Abstract:
An inter-axle differential assembly comprises an input shaft, an output shaft arranged coaxially with respect to each other, differential gearing and a dedicated reversible lubrication pump disposed between the input and output shafts. The reversible gerotor type lubrication pump includes a rotor driven by the input shaft, and an impeller, both disposed within a pump body coupled to a side gear drivingly connected to the output shaft. Thus, the lubrication pump generates lubricant flow only during the differential action between the input shaft and the output shaft, i.e. only when needed and at a flow rate proportional to the speed difference across the differential assembly. An oil flow generated by the lubrication pump is supplied to various components of the inter-axle differential assembly through a gallery of fluid passages.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 09/761,724, filed on Jan. 18, 2001 now U.S. Pat. No. 6,855,083. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates broadly to inter-axle differential assemblies and, more particularly, to a dedicated lubrication pump for an inter-axle differential assembly. 
     2. Description of the Prior Art 
     Motor vehicles with solidly connected multiple drive axles are commonly equipped with an inter-axle differential assembly, commonly arranged in a vehicular transmission transfer case or tandem axle power divider to allow torque balance between the drive axles during the vehicle cornering, to compensate for tire size differences, etc., i.e. when there is any physical requirement for speed difference between the drive axles. The inter-axle differential assemblies are widely employed for tandem drive axles of heavy-duty trucks for on-and off-road service as a power divider. 
     These motor vehicles are, on occasion, driven in situations where there may be unequal traction conditions between the tires of the different drive axles. If the traction condition at any tire falls below that required for sufficient traction effort, high-speed inter-axle differential conditions may occur. These high-speed differential conditions may be potentially severely damaging to critical differential assembly components, such as shaft bearing surfaces as well as rolling contact surfaces of the differential assembly, due to lack of lubrication. 
     In such drive axles it is common to have a supply of lubricant in a transfer case or axle housing and to provide positive lubricant pressure to the input and output shaft journals and the inter-axle differential that are disposed above the level of lubricant in the housing to prevent damaging the differential gear components during these high speed differential conditions. However, current lubrication pumps for differential assemblies are driven continuously while the vehicle is in motion, although lubrication supply is only needed during occasional conditions of relatively high-speed levels of differential action as it is well known to those skilled in the art. The continuously driven lubrication pump operates and consumes engine power irrespective of the amount of lubrication needed by the shaft journals and other components of the inter-axle differential, thus causing unnecessary parasitic losses in a vehicle power transmission and increasing fuel consumption. 
     Thus it has been desired to provide a low-cost and convenient way to incorporate a lubricant pump for providing positive flow of lubricant to the shaft journals and the inter-axle differential assembly only as required. 
     SUMMARY OF THE INVENTION 
     The present invention alleviates the drawbacks of the prior art. The present invention provides an inter-axle differential assembly having a dedicated lubrication pump. The lubrication pump is drivingly coupled to two differentially rotating members of the differential assembly, and, thus, supplies lubricant only when differential action occurs. The hydraulic pump provides volumetric flow of lubricant that varies in direct proportion to the relative (or differential) rotational speed of the rotating members. 
     In accordance with the preferred embodiment of the present invention, the inter-axle differential assembly comprises an input shaft, an output shaft arranged coaxially with respect to each other, a differential gearing and the dedicated lubrication pump disposed between the input and output shafts. The lubrication pump is provided solely for the purpose of lubricating the shaft journals and the inter-axle differential gearing, and only when needed, i.e. the pump generates lubricant flow only during the differential action between the input shaft and the output shaft, and at a flow rate in proportion to the speed differential. 
     In accordance with the preferred embodiment of the present invention, the pump is of the gerotor type, and the differential is of the bevel gear type. However, other types of pumps, such as gear or vane type pumps, are within the scope of the present invention, as well as other types of differentials, such as the spur gear type. The lubrication pump includes a rotor driven by the input shaft, and a housing coupled to a side gear drivingly connected to the output shaft. An oil flow generated by the lubrication pump is supplied to the shaft journals and the inter-axle differential gearing through a gallery communicating with passages in the input and output shafts which supply lubricant to the journals for these shafts and to the inter-axle differential assembly. 
