Abstract:
An articulated joint includes a first rotational member and a second rotational member coupled with and positioned generally coaxial to the first rotational member. The joint also includes a boot. The boot is selectively deformable in response to an increase in pressure in a joint chamber to increase the volume of the joint chamber. The volume of the joint chamber is selectively changed due to, at least in part, relative movement of the boot end to the second rotational member.

Description:
TECHNICAL FIELD  
     The present invention generally relates to constant velocity joints with flexible boots. 
     BACKGROUND ART 
     Constant velocity joints (CV joints) are common components in vehicles. Constant velocity joints are often employed where transmission of a constant velocity rotary motion is desired or required. CV joints are typically greased or otherwise lubricated for the life of the component. The joints are sealed to retain the grease or lubricant inside the joint while keeping contaminants and foreign matter, such as water and dirt, out of the joint. Moreover, a sealing boot, which may be made of rubber, thermoplastic, silicone material, or the like, usually encloses the internal components of the CV joints thus closing an open end. Additionally, a second open end may also be enclosed with an internal cover to close off the CV joint from the contaminants. 
     During operation, a CV joint may create excess internal pressure in the inner chamber of the joint. This is usually the result of temperature, which may be generated during operation. In such instances, it is often desirable to vent pressurized gases from the chamber of the joint to the outer atmosphere to reduce the internal temperature of the joint. The venting prevents undesirable pressure build-up during operation of the joint that could damage or compromise components such as the sealing boot. Consequently, many CV joints include a means for venting. An example of known venting means include a small hole in the center of the grease cap. However, this venting technique may allow an unwanted release of the grease or lubricant and/or the introduction of contaminants into the joint. 
     A joint may also be sealed without a vent valve or other vent. However, the relative pressure differences created within the boot and joint assembly by thermal cycling may deform the boot beyond a desirable amount, thereby resulting in premature boot failure. 
     One-way valves have been used to vent internal pressure within a CV joint. However, these valves may result in a negative pressure (a value that is undesirably less than atmospheric) when the joint cools, and may result in an unacceptable amount of stress within the boot, leading to a premature boot failure. 
     In traditional CV joint assemblies, a small end of the boot or neck is secured at a shaft-mating portion to the shaft to prevent any relative movement therebetween. Relative movement between the shaft-mating portion of the boot and the shaft may wear the boot and/or the shaft and may result in sufficient wear to permit grease to undesirably escape the joint chamber, or may permit contaminants to undesirably enter the joint chamber. 
     Thus, a joint may allow grease or other lubricants to undesirably leak from joint chamber while permitting undesired contaminants to enter during normal operations. What is needed, therefore, is a constant velocity joint that can accommodate the pressure changes within a joint chamber of a joint assembly while reducing or eliminating any loss of lubricants and introduction of contaminants. 
     DISCLOSURE OF THE INVENTION  
     An articulated joint includes a first rotational member and a second rotational member coupled with and positioned generally coaxial to the first rotational member. The joint also includes a boot. The boot is selectively deformable in response to an increase in pressure in a joint chamber to increase the volume of the joint chamber. The volume of the joint chamber is selectively changed due to, at least in part, relative movement of the boot end to the second rotational member. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings. Components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout several views. 
         FIG. 1  is a partially sectioned view of a constant velocity joint. 
         FIG. 2  is a sectional view of a boot for the joint of  FIG. 1 . 
         FIG. 3  is a partially sectioned view of a constant velocity joint according to an embodiment of the present invention. 
         FIG. 4  is a sectional view of a boot for the joint of  FIG. 3 . 
         FIG. 5  is an enlarged sectional view of portion  5  of  FIG. 3 . 
         FIG. 6  is a partially sectioned view of the constant velocity joint of  FIG. 3 , illustrated in a second configuration. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, exemplary constant velocity joints are shown. The illustrated constant velocity joints and joint chambers may be fixed constant velocity joints of the monoblock style that may be used with a propeller shaft (propshaft) of a vehicle. It should be noted, however, that any type of constant velocity joints and constant velocity joint chambers, including without limitation, tripod, fixed tripod, or the like may be used in accordance with the present invention. That is, one of ordinary skill in the art will recognize the advantages realized by the invention in substantially all types of constant velocity joints, and, therefore the invention should not be limited to the illustrated embodiments. 
       FIG. 1  illustrates a prior art CV joint  20  having a central axis A-A. CV joint  20  includes driven end  22  and a driving end  24 . CV joint  20  further includes a joint assembly  26  coupled to a shaft  28  with a boot cover assembly  30  connected therebetween. CV joint  20  further includes a grease cover  32  that seals the driving end  24 . Boot cover assembly  30  includes a metal cover  34  and a flexible boot  36 . A portion of metal cover  34  is crimped onto boot  36  for attachment thereto. Boot cover assembly  30  and grease cover  32  protect the moving parts of CV joint  20  during operation by retaining the grease or lubricant inside the joint while keeping contaminants and foreign matter, such as water and dirt, out of the joint assembly  26 . 
