Wheel support bearing assembly with sensor and in-wheel motor integration

A wheel support bearing assembly with sensor and in-wheel motor integration, that can sense with improved accuracy the forces acting on a contact point between a wheel and a road for precise control of an electric motor unit and/or a vehicle. The bearing assembly includes a bearing unit that rotatably supports a hub of a drive wheel, an electric motor unit, and a reduction gear unit between the electric motor unit and the bearing unit. A sensor unit is associated with an outer ring of the bearing unit. The sensor unit includes a strain generator and at least one measuring sensor attached to the strain generator. The strain generator includes a thin plate including at least two fixation contact segments fixed in contact with an outer diameter surface of the outer ring.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wheel support bearing assembly with sensor and in-wheel motor integration, in which a sensor that senses forces acting on a contact point between a drive wheel and a road surface is integrated into a wheel support bearing assembly of in-wheel motor type which includes a combination of a bearing unit, a reduction gear unit and an electric motor unit.

2. Description of Related Art

For driving stability control of an electric automotive vehicle equipped with a wheel support bearing assembly of in-wheel motor type that includes a combination of a bearing unit, a reduction gear unit, an electric motor unit and a brake unit, a technique has been proposed which uses a sensor to measure the forces along three axes perpendicular to each other, that act on a contact point between a drive wheel and a road surface. The measurements are based on the status of at least one of the following elements: the bearing unit; the electric motor unit; the reduction gear unit; and the brake unit (see Patent Document 1 listed below).

PRIOR ART LITERATURE

A wheel support bearing assembly of in-wheel motor type disclosed in Patent Document 1 includes a bearing unit and a load sensor associated with a stationary raceway member of the bearing unit to sense the respective forces that act along three axes. The sensitivity of the load sensor employed in this assembly, with which the respective loads acting along the three axes are sensed, leaves room for improvement. In particular, a load sensor employed in a wheel support bearing assembly of in-wheel motor type where a bearing unit is coupled via a reduction gear unit to an electric motor unit, is more susceptible to drifts in output signals, since the bearing unit is subject to the heat generated by the electric motor unit and the reduction gear unit. This results in more sensing errors and leads to load sensing with poor accuracy.

For application of load sensors in a wheel support bearing assembly, a sensor unit has been proposed which includes a strain generator including a thin plate and also includes a strain sensor on the thin plate (see Patent Document 2 listed above). Such a sensor unit has never been implemented in a wheel support bearing assembly of in-wheel motor type.

SUMMARY OF THE INVENTION

An object of the invention is to provide a wheel support bearing assembly with sensor and in-wheel motor integration, that can sense with improved accuracy the respective forces along three axes that act on a contact point between a drive wheel and a road surface and is therefore effective for precise control of an electric motor unit and/or a vehicle.

The present invention provides a wheel support bearing assembly with sensor and in-wheel motor integration. The assembly includes a bearing unit that rotatably supports a hub of a drive wheel. The bearing unit includes an outer ring that forms a stationary raceway member. The outer ring has an outer diameter surface. The assembly also includes an electric motor unit that forms a drive source to rotate the drive wheel as well as a reduction gear unit that is interposed between the electric motor unit and the bearing unit. The assembly further includes a sensor unit that includes a strain generator as well as at least one measuring sensor attached to the strain generator. The sensor unit is associated with the outer ring. The strain generator includes a thin plate that includes at least two fixation contact segments fixed in contact with the outer diameter surface of the outer ring.

In this construction, a sensor unit includes a strain generator as well as at least one measuring sensor attached to the strain generator, with the sensor unit being associated with the outer ring forming the stationary raceway member, and with the strain generator including a thin plate that includes at least two fixation contact segments fixed in contact with the outer diameter surface of the outer ring. This allows the sensor unit to sense with improved accuracy strain of the outer ring of the bearing unit, that may be caused by forces acting on a contact point between a drive wheel and a road surface. Therefore, a plurality of sensor outputs from the sensor unit can be used to computationally estimate with precision the loads along three axes that act on the contact point between the drive wheel and the road surface, that are effective for precise control of the electric motor unit and/or a vehicle.

In the present invention, the outer diameter surface of the outer ring may have upper, lower, right and left surface portions that correspond to upper and lower locations as well as right and left locations relative to a tire contact surface with a road, and the sensor unit may be associated with the outer ring at each of the upper, lower, right, and left surface portions.

Such arrangement of four sensor units allows for estimation with further precision of the respective loads along the three axes—that is, a vertical load Fz, a load Fx representing a drive force and/or a brake force, as well as an axial load Fy, acting on a contact point between a drive wheel and a road surface.

In the present invention, the sensor unit may include one sensor and two fixation contact segments.

In the present invention, the sensor unit may include two sensors and three fixation contact segments.

In the present invention, a plastic molding may be provided in proximity to where the sensor unit is disposed, that renders the sensor unit waterproof.

In the present invention, the sensor unit may be associated with the outer ring at an outboard side of the outer diameter surface and a cover may be provided that protects the outboard side of the outer diameter surface.

In the present invention, a signal processor unit may be associated with the outer ring of the bearing unit, a casing of the reduction gear unit, or a casing of the electric motor unit, with the signal processor unit including loads estimator circuitry that estimates loads acting on the drive wheel based on sensor output signals from the sensor unit.

In this construction, the wheel support bearing assembly includes a signal processor unit with which sensor output signals from the sensor unit can be processed to generate loads data for external output. This eliminates the need to transmit weak sensor output signals via a cable to the outside of the wheel support bearing assembly, thereby allowing for a simplified configuration of an electromagnetic shield for such a cable.

In the above construction, the signal processor unit may be associated with a stationary member other than the outer ring of the bearing unit, with the outer ring of the bearing unit including a flange for mounting the outer ring to the casing of the reduction gear unit, the flange having a hole formed therein, and a sensor cable being drawn out of the hole and wired to the signal processor unit for transmission of the output signals from the sensor unit to the signal processor unit.

