Patent Publication Number: US-7213555-B2

Title: Automatic choke

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an automatic choke, and more particularly to an automatic choke capable of controlling air-fuel ratio favorably corresponding to temperature in the process of engine temperature rise after starting. 
   2. Description of the Related Art 
   An automatic choke used when starting a cold engine is designed to control a solenoid actuator or diaphragm actuator for operating a choke valve according to the temperature detected by a temperature detecting element such as thermostat. When starting a cold engine, by controlling the air-fuel ratio in a direction of concentrating the mixed air by the automatic choke, the engine can be started stably. 
   For example, Japanese Patent Application Laid-Open No. 5-280425 relates to a case of detecting a cold engine by a sensor composed of thermistor for issuing a detection signal corresponding to the temperature of the cylinder head, and discloses an automatic choke in which the choke solenoid is automatically actuated only in cold state for actuating the choke when starting up the engine, while the throttle valve is fully closed. 
   As in the device disclosed in the patent document, it is general to control the choke valve by using solenoid actuator. However, since the solenoid is controlled either in on or off state, near the end of the choke period, that is, when the necessary choke period is nearly over, it tends to be over-choke (insufficient opening of choke valve). 
   By contrast, using a bimetal as an actuator, it has been attempted to control the choke valve continuously. However, since the bimetal is poor in response to temperature changes, the choke releasing timing is delayed both when starting a cold engine and when restarting a warm engine, thus it only consumes time while sufficient output is not obtained. 
   SUMMARY OF THE INVENTION 
   It is hence an object of the present invention to present an automatic choke capable of controlling the choke valve accurately and finely while following up the engine temperature. 
   It is a first aspect of the invention to present an automatic choke for controlling the opening degree of a choke valve provided in an intake passage of engine upon start of engine in which it comprises a stepping motor is provided for controlling the opening degree of the choke valve, wherein the choke valve is driven to the fully closed side for initializing the stepping motor when the power source for starting the engine is turned on. 
   It is a second aspect of the invention to present the automatic choke, in which the opening degree of the choke valve upon start of engine is determined on the basis of the temperature information representing the engine temperature upon start of engine, and the time until releasing the choke corresponding to fully opening the choke valve from the opening degree of the choke valve upon start of engine is determined on the basis of the temperature information. 
   It is a third aspect of the invention to present the automatic choke, in which a stepping motor is provided for controlling the opening degree of the choke valve, wherein the choke valve is driven to the fully closed side when the preset start opening degree of the choke valve is at the fully closed side from the reference opening degree and the choke valve is driven to the fully opened side when the preset start opening degree of the choke valve is at the fully opened side from the reference opening degree, for initializing the stepping motor when the power source for starting the engine is turned on. 
   According to the first aspect of the invention, the stepping motor driven in open loop can be securely initialized to fully closed side of the choke valve. Since the stepping motor has been initialized at the fully closed side of the choke value so as to be appropriate when starting up, the choke valve can be quickly turned to the preset opening degree upon start. 
   According to the second aspect of the invention, the engine is started at a proper opening degree of the choke valve determined depending on the engine or engine ambient temperature. Since the choke is released gradually by the stepping motor, over-choke and drop of air-fuel ratio near the end of choke valve fully opened side can be suppressed. 
   According to the third aspect of the invention, when starting the stepping motor driven in open loop, it can be initialized securely. In particular, depending on whether the start opening degree of the choke valve is closer to the fully closed side or to the fully opened side from the reference opening degree, the stepping motor for driving the choke valve is initialized either at the fully closed side or at the fully opened side of the choke valve. That is, since the choke valve is positioned and initialized preliminarily at the start opening degree side, after initializing the stepping motor, the choke valve can be moved in a short time up to the start opening degree. Therefore, after manipulation for engine start, the choke valve can be immediately moved to the start opening degree, and the starting performance is enhanced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of system configuration of an automatic choke in an embodiment of the present invention. 
       FIG. 2  is a flowchart of operation of a choke control unit. 
       FIG. 3  is a flowchart of modified example of initializing process of a stepping motor. 
       FIG. 4  is a table showing an example of pulse rate of the stepping motor corresponding to the engine temperature. 
       FIG. 5  is a diagram showing position of the choke valve at various engine temperature levels upon start of the engine. 
       FIG. 6  is a block diagram of essential functions of a choke controller. 
       FIG. 7  is a diagram showing an example of a choke release time corresponding to the engine temperature. 
