Suspension system design method

Abstract

The invention belongs to the technical field of suspension vibration reduction, and particularly relates to a suspension system design method which comprises the following steps: determining the load gravity center of a whole vehicle according to the overall arrangement requirement, preliminarily arranging an action system, and respectively arranging a wheel train and a suspension guide mechanism. In the aspect of wheel train arrangement, according to the principle that the load gravity center and the elastic center coincide as much as possible, the wheel train position is preliminarily arranged, random road excitation is generated, an equivalent linear dynamics model of a vehicle is established, and dynamics matching calculation is carried out. In the aspect of suspension guide mechanism arrangement, a hydro-pneumatic suspension mathematical model is generated, the determined suspension damping ratio is input into the hydro-pneumatic suspension mathematical model to guide damping valve design and generate nonlinear damping characteristics, and meanwhile, the calculated axle loads are input into the hydro-pneumatic suspension mathematical model to generate nonlinear damping characteristics. The method is used for generating and calculating non-linear elastic characteristics and comprehensively evaluating whether vehicle body vibration response characteristics, suspension heat balance temperature rise characteristic curves and key and heavy part reliability analysis results meet design index requirements or not.

Description

Technical Field

[0001] The invention belongs to the technical field of suspension vibration reduction, and in particular relates to a suspension system design method. Background Art

[0002] The suspension system is usually composed of elastic elements, damping elements and guide mechanisms. Its function is to bear the weight of the vehicle body and the power transmission system; to transmit, bear and alleviate the various reaction forces and torques acting on the moving mechanism by the road surface; to reduce the impact and vibration of the vehicle body caused by uneven road excitation; and to provide a relatively stable support platform for the upper system while ensuring the off-road maneuverability of the vehicle.

[0003] With the continuous development of technology, suspension technology has changed from traditional linear characteristics to strong nonlinear characteristics, which can double the elastic buffer force and dynamic potential at the end of the stroke. Tests have shown that the average off-road speed of the vehicle can be increased by at least 30%. For the representative of nonlinear suspension - oil-gas suspension, the off-road maneuverability of the equipment can be significantly improved even in a passive state, which has become an important development direction.

[0004] However, due to many technical difficulties such as vibration energy dissipation, large-load-bearing-force guidance, hydraulic locking leakage, transient impact locking, etc., the promotion and application in military and civilian fields are limited. At the same time, there is a lack of corresponding design and test specifications and standards, and there is an urgent need to carry out relevant research work. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] The technical problem to be solved by the present invention is: how to provide a suspension system design method.

[0007] (II) Technical solution

[0008] In order to solve the above technical problems, the present invention provides a suspension system design method, which comprises the following steps:

[0009] Step 1: First, determine the load center of gravity of the vehicle according to the overall layout requirements, make a preliminary layout of the motion system, and carry out the layout of the wheel system and the suspension guide mechanism respectively;

[0010] Step 2: In terms of the gear train arrangement, preliminarily arrange the position of the gear train according to the principle that the load center of gravity and the elastic center coincide as much as possible. Grouped by front and rear, the off-road vehicle is configured with a front and rear wheel load distribution ratio of 6:4. First, generate a random road surface excitation, establish an equivalent linear dynamic model of the vehicle, use the road surface model as the input of the equivalent linear dynamic model, conduct suspension characteristic check and analysis, input the suspension equilibrium position stiffness and damping characteristic parameters into the calculation program in the form of arrays respectively, conduct array combination to carry out dynamic matching calculation, input the expected maximum driving speed, monitor the key vibration response conditions including the sprung mass, unsprung mass, suspension relative travel, and vehicle body stability, calculate the time-domain and frequency-domain response data respectively, and use the root mean square value and the maximum vibration response data as the basis for evaluation to judge whether the vibration threshold is met;

[0011] It is set that the root mean square value of the sprung mass acceleration vibration response is less than 0.3g, the maximum impact acceleration vibration response is less than 3.5g, the suspension vibration response travel is not greater than the full suspension travel, and the dynamic load of the unsprung mass is less than the unsprung mass itself;

[0012] Then, establish a thermodynamics model of the suspension system. At the same time, input the maximum driving speed and the road surface model into the thermodynamics model to realize the joint operation of the vehicle equivalent linear dynamic model and the thermal model. Take the thermal equilibrium temperature T < T0 = 150°C as the evaluation threshold. Through the comprehensive evaluation of the vehicle vibration threshold and the suspension thermal equilibrium temperature threshold, after the model is repeatedly iterated and calculated to meet the threshold requirements, the suspension damping ratio can be preliminarily determined.

[0013] Step 3: In terms of the suspension guiding mechanism arrangement, preliminarily determine the pull arm length, balance elbow length, distance from the balance elbow axis center to the oil cylinder center line, pull arm installation angle, and connecting rod length according to the action system layout, generate a suspension leverage ratio calculation model, and finally generate a mathematical model of the oil-gas suspension. Input the determined suspension damping ratio into the mathematical model of the oil-gas suspension to guide the damping valve design and generate non-linear damping characteristics. At the same time, input the calculated axle loads of each wheel into the mathematical model of the oil-gas suspension to carry out the generation calculation of non-linear elastic characteristics. Finally, input the calculated non-linear elastic characteristics and damping characteristic curves into the suspension thermal model to complete the calculation of the thermal equilibrium temperature rise characteristic curve.

[0014] Step 4: Input the nonlinear elastic characteristics and damping characteristics, as well as the generated road surface model, into the nonlinear dynamic model of the whole vehicle to perform vibration response verification calculations. The obtained vibration response results are used as the loads of key components of the motion system. Comprehensively evaluate whether the vehicle body vibration response characteristics, suspension thermal balance temperature rise characteristic curve, suspension relative travel and key component reliability analysis results meet the design index requirements. If they do, the suspension matching optimization process ends. If they do not meet the requirements, the program returns to the first step of the motion system layout and re-carries out iterative optimization calculations until the index requirements are met and the best solution is matched.