Where the flange has a hole formed therein and a sensor cable is drawn out of the hole, the casing of the reduction gear unit may have a groove formed therein through which the sensor cable passes. In this case, the sensor cable drawn out of the hole formed in the flange may pass through the groove formed in the casing of the reduction gear unit, to connect to the signal processor unit. A waterproof seal may surround a sensor cable drawn out of the hole. Such a sensor cable that passes through the groove formed in the casing allows for the provision of a waterproof seal having a long extension along the groove, thereby sealing the sensor cable over a longer length thereof than could be sealed when the sensor cable were radially drawn. In other words, more improved sealing effect can be achieved between a surface of the sensor cable and the waterproof seal. Also, the sensor cable can have a greater bending radius than is the case with when the sensor cable were radially drawn. Therefore, even a sensor cable with thick coatings can be wired with ease. Also, the radial sticking-out of a sensor cable can be minimized.

In the present invention, the signal processor unit may at least include: a signal amplifier function to amplify the sensor output signals; a filter function to remove noise components from the sensor output signals; and an AD converter function to convert the sensor output signals from analog to digital.

In this configuration, the sensor output signals from the sensor unit can be converted to digital signals for load estimation and computed loads data can be output in the form of digital data. This minimizes the number of necessary wires, thereby reducing the cost of a cable employed. At the same time, the risk of breaking of wire can be reduced, thereby resulting in improved reliability.

In the present invention, the signal processor unit may further include a processor function that includes: a corrector function to correct the sensor output signals; an average value calculator function to calculate an average value of the sensor output signals; an amplitude value calculator function to calculate an amplitude value of the sensor output signals; and a memory function to store correction parameters for the correction, calculation parameters for the average value calculation and the amplitude value calculation, and calculation parameters that the loads estimator circuitry uses in computing equations where the average value and the amplitude value serve as variables. In this configuration, loads can be computed based on the average value of the sensor output signals and the amplitude value of the sensor output signals. In particular, since such an amplitude value can minimize the temperature-related effects, increase of load computing errors that may be caused by the heat generated by the electric motor unit and/or the reduction gear unit can be prevented, thereby improving the precision in load estimation. Also, with the signal processor unit including such a processor function, different adjustments of correction parameters and calculation parameters for different wheel support bearing assemblies can be made with ease.

In the present invention, a motor controller unit may be provided that controls the electric motor unit, with the motor controller unit including circuitry to which part of functions of the signal processor unit is integrated.

In this configuration, for instance, the same memory circuitry can be used to store therein the parameters necessary for total control of the electric motor unit as well as the respective parameters used by the signal processor unit. This allows for centralized management of information necessary for a wheel support bearing assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1toFIG. 15illustrate the first embodiment of the present invention. To begin with, the first embodiment will be described in general in connection withFIG. 1. The illustrated wheel support bearing assembly with sensor and in-wheel motor integration includes a bearing unit A that rotatably supports a hub of a drive wheel70, an electric motor unit B forming a drive source for rotation, a reduction gear unit C that reduces the rotational speed of the electric motor unit B that is transmitted to the hub, and a brake unit D that applies a brake force to the hub, with these units A to D being arranged along the center axis O of the drive wheel70. Note that the expression “arranged along a/the center axis O” used herein does not necessarily mean that respective components are all located along the center axis O, but rather means that respective components are all operatively positioned with respect to the center axis O. It is to be noted that hereinafter in this specification, terms “outboard” and “inboard” represent one side of the vehicle body away from the longitudinal center of the vehicle body and the other side of the vehicle body close to the longitudinal center of the vehicle body, respectively, when assembled in the vehicle body.

As shown inFIG. 2, the bearing unit A includes an outer ring1having an inner periphery formed with a plurality of rows of respective raceway surfaces3, an inner member2having an outer periphery formed with a plurality of rows of respective raceway surfaces4that face the respective raceway surfaces3, and a plurality of rows of respective rolling elements5interposed between the respective raceway surfaces3,4of the outer ring1and the inner member2. The bearing unit A forms a plural-row, angular contact ball bearing. As such, the rolling elements5are in the form of balls, with each row of the rolling elements5being retained by a retainer6. Each of the raceway surfaces3,4has an arcuate, cross sectional shape. The raceway surfaces3,4are designed to form back-to-back arrangement with corresponding contact angles. The outer ring1and the inner member2define bearing space delimited therebetween that has outboard and inboard ends sealed by seals7,8, respectively.

The outer ring1forms a stationary raceway member. The outer ring1is of one-piece construction that includes an outer periphery including a flange1afor mounting to a casing33of the reduction gear unit C. The flange1aincludes a plurality of circumferential locations formed with respective screw holes14. With attachment bolts15being inserted in bolt insertion holes33aof the casing33and being screwed in the screw holes14, the outer ring1can be attached to the casing33.

The inner member2forms a rotational raceway member. The inner member2includes a hub axle9and an inner ring10. The hub axle9includes a hub flange9afor mounting to the drive wheel70shown inFIG. 1and to a brake ring46. The hub axle9also includes an axle portion9bthat includes an inboard end having an outer periphery to which the inner ring10is mounted. The rows of the raceway surfaces4are formed on the hub axle9and the inner ring10, respectively. Note that the hub axle9corresponds to a “hub” recited in the claims. The hub axle9includes an inboard end that has an outer periphery formed with a stepped segment—stepped to have a smaller diameter to which the inner ring10is mounted—thereby forming an inner ring mount surface12. The hub axle9includes a center having a through bore11formed therein. The hub flange9aincludes a plurality of circumferential locations formed with respective force-fit holes17for hub bolts16. The hub axle9includes a cylindrical pilot portion13that guides the drive wheel70shown inFIG. 1and the brake ring46. The pilot portion13protrudes towards an outboard side from the proximity of a root portion of the hub flange9a. The pilot portion13includes an inner periphery to which a cap18is fitted that closes an outboard end of the through bore11.

As shown inFIG. 1, the electric motor unit B is of a radial gap type that includes a stator23fixed to a tubular casing22and a rotor25associated with an output shaft24, in which a radial gap is provided between the stator23and the rotor25. The output shaft24is supported via two bearings26by the casing22. The electric motor unit B is controlled by a motor controller unit137that includes control circuitry which, for example, includes inverters.

