Abstract:
A bearing assembly which couples a road wheel to a suspension system component on an automotive vehicle includes a hub to which the wheel is attached and a housing which is attached to the suspension system component. The housing has two tapered raceways which surround raceways on cones that are fitted to the hub. Organized in two rows between the raceways of the housing and cones are tapered rollers which roll along the raceways when the wheel rotates. The rollers as they pass over the outer raceway impart minute flexures to the housing and these flexures are monitored by multiple strain sensors on the housing. The strains—and the signals produced by the sensors—reflect conditions at the region of contact between a tire on the road wheel and the road surface over which the tire rolls. When the bearing assembly is used in industrial applications, such as rolling mills or machine tools, the electrical signals generated by the sensors provide indications usable by electronic processors and controllers which analyze these signals to determine the loads placed upon various components within a system which incorporates the bearing assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Continuation-In-Part of application Ser. No. 09/547,129 filed Apr. 10, 2000. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates in general to bearings and, more particularly, to a bearing assembly which monitors forces and torques transmitted through it to provide electrical signals for use by devices which monitor and control vehicular dynamics based upon calculated tire patch loading or to determine the general stresses, strains, and loads placed upon a bearing. 
     There are a number of applications where the loads and types of loads placed on a bearing in operation can provide significant information about the bearing and the objects attached to the bearing. One such application is in the automotive industry where such loading information, in electrical signal form, is vital for the proper application of Vehicular Dynamic Control (“VDC”) systems. Another application is in the steel rolling mill industry where electronic processing and control is used to manipulate the speed and torque of rollers during the rolling process. Yet another application is the machine tool industry where programmable controllers and processors monitor and control the speed of spindles in milling, cutting, and drilling machines. 
     In the automotive industry, many vehicles of current manufacture come equipped with antilock braking systems. A system of this type monitors the rotation of the wheels on a vehicle and, when the brakes of the vehicle are applied, relaxes the braking force at any wheel which locks up and skids. This reduces the tendency of the vehicle to veer off course when the traction at the wheels differs and makes the vehicle easier to steer under such circumstances. A few vehicles have traction control systems. This type of system monitors the rotation of driven wheels and distributes the tractive effort between those wheels, so that one does not break loose and spin. While both systems enable the driver of a vehicle to maintain better control over the vehicle, other factors influence the operation of the vehicle and, notwithstanding the successful operation of an antilock braking system and a traction control system, those other factors may still cause a vehicle to go out of control. 
     Significant among those other factors are the centrifugal forces encountered by a vehicle when it negotiates a turn—forces which act laterally on the vehicle. The friction between the vehicle tires and the road surface, that is at the so-called “tire contact patches”, resists these forces, but sometimes the friction may not be enough and the vehicle will slide, and perhaps go out of control, particularly if operated by one having poor driving skills. Then again, the frictional forces at the tire contact patches may prevent sliding, but the centrifugal force generated by the turn, inasmuch as it acts at the center of gravity, which is above the tire contact patches, may be sufficient to topple the vehicle. 
     Automobile manufactures have turned to VDC systems to prevent automobiles from going out of control in turns. The typical VDC system relies on a yaw sensor which measures the rate of change in yaw (rotation of the vehicle about its vertical axis) and a lateral acceleration sensor to, in effect, measure the centrifugal force imposed on the vehicle as a consequence of negotiating the turn. A VDC system also takes into account the angular velocity of the road wheels, the position of the steering wheel, and the power delivered by the engine. The typical VDC system analyzes the information and modulates the operation of the engine, as well as the brakes, to better maintain control of the vehicle in the turn. 
     The more sophisticated VDC systems also factor into the real time analysis estimated loads at the individual wheels and thus seek to evaluate conditions at the tire contact patches. But when negotiating a turn, each tire contact patch experiences forces and torques that do not comport with simple analytical procedures. Thus, measuring the displacement of a shock absorber piston, for example, does not give a very reliable indication of conditions that exist at the tire contact patch below that shock absorber. Certainly, it provides no indication of the torque at the tire contact patch, much less of the location at which the resultant of the force at the tire contact patch is acting. 
