Patent Publication Number: US-2022227219-A1

Title: Axle assembly for low floor vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/630,757, entitled “AXLE ASSEMBLY FOR LOW FLOOR VEHICLE,” which was filed on Jan. 13, 2020 and which issued on Apr. 5, 2022 as U.S. Pat. No. 11,292,332, and which is a national stage entry under 35 U.S.C. § 371(b) of PCT International Application No. PCT/US2018/041876, filed Jul. 12, 2018, which claims the benefit of and priority to U.S. Provisional Application No. 62/531,737, filed Jul. 12, 2017, and to U.S. Provisional Application No. 62/669,729, filed May 10, 2018, the disclosures of each of which are hereby incorporated by reference in their entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     The present invention relates to vehicle axle assemblies, and more particularly, to an axle assembly for use with a low floor vehicle. 
     BACKGROUND 
     In order to aid ingress and egress, it is oftentimes ideal for a vehicle to have a floor that is as low as possible. Busses and people carriers, commonly called low floor vehicles, are examples of vehicles that benefit from a low floor height. By minimizing the floor height, a step at a door of the vehicle may be eliminated, which in turn allows passengers easier ingress and egress of vehicle passengers. Furthermore, elimination of steps is especially beneficial to disabled passengers, and passengers with strollers. Increasingly, manufacturers have turned to electric and hybrid propulsion systems for low floor vehicles for increased performance and efficiency. In order to have the floor of the vehicle as low as possible, the drivetrain components are relocated so as to reduce intrusions into the vehicle floor. 
     At least some known low floor vehicles include wheel assemblies driven by electric motor having the electric rotor connected directly to the axle shaft of the wheel assembly. Because these electric motors are connected directly to the axle shaft, the orientation of the electric motor reduces the amount of space available across the wheel assembly, thus reducing the floor space available for the low floor vehicle. Accordingly, a new axle assembly is required to increase the spacing between wheel assemblies and provide larger floor areas. 
     The present invention is aimed at one or more of the problems identified above. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an axle assembly for a low floor vehicle with increased performance and efficiency. 
     In one embodiment of the present invention, an axle assembly is provided. The axle assembly includes an axle housing and a drive unit for driving a wheel assembly. The drive unit includes an axle shaft, a wheel end assembly, an electric machine, and a transmission unit. The axle shaft extends along an axle centerline axis between a first axle end and a second axle end. The wheel end assembly is coupled to the first axle end. The electric machine is positioned within the axle housing and includes a rotor shaft, a drive pinion coupled to the rotor shaft, and an electric motor for rotating the rotor shaft. The rotor shaft extends along a rotor shaft centerline axis that is orientated parallel to the axle centerline axis. The transmission unit is positioned within the axle housing and is configured to transfer torque from the electric machine to the axle shaft. The transmission unit includes an output assembly and an offset gear reduction assembly. The output assembly is coupled to the second axle end such that a rotation of the output assembly rotates the axle shaft. The offset gear reduction assembly is coupled to the output assembly and the drive pinion of the electric machine for transferring torque from the electric machine to the output assembly. 
     In another embodiment of the present invention, an axle housing is provided. The axle housing is configured to be used with an axle assembly that includes a drive unit including an electric machine, a transmission unit, and an inverter assembly. The axle housing includes a first outer section, a second outer section, and a bridge section extending between the first outer section and the second outer section. The first outer section includes a gearbox including an inner surface that defines a cavity configured to receive the electric machine and the transmission unit therein. The bridge section includes a cradle assembly coupled to the gearbox. The cradle assembly includes an inner surface that defines a support chamber configured to receive the inverter assembly therein. 
     In yet another embodiment of the present invention, a vehicle is provided. The vehicle includes a vehicle frame and an axle assembly coupled to the vehicle frame. The axle assembly includes an axle housing, a first drive unit, and a second drive unit. The axle housing includes a bridge section extending between a first outer section and an opposite second outer section. The first outer section includes a first gearbox and the second outer section includes a second gearbox. The bridge section includes a cradle assembly that is coupled to the first gearbox and the second gearbox. The cradle assembly includes an inner surface that defines a support chamber within the cradle assembly. The first drive unit is adapted to be coupled to a first wheel assembly. The first drive unit includes a first electric machine, and a first transmission unit. The first electric machine is positioned within the first gearbox. The first electric machine includes a drive pinion that is coupled to a rotor shaft. The first transmission unit is positioned within the first gearbox and includes an output assembly and an offset gear reduction assembly that is coupled to the output assembly and the drive pinion of the first electric machine for transferring torque from the first electric machine to the output assembly. A first axle shaft is coupled to the output assembly and extends outwardly from an outer surface of the first gearbox. The second drive unit is adapted to be coupled to a second wheel assembly. The second drive unit includes a gear reduction and a second axle shaft that is oriented coaxially with the first axle shaft along an axle centerline axis. The gear reduction is positioned within the second gearbox. The second axle shaft extends outwardly from the second gearbox towards the second wheel assembly. An inverter assembly is positioned within the support chamber of the cradle assembly and is coupled to the first electric machine for providing electrical power to the first electric machine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG. 1  is an elevation view of an axle assembly for a low floor vehicle, according to embodiments of the present invention. 
         FIGS. 2-5  are perspective views of the axle assembly shown in  FIG. 1 . 
         FIG. 6  is a top view of the axle assembly shown in  FIG. 2 . 
         FIG. 7  is a bottom view of the axle assembly shown in  FIG. 2 . 
         FIG. 8  is an elevation view of a front portion of the axle assembly shown in  FIG. 2 . 
         FIG. 9  is an elevation view of a rear portion of the axle assembly shown in  FIG. 2 . 
         FIG. 10  is an elevation view of a right side of the axle assembly shown in  FIG. 2 . 
         FIG. 11  is an elevation view of a left side of the axle assembly shown in  FIG. 2 . 
         FIGS. 12-13  are perspective views of the axle assembly shown in  FIG. 1 . 
         FIG. 14  is a top view of the axle assembly shown in  FIGS. 12-13 . 
         FIG. 15  is a bottom view of the axle assembly shown in  FIGS. 12-13 . 
         FIG. 16  is perspective view of a portion of the axle assembly shown in  FIG. 2 . 
         FIG. 17  is a top view of the axle assembly shown in  FIG. 16 . 
         FIG. 18  is a bottom view of the axle assembly shown in  FIG. 17 . 
