GB2090643A - Hydraulic shock absorber base valves - Google Patents

Abstract

A telescopic hydraulic shock absorber base valve assembly 22 has a hollow pressed-metal pin 47 which has a flange 49 to hold a recuperation valve spring 39 and provides a guide for a compression valve member 52 to which fluid can pass through an opening 58 in the pin. <IMAGE>

Description

SPECIFICATION Improvements relating to hydraulic shock absorbers This invention relates to base valve assemblies for telescopic hydraulic shock absorbers.

A typical shock absorber includes an inner working cylinder, an annular oil reservoir surrounding the working cylinder and a base valve assembly at the bottom of the working cylinder to control the flow of oil between the working cylinder and the reservoir.

In one form of base valve assembly which is described in our British patent specification no. 1 1 51 6 836 a recuperation valve is in the form of an annular disc whose lifting movement is guided by a castellated annular projection on the valve body and the recuperation valve spring is also located by this projection and is held in place by an abutment washer which is held in position by the head of a solid valve pin which extends through the valve body and has a waisted portion to provide an annular clearance between a part of the valve pin and the valve body in communication with the gaps between the castellations in the projection.In another construction described in British patent specification no. 1 020 225 the recuperation valve and valve spring are again retained by an annular component or washer held in position by the head of a machined valve pin but in this case the retainer is a cup-shaped member and sits in an axial aperture in the valve body while the pin has a machined blind bore which communicates with the clearance between the pin and the aperture through the valve body by means of a radial port.

It is an object of the invention to simplify the manufacture and assembly of a base valve assembly while at the same time affording functional advantages.

Broadly the present invention consists in a telescopic hydraulic shock absorber including a base valve assembly comprising a hollow pressed metal pin having a flange to hold a recuperation valve spring and providing a guide for a compression valve to which fluid can pass through an opening in the pin.

According to another aspect a telescopic hydraulic shock absorber includes a base valve assembly comprising a valve body having a recuperation passage extending therethrough, an annular recuperation valve normally closing the recuperation passage, an annular recuperation valve spring biasing the recuperation valve to the closed position, a hollow pressed metal valve pin which extends through a central aperture in the valve body and is closed at the lower end, a flange on the upper end of the pin retaining the recuperation valve spring, a compression valve reciprocatable on the outside of the valve pin, a compression valve spring extending between the compression valve and a compression valve spring seat carried by the pin to bias the compression valve against a compression valve seat on the valve body, and an opening in the pin to afford communication between the interior of the valve pin and a space between the valve pin and the compression valve seat.

It will be seen that the assembly has a fewer number of parts than previous similar assemblies, the valve pin itself serving to provide a seat for the recuperation valve spring. The production of the pin by pressing has considerable advantages over machining as used hitherto since it is cheaper and produces a component having less weight and having the possibility of a much increased flow passage cross-section therethrough.

The compression valve spring seat can be easily attached to the valve pin with little effort and expenditure of energy by providing a hollow portion such as a spigot on the valve pin which is passed through an aperture in the valve spring seat and is then deformed to retain the valve spring seat on the pin.

The pin may have a shank portion passing through the said central aperture and a head portion providing a shoulder abutting a surface on the valve body. In one such arrangement the shank portion is fit in the central aperture and the opening in the pin is located below the aperture while in another such construction the head is a fit in a rebate in the central aperture and there is a clearance between the shank and the central aperture into which the opening opens. While the opening may be radial and formed in the shank it may alternatively be formed in the shoulder so that it can be manufactured by a tool movable in an axial direction.

In a particularly cheap and simple version the compression valve is a pressed metal component comprising a sleeve portion sliding on the outside of the shank and a flange portion engaging a valve seat on the valve body.

The invention may be carried into practice in various ways but one shock absorber and two modifications thereof all embodying the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through the shock absorber; Figure 2 is a longitudinal section to a larger scale of the region of the shock absorber incorporating the base valve with some parts omitted for simplicity; Figure 3a is a longitudinal half-section similar to Figure 2 of a first modified base valve; Figure 3b is a longitudinal half-section similar to Figure 3a of a second modified base valve; and Figure 4 is a fragmentary plan view of the base valve shown in Figure 3a.

