Damping force generating device for an oil damper

A damping force generating device for an oil damper including a hydraulic cylinder, a sub-tank having in the interior thereof an oil chamber and a gas chamber, and a first oil passage which hydraulically connects the hydraulic cylinder to the oil chamber. The damping force generating device comprises a valve seat having second and third oil passages for passing therethrough an operating oil when it is flowing in first and second directions of the first oil passage, respectively; a first valve for opening and closing the second oil passage; and a second valve for opening and closing the third oil passage. The first or second valve comprises a valve body, a mechanism for normally urging the valve body in a closing direction, and an urging force adjusting arrangement for adjusting the urging force of the urging mechanism from the exterior. The damping force generating device is simplified in structure and provides for a reduction in size of the oil damper as well as facilitated adjustment of the damping force.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a damping force generating 
device for an oil damper used as a rear cushion in two-wheeled motor 
vehicles or the like. More particularly, the invention relates to a 
damping force generating device for an oil damper provided with a sub-tank 
having a gas chamber which is separate from a cylinder in which a piston 
is slidably inserted. 
2. Description of Relevant Art 
There has been known an oil damper of the type having a single cylinder 
provided with a sub-tank in which a volumetric change in the interior of 
the cylinder caused by a sliding motion of a piston therein, i.e., a 
volumetric change therein corresponding to an intruding or retreating 
volume of a piston rod, is compensated by a volumetric change of gas in 
the sub-tank, by hydraulically connecting the cylinder with the sub-tank. 
Recently, in two-wheeled motor vehicles or the like, there has been a 
tendency to adopt a single rear cushion and mount it under a seat 
positioned centrally of the vehicle body, or thereabout. However, if the 
foregoing oil damper provided with a sub-tank is used for a rear cushion 
of this type, the structure of the damper, particularly the sub-tank, 
becomes complicated and large in size, and it is difficult to selectively 
change the damping characteristic of the damper. Thus, use of such an oil 
damper has not always been desirable from the standpoint of maintenance. 
The present invention effectively overcomes the foregoing problems 
attendant the conventional oil damper. 
SUMMARY OF THE INVENTION 
The present invention provides a damping force generating device for an oil 
damper including a hydraulic cylinder, a sub-tank provided in the interior 
thereof with an oil chamber and a gas chamber, and a first oil passage 
which hydraulically connects the hydraulic cylinder to the oil chamber in 
the sub-tank. The damping force generating device comprises a valve seat 
disposed in the first oil passage and having at least one second oil 
passage for passing therethrough an operating oil when it is flowing in a 
first direction from the hydraulic cylinder toward the oil chamber in the 
sub-tank, and at least one third oil passage for passing therethrough the 
operating oil when it is flowing in a second direction from the oil 
chamber in the sub-tank toward the hydraulic cylinder. A first valve means 
is provided for opening the second oil passage when the operating oil 
flows in the first direction and closing it when the operating oil flows 
in the second direction, and a second valve means is provided for closing 
the third oil passage when the operating oil flows in the first direction 
and opening it when the operating oil flows in the second direction. The 
first or second valve means comprises a valve body, means for normally 
urging the valve body in the closing direction, and urging force adjusting 
means for adjusting from the exterior the urging force of the urging 
means. 
It is an object of the present invention to provide a damping force 
generating device capable of contributing to the simplification of 
structure and reduction in size of an oil damper. 
It is another object of the present invention to provide a damping force 
generating device for an oil damper capable of adjusting the damping force 
easily and thus affording favorable maintenance characteristics. 
The above and further objects, details and advantages of the present 
invention will become apparent from the following detailed description of 
preferred embodiments thereof, when read in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
With reference to FIG. 1, a piston rod 3 is inserted from below into a 
cylinder 2 of an oil damper 1, and a piston 4 which is slidable within the 
cylinder 2 is fixed to the upper end of the piston rod 3. A valve 
mechanism 5 which is a known damping force generating mechanism is 
attached to the piston 4. 
In the interior of the lower portion of the cylinder 2 are fitted an oil 
seal 6 and a rod guide 7 which are in sliding contact with the outer 
periphery of the piston rod 3. On the outer periphery of the cylinder 2 
are fitted an upper spring shoe 8 and a spring adjuster 9, with an upper 
mounting member 10 being fixed to the upper end of the cylinder 2. 
