EP0067485B1

EP0067485B1 - Sawing device

Info

Publication number: EP0067485B1
Application number: EP82200709A
Authority: EP
Inventors: Jan Wilhelmus Leemans; Jan Peter Houben
Original assignee: Skil Nederland BV
Current assignee: Skil Nederland BV
Priority date: 1981-06-11
Filing date: 1982-06-09
Publication date: 1987-05-06
Also published as: NO152537C; NO821914L; EP0067485A2; NL8102814A; EP0067485A3; DE3276228D1; NO152537B

Description

The invention relates to a sawing device mainly comprising a housing with handles, a motor accommodated in said housing and driving through a transmission with a starting clutch, a sprocket for a sawing chain passed around a guide and comprising a mechanism for putting said drive out of operation, said mechanism having a member for actuating a second clutch arranged between the motor and said starting clutch of the transmission provided with a cam surface for the axial movement of one part of the second clutch, and being retained against a biasing spring force by means of a releasable safety pawl in a position in which the second clutch is in engagement, said pawl being controlled by a mass of inertia, formed by a manually operable lever rotatably arranged around an axis transverse of the sawing chain blade.
A sawing device as set forth in the preamble is known from US-A-3.839.795. The releasable safety pawl in the sawing device is controlled by the handle having its pivot located such that the length of the handle is relatively short. However in case of emergency, for instance when the chain saw "bites" it is necessary that the safety clutch will be activated without manual operation. Therefore one needs a certain mass of the handle giving enough moment of inertia to control a safety pawl. A short length asks for a relatively high weight of the mass, contributing to the total weight of the sawing device. This is disadvantage for the maniability of said device.
The invention has for its object to overcome above mentioned disadvantage and to provide a device having a mechanism such that upon actuation thereof the chain stops substantially without delay without the need for the motor to held.
This device is distinguished in that the lever is rotatable around an axis underneath the sawing chain blade, said lever being coupled to said pawl through a lost-motion member and that the plate member is pivotable about an axis parallel to the driving shaft and is provided with a relief rim for the axial movement of one part of the clutch.
Thanks to the pawl and lost-motion mechanism the control-member can be displaced by the bias force immediately after the pawl is released, said control-member putting the clutch out of operation. Thus the drive between motor and sprocket is interrupted.
In a preferred embodiment the device is distinguished in that the control plate member, the pawl and the biasing spring are accommodated in a closed housing part, which is releasably connected with the housing part comprising the motor and the drive.
This structure ensured an easily removable sub-housing, so exposing the change sprocket for easily mounting a new chain. Further the safety mechanism remains free of dust and dirt, for example carried along by the sawdust.
The invention will be described more fully with reference to the embodiment shown in the Figures.
The drawing shows in

Fig. 1 a perspective view of the sawing device,
Fig. 2 a side elevation of the control-member used in the sawing device of Fig. 1,
Fig. 3 a sectional view taken on the line III-III in Fig. 2.

