GB2219840A - Hydraulic damper - Google Patents

Abstract

A hydraulic damper comprises a cylinder (1), a piston (21), first and second oil passages (22,23) formed in the piston and extending parallel to the axis of the piston, the second passage (23) being located radially outward of and circumferentially displaced from the first passage (22), first and second valve seats (24,25) respectively formed on the first and second end surfaces of the piston, the first valve seat (Fig. 6) being configured such as to separate the openings of the first and second passages in the radial direction of the piston and enclosing the opening of the first passage, the second valve seat (Fig.7) being arranged so as to separate the openings of the first and second passages in the circumferential direction of the piston and surrounding the opening of the second passage, and first and second disc valves (26,29) associated with the first and second valve seats, the first disc valve and the first valve seat being arranged such as to cause an initial deflection in the first disc valve in the valve-closed position. <IMAGE>

Description

HYDRAULIC DAMPER This invention relates to a hydraulic damper which is desirably employed in a vehicle in order to absorb vibration acting thereon, and more particularly relates to a hydraulic damper in which the extension side disc valve is given an initial deflection so that the damping force characteristic is improved.

One conventional type of hydraulic damper is illustrated in Figs. 1 to 3.

In the figures, reference numeral 1 designates a cylinder which constitutes a body of a hydraulic damper and reference numeral 2 designates a piston rod. One end of the piston rod 2 is inserted into the cylinder 1, while the other end thereof extends outside the cylinder 1. On the side of the first end are formed an annular shoulder portion 2A and a small diameter portion 2C axially extending from the shoulder portion 2A and provided with a male screw 2B formed on the distal end thereof. Shown at 3 is a piston slidably disposed in the cylinder 1 and partitioning the interior of the cylinder 1 into two oil chambers A and B.

The piston 3 is fitted on the small diameter portion 2C of the piston rod and secured thereto by means of a nut 14.

The piston 3 has first oil passages 4A formed therein. The location of the first oil passages 4A is such that they are circumferentially spaced apart from each other by 90 degrees, extend substantially parallel with the axis of the piston 3, and open onto the opposite end surfaces 3A and 3B of the piston 3. The piston 3 also has second oil passages 4B formed therein. The second oil passages 4B are formed in a similar manner to the first passages 4A and, as best shown in Figs. 2 and 3, are so located that each of them is at a circumferentially intermediate position between two adjacent first oil passages 4A. Shown at 5 is a first valve seat formed on the first end surface 3A of the piston 3 with a generally cross-like shape and projecting axially therefrom.As best shown in Fig. 2, the first valve seat 5 consists of an annular valve seat portion 5A formed around an opening of a through bore 3C through which the small diameter portion 2C of the piston rod 2 is inserted and four sector-shaped valve seat portions 5B formed to extend outwardly of the annular valve seat portion 5A such as to surround respective openings of the first oil passages 4A in the first end surface 3A. Each sector-shaped valve seat portion 5B is provided with a small groove 6 cut into its outer accurate portion, which groove 6 serves as an orifice (to be explained later). Reference numeral 7 designates a second valve seat formed on the second end surface 3B of the piston 3.As best shown in Fig. 3, the second valve seat 7 is similar to the first valve seat 6 in shape and consists of an annular valve seat portion 7A and four sector-shaped valve seat portions 7B. It is, however, arranged to be angularly displaced by 45 degrees relative to the first valve seat 5 so as to surround the openings of the second oil passages 4B in the second end surface 3B.

Reference numeral 8 designates a contraction side disc valve disposed on the first end surface 3A side and adapted to be seated on and separated from the first valve seat 5. The contraction side disc valve 8 consists of a plurality of planar metal discs and is sandwiched between the first valve seat 5 and a retainer 9 through a washer, as shown in Fig. 1. Shown at 11 is an extension side disc valve disposed on the second end surface 3B side and adapted to be seated on and separated from the second valve seat 7.

