Abstract:
The universal joint features caps that allow the insertion of grease without removal of the caps. Inside each cap is a bushing that replaces the bearings used in other universal joints. One embodiment of the universal joint features a device for protecting a rubber o-ring which fits inside the caps and around the pins. Another aspect of the universal joint features an arrangement for cleaning the grease under the cap. Another aspect of the universal joint is a stronger material that can withstand more extreme driving conditions.

Description:
PRIORITY CLAIM 
   This application claims the benefit of U.S. Provisional Application No. 60/363,056 filed Mar. 8, 2002 entitled “Universal Joint.” 

   FIELD OF THE INVENTION 
   The present invention relates to an improved universal joint for joining two shafts. 
   BACKGROUND OF THE INVENTION 
   Universal joints, also known as U-joints or Cardan joints, are used to couple two shafts and facilitate the transfer of force from one shaft to the next. Typically, each shaft will have a double yoke ending on the ends to be joined. A cross-shaped universal joint with four arms, or pins, connects the two shafts by placing one pin in each of the four yokes. This type of connection allows each shaft to rotate on an independent, and sometimes dynamic, axis. 
   Universal joints are found in industrial, military, and consumer applications. Typical products using universal joints include boats, cars, planes, generators, and other situations in which two shafts must be connected by a flexible joint. Common applications in vehicles include the drive-train and steering system. Often the forces transmitted with a universal joint are extremely large. Some of the most common applications in which universal joints are used in extreme conditions is four-wheel drive, off-road automobile driving and automobile and boat racing. 
   Four-wheel, off-road driving has become an increasingly popular pastime in recent years. Numerous clubs, magazines, and auto-part makers dedicate significant attention to the growing niche of extreme off-road driving. Many enthusiasts consider off-road driving the ultimate test of automotive engineering. Vehicles and components are literally driven to their breaking points in difficult driving conditions. 
   Off-road driving applications include driving through small rivers, over large rocks, through sand, through mud, through snow, over fallen trees, and even over other cars, Four-wheel-drive vehicles are most common for these types of applications. Even most four-wheel-drive vehicles require significant modifications from the factory-produced models to handle treacherous off-road driving conditions. 
   Numerous companies produce after-market products designed to allow cars and trucks to handle off-road driving conditions. Typical products added to a vehicle to allow off-road driving include rugged tires, stronger axles, heavy-duty shock absorbers, gear differentials, and transfer cases. Even with the best modifications and the most skillful drivers, component failures are commonplace. 
   Universal joints are among the more common trouble-areas for off-road vehicles. In automotive applications, universal joints are used in a number of places and are particularly important for connecting a vehicle&#39;s drive shaft and axles. In such applications, the universal joints can be subjected to extreme forces as the connected shafts spin with high torque and high rpm. 
   When the universal joint leading to one particular axle fails, the force from the drive shaft can no longer be distributed that axle. Such a failure will render the associated tire immobile. When a vehicle suffers a universal joint failure, the vehicle will frequently need to be will towed to a repair facility. Furthermore, the types of repairs required after a vehicle suffers a universal joint failure generally need to be performed in a repair facility with sophisticated lifts and other equipment making such repairs very expensive. Moreover, failure of a universal joint often results in other problems such as broken axles or broken drive shafts. 
   SUMMARY OF THE INVENTION 
   The present invention is an improved universal joint that resists failure even under extremely harsh conditions. One aspect features a universal joint for use in off-road and/or racing vehicles with an improved design making the universal joint stronger and more suitable to harsh conditions than any other joint on the market today. Some embodiments employs improved material selections to increase the durability of the improved universal joint. Another feature includes a bronze bearings to reduce friction between the pins and the caps of the universal joint. Another feature describes a cap for a universal joint that has a grease injection point. Another feature describes a pin on a universal joint that has conduits through which grease can flow and be distributed around the pin and bearing. Another feature is a cap that allows the insertion of grease without removal of the cap or joint. Another feature is a method of injecting grease into the cap of a universal joint to lubricate the cap and to flush out dirt or other debris. Some embodiments feature replacement or after-market universal joints for connecting two shafts in an automobile and include a body with at least one clearance groove to facilitate installation, pins oriented in a cross shape with the body, a lubrication conduit, caps covering the pins, bushings to reduce friction between the caps and the pins as the pins and caps are free to rotate about one another, and a grease fitting that allows insertion of grease or other lubricants or cleaners inside the cap without removal of the cap. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of one embodiment of the present invention. 
