Chain saw with tensioning assembly

Abstract

FIG. 2 1 / 4 12 26 14 22 7 16 84 18 30 20 28 7 80 82 70 8610 FIG. 1 10 32 34 26 14 12 22 70 20 44 46 46 42 24 48 50 52 56 16 64 28 54 58 20 26 20 14 12 25 F eb 2 02 6Feb 2026 1 / 4 12 2026201412 25 14 26 22 7 7 82 18 70 28 FIG. 1 86 14 32 12 C © 28 0 70 44 52 56 42 FIG. 2

Description

Statement of corresponding applications This application is based on European Patent Application No. 25169187.9, the entire contents of which are incorporated herein by reference. Field of Invention The invention relates to a chain saw. Background Chain saws are used for cutting purposes, in particular for wood, and can be implemented as handheld tools or used on tree harvesters for felling trees or cutting trunks. The chain saw comprises a sprocket driven by a motor and a guide bar around which the chain is entrained. The chain has links with cutting elements. During operation, the chain wears and lengthens. To adapt for this lengthening process, the position of the guide bar can be adjusted. US 3 194 284 A, considered as generic, describes a chain saw with tensioning means. A guide bar holding at its distal end an idler sprocket has on its proximal end on its longitudinal axis a longitudinal slot through which threaded studs extend. The studs are also mounted to a frame plate supporting the driven sprocket and the guide bar is sandwiched between the frame plate and a cover plate. The guide bar is thus movable along the slot. To bias the guide bar away from the frame plate to tension the chain, a tensioning mechanism with a compression spring and an adjustable screw is provided. The screw extends parallel to the slot and is rotatably supported on the cover plate. A nut, non-rotatably supported on the cover plate, has a thread interacting with the thread of the screw, such that rotation of the screw moves the nut along the direction of the slot. Between the nut and a lug member projecting into an aperture within the guide bar, the compression spring is clamped. The spring is thus with one end coupled via the lug to the guide bar and with the other end coupled via the nut and the screw to the cover plate and the frame plate. The slot and the movement direction of the lug are parallel but offset in a direction transversely to the longitudinal axis of the guide bar within the plane of the guide bar. DE 10 2019 121 221 B4 shows a very similar chain saw. WO 2015 / 038011 A1 shows another chain saw apparatus with a driven sprocket and a chain supported on a guide bar. A bar holder holding the guide bar is attached movably to a mount of the saw apparatus. The bar holder has a T-shaped profile with the central part engaging into a slot of the mount, such that the bar holder with the guide bar can move within the slot away and towards the mount. A tensioner urges the bar holder and thus the bar to move away from the mount to tension the chain. During operation, the piston is under hydraulic pressure that urges the piston to move the bar 2026201412   25 Feb 2026 holder towards the distal end. The slot and the piston movement both extend parallel to the longitudinal axis of the guide bar, while the piston is offset from the plane of the guide bar. Object of the technology A disadvantage of the assembly shown in US 3 194 284 A and DE 10 2019 121 221 B4 is that the point, where the force of the spring is introduced by the lug into the guide bar is transversely offset from the longitudinal axis of the guide bar. This creates canting and frictional forces. The arrangement of WO 2015 / 038011 A1 has the tensioner on the longitudinal axis of the guide bar, however, requires an expensive hydraulic tensioner needing hydraulic lines at a position where no access for an operator is possible. It is an object of the technology to solve one or more of these problems. Alternatively, it is an object of the technology to at least provide the public with a useful choice. Summary The present invention is defined by the claims. A chain saw comprises: a mount supporting a sprocket driveable to rotate around an rotation axis; a guide bar having a longitudinal axis extending through a distal end of the guide bar and the rotation axis of the sprocket, the guide bar movable along the longitudinal axis with respect to the mount, the guide bar and the sprocket lying in a common plane; a chain trained around the sprocket and the guide bar; a tensioning mechanism comprising a spring, a support rigidly connected to the mount, a tensioning screw and a tension bolt which is rigidly connected to the guide bar, wherein the spring biases the guide bar away from the mount along the longitudinal axis with a force that is adjustable by the tensioning screw, wherein the tension screw extends parallel to the longitudinal axis of the guide bar; wherein the tensioning mechanism is, with respect to a direction oriented in the common plane transversely to the axis, aligned with the axis. In other words, the tension mechanism can be offset from the axis of the guide bar in the direction transversely to the plane of the guide bar, but not in the direction lying in the plane of the guide bar and extending transversely to the axis thereof. This means that the tensioning forces are centrically introduced into the guide bar, not like in the prior art according to US 3 194 284 A and DE 10 2019 121 221 B4 in an eccentric manner causing potentially problems with canting and binding in the plane of the guide bar. The proposed tensioning mechanism is compact and simple and can be easily accessed for adjustment of the tensioning screw. The tensioning mechanism continuously biases the guide bar 2026201412   25 Feb 2026 towards the distal end during operation, not only during adjustment of the guide bar position. In examples, the spring is a compression spring and the tensioning screw pulls the tension bolt, which is closer to the sprocket than the support, towards the support, wherein the spring is provided between the tensioning screw and the tension bolt or between the tensioning screw and the support. In examples, the