Abstract:
Provided is an internal combustion engine for improving fuel-economy performance in any of the case where supercharging performed by an electric supercharger is required and the case where the supercharging is not required. The internal combustion engine includes: an electric supercharger; a supercharger; an electric motor; and a controller, the electric supercharger being for compressing an intake air by rotation of the supercharger caused with rotation of the exhaust turbine by an exhaust gas energy to perform supercharging and for rotationally driving the supercharger with electric-motor assistance by the electric motor; an exhaust bypass passage provided to bypass the exhaust turbine; and an opening and closing the exhaust bypass passage unit. In the internal combustion engine, the opening and closing the exhaust bypass passage unit opens the exhaust bypass passage until the supercharging is started by the electric supercharger.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an internal combustion engine including a supercharger provided on an intake passage, which is electric-motor-assisted by an electric motor. 
         [0003]    2. Description of the Related Art 
         [0004]    For improving fuel economy of automobiles, a technology of providing a supercharger, which is driven by an electric motor, on an intake passage to increase an output of an engine (internal combustion engine) is known. The electric motor is provided on a shaft of a turbine and a compressor and has the following characteristics. The electric motor rotates in the case where a desired supercharging pressure is not obtained because of the shortage of an exhaust gas when supercharging is required or in the case where the supercharger rotates at a low speed. In the case where the turbine is rotated by the exhaust gas to successfully obtain the desired supercharging pressure, the electric motor is rotated by the exhaust gas. 
         [0005]    On the other hand, when the supercharging is required, a mechanism including a turbine on an exhaust passage converts an exhaust gas energy into a rotational energy by the turbine to drive a compressor coupled to the turbine through an intermediation of a rotary shaft, thereby performing supercharging work. However, when the supercharging is not required or high load is applied, the turbine acts as an exhaust resistance. As a result, fuel-economy performance is degraded. 
         [0006]    Moreover, a turbocharger generally includes a valve called a west gate valve for causing the exhaust gas to bypass the turbine to prevent the load from being too high due to the exhaust gas when the engine is operated with high load. Therefore, the turbocharger has a flow path for causing the exhaust gas to bypass the turbine when the load is high. In this manner, the exhaust gas is caused to bypass a turbine wheel to prevent the exhaust resistance from increasing until the supercharging pressure rises (for example, see JP 2005-171896 A). 
         [0007]    In this case, there is no exhaust resistance because the exhaust bypass path is opened to cause the exhaust flow to bypass the turbine wheel until the supercharging pressure rises. However, it is necessary to increase the supercharging pressure by the rotation of the electric motor in the meantime, resulting in consumption of a significant amount of power. Therefore, there is a problem that the fuel-economy performance is likely to be consequently degraded. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is devised to solve the problem described above, and has an object of providing an internal combustion engine for improving fuel-economy performance in any of the case where supercharging performed by an electric supercharger is required and the case where the supercharging is not required. 
         [0009]    The internal combustion engine according to the present invention includes: an electric supercharger including: an exhaust turbine provided on an exhaust passage; a supercharger connected to the exhaust turbine through an intermediation of a rotary shaft; an electric motor connected to the rotary shaft; and a controller for controlling the electric motor, the electric supercharger being for compressing an intake air by rotation of the supercharger caused with rotation of the exhaust turbine by an exhaust gas energy to perform supercharging and for rotationally driving the supercharger with electric-motor assistance by the electric motor; an exhaust bypass passage provided to bypass the exhaust turbine; and means for opening and closing the exhaust bypass passage, and in the internal combustion engine, the means for opening and closing the exhaust bypass passage opens the exhaust bypass passage until the supercharging is started by the electric supercharger. 
         [0010]    The internal combustion engine according to the present invention provides the following effects. When the supercharging performed by the electric supercharger is not required, the exhaust flow is caused to bypass the exhaust turbine to lower an exhaust resistance, thereby improving fuel-economy performance. On the other hand, when the supercharging performed by the electric supercharger is required, the exhaust bypass passage is quickly closed to allow the exhaust turbine to be rotated by the exhaust gas. Then, the supercharger is rotated with a combination of an exhaust gas energy and an energy of the electric motor to control a supercharging pressure to a target supercharging pressure, thereby improving the fuel-economy performance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    In the accompanying drawings: 
           [0012]      FIG. 1  is a diagram illustrating an overall configuration of an internal combustion engine according to a first embodiment of the present invention; 
           [0013]      FIG. 2  is a flowchart illustrating an operation of a controller for an electric supercharger according to the first embodiment of the present invention; 
           [0014]      FIG. 3  is a graph illustrating operating points of the internal combustion engine according to the first embodiment of the present invention; and 
           [0015]      FIG. 4  is a time chart for describing a specific operation according to the first embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    Hereinafter, a preferred embodiment of a controller for an internal combustion engine according to the present invention is described with reference to the drawings. 
