Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a tripod type constant velocity universal joint used in a power transmitting section of automobiles, aircraft, ships, and industrial machinery.  
           [0003]    2. Description of the Related Art  
           [0004]    For example, among constant velocity universal joints used as means for transmitting a rotational power of an automobile engine to its wheels at a constant speed is a tripod type constant velocity joint. This tripod type constant velocity universal joint connects a driving side shaft and a driven side shaft together and can transmit a rotational torque between them at a constant velocity even if there is an operating angle between them. The tripod type constant velocity universal joint even permits a relative displacement in an axial direction.  
           [0005]    [0005]FIG. 15 and FIG. 16 show a fundamental structure of a tripod type constant velocity universal joint. This constant velocity universal joint is composed of, as essential structural members, a tripod member  2  with three radially projecting leg shafts  1 , an outer joint member  5  with three axially extending track grooves  3  formed on the inner circumferential surface of the outer joint member, and rollers  7 . Each of the track grooves  3  has at both sides axially extending roller guide surfaces  4 . The rollers  7  are mounted on the leg shafts  1  of the tripod member  2  through a plurality of needle rollers  6  and positioned in the track grooves  3  of the outer joint member. The rollers  7  are guided on their external circumferential surfaces by the roller guide surfaces  4  provided at the both sides of the track grooves.  
           [0006]    The tripod member  2  is fitted over a serration part (or spline part) formed on an end part of the other shaft, not shown, and is secured. As shown in FIG. 17, a plurality of the needle rollers  6  are arranged, so that they can rotate, on an outer circumferential surface of the leg shaft  1  of the tripod member  2 . The needle rollers  6  are limited with respect to their displacement on the leg shaft  1  in the axial direction by washers  8  and  9  installed at the base and top parts of the leg shaft  1 , and a retaining ring  10  secured at the top part of the leg shaft  1 . The outer circumferential surface of the leg shaft  1  of the tripod member  2  has a cylindrical shape, and rollers  7  are fitted over the outer circumferential surface of the leg shaft  1  through the needle rollers  6  so that they can rotate. The inner circumferential surface of the roller  7  has a cylindrical shape-and the outer surface thereof has a genuine partial sphere shape.  
           [0007]    The outer joint member  5  forms a cylindrical cup with one end open and the other end closed, with the other shaft, not shown, being integrally provided at the other end of the outer joint member. Three axial track grooves  3  are formed on the circumference around a center shaft at intervals of 120 degrees on the inner circumferential surface of the outer joint member  5 . At both sides of each track groove  3  are the two roller guide surfaces  4 , and, as shown in FIG. 18, the roller guide surface  4  makes angular contact with the roller  7  at two points A and B. This is done by forming the roller guide surface  4  in the shape of a gothic arch.  
           [0008]    In this tripod type constant velocity universal joint, power is transmitted by the connection between the roller guide surfaces  4  of the outer joint member  5  and the rollers  7  of the tripod member  2 . The rollers  7  absorb plunging by rotating along the roller guide surfaces  4 . In the case of power transmission when the axis of the outer joint member  5  and the axis of the tripod member  2  are aligned, or an operating angle is 0 degree, the point of intersection of the axes of each leg shaft  1  is located on the axis of the outer joint member  5 . In this way the rollers  7  rotate while maintaining dual contact points with the roller guide surfaces  4 . When there is an operating angle, although the magnitude of the contact force fluctuates depending on the rotational phase, the operation of the tripod type constant velocity universal joint is stable because the rollers and the roller guide surfaces  4  are always in contact with each other at the two points A and B.  
           [0009]    The tripod type constant velocity universal joint described above is a sliding type in which relative displacement, caused by plunging, between the two shafts in the axial direction is allowed. Torque is transmitted by connecting the tripod member  2  with one shaft, connecting the outer joint member  5  with the other shaft, and positioning the leg shafts  1  of the tripod member  2  in the track grooves  3  of the outer joint member  5 . In this construction, the tripod member  2  is provided with the three leg shafts  1  projecting in an axial direction, and the outer joint member  5  is provided with the three track grooves  3  extending in the axial direction.  
           [0010]    In this tripod type constant velocity universal joint, because the roller  7  and the roller guide surface  4  are in angular contact at the points A and B, and the roller  7  does not contact with the center part and both sides of the roller guide surface  4 , a strong edge load is not created, the needle rollers  6  do not become skew, and friction resistance does not increase. Furthermore, because of lower eccentric load, rotational moment caused in the roller  7  acting at a right angle to the leg shaft  1  around the axis thereof can be decreased, and frictional force and induced thrust that cause vibration can be reduced. Also, movement in the axial direction when transmitting rotational torque with an operating angle becomes smooth, so that induced thrust is reduced.  
