Tensioner for an accessory drive of a motor vehicle and accessory drive including such a tensioner
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MUVIQ SRL
- Filing Date
- 2025-12-19
- Publication Date
- 2026-07-02
Smart Images
Figure IB2025063217_02072026_PF_FP_ABST
Abstract
Description
[0001] " TENSIONER FOR AN ACCESSORY DRIVE OF A MOTOR VEHICLE AND ACCESSORY DRIVE INCLUDING SUCH A TENSIONER"
[0002] Cross-Reference to Related Applications This Patent Application claims priority from Italian Patent Application No. 102024000029739 filed on December 23, 2024, the entire disclosure of which is incorporated herein by reference.
[0003] Technical Field
[0004] The present invention relates to a tensioner for an accessory drive of a motor vehicle and an accessory drive including such a tensioner.
[0005] Background Art
[0006] As is known, an accessory drive of an internal combustion engine comprises a first pulley connected to a drive shaft of the engine, a second pulley connected to a shaft of an electrical machine, and may comprise one or more pulleys for driving other accessories, e. g. the compressor of the air conditioning. The accessory drive also comprises a belt for transmitting motion between the aforementioned pulleys and a tensioner configured to ensure a correct minimum belt tension level and prevent slippage between the belt and the pulleys.
[0007] In conventional accessory drives, wherein the electrical machine is an alternator (electrical generator) driven by the engine, the tensioner acts on the slack span of the belt, i. e. the span downstream of the engine and upstream of the alternator with reference to the motion direction of the belt.
[0008] In motor vehicles, instead of the conventionalalternator, a reversible electrical machine is increasingly being used which can operate, besides in the conventional generator mode, according to further modes, e. g. as regenerative brake (the so-called "recovery" condition), or as supplementary engine acting in combination with the internal combustion engine (the so-called "boost" condition).
[0009] The use of a reversible electrical machine entails that the span of the belt which is taut under operating conditions wherein the electrical machine is driven by the engine becomes the slack span when the drive torque is supplied by the electrical machine.
[0010] Therefore, various solutions have been developed which allow to ensure the correct tensioning of both spans of the belt.
[0011] For example, a solution is to use a two-arm tensioner carrying respective tensioning pulleys.
[0012] In particular, according to a known solution, the tensioner comprises a base configured to be fixed to a fixed support structure; a first arm rotatable with respect to the base about a first axis; a second arm rotatable about a second axis; a first tensioning pulley carried by the first arm and rotatable with respect to the first arm about a first pulley axis; a second tensioning pulley carried by the second arm and rotatable with respect to the second arm about a second pulley axis; elastic means acting on the first arm and on the second arm to push the first tensioning pulley and the second tensioning pulley into contact with respective spans of the belt.
[0013] The first arm and the second arm may be substantiallyrod-shaped or ring-shaped. Furthermore, the first axis and the second axis may be coincident or be distinct from each other.
[0014] Some problems associated with the known solutions are the difficulty of decreasing slippage between the belt and the pulleys of the accessory drive and increasing torque transmissibility under positive and negative torque conditions of the electrical machine.
[0015] A purpose of the present invention is to provide a tensioner for an accessory drive, which allows he aforementioned problems to be overcome.
[0016] Disclosure of the Invention
[0017] The above purpose is achieved by a tensioner for an accessory drive as claimed in claim 1.
[0018] The present invention further relates to an accessory drive as claimed in claim 15.
[0019] Brief Description of the Drawings
[0020] For a better understanding of the present invention, some preferred embodiments are described hereinafter, by way of non-limiting example and with reference to the accompanying drawings, wherein:
[0021] - Figure 1 is a schematic top view of an engine provided with an accessory drive with a tensioner according to the present invention;
[0022] - Figure 2 is a schematic front view of the accessory drive of Figure 1;
[0023] - Figure 3 is a front view of the tensioner of Figure 1;
[0024] - Figure 4 is an exploded perspective view of the tensioner of Figure 1;- Figure 5 is a schematic front view of the tensioner of Figure 1, wherein the tensioner parameters are indicated;
[0025] - Figure 6 is a schematic view of a detail of Figure 5; - Figure 7 is a graph representative of tensioner torque as a function of an angular distance between a first tensioning pulley and a second tensioning pulley of the tensioner;
[0026] - Figure 8 is a graph representative of the tensioner torque, at a predetermined maximum angular distance between the first tensioning pulley and the second tensioning pulley, as a function of a parameter of Figure 5; and
[0027] - Figures 9 and 10 are respective graphs representative of tensions of a belt of an accessory drive as a function of a torque of the electrical machine of the accessory drive, as the parameters in Figure 5 vary.
[0028] Detailed Description of the Invention With reference to Figures 1 and 2, there is indicated by 1 an accessory drive of an internal combustion engine 2.
[0029] The accessory drive 1 comprises a first pulley 3 connected to a drive shaft 4 of the engine 2, of axis EA, a second pulley 5 connected to a shaft 6 of an electrical machine 7, of axis MA, and a belt 8 connecting the first pulley 3 and the second pulley 5. The accessory drive may comprise other pulleys (not illustrated) for driving other accessories of the engine 2, such as a compressor of the conditioning system.
