Oil bath encoder seal

An oil lubricated rotating hub (14) and stationary spindle (12) assembly includes an oil bath seal (16, 16′) for establishing a dynamic sealing interface between the hub (14) and spindle (12). A wheel sensor assembly includes a variable reluctance senor (54) targeted at an encoder ring (56, 56′) which is integrated into the oil bath seal (16, 16′). The encoder ring (56, 56′) is of the permanent magnet type including a plurality of magnetically polarized sectors alternating between North and South polarities. The use of an encoder style target (56, 56′) in combination with a variable reluctance sensor (54) enables improved slow speed sensing with relatively large air gap spacing between the exposed (58, 58′) of the encoder ring (56, 56′) and the head of the VR sensor (54). Furthermore, the encoder ring (56, 56′) enables use of less expensive, lighter materials for the oil bath seal carrier (20, 20′).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention relates generally to a vehicular wheel hub assembly including an integrated oil seal and speed sensor feature.

2. Related Art

Vehicle speed sensors integrated into a wheel assembly have many useful purposes. One common use for a speed sensor assembly is to cooperate with the vehicle anti-lock braking system. During a vehicle braking condition, a speed signal generated by pulsed electrical signals from the speed sensor assembly is sent to an on-board computer that responds to the drop in vehicle speed. If a wheel lock-up condition is anticipated, the computer directs a valve in the brake system to relieve or modulate the fluid pressure within the brake assemblies at the wheel thereby preventing an undesired wheel lock-up condition. When the computer determines that a lock-up condition is no longer imminent, the braking pressure is returned to normal operation.

In the case of larger trucks and commercial vehicles, it is common to incorporate a so-called oil bath seal between the rotating hub and its stationary spindle to keep lubricating fluid contained within the confines of the roller bearing assemblies. For such applications in which a vehicle speed sensor is desired, it has been taught to incorporate the target portion of the speed sensor assembly into the oil bath seal. In other words, the target for the speed sensor assembly is mounted to that part of the oil bath seal which rotates with the hub about the stationary spindle. The stationary portion of the sensing device, i.e., the sensor per se, is directed at the target in close proximity so that electrical pulses can be generated as the hub rotates, which electrical pulses are then converted into vehicle speed.

According to prior art techniques, speed sensor assemblies such as used in vehicle wheel systems fall into two general categories, namely variable reluctance and inductive type sensor systems. A variable reluctance sensor is a passive device which projects a magnetic field through a coil toward a ferrous target which serves as an actuator. As the actuator target moves, its discontinuities in the form of gear teeth, blades, etc., excite a voltage in the coil, thus producing an electrical sinusoidal wave current with frequency and voltage proportional to the target velocity. As each discontinuity passes by the pickoff coil, it generates a pulse and a pulse train as cycles are repeated. Variable reluctance type sensors are sometimes preferred for the comparatively large voltage amplitudes generated in operation.

Inductive sensors, while somewhat similar in configuration to the variable reluctance type and which generate the same type of signal, are nevertheless distinguished in that its inductive pickoff coils have no internal permanent magnet. Rather, an inductive sensor relies on external magnetic field fluxuations, such as a rotating permanent magnet in order to generate signal pulses. The rotating permanent magnet is often referred to as an encoder ring, and has never been used with the older-style VR sensor because the magnetic flux field produced by the encoder ring has been thought too weak to produce sufficient signal strength.

While both types of sensor assemblies have been proposed for use in vehicle wheel sensing applications, the large truck or commercial vehicle applications in which an oil bath seal is used in connection with a rotating hub and spindle assembly more typically make use of the variable reluctance (VR) type sensor configuration. The target for a VR system, which is also referred to as a tone ring, may be integrated with an oil bath seal. The tone ring is characterized by its thick, gear-like teeth or otherwise crenulated ring-like features. One example of a variable reluctance sensor for use in this type of application may be found in U.S. Pat. No. 5,476,272 to Hixon, grated Dec. 19, 1995 and assigned to the Assignee of this invention.