     Bearing assemblies exist which incorporate the use of strain gages to provide certain information regarding various bearing loads. For example, an antifriction rolling bearing disclosed in U.S. Pat. No. 5,140,849 issued Aug. 25, 1992, uses two strain gages to monitor the general loads applied to a bearing. This bearing, however, is unable to provided the multi-faceted data needed by high level VDC electronic systems or by the processor controlled systems in the rolling mills industry or the machine tool industry. 
     U.S. Pat. No. 4,748,844 discloses a load detection device more related to the automotive industry. That device consists of a multi-component load cell structure fixed to a hub on which a road wheel is mounted, the load cell structure being attached so as to rotate with the tire of the wheel. While that device provides some signal benefits, this device cannot provide signals indicating all loads and all torques required to enable a high level VDC electronic device to function properly. In particular, that device mounts all of its strain gages in only one plane which is perpendicular to the axis about which the wheel rotates. As a result, the signals from the strain gages on that device are unable to detect the forces tending to cause a vehicle to skid sideways or to roll the vehicle over. 
     Therefore, while the automotive industry is continuing to develop electronic devices which assist the driver to maintain control of his vehicle through various combinations of brake application and continuous suspension adjustment, the more sophisticated of these systems require reliable input signals indicating the full spectrum of loading which are indicative of the loads exerted at the tire contact patch. 
     Similarly, the rolling mill and machine tool industry utilize various forms of process controls which require monitoring of the loads placed on bearings. Specifically, rolling mills need bearing feedback regarding indications of belt slipping on rollers or indications that a particular set of rollers is experiencing higher loads and torques. Computer controlled machine tools need to monitor the amount of torque being experienced by a bearing supporting a spindle in order to assess whether cutting and drilling tools have become dull or whether the cutting or drilling speeds exceed the limits established for proper machining operations. 
     SUMMARY OF THE INVENTION 
     The present invention resides in a bearing assembly that couples a road wheel to a suspension system component on an automotive vehicle. The bearing assembly includes a hub to which the road wheel is attached and a housing which is attached to the suspension system component. The hub rotates in the housing on rolling elements which are arranged in two rows, with each row being between opposed raceways on the hub and housing. The rolling elements impart minute flexures to the housing, and the flexures are detected by strain sensors attached to the housing. In one embodiment the sensors are located at 90° intervals around each raceway of the housing. In another they are on a flange at which the housing is attached to the suspension system component. In still another they are located along an intervening surface that lies between the two raceways of the housing. The invention also resides in the bearing assemblies of the several embodiments apart from a wheel and suspension system component. Additionally, the present invention resides in a bearing assembly equipped with strain sensors used to generate electrical signals of a type and mode which are usable by various types of electronic processing and controlling devices which require such electrical signals to calculate loads within the mechanical system in which the bearing is incorporated. 
     The invention also resides in the method of using strain sensors to generate electrical signals of a type and mode which are usable by other automotive devices which function to provide dynamic control of a vehicle under various loading conditions, or by other electronic devices in the rolling mill industry or the machine tool industry. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a road wheel showing the several forces and torques that act on it; 
     FIG. 2 is a sectional view of a bearing assembly constructed in accordance with and embodying the present invention; 
     FIG. 3 is a plan view of one of the sensor modules for the bearing assembly; 
     FIG. 4 is a plan view of a sensor for the sensor module of FIG. 3; 
     FIG. 5 is a perspective view of the housing for the bearing assembly; 
     FIG. 6 is an end view of a housing for a modified bearing assembly; 
     FIG. 7 is an expanded view showing the sensor modules of the modified bearing assembly in a single plane; and 
     FIG. 8 is an end view of a housing for another modified bearing assembly; 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, a road wheel W (FIG.  1 ), which supports an automotive vehicle on a road surface, experiences several forces F and torques T when the wheel W rolls along the road surface. First there is the vertical force F v  which generally represents the weight of the vehicle and any inertial forces generated by irregularities in the road surface and by braking. The wheel W also experiences horizontal forces F h  which act generally in the direction the wheel is headed. Also, there are thrust loads F t , which are forces directed axially, that is in the direction of the axis X of rotation. Then there is the vertical torque T v , that is to say, torque about an axis passing vertically through the wheel W and sometimes referred to as the steering torque. Finally, horizontal torque T h , sometimes referred to as the overturning moment, which acts about an axis passing horizontally through the wheel W in the direction of advance for the wheel W. Altogether the current invention measures the loads for five degrees of freedom which include three forces, F v , F h , and F t , and two moments, T v  and T h . 
