A design method for the center of mass of a whole vehicle and the ground line

Abstract

The present invention discloses a design method for the vehicle center of mass and the ground line, belonging to the technical field of early-stage vehicle development, and comprising the following steps: establishing a vehicle coordinate system; establishing a parametric model; calculating relevant parameters according to the curb weight and the front axle load ratio, and finally calculating the positions of the center of mass in the X direction and the Z direction in the unloaded state respectively according to the front and rear wheel loads and the unloaded ground line obtained in S9; this design method completes the three-dimensional data of the vehicle center of mass and the ground line based on the knowledge engineering module of CATIA software. This design method is based on parametric design, uses the TOP-DOWN design concept, and can drive the operation of the entire model through the pre-set parameters, providing strong support for the early-stage vehicle development and design; this design method is developed based on CATIA software, can be used alone or in synchronization with other product components, saves the early-stage vehicle development time, shortens the vehicle development cycle, and helps to improve the vehicle development efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of pre - development of automobiles, and particularly relates to a design method for the center of mass of a whole vehicle and the ground line. Background Art

[0002] Currently, the calculation models for the center of mass of a traditional whole vehicle and the ground line are two separate models, and most of them are developed based on Excel in Microsoft Office software. Although they can calculate the positions of the center of mass and the ground line, they have the following deficiencies:

[0003] First, since the traditional whole - vehicle center - of - mass and ground - line models are independent of each other, they cannot cooperate during the calculation process, resulting in insufficient calculation accuracy.

[0004] Second, during the development of a whole vehicle, the center of mass and the ground line under multiple different loads are required. The adjustment process is cumbersome and the workload is large.

[0005] Third, every time the whole - vehicle load is adjusted, it cannot be reflected in CATIA, and the visualization degree is low, which cannot strongly support the whole - vehicle development work.

[0006] Therefore, a calculation model for the center of mass of a whole vehicle and the ground line, which is newly developed based on CATIA software, is needed to solve the above problems. Summary of the Invention

[0007] In order to overcome the above - mentioned defects existing in the prior art, the present invention provides a design method for the center of mass of a whole vehicle and the ground line. This model is based on CATIA software, uses the TOP - DOWN design and development concept and parametric design method, has a strong visualization degree, and the center of mass of the whole vehicle and the ground line can be synchronized and coordinated in real time, and is highly integrated into the whole process of vehicle design.

[0008] The present invention is realized through the following technical solutions:

[0009] A design method for the center of mass of a whole vehicle and the ground line includes the following steps:

[0010] Step S1: Establish a whole - vehicle coordinate system;

[0011] Step S2: Establish a parametric model;

[0012] Further, for the establishment of the parametric model, the specific parameters include the position of the center of mass of the whole vehicle when unloaded, the curb weight, the front - to - rear axle load ratio under the curb - weight state, the lengths of the front and rear axle loads, the number of seats and the corresponding R - points of the seats, the positions of the front and rear wheel centers and the luggage center of mass under the design load. Input the above parameters into CATIA software, and realize the establishment of the parametric model through the knowledge - engineering module.

[0013] Step S3: Calculate the front and rear axle loads under the curb - weight state according to the curb weight and the front - axle load ratio.

[0014] Further, the front axle load in the curb state = curb mass * corresponding front axle load ratio;

[0015] The rear axle load in the curb state = curb mass - front axle load in the curb state;

[0016] Step S4: According to the curb mass, the rear axle load mass in the curb state, and the seat loading form in the design load state, combined with the X-direction moment balance theory, the design load and the front and rear axle loads in the design load state, the full load and the front and rear axle loads in the full load state are obtained:

[0017] Further, the design load = curb mass + 75 * (design load of the number of people in the first row + design load of the number of people in the second row);

[0018] The rear axle load in the design load state = rear axle load in the curb state + [(75 * design load of the number of people in the first row * X-direction dimension of the R point of the first row member's seat from the front wheel center - 50 mm) + (75 * design load of the number of people in the second row * X-direction dimension of the R point of the second row member's seat from the front wheel center)] / wheelbase dimension;

[0019] The front axle load in the design load state = design load - rear axle load in the design load state.

