Patent Publication Number: US-11047347-B2

Title: Exhaust gas recirculating device

Description:
TECHNICAL FIELD 
     The present disclosure relates to an exhaust gas recirculation device including a reed valve. 
     BACKGROUND ART 
     In order to reduce NOx in exhaust gas from an engine, an exhaust gas recirculation (hereinafter also referred to as “EGR”) device that recirculates the exhaust gas to the engine is widely used. 
     The EGR device can adjust the mass flow rate of the returning EGR gas by controlling an EGR valve provided in an EGR passage. In some of the engine specifications, the differential pressure between the inlet and outlet of the EGR valve is small and may become negative depending on the driving condition. In such an engine, a reed valve (check valve) is provided at a connection position between the EGR passage and an intake passage of the engine to prevent the backflow of the EGR gas, and at the same time, the EGR gas is pumped out by using periodic differential pressure change caused by pulsation of intake/exhaust stroke of the cylinder. As such a reed valve, mainly a reed-type one-way valve is used (see PTLs 1 and 2). 
     CITATION LIST 
     Patent Literature 
     PTL1 
     
         
         Japanese Patent Application Laid-Open No. 2000-249004
 
PTL2
 
         Japanese Patent Application Laid-Open No. 2001-132557 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In an EGR device using the above described reed valve, the opening/closing sound of the reed valve resonates in the EGR passage, so that an unusual noise (like shuffling sound) may be generated. If this sound is heard from the outside, the product quality may be deteriorated. 
     An object of the present disclosure is to provide an exhaust gas recirculation device capable of suppressing an unusual noise caused by a reed valve. 
     Solution to Problem 
     An aspect of the present disclosure is an exhaust gas recirculation device for returning a part of exhaust gas from an engine to an intake side of the engine through an EGR passage, and the exhaust gas recirculation device includes: 
     a reed valve provided at a connection position between the EGR passage and an intake passage of the engine; 
     an EGR valve provided at the EGR passage; and 
     an EGR duct that forms a passage connecting the EGR valve and an EGR cooler, the EGR duct being a portion of the EGR passage, 
     in which the EGR duct is formed so as to suppress resonance of opening/closing sound generated by the reed valve, the resonance being inside the EGR passage. 
     Advantageous Effects of Invention 
     The present disclosure can suppress an unusual noise caused by a reed valve since the EGR duct is formed so as to suppress resonance, inside an EGR passage, of opening/closing sound generated by the reed valve. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  schematically illustrates the overall configuration of an embodiment; 
         FIG. 2  is a perspective view illustrating a state of an EGR duct, an EGR valve, and an intake duct according to the embodiment; 
         FIG. 3  is a perspective view illustrating a state of an EGR duct, an EGR valve, and an intake duct of a conventional art; 
         FIG. 4  shows frequency characteristics observed on the inlet side of the EGR valve (i.e., on the EGR duct side); and 
         FIG. 5  is a perspective view illustrating a state where the EGR duct is fixed according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. 
     Although an in-line four-cylinder diesel engine will be described as an example in the embodiment, the present invention is not limited to a diesel engine but can also be applied to a gasoline engine. In addition, the number of cylinders in the engine and the arrangement of the cylinders are not limited, either. For the drawings, the dimensions are adjusted so as to make configurations easily understandable, and the ratio of the plate thickness, width, length or the like of each member or part does not necessarily match that of actually manufactured member or part. 
     As illustrated in  FIG. 1 , engine (internal combustion engine)  1  is provided with engine body  2 , exhaust passage Ex, intake passage In, and EGR (exhaust gas recirculation) passage Eg. Engine  1  is further provided with exhaust manifold  3 , inlet manifold  4 , turbocharger  5  including variable turbine  5   a  and compressor  5   b , air cleaner  6 , intercooler  7 , intake throttle  8 , intake duct  8   a , after-treatment device  9  including DOC (diesel oxidation catalyst)  9   a  and DPF (collecting device)  9   b , and EGR device  10 . 
     EGR device  10  is provided with EGR cooler  11 , EGR valve  12 , and reed valve (check valve)  13 . EGR cooler  11  and EGR valve  12  are connected by EGR duct  14 . 
     Engine  1  is a so-called high-pressure EGR system in which EGR gas is returned from the exhaust gas upstream side of turbocharger  5 . Therefore, the differential pressure between the inlet and outlet of EGR valve  12  becomes small, and even becomes negative depending on the driving condition. In the present embodiment, reed valve  13  is provided at a connection position between EGR passage Eg and intake passage In of engine  1  to prevent the backflow of the EGR gas, and at the same time, the EGR gas is pumped out into intake passage In by using periodic differential pressure change caused by pulsation of intake/exhaust stroke of the cylinder. 
