Optimization method of automobile crash performance based on VPI and OLC

Abstract

The present invention discloses a method for optimizing automobile collision performance based on VPI and OLC, comprising the following steps: 1: the initial velocity V0 of the vehicle collides with a rigid wall, the average deceleration is A0, the VPI curve and the OLC curve are fitted, and the linear regression formula of VPI for OLC is obtained; 2: OLC remains unchanged, by optimizing and further optimizing the collision performance of the vehicle body structure, the average deceleration of the vehicle is reduced, and the rebound speed is relatively increased; 3: the average deceleration and rebound speed of the vehicle body structure after the collision performance optimization are recalculated, and it is determined whether the average deceleration and rebound speed of the vehicle meet the relationship between VPI and OLC. If not, return to step 2 for further optimization; if satisfied, the optimization is completed. The present invention uses the linear regression formula of VPI for OLC, and under the premise that OLC remains unchanged, guides the crashworthiness design of the vehicle body structure through the change law of VPI.

Description

Technical Field

[0001] The invention relates to a collision design method for an automobile body structure, and in particular to an optimization method for automobile collision performance based on VPI and OLC. Background Art

[0002] VPI (Peak vehicle pulse index) is a method for approximately deriving the peak chest acceleration of the occupants in the vehicle through the acceleration curve of the vehicle during a collision.

[0003] OLC (Occupant loading criterion) is a method to approximate the average chest acceleration of the occupants in the vehicle through the speed change curve of the vehicle during a collision.

[0004] Although VPI and OLC indexes are widely used by major automobile companies to evaluate the overall performance of vehicle collisions when designing automobile body structures, both VPI and OLC indexes are used separately, and only a single value can be obtained through VPI or OLC index to evaluate vehicle collision performance. For example: a certain brand of automobile uses VPI index to evaluate vehicle collision performance, and its VPI target is no higher than 50g, that is, the peak value of the approximate occupant chest acceleration obtained through the vehicle collision acceleration curve is no higher than 50g; another brand of automobile uses OLC index to evaluate vehicle collision performance, and its OLC target is no more than 27g, that is, the average value of the occupant chest acceleration obtained through the vehicle collision speed-time curve is no higher than 27g. The numerical size of VPI and OLC can only qualitatively analyze whether the overall acceleration curve during the vehicle collision process is soft or hard, but it is impossible to know whether there is still specific optimization space for the front energy absorption structure and support structure of the vehicle, and it is impossible to accurately evaluate the vehicle collision performance, nor is it helpful for the optimization of the body structure design.

[0005] When designing the collision of the vehicle body structure based on the VPI or OLC index, in order to ensure the safety of the vehicle, the rebound speed will be reduced as much as possible and the structural energy absorption will be increased to the maximum. Therefore, it is necessary to arrange high-strength materials at the front end of the vehicle (such as the energy absorption box), the front end and the middle part of the longitudinal beam and other energy absorption parts to meet the energy absorption efficiency requirements, so as to avoid chest injuries of the occupants in the vehicle caused by vehicle intrusion and excessive rebound in the later stage. However, this method needs to be based on progressive axial folding, so the structure and material distribution need to be based on the principle of weak front and strong rear, otherwise the front energy absorption structure will be at risk of instability. In addition, since it is necessary to arrange high-strength materials at the front and middle parts of the vehicle energy absorption box and the longitudinal beam, it is inevitable that the rear part of the longitudinal beam will be required to have a greater structural strength, so the weight of the materials will be accumulated on the path of the energy absorption box and the longitudinal beam, and the vehicle cost will increase. At the same time, since the acceleration curve in the middle section of this method is relatively high, and the occupant's chest has been restrained and pre-tightened by the seat belt at this time, and is squeezed backward by the airbag and the steering column, it is easy to cause the occupant's chest acceleration to couple with the body acceleration. Summary of the invention

[0006] The purpose of the present invention is to provide an optimization method for automobile collision performance based on VPI and OLC, using the linear regression formula of VPI for OLC, and guiding the crashworthiness design of the vehicle body structure through the change law of VPI under the premise that OLC remains unchanged.

[0007] The present invention is achieved in that:

[0008] A method for optimizing automobile collision performance based on VPI and OLC comprises the following steps:

[0009] Step 1: When the initial velocity of the vehicle and the occupants is V0, the vehicle collides with a rigid wall and generates an acceleration -A0 in the direction directly in front of the vehicle, that is, the average deceleration of the vehicle is A0. The VPI curve and the OLC curve are fitted to obtain the linear regression formula of VPI for OLC.

[0010] Step 2: Under the premise of OLC unchanged, by optimizing the collision performance of the vehicle body structure and further optimizing it, the average deceleration A0 of the vehicle is reduced and the rebound speed V is relatively increased. r ;

[0011] Step 3: Recalculate the average vehicle deceleration A0 and rebound velocity V of the body structure after collision performance optimization r , determine the vehicle's average deceleration A0 and rebound speed V r Whether the relationship between VPI and OLC is satisfied, if not, return to step 2 to further optimize the collision performance of the vehicle structure; if satisfied, the optimization of the collision performance of the vehicle structure is completed.

