Abstract:
In a control apparatus for a general-purpose internal combustion engine including a generator as a power supply, the generator includes a main generator coil supplying power to the stepping motor, and an auxiliary generator coil supplying power to an ignition device of the engine. The apparatus includes ignition timing controller for, when starting the engine by a manual starter, detecting that an engine speed reaches or exceeds a predetermined engine speed not exceeding a connecting rotation speed of a centrifugal clutch to retard an ignition timing of the engine, thereby suppressing increase in the engine speed to less than the connecting rotation speed, and for restoring the ignition timing to its normal timing after a predetermined time elapses from start of retarding the ignition timing. Accordingly, it suppresses overshooting of an engine speed above the connecting rotation speed even if a delay occurs in closing a throttle valve by a delay in activating the motor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improvement of a control apparatus for a general-purpose internal combustion engine having an output shaft connected via a centrifugal clutch to a load device, the control apparatus comprising a manual starter, a carburetor having a throttle valve for opening and closing an intake passage, and a stepping motor for controlling opening and closing of the throttle valve, in which the internal combustion engine is started from a full-open position of the throttle valve and, after the start of the engine, the stepping motor is activated so as to close the throttle valve from the full-open position. 
     2. Description of the Related Art 
     Such a control apparatus for a general-purpose internal combustion engine is known as disclosed in, for example, Japanese Patent Application Laid-open No. 2012-140878. 
     SUMMARY OF THE INVENTION 
     With the control apparatus for a general-purpose internal combustion engine disclosed in Japanese Patent Application Laid-open No. 2012-140878, the engine includes a battery as a power supply and thus, after start of the engine, a stepping motor is immediately activated by electric power from the battery to close a throttle valve to a predetermined opening, which thus enables suppressing that an engine speed overshoots to or more a connecting rotation speed of a centrifugal clutch. However, in the case of an internal combustion engine including a generator without having the battery as the power supply, a slow rise in an output from the generator, when starting the engine by a manual starter, may cause a delay in activation of the stepping motor and hence a delay in closing of the throttle valve, thus leading to the engine speed overshooting above the connecting rotation speed of the centrifugal clutch. Accordingly, engine stall may occur by connection shock of the centrifugal clutch. 
     The present invention has been made in view of the above-mentioned circumstances. An object of the present invention is to provide a control apparatus for a general-purpose internal combustion engine including a generator as a power supply, in which, even if a delay in closing of a throttle valve is caused by a delay in activation of a stepping motor when starting the engine by a manual starter, the engine can be surely started by suppressing overshooting of an engine speed above a connecting rotation speed of a centrifugal clutch and after starting the engine, the engine speed can be stabilized at an idling speed. 
     In order to achieve the object, according to a first aspect of the present invention, there is provided a control apparatus for a general-purpose internal combustion engine having an output shaft connected via a centrifugal clutch to a load device, the control apparatus comprising a manual starter, a carburetor having a throttle valve for opening and closing an intake passage, and a stepping motor for controlling opening and closing of the throttle valve, in which the internal combustion engine is started from a full-open position of the throttle valve and, after the start of the engine, the stepping motor is activated so as to close the throttle valve from the full-open position, wherein the control apparatus further comprises: a generator as a power supply of the engine, the generator including a main generator coil for supplying power to the stepping motor, and an auxiliary generator coil for supplying power to an ignition device of the engine; and ignition timing control means for, when starting the engine by a manual starter, detecting that an engine speed of the engine is equal to or more than a predetermined engine speed which is equal to or less than a connecting rotation speed of the centrifugal clutch, and retarding an ignition timing of the engine so as to suppress increase in the engine speed of the engine to less than the connecting rotation speed of the centrifugal clutch, and also for restoring the ignition timing to its normal timing after a lapse of a predetermined time from start of retarding the ignition timing. 
