GB2221011A

GB2221011A - Hydraulic damper

Info

Publication number: GB2221011A
Application number: GB8912675A
Authority: GB
Inventors: Keiichi Shimizu; Hideaki Ando; Yoshiji Yamada
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1988-06-03
Filing date: 1989-06-02
Publication date: 1990-01-24
Anticipated expiration: 2009-06-02
Also published as: GB2221011B; DE3918080A1; FR2632371A1; FR2632371B1; GB8912675D0

Description

- 1 HYDRAULIC DAMPER W ?5 n r) n 1 41- /1011

The field of the present invention is hydraulic dampers mounted on a suspension system in an automobile to provide a damping force to the operation of the suspension system, and more particularly, an improvement in a hydraulic damper comprising at least two oil chambers, a partition member for partitioning the two oil chambers and having a flow path which permits the communication between the oil chambers, and a damping valve provided in the partition member to control the oil flow produced in the flow path.

Incidentally, the term "oil" is used herein to mean any kind of fluid material appropriate for use with a dr.

There is such a conventionally known hydraulic damper comprising a cylinder internally filled with an oil, a piston serving as a partition member which divides the interior of the cylinder into an upper and a lower oil chamber and has a flow path permitting the communication between the oil chambers, and a damping valve provided in the piston to control the oil flow produced between the upper and lower oil chambers through the flow path during upward or downward movement of the piston (for example, see Japanese Patent Application Laid-open No.117169/78).

In this case, the damping valve used is one including a valve seat which is formed in the piston and to which the flow path is opened, the piston being provided with a resilient valve plate which opens and closes the flow path in cooperation with the valve seat, and an opening degree 2 regulating member for regulating the degree of opening of the valve plate.

In the conventional hydraulic damper, the restricting portion of the flow path defined between the valve plate and the valve seat is constant in a condition of the degree of opening of the valve plate being regulated by the opening degree regulating member and hence, the damping force obtained thereby is unconditionally determined by the velocity of the piston. If a desired damping force is obtained depending upon the velocity of the piston, the range of applications of the damper is advantageously widened.

According to the present invention there is provided a hydraulic damper comprising at least two oil chambers, a partition member for partitioning the two oil chambers and having a flow path which permits communication between the oil chambers, and a damping valve provided in the partition member to control an oil flow produced in the flow path, wherein said damping valve cises a resilient valve plate supported on said partition member so as to be normally maintained in a neutral position and,.

when a difference in pressure is developed between said two oil chambers, to flex at a free end thereof from the neutral position toward a lower pressure side, and a control wall formed on said partition member in opposition to said free end of the valve plate to define a restricting or throttling portion of said flow path between the control wall and the free end of said valve plate.

With the above construction, the restricting or throttling portion of the flow path can be controlled to a desired opening degree corresponding to a difference in pressure between the two oil chambers by formation of the control wall into any arbitrary shape,. thereby freely providing any damping force characteristic. This easily accommdates various demands for the damping force characteristic.

Moreover, a single damping valve enables a contraction damping force and an expansion damping force to be generated. This makes it possible to reduce the number of parts to one half, leading to a large contribution to a reduction in cost. Whenever the contraction and expansion of the damper are rapidly repeated, the restricting portion of the flow path is controlled from the state in the neutral position by the resilient valve plate and thus, a stable damping performance is obtained at all times.

In addition to the above construction, if the supporting lengths of a pair of support members supporting the resilient valve plate on the opposite sides are different from each other, the flexing loads on the resilient valve plate are differentiated in the opposite directions, so that the damping force characteristic during contraction and expansion of the hydraulic damper can be varied.

Alternatively, if the control wall is formed of a flat top portion opposed to the free end of the resilient valve plate which is in the neutral position, and inclined portions lying on the opposite sides of the top portion and connected to the top portion, with angles of inclination of the inclined portions being different from each other, the above-described damping force characteristic can be likewise varied.

In addition to the above construction, if a plurality of resilient valve plates each having a plurality of notches opened in its outer peripheral edge are put one on another so that the two oil chambers cannot communicate with each other through the notches, each of the resilient valve plates can be flexed without being distorted. The flexing characteristic is satisfactory and therefore, it.is possible to provide a damping force which is always stable.

Further, if means is provided for adjusting the relative position between the resilient valve plate and the control wall, it is possible to vary the characteristic of opening degree of the restricting portion with respect to the displaced amount of the free end of the valve plate and hence, the damping force characteristic can be adjusted.

