TORSION FILTERING MECHANISM HAVING A CAM TRACK

Abstract

A torsion filtering mechanism (22) has a first rotating member (24), a second rotating member (26) movable with respect to the first rotating member (24), a cam track (60) rotating with one (24) of the rotating members, and at least one associated cam follower (36) carried by the other (26) rotating member. The cam track (60) has, in a section plane perpendicular to the axis of revolution, a profile constituted by a plurality of circular arcs (A0, A1, A2, A3, A4) adjacent pairwise and having an intersection point pairwise. Any two adjacent circular arcs from among the circular arcs have different finite or infinite radii of curvature, and indistinguishable tangents at the intersection point.

Claims

1. A torsion filtering mechanism (22) for a torque transmission device (16), in particular for an automobile, in particular for a clutch device, the torsion filtering mechanism (22) comprising: a first rotating member (24) capable of rotating around an axis of revolution (100) of the torsion filtering mechanism (22); a second rotating member (26) capable of rotating around the axis of revolution (100) and oscillating with respect to the first rotating member (24); at least one cam track (60) carried by one (24) of the first and second rotating members, the cam track (60) being capable of rotating around the axis of revolution (100) with the rotating member (24) carrying the cam track (60), and being elastically connected to the rotating member (24) carrying the cam track (60), in order to exhibit a degree of freedom of movement with respect to the rotating member (24) carrying the cam track (60); and at least one cam follower (36) associated with the cam track (60) and carried by the other (26) of the first and second rotating members, the cam follower (36) being capable of traveling along the cam track (60) between a retrograde end of the cam track and a forward end of the cam track, while causing a variable displacement of the cam track (60) with respect to the rotating member (24) carrying the cam track (60), wherein the cam track (60) has, in a section plane perpendicular to the axis of revolution, a profile having a plurality of circular arcs (A0, A1, A2, A3, A4) adjacent pairwise and having an intersection point pairwise, the profile being such that at least two adjacent circular arcs from among the circular arcs (A0, A1, A2, A3, A4) have different finite or infinite radii of curvature, and indistinguishable tangents at the intersection point.

2. The torsion filtering mechanism according to claim 1, wherein the profile is such that every pair of adjacent circular arcs from among the circular arcs (A0, A1, A2, A3, A4) is constituted by circular arcs having different finite or infinite radii of curvature, and indistinguishable tangents at the intersection point.

3. The torsion filtering mechanism according to claim 1, wherein the plurality of circular arcs (A0, A1, A2, A3, A4) is constituted by at most ten circular arcs.

4. The torsion filtering mechanism according to claim 1, wherein the plurality of circular arcs (A0, A1, A2, A3, A4) comprises at least three circular arcs.

5. The torsion filtering mechanism according to claim 4, wherein at least one circular arc of the profile has a circular arc adjacent the forward end of the cam track from among the circular arcs (A0, A1, A2, A3, A4) of the profile, and a circular arc adjacent the retrograde end of the cam track from among the circular arcs (A0, A1, A2, A3, A4) of the profile, and has a radius greater than the radius of the circular arc adjacent the forward end of the cam track and greater than the radius of the circular arc adjacent the retrograde end of the cam track.

6. The torsion filtering mechanism according to claim 4, wherein at least one circular arc of the profile has a circular arc adjacent the forward end of the cam track from among the circular arcs (A0, A1, A2, A3, A4) of the profile, and a circular arc adjacent the retrograde end of the cam track from among the circular arcs (A0, A1, A2, A3, A4) of the profile, and has a radius less than the radius of the circular arc adjacent the forward end of the cam track and less than the radius of the circular arc adjacent the retrograde end of the cam track.

7. The torsion filtering mechanism according to claim 1, wherein the cam track (60) faces radially in a direction of abutment against the cam follower (36); the cam follower (36) defines a pitch circle (G) for contact with the cam track (60), centered on the axis of revolution (100); and in at least one reference position of the filtering mechanism (22), the profile is at a positive or zero distance from the pitch circle (G), measured in the abutment direction, at every point.

8. The torsion filtering mechanism according to claim 7, wherein in the reference position, the cam follower (36) is in abutment against a so-called reference circular arc (A0) of the profile at a so-called reference contact point (E), the line normal to the reference circular arc (A0) at the reference contact point (E) intersecting the axis of revolution (100).

9. The filtering mechanism according to claim 8, wherein when the filtering mechanism (22) is in the reference position, at least one of the circular arcs (A0, A1, A2, A3, A4) of the profile moves closer to the pitch circle (G) while moving away from the reference contact point.

10. The torsion filtering mechanism according to claim 1, wherein the cam track (60) faces radially outward and the cam follower (36) is arranged radially outside the cam track (60).

11. The torsion filtering mechanism according to claim 8, wherein the reference circular arc (A0) has a finite or infinite radius that is always greater than the radius of the pitch circle (G).