[0012] The step 1 also includes:

[0013] Step 1.1: Calculate the VPI curve. The calculation formula is:

[0014]

[0015] Among them, a max It is the peak chest acceleration of the occupants during the collision;

[0016] w is the angular frequency, m is the mass of the occupant in the vehicle, k is the elastic coefficient of the restraint system;

[0017] t0 is the time from the moment the vehicle hits the rigid wall to the moment the vehicle restraint system starts to work. δ is the free flight distance of the occupants in the vehicle before the vehicle restraint system acts;

[0018] Step 1.2: Calculate the OLC curve using the following formula:

[0019] OLC=a (18)

[0020] Where a is the constant deceleration of the occupants in the vehicle during the collision;

[0021] Step 1.3: Under certain vehicle initial velocity, rebound velocity and vehicle average deceleration, fit the VPI curve and OLC curve to obtain the relationship formula between VPI and OLC: y = Qx (28)

[0022] Where y represents VPI, x represents OLC, Q represents the relationship coefficient between VPI and OLC, Q≈2, that is, VPI≈2*OLC;

[0023] Under the premise that V0 and OLC remain unchanged, as the rebound speed V r increases, the relationship coefficient Q decreases monotonically, and the correlation coefficient R between VPI and OLC 2 It increases monotonically and approaches 1 infinitely.

[0024] The method for optimizing the collision performance of a vehicle body structure comprises:

[0025] (i) Increase the support structure of the root of the vehicle longitudinal beam and the firewall, and use materials with high yield stress and low elastic modulus at the front of the root of the longitudinal beam to increase the rebound speed;

[0026] (ii) Firewalls and inner and outer reinforcement beams of firewalls are made of high-strength and high-hardening materials with low yield strength ratio to improve rebound speed;

[0027] (iii) Increase the crumple space of the front cabin of the vehicle, reduce the vehicle deceleration in the early stage, and prepare for the rebound in the later stage;

[0028] (iv) Increase the length of the front overhang, increase the length and strength of the crash box, and reduce the strength of the middle part of the longitudinal beam so that the longitudinal beam can be mainly bent and collapsed as much as possible.

[0029] The method of increasing the crumple space of the front cabin of the vehicle in the method (iii) includes increasing the length of the front overhang, using a full subframe or using a cast aluminum subframe.

[0030] When the crumple space of the front cabin of the vehicle is increased by increasing the front overhang length in the method (iii), the method (iv) can be further adopted.

[0031] The priority levels of the methods (i)-(iv) described above are gradually reduced.

[0032] When further optimizing the collision performance of the vehicle structure, according to the priority level of the collision performance optimization methods (i)-(iv) of the vehicle body structure, optimization methods are gradually added from (i) to (iv), that is, when method (i) cannot meet the design requirements of the collision performance, return to step 2 and add method (ii) to further optimize the collision performance of the vehicle body structure; if the design requirements of the collision performance still cannot be met after adding method (ii), return to step 2 and add method (iii) to further optimize the collision performance of the vehicle body structure; if the design requirements of the collision performance still cannot be met after adding method (iii), return to step 2 and add method (iv) to further optimize the collision performance of the vehicle body structure.

[0033] In the step 2, when OLC≤35g, the collision performance of the vehicle body structure is optimized; when OLC>35g, the stiffness k of the restraint system of the vehicle is reduced and the collision performance of the vehicle body structure is optimized.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention obtains the linear regression formula of VPI for OLC and the linear regression correlation coefficient R under the premise of different initial velocities and rebound velocities by linear regression, and evaluates the correlation between VPI and OLC by the size of the linear regression correlation coefficient. It can be concluded that the rebound speed of vehicles at the same collision speed is different due to different structural designs, which makes the relationship between VPI and OLC change locally. From this local change, it can be inferred what changes need to be made to the vehicle body, which solves the fundamental problem of blindly using VPI or OLC index alone but severing the relationship with the vehicle body.

[0036] 2. The present invention uses the relationship between VPI and OLC to deduce that, under the premise that OLC remains unchanged, the greater the rebound speed, the smaller the VPI, and thus the smaller the acceleration of the occupant's chest. Therefore, under the premise of reducing the VPI, the rebound speed can be increased by adding support structures at the rear end of the longitudinal beam and in front of the passenger compartment while keeping the OLC unchanged. Different from the prior art that simply requires that the front cabin of the vehicle must have sufficient energy-absorbing parts, the present invention needs to provide additional space while partially reducing the front cabin energy-absorbing parts so that the rebound speed of the vehicle can be increased and the VPI can be reduced while keeping the OLC unchanged.

[0037] 3. The present invention obtains the key methods and ideas for vehicle collision design by analyzing the intrinsic connection between VPI and OLC, and proposes a new concept for vehicle body structure design and development, which solves the dilemma that the industry cannot use both VPI and OLC indexes from the perspective of vehicle body design. At the same time, it also helps design engineers to reasonably develop vehicles with excellent collision resistance for different markets by quantifying design parameters.