Because of the fundamental differences between the variable reluctance-type sensors and the inductive-type sensors, during maintenance operations when an oil bath seal is removed, it is required that its replacement include a tone ring style target for the variable reluctance sensor having the same number of teeth or crenulations as the part it is replacing. And while the tone ring style target designs have become somewhat disfavored because of their comparatively lower durability, thickness/weight and susceptibility to debris accumulation and corrosion, changing to an inductive type sensor would require the added expense and labor of also changing its inductive pickoff coil to the type used in an inductive-type sensor assembly. Accordingly, once a variable reluctance type sensor assembly is installed in a vehicle, subsequent maintenance operations continue to require an older style disfavored tone ring type target even though industry preferences are moving toward an inductive type sensor assembly.

SUMMARY OF THE INVENTION

The subject invention comprises an oil lubricated rotating hub and stationary spindle assembly comprising a spindle defining a rotary axis. A hub is supported on the spindle for rotation about the axis. An oil bath seal establishes a dynamic sealing interface between the hub and the spindle. The oil bath seal includes a metallic carrier fixed relative to the hub and a flexible sealing element extending from the carrier for establishing a fluid impervious seal during relative rotation between the hub and the spindle. An annular encoder ring is disposed on the carrier and is positioned concentrically about the axis. The encode ring has an exposed face comprising a plurality of magnetically polarized sectors alternating between North and South polarities. A variable reluctance sensor is disposed adjacent the encode ring for projecting a magnetic field toward the polarized sectors and producing a sinusoidal wave current in response to the movement of the polarized sectors therethrough. The sinusoidal wave current has a frequency which is proportional to the rotational velocity of the hub.

Accordingly, the subject invention advantageously makes use of an encoder ring style target which is used on inductive sensor type assemblies and has become more favorable in use due to its lower cost, compact size, lightweight and durability as compared with the prior art tone ring style targets. However, the sensor used with the subject encoder ring is a variable reluctance (VR) type sensor which, according to the prior art, has been used before only in connection with a thicker tone ring style target. Thus, the subject invention unites an encoder ring style target with a variable reluctance type sensor to produce the signal used to calculate vehicle speed. This novel approach allows service operators to replace old style tone ring type targets with the newer, preferred encoder style ring when the oil bath seal is replaced on the vehicle.

According to another aspect of the invention, an oil bath seal is provided of the type for establishing a dynamic sealing interface between a rotating hub and a stationary spindle. The oil bath seal comprises a metallic carrier including a carbon steel flange. A flexible sealing element is fixedly joined to the carrier for establishing a fluid impervious seal against an opposing surface, such as a wear sleeve or the spindle per se. An annular encoder ring is fixed to the flange concentrically about the axis. The encoder ring has an exposed face comprising a plurality of magnetically polarized sectors alternating between North and South poles. A carbon steel flange includes a pilot feature for locating the encoder ring on the flange in a centered condition relative to the axis. Accordingly, the subject oil bath seal can be more rapidly produced, in that the pilot feature allows rapid locating and placement of the encoder ring on the flange in a perfectly centered condition.

According to yet another aspect of the invention, a method for replacing an oil bath seal includes the steps of providing a stationary spindle, providing a hub rotatably supported upon the spindle, providing a used oil bath seal in the interstitial space between the hub and the spindle, the used oil bath seal having an integrated tone ring style target for a variable reluctance sensor, removing the used oil bath seal, and installing a new oil bath seal in the interstitial space between the hub and spindle, the new oil bath seal having an encoder ring style target comprising a plurality of magnetically polarized sectors alternating between North and South polarity. According to the subject method, a new oil bath seal assembly having a preferred encoder ring style target is used as a replacement for an old style tone ring style target. The variable reluctance sensor unit associated with the old style tone ring can be reused even though the style of target has been changed to that which has, according to prior art teachings, been used only in connection with inductive type sensors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the Figures, wherein like numerals indicate like or corresponding parts through the several views, a simplified cross-sectional view of an oil lubricated rotating hub and stationary spindle assembly is generally shown at10. The assembly10, which may be of a truck axle-wheel type, includes a stationary axle or spindle, generally indicated at12, and a rotating wheel hub, generally indicated at14. The hub14is supported on the spindle12for rotation about a central axis “A”. InFIG. 1, only that half of the assembly10above the central axis “A” is depicted, it being understood that the lower half is a mirror image.

