Abstract:
An electric wheel motor cooling system includes first and second electric wheel motors and gear reducers which use hydraulic fluid for cooling and lubrication. Each of the electric wheel motor housings includes a sump and a scavenge pump for return of hydraulic fluid to the hydraulic fluid reservoir. A remotely located hydraulic pump interconnected with the hydraulic fluid reservoir supplies and powers first and second locally located hydraulic motors which supply the electric motors and gears with an equal flow of lubricating and cooling oil. The first and second hydraulic motors, in turn, drive a common output shaft which, in turn, drives first and second scavenge pumps. The first and second scavenge pumps have a higher fluid flow rate than the hydraulic motors ensuring that oil is removed from the first and second electric wheel motor housings thus eliminating any churning losses of the motors or gears.

Description:
FIELD OF THE INVENTION 
     The invention is in the field of wheel motors and gearboxes which drive an electric vehicle. 
     BACKGROUND OF THE INVENTION 
     Electric wheel drive systems used in off-highway machinery require a flow of coolant such as hydraulic oil to maintain an optimum operating temperature. Oil cooling is advantageous because it can provide both cooling and lubrication. Since churning losses can reduce efficiency, especially at higher speeds, dry sump systems are a preferred approach for implementing these cooling and lubrication systems. 
     Implementation of a dry sump system in a simple form requires providing a supply and a scavenge pump at each wheel motor site and providing a means for powering these pumps. To simplify the systems, the required pumps can be ganged together so that a single power source can be used, but providing this power source and controlling it adds complexity and is undesirable. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is to facilitate construction of an electric wheel drive system that can be installed on a vehicle with minimal interface and connectivity requirements. The key aspect of this invention is that the power source for the dry sump system is provided by the cooling and lubricating fluid which is supplied from a remotely mounted reservoir and pump. With this arrangement the dry sump components can be mounted near the electric drives (for example packaged within a common axle housing) and the entire assembly can be cooled and lubricated via a single supply and return line. 
     The system described in this invention performs two functions. It divides the supply fluid for distribution to the wheel drive sites and it provides a means to use the energy in the fluid supply to drive one or more scavenge pumps as needed to assure that fluid levels in the sumps are kept away from rotating components. 
     A flow divider provides parallel flow to a set of constant displacement motors that have their drive shafts connected together. The output flow from the motors will be split in direct ratio to the motor displacements (e.g. for two equal displacement pumps the flow will be evenly split). In addition to splitting the flow, these motors can now be used to drive one or more scavenge pumps that form the remainder of the system. 
     In one example, tandem positive displacement motors are used to power two scavenge pumps in housings that form an axle. The tandem positive displacement motors divide the flow equally to each wheel motor and provides power to the scavenge pumps. The two positive displacement motors are combined with the two scavenge pumps into a single four-section unit. The four section unit shares a common shaft and has common motor inlets and pump outlets to minimize the number of fluid connections. 
     Hydraulic motors and pumps intended for high pressure use (e.g. 2000 to 5000 PSI) are built with tight fitting, tight tolerance parts. In particular, the side clearances on the gears have tight tolerances. The tight tolerances are needed to maintain low leakage across the hydraulic units at the high pressures being used. However their tight fits also result in high frictional losses. 
     At very high pressures, the frictional losses are acceptable relative to the power levels (pressure×flow rate). At the lower pressure levels (several hundred psi) being used for cooling and lubrication herein, the losses resulting from these tight fits is very high relative to the useful work being done. Therefore hydraulic units with looser fits (more side clearance on the gears, etc.) and lower frictional losses would be more appropriate for these lower pressure applications. 
     Losses in the cooling and lubrication system are not an insignificant issue. These losses may be on the order of 1 kW each for the axles and the generator in a typical off-highway machine. This is large relative to the overall drive train power levels that are on the order of 200 kW. This is of particular concern for a system that has a primary purpose of improving efficiency. 
