GB2027517A

GB2027517A - Combined fluid damper and elastomeric spring unit

Info

Publication number: GB2027517A
Application number: GB7927606A
Authority: GB
Original assignee: South African Inventions Development Corp
Current assignee: South African Inventions Development Corp
Priority date: 1978-08-09
Filing date: 1979-08-08
Publication date: 1980-02-20
Also published as: JPS5524299A; AU4976879A; DE2932131A1; ZA784514B; FR2433135A1

Abstract

A damper device comprises a plunger member 106 movable within a cylinder member 100 and sealed thereto by an elastomeric annulus 110 secured to the members so that relative movement of the members is resiliently restrained. The cylinder member 100 defines with the elastomeric annulus and the plunger member a sealed space which contains a hydraulic fluid and which is divided into two variable volume chambers 142 and 144 by a partition 108 past or through which restricted flow of the hydraulic fluid is permitted. In the example of Figure 2 the sealed space is located between the elastomeric annulus 110 and a closed end 102 of the cylinder 100, and the partition 108 is fixed on the plunger member 106. In other examples (Figures 1 and 4) the sealed space is located between the elastomeric annulus 110 and a further similar elastomeric annulus axially spaced therefrom and also secured to the plunger and cylinder members. In this case the partition is fixed to the cylinder member and, if desired, at least one piston having a restricted flow passage therethrough may be secured to the plunger to sub-divide the space into further variable volume chambers. <IMAGE>

Description

SPECIFICATION Damper device This invention relates to a damper device which can, with slight modification, also be constructed to provide a pre-determined resilient restraint against relative movement of two members.

The invention seeks to provide a device as mentioned above which is of inexpensive, reliable and compact construction.

According to the invention a damper device comprises a cylinder member; a piston member movable in the cylinder member and protruding from at least one end thereof; an elastomeric annulus secured in a fluid tight manner to the cylinder member and to the piston member and providing a predetermined resilient restraint against relative axial movement of the piston member and the cylinder member; means forming a sealed space between itself, the piston member, the cylinder member and the elastomeric annulus; and means partitioning the sealed space into at least two variable volume spaces that are in communication with one another through at least one opening in the partitioning means that permits restricted flow of hydraulic fluid between the variable volume spaces.

The means forming the sealed space may provide a further seal between the piston member and the cylinder member in the event that the piston member passes through both ends of the cylinder member or may provide a closure to the other end of the cylinder member when the piston member passes through one end only of the cylinder member.

The sealed space forming means may be solid or may be elastomeric as desired.

The partitioning means may be an annulus integral with one of the piston and cylinder members and extending in a radial direction to be adjacent the other of the members to form an annular gap of predetermined clearance through which a restricted flow of hydraulic fluid is permitted. Alternatively the partitioning means may be an annulus integral with one of the members and slidably sealed to the other member with holes being formed through the annulus through which a restricted flow of hydraulic fluid is permitted. This latter alternative is preferred as it is a relatively simpler matter to drill holes accurately of a desired diameter than it is to machine the annulus and sleeve or piston members to form the required annular gap.

The elastomeric annulus may be secured in a fluid tight manner to at least one of the members by means of a sleeve bonded to the annulus and slidable on the member, the sleeve being secured to the member by being compressed between two opposed lands provided on the member, with the structure forming one of the lands being movable.

One of the lands may be formed as a step in the member and the other land may be provided by an annular rib on a threaded part which may be screwed on the member into engagement with the member or which may be a washer that slides on the member and may be forced axially relatively to the member by an appropriate securing means. This construction facilitates speedy and simple repair of the elastomeric annulus should this be required. The annulus may also be bonded directly on to one or both of the members using a suitable adhesive which is later cured - this ensures a good seal without having to resort to O-rings or other sealing means. The elastomeric annulus is a particularly advantageous construction as it provides an effective seal between the piston and cylinder members while permitting controlled relative movement of these members.

The predetermined resilient restraint provided by the elastomeric annulus may take two forms. In a first form the restraint is significant so that the device operates both as a spring and a damper, i.e.

also provides springing between two relatively movable members connected to each other by the device of the invention. In a second form the restraint is slight so that the annular member merely forms a flexible plunger and the spring effect may be ignored.

