U.S. patent application number 09/725759 was filed with the patent office on 2001-08-02 for damping force control type hydraulic shock absorber.
Invention is credited to Matsumoto, Takuya, Nezu, Takashi.
Application Number | 20010010279 09/725759 |
Document ID | / |
Family ID | 18339526 |
Filed Date | 2001-08-02 |
United States Patent
Application |
20010010279 |
Kind Code |
A1 |
Matsumoto, Takuya ; et
al. |
August 2, 2001 |
Damping force control type hydraulic shock absorber
Abstract
A damping force control type hydraulic shock absorber capable of
generating stable damping force even if the flow rate of hydraulic
fluid changes sharply. A slider is slidably fitted in a piston
bolt. Valve members are secured to both ends of the slider to form
extension and compression pressure control valves for controlling
the pressure of hydraulic fluid between upstream and downstream
ports provided in the piston bolt. Hydraulic fluid chambers at the
respective ends of the valve members are cut off from the
downstream ports of the extension and compression pressure control
valves by flange portions of the valve members. When the flow rate
of hydraulic fluid increases sharply, even if the pressure in the
downstream ports changes sharply owing to the flow resistance in
check valves on the downstream side of the downstream ports, the
pressure is not transmitted to the hydraulic fluid chambers.
Therefore, there is no possibility of the slider moving under the
influence of such a pressure change. Accordingly, stable damping
force can be obtained.
Inventors: |
Matsumoto, Takuya;
(Chiba-ken, JP) ; Nezu, Takashi; (Tokyo,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
Suite 800
2033 "K" Street, N.W.
Washington
DC
20006
US
|
Family ID: |
18339526 |
Appl. No.: |
09/725759 |
Filed: |
November 30, 2000 |
Current U.S.
Class: |
188/280 |
Current CPC
Class: |
F16F 9/46 20130101 |
Class at
Publication: |
188/280 |
International
Class: |
F16F 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 1999 |
JP |
340704/1999 |
Claims
What is claimed is:
1. A damping force control type hydraulic shock absorber
comprising: a cylinder having a hydraulic fluid sealed therein; a
piston slidably fitted in said cylinder; a piston rod connected at
one end thereof to said piston, the other end of said piston rod
extending to an outside of said cylinder; a hydraulic fluid passage
for passing the hydraulic fluid in response to sliding movement of
said piston; a damping force control valve for controlling damping
force by controlling flow of the hydraulic fluid through said
hydraulic fluid passage; and a mechanism for actuating said damping
force control valve, wherein said damping force control valve is a
variable pressure control valve comprising a cylindrical sleeve
having an upstream port and a downstream port in the side wall
thereof and a slider valve slidably received in the sleeve and
including a valve member which controls flow of the hydraulic fluid
between said upstream and down stream ports by the movement of said
slider valve, said valve member having an upstream end portion and
a downstream end portion, and wherein a hydraulic fluid chamber
formed on the side of said downstream end portion of said valve
member is cut off from said downstream port.
2. A damping force control type hydraulic shock absorber according
to claim 1, wherein said downstream end portion of said valve
member sealingly engages with an inner wall of said cylindrical
sleeve so that said hydraulic fluid chamber is cut off from said
downstream port.
3. A damping force control type hydraulic shock absorber according
to claim 1, further comprising a pilot operated type damping valve
disposed in said hydraulic fluid passage on the upstream side of
said upstream port of the sleeve and including a disk valve which
opens depending on the pressure of the hydraulic fluid applied
thereto to thereby generating a damping force and a pilot chamber
formed on the downstream side of said disk valve and communicating
with said upstream port.
4. A damping force control type hydraulic shock absorber
comprising: a cylinder having a hydraulic fluid sealed therein; a
piston slidably fitted in said cylinder; a piston rod connected at
one end thereof to said piston, the other end of said piston rod
extending to an outside of said cylinder; a hydraulic fluid passage
for passing the hydraulic fluid in response to sliding movement of
said piston; a damping force control valve for controlling damping
force by controlling flow of the hydraulic fluid through said
hydraulic fluid passage; and a mechanism for actuating said damping
force control valve, wherein said damping force control valve is a
variable pressure control valve comprising: a cylindrical sleeve
having extension side upstream and downstream ports and compression
side upstream and downstream ports in the side wall of the sleeve a
slider valve slidably received in the sleeve and including
extension and compression valve members each of which controls flow
of the hydraulic fluid between said upstream and downstream ports
by the movement of said slider valve, each of said valve members
having an upstream end portion and a downstream end portion, and
wherein a hydraulic fluid chamber formed on the side of said
downstream end portion of each said valve member is cut off from
said downstream port.