       FIG. 2  is a perspective view of another embodiment of the universal joint of the present invention in which the pins are removable. 
       FIG. 3  is a perspective view of another embodiment of the universal joint showing the caps. 
       FIG. 4  is a perspective view of the caps of some embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Shown in  FIG. 1  is one embodiment of an improved universal joint  10  constructed in accordance with the invention. The joint  10  includes a body  12  and a plurality of pins  14 . The joint  10  is designed for installation into the yokes of two shafts such as the various shafts used in an automobile&#39;s drivetrain. The joint  10  may be sold as an after-market product to replace original equipment manufacturer universal joints or it may be included as original equipment in applications where two shafts are joined. 
   Each pin  14  includes a first end  16 , a second end  18 , and an elongate surface  20 . The elongate surface  20  is substantially smooth and cylindrical in shape. The first end  16  of each pin  14  communicates with the body  12 , and the second end  18  of each pin  14  is spaced away from the body  12 . In the embodiment depicted in  FIG. 1 , four pins  14  are oriented with the body  12  in a cross shape. The second end  18  optionally includes at least one conduit  22 . 
   In some embodiments, the body  12  and pins  14  are formed from a single piece of material. For example, with some embodiments, the body  12  and pins  14  are milled from a single ingot. For other embodiments, the metal is cast in a joint shaped mold such that only the pins  14  need to be milled. In embodiments such as those depicted in  FIG. 2 , the pins  14 ′ are removably secured to the body  12 ′. Any number of mechanical attachments may be used to secure the pins  14 ′ to the body  12 ′. The pins  14 ′ may be secured in the body with a retaining mechanism such as a ring clamp (not shown). 
   The body  12  has a thickness A and the pins  14  have a diameter D. The thickness A of the body  12  and the diameter D of the pins  14  vary depending on the application for which the joint is to be used. Universal joints are sized to match the yokes of the shafts which are to be joined, and, generally, larger shafts have larger yokes and require joints with greater thicknesses and greater diameters. 
   The joint  10  of the present invention may also include a plurality of caps  15 ,  15 ′ as shown in  FIGS. 2 and 3 . The caps  15  include an open end and a closed end, and the caps are removably attached to the pins  14 . An inner surface  26  of each cap  15  is substantially smooth and is designed to communicate with a pin  14 . The inner surface  26  may include a friction reducing element  28  such as a bushing or bearings. In many embodiments, the inner surface  26  is a bronze bushing  30 , as shown in  FIG. 4 . Some embodiments may include brass bushings. The inner diameter Z of the caps  15  is slightly larger than the diameter of the matching pin  14 . A cap  15  and a matching pin  14  fit snugly together, but the cap  15  is free to rotate about the pin  14 . Grease or other lubricants may be present between the cap  15  and pin  14 . 
   Typically, one cap  15  is used for each pin  14 . For example,  FIG. 2  shows four caps  15  communicating with the four pins  14 . As shown in  FIG. 4 , each cap  15  has an outer diameter Y and an inner diameter Z. 
