CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/171,485 filed on Feb. 3, 2014 which is a continuation of U.S. Pat. No. 8,672,077, issued on Mar. 18, 2014, each of which is incorporated by reference in its entirety. 
    
    
     FIELD 
     The invention relates to vehicles, and, more particularly to electric motorcycle frames. 
     BACKGROUND 
     Recent advances in electric vehicle technology have resulted vehicles that have comparable performance characteristics compared to internal combustion engine vehicles. Unfortunately, one key component, the battery, remains stubbornly expensive, resulting in costly electric cars. One cannot possibly justify the price of a new electric car compared to a similarly equipment gasoline or diesel model. If, instead, one develops the lightest possible vehicle, the electric equation just might make sense. 
     The lightest practical vehicle is either a motocross bike, a street legal equivalent, the enduro, or it&#39;s fully street focused version, the supermoto. Such bikes often weigh a little over 100 kg. By minimizing weight, the battery requirements are minimized, and, consequently, the price as well. 
     Several companies have seen the light and jumped into the fray. Unfortunately, their efforts have come up short. Many save the expense of designing a new chassis from scratch, and, instead, shoehorn an electric motor and battery pack in a frame that was originally designed for and internal combustion engine. The results have been mediocre, underpowered bikes with limited range and questionable handling. 
     The published US patent application 2011/0036657 A1 by Bland et al. (subsequently referred to as Bland) assigned to Brammo Inc. discloses a straight electric motorcycle chassis that comprises two sides that enclose the headstock and allow attachment of batteries from above and below. Bland places the motor at the axis of the drive sprocket, with no transmission, subsequently requiring a big, heavy electric motor to generate enough torque. The motor is also fully stressed, resulting in high maintenance costs related to motor repair or replacement. In addition, the batteries are insufficient for a reasonable top speed and range. Zero Motorcycles, from Scotts Valley, Calif., manufactures an electric motorcycle frame using a combination of tubular and hydroformed aluminum pieces that are welded together. The myriad disadvantages of welded aluminum frames are discussed in the description, below. Like the teachings of Bland, the Zero batteries are insufficient for a reasonable top speed and range. 
     KTM of Austria and Quantya of Switzerland both employ welded bent steel tube perimeter frames, which can be heavy. 
     All of the electric motorcycle manufacturers discussed above use air cooled electric motors. Compared to liquid cooled electric motors, air cooled electric motors have lower peak power outputs and vastly lower continuous power outputs. 
     Given growing consumer demand for high performance, low cost electric vehicles, there is a need for a new electric motorcycle developed around a new type of chassis. 
     SUMMARY 
     The current invention relates to a vehicle frame, or chassis, and its manufacture. In one embodiment the frame comprises two cast aluminum structures that can be bolted together. The frame structures can each be cast in one piece and finish machined with one fixturing. The frame casting can include an integral motor housing that may be fully stressed and act as a torsion tube. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a motorcycle. 
         FIG. 2  shows motorcycle parts that attach to a motorcycle frame. 
         FIG. 3  shows motorcycle parts that attach to a motorcycle frame. 
         FIG. 4  shows a rear part of a motorcycle frame. 
         FIG. 5  shows a rear part of a motorcycle frame. 
         FIG. 6  shows a rear part of a motorcycle frame. 
         FIG. 7  shows a rear part of a motorcycle frame. 
         FIG. 8  shows a front part of a motorcycle frame. 
         FIG. 9  shows a front part of a motorcycle frame. 
     
    
    
