Trimmer head for use in flexible line rotary trimmers having improved line loading mechanism

#The present invention relates to an improved trimmer head for use in flexible line rotary trimming devices used to trim grass, weeds and other vegetation. More particularly, the invention is directed to an improvement in the line loading of both “bump-feed” type trimmer heads such as those disclosed in U.S. Pat Nos. 4,458,419 and 4,959,904 and the more simple manually operated heads such as that disclosed in U.S. Pat. No. 4,145,809, the contents of said patents being incorporated herein by reference as though fully set forth below.

#Trimmer heads used in flexible line rotary trimmers generally carry one or two lengths of flexible nylon cutting line wrapped about an interior spool with the ends of the line or lines projecting outwardly through opposed apertures in the side wall of the trimmer head. The head is threadably mounted on the end of an elongated shaft and rotated at a high velocity by a gas or electric motor so that the ends of the cutting line project radially from the head and sever weeds or other vegetation. When cutting line projecting from the head breaks off or becomes overly worn, it must be severed and fresh line extended from the spool through the line outlet eyelets in the side of the housing. Bump-feed type heads include a line feed-out mechanism which responds to a bump on the ground intentionally applied by the operator to feed out a measured length of fresh cutting line which is typically cut to the desired length by a knife blade projecting from a shield attached to the trimmer above the cutting head and spaced a predetermined distance from the perimeter of the trimmer head housing. Manual heads do not include any such line feed-out mechanism. A fastening nut that holds the housing portion of the trimmer head to the spool must be loosened so that the spool can be separated from the housing and manually rotated relative to the housing to pay out additional cutting line. The spool and housing are then re-secured by the fastening member.

#In both bump-feed and manual heads, the length or lengths of cutting line are typically wound onto the spool by hand. As most cutting heads employ two lengths of line projecting from opposed sides of the cutting head, care must be taken during the winding of the spool to avoid crossing or otherwise tangling of the two lines within the spool which interferes with the paying out of fresh line. This is particularly important in bump-feed heads where centrifugal force is utilized to pull the new lengths of line from the spool during use as the head is being bumped against the ground as any line tangle will interfere with the proper feeding of the line. Difficulty in properly loading the line on the spool is the most common complaint of home users of flexible line trimmers. It also is a time consuming task for the professional user.

#FIG. 1 is a perspective view of a first embodiment of the trimmer head of the present invention shown secured to the drive bolt of a rotary trimmer.

#FIG. 2 is an exploded perspective view of the various elements comprising the embodiment of the trimmer head of the present invention illustrated in FIG. 1.

#FIG. 3 is a cross-sectional view of the trimmer head housing of the present invention taken along line 3-3 in FIG. 2.

#Referring now in detail to the drawings, a first embodiment of a bump-feed type trimmer head 10 of the present invention is shown in FIG. 1 mounted on the extended end of a rotatable drive shaft 12 on a gasoline or electric powered rotary trimmer (not shown). The trimmer head 10 generally comprises a housing 14, a spool 16 for carrying one or more lengths of coiled monofilament nylon cutting line 17, a cam member 18, a cam follower 20, a coil spring 22, a drive bolt 24 and a retaining nut 25. The trimmer housing 14 is preferably formed by injection molding a nylon 6 copolymer and defines a circular upper wall 26, a cylindrical depending skirt 28 and a centrally disposed tubular extension 30 depending from upper housing surface 26 into the interior of the housing about the central axis of rotation “Y” of the head. The tubular extension 30 in the trimmer head housing 14 defines an annular outer shoulder 32 for coil spring 22 and an axial channel 34 through which the drive bolt 24 extends. Channel 34 is configured to create a mating fitment with both the drive bolt 24 and cam member 18. The upper end portion 36 of channel 34 is preferably square in cross-section; the central portion 38 is of a constant radius and the lower portion 40 is hexagonal in cross-section.

#As seen in FIGS. 2 and 9, the drive bolt 24 defines a square head portion 24a which is received within the correspondingly configured upper portion 36 of channel 34, a cylindrical body portion 24b that extends through the central cylindrical portion 38 of channel 34, and a lower shaft portion 24c that projects from the larger diameter body portion 24b and extends through and projects from the lower hexagonal portion 40 of channel 34. The drive bolt also defines an internally threaded cylindrical bore 24d extending axially through the head portion 24a and a substantial part of central portion 24b for threaded engagement with the drive shaft 12 of the trimmer. Thus, with the drive bolt 24 disposed in channel 34 and in threaded engagement with the drive shaft 12, rotation of the drive shaft imparts corresponding rotation to the drive bolt 24 and housing 14 due to the interference fit between the square head portion 24a of the drive bolt and the upper portion 36 of channel 34 defined by housing extension 30.

#It should be noted that the head portion of the drive bolt and the cross-section of the upper portion of the axially depending tubular member could be formed of shapes other than square to form the desired interference fit. For example, they could both be hexagonally shaped and rotation of the drive bolt would still be imparted to the trimmer head.