Motor vehicle body with a deformation element and a longitudinal member

Abstract

Body for a motor vehicle with a longitudinal member made of a fiber-reinforced plastic composite material, characterized in that the body further comprises a deformation element, wherein the deformation element is designed such that it can absorb collision energy by failure in a low relative speed range of the motor vehicle, and wherein the longitudinal member is designed such that it can absorb collision energy by brittle failure in a high relative speed range of the motor vehicle, wherein a longitudinal member initial failure force level (F3), at which the longitudinal member first begins to fail, is greater than a longitudinal member average failure force level (F4), at which the longitudinal member fails in a further course, wherein a deformation element initial failure force level (F1;F1'), at which the deformation element first begins to fail, and a deformation element average failure force level (F2; F2'), at which the deformation element fails in a further course, is smaller than the longitudinal beam initial failure force level (F3), and wherein the deformation element average failure force level (F2; F2') is smaller than the longitudinal beam initial failure force level (F3) and larger than a force level corresponding to a longitudinal beam average failure force level (F4) reduced by 10%.

Description

[0001] The present invention relates to a body of a motor vehicle according to the preamble of claim 1, in particular with a deformation element and a longitudinal member made of a fiber-plastic composite material.

[0002] A conventional motor vehicle typically consists of a front end, a rear end, and a passenger cell arranged between them. The design of the front end takes particular account of a head-on collision between the vehicle and a collision obstacle. A collision-relevant structure of the vehicle that can sufficiently dissipate collision energy to protect vehicle occupants is also called a crash structure. The collision-relevant structure of the front end is often defined, among other things, by two front longitudinal members (also called engine mounts in front-engine vehicles), deformation elements arranged at the front ends of the longitudinal members (also called "crash boxes"), and a bumper with a bumper cross member.The deformation elements are generally designed for a low-speed collision and are intended to protect the rest of the front-end structure, in particular the front side members, from damage. Thus, in a low-speed collision, it is usually only the bumper with the bumper cross member and the deformation elements that suffer energy-absorbing damage and can be easily replaced for repair. In a high-speed collision, the rest of the front-end structure, in particular the front side members, must also dissipate collision energy. The front side members are usually made of steel in a shell construction. The crash boxes are often made of aluminum. The failure of the front side members made of steel is characterized by plastic deformation, with the force level decreasing as the deformation progresses, i.e. with increasing deformation.The force level at which the crash boxes fail is typically selected to be at least 20% lower than the force level at which plastic failure of the front steel longitudinal member sets in. This makes the force level at which the crash boxes fail relatively low, so that a relatively long deformation path of the crash boxes is required to sufficiently dissipate the collision energy in a low-speed collision.

[0003] It is known to design body structural members for a motor vehicle body in such a way that they fail by absorbing collision energy in the event of a collision. Body structural members made of metallic materials are designed in such a way that they deform appropriately over a designated distance when a predetermined force level is exceeded. However, for body structural members made of fiber-reinforced plastic, dissipation of collision energy through deformation plays no role. Adequate dissipation of collision energy in a body structural member made of fiber-reinforced plastic is brittle failure. A failure of this type is known, for example, as "crushing." In the "crushing" failure mechanism, a more or less complete disintegration (pulverization or fragmentation or also called splintering) of the body structural member occurs, primarily in brittle fracture.Another form of "crushing" is a defined deflection of the material by 180° directly at an impact surface, whereby this deflection is also referred to as peeling or skiving. During crushing, a fiber fracture mechanism in combination with friction is used to dissipate the kinetic collision energy. Both of these failure mechanisms function effectively in a frontal impact, in which the force on the body structure support is perpendicular to a support cross-section. There are all sorts of intermediate forms of failure between the aforementioned types of "crushing" failure, which basically differ in terms of more or less fine-grained fiber fracture. The more fine-grained the failure, the higher the collision energy absorption capacity at failure, or the higher the load / force at which failure occurs.

[0004] DE 10 2010 052 794 A1 relates to a device for improving occupant protection of a motor vehicle with a front longitudinal member structure and a deformation element that deforms at a lower force level than the longitudinal member structure.

[0005] Furthermore, DE 198 47 866 A1 describes a longitudinal member connection between a front longitudinal member designed as a deformation element and a rear longitudinal member with a node element connecting them, which can be inserted into at least one of the longitudinal members.

[0006] Furthermore, DE 103 29 461 A1 shows an engine mount with a first section and a second section which has a thinner wall thickness than the first section, so that the engine mount has two deformation areas with different force levels and energy absorption capacities.

