EP0677361A1

EP0677361A1 - Chain saw with compact brake

Info

Publication number: EP0677361A1
Application number: EP94116795A
Authority: EP
Inventors: Mark Earnest Baer; Robert Lent Creveling, Jr.; David Eugene Ebersole
Original assignee: Mcculloch Corp
Current assignee: Mcculloch Corp
Priority date: 1994-03-22
Filing date: 1994-10-25
Publication date: 1995-10-18
Also published as: AU1168895A; SE9501047L; CA2118472A1; SE9501047D0

Abstract

A chain saw includes a chain brake mechanism (2) which uses the periphery (32) of a cup-shaped reduction gear (30) as a braking surface. One embodiment uses a separate brake drum (96) which surrounds the cup gear. An alternative embodiment uses the cup gear itself as the braking surface.

Description

Field of the Invention

The present invention relates to chain saws, and more particularly, to a chain braking arrangement for chain saws.

Background

Chain saws are prone to exhibit a phenomenon called "kickback." Kickback typically occurs when the tip of the saw contacts the wood being cut, or another solid object, resulting in a violent upward motion which can endanger the operator. The risk of injury can be minimized by stopping the saw chain whenever a kickback occurs or whenever the operator is at risk of coming into contact with the saw chain.
Various chain braking arrangements have been discovered and are disclosed in the prior art. Some devices use a safety handle which actuates the chain brake when the handle is struck by the operator's hand or wrist. Other braking devices use an inertial sensor to actuate the brake when a kickback or other violent motion of the saw occurs. Both such devices are disclosed in Todero, U.S. Pat. No. 4,420,885.
Moore, U.S. Pat. Nos. 3,739,475 and 3,793,727 disclose a braking arrangement which uses a brake drum and brake shoes. The brake drum is fixedly connected to a chain sprocket which drives a saw chain, and the brake shoes make frictional contact with the outer circumference of the brake drum to stop the saw chain.
Hirschkoff, U.S. Pat. No. 4,059,895 discloses a band brake for a chain saw comprising a flexible metallic band which is wrapped around a brake drum. One end of the band is fixed to the chain saw casing or chassis. The other end is attached to a mechanical linkage via a biasing means, typically a spring. In a brake-off condition, the band is loosely wound around the brake drum, and is not in contact therewith. In a brake-on condition, the band is tightened around the brake drum by the biasing means such that the friction between the band and the brake drum stops the saw chain substantially instantaneously.
Wieland et al., U.S. Pat. No. 4,662,072 discloses a band brake for a chain saw wherein a brake drum is located on a motor drive shaft. This patent alternatively discloses that the brake drum can be located elsewhere in the drive train of the saw. Other prior art designs use the outer casing of a centrifugal clutch as the brake drum. See, e.g., Hirschkoff, U.S. Pat. No. 4,026,392.
Typically, chain saw brakes are only used in the event of a kickback or other violent motion of the saw. In the future, it is anticipated that one or more regulatory agencies will require that chain saw brakes must be activated whenever the throttle or trigger is released. Wieland et al., U.S. Pat. No. 4,680,862 discloses a chain saw comprising an electric coasting brake in addition to a mechanical safety brake. Such an arrangement ensures that the operator will not come into contact with a moving saw chain as the saw chain coasts to a stop after the throttle or trigger is released. Further, it may be desirable to use the safety brake itself as a coasting brake. However, this will require an extremely durable brake mechanism since the brake will be applied at least once every time the saw is used.
Many saws, especially those with electric motors as their means for motive power, use a reduction gear to ensure that the saw chain is driven at an optimal speed. In order to produce a saw with a compact design, chain saws using a cup-shaped or ring-shaped gear have been developed. Such a gear is generally cylindrical in shape and has teeth disposed on the inner surface of a circumferential wall of the gear which are engaged by a motor-driven pinion. A cup gear is disclosed in Haupt et al., U.S Pat. No. 3,857,179 and in the above-noted Wieland et al. '072 patent. A ring gear is disclosed in Irgens, U.S Pat. No. 3,669,162.
Cup gears and ring gears have numerous advantages over conventional gears, such as the conservation of space in the chain saw housing. Cup gears also protect the gear and pinion mechanisms from contaminants, such as sawdust and dirt. As discussed in the Irgens '162 patent, cup gears and ring gears can also reduce the torque on the drive shaft by minimizing the moment arm acting on the drive shaft. In addition, cup gears and ring gears have relatively large rotational moments of inertia, when compared to conventional gears with external teeth. As discussed in the Haupt et al. '179 patent, this results in enhanced performance of the chain saw, especially at low speeds.