The interior of the cylinder 2 is partitioned by the piston 4 into an upper 
operating chamber S.sub.1 and a lower operating chamber S.sub.2, both 
chambers S.sub.1 and S.sub.2 being filled with an operating oil. 
To the lower end of the piston rod 3 is fixed a lower spring shoe 12, with 
a cushion spring 14 being stretched between the lower spring shoe 12 and 
the upper spring shoe 8 as shown in FIG. 1. 
The upper end of the cylinder 2 is connected, for example, to the vehicle 
body side through the upper mounting member 10, while the lower end of the 
rod 3 is connected to the vehicle wheel side through the lower mounting 
member 13, with the cylinder 2 and the piston rod 3 being adapted to 
expand and contract relative to each other. 
The structure of the piston 4 and that of the valve mechanism 5 are known, 
and thus detailed description thereof is omitted. 
Outside the cylinder 2 is separately provided a sub-tank 15 as shown in 
detail in FIG. 2, the sub-tank 15 and the cylinder 2 being interconnected 
through a pipe 16. 
As shown in FIG. 2, the interior of the sub-tank 15 is partitioned by a 
flexible partition member (bladder) 17 into an oil chamber S.sub.3 and a 
gas chamber S.sub.4, with air at a predetermined pressure being sealed in 
the gas chamber S.sub.4 through an air valve 18. 
In an end plate 19 of the sub-tank 15 are formed oil passages 20, 21 and 22 
which provide communication between the oil chamber S.sub.3 in the 
sub-tank and the upper operating chamber S.sub.1 of the cylinder 2, with a 
damping force generating device 30 according to the present invention 
being fixedly mounted in an intermediate position relative to the oil 
passages 20-22. 
Construction of the damping force generating device 30 will now be 
described with reference to FIG. 3, wherein reference numeral 31 denotes a 
valve seat, with a valve seat cap 32 being threadedly engaged with the end 
plate 19 through threads 32a in a position above the valve seat 31. 
A hole 33 is formed centrally of a partition wall 31a of the valve seat 31, 
and outside the hole 33 are radially formed a plurality of holes 34. 
Further, on the upper surface of the partition wall 31a is mounted a first 
check valve 36 having a plurality of holes 35 corresponding to the holes 
34, while on the lower surface of the partition wall 31a is mounted a 
second check valve 38 having a centrally located hole 37 corresponding to 
the hole 33. The check valve 38 is urged upwardly, i.e., in a closing 
direction, by means of a valve spring 40 which is mounted in a compressed 
state between the check valve 38 and a stopper ring 39. 
In the interior of the valve seat cap 32 a rod 41 is threadedly engaged 
with the cap 32 through threads 41a formed on the lower portion of the rod 
41, and thus the rod 41 is rotatable with respect to the valve seat cap 
32. To the upper end of the rod 41 is fixed an adjusting dial 42 by a 
machine screw 43. In substantially hemispherical grooves 42a formed in the 
back of the adjusting dial 42 are engaged balls 45 which are resiliently 
held by springs 44. By the engagement of the balls 45, a click is imparted 
to the rotation of the adjusting dial 42, and at the same time the 
loosening of the dial 42 is prevented and thus the loosening of the rod 41 
is prevented. 
Further, an oil chamber S.sub.5 is formed in the interior of the lower 
portion of the valve seat cap 32, and a plurality of holes 46 are formed 
in the cap 32 around the oil chamber S.sub.5, so that the oil chamber 
S.sub.5 communicates with the oil chamber S.sub.3 in the sub-tank 15 
through the holes 46 and oil passage 22. 
Moreover, within the oil chamber S.sub.5 is disposed a coil spring 47 in a 
compressed state between the rod 41 and the first check valve 36 mounted 
on the upper surface of the partition wall 31a of the valve seat 31. By 
the spring 47 the first check valve 36 is normally urged downwardly, i.e., 
in a closing direction. 
In FIG. 3, the rod 41 is positioned so as to be most remote from the first 
check valve 36 and therefore the urging force of the spring 47 is at a 
minimum value. 
The operation of the oil damper 1 will now be described hereinbelow. 
A compression stroke of the piston 4 will be explained with reference to 
FIGS. 1 through 4. In FIG. 1, as the piston 4 moves up relative to the 
cylinder 2, the oil in the upper operating chamber S.sub.1 of the cylinder 
2 flows through the valve mechanism 5 into the lower operating chamber 
S.sub.2 and a damping force is generated within the cylinder 2 by the flow 
resistance of the oil passing the valve mechanism 5. 
