Patent Publication Number: US-2019170058-A1

Title: Turbocharged engine and method of operating turbocharged engine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a turbocharged engine in which a throttle valve and a wastegate valve are electronically controlled, and to a method of operating the turbocharged engine. 
     2. Description of the Related Art 
     When obtaining the full-load performance of a turbocharged gasoline engine, a throttle opening degree is conventionally operated at wide-open throttle (WOT) except in a low-rotation range (e.g., 3,000 rpm or less). Torque control is performed by adjusting the supercharging pressure of the turbocharger by increasing/decreasing the opening degree of a wastegate valve. 
     Generally, the compressor of a turbocharger to be used in this kind of an engine is designed so that the maximum efficiency is obtained at an air flow rate about half that when the engine generates the maximum output. Therefore, if the air flow rate exceeds half of the air flow rate required to generate the maximum output, the compressor is used in a low-efficiency state. 
     In the conventional turbocharged engine, the compressor efficiency is low in a full-load operation range as an engine operation range in which the output is relatively high, and this makes it difficult to further increase the engine output. The full-load operation range is an operation range in which the engine rotation range is at a higher rotation than a predetermined middle speed rotation range, and the engine load is larger than a predetermined threshold. The middle speed rotation range is a rotation range between a low rotation range including an idling rotation and a high rotation range including a maximum rotation. 
     SUMMARY OF THE INVENTION 
     Preferred Embodiments of the Present Invention 
     increase compressor efficiency when an engine operation range is in a full-load operation range, thus further increasing engine output. 
     According to a preferred embodiment of the present invention, a turbocharged engine includes an intake port including a downstream end connected to a combustion chamber, a surge tank in communication with an upstream end of the intake port, an exhaust port including an upstream end connected to the combustion chamber, an exhaust passage in communication with a downstream end of the exhaust port, a turbocharger including a turbine installed in the exhaust passage and a compressor that rotates together with the turbine, a control valve that controls a supercharging pressure of the turbocharger, an intake passage that guides air discharged from the compressor to the surge tank, a throttle valve installed in the intake passage, and a controller configured or programmed to control operations of the control valve and the throttle valve, wherein the controller is configured or programmed to control the throttle valve to set a maximum opening degree of the throttle valve to an opening degree closer to a closing-side than a full-throttle opening degree, i.e., less than full-throttle, such that a compressor efficiency of the compressor is higher than a full-throttle compressor efficiency when an engine operation range is in a full-load operation range. 
     A method of operating a turbocharged engine according to a preferred embodiment of the present invention includes operating a turbocharged engine including a turbocharger that supercharges air in an intake passage of an engine including a throttle valve including determining whether or not an engine operation range is in a full-load operation range, controlling a supercharging pressure of the turbocharger to a predetermined supercharging pressure by using a control valve, when the engine operation range is not in the full-load operation range, and controlling the supercharging pressure of the turbocharger to a predetermined supercharging pressure by using the control valve, and controlling the throttle valve to set a maximum opening degree of the throttle valve to an opening degree less than a full-throttle opening degree, such that a compressor efficiency of a compressor is higher than a full-throttle compressor efficiency when the engine operation range is in the full-load operation range. 
     According to a preferred embodiment of the present invention, a pressure difference is produced between the upstream side and the downstream side of the throttle valve when the engine operation range is in the full-load operation range. In this state, the pressure of the compressor outlet is higher than that in a full-throttle position, provided that the supercharging pressure is the same as that in the full-throttle position. That is, the pressure ratio, which is the ratio of the compressor outlet pressure to the compressor inlet pressure, is higher than that in the full-throttle position. This means that the compressor efficiency rises. 
     When the compressor efficiency rises, the work of the compressor is reduced. Accordingly, the work of the turbine is reduced, and thus the engine exhaust loss is reduced, so that gas exchange is efficiently performed. Consequently, engine combustion improves, and the engine output increases. Also, since the work of the compressor is reduced, the outlet temperature of the compressor decreases, and this decreases the air intake temperature. As a consequence, knocking in the engine is significantly reduced or prevented, and the ignition timing is able to be advanced so that the engine output is further increased. 
     Accordingly, preferred embodiments of the present invention increase the compressor efficiency when the engine operation range is in the full-load operation range, thus further increasing the engine output. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the configuration of a turbocharged engine according to a preferred embodiment of the present invention. 
         FIG. 2  is a graph showing experimental data. 
         FIG. 3  is a flowchart for explaining a method of operating the turbocharged engine according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turbocharged engines and methods of operating the turbocharged engines according to preferred embodiments of the present invention will be explained in detail below with reference to  FIGS. 1 to 3 . 
     An engine  1  shown in  FIG. 1  is preferably a 4-cycle single-cylinder engine or 4-cycle multi-cylinder engine, for example, and includes a cylinder  2 , a piston  3 , and a cylinder head  4 . 
