GB1583278A - Shock absorbers - Google Patents

Description

(54) SHOCK ABSORBERS (71) We, JONAS WOODHEAD LIMITED, a Company registered under the laws of England, of 177 Kirkstall Road, Leeds LS4 2AQ, Yorkshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to shock absorbers, otherwise known as vibration dampers, of the two-tube type, that is to say of the type comprising an inner tube bounding a working cylinder and an outer tube bounding an annular reservoir. The invention relates particularly, but not exclusively, to such shock absorbers for installation between the sprung and unsprung masses of motor vehicles.

It has long been the practice to include baffles in the reservoirs of two-tube hydraulic shock absorbers to suppress surge of the working fluid, the baffle often being in the form of an annular ring member covering almost the entire radial dimension of the reservoir. In one form of baffle the ring is mounted and located upon the working cylinder and assembled, together with the working cylinder, into the outer tube with which it forms a small clearance. In another construction, the ring is pressed into and located within the outer cylinder prior to assembly of the working cylinder into the reserve tube, the ring then forming a small clearance with the working cylinder. The baffle is positioned so that in use it is slightly below the normal working fluid level in the reservoir and serves either or both of two purposes. The first is to suppress mixing of the gas in the reservoir with the liquid to cause aeration. The second is to control the tendency of the working fluid to be thrown away from the lower end of the reservoir as the lower end of the shock absorber is agitated by road surface irregularities to produce voids at the interconnections normally provided between the working cylinder and the lower end of the reservoir.

It has now been proposed, for reasons which include weight saving and material economies, to use a smaller end closure member at least at that end of the outer tube through which the baffle is introduced and to reduce the diameter of the corresponding end of the outer tube to engage the smaller component. This development presents difficulties in making a satisfactory installation of either of the aforementioned types of baffle. It would be possible to instal the baffle before reducing the dimension of the outer tube as by swaging, but this complicates the manufacturing process and obstructs cleaning of the tube.

According to one aspect of the present invention, a two-tube hydraulic shock absorber comprises an inner tube bounding a working cylinder and an outer tube bounding an annular reservoir, the outer tube having at least at one end an end portion of smaller diameter than a central portion thereof, and an annular baffle ring carried on the outside of the inner tube and having dimensions in directions transverse to the axis of the inner tube such that the ring cannot pass freely through the said one end portion, the baffle ring being sufficiently resilient to permit passage of the baffle ring on the inner tube past the said one end portion. Thus, the inner tube with the baffle attached can be introduced into the outer tube which already has a reduced end by deformation of the baffle by an amount to permit such passage, the resilience of the baffle restoring the baffle to its original shape. Thus, according to a second aspect of the present invention, a method of assembling a two-tube shock absorber comprises providing an inner tube bounding a working cylinder and an outer tube bounding an annular reservoir and having at least at one end an end portion of smaller diameter than a central portion thereof, attaching to the outside of the inner tube an annular baffle ring at least part of which is resiliently flexible and which has dimensions in directions transverse to the axis of the inner tube such that the ring cannot pass freely through the said end portion, and telescoping the inner tube within the outer tube while temporarily flexing the ring to cause it to pass through the said end portion into the central portion.

The baffle may take various forms. For example, it may comprise a support ring in contact with the outside of the inner tube and a flexible skirt projecting outwardly from the ring. In one such arrangement the skirt is thinner than the ring so that the ring has adequate strength and the skirt has adequate flexibility. Flexibility may be increased if the skirt is provided with notches such as radial notches in its outer periphery. While the skirt may project radially, the skirt may be inclined in one direction or the other to facilitate insertion of the baffle into the outer tube or for some other purpose. For example, where, as is usually the case, the working cylinder contains a working piston attached to a piston rod which projects from one end only of the working cylinder and that end is the end which is normally upwards when the shock absorber is in use, the skirt may be inclined outwardly and away from that end, i.e. downwardly, so that the impact of hydraulic fluid thrown upwards during use will tend to deflect the skirt to a more nearly radial condition so that the clearance between the outer periphery of the skirt and the inner wall of the outer tube will be reduced.