tensioning screw has a head abutting the support, a nut interacts with a thread of the tensioning screw and the spring, which surrounds the tensioning screw, is clamped between a tension block abutting or integral with the nut and the tension bolt. In examples, the tension screw has a thread interacting with a nut abutting the tension bolt or a thread within the tension bolt and the spring is clamped between the head of the tension screw and the support. In examples, the tensioning mechanism is offset from the axis in the direction extending transversely to the plane of the guide bar. In examples, the tension bolt is mounted to a mounting block connected to the guide bar, the mounting block slidably supported in a direction parallel to the axis in a recess of the mount. In examples, the mounting block is slidably supported on the mount by means of grooves and ridges extending parallel to axis. In examples, the grooves and ridges are offset from the axis in the direction extending in the plane of the guide bar and transverse to the axis. In examples, the guide bar is clamped between the mounting block and a clamping block. In examples, the mounting block and the clamping block are connected by bolts extending through a slot in guide bar extending along axis. In examples, the support bridges a distal end of an open slot of the mount, the slot extending parallel to axis and the tensioning mechanism is located within the slot. In examples, the slot is open towards the recess. In examples, the spring is a urethane spring or a coil spring or a spring washer stack. In examples, radially between the spring and the tensioner screw a cylinder is provided which cylinder is, in axial direction, shorter than the compressed spring. 2026201412   25 Feb 2026 In examples, the proximal end of the tensioning screw is received in a bore of the mount. Brief description of the drawings Embodiments of the invention described in more detail below are shown in the drawings. It shows: Fig. 1 a top view of a chain saw, Fig. 2 the chain saw of fig. 1 in an exploded view from top, Fig. 3 the chain saw of fig 1 in an exploded view from bottom, Fig. 4 a chain tensioner of the chain saw in exploded view, Fig. 5 the chain tensioner of fig. 4 in assembled state, Fig. 6 a section through the chain tensioner of fig. 5 along lines 6-6 of fig. 5, Fig. 7 a section through the chain saw along lines 7-7 of fig. 1, and Fig. 8 a view of a second embodiment of the tensioning mechanism. Detailed description of embodiments of the technology Figs. 1 to 3 show a chain saw 10 with a mount 12 supporting a sprocket 18 driven around its axis 84 by a motor 16. The mount 12 is rotatable by an actuator 14, such that the chain saw 10 can be moved between an operative position for cutting trees and an inoperative, retracted position. The chain saw 10 can be, generally without actuator 14, be embodied as a hand-held tool, or be mounted in a forestry machine, for example in a harvester head. When mounted on a harvester head, chain saw 10 is usually in a horizontal position shown from top in fig. 1 and 2 and from bottom in fig. 3. The chain saw 10 further comprises an elongated guide bar 22 around which a chain 20 is trained. The chain 20 is also trained around the sprocket 18. Chain 20 is shown only in a schematic manner and has links with cutting elements. Guide bar 22 and sprocket 18 are located in a common plane 80, in which also chain 20 lies. Guide bar 22 is movable along its (imaginary) longitudinal axis 70, which runs through the distal end 86 of guide bar 22 and though the axis 84 of sprocket 18, with respect to mount 12 and thus to 2026201412   25 Feb 2026 sprocket 18, biased towards the distal end (to the right side in fig. 1 and 3) to tension the chain 20 by means of a spring 52. The tensioning mechanism is shown in more detail in figs. 2 to 7, with a second embodiment shown in fig. 8. Guide bar 22 has at its proximal end a longitudinal slot 40, open towards the proximal end. The slot 40 receives bolts 28, 30 connecting a mounting block 24 on the side of the guide bar 22 facing the motor 16 and a clamping block 26 on the other side of the guide bar 22. Mounting block 24 has a ridge 60 engaging into slot 40 for centering mounting block 24 on the slot 40. Bolts 28 and 30 are screwed into corresponding threaded bores 62, 65 in mounting block 24. Nuts 32, 38 and washers 34, 36 clamp guide bar 22 between mounting block 24 and clamping block 26. During operation, mounting block 24 is thus fixed to guide bar 22. When the nuts 32, 38 are loosened, mounting block 24 and clamping block 26 can be moved along slot 40, i.e., along the longitudinal axis of guide bar 22, for adjusting or maintenance purposes and / or chain replacement. Once adjusted, the nuts 32, 38 are fixed again to make the chain saw 10 ready for operation. During operation, no adjustment of guide bar 22 along slot 40 - in particular due to a lengthening chain 20 - is foreseen, since the tensioning mechanism described in the following automatically adjusts the guide bar 22. Slot 40 could also be replaced by two bores for bolts 28, 30 within guide bar 22. Mounting block 24 is slidably supported in the mount 12 along the longitudinal axis 70 of guide bar 22. In a cuboidal recess 68 of mount 12, longitudinal ridges 66 are provided, engaging into grooves 64 of mounting block 24. Ridges 66 and grooves 64 are provided on both sides of mounting block 24, which sides are shown in fig. 3 on bottom and top of mounting block 24 and mount 12. The ridges 66 and grooves 64 thus are aligned parallel to the longitudinal axis 70 of guide bar 22 and offset in the transverse direction in the plane of the guide bar 22 and allow mounting block 24 to move along longitudinal axis 70 in a sliding, guided manner. Additionally, mount 12 has a slot 56 at its center, extending along the longitudinal axis 70 of guide bar 22 and open to recess 68. In slot 56, the main parts of the tensioning mechanism are received. The tensioning mechanism connects mounting block 24 and mount 12 in a manner to bias mounting block 