DE102012217653B4 - Bumper support made of a composite material - Google Patents

Abstract

Bumper support (12) made of a composite material for a motor vehicle (11), wherein- at least one retaining cable (18, 23), in particular a retaining cable (18, 18a-d), is fastened to the bumper support (12) by at least one retaining fastening (19, 19f, 19r),- the at least one retaining cable (18, 18a-d) is hollow,- at least one retaining cable (18, 18a-d) is positioned in a tapered bore (24) of the corresponding retaining fastening (19, 19f, 19r), and- a tapered pin (29) is positioned in an opening (28) of a free end (25) of a respective retaining cable (18, 18a-d) such that the tapered pin (29) and the tapered bore (24) form a tapered joint with the retaining cable (18, 18a-d) therebetween.

Description

The invention relates to a bumper support made of a composite material for a motor vehicle. The invention also relates to a motor vehicle having at least one bumper support made of a composite material. The invention applies in particular to passenger cars.

Internal, undisclosed experiments indicate that there are problems with the use of composite bumper beams in crashes where the bumper beam is either damaged or proactively designed to break into two or more pieces to absorb the forces entering the backup structure. During a crash, it is undesirable to have large sections of the bumper beam separate from the rest of the vehicle structure. When the composite bumper beam is attached to composite Low Speed Energy Absorbers (LSEA), the composite Low Speed Energy Absorber will shatter into dust, streaks, and other small sized pieces with no tangible structural attributes after impact.

As in 1 visible, a bumper beam made of a composite material 2 of a passenger car 1 is connected at connecting sections 7 to two low speed energy absorbers 3 by respective fastening devices 4. These connections remain intact in low speed collisions, but in more severe collisions the connections effectively separate due to the total amount of splintered material in the vicinity of the connections, including the connecting sections 7. In 2 a bumper beam 1 is shown, which breaks in the event of an impact at higher forces. In 3 a severed central portion 5 of the composite bumper beam may fly away from the vehicle 1, while side end portions 6 may be connected to the low speed energy absorbers 3 (as shown). Separation of portions such as the central portion 5 from the composite bumper beam 2 would particularly occur in a low side overlap, high speed event where there is the potential for significant rollover and rotation of the motor vehicle after impact.

It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide a bumper support made of a composite material for a motor vehicle which behaves more safely in the event of an impact.

The object is achieved by the subject matter according to the independent claims. Advantageous embodiments can be derived in particular from the dependent claims.

The object is achieved by a bumper beam made of a composite material for a motor vehicle, in which at least one retaining cable is attached to the bumper beam. The at least one retaining cable can hold back sections of the bumper beam that have broken off during an impact. These sections are therefore prevented from flying away from the motor vehicle, which in turn increases safety, for example for people present. In other words, this bumper beam made of a composite material facilitates the use of light, brittle materials in the event of a frontal crash. These materials are exceptionally efficient at absorbing energy, while preventing large pieces of debris from causing further hazards.

In addition, at least one tether is secured to the bumper beam by at least one tether mount. The at least one tether is hollow. At least one tether is positioned in a tapered bore of a respective tether mount. A tapered pin is positioned in an opening of a free end of a respective tether such that the tapered pin and the tapered bore form a tapered joint with the tether therebetween.

Thus, the tapered pin and respective bore form a tapered joint in which the tether is held in an interference fit within the tapered joint. The advantages of this approach are simplicity of fixation and minimal damage to the tethers, ensuring the highest pull-out load for the minimum weight. Several fixing difficulties are avoided when very high loads are concentrated at the ends of the tethers, which are susceptible to tearing out of a mechanical fixation and local crimping of the material used in the tether, causing premature failure at the high loads encountered at the impact.

A bumper beam made of a composite material can in particular be a bumper beam made of fiber composite materials. The fiber composite material can be, for example, a carbon fiber reinforced plastic or a glass fiber reinforced plastic.

The bumper beam may be an elongated member or structure that is hollow or has an open cross-section. The The bumper beam may in particular be a tubular element. A cross-sectional shape of the bumper beam is not limited and may, for example, be an open C-cross-section, hat cross-section, circular, oval or angular, in particular rectangular cross-section. The size and/or cross-sectional shape of the bumper beam may vary along its length. The bumper beam may be linear and/or curved along its centerline or may have a linear or curved centerline.