         FIGS. 19 and 20  are perspective views of a cradle assembly that may be used with the axle assembly shown in  FIG. 2 , according to embodiments of the present invention. 
         FIGS. 21-22  are top views of the cradle assembly shown in  FIG. 19 . 
         FIG. 23  is a bottom view of the cradle assembly shown in  FIG. 19 . 
         FIG. 24  is front view of the cradle assembly shown in  FIG. 19 . 
         FIG. 25  is rear view of the cradle assembly shown in  FIG. 19 . 
         FIGS. 26 and 27  are side views of the cradle assembly shown in  FIG. 19 . 
         FIG. 28  is a perspective view of a top cover that may be used with the cradle assembly shown in  FIG. 19 . 
         FIG. 29  is a view of a top surface of the top cover shown in  FIG. 28 . 
         FIG. 30  is a side view of the top cover shown in  FIG. 28 . 
         FIG. 31  is a view of a bottom surface of the top cover shown in  FIG. 28 . 
         FIG. 32  is a perspective view of a bottom cover that may be used with the cradle assembly shown in  FIG. 19 . 
         FIG. 33  is a view of a top surface of the bottom cover shown in  FIG. 32 . 
         FIG. 34  is a side view of the bottom cover shown in  FIG. 32 . 
         FIG. 35  is a view of a bottom surface of the bottom cover shown in  FIG. 32 . 
         FIGS. 36 and 37  are perspective views of a gearbox that may be used with the axle assembly shown in  FIG. 2 , according to embodiments of the present invention. 
         FIGS. 38-41  are side views of the gearbox shown in  FIG. 36 . 
         FIG. 42  is a top view of the gearbox shown in  FIG. 36 . 
         FIG. 43  is a bottom view of the gearbox shown in  FIG. 36 . 
         FIG. 44  is a perspective view of a gearbox housing that may be used with the gearbox shown in  FIG. 36 , according to embodiments of the present invention. 
         FIGS. 45-48  are side views of the gearbox housing shown in  FIG. 44 . 
         FIG. 49  is a top view of the gearbox housing shown in  FIG. 44 . 
         FIG. 50  is a bottom view of the gearbox housing shown in  FIG. 44 . 
         FIGS. 51-52  are perspective views of a gearbox cover that may be used with the gearbox shown in  FIG. 36 , according to embodiments of the present invention. 
         FIG. 53  is a cutaway perspective view of a gearbox housing and a drive unit that may be used with the axle assembly shown in  FIG. 2 , according to embodiments of the present invention. 
         FIGS. 54-55  are schematic views of a drive unit that may be used with the axle assembly shown in  FIG. 2 . 
         FIG. 56  is a cross-sectional view of a drive unit that of  FIG. 54 , shown in a first reduction ratio. 
         FIG. 57  is a cross-sectional view of the drive unit of  FIG. 54  shown in a second reduction ratio. 
         FIG. 58  is a block diagram of axle assembly shown in  FIG. 2 . 
         FIGS. 59-64  are perspective views of the drive unit shown in  FIG. 54 , according to embodiments of the present invention. 
         FIG. 65  is a top view of the portion of the drive unit shown in  FIGS. 59-64 . 
         FIG. 66  is a bottom view of the portion of the drive unit shown in  FIGS. 59-64 . 
         FIG. 67  is a side view of the portion of the drive unit shown in  FIGS. 59-64 . 
         FIG. 68  is an elevation view of a front portion of the portion of the drive unit shown in  FIGS. 59-64 . 
         FIG. 69  is an elevation view of a rear portion of the portion of the drive unit shown in  FIGS. 59-64 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     DETAILED DESCRIPTION 
     The present invention is directed to an electric drive axle assembly for a low-floor or ultra-low floor (no step) vehicle. The vehicle is generally a high occupancy or heavy-duty vehicle with electric (all-battery or may be a hybrid) propulsion. The invention allows a compact packaging for two 2-speed transmission unit, two electric motors and two wheelhub reduction gears for a low floor vehicle. Having 2-speeds in the transmission unit will allow vehicle performance improvement for top speed and motor efficiency. Integrating the electric motor on the side of the transmission unit (e.g., parallel and adjacent) helps package the system compactly. Using a set of parallel shaft gears for reduction allows an offset to package the motor. The two-speed transmission unit will be integrated within the axle housing. 
     The electric drive axle may include two motors, two 2-speed transmission units, two hub reduction gears and an external axle housing, wherein the motors are used for providing power for driving each wheel. The electric drive axle may include an electric motor with a rotor shaft driving an offset gearing reduction. The output of the offset gearing reduction will input power to a shaft with several bearings, a selectable synchronizer/clutch and two gears, which pair with two gears on the output shaft of the transmission, respectively. The synchronizer will select speeds for two ratios, which will transmit power to the output shaft with either gear pairs in the transmission. The output shaft of the transmission will couple to the input of the wheel hub planetary drive sun gear. In the wheel hub planetary drive, the ring gear will be held stationary while the planet carrier will output power to the wheels as in conventional wheel hub drives. Two electric motors, two 2-speed transmission units and two planetary wheel hub drives are on one axle. The axle housing will integrate each electric motor and transmission compactly and transmit vehicle loads to suspension components. 
     With reference to  FIGS. 1-15 , the present invention includes an axle assembly  10  for a low floor vehicle. The axle assembly  10  includes an axle housing  12  that is coupled to a vehicle frame  11 . The axle housing includes a bridge section  14  and outer sections  16  arranged at opposite ends of the bridge section  14 . Each outer section  16  is spaced laterally from the other relative to the vehicle. In the illustrated embodiment, the axle housing  12  includes a first outer section  16   a  and a second outer section  16   b . The bridge section  14  extends between the first outer section  16   a  and the second outer section  16   b.    
     The axle assembly  10  further includes suspension arms  18  coupled to the axle housing  12 , which may be used to attach the axle assembly  10  to the vehicle. Additionally, tie-rods  20  movably attach the axle assembly  10  to the vehicle. The vehicle may be an electric vehicle or a hybrid vehicle with an electric motor and internal combustion generator/motor. Advantageously, the suspension arms  18  may be configured to retrofit the axle assembly  10  to a vehicle. For example, a low floor bus originally equipped with a traditional axle assembly may utilize the axle assembly  10  in place of the traditional axle assembly. 
