Device for producing damping force in hydraulic shock absorbers

A device for producing the damping force in a hydraulic shock absorber comprising a non-return valve element adapted to open in the compression stroke so as to permit the free flow of working oil, a leaf valve element adapted to deflect downwards under the pressure of the working oil flowing through the holes formed in the non-return valve element during the expansion stroke, thereby providing the damping force, and a support shim interposed between the non-return valve element and the leaf valve element. The leaf valve element and the support shim are interposed between a piston and a valve stop. The support shim has such an outer diameter that its outer periphery is in contact or in slightly radially inwardly spaced relationship with the inner circle of the annulus containing the holes of the non-return valve, whereby the variations in damping force produced by the deflections of the leaf valve element may be avoided, the service life or durability of the leaf valve element may be improved and the shock may be eliminated when the non-return valve element is closed.

BACKGROUND OF THE INVENTION 
The present invention relates to generally a piston valve device for 
producing the damping force in a hydraulic shock absorber and more 
particularly an improvement of a piston valve device for producing the 
damping force in a hydraulic shock absorber of type comprising a 
non-return valve element adapted to be opened during the compression 
stroke so as to permit the free flow of the working oil and a leaf valve 
element adapted to deflect downwards during the expansion stroke under the 
pressure of the working oil flowing through a plurality of holes formed 
through the non-return valve element, thereby producing the damping force, 
the improvement being capable of eliminating the variations in damping 
force, enhancing the durability of the leaf valve element and eliminating 
the shock produced when the non-return valve is closed, thereby offering a 
good riding quality when the hydraulic shock absorber is used on an 
automotive vehicle or a motorcycle. 
The damping force producing piston valve device of the type described is 
disclosed in for instance U.S. Pat. No. 2,060,590, granted to J. E. 
Padgett, Nov. 10, 1936 and particularly in FIGS. 4 and 7 of the 
accompanying drawings thereof. However, the shock absorbing means 
disclosed therein has some defects to be described below. 
During the compression stroke, the working fluid is forced upwardly through 
the passages 26 of the piston causing the flexible plate 29 (the leaf 
valve element) to be held in face to face contact with the rigid plate 28 
(the non-return valve element) and causing both plates to move upwardly 
together away from the piston body. This lifting of the valve elements 
causes the rigid valve plate to separate from the annular seat, thereby 
allowing the working oil to flow upwardly around the outer edge of the 
rigid plate into the upper chamber 15 of the working cylinder. During the 
expansion stroke, the rigid valve plate 28 is seated against the piston 
body so that the working oil can be displaced downwardly through the 
piston only through the orifices of the rigid plate. The flexible plate 29 
normally closes the orifices 32, but when the pressure acting on the 
flexible plate through the orifices increases sufficiently the flexible 
plate is sprung away from the rigid plate and a restricted displacement of 
fluid downwardly into the chamber 16 takes place. This restricted transfer 
of working oil produces a shock absorbing action. Since the leaf or 
flexible valve element is movable relative to the valve stop or guide 33, 
a clearance must be left between the valve stop or guide and the leaf or 
flexible valve element. As a result, in the case of the expansion stroke, 
the leaf or flexible valve element is forced to displace itself radially 
by a distance equal to the clearance. This means that during every 
expansion stroke, the portion of the leaf of flexible valve element in 
contact with the ridge 53 of the shoulder 52 of the piston is shifted so 
that the variations of the damping force result. The variations in the 
damping force are pronounced especially when the difference between the 
outer and inner diameters of the leaf or flexible valve element is small. 
The damping force variation problem described above may be overcomed by 
securely clamping the leaf or flexible valve element between the valve 
stop or guide and the piston. However, if the leaf or flexible valve 
element is clamped, it is forced to deflect upwards even during the 
compression stroke so that as the hydraulic shock absorber compresses and 
expands, the leaf or flexible valve element is forced to deflect it self 
upwards and downwards. As a result, the earlier breakdown of the leaf or 
flexible valve element due to fatique results. 
