Abstract:
A brake rotor for a vehicle is provided with one or more visual wear indicators on brake contact surfaces to allow easy visual inspection of brake rotor condition without the need for measurement tools. The inventive visual wear indicator system is not obtrusive and as such removes only a relatively small amount of brake contact surface to form a recessed surface at a depth of a predetermined minimum useable rotor thickness. With this inventive rotor, one can visually inspect the condition of a brake rotor and readily determine whether the rotor requires replacement or remachining. The visual wear indicator is provided on a brake contact surface of the rotor solely within a brake contact region so as to provide an accurate reflection of the condition of the rotor in areas where wear will occur. The visual indicator may be provided on only one, but preferably both, sides of the rotor and may take numerous forms, such as a cylindrical bore, a more complex shape, an annular groove or even an eccentric groove. For additional visibility, the visual wear indicator may be colored for additional contrast. The visual wear indicator may also be coated to prevent rusting.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The invention relates to a disk brake rotor with a wear indicator that does not adversely affect operation of the rotor yet allows easy visual inspection of wear.  
           [0003]    2. Description of Related Art  
           [0004]    Conventional disk brake rotors generally include a pair of mutually spaced-apart annular disks that form two opposed planar brake contact surfaces. These opposed brake contact surfaces receive braking force as applied by a brake caliper through two opposed brake pads. These rotors encounter frictional forces and heat build up each and every time the brakes are applied. Over time, these rotors (as well as the pads) wear or are damaged due to heat degradation and material fatigue caused by the cyclical application of frictional brake forces. Eventually, both the brake pads and the brake rotors become worn to a point where replacement is warranted or necessary. The full life expectancy of these brake pads and rotors cannot be determined with precision in advance as it is dependent upon many variables. In view of this, most vehicle manufacturers and brake component manufacturing companies recommend periodic inspection of brake components.  
           [0005]    For inspection or indication purposes, brake pads routinely include metal wear indicators located to one side of the brake pad. These indicators extend along a thickness of the brake pad by a distance corresponding to a predetermined minimum wear depth. Even if the brake pads are not completely worn out, visual inspection of the brake pads can be easily performed by viewing these indicators and ascertaining whether the pads are worn sufficiently to warrant replacement. Moreover, such brake pads often exhibit an audible sound when the brakes are sufficiently worn to a point where the metal indicators contact the rotor surface during braking. More complex indicators on some vehicles activate circuits that illuminate a warning indicator when brake pads on a vehicle are worn beyond acceptable tolerances. As such, visual or audible indication of brake pad life can be rather easily determined.  
           [0006]    The wear on brake rotors is not as readily ascertainable. Visual wear of a brake rotor is hard to ascertain. Each brake rotor is designed for a particular application and has a minimum dimensional thickness after which time the brake rotor no longer operates as desired and is susceptible to unacceptable, and perhaps even dangerous warpage, cracking or reduced braking capability. Some rotors are single use rotors, designed with relatively thin rotor surfaces. Upon sufficient wear, these rotors are intended to be replaced. Other rotors are designed with sufficient rotor thickness such that, after extended use, they can be machined or “turned” one or more times by known conventional equipment back to a smooth, flat surface to eliminate uneven wear patterns, and continue in use. This remachining of the brake contact surfaces of these rotors can be repeated until the rotor has reached a design minimum rotor thickness. As brake rotors often last much longer than the average brake pads, most people servicing brake systems visually inspect the brake pads only and do not measure the wear on the rotors until the pads require replacement.  
           [0007]    While a rotor with a severely warped, pitted or scored contact surface may be quickly identified by a trained mechanic&#39;s eye, the remaining life of most rotors, without serious defects, cannot be so readily determined visually. This is because the remaining life cannot be determined from a cursory review of the contact surfaces, which if the rotors are used properly, will wear down uniformly. Moreover, as different rotors have differing dimensions and minimal thickness design criteria, conventional inspection techniques have typically involved precise measurements of the rotor contact surfaces using a micrometer for both rotor thickness and rotor runout (determination of an out-of-round condition). The resultant readings determine whether the rotor:  1 ) needs replacement,  2 ) is within acceptable tolerances, or  3 ) has sufficient remaining thickness to be machined back to a smooth brake surface.  
