Tensioners for internal combustion engine accessory drives

Abstract

A tensioner for a belt drive of a motor vehicle engine, comprising: a fixed component configured to be constrained to the engine and provided with a pin defining a rotation axis; an arm having a hub portion hinged on the pin and rotatable about the axis and an end portion rotatably supporting a pulley, the pulley being configured to cooperate with a drive belt; a main spring interposed between the fixed component and the arm to exert a thrust on the arm, thereby rotating the arm toward the belt; at least one rolling bearing, supporting the arm on the pin; and a pair of damping devices, the pair of damping devices exerting opposite actions on the arm, thereby minimizing the load on the bearings.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the priority of Italian Patent Application No. 102019000011160, filed on July 8, 2019, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a tensioner for a belt drive and, in particular, but not exclusively, to a tensioner for an accessory drive of an industrial vehicle.

[0004] As is known, a tensioner for an accessory drive comprises a fixed part configured to be fixed to the engine and defining a rotating pin; an arm rotatably supported on the rotating pin and carrying a pulley at one end thereof, the pulley being designed to cooperate with a drive belt; and a spring acting on the arm to tension the belt. Background Art

[0005] Known tensioners of the type described above must meet certain basic requirements designed to optimize the life of the tensioner and the belt. In particular, the arm must remain in perfect alignment, that is, it must rotate in a plane orthogonal to the pin axis and not be subject to out-of-plane vibrations that would cause noise, premature wear, and, most likely, belt disengagement.

[0006] The alignment function is usually fulfilled by one or more bushings made of plastic or composite material, which have the function of a plain bearing for radially and axially supporting the arm on the pin.

[0007] The bushing is susceptible to wear; therefore, the tensioner has a limited life span, which is shorter than the life span of the vehicle.

[0008] WO 2015 / 092718 A1 describes a tensioner in which, in order to extend their service life, the bushings are replaced by rolling bearings. In the tensioner described therein, arm vibrations are damped by a C-shaped spring which exerts a tilting moment on the arm which must be balanced by the bearing.

[0009] The object of the present invention is to provide a tensioner of the above-mentioned type, which is provided with an improved damping system which optimizes the load conditions of the bearings. Summary of the Invention

[0010] The above objects are achieved by a tensioner for a belt accessory drive of a motor vehicle engine, the tensioner comprising:

[0011] - a fixing member comprising a base configured to be fixedly secured relative to the engine and a pin defining an axis of rotation;

[0012] - an arm having a hub portion hinged on a pin and rotatable about an axis and an end portion rotatably supporting a pulley configured to cooperate with a transmission belt;

[0013] - a coil spring interposed between the fixed part and the arm to exert a thrust on the arm so as to cause said arm to rotate towards the belt;

[0014] - at least one rolling bearing, at least one rolling bearing interposed between the arm and the pin; and

[0015] - a damping member for damping vibrations of the arm around the pin,

[0016] Characterized in that the damping member comprises a first damping device and a second damping device which exert opposite axial actions on the arm and comprise respective spring elements which exert axial loads in mutually opposite directions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] For a better understanding of the present invention, preferred embodiments are described below by way of non-limiting examples with reference to the accompanying drawings, in which:

[0018] Figure 1 is a perspective view of a tensioner according to the present invention;

[0019] Figure 2 It is along Figure 1 A cross-sectional view of the tensioner taken along line II-II in FIG.

[0020] Figure 3 yes Figure 1 Exploded perspective view of the tensioner. DETAILED DESCRIPTION

[0021] With reference to the drawings, reference numeral 1 generally designates a tensioner for an accessory drive of an industrial vehicle.

[0022] The tensioner mainly includes:

[0023] A fixing component 2, the fixing component 2 being designed to be fixed to a vehicle engine;

[0024] An arm 3 rotatable about an axis A relative to the fixed component 2 ;

[0025] a pulley 4 rotatably carried by the arm 3 at its end 9 and designed to cooperate with a belt (not shown); and

[0026] A coil spring 5 is secured at respective ends (in a known manner and not shown) to the fixed part 2 and the arm 3 to exert a spring load on the arm 3 , thereby urging the pulley 4 into contact with the belt and maintaining a predetermined tension thereon.

