Device for tensioning a fastening

Abstract: The present invention relates to a device for automatic tensioning of a fastening (4), which is adapted to hold a load on a vehicle. The device has a fastening drum (2) for receiving the fastening, a tensioning means (6) for manual tensioning of the fastening and a mechanical retensioning means (8) for automatic increase of the tension of the fastening. The tensioning means and the retensioning means are via a coupling means (10) connected to the fastening drum for rotation thereof in a direction of tensioning. The tensioning means is via the coupling means connected to the retensioning means for activation thereof. The retensioning means comprises a power-storing means (62, 64), in which power is stored during activation and is released automatically for increasing the tension of the fastening. When the tensioning means is operated, its motion is transferred via the coupling means either to the fastening drum or to the retensioning means. When the tensioned fastening slackens, the retensioning means acts via the coupling means on the fastening drum for elimination of the slack.

Description: FIELD OF THE INVENTION The present invention relates to a device for tensioning a fastening according to the preamble to claim 1 in the appended claims. BACKGROUND ART For holding a load on a vehicle, use is made of some kind of fastening, such as a tightening strap or a chain, which is laid across the load and tensioned with a certain amount of force. In certain transports, above all of forestry products, such as timber and pulp wood, pipes and the like, there is the problem of the load settling, which makes it necessary to increase the tension of fastening. Tensioning devices with automatic increase of the tension are available on the market. In most cases, they are provided with hydraulic or pneumatic means for increasing the tension, such as the tensioning devices according to SE-437,495, SE-413,182 and SE-438,126. These devices suffer from the obvious drawback that they can be used merely on vehicles having hydraulic or pneumatic systems, unless special compressors or hydraulic pumps are arranged, which involves great additional expenses. However, tensioning devices with mechanical, automatic increase of the tension are available, which thus do not suffer from the above-mentioned drawback and which besides become more reliable in service than the above-mentioned devices. Such tensioning devices are disclosed in e.g. US-2,946,563 and US-3,077,791. These devices are composed as follows. A manually operable tensioning means is connected to a retensioning means, which in turn is connected to a strap drum. The tensioning means comprises a handle which is operated to rotate the strap drum for rolling up and tensioning the strap which extends round the load. The retensioning means comprises a helical spring. The helical spring is coaxial with the longitudinal axis of the drum. The tensioning means is connected to one end of the spring and the drum to the other end thereof. When the handle is operated and the slack in the strap has been taken up, the helical spring is tensioned and in turn rotates the drum. When the load changes during transport such that the strap slackens, the spring turns the drum such that the strap is tensioned. This composition of the tensioning device makes it difficult to dimension the helical spring. Since the force tensioning the strap is supplied from the handle via the helical spring to the drum, the spring must be thick to withstand the strain because the strap is to be tensioned with great force in order to hold timber and other types of heavy load in place. At the same time it is desirable to have a fairly great retensioning length, which requires many turns of the spring. Consequently this prior-art composition necessitates a helical spring which both has many turns and is thick. It is desirable, however, that the spring does not need too much space, which will be the case if these requirements are to be satisfied completely. The described prior-art devices are both compromises, which above all have too small a retensioning length. The device according to US-3,077,791 besides is not sufficiently strong. SUMMARY OF THE INVENTION The object of the invention therefore is to provide a tensioning device with automatic, mechanical increase of tension, which is strong, has a great retensioning length and sufficient retensioning force. The object is achieved by means of a device according to the invention as defined in the characterising portion of claim 1. Preferred embodiments of the invention are defined in the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the accompanying drawings, in which Fig. 1 is a top plan view of an embodiment of the device according to the invention; Fig. 2 is a side view of the embodiment in Fig. 1, certain parts being broken away; Fig. 3 is a sectional view along line A-A in Fig. 2; and Fig. 4 is a sectional view along line B-B in Fig. 2. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE DEVICE ACCORDING TO THE INVENTION Fig. 1 shows an embodiment of an inventive device for automatic tensioning of a fastening. The device will below be referred to as tensioning device. The tensioning device comprises a frame 1, which supports the construction, a fastening drum 2 for receiving a fastening 4, which in this embodiment is a strap 4 fixed in the fastening drum 4 (Fig. 3). The fastening drum 2 is therefore referred to as strap drum 2. The tensioning device further comprises a tensioning means 6 for manual tensioning of the strap 4, and a retensioning means 8 for automatic increase of the tension of the strap 4. The strap drum 2, the tensioning means 6 and the retensioning means 8 are interconnected via a common coupling means 10, the tensioning means 6 and the retensioning means 8 each being adapted to separately rotate the strap drum 2 about its axis in a direction of tension for winding the strap 4 onto the drum 2. As is evident from Fig. 3, the coupling means 10 comprises first, second and third transmission means 32, 34, 36. The first transmission means 32 is connected to the tensioning means 6. The second transmission means 34 is connected to the strap drum 2. The third transmission means 36 is connected to the retensioning means 