[0038] The present invention uses the linear regression formula of VPI for OLC and the linear regression correlation coefficient R, and evaluates the correlation between VPI and OLC by the size of the linear regression correlation coefficient. Under the premise that OLC remains unchanged, the variation law is obtained according to the value range of VPI to guide the crashworthiness design of the vehicle body structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flow chart of a method for optimizing automobile collision performance based on VPI and OLC of the present invention;

[0040] Figure 2 This is a typical mechanical model diagram of the movement of passengers in a car;

[0041] Figure 3 It is the vehicle collision speed time curve and OLC curve;

[0042] Figure 4 It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average deceleration of the vehicle is 25g, and the rebound velocity is 1m / s;

[0043] Figure 5 It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average vehicle deceleration is 25g, and the rebound velocity is 3m / s;

[0044] Figure 6It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average deceleration of the vehicle is 25g, and the rebound velocity is 5m / s;

[0045] Figure 7 It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average deceleration of the vehicle is 25g, and the rebound velocity is 2m / s;

[0046] Figure 8 It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average vehicle deceleration is 25g, and the rebound velocity is 4m / s;

[0047] Fig. 9 It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average vehicle deceleration is 25g, and the rebound velocity is 6m / s;

[0048] Fig.10 It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average deceleration of the vehicle is 25g, and the rebound velocity is 7m / s;

[0049] Fig.11 It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average vehicle deceleration is 25g, and the rebound velocity is 8m / s;

[0050] Fig.12 It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average vehicle deceleration is 25g, and the rebound velocity is 9m / s;

[0051] Fig.13 It is a linear regression curve diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average vehicle deceleration is 25g, and the rebound velocity is 10m / s;

[0052] Fig.14 It is a linear regression curve superposition diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention when the initial velocity is 13.89m / s, the average vehicle deceleration is 10-46g, and the rebound velocity is 1-10m / s;

[0053] Fig.15It is a principle diagram of the optimization method of automobile collision performance based on VPI and OLC of the present invention, in which OLC remains unchanged and the rebound speed increases;

[0054] Fig.16 It is a graph showing the relationship between the yield strength ratio and the resilience performance of the materials used in the vehicle restraint system. DETAILED DESCRIPTION

[0055] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0056] Please see attached Figure 1 , a method for optimizing automobile collision performance based on VPI and OLC, comprising the following steps:

[0057] Step 1: Fit the VPI curve and the OLC curve to obtain the linear regression formula of VPI to OLC.

[0058] Step 1.1: When the initial velocity of the vehicle and the occupants is V0, the vehicle collides with a rigid wall and generates an acceleration -A0 in the direction directly in front of the vehicle (i.e., the average deceleration of the vehicle is A0, which is a constant value. A0 is determined during vehicle design and development, and A0 varies for different models and configurations). Calculate the VPI curve using the following formula:

[0059]

[0060] Among them, a max It is the peak chest acceleration of the occupants during the collision;

[0061] w is the angular frequency, m is the mass of the occupant in the vehicle, k is the elastic coefficient of the restraint system;

[0062] t0 is the time from the moment the vehicle hits the rigid wall to the moment the vehicle restraint system starts to work. δ is the free flight distance of the occupants before the vehicle restraint system takes effect.

[0063] The derivation process of formula (1) is as follows:

[0064] Please see attached Figure 2 , attached Figure 2It is a typical mechanical model of the movement of passengers in the car, that is, a spring (vehicle restraint system)-mass (passenger mass in the car) system with 2 degrees of freedom. According to the regulations of different countries or the NCAP (New Car Assessment Program, i.e., new car collision test) requirements, there are two speeds, 50kph and 56kph. Here, the initial velocity of the vehicle and the passenger is set as V0, which is set to 50kph (i.e., 13.89m / s); when the vehicle collides with the rigid wall, it generates an acceleration -A0 in the forward direction, where -A0 is a constant value, set to 25g. For vehicles with the same initial velocity, A0 will be very different due to different acceleration targets set during automobile development or different structural differences. However, in the same crumple space, the greater the initial velocity, the greater the average acceleration. The purpose of optimizing the vehicle body structure is to find the optimal solution in the same space, reducing the average acceleration of the vehicle body while reducing the intrusion of the passenger compartment. The occupant in the car with a mass of m is subjected to the force from the restraint system, where the mechanical characteristics of the restraint system are reflected by a linear spring (elastic coefficient k) that only generates force in the compressed state and does not generate force in the stretched state. Assuming that the free flight distance of the occupant in the car before being restrained by the restraint system is δ, the occupant in the car moves at a constant speed V0 from the moment of the collision to before being restrained by the restraint system. Here, since the mass of the vehicle is greater than the mass of the occupant in the car, it can be considered that the movement of the vehicle is not affected by the movement of the occupant in the car.

