Abstract:
A vehicle including a movable element and an electric machine either driving or being driven by the movable element. The electric machine having first and second housing portions and a stator. The second housing portion is engaged with the first housing portion. The stator being coupled to the first housing portion and the second housing portion by way of compressive force applied to the stator by and between the first housing portion and the second housing portion.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to electric machines, and, more particularly, to a method and apparatus for securing the stator of an electric motor or generator to a housing. 
       BACKGROUND OF THE INVENTION 
       [0002]    An electric motor is an electromagnetic/mechanical device that converts electrical energy into mechanical energy. Conversely an electric generator is an electromagnetic/mechanical device that converts mechanical energy into electrical energy. Electrical machines such as electric motors and generators operate through the interaction of ferrous materials and magnetic fields and current carrying conductors to thereby generate the mechanical force or electricity respectively. Electric motors are found in applications as diverse as pumps, blowers, fans, machine tools, household appliances, power tools, disc drives in computers and the like. Electrical motors come in various sizes from small motors that are utilized in watches to rather large electric motor/generators utilized in locomotive engines. 
         [0003]    A rotor of an electric motor is typically the rotating part of the motor and it rotates due to the magnetic fields that are arranged in the motor so that a torque is developed about the axis of the rotor. A stator is the stationary part within which the rotor rotates. The electromagnetic interaction between the stator and rotor cause the rotor to rotate and convey the motion and torque to some element connected to the shaft that typically runs through the rotor. The electromagnetic interaction causes a torque in the rotor and a generally opposite torque in the stator. Stators are typically made with a stack of oriented laminations that have electrical windings passing therethrough and the stator is most commonly secured to the housing by a hot drop process. The hot drop process involves heating the housing to an elevated temperature, thereby causing the housing to expand and the stator is then dropped into the heated housing with the dimensions of the housing and stator being such that as the housing cools an interference fit results, with there being a radial compressive force exerted upon the stator by the contracted housing. The hot drop process requires a large amount of energy to heat the housings. 
         [0004]    Another way in which a stator is secured to the housing is by way of bolts that extend through the housing and the laminations of the stator to thereby immobilize the stator relative to the housing. This has the problem of reducing the effectiveness of the laminations, since holes to accommodate the bolts are needed, which extend through the laminations. 
         [0005]    What is needed in the art is an efficient, energy-saving method and apparatus for connecting the stator to the housing of an electric machine. 
       SUMMARY 
       [0006]    The present invention provides a method and apparatus for connecting the stator to the housing of an electric machine. 
         [0007]    The invention in one form is directed to a vehicle including a movable element and an electric machine either driving or being driven by the movable element. The electric machine having first and second housing portions and a stator. The second housing portion is engaged with the first housing portion. The stator being coupled to the first housing portion and the second housing portion by way of compressive force applied to the stator by and between the first housing portion and the second housing portion, or by fasteners which retain the first housing portion to the second housing portion. 
         [0008]    The invention in another form is directed to an electric machine having first and second housing portions and a stator. The second housing portion is engaged with the first housing portion. The stator being coupled to the first housing portion and the second housing portion by way of compressive force applied to the stator by and between the first housing portion and the second housing portion. 
         [0009]    The invention in yet another form is directed to a method of securing a stator in an electric machine, the method including the steps of positioning the stator, positioning a second housing portion and applying compressive force. The positioning the stator step includes positioning the stator in a first housing portion such that a portion of a lamination on one end of the stator directly encounters a part of the first housing portion in an axial direction. The positioning a second housing portion step includes the positioning of the second housing portion against another lamination on an opposite end of the stator. The applying compressive force step includes applying an axial compressive force against the lamination and the other lamination to thereby preclude movement of the stator relative to the housing portions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0011]      FIG. 1  illustrates a vehicle that utilizes an embodiment of an electric machine that is constructed using the structure and method of the present invention; 
           [0012]      FIG. 2  is a cross-sectional schematical view of an embodiment of the electric machine utilized in the vehicle of  FIG. 1 ; 
           [0013]      FIG. 3  is a cross-sectional schematical view of another embodiment of the electric machine utilized in the vehicle of  FIG. 1 ; and 
           [0014]      FIG. 4  is an end view of the electric machine of either  FIG. 2  or  3 . 
       
    
    
       [0015]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION 
       [0016]    Referring now to the drawings, and more particularly to  FIG. 1 , there is illustrated a vehicle  10 , which may be in the form of an agricultural machine, a construction machine, a forestry machine or other vehicle. Vehicle  10  includes a chassis  12  with moveable elements  14  in the form of wheels that are either directly or indirectly driven by at least one electric machine  16  that either supplies electrical power or is supplied electrical power by way of a power source such as an engine  18 . Electrical machine  16  may be either an electric motor, or an electric generator. Actually vehicle  10  may have at least one of both a motor and generator that are constructed by the method using the structural attributes of the present invention. Electrical power from the electric power source is applied, under the control of the machine operator, to electric machine  16  to drive driven devices  14 . 
