Patent Application
20080193320
The present invention relates to automotive clutch or transmission components and, more particularly, to so called one way clutches wherein one or more struts provide a mechanical coupling between opposed clutch faces and a pair of coaxially rotateable members, with a method for manufacturing and measuring such components.
As explained in U.S. Pat. No. 6,571,926, in such one way clutches, a driving member engages a driven member.
The manufacture of such automotive components is set forth in pending U.S. patent application Ser. No. 11/585,297 filed Oct. 23, 2006, and assigned to the assignee of the present application.
A thin flat strut is carried within each of the driving members' pockets such that a first longitudinal end may readily engage and bear against the shoulder defined by the corresponding recess in the driving member. The struts second, opposite longitudinal end is urged by spring force toward and against the driven member, thereby contacting a complimentary surface on the driven member.
The materials and processing of such clutch components use high hardenability metals to produce the clutch components. Such materials can be used as backing plates' in automotive transmissions. The metallic micro structure of such currently used materials is nearly 100% martensite which is strong and wear resistant. However, because the subject clutch component operates in a contacting environment generating extreme heat, the clutch component is also susceptible to damage and localized injury from hot spots. Such hot spots are produced by interaction with mating friction plates made from a variety of friction materials. Temperatures in these hot spot zones can approach 1500° F. (815° C.) or more. Because the currently used materials are highly hardenable and the hot spot temperatures may exceed the critical temperature or austentizing temperature for steel, the metal in the area of the hot spots can be readily transformed into untempered martensite. Such untempered martensite areas on the backing plate face of the clutch component can be an initiation site for brittle fractures which can readily propagate causing ultimate clutch component failure.
It is also a concern in the manufacture of such automotive components using powder metallurgy techniques that the warpage and possible distortion on the automotive components may result in the component not being completely flat in surface that are desired to be flat within tolerance. The sintering and heat treating or tempering processes are particularly of concern when the die compacted blank is then subsequently sintered in and heat treated, their can be a resulting warpage or distortion.
Accordingly, it is an object of the present invention to provide an improved automotive component that can withstand the temperatures generated in a clutch or brake in a transmission environment, and further that is free of warpage or distortion within desired tolerance.
It is another object of the present invention to provide a method of manufacturing an automotive component that can withstand the temperatures generated in a clutch or brake transmission component by use of powder metallurgy techniques including, die compacting, sintering, quenching and subsequent measurement of the automotive component to assure freedom from warpage and distortion within accepted tolerance.
In a preferred method of manufacturing an automotive component in accordance with the present invention, a low alloy constituent, low hardenability material is utilized that accordingly requires a more aggressive cooling or quenching operation to produce a strong martensitic wear resistant hard structure. The preferred method includes the traditional powder metallurgy operation of die compacting and sintering that is followed by a quenching operation wherein the sintered material is quenched in an environment of a cooling rate that results in a metallic microstructure that is 50-80% martensitic, 20-50% bainitic with a small portion of fine pearlite, generally less than 10%. Quenching may include other quench methods than atmospheric. Because this material does not have high relative hardenability and transform as readily to martensite at a quench rate between 1.9° F. and 5.5° F. per second, untempered martensite is not formed by localized hot spots in the operation of the automotive component. Because there is almost no untempered martensite in the metallic microstructure, resulting from high localized temperatures fracture initiation sites are sufficiently reduced. The service life of the automotive transmission or clutch brake component such as a backing plate is greatly extended. Further, the resulting micro structure from reduction in hardenability reduces the material's propensity to crack propagation in the finished component.
The method of manufacturing an automotive component in accordance with an embodiment of the present invention includes the initial provision of a metal pre alloy powder comprising, by weight, 0.35-0.55% nickel, 0.50-0.85% molybdenum, with the balance essentially iron, admixing an additional metal powder of 0.60-0.90% carbon and 1.0-3.0% copper metal powder to form an admixed metal powder. A suitable lubricant is added to the metal powder mixture to form a lubricated admixed metal powder. The lubricant is one of an EBS (Ethylene bis-stearamide) wax, metal stearates or other lubricant suitable for use in die compaction of metal powders.