Summary of the Invention

According to one aspect of the present invention, a cup gear is utilized as a braking structure in a chain saw. More specifically, a pinion driven by a drive shaft of a motive power means drives a cup gear which in turn drives a chain sprocket. The cup gear carries a braking surface which is acted upon by a braking means to selectively bring the saw chain to a halt.
The braking surface can be an outer circumferential surface of the cup gear. Alternatively, the braking surface can be an outer circumferential surface of a brake drum secured to the outside of the cup gear. An electric motor can be used as the motive power means in a chain saw embodying the present invention, and a brake band can be used as the braking means. The pinion can be directly driven by the drive shaft for rotation therewith at all times during operation of the chain saw. Similarly, the chain sprocket can be directly driven by the cup gear for rotation therewith at all times during the operation of the chain saw. A mechanical linkage may be used to activate the braking means.
In an embodiment of the present invention, a band brake is used in an electric chain saw having a cup gear as a reduction gear. The band brake comprises a flexible metallic band having two ends and a brake drum fixedly attached to the outer surface of the cup gear. A mechanical linkage is used to actuate the band brake. The mechanical linkage comprises a pivotally mounted safety brake lever which carries a pin engaging a cam follower plate attached to the brake band. During a brake-on condition, a helical compression spring biases the brake band in tension tightly around the brake drum.
The present invention allows for significant weight reduction in the chain saw braking mechanism. The invention also provides for a compact braking configuration, thereby reducing the width of the chain saw and the effective moment arm acting on the drive shaft during braking. Furthermore, a chain saw constructed in accordance with one embodiment of the present invention wherein the outer circumference of the cup gear is used as a braking surface will have fewer parts, thereby reducing manufacturing costs.
Other features and advantages are inherent in the apparatus claimed and disclosed or will become apparent to those skilled in the art from the following detailed description in conjunction with the accompanying drawings.

Brief Description of the Drawings

Fig. 1 is a perspective view, taken from the rear and above, of a chain saw embodying the present invention;
Fig. 2 is a fragmentary elevational view of the chain saw of Fig. 1 with the gear housing removed and portions broken away illustrating a chain brake mechanism in the brake-off position;
Fig. 3 is a view similar to Fig. 2 illustrating the chain brake mechanism in the brake-on position;
Fig. 4 is a cross-sectional view taken generally along the lines 4-4 of Fig. 2 of the chain brake mechanism and pinion together with a motor; and
Fig. 5 is a view similar to Fig. 4 of an alternative embodiment of the present invention.