     A wheel  22  is coupled to each end of the axle assembly  10  to support the vehicle and transfer motive power to a road surface. In the embodiment shown, the axle assembly  10  is a dual wheel configuration with a pair of wheels  22  coupled to each end of the axle assembly  10 . Each wheel  22  defines an axis of rotation  24 . The axis of rotation  24  of each wheel  22  is generally aligned. 
     The axle assembly  10  further includes a wheel drive unit  26  coupled to each outer section  16  of the axle housing  12 . Each of the wheel drive units  26  is configured to independently drive one of the wheels  22 . Each drive unit  26  may operate the respective wheel  22  at a different speed during a turning maneuver of the vehicle, or in response to available traction at each wheel  22 . Each wheel drive unit  26  includes an electric machine  28 , a transmission unit  30 , and a wheel end assembly  32 . The axle housing  12  integrates the electric machine  28  and transmission unit  30  compactly and transmits vehicle loads to the tie-rods  20  and suspension arms  18 . The transmission unit  30  allows the vehicle to have an increased top speed while operating more efficiently at low speeds. 
     As shown in  FIGS. 1-2 , the bridge section  14  is arranged between each outer section  16  of the axle housing  12 . It is desirable for a height of a low floor to be both as low as possible, and a width to be as wide as possible in order to maximize capacity of the vehicle. As such, the bridge section  14  is offset from the axis of rotation  24  of the wheels  22  in order to decrease the height of the low floor of the vehicle. The outer sections  16  are configured to support the wheel drive units  26  within the axle housing. Each outer section  16  has a width, which must be decreased in order to increase the width of the low floor of the vehicle. The bridge section  14  may be integrally formed with the outer sections  16  or may be coupled to the outer sections  16  using methods commonly used in the art. For example, the bridge section  14  may be welded, pressed, or bolted to the outer sections  16 . The bridge section  14  may be hollow or solid. 
     The axle assembly  10  may further include a braking system for the vehicle. The braking system may include an air cylinder  34 , brake hoses, brake drums, brake rotors, brake calipers, and the like. In the embodiment shown, the air cylinders  34  are coupled to the axle housing  12  and arranged near each of the outer sections  16 . The air cylinders  34  may be coupled to brake shoes directly or through a linkage. 
     Referring now to  FIGS. 3-2 and 53-69 , the wheel drive unit  26  is shown with the axle housing  12  removed. The drive unit  26  includes an axle shaft  36  coupled to the transmission unit  30  and the wheel end assembly  32 . The axle shaft  36  extends along an axle centerline axis  37  that defines the axis of rotation  24  between a first axle end  36   a  and a second axle end  36   b  (shown in  FIG. 59 ). 
     The transmission unit  30  is coupled to both the electric machine  28  and the axle shaft  36 , and the wheel end assembly  32  is coupled to the wheel  22 . As such, torque generated by the electric machine  28  is transferred through the transmission unit  30  to the wheel end assembly  32 , and then to the wheel  22 . The drive unit  26  further includes a spindle  38  (shown in  FIG. 54 ) coupled to the axle housing  12 . The axle shaft  36  is disposed in the spindle  38  between the wheel end assembly  32  and the transmission unit  30 . As will be discussed in further detail below, the transmission unit  30  has two reduction ratios, which may be selectively engaged by an operator of the vehicle, or a transmission controller. 
     The electric machine  28  generates torque to drive the wheels  22 . The electric machine  28  includes a rotor shaft  40  that protrudes from an electric motor  41 . A drive pinion  42  is fixed to the rotor shaft  40 . The rotor shaft  40  extends along a rotor shaft centerline axis  44  that defines a rotational axis that extends through the electric machine  28 . The rotor shaft centerline axis  44  is orientated parallel to the axle centerline axis  37 . The electric machine  28  may be a DC or AC motor, brushed or brushless, and other types commonly known in the art. 
     The electric machine  28  is oriented such that the rotor shaft  40  protrudes away from the respective wheel  22  with the rotor shaft centerline axis  44  of the rotor shaft  40  arranged parallel to the axis of rotation  24  of the wheels  22 . The electric machine  28  is spaced a distance longitudinally from the axis of rotation  24  of the wheels  22 . 
     By orienting the electric machine  28  such that the rotor shaft  40  protrudes away from, and is longitudinally spaced from the axis of rotation  24  the respective wheel  22 , packaging space within the outer sections  16  of the axle housing  12  is increased without increasing the width of the outer sections  16 . The increased packaging space within the outer sections  16  allows the transmission unit  30  to be arranged adjacent to the electric machine  28 . Preferably, the overall width of the electric machine  28  is substantially similar to the overall width of the transmission unit  30 . As such, the packaging space is not materially affected by the introduction of the electric machine  28 . Stated another way, with the transmission unit  30  arranged adjacent to the electric machine  28  the width of the low floor may be wider than if the transmission unit  30  was arranged otherwise. Furthermore, the increased packaging space allows for the transmission unit  30  to be configured with multiple reduction ratios. Aligning each of the axes of rotation  24 ,  44  in a parallel manner increases the efficiency of the transmission unit  30 . 
     As mentioned above, the drive unit  26  includes the transmission unit  30 . The transmission unit  30  has a first reduction ratio and a second reduction ratio. The transmission unit  30  includes the output assembly  43  and an offset gear reduction assembly  45  that is coupled to the output assembly  43  and the drive pinion  42  of the electric machine  28  for transferring torque from the electric machine  28  to the output assembly  43 . The output assembly  43  includes an output shaft  48  and a plurality of output gears that are fixedly coupled to the output shaft  48 . The offset gear reduction assembly  45  includes an idler shaft  46  that is orientated substantially parallel with the output shaft  48 , and a plurality of idler gears that are rotatably coupled to the idler shaft  46 , and a shift mechanism  50 . Each idler gear is configured to mesh with a corresponding output gear such that a rotation of an idler gear causes a rotation of the corresponding output gear. The shift mechanism  50  is coupled to the idler shaft  46  for selectively transferring torque from the idler shaft  46  to the plurality of idler gears. 
     The idler shaft  46  and the output shaft  48  each have two ends rotatably supported by bearings  52  in the drive unit  26 . A drive wheel  54  is fixed to the idler shaft  46  and meshes with the drive pinion  42 . The drive wheel  54  transfers torque to the idler shaft  46  from the drive pinion  42 . 
