Abstract:
The exhaust emission of a hybrid vehicle is improved by providing a technology of achieving effective functioning of a regenerative catalytic apparatus by utilizing a feature of the hybrid vehicle of being driven by selectively operating an internal combustion engine and an auxiliary power source. The regenerative catalytic apparatus in a hybrid vehicle is provided with a hybrid mechanism for driving the vehicle by selectively operating an internal combustion engine and an auxiliary power source; an exhaust-purifying catalyst provided in an exhaust passage of the internal combustion engine for purifying exhaust flowing in the exhaust passage; and heat-storage mechanism for storing heat generated in the internal combustion engine while the internal combustion engine is in an operating state, and utilizing the stored heat to suppress decrease in the temperature of the exhaust-purifying catalyst after the internal combustion engine is stopped.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a technology for improving exhaust emission of a hybrid vehicle that is driven by selectively utilizing an internal combustion engine and an auxiliary power source. 
     In recent years, internal combustion engines mounted in automobiles and the like are required to discharge the exhaust into the air after sufficiently removing harmful gas components such as carbon monoxide (CO), nitrogen oxide (NOx) and hydrocarbon (HC) that are contained in the exhaust. To satisfy the aforementioned requirement, there has been a well known technology of providing, in an exhaust passage of the internal combustion engine, an exhaust-purifying catalyst for removing the harmful gas components contained in the exhaust. 
     For example, such an exhaust-purifying catalyst includes a three-way catalyst that is formed by coating a surface of a ceramic carrier with alumina and carrying a platinum-rhodium-based precious metal catalytic substance on the alumina surface. 
     When the exhaust introduced into the three-way catalyst has an air-fuel ratio close to the stoichiometric air-fuel ratio, the three-way catalyst reacts hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust with oxygen (O 2 ) therein, thereby oxidizing hydrocarbon (HC) and carbon monoxide (CO) into water (H 2 O) and carbon dioxide (CO 2 ). At the same time, the three-way catalyst reacts nitrogen oxide (NOx) contained in the exhaust with hydrocarbon (HC) and carbon monoxide (CO) therein, thereby reducing nitrogen oxide (NOx) into water (H 2 O), carbon dioxide (CO 2 ) and nitrogen (N 2 ). 
     Such a three-way catalyst provided in the exhaust passage of the internal combustion engine removes carbon monoxide (CO), nitrogen oxide (NOx) and hydrocarbon (HC) contained in the exhaust of the internal combustion engine. Therefore, such harmful gas components can be suppressed from being discharged into the air. 
     The three-way catalyst is active at a predetermined active temperature (e.g., 300° C. to 500° C.) or higher. Therefore, if the temperature of the three-way catalyst is less than the predetermined temperature such as upon cold-starting of the internal combustion engine, the harmful gas components in the exhaust cannot be sufficiently removed. 
     In view of the foregoing problem, Japanese Laid-Open Patent Publication No. 10-236147 has proposed a regenerative catalytic apparatus. The regenerative catalytic apparatus described therein includes a honeycomb catalytic body provided within a heat-insulating container, a plurality of cylindrical heat-storage containers disposed in parallel within the catalytic body along the exhaust-flowing direction, and a heat-storage material provided in each cylindrical heat-storage container. While the internal combustion engine is in the operating state, the heat of the exhaust is stored in the heat-storage material. After the internal combustion engine is stopped, decrease in the temperature of the catalytic body is suppressed by utilizing the heat-insulation effect of the heat-insulating container and the heat stored in the heat-storage material. Thus, the catalytic body is activated early in the next starting of the engine. 
     In such a regenerative catalytic apparatus, the amount of heat stored in the heat-storage material depends on the operating state of the internal combustion engine. The operating state of the internal combustion engine in turn depends on the running conditions of the vehicle. Therefore, the amount of heat stored in the heat-storage material depends on the running conditions of the vehicle. Accordingly, the heat-storage material has not necessarily stored a specific amount of heat or more at the time the internal combustion engine is stopped. As a result, it may be difficult to retain the catalytic body at a specific temperature or higher until the engine is started subsequently. 
     In recent years, in order to reduce the fuel consumption, the amount of exhaust emission, or noise of the internal combustion engines mounted in the automobiles and the like, a hybrid vehicle has been developed, which includes two driving sources, i.e., an internal combustion engine and an electric motor, and which is driven by selectively operating the internal combustion engine and the electric motor. 
     In such a hybrid vehicle as well, it is important to remove harmful gas components contained in the exhaust emitted from the internal combustion engine before the exhaust is discharged into the air. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to improve exhaust emission of a hybrid vehicle by providing a technology of achieving effective functioning of a regenerative catalytic apparatus by utilizing a feature of the hybrid vehicle of being driven by selectively operating an internal combustion engine and an auxiliary power source. 
     In order to achieve the object, a regenerative catalytic apparatus in a hybrid vehicle according to the present invention is provided with a hybrid mechanism for driving the vehicle by selectively operating an internal combustion engine and an auxiliary power source; an exhaust-purifying catalyst provided in an exhaust passage of the internal combustion engine for purifying exhaust flowing in the exhaust passage; and heat-storage means for storing heat generated in the internal combustion engine while the internal combustion engine is in an operating state, and utilizing the stored heat to suppress decrease in the temperature of the exhaust-purifying catalyst after the internal combustion engine is stopped. 
     In such a regenerative catalytic apparatus in the hybrid vehicle, the hybrid mechanism drives the vehicle only by an output of the auxiliary power source, only by an output of the internal combustion engine, or by both outputs of the internal combustion engine and the auxiliary power source, as required. 
