Patent Publication Number: US-7210452-B2

Title: Control apparatus of internal combustion engine

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a control apparatus of an internal combustion engine, and particularly to a control apparatus of an internal combustion engine for preventing trouble of a throttle valve of the internal combustion engine freezing up. 
   2. Description of the Related Art 
   In winter, trouble sometimes arises of dew condensing on the throttle valve of an internal combustion engine of an automotive vehicle and water droplets forming as a result of this dew condensation then freezing and the throttle valve freezing up. As processes by which this trouble of throttle valve freezing occurs, the following examples are known. 
   When an internal combustion engine is running, a flow of air in an intake pipe is constricted by a throttle valve. As a consequence of this flow of air being constricted by the throttle valve, the flow speed of the air in the intake pipe increases sharply in the vicinity of the throttle valve. Along with the increase in the flow speed, the air flowing through the vicinity of the throttle valve is sharply reduced in pressure, and the temperature of that air falls. In environments where the outside temperature is low, in places where the humidity is high such as on sea coasts and by rivers, when the internal combustion engine is operated from cold to warm, as a consequence of the reduction in pressure of the air in the vicinity of the throttle valve and the fall in air temperature, water vapor in the intake air condenses as dew on the throttle valve to form water droplets, and these water droplets freeze. 
   When the internal combustion engine is running, with the flow of air in the intake pipe being constricted by the throttle valve, the pressure in the intake pipe is reduced by the internal combustion engine, and when the internal combustion engine is stopped in this state, because the pressure in the intake pipe rises to atmospheric pressure, air flows into the intake pipe. When at this time the throttle valve is fully closed, a phenomenon of gas in the combustion chambers of the internal combustion engine flowing back into the intake pipe through the intake valves of the internal combustion engine occurs; in an internal combustion engine equipped with an exhaust recirculating device for recirculating exhaust gas into the intake pipe, a phenomenon of post-combustion gas in the combustion chambers flowing into the intake pipe through the exhaust recirculating device occurs; in a vehicle equipped with a positive crankcase ventilation device, a phenomenon of gas in the crankcase of the internal combustion engine flowing into the intake pipe through the positive crankcase ventilation device occurs; and in an internal combustion engine equipped with a fuel transpiration gas circulating device, a phenomenon of gas in the fuel tank flowing into the intake pipe through the fuel transpiration gas circulating device occurs. 
   Because these gases flowing into the intake pipe are all high-temperature, high-humidity gases, the intake pipe becomes filled with high-temperature, high-humidity gas. When in this state a throttle body incorporating the throttle valve is cooled by a low outside air temperature, the high-temperature, high-humidity gas in contact with the inner surface of the throttle body is cooled, water vapor in the gas condenses on the inner surface of the throttle body, and water droplets form. And also when high-temperature, high-humidity gas flows into a throttle body already cooled by low-temperature outside air, because this high-temperature, high-humidity gas makes contact with the inner surface of the cooled throttle body, the high-temperature, high-humidity gas is cooled, water vapor in the gas condenses on the inner surface of the throttle body, and water droplets form. And trouble arises of water droplets condensed on the inner surface of the throttle body collecting at the bottom of the throttle valve under gravity and surface tension and then freezing at the bottom of the throttle valve as the outside air temperature falls and causing the throttle valve to freeze up. 
   When this trouble of the throttle valve freezing occurs, as a result of the intake passage of the internal combustion engine being blocked, a situation in which good startability cannot be ensured when an attempt is made to start the internal combustion engine arises, and there is a risk of the vehicle becoming immobile. 
   Related art concerned with this problem includes JP-A-59-188050 (Related Art 1) and JP-A-2000-320348 (Related Art 2). In Related Art 1, in an apparatus in which while an internal combustion engine is running a target throttle aperture corresponding to the operating state of the engine is obtained and the aperture of a throttle valve is regulated to this target throttle aperture by means of an actuator, when the engine is operating in a low outside air temperature the throttle valve is oscillated in the vicinity of the target throttle aperture to remove water droplets condensed on the throttle valve and thereby prevent trouble of the throttle valve freezing. 
   In Related Art 2, in an apparatus in which while an internal combustion engine is running a target throttle aperture corresponding to the operating state of the engine is obtained and the aperture of a throttle valve is regulated to this target throttle aperture by means of an actuator, when the engine is started in a low outside air temperature, in a state before the internal combustion engine proceeds to full combustion, to prevent trouble of the throttle valve freezing, the throttle valve is made to oscillate greatly by the target throttle aperture being made to fluctuate greatly. 
   Related Art 1: JP-A-59-188050 
   Related Art 2: JP-A-2000-320348 
   However, in Related Art 1, although water droplets condensing as dew on the throttle valve while the engine is running can be removed, it is not possible to prevent dew condensation and freezing of water droplets forming as a result of this dew condensation after the-engine stops, and it is impossible to eliminate trouble of the throttle valve freezing after the internal combustion engine stops. 
   And, if condensed water droplets freeze 100% and the throttle valve reaches a throttle-frozen state, to oscillate the throttle valve to eliminate this throttle-frozen state a large shear torque is necessary, and with actuators normally used the situation often arises that the shear torque is insufficient and the freezing cannot be overcome. In Related Art 1, 2, because freezing of the throttle valve due to freezing of water droplets cannot be eliminated with certainty, the problem arises that sure startability cannot be guaranteed and it is difficult to prevent certainly a situation of the vehicle becoming immobile. 
   And, when a frozen throttle valve is oscillated forcefully, there is a risk of stress accompanying that oscillation causing damage to the throttle valve and its drive mechanism. And when an excessive current flows through a motor for driving the throttle valve, there is a risk of the drive motor burning out. 
   SUMMARY OF THE INVENTION 
   The present invention was made in view of the problems described above, and provides a control apparatus of an internal combustion engine with which, while the internal combustion engine is stopped, it is possible to prevent trouble of a throttle valve freezing. 
   The invention provides a control apparatus of an internal combustion engine including: a battery ancillary to the internal combustion engine; a control unit for receiving power from the battery and controlling the internal combustion engine; and a throttle valve drive device for receiving power from the battery and driving a throttle valve of the internal combustion engine, the control apparatus of the internal combustion engine regulating the valve aperture of the throttle valve by controlling the throttle valve drive device while the internal combustion engine is running, wherein while the internal combustion engine is stopped the control unit receives power from the battery and performs a probability determination of whether or not the probability of the throttle valve freezing is high, and when while the internal combustion engine is stopped it determines that the probability of the throttle valve freezing is high the control unit, before the throttle valve reaches a throttle-frozen state, controls the throttle valve drive device so that the throttle valve drive device receives power from the battery and executes a freeze protection operation of oscillating the valve aperture of the throttle valve. 
   In a control apparatus of an internal combustion engine according to the invention, because when the internal combustion engine is stopped the control unit receives power from a battery and performs a probability determination of whether or not the probability of a throttle valve freezing is high and when the control unit determines that the probability of the throttle valve freezing is high, before the throttle valve reaches a throttle-frozen state, it controls the throttle valve drive device so that the throttle valve drive device receives power from the battery and executes a freeze protection operation of oscillating the valve aperture of the throttle valve, without adding a special control unit for throttle freeze protection operation it is possible certainly to prevent the throttle valve from freezing while the internal combustion engine is stopped and it is possible to provide sure startability and certainly prevent the vehicle from becoming immobile. And, damage to the throttle valve and the throttle mechanism and burning out of the throttle valve drive device can also be prevented. Furthermore, because freezing protection operation is not carried out when the probability of freezing of the throttle valve occurring is low, battery energy can be saved and the lives of the throttle valve, the throttle mechanism and the throttle valve drive device can be extended. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view showing a first preferred embodiment of a control apparatus of an internal combustion engine according to the invention; 
       FIG. 2  is a control flow chart showing a throttle freeze protection operation in the first preferred embodiment; 
       FIG. 3  is a control flow chart showing a throttle freeze protection operation in a second preferred embodiment of a control apparatus of an internal combustion engine according to the invention; 
       FIG. 4  is a control flow chart showing a throttle freeze protection operation in a third preferred embodiment of a control apparatus of an internal combustion engine according to the invention; 
       FIG. 5  is a control flow chart showing a throttle freeze protection operation in a fourth preferred embodiment of a control apparatus of an internal combustion engine according to the invention; 
       FIG. 6  is a control flow chart showing a throttle freeze protection operation in a fifth preferred embodiment of a control apparatus of an internal combustion engine according to the invention; 
       FIG. 7  is a control flow chart showing a throttle freeze protection operation in a sixth preferred embodiment of a control apparatus of an internal combustion engine according to the invention; 
       FIG. 8  is a control flow chart showing a control operation of a standby timer in a seventh preferred embodiment of a control apparatus of an internal combustion engine according to the invention; 
       FIG. 9  is a control flow chart showing a throttle freeze protection operation in the seventh preferred embodiment; 
       FIG. 10  is a flow chart showing a control operation of a standby timer and an interval timer in an eighth preferred embodiment of a control apparatus of an internal combustion engine according to the invention; 
       FIG. 11  is a control flow chart showing a throttle freeze protection operation in the eighth preferred embodiment; and 
       FIG. 12  is a control flow chart showing a throttle freeze protection operation in a ninth preferred embodiment of a control apparatus of an internal combustion engine according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A number of preferred embodiments of a control apparatus of an internal combustion engine according to the invention will be described below with reference to the accompanying drawings. 
   First Preferred Embodiment 
     FIG. 1  is an overall construction view showing a first preferred embodiment of a control apparatus of an internal combustion engine according to the invention. The internal combustion engine control apparatus of this first preferred embodiment is a control apparatus of an internal combustion engine mounted in an automotive vehicle. The internal combustion engine control apparatus of the first preferred embodiment shown in  FIG. 1  has an internal combustion engine  10  and a control system  60  of this internal combustion engine  10 . 
   The internal combustion engine  10  has an internal combustion engine proper  20 , an intake system  30 , an exhaust system  40 , and an exhaust recirculating device  50 . The internal combustion engine proper  20  has a cylinder  23  with a piston  21  and a combustion chamber  22 . An intake valve  24 , an exhaust valve  25  and a spark plug  26  are provided in the combustion chamber  22 . The intake valve  24  and the exhaust valve  25  are opened and closed by a cam (not shown). When the intake valve  24  opens, a mixture of air and fuel is supplied from the intake system  30  into the combustion chamber  22 . The spark plug  26  ignites the mixture supplied into the combustion chamber  22  and causes the mixture to combust inside the combustion chamber  22 . The piston  21  is driven by this combustion of the mixture. When the exhaust valve  25  is opened, exhaust gas is discharged from the combustion chamber  22  into the exhaust system  40 . 
