DE102011113823B4 - Bumpers for a motor vehicle - Google Patents

Abstract

Bumpers (1) for a motor vehicle with at least two mutually spaced tubular or box-shaped deformation bodies (2), the central or longitudinal axes of which are aligned parallel to the direction of travel of the motor vehicle in the assembled state, and with a plurality of tubular cross members (3.1, 3.2, 3.3, 3.4 ), which are arranged one above the other and connected to the deformation bodies (2), the cross members (3.1, 3.2, 3.3, 3.4) being formed from a group of at least three cross members, characterized in that the deformation bodies (2) and the cross members ( 3.1, 3.2, 3.3, 3.4) are made of steel, the cross members (3.1, 3.2, 3.3, 3.4) being connected to the deformation bodies (2) via fastening means (4), the bottom cross member (3.4) having a smaller wall thickness than has at least one of the other cross members (3.1, 3.2, 3.3), the wall thickness of the bottom cross member (3.4) being at least 0.6 times and at most 0.9 times The wall thickness of the cross member (3.1, 3.2 or 3.3) corresponds to the highest wall thickness, with all cross members (3.1, 3.2, 3.3, 3.4) each having a tensile strength of at least 780 MPa, and the deformation resistance and / or tensile strength of the cross member Remove gradually from the top cross member (3.1) in the direction of the bottom cross member (3.4).

Description

The invention relates to a bumper for a motor vehicle, in particular a front bumper, with at least two mutually spaced tubular or box-shaped deformation bodies, the central or longitudinal axes of which, in the assembled state, are oriented essentially parallel to the direction of travel of the motor vehicle, and with a plurality of tubular cross members, one above the other arranged and connected to the deformation bodies (so-called crash boxes), the cross members being formed from a group of at least three cross members.

Such a bumper is from the US 2011/0109122 A1 known. The US 2011/0109122 A1 discloses a method of manufacturing a crash management system for a vehicle, having at least a first cross member and two shock absorbing components connected to the first cross member and a second cross member integral with the first carrier. The crash management system is made from an extruded profile that has a closed or semi-closed configuration. The extruded profile, which is made of aluminum or an aluminum alloy, is cut to length and has a plurality of adjacent, longitudinally formed chambers (cross members) which are connected to one another via webs. A bumper with integrated crash boxes is made from the cut profile. To form the crash boxes in one piece, the webs connecting the chambers (cross members) are severed in regions and at least one of the cross members is bent accordingly at the ends of the profile.

Most rear-end collisions of passenger cars occur at speeds below 20 km / h. This leads to vehicle damage in the front and rear area. In recent years, crash repair tests have been developed in the insurance industry with the aim of reducing damage to cars in typical rear-end collisions. On the basis of these tests, among other things, car insurance companies nowadays classify passenger cars. The automobile manufacturers take this test into account when developing new car models. However, minimizing vehicle damage in the event of a rear-end collision requires that the bumpers of the vehicles involved in the rear-end collision are geometrically compatible. Because the crossbeams of the bumpers are relatively narrow and are arranged at different heights, the result is that the bumpers do not meet and can slip or penetrate into the soft structures of the other vehicle. In these cases, repair costs can be significantly higher than for vehicles whose bumpers meet and absorb the impact energy as intended.

But even if the bumpers meet, it is also important for minimizing the damage to the vehicle that the impact-related displacement (deformation) of the cross member of the bumper does not exceed a certain amount, for example 100 mm, since otherwise the engine unit, in particular the radiator, is damaged. So far, conventional motor vehicle bumpers have generally not been designed for this requirement.

Another requirement when developing new automobiles is to minimize vehicle weight to reduce fuel consumption. For this reason, aluminum bumpers are installed in many motor vehicles. Although these bumpers are relatively light in weight, they have the disadvantage of relatively high material costs.