[0020] Further, the full load = curb mass + 75 * (full load of the number of people in the first row + full load of the number of people in the second row + 1);

[0021] The rear axle load in the full load state = rear axle load in the curb state + {[75 * full load of the number of people in the first row * (X-direction dimension of the R point of the first row member's seat from the front wheel center - 50 mm)] + 75 * full load of the number of people in the second row * X-direction dimension of the R point of the second row member's seat from the front wheel center) + luggage centroid position} / wheelbase dimension;

[0022] The front axle load in the full load state = full load - rear axle load in the full load state.

[0023] Step S5: The natural frequencies n1 and n2 of the front and rear parts of the vehicle body can be expressed by the following formula:

[0024]

[0025] In the formula, c1 and c2 are the front and rear suspension stiffnesses (N / cm); m1 and m2 are the masses above the front and rear suspension springs (kg).

[0026] Step S6: According to the front and rear suspension stiffnesses, the Z-direction positions of the front and rear wheel centers in the full load and no-load states are obtained;

[0027] Further, the front wheel center in the no-load state = (front axle load in the curb weight state - front axle load in the design load state) * 9.8 mm / front suspension stiffness C1;

[0028] The front wheel center in the full-load state = (front axle load in the full-load state - front axle load in the design load state) * 9.8 mm / front suspension stiffness C1;

[0029] The rear wheel center in the no-load state = (rear axle load in the curb weight state - rear axle load in the design load state) * 9.8 mm / rear suspension stiffness C2;

[0030] The rear wheel center in the full-load state = (rear axle load in the full-load state - rear axle load in the design load state) * 9.8 mm / rear suspension stiffness C2;

[0031] Step S7: According to the European Tyre and Rim Technical Organization Standard Manual, calculate the static radius and stiffness of the tyre;

[0032] Further, according to the formula:

[0033] In the formula:

[0034] R S - Theoretical static radius

[0035] dr - Nominal diameter of the rim

[0036] d - Design outer diameter of the new tyre

[0037] F R - Coefficient, which is 0.78 (0.70 for CT tyres)

[0038] The static radius of the tyre = nominal radius of the rim + 0.78 * (design outer radius of the new tyre - nominal radius of the rim);

[0039] The stiffness of the tyre = tyre load * 1 mm / (free radius of the tyre - static radius of the tyre);

[0040] Step S8: Calculate the front and rear tyre radii under three load states of no-load, design load and full-load:

[0041] Further, the front tyre radius in the no-load state = static radius of the tyre + (tyre load - front axle load in the curb weight state / 2) / tyre stiffness * 1 mm;

[0042] The rear tyre radius in the no-load state = static radius of the tyre + (tyre load - rear axle load in the curb weight state / 2) / tyre stiffness * 1 mm;

[0043] The front tyre radius in the design load state = static radius of the tyre + (tyre load - front axle load in the design load state / 2) / tyre stiffness * 1 mm;

[0044] The radius of the rear wheel under the design load condition = the static radius of the tire + (the tire load - the rear axle load under the design load condition / 2) / the tire stiffness * 1 mm;

[0045] The radius of the front wheel under the full load condition = the static radius of the tire + (the tire load - the front axle load under the full load condition / 2) / the tire stiffness * 1 mm;

[0046] The radius of the rear wheel under the full load condition = the static radius of the tire + (the tire load - the rear axle load under the full load condition / 2) / the tire stiffness * 1 mm.