[0065] Vehicle acceleration for

[0066] Vehicle speed for

[0067] Where, t is the collision time;

[0068] The displacement X of the vehicle is:

[0069] exist At this moment, the vehicle restraint system begins to work, that is, the occupants in the car are subjected to the force of the spring, and the motion equation of the occupants in the car is:

[0070]

[0071] Where x is the displacement of the occupant relative to the ground reference system, X is the displacement of the vehicle relative to the ground reference system, is the second-order derivative of the occupant's fulcrum displacement with respect to time.

[0072] therefore

[0073] in

[0074] Assuming that the displacement of the occupant relative to the vehicle is x′=xX, formula (6) can be rewritten as:

[0075]

[0076] in, It is the second-order derivative of the displacement of the occupant relative to the vehicle with respect to time.

[0077] If the acceleration of the vehicle in this model is the average acceleration, then Substituting into formula (7), we get

[0078] Where x' is the displacement of the occupant relative to the vehicle.

[0079] Introduce the unknown coefficients A and B into the solution of formula (8):

[0080]

[0081] Assuming that the initial condition is that the spring and the mass start to contact at t = t0, we get:

[0082] x′(t0)=δ (10)

[0083]

[0084] Substituting formula (10) and (11) into formula (9), we obtain:

[0085] Therefore, formula (9) can be rewritten as:

[0086] Formula (11) can be rewritten as:

[0087] Formula (7) can be rewritten as:

[0088] Therefore, the acceleration of the occupants in the car is: Right now

[0089]

[0090] In order to find the maximum value of the occupant's chest deceleration a max , rewrite formula (15) as:

[0091]

[0092] in,

[0093] Therefore, the maximum value of the occupant chest deceleration can be obtained from formula (16):

[0094]

[0095] According to the definition of VPI, the stiffness of the restraint system is: the stiffness of the 1kg dummy mass is a fixed value of 2500N / m, and the free travel of the occupant in the vehicle is 30mm. Then when the average deceleration of the vehicle A0 = 25g:

[0096]

[0097]

[0098]

[0099] Step 1.2: When the initial velocity of the vehicle and the occupants is V0, the vehicle collides with a rigid wall and generates an acceleration of -A0 in the direction directly in front of the vehicle (i.e., the average deceleration of the vehicle is A0). The OLC curve is calculated using the following formula:

[0100] OLC=a (18)

[0101] Where a is the constant deceleration of the occupants in the vehicle during the collision.

[0102] The derivation process of formula (18) is as follows:

[0103] Please see attached Figure 3 , attached Figure 3 The vehicle collision speed time curve and OLC curve. The initial velocity of the vehicle is V0. When the vehicle collides with a rigid wall, it generates an acceleration of -A0 in the forward direction, where -A0 is a constant value. Figure 3 The speed-time deceleration curve of the vehicle can be expressed as: y=V0-A0t, where t is time.

[0104] At this time, assuming that the initial velocity of the occupant in the car is V0, according to the definition of OLC, the free flight distance before the vehicle's restraint system takes effect is 65mm, which is Figure 3 The area S1 enclosed by the horizontal dotted line and the vehicle speed time deceleration curve is shown. Then the restraint system begins to act on the occupants in the vehicle and decelerates uniformly at a constant deceleration a. Under the action of the restraint system, the deceleration equation of the occupants in the vehicle is: y = V0′-at (19)

[0105] Among them, V0' is the speed of the occupants in the car, and t is the time.

[0106] According to the definition of OLC, the travel of the occupants in the vehicle under the action of the restraint system is 235mm, that is, Figure 3The area S2 enclosed by the speed-time deceleration curve of the occupants in the vehicle and the speed-time deceleration curve of the vehicle, the following derivation process can be obtained from the above conditions:

[0107]

[0108] Among them, t0 is the moment when the vehicle's restraint system starts to take effect.

[0109] In order to obtain Figure 3 V0′ in the deceleration equation of the occupant in the vehicle can be replaced by the boundary condition (t0, V0) at the end point of the occupant's free flight into y=V0 - A0t, the deceleration equation of the occupants in the car is:

[0110] y = (V0 + at0) - at (21);

[0111] Then the coordinates of the intersection of the speed-time deceleration curve of the occupant in the vehicle and the speed-time deceleration line of the vehicle body rebound (t r ,V r ) into formula (21), we can get:

[0112]

[0113] Among them, t r is the rebound time of the occupants in the vehicle, V r is the rebound velocity of the occupants in the vehicle.

[0114] Similarly, the coordinates of the intersection of the vehicle body speed time deceleration curve and the vehicle body rebound speed time deceleration straight line (t r ',V r Substituting y=V0-A0t, we can get:

[0115]

[0116] Among them, t r ' is the rebound time of the vehicle, V r ' is the rebound speed of the vehicle.