[0007] Furthermore, the generic prior art DE 10 2011 113 441 A1 shows a body with a longitudinal member made of fiber composite material.

[0008] It is the object of the present invention to provide a body of a motor vehicle with a deformation element and a longitudinal member, the crash structure of which has a short deformation path with sufficient dissipation of collision energy.

[0009] This object is achieved by a body having the features of patent claim 1. Preferred developments of the invention are listed in the dependent patent claims.

[0010] A motor vehicle body according to the invention has a longitudinal member made of a fiber-reinforced plastic composite material and a deformation element. Such a deformation element is also called a crash box or impact energy absorption element. The deformation element is designed such that it can absorb collision energy through failure in a low relative speed range of the motor vehicle. Relative speed refers to the speed of the motor vehicle relative to a collision opponent. For a rigid, stationary collision opponent, the relative speed corresponds to the speed of the motor vehicle. The longitudinal member is designed such that it can absorb collision energy through brittle failure in a high relative speed range of the motor vehicle. The longitudinal member can preferably absorb collision energy at a substantially constant force level.The high relative speed range preferably borders on the low relative speed range. A longitudinal member initial failure force level, at which the longitudinal member first begins to fail—after initial elastic deformation—is greater than a longitudinal member average failure force level, at which the longitudinal member fails in a further course. Furthermore, a deformation element initial failure force level, at which the deformation element first begins to fail, and a deformation element average failure force level, at which the deformation element fails in a further course, are smaller than the longitudinal member initial failure force level. Furthermore, the deformation element average failure force level is smaller than the longitudinal member initial failure force level and greater than a force level corresponding to a longitudinal member average failure force level reduced by 10%, preferably 5%.

[0011] The aforementioned brittle failure of a fiber-reinforced plastic (FRP) composite longitudinal member is also referred to as "crushing." In the "crushing" failure mechanism, a more or less complete disintegration (pulverization, fragmentation, or also called shattering) of the fiber-reinforced plastic material occurs, primarily in brittle fracture. The more fragmented the failure, the greater the collision energy absorption capacity at failure, or the higher the load / force at which failure occurs.

[0012] The use of a fiber-reinforced plastic composite material for the longitudinal member makes it possible to achieve a comparatively constant failure force level after the initial failure force level—particularly compared to metallic materials. Since, according to the invention, the deformation element's average failure force level is selected to be relatively high, namely at least greater than a longitudinal member's average failure force level reduced by 10%, preferably 5%, the deformation element dissipates collision energy at a relatively high force level, thereby reducing the required deformation path. This, in turn, has the advantage that the crash structure, for example, the front end of the motor vehicle, can be significantly shorter. The motor vehicle can be designed smaller overall, or a passenger cell can be designed larger while maintaining the same overall size.The invention is made possible in particular by the fact that the longitudinal member is formed from a fiber-reinforced plastic composite material whose initial failure force level can be adjusted to a relatively high level, so that, despite a deformation element average failure force level that is close to the longitudinal member average failure force level, the probability that the longitudinal member begins to fail before the collision energy dissipation potential of the deformation element is exhausted is very low. This ensures with a high degree of probability that the longitudinal member will not be irreversibly damaged in a low-speed collision and that the deformation element will not fail completely first.

[0013] According to a preferred development of the invention, the deformation element average failure force level is equal to or greater than the longitudinal member average failure force level.

[0014] This makes it possible to choose an even shorter deformation path of the deformation element with the same collision energy dissipation potential.

[0015] According to a further preferred development of the invention, the deformation element average failure force level is smaller than a longitudinal member average failure force level increased by 10%.

[0016] This ensures that the deformation element average failure force level does not come too close to the longitudinal member initial failure force level and that failure of the longitudinal member does not begin unintentionally.

[0017] The deformation element can be designed in such a way that it fails plastically and / or brittlely.

[0018] The deformation element can preferably consist of a fiber-plastic composite material.

[0019] This could potentially make the deformation element lighter. Furthermore, the failure force level of the deformation element can be kept relatively constant, allowing the deformation path of the deformation element to be used particularly efficiently to absorb collision energy.

[0020] Advantageously, the deformation element is arranged between a bumper cross member and a front end of the longitudinal member.

[0021] According to a further development, the deformation element can be designed to be replaceable by means of detachable fastening means.

[0022] This makes it possible to easily replace the damaged deformation element at low cost, particularly in the case of a low-speed collision.