       FIG. 8  is a graph showing an example of the choke release time corresponding to the engine temperature. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, the invention is specifically described below.  FIG. 1  is a block diagram of system configuration of an automatic choke in an embodiment of the present invention. In the diagram, an engine  1  is used as a driving source of a generator. The engine  1  includes a temperature sensor  2  for detecting the engine temperature. The temperature sensor  2  is provided, for example, on a cylinder head  2   a . The cylinder head  2   a  includes an ignition plug  3 , an intake valve  4 , and an exhaust valve  5 . 
   A carburetor  7  is connected to an intake tube  6  having the intake valve  4 . The carburetor  7  includes a throttle valve  8  disposed at the downstream side, and a choke valve  9  disposed at its upstream. The throttle valve  8  is driven by a stepping motor  10  and opened or closed, and the choke valve  9  is driven by a stepping motor  11  and opened or closed. 
   The engine  1  is coupled to a generator  12 . The generator  12  is driven by the engine  1 , and generates alternating current. This alternating current is rectified, and converted into a specified frequency (commercial frequency of 50 or 60 Hz) by an inverter  13 , and a commercial supply voltage is produced. 
   The generator  12  serving also as starter motor of the engine  1  comprises an outer rotor  12   a  having a magnet mounted on the inner circumference of a flywheel coupled to a crankshaft  1   a  of the engine  1 , and a stator  12   b  on which power generating coil is wound. The crankshaft  1   a  may be coupled to a recoil starter (not shown) for manual starting. 
   The outer rotor  12   a  of the generator  12  includes a reluctor  14  for detection of ignition timing, and a before top dead center sensor (BTDC sensor)  15  for detecting the reluctor  14  is provided around the outer rotor  12   a.    
   The ignition timing of the ignition plug  3  and opening degree of the choke valve  9  are controlled by an operation controller  16 . A choke controller  17  outputs a control signal for driving the stepping motor  11  depending on the engine temperature detected by the temperature sensor  2  and the engine speed detected by the output of the BTDC sensor  15 . According to this control signal, the stepping motor  11  operates the choke valve  9  so as to obtain an appropriate the air-fuel ratio corresponding to the temperature. The control operation of the choke controller  17  is described later. 
   The stepping motor  10  is controlled by an electronic governor so as to maintain the engine speed at a specified reference speed. The reference speed is variable with the magnitude of the load (the electrical load connected to the output side of the inverter  13 ). 
   An ignition controller  18  controls the ignition timing appropriately on the basis of the alternating-current waveforms of the BTDC sensor  15  and generator  12 . Waveform shapers  19 ,  20  shape the output waveform from the BTDC sensor  15  and alternating-current output waveform from the generator  12 , respectively. The ignition timing is controlled by the timing of waveform supplied from the waveform shapers  19 ,  20 , but this is not essential point of the invention and the detail is omitted. 
   A power supply unit  21  supplies necessary power to the operation controller  16 , and includes a battery  25 , and a regulator for regulating the rectified voltage of the generator  12  (input side voltage of the inverter  13 ) at specified voltage. The operation controller  16  may also include a liquid crystal display  22  for displaying the running state of the generator  12  and the like. For remote control of the generator  12 , an interface  24  may be provided for connection of a remote controller  23 . The choke controller  17  and ignition controller  18  may be composed of microcomputers. 
     FIG. 2  is a flowchart of operation of the choke controller  17 . This process is started when the power supply unit  21  is energized by the electric power supplied from the battery  25 . When the battery  25  has been overdischarged, the engine  1  is turned by the recoil starter, and the power supply unit  21  is energized by the power generation output from the generator  12  at this time. 
   First, at step S 1 , the detected temperature by the temperature sensor  2  is read in. At step S 2 , the position of the choke valve  9  (start opening degree or start opening angle) corresponding to the detected temperature is determined. The start opening degree is read out, for example, from a predetermined table as shown in  FIG. 5 . The position of the choke valve  9  is indicated by the number of steps to be supplied to the stepping motor  11 . The detail of  FIG. 5  is described later. 
   At step S 3 , for example using a predetermined table as shown in  FIG. 7 , the working time until release of choke corresponding to the engine temperature (basic choke release time) is determined. The detail of  FIG. 7  is described later. 
   At step S 4 , first the stepping motor  11  is driven in order to initialize, and the stepping motor  11  is driven for rotating the choke valve  9  until start opening degree. 
