GB2157808A

GB2157808A - A telescopic shock absorber

Info

Publication number: GB2157808A
Application number: GB08509272A
Authority: GB
Inventors: Ludwig Axthammer
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1984-04-21
Filing date: 1985-04-11
Publication date: 1985-10-30
Also published as: GB8509272D0; FR2563303A1; DE3415080A1

Abstract

In a telescopic shock absorber the piston unit comprises a piston member 18 having an end face 26 perpendicular to the axis of the shock absorber and a valve plate stack 24 on said end face. This valve plate stack partially covers one exit of a passage 20 extending through the piston member. One valve plate 24a is provided with an axial projection. This axial projection engages the end face 26 or a further valve plate 24c4. The central zone of the valve plate is urged towards the end face. The non-planar valve plate is under pre-stress which pre-stress affects the flow behaviour of fluid through the passage. <IMAGE>

Description

SPECIFICATION A telescopic shock absorber BACKGROUND OF THE INVENTION This invention relates to a valve arrangement for a telescopic shock absorber or vibration damper arranged between the axle and the body of a vehicle.

Especially in the case of centrally clampedin resilient valve discs or valve plates, a frequently desired "degressive" characteristic curve can be achieved only at high construction cost. The valve plates should if possible be of plane formation, since this is very simple in production technique.

STATEMENT OF THE PRIOR ART In order to pre-stress the centrally clampedin resilient valve plates it is known to make the end face of a valve member or piston member conical so that plane spring plates can be pre-stressed. Such a formation is very expensive, since an exact maintenance of the slope of the conical form is necessary and for every variation of the pre-stress a valve member with a different slope of the cone must be provided.

OBJECT OF THE INVENTION A primary object of the present invention is to provide a valve arrangement for a telescopic shock absorber in which the damping characteristic of the valve arrangement can be adjusted in a simpie way.

It is a further object of the present invention to permit such easy adjustment of the damping characteristic while using at least to a large extent substantially planar valve plates and/or a substantially planar end face of the piston member.

A further object of the invention is to provide a highly reliable valve arrangement.

SUMMARY OF THE INVENTION In view of the above objects, a shock absorber comprises a cylinder having an axis and defining a cavity therein. A piston rod extends inward and outward of the cavity. A piston unit is fastened to the piston rod within the cavity and defines two working chambers within the cavity. The piston unit comprises a piston member. The piston member comprises at least one passage extending between the working chambers. The piston member has at least one end face substantially perpendicular to the axis. The passage has at least one exit opening into the end face. The exit is at least partially covered by a valve plate unit. The valve plate unit comprises a non-planar valve plate having a first main face and a second main face. The non-planar valve plate has a central zone, an intermediate zone, and a peripheral zone.The valve plate unit in the central zone is urged towards the end face.

The peripheral zone of the non-planar valve plate is provided with at least one axial projection projecting beyond the first main face.

This axial projection engages with axial pressure either the end face of the piston member or a side face of a further plate.

The non-planar valve plate has the main function to vary the pre-stress of further valve plates. Therefore, this non-planar valve plate can be made of any material, e.g. plastic material and need not have a spring characteristic by itself. It is however of particular advantage to provide a valve plate which is resilient by itself such that the valve plate unit comprising the non-planar valve plate and further valve plates can be provided with small axial dimension for a required pre-stress.

According to a further aspect of the invention, the non-planar valve plate is flat before installation, and the projection is formed in the region of its external diameter by an annular bead. In this case, the annular bead is produced in a simple manner by stamping of the plate, e.g. such that a cranked zone is obtained. On the other hand, it is readily possible to provide the projection by a ring connected with the non-planar valve plate.

The non-planar valve plate can also be produced from synthetic plastic material.

By different arrangements of the non-planar valve plate and further esilient valve plates it is readily possible to obtain different damping force characteristic curves. Thus in accordance with the present invention it is readily possible that the non-planar valve plate comes to abut with one side face on the piston member or that the non-planar valve plate is arranged between further valve plates or partial units of further valve plates.

There is also extensive freedom as regards the shape of the non-planar valve plate. Thus this nonplanar valve plate can comprise several projections or protuberances made in dog form in the region of the external diameter.

Moreover it can be of advantage if the nonplanar valve plate is provided with piercings or perforations.

