Abstract:
A method is provided for optimally engineering a toroidal transmission having a desired input/output ratio to implement the desired ratio of the transmission while meeting the torque and efficiency requirements of the design. Nanoparticle technology is used to manufacture the stator walls to replace the cutting and milling procedures now in use. A novel Mitchell bearing sleeve and its particular hydrodynamic lubrication and cooling method are proposed herein, as well as the introduction of a novel, ultra smooth, amorphous non-oxidizing contact sleeve material used to form the contact sleeve of the drive rollers. A novel self-lubricating system is further provided that includes an oil reservoir disposed within an output shaft of the transmission.

Description:
RELATED APPLICATION  
       [0001]     This application is a continuation of U.S. application Ser. No. 10/704,361, filed Nov. 7, 2003, which claims the benefit of U.S. Application No. 60/427,088, filed on Nov. 15, 2002, the entire teachings of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Over many years, this inventor pursued various implementations of toroidal devices beginning with systems that would have an electronic output (missile nose cone signal transmitters), to very high reduction positioning devices (radar and telescopes), and, lately, to compact, high-torque power XYZ transmissions that can be used in, for example, trucks, automobiles, and marine vessels. Exemplary embodiments of toroidal drive transmissions are disclosed in U.S. Reissue Patent 26,476, issued on Oct. 8, 1968; U.S. Pat. No. 4,297,919, issued on Nov. 3, 1981; 5,784,923, issued on Jul. 28, 1998; and 5,863,273, issued on Jan. 26, 1999. The entire teachings of the above documents are incorporated herein by reference.  
         [0003]     A transmission of the type described in the above patents is depicted in  FIG. 1 . The load-sharing elements in this type of transmission comprise rotor units  10 , each of which includes a hub  12 , a ring  14  rotatably mounted coaxially to the hub, and a plurality of fingers  16  or rotor unit arms extending radially outward from the ring. The fingers are terminated by drive rollers  18 . The rotors  10  are mounted via the hubs  12  to a large ring  20 , which can be referred to as a yoke, centered on the common rotary axis of the transmission input and output shafts  22  and  24 . The drive rollers  18  of radially extending inner fingers  16  of the rotor units  10  engage in the grooves of a worm  26  connected to the input shaft  22 , and the ring  20  to which the rotor units  10  are mounted is connected by arms  28  to the output shaft  24 .  
         [0004]     The outer fingers  16  of the rotor units  10  engage in grooves or races  32  inscribed in the interior of a transmission housing  34 . When the drive worm  26  is rotated by the input shaft  22 , the various rotor units  10  are caused to rotate about their respective hubs  12 . Since the rotors  10  also engage in the stator races  32 , rotation of those rotors  10  causes the rotors to advance along the races which, in turn, causes the ring  20  to which the rotor units are attached to precess about the rotary axis of the transmission. Since the ring  20  is connected to the output shaft by arms  28 , when the ring  20  rotates, so does the output shaft  24 .  
       SUMMARY OF THE INVENTION  
       [0005]     It is proposed to introduce nanoparticle technology to manufacture the stators to replace the cutting and milling procedures now in use. Since the hardness of nanoparticles increases with the square of the decrease in particle size, enormous benefits for durability are gained when Hot Isostatic Pressing (HIP) procedures are applied combined with surface nitriding. Further, this manufacturing process involves “zero waste”, and enables the production of technically superior and economically attractive products.  
         [0006]     A severe durability limit has existed in past toroidal products caused by the seemingly unavoidable use of needle bearings at the rotor arms. When the XYZ transmission operates at high input speeds, for example, 20,000 to 100,000 rotations per minute (rpm), the needles in the needle bearing turn at profound rpm rates, for example, 200,000 rpm.  
         [0007]     A novel Mitchell bearing sleeve and its particular hydrodynamic lubrication and cooling method are proposed herein, as well as the introduction of a novel, ultra smooth, amorphous contact sleeve material used to form the contact sleeve of the drive rollers. In a particular embodiment, Tri-X material (manufactured by XMX Corporation of Waltham, Mass.) is used to form the contact sleeve. In a particular embodiment, Tri-X material has a melting temperature over about 3,000° C. (5,500° F.). Substantial limitations have thus been overcome, which allows operation of the transmission at high torques at high speeds without sustaining thermo-mechanically caused contact pressure damage.  