As shown inFIG. 2andFIG. 3, the reduction gear unit C includes a cycloidal reduction gear. Hence, the reduction gear unit C includes two curve plates34a,34beach having an outer shape that is defined by a smooth, wavy trochoidal curve, and the reduction gear unit C also includes an output shaft32including eccentric portions32a,32bto which the curve plates34a,34b, respectively, are mounted via respective bearings35. The reduction gear unit C also includes a plurality of outer pins36that are extending between inboard and outboard side walls of the casing33and each guiding, at an outer periphery side thereof, the eccentric motions of the curve plates34a,34b. The reduction gear unit C further includes an output shaft37mounted by spline to the through bore11of the hub axle9for integral rotation, and also includes a plurality of inner pins38attached to the output shaft37. The curve plates34a,34binclude a plurality of through holes39formed therein to which the respective inner pins38are inserted. Note that the input shaft32is coupled by spline with the output shaft24of the electric motor unit B for integral rotation. Also note that the input shaft32has opposite ends supported via two respective bearings40by the casing33and an inner diameter surface of the output shaft37, respectively. Preferably, a trochoidal curve that defines the outer shapes of the curve plates34a,34bis a cycloidal curve. However, such a trochoidal curve may be any other type of trochoidal curve. Note that the term “cycloidal reduction gear” used above encompasses such a trochoidal reduction gear as discussed above, in which a trochoidal curve defines the outer shapes.

Rotation of the output shaft24of the electric motor unit B shown inFIG. 1causes eccentric motions of the respective curve plates34a,34bassociated with the input shaft32that rotates integrally with the output shaft24. The eccentric motions of the respective curve plates34a,34bare transmitted via the engagement between the inner pins38and the through holes39, to the inner member2that includes a hub of a wheel, causing rotation of the inner member2. The rotational speed of the inner member2is reduced with respect to that of the output shaft24. For instance, a single stage cycloidal reduction gear can achieve a reduction ratio of no less than 1/10.

The two curve plates34a,34bare mounted to the respective eccentric portions32a,32bof the input shaft32, 180° out of phase from each other so as to cancel out the mutual eccentric motions. The eccentric portion32aincludes a side to which a first counterweight41is mounted, and the eccentric portion32bincludes a side to which a second counterweight41is mounted, with these sides of the eccentric portions32a,32bbeing opposite to each other. The first counter weight41is offset in a direction opposite to the direction in which the eccentric portion32ais offset, and the second counter weight41is offset in a direction opposite to the direction in which the eccentric portion32bis offset, so as to cancel out the vibrations caused by the eccentric motions of the respective curve plates34a,34b.

As shown inFIG. 4, the outer pins36and inner pins38include bearings42,43mounted thereto, respectively. The outer rings42a,43aof the bearings42,43rollingly contact the outer peripheries of the curve plates34a,34band the inner peripheries of the through bores39, respectively. This reduces the contact resistance between the outer pins36and the outer peripheries of the curve plates34a,34bas well as the contact resistance between the inner pins38and the inner peripheries of the through bores39. As a result, the eccentric motions of the curve plates34a,34bcan be smoothly transmitted to the inner member2, causing rotation of the inner member2.

As shown inFIG. 5, the brake unit D includes a manipulator48. The manipulator48includes a brake ring46that is attached to the hub flange9atogether with the drive wheel70and also includes brake pad(s)47that can frictionally contact the brake ring46. The brake unit D also includes a drive49that actuates the brake pad(s)47. The drive49forms an electric brake equipment that includes as a drive source an electric brake motor50. The brake ring46includes a brake disc. A pair of brake pads47are positioned to sandwich the brake ring46therebetween. One of the brake pads47is fixed to a brake frame51. The other of the brake pads47is attached to an advance/retraction member52that is associated with the brake frame51to be advanceable and retractable in a linear fashion. The advance/retraction member52confronts the brake ring46in a direction, in which the advance/retraction member52advances towards or retracts away from the brake ring46. The advance/retraction member52is locked from rotation relative to the brake frame51.

The drive49includes, in addition to the electric brake motor50, a ball screw53that converts the rotational output of the electric motor50to a back-and-forth linear motion and transmits it to the brake pad(s)47as a brake force. The output of the electric motor50is transmitted to the ball screw53via a reduction gear and transmission mechanism58. The ball screw53includes a screw shaft54and a nut55. The screw shaft54is supported via bearings57by the brake frame51such that the screw shaft54can only rotate, and the nut55is fixed to the advance/retraction member52. The advance/retraction member52and the nut55may be of one-piece construction.

The ball screw53includes, in addition to the screw shaft54and the nut55, a plurality of balls56interposed between a first thread raceway formed in an outer peripheral surface of the screw shaft54and a second thread raceway in an inner peripheral surface of the nut55, with the first and second thread raceways confronting each other. The nut55includes a circulation mechanism (not shown) including a continuous path that circulates the balls56placed between the screw shaft54and the nut55, with the continuous path including no ends. The circulation mechanism may be of an external circulation type which includes a return tube and/or a guide plate. The circulation mechanism may be of an internal circulation mechanism which includes an end cap and/or a deflector. Since the ball screw53only makes back-and-forth motion over a short distance, the ball screw53may be of a type without the above circulation mechanism, for example, a retainer type which includes a retainer (not shown) that retinas a plurality of balls56placed between the screw shaft54and the nut55.

The reduction gear and transmission mechanism58includes a train of gears and reduces the rotational speed of the electric brake motor50and transmits it to the screw shaft54of the ball screw53. In the illustrated example, the reduction gear and transmission mechanism58includes a first gear59associated with an output shaft of the electric motor50and also includes a second gear60that is associated with the screw shaft54to mesh with the first gear59. In another example (not shown), the reduction gear and transmission mechanism58may include, for example, a worm and a worm wheel.

The brake unit D includes an actuator62configured to control the electric motor50based on the actuation by an actuation member61such as a brake pedal. The actuator62includes anti-lock controller circuitry65. The actuator62includes the aforementioned actuation member61, a sensor64that can detect the amount as well as the direction of the actuation by the actuation member61, and a controller63that controls the electric motor50according to the detection signals from the sensor64. The controller63contains the aforementioned anti-lock controller circuitry65. The controller63includes a motor control signal generator (not shown) that generates a motor control signal and also includes motor drive circuitry (not shown) that can control a motor current based on the motor control signal.