     DESCRIPTION 
       FIG. 1  shows a motorcycle  100 . The motorcycle  100  shown is an off road or motocross bike. Motorcycles  100  comprise motocross bikes, road bikes, three wheeled bikes, and four wheeled bikes. Any three or four wheeled vehicle where the rider straddles the seat  114  of the vehicle is considered a motorcycle. Scooters are also considered motorcycles. The motorcycle  100  shown in  FIG. 1  comprises an electric motorcycle, and, therefore has an electric motor and a battery box  112 . 
       FIG. 2  shows motorcycle parts that attach to a motorcycle frame  144 . Shown are a shroud  102 , also known as a fairing, a seat  114 , a rear subframe  116 , a rear shock  140 , a swing arm  138 , a rear suspension linkage  130 , a skid plate  142 , a battery box  112 , a motor cover  122 , a sprocket  136 , and a fork  134 . Also shown are the frame structure  200  and the second frame structure  300 . 
       FIG. 3  shows motorcycle parts that attach to a motorcycle frame  144 . Shown are a radiator  104 , a water pump  128 , a footpeg  126 , a rear master cylinder  124 , and a gear cover  120 . Also shown are the frame structure  200  and the second frame structure  300 . 
     A frame  144  for a motorcycle can be made as a single piece or several pieces that are attached together. The example frame  144  shown in  FIGS. 2-3  is a two piece frame  144  comprising the frame structure  200 , also known as a rear bulkhead, and the second frame structure  300 , also known as a front bulkhead. The two piece frame  144  design allows the frame structure  200  and the second frame structure  300  to each be cast as a single piece, finish machined in one fixture, and attached together. 
     Using only one fixture per structure reduces time required for machining and increases accuracy of the machined surfaces. Milling machines large enough for a single structure can be cost prohibitive. Utilizing two structures, rather than a single structure, reduces the size of milling machine required to complete the operation, reducing capital costs. In addition, separating the structure into two pieces can allow machine access to additional areas of the casting, allowing more features to be integrated and reducing the complexity of fixturing and machining. Casting a single frame unit may also be quite complicated and more costly that two smaller frame castings. 
     A typical 3-axis milling machine setup involves clamping the workpiece in a vise where only one face is exposed for cutting at a time. A 4-axis mill setup clamps the workpiece in a rotary fixture. This allows the machine to work on virtually all faces of the workpiece that are perpendicular to the axis of rotation. Thus, by using a 4-axis milling machine, such as a horizontal milling machine with a rotary axis for the workpiece fixture, one can finish machine all of the features, or interface areas, within the tolerance specification for the frame structure  200  and the second frame structure  300  listed below and seen in  FIGS. 4-9  with one fixturing per piece, each saving considerable time and expense. 
     In one embodiment, the frame  144  may be manufactured by casting both the frame structure  200  and the second frame structure  300  each as a single casting from  206  aluminum alloy. The frame structure  200  and the second frame structure  300  castings are then separately mounted in respective fixtures and features are finish machined in at least one working plane.  206  aluminum has some corrosion issues, so conversion coating, a process including an acid dip and passivation, followed by priming and painting would resolve those issues. Other suitable casting aluminum alloys include  201 ,  204 ,  356 , and  357 . In another embodiment, a one piece frame may be manufactured by casting the frame  144  as a single casting with most or all of the features and mounting points included in  FIGS. 2-8  and then finish machined. In yet another embodiment, the frame structure  200  may be cast and finish machined as described above, while the second frame structure  300  may be fabricated in another manner, such as milled from billet aluminum or created by welding two or more parts together. Welding allows one to build a trellis frame structure out of steel, titanium, or aluminum or to build a twin spar aluminum frame structure commonly used for motorcycles. Alternatively, the second frame structure  300  may be built out of a composite material such as carbon fiber. 
     The embodiment of the frame  144  shown in  FIG. 3  with the frame structure  200  and the second frame structure  300  comprises a weldless design. Welding frame components can take a considerable amount to time to accurately fixture and weld together. Welding adds expense due to inconsistencies in weld quality that require a safety margin or more robust and heavy structure to compensate for these inconsistencies. Welding can also result in stress build up and distortion in a structure requiring secondary heat treatment and straightening. 
       FIG. 4  shows a rear part of a motorcycle frame  144 . The frame structure  200  includes frame mounts  202 , a gear cover mount  206 , rear subframe mounts  208 , linkage mounts  210 , rear master cylinder mounts  212 , battery bolt holes  214 , skid plate mounts  216 , footpeg mounts  218 , a rear brake lever mount  220 , shroud mounts  222 , a bottom coolant port  238 , an oil sump  232 , a right side  240 , a motor housing  244 , an output shaft housing  246 , a vent hole  248 , and a shock mount bolt hole  254 . 
       FIG. 5  shows a rear part of a motorcycle frame  144 . The frame structure  200  includes shock mounts  204 , a motor cover mount  224 , a pass through hole  226 , swing arm mounts  228 , a top coolant port  230 , a left side  242 , a motor housing  244 , an output shaft housing  246 , a vent hole  248 , and a structural rib  250 . 
     The left and right sides  242 ,  240  shown in  FIGS. 4, 5  are a type of side structure that connects the motor housing  244 , which may act as a torsion tube, to mounting points for other components or to other frame features. The sides  242 ,  240  are shown as part of a single casting, but may also be a welded trellis structure or a composite structure. It is also possible to use only one side structure in the middle of the frame to connect the motor housing  244  to other features and mounting points. 
       FIG. 6  shows a rear part of a motorcycle frame  144 . The frame structure  200  includes an oil sump  232 , a drain plug port  234 , a bottom coolant port  238 , a motor housing  244 , an output shaft housing  246 , structural ribs  250 , and battery box mounts  252 . 
       FIG. 7  shows a rear part of a motorcycle frame  144 . The frame structure  200  includes a pass through hole  226 , a motor housing  244 , and an output shaft housing  246 . 