       First Embodiment 
       [0017]      FIG. 1  is a schematic configuration diagram of an internal combustion engine including an electric supercharger according to a first embodiment of the present invention. 
         [0018]    The internal combustion engine, that is, an engine  1  of the present invention is a multi-cylinder engine. However,  FIG. 1  illustrates a cross section of only one of the multiple cylinders. 
         [0019]    The engine  1  is of a type that injects a fuel into a cylinder  18  by an injector  12 . A larger amount of intake air is supercharged by a supercharger (compressor impeller)  13  with electric-motor assistance of an electric motor  14  described below. In this manner, not only an increase in output but also an increase in fuel economy can be realized. 
         [0020]    The engine  1 , to which the present invention is applied, is not only a direct injection engine for injecting the fuel into the cylinder  18 . The present invention is also applicable to a port injection engine for injecting the fuel into an intake passage  17  at downstream of a throttle valve  8 . 
         [0021]    The electric motor  14  is located on a shaft of an exhaust turbine (turbine wheel)  15  driven by an exhaust gas and a supercharger  13 . The supercharger  13 , the electric motor  14 , and the exhaust turbine  15  constitute an electric supercharger (electric-motor-assisted turbocharger). 
         [0022]    In the engine  1 , after a waste, a dust, and the like are first removed from an intake air by an air cleaner  3 , the intake air flows into a downstream passage  2  in which the supercharger  13  is provided. The air supercharged by the supercharger  13  then flows from an upstream passage  4  into an intercooler  7 . 
         [0023]    The intercooler  7  lowers a temperature of the intake air, which is increased with an increase in pressure caused by the supercharging, thereby improving filling efficiency. Then, the air supercharged through the throttle valve  8  is sucked into the cylinder  18 . 
         [0024]    An intake valve  9  is opened to fill the cylinder  18  with the supercharged air. Then, the fuel is ignited by an ignition plug  10  to be combusted. An exhaust gas generated when the fuel combusts is exhausted from an exhaust valve  11 . Here, an exhaust passage branches into two passages, that is, an exhaust passage  22  leading to the exhaust turbine  15  and an exhaust bypass passage  5 . Exhaust gas flow rate adjusting means  6  which can adjust a flow rate of the exhaust gas in the exhaust bypass passage  5  is provided on the exhaust bypass passage  5 . The exhaust gas flow rate adjusting means  6  receives a signal from a controller  16  for the electric supercharger to adjust the flow rate of the exhaust gas. A feature of the present invention resides in the exhaust gas flow rate adjusting means  6 , and hence the details thereof are described below. An exhaust gas purification catalyst  21  for purifying the exhaust gas is connected to the exhaust bypass passage  5 . 
         [0025]    Next, the exhaust gas flow rate adjusting means  6  which receives the signal from the controller  16  for the electric supercharger to adjust the flow rate of the exhaust gas and the electric motor  14  are described in detail. 
         [0026]    The controller  16  for the electric supercharger receives command values of the number of engine revolutions, a degree of opening of an accelerator, power supplied to the electric supercharger, an intake pressure, the amount of intake air, and the like to drive the electric motor  14 . More specifically, if a current to be supplied can be detected, the power to be supplied to the electric supercharger can be calculated by a multiplication of the supplied current by a voltage value. 
         [0027]    The intake pressure can be obtained, for example, by providing a pressure sensor in the intake passage  17  at the downstream of the throttle valve  8 . 
         [0028]    The amount of intake air can be obtained, for example, by providing an air flow sensor on the downstream side of the air cleaner  3 . 
         [0029]    Next, an operation of the electric motor  14  is described. 
