Tensioner for an accessory drive of a motor vehicle and accessory drive comprising such a tensioner

Abstract

A tensioner for an accessory drive of an internal combustion engine (2), comprising a belt (8) at least on a first pulley (3) connected to a drive shaft (4) of the engine (2) and on a second pulley (5) connected to an electric motor (7), the tensioner comprising: a base (11) configured to be fixed to a housing (13) of the electric motor; a first ring (15) rotating with respect to the base (11) about a first axis (A1); a second ring (20) rotating with respect to the first ring (15) about a second axis (A2) different from the first axis (A1); a first tension pulley (23) carried by the first ring (15) and rotating with respect to it about its own axis (PA1); a second tension pulley (27) carried by the second ring (20) and rotating with respect to it about its own axis (PA2); and elastic means (34) acting on the first and second rings (15; 20) to push the first and second pulleys (23, 27) into contact with respective spans (8a; 8b) of the belt.

Description

[0001] Cross-references to related applications

[0002] This patent application claims priority to Italian Patent Application No. 102020000015877, filed on July 1, 2020, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to a tensioner for an accessory drive for a motor vehicle and an accessory drive including such a tensioner. Background Technology

[0004] An accessory drive for an internal combustion engine typically includes pulleys connected to a drive shaft, pulleys connected to a motor shaft, and may include one or more pulleys for driving other accessories, such as a regulating system compressor. The accessory drive also includes a belt and tensioner for transmitting motion between the aforementioned pulleys, the tensioner being configured to ensure the correct minimum tension level of the belt and prevent slippage between the belt and pulleys.

[0005] In a conventional accessory drive where the motor is an alternator driven by an engine, the tensioner acts on the slack span of the belt, which is the span relative to the direction of belt movement that is downstream of the engine and upstream of the alternator.

[0006] In motor vehicles, reversible motors are increasingly being used to replace traditional alternators; these reversible motors can operate not only in the traditional generator mode, but also in other modes, such as as a regenerative brake (recuperation condition) or as an auxiliary motor that operates in conjunction with an internal combustion engine (boost condition).

[0007] By using a reversible motor, the span of a belt that is taut under motor-driven operating conditions becomes a slack span when the motor delivers torque.

[0008] Therefore, various solutions were designed to ensure the correct two spans of the tension band.

[0009] One solution includes, for example, using a tensioner with two arms hinged to a common pin and carrying respective pulleys. The arms are subjected to a spring force that tends to bring them closer together to maintain contact between the pulleys and the belt for the corresponding span. An example of this solution is described in EP 1581753-A. The common axis of the two arms is arranged within the path of the belt.

[0010] The overall dimensions of the base on which the arm pivots and the springs arranged around the common hinge axis of the arm make this solution unsuitable for applications with space constraints within the belt path, such as, for example, when the drive has only two pulleys. Furthermore, the arm arrangement is not optimal in terms of the resultant force acting on the pulleys.

[0011] Another solution involves mounting the tensioner on the motor.

[0012] According to known solutions, the tensioner includes: a base configured to be fixed to a motor; a first annular element that rotates relative to the base about the motor axis and carries a first pulley; and a second annular element that rotates relative to the base about the motor axis and carries a second pulley.

[0013] A spring acts between two annular elements, configured to apply a spring force between the elements to maintain the first and second pulleys in contact with the belt for the corresponding span.

[0014] A drawback associated with the above solutions is that they require operation at relatively high belt tension to allow for optimal performance under recovery and boost conditions.

[0015] According to another known solution, the tensioner includes: a base configured to be fixed to a motor, an annular element surrounding the axis of the motor relative to the base and carrying a first pulley, and an arm hinged to the annular element and carrying a second pulley.

[0016] The problem associated with this solution is that it is difficult to obtain symmetrical characteristics under both positive and negative torque conditions of the motor. Summary of the Invention

[0017] The object of the present invention is to produce a tensioner for an accessory drive that does not have the disadvantages associated with the aforementioned known tensioners.