         [0008]     Unlike in other gear transmissions that need an external oil pump to transport lubricating oil to points of high stress and high temperature, an embodiment of the present invention includes a device that facilitates the self-circulation of the lubricant. In the present invention, a lubricant such as oil, is provided in an internal reservoir inside the slower output shaft, and self-circulated to each rapidly spinning rotor unit and its rotating arms including its drive rollers at the end of each arm.  
         [0009]     The engineering design of the present XYZ transmission departs radically from other gear transmissions whose proper functioning relies on maintaining tangential contact of the pitch diameters, under constant temperature, to assure proper tooth engagement. One aspect of the present invention allows wide latitude of temperatures and, therefore, expansions in the transmission in which the pitch diameter is permitted to change without affecting the precise engagement between rotor elements or rotor units and grooves. The rotor arms merely move deeper or less deep in the stator grooves without opening gaps between teeth or increasing their noise.  
         [0010]     The input/output ratio of the XYZ transmission is determined by the number of rotations any rotor element makes as it precesses 360° in the stator multiplied by the number of revolutions the central drive worm must make to cause one rotation of the rotor unit. With a given size of a transmission, a wide range of ratios can be attained, typically covering the span of 12:1 to 98:1 using the above variables. Each different transmission ratio causes different lead angles of the grooves in the worm and the stator, which in turn require varied-positioning mounting angles for the rotor units on the yoke of the output shaft.  
         [0011]     To obtain the mathematically mandatory lead and positioning angles, extensive inventive work was completed in XYZ space to devise the software for correctly machining the parts and fitting the rotor arms into the intersecting different lead angle grooves. Again, this fit demands XYZ three-dimensional precision or the entire principle does not work.  
         [0012]     Accordingly, one aspect of the present invention includes software quintessential for machining and polishing the various grooves and machine components as well as for making the sinter forms for nanopowder forms whose sintered components are then Hot Isostatically Pressed (HIP&#39;d). 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of various embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0014]      FIG. 1  is a perspective view partially broken away of a conventional toroidal power transmission.  
         [0015]      FIG. 2  is a diagram of machine for manufacturing monodispersed metal nanosize particles.  
         [0016]      FIG. 3  is partial cross-sectional view of a toroidal transmission implemented in an embodiment of the present invention.  
         [0017]      FIG. 4  is a partial cross-sectional view of a stator housing illustrating flared surfaces adjacent a split line in accordance with an embodiment of the present invention.  
         [0018]      FIG. 5  is a cross-sectional view of the self-lubricating drive roller sleeve bearing taken at the line  5 - 5  in  FIG. 7 .  
         [0019]      FIG. 6  is a partial sectional view of a toroidal power transmission in accordance with an embodiment of the present invention.  
         [0020]      FIG. 7  is a partial longitudinal sectional view of the self-lubricating drive roller sleeve bearing of an embodiment of the present invention.  
         [0021]      FIG. 8  is a perspective view of a rotor unit implemented in an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     A description of embodiments of the invention follows.  
         [0023]     To create a high-torque, high-speed, durable-under-heavy-load, advanced XYZ transmission, several inventions became necessary to achieve this heretofore elusive goal.  
         [0024]     The first step was to invent a manufacturing process for making monodispersed, cube geometry, metal nanosize particles.  FIG. 2  is illustrative of a vessel  52  used to form the nanosize particles. In this new process, metal  40 , such as titanium or other suitable material, for example, aluminum, is vaporized inside a protective environment by laser beam  42  or electron beam energy. In a particular embodiment, the laser beam  42  can be generated by a CO 2  10 KW laser. Vapor droplets  44  are allowed to escape radially from the vaporization chamber (via slits  49 ) in a laminar stream into surrounding environment. Due to the geometry of a radial/conical slit in the body member  51 , the velocity of the vapor droplets  44  slows down as, simultaneously, the temperature drastically drops because of the radial expansion and vertically increasing height of the circumferential slits  49 . This causes the solidification of the tiny liquid droplets (into particles  48 ) before they are swept away by an inert gas stream  46 . The gas stream  46  flows toward one or more cryogenic pumps  50 , which can be alternating cryogenic pumps, in whose ice receptacle  53 , such as argon ice, the particles  48  become embedded.  
         [0025]     The gas stream  46  can include additional elements, such as hexamethyldisolaxane (HMDS), or one or more monomers. In this embodiment, there are two or more cryopumps  50  so that this device is capable of continuously producing particles  48 . Scorotron can be used to negatively charge the particles  48  so that they repel one another to avoid clumping of the particles.  