24 and thus guide bar 22 along longitudinal axis 70 towards the distal end of guide bar 22. A support 44 bridges over the outer end of slot 56 of mount 12 and is fixed there by bolts 46 on both sides. A tensioner screw 42 extends within slot 56 along longitudinal axis 70 towards center of sprocket 18 and has a head 74 abutting support 44. Tensioner screw 42 goes through a tension bolt 48, a cylinder 50 radially surrounded by a compression spring 52, a tension block 54 and a nut 58 and has its proximal end centered in a bore 72 in mount 12. The thread of tensioner screw 42 only interacts with nut 58 and is freely rotatable with respect to tension bolt 48, cylinder 50, tension block 54 and bore 72. When the head 74 of tensioner screw 42 is turned, nut 58 moves along longitudinal axis 70 of guide bar 22. The axial length of cylinder 50 is shorter than the axial length of compression 2026201412   25 Feb 2026 spring 52 when the latter is in the maximal compressed state. In an embodiment not shown, nut and tension block 54 could be provided as a unitary part or be permanently fixed together. Tension bolt 48 is closer to sprocket 18 than support 44, thus pulling the tension bolt 48 towards support 44 moves guide bar 22 along axis 70 away from sprocket 18, towards the distal end 86 of guide bar 22. Tension bolt 48 is fixed to mounting block 24, as shown in fig. 4. Compression spring 52 is clamped between tension block 54 and tension bolt 48 and supported on cylinder 50. Nut 58 is rotationally fixed on tension block 54. This means that in assembled state of the tensioning mechanism, tensioner screw 42 compresses compression spring 52 between tension block 54 and tension bolt 48 and turning the head 74 of tensioner screw allows adjustment of the force of spring 52. Spring 52 is in an embodiment a urethane spring, but it should be noted that any type of compression spring can be used, for example a helicoidal spring or a spring washer stack. A force acting on guide bar 22 along axis 70 is transmitted via mounting block 24 and tension bolt 48 to spring 52 and from spring 52 via tension block 54, nut 58, tensioner screw 42, support 44 to mount 12. The entire tensioning mechanism, as described in the two preceding paragraphs, is aligned parallel with the longitudinal axis 70 of guide bar 22, only offset in the direction running transversely to the common plane 80 of guide bar 22 and sprocket 18 (and chain 20, this direction extends transversely to the plane of the drawings of fig. 1, 6 and 8), but not in the direction 82 within the plane of the guide bar 22 extending transversely to axis 70, cf. fig. 1. This has the advantage that the tension mechanism does not generate canting or blocking forces within the plane 80 of the guide bar 22. Also, the tensioning mechanism is relatively compact and located at a position where head 74 of tensioner screw 42 can be easily reached. A shown in the second embodiment of fig. 8, showing a similar view as fig. 6, with corresponding parts having the same reference numerals, it is also possible to mount spring 52 between the support 44 and the head 74 of the tensioning screw 42, preferably with a washer 76 and the tension block 54 sandwiched between head 74 and spring 52. Protruding walls 78 on support 44 prevent spring 52 from rotating around tensioning screw 42. A nut 58, blocked against rotation for example by suitable, noncircular features on nut 58 interacting with corresponding features on tension bolt 48, abuts tension block 48 on the side opposite of support 44 and spring 52. Here, spring 52 also encloses cylinder 50. It would also be possible to include nut 58 into tensioning bolt 48, i.e., by providing tensioning bolt 48 with a thread interacting with the thread of tensioning screw 42. Mounting block 24 is the same as in the first embodiment. The second embodiment works generally in the same manner as the first embodiment. The force of spring 52 is on one hand transmitted by support 44 to mount 12 and thus to sprocket 18, and on the other hand by tension block 54, washer 76, tensioning screw 42, nut 58, tension bolt 48, mounting block 24 and bolts 28, 30 to guide bar 22. Turning the head 74 of tensioning screw 42, which pulls the 2026201412   25 Feb 2026 tension block 42 and thus the guide bar 22 away from mount 12 and sprocket 18 against the force of spring 52 (like in the first embodiment, the main difference being the location of spring 52 between support 44 and head 74 in the second embodiment, while spring 52 is between tension bolt 48 and tension block 54 in the first embodiment), varies also in this embodiment the tension of spring 52 and thus the bias of guide bar 42 away from sprocket 18. It should be noted that in another embodiment, not shown, the bolts 28 and 30 are inserted into bores 62, 65 from the side of mounting block 24 shown on top in fig. 4 and 5, before the tension screw 42 is inserted. In this embodiment, the bolts 28, 30 have heads protruding beyond the edge of holes 62, 65 to have the bolts 28, 30 fixed in axial direction. The bolts 28, 30 also have features on their head and / or on their shaft in the vicinity of their head, interacting with features in holes 62, 65, like noncircular or rectangular elements (locational fit), to avoid that bolts 28, 30 rotate around their axes and thus nuts 32, 38 can be tightened to fix mounting block 24 and clamping block 26 together. To be able to insert bolt 28 from the top in fig. 4 and 5, tension bolt 48 has on its side facing towards support 44 a concave recess. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”. The entire disclosures of all applications, patents and publications cited above, if any, are herein incorporated by reference. Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world. The technology may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features. Where in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth. It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the technology and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the present technology.

