FR2775921A1 - MANUALLY GUIDED WORKING INSTRUMENT COMPRISING A TRANSMISSION SHAFT ROTATING IN A SMOOTH BEARING OF A PROTECTIVE TUBE - Google Patents

Abstract

The drive shaft of this device connects a heat engine to a tool and rotates in a direction prefixed in the plain bearing.A helical grease transport groove is formed between the outer lateral surface of the drive shaft (3) and the coaxial bearing surface, directed towards it, of the plain bearing (7). The groove rises in the opposite direction to the direction of rotation of the shaft (3) and extends over at least part of the length of this shaft. The plain bearing (7) is formed in particular by a bearing tube extending over the entire length of the protective tube (1). At least part of the grease (16) accumulating around the generally lower end (40) of the shaft (3) is thus transported upwards towards the motor, which ensures more regular lubrication of the tree. Applicable in particular to brushcutters.

Description

The invention relates to a manually guided working instrument, in

  particular a brushcutter, comprising a protective tube receiving a transmission shaft which is moved at a first end by a drive motor and connected at a second end to a working tool, the transmission shaft rotating in a direction of rotation prefixed in a plain bearing of the protective tube. Such devices, manually guided, are equipped with a protective tube or guide tube, also called a "handle", of straight or curved shape, and are used in particular as brushcutters to thin out the undergrowth, cut weeds or similar work, or as pruners to prune trees. The guide tube forms a protective tube in which is disposed a bearing tube, forming a smooth bearing, in which the transmission shaft is rotatably mounted as in a plain bearing of the usual type. Especially if the guide tube is curved, the transmission shaft can also consist of a flexible shaft.

  To lubricate the shaft / tube rubbing couple-

  bearing, grease is introduced under pressure into the clearance between them. Under the effect of heat and during the operation of the appliance, the fat becomes fluid and tends, for example under the effect of

  gravity, to flow to lower areas.

  As a brushcutter is regularly held in an operating position in which the drive motor placed at one end of the protective tube forms the highest point and the cutting head placed at the other end of the protective tube and comprising the tool forms the lowest point, fat accumulates during operation in the

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  area of the lower end, for example in the area of the cutting head. On the other hand, a lack of grease can occur in the parts of the bearing tube located closer to the drive motor, which can cause damage. In the case of brushcutters carried on the back, a flexible shaft part is provided between the guide tube and the heat engine in order to allow

  rotary movements between the guide tube and the motor.

  The flexible shaft part consists of a flexible protective tube in which is held a transmission shaft made of a wound wire shaft for example. The winding direction is prefixed by the direction of rotation of the shaft. This type of shaft has the effect that the grease introduced under pressure between it and the flexible protection tube is transported in the

  direction of the length of the shaft towards the tube-

  rigid guide. A large accumulation of grease can therefore occur at the level of the bearing provided in

  the connection area of the rigid guide tube, which can damage this bearing.

  The object of the invention is to provide provisions, on manually guided working instruments of the generic type indicated at the start, for lubricating the drive shaft in the protection tube, provisions which must guarantee sufficient lubrication for a long period of time. on duty. According to the invention, this is obtained by the fact that a helical-shaped transport groove, surrounding the axis of the protective tube or guide tube, is formed in the region of the outer lateral surface of the shaft. transmission and the coaxial bearing surface directed towards it of the plain bearing, helical groove which rises in direction

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  opposite to the direction of rotation of the shaft and extends over

  at least part of the length of this tree.

  By the transport groove, rising in the opposite direction to the prefixed direction of rotation of the drive shaft, lubricant is transported from one end, located lower, for example, against gravity, up to the another end, located higher for example, which guarantees the lubrication of the shaft in the plain bearing over essentially the entire axial length thereof. Whatever the reasons for which the grease flows towards one end of the drive shaft, the transport groove according to the invention in return transports a quantity of grease which is at least sufficient for the

lubrication.

  For this purpose, the helical transport groove should extend over the entire length of the guide tube into the bearing surface of the plain bearing or

  in the lateral surface facing it from the tree.

  It may be advantageous to make the helical groove open at its ends, in which case the groove therefore opens freely at the ends.

  bearing tube and shaft.

  In order to ensure sufficiently intense reverse transport of the lubricant, the helical groove has a helix angle of at least 5, preferably 250. It may be advisable to provide a single helical groove with a steep slope or else several helices mutually nested, advantageously having a lower slope, for example under

the shape of a double helix.

