Patent Application
20170073790
The present disclosure relates generally to components formed from ultra-high strength steel, such as boron steel, and method of forming the same.
Ultra-high strength steel is currently used in building construction and static automotive structures (e.g. vehicle bodies and frames). The use of ultra-high strength steel generally allows the weights of these structures to be reduced. Additionally, in automotive structures, the ultra-high strength steel enables the absorption of impact energy and minimizes intrusion into occupant seating areas. Although ultra-high strength steel can be made extremely strong, other properties such as formability, weldability, and impact toughness may be negatively affected, resulting in structures which may be more prone to cracking and fracture.
Power transmission components for automotive vehicles, such as clutch assemblies having clutch plates within a clutch housing and clutch hub are well-known. Such clutch housings have a generally cylindrical or cup-shaped body and an open end. The cylindrical or cup-shaped body is formed from a sheet metal blank and has a plurality of spline teeth formed thereon. The clutch plates fit within the clutch housing and engage the spline teeth. The clutch hub can also be a formed sheet metal component and is typically connected to a transmission shaft.
Powertrain components including clutch housings and hubs are commonly made of aluminum or high strength low alloy steel (HSLA) rather than ultra-high strength steel, such as boron steel. Aluminum or HSLA steel is used primarily because of its formability. Specifically, these types of materials are high strength materials which can achieve a specific geometric dimension or shape and have a specific tolerance required. Consequently, aluminum or HSLA may be used in powertrain components including parts of an automatic transmission easily, efficiently, and at a low-cost.
Typically, components such as clutch housings and hubs made of aluminum or HSLA are formed using one or a combination of cold-forming or stamping processes and thermal heat treatments to obtain the desired shape, performance, and strength characteristics. Additionally, the structures such as the plurality of spline teeth of the clutch housing may be formed easily by using a series of rollers. Similar processes also may be used to form other powertrain components such as planetary carriers used in differentials and various covers used in a vehicle powertrain.
Ultra-high strength steel lacks formability using the conventional cold-forming technologies discussed above. Use of conventional cold-forming technologies with ultra-high strength steel typically does not result in the formation of required geometric dimensions and tolerances. However, there is a desire by manufacturers and suppliers to utilize ultra-high strength steel in forming automotive components such as power transmission components for similar reasons as those discussed above when used in static applications of automotive structures (e.g. reduced component weight and improved absorption of impact energy).
As such, a need exists for components, such as clutch housings and hubs, to be formed from ultra-high strength steel, such as boron steel. Additionally, there is a need for a method for forming the same.
This section provides a general summary of the inventive concepts associated with the present disclosure and is not intended to represent a comprehensive disclosure of its full scope or all of its features, object, aspects and advantages. Components formed with ultra-high strength steel and a method of forming these components from ultra-high strength steel are provided.
In accordance with an aspect of present disclosure, a method for forming a component utilizing ultra high strength steel includes the steps of providing a flat blank of ultra high strength steel. The method proceeds by forming the flat blank into an unfinished shape of a component. Next, the method includes the steps of providing an inert atmosphere and heating the unfinished shape of the component in the inert atmosphere. Then, forming a finished shape of the component using a quenching die.
In accordance with an aspect of present disclosure, a component of ultra high strength steel is produced by providing a flat blank of ultra high strength steel. Next, forming the flat blank into an unfinished shape of the component. This is followed by providing an inert atmosphere and heating the unfinished shape of the component in the inert atmosphere. Then, forming a finished shape of the component using a quenching die so as to obtain the component.
In accordance with an exemplary embodiment of a component constructed in accordance with the present disclosure, there is provided a clutch housing. The clutch housing has a cylindrical or cup-shaped body and an open end.
In accordance with this exemplary embodiment of the present disclosure, a method for forming the clutch housing from ultra-high strength steel includes cold-forming the body of the clutch housing, heat treating in an inert atmosphere, and quenching using a water cooled quenching die to form and finalize the cylindrical or cup-shaped body. The ultra-high strength steel forming the body of the clutch housing may be boron steel.
