EP1933999B1 - Equipment for producing a closed-section cross-member, comprising an adaptable-length punch and/or matrix, and corresponding production method - Google Patents

Abstract

Tooling for the fabrication of a crosspiece with a closed section for connecting two longitudinal arms of a motor vehicle axle comprises a die (3) cooperating with a punch (2) for forming on the closed section of the crosspiece a lengthwise zone of torsion (L) and a mechanism for retaining the crosspiece in position. The die and/or the punch are adaptable in length to enable the length of the zone of torsion to be adapted. An independent claim is also claimed for the fabrication of a crosspiece with a closed section.

Description

The field of the invention is that of motor vehicles. More specifically, the invention relates to a tool for manufacturing a cross member with a closed section according to the preamble of claim 1, and a method of manufacturing such a cross member according to the preamble of claim 7 for the flexible axles for motor vehicles. Such tooling and such a method are known from the document EP 1 134 047 .

It is recalled that generally refers to a flexible axle axle designed to form a torsion element between two wheels.

Conventionally, a flexible axle comprises two longitudinal arms each carrying a wheel mounting bracket and connected by a transverse connecting member called cross member or profile.

During the design of an axle, two sizes are considered, among others, to assess the quality of the axle: bending and torsion.

The principle of flexible axles reconciles a high stiffness in bending and a relative flexibility in torsion. In general, it is through the geometry of the section of the cross member, via its bending and torsional inertia, that the desired compromise between flexural stiffness and (relative) torsional flexibility is achieved.

Recent years have seen a significant roll-out of flexible axle technology in the lower and mid-range segments of the automotive industry, thanks to numerous advantages, including an excellent performance / architecture compromise, and economical implementation using mainly welded type assemblies.

These advantages lead the ground designers to continually push the technique to its limits. The flexible axles are indeed tainted with a number of limitations among which a delicate compromise between longitudinal and transverse stiffness and durability conditioned by the endurance resistance of each of their components, subjected to significant elastic deformations.

The permanent rise in the requirements of comfort and driving pleasure, in particular, guides the design of flexible axles towards solutions. consisting in introducing a torsional stiffness between the two trailing arms, commonly called "anti-roll bar" or "ADB", in order to limit the tilt of the vehicle when cornering while preserving a great vertical flexibility of the train, guarantor of the filtering imperfections of the roadway to the cash register.

But the permanent widening of the scope of application of the soft-axle technology towards mass-produced vehicles (big sedan, minivan or commercial vehicle) without compromising on the quality of service, brings the most demanded components closer and closer to each other. absolute operating limits, be it the static resistance to incidental forces, or the fatigue resistance to a load cycle representative of the life of the train.

The connecting element, or through, is therefore one of the most difficult components to develop, especially in terms of endurance and behavior.

Currently, on the flexible axles, the crossbar connecting the longitudinal arms is made according to two different technologies.

According to a first technology, the crossbar is made from a folded sheet metal element (or stamped) so as to provide a section having a shape of "U", "V" or "L". These sleepers generally require to be associated with an anti-roll bar, providing torsional stiffness to the axle.

The second technology is to integrate the anti-roll stiffness function with the crossbar.

In this case, the cross is manufactured from a tube generally having a circular section, the tube being subjected at least in its central part to a deformation step (at the end of which a portion of the wall is crushed against another portion of the wall) to obtain the desired stiffness in torsion and flexion (examples: Peugeot 806 (registered trademarks) or Opel Zafira (registered trademarks)).

The diversity of anti-roll stiffness according to the needs is ensured by modification of the shape of the section of the cross-member and / or modification of the thickness of the tube.

The invention applies to sleepers made according to this second technology, these being commonly referred to as "closed-profile sleepers" or "closed-section sleepers".

In general, all the flexible axles using a tube crossbar have in their central region a concavity having a section in the shape of "U" or "V".

The cross tube is only deformed in a transverse portion to reduce torsional stiffness, and retains stronger torsion sections (eg circular) at the ends, to facilitate connection to the suspension arm by welding.