     For example, when the amount of heat stored in the heat-storage means is less than a desired amount, the hybrid mechanism drives the vehicle by mainly utilizing the output of the auxiliary power source, as well as controls the operating state of the internal combustion engine so as to increase the amount of heat in the heat-storage means. 
     In this case, since the hybrid vehicle is driven mainly by the output of the auxiliary power source, the vehicle runs independently of the operating state of the internal combustion engine. On the other hand, the operating state of the internal combustion engine is controlled merely in order to increase the amount of heat in the heat-storage means, regardless of the running conditions of the hybrid vehicle. As a result, the heat-storage means can always store the desired amount of heat or more, irrespective of running conditions of the hybrid vehicle. 
     Consequently, the heat-storage means stores the desired amount of heat or more whenever the internal combustion engine is stopped. Therefore, decrease in the temperature of the exhaust-purifying catalyst can be reliably suppressed after the internal combustion engine is stopped. Thus, the exhaust emission at re-start of the internal combustion engine can be improved, as well as the fuel consumption for warming up the exhaust-purifying catalyst can be reduced. 
     A regenerative catalytic apparatus in a hybrid vehicle according to the present invention may be provided with a hybrid mechanism for driving the vehicle by selectively operating an internal combustion engine and an auxiliary power source; an exhaust-purifying catalyst provided in an exhaust passage of the internal combustion engine for purifying exhaust flowing in the exhaust passage; heat-storage means for storing heat generated in the internal combustion engine while the internal combustion engine is in an operating state, and utilizing the stored heat to suppress decrease in the temperature of the exhaust-purifying catalyst after the internal combustion engine is stopped; and engine control means for controlling the operating state of the internal combustion engine through the hybrid mechanism so that the amount of heat stored in the heat-storage means becomes equal to or more than a predetermined amount. 
     In such a regenerative catalytic apparatus in the hybrid vehicle, when the amount of heat stored in the heat-storage means is less than the predetermined amount, the engine control means controls the operating state of the internal combustion engine through the hybrid mechanism so that the heat generated in the internal combustion engine is stored in the heat-storage means. 
     At this time, the hybrid mechanism drives the vehicle by mainly utilizing an output of the auxiliary power source. More specifically, the hybrid mechanism controls the operating state of the internal combustion engine according to a request from the engine control means, as well as controls the auxiliary power source so as to satisfy the running conditions of the vehicle. 
     In this case, the hybrid vehicle is driven mainly by the output of the auxiliary power source independently of the operating state of the internal combustion engine. In other words, the operating state of the internal combustion engine is controlled merely in order to store the heat in the heat-storage means irrespective of the running conditions of the vehicle. As a result, the heat-storage means always stores the predetermined amount of heat or more, regardless of the running conditions of the vehicle. Thus, the heat-storage means stores the predetermined amount of heat or more at the time the internal combustion engine is stopped. Consequently, after the internal combustion engine is stopped, decrease in the temperature of the exhaust-purifying catalyst is prevented by the predetermined amount of heat or more stored in the heat-storage means. 
     The regenerative catalytic apparatus in the hybrid vehicle according to the present invention may further include temperature-detecting means for detecting a temperature of the heat-storage means. In this case, the engine control means may determine the amount of heat stored in the heat-storage means by using a detection value of the temperature-detecting means as a parameter. More specifically, the engine control means may determine that the amount of heat stored in the heat-storage means is the predetermined amount or more when the detection value of the temperature-detecting means is a predetermined value or more, and may determine that the amount of heat stored in the heat-storage means is less than the predetermined amount when the detection value of the temperature-detecting means is less than the predetermined value. 
     The engine control means may control the operating state of the internal combustion engine so as to increase the amount of heat generated in the internal combustion engine, when the detection value of the temperature-detecting means is less than the predetermined value. Moreover, the engine control means may control the operating state of the internal combustion engine into a normal operating state, when the detection value of the temperature-detecting means is the predetermined value or more. Further, the engine control means may be adapted to inhibit the stopping of operation of the internal combustion engine when the internal combustion engine is in the operating state and the detection value of the temperature-detecting means is less than the predetermined value, and to allow the stopping of operation of the internal combustion engine when the detection value of the temperature-detecting means is the predetermined value or more. 
     The heat-storage means according to the present invention may include a heat-storage material for storing heat of the exhaust emitted from the internal combustion engine. In this case, the engine control means may control the operating state of the internal combustion engine so as to increase the temperature of the exhaust emitted from the internal combustion engine, when the detection value of the temperature-detecting means is less than the predetermined value. 
     For example, the exhaust temperature of the internal combustion engine can be increased by retarding the ignition timing, increasing a fuel injection quantity and an intake-air quantity, or the like. Note that, in the case where the internal combustion engine is provided with a variable valve mechanism capable of varying the opening/closing timing of an exhaust valve, the exhaust temperature of the internal combustion engine may be increased by advancing the opening timing of the exhaust valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing a structure of a hybrid mechanism that is mounted in a hybrid vehicle to which a regenerative catalytic apparatus according to the present invention is applied; 
     FIG. 2 is a diagram showing a structure of a regenerative exhaust-purifying mechanism; 
     FIG. 3 is a flowchart illustrating a heat-storage control routine; and 
     FIG. 4 is a diagram showing another embodiment of the regenerative exhaust-purifying mechanism. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, specific embodiments of a regenerative catalytic apparatus in a hybrid vehicle according to the present invention will be described referring to the accompanying drawings. 
