SE459240B - BRAKE SYSTEM FOR CHAIN SAW - Google Patents

Description

459 240 10 15 20 25 30 35 the two brake shoes in contact with the outside of the clutch housing. The yoke is connected with a push rod to a safety rod, which is attached to the front handle of the saw, and it is held by a spring in a position where the brake shoes do not rest. If the saw throws and the user's hand or arm strikes the safety bar, the brake shoes are pressed with wedge action against the clutch drum, whereby the chain stops.

This construction has several disadvantages, including that it can be difficult to get the brake shoes to release again once they are engaged, due to the fact that they are wedged. In addition, this braking system is quite heavy.

Another example of the use of brake shoes is in U.S. Patent No. 3,793,727, "Chain Saw Safety Method and Apparatus", by H. E. Moore.

Later constructions are based on flexible brake bands, for example U.S. Patent No. 3,776,331, "Brake-Device For Power Saws", by L. Gustafsson. In this construction, a flexible band lies loosely around the coupling drum with one end attached to the motor housing. The other end of the belt is attached to one end of a lever, the point of rotation of which lies in front of the front handle of the saw. A ratchet is rotatably attached to this lever and can hook into a pin attached to the motor housing.

A spring, which is located between the lever and the motor housing, biases the chin in the hooked position and at the same time pulls the lever towards the braking position. When the lever moves, the hook is released from the pin and the spring pulls the lever to the braking position. This construction is admittedly simpler than the one described before, but since the spring in the case of an unbraked chain must at the same time both lock the hook and pull the lever towards the braking position, it becomes difficult to determine the appropriate spring force. If the spring is too tightly tensioned, it becomes difficult to release the ratchet, and if it is too loosely tensioned, the flexible brake band may not provide sufficient braking force to stop the chain moving fast enough.

It is therefore desirable to allow the spring to bias the safety lever (sensing arm) to the unbraked condition only when the lever is in that position and to allow the spring to actuate the lever to its braking position only when it assumes this position. If this is the case, there is always a positive force that maintains the desired condition. This object has been achieved in a design presented in U.S. Patent No. 3,934,345, "Snap Acting Over Center Chain Saw Safety Brake And Method Of Operation Thereof", by S. Hirschkoff. This construction means that a safety handle is attached to the motor housing and in the activated position pulls a flexible brake band towards the outside of the clutch drum. One end of a guide rod is attached to the motor housing, so that the rod can both be rotated and displaced axially and its other end runs in a groove. The control rod is pressed by a spring against the safety handle. The relative position of the groove, the rod and the pivot point of the handle means that the force line of the spring goes below the pivot point of the handle at the unbraked state, and that the spring thereby tries to keep the handle in this state, while, when the handle is in the braking position, the spring line pivot point and the spring thus holds the handle in this position. Although this construction provides tipping lock function, it is heavy and quite expensive to manufacture.

All the constructions described above are based on the user's hand or arm activating the mechanism in case the saw throws. However, constructions have been made that are based on the system sensing the saw's angular acceleration during a throw and stopping the chain without the user having to actuate the safety handle manually. An example of this is found in U.S. Patent No. 3,923,126, "Band Type Brake In A Chain Saw", by E.J. Bidenset. In this construction there is an inertial sensor in the form of a guide rod and a first lever, which are connected to each other and which are hingedly attached to the motor housing. This first lever affects a second lever, which is also hingedly attached to the motor housing, and these two are pressed against each other by a spring. The other lever has an arm which ends against a brake band which is pulled by a spring towards its braking position. If a throw occurs, the inertia of the handlebar and the first lever cause them to release contact with the end of the brake band.

In another embodiment, the second lever is directly attached to one end of the brake band and the chain is braked as soon as the lever is rotated.

This is a complicated and expensive construction and it requires great care in assembly. Since the control rod must also function as a safety bar and be able to apply the brake when it comes into contact with the user's hand or arm, it becomes difficult to set the correct one due to the forces of inertia when throwing being considerably less than the force applied by the user. sensitivity, If you set high sensitivity, the result is that the saw is braked carefully as soon as you touch the handlebar.

Other engine saw brakes of interest are described in U.S. Patent Nos. 3,937,306; "Automatic Brake Actuator For A Chain Saw" Näslund et al; 3 964 333,, by Ulf Vilhelm "Safety Braking Mechanism For A Portable Chain Saw", by S. Hirschkoff; and 4,121,339, "Safety Brake Mechanism For Chain Saw", by M. Nikolich.

The main object of the present invention is therefore to provide a chain brake for chainsaws which is compact, light and reliable.

