GB2507415A - A method for including crash, durability and noise simulation in vehicle white body design - Google Patents

Abstract

A method for designing a body in white of a vehicle, in particular a passenger vehicle, the method comprising at steps in which parts of the body in white are identified with regard to the noise characteristics of the vehicle, the durability characteristics of the body in white and the crash characteristics of the body in white, the parts being optimized after evaluation of the thickness of the part with respect to each characteristic and the optimised final set of parts being obtained by combining sensitivity values respectively characterising the sensitivities of the set of parts with regard to the characteristics of noise, durability and crash. This provides improved use of computer assisted engineering (CAE) in the design process of a body in white.

Description

Method for Designing a Body in White of a Vehicle The invention relates to a method for designing a body in white of a vehicle, in particular a passenger vehicle.

A body in white light weight optimal design method can be found in CN 102938004, the method comprising a first step in which discretized material parameters according to current materials in storage are established. The method also comprises a second step in which a part of a body in white to carry out weight reduction is selected. The method further comprises a third step in which it is judged whether the part after the weight reduction meets property requirements or not. Moreover, in the third step the part after the weight reduction is selected, the part meeting the property requirements as a design variant. In a fourth step a free mode analysis is carried out on the body in white before the weight reduction and a basic frequency, a one-step torsion frequency, and a one-step bending frequency are obtained. In a fifth step, the basic frequency, the one-step torsion frequency, and the one-step bending frequency are used as limitation conditions for designing the variant and the lightest mass is used as a target function to optimize each part, so as to obtain a new body in white.

In US 5729463 a method and a system for designing and producing a light weight automobile vehicle body can be found. In the method, structural performance targets are selected, a beam model analysis is conducted, and a body in white design is developed.

Furthermore, a framework type minibus structure can be found in CN 202006833 U. It is an object of the present invention to provide a method for designing a body in white of a vehicle, the method allowing for developing and designing a body in white which is particularly light and meets predeterminable requirements in a particularly short time.

This object is solved by a method having the features of patent claim 1. Advantageous embodiments with expedient and non-trivial developments of the invention are indicated in the other patent claims.

The method according to the present invention serves for designing a body in white of a vehicle, in particular a passenger vehicle. The method according to the present invention comprises a first step in which a first number of parts of the body in white is selected.

There is no restriction of the number of the parts to be selected.

The method comprises a second step in which a first set of parts of the body in white is subjected to a first evaluation regarding the noise characteristics of the vehicle. By means of the first evaluation second number of parts being sensitive with regard to the noise characteristics is identified. In other words, the parts of the second number of parts are particularly relevant for a noise level occurring during operation of the vehicle.

Furthermore, in the second step the second number of parts is subtracted from the first number of parts. The remaining parts form a second set of parts of the body in white.

The method also comprises a third step in which the second set of parts is subjected to a second evaluation regarding the durability characteristics of the body in white. Thereby, a third number of parts being sensitive with regard to the durability characteristics is identified. In other words, the durability of the body in white particularly depends on the third number of parts. Moreover, in the third step the third number of parts is subtracted from the first number of parts. The remaining parts form a third set of parts of the body in white.

The method further comprises a fourth step in which the third set of parts of the body in white is subjected to a third evaluation regarding the crash characteristics of the body in white, thereby identifying a fourth number of parts being sensitive with regard to the crash characteristics. In other words, the crash characteristics of the body in white mainly depend on the fourth number of parts. In the fourth step, the fourth number of parts is subtracted from the first number of parts. The remaining parts form a fourth set of parts of the body in white In each evaluation, the thickness of the respective set of parts is optimized with regard to the respective characteristics. This means in the steps parts being sensitive with regard to the respective discipline (noise characteristics, durability characteristics, and crash characteristics) are not only identified but also optimized with regard to their thickness.

Thereby, the respective thickness and, thus, the respective weight can be minimized, the parts still meeting predeterminable requirements or criteria with regard to the respective discipline. In other words, the weight of the body in white can be minimized but the body in white still has particularly good noise characteristics, durability characteristics and crash characteristics.

