WO2018096485A1

WO2018096485A1 - Clamping device for tensioning of belts incorporating flexures

Info

Publication number: WO2018096485A1
Application number: PCT/IB2017/057366
Authority: WO
Inventors: Nilanjan Sen; John BANGURA; Sudipto Mukherjee; Sandeep Bhat; Amitabh Saran
Original assignee: Altigreen Propulsion Labs Private Limited
Priority date: 2016-11-24
Filing date: 2017-11-23
Publication date: 2018-05-31

Abstract

The present invention describes a clamping device and a tensional system wherein the pulley bearing arms, rotational bearing and spring are all merged into a single contiguous element (to be called the Monolithic Flexure) which allows a smaller design envelope while achieving the performance characteristics desired of belt 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. The use of this monolithic-flexure based clamping device, as a belt tensioner, is one embodiment of this design. 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.

Description

CLAMPING DEVICE FOR TENSIONING OF BELTS INCORPORATING

FLEXURES

FIELD OF INVENTION

[0001] The present invention relates to a clamping device comprising single contiguous element which can be used as a belt tensioner achieving the performance characteristics desired of belt tensioners.

BACKGROUND OF THE INVENTION

[0002] A conventional accessory drive system consists of a single belt wrapped around a set of pulleys mounted on accessory units such as the alternator, water pump and air conditioning unit all driven by a pulley connected to the engine crankshaft.

[0003] Belt starter alternator systems have become increasingly popular over the last decade. They support additional functions such as engine start, brake regeneration and boost operation thus increasing the efficiency / fuel economy of the engine. Such systems differ from conventional accessory drive systems because the drive torque does not always come from the engine, which is at times driven by a motor generator unit (hereby known as MG). During normal operation, the engine crankshaft provides torque for rotating the MG unit, or starter generator, providing taut and slack sides of the belt on opposite sides of the MG pulley. During engine starting or boosting operation, the MG unit transfers power to the system causing the slack and taut sides of the belt to switch positions.

[0004] In conventional accessory drive systems and belt starter alternator systems, a tensioner serves to maintain a specified minimum tension in the belt in the face of geometric and temperature variations. The tensioner also maintains the angle of wrap of the belt around target pulleys. For a belt starter alternator system, during torque reversal, the side of the belt which is under low tension changes and hence special systems are required. The assembly of a conventional accessory drive system or a belt alternator system along with the tensioner(s) is hereby referred to as a Front End Accessory Drive (FEAD). [0005] To accommodate torque reversal for a belt starter alternator system, two belt tensioners are required to engage the belt on opposite sides of the MG pulley. Two mechanical belt tensioners working independently of each other are in use in systems such as the Saturn VUE hybrid which utilizes a dual tensioner described in Patent Application Publication US20060287146.

[0006] An alternative design, which uses two tensioners (pulley and arm) fixed to a frame that can swivel about an axis of rotation (which may coincide with MG axis of rotation), have been developed by Schaeffler (US20150369347A1), Mubea, Bayer Motor Works (Patent EP1420192A2) and others. All of these designs incorporate a bearing which allows the tensioner frame to swivel about the axis of rotation, a discrete spring (embodied as an arc/torsion/curved-leaf spring) to provide the tensioning force on the belt via the tensioner pulleys and pulley bearing arms which connect the tensioner pulleys to the rotational bearing. [0007] A limitation of the existing designs is that the entire assembly of independent pulley bearing arms, rotational bearing and spring necessitate a large space for the tensioner which may or may not be available inside the FEAD.

[0008] We propose a solution where the pulley bearing arms, rotational bearing and spring are all merged into a single contiguous element (to be called the Monolithic Flexure) which allows a smaller design envelope while achieving the performance characteristics desired of belt 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. The use of this monolithic-flexure based clamping device, as a belt tensioner, is one embodiment of this design.

[0009] 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.

SUMMARY OF THE INVENTION [0010] The invention describes a tensioner system comprising of the following:

1. A Monolithic Flexure (MF) that is attached to an external frame.

2. Two tensioner pulleys which engage with the slack and taut side of the belt respectively. 3. The tensioner pulleys are connected to the Monolithic Flexure (MF).

4. A design of the MF that enables the tensioner pulleys to rotate together about the frame in excess of 10 degrees, thus performing the function of a rotational bearing over a limited range.

5. A design of the MF such that the distance separating the tensioner pulleys can change on application of force, thus performing the function of the spring element for the tensioner.

BRIEF DESCRIPTION OF THE DRAWINGS [0011] Figure 1 shows an example of a Front End Accessory Drive along with the tensioner mounted on the MG.

[0012] Figure 2 shows two examples of the tensioner using two types of flexures. DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring now to the drawings in detail, in Fig la and lb, 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 lb, 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.