Another object of this invention is to make a chain brake for chainsaws, where the safety bar is pre-tensioned in either the unbraked position or the braking position.

Furthermore, the invention relates to a chain brake for chainsaws which provides full braking effect even in the event of a small change in position of the safety bar.

The invention further relates to a chain brake for chainsaws which can brake the saw chain both manually and automatically.

The present invention relates to a safety brake for chainsaws, the main purpose of which is to protect the user from injuries in connection with the saw throwing. Generally, a chainsaw consists of a motor housing with a grip handle; an engine mounted in the housing; a saw chain, a saw bar directed forward from the motor housing and along which the saw chain runs; and a rotary transmitting device for driving the saw chain. The safety brake device according to the present invention comprises a sensing arm or a sensing device which is rotatably attached to the motor housing. In one embodiment, the sensing arm has a projection in the form of a pin. A part of the sensing arm is located in front of the grip handle when the saw is in operation and is designed so that it tilts from a first position to a second when it receives a blow from the operator. A flexible brake band is located around the outside of the rotary transfer member or brake drum. One end of the brake band is attached to the motor housing and its other end is connected to the sensing arm, preferably by means of a pin, in such a way that when the sensing arm moves from position one to position two the flexible brake band is moved from a position where it is not in contact with the brake drum to a position where it brakes the drum. A locking device is hingedly mounted to the motor housing and designed to be able to hook onto the projection of the sensing arm. A biasing device (or a tension spring) is attached to the locking device with one end of it in such a way that the locking device resiliently holds the sensing arm in position one when the arm is in this position, and resiliently holds the arm in its position two, when it is in position in this mode.

Thus, when the saw user strikes the sensing arm in the manner typical of a throw of the saw, the sensing arm will move from position one to position two and thus stop the movement of the saw chain, before the chain has come into contact with the user.

In addition, it is possible in a second embodiment to include in the construction a sensing device which reacts to the acceleration which the saw receives during a throw. This acceleration sensor can suitably consist of a combed rod, which is mounted hingedly in the motor housing. In this embodiment, the above-mentioned locking device has been provided with a lever which can abut against the cam on the rod. When the saw throws, the saw will rotate relative to the rod, because the rod has inertia and strives to resist acceleration. The result is that the cam moves on the lever and that the sensing arm in turn moves from position one to position two and stops the chain.

A third embodiment instead comprises a first pin mounted on the locking device and a second projection on the sensing arm. This committee has a U-shaped recess that fits this first pin. The second end of the flexible brake band is normally in this third embodiment attached to a second pin which is also located on the locking device.

A fourth embodiment of the present invention comprises the acceleration sensing mechanism described above together with the locking mechanism in the third embodiment.

Fig. 1 is a side view of a part of a chainsaw according to the present invention; Fig. 2 is a front view of the saw of Fig. 1; Fig. 3 is a side view of a safety braking system forming part of the chainsaw, where the system is in the non-braking condition; Fig. 4 is a front view of the safety brake system, taken along line 4-4 of Fig. 1; Fig. 5 is a view of the same kind as Fig. 3, showing the safety brake system in its braking condition; Fig. 6 is a view of the same kind as Fig. 3, showing a second embodiment of the safety braking system in both its braking and non-braking condition; Fig. 7 is a side view of a chainsaw, showing a third embodiment of the present invention; Fig. 8 is a side view of the safety brake system of Fig. 7 shown in its braking condition; and Fig. 9 is a side view of the safety brake system of Fig. 7, showing a fourth embodiment of the present invention in both braking and non-braking conditions.

Fig. 1 is an external side view of a portable chainsaw, while Fig. 2 is a front view of the same saw. The saw 10 comprises a housing 12 with an internal combustion engine or other engine (not shown in the figure) mounted in a conventional manner. On the rear part of the housing 12 is a control handle 14 and near the front of the housing is a grip handle 16. The grip handle consists of an upper part 18 and side parts 20 and 22.

A saw bar or chain support 24 protrudes from the housing 12 and carries a saw chain 26 which moves in a closed path around the same. The saw chain is propelled by the internal combustion engine via a suitable power or rotation transmitting device. The power transmission device is not in itself a part of the present invention, so any conventional power transmission device may be used, for example according to U.S. Patent No. 2,947,399, "Centrifugally Activated Friction Clutch", by HE Moore or according to U.S. Patent No. 3,385,411 , "Centrifugal Clutch Accuator And Spring Retainer", by RL Collins.

The power transmission usually includes a chain drive driven by the motor shaft, around which the saw chain 26 runs. As the sprocket rotates, the saw chain is driven to run along the saw blade 24 and back around the sprocket in a closed loop.

