Patent Publication Number: US-6701628-B2

Title: Guide bar for a portable handheld work apparatus

Description:
BACKGROUND OF THE INVENTION 
     A known guide bar includes guide plates on respective longitudinal sides of the guide bar in the region of the guide bar tip. The guide plates laterally extend beyond the guide paths formed by a guide groove in the guide bar. The radial projection of the guide plates with respect to the guide groove is so provided that the chain links of a saw chain are substantially laterally covered and only the cutting links of the saw chain extend beyond the edge of the guide plates. The saw chain is guided in the guide groove of the guide bar. In this way, it is ensured that the penetration depth of the cutting links into the material to be cut is reduced during plunge cutting work. Difficulties with respect to the manipulation during plunge cutting work are intended to be reduced thereby. 
     Too large a projection of the guide plates leads, however, to a reduction of the cutting power and plunge cutting work during tree maintenance is thereby hindered. On the other hand, if the projection of the guide plates (especially in the direction-changing region of the guide bar) is too low, then the manipulation of the motor-driven chain saw is made more difficult thereby. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a guide bar wherein the guidance of the saw chain is improved while maintaining a good cutting power during plunge cutting work and the guide bar can be used for saw chains of different configuration. 
     The guide bar of the invention is for a portable handheld work apparatus including a motor-driven chain saw or overhead branch cutter, the guide bar being for a saw chain including cutting links, lateral connecting links and center drive links pivotally connected to each other via rivets or pins with the drive links having respective rakers formed thereon. The guide bar includes: an elongated planar base body defining an outer periphery wherein a peripheral guide groove is provided for receiving the rakers therein and for guiding the saw chain along the outer periphery; the guide bar having guiding surfaces along the outer periphery for supporting the lateral connecting links and the cutting links and the guiding surfaces being separated from each other by the guide groove; the guide bar having a direction-changing section at the outer free end thereof for guiding the saw chain over the outer free end of the guide bar; guide plates mounted on the base body in the direction-changing section and extending radially beyond the guiding surfaces to laterally cover the connecting links and the cutting links of the saw chain; an idler sprocket rotatably mounted in the direction-changing section; the guide plates being configured as rotating left and right guide discs and the guide discs being connected to the idler sprocket so as to rotate therewith; and, the left guide disc having a set of radially projecting first sections and the right guide disc having a set of radially projecting second sections arranged offset with respect to corresponding ones of the first sections. 
     According to the invention, the guide plates in the direction-changing section (at the tip of the guide bar) are configured as rotating guide discs and are connected to the idler sprocket so as to rotate therewith. In this way, a reliable guidance of the guide bar on a motor-driven chain saw or an overhead branch cutter is combined with good cutting power with the aid of the guide plates on the guide bar. In lieu of a circularly-shaped edge, the guide discs include sections which project radially and each cutting link of the saw chain comes partially into overlapment with a radially projecting section. The radially projecting sections can have an outline which is rectangular, rhombic, trapezoidal or define a polygon in another manner. 
     The left and right guide plates on the direction-changing section of the guide bar alternately overlap a cutting link because of the arrangement of the radially projecting sections offset in the running direction. The cutting links each have a front cutting edge running essentially radially and this cutting edge has a contour laterally offset to the outside referred to the running direction of the saw chain and therefore projects axially beyond the outer surfaces of the guide discs in the region of the cutouts between the radially extending sections. Referred to the running direction of the saw chain, a depth limiter is positioned ahead of the front cutting edge. It can be advantageous to so arrange the radially projecting sections that they axially overlap the depth limiter. Alternatively to this, it is, however, also possible to so place the saw chain that the depth limiters are disposed in the region of a radial edge of the radially projecting section of the opposite-lying guide disc. The radial edge runs ahead when viewed in the peripheral direction. With the above-mentioned constructive measures, the function of the depth limiter as an element, which limits the penetration depth of the particular cutting link, is supported by the arrangement of one of the radially projecting sections to the depth limiter and the manipulation of the saw chain is simplified. On the other hand, the cutting power of each front cutting edge is not hindered by the radially projecting sections and therefore a good cutting power especially in plunge cutting operations is ensured. 
