Abstract:
A generator control device controls a generator that is driven by an engine to charge a battery and supply electric power to electric loads. In the generator control device the following steps are carried out: calculating a required electric power; calculating a difference rate that is a difference in an amount of a hazardous gas component of engine exhaust gas between a first case in which the generator generates the required electric power and a second case in which the generator does not generate an electric power divided by the electric power and controlling the generator to generate the required electric power if the difference is equal to or smaller than a first reference value.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is based on and claims priority from Japanese Patent Application 2005-162648, filed Jun. 2, 2005, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a generator control device that controls a generator so as to effectively reduce hazardous components of engine exhaust gases.  
         [0004]     2. Description of the Related Art  
         [0005]     Usually, a vehicle-mounted generator is controlled by controlling its field current according to a battery condition so that the battery does not become over-discharged, as shown in JP-A 2000-4502 or U.S. Pat. No. 6,621,250. Because the generator is driven by an engine, the fuel consumption of the engine increases as the load of the engine becomes heavier. As the engine load increases due to increase in the output electric power of a generator, more hazardous gas components such as NOx component are emitted from the engine.  
         [0006]     U.S. Pat. No. 5,336,932A discloses an engine control device to operate a generator only when the fuel consumption can be controlled within a low level. However, it is difficult to limit the hazardous components when a large amount of electric power is required generated.  
       SUMMARY OF THE INVENTION  
       [0007]     Therefore, a main object of the invention is to provide an improved generator control device that can control hazardous components emitted from an engine when a generator is operated.  
         [0008]     According to a feature of the invention, a generator control device for controlling a generator that is driven by an engine includes first means for calculating a required electric power, second means for calculating a difference relating to an amount of a hazardous gas component of engine exhaust gas between a first case in which the generator generates the required electric power and a second case in which the generator does not generate an electric power, and third means for controlling the generator to generate the required electric power if the difference is equal to or smaller than a first reference value.  
         [0009]     Thus, a hazardous component can be controlled at a low level. The battery is mainly charged while the emission of hazardous components is within a low level.  
         [0010]     Preferably the second means calculates a difference rate (CEM) in an amount of a hazardous component per an electric power to be generated. The difference rate makes the calculation easier. The third means may further detect current charged into and discharged from the battery, calculate a battery charge ratio, and control the generator to charge the battery if the battery charge ratio is not larger than a second reference value even if the difference rate is larger than the first reference value.  
         [0011]     In addition, the second means may calculate a difference between a first amount of fuel consumption when the generator generates no electric power and a second amount of fuel consumption when the generator generates a required electric power so as to provide the difference rate, and the third means may control the generator according to an increase in fuel consumption. In this case, the third means may control the generator to operate in one of a fuel-economic generation range and an emission control generation range according to a predetermined condition. Further, the third means may control the generator to operate according to electric power consumption, or engine operating condition.  
         [0012]     The second means may include correction means for correcting the difference relating to an amount of hazardous gas component according to engine coolant temperature, or EGR condition. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings:  
         [0014]      FIG. 1  is a block diagram of a generator control system that includes a generator control device according to the first embodiment of the invention;  
         [0015]      FIG. 2  is a graph showing a relationship between amounts of NOx component emitted from an engine and engine torques;  
         [0016]      FIG. 3  is a flow diagram of a generation control routine of the generator control device according to the first embodiment;  
         [0017]      FIG. 4  is a graph showing a relationship between fuel consumption rates and engine torques;  
         [0018]      FIG. 5  is a flow diagram of a portion of a generation control routine of the generator control device according to the second embodiment of the invention;  
         [0019]      FIG. 6  is a flow diagram of the rest of the generation control routine of the generator control device according to the second embodiment;  
         [0020]      FIG. 7  is a flow diagram of a portion of a generation control routine of the generator control device according to the third embodiment of the invention;  
         [0021]      FIG. 8  is a map defining a relationship between engine rotation speeds and engine torques;  
         [0022]      FIG. 9  is a flow diagram of a generation control routine of the generator control device according to the fourth embodiment of the invention;  
         [0023]      FIG. 10  is an electronic circuit formed on a circuit board according to the fifth embodiment of the invention; and  
         [0024]      FIG. 11  is a flow diagram of a generation control routine of the generator control device according to the fifth embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]     A generator control device according to the first embodiment of the invention will be described with reference to  FIGS. 1-3 .  
