Cross-Reference to Related Applications

This Patent Appl ication claims priority from Italian Patent Application No . 102022000015750 filed on July 26 , 2022 the entire disclosure of which is incorporated herein by reference .

Technical Sector

The present invention relates to a tensioner for an accessory drive o f a motor vehicle and to an accessory drive including such a tensioner .

Background

The accessory drive of an internal combustion engine generally comprises a pulley connected to the drive shaft , a pulley connected to the shaft of the electrical machine and may comprise one or more pulleys for driving other accessories , such as for example the compressor of the air conditioning system . The accessory drive also comprises a belt for the transmission of the motion between the aforementioned pulleys and a tensioner adapted to ensure a correct minimum level of tension of the belt and avoid slippages between the same and the pulleys .

In conventional accessory drives , in which the electrical machine is an alternator driven by the engine , the tensioner acts on the loose span of the belt , i . e . the span placed downstream of the engine and upstream of the alternator with reference to the direction of motion of the belt .

In motor vehicles , a reversible electrical machine is increasingly used instead of the conventional alternator, which can operate - in addition to the conventional generator mode - according to further modes , for example as a regenerative brake ( so-called " recovery" condition) , or as an additional motor acting in combination with the internal combustion engine ( so-called "boost" condition) .

The use of a reversible electrical machine means that the span of the belt that is tensioned in the operating conditions in which the electrical machine is dragged by the engine becomes the loose span when the driving torque is delivered by the electrical machine .

Various solutions have therefore been developed that allow to ensure the correct tensioning of both spans of the belt .

One solution for example consists in using a tensioner with two arms hinged in a common pin and bearing respective pulleys . The arms are subj ected to the elastic force of a spring that tends to bring them closer together so as to keep the pulleys in contact with the respective spans of the belt . 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 .

The encumbrance of the base on which the arms are articulated and of the spring arranged around the common axis of articulation of the arms themselves are such that they make this solution unsuitable for applications where there are packaging constraints within the path of the belt, such as for example in the case where the drive provides only two pulleys . Furthermore , the arrangement of the arms with respect the resultants of the forces acting on the pulleys is not optimal .

Another solution consists in mounting the tensioner on the electrical machine .

According to a known solution, the tensioner comprises a base adapted to be fixed to the electrical machine , a first annular element rotatable with respect to the base about the axis of the electrical machine and bearing a first pulley, and a second annular element rotatable with respect to the base about the axis of the electrical machine and bearing a second pulley . A spring acts between the two annular elements which is adapted to exert an elastic force between the elements themselves and is adapted to maintain the first and second pulleys in contact with respective spans of the belt .

A drawback connected with the aforementioned solution is the need to operate at a relatively high tension of the belt to allow an optimal operation in the recovery and boost conditions .

According to another known solution, the tens ioner comprises a base adapted to be fixed to the electrical machine , an annular element with respect to the base about the axis of the electrical machine and bearing a first pulley, and an arm hinged to the annular element and bearing a second pulley .

Aim of the present invention is to reali ze a tensioner of the latter type for an accessory drive , which presents a better ef ficiency and allows to reduce losses in the accessory drive .

Disclosure of the Invention

The above aim is achieved by a tensioner for an accessory drive as claimed in Claim 1 .

A further aim of the present invention is the reali zation of an accessory drive with reduced losses .

This aim is achieved by an acces sory drive as claimed in Claim 15 .

Brief Description of the Drawings

For a better understanding of the present invention, a preferred embodiment is described, by way of non-limiting example only, with reference to the accompanying drawings , in which :

Figure 1 is a schematic front view of an accessory drive comprising a tensioner according to the invention;

Figure 2 is a front view of the tensioner of Figure 1 ;

Figure 3 is a section along line I I I - I I I of Figure 2 ;

Figure 4 is a partial section taken along line IV- IV of Figure 2 ;

Figure 5 is a partial section taken along line V-V of Figure 2 ;

Figures 6 and 7 are graphs showing the energy spent to operate the accessory drive of Figure 1 as a function of the geometric parameters of the tensioner ;

Figure 8 is a schematic front view of an accessory drive comprising a tensioner in a di f ferent embodiment of the present invention; and

Figures 9 and 10 are graphs showing the energy spent to operate the accessory drive of Figure 8 as a function of the geometric parameters of the tensioner ;

Figure 11 is a schematic front view of an accessory drive comprising a tensioner according to a third embodiment of the invention;

Figure 12 is a front view of the tensioner of Figure 11 ;

Figures 13 and 14 are sections according to lines XI I I - XI I I and XIV-XIV of Figure 11 .

