Abstract:
A turbofan jet engine having a housing and an engine core disposed in the housing. The engine core includes at least a compressor, turbine, and a drive shaft. The drive shaft defines a drive shaft axis. A plurality of fans are disposed in the housing and each is rotatable about a separate fan axis. Each of the fan axes are axially offset from the drive shaft axis. The turbofan jet engine further includes a drive system operably interconnecting the engine core and fans so as to rotatably drive the fans and selectively disengage select fans from the engine core.

Description:
FIELD OF THE INVENTION 
     The present invention relates to bypass turbofan jet engines and, more particularly, relates to a high bypass-ratio turbofan jet engine having a plurality of non-coaxial fans. 
     BACKGROUND OF THE INVENTION 
     As is well known in the art, turbofan jet engines are often used for aircraft propulsion. The turbofan jet engines generally include a turbine section that is designed to drive at least one compressor and a bypass fan. The bypass fan is typically a low-pressure compressor of large diameter, which is disposed upstream of the main compressor. The bypass fan is further arranged in coaxial relationship with a drive shaft or spool powered by the turbine. 
     Despite the popularity and successfulness of today&#39;s turbofan jet engine, it is accurate to say that the current state-of-the-art in engine development is one of infinitesimally small improvements. Improvements in the art are often limited by the reluctance to modify such a successful design. However, in this regard it can be appreciated that there are structural limits imposed on today&#39;s turbofan designs in light of current material advancements. 
     By way of background, turbofan jet engines typically have a coaxial design in that the bypass fan, the compressor, and the turbine sections rotate about a common axis on two or three coaxial shafts or spools. It is generally accepted that by increasing the bypass fan diameter or employing counter-rotating fans, one can improve the bypass ratio and, thus, the turbofan jet engine efficiency. However, there are number of disadvantages associated with these design techniques. For example, by increasing the bypass fan diameter, the diameter of the nacelle is also increased. The increased size of the nacelle in turn increases the drag and weight associated with the nacelle and the support strut. 
     Furthermore, the increased nacelle diameter may also cause ground clearance problems leading to undesirable configuration characteristics. Any type of oversized engine configuration inhibits the engines use in vertical take-off and landing designs. Still further, large diameter bypass fans further require extensive shielding in the event of a blade-out so as to contain the blades within the engine housing, also known as blade containment. Such blade containment requires robust materials that add significant weight to the aircraft. Alternatively, the addition of counter-rotating fans increases the complexity of the turbofan jet engine and further increases the buzz-saw noise from the front of the engine, which is undesirable. 
     During operation of conventional turbofan jet engines, it is necessary to shut down the engine in the event of a failure of the bypass fan stage. During the shutdown process, due to the sheer size of the bypass fan, the engine experiences very high blade-out loads further necessitating the aforementioned blade containment shielding. 
     Although conventional turbofan jet engines are quite safe and reliable, the efficiency of the design and associated components have been maximized. That is, the size, arrangement, and materials used generally limit further major advancements in turbofan jet engine design. Accordingly, in order to provide improved engine efficiency, there exists a need in the relevant art to change from the basic coaxially arranged turbofan jet engine design. 
     SUMMARY OF THE INVENTION 
     According to the principles of the present invention, a turbofan jet engine having an advantageous design is provided. The turbofan jet engine includes a housing and an engine core disposed in the housing. The engine core includes at least a compressor, turbine, and a drive shaft. The drive shaft defines a drive shaft axis. A plurality of fans are disposed in the housing and each is rotatable about a separate fan axis. Each of the fan axes are axially offset from the drive shaft axis. The turbofan jet engine further includes a drive system operably interconnecting the engine core and fans so as to rotatably drive the fans and selectively disengage select fans from the engine core. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a plan view illustrating a high bypass multi-fan jet engine according to the principle of a first embodiment; 
     FIG. 2 is a front view illustrating the high bypass multi-fan jet engine according to the principle of a first embodiment; 
     FIG. 3 is a front view illustrating the high bypass multi-fan jet engine according to the principle of a second embodiment; 
     FIG. 4 is a plan view illustrating the high bypass multi-fan jet engine according to the principle of the second embodiment; 
     FIG. 5 is a front view illustrating the high bypass multi-fan jet engine according to the principle of a third embodiment; 
     FIG. 6 is a plan view illustrating the high bypass multi-fan jet engine according to the principle of the third embodiment; 
     FIG. 7 is a front view illustrating the high bypass multi-fan jet engine according to the principle of a third embodiment; 
     FIG. 8 is a front view illustrating the high bypass multi-fan jet engine according to the principle of a fourth embodiment; and 
     FIG. 9 is a plan view illustrating the high bypass multi-fan jet engine according to the principle of the fourth embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. In fact, it is anticipated that the principles of the present invention may be equally applicable to a wide variety of turbofan jet engines. Accordingly, the present invention will be described in connection with a conventional high bypass-ratio turbofan jet engine with the following differences described below. Therefore, in the interest of brevity, the specific components and operation of the engine core will not be described herein. 