In the second step, the third step and the fourth step, the identified and optimized parts are subtracted from the first number of parts, the remaining parts forming a respective sot of parts which can be used for further evaluations and, thus, optimizations. This means the respective evaluation serves for finding out the optimal thickness of the respective part so that the respective part or the body in white as a whole meets predeterminable characteristics with a thickness, in particular wall thickness as little as possible so that the weight of the respective parts and the body in white as a whole can be kept particularly low.

By conducting the steps consecutively and by filtering or eliminating some of the pails after the first evaluation and before the second evaluation and after the second evaluation and before the third evaluation the respective thickness of the parts can be optimized in a particularly short time. Simultaneously, the parts and the body in white as a whole meet all the predeterminable requirements so that the body in white has particularly advantageous noise characteristics, crash characteristics and durability characteristics.

The method according to the present invention also has a fifth step in which a final set of optimized parts is obtained by combining sensitivity values which respectively characterize the sensitivities of the respective set of parts with regard to the noise characteristics, the durability characteristics, and the crash characteristics.

The noise characteristics are also referred to as "noise, vibration, harshness" or NVH".

NVH (noise vibration harshness) is a common term for vibrations which can be acoustically noticed as sounds and/or haptically noticed as movements by passengers of the vehicle. The better the noise characteristics are the less vibrations occur and/or can be noticed by the passengers.

Further advantages, features, and details of the invention derive from the following description of a preferred embodiment as well as from the drawing. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respective indicated combination but also in other combination or taken alone without leaving the scope of the invention.

The drawing shows in: Fig. 1 a flow diagram illustrating a method for designing a body in white of a vehicle, in particular a passenger vehicle; Fig. 2 a matrix for illustrating a crash sensitivity evaluation process for determining the sensitivity of parts of the body in white with regard to crash characteristics of the body in white; Fig. 3 a table for illustrating the crash sensitivity evaluation process; Fig. 4 a table of pads of the body in white, wherein a respective thickness of the parts is optimized by the method; and Fig. 5 three tables for illustrating an evaluation process guideline by means of which a cumulative response influence value for each part can be determined.

Fig. 1 shows a flow diagram illustrating a method for designing a body in white of a vehicle, in particular a passenger vehicle. As will be described in the following, a CAE (Computer-Added Engineering) process is used to design the body in white, in particular to optimize a respective thickness of parts of the body in white.

In a first step Si, the body in white is provided as a computer model. Furthermore, a selection of parts from the whole vehicle, in particular the body in white is done based on, for example, engineering judgment and/or predeterminable criteria. For example, big parts having a good weight saving potential are considered for optimization. Small parts can be omitted. However, there is no restriction on the number of parts to be selected for optimization. In other words, in the first step Si a first number of parts of the body in white is selected.

In a second step S2, a first set of parts of the body in white is subjected to a first evaluation regarding the noise characteristics of the vehicle. The first set of parts can comprise the first number of parts or a subset of parts from the first number of parts. By means of the first evaluation a second number of parts being sensitive with regard to the noise characteristics is identified. Moreover, the second number of parts is subtracted from the first number of parts, the remaining parts forming a second set of parts of the body in white.

The number of the parts of the second set of parts is less than the first number of parts.

The second number comprises parts which are NVH sensitive parts. In the first evaluation predeterminable load cases are investigated so that Eigen frequencies and point mobilities of the body in white can be determined. In particular, within the determination of the body in white Figen frequencies, sensitive parts for torsion and bending modes are identified. Moreover, an optimization is carried out using gradient based approach (Nastran SOL 200), wherein an objective function to minimize the respective weight of the parts is used. Within the determination of the body in white point mobilities, a respective optimized thickness from the previous step is evaluated for the body in white point mobilities. Moreover, further optimization of the thickness is carry out based on operating deflection shape studies.