     Alternatively, the pump housing is coupled directly to the output shaft. 
     Therefore, the inter-axle differential assembly in accordance with the present invention includes the dedicated lubrication pump, compactly disposed between the input and output shafts, that lubricates the differential assembly components only when needed, thus providing better efficiency and lower fuel consumption. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings, wherein: 
         FIG. 1  is a longitudinal cross-sectional view of a tandem axle power divider that houses an inter-axle differential of the present invention; 
         FIG. 2  is a longitudinal cross-sectional view of the inter-axle differential in accordance with the first embodiment of the present invention; 
         FIG. 3  is a longitudinal cross-sectional view of a portion of the inter-axle differential in accordance with the first embodiment of the present invention showing a preferred embodiment of a gerotor lubrication pump; 
         FIG. 4  is a longitudinal cross-sectional view of a portion of the inter-axle differential in accordance with the first embodiment of the present invention showing alternative embodiment of the gerotor lubrication pump; 
         FIG. 5  is a longitudinal cross-sectional view of a portion of the inter-axle differential in accordance with the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will now be described with the reference to accompanying drawings. 
     Referring to  FIG. 1 , an inter-axle differential assembly  10  of the present invention disposed in a housing  4  of a tandem axle power divider indicated generally at  2 , is illustrated. The housing  4  is ordinarily provided with a supply of lubricant, such as lubrication oil, therein. 
     The inter-axle differential assembly  10  in accordance with the first embodiment of the present invention, illustrated in detail in  FIG. 2 , comprises an input shaft  14  rotatably supported in a bearing assembly indicated generally at  16 , a differential spider  32  drivingly coupled to the input shaft  14  and provided with a plurality of pinion gears  34  rotatably mounted thereon, a first side gear  20  and a second side gear  44  meshing with the pinion gears  34 , an output shaft  30  drivingly connected to the first side gear  20 , and a dedicated lubrication pump  50  disposed between the input shaft  14  and the output shaft  30  and solely for the purpose of lubricating components of the inter-axle differential assembly  10  during the differential action between the input shaft  14  and the output shaft  30 . 
     The input shaft  14  rotatably supported in a bearing assembly indicated generally at  16 , and has a yoke  18  attached thereto, which is adapted for receiving torque from a vehicle driveline (not shown). The differential spider  32  drivingly engages the input shaft  14  by any appropriate means, preferably through a spline connection  36 . Thus, input torque is transmitted directly to the differential spider  32 . In most applications, the number of the pinion gears  34  will be four, but the number can be as low as two and can be higher than four, although most practical applications would probably not contain more than six pinion gears. 
     The first side gear  20  is journalled in a second bearing assembly indicated generally at  22 , and has a reduced diameter pilot portion  24  of the input shaft  14  journalled therein. The first side gear  20  includes a flange portion  26  integrally formed with a sleeve portion  28 . The flange portion  26  is provided with a plurality of side gear teeth  27  formed thereon for meshing with the pinion gears  34 . The sleeve portion  28  of the first side gear  20  is drivingly coupled with the output shaft  30 . An outboard end of the output shaft  30  is adapted for connection to the rear drive axle (not shown) of the motor vehicle. 
     The second side gear  44  is rotatably mounted to the input shaft  14  by a sleeve bearing or bushing  48  for free rotation thereon. It will be appreciated that any other appropriate type of bearings, such as needle bearings, are also applicable. The second side gear  44  has a plurality of gear teeth  46  thereon engaging the pinion gears  34 . 
     A lubrication pump  50 , in accordance with the first embodiment of the present invention, is disposed between the input shaft  14  and the output shaft  30  of the inter-axle differential  10  within the sleeve portion  28  of the first side gear  20 . In the preferred embodiment, the lubrication pump  50  is a gerotor pump. 
