Patent Description:
<CIT> discloses a reciprocating mower oscillating a pair of mowing blades in mutual anti-phase about a common oscillation axis. Such a mower facilitates convenient mowing of soft grass as well as small shrubs with a very low risk of kicking off pebble-stones. Similar reciprocating mowers are disclosed in each of <CIT>, <CIT>, <CIT>, and <CIT>. There is however a need for a more ergonomic and user-friendly mower.

It is an object of the present invention to solve, or at least mitigate, parts or all of the above mentioned problems. To this end, there is provided, according to a first aspect, a reciprocating mower unit configured to be driven by a drive unit via a transmission shaft arranged within a transmission tube, the reciprocating mower unit comprising: a housing; a reduction gear arranged within the housing, the reduction gear being configured to receive an input rotary motion from the transmission shaft at a first, relatively higher, rotation speed, and deliver an output rotary motion to a gear output shaft at a second, relatively lower, rotation speed; a crank mechanism arranged within the housing, the crank mechanism being configured to convert the output rotary motion of the gear output shaft to an oscillating motion of a pair of mowing blades oscillating in mutual anti-phase about a common oscillation axis; and an input shaft for receiving said input rotary motion from the transmission shaft, wherein the input shaft is provided with a coupling interface for releasably coupling the input shaft to the transmission shaft. Such a reciprocating mower unit permits coupling and de-coupling of the reciprocating mower unit to/from the transmission shaft, which allows connecting the reciprocating mower unit to different drive units, and vice versa. Thereby, the versatility of the reciprocating mower unit as well as the drive unit is increased.

According to an embodiment, the coupling interface may comprise splines for axially sliding into rotational engagement with mating splines of the transmission shaft. One of the input shaft and the transmission shaft may comprise a socket provided with inner splines, whereas the other of the input shaft and the transmission shaft may be provided with outer splines.

According to an embodiment, the housing may comprise a clamping arrangement for clamping the housing to the transmission tube.

According to a second aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a vegetation cutter system comprising: a drive unit comprising a motor and a transmission shaft arranged within a transmission tube; a reciprocating mower unit as defined above; and a clearing saw unit configured to rotate a clearing saw blade, wherein the reciprocating mower unit and the clearing saw unit are configured to be alternatingly connected to the transmission shaft.

According to a third aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a reciprocating mower unit configured to be driven by a drive unit via a transmission shaft arranged within a transmission tube, the reciprocating mower unit comprising: a housing; a reduction gear arranged within the housing, the reduction gear being configured to receive an input rotary motion from the transmission shaft at a first, relatively higher, rotation speed, and deliver an output rotary motion to a gear output shaft at a second, relatively lower, rotation speed; and a crank mechanism arranged within the housing, the crank mechanism being configured to convert the output rotary motion of the gear output shaft to an oscillating motion of a pair of mowing blades oscillating in mutual anti-phase about a common oscillation axis, wherein the reduction gear is a two-stage reduction gear comprising a first gear connected to corotate with the input shaft, a second gear in mesh with the first gear, a third gear connected to corotate with the second gear, and a fourth gear configured to co-rotate with a crank of the crank mechanism, the fourth gear being in mesh with the third gear, wherein the first gear has a first number of teeth, the second gear has a second number of teeth, the third gear has a third number of teeth, and the fourth gear has a fourth number of teeth, wherein the second number of teeth is greater than the first number of teeth, and the fourth number of teeth is greater than the third number of teeth. Such a two-stage reduction gear permits obtaining a high reduction ratio with a compact volume in the reciprocating mower unit, which reduces the need for any reduction gear in the drive unit. Thereby, the manufacturing cost of the drive unit may be reduced, since the same type of drive unit may be used for e.g. rotary clearing saws. Moreover, if the reciprocating mower unit is provided with a coupling interface as defined hereinabove, a modular system may be obtained, allowing changing between rotary and reciprocating mower units using the same drive unit. According to an embodiment, the drive unit of such a modular system is entirely free from any reduction gear, such that the transmission shaft is rotated at the rotary speed of the motor. According to an embodiment, the first and second gears may be bevel gears. Thereby, the rotation axis of the first gear may be inclined relative to the common oscillation axis by an inclination angle, which permits connecting to an inclined transmission shaft. According to examples, the inclination angle may be between <NUM>° and <NUM>°, or between <NUM>° and <NUM>°.

