Shock absorber with damping valve structure having wide range variable damping characteristics

A variable damping characteristics shock absorber includes a piston provided with first and second disc valves. Within a piston, an annular space is defined between the first and second disc valves. The annular space is selectively communicated with upper and lower fluid chambers defined in a shock absorber cylinder tube via a by-pass path. A variable orifice formed by means of a rotary valve is provided in the by-pass path.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a shock absorber having variable 
damping characteristics. More specifically, the invention relates to a 
variable damping characteristics valve assembly, which is suitable for use 
in an automotive suspension system. 
2. Description of the Background Art 
Japanese Patent First (unexamined) Publication (Tokkai) Showa 58-81243 
discloses a shock absorber laving two way damping characteristics for both 
piston bounding and rebounding strokes. In order to provide variable 
damping characteristics for both in piston bounding and rebounding 
strokes, a first piston has a first bounding and rebounding damping valve, 
and a second piston has a second bounding and rebounding damping valve. 
The first and second pistons are arranged in tandem fashion. An 
intermediate chamber is defined between the first and second pistons. The 
intermediate chamber is selectively connected to upper and lower fluid 
chambers of the shock absorber via a switching valve. By switching a fluid 
connection between the intermediate chamber and one of the upper and lower 
fluid chambers only one of the first and second bounding and rebounding 
values in one of the first and second pistons is active for generating 
damping force. 
With the shown construction, since the intermediate chamber is common for 
both piston bounding and rebounding strokes, it is not possible to control 
damping characteristics for the piston bounding stroke and the piston 
rebounding stroke independent of each other. Furthermore, in the shown 
construction, since first and second pistons are required, the number of 
parts is unnecessarily great, causing higher cost and requiring complex 
assembling operation, which causes inefficiency in manufacturing. In 
addition, due to the presence of the first and second damping valves in 
the first and second damping pistons, the overall length of the shock 
absorber becomes excessive. 
On the other hand, Japanese Patent First (unexamined) Publication (Tokkai) 
Showa 58-116213 discloses a variable damping characteristics shock 
absorber. The shown shock absorber is provided with a damping valve for a 
piston bounding or compression stroke, which damping valve will be 
hereafter referred to as the "bounding stroke damping valve" and a damping 
valve for piston rebounding or expansion stroke, which will be hereafter 
referred to as "rebounding stroke damping valve. One or more fluid 
passages are provided in parallel to the aforementioned damping valves. A 
non-return valve is disposed in the fluid path for permitting fluid flow 
only in the piston bounding stroke. A by-pass passage is formed by-passing 
the non-return valve. A variable orifice is provided in the by-passing 
passage for restricting the fluid flow rate through the by-pass passage. 
The variable orifice is formed by means of a rotary valve. The rotary 
valve is rigidly coupled with a control rod which can be rotatingly driven 
for adjusting the damping characteristics. 
With the construction set forth above, the working fluid in a lower fluid 
chamber of the shock absorber flows through bounding stroke damping valve, 
through the variable orifice and through the non-return valve during the 
piston bounding or compression stroke. In each of the working fluid flow 
routes set forth above, a restriction for the fluid flow is provided for 
generating damping force. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a variable 
damping characteristics hydraulic shock absorber which can solve the 
drawback in the prior proposed variable damping characteristics shock 
absorber. 
Another object of the invention is to provide a variable damping 
characteristics shock absorber which can provide a wide range variation of 
damping characteristics, which range is much wider than that in the prior 
proposed shock absorbers. 
A further object of the present invention is to permit the variable damping 
characteristics shock absorber to adjust the damping characteristics 
independently of respective piston stroke direction. 
In order to accomplish the aforementioned and other objects, a variable 
damping characteristics shock absorber, according to the present 
invention, includes a piston provided with first and second disc valves. 
Within a piston, an annular fluid space is defined between the first and 
second disc valves. The annular fluid space is selectively communicated 
with upper and lower fluid chambers defined in a shock absorber cylinder 
tube via by-pass path. A variable orifice formed by means of a rotary 
valve is provided in the by-pass path. 