         [0026]     As shown in  FIG. 1 , a generator control device  11  according to the first embodiment of the invention is connected to a battery  12  via a key switch  13 , an engine ignition system  14 , a fuel injection system  15 , an alternator (ac generator)  16  and a current sensor  17 . The generator control device  11  is powered by the battery  12  to control the ignition system  14 , the fuel injection system  16  as well as the generator  16 . The generator control device  11  calculates a charge ratio SOC of the battery  12  and controls the generator  16  according to the charge ratio SOC. In the calculation of the charge ratio SOC, each amount of current charged into or discharged from the battery  12  is accumulated. That is, the amount of the current charged into the battery  12  is added, and the amount of the current discharged from the battery  12  is subtracted.  
         [0027]     As shown in  FIG. 2 , the amount of the NOx component that is emitted from an engine varies as the engine torque changes. If the engine rotation speed is constant, the increase rate of the NOx component becomes higher when the engine rotation speed is low. On the other hand, the increase rate of the NOx component becomes lower than the increase rate of the engine torque when the engine rotation speed is high.  
         [0028]     When the generator  16  generates a certain amount of electric power, a corresponding generation torque is added to the engine, resulting in change in the engine operating condition. This changes emission of the NOx component. Therefore, it is possible to control the emission of the NOx component by selecting the engine operating condition.  
         [0029]     The generator control device  11  operates according to a generation control routine shown in  FIG. 3 . The control routine is repeated at a certain cycle, such as 8 ms.  
         [0030]     Firstly, at step S 101 , certain engine conditions, such as an engine rotation speed, an intake air ratio and a required electric power, are read. Incidentally, a required electric power is calculated based on a difference in the current charge ratio SOC between a current ratio and a target ratio.  
         [0031]     Thereafter, a current engine torque is calculated from current engine conditions at S 102 . Subsequently, a required electric power is converted into the term of a required generation torque to generate the required electric power, which is stored into a RAM of the control device  11  at S 103 . At the next step S 104 , whether the alternator  16  is generating electric power or not is examined.  
         [0032]     If the result of the examination at S  104  is Yes, the step goes to S 105 , where a current generation torque is calculated from the currently generated electric power and is stored into the RAM of the control device  11 . Subsequently at S 106 , the current generation torque is subtracted from the current engine torque to get an engine torque without electric generation, which is a torque necessary for the engine to operate when the alternator does not generate electric power.  
         [0033]     If the result of the examination at S 104  is No on the other hand, the step goes to S 107 , where it is determined that the current engine torque is the engine torque without electric generation.  
         [0034]     At the next step S 108 , the current engine torque calculated at S 102  and the required generation torque calculated at S 103  are added together to get an engine torque with electric generation, which is a torque necessary for the engine to operate when the alternator generates electric power.  
         [0035]     At the next step S 109 , a no-generation emission rate of hazardous components (g/s) that corresponds to a current engine rotation speed and the engine torque without electric generation is calculated based on a map shown in  FIG. 2 . The no-generation emission rate corresponds to an emission rate of hazardous components when the alternator  16  does not generate electric power. Incidentally, the map stores emission rates of hazardous components that are measured at normal engine operating conditions beforehand.  
         [0036]     Thereafter, the step goes to S 110 , where a generation emission rate of hazardous components (g/s) that corresponds to a current engine rotation speed and the engine torque with electric generation is calculated based on the map. The generation emission rate corresponds to an emission rate of hazardous components when the alternator  16  generates an amount of electric power.  
         [0037]     At the next step S 111 , a difference between the generation emission rate of hazardous components and no-generation emission rate of hazardous components is divided by a current electric power generated by the alternator  16  to obtain a difference rate CEM (g/s.kw). That is: 
 
 CEM  g/s·kw=( RC 1- RC 2)/ P, 
 
 wherein RC 1  is a rate of hazardous components emitted while the alternator  16  is generating an electric power P, RC 2  is a rate of hazardous components emitted while the alternator  16  is not generating electric power. 