[0047] Step S9: On the Y0 plane, with the front and rear wheel centers obtained in step S6 as the centers, and with the front and rear wheel radii under the three load conditions obtained in step S8 as the radii, draw three arcs of the front and rear wheels respectively in the CATIA software. The tangents of the arcs are the ground lines;

[0048] Step S10: According to the front and rear wheel loads and the unloaded ground line obtained in S9, find the positions of the mass centers in the X direction and Z direction under the unloaded condition respectively:

[0049] Furthermore, the dimension of the mass center in the X direction from the front axle under the unloaded condition = the wheelbase dimension * the rear axle load under the curb weight condition / the curb weight;

[0050] After translating the unloaded ground line upward by 580 mm along the Z direction, it is the position of the mass center in the Z direction under the unloaded condition;

[0051] Step S11: According to the front and rear wheel loads and the moment balance formula, find the positions of the mass centers in the X direction and Z direction under the design load and full load conditions respectively;

[0052] Furthermore, step S11 is specifically as follows:

[0053] S111: The dimension of the mass center in the X direction from the front axle under the load condition = the wheelbase dimension * the rear axle load under the design load condition / the design load;

[0054] S112: According to the moment balance formula, after conversion, find the dimension of the mass center in the Z direction relative to the mass center under the unloaded condition under the design load condition:

[0055]

[0056] In the formula:

[0057] h: The height of the mass center from the ground;

[0058] gi: The mass of each assembly (or load);

[0059] hi: The height of each assembly (or load) from the ground;

[0060] The offset dimension of the center of mass in the Z direction relative to the center of mass in the unloaded state under the design load condition = (kerb weight * the distance from the center of mass in the unloaded state to the ground line under the design load in the Z direction + 75 * the design load of the number of people in the first row * (the distance from the R point of the people in the first row to the ground line under the design load in the Z direction + 260 mm) + 75 * the design load of the number of people in the second row * (the distance from the R point of the people in the second row to the ground line under the design load in the Z direction + 260 mm)) / the design load - the distance from the center of mass in the unloaded state to the ground line under the design load in the Z direction

[0061] 260 mm: The distance in the Z direction from the center of mass of a person to the R point of the person

[0062] S113: Calculate the dimension of the center of mass in the X direction from the front axle under the full load condition based on the front and rear wheel loads

[0063] The distance of the center of mass in the X direction from the front axle under the full load condition = wheelbase dimension * the rear axle load under the full load condition / full load mass

[0064] S114: Based on the moment balance formula, after conversion, calculate the offset dimension of the center of mass in the Z direction relative to the center of mass in the unloaded state under the full load condition

[0065] The offset dimension of the center of mass in the Z direction relative to the center of mass in the unloaded state under the full load condition = (kerb weight * the distance from the center of mass in the unloaded state to the ground line under the design load in the Z direction + 75 * the full load of the number of people in the first row * (the distance from the R point of the people in the first row to the ground line under the design load in the Z direction + 260 mm) + 75 * the full load of the number of people in the second row * (the distance from the R point of the people in the second row to the ground line under the design load in the Z direction + 260 mm) + 75 * the distance from the center of mass of the luggage to the ground line under the design load in the Z direction) / full load mass - the distance from the center of mass in the unloaded state to the ground line under the design load in the Z direction

[0066] 260 mm: The distance in the Z direction from the center of mass of a person to the R point of the person

[0067] Step S12: On the Y0 plane, draw the center of mass in CATIA using the design load and the center of mass position parameters under the full load condition calculated in step S10

[0068] Step S13: On the Y0 plane, measure the distance from each center of mass to the corresponding ground line in CATIA according to the design load and the center of mass position parameters under the full load condition calculated in step S10

[0069] Compared with the prior art, the advantages of the present invention are as follows

[0070] A design method for the vehicle center of mass and ground line based on the knowledge engineering module of CATIA software to complete the three-dimensional data of the vehicle center of mass and ground line. This design method is based on parametric design, applying the TOP-DOWN design concept, and the parameters set in the early stage can drive the operation of the entire model, providing strong support for the early-stage development and design of the vehicle. This design method is developed based on CATIA software, which can be used alone or in synchronization with other product components, saving the early-stage development time of the vehicle, shortening the vehicle development cycle, and helping to improve the vehicle development efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0072] Figure 1 Schematic diagram of the design positions of various parameters under the design load;

[0073] Figure 2 Schematic diagram of the front and rear wheel center positions in different states;

