FI81987C - ANORDINATION VID EN MOTORSAOG. - Google Patents

Description

81987

This invention relates to the field of chain saws, and more particularly to a saw chain braking system.

Hand-held Chainsaws typically comprise a housing supporting 5 motors, a blade plate projecting forward from the housing, and a motorized saw chain for endless movement around the blade plate. The chainsaw is intended for use by a sawman who grips it with both hands. Typically, the sawman holds the gripper handle mounted on the housing with one hand and grips the trigger handle of the housing with the other hand to actuate the trigger-throttle lever mechanism.

In some cases of sawing, the saw chain may encounter a resistance that causes the blade plate to pop up in a manner commonly referred to as a kickback.

Usually the main method of handling this kickback. sex has been to arrange a chain brake that can act they ti start kickback, stopping the chain with the brake before 20 contact with the saw.

:: Most chainsaws include a centrifugal clutch between the engine and the chain drive sprocket. A typical V coupling is disclosed in U.S. Patent No. 2,941,411, "Centrifugal Clutch Actuator and Spring Retainer" (R.L.

25 Collins).

Because the drive sprocket is usually attached to the clutch housing, this typically acts as a brake drum in most braking systems.

/ As an example of such a braking system. . Mention may be made of U.S. Patent 3,739 * <75, "Chain Saw Safety: / Method And Apparatus", (H.E. Moore). Moore provides a pin that engages pivotally mounted brake shoes rotatably mounted on the saw housing. The brake shoe has tapered surfaces adapted to contact the protrusions mounted on the housing 35 and as the clamp rotates, the brake shoes are forced into contact with the circumference of the clutch housing. The pin is connected to a safety bar which is placed on the front gripper handle via a push rod and is forced by a spring to retract the brake shoes. If the saw "kicks back" and the sawer's hand or arm strikes the safety bar, the brake shoes are forced into the clutch drum and wedge-5 into place, stopping the chain.

There are several disadvantages to this design, one of which is that once the brake shoes are engaged, they are difficult to retract because they are wedged into place. In addition, the braking system is relatively heavy. Another example of the use of brakes can be found in U.S. Patent 3,793,727, "Cain Saw Safety Method And Apparatus" (H.E. Moore).

Subsequent structures have used flexible brake belts, e.g., U.S. Patent 3,776,331, "Brake-Device For Power 15 Saws," (L. Gustafson). In this construction, the flexible belt is loosely wrapped around the clutch drum, with one end of the belt attached to the housing. The opposite end of the belt is attached to one end of a lever arm, which lever arm is pivotally mounted in the housing in front of the gripper handle, with the other end of the flexible brake belt being attached immediately thereto. A lever is articulated to the lever and is adapted to engage a pin mounted in the housing. A spring mounted between the lever and the housing forces the latch to the locked position and also forces the lever to the brake-25 position. As the lever moves, the latch is forced past the pin and the spring continues to force the lever to the brake position. Although this structure is simpler than the above-mentioned structures when the braking device is in the unbraked state, the spring forces the latch to the locking position and the lever to the braking position. This makes the right choice of spring strength or hard. If the spring produces too much force, it becomes difficult to release the safety lever from the latch, and if the spring is too weak, the braking force produced by the flexible belt cannot stop the chain fast enough, which is desirable.

Therefore, it is desirable for the spring to hold the safety lever (sensor lever) in the unbraked position only when it is in this position and to force the lever to the braking position only when it is in this position. This ensures that there is always a coercive force that maintains the desired position. This is accomplished by the structure disclosed in U.S. Patent 3,934,345, "Snap-Acting Over Center Chain Saw Brake And Method Of Operation Thereof," (S. Hirschkoff). In this construction, the safety lever is typically mounted on the saw housing and in the operating position keeps the flexible belt in frictional contact with the clutch drum 10. The handlebar is mounted at one end both slidably and pivotally into the housing and at the opposite end into a curved slot or groove. The spring forces the handlebar towards the safety arm. The local connection between the gap, the handlebar and the pivot point of the arm is such that in the unbraked state of the jar-15 the spring angle is below the pivot point, forcing the safety arm to the unbraked position and when the safety arm is in the . Although this structure provides a completely satisfactory key locking function, it is heavy and quite expensive to manufacture.