     An important aspect of the invention is that the supply pump is not part of the common shaft system. Instead, the supply pump (which also provides the power for the system, namely, the hydraulic motors and the scavenge pumps) is remotely located from the axle assembly; for example, the supply pump is a part of the engine-driven accessories. 
     There are a wide variety of hydraulic pumps and motors that can be used in the invention. 
     It is an object of the invention to provide a simple and flexible method for managing the cooling and lubricating system for vehicles incorporating one or more electric drive axles. 
     It is an object of the invention to provide an electric wheel motor cooling system which minimizes the usage of space near the wheel motors. 
     It is an object of the invention to provide an electric wheel motor cooling system which is also used for cooling a gear reducer located in proximity to the electric wheel motors. 
     It is an object of the invention to provide an electric wheel motor cooling system which employs a remotely located pump which drives locally mounted constant displacement hydraulic motors which divide the flow of hydraulic fluid equally between the electric wheel motors and gear reducers. 
     It is an object of the invention to provide an electric wheel motor cooling system which employs a remotely located pump which drives locally mounted constant displacement hydraulic motors which drive one or more locally mounted scavenge pumps. 
     It is an object of the invention to provide an electric wheel motor cooling system which employs one or more locally mounted scavenge pumps which remove cooling and lubrication oil from the electric wheel housings and returns it to the hydraulic oil reservoir. 
     It is an object of the invention to provide an electric wheel motor cooling system which employs a remotely located pump which drives locally mounted constant displacement hydraulic motors which drive one or more locally mounted scavenge pumps, and, the scavenge pumps have a pumping flow capacity greater than the constant displacement hydraulic motors ensuring that the scavenge sumps are evacuated and that hydraulic fluid is removed and does not impede the rotation of the electric motors and/or the gear reducer. 
     It is an object of the invention to provide an electric wheel motor cooling system wherein locally mounted constant displacement hydraulic motors are coupled together such that they rotate together. 
     It is an object of the invention to provide an electric wheel motor cooling system which employs a remotely located pump which drives locally mounted constant displacement hydraulic motors which are coupled and rotate together which, in turn, are coupled to one or more scavenge pumps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross section of an axle illustrating the first and second scavenge sumps located in the first and second wheel motor housings and the first and second scavenge pumps removing hydraulic fluid therefrom. 
         FIG. 2  is a cooling system schematic for a single axle with lubrication and cooling fluid supplied from a reservoir by a first supply pump, and the lubrication and cooling fluid is subsequently divided between first and second wheel motors by a first constant displacement hydraulic motor and a second constant displacement hydraulic motor, a first scavenge pump (powered by the first constant displacement hydraulic motor and the second constant displacement hydraulic motor) associated with a first sump of the first wheel motor returns fluid to the reservoir, and a second scavenge pump (powered by the first constant displacement hydraulic motor and the second constant displacement hydraulic motor) associated with a second sump of the second wheel motor returns fluid to the reservoir. 
         FIG. 3  is a cooling system schematic for a single axle with lubrication and cooling fluid supplied from a reservoir by a first supply pump, and the lubrication and cooling fluid is subsequently divided between first and second wheel motors by a first constant displacement hydraulic motor and a second constant displacement hydraulic motor, and a common scavenge pump powered by the first and second hydraulic motors, the common scavenge pump fed from the sumps of the first and second wheel motors and returning fluid to the reservoir. 
         FIG. 4  is a cooling system schematic similar to  FIG. 2  illustrating, among other things, first and second axles with: lubrication and cooling fluid supplied to the first axle from a reservoir by a first supply pump, and, lubrication and cooling fluid supplied to the second axle from a reservoir by a second supply pump;  FIG. 4  further illustrates: a first coupling interconnecting first and second hydraulic motors associated with the first axle with first and second scavenge pumps; and, a second coupling interconnecting third and fourth hydraulic motors associated with the second axle with third and fourth scavenge pumps. 