The shock absorber shown in Figures 1 and 2 is of the two-tube type having an inner working cylinder 10 in which a working piston 12 is slidable and an outer cylinder 14 which is co-axial with the inner cylinder 10 and forms with the inner cylinder an annular reservoir. The top ends of the cylinders 10 and 14 are closed and maintained in co-axial relationship by a seal assembly 1 6 and a piston rod guide 1 8 through which extends the piston rod 20 carrying the working piston 1 2 at its lower end. The bottom end of the inner cylinder 10 is fitted with a base valve assembly 22 which is shown in greater detail in Figure 2 and includes a compression valve and a recuperation valve.The bottom end of the outer cylinder 14 is closed by a base cap 24 having circumferentially spaced portions 25 deformed inwards, the base valve assembly 22 abutting the inside of the inwardly deformed portions to maintain the inner cylinder co-axial with the outer cylinder.

The base cap 24 and the top end of the piston rod 20 are provided with eyes 26 by which the shock absorber is connected to the parts between which vibration is to be damped such as the body and road wheel respectively of a motor vehicle.

The working piston 12 is provided with passages (not shown) which extend from one side of the piston to the other and are normally closed by two spring loaded valves (not shown). The inner working cylinder 10 and part of the annular reservoir are filled with oil; the remainder of the annular reservoir contains air at about atmospheric pressure. In an alternative construction the inner working cylinder and the annular reservoir are filled with oil and gas under pressure and in contact with one another.

In operation, downward movement of the working piston 12 in the cylinder 10 results in a flow of oil from the space below the piston to the space above the piston through one of the spring loaded valves in the piston and there is also a flow of oil from the working cylinder 10 to the annular reservoir corresponding to the displacement of the piston rod 20 through the compression valve in the base assembly 22. When the piston 12 moves upwards in the cylinder 10 oil flows from the space above the piston through the other spring loaded valve in the piston to the space below the piston and there is also a flow of oil from the annular reservoir to the space below the piston through the recuperation valve in the base assembly 22.

The construction of the base valve assembly 22 will now be described in greater detaii with reference to Figure 2. The assembly includes a valve body 31 which very generally has the shape of an inverted cup with a generally cylindrical side wall 32 and a base wall 33. The valve body is manufactured from sintered metal. Its outside surface includes a rebate 34 which receives the bottom end of the inner working cylinder 10.

Extending through the valve body 31 are three arcuate slots 35 which lie between two concentric valve seats 36, 37 on the upper surface of the valve body. The valve seats are overlain by a flat annular disc 38 constituting the recuperation valve. This valve is normally held in contact with the valve seats 36, 37 by a recuperation valve spring 39 which comprises a central ring or hub portion 41 having five fingers 42 which extend radially outwardly and are normally inclinded slightly downwardly into contact with the recuperation valve 38.

In the upper surface of the valve body there is a well 43 providing a shoulder 44 and a cylindrical bore 45 extends through the bottom wall of the well. Passing through the bore is a hollow valve pin 46 which is manufactured of pressed metal and comprises a cylindrical shank portion 47, a cylindrical head portion 48 of greater diameter than the main portion 46 and an outwardly extending upper flange 49. The opening in the recuperation valve 38 fits around the head portion 48 and is radially located thereby.The shoulder 51 between the shank and head portions of the valve pin engages with the shoulder 44 forming the base of the well 43 while the upper part of the shank portion 47 of the pin is a close fit in the bore 45 so that a combination of the contact between the shoulders 51,44 and the contact between the shank portion 47 and the bore 45 accurately and firmly locate the pin in the valve body both axially and radially. The hub portion 41 of the recuperation valve spring 39 is located beneath the flange 49 at the top of the pin so that the spring is normally under some pre-compression to hold the valve 38 against the seats 36, 37.

A compression valve 52 is provided by an annular member comprising a cylindrical wall 54 and an inwardly directed flange 53. The upper edge 55 of the cylindrical wall engages the under surface of the base wall 33 of the valve body 31 which thus forms a valve seat and the inner cylindrical surface 56 of the flange 54 slides on the outer surface of the shank portion 47 of the pin. The annular space 57 between the compression valve and the pin is in communication with the interior of the pin through a single rectangular window 58.The valve 52 is held with its edge 55 in contact wtih the valve body by means of a compression valve spring 59, the upper end of which engages the underside of the compression valve and the lower end of which engages a cup member 61 which is attached to the bottom end of the pin 46 by means of a spigot portion 62 which is passed through an aperture 63 in the cup member and is then compressed, to rivet or clinch the cup member to the pin. The undeformed shaped of the spigot is shown in broken lines.

On compression, the pressure built up in the lower part of the working cylinder 10 will be applied to the flange 53 of the compression valve 52 and when this pressure is sufficient to overcome the force of the valve spring 59 the valve will move downwards to allow oil to pass into the reservoir. On rebound, pressure will be applied to the recuperation valve 38 and when this pressure is sufficient to overcome the force of the recuperation valve spring 39 the valve will lift off the seats 36 and 37 to allow oil to return from the reservoir to the lower part of the working cylinder.