An oil bath seal, generally indicated at16, establishes a dynamic sealing interface between the hub14and the spindle12. In a typical arrangement, oil or other lubricating fluid will be contained in the interstitial space between the hub14and the spindle12on the left side of the oil bath seal16as view fromFIG. 1, whereas the right hand side of the oil bath seal16will be exposed to ambient air. A tapered roller bearing assembly18provides the rotational support for the hub14upon the spindle12. The roller bearing assembly18is contained on the oil side of the oil bath seal16, so that it receives continuous lubrication during operation. Additional taper roller bearing assemblies18may be provided for added stability and as may be specified.

Referring now toFIG. 2, the oil bath seal16is shown in greater detail including a formed metal case or carrier20preferably fabricated from a carbon steel material. The carrier20is fixed relative to the hub14so that it rotates with the hub about the spindle12and its axis “A”. This fixation is accomplished by press fitting a cylindrical outer wall section22of the carrier20within a correspondingly shaped female feature of the hub14. A flow-on-gasket24can be applied to the outer wall22to perfect a fluid tight seal and improve retention within the hub14. A cylindrical inner wall26is integrally connected to the outer wall22through an elbow feature28. The carrier20further includes a radially extending shelf30extending from the inner wall26. Opposite the shelf30, extending radially outwardly from the outer wall22, is a flange32.

The oil bath seal16further includes a flexible sealing element extending from the carrier12for establishing a fluid impervious seal during relative rotation between the hub14and the spindle12. The flexible sealing element can take many forms. InFIG. 2, the flexible sealing element is depicted as a bonded polytetrafluoroethylene (PTFE) type seal34which is bonded to the shelf30. These well-known hydrodynamic style seals34provide long service life in oil bath seal applications. In additional to the bonded PTFE seal34, the flexible sealing element may also include an inner radial dust lip36, and outer radial dust lip38, a first radial extending axial dust lip40and a second radial extending axial dust lip42. All of these dust lip seals36-42contribute to the dynamic sealing interface so as to maintain a clean separation between the oil inside the rotating hub14and the air outside. Preferably, the dust lips36-42are formed simultaneously with the operation of bonding the PTFE seal34to the shelf30in an over-molding operation. Thus, the particular elastomeric formula used to bond the PTFE seal34to the shelf30may be suitable to create the various dynamic dust lips36-42, or in the alternative some intermediate bonding agent may be necessary to achieve a good adhesion for the PTFE seal34.

The oil bath seal16of the preferred embodiment also includes a wear sleeve44which is nested with the carrier20. The wear sleeve44is provided with an annular running surface46concentrically disposed about the axis “A”. The various seal and lip features of the sealing element are held in dynamic engagement with the running surface46during rotation of the hub14. As shown inFIG. 2, the running surface46is contoured to provide both radial and axial engagement surfaces against which the PTFE seal34and the dust lips36-42engage, thereby creating a barrier for oil migration to the air side of the oil bath seal16as well as against dust infiltration from the air side. An axial thrust pad48may be formed simultaneously with the over-molding operation on the carrier20to provide a spaced bumper against which the running surface46engages, thereby preventing over-compression of the axial dust lips40-42and misalignment of all the sealing element features with respect to the wear sleeve44. The internal diameter of the wear sleeve44can be over-molded with an elastomer formation50to perfect a fluid impervious, tight-fitting engagement with the stationary spindle12.

The wear sleeve44is an optional feature, however as some applications for an oil bath seal may employ integral features of the spindle12against which to establish sealing contact with the various flexible sealing elements. In the example depicted inFIGS. 1 and 2, however, the oil bath seal16is provided with an integral wear sleeve44which is preferably of the unitized variety, meaning that the wear sleeve44is permanently joined to the oil bath seal16. This unitizing effect is accomplished by a keeper52which prevents separation of the wear sleeve44from the carrier20. The keeper52, in this embodiment, comprises an L-shaped ring crimped in position to the oil side of the wear sleeve44after the carrier20has been properly seated on the running surface46.