The lubricated admixed metal powder is then die compacted, usually at a pressure of between 40 and 65 tons per square inch in the forming die. The die compacted metal blank is then placed on a precision ground flat ceramic support structure and sintered in an atmosphere of nitrogen and hydrogen mixture or other atmosphere suitable for sintering and sinter hardening. An equivalent of the ceramic support structure, such as a silica or firebrick arrangement could also be used. The sintering operation itself is usually conducted at a temperature above 2000° F. (1090° C.), and most usually at a temperature between 2000° F. (1090° C.) and 2350° F. (1290° C.) for a period of at least 10 minutes. The sintered metal blank itself is then cooled or quenched usually while remaining on the ceramic support structure in a quenching or cooling operation that reduces the temperature of the sintered blank at a rate of 1.9° F./sec. (1.05° C./sec.) and 5.5° F./sec. (3.05° C./sec.) metal blank from between 1600° F. (870° C.) to 2000° F. (1090° C.), to a temperature of between 450° F. (230° C.) and 500° F. (260° C.). The quenched metal blank is then tempered at a temperature of between 350° F. (175° C.) and 450° F. (230° C.) for at least one hour to properly temper the quenched metal blank.
Either before or after tempering, the quenched metal blank is placed on a measuring gauge which includes support pads and probes. These support pads are usually three in number to support the quenched metal blank in a reference plane. The probes are multiple in number, with a usual number totaling twelve, and either contact the quenched metal blank or else utilize a laser or similar measuring device to determine the relative flatness, or roundness or perpendicular structure as desired of the quenched metal blank. Usually such measuring probes are in pairs such that a measuring reading near an internal diameter and near an external diameter may be taken. The signals from the probes are analyzed in a processing unit such as a computer and the relative flatness, roundness, perpendicular structure and other desired physical attributes of the quenched metal blank are then compared to determine if the quenched metal blank is within tolerance.
In the drawings,
Referring to
More specifically, in the exemplary clutch assembly 10, the driving member 12 has a clutch face 22 that defines a first reference surface 24 that extends generally normal to the driving member's rotational axis 16. A plurality of recesses are defined in clutch face 22 of driving member 12, with each recess including a load-bearing shoulder that is operative to abuttingly engage a first end of a given strut 18 when the driving member 12 rotates in a first direction. While this embodiment of the invention contemplates any suitable configuration for the recesses of the driving member 12, in the exemplary clutch assembly 10 each recess 26 of the driving member 12 is adapted to receive a respective one of the assembly's struts 18. In such arrangement, struts 18 are nominally carried by the driving member 12 for rotation therewith about the axis 16.
Driven member 14 similarly includes a clutch face 34, in close-spaced opposition to the clutch face 22 of the driving member 12. Clutch face 34 also includes a reference surface 36 that extends generally normal to the driven member's rotational axis 16. The driven member's clutch face 34 also includes a plurality of recesses 38 which exceed the number of recesses in the driving member 12. Each of the driven member's recesses 38 is adapted to receive the second end of a given strut 18 when the strut's second end is urged into recess 38. Such urging is typically by a spring seated beneath the strut 18 in the driving members recess. Each of the driven member's recesses 38 includes a load-bearing shoulder 46 that is operative to engage the second end of a given strut 18 when the driving member 12 rotates in the first direction relative to the driven member 14. Driver member 14 includes a back face friction plate. This back face is subjected to intense localized heating in use.
The material for the clutch or transmission components of the present invention is a low alloy, low hardenability material that is subjected to an aggressive cooling or quenching operation to produce a strong martensitic, wear resistant metallic structure. The method of the present invention results in clutch or transmission components that have the desired properties.