This means the respective thickness, in particular wall thickness of the parts is optimized with regard to the noise characteristics in the first evaluation. The optimization of the wall thickness can be understood as a reduction of the thickness which is also referred to as "gauge down". By reducing the thickness the weight of the respective part can be reduced. However, the thickness reduction is carried out with regard to the noise characteristics so that the actual noise characteristics of the respective parts meet predeterminable characteristics or characteristic values so that the second number of parts can be designed particularly light on the one hand but still meet predeterminable targets or requirements on the other hand.

In other words, in the second step S2 a first set of parts is subjected to NVH evaluation since the turnaround time for NVH evaluations and optimizations is faster and the NVH calculations are linear in their behaviour. At the end of the second step S2, NVH sensitive parts are identified and optimized. These NVH optimized parts are subtracted from the first number of parts. The remaining parts form a second set of parts used for further evaluations.

After the second step S2, this means after the first evaluation the second number of parts is NVH optimized. In a third step S3 of the method the second set of parts is subjected to a second evaluation regarding the durability characteristics of the body in white, thereby identifying a third number of parts being sensitive with regard to the durability characteristics. Furthermore, the third number of parts is subtracted from the first number of parts, the remaining parts forming a third set of parts of the body in white. The third step S3 is conducted after the second step S2. As can be seen from Fig. 2, the first evaluation is also referred to as NVH evaluation', wherein the second evaluation is also referred to as durability evaluation". In the second evaluation (durability evaluation), predeterminable load cases are investigated to determine the static stiffness and the durability of the body in white. Within the determination of the static stiffness of the body in white, the optimized thickness from the NVH evaluation is evaluated for the static stiffness. Moreover, a further thickness optimization is conducted based on sensitivity studies.

Within the determination of the durability of the body in white, the optimized set of thickness from the previous step is evaluated for the durability of the body in white.

Furthermore, parts being sensitive for base material and spot weld damage are identified using Nastran SQL 200, these parts being further optimized. After the third step S3, the third number of parts is optimized with regard to NVH and the durability of the body in white.

In other words, in the third step S3 the second set of parts is subjected to durability evaluations. At the end of the third step S3, NVH and durability sensitive parts are identified and optimized. These NVH and durability optimized parts are subtracted from the first number of parts. The remaining parts form a third set of parts used for further evaluations.

In a fourth step S4 the third set of parts of the body in white is subjected to a third evaluation regarding the crash characteristics of the body in white thereby identifying a fourth number of parts being sensitive with regard to the crash characteristics. Moreover, the fourth number of parts is subtracted from the first number of parts, the remaining parts forming a fourth set of parts of the body in white. In each of the evaluations the thickness of the respective set of parts is optimized with regard to the respective characteristics. The third evaluation is also referred to as "crash evaluation", the third evaluation regarding the crash characteristics of the body in white. As can be seen from Fig. 1, the fourth step 54 is conducted after the third step S3.

In the fourth step 54, predeterminable load cases are investigated such as IIHS side and rear impact, Euro ENCAP pole impact, rear repair crash, roof drop, and FMVSS3O1.

Within the load cases, the optimized thickness from the NVH evaluation and the durability evaluation is evaluated with regard to the crash characteristics. Sensitive parts for each load case are identified, preferably, by using a diagonal matrix approach. A robust post processing is used in which a combination of automatic response extraction and manual visualization of energy and deformation plots are used. A performance ranking of each part is conducted in order to conduct a subjective and objective response rating.

Furthermore, parts sensitive with regard to crash characteristics are filtered based on performance ranking.

Thus, the method allows for creating a combination of sensitivity information with regard to the noise characteristics, the durability characteristics and the crash characteristics to obtain a final optimized set of parts each having a final optimized thickness. Thus, the final optimized parts are particularly light yet meeting predeterminable targets so that the body in white as a whole has particularly advantageous noise characteristics, durability characteristics and crash characteristics.

In other words, in the fourth step S4 the third set of pads is subjected to crash evaluations. At the end of the fourth step 54, NVH and durability and crash sensitive parts are identified and optimized. The NVH and durability and crash optimized parts are subtracted from the first number of parts. The remaining parts form a fourth number of parts or a fourth set of parts used for further optimization.

