GB2324354A

GB2324354A - Homokinetic universal joint

Info

Publication number: GB2324354A
Application number: GB9815486A
Authority: GB
Inventors: Hiroki Terada; Masaru Komatsu; Hiroyuki Matsuoka; Tetsuro Kadota; Yoshimasa Ushioda; Yukio Asahara
Original assignee: NTN Corp; NTN Toyo Bearing Co Ltd
Current assignee: NTN Corp
Priority date: 1995-02-27
Filing date: 1996-01-05
Publication date: 1998-10-21
Anticipated expiration: 2016-01-05
Also published as: GB9815486D0; GB2324354B

Abstract

A homokinetic universal joint comprises an outer ring (1) having three axial track grooves (1a) formed in an inner periphery thereof, and a tripod member (2) having three radially projecting trunnions (2a). Each trunnion (2a) has rotatably fitted thereon an inner roller (3) having a part-spherical outer surface (3b) and an outer roller (4) having a part-spherical outer surface and an inner surface (4a) in circumferential linear contact with the outer surface (3b) of the inner roller. The tripod member (2) is received in the inner periphery of the outer ring (1) and the outer rollers (4) of the tripod member (2) are rollingly mounted in the track grooves (1a) in the outer ring. The generatrix radius (R1) of the outer surface (30) of the inner roller (3) is smaller than a maximum radius (R2) of the outer surface of the inner roller.

Description

SPECIFICATION HOMOKINETIC UNIVERSAL JOINT BACKGROUND OF THE INVENTION The present invention relates to a homoklnetic unlversal joint used for power transmlsslon in automobiles and varlous industrial machlnes, and partlcularly to a tripod type homoklnetic unlversal joint.

A tripod type homokinetic unlversal joint comprlses a tripod member having three radially projecting trunnions disposed at circumferential intervals of 120- , and an outer ring having track grooves in whlch the three trunnions of said tripod member are fltted for Integral rotation, the joint having features that even if two shafts take an operating angle, the torque is transmitted at homoklnetic and that it allows axial relative dlsplacement.

In homokinetic universal joints of thls type. there Is provlded an arrangement whereln spherical rollers are rotatably fltted on the trunnions In order to decrease the frictional resistance between the trunnions and the track grooves. Recently, further improvements have been made to provide an arrangement, as shown in Flg. 8, wherein each trunnion 2a of a tripod member 2 has rotatably fitted thereon an inner roller 3' having a spherical outer surface and an outer roller 4' having a spherical outer surface and a cylindrical inner surface in linear contact with the outer surface of the Inner roller 3'.

In the same figure. the outer ring 1 is in the form of a substantlally cyllndrlcal cup whlch is open at one end and closed at the other, wherein a shaft 5 is integrally installed at the other end and three axial track grooves 1a' are formed in the inner periphery at intervals of 120 The tripod member 2 is fltted on a serrated portlon (or splined portlon) 6a formed on one end of a shaft 6 and held against slipping off between a step portlon 6b and a cllp 6c. The three trunnions 2a of the tripod member 2 are fltted in the track grooves la' of the outer ring 1. The torque transmission between the outer ring 1 and the tripod member 2 is effected through contact between the outer surfaces of the outer rollers 4' and the track grooves la'.

For axlal displacement of the outer ring 1 and the tripod member 2, the outer rollers 4' are gulded along the track grooves la', and for angular displacement, the outer surfaces of the inner rollers 3' are gulded along the inner surfaces of the outer rollers 4', ensurlng smooth dlsplacement.

The conventional arrangement shown in Flg. 8, in whlch the inner roller 3' and outer roller 4' are mounted on the trunnlons 2a, is advantageous over the arrangements prlor thereto in that the induced thrust Is low which is produced durlng torque transmission with the outer ring 1 and the tripod member 2 taklng an operating angle. The reason is that in a conventlonal arrangement In whlch spherical rollers are mounted on the trunnion, whlle taklng an operating angle. the spherical rollers which make axlal slide movement with inclination are in direct contact with the track grooves of the outer ring, the slide resistance is hlgh, whereas in the arrangement shown in Fig. 8, slnce relatlve displacement is allowed between the inner rollers 3' and the outer rollers 4', the outer rollers 4' have only to make substantially constant axlal movement alone along the track grooves la' of the outer ring 1, with the result that the thrust reslstance Is decreased.