     As best seen in FIGS. 1 and 2, a high bypass multi-fan engine  10  is illustrated in accordance with the principles of the present invention. Briefly, engine  10  generally includes a diffuser  12  disposed upstream from a compressor  14 , a combustor  16 , a turbine  18 , and a nozzle  20 . As may be readily seen in FIG. 1, diffuser  12 , compressor  14 , combustor  16 , turbine  18 , and nozzle  20  are generally arranged in a coaxial arrangements about at least one shaft  22  extending along an axis A—A (hereinafter, these components are generally referred to as engine core  24 ). It should be appreciated that variations in design of the aforementioned components is to be regarded as being within the scope of the present invention. For example, it is common to use multistage compressors to generate the high bypass-ratios commonly associated with these designs. 
     Still referring to FIGS. 1 and 2, engine  10  further includes a fan stage  26  having a plurality of fans  28  disposed upstream from engine core  24 . The plurality of fans  28  are disposed within a fan cowl and diffuser  30 . Each of the plurality of fans  28  includes a plurality of fan blades  32  extending radially outward from a fan hub  34 . Each of the plurality of fans  28  is adapted to rotate about an individual axis separate from the remaining plurality of fans  28 . That is, fan  28   a  rotates about an axis a—a, fan  28   b  rotates about an axis b—b, fan  28   c  rotates about an axis c—c, and fan  28   d  rotates about an axis d—d (FIG.  1 ). 
     Each of the plurality of fans  28  is further driven using a gearbox drive system  36  operably coupled between shaft  22  and each of the plurality of fans  28 . However, it should be understood that gearbox drive mechanism  36  may be operably coupled to additional shafts operating within the engine core  24  in order to balance the load requirements and/or provide redundant mechanisms in the event of a failure. According to a first embodiment, gearbox drive system  36  may include mechanical structure capable of transmitting the drive force between shaft  22  and fan hub  34 . Alternatively, gearbox drive system  36  may include conduit to drive each of the plurality of fans  28  in response to bleed air from compressor  14 . 
     Gearbox drive system  36  further includes a disengagement system  38  operably coupled to each of the plurality of fans  28  to permit the selective and discrete disengagement of any one of the plurality of fans  28  in the event of a failure. This arrangement permits engine  10  to continue to operate, albeit at a reduced efficiency, in emergencies. In a conventional turbofan jet engine, failure of the fan stage would necessitate the shutdown of the entire engine. However, according to the present invention, engine  10  may continue to operate. 
     As best seen in FIG. 1, fan cowl and diffuser  30  may include a plurality of fan flow exhausts  40  extending from a rearward end thereof. The fan flow exhausts  40  permit the flow of at least a portion of the air therethrough. 
     As should be appreciated from the foregoing, the plurality of fans  28  may be arranged in any one of a number of various configurations, which are tailored to the specific application. For example, as seen in FIGS. 3 and 4, the plurality of fans  28  may be arranged symmetrically about engine core  24 . Alternatively, the plurality of fans  28  may be arranged asymmetrically or to one side of engine core  24  (FIGS.  5  and  6 ). Still further, the plurality of fans  28  may be further arranged such that axis A—A is offset from a plane extending through axes a—a, b—b, c—c, and d—d (FIG.  7 ). In fact, the axes of the plurality of fans  28  may be at any angle relative to each other as illustrated in FIGS. 8 and 9. For example, fan  28   a  may be directed in a direction 90 degrees relative to fans  28   b  and  28   c . However, it should be readily appreciated that at least one of the plurality of fans  28  may be coaxially aligned with engine core  24 , as illustrated in FIGS. 5 and 6 where core  24 ′, shown in phantom, is coaxially aligned with the center fan  28 . 
     As should be appreciated from the foregoing discussion and figures, each of the plurality of fans  28  is considerably smaller than a conventional single fan turbofan jet engine. As the fans become smaller, the stresses and the material demands are reduced, thereby the need for exotic materials may be relaxed. Furthermore, smaller fans also produce much smaller blade-out loads due to lower energy and lighter weight, therefore the robustness and weight of the associated blade containment system may be dramatically reduced. Such reduction in the robustness and weight of the blade containment system may provide substantial weight savings in the aircraft. Still further, smaller fans are more easily manufactured and transported in larger numbers, thus providing reduced manufacturing costs. 
     The high bypass multi-fan engine of the present invention provides many important advantages over conventional bypass turbofan jet engine designs. By way of non-limiting example, the present invention provides for the reduction of installation weight, operational noise production, improved range, improved payload capability, improved safety, improved design flexibility, and dramatically reduced manufacturing and operational costs. Additionally, the present invention provides a method of producing bypass ratios which are consistent with today&#39;s technology or those that can not be achieve solely with today&#39;s technology. By way of non-limiting example, the present invention can provide bypass ratios up to and great than 9:1. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.