A tether may in particular be a tether that extends along the length of the bumper beam. The tether is "lateral" in its extension relative to the motor vehicle. Where the motor vehicle is typically considered to extend "longitudinally" from the rear to the front, the bumper beam extends transversely thereto in a "lateral" direction. This lateral direction relative to the motor vehicle therefore coincides at least approximately with the centerline of the bumper beam.

The bumper support can have one or more retaining cables depending on the required restraining force. The retaining cables can in particular be attached to the bumper support, e.g. individually or in one or more groups.

The bumper support can be used on the front or rear of a motor vehicle, i.e. it can be part of a front or rear bumper.

In a further embodiment, the retaining cable is attached or fixed to an outer side or the exterior of the bumper support. In order to avoid separation of the bumper support from the retaining cable in the event of an impact, the retaining cable can then be attached to the bumper support at predetermined distances, for example by means of corresponding hooks or eyelets.

According to another embodiment, at least one retaining cable runs inside the bumper support if the bumper support is hollow. This has the advantage that detached sections of the bumper support can be held back by the at least one retaining cable without any additional means. This greatly facilitates the installation of the retaining cables. In addition, the at least one retaining cable is protected by the bumper support if no impact has occurred.

According to a further embodiment, the bumper beam comprises a plurality of connecting sections for fastening the bumper beam to at least one support element, wherein at least one tether is fastened to lateral end sections of the bumper beam positioned laterally outside the connecting sections. This enables retention of the detached sections of the bumper beam with any length between the connecting sections. This practically means that most or all of the detached sections can be retained in the event of a frontal impact at low speed. But also parts can be retained laterally outside the connecting sections if either a tether passes through them or if the tethers are fastened to this section. The retention of the detached sections of the bumper beam can therefore also be improved in the event of a high-speed impact and/or an impact with a small lateral overlap.

However, the position of attachment of the tethers to the bumper beam is not limited and may, for example, include attaching the tethers to a connecting portion or even a middle portion.

A connecting portion may generally be any region, section or part of the bumper beam that helps or enables the bumper beam to be attached or connected to at least one support member. A connecting portion may, for example, include one or more openings for the support member, holes for inserting a bolt or screw, one or more clips or clamps for clipping or locking the bumper beam to the at least one support member, etc.

It is yet another embodiment that the at least one support cable is slack, i.e. not taut between its support attachments. This allows a large differential brush removal in an offset (i.e. not quite frontal) load case.

The object is also achieved by a motor vehicle having at least one bumper beam made of a composite material as described above. The bumper beam can be part of a front or rear bumper. The motor vehicle can be a passenger car, but is not limited thereto, and can, for example, also be part of a truck, in particular a pickup truck, etc.

It is an embodiment that the motor vehicle has at least one bumper carrier made of a composite material, wherein the bumper carrier has a plurality of connecting sections in order to fasten the bumper carrier to at least one support element, wherein at least a retaining cable is attached to lateral end portions of the bumper beam that are positioned laterally outside the connecting portions. The bumper beam can be attached to at least one support element by at least one attachment device, wherein at least one retaining cable is attached to at least one of the attachment devices. This provides the advantage that some of the load exerted on the retaining cables by a detached portion can be absorbed by the attachment device or devices. In addition, the retaining cables are now positioned more precisely.

Another embodiment is that the at least one support element has at least one low-speed energy absorber (LSEA), in particular a composite material low-speed energy absorber. This allows very effective energy absorption. The low-speed energy absorber can be a crash box.

It is yet a further embodiment that at least one support element is attached to a high speed energy absorber (HSEA) and the fastening device for attaching at least one support element to the bumper beam is connected to the respective high speed energy absorber by longitudinal support cables, which can in particular run through the respective support element. This allows the retention of the bumper beam or detached parts or sections thereof even in the event that the low speed energy absorbers have been crushed or have otherwise lost their structural integrity due to an impact, for example during a high speed impact. The fastening devices therefore act as connecting elements between the support cables and the longitudinal support cables.

The high-speed energy absorber can, for example, be a crash box positioned in front of a body side member or can be part of a body side member.