     The left side  242  and right side  240  of the frame structure  200  flank the motor housing  244  and output shaft housing  246 . The housings  244 ,  246  may extend beyond the external wall of the sides  240 ,  242 , or the housings  244 ,  246  may be contained by the sides  240 ,  242 . Alternately, one or more sides may be connected to the middle of the housings  244 ,  246 . The housings  244 ,  246  may be fully stressed and may act as torsion tubes to add rigidity to the frame structure  200 . Cylinders are the best structure to use for a torsion tube due to its polar moment of inertia, but other shapes can be used if appropriate. The motor housing  244  be designed to receive a motor, preferably a liquid cooled electric motor. The housing  244  may have a top coolant port  230  and a bottom coolant port  238  to allow the circulation of a coolant between the motor housing  244  and the motor. 
     When the motor housing  244  is used as an outer water jacket for containing coolant between itself and the motor, the motor can be contained by an inner water jacket. In this case, the motor and the inner water jacket are not required to be stressed members, while the motor housing  244  may be fully stressed. 
     A motor cover  122  may be attached to a motor cover mount  224  on the frame structure  200  in order to seal the motor from the elements. Likewise, a gear cover  120  may be attached to a gear cover mount  206  in order to seal the motor and/or gear reduction assembly from the elements. A shroud  102  or fairing may be attached to shroud mounts  216 ,  304 . A seat  114  may be attached to seat plate mounts  324  via a seat clip and to the rear subframe  116 . The rear subframe  116  may be attached to rear subframe mounts  208 . A rear shock  140  may be attached to shock mounts  204 . A swing arm  138  may be attached to swing arm mounts  228 . Rear suspension linkages  130  may be attached to linkage mounts  210 . 
     A skid plate  142  may be attached to skid plate mounts  216  in order to protect the a battery box  112 . A battery box  112  may be attached to battery box mounts  252  and secured with bolts passing through the battery bolt holes  214 . Any feature that generally aids in the attachment of the battery box  112  to the frame  144  may be generally referred to as a battery box mount. The battery box  112  may be a semi stressed member when attached to the frame structure  200 , thereby adding rigidity to the frame  144  when attached while being removable without compromising the structural integrity of the frame  144  or having the rest of the motorcycle  100  lay in pieces when the battery box  112  is removed, as would be the case if the battery box  112  where fully stressed. A sprocket  136  may drive a chain to drive the rear wheel and may also be attached to an output shaft that is housed in the output shaft housing  246 . 
     One or more pass through holes  226 , or openings, may be used to allow passage of hoses and wires. Adding a pass through hole  226  on the motor housing  244 , as seen in  FIG. 7 , allows the wires that power the motor to be routed internally in the frame  144 , a more attractive and safer solution than routing power wires externally. An o-ring or equivalent seal between the motor housing  244  and the motor can prevent coolant from entering the chamber where the power wires connect to the motor. A rubber gasket or equivalent is preferably set in the pass through hole  226  to form a seal between the motor housing  244  and the wires and to provide strain relief. 
     One or more vent holes  248 ,  308  allow air to flow through the radiator  104  and to exit the frame  144 . One or more structural ribs  250  may be added to the frame structure  200  to increase rigidity. 
     An oil sump  232  may be placed in the output shaft housing  246  to provide lubrication for a gear reduction. The oil sump  232  can be drained via a drain plug port  234 . An oil level sight and oil fill port may be integrated into the gear cover  120 . A water pump  128  may be attached to a water pump mount  236 , the water pump  128  circulating a coolant to the motor and optionally to the motor control unit and the battery. 
       FIG. 8  shows a front part of a motorcycle frame  144 . The second frame structure  300  includes frame mounts  302 , shroud mounts  304 , a headstock structure  306 , vent holes  308 , a right side  310 , a structural rib  314 , battery box mounts  316 , skid plate mounts  318 , steering stop mounts  320 , radiator mounts  322 , seat plate mounts  324 , and a mounting plane  326 . The headstock structure  306  is designed for receiving a fork  134 . The headstock structure  306  may be a tube as shown in  FIG. 8  or any other structure that holds upper and lower bearings that receive a fork  134 . A box construction type headstock structure  306  may be used to allow greater airflow through the front of the motorcycle  100 . 
       FIG. 9  shows a front part of a motorcycle frame  144 . The second frame structure  300  includes frame mounts  302 , shroud mounts  304 , a headstock structure  306 , a left side  312 , a structural rib  314 , battery box mounts  316 , skid plate mounts  318 , steering stop mounts  320 , radiator mounts  322 , seat plate mounts  324 , and an access hole  328 . The headstock structure  306  may receive a fork  134 . The left and right sides  312 ,  310  are attached to the headstock structure  306 . A structural rib  314  attaches to the left and right sides  312 ,  310 , aids in structural rigidity, and helps keep the left and right sides  312 ,  310  in place during the casting and finish machining process. The seat plate mounts  324  may receive a plate or clip that receives the seat  114 . The access hole  328  can allow access to the radiator fill cap. The battery box mounts  316  may receive a battery box  112 . The skid plate mounts  318  may receive a skid plate  142 . The steering stop mounts  320  may receive steering stops. The radiator mounts  322  may receive a radiator  104 . 
     In addition to having the ability to cool the motor with a coolant, the frame  144  itself can act as a heat sink. Aluminum is a very good heat conductor, and the shape of the frame structure  200  allows excess head to travel from the motor housing  244  to the left and right sides  242 ,  240  of the frame structure  200  where the heat may be dissipated via air convection, conduction to attached parts, or radiation. 
     The left and right sides  242 ,  240  of the frame structure  200  as shown in  FIGS. 4-7  comprise a perimeter frame construction to allow for the connection of parts including the rear swingarm  138 , rear suspension linkage  130 , rear shock  140 , rear subframe  116 , and fork  134 . Alternate constructions include a trellis frame construction and a composite frame construction. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 Reference Numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 100 
                 motorcycle 
               
