Background to the invention

Technical field

The present invention relates to a method, according to the preamble of Claim 1, for absorbing a shock-like load. Wire- rope isolators are used for reducing shock-like loads (e.g., in military vehicles and warships) . Shock isolators are generally used for reducing a shock-like load. The invention also relates to a shock absorber for implementing the method. Description of the prior art

The defence forces of many countries are using shock isolators

(e.g., wire-rope isolators) to protect against impact loads

(for example, in ships, for protection against bottom mines and torpedoes) .

There are various types of shock isolators . USA patents 5,549,285 and 6120014 and JP application publication JP02272160 disclose examples of wire-rope isolators. A wire- rope isolator consists of wire-rope loops, the upper and lower parts of which are secured between metal plates. Other types of isolator, such as air springs and rubber isolators, can often be used in place of a wire-rope isolator. Due to the limited nature of a flexible element, a shock absorber, such as a wire-rope isolator, equipped with a flexible element has a limited range of flexibility between maximum compression and maximum tension. The tension side is typically progressive, i.e. non-linear, requiring an increasing force against displacement. When isolating from a shock-like load, a typical weakness of shock isolators (e.g., wire-rope isolators) are their great increase in rigidity, when the isolator is subject to a tensile force.

Summary

The present invention is intended to eliminate the drawbacks of the known solution models . The characteristic features of the invention are stated in the Claims . According to the method, the area of the said tension side is corrected with a consecutive flexible additional part, by means of which the progressive flexibility of the tension side is made to be more linear and to correspond to the flexibility of the compression side, the additional part being otherwise rigid. The invention eliminates the typical problem of a shock isolator under a shock-like load and gives better protection for the isolated object. In addition, in a preferred embodiment, the isolator is constructed in such a way that the isolation of high frequencies (e.g., more than 50 Hz) will improve substantially.

The invention significantly improves the isolation capability of shock isolators. The additional flexible part according to the invention can be retro-installed in principle in any traditional shock isolator whatever and will substantially improve its existing isolation capability under a shock-like load.

The invention reduces a shock-like load from the object being protected to about one-half, or, in some cases, even to one- quarter. This significant reduction assists in, for example, maintaining the functioning of the sensitive electronic devices in a ship, if a mine or bomb explodes near the ship, or if a vehicle drives into a pothole or stone at high speed.

The invention increases the possibilities to use shock isolators in civilian applications, in which impact loading occurs .

The additional flexible part (ADDI) according to the invention is a flexible part, which is secured to the upper or lower parts of the isolator.

In a group of preferred embodiment, the additional flexible part (ADDI) consists of one or two plates, which are connected to each other. Part of the plate or lower plate is attached, for example, by bolted connections, to the upper part of the shock isolator while the additional-flexibility part or upper plate is correspondingly attached to the object being protected. The plates are dimensioned in such a way that the plates remain attached under normal loading, but separate from each other under a shock-like loading (e.g., a specific frequency of 10 Hz in the spring mass, or more than 2G) . Normally, a shock-like loading goes through the shock isolator, until it would come under tension, when the isolator carries the load, thus avoiding the shock isolator going to the tension side. In addition, the upper plate of the isolator can be made from a rubbery material, or a rubbery material, which isolates the higher frequencies, can be installed between the plates of the isolator. Brief description of the drawings

Figure 1 shows a perspective view of a shock isolator according to a first embodiment of the invention, Figure 2 shows a side view of the embodiment of Figure 1 as well as an enlargement of a detail, Figure 3 shows a second embodiment of the invention,

Figures 4 and 5 show the elastic plates used in the embodiments of Figures 2 and 3 ,

Figure 6 shows the principle of the method according to the invention,

Figures 7a and 7b show tests comparing embodiments according to the invention,

Figures 8a, 8b, and 8c show the behaviour of a wire-rope isolator carrying a conventional load, during excitation,

Figures 8d, 8e, and 8f show correspondingly the behaviour of an embodiment according to the invention, during excitation,

Figures 9 and 10 show correspondingly two variations and their operation from excitation,

Figures 11a, lib, and 11c show the isolator group in operation as in Figure 1 ,

Figures lid, lie, and llf show the isolator group in operation together with two additional flexible parts,

Figures 12a, 12b, 12c and 12d show some other types of flexible plate.

Detailed description of the invention

In the typical arrangement of a shock absorber according to Figure 1, the wire-rope absorber 10 is attached to a base plate 9, which is, in turn, attached to the base by bolts 7 (Figure 2). As such, the attachment can be freely of any form, as long as it is sufficiently strong. Thus, alternatively the wire-rope absorber attachment can also take place, for example, to an L-beam welded to the hull of a ship, or some other frame.

In the wire-rope absorber 10, there is a selected number of rounds of wire-rope 14, which are secured tightly to upper and lower clamp beams 12, 16, so that between them there are numerous separate 'springs', i.e. lengths of wire rope.

In the embodiment of Figure 1, the additional-flexible part 20 comprises two plates 22, 24 secured to each other at a distance apart, the lower plate 22 of which is attached by bolts 15 to the wire-rope absorber 10 and the upper plate 24 to the load 11, the flexing range being limited essentially to only the tension side.

