Tensioner with dual damping system for belt drive

Abstract

Tensioner comprising a fixed part (2) provided with a pivot (4) defining an axis (A), an eccentric arm (5) rotatably mounted on the pivot (4) about the axis (A), a pulley (6) rotatable about an axis (B) defined by the arm (5) and configured to cooperate with a timing belt, a first spring-damper assembly (7) interposed between the arm (5) and the fixed part (2), and a second spring-damper assembly (11) configured to act between the arm (5) and the fixed part (2) starting from a predetermined angle of rotation of the arm (5) with respect to the fixed part (2).

Description

[0001] Cross-references to related applications

[0002] This patent application relates to Italian patent application No. 102021000014756, filed on June 7, 2021, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to a tensioner for a belt drive device in a motor vehicle, particularly for a timing system. Background Technology

[0004] A known tensioner includes a fixed portion with a pivot, a movable arm rotatably mounted on the pivot, and a pulley carried by the movable arm and intended to engage with a belt. In the case of a tensioner for a timing belt, the movable arm typically includes an eccentrically pivotally mounted element that houses a spring. A damping element, typically defined by a bushing, is also present between the fixed portion and the movable arm to dampen oscillations of the movable arm.

[0005] "Installation position" is defined as the maximum deviation between the arm and the belt, in which case the arm can be easily installed, while "nominal position" is defined as the static balance of the tensioner under nominal conditions under the elastic force of the spring and belt.

[0006] Typically, tensioners dampen vibrations symmetrically, meaning they exhibit substantially equal hysteresis cycles during the loading and unloading phases of the tensioner. A limitation of such tensioners is the requirement for a certain angular distance between the nominal and installed positions to allow for belt mounting. However, in some boom drives, it is necessary to limit the angular displacement of the boom toward the installed position during operating conditions to keep the boom below a certain angle and prevent belt tooth skipping. In known tensioners, this can be achieved using a one-way clutch positioned between the boom and the fixed part of the tensioner. This necessitates additional components.

[0007] The purpose of this invention is to provide a tensioner that can overcome the above-mentioned problems. Summary of the Invention

[0008] The above objective is achieved by a tensioner. The tensioner includes: a fixed part having a pivot defining an axis (A); an eccentric arm rotatably mounted on the pivot about the axis (A); a pulley rotatable about an axis (B) defined by the arm and configured to engage with a timing belt; a first spring-damper assembly disposed between the arm and the fixed part; and a second spring-damper assembly configured to act between the arm and the fixed part starting from a predetermined angle of rotation of the arm relative to the fixed part.

[0009] The tensioner according to the invention is characterized by a dual-damping system, wherein a second asymmetric damping system provides a virtual stop to the arm in the direction toward the installation position after the nominal position. The tensioner allows manual rotation of the arm until the installation position is reached. However, during engine operating conditions, the tensioner only allows a predetermined amount of arm angular displacement in the direction opposite to the belt tensioning direction. Attached Figure Description

[0010] To better understand the present invention, preferred embodiments are described below by way of non-limiting examples and with reference to the accompanying drawings, wherein:

[0011] - Figure 1 This is an axial sectional view of the tensioner according to the present invention;

[0012] - Figure 2 yes Figure 1 Exploded perspective view of the tensioner;

[0013] - Figure 3 , Figure 4 , Figure 5 yes Figure 1 Partial cross-sectional views of the tensioner in various operating positions; and

[0014] - Figure 6 It is a graph showing the torque of the tensioner as the rotation angle of the tensioner arm changes. Detailed Implementation

[0015] refer to Figure 1 , Figure 1 A tensioner, indicated by 1, is manufactured according to the present invention and is applicable to the timing system of an engine. The tensioner 1 includes: a fixing part 2, the fixing part 2 being provided with a base 3 and a pivot 4 fixed relative to the base 3 and defining an axis A; an eccentric arm 5, the eccentric arm 5 being rotatable about the pivot 4; and a pulley 6, the pulley 6 being rotatable about an axis B defined by the arm 5 and configured to engage with a timing belt (not shown).

[0016] The tensioner 1 further includes a first spring-damper assembly 7 and a second spring-damper assembly 11 disposed between the fixed part 2 and the arm 5, as will be further described below. In this specification, a “spring-damper assembly” is defined as an assembly that includes an elastic element (such as a spring) and a damping element (such as a bushing) that work together.