The sawing device shown in Fig. 1 mainly comprises a housing 1 with two handles 2, 3, said housing accommodating a motor, for example, an electric motor and a drive for a sawing chain 5 passed around a master blade 4.
Figs. 2 and 3 show more in detail the drive which comprises a gear wheel transmission 6 rotating a main driving shaft 7. At the end remote from the pinion 6 the driving shaft 7 is provided with a claw clutch 8, the outer part 8' of which is non-rotatably, but slidably arranged on said end of the shaft. The inner part 8" is rotatably journalled on the shaft 7 and constitutes the core of a centrifugal clutch 9, which is coaxial with the driving shaft 7. The housing 10 of the centrifugal clutch is connected with a sprocket 11. The centrifugal clutch comprises centrifugal shoes 12, which come into contact upon rotation of the inner part 8" with the housing 10.
The part 8' of the claw clutch can be displaced by a control-member formed by a plate 13 (see Fig. 2), which is pivotable about'a a shaft 14 and accommodated in a releasable housing part 15. The shaft 14 is parallel to the main driving shaft 7. The plate has a reniform opening 32, which is narrow at the top end and has a relief rim 16 gripping below the collar 17 of the part 8' of the claw clutch. The width of the opening 32 exceeds the diameter of the collar 17 of the part 8'.
The plate 13 is movable up and down in the housing part 15 around the spindle 14 by means of a handle 18 against the action of a bias force supplied by a tensile spring 19 stretched between a point 20 of the plate and a point of engagement 21 of the housing part 15.
On the right-hand side (see Fig. 2) below the housing part 15 holds a spindle 22 of square cross-section.'The spindle 22 is journalled at 23 in the housing part 24 of the housing 1 comprising the motor and the transmission gear. The spindle 23 is bent over upwards and terminates in a handle 25 located in front of and near the handle 2 of the sawing deviαe.
The end of the spindle 23 located in the housing part 15 extends into a sleeve 26, which is rotatably journalled in the housing part 15. The sleeve has a pawl 27, which can be bought into contact with a nose 28 of the control-plate 13.
The continuous hole in the sleeve 26 has a star-shaped cross-section such that a turn of the handle 25 in the direction of the arrow P1, that is to say, away from the handle 2 ensures a turn of the sleeve 26 and hence a turn of the pawl 27. In the reverse sense, however, a free stroke is ensured.
On the side facing the centrifugal clutch the control-plate 13 has a skid 29, which in the lowermost position of the plate 13 shown in Fig. 2 by broken lines comes into contact with the housing 10 of the centrifugal clutch which is linked to the sprocket 11.
The device operates as follows.
After the handle 18 is moves upwards, the plate 13 is turned upwards around the pin 14 so that the claw clutch parts 8' and 8" engage one another. Then the connection between the main driving shaft 7 and the central part of the centrifugal clutch is established. After the motor is started, for example, by means of the conventional switches near the handle 3, the centrifugal clutch will become operative as a result of the rotation and the sprocket will rotate so that the chain 5 is moved along the blade 4 in the direction of the arrow P2.
Switching off normally occurs by changing over the main switch near the handle 3 so that the motor stops and the centrifugal clutch gets out of operation at a given number of revolutions.
In the event of an emergency stop the user can move the handle 25 in the direction of the arrow P1 so that the pawl 27 turns in clockwise direction and the plate 13 is moved downwards by the tensile spring 19. This results in that the claw clutch parts 8' and 8" are drawn away from one another so that the link of the main driving shaft 7 to the centrifugal clutch is interrupted.
The skid 29 then comes into contact with the housing 10 of the centrifugal clutch so that the sprocket and hence the chain 5 are immediately halted. The motor can run on in an unaltered manner.
Even if the user does not touch the lever 25, the housing may be thrust upwards in the direction of the arrow P3 as the result of an abrupt shock, for example, due to "biting" of the saw at the tip, so that owing to inertia the handle 25 with the lever moves in the direction of the arrow P1 with respect to the housing 1. Then the mode of switching off is the same. As soon as the cause of the emergency stop is repaired, the user can again move the lever 18 upwards so that the claw clutch 8 becomes operative and the saw can again be used.
The maintenance of the whole device is facilitated by accommodating the entire safety mechanism comprising the plate 13, the pawl 27, the spring 19 in the separate housing part 15, which has a separating wall 30 on the inner side. The partition 30 is releasably fastened by bolts 31 in the housing part 15 and constitutes an effective screen between the sprocket 11 drawing in the sawdust and the compartment in the housing 15. The partition 30 has an opening which is sufficiently large for passing the housing 10 of the centrifugal clutch, and in the engaged state of the claw clutch 8 the width of the reniform opening 15 is such that the housing part 15 with the partition 30 can be removed so that the claw clutch, the centrifugal clutch and the sprocket are freely accessible.
The invention is not limited to the embodiment described above. For example, the inertia mass formed by a lever may have a different shape and it need not be manually operable. The star-shaped hole in the sleeve 26 may be square or have a different shape. The claw clutch may be a dry-plate coupling.

Claims

1. A sawing device mainly comprising a housing (1) with handles (2, 3), a motor accommodated in said housing and driving through a transmission with a starting clutch (9), a sprocket for a sawing chain (5) passed around sawing chain blade (4) and comprising a mechanism for putting said drive out of operation, said mechanism having a member (13) for actuating a second clutch (8) arranged between the motor and said starting clutch (9) of the transmission provided with a cam surface (16) for the axial movement of one part (8, 7) of the second clutch (8), and being retained against a biasing spring (19) force by means of a releasable safety pawl (27) in a position in which the second clutch is in engagement, said pawl (27) being controlled by a mass of inertia, formed by a manually operable lever (25) rotatably arranged around an axis (2) transverse of the sawing chain blade (4), characterized in that the lever (25) is rotatable around an axis (23) underneath the sawing chain blade (4), said lever (25) being coupled to said pawl (27) through a lost-motion member (26) and the plate member (13) is pivotable about an axis (14) parallel to the driving shaft (7) and is provided with a relief rim (16) for the axial movement of one part of the clutch (8).

2. A device as claimed in claim 1, characterized in that the control plate member (13) the pawl (27) and the biasing spring (19) are accommodated in a closed housing part (15, 30), which is releasably connected with the housing part (24) comprising the motor and the drive.