Patent Application
20060023985
None.
Not Applicable.
This invention relates to bearings and more particularly to a bearing system containing a piezoelectric device for controlling the setting of the bearings in the system.
Tapered roller bearings and some other antifriction bearings with inclined raceways, such as angular contact ball bearings, have the capacity to transfer thrust (axial) loads as well as radial loads. When two single row bearings of this type are mounted in opposition, the bearing system so formed has the capacity to transfer or take thrust loads in both directions, and of course radial loads. Moreover, the bearings can be adjusted against each other so that the setting for the bearings can be varied between end play and preload.
When a bearing system operates with end play, clearances, both radial and axial, exist within one or both of its bearings, that is to say the rolling elements of at least one of the bearings do not seat against their raceways for the full circumferences of those raceways. This produces instability in that which rotates on the bearing or, in other words, the axis of rotation is not entirely fixed. However, wear in the bearing is minimal when the bearings are in end play.
When a bearing system operates in preload, the rolling elements of both bearings contact their raceways for the full circumferences of those raceways. This brings stability to the system. But preload increases friction and wear in the bearings, and heavy preloads can induce early failure.
Most equipment that utilizes opposed antifriction bearings operates more efficiently with the bearings set to light preload. However, in some applications, a variance in the preload or even a variance between end play and preload would seem desirable. For example, the opposed bearings that couple the road wheel of an automotive vehicle to the suspension system of the vehicle require little preload and only moderate stability when the vehicle travels straight at moderate speeds. But when the vehicle negotiates turns, particularly at high speeds, the bearing system for the wheel should have greater stability.
Many times, shafts and the bearings which support them are made from steel, while the housings which enclose them are made from aluminum. The differential thermal expansion and contraction which ensues can disrupt bearing settings. Compensating devices exist, but are not entirely satisfactory.
Also, manufacturers of equipment that utilizes rotating components supported on opposed antifriction bearings need to know the optimum setting for the bearing—a setting that will perhaps produce the least noise in gears—and to determine this with multiples setups established by shims of varying thickness is a time-consuming and imprecise procedure.
To be sure, hydraulic systems exist for varying preload—and end play—in bearings systems formed by opposed single row bearings. However, these systems react somewhat sluggishly, consume considerable space, and require complex fluid devices to vary pressure.
Referring now to the drawings, a bearing system A, shown in
Considering the shaft 2 first, it has a bearing seat 20 which leads up to a shoulder 22 for the head bearing 6. Shaft 2 also has a smaller bearing seat 24 for the tail bearing 8 and a threaded end 26 beyond the seat 24. The shaft 2 carries a collar 28 which forms a shoulder at one end of the smaller bearing seat 24. The collar 28 is positioned with a nut 30 that threads over the threaded end 26.
The housing 4 includes a counterbore 36 which at one end opens into the interior of the housing 4 and at an opposite end leads up to a shoulder 38. The counterbore 36 contains the actuator 10 and also serves as another bearing seat for the head bearing 6. The counterbore 36 surrounds the bearing seat 20 for the shaft 2. The housing 4 also has another counterbore 40 which at one end opens out of the housing 4 and at its opposite end leads up to a shoulder 42. The counterbore 40 contains the piezoelectric actuator assembly 12 and serves as a bearing seat for the tail bearing 8. Counterbore 40 surrounds the bearing seat 24 for the shaft 2.
Each bearing 6 and 8 includes an inner race in the form of a cone 48, an outer race in the form of a cup 50, and rolling elements in the form of tapered rollers 52 organized in a single row between the cone 48 and the cup 50. The cone 48 has a tapered raceway 56 which is presented outwardly away from the axis X and a thrust rib 58 at the large end of the raceway 56. The thrust rib 58 leads out to a back face 60 that is squared off with respect to the axis X. The cup 50 has a tapered raceway 62 that is presented inwardly toward the axis X and toward the raceway 56 of the cone 48. The raceway 62 at a small end leads out to a back face 64 that is also squared off with respect to the axis X. The tapered rollers 52 lie in a row between the raceways 56 and 64, with their tapered side faces contacting the raceways 56 and 62 and their large ends bearing against the thrust rib 58 on the cone 48. Generally speaking, line contact exists between the side face of each roller 52 and the tapered raceways 56 and 62.
The thrust rib 58 prevents the rollers 52 from moving up the raceways 56 and 62 and being expelled from the annular space that they occupy between the raceways 56 and 62. The tapered rollers 52 are on apex, meaning that the conical envelopes within which their side faces lie have their apices at a common point along the axis X. Likewise, the conical envelopes in which the tapered raceways 56 and 62 lie have their apices at the same point.