 
         [0038]     Thus, an increase or decrease in the hazardous components per a unit of generated electric power can be calculated. Thereafter, the step goes to S 112 , where the difference rate CEM is compared with a preset reference value Ref  1 .  
         [0039]     If the difference rate CEM is equal to or smaller than the reference value Ref 1 , Yes is issued, so that the step goes to S 113 , where a command electric power is set to the required electric power. In other words, it is determined that the increase in the hazardous components is within an allowable range.  
         [0040]     If the difference rate CEM is larger than the reference value Re 1 , No is issued, so that the step goes to S 114 , where the charge ratio SOC of the battery  12  is compared with a reference value Ref  2 .  
         [0041]     If the charge ratio SOC is equal to or smaller than the reference value Ref  2 , the step goes to S 113 , where the required electric power is set to the command electric power, as it is determined that the battery  12  is not normally charged. Therefore, the alternator  16  is controlled to generate an electric power sufficient to charge the battery  12  to increase the charge ratio SOC irrespective of increase in the difference rate CEM.  
         [0042]     If, on the other hand, the charge ratio is larger than the reference value Ref  2 , the step goes to S 115 , where the command electric power is set to 0. Accordingly, the alternator is controlled to stop generation to decrease the hazardous components.  
         [0043]     A generator control device according to the second embodiment of the invention will be described with reference to  FIGS. 4-6 .  
         [0044]     As shown in  FIG. 4 , the fuel consumption rate varies with the engine rotation speed and the engine torque. In particular, the fuel consumption rate significantly increases as the torque increases. Therefore, it is useful to take a fuel consumption increase rate into account in addition to the difference rate CEM described above. The fuel consumption increase rate is a difference rate CFC (g/s.kw) in the fuel consumption rate between a condition in which the alternator generates an electric power and a condition in which the alternator generates an electric power that is divided by a current electric power generated by the alternator  16 .  
         [0045]     The generator control device  11  operates according to a generation control routine shown in  FIGS. 5 and 6 . The control routine is repeated at a certain cycle, such as 8 ms. The control routine includes the same steps S 101 -S 111  for providing the difference rate CEM as the control routine of the generator control device according to the first embodiment. At the next step S 212 , a no-generation fuel consumption rate (g/s) that corresponds to a current engine rotation speed and the engine torque without electric generation is calculated based on a map shown in  FIG. 4 . The no-generation fuel consumption rate corresponds to a fuel consumption rate when the alternator  16  does not generate electric power. The no-generation fuel consumption rates are measured at normal engine operating conditions and stored into the map beforehand.  
         [0046]     Thereafter, the step goes to S 213 , where a generation fuel consumption rate (g/s) that corresponds to a current engine rotation speed and the engine torque with electric generation is calculated based on the map. The generation fuel consumption rate corresponds to a fuel consumption rate when the alternator  16  generates an amount of electric power.  
         [0047]     At the next step S 214 , the fuel consumption increase rate is calculated as follows: 
 
 CFC  (g/s·kw)=( FC 1- FC 2)/ P, 
 
 wherein FC 1  is a rate of the fuel consumption while the alternator  16  is generating an electric power P, FC 2  is a rate of the fuel consumption while the alternator  16  is not generating electric power. 
 
         [0048]     Thereafter the step goes to S 215 , where a mean value of electric power consumption is calculated by means of annealing process or the like. At the next step S 216 , whether the mean value of the electric power consumption is equal to or larger than a predetermined value Pr 1  or not is examined.  
