Patent Publication Number: US-2013240279-A1

Title: Hybrid tandem drive axle of a truck vehicle

Description:
TECHNICAL FIELD 
     This disclosure relates to truck vehicles, particularly to truck vehicles having tandem drive axles. 
     BACKGROUND 
     Certain truck vehicles have a tandem drive axle comprising a first drive axle that is forward of a second drive axle. One of the purposes of having a tandem drive axle is for enabling the vehicle to carry a larger load because the load weight is distributed to the underlying road service through a greater number of wheels. 
     In one type of tandem drive axle, the first drive axle is coupled by a drivetrain to a combustion engine for propelling driven wheels of the first drive axle. The second drive axle is mechanically coupled to the drivetrain and/or the first drive axle so that driven wheels of the second drive axle are also driven by the combustion engine. When the axles are operated in a 1:1 ratio, the wheels will rotate in unison due to the mechanical coupling when steered wheels at the front of the vehicle are steering the vehicle in a straight line. If there is a difference in diameter between the tire on the first drive axle on one side of the vehicle and the tandem tire on the same side of the vehicle, there can be mismatch in circumference of the tires in the first and second axles, causing friction between the gears between the axles and also causing friction and slip between tandem tires and the underlying road surface. Tire friction can accelerate tire wear and the friction in the gears can impair fuel economy. When the vehicle is being turned by the steered wheels, differential gear mechanisms of the respective drive axles will allow wheels on opposite sides of each drive axle to rotate at slightly different speeds. 
     Another type of tandem drive axle comprises a driven axle and a non-driven axle. When the non-driven axle is rearward of the driven axle, the non-driven axle is sometimes referred to as a tag axle. When the non-driven axle is in front of the driven axle, the non-driven axle is sometimes referred to as a pusher axle. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure relates to a truck vehicle comprising a chassis having a length extending front to rear, a right side, and a left side. 
     Front steerable wheels are suspended from the chassis on the right and left sides for steering the truck vehicle. 
     A combustion engine is supported on the chassis. 
     A tandem rear axle is suspended from the chassis rearward of the front steerable wheels and comprises a first drive axle comprising at least one driven wheel on the right side and at least one driven wheel on the left side and a second drive axle rearward of the first drive axle and comprising at least one driven wheel on the right side and at least one driven wheel on the left side. 
     A drivetrain couples the combustion engine to the first drive axle for driving the at least one driven wheel on the right side and the at least one driven wheel on the left side of the first drive axle. 
     A prime mover other than the combustion engine drives the at least one driven wheel on the right side and the at least one driven wheel on the left side of the second drive axle. 
     Examples of prime movers are electric motors and hydraulic motors. 
     The present disclosure also relates to a method of propelling a truck vehicle that comprises a chassis having a length extending front to rear, a right side, and a left side, front steerable wheels suspended from the chassis on the right and left sides for steering the truck vehicle, a combustion engine supported on the chassis, a tandem rear axle suspended from the chassis rearward of the front steerable wheels and comprising a first drive axle comprising at least one driven wheel on the right side and at least one driven wheel on the left side and a second drive axle rearward of the first drive axle and comprising at least one driven wheel on the right side and at least one driven wheel on the left side, a drivetrain coupling the combustion engine to the first drive axle for driving the at least one driven wheel on the right side and the at least one driven wheel on the left side of the first drive axle. 
     The method comprises operating a prime mover other than the combustion engine for driving the at least one driven wheel on the right side and the at least one driven wheel on the left side of the second drive axle. 
     Examples of prime movers are electric motors and hydraulic motors. 
     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 schematic diagram depicting a top plan view of a truck vehicle chassis. 
         FIG. 2  is an enlarged view of a portion of  FIG. 1  showing a first embodiment. 
         FIG. 3  is a view similar to  FIG. 2  showing a second embodiment. 
         FIG. 4  is a view similar to  FIG. 2  showing a third embodiment. 
         FIG. 5  is a view similar to  FIG. 2  showing a fourth embodiment. 
         FIG. 6  is a view similar to  FIG. 2  showing a fifth embodiment. 
