Patent Publication Number: US-10309362-B2

Title: Starter device for an internal combustion engine and handheld work apparatus having an internal combustion engine and said starter device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority of German patent application no. 10 2015 001 119.7, filed Jan. 29, 2015, the entire content of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a starter device for an internal combustion engine, having an actuating device which has to be set in rotation in order to start the internal combustion engine, and having an entrainer, which has at least one coupling device for coupling to a crankshaft of the internal combustion engine. The entrainer and the actuating device are mounted rotatably about a rotational axis and a damper spring is arranged in operative connection between the entrainer and the actuating device. The starter device has at least one stud, on whose outer periphery the damper spring is mounted. The damper spring is a hinge spring wound from a spring wire, wherein the spring wire, in a sectional plane containing the rotational axis, has a cross section, wherein the spring wire has in the cross section an axially measured width and a radially measured thickness. The spring wire has a radially inner-lying inner side and a radially outer-lying outer side. The cross section of the spring wire on the inner side of the spring wire is rounded. The invention further relates to a handheld work apparatus having an internal combustion engine and having a starter device. 
     BACKGROUND OF THE INVENTION 
     From EP 1 312 798 A2, a starter device for starting an internal combustion engine, which starter device has a damper spring, is known. One end of the damper spring is coupled to a rope pulley, and the other end of the damper spring is connected by a coupling device to a component that rotates with the crankshaft. The spring wire of the damper spring has a circular cross section. 
     It has been shown that starter devices having damper springs of circular cross section are comparatively insensitive to dirt. However, in the case of a circular cross-sectional area of the spring wire, the section modulus against bending is comparatively small, for instance, in relation to rectangular cross-sectional areas. In order to obtain the same spring constant, a damper spring of circular spring cross section must therefore have a larger outer diameter than a damper spring of rectangular cross section. A starter device having a damper spring of rectangular cross section is known, for instance, from U.S. Pat. No. 7,963,266. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a starter device having a robust structure and a low weight. A further object of the invention is to provide a handheld work apparatus having an internal combustion engine and having a starter device. 
     With respect to the starter device, this object is achieved by a starter device wherein at least a portion of the cross section of the spring wire on the outer side of the spring wire runs straight. With respect to the handheld work apparatus, the object is achieved by a handheld work apparatus having an internal combustion engine and having a starter device for the internal combustion engine, wherein the starter device includes an actuating device, which has to be set in rotation in order to start the internal combustion engine, and an entrainer, wherein the entrainer has at least one coupling means for coupling to a crankshaft of the internal combustion engine. The entrainer and the actuating device are mounted rotatably about a rotational axis and a damper spring is arranged in operative connection between the entrainer and the actuating device. The starter device has at least one stud, on whose outer periphery the damper spring is mounted. The damper spring is a hinge spring wound from a spring wire, wherein the spring wire, in a sectional plane containing the rotational axis, has a cross section. The spring wire in cross section has an axially measured width and a radially measured thickness. The spring wire has a radially innermost inner side and a radially outermost outer side and the cross section of the spring wire on the inner side of the spring wire is rounded and at least a portion of the cross section on the outer side of the spring wire runs straight. 
     For the damper spring of the starter device, at least a portion of the cross section of the spring wire on the outer side of the spring wire runs straight. As a result of the straight portion, the section modulus of the spring wire against bending is increased. Accordingly, a damper spring of smaller outer diameter can be used than is the case with a damper spring having the same spring constant and a round spring wire cross section. Since the cross section of the spring wire on the inner side of the spring wire is rounded, the attachment and compaction of dirt deposits on the inner side of the spring wire, and on the outer side of the at least one stud on which the damper spring is mounted, is avoided. If the damper spring performs movements in the direction of the rotational axis, then dirt deposits on the inner side of the spring wire, which are disposed between the spring wire and the stud, are removed and not compacted on the outer periphery of the stud. Due to the rounding on the inner side of the spring wire, a softer performance of the starter device in relation to a damper spring of rectangular cross section is achieved if the damper spring is pulled to the limit on the stud since the rounded cross section on the inner side promotes a slight deformation of the stud, whereby a higher elasticity of the arrangement is achieved. Since the damper spring is rounded on its inner side, damaging of the stud by innermost edges of the damper spring is avoided. 
     The terms “radially” and “axially” relate to the rotational axis of entrainer and actuating device. The radially measured thickness is thus measured parallel to the rotational axis, and the radially measured thickness is measured perpendicular to the rotational axis. 
