Abstract:
There is provided an air supply apparatus for an engine comprising a plurality of exhaust pipes and catalysts arranged in the exhaust pipes, respectively, the apparatus comprising devices for supplying air into the interior of the corresponding exhaust pipes upstream of the corresponding catalysts, respectively.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an air supply apparatus.  
         [0003]     2. Description of the Related Art  
         [0004]     JP Unexamined Patent Publication (Kokai) No. 2003-336521 discloses an apparatus for warming up a catalyst of an engine. The engine disclosed in the above-mentioned publication comprises two exhaust pipes, and a catalyst is arranged in each exhaust pipe. Further, air is supplied to the catalysts from an air pump in order to increase the temperatures of the catalysts. In the catalysts, a hydrocarbon included in an exhaust gas burns by reacting with the air supplied from the air pump to the catalysts. Thereby, the temperature of each catalyst is increased.  
         [0005]     In this connection, it is not preferred to employ a large air pump as the air pump for supplying the air to the catalysts. However, when a small air pump is employed in order to supply the air to a plurality of catalysts, the amount of air supplied by the air pump is insufficient to increase the temperature of each catalyst.  
         [0006]     The object of the invention is to provide an air supply apparatus which can supply a large amount of air to the exhaust pipes.  
       SUMMARY OF THE INVENTION  
       [0007]     According to the first aspect of the invention, there is provided an air supply apparatus for an engine comprising a plurality of exhaust pipes and catalysts arranged in the exhaust pipes, respectively, the apparatus comprising devices for supplying an air into an interior of the corresponding exhaust pipes upstream of the corresponding catalysts, respectively.  
         [0008]     According to the second aspect of the invention, the air supply devices can be independently controlled.  
         [0009]     According to the third aspect of the invention, each air supply device comprises an electrically-activated air pump, an air flow control valve and a check valve, the air pumps can be independently controlled and the air flow control valves can be independently controlled.  
         [0010]     According to the fourth aspect of the invention, each air supply device comprises at least one electrically-activated air pump, and when a plurality of the air pumps must be activated, the air pumps are activated at different times.  
         [0011]     According to the fifth aspect of the invention, when a plurality of the air pumps must be activated, at least one of the air pumps is activated and when a predetermined time period has elapsed after the at least one air pump is activated, the remaining air pumps are activated.  
         [0012]     According to the sixth aspect of the invention, the apparatus comprises a battery for activating the air pumps, and when a plurality of the air pumps must be activated, at least one of the air pumps is activated and when the battery can supply an electrical power having a predetermined electrical voltage to the remaining air pumps after the at least one air pump is activated, the remaining air pumps are activated.  
         [0013]     According to the seventh aspect of the invention, there is provided an air supply apparatus for an engine comprising a plurality of cylinder groups, each having a plurality of cylinders, a plurality of exhaust pipes connected to the cylinder groups, respectively, and catalysts arranged in the exhaust pipes, respectively, the apparatus comprising devices for supplying air into an interior of the corresponding exhaust pipes upstream of the corresponding catalysts, respectively.  
         [0014]     According to the eighth aspect of the invention, the engine is a V-type engine comprising a plurality of banks, and the cylinder groups are provided in the banks, respectively.  
         [0015]     According to the ninth aspect of the invention, the air supply devices can be independently controlled.  
         [0016]     According to the tenth aspect of the invention, each air supply device comprises an electrically-activated air pump, an air flow control valve and a check valve, the air pumps can be independently controlled and the air flow control valves can be independently controlled.  
         [0017]     According to the eleventh aspect of the invention, each air supply device comprises at least one electrically-activated air pump, and when a plurality of the air pumps must be activated, the air pumps are activated at different times.  
         [0018]     According to the twelfth aspect of the invention, when a plurality of the air pumps must be activated, at least one of the air pumps is activated and when a predetermined time period has elapsed after the at least one air pump is activated, the remaining air pumps are activated.  
         [0019]     According to the thirteenth aspect of the invention, the apparatus comprises a battery for activating the air pumps and, when a plurality of the air pumps must be activated, at least one of the air pumps is activated and when the battery can supply electrical power having a predetermined electrical voltage to the remaining air pumps after the at least one air pump is activated, the remaining air pumps are activated.  