         [0049]     If the result of the examination at S 216  is Yes, a fuel-economic generation is selected and the step goes to S 217 , where if the fuel consumption increase rate CFC is equal to or smaller than a predetermined value Pr 2  is examined to go to S 218 , if the examination result is Yes, to set the command electric power to the required electric power. In other words, it is determined that the increase in the fuel consumption increase rate is within an allowable range. If the fuel consumption increase rate CFC is not smaller than a predetermined value Pr 2  (No), the step goes to S 219 , where the charge ratio of the battery SOC is compared with a predetermined value Ref  2  to go to S 218  to set the command electric power to the required electric power if the charge ratio SOC is equal to or smaller than Ref  2  (i.e. Yes, battery is considered to be discharged). On the other hand, if the charge ratio SOC is not equal or smaller than Ref  2  (No), the step goes to S 220  to set the command electric power to 0. In other words, it is determined that the charge ratio is within an allowable range.  
         [0050]     If the result of the examination at S 216  is No, a emission control generation is selected and the step goes to S 221 , where if the difference rate CEM is equal to or smaller than the predetermined value Ref  1  is examined to go to S 222 , if the examination result is Yes, to set the command electric power to the required electric power. In other words, it is determined that the increase in the emission increase rate is within an allowable range. If the difference rate CEM is not smaller than the predetermined value Ref 1  (No at S 221 ), the step goes to S 223 , where the battery charge ratio SOC is compared with the predetermined value Ref  2  to go to S 224  to set the command electric power to 0, if the result is No. In other words, it is determined that the charge ratio is within an allowable range. Otherwise, the step goes to S 222  to set the command electric power to the required electric power.  
         [0051]     A generator control device according to the third embodiment of the invention will be described with reference to  FIGS. 7 and 8 .  
         [0052]     In order to select fuel-economic electric generation or emission control generation, the control routine of this embodiment includes steps S 215   a  and S 216   a  instead of the steps S 215  and  216  of the second embodiment. The other steps are the same as those of the second embodiment.  
         [0053]     As shown in  FIG. 8 , the fuel-economic generation range and the emission control generation range are selected by a reference torque curve along which the torque decreases as the engine rotation speed increases.  
         [0054]     At S 215   a , the fuel-economic generation range and the emission control generation range are provided to be selected by the reference torque curve. At the next step S 216   a , the current engine torque is compared with a torque level on the reference torque curve at the same engine rotation speed as the current engine rotation speed.  
         [0055]     If the current engine torque is smaller than the torque level (No), the step goes to S 217  to compare the fuel consumption increase rate CFC with the predetermined value Pr 2 , which is described above. If, on the other hand, the current torque is not smaller than the torque level (Yes) the step goes to S 221  to compare the difference rate CEM with the predetermined value Ref  1  as described above. Thus, as the engine rotation speed increases, the emission control range expands.  
         [0056]     A generator control device according to the fourth embodiment of the invention will be described with reference to  FIGS. 9-11 .  
         [0057]     The emission increase rate varies with the engine coolant temperature, the air intake air temperature, the air-fuel ratio, the EGR ratio, EGR system condition, etc. The generator control device according to the fourth embodiment of the invention controls the generator taking some of the above information into account in addition to the difference rate CEM described above.  
         [0058]     The generator control device  11  operates according to a generation control routine shown in  FIGS. 9-11 . The control routine is repeated at a certain cycle, such as 8 ms. The control routine includes the same steps S 101 -S 108  for calculating torques necessary for the engine to operate when the alternator does and does not generate electric power.  
         [0059]     Thereafter, the step goes to S 309 , where a coolant temperature detected by a temperature sensor is read. At the next step S 310 , a coefficient CCT for correcting coolant temperature is calculated based on data of a map. The coefficient CCT is a function of the coolant temperature, an engine operating condition such as the engine rotation speed and the torque without electric generation. Generally, the rate of NOx component becomes lower and the HC component becomes higher as the coolant temperature decreases. Therefore, the rates of the hazardous components emitted from an engine to be stored in the map are detected after the engine has been warmed up. The coefficient CCT is to correct the rates of the hazardous components according to a current coolant temperature.  
         [0060]     Thereafter, the step goes to S 311 , where the intake air temperature detected by a temperature sensor is read. Subsequently, at S 312 , a coefficient CAT for correcting intake air temperature is calculated based on data of the map. The coefficient CAT is a function of the coolant temperature, an engine operating condition such as the engine rotation speed and the torque without electric generation. Generally, the rate of the NOx component becomes higher as the intake air temperature rises. Therefore, the rates of the hazardous components emitted from the engine to be stored in the map are detected when the intake air temperature is 25° C. The coefficient CAT is to correct the rates of the hazardous components according to a current intake air temperature.  