All of the structures described above operate under the influence of the sawman's hand or arm or other part during kickback. However, they are structures that have tried to feel the angular acceleration of the chain saw in the event of a kickback and stop the chain without the sawman having to manually move the safety lever. An example is U.S. Patent 3,923,126, "Band Type Brake In A Chain Saw," (E.J. Bidenset). In this construction, the continuity sensor in the form of a control member 30 and a first lever connected together are pivotally mounted in the saw housing. The first lever engages the second lever, which is also mounted on the pivot. into the housing and both levers are spring-loaded towards each other. The second lever has an arm which rests against the end of the brake belt, which is forced into the braking space by the spring of the brake belt. During operation, when the kickback occurs, the loads on the control member and the first lever cause them to move freely from the end of the brake belt. In another embodiment, the second lever is attached to the end of the flexible brake belt and thus the second lever immediately brakes the chain.

This structure is complex and expensive to manufacture and requires a lot of maintenance. Since the control member also acts as a safety bar, acting on the contact of the saw's hand or arm, it is difficult to set the correct release level. For these 10 reasons, the continuity due to the kickback is considerably less than the force produced by the saw. If the force level is really very low, the saw will be subjected to the continuous action of the brake due to the temporary contact of the control member.

Some interesting saw braking systems are disclosed in U.S. Patent Nos. 3,937,306, "Automatic Brake Actuator For A Chain Saw" (Ulf Vilhein Naslun et al); 3,964,333, "Safetu Braking Mechanism For A Portable Chain Saw", (S. Hirschkoff) and 4,121,339, "Safety Brake Mechanism 20 For Chain Saw" (M. Nikolich).

Therefore, the main object of the present invention is to provide a chain brake for a chain saw which is small in construction, light in weight and reliable.

Another object of the present invention is to provide a chain brake for a chain saw 25 in which the safety lever is spring-tensioned to one of two positions, one being the unbraked position and the other being the braking position.

It is a further object of the present invention to provide a chain brake for a chain saw which requires only a small movement of the safety lever 30 to provide the full braking effect.

Yet another object of the present invention is to provide a chain brake for a chain saw that provides both hand-contact and automatic chain braking.

The invention provides a safety brake device for a chain saw, which is primarily intended to protect the sawmill from injuries caused by a kickback. Typically, chain saws have a housing, a hand gripper mounted on said housing, a motor supported by said housing, a saw chain, a blade holder projecting forward from said housing to support the saw chain for endless movement, a gearbox from a drive connected to said motor to operate the saw chain and a safety brake device to stop said saw chain. A safety brake device according to the present invention comprises: a feeler arm 10 pivotally mounted in said housing and having a protrusion, a portion of said feeler arm being positioned in front of said gripper handle during operation of a chain saw and adapted to be moved from a first position to a second position; a flexible brake belt having a first second end 15 connected to said housing and a second end to said protrusion such that when the feeler arm moves from said first position to a second position, the flexible brake belt is displaced from said rotational transfer device to frictional brake communication with said rotary transfer device; a latch rotatably mounted in said housing about an axis of rotation and adapted to engage said protrusion of the sensor arm and a tensioning device having one end connected to said latch I for resiliently holding the sensor arm in the first position and the second position.

In this way, when the saw member strikes the feeler arm, typically due to a kickback, the feeler arm moves from the first position to the second position, stopping the movement of the chain before the saw chain comes into contact with the saw-50.