According to one aspect of the invention, a damping valve assembly for a 
hydraulic shock absorber having a hollow cylinder, a piston rod, a piston 
fixed to the piston rod for movement therewith and disposed within the 
internal space of the cylinder for dividing the internal space into first 
and second fluid chambers respectively filled with a working fluid, and a 
communication path defined through the piston for establishing fluid 
communication between the first and second fluid chambers, the damping 
valve assembly comprises: 
the communication path including a first passage component and second, 
passage component cooperative with the first passage component for 
permitting fluid flow from the first fluid chamber to the second fluid 
chamber during a piston stroke compressing the first chamber; 
first flow restriction means responsive to fluid pressure in the first 
passage component, for adjusting a first path area at one end of the first 
passage component; 
second flow restriction means adjusting fluid flow through the second 
passage component, the second flow restriction means including a variable 
orifice means for adjusting a fluid flow rate through the second passage 
component, the variable orifice means being variable of flow path at least 
between a first fully closed position and a second flow restricting 
position for permitting fluid flow in a limited flow rate. 
The second flow restriction means may further include a resilient valve 
member responsive to the fluid pressure in the second passage component 
for adjusting the second path area at one end of the second passage 
component. The second passage component may include a third passage 
component of the communication path for by-passing the resilient valve 
member for establishing direct connection between upstream of the 
resilient valve member and the second fluid chamber for permitting fluid 
flow therethrough and the variable orifice means is provided in the third 
passage component. The first flow restriction means comprises a resilient 
valve member. 
The first and second passage components may be arranged in series, and the 
resilient valve members of the first and second flow restriction means 
define an annular space therebetween, and the third passage component 
connects the annular space to the second chamber by-passing the resilient 
valve member of the second flow restriction means. The by-pass passage may 
have a portion extending through the piston rod. The variable orifice 
comprises a stationary passage component forming a part of the by-pass 
passage and a movable passage component which is movable between a first 
position in alignment with the stationary passage component and a second 
position offset from the stationary passage component. The movable 
component comprises an opening formed through a rotary valve which by 
rotating varies the angular position of the opening between the first and 
second positions. 
The rotary valve may define a first movable passage component and a second 
movable passage component defining a path area smaller than that of the 
first movable passage component, the rotary valve being driven at a first 
angular position where both of the first and second movable passage 
components are out of alignment with the stationary component for 
completely blocking fluid flow through the by-pass path, a second angular 
position where the first movable passage component is aligned with the 
stationary component for minimum flow restriction, and a third angular 
position where the second movable passage component is aligned with the 
stationary component for flow restriction at greater magnitude than that 
at the second angular position. 
In the alternative, the variable orifice may comprise a stationary passage 
component forming a part of the by-pass passage and a movable passage 
component which is movable between a first position in alignment with the 
stationary passage component and a second position placed offset from the 
stationary passage component. The first disc valve is placed in opposition 
to one end of the communication path for openably closing the associated 
end, a spacer ring is disposed between the first and second disc valves 
for defining therebetween the annular space, the spacer ring defines the 
stationary passage component therethrough, and the movable passage 
component is defined through a movable member disposed within the piston 
rod for selectively establishing and blocking fluid communication between 
the annular space and the portion extending through the piston rod. 
The second disc valve operably closes the annular space for selectively 
establishing fluid communication between the first chamber and the annular 
space. The first and second passage components are essentially parallel to 
each other. 
According to another aspect of the invention, a damping valve assembly for 
a hydraulic shock absorber having a hollow cylinder, a piston rod, a 
piston fixed to the piston rod for movement therewith and disposed within 
the internal space of the cylinder for dividing the internal space into 
first and second fluid chambers respectively filled with a working fluid, 
and a communication path defined through the piston for establishing fluid 
communication between the first and second fluid chambers, comprises: 
first and second disk valves disposed within the communication path in 
tandem fashion; 
an annular space defined between the first and second disc valves; 
a by-pass passage defined for by-passing the first disc valve for 
establishing direct communication between the first fluid chamber and the 
annular space; and 
a variable orifice provided within the by-pass passage for adjusting fluid 
flow rate through the by-pass passage. 
