Patent Application
20100021094
Previously designed rod end bearings for vehicle engines mainly incorporated straight pin and clevis (non-misaligning) pivot joints. These pivot joints have multiple drawbacks, including binding, excessive wearing, and corrosion pitting. With many present-day engines requiring tighter tolerances and better responses at high-temperatures, new pivot joint designs are needed.
There have been several unsuccessful attempts at solving the problems described above. For example, rod end bearings with undesirable misalignment (or more free movement in the bearing) have been designed to attempt to avoid binding. Moreover, multiple variants of high-temperature coatings and/or lubricants have been developed to help increase the corrosion and wear resistance. These coatings or lubricants, while increasing lubricity and protecting from corrosion, did not exhibit the life or wear resistance needed to survive the harsh engine environments, extreme vibration, or high exhaust temperature conditions. In addition, attempts were made using high-temperature specialty alloy steels, but the same issues present with the coatings also surfaced with specialty alloy steels: little or no resistance to vibrational wear at high-temperatures. Previous uses of higher temperature plastics have also been unsuccessful, because the materials were either too brittle or not capable of being formed into the shape needed for this high-temperature bearing race.
Therefore, there exists a need for a new high-temperature rod end bearing having resistance to high-temperature, vibration, life cycle, and corrosion.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In accordance with one embodiment of the present disclosure, a high-temperature bearing assembly is provided. The bearing assembly generally includes a housing portion defining a socket, a swivel device disposed in the socket, and a race disposed between the socket and the swivel device, wherein the race is made from a high-temperature plastic.
In accordance with another embodiment of the present disclosure, a high-temperature bearing assembly is provided. The bearing assembly generally includes a housing portion defining a socket, a swivel device disposed in the socket, and a race disposed between the socket and the swivel device. The race is formed from a high-temperature plastic and the race includes a gap, such that the race collapses when the swivel device is crimped in the socket.
In accordance with another embodiment of the present disclosure, a high-temperature bearing assembly is provided. The bearing assembly generally includes a swivel device disposed in a socket, and a race disposed between the socket and the swivel device, wherein the race is made from a high-temperature plastic.
In accordance with another embodiment of the present disclosure, a method of making a high-temperature bearing assembly is provided. The method generally includes forming a race from a high-temperature plastic, wherein the race is formed in a substantially C-shape, and compressing the race around a swivel device to create a swivel assembly. The method further includes inserting the swivel assembly in a socket, such that the race is positioned between the socket and the swivel device, and crimping the swivel assembly in the socket.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
A high-temperature bearing assembly constructed in accordance with one embodiment of the present disclosure may be best understood by referring to
The improved characteristics of a bearing assembly 20 in accordance with embodiments of the present disclosure improve the capabilities of the bearing assembly 20, such as high-temperature and vibration tolerance and life cycle wear. Such high-quality bearings can be used to position highly sensitive electronic controlled sensors and hydraulic or pneumatic actuation systems. In that regard, this positioning is achieved with minimal lost motion, otherwise described as decreased sensitivity or accuracy in the control systems. In the past, many controls were merely required to open or close valves or louvers; however, now with greater focus on emission standards and operating efficiency, exact bearing positioning is required. As described in greater detail below, the bearing assembly 20 described herein helps achieve exact positioning by allowing the controls to place the output where it is expected to register and thus meeting the efficiency needs of various engine control systems throughout the lives of the systems.
In the illustrated embodiment of
In the illustrated embodiment, the bearing 32 can be pressed and crimped into the head 24 in a manner that allows for pivoting movement of the bearing 32 in the head 24. As a result of the swivel motion, the bearing assembly 20 provides a pivot joint between two parts (not shown). In that regard, the first part would be connected to the swivel device 28 and the second part would be connected to the end shank of the housing portion 22.
As mentioned above, the housing portion 22 includes a head 24 and a shaft 26 extending from the head 24. The head 24 includes a socket 40 for receiving the bearing 32. In that regard, the socket 40 has an inner bore 42 that extends through the socket 40, wherein the inner bore 42 has an inner wall 44 and first and second ends 46 and 48. The socket 40 is configured to hold the bearing 32, but allows for pivotal movement of the bearing 32 relative to the head 24. As described in greater detail below with reference to
As best seen in
The shaft 26 of the housing portion 22 extends from the head 24 and may be a threaded shaft of either the female type having a receiving portion 52 (see
As mentioned above, the swivel device 28 may be a spherical ball swivel or a partially spherical ball swivel. In that regard, the swivel device 28 is configured to swivel with appropriate resistance within the socket 40. The swivel device 28 may include an opening 60 through which a bolt or other attaching hardware (not shown) may pass to connect the swivel device 28 to the first part (not shown). In an exemplary vehicle engine application, the first part may be an electronically controlled actuator.
