Hydraulic damper of adjustable damping force type

A hydraulic damper of adjustable damping force type includes a cylinder containing hydraulic liquid therein, a piston working in the cylinder and partitioning the interior thereof into first and second liquid chambers, a piston rod secured to the piston and extending through the first liquid chamber to the outside of the cylinder, a valve mechanism mounted on the piston for generating damping force both in extension and contraction strokes of the damper, and an adjusting mechanism for adjusting the damping force. The adjusting mechanism includes a coaxial bore formed in the piston rod and communicating permanently with the first liquid chamber through a radial hole in the piston rod, a tubular nut for securing the piston to the piston rod, a tubular guide fitted in the tubular nut and having first and second series of circumferentially spaced orifice openings of different effective area, a shutter rotatably disposed in the guide for selectively opening and closing the orifice openings, a control rod secured to the shutter and extending through the bore in the piston rod, a check valve provided in the nut and permitting liquid flow through the first series of orifice openings only in one direction, and the second series of orifice openings forming a passage by-passing the check valve.

BACKGROUND OF THE INVENTION 
This invention relates to a hydraulic damper for use in a vehicle and 
particularly to a hydraulic damper of the kind including a cylinder 
receiving therein hydraulic liquid, a piston working in the cylinder and 
partitioning the interior of the cylinder into first and second chambers, 
a piston rod secured to the piston and extending through the first chamber 
to the outside of the damper, a damping force generating valve device 
mounted on the piston for generating damping force in the extension and 
contraction strokes of the damper, and a damping force adjusting mechanism 
for adjusting the damping force in response to, such, as the running 
condition of the vehicle. 
The damping force generating device may be a single valve acting in both of 
the extension and contraction strokes or may be formed of two separate 
valves acting respectively in the extension and contraction strokes and 
preventing liquid flow in the respective reverse directions. 
A hydraulic damper of the aforementioned kind is widely used in vehicles 
such as automobiles. The projecting end of the piston rod is usually 
connected to a sprung mass of the vehicle such as the chassis and the 
lower end of the cylinder is secured to an unsprung mass such as a wheel 
axle. 
The damping force adjusting mechanism make it possible to adjust the 
damping force of the damper such that the damping force is reduced when 
the vehicle is running on a smooth road, thereby improving driving 
comfort, and that the damping force is increased when the vehicle is 
running on a rough road condition, thereby preventing excessive vertical 
movement of the chassis and preventing the bottoming phenomenon. 
Typically, the damping force adjusting mechanism comprises a control rod 
extending rotatably through the piston rod, a by-pass passage for 
connecting the first and second chambers and by-passing the damping force 
generating valve or valves on the piston, and an adjusting valve or a 
shutter secured to the inner end of the control rod for adjusting the 
effective area of the by-pass passage in response to the rotation of the 
control rod. Further, a check valve is usually provided for changing the 
damping force between the contraction and extension strokes of the damper 
such that the damping force in the contraction stroke of the damper is 
about one half to one third (1/2-1/3) of the damping force in the 
extension stroke. 
When the adjusting valve is adjusted to increase the passage area of the 
by-pass passage, the damping force decreases both in the extension and 
contraction strokes, whereby the desired ratio between the damping forces 
in the contraction and extension strokes cannot be maintained, and the 
decrease in the damping force in the extension stroke deteriorates the 
stability of the driving characteristics. It has been experienced that 
when the damping force of the damper is too small or the characteristic of 
the damper is too soft and the vehicle is running at a high speed, it is 
difficult to control or maintain the direction of the vehicle. 
The check valve closes in the extension stroke and opens in the contraction 
stroke, and thereby reduces liquid flow in the by-pass passage in the 
extension stroke as compared with the contraction stroke. 
Various proposals have been made with respect to such hydraulic dampers, 
and in one such proposal it is not possible to change the damping force 
both in the extension and contraction strokes at desired multiple steps 
independently. 
One of the objects of the present invention is to provide a hydraulic 
damper wherein the damping force in the extension stroke and that in the 
contraction stroke can be set at a plurality of steps and independently 
from each other, whereby it is possible to obtain optimum damping force 
with respect to a particular running condition of the vehicle. 
Another object of the invention is to provide a hydraulic damper having a 
damping force adjusting mechanism which is simple in construction and 
compact in size, particularly in axial length. 
