GB1564824A

GB1564824A - Transmission devices

Info

Publication number: GB1564824A
Application number: GB32164/76A
Authority: GB
Original assignee: Vadetec SA
Current assignee: Vadetec SA
Priority date: 1975-08-01
Filing date: 1976-08-02
Publication date: 1980-04-16
Also published as: NL7608530A; CA1070527A; AR212630A1; AU1644576A; SE421650B; AU500723B2; FR2319821B1; ES450347A1; BR7605013A; FR2319821A1; IT1070634B; SE7608349L

Description

(54) IMPROVEMENTS RELATING TO TRANSMISSION DEVICES (71) We, VADETEC S.A., a Swiss Body Corporate, of 7, Chemin des Charmettes, Lausanne, Switzerland, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a transmission device. More particularly the invention relates to a friction transmission device for transferring power between rotary members such as drive input and drive output shafts.

There are known transmission devices of this type which utilise cooperating elements having rolling surfaces, and which include means for modifying the relative positions of the rolling surfaces so as to vary the transmission ratio. One such transmission or variable drive is disclosed in U.K. Patent 1479765, and comprises a frame, a first element having a first axis, fixed relative to the frame, and a second element having a second axis capable of moving biconically about the first axis with said second axis intersecting said first axis, the apex of the cones of movement being the point of intersection of said axes, said first element having a pair of rolling surfaces disposed about said first axis one each side of the plane passing through the point of intersection of said axes and perpendicular to said first axis, said second element having a pair of rolling surfaces disposed about said second axis, one each side of the plane passing through the point of intersection of said axes and perpendicular to said second axis, the respective rolling surfaces of the first and second elements being engageable in relative rolling contact, when the second axis is moving biconically about the first axis, at points located on each side of the plane passing through the point of intersection of said axes and perpendicular to the first axis, the arrangement being such that, in use of the device, a couple derived from the biconical movement of said second element results in respective force components acting on the second element at the points of contact of the rolling surfaces in the directions of engagement of the respective rolling surfaces.

A transmission device of this type is particularly well suited for the transmission of high power by creating, in a simple manner, the normal contact pressure between the rolling surfaces of the elements. In the preferred embodiments described in U.K. Patent 1479765 this is achieved by obtaining the contact pressure from the couple derived from biconical movement of the second element. This couple may be considered as "gyroscopic".

Furthermore it is possible to avoid undesirable axial thrusts on drive shafts and e.g. on bearings supporting the first or second element. This is achieved by the subdivision into two of the rolling surfaces, so that they are disposed on either side of the point of axes intersection.

In the embodiments of transmission devices disclosed in U.K. Patent 1479765, by varying the angle of axes intersection and thus modifying the position of the points of contact it is possible to vary the ratio of input speed to output speed. There is therefore provided a degree of freedon for the second element in a radial direction parallel to the meridian plane of the first and second axes. This degree of freedom is also necessary so that the second element can tilt under the action of the derived couple and bring the rolling surfaces into driving contact.

In U.K. Patent 1,521,751 there is disclosed a transmission device in which no substantial modification of the angle of axes intersection is necessary to vary the transmission ratio. Thus in U.K. Patent 1,521,751 the rolling surfaces of one of the elements are defined by generatrices inclined oppositely with respect to the axis thereof: in particular such rolling surfaces are defined by cones having an apex halfangle substantially equal to the angle of axes intersection. The transmission ratio can then be varied in a simple manner by moving the points of contact along the cone surfaces. The rolling surfaces of the other element are generally in the form of annuli.

Conical rolling surfaces are known from other transmission devices, for example those disclosed in U.S. Patents 2,319,319; 2,535,409 and 2,405,957. The devices described in these latter Patents only have a single series of rolling surfaces.

In the case of the transmission device of U.S. Patent No. 2,535,409, a conical planet wheel is forced and locked against an annular ring by means of wedges. Such means would appear to be incompatible with a subdivision of the rolling surfaces into two (it is virtually impossible to force support a member at four points). The arrangement would be unable to prevent, even if arranged symmetrically, the development of an axial reaction component; it is virtually impossible to strictly balance the forces of reaction brought about by a member supported by force at four points.

Moreover and correlatively, the wedges provided in the transmission device of U.S.

Patent No. 2,535,409 do not maintain constant an angle of axes intersection. In fact, they imply a certain elasticity of the planet wheel and therefore a certain variation of the angle, without which it would not be possible to maintain the planet wheel supported against the annular ring.

These essentially structural differences lead to a number of disadvantages. More particularly, the bearings which support the rotating members must be designed so as to resist axial forces, and mechanical connections between the rotating members and a transmission frame must be designed to as to permit the variations of the angle of axes intersection and are a source of oscillations or losses which decrease the efficiency of the transmission device.

In the case of the devices disclosed in U.K. Patent 1,521,751, the rolling surfaces are divided into two and are arranged symmetrically, either side of the point of axes intersection. As with the device of U.K.

Patent 1,479,765, this solves the problem of balancing axial reaction forces.

Nevertheless, even though the angle of axes intersection does not vary greatly, the second element must still have a degree of freedom so that it can swing against the first element under the action of the derived couple, and drivingly engage the rolling surfaces.

The necessity of providing a degree of freedom in a radial direction may lead to the following disadvantages: firstly, the second element might oscillate radially when it rolls on the first member, and such radial oscillations of the second member might damage the rolling surfaces and for example cause a lack of stability of an oil film in the contact area of the rolling surfaces. Such oscillations might also cause fluctuations to the contact pressure which would be prejudicial to the satisfactory operation of the transmission device.

Secondly, there is no doubt that it is often difficult, if not sometimes impossible, to obtain mechanical connections (e.g. by gears) between two members which have an uncertain gap between them. In the case the transmission devices disclosed in e.g. U.K.

Patents 1479765 and 1521751 it is necessary to provide in certain contructional forms, mechanical connections between the second elements (or a member associated with the second elements such as supporting means) and auxiliary mechanisms which it is necessary to drive at speeds which are synchronous with the speed of the second axis about the first axis. It may also be necessary to provide in the case of certain contructional variants, other connecting means between e.g. the frame and the second element in order more particularly to stop rotation of the second element about the second axis.

The necessity of maintaining a radial degree of freedom thus complicates the contruction of the various mechanical connections. Furthermore, it should be noted that mechanically, gaps and resulting oscillations are often a source of energy losses by mechanical friction and are a source of wear. This reduces the efficiency of a transmission device, and this is clearly undesirable.

An object of the present invention is to provide a transmission device which may allow for avoidance of the possible disadvantages mentioned above.