In accordance with this exemplary embodiment of the present disclosure, the method for forming components from ultra-high strength steel includes pre-forming or cold-forming a flat blank of steel into a predetermined shape. The predetermined shape may be a cylindrical or cup-shaped body. The step of cold-forming the flat blank of steel may include forming a plurality of spline teeth along the blank of steel. The method may also include heat treating the blank of steel in an inert atmosphere. The inert atmosphere may be an induction oven or an induction chamber. Additionally, heat treating may be partially or completely localized. The method further includes quenching the heat treated blank of steel. Quenching may include forming a plurality of spline teeth along the blank of steel or finalizing the predetermined form using a water cooled quenching die.
In accordance with this exemplary embodiment of the present disclosure, the method for forming components from ultra-high strength steel includes heat treating a blank of steel in an inert atmosphere and quenching the heat treated blank into a predetermined shape.
In accordance with a second embodiment of a component constructed in accordance with the present disclosure, there is provided a clutch hub. The clutch hub has a cup-shaped body and an open end.
In accordance with a third embodiment of a component constructed in accordance with the present disclosure, there is provided a continuously variable transmission (CVT) plunger. The CVT plunger includes a generally bell-shaped body defining a centrally disposed opening.
In accordance with a forth embodiment of a component constructed in accordance with the present disclosure, there is provided a CVT cylinder. The CVT cylinder includes an annular or cylindrically shaped body having a first end and a second end and including a shoulder formed at the first end.
In accordance with a fifth embodiment of a component constructed in accordance with the present disclosure, there is provided a planetary carrier. The planetary carrier comprises a first piece and a second piece joined together by a weld. The first piece includes a plurality of legs extending longitudinally. A plurality of apertures are circumferentially disposed in a spaced relationship to each other about the perimeter of each piece.
In accordance with a sixth embodiment of a component constructed in accordance with the present disclosure, there is provided a reaction shell. The reaction shell comprises a body including a cylindrical first portion of a first diameter and a cylindrical second portion of a second diameter being larger than the first diameter. A plurality of radially outwardly extending spline teeth are disposed about the cylindrical second portion.
In accordance with a seventh embodiment of a component constructed in accordance with the present disclosure, there is provided a differential housing. The differential housing is generally cup or drum shaped with a tubular neck portion defining a central opening a plurality of arms extending radially and longitudinally from the neck portion.
In accordance with a eighth embodiment of a component constructed in accordance with the present disclosure, there is provided a differential cover. The differential cover comprises a generally bell shaped body extending between a generally cylindrical first end and an opposite annular second end. A ring gear is attached to the second end of the cover.
In accordance with an ninth embodiment of a component constructed in accordance with the present disclosure, there is provided a torque converter cover. The torque converter cover comprises a front portion and a back portion. The front portion is generally drum-shaped and includes a radial wall and an integral cylindrical portion with an inner surface that extends longitudinally from the radial wall. The back portion is ring shaped and has a center opening and a curved cross-section or half round shape.
In accordance with a tenth embodiment of a component constructed in accordance with the present disclosure, there is provided an oil pan. The oil pan comprises a generally rectangular base with a side wall disposed around the periphery of the base and extending generally perpendicularly from the base to an upper continuous flange adapted to be secured under the block of an engine.
The aspects disclosed herein provide various advantages. For example, the components are more lightweight as a result of a reduced cross section resulting from increased material strength than conventional components using HSLA steel. The components have increased tolerance from using ultra-high strength steel than conventional components. The method is more cost efficient and reduces cost due to component trimming using water cooled quenching unlike the conventional methods which require additional trimming such as laser trimming. In other words, there is a reduced die wear and maintenance based on the resulting lower cutting forces from using water cooled quenching. Additionally, there is an improved component reliability due to the reduction of crack initiations due to soft component trimming and an increased manufacturing flexibility using localized induction heating.
Other advantages of the present disclosure will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Detailed examples of the present disclosure are disclosed herein; however, it is to be understood that the disclosed examples are merely exemplary and may be embodied in various and alternative forms. It is not intended that these examples illustrate and describe all possible forms of the disclosure. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure.