     The wheel W has a rim  2  and a tire  4  mounted on the rim  2 . The tire  4  contacts the road surface along a tire contact patch  6 , where the tire  4  experiences the forces F and torques T. The magnitude of the forces and torques indicate conditions at the tire contact patch  6  and, when evaluated with other conditions in real time, provide a good representation of the capacity of the vehicle to remain under control, or, on the other hand, go out of control. 
     The wheel W is coupled to a component C (FIG. 2) of the suspension system for the vehicle at a bearing assembly A which enables the wheel W to rotate about the axis X while transferring loads between the wheel W and suspension system component C. Typically, the suspension system component C is a steering knuckle. The bearing assembly A includes a hub  12  to which the wheel W is attached, a housing  14  which is secured to the suspension system component C, and a bearing  16  which is located between the hub  12  and housing  14  and enables the hub  12  to rotate on the housing  14  with minimal friction. To accommodate the housing  14 , the suspension system component C is provided with a through bore  18  and a machined end face  20 . For the most part, the housing  14  fits partially into the bore  18  and against the end face  20 . The bearing  16  is contained within the housing  14 . The hub  12  extends into the bearing  16  where it is confined both axially and radially. 
     More specifically, the hub  12  includes a flange  26  and a hollow spindle  28  which projects from the flange  26  at a shoulder  30  located on the back face of the flange  26 . Outwardly from the shoulder  30 , the flange  26  is fitted with lug bolts  32  which project axially from its other face and pass through the rim  2  of the road wheel W. Beyond the wheel W, lug nuts  34  are threaded over the bolts  32  to secure the wheel W to the hub  12 . 
     At its end remote from the flange  26 , the spindle  28  is upset, that is, deformed outwardly in the provision of a formed end  36  having an abutment face  38  that lies perpendicular to the axis X and is presented toward the shoulder  30 . The bearing  16  is captured between the shoulder  30  on the flange  26  and the face  38  of the formed end  36 . 
     The bearing  16  includes an inner race in the form of two cones  40  which fit around the spindle  28 , there being an interference fit between each cone  40  and the spindle  28 . Each cone  40  has a tapered raceway  42  that is presented outwardly away from the axis X, a thrust rib  44  at the large end of its raceway  42 , and a back face  46 , which is squared off with respect to the axis X on the end of the thrust rib  44 . The inboard cone  40  is somewhat longer than the outboard cone  40  by reason of a cylindrical cone extension  48  which projects beyond the small end of its raceway  42 . The cone extension  48  may serve as a seat for a target wheel that is monitored by a speed sensor in the housing  14 . The inboard cone  40  at its cone extension  48  abuts the small end of the outboard cone  40  along the spindle  28 , that is to say, the two cones  40  abut at their front faces. The back face  46  of the outboard cone  40  abuts the shoulder  30  that lies along the flange  16 , whereas the back face  46  of the inboard cone  40  abuts the end face  38  on the formed end  36 . 
     In addition to the cones  40 , the bearing  16  includes tapered rollers  54  arranged in two rows, there being a separate row around each cone  40 . Actually, the rollers  54  extend around the raceways  42  for the cones  40 , there being essentially line contact between the tapered side faces of the rollers  54  and the raceways  42 . The large end faces of the rollers  54  bear against the thrust ribs  46 . The rollers  54  of each row are essentially on apex, which means that the envelopes in which their tapered side faces lie have their apices located at a common point along the axis X. Each row of rollers  54  has a cage  56  to maintain the proper spacing between the rollers  54  in that row. 