When the saw 10 is used, the user holds with one hand the operating handle 14 and with the other the gripping handle 16. The gripping handle 16 is used primarily to handle and exert force on the saw, while the operating handle 14 is used to stabilize the saw and control the speed of the chain. by means of a trigger-type gas control 28 28. The user can grasp different parts of the grip handle 16 to move the saw chain in the correct position.

A throw of the saw can, as mentioned above, occur without prior warning. A chain brake system according to the present invention is intended to minimize the consequences of a throw.

In a preferred embodiment, the safety brake system, generally indicated by the designation 29, comprises a sensing arm or means 30, which is hingedly attached about the horizontal axis of rotation 31. The sensing arm is generally a bracket in the form of an inverted U (see Fig. 2) with two largely vertical parts 32 and 33 and a horizontal part 34.

The side part 32 is hingedly attached to the motor housing 12 at its end 35 by means of a screw 36 and can be rotated about the shaft 31. The sensing arm is thus located in front of the grip handle 16. Its second vertical part 33 is also hingedly attached to the motor housing.

Briefly, the sensing arm 30 has been placed between the grip handle 16 and the saw chain 26 and is intended to be actuated by the user's arm or hand. It is clear, however, that the sensing arm 30 is forced to pivot forward when the user strikes it.

From Figs. 1 and 2 together with 3 and 4 it can be seen that the sensing arm 30 has a projection in the form of a pin 38 which cooperates with a recess 39 in the motor housing 12.

The brake device 29 comprises a flexible brake band 40 one end 41 is fastened around a pin 42, which in its, which is attached to the motor housing 12. The brake band 40 is located around the outside 44 of the brake drum 46 and its other end 47 is fastened to the pin 38 The brake drum 46 consists of a rotating member which is so connected to the power transmission of the saw (which is not shown in the figures) that when braking forces act on the drum, the chain is braked. coupled to a shaft 48 The drum 46 may, for example, be driven by the motor or a gear driven by the chain. If centrifugal couplings are used (eg of the type described in the previously mentioned patents by Moore et al. And by Collins) the coupling housing can instead serve as a brake drum.

Any housing rotates the drum 46 as the saw motor and power transmission drive the saw chain around. If braking forces are exerted on the drum 46, these will be transmitted, so that the saw chain is braked. It should be noted that during normal use of the saw, the brake drum rotates freely and does not affect or impede the transmission of power between the motor and the saw chain.

A locking device 50 is rotatably attached to a pin 51 which is located in the motor housing 12. Its axis of rotation has been designated in the figure 52. The locking means cooperates with the sensing arm in that a recess 54 in the locking device 50 fits against the pin 38 (the pin 38 thus becomes the part of the sensing arm which is locked by the locking device). A biasing device in the form of a tension spring 60 is attached at its one end 62 to the motor housing 12 with a spring bracket 64, while its other end 66 engages in a recess 67 in the locking device 50.

Thus, as shown in Figs. 3 and 4, the pin 38 will hold the detent 50 in such a position that the force line 70 of the spring force in the spring 60 runs on the same side of the axis of rotation 52 of the detent on which the pin 38 rests when the sensing arm 30 is in its non-braking or first position. The arm 30 is then resiliently held in its first position by the spring force. The spring 60 will resiliently hold the sensing arm 30 in this first position as long as its line of force continues to lie on the same side of the axis of rotation 52 of the pin 51.

The brake band 40, of course, does not exert any braking force on the brake drum 46 in this position.

Fig. 5, which corresponds to Fig. 3, shows the sensing arm 30 in its second, braking position. This position is assumed if the saw user displaces the sensing arm 30 by striking it at a throw as above. When the arm 30 is moved from position one to position two, the braking position, the pin 38, which is attached to the arm, forces the locking device 50 to turn (in Fig. 5, the direction of rotation becomes clockwise), since the pin in question is located in the recess 54 in the locking device 50. As the pin 38 moves, the brake band 40 is forced into contact with the outside 44 of the brake drum 46, the brake drum 46 is prevented from rotating and the chain 26 is stopped. At the same time, the locking device 50 changes position, so that the force line 70 of the spring 60 459 240 10 will lie on the other side of the axis of rotation S2 of the locking device 50. In this position, the spring 60 resiliently retains the arm 30 in its second position. To return the sensing arm 30 to its first position, it is sufficient for the user to exert a force on the arm which overcomes the force of the spring 60.