     Grease cover  32  includes a vent valve aperture  38 , as discussed in greater detail below. 
     Joint assembly  26  includes a cage  40 , an outer race  42 , an inner race  44 , and a plurality of balls  46 . Cage  40  retains balls  46  between the outer race  42  and the inner race  44  in a generally equally spaced circumferential orientation. Shaft  28  is splined to the inner race  44  to allow axial movement therebetween. 
     Collectively, at least the shaft  28 , boot cover assembly  30 , outer race  42 , and the grease cover  32  form a joint chamber  48 . Joint chamber  48  contains grease or other lubricant (not shown) for lubrication between cage  40 , outer race  42 , inner race  44 , and balls  46 . A vent valve  50  for equalizing pressure on either side of grease cover  32  is positioned within the vent valve aperture  38 . Vent valve  50  includes a cylindrical body  52  having an aperture  60  formed therein. 
     With continual reference to  FIG. 1  and specific reference to  FIG. 2 , the boot  36  includes a contoured body of revolution  62  having a small end  64 , a large end  66 , a middle portion  68 , and a curved portion  70 . As illustrated in  FIG. 1 , the small end  64  is coupled to the shaft  28  and the large end  66  is crimped to the metal cover  34 , which is, in turn, coupled to outer race  42 . Small end  64  is axially secured to the shaft  28  with a conventional type of clamp connector or any other suitable means to restrict any relative axial movement between the small end  64  and the shaft  28 . 
     During vehicle operation, CV joints  20  are typically heated due to the rotation and resulting friction between moving parts. Pressure within the joint chamber  48  typically increases due to the heat of operation, and the lubricants are typically softened and have a lower viscosity due to the heat. When a vehicle is parked on a relatively horizontal surface the shaft  28  is generally horizontal and the level of grease within joint chamber  48  is below the vent valve  50 , allowing any excess pressure generated within joint chamber  48  to vent to the atmosphere while preventing the loss of lubricants through aperture  60 . However, periodically, the vehicle may be parked on an incline resulting in the shaft  28  positioned at an angle relative to a horizontal plane, and the aperture  60  located below the level of lubricant within the joint chamber  48 . When this occurs, grease or other lubricants may escape through the aperture  60 . 
     Generally, when the CV joint  20  is rotating at high speed, the lubricants rotate with the joint and are forced outward from the axis A-A. During this dynamic operating condition, lubricants will typically not escape through aperture  60 . 
     When the CV joint is operating at lower speeds, the force of gravity on a portion of the lubricant may overcome the angular momentum of the lubricant and cause the lubricant to slump toward the shaft  28 . The lubricant may free-fall or migrate toward axis A-A. When this occurs, lubricant may escape through aperture  60 . 
     When a joint, such as CV joint  20 , is heated during operation and then permitted to cool, a vent, such as the aperture  60  in vent valve  50 , which permitted air to escape during any pressure increase in the joint chamber  48 , will permit air to enter the joint chamber  48  as the pressure within the joint chamber  48  falls below ambient pressure. However, this air entering the joint chamber  48  may bring entrained contaminants including moisture that may affect the operation of the joint. By way of example, moisture that enters the joint chamber  48  may react with the grease and drive a chemical reaction that undesirably changes the grease thereby degrading the properties of the grease. 
       FIG. 3  illustrates a CV joint  120  having a central axis B-B. CV joint  120  has a driven end  122  and a driving end  124 . CV joint  120  further includes a joint assembly  126  that is coupled to a shaft  128 . A boot cover assembly  130  is connected between the joint assembly  126  and the shaft  128 . A grease cover  132  seals the driving end  124  of CV joint  120 . Boot cover assembly  130  includes a metal cover  134  and a flexible boot  136 . The shaft  128  is defined, in part, by a generally cylindrical shaft outer surface  138  ( FIG. 5 ), as discussed in greater detail below. 
     Joint assembly  126  includes a cage  140 , an outer race  142 , an inner race  144 , and a plurality of balls  146 . As illustrated, shaft  128  is splined to inner race  144  and may be formed integrally to the inner race  144 . 
     Collectively, at least the shaft  128 , boot cover assembly  130 , outer race  142 , and the grease cover  132  form a joint chamber  148 . The joint chamber  148  contains grease or other lubricant (not shown). 
     With continual reference to  FIG. 3  and specific reference to  FIG. 4 , the boot  136  includes a contoured body of revolution  162  having a first portion, or a small end,  164 , a large end  166 , a middle portion  168 , and a curved portion  170 . As best illustrated in  FIG. 3 , the small end  164  is coupled to shaft  128  and large end  166  is crimped to metal cover  134 , which is, in turn, coupled to outer race  142 . While the boot  136  is illustrated with one hemi-torodial portion such as the curved portion  170 , it will be understood that the boot  136  may also include a plurality of generally hemi-torodial portions, such as illustrated in commonly assigned U.S. patent application Ser. No. 11/452,150. 