According to a further aspect of the invention, a piston assembly for a 
hydraulic shock absorber having a hollow cylinder, a piston rod to which 
the piston is fixed for movement therewith, the piston being disposed 
within the internal space of the cylinder for dividing the internal space 
into first and second fluid chambers respectively filled with a working 
fluid, and defining fluid communication between the first and second fluid 
chambers, comprises: 
a first fluid path means for permitting fluid flow from the first chamber 
to the second chamber during a piston stroke compressing the first 
chamber; 
a first flow restricting means associated with one end of the first fluid 
path for resiliently closing the one end, the first flow restricting means 
being responsive to a fluid pressure in the first fluid path overcoming 
the resilient force thereof for forming a first flow restricting path for 
permitting a limited magnitude of fluid flow therethrough from the first 
chamber to the second chamber; 
a second fluid path means for permitting fluid flow from the first chamber 
to the second chamber during the piston stroke compressing the first 
chamber; 
a second flow restricting means associated with the second fluid path for 
varying the path area thereof for causing flow restriction, the second 
flow restriction means being operable at least between a first position 
for completely blocking fluid communication from the second fluid passage 
means and a second position for permitting fluid flow through the second 
fluid passage in a controlled magnitude of flow rate.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, particularly to FIG. 1, the first embodiment 
of a variable damping characteristics shock absorber, according to the 
present invention, defines an internal space filled with a working fluid 
within a cylinder tube 1. A piston 2 is disposed within the internal space 
of the cylinder tube 1 and separates the internal space into upper and 
lower fluid chambers 1a and 1b. The piston 2 is connected to the lower end 
of a piston rod 3. The piston rod 3 extends through the cylinder tube 1 
and connects to a vehicular body at its upper end. On the other hand, the 
cylinder tube 1 is connected to a suspension member which rotatably 
supports a road wheel. 
The piston 2 defines a first communication path 2a and a second 
communication path 2b. These communication paths 2a and 2b are arranged in 
parallel to each other. The first communication path 2a has a lower end 
exposed to the lower fluid chamber 1b and opening in the vicinity of the 
circumferential edge portion of the piston 2. The upper end of the path 2a 
opens to an annular groove 2c formed on the upper surface of the piston 2. 
The annular groove 2c extends in parallel to an annular groove 2e and is 
separated therefrom by an annular land 2d. On the other hand, the second 
communication path 2b has an upper end exposed to the upper fluid chamber 
1a in the vicinity of the upper circumferential edge portion of the piston 
2. The lower end of the path 2b is communicated with an annular groove 2f 
formed on the lower surface of the piston. The annular groove 2f is formed 
in parallel relationship with an annular groove 2h separated therefrom by 
an annular land 2g. 
Opposing the upper surface of the piston 2, a bounding stroke damping valve 
assembly including a first bounding stroke damping valve 41 and a second 
bounding stroke damping valve 42 is provided. Similarly, opposing the 
lower surface of the piston 2, a rebounding stroke damping valve assembly 
including a first rebounding stroke damping valve 71 and a second 
rebounding stroke damping valve 72 is provided. The damping valves 41, 42 
and 71, 72 are fixedly mounted on the piston rod 3 together with the 
piston 2, by means of a fastening nut 9. 
Both of the first and second bounding stroke damping valves 41 and 42 are 
provided for establishing fluid communication between the first 
communication path 2a and the upper fluid chamber 1a. Specifically, the 
first bounding stroke damping valve 41 is seated on a valve seat surface 
2j for closing the upper end of the annular groove 2c. As seen from FIG. 
1, the second bounding stroke damping valve 42 is provided in spaced apart 
relationship to the first bounding stroke damping valve 41 via a spacer 
ring 5. The second bounding stroke damping valve 42 is seated on a seat 
surface 2k formed on the outer circumferential land. Between the first and 
second bounding stroke damping valves 41 and 42, a bounding stroke annular 
space 6 is defined. 