In the conventlonal arrangement shown in Flg. 8 although the induced thrust is lower than that In prlor arrangements.

there has been a limit In further decreaslng It. We have conducted experlments to investigate the cause and found that when the inner rollers 3' make inclination while contactlng the Inner surfaces of the outer rollers 4' when taking an operatlng angle. the outer rollers 4' also tend to follow the movement of the Inner rollers 3' due to the frictlonal reslstance therebetween. At thls time, as shown enlarged in Flg. 9, the contact stresses increase whlch are produced in the area of contact A between the flange portion lb' on the outer portlon of the track groove la' of the outer ring 1 and the end surface 4c' of the outer roller 4' assoclated with the distal end of the trunnion and In the area of contact B between the inner portlon (opposlte to the flange) of the track groove la' on the non-loaded slde of the outer ring 1, it being believed that the limitatlon Is imposed by the fact that the rolllng resistance of the outer rollers 4' Increases owlng to the frictlonal force produced in these areas of contact A and B.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention Is to provide a tripod type homokinetic unlversal jolnt wherein the induced thrust which is produced during torque transmission between the outer ring and the tripod member taklng an operatlng angle is further decreased, thus further decreaslng vibration.

In a homokinetle universal jolnt accordlng to Claim 1, the inner surface of the outer roller Is shaped such that a load component directed to the dlstal end of the trunnion is produced In the area of contact between It and the outer surface of the inner roller. This load component presses the outer roller toward the dlstal end of the trunnion, whereby, in the non-loaded reglon of the track groove of the outer ring, the contact stress produced in the area of contact on the inner slde is decreased. As for such shape of the inner surface of the outer roller, it is posslble to employ a conlcal taper surface gradually decreased In dlameter toward the dlstal end of the trunnion (Clalm 2), a concave surface with the generatrix center located at a point offset toward the proxlmal end of the trunnion with respect to the generatrlx center of the outer surface of the inner roller (Clalm 3), a convex surface with the generatrlx center located at a polnt offset toward the dlstal end of the trunnion with respect to the generatrlx center of the outer surface of the Inner roller (Claim 4), a composlte surface comprising a conical taper surface gradually decreased in dlameter toward the dlstal end of the trunnion and a convex surface (Clalm 5), and a composite surface comprising cylindrical and convex surfaces (Clalm 6).

In a homokinetic universal jolnt accordlng to Claim 7, the generatrlx radius of the outer surface of the Inner roller is smaller than the maxlmum radius of said outer surface. The contact oval in the area of contact between the outer surface of the inner roller and the inner surface of the outer roller becomes smaller, decreaslng the frlctional resistance in the area of contact, with the result that partlcularly the inclination of the outer roller durlng application of an operating angle Is suppressed.

In a homokinetle universal jolnt according to Clalm 8, the track grooves of the outer ring contact the outer surfaces of the outer rollers but do not contact the end surfaces of the outer rollers assoclated with the dlstal ends of the trunnions. During torque transmission between the outer ring and tripod member taklng an operatlng angle, even if the outer rollers incline while following the dlsplacement of the inner rollers. there Is no contact stress produced between thelr end surfaces assoclated with the distal ends of the trunnions and the track grooves.

In a homokinetic universal joint accordlng to Claim 9, the portlon of the outer roller assoclated with the dlstal end of the trunnion is wldthwlse expanded. When the outer rollers axially move whlle taklng an operatlng angle along the track grooves. the inclination of the outer rollers is suppressed when the outer rollers follow the movement of the inner rollers.

In addition, two or more of the arrangements of Clalms 1 (or 2, or 3, or 4, or 5, or 6), 7, 8 and 9 may be optionally comblned.

