
fitted on the inner peripheral surface of the inner cylinder 1 with the 
piston rod 4 being inserted into the rod hole 71. The outer flat section 
72b of the flange 72 is then engaged with the inner upper peripheral 
surface of the outer cylinder 5 and inner flat section 72c contacts with a 
top edge of the inner cylinder 1. 
The outer peripheral surface of the annular reinforcement 11a of the oil 
seal 11 is engaged with the inner surface of the outer cylinder 5 so as to 
be placed on the outer flat section 72b. 
Subsequently, the upper end portion of the outer cylinder 5 is crimped. 
This crimp provides thrusting force in an axial direction to the rod guide 
7 from the flange 72 through the oil seal 11 to transmit it to the 
cylinder engaging section 73. 
With this arrangement, suitable installation of the rod guide 7 is 
accomplished with engagement between the flange 72 and the outer cylinder 
5, between the engaging section 73 and the inner cylinder 1, and between 
the rod supporting section 74 and the piston rod 4. 
In operation, exertion of lateral force on the piston rod during sliding 
causes it to be inclined, as shown in FIG. 3, while locally pressing the 
rod supporting section 74 of the rod guide 7. This causes the rod 
supporting section 74 to be deformed according to the inclination of the 
piston rod 4 to reduce pressure locally acting on the piston rod 4 (as 
compared to without the inclination) due to a certain degree of flexural 
rigidity of the rod supporting section provided by the gap h between the 
annular wall 75a and the inner cylinder 1 and flexibility of the plate 
member forming the rod supporting section 74. 
It will be appreciated that friction created during piston sliding is 
reduced to achieve smooth displacement of the piston rod and improved 
durability. 
During rebounding stroke of the piston rod 4, compression of the rebound 
rubber 3 against the stopper 5 below the rod guide 7 absorbs the 
rebounding force. 
Referring to FIG. 4, an alternate embodiment of the present invention is 
shown. The same construction as the first embodiment will not be described 
here again. This embodiment is different from the first embodiment in the 
following points. 
A rod guide 7 is provided with a circular plate member to form an annular 
flange 72. All outer peripheral surfaces of the flange 72 are engaged with 
an outer cylinder 5. A leaked oil path 271 is formed in the flange 72 at a 
position outside a contact point with a check lip 11c. 
A rod supporting section 74 includes only a guide bushing 9 without a guide 
seal ring and a stopper as utilized in the first embodiment. A gap h is 
defined between an outer annular wall 74a of the rod supporting section 74 
and an inner periphery of an inner cylinder 1. 
Referring to FIG. 5, a third embodiment of the invention is shown which 
excludes a guide bushing, a guide seal ring, and a stopper so that a 
supporting annular wall 74b of a rod supporting section 74 directly 
contacts with a piston rod 4. A leaked oil path 271 is, similar to the 
second embodiment, provided above the rod guide 7. 
Referring to FIG. 6, a fourth embodiment of the invention is shown. This 
embodiment is substantially the same as the second embodiment, but differs 
in that a reinforcement 12 is interposed between an upper portion of an 
inner cylinder 1 and a flange 72 supporting a guide seal ring 11. The 
reinforcement 12 includes annular plates 12a and 12b of L-shaped cross 
section which engages with a lower surface of an inner flat plate 72c of 
the flange 72 and an outer peripheral surface of a wall 72d. An inner end 
portion of the annular plate 12a is inserted between a top end of a 
cylinder and the inner flat plate 72c of the flange 72. The wall 72d of 
the flange 72 is fitted into an inner surface of the annular plate 12b. 
Additionally, a leaked oil path 51 is defined with a cut-out portion 51a 
formed in an outer periphery of the outer flat plate 72b and a 
communication groove 51b formed in a lower outer periphery of the 
reinforcement 11a. 