5. A damping force control type hydraulic shock absorber according
to claim 4, wherein said downstream end portions of said valve
members sealingly engage with an inner wall of said cylindrical
sleeve so that said hydraulic fluid chambers are cut off from said
downstream ports.
6. A damping force control type hydraulic shock absorber according
to claim 4, wherein said actuating mechanism includes a solenoid
device having an actuating rod which engages with one of said valve
members and a spring which engages the other of said valve members
for biasing the slider valve against said actuating rod.
7. A damping force control type hydraulic shock absorber according
to claim 6, wherein said hydraulic fluid chambers on the downstream
end portions of said valve members are communicated with each other
through a passage formed in said slider valve.
8. A damping force control type hydraulic shock absorber according
to claim 4, wherein said slider valve includes a cylindrical slider
body with said valve members being press fit into said slider
body.
9. A damping force control type hydraulic shock absorber according
to claim 6, wherein said valve members have elongated portions
extending so as to engage with each other.
10. A damping force control type hydraulic shock absorber according
to claim 4, further comprising extension side and compression side
pilot operated type damping valves, each damping valve being
disposed in said hydraulic fluid passage on the upstream side of
the associated upstream port of the sleeve and including a disk
valve which opens depending on the pressure of the hydraulic fluid
applied thereto to thereby generating a damping force and a pilot
chamber formed on the downstream side of said disk valve and
communicating with said upstream port.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to damping force control type
hydraulic shock absorbers attached to suspension systems of
automobiles or other vehicles. More particularly, the present
invention relates to a damping force control type hydraulic shock
absorber capable of appropriately controlling damping force in
accordance with the road surface conditions, vehicle running
conditions, etc. with a view to improving the ride quality and the
steering stability.
[0002] In general, a damping force control type hydraulic shock
absorber includes a cylinder having a hydraulic fluid sealed
therein. A piston connected with a piston rod is slidably fitted in
the cylinder. The hydraulic fluid is caused to flow through a
hydraulic fluid passage by sliding movement of the piston in the
cylinder. The flow of hydraulic fluid is controlled by a damping
force generating mechanism formed from orifices and disk valves to
generate damping force, and the damping force is controlled by
changing the flow path area with a damping force control valve.
[0003] The assignee disclosed a damping force control type
hydraulic shock absorber in the specification of Japanese Patent
Application No. Hei 11-121787. The disclosed damping force control
type hydraulic shock absorber has a variable pressure control valve
in which a slider valve is slidably fitted in a cylindrical sleeve,
and the flow of hydraulic fluid through ports provided in the side
wall of the sleeve is controlled in accordance with the position of
the slider valve, thereby controlling damping force.
[0004] More specifically, an enlarged-diameter portion is formed in
the inner wall of the sleeve. A disk valve body supported by the
slider valve is seated on a shoulder provided by the
enlarged-diameter portion. The plunger of a solenoid pushes the
slider valve in the direction for closing the variable pressure
control valve, that is, in a direction in which the disk valve body
is pressed against the shoulder. The pressure of hydraulic fluid
for opening the variable pressure control valve is determined from
the relationship between the magnitude of pressing force of the
plunger and the pressure of hydraulic fluid applied to the disk
valve body.
[0005] However, the damping force control type hydraulic shock
absorber disclosed in the above-described specification suffers
from the following problem. Because each end of the slider valve is
disposed in a hydraulic fluid chamber communicating with a
hydraulic fluid passage on the downstream side of the variable
pressure control valve, the change in the pressure in the hydraulic
fluid chambers influences the slider valve. When the flow rate of
hydraulic fluid flowing through the variable pressure control valve
increases sharply, the pressure in the downstream-side hydraulic
fluid chamber rises sharply. This causes imbalance between the
pressures in the hydraulic fluid chambers at the two ends of the
slider valve. As a result, the slider valve moves undesirably.