[0023] The longitudinal member can advantageously be a front longitudinal member or a rear longitudinal member. A front bumper cross member with an intermediate deformation element can be arranged on the front longitudinal member. A rear bumper cross member with an intermediate deformation element can be arranged on the rear longitudinal member. The front longitudinal member and / or rear longitudinal member and associated deformation elements can be arranged in pairs. In other words, the body can have a left and a right front longitudinal member and / or a left and a right rear longitudinal member with associated deformation elements.

[0024] Preferably, the longitudinal member may consist of a fiber-plastic composite material with carbon fibers.

[0025] This is advantageous because carbon fibers offer high tensile strength while being comparatively lightweight. This makes it possible to design a particularly short crash structure while maintaining the same level of occupant safety.

[0026] The fiber-reinforced plastic composite is advantageously constructed with continuous fibers. Continuous fibers enable particularly high strength of the longitudinal member and thus a higher failure force level, which also enables a particularly short crash structure.

[0027] Preferably, the longitudinal member fails at an essentially constant force level.

[0028] The above-described developments of the invention can be combined with one another as far as possible and reasonable.

[0029] A brief description of the figure follows. Fig. 1 is a schematic diagram of a force curve over a deformation path of a deformation element and a longitudinal member according to a first embodiment of the present invention. Fig. 2 is a schematic diagram of a force curve over a deformation path of a deformation element and a longitudinal member according to a second embodiment of the present invention.

[0030] A first embodiment and a second embodiment of the present invention are described below with reference to Fig. 1 and Fig. 2 explained.

[0031] According to the first exemplary embodiment, a motor vehicle body has a front longitudinal member made of a fiber-reinforced plastic composite material and a deformation element. The front longitudinal member is reinforced, in particular, with continuous carbon fibers. The deformation element is mounted between a front bumper cross member and a front end of the longitudinal member. The deformation element of the first exemplary embodiment is made of a brittle-failing fiber-reinforced plastic composite material.

[0032] The deformation element is designed in such a way that it can absorb collision energy in the event of a collision at low speed, for example less than 25 km / h or 20 km / h or 15 km / h or any value in between, in particular 16 km / h, without irreversibly damaging the longitudinal member arranged behind it.

[0033] In Fig. Figure 1 shows a schematic diagram of a force curve in the event of a frontal collision of the motor vehicle at high relative speed with a collision obstacle over a deformation path of the deformation element and the longitudinal member. The deformation element fails after initial elastic deformation upon reaching a deformation element initial failure force level F1 by so-called crushing. After exceeding the deformation element initial failure force level F1, the deformation element fails at an approximately continuously constant deformation element average failure force level F2, which is lower than the deformation element initial failure force level F1. A failure force curve 5 of the deformation element is indicated by a dashed line in Fig. 1, with the line shown in an idealized manner. In fact, the failure force curve can also fluctuate somewhat, although the failure force curve is subject to considerably less fluctuation than in a plastically deforming deformation element described in the second embodiment. The maximum deformation path of the deformation element is indicated by x1 in the diagram.

[0034] As soon as the collision energy dissipation potential or the deformation potential of the deformation element is exhausted, failure of the longitudinal member sets in. A failure force curve 7 of the longitudinal member is shown in Fig. 1 is shown with a solid line. Here, the force initially increases during elastic deformation of the longitudinal member to a longitudinal member initial failure force level F3, at which the longitudinal member begins to fail. In particular, the longitudinal member fails brittlely due to the crushing already described above. Another force curve at which the longitudinal member fails is indicated by the longitudinal member average failure force level F4, where after the initial failure, the force curve is relatively constant, especially in comparison to a longitudinal member made of a metallic material that fails plastically. The failure force curve 7 is shown in Fig. 1 is shown ideally. The longitudinal member's average failure force level F4 is lower than the longitudinal member's initial failure force level F3. The maximum deformation path of the longitudinal member is indicated by x2 in the diagram.

[0035] A collision energy that can be absorbed by the system of deformation element and longitudinal member is indicated by the hatched area in the diagram.

[0036] In the diagram, the deformation element initial failure force level F1 and the deformation element average failure force level F2 are each lower than the longitudinal member initial failure force level F3. This prevents the longitudinal member from failing before the deformation element completely fails. To ensure this in every case, the distance between force levels F1 and F2 and the longitudinal member initial failure force level F3 is chosen to be sufficiently large.