     In addition to the drive wheel  54 , two idler gears  56 ,  58  are rotatably supported on the idler shaft  46 . A first idler gear  56  corresponds to the first reduction ratio of the transmission unit  30 , and a second idler gear  58  corresponds to the second reduction ratio of the transmission unit  30 . Each of the idler gears  56 ,  58  can spin freely on the idler shaft  46  such that when the corresponding reduction ratio is not engaged, no torque is transferred between the idler shaft  46  and the idler gear  56 ,  58 . As will be discussed in further detail below, each idler gear  56 ,  58  includes a splined portion engageable with the shift mechanism  50  to rotatably couple the idler gear  56 ,  58  to the idler shaft  46 . 
     The shift mechanism  50  of the transmission unit  30  includes a shift ring  60 , a shift fork  61 , and an actuator  63  (shown in  FIGS. 59-61 ). The shift ring  60  is slideable along the idler shaft  46  between the first idler gear  56  and the second idler gear  58 . The shift ring  60  is rotatably coupled to the idler shaft  46  such that the shift ring  60  and the idler shaft  46  rotate at the same speed. The shift ring  60  includes at least one splined portion engageable with the splined portion of either of the idler gears  56 ,  58 . Additionally, the shift ring  60  defines a groove  62  configured to engage the shift fork  61 . 
     The shift fork  61  is coupled to the actuator  63  and movable to select the first reduction ratio and the second reduction ratio. The shift fork  61  is engaged with the shift ring  60  such that the shift fork  61  is capable of moving the shift ring  60  into engagement with one of the idler gears  56 ,  58 . Additionally, the shift fork  61  may be movable into a neutral position where neither of the idler gears  56 ,  58  are engaged with the shift ring. The shift mechanism  50  may further include a synchronizer to aid shifting. The actuator may be controlled manually or automatically. The actuator may be responsive to hydraulic pressure, pneumatic pressure, or electronic signals generated by a transmission control module. Alternatively, the actuator may include a mechanical linkage controlled by the vehicle operator. 
     The transmission unit  30  further includes two output gears  64 ,  66 . Each of the output gears  64 ,  66  is coupled to the output shaft  48 , a first output gear  64  engaged with the first idler gear  56 , and a second output gear  66  engaged with the second idler gear  58 . The output gears  64 ,  66  are rotatably fixed to the output shaft  48  such that the output gears  64 ,  66  and the output shaft  48  rotate at the same speed. The output shaft  48  defines a bore extending therethrough. The bore is configured to receive the axle shaft  36  and may be splined or keyed such that the axle shaft  36  and the output shaft  48  rotate at the same speed. As mentioned above, the axle shaft  36  is disposed in the spindle  38  and coupled between the wheel end assembly  32  and the transmission unit  30 . 
     The wheel end assembly  32  is arranged at an end of the spindle  38  opposite the transmission unit  30 . The wheel end assembly  32  includes a wheel hub  68  having a wheel flange  70 . The wheel hub  68  is rotatably supported on the spindle  38  by a pair of hub bearings  72 . The wheels  22  may be secured to the wheel flange  70  using bolts, nuts, and other fasteners known in the art. 
     Each wheel end assembly  32  further includes a planetary reduction  74 , which increases torque to drive the wheels  22 . The planetary reduction  74  includes a sun gear  76 , a planet carrier  78 , a plurality of planet gears  80 , and a ring gear  82 . The ring gear  82  is coupled to the spindle  38 . The sun gear  76  is coupled to the end of the axle shaft  36  and disposed in the ring gear  82 . The ring gear  82  is fixed relative to the sun gear  76 . 
     The plurality of planet gears  80  are rotatably coupled to the planet carrier  78 . The planet carrier  78  is arranged adjacent to the ring gear  82  with each planet gear  80  disposed in the ring gear  82 . Each planet gear  80  engages both the ring gear  82  and the sun gear  76 . When the axle shaft  36  rotates the sun gear  76 , the sun gear  76  rotates each planet gear  80 , which in turn rotates the planet carrier  78 . The planet carrier  78  is coupled to the wheel hub  68  such that the planet carrier  78  and the wheel hub  68  rotate at the same speed. 
     Referring specifically to  FIG. 56 , the drive unit  26  is shown with the transmission unit  30  in the first reduction ratio and a torque path showing torque transfer through the drive unit  26 . Torque is generated in the electric machine  28  to rotate the rotor shaft  40  and the drive pinion  42 . The drive pinion  42  rotates the drive wheel  54  coupled to the idler shaft  46 . The idler shaft  46  rotates the shift ring  60 , which is engaged with the first idler gear  56 . The first idler gear  56  is engaged with the first output gear  64  to transfer rotation to the output shaft  48  and axle shaft  36 . Rotation of the axle shaft  36  is further transferred through the planetary reduction  74  to the wheels  22 . 
     Referring now to  FIG. 57 , the drive unit  26  is shown with the transmission unit  30  in the second reduction ratio and a torque path showing torque transfer through the drive unit  26 . Torque is generated in the electric machine  28  to rotate the rotor shaft  40  and the drive pinion  42 . The drive pinion  42  rotates the drive wheel  54  coupled to the idler shaft  46 . The idler shaft  46  rotates the shift ring  60 , which is engaged with the second idler gear  58 . The second idler gear  58  is engaged with the second output gear  66  to transfer rotation to the output shaft  48  and axle shaft  36 . Rotation of the axle shaft  36  is further transferred through the planetary reduction  74  to the wheels  22 . 
     In some embodiments, the drive unit  26  includes the axle shaft  36  extending along the axle centerline axis  37  between a first axle end  36   a  and a second axle end  36   b . The wheel end assembly  32  is coupled to the first axle end  36   a . The electric machine  28  includes the rotor shaft  40 , the drive pinion  42  coupled to and end of the rotor shaft  40 , and the electric motor  41  for rotating the rotor shaft  40 . The rotor shaft  40  extends along the rotor shaft centerline axis  44  that is orientated parallel to the axle centerline axis  37 . The transmission unit  30  is configured to transfer torque from the electric machine  28  to the axle shaft  36 . 
     In the illustrated embodiment, the electric machine  28  is positioned adjacent to the transmission unit  30 , and the electric motor  41  is positioned between the drive pinion  42  and the wheel end assembly  32 . The transmission unit  30  includes the output assembly  43  that is coupled to the second axle end  36   b  such that a rotation of the output assembly rotates the axle shaft  36 . The offset gear reduction assembly  45  is coupled to the output assembly  43  and the drive pinion  42  of the electric machine  28  for transferring torque from the electric machine to the output assembly. 