         [0020]     According to the fourteenth aspect of the invention, there is provided an air supply control apparatus of an engine for supplying an air into interiors of exhaust pipes in which catalysts are arranged, respectively, the apparatus comprising an air supply control device for controlling air supply devices for supplying an air into interiors of the corresponding exhaust pipes upstream of the corresponding catalysts, respectively, the air supply control device can control the air supply devices independently to activate the air supply devices to supply an air into the corresponding exhaust pipes upstream of the corresponding catalysts.  
         [0021]     According to the fifteenth aspect of the invention, there is provided a method of controlling air supply devices of an engine for supplying an air into interiors of exhaust pipes upstream of corresponding catalysts which are arranged in the exhaust pipes, respectively, comprising: controlling the air supply devices independently to activate the air supply devices to supply an air into the interiors of the corresponding exhaust pipes upstream of the corresponding catalysts. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The present invention may be more fully understood from the description of the preferred embodiments of the invention set forth below together with the accompanying drawings, in which:  
         [0023]      FIG. 1  is a view of an engine provided with an air supply apparatus of the invention;  
         [0024]      FIG. 2  is a routine for controlling the activation of air pumps according to the first embodiment;  
         [0025]      FIG. 3  is a routine for controlling the activation of air pumps according to the second embodiment;  
         [0026]      FIG. 4  is a view of an engine with an air supply apparatus of the invention; and  
         [0027]      FIG. 5  is a view of a V-type engine with an air supply apparatus of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     The embodiments of the invention will be explained by referring to the drawings.  FIG. 1  shows an engine provided with an air supply apparatus of the invention. In  FIG. 1, 1  denotes a body of the engine, and # 1 , # 2 , # 3  and # 4  denote first, second, third and fourth cylinders, respectively. Fuel injectors  21 ,  22 ,  23  and  24  are provided to the cylinders, respectively. The cylinders are connected to an intake pipe  4  via intake branch pipes  3 , respectively. The first and fourth cylinders are connected to a first exhaust branch pipe  5 . The second and third cylinders are connected to a second exhaust pipe  6 . That is, when the group of the first and fourth cylinders is referred to as a—first cylinder group—and the group of the second and third cylinders is referred to as a—second cylinder group, the first cylinder group is connected to the first exhaust branch pipe  5  and the second cylinder group is connected to the second exhaust branch pipe  6 . The first and second exhaust branch pipes  5  and  6  are connected to a common exhaust pipe  7 .  
         [0029]     The first exhaust branch pipe  5  forms a single pipe (hereinafter referred to as a—single pipe portion—) at its downstream area and is divided into two pipes (hereinafter referred to as—divided pipe portions—) at its upstream area. The divided pipe portions of the first exhaust branch pipe  5  are connected to the first and fourth cylinders, respectively. Similarly, the second exhaust branch pipe  6  forms a single pipe (hereinafter referred to as a—single pipe portion—) at its downstream area and is divided into two pipes (hereinafter referred to as—divided pipe portions—). The divided pipe portions of the second exhaust branch pipe  6  are connected to the second and third cylinders, respectively.  
         [0030]     Three-way catalysts  8  and  9  are arranged in the single pipe portions of the exhaust branch pipes  5  and  6 , respectively. A catalyst  10  for purifying specific components included in an exhaust gas is arranged in the exhaust pipe  7 . Three-way catalysts  8  and  9  purify nitrogen oxide (NOx), carbon monoxide (CO) and hydrocarbon (HC) at high purification ratio when the temperature of the catalyst is higher than a certain temperature, i.e. the activation temperature, and the air-fuel ratio of the exhaust gas flowing into the catalyst is around the stoichiometric air-fuel ratio.  