           [0008]    Such rotor inspections require expensive and properly calibrated equipment. Moreover, such inspections require knowledge of the appropriate minimum rotor thickness for a particular rotor, which is primarily determined by the rotor manufacturer. This information is often stamped on non-contact surfaces of the rotor or may be published in appropriate literature. However, such literature may be unavailable to a typical vehicle owner. Moreover, even stamped tolerances are often difficult to determine. This is because by the time that sufficient time and braking cycles and wear have occurred to warrant inspection, rust and environmental exposure may have obscured such markings beyond recognition. Further, even upon ascertaining the proper minimum tolerance information, prior inspection techniques required precise micrometer measurements, which cannot be performed by many persons who service vehicles. As such, rapid and accurate inspection of rotors has not been attainable with conventional rotor technology.  
           [0009]    Thus, there is a need for a brake rotor that is capable of visual inspection to determine remaining useful life or uneven wear.  
         SUMMARY OF THE INVENTION  
         [0010]    The invention overcomes the problems with the prior art by providing a visual indicator of rotor condition without the need for measurement tools.  
           [0011]    These and other objects of the invention are overcome by a brake rotor for a vehicle brake system having a visual wear indicator, comprising: a central hub rotatably mountable to a vehicle for rotation about an axis; and at least one radially extending annular disk extending radially from the central hub, the at least one annular disk including inboard and outboard planar brake contact surfaces, the inboard and outboard brake contact surfaces being of a predetermined surface roughness, wherein at least one visual wear indicator is formed on at least one of said inboard and outboard brake contact surfaces solely within a brake contact region of the brake contact surfaces that will be worn due to brake pad contact during use, the visual wear indicator including a recessed surface substantially parallel to the brake contact surface that is at a depth corresponding to a minimum useable thickness of the rotor.  
           [0012]    These and other objects are also achieved by a method of forming a visual wear indicator on a brake rotor, comprising the steps of: forming a brake rotor with a central hub rotatably mountable to a vehicle and at least one radially extending annular disk extending radially from the central hub, the at least one annular disk including inboard and outboard planar brake contact surfaces rotatable about an axis of rotation; forming at least one visual wear indicator on at least one of said inboard and outboard brake contact surfaces solely within a brake contact region of the brake contact surfaces that will be worn due to brake pad contact during use, the visual wear indicator including recessed surface substantially parallel to the brake contact surface that is at a depth corresponding to a minimum useable thickness of the rotor; and processing the inboard and outboard brake contact surfaces to have a predetermined surface roughness.  
           [0013]    It is believed that for best retention of braking benefits, a visual wear indicator system is needed that is not obtrusive. That is, the wear indicator should not remove much rotor material, so as to maximize rotor mass and surface area. Moreover, the visual wear indicator needs to be provided on a contact surface of the rotor that is contacted by the brake pad so as to be an accurate reflection of rotor surface wear.  
           [0014]    The inventive visual wear indicator in a first embodiment of the invention takes the form of a simple counterbore formed on an exterior contact surface of the rotor intermediate radial extremities of the contact surface. Such a location is selected so as to be within an area that is contacted by a brake pad. There may be a counterbore provided diametrically opposite the first bore. This may assist in rotor balancing, but may be unnecessary if the amount of material removed is minimal. The counterbores are preferably formed on opposite surfaces (i.e., one on the outboard rotor surface and one on the inboard rotor surface), but may be formed on the same side. If provided on the same side, they should be provided on both the outboard and inboard rotor surfaces so that both surfaces can be visually checked for wear.  
           [0015]    The inventive visual wear indicator in a second embodiment of the invention takes the form of an annular groove provided in the rotor contact surface. Such an annular groove is preferably formed on both the inboard and outboard rotor surfaces so that both surfaces can be inspected for wear.  