Yet further, if the resilient valve plate and a portion of the control wall which define the restricting portion are integrally formed, the restricting portion can be always maintained to a proper size without reception of an influence of assmebly error during mounting of the damping valve on the damper. This can largely contribute to stabilizing the damping force characteristic.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig.1 is a side view in longitudinal section of - 5 relevant portion of a hydraulic damper for an automobile according to a first embodiment of the present invention; Fig.2 is an enlarged view of portions in and around a damping valve shown in Fig.1; Figs.3(a) and (b) to Figs.7(a) and (b) are longitudinal sectional views illustrating modifications to the damping valve and graphs illustrating their damping force characteristics; Fig.8 is a longitudinal sectional view similar to Fig.2, but illustrating a second embodiment of the present invention; Fig.9 is a longitudinal sectional view substantially similar to Fig.2, but illustrating a third embodiment of the present invention; Fig.10 is a longitudinal sectional view similar to Fig.2, but illustrating a fourth embodiment of the present invention; Fig.11 is a sectional view takn along a line XI-XI in Fig.10; Fig.12 is an exploded perspective view of a resilient valve plate; Fig.13 is a longitudinal sectional view similar to Fig.2, but illustrating a fifth embodiment of the present invention; Fig.14 is a pgrspective view of a single circular leaf spring material used for forming a valve plate and the like; Fig.15 is a side view in longitudinal section of a relevant portion of a hydraulic damper for an automobile according to a sixth embodiment of the present invention; 0 Fig.16 is an enlarged view of a portion indicated by an arrow XVI in Fig.15; Fig.17 is a longitudinal sectional view similar to Fig.9, but- illustrat ing a seventh embodiment of the present invention; and Fig.18 is a longitudinal sectional view similar to Fig.9, but illustrat ing an eighth entodizent of the present invention.

Several eiments of the present invention will now be described with zeference to the accnying drawings, wherein the corresponding portions are designated by the same reference numerals and characters throughout the embodinents.

First, description will be made of a first eiwent of the present invention shown in Figs.1 and 2. Referring to Fig.1, a hydraulic dr 1 conprises an outer casing 2, a cylinder 3 contained in and concentrically secured to the outer casing 2 and internally filled with an oil, and a piston which is connected to a piston rod 4 projecting upward through the outer casing 2 and which is slidably received in the cylinder 3. The piston 5 divides the interior of the cylinder 3 into two upper and lower oil chaniDers 6 and 7, and the outer casing 2 and the cylinder 3 define an oil reservoir 8 therebetween. Air or an inert gas is confined at a predetermined pressure in a space above an oil level within the oil reservoir 8.

The piston 5 is provided with a flow path 16 permitting the cormunication between the upper and lower oil chrs, and with a danping valve 9 for con trolling the flowing of the oil through the flow path 16 between the oil chambers 6 and 7 to generate a.damping force.

A partitioning member 17 securely clamped between the cylinder 3 and a bottom wall of the outer casing 2 is provided with an orifice 10 which controls the flowing of i the oil between the lower oi-l chamber 7 and the oil reservoir 8 to generate a damping force, particularly during mediumand high-speed expansion and contraction of the damper 1.

An upper mounting member 11 for mounting on a vehicle body is secured to an upper end of the piston rod 4, and a lower mounting member 12 for mounting on a wheel-supporting arm Is secured to a lower end of the outer casing 2. A coiled suspension spring 15 is provided in compression between an upper spring seat formed on a lower surface of the upper mounting member 11 and a lower spring seat 14 fixedly mounted on an outer periphery of the outer casing 2.

The flow path 16 and the damping valve 9 will be described below with reference to Fig.2.

The piston 5 is cup-shaped with an end wall 5a having a plurality of through holes 20 being faced upward, and the flow path 16 is formed by a hollow portion 21 of the piston 5 and the through holes 20., Contained in the hollow portion 21 of the piston 5 are, in sequence from the above, an upper spacing tube 22, an upper circular support plate 24, a plurality of circular valve plates 26, a lower circular support plate 25 and a lower spacing tube 23, and these components, together with the end wall 5a of the piston 5, are centrally penetrated,by a smaller diameter end portion 4a of the piston rod 4 and are secured to the piston rod 4 by a nut 27 threadedly engaged on the smaller diameter end portion 4a. The valve plate 26 is made of a leaf spring material and has a diameter larger than those of the upper and lower support 8 is plates 24 and 25. The upper support plate 24 is formed to have a diameter smaller than that of the lower support plate 25. That Ist the length of the support plate 24 for supporting the valve plate 26 is set shorter than that of the lower support plate 25.

On the other hand, an inner peripheral surface of the piston 5 is formed with an annular control wall 28 which defines a restricting or throttling portion 16a of the flow path 16 between the wh11 and an outer peripheral end, i.e., free end of the valve plate 26 opposed to the wall.