         FIG. 7  is a view similar to  FIG. 2  showing a sixth embodiment. 
         FIG. 8  is a view similar to  FIG. 1  showing a truck vehicle chassis have a tandem rear axle with dual wheels. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  show a truck vehicle chassis  10  having a length extending front to rear, a right side, and a left side. Chassis  10  comprises a frame  12  having right side rail  14  extending front to rear, a left side rail  16  extending front to rear, and cross-members  18 ,  20  bridging the side rails. 
     Right and left front steerable wheels  22 ,  24  respectively are suspended from frame  12  on the right and left sides for steering the truck vehicle. 
     A combustion engine  26  is supported on frame  12 . 
     A tandem rear axle  28  is suspended from frame  12  rearward of front steerable wheels  22 ,  24 . Tandem rear axle  28  comprises a first drive axle  30  comprising at least one driven wheel  32  on the right side and at least one driven wheel  34  on the left side and a second drive axle  36  rearward of first drive axle  30 . Second drive axle  36  comprises at least one driven wheel  38  on the right side and at least one driven wheel  40  on the left side. All wheels comprise pneumatic tires. 
     A drivetrain  42  couples combustion engine  26  to first drive axle  30  for driving driven wheels  32 ,  34 . Drivetrain  42  comprises a transmission  44  having an input coupled to an output of combustion engine  26 . Drivetrain  42  further comprises a driveshaft  46  coupled to first drive axle  30 . 
     First drive axle  30  comprises a differential gear mechanism housed within a casing  48 . Driveshaft  46  is coupled to an input of the differential gear mechanism. Within casing  48  right and left axle shafts extend from the differential gear mechanism to right and left driven wheels  32 ,  34 . 
     Second drive axle  36  comprises a differential gear mechanism housed within a casing  50 . Within casing  50  right and left axle shafts extend from the differential gear mechanism to right and left driven wheels  38 ,  40 . 
     An electric motor  52  has an output shaft  53  coupled to an input of the differential gear mechanism housed within casing  50 . The motor housing may be fastened to casing  50  in any suitable appropriate way or the motor may be mounted remotely and coupled by a suitable coupling to the input of the differential gear mechanism. A battery bank  54  of D.C. batteries is supported from left side rail  16  on a tray  56 , and the positive and negative battery bank terminals are coupled by electric cables  58 ,  60  to a controller  66  which is in turn coupled by electric cables  58 A,  60 A to input terminals  62 ,  64  of electric motor  52 . Controller  66  controls the direction and magnitude of power flow between electric motor  52  and battery bank  54  while monitoring battery bank voltage and current flow between the two as will be more fully explained later. 
     Controller  66  also receives electrical data for various parameters associated with operation of combustion engine  26 , transmission  44 , first drive axle  30 , second drive axle  36 , and electric motor  52 . 
     At times, controller  66  controls current flow from battery bank  54  to electric motor  52  to cause driven wheels  38 ,  40  to driven by electric motor  52  through the differential gear mechanism as a function of at least one parameter characterizing operation of combustion engine  26  and/or first drive axle  30 . For example, motor  30  may be controlled to cause driven wheels  38 ,  40  to rotate at the same speed as the respective tandem wheel  32 ,  34 . 
     Controller  66  can also place drive axle  30  and drive axle  36  in any of selectable operating modes, an example of which is a first mode in which traction force for propelling the truck vehicle is provided only by combustion engine  26  operating drive axle  30 , a second mode in which traction force for propelling the truck vehicle is provided only by the electric motor  52  operating drive axle  36 , and a third mode in which traction force for propelling the truck vehicle is provided both by combustion engine  26  operating drive axle  30  and by electric motor  52  operating drive axle  36 . 
     At times, controller  66  and electric motor  52  can operate in a regenerative braking mode to recover energy and deliver some of that energy into re-charging battery bank  54 . For example, if a driver of the truck vehicle steps on a brake pedal to decelerate the truck vehicle, service brakes associated with driven wheels  32 ,  34  will be applied while controller  66  causes electric motor  52  to operate as a generator that delivers electricity back to controller  66  which in turn uses that electricity to re-charge battery bank  54 . It should be mentioned that electric motor may be either a DC motor or an AC motor, and that the interface between motor  52  and battery bank  54  may comprise electrical equipment such as an inverter or converter for electrical compatibility between motor  52  and battery bank  54 . 