Thus, according to the invention, there is provided a transmission device having a frame, drive input means, drive output means, and means interconnecting said input and output means including a first element having a first axis fixed relative to the frame, a second element having a second axis intersecting said first axis at a predetermined angle established by supporting means for said second element, said second axis being capable of moving biconically about the first axis with the apex of the cones of movement being the point of intersection of said axes, said first element having a pair of rolling surfaces disposed about said first axis one each side of the plane passing through the point of intersection of said axes and perpendicular to said first axis, said second element having a pair of rolling surfaces disposed about said second axis one each side of the plane passing through the point of intersection of said axes and perpendicular to said second axis, means for urging the respective rolling surfaces of the first and second elements into relative rolling engagement at points of contact located on each side of the plane passing through the point of intersection of said axes and perpendicular to the first axis, the rolling surfaces of at least one of said elements being defined by generatrices inclined oppositely with respect to the axis thereof and symmetrically with respect to the point of intersection of said first and second axes, and means for varying the spacing of the points of contact from said point of intersection so as to give a variable ratio of rolling surface radii.

By means of such an arrangement, the angle of axes intersection can be positively established by the supporting means. No degree of freedom to provide the contact pressure for the rolling surfaces, is necessary. The angle of axes intersection is fixed at a predetermined value, although it could be adjustably so, and in the embodiments particularly described herein, a variation in the transmission ratio involves no variation of the angle from this predetermined value.

The supporting means can be constructed in different ways. In all cases though, they must establish and maintin the predetermined angle of intersection. There may therefore be two series of bearings or journals; the first permitting rotation of the supporting means and the second element about the first axis and the second permitting a rotation of the second element about the second axis, and relative to the supporting means. The two series of bearings will have their axes inclined to one another.

Although the predetermined, or fixed, angle of axes intersection is established, this does not exclude the possibility of this being adjustable, as mentioned above. Thus whilst the second element is not free to swing about the point of axes intersection, it might be possible for it to be adjustable so as to assume several different predetermined inclinations relative to the first axis. For each of these inclinations the second element will have no degree of radial oscillatory freedom relative to the first element. Such adjustment could be in order to vary the transmission ratio, for example, and would be effected directly or indirectly by an appropriate mechanism.

Considering now a mechanical analysis of the forces developed at the points of contact, in the devices of e.g. U.K. Patents 1,479,765 and 1,521,751-where the angle of intersection has a degree of freedom torque or couple is applied to the first or second element and generates a force at the contact points of the rolling surfaces which in normal operation prevents sliding of the rolling surfaces relative to one another.

In a transmission in accordance with the present invention however, a torque applied to the second element produces no normal force or pressure at the contact points urging the rolling surfaces together, because movement of the second element around the point of axes intersection is prevented.

Therefore, positive systems, i.e. various mechanical arrangements, are provided for urging the rolling surfaces against each other.

As regards variation of the transmission ratio without altering the angle of axes intersection, reference will now be briefly made to the principle of the transmission ratio variation mechanism. The kinematic equation, or transmission equation is: R, iii-h+(-B)-- =O 2 or R, *a'* 2 in which: ii designates the rotational speed of the second axis about the first axis; designates the rotational speed of the second element about the second axis.

measured in an absolute reference frame linked with the transmission device frame; ,B* designates the rotational speed of the second element about the second axis in a rotary reference frame linked to the first axis and to the second axis; there thus exists the relationship O * O O consequently, when A=0 the second element is fixed against rotation about the second axis, but nutates at a speed & relative to the first axis.

w designates the rotational speed of the first element about the first axis when such is permitted.

R, designates the radius of the circle described by one of the contact points on the considered rolling surface of the second element and; R2 designates the radius of the circle described by one of the contact points of the considered rolling surface of the first element.

This equation was defined in the aforementioned U.K. Patent No. 1479765.

It is clear that a modification of the positions of contact points causes a variation in the ratio of R,/R2 and therefore a variation in the ratio between any two of the speeds & , p , and w. It will be shown hereinafter how it is possible to remove uncertainties appearing in the case where the first element is mounted for rotation at the speed w.

Thus, by moving the points of contact along the inclined generatrices of the relevant element, there may be effected a variation in the transmission ratio.

Preferably the rolling surfaces of one of the elements are conical, whilst those of the other element have a substantially annular configuration. A particularly advantageous arrangement may be obtained if the conical surfaces have an apex half angle which is substantially equal to the angle of axes intersection.

The term "conical" used herein signifies that the generatrices of the rolling surfaces, viewed in a meridian plane passing through the axis of revolution of the rolling surfaces do not greatly vary from a straight line. This also means that the angles of the tangents to these generatrices relative to the respective axis of revolution, do not vary substantially from an average value called the "apex halfangle" of the cone.

Thus, the term "apex half-angle of the cone need not be understood in the strictest literal sense of the word and must not be limited to the simple designation of cones or truncated cones, whose generatrices are straight lines.

In the same way the term "annular," used for defining the shape of the other rolling surfaces, need not be interpreted as limited to strictly cylindrical structures, generated by straight lines.

In other words, the annular rolling surfaces, namely the functional parts of the annular rolling surfaces which come into contact with the conical rolling surfaces, need only be e.g. substantially cylindrical, the average tangent at their generating line being substantially parallel to their axis of revolution.

The combination of substantially conical rolling surfaces and substantially cylindrical annular rolling surfaces can lead to the same result as strictly conical and cylindrical' rolling surfaces, i.e. a modification of the transmission ration without modifying the angle of axes intersection whilst providing other advantages which will be described with reference to particular embodiments.

As a result of this arrangement and construction of the rolling surfaces the transmission ratio may be varied by axially moving the annular rolling surfaces and/or the conical rolling surfaces relative to one another to modify the position of the contact points and therefore the transmission ratio.

In a preferred embodiment of a transmission device in accordance with the present invention, the annular rolling surfaces are mounted so as to be axially movable and the means for modifying the position of the contact points between the rolling surfaces comprises members for shifting the annular rolling surfaces.

As a result of this particular construction, it is possible to vary the transmission ratio by axially displacing the annular rolling surfaces along the generating lines of the cones parallel to the axis of revolution of the annular surfaces.

According to another feature of another embodiment, the conical rolling surfaces are mounted in axially movable manner and the means for modifying the position of the contact points between the rolling surfaces comprises means for shifting the conical rolling surfaces so as to vary their spacing.

As a result of this particular contruction, the gap between the second element and the first element may be modified symmetrically or asymmetrically in such a way that in the first case the annular rolling surfaces, loaded by a system creating the contact pressure, can move until they abut against the conical rolling surfaces; or in such a way that the second case, the contact pressures at the points of contact, on either side of the point of axes intersection are unbalanced and give rise to an axial component which is able to displace the annular rolling surfaces.

As regards establishment of the contacts pressure between the rolling surfaces, preferably those of one of the elements are mounted in an axially movable manner and means are provided for loading such surfaces against those of the other element by means of an axially directed force.

