Patent Publication Number: US-2022221039-A1

Title: System, method and apparatus for metallic gear hub with metallic teeth having outer polymer layer

Description:
BACKGROUND OF THE DISCLOSURE 
       FIG. 1  depicts a conventional worm gear  11  having an outer plastic ring  13  that is bonded or molded to an inner steel hub  15 . The outer diameter  17  of the steel hub  15  is smaller than the root diameter  19  of the gear teeth  21 . The gear teeth  21  are formed entirely from plastic and are coupled to a worm shaft  23 . Plastic teeth are beneficial for better noise, vibration and harshness (NVH) performance, but plastic teeth have durability limitations. As customer demand for output torque increases, a more robust gear solution is needed. Although these solutions are workable, improvements in gear design continue to be of interest. 
     SUMMARY OF THE DISCLOSURE 
     Embodiments of a system, method and apparatus for a gear are disclosed. For example, a metallic gear hub can include an axis of rotation and metallic gear teeth. The metallic gear teeth can be smaller than a final gear teeth size of the gear. The metallic gear teeth can be co-planar with the axis. In addition, the metallic gear teeth can be non-orthogonal to the axis. A polymer layer can be located on the metallic gear teeth to form polymer gear teeth on the metallic gear teeth. The polymer gear teeth can form the final gear teeth size of the gear. 
     Embodiments of a method of forming a gear can include forming a metallic gear hub with metallic gear teeth that are smaller than a final gear teeth size of the gear. The method can include blasting the metallic gear hub to a desired surface finish and applying a primer to the metallic gear teeth. The method can further include heating the metallic gear hub and dipping the metallic gear teeth in a fluidized bed of polymer powder and forming a polymer coating on the metallic gear teeth. The method can conclude by processing the polymer coating on the metallic gear teeth to the final gear teeth size of the gear. 
     The foregoing and other objects and advantages of these embodiments will be apparent to those of ordinary skill in the art in view of the following detailed description, taken in conjunction with the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the embodiments are attained and can be understood in more detail, a more particular description can be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments and therefore are not to be considered limiting in scope as there can be other equally effective embodiments. 
         FIG. 1  is an illustration of a conventional worm gear drive system. 
         FIGS. 2A through 2F  are a series of images depicting embodiments of a gear and method of forming the gear. 
         FIGS. 3A through 3C  are a series of images depicting alternative embodiments of a gear and method of forming the gear. 
         FIGS. 4A through 4C  are a series of images depicting other embodiments of a gear and method of forming the gear. 
         FIG. 4D  is an enlarged view of a portion of the gear of  FIG. 4C , with some of the polymer not shown to reveal the metallic teeth inside the polymer. 
         FIGS. 5A through 5C  are a series of images depicting different embodiments of a gear and method of forming the gear. 
         FIGS. 6A through 6C  are enlarged schematic images of portions of embodiments of a gear. 
         FIG. 7  is a diagram of a coordinate system for a gear. 
         FIGS. 8A through 8D  are isometric views of an embodiment of a gear and method of forming the gear. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 2-8  depict various embodiments of a system, method and apparatus for a metallic (e.g., steel) gear hub with metallic teeth having a polymer outer layer that can comprise extensions on the metallic teeth. For example,  FIGS. 2A-2F  illustrate a series of images depicting embodiments of a gear and method forming the gear. Forming the gear can involve, for example, a press fit and heat, such as induction heat. Versions can include forming a polymer outer ring  101  ( FIG. 2A ), such as by injection molding. The polymer outer ring  101  can include inner plastic teeth  103 . 
     In addition, a metallic gear hub  105  ( FIG. 2B ) with outer metal teeth  107  can be formed. The metallic gear hub  105  can be cast, forged, formed by powder metallurgy (PM), etc. The metal teeth  107  of the metallic gear hub  105  can be blasted (e.g., sand blasted) to a desired finish. The metal teeth  107  can have an adhesion promoter applied to them. As shown in  FIG. 2C , the polymer outer ring  101  can be pressed (e.g., press fit) onto the metallic gear hub  105  to form a ring and hub assembly  109 . The ring and hub assembly  109  can be heated (e.g., induction heated) to bond the polymer outer ring  101  to the metallic gear hub  105  to form a gear blank  111  ( FIG. 2D ). After the edges and outside diameter of the gear blank  111  are trimmed to final dimensions, the gear blank  111  can be pressed onto a shaft  113  to form a gear assembly  115  ( FIG. 2F ). The metallic gear hub  105  can include a locating or timing notch  117  ( FIG. 2E ) that can be used to properly align the gear assembly  115  in a gear teeth cutting machine (e.g., a hobbing machine) to cut the final gear teeth in the gear assembly  115  to form a final product. The hobbing machine can include a plunger, such as a spring-actuated plunger, to engage the timing notch  117 . 