In a manner similar to the bounding stroke damping valves 41 and 42, the 
rebounding stroke damping valves 71 and 72 are respectively seated on seat 
surfaces 2m and 2n. An annular spacer ring is disposed between the 
rebounding stroke damping valves 71 and 72 for defining a rebounding 
stroke annular space 8 between the rebounding stroke damping valves. 
In order to communicate the upper fluid chamber 1a with the bounding stroke 
annular space 6, a bounding stroke bypass passage 10 is defined. The 
bounding stroke bypass passage 10 comprises a radial path 5a defined in 
the spacer ring 5, an axial, bore 3a defined in the piston rod 3 
communicated with the radial path via a radial opening 3b formed through 
the piston rod wall, and a radial opening 3c opening the outer end thereof 
to the upper fluid chamber 1a. 
In a manner similar to the above, a rebounding stroke bypass passage 11 is 
defined for establishing, fluid communication between the rebounding 
stroke annular space 8 and the lower fluid chamber 1b. The rebounding 
stroke bypass passage 11 comprises a radial path 7a defined through the 
spacer ring 7, the axial bore 3a, and a radial opening 3d. 
An essentially cylindrical rotary valve 12 is disposed within the axial 
bore 3a for rotation therein. The rotary valve 12 defines a hollow space 
therein which is separated into an upper section and a lower section by a 
partition 12a. The upper section serves as a damping characteristics 
switching valve for the piston bounding stroke, and the lower section 
serves as a damping characteristics switch valve for the piston rebounding 
stroke. A bounding stroke SOFT mode orifice 12d and a bounding stroke 
MEDIUM mode orifice 12e are formed through circumferentially offset 
portions to each other in the upper section of the rotary valve 12. As 
will be appreciated, the bounding stroke SOFT mode orifice 12d defines a 
greater path area than the bounding stroke MEDIUM mode orifice 12e, as 
shown in FIGS. 2 through 4. The fluid flow path area of the bounding 
stroke MEDIUM mode orifice 12e is so determined as to provide smaller flow 
restriction than is provided by the second bounding stroke damping valve 
42 so that the damping force to be created in the orifice 12 is to be 
smaller than that of the second bounding stroke damping valve. 
Similarly to the above, rebounding stroke SOFT mode orifice 12f and 
rebounding stroke MEDIUM mode orifice 12g are formed through 
circumferentially offset portions to each other in the lower section of 
the rotary valve 12. As will be appreciated, the rebounding stroke SOFT 
mode orifice 12f defines a greater path area than the rebounding stroke 
MEDIUM mode orifice 12g, as shown in FIGS. 5 through 7. The fluid flow 
path area of the rebounding stroke MEDIUM mode orifice 12f is so 
determined as to provide smaller flow restriction than is provided by the 
second rebounding stroke damping valve 72 so that the damping force to be 
created in the orifice 12 is to be smaller than that of the second 
rebounding stroke damping valve. 
The rotary valve 12 is rigidly fixed to the lower end of the rotary shaft 
13 which is rotatingly driven by means of a driving actuator 14 which may 
comprise an electric motor. The driving actuator 14 is electrically 
connected to a mode selector switch 16 which is manually operable for 
selecting the damping mode of the shock absorber. As is shown, the mode 
selector switch 16 in the shown embodiment can be operated between three 
mode positions, i.e. HARD mode position, MEDIUM mode position and SOFT 
mode position. The mode selector switch 16 generates a mode selector 
command for driving the actuator 14 to place the rotary valve 12 at a 
predetermined angular position corresponding to one of the selected 
damping modes specifically, when the HARD mode is selected, the rotary 
valve 12 is placed at an angular position where all of the orifices 12d, 
12e and 12f and 12g are out of communication with the radial openings 3c 
and 3d of the piston rod, as shown in FIGS. 4 and 7. Therefore, at %his 
rotary valve position, fluid communication through each of the bounding 
and rebounding stroke bypass passages 10 and 11 is blocked. At this time, 
the working fluid in the annular spaces 6 and 8 flows only through the 
corresponding one of the second bounding stroke damping valve 42 and the 
second rebounding stroke damping valve 72. As a result, the path area for 
the working fluid to flow between the upper and lower fluid chambers 
becomes minimum for generating the greatest damping force. 
