DE2302657A1 - ENERGY ABSORBERS - Google Patents

Description

Energy absorber

Priorities: Norway from 19.1.1972 and 1.3.1972

The invention relates to hydraulic energy absorbers Design in which a piston with no holes is arranged in a cylinder filled with liquid is.

An energy absorber of this type is described for example in US Patent 2,333,095 (GH Dowty) and includes a container filled with a compressible fluid cylinder and a perforated plunger, _λ entering one end of the cylinder and is mounted on a piston rod which by extends outside through an Eohrung in the cylinder front closure. This forehead closure preferably comprises sealing devices which prevent liquid from escaping from the cylinder.

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ORIGINAL INSPECTED

It is necessary to use a compressible element in an energy absorber of this type. In addition to the relatively small deformations that occur in the cylinder itself when the plunger is pressed in, the additional volume formed by the piston rod part must be provided by compressing the contents ¹ DZVT. is squeezed. The degree of compression will then depend on how far the plunger and the piston rod have been priced inwards, i.e. it will also depend on the ratio between the cross-sectional areas of the piston rod and the internal volume of the cylinder. Certain dimensions of the cylinder can therefore reduce the proportion of the damping force due to compression can be selected by giving the piston rod a suitable diameter. When loaded, i.e. when the plunger penetrates the cylinder, the increasing pressure in the cylinder is approximately balanced on both sides of the plunger and the plunger and piston rod are then subjected to a restoring force that is equal to the product of the fluid pressure and the cross-sectional area of the piston rod.

The shock absorber known from US Pat. No. 2,333,095, on the one hand, and the measure according to the invention, on the other hand, have one feature in common, which is the use of a liquid and the fact that the compression of at least part of the cylinder content provides a restoring force, which means that ₍ Every compression of the absorber generates a force which tries to bring the absorber back into its unloaded state. The liquid can be compressible and a compact

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pressibies element "form.

The cylinder is filled with liquid under atmospheric conditions. Pressure before the piston and the forehead lock are provided an infinitesimal small force is theoretically capable of a small compression of the ! compress iblen element to bring about. To prevent, that the absorber rattles, for example, or ux to achieve that the compression only by an active Krafx takes place above a certain minimum, the Earth the absorber arranged with precompression, d. H. the attachment of plunger and forehead closure can through a suitable compression of the cylinder contents can be carried out. This is a well-known principle in shock absorbers.

A number of ways are available to obtain compressibility. Besides using a compressible fluid, as described in the said US patent, the cylinder can be a resilient Element contain, for example, a spring-loaded piston that presses against the liquid, a compressibie Loading of a solid material such as rubber or plastic (cellular plastic) or a gas load or filling, which is optionally enclosed in a flexible envelope within the cylinder. The 'springy Element can also be located in a separate chamber in fluid communication with the cylinder. That Resilience can also be achieved through a combination of elements, so can the liquid itself Be cosipressible and resilient together with another

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ORIGINAL INSPECTED

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The measure according to the invention is obviously not depending on a certain type of resilient element and it should continue to be clear that the given Examples are not "limiting to the invention. What is essential and what even with other devices." as the mentioned can be brought about is the compensation of the volume in the cylinder during Compression occurring piston rod, this compensation being carried out by means of an elastic element can be.

The choice of the resilient element can be essential for the characteristics of the absorber. In absorbers of the type described, the damping force results from two main components, that is the force resulting from the above-mentioned compression, which is called the resilient force in the following, and the viscose damping force that arises when the liquid flows through the holes in the plunger. The resulting damping force depends on several factors such as the shape, size and number of holes in the plunger, the relative speed of the plunger and cylinder, the viscosity of the liquid, the compressibility of the liquid and the spring force of the resilient element. The main purpose of the invention is to create a Dä rrr fungskraftcharakteristik which is more favorable for a certain purpose than the known absorber and in particular this should be achieved by the invention as possible due to special properties of the liquid.

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The "accompanying drawing is a diagram and shows the course of the damping force K over the length of the stroke s for a known type of liquid absorber, for example for certain oils, the compressibility of which is about 10-20 $> ■ . The filling can also consist of an incompressible fluid or a compressible element. The diagram also shows a force corresponding to a pre-compression. The resulting force K is equal to the sum of the spring force ΐ and the viscous damping D. The diagram also shows the relative speed ν between plunger and Cylinder.