Further features and advantages of the invention will become apparent from the following description made with reference to the accompanying drawings, in which: Figure 1 shows a schematic sectioned view of a spring-damper device of the invention; Figure 2 shows a schematic view of a variant of the spring-damper device of the invention; Figure 3 shows a schematic, partly sectioned, pictorial view of an application of the device of Figure 2 to a drawgear suitable for use between railroad cars; Figure 4 shows a damper device constructed to have a substantially linear damping factor in its "working range" as described below; and Figure 5 is a graph schematically illustrating the performance of the device of Figure 4.

Figure 1 shows a spring-damper device of the invention comprising a piston 10, a cylinder 12 which receives the piston 10 therethrough, two elastomeric annuli 14 each secured in a fluid tight manner to the piston 10 and cylinder 12, and screwed on end caps 16 for the cylinder 12. The device further includes partitioning means provided by annuli 18 and 20 of which the annuli 18 are integral with the piston 10 while the annulus 20 is integral with the cylinder 12. An annular gap 22 is formed between the annulus 18 and the cylinder 12 and an annular gap 24 is formed between the annulus 20 and the piston 10. As will be seen from the drawings four variable volume spaces 26,28,30 and 32 are formed between the annuli 14, the cylinder 12, the piston 10, and the annuli 18 and 20.

The variable volume spaces are filled with a suitable hydraulic fluid, such as oil, paraffin, water, brake fluid and the like, as desired.

In greater detail the device of Figure 1 is made up as follows. The piston 10 includes a central rod 34 a portion of which is threaded to engage a nut 36 as shown. Spaced from the thread portion is an enlarged diameter portion 38 with the junction between the portion 38 and the rod 34 forming an abutment shoulder or land 40. Fitted to the rod 34 and squeezed between the shoulder 40 and the nut 36 are the following elements proceeding from left to right:- a sleeve 42, the annulus 14, a bush 44 which is integral with annulus 18, another bush 44 which is integral with the other annulus 18 and then the second annulus 14. Each annulus 14 comprises an inner sleeve 46 of metal or appropriate plastics, a co-axial outer sleeve 48 and a body of elastomeric material 50. The inner sleeve 46 is compressed between opposed ends of the sleeve 42 and the bush 44.To ensure good sealing an O-ring 52 is provided between the rod 34 and the inner sleeve 46, a suitable groove 54 being formed in the rod 34. With regard to the cylinder 12 each annulus 14 is sealed to the cylinder 12 in a fluid tight manner by having the outer sleeve 48 compressed between a shoulder 56 formed in the cylinder 12 and a washer 58 which abuts a skirt 60 on the cap 16.

In practice, the device of Figure 1 is used for providing springing and damping between two relatively movable parts by securing one part to the cylinder 12 and the other part to the piston 10. When the parts move relatively to one another the annuli 14 are stressed in shear and the volumes of the spaces 26 to 32 to vary because the annuli 14 act as plungers. As these volumes vary fluid flows between these spaces through the gaps 22 and 24. These gaps inhibit the flow of the hydraulic fluid so that damping takes place. Clearly the amount of damping depends on the sizes of the gaps 22 and 24.

In a variant of the device of Figure 1 which has not been shown, since it is readily apparent to any person, seals, such as O-rings, are provided to seal the gaps 22 and 24. Then holes are formed through the annuli 18 and 22 through which the fluid can flow in a controlled manner.

Figure 2 shows a spring-damper device of the invention including a cylinder 100 having one end closed by an end wall 102 and provided with mounting flanges 104. A piston 106 having an annular fiange 108 is fitted into the cylinder 100. An elastomeric annulus 110 composed of concentric cylinders of rubber 112 and metal 114 that increase the sheer stiffness of the annulus is secured to the cylinder 100 and piston 106 in fluid tight manner.