Still referring to
In accordance with embodiments of the present disclosure, the race 30 is designed to be reliable in harsh engine environments, extreme vibration, and/or high exhaust temperature conditions. In one embodiment, the race 30 is made from a high-temperature plastic. In another embodiment, the race 30 may have high-temperature resistance up to at least about 450 degrees F. In another embodiment, the race 30 may have high-temperature resistance up to at least about 550 degrees F. In another embodiment, the race 30 may have high-temperature resistance up to at least about 650 degrees F. In another embodiment, the race 30 may have high-temperature resistance up to at least about 750 degrees F. In another embodiment, the race does not vary more than 5% from its original shape and size over time, for example, under a low load of about 10 lbs during life cycle testing.
The race 30 is suitably made from a high-temperature plastic having some ductility that can be formed, for example, by injection molding or direct compression molding into a suitable design. One suitable high-temperature plastic is a thermoplastic polymer. A non-limiting example of a suitable high-temperature, high-performance plastic is VICTREX®PEEK™ polyether-ether-ketone thermoplastic (PEEK). The plastic can be molded, for example, by injection molding, into the desired shape of the race, and then can be subsequently inserted into the socket 40 together with the swivel device 28 and crimped into place (see
Another suitable race material is a polyimide plastic. A non-limiting example of a suitable high-temperature polyimide plastic is DUPONT™ VESPEK® polyimide-based polymer. Other grades and brands of polyimide plastics are also within the scope of the present disclosure. Polyimides have high-temperature resistance up to about 650 degrees F. with excursions up to about the mid-700 degree F. range. However, such polyimide materials must be formed by direct compression molding under high pressure, rather than being injection molded, and may require secondary machining after being formed.
In accordance with embodiments of the present disclosure, the race 30 is required to retain its strength in both the axial and radial directions at temperatures of up to and including about 700 F. In a preferable embodiment, the heat deflection temperature of the race is at least approximately the same as the designed maximum operating temperature of the system in which the bearing assembly 20 will perform, for example, at least about 450 F, at least about 550 F, at least about 650 F, at least about 750 F, etc., depending on the application requirements. In addition to strength, the race is required to resist vibration and life cycle wear. In a preferable embodiment, the race has less than a 5% change from its initial free motion limits.
As described in greater detail below in EXAMPLES 1 and 2, the inventors have found that high-temperature and life cycle performance of ceramic, metal-on-metal including high-temperature coatings, and plastics having low glass transition or heat deflection temperatures did not perform as well as the plastic materials described herein. In general, the inventors have found that low glass transition or heat deflection temperature plastics deform at high-temperatures, ceramics crack under high loads, and metal-on-metal wears under life cycle testing to affect the key characteristics of the bearing assembly (torque and free motion). Moreover, metal-on-metal bearings have a tendency to corrode and bind in extreme conditions.
As best seen in the illustrated embodiment, the race 30 may be formed with a gap 64, for example, in a C-shaped design to help accommodate for differences in ductility in the race material, as well as in the various assembly methods (see
The size of the gap 64 in the C-shaped design depends on several factors, including but not limited to the specific application for the bearing assembly 20, expected expansion or swelling in the materials of the head 24, swivel device 28, or the race 30, etc. In one non-limiting example, the gap 64 may be sized to be up to about 0.020 inches. It should be appreciated that, while shown as a C-shaped design, the race 30 may also be designed to have more than one gap, for example, the race may be comprised of two or more parts that together define a race having a substantially circular cross-section. The advantage of the C-shaped design is that it allows for a gap 64 without requiring multiple parts. The collapsability and conformity characteristics of the C-shaped race 30 were shown to be consistent even at high-temperatures when plastics usually become susceptible to deformation at load.
Methods of making the bearing assembly 20 described above will now be described in greater detail. As mentioned above, the race 30 may be formed, for example, by injection molding or direct compression molding, into a suitable shape. If formed by the compression molding, the race will likely require secondary machining during formation to meet the desired specifications.
Referring to
When the race 30 and swivel device 28 are inserted in the socket 40, the torque of the bearing assembly 20 is tested using a test press that moves the swivel device 28 relative to the socket 40 to achieve the desired torque without limited free movement in the socket 40. When the desired torque is achieved, the crown 62 is crimped in place to maintain the swivel device 28 and race 30 in the socket 40 at the desired torque (see
As discussed above, increased sensitivity and accuracy in control systems have become important in bearing applications. It should be appreciated that the exactness of the torque measurements achieved by the methods of making the bearing assembly described herein allow for accurate control systems and prevent undesirable misalignment (or free movement) in the bearing assembly 20.
In some high-temperature applications, the inventors have found that the race material may have some expansion during use. This expansion affects the desired resistance between the swivel device 28 and the socket 40 during use. In order to address this problem, the race 30 is configured in the C-shaped design, with a gap 64 to allow for swelling or expansion into the gap 64. In addition, the race 30 may also be pre-baked before use in the bearing assembly 20 to a high-temperature of about 700 degree F. Such a pre-bake anneals the race 30 and prevents additional expansion during use. However, it should be appreciated that the pre-bake annealing is not required in all application because of variations in temperature and loading during application, which also affects the capabilities and requirements of the bearing assembly.