When the rotary valve 12 is in the HARD mode position, the working fluid in 
the lower fluid chamber 1b flows through the first communication path 2a, 
the annular groove 2c, a flow restricting gap formed between the 
circumferential edge of the first bounding stroke damping valve 41 and the 
seat surface 2j, the bounding stroke annular space 6 and the flow 
restricting gap formed between the circumferential edge of the second 
bounding stroke damping valve 42 and the seat surface 2k, during piston 
bounding stroke. On the other hand, the working fluid in the upper fluid 
chamber 1a flows into the lower fluid chamber 1b via the second 
communication path groove 2b, the annular groove 2f, the flow restricting 
gap formed between the circumferential edge of the first rebounding stroke 
damping valve 71 and the seat surface 2m, the rebounding stroke annular 
space 8, and the flow restricting gap formed between the circumferential 
edge of the second rebounding stroke damping valve 72 and the seat surface 
2n during piston rebounding stroke. 
When the SOFT mode is commanded through the mode selector switch 16, the 
rotary valve 12 is driven to rotate to the angular position for aligning 
the bounding and rebounding stroke SOFT mode orifices 12d and 12f with the 
radial openings 3b and 3d, as shown in FIGS. 2 and 5. Then, the flow path 
for the working fluid flowing between the upper and lower fluid chamber 
via one of the communication paths 10 and 11 becomes maximum for minimum 
fluid flow resistance. At the same time, since corresponding bounding and 
rebounding annular spaces 6 and 8 communicate with the upper and lower 
fluid chambers 1a and 1b via the stroke damping valves 42 and 41, the 
overall fluid flow path area defined by placing the rotary valve at the 
SOFT mode position becomes maximum for the smallest damping force to be 
produced. 
When the rotary valve 12 is in the SOFT mode position, the working fluid in 
the lower fluid chamber 1b flows into the upper fluid chamber 1a through 
two routes during the piston bounding stroke. One route extends through 
the first communication path 2a, the annular groove 2c, a flow restricting 
gap formed between the circumferential edge of the first bounding stroke 
damping valve 41 and the seat surface 2j, the bounding stroke annular 
space 6 and the flow restricting gap formed between the circumferential 
edge of the second bounding stroke damping valve 42 and the seat surface 
2k, during piston bounding stroke. The other route is established through 
the bounding stroke communication path 10 extending from the bounding 
stroke annular space 6 and the upper fluid chamber 1a via the bounding 
stroke SOFT mode orifice 12d. On the other hand, the working fluid in the 
upper fluid chamber 1a flows into the lower fluid chamber 1b through two 
routes during the piston rebounding stroke. One route is established 
through the second communication path 2b, the annular groove 2f, the flow 
restricting gap formed between the circumferential edge of the first 
rebounding stroke damping valve 71 and the seat surface 2m, the rebounding 
stroke annular space 8, and the flow restricting gap formed between the 
circumferential edge of the second rebounding stroke damping valve 72 and 
the seat surface 2n. The other route is established through the rebounding 
stroke bypass passage 11 via the rebounding mode SOFT stroke orifice 12f. 
Similarly, when the MEDIUM mode is commanded through the mode selector 
switch 16, the rotary valve 12 is driven to rotate to the angular position 
for aligning the bounding and rebounding stroke MEDIUM mode orifices 12E 
and 12G with the radial openings 3b and 3d, as shown in FIGS. 3 and 6. 
Then, the flow path for the working fluid flowing between the upper and 
lower fluid chamber via one of the communication paths 10 and 11 becomes 
smaller than that in the SOFT mode for greater fluid flow resistance. At 
the same time, since corresponding bounding and rebounding annular spaces 
6 and 8 communicate with the upper and lower fluid chambers 1a and 1b via 
the stroke damping valves 42 and 72, the overall fluid flow path are 
defined by placing the rotary valve at the MEDIUM mode position becomes 
smaller than that in the SOFT mode for the medium damping force to be 
produced. In this mode, the secondary routes discussed with respect to the 
SOFT mode fluid flow are established via the bounding and rebounding 
stroke MEDIUM mode orifices 12e and 12g in place of the orifices 12d and 
12f. 