8. The transmission means 32, 34, 36 constitute a planetary gear, or differential, the third transmission means 36 comprising a planet carrier 38 with two opposed planet wheels 40, 42, which are rotatably connected to the planet carrier 38. The first transmission means 32 comprises a gear wheel 46 meshing with the two planet wheels 40, 42 and arranged concentrically in relation thereto. The planet wheels 40, 42 thus rotate along the circumference of the gear wheel 46. The second transmission means 34 comprises a gear ring 48 meshing with the two planet wheels 40, 42 and arranged concentrically in relation thereto. Thus the gear rim 48 rotates externally of the planet wheels 40, 42. The gear wheel 46 is fixedly connected to a first transmission shaft 50 included in the first transmission means 32. Moreover, a first locking wheel 52 is fixedly arranged on the first transmission shaft 50 at the one outer end thereof. The planet carrier 38 is fixedly connected to a second transmission shaft 54 included in the third transmission means 36 at one inner end of the transmission shaft 54. A first sprocket 56 included in the retensioning means 8 is fixedly connected to the second transmission shaft 54 at the other outer end thereof. Further the second transmission shaft 54 is rotatably connected to or supported at the other inner end of the first transmission shaft 50. As is best seen from Fig. 2, the retensioning means 8 further comprises a second sprocket 58, a chain 60 passing over the sprockets 56, 58, and a power-storing means in the form of two gas-operated springs 62, 64. The one ends 66, 68 of the gas-operated springs 62, 64 are connected to the chain 60 and their other ends 70, 72 are fixed in the frame 1. The strap drum 2 is rotatably connected to, i.e. supported by, the first transmission shaft 50 between the first locking wheel 52 and the gear wheel 46. A second locking wheel 78 is included in the strap drum 2. The tensioning means 6 comprises, in addition to said first locking means 52, a lever seat 80, which is arranged in the outer end of the first transmission shaft 50 and which has a hexagonal projection for engaging a lever, for instance a box key. The embodiment of the invention as described above functions as follows. In order to tension the strap 4, the lever seat 80 is rotated by means of the lever, whereby the first transmission means, i.e. the shaft 50 and, thus, the gear wheel 46, rotates clockwise in Fig. 1, i.e. in the direction indicated by arrow S. The rotation is transferred either via the third transmission means 36 and the second transmission means 34 to a motion of the strap drum 2 for winding on the strap 4, or via the third transmission means 36 to a motion of the retensioning means 8 for storing of power in the gas-operated springs 62, 64 by their being compressed. The coupling means 10 strives, through its planetary gear design, for equilibrium of moments between the gear wheel 46 and the gear rim 48. Thus, the motion of the first shaft 50 is transferred to that of the second and third transmission means 34, 36 which applies the lowest braking moment to the first transmission means 32. This implies that the strap 4 is first tensioned by the strap drum 2 rotating counterclockwise until the force in the strap 4 is so great that an equilibrium of moments is achieved in the planetary gear. If the tensioning operation is then continued, the retensioning means 8 will instead be activated. Power is stored in the power-storing means 62, 64 by the chain 60 being driven by the first sprocket 56 such that the gas-operated springs 62, 64 are compressed. The first transmission shaft 50 is prevented from rotating counterclockwise by a first catch 90, which is biased to engagement with the tooth of the first locking wheel 52. The catch 90 is rotatably arranged in the frame 1. The strap drum 2 is prevented from rotating clockwise by a second catch 92 which is biased to engagement with the tooth of the second locking wheel 78. The catch 92 is rotatably arranged in the frame 1. When the strap 4 and the springs 62, 64 are tensioned and the tensioning action is interrupted, the planet carrier 38 with its planet wheels 40, 42 will act as a coupling between the gear wheel 46 and gear rim 48. The springs 62, 64 try to rotate the transmission shaft 54 counterclockwise, seen in Fig. 1. Owing to the catch 90, the gear wheel 46 is prevented from rotating as well. The planet carrier 38 therefore strives to turn the gear rim 48 counterclockwise via the planet wheels 40, 42 and thereby strives to tension the strap 4. In order to slacken the strap 4, a releasing device is operated, which comprises a first and a second releasing means 96, 98 and a shaft 94, on which they are jointly arranged. When the shaft 94 is rotated counterclockwise in Fig. 1, the releasing means 96, 98 actuate the catches 90, 92 for releasing the same from the locking wheels 52, 78. ALTERNATIVE EMBODIMENTS The embodiment of the invention described above is an illustrative example only. Many modifications are feasible within the scope of the invention as defined in the claims. Thus the retensioning means can be provided with some other type of power-storing means, such as helical spring, a screw spring or some other power-storing mechanism which strives to return to the starting position. The solution involving gas-operated springs, however, confers the advantage that the return motion is dampened. It should also be emphasised that two springs are arranged for economical reasons since precisely in this case it is less costly to have two smaller springs than one larger. It goes without saying that it is sufficient to arrange one spring having suitable dimensions. The retensioning means can further be designed in some other fashion and operate according to some principle other than a chain which tensions a spring. However, the solution is advantageous in its simple design, acting directly on the transmission shaft 54. The coupling means may have a different design, which yields the same basic function, i.e. in one operation the strap is tensioned and the retensioning means is activated, and the retensioning means acts on the strap via the coupling means. The various parts of the planetary gear can be designed in some other manner while achieving the same function.