The aspects disclosed herein include components made of ultra-high strength steel and a method of forming components utilizing ultra-high strength steel. In particular, the components may be for example, lightweight automatic clutch hubs and housings, planetary gear carriers, or torque convertor covers made of boron steel and cold formed in their unhardened state to near net-shape via an “indirect method” and finished sized i.e. net-shaped via heat assisted calibration (HAC) to achieve 40 to 60% mass reduction of rotating inertia. According to an aspect, the lightweight pre-formed boron steel components (with or without a plurality of spline teeth) are subsequently heated in an inert atmosphere and rapidly transferred to a water-cooled quenching die to minimize oxidation and resulting in a fine-grained martensitic component material structure. The die quenching tool enables net shape processing within geometric dimensions and tolerance requirements.
As those of ordinary skill in the art will understand various features of the present disclosure as illustrated and described with reference to any of the Figures may be combined with features illustrated in one or more other Figures to produce examples of the present disclosure that are not explicitly illustrated or described. The combinations of features illustrated provide representative examples for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations.
Example embodiments of components formed from ultra-high strength steel constructed in accordance with the present disclosure will now be more fully described. These example embodiments are primarily directed to powertrain components. Moreover, each of the exemplary embodiments is provided so that this disclosure is thorough and fully conveys the scope of the inventive concepts, features and advantages to those skilled in the art. To this end, numerous specific details are set forth to provide a thorough understanding of each of the embodiments associated with the present disclosure. However, as will be apparent to those skilled in the art, not all specific details described herein need to be employed, the example embodiments may be embodied in many different forms, and that neither should be construed or interpreted to limit the scope of the disclosure.
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The method discussed above may also include, but is not limited to cold-forming the clutch housing 10 without a plurality of spline teeth 16, heat treating the unfinished shape of the clutch housing 10 using localized induction heating, and forming and sizing the plurality of spline teeth 16 using the quenching die. Alternatively, the method may include pre-forming/cold-forming the clutch housing 10 with a plurality of spline teeth 16, heating the unfinished shape of the clutch housing 10 in an inert environment, and sizing and finalizing the shape of the housing 10 in the quenching die. Similarly, planetary gear carriers and other components may be partially or completely cold formed and then heated using either localized or entire part heating.
In addition to the clutch housing 10 disclosed above, other embodiments of components from ultra-high strength steel constructed in accordance with the present disclosure are described in more detail below.
In each embodiment of the present disclosure, the components may be formed from 22MnB5 steel, however, it should be understood that the amount of boron (B5-B50) may be selected depending on the type of component or strength desired. Additionally, the amount of other materials which comprise the ultra-high strength steel, such as carbon, may cause variation in the martensitic percentage and hardness after quenching. During the heat treatment, the heating temperature is approximately 850-950degrees C. More specifically, the target heating temperature for 22MnB5 steel is 900 degrees C., however, the heating temperature may be increased as the amount of boron is increased. As described above, the heat treating may be partially or completely localized. The heating method may be induction or by other techniques. When it is desirable to localize strength in one particular area of a component, the heat treatment may be localized to that area. In other instances, localized heat treatment may be used for sections of a component having a thicker cross section.
During the quenching step that may be used in forming each embodiment of the present disclosure, the quench press/die defines the final shape of the part. The release temperature may range between approximately 150-250 degrees C., with a preferred target temperature of 200 degrees C. The components generally remain in the quench press/die for approximately 6-20 seconds depending on the cross sectional thickness and desired strength.
In general, materials having a strength of approximately 1000 Mpa will crack or spring back during cold forming, therefore the methods described in the present disclosure are advantageous when forming such high strength materials. Additionally, due to a reduction of cross section, the geometry of components formed with heat assisted calibration (HAC) methods disclosed herein may be more complex (i.e. ribs). Consequently, the manufacturing of some components (e.g. planetary carrier described in the fifth embodiment above) that is not possible using cold forming is made possible with HAC processes.
While examples of the disclosure have been illustrated and described, it is not intended that these examples illustrate and describe all possible forms of the disclosure. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. Additionally, the features and various implementing embodiments may be combined to form further examples of the disclosure.
This PCT application claims the benefit of, and priority to, U.S. Provisional Application Ser. No. 61/970,008 filed Mar. 25, 2014, and also to U.S. Provisional Patent Application Ser. No. 62/108,793, filed Jan. 28, 2015, the entire disclosures of each of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2015/000175 | 3/25/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61970008 | Mar 2014 | US | |
| 62108793 | Jan 2015 | US |