         [0017]    Now, additionally referring to  FIG. 2  there is illustrated electric machine  16  having housing portions  20  and  22  that are engaged with each other in a sliding fashion, held together with fasteners  24  in the form of bolts that pass through part of housing portion  20  and are threaded into a part of housing portion  22 . A shaft  26  extends through at least one of housing portions  20  and  22 , having a rotor  28  attached thereto. A stator  30  is connected to housing portions  20  and  22 . Stator  30  includes laminations  32  and windings  34 , which extend through laminations  32 . Laminations  32  are generally pieces of ferrous metal that are stacked together and electric conductors in the form of windings  34  are wound so as to have a desired geometry for the induction of magnetic fields into laminations  32  or for the passing of the magnetic fields through the loops of windings  34 . The portion of windings  34  illustrated to the sides of stator  30  may be referred to as end windings or as end turns that extend beyond laminations  32  into cavity  36 , but for the sake of explanation of the present invention, windings  34  are shown schematically, the details of which vary depending on motor or generator specifics. This being a schematical representation, the proportional sizes of rotor  28  and stator  30  may not reflect actual proportions of each of these elements. 
         [0018]    Housing portion  20  has an annular protrusion  38  that extends radially inward and provides a shoulder against which a radially outward portion of laminations  32  come into contact. In a similar manner, housing portion  22  has a protrusion  40  that extends radially inward to contact a lamination on the opposite side of stator  30 , relative to the lamination which protrusion  38  contacts. Fasteners  24  are torqued so that the tensile force that exists in fasteners  24  results in a compressive force applied to laminations  32  by way of protrusions  38  and  40  to thereby hold stator  30  from moving relative to housing portions  20  and  22 . Stator  30  is engaged and torsionally coupled or connected to housing portions  20  and  22  by the compressive force applied thereby. 
         [0019]    The section of housing  20  that is radially outward from laminations  32  does not provide an interference fit with stator  30  and any interaction therebetween is insufficient to secure stator  30  to housing portion  20 . This section may actually have a slight taper to allow for the ease in assembly and to guide stator  30  so that it is well centered in housing  20  as stator  30  encounters protrusion  38 . As shown in  FIG. 3  this section may be spaced apart from stator  30 , which may serve as a cooling channel. 
         [0020]    Now, additionally referring to  FIG. 3 , there is illustrated an electric machine  116 , which is similar in construct to that illustrated in  FIG. 2 , with the reference numbers being the same for the same parts and increased by  100  for parts that, although somewhat different, are significantly similar in their utility. Here housing portion  122  extends along the side of a radially outward portion of an end lamination. Again stator  30  is compressively held in position by the axial force applied thereto by housing portions  120  and  122 , and fasteners  124 . 
         [0021]    Fasteners  24  and  124  are illustrated as bolts, yet other fasteners are also contemplated to provide the compressive force applied to stator  30 . Housing portions  20  and  22 , as well as  120  and  122  are sealed together respectively by  0 -rings  42  and  142 . Cavity  36  may include gearing, such as a transmission or other elements used in electric machines  16  and  116 , with shaft  26  not extending directly from rotor  28  through housing  22 / 122  as illustrated. Further, at least one of the housing portions may be integral with other constructs of vehicle  10 , and/or the housing portions may enclose other components, not illustrated. Electrical interconnections and conductors have been purposely omitted from the figures for the sake of clarity, for ease of focusing on an explanation of the present invention. 
         [0022]    No fasteners or other elements pass through stator  30  to secure stator  30  to housing portions  20 ,  22 ,  120  or  122 . Stator  30  is held from axial and rotational movement by the compressive force from the housing portions and the tension force from the fasteners as discussed herein. The axial force in conjunction with the friction between housing portions  20 ,  22 ,  120 ,  122  act together to torsionally restrain stator  30  relative to the respective housing portions. 
         [0023]    Now, additionally referring to  FIG. 4 , there is shown an end view of electric machine  16 ,  116 . This view illustrates the distribution of fasteners  24  or  124 , which may be symmetrically or asymmetrically arranged about a radially outer portion of housing portion  20 ,  120 , not extending through the body of electrical machine  16  or  116 . 
         [0024]    The present invention provides for the radial piloting and axial alignment of stator  30  and of torque transmittal for electric machines  16  and  116 . Stator  30  is located radially (piloted) as it is axially inserted into housings  20 ,  120  by a controlled clearance fit between the outer portion or outer diameter of stator  30  and the inner corresponding diameter of housings  20 ,  120 . The axial location of stator  30 , and the transmittal of torque thereto is accomplished by the clamping of stator  30  between the shoulders  38  and  40 ,  138  and  140  of the two adjacent housings. The particular configuration discussed herein allows for the use of a radial seal, such as O-ring  42 ,  142  between the two adjacent housings thereby providing a cost-effective seal and allowing the assembly to accommodate length variations of the stack of laminations  32  within production tolerances, while preventing leakage and allowing stator  30  to be clamped tightly for torque transmittal. 
         [0025]    Advantageously, the present invention allows for ease of assembly and disassembly. 
         [0026]    This provides for ease in rebuilding electrical machines  16 ,  116  as well as providing for easier recycling of the components when refurbishment is not practical or desired. This allows for a financial and environmental advantage over the current state of the art. 
         [0027]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.