     FIG. 1 is a schematic diagram showing a structure of a hybrid mechanism that is mounted in a hybrid vehicle to which a regenerative catalytic apparatus according to the present invention is applied. 
     The hybrid mechanism shown in FIG. 1 includes two driving sources, i.e., an internal combustion engine  100  and an electric motor  200  serving as an auxiliary power source according to the present invention. 
     The internal combustion engine  100  is a four-cycle, four-cylinder gasoline engine. The internal combustion engine  100  is provided with spark plugs  3  that face respective combustion chambers (not shown) of cylinders  2 . The internal combustion engine  100  is also provided with a crank-position sensor  16  for outputting a pulse signal every time when a crankshaft serving as an engine output shaft is rotated by a predetermined angle (e.g., 30 degrees), and a water-temperature sensor  17  for outputting an electric signal corresponding to the temperature of cooling water flowing in a water jacket (not shown) formed in the internal combustion engine  100 . 
     Inlet branch pipes  4  are connected to the internal combustion engine  100 . The inlet branch pipes  4  communicate with the respective combustion chambers of the cylinders  2  through respective inlet ports (not shown). A fuel injection valve  5  is attached to each inlet branch pipe  4  so that an injection nozzle thereof faces the corresponding inlet port. 
     The inlet branch pipes  4  are connected to a surge tank  6 , which in turn is connected to an inlet pipe  7 . A throttle valve  8  for adjusting the flow rate of the intake air flowing in the inlet pipe  7  is provided in the inlet pipe  7 . 
     The throttle valve  8  is provided with an actuator  9  formed by a stepper motor and the like for opening and closing the throttle valve  8  according to the magnitude of an applied current, and a throttle-position sensor  10  for outputting an electric signal corresponding to the opening of the throttle valve  8 . 
     An airflow meter  11  for outputting an electric signal corresponding to the mass of the fresh air flowing in the inlet pipe  7  is provided in the inlet pipe  7  upstream of the throttle valve  8 . 
     Exhaust branch pipes  12  are connected to the internal combustion engine  100 . The exhaust branch pipes  12  communicate with the respective combustion chambers of the cylinders  2  through respective exhaust ports (not shown). The exhaust branch pipes  12  are connected to an exhaust pipe  13 , which in turn is connected to a muffler (not shown) in the downstream of the exhaust pipe  13 . 
     A regenerative exhaust-purifying mechanism  14  for removing harmful gas components within the exhaust is disposed in the exhaust pipe  13 . As shown in FIG. 2, the regenerative exhaust-purifying mechanism  14  is formed by a cylindrical body having a dual structure wherein an inner cylinder  140  and an outer cylinder  141  are coaxially disposed. The inner cylinder  140  is a cylindrical body having a diameter larger than that of the exhaust pipe  13 . The outer cylinder  141  is a cylindrical body having an inner diameter larger than the outer diameter of the inner cylinder  140 . 
     The inner cylinder  140  includes therein an exhaust-purifying catalyst  142  having an outer diameter that is substantially the same as the inner diameter of the inner cylinder  140 . For example, the exhaust-purifying catalyst  142  may be a three-way catalyst, an occlusion reduction NOx catalyst, a selective reduction NOx catalyst, or an oxidation catalyst. The three-way catalyst will be described as an example in the present embodiment. 
     The three-way catalyst  142  is formed by a grid-like ceramic carrier of cordierite having a plurality of through-holes extending along the exhaust-flowing direction, and a catalytic layer that is coated over a surface of the ceramic carrier. For example, the catalytic layer is formed from a platinum-rhodium (Pt—Rh)-based precious metal catalytic substance carried on a surface of porous alumina having a plurality of pores. 
     The three-way catalyst  142  thus formed is activated at a predetermined temperature (e.g., 300(C) or higher. When the air-fuel ratio of the exhaust introduced into the three-way catalyst  142  is within a predetermined range (catalytic purification window) close to the stoichiometric air-fuel ratio, the three-way catalyst  142  reacts hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust with oxygen (O 2 ) therein, thereby oxidizing hydrocarbon (HC) and carbon monoxide (CO) into water (H 2 O) and carbon dioxide (CO 2 ). At the same time, the three-way catalyst  142  reacts nitrogen oxide (NOx) in the exhaust with hydrocarbon (HC) and carbon monoxide (CO) therein, thereby reducing nitrogen oxide (NOx) into water (H 2 O), carbon dioxide (CO 2 ) and nitrogen (N 2 ). 
     The inner cylinder  140  has a heat-storage material  143  on its peripheral wall. The heat-storage material  143  includes a phase-change material such as lithium chloride and sodium chloride as a base material. A vacuum space  144  is formed between the heat-storage material  143  and the outer cylinder  141  (hereinafter, the space  144  is referred to as a vacuum heat insulating layer  144 ). The vacuum h eat insulating layer  144  may have a constant degree of vacuum. Alternatively, the degree of vacuum may be adjusted as required. 
     The outer cylinder  141  is provided with a heat-storage-material temperature sensor  145  for outputting an electric signal corresponding to the temperature of the heat-storage material  143 . This heat-storage-material temperature sensor  145  constitutes the temperature-detecting means according to the present invention. 
     In such a regenerative exhaust-purifying mechanism  14 , while the internal combustion engine  100  is in the operating state, the heat of the exhaust passing through the inner cylinder  140  is transmitted through a wall surface of the inner cylinder  140  to the heat-storage material  143 , and stored in the heat-storage material  143 . 