[0015] In addition, the present invention also provides a suspension system design method, characterized in that the method clarifies the load center of gravity of the entire vehicle according to the overall layout requirements, performs a preliminary layout of the motion system, and separately carries out the wheel system layout and the suspension guide mechanism layout.

[0016] In terms of wheel arrangement, the method preliminarily arranges the wheel position according to the principle that the load center of gravity and the elastic center are as close as possible, generates random road excitation, establishes an equivalent linear dynamic model of the vehicle, and performs dynamic matching calculation;

[0017] In terms of suspension guide mechanism arrangement, the method generates a mathematical model of an oil-gas suspension, inputs a determined suspension damping ratio into the mathematical model of the oil-gas suspension to guide the design of a damping valve and generate nonlinear damping characteristics, and simultaneously inputs the calculated axle loads of each wheel into the mathematical model of the oil-gas suspension to perform generation calculations of nonlinear elastic characteristics, and comprehensively evaluates whether the vehicle body vibration response characteristics, the suspension thermal balance temperature rise characteristic curve, and the reliability analysis results of key components meet the design index requirements.

[0018] (III) Beneficial effects

[0019] In view of the situation of the existing technology, the present invention proposes a suspension system design method, which can significantly improve the product design accuracy from clear demand input to theoretical modeling, parameter optimization, guide mechanism design, reliability strength analysis, etc., realize the transformation from empirical design to predictive design, and effectively shorten the new product design cycle and reduce R&D costs.

[0020] Compared with the prior art, the present invention aims at the situation that there is no corresponding standard for oil-gas suspension design. The present invention proposes a complete suspension system design method and process. It proposes to first simulate the smoothness and handling stability of driving under different road conditions and vehicle speeds in the frequency domain through an equivalent linear vehicle dynamics model, respectively monitor the root mean square value of the vehicle body vibration acceleration, pitch angular velocity and relative travel of each wheel suspension, analyze the vibration response under different road conditions and vehicle speeds with the change of stiffness and relative damping coefficient, compile an autonomous optimization algorithm to finally determine the ideal elastic and damping characteristics of each wheel, and input it into the oil-gas suspension dynamics model as the design basis of structural parameters. Combined with the structural characteristics of key elements such as shock absorbing valves, guide mechanisms and energy storage devices, the nonlinear elastic characteristics and damping characteristics with valve opening function are simulated and calculated to obtain accurate external characteristic curves. Further, the determined characteristic data is input into the nonlinear dynamics model of the whole vehicle, and the time domain nonlinear vibration response analysis is carried out to output the load of key components, which can be used as the basis for reliability analysis. At the same time, the influence of nonlinear and asymmetric characteristics on the vibration of the whole vehicle is systematically studied, and the ideal state is achieved through repeated iterations. During the simulation process, it was proposed for the first time to conduct joint calculations with the thermodynamic model, using the thermal equilibrium temperature as the threshold to avoid the problem of overheating and failure of the suspension system.

[0021] A more comprehensive evaluation method is proposed for the optimization and matching of suspension characteristics. Since special vehicles have a longer body, are in a multi-wheel coupling state, and have a bad road surface, they are significantly different from ordinary vehicles. In actual use, the pitch angle vibration and the vertical vibration response of the vehicle body have a greater impact on the feelings of the driver and passengers. The interaction force between the wheels and the ground determines the safety of the vehicle during high-speed driving. It is necessary to avoid the problem of insufficient ground adhesion due to the suspension jump stroke not being reset in time. The relative travel index of the suspension is used as a threshold to determine whether the vehicle will have rigid breakdown under extreme impact conditions, resulting in a decrease in maneuverability. In addition, the thermal balance temperature threshold of the suspension body is introduced in the process of optimizing and matching characteristics to avoid excessive damping that causes overheating and failure of the suspension system. Taking into account the above influencing factors, a comprehensive evaluation method is formulated according to the characteristics of special vehicles and driving conditions, which provides strong support for improving the comprehensive driving performance of vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Design process for oil-gas suspension system solution;

[0023] Figure 2 Calculation process for characteristics of oil-gas suspension system;

[0024] Figure 3 Optimize the matching process for nonlinear suspension system parameters;

[0025] Figure 4is the acceleration response of the vehicle body center of mass vibration at different natural frequencies;

[0026] Figure 5 is the acceleration response of the center of mass vibration of the vehicle body with different damping ratios;

[0027] Figure 6 The vibration acceleration response of sprung mass for different stiffness control methods;

[0028] Figure 7 Suspension relative travel for different stiffness control methods;

[0029] Figure 8 The acceleration response of unsprung mass vibration for different stiffness control methods;

[0030] Fig. 9 It is a single wheel suspension dynamics model;

[0031] Fig.10 is the amplitude-frequency characteristic of the sprung mass displacement excitation on the road surface;

[0032] Fig.11 is the amplitude-frequency characteristic of the unsprung mass displacement on the road surface excitation;

[0033] Fig.12 The amplitude-frequency characteristic of the road surface excitation caused by the relative travel of the suspension;

[0034] Fig.13 The frequency domain characteristics of sprung acceleration are compared;

[0035] Fig.14 Comparison of sprung acceleration time domain characteristics. DETAILED DESCRIPTION

[0036] In order to make the purpose, content, and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings and examples.

[0037] In order to solve the above technical problems, the present invention provides a suspension system design method, which comprises the following steps:

[0038] Step 1: First, determine the load center of gravity of the vehicle according to the overall layout requirements, make a preliminary layout of the motion system, and carry out the layout of the wheel system and the suspension guide mechanism respectively;

[0039] Step 2: In terms of the gear train arrangement, preliminarily arrange the position of the gear train according to the principle that the load center of gravity and the elastic center should coincide as much as possible. Grouped by front and rear, the off-road vehicle is configured according to the front and rear wheel load distribution ratio of 6:4. First, generate a random road surface excitation, establish an equivalent linear dynamic model of the vehicle, use the road surface model as the input of the equivalent linear dynamic model, carry out the suspension characteristic check and analysis, input the suspension equilibrium position stiffness and damping characteristic parameters into the calculation program in the form of arrays respectively, carry out the dynamic matching calculation in an array combination, input the expected maximum driving speed, monitor the key vibration response conditions including the sprung mass, unsprung mass, relative suspension travel, and vehicle body stability, calculate the time-domain and frequency-domain response data respectively, and use the root mean square value and the maximum vibration response data as the basis for evaluation to judge whether the vibration threshold is met;