     Advantageously, the inner side of the spring wire runs in a continuous radius. Advantageously, the radius of the inner side of the spring wire is larger than half the width of the spring wire. As a result of the enlarged radius compared with a spring wire of circular cross section, the section modulus against bending is increased, whereby the overall weight of the arrangement can be reduced yet the damping characteristics remain the same. 
     Advantageously, the portion in which the outer side of the spring wire runs straight extends over at least 30% of the width of the spring wire. Advantageously, the straight portion on the outer side of the spring wire extends over at least 50%, particularly preferably over at least 70% of the width of the spring wire. Therefore, a large increase in section modulus in relation to a spring of round cross section, and at the same time a small outer diameter and thus a low weight of the damper spring, is achieved. In the straight portion, the outer side of the spring wire here advantageously runs parallel to the rotational axis of the starter device. The spring wire advantageously has transverse sides running transversely to the rotational axis, wherein at least a portion of the cross section on the transverse sides of the spring wire runs straight. The transverse sides are that region of the cross section which connects the inner side and the outer side. The straight portion on the transverse sides of the cross section of the spring wire here advantageously runs perpendicular to the rotational axis of the starter device. As a result of the straight portion on the transverse sides, a good mutual lateral contact of adjacent coils of the damper spring is obtained. Sliding of adjacent coils one over another, as can occur in the linear contact of helical springs of round cross section, is thereby largely avoided. 
     At the transition of the outer side into the transverse sides, the cross section of the spring wire advantageously extends with a radius. The radius with which the outer side passes into the transverse sides is here advantageously markedly smaller than the radius on the inner side. Advantageously, the radius with which the outer side passes into the transverse sides is smaller than one-quarter of the width of the spring wire. The thickness of the spring wire, measured perpendicular to the rotational axis, is advantageously at least as large as the width of the spring wire, measured parallel to the rotational axis. Particularly advantageously, the thickness of the spring wire is greater than the width. Hence, an increased section modulus against bending, and thus a higher spring constant, with the same outer diameter of the damper spring is achieved. The weight of the starter device can thereby be kept small overall. 
     Advantageously, the entrainer and the actuating device have respective studs and the damper spring is disposed on the outer periphery of the two studs. The damper spring advantageously has a substantially constant coil diameter. Accordingly, a simple structure and a uniform damping effect over the whole of the starter path are obtained. The coil diameter here corresponds to the outer diameter of the damper spring. Advantageously, the damper spring is held with a first, inwardly bent end on the actuating device and with a second, inwardly bent end on the entrainer. A simple, compact structure of the arrangement is thereby obtained. In order largely to avoid the accommodation of dirt deposits on the outer periphery of the stud, it is advantageously provided that at least one stud has depressions on its outer periphery. Dirt, which has collected between the damper spring and the stud, can pass into the depressions. In this way, the working of the starter device is not impeded by the dirt deposits. 
     A simple structure is obtained if the at least one coupling means on the entrainer includes a pivotably mounted pawl, which, for the coupling of the starter device to the crankshaft of the internal combustion engine, cooperates with a cam contour, wherein the cam contour is connected in a rotationally secure manner to the crankshaft so as to rotate therewith. The actuating device is advantageously a rope pulley, which is manually set in rotation by a starter rope or pull rope. Advantageously, a plurality of pawls, in particular two pawls, are provided. 
     The starter device is advantageously intended for a handheld work apparatus having an internal combustion engine. 
    
    
     
       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; 
         FIG. 2  is a schematic section view through the motor-driven chain saw of  FIG. 1 ; 
         FIG. 3  is an exploded representation of the starter device of the motor-driven chain saw of  FIGS. 1 and 2 ; 
         FIG. 4  is a perspective view of the starter device of  FIG. 3 ; 
         FIG. 5  is a schematic of the coupling means of the starter device of  FIGS. 3 and 4 ; 
         FIG. 6  is a schematic through the starter device; 
         FIG. 7  is a schematic side elevation view of the studs of the starter device; 
         FIG. 8  is a section view showing the cross section of the spring wire of the damper spring of the starter device; and, 
         FIGS. 9 and 10  are schematics of embodiments of the cross section of the spring wire of the damper spring. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
       FIG. 1  shows a motor-driven chain saw as a work apparatus having a starter device. The motor-driven chain saw  1  is configured as a handheld, manually operated work apparatus and has a housing  2 , on which a rear handle  3  and a bale handle  4  are mounted. The motor-driven chain saw  1  has a guide bar  5  on which a saw chain  6  is rotatingly driven. Projecting from the housing  2  is a starter handle  7  of a starter device  8  shown schematically in  FIG. 2 . 