[0014] The tensioner 8, consists of two tensioner pulleys 13 and 14 mounted on the Monolithic Flexure 21 (as in Fig 2a), or connected to it via arms 19 and 20 (in Fig 2b) 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 outward 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.

[0015] As fabricated, the tensioner 8 is designed such that the tensioner pulleys 13 and 14 are closer to each other than in operation. During installation, the pulley bearing arms 11 and 12 are pushed outwards to increase the gap between the tensioner pulleys 13 and 14, to allow installation with the belt 7 as shown in Fig lc. In the figure, the dotted lines show the deformed, outward positions of the pulley bearing arms 11 and 12 and the corresponding positions of the tensioner pulleys 13 and 14. The pulley bearing arms thus clamp back on the belt 7 providing the designed pre-tension in the belt. The belt wrap angle around the MG pulley 5 is thus enhanced.

[0016] When the engine crankshaft pulley 1 is providing the drive torque, while running in the clockwise direction, the belt section running from pulley 1 to MG pulley 5 via pulley 6 will be slack and have lower tension compared to the belt section running from MG pulley 5 to engine crankshaft pulley 1 via pulleys 2 and 3. The taut side of the belt will then push more on the tensioner pulley 13 than the slack side will push on pulley 14. The rotating stage 10 of the tensioner 8 is designed to swivel in direction of the net moment and moves counter clockwise. Tensioner pulley 14 thus achieves the designed function of increasing tension of the slack side of the belt. The rotating stage 10 continues to swivel until there is an equilibrium between the forces on the tensioner pulleys.

[0017] When the MG pulley 5 is providing the driving torque the above described mechanism is reversed. The slack and taut sides of the belt get reversed and the rotating stage 10, swivels clockwise to tension the slack side and arrive at a force equilibrium.

[0018] The rotating stage 10 is connected to the fixed stage 9 through a designed series of thin sections (called flexures), 15, 16, 17 in Fig 2a, including curved beam sections, 18 in Fig 2b. In both cases 2a and 2b, rotation of stage 10 w.r.t to the fixed stage 9 is achieved by a special arrangement of flexures 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 (<lNm/rad) i.e. any rotation of stage 10 requires the application of only a small proportional external moment on the same. This is achieved by either increasing the length of the flexure, reducing the thickness of the flexure or using a material of lower stiffness.

[0019] The tensioner pulleys 13 and 14, by a special design of flexures, are allowed to swivel/move in the plane perpendicular to the MG axis of rotation while balancing the changes in tension of the belt 7. However, it is possible that there are external forces/ moments which can cause the tensioner pulleys 13 and 14 to move in/out of the working plane. These external forces/moments can come from external vibrations, improper assembly or other causes. It is therefore desirable that the flexures also provide stiffness against these forces. In the design shown in Fig. 2a, flexure pairs 15 and 16 are placed some distance apart, thereby increasing the stiffness against any undesirable translation or rotation of the tensioner pulleys out of the working plane of the pulleys.

Examples

1. A tensioner with designed series of locally thinned sections (flexure elements), configured to allow specific motion of the tensioner through elastic deformation.

• The flexure elements permit a rotation of atleast +/- 10 deg. The rotational compliance of the flexure elements along the desired rotation axis is less than 1 Nm/deg.

• The flexure elements can be of several geometries, including but not limited to a straight leaf flexure and a curved beam flexure.

2. A tensioner which in addition to the aforementioned elastic action can also be guided by slide/roll of surfaces in contact.

3. A tensioner with pulley bearing arms extended from the main body to push the tensioner pulleys against the belt and acting as the spring by elastic action. The pulley bearing arm can be made of any deformable solid material including but not limited to: • Steel/ Aluminium flexure(s) in series with solid steel/aluminium arm(s) where the flexure acts as the spring.

• Plastic flexible arm where the entire length flexes elastically and acts as a spring. 4. A tensioner with designed series of flexure elements configured to resist undesirable motions i.e. any rotation/translation that forces the tensioner pulleys out of the plane normal to the MG axis of rotation. The geometric arrangement of the said flexures are designed to provide stiffness against out of the plane forces. 5. A tensioner which operates purely by the mechanism of flexure. The flexure mechanism can also be an assembly of smaller flexure mechanisms each of which are designed to perform one or more of the aforementioned functions of the tensioner.

6. Said flexure mechanism can be monolithic. The flexure mechanism is made as a single contiguous block by EDM, waterjet cutting, laser cutting, 3D printing or other means.

7. A tensioner which can be bolted/pinned to a fixed frame on the belt system for easy assembly. The stationary stage of the flexure design is bolted/pinned to the fixed frame via designed mounting points such that the translating/rotating parts are free to move.

8. A tensioner with designed series of flexure elements configured to allow slight adjustments during assembly. There can be geometric variances, caused by manufacturing/assembly errors, in the mounting points on the fixed frame. The flexures therefore allow for compensating adjustments during assembly.