         [0026]     When the ice evaporates after its removal from the cryopump  50 , only a heap of non-pyrolytic nanopowder  48  remains, ready for further processing. By controlling droplet velocities, thermal gradients, and pressure differentials, as well as assuring laminar flow conditions (to avoid droplet collisions), it is possible to produce monodispersed, i.e., same size, non-agglomerated particles  48  of identical shape, chemistry, morphology, and particle surface properties. Additives such as lanthanum material can be used to form cubic geometry of the particles  48 . In the embodiment in  FIG. 2 , nitrogen is fed into the member  51  on opposite sides to force the vapor droplets  44  into the slit  49 . Oxygen can be used also, for example, to form glass particles. The particles  48  possess a mechanical hardness that is inversely proportional to the particle size  
         (     H   =       C   2     ⁢       1   S           )     .       
 
         [0027]     When Hot-Isostatically Pressed, the particles  48  collectively form a strong particulate body without interstitial vacancies between crystallites. The particles  48  can be placed in a separate autoclave vessel where heat and pressure are applied to the particles which causes them to begin to grow together, but are stopped short of becoming a single crystal block. In other words, the crystalline boundaries are still discernible, even though the intergrowth process has begun already. This stoppage is attained by the timely pressure release in the vessel  52  and the simultaneous temperature drop in the vessel. The result is a durable power transmission component (stators) which renders the high-performance, low-cost aspects the invention transmission requires. Cracks are prohibited from propagating throughout the hardened material. In a particular embodiment, TiN, Al 2 O 3 N 2  (ALON), or other suitable hard material as formed, can be used to form the contact surface of the stator upon which the drive rollers engage. In a particular embodiment, the contact surface is usable in the transmission up to about 1,900° C. (3,500° F.).  
         [0028]     To overcome limitations, such as speed and life, which are innate in normal needle bearings, novel sleeve bearings associated with each drive roller of the fingers of the rotor units are provided. The sleeve bearings together with the novel oil-feeding feature of the present invention offer low friction performance and high speed running and heat dissipation capability. These properties are obtained by choosing a metal alloy suitable for this purpose. In one embodiment, a metal alloy is provided whose melting temperature lies over about 3,000° C. (5,500° F.), whose surface is very smooth and slippery even without oil, but whose surface tension is substantially oleophilic to assure the uniform presence of an oil film. In a particular embodiment, Tri-X material manufactured by XMX Corporation is used to form at least a portion of the contact sleeve.  
         [0029]     Apart from its unique morphology, the geometric shape of the contact sleeve  60  and mounting pins  64  of the drive rollers  82  are believed to be novel in this application. In the embodiment illustrated in  FIGS. 5 and 7 , the geometry of the mounting pin  64  of the rotor unit arm  80  is configured to provide hydrodynamic lubrication between the pin  64  and the contact sleeve  60 , that is, an oil film separates the pin  64  and sleeve  60  during dynamic or running conditions.  
         [0030]     In other embodiments, the inner bore of the contact sleeve  60 , unlike journal bearings with a circular hole, can be shaped to enable the formation of an oil wedge in the partially conical gap. In a particular embodiment, the wedge  88  has a surface area of about 5.0 mm 2  and a contact surface of 0.5 mm 2  where the sleeve  60  contacts the stator surface. At stand-still condition, the oil is attracted via capillary action into the narrow spaces between the bore of the sleeve  60  and the pin  64  on which it is mounted. Under running conditions, however, a dynamic situation takes over that causes the oil from the several grooves to be sucked into the wedge spaces  88  while running under load to be also continuously centrifugally expelled.  
         [0031]     As illustrated in a partial cross-sectional view of the transmission in  FIG. 6 , the oil flow through the sleeve  60  bearings “cools” the metal surfaces as the oil flows centrifugally through the sleeves  60  to the outer perimeter of the drive rollers  82  of the rotor unit arms  80 . From there, the oil returns, due to differential oil pressure, to its supply reservoir  102  that can be located within the hollow, slowly turning output shaft  100 . In a particular embodiment, a respective supply tube  58  fluidly connects the oil reservoir  102  to a central hub of each rotor unit  90 .  
         [0032]     As shown in  FIGS. 6 and 7 , an oil-feed channel  66  in each rotor arm  80  allows the oil to be delivered between each mounting pin  64  and its respective sleeve  60  to provide the hydrodynamic lubrication. As the rotor arms  80  rotate through the toroidal path, centrifugal force moves the oil up through each supply tube  58 , through rotor arms  80  and through the drive rollers  82 . From there, the oil flows down along grooves or races  94  of the stator housing  96 , through a connecting ring channel  104 , and into the oil reservoir  102 . This self-pumping, self-cooling lubrication system offers major advantages over and above any other high-performance transmission.  