     According to the first aspect of the present invention, at the time of start of the engine by the manual starter, the ignition timing control means detects an increase in the engine speed to the predetermined engine speed which is lower than the connecting rotation speed of the centrifugal clutch, and retards the ignition timing so as to suppress overshooting of the engine speed above the connecting rotation speed of the centrifugal clutch. Also, the ignition timing control means restores the ignition timing to its normal timing after the lapse of the certain time from the start of retarding the ignition timing so as to enable stabilizing the engine speed at an idling speed. 
     According to a second aspect of the present invention, in addition to the first aspect, the number of pulses generated by the auxiliary generator coil from the start of retarding the ignition timing is used in place of the predetermined time. 
     According to the second aspect of the present invention, the number of pulses generated by the auxiliary generator coil from the start of retarding the ignition timing is used in place of the predetermined time. Accordingly, the ignition timing control means can detect the lapse of the certain time from the start of retarding the ignition timing, without using a special timer. 
     The above and other objects, characteristics and advantages of the present invention will be clear from detailed descriptions of the preferred embodiment which will be provided below while referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a general-purpose internal combustion engine according to an embodiment of the present invention. 
         FIG. 2  is a plan view of a throttle and choke control device provided in a carburetor of the internal combustion engine. 
         FIG. 3  is an enlarged sectional view of an essential part of  FIG. 2 . 
         FIG. 4  is a diagram showing a generator of the internal combustion engine and an electric circuit related to the generator. 
         FIG. 5  is a flowchart illustrating an operating status of ignition timing control means in  FIG. 4 . 
         FIG. 6  is a diagram for comparing an engine speed characteristic of the present invention and that prior to the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described below with reference to the accompanying drawings. 
     Firstly, as illustrated in  FIG. 1 , a general-purpose internal combustion engine E is equipped at its front face side with a recoil starter  5  capable of cranking a crankshaft  4 , and also, a load device L such as a snow-removal device or the like is connected via a centrifugal clutch  2  to an output end of the crankshaft  4 . Also, a carburetor C which supplies an air-fuel mixture formed by intake air from an air cleaner A to a suction port of the internal combustion engine E is attached to a cylinder head  1  of the engine E. 
     As illustrated in  FIG. 2 , the carburetor C has an intake passage  12  communicating with an intake port of the engine E, and the intake passage  12  is provided with a choke valve  14  and a throttle valve  15  in this order from an upstream side of the intake passage  12 , that is, from the air cleaner A side, and a fuel nozzle (unillustrated) is opened to a venturi portion of the intake passage  12  in an intermediate portion between the valves  14 ,  15 . The choke valve  14  and the throttle valve  15  are both configured with butterfly-type valves which are opened and closed by rotation of valve shafts  14   a ,  15   a , respectively. 
     A throttle and choke control device D for automatically controlling openings of the choke valve  14  and the throttle valve  15  is mounted on an upper portion of the carburetor C. Hereinafter, the valve shaft  14   a  of the choke valve  14  will be called the choke valve shaft  14   a , and the valve shaft  15   a  of the throttle valve  15  will be called the throttle valve shaft  15   a.    
     The throttle and choke control device D will be described with reference to  FIGS. 2 and 3 . 
     A casing  16  of the throttle and choke control device D is integrally formed with an upper sidewall of the carburetor C and an upper surface of the casing  16  is opened. The opened surface is normally closed by a cover plate (unillustrated). 
     The casing  16  houses therewithin a stepping motor  17 , a throttle valve opening-closing mechanism  18  arranged between the stepping motor  17  and the throttle valve shaft  15   a  so as to open or close the throttle valve  15  according to activation of the stepping motor  17 , and a choke valve opening-closing mechanism  19  which is driven by an output from the stepping motor  17  so as to open and close the choke valve  14 . 