Detailed Description of the Invention

With reference to Figure 1 , 1 denotes an accessory drive of an internal combustion engine 2 .

The accessory drive 1 comprises a first pulley 3 connected to a drive shaft 4 of the engine 2 , having axis EA, a second pulley 5 connected to a shaft 6 of an electrical machine 7 , having axis MA, and a belt 8 connecting the first pulley 3 and the second pulley 5 together . Optionally, the accessory drive 1 may comprise other pulleys for dragging other accessories of the engine 2 . Figure 1 shows by way of example a third pulley 9 of a compressor of the air conditioning system .

The accessory drive 1 further comprises a tensioner 10 mounted on the electrical machine 7 and comprising ( Figures 2-5 ) : an annular base 11 integrally comprising a flat flange 12 adapted to be fixed to a casing 13 of the electrical machine 7 ( Figure 1 ) and an annular collar 14 , having axis TA, not coincident in use with the axis MA as will be better described below, extending axial ly cantilevered from the flange 12 ; a main ring-shaped arm 15 (hereinafter " ring 15" ) having axis TA rotatably supported on the base 11 around the collar

14 ( figs . 3 - 5 ) ; a first tensioning pulley 16 carried by an external radial appendage 17 ( Fig . 5 ) of the ring 15 and rotatable with respect to it about an axis PAI parallel to the axes MA and TA; a tensioning arm 18 rotatably supported on the ring 15 and rotatable with respect to it about an axis AA parallel to the axes MA and TA and circumferentially spaced with respect to the axis PAI ; and a second tensioning pulley 19 carried by the tensioning arm 18 and rotatable with respect to it about an axis PA2 parallel to the axes MA and TA.

More speci fically, the ring 15 is axially interposed between a lower bushing 21 that supports it axially on the flange 12 and radially with respect to the collar 14 of the base 11 and an upper damping ring 22 forced against the ring

15 by an elastic or " flexplate" stop ring 23 . The stop ring 23 is locked on the collar 14 of the base 11 by means of a thread-rolling operation so as to be conically deformed and exert an axial force on the damping ring 22 .

The tensioning arm 18 i s rotatably mounted on a pin 24 having axis AA extending axially cantilevered from the ring 15 .

For this purpose , the tensioning arm 18 is provided with a hub 25 provided with a through hole 26 having axis AA and defining a cylindrical seat 27 coaxial to the hole 26 and axially open towards the ring 15 .

The pin 24 engages the hole 26 of the hub 25 with interposition of radial and axial support bushings 28 , and is axially locked by a stop ring 28 ' fitted on a free end of the pin 24 .

A torsion spring 29 , having its own end portion 30 housed in the seat 27 of the hub 25 and constrained to its own opposite end (not visible in the figures ) exerts on the tensioning arm 18 a force tending to bring the pulleys 16 and 19 closer together, thus keeping them in contact with the respective spans 8a, 8b of the belt 8 arranged on opposite sides of the second pulley 5 ( respectively downstream and upstream of the second pulley 5 considering the direction of motion of the belt 8 , which is clockwise with reference to Figure 1 ) .

According to the present invention, the axis TA of rotation of the ring 15 is not coincident with the axis MA of the pulley 5 o f the electrical machine 7 . In particular, the axis TA is di splaced with respect to the axis MA on the opposite side with respect to the direction of the resultant HL ( Fig . 1 ) of the forces exerted by the belt 8 on the second pulley 5 ( "hub load" ) under static equilibrium conditions .