According to one or the other of the technologies just mentioned, the crossbar of a flexible axle is characterized by a high stiffness in bending and a low torsion stiffness, the latter must be precisely calibrated (associated with the anti-roll stiffness of the axle.

In the case of closed section cross members, all the stiffness is ensured by the cross member, whose torsional inertia has been carefully adjusted according to the anti-roll stiffness required by the specifications. As a result, the tolerance on the anti-roll stiffness of the axle is integrally associated with that of the crossbar itself.

When manufacturing closed-section axle crosspieces (by deformation of a tube), the manufacturer is generally faced with the difficulty of respecting the tolerance on the anti-roll stiffness expressed by the car manufacturer through a booklet charges.

One of the factors influencing the anti-roll stiffness is the dispersion over the thickness of the tube.

The problem is to decrease the sensitivity of the anti-roll stiffness of the axle to the dispersions on the thickness of the tube.

The order of magnitude is such that a dispersion of +/- 0.1 mm the thickness of the tube can generate of the order of three times the tolerance interval of the anti-roll stiffness of the axle of the specifications.

Several solutions have been made to this problem of controlling the anti-roll stiffness of a torsion axle with a closed section.

A first solution is to work with tube suppliers to control dispersions on the thickness of the tube (from a rolling process and welding), using a sorting method.

The potential of this solution turns out to be relatively limited in practice.

According to a second solution, tubes from a rolling and welding process are used, to which a re-stretching is subsequently applied to improve the tolerance on the thickness.

This solution is effective, but the associated cost is important. This increases the overall cost of the axle, which is most often incompatible with the requirements of motor vehicle manufacturers.

According to another solution, a hot stamping process is used which makes it possible to better control the geometry of the sections formed.

However, practice shows that this technique does not reduce the sensitivity to dispersions on the thickness.

According to yet another solution, the tube sheets are connected at each end of the cross-member by a "clinching" method (puncturing of one sheet in the other by punching).

This solution makes it possible to better control the dispersion over the effective length of the working section (the lowest torsion section of inertia), but does not compensate for the dispersions on the thickness of the tube.

The invention particularly aims to overcome the disadvantages of the prior art.

More specifically, the object of the invention is to propose a tool for manufacturing a closed-section cross member for a flexible axle according to claim 1 which makes it possible to better control the dispersion of the torsion stiffness of the crossbar compared with the solutions of the prior art.

The invention also aims to provide such a tool that is simple in design and easy to implement.

The invention also aims to propose a method of manufacturing such a cross member, according to claim 7.

These objectives, as well as others which will appear later, are achieved thanks to the invention which has for object a tool for manufacturing a cross-section with a closed section intended to connect two longitudinal arms of a flexible axle of a motor vehicle said tooling comprising at least one die intended to cooperate with a punch to form on said closed section of said crosspiece a torsion zone length, and means for holding said crosspiece in position, characterized in that said matrix and / or said punch are adaptable in length to adapt said length of said torsion zone.

An adaptive system is thus obtained which makes it possible to vary the length of the torsion zone (also called the "working zone") of the cross member and, consequently, its torsion stiffness.

Such a variation in the length of the torsion zone can be obtained by simple adjustment of the dimensions of the die and the punch of the forming tool, this in an integrated way to the tooling as it will appear more clearly later.

According to a preferred solution, said matrix and said punch each comprise at least two parts that may be spaced apart / close to each other.

In this way, a particularly simple and effective solution is obtained for adapting the tooling according to the torsional stiffness sought for the crossmember.

According to a first embodiment, said two parts of said die and / or said punch may be actuated by at least one jack.

According to a second embodiment, said two parts of said matrix and / or said punch are maintained in the extension of one another using screwing means.

In this case, the tooling preferably comprises a set of shims capable of being interposed between said two parts of said die and / or said punch.

The set of shims can then comprise a variety of shims of different thicknesses to cover a given amplitude, with the desired accuracy.

According to an advantageous solution, said means for holding in position comprise at least one variable-displacement mandrel.

Such mandrels contribute to the modularity of the tooling, allowing to adapt it according to both the thickness of the cross member and its length.