[0017] The base 3 is essentially an annular plate with an axis A. The base 3 has a first annular protrusion 12 at its inner annular edge and a second annular protrusion 13 extending in an axial direction at its outer annular edge. A pivot 4 is mounted within the first annular protrusion 12 and, together with the base 3, defines a fixing portion 2, which is easily secured to the engine by a screw (not shown) passing through the axis A of the pivot 4, and a protrusion 14, which extends from the base 3 in an axial direction opposite to that of the protrusions 12 and 13 and is easily engaged with a seat present in the engine.

[0018] The first spring-damper assembly 7 includes a main spring 15 positioned between the fixed part 2 and the arm 5, and a damping bushing 16.

[0019] Arm 5 includes an eccentric portion 17, which is rotatably mounted on the end of pivot 4 opposite to base 3 via damping bushing 16, and has an inner cylindrical A-axis surface in radial contact with damping bushing 16 and an outer cylindrical B-axis lateral surface on which pulley 6 is mounted via bearing 21.

[0020] Arm 5 further includes a bell-shaped portion that opens toward and faces the base 3, the bell-shaped portion being connected to the eccentric portion 17 via a radial annular intermediate wall 22. The bell-shaped portion and the base 3 define a chamber 23.

[0021] The main spring 15 is a helical torsion spring, such as a helical torsion spring with a circular cross-section. The helical torsion spring is coaxially housed in the chamber 23 and axially positioned between the base 3 and the intermediate wall 22 of the arm 5. The main spring 15 includes a radially oriented first end 24 and a second end 25. The first end 24 of the main spring 15 engages in the radially penetrating seat 18 of the second annular protrusion 13 of the base 3. The second end 25 of the main spring 15 engages in a radially through-hole (not shown) in the bell-shaped portion of the arm 5.

[0022] The second spring-damper assembly 11 is axially housed in a chamber 23 between the base 3 and the intermediate wall 22 of the arm 5 and radially between the pivot 4 and the main spring 15. The second spring-damper assembly 11 includes a fixed housing 26, a second spring 27, and a bushing 31.

[0023] The housing 26, forming part of the fixing part 2, is cup-shaped and includes an annular base portion 28 and an outer A-axis tubular wall 30. The annular base portion 28 is fitted onto the pivot 4 and rigidly connected to the base 3, for example, by engaging a corresponding seat of the base portion of the housing 26 through an axial protrusion 29 of the base 3. The outer A-axis tubular wall 30 extends axially from the base portion toward the intermediate wall 22 of the arm 5. The housing 26 can be made of various materials, such as plastic (possibly with internal metal inserts to increase mechanical strength), metal, or composite materials.

[0024] Bushing 31 is a conical damping bushing mounted on pivot 4 and includes a conical wall 39 and an annular end flange 40 extending radially outward from the conical wall 39. The conical wall 39 has a radially inward surface 32 and a radially outward surface 33. Surface 32 is in radial contact with the middle portion of pivot 4 and has a series of axial grooves 41. Surface 33 of bushing 31 is substantially conical, having a diameter decreasing from flange 40 toward the base portion 28 of housing 26, and is adapted to interact with the second spring 27. Bushing 31 is axially cut along one of its generatrices to be radially flexible. On the side opposite to the cut relative to axis A, bushing 31 has an axial protrusion 38, which is preferably provided with an axial groove 42 extending in the opposite direction relative to base 3 and received with an angular clearance within a circumferential groove 44 of arm 5.

[0025] The auxiliary spring 27 is a helical torsion spring, such as a helical torsion spring with a rectangular cross-section. The helical torsion spring is coaxial with the pivot 4 and mounted around the bushing 31, radially positioned between the conical wall 39 of the bushing 31 and the tubular wall 30 of the housing 26. The auxiliary spring 27 includes an axially pointing first end 34 and a second end 35. The first end 34 of the second spring 27 engages an axially pointing through-hole in the base portion 28 of the housing 26. The second end 35 of the auxiliary spring 27 engages an axial seat portion of the bushing 31, preferably in an axial groove 42 of the protrusion 38. The second spring 27 is mounted within the housing 26 with a radial preload.

[0026] The main spring 15 applies an elastic torque to the arm 5 so as to maintain the arm 5 in a “free arm” position defined by the contact between the protrusion 38 of the bushing 31 and the first end 45 of the groove 44 of the arm 5 itself when there is no load on the pulley 6.