     With specific reference to  FIG. 5 , the small end  164  includes a channel  174  formed therein and a scraper  176  extending therefrom to a small end surface  178 . The channel  174  includes a generally cylindrical seal mating wall  180 , a generally annular first seal retaining wall  182 , and a generally annular second seal retaining wall  184 . With reference to  FIGS. 3-5 , the boot  136  also includes an inside boot surface  186  and an outside boot surface  188 . 
     The small end  164  is axially moveable relative to the shaft  128  and includes a radial shaft seal  190  interposed between the small end  164  and the shaft  128 . The radial shaft seal  190  includes an annular seal body  192  and a tensioning member  194 . The seal body  192  includes a generally cylindrical boot mating portion  200 , a first sealing portion  202 , and a second sealing portion  204 . As illustrated in  FIG. 5 , the seal body  192  is coupled to the shaft  128  in an interference fit such that at least a portion of first sealing portion  202 , and the second sealing portion  204  of the seal body  192  are outwardly deformed as the seal body  192  is installed onto the shaft  128 . 
     As will be appreciated, articulation of the joint  120  where the axis of the shaft  128  is not co-axial with the axis of the outer race  142  may result in a change in the volume of the joint chamber  148 . Movement between the small end  164  and the shaft  128  may reduce this change in volume of the joint chamber  148  during joint articulation to prevent an undesirable change in the pressure within the joint chamber  148 . 
     Additionally, if a boot similar to the boot  136  is used on a plunging joint, joint plunge may affect the volume of the joint chamber  148  as the shaft moves axially relative to a outer race  142 . Accordingly, movement between the small end  164  and the shaft  128  may reduce this change in volume of the joint chamber  148  during joint plunge to prevent an undesirable change in the pressure within the joint chamber  148 . 
       FIG. 3  illustrates the CV joint  120  in a first configuration where the pressure within the joint chamber  148  is generally equal to the ambient (outside the joint chamber  148 ) pressure. In this first configuration, a distance between the outer race  142  and the small end surface  178  is illustrated as a distance L 1 . 
       FIG. 6  illustrates the CV joint  120  in a second configuration. In the second configuration, the joint chamber  148  has a greater volume than the volume of the joint chamber  148  in the first configuration. One explanation for the greater volume in the second configuration may be that fluids, such as air, within joint chamber  148  may have expanded due to heat during operation of the joint  120 . In this second configuration, a distance between the outer race  142  and the small end surface  178  is illustrated as a distance L 2 . As illustrated, the distance L 2  is greater than the distance L 1 . 
     During operation of CV joint  120 , heat buildup in joint chamber  148  increases the temperature of the fluids (grease, air, and the like) contained within the joint chamber  148 . As the temperature of these fluids increases, the pressure of these fluids within joint chamber  148  increases, due primarily to the expansion of the fluids that are gasses. This increased pressure is exerted on the boot  136 , and results in a force FE acting on the inside boot surface  186  (and on the seal  190 ) that urges the small end  164  of the boot  136  to move in the direction of arrow PI. When the pressure within the joint chamber  148  rises sufficiently above the ambient pressure, the force FE ( FIG. 5 ) increases. When the force FE increases above a magnitude required to overcome a frictional force FF ( FIG. 5 ) between the seal  190  and the shaft  128 , then the small end  164  of the boot  136  may move relative to the shaft  128  such that the boot  136  moves from the first configuration and toward the second configuration. 
     After operation of the CV joint  120 , the temperature of CV joint  120  will typically lower to ambient temperature. As the temperature of the air within joint chamber  148  decreases, the pressure of this air decreases. As the pressure within the joint chamber  148  decreases, a return force FR ( FIG. 3 ) (due to negative pressure within the joint chamber  148 ) is exerted on the boot  136  (generally at curved portion  170 ) generally in the direction of arrow PD ( FIG. 6 ). As the pressure within the joint chamber  148  further decreases, the force FR will increase to a magnitude sufficient to overcome a frictional force between the seal  190  and the shaft  128 . This return force FR will urge the small end  164  to move relative to the shaft  128  generally in the direction of the arrow PD. As the small end  164  moves relative to the shaft  128  generally in the direction of the arrow PD, the volume within the joint chamber  148  is decreased, thereby increasing the pressure within the joint chamber  148  to a pressure that is closer to ambient pressure. 
     As will be appreciated, the frictional force, FR, and FE are not constants, but vary with operation of the joint  120 . That is, the frictional force may vary whether the force is generated due to a sliding or a static friction. The forces FR and FE necessarily change with a change in the pressure within the joint chamber as compared to the ambient pressure. 