The internal diameter of the collar 14 is dimens ioned so as to allow mounting the tensioner 10 on the electrical machine 7 in the presence of the second pulley 5 , the encumbrance of which is schematically indicated with a dotted line in Figure 3 . This diameter must therefore be at least equal to the outer diameter of the second pulley 5 plus twice the distance between the axes TA and MA (hereinafter " eccentricity" )

Figure 6 is a graph showing the values of the energy spent to operate the drive 1 during a WLTP homologation cycle for various positions A, B, ..., H of the axis TA around the axis MA, expressed in terms of equivalent emissions [ g CCh/ km] , and in the condition where the axis TA coincides with MA ( eccentricity 0 ) . Each of the positions A, B, ..., H has an eccentricity equal to 8 mm, and the various positions are angularly equally spaced from one another by 45 ° , as shown in the following table :

TABLE 1

By looking at the values associated with the graph, it is evident that points with eccentricity facing the opposite side with respect to the hub load HL have loss values lower than a condition without eccentricity (point MA) .

According to a preferred embodiment of the invention, the axis TA lies in an angle of 180 ° , and more preferably of 90 ° , with a vertex coincident with MA and having as bisector the line of action of the hub load HL . This 90 ° angle is highlighted in Figure 6 with a cross hatching .

The optimal point 0, with which the lower losses are associated, is displaced, with respect to the line of action of the hub load HL, from the opposite side to the tensioning arm 18 . In other words , in the embodiment of Figures 1-5 , in which the tensioning arm 18 is to the left of the hub load HL, the condition of optimal eccentricity to minimise the energy spent in the homologation cycle is to the right of the line of action of the hub load HL .

Figure 7 is a graph showing the values of the energy spent to operate the drive 1 during a WLTP homologation cycle , expressed in terms of equivalent emissions [ g CCd/ km] , as a function of the eccentricity rTA of the axi s TA with respect to the axis MA and of the angle aTA, i . e . the direction of the eccentricity (measured in ° starting from the axis of the abscissa of the graph) : it can be clearly seen how this energy decreases with increasing eccentricity and has a minimum .

In this case under examination, the minimum ( 3 , 467 g CCh/ km) is in aTA = 38 . 18 ° for an eccentricity equal to 8 mm .

Clearly, the eccentricity cannot be increased indefinitely to avoid interference between the ring 15 and the second pulley 5 and to contain the encumbrance of the tensioner 10 during operation .

Figure 8 shows a di f ferent embodiment of the present invention, in which the first tensioning pulley 16 carried by the ring 15 acts on the span 8b of the belt 8 and the second tensioning pulley 19 carried by the tensioning arm 18 acts on the span 8a of the belt 8 . In other words , the tensioning arm 18 is in this case to the right o f the line of action of the hub load HL and the first tensioning pulley 16 is to the left .

Figures 9 and 10 are equivalent to Figures 6 and 7 and entirely congruent results are present in them .

The points A, B, ..., H were selected with the same criteria ( 8mm of eccentricity with an angular pitch of 45 ° around the axis MA) .

TABLE 2

Also in this case , by looking at the values associated with the graph of Figure 9 , it is evident that points with eccentricity facing the opposite side with respect to the hub load HL have loss values lower than a condition without eccentricity (point MA) .

According to a preferred embodiment of the invention, the axis TA lies in an angle of 180 ° , and more preferably of 90 ° , with a vertex coincident with MA and having as bisector the line of action of the hub load HL . This 90 ° angle is highlighted in Figure 9 with a cross hatching .

The optimal point 0, with which the lower losses are associated, is displaced, with respect to the line of action of the hub load HL, from the opposite side to the tensioning arm 18 . In other words , in the embodiment of Figure 8 , in which the tensioning arm 18 is to the right of the hub load HL, the condition of optimal eccentricity to minimise the energy spent in the homologation cycle is to the left of the line of action of the hub load HL .

The graph of Figure 10 shows even more clearly how the energy spent to operate the drive 1 decreases with increasing eccentricity and has a minimum .

In this case , for an eccentricity of 8 mm the minimum ( 3 , 237 g CCh/ km) is in aTA = 59 . 22 ° .