         FIG. 5  is a cooling system schematic similar to  FIGS. 1 and 4  illustrating, among other things, first and second axles with: lubrication and cooling fluid supplied to the first axle from a reservoir by a first supply pump, and, lubrication and cooling fluid supplied to the second axle from a reservoir by a second supply pump. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic cross section  100  of an axle illustrating the scavenge sumps and the scavenge pumps for removal of the lubricating and cooling oil from the first wheel motor housing  104  and the second wheel motor housing  105 .  FIG. 1  illustrates centrally located housing  101  in an axle between the first wheel motor  104 M and the second wheel motor  105 M. Intermediate housing  102  resides between the centrally located housing  101  and the first wheel housing  104 . Intermediate housing  103  resides between the centrally located housing  101  and the second wheel housing  105 . First wheel housing  104  includes the first wheel motor  104 M and the first wheel housing scavenge sump  104 S. Second wheel housing  105  includes second wheel motor  105 M and the second wheel housing scavenge sump  105 S. Conduit  212  for conveying fluid from the sump  104 S to the housing  108  for scavenge pumps  204 ,  205 . Conduit  215  for conveying fluid from the sump  105 S to the housing  108  for scavenge pumps  204 ,  205 . 
       FIG. 1  also illustrates a gear reducer for reducing the speed of the driven wheel and increasing the torque to the driven wheel. The gears of the gear reducer, the bearings of the gear reducer, the bearings of the electric motor, and the electric motor all require lubrication and cooling oil. 
       FIG. 2  is a cooling system schematic  200  for a single axle with lubrication and cooling fluid  299  supplied from a reservoir  210  by a first supply pump  201 , and the lubrication and cooling fluid  299  is subsequently divided between first wheel motor  104 M and second wheel motor  105 M by a first constant displacement hydraulic motor  202  and a second constant displacement hydraulic motor  203 , a first scavenge pump  204  (powered by the first constant displacement hydraulic motor  202  and the second constant displacement hydraulic motor  203 ) associated with a first sump  104 S of the first wheel motor  104 M returns fluid to the reservoir  210 , and a second scavenge pump  205  (powered by the first constant displacement hydraulic motor  202  and the second constant displacement hydraulic motor  203 ) associated with a second sump  105 S of the second wheel motor  105 M returns fluid to the reservoir  210 . The first supply pump  201  can be located near the vehicle engine (not shown) thus saving space near the wheel motors  104 M,  105 M. 
     Referring to  FIG. 2 , one of the important aspects of the invention is that a pair of constant displacement hydraulic motors  202 ,  203  coupled together by a common shaft  202 D is used as a flow divider to supply electric motors  104 M,  105 M on both sides of an axle while simultaneously providing a drive means for a pair of scavenge pumps  204 ,  205 . An important aspect of the invention is that the supply pump  201  is not part of the common shaft system. Instead, the supply pump  201  (which also provides the power) is remotely located from the axle assembly; for example, the supply pump is a part of the engine-driven accessories. 
     Feed line  213  communicates hydraulic fluid from first constant displacement hydraulic motor  202  to first wheel motor  104 M. Feed line  214  communicates hydraulic fluid from first constant displacement hydraulic motor  203  to first wheel motor  105 M. 
     Still referring to  FIG. 2 , the supply pump suction line  201 S feeds oil  299  from oil (hydraulic fluid) reservoir  210  to the pump  201 . Interconnecting line  201 L communicates oil flow between supply pump  201  and header  211 . Header  211  supplies branch line  202 L interconnecting header  211  and constant displacement hydraulic motor  202  and header  211  also supplies branch line  203 L interconnecting header  211  and constant displacement hydraulic motor  203 . Hydraulic motors  202 ,  203  receive equal flow from their respective branch lines  202 L,  203 L at equal pressure dividing the flow from pump  201  to supply the lubrication needs of motors  104 M,  105 M. Hydraulic motors  104 M,  105 M are not immersed in lubricating oil thus there are no churning losses due to oil in the motor housings  104 ,  105 . Similarly, the associated gear reducers are not immersed in oil. 