               
                 102 
                 shroud 
               
               
                 104 
                 radiator 
               
               
                 106 
                 steering dampener 
               
               
                 108 
                 steering stop 
               
               
                 110 
                 skid plate 
               
               
                 112 
                 battery box 
               
               
                 114 
                 seat 
               
               
                 116 
                 rear subframe 
               
               
                 118 
                 shock 
               
               
                 120 
                 gear cover 
               
               
                 122 
                 motor cover 
               
               
                 124 
                 rear master cylinder 
               
               
                 126 
                 foot peg 
               
               
                 128 
                 water pump 
               
               
                 130 
                 rear suspension linkage 
               
               
                 134 
                 fork 
               
               
                 136 
                 sprocket 
               
               
                 138 
                 swing arm 
               
               
                 140 
                 shock 
               
               
                 142 
                 skid plate 
               
               
                 144 
                 frame 
               
               
                 200 
                 frame structure 
               
               
                 202 
                 frame mount 
               
               
                 204 
                 shock mount 
               
               
                 206 
                 gear cover mount 
               
               
                 208 
                 rear subframe mount 
               
               
                 210 
                 linkage mount 
               
               
                 212 
                 rear master cylinder mount 
               
               
                 214 
                 battery bolt hole 
               
               
                 216 
                 skid plate mount 
               
               
                 218 
                 footpeg mount 
               
               
                 220 
                 rear brake lever mount 
               
               
                 222 
                 shroud mount 
               
               
                 224 
                 motor cover mount 
               
               
                 226 
                 pass through hole 
               
               
                 228 
                 swing arm mount 
               
               
                 230 
                 top coolant port 
               
               
                 232 
                 oil sump 
               
               
                 234 
                 drain plug port 
               
               
                 236 
                 water pump mount 
               
               
                 238 
                 bottom coolant port 
               
               
                 240 
                 right side 
               
               
                 242 
                 left side 
               
               
                 244 
                 motor housing 
               
               
                 246 
                 output shaft housing 
               
               
                 248 
                 vent hole 
               
               
                 250 
                 structural rib 
               
               
                 252 
                 battery box mount 
               
               
                 254 
                 shock mount bolt hole 
               
               
                 300 
                 second frame structure 
               
               
                 302 
                 frame mount 
               
               
                 304 
                 shroud mount 
               
               
                 306 
                 headstock tube 
               
               
                 308 
                 vent hole 
               
               
                 310 
                 right side 
               
               
                 312 
                 left side 
               
               
                 314 
                 structural rib 
               
               
                 316 
                 battery box mount 
               
               
                 318 
                 skid plate mount 
               
               
                 320 
                 steering stop mount 
               
               
                 322 
                 radiator mount 
               
               
                 324 
                 seat plate mount 
               
               
                 326 
                 mounting plane 
               
               
                 328 
                 access hole
This invention comprises a frame for an electric motorcycle. Electric motorcycles have vastly different component requirements compared to internal combustion engine motorcycles, and, therefore, require a radical redesign of the frame in order to maximize the efficiency of the system.