The control wall 28 is formed of a flat top portion a and inclined portions b and c connected respectively to opposite sides of the top portion a so as to have an angle section. The top portion a serves to minimize the degree of opening of the throttling or restricting portion 16a in opposition to the outer peripheral end of the valve plate 26 assuming a neutral position in a free state.

The operation of this embodiment will be described below.

When an axial compression load is applied to the damper 1 to cause the piston 5 to move downward within the cylinder 3, the oil In the lower oil chamber 7 Is passed through the flow path 16 into the upper oil chamber 6, wherein the flow of oil Is throttled or restricted in the throttling or restricting portion 16a, which is minimum in degree of opening at the beginning, between the valve plate 26 and the control wall 28, so that the hydraulic pressure in the lower oil chamber is raised to generate'a damping 9 - f orce.

The hydraulic pressure developed in the lower oil chamber 7 in this manner acts on a lower surface of the valve plate 26 and hence, when that hydraulic pressure is raised in excess of a predetermined value, the valve plate 26 is flexed upwardly about a peripheral edge of the upper support plate 24, so that the free end, i.e., outer peripheral end thereof is displaced upwardly describing an arc as shown in a broken line in Fig.3(a). When the free end of the valve plate 26 thus becomes opposed to the inclined portion b of the control wall 28, the degree of opening of the restricting portion 16a is increased. Therefore, the rate of increase in generated damping force decreases with the increase in downward speed of the piston 5, as shown in Fig.3(b).

Then, when the compression load is removed, the damper 1 is expanded by a repulsive force of the suspension spring 15. In this case, when the difference in pressure between the oil chambers 6 and 7 has disappeared before starting of such expansion, the valve plate 26 immediately returns to the original free state by Its own resilience to assume a neutral position, thereby again minimizing the degree of opening of the restricting portion 16a. Therefore, when the expansion of the damper 1, i. e., the upward movement of the piston 5 is started, the oil flow, as the oil is passed from the upper oil chamber 6 into the lower oil chamber 7, is restricted by the restricting portion 16a as during the contraction of the damper 1, so that the hydraulic pressure in the upper oil chamber 6 is raised, thereby ensuring that a damping force is reliably generated.

The hydraulic pressure in the upper oil chamber 6 acts on an upper surface of the valve plate 26 and hence, when such hydraulic pressure is increased in excess of a predetermined value, the valve plate 26 is flexed downwardly about a peripheral edge of the lower support plate 25. With the increase in amount of valve plate flexed, in other words, with the increase in upward movement of the piston 5, the degree of opening of the restricting portion 16a increases, and the rate of increase in damping force correspondingly decreases.

It should be noted that because the amount of valve plate 26 projecting from the lower support plate 25 is smaller than from the upper support plate 24 due to setting of the size of the upper and lower support plates 24 and 25 as described above, the load flexing the v alve plate 26 downwardly is larger than the upwardly flexing load and hence, the damping force provided at this time is larger than that provided during contraction of the damper 1.

On the other hand, the flowing of the oil is permitted between the lower oil chamber 7 and the oil reservoir 8 through the orifice 10 in accordance with a variation in that volume of the piston rod 4 which occupies the inside of the cylinder 3 due to upward and downward movement of the piston 5, and when the flow velocity exceeds a predetermined value, the damping force is generated by the resistance of the orifice 10.

Any of Figs.4(a), 5(a), 6(a) and 7(a) illustrate modifications to the control wall 28, and Figs.4(b), 5(b), 6(b) and 7M illustrate damping characteristics associated with the modifications.

M attention should particularly be paid to the structure that the angle d, of the upper inclined portion b is set larger than the angle P of the lower inclined portion c in the control wall 28 having the angle section shown in Fig.7(a).

In doing so, when the valve plate 26 is flexed upwardly, the extent of increase in degree of opening of the restricting portion 16a is larger than when the valve plate 26 is flexed downwardly, and therefore, the damping force provided during contraction of the damper 1 can be more weakened than that provided during expansion.

Pig.8 illustrates a second embodiment of the present invention, and only arrangements different from those in the first embodiment will be described below.

An adjusting plate 30 as adjusting means is interposed between the upper spacing tube 22 and the upper support plate 24, and a single or a plurality of (two, in the illustrated embodiment) first auxiliary plate(s) 31,, 31 2 having a resilience as sub valve plate(s) is or are also interposed between the upper support plate 24 and a single valve plate 26 as a main valve plate.

Further, a single or a plurality of (two, In the illustrated embodiment) second auxiliary plate(s) 32,, 32 2 having a resilience as sub valve plate(s) is or are interposed between the valve plate 26 and the lower support plate 25.