     The housing  14  surrounds the spindle  28  as well as the two cones  40  and the two rows of rollers  54 . It forms part of the bearing  16  in that is has tapered raceways  58  which are presented inwardly toward the axis X. In that sense, the housing  14  constitutes the outer race of the bearing  16 . The raceways  58  on the housing  14  taper downwardly toward a cylindrical intervening surface  59  which separates them. The rollers  54  likewise lie along the raceways  58  of the housing  14 , there being essentially line contact between the raceways  58  and the tapered side faces of the rollers  54 . At their large ends, the raceways  58  open into short end bores  60  in which the thrust ribs  44  of the two cones  40  are located. Thus, each end of the bearing  16  has an annular space, with that space being between the thrust rib  44  at that end and the surrounding surface of the end bore  60 . 
     The housing  14  has an exterior surface  62  that is generally cylindrical and also a triangular or rectangular flange  64  that projects from the surface  62  generally midway between its ends. In the region behind the flange  64 , the diameter of the surface  62  is slightly less than the diameter of the through bore  18  in the suspension system component C. This portion of the housing  14  fits into the bore  18  with some clearance, while the back face of the flange  64  bears against the end face  20  on the component C. The housing  14  is secured firmly to the component C with bolts  66  that pass through the latter and thread into the flange  64  on the former. 
     The annular spaces at the ends of the bearing  16  are closed with seals  68  which fit into the end bores  60  of the housing  14  and around the thrust ribs  44  of the cones  40 . U.S. Pat. No. 5,022,659 discloses suitable seals for both locations. 
     The formed end  36  unitizes the assembly A. But the hub  12  does not always have the formed end  36 . Initially, the spindle  28  of the hub  12  extends from the shoulder  30  all the way to its free end as a cylindrical surface. The two cones  40 , with their complements of rollers  54  and with the housing  14  captured between the rollers  54  of the two rows, are installed over the cylindrical surface of the spindle  28  and advanced until the back face  46  of the outboard cone  40  comes against the shoulder  30  at the other end of the spindle  28 . When the cones  40  are so positioned, a portion of the spindle  28  projects beyond the back face  46  of the inboard cone  40 . This portion is deformed into the formed end  36 . PCT application GB 98/01823 (International Publication No. WO98/58762) discloses a rotary forming process for upsetting the initially extended end of the spindle  28  and converting that end into the integral formed end  36  which in effect unitizes the entire assembly A. 
     Other means may secure the two cones  40  on the spindle  28  as well. For example, the end of the spindle  28  may have threads and a nut engaged with those threads and turned down against the back face  46  of the inboard cone  40 . 
     When the assembly A is so unitized, its bearing  16  exists in a condition of slight preload. Actually the spacing between the inner raceways  42  on the cones  40  determines the setting of the bearing  16 , and that spacing depends on the length of the cone extension  48  for the inboard cone  40 , inasmuch as the rotary forming procedure which produces the formed end  46  drives the inboard cone  40  toward the outboard cone  40  with enough force to cause the cone extension  48  on the former to abut the small end of the latter. A nut threaded over the spindle  28  and turned down snugly against the back face  46  of the inboard cone  40  will have the same effect. 
     The forces F v , F h  and F t  and the torques T v  and T h  which act upon the wheel W reflect conditions at the tire contact patch  6 . For example, a balanced thrust load F t  will reflect travel in a straight line and will represent somewhat more than the preload in the bearing  16 . On the other hand, a larger unbalanced thrust F t , that is more in one direction than the other, will indicate a turn or perhaps a significant inclination of the vehicle to one side or the other. An increase in the vertical force F v  will reflect a turn or the application of brakes if the wheel W is at the front of the vehicle. 
     The forces F v , F h , F t  and the torques T v  and T h  which the wheel W experiences are transferred to the suspension system component C through the bearing assembly A, so the bearing assembly A experiences those forces F and torques T as well. The forces F and torque T manifest themselves in minute expansions and contractions of the housing  14 , and these minute expansions and contractions are detected at sensor modules M (FIG. 5) which are attached to the exterior surface  62  of the housing  14  immediately outwardly from both its raceways  58 . Actually, the tapered rollers  54  transfer the forces F and torques T from the cones  40  to the housing  14  and as they roll along the raceways  58 , impart the expansions and contractions in the bearing  16 . Those expansions and contractions transfer to the exterior surface  62  and to the locations of the sensors M along that surface  62 . 