     The output assembly  43  includes the output shaft  48  coupled to the second axle end  36   b  and orientated co-axially with the axle shaft  36 . The plurality of output gears  64 ,  66  are fixedly coupled to the output shaft  48 . The offset gear reduction assembly  45  includes the idler shaft  46  that is orientated substantially parallel with the output shaft  48 . The plurality of idler gears  56 ,  58  are rotatably coupled to the idler shaft  46 . Each idler gear  56 ,  58  is configured to mesh with a corresponding output gear  64 ,  66  such that a rotation of an idler gear causes a rotation of the corresponding output gear. The shift mechanism  50  is coupled to the idler shaft  46  for selectively transferring torque from the idler shaft  46  to the plurality of idler gears  56 ,  58 . The drive wheel  54  is coupled to an end of the idler shaft  46  and is configured to mesh with the drive pinion  42  of the electric machine  28  for transferring torque from the electric machine  28  to the idler shaft  46 . 
     In the illustrated embodiment, as shown in  FIG. 68 , the idler shaft  46  is spaced a first horizontal distance H 1  from the rotor shaft  40  and second horizontal distance H 2  from the axle shaft  36  along a horizontal axis X such that the idle shaft  46  is orientated between the axle shaft  36  and the rotor shaft  40  along the horizontal axis X. In the illustrated embodiment, the first horizontal distance H 1  is greater than the second horizontal distance H 2 . In some embodiments, the first horizontal distance H 1  is equal to, or less than, the second horizontal distance H 2 . The idler shaft  46  is also positioned a first vertical distance V 1  below the output shaft  48  and the axle shaft  36 , and a second vertical distance V 2  below the rotor shaft  40  along a vertical axis Z. In the illustrated embodiment, the first vertical distance V 1  is greater than the second vertical distance V 2 . In some embodiments, the first vertical distance V 1  is equal to, or less than, the second vertical distance V 2 . 
     In some embodiments, the transmission unit  30  includes a 2-speed transmission including the plurality of output gears including the first output gear  64  and the second output gear  66  spaced along the output shaft  48 . The plurality of idler gears includes the first idler gear  56  meshed with the first output gear  64  and the second idler gear  58  meshed with the second output gear  66 . 
     In the illustrated embodiment, the wheel end assembly  32  includes the wheel hub  68  adapted to be coupled to at least one wheel  22 , and the wheel hub planetary drive  74  coupled to the axle shaft  36  and to the wheel hub  68  for transferring torque from the axle shaft  36  to the wheel hub  68 . The wheel hub planetary drive  74  includes the planetary gear having the sun gear  76  of the planetary gear coupled to the axle shaft  36 . The planet carrier  78  of the planetary gear is coupled to the wheel hub  68 , and the ring gear  82  of the planetary gear is coupled to the hub spindle  38  and is held stationary with respect to the planet carrier  78  and the sun gear  76 . 
     Referring to  FIGS. 2 and 58 , in some embodiments, the axle assembly  10  may include a first drive unit  100  for driving a first wheel assembly  102 , and a second drive unit  104  for driving a second wheel assembly  106 . The first drive unit  100  and the second drive unit  102  each include a drive unit  26 . The first drive unit  100  includes a first axle shaft and the second drive unit  104  includes a second axle shaft oriented coaxially with the first axle shaft along the axle centerline axis  37  that defines the axis of rotation  24 . 
     In one embodiment, the axle assembly  10  may include an inverter device  108  coupled to each of the first and second drive units  100  and  104 , and a controller  110  for operating the electrical inverter device  108  and the drive units  100  and  104 . Each inverter device  108  is coupled to one or more batteries  112  for supplying electrical power to the inverter electrical inverter  108 . Each controller  110  is coupled to a VMU unit  114 . In one embodiment, the first drive unit  100  is configured to operate independently from the second drive unit  104 . In addition, each controller  110  is programmed to operate the corresponding motor assemblies at a variable speed. For example, in one embodiment, the VMU  114  may be programmed to transmit signals to each controller  110  such that, during operation, the controller  110  of the first drive unit  100  may operate the drive unit of the first drive unit  100  at a first rotational speed, and the controller  110  of the second drive unit  100  may operate the drive unit of the second drive unit  104  at a second rotational speed that is different than the first rotational speed of the first drive unit  100 . In addition, during operation, only one of the motor assemblies may be operated to drive the corresponding wheel assembly with the other drive unit allowing the corresponding wheel assembly to spin freely. This provides the axle assembly  10  with the capability of not driving one of the electric motors when the load requirements are low. This can be done through the controller that doesn&#39;t send power to one of the motors, or can be done mechanically to disconnect the motor. Disconnection can be through a neutral position as part of a speed change mechanism, or through a clutch or the like. When in this mode, the axle assembly  10  operates to drive only one wheel on one side of the vehicle. For example, in a tandem axle configuration (four wheels), the axle assembly  10  may operate to generate power that can be alternated between different motors based on needs and loads. 
     Referring to  FIGS. 2-52 , in the illustrated embodiment, each outer section  16  includes a gearbox  116  that includes a gearbox housing  118  and a gearbox cover  120 . The bridge section  14  includes a cradle assembly  122  that is coupled to each gearbox housing  118 . The cradle assembly  122  includes a cradle frame  124 , a top cover  126  that is removably coupled to a top portion  128  of the cradle frame  124 , and a bottom cover  130  that is removably coupled to a bottom portion  132  of the cradle frame  124 . The cradle frame  124  includes an inner surface  134  that defines a cavity  136  that extends through the cradle frame  124 . The top cover  126  extends across the top portion  128  of the cradle frame  124  and the bottom cover  130  extends across the bottom portion  132  of the cradle frame  124  to enclose the cavity  136  to form a cradle chamber  138 . The cradle chamber  138  is sized and shaped to receive one or more electrical inverter devices  108  that are positioned within the cradle chamber  138 . In some embodiments, the cradle assembly may be built with the inverters inside or may be assembled without the inverters inside the cradle chamber. 