     The reversible unidirectional flow gerotor pump  50 , well known in the prior art and illustrated in detail in  FIG. 3 , comprises a rotor  52  having a plurality of external teeth, an impeller  54  having a plurality of internal teeth which are in meshing engagement with external teeth of the rotor  52 , and a pump body  56  housing the rotor  52  and the impeller  54 . The rotor  52  is eccentrically arranged relative to the impeller  54  and is drivingly connected to the input shaft  14  through a rotor shaft  58  having a substantially smaller diameter then the pilot portion  24  of the input shaft  14 , as seen in  FIG. 2 . In general, the rotor  52  has one less tooth than the impeller  54 , such that driving of the rotor  52  will in turn cause driving of the impeller  54 . The pump body  56  is secured to the side gear  20  within its sleeve portion  28  by means of a pin  64  received in an arcuate groove  65  formed in the pump body  56 . An inlet port  60  and an outlet port  62  are formed in the pump body  56 . Relative rotation of the rotor  52  to the impeller  54  thus provides a series of variable volume chambers within pump  50 , resulting in the build up of fluid pressure and pumping of lubricant in response to relative rotation of the rotor  52  and impeller  54 , and thus in response to differential rotation between the input shaft  14  and the first side gear  20 . Obviously, volumetric flow of lubricant produced by the lubrication pump varies in direct proportion to the differential rotational speed of the input and output shafts. 
     The pump body  56  is housed within the sleeve portion  28  of the first side gear  20  and located angularly by the pin  64  in the arcuate groove  65  formed in an outer peripheral surface of the pump body  56 . The groove  65  extends angularly around 90° of the outer peripheral surface of the pump body  56 . Consequently, the pump body  56  is allowed to rotate 90° relative to the first side gear  20  depending on a relative direction of rotation of the rotor  52  with respect to the first side gear  20 . In this way, the pump body  56  exchanges positions of the inlet port  60  and the outlet port  62  relative to the first side gear  20  in order to provide a reversible pumping function. Thus, the switching of ports  60  and  62  allows the pump  50  to provide a unidirectional flow of lubricant regardless of the direction of the rotation of the rotor  52 . 
     Referring again to  FIGS. 2 and 3 , the lubricant under pressure flows from the outlet port of the lubrication pump  50  (the second port  62  in  FIG. 3 ) through a gallery of fluid passages including a passage  70  provided in the input shaft  14  to lubricate the components of the inter-axle differential  10  via a number of cross passages, such as a cross passage  72  for lubricating the sleeve bearing  48 . Additionally, the inter-axle differential assembly  10  may have supplemental lubricant delivery means, such as a splash diversion and delivery channels (not shown). 
     The inlet port  60  of the pump  50  is in fluid communication with an inlet passage  76  provided in a differential support carrier  75 , trough an inlet cross passage  78  in the sleeve portion  28  of the first side gear  20  between seal rings  80 . Alternatively, as shown in a lower portion of  FIG. 3 , pair of annular lip seals  80 ′ may be used to seal the inlet passage  76 . The inlet passage  76  is in turn fluidly connected to the supply of lubricant disposed in the housing  4  of the tandem axle power divider  2 , and may be fitted with a check valve (not shown) or an elevated oil reservoir (not shown) to aid in pump priming. 
     It will be appreciated that any other appropriate types of reversible unidirectional flow hydraulic pumps such as gear, vane or wobble pin type, well known in the prior art, are within the scope of the present invention. 
       FIG. 4  illustrates an alternative embodiment of the reversible gerotor lubrication pump used in the inter-axle differential assembly  10  in accordance with the first embodiment of the present invention. An inboard end  15  of the input shaft  14  is rotatably supported in the sleeve portion  28  of the first side gear  20 . A dedicated lubrication pump  150 , preferably a conventional gerotor pump of reversible unidirectional flow type, is disposed within the sleeve portion  28  of the first side gear  20  adjacent to the inboard end  15  of the input shaft  14 . The lubrication gerotor pump  150  comprises a rotor  152 , an impeller  154 , and a port plate  157  having a first port  160  and a second port  162 . The rotor  152  is drivingly connected to the input shaft  14  through a rotor shaft  158 . An outlet passage  163  is formed within the tubular rotor shaft  158 . 