According to an embodiment, the first gear may have <NUM>-<NUM> teeth; the second gear may have <NUM>-<NUM> teeth; the third gear may have <NUM>-<NUM> teeth, and the fourth gear may have <NUM>-<NUM> teeth.

According to a fourth aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a reciprocating mower unit configured to be driven by a drive unit via a transmission shaft arranged within a transmission tube, the reciprocating mower unit comprising: a housing; a reduction gear arranged within the housing, the reduction gear being configured to receive an input rotary motion from the transmission shaft at a first, relatively higher, rotation speed, and deliver an output rotary motion to a gear output shaft at a second, relatively lower, rotation speed; and a crank mechanism arranged within the housing, the crank mechanism being configured to convert the output rotary motion of the gear output shaft to an oscillating motion of a pair of mowing blades oscillating in mutual anti-phase about a common oscillation axis, the crank mechanism comprising, for each of the mowing blades, a respective four-bar linkage configured to oscillate the respective blade in response to rotation of the gear output shaft, each of the four-bar linkages comprising a fixed link between a rotation axis of the gear output shaft and the common oscillation axis; a respective input link configured as a crank attached to the gear output shaft; a respective output link configured as a crank journaled to pivot about the common oscillation axis; and a respective coupler link interconnecting the respective input and output links, wherein, for each of said four-bar linkages, a link ratio between the input link and the fixed link is at least <NUM>:<NUM>. It has been found that using such a link ratio, a relatively low level of vibrations of the tool may be obtained, resulting in a better work environment. According to an embodiment, the link ratio between the input link and the fixed link is at least <NUM>:<NUM>. The link ratio may, according to a typical example, be between <NUM>:<NUM> and <NUM>:<NUM>. A typical length of the input link may, for example, be between <NUM>,<NUM> and <NUM>. A typical length of the fixed link may, for example, exceed <NUM>. Alternatively or additionally, the fixed link may be shorter than about <NUM>. The reciprocating mower unit may be provided with a coupling interface and/or a two-stage reduction gear as defined hereinabove.

According to an embodiment, the reciprocating mower unit may have a link ratio between the input link and the coupler link of at least <NUM>:<NUM>. It has been found that using such a link ratio, a relatively low level of vibrations of the tool may be obtained in combination with a compact and efficient reciprocating mower unit, resulting in a more ergonomic reciprocating mower unit. According to an embodiment, the link ratio between the input link and the coupler link is between <NUM>:<NUM> and <NUM>:<NUM>. A typical length of the coupler link may, for example, be between <NUM> and <NUM>. A typical length of the output link may, for example, be between <NUM> and <NUM>.

According to a fifth aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a reciprocating mower unit configured to be driven by a drive unit via a transmission shaft arranged within a transmission tube, the reciprocating mower unit comprising: a housing; a reduction gear arranged within the housing, the reduction gear being configured to receive an input rotary motion from the transmission shaft at a first, relatively higher, rotation speed, and deliver an output rotary motion to a gear output shaft at a second, relatively lower, rotation speed; and a crank mechanism arranged within the housing, the crank mechanism being configured to convert the output rotary motion of the gear output shaft to an oscillating motion of a pair of mowing blades oscillating in mutual anti-phase about a common oscillation axis, wherein the crank mechanism is configured to oscillate each respective mower blade about the common oscillation axis at an oscillation angle of less than <NUM>°. Thereby, a low level of vibration may be obtained. An oscillation angle of between <NUM>° and <NUM>° has been found to result in a particularly good balance between mowing efficiency and vibration. The reciprocating mower unit may be provided with a coupling interface and/or a two-stage reduction gear and/or a four-bar linkage as defined hereinabove.