Detailed Description of the Drawings

Referring to Fig. 1, a chain saw 10 includes a saw chain 12, a guide bar 13, a rear handle 14, a front handle 16, a motor housing 18, a gear housing 19, and a safety brake lever 20.
Figs. 2 and 4 show a braking and drive mechanism 21 of the present invention in a first or brake-off position or configuration. A pinion 22 is fixedly attached to a motor drive shaft 24 which is driven by a motor 25. A plurality of pinion teeth 26 disposed on the pinion 22 engage a plurality of cup gear teeth 28 disposed on an inner surface 30 of a cylindrical wall 32 of a cup gear 34. A chain sprocket 36 is fixedly attached to the cup gear 34. The chain sprocket 36 drives the saw chain 12 as it moves along the guide bar 13. It should be noted that the bottom side of the saw chain 12 moves toward the chain sprocket 36. Thus the chain sprocket 36, cup gear 34, and pinion 22 all rotate in a clockwise direction as indicated in Fig. 2 by an arrow 37.
Although a chain saw powered by an electric motor 25 is depicted in the drawings, the present invention is also applicable to chain saws powered by internal combustion engines.
Referring to Fig. 4, the braking and drive mechanism 21 comprises a brake band 38 disposed around a brake drum 40. The brake drum 40 is rigidly attached to the cup gear 34 by a plurality of stamped bosses 42 which extend into a plurality of corresponding bores 44 in the cup gear 34. Each boss 42 includes an enlarged head 46 which, together with an axial face 48 of the brake drum 40, capture the cup gear 34 therebetween. Alternatively, the brake drum 40 could be secured to the cup gear 34 by another means of attachment, such as bolts, screws, or rivets.
A motor housing partition 50 separates the motor 25 from the braking and drive mechanism 21. As seen specifically in Fig. 2, an angle bracket 51 having a vertical portion 52 and a horizontal portion 54, and a guide bar support 56 protrude from the motor housing partition 50 and form a channel 58 therebetween. A fixed end 60 of the brake band 38 is bent at approximately a right angle so that it fits in the channel 58 and bears against the vertical portion 52 of the angle bracket 51. Other means of securing the fixed end 60 of the brake band 38 may alternatively be used. A moveable end 62 of the brake band 38 is secured by any suitable means to a cam follower plate 63.
One suitable means of attachment comprises the following arrangement. The moveable end 62 of the brake band 38 may be twisted 90 degrees so that it aligns with an outward facing surface 64 of the cam follower plate 63. The moveable end 62 of the brake band 38 may be attached to the cam follower plate 63 by a post (not shown) extending from the cam follower plate 63 which engages a hole (not shown) in the moveable end 62 of the brake band 38.
The cam follower plate 63 is pivotally mounted to the motor housing partition 50 by a cam follower plate mounting pin 65.
A fixed end 66 of a helical compression spring 68 is fixed within a retaining hole 70 in the motor housing partition 50. A moveable end 72 of the helical compression spring 68 bears against a rearward side 73 of the cam follower plate 63, and may also be attached thereto by any suitable means. A roller pin 74 carried by the safety brake lever 20 engages a forward side 75 of the cam follower plate 63. The safety brake lever 20 is pivotally mounted to the motor housing partition 50 by a safety brake lever mounting pin 76.
In the brake-off configuration (as depicted in Fig. 2), the safety brake lever 20 is disposed in a substantially upward or vertical position and the roller pin 74 engages an indentation 78 and a lobe 80 on the cam follower plate 63 such that the cam follower plate 63 is prevented from rotation about the cam follower plate mounting pin 65. Thus, the helical compression spring 68 is in a compressed state and the brake band 38 is loosely wrapped around the brake drum 40 such that the brake band 38 is not in contact therewith.
As seen in Fig. 2, an arm 82 on the safety brake lever 20 engages a first arm 84 of a brake switch actuator 86 pivotally mounted on the motor housing partition 50 at a brake switch actuator mounting pin 88. A second arm 90 of the brake switch actuator 86 engages a spring-loaded plunger 92 of a microswitch 94. The microswitch 94 is configured such that electrical power is supplied to the motor 25 (Fig. 3) when the plunger 92 is depressed. The plunger 92 is pushed outward from the microswitch 94 by a spring (not shown) such that the plunger 92 is extended and the microswitch 94 is open in the absence of pressure on the plunger 92.
A second or brake-on position or configuration is depicted in Fig. 3. When the safety brake lever 20 is pushed forward (to the right in Figs. 2 and 3), for example by a user's hand during a kickback condition, the roller pin 74 moves upwardly, releasing the cam follower plate 63 for clockwise rotation under the influence of the force applied by the helical compression spring 68. The brake band 38 thus is pulled tightly around the brake drum 40 and the friction between the brake band 38 and a cylindrical flange 96 (Fig. 4) of the brake drum 40 brings the saw chain 12 (not shown in Fig. 3) quickly to a halt.
In addition, in the brake-on position, the plunger 92 of the microswitch 94 is extended and the microswitch 94 is open. Thus, electrical power is cut off from the motor 25 when the safety brake lever 20 is in the brake-on position.
As seen in Fig. 4, the brake drum 40 surrounds the cup gear 34 and the cylindrical flange 96 of the brake drum 40 provides a braking surface 97 with which the brake band 38 comes into frictional contact during braking. Although not necessary, the cylindrical flange 96 of the brake drum 40 may be radially spaced outwardly from an outer cylindrical surface 98 of the cup gear 34. This separation facilitates air flow around the cylindrical flange 96 of the brake drum 40 for better cooling. Also, it helps minimize heat transfer from the brake drum 40 to the cup gear 34. As a result, the cup gear 34 can be made of a less durable, more inexpensive material, such as plastic.
Fig. 5 shows an alternative embodiment of the present invention wherein elements common to Figs. 2-4 are assigned like reference numerals. In this embodiment, an outer surface 198 of a cup gear 134 is utilized as a braking surface. In such a design, the cup gear 134 must be manufactured from a durable material, such as steel. Although this design results in more weight in the cup gear 134, the absence of a separate brake drum (40 in Fig. 4) simplifies the manufacture of the chain saw. Also, the additional inertia of a heavier cup gear 134 improves performance of the saw at low speeds.
Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure may be varied substantially without departing from the spirit of the invention, and the exclusive use of all modifications which come within the scope of the appended claims is reserved.

