BRAKING AND HOLDING DEVICE FOR DISPLACEABLE RODS

Abstract: Braking and holding device for displaceable rods such as the rods (4) in telescopic positioning and holding devices in which the rod is required to be braked in conjunction with its displacement for the purpose of extending or retracting the device. Braking is provided by means of a bush (24, 26) made from an elastic rubber material which is held by compression around the rod (4). The bush is made from a material exhibiting frictional properties such that braking appropriate to the intended purpose is provided.

Description: Braking and holding device for displaceable rods Technical field: The present invention relates to braking and holding devices for displaceable rods. It often happens in a large number of contexts that there is a wish to have a positioning or movement facility and that a mechanism is arranged for this purpose. Such a mechanism will often include a rod which is capable of displacement in relation to another part of the mechanism. It is usual in such a case for the rod together with the other part to be executed as a telescopic arrangement; one of the parts is thus executed as a tube into which the other part can be inserted. Mechanisms of this kind are encountered to a very great extent in adjustable—height chairs, especially work chairs, and in openable hatches, especially hatches having a horizontal hinge such as those used as luggage compartment covers and the openable hood lids - of motor vehicles. In both the aforementioned cases a gravitational force is imposed on the devices for the purpose of their adjustment, to different " heights in the case of chairs and from the closed to the open position in the case of covers, said gravitational force having to be compensated for without sacrificing the movement facility as a consequence. The devices required for this purpose accordingly take the form of some kind of lock or brake enabling the desired positions of adjustment to be retained securely, and a brake which will damp the movement in the direction of the gravitational force, and frequently in addition a balancing arrangement which will partly counterbalance the gravitational force in such a way that the whole of the supported weight need not be lifted by the movement against the gravitational force. Background: • Previously disclosed is the use of a so-called gas spring in order to achieve these functions, this being a device in which a volume of gas sealed inside a cylinder is used in order to provide the necessary spring force to counteract the gravitational force. A positioning function may be achieved at the same time by the use of OMPI .-4 _ WSPO a valve to increase or reduce the quantity of gas in the cylinder. The flow of the gas may also be utilized to provide gentle, braked movement. The aforementioned positioning function is necessary in the case of chairs, whereas in the case of covers all that may often be required are two normal positions, these being the closed position and the fully open position. Technical problem: A gas spring consisting of a cylinder, a piston, valves and organs for the transmission of the force and the arresting of the gas spring results in a relatively high cost price, however. It is of interest, therefore, to produce a different type of device by means of which the aforementioned functions can be achieved and which is able to replace gas springs in applications such as adjustable chairs and covers such as luggage compartment covers of motor vehicles. A further disadvantage of gas springs is that they have been found to be subject to the risk of bursting caused by the internal gas pressure. Accidents have occurred. The solution: In the present invention the aforementioned problem has been solved by means of a mechanism which operates entirely by the friction present between surfaces- with the assistance of a spring mechanism, whereby a braking and springing function identical with that of gas springs can be achieved by simple and robust means without the aforementioned risk of bursting. The object of the invention is to provide an arrangement capable of satisfying the aforementioned need by means of a simple and robust arrangement capable of being manufactured at low cost. Brief description of the drawings: In the accompanying drawings are illustrated three embodiments of the invention. Figure 1 shows a positioning arrangement for a frame for an adjustable—height chair in a longitudinal section along the line I—I in Figure 2. Figure 2 shows the arrangement in a section along the line II—II in Figure 1. Figure 3 shows the arrangement in a section along the line III—III in Figure 2. Figure _OMPl 4 shows the second embodiment, which is also a chair frame shown in longitudinal section. Finally, Figure 5 shows the third embodiment which relates to an arrangement for holding open covers such as luggage compartment covers as a central longitudinal section. Best mode of carrying out the invention: Chairs, for example work chairs, which are adjustable in height are usually