Figure 11 schematically shows an accessory drive 1 completely analogous to the drive previously described and provided with a tensioner 40 according to a third embodiment of the invention .

The tensioner 40 ( Figures 12 - 14 ) is functionally equivalent to the tensioner 10 described with reference to Figures 2 to 5 , and is described below insofar as it di f fers structurally therefrom, using the same reference numerals to identi fy parts equal to or corresponding to parts already described .

The tensioner 40 comprises a base 11 integrally comprising an arcuate flange 12 facing in use a circumferential portion of the casing of the electrical machine (not shown) and adapted to be fixed to said casing by means of a plurality of screws 41 . The base 11 further comprises an annular collar 14 extending on a plane parallel to the plane of the flange 12 and connected cantilevered to it by a step-like j oining portion 42 .

The collar 14 , having axis TA not coincident in use with the axis MA as will be better described below, is axially spaced from the flange 12 so as to extend, in an axial direction, beyond the second pulley 5 , so as to axially face it .

The tensioner 40 further comprises , in a manner analogous to what is described for the tensioner 10 : a main arm 15 having axis TA rotatably supported by the collar 14 ( Figures 13 and 14 ) ; a first tensioning pulley 16 carried by an external radial appendage 17 ( Figures 12 and 14 ) of the main arm 15 , rotatable with respect to it about an axis PAI parallel to the axes MA and TA and cooperating with the span 8a of the belt 8 ; a tensioning arm 18 rotatably supported on the main arm 15 and rotatable with respect to it about an axis AA parallel to the axes MA and TA and circumferentially spaced with respect to the axis PAI ; and a second tensioning pulley 19 carried by the tensioning arm 18 , rotatable with respect to it about an axis PA2 parallel to the axes MA and TA and acting on the span 8b of the belt 8 .

The modes of connection of the main arm 15 with the collar 14 and of the tensioning arm 18 with the main arm 15 are equivalent to what is described with reference to the tensioner 10 .

According to the present invention, as already pointed out , the axis TA of rotation of the main arm 15 of the tensioner 40 is not coincident with the axis MA of the second pulley 5 of the electrical machine 7 . In particular, the axis TA is displaced with respect to the axis MA on the opposite side with respect to the direction of the resultant HL ( Fig . 11 ) of the forces exerted by the belt 8 on the second pulley 5 ( "hub load" ) under static equilibrium conditions .

The relative arrangement of the axes TA, MA, PAI and PA2 is identical to that of the corresponding axes of the tensioner 10 , and the kinematic and dynamic behaviour of the tensioner 40 is quite similar to that of the tensioner 10 . As far as energy saving and eccentricity optimisation are concerned, therefore , the same data set out above with reference to the tensioner 10 applies .

Since in this case the collar 14 and the main arm 15 are arranged facing the second pulley 5 instead of around it , no constraints on the dimensioning thereof in a radial direction are caused . This allows to release the dimensioning and positioning o f the collar 14 and of the main arm 15 from the eccentricity value , which can then be increased without increasing the radial encumbrance of the tensioner 40 .

According to an embodiment variant of the tensioner 40 , the first tensioning pulley 16 carried by the main arm 15 acts on the span 8b of the belt 8 and the second tensioning pulley 19 carried by the tensioning arm 18 acts on the span 8a of the belt 8 . In other words , the tensioning arm 18 is in this case to the right of the line of action of the hub load HL and the first tensioning pulley 16 is to the left .

According to a further variant embodiment , the main arm 15 and/or the tensioning arm 18 can be supported by a rolling bearing instead of by a sliding bearing .

From an examination of the characteristics of the invention, the advantages that it allows to obtain are evident . In particular, by arranging the axis of the ring 15 in an eccentric position with respect to the axis of the electrical machine it is possible to obtain advantages with regard to the energy spent for operating the accessory drive and, therefore , savings on emissions . Finally, it is clear that modi fications and variations can be made to the embodiments described that do not depart from the scope of protection defined by the Claims .

For example , the homologation cycle could be a homologation cycle of other type than the aforementioned WLTP homologation cycle .