The subject oil bath seal16is configured to cooperate with a wheel speed sensor assembly, such as may be used for sensing or detecting the wheel speed. Referring again toFIG. 1, the wheel speed sensor assembly is shown including a stationary sensor54of the variable reluctance (VR) type. The VR sensor54is affixed in any known fashion to a non-illustrated mounting structure carried by the spindle12, which results in a stationary mounting of the VR sensor54. The VR sensor54is of the typical strain-based variety which projects a magnetic field through an internal coil. An alternating voltage is generated in the coil through fluxuations in the magnetic field.

In prior art configurations, the teeth of a tone-ring type target excite a voltage in the coil, thus producing an electrical sinusoidal wave current. However, in the subject invention, the more traditional tone ring type target is substituted with an encoder ring56such as found only in inductive sensor systems. The encoder ring56is an annular member disposed on the carrier20and positioned concentrically about the axis “A”. Concentricity is assured through use of an appropriate piloting feature, such as an outer lip overhanging the edge of the carrier flange32, or by extension of the elastomeric over-mold material up to the inside diameter of the encoder ring56. The encoder ring56has an exposed face58comprising a plurality of magnetically polarized sectors alternating between North and South polarities. The VR sensor54is positioned proximate the exposed face58of the encoder ring56and projects its magnetic field toward the polarized sectors so as to produce a sinusoidal wave current in response to movement of the polarized sectors through the magnetic field. The sinusoidal wave current will have a frequency which is proportional to the rotational velocity of the hub14.

The polarized sectors are perhaps best illustrated inFIG. 4and are formed by a continuous annular strip of permanent magnets disposed on the flange32in full surface-to-surface contact. The encoder ring56can overlie the outer-most edge of the flange32as shown inFIG. 2, or not as shown inFIG. 4. Preferably, although not necessarily, the encoder ring56is of the elastomer based ceramic magnetic type whose general composition is known from gasketing and other sheet type applications of such magnets. Alternatively, the encoder ring56can be formed in an over-molding operation with the magnetic qualities imparted in a subsequent magnetizing operation. About the circumference of the flange32, the encoder ring56may be divided into any number of polarized sectors provided the number of such sector is even and their arcuate dimension is substantially equal. Each sector presents a North or South polarization on the exposed face58which is different from that of the adjacent sectors, such that the exposed face58alternates in North-South increments regularly about its circumferential measure. The axial thickness of the encoder ring56may be distinguished by a median line60which, although not visible, represents a polarity reversal within each sector toward the back side of the encoder ring56.

Because the magnetic strength of such encoder rings56are fairly weak, the amount of fluxuation in the magnetic field produced by the VR sensor54would typically be too weak to detect. However, because the flange32is composed of a carbon steel material and backs the encoder ring56in full surface-to-surface contact, the magnetic field strength produced by the encoder ring56, looping between adjacent poles or sectors, is substantially enhanced to the point where the VR sensor54is capable of detecting and being influenced by the magnetic discontinuities. Thus, an electrical sinusoidal wave current is produced through the magnetically enhanced fields of the encoder ring56, resulting from the full surface-to-surface backing by the carbon steel flange32. Accordingly, a gain in the flux amplitude of the encoder ring56is achieved when it is backed by the carbon steel flange32.

FIG. 5illustrates an alternative embodiment of the subject encoder ring56which including a plurality of radial grooves62disposed in the exposed face58. One groove62is associated with each of the polarized sectors, and extends radially along the line of separation between adjacent polarized sectors. The depth of the grooves62may be varied to suit a particular application, but in the preferred embodiment they will have an axial depth measured from the exposed face58less than or equal to ⅔ of the axial thickness of the encoder ring56. The grooves62have an affect of accentuating the magnetic field created by the encoder ring56so as to sharpen the wave form of electrical sinusoidal wave current produced when the hub14is rotated. Thus, it is possible that more accurate pulses can be generated for use in the vehicle wheel speed sensor system.

InFIG. 6, an alternative embodiment of the grooves62′ is depicted. In this case, the grooves62′ are again radially disposed through the exposed face58, but instead of being placed along the line of separation between adjacent polarized sectors, each groove62′ is disposed centrally within each polarized sector, thereby dividing its polarized face into two half sectors. Like the boundary line grooves62shown inFIG. 5, the sector-bisecting grooves62′ accentuate the magnetic field created by the encoder ring56and thereby improve the sensing quality.