executed with a central, vertical upright attached at its lower end to a foot having a number of star—shaped projecting legs and supporting at its upper part a seat, in this case with a back—rest and an arm— est. The upright is so arranged for this purpose as to be capable of being extended or retracted telescopically, thereby enabling the height of the seat above the surface on which the feet are resting to be adjusted. Now there exists a requirement that the adjustment of such a chair shall be capable of being performed in a very straightforward manner simply by releasing the mechanism when one is seated on the chair, whereupon adjustment is made either by the application of pressure to the chair until the upright has retracted to the point at which the desired height is reached, or by reducing the load on the seat allowing a spring force to push the seat upwards so that it can then be locked in a new height position. An associated requirement is that the movement shall be braked. The ability of the seat to fall freely downwards if the locking mechanism is released and if pressure is applied to the chair shall be prevented, since this may cause personal injury. In Figure 1 is shown an upright 1 of the aforementioned type. It exhibits a sleeve in the form of a tube 2 which at its upper end supports an attachment 3 for the chair seat. Inside the tube 2 is arranged in such a way as to be capable of displacement a rod . 4 , the outer end of which is attached to a frame for the legs, although this is not shown in the Figure. The attachment 3 supports a control organ 5 , the rotation of which, for instance by means of a lever not shown here, enables the mechanism which locks the tube 2 and the rod 4 to each other to be released so as to permit the adjustment of the aforementioned two elements in relation to each other and thus to permit the height of the seat to be adjusted. The outer element described here corresponds to the aforementioned arrangements in previously disclosed chair frames. The rod 4 supports at its inner end a plate 6 which, in the manner of a piston, is able to move inside the tube 2 . Against the plate 6 rests a powerful compression spring 7 , the other end of which bears against an end plate 8 at the end of the tube which faces the attachment 3 . The plate 6 exhibits a hole 9 through which there extends a rod 10 . The rod 10 is supported via a plate 11 by a short rod 12 , which is supported in such a way as to be capable of displacement in a hole 13 in the plate 8 . A loading is applied to the rod 12 by means of a compression spring 14 which is held between the plate 11 and the plate 8 . The rod 12 projects by its outer end beyond the end of the tube 2 , where it exhibits a connecting element 15 to the control organ 5 . The control organ is connected to an eccentric shaft 16 which runs with its eccentric cam through the connecting element 15 . In this way the rotation of the control organ 5 will cause the rod 12 and with it the rod 10 to be raised against the effect of the spring 14 , or else the rod can be forced downwards so as to complement the effect of the force of the spring 14 . The rod 4 is enclosed at the lower end of the tube 2 by a braking and locking element 18 . This consists of a sleeve 19 with end plates 20 and 21 which exhibit holes 22 suitable to guide the rod 4 . The sleeve 19 also exhibits a hole 23 which is sufficiently large to provide a clearance with the rod 4 . In this clearance is inserted a bushing 24 which, unlike the other component parts of the arrangement which are made of steel or some other hard material, is made of elastic rubber. The rubber bushing 24 is enclosed in a thin metal ring 28 . The lower end plate 21 on the sleeve 19 is connected to a second sleeve 25 with an inward—flanged lower edge. In the space formed by this sleeve is inserted a second rubber bushing 26 having a central hole 27 which is so executed as to be under—sized by a certain amount in relation to the rod 4 , so that it will be caused to press against the latter by the elasticity of the rubber. In the uncompressed state, however, the hole tapers slightly outwards towards the top, and thus towards the inside of ' BUR£4ϋ _QA.PI the tube 2.. In this way the contact with the lower edge of the bushing is greater than that with the upper edge. The conicity may even be so great as to provide free play at the upper edge, in the manner indicated in Figure 1. It may be appreciated from Figure 2 that the rubber bushing 24 is slotted by means of a groove 30 , which is also true of the inner metal ring 28 . In line with the groove 30 is a recess 33 in the sleeve 19 in its hollow wall 23 . Into this groove project two wings 31 and 32 on the ring 28 . The wing 31 is in this case designed to rest against one of the end walls 34 of the recess 33 , whereas the wing 32 exhibits free play with the other end wall 35 of the space. The latter end wall is arranged at an angle, unlike the former end wall, so that the space between the wall and the wing 32 widens outwards in an upward direction. Into