Hydraulic shock absorber

A hydraulic shock absorber comprising a cylinder, a partition member for partitioning the interior of the cylinder into two chambers and a damping force generating mechanism for regulating the oil flow through a communication passageway formed through the partition member and connecting the two chambers with each other. The damping force generating mechanism comprises a disk valve seated on a seat formed on the partition member and adapted to open in response to the oil pressure in the communication passageway; a damping force regulating chamber arranged on the side of the disk valve remote from the partition member; an oil passageway for connecting the damping force regulating chamber to the communication passageway; an orifice disposed in the oil passageway to restrict the area of the oil passageway for oil flow therethrough; and fulcrum member arranged in the damping force regulating chamber and in contact with the disk valve for providing a fulcrum for the disk valve to deflect. The fulcrum member is designed such that the contact position in which the fulcrum member contacts with the disk valve is shifted in the radially outward direction of the disk valve in response to increase in the pressure of oil which flows into the damping force regulating chamber through the orifice.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a hydraulic shock absorber for use in a 
vehicle. 
2. Description of the Related Art 
Japanese Patent Publication No. 42-17787, discloses a hydraulic shock 
absorber which is constructed with the aim of providing both operating 
stability and riding comfort to generate a normal damping force in 
response to a low frequency vibration applied to a car and a little or no 
damping force in response to a high frequency vibration. 
As shown in FIG. 1, in such a hydraulic shock absorber, an upper pressure 
chamber 4 and a lower pressure chamber 5 are arranged on the upper and 
lower sides of a valve 3 which closes an oil passageway 2 formed in a 
piston 1. A chamber 6 partitioned on the upper side of the piston 1 
communicates with the lower pressure chamber 5 via an oil chamber 7 whose 
volume varies with the internal pressure. An orifice 8 is arranged between 
the chamber 0 and the oil chamber 7. 
According to the above construction of the hydraulic shock absorber, when 
frequency of a pressure change in the chamber 6 on the upper side of the 
piston 1 is low, a large amount of oil flows through the orifice 8 and the 
oil chamber 7 to the lower pressure chamber 5 to increase the oil pressure 
in the lower pressure chamber 5. This results in augmenting a force acting 
in a direction so as to close the valve 3, thereby generating a normal 
damping force. 
On the contrary, when frequency of the pressure change in the chamber 6 is 
high, the orifice 8 restricts the oil flow to the oil chamber 7, thus 
limiting the pressure increase in the oil chamber 7. Since the pressure in 
the lower pressure chamber S becomes lower than that in the upper pressure 
chamber 4, the degree to which the valve 3 opens increases, whereby a 
little damping force is generated. 
Such a conventional hydraulic shock absorber as described above has the 
following problems. 
Since the hydraulic shock absorber requires a free piston 9 or a diaphragm 
so that the volume of the oil chamber 7 changes according to internal 
pressure, machining of the hydraulic shock absorber demands precise 
dimensional tolerances. In addition, the complicated structure causes high 
production costs. 
Further, in order to secure the volume of the oil chamber 7, the oil 
chamber 7 should be arranged to extend long in the upper and lower 
directions (along the axial direction). This leads to a hydraulic shock 
absorber which is long in the total length and therefore difficult to 
miniaturize. 
Moreover, either the extension stroke of the hydraulic shock absorber or 
the contraction stroke is only controlled. (The hydraulic shock absorber 
shown in FIG. 1 is adapted to control the extension stroke.) The identical 
two systems, disposed symmetrically with the upper and lower parts, would 
control the extension and contraction strokes. This is, however, 
impractical due to a hydraulic shock absorber extending lengthwise in the 
axial direction. 
SUMMARY OF THE INVENTION 
The present invention overcomes the above-described problems and its object 
is to provide a simpler-structured hydraulic shock absorber which permits 
generating damping forces of various magnitudes corresponding to the 
frequency of vibrations applied to the car. 
A hydraulic shock absorber according to the present invention comprises a 
damping force generating system which regulates the oil flow developed in 
a communication passageway to generate a damping force, the communication 
passageway connecting to two chambers formed by a partition member in a 
cylinder, the damping force generating system comprising a disk valve 
which opens in response to the oil pressure in the communication 
passageway, the disk valve being seated on a seat formed on the partition 
member, a damping force regulating chamber arranged on the opposite side 
of the partition member with respect to the disk valve, and an oil 
passageway for connecting the damping force regulating chamber to the 
communication passageway. The damping force generating system further 
comprises an orifice disposed in the oil passageway to restrict the area 
through which the oil flows in the oil passageway and fulcrum means in 
contact with the disk valve for providing the fulcrum of the disk valve 
for deflecting, the fulcrum means being arranged in the damping force 
regulating chamber such that the contact position of the fulcrum means 
with the disk valve is altered in radially outward direction of the disk 
valve in response to the increase in the oil pressure in the damping force 
regulating chamber. 