The extension side disc valve 11 also consists of a plurality of planar metal discs and is sandwiched between the second valve seat 7 of the piston 3 and a retainer 12 through a washer 13. Reference numeral 14 is a nut engaging with the male screw 2B of the piston rod 2. The nut 14 is threaded onto the male screw 2B after the retainers 9 and 12, disc valves 8 and 11 and piston 3 have been fitted on the small diameter portion 2C of the piston rod 2 in turn, as shown in Fig. 1, and is tightened so as to sandwich and position those parts in place.

An explanation will now given with respect to the operation of a conventional hydraulic damper provided with a structure such as that explained above.

In an extension stroke where the piston 3 moves in the direction shown by arrow C, oil in the chamber A flows into the spaces surrounded by the first valve seat 5 through the orifices 6, and then flows into the oil chamber B through the first oil passages 4A. When flowing through the orifices 6, the oil flow meets with strong resistance so that large damping force is generated. When the speed of the piston 3 becomes faster, the oil in the chamber A acting on the extension side disc valve 11 through the second oil passages 4B deflects the disc valve 11 to separate it from the second valve seat 7. Thus, oil in the chamber A is allowed to flow into the chamber B through both the first and second oil passages 4A and 4B, generating predetermined damping force.

In a contraction stroke where the piston 3 moves in the direction shown by arrow D, oil in the oil chamber B flows into the spaces surrounded by the first valve seat 5 through the first oil passages 4A, and then flows into the oil chamber A through the orifices 6. At that time, the orifices 6 serve to generate relatively large damping force.

When the piston 3 is displaced faster, the oil from the oil chamber B deflects the contraction side disc valve 8 to separate it from the first valve seat 5 and flows into the chamber A, generating predetermined damping force.

It is noted that, in the conventional hydraulic damper as explained above, the first and second oil passages 4A, 4B are formed in the piston 3 so as to extend parallel to the axis of the piston and that the first and second valve seat 5, 8 are formed on and extend axially from the first and second end surfaces 3A, 3B of the piston 3, respectively, such as to surround the openings of the first oil passages 4A in the first end surface 3A of the piston 3 and the openings of the second oil passages 4B in the second end surface 3B, respectively. It is therefore possible to make the piston 3 of sintered metal or synthetic resin by molding, in which the ability of the piston 3 (moldings) to be separated from the mold is substantially improved.

Further, by forming the valve seats 5 and 7, the total number, for example eight, of oil passages can easily be divided into four extension side oil passages and four contraction side oil passages.

The conventional hydraulic damper explained above suffers, however, from the following problem.

A hydraulic damper for use in a vehicle is generally arranged such that the damping force generated in extension strokes become larger than that in contraction strokes so that an improved ride is obtainable.

In the prior art hydraulic damper explained above, the valve seats 5 and 7 are respectively formed on the opposite end surfaces 3A and 3B of the piston 3 and comprise annular valve seat portions 5A and 7A and sector-shaped valve seat portions 5B and 7B, respectively. Even if, therefore, for the purpose of making the damping force in extension strokes larger than that in contraction strokes, a height difference is given between the annular valve seat portion 7A and the sector-shaped valve seat portions 7B by changing the heights thereof so that an initial deflection is given to the extension side disc valve 11, a gap appears between the disc valve 11 and each radially extending portion 7B1 of the sector-shaped valve seat portions 7B, so that, even in the valve-closed condition, oil leaks through the gap. It is therefore impossible to establish a desired damping force characteristic.

The present invention has been accomplished in order to solve the problem mentioned above. Accordingly, it is an object of the invention to provide a hydraulic damper wherein an initial deflection is caused in a disc valve while at the same time preventing any gap from appearing between the disc valve and a valve seat, thereby improving the damping force characteristic of the damper.