The connection to the cylinder 100 involves a rim 116 which is externally threaded to engage correspond ing threads on the cylinder 100 and which is internally bonded to the outermost rubber cylinder 112. The connection to the piston 106 involves a shoulder 18 formed on the piston and a circlip or collar 120 which engages the piston 106 and clamps the innermost metal sleeve 114 between itself and the shoulder 118. Suitable O-rings 122 and 124 are provided as shown. A coil spring 125 is provided to bias the annulus 108 away from the wall 102. An axial projection 126 on the piston 106 fits into an inner sleeve 128 mounted on the wall 102 by a cylindrical hollow turret 130. A space 132 for air is formed between the end of the projection 126, the interior of the turret 130 and the sleeve 128. A sealing plug 134 of rubber or neoprene is provided in a bore in the space 132.

Aspring-loaded one-way valve 136 is provided in the annular flange 108.

A cylindrical clearance space or gap 138 is formed between the periphery of the flange 108 and the internal walls of the cylinder 100. The dimensions of this gap are so selected to allow a pre-determined restricted flow of fluid between variable volume spaces 144 and 142 formed in the cylinder to either side of the annular flange 108. Thus, when the piston 106 is forced into the cylinder 100 the elastomeric annulus 110 and coil spring 124 resiliently oppose this movement and at the same time fluid flows from the chamber 142 to the chamber 144 through the gap 138 in a controlled manner to effect damping of the movement of the piston relatively to the cylinder. On the return stroke, i.e. under the influence of the annulus 110 and spring 124, the one way valve 136 opens and allows the hydraulic fluid to pass readily from the chamber 144 to the chamber 142.

The interior of the cylinder 110 is tapered from its open end to the end wall 102. This taper is too slight to be shown on the drawings. The taper has the effect of giving soft cushioning or damping initially and progressively getting harder towards the limit of the stroke. This is a further advantageous feature of the invention.

Figure 3 shows an application of the springdamper of Figure 2 as applied to a drawgearwhich is usually provided in the coupling between railroad cars. As shown pictorially, since the parts are substantially standard, one of the cars, i.e. the one provided with the drawgear, is fitted with a frame 150 which supports the cylinder 100 by means of stops 152. A conventional yoke 154 is also supported on the frames 150, but in this event for longitudinal movement in one direction only from a rest position.

Longitudinal movement in the other direction is prevented buy a plate 156 which abuts further stops 158 which define the rest position. The plate 156 abuts the piston 106. A buffer 160 of another railway truck, when the trucks collide, first into the yoke 154 and pushes against the plate 156 which, in turn, forces the piston 106 into the cylinder 100. Move ment of the piston into the cylinder is resiliently opposed and is damped as discussed above with reference to Figure 2.

Figure 4 shows a damper device of the invention which is constructed to have a linear damping factor and in which the restraints offered by the elastomer ic annuli are largely unimportant with respect to the functioning of the device. There is some similarity between this device and the device of Figure 1 so that parts which are similar to those shown in Figure 1 have been given the same reference numerals but with the prefix of 200. The drawing shows a piston member 210 composed of a central rod 234 formed with an enlarged diameter portion 238 at one end and a step or shoulder 240 formed between the rod 234 and enlarged diameter portion 238. A nut 236 engages a threaded portion on the rod 234 and squeezes between itself and the shoulder 240 the following elements in order:- a sleeve 242, an elastomeric annulus 214, a further sleeve 244, and a further annulus 214. The annuli 214 are bonded to the rod 234 using a suitable adhesive, such as an epoxy adhesive, which is then cured. The piston 210 is movable within a cylinder 212 and is guided therein by means of end caps 216 fitted to each end of the cylinder. The cylinder 212 is also formed with a central annulus 220 which extends radially inwardly from the wall of the cylinder to the sleeve 244 and is sealed thereto by a suitable O-ring 248. The radially outer edges of the annuli 214 are bonded to the inner walls of the cylinder and are also clamped between a washer 258, which abuts a skirt 260 on the end caps 216, and a shoulder 256 formed internally in the cylinder 212. Two chambers 226 and 228 are formed between the piston rod, annuli 214, cylinder 212 and annulus 220, with these chambers being in communication with each other through holes 262 bored through the anulus 220.Holes 264 are formed through the cylinder 212 to permit filling of the chambers 226 and 228 with a suitable hydraulic fluid, such as oil, brake-fluid, water and the like.