Embodiments of the invention wlll now be descrlbed with reference to the accompanylng drawings, in whlch; Flg. 1 is a cross-sectional view (figure a) showlng an embodiment, a partial enlarged cross-sectional view (figure b) showing a perlpheral portlon of a track groove in the figure a, and a view (figure c) showlng a component of force produced in an area of contact between an inner roller and an outer roller; Flg. 2 is a cross-sectional vlew (flgure a) showlng another embodlment, and a partlal enlarged cross-sectlonal view (figure b) showlng a peripheral portion of a track groove in the flgure a; Flg. 3 is a partial enlarged cross-sectlonal view showing a perlpheral portlon of a track groove In another embodiment; Flg. 4 is a partlal enlarged cross-sectlonal view showing a peripheral portlon of a track groove in another embodlment; Fig. 5 is a partlal enlarged cross-sectional vlew showing a perlpheral portion of a track groove In another embodiment; Fig. 6 is a partlal enlarged cross-sectional view showlng a perlpheral portlon of a track groove in another embodlment; Fig. 7 is a graph showing the results of measurements of the induced thrust; Flg. 8 is a longitudinal sectlonal vlew (figure a) showlng a conventional arrangement, and a cross-sectional view (figure b) thereof; and Flg. 9 is an enlarged cross-sectional vlew showing a perlpheral portion of a trunnion in Flg. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS In the drawings, members and parts whlch are substantially the same as those in a conventlonal arrangement shown in Flgs. 8 and 9 are denoted by the same reference characters to omit a repetltlve description thereof.

As shown in Flg. 1, an inner roller 3 is rotatably fitted on a trunnion 2a of a tripod member 2 through a plurallty of needle rollers 7 and held In position agalnst slipping off the trunnion 2a by a slip-off preventing ring 8 and a stopper ring 9 mounted on the dlstal end of the trunnion 2a. As shown in Flg. 1 (b). the Inner surface 3a of the Inner roller 3 is a cyllndrlcal surface, and the outer surface 3b thereof Is a spherical surface. In this embodiment, the generatrlx of the outer surface 3b is an arc of radius R1 with the generatrlx center dlsposed at a point 01 offset toward the outer slde by a predetermlned amount from the radius center 02 of the maxlmum radius R2 of the inner roller 3, the generatrlx radius R1 being smaller than the maximum radius R2 of the outer surface 3b. The generatrlx of the outer surface 3b Is a circular arc line appears in the cross sectlon of the Inner roller 3 in Flg.

l(b). Thus, In thls specification, the word "generatrlx" means a line appears in the cross section In Flg. 1 -- Flg.

6.

An outer roller 4 is rotatably fltted on the outer surface 3b of the inner roller 3. In thls embodlment, the inner surface 4a of the outer roller 4 is a conlcal taper surface gradually decreased in diameter toward the distal end of the trunnion 2a and, therefore, the inner surface 4a and the outer surface 3b of the outer roller 3 are in linear contact with each other and hence relatlve dlsplacement between them is permltted. In addltlon, the conical taper angle of the inner surface 4a is preferably 0.1 - 3 degrees, for example. The outer surface 4b of the outer roller 4 is a spherical surface of generatrix radius R3 with the generatrlx center disposed at a point 03.

The track groove la of the outer ring 1 Is depicted substantlally V-shaped or double-spherically shaped (Gothic arch-shaped), but unlike the conventlonal arrangement shown in Figs. 8 and 9, there is no flange on its outer slde. As a result, the track groove la makes angular contact at two polnts p and q with the outer surface 4b of the outer roller 4, not with the end surface 4c of the outer roller 4 assoclated with the distal end of the trunnion.

The homokinetic unlversal jolnt of this embodiment has the arrangement descrlbed above, whereby the induced thrust is decreased as follows.

That is, (1) the shape is such that the track groove la of the outer ring 1 makes angular contact at two points p and q with the outer surface 4b of the outer roller 4 and do not make contact with the end surface 4c of the outer roller 4 associated with the distal end of the trunnion.

Therefore, when torque Is transmitted between the outer ring 1 and the tripod member 2 taking an operating angle. even If the outer roller 4 is inclined as it follows the displacement of the inner roller 3, there will be no contact stress produced between the end surface 4c and the track groove la. Therefore, as compared with the conventional arrangement, the axial sllde reslstance is decreased and so is the induced thrust.