The DE 10 2007 001 966 A1 discloses a bumper system for a motor vehicle, with a bumper cross member which is held on a rigid frame of the motor vehicle via deformation bodies (crash boxes). Furthermore, the bumper system comprises a deformable bumper outer skin and a support part supporting the lower region of the outer skin, which has at least a large part of its length two vertically spaced cross members. The two crossbeams are preferably connected to one another in one piece and realized in the form of a carrier part which is produced as an injection molded part made of plastic. The carrier part is designed in such a way that it offers effective pedestrian protection and should keep the strain on the pedestrian knee low in the event of an accident.

From the DE 10 2004 056 956 B4 a bumper is known which has at least two round tubes as cross members, which are arranged one above the other in the vertical direction and are connected to one another between side frames (crash boxes) by a plate-shaped clamp. The bracket is provided on the front of the tubes and welded to them. It has upper and lower curved end sections which are adapted to the outer shape of the tubes. The tubes are connected to the side frames via support elements which have arcuate cutouts for the form-fitting reception of the tubes.

The present invention has for its object to provide a bumper of the type mentioned, its cross member offer a relatively high resistance to deformation, so that in the event of a rear-end collision at speeds of less than 20 km / h, the crossbeams can be deliberately limited to be moved back and the bumper of the vehicle involved in the collision largely prevents the bumper from going under or over it. At the same time, the bumper should have a relatively low weight.

This object is achieved by a bumper with the features of claim 1.

The bumper according to the invention is characterized in that the deformation bodies and the crossbeams are made of steel, the crossbeams being connected to the deformation bodies via fastening means, the lowermost crossbeam having a smaller wall thickness than at least one of the other crossbeams, the wall thickness being at least that Corresponds to 0.6 times and at most 0.9 times the wall thickness of the cross member with the highest wall thickness, with all cross members each having a tensile strength of at least 780 MPa, and wherein the deformation resistance and / or the tensile strength of the cross members from the top cross member in the direction remove the bottom cross member gradually.

The solution according to the invention is based on the knowledge that, with regard to a typical rear-end collision at a speed of less than 20 km / h, there is a deliberate, limited backward displacement of the cross member area of the bumper, as well as a high degree of security against the bumper being driven under or over, and also a considerable reduction in weight of the bumper can be achieved if the bottom cross member has a smaller wall thickness than at least one of the cross members arranged above in a bumper of the type mentioned.

The bumper defined in claim 1 thus fulfills the requirements of the above-mentioned crash repair test developed by the insurance industry and is also characterized by a relatively low weight.

The deformation body and the cross member of the bumper according to the invention are made of steel according to the invention. Steel is particularly characterized by good cold formability and a proven and cost-effective weldability. In addition, the material steel offers the possibility of achieving higher strengths than, for example, aluminum. It is also conceivable to use heat-treatable steels, such as, for example, manganese-boron steels, which can be continuously hardened as cross members or can have different strengths locally. According to the invention, all cross members have a tensile strength of at least 780 MPa. At least the lowermost cross member of the bumper according to the invention is preferably made of high-strength steel with a tensile strength of at least 1200 MPa, preferably of at least 1400 MPa.

Depending on the requirements and with a view to a relatively low weight, different material grades and / or wall thicknesses can be used. In particular, by using steels with tensile strengths of at least 780 MPa, at least the lowest cross member with a smaller wall thickness can be produced (0.9 times the wall thickness of the cross member with the highest wall thickness). If steels with tensile strengths of at least 1200 MPa are considered, the wall thickness can be reduced further, at least by or to 0.6 times, preferably 0.7 times the wall thickness of the cross member with the highest (greatest) wall thickness.

A further preferred embodiment of the bumper according to the invention provides that at least the uppermost cross member ends on the outer sides of the deformation bodies. This length limitation of the uppermost cross member or at least one other cross member of the other cross members serves the purpose of minimizing the weight of the bumper. The cross member in question can end at a short distance from the outside of the respective deformation body. The distance or projection of the end of the cross member relative to the outside of the deformation body is preferably less than or equal to the outside diameter or the largest profile outside width of the cross member in question. In a particularly preferred manner, at least the uppermost cross member is essentially flush in its longitudinal extent with the two outer sides of the deformation bodies.