It should be appreciated that, though the shown embodiment is directed to 
manual selection of the damping characteristics of the shock absorber 
through the manually operable mode selector switch, it may be possible to 
command the damping mode in automatic manner depending upon vehicle 
driving conditions, such as vehicular speed, vehicular acceleration and 
deceleration magnitude, lateral force to be exerted on the vehicle, 
rolling magnitude and so forth. 
FIG. 8 shows a second embodiment of the variable damping characteristics 
shock absorber according to the present invention. The shown embodiment is 
different from the former embodiment in the construction of the piston 
assembly and the fluid path. In the shown embodiment, the piston assembly 
includes first and second piston bodies 109 and 112 provided in axial 
alignment with each other and mounted on the lower end of the piston rod 3 
via a stud 104 engaging with a fastening nut 105 which is rigidly fixed to 
the lower end of the piston rod 3. The first piston body 109 is formed 
with an annular groove 109b on the upper surface thereof. The annular 
space 109b is closed by a second bounding stroke damping disc valve 108 
mounted with a ring washer 107 and a retainer disc 106. The outer end of a 
radially extending bounding stroke bypass passage 109a opens to the 
annular groove 109b. The inner end of the radially extending opening 109a 
opens to an annular chamber 109c defined by the inner circumference of the 
first piston body 109 and the central portion of the damping disc valve 
108. The annular chamber 109c is communicated with an axially extending 
bore 104a defined in the stud 104 via a radial path 104b and an upper 
radial opening 120a formed through a rotary valve body 120. 
On the other hand, the second piston body 112 is formed with a bounding 
stroke communication path 112a, a rebounding stroke first communication 
path 112b and a rebounding stroke second communication path opening 112c. 
The lower end of the bounding stroke communication path opening 112a is 
exposed to the lower fluid chamber 1b. On the other hand, the upper end of 
the bounding stroke communication path 112a is opened to a groove 112f 
formed on the upper surface of the second piston body 112, which annular 
groove 112f is closed by a first bounding stroke damping disc valve 111 
and thus in fluid communication with the upper fluid chamber 1a as this 
valve 111 opens. On the other hand, the rebounding stroke first 
communication path 112b has an upper end opening to a radially extending 
cut-out 112f, and a lower end opening to an inner annular groove 112g. A 
rebounding stroke bypass passage 112c opens to an annular chamber 119 
defined between the inner circumference of the piston body 112 and the 
outer periphery of the stud 104 at the upper end, which annular chamber 
119 is in fluid communication with the axial bore 104a via a radial path 
104c and the lower radial opening 120b, and to the outer annular groove 
118 at the lower end thereof. The inner annular groove 112g is closed by a 
first rebounding stroke damping disc valve 113. The outer annular space 
118 is closed by a second damping disc valve 115. A spacer ring 114 is 
positioned between the first damping disc valve 113 and the second damping 
disc valve 115. 
A first passage component includes the bounding stroke communication path 
112a extending from the lower fluid chamber 1b to the groove 112f. A 
second passage component has two branches, a first branch from the annular 
space 118, past the disc valve 115 to the lower fluid chamber 1b, and a 
second branch from the annular space 118 through the bounding stroke 
bypass passage 112c, the radial path 104c the orifice 120b and the axial 
bore 104a. The second branch of the second passage component comprises a 
third passage component, which defines a bypass passage bypassing the disk 
valve 115. 
With the shown construction, the working fluid in the lower fluid chamber 
1b flows into the upper fluid chamber 1a through two routes C.sub.1 and 
C.sub.2 during the piston bounding stroke. On the other hand, the working 
fluid in the upper fluid chamber 1a flows into the lower fluid chamber 
through two routes D.sub.1 and D.sub.2 during the piston rebounding 
stroke. 