[0027] Tensioner 1 ( Figure 2It further includes a locking pin 37 for locking the arm 5 in a mounting position relative to the "free arm" position, resisting rotation by the spring action of the main spring 15 and the auxiliary spring 27, as will be better described below. The locking pin 37 is received in the radial through-hole 43 of the arm 5 and holds the arm 5 in a fixed relative position to the base 3 in the mounting configuration of the tensioner 1.

[0028] Finally, the tensioner 1 includes a dust cover 36, which is axially positioned between one end of the arm 5 and the head of the pivot 4, and extends radially to protect the bearing 21.

[0029] The operation of the tensioner 1 is described starting from the "free arm" position defined by the contact between the protrusion 38 of the bushing 31 and the first end 45 of the groove 43, as described above. Figure 3 ).

[0030] As the belt load increases, arm 5 rotates towards the mounting position against the reaction torque of the main spring 15. The angular clearance connection between arm 5 and bushing 31 allows for rotational movement of arm 5 in the first part ( Figure 6 In segment a) of the curve diagram, only the first spring damping assembly 7 is involved. Specifically, the main spring 15 operates with a first slope defined by the stiffness of the main spring 15, and its elastic deformation increases linearly with the increase of the relative angle.

[0031] When a predetermined angle is reached, depending on the angular width of the groove 44, the arm 5 tangentially abuts against the protrusion 38 of the bushing 31 at the second end 46 of the groove 44. Figure 4 The stiffness 15 of the main spring is selected such that this condition corresponds to the nominal position of the tensioner 1, which is determined by balancing the action exerted by the main spring 15 and the belt under nominal conditions.

[0032] From this position onward, as the belt load increases, the second spring-damper assembly 11 also comes into play. Specifically, the auxiliary spring 27, which has a greater stiffness than the main spring 15, also comes into play. Because the auxiliary spring 27 is preloaded and it is necessary to overcome this preload, the curve ( Figure 6 The second section b is presented, which has a very high initial slope. The coil is detached from the tubular wall 30 while being compressed. As the number of coils increases and therefore as the free length of the auxiliary spring 27 increases, the slope gradually decreases until the auxiliary spring 27 is completely detached from the tubular wall 30.

[0033] As the relative angle increases further, bushing 31 rotates against the action of the two springs 15 and 27. Therefore, the curve ( Figure 6 The third segment c presents a slope defined by the sum of the stiffnesses of two springs 15 and 27 acting in parallel.

[0034] During its own compression, the auxiliary spring 27 gradually and smoothly winds around the bushing 31, thereby creating radial contact coil by coil. Due to its axial cutting, the bushing 31 is then gradually tensioned on the pivot 4. Thus, proportional radial damping is achieved between the bushing 31 and the pivot 4.

[0035] The behavior of tensioner 1 as the load applied by the belt changes has been described; it is now appropriate to describe its actual behavior in use.

[0036] Specifically, the installation of tensioner 1 on the engine occurs at the installation location ( Figure 5 The installation position is kept stable by locking pin 37.

[0037] After the belt is installed, locking pin 37 is pulled out, and arm 5 moves to its nominal position under the action of springs 15 and 27. Figure 4 ).

[0038] Under dynamic conditions, during engine operation, the two spring-damper assemblies 7, 11 achieve asymmetric damping of the movement of arm 5, depending on the direction in which such movement leaves the nominal position.

[0039] Specifically, when arm 5 rotates toward the "free arm" position, only the first spring-damper assembly 7 engages, and therefore the damping is determined solely by the damping bushing 16. Conversely, when arm 5 rotates toward the mounting position, the second spring-damper assembly 11 also engages, thus resulting in an increase in both the elastic stiffness and damping acting on arm 5.

[0040] refer to Figure 6 The asymmetric damping is evident, where the curves show the different hysteresis levels resulting from the different damping conditions described above.

[0041] The advantages of the present invention become clear when examining the characteristics of the tensioner 1.

[0042] Specifically, the tensioner 1 asymmetrically dampes the vibration of the arm 5. This is possible due to the second spring-damper assembly 11, which, due to the combination of the preloaded auxiliary spring 27 and bushing 31, creates a region with high stiffness and damping.