French Patent No. 1,227,486 discloses a transmission device comprising a conical roller which can be displaced axially by a small amplitude under the action of the spring. It should be noted however that this transmission device does not have two pairs of rolling surfaces arranged e.g.

symmetrically in such a way that the axial forces of reaction may be eliminated and that the spring does not create a contact pressure but belongs either to a disengaging mechanism or to a wear-compensation mechanism. Thus the spring does not develop a contact pressure between the roller and a ring so as to ensure driving engagement without sliding. Driving is in fact produced by "simple adhesion" of the smooth surfaces.

It should be noted here that in preferred embodiments of the present invention the fact that the contact pressure is created by a system which is independent of the kinematic operating conditions provides the advantage of permanently maintaining an adequate contact pressure, even in transient states when the speeds a, p.* and w can vary. Where the contact pressure is provided by e.g. gyroscopic forces, as disclosed for example in U.K. Patent No. 1,479,765, it is sensitive to accidental variations of the kinematic conditions. In this connection, the use of an independent system constitutes an advantage.

It should also be noted that the fact that the angle of axes intersection is fixed facilitates the provision of an independent system for creating the contact pressure.

Therefore, as the second element has a fixed orientation, it is possible to utilize it for pressing the rolling surfaces thereof.

The system for creating the contact pressure can be constructed in various ways.

In the case of certain embodiments, the loading of the rolling surfaces mounted in axially movable manner can have an intertial origin. In this case, the rolling surfaces mounted in axially movable manner are preferably those of the second element and are formed on two annular rings, whose axis is the second axis, inserted between the first element and the second element and which are mounted for rotation, at the speed p*, with the second element. The annular rings have a chosen mass and geometry, and the rolling surfaces of the first element have a chosen profile, such that two axial forces are developed and have the effect of axially displacing the annular rings towards the rolling surfaces of the first element and of creating the contact pressure.

In the case of other embodiments, the means for loading the rolling surfaces mounted in axially movable manner can comprise a resilient system. In this case, in one preferred arrangement, the rolling surfaces of the second element are mounted in an axially movable manner; and the rolling surfaces of the first element are two truncated cones juxtaposed at their bases, whose apex half-angle is slightly less than the angle of axes intersection. The means for axially loading the two rolling surfaces of the second element against those of the first element to create the contact pressure then comprises two spring systems, each acting at one end on the second element and at the other end on the axially movable rolling surfaces of the second element.

In the case of other embodiments, the means for loading the rolling surfaces mounted in axially movable manner for creating the contact pressure comprises ramps and in this case preferably the two rolling surfaces of the second element surround the first element. and the two rolling surfaces of the first element are mounted in axially movable manner on the first element and are two truncated cones juxtaposed at their bases, whose apex halfangle Is equal to the angle of axes intersection.

The means for axially loading the rolling surfaces of the first element against the rolling surfaces of the second element then preferably comprises a system of ramps integral with the first element and cooperating with complementary ramps integral with the rolling surfaces of the first element.

Preferably. in this case, the ramps are of a helical type, in such a way that the rolling surfaces of the first element are automatically screwed onto the first element during the operation of the transmission device.

These particular contructions of the system which creates the contact pressure by means of ramps integral with either of the elements have the substantial advantage of preventing relative slipping of the rolling surfaces under the action of the output torque (or a driving or reactive torque) of an excessive nature. Thus, the contact pressure created by such a system of ramps may be directly proportional to the output torque, so that the contact pressure is continually adapted to the value of this torque, whatever it is.

Variation of the transmission ratio may by connected with the creation of the contact pressure, because in one case it is a question of finding solutions permitting the modification of the position of the points of contact and in the other it is a question of the contact pressure at these points.

However, an advantage of the arrangements described hereinbefore is that the problems become compatible with one another.

Thus, for example, it is possible to combine the inertial loading means for the annular rolling surfaces which creates the contact pressure, with the means permitting an axial shifting of the conical rolling surfaces witil a view to modifying the position of the contact points.

In the same way. it is possible to combine the resilient systems loading the annular rolling surfaces, which create the contact pressure. with the means which axially shift the conical rolling surfaces. For example, in this case, these means can be hydraulic and comprise chambers adapted to receive fluid under pressure.

Moreover, it is possible to combine the systems of ramps loading the conical rolling surfaces, which create the contact pressure, with means which axially shift the annular rolling surfaces with a view to modifying the position of the contact points. For example, in this case, such shifting means can comprise connections by gear trains.

However, other permutations and combinations are possible.

It should be noted that the system creating the contact pressure axially loads the rolling surfaces of the element in question without in practice displacing them, in such a way as to create the contact pressure, the action thereof being permanent. On the other hand the means for modifying the position of the contact points shifts the axial position of the rolling surfaces in such a way as to modify the ratio of the rolling surface radii is only used when it is necessary to vary the transmission ratio, so that its action is temporary.

It is generally necessary to provide mechanical connections between various members in the transmission device, such as between the drive means, e.g. an input shaft, and the second element or the supporting means, or between e.g. an output shaft and the first or second element, or finally between the second element and the frame or between the second element and the first element so as to link the speeds (, A* w) or at least two of them.

Furthermore, there may be necessary mechanical connections between auxiliaries of the transmission device, or the motor operating the transmission device, and the second element in order to synchronize the operations of the auxiliaries with those of the transmission device.

The provision of the various mechanical connections involves different solutions depending on the advantages which it is desired to obtain, or depending on the disadvantages which it is desired to avoid.

Moreover, different solutions can be envisaged according to the nature of the members which are to be connected or, alternatively, the same solution can be used for connecting members of a different type.

In certain preferred embodiments conical gears are used, having as their apex the point of axes intersection.

According to one embodiment, this mechanical connection, involving conical gear trains forms a connection between a drive shaft and the second element.

According to another embodiment which can be used when the first element is mounted so as to rotate about the first axis, a mechanical connection by conical gear trains is placed between the second element and the frame in such a way as to link the speeds & and A* According to a still further embodiment which can also be used when the first element rotates at speed w about the first axis, a mechanical connection by conical gear trains is provided between the first and second elements in such a way as to link in rotation the speeds & , p, and w or at least two of them.

Preferably, the conical gear train comprises two conical gears witht their apex being the point of axes intersection one integral in rotation with the second element and the other linked in rotation with one of the following members, namely the frame, drive shaft, the first element or the supporting means.

The problem of connections between the supporting means and a rotatry drive shaft does not present a difficulty because the angle of axes intersection is fixed. It has already been seen that the supporting means may rotate about the first axis. It is therefore simple to link such means in rotation with the rotary drive shaft, preferably mounted axially on the first axis.

This system can also be used for driving auxiliaries of the transmission device or e.g.

a motor driving the transmission device.

In a similar way, the problem of connections between a rotary drive shaft and the first element when the latter rotates about the first axis does not present a difficulty. It is possible to link in rotation, the first element with the drive shaft, which is more particularly mounted coaxially on the first axis.

The expression "linked in rotation" used herein relates to identical angular velocities, or in a constant given ratio, or in a variable given ratio, whereas the expression "integral in rotation'' relates to identical speeds.