In order to accomplish the above object, a hydraulic damper according to the present invention comprises a cylinder, a piston rod having one end inserted into the cylinder and the other end extending to the outside of the cylinder, a piston slidably disposed in the cylinder and secured to the one end of the piston rod, the piston having opposite first and second end surfaces and partitioning the interior of the cylinder into two oil chambers, a first oil passage formed in the piston and extending parallel to the axis of the piston, the first oil passage opening onto the first and second end surfaces of the piston, a second oil passage formed in the piston and extending parallel to the axis of the piston, the second oil passage opening onto the first and second end surfaces of the piston and being located radially outward of and angularly offset from the first oil passage, a first valve seat formed on the first end surface of the piston concentrically with the piston, the first valve seat being arranged such as to define a partition separating the openings of said first and second oil passages which open onto the first end surface of the piston from each other in the radial direction of the piston and surrounding the opening of the first oil passage which opens onto the first end surface of the piston, a second valve seat formed on the second end surface of the piston, the second valve seat being arranged such as to define a partition separating the openings of the first and second oil passages that open onto the second end surface of the piston from each other in the circumferential direction of the piston and surrounding the opening of the second oil passage that opens onto the second end surface of the piston, a first disc valve disposed on the side of the first end surface such as to be seated on and separated from the first valve seat, and a second disc valve disposed on the second end surface of the piston such as to be seated on and separated from the second valve seat, the first valve seat and the first disc valve being so designed that an initial deflection is caused in the first disc valve when the first disc valve is seated on the first valve seat.

One of main features of the present invention is the provision of a hydraulic damper in which a valve seat is formed on one end surface of a piston concentrically with the piston. In such a damper, it is possible to eliminate any gap between a disc valve and the valve seat such as appears in the conventional damper when an initial deflection is caused in the disc valve, thereby preventing any leakage of oil in the valve-closed condition.

Other features and advantages of the present invention will be apparent from the following description taken in connection with the accompanying drawings wherein: Fig. 1 is an elevational sectional view showing a main portion of a conventional hydraulic damper; Figs. 2 and 3 are sectional views taken along lines I-I and II-II in Fig. 1, respectively; Fig. 4 is an elevational sectional view similar to Fig. 1 but showing a hydraulic damper according to a preferred embodiment of the present invention; Fig. 5 is a vertical sectional view of the piston shown in Fig. 4; and Figs. 6 and 7 are right and left side elevational views of the piston shown in Fig. 5, respectively.

Before explaining the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of being applied in other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

Referring now to Figs. 4 to 7, a preferred embodiment of the invention will be explained. The same references will be used to designate elements which are the same as those of the prior art shown in Figs. 1 to 3 and detailed explanation thereof will be omitted.

In the figures, reference numeral 21 designates a piston fixed to a small diameter portion 2C of a piston rod by means of a nut 14 and partitioning the interior of a cylinder 1 into two oil chambers A and B. The piston 21 is thick and disc-like in shape and made of sintered metal or synthetic resin by molding. The piston 21 is provided at its center with a through bore which extends axially and into which the small diameter portion 2C of the piston rod 2 is fitted. Shown at 22 are first or extension side oil passages formed in the piston 21 and extending parallel to the axis of the piston 21. The first oil passages 22 are located in a relatively inner part of the piston 21 in the radial direction and open onto the opposite or first and second end surfaces 21A and 21B of the piston 21.Although various shapes can be employed with the first oil passages 22, in the preferred embodiment these oil passages are circular in cross section. Although the number and location of the first oil passages can be changed as required, three first oil passages are provided in the preferred embodiment and these are circumferentially and equidistantly spaced apart from each other. As best shown in Fig. 6, the first oil passages 22 are located such as to open onto the first end surface 21A in an area between an annular valve seat portion 24A and a circular valve seat portion 24B which will be explained later.

The piston 21 is also provided with three second or contraction side oil passages formed therein and extending parallel to the axis of the piston 21. The second oil passages 23 are located on the radially outer side of the first oil passages and each extends arcuately for a predetermined distance in the circumferential direction of the piston 21. The second oil passages 23 are angularly offset relative to the first oil passages 22 such as to alternate therewith in the circumferential direction. The second oil passages 23 open onto the first end surface 21A outside the area of the circular valve seat portion 24B, as shown in Fig. 6, and onto the second end surfaces 21B within spaces surrounded by an annular valve seat portion 25A and three sector-shaped valve seat portions as shown in Fig. 7.

Although it is stated in the above explanation that the first and second oil passages 22, 23 extend parallel to the axis of the piston 21, it should be noted that the terminology "parallel to the axis of the piston 21" is used to include not only the case in which the passages 22, 23 are exactly parallel to the axis but also causes in which the passages 22, 23 are formed with a draft such as is required in molding or with a slant which still allows separation of moldings from the mold.