         [0061]     Thereafter, the step goes to S 313 , where if an EGR valve erroneously opens or not is examined by an EGR diagnosis function that is included in the control device  11 . If the result is Yes, the step goes to S 314 , where an EGR ratio that corresponds to the present engine condition is provided by means of a map or the like. If, on the other hand, the result of S  313  is No, the step goes to S  315 , where if an EGR valve erroneously closes or not is examined by the EGR diagnosis function to go to S 316  if the result is Yes, where the EGR ratio is set to 0 or to go S 317  if the result is No, where the EGR ratio detected by an EGR ratio sensor is read.  
         [0062]     Thereafter, the step goes to S 318 , where a coefficient CEGR for correcting EGR ratio is calculated based on data of the map. The coefficient CEGR is a function of the EGR ratio, an engine operating condition such as the engine rotation speed and the torque without electric generation. Generally, the rate of NOx component decreases and the HC component increases as the EGR ratio increases. Therefore, the rates of the hazardous components emitted from the engine to be stored in the map are detected after the engine has been warmed up. The coefficient CEGR is to correct the rates of hazardous components that are stored in the map according to a current EGR ratio.  
         [0063]     Thereafter, the step goes to S 319 , where an air-fuel ratio detected by a air-fuel ratio sensor is read. At the next step S 320 , a coefficient CAF for correcting the air-fuel ratio is calculated based on data of the map. The coefficient CAF is a function of the air fuel ratio, an engine operating condition such as the engine rotation speed and the torque without electric generation. Generally, the rate of NOx component increases as the air-fuel mixture becomes leaner, but decrease as the air-fuel mixture becomes more leaner. Therefore, the rates of the hazardous components emitted from the engine to be stored in the map are detected at a predetermined air-fuel ratio (e.g. theoretical air-fuel ratio). The coefficient CAF is to correct the rates of hazardous components that are stored in the map according to a current air-fuel ratio.  
         [0064]     Subsequently, the step goes to S 321  shown in  FIG. 11 , where a basic no-generation emission rate of hazardous components (g/s) that corresponds to a current engine rotation speed and the engine torque without electric generation is read from a map as shown in  FIG. 2 . An actual no-generation emission rate of hazardous components (g/s) is obtained by multiplying the basic no generation emission rate by the correction coefficients CCT, CAT, CEGR and CAF. That is:  
         [0065]     actual no-generation emission rate of hazardous components (g/s) =basic no-generation emission rate of hazardous components (g/s)×CCT×CAT×CEGR×CAF  
         [0066]     Then the step goes to S 322 , where a basic generation emission rate of hazardous components (g/s) that corresponds to a current engine rotation speed and the engine torque with electric generation is calculated based on the map. The basic generation emission rate corresponds to an emission rate of hazardous components when the alternator  16  generates an amount of electric power. An actual generation emission rate of hazardous components (g/s) is obtained by multiplying the basic generation emission rate by the correction coefficients CCT, CAT, CEGR and CAF. That is:  
         [0067]     actual generation emission rate of hazardous components (g/s)=basic generation emission rate of hazardous components (g/s)×CCT×CAT×CEGR×CAF  
         [0068]     At the next step S 111 , a difference rate CEM (g/s.kw) between the actual generation emission rate of hazardous components and actual no-generation emission rate of hazardous components is divided by a current electric power generated by the alternator  16  as described above.  
         [0069]     The following steps are the same as the steps described in the first embodiment.  
         [0070]     As a modification, the step S 111  shown in  FIG. 3  or S 211  shown in  FIG. 5 , the difference rate CEM (g/s.kw) may be corrected by one, some or all of the engine coolant temperature, the intake air temperature, the air-fuel ratio, the EGR ratio, or conditions (errors) of an EGR system. It is also useful to correct the difference rate CEM by a variable valve timing.  
         [0071]     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.