         [0031]     The catalyst  10  positioned downstream of the three-way catalysts  8  and  9  may be a NOx catalyst for purifying NOx. The NOx catalyst carries NOx by absorbing or storing the NOx when the temperature of the NOx catalyst is higher than a certain temperature, i.e. the activation temperature and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is greater (i.e. leaner) than the stoichiometric air-fuel ratio. On the other hand, the NOx catalyst reduces and purifies the NOx when the temperature of the NOx catalyst is higher than the activation temperature and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is the stoichiometric air-fuel ratio or smaller (richer) than the stoichiometric air-fuel ratio.  
         [0032]     Air pipes  11  and  12  are connected to the single pipe portions of the exhaust branch pipes  5  and  6  upstream of the three-way catalysts  8  and  9 , respectively. In the direction away from the single pipe portions, check valves  13  and  14 , air flow control valves  15  and  16 , air pumps P 1  and P 2  and air filters  17  and  18  are arranged in the air pipes  11  and  12 , respectively. Pressure sensors  19  and  20  for detecting the pressure of the air in the air pipes  11  and  12  are arranged in the air pipes  11  and  12  between the air flow control valves  15  and  16  and the air pumps P 1  and P 2 , respectively. A common battery B supplies an electrical power to the air pumps P 1  and P 2  to activate them. Therefore, in this embodiment, electrically-activated air pumps are employed as the air pumps.  
         [0033]     The air pumps P 1  and P 2  take in air through the air filters  17  and  18  and discharge the air toward the single pipe portions of the exhaust branch pipes  5  and  6 . Further, the air pumps P 1  and P 2  can be independently controlled. The air flow control valves  15  and  16  control the supply of the air discharged by the air pumps P 1  and P 2  to the single pipe portions of the exhaust branch pipes  5  and  6 . When the air flow control valves  15  and  16  are opened, the air is supplied to the single pipe portions of the exhaust branch pipes  5  and  6  from the air pumps P 1  and P 2 . On the other hand, when the air flow control valves  15  and  16  are closed, the supply of the air to the single pipe portions of the exhaust branch pipes  5  and  6  from the air pumps P 1  and P 2  is stopped. The check valves  13  and  14  prevent the air from flowing from the exhaust branch pipes  5  and  6  to the air pumps P 1  and P 2 .  
         [0034]     In the first embodiment, the air pumps P 1  and P 2  can be independently controlled and are provided for the three-way catalysts  8  and  9 , respectively, and thus the air can be supplied to the three-way catalyst  8  and  9 , respectively, so as to satisfy the various requirements relating to the three-way catalysts  8  and  9 .  
         [0035]     In  FIG. 1 , an electronic control unit (ECU)  100  comprises an input port  102 , an output port  103 , CPU (microprocessor)  104 , ROM (read only memory)  105  and RAM (random access memory)  106 , which are connected each other by a bidirectional bus  101 . The pressure sensors  19  and  20  are connected to the input port  102  and the outputs of the pressure sensors  19  and  20  are input into the input port  102 . The output port  103  is connected to the air flow control valves  15  and  16 , fuel injectors  21 - 24  and the air pumps P 1  and P 2 .  
         [0036]     In the first embodiment, when both of the air pumps P 1  and P 2  must be activated, first, one of the air pumps P 1  and P 2 , for example, the air pump P 1  is activated and the other air pump, i.e. the air pump P 2  is not activated. Then, when a predetermined time period has elapsed after the air pump P 1  is activated, the air pump P 2  is activated. That is, in the first embodiment, when both of the air pumps P 1  and P 2  must be activated, they are activated at different times.  
         [0037]     The activation of the air pumps according to the first embodiment is advantageous. In particular, in the case wherein the common battery B supplies an electrical power to the air pumps P 1  and P 2 , if both of the air pumps P 1  and P 2  are activated simultaneously, the electrical voltage which the battery B can supply to the air pumps is largely decreased. Such a large decrease in the electrical voltage of the battery B is not preferred as the electrical power of the battery B is generally also used to energize the lamps and the audio system of the automotive vehicle. On the other hand, when the air pumps P 1  and P 2  are activated at the different times, the electrical voltage of the battery is not largely decreased.  