this space projects the rod 10 with a wedge—shaped section 36 . The embodiment in accordance with Figure 4 also exhibits a rod, in this case identified by the reference designation 55 , and a sleeve 56 consisting of an outer tube 57 and an inner tube 58 . The embodiment in accordance with Figure 4 is also intended to be used as a chair frame. The rod 55 exhibits at its upper end a plate 59 which, in the manner of a piston, is able to move inside the inner tube 58 . Above the plate 59 is present a compression spring 60 , the upper end of which rests against an inward—flanged part 61 of the tube 58 . Above the inward—flanged part 61 is present a control organ 62 with an outer part 63 , not shown in its entirety here, having a ' handle or similar, and an inner part 64 . The control organ 62 is pivotally mounted about a pin 65 which is attached to the outer tube 57 , which in turn is connected to the inner tube 58 . Inside the inner tube 58 is situated the braking and holding mechanism in accordance with the invention. This consists of a first sleeve 66 made of a material with a low coefficient of friction. It is held in position by being supported against a shoulder 67 in the tube 58 . The sleeve exhibits inner, upward and inward inclined surfaces 68 . These surfaces are assumed to be plane, but may also be conical. Beneath the sleeve 66 is present a sleeve δ 69 with an upper side wall 70 , the inside of which is essentially plane, and a lower side wall 71 , the inside of which is conical. The sleeve 69 is held between the sleeve 66 and an inward—flanged part 72 of the tube 58 . In the sleeve 69 is inserted a rubber bushing 81 which encloses the rod 55 . In the sleeve 66 are inserted two gripping jaws 73 , the outer surfaces 74 of which are shaped so as to make contact with the surfaces 69 in the sleeve 66 , and the inner surfaces 75 of which are shaped so as to make contact with the preferably cylindrical rod 55 . The gripping jaws 73 are each supported by a thin, flexible rod 76 , said two rods extending through holes 77 in the plate 59 and being connected to a central rod 78 having an upper head 79 above the inward—flanged part 61 of the tube 58 , through which the rod 78 extends. Between the head 79 and the inward—flanged part 61 is present a spring washer 80 . Its spring force is greater than the spring force of the spring 60 . The head 79 can be influenced by means of the inner part 64 of the control organ 62 . The embodiment of the arrangement illustrated in Figure 5 consists of a telescopic equalizer spring and braking arrangement intended, for example, for covers such as luggage compartment covers for motor vehicles, and is identified as a whole by the reference designation 40 in the Figure. This arrangement also exhibits an outer sleeve in the form of a tube 41 in which a rod 42 is so arranged as to be capable of being displaced. The sleeve, and accordingly the tube 41 are designed to be attached, for example, to the chassis of a motor vehicle by means of a fastening lug 43 , and the rod 42 is designed to be attached, for example, to a luggage compartment cover by means of a fastening lug 44 . The cover is able in this way to be opened and closed by extending and retracting the device 40 . The rod 42 supports at its upper end a plate 45 against which rests a compression spring 46 , the other end of which rests against an end wall 47 attached inside the tube 41 . The rod is controlled at its outer end by means of a second end wall 48 attached inside the tube 41 . The end wall 48 exhibits an inner sleeve—shaped part 49 in which a rubber bushing 50 is pressed securely into position by indentation of the inward—facing edge of the sleeved-shaped part. The rubber bushing 50 is also so arranged as to make contact with the corresponding rod, being in this case the rod 42 , through the elasticity of the rubber, and is in this way so arranged as to make firmer contact via its part which faces towards the end wall 48 than with the opposite end of the hole 51 through the bushing which faces inwards towards the tube 41 . It has been demonstrated in connection with the invention that it is possible to achieve highly suitable braking by utilizing the friction of the rubber against steel. This calls for various factors to be accurately matched, however, such- as the hardness, the clamping and the quality of the rubber, and for a suitable surface on the steel surface against which it runs. It has also been found that the possibility exists to achieve varying braking force in varying directions of movement- through the aforementioned varying pressure applied by the rubber body at its two ends. A kind of locking effect is obtained in this way, since the rubber body attempts to open as the steel rod moves in one direction, whereas it attempts to close as the steel rod moves in the other direction. Complete arrest will not occur, however, because of the elasticity of the rubber body. It is also possible to regulate the braking effect by causing the rubber body to be applied in a more or less hard