[0027] More specifically, the fixing member 2 comprises a base plate 6 designed to rest on an engine surface, and a substantially hollow cylindrical pin 7 having an axis A, driven into a central hole 8 of the base plate 6 and extending cantilevered therefrom.

[0028] The fixing member 2 is designed to be fixed to the engine by means of screws (not shown) installed through the pins 7 .

[0029] The arm 3 comprises a hub portion 10 opposite the end 9 carrying the pulley 4 , the hub portion 10 having a substantially hollow cylindrical shape and comprising an outer wall 11 and an inner wall 12 forming between them an annular cavity 13 open towards the base plate 6 .

[0030] The arm 3 is supported on the fixed part 2 by a pair of rolling bearings 14 and 15, preferably ball bearings, interposed radially between the inner wall 12 of the hub portion 10 of the arm 3 and the pin 7. Conveniently, each of the bearings 14, 15 has an inner ring 16 driven onto the pin 7 and an outer ring 17 driven into the inner wall 12; the two inner rings 16 and the two outer rings 17 are axially adjacent to each other.

[0031] The inner ring 16 of the bearing 14 is in axial abutment with the annular shoulder 19 of the base plate 6 surrounding the pin 7, and the inner ring 16 of the bearing 15 is in axial abutment with the annular shoulder 20 of the pin 7 near its free end 21; the outer ring 17 of the bearing 15 is in axial abutment with the inner annular shoulder 24 of the inner wall 12, and the outer ring 17 of the bearing 14 is held axially against the outer ring 17 of the bearing 15 by an elastic ring 25, which is housed in an inner seat 26 located at one end of the inner wall 12.

[0032] According to the invention, the tensioner 1 comprises a first damping device 27 and a second damping device 28 , with axial action, interposed between the fixed part 2 and the arm 3 , for damping the vibrations of the arm 3 .

[0033] According to the example shown, first damping device 27 is housed in a compartment axially bounded by a head surface 30 of the outer wall 11 of the hub portion 10 of arm 3 (hereinafter referred to as "surface 30 of arm 3 for the sake of simplicity") and a peripheral edge 31 of base plate 6, radially outwardly bounded by a cylindrical axial projection 32 at the end of outer wall 11, and inwardly bounded by an annular axial projection 33 of base plate 6. First damping device 27 essentially comprises a first damping ring 34, which is arranged in axial abutment against surface 30 of arm 3, with the possibility of relative sliding, and a first coil spring 35, which rests axially against peripheral edge 31 of base plate 6 and generates a predetermined axial load on first damping ring 34, which is designed to remain against surface 30 of arm 3. Conveniently, to prevent premature wear of first damping ring 34, a first metal washer 36 is interposed between first damping ring 34 and first coil spring 35.

[0034] The second damping means 28 are axially comprised between the shoulder 24 of the inner wall 12 and an end cap 37 fixed on the free end 21 of the pin 7 , abutting against the shoulder 20 , by pressing the pin.

[0035] The second damping device 28 mainly comprises a second damping ring 38, which bears axially against the shoulder 24, and a second coil spring 39, which bears axially against the end cap 37 and generates an axial load on the second damping ring 38. Conveniently, in order to avoid premature wear of the second damping ring 38, a metal washer 40 is interposed between the second damping ring 38 and the second coil spring 39.

[0036] To achieve the most consistent damping possible, the friction between the damping rings 34, 38 and the corresponding surfaces of the arm 3 should be as low as possible. A suitable material for the damping rings 34, 38 is a PA46+PTFE-based thermoplastic material, such as Stanyl® TW371 from DSM Engineering Plastics BV. Lubricant is preferably applied between the rings and the corresponding surfaces of the arm in relative sliding contact to reduce the coefficient of friction. The optimal coefficient of friction is between 0.1 and 0.2.

[0037] The coil spring 5 is subjected to a combination of torsional and compressive loads in use and therefore exerts an axial thrust tending to axially separate the arm 3 from the base plate 6. Conveniently, the spring loads exerted in use by the first and second coil springs 35, 39 are different so as to balance the axial thrust exerted by the coil spring 5. In particular, the axial load exerted by the first coil spring 35, corresponding to the axial load of the coil spring 5, is lower than the axial load exerted by the second coil spring 39, so that during installation of the tensioner 1, no axial load corresponding to the moderate load of the coil spring 5 is exerted on the bearing 14.