   A cooling water temperature sensor  27  is provided in the cylinder  23 . This cooling water temperature sensor  27  includes an engine temperature detecting means of the internal combustion engine. This cooling water temperature sensor  27  detects the temperature of cooling water of the internal combustion engine supplied to the cylinder  23  and outputs engine temperature information Tw proportional to this cooling water temperature. The cooling water temperature is proportional to the temperature of the cylinder  23 , and the engine temperature information Tw has a size proportional to the temperature of the internal combustion engine proper  20 . 
   The intake system  30  has an intake pipe  31 , an air filter  32 , a throttle body  33  and a fuel injection valve  37 . The intake pipe  31  is connected to the combustion chamber  22  via the intake valve  24 . The throttle body  33  is disposed in the intake pipe  31  on the downstream side of the air filter  32 . This throttle body  33  has a throttle valve  34 , a throttle position sensor  35  and a throttle valve drive device  36 . 
   The throttle valve  34  is disposed so as to cross an intake passage inside the intake pipe  31 , and rotates about a rotary shaft  34 A to open and close the intake passage inside the intake pipe  31 . In  FIG. 1  the throttle valve  34  is shown in a fully closed state, and in this state the throttle valve aperture is 0% and the intake passage is blocked. In  FIG. 1 , when the throttle valve  34  rotates in the clockwise direction about the rotary shaft  34 A, the throttle valve aperture increases. When the throttle valve  34  has become parallel with the intake passage, the throttle valve  34  is fully open, and the throttle valve aperture is 100%. The throttle valve aperture is regulated between 0 and 100%. When the throttle valve aperture is 50%, the throttle valve  34  is half open. 
   The throttle position sensor  35  and the throttle valve drive device  36  are ancillary to the throttle valve  34 . The throttle position sensor  35  is disposed facing the throttle valve  34  outside the intake pipe  31 , and generates throttle position information Sp proportional to the position of the throttle valve  34 , that is, the throttle valve aperture. The throttle valve drive device  36  consists of for example a throttle drive motor. This throttle valve drive device  36  is also disposed facing the throttle valve  34  outside the intake pipe  31 , and rotates the rotary shaft  34 A to turn the throttle valve  34  about the axis of the rotary shaft  34 A. The throttle valve aperture is regulated by this throttle valve drive device  36 . 
   The fuel injection valve  37  is disposed inside the intake pipe  31  in the vicinity of the intake valve  24  in the internal combustion engine proper  20 . This fuel injection valve  37  injects a calculated amount of fuel immediately in front of the intake valve  24  and thereby creates a mixture of air and fuel. By the amount of fuel injected by the fuel injection valve  37  being calculated, the air-fuel ratio of this mixture is regulated to approach a theoretical air-fuel ratio. 
   An airflow sensor  38  and an intake air temperature sensor  39  are disposed in the intake pipe  31  upstream of the throttle valve  34 . The airflow sensor  38  detects the flowrate of air supplied to the combustion chamber  22  through the throttle valve  34  and outputs intake airflow information Va proportional to this flowrate. The intake air temperature sensor  39  constitutes intake air temperature detecting means. This intake air temperature sensor  39  detects the temperature of air flowing into the combustion chamber  22  through the throttle valve  34  and outputs intake air temperature information Ta proportional to this air temperature. 
   The exhaust system  40  has an exhaust pipe  41 . This exhaust pipe  41  is connected to the combustion chamber  22  via the exhaust valve  25 . 
   The exhaust recirculating device  50  has an exhaust recirculating passage  51  and a recirculating valve device  52 . The exhaust recirculating passage  51  connects the exhaust pipe  41  to the intake pipe  31  downstream of the throttle valve  34 . This exhaust recirculating passage  51  recirculates some of the exhaust gas in the exhaust pipe  41  to the intake pipe  31  so that it is fed into the combustion chamber  22  with the mixture gas and lowers the combustion temperature inside the combustion chamber  22 , whereby harmful components in the exhaust gas are reduced. The-recirculating valve device  52  includes the recirculating valve and a drive device thereof, and the recirculating valve is disposed as to cross the exhaust recirculating passage  51 . The recirculating valve device  52  controls the exhaust recirculating passage  51  in correspondence with its valve aperture and thereby regulates the amount of exhaust gas recirculated to the intake pipe  31 . 
   The control system  60  has a battery  61  ancillary to the internal combustion engine  10 , a throttle opening/closing control device  70  connected between this battery  61  and the throttle valve drive device  36 , and a control unit  80  that receives a supply of electrical power from the battery  61 . The battery  61  is for example a 12V system battery, and in a normal state has an output voltage of approximately 13V. The throttle opening/closing control device  70  opens and closes power supply paths between the battery  61  and the throttle valve drive device  36 . These power supply paths include a direct power supply path  72  and an ignition power supply path  73 . An ignition switch  74  that is ON while the internal combustion engine  10  is running is connected to the ignition power supply path  73 . While the internal combustion engine  10  is running, power is supplied from the battery  61  to the throttle valve drive device  36  via the ignition power supply path  73  and via the throttle opening/closing control device  70 , and when the internal combustion engine  10  is stopped, power is supplied from the battery.  61  to the throttle valve drive device  36  via the direct power supply path  72  and the throttle opening/closing control device  70 . The throttle opening/closing control device  70  can be incorporated directly into the control unit  80 . 
   The control unit  80  is-constructed using for example a microcomputer. The control-unit  80  receives a supply of power from the battery  61  via the direct power supply path  72  and the ignition power supply path  73 . The direct power supply path  72  connects the battery  61  and the control unit  80  together at all times. When the internal combustion engine  10  is stopped, because the ignition switch  74  is OFF, the control unit  80  receives power from the battery  61  via the direct power supply path  72 . 
   The engine temperature information Tw from the cooling water temperature sensor  27 , the throttle position information Sp from the throttle position sensor  35 , the intake airflow information Va from the airflow sensor  38  and the intake air temperature information Ta from the intake air temperature sensor  39  are inputted to the control unit  80 . Also ancillary to the control unit  80  are an accelerator position sensor  81 , an environmental temperature sensor  82 , date/time information outputting means  83 , and a location sensor  84 . In correspondence with the position of an accelerator pedal operated by a driver of the automotive vehicle, the accelerator position sensor  81  outputs accelerator position information Ap proportional to the amount by which this accelerator pedal is being depressed. 
   The environmental temperature sensor  82  constitutes environmental temperature detecting means. This environmental temperature sensor  82  detects the environmental temperature around the internal combustion engine  10  and generates environmental temperature information Tc proportional to this environmental temperature. Specifically, this environmental temperature sensor  82  detects the air temperature inside the engine compartment of the vehicle, the air temperature around the intake pipe  31  in the vicinity of the throttle valve  34 , or the surface temperature of the intake pipe  31  in the vicinity of the throttle valve  34 . 
   The date/time information outputting means  83  outputs date/time information DT including date information and time information corresponding to a calendar. This date/time information outputting means  83  can alternatively be incorporated directly into the control unit  80 . The location sensor  84  detects the location of the internal combustion engine  10  on a map and outputs location information Lo corresponding to this location. The accelerator position information Ap, the environmental temperature information Tc, the date/time information DT and the location information Lo are also inputted to the control unit  80 . 
   The control unit  80  performs control of a fuel injection quantity of the fuel injection valve  37 , control of the exhaust gas recirculation flow of the exhaust recirculating device  50 , control of a target throttle valve aperture of the throttle valve  34 , and control of the throttle freeze protection operation of the throttle valve  34 . The control of the fuel injection quantity, the control of the exhaust gas recirculation flow and the control of the target throttle valve aperture are performed while the internal combustion engine  10  is running, and the control unit  80  receives power from the battery  61  via the ignition power supply path  73  and the ignition switch  74  to perform this control. The control of the throttle freeze protection operation is performed when the internal combustion engine  10  is stopped, and the control unit  80  receives power from the battery  61  via the direct power supply path  72  to perform this throttle freeze protection operation control. 
   In the control of the fuel injection quantity, the control unit  80  calculates a fuel injection quantity appropriate to the intake air mainly on the basis of the engine temperature information Tw, the intake airflow information Va and the intake air temperature information Ta, and, in synchrony with information on the angular position of the internal combustion engine  10  from a crank angle sensor (not shown), feeds a fuel injection time corresponding to that calculated fuel injection quantity to the fuel injection valve  37 . In the control of the exhaust gas recirculation flow, the control unit  80  calculates a valve aperture of the recirculating valve device  52  mainly on the basis of information on the speed of the internal combustion engine  10  from the crank angle sensor (not shown), the intake airflow information Va and the engine temperature information Tw, and drives this recirculating valve device  52  to that calculated valve aperture. In the control of the target throttle valve aperture, the control unit  80  calculates a target throttle valve aperture mainly on the basis of the accelerator position information Ap and the throttle position information Sp, and on the basis of this target throttle valve aperture feeds a target valve aperture control signal St to the throttle opening/closing control device  70  and thereby controls the throttle valve drive device  36  to the target valve aperture. 
   In the throttle freeze protection operation control, using the environmental temperature information Tc, the engine temperature information Tw, the intake air temperature information Ta, the date/time information DT or the location information Lo of when the internal combustion engine  10  is stopped, or using a drive level of the recirculating valve device  52  of when the internal combustion engine  10  is running, on the basis of these the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, and when it determines that the probability of the throttle valve  34  freezing is high it feeds a throttle freeze protection signal Sf to the throttle opening/closing control device  70  and supplies power from the battery  61  to the throttle valve drive device  36  through this throttle opening/closing control device  70  and causes it to perform a throttle freeze protection operation of oscillating the throttle valve aperture. 
   Next, the operation of the apparatus described above will be described. While the internal combustion engine  10  is running, a driver operates the accelerator pedal (not shown). The amount of depression of the accelerator pedal is converted into accelerator position information Ap by the accelerator position sensor  81  and inputted to the control unit  80 . The control unit  80  calculates a target valve aperture of the throttle valve  34  on the basis of the inputted accelerator position information Ap and throttle position information Sp, and supplies a target valve aperture control signal St corresponding to this target valve aperture to the throttle opening/closing control device  70 . In accordance with the target valve aperture control signal St, the throttle opening/closing control device  70  controls the throttle valve drive device  36  to regulate the valve aperture of the throttle valve  34  to the target valve aperture. 