       FIG. 3  shows a second embodiment that differs from the one of  FIGS. 1 and 2  in that electric motor  52  is integrated with drive axle  36  as an in-line motor for directly driving both driven wheels  38 ,  40 . 
       FIG. 4  shows a third embodiment that differs from the one of  FIG. 3  in that electric motor  52  is integrated with drive axle  36  as an in-line motor for directly driving one of the driven wheels  38 ,  40  while an additional electric motor  68  is integrated with drive axle  36  as an in-line motor for directly driving the other of the driven wheels  38 ,  40 . Each motor  52 ,  58  is powered by battery bank  54  and independently controlled by controller  66 . 
       FIG. 5  shows a fourth embodiment that differs from the one of  FIGS. 1 and 2  in that electric motor  52  is replaced by a hydraulic motor  70  having an output shaft  72  coupled to an input of the differential gear mechanism housed within casing  50 . The truck vehicle comprises a hydraulic energy storage system  74  for operating hydraulic motor  70 . Examples of such a power supply are hydraulic pumps and hydraulic accumulators which may be mounted on, or integrated with, the motor itself or mounted in any suitable location and coupled to the motor by hydraulic fluid lines. Controller  66  controls hydraulic motor operation in a manner appropriate to the particular motor, such as by control of stroke or displacement. 
     Hydraulic motor  70  may also at times be operated as a pump that provides energy recovery during vehicle braking, analogous to the energy recovery from electric motor  52 , except that hydraulic fluid is pumped into the hydraulic energy storage system. 
       FIG. 6  shows a fifth embodiment that differs from the one of  FIG. 5  in that hydraulic motor  70  is integrated with drive axle  36  as an in-line motor for directly driving both driven wheels  38 , 40 . 
       FIG. 7  shows a seventh embodiment that differs from the one of  FIG. 6  in that hydraulic motor  70  is integrated with drive axle  36  as an in-line motor for directly driving one of the driven wheels  38 ,  40  while an additional hydraulic motor  76  is integrated with drive axle  36  as an in-line motor for directly driving the other of the driven wheels  38 ,  40 . Each motor  70 ,  76  is powered by hydraulic power supply  74  and independently controlled by controller  66 . 
       FIG. 8  shows a truck vehicle chassis  10  that is like the one shown in  FIG. 1  except for tandem rear axle  28  having dual right wheels and dual left wheels on each axle  30 ,  36 , a common architecture for Class 8 trucks. 
     Because the two driven axles of the disclosed tandem axle are driven from different power sources, the disclosed tandem axle may provide improved fuel economy by the elimination of friction that might occur between the axles that are directly coupled due to tire rotational mismatch. Certain existing tandem rear axle truck vehicles can be modified to one of the disclosed tandem axle embodiments without significantly disturbing the configuration of the existing engine, transmission, drive shaft, and first drive axle. The ability to associate an electric motor or a hydraulic motor with a second drive axle can even be accomplished in a short wheel base truck vehicle. 
     The disclosed hybrid tandem axle provides a redundant traction drive for a truck vehicle because a failure of one prime mover or its drive axle does not necessarily affect the ability of the other prime mover and its drive axle to propel the vehicle. Furthermore, a truck vehicle can operate using the second drive axle alone thereby avoiding the need to use the combustion engine in certain situations. 
     In each of the disclosed embodiments, the second drive axle  36  can provide not only traction drive for propelling the truck vehicle but when a driver applies service brakes, the second drive axle can be used for regenerative braking. This affords the opportunity for different modes of braking as well as different modes of propulsion. 
     When a driver applies service brakes of the vehicle in a first mode of tandem rear axle braking, only the service brakes of wheels  32 ,  34  are applied without any regenerative braking of wheels  38 ,  40 . In a second mode, the service brakes of wheels  32 ,  34  are applied concurrent with regenerative braking of wheels  38 ,  40 . In a third mode only regenerative braking of wheels  38 ,  40  occurs.