Patent Application
20070153472
The present invention relates generally to electric power operated hand tools and specifically to a chainsaw having a unitary chassis design for stability, rigidity and ease of assembly, an improved chain bar retaining system and improved strain relief for electrical wiring supplying power to the chainsaw motor.
Lightweight and portable power tools have become popular consumer items as the number of people who own and maintain their own homes has grown over the past decades. Specifically, lightweight electrically powered chainsaws and other electrical power tools have proliferated due to the need for light tree and branch trimming and the widespread commercialization of consumer-grade saws. Electrically powered saws are preferred by many consumers over conventional two-cycle motor type saws since they obviate the need for mixing oil and gas as required for most two-cycle systems, are much quieter to use, and are usually lighter in weight.
Most conventional power saws utilize a continuous loop-type chain driven by a drive sprocket secured to an end of a rotating shaft, which is in turn driven by an electric motor or alternatively an internal combustion engine. The chain travels along a groove in the perimeter of an elongated guide bar having one end secured to the saw proximate the drive sprocket.
Many prior art chain saws utilize guide bars that are secured to a chassis or plate securely mounted within the saw assembly. Guide bars are required to be capable of motion along their longitudinal axis to enable proper tensioning of the chair that rotates around the perimeter of the guide bar. As the saw is used the chain necessarily stretches to a certain degree, thereby causing a loose fit between the rotating chain and the guide bar. When this fit becomes too loose it poses a danger to a user since a rapidly moving chain may “jump” off the guide bar.
Accordingly, a wide variety of chain tensioning systems have been implemented in the prior art. Most of these systems involve moving or biasing the guide bar forward, away from the drive sprocket along its longitudinal axis thereby taking up any slack in a loose chain. To effect motion of this type, guide bars typically comprise a slotted portion that is placed over a pair of threaded posts that protrude outwardly from the chainsaw having one end secured to the chassis, and one end free to accept a nut having complementary threads. The nuts are then tightened down against the guide bar to hold it securely to the chassis. An example of such a system is shown in U.S. Pat. No. 5,353,506 to Müller et al.
In the aforementioned prior art systems it is difficult for one person to adjust chain tension since one or more screws or bolts must be loosened, the guide bar must be biased into the proper position and held there, then the screws or bolts must be tightened while holding the guide bar in place. This operation often requires more dexterity than most users possess.
A further difficulty with prior art power tool systems that operate on electrical power is the tendency of the necessary cord carrying electrical power to the tool via electrical conductors to suffer failure due to strain from repetitive use or even a catastrophic single event. Obviously the failure of an electrical cord or cords can be quite dangerous to the user and those in the immediate vicinity. Specifically, many cord assemblies fail at the point where they enter the power tool, since this point is subject to a great deal of flexing and twisting. Accordingly, many manufacturers have developed strain relief systems to protect electrical conductors enclosed therein from damage.
Various standards have been developed to guide manufacturers in the proper design of power cords and their concomitant strain relief systems. ANSI requirements and those requirements promulgated by organizations such as UL and CSA for alternating current powered products aid manufacturers in developing integrity in the power cord and its retention within the tool.
Typically, prior art strain relief devices comprise power wiring encapsulated within a molded portion that is then captured between two halves of the tool housing, and held in place by compressive force as the housing halves are held together with fasteners or adhesives. These molded portions often employ various and sundry flanges or grooves that engage slots or protrusions in the housing halves to retain the strain relief
One difficulty with prior art strain relief systems is that the strain relief is typically integrally molded to the power cord using relatively soft, elastic material that is thence captured by relatively hard, inflexible molded housings. The use of these materials makes consistent strain relief/housing mating difficult, since much of the fit is dependent on production tooling wear, molding peculiarities and the like. Accordingly, there is a need for a robust strain relief system for a power tool that minimizes production material and labor costs while maximizing system integrity over a wide variety of manufacturing platforms.
Finally, many commercially available power tools utilize a “split-case” design for housing and protecting the tool motor and power components wherein the motor is disposed and secured in a first half and, in the case of a chainsaw, the sprocket and cover are disposed in a second, mating half. The two halves are usually molded from a high impact plastic and have complimentary fasteners such as slots and tabs to secure to halves together, typically along a central longitudinal seam.