[0030] The accessory drive 1 further comprises a tensioner 11 comprising a base 12 configured to be attached to a fixedsupport structure 13, a first arm 21 rotatable with respect to the base 12 about a first axis Al, a second arm 22 rotatable about a second axis A2, a first tensioning pulley 31 carried by the first arm 21 and rotatable with respect to the first arm 21 about a first pulley axis PA1, and a second tensioning pulley 32 carried by the second arm 22 and rotatable with respect to the second arm 22 about a second pulley axis PA2.
[0031] In particular, the support structure 13 may be a bracket attached to the engine 2 in an area internal or external to the belt 8, or a portion of the engine 2 itself in such area, or a casing of the electrical machine 7. Therefore, the base 12 may be attached internally or externally to the belt 8.
[0032] In the illustrated embodiment, the tensioner is mounted on the electrical machine 7 and the support structure 13 is a casing of the electrical machine 7.
[0033] In the illustrated embodiment (Figure 3), the first arm 21 comprises a first ring 41, rotatable with respect to the base 12 about the axis Al, and the second arm 22 comprises a second ring 42, rotatable about the axis A2.
[0034] In particular (Figure 4 ), the base 12 integrally comprises a flat flange 51 configured to be attached to the casing 13 of the electrical machine 7 and an annular collar 52, of axis Al coincident in use with the axis MA, extending axially cantilevered from the flange 51.
[0035] The first ring 41 is rotatably supported on the base 12 about the collar 52 via a first bushing 53 having a flat annular portion 54 and a cylindrical portion 55, of axis Al, radially interposed between the first ring 41 and the collar
[0036]
[0037] The second ring 42 is rotatably supported by the first ring 41 via a second bushing 56 and a third bushing 57.
[0038] The base 12 and the rings 41, 42 have an internal diameter greater than the diameter of the second pulley 5 so as to allow the tensioner 11 to be mounted on the electrical machine 7 in the presence of the second pulley 5.
[0039] The first ring 41 comprises an external radial appendage 61 rotatably supporting the first tensioning pulley 31 of the tensioner 11, of axis PA1, via a pivot 62 and a bearing 63. The second ring 42 comprises an external radial appendage 64 rotatably supporting the second tensioning pulley 32 of the tensioner 11, of axis PA2, via a pivot 65 and a bearing 66.
[0040] The first tensioning pulley 31 and the second tensioning pulley 32 are configured to cooperate with respective spans 8a, 8b of the belt 8 arranged respectively downstream and upstream of the second pulley 5 according to the advancement direction of the belt 8 (clockwise, with reference to Figure 2 ).
[0041] In the illustrated embodiment, the second ring 42 rotates relative to the first ring 41 about the axis A2 which is parallel to the axis Al and distinct therefrom. The axis A2 is arranged inside the first ring 41 and orbits about the axis Al as the first ring 41 rotates.
[0042] The tensioner 11 also comprises a traction spring 71 extending along a spring axis SA and acting on the first arm 21 and the second arm 22 to push the first tensioning pulley 31 and the second tensioning pulley 32 into contact with respective spans 8a, 8b of the belt 8.
[0043] The spring 71 comprises a first end 81 constrained tothe first arm 21 at a first constraint point Pl and a second end 82 constrained to the second arm 22 at a second constraint point P2.
[0044] Preferably, the first arm 21 comprises a first constraint element 91 defining the first constraint point Pl, and the second arm 22 comprises a second constraint element 92 defining the second constraint point P2.
[0045] In particular, the first constraint element 91 comprises a first projection to which the first end 81 of the spring 71 is constrained, and the second constraint element 92 comprises a second projection to which the second end 82 of the spring 71 is constrained.
[0046] Preferably, the first constraint element 91 comprises a first pivot 101 extending along a first pivot axis PPA1 on which the first constraint point Pl lies, and the second constraint element 92 comprises a second pivot 102 extending along a second pivot axis PPA2 on which the second constraint point P2 lies.
[0047] Conveniently, the first pivot axis PPA1 is parallel to the first axis Al and the second pivot axis PPA2 is parallel to the second axis A2. Preferably, the first pivot axis PPA1 and the second pivot axis PPA2 are parallel to each other and orthogonal to the spring axis SA.
[0048] Preferably, the first arm 21 comprises a first appendage 111 configured to carry the first pivot 101, and the second arm 22 comprises a second appendage 112 configured to carry the second pivot 102.
[0049] In particular, the first appendage 111 extends substantially orthogonally to the first axis Al, and the second appendage 112 extends substantially orthogonally tothe second axis A2.
[0050] In the illustrated embodiment, the first appendage 111 is an outer radial appendage extending from the first ring 41 and the first pivot 101 extends axially cantilevered from the first appendage 111, and the second appendage 112 is an outer radial appendage extending from the second ring 42 and the second pivot 102 extends axially cantilevered from the second appendage 112.
[0051] Conveniently, the second appendage 112 is axially interposed between the base 12 and the first appendage 111, and comprises an axial projection 113 configured to selectively cooperate with a projection 114 extending axially from the first ring 41 and a projection 115 extending axially from the first appendage 111. In particular, the axial projection 113 is angularly interposed between the projection 114 and the projection 115 and is configured to define respective angular end stops to the relative rotation between the first arm 21 and the second arm 22. In particular, the angular distance between the first tensioning pulley 31 and the second tensioning pulley 32 is maximum (and the traction of the spring 71 is maximum) when the axial projection 113 abuts against the projection 114, and the angular distance between the first tensioning pulley 31 and the second tensioning pulley 32 is minimum (and the longitudinal expansion of the spring 71 is minimum) when the axial projection 113 abuts against the projection 115 (as in Figure 3).
