Patent Publication Number: US-2004055814-A1

Title: Engine noise control system

Description:
REFERENCE TO RELATED APPLICATIONS  
     [0001] The present invention claims priority to U.S. Provisional Patent Application No. 60/389,581, filed Jun. 18, 2002. 
    
    
     
       TECHNICAL FIELD  
       [0002] The present invention relates to noise control systems, and more particularly to a system that controls noise in a valve actuation inlet for an engine.  
       BACKGROUND OF THE INVENTION  
       [0003] There are currently engines designed to operate in two or more modes where different numbers of cylinders are fired during each mode. For purposes of illustration only, the example described below addresses an engine having eight cylinders and that operates in two modes, one using all eight cylinders and one using only four out of the eight cylinders. However, the description below is applicable to any engine having any number of cylinders and any number of operating modes with any number of cylinders switched on and off.  
       [0004] During a low power mode, four out of the eight cylinders may be operated, creating an engine sound having predominantly low frequency components. In one embodiment, the signature of the engine noise is predominated by the firing frequency of the engine, which is around twice the engine rotational speed. Typically, the frequency range during this mode is 33 to 170 Hz as the engine runs from idle to 5000 rpm. When the engine mode is operated in a high power mode, where all eight cylinders are operating, the additional cylinders change the engine noise characteristic by increasing the frequency to, typically, four times the engine speed (e.g., around 100 to 400 Hz in the primary engine firing range).  
       [0005] However, currently known noise control systems are not able to adapt their noise control properties to handle the noise characteristic of different engine operating modes. This causes significant noise character changes as the engine mode switches while the noise control system does not follow suit.  
       [0006] There is a desire for a noise reduction system that can reliably control noise in an engine having more than one operating mode generating different noise characteristics.  
       SUMMARY OF THE INVENTION  
       [0007] The present invention is directed to an engine noise reduction system comprising a valve disposed in an engine air inlet. The valve is biased by a resilient member in a closed position to restrict the amount of air flowing through the air inlet. When the engine is operating in a first mode that draws an increased amount of air through the inlet, vacuum pressure generated by the increased air flow overcomes the biasing force in the resilient member and forces the valve open, maximizing air flow through the inlet.  
       [0008] When the engine operates in a second mode that requires less air, the reduced air flow reduces the vacuum pressure in the inlet to a level below the biasing force of the resilient member. The biasing force then closes the valve, reducing the amount of air available for transmitting engine noise through the inlet.  
       [0009] As a result, the inventive system can allow the maximum amount of air to reach the engine for a given engine operating mode while minimizing engine noise, particularly low-frequency noise generated during the second mode. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010]FIG. 1 is a representative diagram of a system having a noise control mechanism according to one embodiment of the invention;  
     [0011]FIG. 2 is perspective view of an air inlet having a noise control mechanism according to one embodiment of the invention;  
     [0012]FIG. 3 is a section view of the noise control mechanism during a first engine operating mode; and  
     [0013]FIG. 4 is a section view of the noise control mechanism during a second engine operating mode. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
     [0014]FIG. 1 is a representative diagram illustrating a relationship between an air inlet  100  and a noise control mechanism  102  according to one embodiment of the invention. The air inlet  100  is connected to an engine  104 , and the noise control mechanism  102  controls air flow through the inlet as well as the amount of noise exiting the inlet. In one embodiment, the noise control mechanism  102  comprises a valve  106  movably supported within the inlet  100  by a support  107  connected to a resilient member  108 , which biases the valve  106  in a first position. The support  107  can be any known support structure, such as a separate support shaft or support protrusions integrally connected to and extending from the valve  106 . Further, the resilient member  108  can be any device, such as a coil spring or a leaf spring, that moves the valve  106  in the desired manner. In one embodiment, the valve  106  is positioned so that it closes off approximately half of the air inlet  100  when it is in the first position.  
     [0015]FIG. 2 is a perspective view of the air inlet  100  and the noise control mechanism  102  according to one embodiment of the invention. Generally, the invention attenuates noise by changing acoustic impedance through the inlet  100  based on the operating mode of the engine. The valve  106  is positioned to increase airflow during a first engine operating mode where most or all of the cylinders are operating (e.g., 8 cylinders) and to restrict airflow during a second engine operating mode where fewer of the cylinders are operating (e.g., 4 cylinders).  
     [0016] More particularly in this example, when all of the cylinders in the engine  104  are running, the valve  106  moves to an open position (FIG. 3) to maximize the amount of air flowing through the entire air inlet  100 , allowing the engine  104  to operate at its maximum power. When the engine  104  switches to the second operating mode, which uses less than all of the cylinders, the valve  106  moves to a closed position (FIG. 4), restricting air flow through the inlet  100  and therefore to the engine  104 . Although it is desirable to maximize air flow at all times, this air flow restriction does not adversely affect engine operation because the amount of air required by the engine  104  in the second operating mode is significantly less than in the first mode due to the reduced number of operating cylinders.  
     [0017] The valve  106  rotates about the shaft  107 . The resilient member  108  connected to the shaft  107  biases the valve  106  in the closed position in this embodiment. When the engine  104  operates in the first mode with all cylinders firing, the air drawn by the engine  104  and the resulting pressure characteristic within the air inlet  100  overcomes the biasing force in the resilient member  108  and forces the valve  106  to the open position (FIG. 3). In other words, the increased air requirements by the engine  104  when it is operating in the first mode increases the air flow and the vacuum pressure in the inlet  100 , forcing the valve  106  open.  
     [0018] When the engine  104  is operating in the second mode, however, the air drawn by the engine  104  is reduced, reducing the air flow and vacuum pressure inside the inlet  100 . The biasing force of the resilient member  108  is calibrated so that it will overcome the vacuum pressure in the inlet  100  when the engine  104  is operating in the second mode, forcing the valve  106  to move to the closed position. The actual amount of biasing force in the resilient member  108  can be determined through experimentation via any known method.  
     [0019] It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.