The elastomeric annul 214 are constructed to form a suitable seal between the piston and the cylinder while at the same time providing the means or plungers for moving the hydraulic fluid in the chambers 226 and 228 between each other. A significant feature is that the annuli 214 have a stiffness which is capable of generating pressure in either of the chambers 226 and 228 but which, when this pressure tends to exceed a value predetermined by the stiffness of the annuli, bulge resiliently outwardly as a result of the pressure, so that the pressure remains substantially constant at that predetermined maximum value. Thus the damper of Figure 4 provides a predetermined maximum damping factor above which the device acts resiliently in accordance with the resilience of the annuli 214.

Hence, the damper is suitable for use in a structure which can accommodate certain forces only, so that when the piston and cylinder move rapidly with respect to each other resistance to this movement is limited to a set maximum. Another important feature of the device is that even before reaching the stage where the annuli 214 bulge outwardly, the annuli deform resiliently - but without bulging - as the pressure increases. As will be explained below this ensures that the damper has a constant 'damping factor".

As is well known in the art the resistance of a damper increases when the relative velocity of the cylinder and piston increases. In other words the damping force of the device increases as the relative velocity increases. Unless care is taken this rate of increase of force is not linear and if the communication between the chambers in the damper is a fixed cross-section opening the damping factor will increase with increasing velocity. For this reason known damping devices provide spring biassed valves for the flow openings for fluid, but this is not convenient, is expensive, and is unreliable. This invention, on the other hand, relies on the resilience of the annuli 214 to produce a device with a constant damping factor and, in addition, a device which has a maximum damping force.Moreover construction and assembly of the device are relatively easy and, since simple rugged elements are used, the device will be reliable in use.

Figure 5 shows a graph illustrating the relationship of the "damping force" of the device of Figure 4 in relation to piston velocity with respect to the cylinder. The "damping factor" is the slope of the curve at any particular point. Thus in the present example the holes 262 are made sufficiently large that for low piston velocities the device offers substantially no resistance to the relative movements of piston and cylinder. When a particular relative velocity is reached then there is resistance to fluid passing through the openings 262 and the device offers a resistance; this is known as the "damping force".

The damping force increases with increasing velocities until a maximum is reached whereafter the annuli bulge outwardly so that the damping force remains constant. As shown there is a range of velocities in which the curve is substantially straight and in which, therefore, the damping factor is substantially constant; this is the "working range" of the device. In this working range the device has a linear damping characteristic. As will be appreciated this working range can be varied as desired. For example the range of low speeds for which the device is ineffective, i.e. does not provide any damping force, can be controlled by varying the size of the openings 262. The damping factor, i.e. the slope of the graph, in the medium velocity range, can be controlled by varying the resilience or construction of the annuli 214.Also, the maximum damping force of the device can be controlled by suitably constructing or varying the resilience of the annuli 214.

While considerable emphasis has been placed on the structure of the preferred embodiments herein illustrated and described, it will be appreciated that many changes can be made in the structures and structural inter-relationships shown without departing from the principles of the present invention. In this respect, for example, in the embodiment of Figure 2 instead of having a solid end wall 102, a turret 130 formed with a space and a protrusion on the piston which moves into the recess in the turret, the end wall 102 may be made of a flexible material, such as another elastomeric disc. Also the number of annuli forming partitions in each of the embodiments illustrated can be varied as desired. These and other changes will be suggested to or be obvious to those skilled in the art from the foregoing description of the preferred embodiments, as will other embodiments of the invention, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the present invention and not as limiting.

Claims

1. A damper device comprising a cylinder member; a piston member movable in the cylinder member and protruding from at least one end thereof; an elastomeric annulus secured in a fluid tight manner to the cylinder member and the piston member and providing a predetermined resilient restraint against relative axial movement of the piston member and cylinder member; means forming a sealed space between itself, the piston member, the cylinder member, and the elastomeric annulus; and means partitioning the sealed space into at least two variable volume spaces that are in communication with one another through at least one opening in the partitioning means that permits restricted flow of a hydraulic fluid between the variable volume spaces.

2. A damper device as claimed in claim 1, in which the piston member passes through both ends of the cylinder member and in which the means forming the sealed space comprises a second elas tomericannulussecured in a fluid tight manner to the piston member and the cylinder member.