[0052] Conveniently, the spring 71 is a helical spring whose axis is the spring axis SA. In other words, the spring 71 is helix-shaped, i. e. a line wound about a rotational solidwhose axis is the spring axis SA. Each winding of the spring 71, i. e. each portion of the helix corresponding to one revolution about the spring axis SA, is referred to as a coil. Each half winding of the spring 71, i. e. each portion of the helix corresponding to a half revolution about the spring axis SA, is referred to as a half coil.
[0053] Conveniently, the spring 71 comprises a first end portion 121 and a second end portion 122.
[0054] In particular, the first end portion 121 and the second end portion 122 comprise respective pluralities of coils defining opposite ends of the spring 71 along the spring axis SA.
[0055] Conveniently, the spring 71 comprises a central portion 123 interposed between the first end portion 121 and the second end portion 122.
[0056] Conveniently, the spring 71 is obtained from a wire having a constant diameter.
[0057] Preferably, the tensioner 11 further comprises a first end element 131 operatively interposed between the spring 71 and the first arm 21, and a second end element 132 operatively interposed between the spring 71 and the second arm 22.
[0058] The first end element 131 comprises a first plate 141 having first holes 151 configured to house at least one coil 121' of the first end portion 121.
[0059] In particular, the first holes 151 are arranged on opposite sides with respect to the spring axis SA. The first holes 151 define respective through seats for respective portions of the coil 121', which is the last coil ( i. e. the end coil) of the first end portion 121. Preferably, the firstholes 151 define respective through seats for respective portions of at least one other coil, consecutive to the coil 121 ', of the first end portion 121.
[0060] The second end element 132 comprises a second plate 142 having second holes 152 configured to house at least one coil 122' of the second end portion 122.
[0061] In particular, the second holes 152 are arranged on opposite sides with respect to the spring axis SA. The second holes 152 define respective through seats for respective portions of the coil 122', which is the last coil ( i. e. the end coil) of the second end portion 122. Preferably, the second holes 152 define respective through seats for respective portions of at least one other coil, consecutive to the coil 122 ', of the second end portion 122.
[0062] The first plate 141 and the second plate 142 are coplanar and lie on a plane comprising the spring axis SA.
[0063] In other words, the first plate 141 and the second plate 142 lie on the same plane on which the spring axis SA also lies.
[0064] Preferably, such plane is orthogonal to the first axis Al and the second axis A2. Therefore, the spring axis SA is orthogonal to the first axis Al and the second axis A2.
[0065] Preferably, the spring 71 is a cylindrical helix, i. e. it extends along a cylinder whose axis is the spring axis SA. In other words, the spring 71 is defined by a line wound about a cylinder whose axis is the spring axis SA.
[0066] Preferably, the first holes 151 are least four and the second holes 152 are least four.
[0067] Conveniently, the number of first holes 151 is equal to the number of second holes 152.Preferably, the first plate 141 has a first hooking hole and the first pivot 101 is configured to engage the first hooking hole, and the second plate 142 has a second hooking hole and the second pivot 102 is configured to engage the second hooking hole.
[0068] Conveniently, the first hooking hole is dimensioned to allow the rotationally free coupling between the first end element 131 and the first arm 21, in particular between the first plate 141 and the first pivot 101. Similarly, the second hooking hole is dimensioned to allow the rotationally free coupling between the second end element 132 and the second arm 22, in particular between the second plate 142 and the second pivot 102.
[0069] Preferably, the first hooking hole and the second hooking hole have respective diameters equal to each other, and the first pivot 101 and the second pivot 102 have respective diameters equal to each other.
[0070] Preferably, the first hooking hole is a through hole passed through by the first pivot 101. Similarly, the second hooking hole is a through hole passed through by the second pivot 102.
[0071] Conveniently, with reference to the spring axis SA, the first end portion 121 is interposed between the first hooking hole and the central portion 123, and the second end portion 122 is interposed between the second hooking hole and the central portion 123.
[0072] Preferably, the first hooking hole and the second hooking hole are arranged along the spring axis SA.
[0073] In particular, the first hooking hole and the second hooking hole have respective centres belonging to the springaxis SA.
[0074] Preferably, the tensioner 11 comprises a first bushing 161 interposed between the first pivot 101 and the first plate 141 and a second bushing 162 interposed between the second pivot 102 and the second plate 142.
[0075] In Figures 5 and 6, some parameters of the tensioner 11 are indicated.
[0076] In particular, the parameters of the tensioner 11 comprise the following (linear) distances:
[0077] - l1: distance between the first axis Al and the first constraint point Pl;
[0078] - l'1: distance between the first axis A1 and the first pulley axis PA1;
[0079] - l2: distance between the second axis A2 and the second constraint point P2;
[0080] - l'2: distance between the second axis A2 and the second pulley axis PA2.