     The cylinder head  4  defines a combustion chamber  5  in cooperation with the cylinder  2  and piston  3 . The combustion chamber  5  is surrounded by the cylinder  2 , piston  3 , and cylinder head  4 . 
     The cylinder head  4  includes an intake port  6  and an exhaust port  7 , and further includes an intake valve  8 , an exhaust valve  9 , an ignition plug  10 , a fuel injector  11 , and the like. The downstream end of the intake port  6  communicates with the combustion chamber  5 , and the upstream end thereof communicates with a surge tank  12 . The upstream end of the exhaust port  7  communicates with the combustion chamber  5 , and the downstream end thereof communicates with an exhaust passage  13 . 
     The intake valve  8  opens and closes the downstream end of the intake port  6 . The exhaust valve  9  opens and closes the upstream end of the exhaust port  7 . 
     The fuel injector  11  injects fuel into the combustion chamber  5 . A controller  14  (to be described below) is configured or programmed to control the operations of the ignition plug  10  and fuel injector  11 . 
     The surge tank  12  is connected to a compressor  22  of a turbocharger  21  via a throttle valve  15  and an intake passage  17  including an intercooler  16  and the like. Air discharged from the compressor  22  is guided to the surge tank  12  through the intake passage  17 . 
     The surge tank  12  includes an intake pipe pressure sensor  23  that senses the internal pressure of the surge tank  12 . The intake pipe pressure sensor  23  transmits the sensed pressure as data to the controller  14 . 
     The throttle valve  15  includes an electric valve that controls the flow rate of air flowing through the intake passage  17 , and is located in the intake passage  17  between the surge tank  12  and intercooler  16 . The throttle valve  15  operates based on a control signal transmitted from the controller  14 . The controller  14  sets the opening degree of the throttle valve  15 . 
     The intercooler  16  cools air supplied from the compressor  22 . 
     The turbocharger  21  includes a turbine  24  located in the exhaust passage  13 , and the compressor  22  which rotates together with the turbine  24 . 
     The compressor  22  draws air from an air cleaner  25 , compresses the air, and discharges the air toward the intercooler  16 . 
     The turbine  24  of the turbocharger  21  rotates as the exhaust gas passes through the turbine  24 . A wastegate valve  26  in the turbocharger  21  controls the amount of exhaust gas which passes through the turbine  24 . The controller  14  controls the operation of the wastegate valve  26 . In the present preferred embodiment, the wastegate valve  26  corresponds to a control valve. 
     The controller  14  controls the operation of the engine  1 , i.e., controls the rotational speed of the engine  1  based on the operation amount of an accelerator pedal  27  which is operated by a driver (not shown). When controlling the rotational speed of the engine  1 , the controller  14  operates based on an operation method described in the flowchart shown in  FIG. 3 . 
     The operation method of the engine  1  will be explained below by including a detailed explanation of the operations performed by the controller  14 . 
     The controller  14  starts the operation when a start switch  31  (see  FIG. 1 ) is operated (step S 1 ). The controller  14  starts a starter motor (not shown), and starts the engine  1  by controlling the operations of the ignition plug  10  and fuel injector  11 . 
     Then, the controller  14  determines whether the current engine operation range is in a full-load operation range (step S 2 ). The full-load operation range is an operation range in which the engine rotation range is at a higher rotation than a middle-speed rotation range, and the engine load is larger than a predetermined threshold. The middle-speed rotation range is a rotation range between a low-speed rotation range including an idling rotation and a high-speed rotation range including a maximum rotation. Step S 2  corresponds to a determination step according to a preferred embodiment of the present invention. Although not shown, the current engine operation range is sensed using, e.g., a sensed value from a rotational speed sensor that senses the rotational speed of a crank shaft. 
     If the rotational speed of the engine  1  is less than a predetermined low rotational speed or if the rotational speed is not less than the low rotational speed but the operation amount of the accelerator pedal  27  is smaller than a predetermined threshold (the load is small), it is determined in step S 2  that the engine rotation range is the low-speed rotation range. The low rotational speed described above is, for example, about 3,000 rpm. 
     If the current engine operation range is not in the full-load operation range, supercharging pressure control is performed (step S 3 ). Therefore, the process advances to step S 3  if the engine rotation range is the low-speed rotation range as described above. In the present preferred embodiment, step S 3  corresponds to a supercharging pressure control step according to a preferred embodiment of the present invention. 
     Supercharging pressure control controls the supercharging pressure of the turbocharger  21  to a predetermined supercharging pressure by using the wastegate valve  26 . The supercharging pressure of the turbocharger  21  is equivalent to the air pressure on the throttle valve downstream side which is sensed by the intake pipe pressure sensor  23 . Also, a predetermined supercharging pressure described herein is a supercharging pressure based on the operation amount of the accelerator pedal  27 , the rotational speed of the engine  1 , and the like. A value read out from a map (not shown) may be used as the predetermined supercharging pressure. The map may be stored in a memory  32  (see  FIG. 1 ) of the controller  14 . 