         [0038]     In the first embodiment, when the temperatures of the three-way catalysts  8  and  9  are lower than a predetermined temperature (in particular, an activation temperature at which the three-way catalyst can purify the NOx, CO and HC), for example, at engine starting, it is judged that both of the air pumps P 1  and P 2  must be activated. In other words, when the engine is driven and the air is supplied from the air pumps to the three-way catalysts (at this time, the air flow control valves  15  and  16  are opened), the HC included in the exhaust gas burns with the supplied air in the three-way catalysts to increase the temperatures of the three-way catalysts. Therefore, when the temperatures of the three-way catalysts are lower than the activation temperature and air is supplied from the air pumps to the three-way catalysts, the temperatures of the three-way catalysts are increased to the activation temperature.  
         [0039]     Further, in the first embodiment, the above-mentioned predetermined time period between the activation of the first air pump P 1  and the activation of the second air pump P 2  may be determined on the basis of the voltage of the battery B and/or the temperature of the cooling water for cooling the engine and/or the temperature of the ambient air. In particular, when the voltage of the battery B is smaller than the standard voltage, the activation of the second air pump P 2  should be delayed until the voltage of the battery B becomes the standard voltage. Therefore, in the case wherein the above-mentioned predetermined time period is determined on the basis of the voltage of the battery B, the predetermined time period is set to a long time period in inverse proportion to the voltage of the battery B with reference to the standard voltage.  
         [0040]     Moreover, when the temperature of the cooling water for cooling the engine or the ambient air is low, the temperatures of the three-way catalysts are also low at engine starting, and thus the temperatures of the three-way catalysts should be largely increased. Therefore, in the case wherein the above-mentioned predetermined time period is determined on the basis of the temperature of the cooling water or the ambient air, in particular, immediately after the engine starts, the predetermined time period is set to a short time period in proportion to the temperature of the cooling water or the ambient air.  
         [0041]      FIG. 2  shows an example of the routine for controlling the air pumps according to the first embodiment. In the routine shown in  FIG. 2 , at step  10 , it is judged if the air must be supplied to the three-way catalysts  8  and  9  by activating both of the air pumps P 1  and P 2 . In this connection, for example, when the temperature of each three-way catalysts is lower than the activation temperature and the amount of the exhaust gas discharged from each cylinder is smaller than a predetermined amount, it is judged that the air must be supplied to the three-way catalysts  8  and  9 . (In this connection, if the air is supplied from the air pumps to the exhaust branch pipe when the amount of the exhaust gas discharged from each cylinder is greater than the predetermined amount, the exhaust gas may flow back toward the cylinders.)  
         [0042]     When it is judged that the air must not be supplied to the three-way catalysts  8  and  9  at step  10 , the routine proceeds to step  15  where the activation of the first air pump P 1  is kept stopped when it is not activated or the activation of the first air pump P 1  is stopped when it is activated. Next, the routine proceeds to step  16  where the activation of the second air pump P 2  is kept stopped when it is not activated or the activation of the second air pump P 2  is stopped when it is activated.  
         [0043]     On the other hand, when it is judged that the air must be supplied to the three-way catalysts  8  and  9  at step  10 , the routine proceeds to step  11  where it is judged if the air pumps P 1  and P 2  are in a condition wherein the activation of the air pumps P 1  and P 2  is allowed. In particular, when the air pumps have been activated for long time, the temperatures of the air pumps are relatively high. Therefore, under the circumstances, if the air pumps are activated, they may be burned out. Further, if the air pumps are activated shortly after the activation of the air pumps is stopped, the activation and the stoppage of the air pumps are repeated in a short time interval, and thus the drivers of the air pumps are deteriorated.  
         [0044]     Therefore, at step  11 , it is judged that the air pumps P 1  and P 2  are in a condition wherein the activation of the air pumps P 1  and P 2  is allowed when the air pumps had been activated for short time, and/or when a time long enough to decrease the temperatures of the air pumps to a sufficient low temperature has elapsed after the activation of the air pumps were stopped although the air pumps had been activated for long time, and/or when a long time has elapsed after the air pumps were stopped such that the drivers of the air pumps are not deteriorated.  