According to the above-mentioned structure, as the frequency of the 
pressure change in the chamber partitioned by the partition member 
increases, the orifice arranged in the oil passageway limits the oil 
pressure increase in the damping force regulating chamber. As the oil 
pressure in the damping force regulating chamber increases, a position at 
which the fulcrum means contacts the disk valve shifts in a radially 
outward direction. For which reason, the fulcrum of the valve for 
deflecting when the valve is opened shifts in correspondence to the 
frequency, thereby regulating the damping force. 
That is, when the orifice restricts the oil pressure increase in the 
damping force regulating chamber (when the frequency is high), the 
position of the fulcrum of the valve for deflecting shifts radially 
inward, and when the orifice does not restrict the oil pressure increase 
in the damping force regulating chamber (when the frequency is low), the 
position of the fulcrum of the valve shifts radially outward. For these 
reasons, when the frequency of the vibration applied to the car is high, 
the hydraulic shock absorber is capable of generating a small amount of 
damping force, while on the contrary, when the frequency is low, it is 
capable of generating a large amount of damping force. 
Other objects and features of the present invention will become apparent 
from the following detailed description of the preferred embodiments when 
read together with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention will now be described with 
reference to FIGS. 2 to 4. 
As shown in FIG. 2, a piston 13, serving as a partition member attached to 
a small diameter section 12 of a piston rod 11, is slidably fitted with 
the aid of a piston ring 14 in a cylinder 10. The piston 13 divides the 
inside of the cylinder 10 into an upper chamber 15 and a lower chamber 10. 
The piston 13 is provided with an extension side communication passageway 
17 and a contraction side communication passageway 18 communicating the 
upper chamber 15 and the lower chamber 16 with each other. One end of the 
extension communication passageway 17 is open to the upper chamber 15 and 
the other end is open to an annular groove 10 which is formed in the end 
face on the lower side of the piston 13. One end of the contraction 
communication passageway 18 is open to the lower chamber 10 and the other 
end is open to an annular groove 20 which is formed in the end face on the 
upper side of the piston 13. 
An extension side damping force generating mechanism 23, which generates 
damping force when the piston 13 is expanded, is arranged downstream of 
the extension communication passageway 17, i.e., on the lower side of the 
piston 13. 
The construction of the extension side damping force generating mechanism 
23 will now be described. 
A disk valve 25 is seated on a seat 24 formed in the end face on the lower 
side of the piston 18. The disk valve 25 and the above-mentioned annular 
groove 19 constitute a pressure room 28 for receiving oil used for 
applying the oil pressure to the disk valve 25. Moreover, the pressure 
room 26 communicates with the lower chamber 19 through an orifice 
passageway 27 formed on the seat 24 of the piston 13. 
A holder 29, having a recess 28 open to the disk valve 25, is disposed on 
the side of the disk valve 25 remote from the piston 13. A damping force 
regulating chamber 31 is defined by the recess 28 and a fulcrum means 30 
which will be described later in detail. The damping force regulating 
chamber 31 communicates with the aforesaid pressure room 26 via an oil 
passageway 35. The passageway 35 comprises a cutaway passageway 32 formed 
in the inner wall of the annular groove 19 of the piston 13, a chamfer 33 
(see FIG. 3) formed in the small diameter section 12 of the piston rod 11 
and a passageway 34 formed in the holder 29. A check valve 38 comprising a 
disk valve 37 is arranged in the passageway 34 and an orifice 38 is formed 
in the disk valve 37. The check valve 38 reduces the oil flow from the 
pressure chamber 26 to the damping force regulating chamber 31 by means of 
the orifice 36 to limit the oil pressure increase in the damping force 
regulating chamber 31, while allowing the disk valve 37 to open wide so 
that the oil in the damping force regulating chamber 31 smoothly returns 
to the pressure chamber 26. 
The fulcrum means 30 comprises a spherically-shaped backup disk 39 arranged 
so as to contact the disk valve 25 and a retainer 40 fitted on the 
internal circumference of the outer wall of the recess 28 of the 
above-mentioned holder 20. The fulcrum mean 30 further comprises an 
elastic member 41 for pressing the retainer 40 against the backup disk 39 
and for sealing the gap between the damping force regulating chamber 31 
and the lower chamber 16. A part of the retainer 40, the part coming into 
contact with the backup disk 39, is formed in the shape of a 
curved-surface so that the backup disk 39 can be smoothly deformed. The 
retainer 40 is fixed by baking to the elastic member 41. Although, in the 
embodiment shown in FIG. 2, a supporting member 42 is employed to support 
the backup disk 39, the holder 29 may alternatively directly support the 
backup disk 39 without the supporting member 42. 
