Abstract:
A bearing arrangement includes a bearing outer element that defines a first plurality of races opening radially inwardly, a bearing inner element that defines a second plurality of races opening radially outwardly, and a bearing middle element defining a third plurality of races at its radially outer surface thereof and a fourth plurality of races at its radially inner surface thereof. Rolling elements are receivable in the races. The bearing middle element includes an axial protrusion at least at one end thereof that can be received in a housing with respect to which the bearing outer and inner elements are rotatable.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The automotive industry is increasingly focusing on reducing parasitic losses in power transmission systems to improve fuel economy. One way to achieve such a reduction is to transform each system powered by an engine belt so that it can be turned on and off as needed. This is often accomplished by multiple bearings and clutches. For example, in a water pump application, having an “off” setting is beneficial during initial operation of an engine to permit heating of the engine to a steady operational temperature more quickly so that the engine burns fuel more efficiently. 
     Packaging, thermal expansion, and assembly stack-up tolerances create issues for the design and manufacture of a clutched system in various applications. These issues are addressed by the present invention. 
     2. Description of Related Art 
     Bearings involved in clutched water pumps, which involve relatively new technology, are similar to bearings used in compressors, which involve mature technology. Typically, one bearing, or a set of bearings, is used to support a shaft that rotates an impeller blade in a water pump, while another bearing, or another set of bearings, is used to allow an engine pulley to rotate. A clutch system connects the shaft to the pulley, allowing them to rotate together. When the clutch is disengaged, the pulley bearing rotates along with the engine, but the shaft bearing of the water pump does not rotate. 
     Current bearing assemblies typically require multiple layers to work perfectly with each other for ideal function. The layers typically required for a clutched water pump include a pulley bearing outer ring, a rolling element layer, a pulley bearing inner ring, an aluminum pump housing, a shaft bearing outer ring, another rolling element layer, and a shaft. For other applications, there may also be a bearing inner ring between the innermost rolling elements and the shaft. 
     SUMMARY OF THE INVENTION 
     Certain issues are addressed by way of the present invention, which combines two sets of bearings into one layered set. As will be described, a bearing design according to the invention eliminates two layers, requiring only a bearing outer ring, a rolling element layer, a bearing middle ring, another rolling element layer, and a shaft. 
     In clutched water pump and compressor systems, concentricity control of pulley bearings relative to shaft bearings is a concern. In such a system, the clutch rotates about the axis created by the pulley and pulley bearing. When the clutch is active, the shaft in the water pump bearing will also be rotating, ideally on the same axis. If the two bearings are not concentric on the same axis, the shaft will be forced to tilt back and forth as it is rotated off-center by the clutch. Concentricity control is improved according to the invention, since, with the new design, the two bearings are combined, allowing for dimensional monitoring and adjustment at the time of bearing production. The bearing system is also built as one unit, and does not depend on press-fit connections with another material source, which are complicated by thermal effects. 
     Complying with design envelope constraints for the bearings is also a concern in water pump systems. It is less of an issue in compressor systems, since, in compressor systems, design envelope constraints on space and function generally allow the shaft to be placed between two small single-row bearings with no cantilever, and the compressor configuration typically allows the single-row bearings to be placed rearward of the pulley bearing so that there is no sandwiched layer of pump housing material. In a clutched water pump, an impeller blade is cantilevered from the shaft in the water pump bearing. Due to pump housing design and design envelope space, the water pump bearing has to fit inside the clutch pulley bearing inner diameter with enough extra space for a housing layer between the two bearings. 
     Design envelope constraint compliance for the bearing set is improved with the new design. Current technology requires a pump housing wall thickness of 6 millimeters or greater for aluminum housings. Elimination of the pump wall layer saves 6 millimeters per side for a total of at least 12 millimeters on the diameter. Combining the outer race of the shaft bearing and the inner race of the pulley bearing into one race results in further space efficiency, potentially reducing the packaging space another 3 millimeters or more. Combined space efficiencies can reduce total required packaging space by 15 millimeters or more. 
     Thermal expansion of the system is an additional concern. Typically, pump housings are made of aluminum to save vehicle weight. Aluminum expands at a different rate than steel as the pump water increases in temperature. This characteristic causes changes in the press or slip fits of the bearings to the aluminum housing and affects the bearing radial internal clearances of each bearing at different rates. Thermal expansion concerns are addressed by the new design. The expansion rate of aluminum relative to steel no longer affects the radial internal clearance of the bearing combination. Reducing this variance leads to more control over system life and location stability for clutch components, seals, and impellers. Each of these characteristics is affected by the bearing&#39;s internal clearance. 