SUMMARY OF THE INVENTION 
The present invention provides a hydraulic damper of adjustable damping 
force type including a cylinder containing hydraulic liquid therein, a 
piston working in the cylinder and partitioning the interior thereof into 
two chambers, a piston rod secured to the piston and extending through one 
of the liquid chambers to the outside of the cylinder, a valve mechanism 
mounted on the piston for generating damping force both in extension and 
contraction strokes of the damper, and an adjusting mechanism provided 
independently from the valve mechanism and including a passage having a 
plurality of orifice openings having different effective areas, a shutter 
cooperating with the orifice openings for selectively opening and closing 
the orifice openings and being operable from the outside of the damper, 
and a check valve for controlling the liquid flow through the passage 
during either one of extension and contraction strokes of the damper. A 
tubular member is mounted on the inner end of the piston rod, a guide is 
fitted in the tubular member for rotatably receiving therein the shutter, 
and a control rod extends through the piston rod and is connected to the 
shutter. The orifice openings are formed in the guide, the check valve 
opens or closes in response to the direction of flow passing through the 
orifice opening(s), and a plurality of orifice passages having different 
passage areas are provided between the shutter and the guide and not 
passing through the check valve, such orifice passages being selectively 
opened and closed by the shutter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The hydraulic damper shown in FIG. 1 comprises a cylinder 1 containing 
therein hydraulic liquid, a piston 3 working in the cylinder 1 and 
partitioning the interior thereof into two liquid chambers A and B, and a 
piston rod 2 secured to the piston 3 and extending through one liquid 
chamber B and projecting to the outside through one end (not shown) of the 
cylinder 1. On opposite surfaces of the piston 3, there are provided disc 
valves 4 and 5 acting respectively as a damping force generating device of 
an extension side and a damping force generating device of a contraction 
side. When the piston 3 and the piston rod 2 move in the direction of 
arrow X or in an extending direction at a speed higher than a 
predetermined speed, the disc valve 4 deflects and generates a damping 
force. Similarly the disc valve 5 acts to generate a damping force in the 
contraction stroke, i.e. during movement in the direction of arrow Y. 
A tubular member 6 is threadingly secured to the piston rod to act as a nut 
fixing the piston 3 and the disc valves 4 and 5 on the piston rod 2. A 
space 7 is defined in the tubular member 6 for receiving therein a damping 
force adjusting mechanism according to the invention. A closure plate 8 is 
secured to the tip end of the tubular member 6 to close the space 7. A 
guide 11 consisting of a passage forming portion 9 and a valve forming 
portion 10 is fitted and secured to the inner circumferential wall of the 
tubular member 6 by force fitting or the like process. A shutter 12 is 
rotatably fitted in the guide 11. A control rod 13 is secured to the 
shutter 12 and extends through a coaxial bore 14 in the piston rod 2, with 
the outer end (not shown) of the rod 13 being located outside of the 
piston rod and being connected to a driving device (not shown) such as an 
electric motor or a solenoid. 
An annular liquid chamber 15 is formed between the inner circumference of 
the tubular member 6 and the passage forming portion 9 of the guide 11, 
and the liquid chamber 15 is permanently communicated through a plurality 
of openings 16 in the tubular member 6 with the liquid chamber A. As shown 
in FIG. 2, there are provided four orifice passages 17, 18, 19 and 20 
having different passage areas respectively in the passage forming portion 
9 of the guide 11. One end of each orifice passage opens permanently to 
the liquid chamber 15 and the other end thereof opens to the surface 
engaging with the shutter 12. As shown in FIG. 3, a groove 21 is formed in 
the outer circumference of the shutter 12 which, as will be described 
hereinafter, selectively opens and closes the orifice passages 17 and 18 
upon rotation of the shutter 12, thereby communicating the liquid in the 
liquid chamber A with a liquid chamber 22 which is defined in the inner 
space of the shutter 12. A plurality of openings 23 are formed in a 
radially extending wall of the generally cup-shaped shutter 12 and, the 
openings 23 are communicated with a plurality of openings 24 formed in the 
valve forming portion 10 of the guide 11 through an annular space defined 
between the inner surface of the valve forming portion 10 and adjacent 
surface of the radial wall of the shutter 12. A check valve 26 is provided 
to cooperate with the openings 24 for permitting liquid flow from the 
openings 24 to a liquid chamber 25 which is formed between the valve 
forming portion 10 of the guide 11 and the inner surface of the tubular 
member 6 and preventing liquid flow in the opposite direction. A spring 27 
normally presses the check valve 26 toward the closed condition. The 
liquid chamber 25 is permanently communicated with the liquid chamber B 
through the coaxial bore 14 and a radial hole 28 in the piston rod 2. 