     Drive link  202 D between the first constant displacement hydraulic motor  202  and the second constant displacement hydraulic motor  203  couples the constant displacement hydraulic motor together. Drive link  204 D between constant displacement hydraulic motor  203  and scavenge pump  204  is illustrated in  FIG. 2 . Drive link  204 D drives scavenge pumps  204 ,  205 . Arrows on the motors  202 ,  203  indicate the direction of flow therein. Arrows on the pumps  204 ,  205  indicate the direction of flow therein. 
     Feed line  212  conveys hydraulic fluid (oil) from the first constant displacement hydraulic motor  202  to the first wheel motor  104 M. Feed line  214  conveys hydraulic fluid (oil) from the second constant displacement hydraulic motor  203  to the second wheel motor  105 M. 
     Drive link  205 D couples the first scavenge pump  204  and the second scavenge pump  205  together. First and second scavenge pumps  204 ,  205  are driven by link  204 D powered by motors  202 ,  203 . Hydraulic motors  202 ,  203  and scavenge pumps  204 ,  205  include unnumbered arrows which indicate the direction of the hydraulic oil flow. The unnumbered arrows are used in  FIGS. 2-5 . 
     Still referring to  FIG. 2 , suction line  212  conveys hydraulic oil (fluid) from first wheel housing scavenge sump  104 S to scavenge pump  204  and suction line  215  conveys hydraulic oil (fluid) from second wheel housing scavenge sump  105 S to scavenge pump  205 . Discharge header  206  is fed from scavenge pump  204  discharge line  204 L and from scavenge pump  205  discharge line  205 L. Return line  217  conveys hydraulic fluid from the discharge header  206  to the reservoir  210 . Hydraulic pump  218  is fed from reservoir  210  and pumps hydraulic oil into and through hydraulic cooler  219  and through return line  220 . 
       FIG. 3  is a cooling system schematic  300  for a single axle with lubrication and cooling fluid  299  supplied from a reservoir  210  by a first supply pump  201 , and the lubrication and cooling fluid  299  is subsequently divided between first and second wheel motors  104 M,  105 M by a first constant displacement hydraulic motor  202  and a second  203  constant displacement hydraulic motor, common scavenge pump  204  powered by the first and second hydraulic motors  202 ,  203 , the common scavenge pump  204  fed from the sumps  104 S,  105 S of the first  104 M and second  105 M wheel motors and returning fluid  299  to the reservoir  210 . 
     Still referring to  FIG. 3 , housing  108 A illustrates flow dividing constant displacement hydraulic motors  202 ,  203  and common scavenge pump  204 . A common suction line  220 C feeds scavenge pump  204 . Common suction line  220 C is fed by suction lines  220 L,  220 R from sumps  104 S,  105 S. Discharge line  220 D of scavenge pump  204  leads to oil reservoir  210 . Suction line  220 L from first wheel housing scavenge sump  104 S supplies oil to scavenge pump common line  220 C and suction line  220 R from second wheel housing scavenge sump  105 S supplies oil to scavenge pump common line  220 C in  FIG. 3 . 
       FIG. 4  is a cooling system schematic  400  similar to  FIG. 2  illustrating, among other things, first  401  and second  402  axles with: lubrication and cooling fluid  299  supplied to the first axle  401  from the reservoir  210  by a first supply pump  201 , and, lubrication and cooling fluid  299  supplied to the second axle  402  from the reservoir  210  by a second supply pump  201 A. Second supply pump  201 A is preferably located near the vehicle engine in the example of  FIGS. 4 and 5 . Interconnecting line  201 M conveys fluid between supply pump  201 A and header  211 . First supply pump  201  is preferably located near the vehicle engine (which can be an internal combustion engine) in the examples of  FIGS. 1-5 . 