A certain upper limit for the maximum power E ^ „_ makes it possible to achieve an efficiency for absorbers of this type to define. Through the force of K “and

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the jj & nge of the stroke s becomes the maximum available energy that can be absorbed by the absorber, equal to K _ = xs. This is indicated in the diagram by a rectangle with height K and length s. The performance of the absorber can then be defined as the fraction of this energy that the absorber can absorb with the same maximum force and the same length of the stroke.

For some purpose it is desirable to have the greatest possible efficiency. This is for example of importance in collisions between vehicles. Eei such a cushioning for the purpose of harm It is to prevent or limit on motor vehicles and / or people and animals in the motor vehicles

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essential that the delay at the moment of the collision doesn't get too big. Such is the maximum contraction force limited. Due to the weight, appearance and size of the motor vehicle, it is also desirable to optimize the damping system in terms of dimensions and se E.g. a limit was set with regard to the length of the stroke for the absorber.

The above-mentioned example does not mean any 3egrer.zu.nr: ■ for the use of the absorber according to the invention, only serves to explain a case in which the damping force K acts as gently as possible.

It is a known fact that viscous damping increases with the flow rate of the liquid through the holes in the plunger at a roughly constant viscosity, i.e. Newton's liquid, increases. Based It will be seen from the drawing that the efficiency of the absorber increases when the damping force K is increased could before and after it has reached its maximum value K. One possibility is to increase the suspension force F by adding a higher compression either through increased pre-compression, a thicker piston rod (in relation to the cylinder diameter) or both are exposed.

Pre-compression beyond a certain limit is not desirable. An increase in the spring force would also to a higher degree of resilience according to Sta.3 lead, which is sometimes undesirable.

A combination of resilient elements can be a favorable

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They have an influence on the characteristics of the absorber, as an element can be relatively easily compressible and can result in a small spring force over part of the stroke, whereupon a heavier compressible Έ! βζβώ. ± must be compressed by continuing to compress the absorber. As a result, the spring force increases relatively strongly towards the end of the stroke su and compensates for the decreasing viscous damping force. In this way the efficiency of the absorber can be increased.

Another way to increase the absorber characteristics change, which is essential according to the invention, is the viscous damping force D before and after Increase maximum point.

This can be achieved by using a liquid which is Bingaam-plastic, which means that, in contrast to the Newton ¹ see liquid, the liquid must be subjected to a certain shear stress before it begins to flow through an opening of a certain dimension, for example.

For a better understanding of the influence of the Ingham plasticity In an absorber of this type one can have the advantage that the plunger is constant during the stroke against the liquid, which is roughly at rest, regardless of possible compression. During the day During the stroke, the liquid will flow through the relatively small holes in the plunger. Is this liquid binghamplastic so this flow is not triggered until the

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liquid exposed to a certain shear stress is. If this shear stress is reached, the liquid theoretically flows through the holes at a constant rate Speed when a constant viscosity is assumed. This, in turn, should be at a constant viscosity. * However, this is based on the assumption that: 3 the liquid, because of its compressibility, compensates for the fact that the speed of the plunger is related to of the cylinder is not constant during the stroke. In fact, the shear stress increases at the beginning of the stroke up to a value that is slightly higher than the vert required to start flow through the holes, whereupon the shear stress should decrease towards the limit value. Once this limit is reached, the flow stops.

In the drawing, in which an imaginary course of the bending force K is shown, F is the spring force which results from the compression of the cylinder contents; D is the viscous damping force using a Newtonian fluid and D ¹ is the viscous damping force using a Bingharu plastic fluid. The force K ¹ is the sum of the forces D ¹ and F. Kit of the same xaximal force K leads the Bingham plastic liquid to an efficiency better than that of the Newtonian liquid.