The invention also relates to a method of manufacturing a cross-section with a closed section intended to connect two longitudinal arms of a flexible axle of a motor vehicle, using a tool comprising at least one die intended to cooperate with a punch. to form on said closed section of said cross member a torsion zone length, and means for holding said crosspiece in position, characterized in that it comprises a step of adjusting the length of said matrix and / or said punch in order to adapting said length of said torsion zone.

Preferably, the method comprises a preliminary step of calculating said length of said torsion zone as a function of the desired torsional stiffness for said cross-member and the wall thickness of said section.

According to an advantageous solution, the method comprises a step of adjusting the stroke of two mandrels forming said holding means in position.

• les figures 1 à 3 sont chacune une vue d'une étape de fabrication d'une traverse à section fermée selon l'art antérieur ;
• les figures 4a, 4b, 5 et 6 sont des vues permettant d'illustrer l'influence de la zone de torsion d'une traverse sur la raideur de torsion de celle-ci ;
• la figure 7 est une vue schématique du principe général de l'invention ;
• la figure 8 est une vue schématique d'un mode de réalisation préférentiel de l'invention ;
• les figures 9 à 11 sont des graphes illustrant un exemple d'intervalle de tolérance de raideur de torsion obtenu grâce à l'invention en fonction d'une dispersion d'épaisseur et d'une variation de longueur travaillante données.

Other characteristics and advantages of the invention will emerge more clearly on reading the following description of a preferred embodiment of the invention given by way of illustrative and nonlimiting example, and the appended drawings in which:

• the Figures 1 to 3 are each a view of a manufacturing step of a cross section closed according to the prior art;
• the Figures 4a, 4b, 5 and 6 are views for illustrating the influence of the torsion zone of a cross member on the torsion stiffness thereof;
• the figure 7 is a schematic view of the general principle of the invention;
• the figure 8 is a schematic view of a preferred embodiment of the invention;
• the Figures 9 to 11 are graphs illustrating an example of a torsion stiffness tolerance range obtained by the invention as a function of a thickness dispersion and a given working length variation.

With reference to Figures 1 to 3 it will be recalled that a cross-section with a closed section is manufactured according to the prior art from a tube 1 on which, by means of a press, it acts by deforming its section to produce a torsion zone.

The conventional tooling comprises a punch 2 and a die 3 actuated by a press and intended to cooperate to form the torsion zone, and mandrels 4 intended to bear against the ends of the tube 1.

In an initial phase, the tube is placed in the press, and the mandrels are advanced against the tube so as to lock it; then we close the press.

The figure 2 illustrates the forming step of the torsion zone over a fixed and fixed length, the die 3 and the punch 2 crushing between them the tube.

At the end of the forming step, the press is opened (the die 3 and the punch 2 are therefore spaced apart from one another) and the mandrels are moved away from the tube ( figure 3 ).

With reference to Figures 4a and 4b , it is recalled that the torsion zone of a closed-section crosspiece denotes the zone L corresponding to the portion central of the cross.

For such a cross, the geometric profile of the section of the tube, the thickness of the tube and the length of the torsion zone are factors of order 1 for obtaining the torsional stiffness of the crossbar.

Moreover, for a constant section profile and tube thickness, the variation of the length ΔL of the torsion zone varies the torsion stiffness R of the crossbar in the following way: if L increases, R decreases, and conversely .

Thus, when the length of the torsion zone L is minimal, the crossbar has a maximum torsion stiffness ( figure 5 ). Conversely, when the length of the torsion zone L is maximum, the crossbar has a minimum torsional stiffness ( figure 6 ).

As mentioned above, the principle of the invention illustrated by the figure 7 lies in the fact of making the punch 2 and the matrix 3 adaptable in length so that they allow variations in length ΔL corresponding to the length of the desired torsion zone.

To do this, according to the embodiment illustrated by the figure 8 , the punch 2 and the die 3 each have two parts, respectively 2a, 2b and 3a, 3b may be moved closer or spaced apart from each other to obtain a variation ΔL.

The spacing between the parts 2a, 2b on the one hand, and the parts 3a, 3b on the other hand, is obtained by interposing between them one or more shims 6.