On the upper side of the piston 13 is arranged a contraction side damping 
force generating mechanism 23a, which controls the oil flow in the 
contraction communication passageway 18 to generate the damping force. 
Since the construction of the contraction side damping force generating 
mechanism 23a is the same as that of the extension side damping force 
generating mechanism 23, the corresponding components thereof are 
designated by the same numerals of the components of the extension side 
damping force generating mechanism 23 except that the numerals are 
succeeded by "a", and the explanation thereof is therefore omitted. In 
this embodiment, the rigidity of the disk valve 25a of the contraction 
side damping force generating mechanism 23a is designed to be less than 
the rigidity of the disk valve 25 of the extension side damping force 
generating mechanism 23. 
The operation of the above-constructed hydraulic shock absorber will now be 
described. 
For example, because of the increased frequency of pressure change in the 
upper and lower chambers 15, 16 while a car is running on a rough road, 
the orifices 36, 36a disposed in the oil passageways 35, 35a limit the 
pressure increase in the damping force regulating chambers 31, 31a. For 
this reason, the positions of the outer edges of the portion of the backup 
disks 39, 39a in contact with the disk valves 25, 25a, shift in a radially 
inward direction of the disk valves 25, 25a (the state shown in FIG. 2). 
Since these contact edges act as the fulcrums for the disk valves 25, 25a, 
respectively, when the valves 25, 25a are opened, a small amount of the 
damping force is generated as shown by lines A1-A2 and a1-a2 in FIG. 4. 
Furthermore, because of the decreased frequency of pressure change in the 
upper and lower chambers 15, 16 while the car is running on a even road, 
the orifices 30, 31a do not limit the pressure increase in the damping 
force regulating chambers 31, 31a. For this reason, the oil pressure in 
the damping force regulating chambers 31, 31a increases, thereby causing 
the retainers 40, 40a to press the backup disks 39, 39a against the disk 
valves 25, 25a. The positions of the outer edges of the backup disks 39, 
39a in contact with the disk valves 25, 25a, respectively, shift in a 
radially outward direction of the disk valves 25, 25a. Thus, the positions 
of the fulcrums of the disk valves 25, 25a shift outward when the valves 
25, 25a are opened. For this reason, a large amount of the damping force 
is generated, as shown by the lines B1-B2 and b1-b2 in FIG. 4. Since the 
force with which the retainers 40, 40a respectively press the backup disks 
39, 39a is proportional to the magnitude of the oil pressure in the 
damping force regulating chambers 31, 31a, respectively, the damping force 
is reduced proportionally and gradually in accordance with the increase in 
the frequency, as indicated by the broken lines in FIG. 4. 
As has been described above, the damping force is regulated: it is 
decreased in the case of a high frequency, while on the contrary it is 
increased in the case of a low frequency. For this reason, the damping 
force is decreased while the car is running on a rough road or the like, 
thereby improving riding comfort. On the other hand, the damping force is 
increased while the car is running on a even road, thereby improving 
operating stability. Hence, comfort in riding and operating stability are 
both provided by the above combined mechanism. 
Other embodiments will now be described. Only fulcrum means will be 
explained in detail, since the structure of the fulcrum means in the 
respective other embodiments is only different from that of the 
above-described fulcrum means and the structure of other parts is the same 
as that of the first embodiment. The same components as in the first 
embodiment are indicated by the same numerals, the explanation thereof 
being omitted. 
The second embodiment will now be described with reference to FIG. 5. As 
shown in FIG. 5, a fulcrum means 45 is press-fitted inside the recess 28 
of the holder 29. The fulcrum means 45 comprises an annular metal ring 43 
and a rubber member 44 substantially formed in a parallelogram shape in 
cross section and attached, by baking, to the internal circumference of 
the annular metal ring 43. The internal circumference portion of the 
rubber member 44 contacts the disk valve 25 and the metal ring 43 on the 
external circumference of the rubber member 44 are fixed to the retainer 
40. The rubber member 44 is forced against the disk valve 25 by the oil 
pressure within the damping force regulating chamber 31 formed between the 
recess 28 and the rubber member 44. As the oil pressure increases, the 
area in which the rubber member 44 is in contact with the disk valve 25 
expands, thereby altering the position of the fulcrum of the disk valve 
25, for deflecting, to open. 