The plates 22 and 24 are attached at their edges to each other by means of a spacer 28. The plates 22 and 24 and spacer (steel plate) are pressed tightly together by the bolts 24.1 and nuts 22.1. However the lower plate 22 is first attached to the upper clamp beam 16 with an auxiliary strip 26 (steel plate). In Figure 1, all that is visible of the countersunk bolt 15 is head of the nut tightening it from below. Correspondingly, in this construction the upper plate 24 is attached with a strip 32 to the load 11 (e.g., the device frame that must be protected). After this, the plates 22, 24 with the spacers 28 between them can be set opposite to each other and attached to each other.

In Figure 2, the same construction is shown in greater detail, using also an enlarged detail, in which the auxiliary strips 26 and 27 used in the attachment of the plates 22 and 24, as well as the countersunk bolts 15 and 17, can be clearly seen.

Also drawn in Figure 2 is the flexible length L in principle of the additional-flexible part, the ends of which form the force connections CI and C2 to the wire-rope absorber and correspondingly to the load. In Figure 1, the flexible length L is on both sides and both plates continue past the force connections CI and C2. Between the force connections CI and C2 is a flexible part, which is preferably attached to only one surface. It can be formed of several layers of a suitable tape. It prevents high-frequency interference from arising, if the force connections Cl and C2 strike each other. The displacement of the force connection Cl and C2 is prevented on the compression side, but on the tension side they can separate. This rule concerns all the embodiments. As such, the operation is not greatly disturbed, even though the zero point of the additional flexible part 20 deviates to some extent from the zero point of the basic isolator.

In the embodiment of Figure 3, each shock absorber comprises a one-sided additional flexible part 20'. The lower plate 22' is attached to the upper clamp beam 16 of the wire-rope absorber 10 and the upper plate 24', together with a spacer 32, to the load.

Because the plates 22' and 24' are rigidly secured at their ends to both the wire-rope absorber and the load, the specific rigidity of the static support is only slightly more flexible than the preceding case. In this case, the plates 22' and 24' are thicker, in order to achieve the same performance value.

Figure 4 is used to explain the dimensioning of the shock absorber of Figures 1 and 2. The shock absorber is dimensioned for a load of 15 kg. The manufacturer of the wire-rope absorber is Armeka Oy, Finland. Its product code is 146 - 74/80 - 6/10 - I, which refers to the following dimensions: Length of the wire-rope absorber 147 mm, height/width 70/85 mm, wire-rope diameter 6 mm and rounds 10. The additional flexible part 20 (ADDI) plate is a steel plate Fe52, yield strength 335 MPa. The plate's length is 170 mm, its width 150 mm, and its thickness 1 mm.

The dimensioning of the shock absorber of Figure 3 is correspondingly explained with the aid of Figure 5. The wire- rope absorber is the same as the previous one. A steel plate Fe52, yield strength 335 MPa, is used as the plate of the additional flexible part (ADDI) . The plate's length is 150 mm, its width 105 mm, and its thickness 2 mm.

The operating principle of the invention can be understood with the aid of Figure 6. The broken lines show the flexibility of a typical wire-rope isolator relative to force. It will be noted immediately that the curve is nearly linear on the compression side. On the tension side, on the other hand, the wire-rope absorber is quite non-linear after displacement (in this case, 15 mm) . After that, the curve drops rapidly downwards, i.e. an increasing amount of force is required to achieve displacement. Some other types of shock isolators display the same phenomenon.

When an additional flexible part (ADDI) according to the invention is added to this configuration consecutively with the wire-rope isolator, the flexibility of the tension side of the flexibility curve is corrected to become nearly linear and to correspond to the flexibility of the compression side. An impact loading normally goes through the wire-rope isolator, until it becomes under tension, when the looser springs (or other elements) of the ADDI carry the load and the wire-rope isolator is prevented from going to the tension side.

It can be easily concluded from this figure, that the additional flexibility of the ADDI need not necessary start from zero, instead it is sufficient to start from somewhere close to it, for example from the linear initial part of the tension side of the wire-rope isolator.

It can also be concluded from Figure 6 that the invention is suitable for use in connection with any shock isolator whatever with a similar flexing property, when the ADDI will correct the flexing to be linear on the tension side.

The test results of Figures 7a and 7b will be explained later.

In Figures 8a, 8b, and 8c, the following reference numbering is used: load 11, conventional wire-rope absorber 10, and base 9. In Figure 8a, the base is in a state of rest. In Figure 8b, the base rises as a result of an impact, when the wire-rope absorber 10 is compressed. In Figure 8c, the base has dropped below the normal level, so that the wire-rope absorber is forced to stretch higher.

The same stages are shown in Figures 8d, 8e, and 8f, with the additional flexible part (ADDI) according to the invention. In the rest state and in the compression, i.e. pushing stage, the additional flexible part is closed. However, in the tension state (Figure 8f) the additional flexible part truly flexes and the main flexing takes place in it.