     As mentioned previously, operation of CV joint  120  generally results in the lubricant within joint chamber  148  migrating away from axis B-B within CV joint  120  as a centrifugal force is imparted upon the lubricant. The lubricant will generally be held within the joint chamber  148  in an annular configuration that is positioned farthest from axis B-B by a centripetal force imparted to the lubricant by at least outer race  142 , metal cover  134 , and the outer portions of grease cover  132 . In this annular configuration, the lubricant will contact balls  146  which are preferably constructed of a metal. As the lubricant tends to cling to metals, and balls  146  rotate along an axis generally parallel to axis B-B, a portion of the lubricant will generally be interposed between balls  146 , cage  140 , outer race  142 , and inner race  144  during operation of CV joint  120 . 
     During high-speed operation, the centrifugal force acting on the lubricant will generally be greater than the force due to gravity on the lubricant and thus prevent the lubricant from migrating toward axis B-B. In relatively slow-rotational operation, the force due to gravity acting on the lubricant may be sufficient to cause a portion of the lubricant to slump where a portion of the lubricant falls toward axis B-B during rotation of CV joint  120 . This slumping may occur as a migration of lubricant along grease cover  132  toward axis B-B as CV joint  120  rotates, or may occur as a portion of lubricant clings to itself (tackifier) and releases from other portions of lubricant and/or CV joint  120  and is free to fall in a generally arcuate path toward axis B-B. Thus, during lower speed operation, a portion of the lubricant may migrate toward the axis B-B. 
     In a static, non-rotating, state, the CV joint  120  at ambient temperature will generally contain a lubricant that clings to both itself and internal portions of CV joint  120  such that the lubricant (typically grease) will not flow. During operation of CV joint  120 , the lubricant may shear soften and experience a reduction in viscosity. This reduction in viscosity may cause the lubricant to flow more readily until the lubricant sufficiently cools after operation. 
     When CV joint  120  has been operated sufficiently to shear soften the lubricant (generally at an increased ambient temperature and under harsh operating conditions) and CV joint  120  is not rotating, a portion of the lubricant may flow from the annular position of operation (mentioned above) to lower portions of the joint chamber  148  as a result of the effects of gravity. As the lubricant flows, the level of the lubricant will preferably not reach the axis B-B when axis B-B is generally horizontal. When axis B-B is not horizontal, (such as, for example, when the vehicle is parked on an incline) the level of the lubricant may move closer to the axis B-B. At an extreme incline, where axis B-B is far from horizontal, the level of the heated, lower viscosity lubricant may flow toward axis B-B and reach a center portion of the grease cover  132 . 
     The elimination of a vent valve within the joint  120  will restrain the fluids within the joint chamber  148  from escaping from the joint chamber  148  and will reduce or eliminate contaminants from entering the joint chamber  148 . The relative movement between the small end surface  178  and the shaft  128  permits the pressure within the joint chamber  148  to equalize close to the ambient pressure, thereby preventing the pressure within the joint chamber  148  to increase or decrease to an undesired value. 
     In the embodiment illustrated the scraper  176  contacts the shaft surface  138 , at least when the scraper  176  moves in the direction of the arrow PI, to move contaminants away from the shaft seal  190 . However, the scraper may not be in constant contact with the outer shaft surface  138  at all times during operation, since the rotation of the joint  120  will tend to prevent the presence of solid or particulate contamination from accumulating on the shaft surface  138  (due to the angular acceleration). Additionally, the scraper  176  may be integrally molded on the boot  136 , and/or may be constructed of a different material than the boot, such as a high density polyethylene (HDPE) or other suitable material. 
     The joint  120  may be sealed with a predetermined amount of grease or other lubricant. With the elimination of a vent valve, the lubricant within the joint  120  may have a nitrogen blanket, or other gas, to prevent breakdown of the lubricant. 
     The pressure differential across the boot  136  will be greater than the pressure differential across a boot in a vented joint, but less than the pressure differential across a conventional sealed joint. Accordingly, the joint  120  may experience less infiltration of contaminants than a vented joint, such as joint  20 , while experiencing less boot stress than a conventional sealed joint. 
     As illustrated, the small end  164  is a generally cylindrical first boot end portion that is sealed to the outer shaft surface  138  while permitting the first boot end portion to move generally parallel to the axis B-B relative to the shaft  128 . 
     The material for the boot  136  is preferably a flexible material, and may be plastic, nylon or any elastomer, such as hydrogenated nitrile butadiene rubber (HNBR), chloroprene rubber, silicone, or thermoplastic elastomer (TPE). 
     The preceding description has been presented only to illustrate and describe exemplary embodiments of the methods and systems of the present invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope. The scope of the invention is limited solely by the following claims.