GB2335625A

GB2335625A - Chain saw with brake/clutch assembly

Info

Publication number: GB2335625A
Application number: GB9906033A
Authority: GB
Inventors: Egbert Steinbrueck; Juergen Dolata; Heiko Below
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1998-03-24
Filing date: 1999-03-16
Publication date: 1999-09-29
Anticipated expiration: 2019-03-16
Also published as: GB9906033D0; IT1311740B1; ITMI990527A1; GB2335625B; DE19812860A1; FR2776559A1

Abstract

In order to achieve low-noise transmission, vibration damping and a lubrication-free transmission unit in a chain saw, in particular an electric chain saw, with a saw chain, which is driven by a sprocket wheel (26), a motor driving the sprocket wheel (26), a transmission unit comprising a separating clutch (34) and disposed between the driven shaft of the motor and the sprocket wheel, and with a chain brake (50), which can be activated upon disengagement of the separating clutch (34), the transmission unit is formed as a belt transmission (25), the belt wheel (30) of which is disposed coaxially with the sprocket wheel (26), and the separating clutch (34) is disposed between the belt wheel (30) and the sprocket wheel (26), so that impact loading when the chain saw is turned off, which is harmful to the belt transmission (25), is prevented and at the same time only a small braking moment is required to brake the sprocket wheel (26).

Description

2335625 1 Chain s The invention is based on a chain saw, in particular an

electric chain 5 saw, of the type defined in the preamble of claim 1.

In a known chain saw of this kind (EP 0 743 147 AI) the transmission unit disposed between the driven shaft of the electric motor and the sprocket wheel driving the saw chain is a bevel gear with a bevel gear pinion nonrotatably seated on the driven shaft and a ring gear meshing with the latter and non-rotatabIy seated on a sprocket wheel shaft. The sprocket wheel is non-rotatably connected to a clutch member of the separating clutch, which is disposed coaxially with the sprocket wheel shaft, and is seated on the sprocket wheel shaft in a rotatable, axially stationary manner. The other clutch member is connected in a non-rotatable, yet axially displaceable manner to the sprocket wheel shaft and can be axially displaced by means of the disengaging device for disengaging the clutch. The two clutch members are maintained 'm engagement with one another by means of a clutch spring formed as a compression spring. The chain brake comprises a brake drum which is firmly connected to the sprocket wheel and around which a brake band winds. The brake band can be tensioned by means of a hand guard which is pivotably disposed at the machine housing, so that depending on the pivot position of the hand guard, it securely brakes the brake drum or releases the latter, whereby the brake drurn can turn away unimpeded below the brake band. The chain brake also comprises a brake shoe which lies inside the brake drum and which is applied to the inner wall of the brake drum when the separating clutch is disengaged by the disengaging device. The disengaging device comprises an electromagnet which disengages the separating clutch when the electric motor is turned off and at the same time applies the brake shoe to the brake drum, so that the sprocket wheel is braked.

2 The chain saw according to the invention with the features of claim 1 combines the advantages of a belt drive with those of a clutch, without having to tolerate the respective disadvantages at the same time. The belt drive has the advantages of low-noise transmission, absence of lubrication and vibration damping. The clutch escapes the disadvantages of the belt drive, i.e the impact loads, which are harmful to it when the chain saw is turned off and the saw chain securely braked. The belt is relieved through the separating clutch opening when the chain brake responds, so that the inertial moment of the motor no longer acts on the sprocket wheel shaft and the belt wheel can rotate freely. The braking moment required to brake the sprocket wheel is at the same time substantially smaller, as the inertial mass of the motor does not have to be braked and the braking moment is not applied via the belt drive. The clutch can simultaneously be used as a safeguard against overload.

Advantageous developments of and improvements to the chain saw presented in claim 1 are possible through the measures specified in the additional claims.

According to a preferred embodiment of the invention the sprocket wheel is non-rotatably connected to a rotatably mounted sprocket wheel shaft, and the belt wheel is seated loosely on the sprocket wheel shaft. One clutch member of the separating clutch is formed at the belt wheel and the other clutch member is held in a non-rotatable and axially displaceable manner on the sprocket wheel shaft. The clutch members are maintained in engagement with one another by a clutch spring which is axially supported on the sprocket wheel shaft. These measures enable the belt drive and clutch to be produced inexpensively.