[0040] It is specified that the root mean square value of the sprung mass acceleration vibration response is less than 0.3g, the maximum impact acceleration vibration response is less than 3.5g, the suspension vibration response travel does not exceed the full suspension travel, and the dynamic load of the unsprung mass is less than the unsprung mass itself;

[0041] Then, establish a thermodynamics model of the suspension system. At the same time, input the maximum driving speed and the road surface model into the thermodynamics model to realize the joint operation of the vehicle equivalent linear dynamic model and the thermal model. Take the thermal equilibrium temperature T < T0 = 150°C as the evaluation threshold. Through the comprehensive evaluation of the vehicle vibration threshold and the suspension thermal equilibrium temperature threshold, after the model is repeatedly iterated and calculated to meet the threshold requirements, the suspension damping ratio can be preliminarily determined.

[0042] Step 3: In terms of the suspension guiding mechanism arrangement, preliminarily determine the pull arm length, balance elbow length, distance from the balance elbow axis center to the oil cylinder center line, pull arm installation angle, and connecting rod length according to the layout of the running gear system, and generate a suspension leverage ratio calculation model. Finally, generate a mathematical model of the oil-gas suspension. Input the above-determined suspension damping ratio into the mathematical model of the oil-gas suspension to guide the damping valve design and generate the nonlinear damping characteristics. At the same time, input the calculated axle loads of each wheel into the mathematical model of the oil-gas suspension to carry out the generation calculation of the nonlinear elastic characteristics. Finally, input the calculated nonlinear elastic characteristics and damping characteristic curves into the suspension thermal model to complete the calculation of the thermal equilibrium temperature rise characteristic curve.

[0043] Step 4: Input the nonlinear elastic characteristics and damping characteristics, as well as the generated road surface model, into the nonlinear dynamic model of the whole vehicle to perform vibration response verification calculations. The obtained vibration response results are used as the loads of key components of the motion system. Comprehensively evaluate whether the vehicle body vibration response characteristics, suspension thermal balance temperature rise characteristic curve, suspension relative travel and key component reliability analysis results meet the design index requirements. If they do, the suspension matching optimization process ends. If they do not meet the requirements, the program returns to the first step of the motion system layout and re-carries out iterative optimization calculations until the index requirements are met and the best solution is matched.

[0044] In addition, the present invention also provides a suspension system design method, characterized in that the method clarifies the load center of gravity of the entire vehicle according to the overall layout requirements, performs a preliminary layout of the motion system, and separately carries out the wheel system layout and the suspension guide mechanism layout.

[0045] In terms of wheel arrangement, the method preliminarily arranges the wheel position according to the principle that the load center of gravity and the elastic center are as close as possible, generates random road excitation, establishes an equivalent linear dynamic model of the vehicle, and performs dynamic matching calculation;

[0046] In terms of suspension guide mechanism arrangement, the method generates a mathematical model of an oil-gas suspension, inputs a determined suspension damping ratio into the mathematical model of the oil-gas suspension to guide the design of a damping valve and generate nonlinear damping characteristics, and simultaneously inputs the calculated axle loads of each wheel into the mathematical model of the oil-gas suspension to perform generation calculations of nonlinear elastic characteristics, and comprehensively evaluates whether the vehicle body vibration response characteristics, the suspension thermal balance temperature rise characteristic curve, and the reliability analysis results of key components meet the design index requirements.

[0047] Example 1

[0048] In this embodiment, the suspension system not only needs to be designed with a highly compact integrated structure, but also needs to carry out special dynamic modeling research to clarify the influence of parameters such as wheel rubber deformation, positioning parameters and hard point coordinates of various structural parts, and cylinder layout on the smooth transmission of suspension force, so as to avoid the problem of excessive lateral force and eccentric wear of the piston and hinge point, so as to achieve smooth and efficient transmission of ground impact excitation.

[0049] On the basis of effectively solving the stress problem of suspension system structural parts, it is also necessary to sort out the complete suspension system design process and method, and formulate a systematic evaluation index system, so as to ensure the reliability and stability of the actuator while achieving efficient isolation of ground impact excitation. This requires the reasonable matching of elasticity and damping characteristics to effectively suppress the vibration energy from the outside world. The function of the elastic element is mainly as an energy storage device, usually through the deformation of the spring or accumulator to achieve the purpose of absorbing part of the vibration energy and realize the buffering function, but it cannot dissipate the energy and needs to be released in the next vibration cycle. The damping element throttles the oil at high speed through the damping valve system, which can convert the vibration energy into heat energy for dissipation. The elasticity and damping characteristics of the passive suspension have been determined at the beginning of the design. Usually, a compromise design is made based on various working conditions, striving to meet the use requirements under different driving conditions. However, once the characteristic parameters are determined at the beginning of the design, they cannot be adjusted, and it is impossible to achieve the best use state on various road surfaces. Therefore, on the basis of formulating the suspension system design methods and processes, it is necessary to further carry out the optimization matching and coordinated control research of the suspension characteristics, which is also the key to fully realizing the buffering and vibration isolation performance. It is also necessary to clarify the best matching scheme of suspension elasticity and damping characteristics under different road conditions and vehicle speed conditions, so as to achieve the purpose of significantly reducing the vehicle vibration response.