[0081] Furthermore, the tensioner 11 parameters comprise the following angular distances (i. e. angles):
[0082] - a1: angular distance between a conjunction between the first constraint point P1 and the first axis A1 and a conjunction between the first pulley axis PA1 and the first axis A1;
[0083] - a2: angular distance between a conjunction between the second constraint point P2 and the second axis A2 and a conjunction between the second pulley axis PA2 and the second axis A2.
[0084] In the illustrated embodiment, the first axis Al is distinct from the second axis A2, which orbits about the axis Al as the first arm 21 rotates.In particular, the parameters indicated in Figure 6 comprise:
[0085] - l12: distance between the first axis Al and the second axis A2;
[0086] - a12: angular distance between a conjunction between the second axis A2 and the first axis A1 and a conjunction between the first pulley axis PA1 and the first axis A1.
[0087] At least one of the following relations applies:
[0088] l1> l'1
[0089] l2> l'2
[0090] In particular, the distance between the first axis Al and the first constraint point Pl is greater than the distance between the first axis Al and the first pulley axis, and / or the distance between the second axis A2 and the second constraint point P2 is greater than the distance between the second axis A2 and the second pulley axis PA2.
[0091] Preferably, at least one of the following relations applies:
[0092] l1≤ l1,max
[0093] l2≤ l2,max
[0094] wherein:
[0095] - liimax ‘ maximum distance between the first axis Al and the first constraint point Pl;
[0096] - l2,max: maximum distance between the second axis A2 and the second constraint point P2.
[0097] In particular, the distance between the first axis Al and the first constraint point Pl is less than or equal to the maximum distance l1,max, and / or the distance between the second axis A2 and the second constraint point P2 is lessthan or equal to the maximum distance l2,max. In particular:
[0098] - l1,maxis chosen so that the derivative of a curve representative of a torque of the tensioner, at a predetermined maximum angular distance between the first tensioning pulley 31 and the second tensioning pulley 32, as a function of the distance between the first axis A1 and the first constraint point P1 is equal to a first predetermined threshold;
[0099] - l2,maxis chosen so that the derivative of a curve representative of a torque of the tensioner, at a predetermined maximum angular distance between the first tensioner pulley 31 and the second tensioner pulley 32, as a function of the distance between the second axis A2 and the second constraint point P2 is equal to a second predetermined threshold.
[0100] Conveniently, the first predetermined threshold may be equal to the second predetermined threshold.
[0101] With reference to
[0102]
[0103] and l1,max, after choosing the predetermined maximum angular distance between the first tensioning pulley 31 and the second tensioning pulley 32 and the first predetermined threshold, the curve representative of the tensioner torque as a function of l1is considered, and l1,maxis chosen so that the (first) derivative of the curve at the point where l1= l1,maxis equal to the first predetermined threshold.
[0104] With reference to l2and l2,maxr after choosing the predetermined maximum angular distance between the first tensioning pulley 31 and the second tensioning pulley 32 and the second predetermined threshold, the curve representativeof the tensioner torque as a function of l2is considered, and l2,maxis chosen so that the (first) derivative of the curve at the point where l2= l2,maxis equal to the second predetermined threshold.
[0105] Preferably, at least one of the following relations applies:
[0106] / — 1 5. / '
[0107]
[0108] ^2, max ~ ’ ^2
[0109] In particular, the maximum distance between the first axis Al and the first constraint point Pl is 150% of the distance between the first axis Al and the first pulley axis PA1, and / or the maximum distance between the second axis A2 and the second constraint point P2 is 150% of the distance between the second axis A2 and the second pulley axis PA2.
[0110] Preferably, at least one of the following relations applies:
[0111] 1,1 · l'1≤ l1≤ l1,max
[0112] 1
[0113]
[0114] ,1 ' I2 — l2≤ l2,max
[0115] In particular, the distance between the first axis Al and the first constraint point Pl is greater than or equal to 110% of the distance between the first axis Al and the first pulley axis PAI and less than or equal to the maximum distance between the first axis Al and the first constraint point Pl, and / or the distance between the second axis A2 and the second constraint point P2 is greater than or equal to 110% of the distance between the second axis A2 and the second pulley axis PA2 and less than or equal to the maximum distance between the second axis A2 and the second constraint point P2.
[0116] Preferably, at least one of the following relationsapplies:
[0117] 1,2 · l'1≤ l1≤ l1,max
[0118]
[0119] 1,2 · l'1≤ l1≤ l1,max
[0120] 1.2 • Z2 — l2≤ l2,max
[0121] In particular, the distance between the first axis Al and the first constraint point Pl is greater than or equal to 120% of the distance between the first axis Al and the first pulley axis PAI and less than or equal to the maximum distance between the first axis Al and the first constraint point Pl, and / or the distance between the second axis A2 and the second constraint point P2 is greater than or equal to 120% of the distance between the second axis A2 and the second pulley axis PA2 and less than or equal to the maximum distance between the second axis A2 and the second constraint point P2.
[0122] Preferably, at least one of the following relations applies:
[0123] 1,3 · l'1≤ l1≤ l1,max
[0124]
[0125] 1,3 · l'1≤ l1≤ l1,max
[0126] 1,3 · l'2≤ l2≤ l2,max
[0127] In particular, the distance between the first axis Al and the first constraint point Pl is greater than or equal to 130% of the distance between the first axis Al and the first pulley axis PAI and less than or equal to the maximum distance between the first axis Al and the first constraint point Pl, and / or the distance between the second axis A2 and the second constraint point P2 is greater than or equal to 130% of the distance between the second axis A2 and the second pulley axis PA2 and less than or equal to the maximum distance between the second axis A2 and the second constraint point P2.