[0117] The area S2 can be obtained by Figure 3 Subtract the areas of the two right triangles in , that is:

[0118]

[0119] Substituting formula (22) and (23) into formula (24), we can obtain:

[0120]

[0121] At the same time, substituting the free flight distance of the passengers in the vehicle, 0.065 m, into formula (20) yields:

[0122]

[0123] Substituting formula (26) into formula (25), we can get:

[0124]

[0125] When a vehicle collides with a rigid wall at an initial velocity of 50 kph, V0 = 13.89 m / s. After the vehicle restraint system structure absorbs energy, it decelerates. The rebound velocity of the vehicle is usually between 1 m / s and 5 m / s. For the convenience of calculation, the rebound velocity of the vehicle is temporarily taken as V r =1.11m / s, then when the average vehicle deceleration A0 = 25g, OLC is equal to:

[0126]

[0127] Step 1.3: The vehicle hits a rigid wall at 50 kph, with an average vehicle deceleration A0 of 25 g and a rebound velocity V r When it is 1.11m / s, VPI=56.7g≈2*28.83g=57.66g, that is, VPI≈2*OLC.

[0128] When the rebound speed V r When y is 1m / s, y=2.255x, R 2 =0.392, where y represents VPI, x represents OLC, and R 2 is the correlation coefficient, and its linear regression curve is shown in the attached figure. Figure 4 shown.

[0129] When the rebound speed V r When it is 3m / s, y=2.056x, R 2 =0.972, where y represents VPI, x represents OLC, and R 2 is the correlation coefficient, and its linear regression curve is shown in the attached figure. Figure 5 shown.

[0130] When the rebound speed V r When it is 5m / s, y=1.931x, R 2 =0.989, where y represents VPI, x represents OLC, and R 2 is the correlation coefficient, and its linear regression curve is shown in the attached figure. Figure 6 shown.

[0131] From the above relationship and the attached Figure 4 To Attachment Figure 6 It can be seen that the relationship between VPI and OLC basically satisfies the relationship VPI≈2*OLC, and the linear regression correlation coefficient also shows that the two have extremely high correlation.

[0132] Step 1.4: The vehicle collides with a rigid wall at 50 kph. When the average deceleration A0 of the vehicle is 10-46 g, the rebound velocity V r When the rebound speed is 1-10 m / s (1-10 m / s can basically cover the rebound speed of all brands and models of vehicles in the prior art, so the rebound speed in the range of 1-10 m / s is highly representative), the VPI curve and the OLC curve are fitted to obtain the relationship formula between VPI and OLC: y=Qx(28).

[0133] Among them, y represents VPI, x represents OLC, and Q represents the relationship coefficient between VPI and OLC, as shown in the attached figure. Figure 4-13 Its linear regression curve is shown in the attached Fig.14 shown.

[0134] From the relationship between VPI and OLC: y = Qx, we can know that when V0 = 13.89m / s, as the rebound speed V r increases, the relationship coefficient Q decreases monotonically, and the correlation coefficient R between VPI and OLC 2 It increases monotonically and approaches 1 infinitely, indicating that VPI and OLC are highly correlated.

[0135] Specifically, when the average vehicle deceleration A0 is 10-46g, the rebound speed V r In the working range surrounded by the workpiece with a change of 1-10m / s, the correlation coefficient Q≈2 and varies between 1.785-2.255, and the correlation coefficient R 2 Varies between 0.933 and 0.995, and all curves are superimposed on the Fig.14 middle.

[0136] Therefore, according to formula (28) and the attached Fig.14 The following conclusion is drawn: Under the premise that OLC remains unchanged, the rebound speed V r The larger the value, the smaller the VPI. Fig.14 It can be seen that when OLC is equal to the more commonly used value of 30g, the VPI changes between 54g and 63g, which is close to a change of 10g. At the same time, the vehicle average deceleration A0 changes between 24g and 29g. Since the VPI curve shows a high correlation with the occupant chest acceleration, this 10g VPI change range will have a great impact on the occupant chest acceleration.

[0137] Under the condition of different initial collision velocities V0, the VPI curve and OLC curve at the initial velocity V0 can be fitted through the above steps. By bringing different initial velocity V0 values ​​into the above derivation process, the conclusion that VPI≈2*OLC can also be obtained, which will not be repeated here.

[0138] Step 2: From formula (28) and the attached Fig.14 It can be seen that when OLC>35g, VPI will change between 63-90g, reducing the stiffness k of the vehicle's restraint system, and under the premise of unchanged OLC, by optimizing and further optimizing the collision performance of the body structure, reducing the average deceleration A0 of the vehicle, reducing the energy absorption of the early vehicle, increasing the collapse of the vehicle, and relatively increasing the rebound speed V r , which is conducive to improving optimization efficiency. Reducing the stiffness k of the vehicle's restraint system includes: increasing the collapse of the steering column, increasing the diameter of the airbag's vent hole, reducing the force limit penalty of the seat belt, and a series of other optimizations for the occupant restraint system.

[0139] The larger the OLC is, the larger the design range of VPI is. Therefore, the value of VPI can be reduced by designing the stiffness k of the constraint system, which has a positive effect on VPI. The acceleration waveform of the vehicle body will promote the subsequent optimization of the constraint system.

[0140] When OLC is less than or equal to 35g, under the premise of OLC unchanged, by optimizing the collision performance of the vehicle body structure and further optimizing it, the average deceleration A0 of the vehicle is reduced, the energy absorption of the vehicle in the early stage is reduced, the collapse of the vehicle is increased, and the rebound speed V is relatively increased. r .