  Other characteristics and advantages of the invention will emerge more clearly from the

  description which follows of non-exemplary embodiments

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  limiting, as well as the accompanying drawings, in which: - Figure 1 is a schematic representation of a working instrument carried by an operator and guided manually by him; - Figure 2 is a schematic axial section of the guide tube of the apparatus according to Figure 1; - Figure 3 is a schematic perspective view of a bearing tube disposed in the guide tube according to Figure 2; - Figure 4 is an axial section of the bearing tube according to Figure 3; - Figure 5 is a schematic perspective view of a drive shaft provided between the drive motor and the cutting tool of an instrument according to the invention; and FIG. 6 is a side view of the drive shaft according to FIG. 5 and of part of the

  bearing tube, shown in section.

  The working instrument shown as

  example is a brushcutter comprising a tube-

  guide or handle 1 which can be straight or curved and has at a first end 5 a drive motor 6 and, at a second end 4, a cutting head 2 provided with a cutting tool in the form of a wire section 9 which is oriented radially under the effect of centrifugal force during operation. In the region of the first end 5, a strap 12 is fixed with the aid of which the device can be carried by an operator 11. Between the first and the second end 4, a handlebar 14 is fixed on the handle 1 for hold and guide the device. This handlebar has two handles including the one on the right,

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  designated 14a, is produced as a rotary handle connected by a flexible gas control cable to the drive motor 6, constituted by a heat engine. It can be a two-stroke engine, a four-stroke engine or a combination of these two

types of motors.

  As can be seen in FIG. 2, the guide tube 1 forms a protective tube for the transmission shaft 3, rotating in a smooth bearing 7. The latter is formed by a bearing tube which advantageously extends over the entire length of the guide tube 1 and is fixed - as shown in FIG. 3 - roughly centrally in the protective tube by means of radial ribs 17, which in particular also provides in the curved part of the protective tube a good rotary assembly of the shaft 3. In the region of the first end 5, the shaft 3 is fitted together in rotation by a coupling part 10 in a complementary receiving part 30 of a bell clutch 31, inside which act clutch elements driven in rotation by the heat engine 6. In the region of the other end 4 of the guide tube 1, the shaft 3 is secured in rotation with the head cutting 2, so that this head is rotated when when the clutch housing 31 turns and the cutting line 9, intended as a working tool, is oriented radially under

the effect of centrifugal force.

  The bell 31 is conveniently part of a centrifugal clutch of the drive motor 6, so that this clutch only engages from a determined speed of rotation of the motor

  thermal to rotate the cutting head 2.

  FIG. 1 represents the operating position generally provided for the

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  brush cutter 13. In this position, the end 4 is located lower than the other end 5, which amounts to saying that the motor 6 is generally placed higher than the cutting head 2. If the appliance is used as pruner for cutting branches high, the cutting head is usually located higher than the engine. In the case of a brushcutter that can be carried on the back, a flexible shaft is provided between a rigid guide tube and the motor carried on the back, a flexible shaft which allows relative movement between the motor and the guide tube. This flexible shaft consists of a flexible transmission shaft rotating in a flexible protective tube forming at the same

time the tube-bearing.

  To lubricate the shaft 3 in the plain bearing 7 formed by the bearing tube, grease is provided in the clearance 20 between their respective sliding surfaces in mutual contact. As the grease is heated by external heat or by the relative movement between the external lateral surface 33 of the shaft 3 and the internal lateral surface 27, coaxial with it, of the plain bearing 7, it tends, in the operating position usual illustrated in Figure 1, to flow by gravity towards the lower end 4. An accumulation of grease 16 is thereby formed at the lower end 4 of the

guide tube 1.

  The invention provides a groove 41 for return transport of grease, acting in the opposite direction to the direction of gravity flow of the grease between the bearing tube 7 and the shaft 3, which rises helically in the opposite direction to the direction of prefixed rotation 22 of the shaft 3 from the end 4, located lower, towards the other end 5 of the guide tube, located

upper.

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  As shown in Figures 3 and 4, the groove 41 for return transport of grease can be formed in the bearing tube 7 constituting the plain bearing for the shaft. As can be seen in the sectional representation according to Figure 4, the groove 41 - having a helical shape extending around the axis 21 of the guide tube 1 - rises evenly at a helix angle 42 , which is for example 5 and preferably 25 or more. FIG. 4 therefore schematically shows that a transport groove 41 is thus formed in the region of the sliding surfaces in mutual contact (bearing surface 27 and lateral surface 33), groove having in cross section a shape in part of a circle, in particularly in a circle segment and by which a grease transport effect is obtained directed in the opposite direction to the direction of flow by gravity. This guarantees that the bearing system between the drive shaft and the bearing tube does not turn dry after a certain number of hours of operation; Lubrication intervals that may be necessary can be extended. It is appropriate that the helical groove 41 extends over the entire length of the bearing tube 7 and the guide tube 1, so that a return of grease to the end 5 and consequently lubrication of the tree

  3 over its entire length are insured.

