Abstract:
In accordance with exemplary embodiments, a drive system is provided for an electric or hybrid electric vehicle that provides reduces electromagnetic emissions. The system includes, but is not limited to, an electric motor and a transmission having a collar for receiving a portion of a drive shaft. The collar has an inside diameter proportioned to an outside diameter of the drive shaft to cause capacitive coupling between the transmission and the drive shaft thereby reducing electromagnetic emissions along the drive shaft.

Description:
TECHNICAL FIELD 
       [0001]    The technical field generally relates to systems and methodologies for a drive system for electric and hybrid electric vehicle, and more particularly, to systems and methodologies for a drive system that provides reduced electromagnetic emissions. 
       BACKGROUND 
       [0002]    Electric and hybrid vehicles typically include alternating current (AC) electric motor(s) that are driven by a direct current (DC) power source, such as a high voltage battery pack. The battery pack provides direct current to inverter module(s), which perform a rapid switching function to convert the DC power to AC power which drives the AC electric motor(s). 
         [0003]    The rapid switching of the inverters can also produce electromagnetic interference (EMI) that is manifested as conducted interference or radiated emissions that may impede the proper operation of radio receiving or other electronic equipment in the vehicle. Additionally, EMI may be radiated from the vehicle to the surrounding environment, which may exceed permitted EMI levels in some countries. Accordingly, it is desirable to provide a simple, reliable and cost effective solution to EMI emissions in electric or hybrid electric vehicles. Additionally, other desirable features and characteristics of the present invention will become apparent from the subsequent description taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
       BRIEF SUMMARY 
       [0004]    In accordance with an exemplary embodiment, a drive system is provided for an electric or hybrid electric vehicle that provides reduces electromagnetic emissions. The system comprises an electric motor and a transmission having a collar for receiving a portion of a drive shaft. The collar has an inside diameter proportioned to an outside diameter of the drive shaft to cause capacitive coupling between the transmission and the drive shaft thereby reducing electromagnetic emissions along the drive shaft. 
         [0005]    In accordance with another exemplary embodiment, a drive system is provided for an electric or hybrid electric vehicle that provides reduces electromagnetic emissions. The system comprises an electric motor and a transmission coupled to a drive shaft. A bushing is coupled to the transmission and extends around at least a portion of the drive shaft. The bushing has an inside diameter proportioned to an outside diameter of the drive shaft to cause capacitive coupling between the transmission and the drive shaft thereby reducing electromagnetic emissions along the drive shaft. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]    The inventive subject matter will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0007]      FIG. 1  is an illustration of a vehicle according to an exemplary embodiment; 
           [0008]      FIG. 2  is illustration of transmission case suitable for use in the vehicle of  FIG. 1  in accordance with an exemplary embodiment; and 
           [0009]      FIG. 3  is an illustration of collar or bushing suitable for use with the transmission case of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    The following detailed description is merely exemplary in nature and is not intended to limit the subject matter of the disclosure or its uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
         [0011]    The following description refers to elements or features being “connected” or “coupled” together. As used herein, “connected” may refer to one element/feature being directly joined to (or directly communicating with) another element/feature, and not necessarily mechanically. Likewise, “coupled” may refer to one element/feature being directly or indirectly joined to (or directly or indirectly communicating with) another element/feature, and not necessarily mechanically. However, it should be understood that although two elements may be described below, in one embodiment, as being “connected,” in alternative embodiments similar elements may be “coupled,” and vice versa. Thus, although the schematic diagrams shown herein depict example arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment. It should also be understood that  FIGS. 1-3  are merely illustrative and may not be drawn to scale. 