     Analogous conventional bearings consist of two rings of metal forming inner and outer races. The rings are separated by rolling elements. By way of this invention, the need for two bearings, and a total of four rings, is eliminated; instead, one bearing, and a total of three rings, can be used. This allows for smaller packaging space and better manufacturing control of the manner in which the rolling elements act relative to each other. Better control of radial internal clearance, shaft tilt, and free rock can also be maintained. One application of this bearing would provide benefit to a clutch system by maintaining better angular control between a clutch plate and a pulley. By having the bearing elements self-contained in one package, negative effects of multiple interfaces and thermal expansion are also reduced. 
     Although the focus of this disclosure may appear to be on water pump applications, this technology can be used in any application requiring concentric bearings to provide inner and outer ring rotation and a stationary middle section. The invention is also applicable, for example, to pulleys, fans, and other elements involving engagement and disengagement functions. 
     In a particular configuration of the invention, a bearing arrangement includes a bearing outer element that defines a first plurality of races opening radially inwardly, a bearing inner element that defines a second plurality of races opening radially outwardly, and a bearing middle element defining a third plurality of races at its radially outer surface thereof and a fourth plurality of races at its radially inner surface thereof. Rolling elements are receivable in the races, and the bearing middle element includes an axial protrusion at least at one end thereof that can be received in a housing with respect to which the bearing outer and inner elements are rotatable. 
     The bearing outer and middle elements are rings in this configuration, while the bearing inner element is a shaft. The axial protrusion may have a flat surface defined thereon to prevent rotation of the bearing middle element relative to the housing. A press fit may be used to connect the axial protrusion within an opening of the housing, and the axial protrusion may also include a groove at a distal end thereof to receive a retaining ring that secures the axial protrusion within an opening of the housing. The third and fourth pluralities of races are offset relative to one another in an axial direction for compact construction, and the axial protrusion defines a circumferentially extending wall against which the housing is abuttable upon reception of the end of the axial protrusion in the housing. 
     A process of securing the bearing arrangement to the housing is also disclosed. 
     The resulting two-level bearing configuration thus has an outer race, a rolling element layer, a middle race, another rolling element layer, and an inner race, which may be formed by the shaft. The bearing levels or layers are separated by two rows of rolling elements. By holding the middle race or layer fixed in the housing, both the outer ring and the shaft are free to rotate independently of each other. The outer ring and the shaft can be made to run simultaneously when a clutch mechanism is applied between a hub pressed on the shaft and a pulley pressed on the outer ring. The design will also use grease, seals, and, optionally, two rubber O-rings, although these portions of the design are not considered new developments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view, partly in cross section, of a conventional bearing configuration. 
         FIG. 2  is a view, similar to that of  FIG. 1 , showing a bearing configuration according to the invention. 
         FIG. 3  is an enlarged view of a part of the conventional configuration of  FIG. 1  with section lines omitted for clarity. 
         FIG. 4  is an enlarged view similar to that of  FIG. 3  but of the bearing configuration shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of the conventional bearing configuration shown in  FIGS. 1 and 3  will first be provided in order to facilitate an understanding of the advantages provided by the invention. 
     The conventional bearing configuration illustrated in  FIGS. 1 and 3  includes a first, outer bearing  10  and a second, inner bearing  12 . The outer bearing  10 , as illustrated, is composed of an outer bearing outer ring  14 , rolling elements  16 , and an outer bearing inner ring  18 . The inner bearing  12 , as illustrated, is composed of an inner bearing outer ring  20 , rolling elements  22 , and a central shaft  24 . A pump housing  26 , typically constructed of aluminum or other such material and partially illustrated in  FIGS. 1 and 3 , is interposed between the inner bearing outer ring  20  and the outer bearing inner ring  18  to support those rings. 
     As best seen in the enlarged view provided by  FIG. 3 , each of the rolling elements  16  travels within an outer bearing outer race  28  formed in the outer ring  14  and a corresponding outer bearing inner race  30  formed in the inner ring  18 . Each of the rolling elements  22 , similarly, travels within an inner bearing outer race  32  formed in the outer ring  20  and a corresponding inner bearing inner race  34  formed directly in the shaft  24 . An appropriate retainer or separator (not shown) maintains the proper spacing between adjacent rolling elements  16  and  22  of each set of rolling elements. 