According to an advantageous embodiment of the invention the clutch 2.5 member which is engaged with the sprocket wheel shaft comprises a clutch plate and a coaxial hub which is integral with the latter, is nonrotatably seated on the sprocket wheel shaft and is axially displaceable. The chain brake comprises a brake disc, which is seated loosely on the hub and pressed against the clutch plate by means of 3 a pressure spring, and a stationary stop, which is disposed such that the brake disc strikes against this in the rotational direction and is retained when the clutch member is displaced axially on the sprocket wheel shaft to disengage the separating clutch. The saw chain is braked extremely quickly by the braking power occurring between the brake disc and the clutch member. These construction measures result in an inexpensive, producible braking mechanism. The brake disc may alternatively be integrally formed with the displaceable clutch member. In this case the saw chain is brought to an abrupt standstill when the chain brake responds. This alternative construction produces a chain brake which has advantages in terms of cost and which is highly suitable for braking just small inertial moments.

The invention is illustrated in detail in the following description on the basis of an embodiment represented in the drawings, in which:

Figure 1 is a diagrammatic side view of a chain saw with individual components provided within the scope of the invention; Figure 2 is a diagrammatic section along the line II-El in Figure 1; Figure 3 is a diagrammatic view from below of a brake disc in Figure 2.

The chain saw represented in Figure 1 just in basic form and just with the components which are of interest within the scope of the invention comprises a housing 10, at the rear end of which a first handle 11 is formed and on the front end face of which support teeth 12 are formed to apply the chain saw to the workpiece which is to be sawn. A second handle 13 is disposed near the end face of the housing 10 on the top side thereof and extends like a bow transversely to the longitudinal axis of the housing 10, i.e. in the direction of the depth of the drawing page in Figure 1.

A hand guard 14 is mounted in front of the second handle 13 and can be pivoted about a pivot point 60 fixed in the machine housing 10 into two pivot positions, in one pivot position of which the saw chain, which is not shown here and is guided on a so-called sword, is securely braked by means of a chain brake 50, to be fflustrated 4 in detail in the following, and in the other pivot position of which the saw chain is released. The saw chain is released when the hand guard 14 is in the position represented in the drawing. The saw chain is securely braked by pivoting the hand guard 14 in the direction of the arrow 15 in Figure 1. The chain brake 50 (Figure 2) actuated by the hand guard 14 serves to prevent the operator being injured by the saw chain due to a sudden rebound, so-called kick back, of the chain saw when in operation. If such a rebound occurs, the hand guard 14 strikes against the operator's hand, which clasps the second handle 13, so as to pivot into the other pivot position and actuate the chain brake 50. A switching key 17 for operating an on-off switch 18 projects from the underside, over which a guard bow 16 extends at a spacing, of the first handle 11. The electrical on-off switch 18 is disposed in the circuit of an electric motor, which is not shown here, for driving the saw chain, the on-off switch 18 being tumed on by pressing the switching key 17 into the handle 11 and turned off by releasing the switching key 17. Once the switching key 17 has been released, it is is pivoted out again by a compression spring 19.

The on-off switch 18 is operated by means of a switching or traction member 20, which moves with a wedge face 201 over a ram 21 bearing electrical switching contacts and in the process displaces this axially such that the switching contacts close the circuit. The traction member 20 is held on one side by a tension spring in its normal position, in which the on-off switch 18 is open, and displaced against the force of the tension spring 22 by a traction means, here formed as a traction band 23, installed in the housing 10. The switching key 17 is provided with an extension 24, which lies transversely against the traction band 23 when the switching key 17 is in the off position. When the switching key 17 is pivoted, the extension 24 forms a loop in the traction band 23, whereby the traction band 23 is shortened, and thereby exerts a tractive force on the traction member 20 for switching the on-off switch 18. For safety reasons a two-hand switching arrangement may be provided to turn on the electric motor, for which purpose an identical switching key 17 with an extension 24' is disposed in the second handle 13. When the switching key 17 is operated, the extension 24' similarly deflects the traction band 23 while forming a loop transversely to the direction in which it extends. The taut length of the traction band 23 and the displacement paths of the extensions 24, 24' are then adapted to one another such that the traction member 20 can only move over the entire displacement path to close the on-olf switch 18 by twice forming a loop in the traction band 23.