The invention may be carried into practice in various ways but one two-tube hydraulic shock absorber embodying the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a partial longitudinal section of the shock absorber; Figure 2 is a plan view of the baffle of the shock absorber; Figure 3 is a partial longitudinal section of a first alternative baffle; and Figure 4 is a view similar to Figure 3 of a second alternative baffle.

The shock absorber shown in Figures 1 and 2 of the drawings comprises an inner tube 1 bounding a working cylinder 2 containing a piston 3 having passages and valves (not shown) which permit but restrict flow of hydraulic fluid from each side of the piston to the other side. The piston is attached to one end of a piston rod 4 which passes out through the upper end of the working cylinder 2 through a seal assembly 5 contained within an end cap 6. Surrounding the inner tube 1 is an outer tube 7 forming an annular chamber 8 which forms an annular reservoir which is in communication with the bottom of the working cylinder 2 through non-return base and recuperation valves (not shown).

The outer tube 7 has a central portion 9 of constant diameter and is swayed down at the top end as can be seen in Figure 1. The end portion 11 at the upper end is secured to the end cap 6 and the end portion at the lower end is secured to a corresponding end cap, not shown, for example by welding.

Surrounding the inner tube 1 and secured thereto as a press fit is an annular baffle ring 12 comprising a support portion 13 and a skirt portion 14 which extends radially outwardly from the upper end of the support portion. As can be seen from Figure 1, the skirt portion 14 is substantially thinner than the ring portion 13 so that the skirt portion is resiliently flexible while the support portion is sufficiently robust to grip the inner tube 1 and adequately to support the skirt portion. It can be seen from Figure 2 that the skirt portion 14 is formed with a number of V-shaped circumferentially spaced notches 15.

In the assembly of the shock absorber shown in Figures 1 and 2 the baffle ring 12 is pressed over the inner tube 1 and is forced along the tube to the position shown in Figure 1. The piston 3 with the piston rod 4, the seal assembly 5 and the end cap 6 are then assembled to the inner tube 1 and the resulting assembly is then telescoped into the outer tube 7 through the upper end, the outer tube already having at this stage the base cup secured to its bottom end. The diameter of the skirt portion 14 of the baffle ring 12 is greater than the inner diameter of the reduced portion 11 of the outer tube 7 but is able to deform resiliently sufficiently to permit the baffle ring to be moved past the end portion 11 whereafter it springs back to the flat condition shown in Figure 1. The notches 15 are provided to reduce the stress necessary to allow the skirt 14 to pass the end portion 11 to avoid the skirt portion taking a permanent set due to excessive distortion.

Figure 3 shows another form of baffle ring 21 which may be substituted for the construction shown in Figures 1 and 2 but is adapted for assembly from the bottom end of the outer tube 7 prior to attachment of the base cup. In this case, both ends or only the bottom end of the outer tube 7 are reduced. The baffle ring comprises a cylindrical portion 22 from the bottom end of which a flange extends outwardly, the inner portion 23 of the flange being normal to the axis of the inner tube 1 while the outer portion 24 is inclined downwardly to assist entry of the baffle ring into the outer tube.

The baffle ring 25 shown in Figure 4 is similar to that shown in Figure 3 but the skirt portion has no section which is radial but is all downwardly inclined and extends from the upper end of the sleeve portion 26.

The constructions shown in Figures 3 and 4 with skirt portions which are inclined downwardly are arranged so that any deflection upwards which occurs due to surge of the working fluid will diminish the clearance between the periphery of the skirt portion and the outer tube 7, in contrast to the effect of such a deflection of the baffle ring shown in Figures 1 and 2 where any deflection will increase the clearance and hence the area of the fluid flow path between the baffle ring and the outer tube.

The baffle rings described above may be made of plastics material, for example nylon.

WHAT WE CLAIM IS:- 1. A two-tube hydraulic shock absorber comprising an inner tube bounding a working cylinder and an outer tube bounding an annular reservoir, the outer tube having at least at one end an end portion of smaller diameter than a central portion thereof, and an annular baffle ring carried on the outside of the inner tube and having dimensions in directions transverse to the axis of the inner tube such that the ring cannot pass freely through the said one end portion, the baffle ring being sufficiently resilient to permit passage of the baffle ring on the inner tube past the said one end portion.

