Abstract:
A structural electric tandem axle module ( 13 ) for propelling a vehicle such as a large vocational vehicle without applying torque to the chassis frame of the vehicle as the module operates.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to wheeled vehicles, especially large vocational vehicles. More particularly, the invention relates to a tandem axle module which delivers torque to wheels of a tandem axle for propelling a vehicle. 
     SPONSORSHIP 
     This invention has been sponsored by the National Research Council Canada but is solely owned by the inventor. 
     BACKGROUND OF THE INVENTION 
     A typical chassis frame of a commercial truck, a motor bus, a motor coach, and many military vehicles is an assembled structure having right and left longitudinal side rails joined together by transverse cross members. Consequently, the central portion of such a chassis frame is mostly an open structure which allows the frame to twist longitudinally and exhibit torsional compliance when the vehicle traverses uneven surfaces and when torque is transferred from a driveline to the frame. 
     A typical driveline of commercially manufactured trucks is headed by an internal combustion engine and extends longitudinally from front to rear of the truck with the engine crankshaft rotating about a longitudinally extending axis. When the engine is accelerated to accelerate the truck, the engine transfers equal torque through the driveline to the wheels and to the frame. Although the frame is torsionally compliant, certain torsionally rigid components, such as compressed air tank cylinders and cylindrical fuel tanks are often mounted on the frame&#39;s side rails. 
     As a truck travels over an uneven surface, the suspension system transfers torque into side-rail-mounted components which, like a fuel tank, have closed, torsionally rigid, cross sections. Over time, torque applied to a chassis frame can result in a condition sometimes referred to as “fuel tank walking.” That condition is characterized by a fuel tank turning within its mounting straps and in the extreme, disappearance of a fuel tank fill tube underneath the truck cab. 
     A commercial truck also comprises a body mounted on the chassis frame. A typical truck body comprises a cab and a front engine compartment hood. The cab is a torsionally rigid structure which is also subjected to repeated twisting by torsion being applied to the chassis frame by the engine. The front engine compartment hood is also a torsionally rigid structure. Those body components can, over time, experience micro fractures which can propagate to the point of causing catastrophic component failure—all attributable to the repeated absorption of engine-induced torsion. Broken hood hinges are one example of such failures. 
     SUMMARY OF THE INVENTION 
     The present invention provides a solution for mitigating the aforementioned consequences of repeated torsion absorption by a chassis frame, consequences which include not only failure of frame-mounted components like compressed air tanks and fuel tanks but also failures in the chassis frame itself, such as the frame&#39;s side rails, in various chassis components associated with the frame, such as transverse torque rods, and in various body components like hood hinges. 
     Briefly, mitigation of the aforementioned consequences of repeated torsion absorption is achieved through a structural electric tandem axle module which when propelling a vehicle does not transfer torque to the chassis frame. 
     The module comprises a dual-rotor electric motor. One rotor delivers torque through a differential gear mechanism of a front tandem axle to wheels at the axle&#39;s ends. The other rotor delivers torque through a differential gear mechanism of a rear tandem axle to wheels at the axle&#39;s ends. 
     The shafts of the respective rotors deliver equal torques to the respective differentials, but in opposite directions of rotation. Because the rotors are forced to rotate in opposite directions by the same electromagnetic force acting between them, the sum of the torques delivered to the two tandem axles by the rotors is two times greater than the torque output of a conventional truck transmission driveline. 
     In the conventional art, one half of the rotational mechanical torque is wasted in repeatedly elastically deforming the chassis frame rails and stressing frame and frame-mounted components to the point that they will eventually fail. 
     The disclosed structural electric tandem axle module eliminates this waste of energy and its inherent consequences. In doing so, the disclosed module endows a vehicle with enhanced road handling characteristics by allowing each rigid dual wheel axle to pivot about a longitudinal center line of the vehicle while maintaining secure mechanical articulation and full tire contact with road surfaces. 
     The module is maintenance-friendly because it is a self-contained unit which can be quickly replaced in the field or in a maintenance facility. 
     The dual rotor and the structural casing which houses it provide for rigid axle rotational articulation about the module&#39;s centerline while canceling out mechanical torque input to the chassis frame, thereby eliminating the problems caused by engine-induced torque input the chassis frame, including overloading the right front steered wheel and tire which occurs in conventional trucks. 
     The module that can be used in various on-road and off-road applications including: commercial vehicles such as trucks, buses, and motorcoaches; military, agricultural, construction, and rail vehicles; and vehicles which are connected to an electrical distribution grid, such as electric rail lines. 
     The module can enhance vehicle efficiency by energy recovery during vehicle braking and it may offer opportunities for weight reduction by enabling use of lighter weight frame rails. Common modules for various vehicles can provide economies of scale in mass-production manufacture of modules. 