     In the regenerative exhaust-purifying mechanism  14 , while the internal combustion engine  100  is stopped, the vacuum heat insulating layer  144  blocks heat radiation from the three-way catalyst  142  and the heat-storage material  143 , as well as the heat stored in the heat-storage material  143  is transmitted to the three-way catalyst  142 . Thus, decrease in the temperature of the three-way catalyst  142  is suppressed. 
     Referring back to FIG. 1, the exhaust pipe  13  is provided with an air-fuel-ratio sensor  15  upstream of the regenerative exhaust-purifying mechanism  14 . The air-fuel-ratio sensor  15  outputs an electric signal corresponding to the air-fuel ratio of the exhaust introduced into the three-way catalyst  142  of the regenerative exhaust-purifying mechanism  14 . 
     For example, the air-fuel-ratio sensor  15  is formed by a solid electrolyte portion formed from zirconia (ZrO 2 ) burned into a cylindrical shape, an outer platinum electrode covering the outer surface of the solid electrolyte portion, and an inner platinum electrode covering the inner surface of the solid electrolyte portion. When a voltage is applied between the electrodes, the air-fuel-ratio sensor  15  outputs a current of a magnitude proportional to the oxygen concentration in the exhaust gas (concentration of unburned fuel components when the air-fuel ratio is richer than the stoichiometric air-fuel ratio) resulting from migration of oxygen ions. 
     The crankshaft of the internal combustion engine  100  is coupled to an output shaft  18 , which in turn is coupled to a power-dividing mechanism  19 . The power-dividing mechanism  19  is mechanically connected to a generator  20  and a rotary shaft (motor rotary shaft)  200   a  of the electric motor  200 . 
     For example, the power-dividing mechanism  19  is formed by an planetary gear that is provided with a planetary carrier rotatably carrying a pinion gear, a ring gear disposed outside the planetary carrier, and a sun gear disposed inside the planetary carrier. A rotary shaft of the planetary carrier is coupled to the output shaft  18 , a rotary shaft of the ring gear is coupled to the motor rotary shaft  200   a , and a rotary shaft of the sun gear is coupled to the generator  20 . 
     A reduction gear  21  is coupled to the motor rotary shaft  200   a  of the electric motor  200 , and wheels  24 ,  25  serving as driving wheels are coupled to the reduction gear  21  through respective drive shafts  22 ,  23 . The reduction gear  21  is formed by a combination of a plurality of gears. The reduction gear  21  reduces the rotational speed of the motor rotary shaft  200   a , and transmits the reduced rotational speed to the drive shafts  22 ,  23 . 
     The generator  20  is electrically connected to an inverter  26 , which in turn is electrically connected to a battery  27  and the electric motor  200 . 
     The generator  20  is formed by an alternating-current-synchronous motor. The generator  20  generates electric power by converting kinetic energy, which is input thereto from the internal combustion engine  100  through the power-dividing mechanism  19 , into electric energy in response to application of an exciting current. 
     The generator  20  serves as a starter motor of the internal combustion engine  100  when driving electric power is applied from the battery  27  upon starting of the internal combustion engine  100 . 
     The battery  27  is formed by a plurality of nickel-hydrogen batteries connected in series with each other. The battery  27  is provided with an SOC (State Of Charge) controller  28  for calculating a state of charge of the battery  27  from an integrated value of the amounts of discharge current and charging current of the battery  27 . 
     The electric motor  200  is formed by an alternating-current-synchronous motor. When the electric power generated by the generator  20  and/or the electric power of the battery  27  is applied to the electric motor  200 , the electric motor  200  rotates the motor rotary shaft  200   a  with the torque corresponding to the magnitude of the applied electric power. 
     The electric motor  200  serves as a generator during deceleration of the vehicle, and performs so-called regenerative power generation. More specifically, the electric motor  200  converts kinetic energy transmitted from the wheels  24 ,  25  to the motor rotary shaft  200   a  through the drive shafts  22 ,  23  and the reduction gear  21  into electric energy. 
     The inverter  26  is a power-converting apparatus formed by a combination of a plurality of power transistors. The inverter  26  selectively performs application of the electric power generated by the generator  20  to the battery  27 , application of the electric power generated by the generator  20  to the electric motor  200 , application of the electric power stored in the battery  27  to the electric motor  200 , and application of the electric power regenerated by the electric motor  200  to the battery  27 . 
     In the present embodiment, the generator  20  and the electric motor  200  are each formed by the alternating-current-synchronous motor. Therefore, when the electric power generated by the generator  20  is to be applied to the battery  27 , the inverter  26  converts an AC voltage generated by the generator  20  into a DC voltage, and then applies the DC voltage to the battery  27 . When the electric power of the battery  27  is to be applied to the electric motor  200 , the inverter  26  converts a DC voltage of the battery  27  into an AC voltage, and then applies the AC voltage to the electric motor  200 . When the electric power regenerated by the electric motor  200  is to be applied to the battery  27 , the inverter  26  converts an AC voltage regenerated by the electric motor  200  into a DC voltage, and then applies the DC voltage to the battery  27 . 
     Such a hybrid mechanism is further provided with an electronic control unit (E-ECU)  29  for controlling the internal combustion engine  100 , and an electronic control unit (H-ECU)  30  for generally controlling the entire hybrid mechanism. 
     The H-ECU  30  is connected through electric wiring to an accelerator-position sensor  31  for outputting an electric signal corresponding to the operation amount of an accelerator pedal (not shown) and the SOC controller  28 . Thus, the H-ECU  30  can receive an output signal (accelerator opening signal) of the accelerator-position sensor  31  and an output signal (signal indicating the state of charge of the battery  27 ) of the SOC controller  28 . 