The operating oil, in an amount corresponding to the intruding volume of 
the piston rod 3 into the cylinder 2, is introduced through the pipe 16 
into the oil chamber S.sub.3 in sub-tank 15. The oil thus introduced 
through the pipe 16 then flows through the oil passages 20 and 21 and 
further passes through the hole 37 of the second check valve 38 and the 
central hole 33 of the valve seat 31, as shown in FIG. 4, and forces open 
the first check valve 36 upwardly against the spring 47 by virtue of its 
pressure. Then the oil flows through the plurality of holes 35 of the 
first check valve 36, oil chamber S.sub.5, the plurality of holes 46 and 
finally through the oil passage 22 into the oil chamber S.sub.3 in the 
sub-tank and compresses the air in the gas chamber S.sub.4. 
A damping force is generated within the damping force generating device 30 
by the flow resistance induced when the operating oil passes through the 
check valves 36 and 38, and this damping force can be selectively adjusted 
by turning the adjusting dial 42 in either a clockwise or counterclockwise 
direction to move the rod 41 up or down relative to the cap 32, thereby 
changing the set length of the valve spring 47 and thus changing the 
urging force of the spring 47. 
An expansion stroke of the piston 4 will now be explained with reference to 
FIGS. 1 through 3 and 5. In FIG. 1, when the piston 4 moves down relative 
to the cylinder 2, the oil in the lower operating chamber S.sub.2 of the 
cylinder 2 flows through the valve mechanism 5 into the upper operating 
chamber S.sub.1, and at this time a required damping force is generated 
within the cylinder 2. 
At this time, moreover, the operating oil corresponding to the retreating 
volume in the cylinder 2 caused by the downward movement of the piston rod 
3 must be replenished from the oil chamber S.sub.3 in the sub-tank 15 into 
the cylinder 2 through the pipe 16. That is, the oil in the sub-tank oil 
chamber S.sub.3 flows through the oil passage 22, holes 46, oil chamber 
S.sub.5, then, as shown in FIG. 5, passes through the plurality of holes 
35 of the first check valve 36 and the plurality of holes 34 of the valve 
seat 31, and forces down the second check valve 38 against the valve 
spring 40 by virtue of its pressure. The oil then flows through the 
central hole 37 of the check valve 38, oil passages 21, 20 and pipe 16 and 
finally into the cylinder 2. Also in this case, a required damping force 
is generated within the device 30 by the flow resistance induced when the 
operating oil passes through the check valves 36 and 38. As a result of 
flow of the oil in the sub-tank oil chamber S.sub.3 into the cylinder 2, 
the air in the gas chamber S.sub.4 expands. 
Thus, the damping force generating device 30 generates a damping force in 
both compression and expansion strokes, and this damping force (in this 
embodiment the damping force in the compression stroke) can be selectively 
adjusted by a simple operation from the exterior, which is convenient for 
maintenance of the damper. 
Moreover, the damping force generating device 30 of the present invention, 
by merely attaching it to sub-tank 15, can provide a damping force between 
the cylinder side oil chamber S.sub.1 and the oil chamber S.sub.3 in the 
sub-tank 15. Therefore, by only a simple mcdification of the structure of 
a conventional sub-tank, it becomes possible to put the device 30 to 
practical use, and the device 30 itself can be simplified in its structure 
and reduced in its size, thus permitting even reduction in size of the 
sub-tank. 
In the above-described embodiment, as shown in FIG. 3, the first valve 36 
is normally urged in the closing direction by means of the coil spring 47 
to adjust the damping force in the compression stroke of the piston, i.e., 
to adjust the flow path resistance of the valve 36, and such urging force 
is adjusted by the rod 41 and the adjusting dial 42. 
However, a coil spring can be readily adopted as the spring 40 of the 
second valve 38, with its urging force being made adjustable by virtue of 
the same construction as in the foregoing embodiment, whereby the damping 
force in the expansion stroke of the piston can be adjusted. 
Furthermore, it will be understood that the spring in question is not 
limited to a coil spring and that any other suitable spring may 
alternatively be employed. 
Although there have been described what are at present considered to be the 
preferred embodiments of the invention, it will be understood that the 
present invention may be embodied in other specific forms without 
departing from the spirit or essential characteristics thereof. The 
present embodiments are therefore to be considered in all respects as 
illustrative, and not restrictive. The scope of the invention is indicated 
by the appended claims rather than by the foregoing description.