According to a sixth aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a reciprocating mower unit configured to be driven by a drive unit via a transmission shaft arranged within a transmission tube, the reciprocating mower unit comprising: a housing; a reduction gear arranged within the housing, the reduction gear being configured to receive an input rotary motion from the transmission shaft at a first, relatively higher, rotation speed, and deliver an output rotary motion to a gear output shaft at a second, relatively lower, rotation speed; a crank mechanism arranged within the housing, the crank mechanism being configured to convert the output rotary motion of the gear output shaft to an oscillating motion of a pair of mowing blades oscillating in mutual anti-phase about a common oscillation axis; and a grounding body defining a lowermost face for resting against the ground when the reciprocating mower unit is in use, wherein the grounding body is rotationally decoupled, with regard to turning about the common oscillation axis, from each mowing blade of said pair of mowing blades. Thereby, vibrations of the tool may be reduced, which results in a better user experience. The reciprocating mower unit may be provided with a coupling interface and/or a two-stage reduction gear and/or a four-bar linkage and/or an oscillation angle as defined hereinabove. Optionally, the grounding body may be rotationally decoupled also from the housing.

According an embodiment, the grounding body may have a circular outer shape, as seen along the common oscillation axis. The grounding body may be made of plastic.

According to an embodiment, the grounding body may be axially carried by a blade reciprocation shaft.

According to an embodiment, the grounding body may be axially held through a central opening of the grounding body between an upper axial stop and a lower axial stop, wherein an axial distance between the upper and lower axial stops exceeds the thickness of the grounding body adjacent the central aperture. The upper axial stop may be defined by a downwards facing shoulder of the mowing blade reciprocation shaft. The lower axial stop may be defined by a fastening arrangement in abutment with a lower shoulder of the mowing blade reciprocation shaft. The fastening arrangement may comprise, for example, a threaded element, such as a screw or a nut, holding a washer tightly into abutment with the lower axial shoulder. The central opening of the grounding body may be sufficiently larger than e. g any blade reciprocation shaft penetrating therethrough to allow free rotation of the grounding body relative to the blade reciprocation shaft.

According to a seventh aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a method of operating a reciprocating mower unit, comprising: driving a pair of mowing blades to oscillate in a guided mutual anti-phase motion about a common oscillation axis; and allowing a grounding body, axially held by the reciprocating mower unit at a bottom face thereof, to remain stationary.

According to an eighth aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a method of operating a reciprocating mower, comprising: operating a motor of a drive unit at a rotation speed of more than <NUM> revolutions per minute; operating a transmission shaft having a length of at least <NUM> metre at the rotation speed of the motor; driving a first reduction gear step with an output rotary motion of the transmission shaft; driving a second reduction gear step with an output rotary motion of the first reduction gear step; and converting output rotary motion of the second reduction gear step to an oscillating motion of a pair of mowing blades.

It is noted that embodiments of the invention may be embodied by all possible combinations of features recited in the claims. Further, it will be appreciated that the various embodiments described for the devices are all combinable with the methods, and vice versa.

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and nonlimiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.

<FIG> illustrates a handheld reciprocating mower <NUM> comprising a drive unit <NUM> and a reciprocating mower unit <NUM>. The drive unit <NUM> comprises a transmission tube <NUM>, and a motor <NUM> attached to a first end 16a of the transmission tube <NUM>. The motor <NUM>, which is configured to drive the reciprocating mower unit <NUM> via a transmission shaft (not illustrated) inside the transmission tube <NUM>, may be e.g. an internal combustion engine or an electric motor. The drive unit is further provided with a pair of handles 20a, 20b for holding the reciprocating mower <NUM>, and a trigger <NUM> for controlling a rotary speed of the motor <NUM>, which in the case of an internal combustion engine is typically operated at a speed exceeding <NUM> revolutions per minute (rpm). The reciprocating mower unit <NUM> is attached to a second end 16b of the transmission tube <NUM>, opposite the first end 16a, such that an operator standing in an upright position, and holding the reciprocating mower <NUM> by the two handles 20a, 20b, may conveniently position the reciprocating mower unit <NUM> close to the ground and at a safe distance from his/her feet, for mowing e.g. grass and other vegetation. For the purpose, the transmission tube typically has a length exceeding about <NUM> metre.