     The H-ECU  30  is connected to the generator  20 , the inverter  26  and the electric motor  200  through electric wiring, and is also connected to the E-ECU  29  through a bilateral communication line. The H-ECU  30  is capable of controlling the generator  20 , the inverter  26  and the electric motor  200  based on the output signals of the accelerator-position sensor  31 , the SOC controller  28  and the like, and is also capable of controlling the internal combustion engine  100  through the E-ECU  29 . 
     For example, the H-ECU  30  starts the internal combustion engine  100  when an ignition switch is change-over from OFF to ON. More specifically, the H-ECU  30  controls the inverter  26  so as to apply the driving electric power from the battery  27  to the generator  20 , thereby causing the generator  20  to serve as a starter motor. In addition, the H-ECU  30  transmits an engine-start request signal to the E-ECU  29  so as to operate the spark plugs  3 , the throttle valve  8  and the fuel injection valves  5 . 
     In this case, in the power-dividing mechanism  19 , the sun gear coupled to the generator  20  is rotated, whereas the ring gear coupled to the wheels  24 ,  25  is stopped. Therefore, almost all of the rotational torque of the sun gear is transmitted to the planetary carrier. 
     The planetary carrier of the power-dividing mechanism  19  is coupled to the output shaft  18  of the internal combustion engine  100 . Therefore, when the planetary carrier is rotated in response to the rotational torque of the sun gear, the output shaft  18  is also rotated correspondingly. At this time, the E-ECU  29  operates the spark plugs  3 , the throttle valve  8  and the fuel injection valves  5 , whereby cranking of the internal combustion engine  100  is implemented. Thus, the internal combustion engine  100  is started. 
     When the temperature of cooling water is raised to a predetermined temperature or higher after starting of the internal combustion engine  100 , the H-ECU  30  determines that the internal combustion engine  100  has been warmed up, and transmits an engine-stop request signal to the E-ECU  29  so as to stop the internal combustion engine  100 . 
     If the vehicle is stopped while the ignition switch is on, the H-ECU  30  transmits the engine-stop request signal to the E-ECU  29  so as to stop the internal combustion engine  100 , as well as controls the inverter  26  so as to discontinue rotation of the electric motor  200 . 
     However, there may be a case where an output signal value (signal value indicating the state of charge of the battery  27 ) of the SOC controller  28  is less than a predetermined reference value when the vehicle is stopped, an auxiliary machinery (such as a compressor of an in-vehicle air-conditioner) that is driven with a part of the torque output from the internal combustion engine needs to be operated, or the internal combustion engine  100  or an exhaust-purifying system needs to be warmed up. In such a case, the H-ECU  30  inhibits the internal combustion engine  100  from being stopped or transmits the engine-start request signal to the E-ECU  29  so as to restart the stopped internal combustion engine  100 . 
     When the vehicle having been stopped is started, the H-ECU  30  controls the inverter  26  so as to apply the driving electric power from the battery  27  to the electric motor  200 . When the driving electric power is supplied from the battery  27  to the electric motor  200 , the motor rotary shaft  200   a  of the electric motor  200  is rotated. Then, the rotational torque of the motor rotary shaft  200   a  is transmitted to the wheels  24 ,  25  through the reduction gear  21  and the drive shafts  22 ,  23 , whereby the vehicle starts moving. 
     Note that there may be a case where the output signal value of the SOC controller  28  is less than the predetermined reference value when the vehicle is started, the auxiliary machinery such as the compressor of the air-conditioner needs to be operated, or the internal combustion engine  100  or the exhaust-purifying system needs to be warmed up. In such a case, the H-ECU  30  transmits the engine-start request signal to the E-ECU  29  so as to start the internal combustion engine  100 . 
     When the internal combustion engine  100  is started in order to charge the battery  27 , operate the auxiliary machinery, or warm up the internal combustion engine  100  or the exhaust-purifying system upon starting the vehicle, the H-ECU  30  controls the inverter  26  so as to apply the exciting current from the battery  27  to the generator  20 , thus causing the generator  20  to operate as a generator. 
     In this case, the output shaft  18  is rotated by the torque that is output from the internal combustion engine  100 . The rotational torque of the output shaft  18  is transmitted to the planetary carrier of the power-dividing mechanism  19 , and distributed from the planetary carrier to the sun gear and the ring gear. 
     The rotational torque distributed from the planetary carrier to the sun gear is transmitted to the generator  20  coupled to the sun gear. The generator  20  generates electric power by converting the kinetic energy transmitted from the sun gear into electric energy. The electric power generated by the generator  20  is distributed to the battery  27  and the electric motor  200  by the inverter  26 . 
     The rotational torque distributed from the planetary carrier to the ring gear is transmitted to the motor rotary shaft  200   a  coupled to the ring gear. 
     As a result, the motor rotary shaft  200   a  is rotated by the torque output from the electric motor  200  plus the rotational torque transmitted from the ring gear. The rotational torque of the motor rotary shaft  200   a  is transmitted to the wheels  24 ,  25  through the reduction gear  21  and the drive shafts  22 ,  23 . 
     When the state of the vehicle is shifted from starting to the normal running, the H-ECU  30  controls the E-ECU  29  so as to render the torque output from the internal combustion engine  100  at desired target torque. In addition, the H-ECU  30  stops supplying the driving electric power from the battery  27  to the electric motor  200 , and controls the inverter  26  so as to apply the exciting current from the battery  27  to the generator  20 . 