Here, the first auxiliary plate 311. 31 2 is formed with a diameter smaller than that of the valve plate 26 and 0 larger than that of the upper support plate 24, and the diameter of the upper auxiliary plate 31 2 Is smaller than that of the lower auxiliary plate 31 1 The second auxiliary plate 321, 32 2 Is formed with a diameter smaller than that of the valve plate 26 and larger than that of the lower support plate 25, and mreover the diareter of the lower auxiliary plate 32 2 is smaller than that of the upper auxiliary plate 32 1 Further, the diameters of the first and second auxiliary plates 311. 31 2 and 32,.. 32 2 are different froM each other, and in the illustrated embodiment, the diameter of the first auxiliary plate 311. 31 2 is smaller than that of the corresponding second auxiliary plate 321.. 32 2 The control wall 28 opposed to the outer peripheral end of the valve plate 26 has a profile similar to that shown in Fig.7(a).

Other arrangements are similar to those in the previous embodiment.

According to this embodiment, when the valve plate 26 is flexed upwardly or downwardly by a difference in pressure between the oil chambers 6 and 7, the first auxiliary plates 31 1 and.31 2 or the second auxiliary plates 32 1 " and 32 2 are also flexed, wherein the load flexing the valve plate 26 upwardly is smaller than the downwardly flexing load, because the diameter of the first auxiliary plate 31,, 31 2 is smaller than that of the corresponding second auxiliary plate 321. 32 2 Consequently, it is possible for the damper 1 to exhibit a larger damping force during expansion than during contraction.

13 - In addition, if the adjusting plate 30 is replaced by one having a different thickness, it is possible to freely adjust the axially relative position of the valve plate 26 to the control wall 28, thereby adjusting the damping force characteristic. It should be noted that even a replacement of the upper spacing tube 22 by one having a different axial length enables a similar effect to be obtained.

Fig.9 illustrates a third embodiment of the present invention, which is of a construction similar to that in the second embodiment, except that interposed between the valve plate 26 as the main valve plate and the first and second auxiliary plates 31 1 and 32 1 as sub valve plates adjacent the valve plate 26 are extremely thin spacer plates s and s having a diameter smaller than those of the auxiliary plates 31 1 and 32 1 In this figure, the portions corresponding to those in the previous second embodiment are designated by the same reference numerals and characters.

According to this embodiment, in a free state of the the valve plate 26, very small clearances are produced radially outside the spacers s and s between the valve plate 26 and the first and second auxiliary plates 31 1 and 32 1 and hence, when the valve plate 26 is flexed along with the first auxiliary plate 311, 31 2 or the second auxiliary plate 321 32 2 toa lower pressure side due to a difference ii pressure between the oil chambers 6 and 7, it can be reliably peeled off from the second auxiliary plate 32 1 or the first auxiliary plate 31 1 on a higher pressure side. This leads to stabilizing of the damping force characteristic, because the auxiliary plate on the higher pressure side exerts no influence on the flexing rigidity of the valve plate 26 from the beginning of flexing of the valve plate 26.

Figs.10 to 12 illustrate a fourth embodiment of the present invention, and only arrangements different from those in the previous embodiments will be described below.

A damping valve 9 has a valve plate 126 which is clamped on a smaller diameter end 4a of a piston rod 4 by an upper support plate 24and a lower support plate 25 having a diameter larger than that of the plate 24. The valve plate 126 is comprised of a plurality of (two, in the illustrated embodiment) annular resilient leaf spring plates 142 put one on another and each having a plurality of slit-like notches 141 opened in its outer peripheral edge. The resilient plates 142 are disposed with their respective notches 141 misaligned circumferentially. In order to provide such a disposition, a flat surface 143 formed on one side of the smaller diameter end portion 4a of the piston rod 4 is engaged with a flat surface 145 formed on one side of a central bore 144 in each of the resilient plates 142.

In this embodiment, when a difference in pressure is developed between the oil chambers 6 and 7, the valve plate 126 is flexed upwardly or downwardly. In this case, the plurality of resilient plates 142 forming the valve plate 126 are flexed with their respective notches 141 being gradually narrowed and hence, no strain is produced in each of the resilient plates 142. Moreover, the pressure cannot be escaped through the notches 141, because the respective notches 141 of the resilient plates 142 are misaligned from one another without communication with one another.

Figs.13 and 14 illustrate a fifth embodiment of the present invention.

With this embodiment, a damping valve 9 provided in a hollow portion of a piston 5 includes a valve plate 226 which is formed with a diameter larger than those of upper and lower support plates 24 and 25.

An inner peripheral surface of the piston 5 is provided with a control wall 228 which opposes an outer peripheral end of the valve plate 226 to define therebetween a restricting portion 16a of a flow path 16.

