CN220523180U

CN220523180U - Device for a motor vehicle drive train

Info

Publication number: CN220523180U
Application number: CN202190000848.8U
Authority: CN
Inventors: C·鲍迪诺; L·赞科; R·弗加里
Original assignee: Valeo Embrayages SAS
Current assignee: Valeo Embrayages SAS
Priority date: 2020-11-06
Filing date: 2021-11-04
Publication date: 2024-02-23
Anticipated expiration: 2031-11-04
Also published as: WO2022096609A1; FR3116093A1; EP4240988A1; FR3116093B1

Abstract

The utility model discloses a device (10) for a motor vehicle drive train, comprising: -a rotating element (3) for rotatable mounting about a rotation axis (X), the rotating element (3) comprising a radial portion (7) and a cylindrical skirt (8) of radial dimension (Ep) extending from the radial portion (7), -an annular cover (9) arranged together with the rotating element (3) to enclose the elastic member (5), wherein the cylindrical skirt (8) and the cover (9) each comprise positioning means (80, 90) which co-act in such a way as to position the cover (9) on the rotating element (3), the positioning means (80, 90) of the cylindrical skirt (8) and the cover (9) being fixed together by welding.

Description

Device for a motor vehicle drive train

Technical Field

The present utility model relates to the field of vehicle drive trains, and more particularly to devices fitted to vehicle drive trains. In particular, the utility model relates to dual mass flywheels.

Background

It is known practice to equip a vehicle transmission with a dual mass flywheel comprising a main flywheel and a secondary flywheel coaxial and rotatable with respect to each other, in order to filter in particular the vibrations caused by the non-cyclical behaviour upstream of the gearbox. The primary and secondary flywheels are rotatably coupled by an elastic member so that torque can be transmitted and non-circulation between the primary and secondary flywheels is suppressed.

In a known manner, the main flywheel comprises a rotating element for fixing to, for example, a crankshaft of an internal combustion engine, and a cover for housing the elastic member. Document DE102018128216A1 discloses such a main flywheel of a dual mass flywheel, wherein the cover and the rotating element are rigidly fixed end-to-end, using laser welding for optimal welding. However, this solution has drawbacks.

The laser welding method allows the outer circumferences of the cap and the rotating element to be assembled end-to-end, but due to the lack of filler material and the finesse of the beam of the laser source, the gap between the parts is required to be very small and have an acceptable geometric profile. However, manufacturing these components by cutting and stamping can produce shapes that are not suitable for laser welding.

Additional machining operations are required to make the shapes compatible and the gaps between the parts are also acceptable for laser welding. Furthermore, the end-to-end assembly of the components within the device is cumbersome and forces the main flywheel to use additional components, such as inertia rings attached to the cover surface by welding. The assembly steps and the production of such devices forming the main flywheel are therefore costly.

Disclosure of Invention

It is a particular object of the present utility model to provide a simple, efficient and economical solution to this problem.

To this end, according to a first aspect, the utility model proposes a device for a motor vehicle drive train, comprising:

a rotating element intended to be rotatably mounted about a rotation axis, the rotating element comprising a radial extension and a cylindrical skirt extending from the radial extension,

an annular cover arranged with the rotating element to enclose the elastic member,

wherein the cylindrical skirt and the cap each comprise positioning means which co-act in such a way as to position the cap on the rotating element, said positioning means of the cylindrical skirt and cap being fixed together by welding.

Thanks to these features, the device can simplify the installation and assembly of the cover on the rotating element. By forming the locating means on each component, the cap is simply and quickly axially located on the cylindrical skirt, even manually, without the need for preparation work or additional operations. Their co-action provides in particular angular indexing of the cap on the cylindrical skirt for the positioning means, for example by complementation of the shape. Such a positioning means provides greater geometric tolerances in the manufacture of the component while preventing abutment problems between the cap and the cylindrical skirt, for example due to laser welding assembly defects.

The assembly of the positioning device is also carried out in a simple manner in a single welding operation without the need for post-operation finishing, such as welding with filler material or arc welding. Fixing the positioning means together in this way makes it possible to rigidly fix the cap to the cylindrical skirt.

The cost is obviously reduced. Simplifying and optimizing the design and assembly of these components. The individual components may combine multiple functions, for example, the end of the cylindrical skirt of the rotary element may be brought into engagement with the motor ring gear by interference or welding, thereby reducing the number of components present in the device. It is also possible to simplify the design of the cover to its most basic form in order to reduce its volume, weight or to simplify its assembly in such a device.

Such a device according to the first aspect of the utility model may comprise one or other of the following features, alone or in combination:

advantageously, a cylindrical skirt may surround the cap. Thus, the cap may be contained within the cylindrical skirt of the rotary element. The advantage here is that the volume of the two parts is limited by the radial arrangement of the cap within the cylindrical skirt of the rotating element.

The positioning means of the cover are formed by the outer diameter D3 of the cover. The advantage here is that the volume of the two parts is limited by the radial arrangement of the cap within the cylindrical skirt of the rotating element. The positioning means of the cap may be arranged substantially along a layout circle C2, which may be equal to or greater than the outer diameter of the cap, in particular between the outer diameter of the cap and the inner diameter of the cylindrical skirt;

In particular, the positioning means of the cylindrical skirt may be formed by an inner diameter D1 of the cylindrical skirt, so as to limit its volume. The positioning means of the cylindrical skirt may be arranged substantially along a layout circle C1 located between the inner and outer diameters of the cylindrical skirt. The shape of the cover can be simplified, for example completely contained in a plane P perpendicular to the axis X, that is to say without axially recessed, offset or deformed portions;

in particular, the positioning means of the cylindrical skirt and of the cap may be arranged substantially along the same layout circle, which may be between the inner diameter of the cylindrical skirt and the outer diameter of the cap. Such positioning means are therefore located at the same radial distance from the axis of rotation. As a result, uniform radial support is provided for the assembly of the components by the positioning means acting in concert at only certain points on the components.

These devices perform a number of functions: the positioning means of the parts co-act to ensure at the same time axial support, centring and angular indexing of the cap on the cylindrical skirt.