   The flow of air supplied to the combustion chamber  22  through the intake pipe  31  is measured by the airflow sensor  38  and inputted to the control unit  80  as the intake airflow information Va. The temperature of the air supplied to the combustion chamber  22  through the intake pipe  31  is measured by the intake air temperature sensor  39  and inputted to the control unit  80  as the intake air temperature information Ta. The temperature of the cooling water supplied to the cylinder  23  is detected by the cooling water temperature sensor  27  and inputted to the control unit  80  as the engine temperature information Tw. 
   The control unit  80  calculates a fuel injection quantity on the basis of the intake airflow information Va, the intake air temperature information Ta and the engine temperature information Tw, and, at an angular position based on angular position information inputted from the crank angle sensor (not shown), injects that fuel injection quantity through the fuel injection valve  37 . As a result of this injection of fuel, a mixture of air flowing in through the intake pipe  31  and fuel supplied through the fuel injection valve  37  is formed. This mixture flows into the combustion chamber  22  of the internal combustion engine  10  through the intake valve  24 ; is compressed; is ignited by a spark created by the spark plug  26 , which is driven by the control unit  80 ; combusts; and exerts a driving torque through the piston  21  of the internal combustion engine  10 . 
   Exhaust gas from the combustion is discharged through the exhaust valve  25  into the exhaust pipe  41 . Some of this exhaust gas flows into the exhaust recirculating passage  51  of the exhaust recirculating device  50 . The control unit  80  calculates an exhaust recirculation quantity on the basis of speed information of the internal combustion engine  10  inputted from the crank angle sensor (not shown), the intake airflow information Va inputted from the airflow sensor  38 , and the engine temperature information Tw inputted from the intake air temperature sensor  39 , and regulates the valve aperture of the recirculating valve device  52  in correspondence with this exhaust recirculation quantity to control the exhaust recirculating passage  51 . As the exhaust recirculating passage  51  is regulated by the recirculating valve device  52 , exhaust gas from combustion flowing into the exhaust recirculating passage  51  flows into the intake pipe  31  under the negative pressure in the intake pipe  31 . 
   In the first preferred embodiment, when the internal combustion engine  10  is stopped, the control unit  80  receives a supply of power from the battery  61  through the direct power supply path  72  and performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, on the basis of the environmental temperature information Tc from the environmental temperature sensor  82 . When the inputted environmental temperature information Tc is below a predetermined value Tc 0  (for example 0° C.), the control unit  80  determines that the probability of the throttle valve  34  freezing is high and controls the throttle opening/closing control device  70  to perform a throttle freeze protection operation. 
   In this throttle freeze protection operation, the control unit  80  sends the throttle freeze protection signal Sf to the throttle opening/closing control device  70 . The throttle opening/closing control device  70  causes the throttle valve drive device  36  to execute the throttle freeze protection operation on the basis of the throttle freeze protection signal Sf from the control unit  80 . In this throttle freeze protection operation, the throttle valve drive device  36  receives a supply of power from the battery  61  through the throttle opening/closing control device  70  and oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation will now be explained with reference to the flow chart shown in  FIG. 2 .  FIG. 2  is a control flow chart of the throttle freeze protection operation in the first preferred embodiment, and is executed at intervals of a predetermined time (for example every 20 ms). This throttle freeze protection operation of  FIG. 2  includes seven steps S 101  to S 107 . 
   First, in step S 101 , the control unit  80  determines on the basis of for example the signal from the crank angle sensor (not shown) whether the internal combustion engine  10  has stopped, and if this determination result is No processing proceeds to step S 102  and sets an end flag to “0” and the routine ends. If the internal combustion engine  10  has stopped and the determination result of step S 101  is therefore Yes, processing proceeds to step S 103  and determines whether the end flag is “1”. If the determination result of step S 103  is Yes, it is inferred that the freeze protection operation of the throttle valve  34  has ended and the routine ends. When the end flag is not “1”, the determination result of step S 103  is No and processing proceeds to step S 104 . 
   In step S 104 , the environmental temperature information Tc from the environmental temperature sensor  82  is read in, and processing proceeds to the following step S 105 . In step S 105 , it is determined whether the environmental temperature information Tc inputted from the environmental temperature sensor  82  is below the predetermined value Tc 0  (for example 0° C. or less). When the environmental temperature information Tc inputted from the environmental temperature sensor  82  is not below the predetermined value Tc 0 , the determination result of step S 105  is No, it is inferred that it is not necessary to carry out a throttle freeze protection operation, and the routine ends. When the environmental temperature information Tc inputted from the environmental temperature sensor  82  is below the predetermined value Tc 0 , the determination result of step S 105  is Yes, it is inferred that it is necessary to carry out a throttle freeze protection operation, and processing proceeds to the following steps S 106 , S 107 . In step S 106  the end flag is set to “1”, and in step S 107  a throttle freeze prevention opening/closing drive command flag is set to “1” and the routine ends. 
   When the throttle freeze prevention opening/closing drive command flag is “1”, in accordance with a control program (not shown) the control unit  80  supplies a throttle freeze protection signal Sf to the throttle opening/closing control device  70 , and on the basis of this throttle freeze protection signal Sf the throttle opening/closing control device  70  executes a throttle freeze protection operation. In this throttle freeze protection operation, the throttle valve drive device  36  oscillates the valve aperture of the throttle valve  34 . 
   On the basis of the throttle freeze protection signal Sf, in accordance with a control program (not shown) the throttle opening/closing control device  70  controls the throttle valve drive device  36  so as to change the throttle aperture for example from fully closed→half open→fully open→half open→fully closed. In this case, in accordance with the throttle freeze protection signal Sf the throttle opening/closing control device  70  controls the throttle valve  34  to perform one opening and closing movement in which it goes from fully closed to fully open and back to fully closed. 
   However, alternatively, when the internal combustion engine  10  is stopped the throttle opening/closing control device  70  may preparatorily bring the throttle valve  34  to a half-open state, and then, on the basis of the throttle freeze protection signal Sf, when the throttle freeze prevention opening/closing drive command flag is “1”, control the throttle valve drive device  36  so that the throttle valve aperture changes from half open→fully open→half open→fully open→half open. In this case, the throttle opening/closing control device  70  controls the throttle valve  34  to perform one opening and closing movement in which it goes from half open to fully open and back to half open. 
   Or, the throttle valve aperture may be controlled to change from half open→fully open→half open→fully closed →half open, or the throttle valve aperture may be controlled to change from half open→fully closed→half open→fully closed→half open. In these cases, the throttle opening/closing control device  70  performs control to effect one opening and closing movement in which the throttle valve aperture goes from half open to fully closed and back to fully open. 
   When the internal combustion engine  10  is stopped, before the throttle valve  34  freezes, the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, and when this probability is high it causes a throttle freeze protection operation to be executed before the throttle valve  34  becomes frozen. Freezing of the throttle valve  34  occurs as a result of dew condensation occurring on the throttle valve  34  and water droplets arising from this dew condensation then freezing. The state of water droplets arising from dew condensation on the throttle valve  34  having frozen 100% will be called the state of the throttle valve being frozen, that is, the throttle-frozen state. The throttle freeze protection operation conducted by the control unit  80  is executed before the water droplets arising from dew condensation have frozen 100%, and indeed before a semi-frozen state is reached in which the water droplets have frozen about 50%. 
   If a throttle freeze protection operation is executed when the water droplets arising on the throttle valve  34  from dew condensation are in a 0% frozen state, because by that throttle freeze protection operation it is possible to shake off the water droplets formed by dew condensation on the throttle valve  34 , the throttle valve  34  can be prevented from progressing to a throttle-frozen state. And if the throttle freeze protection operation is executed with the water droplets condensed as dew on the throttle valve  34  in a semi-frozen state in which they are 50% frozen, because by that throttle freeze protection operation the water droplets having condensed as dew on the throttle valve  34  and ice formed by about half of that water freezing can be shaken off, similarly the throttle valve  34  can be prevented from progressing to a throttle-frozen state. 
   In the probability determination of whether or not the probability of the throttle valve  34  freezing is high, it is determined that the probability of the throttle valve  34  freezing is high when the environmental temperature information Tc is below the predetermined value Tc 0  (for example 0° C.), and the predetermined value Tc 0  in this probability determination is set so that if dew condensation on the throttle occurs, the throttle freeze protection operation is executed before those water droplets reach a semi-frozen state. As a result, in the throttle freeze protection operation, the throttle valve drive device  36  is prevented from consuming excessive energy, and damage to the throttle valve drive device  36  and the throttle valve  34  and its drive mechanism can also be avoided. 
   As described above, in the first preferred embodiment, because a throttle freeze protection operation of the throttle valve  34  is carried out and water droplets having formed on the throttle valve  34  and ice resulting from these water droplets partially freezing are removed before the throttle valve  34  freezes, freezing of the throttle valve can be prevented, and it is possible to guarantee sure startability and to prevent certainly a situation of the vehicle becoming immobile. And, damage of the throttle valve  34  and its throttle mechanism, and burning out of the throttle valve drive device  36 , can be prevented. Furthermore, because no throttle freeze protection operation is carried out when the probability of the throttle valve  34  freezing is low, energy can be saved and the lives of the throttle valve  34 , its throttle mechanism, and the throttle valve drive device  36  can be extended. 
   And, in this first preferred embodiment, because when the probability of the throttle valve  34  freezing is high the control unit  80  causes a throttle freeze protection operation to be carried out by supplying power from the battery  61  to the throttle valve drive device  36 , the throttle freeze protection operation can be carried out when the internal combustion engine  10  is stopped by using the throttle valve drive device  36  provided for driving the throttle valve  34  when the internal combustion engine  10  is running, and thus the throttle freeze protection operation can be performed without a special throttle valve driving device being added. 
   Second Preferred Embodiment 
   In this second preferred embodiment, the probability determination of whether or not the probability of the throttle valve  34  freezing is high is carried out using the intake air temperature information Ta from the intake air temperature sensor  39  shown in  FIG. 1 , and when that probability is high, a throttle freeze protection operation is carried out. Whereas in the first preferred embodiment the environmental temperature information Tc from the environmental temperature sensor  82  was used, in the second preferred embodiment the intake air temperature sensor  39  is used instead of the environmental temperature sensor  82 . Otherwise, it is the same as the first preferred embodiment. Because the overall construction, and operation when the internal combustion engine  10  is running, of this second preferred embodiment are the same as in the first preferred embodiment, a description of these will be omitted. 