Claims: A device for tensioning a fastening (4) which is adapted to hold a load on a vehicle, the device comprising a fastening drum (2) for receiving the fastening, a tensioning means (6) for manual tensioning of the fastening and a mechanical retensioning means (8) for automatically increasing the tension of the fastening, the tensioning means being connected to the retensioning means for activating the same, and the retensioning means comprising a power-storing means (62, 64), in which power is stored during activation and is released automatically for increasing the tension of the fastening, characterised in that it further comprises a coupling means (10), that the tensioning means (6) is connected to the retensioning means (8) via the coupling means (10) for effecting said activation, and that both the tensioning means and the retensioning means are connected to the fastening drum (2) via the coupling means for rotating the fastening drum in a tensioning direction, the tensioning motion of the tensioning means being transferred via the coupling means either to the fastening drum or to the retensioning means. A device as claimed in claim 1, characterised in that the coupling means (10) comprises a first transmission means (32) connected to the tensioning means (6), a second transmission means (34) connected to the fastening drum (2) and a third transmission means (36) connected to the retensioning means (8), which are mutually arranged in a planetary gear configuration. A device as claimed in claim 2, characterised in that a motion of the tensioning means (6) is transferable via the first transmission means (32), the third transmission means (36) and the second transmission means (34) to a motion of the fastening drum (2) and via the first transmission means and the third transmission means to a motion of the retensioning means (8). A device as claimed in claim 2 or 3, characterised in that the coupling means (10) comprises a planetary gear, the third transmission means (36) comprising a planet carrier (38) with two opposed planet wheels (40, 42) which are rotatably connected to the planet carrier (38), the first transmission means (32) comprising a gear wheel (46) meshing with the two planet wheels (40, 42) and arranged concentrically thereto, the second transmission means (34) comprising a gear rim (48) meshing with the two planet wheels (40, 42) and arranged concentrically thereto, and a motion of the tensioning means in each moment being transferred to that one of the second and third transferred means which applies the lowest braking moment to the first transmission means. A device as claimed in any one of the preceding claims, characterised in that it comprises a releasable locking device (90, 92, 94, 96, 98) which locks the motion of both the tensioning means (6) and the fastening drum (2) in any direction of rotation, the locking device comprising a first catch (90) engaging a first locking wheel (52) associated with the tensioning means, and a second catch (92) engaging a second locking wheel (78) associated with the fastening drum. A device as claimed in claim 5, characterised in that the locking device comprises a releasing device having a first and second releasing means (96, 98) and a shaft (94), on which the releasing means are jointly arranged, the releasing device being manually operable for releasing the catches by the releasing means actuating the catches (90, 92) for releasing the same from the locking wheels (52, 78). A device as claimed in any one of the preceding claims, characterised in that the power-storing means (62, 64) of the retensioning means (8) consists of at least one gas-operated spring (62 or 64). A device as claimed in claim 7, characterised in that the retensioning means (8) comprises a first sprocket (56) connected to the coupling means (10), a second sprocket (58) and a chain (60), which passes over the sprockets and is connected to said at least one gas-operated spring.

Inventors: JOENSSON PER-ANDERS, JOENSSON, PER-ANDERS, Jönsson, Per-Anders
Applicants: JONSSON & PAULSSON IND AKTIEBO, JONSSON & PAULSSON INDUSTRI AKTIEBOLAG
Application year: 1997
Main classification: B60P7
IPC codes: B60P7