Further, slnce the Inner surface 4a of the outer roller 4 is a conlcal taper surface gradually decreased in diameter toward the distal end of the trunnion, (2) a component of force F is produced in the area of contact S between the inner surface 4a and the outer surface 3b of the inner roller 3. presslng the outer roller 4 toward the distal end of the trunnion (see Fig. 1 (c)). Because of thls force component F, in the reglon of the track groove la on the nonloaded side of the outer ring 1, the contact stress produced In the contact area on the inner side (the portlon B shown in the flgure 9) is decreased. As a result, as compared with the conventional arrangement, the axlal sllde reslstance is decreased and so is the induced thrust.

Further, (3) slnce the generatrix radius R1 of the outer surface 3b of the inner roller 3 is smaller than the maximum radius R2, the contact oval In the area of contact S between the outer surface 3b of the inner roller 3 and the inner surface 4a of the outer roller 4 becomes smaller, decreaslng the frictional resistance in the area of contact S, with the result that partlcularly the inclination of the outer ring 4 during application of an operatlng angle is suppressed. As a result, as compared with the conventlonal arrangement, the axial slide reslstance is decreased and so Is the Induced thrust.

In a homokinetic unlversal joint shown in Flg. 2. the portlon of the outer roller 4 assoclated with the dlstal end of the trunnion is widthwise expanded. The outer 4b of the outer roller 4 Is asymmetrlcal with respect to the spherical surface center H thereof. Since there is no flange in the outer side of the track groove la of the outer ring 1, the track groove la does not contact the end surface 4c of the outer roller 4 assoclated with the dlstal end of the trunnion even if the portlon of the outer roller 4 assoclated with the dlstal end of the trunnion is widthwise expanded. The rest of the arrangement is the same as that shown in Flg. 1.

Wlth the above arrangement, in the homokinetic universal joint accordlng to thls embodlment also, the induced thrust is decreased in the same manner as descrlbed in the above (1).

(2) and (3), and at the same time, the portion of the outer roller 4 associated with the distal end of the trunnion is widthwise expanded; therefore, when the outer roller 4 axially moves along the track groove la while taklng an operatlng angle, the inclination of the outer roller 4 is suppressed whlch is produced when the outer roller 4 tends to incline as it follows the movement of the inner roller 3. Thus, the decrease of the induced thrust is further effectlvely attained.

Induced thrusts were measured on the homokinetic unlversal joint In the embodiment shown In Flg. 2 and the conventlonal joint shown in Flgs. 8 and 9. The result is shown in Fig. 7. In Flg. 7, the line X indicates the present inventive article and the line Y indicates a conventional article. As shown in the same figure. the conventlonal article Y exhibited that the induced thrust increased with increasing joint angle (operating angle) and that it tended to sharply increase partlcularly from the tlme when the joint angle reached a predetermined value. In contrast, in the present inventive article X, the induced thrust maintained a substantially constant low level.

without any tendency to increase sharply in connectlon with the jolnt angle.

Homokinetic universal jolnts shown in Figs. 3 through 6 are the same in basic arrangement as the one shown in Fig. 2 and have thelr induced thrusts decreased in the same manner as mentloned in (1), (2), (3) and (4) above, but differ in the shape of the inner surface 4a of the outer roller 4 from the arrangement shown in Fig. 2.

The homokinetic unlversal jolnt shown in Flg. 3 Is designed such that the inner surface 4a of the outer roller 4 is a concave surface of generatrlx radius R4 with the generatrlx center located at a point 04 whlch is offset toward the outer diameter slde beyond the radius center 02 of the outer surface 3b of the inner roller 3 and the proximal end of the trunnion 2a with respect to the generatrix center 01 of the outer surface 3b of the inner roller 3. Slnce the inner surface 4a of the outer roller 4 is such a concave surface, (2) a component of force F Is produced in the area of contact S between the inner surface 4a and the outer surface 3b of the inner roller 3, presslng the outer roller 4 toward the distal end of the trunnion.