The anti-lock controller circuitry65adjusts, based on the rotation of the drive wheel70shown inFIG. 1, a brake force applied by the electric motor50to prevent locking-up of rotation of the drive wheel70during braking caused by the actuation of the actuation member61. During braking, the anti-lock controller circuitry65determines the rotational speed of the drive wheel70shown inFIG. 1. When the anti-lock controller circuitry65detects, based on the rotational speed, locking-up of rotation of the drive wheel70shown inFIG. 1or a sign thereof, the anti-lock controller circuitry65lowers the drive current to the electric motor50or causes the electric motor50to generate a temporary rotational output in the opposite direction. In this way, the anti-lock controller circuitry65adjusts the brake force, i.e. a clamp force applied by the brake pad(s)47. The rotational speed of the drive wheel70is determined based on the output from an RPM sensor87that is associated with the electric motor unit B.

A shown inFIG. 1, to the hub flange9aof the bearing unit A is attached the drive wheel70together with the brake ring46. The drive wheel70includes a wheel71and a tire72mounted on a periphery of the wheel71. With the brake ring46being sandwiched between the hub flange9aand the wheel71and with the hub bolts16force-fitted in the force-fit holes17in the hub flange9abeing screwed to the wheel71, the drive wheel70as well as the brake ring46can be secured to the hub flange9a.

The outer ring1, which forms the stationary raceway member, has an outer diameter surface, with which four sensor units120may be associated.FIG. 6shows a front elevational view of the outer member1as viewed from an outboard side. In the figure, the sensor unit(s)120are associated with the outer ring1at upper, lower, right, and left surface portions thereof, respectively, that correspond to upper and lower locations as well as right and left locations relative to a tire contact surface with a road.

As shown in the enlarged plan view ofFIG. 7and the enlarged cross sectional view ofFIG. 8, each of the sensor unit(s)120includes a strain generator121and a strain sensor122attached to the strain generator121to sense strain of the strain generator121. The strain generator121includes a metallic, elastically deformable thin plate such as a steel plate, having a thickness no greater than 3 mm. The thin plate is a substantially stripe-shaped as viewed in a plan view and has a width that is uniform over an entire length thereof. The thin plate includes a center with opposite side edges thereof having respective cutout(s)121b. The strain generator121includes opposite ends thereof including two fixation contact segments121a(FIG. 8) fixed, via respective spacers123, in contact with the outer diameter surface of the outer ring1. The strain sensor122is affixed on a portion of the strain generator121where higher strain is produced in response to loads along respective directions. In the figure, such a portion is a center of the strain generator121which is sandwiched, from outer surface sides thereof, by the cutout(s)121bformed in the opposite side edges. And the strain sensor122senses circumferential strain that is produced near the cutout(s)121b.

Preferably, the strain generator121does not plastically deform under a condition where the maximum possible force—the maximum possible external force that acts on the outer ring1which forms the stationary raceway member or the maximum possible force that acts between the tire and a road surface—affects the strain generator121. This is because plastic deformation of the strain generator121leads to less transmission of deformation of the outer ring1to the sensor unit120, thereby undesirably affecting the measurement of strain. The phrase “the maximum possible force” refers to an abnormally strong force of the maximum level that may be applied to the bearing unit A, but which is acceptable in the sense that the bearing unit A can recover, after removal of that force, a normal function as a bearing unit (assuming that recovery of the function of a sensor system is irrelevant, here).

Each of the sensor unit(s)120is associated with the outer ring1such that the two fixation contact segments121aof that strain generator121are positioned at substantially the same axial coordinate of the outer ring1and also circumferentially spaced apart from each other. The fixation contact segments121aare fixed, via respective spacers123, by respective bolts124with the outer diameter surface of the outer ring1. Each of the bolts124is inserted in a bolt insertion hole125radially perforated in the fixation contact segment121a, and through a bolt insertion hole126formed in a spacer123, to screw in a screw hole127formed in an outer periphery of the outer ring1.

Such fixation of the fixation contact segments121ato the outer diameter surface of the outer ring1via spacers123allows for a space to be formed between the outer diameter surface of the outer ring1and a center of the thin plate of the strain generator121where the cutout(s)121bare formed. This facilitates deformation with strain near the cutout(s)121b. Here, the axial coordinate at which the fixation contact segments121aare located is an axial coordinate within the proximity of where an outboard raceway surface3of the outer ring1is located. The phrase “a/the proximity of where an outboard raceway surface3of the outer ring1is located” used herein refers to a range, as shown inFIG. 2, from where an outboard raceway surface3is formed to a mid-location between inboard and outboard raceway surfaces3. The outer diameter surface of the outer ring1includes a flat portion1bwith which the spacers123fixedly contact.

In another example as shown in the cross sectional view ofFIG. 9, the outer diameter surface of the outer member1has a groove1cformed therein, at a mid-location of two portions of the outer diameter surface, with the two portions being where the two respective fixation contact segments121aof the strain generator121are fixed. This also allows for a space to be formed, without the spacers123, between the outer diameter surface of the outer ring1and a mid-location of the two fixation contact segments121a, with the mid-location corresponding to where the cutout(s)121bare formed in the strain generator121.

In yet another example as shown inFIG. 10, the strain generator121may include a substantially stripe-shaped configuration as viewed in a plan view which does not include such cutout(s)121bas in the example ofFIG. 7.

A variety of strain sensors122may be used. For example, a strain sensor122includes a metallic foil strain gauge. In that case, the strain sensor122is adhesively fixed on a strain generator121in general.

A strain sensor122may include a thick-film resistor formed on a strain generator121.FIG. 11shows such a construction of a sensor unit120. The illustrated sensor unit120includes a strain generator121, an insulation layer150formed on a sensor mount surface121A of the strain generator121, a pair of electrodes151,151formed on the opposite sides of a surface of the insulation layer150, a strain measurement resistor152, which forms a strain sensor, on the insulation layer150between the electrodes151,151, and a protective film153formed on the electrodes151,151as well as on the strain measurement resistor152.