   The thickness A of the body  12  and the diameter D of the pins  14  of the embodiment shown in  FIG. 1  are greater than the thicknesses and diameters of comparable prior art universal joints. For example, one common type of axle used for automobiles has yokes with yoke hole diameters of 1.1875 inches. Prior art universal joints used with this type of axle have pin diameters of 0.767 inches and a body thickness of 0.954 inches. In contrast, the diameters D of the pins  14  which match axles with yoke hole diameters of 1.1875 inches are in the range of approximately 0.77 inches to 0.9 inches. More preferably, the pin diameters D matching this type of axle range from approximately 0.84 inches to 0.87 inches. More preferably, the pin diameter D for this type of axle is approximately 0.86 inches. In some arrangements, the pin diameter D can range from 0.8 inch to 0.9 inch and, in other arrangements, the pin diameter D can range from 0.7 inch to 0.9 inch. In one arrangement, the pins have a diameter of about 0.7 inch. The thickness A that matches this type of axle can range from approximately 1 inch to 1.5 inches. More preferably, the thickness A that matches this type of axle is approximately 1.312 inches. In some arrangements, the thickness A can range from 1 inch to 1.4 inches, in other arrangements, the thickness A can range from 1.1 inches to 1.5 inches and, in yet other arrangements, the thickness A can range from 1.15 inches to 1.4 inches. As explained in more detail below, installation can be more difficult with the increased thickness and clearance cut  50  is designed to facilitate installation. 
   As another example, another common type of axle has yokes with yoke hole diameters of 1.375 inches. Prior art universal joints used for this type of axle have pins with 0.893 inch diameters and a body thickness of 1.050 inches. The diameters D of the pins  14  which match axles with yoke hole diameters of 1.375 inches are in the range of approximately 0.96 inch to 1.1 inches. More preferably, the pin diameters D matching this axle range from approximately 0.97 inch to 1.05 inches. More preferably, the pin diameter D is approximately 0.98 inch. In some arrangements, the pin diameter D can range from 0.9 inch to 1 inch and, in other arrangements, the pin diameter D can range from 0.95 inch to 1 inch. In one arrangement, the pins have a diameter of 0.9 inch. In another arrangement, the pins have a diameter of 0.95 inch. The thickness A that matches this type of axle can range from approximately 1.1 inches to 1.35 inches. More preferably, the thickness A that matches this type of axle can range from approximately 1.2 inches to 1.3 inches. More preferably, the thickness A that matches this type of axle is approximately 1.25 inches. In some arrangements, the thickness A can range from 1 inch to 1.4 inches, in other arrangements, the thickness A can range from 1.1 inches to 1.5 inches and, in yet other arrangements, the thickness A can range from 1.15 inches to 1.4 inches. 
   In many embodiments, the ratio of the cap diameter Z to the pin diameter D is in the range of approximately 1.52:1 to 1.25:1. More preferably, the ratio of the cap diameter Z to the pin diameter D is in the range of approximately 1.5:1 to 1.3:1. Most preferably, the ratio of the cap diameter Z to the pin diameter D is in the range of approximately 1.4:1 to 1.35:1. In some embodiments, the cap outer diameter can be about 1.19 inches and, in other embodiments, the cap outer diameter can be about 1.38 inches. 
   Another novel feature of the joint  10  is the ability to rebuild the joint  10 . Friction can cause the pins  14  and caps  15  to wear. In part because of the increased thickness of the pins  14 , the pins can be milled to a smaller diameter and mated with a new cap  15  and/or a new bushing  30 . The joint  10  can then be reinstalled. One method of rebuilding the universal joint  10  is to machine the pins  12  to a diameter that is 0.010 inch smaller then the original diameter. Some embodiments of the universal joints  10  include caps  15  with increased thicknesses or bushings  30  with an increased thickness to match the reduced thicknesses of the pins  14 . 
   A retaining element  32  can be applied to hold the cap in place on the pin and inside the yoke.  FIG. 3  shows a ring clip holding the cap in place. The yokes of an axle communicate with the caps  15  such that relative movement of the cap  15  within the yoke is substantially prevented. In some embodiments the caps  15  may be welded inside the yokes in addition to or in place of the retaining element  32 . Embodiments that feature removable pins  14  may include a second retaining element. 