         [0033]     The persistent problem of shifting gear engagement pitch at varying pitch diameters due to thermal expansion of the gears and variations in shaft distances within the housing, with increases in the attendant gear noise and tooth wear, is overcome in the present invention transmission by the radial mounting of the rotor units  90 . By suitably positioning the rotor units  90  on their yoke  92  mounts, these rotors  90  can move deeper or less deeply into the running grooves (stator and worm) without affecting the proper engagement (see  FIG. 3 ).  
         [0034]     To accommodate various input/output ratios within a given space, several variables are available to the engineer (all of which are interrelated): the number of threads or grooves on the worm; the number of arms on the rotor elements; and the number of toroidal grooves in the stator.  
         [0035]     In other embodiments, the stator housing  96  can include a first or top section  106  and a second or bottom section  108  that meet at a split line  110  to form the enclosed housing ( FIG. 4 ). If the two sections  106 ,  108  are not lined up in a precise fashion, the grooves or races  32  defined by the sections are also not lined up, resulting in a non-smooth surface over which the contact sleeves  60  pass, which can result in noisy operation of the transmission.  
         [0036]     In specific embodiments, each section  106 ,  108  can be beveled or flared adjacent to the split line  110  in surfaces  112  that form the races  32 . In one embodiment, the surfaces  112  are inclined  114  at about one degree and begin  116  at about 20 micrometers (0.79 mils) from the split line  110 . Surfaces  112  provide a smoother transition for the sleeves  60  as they roll along the races  32  when the sections  106 ,  108  are not perfectly aligned.  
         [0037]     Similarly, the races  32  and/or grooves in the worm  26  can be tapered or bevel adjacent to where the sleeves  60  pass from the grooves in the worm  26  to the races  32  to provide a smooth transition even when the sections  106 ,  108  are not perfectly aligned. As illustrated in  FIG. 3 , an exemplary race  32  is shown having beveled or flared surfaces  118  that facilitate a smooth transition of the sleeves  60  exiting the grooves in the worm  26  and entering the races  32 . In a particular embodiment, surfaces  118  can be about 1.5 mm (0.06 inches) long  120  and inclined  122  at about one degree.  
         [0038]     In a particular embodiment, a method is provided for optimally designing a toroidal transmission, having a desired input/output ratio given the desired reduction or input/output ratio of the transmission, for example, 25:1, a design which maximizes torque of the transmission is determined as follows. Torque is measured as turning moment Md=C*(Hp/rpm), where C is 7.162, HP is horsepower (the rate at which work is done), and rpm is revolutions per minute of the torque conveying input or output shaft, whichever is of interest.  
         [0039]     For a given reduction ratio and torque, a first step is to approximate diameters of the stator, worm, and sleeve pins and strength of the roller arms that can handle the required torques (input/output) (see  FIG. 8 ). Typically, the worm diameter is about one-third the total diameter of the transmission at its widest part. Based on worm diameter, the total number of rotor arms that can physically fit without dimensional interference simultaneously around the worm is determined. This depends on the sleeve outer diameter chosen for the drive rollers of the rotor units. In turn, the sleeve outer diameter chosen determines the width of the toroidal grooves in the stator as well as the width of the worm groove.  
         [0040]     So upon choosing a sleeve outer diameter, the width of the helical stator grooves, but not their number, and the width of the worm groove are determined. The circumference of the stator (calculated from the diameter determined in the first step above) then dictates the total number of stator grooves at the determined width (about the same as the chosen sleeve outer diameter) and with respective wall thickness between grooves possible. Candidate designs (having (i) n total number of stator grooves at the determined width and (ii) M wall thickness between grooves) are analyzed for stability and ranked. As such, threshold thinness (optimal thickness) M and bending strength of the stator walls which form stator grooves are determined such that the stator walls do not fail, i.e., break, during transmission use. To achieve a compact design for the required ratio, the roller elements must make multiple revolutions, such as three, four, or five, which, based on the number of arms a roller sleeve possesses, determines the outside diameter of the stator assuming each runs in a single set or multiple set of grooves.  
         [0041]     As mentioned previously, the chosen sleeve (driver roller) outer diameter dictates the maximal number of rotor arms, and hence rotor units, that can simultaneously fit around the worm. The desired number of rotor units is optimized based on load sharing requirements. This in turn requires consideration of rotor unit design which includes rotor unit dimensions, number and strength of arms of each rotor unit, and angular placement of the rotor units on the yoke. Rotor unit dimensions are determined to provide sufficiently robust rotor units including a total number of arms of each rotor unit. The rotor units are mounted on the yoke at precise positions such that drive rollers of the rotor units are in rolling engagement with the stator grooves or races and worm grooves. More specifically, the drive rollers of each rotor arm are configured to be in rolling engagement with respective separate grooves (either stator side races or worm side groove) at a given moment.  