  In order to promote the return transport of the lubricant 16 which has been deposited for example in the area of the end 4, it is provided that the shaft 3 protrudes by its end 40 from the bearing tube 7 in the area of the accumulation of grease, which promotes the entry of lubricant into the groove 41, open at its end. In the prefixed operating position of the device as a brush cutter,

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  the end 40 of the shaft is therefore placed lower than the other end 50, towards which the groove 41 rises from the end 40, see in particular the figures

1 and 2.

  In the embodiment according to the figure, the transport groove 41 is formed not in the bearing surface 27 - preferably over the entire axial length of this surface - of the tube 7 forming a smooth bearing, but in the outer lateral surface 33 of the shaft 3. Again, the groove preferably extends over the entire axial length of this surface, but at least in the region of the bearing tube 7. The embodiment of the grease transport groove 41 is the same as that provided for the groove in the bearing tube 7 of the previous example. The lower end 40 of the shaft 3 protrudes again from the accumulation of lubricant 16 in the region of the lower end 4 of the guide tube 1, which promotes the entry of lubricant into the groove 41 and its transport back towards the upper end 5 of the guide tube 1 and the end

  upper 50 of the drive shaft 3.

  It may be advisable to provide only one helical groove 41, but it is advantageous to provide an additional helical groove 44, offset by 180 in the direction of rotation relative to the first, as indicated in broken lines on the

  figure 6. Such a double propeller allows to obtain -

  even if the helix angle is small - good transport

  and a high flow rate of lubricant returned.

  It is advantageous that the bearing tube 7 is made of plastic, in which case the helical groove 41 may already be formed in this tube during manufacture. If a flexible wire shaft 3 for springs or the like is provided, it is

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  preferably that the groove 41 for the return transport of the grease is formed in the bearing surface 27 of the bearing tube 7. It may be advantageous to

  make the shaft 3 also made of plastic.

Claims (11)

  1. Manually guided working instrument, in particular a brush cutter, comprising a protective tube receiving a transmission shaft (3) which is moved at a first end (5) by a drive motor (6) and connected at a second end (4) to a working tool (9), the drive shaft (3) rotating in a direction of rotation (22) prefixed in a plain bearing of the protective tube (1), characterized in that a groove of transport (41) of helical shape, surrounding the axis (21) of the protective tube or guide tube (1), is formed in the region of the outer lateral surface (33) of the drive shaft (3) and of the coaxial bearing surface (27) directed towards it, of the plain bearing (7), helical groove which rises in the opposite direction to the direction of rotation (22) of the shaft (3) and extends over a   at least part of the length of this tree.   2. Working instrument according to claim 1, characterized in that the transport groove (41) is formed in the bearing surface (27) of the plain bearing (7) and preferably extends over   the entire axial length of this surface.   3. Working instrument according to claim 1 or 2, characterized in that the transport groove (41) is formed in the outer lateral surface (33) of the drive shaft (3) and preferably extends over any the axial length of this surface.   4. Working instrument according to one of   Claims 1 to 3, characterized in that the groove   transport (41) is open at its ends.   5. Working instrument according to one of the   Claims 1 to 4, characterized in that the groove   transport (41) has a helix angle (42),   measured relative to the axis (21) of the protective tube (1), of about 5, preferably 25 or more.   6. Working instrument according to one of   Claims 1 to 5, characterized in that, in a prefixed operating position of the instrument,   one end (40) of the drive shaft (3) is located lower than the other end (50) and that the transport groove (41) rises from the end 10 (40) located lower towards the end (50) located higher. 7. Working instrument according to one of   Claims 1 to 6, characterized in that the groove   transport (41) is formed of a single propeller.   8. Working instrument according to one of   Claims 1 to 6, characterized in that the groove   transport (41) is formed by several propellers, in particular of a double propeller.   9. Working instrument according to one of the   Claims 1 to 8, characterized in that the tube   protection (1) is made of plastic.   10. Working instrument according to one of   Claims 1 to 9, characterized in that the groove   transport (41) has in cross section a shape of part of a circle, in particular in a segment of a circle. 11. Working instrument according to one of   Claims 1 to 10, characterized in that the bearing   smooth is a bearing tube (7) arranged inside the protective tube (1).