Claims:WE CLAIM:

1. A clamping device, consisting of a monolithic flexure comprising:
a. a part of the volume which is substantially fixed comprising of designed zones of locally thinned sections (flexure elements), a plurality of fixation holes and a plurality of curved and straight surfaces, to be called the “fixed component”;
b. part of the volume, which deforms with respect to the fixed component, comprising of designed zones of locally thinned sections (flexure elements), a plurality of curved and straight surfaces and a pair of clamping-arms, to be called the “movable component”;

wherein:
said flexure elements are configured to allow said movable component to rotate, relative to said fixed component, about an axis not physically located on the volume of said monolithic flexure;

said pair of clamping-arms on said movable component provide equal and opposing force on interacting object(s) and said movable component rotates to adjust for in-plane movement of said interacting object(s).

the deforming geometry of said flexure elements and said pair of clamping arms can be described on a plane perpendicular to said axis of rotation.

the axial length of said flexure elements provide the only stiffness in said monolithic flexure, against motion parallel to said axis of rotation.

2. A clamping device as claimed in claim 1 and additional flexure element(s), out-of-plane of the said monolithic flexure, consisting of
a. designed zones of substantially planar thin section(s)
b. atleast two zone of locally thickened sections separated by one or more zones of said substantially planar thin sections
wherein:
one zone of locally thickened section is rigidly located to said movable component of clamping device.
one zone of locally thickened section is rigidly fixated w.r.t said fixed component of clamping device.
said substantially planar thin sections are arranged such that out-of-plane-motion of said movable component, parallel to said axis of rotation, causes in-plane deformation of said sections.
said substantially planar thin sections are arranged such that in-plane-motion of said movable component causes out-of-plane deformation of said sections.

3. The clamping device as claimed in claim 2, wherein said movable component executes in-plane rotation about said fixed component till the curved (or straight) surface(s) of said movable component engages with the curved (or straight) surface(s) of said fixed component thereby restricting further rotation.

4. The clamping device as claimed in claim 1, wherein said movable component, occupies the same axial length, along said rotation axis, as said fixed component.

5. The clamping device as claimed in claim 2, wherein said flexure elements, occupies at least the same axial length, along said rotation axis, as said fixed component.

6. The clamping device as claimed in claim 1, wherein said flexure elements are configured to allow adjustment of said fixation holes relative to each other.
, Description:CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is an improvement in or modification of Indian application titled “CLAMPING DEVICE FOR TENSIONING OF BELTS INCORPORATING FLEXURES”, Indian application number 201641040269, dated November 24, 2016, which has now been granted as Indian patent 307870 on February 22, 2019.

FIELD OF INVENTION
[0002] The present invention relates to an improved clamping device comprising monolithic flexure elements which can be used as belt tensioners, achieving enhanced performance characteristics desired of belt tensioners.

BACKGROUND
[0003] Parent patent application IN201641040269 describes a clamping device for tensioning of belts. The device described involves a single contiguous element defined as ‘monolithic flexure’ which rotates about a fixed point (on the frame) and deforms to change the gap between two pulleys mounted on the arm. The monolithic flexure has dimensional features with varying cross-sectional area. These features, with varying thickness, allow the monolithic flexure to be relatively compliant in selective degree(s) of freedom, but relatively stiff in the complimentary degree(s) of constraint.

[0004] Flexures are elements that incorporate dimensional variation across sections of elastic materials to be relatively compliant in selective degree(s) of freedom, but relatively stiff in the complimentary degree(s) of constraint. Flexure based systems are advantageous in reducing part counts in assemblies by eliminating conventional joints and hence requirement of conventional bearings.

[0005] Thus, the pulley bearing arms, rotational bearing and spring of a dual- belt tensioner, are all merged into the monolithic flexure which allows a smaller design envelope while achieving the performance characteristics desired of dual tensioners. The monolithic flexure designed, works as a clamping device on the belt and is used to provide the necessary tensioning force on the belt.

[0006] A feature of the monolithic flexure embodiment described in the patent, is that the deforming geometries of the individual dimensional features can be described in a single ‘principal plane’ perpendicular to the required rotation axis of the monolithic flexure. The said plane is also substantially parallel to the plane defined by the midline of the belt. The deformations of the features(s) in this plane allow the monolithic flexure to adjust itself to changes in tension forces in the belt.

[0007] The geometry described as extrusion of the features perpendicular to this plane, in the direction of rotation axis in both directions, determine the stiffness of the monolithic flexure to forces and moments that cause deformations perpendicular to the plane. All out of plane motions are to be constrained and the thickness of the extrusion then defines the relative rigidity of the device to these degree(s) of constraint.

[0008] Typically, when used as a dual-belt tensioner in vehicles, the axial space available is limited to the width of the belt. Thus, the extrusion length is limited and consequently limits the rigidity of the device in the desired degree(s) of constraint. Since the forces and moments causing deflections in the constraint direction are an order less than the belt tension forces, the resultant deformations do not necessarily affect the performance of the dual-belt tensioner. An example would be when the midline of the belts is offset from the principal plane of the monolithic flexure. The resultant of the belt tension forces is then parallel and offset from the principal plane of the monolithic flexure thus creating a bending moment. If the resultant force is pointing away from the fixation points of the monolithic flexure the resultant bending moment will try to reduce the offset and stabilise the dual-belt tensioner.

[0009] However, if the resultant force is pointing towards the fixation points, the resultant bending moment will tend to increase the offset which will further increase the bending moment and deformations. As a result, the monolithic flexure and the pulleys attached to it will swivel and eventually slip away from the belt. To avoid this unstable behaviour the stiffness of the monolithic flexure against deformations parallel to the rotation axis is to be increased.