In general, a method of manufacturing an automotive component in accordance with one aspect of the present invention comprises the steps of providing an initial pre alloy metal powder comprising, by weight, 0.35-0.55% nickel, 0.50-0.85% molybdenum, with the balance essentially iron. Then an additional 0.60-0.90% carbon, 1.0-3.0% copper metal powder are admixed to the initial metal powder to form an admixed metal powder. A suitable lubricant is added in accordance with powder metal practice to form a lubricated, admixed metal powder. The lubricated admixed metal powder is then die compacted, typically at a pressure of between 40 and 65 tons per square inch, to form a die compacted metal blank. The die compacted metal blank is then sintered to form a sintered metal blank. The die compacted metal blank is placed on a precision ground of otherwise flat ceramic fixture 11. The flat face of the die compacted metal blank is in contact with the flat ceramic fixture 11. Such sintering typically is conducted at a temperature above 2000° F. (1090° C.), and more typically at a temperature between 2000° F. (1090° C.) and 2350° F. (1290° C.). The sintered metal blank, which is, in one embodiment of the present invention, either the driven or driving clutch component mentioned above, is then cooled or quenched to form a cooled metal blank, usually while the sintered metal blank remains on the flat ceramic fixture 11. The quenching or cooling operation reduces the temperature of the sintered metal blank from between 1600° F. (870° C.) to 2000° F. (1090° C.) to a temperature of 450° F. (230° C.) and 500° F. (260° C.). It is desirable that such cooling or quenching be conducted at a rate between 1.9° F. (1.05° C.) and 5.5° F. (3.05° C.) per second. The cooled or quenched metal blank is then tempered at a temperature of between 350° F. (175° C.) and 450° F. (230° C.) for at least one hour. The resulting automotive component has a microstructure that is 50-80% martensitic, 20-50% bainitic, and a small percentage, usually less than 10%, fine pearlite.
Because this resulting automotive component material does not transform as readily to martensite, the component does not respond to localized hot spots in clutch or transmission automotive service. Because there is almost no untempered martensite, the resulting microstructure, which is up to 50% bainitic, eliminates fracture initiation sites thereby extending the serviceable life of the clutch or transmission component. Reduction in hardenablity, as compared to the high hardenability materials previously used in such clutch brake or transmission components, reduces the materials propensity to re-hardening which further prohibits crack development and propagation.
Either before or after tempering, the cooled metal blank or tempered metal blank, as appropriate, is placed on a measuring device 55. The measuring device 55 usually includes three supports 51 such that the quenched metal blank is held in a reference plane. A plurality of probes 53 then either contact the quenched or tempered metal blank to determine whether warpage or distortion has occurred to the point that the desired flatness of the quenched or tempered metal blank is out of tolerance. Alternately, the probes 53 can be designed to emit a laser or similar signal to obtain the similar surface configuration information from the quenched or tempered metal blank.
The signals from the probes 53 are transmitted to a computer wherein the shape of the desired surfaces of the quenched or tempered metal blank are compared to reference to determine whether the flatness of the quenched or tempered metal blank is within tolerance.
Alternately, the probes 53 can be designed to contact edges or perpendicular structures on the quenched or tempered metal blank to measure roundness or perpendicularity of the extended sections of the quenched or tempered metal blank. Similar signals from the probes 53 are processed and compared to reference information to determine whether the roundness or perpendicularity of the extended structure is within tolerance.
Such a measuring technique provides a rapid determination whether the quenched or tempered metal blank is within tolerance for flatness, roundness, perpendicularity, or other design parameters. The support 51 of the die compacted metal blank on the machined flat ceramic support greatly contributes to the flatness, roundness, and perpendicular symmetry of the die compacted metal blank through the sintering operation. The probes 53 are usually twelve in number, including pairs that are separated into an inner set of probes that obtain readings from an inner diameter of the automotive component, and an outer set of probes that obtain reading from an outer diameter of the automotive component.
Certain examples of the method of carrying out the present invention follow:
In a method of manufacturing an automotive clutch component, an initial pre alloy metal powder of particle sizes between 250 and 1 micron was provided comprising, by weight, 0.45% nickel, 0.65% molybdenum, with the balance essentially iron.