3. A damper device as claimed in claim 1, in which the piston member passes through only one end of the cylinder member and in which the means forming the sealed space forms a closure for the other end of the cylinder member.

4. A damper device as claimed in claim 3, in which the closure is solid and is substantially non-deformable.

5. A damper device as claimed in claim 3, in which the sealed space forming means is a further elastomeric annulus.

6. A damper device as claimed in any of claims 1 to 5, in which the elastomeric annulus comprises an annulus of elastomeric material and at least inner and outer sleeves of a material relatively harder than the elastomeric material, each of the sleeves being bonded to the anulus of elastomeric material.

7. A damper device as claimed in any of claims 1 to 6, in which the elastomeric annulus is bonded to at least one of the piston and cylinder members.

8. A damper device as claimed in any of claims 1 to 6, in which the elastomeric annulus has at least one of its radially inner and outer ends clamped to the piston member or cylinder member, respectively.

9. A damper device as claimed in claim 8, in which the elastomeric annulus is clamped by means of two opposed lands provided on the member, at least one of the lands being movable to squeeze the elastomeric element between itself and the other land.

10. A damper device as claimed in any of claims 1 to 9, in which the device acts as a combined spring and damper in that the stiffness of the elastomeric annulus is such as to provide a desired resilient restoring force when it is deflected in shear.

11. A damper device as claimed in claim 10, in which at least one concentric sleeve of material that is relatively harder than the elastomeric material of the annulus is embedded in and bonded to the elastomeric material to increase its shear stiffness.

12. A damper device as claimed in either of claims 10 or 11, in which further spring means is provided inside the cylinder to increase the resilient restraint offered by the device when the piston and cylinder members are moved relatively to one another.

13. A damper device as claimed in claim 12, in which the further spring means includes a coil spring that acts between a partitioning means secured to one of the members and a fixed part on the other of the members.

14. A damper device as claimed in any of claims 1 to 9, in which the device acts substantially as a damper only and the resilient restoring forces provided by the elastomeric annulus are largely ignorable in that the elastomeric annulus is constructed to deflect under pressure of a hydraulic fluid in the variable volume space of which the elastomeric annulus forms one wall such that the pressure in this space increases in a controlled manner.

15. A damper device as claimed in claim 14, in which the elastomeric annulus is constructed to deflect in such a manner that the damping factor of the device is substantially constant over a desired range.

16. A damper device as claimed in either of claims 14 or 15, in which the elastomeric annulus is constructed to deflect in such a manner that the pressure in the sealed space of which the elastomeric annulus forms one wall is prevented from exceeding a predetermined maximum value, whereby the damper device provides a damping force which does not exceed a predetermined maximum value.

17. A damper device as claimed in any of claims 1 to 16, in which the partitioning means comprises a stiff annulus integral with one of the piston and cylinder members and extending in a radial direction to be adjacent the other of the members to form an annular gap of predetermined clearance between itself and the other member through which a restricted flow of hydraulic fluid is permitted.

18. A damper device as claimed in claim 17, in which the member that is movable with respect to the annulus has a tapered surface so that the width of the annular gap varies axially along the damper device, whereby the damping force varies with increasing displacement.

19. A damper device as claimed in any of claims 1 to 16, in which the partitioning means comprises a stiff annulus integral with one of the members and slidably sealed to the other member with holes being formed through the annulus through which a restricted flow of hydraulic fluid is permitted.

20. A damper device as claimed in claim 19, in which a one-way valve is provided in at least some of the holes to control the flow of liquid through the holes in the annulus of the partitioning means.

21. A damper device as claimed in any of claims 1 to 20, in which the partitioning means includes a first stiff annulus fixed to one of the members and extending towards the other of the members and two further stiff annuli, one being on each side of the first annulus and each being fixed to the member movable relatively to the member to which the first annulus is secured, so as to form four variable volume spaces in communication with one another through at least one opening formed in each annulus providing restricted flow paths for hydraulic fluid.

22. A damper device substantially as herein described with reference to any of Figures 1, or 2 and 5, or 3, or 4 or substantially as illustrated in any of Figures 1 to 4 of the drawings.