**: In addition, according to another embodiment, an acceleration sensor or means is provided for sensing the acceleration of a chainsaw due to a kickback. Preferably, the acceleration sensor comprises a rod mounted on the cam and pivotally mounted in the housing. The above-mentioned latch is provided with a lever for detachable coupling. When a kickback occurs, the chain saw rotates 6 81987 relative to the rod because the rod has continuity and tends to resist acceleration. This causes the cam to rotate the lever, which in turn causes the feeler arm to move from the first position to the second position, 5 stopping the chain.

In the third embodiment, instead, the first pin is mounted on the latch and the feeler arm comprises a different protrusion, whereby the U-shaped groove is engaged with this first pin. In this third embodiment, one end of the flexible brake belt is typically connected to a second pin mounted on the latch.

A fourth embodiment of the present invention includes the acceleration sensing device described above in conjunction with a saw mechanism according to the third embodiment.

Fig. 1 shows a side view of a part of a chain saw according to the present invention, Fig. 2 shows a front view of a chain saw shown in Fig. 1, Fig. 3 shows a side view of a safety braking system forming a part of a chain saw which is not a braking mode. Fig. 4 shows an end view of the emergency braking system, seen along line 4-4 in Fig. 1, Fig. 5 shows the emergency braking system in the braking state in the same way as Fig. 3; Fig. 6 shows, in the same way as Fig. 3, a second embodiment of the safety braking system in both unbraked and braked condition, Fig. 7 shows a side view of a part of a chain saw according to the third to 30th embodiments of the present invention, Fig. 8 shows a side view of the safety braking system and Figure 9 is a side view of a safety braking system according to a fourth embodiment of the invention in both the unbraked and braked states.

• Figure 1 shows a side view of a part of a portable chain saw and Figure 2 shows a front view of the 7 81987 chain saw shown in Figure 1. The chain saw 10 includes a housing, i.e. a frame 12, which in the usual way supports an internal combustion engine or an engine device (not shown). The housing 12 includes a guide handle 14 mounted at the rear of the housing and a grip handle 5 or means 16 mounted near the front of the housing. The gripping handle comprises a top part 18, 20 and side parts 22.

Extending from the housing 12 is a blade plate, i.e. a blade holder 24, which supports a sawing or cutting chain 26 for endless rotation. The internal combustion engine drives this sawing-10 chain suitably via a gearbox or a device for transferring rotation from the internal combustion engine. The gearbox per se is not part of the invention, as any suitable conventional gearbox may be used, for example as disclosed in U.S. Patent No. 2,947,399 »" Centrifugal Clutch Actuator And Spring Retainer "(R.L. Collins).

Typically, the transmission includes a sprocket which is rotated by a drive shaft of the motor and around which a saw chain 26 is arranged. Rotation of the sprocket drives the saw chain in an endless manner around the blade plate 24.

When the chain saw 10 is used, the saw handles the guide handle 14 with one hand and the grip handle 16 with the other hand. This grip handle 16 is primarily used to handle the chain saw to apply pressure thereto, while the guide handle 14 is used to stabilize the saw 25 and control the saw chain speed. The saw can grasp 16 different points of the grip handle to properly orient the saw chain.

As mentioned earlier, the kickback phenomenon occurs without warning. To reduce kickback effects, the present invention provides a chain saw brake system.

In a preferred embodiment, the safety brake system or device, generally indicated by reference numeral 29, comprises a feeler arm or member 30 pivotally mounted for pivoting movement about a geometric axis of rotation 31. The feeler arm is usually an upside-down U-shaped member (see Figure 2), where 8 81987 has substantially vertical side portions 32, 33 and a horizontal top 34. The side portion 32 is pivotally mounted at its end 35 in a housing 12 by a bolt 36 and pivots about a shaft 31 . Thus, the feeler arm is placed in front of the gripper handle 16. The second side part 33 is also pivotally mounted in the housing.

Briefly, the feeler arm 30 is arranged to be between the gripper handle 16 and the saw chain 26 so that it can be touched by the sawer's arm or hand. In any case, it will be appreciated that the feeler arm 30 has been developed to be pivotable when the sawer's hand strikes it.