Reference numeral 24 designates a first valve seat formed on and projecting from the first end surface 21A of the piston 21. The first valve seat comprises the annular valve seat portion 24A formed around the opening of the bore 21A and the circular valve seat portion 24B spaced outward from the annular valve seat portion 24A by a predetermined distance and formed concentrically therewith. As best shown in Fig. 6, the circular valve seat portion 24B defines a partition which separates the openings of the first and second oil passages 22, 23 opening in the first end surface 21A on the inner and outer side of the partition, respectively. The openings of the first oil passages 22 are located in the area between the annular and the circular valve seat portions.The circular valve seat portion 24B axially projects slightly higher than the annular portion 24A to produce a height difference therebetween, so that an initial deflection is caused in an extension side disc valve in the valve-closed position, as will be explained later.

Reference numeral 25 designates a second valve seat formed on and projecting from the second end surface 21B of the piston 21. The second valve seat 25 comprises an annular valve seat portion 25A formed around the bore 21A and three sector-shaped valve seat portions 25B circumferentially spaced from each other. As best shown in Fig. - 7, the openings of the second oil passages 23 opening in the second end surface 21B are located in the respective spaces surrounded by the annular and the sector-shaped portions, while the openings of the first oil passages 22 are respectively located between the adjacent two sector-shaped portions.

Each sector-shaped portion 25B has the same height as the annular portion 25A.

Reference numeral 26 designates a first or extension side disc valve disposed on the first end surface 21A side such as to be seated on and separated from the circular valve seat portion 24B of the first valve seat 24. The first disc valve 26 is sandwiched between the valve seat 24 and a retainer 27 through a washer 28. Due to the height difference between the annular portion 24A and the circular portion 24B, the first disc valve 26 is given an initial deflection when seated on the valve seat 24, so that the first disc valve 26 is closely seated on the circular valve seat portion 24B around the entire circumference with a predetermined spring load, thus preventing any gap from appearing between the disc valve 26 and the annular valve seat portion 24B.The first disc valve 26 consists of four discs, the inner-most one of which is provided with a cutout which serves as an orifice permanently communicating the chamber B with the chamber A through the first oil passages 22. The disc valve 26 is formed with a diameter smaller than that of a second or contraction side disc valve 29 which will be explained later. Thus the first disc valve 26 has a spring constant larger than that of the second disc valve 29.

The second disc valve 29 is disposed on the second end surface 21B side such as to be seated on and separated from the sector shaped valve seat portions 25B of the second valve seat 25. The second disc valve 29 consists of three discs and therefore has a spring constant smaller than that of the first disc valve 26. The second disc valve 29 is sandwiched between the valve seat 25 and a retainer 30 through a washer 31. The retainer 30 abuts against an annular shoulder portion 2A of the piston rod 2 and cooperates with the retainer 27 to hold and to position in place the disc valves 26, 29 and the piston 21 and so on which are disposed therebetween, as shown in Fig. 4, when the nut 14 is threaded on the male screw 2B of the piston rod 2.

The hydraulic damper of the preferred embodiment with the structure mentioned above operates in essentially the same way as in the prior art hydraulic damper explained before.

In the hydraulic damper according to the preferred embodiment, however, the first seat valve 24 formed on the first end surface 21A of the piston 21 comprises the annular valve seat portion 24A and the circular valve seat portion 24B arranged concentrically with the annular portion 24A and those two portions are arranged such that the circular portion 24B axially projects slightly higher than the annular portion 24A, so that the first or extension side disc valve 26 is given an initial deflection when mounted, thereby enabling close contact of the first disc valve 26 with the circular valve seat portion 24B around the entire circumference thereof in the valve-closed position, and thus preventing any gap from appearing therebetween.

Even if one or more of the discs which constitute the disc valve 26 involves some unevenness due to waviness, warping or the like, the disc valve 26 is given an initial deflection through the arrangement of the valve seat 24 and closely abuts against the circular valve seat portion 24B around the entire circumference thereof with a predetermined spring load, thereby preventing any gap from appearing between the disc valve 26 and the valve seat 24 and thus preventing any leakage of oil.