[0018] The above objective is achieved by the tensioner for the accessory drive according to claim 1. Attached Figure Description

[0019] To better understand the invention, preferred embodiments are described by way of non-limiting examples and with reference to the accompanying drawings, wherein:

[0020] Figure 1 This is a schematic top view of an engine equipped with an accessory drive with a tensioner according to the present invention;

[0021] Figure 2 yes Figure 1 A schematic front view of the accessory driver;

[0022] Figure 3 yes Figure 1Front view of the first embodiment of the tensioner;

[0023] Figure 4 It is along Figure 3 A partial 3D view taken from line IV-IV;

[0024] Figure 5 It is based on Figure 3 The cross section of line VV;

[0025] Figure 6 and Figure 7 yes Figure 3 An exploded perspective view of the tensioner in opposite axial directions;

[0026] Figures 8 to 13 It is a comparative illustration of quantities related to various embodiments of the present invention;

[0027] Figures 14 to 18 It is a diagram. Figure 5 Schematic partial cross-sectional view of the detailed embodiment variation;

[0028] Figure 19 and Figure 20 These are front views of the tensioner according to the present invention and the second embodiment, respectively. Detailed Implementation

[0029] refer to Figure 1 and Figure 2 The attached figure shows the accessory drive of the internal combustion engine 2, with reference numeral 1 indicating the accessory drive.

[0030] The accessory drive 1 includes: a first pulley 3 connected to the drive shaft 4 of the engine E, having an axis EA; a second pulley 5 connected to the shaft 6 of the motor 7, having an axis MA; and a belt 8 connecting the first pulley 3 and the second pulley 5 to each other. The accessory drive may include other pulleys (not shown) for driving other accessories of the engine 1, such as, for example, a regulating system compressor.

[0031] The accessory drive 1 also includes a tensioner 10, which is mounted on the motor 7 and includes ( Figures 3-7 ):

[0032] The base 11 integrally includes a housing 13 configured to be fixed to the motor 7. Figure 1 and Figure 5 The flat flange 12 and the annular collar 14 have an axis A1 that coincides with the axis MA during use and extends axially from the flange 12 in a cantilever manner.

[0033] The first ring 15 is rotatably supported on the base 11 around the collar 14 by means of a first bushing 16, the first bushing 16 having a flat annular portion 17 axially inserted between the first ring 15 and the flange 12 and a cylindrical portion 18 having an axis A1 axially inserted between the first ring 15 and the collar 14. Figure 5 );as well as

[0034] The second ring 20 is rotatably supported on the base 11 by means of a bushing 21 surrounding the first ring 15, the bushing 21 surrounding its inner edge and having a C-shaped cross section in at least the main part of its circumference for this purpose; the bushing 21 is properly pressed against the inner edge of the second ring 20.

[0035] The base 11 and rings 15, 20 have an inner diameter larger than the diameter of the second pulley 5, so as to allow the tensioner 10 to be assembled onto the motor 7 in the presence of the second pulley 5 (see...). Figure 5 (The overall dimensions of pulley 5 are schematically shown by dashed lines).

[0036] The first ring 15 includes a radially outer attachment 22, which rotatably supports the first pulley 23 of the tensioner 10 having an axis PA1 by means of a pin 24 and a bearing 25. The second ring 20 includes a tubular axial attachment 26, which extends cantileveredly from the opposite side of the flange 12 of the base 11, and the second pulley 27 of the tensioner 12 having an axis PA2 is rotatably mounted on the tubular axial attachment 26 by means of a pin 28 and a bearing 29.

[0037] The first pulley 23 and the second pulley 27 are configured according to the belt feed direction (clockwise, see reference). Figure 2 It cooperates with the corresponding portions 8a and 8b of the belt arranged upstream and downstream of the second pulley 5, respectively.

[0038] According to the invention, the second ring 20 rotates relative to the first ring 15 about an axis A2 that is parallel to but different from the axis A1. The axis A2 is arranged within the first ring 15, and rotates about the axis A1 as the first ring 15 rotates. For this purpose, the first ring 15 has a cylindrical inner surface 30 with axis A1 that rotates about the cylindrical portion 18 of the bushing 16, and an eccentric cylindrical outer surface 31 with axis A2 that radially supports the bushing 21.

[0039] The first ring 15 and the second ring 20 define the corresponding housings 32 and 33 for the spring 34, the purpose of which is to generate elastic force to keep the pulleys 23 and 27 in contact with the belt 8, thus maintaining a predetermined tension level in the belt 8 during use.