           [0011]    However, conventional tripod type constant velocity universal joints are usually mounted on vehicles operating at low angles, for example equal to or less than 4 degrees, and for vehicles operating at high angles, for example equal to or more than 7 degrees, tripod type constant velocity universal joints of a double roller type are used taking into consideration a higher level of vibration in such applications. The conventional tripod type constant velocity universal joints described above correspond to a single roller type.  
           [0012]    A tripod type constant velocity universal joint of a double roller type is provided with a roller assembly each contained as a unit. The roller assembly is composed of a circular inner roller which is fitted over the outer circumferential surface of a leg shaft, and an outer roller positioned within the track groove which rotates in the axial direction of an outer joint member. Needle rollers are interposed between the inner and outer rollers. Within the roller assembly the inner and outer rollers are individually rotatable.  
           [0013]    In this tripod type constant velocity universal joint, the roller assembly composed of the inner and outer rollers can swing freely with respect to the leg shaft. Therefore, when transmitting a rotational force at a high operating angle between the outer joint member and the tripod member, the roller assembly can rotate only in the axial direction of the outer joint member, and the vibration inducing force of the outer joint member can be absorbed by the rotation of the needle rollers, so that sliding resistance can be reduced. Furthermore, the moment acting to incline the roller assembly during operation becomes smaller, the roller assembly can maintain its posture, resistance between the outer joint member and the roller assembly during rotation becomes smaller, and induced thrust can be reduced.  
           [0014]    However, because a tripod type constant velocity universal joint of a double roller type has a structure provided with the roller assemblies composed of inner and outer rollers, using a tripod type constant velocity universal joint of this type in a vehicle which operates at a low angle causes the cost to increase.  
         SUMMARY OF THE INVENTION  
         [0015]    An object of the present invention is to enable the use of a tripod type constant velocity universal joint in vehicles operating at high angles, without causing an increase in costs, by reducing the level of vibration even at high operating angles.  
           [0016]    A tripod type constant velocity universal joint in accordance with the present invention is composed of an outer joint member with three track grooves, which extend in its axial direction around the circumference, on the inner surface of the outer joint member, and a tripod member with three radially projecting leg shafts around the circumference of the tripod member. Rollers are mounted on each leg shaft, so that they can rotate, through a plurality of needle rollers, and positioned in the track grooves of the outer joint member. The rollers are guided at their outer circumferential surfaces by roller guide surfaces provided on both sides of the track grooves. In this construction, grooves extending along the track grooves are formed on the roller guide surfaces at the points where the rollers contact.  
           [0017]    In a tripod type constant velocity universal joint in accordance with the present invention, because the grooves extending along the track grooves are formed on the roller guide surfaces at the points where the rollers contact, the grooves formed on the roller guide surfaces function as pockets for grease supplied inside the constant velocity universal joint. By the grease in the pockets improves the lubrication, the sliding resistance and induced thrust between the roller guide surfaces and the rollers are reduced, so that the level of vibration is lowered. As a result, the level of vibration can be reduced in a tripod type constant velocity universal joint of a single roller type even when operating at high angles. In this way it becomes possible to use the joint in a vehicle operating at high angles without causing an increase in costs.  
           [0018]    To achieve this lowered level of vibration, it is preferable that the following are added to the structure of the tripod type constant velocity universal joint:  
           [0019]    1. Clearance between the outer circumferential surface of the roller and the track groove is widened by an amount equal to a reduction in the clearance caused by inclination of the roller. The widening is achieved by making the outer circumferential surface of the roller in a spherical shape, and making the outer circumferential surface of the roller in cross section an arc shape with its center of curvature shifted radially outward from the axis of the roller.  
           [0020]    2. The roller guide surface and the roller are in angular contact at two points.  
           [0021]    3. The outer circumferential surface of the leg shaft is crowned.  
           [0022]    4. The inner circumferential surface of the roller is crowned.  
           [0023]    5. The outer circumferential surface of the leg shaft is formed in an elliptical cylinder shape in the embodiments of FIG. 1 and FIG. 3.  
           [0024]    6. The ends of the needle roller are formed in a convex shape. 
       
    
    
       [0025]    The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.  