[0141] Please see attached Fig.15 , the area enclosed by the dotted line OLC and the solid line A0 must be equal to the area enclosed by the dotted line OLC and the dashed line A0' (A0' is the average vehicle deceleration after reduction under the premise of unchanged OLC, and A0>A0'), that is, S3=S4, which can satisfy the premise of unchanged OLC, reduce the energy absorption of the middle part of the vehicle, increase the rebound speed of the vehicle, and thus reduce the VPI. Another explanation for the further reduction of VPI is the decrease in the average deceleration of the vehicle. Under the premise of unchanged OLC, based on the starting point that the greater the rebound speed, the smaller the VPI will be, a new vehicle structure that meets the vehicle collision requirements can be designed.

[0142] The method for optimizing the collision performance of a vehicle body structure comprises:

[0143] (i) Increase the support structure of the root of the vehicle longitudinal beam and the firewall, and use materials with high yield stress and low elastic modulus at the front of the root of the longitudinal beam, so that the material is easier to rebound before reaching yield in the later stage of the collision, thereby helping the vehicle to rebound and increase the rebound speed. Preferably, an aluminum alloy casting made of A356 HPDC high pressure die casting can be used as the support structure of the root of the longitudinal beam to obtain a higher rebound speed. The characteristic of A356 HPDC is that the Young's modulus is only 1 / 3 of that of steel, but the overall rigidity of the structure is high and it is difficult to reach the overall yield point.

[0144] (ii) The firewall and the inner and outer reinforcement beams of the firewall are made of materials with low yield strength, high strength and high hardening performance, which can increase the elastic part of the material after unloading, so as to help the vehicle rebound later and increase the rebound speed. Preferably, the material with low yield strength, high strength and high hardening performance can be DP800 or DP1000 stamping parts, which can increase the rebound effect of the vehicle later.

[0145] For the influence of materials with different yield ratios on material springback, please refer to the attached Fig.16 In the figure, the solid line is the material with higher yield strength, and the dotted line is the material with lower yield strength. Fig.16 It can be seen that the greater the yield strength ratio of the material, the greater the springback.

[0146] (iii) Properly increase the crumple space of the front cabin of the vehicle, for example, by increasing the length of the front overhang, using a full subframe or a cast aluminum subframe, etc. This can minimize the vehicle deceleration in the early stages and prepare for the rebound in the later stages. In the middle stages of a collision, using brittle materials such as a cast aluminum subframe in the middle of the vehicle's front energy-absorbing structure can reduce the average acceleration in the middle stages of a collision.

[0147] (iv) Increase the length of the front overhang, increase the length and strength of the crash box, and reduce the strength of the middle part of the longitudinal beam, so as to achieve the purpose of reducing the mid-term energy absorption and mid-term average acceleration, so that the longitudinal beam can be mainly bent and collapsed as much as possible.

[0148] Although both methods (iii) and (iv) are based on increasing the front cabin space, method (iii) is a method that uses brittle structural parts such as cast aluminum subframes as compensation to reduce mid-term acceleration; while method (iv) is also a method of increasing the front cabin space, but it mainly focuses on increasing the front overhang length, increasing the energy absorption in the initial stage, and then reducing the average mid-term acceleration by weakening the middle part of the longitudinal beam. When the crumple space of the front cabin of the vehicle is increased by increasing the front overhang length in method (iii), method (iv) can be further adopted, and method (iii) and method (iv) are combined to improve the optimization effect.

[0149] The above four methods are the best optimization methods suitable for the inference results in step 1, but the collision performance optimization methods of the vehicle body structure are not limited to the above four methods. Other methods can also be used to optimize the collision performance of the vehicle body structure, which will not be repeated here.

[0150] Since the most direct methods to increase the rebound speed are methods (i) and (ii), and methods (iii) and (iv) are to increase the rebound speed by increasing the crumple space while reducing the mid-term energy absorption, the priority levels of methods (i)-(iv) are gradually reduced.

[0151] Step 3: CAE and other calculation software can be used to recalculate the average vehicle deceleration A0 and rebound speed V of the body structure after collision performance optimization. r , determine the vehicle's average deceleration A0 and rebound speed V r Whether the relationship between VPI and OLC is satisfied, if not, return to step 2 to further optimize the collision performance of the vehicle structure; if satisfied, the optimization of the collision performance of the vehicle structure is completed.

[0152] When further optimizing the collision performance of the vehicle structure, according to the priority level of methods (i)-(iv), optimization methods are gradually added from (i) to (iv). That is, when method (i) cannot meet the design requirements of the collision performance, return to step 2 and add method (ii) to further optimize the collision performance of the vehicle body structure. If the design requirements of the collision performance still cannot be met after adding method (ii), return to step 2 and add method (iii) to further optimize the collision performance of the vehicle body structure. If the design requirements of the collision performance still cannot be met after adding method (iii), return to step 2 and add method (iv) to further optimize the collision performance of the vehicle body structure.