     More specifically, the H-ECU  30  calculates driving torque required by the driver (hereinafter, referred to as required driving torque) from an output signal (accelerator opening) of the accelerator-position sensor  31  and an output signal (vehicle speed) of a vehicle-speed sensor (not shown). Then, the H-ECU  30  determines the torque to be output from the internal combustion engine  100  (hereinafter referred to as a required engine torque) and the torque to be output from the electric motor  200  (hereinafter referred to as a required motor torque) in order to satisfy the required driving torque. 
     The H-ECU  30  transmits the required engine torque to the E-ECU  29 , as well as controls the inverter  26  according to the required motor torque. At this time, the H-ECU  30  controls the revolution speed of the generator  20  by adjusting the magnitude of the exciting current applied to the generator  20 . Thus, the H-ECU  30  controls the revolution speed (hereinafter, also referred to as engine speed) of the internal combustion engine  100 . 
     For example, the required engine torque transmitted from the H-ECU  30  to the E-ECU  29  is a value obtained by using the intake-air quantity and revolution speed of the internal combustion engine  100  as parameters. In this case, the H-ECU  30  has a map indicating the relation between the intake-air quantity, engine speed and engine torque. The H-ECU  30  specifies from the map the intake-air quantity and engine speed corresponding to the desired engine torque, and transmits the specified intake-air quantity and engine speed to the E-ECU  29  as the required engine torque. 
     The E-ECU  29  determines the throttle opening, fuel injection quantity, fuel injection timing and ignition timing according to the required engine torque received from the H-ECU  30 , and controls the actuator  9 , the fuel injection valves  5  and the spark plugs  3  accordingly. 
     Note that, if the battery  27  needs to be charged during normal running of the vehicle, the H-ECU  30  controls the E-ECU  29  so as to increase the torque output from the internal combustion engine  100 , as well as controls the inverter  26  so as to increase the exciting current applied from the battery  27  to the generator  20 . Thus, the amount of power generation is increased while assuring the required driving torque. 
     During acceleration of the vehicle, the H-ECU  30  calculates the required driving torque, required engine torque and required motor torque as it does during normal running of the vehicle as described above. Then, the H-ECU  30  controls the internal combustion engine  100  through the E-ECU  29 , as well as controls the electric motor  200  through the inverter  26 . 
     The H-ECU  30  controls the inverter  26  so as to apply not only the electric power generated by the generator  20  but also the electric power of the battery  27  to the electric motor  200 , thus increasing the torque output from the electric motor  200 . 
     During deceleration or braking of the vehicle, the H-ECU  30  transmits the engine-stop request signal to the E-ECU  29  so as to stop the internal combustion engine  100  (i.e., so as to stop fuel injection control and ignition control). In addition, the H-ECU  30  controls the inverter  26  so as to stop the generator  20  and the electric motor  200 . 
     Then, the H-ECU  30  controls the inverter  26  so as to apply the exciting current from the battery  27  to the electric motor  200 . Thus, the electric motor  200  functions as a generator, and performs regenerative power generation. More specifically, the electric motor  200  converts kinetic energy transmitted from the wheels  24 ,  25  through the drive shafts  22 ,  23  and the reduction gear  21  to the motor rotary shaft  200   a  into electric energy. The battery  27  is charged with the electric power regenerated by the electric motor  200  through the inverter  26 . 
     The E-ECU  29  is connected through electric wiring to various sensors such as the throttle-position sensor  10 , the airflow meter  11 , the air-fuel-ratio sensor  15 , the crank-position sensor  16 , the water-temperature sensor  17  and a heat-storage-container water-temperature sensor  38 , so that the E-ECU  29  can receive respective output signals of such sensors. 
     The E-ECU  29  is connected through electric wiring to the spark plugs  3 , the actuator  9 , the fuel injection valves  5 , a first control valve  35 , a second control valve  36 , an electric water pump  37  and the like. Thus, the E-ECU  29  performs ignition control, throttle control, fuel injection control, and heat-storage control, based on the output signals of the above-mentioned sensors and the request from the H-ECU  30 . 
     For example, in the fuel injection control, the E-ECU  29  determines the fuel injection quantity (TAU) according to the following expression for calculating the fuel injection quantity: 
     
       
           TAU=TP * FWL *  ( FAF+FG ) * [ FASE+FAE+FOTP +FDE ( D )] *  FFC+TAUV   
       
     
     where 
     TP: basic injection quantity; 
     FWL: increased quantity for warming-up; 
     FAF: air-fuel-ratio feedback correction coefficient; 
     FG: air-fuel-ratio learning coefficient; 
     FASE: increased quantity after starting; 
     FAE: increased quantity for acceleration; 
     FOTP: increased OTP quantity; 
     FDE(D): increased quantity (decreased quantity) for deceleration; 
     FFC: fuel-cut return correction coefficient; and 
     TAUV: invalid injection time. 
     The E-ECU  29  determines the operating state of the internal combustion engine  100  by using the output signal values of the sensors as parameters. Based on the determined engine operating state and a map pre-stored in a ROM (Read Only Memory) within the E-ECU  29 , the E-ECU  29  calculates the basic injection quantity (TP), increased quantity for warming-up (FWL), increased quantity after starting (FASE), increased quantity for acceleration (FAE), increased OTP quantity (FOTP), increased quantity for deceleration (FDE(D)), fuel-cut return correction coefficient (FFC), invalid injection time (TAUV) and the like. 
     Moreover, the E-ECU  29  calculates the air-fuel-ratio feedback correction coefficient (FAF) by determining whether or not the conditions of the air-fuel-ratio feedback control are satisfied. 