One difficulty with these prior art tool designs is that the two cover halves are prone to breaking apart along the seam when the tool is subjected to a sharp impact, such as from being dropped or struck. Furthermore, these split case designs require a large amount of production tooling and high labor cost to assemble since their designs are relatively complex. Accordingly, there is a need in the art for a power tool having a design that obviates the disadvantages inherent in conventional split-case designs.
In order to obviate the above-mentioned problems, a power tool is provided that utilizes a unitary housing construction wherein a single unitary chassis is provided for the mounting of various components that acts to both enhance the overall strength and rigidity of the tool as well as reduce manufacturing costs.
Furthermore, the present invention incorporates a novel guide bar design for use in conjunction with a chainsaw power tool embodiment that provides for positive and facile retention of the guide bar to the chainsaw as well as a convenient mechanism for adjusting chain tension. The retention system incorporates a mounting pin and a keyed retaining pin, both of which engage apertures or a slot in a guide bar wherein the guide bar is compressively engaged by simple rotational motion of the retaining pin.
The present invention further comprises an electrically operated power tool having a novel strain relief system that employs an integrally molded relief cord having a central aperture or bore for routing power wiring, wherein the strain relief bore is advantageously engaged by a protruding post or pin of the power tool thereby enabling use of the strain relief with a wide variety of electrical devices and in a wide variety of strain relief applications.
Other features, objects and advantages of the present invention will become apparent from reading the detailed description of the preferred embodiments taken in conjunction with the attached drawing Figures.
Referring now to
The unitary chassis 20 of the present invention may be molded from, for example, a high impact plastic compound such as polyethylene, polycarbonate, nylon, or the equivalent thereof having integrally molded attachment points 22 to which necessary tool components are mounted. For purposes of this specification reference will be made to an electric chain saw power tool 10. However, one of ordinary skill in the art will recognize that the present invention may be utilized in a wide variety of applications and is not limited to the environment of a chainsaw.
As seen in
Chassis 20 may further comprise a plurality of integrally molded bumper spikes 60 extending outwardly from a forward portion of chassis 20 proximate guide bar 7 to facilitate gripping a tree branch or other item being cut by the tool 10. This feature of the invention obviates the need to secure a separate bumper spike assembly to chassis 20 as is the case with prior art devices, thereby reducing assembly time and cost.
In one embodiment of the present invention unitary chassis 20 central member 30 may comprise an integrally molded I-beam that is disposed substantially the entire length of chassis 20 to provide enhanced rigidity thereto. I-beam shaped central member 30 may be molded such that a lower portion 32 thereof is disposed along and forms the bottom of chassis 20.
In a further embodiment of the present invention as shown in
Referring now to drawing
Retaining pin 110 further comprises a second end 118 having a flared head 120 thereon having wing portions 122 extending therefrom. Retaining pin 110 second end 118 is positioned to extends outwardly towards the guide bar 7 side of chassis 20. Wing portions 122 are shaped such that a slot 9 of guide bar 7 may be positioned over flared head 120 when pin 110 is rotated in a first direction, and such that when pin 110 is rotated in a second direction wing portions 122 rotate over the edges of slot 9 to contact the guide bar 7 proximate the slot 9 thereof, as best seen in
Retaining pin 110 flared head 120 may further include a slot 124 therein to accept a conventional straight blade screwdriver or the like thereby permitting easy rotation of retaining pin 110. Additionally, wing portions 122 may be elongate in shape to permit them to be readily grasped and turned between the thumb and forefinger of a user. Additionally, retaining pin 110 has an overall length such that when rotated, the wing portions 122 engage guide bar 7 and compressively force it against chassis 20.