Has the use of a Biigiam plastic liquid also has a further significant influence, since this reduces the risk of leakage. This is especially important for Absorber with pre-compression, with which leaks easily, the same

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if they are in the wrong position "can occur. The fact that the pre-compression is below the pressure "some seal design does The shear stress necessary for the fluid flow to begin to flow through the seal " is such that licking theoretically under conditions of rest " will not occur. The use of Bingham plastic Liquid has proven to be very beneficial in practice, in order to prevent leaks, especially in the case of absorbers that are very rarely used.

An exemplary embodiment of the invention comprises one. Absorber with lonely plastic liquid, both de.:, the liquid is also thixotropic, which means that the liquid viscosity changes as the liquid changes is exposed to a stirring movement. When the liquid is at rest, its viscosity is high. By Stirring will decrease the viscosity and become very low even for a period of time after the stirring is stopped has remained and then to the original value after it has been at rest for a certain period of time, to return. First, this will further reduce the risk of leakage. There is another essential effect in that the return movement of the plunger after a stroke will take place with less resistance than if a non-thixotropic liquid was exposed to a Viscosity would be used which gives the same maximum force as the thixotropic liquid. During the stroke forms the flow of liquid through the holes in the Plunger a kind of agitation and the viscosity of the liquid will decrease. The viscous damping during the The return movement decreases because this damping is

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decrease in viscosity. Thus, a Return movement achieved by means of a smaller spring force will. Sufficient spring force can be. so achieve at a lower fluid pressure, what is desirable from both a functional and structural point of view Reasons is. The reason for the low viscosity maintained during the return stroke is that the thixotropic effect depends on time. Subsequent to a stirring or agitation process and thus a decrease in the viscosity the liquid must rest for a certain period of time before the maximum viscosity becomes attainable again. This imposes a limitation on the use of the absorber, as it is extremely suitable for shock absorption, which occurs in such long time intervals occurs that the maximum viscosity is reached before the next shock occurs.

The Bingham plasticity and the thixotropic effect can be created by adding highly dispersive IC materials, for example, to common shock absorber fluids or silicone oil or other compressive fluids. Typical examples of such materials are SiOp and AlpO ^. However, it is not you for .erfindungsgemäße I'Iaßnahme importance which liquid or which additives are verweilet if only the liquid Bingham-plastic can be made if appropriate also thixotropic and is suitable for use in energy absorbers.

As an example of liquid in an energy absorber

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According to the invention, silicone oil should be mentioned which, in its pure state, has a viscosity between 10,000 and 100,000 cS (centistckes) and to which 5 to 15 percent by weight SiO _{2 has been} added.

A suitable silicone oil was Dow Corning 200 and 210 scwie uses SiOp, which is marketed under the name Cabcsil will.

Ali SAYING]

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Claims (10)

Claims ί Iy Hydrauliseher shock absorber and the other end of the cylinder sealed with a cylinder, an inner piston with at least one hole "or a bore, which is mounted on a ^ piston rod which extends outwardly through a bore in an end cap of the 'cylinder, and the contents of the cylinder yields resiliently against the entering volume of the piston rod by compression of the energy absorber and consists at least partially of a liquid, characterized in that the liquid has Binghar plastic properties. 2. Energy absorber according to claim 1, characterized in that the liquid is compressive. 3. Energy absorber according to claim 1 or 2, characterized in that the cylinder also has at least one Contains koxpressibles non-liquid element. 4. Energy absorber according to one of claims 1 to 3, characterized in that the cylinder content is the entire Cylinder volume, with the piston in the outer position, fills. 5- energy absorber according to claim 4, characterized in that that the contents of the cylinder, when the piston is in its outer position, can be seen beyond the atmosphere Has pressure. 309831/0462 6. Energy absorber according to one of claims 1 to 5, characterized in that the liquid is thixotropic
is. 7. Energy absorber according to one of claims 1 to 6, characterized in that the liquid is a silicone oil is. 8. Energy absorber according to one of claims 1 "to 7, characterized in that the liquid contains Al ₂ O ^. 9. Energy absorber according to one of claims 1-7,
characterized in that the liquid contains _{SiO 2.} 10. Energy absorber according to claim 8, characterized in that the liquid is a silicone oil, which in the pure state has a viscosity between 10,000 and
100,000 cS (Centistokes) and to which between 5 and 15 percent by weight SiOp were added. 309831/0462 Blank page