     The cradle frame  124  includes a forward member  140 , a rear member  142 , a first side member  144  and an opposite second side member  146 . The first side member  144  and the second side member  146  extend along a longitudinal axis  148  and are spaced a distance apart along a transverse axis  150  that is perpendicular to the longitudinal axis  148 . In the illustrated embodiments, the transverse axis  150  is substantially parallel to the axis of rotation  24  of each wheel  22 . The forward member  140  is coupled between the first side member  144  and the second side member  146  to form a front portion  152  of the cradle frame  124 . The rear member  142  is coupled between the first side member  144  and the second side member  146 , and is spaced a distance from the forward member  140  along the longitudinal axis  148  to form a rear portion  154  of the cradle frame  124 . 
     The first side member  144  and the second side member  146  each include one or more cable access openings  156  that extend through the side members. The cable access opening  156  is sized and shaped to receive a plurality of electrical cables therethrough to allow electrical and communication cables to extend from the electrical inverter devices  108  positioned within the cradle chamber  138  to an area outside the cradle chamber  138 . The electrical and communication cables may include, but are not limited to, 3 phase cables, two DC cables, a motor connection cable, and customer interface cable. 
     A pair of forward mounting flanges  158  extend outwardly from opposite ends of the forward member  140 . Each forward mounting flange  158  includes a mounting member  160  and a support arm  162  that is coupled between the mounting member  160  and the forward member  140 . The mounting member  160  is spaced a distance outwardly from an outer surface  164  of a corresponding side member  144 ,  146  as measured along the transverse axis  150 . The mounting member  160  includes a planar mounting surface  166  that is configured to engage an outer surface of a corresponding gearbox housing  118 . The planar mounting surface  166  is orientated substantially parallel to the outer surface  164  of the corresponding side members  144 ,  146 . 
     Referring to  FIGS. 24-27 , in the illustrated embodiment, the forward member  140  includes a top surface  168  and a bottom surface  170 , and includes a height  172  measured between the top surface  168  and the bottom surface  170  along a vertical axis  174 . The mounting member  160  includes a bottom surface  176  and a top surface  178  and the planar mounting surface  166  extending between the bottom surface  176  and the top surface  178 . The planar mounting surface  166  includes a height  180  measured between the top surface  178  and the bottom surface  176  of the mounting member  160  along the vertical axis  174 . The bottom surface  176  of the mounting member  160  is substantially flush with the bottom surface  170  of the forward member  140 . The top surface  178  of the mounting member  160  is spaced a vertical distance from the top surface  168  of the forward member  140  such that the height  180  of the mounting surface  166  is greater than the height  172  of the forward member  140 . A plurality of fastener openings extending through the planar mounting surface  166  of the mounting member  160 . Each fastener opening is sized and shaped to receive a fastener such as, for example, a bolt and/or screw, therethrough to couple the cradle frame  124  to the gearbox housing  118 . 
     In addition, the support arm  162  includes an arcuate top surface  182  that extends between the top surface  178  of the mounting member  160  and the top surface  168  of the forward member  140 . The support arm  162  also includes an arcuate outer surface  184  and an arcuate inner surface  186 . The arcuate inner surface  186  defines a gap  188  between the mounting member  160  and a side member outer surface  164  of the corresponding side members  144 ,  146 . The gap  188  is sized and shaped to receive a portion of the gearbox housing  118  therein to facilitate coupling the cradle frame  124  to the gearbox housing  118 . 
     Referring to  FIGS. 19-23 , in the illustrated embodiment, the forward member  140  also includes a suspension arm support assembly  190  that extends outwardly from the outer surface of the forward member  140 . The outer surface of the forward member  140  includes an arcuate shape that defines a pair of slots  192  between opposing ends of the suspension arm support assembly  190  and the forward member outer surface. Each slot  192  is sized and shaped to receive an end of a tie-rod  20 , and a mounting surface  194  is defined at each end of the suspension support arm assembly  190  to facilitate coupling the tie-rod  20  to the suspension arm support assembly  190 . The forward member outer surface includes recessed portions  196  that are positioned with respect to at each end of the suspension support arm assembly  190 . Each recessed portion  196  is sized and shaped to receive an end of a tie-rod  20  such that each tie-rod  20  extends outwardly from the forward member  140  at an oblique angle. 
     In the illustrated embodiment, a pair of rear mounting flanges  198  extend outwardly from opposite ends of the rear member  142 . Each rear mounting flange  198  includes a rear mounting member  200  and a rear support arm  202  that is coupled between the rear mounting member  200  and the rear member  142 . The rear mounting member  200  is spaced a distance outwardly from the corresponding side member outer surface  164  as measured along the transverse axis  150 . The rear mounting member  200  also includes a rear planar mounting surface  204  that is configured to engage an outer surface of a corresponding gearbox housing  118 , and is orientated substantially parallel to the side member outer surface  164  and the planar mounting surface  166  of the forward mounting member  160 . 
     In the illustrated embodiment, the planar mounting surface  166  of the forward mounting member  160  and the rear planar mounting surface  204  that are positioned on the same side of the cradle frame  124  are orientated within the same plane to facilitate coupling the cradle assembly  122  to the corresponding gearbox housing  118 . In addition, the rear planar mounting surface  204  includes a height  206  measured along the vertical axis  174  that is substantially similar to the height of the corresponding planar mounting surface  166  of the forward mounting member  160 . In one embodiment, the forward mounting member  160  includes a length  302  (shown in  FIG. 21 ) defined along the longitudinal axis  148 , and the rear mounting member  200  includes a length  304  defined along the longitudinal axis  148  that is longer than the length  302  of the forward mounting member  160 . 
     Each rear mounting member  200  includes a plurality of fastener openings extending through the rear planar mounting surface  204  that are sized and shaped to receive a fastener such as, for example, a bolt and/or screw, therethrough to couple the cradle frame  124  to the gearbox housing  118 . Similar to the forward mounting member  160 , each rear support arm  202  includes an arcuate top surface that extends between a top surface of the rear mounting member  200  and a top surface of the rear member  142 . The rear support arm  202  also includes an arcuate outer surface and an arcuate inner surface. The arcuate inner surface of the rear support arm  202  defines a gap  208  between the rear mounting member  200  and the corresponding side member outer surface  164  that sized and shaped to receive a portion of the gearbox housing  118  therein. 
     Referring to  FIGS. 28-35 , in the illustrated embodiment the top cover  126  and the bottom cover  130  each include a plate  210  that includes an outer surface  212  and an inner surface  214  that extend between extend between a front endwall  216  and a rear endwall  218  along the longitudinal axis  148 , and between opposing side endwalls  220  along the transverse axis  150 . Each front endwall  216  includes an arcuate shape that matches the arcuate shape of the inner surface of the forward member  140 . The top cover  126  and the bottom cover  130  each include a plurality of fastening tabs  222  extend outwardly from the side endwalls  220  and the rear endwall  218 . Each fastening tab  222  includes an opening extending therethrough that is sized and shaped to receive fastener to facilitate coupling the top cover  126  to the cradle frame  124 . 