[0128] Preferably, at least one of the following relationsapplies:
[0129] 1,4
[0130]
[0131] 1,4 · l'1≤ l1≤ l1,max
[0132] 1,4 · l'2≤ l2≤ l2,max
[0133] In particular, the distance between the first axis Al and the first constraint point Pl is greater than or equal to 140% of the distance between the first axis Al and the first pulley axis PAI and less than or equal to the maximum distance between the first axis Al and the first constraint point Pl, and / or the distance between the second axis A2 and the second constraint point P2 is greater than or equal to 140% of the distance between the second axis A2 and the second pulley axis PA2 and less than or equal to the maximum distance between the second axis A2 and the second constraint point P2.
[0134] Preferably, an angular distance between a conjunction between the first constraint point Pl and the first axis Al and a conjunction between the first pulley axis PAI and the first axis Al and an angular distance between a conjunction between the second constraint point P2 and the second axis A2 and a conjunction between the second pulley axis PA2 and the second axis A2 are chosen as a function of a predetermined torque of the tensioner under nominal conditions.
[0135] In particular, the angle a (i. e. the angular distance between a conjunction between the first constraint point Pl and the first axis Al and a conjunction between the first pulley axis PAI and the first axis Al ) and the angle a2(i. e. the angular distance between a conjunction between the second constraint point P2 and the second axis A2 and a conjunction between the second pulley axis PA2 and the second axis A2 )are chosen so that the tensioner 11 provides a predetermined torque when it is under nominal conditions, i. e. when the torque of the electrical machine 7 is zero and the belt 8 is stationary (i. e. it is not transmitting motion between the pulleys of the accessory drive).
[0136] Preferably, such predetermined torque is chosen to be equal to the torque provided, under nominal conditions, by a tensioner similar to the tensioner 11 but comprising a torsion spring (i. e. a spring that provides an elastic torque as a function of angular displacement) instead of the traction spring 71.
[0137] Figures 7 to 10 are graphs relating to the tensioner 11 as certain parameters indicated in Figures 5 and 6 vary.
[0138] In particular, the tensioner 11 comprises the following parameters:
[0139] - l'1= 90 mm;
[0140] - l2= 90 mm;
[0141] - Z12= 5 mm;
[0142] - a12= 100° clockwise from the conjunction between the first pulley axis PAI and the first axis Al;
[0143] - stiffness of traction spring 71 equal to 15 N / mm. Furthermore, for the graphs in Figures 7 to 9, the following parameters are chosen and kept constant:
[0144] - l2= 95 mm;
[0145] - a2= 155° clockwise from the conjunction between the second pulley axis PA2 and the second axis A2.
[0146] Therefore, for the graphs in Figures 7 to 9 the relation l2> l'2, in particular l2≅ 1,1 · l'2, applies.
[0147] The graph in Figure 7 is representative of the torque of the tensioner 11 as a function of the angular distancebetween the first tensioning pulley 31 and the second tensioning pulley 32.
[0148] In particular, in the graph in Figure 7 there is a straight line representative of the torque provided by a tensioner having the same parameters as the tensioner 11, but comprising a torsion spring ( i. e. a spring that provides elastic torque as a function of angular displacement) instead of the traction spring 71.
[0149] Furthermore, in the graph in Figure 7 there is a plurality of curves representative of the respective torques provided by the tensioner 11 as l1and α1vary.
[0150] In particular, after choosing l1, α1is chosen so that the curve with such l1and α1intersects the aforementioned straight line when the tensioner 11 is under nominal conditions, which correspond e.g. to an angular distance between the first tensioning pulley 31 and the second tensioning pulley 32 of approximately 45° and a torque supplied by the tensioner 11 of approximately 15 Nm.
[0151] In particular, the curves have the following values of l and a:
[0152] - 1- = 85 mm and a = 133,5°, thus
[0153]
[0154] = 0,9 • l';
[0155] - 1- = 100 mm and a = 140°, thus
[0156]
[0157] = 1,1 • l';
[0158] - l1= 115 mm and α1= 146°, thus l1≅ 1,3 · l'1;
[0159] - l1= 125 mm and α1= 150,5°, thus l1≅ 1,4 · l'1;
[0160] - l1= 135 mm and α1= 154,5°, thus l1≅ 1,5 · l'1;
[0161] - l1= 145 mm and α1= 159°, thus l1≅ 1,6 · l'1;
[0162] - l1= 155 mm and α1= 164°, thus l1≅ 1,7 · l'1.
[0163] Considering a predetermined maximum angular distance between the first tensioning pulley 31 and the second tensioning pulley 32, e. g. 70°, the torque of the tensioner11 increases as
[0164]
[0165] increases.
[0166] In particular, the graph in Figure 8 is representative of the torque of the tensioner 11 at the predetermined maximum angular distance between the first tensioning pulley 31 and the second tensioning pulley 32, e. g. 70°, as a function of l.
[0167] The curve representative of this torque is substantially a branch of a parabola having negative concavity (and thus negative second derivative), and the ( first) derivative of the curve at a point is positive and decreases as l increases.