Furthermore, there is another problem. That is, when the compression stroke 
changes to the expansion stroke so that the non-return or rigid valve 
element is closed, the flow of the working oil is cut off instantaneously 
even though for a very short time interval until the downward deflection 
of the leaf or flexible valve element starts, thus resulting in shock 
causing the degradation of the riding quality. 
SUMMARY OF THE INVENTION 
One of the objects of the present invention is therefore to provide a 
piston valve device for producing the damping force in a hydraulic shock 
absorber which is simple in construction yet capable of substantially 
overcoming the above and other problems encountered in the prior art 
devices. 
According to the present invention, the above and other objects thereof may 
be accomplished by the provision of a support shim which is interposed 
between a non-return valve element and a leaf valve element, securely held 
in position between a valve stop and a piston together with the leaf valve 
element and has such an outer diameter that its outer periphery or edge is 
in contact with or in slightly radially inwardly spaced relationship with 
the inner circle of the annulus containing a plurality of equiangularly 
spaced holes formed through the non-return valve element. 
Since the leaf valve element is securely clamped together with the support 
shim between the valve stop and the piston so that it may defects 
downwards always along a predetermined deflection line during the 
expansion stroke, whereby the damping force may be always well stabilized. 
Furthermore, the support shim serves to restrict the upward deflection of 
the leaf valve element during the compression stroke. Thus, the repetitive 
upward and downward deflections of the leaf valve element can be avoided, 
whereby the breakdown due to fatique may be prevented. 
Furthermore, even when the non-return valve is closed, there may be left a 
passage for permitting the restricted flow of the working oil between the 
leaf valve element and the non-return valve element so that the shock 
which is accompanied by the closure of the non-return valve element when 
the compression stroke changes to the expansion stroke may be 
substantially eliminated or reduced to a minimum. 
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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment, FIG. 1 
Referring to FIG. 1, a hydraulic shock absorber has a piston rod 12 
operatively connected to a piston 10 which is slidably fitted into a 
cylinder 14 and divides the latter into an upper working chamber and a 
lower working chamber both of which are filled with the working oil. 
The piston rod 12 has a reduced-diameter lower end portion, and four major 
parts; that is, an annular shim 18, leaf valve elements 20, a support shim 
22 and a valve stop 26 with an upper flange 24 being interposed between 
the shoulder 16 between the large-diameter and small-diameter portions of 
the piston rod 12 and the piston 10. These four major parts 18, 20, 22, 26 
may be supplied in the form of a sub-assembly so as to facilitate the 
assembly with the piston rod 12 and piston 10. The lower end of the 
reduced-diameter lower portion of the piston rod 12 is securely fastened 
to the piston 10 with a nut 28. 
A non-return valve element 30 is slidably fitted over the valve stop 26 and 
is in the form of an annular rigid plate or disk. A spring member 32, 
which has a relatively small force, is fitted over the valve stop 26 above 
the non-return valve element 30 normally biases the latter towards the 
piston 10. The non-return valve element 30 is formed with a plurality (two 
in FIG. 1) of holes 34 in such a manner that they will not offer any 
substantial resistances to the working oil flowing through them. 
The piston 10 has an annular ridge 36 extended upright from the crown 
portion, a plurality of relatively large-diameter through holes 38 (only 
two being shown in FIG. 1) and a sealing member on ring 40 fitted into an 
annular groove formed in the outer peripheral wall of the piston 10. The 
annular ridge or wall 36 of the piston 10 supports the non-return valve 
element 30 adjacent at its outer periphery. That is, the top annular 
surface of the annular ridge or wall 36 of the piston 10 serves as an 
outer valve seat 42 for the non-return valve element 30. 
The support shim 22 is in the form of an annular rigid plate or disk with 
an outer diameter equal to or less than the diameter of a circle along 
which are located the centers of the equiangularly spaced holes 34 of the 
non-return valve element 30 minus the diameter of these holes 34. 