In order to balance forces of reaction on bearings supporting the second element the arrangement is preferably such that the biconical movement of the second element creates a couple which wholly or partly balances the forces applied to the second element by the system creating the contact pressure. Such a couple should have a direction and an intensity which is sufficient to relieve stresses on e.g. bearings inserted between the supporting means and the second element. Such bearings permit the latter to rotate about the second axis, whilst maintaining it inclined by the predetermined angle. As a result, it is possible to lighten the material construction of these bearings and decrease the mechanical

The elementary forces of inertia which are developed in the mass of the second element can be reduced, by applying the general laws of mechanics, to a torque and to a force applied at the point of axes intersection.

In case where the centre of gravity of the second element substantially coincides with the point of axes intersection the force applied at this point is substantially zero. In the converse, the force applied at the point will be a rotary force located in plane perpendicular to the first axis. Thus by arranging for the centre of gravity of the second element to be adjacent the point of axes intersection, there maybe eliminated forces applied at that point which load bearings for the element.

The torque, can be mathematically characterized by a vector, whose direction is perpendicular to the plane containing the first and second axes. The torque has a tendency to swing the second element about an axis perpendicular to the plane containing the first axis and the second axis, but since the angle of intersection is fixed, no movement is possible.

Preferably, the second element is a solid of revolution about the second axis, having a transverse plane of symmetry perpendicular to the second axis at the point of axes intersection. In the case of this embodiment, it is possible to calculate, by applying conventional laws of the mechanics of solids, the moment of this torque (the modulus of the vector), said moment being given by the following formula: Cl=(J1J3)C1f2 sin a cos aJ3CE(O sin a In this formula: J, and J3 respectively designate the moments of inertia of the second element relative to the second axis and relative to an axis passing through the point of axes intersection and perpendicular to said second axis; and a designates the angle of intersection of the second axis with the first axis; This formula gives the intensity of the movement of the gyroscopic torque resulting from the forces of inertia and relative thereto the following comments are made: a) it has been set out in two parts in such a way as to show in the first part the contribution of intertial effects which can be caller "centrifugal". Thus, when h=-b.

(when p*=0), the second part of the expression disappears, only leaving the first part, which is independent of the rotational speed of the second member about the second axis.

It should be noted that In general in the transmission devices described herein p,=o, or in other words =,B*.

b) The expression for the moment of the torque is an algebraic sum. This couple can therefore depending on the value of each of the parameters, either act in a direction which would tend to apply the second element to the first, or, conversely act in a direction which would tend to oppose the second element being supported on the first.

The different parameters such as the shape and mass of the second member (J" J3), the rotational speed (, p) and the angle of axes intersection, should preferably, for each variant, be proportioned so as to obtain a torque having a direction and an intensity sufficient for balancing totally or partially the reactive torque produced by a mechanical system creating the contact pressures between the rolling surfaces linked with the power to be transmitted by the transmission device.

The calculation of the structural and kinematic paramenters of the second element falls within the scope of one skilled in the art.

In order to balance reactive forces on the frame, in accordance with a further preferable feature the supporting means is arranged to develop a torque with an inertial origin which serves to wholly or partly balance the forces produced by a system creating the contact pressures on the first element and consequently on the frame.

The inertially developed torque depends on the arrangement and distribution of the masses forming the supporting means.

Different members of which the transmission device is comprised can be arranged in different ways depending on the problems it is wished to meet or advantages which it is desired to additionally obtain.

Firstly, the relative positions of the first element and the second element can vary.

The first element can be contained within the second element, which is then a hollow body; conversely, the second element can be contained within the first element which on this occasion is hollow. The rolling surfaces can in turn be concave or convex in a transverse plane.

Secondly, a large variety of rolling surface forms are possible. Conical rolling surfaces can be mounted on the first element or on the second element. In the meridian planes (i.e. in a radial plane passing through the axes of revolution of the rolling surfaces) the generating lines of the rolling surfaces can either be convex or concave The choice of the radii of curvature of the rolling surfaces in the transverse or meridian planet make it possible, all things being equal obtain different output speed -anges for 1 ill same variation amplitude of the rolling surface radii ratio, different variation laws of the transmission power as a function of the output speed and transmission devices with different dimensions.

Thirdly, many mechanisms creating the contact pressure are conceivable.

Fourthly, input and output means can be realized in different ways. There can be main drive shafts (input shaft or output shaft or vice versa). The main drive shafts can be linked in rotation respectively either with the first or second elements or the second element or supporting means. It is not indispensible for the input and output means to be respectively linked in rotation with the first and second elements, so that one can be linked with the rotary movement of speed p* of the second element about its own axis, the second axis, and the other can be linked at the speed ci of the second element about the first axis.

Fifthly, the first element can either be fixed or can rotate about the first axis.

In the case where the first element rotates about the first axis, at speed w, the general kinematic transmission equation: R1 R2 =0 R2 which was defined in U.K. Patent No.

1,479,765 leads to indefiniteness. Several possible speeds p correspond to a speed & , depending on the values of w. To remove this indefiniteness and as disclosed in U.K.

Patent No. 1,479,765 various solutions are possible.

One solution consists of connecting in rotation the first element to e.g. a main drive shaft, and stopping the rotation of the second element relative to the frame (fi=0 13*=a) or stopping the rotation of a main drive shaft connected to the second element.

It has already been seen how it is possible to produce the mechanical connections between the second element and the frame or between the second element and a main drive shaft to achieve this result, e.g. by means of bevel gears or a flexible transverse member.

Another solution consists of connecting at least two of the speeds ( & , p*, w) by means of mechanical connections.

Thus, the speeds ez, ,B*, w are interconnected by two equation systems. On the one hand, the general kinematic transmission equation: R1 k-h+(-) =0 R2 and on the other hand the equation due tothe mechanical connection which can be of the type: F( & , ss*, w)=0 in the case of an epicyclic connection for example or of the type: g(7 ss*)=0 or even of the type: h( & , w)=0 i(w. p,*)=0 This system of equations makes it possible to determine the output speed of the transmission device as a function of the input speed for a predetermined value of the rolling surface radii ratio. Thus, only a single ouput speed corresponds td one input speed.

The mechanical connections linking the speeds & , p, w provide particular advantages. As has been seen, the torque induced by the biconical movement of the second element varies as a function of the speeds of the second element about the second axis and of the second axis about the first axis. Therefore, the mechanical connections make it possible to modify the evolution of the gyroscopic torque as a function of the output speed. Thus, it is possible to correlatively obtain output torques which are better adapted to the different cases of utilization (constant torques, etc.).

The mechanical connections connecting the speeds & , p*, w in the same way as the mechanical connections linking the first and second elements, as well as the supporting means to the main drive shaft i.e. input or output shafts of the transmission device, can be formed in different ways, e.g. by means of bevel gear trains with their apex the point of axes intersection or by means of a flexible transverse member, or by means of sliding articulations mounted on an extension integral with the second member.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 is a longitudinal sectional view through a first embodiment.