Referring further to Figures 1 and 2, and further to Figures 3 and 4, it can be seen that the feeler arm 30 comprises a protrusion in the form of a rigid pin 38 passing through a notch 39 in the housing 12.

The brake device 29 comprises a flexible brake belt 40 attached at one end 41 to the housing 12 by a pin 42. The brake belt 40 is positioned around the circumferential surface 44 of the brake drum 46 and is attached at its other end 47 to a pin 38. The brake drum 46 comprises a rotating member connected to a chain saw to the gearbox (not shown) so that: · the braking forces applied to the drum will slow down the saw chain. The drum 46 may be connected, for example, to a shaft 48 driven by a motor or to a sprocket which drives a saw chain. Alternatively, in cases where centrifugal clutches are used (such as those described in the aforementioned Moore et al. And Collins patents), the clutch cup may advantageously act as a brake drum. In any case, when the chain saw motor and gearbox circulate the saw chain and the drum 46 also rotates. When a braking force must be applied to the drum 46, this force is transmitted to brake the saw chain. However, it should be noted that under normal operating conditions, the brake drum is freely rotating and does not interfere with or restrict the transmission of the saw chain.

35 The housing 12 is rotatably mounted by a latch 50 via a pin 51 and thus has a pivot shaft 52. The latch *: 50 is adapted to be gripped by a feeler arm 30, which is obtained by making a notch 54 in the latch 50 which is adapted to engage the pin 38 (thus the pin 38). 38 acts as a latch engagement means for the sensing arm). A tensioning means, in the form of a tension spring 60, is mounted at one end 62 to the housing 12 via a bracket 64 and at its other end 66 engages a slot 67 in the latch 50.

As shown in Figures 3 and 4, with the feeler arm 30 in the unbraked, i.e. first position, the pin 38 positions the latch 50 so that the force 10 provided by the spring 60 acts along the force shaft 70 (on the same side of the shaft 52 as the pin 38). Thus, the feeler arm 30 is resiliently retained to conform to the first position. The spring 60 resiliently retains the sensor arm 30 in the first position as long as the spring force shaft 70 remains on the same side of the rotation shaft 52 of the ta-15 pin 51. Naturally, the brake belt 40 remains out of frictional braking communication with the brake drum 46.

Fig. 5, which corresponds to Fig. 3, shows the sensor arm 30 in the second position, i.e. in the braking position. This is achieved when the sawman moves the tactile arm 30 due to the impact of his · 'hand on the tactile arm during the aforementioned kickback event. When the feeler arm 30 moves to the first. from one position to another, i.e. the braking position, the pin 38 attached to it, while in the notch 54 of the latch 50, causes the latch to rotate (as shown in Figure 5 counterclockwise). As the pin 38 moves, the brake belt 40 comes into contact with the surface 44 of the brake drum 46, preventing rotation of the drum and stopping the chain 26. At the same time, the latch 50 pivots to a position where the force shaft 70 of the spring 60 moves 30 to the opposite side. In this state, the spring 60 flexibly tends to hold the feeler arm:: 30 in a second position.

To return the feeler arm 30 to the first position, the sawer only needs to apply sufficient force to the feeler arm 35 to overcome the force of the spring 60.

:: · Although such a braking system 29 has many advantages, such as low cost, high reliability, low weight, and the ability to provide a flexible holding force to retain the sensor arm 30 when in either the first or second position, the safety system the properties can be further improved by attaching a second mechanism 5 for braking the chain, which mechanism does not require the hand of the saw to hit the safety arm. As shown in Fig. 6, an acceleration sensing system may be provided, generally indicated at 80, which will sense the acceleration due to the kickback of the chain saw.

The acceleration sensing system or device 80 comprises a sensing rod 81 which is pivotally connected to the housing 12 by a pivoting bracket 82. The sensing rod 8l comprises a cam surface 83 · The latch 50 'is provided with a lever arm 84 adapted to contact the cam surface 83. zero 86. Although the weight 86 may be secured in place for a reason to be considered later, it may be desirable for it to be movably engaged with the sensor rod 81 and may be selectively secured at a predetermined position in said sensor rod 8l by a bracket or set screw 87.