Unlike the previously-described embodiments, the control wall 28 is comprised of a first annular angle portion 229 integrally formed on the inner peripheral surface of the piston 5, a second annular angle portion 230 formed on an annular member 231 threadely engaged with the inner peripheral surface of the piston 5, and a ring member 232 securely clamped between both the angle portions 229 and 230. Tops of the angle portions 229 and 230 and an inner peripheral surface of the ring member 232 are formed into a substantially continuous flat-surface.

As shown in Fig.14, the valve plate 226 and the ring member 232 are rade of a single circular leaf spring material 209.

More specifically, a mounting hole 233 is made in a central portion of the single circular leaf spring material 209, so that the smaller diameter end 4a of the piston rod 4 is passed through the hole 233. A plurality of arcuate slits 234 corresponding to the restricting portion 16a are also cut in an outer periphery of the leaf spring material 209 in such a manner that they are arranged on a circumferential line concentric with the mounting hole 233. Further, rectilinear slits'235 are cut in an intermediate portion of the leaf spring-material 209 to extend diametrically from opposite ends of each circular slit 234 to near the mounting hole 233.

Thus, the valve plate 226 is comprised of a boss portion 236 having the munting hole 233, and a plurality of farr-shaped valve pieces 237 each surrounded by the arcuate slit 234 and the rectilinear slits 235, and the boss portion 236 is secured to the smaller diameter end 4a of the piston rod 4.

In addition, the ring member 232 is formed by an annular portion located outside the arcuate slits 234, i.e., a portion forming a portion of the control wall 228, and the ring member 232 and the boss portion 236 are integrally connected to each other by a plurality of connecting pieces 238 each extending radially between the adjacent valve pieces 237.

Because the valve plate 226 and the ring member 232 are made from a single leaf spring material and moreover, the boss portion 236 of the valve plate 226 and the ring member 232 are-integrally interconnected through the connecting pieces 238 in this manner, the relative positional relationship between the valve plate 226 and the ring member 232 is always constant before and after mounting and therefore, the restricting portion 16a defined by the arcuate slits 234 between the valve plate 226 and the ring member 232 is not influenced at all by an assembly error produced upon mounting of the damping valve 9 and always maintains a proper size, thereby enabling the damping force characteristic to be stabilized.

While description has been made of the embodiments with the damping valve provided in the piston, a damping valve may be provided, in place of the orifice, in the partition member interposed between the lower oil chamber 7 and the oil reservoir 8.

A sixth embodiment shown in Figs.15 and 16 is such one example, wherein two damping valves are provided: one being in a piston 5 which partitions upper and lower oil chambers 6 and 7; and the other being between the lower oil chamber 7 and the oil reservoir 8.

The damping valve 9 provided in the piston 5 may be of any of the constructions in the previously-described first to fifth embodiments, and the description thereof is omitted.

In a partition member 312 clamped between the lower end of the cylinder 3 and the bottom wall of the outer casing 2, there are a flow path 313 permitting the communication between the lower oil chamber 7 and the oil reservoir 8, and a damping valve 314 which controls the oil flowing between the lower oil chamber 7 and the oil reservoir 8 through the flow path 313 during contraction and expansion of the danper 1 to generate a damping force.

The flow path 313 and the damping valve 314 provided in the partition member 312 will be described below with reference to Fig.16.

The partition member 312 comprises a cylindrical portion 312a received in the cylinder 3, and a flange 312b formed around an outer periphery of a lower end of the cylindrical portion 312a and securely clamped between the lower end of the cylinder 3 and the bottom wall of the outer casing 2. The cylindrical portion 312a is provided with an upper chamber 320 opened at its upper surface, and a lower chamber 321 opened at its lower surface. A plurality of through holes 323 are made in a partition wall 322 partitioning the chambers 320 and 321 and permit the communication between the chambers. A plurality of notches 324 are also provided in a lower surface of the flange 312b to permit the communication between the lower chamber 321 and the oil reservoir 8. The flow path 313 is formed by the upper chamber 320, the lower chamber 321, the through holes 323 and the notches 324.

Contained in the upper chamber 320 are, in sequence from the below, a lower spacing tube 325, a lower circular support plate 326, a single auxiliary plate 328 as a sub valve plate, a circular valve plate 327 as a main valve plate, an upper'Circular support plate 329, and an upper spacing tube 330. These components are fixed on the partition wall 322 by a bolt 331 stood on the partition wall 322 and a nut 332 threadedly engaged with an upper end of the bolt 331.

Either of the main and sub valve plates 327 and 328 are made of a leaf spring material, wherein the lower sub valve plate 328 is formed to have a diameter smaller than that of 19 - the upper main valve plate 327. The lower support plate 326 is formed to have a diameter smaller than that of the sub valve plate 328 and further, the upper support plate 329 i 0 0 formed with a diameter smaller than that of the lower support plate 326. In other words, the supporting length of the upper support plate 329 for the main valve plate 327 is set shorter than the supporting length of the lower support plate 326 for the sub valve plate 328.