     For example, the conditions of the air-fuel-ratio feedback control are as follows: cooling water has a predetermined temperature or higher; the internal combustion engine  100  is in the non-start state; correction to increase the fuel injection quantity after starting is not executed; correction to increase the fuel injection quantity for warming-up is not executed; correction to increase the fuel injection quantity for acceleration is not executed; correction to increase the OTP quantity for preventing a component of an exhaust system such as the three-way catalyst  142  from being heated is not executed; the fuel-cut control is not executed; and the like. 
     If such conditions of air-fuel-ratio feedback control are not satisfied, the E-ECU  29  calculates the fuel injection quantity (TAU) by using the air-fuel-ratio feedback correction coefficient (FAF) as “1.0.” 
     If such conditions of air-fuel-ratio feedback control are satisfied, the E-ECU  29  receives an output signal of the air-fuel-ratio sensor  15 . Then, based on the received output signal and the response delay time of the air-fuel-ratio sensor  15 , the E-ECU  29  determines whether an actual air-fuel ratio of the exhaust is leaner or richer than the stoichiometric air-fuel ratio. 
     When the E-ECU  29  determines that the actual air-fuel ratio of the exhaust is richer than the stoichiometric air-fuel ratio, the E-ECU  29  corrects the air-fuel-ratio feedback correction coefficient (FAF) so as to reduce the fuel injection quantity (TAU). On the other hand, when the E-ECU  29  determines that the actual air-fuel ratio of the exhaust is leaner than the stoichiometric air-fuel ratio, the E-ECU  29  corrects the air-fuel-ratio feedback correction coefficient (FAF) so as to increase the fuel injection quantity (TAU). 
     The E-ECU  29  performs upper-limit guard processing and lower-limit guard processing on the air-fuel-ratio feedback correction coefficient (FAF) thus obtained, and calculates the fuel injection quantity (TAU) by substituting the resultant air-fuel-ratio feedback correction coefficient (FAF) for the above-mentioned expression for calculating the fuel injection quantity. 
     In the heat-storage control, the E-ECU  29  receives an output signal value (temperature of the heat-storage material) of the heat-storage-material temperature sensor  145  of the regenerative exhaust-purifying mechanism  14 , and determines whether or not the heat-storage material has at least a predetermined temperature. 
     If the temperature of the heat-storage material is the predetermined temperature or higher, the E-ECU  29  determines that the amount of heat stored in the heat-storage material  143  is a desired amount or more, and executes normal control. On the other hand, if the temperature of the heat-storage material is less than the predetermined temperature, the E-ECU  29  determines that the amount of heat stored in the heat-storage material  143  is less than the desired amount. Then, the E-ECU  29  controls the operating state of the internal combustion engine  100  so as to increase the amount of heat generated by the internal combustion engine  100 , and specifically, to increase the temperature of the exhaust emitted from the internal combustion engine  100 . 
     When the E-ECU  29  arbitrarily controls the operating state of the internal combustion engine  100  so as to increase the exhaust temperature, a change in the operating state of the internal combustion engine  100  may affect the running state of the vehicle, whereby drivability may possibly be degraded. 
     Then, in the present embodiment, the E-ECU  29  notifies the H-ECU  30  of the start to execute the heat-storage control if the operating state of the internal combustion engine  100  needs to be controlled in the heat-storage control so as to raise the exhaust temperature. The H-ECU  30  responsively idles the internal combustion engine  100 , and controls the revolution speed of the generator  20  so as to drive the vehicle only with the output of the electric motor  200 . 
     According to such control, the operating state of the internal combustion engine  100  does not affect the running state of the vehicle. Therefore, the E-ECU  29  can control the operating state of the internal combustion engine  100  independently of the running conditions of the vehicle. Accordingly, the E-ECU  29  can arbitrarily control the operating state of the internal combustion engine  100  merely in order to raise the exhaust temperature. 
     Hereinafter, the heat-storage control according to the present embodiment is described in detail. 
     In executing the heat-storage control, the E-ECU  29  executes a heat-storage control routine as shown in FIG.  3 . This heat-storage control routine is pre-stored in a storage device such as the ROM included in the E-ECU  29 , and repeatedly executed by the E-ECU  29  at predetermined time intervals while the ignition switch is on. 
     In the heat-storage control routine, the E-ECU  29  first determines in Step S 301  whether or not the internal combustion engine  100  is in the operating state. 
     If the E-ECU  29  determines in Step S 301  that the internal combustion engine  100  is in the operating state, the E-ECU  29  proceeds to Step S 302 , and receives an output signal T of the heat-storage-material temperature sensor  145 . 
     In Step S 303 , the E-ECU  29  determines whether or not the output signal value T of the heat-storage-material temperature sensor  145  is at least a predetermined temperature TS. 
     If the E-ECU  29  determines in Step S 303  that the output signal value T of the heat-storage-material temperature sensor  145  is the predetermined temperature TS or higher, the E-ECU  29  terminates execution of the routine. 
     On the other hand, if the E-ECU  29  determines in Step S 303  that the output signal value T of the heat-storage-material temperature sensor  145  is less than the predetermined temperature TS, the E-ECU  29  proceeds to Step S 304 . 