It is yet another embodiment that the at least one retaining cable and/or the at least one longitudinal retaining cable is wound around the respective fastening device. This allows for a simple but effective installation.

For a more even load distribution across multiple tethers and therefore for a more robust design, one embodiment is that at least two groups of tethers are attached to the bumper beam, each group comprising at least two tethers attached to a common set of outer tether attachments. In particular, the outer tether attachments are attached to opposite sides of the bumper beam, in particular to a front and a rear of the bumper beam. For an even more even load distribution, the tethers of each group are partially connected to or held by (e.g. wrapped around) an upper end portion of the attachment devices, and another part is held by (e.g. wrapped around) a lower end portion of the attachment devices.

Preferably, the holding ropes and/or longitudinal holding ropes are made from a material with high tensile strength, in particular from an ultra-high-strength material with high elasticity. It is an advantageous embodiment that the holding ropes are made from plastic fiber, but could also contain metallic wires. A holding rope can in particular be a hollow holding rope. The holding rope can in particular be braided, in particular have a braided fiber structure.

According to an advantageous embodiment, the at least one holding rope can be made of a synthetic fiber.

Advantageously, the taper angle of the tapered pin and the tapered bore is not greater than 5°, in particular not greater than 2.5°, in particular it is approximately 2°.

Advantageously, the tapered pin has a handle at its larger end.

According to a further advantageous embodiment, the holding fastening has a plurality of tapered bores, in particular parallel, laterally aligned tapered bores.

Preferably, the retaining fastening is a separately manufactured element. Alternatively, the retaining fastening can be integrated into the bumper cross member.

• - Führen eines freien Endes eines Halteseils durch ein kleineres Ende einer verjüngten Bohrung einer Haltebefestigung,
• - Einführen eines verjüngten Stifts in eine Öffnung des freien Endes des Halteseils mit seinem kleineren Ende zuerst und
• - Zurückziehen des Halteseils durch die verjüngte Bohrung.

A particularly advantageous method for assembling the bumper cross member made of a composite material comprises the following steps:

• - guiding a free end of a holding cable through a smaller end of a tapered hole of a holding fixture,
• - Insert a tapered pin into an opening in the free end of the tether with its smaller end first and
• - Pull back the retaining cable through the tapered hole.

• 1 zeigt eine perspektivische Ansicht eines Stoßfängerträgers gemäß Stand der Technik aus einem Verbundmaterial eines Personenkraftwagens,
• 2 offenbart einen Stoßfängerträger gemäß Stand der Technik, der bei einem Aufprall bei höheren Kräften bricht,
• 3 zeigt, wie ein abgetrennter mittlerer Abschnitt des Stoßfängerträgers gemäß Stand der Technik aus einem Verbundmaterial von dem Fahrzeug wegfliegt,
• 4 zeigt eine perspektivische Ansicht einer vorderen Crashstruktur eines Personenkraftwagens gemäß der Erfindung, die einen Stoßfängerträger aus einem Verbundmaterial und zwei Low Speed Energy-Absorber vor einem Aufprall aufweist,
• 5 zeigt eine perspektivische Ansicht der vorderen Crashstruktur aus 4 ohne den Stoßfängerträger aus dem Verbundmaterial und ohne die beiden Low Speed Energy-Absorber,
• 6 zeigt eine perspektivische Detailansicht eines Low Speed Energy-Absorbers der vorderen Crashstruktur aus 4 ohne den Stoßfängerträger aus einem Verbundmaterial,
• 7 zeigt eine perspektivische Ansicht einer vorderen Crashstruktur aus 4 nach einem frontalen Aufprall,
• 8 zeigt anhand einer vergrößerten Ansicht einer Haltebefestigung der vorderen Crashstruktur aus 4 einen ersten Schritt des Befestigens von entsprechenden Halteseilen an der Haltebefestigung,
• 9 zeigt in einer ähnlichen Ansicht wie 8 einen zweiten Schritt des Befestigens der entsprechenden Halteseile an der Haltebefestigung,
• 10 zeigt in einer ähnlichen Ansicht wie 8 einen dritten Schritt des Befestigens der entsprechenden Halteseile an der Haltebefestigung und
• 11 zeigt in einer ähnlichen Ansicht wie 8 einen vierten Schritt des Befestigens der entsprechenden Halteseile an der Haltebefestigung.