Accordingly, there is likelihood of damping force becoming
unstable.
SUMMARY OF THE INVENTION
[0006] The present invention was made in view of the
above-described circumstances. An object of the present invention
is to provide a damping force control type hydraulic shock absorber
capable of generating stable damping force even if the flow rate of
hydraulic fluid changes sharply.
[0007] To attain the above-described object, the present invention
provides a damping force control type hydraulic shock absorber
including a cylinder having a hydraulic fluid sealed therein. A
piston is slidably fitted in the cylinder. A piston rod is
connected at one end thereof to the piston. The other end of the
piston rod extends to the outside of the cylinder. A hydraulic
fluid passage passes the hydraulic fluid in response to sliding
movement of the piston. A damping force control valve controls
damping force by controlling the flow of hydraulic fluid through
the hydraulic fluid passage.
[0008] The damping force control valve is a variable pressure
control valve having a slider valve slidably fitted in an
approximately cylindrical sleeve to control the pressure of
hydraulic fluid between upstream and downstream ports provided in
the side wall of the sleeve by movement of the slider valve. A
hydraulic fluid chamber on the downstream end portion of the slider
valve in the sleeve is cut off from the downstream port.
[0009] With the above-described arrangement, the pressure of
hydraulic fluid between the ports in the sleeve does not act on the
hydraulic fluid chamber on the downstream end of the slider valve.
Therefore, there is no possibility of the slider valve being moved
by the pressure of hydraulic fluid between the ports in the
sleeve.
[0010] In the damping force control type hydraulic shock absorber
according to the present invention having the above-described
arrangement, the damping force control valve may be a pilot valve
of a pilot operated type damping valve that generates damping force
in accordance with sliding movement of the piston.
[0011] With the above-described arrangement, the pilot pressure
changes as a result of the control of the damping force control
valve, causing valve-opening characteristics of the pilot operated
type damping valve to change.
[0012] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description of the preferred embodiments thereof, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a vertical sectional view of an essential part of
a damping force control type hydraulic shock absorber according to
a first embodiment of the present invention.
[0014] FIG. 2 is an enlarged view showing a piston bolt and
associated members constituting a damping force control valve of
the damping force control type hydraulic shock absorber shown in
FIG. 1.
[0015] FIG. 3 is an enlarged view showing a piston bolt and
associated members constituting a damping force control valve of a
damping force control type hydraulic shock absorber according to a
second embodiment of the present invention.
[0016] FIG. 4 is an enlarged view showing a piston bolt and
associated members in a modification of the second embodiment shown
in FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Embodiments of the present invention will be described below
in detail with reference to the accompanying drawings.
[0018] A first embodiment will be described with reference to FIGS.
1 and 2. As shown in FIG. 1, a damping force control type hydraulic
shock absorber 1 according to the first embodiment includes a
cylinder 2 having a hydraulic fluid sealed therein. A piston 3 is
slidably fitted in the cylinder 2. The piston 3 divides the inside
of the cylinder 2 into two chambers, i.e. a cylinder upper chamber
2a and a cylinder lower chamber 2b. An approximately cylindrical
piston bolt 4 (sleeve) is inserted into the piston 3 and secured by
using a nut 5. The piston bolt 4 has a large-diameter portion 4a at
the proximal end thereof. A solenoid casing 7 connected to one end
portion of a hollow piston rod 6 is screwed onto the large-diameter
portion 4a of the piston bolt 4. The other end portion of the
piston rod 6 extends through the cylinder upper chamber 2a and
further through a rod guide (not shown) and an oil seal (not
shown), which are fitted to the upper end portion of the cylinder
2, and projects to the outside of the cylinder 2. It should be
noted that the cylinder 2 is provided with a reservoir or a gas
chamber to compensate for a volumetric change in the cylinder 2 due
to extension and contraction of the piston rod 6.