     One general aspect of the invention relates to the subject matter set forth in independent Claim  1 . 
     Another general aspect of the invention relates to the subject matter set forth in independent Claim  7 . 
     Further aspects are set forth in the various dependent Claims. 
     The foregoing summary, accompanied by further detail of the disclosure, will be presented in the Detailed Description below with reference to the following drawings that are part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a truck vehicle. 
         FIG. 2  is a top plan view of a structural electric tandem axle module in the truck vehicle. 
         FIG. 3  is cross section view through a portion of a structural electric tandem axle module taken in the same direction as  FIG. 2  and enlarged. 
         FIG. 4  is a left side elevation view of another truck vehicle. 
         FIG. 5  is a perspective view of a differential mechanism by itself. 
         FIG. 6  is a fragmentary view of a modification. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a truck vehicle T like the one shown in FIG. 7 of Pub. No. US 2012 0152631. 
     Truck vehicle T has a chassis frame F which provides underlying support for an engine and cooling module support frame  8  which itself provides underlying support for a transverse-mounted dual-engine, variable power drive  100 . Chassis frame F has a right side rail RSR and a left side rail LSR. 
     Drive  100 , as described in Pub. No. US 2012 0152631, comprises a starboard side turbodiesel propulsion engine  1 , a starboard side hydraulic internal wet-disk clutch  2 , an electric generator  3 , a port side hydraulic internal wet-disk clutch  4 , a port side turbodiesel propulsion engine  5 , a starboard side engine exhaust stack  6 , including a diesel particulate filter (DPF) and optional exhaust treatment apparatus, and a port side engine exhaust stack  7 , including a diesel particulate filter (DPF) and optional exhaust treatment apparatus. 
     Support frame  8  and the components which it supports can be covered by a cover which is shown in open position in  FIG. 1  to provide service access to drive  100 . The cover comprises movable starboard and port side clamshell halves  9 ,  10  which are swung closed to cover the drive. Exhaust stacks  6 ,  7  are shaped to place their tailpipes outside the cover when the cover is closed. 
     Truck vehicle T comprises a cab C having an interior compartment for a driver of the vehicle. Right and left front steerable wheels  11 ,  12  respectively are suspended from chassis frame F on right and left sides for steering truck vehicle T. A structural electric tandem axle module  13  is mounted on chassis frame F rearward of cab C. Supported on chassis frame F over module  13  is a fifth wheel  14  to which a trailer (not shown) can be connected for towing by truck vehicle T. 
       FIG. 2  shows structural electric tandem axle module  13  to comprise a front drive axle  15  and a rear drive axle  16 . Between the two axles  15 ,  16  is a succession of structural elements fastened together to form a structurally rigid housing  17  at opposite lengthwise ends of which drive axles  15  and  16  are respectively mounted. Housing  17  is securely mounted on chassis frame F between right side rail RSR and left side rail LSR. 
     The structural elements forming rigid housing  17  comprise, in order from front to rear, a front drive axle pivot bearing  18 , a brush holder ring  19 , an electric motor casing  20 , and a rear drive axle pivot bearing  21 .  FIG. 3  shows electric motor casing  20  to comprise a first part  20 A and a second part  20 B. First part  20 A has an end wall confronting brush holder ring  19  and a cylindrical side wall extending to an open end which is closed by second part  20 B. 
     Front drive axle  15  comprises a front differential casing  22  which encases a front differential gear mechanism  23  and which at an end toward brush holder ring  19  has a circular flange  24  which is supported by front drive axle pivot bearing  18  for pivotal motion about a longitudinal axis  25  of module  13 . 
     Rear drive axle  16  comprises a rear differential casing  26  which encases a rear differential gear mechanism  27  and which at an end toward second part  20 B of motor casing  20  has a circular flange  28  which is supported by rear axle pivot bearing  21  for pivotal motion about axis  25 . 
     Front drive axle  15  has a left front drive shaft  29  extending from front differential gear mechanism  23  to a left front axle wheel hub  30  on which left front axle wheels  31  are mounted and a right front drive shaft  32  extending from front differential gear mechanism  23  to a right front axle wheel hub  33  on which right front axle wheels  34  are mounted. Left front drive shaft  29  is coupled to wheel hub  30  so that both rotate in unison. Right front drive shaft  32  is coupled to wheel hub  33  so that both rotate in unison. 
     Rear drive axle  16  has a left rear drive shaft  35  extending from rear differential gear mechanism  27  to a left rear axle wheel hub  36  on which left rear axle wheels  37  are mounted and a right rear drive shaft  38  extending from rear differential gear mechanism  27  to a right rear axle wheel hub  39  on which right rear axle wheels  40  are mounted. Left rear drive shaft  35  is coupled to wheel hub  36  so that both rotate in unison. Right rear drive shaft  38  is coupled to wheel hub  39  so that both rotate in unison. 