[0050] Suspension system optimization matching flow chart as follows Figure 1As shown in the figure, first, the overall vehicle load center of gravity is determined according to the overall layout requirements, the action system is preliminarily laid out, and the wheel system layout and the suspension guiding mechanism layout are carried out separately. In terms of the wheel system layout, the position of the wheel system is preliminarily arranged according to the principle that the load center of gravity and the elastic center should coincide as much as possible. Usually, it is grouped by front and rear. Off-road vehicles are configured according to the front and rear wheel load distribution ratio of 6:4 to ensure the front wheel grounding ability during high-speed off-road. To facilitate setting characteristic parameters, first, a random road surface excitation is generated, and an equivalent linear dynamic model of the vehicle is established. The road surface model is used as the input of the equivalent linear dynamic model to carry out suspension characteristic checking and analysis. The suspension equilibrium position stiffness and damping characteristic parameters are input into the calculation program in the form of arrays respectively, and an array combination is carried out to carry out dynamic matching calculation. The expected maximum driving speed is input, and the key vibration response conditions such as the sprung mass, unsprung mass, relative suspension travel, and vehicle body stability are monitored. The time-domain and frequency-domain response data are calculated respectively, and the root mean square value and the maximum vibration response data are used as the basis for evaluation to judge whether the vibration threshold is met. According to experience, the root mean square value of the sprung mass acceleration vibration response should be less than 0.3g, the maximum impact acceleration vibration response should be less than 3.5g, the suspension vibration response travel should not be greater than the full suspension travel to avoid hitting the limiter, and the dynamic load of the unsprung mass should be less than the unsprung mass itself to avoid the driving safety problem of the wheel leaving the ground. A thermodynamics model of the suspension system is established, and at the same time, the maximum driving speed and the road surface model are input into the thermodynamics model to realize the joint operation of the vehicle equivalent linear dynamic model and the thermal model. The thermal equilibrium temperature T < T0 = 150°C is used as the evaluation threshold to carry out the optimization and matching of the stiffness and damping parameters to ensure that the suspension temperature will not be too high and cause seal failure when the vehicle is driving at high speed on a complex road surface. Taking the suspension thermal equilibrium threshold as the threshold for the optimization and matching of characteristic parameters is proposed for the first time and has played an important guiding role in the project development process. Through the comprehensive evaluation of the vehicle vibration threshold and the suspension thermal equilibrium temperature threshold, after the model is repeatedly iterated and calculated to meet the threshold requirements, the suspension damping ratio can be preliminarily determined.

[0051] In terms of the suspension guiding mechanism layout, the 1. pull arm length, 2. balance elbow length, 3. distance from the balance elbow axis to the cylinder center line, 4. pull arm installation angle, and 5. connecting rod length are preliminarily determined according to the layout of the action system, and a suspension leverage ratio calculation module is generated, and finally a mathematical model of the hydro-pneumatic suspension is generated. The determined suspension damping ratio is input into the hydro-pneumatic suspension mathematical model to guide the design of the damping valve and generate a non-linear damping characteristic. At the same time, the calculated wheel axle loads of each wheel are input into the hydro-pneumatic suspension mathematical model to carry out the generation calculation of the non-linear elastic characteristic. The calculated non-linear elastic characteristic and damping characteristic curves are input into the suspension thermal model to complete the calculation of the thermal equilibrium temperature rise characteristic curve.

[0052] The nonlinear elastic characteristics and damping characteristics, as well as the generated road surface model, are input into the nonlinear dynamic model of the whole vehicle for further vibration response verification calculation. The obtained vibration response results can be used as the load of key components of the action system, for reliability analysis of key parts, and to guide the engineering design of the actuator. Comprehensively evaluate whether the vehicle body vibration response characteristics, suspension thermal balance temperature rise characteristic curve, suspension relative travel and key parts reliability analysis results meet the design index requirements. According to experience, the suspension thermal balance temperature is set to 150°C, which can meet the vibration reduction requirements of various complex roads. If the design index requirements are met, the suspension matching optimization process ends. If the requirements are not met, the program returns to the first step of the action system layout and re-carries out iterative optimization calculations until the index requirements are met and the best solution is matched.

[0053] To further optimize the suspension system structure and design an integrated solution, we first need to conduct a qualitative analysis of the main components of the suspension. Starting from the overall layout of the vehicle, we can determine that the main design elements of the suspension system include the balance elbow, rocker arm, connecting rod, oil and gas spring and other components. Then, combined with the suspension system design theory, we will conduct an engineering design, considering the rigid constraint connection between the balance elbow and the vehicle body of the integrated suspension system and the setting of the slewing pair. The design process is as follows: Figure 2 shown.

[0054] According to the overall layout requirements and the load distribution of each wheel position, the requirements of the dynamic and static travel, static balance position, etc. of the suspension vibration isolation system are first refined, and the vertical stiffness of the static balance position of the nonlinear suspension is checked and calculated by load and static travel, and the natural frequency is set between 1-1.3Hz. The reason for setting it in this range is mainly to take into account the particularity of the nonlinear characteristics of the suspension. It can not only ensure that the suspension has low stiffness and good ride comfort when moving near the balance position, but also when the movement travel is increased, with the nonlinear increase of the elastic force value, it can also generate sufficient dynamic specific potential energy at the end of the travel to prevent the phenomenon of rigid collision with the limiter.

[0055] Then, the oil-gas spring characteristics matching and the hard point coordinates of the guide mechanism are designed respectively. Kinematic simulation analysis is carried out with the layout space and suspension geometric kinematics as constraints, and the hard point design of the suspension vibration isolation system is carried out. The constructed dynamic model is used for iterative optimization. The optimal hard point coordinates are determined with the minimum lateral force on the piston as the evaluation criterion. Then the guide mechanism is designed according to the hard point coordinates, and the topological optimization of the guide mechanism is carried out through finite element analysis. At the same time, the oil-gas spring characteristics are matched, and the key parameters such as the oil-gas spring cylinder diameter, piston stroke, and air chamber volume are determined according to the design requirements such as bearing capacity and frequency deviation. The corresponding nonlinear stiffness model and adjustable damping valve system damping characteristic model are constructed in combination with the suspension thermodynamic model, and the structural parameters of the key components of the oil-gas spring are determined. Finally, the structural design of the suspension system is carried out in combination with the design scheme of the oil-gas spring and the guide mechanism. The ultimate impact load is input for finite element analysis, and the strength of its key components is checked. The process of iterative hard point coordinates, structural parameters, and strength analysis is finally formed. A highly compact nonlinear suspension system solution is finally formed.