   As shown in  FIG. 4 , the caps  15  may also include an aperture  34 . The aperture  34  allows the grease or other lubricants and cleaners to be injected to the inner surface  26  of the cap  15  without removing the cap  15  from the pin  14 .  FIG. 4  shows an embodiment in which a grease fitting  36  communicates with the aperture  34 . The grease fitting  36  includes a port  38  through which grease, other lubricants, or other fluids may pass. A valve  40  inside the grease fitting  36  prevents grease from escaping from the port  38  and opens to allow grease into the cap  15  when grease is injected. Thus, grease can be inserted through the grease fitting  36 , but grease typically cannot flow out of the grease fitting  36 . In some embodiments, the grease fittings  36  feature a low profile head  52  that is designed to avoid interference with the movement of the yokes of a shaft. In some embodiments, the head  52  of the grease fitting  36  is machined to a smaller thickness to ensure that it will not contact the yokes of a shaft. In embodiments in which the pins  14  include conduits  22 , the conduits  22  direct the flow of grease, other lubricants, and/or cleaning agents as needed to lubricate the inner surface  26  of a cap  15  and/or flush dirt, moisture, and debris away from the pin  14 . 
   In some embodiments, the aperture  34  is drilled into the cap  15 . The aperture  34  is then be tapped to receive a threaded grease fitting  36 . The grease fitting  36  can then be screwed into place. In some embodiments, a fitting clearance  42  is drilled into the second end  18  of the pin  14 , thereby preventing the grease fitting from reaching the pin. 
   Even with lubrication, friction between the caps  15  and/or bushings  30  and the pins  14  creates heat. Another novel aspect of the embodiment shown and described is the allowance for expansion of the metal pieces caused from this heat. A spacing device  44  such as an o-ring as shown in  FIG. 3  aides in allowing this expansion. In some embodiments, the spacing device is a rubber o-ring  46 . In some embodiments, the cap  15  includes a protective element  54  that covers the spacing device  44  and prevents rocks, sticks, or other debris from contacting the spacing device  44 . Another embodiment of the invention shown in  FIG. 4  presents a cap  15  in which a bottom edge  56  of the cap  15  is extended in length and has an o-ring groove  58  on its inside diameter. The o-ring groove  58  allows the o-ring  46  to fit inside the cap  15  so that the o-ring  46  is substantially protected from contact with foreign objects. Covering the o-ring  46  in this method helps to prevent damage to the o-ring  46  from sticks, rocks, and other debris that may otherwise come in contact with the o-ring  46 . 
   Another novel feature of some embodiments of this invention is the ability to flush grease, dirt, moisture, and other debris from inside the cap  15  without removing the cap  15 . Injecting sufficient quantities of new, clean grease through the aperture  34  allows old grease and debris to be flushed out of the cap  15 . 
   Methods of installing the universal joint  10  are also disclosed herein. For embodiments of a universal joint which feature removable pins such as the one shown in  FIG. 2 , the body is first positioned between the yokes of one shaft and pins are inserted through the holes in the yokes. Next, the yokes of the second shaft are positioned such that the hole of the yokes line up with the pin holes  48  in the body  12  and the remaining pins are inserted. Any retaining elements are then added. 
   To install some other embodiments, the body  12  is first positioned within the yokes of one shaft. In embodiments with clearance cuts  50 , the pin  14  nearest the clearance cut  50  is positioned inside one of the yokes. The joint  10  is then tilted such that the clearance cut  50  is moved toward the yoke. The additional clearance from the clearance cut  50  allows the body  12  to be positioned within the yokes and allows a second pin  14  on the opposite side of the body  12  to be inserted into the other yoke. This process is then repeated for the second set of yokes. With the joint  10  in position, one cap  15  is passed through each yoke and positioned over each pins  14 . The caps  15  are then secured in place, for example, by welding them to the yokes or adding a retaining element  32 . To remove the joint  10 , the reverse procedure can be employed. 
   In one embodiment, the improved universal joint  10  are made of 4340 Mod 300M Chrome-Moly. The metal used in one embodiment has a hardness of 53 Rockwell C. Other materials could be used to make the universal joint  10 . The bushings  30  in one embodiment are made of bronze. 
   For purposes of summarizing the invention, certain aspects, advantages, and novel features of the invention are described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
   The drawings and the associated descriptions are provided to illustrate embodiments of the invention, and not to limit the scope of the invention.