Claims

1. A chain saw comprising:a mount supporting a sprocket driveable to rotate around an rotation axis;a guide bar having a longitudinal axis extending through a distal end of the guide bar and the rotation axis of the sprocket, the guide bar movable along the longitudinal axis with respect to the mount, the guide bar and the sprocket lying in a common plane;a chain trained around the sprocket and the guide bar;a tensioning mechanism comprising a spring, a support rigidly connected to the mount, a tensioning screw and a tension bolt which is rigidly connected to the guide bar, wherein the spring biases the guide bar away from the mount along the longitudinal axis with a force that is adjustable by the tensioning screw, wherein the tension screw extends parallel to the longitudinal axis of the guide bar;characterized in that the tensioning mechanism is, with respect to a direction oriented in the common plane transversely to the axis, aligned with the axis.

2. The chain saw according to claim 1, wherein the spring is a compression spring and the tensioning screw pulls the tension bolt, which is closer to the sprocket than the support, towards the support, wherein the spring is provided between the tensioning screw and the tension bolt or between the tensioning screw and the support.

3. The chain saw according to claim 2, wherein the tensioning screw has a head abutting the support, a nut interacts with a thread of the tensioning screw and the spring, which surrounds the tensioning screw, is clamped between a tension block abutting or integral with the nut and the tension bolt.

4. The chain saw according to claim 2, wherein the tension screw has a thread interacting with a nut abutting the tension bolt or a thread within the tension bolt and the spring is clamped between the head of the tension screw and the support.

5. The chain saw according to one of claims 1 to 4, wherein the tensioning mechanism is offset from the axis in the direction extending transversely to the plane of the guide bar.

6. The chain saw according to one of claims 1 to 5, wherein the tension bolt is mounted to a mounting block connected to the guide bar, the mounting block slidably supported in a direction parallel to the axis in a recess of the mount.

7. The chain saw according to claim 6, wherein the mounting block is slidably supported on the mount by means of grooves and ridges extending parallel to axis.2026201412   25 Feb 20268. The chain saw according to claim 7, wherein the grooves and ridges are offset from the axis in the direction extending in the plane of the guide bar and transverse to the axis.

9. The chain saw according to one of claims 6 to 8, wherein the guide bar is clamped between the mounting block and a clamping block.

10. The chain saw according to claim 9, wherein the mounting block and the clamping block are connected by bolts extending through a slot in guide bar extending along axis.

11. The chain saw according to one of the preceding claims, wherein the support bridges a distal end of an open slot of the mount, the slot extending parallel to axis and the tensioning mechanism is located within the slot.

12. The chain saw according to claim 11, when appended to claim 6, wherein the slot is open towards the recess.

13. The chain saw according to one of the preceding claims, wherein the spring is a urethane spring or a coil spring or a spring washer stack.

14. The chain saw according to claim 13, wherein radially between the spring and the tensioner screw a cylinder is provided which cylinder is, in axial direction, shorter than the compressed spring.

15. The chain saw according to one of the preceding claims, wherein the proximal end of the tensioning screw is received in a bore of the mount.

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