       BRIEF EXPLANATION OF THE DRAWINGS  
       [0026]    In the accompanying drawings:  
         [0027]    [0027]FIG. 1 shows a cross sectional view of a tripod type constant velocity universal joint in accordance with an embodiment of the present invention with oil grooves formed on roller guide surfaces;  
         [0028]    [0028]FIG. 2 is an enlarged cross sectional view of an essential part showing a roller and a roller guide surface of the embodiment presented in FIG. 1;  
         [0029]    [0029]FIG. 3 shows a cross sectional view of a tripod type constant velocity universal joint in accordance with another embodiment of the present invention with roller guide surfaces in cross section forming a polygon shape;  
         [0030]    [0030]FIG. 4 is an enlarged cross sectional view of an essential part showing a roller and a roller guide surface of the embodiment presented in FIG. 3;  
         [0031]    [0031]FIG. 5 is a characteristics diagram showing the relationship between induced thrust and operating angles;  
         [0032]    [0032]FIG. 6 is another embodiment of the present invention, showing a tripod type constant velocity universal joint with the outer circumferential surfaces of the leg shafts and inner circumferential surfaces of the rollers crowned, and both ends of the needle rollers formed in a convex shape;  
         [0033]    [0033]FIG. 7 is an enlarged cross sectional view of an essential part showing a leg shaft, a needle roller and a roller of the embodiment in FIG. 6;  
         [0034]    [0034]FIG. 8 is a characteristics diagram showing the relationship of induced thrust relative to operating angle presented in the embodiment in FIG. 6;  
         [0035]    [0035]FIG. 9 is still another embodiment of the present invention, showing a tripod type constant velocity universal joint, wherein the outer circumferential surface of a roller in cross section forms an arc shape with the center of curvature shifted radially outward from the axis of the roller;  
         [0036]    [0036]FIG. 10 is a cross sectional side view of the tripod type constant velocity universal joint in the embodiment in FIG. 9, showing a state in which the roller is inclined in the axial direction of an outer joint member;  
         [0037]    [0037]FIG. 11 is a further embodiment of the present invention showing a cross sectional view of a tripod type constant speed universal joint, in which the outer circumferential surface of the roller in cross section forms an arc shape with the center of curvature thereof shifted radially outward from the axis of the roller, the outer circumferential surface is formed in an elliptical cylinder, and the outer circumferential surface of the leg shaft and inner circumferential surface of the roller are crowned;  
         [0038]    [0038]FIG. 12 is a cross sectional side view of the tripod type constant velocity universal joint in the embodiment in FIG. 11, showing a state in which the roller is inclined in the axial direction of an outer joint member;  
         [0039]    [0039]FIG. 13 is an enlarged cross sectional view of an essential part showing the leg shaft, the outer surface of which forms an elliptical cylinder, the needle rollers, and the inner surface of the roller of the embodiment shown in FIG. 11;  
         [0040]    [0040]FIG. 14 is a characteristics diagram showing the relationship between the induced thrust and the operating angle in the embodiments of FIG. 9  and FIG. 10, and FIG. 11 to FIG. 13;  
         [0041]    [0041]FIG. 15 is a cross sectional view showing a conventional tripod type constant velocity universal joint;  
         [0042]    [0042]FIG. 16 is a cross sectional side view of the conventional tripod type constant velocity universal joint presented in FIG. 15;  
         [0043]    [0043]FIG. 17 is an enlarged cross sectional view of an essential part of the conventional tripod type constant velocity universal joint in FIG. 15, showing a leg shaft, a needle roller, and a roller; and  
         [0044]    [0044]FIG. 18 is an enlarged cross sectional view of an essential part of the conventional tripod type constant velocity universal joint in FIG. 15, showing a roller and a roller guide surface. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]    An embodiment shown in FIG. 1 is a tripod type constant velocity universal joint of a single roller type. This constant velocity universal joint is composed of, as essential structural members, a tripod member  12  with three radially extending leg shafts  11 , an outer joint member  15  with three axially extending track grooves  13  formed on the inner circumferential surface of the outer joint member, and rollers  17 . Each of the track groove  13  have, at both sides, axially extending roller guide surfaces  14 . The rollers  17  are mounted on the leg shafts  11  of the tripod member  12  through a plurality of needle rollers  16  and positioned in the track grooves  13  of the outer joint member  15 . The rollers  17  are guided on their external circumferential surfaces by the roller guide surfaces  14  provided at both sides of each of the track grooves.  