[0040] Spring 34 ( Figures 3-5The spring 34 is an arc-shaped helical compression spring arranged circumferentially relative to rings 15 and 20. Housings 32 and 33 consist of radial attachments to the respective rings 15 and 20 and house the respective ends 34a and 34b of the spring 34. Housings 32 and 33 define respective circumferential channels 35 having a U-shaped cross-section and are closed on opposite circumferential sides by respective radial walls 36, which define corresponding shoulders for opposite ends of the spring 34. A corresponding protrusion 37 for centering the spring 34 extends from the wall 36. Within the channel 34, a half-shell 38 made of plastic is housed; the half-shell houses the spring 34 to prevent direct contact between the spring and housings 32 and 33.

[0041] The first ring 15 passes through the disc spring 43 ( Figures 5-7 The disc spring 43 is axially locked to the flange 12 of the base 11 and is axially compressed between the annular end edge 44 of the collar 14 of the base 11 and the first ring 15. To avoid direct contact between the disc spring 43 and the first ring 15, the spring 43 is provided with a coating 45 made of plastic material covering its outer edge.

[0042] The tubular fitting 26 of the second ring 20 is arranged in the recess 45 obtained on the periphery of the first ring 15. Figure 6 Within the spring 34, the relative rotation between rings 15 and 20 is limited, which are located between the free arm position corresponding to the maximum longitudinal expansion of the spring 34 and the load stop position corresponding to the maximum compression of the spring 34.

[0043] The first ring 15 has a protrusion 47 at the bottom. Figure 7 The protrusion 47 is configured to slidably engage the arcuate groove 48 of the flange 12 of the base 11 to limit the rotation angle of the first ring 15 relative to the base 11.

[0044] In the absence of a reaction force from belt 8, spring 34 tends to hold rings 15 and 20 in the free arm position. To allow for easy assembly of belt 8, rings 15 and 20 are secured by locking pin 49 before installation. Figure 3-5 They are locked in relative angular mounting positions, with locking pin 49 engaging their respective holes 50, 51. The mounting position is appropriately close to the load-stopping position.

[0045] Once the belt is installed, pin 49 is removed, and the tensioner reaches its maximum tension under the action of spring 34. Figure 2 The nominal position is schematically shown, in which the two pulleys 23 and 27 are symmetrical with respect to the bisector line H of the winding angle θ of the belt 8 on the pulley 5, and coincide with the direction of the resultant tension force of the belt 8 on the pulley 5 under nominal conditions.

[0046] The operation of tensioner 10 is as follows.

[0047] Under normal operating conditions, engine 2 delivers torque and motor 7 is driven and operated as an alternator. Under these conditions, the belt span 8b is the taut span, and span 8a is the slack span.

[0048] Compared to Figure 2 At the nominal position shown, the tensioner 10 rotates clockwise about axis A1 because the tension span 8b transmits the hub load to pulley 27. Under the thrust of the spring 34, which tends to move pulleys 23 and 24 closer to each other, pulley 23 acts on the slack span 8a, maintaining the same preset minimum tension value as the torque changes.

[0049] In boost mode, motor 7 delivers power (positive torque) added to the power of engine 2. This tends to decrease the tension in the belt span 8b and increase the tension in the belt span 8a. On the other hand, in recovery mode, motor 7 absorbs mechanical energy (negative torque), and therefore the tension in the belt span 8a tends to decrease.

[0050] Using a rotating axis A2 of the second ring 20, which is different from the axis A1 of the first ring (as described, it coincides with the axis MA of the motor 7 in use), allows for reduced installation tension of the belt 8 and torque transmission capacity within the slack span (understood as the span of each slack in operation).

[0051] Figure 8 This is a graph showing the different positions of axis A2 relative to axis A1 (where the X and Y axes represent coordinates in mm measured from the axis of the drive shaft), denoted as N1-N10. A1 represents a comparative example where axis A2 coincides with axis A1 of motor 7 (coordinates 210; 155 relative to the axis of the drive shaft).

[0052] Figure 9 This indicates that, in response to Figure 8 The points in the curve represent the tension trend in the relaxation span of belt 8 as the torque of motor 7 changes (negative torque values ​​indicate recovery mode, and positive values ​​indicate boost mode).

[0053] A torque value of 0 corresponds to the installation tension, which is the same for all examples (315N). In this case, line A1 also represents a comparative example where axis A1 and axis A2 coincide.