On the other hand, an inner peripheral surface of the upper chamber 320 is formed with an annular projection 333 (control wall) which defines aretricting portion 313a of the flow path 313 in an opposed relation to an outer peripheral end of the main valve plate 327. The projection 333 has a vertically central portion formed into a flat top portion a', and vertically opposite side portions formed into inclined portions bl and c'. The top portion a' serves to minimize the degree of opening of the restricting portion 323a in opposition to the main valve plate 327 occupying a neutral position in a tree state. The inclined portion bl has an angle of inclination set larger than that of the inclined portion c'.

The operation of this embodiment will be d:escribed below.

When an axial compression or expansion load is applied to the damper 1, causing the piston 5 to move upwardly or downwardly within the cylinder 3, flowing of an oil occurs between the upper and lower oil chambers 6 and 7 via the flow path 16 in the piston 5. In this case, the oil flow is controlled in the flow path 16 by the damping valve 9, so that the oil pressure in the lower or upper oil chamber 7 or 6 is raised, and as a result, a contraction or expansion damping force is generated.

During downward movement of the piston 5, the oil of an amount corresponding to the volume of piston rod 4 entering the cylinder 3 is passed from the lower-oil chamber 7 via the flow path 313 in the partition member 312 into the oil reservoir S. In this case, the oil flow is restricted or throttled at the restricting portion 313a between the main valve plate 327 and the projection 333, which has been of a minimal degree of opening at the beginning. This also causes the oil pressure in the lower oil chamber to be raised to generate a contraction damping force.

The oil pressure developed in the lower oil chamber 7 acts on the upper surface of the main valve plate 327, and when such oil pressure is raised in excess of a given value, the main valve plate 327 is flexed downwardly along with the sub valve plate 328 about the peripheral edge of the lower support plate 326. With the increase in amount of flexure, the degree of opening of the restricting portion 313a increases, and correspondingly, the degree of increase in contraction damping force is controlled.

During upward movement of the piston 5, the oil of an amount corresponding to the volume of piston rod 4 protruding out of the cylinder 3 is returned from the oil reservoir 8 via the flow path 313 into the lower oil chamber 7. In this case, as soon as the difference in pressure between the oil reservoir 8 and the lower oil chamber 7 has become zero before starting of upward movement of the piston L 0 W !5 5, the main valve plate 327 is returned along with the sub valve plate 328 to its original free state to occupy a neutral position shown, thereby again minimizing the degree of opening of the retriction portion 313a. Therefore, upon starting of upward movement of the piston, the oil flow is restricted in the restricting portion 313a as with the downward movement of the piston 5 when the oil is returned from the oil reservoir 8 into the lower oil chamber 7, so that the reduction in pressure in the lower oil chamber 7 advances to ensure generation of an expansion damping force.

When the pressure in the lower oil chamber 7 is reduced to less than a predetermined value, only the main valve plate 327 is flexed upwardly not with the sub valve plate 328 about the peripheral edge of the upper support plate 326. With the increase in amount of flexure, the degree of opening of the restricting portion 313a increases and correspondingly, the degree of increase in expansion damping force is controlled.

Now, owing to the dimensions of the upper and lower support plates 329 and 326 set in the above manner, the main valve plate 327 protrudes in a larger- amount from the upper support plate 329 than that protruding from the lower support plate 326 and moreover, protrudes more outwardly than does the sub valve plate 328, so that it can be flexed upwardly alone. Accordingly, the load of flexing of the main valve plate 327 upwardly alone is smaller than the load of flexing of the rain valve plate 327 along with the sub valve plate 328 downwardly and thus, the damping force obtained is during upward movement of the piston 5 is far smaller than that obtained during downward movement of the piston 5.

Figs. 17 and 18 show seventh and eighth embodiments according to the present invention and these embodiments differ from the afore-rentioned third embodiment in that other means are used for facilitating flexure of a resilient valve plate toward a lower pressure side in place of the spacer of the third embodiment.

In case of the seventh embodiment shown in Fig. 17, in place of the spacer s, flexible, porous plates 435 are interposed between a valve plate 26 and first and second auxiliary plates 31 1 and 31 2' respectively.

