Abstract:
A spark plug guard can be switched between a spark-plug covering position to protect a spark plug and a spark-plug opening position. An operator displaces the spark plug guard from the spark-plug covering position to the spark-plug opening position, thereby obtaining a wide working space to perform the maintenance and inspection of the spark plug efficiently. The spark plug guard has a function of fixing a predetermined part in the spark-plug covering position. Consequently, the need for a part fixing member which was conventionally required for fixing the predetermined part to the engine body is eliminated, thus contributing to a decrease in the weight of the whole internal combustion engine and to cost reduction.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a power working machine equipped with an internal combustion engine having a spark plug. The present invention also concerns a spark plug guard for protecting the spark plug. 
   2. Description of the Related Art 
   Some portable working machines such as brush cutters and hedge trimmers are equipped with an internal combustion engine, such as a small air-cooled two-stroke cycle gasoline engine, as a prime mover for driving a cutting blade (a working member). The internal combustion engine has a spark plug at the head of a cylinder constituting the engine body. The terminal of the spark plug projecting outward from the cylinder head is covered with a detachable plug cap, to which an ignition high-tension lead is connected, for protection. 
   In order to protect the spark plug perfectly, it is preferable to provide a spark plug guard for covering above the plug cap. This is for the purpose of preventing damage to the spark plug by the contact of the plug cap with articles during transportation of the portable working machine by track or the like, during depositing in storage, or during replacement of the cutting blade with the internal combustion engine placed upside down on the ground. 
   However, if the spark plug guard is secured to the engine body with screws and so on, troublesome detachment work of the spark plug guard is required during maintenance of the spark plug, thus resulting in a decrease in workability. 
   Also, if a part designed specifically for protection of the spark plug is mounted to the engine body, the machine increases in weight correspondingly, thus going against the demand for compact and lightweight portable working machines and causing an increase in cost. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in consideration of the foregoing problems. Accordingly, it is an object of the present invention to provide a power working machine and a spark plug guard capable of contributing to an increase in maintenance workability of a spark plug, weight reduction of the entire internal combustion engine, and cost reduction. 
   In order to attain the above object, a power working machine according to the present invention is equipped with an internal combustion engine having a spark plug, comprising a spark-plug guard capable of switching between a spark-plug covering position to cover the spark plug for protection and a spark-plug opening position to be apart from the spark plug to facilitate access to the spark plug, the spark plug guard having a part fixing function of fixing a predetermined part to a body of the internal combustion engine in the spark-plug covering position. 
   According to the present invention, during the maintenance of the spark plug, an operator displaces the spark plug guard from the spark-plug covering position to the spark-plug opening position. Therefore, the covered state of the spark plug by the spark plug guard is easily released to provide a wide working space, thus facilitating maintenance and inspection of the spark plug. 
   The spark plug guard also includes a function of fixing the predetermined part in addition to a function of protecting the spark plug. Therefore, fitting means, which were necessary for securing the predetermined part to the engine body, become unnecessary, so that the entire internal combustion engine can be reduced in weight and cost. 
   The spark plug guard may be arranged on either side of the engine body and the predetermined part. 
   The way of displacement of the spark plug guard may be of slide type, rotation type, pivot type, draw type and so on. 
   As a preferable embodiment, the spark plug guard may comprise an attachment section to either one of the engine body and the predetermined part; and an engagement section engageable with the other one of the engine body and the predetermined part. In this case, when the spark plug guard is attached to either one of the engine body and the predetermined part and the engagement section is attached to the other one of the engine body and the predetermined part, the spark plug guard is brought into the spark-plug covering position, thereby fixing the predetermined part to the engine body. 
   As a preferable embodiment, the predetermined part may be fixed to the engine body via a toggle mechanism. With such an arrangement, the predetermined part can easily be fixed by the spark plug guard, and also the fixed state is stable; thus, it is preferable. 
   As a preferable embodiment, the predetermined part may be a cleaner cover for covering an air cleaner of the internal combustion engine. With such an arrangement, since relatively frequent opening and closing operation of the cleaner cover can quickly be performed with less effort, the maintenance and inspection of the air cleaner can also be performed efficiently. 
   As a preferable embodiment, the spark plug guard may further comprise a finger hole for an operator to engage the finger therewith in displacement from the spark-plug covering position to the spark-plug opening position. With such an arrangement, the operator (worker) can easily switch the position of the spark plug guard, and the spark plug guard itself is reduced in weight; thus, it is more preferable. 
