WO1995012767A1

WO1995012767A1 - Tripode type constant velocity ratio universal joints

Info

Publication number: WO1995012767A1
Application number: PCT/GB1994/002263
Authority: WO
Inventors: Stephen Charles Bartlett; Richard Anthony Lloyd
Original assignee: Gkn Automotive Ag
Priority date: 1993-11-06
Filing date: 1994-10-17
Publication date: 1995-05-11
Also published as: FR2712050B1; FR2712050A1; GB9322917D0; JPH09504595A

Abstract

A tripode type constant velocity ratio universal joint has the arms (19) which carry the rollers (21) of one joint member (11), and/or the tracks (15) of the other joint member (10) in which the rollers (21) engage, inclined so as substantially to elliminate third-order transmission error from the joint.

Description

Title: Tripode Type Constant Velocity Ratio Universal Joints

Description of Invention

This invention relates to constant velocity ratio (homo inetic) universal joints of the tripode type, such a joint comprising a first joint member having a rotational axis and three tracks equally circumferentially spaced about its rotational axis and extending lengthwise of the joint member; and a second joint member having a rotational axis and three arms equally circumferentially spaced about its rotational axis and extending substantially radially relative to such rotational axis into the tracks of the first joint member, each arm carrying a respective roller having an external surface which engages opposed side portions of the associated track, and each roller being able to move within its associated track such that the first and. second joint members are able to undergo relative articulation. Such a joint will hereafter be referred to as a tripode-type joint of the kind specified.

Tripode-type joints of the kind specified are widely used in motor vehicle drive lines, for example as the inboard and/or the outboard universal joints of drive shafts extending laterally to drivable wheels of a vehicle. A type of joint of the kind specified usually used as an inboard universal joint of a driveshaft provides for the first and second joint members to be able to move axially relative to one another as well as to undergo relative articulation. The relative axial movement ("plunge") in the joint is necessary to accommodate length variations in the driveshaft which occur as a result of vehicle suspension movement. Joints used as the outboard universal joints in driveshafts of front- wheel drive vehicles are of a construction which does not enable them to accommodate plunge but does enable them to articulate to a much greater angle than is possible with plunging inboard joints, in order to accommodate steering of the front wheels of a vehicle.

In a conventional tripode joint of the kind specified, the tracks in the first joint member extend parallel to the rotational axis of such joint member. The arms of the other joint member are perpendicular to the rotational axis of the other joint member. There have been proposals for tripode joints in which the tracks and arms are at other orientations, for example US 3 990 267 shows a tripode joint wherein the tracks of one joint member are skewed relative to the rotational axis thereof, for the purpose of generating an axial force when the joint transmits torque. It has been proposed, in JP Utility Model publication 63- 115927, that the arms of the inner joint member should be inclined at an angle other than 90° to the rotational axis of the joint member, but this does not eliminate the transmission error described hereafter. The inclination of the arms of the inner joint member is intended to reduce axial forces arising between the two joint members.

Although commonly referred to as a constant velocity ratio (homokinetic) universal joint, the conventional tripode joint of the kind specified only behaves as a truly constant velocity ratio joint if it is installed in such a way that rotation of the joint when articulated does not cause a change in the inclination of the rotational axis of the inner joint member relative to the axis of the outer joint member. If not installed thus, and one joint member is rotated at a constant angular velocity, when the joint is articulated the angular velocity of the other joint member will cyclically decrease and increase, although the mean angular velocity of both joint members is, of course, the same. This deviation of the joint from true constant velocity characteristics, referred to herein as transmission error, is predominantly third order, being a sinusoidal variation with a frequency of three times the rate of rotation of the joint. There are other orders of transmission error, but Fourier analysis shows that, for a geometrically perfect joint having no other geometric distortions, the third order component represents 99.8% of the RMS value of all transmission errors. The transmission error arises from the orbital motion which the centre of one joint member is caused to undergo if the rotational axis of the other joint member is held fixed. If the opposite end of a shaft connected to the one joint member is constrained to rotate about a fixed point the inclination of such shaft must change. If such shaft were (theoretically) infinitely long the change in inclination would be zero, or a change in shaft inclination can be avoided if a tripode-type joint is used at the other end of the shaft, providing the arms of the joint members of the two joints are in phased relationship with one another and the articulation angles and pitch circle radius of the tracks of the two joints are such that the orbital motion at one end of the shaft is of the same magnitude as that at the other end. Although the shaft connecting the two joints is still subject to an orbiting motion about its nominal axis it remains parallel to such axis and its angular velocity does not fluctuate.

When used in motor vehicles, particularly passenger cars, the transmission characteristics of universal joints in terms of not causing any vibrations in the vehicle drive line are of great importance, to reduce noise, vibration and harshness detectable by persons travelling in the vehicle.