         [0045]     When it is judged that the air pumps P 1  and P 2  are not in a condition wherein the activation of the air pumps P 1  and P 2  is allowed at step  11 , steps  15  and  16  are performed. On the other hand, when it is judged that the air pumps P 1  and P 2  are in a condition wherein the activation of the air pumps P 1  and P 2  is allowed, the routine proceeds to step  12  where the first air pump P 1  is activated. Next, the routine proceeds to step  13 .  
         [0046]     At step  13 , it is judged if the elapsed time period T after the first air pump P 1  is activated has reached a predetermined time period Tth determined as explained above. When it is judged that the elapsed time period T has reached the predetermined time period Tth at step  13 , the routine proceeds to step  14  where the second air pump P 2  is activated. On the other hand, when it is judged that the elapsed time period T has not reached the predetermined time period Tth, step  16  is performed.  
         [0047]     The second embodiment of the invention will be explained. In the second embodiment, when both of the air pumps P 1  and P 2  must be activated, first, the first air pump P 1  is activated and the second air pump P 2  is not activated. At this time, it is judged if the voltage of the battery B is greater than the standard voltage. When it is judged that the voltage of the battery B is greater than the standard voltage, the second air pump P 2  is activated. On the other hand, when it is judged that the voltage of the battery B is smaller than the standard voltage, the activation of the air pump P 2  is delayed until the voltage of the battery B becomes the standard voltage. According to the second embodiment, when both of the air pumps must be activated, the air pumps are activated at different times.  
         [0048]     The control of the activation of the air pumps according to the second embodiment provides advantages similar to those provided by the first embodiment. Further, in the second embodiment, the time to activate the second air pump after the first air pump is activated is determined only on the basis of the voltage of the battery B which is the most important parameter to be considered. Therefore, according to the second embodiment, simple control of the air pumps can prevent the voltage of the battery from being largely decreased.  
         [0049]      FIG. 3  shows an example of the routine for controlling the air pumps according to the second embodiment. In the routine shown in  FIG. 3 , at step  20 , similar to step  10  of the routine shown in  FIG. 2 , it is judged if the air must be supplied to the three-way catalysts  8  and  9  by activating both of the air pumps P 1  and P 2 . When it is judged that the air must not be supplied to the three-way catalysts  8  and  9  at step  20 , the routine proceeds to step  25  where the activation of the first air pump is kept stopped when it is not activated or the activation of the first air pump is stopped when it is activated. Next, the routine proceeds to step  26  where the activation of the second air pump is kept stopped when it is not activated or the activation of the second air pump is stopped when it is activated.  
         [0050]     On the other hand, when it is judged that the air must be supplied to the three-way catalysts  8  and  9  at step  20 , the routine proceeds to step  21  which is similar to step  11  of the routine shown in  FIG. 2  where the air pumps P 1  and P 2  are in a condition wherein the activation of the air pumps P 1  and P 2  is allowed. When it is judged that the air pumps are not in a condition wherein the activation of the air pumps is allowed, steps  25  and  26  are performed. On the other hand, when it is judged that the air pumps are in a condition wherein the activation of the air pumps is allowed, the routine proceeds to step  22  where the first air pump P 1  is activated. Next, the routine proceeds to step  23 .  
         [0051]     At step  23 , it is judged if the voltage V of the battery B is greater than the standard voltage Vth. When it is judged that the voltage V of the battery B is greater than the standard voltage Vth at step  23 , the routine proceeds to step  24  where the second air pump P 2  is activated. On the other hand, when it is judged that the voltage V of the battery B is smaller than the standard voltage Vth, step  26  is performed.  
         [0052]     In the above-explained embodiments, the engine has two exhaust branch pipes and two three-way catalysts arranged in the exhaust branch pipes, respectively. However, the invention can be also applied to the engine having three or more exhaust branch pipes and the corresponding number of three-way catalysts arranged in the exhaust branch pipes, respectively.  