   As a preferable embodiment, the finger hole may face a plug cap put on the spark plug in the spark-plug covering position. In this case, the finger hole serves as an air-circulating channel toward the plug cap, providing a cooling effect of the spark plug; thus, it is more preferable. 
   As a preferable embodiment, the finger hole may be arranged in the position for a tool inserted therethrough to be able to reach a control section of a carburetor of the internal combustion engine. With such an arrangement, the spark plug guard does not obstruct the operation of controlling the flow rate of the fuel in the carburetor; thus, it is preferable. 
   As a preferable embodiment, the internal combustion engine may comprise an engine cover including a first cover and a second cover joined with each other, the first cover including the spark plug guard, the spark plug guard including an engagement section to the second cover for bringing the engagement section into engagement with the second cover, and the spark plug guard being displaced to the spark-plug covering position, so that the first cover and the second cover being joined with each other. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a general perspective view of a brush cutter as an example of a power working machine according to an embodiment of the present invention; 
       FIG. 2  is a partly cutaway enlarged view seen from the direction of arrow II of  FIG. 1 , showing essential parts of an internal combustion engine; and 
       FIG. 3  is a general perspective view of a spark plug guard in FIG.  2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a portable brush cutter  1  as a working machine according to an embodiment of the present invention includes a rotary cutting blade  3  as a power working member at the front end  2   a  of an operating rod  2  extending longitudinally, and includes an internal combustion engine such as a small air-cooled two-stroke cycle gasoline engine  4  at the rear and  2   b  of the operating rod  2 . The driving force by the internal combustion engine  4  is transmitted to the cutting blade  3  via a transmission shaft  5  extending through the operating rod  2 . An appropriate type of centrifugal clutch  6  is interposed between the internal combustion engine  4  and the transmission shaft  5 . When the rotation speed of the internal combustion engine  4  exceeds a certain value, the rotation driving force is outputted to the cutting blade  3 . 
   The operating rod  2  has a hanging ring  7  near the rear end  2   b.  An operator can hold the brush cutter  1  on his/her shoulder in a balanced manner by hanging a shoulder belt (not shown) on the hanging ring  7 . 
   The operator holds front and rear grips  8  and  9  made of rubber or the like and attached on the operating rod  2  with hands, and cuts the grass while operating a throttle lever  10  arranged at the front of the rear grip  9  and swinging the front end  2   a  of the operating rod  2  from side to side. 
   Referring to  FIG. 2 , the internal combustion engine  4  is equipped with an engine body  14  including a cylinder  11 , a carburetor  12 , an air cleaner  13 , a crank casing (not shown); and an engine cover  15  for covering the periphery of the engine body  14 . The cylinder  11  has a spark plug  16  attached to a head  11   a  thereof. An end  17  near the terminal of the spark plug  16  extends outwardly and diagonally upward from the cylinder  11 , to which a plug cap  18  made of rubber or the like and connecting to an ignition high-tension lead (not shown) is fitted. 
   Air that was purified with the air cleaner  13  is mixed with lubricant-containing fuel atomized by the carburetor  12  and is supplied to the cylinder  11  regularly by reciprocating slide motion of a piston (not shown) placed in the cylinder  11 . 
   The engine cover  15  is formed of a combination of covers integrally molded of a synthetic resin material having appropriate heat resistance and strength. For example, the engine cover  15  has a body cover  19  for covering the cylinder  11  and the periphery as a main body, a carburetor cover  20  for mainly covering the carburetor  12 , and a cleaner cover  21  for covering the air cleaner  13  held by the carburetor cover  20 . In this embodiment, the carburetor cover  20  is joined to the body cover  19  that is a first cover which is attached directly to the engine body  14 ; and the cleaner cover  21  that is a second cover is joined to the carburetor cover  20 . 
   The body cover  19  includes a fixed guard  23  for covering an opening-side half  18   a  of the plug cap  18 . The fixed guard  23  covers above the plug cap  18  together with a spark plug guard  25  having a moving guard  24  to protect the spark plug  16  in cooperation with the spark plug guard  25 . 