Of course, the number and the thickness of the shims are chosen according to the desired ΔL.

The parts 2a, 2b of the punch are held together with the wedges 6 by means of threaded rods 5. The same goes for the parts 3a, 3b of the die with the wedges 6.

Furthermore, the mandrel races 4 are controlled by hydraulic cylinders (not shown) ensuring the translation of the mandrels.

It is noted that the adaptation of the lengths of the punch and the die can be obtained hydraulically, for example using embedded cylinders, according to another conceivable embodiment.

The adaptive adjustment of the tooling that has just been described is performed between each burst of production (a burst being defined by a batch of tubes characterized by an average thickness value of the tubes), in press, with or without partial dismantling. tooling.

Prior to the adjustment of the tooling, the length of the torsion zone is calculated as a function of the thickness of the tube, this for a stiffness fixed by specifications.

Such tooling therefore allows, in terms of production, to form parts in bursts.

The Figures 9 to 11 are graphs illustrating an example of a torsion stiffness tolerance range obtained by the invention as a function of a thickness dispersion and a given working length variation.

The graph of the figure 9 indicates a thickness dispersion (between 3.35 mm and 3.55 mm) on a batch of tubes.

The graph of the figure 10 indicates working length variations (corresponding to the length of the torsion zone).

The graph of the figure 11 indicates the output data for torsional stiffness.

In the example above, the variation in working length (denoted L on the figure 4a ) between 618 and 700 mm makes it possible to respect a tolerance tolerance of stiffness of ± 2 m.daN / ° for a tolerance on the thickness of the tube of ± 0,1 mm.

Without the length adaptation of the working zone (that is to say with the techniques of the prior art), the dispersion of the thickness of the tube results in a torsional stiffness dispersion of ± 7.25 m.daN / ° (± 8%).

Claims (9)

1. Tooling for manufacturing a closed-section cross-member intended to connect two longitudinal arms of a motor vehicle non-rigid axle, said tooling comprising at least one die (3) intended to collaborate with a punch (2) to form, on said closed section of said cross-member, a length (L) of torsion zone, and means for holding said cross-member in position, characterized in that said die (3) and/or said punch (2) are length-adjustable so that said length of said torsion zone (L) can be adapted.
2. Tooling for manufacturing a closed-section cross-member according to Claim 1, characterized in that said die (3) and said punch (2) each comprise at least two parts (3a), (3b), (2a), (2b) that can be moved away from/toward each other.
3. Tooling for manufacturing a closed-section cross-member according to Claim 2, characterized in that said two parts (3a), (3b), (2a), (2b) of said die (3) and/or of said punch (2) can be actuated by at least one actuating cylinder.
4. Tooling for manufacturing a closed-section cross-member according to Claim 2, characterized in that said two parts (3a), (3b), (2a), (2b) of said die (3) and/or of said punch (2) are held in the continuation of one another using screwing means (5).
5. Tooling for manufacturing a closed-section cross-member according to Claim 4, characterized in that it comprises a set of shims (6) which can be interposed between said two parts (3a), (3b), (2a), (2b) of said die (3) and/or of said punch (2).
6. Tooling for manufacturing a closed-section cross-member according to any one of Claims 1 to 5, characterized in that said holding means comprise at least one variable-travel clamp (4).
7. Method for manufacturing a closed-section cross-member intended to connect two longitudinal arms of a motor vehicle non-rigid axle, using tooling comprising at least one die (3) intended to collaborate with a punch (2) to form, on said closed section of said cross-member, a length (L) of torsion zone, and means for holding said cross-member in position, characterized in that it comprises a step of adjusting the length of said die (3) and/or of said punch (2) so as to adapt said length of said torsion zone (L).
8. Method of manufacturing a closed-section cross-member according to Claim 7, characterized in that it comprises a prior step of calculating said length of said torsion zone (L) according to the desired torsional stiffness of said cross-member and according to the wall thickness of said section.
9. Method of manufacturing a closed-section cross-member according to either of Claims 7 and 8, characterized in that it comprises a step of adjusting the travel of two clamps (4) that form said holding means.

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