           [0016]    Alternative exemplary embodiments are also provided and described. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The foregoing and further objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein:  
         [0018]    [0018]FIG. 1 is a side view of a brake rotor according to a first embodiment of the invention;  
         [0019]    [0019]FIG. 2 is a cross-sectional view of the brake rotor of FIG. 1 taken along line  22 ;  
         [0020]    [0020]FIG. 3 is a side view of a brake rotor according to another invention of the invention;  
         [0021]    [0021]FIG. 4 is a cross-sectional view of the brake rotor of FIG. 3 taken along line IVIV;  
         [0022]    [0022]FIG. 5 is a side view of a brake rotor according to a further alternative embodiment of the invention; and  
         [0023]    FIGS.  6 - 9  are illustrative additional exemplary visual wear indicator configurations according to the invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]    A first embodiment of the invention will be described with reference to FIGS.  1 - 2 , in which a brake rotor  100  is shown having two opposed brake contact surfaces  110  of a diameter A formed on annular disks  190 , a center mounting hub  120  of a diameter B having mounting features  130  circumferentially spaced about a central axis, a central aperture  140  of a diameter D, and one or more visual wear indicator bore(s)  150  located within a brake region  160  at radius C/ 2  from the central axis.  
         [0025]    Aperture  140  of rotor  100  accommodates mounting on an extending shaft of a wheel axle or steering hub of a vehicle, such as an automobile, truck, motorcycle or other land vehicle, i.e., the shaft is received within aperture  140 . Mounting features  130  on mounting hub  120  are typically a through bore sized to receive an appropriate wheel stud. Such bores usually have a conventional configuration, such as  4 ,  5 ,  6 ,  8  or more through bores equally spaced about the center axis at a predefined bolt circle diameter. For example, an exemplary embodiment is shown with a  5  bolt pattern spaced on a 4.250″ bolt circle, which is a conventional configuration for many U.S. vehicles. However, other conventional mounting features can be readily substituted as these features do not form an essential part of the invention.  
         [0026]    Brake rotors  100  are usually formed or molded from cast iron, but have recently been formed of other metals and composite materials, such as aluminum, titanium, carbon fiber, and impregnated polymer composites. The exact material is not critical to the invention and may be any conventional or subsequently developed composition found suitable as a brake rotor surface. Preferably, but not necessarily, the rotor is of a unitary construction formed of a single material, which may be a composite steel or other suitable material.  
         [0027]    At least one and preferably two radially extending axial disks  190  extend from hub  120  and form brake contact surfaces  110 . These disks are usually molded to a certain overdimension (i.e., increased thickness) and then precision machined by known conventional milling machinery to have industry defined planar contact surfaces of (1) a certain surface roughness, such as, for example  125  Ra, and (2) dimensional accuracy (lateral runout). However, the inventive brake rotors  100  are further formed with one or more visual wear indicator bores  150  on at least the outboard contact surface  110  and preferably on both outboard and inboard contact surfaces  110  as shown.  
         [0028]    The ability of the brake rotor  100  to dissipate heat generated by the braking forces is critical to proper operation of the braking system. Brake rotors are essentially a heat sink. As logic dictates, a larger brake rotor is generally able to accommodate more heat dissipation. However, as the diameter of rotors is often limited by the wheel size and the like in vehicles, brake rotors typically are provided with an internal vane structure, best shown in FIGS.  1 - 2 , that consists of thin, spaced radially extending vanes  170  between the two annular disks  190  that define the contact surfaces  110 . Air flow paths  180  are defined between adjacent vanes  170  that assist in air cooling of the rotors. Details of such vanes structures are well known and do not form an essential part of the invention. Accordingly, further description is omitted.  
         [0029]    Because bigger rotors accommodate more cooling, most brake rotors have a full contact face surface (surface  110 ) to maximize rotor mass, contact surface area and associated heat transfer and dissipation properties. However, some rotor designs of recent years have begun implementing different configurations, including “crossdrilled” designs that attempt to improve cooling and slotted rotors that attempt to improve brake pad cleaning.  