InFIG. 3, an alternative configuration for the subject oil bath seal is generally indicated at16′. In connection withFIG. 3, the prime designation is used to identify features identical to or readily corresponding with those described above in connection with the other figures. Thus, the oil bath seal16′ ofFIG. 3includes a carrier20′ having a flange32′ upon which an encoder ring56′ is attached by bonding. In this example, the encoder ring56′ does not include the overhanging outer lip feature depicted inFIG. 2. Rather, the location of the encoder ring56′ is accomplished by a pilot64′ formed on the flange32′. The pilot64′ can be a separate feature or integrally molded with the dust lips36′-42′. In lieu of the overhanging outer lip, the pilot64′ serves as the sole centering feature, having an outer edge which corresponds to the inner diameter of the encoder ring56′, so that it can be readily placed on and bonded to the flange32′. For this purpose, an adhesive66′ can be used to achieve satisfactory bonding. The adhesive66′ may, for example, comprise a 0.005-0.025 inch thick elastomeric film, which may or may not be pre-magnetized. In fact, the adhesive66′ may be intentionally non-magnetic. In this alternative embodiment, a soft unitizing configuration is achieved by use of a non-contacting retention lip68′ which overhangs an upstanding part or radially outwardly projecting end flange45of the wear sleeve44′. The soft flexible unitizing retention lip68′ functions as the keeper in this embodiment by capturing the end flange45which is pushed past the lip68′ as illustrated inFIG. 3, thereby eliminating the rigid formation shown inFIG. 2.

It will be appreciated that the various alternative configurations shown inFIGS. 3,5and6can be interchanged with one another and with features shown in the preferred embodiment ofFIGS. 2 and 4. Furthermore, other types of sealing arrangements and formations of the carrier20and wear sleeve44are possible, depending largely upon the intended application.

A particular advantage of an encoder ring style target for the VR sensor54can be seen inFIGS. 2 and 3, wherein the air side of the oil bath seal16,16′ is substantially encased in corrosion resistant material. This fact is enhanced by use of the pilot feature64,64′ which, by virtue of the over-molded elastomer, provides substantial sealing integrity and protection for the exposed carbon steel component. Furthermore, because an encoder ring56,56′ can be made substantially thinner than a prior art tone ring which demanded discernable discontinuities such a gear teeth or crenulations, the carrier20,20′ can be made from substantially thinner and less costly material. Thus, by protecting the exposed surfaces on the air side of the carrier20,20′ with elastomeric over-molding and by the corrosion resistant encoder ring56, thinner and less expensive sheet metal can be used to form the carrier20, without the need for corrosion resistant coating or paint. Another advantage of the subject encoder ring56,56′ results from the permanent magnetic quality of this type of target. More particularly, the permanent magnet encoder ring56,56′ will attract ferrite particles which may otherwise fall into the oil bath seal16,16′ and degrade the flexible sealing element.

Another significant advantage of the subject invention which combines the encoder ring56,56′ with a VR sensor54resides in its ability to demonstrate acceptable voltage signal performance at minimum wheel speeds, and at relatively large air gaps. For example, as depicted in the table below, testing conducted to compare the voltage output produced by a prior art tone ring in combination with its VR sensor was made against the subject encoder ring56,56′ placed into service with the same VR sensor54. The tests were conducted at wheel speeds of 30, 50 and 100 rpm, and each wheel speed was measured at air gaps (i.e., axial spacing between the VR sensor54and the exposed face58,58′) of 0.01, 0.02 and 0.03 inches.

As shown above, while the peak voltage produced by the subject encoder ring56,56′ is lower than that produced by a prior art tone ring at the lower air gap spacings, it is noteworthy that the subject encoder ring56,56′ achieves less overall signal loss as the air the gap increases. Furthermore, the subject encoder ring56,56′ maintains significantly higher voltage amplitudes at slower wheel speeds with the larger air gap, thereby enabling more accurate speed sensing at lower speeds.