[0019] The piston 3 is provided with an extension hydraulic fluid
passage 8 and a compression hydraulic fluid passage 9 for
communication between the cylinder upper and lower chambers 2a and
2b. An extension damping force generating mechanism 10 is provided
between the piston 3 and the nut 5 to control the flow of hydraulic
fluid in the extension hydraulic fluid passage 8. A compression
damping force generating mechanism 11 is provided between the
piston 3 and the large-diameter portion 4a of the piston bolt 4 to
control the flow of hydraulic fluid in the compression hydraulic
fluid passage 9.
[0020] The extension damping force generating mechanism 10 will be
described below. An annular valve seat 12 projects from an end
surface of the piston 3 that faces the cylinder lower chamber 2b. A
disk valve 13 (a pilot operated type damping valve) is seated on
the valve seat 12. An annular fixing member 14 is mounted on the
piston bolt 4 between the piston 3 and the nut 5. A movable ring 15
is slidably fitted on the outer periphery of the fixing member 14.
The movable ring 15 is pressed to abut on the disk valve 13 by
spring force of a disk-shaped plate spring 16 clamped between the
fixing member 14 and the nut 5. A pilot chamber 17 is formed
between the disk valve 13 and the fixing member 14 so that the
pressure in the pilot chamber 17 acts on the disk valve 13 in the
direction for closing it. The pilot chamber 17 is communicated with
the extension hydraulic fluid passage 8 through a fixed orifice 18
provided in the disk valve 13. The pilot chamber 17 is also
communicated with the other side of the fixing member 14 by ports
19 and 20 provided in the side wall of the piston bolt 4 through an
extension pressure control valve 21 (a damping force control valve,
or a variable pressure control valve) provided inside the piston
bolt 4. The pilot chamber 17 is further communicated with the
cylinder lower chamber 2b through a check valve 22 formed from a
disk valve superimposed on the plate spring 16.
[0021] The compression damping force generating mechanism 11 will
be described below. An annular valve seat 23 projects from an end
surface of the piston 3 that faces the cylinder upper chamber 2a. A
disk valve 24 (a pilot operated type damping valve) is seated on
the valve seat 23. An annular fixing member 25 is mounted on the
piston bolt 4 between the large-diameter portion 4a and the piston
3. A movable ring 26 is slidably fitted on the outer periphery of
the fixing member 25. The movable ring 26 is pressed to abut on the
disk valve 24 by spring force of a disk-shaped plate spring 27
clamped between the fixing member 25 and the large-diameter portion
4a. A pilot chamber 28 is formed between the disk valve 24 and the
fixing member 25 so that the pressure in the pilot chamber 28 acts
on the disk valve 24 in the direction for closing it. The pilot
chamber 28 is communicated with the compression hydraulic fluid
passage 9 through a fixed orifice 29 provided in the disk valve 24.
The pilot chamber 28 is also communicated with the other side of
the fixing member 25 by ports 30 and 31 provided in the side wall
of the piston bolt 4 through a compression pressure control valve
32 (a damping force control valve, or a variable pressure control
valve) provided inside the piston bolt 4. The pilot chamber 28 is
further communicated with the cylinder upper chamber 2a through a
check valve 33 formed from a disk valve superimposed on the plate
spring 27.
[0022] The extension and compression pressure control valves 21 and
32 will be described below with reference mainly to FIG. 2. The
piston bolt 4 has a small-diameter bore 34 in the center thereof.
The ports 19 and 30 open into the small-diameter bore 34.
Large-diameter bores 35 and 36 are formed at both ends of the
small-diameter bore 34. The ports 20 and 31 open into the
large-diameter bores 35 and 36, respectively. Annular valve seats
37 and 38 are formed by step portions between the small-diameter
bore 34 and the large-diameter bores 35 and 36. A cylindrical
slider 39 is slidably fitted in the small-diameter bore 34 of the
piston bolt 4. Annular valve chambers 40 and 41 are formed between
the small-diameter bore 34 and small-diameter portions formed at
both ends of the slider 39. The valve chambers 40 and 41
communicate with the ports 19 and 30, respectively. Valve members
42 and 43 are secured to both ends of the slider 39. The valve
members 42 and 43 are adapted to rest on or separate from the valve
seats 37 and 38, respectively. The valve members 42 and 43 are each
in the shape of a cylindrical member, one end of which is almost
closed. Each of the valve members 42 and 43 has a projecting
portion at the bottom thereof. The projecting portion is
press-fitted into the slider 39. Annular valve chambers 44 and 45
are formed between the valve members 42 and 43 and the
large-diameter bores 35 and 36, respectively. The valve chambers 44
and 45 communicate with the ports 20 and 31, respectively. The
valve members 42 and 43 have flange portions 46 and 47 extending
from the outer peripheries of the open ends thereof. The flange
portions 46 and 47 are slidably fitted in the large-diameter bores
35 and 36, respectively. The slider 39 and the valve members 42 and
43 constitute a slider valve according to the present
invention.