fashion, to the point at which complete locking is achieved for the forces present. By the aforementioned means it is possible to achieve a braking effect such that smooth and non—jerky movement is achieved, in a more or less identical fashion to that achieved by considerably more complicated pneumatic or hydraulic arrangements. With the upright 1 for a chair frame shown in Figures 1—3 it is possible to achieve complete locking at the level of the forces which are generated and which are represented essentially by the mass of the chair seat and the mass of the person imposing a load on same. This locking will be achieved if the rod 12 is not actuated, so that the spring 14 is able to exert its full force against the rod 10 via the washer 11 . In this case its wedge—shaped, lower OMPI *- . part 36 will be forced between the surface 35 and the wing 32 . In this way the wing 32 is affected by a force directed towards the second wing 31 (see Figure 2), producing a tightening of the sleeve 28 and thus of the rubber bushing 24 against the rod 4 . If an appropriate force is provided in the spring 14 and if other factors such as the angle of taper of the part 36 are matched, the aforementioned complete locking can be achieved under the aforementioned circumstances. The rubber bushing 24 need not, however, absorb the loading force in its entirety, since a frictional force is also generated in the rubber bushing 26 , which is permanently tightened around the rod 4 and which is able in this way to assure an invariable initial braking effect. As has already been mentioned this braking effect can be varied in different directions by producing variations in the contact pressure of the rubber bushing along the hole 27 . In this case the conicity to which this variable tightening is attributable has been selected in such a way that greater force is required to force the rod 4 into the tube 2 than to force it out. This means that the braking effect will be greater for compression caused by a load being imposed on the seat than for the seat being raised with the help of the spring 7 . In this way the counterforce against the spring will be lower at the same time as powerful braking of the downward movement of the seat will be achieved. The above has, of course, been selected only as one example of the aforementioned possible function. By specifying a very strong spring 7 the even tightening of the rubber bushing 26 may be more appropriate, so that identical braking force is obtained in both directions, or alternatively tightening of a kind opposite to that described above, so that greater resistance is obtained when the spring is extended than when it is compressed. The latter may be appropriate in the case of springs which are so strong that to all intents and purposes the whole of the applied gravitational force is counterbalanced. If a change is to be made to the arrangement, requiring the rod 4 to be displaced in relation to the tube 2 , the rod 12 is raised with the help of the control organ 5 via the eccentric shaft 16 . This will cause the rod 10 to move upwards, and the pressure exerted by the wedge—shaped part 36 on the wing 32 will reduce. In this way the clamping of the rubber bushing 24 against the rod 4 will be reduced. With the help of the control organ the remaining braking force can be adjusted to the initial value determined by the braking force exerted by the rubber bushing 25 . Once the desired height has been reached, the bushing 24 is once more locked by releasing the control organ, allowing the spring 24 to exert its full effect. The effect of the spring can also be amplified by moving the control organ 5 in the opposite direction to the direction of release. The mechanism may be varied in different ways. The rubber bushing 24 itself may be subjected to a loading in the direction of tightening, with the result that the control organ, instead of counteracting the tightening of the bushing, will instead release it from the effect of the aforementioned clamping forces. The bushing may, as an alternative, have imparted to it a certain basic degree of tightening, which may be increased with the help of the control mechanism. The additional rubber bushing 25 can be dispensed with in this way under certain circumstances. Although the mechanism illustrated in Figures 1—3 is intended primarily for chair frames, it can conceivably also be adapted to suit other purposes, for example those, in which the actuating force is less than that achieved in chairs designed to carry a single person. If it is assumed that the embodiment in accordance with Figure 4 also forms part of a chair frame, then the application of a load to the chair will cause the sleeve 56 and with it the tubes 57, 58 to be subjected to a force, shown in the Figure to run in a downward direction, which will attempt to push the rod 55 into the tube 58 . The spring 60 will, on the other hand, attempt to push the rod out of the tube. Any movement will cause braking to occur by means of the rubber bushing 81 in the manner previously