[0074] Figure 3 Schematic diagram of the ground line in different states;

[0075] Figure 4 Schematic diagram of the center of mass position in different states;

[0076] Figure 5 Schematic diagram of the center of mass height in different states. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0077] To clearly and completely describe the technical solutions of the present invention and their specific working processes, in combination with the accompanying drawings of the specification, the specific embodiments of the present invention are as follows:

[0078] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0079] Example 1

[0080] This example provides a design method for the vehicle center of mass and the ground line, including the following steps:

[0081] Step S1: Establish a vehicle coordinate system;

[0082] In the early stage of development, the various professional groups carry out collaborative design, and unified coordinate systems for data are required so that other relevant professional groups can call correct and reasonable data as boundaries when referring. For newly developed vehicle models, according to the wheel center 1000 in front, 1000 below, and the vehicle longitudinal symmetry plane as Y = 0 under the design load, set the vehicle coordinate system in the CATIA software. Since the current project has a large dependence on the reference vehicle, the initial coordinate system is mostly established on the principle of being consistent with the basic vehicle coordinate system.

[0083] Step S2: Establish a parametric model;

[0084] For the establishment of the parametric model, the specific parameters include the vehicle unloaded center of mass position, curb weight, front and rear axle load ratios under the curb weight state, front and rear axle load lengths, number of seats and the corresponding seat R points, design load front and rear wheel centers and luggage center of mass position. Input the above parameters into the CATIA software, and realize the establishment of the parametric model through the knowledge engineering module.

[0085] Step S3: Calculate the front and rear axle loads under the curb weight according to the curb weight and the front axle load ratio;

[0086] Curb weight in this example: 2700 kg;

[0087] Front axle load ratio: 0.52;

[0088] n1 - Front suspension natural frequency: 1 (empirical value range 0.8 - 1.15);

[0089] n1 - Front suspension natural frequency: 1.1 (empirical value range 0.98 - 1.3);

[0090] Number of people in the first row - Design load: 2 (the design load state of a 5 - seat vehicle is 2 people in the first row and 1 person in the second row);

[0091] Number of people in the second row - Design load: 1;

[0092] Number of people in the first row - Full load: 2 (the full load state of a 5 - seat vehicle is 2 people in the first row and 3 people in the second row);

[0093] Number of people in the second row - Full load: 3;

[0094] Full load front spring - under mass coefficient: 0.11 (independent suspension reference average value 0.11);

[0095] Unsprung mass coefficient after full load: 0.009 (reference mean value of independent suspension is 0.09);

[0096] Tire load: 825;

[0097] Dimension of tire free radius, according to tire selection, the dimension is 340 mm;

[0098] Nominal diameter of rim, according to tire selection, the dimension is 215.9 mm;

[0099] Height of center of mass - unloaded: 580 (determine the position of the vehicle's center of mass when unloaded according to the benchmark vehicle and development experience value);

[0100] The front axle load in the curb weight state = curb weight * corresponding front axle load ratio = 1404;

[0101] The rear axle load in the curb weight state = curb weight - front axle load in the curb weight state = 1296;

[0102] Step S4: According to the curb weight, the rear axle load mass in the curb weight state, and the seat load-bearing form in the design load state, combined with the X-direction moment balance theory, thus calculate the front and rear axle loads in the design load and design load state, the full load and the front and rear axle loads in the full load state:

[0103] The design load = curb weight + 75 * (design load of the number of people in the first row + design load of the number of people in the second row) = 2925;

[0104] The rear axle load in the design load state = rear axle load in the curb weight state + [(75 * design load of the number of people in the first row * X-direction dimension from the R point of the first row member's seat to the front wheel center - 50 mm) + (75 * design load of the number of people in the second row * X-direction dimension from the R point of the second row member's seat to the front wheel center)] / wheelbase dimension = 1428;

[0105] The front axle load in the design load state = design load - rear axle load in the design load state = 1497.