[0023] A proportional solenoid 48 is provided in the solenoid
casing 7. An actuating rod 50 is connected to a plunger 49 of the
proportional solenoid 48. The distal end portion of the actuating
rod 50 is inserted into the valve member 43 secured to one end of
the slider 39. The distal end of the actuating rod 50 abuts on the
bottom of the valve member 43. An adjusting screw 51 and a lock nut
52 are screwed into the large-diameter bore 35 at the distal end of
the piston bolt 4 to close the opening of the large-diameter bore
35. A return spring 53 (compression spring) is interposed between
the valve member 42 secured to the other end of the slider 39 and
the adjusting screw 51. Lead wires 55 of a coil 54 of the
proportional solenoid 48 extend through the hollow piston rod 6 to
the outside of the cylinder 2. Thus, electric power can be supplied
to the coil 54 from a connector 56 connected to the distal ends of
the lead wires 55.
[0024] A hydraulic fluid chamber 57 is formed between the valve
member 42 and the adjusting screw 51 in the large-diameter bore 35.
The hydraulic fluid chamber 57 is cut off from the valve chamber 44
by the flange portion 46. A hydraulic fluid chamber 58 is formed at
the rear side of the valve member 43 in the large-diameter bore 36
to communicate with the inside of the proportional solenoid 48. The
hydraulic fluid chamber 58 is cut off from the valve chamber 45 by
the flange portion 47. The hydraulic fluid chambers 57 and 58 are
communicated with each other through a hydraulic fluid passage 59
in the slider 39 and through hydraulic fluid passages 60 and 61
formed in the respective projecting portions of the valve members
42 and 43 and further through an orifice passage 62 provided in the
distal end portion of the actuating rod 50 of the proportional
solenoid 48. It should be noted that the fit between the
large-diameter bores 35 and 36 and the flange portions 46 and 47 of
the valve members 42 and 43 allows a slight leakage of hydraulic
fluid as caused by a volume change due to a change in temperature
or the like of the hydraulic fluid in the hydraulic fluid chambers
57 and 58.
[0025] The following is a description of the operation of this
embodiment arranged as stated above.
[0026] During the extension stroke of the piston rod 6, as the
piston 3 moves, the hydraulic fluid in the cylinder upper chamber
2a is pressurized. Consequently, before the disk valve 13 of the
extension damping force generating mechanism 10 opens (in a low
piston speed region), the hydraulic fluid in the cylinder upper
chamber 2a flows to the cylinder lower chamber 2b through the
extension hydraulic fluid passage 8, the fixed orifice 18 in the
disk valve 13, the pilot chamber 17, the port 19, the extension
pressure control valve 21, the port 20 and the check valve 22. When
the pressure in the cylinder upper chamber 2a reaches the valve
opening pressure of the disk valve 13 (a high piston speed region),
the disk valve 13 opens to allow the hydraulic fluid from the
extension hydraulic fluid passage 8 to flow directly into the
cylinder lower chamber 2b.
[0027] Thus, before the disk valve 13 opens (in the low piston
speed region), damping force is generated by the fixed orifice 18
and the extension pressure control valve 21. The degree of opening
of the extension pressure control valve 21 is determined by the
balance between force exerted on the valve member 42 by the
pressure of hydraulic fluid in the valve chamber 40 and thrust
derived from the return spring 53 and the proportional solenoid 48.
Therefore, damping force before the disk valve 13 opens (in the low
piston speed region) can be controlled directly by controlling the
electric current supplied to the coil 54 independently of the
piston speed.