Advantageously, the positioning means of the cap may have a shape complementary to those of the cylindrical skirt;

the positioning means of the cylindrical skirt and of the cap can be fixed together by means of a weld. Thus, a weld may be produced at least partially at said positioning means of the cylindrical skirt and the cap. The weld may extend at least partially around the rotation axis X, in particular at least 240 degrees. The weld may extend continuously over 360 degrees around the axis X, thereby ensuring a fixed assembly of the positioning device in axial and angular directions. Thus, the entire cap is rigidly fixed to the cylindrical skirt;

The weld seam may be produced by filler material welding;

the weld seam can preferably be produced by arc welding, in particular by cold welding. The advantage of such arc welding is that the heat release (principle of cold welding) is reduced. This reduces deformation and increases the tolerance at the fit-gap J, especially at the positioning means of the two parts. Thus, no preparation work is required to position the cylindrical skirt and cap, or post-operation finishing is performed on these components;

the rotary element and the positioning means of the cylindrical skirt may be formed as a single piece, made in one piece. The positioning means of the cylindrical skirt may be integral with the cylindrical skirt;

the cover and the positioning means of the cover may be formed as a single piece made in one piece. The positioning means of the cylindrical skirt may be integral with the remainder of the cap;

the cylindrical skirt may comprise a specific profile intended to interact with the positioning means of the cap;

the cap may comprise a specific profile intended to interact with the positioning means of the cylindrical skirt;

the positioning means can be realized by pressing the cylindrical skirt and the cap respectively. Preferably, the positioning means may be manufactured by stamping or machining the rotating element and the cover, respectively. This has the advantage that the devices are produced partly rather than over the whole part. Simplifying manufacture, particularly by limiting machining or stamping to only areas where locating means will or will not be formed on each component;

Alternatively, said positioning means of the cylindrical skirt and of the cap may be formed by cutting, stamping or any other method known to the person skilled in the art;

the cylindrical skirt and the cap of the rotating element may each comprise at least three positioning means, preferably angularly distributed, in particular regularly distributed, about the axis. Thus, the cap is uniformly supported on the surface of the skirt. The lack of parallelism of the components is limited. In other words, the positioning of the components is more accurate and stable.

These components are relatively inexpensive;

the positioning means of the cylindrical skirt may be of identical shape;

the positioning means of the cover may be of identical shape;

the number of positioning means per component may be even or odd.

Preferably, the cylindrical skirt and the cap of the rotating element may comprise the same number of positioning means. Thus, the positioning means may be arranged radially and/or axially facing each other to facilitate indexing during assembly;

advantageously, the cylindrical skirt and the cap of the rotating element may each comprise a limited number of positioning means, for example less than five, preferably equal to three, per component. Note that the fewer (limited in number) positioning devices, the easier it is to adjust the production parameters and tools to obtain a very flat surface for contact between the components. The positioning means are advantageously limited according to, for example, the size and shape of the positioning means;

In a first variant, the positioning means of the cap may be a support lug that positions a radial portion of the cap with respect to the cylindrical skirt of the rotating element;

in a second variant, the cylindrical skirt may form at least one support seat, the cover forming at least one protrusion, the cylindrical skirt and the cover interacting by positioning the respective protrusions on the respective support seats. The support seat and the protrusion form positioning means for the cylindrical skirt and the cap;

in particular, the cylindrical skirt forms at least two support seats and the cap forms at least two projections, the cylindrical skirt and the cap interacting by positioning said respective projections on said respective support seats. In other words, the positioning means of the cylindrical skirt and of the cap may be protrusions on the cap, which are positioned on a support seat formed in the cylindrical skirt of the rotating element. The advantage of these protrusions is that they ensure a larger surface area for centring the cap with the cylindrical skirt, in particular by reducing the radial distance between the parts to an absolute minimum. The volume and material requirements of such a component are therefore limited only by the co-action of the projection and the support seat.

The support seat can be made by machining the cylindrical skirt, i.e. by machining specific areas of the support seat. Alternatively, the support seat may be made by stamping a cylindrical skirt;

The protrusions may be made by machining the rest of the cover, i.e. by machining the spaces between adjacent protrusions on the cover. Alternatively, the protrusions may be made by stamping the cover.

The projection on the cap may have a shape complementary to the support seat on the cylindrical skirt. This simplifies manual centering and indexing of the cap, requiring no special tools prior to welding;

the projection may comprise a plurality of support surfaces for accommodation on the support seat;

the protrusions are solid portions, convex in shape, and may be of the same shape. The protrusions may thus extend discontinuously in the circumferential direction about the axis X;

in particular, each protrusion may open radially outwards;

the protrusions on the cover may have a convex shape;

the projection may for example have a circular shape and extend radially outwards from the outer diameter of the cap, that is to say in the direction of the cylindrical skirt;

as a variant, the protrusions may have a polygonal shape, for example triangular, rectangular or trapezoidal. For example, in a plane orthogonal to the axis X, each protrusion may be a protrusion in the form of a tooth;

the term "support seat" refers in particular to an open recess formed in the cylindrical skirt in order to house at least one positioning means of the cap. For the positioning means of the mounting and positioning cover, the depth of the recess is such that it is different from a simple notch or score;

Preferably, the cylindrical skirt may have a maximum thickness Ep measured along a reference axis, and the support seat may have a depth measured along another axis parallel to the reference axis. In particular, the reference axis is in a radial direction;

the depth of the support seat may be the largest dimension of the support seat in the radial direction;

the depth of the support seat may be between 15% and 70% of the maximum thickness Ep of the cylindrical skirt;

the depth of the support seat may be between 25% and 65% of the maximum thickness Ep of the cylindrical skirt.

For example, it may be equal to or greater than 35% of the maximum thickness Ep of the cylindrical skirt;

in particular, it may be between 30% and 60% of the maximum thickness Ep of the cylindrical skirt.

For all these ranges of values, the depth (for example the radial dimension) of the support seat is sufficient and limited with respect to the rest of the cylindrical skirt, so as to be established to accommodate the positioning means of the cap. Outside this range of values, the cylindrical skirt of the rotating element may be damaged during assembly with the cover or during operation on the vehicle, or may be insufficiently sized to support the protrusion. These numerical ranges thus offer the additional possibility of reducing the radial volume without causing problems in terms of supporting, centring or irreversibly damaging the cylindrical skirt of the containing cap;

Preferably, the support seat may be hollow, concave, and may be of the same shape. The support seat may extend discontinuously in a circumferential direction around the axis X;

in particular, each support seat can open radially inwards;

the support seat may be a housing, an opening, a cavity or a recess in the material;

preferably, the support seat on the cylindrical skirt may have a concave shape. The support seat may have a circular shape and extend from the inner diameter of the cylindrical skirt, that is to say in the direction of the cap.