[0168] The graph in Figure 9 is representative of the tension of the belt 8 as a function of the torque of the electrical machine 7.
[0169] Conveniently, the torque of the electrical machine 7 is less than zero when the electrical machine 7 operates as a regenerative brake (the so-called "recovery" condition), and the torque of the electrical machine 7 is greater than zero when the electrical machine 7 operates as a supplementary engine acting in combination with the internal combustion engine 2 (the so-called "boost" condition).
[0170] In particular, the tension of the span 8a (which is downstream of the second pulley 5 and thus of the electrical machine 7 ) is relatively higher in the recovery condition and relatively lower in the boost condition, and the tension of the span 8b (which is upstream of the second pulley 5 and thus of the electrical machine 7 ) is relatively lower in the recovery condition and relatively higher in the boost condition.
[0171] Conveniently, the span 8a is the taut span in therecovery condition and is the slack span in the boost condition, and the span 8b is the slack span in the recovery condition and is the taut span in the boost condition.
[0172] In the graph in Figure 9 there is a plurality curves representative of the tensions of the spans 8a and 8b as l and a change.
[0173] In particular, the curves have the following values of l and a:
[0174] - l₁ = 85 mm and α₁ = 133,5°, thus l₁ ≅ 0,9 · l'₁;
[0175] - l₁ = 90 mm and α₁ = 135°, thus l₁ = l'₁;
[0176] - l₁ = 125 mm and α₁ = 150,5°, thus l₁ ≅ 1,4 · l'₁.
[0177] The graph in Figure 9 shows that, with the same torque of the electrical machine 7, the tension of the slack span (i. e. the span 8a in the boost condition and the span 8b in the recovery condition) is higher when
[0178]
[0179] In particular, the tension of the slack span increases as l₁ increases, and thus as the ratio l₁ / l'₁ increases.
[0180] The graph in Figure 10 is representative of the tension of the belt 8 as a function of the torque of the electrical machine 7.
[0181] The considerations on the electrical machine 7 and the tensions of the spans 8a and 8b with reference to the graph in Figure 9 apply mutatis mutandis with reference to the graph in Figure 10.
[0182] Unlike the graph in Figure 9, for the graph in Figure 10 the following parameters are chosen and kept constant:
[0183] - l₁ = 115 mm;
[0184] - a = 146° clockwise from the conjunction between the first pulley axis PAI and the first axis Al.
[0185] Therefore, for the graph in Figure 10, the relation l >l'₁, in particular l₁ ≅ 1,3 · l'₁, applies.
[0186] In the graph in Figure 10 there is a plurality of curves representative of the tensions of the spans 8a and 8b as l2and a2change.
[0187] In particular, the curves have the following values of l2and a2:
[0188] - l₂ = 85 mm and α₂ = 165°, thus l₂ ≅ 0,9 · l'₂;
[0189] - l₂ = 95 mm and α₂ = 155°, thus l₂ ≅ 1,1 · l'₂;
[0190] - l₂ = 110 mm and α₂ = 145°, thus l₂ ≅ 1,2 · l'₂.
[0191] The graph in Figure 10 shows that, with the same torque of the electrical machine 7, the tension of the slack span (i. e. the span 8a in the boost condition and the span 8b in the recovery condition) is higher when l₂ > l'₂.
[0192] In particular, the tension of the slack span increases as l₂ increases, and thus as the ratio l₂ / l'₂ increases.
[0193] The operation of the tensioner 11 is the following.
[0194] Under normal operating conditions, the engine 2 supplies drive torque and the electrical machine 7 is driven and operates as an alternator. In this condition, the span 8a of the belt 8 is the taut span and the span 8b is the slack span.
[0195] With respect to the nominal position illustrated in Figure 2, the tensioner 11 rotates counter-clockwise about the axis Al by effect of the hubload transmitted by the taut span 8a to the pulley 31. Under the thrust of the spring 71, tending to bring the pulleys 31 and 32 close to each other, the pulley 32 acts on the slack span 8b keeping a minimum predetermined tension value in such span as the torque varies.
[0196] In boost mode, the electrical machine 7 supplies drivepower (positive torque) which adds to that of the engine 2. This tends to reduce the tension in the span 8a and increase the tension in the span 8b of the belt 8. Conversely, in recovery mode, the electrical machine 7 absorbs mechanical power (negative torque), and thus the tension in the belt 8 span 8b tends to decrease.
[0197] Conveniently, the use of a rotation axis A2 of the second ring 42 distinct from the axis Al of the first ring 41 (coincident in use, as mentioned, with the axis MA of the electrical machine 7 ) allows to obtain a reduction in the installation tension of the belt 8 with the same torque transmission capability in the slack span (understood as the slack span from time to time depending on the operating conditions).
[0198] In view of the foregoing, the advantages of the present invention are evident.
[0199] In particular, the fact that the tensioner 11 comprises the traction spring 71 and that l₁ > l'₁ and / or l₂ > l'₂ applies allows to maximise the tension of the slack span (understood as the slack span from time to time depending on the operating conditions). This in turn allows to decrease the slippage between the belt 8 and the pulleys of the accessory drive 1 and an increase in torque transmissibility under positive and negative torque conditions of the electrical machine 7.