     The top portion  128  of the cradle frame  124  includes a top grove  224  that is defined along a perimeter of the cavity  136  adjacent the cradle inner surface  134  that is sized and shaped to receive a portion of an outer edge of the top cover  126  such that the outer surface  212  of the top cover  126  is positioned substantially flush with the top surface of the forward member  140 , rear member  142 , and side members  144 ,  146  of the cradle frame  124 . A plurality of positioning slots  226  are defined along the top surfaces of the rear member  142  and side members  144 ,  146 . Each positioning slot  226  is sized and shaped to receive a corresponding fastening tab  222  therein. The top surfaces of the rear member  142  and side members  144 ,  146  include an opening defined within each positioning slot  226  to receive a fastener therein to facilitate coupling the top cover  126  to the cradle frame  124 . 
     Similarly, the bottom portion  132  of the cradle frame  124  includes a bottom grove  228  that is defined along a perimeter of the cavity  136  adjacent the cradle inner surface  134  that is sized and shaped to receive a portion of an outer edge of the bottom cover  130  such that the outer surface  212  of the bottom cover  130  is positioned substantially flush with the bottom surface of the forward member  140 , rear member  142 , and side members  114 ,  146  of the cradle frame  124 . A plurality of positioning slots  230  are defined along the bottom surfaces of the rear member  142  and side members  144 ,  146  for receiving a corresponding fastening tab  222  therein. An opening is defined within each positioning slot  230  to receive a fastener therein to facilitate coupling the bottom cover  130  to the cradle frame  124 . 
     The top cover  126  also includes a plurality of openings  232  extending through the plate  210  and are sized and shaped to receive fasteners therethrough to facilitate mounting the electrical inverter devices  108  within the cradle chamber  138 . 
     Referring to  FIGS. 36-52 , in the illustrated embodiment, the gearbox  116  includes the gearbox housing  118  and the gearbox cover  120 . The gearbox housing  118  includes a body  234  including a plurality of walls having an inner surface  236  and an outer surface  238 . The inner surface  236  defines a gearbox cavity  240  that is sized and shaped to receive the drive unit  26  therein. The outer surface  238  extends between a front-side portion  242  and a back-side portion  244  along the transverse axis  150 , and between a forward portion  246  and a rear portion  248  along the longitudinal axis  148 . 
     The front-side portion  242  of the gearbox housing  118  includes a first mounting surface  250  positioned adjacent to the forward portion  246  and a second mounting surface  252  positioned adjacent to the rear portion  248 . The first mounting surface  250  includes a substantially planar surface having a shape matching the shape of the planar mounting surface  166  of the forward mounting flange  158 . The second mounting surface  252  includes a substantially planar surface having a shape matching the shape of the planar mounting surface of the rear mounting flange  204 . The first mounting surface  250  and the second mounting surface  252  each include a plurality of fastener openings extending through the gearbox housing  118  and are sized and shaped to receive corresponding fasteners therein to facilitate coupling the gearbox housing  118  to the cradle frame  124 . In the illustrated embodiment, the forward mounting flange  158  is adapted to be coupled to the gearbox housing  118  at the first mounting surface  250  adjacent to the forward portion  246 , and the rear mounting flange  198  is adapted to be coupled to the gearbox housing  118  at the second mounting flange  252  adjacent to the rear portion  248 . 
     A shaft opening  256  extends through the back-side portion  244  and is sized and shaped to receive the axle shaft  36  therethrough. A motor opening  258  also extends through the back-side portion  244  and is sized and shaped to receive a portion of the electric machine  28 . 
     In the illustrated embodiment, the forward portion  246  and the rear portion  248  each include a upper support flange  260  and a lower support flange  262  that is spaced a distance from the upper support flange  260  along the vertical axis  174 . The upper support flange  260  and the lower support flange  262  are configured to couple the gearbox housing  118  to a suspension arm  18  extending outwardly from the gearbox housing  118  to facilitate coupling the axle assembly  10  to the vehicle. The forward portion  246  includes a suspension arm support flange  264  that is positioned above the upper support flange  260  along the vertical axis  174 . The suspension arm support flange  264  is adapted to couple a tie-rod  20  to the gearbox housing  118  and is orientated such that the tie-rod  20  extends outwardly from the gearbox housing  118  substantially parallel to the longitudinal axis  148 . 
     The front-side portion  242  also includes a mounting shoulder  266  extending outwardly from an outer surface of the front-side portion  242 . The mounting shoulder  266  extends around a perimeter of the opening and includes a planar front surface  268 . A plurality of holes are defined along the front surface  268  for receiving corresponding fasteners therein to facilitate coupling the gearbox cover  120  to the gearbox housing  118 . 
     The gearbox cover  120  includes a body  270  including an outer surface  272  having a shape that substantially matches the shape of the mounting shoulder  266 . The gearbox cover  120  includes a plurality of openings  274  extending around a perimeter of a mounting surface of the body  270  that are sized and shaped to received fasteners therethrough to facilitate coupling the gearbox cover  120  to the gearbox housing  118 . The gearbox cover  120  is adapted to be coupled to the gearbox housing  118  to enclose the drive unit within the gearbox cavity  240 . The mounting shoulder  266  includes a positioning groove  276  defined along the front surface  268 . The gearbox cover  120  includes a positioning lip that extends outwardly from a surface of the gearbox cover  120  and is configured to engage the positioning groove  276  to facilitate coupling the gearbox cover  120  to the gearbox housing  118 . The mounting shoulder  266  extends outwardly a distance from the front-side portion  242  along the transverse axis  150  such that the gearbox cover  120  is positioned within a gap  278  defined between the forward mounting flange  158  and the corresponding rear mounting flange  198  when the gearbox  116  is mounted to the cradle frame  124 . 