As a variant, the support seat may have a polygonal shape, for example triangular, rectangular or trapezoidal;

advantageously, the support seat may have a stepped shape hollowed out from the end edge of the cylindrical skirt along an axis orthogonal to the rotation axis X. Thus, the distal portion of the support seat is hollowed out to a greater depth than the proximal portion of the same support seat. In this case, the ends of the protrusions bear on the distal end portion of the support base. In other words, the distal portion of the support base defines the bottom of the support base. Preferably, the remaining space in the distal portion may partially accommodate the weld.

In particular, the gap between the distal portion of the support seat and the end edge of the cylindrical skirt is such that it defines a radial edge of the support seat. Thus, the support seat may comprise a radial edge extending from an end edge of the cylindrical skirt to a bottom of the support seat;

In other words, the support seat may comprise:

the end of the projection bearing against a distal portion, called the bottom, of the end edge of the cylindrical skirt, the remaining space of the bottom of the support seat partly housing the weld,

the radial edge on which the raised support surface bears, the radial edge of the support seat extending from the end edge of the cylindrical skirt to the bottom of the support seat.

A support seat having this shape has the advantage of being simple to produce, in particular by punching or removing material, for example by machining. The radial edge of the support seat makes it possible to position and retain the protuberance of the cap on the cylindrical skirt, while the distal portion of the support seat makes it possible to center the protuberance of the cap with respect to the cylindrical skirt.

The space delimited by the distal portion (bottom of the support seat) also has the advantage of partly housing the weld of the fixed positioning device, thus optimizing the volume of the assembled component;

the cross-section of the support seat may be substantially rectangular or hollow semi-cylindrical, hemispherical or fluted. For example, in a plane orthogonal to the axis X, the support seat may be a circular or circular cavity or recess;

in particular, the cross section of the support seat may be semicircular;

In particular, one lateral support surface of the projection may be housed on a radial edge of the support seat, while the other lateral support surface may receive the weld;

in particular, the radial edges of the support seat and the weld seam may be arranged axially on either side of the cover, thereby rigidly fixing the protrusion of the cover to the support seat;

in other words, defining a plane P passing through the cover and the axis X, the radial edges of the support seat and the weld may be axially arranged on either side of the plane P. Due to its characteristics, the cap is axially positioned and fixed to the cylindrical skirt on one side by the weld joining the cap to the distal portion of the support seat and on the other side by the abutment of the radial edge of the support seat on the cap. This arrangement therefore has the advantage of keeping the cover stationary, limiting the lack of parallelism between the components.

In particular, the weld seam may be partly co-arranged on the first support surface of the protrusion and on the distal end portion of the support seat, so as to rigidly fix the protrusion and the support seat;

advantageously, one of the raised support surfaces may form a groove or rib with the cap, said groove or rib interacting with the end edge of the cylindrical skirt and/or with the support seat;

in particular, the groove or rib may interact with a radial edge of the support seat.

The advantage of these shapes is that their interaction is simplified, for example:

or by housing protruding ribs on the end edges and on a portion of the support seat, called radial edge,

or by receiving a portion of the support seat in a recess of the projection, called radial edge;

in particular, said grooves or ribs may have a shape complementary to said radial edges, their mutual abutment also simplifying the centring of the cap on the cylindrical skirt;

the cover may comprise support bosses arranged to receive the elastic member, the positioning means of the cover and of the bosses being alternately distributed about the axis X;

the positioning means and the boss of the cover may be angularly arranged in a regular or irregular distribution about the axis X;

in particular, the space between two immediately adjacent bosses on the cover may comprise a series of at least two positioning means of the cover, in other words a series of at least two protrusions between two immediately adjacent bosses;

the positioning means of the cylindrical skirt may form a reinforcement to prevent rotation of the cap with respect to the cylindrical skirt;

the rotating element may mount an inertia ring on the cylindrical skirt to facilitate assembly on the cylindrical skirt instead of on the cap;

According to a second aspect, the utility model also relates to a device according to any of the preceding features, said device being capable of forming a torsional damper. In particular, the device may be a dual mass flywheel comprising:

a main element, called main flywheel, formed by said rotating element and said cover, said main flywheel being intended to be rotated by a drive shaft,

-a secondary element, called secondary flywheel, capable of interacting with the driven shaft, and

-an elastic member rotationally elastically coupling the primary flywheel and the secondary flywheel.

According to a second aspect, the advantage is, inter alia, that the components of the main flywheel are assembled end-to-end without using additional components to ensure optimal compactness of the components and larger manufacturing tolerances.

According to a third aspect, the utility model also proposes a method for assembling a device for a motor vehicle drive train, comprising at least the following steps:

a) Assembling the cylindrical skirt of the rotating element and the cap together such that at least one first positioning means formed by the cylindrical skirt and at least one second positioning means formed by the cap are associated with each other by shape complementation;

b) Pressing the cap and the cylindrical skirt against each other and holding them under axial pressure;

c) The first positioning device and the second positioning device are welded together.

According to this third aspect of the utility model, the mechanical assembly of the parts end-to-end is achieved by positioning and centering the cap on the cylindrical skirt and then performing the welding operation without any additional machining, post-operation finishing or preparation for positioning the parts end-to-end.

Thanks to these features, the positioning means of the two parts provide greater geometric manufacturing tolerances, while preventing problems of abutment between the parts due to defects of the laser welding assembly. The tolerance of the component fit-up gap increases. Geometric constraints on the end-to-end surfaces, in particular concentric flatness, are no longer imposed on the parts to be assembled.

Finally, the cost of this method is thus significantly reduced. Simplifying and optimizing the design and assembly of these components.

In step b), the interaction between the positioning means may take the form of a complementary shape;

in step c), all positioning means of the two parts can be welded together with the cylindrical skirt and the cap by a single weld in a single welding operation;

in step c), a weld may be produced with a filler material;

Preferably, in step c), the weld seam may be produced by arc welding, in particular by cold welding. An advantage of this arc welding method (or CMT for cold metal transfer) is that it reduces the heat release (principle of cold welding). This benefit correspondingly reduces distortion and increases tolerance at the mating gap J, particularly at the two component positioning device. Thus, no preparation work is required to position the cylindrical skirt and cap, or post-machining or finishing is performed on both components;

according to a third aspect, such an assembly method may further comprise one or other features described in the first and second aspects, alone or in combination:

in particular, the cylindrical skirt and the cap of the rotating element may each comprise at least three positioning means, preferably angularly distributed, in particular regularly distributed, about the axis.