   In this second preferred embodiment, after the internal combustion engine  10  stops, when the intake air temperature information Ta inputted from the intake air temperature sensor  39  is below a predetermined value (for example 0° C.), the control unit  80  determines that the probability of the throttle valve  34  freezing is high and sends a throttle freeze protection signal Sf to the throttle opening/closing control device  70 . And in accordance with the throttle freeze protection signal Sf from the control unit  80 , the throttle opening/closing control device  70  drives the throttle valve drive device  36  to oscillate the throttle valve  34 . 
   The throttle freeze protection operation of this second preferred embodiment will now be explained with reference to the flow chart of  FIG. 3 .  FIG. 3  is a control flow chart of the throttle freeze protection operation of the second preferred embodiment, and the control routine of this  FIG. 3  is executed at intervals of a predetermined time (for example every 20 ms). The control flow chart of  FIG. 3  includes seven steps, S 201  to S 207 . Steps S 201 , S 202  and S 203  are the same as steps S 101 , S 102  and S 103  in  FIG. 2  and will not be described again here. 
   In step S 203 , when the end flag is not “1”, because the determination result of step S 203  is No, processing proceeds to the next step S 204  and reads in the intake air temperature information Ta of inside the intake pipe  31  from the intake air temperature sensor  39 . In the following step S 205 , it is determined whether the intake air temperature information Ta of inside the intake pipe  31  inputted from the intake air temperature sensor  39  is below a predetermined value Ta 0  (for example below 0° C.). When the intake air temperature information Ta is below the predetermined value Ta 0 , the determination result of step S 205  is No, it is inferred that it is not necessary to carry out a throttle freeze protection operation, and the routine ends. When the intake air temperature information Ta is below the predetermined value Ta 0 , the determination result of step S 205  is Yes, it is inferred that it is necessary to carry out a throttle freeze protection operation, and in the next step S 206  the end flag is set to “1”, in step S 207  the throttle freeze prevention opening/closing drive command flag is set to “1”, and the routine ends. 
   In this second preferred embodiment also, when the throttle freeze prevention opening/closing drive command flag is “1”, in accordance with a control program (not shown) the control unit  80  supplies a throttle freeze protection signal Sf to the throttle opening/closing control device  70 , and on the basis of this throttle freeze protection signal Sf the throttle opening/closing control device  70  executes a throttle freeze protection operation. In this throttle freeze protection operation, the throttle valve drive device  36  oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this second preferred embodiment is the same as the throttle freeze protection operation in the first preferred embodiment, and by this throttle freeze protection operation it is possible to prevent freezing of the throttle valve  34 . 
   In this second preferred embodiment also, when the internal combustion engine  10  is stopped, before the throttle valve  34  freezes, the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high,and, when it determines that this probability is high, causes a throttle freeze protection operation to be executed before the throttle valve  34  reaches a throttle-frozen state. Freezing of the throttle valve  34  occurs as a result of dew condensing on the throttle valve  34  and water droplets arising from this dew condensation then freezing. The state of water droplets arising from dew condensation on the throttle valve  34  having frozen 100% is here called the state of the throttle valve being frozen, that is, the throttle-frozen state. The throttle freeze protection operation conducted by the control unit  80  is executed before the water droplets arising from dew condensation have frozen 100%, and indeed before the water droplets reach a semi-frozen state in which they have frozen about 50%. 
   If a throttle freeze protection operation is executed when the water droplets arising on the throttle valve  34  from dew condensation are in a 0% frozen state, because by that throttle freeze protection operation it is possible to shake off the water droplets formed by dew condensation on the throttle valve  34 , the throttle valve  34  can be prevented from progressing to a throttle-frozen state. And if the throttle freeze protection operation is executed with the water droplets condensed as dew on the throttle valve  34  in a semi-frozen state in which they are 50% frozen, because by that throttle freeze protection operation the water droplets having condensed as dew on the throttle valve  34  and ice formed by about half of that water freezing can be shaken off, similarly the throttle valve  34  can be prevented from progressing to a throttle-frozen state. 
   In the probability determination of whether or not the probability of the throttle valve  34  freezing is high, it is determined that the probability of the throttle valve  34  freezing is high when the intake air temperature information Ta is below the predetermined value Ta 0  (for example 0° C.), and the predetermined value Ta 0  in this probability determination is set so that if dew condensation on the throttle occurs, the throttle freeze protection operation is executed before those water droplets reach a semi-frozen state. As a result, in the throttle freeze protection operation, the throttle valve drive device  36  is prevented from consuming excessive energy, and damage to the throttle valve drive device  36  and the throttle valve  34  and its drive mechanism can also be avoided. 
   The intake air temperature sensor  39  is a sensor used to calculate the fuel injection quantity of the fuel injection valve  37 . In this second preferred embodiment, because the probability determination of whether or not the probability of the throttle valve  34  freezing is high is carried out on the basis of the intake air temperature information Ta inputted from the intake air temperature sensor  39 , without any special sensor being added, freezing of the throttle valve  34  can be prevented without any increase in cost being incurred. 
   Third Preferred Embodiment 
   In this third preferred embodiment, a probability determination of whether or not the probability of the throttle valve  34  freezing is high is carried out using the engine temperature information Tw from the cooling water temperature sensor  27  shown in  FIG. 1 , and when that probability is high, a throttle freeze protection operation is carried out. Whereas in the first preferred embodiment the environmental temperature information Tc from the environmental temperature sensor  82  was used, in the third preferred embodiment the cooling water temperature sensor  27  is used instead of the environmental temperature sensor  82 . Otherwise, it is the same as the first preferred embodiment. Because the overall construction, and operation when the internal combustion engine  10  is running, of this third preferred embodiment are the same as in the first preferred embodiment, a description of these will be omitted. 
   In this third preferred embodiment, after the internal combustion engine  10  stops, when the engine temperature information Tw inputted from the cooling water temperature sensor  27  is below a predetermined value Tw 0  (for example 0° C.), the control unit  80  determines that the probability of the throttle valve  34  freezing is high and sends the throttle freeze protection signal Sf to the throttle opening/closing control device  70 . In accordance with the throttle freeze protection signal Sf from the control unit  80 , the throttle opening/closing control device  70  drives the throttle valve drive device  36  and thereby oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this third preferred embodiment will now be described with reference to the flow chart shown in  FIG. 4 .  FIG. 4  is a control flow chart of the throttle freeze protection operation in the third preferred embodiment, and the control routine of this  FIG. 4  is executed at intervals of a predetermined time (for example every 20 ms). The control flow chart of  FIG. 4  includes seven steps S 301  to S 307 . Steps S 301 , S 302  and S 303  are the same as steps S 101 , S 102  and S 103  of  FIG. 2  and will not be described again here. 
   In step S 303 , when the end flag is not “1”, because the determination result of step S 303  is No, processing proceeds to the next step S 304  and reads in the engine temperature information Tw from the cooling water temperature sensor  27 . In the following step S 305 , it is determined whether the engine temperature information Tw is below the predetermined value Tw 0  (for example below 0° C.). When the engine temperature information Tw is not below the predetermined value Tw 0 , the determination result of step S 305  is No, it is inferred that it is not necessary to carry out a throttle freeze protection operation, and the routine ends. When the engine temperature information Tw is below the predetermined value Tw 0 , the determination result of step S 305  is Yes, it is inferred that it is necessary to carry out a throttle freeze protection operation, in the following step S 306  the end flag is set to “1”, in step S 307  the throttle freeze prevention opening/closing drive command flag is set to “1”, and then the routine ends. 
   In this third preferred embodiment also, when the throttle freeze prevention opening/closing drive command flag is “1”, in accordance with a control program (not shown) the control unit  80  supplies a throttle freeze protection signal Sf to the throttle opening/closing control device  70 , and on the basis of this throttle freeze protection signal Sf the throttle opening/closing control device  70  executes a throttle freeze protection operation. In this throttle freeze protection operation, the throttle valve drive device  36  oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this third preferred embodiment is the same as the throttle freeze protection operation in the first preferred embodiment, and by this throttle freeze protection operation it is possible to prevent freezing of the throttle valve  34 . 
   In this third preferred embodiment also, when the internal combustion engine  10  is stopped, before the throttle valve  34  freezes, the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, and, when it determines that this probability is high, causes a throttle freeze protection operation to be executed before the throttle valve  34  reaches a throttle-frozen state. Freezing of the throttle valve  34  occurs as a result of dew condensing on the throttle valve  34  and water droplets arising from this dew condensation then freezing. The state of water droplets arising from dew condensation on the throttle valve  34  having frozen 100% is here called the state of the throttle valve having frozen, that is, the throttle-frozen state. The throttle freeze protection operation conducted by the control unit  80  is executed before the water droplets arising from dew condensation have frozen 100%, and indeed before the water droplets reach a semi-frozen state in which they have frozen about 50%. 
   If a throttle freeze protection operation is executed when the water droplets arising on the throttle valve  34  from dew condensation are in a 0% frozen state, because by that throttle freeze protection operation it is possible to shake off the water droplets formed by dew condensation on the throttle valve  34 , the throttle valve  34  can be prevented from progressing to a throttle-frozen state. And if the throttle freeze protection operation is executed with the water droplets condensed as dew on the throttle valve  34  in a semi-frozen state in which they are 50% frozen, because by that throttle freeze protection operation the water droplets having condensed as dew on the throttle valve  34  and ice formed by about half of that water freezing can be shaken off, similarly the throttle valve  34  can be prevented from progressing to a throttle-frozen state. 
   In the probability determination of whether or not the probability of the throttle valve  34  freezing is high, it is determined that the probability of the throttle valve  34  freezing is high when the engine temperature information Tw is below the predetermined value Tw 0  (for example 0° C.), and the predetermined value Tw 0  in this probability determination is set so that if dew condensation on the throttle occurs, the throttle freeze protection operation is executed before those water droplets reach a semi-frozen state. As a result, in the throttle freeze protection operation, the throttle valve drive device  36  is prevented from consuming excessive energy, and damage to the throttle valve drive device  36  and the throttle valve  34  and its drive mechanism can also be avoided. 
   The cooling water temperature sensor  27  is also a sensor used to calculate the fuel injection quantity of the fuel injection valve  37 . In this third preferred embodiment, because the probability determination of whether or not the probability of the throttle valve  34  freezing is high is carried out on the basis of the engine temperature information Tw inputted from the cooling water temperature sensor  27 , without any special sensor being added, as in the second preferred embodiment freezing of the throttle valve  34  can be certainly prevented without any increase in cost being incurred. 