The operation of the hydraulic shock absorber according to the second 
embodiment is the same as that of the hydraulic shock absorber in the 
first embodiment. 
The third embodiment will now be described with reference to FIG. 6. 
An annular and flat elastic tube 46, which acts as a fulcrum means, is 
fitted into the recess 28 of the holder 29. The internal circumference of 
the tube 46 contacts the disk valve 25 and the external circumference of 
the tube 46 is positioned in the recess 28 by means of a projection 47 
formed on the holder 29. The tube 46 is pressed against the disk valve 25 
by the oil pressure in the damping force regulating chamber 31 defined by 
the recess 28 and the tube 46. As the oil pressure increases, the area in 
which tube 46 is in contact with the disk valve 25 expands outwardly. 
thereby shifting the position of the fulcrum for the disk valve 25 to 
deflect to open. The operation of the hydraulic shock absorber according 
to the third embodiment is the same as that of the hydraulic shock 
absorber in the first embodiment. 
The forth embodiment will now be described with reference to FIG. 7. 
In this embodiment, an O ring 48 fitted into the recess 28 of the holder 29 
acts as a fulcrum means. The O ring 48 is expanded in diameter in response 
to the oil pressure increase in the damping force regulating chamber 31. 
This causes the contact face of the ring 48 to shift in a radially outward 
direction and alter accordingly the position of the fulcrum of the disk 
valve 25 for deflection. In this embodiment, the structures of an oil 
passageway and the check valve arranged in the oil passageway are 
different from those in the first embodiment. The oil passageway 49 is 
formed by a gap between the external circumference of the small diameter 
section 12 of the piston rod 11 and the internal circumferences of piston 
13, the disk valve 25, the holder 29 and the disk valves 50, 51. As shown 
in FIG. 8, projections 52 are formed in the internal circumference sides 
of the following members, the piston 13, the disk valve 25, the holder 29 
and the disk valves 50, 51, respectively. The projections 52 are in 
contact with the small diameter section 12 of the piston rod 11 to 
determine the position of each of the members with respect to the 
diametrical direction. A check valve 53 comprises two disk valves 50, 51 
and an orifice 54 with a cutaway formed in the disk valve 50. The orifice 
54 restricts the oil flow from the pressure chamber 26 to the damping 
force regulating chamber 31, while the disk valves 50, 51 are opened wide 
so that the oil in the damping force regulating chamber 31 returns quickly 
to the pressure chamber 26. The operation of the hydraulic shock absorber 
according to the forth embodiment is the same as that of the hydraulic 
shock absorber in the first embodiment. 
In the above-described embodiments, the damping force generating mechanism 
according to the present invention is arranged on the piston 13. This 
invention, however, is not limited to this arrangement. For example, the 
damping force generating mechanism may be arranged on the bottom portion 
of a double tube type hydraulic shock absorber. That is, the damping force 
generating mechanism may be arranged in such a manner that it regulates 
the oil flow in the communication passageway formed through a partition 
member, which is a partition between the interior of the inner tube and a 
space defined between the inner and outer tubes. 
Although, in the embodiments described above, the present invention is 
applied to both an expansion side damping force generating mechanism and a 
contraction side damping force generating mechanism, the invention may be 
applied to either one of them only. 
As has been described in detail, in the present invention, a communication 
passageway of a partition member communicates with a damping force 
regulating chamber defined on the side of a disk valve remote from the 
partition member through an oil passageway provided with an orifice 
disposed midway thereof. A fulcrum means is disposed in the damping force 
regulating chamber to act as a fulcrum for the disk valve to deflect to 
open. The fulcrum means are designed such that the position of the fulcrum 
shifts in response to the increase in the oil pressure in the damping 
force regulating chamber. The magnitude of the damping force can, 
therefore, be regulated in response to the frequency of a pressure change 
in the damping force regulating chamber. 
Further, in the above-mentioned construction, the construction of the 
hydraulic shock absorber is simplified and the production costs thereof 
are reduced, since the shock absorber does not need a long oil chamber 
extending in the axial direction of the piston and a free piston in the 
oil chamber, as in the case of the conventional hydraulic shock absorber. 
Moreover, it is possible to miniaturize the hydraulic shock absorber in 
the length. As a result, the application of the present invention to both 
extension and contraction side damping force generating mechanisms does 
not lead to a lengthened shock absorber. 
In addition, it is possible to provide a hydraulic shock absorber with a 
high degree of freedom for setting damping force characteristics, for the 
damping force characteristics can be changed by only modifications to the 
fulcrum means being made. 
The invention has been described in detail with particular reference to the 
preferred embodiments thereof, but it will be understood that variations 
and modifications of the invention can be made within the spirit and scope 
of the invention.