Fig. Ia is a cross-sectional view on the line a-a of Fig. 1.

Fig. 2 is a longitudinal sectional view through a second embodiment.

Fig. 3 is a force diagram relating to the embodiment of Fig. 2 Fig. 4 is a longitudinal sectional view through a third embodiment.

Fig. 4a is a cross-sectional view on the line b-b of Fig. 4.

Fig. 5 is a longitudinal sectional view through a fourth embodiment.

Fig. Sa is a partial perspective view of part of the embodiment of Fig. 5.

Fig. 6 is a longitudinal sectional view through a fifth embodiment similar to that of Figs. 2 and 3.

Fig. 7 is a longitudinal sectional view through a sixth embodiment similar in some respects to that of Fig. 4 and 5; and Fig. 7a is a detailed perspective view of the means for modifying the position of the contact point in the case of the embodiment of Fig. 7.

The transmission device of Figs. I and la comprises a fixed frame A having at either end two substantially planar sides A1 and A joined by a casing A3, which has a generally cylindrical shape.

A first metallic element 2 and a second metallic element 3 are rotatably mounted on said frame via bearings.

The first element 2 extends along a first axis 7 which is the longitudinal axis of the transmission device, being fixed relative to the frame A. The first element comprises two symmetrical conical half portions 4 and 5, having respective conical rolling surfaces 8 and 9. These two half portions are mounted on an output shaft 11 coaxial with the first axis 7 and are axially movable relative to one another. Keys 22a and 22b respectively interlock the two half portions 4 and 5 and the shaft 11 so as to turn therewith.

Between the inner wall of portions 4 and 5 and the outer surface of shaft 11 are provided respective annular chambers 14a and l4b, which communicate with the outside by pipes 17a, 17b and 15 provided to this end in the shaft 11. A radial bore 18 in shaft 11 makes it possible to introduce a pressurized fluid into the chambers 14a and 14b even when shaft 11 rotates, via an annular space 6 and supply pipe 6'. Gaskets 21a, 21b, 2lc, 21d, 21e and 2lf ensure the sealing of the system of annular chambers and the various supply pipes. The introduction of a pressurized fluid into the annular chambers has the effect of simultaneously axially displacing the two portions 4 and 5 thereby moving the rolling surfaces 8 and 9 apart.

The frustum-shaped rolling surfaces 8 and 9 are of revolution about the first axis 7 and are disposed symmetrically on opposite sides of a plane 10 which is perpendicular to the first axis 7 a point S on said axis. The large bases of each of the truncated cones face one another.

Shaft 11 is supported by the frame at each of its ends by a system of bearings comprising a first series of roller bearings la and Ib coaxial with the axis 7. In order to facilitate the assembly of the first element and the shaft 11 supporting the same, the end of shaft 11 is disassemblable by means of a system of rings 23a, 23b, and a bolt 24.

A support 13 is mounted for rotation about the first axis 7 by means of a system of bearing 25a and 25b inserted between the frame A (sides A, and A2 respectively) and the support. The bearings la and lb mentioned hereinbefore are themselves mounted within the support 13 in the transverse plane of bearings 25a and 25b at each of the ends of the transmission device, in such a way that the first element 2 can rotate relative to support 13, which can itself rotate relative to frame A. The support 13 has a tube like, substantially cylindrical portion extending between its ends.

The substantially cylindrical support 13 is inclined relative to the longitudinal axis 7 of the transmission device. The second element is supported by support 13 via needle and ball bearings 26a, 26b, and 26c.

This latter bearing serves to axially position the second element 3 relative to the support 13.

The second element 3 is a substantially cylindrical solid of revolution and is rotatable relative to the support 13 about a second axis 12 passing through the point S on the first axis 7 and inclined by constant fixed angle a relative to the latter. In the case of this embodiment, the half-angles at the apices of the conical frustums forming the rolling surfaces of the first element are slightly smaller than the above-defined angle a. The significance of this will be shown hereinafter with reference to the description of the operation of the transmission device.

The second element 3 comprises two rolling surfaces 19 and 20 which are of revolution about the second axis 12 and are symmetrically disposed on either side of a plane 16 perpendicular to said second axis at point S. These rolling surfaces are formed on two annular rings 27 and 28 which are axially movable relative to one another, along the second axis 12 within a cylindrical body 3a of the second element, but they are integral in rotation with the second element 3.

A mechanical system comprising a plurality of coil springs 29a and 29b axially biases the rolling surfaces 19 and 20 of the second element in such a way as to urge them with a sufficient force at two contact points P1 and P2 respectively against the rolling surfaces 8 and 9 of the first element 2. These springs are fitted along the inner wall of the second element 3 and act respectively between flanges 30a and 30b located at the two ends of the second element 3 and their respective annular rings 28 and 27. The exact function of this spring system will be described hereinafter.

A bevel gear 31 of apex S is integral in rotation with the second element 3 and meshes with a bevel gear 32 of apex S integral in rotation with the casing A3 of the frame. An input drive shaft 33 is integral in rotation with support 13, said shaft 33 being coaxial with axis 7.

The operation of this embodiment will now be described.

The conical or frustum-shaped rolling surfaces 8 and 9 are in rolling frictional contact at P1 and P2 with the rolling surfaces 19 and 20 of the second element. The specific contact pressure is created by the system of springs 29a and 29b. These springs and the half-angle at the apex of the frustum-shaped rolling surfaces 8 and 9 are designed to create a normal force FN sufficient to transmit the input torque, without any slipping of the rolling surfaces relative to one another.

Under the action of input torque applied to the input shaft 33, rolling surfaces 19 and 20 are rotated on the one hand at the speed ,B* about their own axis, the second axis, and on the other are given a conical movement of apex S about the first axis 7 at speed & .

The above-defined speeds p*, & , and the speed w of the first element about axis 7 are interconnected by the previously defined relationship: R, ww =0 R2 R, and R2 are as shown on Fig. 1.

In the case of the present embodiment, the bevel gears 31 and 32 of apex S, which are respectively integral with the second member 3 and the frame A, have the effect of linking in rotation the speeds h and'3 in such a way that the latter are in a constant ratio. Consequently, for a given input speed h there is only a single output speed w at which the output shaft 11 of the transmission device can be driven.

The mass of the second element 3 is distributed in such a way that the centre of gravity of the second element coincides with the point S on the first and second axes and the main moments of inertia J, and J3 of the second element have values related to the speeds a and'3 and the slope angle a in such a way that a torque is developed having a direction and intensity sufficient for wholly or partly balancing the reactive torque associated with the normal forces FN.

Thus, the bearings 26a, 26b and 26c which support the second element, only receive relatively low or zero radial forces during operation.

Furthermore, as a result of the symmetrical arangement of the rolling surfaces, bearings la, lb, 25a and 25b supporting the main drive shafts receive no axial reaction.

The way in which input-output speed ratio can be varied by modifying the ratio R, and R2 will now be described.