Turning now to <FIG>, the reciprocating mower unit <NUM> comprises a housing <NUM> provided with a clamping arrangement <NUM> for clamping the housing <NUM> onto the transmission tube <NUM> (<FIG>). The clamping arrangement comprises a slit <NUM> in the housing <NUM>, and a clamping screw <NUM> configured to press the slit <NUM> together. A crank mechanism (not illustrated) is arranged within the housing <NUM> underneath a top cover <NUM>; the crank mechanism is configured to oscillate a pair of mowing blades 32a, 32b in mutual anti-phase about a common oscillation axis A1. The crank mechanism is configured to oscillate a first, lower mowing blade 32a of the pair of mowing blades between end positions defined by a first oscillation angle α<NUM>, and a second, upper mowing blade 32b of the pair of mowing blades between end positions defined by a second oscillation angle α<NUM>. Typically, α<NUM> and α<NUM> may be substantially the same; in the illustrated example, α<NUM> = α<NUM> ≈ <NUM>°. The oscillation angle approximately corresponds to half the cutting tooth pitch P, i.e. the mowing blades 32a, 32b move relative to each other such that each cutting tooth 34b of the upper mowing blade 32b alternatingly overlaps with two adjacent cutting teeth 34a of the lower mowing blade 32a, and vice versa, so as to shear off vegetation caught in the gap <NUM> therebetween.

<FIG> illustrates the drive unit <NUM>, the reciprocating mower unit <NUM>, and a clearing saw unit <NUM>. The drive unit <NUM> comprises, at the second end 16b of the transmission tube <NUM>, a cutter unit interface 40a, and each of the reciprocating mower unit <NUM> and the clearing saw unit <NUM> comprises a respective drive unit interface 40b configured to mate with the cutter unit interface 40a of the drive unit <NUM>. Thereby, the drive unit <NUM>, the reciprocating mower unit <NUM>, and the clearing saw unit <NUM> make up a modular vegetation cutter system <NUM> allowing the reciprocating mower unit <NUM> and the clearing saw unit <NUM> to be alternatingly connected to the drive unit <NUM>. Even though the reciprocating mower unit <NUM> may be well suited for grass and small shrubs, in particular in situations where ricocheting pebbles may cause damage, the rotary clearing saw unit <NUM>, configured to rotating a circular clearing saw blade <NUM> at a high rotary speed, may be better suited for thicker shrubs and in situations where a higher cutting speed is desired. Thanks to the modular system <NUM>, both alternatives may be available to the operator at a low weight and volume.

<FIG> illustrates the cutter unit interface 40a of the drive unit <NUM> and the drive unit interface 40b of the reciprocating mower unit <NUM> in greater detail. It will be appreciated that the drive unit interface 40b of the clearing saw unit <NUM> may be identical to that of the reciprocating mower unit <NUM>. For clarity of illustration, the respective outlines of the transmission tube <NUM> of the drive unit <NUM> and the housing <NUM> of the reciprocating mower unit <NUM> are illustrated with dashed lines. The transmission shaft <NUM> is arranged inside the transmission tube <NUM>, and is connected to be rotated by the motor <NUM> (<FIG>) of the drive unit <NUM>. A free end <NUM> of the transmission shaft <NUM> is provided with outer splines <NUM> extending axially along the transmission shaft <NUM>. The drive unit interface 40b comprises a transmission tube socket <NUM> for matingly receiving the free second end 16b of the transmission tube <NUM>, and the clamping arrangement <NUM> allows decreasing the width of the slit <NUM> in the housing <NUM> such that the transmission tube <NUM> is firmly clamped in the transmission tube socket <NUM> of the housing <NUM>. The drive unit interface 40b further comprises an input shaft <NUM> having a transmission shaft socket <NUM> provided with inner splines <NUM>, for receiving the splined end <NUM> of the transmission shaft <NUM>. A bearing arrangement <NUM> radially supports the input shaft <NUM> within the housing <NUM>.