The above-described properties, features and advantages of the present invention and the manner of their implementation will be described in more detail by the following schematic description of a specific embodiment, which is explained in conjunction with the figures. Similar and functionally similar elements in the figures may have the same reference numerals.

• 1 shows a perspective view of a bumper beam according to the prior art made of a composite material of a passenger car,
• 2 discloses a bumper beam according to the prior art which breaks in the event of an impact at higher forces,
• 3 shows how a severed central section of the bumper beam according to the prior art made of a composite material flies away from the vehicle,
• 4 shows a perspective view of a front crash structure of a passenger car according to the invention, which has a bumper beam made of a composite material and two low speed energy absorbers before an impact,
• 5 shows a perspective view of the front crash structure from 4 without the composite bumper support and without the two Low Speed Energy Absorbers,
• 6 shows a perspective detailed view of a Low Speed Energy Absorber of the front crash structure from 4 without the bumper support made of a composite material,
• 7 shows a perspective view of a front crash structure from 4 after a frontal impact,
• 8th shows an enlarged view of a retaining fixture of the front crash structure from 4 a first step of attaching appropriate retaining ropes to the retaining fixture,
• 9 shows in a similar view as 8th a second step of attaching the corresponding retaining ropes to the retaining fixture,
• 10 shows in a similar view as 8th a third step of attaching the corresponding retaining ropes to the retaining fixture and
• 11 shows in a similar view as 8th a fourth step of attaching the corresponding retaining ropes to the retaining fixture.

4 shows a perspective view of a front crash structure of a passenger car 11, which has a bumper beam 12 made of a composite material and two low speed energy absorbers 13 before an impact. The bumper beam 12 made of a composite material has the basic shape of a hollow body with a rectangular cross-section. A middle section 15 of the bumper beam 12 made of a composite material runs at least approximately straight, while its two lateral end sections 16 are slightly bent towards the main body of the vehicle 11. A corresponding center line C is therefore also partly straight and partly bent. The bumper beam 12 made of a composite material consists of a fiber-reinforced plastic, in particular of a carbon fiber-reinforced plastic. The bumper beam 12 made of a composite material can be used on the front or the rear of the vehicle 11, that is to say can be part of a front bumper or a rear bumper.

The low-speed energy absorbers 13 are shaped as short hollow bodies with a rectangular cross-section. The low-speed energy absorbers 13 are aligned in the longitudinal direction of the vehicle 11. The low-speed energy absorbers 13 are also made of fiber-reinforced plastic, in particular carbon-fiber-reinforced plastic.

At a respective connecting portion 27 of the bumper beam 12, a front portion of the low speed energy absorbers 13 is inserted into a rear opening (not shown) of the bumper beam 12 made of a composite material and fixed to the bumper beam 12 by fastening devices comprising a bolt or screw 14 which is simultaneously passed through the bumper beam made of a composite material 12 and the low speed energy absorber 13. A rear portion of the low speed energy absorbers 13 is connected to a respective main high speed energy absorber 17. The main high speed energy absorber 17 can also be made of fiber-reinforced plastic, in particular of carbon fiber-reinforced plastic.

Inside the bumper beam 12 made of a composite material there run support cables 18 which are attached or fixed to the end portions 16 of the bumper beam 12 by (external) support attachments 19, of which only a rear external support attachment 19, 19r attached to a rear side 20 of the bumper beam 12 is shown. The external support attachments 19 can be mounted on the bumper beam 12 made of a composite material, for example by rivets 21, screws, bolts and/or adhesive etc. As an example, rivets 21 are shown attached to external support attachments 19, 19f on a front side 22 of the bumper beam 12. The support ropes 18 are made of high-strength, braided synthetic fibers with high elasticity.

5 shows a perspective view of the front crash structure of the 4 without the bumper support 12 made of a composite material and without the two low speed energy absorbers 13. Four retaining cables 18a, 18b, 18c, 18d are attached to the bumper support 12. The retaining cables 18a-d are each arranged in two groups of two retaining cables 18a, 18b and 18c, 18d. Each retaining cable 18a, 18b, 18c and 18d of each group is each attached by a common set of external retaining fastenings 19r and 19f.