   Fourth Preferred Embodiment 
   In this fourth preferred embodiment, the probability determination of whether or not the probability of the throttle valve  34  freezing is high is carried out using the date/time information DT from the date/time information outputting means  83  shown in  FIG. 1 , and when that probability is high, a throttle freeze protection operation is carried out. Whereas in the first preferred embodiment the environmental temperature information Tc from the environmental temperature sensor  82  was used, in the fourth preferred embodiment the date/time information outputting means  83  is used instead of the environmental temperature sensor  82 . Otherwise, it is the same as the first preferred embodiment. Because the overall construction, and operation when the internal combustion engine  10  is running, of this fourth preferred embodiment are the same as in the first preferred embodiment, a description of these will be omitted. 
   In this fourth preferred embodiment, after the internal combustion engine  10  stops, when the date/time information DT inputted from the date/time information outputting means  83  is in a predetermined date range and time range, the control unit  80  determines that the probability of the throttle valve  34  freezing is high and sends the throttle freeze protection signal Sf to the throttle opening/closing control device  70 . In accordance with the throttle freeze protection signal Sf from the control unit  80 , the throttle opening/closing control device  70  drives the throttle valve drive device  36  and thereby oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this fourth preferred embodiment will now be described with reference to the flow chart shown in  FIG. 5 .  FIG. 5  is a control flow chart of the throttle freeze protection operation in the fourth preferred embodiment, and the control routine of this  FIG. 5  is executed at intervals of a predetermined time (for example every 20 ms). The control flow chart of  FIG. 5  includes seven steps S 401  to S 407 . Steps S 401 , S 402  and S 403  are the same as steps S 101 , S 102  and S 103  of  FIG. 2  and will not be described again here. 
   In step S 403 , when the end flag is not “1”, because the determination result of step S 403  is No, the control unit  80  proceeds to the next step S 404  and reads in the date/time information DT from the date/time information outputting means  83 . In the following step S 405 , it is determined whether the date information and time information included in the date/time information DT are in a predetermined date range and time range, for example between November and March and between 10 pm and 8 am. When the date information and time information included in the date/time information DT are not in the predetermined date range and time range, the determination result of step S 405  is No, it is inferred that it is not necessary to carry out a throttle freeze protection operation, and the routine ends. When the date information and time information included in the date/time information DT are in the predetermined date range and time range, the determination result of step S 405  is Yes, it is inferred that it is necessary to carry out a throttle freeze protection operation, in step S 406  the end flag is set to “1”, in the following step S 407  the throttle freeze prevention opening/closing drive command flag is set to “1”, and then the routine ends. 
   In this fourth preferred embodiment also, when the throttle freeze prevention opening/closing drive command flag is “1”, in accordance with a control program (not shown) the control unit  80  supplies a throttle freeze protection signal Sf to the throttle opening/closing control device  70 , and on the basis of this throttle freeze protection signal Sf the throttle opening/closing control device  70  executes a throttle freeze protection operation. In this throttle freeze protection operation, the throttle valve drive device  36  oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this fourth preferred embodiment is the same as the throttle freeze protection operation in the first preferred embodiment, and by this throttle freeze protection operation it is possible to prevent freezing of the throttle valve  34 . 
   In this fourth preferred embodiment also, when the internal combustion engine  10  is stopped, before the throttle valve  34  freezes, the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, and, when it determines that this probability is high, causes a throttle freeze protection operation to be executed before the throttle valve  34  reaches a throttle-frozen state. Freezing of the throttle valve  34  occurs as a result of dew condensing on the throttle valve  34  and water droplets arising from this dew condensation then freezing. The state of water droplets arising from dew condensation on the throttle valve  34  having frozen 100% is here called the state of the throttle valve having frozen, that is, the throttle-frozen state. The throttle freeze protection operation conducted by the control unit  80  is executed before the water droplets arising from dew condensation have frozen 100%, and indeed before the water droplets reach a semi-frozen state in which they have frozen about 50%. 
   If a throttle freeze protection operation is executed when the water droplets arising on the throttle valve  34  from dew condensation are in a 0% frozen state, because by that throttle freeze protection operation it is possible to shake off the water droplets formed by dew condensation on the throttle valve  34 , the throttle valve  34  can be prevented from progressing to a throttle-frozen state. And if the throttle freeze protection operation is executed with the water droplets condensed as dew on the throttle valve  34  in a semi-frozen state in which they are 50% frozen, because by that throttle freeze protection operation the water droplets having condensed as dew on the throttle valve  34  and ice formed by about half of that water freezing can be shaken off, similarly the throttle valve  34  can be prevented from progressing to a throttle-frozen state. 
   In this fourth preferred embodiment, in the probability determination of whether or not the probability of the throttle valve  34  freezing is high, it is determined that the probability of the throttle valve  34  freezing is high when the date information and time information of the date/time information DT are in a predetermined date range and time range, and the predetermined date range and time range in this probability determination are set so that if dew condensation on the throttle occurs, the throttle freeze protection operation is executed before those water droplets reach a semi-frozen state. As a result, in the throttle freeze protection operation, the throttle valve drive device  36  is prevented from consuming excessive energy, and damage to the throttle valve drive device  36  and the throttle valve  34  and its drive mechanism can also be avoided. 
   The predetermined date range and time range may alternatively be set in a combination, such as for example from 11 pm to 6 am in autumn and from 8 pm to 9 am in winter. 
   In this fourth preferred embodiment, because a throttle freeze protection operation is executed in seasons and time periods when freezing of the throttle valve  34  occurs the most readily, such as on winter nights, freezing of the throttle valve  34  can be prevented with energy being saved as well. 
   Fifth Preferred Embodiment 
   In this fifth preferred embodiment, the probability determination of whether or not the probability of the throttle valve  34  freezing is high is carried out using the location information Lo from the location sensor  84  shown in  FIG. 1 , and when that probability is high, a throttle freeze protection operation is carried out. Whereas in the first preferred embodiment the environmental temperature information Tc from the environmental temperature sensor  82  was used, in the fifth preferred embodiment the location sensor  84  is used instead of the environmental temperature sensor  82 . Otherwise, it is the same as the first preferred embodiment. Because the overall construction, and operation when the internal combustion engine  10  is running, of this fifth preferred embodiment are the same as in the first preferred embodiment, a description of these will be omitted. 
   In this fifth preferred embodiment, after the internal combustion engine  10  stops, when the location information Lo inputted from the location sensor  84  is in a predetermined location range, the control unit  80  determines that the probability of the throttle valve  34  freezing is high and sends the throttle freeze protection signal Sf to the throttle opening/closing control device  70 . In accordance with the throttle freeze protection signal Sf from the control unit  80 , the throttle opening/closing control device  70  drives the throttle valve drive device  36  and thereby oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this fifth preferred embodiment will now be described with reference to the flow chart shown in  FIG. 6 .  FIG. 6  is a control flow chart of the throttle freeze protection operation in the fifth preferred embodiment, and the control routine of this  FIG. 6  is executed at intervals of a predetermined time (for example every 20 ms). The control flow chart of  FIG. 6  includes seven steps S 501  to S 507 . Steps S 501 , S 502  and S 503  are the same as steps S 101 , S 102  and S 103  of  FIG. 2  and will not be described again here. 
   In step S 503 , when the end flag is not “1”, because the determination result of step S 503  is No, the control unit  80  proceeds to step S 504  and reads in the location information Lo on where the internal combustion engine is located from the location sensor  84 . In the following step S 505 , it is determined whether the location information Lo is in a predetermined location range (for example a cold region such as Hokkaido). When the location information Lo is not in the predetermined location range, the determination result of step S 505  is No, it is inferred that it is not necessary to carry out a throttle freeze protection operation, and the routine ends. When the location information Lo is in the predetermined location range, the determination result of step S 505  is Yes, it is inferred that it is necessary to carry out a throttle freeze protection operation, in step S 506  the end flag is set to “1”, in step S 507  the throttle freeze prevention opening/closing drive command flag is set to “1”, and then the routine ends. 
   In this fifth preferred embodiment also, when the throttle freeze prevention opening/closing drive command flag is “1”, in accordance with a control program (not shown) the control unit  80  supplies a throttle freeze protection signal Sf to the throttle opening/closing control device  70 , and on the basis of this throttle freeze protection signal Sf the throttle opening/closing control device  70  executes a throttle freeze protection operation. In this throttle freeze protection operation, the throttle valve drive device  36  oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this fifth preferred embodiment is the same as the throttle freeze protection operation in the first preferred embodiment, and by this throttle freeze protection operation it is possible to prevent freezing of the throttle valve  34 . 
   In this fifth preferred embodiment also, when the internal combustion engine  10  is stopped, before the throttle valve  34  freezes, the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, and, when it determines that this probability is high, causes a throttle freeze protection operation to be executed before the throttle valve  34  reaches a throttle-frozen state. Freezing of the throttle valve  34  occurs as a result of dew condensing on the throttle valve  34  and water droplets arising from this dew condensation then freezing. The state of water droplets arising from dew condensation on the throttle valve  34  having frozen 100% is here called the state of the throttle valve having frozen, that is, the throttle-frozen state. The throttle freeze protection operation conducted by the control unit  80  is executed before the water droplets arising from dew condensation have frozen 100%, and indeed before the water droplets reach a semi-frozen state in which they have frozen about 50%. 
   If a throttle freeze protection operation is executed when the water droplets arising on the throttle valve  34  from dew condensation are in a 0% frozen state, because by that throttle freeze protection operation it is possible to shake off the water droplets formed by dew condensation on the throttle valve  34 , the throttle valve  34  can be prevented from progressing to a throttle-frozen state. And if the throttle freeze protection operation is executed with the water droplets condensed as dew on the throttle valve  34  in a semi-frozen state in which they are 50% frozen, because by that throttle freeze protection operation the water droplets having condensed as dew on the throttle valve  34  and ice formed by about half of that water freezing can be shaken off, similarly the throttle valve  34  can be prevented from progressing to a throttle-frozen state. 
   In this fifth preferred embodiment, in the probability determination of whether or not the probability of the throttle valve  34  freezing is high, it is determined that the probability of the throttle valve  34  freezing is high when the location information Lo is in a predetermined location range, and the predetermined location range in this probability determination is set so that if dew condensation on the throttle occurs, the throttle freeze protection operation is executed before those water droplets reach a semi-frozen state. As a result, in the throttle freeze protection operation, the throttle valve drive device  36  is prevented from consuming excessive energy, and damage to the throttle valve drive device  36  and the throttle valve  34  and its drive mechanism can also be avoided. 