     All wheels comprise pneumatic tires  41 . 
     Structural electric tandem axle module  13  further comprises an outer rotor  42  and an inner rotor  43  which collectively form an electric motor. 
     Outer rotor  42  has an outer rotor shaft  44  journaled for low-friction rotation about axis  25  via taper bearing assemblies  45 ,  46  situated in respective bearing mounts in housing  20 . Between taper bearing assemblies  45 ,  46 , outer rotor  42  comprises a permanent magnet assembly  47  which is disposed within motor casing  20  and which rotates with outer rotor shaft  44 . At one end beyond taper bearing assembly  46 , outer rotor shaft  44  has a bevel pinion gear  48  which couples outer rotor  42  with rear differential gear mechanism  27 . 
     Inner rotor  43  has an inner rotor shaft  49  arranged for rotation about axis  25 . One taper bearing assembly  50  is situated in a bearing mount in brush holder ring  19  to provide a first point of support for low-friction rotation of inner rotor shaft  49  about axis  25 . At one end beyond taper bearing assembly  50 , inner rotor shaft  49  has a bevel pinion gear  51  which couples inner rotor  43  with front differential gear mechanism  23 . 
     The end of outer rotor shaft  44  which is supported by taper bearing assembly  45  comprises a clearance hole concentric with axis  25 . Inner rotor shaft  49  extends from the end supported by taper bearing assembly  50  and passes through that clearance hole to an opposite end where a second point of support for low-friction rotation of inner rotor shaft  49  about axis  25  is provided by a taper bearing assembly  52  which is itself situated in a frame of outer rotor  42  which also supports permanent magnets of permanent magnet assembly  47 . The clearance hole is sealed by a seal between the two rotor shafts. Consequently, both rotors  42 ,  43  are supported for rotation about axis  25 . 
     Inner rotor  43  comprises an armature  53  which is supported on, and rotates with, inner rotor shaft  49 . Brush holder ring  19  houses an inner rotor slip ring wheel  54  which is mounted on, and rotates with, inner rotor shaft  49 . Inner rotor slip rings  55 ,  56  are axially spaced apart and extend circumferentially around the outside of inner rotor slip ring wheel  54 . Inner rotor electric brushes  57 ,  58  on an inner wall of brush holder ring  19  are biased into contact with respective slip rings  55 ,  56 . 
     Armature  53  comprises a frame on which an inner rotor armature winding is disposed. The inner rotor armature winding is electrically connected to slip rings  55 ,  56 , enabling the winding to connect through the slip rings and brushes  57 ,  58  to electric terminations housed within a compartment  59  ( FIG. 2 ) of motor casing  20  which is closed by a removable cover  60  on the casing&#39;s exterior. 
     Differential gear mechanisms  23 ,  27  are essentially identical. As shown in  FIG. 5 , each mechanism comprises a ring gear  61  mounted on a ring gear carrier  62  which is journaled for rotation on the respective differential casing  22 ,  26  about the axis of the respective differential&#39;s two drive shafts  29 ,  32  and  35 ,  38 . Each differential gear mechanism further comprises a left side gear  63  and a right side gear  64 . 
     The left side gear  63  of the respective differential gear mechanism  23 ,  27  is rotationally coupled to the respective left drive shaft  29 ,  35  by mutually engaged splines, and the right side gear  64  of the respective differential gear mechanism  23 ,  27  is rotationally coupled to the respective right drive shaft  32 ,  38  by mutually engaged splines. Two aligned spider gears  65 ,  66  are supported for independent rotation on opposite sides of a cage  67  which is part of ring gear carrier  62 . 
     The two side gears  63 ,  64  can rotate on the respective ring gear carrier  62  via their own respective bearing about the common axis of the respective drive axle&#39;s drive shafts. 
     Each pinion  48 ,  51  meshes with the respective ring gear  61 . Rotation of pinion  51  about axis  25  rotates ring gear  61  of differential gear mechanism  23 , including cage  67 . The rotation of ring gear  61  is imparted to the respective side gears  63 ,  64  because spider gears  65 ,  66  are in mesh with both side gears. The two drive shafts of each drive axle will rotate at equal speeds when the vehicle is being steered in a straight line, but the differential gear mechanism will allow one drive shaft to rotate at a slower speed than the other when the vehicle is being steered to turn in the direction of the slower rotating drive shaft. 