Thus, it should be understood that the method for assembling the device comprises at least the following steps:

a) Assembling the cylindrical skirt of the rotating element and the cap together such that the first positioning means (preferably at least three) formed by the cylindrical skirt and the at least three second positioning means (preferably at least three) formed by the cap are associated with each other by shape complementation;

c) The first and second positioning means are welded together, in particular in pairs.

Drawings

The utility model will be better understood from the following description of specific embodiments thereof, with reference to the accompanying drawings, and further objects, details, features and advantages of the utility model will become more apparent, the description being provided by way of non-limiting illustration only:

figure 1 is a rear perspective view of a device for forming a torsional damper according to a first embodiment of the utility model;

fig. 2 is an axial section of the device according to the first embodiment shown in fig. 1;

fig. 3 is an exploded perspective view of the device according to the first embodiment shown in fig. 1;

fig. 4 is a detailed perspective view of a rotating element according to the first embodiment shown in fig. 1;

fig. 5 is a detailed perspective view of the cover according to the first embodiment shown in fig. 1;

fig. 6A, 6B and 6C depict a method for assembling a device according to the first embodiment shown in fig. 1;

fig. 7 is an axial section of a device according to a second embodiment of the utility model.

Detailed Description

"vehicle" is understood to mean a motor vehicle, including not only a passenger car, but also an industrial vehicle, in particular a heavy goods vehicle, a public transport vehicle or an agricultural vehicle, as well as any transport device capable of transporting living beings and/or objects from one place to another.

In the following description and claims, by way of non-limiting example and for the sake of understanding, the term "inner/inner" or "outer/outer" will be used with respect to the axis X and in a radial direction orthogonal to said axial direction; the terms "rear" AR and "front" AV will be used to define the relative position of one element with respect to the other element in the axial direction, the element intended to be placed close to the combustion engine being denoted rear, the element intended to be placed close to the gearbox being denoted front.

Unless otherwise indicated, "axial" means "parallel to the axis of rotation X of the balance cover or dual clutch", "radial" means "along a transverse axis intersecting the axis of rotation of the dual wet clutch", and "angled" or "circumferential" means "about the axis of rotation X of the torsional damping device". Here, the thickness is measured along the rotation axis X.

Fig. 1 to 5 show a first embodiment of a torsional damper 1 of a drive train, in particular comprising a device 10 of the drive train. The device comprises a main flywheel 2 and a secondary flywheel 4 rotatably mounted relative to each other about an axis X. As shown in fig. 2, the torsional damper 1 further comprises an elastic member 5 arranged to transmit torque and to dampen the rotational non-circulation between the primary flywheel 2 and the secondary flywheel 4. Thus, the elastic member 5 is installed between the main flywheel 2 and the sub flywheel 4, rotatably connecting them.

The main flywheel 2 comprises a rotary element 3 for fixing to the end of the engine crankshaft. In fig. 2, it comprises a hub 6, a radial portion 7 extending radially outwardly from the hub 6, and an axial cylindrical skirt 8 extending from the outer circumference of the radial portion 7 forward AV.

The rotating element 3 is provided with holes, for example as shown in fig. 2, for the passage of fixing screws to fix the rotating element 3 to the engine crankshaft. The main flywheel 2, in particular the rotary element 3, is thus fixed to, for example, the end of the engine shaft for rotation by the engine crankshaft.

Furthermore, the rotating element 3 may be equipped with a target, not shown, which is arranged opposite to a sensor, not shown. The sensor is capable of emitting a signal representative of the angular position and/or velocity of the target. This type of sensor may in particular inform the vehicle computer of the position of the crankshaft, which allows the vehicle computer to control the injection of fuel correctly and, for a gasoline engine, the ignition of the spark plug.

Furthermore, the main flywheel 2 comprises a cap 9 having an annular shape and an axis X, which is fixed to the front end AV of the cylindrical skirt 8, as shown in fig. 1 to 3. The cap 9 defines, together with the radial portion 7 and the cylindrical skirt 8, an annular chamber 30, in which the elastic member 5 is housed. The elastic member 5 is, for example, a curved coil spring distributed circumferentially around the axis X.

Each elastic member 5 extends circumferentially between two support lugs of the web 11, as shown by the broken line in fig. 2, the web 11 rotating as a whole with the secondary flywheel 4 and the two support rims carried by the primary flywheel 2. Preferably, each support rim carried by the main flywheel 2 is constituted, for example, by two bosses 12, 13 formed in the cover 9 and in the radial portion 7 of the rotary element 3, respectively. Fig. 3 shows a boss 13 formed in the radial portion 7 of the rotary element 3, while fig. 1 and 3 show a boss 12 formed in the cover 9.

The cover 9 comprises bosses 12, each boss 12 being able to form a support edge of the elastic member 5 together with a facing boss 13 provided in the radial portion 7 of the rotary element 3.

Thus, in operation, each elastic member 5 abuts at a first end against a support edge carried by the rotary element 3 and at a second end against a support lug (not shown) carried by the web 11, ensuring torque transmission between the rotary element 3 and the secondary flywheel 4.

According to a variant embodiment, not shown, the web 11 is not directly fixed to the secondary flywheel 4, but is rotatable about the axis X with respect to the secondary flywheel 4. In this case, torque is transmitted between the web 11 and the secondary flywheel 4 by one or more additional elastic members.

The secondary flywheel is intended to form a reaction plate of a clutch (not shown) connected to the input shaft of the gearbox. By means of bearings 14, for example ball bearings as shown in fig. 2, the secondary element 4 is centered and rotationally guided on the primary flywheel 2, in particular on the rotary element 3.

Furthermore, the device 1 comprises a protection ring 22 attached to the rotating element 3 to protect the annular starter ring gear from deformations that might damage it. In fig. 2, the cylindrical skirt 8 has a shoulder formed in the rear edge of said cylindrical skirt 8, in which shoulder the protection ring 22 is mounted. The protection ring 22 further comprises an axial protection 24, in this case constituted by an annular flange projecting radially outwards with respect to the inner support. The axial protection 24 makes it possible to protect the cylindrical skirt 8 from axial impacts. The protection ring 22 is rigidly fixed to the rotating element 3, for example by a tight fit (for example by a shrink fit) in a shoulder formed in the rear edge of the cylindrical skirt 8.