[0056] On the basis of forming a specific implementation plan for the suspension system, further detailed characteristic calculations of the suspension system are carried out. The process is as follows: Figure 3 First, input the vehicle weight G, vehicle bottom height from the ground H, balance elbow axis distance from the vehicle bottom E, balance elbow length R, road wheel diameter D, number of road wheels n, dynamic stroke f d 、Static stroke f j , coordinates of the upper hinge point (x1, y1), length of the pull arm r, angle between the pull arm and the balance elbow β, piston area A h , the initial gas column length h0, calculate the angle α between the balance elbow and the horizontal line, further calculate the oil-gas spring piston stroke s and lever ratio i in sequence, according to the initial gas column length h0, and use the gas state equation to deduce the gas pressure p of the oil-gas spring at any position, and use the calculated gas pressure p and piston area A h Multiply them to get the nonlinear elastic characteristics of the oil-gas spring, and then multiply them with the lever ratio i to further get the elastic characteristics of the suspension system. The generation of nonlinear elastic characteristic curves can be achieved through autonomous programming. The natural frequency of the sprung mass at the static equilibrium position and the dynamic potential energy at the end of the suspension system stroke are calculated respectively, and a vehicle dynamics model is established to check and calculate the ride comfort and driving stability of the vehicle, and judge according to the vibration response results of the vehicle dynamics simulation. If the acceleration vibration response is greater than the set threshold, it is necessary to increase the initial inflation pressure p0, repeat the calculation of the characteristics, and input them into the vehicle dynamics model for analysis again until the threshold setting requirements are met. In addition, if the relative travel of the suspension is greater than the set threshold, it means that the suspension buffering capacity is insufficient, and it is necessary to reduce the initial inflation pressure p0, and iteratively calculate the characteristics and input them into the vehicle dynamics model for analysis until the threshold setting requirements are met.

[0057] In order to make the vehicle have good driving performance on various complex roads, it is necessary to further study the control method of suspension stiffness and damping characteristics. After adopting the technical solution of oil-gas suspension, stiffness adjustment becomes possible by adjusting the high-pressure gas volume.

[0058] The adjustment of stiffness characteristics is mainly reflected in two aspects: static adjustment and dynamic adjustment during driving. In terms of static adjustment, the internal working pressure of the oil-gas suspension is first collected through sensors, the wheel load state is calculated, and the suspension accumulator is charged and discharged through the hydraulic pneumatic system. The vehicle body frequency deviation is adjusted to a reasonable range (set to 1Hz-1.3Hz) using the gas state equation. After the gas volume adjustment is completed, it is necessary to consider that the vehicle body posture will also change accordingly. Therefore, it is necessary to formulate a control algorithm to drive the vehicle posture adjustment hydraulic valve group to charge and discharge the suspension cylinder, so as to achieve the target position of the vehicle bottom height from the ground to meet the driving requirements. The static adjustment of stiffness characteristics can effectively solve the problem of vehicle driving performance changes caused by the large difference between empty and full load conditions, and meet the use requirements under various load conditions.

[0059] In terms of dynamic adjustment of stiffness characteristics during driving, a suspension system dynamics model is established to carry out simulation analysis of the optimal matching of stiffness and damping characteristics, such as Figure 4-Figure 5 As shown in the figure, as the natural frequency, i.e. the suspension stiffness, decreases, the root mean square of the body vibration acceleration also decreases, and the sensitivity of the change is significantly greater than the effect of the damping ratio on it, but it will also increase the relative travel of the suspension. Figure 4 It can be seen that the root mean square acceleration of the vehicle body vibration will gradually decrease with the increase of the damping ratio. When the damping ratio reaches about 0.5, the root mean square acceleration reaches the minimum. As the damping ratio continues to increase, the root mean square acceleration gradually shows an increasing trend, that is, there is a nonlinear trend, which means that under specific road conditions and vehicle speeds, the optimal suspension damping can usually be selected. Figure 5 It can be seen that the root mean square acceleration of the vehicle body vibration will increase with the increase of the natural frequency, that is, the suspension stiffness, and basically presents a simple linear relationship, which means that when the relative travel of the suspension allows, reducing the stiffness can achieve the effect of suppressing the vehicle body vibration.

[0060] Based on the above matching analysis results, the vibration response of the suspension system in the time domain was further studied. The suspension stiffness was increased by 2 times, i.e., the high stiffness state, and the suspension stiffness was reduced to 0.5 times, i.e., the low stiffness state. The suspension stiffness was adjusted according to the stroke change, i.e., the stroke-varied stiffness state, and the acceleration-varied stiffness state, which further considered the body acceleration response, was determined. The control method of the stroke-varied stiffness is as follows:

[0061]

[0062] Where k is the target suspension stiffness, k bis the passive suspension stiffness, s is the suspension response travel, and s0 is the set suspension range travel.

[0063] The control method of acceleration variable stiffness is as follows:

[0064]

[0065] Where: is the sprung mass acceleration; Preset threshold value for acceleration.

[0066] A comparative analysis of vibration responses based on vehicle dynamics was conducted, and the results are as follows: Figure 6 As shown in the figure, it can be seen that with the increase of suspension stiffness, the body vibration acceleration also shows a significant increasing trend, and when the stiffness decreases, it shows a significant downward trend. Compared with the passive suspension, the travel variable stiffness and acceleration variable stiffness control methods have obvious advantages in suppressing the body vibration acceleration, and are comparable in suppressing the relative travel of the suspension and the acceleration of the unsprung mass, such as Figure 7-Figure 8 Compared with the traditional passive suspension, the realization of the adjustable stiffness function significantly expands the dimension of suspension characteristic adjustment and the amplitude of vibration response suppression, laying the foundation for the research and development of intelligent suspension vibration reduction technology.

[0067] It should be noted that in the process of dynamically adjusting the suspension stiffness characteristics during driving, it is necessary to accurately monitor the filling and releasing volume of the high-pressure gas in the suspension air chamber, and at the same time compensate the amount of oil in the oil-gas suspension oil chamber through the vehicle posture hydraulic adjustment system. That is, the vehicle posture hydraulic adjustment system needs to drain oil when the air chamber is inflated, and needs to fill oil when the air chamber is deflated, so as to ensure the stability of the vehicle body posture.