As shown inFIG. 2, the sensor unit(s)120associated with the outer ring1at the outer diameter surface thereof is/are covered by a protective cover90. Note that the protective cover90is omitted inFIG. 6. The protective cover90is of a tubular configuration having an inner diameter that increases towards an inboard side. In particular, the protective cover90is of a cylindrical configuration with an inboard side having a larger diameter and with an outboard side, half of which shrinks towards an inner diameter side to have a smaller diameter. The protective cover90includes an inboard end mounted to an outer diameter surface of the flange1aof the outer ring1via an O-ring91. The protective cover90also includes an outboard end mounted to the outer diameter surface of the outer ring1. A material for the protective cover90includes a metallic material such as a stainless steel and/or a resinous material such as PA66+GF. The flange1aof the outer ring1includes the outer diameter surface including a circumferential groove1dformed therein to which an O-ring can be fitted. With the O-ring91being fitted to the groove1d, not only the O-ring91can be axially positioned but also the space between the inboard end of the protective cover90and the outer diameter surface of the flange1aof the outer ring1can be reliably sealed. A proximity to where sensor unit(s)120is/are disposed is provided with a plastic molding that renders the sensor unit(s)120waterproof.

Such a protective cover90within which the sensor unit(s)120is/are fixedly associated with the outer ring1at the outer diameter surface thereof prevents corrosion, due to an external environment, of where the sensor unit(s)120is/are fixed, which may lead to instability of such fixations. As a result, the sensor unit(s)120can operate without any malfunctions, despite its/their use in the wheel support bearing assembly which operates where the suspension system thereof is subject to a severe environment.

Each of the sensor unit(s)120includes a signal cable (sensor cable)129that connects to a signal processor unit130. The signal processor unit130includes loads estimator circuitry133(FIG. 12) that estimates loads acting on the drive wheel70based on sensor output signals from the respective sensor unit(s)120. In the illustrated example, the signal processor unit130is associated with the casing33of the reduction gear unit C at an outboard end, outer diameter surface thereof. The signal processor unit130may be associated with the outer ring1at the outer diameter surface thereof along with the sensor unit(s)120. The signal processor unit130may be associated with the casing22of the electric motor unit B at an outer diameter surface thereof.

A shown inFIG. 2, the flange1aof the outer ring1has cable insertion hole(s)92that are axially perforated therein, out of which the signal cable(s)129of the respective sensor unit(s)120is/are drawn. The cable insertion hole(s)92is/are filled with an elastic filler93such as a molding plastic after the signal cable(s)129is/are drawn out of it/them. The signal cable(s)129out of the cable insertion hole(s)92pass(es) through respective cable guide cutout(s)33bformed in an outboard end of the casing33of the reduction gear unit C and is/are drawn to the signal processor unit130. A waterproof seal94surrounds the respective signal cable(s)129for waterproof thereof. The cutout(s)33bmay be through hole(s) open at an outer diameter surface of the casing33. As such, penetration of, for example mud or salty water, from outside through the cable insertion hole(s)92into the protective cover90can be prevented. The wiring from the sensor unit(s)120to the signal processor unit130may be designed in such a way to extend inside the casing33of the reduction gear unit C. Thus, the signal cable(s)129may connect to the signal processor unit130without being exposed to the external environment. In this case, since the signal cable(s)129is/are not exposed to the external environment, penetration paths of, for example mud, can be reduced to a minimum level, thereby resulting in improved waterproof as well as improved reliability.

FIG. 12shows a block diagram of a schematic configuration of the signal processor unit130. The signal processor unit130includes preprocessor circuitry131, average value and amplitude value calculator circuitry132, loads estimator circuitry133, parameters memory circuitry134, and communications circuitry135that includes an I/F function. The preprocessor circuitry131includes a signal amplifier function to amplify sensor output signals from the respective sensor unit(s)120, a filter function to remove noise components from the sensor output signals, and an AD converter function to convert the amplified and filtered sensor output signals from analog to digital. Since weak sensor output signals from the sensor unit(s)120are converted into digital signals by the sensor processor unit130arranged in proximity to the sensor unit(s)120, the sensor output signals are less subject to noises, thereby resulting in improved sensing accuracy. The average value and amplitude value calculator circuitry132includes average value calculator function and amplitude value calculator function to calculate average value and amplitude value, which will be more described later, of the sensor output signals out of the preprocessor circuitry131, and also includes a corrector function to correct, for example, the calculated average value. The loads estimator circuitry133includes loads estimator function to estimate loads acting on the drive wheel70based on the average value and amplitude value calculated by the average value and amplitude value calculator circuitry132. Hence, the signal processor unit130performs all computations that are based on the sensor output signals from the sensor unit(s)120. This results in improved usability. This also minimizes the number of external wires, thereby resulting in improved reliability.

Each of the sensor unit(s)120is associated with the outer ring1at an axial coordinate within the proximity of where an outboard raceway surface3of the outer ring1is located. As a result, the output signals from the respective strain sensor(s)122include influences from the rolling elements5that move in the proximity of where the respective sensor unit(s)120is/are disposed. Therefore, the amplitude of the sensor output signals reaches a maximum value thereof when the rolling elements5move in the closest proximity to the strain sensor122of the sensor unit120, and the amplitude declines as the rolling elements5move away from that location. Accordingly, during the operation of the bearing assembly, the sensor output signals have a waveform similar to a sinusoidal wave such as shown inFIG. 13whose amplitude changes in a period that corresponds to a pitch of the rolling elements5. Here, the average value and amplitude value calculator circuitry132calculates an amplitude value (AC component) from the sensor output signals as well as an average value of the amplitude (DC component) of the sensor output signals, as data with which to determine loads.