     In one embodiment, each sensor module M includes (FIGS. 3 &amp; 4) a strain gage  70  that basically consists of a carrier matrix  72  and two foil resistance elements  74  and  76 . It should be noted that while the description of this embodiment describes the use of bonded resistance strain gauge sensors which operate by changing resistance values, other types of strain sensors such as mechanical sensors, photoelectric sensors, optical sensors, capacitance sensors, inductance sensors, and semiconductor sensors are also equally suitable. In this embodiment, however, the carrier matrix  72  is formed from a suitable polymer, such as polyimide, that itself is capable of expanding and contracting with the housing  14 . It is bonded to the exterior surface of the housing  14  with a suitable adhesive. Each foil resistance element  74  and  76  is formed from a suitable metal foil, such as constantan foil, which is bonded to the carrier matrix  72  such that it experiences the same expansions and contractions as the matrix  72 . Each resistance element  74  and  76  has several parallel legs  78  and end loops  80  connecting the ends of the adjacent legs  78 . The outermost legs  78  terminate at tabs  82 . The elements  74  and  76 , while both being on the matrix  72 , are electrically isolated from each other. Moreover, the legs  78  of the element  74  are oriented at 90° with respect to the legs  78  of the element  76 . The resistance of each leg  78  varies when it undergoes the expansions and contractions experienced by the carrier matrix  72 , and the resistance of each element  74  and  76  undergoes an even greater change in resistance, inasmuch as it consists of multiple legs  78  connected in series. The matrix  72  electrically isolates the elements  74  and  76  from the metal housing  14 , yet transmits the minute expansions and contractions of the housing  14  to the legs  78  of the elements  74  and  76 . 
     In addition to its sensor  70 , each sensor module M includes a temperature compensator  84  and a terminal block  86 . The temperature compensator  84  should operate at the same temperature as the sensor  70 , and to this end, should be located on the housing  14  adjacent to the sensor  70 , even on the carrier matrix  72  of the sensor  70 . In this regard, the resistances of the resistance elements  74  and  76  not only vary with expansions and contractions of the matrix  72 , but also with temperature. The temperature compensator  84  is connected to the resistance elements  74  and  76 , either through a bridge circuit or through a processor, such that it compensates or offsets changes in the resistances of the elements  74  and  76  attributable to temperature variations. Thus, the signals derived from the resistance elements  74  and  76  reflect only variations in strain. The terminal block  86  contains terminals  88  to which the tabs  82  on the resistance elements  74  and  76  are connected and to which the temperature compensator  84  is likewise connected, all through leads. The terminals  88  are in turn connected to a processor for evaluating and processing the signals produced by the resistance elements  74  and  76  and the temperature compensator  84 . 
     Four sensor modules M are attached to the exterior surface  62  of the housing  14  radially outwardly from the outboard raceway  58  and they are arranged at 90° intervals, (FIG. 5) one being with its sensor  70  at the top of the surface  62 , another with its sensor  70  at the bottom of the surface  62  and the other two with their sensors  70  at the sides of the surface  62 . The remaining four sensor modules M are also attached to the exterior surface  62 , but they are located radially outwardly from inboard raceway  58 . They too are located at 90° intervals, with their sensors  70  being at the top, bottom and sides of the surface  62 . In other words, the sensors  70  are arranged in two rows, with the sensors in each row being located 0°, 90°, 180°, and 270°, 0° being top center. In each of the sensors  70  of the eight modules M, the legs  78  of the resistance element  74  for that sensor  70  extend circumferentially, whereas the legs  78  of the element  76  extend axially with respect to the bearing housing  14 . 