2. A shock absorber as claimed in Claim 1 in which the baffle comprises a support ring in contact with the outside of the inner tube and a flexible skirt projecting outwardly from the ring.

3. A shock absorber as claimed in Claim 2 in which the skirt is thinner than the ring.

4. A shock absorber as claimed in Claim 2 or Claim 3 in which the skirt projects radially from the support ring.

5. A shock absorber as claimed in Claim 2 or Claim 3 or Claim 4 in which the skirt has notches in its outer periphery.

6. A shock absorber as claimed in Claim 2 or Claim 3 in which the working cylinder contains a working piston attached to a piston rod which projects from one end only of the working cylinder and the skirt is inclined outwardly and away from that end.

7. A two-tube hydraulic shock absorber substantially as described herein with reference to Figures 1 and 2 of the accompanying drawings.

8. A shock absorber as claimed in Claim 7 modified substantially as described herein with reference to Figure 3 or to Figure 4 of the accompanying drawings.

9. A method of making a two-tube hydraulic shock absorber comprising providing an inner tube bounding a working cylinder and an outer tube bounding an annular reservoir and having at least at one end an end portion of smaller diameter than a central portion thereof, attaching to the outside of the inner tube an annular baffle ring at least part of which is resiliently flexible and which has dimensions in directions transverse to the axis of the inner tube such that the ring cannot pass freely through the said end portion, and telescoping the inner tube within the outer tube while temporarily flexing the ring to cause it to pass through the said end portion into the central portion.

10. A method of making a two-tube hydraulic shock absorber substantially as described herein with reference to Figures 1 and 2 of the accompanying drawings.

11. A method as claimed in Claim 10 modified substantially as described herein with reference to Figure 3 or to Figure 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. between the periphery of the skirt portion and the outer tube 7, in contrast to the effect of such a deflection of the baffle ring shown in Figures 1 and 2 where any deflection will increase the clearance and hence the area of the fluid flow path between the baffle ring and the outer tube. The baffle rings described above may be made of plastics material, for example nylon. WHAT WE CLAIM IS:-

1. A two-tube hydraulic shock absorber comprising an inner tube bounding a working cylinder and an outer tube bounding an annular reservoir, the outer tube having at least at one end an end portion of smaller diameter than a central portion thereof, and an annular baffle ring carried on the outside of the inner tube and having dimensions in directions transverse to the axis of the inner tube such that the ring cannot pass freely through the said one end portion, the baffle ring being sufficiently resilient to permit passage of the baffle ring on the inner tube past the said one end portion.

2. A shock absorber as claimed in Claim 1 in which the baffle comprises a support ring in contact with the outside of the inner tube and a flexible skirt projecting outwardly from the ring.

3. A shock absorber as claimed in Claim 2 in which the skirt is thinner than the ring.

4. A shock absorber as claimed in Claim 2 or Claim 3 in which the skirt projects radially from the support ring.

5. A shock absorber as claimed in Claim 2 or Claim 3 or Claim 4 in which the skirt has notches in its outer periphery.

6. A shock absorber as claimed in Claim 2 or Claim 3 in which the working cylinder contains a working piston attached to a piston rod which projects from one end only of the working cylinder and the skirt is inclined outwardly and away from that end.

7. A two-tube hydraulic shock absorber substantially as described herein with reference to Figures 1 and 2 of the accompanying drawings.

8. A shock absorber as claimed in Claim 7 modified substantially as described herein with reference to Figure 3 or to Figure 4 of the accompanying drawings.

9. A method of making a two-tube hydraulic shock absorber comprising providing an inner tube bounding a working cylinder and an outer tube bounding an annular reservoir and having at least at one end an end portion of smaller diameter than a central portion thereof, attaching to the outside of the inner tube an annular baffle ring at least part of which is resiliently flexible and which has dimensions in directions transverse to the axis of the inner tube such that the ring cannot pass freely through the said end portion, and telescoping the inner tube within the outer tube while temporarily flexing the ring to cause it to pass through the said end portion into the central portion.

10. A method of making a two-tube hydraulic shock absorber substantially as described herein with reference to Figures 1 and 2 of the accompanying drawings.

11. A method as claimed in Claim 10 modified substantially as described herein with reference to Figure 3 or to Figure 4 of the accompanying drawings.