[0200] The fact that the relations l₁ > l'₁ and l₂ > l'₂ apply jointly allows to further increase the tension of the slack span, which increases as l₁ (and thus the relation l₁ / l'₁) and l₂ (and thus the relation l₂ / l'₂) increase.
[0201] The fact that l < llmaxand / or l2< l2imaxapplies, bychoosing
[0202]
[0203] l₁ ≤ l₁,max and / or l₂ ≤ l₂,max as specified above, allows to indirectly limit the maximum tension of the belt 8. This in turn allows to limit the loads on the components of the accessory drive, thus increasing their service life.
[0204] The fact that 1,1 · l'₁ ≤ l₁ ≤ l₁,max and / or 1,1 · l'₂ ≤ l₂ ≤ l₂,max applies allows to further increase the tension of the slack span, which increases as l₁ (and thus the ratio l₁ / l'₁) and / or l₂ (and thus the ratio l₂ / l'₂) increases, while at the same time limiting the maximum tension of the belt 8.
[0205] The fact that 1,2 · l'₁ ≤ l₁ ≤ l₁,max and / or 1,2 · l'₂ ≤ l₂ ≤ l₂,max applies allows to further increase the tension of the slack span, which increases as l₁ (and thus the ratio l₁ / l'₁) and / or l₂ (and thus the ratio l₂ / l'₂) increases, while at the same time limiting the maximum tension of the belt 8.
[0206] The fact that 1,3 · l'₁ ≤ l₁ ≤ l₁,max and / or 1,3 · l'₂ ≤ l₂ ≤ l₂,max applies allows to further increase the tension of the slack span, which increases as l₁ (and thus the ratio l₁ / l'₁) and / or l₂ (and thus the ratio l₂ / l'₂) increases, while at the same time limiting the maximum tension of the belt 8.
[0207] The fact that 1,4 · l'₁ ≤ l₁ ≤ l₁,max and / or 1,4 · l'₂ ≤ l₂ ≤ l₂,max applies allows to further increase the tension of the slack span, which increases as l₁ (and thus the ratio l₁ / l'₁) and / or l₂ (and thus the ratio l₂ / l'₂) increases, while at the same time limiting the maximum tension of the belt 8.
[0208] If present, the first end element 131 and the second end element 132, in particular the first plate 141 comprising the first holes 151 and the second plate 142 comprising the second holes 152, allow to drastically reduce the risk of deterioration or even breakage of the spring 71, both during installation of the belt 8 and in use. Indeed, in such acase, the spring 71 does not have respective hook-shaped ends and hooked, respectively, to the first arm 21 and the second arm 22. Conversely, at least one coil 121 ' of the first end portion 121 is housed in the first holes 151 of the first plate 141 and at least one coil 122 ' of the second end portion 122 is housed in the second holes 152 of the second plate 142, allowing for better distribution of the traction load. Furthermore, the fact that the first plate 141 and the second plate 142 are coplanar and lie on a plane comprising the spring axis SA allows to indirectly define the spring axis SA, and thus the orientation of the spring 71, with respect to the arms 21, 22, avoiding undesirable mechanical moments.
[0209] Finally, it is clear that modifications may be made to the tensioner 11 without departing from the scope of protection defined by the claims.
[0210] For example, the first constraint point Pl may be defined by a first hole (e. g. present on the first ring 41 or on an outer radial appendage of the first ring 41 ) to which the first end 81 of the spring 71 is constrained, and the second constraint point P2 may be defined by a second hole (e. g. present on the second ring 42 or on an outer radial appendage of the second ring 42 ) to which the second end 82 of the spring 71 is constrained.
[0211] The first axis Al and the second axis A2 may be coincident with each other. In such a case, the first ring 41 and the second ring 42 are rotatable with respect to the base 12 about a common axis.
[0212] The first arm 21 and the second arm 22 may be substantially rod-shaped instead of ring-shaped. In such acase, the first arm 21 and the second arm 22 may be hinged to the base 12 about their respective axes, distinct from or coincident with each other, or one of the first arm 21 and the second arm 22 may be hinged to the base 12 and carry, hinged to it, the other one of the first arm 21 and the second arm 22.
Claims
CLAIMS1. Tensioner for an accessory drive of an internal combustion engine ( 2 ), the accessory 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 an electrical machine ( 7 ), and a belt ( 8 ) wound at least on the first pulley ( 3 ) and the second pulley ( 4 ), the tensioner ( 1 ) comprising:- a base ( 12 ) configured to be fixed to a fixed support structure ( 13 );- a first arm ( 21 ) rotatable with respect to the base ( 12 ) about a first axis (Al );- a second arm ( 22 ) rotatable about a second axis (A2 ); - a first tensioning pulley ( 31 ) carried by the first arm ( 21 ) and rotatable with respect to the first arm ( 21 ) about a first pulley axis ( PAI );- a second tensioning pulley ( 32 ) carried by the second arm ( 22 ) and rotatable with respect to the second arm ( 22 ) about a second pulley axis ( PA2 );- a traction spring ( 71 ) extending along a spring axis ( SA) and acting on the first arm ( 21 ) and the second arm ( 22 ) to push the first tensioning pulley ( 31 ) and the second tensioning pulley ( 32 ) into contact with respective spans ( 8a, 8b ) of the belt ( 8 ), wherein the spring ( 71 ) comprises a first end ( 81 ) constrained to the first arm ( 21 ) at a first constraint point ( Pl ) and a second end ( 82 ) constrained to the second arm ( 22 ) at a second constraint point ( P2 ),wherein at least one of the following relations applies:> li'l2> l'2wherein:- l₁: distance between the first axis (A1) and the first constraint point (P1);-: distance between the first axis (Al ) and the first pulley axis ( PAI );- l2: distance between the second axis (A2 ) and the second constraint point ( P2 );- l2: distance between the second axis (A2 ) and the second pulley axis ( PA2 ).
