GB2107821A

GB2107821A - Hydraulic damper with rebound bump stop

Info

Publication number: GB2107821A
Application number: GB08221966A
Authority: GB
Inventors: Ieaki Miura
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1981-07-31
Filing date: 1982-07-29
Publication date: 1983-05-05
Also published as: JPS5819148U

Abstract

A hydraulic damper comprises a cylinder 4, a piston 2 working in the cylinder and partitioning the interior thereof into upper and lower chambers, a piston rod 3 secured to the piston and extending through the upper chamber and a rod guide 6 to the outside, and a valve mechanism 7 mounted on the upper side of the piston for generating a damping force in the extension stroke of the damper. An annular bumping rubber 5 is disposed in the upper chamber for preventing the piston from bumping against the rod guide when the piston moves excessively toward the rod guide in the extension stroke of the damper, and a retainer guide 8 is mounted on the piston rod. The retainer guide includes a radial flange on the upper end to define thereon a generally dish-shaped surface for engaging with the bumping rubber and to engage with a downwardly facing shoulder of the piston rod, and a downwardly extending stem encircling the piston rod with the lower end engaging with the piston thereby locating the valve mechanism. A process for manufacturing the retainer guide is also disclosed. <IMAGE>

Description

SPECIFICATION Hydraulic damper This invention relates to a hydraulic damper and, particularly, to a hydraulic damper of the kind including a cylinder, a piston working in the cylinder and partitioning the interior thereof into upper and lower oil chambers, a piston rod secured to the piston and extending through the upper oil chamber to the outside, a rod guide closing the upper end of the cylinder and passing slidably therethrough the piston rod, and a valve mechanism mounted on the upper side of the piston and generating a damping force in the extension stroke of the damper.

The hydraulic damper of the aforementioned kind is publicly known as shown for example in Japanese Patent Publication 7782/1969. The damper shown in the Japanese Patent works satisfactorily, however, when an excessively large force acts on the damper in the extending direction, or when the upper oil chamber is not fully filled with oil and a force acts on the damper in the extending direction, the piston will sometimes move excessively in the upward direction and bump against the rod guide thereby injuring the valve mechanism or the piston. Such shortcomings can be avoided by providing a bumping rubber between the rod guide and the piston which is resiliently compressed when the piston excessively approaches the rod guide thereby preventing the piston from bumping against the rod guide.The bumping rubber is formed of rubber or the like material and has an annular configuration encircling the piston rod. It is required to provide a generally dish-shaped retainer for supporting the bumping rubber on the piston.

In the aforesaid Japanese Patent, there is provided a retainer guide having a generally cylindrical configuration and fitted on a small diameter portion of the piston rod. The upper end of the retainer guide engages with a downwardly facing shoulder of the piston rod and the lower end thereof engages with the upper end surface of the piston. Thus, the retainer guide acts to provide a space for mounting the valve mechanism and to guide a movable member of the valve mechanism, and is usually formed of a sintered metal.

For incorporating the bumping rubber in such prior art damper, there are problems that it is necessary to increase the length of the small diameter portion of the piston rod by the thickness of the dish-shaped retainer, and to increase the strength of the retainer guide.

The present invention aims to solve problems in incorporating a bumping rubber in the hydraulic damper of the aforementioned kind and, the hydraulic damper according to the invention comprises a unitary retainer guide having a radial flange on the upper end defining thereon a generally dish-shaped surface for engaging with the bumping rubber, and a downwardly extending stem encircling the piston rod with the lower end engaging with the piston.

The present invention further provides a method for manufacturing the retainer guide which comprises steps of preparing a circular, solid metal rod, coining one end of the metal rod to form a radial flange having a generally dish-shaped surface on said one end, forming central bores extending from opposite ends of said metal rod coaxially and alternatively, and finally forming an axial bore extending through the retainer guide.

Further objects and advantages of the invention will become apparent from the following detailed description taken with reference to accompanying drawings, in which: Fig. 1 is a longitudinal sectional view of a hydraulic damper according to the invention; Fig. 2 is a sectional view of a retainer guide incorporated in the hydraulic damper of Fig. 1; Fig. 3 is a partial sectional view of a prior art hydraulic damper; and Fig. 4A through Fig. 4F are schematic views showing a press forming process for manufacturing the retainer guide of Fig. 2.

The hydraulic damper shown in Fig. 1 comprises a piston 2 secured to a rod 3. The piston 2 works in a cylinder 4 and partitions the interior of the cylinder 1 into upper and lower oil chambers. The rod 3 extends through the upper oil chamber and a rod guide 6 to the outside. A valve mechanism 7 is mounted on the piston 2 for generating a damping force in the extension stroke of the damper. A second valve mechanism is provided on the lower end of the cylinder 4 and generates a damping force in the contraction stroke of the damper. A reservoir chamber containing therein gas and oil is defined by an annular space between the outer circumference of the cylinder 4 and a coaxial outer tube, and is communicated with the lower oil chamber through the second valve mechanism.

There is provided a bumping rubber 5 in the upper oil chamber for preventing the direct contact between the piston 2 and the rod guide 6 when the rod 3 moves to the most extended position and relieving the shock. The bumping rubber has a short cylindrical configuration and is fitted on the rod 3. A retainer guide 8 is mounted on the piston rod 3 with the upper end engaging with a downwardly facing annular shoulder defined at a diametric step on the piston rod 3, and the lower end of the retainer guide 8 engages with the piston 2, further, the retainer guide 8 has a radial flange 10 on the upper end portion which defines a generally dish-shaped or recessed surface for engaging with the bumping rubber 5. A cylindrical stem portion 9 of the retainer guide 8 encircles a small diameter portion of the piston rod 3 and integrally extends from the flange portion 10.The outer circumference of the stem portion 9 in the embodiment is utilized to locate and guide the valve mechanism 7. A tightening nut threadingly engaging with the piston rod 3 clamps the piston 2 and the retainer guide 9 against the shoulder of the piston rod 3.