<FIG> illustrates the housing <NUM> of the reciprocating mower unit <NUM> (<FIG>) with its cover <NUM> (<FIG>) removed, revealing a reduction gear <NUM> and a crank mechanism <NUM>. The reduction gear <NUM> is configured to reduce the rotary speed delivered by the input shaft <NUM> (<FIG>) to a lowered rotary speed of a gear output shaft <NUM>, which drives the crank mechanism <NUM> for reciprocating the blades 32a, 32b (<FIG>). The gear output shaft <NUM> is configured to rotate about a gear output shaft rotation axis A2, and thereby rotate a first, upper, input crank, configured as a first, upper, crankpin 60a formed on the gear output shaft <NUM>. The upper input crankpin 60a defines the input link of a first, upper, four-bar linkage, comprising the upper input crankpin 60a, an upper coupler link 62a, and an upper output crank 64a which is configured to reciprocate about the common oscillation axis A1 in response to rotating the upper input crankpin 60a about the gear output shaft rotation axis A2. The upper coupler link 62a is pivotally coupled to the upper input crankpin 60a and an upper output crankpin 66a of the output crank 64a, but otherwise floating. The fourth link of the upper four-bar linkage is defined by the fixed link between the gear output shaft rotation axis A2 and the common oscillation axis A. The fixed link is physically represented by the housing <NUM>, which holds the gear output shaft rotation axis A2 and the common oscillation axis A1 in fixed relationship with each other.

<FIG> schematically illustrates the operation of the upper four-bar linkage <NUM>. The four-bar linkage is illustrated in two positions, one of which is drawn in broken lines. The rotation of the input link 60a about the gear output shaft rotation axis A2 moves the coupler link 62a, which in turn pivots the output link 64a about the common oscillation axis A1 in a reciprocating manner. The fixed link <NUM> does not move. According to the illustrated example, the input link 60a has a length of about <NUM> (i.e. the radial centre of the crank pin is offset from the radial centre of the gear output shaft (=axis A2) by about <NUM>), the coupler link 62a has a length of about <NUM> (i.e. the distance between the pivot axes is about <NUM>), the output link 64a has a length of about <NUM>, and the fixed link <NUM> has a length of about <NUM>.

<FIG> illustrates the reduction gear <NUM> and the crank mechanism <NUM> with the housing <NUM> (<FIG>) removed. The reduction gear <NUM> is a two-stage reduction gear comprising a first gear <NUM> attached to the input shaft <NUM>, a second gear <NUM> attached to an intermediate shaft <NUM> and in mesh with the first gear <NUM>, a third gear <NUM> attached to the intermediate shaft <NUM> to co-rotate with the second gear <NUM>, and a fourth gear <NUM> attached to the gear output shaft <NUM> and in mesh with the third gear. The first and second gears <NUM>, <NUM> are bevel gears; in the view of <FIG>, they are illustrated without teeth for ease of illustration. In the illustrated example, the first gear <NUM> has <NUM> teeth; the second gear <NUM> has <NUM> teeth; the third gear <NUM> has <NUM> teeth; and the fourth gear <NUM> has <NUM> teeth. Thereby, there is a first reduction in rotary speed at the engagement between the first and second gears <NUM>, <NUM>, defining a first stage of said two-stage reduction gear, and a second reduction in rotary speed at the engagement between the third and fourth gears <NUM>, <NUM>, defining a second stage of said two-stage reduction gear. Upper and lower ends of the intermediate shaft <NUM> and the gear output shaft <NUM> are journaled in bearings <NUM>, even though only the lower bearings are illustrated in the view of <FIG> also illustrates the first, upper four-bar mechanism of the crank mechanism <NUM> along with a second, lower, four-bar mechanism which, however, is better illustrated in the exploded view of <FIG>.

Turning to <FIG>, the second, lower, four-bar mechanism is also driven by the gear output shaft <NUM>. An input crank, configured as a second, lower crankpin 60b formed on the gear output shaft <NUM>, defines the input link of the second, lower, four-bar linkage. The lower crankpin 60b is out of phase with the upper crankpin 60a, with regard to rotation about the gear output shaft rotation axis A2, by <NUM>°. The lower four-bar linkage comprises the lower input crankpin 60b, a lower coupler link 62b, and a lower output crank 64b which is configured to reciprocate about the common oscillation axis A1 in response to rotating the lower input crankpin 60b about the gear output shaft rotation axis A2. The lower coupler link 62b is pivotally coupled to the lower input crankpin 60b and a lower output crankpin 66b of the lower output crank 64b, but otherwise floating. The fourth link of the lower four-bar linkage is, similar to the upper four-bar linkage, defined by the fixed link between the gear output shaft rotation axis A2 and the common oscillation axis A1, and is physically represented by the housing <NUM>.