The electric motor, which is not shown, drives via a belt transmission or a belt drive 25, which is preferably formed as a toothed belt drive, a sprocket wheel 26 (Figure 2), which in turn drives the saw chain guided in rotation on a so called saw sword. Ile sprocket wheel 26 is non-rotatably seated on a sprocket wheel shaft 27 mounted in the housing 10. Here the number 28 represents a ball bearing and the number 29 a sliding contact bearing for the sprocket wheel shaft 27. The belt drive 25 comprises a belt wheel 30, which is loosely seated on the sprocket wheel shaft 27, a belt pulley 31 of smaller diameter and a toothed belt 32 which is guided over the circumference of the belt wheel 30 and the belt pulley 3 1. The belt pulley 31 is non-rotatably seated on a driven shaft 33 which, depending on the installed position of the electric motor, may directly be the motor shaft or the output shaft of a bevel gear.

A separating clutch 34 is coaxially seated on the sprocket wheel shaft 27 and connects the belt wheel 30 to the sprocket wheel shaft 27 in a nonrotatable manner in the engaged state, so that the sprocket wheel 26 is driven via the belt drive when the electric motor is running. Of the two clutch members 341, 342 which are non-rotatably engaged with one another, one clutch member 341 is integrally formed with the belt wheel 30, while the other clutch member 342 is held in a non rotatable and axially displaceable manner on the sprocket wheel shaft 27. The two clutch members 341, 342 are maintained in engagement with one another by a clutch spring 35 which is axially supported on the sprocket wheel shaft 27. In detail, the 6 clutch member 342 disposed on the sprocket wheel shaft 27 comprises a clutch plate 36 and a coaxial hub 37, which is integral with the latter and can be displaced Mi diametrical axial grooves 271 in the sprocket wheel shaft 27. The sprocket wheel shaft 27 may alternatively also have a flattened drive face (symbolised as a cross in broken lines in Figure 2), which co-operates in a positive engagement with a correspondingly formed inner face of the hub 37. The clutch spring 35 is supported on one side at the hub 37 and at the other at an abutment 38, which is fixed on the sprocket wheel shaft 27 so that it cannot be displaced axially. The clutch plate 36 bears axially projecting clutch dogs on the end face which is distant from the hub 37, which dogs co-operate with like, projecting clutch dogs formed at the end face of the belt wheel 30 for rotational drive, the clutch dogs either interlocking or lying against one another in the rotational direction. If the clutch dogs are appropriately beveHedL the clutch can be used as a torque or an overload clutch, in which the bevel of the clutch dogs and the clamping force of the clutch spring 3 5 are adapted to one another such that the clutch dogs turn relative to one another against the force of the clutch spring 35 at a predetermined torque. A clutch of this kind is also called an overload clutch.

A disengaging device 40 (Figure 1), which comprises a slide 39 acting on the clutch member 342, is provided to disengage the separating clutch 34. A displacement of the slide 39 in the direction of the arrow 41 in Figure 1 causes a displacement of the clutch member 342 against the force of the clutch spring 35, so that the clutch dogs of the clutch members 341, 342 are disengaged. The belt wheel is thereby uncoupled from the sprocket wheel shaft 27 and the sprocket wheel 26 and can rotate freely on the sprocket wheel shaft 27 when the electric motor is running. The slide 39 may be replaced by a lever which is operated in the same way by the disengaging device 40.