In this way, during the kickback, the rod 81 will resist acceleration due to its inertia, which causes the cam pin 83 to pivot relative to the chain saw. This causes: the latch 50 'to rotate to a position where the force shaft 70 of the spring 60 * moves to the opposite side of the axis of rotation 52 *, thereby causing the spring 60 to resiliently hold the feeler rod 8l in a second position by the latch 50' and move the brake belt 40 to the brake drum surface 46 With 44. By thus incorporating the acceleration sensing system 30, the hand of the sawman need not touch the sensing arm 30 to stop the chain. In addition, the size of the weight 86 and its distance from the joint point by the right choice of the amount of tolerable kickback acceleration can be set to different values.

Figure 7 shows a side view of a part of a chain saw and a third embodiment of a tur-35 brake system. Referring to Figures 7 and 8, the chain saw is generally designated 200 and comprises a housing 201 having a front accessory.

II

81987 and a brake device, generally indicated at 203. This brake device 203 comprises a sensor arm 204 mounted on the housing 201 and pivoting about an axis of rotation 205 from the first position shown in Figure 7 to the second position shown in Figure 8. The feeler arm 204 has a different shape from that shown above and in this embodiment is in the shape of a member 206 having an end 207 with first grooves 208. The brake device 203 further comprises a second shaped latch or lever 210 rotatably mounted in the housing 200. about the axis of rotation 211. The first pin 214 on the lever 210 is mounted for engagement with the first groove 208 in the member 206 of the sensor arm 204. The flexible brake belt 216 is attached at one end 218 to a housing pin 220 mounted inside the housing 201.

The brake belt is positioned around the circumferential surface 222 of the brake drum 224 and is connected at one end 226 to a second pin 228 mounted on the lever 210.

The spring 230 is attached at one end 232 to the housing 201 and at the other end to the second groove 236 in the lever 210. In this way, as in the previous case of the chain brake system 29 shown in Figures 1-6, when the feeler arm 204 moves from the first position, i.e. the jar. -: · .: from the non-rushing position (Fig. 7) to the second position (Fig. 25 8), the groove 208 in the member 206 rotates the lever 210 counterclockwise around the first pin 214, causing the chain to stop. Meanwhile, this movement in turn causes the support shaft 240 of the spring 230 to move from a position tending to hold the feeler arm in the first position and the brake belt 216 away from the circumferential surface 222 of the brake drum 224 to the second position (shown in Figure 8) when the support shaft of the spring 230 211 on the opposite side.

Thus, the spring 230 now requires the sensor arm 204 to be held in the second position and the brake belt 216 in contact with the circumferential surface 222 of the drum 224.

A fourth embodiment of the present invention is shown in Figure 9, wherein the lever 210 optionally includes a lever arm i2 81 987 24 in contact with an optional acceleration sensing system 246, which is similar and operates in the same manner as the acceleration sensing system 80 shown in Figure 6. The acceleration sensing system 246 comprises sensing. -5 a rod 248 pivotally connected to the housing 201 by a bracket 250. The rod 248 has a cam surface 252 that contacts the lever arm 244. The feeler rod 248 is provided with a weight 254 movably engageable with the rod 248 and selectively secured in place by a set screw 106. Thus during the kickback, the rod 248 withstands acceleration due to its inertia, which causes the cam surface 252 to rotate relative to the chain saw. This causes the lever 210 to rotate to a position where the force shaft 240 of the spring 230 moves to the opposite side of the axis of rotation 211, thereby causing the spring 230 to resiliently hold the feeler arm 20¾ in the second, braking position via the lever 210. Thus, with respect to the acceleration sensing system 246, the sawer's hand need not touch the sensing arm 204 to stop the chain. Again, the size of the weight 254 and its distance from the joint point by the right choice of the amount of tolerable kickback acceleration can be set to different values.