The cone 48 of the head bearing 6 fits over the bearing seat 20 of the shaft 2 with an interference fit. A back face 60 of the cone 48 fits against the shoulder 22 at the end of the seat 20. The cup 50 of the head bearing 6 fits into the counterbore 36 in the housing 4 with a slightly loose fit. A back face 60 of cup 50 is presented toward, yet spaced from the shoulder 38 at the end of the counterbore 36. The rollers 52 of the head bearing 6 are disposed between the cone 48 and cup 50 of that bearing 8.
The cone 48 of the tail bearing 8 fits over the other bearing seat 24 on the shaft 2, again with an interference fit. The back face 60 of cone 48 bears against the shoulder formed by the end of the collar 28. The cup 50 of the tail bearing 8 fits into the counterbore 40 in the housing 4 with a slightly loose fit. A back face 64 of the cup 50 is presented toward, yet spaced form the shoulder 42 at the inner end of the counterbore 40. The rollers 52 for the bearing 8 reside between the cone 48 and cup 50 for the bearing.
Each of the piezoelectric actuator assemblies 10 and 12 possesses an annular configuration as shown in
Each piezoelectric actuator assembly 10 and 12 comprises a series of plates 70 arranged face to face to create a stack, and associated electrical leads 72 extending from the stack for connection across an electrical potential of variable voltage. Each plate 70 is formed from a piezoelectric ceramic, and the individual plates 70 are each connected to the leads 72 such that each may be placed across an electrical potential. Each plate 70 produces an electrical potential when compressed, and conversely when an electrical potential is impressed across it, it expands in at least an axial dimension. Typically a single plate 70 is about 0.0035 in. thick. When electrical potential is impressed across the plate 70, the plate 70 will expand axially about 5 μin. Potentials of a lesser magnitude produce less expansion. Therefore, a stack composed of 200 plates 70 will occupy about 0.7 in (200×0.0035 in) and at the most will expand about 0.001 in. (200×5 μin.) when the maximum electrical potential is impressed across each plate 70. The two piezoelectric actuator assemblies 10 and 12 together occupy about 1.4 in. and expand a maximum of 0.002 in. When expanding, each piezoelectric actuator assembly 10 and 12 is capable of producing a force on the order of 1000 lbs.
The piezoelectric actuator assembly 10 fits snugly between associated cup 50 and the shoulder 38 for the counterbore 36 in which the piezoelectric actuator assembly 10 is confined, and likewise the piezoelectric actuator assembly 12 fits snugly between associated cup 50 and the shoulder 42 of the counterbore 40 in which the piezoelectric actuator assembly 12 is located. This is achieved by turning the nut 30 down against the collar 28 while the rollers 52 of the head bearing 6 are seated against the raceway 56 and 62 of that bearing, so no clearances exist in the bearing 6. As the collar 28 advances over the shaft 2, the collar 28 drives the cone 48 of the tail bearing 8 over associated seat 24 on the shaft 2. The advance terminates when the bearings 6 and 8 achieve the correct setting, which typically is zero end play and preload.
The initial setting established by the nut 30 may provide enough stability for most operating conditions under which the shaft 2 rotates. However, certain conditions may require greater stiffness. When the shaft 2 experiences those conditions, an electrical potential is impressed across each piezoelectric actuator assembly 10 and 12—actually across each plate 70—and the piezoelectric actuator assemblies 10 and 12 expand axially. Each piezoelectric actuator assembly 10 and 12 bears against the back faces 64 of the cups 50 for the two bearings 6 and 8 and drive the cups 50 apart. This imparts preload to the bearings 6 and 8, with the magnitude of the preload depending on the magnitude of the electrical potential, up to a maximum expansion of each piezoelectric actuator assembly 10 and 12.
Preferably, the electrical potential impressed across each piezoelectric actuator assembly 10 and 12 from a power source 50 is regulated by a control circuit 100, shown in
Control circuit 100 is preferably configured in the form of a closed loop control system utilizing a parameter associated with each piezoelectric actuator assembly 10 and 12, and may be displaced from the physical location of the bearing system A, as required for each particular application, when suitable electrical connectors 75 to each piezoelectric actuator assembly 10 and 12 are provided.
In a first embodiment, each piezoelectric actuator assembly 10 and 12 is utilized as a resonance device (i.e., a tank circuit) in a standard oscillator circuit (e.g. Colpitts, Pierce, etc.). Selected resonant frequencies of each piezoelectric actuator assembly 10 and 12 provide a measure of a characteristic of the piezoelectric actuator assembly 10 and 12, from which a elongation information for each piezoelectric actuator assembly 10 and 12 from an initial or desired state can be determined by a suitable comparator 104, such as a microprocessor or other logic circuit having sufficient computational capacity. These resonance frequencies typically have much higher frequencies than the structure within which each piezoelectric actuator assembly 10 and 12 is disposed. The comparator 104 is configured in a responsive manner to regulate the electrical potential from the power source 105 impressed on each piezoelectric actuator assembly 10 and 12 to achieve the desired bearing setting.