   The spark plug guard  25  has a protecting function for the spark plug  16  and a part fixing function of fixing a predetermined part of the internal combustion engine  4 , such as the cleaner cover  21 , to the engine body  14 . The spark plug guard  25  can be switched between a spark-plug covering position P 1  to cover the spark plug  16  for protection and a spark-plug opening position P 2  to be apart from the spark plug  16  to facilitate access to the spark plug  16 . The cleaner cover  21  is fixed to the engine body  14  in the spark-plug covering position P 1 . 
   In other words, the spark plug guard  25  serves as a spark-plug protecting member and also as a part-fixing member. Therefore, the spark plug guard  25  serving as a part fixing member can freely be switched between the spark-plug covering position P 1  to fix the cleaner cover  21  to the engine body  14  and the spark-plug opening position P 2  to cancel the fixed state of the cleaner cover  21  to the engine body  14 . The moving guard  24  of the spark plug guard  25  covers the spark plug  16  in the spark-plug covering position P 1  for protection, and is separated from the spark plug  16  to secure a wide working space, thus facilitating access to the spark plug  16 . 
   In this embodiment, the spark plug guard  25  is pivotally attached to and supported by the carburetor cover  20  constituting the first cover together with the body cover  19 . 
   More specifically, referring to  FIGS. 2 and 3 , the spark plug guard  25  is molded in one piece of an appropriate synthetic resin material having low heat conductivity, and includes a main body  27  having a pair of bearing brackets  26 ,  26  facing each other at the lengthwise center thereof, the moving guard  24  formed at one end of the main body  27 , and an engagement claw  28  formed at the other end of the main body  27  and engageable with the cleaner cover  21 . Each of the pair of bearing brackets  26 ,  26  has a bearing hole  30  for relatively rotatably receiving a horizontal first pivot shaft  29 . 
   As shown in  FIG. 2 , the first pivot shaft  29  is integrally joined to a second pivot shaft  32  extending in parallel with the first pivot shaft  29  via a joining piece  31 . The second pivot shaft  32  is fitted in a bearing  33  of the carburetor cover  20  and is supported relatively rotatably. The first pivot shaft  29  can pivot within a predetermined angle while maintaining a certain relative distance from the second pivot shaft  32 . Therefore, the spark plug guard  25 , which is relatively rotatably supported on the first pivot shaft  29  in the pair of bearing brackets  26 ,  26  serving as attachment sections, can pivot around the first pivot shaft  29  and also around the second pivot shaft  32 . 
   The spark plug guard  25  can be formed by an appropriate material such as the synthetic resin having sufficient rigidity to protect the spark plug  16  and elasticity required to work as a toggle latch, which will be described later. 
   On the other hand, the cleaner cover  21  that is a second cover includes, at the upper part, an engagement receiving section  34  engageable with the engagement claw  28  of the spark plug guard  25 . The cleaner cover  21  has a hook-shaped engagement section  35  at the lower end, which is in engagement with a cleaner-cover pivot shaft  36  formed at the lower end of the carburetor cover  20 ; thus, the upper end can pivot around the cleaner-cover pivot shaft  36 . 
   In order to bring the cleaner cover  21  in intimate contact with the carburetor cover  20  of the engine body  14 , the spark plug guard  25  is appropriately rotated around the first pivot shaft  29  and the second pivot shaft  32  with the cleaner cover  21  closed, and the engagement claw  28  is brought into engagement with the engagement receiving section  34  of the cleaner cover  21 . Then, while maintaining the engaging state, the moving guard  24  of the spark plug guard  25  is rotated downwardly. Thus, the spark plug guard  25  pivots around the first pivot shaft  29  and the second pivot shaft  32  clockwise in  FIG. 2  to move the first pivot shaft  29  over line L (dead center) that connects the second pivot shaft  32  and the engagement receiving section  34  of the cleaner cover  21 , where the direction of the reactive force is reversed, thereby being self-locked in the spark-plug covering position P 1  shown by an imaginary line in  FIG. 2  (a toggle mechanism). The spark plug guard  25  connects the cleaner cover  21  to the carburetor cover  20  in the spark-plug covering position PI. More specifically, the spark plug guard  25  fixes the cleaner cover  21  as a toggle latch to the carburetor cover  20  while sandwiching the air cleaner  13  therebetween. 