According to a further aspect of the invention, the non-planar valve plate is formed as a centrally clamped-in leaf spring having a plurality of arms. These arms are adapted to the diameter of the adjacent valve plate upon which the leaf spring acts. Projections or protuberances are provided on these arms.

According to a further feature of the invention the non-planar valve plate is arranged between further valve plates and engages with the abutment face of its projection or protuberance with one of said further valve plates.

According to a further aspect of the invention one resilient valve plate is arranged in an internal space defined by the non-planar valve plate.

The various features of novelty which characterize the invention will be explained in greater detail below by reference to the forms of embodiment represented in the drawings in detail, wherein: FIGURE 1 shows a valve arrangement on a piston member where the valve plates are prestressed for extension damping and compression damping (extension damping occurs when the piston rod moves outward of the cylinder and compression damping occurs when the piston rod moves inward of the cylinder); FIGURE la shows as a detail in crosssection one of the valve plates, namely the non-planar valve plate; FIGURE 2 shows a piston member of a shock absorber with pre-stressed valve plates for extension damping; FIGURE 3 shows a form of embodiment in which a non-planar valve plate provided with a projection comes to abut with an abutment face on the end face of the piston member;; FIGURE 4 shows a non-planar valve plate having two projections made in dog form; FIGURE 5 shows a non-planar valve plate having three projections made in dog form which are uniformly distributed over the cir cu mference; FIGURE 6 shows a centrally clamped-in leaf spring with projections of dog form arranged on the leaf spring ends; FIGURE 7 shows a three-armed leaf spring with projections made in dog form on the ends; FIGURE 8 shows a non-planar valve plate with a plurality of perforations.

DETAILED DESCRIPTION OF THE DRAWING In Figure 1 there is shown a cylinder 10 in which a cavity 1 2 is defined. A piston rod 14 is arranged coaxial with the cylinder 10. This piston rod 14 passes through a piston rod guiding and sealing arrangement at the upper end of the cylinder 10 (not shown). The piston rod 14 is connected within the cavity 12 with a piston unit 1 6 which divides the cavity 1 2 into two working chambers 1 2a and 1 2b. The working chamber 1 2a extends up to the piston rod guiding and sealing arrangement; the working chamber 1 2b extends down to a bottom of the cylinder 10 (not shown).

The piston unit 1 6 comprises a piston member 18. The piston member 18 is provided with two passages or bores 20 and 22.

The bore 20 is effective for the extension damping, i.e. when the piston rod 14 moves upward in Figure 1 such that the fluid, particularly liquid contained in the working chamber 1 2a flows into the working chamber 1 2b.

The bore 22 is effective on compression damping, i.e. when the piston rod 14 is moving downward in the illustration of Figure 1 such that the liquid flows from the working chamber 1 2b into the working chamber 1 2a.

A damping valve 24 is associated with the bore 20. This damping valve 24 comprises a stack of valve plates 24a, 24b, 24c1, 24c2, 24c3 and 24c4. The valve plate 24b can be regarded as a primary partial valve plate unit.

The valve plates 24c1 to 24c4 can be regarded as a secondary partial valve plate unit.

The valve plate 24a is a non-planar valve plate which will be described in more detail below. The damping valve 24 may be regarded also as a valve plate unit. The piston member 1 8 is provided with an end face 26 which is substantially planar and perpendicular to the axis of the piston rod 14. The valve plate 24b is in contact with the end face 26.

All valve plates 24b and 24c1 to 24c4 are planar in the non-assembled condition. These valve plates 24b and 24c1 to 24c4 are of resilient material, more particularly of steel.

The non-planar valve plate 24a comprises a first main face 28 and a second main face 30.

In radial direction one recognizes a central zone 32, an intermediate zone 34 and a peripheral zone 36. The peripheral zone 36 is provided with a projection 38 which projects beyond the first main face 28 and is defined by a crank-shaped deflection having a radially outer end portion 40. The valve plates 24a, 24b and 24c1 to 24c4 are urged towards the end face 26 in the central zone 32 by a nut 42. The deflection 38 is responsible for the amount of pre-stress which the valve plates 24c1 to 24c4 are subject to. The pre-stress which the valve plates 24c1 to 24c4 are subject to is transmitted through the nonplanar valve plate 24a onto the valve plate 24b such that the valve plate 24b is biased towards the end face 26.The non-planar valve plate 24a is planar in its central and intermediate zones and non-planar only due to the crank-shaped deflection which can easily be obtained by stamping or deep drawing.