The transmission error above described is believed to be a factor in the overall characteristics of a tripode-type joint, in terms of excitation of driveline vibrations, and accordingly it is an object of the present invention to reduce such error and the disadvantageous consequences thereof. The absence of speed fluctuations would also be beneficial in specialised applications such as instrument drives or precision mechanisms or in high rotary inertia drives.

According to the present invention, we provide a constant velocity ratio universal joint of the tripode type, comprising a first joint member having a rotational axis and three tracks, equally circumferentially spaced about its rotational axis and extending lengthwise of the joint member; and a second joint member having a rotational axis and three arms equally circumferentially spaced about its rotational axis and extending substantially radially relative to such rotational axis into the tracks of the first joint member, each arm carrying a respective roller having an external surface which engages opposed side portions of the associated track, and each roller being able to move within its associated track such that the two joint members are able to undergo relative articulation, wherein:- 1. the tracks in the first joint member, in respect of their alignment relative to a datum comprising the axis of rotation of the first joint member, and/or

2. the arms of the second joint member, in respect of their alignment relative to a datum comprising a plane perpendicular to the axis of rotation of the second joint member, are so inclined relative to the respective datum as substantially to eliminate the third order transmission error from the joint.

It has been found that, in a tripode universal joint of the kind specified, the third order transmission error is substantially eliminated from the joint if the alignment of the tracks relative to their datum, and the alignment of the arms relative to their datum, bear a relationship which is approximately equal to _β oa ₌r , m = , t.a.._n-, 1 — r - θ track

2 2

where: _θarm >s the angle of inclination of each arm relative to its datum _{θ t}r_ack is the angle of inclination of each track relative to its datum r is the pitch circle radius of the tracks in the first joint member, and L is the length of the shaft which in use is connected to one of the joint members, it being assumed that the installation of the joint is such that the joint member to which the shaft is not connected is constrained to a purely rotational motion without any orbiting of its axis of rotation, whilst the joint member to which the shaft is connected is able to orbit. The length L of the shaft is the distance from the centre of the joint member which is able to orbit and is connected thereto, to a point, which usually will be at or adjacent the other end of the shaft, which is constrained to a purely rotational motion and does not orbit.

The preferred construction of joint according to the invention is one in which β _tr_ack = z_er_o, ^l-^e- the tracks are parallel to the rotational axis of their joint member. A joint member with such a parallel orientation of its tracks is much less expensive to manufacture then a joint member in which the tracks are inclined to the rotational axis of the joint member.

If the angle of inclination of the tracks is zero, i.e. the tracks are parallel to the rotational axis of their joint member, the angle of inclination of each of the arms of the second joint member has a negative value, which means an inclination of the arms from the plane perpendicular to the axis of rotation of the second joint member away from the first joint member, i.e. towards the opposite end of a shaft element connected to the second joint member when a shaft is so connected.

However, the tracks of the first joint member may alternatively be inclined to the rotational axis of their joint member. They may be inclined so as to converge or to diverge as they extend towards the opposite end of the shaft element connected to the second joint member, in which case the arms of the second joint member are inclined at respective angles determined in accordance with the approximate relationship above set forth.

A joint according to the invention may be a plunging type of joint, as used typically as an inboard joint in a motor vehicle lateral driveshaft, in which case it is the first joint member whose rotational axis is constrained against orbiting and the second joint member which is free to orbit and is connected to the shaft whose length is L.

Alternatively, the joint may be of the axially fixed (non-plunging) type as typically used as an outboard universal joint in a motor vehicle lateral driveshaft, in which case it is the second joint member whose rotational axis is constrained against orbiting and the first joint member which is able to orbit and which has the shaft of length L connected thereto.

The invention will now be described by way of example with reference to the accompanying drawings, of which:

Figure 1 illustrates a conventional tripode joint of the kind specified, i.e. one not in accordance with the present invention and the accompanying graph shows the transmission error associated therewith; Figure 2A is a view as Figure 1, showing an embodiment of joint according to the present invention;

Figure 2B shows part of the joint of Figure 2A.

Figure 3 illustrates another type of conventional tripode joint of the kind specified, not in accordance with the present invention; and

Figure 4 shows a joint of the same general type as that of Figure 3, but modified in accordance with the present invention.