12. The torsion filtering mechanism according to claim 1, wherein the cam follower (36) has a follower roller (38).

13. The torsion filtering mechanism according to claim 1, wherein the cam track (60) is formed on a flexible blade (54) having a base (56) fastened to the rotating member (24) carrying the cam track (60).

14. A torsion filtering mechanism according to claim 1, wherein it furthermore comprises: at least one other cam track (60) carried by one (24) of the first and second rotating members, the other cam track (60) being capable of rotating around the axis of revolution (100) with the rotating member carrying the other cam track and being elastically connected to the rotating member carrying the other cam track (60), in order to exhibit a degree of freedom of movement with respect to the rotating member carrying the other cam track (60); and at least one other cam follower (36) associated with the other cam track (60) and carried by the other (26) of the first and second rotating members, the other cam follower (36) traveling along the other cam track (60) causing a variable displacement of the other cam track (60) with respect to the rotating member carrying the other cam track, wherein the other cam track exhibits, in a section plane perpendicular to the axis of revolution, a profile constituted by a plurality of circular arcs (A0, A1, A2, A3, A4) adjacent pairwise, the profile being such that any two adjacent circular arcs from among the circular arcs (A0, A1, A2, A3, A4) have different radii of curvature and one intersection point, and have indistinguishable tangents at the intersection point.

15. The torsion filtering mechanism according to claim 14, wherein the cam track (60) and the other cam track (60) have different profiles.

16. The torsion filtering mechanism according to claim 2, wherein the plurality of circular arcs (A0, A1, A2, A3, A4) comprises at most ten circular arcs.

17. The torsion filtering mechanism according claim 2, wherein the plurality of circular arcs (A0, A1, A2, A3, A4) comprises at least three circular arcs.

18. The torsion filtering mechanism according claim 3, wherein the plurality of circular arcs (A0, A1, A2, A3, A4) comprises at least three circular arcs.

19. The torsion filtering mechanism according to claim 5, wherein at least one circular arc of the profile has a circular arc adjacent the forward end of the cam track from among the circular arcs (A0, A1, A2, A3, A4) of the profile, and a circular arc adjacent the retrograde end of the cam track from among the circular arcs (A0, A1, A2, A3, A4) of the profile, and has a radius less than the radius of the circular arc adjacent the forward end of the cam track and less than the radius of the circular arc adjacent the retrograde end of the cam track.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Other characteristics and advantages of the invention will become evident from a reading of the description below that refers to the attached Figures, in which:

[0048] FIG. 1 is a schematic view of a propulsion assemblage according to an embodiment of the invention, having a dual mass flywheel incorporating a torsion filtering mechanism according to an embodiment of the invention;

[0049] FIG. 2 is a perspective view of a portion of the dual mass flywheel of the propulsion assemblage of FIG. 1;

[0050] FIG. 3 is a frontal view of a portion of the dual mass flywheel of FIG. 2 showing in particular a flexible blade of the filtering mechanism;

[0051] FIG. 4 is a section view of the dual mass flywheel of FIG. 2;

[0052] FIG. 5 is a schematic view of a profile of a cam track of the flexible blade of FIG. 3;

[0053] FIG. 6 is a graph of a characteristic curve of the torque of the filtering mechanism corresponding to the profile of FIG. 5;

[0054] FIG. 7 is a schematic view of an alternative profile to the profile of FIG. 5;

[0055] FIG. 8 is a graph of a characteristic curve of the torque of the filtering mechanism corresponding to the profile of FIG. 7;

[0056] FIG. 9 is a graph of a characteristic curve of the torque of the filtering mechanism corresponding to another profile of the cam track;

[0057] FIG. 10 is a graph of a curve resulting from combining the torque characteristics illustrated in FIGS. 6 and 8.

[0058] For greater clarity, identical or similar elements are labeled with identical reference characters in all the Figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0059] FIG. 1 illustrates a motor vehicle propulsion assemblage 10 having an internal combustion engine 12 whose crankshaft 14 drives a kinematic transmission drivetrain 16 having a dry clutch 18 arranged upstream from a gearbox input shaft 20. Disposed kinematically between crankshaft 14 and friction clutch 18 in kinematic transmission drivetrain 16 is a torsion filtering mechanism 22 that constitutes a dual mass flywheel and has an input member constituted by a primary flywheel 24 integral with crankshaft 14 and an output member constituted by a secondary flywheel 26 integral with a reaction plate of clutch 18 or made as a single piece therewith. Elastic members 28 are interposed between primary flywheel 24 and secondary flywheel 26 so as to operate in the context of angular position fluctuations between primary flywheel 24 and secondary flywheel 26. Crankshaft 14, damping mechanism 22, clutch 18, and input shaft 20 of the gearbox rotate around a single axis of revolution 100.