The bores 20 are not fully covered by the valve plate 24b such that a pre-opening crosssectional area is defined between the outer periphery of the valve plate 24b and the radially outer edges of the bore or bores 20.

Only when a force greater than the prestress force resulting from the non-planar valve plate 24a is exerted by the damping medium upon the valve plate 24b the valve plate 24b is lifted and thus the flow crosssection is enlarged in pressure dependence.

The pre-stress with which the valve plate 24b is pressed against the end face 26 of the piston member 1 8 can be achieved either by the number of the spring plates 24c1 to 24c4 or by the amount of axial deflection of the cranked projection 38.

The construction and manner of operation of the upper damping valve, which co-operates with the bores 22 and serves for compression damping, correspond substantially to what is described above, with the difference that this compression damping valve is effective on downward movement of the piston rod 14 into the cylinder 10.

The form of embodiment according to Figure 2 differs from that according to Figure 1 essentially in that the piston member 11 8 is provided with obliquely proceeding bores 1 20 and 1 22. Analogous parts are designated by the same reference numerals as in Figure 1, increased by 100. These bores 120 and 122, respectively, open in each case into an annular channel 144 and 146, respectively, which are covered by respective valve plate units.

For providing a pre-opening cross-sectional area the valve plate 124by is provided with apertures 148. Also in this embodiment all the valve plates are pressed in the central zone by the nut 142 against the end face 1 26 and the pre-stress is dependent on the degree of axial cranking of the non-planar valve plate 124a.

In Figure 3 analogous parts are designated by the same reference numerals as in Figure 1, increased by 200. According to Figure 3 the centrally clamped-in non-planar valve plate 224a is so installed that it abuts the end face 226 by the radially outer end portion 240 of the crank-shaped deflection 238. In this way the non-planar valve plate 224a forms an annular chamber 250 accomodating the primary partial valve plate unit 224b1, 224b2 which comprises at least one valve plate. The valve plates 224c1 to 224c3 which are flexed through in the installation of the piston member 218 by the nut 242 press upon the second main face 230 of the non-planar valve plate 224a so that the end portion 240 of the crank-shaped deflection is biased against the end face 226 of the piston member 218.This embodiment of invention renders it possible to divide the stack of valve plates into two partial units 224b1, 224b2 contacting the end face 226 without pre-stress and being situated in the annular chamber 250 and a pre-stressed or biased partial unit 224c1 to 224c3 which is supported by the radially outer end portion 240 of the valve plate 224a on the end face 226 of the piston member 218. Such an embodiment is especially suitable when high demands are made of comfort, in that a soft damping is desired in the case of small movements and low piston speeds, while in the case of hard vibration loadings an openign with high pre-stress force is to take place.

In Figures 4 to 8 there are shown advantageous forms of embodiment of the non-planar valve plate 424a, 524a, 624a, 724a, respectively. Analogous parts are designated by the same reference numerals as in Figure 1, increased by 300, 400, 500, 600 and 700 respectively. The non-planar valve plate 324, 424 is provided according to Figures 4 and 5, respectively, with two and three projections 338, 438, respectively, made in dog form.

Figures 6 and 7 show non-planar valve plates in the form of leaf springs 524a and 624a, respectively, the arms of which likewise comprise projections 538 and 638, respectively, of dog form at their ends. In Figure 8 the non-planar valve is provided with projections 738 of dog form and possesses perforations 752 which consist in the present case of circular punched-out portions. The centrally clamped-in non-planar valve plates according to Figures 4 to 8 are preferably installed in the position as shown in Figures 1 and 2. The abutment faces formed by the projections of dog form then come to abut on the valve plate 24c4 and 124c2, respectively.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

It is to be understood that the reference numerals in the claims are only for better understanding and are by no means restrictive.