Referring firstly to Figure 1 of the drawings, the tripode type of universal joint there illustrated comprises an outer, first, joint member indicated generally at 10 and an inner, second, joint member indicated generally at 11. The outer joint member is generally in the form of a hollow component, closed at one end (12) from which end a stub shaft 13 extends for torque transmitting connection of the outer joint member to another component in, for example, a vehicle driveline. The rotational axis of the outer joint member is indicated at 14. From the closed end 12 of the outer joint member there extend three tracks 15, equally circumferentially spaced about the axis of rotation 14 of the joint member. Each track comprises opposed surfaces which are generally in the form of parts of a cylindrical or substantially cylindrical surface. The centre lines of the tracks, as indicated at 16, and which are the central longitudinal axes of the cylinders of which the tracks surfaces form part, are parallel to the rotational axis 14 of the outer joint member. In the illustrated joint the tracks 15 are open towards the external circumference of the outer joint member; in some designs of tripode joint the tracks are not thus open and the outer joint member is in the form of a cup with an unbroken external circumferential surface.

The inner joint member 11 is an annular component, having torque transmitting engagement with a shaft element 17 extending therefrom out of the open end of the outer joint member 10, the rotational axis of the inner joint member and shaft 17 being indicated at 18. Three arms, one of which is shown at 19, extend outwardly from the inner joint member into the tracks 15 in the outer joint member, such arms having respective axes as indicated at 20 for the arm 19, which axes lie in a plane perpendicular to the rotational axis 18 of the inner joint member. Each arm 19 carries a respective roller as seen at 21, which is able to rotate about the arm and move lengthwise of the arm, i.e. axially with respect to the arm axis 20. Each roller 21 has a part-spherical external surface, which enables the roller to tilt within the track 15 in which it engages. This condition is illustrated in Figure 1, in which the joint is in the articulated condition with the rotational axes 14, 18 of the outer and inner joint members inclined to one another.

Joints as shown in Figure 1 typically are used as the inboard joints of laterally extending driveshafts in motor vehicles. When thus used, the outer joint member is constrained to rotation about a fixed axis, i.e. its axis of rotation does not orbit, whilst the inner joint member connected to a driveshaft element is able to orbit.

As hereinbefore described, a transmission error is associated with a conventional tripode joint installed as above described. If one joint member is rotated at a constant angular velocity when the joint is articulated, the angular velocity of the other joint member will cyclically decrease and increase. This transmission error, which is predominantly a third order error, is a sinusoidal variation with a frequency of three times the rate of rotation of the joint, as illustrated in the diagram to the right of the joint shown in Figure 1.

Referring now to Figures 2A and 2B of the drawings, these show an embodiment of universal joint according to the present invention. The basic structure of the joint, comprising an outer joint member and an inner joint member, and associated parts, is the same as that described above and will not therefore be referred to again. The joint differs from the joint of Figure 1, however, in that the arms of the inner joint member are each inclined to a plane perpendicular to the axis of rotation of the inner joint member, at an angle _θ arm ^{to sucn} plane. The arms are inclined towards the opposite end of the shaft 17 extending from the inner joint member 11, and according to the invention the angle of such inclination is approximately equal to tarn — where L is the length of the shaft 17 and r is the pitch circle radius of the tracks in the outer joint member 10. The length L of the shaft is the length from the centre of the inner joint member to a point at the opposite end of the shaft which is regarded as being constrained to a position which is stationary in space, e.g. by being constrained by another universal joint at the opposite end of the shaft, such universal joint being of a type which does not cause any orbiting motion of the opposite end of the shaft to take place.

The embodiment of joint shown in Figure 2 is a preferred one because an outer joint member 10 of the illustrated configuration in which the tracks extend parallel to the rotational axis of the joint member is the easiest form of joint member to manufacture. However, it would alternatively be possible for the tracks to be inclined to the rotational axis 14 so that they diverge or converge relative to one another as they extend from the closed end of the joint member to the open end thereof.

In this case, the alignment Q _track of each of the tracks relative to a datum, which is the axis of rotation of the outer joint member 10, and the alignment Q_aιm of each arm relative to a datum, which is a plane perpendicular to the axis of rotation of the inner joint member, bear a relationship to one another which is approximately equal to _fta-,r,-m_™ _ = - ta_,„n- 1_. — - & track

22_ 2

In the above expression, a positive angle of Q_arm represents an inclination of the arms, as they extend radially outwards, towards the opposite end of the shaft connected to the inner joint member, or in other words towards the open end of the outer joint member, as shown in Figure 2. A negative value of _{θ t}r_ack represents a track which is inclined so that the tracks converge as they extend from the closed end of the outer joint member to the open end thereof, whilst a positive value of e _tr_ack represents a divergent track.

It will be appreciated that, if the tracks were inclined, the pitch circle radius r would vary along the length of the tracks. Approximately to conform to the expression above set forth for the relationship between Q_arm and _{θ t}r_ack, the configuration of the tracks would be a shallow curve. In practice, however, substantial elimination of third order transmission error can be achieved if the tracks are straight and their inclination is determined in accordance with the pitch circle radius thereof at the normal operating position of the inner joint member axially relative to the outer joint member. In typical use of a universal joint in a motor vehicle drive line, most of the axial displacement of the inner joint member from its normal operating position is of small magnitude, with displacements of greater magnitude only rarely arising.