Furthermore, the cylindrical skirt 8 extends axially along the axis X between two sides, in this case between the inner and outer surfaces of the cylindrical skirt 8. The radial dimension Ep of the cylindrical skirt 8 is defined between its two inner and outer sides, that is to say it is measured along a reference axis, in this case in a radial direction.

The inner surface forms an end edge 81 at its end. The outer surface forms an end edge 82 at its end. The end edges 81, 82 define therebetween the outer periphery 15.

The outer periphery 15 is preferably circumferentially continuous about the axis X.

The inner surface, in particular the end edge 81, may define a supporting surface of the cap 9 and it defines an inner diameter D1 of the cylindrical skirt 8, while the end edge 82 defines an outer diameter of the cylindrical skirt 8.

Furthermore, the main flywheel 2 comprises a ring gear (not shown) for rotating the main flywheel 2 using a starter. For example, the ring gear is made in one piece with the rotating element 3, that is to say in one piece, and is preferably integral with the cylindrical skirt 8 at its axial end. For example, the ring gear may be defined by the outer periphery 15 of the cylindrical skirt 8.

Alternatively, the rotating element 3 comprises a ring gear, which is attached to the front surface AV of the cylindrical skirt 8 by welding, in particular formed on the end 15 of the cylindrical skirt 8. In all cases, the arrangement of a ring gear on the cover 9 will be avoided, to limit its deformation and to simplify its shape to an absolute minimum.

Furthermore, the cover 9 extends radially between the radially inner edge 91 and the radially outer edge 92, the simplified shape of which, in particular the rectilinear cross-section of the cover, limits its volume.

Thus, the cover 9 can be entirely contained in a plane P perpendicular to the axis X. In other words, the simplified shape of the cap is such that it does not involve additional manufacturing steps or indeed the recess and axially offset portions. Its radially outer edge 92 extends axially between the two side faces 931 and 932, extending in a radial direction. The first side 931 is located at the front AV of the cover 9 and the second side 932 is located at the rear AR of the cover 9. The first and second sides 931, 932 define a circular-type outer periphery 930 at their radial ends. The outer periphery 900 defines an outer diameter D3 of the cap 9. The thickness Ec of the flange is axially defined between the sides 931 and 932. The cover 9 has a thickness Ec, in this case a thin and/or substantially constant thickness.

In this case, the cylindrical skirt 8 of the rotating element 3 surrounds the cap 9. The cap 9 is thus in this case completely contained within the cylindrical skirt 8. The cap 9 is welded at its radially outer edge 92 to the end edge 81 of the cylindrical skirt 8. In particular, as shown in figures 1, 2 and 6, the outer periphery 930 of the cap 9 is supported on the end edge 81 of the cylindrical skirt 8.

There is a very small fit clearance J between the ends of the parts 3, 9 to be welded, typically less than 1mm, for example about 0.5mm, for which case mechanical assembly by laser welding may lead to unacceptable defects.

To simplify the end-to-end mechanical assembly of the cap 9 on the cylindrical skirt 8, positioning means 80, 90 are respectively formed by the inner end edge 81 of the cylindrical skirt 8 and the outer periphery 930 of the cap 9 to axially position the cap with respect to the cylindrical skirt.

A positioning means 80 of the cylindrical skirt 8 is formed in the inner diameter D1. Thus, a first layout circle C1 centered on the axis X can be defined, along which the positioning means 80 of the cylindrical skirt 8 are arranged substantially. Specifically, the positioning device 80 is defined between an inner diameter D1 and an outer diameter of the cylindrical skirt. The layout circle C1 is also located between the outer diameter and the inner diameter D1 of the cylindrical skirt 8, in particular on the inner diameter D1 of the cylindrical skirt as shown.

In a variant not shown, the positioning means 80 may extend in the direction of the axis X. Thus, the first layout circle of the positioning means of the cylindrical skirt will be between the inner diameter of the cylindrical skirt and the outer diameter of the cap.

The positioning means 90 of the cover 9 are formed by an outer diameter D3. Thus, a second layout circle C2 centered on the axis X may be defined, along which the positioning means 90 of the cover 9 are arranged substantially. In particular, the positioning device 90 may extend outwardly from the outer diameter D3, that is to say in a direction away from the axis X. Thus, the second layout circle C2 may be equal to or greater than the outer diameter D3 of the cap 9, in particular between the outer diameter D3 of the cap 9 and the inner diameter D1 of the cylindrical skirt 8, as shown.

In particular, the outer diameter D3 of the cap 9 is substantially equal to the inner diameter D1 of the cylindrical skirt 8. Thus, the second layout circle C2 may be between the outer diameter D3 of the cap 9 and the inner diameter D1 of the cylindrical skirt 8. In a variant not shown, the positioning means 90 are formed inside the cover, delimited by the inner diameter of the cover 9.

Preferably, the positioning means 80, 90 of the cylindrical skirt 8 and of the cap interact with each other. Thus, the positioning means 80, 90 are co-located along the axis X and they are arranged to bear one on the other in order to center the cap on the cylindrical skirt.

In the example shown, the axial positioning, centering and angular indexing are ensured only at the same point on the cylindrical skirt and cap by their positioning means 80, 90. The co-action of the positioning means 80, 90 is such that it can simultaneously ensure axial support, centering and angular indexing of said positioning means 90 with respect to said positioning means 80.

Furthermore, the positioning means 80, 90 are then fixed together by welding, in particular by means of a single weld 100, which preferably results from arc welding. The weld 100 extends at least more than 140 degrees about the axis X. Advantageously, the weld 100 extends continuously around the axis X, that is to say over 360 degrees. This type of cold welding process will be described in detail in the remainder of the specification.

In the example shown, the cover 9 and the cover are also welded together by means of said weld seam 100. Thus, the outer periphery 930 of the cap 9 abuts against the inner side 81 of the cylindrical skirt 8, so as to be fixed together by the weld 100. Thus, the outer diameter D3 of the cap 9 coincides with the inner diameter D1 of the cylindrical skirt 8, said diameters D1, D3 being located one above the other.

As a result, the first and second circles C1, C2 of the layout of the positioning means 80, 90 for the cylindrical skirt and cap also coincide, forming a single identical layout circle.