     As shown by  FIG. 2 , an internal combustion engine  10  is mounted in the housing  2  of the motor-driven chain saw  1 . The internal combustion engine  10  is advantageously configured as a two-stroke engine or as a mixture-lubricated four-stroke engine. The internal combustion engine  10  has a cylinder  11 , in which a piston  12  is reciprocatingly mounted. The piston  12  drives a crankshaft  13  rotatingly about a rotational axis  14 . In the embodiment shown, a fan wheel  9  is mounted on the crankshaft  13  and serves for moving cooling air for the internal combustion engine  10 . The starter device  8  is in engagement with the fan wheel  9  during the starting process, as is explained in greater detail below. On that side of the internal combustion engine  10 , which faces away from the fan wheel  9 , is disposed a centrifugal clutch  15 , which, when a structurally pregiven rotational speed is exceeded, connects the crankshaft  13  in a rotationally secure manner to a drive sprocket  16 . The drive sprocket  16  serves to drive the saw chain  6  ( FIG. 1 ). 
       FIG. 3  shows the assembly of the starter device  8  in detail. The starter device  8  comprises a rope pulley  18 , which is rotatably mounted in the housing  2  and is coupled by a return spring  17  to the housing  2 . The return spring  17  has an inner end  52 , which is held on the pulley  18 . The outer end of the return spring  17  is held on the housing  2 . The rope pulley  18  has a groove  19  for receiving a pull rope. On the side which projects into the housing  2 , on the rope pulley  18  is formed a receiving space  20  into which projects a stud  21 . The receiving space  20  is delimited by a roughly cylindrical peripheral wall  51 . The rope pulley  18  has a central opening  53 , which receives a bearing shaft (not shown in  FIG. 3 ). 
     As shown in  FIG. 8 , a damper spring  23 , configured as a hinge spring, is provided. A first end  26  of damper spring  23  is suspended from a wall portion  38 . The wall portion  38  is disposed on the base of the receiving space  20 . A second end  27  of the damper spring  23  is connected to an entrainer  24 . Between the rope pulley  18  and the entrainer  24  is disposed a disc  22  having an outer diameter (a). The entrainer  24  has an opening  54 , which likewise receives the bearing shaft. On the entrainer  24 , on the side facing away from the damper spring  23 , are provided two receptacles  28  for accommodating pawls  25 . The pawls  25  are pivotably mounted on the entrainer  24 . The damper spring  23  is disposed largely in the receiving space  20 . The receiving space  20  is largely closed off by the entrainer  24 . Penetration of dirt deposits into the receiving space  20  during operation can hence be largely avoided. 
       FIG. 4  shows the arrangement of the pawls  25  on the entrainer  24  in detail. As shown by  FIG. 4 , a bearing shaft  32  projects through the entrainer  24 . The entrainer  24  and the rope pulley  18  are rotatably mounted on the bearing shaft  32 . The bearing shaft  32  is fixed on the housing  2 . The pawls  25  have respective actuating lugs  35 . In the region of their mounting, the pawls  25  are surrounded by wall portions  31  of the entrainer  24 . Hence, the region of the mounting of the pawls  25  is protected from dirt. In addition, the wall portions  31  form a stop defining the outer pivoting position of the pawls  25 . As shown also by  FIG. 4 , the housing  2  has, adjacent to the starter device  8 , a multiplicity of cooling air openings  29 . Via the cooling air openings  29 , dirt deposits such as chips, dust or the like can also be sucked up during operation. Because of the peripheral wall  51 , the starter device  8  is largely protected from dirt deposits. The peripheral wall  51  is supported by radially outward projecting reinforcing ribs  30 . 
       FIG. 5  shows the arrangement of the actuating lugs  35  on a spring clip  33  fixed onto the bearing shaft  32 . In addition, a cam contour  34  of the fan wheel  9 , with which the pawls  25  cooperate during the starter process, is shown schematically. When the starter rope is pulled, the entrainer  24  rotates, in  FIG. 5 , in the clockwise direction. The actuating lugs  35  thereby move outwards in the spring clip  33  held by friction on the bearing shaft  32 . In this way, the pawls  25  are pivoted outward about their pivot axes  36 . In the outwardly pivoted position, the free ends of the pawls  25  enter into engagement with the cam contour  34  and thereby couple the entrainer  24  in a rotationally secure manner to the fan wheel  9  and the crankshaft  13  so as to rotate therewith. When the starter rope is retracted due to the return spring  17 , the entrainer  24  rotates in  FIG. 5  anti-clockwise. The pawls  25  are thereby pivoted back into the position shown in  FIG. 5  due to the actuating lugs  35  being directed inward in the spring clip  33 . 