         [0030]    With such cross-drilled designs, a series of through bores are drilled all the way through one or both of the annular disks  190  to provide an air flow path from the exterior contact surfaces of the rotor to the interior air flow paths of the internal vane structure. While such through bores increase rotor cooling efficiencies, these through bores may present other problems, such as compromised rotor integrity and increasing the risk of stress cracks. Moreover, if too much material is removed, heat dissipation or other braking properties may be compromised. Such through bores, however, regardless of their effectiveness at brake cooling, cannot serve as wear indicators because the bores go all the way through annular disks  190 .  
         [0031]    The need for a visual wear indicator for brake rotors is discussed above. However, the braking efficiency of the rotor visual wear indicator should not be obtrusive to maximize the efficiency of the rotor. That is, the indicator should not require removal of a large amount of rotor material, to maximize rotor mass and surface area. Moreover, the visual wear indicator(s)  150  needs to be provided on the contact surface  110  in a braking region contacted by a brake pad during use, as it is only this area that is subject to wear.  
         [0032]    There are several possible configurations for the inventive visual wear indicator  150 . In a first embodiment, shown in FIGS.  1 - 2 , the inventive visual wear indicator  150  is a simple counterbore formed partially into contact surface  110  at a location intermediate radial extremities of contact surface  110 . That is, the location is selected to have a radius C/2 that is greater than B/2 and less than A/2 so as to be within a braking contact area contacted by a brake pad, shown in outline form as element  160 , as rotor  100  rotates between opposing brake pads. The size and shape of the counterbore is selected so as to remove only a small amount of rotor material. This reduces the possible detrimental effect of the counterbore on the brake system, e.g., drag, noise, rotor balance and the like.  
         [0033]    By making the counterbore cylindrical as shown, a very economical manufacturing process can be used to form the counterbore. For example, the formed rotor may be fixedly mounted and a simple machine tool such as a drill press with a rotating bit moveable in a single degree of freedom (translatable in one plane) can be used to form the hole. A suitable counterbore may have, for example, a diameter of approximately 0.4″ (11 mm). While the exact size is not critical, the depth of the visual wear indicator is critical as the thickness of the rotor material at the bottom of the counterbore must correspond to a desired minimum useable rotor thickness contemplated by the manufacturer.  
         [0034]    In its simplest form, the visual wear indicator  150  can consist of a single cylindrical counterbore, provided in the outboard brake contact surface  110 . In such a case, it can be presumed that wear on both inboard and outboard brake contact surfaces  110  will be substantially the same. However, as this is not always the case, it is more preferable to provide at least one visual wear indicator  150  on each of the inboard and outboard brake contact surfaces  110 , as shown. Because the amount of material removed in this embodiment is negligible in the context of total rotor mass, on the order of one gram, the visual wear indicators can be provided in the same location(s) on each contact wear surface  110 . However, it may be advantageous to provide the visual wear indicators 180° from each other (diametrically opposite each other) as shown in FIGS. 1 and 2 so as to maintain better rotor balance. However, this may only have significance if the amount of material is relatively large or the weight of the rotor is significantly reduced.  
         [0035]    In the first embodiment, a single isolated visual wear indicator is provided, preferably on each brake contact surface  110 . However, it may be desirable to visually gauge wear around the entire periphery of the rotor. An exemplary embodiment of such is shown in FIGS.  3 - 4  where instead of a single isolated bore, a narrow annular groove  150 ′ is provided that is substantially concentric with hub  120  and the axis of rotor rotation. This provides an enhanced visual wear indicator that can be used to visually ascertain the condition of the rotor at various locations about the rotor surface. Such an embodiment is capable of identifying not only overall wear, but is capable of determining runout problems (i.e., where the rotor is experiencing uneven wear patterns). This groove  150 ′ should, like bore  150 , have a depth such that the thickness of the rotor material at the bottom of the groove corresponds to the minimum useable rotor thickness contemplated by the manufacturer. Also, the width of the groove should be quite small to reduce effect on braking and adverse problems with brake pad contact. A typical exemplary width can be between {fraction (1/16)}″ - {fraction (3/16)}″ wide. As in the first embodiment, annular groove  150 ′ may be provided on each of the inboard and outboard brake contact surfaces  110  and must be located within a brake contact region that is contacted by brake pads  160  during use (i.e., radially located between a lowermost and an uppermost contact edge of brake pad  160  when installed).  