Each porous plate 435 is made of a rubber or synthetic resin material having a continuous porosity structure and has a diameter substantially equal to that of adjacent auxiliary plate 31 1 or 31 2 This porous plate 435 may be held in place by being clamped between the valve plate 27 and the auxiliary plate 31 1, 31 2 or by being bonded to opposed surfaces of these plates 27 and 31if 31 2' In this embodiment, when a difference in pressure is generated between both oil chambers 6 and 7, the oil pressure in a higher pressure side oil chamber acts between the valve plate 26 and that auxiliary-plate 31 1 or 31 2 which is on the higher pressure side through pores provided in the associated porous plate 435, so that the valve plate 26 can flex toward the lower pressure side along with one auxiliary plate only as located on that side, 0 0 without being affected by the other, higher pressure side auxiliary plate.

In the pighth embodiment shown in Fig. 18, a number of through holes 536 are formed through both sides of respective auxiliary plates 31 1' 312, 321 and 32 2 which are in free state brought into direct, intimate contact with the valve plate 26. These through holes 536 may be designed in a preferable manner. They may be, for example, circular-shaped or slits.

The structure according to this embodiment permits the oil pressure in the higher pressure side oil chamber to act also between the valve plate 26 and the auxiliary plate 31 1 or 3L. on the higher pressure side through the number of through holes 536 when a difference in pressure appears between the oil chambers 6 and 7. This serves to eliminate' the influence of the higher pressure side auxiliary plate without relying on the spacer s of the third embodiment or the porous plates 435 of the seventh embodiment. The valve plate 26 can flex toward the lower pressure side along with the lower pressure side auxiliary plate only.

Incidentally, it should be noted that in the foregoing third embodiment projections or bulged portions of spacer type may be formed on the auxiliary plates 31 1 and 31 2 in place of the disclosed spacers s for abutment against the valve plate 26.

0 24 It is to be clearly understood that there are no particular features of the foregoing specification, or of any claims appended hereto, which are at present regarded as being essential to the performance of the present invention, and that any one or more of such features or combinations thereof may therefore be included in, added to, omitted from or deleted from any of such claims if and when amended during the prosecution of this application or in thefiling or prosecution of any divisional application based thereon. Furthermore the manner in which any of such features of the specification or claims are described or defined may be amended, broadened or otherwise modified in any manner which falls within the knowledge of a person skilled in the relevant art, for example so as to encompass, either implicitly or explicitly, equivalents or generalisations thereof.

1

Claims

CLAIMS:

1. A hydraulic damper comprising at least two oil chambers, a partition member for partitioning the two oil chambers and having a flow path which permits communication between the oil chambers, and a damping valve provided in the 0 0 partition member to control an 011 flow produced in the flow path, wherein said damping valve conprises a resilient valve plate supported on said partition member so as to be normally maintained in a neutral position and, when a difference in pressure is developed between said two oil chambers, to flex at a free end thereof from the neutral position toward a lower pressure side, and a control wall formed on said partition member in opposition to said free end of the valve plate to define a restricting or throttling portion of said flow path between the control wall and the free end of said valve plate.

2. A hydraulic damper according to claim 1, wherein the degree of opening of said restricting portion is at minimum when said resilient valve plate is in said neutral position.

3. A hydraulic dr according to claim 1 or 2, wherein said resilient valve plate is clamped on opposite sides thereof by a pair of support members whose supporting lengths for said resilient valve plate are set to be different from each other.

4. A hydraulic damper according to claim 3, wherein said oil chambers comprise an upper oil chamber which becomes a lower pressure side when said hydraulic damper is contracted, and a lower oil chamber which becomes a lower pressure side when said hydraulic damper is expanded, and said support members LO W has supporting lengths set such that the supporting length of the member on the upper oil chamber side is shorter than that of the member on the lower oil chamber side.

5. A hydraulic damper according to claim 3, wherein said oil chambers comprise a chamber which is at a higher pressure when said hydraulic damper is contracted, and an oil reservoir which permits reception and supplement of an oil from and into said chamber depending upon an increase and decrease in pressure within said chamber, and said support members have supporting lengths set such tnat the supporting length of the member.on the side of said chamber is shorter than that of the member on the side of said oil reservoir.

6. A hydraulic damper according to any preceding claim, wherein said resilient valve plate is comprised of a plurality of valve plates put one on another.

7. A hydraulic damper according to claim 6, wherein said valve plates are of the same diameter.

8. A hydraulic damper according to claim 6 or 7, wherein each of said valve plates is provided with a plurality of slit-like notches opened in an outer peripheral edge of the valve plate.

9. A hydraulic damper according to any of claims.1 to 5, wherein said resilient valve plate comprises a main valve plate and at least one sub valve plate having a diameter smaller than that of the main valve plate, said main and sub valve plates being put one on another.

10. A hydraulic damper according to claim 9, wherein said sub valve plates are disposed at least one on each of - 27 opposite sides of said main valve plate.

11. A hydraulic damper according to claim 9 or 10, wherein interposed between said main valve plate and the sub valve plate adjacent said main valve plate is a spacer means having a diameter smaller than that of said adjacent sub valve plate.