[0060] The structure of dual mass flywheel 22 is illustrated in detail in FIGS. 2 to 4. Primary flywheel 24 is made up of a plate 30 on which is fastened a ring gear 32 for connection to a starter (not depicted). Plate 30 of primary flywheel 24 is intended to be mounted, by way of screws 34, on a terminal flange of crankshaft 14. Primary flywheel 24 supports cam followers 36, in this case two in number. Each cam follower 36 is constituted by a roller 38 mounted, by means of a needle bearing or a plain bearing, on a pivot 40 fastened to plate 30, so as to rotate around an axis that is parallel to axis of revolution 100 and is fixed with respect to primary flywheel 24.

[0061] Secondary flywheel 26 forms a solid plate 42 that also constitutes a reaction plate of friction clutch 18. A rolling bearing 44 provides rotational guidance of secondary flywheel 26 with respect to primary flywheel 24. Studs 46 allow plate 42 to be fastened to a clutch cover (not depicted). Secondary flywheel 26 furthermore forms a splined hub 48, which projects axially with respect to plate 42 and onto which is shrink-fitted annular body 50 of a one-piece elastic member 52 having curved flexible blades 54, here two in number. Each flexible blade 54 has a bent base 56 extending substantially radially outward with respect to annular body 50, prolonged by an elongated curved arm 58 which extends circumferentially and on which is formed a cam track 60 facing radially outward and arranged radially inside of, and facing toward, one of rollers 38. Each flexible blade 54 is thus associated with one of rollers 38 that rolls on the associated cam track 60.

[0062] Remarkably, cam track 60 exhibits, in a section plane perpendicular to axis of revolution 100, a profile constituted by a succession of circular arcs, some of which can have an infinite radius and can constitute straight line segments.

[0063] According to the embodiment illustrated in FIG. 5, for example, the profile is constituted by a straight line segment A0 (circular arc of infinite radius), followed successively by four circular arcs A1, A2, A3, and A4 having centers C1, C2, C3, C4 and radii R1, R2, R3, R4 that are different pairwise and in this case increase pairwise, so that R1<R2<R3<R4. At their intersection point, two adjacent circular arcs have a common tangent. Circular arc A1 is also tangent to straight line segment A0. Remarkably, there exists a reference point E of straight line segment A0 for which the line normal to the straight line segment passes through axis of revolution 100 of the filtering mechanism. At this reference point E, the contact load between flexible blade 54 and cam follower 36 is entirely radial with respect to axis of revolution 100, and causes no torque. This is therefore an equilibrium position. This equilibrium position is stable because on either side of reference point E, cam track 60 is located radially outside of pitch circle G defined by the path of the contact point between roller 38 of cam follower 36 and cam track 60 when first rotating member 24 rotates with respect to the second member 26.

[0064] Cam track 60 of FIG. 5 is convex, and circular arcs A0 to A4 are in this case all arranged radially outside pitch circle G with respect to the axis of revolution, at least in the reference position corresponding to contact between roller 38 and reference point E. The centers of curvature and the radii of the successive circular arcs are selected so that in the reference position corresponding to contact between roller 38 and reference point E, the distance between the axis of revolution and a current point on the cam track increases continuously as that point moves away from the reference point.

[0065] This ensures that when the primary flywheel rotates with respect to the secondary flywheel in a direction that will be arbitrarily called the “forward direction,” the roller of the cam follower rolls on the associated cam track while moving away from reference point E and approaching the free end, producing increasing bending of the flexible blade.

[0066] This results in a correlation between torque and angular position which is illustrated by the graph of FIG. 6, in which the abscissa axis represents values for angular position increasing in the forward direction from the position of reference point E, and the ordinate axis represents absolute values for the corresponding static torque. It is evident that the torque is a continuous monotonic increasing function of angular position. In other words, the torque increases, continuously and with no discontinuity, with angular position. It is also evident that the derivative of the aforementioned function is a monotonic continuous increasing function, in other words that the angular stiffness also increases continuously with angular position.

[0067] As applicable, the cam track can continue in a retrograde direction beyond segment A0. In such a case, what has been described here regarding the region of the cam track traveled along by the cam follower when the primary flywheel rotates with respect to the secondary flywheel in the forward direction from reference point E also applies to that portion of the cam track traveled along by the cam follower starting from the equilibrium point when the primary flywheel rotates with respect to the secondary flywheel in the retrograde direction. In this region as well, the cam track is constituted by successive circular arcs co-tangent at their intersection points.

[0068] It thus becomes possible to design a simple cam surface that defines a characteristic curve for angular stiffness with respect to the angular positioning between the primary flywheel and secondary flywheel. In particular, this design using successive circular arcs simplifies dimensional checks in the production process.