Although a braking system such as the described system 29 has many advantages, such as low cost, high reliability, low weight and the ability to resiliently retain the sensing arm 30 in either of its two positions, its safety level can be further increased by allowing the system to include a second mechanism, which can brake the chain without the saw user having to access the safety arm. Fig. 6 shows an acceleration sensing system, designated 80, which can respond to 8CC & 1êI8Cí0H @ 1hos the saw at a throw. The acceleration sensing system or device 80 includes a reaction arm 81 which is rotatably attached to the motor housing 12 with a fastening device 82. On the reaction arm 81 is a cam 83. A locking device 50 'has a lever 84, 20 which abuts the cam 83. On the reaction arm is attached to a weight 86.

The weight 86 can be locked in its position, but as shown below it may be convenient to design it so that it can be displaced along the arm 81 and can be locked in the desired position by means of some fastener such as the locking screw 87. The reaction arm 81 thus comes at a throw to withstand the acceleration due to its mass inertia, which will cause the cam 83 to rotate relative to the saw.

Then the locking device 50 'will change position so that the force line 70 of the spring 60 will lie 30 on the opposite side of the axis of rotation 52 and the spring will via the locking device: 50 * resiliently hold the sensing arm 30 in its second position and force the brake band 40 into contact with the outside of the brake drum 46 I 44. Thus, it does not become necessary for the user to access the sensing arm 30 for the chain to stop if the acceleration sensing system 80 is mounted in the saw. By selecting the weight 86 appropriately and locking it at an appropriate distance from the point of rotation, the system can be triggered only when a selected acceleration level has been exceeded.

Fig. 7 shows a side view of a part of a chainsaw with a third embodiment of the safety brake system. In Figs. 7 and 8, the saw is designated 200 and has a motor housing 201, a grip handle 202 and a braking device 203. The braking device 203 includes a sensing arm 204, rotatably attached to the motor housing 201 with the rotary shaft 205. The arm 204 has two positions, the one shown in Fig. 7 and the other in Fig. 8. The arm 204 has a differently shaped projection 206 than that described above with a first recess 208 in the end 207 of the projection 206. The braking device 203 further includes a differently designed locking device or a lever 210 which is attached to the housing 200 and is rotatable about the shaft 211. On the lever 210 is a pin 214 which cooperates with the first recess 208 in the projection 204 of the sensing arm 204. A flexible brake band is attached with one end 218 to a pin 220 in the motor housing 201 and located around the outside 222 of the brake drum 224. The other end of the belt is attached to a second pin 228 on the lever 210.

One end 232 of a spring 230 is attached to the motor housing 201 and the other end is located on the lever 210 in a second recess 236. In this case, as in the previous system according to Figs. 1-6, the chain will scan when the sensing arm 204 touches from its first, non-braking, position (according to Fig. 7) to its second position (Fig. 8) in that the recess 208 in the projection 206 via the pin 214 rotates the lever 210 counterclockwise. At the same time, this movement causes the force line 240 of the spring 230 to change position so that the spring no longer strives to hold the sensing arm in its first position, where the brake band 216 runs freely from the outside 222 of the brake drum 224 but its force line ends on the other side of the lever 210. with the consequence that the spring 230 now strives to hold the sensing arm 204 in its second position, where the brake band 216 is pulled towards the outside 222 of the brake drum 224.

Fig. 9 shows a fourth embodiment of the present invention, wherein the lever 210 is formed with a lever 244 which communicates with an acceleration sensing system 246, which in design and function is similar to the system 80 shown in Figs. The system 246 comprises a reaction arm 248 by means of a f, which is rotatably attached to the motor housing 201 fastener 250. The reaction arm 248 has a cam 252, against which the lever 244 rests. The arm 248 is provided with a weight 254, which can be moved along the arm and with a locking screw fixed in any position along the arm. In the event of a throw, the arm 248 will thus, due to its inertia, resist the acceleration, with the consequence that the cam 252 will be rotated relative to the saw. Thereby, the lever 210 is rotated to a position where the force line 240 of the spring 230 goes on the other side of the axis of rotation 211 with the result that the spring 230 resiliently via the lever 210 holds the sensing arm 204 in its second, braking position. Then the brake band 216 is also brought into contact with the outside 222 of the brake drum 224. With this acceleration sensing system 246, the saw user thus does not have to access the sensing arm 204 for the chain to stop.

As before, one can set the response sensitivity of the sensing system by selecting the size of the weight 254 appropriately and locking it at an appropriate distance from the pivot point of the reaction arm 248.