Furthermore, the positioning means 80 of the cylindrical skirt 8 have a shape complementary to the positioning means 90 of the cap 9, to manually index the cap on the cylindrical skirt.

Preferably, the cylindrical skirt 8 comprises a limited number of devices, in this case three positioning devices 80 regularly angularly distributed about the axis X. The cover 9 comprises a limited number of devices, in this case three positioning devices 90 regularly angularly distributed about the axis X. In fig. 1 to 3, the positioning devices 80, 90 are arranged axially facing each other, i.e. in pairs, the number of which is the same.

In a variant not shown, two positioning means 90 may interact with the positioning means 80, for example the number of positioning means of the cap is twice that of the cylindrical skirt.

The positioning means 90 of the cover 9 are protrusions 95, that is to say solid portions formed by the outer diameter D3 of the cover 9, extending outwards in the radial direction.

The positioning means 80 of the cylindrical skirt 8 are a supporting seat 85, that is to say a hollow portion formed in the cylindrical skirt 8, in which the protrusion 95 is housed. The term "support" refers to a solid housing whose depth R1 is such that it is distinguished from a simple recess.

In other words, in this case, the support seat 85 comprises a distal portion 851, which is remote from the end edge of the cylindrical skirt 8, so as to be distinct from the proximal portion of said seat 85.

The positioning means 80 of the cylindrical skirt 8 are thus formed in the thickness Ep of the cylindrical skirt 8. Each support seat 85 is a discontinuous shape extending in the circumferential direction, such as a housing. In particular, the support seats extend radially along the depth R1, opening radially inwards so as to receive the projections 95 therein. Furthermore, such a support seat 85 extends axially from the outer periphery 15 along the height H1 so as to form an open casing, in this case open towards the front AV of the device 10, for inserting the projection 95 into the support seat 85 and generally for mounting the cap 9 inside the cylindrical skirt 8. The depth R1 of the support seat 85 is defined radially from the inner diameter D1.

In the example shown, the number of support seats 85 is three, angularly distributed regularly about axis X. The support seats 85 have the same shape, in this case, the same depth R1 and the same height H1.

Also, the number of protrusions 95 is three, regularly angularly distributed. The protrusions 95 have the same shape, in this case the same thickness and radial dimensions. In particular, the shape of the protrusion 95 is defined between the two sides 931, 932 of the cover, in particular in fig. 1 to 6C.

The support seats 85 are obtained by recessing or punching at specific points on the cylindrical skirt 8 where they are to be positioned. This operation is performed partially on the component, not on the entire cylindrical skirt.

Instead, the protrusion 95 is obtained by limiting the recessing or stamping operation only to the area of the cover where no protrusion will be located. The so-recessed or stamped portions define therebetween a protrusion 95. This operation is also performed partly on the part, not on the whole cover.

In a variant not shown, the support seat 85 and/or the protrusion 95 can be produced by forging. They can also be produced by pressing. The advantage in this case is a reduced machining time for producing one-piece components with improved mechanical properties (fiber structure, grain refinement).

In the example shown, the support seat 85 has a stepped shape hollowed out from the end edge 81 of the cylindrical skirt 8 along an axis orthogonal to the rotation axis X, in this case in a radial direction.

Preferably, each support base 85 comprises:

a distal portion 851 defined with respect to the end edge 81 of the cylindrical skirt, called "bottom" of the support seat 85. The distal portion 851 is defined by the diameter of one or more machining tools.

The radial space between the distal portion 851 with respect to the end edge 81 also defines a depth R1.

The distal portion 851 is connected to the end edge 81 of the skirt by a radial edge 852. Radial edge 852 is defined by a depth R1. A radial edge 852 is defined between the inner diameter D1 and the distal portion 851 of the support seat 85.

The distal portion 851 of the support seat 85 may be hollowed out to a greater depth R1 than the proximal portion of the same support seat 85. The distal portion 851 defines an inner diameter D1 along the axis X, which may correspond to half the diameter of a tool for machining. As shown, the distal portion 851 of the cylindrical skirt 8 ensures radial centring of the cap with respect to the axis X.

The support seat 85 is thus open radially outwards in the direction of the axis X inside the device.

In this case, the radial edge 852 of the support seat 85 is axially defined with respect to the outer periphery 15 along a height H1, which is produced by the tool during machining. As shown, this radial portion 852 of the cylindrical skirt 8 ensures axial positioning of the cap 9. The geometry of the support seat thus ensures a reliable positioning and centering of the two parts that overlap each other after assembly.

In particular, the support seat 85 has a semicircular cross section.

In particular, the positioning means 90 of the cover 9 are defined between the outer diameter D3 of the cover and the inner diameter D2 of the support seat. The depth R1 of the support seat 85 is defined between the inner diameter D1 of the cylindrical skirt and the inner diameter D2 of the support seat.

Preferably, the depth R1 of the support seat 85 is between 25% and 60% of the radial dimension Ep of the cylindrical skirt 8 in the radial direction. In the example shown, the depth R1 of the support seat 85 is approximately 43% of the radial dimension Ep of the cylindrical skirt 8.

Specifically, in a variant not shown, the radial edge 852 forms an angle α between 45 degrees and 120 degrees, in particular between 90 degrees and 120 degrees, with the distal portion 851. In the example shown, the angle α is substantially 90 degrees. The positioning means 80 of the cylindrical skirt 8 are formed by a distal portion 851 and a radial edge 852 of the support seat 95. The angle alpha may depend on the head of the tool used in the machining process.

In a variant not shown, the angle α may be strictly greater than 90 degrees, so as to incline the radial edge with respect to the bottom of the support seat.

As an example in fig. 4, the radial edge 852 is connected to the distal portion 851 by a rounded corner 853 (e.g. a circular arc), the rounded corner 853 resulting from the machining of the support seat 95, for example from the head of the tool used. Note that, in order to improve the machining accuracy of the support base, the support base may be machined using a plurality of machining tools having different diameters belonging to the same range. In particular, in this case, the distal portion 851 of the support seat is formed by first and second recessed portions 851', 851 "produced by different machining heads, having slightly different diameters. During the machining operation, the first concave portion 851' of the bottom portion 851 is created by a first tool of larger diameter, while the second concave portion 851 "of the bottom portion 851 is created by a second tool of smaller diameter. In this case, the second recessed portion 851 "receives the entire protrusion 95 and it defines an inner diameter D3 along the axis X.