OBJECTIVE OF THE INVENTION

[0010] We propose a solution where additional flexure(s) in the form of a thin sheet is introduced. The deforming geometry of the flexure is approximately along the rotation axis and is attached to the fixed frame and the monolithic flexure at either ends. This preserves the compliance of the device in the selective degree(s) of freedom, but significantly increase the stiffness in the desired degrees of constraint without increasing the axial space occupied by the monolithic flexure.

SUMMARY OF THE INVENTION
[0011] The invention describes a tensioner system comprising of a Monolithic Flexure (MF) that is attached to an external frame, additional Flexure Element(s) in form of a thin sheet with edge-view containing the rotation axis of the flexure, connecting the Monolithic Flexure (MF) and external frame, two tensioner pulleys which engage with the slack and taut side of the belt respectively, the tensioner pulleys are connected to the Monolithic Flexure (MF), a design of the Flexure Element(s) that preserve the rotational capacity of the Monolithic Flexure thus enabling the tensioner pulleys to rotate together about the frame in excess of 10 degree, and a design of the Flexure Element(s) that prevents the tensioner pulley from slipping away from the belt thus enhancing the stiffness of the Monolithic Flexure in the desired direction.

BRIEF DESCRIPTION OF DRAWINGS
[0012] Figure 1 shows an example of a Front End Accessory Drive along with the tensioner mounted on the MG.

[0013] Figure 2 shows an example of the tensioner described in the previous patent as well as the problem of pulleys tilting away from the belt under a particular use case.

[0014] Figure 3 shows an example of the flexure element introduced to resist the pulley tilt.

DETAILED DESCRIPTION OF EMBODIMENTS
[0015] Referring now to the drawings in detail, in Fig 1a and 1b, 1 indicates the engine crankshaft pulley on a representative FEAD while 2 and 3 would be pulleys for accessories such as water pump and air-conditioner. An idler pulley 6, for the belt drive system is also shown. The tensioner 8, is mounted on to the motor generator 4, such that it pushes the belt 7 in on both sides, thus increasing the belt wrap angle around the motor generator pulley 5. Another design possibility can be, as shown in Fig 1b, where the tensioner is placed circumferentially around the MG pulley 5, without increasing the axial extent of the FEAD. In both cases, there is clearance between the tensioner 8 and the MG pulley 5 so that the MG pulley 5 and belt 7 are free to move.

[0016] Figure 2a, describes one embodiment of the tensioner 8. Said tensioner, consists of two tensioner pulleys 13 and 14 mounted on the Monolithic Flexure 21 via arms 19 and 20 in the same axial extent. The Monolithic Flexure 21, contains two pulley bearing arms 11 and 12, which connect the tensioner pulleys 13 and 14, to the rotating stage 10. The tension in the belt wrapping around the tensioner pulleys 13 and 14 applies a net force 15 and 16, outwards on individual pulleys. The pulley bearing arms 11 and 12 can flex in/out by deforming on the application of force, thereby increasing/decreasing the separation distance between the tensioner pulleys 13 and 14. In steady running, the force due to the pulley bearing arms and the force due to belt tension on the tensioner pulleys are in equilibrium. The Monolithic Flexure 21, also contains a fixed stage 9 that is fixed to the motor housing through the mounting holes 22.

[0017] The rotating stage 10 is connected to the fixed stage 9 through a designed series of thin sections (called flexures), 17, 18. The rotation of stage 10 w.r.t to the fixed stage 9 is achieved by a special arrangement of flexures 17, 18 such that the net deformation of stage 10 is a rotation without significant translation about a desired fixed point on the MG frame. Moreover, these flexures are designed such that stage 10 exhibits a low rotational compliance (<1Nm/rad) i.e. any rotation of stage 10 requires the application of only a small proportional external moment on the same.

[0018] The deforming geometry of the flexures 17, 18 can be described in a principal plane 23, perpendicular to the rotation axis 24. Thus, any forces or moments that create displacement of the rotating stage 10 (and consequently bearing arms 11, 12 and pulleys 13, 14) perpendicular to the principal plane will be resisted only by the stiffness of the flexures 17, 18 in the same direction. This stiffness is proportional to the extruded length of the flexures. Due to the limited axial space available on top of the motor generator 4, the extruded length will be approximately equal to the width of the belt 7. The achievable stiffness of the rotating stage 10 against deformations perpendicular to the principal plane 23 is thus limited.

[0019] Figure 2b, 2c, describes a situation where the resultant 26 of the tension forces 17, 18, is offset from the principal plane 23 and towards the mounting holes 22. In such a case the moment generated will cause the rotating stage 10 perform a swivel motion 27 out of the principal plane 23, and further increase the offset of the belt from the principal plane and thus increasing the moment, till the pulleys 13, 14 slip out of the belt 7.

[0020] A flexure element 25, in the form of a thin sheet, is attached to the rotating stage 10 of the monolithic flexure 21 at one end, as shown in figure 3a. The other end is attached to the motor generator 4. The flexure element is arranged such that it is stiff to deformations perpendicular to the principal plane. This is achieved by keeping the deforming geometry of the flexure element 25, approximately parallel to the rotation axis 24. Any deformation of the rotating stage normal to the principal plane 23, shown in figure 3b, would cause a change in the length of the deforming geometry of the flexure element 25, against which the flexure element can generate a large resisting force. This will prevent the out-of-plane swivelling 27 of the pulleys 13, 14 away from the belt 7, as shown in figure 3c.

[0021] In figure 3c, the edge-view of the thin-sheet of flexure 25 aligns with the rotation axis 24 and perpendicular to the principal plane 23, thus permitting the flexure element to be complaint to rotational deformations in the principal plane 23 about the rotation axis 24.