According to the invention, the deformation resistance and / or the tensile strength of the crossbeam gradually decrease from the uppermost crossbeam in the direction of the lowermost crossbeam. In this way, the material costs of the bumper according to the invention can be reduced, if necessary, and the requirements of the above-mentioned crash repair test developed by the insurance industry can be met.

A further advantageous embodiment of the bumper according to the invention is characterized in that at least the uppermost cross member and the cross member arranged directly underneath are locally connected to one another between the deformation bodies. As a result, the deformation resistance in the upper area of the bumper can be increased further. The local connection of at least the top crossmember and the The cross member arranged directly below can preferably be formed from one or more screw connections. To improve the deformation resistance of the bumper, all cross members can also be connected locally.

With regard to low manufacturing costs, a further preferred embodiment of the bumper according to the invention provides that the cross members or at least the lowermost cross members are / are designed as a rolling profile, optionally as a curved rolling profile. According to an alternative embodiment of the bumper according to the invention, the cross members or at least the lowermost cross member can also be produced from a plurality of sheet metal parts, the longitudinal edges of the respective or top cross member being welded to one another in the butt joint or overlap joint. The latter embodiment offers the possibility of tailoring the cross member in question from sheet metal or sheet metal parts of different wall thickness and / or different material quality.

A further advantageous embodiment of the bumper according to the invention is characterized in that the lowest cross member differs in cross-sectional shape from at least one of the other cross members. This also increases the deformation resistance of the bumper and / or reduces its weight.

If the number of cross members meets the required minimum height of the bumper and a further increase in the deformation resistance is required, remedial measures can be taken according to a further embodiment of the bumper according to the invention by at least one of the cross members being foamed with structural foam.

Further preferred and advantageous embodiments of the bumper according to the invention, in particular front bumper, are specified in the subclaims.

• 1 einen erfindungsgemäßen Stoßfänger für ein Kraftfahrzeug mit zwei stoßabsorbierenden Deformationskörpern (Crashboxen), in Draufsicht;
• 2 den Stoßfänger der 1, in Vorderansicht;
• 3 eine perspektivische Schnittdarstellung des Stoßfängers entlang der Schnittlinie III-III in 2;
• 4 eine Ansicht auf die Schnittfläche der 3; und
• 5 und 6 jeweils eine Querschnittansicht auf übereinander angeordnete Querträger eines erfindungsgemäßen Stoßfängers gemäß zwei weiteren Ausführungsbeispielen.

The invention is explained in more detail below on the basis of a drawing showing several exemplary embodiments. They show schematically:

• 1 a bumper according to the invention for a motor vehicle with two shock-absorbing deformation bodies (crash boxes), in plan view;
• 2 the bumper of the 1 , in front view;
• 3 a perspective sectional view of the bumper along the section line III-III in 2 ;
• 4 a view of the section of the 3 ; and
• 5 and 6 in each case a cross-sectional view of a cross member of a bumper according to the invention arranged one above the other according to two further exemplary embodiments.

In 1 is a bumper 1 shown for a motor vehicle, which is intended in particular for use as a front bumper.

The bumper 1 comprises two tubular or box-shaped deformation bodies 2 , which can also be called crash boxes. Their central or longitudinal axes are aligned essentially parallel to the direction of travel, ie the longitudinal direction of the motor vehicle. The deformation bodies 2 are attached to side members or other parts of the vehicle body. In the illustrated embodiment, the hollow deformation body 2 an essentially rectangular cross-sectional profile. Alternatively, they can also be designed, for example, with an oval or circular cross-sectional profile.

The bumper also includes 1 at least three cross members 3.1 . 3.2 . 3.3 , which are arranged in parallel one above the other and with the deformation bodies 2 are connected by suitable fasteners. The cross beams 3.1 . 3.2 . 3.3 are tubular. For example, they consist of individual tubes and / or closed profiles.