2. Tensioner as claimed in claim 1, wherein at least one of the following relations applies:l1≤ l1,maxl2≤ l2,maxwherein:- liimax ‘ maximum distance between the first axis (Al ) and the first constraint point ( Pl ), wherein liima.x is chosen such that the derivative of a curve representative of a torque of the tensioner, at a predetermined maximum angular di stance between the first tensioning pulley ( 31 ) and the second tensioning pulley ( 32 ), as a function of the distance between the first axis (Al ) and the first constraint point ( Pl ) is equal to a first predetermined threshold;- l2,max: maximum distance between the second axis (A2 ) and the second constraint point ( P2 ), wherein l2imaxis chosen such that the derivative of a curve representative of a torque of the tensioner, at a predetermined maximum angular di stance between thefirst tensioner pulley (31 ) and the second tensioner pulley (32 ), as a function of the distance between the second axis (A2 ) and the second constraint point (P2 ) is equal to a second predetermined threshold.
3. Tensioner as claimed in claim 2, wherein at least one of the following relations applies:l₁,max = 1,5 · l'₁^2, max ~ ’ ^24. Tensioner as claimed in claim 2 or 3, wherein at least one of the following relations applies:1,1 • 11 A l A li max1.1 ' I2 — l2≤ l2,max5. Tensioner as claimed in any of claims 2 to 4, wherein at least one of the following relations applies:1,2 · l'₁ ≤ l₁ ≤ l₁,max1,2 · l'₁ ≤ l₁ ≤ l₁,max1.2 • Z2 — ^2 — ^-2, max6. Tensioner as claimed in any of claims 2 to 5, wherein at least one of the following relations applies:1,3 · l'1≤ l1≤ l1,max1,3 · l'₁ ≤ l₁ ≤ l₁,max1,3 · l'2≤ l2≤ l2,max7. Tensioner as claimed in any of claims 2 to 6, wherein at least one of the following relations applies:1.4 li < li < limax1,4 • V2 < Z2< l2,max8. Tensioner as claimed in any of the preceding claims, wherein an angular distance between a conjunction between the first constraint point (Pl ) and the first axis (Al ) and a conjunction between the first pulley axis (PAI ) and the first axis (Al ) and an angular distance between a conjunction between the second constraint point (P2 ) and thesecond axis (A2 ) and a conj unction between the second pulley axis ( PA2 ) and the second axis (A2 ) are chosen as a function of a predetermined torque of the tensioner under nominal conditions.
9. Tensioner as claimed in any of the preceding claims, wherein the first arm ( 21 ) comprises a first constraint element ( 91 ) defining the first constraint point ( Pl ), wherein the second arm ( 22 ) comprises a second constraint element ( 92 ) defining the second constraint point ( P2 ).
10. Tensioner as claimed in claim 9, wherein the first constraint element ( 91 ) comprises a first pivot ( 101 ) extending along a first pivot axis ( PPA1 ) on which the first constraint point ( Pl ) lies, wherein the second constraint element ( 92 ) comprises a second pivot ( 102 ) extending along a second pivot axis ( PPA2 ) on which the second constraint point ( P2 ) lies.
11. Tensioner as claimed in claim 10, wherein the first arm ( 21 ) comprises a first appendage ( 111 ) configured to carry the first pivot ( 101 ), wherein the second arm ( 22 ) comprises a second appendage ( 112 ) configured to carry the second pivot ( 102 ).
12. Tensioner as claimed in any of the preceding claims, comprising:- a first end element ( 131 ) operatively interposed between the spring ( 71 ) and the first arm ( 21 );- a second end element ( 132 ) operatively interposed between the spring ( 71 ) and the second arm ( 22 ), wherein the spring ( 71 ) comprises a first end portion ( 121 ) and a second end portion ( 122 ),wherein the first end element ( 131 ) comprises a first plate ( 141 ) having first holes ( 151 ) configured to house at least one coil ( 121 ' ) of the first end portion ( 121 ),wherein the second end element ( 132 ) comprises a second plate ( 142 ) having second holes ( 152 ) configured to house at least one coil ( 122 ’ ) of the second end portion ( 122 ),wherein the first plate ( 141 ) and the second plate ( 142 ) are coplanar and lie on a plane comprising the spring axis (SA).
13. Tensioner as claimed in any of the preceding claims, wherein the second axis (A2 ) is coincident with the first axis (Al ).
14. Tensioner as claimed in any of claims 1 to 12, wherein the first arm ( 21 ) and the second arm ( 22 ) comprise, respectively, a first ring (41) and a second ring ( 42 ), the second axis (A2 ) being distinct from the first axis (Al ).
15. 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 electrical machine ( 7 ), a belt ( 8 ) wound at least on the first pulley (3) and the second pulley (5), and a tensioner ( 11 ) as claimed in any of the preceding claims.