The average value calculated by the average value and amplitude value calculator circuitry132includes temperature characteristics of the strain sensor(s)122, temperature-dependent strain of the outer ring1, and/or drift values generated by other factors. The average value and amplitude value calculator circuitry132is configured to correct drifts in the sensor output signals. The parameters memory circuitry134is configured to store correction parameters that can be read from the parameters memory circuitry134for correction of the drifts. The parameters memory circuitry134includes, for example, non-volatile memory. In order to correct temperature-dependent drifts, at least one sensor unit120may include a strain generator121that includes a temperature sensor128such as illustrated by an imaginary line inFIG. 7, and the output signals from the temperature sensor128may be input, along with the sensor output signals from the sensor unit(s)120, via the preprocessor circuitry131to the average value and amplitude value calculator circuitry132, for correction of the drifts. The parameters memory circuitry134may be configured to store information necessary with regard to the temperature sensor128. The computing equations and/or correction parameters that the average value and amplitude value calculator circuitry132uses are configured based on the results obtained in advance from experiments and/or simulations.

The loads estimator circuitry133is configured to estimate loads (a vertical load Fz, a load Fx representing a drive force and/or a brake force, and an axial load Fy) acting on the drive wheel70based on a linear equation where the average value and the amplitude value calculated by the average value and amplitude value calculator circuitry132serve as variables and where the variables are multiplied by respective defined correction coefficients. The parameters memory circuitry134is also configured to store the correction coefficients of the linear equation that can be read from the parameters memory circuitry134. The correction coefficients are configured based on the results obtained in advance from experiments and/or simulations. The loads data obtained by the loads estimator circuitry133are transmitted via the communications circuitry135and output to a higher-order electric control unit (ECU)85(FIG. 15) at a vehicle body, through communication (for example, via CAN bus) with the electric control unit85. If necessary, the loads data may be output in analog voltage. The respective parameters stored in the parameters memory circuitry134may be written from outside via the communications circuitry135.FIG. 14shows a schematic processing flow, starting from the sensor output signals from the sensor unit(s)120up until the estimation of the respective loads Fx, Fy, Fz by the loads estimator circuitry133.

Loads acting between the drive wheel70and the road surface are also applied to the outer ring1which forms the stationary raceway member of the bearing unit A, resulting in deformation of the outer ring1. Hence, the strain generator121of the sensor unit120includes the thin plate that includes two fixation contact segments121afixed in contact with the outer diameter surface of the outer ring1. Thus, strain of the outer ring1is transmitted with ease to the strain generator121in the form of a larger strain thereof, which strain sensor122can sense with excellent accuracy.

In the embodiment under discussion, four sensor units120are associated with the outer ring1at the outer diameter surface having upper, lower, right and left surface portions that correspond upper and lower locations as well as right and left locations relative to the tire contact surface with the road, with each sensor being associated with the outer ring1at each of the upper, lower, right, and left surface portions such that the sensor circuits120are circumferentially spaced apart at equal intervals, 90° out of phase from each other. This allows for estimation with further precision of the loads that act on the bearing unit A, namely the vertical load Fz, the load Fx representing the drive force and/or the brake force, as well as the axial load Fy.

As shown inFIG. 15, the electric control unit85to which the loads data are input includes abnormality determination circuitry84that determines, based on the loads data, possible abnormalities of the road surface conditions and/or of the contact conditions between the drive wheel70and the road surface. Connected to the output of the electric control unit85are the electric motor unit B, the electric motor50of the brake unit D, and a damper unit74of the suspension system73. The electric control unit85outputs, based on the loads data from the signal processor unit130, information related to the road surface conditions and/or to the contact conditions between the drive wheel70and the road surface, to the electric motor unit B, the electric motor50of the brake unit D, and the damper unit74of the suspension system73.

The configuration of the electric control unit85to output, based on the loads data from the signal processor unit130, information related to the road surface conditions and/or to the contact conditions between the drive wheel70and the road surface allows for more precise estimation of road surface conditions and/or of contact conditions with the road. The resultant respective information can be used for control of the electric motor unit B and/or for vehicle attitude control, thereby resulting in improved safety and cost-efficiency. For instance, for smooth cornering of a vehicle, such information is output to the electric motor unit B to control the rotational speed of the right and left drive wheels70. To prevent the locking-up of the drive wheel70under braking, such information is output to the electric motor50of the brake unit D for braking control. To prevent excessive rolling of the vehicle body under cornering or prevent excessive pitching of the vehicle body under acceleration or braking, such information is output to the damper unit74of the suspension system73for suspension control. The abnormality determination circuitry84generates an abnormality signal when one or more of the forces along the respective three axes exceed the respective acceptable limit(s). The abnormality signal may also be used for vehicle control of an automotive vehicle. Moreover, real-time output concerning the forces that acts between the drive wheel70and the road surface can result in much finer attitude control.

In this way, the wheel support bearing assembly with sensor and in-wheel integration includes sensor unit(s)120, each of which includes the strain generator121and one strain sensor122attached to the strain generator121, with the sensor unit(s)120being associated with the outer ring1at an outer diameter thereof, wherein the outer ring1forms the stationary raceway member of the bearing unit A. The strain generator121includes the thin plate that includes two fixation contact segments121afixed in contact with the outer diameter surface of the outer ring1. This allows the sensor unit(s)120to sense with improved accuracy strain of the outer ring1of the bearing unit A, that is caused by forces acting on the contact point between the drive wheel70and the road surface. Therefore, a plurality of sensor output signals from the sensor unit(s)120can be used to computationally estimate with precision the loads Fx, Fy, Fz along three axes that act on the contact point between the drive wheel70and the road surface, that are effective for precise control of the electric motor unit B and/or the vehicle.

Also, in the embodiment under discussion, the signal processor unit130is associated with the casing33of the reduction gear unit C—i.e. associated with the stationary member other than the outer ring1, with the signal processor unit130including the loads estimator circuitry133that estimates loads acting on the drive wheel70based on sensor output signals from the sensor unit(s)120. In this construction, the wheel support bearing assembly includes the signal processor unit130with which sensor output signals from the sensor unit120are processed to generate loads data for external output. This eliminates the need to transmit weak sensor output signals via signal cable(s)129to the outside of the wheel support bearing assembly, thereby allowing for a simplified configuration of an electromagnetic shield for such signal cable(s)129.