         [0053]     Further, the invention can be also applied to the engine shown in  FIG. 4 , having a plurality of cylinder groups (two cylinder groups in the engine shown in  FIG. 4 ) each having a plurality of cylinders (three cylinders in the engine shown in  FIG. 4 ). The embodiment shown in  FIG. 4  will be explained. In  FIG. 4, 1A  and  1 B denote bodies of the engine, respectively and # 1 , # 2 , # 3 , # 4 , # 5  and # 6  denote first, second, third, fourth, fifth and sixth cylinders, respectively. Fuel injectors  31 ,  32 ,  33 ,  34 ,  35  and  36  are provided to the cylinders, respectively. The first, second and third cylinders are connected to an intake pipe  4  via intake branch pipes  3 A, respectively. The fourth, fifth and sixth cylinders are connected to the intake pipe  4  via intake branch pipes  3 B, respectively. Further, the first, second and third cylinders are connected to a first exhaust pipe  5 . The fourth, fifth and sixth cylinders are connected to a second exhaust pipe  6 . That is, when the group of the first, second and third cylinders is referred to as a —first cylinder group—and the group of the fourth, fifth and sixth cylinders is referred to as a—second cylinder group—, the first cylinder group is connected to the first exhaust branch pipe  5  and the second cylinder group is connected to the second exhaust branch pipe  6 . The first and second exhaust branch pipes  5  and  6  are connected to a common exhaust pipe  7 .  
         [0054]     Three-way catalysts  8  and  9  are arranged in the exhaust branch pipes  5  and  6 , respectively. A catalyst  10  for purifying specific components included in the exhaust gas is arranged in the exhaust pipe  7 .  
         [0055]     Air pipes  11  and  12  are connected to the exhaust branch pipes  5  and  6 , respectively. In the direction away from the exhaust branch pipes  5  and  6 , check valves  13  and  14 , air flow control valves  15  and  16 , air pumps P 1  and P 2  and air filters  17  and  18  are arranged in the air pipes  11  and  12 , respectively. Pressure sensors  19  and  20  are arranged in the air pipes  11  and  12  between the air flow control valves  15  and  16  and the air pumps P 1  and P 2 , respectively. A common battery B supplies an electrical power to the air pumps P 1  and P 2  to activate them.  
         [0056]     The check valves, air flow control valves, air pumps, air filters, pressure sensors and battery of the embodiment shown in  FIG. 4  are the same as those of the embodiment shown in  FIG. 1 . Further, the control of the activation of the air pumps of the embodiment shown in  FIG. 4  is the same as that explained referring to  FIGS. 1-3 .  
         [0057]     In  FIG. 4 , an electronic control unit (ECU)  100  comprises an input port  102 , an output port  103 , CPU (microprocessor)  104 , ROM (read only memory)  105  and RAM (random access memory)  106 , which are connected each other by a bidirectional bus  101 . The pressure sensors  19  and  20  are connected to the input port  102  and the outputs of the pressure sensors  19  and  20  are input into the input port  102 . The output port  103  is connected to the air flow control valves  15  and  16 , fuel injectors  31 - 36  and the air pumps P 1  and P 2 .  
         [0058]     In particular, the engine shown in  FIG. 4  may be a V-type engine shown in  FIG. 5 . The V-type engine shown in  FIG. 5  comprises two banks  1 A and  1 B (corresponding to the engine bodies  1 A and  1 B of the embodiment shown in  FIG. 4 , respectively). The cylinder groups (corresponding to the first and second cylinder groups of the embodiment shown in  FIG. 4 , respectively) are provided in the banks  1 A and  1 B, respectively. Each cylinder group has three cylinders (corresponding to the cylinders # 1 -# 3  and # 4 -# 6  of the embodiment shown in  FIG. 4 , respectively). In the V-type engine, the banks  1 A and  1 B are positioned such that the center axis of the cylinders of one of the cylinder groups and the center axis of the cylinders of the other cylinder group cooperate to form “V” shape.  
         [0059]     In case where the invention applies to the V-type engine, the air pumps are provided for the banks, respectively. Therefore, even if small air pumps are employed, the air pumps can supply the air to the three-way catalysts such that the temperatures of the three-way catalysts are increased. Further, when both of the air pumps must be activated, the air pumps are activated at different times, and thus a large decease in the voltage of the battery can be prevented.  
         [0060]     While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention.