The invention relates to a tightener for a track according to the preamble of claim 1. The invention particularly relates to a tightener for a track used in the handling of tracks of work machines. When installing tracks of work machines on top of road wheels and, equivalently, when removing them from top of road wheels, various tighteners and other devices are commonly utilised. The fitting of heavy steel tracks in place requires that the track is tightened relatively tight in order for the track assembly to operate in a correct way. The tightening requires of the tighteners used applying a great pulling force between the ends of the track. At the same time, movement range large enough is required in order to be able to connect the ends of the track also in demanding terrain conditions. Track pads of the track must be kept in the correct position during tightening in order to be able to install connectors between the ends of the track more easily. The tensioning tool of document US2009183489 based on a screw represents a device type, which includes a fixed jaw and a jaw moving in guides. The jaw in the guides is pulled by the screw towards the fixed jaw. A problem of this type of devices are sliding pairs of guides easily damaged in field conditions which, when wearing, cause pausing in operation and seizing of slide surfaces. Furthermore, the position of the track pad cannot be controlled sufficiently in order for the tightening of the track be smooth.

Documents FI7686 and GB2242232A describe hydraulically-operated tightening devices the required fluid pressure of which is delivered by a manual pump or the hydraulics of a work machine. In this area of application, a problem of the hydraulic device is its construction, which is heavier and more complex than that of the mechanical device and its poor applicability to winter conditions. Also in these devices, the position of the track pad cannot be ensured.

The tightening of different ropes and cables employs the so-called rigging screw the construction of which is simple and which is reliable in operation. This construction principle is not directly applicable to track tighteners because the actuators of a conventional rigging screw do not include a ratchet tool reliable enough.

The object of the invention is to introduce a tightener for a track which solves the above problems, eliminates the defects of prior art and provides a tightener for a track which is good of its operating features and reliable in operation. The object is provided with the arrangement according to the invention, which is characterised by what is presented in the claims.

The invention enables a tightener for a track, by means of which in field conditions, it is possible to effectively install tracks in place or remove them in connection with servicing. The tightener for a track includes hooks, which are fitted in the threads of a worm shaft . One half of the worm shaft includes a right-hand thread and the other half a left-hand thread. Between the halves is fitted a ratchet handle by which the worm shaft is rotated. The hooks are provided with a tightening means to lock the track pad and shaped such that the pad is oriented direct in connection with tightening. The ratchet handle consists of a housing within which torsion elements are protected from getting dirty. The torsion elements are most advantageously a gear arranged into connection with the worm shaft and a ratchet latch, which is a toothed segment suitable for contact with the gear. The gear is fitted in the housing such that its outer race rests on the housing during tightening. Then, torsional load is divided more evenly, which decreases the loading of e.g. the worm shaft and its bearing. The ratchet latch can be connected to the torsion arm of the ratchet handle or it can be a separate locking element pivoted to the body of the ratchet handle. The ratchet handle includes a reversing sleeve by which the pivotedly fastened toothed segment is controlled to lock in the desired direction or to remain in the free position. The position of the toothed segment is ensured by a spring in connection with the device.

The invention enables a light and simple tightener for a track. The torsion elements of the tightener for a track are located in the tightly closed housing where they are protected from damages and dirt. The components of the tightener for a track are of simple construction and of low costs. The gear and the toothed segment fitted for contact supply the worm shaft with the torsional force provided with the ratchet handle reliably, because there are several teeth in contact simultaneously.

Some advantageous embodiments of the invention are described in the dependent claims.

Next, the invention will be described in detail by means of some advantageous embodiments and with reference to the enclosed drawings.

Fig. 1 shows an oblique top view of a tightener for a track according to the invention.

Fig. 2 shows an oblique top view of the device of Fig. 1 set between track pads. Fig. 3 shows a ratchet handle of the device according to the invention without a housing cover.

Fig. 4 shows a schematical and partially cut view of the construction of the ratchet handle of the device according to the invention. Fig. 5 shows an alternative implementation of the ratchet handle in which a ratchet latch is integrated in the handle part of the ratchet handle.

Fig. 6 shows an alternative implementation of the ratchet handle in which the ratchet latch is a separate locking element.

Figs. 1-6 show a tightener for a track. The tightener for a track consists of a left- hand hook 1, a right-hand hook 2, a worm shaft 3, and a ratchet handle 4.

The left-hand hook 1 consists of a hook part la and a nut part lb. The nut part lb includes a threaded hole where there is a left-hand thread 3c. The hook part la is provided with a tightening bolt lc which is perpendicular in relation to the threaded hole 3c. The right-hand hook 2 consists of a hook part 2a and a nut part 2b. The nut part 2b includes a threaded hole where there is a right-hand thread 3d. The hook part 2a is provided with a tightening bolt 2c which is perpendicular in relation to the threaded hole 3d.

The nut parts lb, 2b of the hooks 1 and 2 are of the shape of a rectangular prism. Into connection with the nut parts are arranged hook parts la, 2a of the shape of letter C. The tightening bolts lc, 2c are perpendicular in relation to an upper surface lbl, 2b2 of bolt parts lb 1, 2b2 of the hooks. The upper surfaces lbl, 2b2 extend sufficiently far in the direction of the longitudinal axis of the worm shaft, whereby the ridges of the track pad cannot damage the worm shaft. The hooks 1 and 2 are fitted to the worm shaft 3, one half 3a of which includes a left-hand thread and the other half 3b a right-hand thread. Between the halves 3a and 3b is non-rotatably fitted a gear 3e which is concentric in relation to the worm shaft 3.