Fig. 3 shows a prior art hydraulic damper disclosed in the Japanese Patent Publication 7782/1969 wherein a retainer guide 8' formed of a sintered metal is clamped between the downwardly facing shoulder on the piston rod 3 and the upper end of the piston 2.

The hydraulic damper of Fig. 1 further includes an outer tube coaxially encircling the cylinder 1 to define therebetween an annular reservoir chamber, and a second valve mechanism for generating a damping force in the contraction stroke of the damper. The reservoir chamber receives oil in the lower portion and gas in the upper portion, and the second valve mechanism is provided in the lower end of the lower oil chamber and restricts the oil flow from the lower oil chamber to the lower portion of the reservoir chamber in the contraction stroke of the damper, and communicates relatively freely the lower portion of the reservoir chamber with the lower oil chamber in the extension stroke of the damper.

Normally, the bumping rubber 5 simply reciprocates, together with the piston 2, in the cylinder in response to the reciprocating movement of the piston and does not contact with the rod guide 6, however, when the piston 2 moves excessively in the upward direction, the bumping rubber resiliently contact with the rod guide 6 and absorbs the shock of the bumping.

The invention can very easily be applied on existing hydraulic damper such as shown in Fig. 3 by simply mounting the bumping rubber 5 and the retainer guide 8 and removing the retainer guide 8t. The assembling operation is very easy and the increase in the number of parts can be minimized.

The present invention further relates to a method for manufacturing the retainer guide 8, which comprises, as shown in Fig. 2, a radial flange 10 having a dish-shaped upper end surface 11, a generally cylindrical stem 9 extending downward from the flange 11, and a central bore 20.

Fig. 4A through Fig, 4F show the manufacturing process. Firstly, a circular solid metal rod 1 2 is prepared as shown in Fig. 4A. The rod 1 2 is preferably formed of a yieldable metal such as a steel or the like. The rod 12 is cut by any suitable tool by a predetermined length to form a rod member 13 as shown in Fig. 4B. Next, as shown in Fig. 4C, a flange 10 having a generally dishshaped end surface 11 is formed on one end of the rod member 13 by a press forming process, particularly by a coining process wherein upper and lower dies 1 7 and 1 6 of a press cooperate to plastically deform the rod member 1 3 in the cold state.

Thereafter, as shown in Figs. 4D, 4E and 4F, the bore 20 is steppingly formed in the central portion of the member 1 3'. In Fig. 4D, there is provided in an upper die 1 9 a projection 21 in the central portion to form a recess 1 9a in the upper end surface of the member 13'. The lower die 18 is nearly equal to the lower die 1 6 in Fig. 4C. In Fig. 4E, a rod 24 slidably passes through a lower die 22 and is forcibly moved upwards to form a recess 25. It will be noted that the length of the stem portion substantially increases in forming the recess 25. Finally, as shown in Fig. 4F, a retainer guide 8 having the configuration substantially equal to the retainer quide 8 shown in Fig. 2 is manufactured.

If necessary, grinding, finishing or the surface treatment process is performed on the surface of the retainer guide to adjust the roughness on the surface or the accuracy in the dimension.

The retainer guide 8 formed of the aforesaid process has a sufficient strength since the metal is plastically deformed by a cold forging process, thus, it is possible to reliably support the bumping rubber 5 on the piston 2.

As described heretofore, in the hydraulic damper according to the invention, there are provided an annular bumping rubber for preventing the piston from bumping with adjacent end of the cylinder when the piston excessively approaches the end in the extension stroke of the damper, and a retainer guide formed of a cold forging process is mounted on the piston rod to support the bumping rubber above the piston and to locate and guide the damping force generating valve mechanism on the piston, thus, the deformation or the damage of the piston or the retainer guide can reliably be prevented even if the piston should move in the extending direction at an excessively high speed. The retainer guide can easily be manufactured thereby reducing the cost.

The invention is not limited to the embodiment disclosed, and various changes or modifications can be applied within the scope of the invention.

For example, the hydraulic damper may be a singie tube type, and the second valve mechanism for generating a damping force in the contraction stroke of the damper may also be mounted on the piston.

Claims

1. A hydraulic damper comprising a cylinder, a piston working in the cylinder and partitioning the interior thereof into upper and lower chambers, a piston rod secured to the piston and extending through the upper chamber and a rod guide to the outside, a valve mechanism mounted on the upper side of the piston for generating a damping force in the extension stroke of the damper, an annular bumping rubber disposed in the upper chamber for preventing the piston from bumping against the rod guide when the piston moves excessively toward the rod guide in the extension stroke of the damper, and a retainer guide mounted on the piston rod and including a radial flange on the upper end defining thereon a generally dishshaped surface for engaging with the bumping rubber and a downwardly extending stem encircling the piston rod with the lower end engaging with the piston.

2. A process for manufacturing the retainer guide according to Claim 1 wherein the process comprising the steps of preparing a circular, solid metal rod, coining one end of the metal rod to form a radial flange having a generally dish-shaped surface on said one end, forming central bores extending from opposite ends of said metal rod coaxially and alternatively, and finally forming an axial bore extending through the retainer guide.

3. A hydraulic damper substantially as hereinbefore described with reference to, and as illustrated in, Figs. 1, 2 and 4A to 4F of the accompanying drawings.