   The predetermined location range of the location information Lo may alternatively be set for example to anywhere in Hokkaido and over 1000 m above sea level, or anywhere in North America and above latitude 45°, or may be set to any region in a subpolar or polar zone. 
   In this fifth preferred embodiment, because a throttle freeze protection operation is executed in locations where freezing of the throttle valve  34  occurs the most readily, such as cold regions and high-altitude regions, freezing of the throttle valve  34  can be prevented with energy being saved as well. 
   Sixth Preferred Embodiment 
   In this sixth preferred embodiment, the probability determination of whether or not the probability of the throttle valve  34  freezing is high is carried out on the basis of the operation history of the recirculating valve device  52  of the exhaust recirculating device  50  while the internal combustion engine  10  was operating, and when that probability is high, a freeze protection operation of the throttle valve  34  is carried out. Whereas in the first preferred embodiment the environmental temperature information Tc from the environmental temperature sensor  82  was used, in the sixth preferred embodiment the operation history of the recirculating valve device  52  of the exhaust recirculating device  50  is used instead of the environmental temperature sensor  82 . Otherwise, it is the same as the first preferred embodiment. Because the overall construction, and operation when the internal combustion engine  10  is running, of this sixth preferred embodiment are the same as in the first preferred embodiment, a description of these will be omitted. 
   The recirculating valve device  52  of the exhaust recirculating device  50  recirculates exhaust gas from the exhaust pipe  41  to the intake pipe  31  while the internal combustion engine  10  is running, and historical information on the valve aperture of the recirculating valve device  52  while the internal combustion engine  10  is running is stored in memory in the control unit  80 . This valve aperture history of the recirculating valve device  52  is accumulated during running of the internal combustion engine  10 , and it remains even when the internal combustion engine  10  stops, but when operation of the internal combustion engine  10  starts the next time it is reset. In this sixth preferred embodiment, after the internal combustion engine  10  stops, the control unit  80  refers to this valve aperture history of the recirculating valve device  52  pertaining to the previous operation of the internal combustion engine  10  stored in memory, and when the maximum valve aperture is above a predetermined valve aperture (for example above 50%), it determines that the probability of the throttle valve  34  freezing is high and sends the throttle freeze protection signal Sf to the throttle opening/closing control device  70 . In accordance with the throttle freeze protection signal Sf from the control unit  80 , the throttle opening/closing control device  70  drives the throttle valve drive device  36  and thereby oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this sixth preferred embodiment will now be described with reference to the flow chart shown in  FIG. 7 .  FIG. 7  is a control flow chart of the throttle freeze protection operation in the sixth preferred embodiment, and the control routine of this  FIG. 7  is executed at intervals of a predetermined time (for example every 20 ms). The control flow chart of  FIG. 7  includes six steps S 601  to S 606 . Steps S 601 , S 602  and S 603  are the same as steps S 101 , S 102  and S 103  of  FIG. 2  and will not be described again here. 
   In step S 603 , when the end flag is not “1”, because the determination result of step S 603  is No, in step S 604  the control unit  80  determines whether the maximum valve aperture of the recirculating valve device  52  in the previous operation of the internal combustion engine  10  is above a predetermined value (for example 50%). When the maximum valve aperture of the recirculating valve device  52  in the previous operation of the internal combustion engine  10  is not above the predetermined value, the determination result of step S 604  is No, it is inferred that it is not necessary to carry out a throttle freeze protection operation, and the routine ends. When the maximum valve aperture of the recirculating valve device  52  in the previous operation of the internal combustion engine  10  is above the predetermined value, the determination result of step S 604  is Yes, it is inferred that it is necessary to carry out a throttle freeze protection operation, in step S 605  the end flag is set to “1”, instep S 606  the throttle freeze prevention opening/closing drive command flag is set to “1”, and then the routine ends. 
   In this sixth preferred embodiment also, when the throttle freeze prevention opening/closing drive command flag is “1”, in accordance with a control program (not shown) the control unit  80  supplies a throttle freeze protection signal Sf to the throttle opening/closing control device  70 , and on the basis of this throttle freeze protection signal Sf the throttle opening/closing control device  70  executes a throttle freeze protection operation. In this throttle freeze protection operation, the throttle valve drive device  36  oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this sixth preferred embodiment is the same as the throttle freeze protection operation in the first preferred embodiment, and by this throttle freeze protection operation it is possible to prevent freezing of the throttle valve  34 . 
   In this sixth preferred embodiment also, when the internal combustion engine  10  is stopped, before the throttle valve  34  freezes, the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, and, when it determines that this probability is high, causes a throttle freeze protection operation to be executed before the throttle valve  34  reaches a throttle-frozen state. Freezing of the throttle valve  34  occurs as a result of dew condensing on the throttle valve  34  and water droplets arising from this dew condensation then freezing. The state of water droplets arising from dew condensation on the throttle valve  34  having frozen 100% is here called the state of the throttle valve having frozen, that is, the throttle-frozen state. The throttle freeze protection operation conducted by the control unit  80  is executed before the water droplets arising from dew condensation have frozen 100%, and indeed before the water droplets reach a semi-frozen state in which they have frozen about 50%. 
   If a throttle freeze protection operation is executed when the water droplets arising on the throttle valve  34  from dew condensation are in a 0% frozen state, because by that throttle freeze protection operation it is possible to shake off the water droplets formed by dew condensation on the throttle valve  34 , the throttle valve  34  can be prevented from progressing to a throttle-frozen state. And if the throttle freeze protection operation is executed with the water droplets condensed as dew on the throttle valve  34  in a semi-frozen state in which they are 50% frozen, because by that throttle freeze protection operation the water droplets having condensed as dew on the throttle valve  34  and ice formed by about half of that water freezing can be shaken off, similarly the throttle valve  34  can be prevented from progressing to a throttle-frozen state. 
   In this sixth preferred embodiment, in the probability determination of whether or not the probability of the throttle valve  34  freezing is high, it is determined that the probability of the throttle valve  34  freezing is high when the maximum valve aperture of the recirculating valve device  52  in the previous operation of the internal combustion engine  10  is above the predetermined value, and the predetermined value in this probability determination is set so that if dew condensation on the throttle occurs, the throttle freeze protection operation is executed before those water droplets reach a semi-frozen state. As a result, in the throttle freeze protection operation, the throttle valve drive device  36  is prevented from consuming excessive energy, and damage to the throttle valve drive device  36  and the throttle valve  34  and its drive mechanism can also be avoided. 
   If when the internal combustion engine  10  is running the flow of exhaust gas recirculated by the exhaust recirculating device  50  rises above a predetermined level, the probability of the throttle valve  34  freezing after the internal combustion engine  10  stops is high. In this sixth preferred embodiment, because a throttle freeze protection operation is carried out when the probability of the throttle valve  34  freezing is high as a result of exhaust gas recirculation, freezing of the throttle valve  34  can be prevented with energy being saved as well. 
   Although here it was determined whether or not the probability of the throttle valve  34  freezing is high on the basis of the valve aperture history of the recirculating valve device  52  of the previous operation of the internal combustion engine  10 , alternatively an exhaust gas recirculation flow may be calculated from a recirculation valve aperture and an operating state of the internal combustion engine  10  and the probability of the throttle valve  34  freezing then determined on the basis of this. Or, a recirculated exhaust gas flow may be estimated when the internal combustion engine is stopped on the basis of a recirculating valve aperture of immediately before the internal combustion engine  10  stopped, and the probability of the throttle valve  34  freezing then determined on the basis of this. 
   Seventh Preferred Embodiment 
   In this seventh preferred embodiment, the control unit  80  starts the throttle freeze protection operation after a predetermined standby time has elapsed from the time at which the internal combustion engine  10  stopped. Otherwise, it is the same as the first preferred embodiment. 
   In this seventh preferred embodiment, as in the first preferred embodiment, while the internal combustion engine  10  is stopped, when the environmental temperature information Tc inputted from the environmental temperature sensor  82  is below a predetermined value (for example 0° C.), the control unit  80  determines that the probability of the throttle valve  34  freezing is high and sends the throttle freeze protection signal Sf to the throttle opening/closing control device  70 . In accordance with the throttle freeze protection signal Sf, the throttle opening/closing control device  70  drives the throttle valve drive device  36  and thereby applies an oscillating motion to the throttle valve  34 . In this seventh preferred embodiment, when the control unit  80  has determined that the probability of the throttle valve  34  freezing is high, it stands by until a predetermined standby time T 1  (for example 1 hour) has elapsed from the time at which the internal combustion engine  10  stopped, and carries out a throttle freeze protection operation after this standby time T 1  elapses. 
   The throttle freeze protection operation in this seventh preferred embodiment will now be described with reference to  FIG. 8  and  FIG. 9 .  FIG. 8  is a flowchart of standby time timing carried out for the internal combustion engine  10 , executed at intervals of a predetermined time (for example every 500 ms). This flow chart of  FIG. 8  includes two steps S 701 , S 702 . In step S 701 , first it is determined whether a standby timer is at 0, and when the standby timer is at 0, because the determination result of step S 701  is Yes, it is inferred that the standby time T 1  has elapsed, and the routine ends. When the standby timer is not at 0, because the determination result of step S 701  is No, the control unit  80  carries out a decrementing of the standby timer in Step S 702 . 
     FIG. 9  is a control flow chart of the throttle freeze protection operation in the seventh preferred embodiment, executed at intervals of a predetermined time (for example 20 ms). This flow chart includes eight steps S 703  to S 710 . 
   First, in step S 703 , the control unit  80  determines for example on the basis of a signal from the crank angle sensor (not shown) whether the internal combustion engine  10  has stopped, and when the internal combustion engine  10  has not stopped, because the determination result of step S 703  is No, it proceeds to step S 704 , sets the end flag to “0”, sets the standby time to T 1  (for example 1 hour), and then the routine ends. When the internal combustion engine  10  has stopped, because the determination result of step S 703  is Yes, processing proceeds to step S 705  and determines whether the end flag is “1”. When the end flag is “1”, the determination result of step S 705  is Yes, it is inferred that the throttle freeze protection operation has ended, and the routine ends. 