The ratchet handle 4 includes a housing-like body 4a, a torsion arm 4c and a handle 4d at the end of the torsion arm. Within the body 4a is arranged a space for the gear 3e and a ratchet latch 4c2. The body 4a is closed with a cover 4a3 which is fastened to the body by fastening elements 4al and 4a2. The fastening elements are most advantageously a sunk screw 4al which is fitted to threaded holes 4a2 in the body 4a. The worm shaft 3 is fitted to clearance holes 3al in the body 4a and the cover 4a3 such that the gear 3e remains within the housing-like body 4a. The clearance holes 3al simultaneously operate as the bearings of the worm shaft, in connection with which there can be sealing elements (not shown in the figures).

The ratchet latch 4c2 consists of a toothed segment 4c2 suitable for contact with the gear 3e. The toothed segment 4c2 is lightened from its middle section, that is, part of the segment teeth have been removed. The segment 4c2 is fastened to the body 4a via pivots 4c3 such that the ratchet latch can swivel back and forth around the pivot 4c3. This enables the fact that the toothed segment 4c2 can be in contact with the gear 3e alternately from its both ends, whereby the direction of the working movement of the tightener for a track can be reversed.

The ratchet latch 4c2 can be connected to the torsion arm 4c of the ratchet handle or it can be a separate locking element pivoted to the body of the ratchet handle. In the latter case, the torsion arm 4c is fastened fixedly or form- fittingly to the body 4a. The ratchet handle 4 includes a reversing sleeve 4b by which the pivotedly fastened toothed segment 4c2 is controlled to lock in the desired direction or to remain in the free position. The position of the toothed segment is ensured by a spring 4c4 in connection with the device. The spring is most advantageously a pressure spring the springback factor of which is relatively small. The spring 4c4 is fitted within the reversing sleeve 4b.

The reversing sleeve is fitted to the torsion arm 4c and locked in place by a locking element 4c 1, such as a roll pin. The lower edge of the reversing sleeve 4b rests on the ratchet handle 4c2. The lower edge of the sleeve 4b is shaped bevel such that, when rotating the sleeve 180 degrees around its longitudinal axis, the lower edge rests on either of the halves of the ratchet handle or is in a neutral position. On the outer surface of the reversing sleeve is arranged a mark which shows the position of the sleeve in relation to the body of the ratchet handle. When the sleeve is rotated from the middle position 90 degrees in either direction, the spring 4c4 ensures that the ratchet latch remains in contact with the gear 3e.

In an advantageous embodiment, the reversing sleeve 4b is provided with an inner shoulder on which is set to rest a compression spring 4c4 suitably longer than the sleeve of its unsupported length. The sleeve, within which the spring is, is passed from the top to the torsion arm 4c 1 of the ratchet handle and locked in place by a locking element 4c 1. The mutual distance between the centre of the gear 3e and the pivot point 4c3 of the toothed segment 4c2 is in an advantageous embodiment 0.8-1.0 times the reference diameter of the gear. In an advantageous embodiment, the reference diameter of the gear is in the range of 40-60 mm. The gear 3e is fitted to the housing 4a such that its outer race rests on the inner surface of a space in the housing 4a during tightening. Then, loading resulting from the tightening of the ratchet handle is divided more evenly, thus lightening the loading of the other parts in the construction.

The device according to the invention operates in the following way. The hooks 1 and 2 of the tightener for a track are rotated in the worm shaft 3 at a suitable location in order to be able to set the hooks in the track pads. The pads are set to rest on the upper surfaces lbl, 2b 1 in the nut parts lb, 2b of the hook, after which the pads are locked in place by tightening bolts lc.

By the reversing sleeve 4b of the ratchet handle 4, a tightening working movement is selected, whereby the lower edge of the sleeve 4b rests on the other edge of the ratchet latch 4c2 controlling the ratchet latch to contact with the gear 3e in the tightening direction. Depending on the dimensioning of the toothed segment 4c2, the gear 3e and their mutual position, they remain self-operatedly in contact, whereby the spring 4c4 only ensures the contact of the ratchet latch and the gear in the initial situation. As the spring is dimensioned relatively small of its springback factor, it will not prevent the ratchet latch from rising from contact during the return of the ratchet handle. By a back-and-forth movement of the ratchet handle 4, the ends of the track can be provided at a suitable distance from each other in order to be able to install the fastening links of the track in place.

The figures and the description related to them are only intended to illustrate the present invention. Of its details, the device can vary within the scope of the enclosed claims and the inventive idea presented in the description of the invention. It is evident to those skilled in the art that the technical arrangements of the tightener for a track can vary depending on their purpose of use. It is evident to those skilled in the art that the idea of the invention can be applied in a different set of track tighteners. The embodiment of the invention can vary in accordance with conditions of use and customer requirements and within the scope of arrangements implemented in connection with production.