If the tracks in the joint member 10 are inclined, they are preferably inclined, whether in the convergent or the divergent sense, at an angle which is less than approximately _tan'i — • For typical joints and shaft lengths commonly used in automotive applications, this means that the modulus of the angle β tr_ack, is l^ess than about 3° - 4°.

Referring now to Figure 3 of the drawings, this shows a further embodiment of conventional universal joint of the kind specified. This joint comprises a first joint member indicated generally at 30 and a second joint member indicated generally at 31. The joint member 30, which is provided integrally at the end of a shaft element 33 with a rotational axis 34, is a tulip- shaped component affording three tracks 35 equally circumferentially spaced about the axis of rotation 34. Each track comprises opposed surfaces which are generally in the form of parts of a respective cylindrical or substantially cylindrical surface. The centre lines of the tracks, as indicated at 36, and which are the longitudinal central axes of the cylindrical surfaces of which the tracks surfaces form part, are parallel to the rotational axis 34.

The joint member 31 is a cup-shaped component provided at the end of a stub shaft element 37. Within the cup-shaped joint member 31 near the open end thereof there is supported a tripode member which comprises three arms 39 extending radially relative to the rotational axis 38 of the joint member 31. The arms 39 extend through the tracks 35 of the joint member 30 and are connected by a central annular body portion indicated at 40. The arms 39 carry respective rollers as indicated at 41, the rollers being able to rotate about and move lengthwise of their respective arms. The rollers 41 have part-spherical external surfaces which enables them to tilt within the respective tracks 35 they engage, as well as to move axially therealong.

At the end of the joint member 30 nearest the stub shaft 37 of the joint member 31 there is connected a three-legged pressing 42 which abuts the body 40. The body 40 carries a spring loaded button 43, which abuts a portion 32 of the joint member 30. The effect of this is that the two joint members are constrained against relative axial movement (plunge) relative to one another, but are able to undergo relatively large angles of relative articulation.

Also visible in Figure 3 is a flexible sealing boot 44 for retaining lubricant in and excluding dirt from the joint.

Joints as shown in Figure 3 are typically used as the outboard joints of lateral driveshafts in front-wheel drive motor vehicles. In such applications, the joint member 31 is connected to the vehicle wheel and its axis of rotation 38 is not able to orbit. When the joint rotates when articulated, the joint member 30 and adjacent end of the shaft element 33 are subject to orbital motion as above described, with the resultant transmission error.

Figure 4 shows a joint of the same type as Figure 3 but constructed in accordance with the invention. In this joint, the axes of the arms 39, instead of being perpendicular to the axis of rotation 38 of the joint member 31, are inclined to the plane perpendicular to such axis at an angle Q_armThe inclination of the arms is in the same sense as shown in the joint of Figure 2, i.e. as the arms extend outwardly they extend towards the open end of the joint member 30 and the remote end of the stub shaft 37 of the joint member 31. The angle Q_arm is calculated in accordance with the expression above set forth in relation to the joint of Figure 2 of the drawings, with reference to the pitch circle radius r of the tracks 35 of the joint member 30 and the length L of the shaft element 33 connected to the joint member 30. Just as in the joint shown in Figure 2, the tracks 35 may instead of being parallel to the axis of rotation 34 of such joint member be inclined thereto at an angle Q_tr_ack. Preferably the above set forth remarks as to the magnitude of e _tr_ac_k if the tracks are inclined also apply in relation to this type of joint.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A constant velocity ratio universal joint of the tripode type, comprising a first joint member having a rotational axis and three tracks, equally circumferentially spaced about its rotational axis and extending lengthwise of the joint member; and a second joint member having a rotational axis and three arms equally circumferentially spaced about its rotational axis and extending substantially radially relative to such rotational axis into the tracks of the first joint member, each arm carrying a respective roller having an external surface which engages opposed side portions of the associated track, and each roller being able to move within its associated track such that the two joint members are able to move axially relative to one another and undergo relative articulation, wherein:-

1. the tracks in the first joint member, in respect of their alignment relative to a datum comprising the axis of rotation of the first joint member, and/or

2. A universal joint according to Claim 1 wherein the alignment of the tracks and the alignment of the arms bear a relationship

Qarm = tan~ι -Z- - .^{θ trrac/r} as herein defined.

2 2

3. A universal joint according to Claim 2 wherein the modulus of θ rac_k, is l^ess than approximately tan"i —

4. A universal joint according to Claim 3 wherein Q _tr_ack = z_er_o, i.e. the tracks are parallel to the rotational axis of the first joint member.

5. A universal joint substantially as hereinbefore described with reference to Figure 2 or Figure 4 of the accompanying drawings.