   For initialization of the stepping motor  11 , for example, as described specifically below, a driving signal of a predetermined number of steps is supplied to the stepping motor  11  so as to move the choke valve  9  to the fully closed side. In consequence, the choke valve  9  is fully closed. The start opening degree of the choke valve  9  is determined on the basis of this fully closed position. 
   When starting up the engine by driving the starter motor by battery, after initialization of the stepping motor  11 , the choke valve  9  is moved to the start opening degree, and then the engine is started. On the other hand, when power cannot be supplied from battery, since the stepping motor  11  is driven and ignited by the power generation output obtained by manual revolution by the recoil starter, driving of the choke valve  9  and start of the engine are executed almost at the same time. 
   After the engine startup, at step S 5 , it is judged whether the choke valve  9  is opened to half or not. This is judged by the number of pulses supplied to the stepping motor  11  or by the number of steps of the driving signal. If the choke valve  9  is opened to less than half, advancing to step S 6 , the engine speed is detected. The engine speed can be detected on the basis of the output period of the BTDC sensor  15 , but the method of detection is not particularly specified. At step S 7 , the motor driving condition until the choke valve  9  is opened to half is determined. 
   In determination of motor driving condition until half open, the basic choke release time determined at step S 3  (working time from start opening degree to half open) is corrected. In this correction, as the engine speed is higher, the basic choke release time is shortened, and as the engine speed is lower, the basic choke release time is extended. 
   The number of driving pulses supplied to the stepping motor  11  in every driving period (for example, 0.7 sec) is determined on the basis of this driving period and the basic choke release time extended or shortened corresponding to increase or decrease of engine speed. When the number of pulses supplied per driving period is increased, it is fast to move to the choke release side, whereas if the number of pulses supplied per driving period is decreased, it is slow to move to the choke release side. 
   In this way, at step S 7 , the number of pulses or number of steps in every driving period to be supplied to the stepping motor  11  until the choke valve  9  is opened half from start opening degree is determined, and at step S 8 , the stepping motor  11  is driven in the determined motor driving condition (determined number of driving pulses or number of steps). 
   If it is judged at step S 5  that the choke valve  9  is open to half, skipping to step S 9 , it is judged if the choke valve  9  is fully opened or not. Same as in judgement of half open, it is determined by the number of pulses or the number of steps supplied to the stepping motor  11 . 
   If the choke valve  9  is not fully opened, going to step S 10 , the engine speed is detected. At step S 11 , the motor driving condition until the choke valve  9  is opened fully is determined. At step S 11 , too, same as at step S 7 , the basic choke release time by the engine speed (working time from half open to full open) is corrected, and the number of output driving pulses or number of steps in every driving period on the stepping motor  11  is calculated. At step S 12 , the stepping motor  11  is driven in the determined motor driving condition (determined number of pulses or number of steps). When the choke valve  9  is judged to be fully opened, this choke control is terminated. 
   As mentioned above, by driving the choke valve  9  by a specified amount in the fully closing direction at step S 4 , and this position is determined as the initial position of the stepping motor  11 . As a result, the following effects are brought about. For example, due to overdischarge of a battery  25 , if power cannot be supplied to the generator  12  for operating as starter motor from the power supply unit  21 , the recoil starter is operated to start the engine. In this case, if failing to start by the recoil starter, and no power is supplied until the choke valve  9  is fully closed, by such initialization of the choke valve  9 , the position of the choke valve  9  is at leased moved in the fully closing direction. Hence, it is easier to start the engine, and possibility of engine start is higher by next attempt to start. 
   For initialization of the stepping motor  11 , the timing of driving the choke valve  9  in the fully closing direction is not specified, and it may be executed at the first step in this flowchart. In short, to set the choke valve  9  at the start opening degree, the stepping motor  11  may be initialized at the fully closed side of the choke opening degree until the stepping motor  11  is driven. 
   A modified example of initialization of stepping motor  11  at step S 4  is explained.  FIG. 3  is a flowchart of modified example of initialization of the stepping motor  11 . 
   In the diagram, at step S 41 , the pulse rate of the stepping motor  11  is determined depending on the engine temperature. An example of setting table of pulse rate of the stepping motor  11  in relation to temperature is shown in  FIG. 4 . 
   At step S 42 , it is judged if the start opening degree determined at step S 2  is less than the predicted value (for example, half open). If the start opening degree is less than half open, the process goes to step S 43 , and if the start opening degree is half open or more, the process goes to step S 44 . 