The lower output crank 64b is connected to an outer blade reciprocation shaft 80b via splines, to reciprocate the outer blade reciprocation shaft 80b about the common oscillation axis A1. An upper blade carrier 82b is fixedly connected to a bottom end of the outer blade reciprocation shaft 80b. Similarly, the upper output crank 64a is connected to an inner blade reciprocation shaft 80a via splines, to reciprocate the inner blade reciprocation shaft 80a about the common oscillation axis A1 in anti-phase with the outer blade reciprocation shaft 80b. A lower blade carrier 82a is fixedly connected to a bottom end of the inner blade reciprocation shaft 80a. The inner and outer blade reciprocation shafts 80a, 80b are concentric, and the inner blade reciprocation shaft 80a extends axially, from the lower blade carrier 82a, through the outer reciprocation shaft 80b and the lower output crank 64b, to engage with the splines of the upper output crank 62a. Each of the lower and upper blade carriers 82a, 82b holds a respective mowing blade 32a, 32b (<FIG>).

The section of <FIG> illustrates the various components of the reduction gear <NUM> and the crank mechanism <NUM>. Even though the gear output shaft <NUM> is not visible in the section, its rotation axis A2 is indicated in line with the centre of the fourth gear <NUM>. The input shaft <NUM> is inclined in relation to the common oscillation axis A1 of the gear output shaft by an inclination angle α<NUM> of about <NUM>°, to provide for holding the transmission tube <NUM> (<FIG>) at a convenient angle, with the blades 32a, 32b horizontal above the ground.

The section of view <NUM> also illustrates a grounding body <NUM> for resting against the ground when the reciprocating mower unit <NUM> is in use. <FIG> illustrates the grounding body <NUM> in perspective; it has a circular outer shape, as seen along the common oscillation axis A1. and is provided with a circular central aperture <NUM> for receiving a screw <NUM>. A washer <NUM> forms a lower axial stop for the grounding body <NUM>. Referring back to <FIG>, the screw <NUM> engages with an inner thread of the inner blade reciprocation shaft 80a such that the screw <NUM> and the inner blade reciprocation shaft 80a are rigidly connected. The screw <NUM> tightly holds the washer <NUM> against a lower axial end <NUM> of the inner blade reciprocation shaft 80a, whereas the bottom face of the lower blade carrier 82a, which is integrally formed with the inner blade reciprocation shaft 80a, defines an upper axial stop of the grounding body <NUM>. The axial distance between the upper and lower axial stops exceeds the thickness of the grounding body adjacent the central aperture <NUM>. Thereby, the grounding body is rotationally decoupled from both blade reciprocation shafts 80a, 80b as well as from the housing <NUM>.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claim 1:
A reciprocating mower unit (<NUM>) configured to be driven by a drive unit (<NUM>) via a transmission shaft (<NUM>) arranged within a transmission tube (<NUM>), the reciprocating mower unit (<NUM>) comprising:
a housing (<NUM>);
a reduction gear (<NUM>) arranged within the housing (<NUM>), the reduction gear (<NUM>) being configured to receive an input rotary motion from the transmission shaft (<NUM>) at a first, relatively higher, rotation speed, and deliver an output rotary motion to a gear output shaft (<NUM>) at a second, relatively lower, rotation speed; and
a crank mechanism (<NUM>) arranged within the housing, the crank mechanism (<NUM>) being configured to convert the output rotary motion of the gear output shaft (<NUM>) to an oscillating motion of a pair of mowing blades (32a, 32b) oscillating in mutual anti-phase about a common oscillation axis (A1), wherein the reciprocating mower unit (<NUM>) is characterized in comprising an input shaft (<NUM>) for receiving said input rotary motion from the transmission shaft (<NUM>), wherein the input shaft (<NUM>) is provided with a coupling interface (<NUM>) for releasably coupling the input shaft (<NUM>) to the transmission shaft (<NUM>).