An additional 0.7% graphite, and 1.75% copper metal powder of particle sizes between 150 and 1 micron, by weight, were admixed to form an admixed metal powder.
0.5% EBS was added as a lubricant to form a lubricated admixed metal powder.
The lubricated, admixed metal powder was compacted at a pressure of 45 tons per square inch.
The die compacted metal blank was then placed on a machined flat ceramic support and sintered at a temperature 2050° F. for 15 minutes.
The sintered metal blank was then quenched while on the ceramic support metal blank at a rate of 5.4° F. (3.00° C.) per second from an initial temperature of (2000° F.) (1090° C.) to a temperature of (500° F.) (260° C.) per use. The quenched was then tempered at a temperature of (380° F.) (190° C.) for 60 minutes.
The resulting material has a metal microstructure that was 50-55% martensitic, 45-50% bainitic and <5% fine pearlite. The Rockwell hardness of the resulting material was about HRA40.
The tempered metal blank was then placed on a measuring device to determine flatness within tolerance. The tempered metal blank was supported on three support pads. Twelve probes then contacted various sections of the tempered metal blank. Signals from such probes were processed in a computer to determine whether the flatness of the tempered metal blank was within tolerance.
In a method of manufacturing an automotive clutch component, an initial pre alloy metal powder of particle sizes between 250 and 1 microns was provided comprising, by weight, 0.45% nickel, 0.65% molybdenum, with the balance essentially iron.
An additional 0.9% graphite, and 1.75% copper metal powder of particle size between 150 and 1 micron, by weight, were admixed to form an admixed metal powder.
0.5% EBS was added as a lubricant to form a lubricated admixed metal powder.
The lubricated, admixed metal powder was compacted at a pressure of 45 tons per square inch.
The die compacted metal blank was then placed on a ceramic support and sintered at a temperature 2050° F. for 15 minutes.
The sintered metal blank was then quenched while on the ceramic support at a rate of 1.9° F. (1.05° C.) per second from an initial temperature of (2000° F.) (1090° C.) to a temperature of (500° F.) (260° C.) per use. The quenched metal blank was then tempered at a temperature of (380° F.) (1090° C.) for 60 minutes.
The resulting material has a metal microstructure that was 60-65% martensitic, 35-40% bainitic and <5% fine pearlite. The Rockwell hardness of the resulting material was about HRA50.
The tempered metal blank was then placed on a measuring device to determine flatness within tolerance. The tempered metal blank was supported on three support pads. Twelve probes then contacted various sections of the tempered metal blank. Signals from such probes were processed in a computer to determine whether the flatness of the tempered metal blank was within tolerance.
In a method of manufacturing an automotive clutch component, an initial pre alloy metal powder of particle size between 250 and 1 micron was provided comprising, by weight, 0.45% nickel, 0.65% molybdenum, with the balance essentially iron.
An additional 0.9% carbon, and 1.75% copper metal powder of particle size between 150 and 1 micron, by weight, were admixed to form an admixed metal powder.
0.5% EBS was added as a lubricant to form a lubricated admixed metal powder.
The lubricated, admixed metal powder was compacted at a pressure of 45 tons per square inch.
The die compacted metal blank was then placed on a machined flat ceramic support and sintered at a temperature 2050 for 15 minutes.
The sintered metal blank was then quenched while on the ceramic support at a rate of 1.9° F. (1.0° C.) per second from an initial temperature of (2000° F.) (1090° C.) to a temperature of (500 ° F.) (260° C.) per use. The quenched metal blank was then tempered at a temperature of (380° F.) (190° C.) for 60 minutes.
The resulting material has a metal microstructure that was 80% martensitic, 20% bainitic and <1% fine pearlite. The Rockwell hardness of the resulting material was about HRA58.
The tempered metal blank was then placed on a measuring device to determine flatness within tolerance. The tempered metal blank was supported on three support pads. Twelve probes then contacted various sections of the tempered metal blank. Signals from such probes were processed in a computer to determine whether the flatness of the tempered metal blank was within tolerance.