     Difficulties with respect to the manipulation of the guide bar during plunge cutting work do not occur when the radially projecting sections (measured in the peripheral direction of the guide discs) are spaced so far on a particular guide disc that two cutting links partially and one connecting link can come to lie in the cutout between each two radially projecting cutouts. It is practical to so arrange the edges of the radially projecting sections that the edges are angled so as to depart from the perpendicular. Perpendiculars are here understood to be center perpendiculars of the guide discs and parallels to the center perpendiculars of the guide discs. It is seen as practical to configure the cutouts between the radially projecting sections of each guide disc in the peripheral direction approximately as long as the width of the radially projecting sections. To make possible uniform plunge cutting work with the guide bar, it is practical to end the edge of the guide discs with a slight spacing radially below a roof cutting edge of the cutting link. 
     The idler sprocket is surrounded on both sides by side plates in the direction-changing section. These side plates radially project beyond the idler sprocket and axially guide the latter. In each side plate, a bearing is provided for rotatably journalling the idler sprocket and the guide discs which run with the idler sprocket. The guide discs are preferably connected to the idler sprocket so as to rotate therewith and are driven by the movable saw chain. Preferably, the guide discs are fixed at the direction-changing section of the guide bar so as to be exchangeable and can be exchanged with the saw chain. 
     It is practical to provide each guide disc with three or even two radially projecting sections. To be able to use conventional saw chains in combination with the guide bar, it is practical to configure the idler sprocket with a number of teeth which amounts to four times the number of radially projecting sections. In an advantageous embodiment, the idler sprocket has eight or twelve teeth. It can be practical to so configure the guide bar that it can be turned over. For this purpose, the guide discs are configured in their basic outline to be axially symmetrical. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described with reference to the drawings wherein: 
     FIG. 1 is a schematic side elevation view of a motor-driven chain saw equipped with a guide bar according to the invention; 
     FIG. 2 is a side elevation view of the end portion of the guide bar of FIG. 1; 
     FIG. 3 is a perspective view of the end portion shown in FIG. 2; 
     FIG. 4 is a variation of the embodiment shown in FIG. 3; 
     FIG. 5 is a partial cutaway view of the end portion shown in FIGS. 2 and 3; 
     FIG. 6 is an exploded view of the end portion of the guide bar shown in FIG. 3; 
     FIG. 7 is a view of a variation of the end portion of a guide bar according to the invention; and, 
     FIG. 8 is an enlarged view of the end portion of the guide bar of FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     FIG. 1 is a schematic view of a portable handheld work apparatus  2  which is shown here as a motor-driven chain saw  3 . A guide bar  1  for a saw chain  6 , which runs thereon, is fixed to the housing  36  of the motor-driven chain saw  3 . The guide bar  1  is clamped with an attachment end  37  between a sprocket-wheel cover  38  and the housing  36  and is configured essentially of an elongated flat base body  4 . The saw chain  6  is driven by a drive motor  39  of the motor-driven chain saw  3  in the running direction  40 . The drive motor is an internal combustion engine having a reciprocating or rotating piston and is driven in accordance with a two-stroke method or four-stroke method. 
     As shown in FIGS. 2 to  8 , the saw chain  6  comprises connecting links  9 , which are configured as simple side links  41 , and cutting links  8 . Each cutting link  8  includes a front cutting edge  21  which, referred to the running direction  40  of the saw chain  6 , is offset laterally toward the outside. Each cutting link  8  also includes a roof section  42  having a roof cutting edge  32  with the roof section  42  being angled to the center drive link  7 . A depth limiter  23  is provided on the cutting link  8  in running direction  40  ahead of the roof cutting edge  32 . A guide groove  5  is provided in the outer periphery of the guide bar  1  and rakers  11  of the center drive links  7  engage therein. The center drive links  7  as well as the lateral connecting links  9  are pivotally connected to each other with the aid of pins  10 . The pins  10  are configured as rivets in the embodiment shown. The cutting links  8  (especially the front cutting edges  21  of the cutting links  8 ) are arranged alternately on the right and left longitudinal sides of the saw chain  6 . 