The disengaging device 40 is coupled to the hand guard 14 such that, when the hand guard 14 is in the pivot position represented in Figure 1, in which the 7 saw chain is free-g, the disengaging device 40 is inoperative and the separating clutch 34 therefore engaged, and upon pivoting the hand guard 14 in the direction of the arrow 15 the slide 39 of the disengaging device 40 is displaced in the direction of the arrow 41, so that the separating clutch 34 disengages. For this purpose the disengaging device 40 comprises a toggle which is loaded by a compression spring 42 and is formed by a lever 43 1 and the hand guard 14. The toggle joint 44 is fixed on a pin 61 which projects from the hand guard 14 parallel to the pivot axis 60 of the latter and which is guided in an oblong hole 62 formed in the machine housing 10. The lever 43 1 is pivotably mounted at a spacing from the toggle joint 44 at the hinge point 46 on a lever 432, which is fixed at the end to the slide 39 at the hinge point 45.

The end of the traction band 23 which is distant from the traction member 20 is fixed at the hinge point 46, this end having been guided beforehand over a deflection pulley 47 fixed to the housing. If the hand guard 14 is pivoted in the direction of the arrow 15, the toggle joint 44 will pivot in the direction of the arrow 48 until it is stopped at the other end of the oblong hole 62, resulting on the one hand in the slide 39 being displaced in the direction of the arrow 41 and on the other in the hinge point 46 being moved in a way which causes a slack in the traction band 20 such that in spite of the fact that the switching keys 17, 17 are pressed in, the tension spring 22 acting on the traction member 20 pulls the traction member 20 away from the ram 21 and the on- off switch 18 is thus opened.

As initially mentioned, the saw chami is securely braked when the hand guard 14 is pivoted in the direction of the arrow 15, the separating clutch 34 being simultaneously disengaged via the slide 39 of the disengaging device 40, so that the belt drive 25 is uncoupled from the sprocket wheel 26 and the sprocket wheel 26 is braked by means of the chain brake 50.

The chain brake 50 represented in section in Figure 2 has a brake disc 51 (Figure 3), which co-operates with a stop 55. The stop 55 may be fixed in the housing 10 or on the slide 3 9. The brake disc 5 1 is loosely seated on the hub 3 7 of 8 the clutch member 342 and is pressed by means of a Belleville spring assembly 52 against the rear side, which is distant from the clutch dogs, of the clutch plate 36. The Belleville spring assembly 52 is supported at a disc 53, which is fixed on the hub 37 by means of a retaining ring 34. The brake disc 51 shown from below in Figure 3 has two radially projecting lugs 5 11. During operation of the chain saw the brake disc 5 1 rotates with the clutch member 342, and in this case can rotate freely. If the hand guard 14 is actuated and therefore pivots in the direction of the arrow 15 in Figure 1 by means of the sequence described above, the slide 3 9 with its lifting ramps 3 91 travels under the brake disc 51 projecting beyond the clutch plate 36, lifts the brake disc 51 and at the same time displaces the clutch member 342 displaced against the force of the clutch spring 35. The separating clutch 34 disengages, and the brake disc 5 1 moves with its lugs 5 11 into the region of the stationary stop 5 5. One of the lugs 5 11 of the brake disc 5 1 strikes against the stop 5 5. The brake disc 5 1 is retained and slips with respect to the clutch plate 36, and a braking moment which depends on the spring force of the Belleville spring assembly 52, is produced between the brake disc 51 and the clutch plate 36. The sprocket wheel 26, which is non-rotatably connected to the clutch plate 36 via the sprocket wheel shaft 27, is therefore braked very quickly and the saw chain brought to a standstill in a short space of time.

The Belleville: spring assembly 52 is only required to brake high inertial 20 moments and thus damp the striking action of the lugs 511. The braking time can be shortened by increasing the preloading of the Belleville spring assembly 52 or lengthened by reducing the preloading. The preloading force of the Belleville spring assembly 52 is easily changed by adding or removing one or more Belleville spring(s). The brake disc 51 and the clutch plate 36 can be rigidly connected together or produced integrally with one another to brake small inertial moments. In this case it is possible to dispense with the Befleville spring assembly 52, the disc 53 for supporting the Belleville spring assembly 52 and the retaining ring 54 for fixing the 9 disc 53 on the hub 37. The saw chain is brought abruptly to a standstill by actuating the disengaging device 40.