[0043] Furthermore, the preload of the auxiliary spring 27 is controlled by the housing 26. For the same auxiliary spring 27, the smaller the diameter of the tubular wall 30 of the housing 26, the smaller the outer diameter of the auxiliary spring 27, and therefore the greater its preload. Thus, the preload of the auxiliary spring 27 can be easily controlled by conveniently selecting the diameter of the housing 26 or the number of coils of the auxiliary spring 27.

[0044] This allows for the use (and therefore manufacture) of fewer parts compared to a tensioner with a one-way clutch.

[0045] Furthermore, during the movement of tensioner 1 from its nominal position to its installed position, tensioner 1 absorbs most of the energy from the belt due to the resistance torque generated by auxiliary spring 27. In this way, less energy will be retained by the frictional damping in bushing 31 to pivot 4, thereby reducing wear on bushing 31 and increasing its lifespan. This is advantageous compared to known one-way clutch systems, which suppress movement through friction rather than through spring reaction torque because the spring in a one-way clutch is not preloaded.

[0046] Furthermore, another advantage is that when the tensioner 1 is in the installed position or any position within the range between the installed and nominal positions and the belt load stops operating, the higher-stiffness auxiliary spring 27 engages with the main spring 15. This allows for increased kinetic acceleration, thus enabling the tensioner 1 to return to the nominal position more quickly compared to a one-way clutch system. In this situation, the one-way clutch will cease operation as it will only loosen the contact between the pivot and the bushing, and only the main spring will drive the tensioner from the installed position to the nominal position.

[0047] Finally, it is clear that modifications and variations can be made to the tensioner 1 without exceeding the scope of protection defined by the claims.

[0048] For example, the cross section 15 of the main spring is not circular and / or the cross section 27 of the auxiliary spring is not rectangular and is, for example, circular.

[0049] Furthermore, the auxiliary spring 27 has such high stiffness that it can achieve its purpose without preloading, or it can have a different number of coils.

Claims

1. A tensioner, the tensioner comprising: The fixing part (2) is provided with a pivot (4) that defines the axis A; eccentric An eccentric arm (5) rotatably mounted on the pivot (4) about axis A; a pulley (6) rotatable about axis B defined by the eccentric arm (5) and configured to engage with a timing belt; a first spring-damper assembly (7) disposed between the eccentric arm (5) and the fixed portion (2); and a second spring-damper assembly (11) configured to act on the eccentric arm (5) from a predetermined angle of rotation relative to the fixed portion (2). Between the fixed part (2), the second spring-damper assembly (11) includes: a bushing (31) rotatably mounted on the pivot (4) about the axis A; a spring (27) coaxial with the pivot (4), the spring (27) having a first end (34) constrained to the fixed part (2) and a second end (35) constrained to the bushing (31), the spring (27) acting torsionally between the fixed part (2) and the bushing (31), the eccentric arm (5) and the bushing (31) being connected to each other with an angular clearance.

2. The tensioner as claimed in claim 1, wherein, The spring (27) is preloaded and installed between the fixing part (2) and the bushing (31).

3. The tensioner as claimed in claim 1, wherein, The fixing part (2) includes a base (3) attached to the pivot (4) and a tubular outer shell (26) coaxial with the pivot (4) and attached to the base (3).

4. The tensioner as claimed in claim 1, wherein, The bushing (31) applies radial damping to the pivot (4).

5. The tensioner as claimed in claim 4, wherein, The bushing (31) is axially cut along its generatrix.

6. The tensioner as claimed in claim 3, wherein, The spring (27) is a helical spring that is radially interference-fitted inside the housing (26).

7. The tensioner as claimed in claim 6, wherein, The spring (27) has a first end (34) and a second end (35) that are respectively constrained to the fixing part (2) and the bushing (31) and are axially oriented.

8. The tensioner as claimed in claim 6, wherein, The spring (27) has a rectangular or circular cross-section.

9. The tensioner as claimed in claim 6, wherein, The bushing (31) has a conical outer surface adapted to interact with the spring (27).

10. The tensioner as claimed in claim 1, wherein, The connection between the bushing (31) and the eccentric arm (5) with an angular gap is defined by at least one protrusion (38), which extends from one of the bushing (31) and the eccentric arm (5) and loosely engages the circumferential seat obtained between the other of the bushing (31) and the eccentric arm (5).

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