The shutter 12 further has a passage 29 which is defined by an axially 
extending groove formed in the outer circumference of the shutter 12 and, 
as will be described hereinafter, the passage 29 is selectively 
communicated with orifice passages 19 and 20 upon rotation of the shutter 
12. The passage 29 is permanently communicated with the liquid chamber 25 
in the tubular member 6 through a passage 30 connecting the outer and 
inner surfaces of the guide 11. 
The damping force adjusting mechanism according to the invention and having 
the aforesaid constitution comprises a first passage consisting of 
openings 16, the liquid chamber 15, the orifice passage 17 or 18, the 
groove 21, the openings 23, the openings 24, the check valve 26, the 
liquid chamber 25, the bore 14 and the radial hole 28 between the liquid 
chambers A and B passing through the check valve 26 and, a second passage 
consisting of openings 16, the liquid chamber 15, orifice passage 19 or 
20, the passage 29, the passage 30, the liquid chamber 25 and the radial 
hole 28 between the liquid chambers A and B. The effective passage area of 
the first passage is defined by the orifice passage 17 or 18 and the 
effective area of the second passage which by-passes the check valve is 
defined by the orifice passage 19 or 20. The orifice passages 17 and 19 
respectively have passage areas larger than the orifice passages 18 and 
20. The orifice passages 17 and 18 are respectively located at angular 
positions separated by 180 degrees from orifice passages 19 and 20. When 
the shutter 12 is located at position (a) in FIG. 2 with a line connecting 
the groove 21 and the passage 29 being on the line (a), the orifice 
passages 17, 18, 19 and 20 are closed by the shutter 12 and the adjusting 
mechanism takes a fully closed position. When the shutter 12 rotates by 60 
degrees from the position (a) to position (b), the groove 21 and the 
passage 29 of the shutter 12 are located as shown in FIG. 2 and the first 
passage passing through the check valve opens with the passage area being 
defined by the orifice passage 18 and the second passage not passing 
through the check valve opens with the passage area being defined by the 
orifice passage 20, and the adjusting mechanism is in a small area 
position. When the shutter 12 is further rotated by 60 degrees to position 
(c), the first passage passing through the check valve opens with the 
passage area being defined by orifice passage 17 and the second passage 
not passing through the check valve opens with the passage area being 
defined by the orifice passage 19. The adjusting mechanism than is in a 
large area position. 
FIG. 4 shows a modified form wherein orifice passages 17', 18', 19' and 20' 
are formed in the passage forming portion 9 of the guide 11 as shown in 
the drawing. The angles of rotation of the shutter 12 between the fully 
closed position (a') and the small area position (b') and between the 
small area position (b') and the large area position (c') are 120 degrees 
respectively. 
The operation of the first embodiment of the invention will now be 
explained with reference to FIG. 5 to FIG. 7. 
When the shutter 12 is located at small area position (b) in FIG. 2 and the 
piston rod 2 moves in the extending direction or the direction X in FIG. 
1, the pressure in the liquid chamber B increases and the liquid in the 
chamber B flows into the liquid chamber 25 through the radial hole 28 and 
the bore 14. The check valve 26 is maintained in the closed condition and 
the first passage passing through the check valve is maintained closed. 
The liquid in the liquid chamber 25 flows into the liquid chamber A as 
shown by arrow F.sub.1 in FIG. 5, sequentially from the passage 30, 
passage 29, the orifice passage 20, the chamber 15 and openings 16, and 
the orifice passage 20 generates a predetermined damping force. It will be 
understood that when the speed of the piston rod 2 or the piston 3 exceeds 
a predetermined level, the disc valve 4 mounted on the piston 3 opens and, 
a large amount of liquid passes through the disc valve 4, thus, the 
damping force at that condition is mainly defined by the disc valve 4. 
When the piston rod 2 and the piston 3 moves in the direction of arrow Y in 
FIG. 1 or in the contracting direction, the liquid in the chamber A flows 
into the chamber B through the first passage passing through the check 
valve as shown by arrow F.sub.3 in FIG. 6 and also through the second 
passage not passing through the check valve as shown by arrow F.sub.2 in 
FIG. 6. The orifice passages 18 and 20 act to generate damping force. When 
the speed of the piston 3 exceeds a predetermined level, the disc valve 5 
mounted on the piston 3 opens and, thereafter, the damping force is mainly 
determined by the characteristic of the disc valve 5. 
When the shutter 12 takes the large area position (c), the damping force in 
the extension stroke is generated by the orifice passage 19 and the 
damping force in the contraction stroke is generated by the orifice 
passage 19 and the orifice passage 17. The damping force characteristic 
curves in the extension and contraction strokes are more gradient as 
compared respectively with those of the small area position (b). 