In the illustrated embodiments, the bumper has 1 Four cross beams (profiles) arranged in parallel one above the other 3.1 . 3.2 . 3.3 . 3.4 on. However, it can optionally also have more than four or only three tubular cross members 3.1 . 3.2 . 3.3 be provided.

The connection between the cross beams 3.1 . 3.2 . 3.3 . 3.4 and the deformation bodies (crash boxes) 2 is preferably designed as a detachable connection, for example by screw connections. On the front faces of the tubular deformation body 2 are fasteners for this 4 intended. The fasteners 4 consist, for example, of bracket-shaped brackets or webs on the respective deformation body 2 are attached or molded and holes for receiving with the cross members 3.1 . 3.2 . 3.3 . 3.4 connectable bolt 5 or the like. The crossbeam 3.1 . 3.2 . 3.3 . 3.4 are preferably vertically spaced from each other.

The lowest cross member 3.4 differs in terms of its wall thickness and, if applicable, material quality from at least one of the other cross members 3.1 . 3.2 . 3.3 in that it has a smaller wall thickness than the other cross beams 3.1 . 3.2 . 3.3 has, the wall thickness of the cross member to reduce the weight 3.4 at least 0.6 times and at most 0.9 times the wall thickness of the cross member 3.1 . 3.2 or 3.3 with the greatest (highest) wall thickness. The lowest cross member is preferably 3.4 made of a high-strength steel that has a tensile strength of at least 1200 MPa, preferably at least 1400 MPa.

To the weight of the bumper 1 To minimize further is the top cross member 3.1 shorter than the crossbeams below 3.2 . 3.3 . 3.4 , The top crossmember ends accordingly 3.1 on the outside 2.1 the crash boxes (deformation bodies) 2 , preferably being substantially flush with the outsides 2.1 the crash boxes 2 locks or the outsides 2.1 the crash boxes 2 protrudes laterally with a small distance (cf. 1 to 3 ).

In order to further increase the resistance in the upper area of the construction, at least the top crossmember 3.1 and the cross member immediately below 3.2 preferably locally connected to each other in the area of the vehicle center, the local connection also in other areas, for example between the vehicle center and the crash box, as required 2 , can be provided. For example, this is by one or more screw connections 6 realized (cf. 4 ). Alternatively, this local connection from the upper cross member 3.1 and the cross member immediately below 3.2 can also be realized by a positive connection by means of plug pins or locking elements. All cross beams can be used to further increase the resistance to deformation 3.1 . 3.2 . 3.3 . 3.4 of the bumper 1 be locally connected. The local connections can be provided at different locations as required.

The cross beams 3.1 . 3.2 . 3.3 . 3.4 of the bumper according to the invention 1 differ from one another in terms of their resistance to deformation and / or their strength, for example in such a way that the resistance to deformation and / or the tensile strength of the crossmember from the uppermost crossmember 3.1 towards the lowest cross member 3.4 gradually decrease or are essentially identical.

For the production of tubular cross members or profiles 3.1 . 3.2 . 3.3 . 3.4 Both continuous and discontinuous forming processes can be considered. For example, the cross member 3.1 . 3.2 . 3.3 . 3.4 are produced as closed roll profiles by continuous roll forming of sheet metal strips (split strips). Alternatively, the cross member 3.1 . 3.2 . 3.3 . 3.4 but can also be produced discontinuously as a formed part by deep drawing or another suitable forming process and subsequent welding of the longitudinal edges of the sheet metal shells obtained by forming, which are arranged in the butt joint or overlap joint.

In the 5 and 6 are further embodiments of the bumper according to the invention 1 outlined, with the top cross member 3.1 each with respect to its cross-sectional shape of at least one of the other cross members 3.2 . 3.3 . 3.4 different.