[0028] At this time, according to the degree of opening of the
valve member 42, the pressure in the pilot chamber 17, which is on
the upstream side of the valve member 42, changes, and the pressure
in the pilot chamber 17 acts on the disk valve 13 in the direction
for closing it as a pilot pressure. Therefore, it is possible to
control the valve opening pressure of the disk valve 13 together
with the valve opening pressure of the valve member 42. Thus,
damping force in the high piston speed region can be controlled
simultaneously.
[0029] During the compression stroke of the piston rod 6, as the
piston 3 moves, the hydraulic fluid in the cylinder lower chamber
2b is pressurized. Consequently, before the disk valve 24 of the
compression damping force generating mechanism 11 opens (in the low
piston speed region), the hydraulic fluid in the cylinder lower
chamber 2b flows to the cylinder upper chamber 2a through the
compression hydraulic fluid passage 9, the fixed orifice 29 in the
disk valve 24, the pilot chamber 28, the port 30, the compression
pressure control valve 32, the port 31 and the check valve 33. When
the pressure in the cylinder lower chamber 2b reaches the valve
opening pressure of the disk valve 24 (the high piston speed
region), the disk valve 24 opens to allow the hydraulic fluid from
the compression hydraulic fluid passage 9 to flow directly into the
cylinder upper chamber 2a.
[0030] Thus, before the disk valve 24 opens (in the low piston
speed region), damping force is generated by the fixed orifice 29
and the compression pressure control valve 32. The degree of
opening of the compression pressure control valve 32 is determined
by the balance between force exerted on the valve member 43 by the
pressure of hydraulic fluid in the valve chamber 41 and thrust
derived from the return spring 53 and the proportional solenoid 48.
Therefore, damping force before the disk valve 24 opens (in the low
piston speed region) can be controlled directly by controlling the
electric current supplied to the coil 54 independently of the
piston speed.
[0031] At this time, according to the degree of opening of the
valve member 43, the pressure in the pilot chamber 28, which is on
the upstream side of the valve member 43, changes, and the pressure
in the pilot chamber 28 acts on the disk valve 24 in the direction
for closing it as a pilot pressure. Therefore, it is possible to
control the valve opening pressure of the disk valve 24 together
with the valve opening pressure of the valve member 43. Thus,
damping force in the high piston speed region can be controlled
simultaneously.
[0032] When the slider 39 is placed in an intermediate position
where both the valve members 42 and 43 are separate from the valve
seats 37 and 38 by controlling the electric current supplied to the
coil 54 of the proportional solenoid 48, "soft" damping force
characteristics (small damping force) can be obtained during both
the extension and compression strokes of the piston rod 6. By
urging the valve member 42 to press on the valve seat 37 and thus
separating the valve member 43 from the valve seat 38, it is
possible to obtain "hard" damping force characteristics (large
damping force) during the extension stroke and "soft" damping force
characteristics during the compression stroke. By urging the valve
member 43 to press on the valve seat 38 and thus separating the
valve member 42 from the valve seat 37, it is possible to obtain
"soft" damping force characteristics during the extension stroke
and "hard" damping force characteristics during the compression
stroke. Thus, it is possible to obtain extension/compression
inverting damping force characteristics suitable for semi-active
suspension control based on the sky-hook damper theory.
[0033] As has been stated above, the flange portions 46 and 47 of
the valve members 42 and 43 are fitted in the large-diameter bores
35 and 36, respectively, whereby the hydraulic fluid chambers 57
and 58 at the respective ends of the valve members 42 and 43
secured to the slider 39 are cut off from the valve chambers 44 and
45 communicating with the downstream ports 20 and 31 of the
extension and compression pressure control valves 21 and 32.
Accordingly, even if the flow rate of hydraulic fluid increases
sharply and consequently the pressure in the valve chambers 44 and
45 increases temporarily owing to the influence of flow resistance
in the check valves 22 and 33, the pressure is not transmitted to
the hydraulic fluid chambers 57 and 58. Therefore, there is no
possibility of the slider 39 moving under the influence of such a
pressure change. Accordingly, stable damping force can be
obtained.
