Abstract:
A brake rotor has double annular vents with cooling vanes connecting inboard and outboard cheeks of a rotor to a central support ring. Each of the annular vents provides separate passages for cooling the adjacent cheek of the brake rotor and separate inlets are provided for the dual vents from opposite sides of the central support ring. Aligned and staggered vane embodiments and parallel and angled passage embodiments are disclosed. The dual vents increase both the flow rate and the surface area for heat transmission and flow the air closer to the heated cheek surfaces. The staggered vanes improve stiffness and the slanted passages have potential stiffness and heat sink advantages.

Description:
TECHNICAL FIELD 
     This invention relates to rotors for automotive vehicle disk brakes and, more particularly, to rotors having a double row of cooling vents. 
     BACKGROUND OF THE INVENTION 
     It is known in the art relating to automotive vehicle disk brakes to provide vented rotors having a single ring of air passages or cooling vents separated by annularly spaced cooling vanes. The vanes act as impellers that force air through the passages by centrifugal action during rotation of the brake rotor when the vehicle is moving. The vanes also connect the two cheeks of the rotor together and so affect the stiffness of the rotor by their structural characteristics. The air passing through the passages cools the brake rotor and the associated brake pads and thereby extends the life of the pads and improves the braking action of the pads against the rotor. A vented brake rotor has greater surface area per unit of mass of the rotor than an unvented rotor and has higher cooling rates due to both increased air velocity and increased surface area. 
     Two fundamental variables that influence the performance of a vehicle brake rotor are the cooling rate and the heating rate. The higher the cooling rate and the lower the heating rate the lower the braking temperature of a given rotor. Typically, the total width of a brake rotor will be fixed for a given vehicle in advance during the design and development of the vehicle. Increasing the air gap along the rotor axis will increase the cooling rate, however if the air gap along the axis is increased the cheek thickness will have to be reduced which brings down the mass of the rotor. The cooling rate and heating rate are opposing variables for a fixed rotor total width so that increasing one will decrease the other and vice versa. It is a problem then to find the optimum point where both cooling and heating rates are acceptable and rotor performance and pad wear life are maximized. Various changes, such as increasing the number of vanes, modifying vane shape or enhancing brake rotor and pad materials can affect the performance of a disk but may also adversely affect its structural and noise properties. Accordingly, improvements in the performance of the current version of a vented brake rotor generally represent compromises between performance and other required characteristics. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved brake rotor which provides a double row of vents with cooling vanes connecting inboard and outboard cheeks of a rotor to a central support ring. Each of the rows or rings of vents provides separate cooling to the adjacent cheek of the brake rotor and separate inlets are provided for the two rows of vents from opposite sides of the central support ring. 
     The double-vented brake rotor of the invention improves rotor performance in several ways. First, the surface area for heat transmission to the cooling air is increased by the introduction of two cheek faces connected to the central support ring. Second, the air flow rate is increased due to bifurcation of the air passages. Third, the flowing air is brought closer to the heat sources, which are the outer cheek faces. The result is that cooling performance of the new brake rotor is substantially improved. The design is such that the brake rotor is tangentially and axially rigid because the cooling vanes are relatively short and support the cheeks without substantial deflection, which leads to reduced noise propensity. 
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is an axial half cross sectional view of a first embodiment of double vented brake rotor having aligned vanes; 
     FIG. 2 is an isometric view showing the rotor of FIG. 1; 
     FIG. 3 is a view similar to FIG. 1 but showing an alternative embodiment wherein the vanes of one of the vents are angularly staggered relative to the other; 
     FIG. 4 is an isometric view showing the embodiment of FIG. 3; 
     FIG. 5 is a view similar to FIG. 1 showing a third embodiment wherein the vents are slanted inwardly toward their outer radius; and 
     FIG. 6 is a view similar to FIG. 5 showing an alternative embodiment with angularly staggered vanes. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIGS. 1 and 2 of the drawings in detail, numeral  10  generally indicates a first embodiment of a double-vented brake rotor according to the invention. Rotor  10  includes a hub  12  having a generally cylindrical body  14  ending axially outwardly from a radially inwardly extending ring  16  having openings, not shown, for attachment of the hub to a wheel spindle of a vehicle. Adjacent its inner end, the hub  12  is connected with a radially outwardly extending central support ring  18 . 
     An annular brake disk  17  is carried by the hub  12  at its inner end. The brake disk  17  includes a central support ring  18 , which is fixed to the hub  12  and extends radially outward therefrom. The disk  17  further includes inboard and outboard cheeks  22  and  23  respectively, spaced to either side of the support ring  18  to form double inboard and outboard vents  20 , 21 . The inboard and outboard cheeks  22 ,  23  have outer surfaces  24  adapted to be engaged by the brake pads of a disk brake mechanism not shown. Each cheek  22 , 23  is connected axially with the support ring  18  by a ring of angularly spaced vanes  26 , which extend radially and axially to define a plurality of angularly spaced generally radial air passages  28  across the annular vents  20 ,  21 . The passages  28  provide for radial air flow from the inner diameter to the outer diameter of the cheeks  22 , 23 . 