     The assembly of the starter device  8  is shown in detail in  FIG. 6 . The bearing shaft  32  is fixed in the housing  2 . The bearing shaft  32  can, for example, be injection molded onto the housing  2 . The bearing shaft  32  includes a retaining bolt  40 , which has a groove  55  for accommodating the spring clip  33 . The rope pulley  18  has a lug  37 , which engages in the inner end  52  of the return spring  17  and thereby provides a rotationally secure connection between the inner end  52  of the return spring and the rope pulley  18 . In  FIG. 6 , a pull rope  43  is shown schematically in the groove  19  of the rope pulley  18 . Advantageously, one end of the pull rope  43  is held fixedly on the rope pulley  18 , and the other end is held on the starter handle  7  ( FIG. 1 ). 
     The stud  21  of the rope pulley  18  has an inner region  46 , which is journalled on the bearing shaft  32 , and an outer region  49 , on whose outer periphery the damper spring  23  is mounted. The outer region  49  has an outer diameter (c), which in the embodiment shown corresponds to the outer diameter (a) of the disc  22  ( FIG. 3 ). In the embodiment shown, the inner region  46  of the stud  21  has a shoulder  48 , on which the disc  22  is mounted. 
     The entrainer  24  has a stud  42 , which projects in the direction of the rope pulley  18 . The stud  42  has an outer region  50 , on whose outer periphery the damper spring  23  is mounted. The stud  42  has an inner region  47 , which serves for the rotatable mounting of the entrainer  24  on the bearing shaft  32 . Also, the inner region  47  of stud  42  lies with its end against the inner region  46  of the stud  21  adjacent to the outer periphery of the bearing shaft  32  in the embodiment shown. The stud  42  can also bear against the disc  22 , which for its part bears against the stud  21  of the rope pulley  18 . The bearing contact can here be provided against the inner regions ( 47 ,  46 ) or the outer regions ( 49 ,  50 ). As  FIG. 6  also shows, the stud  42  has a wall portion  39 , on which the second end  27  of the damper spring  23  is hooked into. The outer region  50  of the stud  42  has an outer diameter (b). Advantageously, the outer diameter (b) roughly corresponds to the outer diameter (c) of the outer region  49  of the stud  21  and to the outer diameter (a) of the disc  22  ( FIG. 3 ). 
     The damper spring  23  has a radially inner side  56  referred to the rotational axis  14 . This inner side  56  lies facing the studs  21  and  42 . The damper spring  23  also has radially outermost outer side  57 , which lies facing the peripheral wall  51  of the receiving space  20 . As shown by  FIG. 6 , the cross section of the spring wire of the damper spring  23  is configured such that it is rounded off on the inner side  56 . On the outer side  57 , the cross section has a straight region. The damper spring  23  has a coil diameter (f), which corresponds to the outer diameter of the damper spring  23 . 
     In  FIG. 6 , the fan wheel  9  is also shown schematically. The fan wheel  9  has a rim  41 , which is of roughly cylindrical configuration, which, between the peripheral wall  51  and the entrainer  24 , engages in the receiving space  20 , and on the inner side of which is configured the cam contour  34 . 
     During the starting operation, the damper spring  23  is tensioned when the pull rope  43  is pulled. The inner side  56  of the damper spring  23  can here be pulled as far as it will go onto the studs  21  and  42 . If the damper spring  23  is pulled to the limit, then, upon further pulling on the pull rope  43 , the tensile force is transmitted to the crankshaft  13  directly via the coupling device formed by the pawls  25  and the cam contour  34 . If the damper spring  23  is not pulled to the limit, then the force of the damper spring  23  and the force applied to the pull rope  43  by the operator act jointly on the crankshaft  13 . 
     For the avoidance of dirt deposits, the studs  21  and  42  have, on their outer side, a multiplicity of depressions ( 44 ,  45 ), as shown schematically in  FIG. 7 . The depressions ( 44 ,  45 ) can be configured, for instance, as grooves running parallel to the rotational axis  14 . 