described. In order to permit this braking to be different in the two directions, with the load force generally being greater and requiring to be braked more heavily than the spring force, the bushing is able to achieve different contact depending on the direction of movement of the rod 55 . Where use was made of the previously described embodiment, this was achieved by the use of a conical hole in the bushing. In the present case it is achieved by "BUREAU O PI the use of different contact surfaces on both sides of the bushing, these being the plane surface of the end wall 70 and the conical surface of the end wall 71 . This difference means that the bushing will make stronger contact through the increased clamping effect against the rod when it is resting against one of the surfaces, and that it will tilt away from the rod to a greater extent and will thus exhibit reduced contact when it is in contact with the other surface. In the present case the contact will be greatest when the bushing is in contact with the upper surface. Depending on the angles and on the length of the bushing, the opposite situation can also be achieved, on the other hand, as the result of the edge of the bushing turning more towards the braking surface in the case of tilted contact. Braking provided by the bushing is intended, however, only to ensure gentle movement when the arrangement is under load. Definite locking can be achieved by means of the jaws 73 . If these are actually forced upwards by the spring 80 they will be compressed around the rod 55 through the interaction between the surfaces 68 and 74 caused by the jaws attempting to move upwards due to the rods 76 being drawn upwards by the spring 80 . The fact that the sleeve 66 exhibits low friction results in a situation such that the spring force can be relatively low, whereas the pressure against the rod is nevertheless high as a result of the appropriate matching of the angle for the surfaces 68 and 74 . The low friction thus facilitates movement between these surfaces, whereas the higher friction around the rod will increase the locking effect. If it is wished to alter the arrangement, the outer part 63 of the control organ 62 is pulled upwards, thereby causing the inner part 64 to pivot downwards and to force down the head 79 against the effect of the spring 80 . In this way the rods 76 will force down the jaws 73 towards the wider part of the sleeve 66 . In this way the pressure against the rod 55 will be reduced, permitting it to be displaced. The bushing 81 acts as a brake during displacement in the manner previously described. By the appropriate matching of the release of the jaws 73 a supplementary braking effect can be achieved with the help of these. OMPI If the arrangement in accordance with Figure 5 is used in conjunction with an upward—opening cover such as the luggage compartment cover for a motor vehicle, it is arranged in such a way that it is attached between the chassis of the vehicle and the cover, so that the arrangement will be extended as the cover is opened. The spring 46 will in this way counterbalance the weight of the cover. It is often preferred to counterbalance the weight entirely, so that the spring will hold the cover open against the •effect of the gravtitational force which is attempting to close same. In the closed position the spring is thus under compression, and the cover is held in position by a locking mechanism. It is also common practice for the spring to be specified in such a way that it is able to open the cover slightly from its closed position, but is unable to overcome the moment imposed by the gravitational force within a range of movement from an essentially horizontal position of the cover to a more upright position. In this way the entire mass of the cover need not be counterbalanced, although initial opening will still be obtained when the cover is unlocked and the cover will be restrained in the fully open position. From a position close to the open position to a position close to the closed position, however, the moment imposed by the gravitational force will be so great that the force of τhe spring will be overcome and the cover will attempt to drop down. Irrespective of the manner in which balancing is achieved, it is still desirable to brake the movement of the cover in such a way that it cannot drop freely or spring upwards unrestrained. The bushing 50 is provided for this purpose. It operates in the same way as the bushing 26 . Accordingly it is permanently under tension and is able in this way to be executed so as to exhibit the aforementioned varying tension, so that the braking force is greater in one direction than in the other. The direction in which the greater braking force is specified will depend on the nature of the aforementioned balancing. In the case illustrated in Figure 4 the spring 46 is prevented from forcing out the rod 42 too rapidly, whereas in the opposite direction the force necessary to tension the spring is increased insigni icantly by the braking effect of the bushing.