Now turning to
As mentioned above, embodiments of the present disclosure are not limited to rod end bearing assemblies. In the illustrated embodiment, a plate bearing assembly 120 is shown. Referring to
Strength testing in a rod end bearing assembly was performed in two directions at temperatures of up to and including 700 F: axial direction (direction of axis of bore) and radial direction (direction of axis of housing). Several different materials were used for the race in the strength testing, including a ceramic, a nylon plastic, a polyimide, and a PEEK race, as well as a metal-on-metal bearing having a high-temperature coating, such as an electroless nickel TEFLON® coating. The results of the testing are listed below in TABLE 1. The “PASS” or “FAIL” indicators are directed to whether bearing retention loads of about 250 lbs could be sustained through a temperatures cycle from about 68 F (room temperature) up to about 700 F (high-temperature).
The metal-on-metal bearing with a high-temperature coating performed the best in the strength testing test as a result of the all-steel construction. However, metal-on-metal bearings tended to fail in life cycle testing, described below in EXAMPLE 2.
The plastics (nylon, polyimide, and PEEK) and ceramic races had very high ultimate compression strengths, which resulted in the bearing assembly successfully withstanding high loads in the radial direction. Failure mode testing often resulted in a housing or connecting linkage failing before the race and swivel failed under load in the radial direction.
In the axial direction, the differences in strength between the plastic and ceramic races became more prevalent. Due to the low-fracture toughness of ceramics, the ceramics failed almost immediately regardless of temperature. In most tests, the ceramics cracked at loads of 70% less than the other materials (plastics and metal-on-metal).
The ultimate failure mode in unacceptable plastic races (such as nylon) was seen at or near the heat deflection temperatures of the various plastics. Bearing retention loads would be reduced to nearly zero when the material approached the heat deflection temperature due to loss of the race stiffness. Many common polymers, such as nylons, have heat deflection temperatures well below the high-temperature applications of up to and including about 700 F.
In high-grade polyimide and PEEK materials, the heat deflection temperature is considerably higher than required for expected high-temperature applications. Rather than melting, polyimide plastics tend to oxidize over time at high-temperatures (such as over 800 F) and will degrade the binders in the material such that the plastic becomes brittle. Oxidization was not observed in the testing. In that regard, the polyimide race retained over 95% of its original strength from testing that occurred from about -40 F to up to about mid-500 F or to about mid-700 F based on the specific grade of polyimide and the specific loading and application of the bearing. Because the polyimide material does not melt in the temperature range, like the unacceptable plastic races, some oxidation degradation can be acceptable, particularly at low-loading conditions.
Life cycle testing included variants in amount of repetitive (e.g., up to 30 million cycles) cyclic travel (angular movement of the linkage, e.g., 20 degrees sweeps back and forth) through the expected temperature range of the application (e.g., up to and including 700 F). Several different materials were used for the race in the life cycle, including a polyimide race, a PEEK race, and metal-on-metal bearings having various high-temperature coatings, such as electroless-nickel TEFLON® and high-temperature dry film lubricant (moly). Notably, ceramic and nylon races were not tested due to their failure in the strength testing described above in EXAMPLE 1.
The results of the testing are listed below in TABLE 2. The data shows an increase in play or free movement in percentages in bearing assemblies having races made from the various materials after 20,000,000 cycles as temperature cycles from about 70 F (approximately room temperature) to application specific temperature highs, such a about 700 F under a negligible bearing load of less than about 10 lbs.
After life cycle testing, the metal-on-metal bearing with a high-temperature coating consistently wore in key points in the cyclic travel, resulting in undesired changes in torque and undesired changes in the free motion of the bearing assembly. The inventors found that the coatings degraded during cyclic travel as a result of the repetitive movement of two unforgiving metal surfaces making contact with each other at load; therefore, the slope of degradation was drastic. In most tests, the inventors found that the key characteristics (torque and free motion) would change at about 50% of the expected life cycle. Initially, the parts would tighten from an increase in debris in the socket (i.e., shavings or worn particles from the bearing or raceway itself). The torque required to actuate the linkage would increase at this point. As the parts degraded, the wear would accelerate to a point where the free motion was beyond acceptable levels for accurate movement within the system. Data showed that once the coatings were worn (usually within half of the expected life cycle), subsequent wear would increase by 10 fold compared to the initial free movement in the system. At that level of free movement, the swivel itself would likely become dislodged from the raceway. This type of wear was even more profound when subjected to accelerated wear testing that included debris (dust, sand) and/or vibrational testing with temperature cycles.
The plastic materials (e.g., polyimide and PEEK) in these applications do not have the same frictional wear as metal-on-metal due to the self-lubricating characteristics of plastics. In addition, the plastics absorbed the impact stresses during vibrational testing. However, the life cycle test in conjunction with heat cycles (e.g., up to and including 700 F) accelerated the breakdown of the unsuccessful plastics (e.g., nylon). Acceptable polyimide and PEEK materials did not vary more than 5% from their initial free-motion limits.
While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 61/083834, filed on Jul. 25, 2008, the disclosure of which is hereby expressly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61083834 | Jul 2008 | US |