In fig. 2 and 4, the maximum depth R1 of the support seat is defined by the point furthest from the axis X, here belonging to the second recess portion 851. As a variant, this point may belong to the first recessed portion 851'. Furthermore, each protrusion 95 comprises a plurality of support surfaces 950, 951, 952 arranged to be received inside the support base 95.

Specifically, the protrusion 95 extends along the axis X between the two sides 951, 952. The side on the front AV of the protrusion 95 defines a first support surface 951 that partially (with the distal portion 851) co-receives the weld 100. The distal portion 851 of the support seat and the protruding first support surface 951 are arranged adjacent to each other to secure the positioning means 80, 90 together, thereby completing the mechanical assembly of the device 1. The first support surface 951 may define an angle α with the distal portion 851.

The side on the rear AR of the protrusion 95 defines a second support surface 952 of the protrusion 95 that bears or abuts against a radial edge 852 of the support base 95. In this case, the radial edge 852 makes it possible to position and retain the protrusion 95 of the cap 9 inside the cylindrical skirt 8. The radial edge 852 of the support seat 85 and the weld seam 100 are axially arranged on either side of the cap 9, together so that the protrusion 95 of the cap 9 is axially and angularly fixed with respect to the support seat 85 in the cylindrical skirt 8. Thus, a plane P is defined orthogonal to the axis X and passing through the cover, the radial edge 852 and the weld bead 100 being arranged axially on either side of the plane P, at the rear AR and at the front AV of the plane P, respectively.

The first and second support surfaces 951, 952 define axially therebetween a radially outer end 950 of the protrusion 95, which is supported on the distal portion 851 of the support base 95. The distal portion 851 of the support seat 85 makes it possible to center the protrusion 95 on the cap 9 with respect to the cylindrical skirt 8.

Distal portion 851 is sized to receive end 950 of projection 95 and weld 100. The end 950 may be a flat or smooth bearing surface.

In particular, end 950 defines an outer diameter D4 of protrusion 95. The first and second support surfaces 951, 952 are defined between an outer diameter D3 and an outer diameter D4 of the cover. In other words, once the end 950 of the protrusion 95 is mounted to bear on the distal portion 851 of the support seat, the remaining space in the distal portion 851, referred to as the "free space" of the support seat bottom, then partially accommodates the weld 100. The free space formed in the support seat 85 is axially defined between the first support surface 951 and the outer periphery 15 of the cylindrical skirt. In particular, the outer diameter D4 is substantially equal to the inner diameter D3.

In the example shown, the support seat 85 and the projection 95 have in this case complementary shapes, with a male-female-like interaction as shown in fig. 1 to 5. Any type of known interaction of convex-concave shapes is possible.

In particular in fig. 5, each projection 95 has a convex shape, that is to say a convex shape with a circular edge 950 extending in the direction of the support seat 85. Thus, the contours of the first and second support surfaces 951, 952 have a circular shape, preferably the same, e.g. semi-circular. The end 950 of the protrusion 95 has a circular shape, such as a semi-cylindrical shape. In a variant not shown, the end portion may have the shape of a hemisphere.

In particular in fig. 4, each support seat 85 has a concave shape, that is to say a concave shape with a circular edge 950, which circular edge 950 receives a projection 95 of convex shape, in other words a recess having the shape of a hollow semi-cylinder. Thus, the profile of the radial edge 852 has a circular shape, such as a half moon shape. The distal portion 851 of the support seat 85 has a circular shape, such as a hollow semi-cylinder.

In a variant not shown, the bottom can have the shape of a hollow hemisphere.

In a variant not shown, the male-female shape interaction can be applied mutatis mutandis to the positioning means of the male-shaped cylindrical skirt 8 and to the positioning means of the female-shaped cap. All functions described for one component apply to another component.

In the first embodiment, the second support surface 952 of the protrusion 95 is formed in a recess 96 in the protrusion. The grooves 96 are made by machining or stamping. The recess 96 may be defined with respect to the remainder of the cover 9. It ensures a better interaction of the protrusion 95 with the radial edge 852 of the support seat.

As an example in fig. 5, grooves 96 are formed on the protrusions 95 and the radially outer edge 92 of the cover 9. The groove 96 is formed along the axis X and extends axially from the second side 932 of the cover 9. The groove 96 extends radially along a radial dimension R2 from the radially outer edge 92 to an end 950 of the protrusion 95. Preferably, the recess 96 and the radial edge 852 of the support socket have complementary shapes.

In particular, the radial dimension R2 of the recess 96 is strictly greater than the depth R1 of the support seat, for example in this case the radial dimension R2 is half the depth R1 of the support seat. This facilitates manual assembly, creating additional clearance for mounting the protrusion 95 in the support seat 85.

As an example in fig. 5, the grooves 96 extend angularly between edges 960 formed on the radially outer edge 92 of the cover 9.

A method for assembling the device 1 will now be described, as shown in the first embodiment, in particular in fig. 1 to 6C, and comprises at least the following steps:

in a first step (as shown in fig. 6A), a rotating element 3 is provided, comprising a cylindrical skirt 8 with an axis of rotation X, the skirt 8 comprising positioning means 80. There is also provided a cover 9 comprising positioning means 90 adapted to co-interact with the positioning means 80 of the rotating element 3.

In a second step (as shown in fig. 6B), the cap 9 is placed supported on the cylindrical skirt 8 of the rotating element 3 and held thereon under axial pressure, in particular by making the positioning means 80 of the cylindrical skirt 8 interact with the positioning means 90 of the cap 9.

In a third step (as shown in fig. 6C), the positioning means 80, 90 of the cylindrical skirt 8 and the cap 9 are welded, in particular by means of a weld 100, which is produced mainly by cold welding.

In particular in a third step, the positioning means 80, 90 are welded together, advantageously thanks to their complementary shape, preferably so as to ensure at the same time the axial support, centering and angular indexing of said means of the cap with respect to those of the cylindrical skirt.

In particular in the third step, the cylindrical skirt 8 and the cap 9 of the rotating element 3 are additionally welded. The overall profile of the components 3, 9, in particular the profile of their positioning means, is thus welded. In a fourth additional step, the bearing pressure exerted on the cover 9 may be released and/or the assembly may be cooled, in particular at the weld 100.