       FIG. 4  further illustrates a first coupling  203 C associated with a first axle  401 . Specifically,  FIG. 4  further illustrates a first coupling  203 C interconnecting first and second scavenge pumps  204 ,  205  with motors  202 ,  203 . A second coupling  213 C interconnects third and fourth hydraulic motors  202 A,  203 A associated with the second axle  402  with third and fourth scavenge pumps  204 A,  205 A. See  FIG. 4 . Axles  401 ,  402  illustrated in  FIG. 4  are each operated as described hereinabove in regard to  FIG. 2 . Couplings  203 C,  213 C are the functional equivalent of the link  204 D illustrated in  FIG. 2 . 
     The structure and function of the axles  401 ,  402  are identical. Different reference numerals are used for the motors  202 A,  203 A and the scavenge pumps  204 A,  205 A to differentiate between axles  401 ,  402 . Reference numeral  217 A is used for the return line from axles  402  in  FIG. 4  and  FIG. 5 . 
       FIG. 5  is a cooling system schematic  500  similar to  FIGS. 1 and 4  illustrating, among other things, first  401  and second  402  axles with: lubrication and cooling fluid  299  (hydraulic oil) supplied to the first axle  401  from the reservoir  210  by a first supply pump  201 , and, lubrication and cooling fluid  299  supplied to the second axle  402  from a reservoir by a second supply pump  201 A.  FIG. 5  is substantially similar to  FIG. 4  with the exception that links  403 ,  404  other than couplings  203 C,  213 C are used to drive the scavenge pumps  204 ,  205 . 
     Those of skill in the art will recognize that the invention has set forth by way of examples only and that changes may be made to the invention as set forth herein without departing from the spirit and scope of the invention as set forth in the claims. 
     REFERENCE NUMERALS 
     
         
           100  diagrammatic cross section of an axle illustrating a pumping network for the distribution of lubricating oil between first and second wheel motors. 
           101  centrally located housing in an axle between the first wheel motor and the second wheel motor 
           102  intermediate housing between the centrally located housing  101  and the first wheel housing  104   
           103  intermediate housing between the centrally located housing  101  and the second wheel housing  104   
           104  first wheel housing 
           104 M first wheel motor 
           104 S first wheel housing scavenge sump 
           105  second wheel housing 
           105 M second wheel motor 
           105 S second wheel housing scavenge sump 
           108  housing for flow dividing constant displacement hydraulic motors  202 ,  203  and for scavenge pumps  204 ,  205   
           108 A housing for flow dividing constant displacement hydraulic motors  202 ,  203  and for common scavenge pump  204   
           200  cooling system schematic for a single axle with lubrication and cooling fluid supplied from a reservoir by a first supply pump, and the lubrication and cooling fluid is subsequently divided between first and second wheel motors by a first constant displacement hydraulic motor and a second constant displacement hydraulic motor, a first scavenge pump (powered by the first constant displacement hydraulic motor and the second constant displacement hydraulic motor) associated with a first sump of the first wheel motor returns fluid to the reservoir, and a second scavenge pump (powered by the first constant displacement hydraulic motor and the second hydraulic motor) associated with a second sump of the second wheel motor returns fluid to the reservoir. 