     An elastomeric seal  36  is typically interposed between the pump housing  26  and the central shaft  24  to maintain separation of the pump housing interior  38  and the inner bearing  12 . 
     As shown in  FIGS. 2 and 4 , the bearing arrangement or configuration according to this invention includes a first, outer bearing  40  and a second, inner bearing  42 . The outer bearing  40 , as illustrated, is composed of a bearing outer ring  44 , rolling elements  46 , and a bearing middle ring  48 . The inner bearing  42 , as illustrated, is composed of the same bearing middle ring  48 , rolling elements  50 , and a central shaft  52 . A pump housing  66 , partially illustrated in  FIGS. 2 and 4 , is secured to the bearing middle ring  48  in a manner that will become apparent. 
     Each of the rolling elements  46  travels within an outer bearing outer race  54  formed in the bearing outer ring  44  and a corresponding outer bearing inner race  56  formed in the bearing middle ring  48 . Each of the rolling elements  50 , similarly, travels within an inner bearing outer race  58  formed in the bearing middle ring  48  and a corresponding inner bearing inner race  60  formed directly in the shaft  52 . As with the conventional configuration discussed previously, an appropriate retainer or separator (not shown) maintains the proper spacing between adjacent rolling elements  46  and  50  of each set of rolling elements. In this arrangement, an elastomeric seal  62  is interposed between the bearing middle ring  48  and the central shaft  52  to maintain separation of the interior  64  of the pump housing  66  and the inner bearing  42 . The races  58  and  58 , and thus the sets of rolling elements running therein, can be staggered relative to the races  56  and  56  on the bearing middle ring  48  in order to minimize packaging space required. As an added feature, containing the outer bearing  40  and the inner bearing  42  as one unit allows a mechanical seal  62  to be placed on the bearing when it is constructed, thereby eliminating an assembly operation for the pump assembler. 
     The bearing middle ring  48  includes an axial protrusion  68  of reduced outer diameter. When the bearing assembly is in use, that axial protrusion  68  extends into the interior  64  of the pump housing  66 . A circumferentially extending wall  70  is thus defined at the junction of the axial protrusion  68  and the remainder of the bearing middle ring  48 , and a surface  72  of the protrusion  68  extends, in the direction of the interior of the pump housing  66 , away from the circumferentially extending wall  70 . 
     The shaft, bearing rings, and rolling elements of the illustrated bearing configuration are made of SUJ-2 high chromium tool steel or other such material with suitable hardness and wear resistance characteristics. 
     The bearing outer ring  44 , rolling elements  46 , bearing middle ring  48 , rolling elements  50 , and central shaft  52  can be assembled initially to form the two-level bearing. To secure the pump housing  66  and the bearing middle ring  48  together, the distal end of the bearing middle ring  48  is press-fit into and installed to the pump housing  66  by applying pressure to that bearing middle ring only. This assembly procedure prevents the ball rows from brinelling or deforming any of the races. The assembled bearing and pump housing unit prevents leakage of coolant from the interior  64  by way of (1) the frictional press fit connection between the outer diameter of the axial protrusion  68  and the inner diameter of a corresponding protrusion receiving opening in the pump housing  66 , and (2) optionally using a seal, such as the two rubber o-rings  80  shown, between the outer surface of the axial protrusion  68  and the inner surface of the opening in the pump housing  66 . 
     After connection of the two-level bearing to the pump housing  66 , the housing  66  abuts against the wall  70  defined on the axial protrusion  68  for proper positioning. The distal end of the bearing middle ring  48  is retained in the pump housing  66  by (1) the frictional press fit connection between the outer diameter of the axial protrusion  68  and the inner diameter of a corresponding protrusion receiving opening in the pump housing  66 , and (2) optionally providing an appropriately located groove  82  in the outer diameter of the axial protrusion  68  and utilization of a retaining ring (not shown) receivable in that groove  82 . To prevent relative rotation of the bearing middle ring  48  and the pump housing  66 , a portion of the bearing middle ring can have a “D-flat” (a “D” type cross section) instead of being round. 
     By way of the construction described, the pump housing manufacturer benefits by being provided with fewer areas of the housing casting that require machining. More particularly, referring again to  FIG. 3 , the bearing-receiving portion of a conventional pump housing  26  typically requires machining to produce surfaces A, B, C, and D. As is apparent by comparing  FIGS. 3 and 4 , however, a significant reduction in machining is permitted by way of the configuration shown in  FIG. 4 , since only surfaces E and F are needed with a construction according to the present invention. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.