When the shutter 12 takes the fully closed position (a) the first and 
second passages are maintained at closed condition and the damping forces 
in the extension and contraction strokes are defined by the valve 
mechanisms 4 and 5 on the piston 3 as shown by chain lines in FIG. 7. 
The solid lines in FIG. 7 depict the damping force characteristic curves at 
the small area position (b) of the adjusting mechanism, and the broken 
lines depict those at the large area position (c). As shown in FIG. 7, the 
characteristic curves both in the extension and contraction strokes change 
distinctively in three steps. By suitably determing the number, the 
location and passage area of the orifice passages, it is possible to 
adjust optimumly the damping force characteristics in response to the 
running condition of the vehicle, thereby improving driving comfort and 
improving steering characteristics. 
FIGS. 8-11 show a second embodiment of the invention which is generally 
similar to the first embodiment of FIG. 1, and corresponding parts are 
depicted by the same reference numerals and detailed description thereof 
is omitted. 
In FIG. 8, a guide 41 having an integral passage forming portion and a 
valve forming portion is forcibly fitted in the tubular member 6. It will 
be understood that the guide 11 in FIG. 1 also can include an integral 
passage forming portion 9 and the valve forming portion 10 but, 
practically, a tubular passage forming portion 9 and a plate like valve 
forming portion 10 are abuttingly disposed in the tubular member 6, and 
this complicates the manufacturing and assembling operations. A shutter 42 
in FIG. 8 has a pair of axially extending and diametrically opposed slits 
or grooves 43A and 43B in the circumferential wall thereof. The guide 41 
has three sets of orifice passages 44A, 44B; 45A, 45B and 46A, 46B having 
passage areas different from each other, and each set of orifice passages 
is selectively communicated with the liquid chamber 22 within the shutter 
42 upon rotation thereof. The guide 41 further has two orifice passages 47 
and 48 at a location axially spaced from the aforesaid three sets of 
orifice passages. First ends of orifice passages 47 and 48 open 
permanently to the liquid chamber 25 through axially extending grooves or 
passages 49 and 50 formed in the outer circumference of the guide 41. The 
other ends of orifice passages 47 and 48 open selectively to the chamber 
22 through the slit 43A or 43B upon rotation of the shutter 42. 
An opening 51 is formed in the guide 41 to surround the control rod 13 and 
a valve seat 52 is formed on the outer circumference of the opening 51. A 
check valve 53 cooperating with the valve seat 52 is slidably fitted on 
the control rod 13. In the embodiment of FIG. 8, both of the first passage 
passing through the check valve and the second passage not passing through 
the check valve pass through the liquid chamber 22, and thus the second 
passage passes through the orifice passage 47 or 48 and the orifice 
passage 49 or 50. 
By rotating the shutter 42, it is possible to change the damping force 
characteristics by three steps as shown in FIG. 11. Namely, when the 
orifice passages 44A and 44B and the orifice passage 47 are opened (large 
area condition) the damper takes a low damping force condition as depicted 
in broken lines by FIG. 11, and when the orifice passages 45A and 45B and 
orifice passage 48 are opened (small area condition) the damper takes a 
medium damping force condition as shown by solid lines in FIG. 11. When 
the orifice passages 46A and 46B are opened, the damper takes a high 
damping force condition as shown in chain lines by FIG. 11. 
The orifice passages 44A, 44B, 45A, 45B, 46A and 46B controlling the 
passage area of the first passage passing through the check valve are 
formed axially separated from the orifice passages 47 and 48, thus, the 
number, the angular or circumferential location and the passage area can 
be determined freely and independently. 
It will be understood that FIGS. 1 and 8 show the essential portion of the 
damper which may be of the dual tube type or single tube type, and the 
damping force generating valve mechanisms 4 and 5 mounted on the piston 3 
may be replaced by any desired publicly known valve mechanism or valve 
mechanisms. Further, it has been described that the damping force in the 
extension stroke is larger than that in the contraction stroke, but, it is 
possible to provide that the damping force in the contraction stroke is 
larger than that in the extension stroke, in which case the check valve is 
arranged in the reverse direction. The damping force in both embodiments 
changes at three steps, but it is possible to adjust the damping force at 
four or more steps. Further, the shutter 12 shown in FIG. 1 may be 
modified as shown in FIG. 12 wherein axial extension of the groove 29 
shown in FIG. 3 is reduced as shown at groove 29' in FIG. 12. 
As described heretofore, according to the invention, it is possible to 
adjust the damping force in the extension and contraction strokes of the 
damper at a plurality of steps in response to the running conditions of 
the vehicle thereby improving the driving feel and maintaining good 
stability of directional control of the vehicle. Further, adjusting 
mechanism is simple in the construction and is compact in size.