           201  first supply pump which can be located near the vehicle engine 
           201 A second supply pump which can be located near the vehicle engine in  FIGS. 4 and 5   
           201 L interconnecting line between supply-pump  201  and header  211   
           201 M interconnecting line between supply-pump  201 A and header  211   
           201 S supply pump suction line from oil (hydraulic fluid) reservoir  210   
           202  first constant displacement hydraulic motor 
           202 A third constant displacement hydraulic motor 
           202 D drive link between the first constant displacement hydraulic motor  202  and the second constant displacement hydraulic motor  203   
           202 L branch line interconnecting header  211  and constant displacement hydraulic motor  202   
           203  second constant displacement hydraulic motor 
           203 A fourth constant displacement hydraulic motor 
           203 C coupling between the constant displacement hydraulic motors  202 ,  203  and the scavenge pumps  204 ,  205  in  FIG. 4   
           203 D drive link between constant displacement hydraulic motor  203  and scavenge pump  204  in  FIG. 2   
           203 L branch line interconnecting header  211  and constant displacement hydraulic motor  203   
           204  first scavenge pump 
           204 A third scavenge pump 
           204 D drive link between constant displacement hydraulic motors  202 ,  203  and scavenge pumps  204 ,  205   
           204 E drive link between constant displacement hydraulic motors  202 ,  204  and scavenge pumps  204 ,  205   
           204 F drive link between constant displacement hydraulic motors  202 A,  203 A and scavenge pumps  204 A,  205 A 
           205  second scavenge pump 
           205 A fourth scavenge pump 
           205 D drive link between the first scavenge pump  204  and the second scavenge pump  205   
           206  discharge header fed from scavenge pump  204  discharge line  204 L and from scavenge pump  205  discharge line  205 L 
           210  oil (hydraulic fluid) reservoir 
           211  header feeding line  202 L and first constant displacement hydraulic motor  202  and feeding line  203 L and second constant displacement hydraulic motor  203   
           212  suction line from first wheel housing scavenge sump  104 S to scavenge pump  204   
           213  feed line from first constant displacement hydraulic motor  202  to first wheel motor  104 M 
           214  feed line from first constant displacement hydraulic motor  203  to first wheel motor  105 M 
           213 C coupling between the constant displacement hydraulic motors  202 A,  203 A and the scavenge pumps  204 A,  205 A in  FIG. 4   
           215  suction line from second wheel housing scavenge sump  105 S to scavenge pump  205   
           217  return line from the discharge header  206  to the reservoir  210   
           217 A return line in the example of  FIGS. 4 and 5   
           218  hydraulic pump from fed from reservoir  210  and pumping into and through cooler  219   
           219  hydraulic cooler 
           220  return line from hydraulic cooler  219  to reservoir  210   
           220 C common suction line for scavenge pump  204  fed by suction lines  220 L,  220 R from sumps  104 S,  105 S 
           220 D discharge line of scavenge pump  204  in  FIG. 3  leading to reservoir  210   
           220 L suction line from first wheel housing scavenge sump  104 S to scavenge pump common line  220 C in  FIG. 3   
           220 R suction line from second wheel housing scavenge sump  105 S to scavenge pump common line  220 C in  FIG. 3   
           299  hydraulic fluid in the reservoir  210   
           300  cooling system schematic for a single axle with lubrication and cooling fluid supplied from a reservoir by a first supply pump, and the lubrication and cooling fluid is subsequently divided between first and second wheel motors by a first constant displacement hydraulic motor and a second constant displacement hydraulic motor, and a common scavenge pump powered by the first and second hydraulic motors, the common scavenge pump fed from the sumps of the first and second wheel motors and returning fluid to the reservoir. 
           400  cooling system schematic similar to  FIG. 2  illustrating, among other things, first and second axles with: lubrication and cooling fluid supplied to the first axle from a reservoir by a first supply pump, and, lubrication and cooling fluid supplied to the second axle from a reservoir by a second supply pump;  FIG. 4  further illustrates: a first coupling interconnecting first and second hydraulic motors associated with the first axle with first and second scavenge pumps; and, a second coupling interconnecting third and fourth hydraulic motors associated with the second axle with third and fourth scavenge pumps. 
           401  first axle 
           402  second axle 
           500  cooling system schematic similar to  FIGS. 1 and 4  illustrating, among other things, first and second axles with: lubrication and cooling fluid supplied to the first axle from a reservoir by a first supply pump, and, lubrication and cooling fluid supplied to the second axle from a reservoir by a second supply pump.