[0106] The full load = curb weight + 75 * (full load of the number of people in the first row + full load of the number of people in the second row + 1) = 3150;

[0107] The rear axle load in the full load state = rear axle load in the curb weight state + {[75 * full load of the number of people in the first row * (X-direction dimension from the R point of the first row member's seat to the front wheel center - 50 mm)] + 75 * full load of the number of people in the second row * X-direction dimension from the R point of the second row member's seat to the front wheel center) + luggage center of mass position} / wheelbase dimension = 1629;

[0108] The front axle load in the full load state = full load - rear axle load in the full load state = 1521.

[0109] Step S5: The natural frequencies n1 and n2 of the front and rear parts of the vehicle body can be expressed by the following formula:

[0110]

[0111] In the formula, c1 and c2 are the front and rear suspension stiffnesses (N / cm); m1 and m2 are the masses above the front and rear suspension springs (kg).

[0112] C1 - Front suspension stiffness = 39.4384 * n1 - Front suspension offset frequency * Front axle load - Full load * (Full load front spring mass coefficient (Independent suspension reference mean 0.11)) / 1000 = 53.38;

[0113] C2 - Front suspension stiffness = 39.4384 * n2 - Rear suspension offset frequency * Rear axle load - Full load * (1 - Full load rear spring mass coefficient (Independent suspension reference mean 0.09)) / 1000 = 70.75;

[0114] Step S6: Calculate the Z-direction positions of the front and rear wheel centers in the full-load and no-load states according to the front and rear suspension stiffnesses;

[0115] As Figure 2 shown, the front wheel center in the no-load state = (Axle load under curb weight - Axle load under design load state) * 9.8 mm / Front suspension stiffness C1 = -17.14;

[0116] The front wheel center in the full-load state = (Axle load under full load - Axle load under design load state) * 9.8 mm / Front suspension stiffness C1 = 4.29 mm;

[0117] The rear wheel center in the no-load state = (Axle load under curb weight - Axle load under design load state) * 9.8 mm / Rear suspension stiffness C2 = -18.24 mm;

[0118] The rear wheel center in the full-load state = (Axle load under full load - Axle load under design load state) * 9.8 mm / Rear suspension stiffness C2 = 27.93 mm;

[0119] Step S7: Calculate the static radius and stiffness of the tire according to the European Tyre and Rim Technical Organization Standard Manual;

[0120] Furthermore, according to the formula:

[0121] In the formula:

[0122] R S -Theoretical static radius

[0123] dr-Nominal diameter of the rim

[0124] d - Outer diameter of new tire design

[0125] F R - Coefficient, which is 0.78 (0.70 for CT tires)

[0126] The static radius of the tire = Rim nominal radius + 0.78 * (New tire design outer radius - Rim nominal radius) = 312.7 mm;

[0127] The tire stiffness = Tire load * 1 mm / (Tire free radius - Tire static radius) = 30.22;

[0128] Step S8: Calculate the front and rear tire radii under three load conditions of no load, design load, and full load:

[0129] The front tire radius under no load condition = Tire static radius + (Tire load - Front axle load under curb weight / 2) / Tire stiffness * 1 mm = 314.84 mm;

[0130] The rear tire radius under no load condition = Tire static radius + (Tire load - Rear axle load under curb weight / 2) / Tire stiffness * 1 mm = 315.22 mm;

[0131] The front tire radius under design load condition = Tire static radius + (Tire load - Front axle load under design load / 2) / Tire stiffness * 1 mm = 316.77 mm;

[0132] The rear tire radius under design load condition = Tire static radius + (Tire load - Rear axle load under design load / 2) / Tire stiffness * 1 mm = 318.56 mm;

[0133] The front tire radius under full load condition = Tire static radius + (Tire load - Front axle load under full load / 2) / Tire stiffness * 1 mm = 316.38 mm;

[0134] The rear tire radius under full load condition = Tire static radius + (Tire load - Rear axle load under full load / 2) / Tire stiffness * 1 mm = 313.04 mm.