     Each metal tooth  107  of the metallic gear hub  105  can have a tooth size or radial dimension  119  ( FIG. 2B ) relative to a rotational axis  121  of the metallic gear hub  105 . The radial dimension  119  of the metal teeth  107  can be less than a desired final gear tooth size or radial dimension  123  ( FIG. 2F ) of the layer of polymer (e.g., plastic) on an exterior of the metal teeth  107 . 
       FIGS. 3A-3C  illustrate a series of images depicting alternate embodiments of a gear and method of forming the gear. These versions can include molding, such as injection overmolding, a polymer  201  on a metallic gear hub  205 . For this configuration, the metallic gear hub  205  can be cast, forged, PM, etc., with metallic teeth  207 . Like the previous embodiment, the metallic teeth  207  on the metallic gear hub  205  can have a radial dimension  219  ( FIG. 3A ) relative to axis  221  that is less than the desired final gear radial dimension  223  ( FIG. 3C ) to allow for the polymer layer on the exterior of the metallic teeth  207 . The metallic gear hub  205  can be placed in a mold cavity, and polymer  201  can be injection molded on the metallic gear hub  205  to form a gear blank  209  ( FIG. 3B ). As shown in  FIG. 3C , the gear blank  209  can be trimmed to final dimensions, pressed onto a shaft  213 , and then hobbed like the previous design into a final product comprising a gear assembly  215 . 
       FIGS. 4A-4C  depict a series of images illustrating other embodiments of a gear and method of forming the gear. Like other embodiments, this version can include a metallic gear hub  305  (e.g., a stamped metallic gear hub) with a molding (e.g., injection overmolding) of polymer  301 . For this configuration, the metallic gear hub  305  can be formed (e.g., stamped) with metallic teeth  307 . 
       FIG. 4D  is an enlarged view of a portion of the gear of  FIG. 4C , with some of the polymer  301  not shown to reveal the metallic teeth  307  inside the polymer. The metallic teeth  307  can have a radial dimension  319  ( FIGS. 4A and 4D ) relative to axis  321  that is less than the desired final gear tooth radial dimension  323  ( FIGS. 4C and 4D ) to allow for the layer of polymer  301 . The metallic gear hub  305  can be placed in a mold cavity, and the polymer  301  can be molded (e.g., injection molded) over the metallic gear hub  305  to form a gear blank  309  ( FIG. 4B ). The gear blank  309  can be trimmed to final dimensions, pressed to a shaft, and hobbed like the other designs to form a final product comprising a gear assembly  315  ( FIG. 4C ). Alternatively, this gear can be molded into a blank, or molded to its final shape. 
       FIGS. 5A-5C  are a series of images depicting still other embodiments of a gear and method of forming the gear. This version can include a metallic gear hub  405  with a coating, such as a powder-based coating of polymer  401 . For this configuration, the metallic gear hub  405  can be formed with metallic teeth  407 . The metallic teeth  407  of the metallic gear hub  405  can have a metal tooth radial dimension  419  ( FIG. 5A ) that is less than the desired final gear tooth radial dimension  423  ( FIG. 5C ) to allow for a coating thereon, such as a layer of powder coat based polymer  401 . Prior to coating, the metallic gear hub  405  can be blasted (e.g., sand blasted) and a primer can be applied to it. The metallic gear hub  405  can be preheated to a selected temperature and dipped into a fluidized bed of the powder coat material of polymer  401 . The heat and primer can cause the powder to bond to the metallic gear hub  405  to form a gear blank  409  ( FIG. 5B ). After this stage, the metallic gear hub  405  can appear to be a finished gear, but the powder coat process can provide a coating that can be made more uniform to be used as the final gear geometry. The next step can be to press the metallic gear hub  405  to a shaft and hob the gear as described in the previous designs into a gear assembly  415 . 