Also, in the embodiment under discussion, the signal processor unit130includes: the signal amplifier function to amplify the sensor output signals; the filter function to remove noise components from the sensor output signals; and the AD converter function to convert the sensor output signals from analog to digital. In this configuration, the sensor output signals from the sensor unit120are converted to digital signals for load estimation and the loads data are computed and output in the form of digital data. This minimizes the number of necessary wires, thereby reducing the cost of signal cable(s)129employed. At the same time, the risk of breaking of wire can be reduced, thereby resulting in improved reliability.

Moreover, the signal processor unit130further includes the processor function that includes: the corrector function to correct the sensor output signals; the average value calculator function to calculate the average value of the sensor output signals; the amplitude value calculator function to calculate the amplitude value of the sensor output signals; and the memory function to store correction parameters for the correction, calculation parameters for the average value calculation and the amplitude value calculation, and calculation parameters that the loads estimator circuitry133uses in computing equations where the average value and the amplitude value serve as variables. In particular, since such an amplitude value can minimize temperature-related effects, increase of load computing errors that may be caused by the heat generated by the electric motor unit B and/or the reduction gear unit C can be prevented, thereby improving the precision in load estimation. Also, with the signal processor unit130including such a processor function, different adjustments of correction parameters and calculation parameters for different wheel support bearing assemblies can be made with ease.

Also, in the embodiment under discussion, the motor controller unit137may be provided that controls the electric motor unit B, with the motor controller unit137including circuitry to which part of functions of the signal processor unit130is integrated. For example, such part of the functions performed by the circuitry includes one or more of the circuitries131,132,133,134,135described in connection withFIG. 12. In particular, it is preferred that the motor controller unit137include the parameters memory circuitry134. In this configuration, for instance, the parameters memory circuitry134can be used to store therein the parameters necessary for total control of the electric motor unit B as well as the respective parameters used by the signal processor unit130. This allows for centralized management of information necessary for the wheel support bearing assembly.

In the embodiment under discussion, the bearing unit A is a third-generation wheel support bearing unit whose inner member forms part of a hub. The bearing unit A may be a first-generation or second-generation wheel support bearing unit whose inner member and a hub of a wheel are separate components of each other. The bearing unit A may be a tapered rollers type wheel support bearing unit of any generation.

As shown inFIG. 5, the wheel support bearing assembly includes the brake unit D that includes the electric brake equipment which uses the electric motor50to moves the brake pad(s)47. This prevents environmental contamination which may be caused by oil leakage that occurs in a hydraulic brake equipment. Such an electrically-powered brake allows for rapid adjustment of movement of the brake pad(s)47, thereby resulting in improved response in control of the rotational speeds of the left and right drive wheels70under cornering.

Also, the wheel support bearing assembly electrically actuates the damper unit74of the suspension system73, thereby resulting in improved response in suspension control and also resulting in more stable vehicle attitude.

In the above description, the signal processor unit130is configured to estimate the forces acting along three axes between the drive wheel70and the road surface, for output which is used to control the driving of the electric motor unit B, and/or the actuation of the brake unit D, and/or the actuation of the suspension system73. It is more preferred that signals from a steering apparatus be also used for these respective controls, to achieve further adequate control for an actual travel. Furthermore, the wheel support bearing assembly of the invention may be applied to all wheels of the automotive vehicle or may only be applied to one or some of the wheels (i.e. not all of the wheels).

FIG. 16toFIG. 20shows the second embodiment of the invention. In this embodiment, the wheel support bearing assembly with sensor and in-wheel motor integration according to the first embodiment as shown inFIG. 1toFIG. 15is modified to include sensor unit(s)120with the following configuration. As shown in the enlarged plan view ofFIG. 17and the enlarged cross sectional view ofFIG. 18, each of the sensor unit(s)120includes a strain generator121and two strain sensors122attached to the strain generator121to sense strain of the strain generator120. The strain generator121includes three fixation contact segments121afixed, via respective spacers123, in contact with the outer diameter surface of the outer ring1. The three fixation contact segments121aare arranged in a line that extends in a longitudinal direction of the strain generator121. InFIG. 18, a strain sensor122A of the two strain sensors122is located between the fixation contact segment121aon a left end of the strain generator121and the fixation contact segment121aon a center of the strain generator121, whereas the other strain sensor122B of the two strain sensors122is located between the fixation contact segment121aon a center of the strain generator121and the fixation contact segment121aon a right end of the strain generator121. As shown inFIG. 17, the strain generator121includes respective cutout(s)121bformed in opposite side edges at two locations where the respective strain sensors122A,122B are associated with the strain generator121.

Each of the sensor unit(s)120is associated with the outer ring1such that the three fixation contact segments121aof that strain generator121are positioned at substantially the same axial coordinate of the outer ring1and also circumferentially spaced apart from each other. The fixation contact segments121aare fixed, via respective spacers123, by respective bolts124in contact with the outer diameter surface of the outer ring1.

In another example as shown in the cross sectional view ofFIG. 19, the outer diameter surface of the outer ring1may have respective grooves1cformed therein, at respective mid-locations between three portions of the outer diameter surface, with the three portions being where the three respective fixation contact segments121aof the strain generator121are fixed. This also allows for a space to be formed, without the spacers123, between the outer diameter surface of the outer ring1and where the cutout(s)121bare formed in the strain generator121. Other constructions and arrangements of the sensor unit(s)120are similar to those in the first embodiment shown inFIG. 1toFIG. 15.

In the embodiment under discussion, the average value and amplitude value calculator circuitry132of the signal processor unit130in the first embodiment shown inFIG. 1toFIG. 15is modified to compute the sum of the output signals from the two strain sensors122A,122B for each of the sensor unit(s)120, and to take out the sum as an average value. The difference of the output signals from the two strain sensors122A,122B is also computed and the differential value is taken out as an amplitude value.