Claims: Patent Claims: 1. Braking and holding device for displaceable rods such as. the rods (4; 42) in telescopic positioning and holding devices in which the rod is required to be braked in conjunction with its displacement for extending or retracting the device, c h a r a c t e r i z e d in that for the purpose of providing braking is arranged at least one bushing (24, 26; 50) comprising an elastic rubber material which is held by compression around the rod (4; 42) and which is made from a material exhibiting frictional properties such that braking appropriate to the intended purpose is provided. 2. Braking and holding device in accordance with Patent Claim 1, c h a r a c t e r i z e d in that the bushing (24, 26; 50), at least before it is applied to the rod (4; 42), is of a consistency such that the compression exerted against the rod is different at the two ends of the bushing, and in that the bushing will endeavour to open in one direction through being carried along and bent outwards from the rod, whereas in the other direction it will endeavour to close by being bent inwards towards the rod, depending on the direction in which a change between firm and loose occurs in the nature of the contact having regard for the direction of movement. 3. Braking and holding device in accordance with Patent Claim 1, c h a r a c t e r i z e d in that the bushing (81) is situated between two supporting lateral surfaces (70, 71) of mutually varying cone angle, in which case the extreme position is one in which one of the surfaces (70) is plane, thereby causing the bushing, in its efforts to make contact with one of the surfaces as the rod (55) moves in one direction and to make contact with the other surface as the rod moves in the other direction, to adapt its form because of its elasticity, with the result that, in one direction, the extreme case will be that the bushing is plane, so that contact with the rod extending through the bushing will vary because of the different conical deformation of the bushing in the two directions of movement. 4. Braking and holding device in accordance with Patent Claims 1, 2 or 3, c h a r a c t e r i z e d in that it comprises, in OMPI addition to the aforementioned brake bushing (26), which is in essentially invariable contact with the rod (4 ) , at least one other locking device (24), the contact of which with the .rod may vary as a result of the device being clamped to a greater or lesser extent against the rod by means of a control organ (5 ) , in such a way that the strength of the braking may be varied. 5. Braking and holding device intended specifically for adjustable frames, especially for work chairs, and in accordance with Patent Claim 4, c h a r a c t e r i z e d in that the rod (4) can be inserted or withdrawn in relation to a tubular sleeve (2), and in that the sleeve encloses the aforementioned braking bush (26) and the aforementioned locking device (24) with variable contact, said latter bush being in the form of a reversing device and being connected to an actuating organ (10) by means of which the tightness with which it is held around the rod can be regulated, said actuating organ being connected to a control organ (5). 6. Braking and holding device in accordance with Patent Claim 5, c h a r a c t e r i z e d in that the reversing device consists of a slotted bushing (24) and in that the actuating organ consists of a control rod (10) having a wedge—shaped part (36) which runs essentially parallel with the aforementioned displaceable rod (4) and which is capable of being displaced in relation to parts (31, 32) of the bushing (24) to either side. of its slotting (30) in such a way that the effect of the taper will cause the bushing to be compressed to a greater or lesser degree so that the braking function may be varied by means of the control organ (5) connected to the control rod. 7. Braking and holding device in accordance with Patent Claim 6, c h a r a c t e r i z e d in that the adjustable bushing (24) incorporates an outer ring (19) of hard material in which the slotted elastic rubber component (24) of the bushing is retained by a part (31) situated on one side of the slotting (30), whilst the part (32) situated on the other side of the slotting rests against the control rod (10) with one side of its wedge—shaped part (36), whilst the other side of the wedge—shaped part rests against a surface (35) on the outer ring (19) extending obliquely to the direction of displacement, so that the wedge—shaped part is able as _OMPI A the result of movement between said second part and the oblique surface to displace the second part peripherally in order to produce increased or reduced contact of the elastic rubber part (24) of the bushing with the rod (4).

Inventors: PETERSSON BENGT, PETERSSON, BENGT
Applicants: NP NEW PROD NORDINVENT INVEST, N.P. NEW PRODUCTS NORDINVENT INVESTMENT AKTIEBOLAG
Application year: 1984
Main classification: F16F13
IPC codes: A47C3, F16F7, F16F13, F16J10