Simplified Hydraulic Damper

(1) The present invention relates to hydraulic dampers mountable on vehicles or aircraft to damp or alleviate the mechanical vibrations associated therewith.

(2) There has been proposed a hydraulic damper of the gas enclosed type comprising a piston slidably housed in a tube. A piston-rod is fitted to the piston, partitioning the tube into upper and lower chambers, which are filled with oil and which are communicated with each other via a passage provided in the piston-rod. A valve mechanism for generating a damping force in such a hydraulic damper is disclosed, for instance, in Japanese Utility Model Application Laid-open No. 85490/1978. That application proposes an arrangement wherein a leaf valve is disposed between a disk plate slidably installed in a hollow nut. A valve seat is stationarily installed within the hollow nut so as to constitute an expansion-side valve which can also function as a damper, even when the expansion stroke is abrupt (the term "expansion-side damping valve" is herein intended to mean a valve which opens only when the piston-rod moves in the expansion direction, A, relative to the tube). In the proposed hydraulic damper, however, the inside surface of the hollow nut in which the disk plate has to slide must be finished with high precision. Additionally, the disk plate has a tendency to incline and scrape the inside surface of the hollow nut, thereby rendering the damper function unstable. To avoid the above-mentioned difficulties, high precision finishing of the damper parts is demanded as well, increasing the cost of the device.

The primary object of the present invention is to provide a hydraulic damper which is easily produced in that highprecision work is not required.

Another object of the invention is to provide hydraulic damper having reduced production costs because highprecision work is not required.

Still another object of the invention is to provide a hydraulic damper which is simple in structure and stable in performance.

The hydraulic damper according to the present invention is characterized in that the extension-side damping valve is comprised of a disk valve and a valve seat which are fixed within the hollow nut, thereby dispensing with any slidable parts in the hollow nut and thus making it possible to reasonably reduce the production cost of the unit. High-precision work is not required in finishing the inside surface of the hollow nut and stable performance can be guaranteed.

Other objects and features will become apparent from the following description with reference to the attached drawings.

FIG. 1 is a whole longitudinal section view of a hydraulic damper according to the present invention.

FIG. 2 is a longitudinal section view of a piston and a hollow nut shown in FIG. 1.

FIG. 3 is a longitudinal section view of a variation of the piston and hollow nut in the hydraulic damper according to the present invention.

FIG. 4 is a longitudinal section view of another variation of the piston and hollow nut in the hydraulic damper according to the present invention.

FIG. 5 is a whole longitudinal section view of still another enbodiment of the hydraulic damper according to the present invention.

FIGS. 1 and 2 illustrate one embodiment of the present invention. A tube 1 has its bottom end thereof closed. A mounting ring 2 is carried by the bottom end of the tube, and a rod guide 3 and a sealing member 4 are fixed to a top end of the tube. A piston rod 5 is slidably movable in the directions denoted by arrows A and B through the rod guide 3 and the sealing member 4, and projects outside of the tube 1. A mounting ring 6 is secured to the outer end of the piston rod 5. Also, a cap 7 is attached to the outer end of the piston rod 5. A dust cover 8 is attached to the cap 7.

A piston 9 is mounted on the inner end of the piston rod 5 by means of a hollow nut 10 with a cavity screwed to the inner end tip of the piston rod 5. The configuration of this part will be described later. Between the bottom of the tube 1 and the piston 9 there is installed a free piston 11 which is slidable in the directions denoted by arrows A and B. A space defined between the piston 9 and the sealing member 4 constitutes an upper piston chamber 12, while a space defined between the piston 9 and the free piston 11 constitutes a lower piston chamber 13. A space defined between the bottom of tube 1 and the free piston 11 constitutes a pressurized gas chamber 14. The piston chambers are filled with oil, while the gas chamber 14 holds a high-pressure gas sealed therein.

At the inner end of the piston rod 5 there is formed a communicating path 15 which establishes fluid communication between the cavity in the hollow nut 10 and the upper piston chamber 12. Within the piston 9 there is formed a communicating path 16 which established fluid communication between the upper piston chamber 12 and the lower piston chamber 13. On the periphery of the piston rod 5 and at the top of the piston 9 there is installed a contraction-side damping valve 17 (the term "contraction-side damping valve" is herein intended to mean a valve which opens only when the piston-rod moves in the contraction direction, B, relative to the tube). The damping valve 17 comprises a disk valve 18 suitable to open or close the communicating path 16 in the piston 9, a retainer 19 which functions as a fulcrum for deflection of the disk valve 18, and a washer 20 to prevent an excess-deflection of the disk valve 18. The disk valve 18, the retainer 19 and the washer 20 are sandwiched and fixed in a stepped portion 5a in the piston rod 5 and the piston 9. The washer 20 also serves to stop or limit the expansion stroke by bearing against the sealing member 4. The cavity of the hollow nut 10 holds an expansion-side damping valve 21. The expansion-side damping valve 21 comprises a valve seat 23 fixedly mounted in the nut 10 by means of a screw member 22 screwed in the cavity of the hollow nut 10, a disk valve 25 suitable to open or close the communication path 24 formed in the valve seat 23, a retainer 26 to serve as a fulcrum for deflection of the disk valve 25, and a washer 27 to prevent an excess-deflection of the disk valve 25. The valve seat 23, the disk valve 25, the retainer 26 and the washer 27 are sandwiched in the stepped portion 10a in the hollow nut 10 and the screw member 22. Within the screw member 22 there is formed a communication path 28 establishing communication between the inside of the hollow nut 10 and the lower piston chamber 13.