As is apparent from the above explanations, the hydraulic damper according to the embodiment, in which the extension side disc valve 26 is given an initial deflection, can generate extension side damping force which is effectively increased. The damping force characteristic of the damper is therefore positively improved, thus providing substantially improved ride and driving stability. Further, each of the oil passages 22, 23 are formed so as to extend parallel to the axis of the piston. The piston 21 can therefore be formed of sintered metal or synthetic resin by press molding or injection molding, thus resulting in improved efficiency in manufacturing, as well as a reduction in the weight of the piston.

In the embodiment explained above, the cutout 26 is formed in the extension side disc valve to serve as an orifice. However, the sector-shaped portion 25B of the second valve seat 25 may alternatively be provided with an orifice similar to the orifice 6 in the prior art shown in Figs. 1 to 3 and, in that case, the cutout 26A of the extension side disc valve 26 can be omitted.

Although the contraction side oil passages 23 are arcuate in cross section in the above embodiment, they may alternatively take the same circular form as that of the extension side oil passages 22 or any other shape, as desired.

Although the second valve seat 25 comprises the annular valve seat portion 25A and sector-shaped valve seat portions 25B in the above embodiment, the portions which are in the shape of a sector may alternatively be shaped in the form of, for example, a rectangle, a triangle with its base line positioned on the annular valve seat portion side and with its top positioned on the outer circumferential side of the piston 21, a semi-circular, or the like. In other words, the second valve seat may take any configuration which allows it to separate from each other in the circumferential direction of the piston 21, the openings of the extension side passages 22 and the openings of the contraction side passages 23, both of which open onto the second end surface 21B of the piston, and to surround the openings of the contraction side oil passages 23.

As explained above, in a hydraulic damper according to the present invention, a piston can be manufactured by molding since the oil passages are formed such as to extend parallel to the axis of the piston. Further, a valve seat is formed on one end surface of the piston concentrically with the piston and arranged such as to cause an initial deflection in an extension side disc valve. Therefore, even if the extension side disc valve is not completely flat, the disc valve is closely seated on the valve seat with a predetermined spring load to prevent any gap from appearing therebetween, thereby effectively raising the extension side damping force and thus improving the damping force characteristic. As a result, vehicle ride is substantially improved.

Claims (2)

1. A hydraulic damper comprising: a cylinder; a piston rod having one end inserted into the cylinder and the other end extending to the outside of the cylinder; a piston slidably disposed in the cylinder and secured to the one end of the piston rod, saLd piston having opposite first and second end surfaces and partitioning the interior of the cylinder into two oil chambers; a first oil passage formed in the piston and extending parallel to the axis of the piston, said first oil passage opening onto said first and second end surfaces of the piston;.

a second oil passage formed in the piston and extending parallel to the axis of the piston, said second oil passage opening onto said first and second end surfaces of the piston, and said second oil passage being located radially outward of and circumferentially displaced from said first oil passage; a first valve seat formed on the first end surface of the piston concentrically with the piston, said first valve seat bering arranged such as to define a partition separating, in the radial direction of the piston, the openings of said first and second oil passages opening onto the first end surface of the piston from each other and surrounding the opening of said first oil passage opening onto the first end surface of the piston;; a second valve seat formed on .the second end surface of the piston, said second valve seat being arranged such as to define a partition separating, in the circumferential direction of the piston, the openings of said first and second oil passages opening onto the second end surface of the piston from each other and surrounding the opening of said second oil passage opening onto the second end surface of the piston; a first disc valve disposed on the first end surface side of the piston such as to be seated on and separated from said first valve seat; and a second disc valve disposed on the second end surface side such as to be seated on and separated from said second valve seat; said first valve seat and said first disc valve being so designed that an initial deflection is caused in said first disc valve when the first disc valve is seated on the first valve seat.

2. An hydraulic damper substantially as described herein with reference to and as illustrated in Figures 4 to 7 of the accompanying drawings.