         [0046]    The tripod member  12  is fitted over a serration part (or spline part) formed on an end part of the other shaft, not shown, and is secured. A plurality of the needle rollers  16  are mounted on the circumferential surface of the leg shaft  11  of the tripod member  12  so that they can rotate. The displacement of the needle rollers  16  on the leg shaft  11  is limited in an axial direction by washers  18  and  19 , installed at a base and top part of the leg shaft  11 , and retaining ring  20  installed on a top part of the leg shaft  11 .  
         [0047]    The outer joint member  15  forms a substantial cylindrical cup with one end open and the other end closed. The other shaft, not shown, is integrally provided at the other end of the outer joint member, and three axial track grooves  13  are formed on the circumference around a center shaft at intervals of 120 degrees. At the both sides of each track groove  13  are the two roller guide surfaces  14 , and, as shown in FIG. 2, the roller guide surface is in angular contact with the roller  17  at two points C and D by forming the roller guide surface  14  in the shape of a gothic arch.  
         [0048]    In this tripod type constant velocity universal joint, power is transmitted by the connection of the roller guide surfaces  14  of the outer joint member  15  with the rollers  17  of the tripod member  12 . The rollers  17  absorb plunging by rotating along the roller guide surfaces  14 .  
         [0049]    In the case of transmission when the axis of the outer joint member  15  and the axis of the tripod member  12  are aligned, or when an operating angle is 0 degrees, the point of intersection of the axes of each leg shaft  11  is located on the axis of the outer joint member  15 . In this way the rollers  17  rotate while maintaining dual contact points with the roller guide surfaces  14 . When there is an operating angle, although the magnitude of the contact force fluctuates depending on the rotational phase, the operation of the tripod type constant velocity universal joint is stable because the rollers  17  and the roller guide surfaces  14  are always in contact with each other at the two points C and D. In this embodiment, grooves  21  and  22  extending along the track grooves  13  are formed on the two contact points C and D on the roller guide surface that is in contact with the roller  17 , and at the same time a groove  23  extending along each of the track grooves  13  is formed on the intermediate part between the contact points C and D.  
         [0050]    The grooves  21  to  23  formed on the roller guide surface  14  function as pockets for grease supplied inside the constant velocity universal joint. The grease in the pockets improves the lubrication and consequently the induced thrust can be reduced. The term “induced thrust” means thrust force produced by friction inside a constant velocity universal joint when torque is applied to this joint rotating at a certain operating angle. In a tripod type joint induced thrust appears mainly as a strong tertiary component.  
         [0051]    In the embodiment shown in FIG. 1 and FIG. 2, the roller guide surface  14  is provided with the grooves  21  to  23 . However, a structure shown in FIG. 3 and FIG. 4 is also possible. In the embodiment shown in FIG. 3 and FIG. 4, a roller guide surface  14 ′ in cross section forms a polygon shape and the roller  17  makes contact with the roller guide surface at the four points E to H. Clearance formed between each of the four contact points E to H serves, in the same way as the grooves of  21  to  23  described above, as pockets for grease supplied inside the constant velocity universal joint.  
         [0052]    In the embodiments shown in FIG. 1 to FIG. 4, when a conventional type and an improved type (in accordance with the embodiments) are compared as shown in FIG. 5, the improved type has less induced thrust than the conventional type even with larger operating angles. Consequently the improved type can be used for vehicles operating at higher angles.  
         [0053]    [0053]FIG. 6 and FIG. 7 show an embodiment in which an outer circumferential surface  24  of the leg shaft  11 ′ of the tripod member  12  and on an inner circumferential surface  25  of a roller  17 ′ are crowned.  
         [0054]    Crowning the outer circumferential surface  24  of the leg shaft  11 ′ and the inner circumferential surface  25  of the roller  17 ′ increases mutual freedom of movement of the leg shaft  11 ′ and the roller  17 ′ (needle rollers  16 ′ exist between the two) so that the level of vibration can be reduced. This means that the roller  17 ′ is in parallel with track groove  13  as much as possible when it moves, with a reduced inclination, even when there is an operating angle, and as a result the level of vibration can be reduced.  
         [0055]    In the embodiment shown in FIG. 6 and FIG. 7, both the outer circumferential surface  24  of the leg shaft  11 ′ and inner circumferential surface  25  of the roller  17 ′ are crowned. However, a reduction in the level of vibration can be obtained by crowning either of the outer circumferential surface  24  of the leg shaft  11 ′ or the inner circumferential surface  25  of the roller  17 ′.  