     The connecting links  9  glide with their foot sections  43  on the guide surfaces  12  which are arranged on the outer periphery  44  of the guide bar  1  on both longitudinal sides of the guide groove  5 . A left guide plate  15  and a right guide plate  16  in the form of rotating guide discs  17  and  18  are provided on the direction-changing section  14  of the free end or tip  13  of the guide bar. The rotational axis  45  of the guide discs ( 17 ,  18 ) lies on the longitudinal center axis  46  of the guide bar  1 . The guide discs ( 17 ,  18 ) are connected to an idler sprocket  19  so as to rotate therewith and are rotatably entrained by the running saw chain  6 . 
     As shown in FIG. 1, the attachment end  37  of the guide bar  1  includes a longitudinal slot  47  lying on the longitudinal center axis  46 . Clamping bolts, which lie fixedly in the housing  36  of the motor-driven chain saw  3 , extend through the longitudinal slot  47  when fixing the guide bar  1  on the housing  36 . The motor-driven chain saw  3  is guided and held with a forward handle  48  extending over the housing  36  as well as a rearward handle  49 . A hand guard  50  is assigned to the forward handle  48  for protecting an operator of the chain saw  3 . A safety-braking device is activated via the hand guard  50  and brings the saw chain  6 , which runs in the direction of arrow  40 , to standstill in fractions of a second in order to protect the operator against the action of the moving saw chain  6 . A throttle lever  51  is provided in the rearward handle  49  in the grasping region of a hand of the operator and a throttle lever latch  52  is assigned thereto. 
     The direction-changing section  14  of the guide bar  1  is formed of two side plates ( 33 ,  33 ′) as shown in FIGS. 3 and 6. The idler sprocket  19  is mounted between the two side plates ( 33 ,  33 ′) and is configured similarly to a toothed wheel. The rakers  11  of the drive links  7  engage in respective gaps  53  between each two mutually adjacent teeth  35  of the idler sprocket  19 . The outer edges of the side plates ( 33 ,  33 ′) define the guide surface  12  at the direction-changing section  14 . The side plates ( 33 ,  33 ′) are attached to the base body  4  of the guide bar  1  and have respective bearings ( 34 ,  34 ′) which are held in respective bearing holders ( 54 ,  54 ′) of the side plates ( 33 ,  33 ′). This is shown especially in FIGS. 5,  6  and  8 . The base body  4  of the guide bar  1  can be made of solid material (see FIGS. 5 and 6) or can be configured in a light configuration having corresponding cutouts  55  (see FIG.  8 ). 
     The guide discs ( 17 ,  18 ) of the guide bar  1  are configured to have identical outlines. The left guide disc  17  and the right guide disc  18  are arranged on respective outer sides of the side plates ( 33 ,  33 ′) which face away from the idler sprocket  19 . The holders ( 54 ,  54 ′) for the respective bearings ( 34 ,  34 ′) are open toward the respective side plates discs ( 33 ,  33 ′). Each bearing ( 34 ,  34 ′) has an opening  56  for accommodating rivets  63 . 
     As shown schematically in FIG. 6, a particular rivet  63  engages through an opening  57  of the guide discs ( 17 ,  18 ), an opening  56  of the bearings ( 34 ,  34 ′) and a corresponding opening  58  in the idler sprocket  19  as well as a next opening  56  in the bearing  34 ′ of the side plate  33 ′. The rivets  63  project axially beyond the bearing  34 ′ and engage through a correspondingly assigned opening  57  in the guide disc  18  so that the guide discs ( 17 ,  18 ) are connected so as to rotate with the idler sprocket  19 . The idler sprocket  19  accommodates the raker  11  of a drive link  7  in each gap  53  in correspondence to its tooth pitch and the guide discs ( 17 ,  18 ) are connected in specific positions with the idler sprocket  19  so as to rotate therewith. For this reason, a relative movement between the saw chain  6  and the guide discs ( 17 ,  18 ) is reliably prevented. 