[0054] With the same installation tension, Examples N1 and N5-N10 determine increasingly higher relaxation span tensions relative to Comparative Example A1, while in Examples N2, N3, and N4, the relaxation span tensions are lower than the comparative examples, at least under one of the recovery and boost conditions. Among the positive examples, N10 is the best because it exhibits a symmetrical tension curve under both recovery and boost conditions (from...). Figure 9 As can be seen from the curve, the tension value at the extreme point of the torque value is equal to + / - 55 Nm, which is basically the same.

[0055] The installation tension of the belt can be reduced by increasing the tension during the slack span.

[0056] Figure 10 against Figure 9 Example N10 shows a mounting tension that is 50 N lower than the comparison example (265 N instead of 315 N). Examining the graph, it is easy to see that within the normal operating range, from approximately -25 Nm to +25 Nm, there is no risk of slippage, and the tension remains lower than the reference example; this means reduced losses due to friction, thus reducing consumption.

[0057] On the other hand, slippage may occur in the high torque region (>25Nm in the module). Compared with when the axes A1 and A2 coincide, the drive becomes more rigid and the torque transmission capability is improved.

[0058] To clarify the influence of the position of A2 relative to A1 on the tension balance of the relaxation span under recovery and pressurization conditions. Figure 11 Various other examples N11-N16 are shown, corresponding to positions on axis A2 equidistant from axis A1. That is, points N11-N16 lie on a circle centered at A1 (axis A2 coincides with A1). Given the same distance A1-A2 ( Figure 12 Different behaviors correspond to these points, thus deriving that the key factor is not the distance between A1 and A2.

[0059] Experiments have verified that the determining factor for obtaining the symmetrical behavior of the tensioner 10 under both positive and negative torque conditions is, under nominal conditions, the plane identified by axes A1-A2 and the plane containing axis A1 and motor 7 ( Figure 2 The angle formed between the planes of the bisectors H of the winding angle θ of the belt on pulley 5 ( ) and belt 8. It should be noted that... Figure 2 In the symmetrical layout of the drive 1 shown with only two pulleys, the bisector H intersects the axis of the drive shaft EA, but this situation does not usually occur.

[0060] The optimal angle α varies with the winding angle θ, and the relationship determined experimentally is expressed as follows:

[0061] α = -0.2166θ + 97.267 + c,

[0062] Where α and θ are expressed in degrees (°), and c is a variable in the range of +10° to -10°.

[0063] The value c = 0 corresponds to Figure 9 or Figure 10 The curve (tension as a function of torque) is perfectly symmetrical under both positive and negative torque conditions. For the value c = 0, the above linear relationship is as follows: Figure 13 As shown.

[0064] The extreme values ​​of the variable range of c are calculated based on the acceptable asymmetry value equal to 5% of the installation tension in the curves above. In particular, for example N10, with an installation tension of 315 N, the unbalance is 15.21 N for c = +10° and 14.98 N for c = -10°, both values ​​being less than 15.75 (5% of the installation tension).

[0065] Surprisingly, the optimal angle is independent of the diameter of pulley 5 and the layout of the drive.

[0066] Because the pulley system is symmetrical with respect to the bisector H of the winding angle θ, and because the resulting force system is symmetrical, plane P can be indiscriminately positioned on one side or the other of line H (i.e., toward pulley 23 or toward pulley 27), forming an angle α with it in each case. In other words, the two tensioners have corresponding axes A2 positioned on plane P, which is arranged on the opposite side of line H but forms the same angle α with it, exhibiting the same behavior.

[0067] The optimal position of plane P as defined above refers to the nominal position of the tensioner.

[0068] Figures 14 to 18 This is a schematic partial cross-sectional view illustrating an alternative solution for axially and radially supporting rings 15 and 20 on base 11. The same reference numerals are used to denote those already referenced. Figure 3-7 The parts described are the same as or corresponding to the parts described, and refer to Figure 5 The details highlighted in the diagram illustrate the solution. For the sake of brevity, a description of the support bushing is omitted, but whenever there is relative sliding between rings 15 and 20 and relative to base 11 and spring 43, the support bushing must be axially and / or radially inserted in any case to avoid premature wear and control the damping of oscillations.