         [0030]    The controller  16  for the electric supercharger receives a supercharge command value from, for example, an engine computer. At this time, in the case where a supercharging pressure has not reached a necessary supercharging pressure, the electric motor  14  is operated to assist in increasing the supercharging pressure. On the other hand, in the case where a sufficiently large number of revolutions of the exhaust turbine  15  is obtained by the engine exhaust gas, the electric motor  14  may function as a power generator. 
         [0031]    Next, a specific operation is described with reference to a flowchart of  FIG. 2 . 
         [0032]      FIG. 2  illustrates five steps, that is, Steps S 201  to S 205  between START and END. 
         [0033]    First, in Step S 201 , the controller  16  for the electric supercharger loads the number of engine revolutions, the degree of opening of the accelerator, an engine torque, the intake pressure, and the amount of intake air to store them in a memory (not shown) of a microcomputer. 
         [0034]    Next, in Step S 202 , a target supercharging pressure of the electric supercharger is calculated from the number of engine revolutions, the degree of opening of the accelerator, and the engine torque. In this operation, for example, it is sufficient that a necessary supercharge-assist amount obtained from the number of revolutions of the engine, the degree of opening of the accelerator, and the engine torque is prestored in a map or the like to calculate the target supercharging pressure. A more specific operation is described with reference to  FIG. 3 . 
         [0035]      FIG. 3  is a graph illustrating an output characteristic of the internal combustion engine, which illustrates the relation between the number of revolutions of the internal combustion engine, an output torque, and the supercharging pressure. For example, while the internal combustion engine is operated at a point A in  FIG. 3 , the supercharging is not required. Therefore, the target supercharging pressure in Step S 202  is 1 when an atmospheric pressure is 1. The supercharging is not required when the internal combustion engine is operated at the point A as illustrated in  FIG. 3 . Therefore, by using the exhaust bypass passage  5  as the exhaust passage to cause the exhaust gas to bypass the exhaust turbine  15 , the effect that an exhaust resistance is lowered to improve fuel-economy performance is provided. 
         [0036]    On the other hand, when an operating state of the internal combustion engine is changed from the point A to a point B illustrated in  FIG. 3 , the point B is contained in an area where the supercharging is required. Therefore, it is necessary to quickly close the exhaust bypass passage  5  by the exhaust gas flow rate adjusting means  6  to rotate the exhaust turbine  15  with the exhaust gas energy. 
         [0037]    A specific operation at this time is described with reference to  FIG. 4 .  FIG. 4  is a time chart when the operating state of the internal combustion engine transits from the point A to the point B illustrated in  FIG. 3 . 
         [0038]    At a time t 0 , acceleration is started by an operation of the accelerator, which is performed by a driver. At a time t 1 , with an increase in degree of opening of the accelerator, a pressure of an intake pipe starts increasing. At this time, in the case where it is judged that the supercharging is required, the exhaust bypass passage  5  is closed as illustrated in  FIG. 4 . Moreover, at this time, whether or not to perform electric-motor assistance is judged according to the degree of acceleration. When the electric-motor assistance is required, the electric-motor assistance is performed with an electric energy. 
         [0039]    At a time t 2 , when the pressure of the intake pipe reaches the target supercharging pressure and a sufficient amount of the exhaust gas energy is obtained, an assisting force of the electric motor  14  is reduced without lowering the pressure of the intake pipe. 
         [0040]    At a time t 3 , when it is judged that the target pressure of the exhaust pipe can be maintained only with the exhaust gas energy, energization of the electric motor  14  is stopped to perform the supercharging only with the exhaust gas energy. 
         [0041]    Returning to the flowchart of  FIG. 2 , the operation is further described. 
         [0042]    In Step S 203 , it is judged from the operating state of the engine  1  whether or not the supercharging is required. The operation in this step is as described above. When the supercharging is not required, the operation proceeds to Step S 205 . On the other hand, when the supercharging is required, the operation proceeds to Step S 204 . 
         [0043]    In Step S 204 , the exhaust bypass passage  5  is quickly closed to cause the exhaust gas to flow toward the exhaust turbine  15 . In this manner, the electric supercharger operates to perform the supercharging by using the exhaust gas energy. 
         [0044]    In Step S 205 , the exhaust bypass passage  5  is opened. In this manner, the electric supercharger is operated to prevent the exhaust turbine  15  from acting as the exhaust resistance. 
         [0045]    Besides, for example, the engine  1  may include throttle position detecting means for detecting a throttle position of a driver. The amount of assistance by the electric motor  14  may be determined and the exhaust bypass passage  5  may be closed according to an output of the throttle position detecting means. 