In a fifth step S5, a final set of optimized parts meeting all NVH and durability and crash criteria is obtained by combining the sensitivities of all three disciplines (NVH and durability and crash).

In the second step S2, the third step S3 and the fourth step S4 a functional evaluation for each discipline (NVH, durability, crash) is carried out one after the other which helps filter sensitive parts leaving less parts to optimize for the next discipline, i.e. evaluation. This

S

helps create a deeper inside on sensitivity information of every part. Moreover, the method allows for realizing an optimized design and function meeting all requirements with no additional checks. No gauge change, this means no change of the thickness which will deteriorate the NVH target is considered during the durability evaluation and the crash evaluation and optimization studies.

The filtering or elimination of the parts is based on sensitivity information. Figs. 2 and 3 serve for illustrating the crash evaluation which is a crash sensitivity evaluation process.

In order to conduct the crash sensitivity evaluation process, a so-called a diagonal matrix approach or run matrix approach is used. Such diagonal matrix or run matrix is shown in Fig. 2. For determining the crash sensitivity of the parts, a predeterminable number of consecutive simulations runs is conducted. For example, a so-called nominal run is conducted in which a so-called base line model of the body in white is used. In the base line model the parts have a certain thickness. Moreover, a simulation run with all parts is conducted, wherein the parts have a down gauge of 15 % with regard to the simulation run before, in particular the nominal run. Furthermore, simulations runs with individual parts are conducted, the parts having, foi example, a down gauge of 15 %. In Fig. 2, a down gauge of 15% is an example only. The down gauge can be chosen in a need-based manner.

The number of runs depends on the number of design variable subjected to the respective evaluation. In this matrix approach, each part is evaluated one at a time' by down gauging it individually to study its contribution on the total response of outcome.

Each part is down gauged with different values, for example, percentages, for example 15%, 10%, 5% etc.. Down gauge of a part is carried out until the load case criteria are satisfied. There will be one run called worst case scenario" in which all the parts are down gauged to their maximum percentages allowed. There will be one run called nominal run" or base run" in which all the parts have their original thicknesses assigned to them.

Fig 3 shows a table illustrating the crash sensitivity evaluation and elimination of most sensitive parts based on performance ranking criteria. Each part is ranked based on its respective performance in each load case. CR1 (cumulative response index) is used as a performance ranking criteria for elimination of most sensitive parts. The higher the CR1 is the more sensitive the part is with regard to crash responses.

In Fig. 3, "DC" means roof drop load case, "HE" means rear repair crash load case, "SLY means ENCAP pole impact load case, "53" means IIHS side impact load case, and HI" means FMVSS3O1 load case.

Moreover, in Fig. 3, the number "1" indicates a marginal/acceptable deterioration in performance of the part and the number "3" indicates a large/unacceptable deterioration in performace of the part. These numbers are derived from evaluation process guide lines shown in Fig. 5. For example, parts designated with reference sign "P" are most sensitive for crash load cases.

Fig. 4 shows a table in which the individual sensitivity information determined by means of the NVH evaluation, the durability evaluation, and the crash evaluation are combined. In other words, the table shown in Fig. 4 shows a combination of the sensitivities. Each part is down gauged with different percentages (e.g. 15%, 10%, 5% etc.) until the load case criteria is satisfied. In the table shown in Fig. 4, the parts are designated with predeterminable numbers. For example, part 1617201 is down gauged to 15%, 10%, 5%.

But even with 5% down gauge this part could not satisfy the NVH point mobility (PM) loadcase criteria. So this part is again put back to nominal thickness in order to satisfy the NVH point mobility loadcase criteria.

The sensitivity information for each pad across all three disciplines (NVH, durability, crash) are combined to create a first iteration "Iter 1". For example, Part 66371381 deteriorated the performance of "DC" and "SG" loadcase with a down gauge of 15. But, the performance could be fulfilled neither with 10 % nor with 5 % down gauge. So, the thickness of this part should be kept at nominal value in "Iter 1". "Iter 1" is a combination of sensitivity information of all the parts together. To study the combined effect, this set of thickness is once again evaluated for all loadcase criteria (NVH, durability, crash) and further optimized. Hence the final set of optimized thickness are obtained which satisfies all NVH, durability, and crash criteria yielding a light weight body in white. An important note to consider in this evaluation is that no gauge change which will deteriorate the NVH target is considered during durability and crash sensitivity and optimization studies. This avoids going back and forth for checking whether the new gauges optimized during the third step S3 will satisfy load case criteria in the second step S2.