       FIG. 2  is a perspective view illustrating a state of EGR duct  14 , EGR valve  12 , and intake duct  8   a  of the embodiment.  FIG. 3  meanwhile is a perspective view illustrating a state of EGR duct  14   x , EGR valve  12 , and intake duct  8   a  of a conventional art as a comparative example. 
     As apparent from a comparison between  FIG. 2  and  FIG. 3 , EGR duct  14  of the present embodiment has a larger volume than conventional EGR duct  14   x . With this configuration, EGR duct  14  of the present embodiment has a function of a silencer that silences the shuffling sound generated when reed valve  13  opens and closes. 
     In practice, EGR duct  14  is formed so as to suppress resonance, within EGR passage Eg, of opening/closing sound generated by reed valve  13 . That is, the resonance is suppressed by making the volume of the hollow part of EGR duct  14  larger than that of conventional EGR duct  14   x  in the present embodiment. 
       FIG. 4  shows frequency characteristics of opening/closing sound of reed valve  13  observed on the inlet side of EGR valve  12  (i.e., on the EGR duct  14  side).  FIG. 4  reveals that resonance frequencies of the opening/closing sound generated by reed valve  13  exist in the range of 208 to 256 Hz. In the present embodiment, the shape of EGR duct  14  such as a volume is determined so that resonance in EGR duct  14  does not occur at those resonance frequencies. 
     In the present embodiment, EGR duct  14  has a shape such that it does not resonate at a frequency of 200 to 260 Hz. Specifically, the resonant frequency (i.e., resonance frequency of EGR duct  14 ) is adjusted to be lower than 200 Hz by increasing the volume of EGR duct  14  compared to the conventional duct. Such a configuration can prevent the opening/closing sound of reed valve  13  from resonating in EGR duct  14 . 
     Further, EGR duct  14  is formed of a casting in the present embodiment. EGR duct  14  formed of a casting can further suppress leaking of an unusual noise generated by opening/closing of reed valve  13  to the outside via EGR duct  14 . That is, leaking of an unusual noise to the outside can be suppressed by suppressing the loudness of the unusual noise itself in EGR passage Eg with the use of EGR duct  14  having a shape that suppresses the resonance of the opening/closing sound generated by reed valve  13  within the EGR passage, as well as by forming EGR duct  14  from a casting. The unusual noise heard from outside thus can be further suppressed. 
     Forming EGR duct  14  from a casting increases its weight, and thus fixing portion  14   a  for fixing EGR duct  14  to the outside is formed on the outer surface of EGR duct  14  as illustrated in  FIGS. 2 and 5  in the present embodiment. EGR duct  14  is then fixed to, for example, an engine block indicated by a dashed-dotted line via fixing portion  14   a  as illustrated in  FIG. 5 . 
     As described above, the present embodiment can realize exhaust gas recirculation device  10  capable of suppressing an unusual noise caused by reed valve  13  by employing the shape of EGR duct  14  that suppresses the resonance, within EGR passage Eg, of the opening/closing sound generated by reed valve  13 . 
     The embodiment disclosed herein is a mere exemplification for practicing the present invention, and should not be construed as limiting the technical scope of the present invention in any way. Specifically, various modifications are possible without departing from the spirit or main features of the present invention. 
     In the embodiment disclosed herein, resonance frequencies generated by the opening/closing of reed valve  13  exist in the range of 208 to 256 Hz as shown in  FIG. 4 , and thus the resonant frequency of EGR duct  14  (i.e., resonance frequency of EGR duct  14 ) is adjusted to be lower than 200 Hz; however, the resonant frequency of EGR duct  14  (i.e., resonance frequency of EGR duct  14 ) can be set in accordance with resonance frequencies generated by the opening/closing of reed valve  13 . That is, EGR duct  14  can be formed to have a shape such that EGR duct  14  does not resonate (sympathize) at the resonance frequencies generated by the opening/closing of reed valve  13 . 
     This application is entitled to and claims the benefit of Japanese Patent Application No. 2017-122360 filed on Jun. 22, 2017, the disclosure of which including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The exhaust gas recirculation device of the present disclosure is suitable as an exhaust gas recirculation device including a reed valve. 
     REFERENCE SIGNS LIST 
     
         
           1  Engine 
           2  Engine body 
           10  EGR (exhaust gas recirculation) device 
           11  EGR cooler 
           12  EGR valve 
           13  Reed valve 
           14 ,  14   x  EGR duct 
           14   a  Fixing portion 
         Eg EGR (exhaust gas recirculation) passage 
         Ex exhaust passage 
         In Intake passage