In operation, exertion of compression force created by crimping of an upper 
end portion of an outer cylinder 5 or bounding force in an axial direction 
on the flange 72 through the reinforcement 11a of the oil seal 11 causes 
bending stress to be generated on the flange 72 with respect to a top edge 
of the inner cylinder 1 since positions where the axial forces act and the 
top edge of the inner cylinder 1 are shifted radially from each other. The 
flange 72 is deformed by the bending force since it is formed by pressing 
a single plate member to be enlarged resulting in weakened bending 
rigidity. It will be noted that internal residual stress created by the 
crimp of the outer cylinder 5 is reduced to reduce generation of noise 
during operation. 
However, in the embodiments of the invention, rigidity of the reinforcement 
is, as described above, added to the inner flat plate 72b of the flange 72 
and the wall 72d, reducing a bending stress acting on the flange 72. 
With the arrangements of the embodiments, deformation of the flange 72 can 
be prevented to maintain the internal residual stress exerted on the oil 
seal 11 and the rod guide 7 and thus prevent noise from being generated 
during operation. 
Referring to FIG. 7, a fifth embodiment of the invention is shown. This 
embodiment is similar to the fourth embodiment in that a reinforcement 12 
is interposed between a top edge of an inner cylinder 1 and a flange 72, 
but is different in the following respects. 
The length of a vertical wall 12b of the reinforcement 12 is greater or 
equal to that of a vertical wall 72d of the flange 72 to input an axial 
force directly to the reinforcement 12 through an annular reinforcement 
11a and an outer flat plate 72c of the flange 72, virtually preventing the 
bending force from acting on the flange 72. 
Shown in FIG. 8, is the arrangement of a flange 72 of a rod guide 7 and a 
ring reinforcement 11a of an oil seal 11 for defining the leaked oil path 
51 which was previously referred to in FIGS. 6 and 7. 
The flange 72 includes, as shown in FIG. 9, five chamfered surfaces 51a on 
an outer flat section 72c at given intervals. The ring reinforcement 11a 
includes, as shown in FIGS. 10 and 11, two recessed portions 51b at its 
peripheral portions which are diametrically opposed to each other and open 
to the outside. A combination of the chamfered surface 51a and the 
recessed portion 51b defines the leaked oil path 51 connecting between a 
reservoir chamber C and a chamber 10. 
When the oil seal 11 and the rod guide 7 are fitted into an outer cylinder 
5, at least one leaked oil path can be always formed without positioning 
the flange 72 and the ring reinforcement 11a in a circumferential 
direction since the five chamfered surfaces 51a are provided on the flange 
at regular intervals and the two recessed portions 51b are diametrically 
opposed to each other with respect the center of the ring reinforcement. 
The leaked oil path 51 is, as described above, is opened and closed by a 
check lip 11c. 
With the above arrangement, the leaked oil path 51 communicating between 
the reservoir chamber C and the chamber 10 in the inner cylinder 1 
provided with only the chamfered surfaces 51a of the rod guide 7 and the 
recessed portions 51b of the oil seal reinforcement 11a. Thus, the rod 
guide 7, especially the outer flat section 72b, can provide rigidity 
sufficient for receiving loads caused by bounding or rebounding motion of 
a vehicle body. 
While the present invention has been disclosed in terms of the preferred 
embodiment in order to facilitate better understanding thereof, it should 
be appreciated that the invention can be embodied in various ways without 
departing from the principle thereof. Therefore, the invention should be 
understood to include all possible embodiments and modifications to shown 
embodiments which can be embodied without departing from the principle of 
the invention as set out in the appended claims. 
For example, as shown in FIG. 12, four recessed portions 100 may be 
provided in the oil seal reinforcement 11a which are circumferentially 
spaced from each other by regular intervals. Alternatively, an even number 
of recessed portions more than four may be provided. For the rod guide 7, 
an uneven number of chamfered surfaces more than five may be formed. 
Additionally, the relative number of recessed portions to chamfered 
surfaces may be reversed.