[0069] exist Figure 14 In this solution, a disc spring 43 acts between a shoulder 50 integral with the first ring 15 and the second ring 20, applying axial loads in opposite directions to them. In this way, the first ring 15 is axially pushed against the shoulder 44 integral with the base 11 and the second ring 20 is pushed against the base 11.

[0070] exist Figure 15In the solution, there are two disc springs 43a and 43b, which act between the shoulder 44, which is integral with the base 11, and the corresponding rings 15 and 20. This allows for independent control of the rotational damping of the first ring 15 and the rotational damping of the second ring 20.

[0071] exist Figure 16 In this configuration, the first ring 15 is axially supported by the second ring 20, and the disc spring 43 acts between the fixed shoulder 44, which is integral with the base 11, and the first ring 15. Therefore, in this configuration, the axial loads of the first ring 15 and the second ring 20 relative to the spring 43 are arranged in series.

[0072] exist Figure 17 In the solution, there are two disc springs 43a and 43b, one of which acts between the shoulder 44 integrated with the base 11 and the first ring 15, and the other acts between the shoulder 50 integrated with the first ring 15 and the second ring 20.

[0073] at last, Figure 18 One solution is shown in which the spring 43 acts on the first ring 15, which rests on both the base 11 and the second ring 20.

[0074] The solution adopted affects the damping possibilities for controlling the rotation of the first ring 15 and the second ring 20, but does not change the general operation of the tensioner previously described.

[0075] Figure 19 and Figure 20 Tensioner 52 is shown, which will be described below only in the extent that it differs from the described tensioner 10, using the same reference numerals to distinguish it from parts that are the same as or correspond to those already described.

[0076] Since spring 34 is a helical traction spring, it is arranged tangentially to the first ring 15 and the second ring 20 and has corresponding hook-shaped ends 34a, 34b that hook onto the corresponding studs 53, 54, which are integral with the first ring 15 and the second ring 20 and extend axially from their respective external radial attachments 55, 56.

[0077] The positions of the pulley 23 carried by the first ring 15 and the pulley 27 carried by the second ring are opposite to those of the tensioner 10 because the traction spring 34 (rather than the compression spring in the tensioner 10) determines the relative rotation between the two rings 15, 20 in opposite directions. The action of the spring 34 always produces a spring force that tends to keep the pulleys 23, 27 in contact with the belt 8, thereby maintaining a predetermined tension level in the belt 8 during use.

[0078] Upon examination of the tensioners 10, 52 produced according to the present invention, their advantages are obvious.

[0079] In particular, by using tensioner pulleys carried by a first ring rotating about a first axis and a second ring rotating eccentrically relative to the first axis relative to the first axis, the installation tension of the belt can be reduced for the same torque transmission capacity without significantly increasing the overall size and cost of the tensioner.

[0080] Furthermore, when the tensioner is in the nominal position, by arranging the second shaft on a plane that forms a predetermined angle with the bisector of the winding angle, the operation of the drive under both positive and negative torque conditions of the motor can be optimized.

Claims

1. A tensioner for an accessory drive of an internal combustion engine (2), the drive (1) comprising at least a first pulley (3) connected to a drive shaft (4) of the engine (2), at least a second pulley (5) connected to a motor (7), and a belt (8) wound at least on the first pulley and the second pulleys (3, 5), the tensioner (10) comprising: - Base (11), the base (11) being configured to be fixed to the housing (13) of the motor; - First ring (15), the first ring (15) rotates about a first axis (A1) relative to the base (11); - Second ring (20), the second ring (20) rotates relative to the first ring (15) about a second axis (A2) different from the first axis (A1); - First tension pulley (23), the first tension pulley (23) is carried by the first ring (15) and rotates relative to the first ring (15) about its own axis (PA1); - A second tension pulley (27), which is carried by the second ring (20) and rotates relative to the second ring (20) about its own axis (PA2); and - An elastic device (34) acts on the first ring and the second ring (15; 20) to push the first pulley and the second pulley (23, 27) into contact with the corresponding span (8a; 8b) of the belt; The second axis (A2) is located inside the first ring (15), and when the first ring (15) rotates about the first axis (A1), the second axis (A2) rotates about the first axis (A1). Under nominal conditions, the plane passing through the first axis and the second axis (A1; A2) is inclined at a measured angle (α) relative to the bisector of the winding angle of the belt (8) on the second pulley (5) so as to balance the tension in the taut span of the belt (8) under positive torque conditions and negative torque conditions of the motor (7).