   When the end flag is not “1”, the determination result of step S 705  is No, and processing proceeds to the next step S 706 . In step S 706 , it is determined whether the standby timer is at 0, and if the standby timer is not at 0 the determination result of step S 706  is No and the control unit  80  determines it is standing by, and the routine ends. When the standby timer is 0, because the determination result of step S 706  is Yes, processing proceeds to the following step S 707  and reads in the environmental temperature information Tc from the environmental temperature sensor  82 . In the next step S 708 , it is determined whether the environmental temperature information Tc inputted from the environmental temperature sensor  82  is below the predetermined value Tc 0  (for example below 0° C.). When the environmental temperature information Tc is not below the predetermined value Tc 0 , the determination result of step S 708  is No, it is inferred that it is not necessary to carry out a throttle freeze protection operation, and the routine ends. When the environmental temperature information Tc is below the predetermined value Tc 0 , the determination result of step S 708  is Yes, it is inferred it is necessary to carry out a throttle freeze protection operation, in step S 709  the end flag is set to “1”, in step S 710  the throttle freeze prevention opening/closing drive command flag is set to “1”, and the routine ends. 
   In this seventh preferred embodiment, after a standby time T 1  elapses from when the internal combustion engine  10  stops, when the throttle freeze prevention opening/closing drive command flag is “1”, in accordance with a control program (not shown) the control unit  80  supplies a throttle freeze protection signal Sf to the throttle opening/closing control device  70 , and on the basis of this throttle freeze protection signal Sf the throttle opening/closing control device  70  executes a throttle freeze protection operation. In this throttle freeze protection operation, the throttle valve drive device  36  oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this seventh preferred embodiment is the same as the throttle freeze protection operation in the first preferred embodiment, and by this throttle freeze protection operation it is possible to prevent freezing of the throttle valve  34 . 
   In this seventh preferred embodiment, when the internal combustion engine  10  is stopped, after the standby time T 1  elapses from when the internal combustion engine  10  stopped, before the throttle valve  34  freezes, the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, and, when it determines that this probability is high, causes a throttle freeze protection operation to be executed before the throttle valve  34  reaches a throttle-frozen state. Freezing of the throttle valve  34  occurs as a result of dew condensing on the throttle valve  34  and water droplets arising from this dew condensation then freezing. The state of water droplets arising from dew condensation on the throttle valve  34  having frozen 100% is here called the state of the throttle valve having frozen, that is, the throttle-frozen state. The throttle freeze protection operation conducted by the control unit  80  is executed before the water droplets arising from dew condensation have frozen 100%, and indeed before the water droplets reach a semi-frozen state in which they have frozen about 50%. 
   If a throttle freeze protection operation is executed when the water droplets arising on the throttle valve  34  from dew condensation are in a 0% frozen state, because by that throttle freeze protection operation it is possible to shake off the water droplets formed by dew condensation on the throttle valve  34 , the throttle valve  34  can be prevented from progressing to a throttle-frozen state. And if the throttle freeze protection operation is executed with the water droplets condensed as dew on the throttle valve  34  in a semi-frozen state in which they are 50% frozen, because by that throttle freeze protection operation the water droplets having condensed as dew on the throttle valve  34  and ice formed by about half of that water freezing can be shaken off, similarly the throttle valve  34  can be prevented from progressing to a throttle-frozen state. 
   In this seventh preferred embodiment, after the standby time T 1  elapses from when the internal combustion engine  10  stopped, the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, and in this probability determination it is determined that the probability of the throttle valve  34  freezing is high when the environmental temperature information Tc is below a predetermined value Tc 0  (for example 0° C.). In this seventh preferred embodiment, the standby time T 1  and the predetermined value Tc 0  in the, probability determination are set so that if dew condensation on the throttle occurs, after the standby time T 1  elapses, the throttle freeze protection operation is executed before those water droplets reach a semi-frozen state. As a result, in the throttle freeze protection operation, the throttle valve drive device  36  is prevented from consuming excessive energy, and damage to the throttle valve drive device  36  and the throttle valve  34  and its drive mechanism can also be avoided. 
   When the internal combustion engine  10  is running, the temperature of the throttle body  33  including the throttle valve  34  may rise, and in this case dew condensation will not occur immediately after the internal combustion engine  10  stops, but rather dew condensation occurs after a certain time elapses from when the internal combustion engine  10  stopped, when the throttle body  33  including the throttle valve  34  has fully cooled. And, freezing of water droplets does not occur simultaneously with the occurrence of dew condensation, but rather freezing of the water droplets occurs after a certain time elapses from the occurrence of dew condensation, and the throttle valve  34  freezes when these water droplets have frozen approximately 100%. 
   With this seventh preferred embodiment, after the internal combustion engine  10  stops, a freezing prevention operation of the throttle valve  34  can be carried out at the time at which the throttle valve  34  is most likely to freeze, before the throttle valve  34  becomes throttle-frozen, and freezing of the throttle valve can be prevented without fail. 
   Although in the seventh preferred embodiment the standby time T 1  set in the standby timer was fixed, alternatively it may be made to change with the environmental temperature or the like. And whereas in the seventh preferred embodiment the determination of the probability of the throttle valve  34  freezing was carried out on the basis of the environmental temperature information Tc, alternatively it may be carried out on the basis of the intake air temperature information Ta, the engine temperature information Tw, date/time information DT including date information and time information, location information Lo or the valve aperture history of the exhaust recirculating device  50 . In this case also, the standby time T 1 , and the predetermined value Ta 0  of the intake air temperature information Ta, the predetermined value Tc 0  of the environmental temperature information Tc, the predetermined date information and time information of the date/time information DT, the location range of the location information Lo, and the predetermined value of the valve aperture of the recirculating valve device  52  used in the probability determination of whether or not the probability of the throttle valve  34  freezing is high are set so that the throttle freeze protection operation is executed after the standby time T 1  elapses and, even if dew condenses on the throttle, before the water droplets reach a semi-frozen state. 
   Eighth Preferred Embodiment 
   In this eighth preferred embodiment, after a predetermined standby time elapses from when the internal combustion engine  10  stopped, the control unit  80  starts a throttle freeze protection operation of the throttle valve  34  and performs the freeze protection operation K 1  times (K 1  being an integer) at predetermined time intervals. Otherwise, the construction is the same as that of the first preferred embodiment. 
   In this eighth preferred embodiment, while the internal combustion engine  10  is stopped, after a standby time T 1  has elapsed from when the internal combustion engine  10  stopped, when the environmental temperature information Tc inputted from the environmental temperature sensor  82  is below a predetermined value (for example 0° C.), the control unit  80  determines that probability of the throttle valve  34  freezing is high, and at predetermined intervals sends the throttle freeze protection signal Sf to the throttle opening/closing control device  70 , K 1  times. In accordance with the throttle freeze protection signal Sf, the throttle opening/closing control device  70  drives the throttle valve drive device  36  and thereby applies an oscillating motion to the throttle valve  34 . In this eighth preferred embodiment, when the control unit  80  has determined that the probability of the throttle valve  34  freezing is high, it stands by until a predetermined standby time T 1  (for example 1 hour) has elapsed from the time at which the internal combustion engine  10  stopped, and after this standby time T 1  elapses carries out K 1  throttle freeze protection operations with intervals of a predetermined time (for example 30 minutes) between them. 
   Specifically, when the control unit  80  has determined that the probability of the throttle valve  34  freezing is high, it stands by until the standby time T 1  (for example 1 hour) elapses from when the internal combustion engine  10  stopped, and after this standby time T 1  elapses it carries out a first throttle freeze protection operation. And after carrying out the first throttle freeze protection operation, the control unit  80  repeats the throttle freeze protection operation at intervals of a predetermined time (for example 30 minutes). Here, the total number of times the throttle freeze protection operation is carried out is a predetermined number of times K 1  (for example five times) set in an interval counter. 
   The throttle freeze protection operation of this eighth preferred embodiment will now be described with reference to the flow charts shown in  FIG. 10  and  FIG. 11 .  FIG. 10  is a flow chart according to which standby time timing and interval time timing are performed in the eighth preferred embodiment, and is executed at intervals of a predetermined time (for example every 500 ms). This flow chart of  FIG. 10  includes four steps S 801  to S 804 . 
   First, in step S 8   01 , it is determined whether the standby timer is at 0, and when the standby timer is at 0 the determination result of step S 801  is Yes and it is inferred that the standby time T 1  has elapsed. When the standby timer is not at 0 the determination result of step S 801  is No and in step S 802  decrementing of the standby timer is carried out. In the following step S 803 , a determination of whether the interval timer is at 0 is performed. When the interval timer is 0, the determination result of step S 803  is Yes and it is inferred that the interval time as elapsed. When the interval timer is not at 0, the determination result of step S 803  is No, processing proceeds to step S 804 , a decrementing of the interval timer is carried out and then the routine ends. 
     FIG. 11  is a control flow chart of the throttle freeze protection operation in the eighth preferred embodiment, executed at intervals of a predetermined time (for example every 20 ms). This flow chart of  FIG. 11  includes sixteen steps S 805  to S 820 . 
   First, in step S 805 , the throttle control unit  80  determines for example on the basis of a signal from the crank angle sensor (not shown) whether the internal combustion engine  10  has stopped. When the internal combustion engine  10  has not stopped, the determination result of step S 805  is No and processing proceeds to step S 806 . In this step S 806 , the end flag is set to “0”, the standby timer to T 1  (for example 1 hour), a standby end flag to “0”, and an interval counter to K 1  (for example 5times), and then the routine ends. When the internal combustion engine  10  has stopped, the determination result of step S 805  is Yes and processing proceeds to the next step S 807 . In this step S 807 , it is determined whether the end flag is “1”, and when the end flag is “1” the determination result of step S 807  is Yes, it is inferred that the throttle freeze protection operation has ended, and the routine ends. When the end flag is not “1”, the determination result of step S 807  is No, and processing proceeds to the following step S 808 . 
   In this step S 808 , it is determined whether the standby end flag is 1. When the standby end flag is not 1, the determination result of step S 808  is No, and processing proceeds to step S 809 . In this step S 809 , it is determined whether the standby timer is at 0, and when the standby timer is not at 0 the determination result of step S 809  is No and the control unit  80  determines it is standing by, and the routine ends. When the standby timer is 0, the determination result of step S 809  is Yes, processing proceeds to the next step S 810 , in this step S 810  the environmental temperature information Tc is read in from the environmental temperature sensor  82 , and then processing proceeds to the following step S 811 . 