In particular in the third step, the weld 100 is produced by arc welding, in particular by cold welding (CMT for cold metal transfer). This method makes it possible to weld two parts 3, 9 of thin thickness or with a specific profile, with a significant fit gap J between them, which is problematic for end-to-end laser welding. In particular, by interrupting the short arc in a targeted manner (called short circuit), the filler metal is thus deposited precisely between the cap and the cylindrical skirt of the rotating element. The positioning means 80, 90 of the cylindrical skirt 8 and cap 9 will then be welded or brazed end-to-end, very uniformly and without splashing. Heat release and deformation is reduced, particularly at the two-part positioning device 80, 90.

Thus, no preparation work is necessary to position the cylindrical skirt 8 and the cap 9, or to finish machined or operated on these two parts 3, 9.

Fig. 7 shows a second embodiment of the utility model, which is substantially similar to the first embodiment, except that a second support surface 952 of the protrusion 95 is formed in a rib 96' of the protrusion. The rib 96' may be defined with respect to the rest of the cover 9.

In the second embodiment, the ribs 96' are also made by punching or machining the remainder of the cover 9. It ensures a better interaction of the protrusion 95 with the radial edge 852 of the support seat 85. Ribs 96' are formed on the protrusion 95 and the radially outer edge 92 of the cover 9. The rib 96' is formed along the axis X and it extends axially from the second side 932 of the cover 9. The rib 96' extends radially along a radial dimension R2 from the radially outer edge 92 to an end 950 of the protrusion 95.

In particular in fig. 7, the ribs 96' and radial edges 852 of the support base have complementary shapes. Advantageously, the radial edge 852 may comprise a groove, for example formed in the cylindrical skirt 8, for receiving the rib 96' of the protrusion 95. Their shapes are complementary.

In particular, the radial dimension R2 of the rib 96' is strictly greater than the depth R1 of the support seat, for example in this case the radial dimension R2 is half the depth R1 of the support seat. This facilitates manual assembly, creating additional clearance for mounting the protrusion 95 in the support seat 85.

As an example in fig. 7, the grooves 96 extend angularly between edges 960' formed on the radially outer edge 92 of the cover 9.

While the utility model has been described in connection with a number of specific embodiments, it is clear that the utility model is in no way limited thereto and that the utility model includes all technical equivalents of the means described as well as combinations thereof, if these are within the scope of the utility model. In particular, although the utility model has been described above in relation to a torsional damper type device, the device as described above may also be associated with other types of devices, such as rigid or flexible engine flywheels, torque converters, etc.

Use of the verb "to comprise" or "to comprise" does not exclude the presence of elements or steps other than those described in the claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims

1. A device (10) for a motor vehicle drive train, characterized in that the device (10) comprises:

a rotating element (3) intended to be rotatably mounted about a rotation axis (X), the rotating element (3) comprising a radial extension (7) and a cylindrical skirt (8) extending from the radial extension (7),

An annular cover (9) arranged together with the rotating element (3) to enclose the elastic member (5),

wherein the cylindrical skirt (8) and the cap (9) each comprise positioning means (80, 90) which co-act in such a way as to position the cap (9) on the rotating element (3), said positioning means (80, 90) of the cylindrical skirt (8) and the cap (9) being fixed together by welding, and

the cylindrical skirt (8) forms at least two seats (85) and the cap (9) forms at least two projections (95), the cylindrical skirt (8) and the cap (9) interacting by positioning the respective projections on the respective seats.

2. Device (10) according to claim 1, wherein the positioning means (90) of the cap (9) are arranged substantially along a layout circle (C2), in particular between the outer diameter (D2) of the cap (9) and the inner diameter (D1) of the cylindrical skirt (8).

3. Device (10) according to claim 1 or 2, wherein the cylindrical skirt (8) surrounds the cap (9), the positioning means (90) of the cap (9) being formed by the outer diameter (D3) of the cap.

4. Device (10) according to claim 1 or 2, wherein said cylindrical skirt (8) and cap (9) each comprise at least three positioning means (80, 90) angularly distributed about said rotation axis (X), said positioning means (80, 90) being made by punching or machining said rotating element and cap, respectively.

5. The device (10) according to claim 1 or 2, wherein the positioning means (80, 90) of the cylindrical skirt (8) and cap (9) are fixed together by means of a weld (100), the weld (100) extending at least partially around the rotation axis (X).

6. The device (10) according to claim 5, wherein the weld (100) extends continuously over 360 degrees around the rotation axis (X).

7. The device (10) according to claim 5, wherein the weld (100) is produced by welding with a filler material.

8. The device (10) according to claim 1 or 2, wherein the shape of the protrusion (95) is complementary to the shape of the support seat (85).

9. The device (10) according to claim 1 or 2, characterized in that the protrusion (95) on the cover (9) has a convex shape and the support seat (85) on the rotating element (3) has a concave shape.

10. Device (10) according to claim 1 or 2, wherein the cylindrical skirt (8) has a maximum thickness (Ep) measured along a reference axis, and the support seat (85) has a depth (R1) measured along another axis parallel to the reference axis, the depth (R1) being between 25% and 65% of the maximum thickness (Ep).

11. The device (10) according to claim 1 or 2, wherein the support seats (85) have a stepped shape hollowed out from the end edge (81) of the cylindrical skirt (8) along an axis orthogonal to the rotation axis (X), the distal end (851) of a support seat (85) being hollowed out to a greater depth (R1) than the proximal end of the same support seat (85), the support seat (85) having a semicircular cross section.

12. Device (10) according to claim 1 or 2, characterized in that the protrusion (95) comprises a plurality of support surfaces (950, 951, 952) intended to be received on the support seat (85), one of the support surfaces (952) of the protrusion (95) being formed in a groove (96) or a rib (96 ') of the protrusion (95), said groove (96) or rib (96') interacting with the end edge (81) of the cylindrical skirt (8) and/or with the support seat (85).

13. The device (1) according to claim 1 or 2, characterized in that the device (1) is a dual mass flywheel (1) comprising:

-a main flywheel (2) formed by the rotating element (3) and the cover (9), said main flywheel being intended to be rotated by a drive shaft,

-a secondary flywheel (4) capable of interacting with a driven shaft, and

-an elastic member (5) rotationally elastically coupling the primary flywheel (2) and the secondary flywheel (4).

14. The apparatus (10) of claim 7, wherein the weld (100) is produced by arc welding with a filler material.

15. The device (10) according to claim 7, wherein the weld (100) is produced by cold welding with a filler material.