     In Step S 304 , the E-ECU  29  writes “1” to an engine-stop-inhibition-flag storage region that is preset in a RAM (Random Access Memory) included in the E-ECU  29 . The engine-stop-inhibition-flag storage region stores “1” when the state of the regenerative exhaust-purifying mechanism  14  is in a heat-storage-control execution region, i.e., when the operating state of the internal combustion engine  100  is controlled so as to increase the amount of heat stored in the heat-storage material  143 . The engine-stop-inhibition-flag storage region stores “0” when the state of the regenerative exhaust-purifying mechanism  14  is in a heat-storage-control non-execution region. 
     When the engine-stop-inhibition-flag storage region stores “1,” the E-ECU  29  does not stop the internal combustion engine  100  even if it receives an engine-stop request from the H-ECU  30 . 
     After executing step S 304 , the E-ECU  29  proceeds to Step S 305 , and transmits to the H-ECU  30  a signal indicating that execution of the heat-storage control is started. 
     In this case, the H-ECU  30  controls the hybrid mechanism so that the internal combustion engine  100  idles and that the hybrid vehicle runs with the rotational torque output from the electric motor. 
     More specifically, the H-ECU  30  controls the inverter  26  so as to adjust the magnitude of the exciting current applied from the battery  27  to the generator  20 , thereby settling the revolution speed of the generator  20  at a predetermined value. This predetermined value is such a revolution speed that the rotational torque output from the internal combustion engine  100  (rotational torque of the output shaft  18 ) is no longer transmitted to the motor rotary shaft  200   a  in the power-dividing mechanism  19 . 
     On the other hand, the H-ECU  30  calculates required driving torque from an output signal (accelerator opening) of the accelerator-position sensor  31  and an output signal (vehicle speed) of the vehicle-speed sensor, and regards the required driving torque thus obtained as the required motor torque. Then, the H-ECU  30  adjusts the driving electric power applied from the battery  27  or the generator  20  to the electric motor  200  so as to satisfy the required motor torque. 
     Referring back to FIG. 3, after executing Step S 305 , the E-ECU  29  proceeds to Step S 306 , and starts execution of the heat-storage control. In the heat-storage control, the E-ECU  29  increases the exhaust temperature and the amount of heat by increasing the engine speed and intake-air quantity, retarding the ignition timing, or the like. 
     In Step S 307 , the E-ECU  29  again receives the output signal T of the heat-storage-material temperature sensor  145 . 
     In Step S 308 , the E-ECU  29  determines whether or not the output signal value T received from the heat-storage-material temperature sensor  145  in Step S 307  is at least the predetermined temperature TS, i.e., whether or not the temperature of the heat-storage material  143  has increased at least to the predetermined temperature TS. 
     If the E-ECU  29  determines in Step S 308  that the output signal value T of the heat-storage-material temperature sensor  145  is less than the predetermined temperature TS, the E-ECU  29  returns to Step S 306 , and continues to execute the heat-storage control. 
     On the other hand, if the E-ECU  29  determines in Step S 308  that the output signal value T of the heat-storage-material temperature sensor  145  is the predetermined temperature TS or higher, the E-ECU  29  proceeds to Step S 309 , and terminates execution of the heat-storage control. 
     In Step S 310 , the E-ECU  29  transmits to the H-ECU  30  a signal indicating that execution of the heat-storage control is terminated. In this case, the H-ECU  30  controls the hybrid mechanism so as to return the operating state of the internal combustion engine  100  and the electric motor  200  to a normal operating state. 
     After executing Step S 310 , the E-ECU  29  proceeds to Step S 311 , and rewrites the value stored in the engine-stop-inhibition-flag storage region from “1” to “0,” thereby terminating execution of the routine. 
     The E-ECU  29  executes the heat-storage control routine in a manner as described above, whereby an engine control means according to the present invention is implemented, and the operating state of the internal combustion engine  100  can be controlled independently of the running state of the vehicle. Therefore, irrespective of the running state of the vehicle, the operating state of the internal combustion engine  100  can be controlled so as to store the heat in the heat-storage material  143 . 
     As a result, in the regenerative catalytic apparatus in the hybrid vehicle according to the present embodiment, a desired amount of heat or more can always be stored in the heat-storage material  143 . Thus, the heat-storage material  143  stores the desired amount of heat or more whenever the internal combustion engine  100  is stopped. 
     Therefore, according to the regenerative catalytic apparatus in the hybrid vehicle of the present embodiment, decrease in the temperature of the three-way catalyst  142  is prevented by the sufficient amount of heat stored in the heat-storage material  143  after the internal combustion engine  100  is stopped. Thus, the three-way catalyst  142  can be retained at its active temperature or higher until the internal combustion engine  100  is restarted. As a result, the exhaust emission upon starting the internal combustion engine  100  can be improved, as well as the fuel consumption that is required to warm up the three-way catalyst  142  can be reduced. 
     Note that, in the present embodiment, the amount of heat stored in the heat-storage material  143  is determined by using the output signal value (temperature of the heat-storage material  143 ) of the heat-storage-material temperature sensor  145  as a parameter. However, it is also possible to provide instead of the heat-storage-material temperature sensor  145  a catalyst-bed temperature sensor for detecting the bed temperature of the three-way catalyst  142 , and estimate the amount of heat stored in the heat-storage material  143  by using an output signal value of the catalyst-bed temperature sensor as a parameter. 
     Moreover, as shown in FIG. 4, the regenerative exhaust-purifying mechanism  14  may include an electric heater  146  for heating the heat-storage material  143 . In this case, the electric heater  146  may be operated to heat the heat-storage material  143  and the three-way catalyst  142  only when the temperature of the heat-storage material  143  or the three-way catalyst  142  becomes less than a desired temperature, such as when the internal combustion engine  100  has been stopped for a long time.