[0153] When optimizing and further optimizing the collision performance of the vehicle body structure, the optimization sequence of methods (i)-(iv) is preferred, but it is also possible to skip a step in the middle according to the difficulty of the OEM development. For example, if the vehicle body structure can be optimized according to method (i) first, if it is found that the design goal is still not achieved after optimization, methods (ii) and (iii) can be skipped and method (iv) can be used; it is also possible not to optimize method (i) and directly use the following solutions, but the overall priority remains unchanged.

[0154] Embodiment 1:

[0155] When a 2-ton vehicle hits a rigid wall head-on at a speed of V0 = 13.89 m / s, according to formula (28): y = Qx, where Q ≈ 2, combined with the attached Fig.14 The vehicle company set a vehicle development goal of less than 31g OLC and less than 57g VPI. Through the first CAE simulation, it was found that the crushable space of the front cabin of the vehicle was relatively small, only 337mm, and the rebound speed of the vehicle was only 1m / s. According to the kinetic energy theorem: Calculate the average acceleration of the vehicle: A0 = 29 g.

[0156] Where M is the vehicle weight and S is the vehicle crumpling distance.

[0157] Substituting A0 into the calculation formula of VPI, we get VPI=64.84g. Substituting A0=29g and Vr=1m / s into the calculation formula of OLC, we get OLC=30.43g. It can be found that OLC has met the company's specified goals, but VPI=64.84g>target 57g, and the body still needs to be optimized.

[0158] According to optimization method (i): the supporting structure at the root of the longitudinal beam is replaced from sheet metal steel structure to A356 HPDC high pressure die-cast aluminum material. At this time, through a new round of CAE simulation, the rebound speed is increased to Vr = 5m / s, and A0 is reduced to 25g. At the same time, the calculated OLC = 30.69g remains basically unchanged, but VPI is reduced to 56.74g. At this time, both indicators meet the vehicle objectives.

[0159] Embodiment 2:

[0160] When a car weighing 2.5 tons hits a rigid wall head-on at a speed of V0 = 13.89 m / s, according to formula (28): y = Qx, where Q ≈ 2, combined with the attached Fig.14 The vehicle company set a vehicle development goal of less than 35g OLC and less than 65g VPI. Through the first CAE simulation, it was found that the crushable space of the front cabin of the vehicle was relatively small, only 291mm, and the rebound speed of the vehicle was only 2m / s. According to the kinetic energy theorem: The average acceleration of the vehicle is calculated to be A0 = 33 g.

[0161] Where M is the vehicle weight and S is the vehicle crumpling distance.

[0162] Substituting A0 into the calculation formula of VPI, we get VPI=73.9g. Substituting A0=33g and Vr=2m / s into the calculation formula of OLC, we get OLC=34.6g. It can be found that OLC has met the company's specified goals, but VPI=73.9g>target 65g, and the body still needs to be further optimized.

[0163] At this time, the optimization method (iii) is used to increase the crumple space of the front cabin. Specifically, a brittle cast aluminum subframe is used in the middle of the front energy absorption structure of the vehicle. This can reduce the acceleration of the middle part and increase the crumple distance of the middle part of the vehicle. At this time, a new round of CAE simulation results in the rebound speed increasing to V r =4m / s, A0 is reduced to 28g, while OLC = 34.3g is calculated to remain basically unchanged, the crumple distance is also increased to 320mm, but VPI is reduced to 62.8g. At this time, both indicators meet the vehicle goals at the same time.

[0164] Embodiment 3:

[0165] When a car weighing 2.8 tons hits a rigid wall head-on at a speed of V0 = 13.89 m / s, according to formula (28): y = Qx, where Q ≈ 2, combined with the attached Fig.14 The vehicle company set a vehicle development goal of less than 36g OLC and less than 65g VPI. Through the first CAE simulation, it was found that the crushable space of the front cabin of the vehicle was relatively small, only 253mm, and the rebound speed of the vehicle was 3m / s. According to the kinetic energy theorem: Calculate the average acceleration of the vehicle: A0 = 37 g.

[0166] Where M is the vehicle weight and S is the vehicle crumpling distance.

[0167] Substituting A0 into the calculation formula of VPI, we get VPI=81g. Substituting A0=37g and Vr=3m / s into the calculation formula of OLC, we get OLC=38.9g. It can be found that OLC has met the company's specified goals, but VPI=81g>target 65g, and the body still needs to be optimized.

[0168] First, we execute the optimization method (i): replace the supporting structure of the root of the longitudinal beam from sheet metal steel structure to A356HPDC high pressure die-cast aluminum material, and simply increase the vehicle rebound speed. At this time, through a new round of CAE simulation, the rebound speed is increased to Vr = 4.5m / s, A0 is reduced to 34g, and OLC = 38.5g is calculated to remain basically unchanged, the collapse distance remains unchanged at 253mm, and VPI is reduced to 72.9g. At this time, although the two indicators have improved, they still have not reached the predetermined goals.