     In  FIGS. 6A-6C , embodiments of a gear  615  can include a metallic gear hub  605  having an axis of rotation and metallic gear teeth  607   a  and  607   b . The axis of rotation can be parallel to the Y-axis in  FIG. 7 . The metallic gear teeth  607   a ,  607   b  can be oriented or configured relative to any of the X, Y or Z-axes, or rotated in respective roll, pitch and yaw rotational directions. 
     Embodiments of the metallic gear teeth  607   a ,  607   b  can be similar to metallic gear teeth  307  of  FIG. 4 . The metallic gear teeth  607   a ,  607   b  can be smaller than a desired final gear teeth size of the gear  615 . In some versions, the metallic gear teeth  607   a ,  607   b  can be co-planar with the axis. Examples can include metallic gear teeth  607   c  (shown schematically) which are non-orthogonal to the axis. A polymer layer  601  can be formed on the metallic gear teeth  607   a ,  607   b  or  607   c  to form polymer gear teeth thereon, such that the polymer gear teeth comprise the final gear teeth size of the gear  615 . Examples can include net shape molded teeth. 
     In addition, one or more of the metallic gear teeth  607   a ,  607   b ,  607   c  can form an overhang  644  ( FIGS. 4D and 6B ). Versions of the overhangs  644  can help retain the polymer layer  301 ,  601 , respectively, thereon. The overhangs  644  can extend in opposite axial directions on respective ones of the metallic gear teeth  607   a ,  607   b ,  607   c . In some examples, an outer axial dimension between opposite ones of the overhangs  644  can exceed an outer axial dimension of the metallic gear hub  605 . 
     In some embodiments, the contact line  633  on a helical gear or mating worm shaft (not shown) can look like it is illustrated in  FIGS. 6A and 6C . One or more of the shape, length and direction of the metallic gear teeth  607   c  can be complementary to or even match the contact line  633  (as shown in  FIG. 6C ) of the gear  615  to more directly react the load. Thus, metallic gear teeth  607   c  can be configured at an angle instead of in the parallel offset depicted by metallic gear teeth  607   a ,  607   b.    
     The mating worm shaft (not shown) can contact the gear  615  along the contact line  633 . For metallic gear teeth  607   a ,  607   b , the contact line  633  or area can extend beyond the edges of the metallic gear teeth  607   a ,  607   b . This could possibly shear the polymer layer  601  that is not directly supported by the metallic gear hub  605 . This is not true for embodiments having metallic gear teeth  607   c  since the polymer layer  601  would be fully supported along the entire contact line  633 . Some versions of the metallic gear teeth  607   c  can comprise rounded rectangle shapes, as shown. Such design can react directly against the metallic backing of the metallic gear hub  605 . In some examples, the angled teeth can react the load only on every other tooth. In other examples, the contact ratio for worm gears is generally greater than two, so two teeth can always be in contact with the worm gear. 
     For example, the metallic gear teeth  607   c  can be oriented at an acute angle relative to the axis. In some versions, the acute angle can be in a range of about 30 degrees to about 60 degrees. Each of the metallic gear teeth can comprise a shape that is rectangular with rounded corners. Referring to  FIG. 7 , each of the metallic gear teeth  607   c  can be oriented at an acute roll angle relative to neutral, and both pitch and yaw angles of the metallic teeth can be neutral. 
     In some embodiments, at least some of the metallic gear teeth  607   a ,  607   b  can be offset from each other in the axial direction, instead of axially aligned. Some versions of the polymer gear teeth are not offset from each other. The metallic gear teeth  607   a ,  607   b  can comprise an alternating axial pattern on the metallic gear hub  605 . Examples of the polymer gear teeth do not comprise an alternating pattern. 
     Embodiments of the metallic gear teeth  607   a ,  607   b  or  607   c  can comprise a metal axial width, and the polymer gear teeth can comprise a polymer axial width that exceeds it, such as at least double the metal axial width, at least triple or even at least quadruple that of the metallic gear teeth. In one example, the polymer axial width of the polymer gear teeth can be substantially equal to a metallic axial width of the metallic gear teeth. Versions of at least some of the metallic gear teeth can be axially offset from each other, and the polymer gear teeth can be not offset from each other. Examples of the metallic gear teeth can comprise an alternating pattern on the metallic gear hub, whereas the polymer gear teeth may not comprise an alternating pattern in some versions. 