         [0012]      FIG. 1  illustrates a hybrid electric vehicle  20 , according to one embodiment. The vehicle  20  may be any one of a number of different types of vehicle, such as, for example, a sedan, a wagon, a truck, or a sport utility vehicle (SUV), and may be two-wheel drive (2WD), four-wheel drive (4WD), or all-wheel drive (AWD). The vehicle  20  may also incorporate any one of, or combination of, a number of different types of engines, such as, for example, a gasoline or diesel fueled combustion engine, a flex fuel vehicle (FFV) engine (i.e., using a mixture of gasoline and alcohol), a gaseous compound (e.g., hydrogen and/or natural gas) fueled engine, a combustion/electric motor hybrid engine, and an electric motor. 
         [0013]    In the exemplary embodiment of  FIG. 1 , the vehicle  20  includes a frame  22 , four wheels  24 , and an electronic control system  26 . Although not specifically shown, the frame includes a chassis and a body arranged on the chassis that substantially encloses the other components of the vehicle  20 . The wheels  24  are each rotationally coupled to the frame  22  near a respective corner. While  FIG. 1  depicts various electrical and mechanical connections and couplings in a very simplified manner for ease of description, an actual embodiment of vehicle  20  will of course utilize additional physical components and devices that are well known in the automotive industry. 
         [0014]    As illustrated in  FIG. 1 , the vehicle  20  is an AWD hybrid electric vehicle, and further includes a forward actuator  28  coupled to a rear actuator assembly  30  by a drive shaft  56 , and each of the actuators  28  and  30  are coupled to the wheels  24  through multiple axles  58 . The forward actuator  28  includes an internal combustion engine  36 , a forward motor/transmission assembly  38 , a forward power inverter  40  and a lubricating fluid reservoir  41 . The rear actuator  30  includes a rear motor/transmission assembly  44  and a rear power inverter  46 . The electronic control system  26  is in operable communication with a forward actuator assembly  28 , the rear actuator  30 , a battery  34  and inverters  40  and  46 . Although not shown in detail, the electronic control system  26  includes various sensors and automotive control modules, or electronic control units (ECUs) used for reliable and safe operation of the vehicle  20 . 
         [0015]    The forward motor/transmission assembly  38  includes a collar  39 , which may be integrally formed into the case of the forward motor/transmission assembly  38  or may be a separate piece (e.g., bushing) mechanically and electrically coupled to the forward motor/transmission  38 . The collar  39  has an inside diameter proportioned to be slightly larger than the outside diameter of the drive shaft  56 , or at least a portion thereof, such as the slip yoke (discussed in more detail in  FIG. 2 ), which allows the drive shaft  56  to move as necessary as the suspension (not shown) of the vehicle  20  works during operation. The proportioning of the collar (or bushing)  39  and drive shaft  56  (or slip yoke) creates a gap, which causes capacitive coupling between the drive shaft  56  and the forward motor/transmission  38 . The capacitive coupling shunts high frequency currents to chassis (ground) that would otherwise travel along the drive shaft  56  producing electromagnetic radiation or interference (EMI). 
         [0016]    Referring now to  FIG. 2 , the casing  38 ′ of the forward motor/transmission assembly  38  is shown to include an integral collar  39 , which surrounds at least a portion of the slip yoke  56 ′ of the drive shaft  56 . Typically, a universal joint  57  couples the drive shaft  56  to the slip yoke  56 ′ which allows the length of the drive shaft to extend or contract (by virtue of the slip yoke moving in or out of the casing  38 ′) to compensate for the operation of the vehicle&#39;s suspension system. 
         [0017]    As previously mentioned, the inverters ( 40  and  46  of  FIG. 1 ) may cause electromagnetic currents due to the rapid switching operation of the inverters. Such currents would tend to travel along the drive shaft  56 , which may form an antenna (due to the partial inductance of the drive shaft  56 ) that radiates electromagnetic energy (EMI) into the vehicle&#39;s various electronic systems and/or into the surrounding environment. Conventional approaches to reducing EMI include coupling (bolting) conductive cables to various chassis (vehicle ground) points. However, this practice is labor intensive and the cables may degrade with age or fail over the life of the vehicle. 
         [0018]    According to various embodiments, capacitive coupling is created between the casing  38 ′ and the drive shaft  56  (or slip yoke  56 ′) that shunts such currents to chassis (i.e., ground), which provides benefits such as the reduction of EMI. The capacitive coupling is created by a controlled gap formed between the casing  38 ′ and the drive shaft  56  by proportional control of the inside diameter of the collar (or bushing)  39  and outside diameter of the slip yoke  56 ′. Capacitive coupling is possible by providing a lower impedance path for the current than the drive shaft  56  impedance caused by the partial inductance, which can be expressed as: 
         [0000]    
       