Therefore the outer periphery of the support shim 22 is located adjacent 
to the inner circle of the annulus containing a plurality of equally 
spaced holes 34 of the non-return valve element 30. The thickness of the 
support shim 22 is so selected that an orifice passage 44 defined between 
the undersurface of the non-return valve element 30 and the upper surface 
of the leaf valve elements 20 may have suitable dimensions. Furthermore 
the support shim 22 has a function of supporting the non-return valve 
element 30. That is, the upper surface of the support shim 22 serves as an 
inner valve seat 46 for the non-return valve element 30. To this end, it 
is preferable that the upper surface of the support shim 22 is in coplanar 
relationship with the top annular surface of the annular ridge or wall 36 
of the piston 10. As a result, the thickness of the shim 18 is selected 
depending upon the sum of the thickness of the leaf valve elements 20 and 
that of the support shim 22. 
The leaf valve elements 20 are in the form of an annular flexible plate or 
disk with the outer periphery extended the outer circle of the annulus 
containing the holes 34 of the non-return valve element 30. In the first 
embodiment, the leaf valve elements 20 are shown as comprising two disks, 
but it is to be understood that the leave valve element assembly may 
comprises three or more disks or a single disk having a thickness equal to 
the required overall thickness of two or more disks. 
Next the mode of operation of the first embodiment with above construction 
will be described. During the downward stroke of the piston 10 within the 
cylinder 14 which is filled with the working oil; that is, the compression 
stroke of the hydraulic shock absorber, the pressure of working oil below 
the piston 10 increases, thereby forcing the non-return valve element 30 
upwards against the spring member 32. The upper flange 24 of the valve 
stop 26 limits the maximum stroke or lift of the non-return valve element 
30. The non-return valve element 30 is therefore moved away from the outer 
valve seat 42; that is, the annular top surface of the annular ridge or 
wall 36 of the piston 10 and spontaneously the orifice passage 44 which is 
defined between the leaf valve element 20 and the non-return valve element 
30 is increased in dimension. 
Therefore the working oil under the piston 10 may flow through the enlarged 
orifice passage 44, through the holes 34 of the non-return valve element 
30 and the passage opened between the latter and the outer valve seat 42 
into the upper chamber above the piston 10 without experiencing no 
resistance. As a result, the hydraulic shock absorber may be compressed 
without encountering any damping force. 
During the compression stroke of the hydraulic shock absorber, the pressure 
increase in the chamber below the piston 10 also causes the leaf valve 
element 20 to deflect upwards. Since the support shim 22 overlies the leaf 
valve element 20 with the outer periphery 48 of the support shim 22 
extended more radially outwardly than the shim 18 below the leaf valve 
element 20, the support shim 22 serves to limit the upward deflection of 
the leaf valve element 20. That is, the upward deflection of the leaf 
valve element 20 is less than that of the non-return valve element 30. 
During the expansion stroke (that is, when the piston 10 moves upwards in 
FIG. 1), the non-return valve element 30 is forced to abut against the 
outer valve seat 42 and the inner valve seat 46 which is the upper surface 
of the support shim 22. That is, both the outer and inner valve seats 42 
and 46 are closed with the non-return valve element 30. As a result, when 
the piston stroke is relatively slow, the working oil in the upper chamber 
above the piston 10 is forced to flow through the holes of the non-return 
valve element 30, the orifice passage 44 and the through holes 38 of the 
piston 10 into the chamber below the piston 10. In this case, the 
hydraulic shock absorber generates the damping force, the magnitude of 
which is proportional to the square of the piston stroke or speed, due to 
the frictional resistances which the working oil encounters when it flows 
through the orifice passage 44. It follows therefore that thus produced 
damping force is dependent upon the dimensions of the orifice passage 44 
which is defined between the leaf valve element 20 and the non-return 
valve element 30 and more particularly the thickness of the support shim 
22 interposed between them. 