[0068] In view of the fact that the stiffness adjustment system is relatively complex and the fact that the function is achieved by adjusting the high-pressure air volume, it has typical nonlinear and time-lag characteristics, which is not conducive to real-time adjustment. Therefore, it is further proposed to first suppress the acceleration vibration response of the vehicle body by adjusting the suspension stiffness in steps, and then combine it with the damping characteristic control method to achieve the purpose of significantly improving the off-road maneuverability of the vehicle. The realization of stiffness adjustment can effectively solve the use requirements of large changes in sprung mass and special equipment operations.

[0069] Aiming at the adaptive adjustment of suspension damping characteristics, the present invention proposes a frequency-band hybrid control method, such as Fig. 9 As shown in the figure, taking the single-wheel suspension system as the research object, the fixed point of the frequency domain vibration response is derived, and the suspension motion differential equations are first given:

[0070]

[0071] In the formula, m s is the sprung mass, m uis the unsprung mass, is the sprung mass acceleration, is the unsprung mass acceleration, x s is the sprung mass displacement, x u is the unsprung mass displacement, is the sprung mass velocity, is the unsprung mass velocity, x r is the road roughness, k s is the suspension stiffness characteristic, k u is the wheel stiffness characteristic, c s is the suspension damping characteristic.

[0072] Through Laplace transform, we can get:

[0073]

[0074] The functional relationship between the sprung mass and the unsprung mass displacement is derived as follows:

[0075]

[0076] And the functional relationship between the sprung mass and the ground excitation elevation is summarized as:

[0077]

[0078] The fixed point expression of the sprung mass displacement response is obtained by programming:

[0079]

[0080] Depend on Fig.10 As shown, by programming and analyzing the amplitude-frequency characteristics, it can be seen that: ①ω2 and ω3 are related to the suspension stiffness k s is related to the suspension damping c s is independent of, while ω1 is related to the suspension stiffness k s and suspension damping c s are irrelevant and are completely determined by the wheel stiffness k u and unsprung mass m u Determination; ② When the excitation frequency ω is in the range of ω<ω1 or ω2<ω<ω3, the vertical vibration acceleration transmission rate of the vehicle body decreases with the increase of suspension damping, that is, the inhibitory effect of increasing damping on suspension resonance (low-frequency resonance area and high-frequency resonance area) is particularly significant; ③ When the excitation frequency ω is in the range of ω1<ω<ω2 or ω>ω3, the vertical vibration acceleration transmission rate of the vehicle body increases with the increase of suspension damping, which will cause the vehicle's ride smoothness to deteriorate. This is why the passive suspension system needs to compromise in order to improve the vehicle's ride smoothness.

[0081] Furthermore, the frequency domain fixed point expression of the unsprung mass displacement response is derived, and the functional relationship between the unsprung mass displacement and the road elevation excitation is summarized as follows:

[0082]

[0083] set up:

[0084]

[0085] Solving the above equation is equivalent to the following form:

[0086]

[0087] Further sorting:

[0088] {k u (-m s ω 2 +k s )[k u ω-(m u +m s )ω 3 ]} 2 -{(k u ω)[m u m s ω 4 -(k s m s +k u m s +m u k s )ω 2 +k u k s ]} 2 =0 The fixed point expression of the frequency domain of the unsprung mass displacement response is solved by programming:

[0089]

[0090] The amplitude-frequency characteristics of the unsprung mass displacement to the road surface excitation are analyzed by programming, such as Fig.11 As shown, it can be seen that: ①ω4 and ω5 are related to the suspension stiffness k s ① When the excitation frequency ω is in the range of ω<ω4 or ω>ω5, the wheel dynamic deformation transmission rate decreases with the increase of suspension damping. Similarly, increasing damping is beneficial to suppress the resonance of the vehicle. ③ When the excitation frequency ω is in the range of ω4<ω<ω5, the wheel dynamic deformation transmission rate increases with the increase of suspension damping, which will cause the vehicle's road adhesion to deteriorate, indicating that the passive suspension system cannot optimize the wheel dynamic deformation as a whole in the entire frequency band.

[0091] The relationship between the relative travel of the suspension and the road surface excitation elevation is further derived:

[0092]

[0093] set up:

[0094]

[0095] Arrange the transformation into the form of a system of equations:

[0096]

[0097] The frequency domain fixed point expression for solving the relative travel of the suspension is:

[0098]

[0099] Through programming, the amplitude-frequency characteristics of the relative travel of the suspension to the road excitation are analyzed, such as Fig.12 As shown, it can be seen that: ①ω6 and suspension stiffness k s and suspension damping c s ① They are all unrelated, indicating that at this frequency, the suspension dynamic stroke transmission rate is not affected by the suspension force and is a constant value; ② In general, the suspension dynamic stroke decreases with the increase of suspension damping. Similarly, increasing damping is beneficial to suppress vehicle resonance.

[0100] Based on the above analysis of the six fixed points of vehicle body vertical vibration acceleration, wheel dynamic deformation and suspension dynamic travel, it can be seen that from the perspective of frequency, there is a certain consistency in the influence of suspension damping on the transfer characteristics of vehicle body vertical vibration acceleration, wheel dynamic deformation and suspension dynamic travel: ① In both the low-frequency resonance zone and the high-frequency resonance zone, the suspension system needs to provide greater damping to suppress resonance; ② In both the medium-frequency zone and the high-frequency zone, the suspension system needs to provide smaller damping to reduce and improve the vehicle's driving smoothness and road adhesion.

[0101] Although the suspension system usually has two vibration control goals - improving vehicle ride smoothness and road adhesion (while also taking into account the vehicle driving safety goal), and there is only one control quantity, so no matter what control method is used, these two performance indicators cannot be simultaneously optimized. However, from the above analysis of the fixed point of the transmissibility, it can be seen that the transmission characteristics of the suspension damping to the three indicators in the frequency domain are consistent to a certain extent. As long as the frequency intervals are appropriately divided and different controls are applied to different frequency intervals, the overall performance of the suspension can be approximately optimal.