   At step S 43 , the stepping motor  11  is initialized at the fully closed side of the choke valve  9 . That is, the choke valve  9  is turned to the fully closed side at the pulse rate determined at step S 41 . At step S 44 , the stepping motor  11  is initialized at the fully opened side of the choke valve  9 . That is, the choke valve  9  is turned to the fully opened side at the pulse rate determined at step S 41 . 
   In this manner, when the start opening degree determined on the basis of engine temperature is at fully closed side, the choke valve  9  is driven to fully closed position, where the stepping motor  11  is initialized. On the other hand, when the start opening degree determined on the basis of the engine temperature is at fully opened side, the choke valve  9  is driven to fully opened position, where the stepping motor  11  is initialized. Thus, since initialization takes place at a side closer to the start opening degree, the choke valve  9  can be moved to the start opening degree in a shorter time after initialization. 
     FIG. 5  shows the position or start opening degree of the choke valve  9  at various engine temperatures upon start of engine, expressed by the number of steps of the stepping motor  11 . In this example, the choke valve  9  is fully closed (number of steps=110) in an engine temperature range of minus 25° C. to 20° C., and the choke valve  9  is slightly open at engine temperature of 30° C. or higher. The choke valve  9  is half open (number of steps=55) at engine temperature of 60° C., and at higher temperatures the choke valve  9  is opened gradually up to the number of steps of 35. 
   As understood from this diagram, in the modified example of initialization, since at the engine temperature of 60° C. or less, the start opening degree is at closed side from the half open state, the stepping motor  11  is initialized at the fully closed side of the choke valve  9 . Since at the engine temperature of 60° C. or higher, the start opening degree is at opened side from the half open state, and the stepping motor  11  is initialized at the fully opened side of the choke valve  9 . 
     FIG. 6  is a block diagram of essential functions of the choke controller  17  of the embodiment. In a start opening degree setting unit  26 , the start opening degree of the choke valve  9  corresponding to the engine temperature shown in  FIG. 5  is set, and the value of start opening degree corresponding to the engine temperature detected by the temperature sensor  2  is issued. A start opening degree judging unit  27  reads the start opening degree from the start opening degree setting unit  26 , and judges whether at the fully closed side or fully opened side from the planned opening degree (for example, opening degree corresponding to half open). 
   A motor initializing unit  28  supplies a specified number of driving signals for moving the stepping motor  11  to the fully closed position of the choke valve  9  when the start opening degree is at the fully closed side, to the stepping motor  11 . On the other hand, the motor initializing unit  28  supplies a specified number of driving signals for moving the stepping motor  11  to the fully opened position of the choke valve  9  when the start opening degree is at the fully opened side, to the stepping motor  11 . 
   When the stepping motor  11  is initialized by supplying the preset number of steps of driving signals for fully closing or fully opening to the stepping motor  11 , then a choke setting unit  29  supplies the number of steps of driving signals corresponding to the start opening degree to the stepping motor  11 , and sets the choke valve  9  at start opening degree. 
     FIG. 7  is an example showing choke release time corresponding to the engine temperature. This is an example of basic choke release time when the engine speed is controlled by an electronic governor to be at reference speed of 3300 rpm. Therefore, if the reference speed varies with fluctuations of the load connected to the generator  12 , the basic choke release time (working time until half open, and working time from half open to full open) is corrected depending on the engine speed. That is, when the load increases and the engine speed changes somewhat higher than the reference speed, the choke release time is shortened, and when the load decreases and the engine speed changes somewhat lower than the reference speed, the choke release time is extended. Thus, the choke release time is corrected to be appropriate depending on the running condition of the generator  12 , that is, the engine  1 . 
     FIG. 8  shows the graph representing an example of  FIG. 7 . As this graph, the choke release time is determined due to the engine temperature upon start. 
   In this embodiment, the stepping motor is used as the driving source of the choke valve, but not limited to the stepping motor, for example, a servo motor may be similarly used. 
   The engine temperature is represented by the temperature of the cylinder head  2   a , but the engine temperature for choke valve control is not limited to the temperature at this position. For example, a temperature sensor may be installed in an oil pan or water jacket for engine cooling water, and the temperature of lubricating oil or temperature of engine cooling water maybe detected, and used as engine temperature. Besides, any temperature information detected in engine case parts capable of representing the engine temperature may be employed in the choke valve control of the invention.