9. A tensioner designed to be compact (<160 mm dia.) for easy-fitting in congested spaces. Such a small design envelope is only possible by removing the individual elements (such as the tensioner arms, spring, rotational bearing) of the tensioner and combining their functionality into a single structure.

10. A tensioner which fits circumferentially around the MG pulley, i.e. it can be assembled on to the MG without increasing the length of the assembly along the MG rotation axis. 11. A tensioner which responds instantaneously to a switch in operation in the FEAD, quickly adjusting its angular position about the MG axis, to balance the difference in belt tension about the MG pulley.

12. A tensioner consisting of plastic flexure elements, therefore possessing significant self- damping properties. Because of the visco-elastic nature of plastic materials, the tensioner does not suffer from excessive vibrations during operation.

Claims

CLAIMS:

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 22 and a plurality of curved and straight surfaces, to be called the "fixed component" 9; b. a 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" 10; wherein:

said flexure elements are configured to allow said movable component to rotate, relative to said fixed component, about an axis 24 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).

2. The clamping device as claimed in claim 1, 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.

3. The clamping device as claimed in claim 1, wherein said flexure elements are configured to restrict the movement of said movable component in other spatial directions, excluding in-plane rotation, relative to said fixed component.

4. The clamping device as claimed in claim 1, wherein said flexure elements are configured to allow adjustment of said fixation holes 22 relative to each other.

5. The clamping device as claimed in claim 1, wherein said movable component 10, occupies the same axial length, along said rotation axis 24, as said fixed component 9.

6. The clamping device as claimed in claim 1, wherein said pair of clamping arms on movable component, comprising: a. a pair of designed continuous portions 11, 12 with a plurality of straight and curved surfaces; b. an intermediate portion 23, located between said pair of continuous portions, that includes a plurality of curved and straight surfaces; wherein:

said continuous portions are designed for symmetrical stiffness, relative to said intermediate portion, in a plane normal to the axis 24 of said rotation of said movable component; said continuous portions are each designed with a pair of concave 25 and convex 26 surfaces, perpendicular to said plane, to allow designed deflection in said continuous portion within the elastic load limit of the material; said deflection provides a clamping force on the interacting body(s) with which said clamping-arms are in contact.

7. The clamping device as claimed in claim 6, wherein said continuous portions are designed with said pair of concave and convex surfaces such that the shortest chord joining said surfaces is monotonically increasing in the direction of said intermediate section 23.

8. The clamping device as claimed in claim 6, wherein said continuous portions are designed to resist deflection parallel to axis 24 of said rotation.

9. A belt tensioner comprising of the clamping device wherein: said clamping arms have attached pulleys 13, 14; said clamping-arms provide force on different section of a belt 7 via the attached pulleys; and said rotation adjusts against belt movement caused by differences in tension in said belt sections.

10. The belt tensioner as claimed in claim 9, wherein said movable component 10 executes in- plane rotation about the fixed component 9 till the curved (or straight) surface(s) of said movable component meshes with the curved (or straight) surface(s) of said fixed component thereby restricting further rotation.

11. The belt tensioner as claimed in claim 9, wherein said flexure elements are configured to restrict the movement of said movable component in other directions, excluding in-plane rotation, relative to said fixed component.

12. The belt tensioner as claimed in claim 9, wherein said flexure elements are configured to allow adjustment of said fixation holes 22 relative to each other.

13. The belt tensioner as claimed in claim 9, wherein said movable component 10 and pulleys 13, 14 occupy the same axial length, along said rotation axis 24, as said fixed component 9.

14. The belt tensioner as claimed in claim 9, including the pair of arms on said moving component, comprising: a. a pair of designed continuous portions 11, 12 with a plurality of straight and curved surfaces; b. an intermediate portion 23, located between said pair of continuous portions, that includes a plurality of curved and straight surfaces; c. a pair of pulleys 13, 14 each affixed to one end of the continuous portions, furthest away from said intermediate portion; wherein:

said continuous portions are designed for symmetrical stiffness, relative to said intermediate portion, in a plane normal to the axis 24 of said rotation of said movable component; said continuous portions are each designed with a pair of concave 25 and convex 26 surfaces, perpendicular to said plane, to allow designed deflection in said continuous portion within the elastic load limit of the material; said deflection provide the clamping force on external belt 7 via the pulleys.

15. The belt tensioner as claimed in claim 14, wherein said continuous portions are designed with said pair of concave and convex surfaces such that the shortest chord joining said surfaces is monotonically increasing in the direction of said intermediate section.

16. The belt tensioner as claimed in claim 14, wherein said continuous portions are designed to restrict deflection of the pulleys parallel to axis 24 of said rotation.