One tether 18a and 18c of each group is wrapped around an upper end portion of the bolts 14, and the other tether 18b and 18d is wrapped around a lower end portion of the bolts 14. The tethers 18 are slightly slack to allow a large differential crush distance in an offset (i.e., not fully frontal) crash.

Also wrapped around each bolt 14 are two longitudinal retaining cables 23 which are attached to the front of the main high speed energy absorber 17. This ensures that broken sections of the bumper beam 12 are retained even if the structural integrity of the low speed energy absorbers 13 has been destroyed. The front may be an integral part of the main high speed energy absorber 17 or may be an intermediate element, for example a flange. The longitudinal retaining cables 23 may also be made of a high strength plastic fiber with high elongation.

The arrangement of the retaining cables 18 and the longitudinal retaining cables 23 on one of the screws 14 in relation to the Low Speed Energy Absorber 13 is shown in 6 visible in more detail. While the holding cables 18 are wound around the screw 14 outside the low speed energy absorber 13, the longitudinal holding cables 23 run inside the low speed energy absorber 13.

7 shows a perspective view of the front crash structure of the 4 after a full frontal impact at low speed analogous to 3 This time, the detached middle section 15 is held back by the retaining cables 18. In the case shown, the end sections 16 are still firmly connected to the low speed energy absorbers 13. Even if an end section 16 were to break off, the retaining cables 18 would hold it back. Even if the low speed energy absorbers 13 are crushed but the screws 14 are intact, sections of the bumper beam 12 can be held back due to the longitudinal retaining cables 23.

8th shows, by means of an enlarged view of the exemplary retaining fixture 19, 19r, a first step of attaching the respective retaining cables 18c, 18d to the retaining fixture 19r. In this embodiment, the retaining fixture 19 is a separately manufactured bracket which is attached to the bumper beam 12 by the rivet 21 (not shown).

The retaining fixture 19 has two parallel, laterally aligned and tapered bores 24. A free end 25 of the respective retaining cables 18c, 18d has been passed through the smaller end 26s of the bores 24. The bores 24 have only a small taper angle of about 2 degrees (inclusive). The retaining fixture 19 can be made from a number of materials, including metal(s), ceramic and/or plastic, particularly fiber reinforced plastic.

The tethers 18, 18c, 18d are hollow. The tethers 18, 18c, 18d are particularly braided. The tethers 18, 18c, 18d may particularly be made of a plastic fiber based material to which natural fibers and/or metal threads may be added. The hollow braided tethers 18 may include a combination of fiber types, braid angles, etc. to provide the required strength, stiffness and elongation to retain the large sections of debris upon impact.

9 shows a second step of attaching the retaining cables 18c, 18d to the retaining attachment 19r. Now the free ends 25 of the retaining cables 18c, 18d have an opening 28 on their front side into which a respective pin 29 can be inserted as indicated by the corresponding arrows. The pin 29 has a tapered shape with a smaller end 30 to be inserted into the opening first and a wider end connected to a handle 31. The pin 29 has a size and a taper angle comparable to the size and taper angle of the holes 24. The size (in particular its diameter) can be slightly smaller than that of the holes 24 in order to take into account a wall thickness of the retaining cables 18.

10 shows a third step of attaching the retaining cables 18c, 18d to the retaining attachment 19r, wherein the pins 29 have been inserted into the openings 28 up to their effective length, i.e. without the handle 31. The retaining cables 18, 18c, 18d therefore overlap the tapered part of the respective pin 29.

11 shows a fourth step of attaching the tethers 18c, 18d to the retaining fixture 19r. The tethers 18c, 18d have now been retracted through the retaining fixture 19r and its bores 24, allowing the tapered pin 29 to penetrate the wider end 26i of the tapered bore 24 in the retaining fixture 19r.

Because the tapers of the bore 24 and pin 29 have at least approximately similar taper angles, as the tether 18c, 18d is retracted, the tapers are drawn together and the tether 18c, 18d and its braided material are compressed between the surfaces of the taper (i.e., the bore 24 and pin 25) that are mated. Due to the small taper angle of about two degrees (inclusive), the more force is pulled on the tethers 18c, 18d, the greater the perpendicular component to the tethers 18c, 18d. This securely prevents the tethers 18c, 18d from slipping out of the bores 24, even under high forces. Another advantage is that pressure applied to the tethers 18c, 18d under external loading is distributed substantially evenly around the circumference. The forces attempting to crimp the material of the tethers 18c, 18d on certain fibers are reduced and load carrying capacity is therefore increased. The advantages of this approach are the simplicity of attachment and the minimal damage to the tethers 18, ensuring the highest pull-out load for the minimum weight.