[0102] According to the above analysis, the frequency divider γ is designed as follows:

[0103]

[0104] Where: is the rate of change of sprung mass acceleration; α is an intermediate variable, where α=(2πf cross ) 2 , f cross Take the first fixed point frequency

[0105] Assume that Where f>0, then Where f is the actual input frequency, substituting it into the formula yields:

[0106] γ=((2πf) 4 -a 2 )sin 2 (2πft)

[0107] Since α=(2πf1) 2 , when 0<f<f1, γ<0; and when f>f1, γ>0. Based on this, an improved frequency domain hybrid damping control method is given, which can be expressed as:

[0108]

[0109] Where: c f is the adjustable damping value of the suspension; c fmax Maximum adjustable damping for the suspension.

[0110] The evaluation index and vibration control target of the vehicle suspension system are based on the root mean square value of the sprung vibration acceleration, the root mean square value of the wheel dynamic displacement and the comprehensive performance of the suspension system formed by them. The convex function is selected to establish the comprehensive performance evaluation index of the vehicle suspension system, which can be expressed as:

[0111]

[0112] Where ζ and ξ are the weight distribution coefficients of sprung mass acceleration and wheel displacement, respectively, and ζ+ξ=1. The adaptive adjustment of the weight distribution coefficient is realized by fuzzy control method. Q RP_P and Q RP are the root mean square values ​​of the sprung vibration acceleration of the passive and controllable suspension, Q RAP and Q RA are the root mean square values ​​of the dynamic displacements of the passive and controllable suspension wheels, respectively.

[0113] Through programming, the vibration response comparison analysis of different control methods is carried out, and the frequency response characteristics of the vehicle suspension system are analyzed using the sine excitation method. The reference frequency range is 0.011m, referring to the random road surface. -1 <n<2.83m -1, taking the F-class standard random road surface as the excitation input, the time-frequency domain comparison curves and the root mean square value of the sprung vibration acceleration of the passive suspension, skyhook damping control, acceleration damping control and frequency domain hybrid control suspension systems are generated, such as Figure 13-14 As shown in the figure, it can be seen that (1) the ceiling damping has a good inhibitory effect on the sprung vibration acceleration in the low-frequency resonance area, but has an obvious amplification trend in the vibration response in the high-frequency area, and the root mean square value of the sprung acceleration response in the full-frequency domain has increased; (2) ADD damping is not as good as ceiling damping and frequency domain hybrid control in suppressing the sprung vibration acceleration in the low-frequency resonance area, but has a very obvious inhibitory effect on the sprung vibration acceleration in the frequency domain between low-frequency resonance and high-frequency resonance, which is equivalent to frequency domain hybrid control. Therefore, the root mean square value of the sprung acceleration response in the full-frequency domain is attenuated by 1.3% compared with the passive suspension. 14.3%; (3) Compared with ceiling damping and ADD damping control, hybrid control tracks the response characteristics of ceiling damping to sprung vibration acceleration in the low-frequency range, and tracks the response characteristics of acceleration damping control to sprung vibration acceleration in the medium and high-frequency range, indicating that the crossover designed by the improved algorithm is effective; (4) Compared with passive suspension, frequency domain hybrid control can reduce sprung vibration acceleration in most frequency bands, with a RMS attenuation of 16.2% compared with passive suspension, which is more obvious than ceiling damping and ADD damping, thus verifying the effectiveness of the algorithm.

[0114] In summary, the present invention belongs to the technical field of suspension vibration reduction, and specifically relates to a suspension system design method. According to the requirements of the overall layout, the load center of gravity of the whole vehicle is clarified, the action system is preliminarily arranged, and the wheel system layout and the suspension guide mechanism layout are carried out respectively. In terms of wheel system layout, the wheel system position is preliminarily arranged according to the principle of maximally coinciding the load center of gravity and the elastic center, random road excitation is generated, an equivalent linear dynamic model of the vehicle is established, and dynamic matching calculations are carried out. In terms of suspension guide mechanism layout, a mathematical model of oil-gas suspension is generated, and the determined suspension damping ratio is input into the mathematical model of oil-gas suspension to guide the design of the damping valve and generate nonlinear damping characteristics. At the same time, the calculated wheel axle loads are input into the mathematical model of oil-gas suspension to carry out the generation calculation of nonlinear elastic characteristics, and comprehensively evaluate whether the vehicle body vibration response characteristics, the suspension thermal balance temperature rise characteristic curve and the reliability analysis results of key parts meet the design index requirements.

[0115] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A suspension system design method, characterized in that: The method includes the following steps: Step 1: First, clarify the overall vehicle load center of gravity according to the overall layout requirements, conduct a preliminary layout of the running system, and separately carry out the layout of the wheel system and the suspension guiding mechanism; Step 2: In terms of the wheel system layout, preliminarily arrange the position of the wheel system according to the principle that the load center of gravity and the elastic center should coincide as much as possible. Grouped by front and rear, off-road vehicles are configured according to a front and rear wheel load distribution ratio of 6:

4. First, generate a random road surface excitation, establish an equivalent linear dynamic model of the vehicle, use the road surface model as the input of the equivalent linear dynamic model, conduct suspension characteristic checking and analysis, input the suspension equilibrium position stiffness and damping characteristic parameters into the calculation program in the form of arrays respectively, conduct array combination to carry out dynamic matching calculation, input the expected maximum driving speed, monitor the key vibration response conditions including the unsprung mass, sprung mass, suspension relative travel, and vehicle body stability, calculate the time-domain and frequency-domain response data respectively, and use the root mean square value and the maximum vibration response data as the basis for evaluation to judge whether the vibration threshold is met; It is set that the root mean square value of the sprung mass acceleration vibration response is less than 0.3g, the maximum impact acceleration vibration response is less than 3.5g, the suspension vibration response travel is not greater than the full suspension travel, and the dynamic load of the unsprung mass is less than the unsprung mass itself; Then, establish a thermodynamics model of the suspension system, and at the same time input the maximum driving speed and the road surface model into the thermodynamics model to realize the joint operation of the vehicle equivalent linear dynamic model and the thermal model. Take the thermal equilibrium temperature T < T0 = 150°C as the evaluation threshold. Through the comprehensive judgment of the vehicle vibration threshold and the suspension thermal equilibrium temperature threshold, after the model is repeatedly iterated and calculated to meet the threshold requirements, the suspension damping ratio can be preliminarily determined.