     In the illustrated embodiment, the axle housing  12  includes the first outer section  16   a , the second outer section  16   b , and the bridge section  14  extending between the first outer section  16   a  and the second outer section  16   b . The first outer section  16   a  includes the gearbox  116  including the inner surface  236  that defines the gearbox cavity  240  that is sized and shaped to receive the electric machine  28  and the transmission unit  30 . The bridge section  14  includes the cradle assembly  122  that is coupled to the gearbox  116 . The cradle assembly  122  includes the inner surface  134  defining the support chamber  138  that is sized and shaped to receive the inverter assembly  108  therein. In some embodiments, the second outer section  16   b  includes a second gearbox  116  that is coupled to the cradle assembly  122  and configured to support the second drive unit  26  therein. 
     In the illustrated embodiment, the gearbox  116  includes the gearbox housing  118  and the gearbox cover  120  that is removably coupled to the gearbox housing  118 . The cradle assembly  122  is removably coupled to the gearbox housing  118 . 
     The cradle assembly  122  includes the cradle frame  124 . The cradle frame  124  includes the forward member, the rear member, and the pair of opposing side members  144 ,  146  extending between the forward member  140  and the rear member  142  along the longitudinal axis  148 . A first mounting flange  158  extends outwardly from the first side member  144  of the pair of opposing side members and is configured to couple to an outer surface of the gearbox housing  118 . A second mounting flange  198  extending outwardly from the first side member  144  and is configured to couple to the outer surface of the gearbox housing  118 . The first mounting flange  158  is spaced a distance from the second mounting flange  198  along the longitudinal axis  148  to define the gap  278  between the first mounting flange  158  and the second mounting flange  198 . The gearbox cover  120  is positioned within the gap  278  with the gearbox housing  118  coupled to the cradle frame  124 . 
     The cradle frame  124  includes a suspension arm support assembly  190  that extends outwardly from the forward member  140 . The suspension arm support assembly  190  is configured to couple to a tie-rod  20  that is coupled to a vehicle frame. The cradle assembly  122  includes the top cover  126  that is removably coupled to the top portion of the cradle frame  124 . The cradle assembly  122  includes the bottom cover  130  that is removably coupled to the bottom portion of the cradle frame  124 . In some embodiments, the bottom cover  130  is fixedly coupled to the bottom portion. In other embodiments, the cradle frame  124  and bottom cover  130  are formed as a unitary member. In the illustrated embodiment, the cradle frame  124  includes the cable access openings  156  defined through at least one of the pair of opposing side members  144 ,  146 . 
     The gearbox housing  118  includes a body  234  that extends between a first endwall  310  and an opposite second endwall  312 . A pair of first support flanges  314  extend outwardly from the first endwall  310 . The pair of first support flanges  314  are configured to couple to a first mount arm  316  that is coupled to a vehicle frame. A pair of second support flanges  318  extend outwardly from the second endwall  312 . The pair of second support flanges  318  are configured to couple to a second mount arm  320  that is coupled to the vehicle frame. The gearbox housing  118  also includes the suspension arm support flange  264  that is adapted to couple a tie-rod  20  to the gearbox housing  118 . 
     In the illustrated embodiment, the axle assembly  10  is coupled to the vehicle frame  11 . The axle assembly  10  includes the axle housing  12  including the bridge section  14  extending between the first outer section  16   a  and the opposite second outer section  16   b . The first outer section  16   a  includes a first gearbox  116 . The second outer section  16   b  include a second gearbox  116 . The bridge section  14  includes the cradle assembly  122  that is coupled to the first gearbox and the second gearbox. The cradle assembly  122  includes the inner surface that defines the support chamber within the cradle assembly  122 . A first drive unit  100  is adapted to couple to the first wheel assembly  102 . The first drive unit  100  includes a first electric machine  28  positioned within the first gearbox  116 . The first electric machine  28  includes a drive pinion coupled to a rotor shaft. The first transmission unit  30  is positioned within the first gearbox  116  and includes the output assembly  43  and the offset gear reduction assembly that is coupled to the output assembly  43  and the drive pinion of the first electric machine  28  for transferring torque from the first electric machine to the output assembly. The first axle shaft is coupled to the output assembly  43  and extends outwardly from an outer surface of the first gearbox  116 . A second drive unit  102  is adapted to couple to a second wheel assembly  106 . The second drive unit  102  includes a gear reduction and a second axle shaft that is oriented coaxially with the first axle shaft along the axle centerline axis. The gear reduction is positioned within the second gearbox  116 . The second axle shaft extends outwardly from the second gearbox towards the second wheel assembly. An inverter assembly  108  is positioned within the support chamber of the cradle assembly  122 . The inverter assembly is coupled to the first electric machine for providing electrical power to the first electric machine. 
     In one embodiment, the axle assembly  10  may include a 700 mm Walk Through ultra-low floor (ULF) with a 275/70r22.5 Tire, 2 speed: −11.1:1; 19.6:1, Axle Weight Rating of 11,600 kg, and 750,000 mile capable. The axle assembly  10  may also include a 1,000 mm Walk Through ULF with 445/45r22.5 Tire, 2 speed: 11.1:1; 19.6:1, Axle Weight Rating of 10,500 kg, and 750,000 mile capable. The axle assembly  10  may also include a 580 mm Walk Through ULF with 305/70r22.5 Tire, 2 speed: 11.1:1; 19.6:1, Axle Weight Rating of 12,600 kg, and 750,000 mile capable. The axle assembly  10  may also include a 700 mm Walk Through ULF, One Speed, 275/70r22.5 Tire, 1 speed: 15:1, Axle Weight Rating of 11,600 kg, and 750,000 mile capable. The axle assembly  10  may also include a 1,000 mm Walk Through ULF, One Speed with 275/70r22.5 Tire, 1 speed: 15:1, Axle Weight Rating of 10,500 kg, 750,000 mile capable. The axle assembly  10  may also include a 580 mm Walk Through ULF, One Speed with 305/70r22.5 Tire, 1 speed: 15:1, Axle Weight Rating of 12,600 kg, and 750,000 mile capable. 
     A controller, computing device, server or computer, such as described herein, includes at least one or more processors or processing units and a system memory (see above). The controller typically also includes at least some form of computer readable media. By way of example and not limitation, computer readable media may include computer storage media and communication media. Computer storage media may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology that enables storage of information, such as computer readable instructions, data structures, program modules, or other data. Communication media typically embody computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism and include any information delivery media. Those skilled in the art should be familiar with the modulated data signal, which has one or more of its characteristics set or changed in such a manner as to encode information in the signal. Combinations of any of the above are also included within the scope of computer readable media. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings, and the invention may be practiced otherwise than as specifically described.