In an exemplary embodiment, an excitation voltage is applied to piezoelectric actuator assembly 10, 12 to obtain an indication of length. One half of the piezoelectric actuator assembly 10, 12 is supplied with an excitation voltage which is 180° out-of-phase with respect to the excitation voltage supplied to the remaining half. This produces a sinusoidal node shape in the resonance, with nodes in the middle and at each end. Hence one wavelength of this since wave is equivalent to the length of the piezoelectric actuator assembly 10, 12. Since the patterned excitation voltage is of a significantly higher frequency than the larger operating voltage for each piezoelectric actuator assembly 10, 12, it may be superimposed on top of the larger operating voltage.
Optionally, when utilizing the piezoelectric actuator assembly 10 and 12 as a resonance device, a temperature sensor 106 may be operatively disposed to acquire thermal measurements for each piezoelectric actuator assembly 10 and 12. Thermal measurements supplied to the comparator 104 may then be utilized to compensate for thermal effects on the resonant frequencies.
In an alternate embodiment, a sensor 108, such as a pressure gauge, a strain gauge, or a stress gauge, is disposed to provide a measure of a force exerted at a piezoelectric actuator assembly 10 and 12. A signal representative of the measured force is provided to the control circuit 10. The comparator 104 compares the measured force to an initial or desired state for each piezoelectric actuator assembly 10 and 12, and correspondingly regulates the electrical potential from the power source 105 impressed on each piezoelectric actuator assembly 10 and 12 to achieve the desired bearing setting.
In an alternate embodiment, a displacement sensor 110, such as a capacitive sensor, LVDT, or strain gauge, is disposed to provide a measure of a displacement of each piezoelectric actuator assembly 10 and 12 from an initial state. A signal representative of the measured displacement is provided to the control circuit 10. The comparator 104 compares the measured displacement to an initial or desired state for each piezoelectric actuator assembly 10 and 12, and correspondingly regulates the electrical potential from the power source 105 impressed on each piezoelectric actuator assembly 10 and 12 to achieve the desired bearing setting.
As shown in
Turning to
The hub 302 has a flange 314, to which the rim of a road wheel is attached, and a spindle 316 which projects from the flange 314, it leading away from a shoulder 318 and terminating at a formed end 320 or other device for capturing the bearings 306 and 308 on the spindle 316. The housing 304 contains two bearing seats 322 and 324 in the form of counterbores that lead away from shoulders 326. It also has a flange 328 which is fastened to the suspension system component.
The bearing 306 and 308, each have a cone 48, a cup 50, and tapered rollers 52, which basically correspond to the counterparts in the bearings 6 and 8, although the cones 48 have extensions that abut. The cones 48 fit over the spindle 316 with interference fits, the back face 64 of the cone 48 for the outboard bearing 308 being against the shoulder 318 and the back face 64 of the cone 48 for the inboard bearing 308 being against formed end 320. The cup 50 for the outboard bearing 306 and the piezoelectric actuator assembly 310 fits into the bearing seat 322 of the housing 304, with the piezoelectric actuator assembly 310 being interposed between the shoulder 326 for that seat and the back face 64 of the cup 50. The cup 50 for the inboard bearing 308 and the piezoelectric actuator assembly 312 fits into the other bearing seat 324, with the piezoelectric actuator assembly 312 being interposed between the shoulder 326 of that seat and the back face 64 of the cup 50. The cups 50 fit loosely in their respective seats 322 and 324, and the piezoelectric actuator assemblies 310 and 312 expand and contract to displace the cups 50 axially and thereby control the setting of the bearings 306 and 308.
Variations are possible. For example, a bearing system may adjust its setting through the positioning of the cones 48, in which event the piezoelectric actuators would be behind the back faces 60 of the cones 48. Also, a single actuator located behind the back face 64 of only one of the cups 50 or behind the back face 60 of only one of the cones 48 will suffice. Apart from that, actuators similar to the piezoelectric actuator assemblies 10, 12, 310 and 312 may be installed behind the back faces 64 of cups 50 or the back faces 60 of cones 48 in systems having directly mounted bearings, that is to say bearings in which the large ends of the rollers 52 for the two bearings are presented toward each other. Moreover, piezoelectric actuator assemblies similar to the piezoelectric actuator assemblies 10, 12, 310 and 312 may be utilized with bearing systems having other types of bearings that have inclined raceways which enable them to accommodate both axial loads and radial loads, angular contact ball bearings and spherical roller bearings, for example. In any of the bearing systems, the races that do not displace may be formed integral with the components on which they are positioned, in which event the raceways are formed directly on those components. Furthermore any race that undergoes displacement may be subjected to a force exerted by a spring, with that force seeking to seat the rolling elements against their raceways, and may be resisted by a piezoelectric actuator assembly, so the piezoelectric actuator assembly still controls the position of the displaceable race.