The number being designated with reference sign N1" designates a part which particularly affects the rear impact load case. A number designated with reference sign "N2" in Fig. 4 designates a part which particularly affects the side impact load case. For example, the part designated with the number "N2" is a side member of the body in white.

For example, the part designated by the number N1"is a B-pillar of the body in white.

The pads listed in the table shown in Fig. 4 are optimized with regard to their respective thickness and yet satisfy the predeterminable NVH, durability and crash requirements or targets. Thus, the body in white as a whole is particularly light and still has particularly advantageous NVH, durability and crash characteristics.

For example, a colour coding can be used in the table shown in Fig. 4, the colour coding comprising four different colours: yellow, red, green and white. Each cell of the table shown in Fig. 4 can be filled with one of the colours. Each colour indicates a down gauge or a thickness. For example, "white" indicates the nominal thickness. "Yellow" indicates a down gauge of 15%, "red" indicates a down gauge of 10% and "green" indicates a down gauge of "5%".

Fig. 5 shows tables by means of which a process for determining the CR1 can be illustrated. The parts can be classified into grades, wherein each grade corresponds with a weight factor. Moreover, the parts can be classified in order to assign a respective response uncertainty factor (RUF) to the respective part. Furthermore, respective importance factors can be assigned to the parts so that the CR1 can be calculated by multiplying the weight factor, the RUF and the importance factor. By means of the method illustrated by means of the Figs., an optimized design functionally meeting all requirements can be created in a particularly short time.

List of reference sign Si first step S2 second step 53 third step S4 fourth Stepp DC roof drop load case HE rear repair crash load case SL ENCAP pole impact load case SO IIHS side impact load case HI FMVSS3Oi load case CR1 cumulative response influence P parts Ni number N2 number

Claims (3)

1. Claims A method for designing a body in white of a vehicle, in particular a passenger vehicle, the method comprising: -a first step (Si) in which a first number of parts of the body in white is selected, -a second step (52) in which: o a first set of parts of the body in white is subjected to a first evaluation regarding the noise characteristics of the vehicle, thereby identifying a second number of parts being sensitive with regard to the noise characteristics, o the second number of parts is subtracted from the first number of parts, the remaining parts forming a second set of parts of the body in white, -a third step (S3) in which: o the second set of pads is subjected to a second evaluation regarding the durability characteristics of the body in white, thereby identifying a third number of parts being sensitive with regard to the durability characteristics, o the third number of parts is subtracted from the first number of parts, the remaining parts forming a third set of parts of the body in white, -a fourth step (54) in which: o the third set of parts of the body in white is subjected to a third evaluation regarding the crash characteristics of the body in white thereby identifying a fourth number of parts being sensitive with regard to the crash characteristics, o the fourth number of parts is subtracted from the first number of parts, the remaining pads forming a fourth set of parts of the body in white, wherein in each evaluation the thickness of the respective set of parts is optimized with regard to the respective characteristics, -a fifth step (S5) in which a final set of optimized parts is obtained by combining sensitivity values respectively characterizing the sensitivities of the set of parts with regard to the noise characteristics, the durability characteristics, and the crash characteristics.
2. 2. The method according to claim 1, characterized in that in at least one of the steps (Si, S2, S3, S4, S5) at least two consecutive simulation runs are conducted by means of which the respective characteristics of at least one of the parts is simulated, a second one of the runs succeeding a first one of the runs and being conducted with a smaller thickness of the at least one part in comparison with the first run.
3. 3. The method according to claim 2, characterized in that the thickness of the at least one part in the second run is at least 15% less than the thickness of the at least one part in the first run.