Similarly to the previously discussed embodiment, each of the sensor unit(s)120is associated with the outer ring1at an axial coordinate within the proximity of where the outboard raceway surface3of the outer ring1is located. As a result, the output signals a, b from the respective strain sensor(s)122A,122B include influences from the rolling elements5that move in the proximity of where the respective sensor unit(s)120is/are disposed, as shown in (A) through (C) ofFIG. 20. Note that, even when the wheel support bearing assembly is in rest, the output signals a, b from the respective strain sensor(s)122A,122B still include influences from the rest positions of the rolling elements5. The sensor output signals a, b from the strain sensors122A,122B reach maximum values thereof when the rolling elements5move in the closest proximity to the respective strain sensors122A,122B of the sensor unit120(or when the rolling elements5are resting in such locations), and the sensor signals a, b decline as the rolling elements5move away from such locations (or when the rolling elements5are resting in locations away from such locations) as shown in (A) and (B) ofFIG. 20. During the operation of the bearing assembly, the rolling elements5, one after another with a defined pitch P, move past the proximity of where the respective sensor unit(s)120is/are disposed. Accordingly, the output signals a, b from the strain sensors122A,122B have a waveform similar to a sinusoidal wave such as the one illustrated by a solid line in (C) ofFIG. 20with cyclical changes in a period that corresponds to the pitch P of the rolling elements5.

The output signals a, b from the strain sensors122A,122B include influences such as temperature-related influences. In the embodiment under discussion, the sum of the output signals a, b from the two strain sensors122A,122B is calculated to determine the aforementioned average value, and the difference in amplitude between the output signals a, b is calculated to determine the aforementioned amplitude value. In this way, the fluctuation caused by the movement of the rolling elements is cancelled in the average value. Influences such as temperature-related influences that may appear in the respective output signals a, b from the two strain sensors122A,122B are cancelled in the amplitude value. Therefore, the use of the average value and the amplitude value allows for more precise estimation of loads that act on the bearing unit A and/or the tire contact surface with the road.

In (A) through (C) ofFIG. 20, the arrangement of the three fixation contact segments121aare such that they are arranged in a circumferential line and associated with the outer ring1at the outer diameter surface thereof, wherein the outer ring1forms the stationary raceway member. In the figure, the distance between the two fixation contact segments121aon the opposite sides of the arrangement equals the pitch P of the rolling elements5. As a result, the circumferential distance between the two strain sensors122A,122B that are located at respective mid-locations between the neighboring fixation contact segments121ais substantially ½ of the pitch P of the rolling elements5. Therefore, the output signals a, b from the two strain sensors122A,122B are substantially 180° out of phase from each other, and the fluctuation caused by the movement of the rolling elements5is cancelled in the average value that is determined as the sum of the output signals a, b. Influences such as temperature-related influences are cancelled in the amplitude value that is determined as the difference between the output signals a, b.

Note that in (A) through (C) ofFIG. 20, by selecting the distance between the two fixation contact segments121aon the opposite sides of the arrangement to be equal to the pitch P of the rolling elements5and by arranging the strain sensors122A,122B in the respective mid-locations between the neighboring fixation contact segments121a, the circumferential distance between the two strain sensors122A,122B is indirectly made to be substantially ½ of the pitch P of the rolling elements5. In another example, the circumferential distance between the two strain sensors122A,122B may directly be chosen to be substantially ½ of the pitch P of the rolling elements5. Likewise, the circumferential distance between the two stain sensors122A,122B may directly be chosen to be ½+n of the pitch P of the rolling elements5with n being an integer, or to a value that is approximate to that value. In this case, too, the fluctuation caused by the movement of the rolling elements5is cancelled in the average value that is determined as the sum of the output signals a, b from the strain sensors122A,122B, and influences such as temperature-related influences are cancelled in the amplitude value that is determined as the difference between the output signals a, b.

FIG. 21Ashows a front elevational view of a casing33of a reduction gear unit C according to the third embodiment of the invention, as viewed from an outboard side, andFIG. 21Bshows a side view (end elevational view along the line XXIA-XXIA) of a substantial portion fromFIG. 21A. As shown inFIG. 21A, the casing33of the reduction gear unit C includes an outboard end having cable guide cutout(s)33bformed therein, with the cutout(s)33bhaving a shape of a circumferentially extending groove—that is, the cutout(s)33bincluding a circumferential groove. Signal cable(s)129drawn out of cable insertion hole(s)92of the flange1aof the outer ring1pass through the cutout(s)33bthat have/has a shape of a groove, to connect to the signal processor unit130.

The cutout(s)33bof the casing33are located at location(s) out of phase from the signal processor unit130. In the illustrated example, the cutout33bis located at a location about 90° out of phase from the signal processor unit130. From the casing33, a material is cut out starting from a circumferential location P1that confronts the cable insertion hole(s)92and removed along a direction substantially parallel to a tangential direction of the casing33, to form a side surface33baof the groove of the cutout(s)33b. From the casing33, a material is cut out starting from the proximity of the location P1and removed in a radial direction of the casing33, to form an opposite side surface33bbof the groove of the cutout(s)33b. As shown inFIG. 21B, a material is also cut out to form a bottom surface33bcof the groove of the cutout(s)33b, such that the bottom surface33bcextends in a plane perpendicular to an axial direction of the bearing assembly.

A waterproof seal94surrounds signal cable(s)129drawn out of the cable insertion hole(s)92. The waterproof seal94fills the entire groove(s) of the cutout(s)33bof the casing33. Such signal cable(s)129passing through the cutout(s)33bthat have/has a shape of a groove and is/are formed in the casing33allows for sealing the signal cable(s)129over a longer length thereof than could be sealed when the signal cable(s) were radially drawn such as shown inFIG. 2. In other words, more improved sealing effect can be achieved between a surface of the signal cable(s)129and the waterproof seal94. Also, the signal cable(s)129can have a greater bending radius that is the case with when the signal cable(s)129were radially drawn. Therefore, even signal cable(s)129with thick coatings can be wired with ease. Also, the radial sticking-out of signal cable(s)129can be minimized. Accordingly, the entire size of the sensor unit(s) can be reduced.

REFERENCE NUMERALS

1: OUTER RING

22: CASING OF ELECTRIC MOTOR UNIT

33: CASING OF REDUCTION GEAR UNIT

70: DRIVE WHEEL

120: SENSOR UNIT

121a: FIXATION CONTACT SEGMENT

130: SIGNAL PROCESSOR UNIT

137: MOTOR CONTROLLER UNIT