Another embodiment, for example, includes the recognition that a separately manufactured retaining fixture could be replaced by machining the tapered bore(s) directly into the structure, e.g., the bumper beam 12, being retained. This reduces costs by reducing assembly time and minimizing fixtures.

List of reference symbols

1

vehicle

2

Bumper support made of a composite material

3

Low Speed Energy Absorber

4

Connection

5

middle section of the bumper beam made of a composite material

6

Lateral end section of the bumper beam made of a composite material

7

Connecting section

11

vehicle

12

Bumper support made of a composite material

13

Low Speed Energy Absorber

14

screw

15

middle section of the bumper beam made of a composite material

16

Lateral end section of the bumper beam made of a composite material

17

High Speed Energy Absorber

18

Holding rope

18a-18d

Holding ropes

19

Holding fixture

19f

Mounting bracket (front)

19r

Mounting bracket (rear)

20

Back of the bumper support

21

rivet

22

Front of the bumper beam

23

Longitudinal tether

24

Tapered bore

25

Free end of a tether

26s

Smaller end of the tapered bore

261

Wider end of the tapered bore

27

Connecting section

28

Opening the free end

29

Rejuvenating pen

30

Smaller end of the tapered pin

31

Handle

C

Centerline of the composite bumper beam

Claims (11)

Bumper support (12) made of a composite material for a motor vehicle (11), wherein - at least one retaining cable (18, 23), in particular a retaining cable (18, 18a-d), is fastened to the bumper support (12) by at least one retaining fastening (19, 19f, 19r), - the at least one retaining cable (18, 18a-d) is hollow, - at least one retaining cable (18, 18a-d) is arranged in a tapered bore (24) of the corresponding retaining fastening fastening (19, 19f, 19r), and - a tapered pin (29) is positioned in an opening (28) of a free end (25) of a respective retaining cable (18, 18a-d) such that the tapered pin (29) and the tapered bore (24) form a tapered joint with the retaining cable (18, 18a-d) therebetween. Bumper support (12) made of a composite material according to Claim 1 , wherein the at least one holding rope (18, 23) is a braided holding rope. Bumper support (12) made of a composite material according to Claim 1 , wherein the at least one holding rope (18, 23) is made of synthetic fiber. Bumper support (12) made of a composite material according to one of the preceding claims, wherein a taper angle of the tapered pin (29) and the tapered bore (24) is not greater than 5°, in particular not greater than 2.5°, in particular approximately 2°. A bumper beam (12) made of a composite material according to any one of the preceding claims, wherein the tapered pin (29) has a handle (31) at its larger end. Bumper support (12) made of a composite material according to one of the preceding claims, wherein the holding fastening (18, 18a-d) has a plurality of tapered bores (24), in particular parallel, laterally aligned tapered bores (24). Bumper beam (12) made of a composite material according to one of the preceding claims, wherein the retaining fastening (18, 18a-d) is a separately manufactured element. Bumper support (12) made of a composite material according to one of the claims, wherein the retaining fastening (18, 18a-d) is integrated into the bumper support (12). Motor vehicle (11) having at least one bumper support made of a composite material (12) according to one of the preceding claims. Motor vehicle (11) after Claim 9 comprising at least one bumper beam (12) made of a composite material according to Claim 2 wherein the bumper support (12) is fastened to at least one support element (13) by at least one fastening device (14) and wherein at least one retaining cable (18, 23) is fastened to the at least one fastening device (14). Method for assembling a bumper beam (12) made of a composite material according to one of the Claims 1 until 8th , the method comprising the following steps: - guiding a free end (25) of a tether (18, 23) through a smaller end (26s) of a tapered bore (24) of a retaining fixture (19, 19f, 19r); - inserting a tapered pin (29) into an opening (28) of the free end (25) of the tether (18, 23) with its smaller end (30) first; and - retracting the tether (18, 23) through the tapered bore (24).