   In this step S 811 , it is determined whether the environmental temperature information Tc inputted from the environmental temperature sensor  82  is below a predetermined value Tc 0  (for example below 0° C.). When the environmental temperature information Tc is not below the predetermined value Tc 0 , the determination result of step S 811  is No, it is inferred that it is not necessary to carry out a throttle freeze protection operation, and the routine ends. When the environmental temperature information Tc inputted from the environmental temperature sensor  82  is below the predetermined value Tc 0 , the determination result of step S 811  is Yes, it is inferred that it is necessary to carry out a throttle freeze protection operation, and processing proceeds to the following steps S 812 , S 813 , S 814 . In step S 812 , the interval timer is set to T 2  (for example 30 minutes), in step S 813  the standby end flag is set to “1”, in step S 814  the throttle freeze prevention opening/closing drive command flag is set to “1”, and then the routine ends. 
   When the standby end flag is 1, the determination result of step S 808  is Yes, and in the following step S 815  it is determined whether the interval timer is at 0. When the interval timer is not at 0, the determination result of step S 815  is No, the control unit  80  determines that it is standing by, and the routine ends. When the interval timer is 0, the determination result of step S 815  is Yes, and in the next step S 816  a decrementing of the interval counter is carried out, and processing proceeds to step S 817 . In step S 817 , it is determined whether the interval counter is at 0. 
   When the interval counter is not at 0, the determination result of step S 817  is No, processing proceeds to step S 818  and the interval timer is set to T 2 , and in the next step S 820  the throttle freeze prevention opening/closing drive command flag is set to “1”. When the interval counter is 0, the determination result of step S 817  is Yes, in step S 819  the end flag is set to “1”, and in the next step S 820  the throttle freeze prevention opening/closing drive command flag is set to “1”, and the routine ends. 
   In this eighth preferred embodiment, after the standby time T 1  elapses from when the internal combustion engine  10  stopped, when the throttle freeze prevention opening/closing drive command flag is “1”, every time a predetermined interval elapses, up to K 1  times, the control unit  80  supplies a throttle freeze protection signal Sf to the throttle opening/closing control device  70  and on the basis of this throttle freeze protection signal Sf the throttle opening/closing control device  70  executes a throttle freeze protection operation. In this throttle freeze protection operation, the throttle valve drive device  36  oscillates the valve aperture of the throttle valve  34 . 
   In this eighth preferred embodiment, each of the K 1  throttle freeze protection operations carried out at intervals of the predetermined time is the same as the throttle freeze protection operation in the first preferred embodiment, and by these throttle freeze protection operations it is possible to prevent freezing of the throttle valve  34 . 
   In this eighth preferred embodiment, after the standby time T 1  elapses from when the internal combustion engine  10  is stopped, before the throttle valve  34  freezes, the control unit  80  performs a probability determination of whether or not the probability of the throttle valve  34  freezing is high, and, when it determines that this probability is high, causes K 1  throttle freeze protection operations to be executed, each before the throttle valve  34  reaches a throttle-frozen state, with intervals of a predetermined time between them. Freezing of the throttle valve  34  occurs as a result of dew condensing on the throttle valve  34  and water droplets arising from this dew condensation then freezing. The state of water droplets arising from dew condensation on the throttle valve  34  having frozen 100% is here called the state of the throttle valve having frozen, that is, the throttle-frozen state. Each of the K 1  throttle freeze protection operations conducted by the control unit  80  is executed before the water droplets arising from dew condensation have frozen 100%, and indeed before the water droplets reach a semi-frozen state in which they have frozen about 50%. 
   If a throttle freeze protection operation is executed when the water droplets arising on the throttle valve  34  from dew condensation are in a 0% frozen state, because by that throttle freeze protection operation it is possible to shake off the water droplets formed by dew condensation on the throttle valve  34 , the throttle valve  34  can be prevented from progressing to a throttle-frozen state. And if the throttle freeze protection operation is executed with the water droplets condensed as dew on the throttle valve  34  in a semi-frozen state in which they are 50% frozen, because by that throttle freeze protection operation the water droplets having condensed as dew on the throttle valve  34  and ice formed by about half of that water freezing can be shaken off, similarly the throttle valve  34  can be prevented from progressing to a throttle-frozen state. 
   In this eighth preferred embodiment, the standby time T 1 , the interval time T 2 , and the predetermined value Tc 0  of the environmental temperature information Tc used in the probability determination of whether or not-the probability of the throttle valve  34  freezing is high are set so that, after the standby time elapses, and after each time the interval time, elapses thereafter, even if dew condensation on the throttle occurs, the throttle freeze protection operation is executed before those water droplets reach a semi-frozen state. As a result, in the throttle freeze protection operation, the throttle valve drive device  36  is prevented from consuming excessive energy, and damage to the throttle valve drive device  36  and the throttle valve  34  and its drive mechanism can also be avoided. 
   When the internal combustion engine  10  is running, the temperature of the throttle body  33  including the throttle valve  34  may rise, and in this case dew condensation will not occur immediately after the internal combustion engine  10  stops, but rather dew condensation occurs after a certain time elapses from when the internal combustion engine  10  stopped, when the throttle body  33  including the throttle valve  34  is fully cooled. At this time, it often happens that dew condenses in small quantities over a long period after this certain time elapses, and water droplets arising from this dewing freeze gradually. 
   With this eighth preferred embodiment it is possible to carry out a throttle freeze protection operation repeatedly over the period in which dewing is likely to occur, and dew condensation and freezing occurring a little at a time can be removed without fail and freezing of the throttle valve can be prevented without fail. 
   Although in this eighth preferred embodiment the standby time T 1  set in the standby timer, the interval time T 2  set in the interval timer and the predetermined number of times K 1  set in the interval counter are fixed, alternatively they may be made to change with the environmental temperature or the like. And whereas in the eighth preferred embodiment the determination of the probability of the throttle valve  34  freezing was carried out on the basis of the environmental temperature information Tc, alternatively it may be carried out on the basis of the intake air temperature information Ta, the engine temperature information Tw, date/time information DT including date information and time information, location information Lo or the valve aperture history of the exhaust recirculating device  50 . In this case also, the standby time T 1 , the interval time T 2 , and the predetermined value Ta 0  of the intake air temperature information Ta, the predetermined value Tc 0  of the environmental temperature information Tc, the predetermined date information and time information of the date/time information DT, the location range of the location information Lo, and the predetermined value of the valve aperture of the recirculating valve device  52  used in the probability determination of whether or not the probability of the throttle valve  34  freezing is high are set so that the throttle freeze protection operation is executed, after the standby time T 1  elapses and after each time the interval time T 2  elapses thereafter and, even if dew condenses on the throttle, before the water droplets reach a semi-frozen state. 
   Ninth Preferred Embodiment 
   In this ninth preferred embodiment, when the internal combustion engine  10  is stopped, even when the control unit  80  has determined that the probability of the throttle valve  34  freezing is high, if the power supply voltage of the battery  61  is lower than a predetermined value V (for example 11V), throttle freeze protection operation is prohibited. Otherwise, the construction is the same as that of the first preferred embodiment. 
   Specifically, in this ninth preferred embodiment, while the internal combustion engine  10  is stopped, when the environmental temperature information Tc inputted from the environmental temperature sensor  82  is below a predetermined value Tc 0  (for example 0° C.), the control unit  80  determines that the probability of the throttle valve  34  freezing is high. However, in this ninth preferred embodiment, even when the control unit  80  determines that the probability of the throttle valve  34  freezing is high, if the power supply voltage of the battery  61  is lower than a predetermined value V (for example 11V), throttle freeze protection operation is prohibited. The battery  61  is a 12V system battery and normally maintains a power supply voltage of about 13V, and when its voltage falls below 11V the battery  61  is in an over-discharged state. 
   The throttle freeze protection operation in this ninth preferred embodiment will now be described with reference to  FIG. 12 .  FIG. 12  is a control flow chart of the throttle freeze protection operation in the ninth preferred embodiment, executed at intervals of a predetermined time (for example every 20 ms). This flow chart of  FIG. 12  includes nine steps S 901  to S 909 . Steps S 901  to S 905  are the same as steps S 101  to S 105  shown in  FIG. 2  and therefore will not be described again here. 
   In step S 904 , when the environmental temperature information Tc inputted from the environmental temperature sensor  82  is below the predetermined value Tc 0 , the determination result of step S 905  is Yes and it is determined that it is necessary to carry out a throttle freeze protection operation. However, in this case, in the next step S 906 , the power supply voltage of the battery  61  is read in, and in the next step S 907  it is determined whether the power supply voltage of the battery  61  is above a predetermined value V (for example 11v). When the power supply voltage of the battery  61  is not the predetermined value V or more, the determination result of step S 907  is No and then the routine ends. In this case, the throttle freeze protection operation is prohibited. When the power supply voltage of the battery  61  is not the predetermined value V, the determination result of step S 905  is Yes, and in the next step S 908  the end flag is set to “1”, in the following step S 909  the throttle freeze prevention opening/closing drive command flag is set to “1”, and then the routine ends. 
   In this ninth preferred embodiment also, when the throttle freeze prevention opening/closing drive command flag is “1”, in accordance with a control program (not shown), the control unit  80  supplies a throttle freeze protection signal Sf to the throttle opening/closing control device  70  and on the basis of this throttle freeze protection signal Sf the throttle opening/closing control device  70  executes a throttle freeze protection operation. In this throttle freeze protection operation, the throttle valve drive device  36  oscillates the valve aperture of the throttle valve  34 . 
   The throttle freeze protection operation in this ninth preferred embodiment is the same as the throttle freeze protection operation in the first preferred embodiment, and by this throttle freeze protection operation it is possible to prevent freezing of the throttle valve  34 . 
   With this ninth preferred embodiment, when the power supply voltage of the battery  61  ancillary to the internal combustion engine  10  is below a predetermined value V, by prohibiting throttle freeze protection operation by the throttle valve drive device  36  it is possible to prevent over-discharging of the battery  61  caused by throttle freeze protection operation. 
   Although in the ninth preferred embodiment the power supply voltage of the battery  61  at which throttle freeze protection operation is prohibited is fixed, alternatively it may be made to change with the environmental temperature or the like. And whereas in the ninth preferred embodiment the determination of the probability of the throttle valve  34  freezing was carried out on the basis of the environmental temperature information Tc; alternatively it may be carried out on the basis of the intake air temperature information Ta, the engine temperature information Tw, date/time information DT including date information and time information, location information Lo or the valve aperture history of the exhaust recirculating device  50 . 
   A control apparatus of an internal combustion engine according to the invention can be used in all kinds of automotive vehicles, including passenger vehicles and trucks.