     In step S 3 , the controller  14  controls the opening degrees of the throttle valve  15  and wastegate valve  26  using feedback control, so that the actual supercharging pressure of the turbocharger  21  matches the predetermined supercharging pressure. During the supercharging pressure control, the throttle valve  15  and wastegate valve  26  operate so as to obtain a supercharging pressure corresponding to the operation amount of the accelerator pedal  27 , and the rotational speed of the engine  1  changes in accordance with the operation of the accelerator pedal  27 . 
     On the other hand, if in step S 2  the engine rotation range is at a higher rotation than the middle-speed rotation range and the operation amount of the accelerator pedal  27  is not smaller than the above-described threshold, i.e., when the engine operation range is in the full-load operation range, a control using both the above-described supercharging pressure control and a throttle opening degree control to be described below is performed (step S 4 ). In the present preferred embodiment, step S 4  corresponds to a supercharging pressure control/throttle opening degree control combination step according to a preferred embodiment of the present invention. 
     Steps S 2  to S 4  described above are repetitively performed until the start switch  31  is operated again and the engine  1  stops (steps S 5  and S 6 ). 
     The throttle opening degree control performed in step S 4  controls the throttle valve  15  by setting the maximum opening degree of the throttle valve  15  to an opening degree less than the full-throttle opening degree, so that the compressor efficiency is higher than the full-throttle compressor efficiency. In step S 4 , therefore, the controller  14  controls the supercharging pressure of the turbocharger  21  to a predetermined supercharging pressure (equal or substantially equal to the supercharging pressure when performing supercharging pressure control) by using the wastegate valve  26 , and controls the throttle valve  15  by setting the maximum opening degree of the throttle valve  15  to an opening degree less than the full-throttle opening degree so as to satisfy a predetermined condition. The predetermined condition described herein makes the current compressor efficiency higher than the full-throttle compressor efficiency. As is conventionally well known, the compressor efficiency is able be obtained by calculations based on the inlet temperature and inlet pressure of the compressor  22  and the outlet temperature and outlet pressure of the compressor  22 . In the present preferred embodiment, throttle opening degrees by which the control is performed to provide the best compressor efficiency are obtained by calculations and experiments in advance and are mapped and stored in the memory  32  of the controller  14 . 
     When the maximum opening degree of the throttle valve  15  is an opening degree less than the full-throttle opening degree while the engine operation range is in the full-load operation range, a pressure difference is produced between the upstream side and the downstream side of the throttle valve  15 . This state of the engine  1  will be explained with reference to  FIG. 2 .  FIG. 2  is a graph showing data obtained by actually operating the engine  1  according to a preferred embodiment of the present invention. The data shown in  FIG. 2  was obtained when the engine speed was about 6,000 rpm, for example. 
     As shown in  FIG. 2 , when the opening degree of the throttle valve  15  is controlled to be, e.g., 70% while the engine operation range is in the full-load operation range, a supercharging pressure A is equal or substantially equal to that in the full-throttle position (throttle opening degree=100%), and a pressure B at the compressor outlet is higher than that in the full-throttle position. That is, the pressure ratio of the pressure B at the compressor outlet to the pressure (equal or substantially equal to atmospheric pressure) at the compressor inlet is higher than that in the full-throttle position. This means that the compressor efficiency increases, and the experimental results indicate that a compressor efficiency C increases to 58% from 38% in the full-throttle position, as shown in  FIG. 2 . That is, in step S 4 , the controller  14  controls the maximum opening degree of the throttle valve  15  to be less than the full-throttle opening degree so that the current compressor efficiency is higher than the full-throttle compressor efficiency. 
     Since the compressor efficiency increases as described above, the work of the compressor  22  is reduced, so the work of the turbine  24  is reduced. That is, as shown in  FIG. 2 , a compressor outlet temperature D decreases as the compressor efficiency C increases, and the work of the turbine  24  is reduced. When the work of the turbine  24  is reduced, an opening degree E of the wastegate valve  26 , the operation of which is controlled so as to obtain a predetermined supercharging pressure based on the operation amount of the accelerator pedal  27  and the rotational speed of the engine  1 , increases so that a turbine inlet pressure F decreases and a turbine inlet temperature G rises. 
     When the work of the turbine  24  is reduced, the exhaust loss of the engine  1  is reduced so that gas exchange is efficiently performed. As a consequence, the combustion of the engine  1  improves and an output H of the engine  1  is increased. 
     Also, when the work of the compressor  22  is reduced and the outlet temperature D of the compressor  22  decreases as described above, the intake temperature decreases so that knocking is significantly reduced or prevented in the engine  1 . This makes it possible to advance the ignition timing and further increase the engine output. 
     Accordingly, preferred embodiments of the present invention provide a turbocharged engine that further increases the engine output by raising the efficiency of the compressor  22  when the engine operation range is in the full-load operation range, and a method of operating the turbocharged engine. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.