According to Figures 9 and 10, the additional flexible part 20 can be equally easily above or below the basic absorber.

In Figures 11a, lib, and 11c, several configurations are shown, comprising several shock absorbers and their situations, as in Figures 8a - c.

According to Figures lid, lie, and llf , a configuration can be made of several absorbers, which have a common support 36, which carries a chosen number of additional flexible parts 20.

According to Figures 12a, 12b, 12c and 12d, the additional flexible part can be manufactured, if desired, from only a single plate. In this case, the flexible length L is conceptually more complex, but nevertheless analogous with the previous embodiments .

In the version of Figure 12a, four wire-rope absorbers (or similar) are attached to the dark holes. The white holes next to them are attached to the load or base, if the additional flexible part is underneath. In this case too, intermediate absorption is important, even though it must be made in several places. A direct impact by each attachment point on the counter-structure must absolutely be prevented. Now intermediate rubber pieces or similar will possibly be required at each attachment point.

In the version of Figures 12b, two wire-rope isolators are required. In the versions of Figures 12c and 12d, however, a single wire-rope absorber is used.

Mathematical simulation of the wire-rope isolator and ADDI, using WIROSI software

The mathematical simulation was performed using WIROSI software. The rigidity of the isolators was taken from static test results. The aim of the simulation was to compare the response of purely the wire-rope isolators with a situation in which an ADDI absorber was attached to a wire-rope isolator. Three different excitation pulses were used in the simulation:

* half-sine pulse with amplitude 10 g and 18-ms pulse length

* excitation measured in a field test, with a kick-off velocity of 3.8 m/s

* excitation measured in a field test, with a kick-off velocity of 4.6 m/s.

Four isolators (Armeka product code: 216-124/125-10/8-1) were used in the simulations, by means of which a mass of 160 kg was isolated. Using the first test pulse, the wire-rope isolators did not enter tension substantially, so that the responses were similar (wire-rope isolator vs. wire-rope isolator + ADDI) . In the second and third pulses, which were based on field tests, the isolators entered tension and the differences in the responses were significant.

Shock test-table tests for a wire-rope isolator and an ADDI A shock test-table can be used to give a rapidly damping sine shock pulse in the vertical or horizontal direction to the object being studied. The device consists of 16 steel leaf springs. The force is created by pulling the table downwards with two hydraulic cylinders, using the aid of frangible bolts. When the bolt fractures, the table is propelled upwards by the leaf springs, causing a shock-like pulse. The break- impulse displacement of the spring can adjusted by changing the material of the frangible bolt, or by preventing the maximum displacement of the pre-loading. The device's maximum displacement is 26 mm. The amplitude of the shock pulse can be adjusted by changing the span of the leaf springs, or by changing the material of the frangible bolt. The kick-off velocity of the shock used varies from 1.6 to 2.5 m/s. The isolated device was a steel plate, the mass of which was 60 kg and it was isolated using four wire-rope isolators (Armeka product code: 146-74/80-6/10-1) and, in addition ADDI absorbers. The tests were performed at different shock amplitudes and in the results a comparison was made between the isolation with purely wire-rope isolators and wire-rope isolators to which ADDI absorbers were attached. The isolated device with the isolator was attached to the shock test-table.

Results of the shock test-table tests for a wire-rope isolator and ADDI (Figure 7a) The measurements were saved at a 50 kHz display frequency and the results anti-alia filtered at 1 kHz. Two 60 kg steel-plate masses were attached:

* using four wire-rope isolators

* using four wire-rope isolators + ADDI absorbers.

The sizes of the wire-rope isolators were: length - 147 mm, height/width - 70/85 mm, wire-rope thickness - 6 mm, and number of rounds - 10. The ADDI absorber (prototype 4) was manufactured from structural steel Fe52 (yield strength 335 MPa) . Sizes of the ADDI absorber: length - 170 mm, width - 150 mm, and thickness - 1 mm.

Field-test results for a wire-rope isolator and ADDI (Figure 7b)

The field tests were performed on a real warship and using real depth charges . The results are shown on the time plane on the y-axis acceleration [m/s ² ] . Two 30 kg masses were placed next to each other and attached to the ship:

* using two wire-rope isolators

* using two wire-rope isolators + ADDI absorbers (prototype 5) . The sizes of the wire-rope isolators were: length - 147 mm, height/width - 70/85 mm, thickness of wire rope 6 mm, and number of rounds - 10. The ADDI absorber (prototype 5) was manufactured from structural steel Fe52 (yield strength 335 MPa). The sizes of the ADDI absorber were: length - 150 mm, width - 105 mm, and thickness - 2 mm.

PARTS LIST

7 base bolt 19 additional flexible part base / frame 20 intermediate absorber

(rubber) (21')

base plate 21 lower plate (22 ' )

wire-rope absorber 22 upper plate (24 ' )

load to be protected from 23 lower auxiliary strip vibration 24 upper auxiliary strip lower clamp beam 25 spacer strip

attachment bolt 32 strip

wire-rope coils 36 group support

attachment bolt (countersunk)

upper clamp beam flexible length attachment bolt (countersunk) end of L

nut other end of L