[0037] Furthermore, in the illustrated embodiment, the deformation element average failure force level F2 is approximately equal to the longitudinal member average failure force level F4. As a result, the force level at which the deformation element fails is comparatively high, so that sufficient collision energy can be dissipated via the deformation element within the available deformation path x1. The deformation element average failure force level F2 can also be configured in a range from 10% lower than the longitudinal member average failure force level F4 to 10% higher than the longitudinal member average failure force level F4, as long as the longitudinal member initial failure force level F3 is large enough that failure of the longitudinal member does not occur before complete failure of the deformation element.

[0038] The second embodiment of the present invention is described below with reference to Fig. 2, wherein in particular the differences from the first embodiment are described and a description of the similarities to the first embodiment has been essentially omitted.

[0039] According to the second embodiment, a body of a motor vehicle has a front longitudinal member formed from a fiber-plastic composite material and a deformation element which, in contrast to the first embodiment, is formed from an aluminum material.

[0040] In the event of a frontal collision, the deformation element fails essentially plastically after initial elastic deformation upon reaching a deformation element initial failure force level F1'. After exceeding the deformation element initial failure force level F1', the deformation element fails with a strongly fluctuating failure force curve 5', which is characteristic of the failure of an aluminum deformation element. An average value of the fluctuating failure force curve 5' after reaching the initial failure force level F1' is shown in the diagram with a deformation element average failure force level F2'. The deformation element average failure force level F2' is lower than the deformation element initial failure force level F1'. The maximum deformation path of the deformation element is indicated by x1 in the diagram.

[0041] As soon as the collision energy dissipation potential or a deformation potential of the deformation element is exhausted, failure of the longitudinal member sets in. A failure force curve 7 of the longitudinal member according to the second embodiment corresponds to the failure force curve of the longitudinal member according to the first embodiment and is shown in Fig. 2 is shown with a solid line, analogous to the first embodiment. The deformation element initial failure force level F1' and the deformation element average failure force level F2' are each smaller than a longitudinal member initial failure force level F3, with the deformation element average failure force level F2' of the second embodiment being slightly larger than a longitudinal member average failure force level F4.

[0042] Overall, according to the embodiments of the present invention, a relatively large collision energy can be absorbed within the available deformation path x1 + x2, wherein the function of the deformation element to protect the longitudinal member from irreversible damage in collisions at low speeds is maintained.

Claims

[1] Body for a motor vehicle with a longitudinal member made of a fiber-reinforced plastic composite material, characterized byin that the body further comprises a deformation element, wherein the deformation element is designed such that it can absorb collision energy by failure in a low relative speed range of the motor vehicle, and wherein the longitudinal member is designed such that it can absorb collision energy by brittle failure in a high relative speed range of the motor vehicle, wherein a longitudinal member initial failure force level (F3), at which the longitudinal member begins to fail for the first time, is greater than a longitudinal member average failure force level (F4), at which the longitudinal member fails in a further course, wherein a deformation element initial failure force level (F1; F1'), at which the deformation element begins to fail for the first time, and a deformation element average failure force level (F2;F2'), at which the deformation element fails in a further course, are smaller than the longitudinal member initial failure force level (F3), and wherein the deformation element average failure force level (F2; F2') is smaller than the longitudinal member initial failure force level (F3) and greater than a force level corresponding to a longitudinal member average failure force level (F4) reduced by 10%.; [2] Body according to claim 1, characterized by that the deformation element average failure force level (F2; F2') is equal to or greater than the longitudinal member average failure force level (F4). [3] Body according to one of claims 1 or 2, characterized by that the deformation element average failure force level (F2; F2') is smaller than a longitudinal member average failure force level (F4) increased by 10%. [4] Body according to one of claims 1 to 3, characterized bythat the deformation element is designed in such a way that it fails plastically and / or brittlely. [5] Body according to one of claims 1 to 4, characterized by that the deformation element consists of a fiber-reinforced plastic composite material. [6] Body according to one of claims 1 to 5, characterized by that the deformation element is arranged between a bumper cross member and a front end of the longitudinal member. [7] Body according to one of claims 1 to 6, characterized by that the deformation element is designed to be replaceable by means of detachable fastening means. [8] Body according to one of claims 1 to 7, characterized by that the longitudinal member is a front longitudinal member or a rear longitudinal member. [9] Body according to one of claims 1 to 8, characterized by that the longitudinal member is made of a fiber-reinforced plastic composite material with carbon fibers. [10] Body according to one of claims 1 to 9, characterized by that the fiber-reinforced plastic composite material is formed with continuous fibers.

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