The homokinetic unlversal joint shown in Fig. 4 Is deslgned such that the inner surface 4a of the outer roller 4 is a convex surface of generatrix radius R5 with the generatrix center located at a point 05 whlch is offset toward the outer dlameter slde beyond the outer surface 4b of the outer roller 4 and the dlstal end of the trunnion 2a with respect to the generatric center 01 of the outer surface 3b of the inner roller 3. Slnce the inner surface 4a of the outer roller 4 is such a convex surface. (2) a component of force F is produced in the area of contact S between the Inner surface 4a and the outer surface 3b of the inner roller 3, presslng the outer roller 4 toward the distal end of the trunnion.

The homokinetic universal joint shown in Flg. 5 is designed such that the inner surface 4a of the outer roller 4 is a composlte surface comprlslng a conical taper surface 4a1 gradually decreased in dlameter toward the dlstal end of the trunnion 2a and a partlal convex surface 4a2 with the generatrix center located at a polnt 06 whlch is offset toward the outer dlameter side beyond the outer surface 4b of the outer roller 4 with respect to the generatrix center 01 of the outer surface 3b of the inner roller 3. The conical taper surface 4a1 is posltloned on the slde associated with the dlstal end of the trunnion 2a and the partial convex surface 4a2 is positioned on the slde associated with the proximal end of the trunnion 2a. the two surfaces being smoothly continuous with each other. Slnce the inner surface 4a of the outer roller 4 is such a composite surface, (2) a component of force F is produced in the area of contact S between the inner surface 4a and the outer surface 3b of the inner roller 3, presslng the outer roller 4 toward the dlstal end of the trunnion.

The homokinetic unlversal joint shown in Fig. 6 is deslgned such that the inner surface 4a of the outer roller 4 is a composlte surface comprising a cylindrical surface 4a3 and a partial convex surface 4a2 with the generatrlx center located at a polnt 06 which is offset toward the outer diameter slde beyond the outer surface 4b of the outer roller 4 with respect to the generatrlx center 01 of the outer surface 3b of the inner roller 3. The cyllndrlcal surface 4a3 is posltloned on the slde assoclated with the dlstal end of the trunnion 2a and the partlal convex surface 4a2 is posltloned on the slde associated with the proximal end of the trunnion 2a, the two surfaces being smoothly contlnuous with each other. Slnce the inner surface 4a of the outer roller 4 is such a composlte surface, (2) a component of force F is produced in the area of contact S between the inner surface 4a and the outer surface 3b of the inner roller 3, presslng the outer roller 4 toward the dlstal end of the trunnion 2a.

In addition, the embodlment shown in Flg. 1 is designed to decreaase the induced thrust by comblng the elements (1), (2) and (3) mentloned above, whlle the embodlments shown in Figs. 2 through 6 are deslgned to decreaase the induced thrust by combing the elements (1), (2). (3) and (4). However, it is posslble to construct arrangements by using said elements (1), (2), (3) and (4) singly or in comblnatlon, in whlch case also substantial effects can be expected. Further, the shape of the inner surface 4a of the outer roller 4 may also be applled to the arrangement shown in Flg. 1, in whlch case also equlvalent effectes can be expected.

As has been described so far, according to the present inventlon, the induced thrust which is produced durlng transmission of torque whlle the outer ring and the tripod member are taklng an operating angle can be greatly decreased as compared with the conventional arrangement, maklng it posslble to improve the vlbratlon characteristics of this tripod type of homokinetic universal joints.

Claims

1. A homokinetic universal joint comprising an outer ring having three axial track grooves formed in an inner periphery thereof, and a tripod member having three radially projecting trunnions, each trunnion having rotatably fitted thereon an inner roller having a part spherical outer surface and an outer roller having a part spherical outer surface and an inner surface in circumferential linear contact with the outer surface of the inner roller in an area of contact therebetween, said tripod member being received in the inner periphery of the outer ring, the outer rollers of the tripod member being rollingly mounted in the track grooves in the outer ring, wherein a generatrix radius of the outer surface of the inner roller is smaller than a maximum radius of said outer surface of the inner roller.

2. A homokinetic universal joint as claimed in claim I, wherein the inner surface of each outer roller and the outer surface of each inner roller are shaped such that a load component toward a distal end of the trunnion is produced in the area of contact of the inner surface of the outer roller with the outer surface of the inner roller.