[0169] Then continue to follow the optimization methods (iii) and (iv): increase the length of the front overhang and reduce the strength of the middle part of the longitudinal beam, so as to achieve the purpose of reducing the mid-term energy absorption and mid-term average acceleration, so that the longitudinal beam can be mainly bent and collapsed. At this time, a new round of CAE simulation shows that the rebound speed increases to V r =6m / s, A0 is reduced to 29g, and OLC=35.37g is calculated to meet the requirements. The crumple distance is increased to 275mm, and VPI is reduced to 64.8g. At this time, both indicators meet the vehicle goals at the same time.

[0170] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for optimizing automobile collision performance based on VPI and OLC, characterized by: The following steps are involved: Step 1: When the initial velocity of the vehicle and the occupants is V0, the vehicle collides with a rigid wall and generates an acceleration -A0 in the direction directly in front of the vehicle, that is, the average deceleration of the vehicle is A0. The VPI curve and the OLC curve are fitted to obtain the linear regression formula of VPI for OLC. Step 2: Under the premise of OLC unchanged, by optimizing the collision performance of the vehicle body structure and further optimizing it, the average deceleration A0 of the vehicle is reduced and the rebound speed V is relatively increased. r ; Step 3: Recalculate the average vehicle deceleration A0 and rebound velocity V of the body structure after collision performance optimization r , determine the vehicle's average deceleration A0 and rebound speed V r Whether the relationship between VPI and OLC is satisfied. If not, return to step 2 to further optimize the collision performance of the vehicle structure. If satisfied, the collision performance optimization of the vehicle structure is completed. The step 1 also includes: Step 1.1: Calculate the VPI curve. The calculation formula is: Among them, a max It is the peak chest acceleration of the occupants during the collision; w is the angular frequency, m is the mass of the occupant in the vehicle, k is the elastic coefficient of the restraint system; t0 is the time from the moment the vehicle hits the rigid wall to the moment the vehicle restraint system starts to work. δ is the free flight distance of the occupants in the vehicle before the vehicle restraint system acts; Step 1.2: Calculate the OLC curve using the following formula: OLC=a (18) Where a is the constant deceleration of the occupants in the vehicle during the collision; Step 1.3: Under certain vehicle initial velocity, rebound velocity and vehicle average deceleration, fit the VPI curve and OLC curve to obtain the relationship formula between VPI and OLC: y = Qx (28) Where y represents VPI, x represents OLC, Q represents the relationship coefficient between VPI and OLC, Q≈2, that is, VPI≈2*OLC; Under the premise that V0 and OLC remain unchanged, as the rebound speed V r increases, the relationship coefficient Q decreases monotonically, and the correlation coefficient R between VPI and OLC 2 It increases monotonically and approaches 1 infinitely.

2. The method for optimizing automobile collision performance based on VPI and OLC according to claim 1, characterized in that: The method for optimizing the collision performance of a vehicle body structure comprises: (i) Increase the support structure of the root of the vehicle longitudinal beam and the firewall, and use materials with high yield stress and low elastic modulus at the front of the root of the longitudinal beam to increase the rebound speed; (ii) Firewalls and inner and outer reinforcement beams of firewalls are made of high-strength and high-hardening materials with low yield strength ratio to improve rebound speed; (iii) Increase the crumple space of the front cabin of the vehicle, reduce the vehicle deceleration in the early stage, and prepare for the rebound in the later stage; (iv) Increase the length of the front overhang, increase the length and strength of the crash box, and reduce the strength of the middle part of the longitudinal beam so that the longitudinal beam can be mainly bent and collapsed as much as possible.

3. The method for optimizing automobile collision performance based on VPI and OLC according to claim 2, characterized in that: The method of increasing the crumple space of the front cabin of the vehicle in the method (iii) includes increasing the length of the front overhang, using a full subframe or using a cast aluminum subframe.

4. The method for optimizing automobile collision performance based on VPI and OLC according to claim 3, characterized in that: When the crumple space of the front cabin of the vehicle is increased by increasing the front overhang length in the method (iii), the method (iv) can be further adopted.

5. The method for optimizing automobile collision performance based on VPI and OLC according to claim 2, characterized in that: The priority levels of the methods (i)-(iv) described above are gradually reduced.

6. The method for optimizing automobile collision performance based on VPI and OLC according to claim 2 or 5, characterized in that: When further optimizing the collision performance of the vehicle structure, according to the priority level of the collision performance optimization methods (i)-(iv) of the vehicle body structure, optimization methods are gradually added from (i) to (iv), that is, when method (i) cannot meet the design requirements of the collision performance, return to step 2 and add method (ii) to further optimize the collision performance of the vehicle body structure; if the design requirements of the collision performance still cannot be met after adding method (ii), return to step 2 and add method (iii) to further optimize the collision performance of the vehicle body structure; if the design requirements of the collision performance still cannot be met after adding method (iii), return to step 2 and add method (iv) to further optimize the collision performance of the vehicle body structure.

7. The method for optimizing automobile collision performance based on VPI and OLC according to claim 1, characterized in that: In the step 2, when OLC≤35g, the collision performance of the vehicle body structure is optimized; when OLC>35g, the stiffness k of the restraint system of the vehicle is reduced and the collision performance of the vehicle body structure is optimized.

Images