[0135] As Figure 3 shown, Step S9: On the Y0 plane, with the front and rear wheel centers obtained in Step S6 as the centers, and with the front and rear wheel radii under the three load conditions obtained in Step S8 as the radii, draw three arcs of the front and rear wheels respectively in the CATIA software, and the tangents of the arcs are the ground lines;

[0136] Step S10: According to the front and rear wheel loads and the no-load ground line obtained in S9, calculate the positions of the center of mass in the X direction and Z direction under no-load condition respectively:

[0137] The dimension of the centroid distance from the front axle in the X direction under the no-load state = wheelbase dimension * rear axle load under the curb weight state / curb weight = 1648.8 mm;

[0138] After translating the no-load ground line upward by 580 mm along the Z direction, it is the position of the no-load centroid in the Z direction;

[0139] Step S11: According to the front and rear wheel loads and the moment balance formula, respectively calculate the positions of the centroid in the X direction and Z direction under the design load and full-load state;

[0140] Step S11 is specifically as follows:

[0141] S111: The dimension of the centroid distance from the front axle in the X direction under the load state = wheelbase dimension * rear axle load under the design load state / design load = 1676.59 mm;

[0142] S112: According to the moment balance formula, after conversion, calculate the dimension of the centroid in the Z direction relative to the no-load state centroid under the design load state:

[0143]

[0144] In the formula:

[0145] h: The height of the centroid from the ground;

[0146] gi: The mass of each assembly (or load);

[0147] hi: The height of each assembly (or load) from the ground;

[0148] The offset dimension of the centroid in the Z direction relative to the no-load state centroid under the design load state = (curb weight * the distance of the no-load centroid to the design load ground line in the Z direction + 75 * the design load of the number of people in the first row * (the distance of the R point of the people in the first row to the design load ground line in the Z direction + 260 mm) + 75 * the design load of the number of people in the second row * (the distance of the R point of the people in the second row to the design load ground line in the Z direction + 260 mm)) / design load - the distance of the no-load centroid to the design load ground line in the Z direction = 18.93 mm;

[0149] 260 mm: The distance of the human centroid to the R point of the human in the Z direction;

[0150] S113: According to the front and rear wheel loads, calculate the dimension of the centroid distance from the front axle in the X direction under the full-load state:

[0151] The distance of the full-load centroid from the front axle in the X direction = wheelbase dimension * rear axle load under the full-load state / full-load mass = 1776.71 mm;

[0152] S114: According to the moment balance formula, after conversion, the offset dimension of the centroid in the Z direction in the full-load state relative to the centroid in the no-load state is obtained as 30.38 mm:

[0153] The offset dimension of the centroid in the Z direction in the full-load state relative to the centroid in the no-load state = (kerb weight * the distance from the no-load centroid to the design load ground line in the Z direction + 75 * the full-load load of the number of people in the first row * (the distance from the R point of the people in the first row to the design load ground line in the Z direction + 260 mm) + 75 * the full-load load of the number of people in the second row * (the distance from the R point of the people in the second row to the design load ground line in the Z direction + 260 mm) + 75 * the distance from the luggage centroid to the design load ground line in the Z direction) / full-load mass - the distance from the no-load centroid to the design load ground line in the Z direction;

[0154] 260 mm: The distance in the Z direction from the centroid of the person to the R point of the person.

[0155] As Figure 4 shown, step S12: On the Y0 plane, using the design load and the centroid position parameters in the full-load state calculated in step S10, draw the centroid in CATIA;

[0156] As Figure 5 shown, step S13: On the Y0 plane, according to the design load and the centroid position parameters in the full-load state calculated in step S10, measure the distance from each centroid to the corresponding ground line in CATIA.