[0038] Finally, the tensioner 1 comprises a first annular sealing element 41 and a second annular sealing element 42, which are designed to protect the respective damping means 27, 28 from any penetration of dust from the outside. The first sealing element 41 is interposed between the base plate 6 and the cylindrical axial projection 32 of the outer wall 11; the second sealing element 42 is interposed between the inner wall 12 and the peripheral flange 43 of the end cap 37.

[0039] The operation of the tensioner 1 is as follows.

[0040] The arm 3 is supported on the pin 7 in an angularly free manner by bearings 14 , 15 and is subject to the elastic load of the coil spring 5 and the tension of the belt (not shown).

[0041] Due to the variations in the tension of the belt, the arm oscillates about the pin 7. The bearings 14, 15 ensure that the arm 3 rotates parallel to a plane perpendicular to the axis A of the pin 7.

[0042] Under the axial load of the coil springs 35 , 39 , the vibration of the arm 3 caused by the belt tension variation is damped by the relative sliding of the damping rings 34 , 38 and the corresponding surfaces of the arm 3 .

[0043] The purely axial action of the disc springs 35 , 39 not only allows for better damping control but also eliminates any tilting moments on the bearings 14 , 15 .

[0044] Furthermore, since the axial loads of the coil spring 5 and the disc springs 35 and 39 are balanced with each other, the bearings 14 and 15 only bear the hub load caused by the belt transmission.

[0045] Optimization of the load conditions of the bearings extends their life. The tensioner is therefore suitable for "lifetime" applications, where replacement is not scheduled during the service life of the vehicle.

Claims

1. A tensioner for a belt accessory drive of a motor vehicle engine, comprising: a fixed component (2) comprising a base plate (6) configured to be fixedly secured relative to the engine and a pin (7) defining an axis of rotation (A); an arm (3) having a hub portion (10) hinged on the pin (7) and rotatable about the axis (A) and an end portion (9) rotatably supporting a pulley (4), the pulley (4) being configured to cooperate with a drive belt; a coil spring (5) interposed between the fixed part (2) and the arm (3) to exert a thrust on the arm (3) so as to cause the arm to rotate toward the belt; at least one rolling bearing (14, 15) interposed between the arm (3) and the pin (7); as well as a damping member (27, 28) for damping vibrations of the arm (3) around the pin (7), Characterized in that the damping member comprises a first damping device (27) and a second damping device (28), the first damping device (27) and the second damping device (28) exerting opposite axial actions on the arm (3) and respectively comprising spring elements (35, 39) exerting axial loads in directions opposite to each other.

2. The tensioner according to claim 1, characterized in that The axial action of the spring element (35, 39) and the axial action of the coil spring (5) balance each other in order to minimize the axial load on the at least one rolling bearing (14, 15).

3. The tensioner according to claim 1, characterized in that The first damping device (27) and the second damping device (28) respectively comprise a damping ring (34, 38), which cooperates with the corresponding surface of the arm (3) in a sliding manner under the action of the corresponding spring element (35, 39).

4. The tensioner according to claim 1, characterized in that The spring elements (35, 39) are coil springs.

5. The tensioner according to claim 1, characterized in that The hub portion (10) comprises a cylindrical outer wall (11) and a cylindrical inner wall (12), defining an annular cavity (13) therebetween for accommodating the coil spring (5), and the at least one rolling bearing (14, 15) is radially arranged between the pin (7) and the cylindrical inner wall (12).

6. The tensioner according to claim 5, characterized in that The first damping means (27) is arranged between the base plate (6) and the head surface (30) of the cylindrical outer wall (11), and the second damping means (28) is arranged between an end cap (37) integral with the pin (7) and an inner shoulder (24) of the cylindrical inner wall (12).

7. The tensioner according to claim 6, characterized in that The at least one rolling bearing is in axial adjoining relationship with the inner shoulder.

8. The tensioner according to claim 5, characterized in that An annular sealing element (41, 42) is included, which is configured to protect the respective first damping device (27) and the second damping device (28) from dust contamination.

Images