[0034] Next, a second embodiment of the present invention will be
described with reference to FIG. 3. It should be noted that the
second embodiment is similar in structure to the first embodiment
except for the structure of fit between the valve members 42 and 43
and the large-diameter bores 35 and 36. Therefore, members or
portions similar to those in the first embodiment shown in FIG. 2
are denoted by the same reference numerals, and only a part of the
second embodiment in which it differs from the first embodiment
will be described below in detail.
[0035] As shown in FIG. 3, in the second embodiment, the flange
portions 46 and 47 of the valve members 42 and 43 are omitted, but
instead the large-diameter bores 35 and 36 are provided with
small-diameter portions 63 and 64, respectively. The small-diameter
portions 63 and 64 are fitted on the respective outer peripheries
of the valve members 42 and 43, whereby valve chambers 44 and 45
communicating with the ports 20 and 31, respectively, are formed
downstream the extension and compression pressure control valves 21
and 32. With this arrangement, the hydraulic fluid chambers 57 and
58 are cut off from the valve chambers 44 and 45 by the
small-diameter portions 63 and 64. Thus, there is no possibility
that a change in pressure of hydraulic fluid in the valve chambers
44 and 45 will act in the axial direction of the valve members 42
and 43. Accordingly, it is possible to surely prevent undesired
movement of the slider 39 due to a pressure change and hence
possible to obtain stable damping force.
[0036] Next, a modification of the second embodiment will be
described with reference to FIG. 4. In this modification, the
slider 39 and the valve members 42 and 43 as shown in FIG. 3 are
integrated into a slider valve structure, which is halved at an
approximately central portion in the axial direction to provide an
upper (compression side) slider valve 70 and a lower (extension
side) slider valve 71.
[0037] With the above-described arrangement, the combination of the
slider valves 70 and 71 has an approximately similar profile to
that of the combination of the slider 39 and the valve members 42
and 43 in FIG. 3 and thus provides the same advantageous effect as
that in the second embodiment. In addition, it becomes unnecessary
to perform an operation of press-fitting valve members into a
slider as required in the embodiment shown in FIG. 3. Therefore,
there is no likelihood of misalignment, which might otherwise occur
during the press-fitting operation, and the alignment accuracy can
be increased. Consequently, the leakage of hydraulic fluid is
minimized, and the design damping force can be obtained easily.
Furthermore, cost reduction can be attained by eliminating the
press-fitting process. Moreover, because there are no shavings
which would otherwise occur during the press-fitting process, it is
possible to prevent occurrence of a failure in operation due to
foreign matter.
[0038] In order to increase the alignment accuracy in FIG. 4, it is
necessary to drill a hole (slider receiving portion) in the piston
bolt 4 with high accuracy. Accordingly, drilling is carried out
from the axially upper and lower ends of the piston bolt 4 to form
a compression-side hole 72 and an extension-side hole 73. In this
case, because the work (piston bolt 4) is inverted to drill each
hole, misalignment is likely to occur. In this regard, an inner
peripheral groove 74 is provided in an approximately central
portion of the piston bolt 4 to allow misalignment (a step in the
hole) and to accommodate burrs resulting from the drilling
process.
[0039] Although in the first and second embodiments the extension
and compression pressure control valves 21 and 32 are so structured
that the valve members 42 and 43 are seated directly on the
respective valve seats 37 and 38, it is also possible to perform
the valve open-close operation by using flexible disk valves
installed on either the valve members 42 and 43 or the valve seats
37 and 38. In addition, the seat portions of the extension and
compression pressure control valves 21 and 32 can be improved in
sealing properties by coating them with a rubber-based paint, an
elastic resin material or the like.
[0040] As has been detailed above, according to the damping force
control type hydraulic shock absorber of the present invention, the
hydraulic fluid chambers at both ends of the slider valve in the
sleeve of the damping force control valve, which is a variable
pressure control valve, are cut off from the ports provided in the
sleeve. Therefore, the pressure of hydraulic fluid in the ports of
the sleeve does not act on the hydraulic fluid chambers at the two
ends of the slider valve. Accordingly, there is no possibility of
the slider valve moving under the influence of the pressure. Thus,
stable damping force can be obtained.
[0041] It should be noted that the present invention is not
necessarily limited to the foregoing embodiments but can be
modified in a variety of ways without departing from the gist of
the present invention.
* * * * *