         [0042]     The foregoing is accomplished in a particular embodiment by the following steps. Take an initial number of arms per rotor unit (this is the rotor ratio). Compare the rotor ratio to the given reduction ratio, and determine the number of rotations a rotor unit will make in a 360° precessional advance (i.e., one revolution about the stator).  
         [0043]     In the given example, the reduction ratio is 25:1. Say each rotor has 6 arms or the rotor ratio is 6:1. Comparing reduction ratio to rotor ratio gives 25/6=4 rotations of the rotor unit to cause a 360° precessional advance. Because of the epicyclic nature, the transmission ratio will be ±1 depending on the direction of the groove angles.  
         [0044]     Next, multiply the determined number of rotor unit rotations by the number of rotor arms. This product represents the minimal number of stator grooves. In the example, 6 rotor arms× 4  rotations=24 needed stator grooves.  
         [0045]     The total number of stator grooves (the above calculated minimum number or more) are evenly spaced about 360°. The total number of stator grooves is bounded by the stator circumference (π multiplied by the stator diameter previously determined) factoring in groove width (synonymous with the driver roller sleeve outer diameter) and the previously calculated optimal wall thickness M.  
         [0046]     Accordingly, the driver roller sleeve outer diameter dictates (i) stator groove configuration (i.e., maximum number of grooves and wall thickness between grooves, given a stator diameter) and (ii) rotor unit design (i.e., maximum number of rotor units, or number of rotor arms per rotor unit, which determines a minimum number of stator grooves). This is mathematically stated:  
               d   w     ≈       1   3     ⁢     d   s     ⁢           ⁢             d   w     ⁢           ⁢   is   ⁢           ⁢   diameter   ⁢           ⁢   of   ⁢           ⁢   the   ⁢           ⁢   worm                 d   s     ⁢           ⁢   is   ⁢           ⁢   diameter   ⁢           ⁢   of   ⁢           ⁢   the   ⁢           ⁢   stator               n   =     number   ⁢           ⁢   of   ⁢           ⁢   groove   ⁢           ⁢   sets                       Eq   .           ⁢   1                 π   ·     d   s       =       ∑     i   =   1       g   s       ⁢       ·       (       T   w     +     W   g       )     i       ⁢           ⁢           where   ⁢           ⁢     g   s     ⁢           ⁢   is   ⁢           ⁢   number   ⁢           ⁢   of   ⁢           ⁢   stator   ⁢           ⁢   grooves                 T   w     ⁢           ⁢   is   ⁢           ⁢   thickness   ⁢           ⁢   of   ⁢           ⁢   groove   ⁢           ⁢   wall   ⁢           ⁢   at   ⁢           ⁢   groove   ⁢           ⁢   i                 W   g     ⁢           ⁢   is   ⁢           ⁢   width   ⁢           ⁢   of   ⁢           ⁢   groove   ⁢           ⁢   i                       Eq   .           ⁢   2                 given   ⁢           ⁢   Reduction   ⁢           ⁢   ratio   ⁢     /     ⁢   Rotor   ⁢           ⁢   ratio   ×   Number   ⁢           ⁢   of   ⁢           ⁢   arms   ⁢           ⁢   per   ⁢           ⁢   rotor     =     min   ⁡     (     g   s     )               Eq   .           ⁢   3             
 
         [0047]     The above system of equations must be held true while maximizing torque (Md=C*Hp/rpm), maximizing number of arms per rotor unit for maximal load carrying ability and optimizing groove wall stability.  
         [0048]     The toroidal transmission is designed by the present invention to include an optimum number of stator grooves to achieve the desired input/output ratio and at the same time include sufficiently robust stator and worm groove walls.  
         [0049]     In summary, the overall design of the geometric construct shown above is optimized to achieve maximum compactness of the transmission while achieve maximum running efficiency and torque. Embodiments of the toroidal transmission can be implemented in a wide variety of applications, such as automotive wheel drives, helicopter main gearboxes, off-road vehicles, forklift platform drives, agricultural machines, hoists, winches, reverse flow tidal turbines, and wind propeller speed increasers/decreasers.  
         [0050]     While this invention has been particularly shown and described with references to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.