Il

Claims (12)

1. Arrangement at a motor saw 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) and a saw blade (24) directed forward from the motor housing and along which saw chain running in a closed loop, and a rotary transfer device which transmits the motor rotation to movement of the saw chain and safety brake means to stop the saw chain at the rear throw, characterized in that the device comprises a rotatable sensing means (30) rotatably connected to the motor housing (12 ) for sensing the backward throw of the chain saw, and a second sensing device (38) arranged to be rotatable from a first position to a second position at the rear throw; brake means (40) which can be contacted with said rotary transmission means (46) to prevent rotational transmission from the motor to the saw chain, said braking means being movable from a free position with respect to said rotary transmission to a position for frictional braking of said rotary transmission. 25 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; 30. a biasing member (60) having a first end (62) and a second end (66), said first end being connected to the motor housing at a fixed point and said second end being attached to said pivoting means (50) at a definite point spaced from the pivot point (52) to resiliently force said pivotal means to said first position where the pivotal member is in its first position and to resiliently force the pivotal member to the second position where the pivotal member is located in its second position, wherein a conceivable line (70) connecting the bias point of the bias member to the motor housing and the bias point of the bias member on the pivot member is located on one side of said pivot point where the pivot member is in said first position and opposite; side of the pivot point where the rotatable member is in the second position; 10. the rotatable sensing means (30), the separate rotatable means (50) and the biasing means (60) cooperate with said brake means (40) to keep the brake means in a free position with respect to said rotary transmission means when the sensing chain is open when the sensing means is open. in said first position and said rotatable member is in the first position of said rotatable member so that in case of a throwback, the sensing device cooperating with said rotatable member is to move said rotatable member from said first position 20 to said second position of said rotatable member when said sensing means is 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 brake means (40) to keep the brake means in a position for frictional braking contact with said rotary transmission means to thereby prevent the chain from rotating. 2. Device according to claim 1, characterized in that the second sensing means (38) consists of a pin (38) or other projection of the rotatable sensing means (30) and that in the separate rotating means (50) there is a first recess (54) arranged to receive said pin or equivalent. .35 3. Device according to claim 2, characterized in that the other end of the braking means is attached to said pin or corresponding projection. ie 81987 Device according to claim 3, characterized in that the separate rotatable means is provided with a second recess (67) arranged to cooperate with the biasing means, and that the other end of the biasing means is connected to said pivotal means via said second recess. 5. Device according to claim 1, characterized in that the device further comprises an acceleration sensing means (80) attached to the motor housing 10 and provided with a cam (83), which means is adapted 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 releasably abut against said cam, said rotatable member being 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 the rotatable member is connected to reliably press against its first position when the cam is in its first cam position and to resiliently be pressed towards its second position when the cam is in its second cam position. 6. Device according to claim 5, characterized in that the cam-provided acceleration sensing means comprises an arm (81) pivotally connected to the motor housing and on which arm a weight (86) is mounted. 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 attach the weight to the arm in selected positions. Apparatus according to any of the preceding claims, characterized in that the separate rotatable member (210) has a lever (244) which is in communication with the acceleration sensing system (246), which comprises a reaction arm (248) which is pivotally attached to the motor housing (201) by means of a fastener (250). Device according to any of the preceding claims, characterized in that the reaction arm (248) has a cam (252), against which the lever (244) rests. 10. 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 fixed by means of reading means in arbitrary positions along it. 11. Device according to claim 10, characterized in that, in case of throwing the arm, by its inertia, it will withstand acceleration with the result that the cam (252) of the reaction arm will be rotated relative to said position, the locking means being rotated to a position where the biasing means ( 230) power line (240) will extend on the other side of the pivotal axis (211) of the separate pivotal member, with the result that the biasing means will reliably tilt the arm (204) into its second braking position via the locking means. Device according to any of claims 1-11, characterized in that the braking means is a flexible brake band (40).