By injecting a pressurized fluid into the chambers 14a and 14b, it is possible to displace the rolling surfaces 8 and 9, by respectively moving them away from plane 10. In Fig. 1, the rolling surfaces 8 and 9 are shown in their position of maximum spacing.

The available transverse spacing between the rolling surfaces 8 and 9 and the cylindrical body 3a of the second element 3 decreases in proportion to the moving apart of the rolling surfaces. As the slope angle of the second axis relative to the first axis is greater than the half-angle at the apex of the frustum-shaped rolling surfaces 8 and 9, the available transverse space between the rolling surfaces 8 and 9 and the cylindrical body 3a of the second element 3 increases in the directions towards the plane of symmetry 16. Therefore, the axially movable annular rings 27 and 28 on which are provided the rolling surfaces 19 and 20 cannot move back in the direction of plane 16 when the rolling surfaces 8 and 9 are moved away from one another from e.g.

minimum spacing by injecting a pressurized fluid into chambers 14a and 14b. Therefore, the ratio R,/R2 varies, because the radius R2 increases, so that correlatively, bearing in mind the kinematic equation mentioned hereinbefore the speed ratios w and a vary.

Conversly, when the fluid pressure in the chambers 14a and 14b decreases, the rolling surfaces 8 and 9 move towards one another from e.g. the maximum spacing shown in Fig. I and towards plane 10. They are in fact shifted in this direction by the springs 29a and 29b via the annular rings 27 and 28 themselves. They are shifted by the springs whilst the fluid pressure in the chambers does not balance the force exerted by the springs. As a result of the reversible displacement of the rolling surfaces 8 and 9, it is possible to continuously vary in one direction or the other the speed ratio of the transmission device.

With reference to Fig. 2 a second embodiment of the transmission device in accordance with the invention will now be described.

Most of the members described with reference to Fig. 1 are shown in this drawing. They carry the same reference numerals and in particular there are shown frame A, first element 2, second element 3, first axis 7, second axis 12, support 13, rolling surfaces 8 and 9 of the first element and 19 and 20 of the second element, with the constant angle a of the second axis relative to the first axis.

A detailed description will only be provided here of those members whose structure differs from that described hereinbefore. This applies more particularly to the geometry of the rolling surfaces 8 and 9, having a generally conical configuration.

In the case of this embodiment, the means creating the contact pressure between the rolling surfaces has an inertial origin, i.e. the inertial forces which develop in the mass of the annular rings 27 and 28 applies them against the rolling surfaces 8 and 9. Fig. 3 is a force diagram illustrating the forces acting on one of the rolling surfaces. As the annular ring 28 is rotated at speed & about the first axis 7, it is subjected to centrifugal forces, whose resultant at Gp (centre of gravity of the annular ring, located on the second axis 12) is a rotary force Fe (this force depends on the geometry and mass of the annular ring as well as its speed & ). This force can be broken down into an axial component (directed according to the second axis 12) FCa and a radial component Foe,. The axial component FCa has the tendency to displace the annular ring 28 in the direction of arrow F, i.e. to move the ring 28 out of the plane of symmetry 16 of the second element. Therefore, the annular ring is displaced until it engages on the rolling surface 9 of the first element, with an adequate pressure to prevent the slipping of the rolling surfaces 9 and 20, in such a way that the rolling surfaces roll on one another without slipping.

It is known that in order to transmit a given input torque, it is necessary to exert a predetermined normal force FN (this normal force FN is obtained by calculation or experimentally from the torque value to be transmitted). It is possible to calculate or draw the profile of the rolling surface 9 of the first member and define the geometry of the annular ring 28 in such a way that at each contact point between the rolling surfaces 9 and 20, the normal force created by the centrifugal force Fe is equal to the desired normal force FN. Thus, if T is used to designate the tangent at contact point P2 relative to the rolling surface 9 of the first member, said tangent T forms an angle aa with the second axis 12 which is materialized by drawing at P2 the parallel line and the perpendicular line to the first axis 12.

The axial component FNa (in accordance with the second axis 12) of the normal force FN is a function of the above-defined angle Aa: F,,=F,xsin A When balanced, the axial component FN8 must be equal to the axial component FCa created by the centrifugal force: Fca=FNa=Fnxsin .cr Thus, by graphically or numerically solving this equation, it is possible to determine the geometry, the mass of the annular ring and the rotation speed cr, as well as the profile of the rolling surface 9 permitting the creation of the desired normal force FN.

The means for varying the axial position of the rolling surfaces 8 and 9 and the variation of the speed is, in all points identical to that applied with reference to Fig. 1.

Figs. 4 and 4a will now be described which show a third embodiment having a mechanical system for loading the rolling surfaces and creating the contact pressure.

comprising helical ramps. These drawings show many of the members described with reference to Fig. 1 and these carry the same references. A detailed description will be provided hereinafter only of those members having a different structure from those described hereinbefore, more particularly the loading system for the rolling surfaces.

In this embodiment, the rolling surfaces 8 and 9 are truncated cones, whereof the half angle at the apex is equal to the angle a of the second axis relative to the first axis.

Therefore, the available spacing between the cylindrical body 3a of the second element 4 and the rolling surfaces 8 and 9 is constant over the entire length of the rolling surfaces.

The rings 27 and 28 are mounted, in a manner to be described hereinafter, in such a way that they can be axially displaced, along the second axis in the space between surfaces 8 and 9, and body 3a, and are in frictional contact with the rolling surfaces 8 and 9.

The two half portions 4 and 5 on which the rolling surfaces 8 and 9 are formed, are movable on shaft 11 by means of helical ramps 40a and 40b having opposite pitch It is obvious that on rotating the two half portions 4 and 5 relative to the output shaft II in an appropriate direction, there is a tendency to move apart the portions 4 and 5.

This has the effect of reducing the space between the rolling surfaces 8 and 9 and the second element 3. Consequently, on rotating the two portions 4 and 5 in an appropriate direction, the rolling surfaces 8 and 9 may be applied against the rolling surfaces 19 and 20 with a sufficient normal force to transmit the input torque.

A coil spring 40c inserted between the two halves 4 and 5 facilitates the operation of the mechanical system which creates the normal force by pre-loading the rolling surfaces in such a way that they are prevented from sliding on one another on starting or in the case where the output torque is zero.

The annular rings 27 and 28 are mounted so as to slide axially within the cylindrical body 3a of the second element, having a cylindrical shape internally. They are traversed by threaded rods 41, such as 41a, 41b and 41c having opposite pitches, making it possible to axially displace them, to move them closer or further away from each other. These threaded rods 41 are integral with gears 42, such as 42a, 42b and 42c, movable by a crown gear 43 whose axis is the second axis 12. This crown gear 43 is itself integral with a bevel gear 44 of apex S in gear with a further bevel gear 45 of apex S, which rotates about the first axis 7. Bevel gear 45 is integral in rotation with a gear 46 which is in gear with a gear 47, integral with a control rod which rotates about an axis 48, fixed relative to frame A. As a result of this combination of gears, it is possible to control from the outside of the transmission device, the axial position of the annular rings and thus vary the speed ratio of the transmission device, as has already been described with reference to Fig. 1.

