Ladder structure three-level stiffness non-equal length automobile suspension leaf spring and its design method

Abstract

The invention relates to a stepped structure three-level stiffness non-equal length automobile suspension steel leaf spring and a design method thereof, belonging to the technical field of steel leaf springs; the device is a stepped structure, comprising a primary leaf spring, a secondary leaf spring and a tertiary leaf spring, the primary leaf spring, the secondary leaf spring and the tertiary leaf spring are arranged from top to bottom and their effective lengths decrease in sequence; it also comprises a matching three-level stepped leaf spring bracket, the primary leaf spring, the secondary leaf spring and the tertiary leaf spring are designed with different parabolas; the invention ensures that the inherent frequency deviation of the leaf spring is always within a reasonable range from no-load to full-load, thereby ensuring the consistent comfort of the empty and fully loaded vehicle; the three leaf spring leaves reasonably distribute the design stress of the leaf springs at each level according to the load changes they bear, ensuring that the leaf springs at each level have equal strength and equal life design; the leaf springs at each level do not contact each other except the middle part, thereby eliminating the friction between the leaves, reducing the dynamic stiffness and improving the vibration reduction effect of the leaf spring.

Description

Technical Field

[0001] The invention relates to a ladder-structured three-level stiffness non-equal-length automobile suspension steel leaf spring and a design method thereof, belonging to the technical field of steel leaf springs. Background Art

[0002] With the continuous improvement of customers' requirements for product comfort and the need for high-quality development, the inherent frequency deviation of automobile suspension leaf springs is required to be at a lower level. Existing automobile suspension leaf springs usually adopt single-stage or two-stage stiffness, which has the following defects:

[0003] 1. Due to structural reasons, the existing single-stage or two-stage stiffness leaf springs have a no-load bias frequency of 5.8-6.8Hz for single-stage stiffness leaf springs and a full-load bias frequency of 2.3-2.8Hz; the two-stage stiffness leaf springs have a no-load bias frequency of 4.0-5.0Hz and a full-load bias frequency of 2.3-2.8Hz. The no-load bias frequency is relatively high and much higher than the full-load bias frequency, and it is impossible to achieve the ideal state where the no-load bias frequency is equal to the full-load bias frequency, resulting in poor comfort when the car is unloaded;

[0004] 2. The existing single-stage or two-stage leaf springs have large friction between the leaves due to the close fit between the leaves. The dynamic stiffness of the leaf spring is relatively large, especially when the vibration is low-amplitude and high-frequency, the dynamic stiffness can reach 3-5 times the static stiffness, resulting in a sharp reduction in the vibration reduction effect of the leaf spring;

[0005] 3. In the process of increasing load from no-load to full-load, the stiffness of the existing two-stage stiffness leaf spring suddenly changes too much before and after the auxiliary spring contacts, and the inherent bias frequency increases from 2.5-3.0Hz to 6.0-6.5Hz. The sudden increase in the inherent bias frequency causes vehicle shaking and poor comfort. Summary of the invention

[0006] In view of the above deficiencies in the prior art, the technical problem to be solved by the present invention is: to provide a stepped structure three-stage stiffness unequal length automobile suspension leaf spring and a design method thereof, which solves the problem that the existing single-stage or two-stage stiffness automobile suspension leaf spring has a much higher no-load frequency deviation than a full-load frequency deviation, and cannot achieve the ideal state where the no-load frequency deviation is equivalent to the full-load frequency deviation, so that the inherent frequency deviation of the leaf spring is always within a reasonable range in the process from no-load to full-load, thereby ensuring the consistent comfort of the vehicle when it is empty and fully loaded.

[0007] The stepped structure three-level stiffness non-equal length automobile suspension steel leaf spring of the present invention is a stepped structure, comprising a primary leaf spring, a secondary leaf spring and a tertiary leaf spring, wherein the primary leaf spring, the secondary leaf spring and the tertiary leaf spring are arranged from top to bottom and their effective lengths decrease in sequence; the step structure also comprises a matching three-level stepped leaf spring bracket, wherein the three-level stepped leaf spring bracket supports the primary leaf spring, the secondary leaf spring and the tertiary leaf spring according to the load conditions; when unloaded, the three-level stepped leaf spring bracket only supports the primary leaf spring, and as the load increases, the three-level stepped leaf spring bracket supports the secondary leaf spring and the tertiary leaf spring in sequence at different fulcrums;

[0008] The primary leaf spring, secondary leaf spring and tertiary leaf spring are designed with different parabolas. The thickness of the middle parts of the primary leaf spring, secondary leaf spring and tertiary leaf spring are equal. The lower part of the middle part of the primary leaf spring contacts the middle part of the secondary leaf spring, and the lower part of the middle part of the secondary leaf spring contacts the middle part of the tertiary leaf spring. The remaining parts of the leaf springs of each level do not contact each other, so as to eliminate the friction between the leaf spring leaves, reduce the dynamic stiffness and further reduce the inherent frequency deviation.