Retention system 100 further comprises a threaded mounting pin 130 capable of accepting a bolt or the like having complementary threads. A first end 132 of mounting pin 130 is disposed in a mounting pin aperture 68 in chassis 20. A second end 134 of mounting pin 130 extends out through the opposing side of chassis 20. The first end 132 of mounting pin 130 is hexagonal in shape and is designed to fit securely within mounting pin aperture 68 to prevent rotation of mounting pin 130 once installed. Accordingly, mounting pin aperture 68 may also be hexagonal in shape and sized to accept first end 132 of mounting pin 130 thereby preventing its rotation.
Mounting pin 130 has a diameter that permits slot 9 of guide bar 7 to pass over pin 130 such that a nut (not shown) may be secured over second end 134 thence tightened to secure guide bar 7 in place against chassis 20. Furthermore, mounting pin 130 may be spaced from retaining pin 110 along a central longitudinal axis as denoted by the arrow 11 in
In operation guide bar 7 must be periodically adjusted longitudinally in the direction of line 11 to account for the stretching of a chain that rotates around the perimeter of guide bar 7 or alternatively, the installation of a new chain. Retaining pin 110 is initially rotated such that wing portions 122 extending from flared head 120 are capable of passing through slot 9 of guide bar 7. The guide bar slot 9 is then placed over both the retaining pin 110 and the mounting pin 130 thereby permitting guide bar 7 to move longitudinally along pins 110 and 130. Guide bar 9 is thence moved longitudinally to a position where the desired chain tension is achieved.
Once guide bar 7 is satisfactorily positioned, retaining pin 110 is simply rotated into its second position either by inserting a screwdriver in slot 124 or by rotating wing portions 122 by hand, thereby permitting wing portions 122 to contact guide bar 7 proximate slot 9, forcing it against a portion of chassis 20 compressively. Since guide bar 7 is now held in place between wing portions 122 and chassis 20 the nut may be placed over second end 134 of mounting pin 130 and tightened. The retention system 100 of the present invention facilitates this operation by permitting a user to position guide bar 7 with one hand and then rotate retaining pin 110 with a second hand to retain guide bar 7 in place against chassis 20. The user then may release guide bar 7 and use both hands to secure a nut over mounting pin 130.
In an alternative embodiment of the present invention retaining pin 110 keyed end 114 is captured within key slot 66 such that pin 100 is not capable of rotational motion. In this embodiment of the invention flared end 120 of retaining pin 110 is rotatably secured to pin 110 such that it is capable of rotation independent of retaining pin 110. This embodiment of the invention permits the retaining pin 110 to be securely gripped by key slot 66 while permitting its flared end 120 to rotate freely to engage or disengage slot 9 of guide bar 7 as required.
Referring now to drawing
As best seen in
Molded housing 210 may further comprise a first aperture 216 into which power wiring 202 entering housing 210 is routed and at least one second aperture 218 through which power wiring 202 exiting housing 210 passes. Entering power wiring 202 may include a flexible exterior insulator 206 that is integrally molded into housing 210 such that the wiring contained within housing 210 simply forms an integral part thereof until exiting from forward portion 214.
As seen in
Once central bore 212 is positioned over post 70 handle cover 5 is secured to integral handle 58 thereby capturing central bore 212 on post 70 and prohibiting longitudinal or side-to-side movement of molded housing 210. It should be noted that integral handle 58 and handle cover 5 may be shaped to facilitate entry of housing 210 into handle 58 once cover 4 is in place. In operation, since central bore 212 is captured on post 70 power wiring 202 is prevented from any longitudinal or twisting motion, and may only slightly flex upwardly or downwardly as permitted by the forward portion of housing 210 contacting interior portions of integral handle 58. Thus the present invention provides a strain relief system 200 which is vastly superior to prior art systems and simply will not permit twisting or longitudinal motion of power wiring, up to the structural tolerances of housing 210, post 70 and handle 58.
While the present invention has been shown and described herein in what are considered to be the preferred embodiments thereof, illustrating the results and advantages over the prior art obtained through the present invention, the invention is not limited to those specific embodiments. The forms of the invention shown and described herein are to be taken as illustrative only and other embodiments may be selected without departing from the scope of the present invention, as set forth in the claims appended hereto.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11220260 | Sep 2005 | US |
| Child | 11463249 | Aug 2006 | US |