When the piston stroke is increased and the pressure of the working oil 
above the piston 10 exceeds a certain value, the leaf valve element 20 is 
forced to deflect itself downwards along the deflecting line 50; that is, 
the outer periphery of the shim 18, away from the non-return valve element 
30. As a result, the orifice passage 44 is again increased in dimensions 
so that the flow rate of the working oil flowing from the upper chamber 
into the lower chamber increases so that the pressure of the working oil 
above the piston increases in proportion to the piston stroke or speed. 
Thus, the hydraulic shock absorber produces the damping force which is 
proportional in magnitude to the piston stroke or speed. 
At the instant when the hydraulic shock absorber switches from its 
compression stroke to its expansion stroke, the non-return valve element 
30 closes both the outer and inner valve seats 42 and 46 are described 
above, but it is to be emphasized that the flow of the working oil from 
the upper chamber above the piston 10 to the lower chamber is not 
completely shut off, but it may flow through the holes 34 of the 
non-return valve element 30, the orifice passage 44 and the thorugh holes 
38 of the piston as described above. Therefore the shock which tends to be 
felt at the instant the non-return valve 30 is closed may be substantially 
eliminated. 
The leaf valve element 20 is snugly fitted over the reduced-diameter lower 
portion of the piston rod 12 and is securely held in position between the 
shim 18 and the support shim 22 which in turn is abutted against the lower 
end of the valve stop 26. Therefore the leaf valve element 20 is always 
caused to deflect itself downwards along the deflecting line or the outer 
periphery of the shim 18 so that the damping force produced during the 
expansion stroke of the hydraulic shock absorber may be statsifactorily 
stabilized. 
Second Embodiment, FIG. 2 
The present invention may be equally applied to a hydraulic shock absorber 
of the type comprising an outer tube and an inner tube telescopically 
fitted therein as will be described hereinafter with reference to FIG. 2, 
wherein in order to designate parts similar to those shown in FIG. 1, 100 
is added to the reference numerals used in FIG. 1. Since the second 
embodiment shown in FIG. 2 is substantially similar in construction to the 
first embodiment shown in FIG. 1, only the difference between them will be 
described. 
Whereas the hydraulic shock absorber shown in FIG. 1 comprises the piston, 
the piston rod 12 and the cylinder, the hydraulic shock absorber shown in 
FIG. 2 comprises an inner tube 112 upon which is mounted a piston 110 and 
an outer tube 114. 
The sub-assembly comprising a shim 118, a leaf valve element 120, a support 
shim 122 and a valve stop 126 is interposed between the shoulder 116 of 
the inner tube 112 and a nut 128 screwed to the lower end thereof. 
The nut 128 is formed with an annular groove in the outer peripheral wall 
thereof and a seal member consisting of an O-ring and a piston ring is 
fitted in the annular groove. The seal member 140 is made into slidable 
contact with the inner wall of the outer tube 114 and divides the latter 
into a chamber above the piston 110 and a chamber below it. Therefore in 
the second embodiment the piston 110 is not provided with a seal member 
and makes no slidable contact with the inner wall surface of the outer 
tube 114. The through holes 138 of the piston 110 are communicated with 
the chamber below the piston 110 through a recess 152 formed in the top 
surface of the nut 128, a plurality of holes 154 formed through the wall 
of the inner tube 112 and the interior of the inner tube 112. Therefore it 
is apparent to those skilled in the art that the hydraulic shock absorber 
shown in FIG. 2 may produce the damping force in a manner substantially 
similar to that described above with reference to FIG. 1 so that no 
further detailed description shall be made. However, it must be emphasized 
that in the shock absorber of the type shown in FIG. 2, the spacing 
between the outer and inner tubes 114 and 112 cannot be increased beyond a 
certain limit so that the difference between the outer and inner diameters 
of the leaf valve element 120 becomes shorter than that in the shock 
absorber shown in FIG. 1, but the variations in damping force may be 
eliminated because according to the present invention the shim 118 is 
disposed below the leaf valve element 120 so as to restrain its downward 
deflection as described elsewhere.