   When the spark plug guard  25  is in the spark-plug covering position P 1 , the moving guard  24  is positioned above a closing-side half  18   b  of the plug cap  18 . More specifically, the moving guard  24  covers above the plug cap  18  together with the fixed guard  23  formed at the upper part of the body cover  19  to protect the spark plug  16  in cooperation with the fixed guard  23 . Accordingly, direct collision of an article M such as a floor and other equipment with the plug cap  18  can be prevented during cutting work or transportation and housing of the brush cutter  1 ; thus, damage to the spark plug  16  can be prevented and the operator can be protected from heat and high voltage supplied to the spark plug  16  during the operation of the internal combustion engine  4 . 
   During the maintenance of the spark plug  16 , the operator switches the spark plug guard  25  from the spark-plug covering position P 1  to the spark-plug opening position P 2 . Thus, the moving guard  24  is widely separated from the spark plug  16  to release the covered state of the spark plug  16  with the spark plug guard  25  easily, thus facilitating maintenance and inspection of the spark plug  16 , such as detaching the plug cap  18 , using a wide working space thus obtained. 
   The spark plug guard  25  also has a function of joining the cleaner cover  21  to the carburetor cover  20  in addition to a function of protecting the spark plug  16 . Therefore, exclusive parts such as screws for securing the cleaner cover  21  to the engine body  14  are not necessary, so that the entire internal combustion engine  4  can be reduced in weight and cost. 
   Furthermore, according to this embodiment, since it is easy to change the position of the spark plug guard  25  serving as a fixing bracket, the cleaner cover  21  can quickly be opened and closed with less effort as compared with a case by the conventional fixing method using screws and so on. Accordingly, the maintenance and inspection of the air cleaner  13  can also be performed efficiently. 
   Also, since the cleaner cover  21  is fixed to the carburetor cover  20  via the spark plug guard  25  and the toggle mechanism, the fixed state is stable; thus, it is more preferable. 
   In this embodiment, as shown in  FIG. 2 , a spark-plug-guard receiving opening  40  is opened in the form of notch at the upper part of the carburetor cover  20 . The spark plug guard  25  displaces to the spark-plug covering position P 1 , so that most outline of the spark plug guard  25  comes in the plug-guard receiving opening  40 . Accordingly, as shown in  FIGS. 1 and 2 , the outline of the whole internal combustion engine  4  becomes compact, thus facilitating working while carrying it. 
   Referring to  FIGS. 2 and 3 , the spark plug guard  25  has a finger hole  37  suitable for use in pivotal displacement. The finger hole  37  facilitates the pivotal displacement from the spark-plug covering position P 1  in a self-locking state to the spark-plug opening position P 2 . Also, since the spark plug guard  25  itself is decreased in weight by the amount corresponding to the notch of the finger hole  37 , it is more preferable. 
   Referring to  FIG. 2 , in this embodiment, the finger hole  37  is formed in the position to face the plug cap  18  in the spark-plug covering position P 1 . Therefore, the finger hole  37  serves as an air-circulating channel toward the plug cap  18 , thus providing a cooling effect of the spark plug  16 . 
   Moreover, in this embodiment, the finger hole  37  is arranged in the position for a tool such as a screwdriver  38  inserted therethrough to be able to reach a control section  39  of the carburetor  12 . Accordingly, even when the spark plug guard  25  is closed in the spark-plug covering position P 1 , it does not obstruct the operation of controlling the flow rate of the fuel in the carburetor  12 , thus being preferable. 
   The spark plug guard  25  is not limited to the foregoing arrangement, but may be of other known toggle-latch types. 
   The spark plug guard  25  is not limited to the toggle-latch type, but may be one equipped with a moving guard having an attachment section to the carburetor cover  20 , an elastic member such as a spring and rubber connected to the moving guard, and an engagement section attached to the elastic member and engageable with the cleaner-cover  21 . In this case, when the spark plug guard is arranged between the carburetor cover  20  and the cleaner cover  21  against the elasticity of the elastic member, the cleaner cover  21  is fixed to the carburetor cover  20  by the elasticity of the elastic member, and the moving guard covers above the spark plug  16  for protection. 
   Furthermore, contrary to the above described embodiment, the toggle-latch type of spark plug guard may be mounted to the cleaner cover  21 . In this arrangement, the spark plug guard has an engagement section which can engage with an engagement receiving section formed on the carburetor cover  20 , wherein the engagement section is brought into engagement with the engagement receiving section, so that the cleaner cover  21  is fixed to the carburetor cover  20 .