Claims

A chain saw, comprising:
means for developing motive power having a drive shaft;
a pinion connected to the drive shaft for rotation therewith and having pinion teeth;
a rotatable cup gear having internal teeth engaged by the pinion teeth and carrying a braking surface;
a chain sprocket connected to the cup gear for rotation therewith;
braking means surrounding the braking surface; and
means for moving the braking means between a first position wherein the cup gear is free to rotate in response to rotation of the drive shaft and a second position wherein rotation of the cup gear is arrested by the braking means.
The chain saw of claim 1, wherein the braking surface comprises an outer circumferential surface of the cup gear.
The chain saw of claim 1, wherein the braking surface comprises an outer circumferential surface of a brake drum secured to the cup gear.
The chain saw of claim 1, wherein the means for developing motive power is an electric motor.
A chain saw, comprising:
a motor having a drive shaft;
a pinion connected to the drive shaft for rotation therewith and having pinion teeth;
a rotatable cup gear having internal teeth engaged by the pinion teeth;
a chain sprocket connected to the cup gear for rotation therewith;
a brake drum surrounding the cup gear and rotatable therewith at all times during operation of the chain saw;
braking means surrounding the circumference of the brake drum; and
means for moving the braking means between a first position wherein the brake drum and cup gear are free to rotate in response to rotation of the drive shaft and a second position wherein rotation of the brake drum and the cup gear is arrested by the braking means.
The chain saw of claim 5, wherein the braking means comprises a brake band.
The chain saw of claim 5, wherein the pinion is directly driven by the drive shaft for rotation therewith at all times during operation of the chain saw.
The chain saw of claim 5, wherein the chain sprocket is directly driven by the cup gear for rotation therewith at all times during operation of the chain saw.
A chain saw, comprising:
a motor having a drive shaft;
a pinion connected to the drive shaft for rotation therewith and having pinion teeth;
a rotatable cup gear having internal teeth engaged by the pinion teeth;
a chain sprocket connected to the cup gear for rotation therewith;
a brake drum surrounding the cup gear and rotatable therewith at all times during operation of the chain saw;
a brake band surrounding the circumference of the brake drum;
a mechanical linkage for moving the brake band between a first position wherein the brake drum and cup gear are free to rotate in response to rotation of the drive shaft and a second position wherein rotation of the brake drum and the cup gear is arrested by the brake band; and
means for applying a biasing force to the brake band in the second position.
The chain saw of claim 9, wherein the brake drum is rigidly attached to the outer periphery of the cup gear for rotation therewith.
The chain saw of claim 9, wherein the mechanical linkage for moving the brake band comprises a pivotally mounted lever which is coupled to the brake band.
The chain saw of claim 9, wherein the mechanical linkage for moving the brake band comprises a pivotally mounted lever carrying a pin engaging a cam follower plate which is attached to the brake band.
The chain saw of claim 9, wherein the pinion is directly driven by the drive shaft for rotation therewith at all times during operation of the chain saw.
The chain saw of claim 9, wherein the chain sprocket is directly driven by the cup gear for rotation therewith at all times during operation of the chain saw.
The chain saw of claim 9, wherein the applying means is a helical compression spring.