Next, the operation of the hydraulic damper as set forth above is described. First, in the expansion stroke, the piston 9 together with the piston rod 5 move in the direction of arrow A relative to the tube 1. A pressure thereupon builds up in the upper piston chamber 12 and in consequence the disk valve 25 deflects around the retainer 26. The communication path 24 in the valve seat 23 thereby opens. The oil in the upper piston chamber 12 flows into the lower piston chamber 13 via the paths 15,24, the cavity of the hollow nut 10, and the path 28. At the same time, the gas chamber 14 expands to compensate for the changed volume of the pistion rod 5 within the upper piston chamber 12, while the free piston 11 moves in the direction A to compensate for the created negative pressure. Thus, when the oil deflects the disk valve 25 and flows into the path 24, a damping force in the expansion stoke is generated. In the contraction stroke, on the contrary, the piston 9 together with the piston rod 5 move in the direction of arrow B relative to the tube 1. The oil in the lower piston chamber 13 is then caused to flow into the upper piston chamber 12 via the path 16 formed in the piston 9. The pressure of the oil causes the disk valve 18 to deflect around the retainer 19 as the fulcrum, whereupon the path 16 of the piston 9 opens, permitting the oil in the lower piston chamber 13 to go into the upper piston chamber 12 via the path 16. At the same time the gas chamber 14 contracts by a volume equivalent to the volume of intrusion of the piston rod 5 into the upper piston chamber 12, thereby causing the free piston 11 to move in the direction B to compensate for the changed volume of the piston within the tube. As the result of the oil deflecting the disk valve 18 and flowing into the communicating path 16, a damping force in the contraction stroke is generated. In this manner, the damping forces are generated when the oil deflects the disk valve 25 or 18 and flows into the path 24 or 16, respectively. Accordingly, a good damping performance can be attained regardless of the suddenness of the expansion or contraction stroke.

It is obvious that the same effect in the above embodiment can be realized when the disk valve 18 is installed below the piston 9 to open or close the path 16, while the disk valve 25 is installed above the valve seat 23 to open or close the path 24.

In FIGS. 3-5 showing other embodiments of the present invention, the same or similar parts as in the first embodiment are given the same numerals. FIG. 3 illustrates a second embodiment of the present invention. In this embodiment, the separate members, i.e., retainers 19,26 and washers 20,27 (in the first embodiment) are made of the same pieces 31 and 32, respectively. Meanwhile, through-hole 33 is bored in the screw member 22 and into this hole 33 a part 23a of the valve seat 23 (a fixture for the disk valve 25 and the member 32) is pressed.

Thus the number of components can be reduced and a preassembly of parts inside the hollow nut 10 is possible.

FIG. 4 illustrates a third embodiment of the present invention. In this case, through-hole 41 is bored in the valve seat 23. A part 22a of the screw member 22 is pressed into the through-hole 41. The disk valve 25, the retainer 26, and the washer 27 are fitted in advance of the part 22a.

In this way, the whole surface of the valve seat 23 can be easily finished flat.

FIG. 5 illustrates a fourth embodiment of the invention characterized by the non-existence of a free piston in the hydraulic damper without deterioration of the damping effects. In this embodiment, because there is no free piston provided in the hydraulic damper, the body of the hydraulic damper is composed of a double tube consisting of the inner tube 1a and the outer tube 1b; the lower piston chamber 13 is divided into the parts 13a, 13b and 13c; and a pressurized gas chamber 14 is formed in the upper portion of the gap between the inner tube 1a and the outer tube 1b.

The partitioning member 50 separates the lower piston chamber into 13a and 13b, and is installed at the lower end of the inner tube 1a. An orifice 50a to communicate 13a with 13b is bored in the partitioning member 50. The orifice 50a is designed to maintain the liquid pressure during the contraction stroke high enough for the chamber 13a to deflect the damping valve 18. Meanwhile on the underside of the partitioning member 50 there is formed a communicating path 50b, which communicates 13b with 13c. The piston-hollow nut assembly attached to the lower end of the piston rod 5 in FIG. 5 is schematically simplified, but it is essentially the same as the one illustrated in FIG. 2. Thus the present embodiment is functionally the same as the ones illustrated in FIGS. 1 and 2.

As described above, since in the present invention, the expansion-side damping valve is constructed by fixedly providing the disk valves and the valve sheets within the hollow nut, there is no part slidably movable within the hollow nut. Therefore, the inside face of the hollow nut need not be finished with very high precision and a cost reduction can be reasonably achieved without sacrificing the stable operation of the damper.

It is apparent that different variations of the embodiment are feasible without departing from the spirit and scope of the present invention and therefore the present invention is not restricted to the specific embodiments and should be limited only as specified in the attached claims.