         [0046]    Besides, for example, the engine  1  may include atmospheric pressure detecting means for detecting an atmospheric pressure and intake pipe pressure detecting means for detecting a pressure of an intake pipe. The exhaust bypass passage  5  may be closed according to an output of the atmospheric pressure detecting means and an output of the intake pipe pressure detecting means. 
         [0047]    Besides, for example, the engine  1  may include internal combustion engine high-load state detecting means for detecting a high-load state of the internal combustion engine. When the engine  1  is operated in the high-load state, the exhaust bypass passage  5  may be opened to reduce a back pressure if the back pressure becomes excessively high with the exhaust bypass passage  5  being closed. 
         [0048]    Besides, for example, the engine  1  may include internal combustion engine warm-up state detecting means for detecting a warm-up state of the internal combustion engine. When warm-up is required because the engine  1  is just started, the exhaust bypass passage  5  is closed to consciously increase the exhaust resistance. In this manner, the warm-up of the internal combustion engine can be completed earlier. Therefore, in some cases, the fuel-economy performance can be improved by increasing the exhaust resistance when the warm-up is required. As described above, when the internal combustion engine is required to be warmed up or the like, the exhaust bypass passage  5  may be closed even when the supercharging is not required. 
         [0049]    As described above, the exhaust gas flow rate adjusting means  6  is controlled according to various conditions. As a result, an optimal supercharging pressure can be obtained. In addition, when the supercharging is not required, the exhaust gas is caused to pass through the exhaust bypass passage  5  to reduce the exhaust resistance by the exhaust turbine  15 . In this manner, the fuel-economy performance can be improved. 
         [0050]    The exhaust gas flow rate adjusting means  6  can be realized by an electrically driven electromagnetic valve, a check valve, or the like. 
         [0051]    As described above, according to this embodiment, when the supercharging performed by the motor supercharger is not required, the exhaust flow is caused to bypass the exhaust turbine  15 . In this manner, the exhaust resistance is reduced to improve the fuel-economy performance. On the other hand, when the supercharging performed by the motor supercharger is required, the exhaust bypass passage  5  is quickly closed to rotate the exhaust turbine  15  with the exhaust gas. In this manner, the supercharger  13  is rotated with the combination of two energies, that is, the exhaust gas energy and the energy of the electric motor  14  to control the supercharging pressure to the target supercharging pressure. As a result, the fuel-economy performance can be improved. 
         [0052]    Although the operation of the controller  16  for the electric supercharger has been described in this embodiment, the same effects can be obtained even if the controller for the electric supercharger functions as a simple driver for driving the electric motor  14  in the case where the function of the controller for the electric supercharger described above can be provided to, for example, an engine computer or the like. 
         [0053]    Further, in this embodiment, the exhaust bypass passage  5  is quickly closed when the supercharging is required. However, the engine may include exhaust turbine revolution number detecting means for detecting the number of revolutions of the exhaust turbine to adjust the flow rate of the exhaust gas flowing through the exhaust bypass passage  5  according to the number of revolutions of the exhaust turbine. By adjusting the flow rate of the exhaust gas in the exhaust bypass passage  5  according to the number of revolutions of the exhaust turbine as described above, the exhaust turbine  15  is kept rotating (for example, at a constant revolution rate of 20,000 rpm) without acting as the exhaust resistance. In this manner, the supercharging pressure can quickly rise. As a result, the effects of improving driving comfort for the driver are also obtained. 
         [0054]    Further, after passing through the catalyst, the exhaust gas in the exhaust bypass passage  5  is directly released to the atmosphere in this embodiment. However, the present invention can also be carried out by using an EGR passage and an EGR valve. Besides, the present invention can also be carried out by using a conventionally existing west gate valve. Therefore, the present invention can be realized in a known structure which can construct the exhaust bypass passage for causing the exhaust gas to bypass the exhaust turbine  15 . 
         [0055]    Besides, for example, even with a structure including a mechanical turbocharger after the electric supercharger, specifically, a so-called twin-turbo structure, the same effects can be obtained. 
         [0056]    Although this embodiment of the present invention has been described above, the present invention is not limited to the exemplary embodiment described above. It is apparent to those skilled in the art that various embodiments are possible within the scope of the present invention.