In the exemplary embodiment according to 5 has the top cross member 3.1 an essentially circular cross-sectional profile, while the crossbeams arranged underneath 3.2 . 3.3 . 3.4 each have an essentially rectangular or square cross-sectional profile. The corners or edges of the rectangular or square cross members 3.2 . 3.3 . 3.4 are slightly rounded. The bottom crossmember also differs 3.4 of the bumper 1 according to 5 in terms of its wall thickness from the other cross members 3.2 . 3.3 , The wall thickness of the cross member preferably corresponds 3.4 the wall thickness of the tubular cross member 3.1 , The cross beams 3.1 . 3.4 are made of steel with a tensile strength of at least 1200 MPa, preferably at least 1400 MPa. The wall thickness of the cross member 3.1 . 3.4 corresponds to 0.6 times, preferably 0.7 times and at most 0.9 times the wall thickness of the cross members 3.2 . 3.3 ,

In the exemplary embodiment according to 6 has the top cross member 3.1 an oval or elliptical cross-sectional profile, whereas the crossbeams underneath 3.2 . 3.3 . 3.4 have a substantially square or rectangular or circular cross-sectional profile, its wall thickness being that of the cross member 3.4 equivalent.

The connection of the tubular cross members or profiles 3.1 . 3.2 . 3.3 . 3.4 according to the 5 and 6 with the deformation bodies (crash boxes) 2 is preferably like that in the 1 to 3 illustrated embodiment executed. The top cross member 3.1 in the embodiment according to 5 can in turn with the cross member arranged immediately below 3.2 in the area of the vehicle center locally via one or more screw connections or other suitable connecting means 6 , in particular locking means connected; or according to 6 can all cross beams 3.1 . 3.2 . 3.3 . 3.4 be locally connected to one another, the connection to one another not being limited to the center of the vehicle.

Claims (7)

Bumpers (1) for a motor vehicle with at least two mutually spaced tubular or box-shaped deformation bodies (2), the central or longitudinal axes of which are aligned parallel to the direction of travel of the motor vehicle in the assembled state, and with a plurality of tubular cross members (3.1, 3.2, 3.3, 3.4 ), which are arranged one above the other and connected to the deformation bodies (2), the cross members (3.1, 3.2, 3.3, 3.4) being formed from a group of at least three cross members, characterized in that the deformation bodies (2) and the cross members ( 3.1, 3.2, 3.3, 3.4) are made of steel, the cross members (3.1, 3.2, 3.3, 3.4) being connected to the deformation bodies (2) via fastening means (4), the bottom cross member (3.4) having a smaller wall thickness than has at least one of the other cross members (3.1, 3.2, 3.3), the wall thickness of the bottom cross member (3.4) being at least 0.6 times and at most 0.9 fac hen corresponds to the wall thickness of the cross member (3.1, 3.2 or 3.3) with the highest wall thickness, all cross members (3.1, 3.2, 3.3, 3.4) each having a tensile strength of at least 780 MPa, and the deformation resistance and / or the tensile strength of the cross member Remove gradually from the top cross member (3.1) in the direction of the bottom cross member (3.4). Bumper after Claim 1 , characterized in that the lowest cross member (3.4) is made of steel, which has a tensile strength of at least 1200 MPa. Bumper after Claim 1 or 2 , characterized in that at least the uppermost cross member (3.1) ends on the outer sides (2.1) of the deformation body (2). Bumper according to one of the Claims 1 to 3 , characterized in that at least the top crossmember (3.1) and the crossmember (3.2) arranged directly below it are locally connected to one another between the deformation bodies (2). Bumper after Claim 4 , characterized in that the at least local connection of the uppermost cross member (3.1) and the cross member (3.2) arranged directly below it is formed from one or more latching or screw connections (6). Bumper according to one of the Claims 1 to 5 , characterized in that the lowest cross member (3.4) differs in cross-sectional shape from at least one of the other cross members (3.1, 3.2, 3.3). Bumper according to one of the Claims 1 to 6 , characterized in that at least one of the cross members (3.1, 3.2, 3.3, 3.4) is foamed with structural foam.

Images