     The lubricant under pressure flows from the outlet port  162  of the lubrication pump  150  through the passage  170  drilled in the input shaft  14  to lubricate the components of the inter-axle differential  10  via a number of cross passages, such as cross passages  72 . 
     The port plate  157  is located angularly by a pin  164  in an arcuate groove  165  formed on an outer peripheral surface of the port plate  157 . The groove  165  is angularly extended around an outer peripheral surface of the port plate  157  to approximately 180°. Consequently, the port plate  157  is allowed to rotate 180° relative to the first side gear  20  depending on a relative direction of rotation of the pump rotor  152  with respect to the first side gear  20 . In this way, the port plate  157  exchanges positions of the inlet port  160  and the outlet port  162  relative to the first side gear  20  in order to provide a reversible pumping function. Thus, the switching of the ports  160  and  162  allows the pump  150  to provide a unidirectional flow of lubricant regardless of the direction of the rotation of the rotor  152 . 
     The inlet port  160  of the pump  150  is in fluid communication with the inlet passage  76  provided in the differential support carrier  75 , trough an inlet cross passage  78  in the sleeve portion  28  of the first side gear  20  between seal rings  80 . Alternatively, as shown in a lower portion of the  FIG. 4 , pair of annular lip seals  80 ′ may be used to seal the inlet passage  76 . It will be appreciated that any other appropriate sealing device for sealing the inlet passage  76  is within the scope of the present invention. The inlet passage  76  is fluidly connected to the supply of lubricant disposed in the housing  4  of the tandem axle power divider  2 , and may be fitted with a check valve (not shown) or an elevated oil reservoir (not shown) to aid in pump priming. 
     In accordance with the second embodiment of the present invention, illustrated in  FIG. 5 , an inboard end  215  of an input shaft  214  is rotatably supported in a tubular inboard end  231  of an output shaft  230 . A dedicated lubrication pump  250 , preferably of conventional reversible unidirectional gerotor type, is disposed within the tubular inboard end  231  of the output shaft  230  adjacent to the inboard end  215  of the input shaft  214 . The lubrication gerotor pump  250  comprises a rotor  252 , an impeller  254 , and a port plate  257  having an inlet port  260 . The rotor  252  is drivingly connected to the input shaft  214  through a rotor shaft  258 . An outlet port  262  is provided as a passage within the tubular rotor shaft  258 . 
     The lubricant under pressure flows from the outlet port  262  of the lubrication pump  250  through a passage  270  drilled in the input shaft  214  to lubricate the components of the inter-axle differential  10  via a number of cross passages, such as cross passages  272 . The inlet port  260  of the pump  250  is in fluid communication with an inlet passage  276  provided in a differential support carrier  275 , trough an inlet cross passage  178  in the tubular inboard end  231  of the output shaft  230  between seal rings  280 . Alternatively, as shown in a lower portion of the  FIG. 5 , pair of annular lip seals  280 ′ may be used to seal the inlet passage  276 . It will be appreciated that any other appropriate sealing device for sealing the inlet passage  276  is within the scope of the present invention. The inlet passage  276  is fluidly connected to the supply of lubricant disposed in the housing  4  of the tandem axle power divider  2 , and may be fitted with a check valve (not shown) or an elevated oil reservoir (not shown) to aid in pump priming. 
     Therefore, a novel arrangement of the inter-axle differential assembly in accordance with the present invention including the dedicated lubrication pump provides a compact, efficient and low-cost solution for lubricating components of the inter-axle differential assembly only when needed. The present arrangement of the inter-axle differential assembly substantially reduces parasitic losses associated with powering lubrication pumps. 
     The foregoing description of the preferred embodiments of the present invention has been presented for the purpose of illustration in accordance with the provisions of the Patent Statutes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments disclosed hereinabove were chosen in order to best illustrate the principles of the present invention and its practical application to thereby enable those of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated, as long as the principles described herein are followed. Thus, changes can be made in the above-described invention without departing from the intent and scope thereof. It is also intended that the scope of the present invention be defined by the claims appended thereto.