     When the road wheel W rolls over a road surface and carries the suspension system component C with it—as well as the entire vehicle of which the component C is a part—the spindle  28  of the hub  12  rotates in the housing  14 . The cones  40  of the bearing  16 , being fitted to the spindle  28  with an interference fit, likewise rotate. The tapered rollers  54  of the outboard row roll along the raceway  42  of the outboard cone  40  and the outboard raceway  58  of the housing  14 . The tapered rollers  54  of the inboard row roll along the raceway  42  of the inboard cone  40  and the inboard raceway  58  of the housing  16 . As the rollers  54  roll between their respective raceways  42  and  58  they transfer radial loads between the cones  40  and the housing  14 . The radial load exerted by any roller  54  against the outer raceway  58  along which it rolls causes the housing  14  to flex minutely, and this flexure, while existing at the raceway  58 , transfers through the housing  14  to the exterior surface  62  and manifests itself as a slight circumferential, and somewhat smaller, axial elongation of the surface  62  radially outwardly from the line of contact between the roller  54  and the raceway  58 . Thus, each time a loaded roller  58  passes between a sensor  70  and the axis X, the flexure that occurs along its raceway  58  is transmitted to the exterior surface  62  at the sensor  70  where it elongates the parallel legs  78  of the resistance element  74  for sensor  70  and increases the resistance of the resistance element  76 . The magnitude of the change in resistance depends on the load, for a roller which bears against its raceway  58  with a heavy force will impart a greater flexure than one which bears with a lesser force. By comparing the flexure—and thus the roller loads—reflected in the signals from the sensors  70 , one can ascertain conditions at the tire patch  6  in real time. 
     A modified bearing assembly B (FIG. 6) is the same as bearing assembly A in all respects, except the location and orientation of the sensors  70  for the eight sensor modules M. The bearing assembly B has its sensor modules M located along and attached to the outside flange surface  65  of the flange  64  of the housing  14 . FIG. 7 shows an unfolded view of the positions and orientations of the sensors  70  along the outside flange surface  65 . Four of the sensor modules M have their sensors  70  located at 0°, 90°, 180°, and 270° around the outside flange surface  65 , with the very top of the outside flange surface  65  being 0°. These sensors  70  have the legs  78  of their resistance elements  74  extended circumferentially and the legs  78  of their resistance elements  76  extended axially with respect to the housing. The remaining four sensor modules M have their sensors  70  located at 25°, 65°, 155°, and 295° from top center, measuring forwardly and then around. The legs  78  of the resistance elements  74  and  76  in the remaining sensors  70  are oriented at 45° with respect to the circumferential direction and likewise 45° with respect to the axial direction. 
     Another modified bearing assembly D (FIG. 8) also resembles the bearing assembly A in every respect except the location of the sensors  70  for the eight sensor modules M. The bearing assembly D has its sensor modules M located along and attached to the intervening surface  59  that lies between the two raceways  58  of the housing  14 . FIG. 7 shows an unfolded view of the positions and orientations of the sensors  70  along the surface  59 . Four of the sensor modules M have their sensors  70  located at 0°, 90°, 180°, and 270° around the surface  59 , with the very top of the surface  59  being 0°. These sensors  70  have the legs  78  of their resistance elements  74  extended circumferentially and the legs  78  of their resistance elements  76  extended axially with respect to the housing. The remaining four sensor modules M have their sensors  70  located at 25°, 65°, 155° and 295° from top center, measuring forwardly and then around. The legs  78  of the resistance elements  74  and  76  in the remaining sensors  70  are oriented at 45° with respect to the circumferential direction and likewise 45° with respect to the axial direction. In short, the location of the sensors  70  along the intervening surface  59  corresponds to the location of the sensors  70  along the flange surface  65  of the bearing assembly B, and basically, the same holds true with respect to the orientation of the resistance elements  74  and  76  of the sensors  70  (FIG.  7 ). 
     Another embodiment resembles the bearing assembly A in every respect except there is no road wheel W, rim  2 , or hub  12 . Instead, the bearing assembly A is mounted to any rotating shaft installation and the bearing sensors are thereafter used to provide electrical signals indicative of the circumferential, circumferential-axial, axial torque, and shear strains on the bearing generally. Examples of applications which would need such information are process controls for rolling mills and process controls for machine tools. It will be obvious to one skilled in the art of bearing design and bearing use that there are many other applications wherein the loading sustained by a bearing would require the use of a bearing capable of providing electrical signals for monitoring those bearing loads.