TORQUE-LIMITED CHAIN TENSIONING FOR POWER TOOLS

• US 20110167650A1
• Filed: 06/24/2009
• Published: 07/14/2011
• Est. Priority Date: 06/24/2008
• Status: Active Grant

• Current Assignee: Mtd Products Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Mtd Products Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Atchley, Robert, Shymkus, Robert M., Buttery, Jeremy L., Lucas, Delbert E.
• Granted Patent: US 8,595,943 B2
• Time in Patent Office: Days
• US Class Current: 30/386
• CPC Class Codes: B27B 17/14 Arrangements for stretching the chain saw
• CPC Class Codes: F16D 7/022 with a helical band or equivalent member co-operating with a cylindrical torque limiting coupling surface
• CPC Class Codes: F16D 7/025 with flat clutching surfaces, e.g. discs
• CPC Class Codes: F16D 7/04 of the ratchet type similar gearings based on repeated accumulation and delivery of inertia-energy F16H33/08; overload clutches of the ratchet type F16D43/202

Abstract

A chainsaw (100) has a chainsaw body (101), a cutting chain (103) driven by a motor, and a guide bar mounting stud (111) extending from the chainsaw body (101). The chainsaw (100) also has an adjustably connected guide bar (102) having a track for supporting the cutting chain (103) around a periphery of the guide bar (102) and an adjustment pin (114) extending from a side face thereof. The guide bar mounting stud (111) is configured to extend through an elongated slot (112) in the guide bar (102). The chainsaw (100) also has a cam (116) received on the guide bar mounting stud (111) and having an eccentric groove facing the guide bar (102). The adjustment pin (114) is received in the eccentric groove such that rotation of the cam (116) causes the guide bar (102) to move with respect to the chainsaw body (101), thereby tensioning the cutting chain (103). The chainsaw (100) also has a clutch (118) connected to the cam (116) for allowing no more than a predetermined load to be applied to the guide bar (102) for tensioning the cutting chain (103).

Claims

1. A chainsaw powered by a motor housed by a chainsaw body, the chainsaw comprising:

a cutting chain connected so as to be driven by the motor;

a guide bar mounting stud extending from the chainsaw body;

an adjustably connected guide bar having a track for supporting the cutting chain around a periphery of the guide bar, an adjustment pin extending from a side face thereof, and an elongated slot formed therein, wherein the guide bar mounting stud is configured to extend through said slot in the guide bar;

a cam received on the guide bar mounting stud and having an eccentric groove facing the guide bar, wherein the adjustment pin is received in the eccentric groove such that rotation of the cam causes the guide bar to be positioned along its longitudinal dimension with respect to the chainsaw body, thereby tensioning the cutting chain; and

a clutch connected to the cam for allowing no more than a predetermined load to be applied to the guide bar for tensioning the cutting chain.

2. The chainsaw of claim 2 wherein when there is not a sufficient reaction force from the tension of the cutting chain, the cam will turn and the sliding of the adjustment pin in the eccentric groove drives the guide bar in a direction away from the body of the chainsaw, and when sufficient tension exists in the cutting chain, the clutch will begin slipping and prevent the cutting chain from being tensioned further.

3. The chainsaw of claim 2 wherein the clutch comprises a knob mounted on the guide bar mounting stud and rotatable about the axis of the mounting stud.

4. The chainsaw of claim 3 wherein the knob will continue to rotate while the clutch slips to clamp the guide bar down against the chainsaw body.

5. The chainsaw of claim 2 wherein the clutch includes a wrap spring between the knob and the cam to limit the amount of tension which may be supplied to the cutting chain.

6. The chainsaw of claim 2 wherein the clutch includes a first series of magnets, and the cam includes a generally opposed second series of magnets, wherein the first and second series of magnets hold the cam in relation to the clutch until sufficient force is created such that the magnetic forces between the first and second series of magnets are no longer great enough to prevent a slip between the clutch and the cam, thereby limiting the torque that the cam can apply.

7. The chainsaw of claim 2 wherein the clutch includes a ring gear connected to one of the clutch and the cam, and one or more flexible fingers comprising a center gear connected to the other of the clutch or the cam.

8. The chainsaw of claim 7 wherein the fingers are constructed from a plastic material.

9. The chainsaw of claim 7 wherein the ring gear includes directioned teeth, providing slip torque between the ring gear and the fingers that is greater when a knob is rotated in a first direction than that in an opposing direction.

10. The chainsaw of claim 7 wherein when a finger bends past kick-over, the clutch slips.