     In the present instance, inlet air flow to the passages  28  is enhanced by shallow annular grooves or dents  30  provided in the cylindrical body  14  inward of the cheeks  22 ,  23 . As indicated in drawing FIGS. 1 and 2, the vanes  26  of the inboard vent  20  are axially aligned with the corresponding vanes of the outboard vent  21 . 
     Referring now to FIGS. 3 and 4 of the drawings, numeral  32  generally indicates a second embodiment of double-vented brake rotor according to the invention. Rotor  32  is in many respects identical to rotor  10  so that like numerals are used to indicate like parts. 
     Rotor  32  differs from rotor  10  in that the vanes  34  of the inboard vent  35  are angularly staggered fully out of alignment with the vanes  36  of the outboard vent  37 , so that the inboard and outboard passages  38 ,  40  are similarly staggered. Optionally, in modified embodiments, the amount of stagger in the vanes of the dual vents may be varied as desired from a minimal misalignment to full misalignment. Also, the particular configuration of the vanes may take any desired form and may be curved radially or axially if desired for use in either embodiment of the invention as previously described. Further, the vanes of the two vents could be made to differ in size, shape number and/or spacing should such modifications be found to be advantageous. 
     FIG. 5 of the drawings illustrates a third embodiment of brake rotor indicated by numeral  42  and FIG. 6 of the drawings indicates a fourth embodiment of brake rotor indicated by numeral  44 . Both the third and fourth embodiments  42 ,  44  are similar to the previously described rotors  10 ,  32  in being provided with a hub  12 , cylindrical body  14  and a radially inwardly projecting ring  16 , the body including shallow annular grooves or dents  30  similar to those of the first described embodiments. Rotors  42 ,  44  differ from the previous embodiments in that the central support ring  46  and the inboard and outboard cheeks  48 ,  50  are configured to provide annular vents  52 ,  54  which are slanted toward one another as their radial distance from the inner diameter to the outer diameter of the cheeks increases. Thus the thickness of the central support ring is reduced toward the outer diameter while the thickness of the respective cheeks is increased toward their outer diameters. The result is that the vanes  56 ,  58  and the cooling passages  60 ,  62  slant toward one another as the passages extend radially outward to their outer diameters. 
     The embodiments of FIGS. 5 and 6 differ from one another in the same manner as those of the first two described embodiments, namely, in that the vanes  56 ,  58  of rotor  42  of FIG. 5 are aligned longitudinally with the corresponding vanes of the adjacent passages and the vanes  56 ,  58  of rotor  44  are staggered radially out of alignment with one another. The optional variations noted regarding the embodiments of FIGS. 1-4 could also be applied to the embodiments of FIGS. 5 and 6. 
     In operation of all the embodiments described, rotation of the rotor as the vehicle moves causes the vanes of the various embodiments to act as impellers which, through centrifugal action, cause air to flow radially outward through the respective passages adjacent to the inboard and outboard cheeks of the respective brake rotors. The air passing through the passages cools the cheeks of the rotors, the inboard ring of passages cooling the inboard cheek of the rotor and the outboard ring of passages cooling the outboard cheek of the rotor. 
     In all cases the additional air flow generated in the dual passages provides improved cooling of the separate cheeks of the respective rotors so that the temperature of the cheeks caused by the friction of braking is maintained at a generally lower level. This occurs in part because the thickness of the cheeks is reduced so that air flow passes closer to the sources of heat which are the outer surfaces  24  of the cheeks. At the same time the reduced mass of the cheeks allows them to be cooled more quickly when the braking action ceases so that the temperature is maintained at a lower level both during and after braking. Additionally, heat from the inner and outer cheeks is conducted through the vanes into the central support ring and is dissipated to the air flow from the ring surface. All these actions combine to maintain lower temperatures in brake rotors made according to the invention. 
     Staggering of the vanes, as opposed to providing aligned vanes as in the first and third embodiments, appears to provide increased structural rigidity in the brake rotor and therefore to reduce vibration and noise in these embodiments, although this may vary with the extent of angular staggering or other variations not yet evaluated. 
     The slanted vanes and passages of rotors  42  and  44  shown in FIGS. 5 and 6 provide the additional advantage that the cheeks are tapered so they are thicker at their outer edges than at their inner edges and thus provide a greater local mass as the distance toward their outer diameter increases. This provides a greater heat sink for receiving the heat input from rubbing of the brake pads at the outer diameter where the linear speed of the surfaces  24  is greater so that the heat input is greater than at the inner edges of the cheeks. Thus the temperature rise at the outer periphery is smaller during heat input while the air passages still provide increased cooling for carrying away the heat in the inboard and outboard passages which directly cool the inboard and outboard cheeks. 
     A further advantage is that the central support ring  46  is larger at its base and thus provides increased structural support for the cheeks and the associated vanes which are connected to the support ring. In addition, the embodiment of FIG. 6 having the staggered vanes has the potential of being stiffer structurally than the embodiment of FIG. 5 having aligned vanes. 
     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.