       FIGS. 8A-8D  illustrate a series of images depicting alternate embodiments of a gear and method of forming the gear. These versions can include molding, such as injection overmolding, a polymer  801  on a metallic gear hub  805 . For this configuration, the metallic gear hub  805  can be formed as with the other embodiments with metallic teeth  807 . As before, the metallic teeth  807  can have a radial dimension  819  relative to a rotational axis that is less than the desired final gear radial dimension  823  to allow for the polymer layer  801  on the exterior of the metallic teeth  807 . The polymer  801  can be formed on the metallic gear hub  805  in any of the ways or methods described herein. For example, a gear blank can be formed and the gear blank can be trimmed to final dimensions, pressed onto a shaft, and then hobbed like the other designs into a final product comprising a gear assembly. Versions of the metallic teeth can engage the worm shaft even if the polymer layer is not present. Should the polymer fail, such a feature can provide redundancy for providing assistance to the vehicle operator. Thus, metal-to-metal contact can provide assistance to safely leave a roadway. 
     Embodiments of the metallic gear hub can comprise at least one of machined, cast, forged, stamped, hobbed and powder metallurgy. Embodiments of the polymer gear teeth can be at least one of molded, injection molded, pressed, induction heated, powder coated and bonded. Embodiments of the metallic gear hub can comprise a locating notch and the polymer gear teeth can be post-machined relative to the locating notch to form a uniform polymer thickness and the final gear teeth size. Some embodiments can allow for the net shape molding of the final gear teeth dimensions. 
     Embodiments of a method of forming a gear also are disclosed. For example, the method can include forming a metallic gear hub with metallic gear teeth that are smaller than a final gear teeth size of the gear; blasting the metallic gear hub to a desired surface finish; applying a primer to the metallic gear teeth; heating the metallic gear hub and dipping the metallic gear teeth in a fluidized bed of polymer powder; forming a polymer coating on the metallic gear teeth; and then processing the polymer coating on the metallic gear teeth to the final gear teeth size of the gear. 
     Some versions of the method can include injection molding the polymer with internal teeth to form a polymer ring, and attaching the polymer ring to the gear teeth. Other examples of the method can include trimming the polymer coating to a final size and hobbing the polymer coating. 
     Embodiments can include systems, methods and devices that form a polymer gear having teeth with a metallic core. The use of metallic core teeth can increase the robustness and torque-carrying capacity of the gear, while the polymer exterior can help maintain satisfactory NVH performance. 
     This written description uses examples to disclose the embodiments, including the best mode, and also to enable those of ordinary skill in the art to make and use the invention. The patentable scope is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 
     Note that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities can be performed in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed. 
     In the foregoing specification, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention. 
     It can be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “communicate,” as well as derivatives thereof, encompasses both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, can mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items can be used, and only one item in the list can be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C. 
     Also, the use of “a” or “an” are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
     The description in the present application should not be read as implying that any particular element, step, or function is an essential or critical element that must be included in the claim scope. The scope of patented subject matter is defined only by the allowed claims. Moreover, none of the claims invokes 35 U.S.C. § 112(f) with respect to any of the appended claims or claim elements unless the exact words “means for” or “step for” are explicitly used in the particular claim, followed by a participle phrase identifying a function. 
     As used herein, the term “about” or “approximately” applies to all numeric values, whether or not explicitly indicated. These terms generally refer to a range of numbers that one of skill in the art would consider equivalent to the recited values (i.e., having the same function or result). In many instances these terms may include numbers that are rounded to the nearest significant figure. As used herein, the terms “substantial” and “substantially” means, when comparing various parts to one another, that the parts being compared are equal to or are so close enough in dimension that one skill in the art would consider the same. Substantial and substantially, as used herein, are not limited to a single dimension and specifically include a range of values for those parts being compared. The range of values, both above and below (e.g., “+/−” or greater/lesser or larger/smaller), includes a variance that one of skill in the art would know to be a reasonable tolerance for the parts mentioned. 
     Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that can cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, sacrosanct or essential feature of any or all the claims. 
     After reading the specification, skilled artisans will appreciate that certain features which, for clarity, are described herein in the context of separate embodiments, can also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, can also be provided separately or in any subcombination. Further, references to values stated in ranges include each and every possible value within that range.