         
           
             
               
                 
                   L 
                   = 
                   
                     
                       ( 
                       
                         
                           μ 
                            
                           
                               
                           
                            
                           l 
                         
                         
                           2 
                            
                           π 
                         
                       
                       ) 
                     
                      
                     
                       [ 
                       
                         
                           
                             ln 
                              
                             
                                 
                             
                              
                             2 
                              
                             l 
                           
                           τ 
                         
                         - 
                         1 
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0019]    where:
       l is the length of the drive shaft  56 ;   r is the radius of the drive shaft  56     μ is permeability of air.       
 
         [0023]    In one embodiment, the casing  38 ′ has the collar  39  formed integrally into the casing  38 ′. This can be done by precision drilling or boring to tolerances that will be discussed in conjunction with  FIG. 3 . The capacitive coupling is designed to provide a low impedance path to chassis (ground) at the frequency of interest to be reduced or eliminated for control of EMI. Thus, various interfering signals can be reduced or eliminated by control of the diameters of the capacitive interface between the collar  39  and the slip yoke  56 ′. 
         [0024]    Referring to  FIG. 3 , a more detailed illustration of the collar or bushing  39  is shown along with its interface to the slip yoke  56 ′ of the drive shaft  56 . The collar or bushing  39  may extend around all or a portion of the slip yoke  56 ′ to create the capacitive interface there between. Although the slip yoke  56 ′ is illustrated for convenience as a cylinder, it will be appreciated that a commercial embodiment of slip yoke will have a grooved or ribbed surface that couples to a mating interface in the forward motor/transmission ( 38  of  FIG. 1 ). 
         [0025]    In the embodiment illustrated in  FIG. 3 , the collar  39  may be formed as a separate piece (bushing), which would be mechanically and electrically coupled to the casing ( 38 ′ of  FIG. 2 ) such as by press-fitting, bolting or any other suitable coupling mechanism. In an exemplary embodiment, the bushing  39  has a nominal length  60  of 154 mm (which would be the nominal depth if bored into the case  38 ′ in an integrated embodiment), the inside diameter  62  of the bushing (or collar)  39  is nominally 102 mm, and the outside diameter  64  of the slip yoke  56 ′ is nominally 101.8 mm. The proportions of these dimensions creates a gap between the slip yoke  56 ′ and the bushing (or collar)  39  of 0.1 mm. The proportional ratios creates a capacitance, which may be determined as: 
         [0000]    
       
         
           
             
               
                 
                   C 
                   = 
                   
                     ( 
                     
                       
                         2 
                          
                         πɛ 
                          
                         
                             
                         
                          
                         L 
                       
                       
                         ln 
                          
                         
                             
                         
                          
                         b 
                          
                         
                           / 
                         
                          
                         a 
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
       
         
           
             where:
           ε is the permittivity of air;   L is the length  60  of the collar  39 ;   a is the inside diameter  62  of the collar  39 ; and   b is the outside diameter  64  of the slip yoke  56 ′.   
         
           
         
       
     
         [0031]    From equation (2), it will be appreciated that an equivalent capacitance of approximately 8.5 nf is created, which provides a low impedance path of approximately 1.9 ohms to chassis (i.e., ground) at 1 MHz. By using other dimensions, other capacitive values and low impedance paths to chassis can be created depending upon the frequency of interest to be reduced or eliminated. The capacitive coupling at the interface between the collar  39  and the slip yoke  56 ′ is generally of low cost and reliable as there are no additional moving parts or aging parts. The embodiments of the present disclosure thus provide a simple, effective and reliable way to reduce or eliminate EMI in electric or hybrid electric vehicles. 
         [0032]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.