12. A hydraulic daTper according to claim 10 or 11, wherein a plurality of said sub valve plates are disposed at least on one side of said main valve plate, these sub valve plates being formed so as to gradually decrease in diameter away from said main valve plate.

13. A hydraulic damper according to any of claims 10 to 12, wherein said sub valve.plates are set in diameter such that a load for flexing of the main valve plate from the neutral position in one direction isdifferent from a flexing load in the other direction.

14. A hydraulic damper according to claim 13, wherein said sub valve plate disposed on one side of said main valve plate is formed with a diameter smaller than that of the sub valve plate on the other side.

15. A hydraulic danper according to any preceding claim, wherein said control wall has an angled section formed by a flat top portion opposed to the free end of said resilient valve plate when the plate is In said neutral position, and by inclined portions connected to opposite sides of said top portion.

16. A hydraulic damper according to claim 15, wherein one of said inclined portions has an angle of inclination set larger than that of the other inclined portion.

17. A hydraulic damper according to claim 16, wherein said one inclined portion having the larger angle of inclination is disposed on the side of that oil chamber which becomes a lower pressure when said hydraulic damper is contracted.

18. A hydraulic damper according to claim 16. wherein said one inclined portion having the larger angle of inclination is disposed on the side of that - oil chamber which becomes a higher pressure contracted.

19. A hydraulic damper according to claim 17, wherein said partition member is a piston slidably received in a cylinder; said oil chambers comprise an upper oil chamber and a lower oil chamber which are partitioned by said piston; and said one inclined portion is provided on the upper oil chamber side.

20. A hydraulic damper according to claim 18, wherein said partition member is interposed between ends of an outer casing and a cylinder contained in said outer casing; said oil chambers comprise an oil chamber within said cylinder and an oil reservoir defined between said cylinder and said outer casing; and said one inclined portion is provided on the side of said oil chamber within said cylinder.

21. A hydraulic damper according to claim 14, wherein said control wall has an angled section formed by a flat top portion opposed to the tree end of said main valve plate when the main valve plate is in said neutral position, and by inclined walls connected to opposite sides of said top portion, one of said inclined walls having an angle of inclination set larger than that of the other inclined wall, when said hydraulic damper is 1 W and the sub valve plate disposed on the side of the inclined wall having the larger angle of inclination is formed to have a diameter smaller than that of the sub valve plate on the other side.

22. A hydraulic damper according to claim 13, wherein said main and sub valve plates are clamped on their opposite sides by a pair of support plates, one of the support plates on that side where a larger load is required for flexing said main valve plate has a diameter larger than that of the other support member.

23. A hydraulic damper according to claim 1, further including an adjusting means provided in said partition member for adjusting a relative-position between said resilient valve plate and the control wall.

24. A hydraulic damper according to claim 1, wherein said resilient valve plate is integral with a portion of said control wall, and slits are provided between said resilient valve plate and said portion of the control wall for defining said restricting portion of the floiw path.

25. A hydraulic damper according to claim 24, wherein said resilient valve plate is comprised of a plurality of valve pieces circumferentially spaced from one another; a boss portion to be -secured to said partition member is integral with radial inner ends of said valve pieces; and said portion of the control wall is formed in the form of a ring disposed to surround outer peripheries of said valve pieces and integrally connected to said boss portion through connecting pieces.

26. A hydraulic damper according to claim 1, wherein said partition member is a piston slidably received in a 0 cylinder, and said oil chambers comprise an upper oil chamber and a lower oil chamber which are defined within said cylinder by said piston.

27. A hydraulic damper according to claim 1, wherein said partition member is interposed between ends of an outer casing and a cylinder contained in said outer casing, and said oil chambers comprise an oil chamber within said cylinder and an oil reservoir defined between said outer casing and said cylinder.

28. A hydraulic damper according to claim 26, wherein said cylinder is contained in an outer casing; a second partition member is interposed between an oil reservoir defined between said cylinder and outer casing and one of said upper and lower oil chambers; and a second damping valve is provided in said second partition member.

29. A hydraulic damper according to claim 9 or 10, wherein a porous plate is interposed between the main valve plate and the sub valve plate adjacent thereto.

30. A hydraulic damper according to claim 9 or 10, wherein said sub valve plate is formed with a number of through holes so as to penetrate through opposite side thereof.

Published 1990 CL The PatentOffice. State House. 66 71 High Holborn. LondonWC1R4TP. Further copies mkvbe obtained from The Patent Office Sales Branch. St Mary Crky. Orpingtor- Kent BR5 3RD Printed by Multiplex techruques ltd. St Ma-y Crky. Kent. Con. 187