Claims

1. A telescopic shock absorber comprising: a cylinder (10) having an axis and defining a cavity (12) therein; a piston rod (14) extending inward and outward of said cavity (12); and a piston unit (1 6) fastened to said piston rod (14) within said cavity (12) and defining two working chambers (12a, 12b) within said cavity (12); said piston unit (16) comprising a piston member (18); said piston member (18) comprising at least one passage (20) extending between said working chambers (12a, 12b); said piston member (18) having at least one end face (26) substantially perpendicular to said axis; said passage (20) having at least one exit opening into said end face (26); said exit being at least partially covered by a valve plate unit (24);; said valve plate unit (24) comprising a nonplanar valve plate (24a) having a first main face (28) and a second main face (30); said non-planar valve plate (24a) having a central zone (32), an intermediate Zone (34), and a peripheral zone (36); said valve plate unit (24) in said central zone (32) being urged towards said end face (26); said peripheral zone (36) of said non-planar valve plate (24) being provided with at least one axial projection (38) projecting beyond said first main face (28); said axial projection (38) engaging with axial pressure one of said end face and a side face of a further valve plate (24c4) (all Figures).

2. A telescopic shock absorber as set forth in claim 1, said axial projection (38) being defined by a deflection of plate material of said non-planar valve plate (24a) (all Figures).

3. A telescopic shock absorber as set forth in claim 2, said deflection (38) being substantially crank-shaped when regarded in a plane of section containing said axis (Figures 1 to 3), said crankshaped deflection (38) having a radially outer end portion (40) engaging one of said end face and said side face of said further valve plate (24c4).

4. A telescopic shock absorber as set forth in one of claims 1 to 3, said non-planar valve plate (24a) having its second main face (30) in contact with one of said end face and a primary partial valve plate unit (24b) adjacent said end face (26) and having its projection (38) in engagement with a secondary partial valve plate unit (24c1 to 24c4) remote from said end face (26) (Figures 1 and 2).

5. A telescopic shock absorber as set forth in one of claims 1 to 3, said non-planar valve plate (224a) having its projection (238) in engagement with said end face (226) and its primary main face (228) in engagement with one of said end face and a primary partial valve plate unit (224b1, 224b2) adjacent said end face (226) (Figure 3).

6. A telescopic shock absorber as set forth in claim 5, said non-planar valve plate having its secondary main face (230) in contact with a secondary partial valve plate unit (224c1, 224c3) remote from said end face (226) (Figure 3).

7. A telescopic shock absorber as set forth in one of claims 1 to 6, said non-planar valve plate (24a) being made of elastic material like steel (all Figures).

8. A telescopic shock absorber as set forth in one of claims 1 to 7, said non-planar valve plate (324a) having a plurality of projections (338) distributed along its peripheral zone (Figures 4 to 8).

9. A telescopic shock absorber as set forth in one of claims 1 to 7, said non-planar valve plate (24a) having a substantially circular peripheral zone (36), and said deflection (38) extending substantially along the total peripheral length of said peripheral zone (36) (Figures 1 to 3).

10. A telescopic shock absorber as set forth in one of claims 1 to 8, said non-planar valve plate (524a) having a diagonal strip configuration (Figure 6).

11. A telescopic shock absorber as set forth in one of claims 1 to 8, said non-planar valve plate (624a) having a star-shaped configuration (Figure 7).

1 2. A telescopic shock absorber as set forth in one of claims 1 to 11, said non-planar valve plate (724a) being provided with a plurality of perforations (752) in its intermediate zone (Figure 8).

1 3. A telescopic shock absorber as set forth in one of claims 1, 5, 6, 7, 9, said non-planar valve plate (224a) having a circular peripheral zone with a crank-shaped projection (238) extending substantially along the total circumference of said peripheral zone, said crankshaped projection (238) being biased into contact with said end face (226) of said piston member (218), the central zone of said nonplanar valve plate (224a) being in contact with a primary partial valve plate unit (224b1, 224b2) adjacent said end face (226) of said piston member (218), said primary partial valve plate unit (224b1, 224b2) being housed within an annular chamber (250) defined between said end face (226) and said non-planar valve plate (224a) (Figure 3).

14. A telescopic shock absorber as set forth in one af claims 1 to 13, said valve plate unit (24) comprising -when regarded in the disassembled condition-substantially planar valve plates (24b, 24c1, 24c4) except for said nonplanar valve plate (24a), said non-planar valve plate (24a) being also substantially planar except for said axial projection (38) (all Figures).

1 5. A telescopic shock absorber as set forth in one of claims 1 to 14, said end face (26) being substantially planar (Figures 1 to 3).

16. A telescopic shock absorber as claimed in claim 1, substantially as described herein with reference to and as illustrated by any one of the examples shown in the accompanying drawings.