A conventional chain brake with a brake drum and a brake band, as described in the known publication cited at the outset may also be used instead of 5 the chain brake 50 represented in Figure 2.

The disengaging device 40 may also be connected to an electromagnet instead of to the hand guard 14, this magnet being energised when the onoll switch 18 is turned off and operating the slide 39 or lever of the disengaging device 40 as described to disengage the separating clutch 34 and activate the chain brake 50.

Claims

1. Chain saw, in particular an electric chain saw, with a saw chain, which is driven by a sprocket wheel (26), with a motor driving the sprocket wheel (26), in particular an electric motor, with a transmission unit which is disposed between the driven shaft of the motor and the sprocket wheel (26) and in which a separating clutch (34) is disposed, with a disengaging device (40) for the separating clutch (34) and with a chain brake (50), which can be activated upon disengagement of the separating clutch (34), characterised in that the transmission unit is formed as a belt transmission (25), preferably a toothed belt transmission, which comprises a belt wheel (30) coaxial with the sprocket wheel (26), and that the separating clutch (34) is operative between the belt wheel (30) and the sprocket wheel (26)..

2. Chain saw according to claim 1, characterised in that the sprocket wheel (26) is non-rotatably connected to a rotatably mounted sprocket wheel shaft (27), that the belt wheel (30) is seated loosely on the sprocket wheel shaft (27), and that one clutch member (34 1) of the separating clutch (34) is formed at the belt wheel (30), the other clutch member (342) is held in a non-rotatable and axially displaceable manner on the sprocket wheel shaft (27), and the clutch members (341, 342) are maintained in engagement with one another by a clutch spring (35) which is axially supported on the sprocket wheel shaft (27).

9 3. Chain saw according to claim 1 or 2, characterised in that the clutch member (342) which is seated on the sprocket wheel shaft (27) comprises a clutch plate (36) and a coaxial hub (37) which is integral with the latter and is axially displaceable on the sprocket wheel shaft (27).

11 4. Chain saw according to claim 3, characterised in that the clutch members (341, 342) comprise clutch dogs which interlock or lie against one another in the rotational direction and which are in each case moulded integrally onto the end face of the belt wheel (30) and onto the plate face of the clutch plate (36).

5. Chain saw according to one of claims 1 - 4, characterised in that the separating clutch (34) is formed as an overload clutch.

6. Chain saw according to one of claims 1 - 5, characterised in that the 10 disengaging device (40) comprises a slide (39) or lever which acts on the clutch member (342) disposed in a displaceable manner on the sprocket wheel shaft (27) in order to displace this member axially on the sprocket wheel shaft (27).

7. Chain saw according to one of claims 3 - 6, characterised in that the is chain brake (50) comprises a brake disc (5 1), which is seated loosely on the hub (3 7) of the clutch member (342) and pressed against the clutch plate (36) by means of a pressure spring (52) or is integrally formed with the clutch member (342), and a stationary stop (55), which is disposed such that the brake disc (5 1) strikes against this in the rotational direction when the clutch member (342) is displaced axially to 2 0 disengage the separating clutch (34).

8. Chain saw according to claim 7, characterised in that the pressure spring is formed as a Befieville spring assembly (52) which is seated on the hub (37) and is supported between the clutch plate (36) and an abutment (disc 53, retaining 25 ring 54) disposed in an axially stationary manner on the hub (37).

9. Chain saw according to one of claims 6 - 8, characterised in that the slide (39) or lever of the disengaging device (40) is coupled to a hand guard (14), 12 which is disposed on the housing (10) and can be pivoted into two end positions, such that the separating clutch (34) is engaged in one end position of the hand guard (14) and disengaged in the other end position of the hand guard (14).

10. Chain saw according to one of claims 6 - 8, characterised in that the slide (39) or lever of the disengaging device (40) is coupled to the armature of an electromagnet such that the separating clutch (34) is engaged upon the magnet being energised and disengaged upon the magnet being de-energised.

11.

A chain saw substantially as herein described with reference to the accompanying drawings.