         [0056]    Crowning in the range R 89  to R 700  on the outer circumferential surface  24  of the leg shaft  11 ′ is preferred, and in the range R 50  to R 800  on the inner circumferential surface  25  of the roller  17 ′ is preferred. Crowning below R 89  and R 50  causes the surface pressure to become too high, which causes a shorter lifetime of the joint in a load endurance test and lowers durability. Contrary to this, when the crowning is larger than R 700  and R 800  it becomes difficult to obtain a reduction in induced thrust. This means that a reduction of 5% or less in induced thrust is only within an allowance, and the desired reduction cannot be obtained.  
         [0057]    In the preferred crowning range on the outer circumferential surface  24  of the leg shaft  11 ′, which is from R 89  to R 700 , the ratio of the crowning R to the outer diameter d of the leg shaft  11 ′ becomes R/d=5.0 to 39.3.  
         [0058]    In the preferred crowning range on the inner circumferential surface  25  of the roller  17 ′, which is from R 50  to R 800 , the ratio of the crowning R to the inner diameter D of the roller  17 ′becomes R/d=2.2 to 35.2.  
         [0059]    In order to further reduce the level of vibration, it is preferable that the ends  26  of needle rollers  16 ′, provided between the roller guide surface  14  and the roller  17 ′, are formed in a convex shape. A convex shape on the ends  26  of the needle rollers  16 ′ helps reduce sliding resistance and induced thrust. The term “sliding resistance” means the magnitude of axial friction force that occurs when an outer joint member and a shaft mutually slide in a sliding type joint such as a tripod type constant velocity joint.  
         [0060]    In the embodiments shown in FIG. 6 and FIG. 7, as shown in FIG. 8, when a conventional type and a improved type (in accordance with the embodiments) are compared, the improved type has less induced thrust than the conventional type even with a higher operating angle so that the improved type can be used for vehicles operating at higher angles.  
         [0061]    [0061]FIG. 9 and FIG. 10 show an embodiment in which the outer circumferential surface of a roller  17 ″ in cross section forms an arc shape and the centers of curvature O 1  and O 2  are shifted radially outward from an axis O of the roller  17 ″. FIGS.  11  to  13  show an embodiment in which the outer circumferential surface of roller  17 ″ in cross section forms an arc shape with the centers of curvature O 1  and O 2  shifted radially outward from the axis O of the roller, and furthermore, the outer surface of the leg shaft  11 ′ in cross section forms an elliptical cylinder. The outer circumferential surface of the leg shaft  1 l′ and the inner circumferential surface of the roller  17 ″ are crowned.  
         [0062]    In the tripod type constant velocity universal joint of this embodiment, by forming the roller  17 ″ with the outer circumferential surface in an arc cross section with the centers of curvature O 1  and O 2  shifted radially, outward from the axis O of the roller, the force suppressing the inclination of the roller  17 ″ is increased. This means that the roller  17 ″ is in parallel with the track groove  13  as much as possible when it moves, with a reduced inclination, even when there is an operating angle, and as a result the level of vibration can be reduced.  
         [0063]    Making the leg shaft  11 ′ in an elliptical cylinder and crowning the outer circumferential surface of the leg shaft  11 ′ and the inner circumferential surface of the roller  17 ″, enables a swinging motion of the roller  17 ″ on the leg shaft  11 ′ in the axial direction of the leg shaft. Thereby, the roller  17 ″ is in parallel with track groove  13  as much as possible when it moves, with a reduced inclination, even when there is an operating angle, and as a result the level of vibration can be further reduced.  
         [0064]    When the roller  17 ″ is inclined in the axial direction of the leg shaft  11 ″, a contact angle between the roller  17 ″ and the roller guide surface  14  varies and a track clearance becomes smaller. Therefore, it is preferable that, like this embodiment, the outer circumferential surface of the roller  17 ″ in cross section forms an arc shape with the centers of curvature O 1  and O 2  of the outer circumferential surface shifted radially outward from the axis O of the roller. At the same time, the roller guide surface  14  is formed in a shape in which a track clearance can be secured between the track groove  13  and the roller guide surface  14  even when the roller  17 ″ is inclined at a maximum operating angle.  
         [0065]    By doing this, freedom of movement of the roller  17 ″ relative to the roller guide surface  14  is increased and the level of vibration is further reduced.  
         [0066]    In the embodiment shown in FIG. 9 and FIG. 10, and the embodiment in FIG. 11 to  13 , when a conventional type and improved types (in accordance with the embodiments) are compared as shown in FIG. 14, the improved types have less induced thrust than the conventional type even at larger operating angles so that the improved types can be used for vehicles operating at higher angles.  
         [0067]    While there has been described what are at present considered to be preferred embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.

Technology Category: 4