A description will now be provided of Figs. 5 and 5a which shows a fourth embodiment. In the case of this embodiment, the annular rings 27 and 28, on which are provided the rolling surfaces, are positioned externally by the combination of a hydraulic system and a gear train.

This drawing shows many of the members described with reference to the previous drawings. particularly Figs. I and 4 and they carry the same reference numerals.

The half-angle at the apex of the frustums constituting the rolling surfaces 8 and 9 is substantially equal to the angle of the second axis relative to the first axis.

In the case of this embodiment, the mechanical system loading the rolling surfaces and creating the normal force FN is comparable to the described hereinbefore with reference to Fig. 4. It comprises an annular ring 59 mounted integral in rotation with shaft 11 by means of channels. Annular ring 59 has on its sides ramps formed by teeth 59a and 59b which cooperate with ramps having a comp.lementary configuration, also forme main drive shaft 63 which traverses the hollow shaft 11.

In other words, this embodiment differs from that described relative to Figs. 2 and 3 in that the first element is fixed against rotation. One of the main drive shafts 63 is connected in rotation at the speed ce of the second element about the first axis 7. The other main drive shaft 61 is connected in rotation at the speed p* of the second element about the second axis 12 via a bevel gear train of apex S.

A description will now be given of Figs. 7 and 7a which show a further embodiment comparable to that described with reference to Figs. 4 and 5.

In this embodiment, the second element carries the conical rolling surfaces.

The transmission device has a frame A comprising two flat sides A, and A2 at each of the ends, joined by screws to a substantially cylindrical casing A3.

The first element 72 comprising two half portions 74 and 75 with a generally annular configuration is mounted on the said casing. On these two half portions are provided rolling surfaces 78 and 79 which are of revolution about a first axis 77 (the longitudinal axis of the transmission device) and are symmetrically positioned relative to a plane 80 perpendicular to the first axis 7 at a point S on said axis. The two half portions may move axially within the casing along the first axis 77. These two half portions are controlled in axial translation by a manipulating member, whose arrangement will be better understood by referring to the detailed view of Fig. 7a to be described hereinafter.

Within the casing is mounted a second element 73 which also comprises two half portions 73a and 73b on which are respectively provided frustum-shaped rolling surfaces 89 and 90. These two rolling surfaces 89 and 90 are of rotation about a second axis 92 which intersects the first axis 77 at a point S. In addition, they are symmetrically arranged on either side of a plane 86 perpendicular to the second axis at S.

The angle a of the second axis, relative to the first axis, is constant and substantially equal to the half-angle at the apex of the frustum-shaped rolling surfaces.

The two half-portions 73a and 73b are mounted by means of a system of helical ramps 110a and 11 Ob on a hollow shaft 81 coaxial with the second axis 92 (this system of helical ramps has the same functions as the system of helical ramps described with reference to Fig. 4).

This shaft 81 and the second member 73 are mounted so as to rotate about the second axis 92 by meanYof bearings 96a and 96h carried at one of the ends by a support 83a which is freely rotatable about the first axis 7 and at the other end by a support 83b integral in rotation with a main drive shaft 103.

Support 83a is itself supported by bearings 81a mounted in the side A, of the frame.

Support 83b is itself supported by the bearings 81b mounted in the side A2 of the frame.

Shaft 81 and the second element 73 which rotate at speed ss* about the second axis 92 are linked in rotation, via a universal joint 100 with a main drive shaft 104 coaxial to axis 77. This shaft 104 is supported by bearings 105. The univeral joint 100 is located within the hollow shaft 81.

It can be seen that the members comprising this embodiment have similarities with the members described with reference to Figs. 1 to 6. Their relative positioning is not the same, but their structures and functions are comparable.

Therefore, no further detailed description will be provided here of the operation of this embodiment, because it is comparable to that of the previously described embodiments. However, it is briefly pointed out that the shaft 103 rotates support 83b at speed h. As a result, due to the fact that the rolling surfaces 78 and 89 on the one hand and 79 and 90 on the other are respectively maintained loaded against one another at the two points P, and P2, the second element 73 rolls against the first element 72 by rotating on itself at the speed A* about the second axis. Therefore, the main drive shaft 104, linked in rotation with the second element, is driven.

In the same way as in certain of the embodiments already described, the normal force providing the specific frictional contact pressure at P, and P2 is created by the system of helical ramps. In order to facilitate the operation of the helical ramps system on starting, a spring 106, inserted between the two frustum-shaped portions 73a and 73b actuates the rolling surfaces 89 and 90 relative to the rolling surfaces of the first element in such a way that the rolling surfaces are preloaded.

In the same way as previously, the geometry and kinematics of the second element are adapted so as to produce a torque which balances the reactive torque correlative to the normal forces exerted at P, and P2. This arrangement reduces the mechanical stresses, particularly on the bearings, which lightens them or reduces wear thereto.

The manipulating member which axially moves the rolling surfaces 78 and 79 of the first element will now be described with reference to the detailed view of Fig. 7a.

This perspective view shows the cylindrical casing of A2, the first axis 77, and the two half portions 74 and 75 of the first element having an annular configuration on which are formed the rolling surfaces 78 and 79 which are of revolution about the first axis 77. Cylindrical pins 74a and 75a are respectively integral with the two half portions 74 and 75. These two pins slide in longitudinal opening 115 of the casing and cooperate with a system of helical ramps 1 16a and 1 16b of opposite pitch, provided in a sleeve made in two parts 117 and 118 in order to facilitate machining of the ramp.

The sleeve parts 117 and 118 are coaxial with the casing and rotate about the first axis 7. It is obvious that on rotating the sleeve about the axis 77, rolling surfaces 78 and 79 are moved away from one another to a greater or lesser extent in accordance along the first axis 77.

It will thus be seen that, at least in the preferred embodiments, there are provided transmission devices which enable the avoidance of axial thrusts on drive shafts.

The devices are able to transmit high power whilst keeping the rolling surfaces engaged with one another, without sliding. A simple and rapid variation of the transmission ratio is possible. Uncertain clearances between the rolling surfaces can be avoided since the angle of axes intersection is fixed, i.e.

positively established by the supporting means.

The establishment of connections between certain of the members is also simplified.