     The stepping motor  17  is housed and fixed in the casing  16  with a rotor shaft  21  of the stepping motor  17  being parallel to the throttle valve shaft  15   a  and the choke valve shaft  14   a . In addition, the throttle valve opening-closing mechanism  18  includes a pinion gear  22  attached to the rotor shaft  21 , a first intermediate gear  23  in mesh with the pinion gear  22 , a second intermediate gear  24  integrally formed with the first intermediate gear  23  and having a smaller diameter than that of the first intermediate gear  23 , and an output gear  25  attached to the throttle valve shaft  15   a  so as to in mesh with the second intermediate gear  24  and having a larger diameter than that of the second intermediate gear  24 . The first and second intermediate gears  23 ,  24  are rotatably supported by a first supporting shaft  26  mounted to the casing  16  to be parallel to the rotor shaft  21 . The first and second intermediate gears  23 ,  24  and the output gear  25  are configured of sector gears. 
     The choke valve opening-closing mechanism  19  includes a cam  28  having, as a cam surface  28   a , a concavely curved inner peripheral surface formed on an inner side surface of the first intermediate gear  23 , a cam follower  30  rotatably supported by a second supporting shaft  29  provided in the casing  16  in parallel to the first supporting shaft  26 , and having a cam sliding contact portion  30   a  which comes into sliding contact with the cam surface  28   a , a first arm  31  having one end portion rotatably supported by the second supporting shaft  29 , a relief spring  32  formed of a torsion coil spring and attached to the second supporting shaft  29  to be interposed between the cam follower  30  and the first arm  31 , and a second arm  33  fixed to the choke valve shaft  14   a  and interlockingly connected to the other end of the first arm  31 . 
     The other end side of the first arm  31  extends long in a radial direction of the second supporting shaft  29 , and the other end portion of the first arm  31  is provided with a long hole  34  with its major axis oriented in the radial direction of the second supporting shaft  29 . Meanwhile, the second arm  33  is bent in a V-shape with the choke valve shaft  14   a  as the center, and a pin  35  provided at one end portion of the second arm  33  is inserted through the long hole  34  so that the first and second arms  31 ,  33  are interlockingly connected to each other. Thus, the first arm  31  rotates around the second supporting shaft  29  in a counterclockwise opening direction  37  in  FIG. 3  so as to rotate the second arm  33  clockwise, thus enabling rotation of the choke valve  14  in its opening direction. 
     Also, when the stepping motor  17  operates in a direction in which the throttle valve  15  rotates toward its open side so that the first intermediate gear  23  rotates counterclockwise in  FIG. 2 , the cam follower  30  rotates counterclockwise in  FIG. 2  around the second supporting shaft  29  by bringing the cam sliding contact portion  30   a  into sliding contact with the cam surface  28   a  of the cam  28  of the first intermediate gear  23 . The relief spring  32  attached to the second supporting shaft  29  exerts a spring force which biases the cam follower  30  to a side on which the cam sliding contact portion  30   a  of the cam follower  30  comes into sliding contact with the cam surface  28   a , that is, in the clockwise direction in  FIG. 2 , so as to bias the first arm  31  to rotate about the second supporting shaft  29  in the counterclockwise direction in  FIG. 2 . The cam follower  30  and the first arm  31  are provided with abutment surfaces  30   b ,  31   a , respectively, which abut against each other by the spring force of the relief spring  32 . 
     Thus, when the cam follower  30  rotates counterclockwise in  FIG. 2  by rotation of the first intermediate gear  23 , the first arm  31  rotates by the spring force of the relief spring  32  in such a way as to follow the cam follower  30 . When the first arm  31  rotates clockwise in  FIG. 2 , that is, in the opening direction of the choke valve  14 , with the cam sliding contact portion  30   a  in sliding contact with the cam surface  28   a , only the first arm  31  rotates clockwise in  FIG. 2 . 