The parts of the base valve assembly are assembled with the components inverted. The valve pin 46 is mounted over a circular mandrel and the remaining components are placed over the pin in sequence. Finally, with the cup member 61 pressed against the end wall of the pin, the spigot 62 is pressed by a riveting tool, the assembly mandrel serving also as an anvil for this operation. The absence of the sub-assemblies and the unidirectional procedure make it possible to dse simple and inexpensive automatic machinery as well as making manual assembly easy.

For many purposes the construction so far described will provide adequate flow characteristics during compression. If a different flow cross-section is required this could be achieved by providing a pin with a window 58 of different size or by adding one or more further windows. However, to avoid the need for manufacturing and stocking pins having windows of different sizes and to provide a means of accurately setting the minimum cross-section flow path up to the compression valve, a separate control ring 65 may be provided. This ring fits in the hollow interior of the head portion 48 bf the pin and has a central aperture 66 of closely controlled size. Rings having differently sized apertures 66 may be used to provide different control characteristics.

Figures 3a and 3b show on a single figure two modified constructions of base valve, both of which are closely similar to that shown in Figures 1 and 2 and for this reason only the difference will be described. In the base valve shown in Figure 3a, i.e. to the left of the vertical centre line, the bore 45a in the base wall 33a of the body member 31 a is of greater diameter than that of the shank portion 47a of the pin 46a so that an annular space 71 occurs between the shank portion and the bore. Circular windows 72 connect this space with the interior of the pin. The pin is radially located by the outer surface of the head portion 48a engaging the cylindrical surface 73 of the well 43a in the valve body.

The compression valve 52a is formed as a pressing having a cylindrical wall 74 which slides on the outside of the shank portion 47a of the pin 46a and an outwardly directed flange portion 75 the upper surface of which engages a valve seat 76 formed on the underside of the base wall 33a of the valve body 31 a.

The second modified base valve assembly which is shown in Figure 3b, i.e. to the right of the vertical centre line, and in Figure 4 is similar to that shown in Figure 3a but in this case windows 77 are formed not in the shank portion 47b of the pin 46!; but in the shoulder portion 516 between the shank portion and the head 48!;. These windows can be more easily manufactured by a fairly robust drill or punch operating axially as compared with the radial windows 58a of the construction shown in Figure 3a. It will be seen that the diameters of the windows are such that somewhat more than half of each of them is obscured by the valve body 316 but they are dimensioned so that the unobscured portions provide the necessary flow cross-section.

Claims (9)

1. A telescopic hydraulic shock absorber including a base valve assembly comprising a hollow pressed-metal pin having a flange to hold a recuperation valve spring and providing a guide for a compression valve to which fluid can pass through an opening in the pin.

2. A telescopic hydraulic shock absorber including a base valve assembly comprising a valve body having a recuperation passage extending therethrough, an annular recuperation valve normally closing the recuperation passage, an annular recuperation valve spring biasing the recuperation valve to the closed position, a hollow pressed metal valve pin which extends through a central aperture in the valve body and is closed at the lower end, a flange on the upper end of the pin retaining the recuperation valve spring, a compression valve reciprocatable on the outside of the valve pin, a compression valve spring extending between the compression valve and a compression valve spring seat carried by the pin to bias the compression valve against a compression valve seat on the valve body, and an opening in the pin to afford communication between the interior of the valve pin and a space between the valve pin and the compression valve seat.

3. A shock absorber as claimed in Claim 2 in which the compression valve spring seat has an aperture therein through which passes a hollow portion of the valve pin which is deformed to retain the valve spring seat on the pin.

4. A shock absorber as claimed in Claim 2 or Claim 3 in which the pin has a shank portion passing through the said central aperture and a head portion providing a shoulder abutting a surface on the valve body.

5. A shock absorber as claimed in Claim 4 in which the shank portion is a fit in the central aperture and the opening in the pin is located below the aperture.

6. A shock absorber as claimed in Claim 4 in which the head is a fit in a rebate in the central aperture and there is a clearance between the shank and the central aperture into which the opening opens.

7. A shock absorber as claimed in Claim 6 in which the opening is formed in the shoulder.

8. A shock absorber as claimed in Claim 6 or Claim 7 in which the compression valve is a pressed metal component comprising a sleeve portion sliding on the outside of the shank and a flange portion engaging a valve seat on the valve body.

9. A hydraulic shock absorber including a base valve assembly, the base valve assembly being constructed and arranged to operate substantially as described herein with reference to Figures 1 and 2 or to Figure 3a or Figure 3b of the accompanying drawings.