2. The tensioner as claimed in claim 1, wherein, The base (11) has an annular configuration, and the inner diameter of the base (11) and the first and second rings (15; 20) is larger than the diameter of the second pulley (5), so that the tensioner (10) can be mounted on the motor (7) without interfering with the second pulley (5).

3. The tensioner as claimed in claim 1, wherein, The base (11) includes an annular collar (14) having an axis that coincides with the first axis (A1), and the first ring (15) is rotatably mounted around the collar (14) by means of a first bushing (16).

4. The tensioner as claimed in claim 3, wherein, The first ring (15) has a cylindrical inner surface (30) and an eccentric cylindrical outer surface (31), the cylindrical inner surface (30) being coaxial with the first axis (A1) and rotating about the first bushing (16), the eccentric cylindrical outer surface (31) being coaxial with the second axis (A2), and the second ring (20) being able to rotate about the cylindrical outer surface (31) of the first ring (15) by means of the second bushing (21).

5. The tensioner as described in any one of claims 1 to 4, wherein, The angle is a function of the winding angle (θ) of the belt (8) on the second pulley (5), and the relationship is as follows: α = -0.2166θ + 97.267 + c, Where α and θ are expressed in degrees (°), and c is a variable contained in the range between +10° and -10°.

6. The tensioner as claimed in claim 1, wherein, The elastic device includes at least one first spring (34) acting between the first ring and the second ring (15; 20).

7. The tensioner as claimed in claim 6, wherein, The first spring (34) is a compression spring having corresponding ends (34a, 34b) which are housed in corresponding housings (32, 33) that are integral with the first ring and the second ring (15; 20), respectively.

8. The tensioner as claimed in claim 7, wherein, The housing (32, 33) consists of radial attachments of the corresponding first ring and second ring (15, 20) and defines a corresponding circumferential channel (35), which is closed at circumferentially opposite ends by a corresponding radial wall (36), which defines a corresponding shoulder for the opposite end of the first spring (34).

9. The tensioner as claimed in claim 6, wherein, The first spring (34) is a compression spring, the ends (34a, 34b) of which are hooked to the attachments of the corresponding first and second rings (15, 20) and arranged tangentially relative to the first and second rings (15, 20).

10. The tensioner of claim 4, comprising at least one second spring (43) that applies an axial load on at least one of the first bushing and the second bushing (16, 21) to dampen rotation of the first ring and the second ring (15, 20).

11. The tensioner of claim 10, wherein the axial load is applied to one of two rings (15, 20), and the other ring is axially inserted between at least a portion of the ring and the base (11).

12. The tensioner as claimed in claim 10, wherein, The second spring (43) is axially inserted between the first ring and the second ring and applies axial loads in opposite directions to the first ring and the second ring. One of the first rings (20) is pushed against the base (11) and the other ring (15) is axially pushed against the shoulder (44) integral with the base (11).

13. The tensioner of claim 10, comprising two second springs (43a, 43b) applying corresponding axial loads on corresponding first and second rings (15, 20).

14. The tensioner as claimed in claim 1, wherein, The first ring and the second ring (15, 20) include corresponding first engagement devices (26, 45) for limiting the relative rotation between the first ring and the second ring (15, 20).

15. The tensioner as claimed in claim 1, wherein, The first ring (15) and the base (11) include corresponding engagement devices (47, 48) for limiting relative rotation between the first ring (15) and the base (11).

16. The tensioner as claimed in claim 1, comprising a locking device (49) for locking the first ring and the second ring (15, 20) at an angle to each other in a relative installation position, the locking device (49) being releasable after installation.

17. The tensioner of claim 16, wherein the locking device (49) includes a pin capable of being inserted into corresponding holes (50, 51) of the first ring and the second ring (15, 20).

18. An accessory drive for an internal combustion engine (2) comprising at least a first pulley (3) connected to a drive shaft (4) of the engine (2), at least a second pulley (5) connected to an electric motor (7), a belt (8) at least wound around the first pulley and the second pulley (3, 5), and a tensioner (10) as claimed in claim 1.

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