[0157] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0158] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0159] Furthermore, any combination can be made between different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A design method for the center of mass of a whole vehicle and the ground line, characterized in that, it includes the following steps: Step S1: Establish a whole vehicle coordinate system; Step S2: Establish a parametric model; Step S3: Calculate the front and rear axle loads under the curb weight condition according to the curb weight and the front axle load ratio; Step S4: According to the curb weight, the rear axle load mass under the curb weight condition, and the seat load-bearing form under the design load condition, combined with the X-direction moment balance theory, calculate the design load, the front and rear axle loads under the design load condition, the full load, and the front and rear axle loads under the full load condition; Step S6: Calculate the Z-direction positions of the front and rear wheel centers under the full load and no-load conditions according to the front and rear suspension stiffnesses; Step S7: Calculate the static radius and stiffness of the tire according to the European Tyre and Rim Technical Organization Standard Manual; Step S8: Calculate the front and rear tire radii under the no-load, design load, and full load conditions; Step S9: On the Y0 plane, with the front and rear wheel centers obtained in Step S6 as the centers and the front and rear wheel radii under the three load conditions obtained in Step S8 as the radii, draw three arcs of the front and rear wheels in the CATIA software respectively, and the tangents of the arcs are the ground lines; Step S10: Calculate the positions of the center of mass in the X direction and Z direction under the no-load condition according to the front and rear wheel loads and the no-load ground line obtained in S9; Step S11: Calculate the positions of the center of mass in the X direction and Z direction under the design load and full load conditions according to the front and rear wheel loads and the moment balance formula respectively; Step S12: On the Y0 plane, draw the center of mass in CATIA with the center of mass position parameters under the design load and full load conditions calculated in Step S10; Step S13: On the Y0 plane, measure the distances from each center of mass to the corresponding ground line in CATIA according to the center of mass position parameters under the design load and full load conditions calculated in Step S10; The dimension of the center of mass from the front axle in the X direction under the no-load condition = wheelbase dimension * rear axle load under the curb weight condition / curb weight; After translating the no-load ground line 580 mm upward along the Z direction, it is the Z-direction position of the no-load center of mass; Step S11 is specifically as follows: S111: The dimension of the center of mass from the front axle in the X direction under the load condition = wheelbase dimension * rear axle load under the design load condition / design load; S112: According to the moment balance formula, after conversion, calculate the dimension of the center of mass in the Z direction relative to the no-load center of mass under the design load condition: Where: h: The height of the center of mass from the ground; gi: The mass of each assembly or load; hi: The height of each assembly or load from the ground; The offset dimension of the center of mass in the Z direction under the design load condition relative to the no-load center of mass = (curb weight * the Z-direction distance from the no-load center of mass to the design load ground line + 75 * the design load of the number of people in the first row * (the Z-direction distance from the R point of the people in the first row to the design load ground line + 260 mm) + 75 * the design load of the number of people in the second row * (the Z-direction distance from the R point of the people in the second row to the design load ground line + 260 mm)) / design load - the Z-direction distance from the no-load center of mass to the design load ground line 260 mm: The Z-direction distance from the center of mass of a person to the R point of the person S113: Calculate the dimension of the center of mass from the front axle in the X direction under the full-load condition based on the front and rear wheel loads: Distance of the center of mass from the front axle in the X direction under full load = Wheelbase dimension * Rear axle load under full-load condition / Full-load mass; S114: Based on the moment balance formula, calculate the offset dimension of the center of mass in the Z direction under the full-load condition relative to that under the no-load condition after conversion: Offset dimension of the center of mass in the Z direction under the full-load condition relative to that under the no-load condition = (Kerb mass * Distance of the center of mass under no load from the design load ground line in the Z direction + 75 * Full-load load of the first row of passengers * (Distance of the R point of the first row of passengers from the design load ground line in the Z direction + 260 mm) + 75 * Full-load load of the second row of passengers * (Distance of the R point of the second row of passengers from the design load ground line in the Z direction + 260 mm) + 75 * Distance of the center of mass of luggage from the design load ground line in the Z direction) / Full-load mass - Distance of the center of mass under no load from the design load ground line in the Z direction; 260 mm: Distance of the center of mass of a person from the R point of the person in the Z direction.