         [0036]    This embodiment also can be manufactured at a relatively inexpensive cost. For example, rotor  100  may be mounted on a rotary jig and a fixed machine tool having a drill bit that is translatable in one dimension is positioned to a desired location and advanced into the rotor to the desired depth while the rotor is rotated by the rotary jig to form the annular groove  150 ′ on rotor  100 .  
         [0037]    Even though the annular groove has minimal width and thus has only limited contact with the brake pad surface, it may be possible that, after extended use, an annular ridge may develop on the brake pads due to the repeated interaction of the brake pad with the annular groove at the same radial location. Such a ridge may create undesirable noise. To avoid this potential problem, the visual wear indicator may be shaped as an eccentric groove  150 ″ that is still substantially concentric with the axis of rotation. See FIG. 5. The exact shape of eccentricity can be varied as desired and does not have to be as complex as that shown. However, the primary purpose of the eccentricity is to vary the radial point of contact with the brake pads during rotation to avoid the formation of an annular ridge.  
         [0038]    The formation of an eccentric groove requires additional machining costs. One exemplary possible manufacture technique would be to provide a bit on a drill jig that is translatable radially and mounting the rotor on a rotatable jig such that during rotation, the bit is translated radially inward or outward to form the eccentric pattern. Alternatively, the groove can be formed by using a multiple axis CNC machine.  
         [0039]    Other variations of an eccentric groove that would eliminate the potential for the formation of annular ridges, as discussed above are an annular groove as in FIG. 3 that is slightly offset from the axis of rotation and an oval groove.  
         [0040]    The invention as described is not limited to the specific embodiments described. Instead, the inventive visual wear indicator and rotor can have various other configurations, such as, for example, those shown in FIGS.  6 - 9 . That is, instead of a simple cylindrical counterbore or annular groove, the counterbore may be square as in FIG. 6. The indicator may also take the form of a more complex shape or shapes, such as the star form in FIG. 7, the hollow milling design in FIG. 8, or even a custom insignia or logo, such as that shown in FIG. 9. The shape of the indicator is not overly important, rather, the location and depth of the visual wear indicator are the critical parameters. That is, the wear indicator should only be provided in a location that is fully contacted by a brake pad during use so that the indicator is a proper indicator of rotor wear in the region that forms a braking surface. Additionally, the wear indicator should have a recessed surface that is substantially parallel to the brake contact surface and the depth of the rotor material at the bottom of the indicator should be equal to or greater than the predetermined minimum useable thickness of the rotor, so as to indicate when the rotor has worn to a point where it is no longer serviceable.  
         [0041]    While not necessary, it is also contemplated that such visual wear indicators  150  may be painted, coated, anodized or the like so as to visually contrast from the remainder of the rotor surface, which in most cases is a dull, polished metallic finish. For example, the wear indicator surface can be applied with a coat of a highly visible or contrasting color, such as red. Obviously, when such coating is to be used, the counterbore depth must be accordingly adjusted to accommodate for a predetermined thickness of the paint or other colored coating. Such a colored coating can have multiple purposes. When the rotor is new, it provides a distinct visual cue that this rotor is different from normal rotors and has the inventive visual wear indicators. Second, as is known, metallic rotors rust during use and exposure to elements. Thus, only those surfaces that are worn down by contact with the brake pads are free of such rust. By coating the wear indicator surface, this surface can be protected from rust build up, which could effect the proper visual indicator function. Further, even to the extent that rust may accumulate on top of the coated visual wear indicator, when the rotor is worn to the true limit of the wear indicator, any such rust or accumulation will be scraped off by the contact with the brake pads until the coating shows through to give a contrasting visual indication that the rotors are worn, which indication may otherwise be obscured if the coating is not provided.  
         [0042]    While the systems of the invention have been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.