     Incidentally, as illustrated in  FIG. 2 , the choke valve shaft  14   a  is offset to one side from the center of the intake passage  12 , and thus, the choke valve  14  when in its fully closed state is in a tilted state in which a side of the choke valve  14  having a larger radius of rotation is located downstream of the intake passage  12  from a side of the choke valve  14  having a smaller radius of rotation. Thus, in a case where the choke valve opening-closing mechanism  19  sets the opening of the choke valve  14  to an opening between full closing and half opening, if intake negative pressure in the internal combustion engine E, which is equal to or more than a certain value, acts on the choke valve  14 , the choke valve  14  is opened to a position where a difference between a rotation moment which the intake negative pressure applies to the side of the choke valve  14  having the larger radius of rotation and a rotation moment which the intake negative pressure applies to the side of the choke valve  14  having the smaller radius of rotation is balanced with a rotation moment applied to the first arm  31  by the relief spring  32 . 
     Also, a temperature sensitive actuator  40  which operates according to ambient temperature is housed and fixed in the casing  16 . The temperature sensitive actuator  40  includes a case  41  in which wax (unillustrated) is sealed, and a piston  42  slidably fitted in the case  41  to bring an inner end of the piston  42  into contact with the wax and having an outer end protruding outward from the case  41 . Accordingly, when the ambient temperature rises, protrusion amount of the piston  42  increases by thermal expansion of the wax. Thus, the outer end of the piston  42  can abut against a pressure receiving portion  30   c  of the cam follower  30 , and thus, when the protrusion amount of the piston  42  is increased so that the piston  42  presses against the pressure receiving portion  30   c , the cam follower  30  rotates in the opening direction of the choke valve  14 . 
     Also, the casing  16  is provided with choke valve forced-closing means  43  capable of manually operating, from outside of the casing  16 , the choke valve  14  toward its closing side. The choke valve forced-closing means  43  includes an operating lever  55  having an intermediate portion rotatably supported by a third supporting shaft  44  provided in the casing  16 , a pressure receiving pin  56  fixedly provided at the other end portion of the second arm  33  in such a way as to face an inner end portion of the operating lever  55  so as to be capable of abutting against the inner end portion thereof, and a return spring (unillustrated) which biases the operating lever  55  to rotate so as to separate from the pressure receiving pin  56 . When the operating lever  55  is rotated against a bias force of the return spring so as to press the pressure receiving pin  56 , the second arm  33  can be forcibly rotated in a closing direction of the choke valve  14 . 
     As illustrated in  FIGS. 1 and 4 , the internal combustion engine E is not equipped with a battery but includes a magnet type generator  45  as a power supply. The generator  45  is driven by the crankshaft  4  and includes a main generator coil  45   a  and an auxiliary generator coil  45   b.    
     An output from the auxiliary generator coil  45   b  is inputted to an ignition device  46  and ignition timing control means  47 , and an output from the ignition timing control means  47  is inputted to the ignition device  46 . The ignition device  46  is switchable between its operating and non-operating states, and the ignition device  46  when in the operating state applies its output to a spark plug  48  of the internal combustion engine E. 
     An output from the main generator coil  45   a  is inputted to an electronic control unit  50 . The electronic control unit  50  includes a power supply circuit  51  and a pulse arithmetic circuit  52  and an engine speed setting device  53  is connected to the electronic control unit  50 . The pulse arithmetic circuit  52  controls the stepping motor  17  to achieve a balance between a desired engine speed set by the engine speed setting device  53  and the number of pulses generated by the main generator coil  45   a , which are obtained via the power supply circuit  51 , so as to open and close the throttle valve  15 , thereby controlling an output from the internal combustion engine E. Accordingly, an engine speed corresponds to the desired engine speed set by the engine speed setting device  53 . Thus, when the ignition device  46  is placed in the non-operating state to stop ignition of the spark plug  48 , the electronic control unit  50  rotates the stepping motor  17  to a full-open position of the throttle valve  15  by using an output by inertial rotation of the generator  45 . 
     Next, an operation of the embodiment will be described. 
     As mentioned above, the electronic control unit  50  rotates the stepping motor  17  to the full-open position of the throttle valve  15  by using the output by the inertial rotation of the generator  45  immediately before stop of rotation of the internal combustion engine E. Accordingly, when the engine E is in its stopped state, the throttle valve  15  is held in the full-open position, and the choke valve  14  is held at an opening according to whether the ambient temperature is high or low, by the temperature sensitive actuator  40 . 