[0069] Successive circular arcs can of course be selected in order to obtain different cam profiles and different variations in torque and angular stiffness.

[0070] FIG. 7, for example, illustrates a profile having four successive circular arcs having radii R0, R1, R2, and R3, such that R0>R, R0>>R1, R1>R2, R2<<R3, R being the radius of pitch circle G, the directly adjacent arcs being co-tangent at their intersection as in the first embodiment. A profile of this kind results in a correlation between torque and angular deflection as illustrated in FIG. 8: the torque is a continuous function of angular deflection, but a function that is not monotonic and can be derived only in sections. It is evident in particular that circular arc A2 having radius R2 corresponds to a negative slope of the curve, i.e. to a negative angular stiffness. This corresponds to a zone of the cam track profile which approaches the pitch circle in the forward direction.

[0071] FIG. 9 illustrates the characteristic curve for torque as a function of angular deflection for a different profile, where R0>R, R1<R0, R2<R1, R3>R2, and R4>R3, but with circular arc lengths different from the previous embodiment so that the angular stiffness remains positive or zero at all points.

[0072] It is apparent that whatever the shape of cam track 60 and the positioning of cam follower 36 on cam track 60, flexible blade 54 is flexed in such a way that the point of contact between cam follower 36 and cam track 60 is on pitch circle G. Since cam track 60 faces radially outward, the stiffness in a given rotation direction at the contact point will be negative if that portion of cam track 60 which will be traveled along from the contact point in that rotation direction is arranged below pitch circle G when cam follower 36 is at the contact point. Conversely, the stiffness is positive if the portion of cam track 60 which is in the vicinity of the contact point, and which will be traveled along starting from the contact point in that rotation direction, is arranged above pitch circle G when cam follower 36 is at the contact point.

[0073] Particularly advantageously, two blades having different profiles can be combined for one torsion filtering mechanism, for example one blade of the type in FIGS. 5 and 6 and one blade of the type in FIGS. 7 and 8. With such a combination it is possible to obtain a resulting torque which is the sum of the torques of each blade, a graph of which is illustrated in FIG. 10. It should be emphasized that the two blades of FIGS. 5 and 7 have been positioned in such a way that they are jointly in their reference position with respect to their respective cam follower.

[0074] Note that the general shape of the curve of FIG. 10 is similar to that of FIG. 9, but that the maximum torque values obtained for the maximum angular deflection of 60° are substantially higher for the mechanism of FIG. 10 having blades with different profiles, than for the mechanism of FIG. 9 having identical blades.

[0075] It is evident that the tangent to the curve of FIG. 10, which represents stiffness, is low in the range of angular deflection from 20° to 40° and higher in the range from 40° to 60°. More precisely, it is evident that in the range between 20° and 40° the angular stiffness is less than 60 Nm/rad. In the range of angular deflection between 50° and 60°, conversely, the angular stiffness is greater than 800 Nm/rad, which allows the filtering mechanism to respond to a wide range of torques between 0 and 450 Nm, with a low stiffness over a significant portion of the angular deflection range for torques less than 50 Nm.

[0076] This result is obtained in particular by combining, over a given angular range (between 30° and 40°), a positive stiffness for the blade of FIG. 5 and a negative one for the blade of FIG. 7, yielding a resulting value of almost zero for the angular stiffness in that angular deflection range.

[0077] It thus becomes possible to design a particularly interesting characteristic using cam profiles that individually remain simple. In particular, this design of each cam profile using successive circular arcs simplifies dimensional checks in the production process.

[0078] The examples depicted in the Figures and discussed above are of course provided only for illustration and are not limiting.

[0079] In the embodiments above, cam track 60 is convex and is disposed radially inside cam follower 36 in a location centered on axis of revolution 100. The proposed solution can be transposed, however, to a concave cam track arranged radially inside the cam follower, as illustrated in the application FR 3000155. It is also transferrable to a concave cam track arranged radially outside the cam follower, as illustrated in application FR 1562316 (not published on the filing date of the present Application).

[0080] The torsion filtering mechanism according to the present invention using (a) flexible blade(s) can constitute a dual mass flywheel as illustrated in FIG. 1. It can also constitute an inertial deflector or a pendulum oscillator arranged in bypass fashion with respect to the torque path.

[0081] Provision is explicitly made that the various embodiments illustrated can be combined with one another in order to propose others. Any characteristic that has emerged for one skilled in the art from the totality of the elements of the Application, and that has been specifically disclosed only in relation to other characteristics identified in one or more embodiments, can be implemented as a variant of said embodiment or embodiments without being combined with all of the other characteristics of that or those embodiments, and/or can be combined, as applicable, with other characteristics proceeding from another embodiment deriving from all the elements of the Application, provided such has not been expressly excluded or technical circumstances do not make such combinations impossible or devoid of purpose.