     The electric motor formed by outer rotor  42  and inner rotor  43  operates to rotate the two rotors at the same speed but in opposite directions about axis  25  as viewed in one direction along axis  25 . The equal, but opposite, rotations occur because of interaction between an inner rotor electromagnetic field pattern created by electric D.C. current flow from electric generator  3  through brushes  57 ,  58  and slip rings  55 ,  56  to the inner rotor armature winding of inner rotor armature  47  and a an outer rotor magnetic field pattern created by powerful permanent magnets, such as rare earth magnets, of permanent magnet assembly  53  of outer rotor  42 . 
     The inner rotor armature winding may comprise individual coil windings which are commutated to the current source as inner rotor  43  turns about axis  25 . By reversing the direction of D.C. source current to the inner rotor armature winding, the rotations of the respective rotors can be reversed. 
     If outer rotor shaft  44  is rotating in a counterclockwise direction as viewed in the direction from bevel pinion gear  48  toward bevel pinion gear  51 , rear axle drive shafts  35 ,  38  will rotate in a direction which causes rear axle wheels  37 ,  40  to rotate in a direction which propels truck vehicle T forward. At the same time, bevel pinion gear  51  is rotating clockwise, causing front axle drive shafts  29 ,  32  and rear axle wheels  37 ,  40  to rotate in a direction which also propels truck vehicle T forward. By reversing the direction of D.C. source current to the inner rotor armature winding, the front axle wheels and the rear axle wheels will propel truck vehicle T in reverse. 
     In other words, the electric motor is operable to cause outer rotor  42  and inner rotor  43  to rotate in opposite directions about the axis as viewed in a direction from one differential gear mechanism toward the other. Consequently, both the left and right drive shafts  29 ,  32  of front tandem axle  15  and the left and right drive shafts  35 ,  38  of rear tandem axle  16  rotate in identical directions of rotation when viewed from a direction transverse to axis  25 , i.e. from a side of truck vehicle T. 
     Temperature of the electric motor can be regulated by controlling flow of coolant through coolant passages in motor casing  20 . 
       FIG. 4  illustrates a truck vehicle having a longitudinal mounting of a dual-engine, variable-power drive. The same reference numerals as used in prior Figs. are used in  FIG. 4  to identify like components. 
     The truck vehicle comprises a chassis frame having a right side rail extending from front to rear, a left side rail LSR extending from front to rear, and various cross-members bridging the side rails and securely fastened to the side rails by Huck fasteners  69 . 
     Front steerable wheels are suspended from the chassis frame. A structural electric tandem axle module  13  is suspended from the chassis frame underneath fifth wheel  14 . The dual-engine, variable-power drive operates module  13  to deliver torque to the wheels of each tandem axle to propel the truck vehicle. 
     The dual-engine, variable power drive module comprises a rear internal combustion engine  102  and a front internal combustion engine  104  at opposite lengthwise ends. Drive  100  also comprises a rear hydraulic internal wet-disk clutch  103 , a front hydraulic internal wet-disk clutch  105 , and an electric generator  106 . 
     Each flywheel is coupled through the respective clutch  103 ,  105  to a respective end of a rotor shaft of electric generator  106  whose housing is fastened to the blocks of engines  102 ,  104  so that the generator is thereby supported by the engine blocks. When a clutch is engaged, it couples flywheel rotation to the rotor shaft of generator  106 , and when a clutch is disengaged, it does not couple flywheel rotation to the shaft of generator  106 . 
     In  FIG. 4  the front of front engine  104  and the front of rear engine  102  face in opposite directions at the far ends of drive  100 . A cooling module  111  for engine  104  is mounted on chassis frame  52  frontally of engine  104 , and a cooling module  113  for engine  102  is mounted on chassis frame  52  rearward of engine  102 . 
     Shown in phantom in  FIG. 4  are a front hood  115  covering engine  104  and having a grill frontally of cooling module  111 . The rear of a day cab is marked at  117  and that of a sleeper cab at  119 . A rear hood  121  covers engine  102  and has a grill rearward of cooling module  113 . The rear hood will extend to the rear of either type of cab. 
     The truck can also provide brake energy recovery by using the driven axle wheels to operate the rotors  42 ,  43  as an electric generator to charge an energy storage device or system, such as a battery, battery bank, or ultra-capacitor. 
       FIG. 6  shows a modification in which the outer rotor, instead of comprising powerful permanent magnets as already described, comprises an outer rotor winding which is supplied with electric current from generator  3  to create an electromagnetic field pattern which interacts with the electromagnetic field pattern created by current flow through the inner rotor armature winding. The electric current to the outer rotor winding is supplied through brushes  122 ,  123  on motor casing  20  and slips rings  124 ,  125  on outer rotor  42 . 
     The suspensions of the front tandem axle and the rear tandem axle can be independent. The right wheel suspension of either axle can be made independent of the left wheel suspension of the same axle by including a CV joint in the operative coupling from the differential to each wheel.