     The damper spring  23  is wound from spring wire  58 .  FIG. 8  shows the cross section of the spring wire  58  of the damper spring  23  in detail.  FIG. 8  here shows a section through the spring wire in a plane containing the rotational axis  14 . In this section plane, the cross section of the spring wire  58  has a thickness (d), which is measured perpendicular to the rotational axis  14  ( FIG. 5 ), and a width (e), which is measured parallel to the rotational axis  14 . On the inner side  56 , the cross section of the spring wire  58  runs in a radius (r) which is greater than half the width (e). Hence the cross section of the spring wire  58  on the inner side  56  is flatter compared with a damper spring of circular cross section. On its outer side  57 , the spring wire  58  has a portion  61 , in which the cross section runs straight. The damper spring  23  is accordingly configured flattened on its outer side  57 . The straight portion  61  here extends over at least 30% of the width (e). In the embodiment shown, the straight portion  61  extends over approximately half the width (e). In the straight portion  61 , the outer side  57  here runs parallel to the rotational axis  14 . The spring wire  58  has transverse sides  59  and  60 , which run roughly perpendicular to the rotational axis  14  ( FIG. 6 ). The transverse sides  59  and  60  connect the inner side  56  to the outer side  57 . In the embodiment shown, the transverse sides  59  and  60  are configured in mirror symmetry to each other. The transverse sides  59  and  60  have respective straight portions  62 . The straight portion  62  advantageously extends over more than 30%, in particular over at least 50% of the thickness (d). The transverse sides  59  and  60  each extend over at a radius (s) into the outer side  57 . The radius (s) is markedly less than the radius (r) and can measure, for instance, 60%, in particular roughly 50% of the radius (r). The radius (s) is here advantageously less than half the width (e), in particular less than 30% of the width (e). 
       FIG. 9  shows an embodiment of a damper spring  63  having a spring wire  68 , which is intended for use in a starter device  8 . The configuration of the damper spring  63  substantially corresponds to that of the damper spring  23 . The spring wire  68  has an inner side  66  and an outer side  67 . On its inner side  66 , the spring wire  68  runs with a radius (r). Also in the embodiment of  FIG. 9 , the radius (r) is greater than half the width (e) of the spring wire  68 . The width (e) of the spring wire  68  here corresponds to the width (e) of the spring wire  58  from  FIG. 8 . The spring wire  68  has a thickness (g) which is less than the thickness (d) of the spring wire  58 . The thickness (g) roughly corresponds to the width (e). On its outer side  67 , the spring wire  68  has a straight portion  71 , which extends over at least 30%, in particular over at least 50% of the width (e). In the embodiment shown, the straight portion  71  extends over more than 70% of the width (e). The outer side  67  passes with a radius (t) into transverse sides  69  and  70  of the spring wire  68 . The radius (t) is markedly less than the radius (s) of the spring wire  58 . The radius (t) advantageously measures less than 20%, in particular less than 15% of the width (e). 
       FIG. 10  shows an embodiment of a damper spring  73 , which has a spring wire  78  and which is intended for use in a starter device  8 . The spring wire  78  has an inner side  76  and an outer side  77 , and transverse sides  79  and  80 . The outer side  77  is configured in accordance with the outer side  57  of the spring wire  58  and has a straight portion  61 , which passes with respective radii (s) into the transverse sides  79  and  80 . The transverse sides  79  and  80  have respective straight portions  82 , which run perpendicular to the rotational axis  14  ( FIG. 6 ). The straight portion  82  advantageously extends over more than 30% of the thickness (g), in the embodiment shown, over roughly 50% of the thickness (g). The thickness (g) roughly corresponds to the width (e). 
     The damper spring  73  occupies the same structural space as a damper spring whose spring wire has a circular cross section of diameter corresponding to the width (e) or the thickness (g). In relation to such a damper spring of circular cross section, the spring wire  78  has however a larger section modulus against bending due to the material accumulation on the outer side  77 . Due to the radius (r), which is greater than half the width (e), a flatter course of the rounding on the inner side  76  is additionally obtained. The damper spring  63  has, in relation to the damper spring  73 , an increased section modulus against bending, and hence a higher spring constant due to the smaller radius (t) and the larger width of the straight portion  71 . 
     The damper spring  23  too has a larger spring constant than the damper spring  73  due to the larger thickness (d). A desired spring constant can be set by an appropriate configuration of the cross-sectional form of the spring wire ( 58 ,  68 ,  78 ). Since the inner side ( 56 ,  66 ,  76 ) is of rounded-off configuration, the susceptibility to the formation of dirt on the inner side is reduced. As a result of the straight portions ( 62 ,  82 ) on the transverse sides ( 59 ,  60 ,  69 ,  70 ,  79 ,  80 ), adjacent coils, when they come to bear one against another, are in mutual contact not only linearly, but over a larger area. This prevents adjacent coils from sliding one over the other. 
     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.