2. A design method for the center of mass of a whole vehicle and the ground line as claimed in claim 1, wherein, for the establishment of the parametric model, the specific parameters include the position of the center of mass of the whole vehicle under no load, the kerb mass, the front and rear axle load ratios under the kerb mass condition, the lengths of the front and rear axles, the number of seats and the corresponding R points of the seats, the positions of the front and rear wheel centers under the design load and the center of mass of the luggage. Input the above parameters into the CATIA software, and realize the establishment of the parametric model through the knowledge engineering module.

3. A design method for the center of mass of a whole vehicle and the ground line as claimed in claim 1, wherein, Front axle load under the kerb condition = Kerb mass * Corresponding front axle load ratio; Rear axle load under the kerb condition = Kerb mass - Front axle load under the kerb condition.

4. A design method for the center of mass of a whole vehicle and the ground line as claimed in claim 1, wherein, Design load = Kerb mass + 75 * (Design load of the first row of passengers + Design load of the second row of passengers); Rear axle load under the design load condition = Rear axle load under the kerb condition + [(75 * Design load of the first row of passengers * (Distance of the R point of the first row of members' seats from the front wheel center in the X direction - 50 mm) + (75 * Design load of the second row of passengers * (Distance of the R point of the second row of members' seats from the front wheel center in the X direction))] / Wheelbase dimension; Front axle load under the design load condition = Design load - Rear axle load under the design load condition.

5. A design method for the center of mass of a whole vehicle and the ground line as claimed in claim 1, wherein, Full-load load = Kerb mass + 75 * (Full-load load of the first row of passengers + Full-load load of the second row of passengers + 1); Rear axle load under the full-load condition = Rear axle load under the kerb condition + {[75 * Full-load load of the first row of passengers * (Distance of the R point of the first row of members' seats from the front wheel center in the X direction - 50 mm)] + 75 * Full-load load of the second row of passengers * (Distance of the R point of the second row of members' seats from the front wheel center in the X direction) + Position of the center of mass of luggage} / Wheelbase dimension; Front axle load under the full-load condition = Full-load load - Rear axle load under the full-load condition.

6. A design method for the center of mass of a whole vehicle and the ground line as claimed in claim 1, wherein, The front wheel center under the no-load state = (front axle load under the curb weight state - front axle load under the design load state) * 9.8 mm / front suspension stiffness C1; The front wheel center under the full-load state = (front axle load under the full-load state - front axle load under the design load state) * 9.8 mm / front suspension stiffness C1; The rear wheel center under the no-load state = (rear axle load under the curb weight state - rear axle load under the design load state) * 9.8 mm / rear suspension stiffness C2; The rear wheel center under the full-load state = (rear axle load under the full-load state - rear axle load under the design load state) * 9.8 mm / rear suspension stiffness C2.

7. A design method for the center of mass and ground line of a whole vehicle according to claim 1, characterized in that, According to the formula: In the formula: R S - Theoretical static radius dr - nominal diameter of the rim d - designed outer diameter of the new tire F R - Coefficient, which is 0.78 The static radius of the tire = nominal radius of the rim + 0.78 * (designed outer radius of the new tire - nominal radius of the rim); The stiffness of the tire = tire load * 1 mm / (free radius of the tire - static radius of the tire).

8. A design method for the center of mass and ground line of a whole vehicle according to claim 1, characterized in that, The front wheel radius under the no-load state = static radius of the tire + (tire load - front axle load under the curb weight state / 2) / tire stiffness * 1 mm; The rear wheel radius under the no-load state = static radius of the tire + (tire load - rear axle load under the curb weight state / 2) / tire stiffness * 1 mm; The front wheel radius under the design load state = static radius of the tire + (tire load - front axle load under the design load state / 2) / tire stiffness * 1 mm; The rear wheel radius under the design load state = static radius of the tire + (tire load - rear axle load under the design load state / 2) / tire stiffness * 1 mm; The front wheel radius under the full-load state = static radius of the tire + (tire load - front axle load under the full-load state / 2) / tire stiffness * 1 mm; The rear wheel radius under the full-load state = static radius of the tire + (tire load - rear axle load under the full-load state / 2) / tire stiffness * 1 mm.

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