FIG. 9 explanatorily shows the routes D.sub.1 and D.sub.2 for permitting 
fluid flow from the upper fluid chamber 1a to the lower fluid chamber 1b 
in the piston rebounding stroke. As can be seen from FIG. 9, the second 
route D.sub.2 in the rebounding stroke is established through the 
rebounding stroke communication path 112b, the annular groove 112g, the 
gap formed between the first rebounding stroke damping disc valve 113 and 
a seat surface 112d, the annular space 118, the rebounding stroke bypass 
passage 112c, the annular chamber 119, the radial path 104c, the radial 
orifice 120b and the axial base 104a. The first route D.sub.1 is 
established by a gap formed between the second rebounding stroke damping 
disc valve 115 and the seat surface 112e, which gap establishes fluid 
communication between the annular groove 118 and the lower fluid chamber 
1b. On the other hand, FIG. 10 explanatorily shows the routes C.sub.1 and 
C.sub.2 for permitting fluid flow from the lower fluid chamber 1 b to the 
upper fluid chamber 1a in the piston bounding stroke. As can be seen from 
FIG. 10, the first route C.sub.1 in the bounding stroke is established 
through the bounding stroke communication path 112a, the groove 112f and a 
gap formed between the first bounding stroke damping disc valve 111. The 
second route C.sub.2 is established through the axial bore 104a, the lower 
radial orifice 120a, the radial path 104b, the radially extending 
rebounding stroke bypass passage 109a, a gap formed between the 
circumferential edge of the second bounding stroke damping disc valve 108 
and the seat surface of the first piston body 109. 
Here, the second bounding stroke damping disc valve 108 has a small 
stiffness for providing low damping characteristics. Similarly, first 
rebounding stroke damping disc valve 113 has a smaller stiffness than the 
second rebounding stroke damping disc valve 115. Though it is not clearly 
shown in the drawings, the rotary valve 120 is provided with a plurality, 
of radial orifices having mutually different path areas to be selectively 
aligned so that the path area for the fluid flow can be varied for 
providing variable damping characteristics. The rotary valve 120 may also 
be placed at an angular position for completely blocking fluid flow. In 
such case, the second routes D.sub.2 and C.sub.2 are shut down in 
rebounding and bounding stroke. Therefore, the harder damping 
characteristics can be obtained by permitting the fluid flow only through 
the first routes D.sub.1 and C.sub.1 in the rebounding and bounding 
strokes, respectively, of the piston. Therefore, even when the rotary 
valve 120 is provided with only one sets of radial orifices 120a and 120b, 
respective two way damping characteristics in the bounding and rebounding 
strokes can be obtained as shown by lines (a) through (d) in FIG. 11. The 
characteristics in FIG. 11 shows substantial improvement achieved in 
comparison with that in the prior art as shown in lines (1) through (4) of 
FIG. 12. 
FIG. 13 shows a third embodiment of the variable damping force shock 
absorber according to the present invention. This embodiment is derived 
from modification of the foregoing second embodiment. In this embodiment, 
a smaller diameter extension 140 is provided in place of the stud 104 in 
the second embodiment. This clearly reduces parts for forming the shock 
absorber and thus reduces production steps and costs Furthermore, 
according to the shown embodiment, the radial extending path 109a and the 
communication path opening 112c are replaced with grooves 109b' and 112c' 
formed on the surfaces of the first and second piston bodies 109 and 112. 
By this, production process can be simplified to be easily performed. 
As can be seen from FIG. 13, the shown embodiment is formed with the 
communication paths 112a and 112b in parallel to the axis of the piston 
rod. This makes machining or molding of the shaped piston easy. 
In addition, the shown embodiment is provided with a retainer 115a mating 
with the disc valve 115. The retainer 115a is biased upwardly to 
constantly urge the establishment of to steady and constant contact 
between the retainer and the disc valve 115 by means of a coil spring. 
While the present invention has been disclosed in terms of the preferred 
embodiments in order to facilitate better understanding of the invention, 
it should be appreciated that the invention can be embodied in various 
ways without departing from the principle of the invention. Therefore, the 
invention should be understood to include all possible embodiments and 
modifications to the shown embodiments which can be embodied without 
departing from the principle of the invention set out in the appended 
claims.