     When starting the internal combustion engine E, first, an idling speed as the desired engine speed is set in the engine speed setting device  53 . Of course, the idling speed is lower than a connecting rotation speed of the centrifugal clutch  2 . Then, when the crankshaft  4  is cranked by operation of the recoil starter  5  in order to start the internal combustion engine E, an air-fuel mixture formed in the intake passage  12  is sucked into the engine E accordingly, and first, the ignition device  46  operates by electric power generated by the auxiliary generator coil  45   b  of the generator  45  so as to generate a spark in the spark plug  48 , thereby making the engine E in a state of complete explosion. Then, the throttle valve  15  is in the full-open position, so that, the engine E sucks a large amount of air-fuel mixture so as to sharply increase the engine speed, thereby becoming in a started state. At this stage, an output voltage from the main generator coil  45   a  of the generator  45  rises sufficiently to place the electronic control unit  50  in an operating state. Thus, the pulse arithmetic circuit  52  of the electronic control unit  50  controls the stepping motor  17  so as to achieve a balance between the idling speed set by the engine speed setting device  53  and the number of pulses generated by the main generator coil  45   a , which are obtained via the power supply circuit  51 , thereby closing the throttle valve  15  to reduce the engine speed to the idling speed. 
     However, the engine speed tends to overshoot above the connecting rotation speed of the centrifugal clutch  2  before the engine speed is stabilized at the idling speed, as indicated by a dashed line (showing an engine speed characteristic prior to the invention) in  FIG. 6 , and this overshooting causes the engine E to stall by connection shock of the centrifugal clutch  2 . 
     In the present invention, therefore, the ignition timing control means  47  operates in the following manner according to a flowchart of  FIG. 5 . Specifically, first, at step  1 , a decision is made as to whether or not the engine E is now in the started state, and, if the decision is made that the engine E is in the started state (YES), processing goes to step  2 , and there, a decision is made as to whether or not an engine speed Ne detected from an output of the auxiliary generator coil  45   b  is increased to or above a predetermined engine speed (for example, 800 rpm) which is lower than the connecting rotation speed of the centrifugal clutch  2 , and, if the decision is made that the engine speed Ne is increased to or above the predetermined engine speed (YES), the processing goes to step  3 , and there, the ignition device  46  is controlled so as to retard an ignition timing. As a result, as indicated by a solid line in  FIG. 6 , torque of the engine E decreases immediately to suppress the above-described overshooting of the engine speed Ne, and the engine speed Ne moves toward the idling speed without exceeding the connecting rotation speed of the centrifugal clutch  2 . 
     Then, the processing goes to step  4 , and there, the ignition timing control means  47  starts counting pulses generated by the auxiliary generator coil  45   b  from start of retarding the ignition timing, and then, at step  5 , a decision is made as to whether or not the number of the counted pulses reaches or exceeds a predetermined number (for example, 30 pulses), and, if the decision is made that the number of the counted pulses reaches or exceeds the predetermined number (YES), in other words, if the decision is made that a substantially certain time t has elapsed from the start of retarding the ignition timing, the processing goes to step  6 , and there, the ignition device  46  is controlled so as to restore the ignition timing to its normal timing. 
     Thus, as indicated by the solid line in  FIG. 6 , the engine speed Ne can be stabilized at the idling speed without exceeding the connecting rotation speed of the centrifugal clutch  2 . 
     After starting the engine, the engine speed setting device  53  is operated to activate the stepping motor  17  as in the conventional way so as to appropriately open and close the throttle valve  15  and the choke valve  14 , thereby obtaining a desired engine speed to drive the load device L. 
     Incidentally, the present invention is not limited to the above-described embodiment and various design changes can be made to the present invention without departing from the gist of the invention. For example, the recoil starter may be replaced by a kick starter.