WHAT WE CLAIM IS: 1. A transmission device having a frame, drive input means, drive output means, and means interconnecting said input and output means including a first element having a first axis fixed relative to the frame, a second element having a second axis intersecting said first axis at a predetermined angle established by supporting means for said second element, said second axis being capable of moving biconically about the first axis with the apex of the cones of movement being the point of intersection of said axes, said first element having a pair of rolling surfaces disposed about said first axis one each side of the plane passing through the point of intersection of said axes and perpendicular to said first axis, said second element having a pair of rolling surfaces disposed about said second axis one each side of the plane passing through the point of intersection of said axes and perpendicular to said second axis, means for urging the respective rolling surfaces of the first and second elements into relative rolling engagement at points of contact located on each side of the plane passing through the point of intersection of said axes and perpendicular to the first axis, the rolling surfaces of at least one of said elements being defined by generatrices inclined oppositely with respect to the axis thereof and symmetrically with respect to the point of intersection of said first and second axes, and means for varying the spacing of the points of contact from said point of intersection so as to give a variable ratio of rolling surface radii.

2. A transmission device as claimed in claim 1 wherein the means for urging the rolling surfaces of said elements against each other includes resilient means acting along the second axis on the rolling surfaces of the second element.

3. A transmission device as claimed in claim I wherein the means for urging the rolling surfaces of said elements against each other incudes means arranged to develop forces of inertia acting along the second axis on the rolling surfaces of the second element.

4. A transmission device as claimed in claim 1 wherein the means for urging the rolling surfaces of said elements against each other includes a system of ramps acting along the first axis on the rolling surfaces of the first element.

5. A transmission device as claimed in claim 1 wherein the means for urging the rolling surfaces of said elements against each other includes a system of ramps acting along the second axis on the rolling surfaces of the second element.

6. A transmission device as claimed in any preceding claim wherein the means for varying the spacing of the points of contact includes a pressurised fluid system acting along the first axis on the rolling surfaces of the first element.

7. A transmission device as claimed in any of claims 1 to 5 wherein the means for varying the spacing of the points of contact indluces a gear system acting along the second axis on the rolling surfaces of the second element.

8. A transmission device as claimed in any of claims 1 to 5 wherein the means for varying the spacing of the points of contact includes a pin and slot arrangement and acts along the first axis on the rolling surfaces of the first element.

9. A transmission device as claimed in any of claims 1 to 5 wherein the means for varying the spacing of the points of contact includes a pressurised fluid system acting on the rolling surfaces of the first element, and a gear system and pin and slot arrangement acting along the second axis on the rolling surfaces of the second element.

10. A transmission device as claimed in claim 3 wherein the rolling surfaces of the first element are conical and the rolling surfaces of the second element are annular.

11. A transmission device as claimed in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. half portions 74 and 75 of the first element having an annular configuration on which are formed the rolling surfaces 78 and 79 which are of revolution about the first axis 77. Cylindrical pins 74a and 75a are respectively integral with the two half portions 74 and 75. These two pins slide in longitudinal opening 115 of the casing and cooperate with a system of helical ramps 1 16a and 1 16b of opposite pitch, provided in a sleeve made in two parts 117 and 118 in order to facilitate machining of the ramp. The sleeve parts 117 and 118 are coaxial with the casing and rotate about the first axis 7. It is obvious that on rotating the sleeve about the axis 77, rolling surfaces 78 and 79 are moved away from one another to a greater or lesser extent in accordance along the first axis 77. It will thus be seen that, at least in the preferred embodiments, there are provided transmission devices which enable the avoidance of axial thrusts on drive shafts. The devices are able to transmit high power whilst keeping the rolling surfaces engaged with one another, without sliding. A simple and rapid variation of the transmission ratio is possible. Uncertain clearances between the rolling surfaces can be avoided since the angle of axes intersection is fixed, i.e. positively established by the supporting means. The establishment of connections between certain of the members is also simplified. WHAT WE CLAIM IS:

1. A transmission device having a frame, drive input means, drive output means, and means interconnecting said input and output means including a first element having a first axis fixed relative to the frame, a second element having a second axis intersecting said first axis at a predetermined angle established by supporting means for said second element, said second axis being capable of moving biconically about the first axis with the apex of the cones of movement being the point of intersection of said axes, said first element having a pair of rolling surfaces disposed about said first axis one each side of the plane passing through the point of intersection of said axes and perpendicular to said first axis, said second element having a pair of rolling surfaces disposed about said second axis one each side of the plane passing through the point of intersection of said axes and perpendicular to said second axis, means for urging the respective rolling surfaces of the first and second elements into relative rolling engagement at points of contact located on each side of the plane passing through the point of intersection of said axes and perpendicular to the first axis, the rolling surfaces of at least one of said elements being defined by generatrices inclined oppositely with respect to the axis thereof and symmetrically with respect to the point of intersection of said first and second axes, and means for varying the spacing of the points of contact from said point of intersection so as to give a variable ratio of rolling surface radii.

11. A transmission device as claimed in

claim 10 wherein the apex half-angle of the conical rolling surfaces is smaller than the angle between the first and second axes.

12. A transmission device as claimed in claim 2 wherein the resilient means includes two helical springs engaging respectively at one end on the second element and at the other end on the rolling surfaces of the second element, said rolling surfaces of the second element being axially movable.

13. A transmission device as claimed in claim 4 wherein the rolling surfaces of the first element are conical and the rolling surfaces of revolution of the second element are annular, and the apex half-angle of each conical rolling surface of revolution is equal to the angle between the first and second axes.

14. A transmission device as claimed in claim 13 wherein the half parts comprising the rolling surfaces of revolution of the first element are screwed by means of helical ramps of opposite slope on a shaft and wherein the two half parts are connected with each other by a helical spring.

15. A transmission device as claimed in any preceding claim wherein said supporting means for said second element is iournalled in the frame for rotation about said first axis and is journalled with said second element for relative rotation of said second element and said supporting means about said second axis.

16. A transmission device as claimed in claim 15 wherein said supporting means for said second element is a torque transmitting member having opposite ends journalled in the frame on said first axis and a tube-like section extending between said opposite ends.

17. A transmission device as claimed in claim 16 wherein said tube-like section is coaxial with said second axis and is journalled directly with said second element on opposite sides of the point of intersection of said first and second axes.

18. A transmission device as claimed in claim 17 wherein said second element includes exterior journal surfaces coaxial with said second axis and wherein the interior of said tube-like section is journalled with said exterior journal surfaces.

19. A transmission device as claimed in claim 16, 17 or 18 wherein said tube-like section extends radially between said first and second elements and is formed with diammetrically opposite, axially spaced openings to enable said rolling surfaces to engage at said points of contact.

20. A transmission device as claimed in claim 15 wherein said second element includes interior journal surfaces coaxial with said second axis and wherein said supporting means for said second element extends within, and is journalled with, said interior journal surfaces.

21. A transmission device as claimed in any preceding claim wherein the arrangement is such that a couple derived from the biconical movement of the second element about the first axis at least partially balances reactive forces resulting from the means urging the rolling surfaces into engagement.

22. Transmission devices, substantially as hereinbefore described.

23. A transmission device substantially as hereinbefore described with reference to Figs. 1 and la; or Figs. 2 and 3; or Figs. 4 and 4a; or Figs. 5 and 5a; or Fig. 6; or Figs. 7 and 7a.