2. The suspension system design method according to claim 1, characterized in that: The method further includes: Step 3: In terms of the suspension guiding mechanism layout, preliminarily determine the pull arm length, balance elbow length, distance from the balance elbow axis center to the oil cylinder center line, pull arm installation angle, and connecting rod length according to the layout of the running system, generate a suspension leverage ratio calculation model, and finally generate a mathematical model of the hydro-pneumatic suspension. Input the determined suspension damping ratio into the mathematical model of the hydro-pneumatic suspension to guide the damping valve design and generate non-linear damping characteristics. At the same time, input the calculated axle loads of each wheel into the mathematical model of the hydro-pneumatic suspension to carry out the generation calculation of non-linear elastic characteristics. Finally, input the calculated non-linear elastic characteristics and damping characteristic curves into the suspension thermal model to complete the calculation of the thermal equilibrium temperature rise characteristic curve.

3. The suspension system design method according to claim 2, characterized in that: The method further includes: Step 4: Input the non-linear elastic characteristics and damping characteristics, and the generated road surface model into the vehicle non-linear dynamic model to conduct vibration response checking calculations. The obtained vibration response results are used as the loads of the key components of the running system; comprehensively evaluate whether the vehicle body vibration response characteristics, the suspension thermal equilibrium temperature rise characteristic curve, the suspension relative travel, and the reliability analysis results of key components meet the design index requirements. If they meet, the suspension matching optimization process ends. If they do not meet the requirements, the program returns to the first step of the running system layout to re-conduct iterative optimization calculations until the best solution that meets the index requirements is matched.

4. The suspension system design method according to claim 3, characterized in that: In view of the existing technology, the suspension system design method, from clear demand input to theoretical modeling, parameter optimization, guide mechanism design, and reliability strength analysis, can significantly improve product design accuracy, achieve the transition from empirical design to predictive design, and effectively shorten the new product design cycle and reduce R&D costs.

5. The suspension system design method according to claim 4, characterized in that: In view of the lack of corresponding specifications and standards for oil-gas suspension design, the method proposes a complete suspension system design method and process. It is proposed that the equivalent linear vehicle dynamics model is first used to simulate the smoothness and handling stability of driving under different road conditions and vehicle speeds in the frequency domain, and the root mean square value of the vehicle body vibration acceleration, pitch angular velocity and relative travel of each wheel suspension is monitored respectively. The vibration response under different road conditions and vehicle speeds varies with the stiffness and relative damping coefficient. An autonomous optimization algorithm is compiled to finally determine the ideal elastic and damping characteristics of each wheel position, which are input into the oil-gas suspension dynamics model as the design basis of structural parameters. The nonlinear elastic characteristics and damping characteristics with valve opening function are simulated and calculated in combination with the structural characteristics of the key elements of the damping valve, guide mechanism and energy storage device, and an accurate external characteristic curve is obtained; the determined characteristic data is further input into the nonlinear dynamics model of the whole vehicle, and the time domain nonlinear vibration response analysis is carried out to output the load of key components as the basis for reliability analysis. At the same time, the influence of nonlinear and asymmetric characteristics on the vibration of the whole vehicle is systematically studied, and the ideal state is achieved through repeated iterations. During the simulation process, it was proposed for the first time to conduct joint calculations with the thermodynamic model, using the thermal equilibrium temperature as the threshold to avoid the problem of overheating and failure of the suspension system.

6. The suspension system design method according to claim 5, characterized in that: The method proposes a relatively comprehensive evaluation method for optimizing and matching suspension characteristics. Since special vehicles have a long body, are in a multi-wheel coupling state, and have a bad road surface, they are significantly different from ordinary vehicles. In actual use, the vehicle pitch angle vibration and the vertical vibration response of the vehicle body have a greater impact on the feelings of the driver and passengers. The interaction force between the wheels and the ground determines the safety of the vehicle during high-speed driving. It is necessary to avoid the problem that the suspension jump stroke cannot be reset in time, resulting in insufficient ground adhesion. The suspension relative stroke index is used as a threshold to determine whether the vehicle will have rigid breakdown under extreme impact conditions, resulting in a decrease in maneuverability. In addition, the thermal balance temperature threshold of the suspension body is also introduced in the process of optimizing and matching characteristics to avoid excessive damping and cause overheating failure of the suspension system.

7. The suspension system design method according to claim 6, characterized in that: Taking all the above factors into consideration, the method develops a comprehensive evaluation method according to the characteristics of special vehicles and driving conditions, which provides strong support for improving the comprehensive driving performance of vehicles.

8. The suspension system design method according to claim 7, characterized in that: The method belongs to the technical field of suspension vibration reduction.

9. A suspension system design method, characterized in that: The method defines the load center of gravity of the whole vehicle according to the overall layout requirements, makes a preliminary layout of the motion system, and respectively carries out the layout of the wheel system and the layout of the suspension guide mechanism.

10. The suspension system design method according to claim 9, characterized in that: In terms of wheel arrangement, the method preliminarily arranges the wheel position according to the principle that the load center of gravity and the elastic center are as close as possible, generates random road excitation, establishes an equivalent linear dynamic model of the vehicle, and performs dynamic matching calculation; In terms of suspension guide mechanism arrangement, the method generates a mathematical model of an oil-gas suspension, inputs a determined suspension damping ratio into the mathematical model of the oil-gas suspension to guide the design of a damping valve and generate nonlinear damping characteristics, and simultaneously inputs the calculated axle loads of each wheel into the mathematical model of the oil-gas suspension to perform generation calculations of nonlinear elastic characteristics, and comprehensively evaluates whether the vehicle body vibration response characteristics, the suspension thermal balance temperature rise characteristic curve, and the reliability analysis results of key components meet the design index requirements.

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