     The guide discs ( 17 ,  18 ), which are shown in FIGS. 2 to  6 , each have three radially projecting sections ( 20 ,  20 ′). The number of teeth  35  of the idler sprocket  19  is twelve in FIGS. 2 to  5 . As shown in FIGS. 2 to  5 , each depth limiter  23  of a cutting link  8  is alternately covered in the axial direction of the rotational axis  45  by a radially projecting section  20  of the left disc  17  and a radially projecting section  20 ′ of the right guide disc  18 . The guide discs ( 17 ,  18 ) move on the outer sides of the side plates ( 33 ,  33 ′) when viewed in the axial direction and project radially beyond the particular guide surfaces  12  of the side plates ( 33 ,  33 ′). The sections  20  of the guide disc  17  are arranged offset to the sections  20 ′ of the guide disc  18  referred to the peripheral direction  28 . The sections  20 ′ are arranged in the center of a cutout  24  between two sections  20 . 
     As shown in FIGS. 3 and 6, the front cutting edge  21  projects through a corresponding cutout  24  between the radially projecting sections ( 20 ,  20 ′) and extends axially beyond the outer surfaces  22  of the guide discs ( 17 ,  18 ) so that the cutting width is somewhat greater than the thickness of the guide bar in the region of the guide discs ( 17 ,  18 ). The front cutting edge  21  projects in this manner because of its cropped form viewed in cross section. In the embodiments shown in FIGS. 2 to  6 , a cutting link  8  comes to lie in a corresponding cutout  24  of a guide disc ( 17 ,  18 ) when viewed in the running direction of the saw chain  6 . The width L (FIG. 2) of the cutout  24  between the radially projecting sections ( 20 ,  20 ′) is in the peripheral direction approximately the same size as the width B of the radially projecting sections ( 20 ,  20 ′) in the peripheral direction  28 . The maximum radius R of the guide discs ( 17 ,  18 ) is so selected that the edge  30  of the guide discs ( 17 ,  18 ) ends at only a small distance  31  radially below the path traveled by the roof cutting edge  32  (see FIGS.  5  and  8 ). The roof cutting edge and front cutting edge of the cutting link  8  laterally project over the edge  30  of the guide discs so that the lateral cut also takes place in the direction-changing section  14  by a cutting tooth  60  of the cutting link  8 . The radially running edges ( 25 ,  26 ) of the radial sections  20  are advantageously configured to be at an angle from the perpendicular  27  or a parallel  61  to the perpendicular  27 . The radial edges ( 25 ,  26 ) extend in the radial direction viewed from the rotational axis  45  to the perpendicular  27  at an angle  62  of &lt;15°, preferably approximately 2° to 5°. The offset arrangement of the cutting links  8  or cutting teeth  60  (when viewed in the peripheral direction  28  and in the running direction  40 ) can be achieved in a simple manner in that the saw chain  6  is placed offset by one tooth  35  of the idler sprocket as shown by a comparison of FIGS. 3 and 4 to each other. In this way, an arrangement with cutting links  8  can be configured whose depth limiter  23  is disposed in the region of the leading edge  25  of the section ( 20 ,  20 ′) (see FIG. 3) or, however, the depth limiter comes to lie in the center region of the cutouts ( 20 ,  20 ′) of the opposite-lying guide disc ( 17 ,  18 ) and is covered thereby (see FIG.  4 ). It can also be practical to configure the radially extending edges ( 25 ,  26 ) of the radially projecting sections  20  as cutting edges. In this way, the guide bar  1  can be turned over and, on the other hand, the chip-producing power of the saw chain  6  is favorably influenced. 
     In all of the embodiments shown, the guide discs ( 17 ,  18 ) are driven by the moved saw chain  6 . 
     The guide discs in FIGS. 2 to  6  each have three radially projecting sections  20  and an idler sprocket  19  whose tooth count can be divided by four; thus, the teeth count of the idler sprocket  19  is twelve teeth  35 . The guide discs ( 17 ,  18 ) of the guide bar, which is shown in FIGS. 6 and 7, each have two radially projecting sections  20  and are driven by an idler sprocket  19  whose teeth count is, in turn, dividable by four; thus, the idler sprocket  19  is driven with eight teeth  35  via the moved saw chain  6 . 
     If a guide bar configured in accordance with the invention is plunged with the free end  13  into wood as it is necessary, for example, with tree maintenance, then too great a depth of penetration of the roof cutting edge  32  into the wood is reliably prevented by the radially projecting sections  20 . 
     It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.