Claims (12)

10 15 20 25 30 35 459 240 13 PATENT REQUIREMENTS A chainsaw device comprising a motor housing (12), a grip handle (16) mounted on the motor housing, a motor mounted in the motor housing, a saw chain (26), a saw bar (24) directed forward from the motor housing and along which the saw chain runs in a closed loop, and a rotary transmission device which transmits the rotation of the motor to movement of the saw chain and safety brake means for stopping the saw chain in the event of reversing, characterized in that the device includes a rotatable sensor (30) rotatably connected to the motor - the housing (12) for sensing backward thrust of the chain saw, and a second sensing means (38) arranged to be rotatable from a first position to a second position during reverse thrust; brake means (40) contactable with said rotary transmission means (46) for preventing rotational transmission from the motor to the saw chain, said brake means being movable from a free position with respect to said rotary transmission to a position for frictional braking of said rotary transmission for to prevent rotation of the saw chain; a separate rotatable member (50) rotatable about a pivot point (52) from a first position of the rotatable member to a second position of the rotatable member; a biasing means (60) having a first end (62) and a second end (66), said first end being connected to the motor housing at a certain point and said second end being attached to said rotatable means (50) at a certain point at a distance from the pivot point (52) to resiliently force said rotatable member to said first position when the rotatable member is in its first position and to resiliently force the rotatable member to the second position when the rotatable member is in its position second position, wherein an imaginary line (70) connecting the fastening point attachment point in the motor housing and the fastening point attachment point on the rotatable member 459 240 10 15 20 25 30 35 14 lies on one side of said pivot point when the rotatable member is in said first position and on the opposite side of the point of rotation when the rotatable member is in the second position; furthermore, the rotatable sensing means (30), the separate rotatable means (50) and the biasing means (60) cooperate with said braking means (40) to keep the braking means in a free position with respect to said rotary transmission means when the saw chain is running, when the sensing means is in position in said first position and said rotatable member is in the first position of the rotatable member so that when recoiled the sensor cooperating with the rotatable member is to move the rotatable member from said first position to said second position of the rotatable member when the sensor moved from said first position to said second position, whereby the rotatable sensing means (30), the separate rotatable means (50) and the biasing means (60) cooperate with said braking means (40) to keep the braking means in a position for friction-braking contact with said rotary transmission. means for preventing the saw chain from rotating. Device according to claim 1, characterized in that the second sensing device (38) consists of a pin (38) or other projection on the rotatable sensing device (30) and that in the separate rotatable member (50) there is a first recess (50). 54) arranged to receive said pin or equivalent. 3. Device according to claim 2, characterized in that the other end of the brake member is attached to said pin or corresponding projection. Device according to claim 3, characterized in that the separate rotatable member is provided with a second recess (67) arranged to cooperate with the biasing member, and that the other end of the biasing member is connected to said rotatable member via said second recess. 10 15 20 25 30 35 459 240 15 Device according to claim 1, characterized in that the device further comprises an acceleration sensing means (80) attached to the motor housing and provided with a cam (83), which means are arranged to react for the acceleration of the saw chain and to move the cam from a first cam position to a second cam position when the acceleration exceeds a certain value, that the separate rotatable member (50 ') is provided with a lever arm (84) arranged to be releasably abutment against said cam, that said rotatable member is arranged to be able to move from said first position in which the lever arm is in contact with the cam to a second position whereby the lever arm is released from the cam, and that the rotatable member is connected to resiliently press against its first position when the cam is in its first cam position and to resiliently press against its second position when the cam is in its second cam position. Device according to claim 5, characterized in that the cam-provided acceleration sensing means comprises an arm (81) which is rotatably connected to the motor housing and on which arm a weight (86) is mounted. 7. Device according to claim 6, characterized in that said weight (86) is movably mounted on the arm and that fastening means (87) are arranged to be able to fasten the weight on the arm in selected positions. Device according to any one of the preceding claims, characterized in that the separate rotatable member (210) has a lever (244) which communicates with the acceleration sensing system (246), which comprises a reaction arm (248), which is rotatably attached to the motor housing (201) by means of a fastener (250). Device according to one of the preceding claims, characterized in that the reaction arm (248) has a cam (252), against which the lever (244) rests. Device according to claim 9, characterized in that the reaction arm (248) is provided with a weight (254), which can be moved along the arm and by means of locking means fixed in arbitrary positions along it. 459 240 16 11. A device according to claim 10, characterized in that during a throw the arm will resist acceleration due to its inertia with the consequence that the cam (252) of the reaction arm will be rotated relative to the saw, the locking device being rotated to a position where the bias The line of force (240) of the actuator (230) will extend on the other side of the axis of rotation (211) of the separate rotatable member with the result that the biasing means via the locking means will resiliently hold the sensing arm (204) in its second, braking position. 10 Device according to one of Claims 1 to 11, characterized in that the brake member consists of a flexible brake band (40). 15 20 25 30 35