[0009] The design method of the stepped structure three-level stiffness non-equal length automobile suspension leaf spring of the present invention comprises the following steps:

[0010] S1. Determine the target frequency deviation of the leaf spring from no-load to full-load according to the smoothness requirements ;

[0011] S2, according to the leaf spring load is no-load load , when only the primary leaf spring is in effect, calculate the target stiffness of the primary leaf spring ; According to the leaf spring load , when the primary leaf spring and the secondary leaf spring work at the same time, calculate the target stiffness of the secondary leaf spring ; Based on the leaf spring load as full load , when the first-stage leaf spring, the second-stage leaf spring and the third-stage leaf spring work at the same time, calculate the target stiffness of the third-stage leaf spring ;

[0012] S3. According to the leaf spring action length L, leaf spring width B installation dimension requirements and the corresponding relationship between the leaf spring parabolic coefficient k and the leaf spring stiffness, the parabolic coefficient k and leaf type parameters of the primary leaf spring, the secondary leaf spring and the tertiary leaf spring are calculated respectively, which specifically includes the following steps:

[0013] S31, preliminarily setting the parabolic coefficient k and leaf type parameters of each level of leaf springs, and calculating the rotation angle θ of each level of leaf springs;

[0014] S32, calculating the deflection ω of the leaf springs at each level according to the calculated rotation angle θ of the leaf springs at each level;

[0015] S33, according to the calculated deflection ω of the leaf springs at each level, calculate the stiffness of the leaf springs at each level respectively ;

[0016] S34, the calculated stiffness Respectively with the target stiffness , , Compare and observe whether the deviation between the two is less than the specified value. If not, readjust the parabola k and the sheet type parameters and repeat steps S31-S34 until the stiffness is meet the requirements;

[0017] S4. Calculate the leaf spring design stress based on the adjusted leaf spring parabola coefficient k and leaf shape parameters. ;

[0018] S5. Calculate the impact stress of leaf springs using the energy conversion principle ;

[0019] S6. Calculate the design stress and impact stress , check with the leaf spring design specification value. If it does not meet the requirements, readjust the leaf spring raw material thickness, end thickness and other parameters, repeat steps S31-S6, re-iterate and calculate the parabola coefficient k and leaf shape parameters, and recalculate the design stress and impact stress , until the design requirements are met;

[0020] S7. Calculate the leaf spring frequency deviation , see if it meets the requirements, if not, adjust the leaf spring raw material thickness, end thickness and other parameters, repeat steps S31-S8, and iterate the calculation repeatedly until the design requirements are met;

[0021] S8. According to customer requirements or leaf spring standard requirements, determine the installation dimensions such as center bolt, middle gasket, end width, etc., and draw the leaf spring assembly drawing.

[0022] Preferably, in step S2, the primary leaf spring target stiffness The calculation formula is:

[0023] = (I)

[0024] Secondary leaf spring target stiffness The calculation formula is:

[0025] = (II)

[0026] Target stiffness of three-stage leaf spring The calculation formula is:

[0027] = (III)

[0028] in, is the target frequency deviation of the leaf spring, is the no-load load, is the load when the primary leaf spring and the secondary leaf spring act at the same time, For full load, is the acceleration due to gravity.

[0029] Preferably, in step S31, the leaf spring rotation angle The calculation formula is:

[0030] = (IV)

[0031] Among them, M is the bending moment of the corresponding section of the leaf spring, E is the elastic modulus of the material, I is the moment of inertia of the corresponding section of the leaf spring, and L is the effective length of the leaf spring. is the distance between the corresponding section and the center of the leaf spring, is the number of leaf springs, B is the width of the leaf spring, is the arc coefficient of the corresponding section, is the leaf spring thickness, is the load;

[0032] When it is located in the middle straight section of the leaf spring, = thickness of raw material;

[0033] When it is in the transition section of the leaf spring, = Raw material thickness - ( - middle straight length) × (raw material thickness - parabola starting point thickness) / transition section length;

[0034] When located on the parabola segment of the leaf spring,

[0035] =k ; (V)

[0036] Where, k is the parabola coefficient of the leaf spring;

[0037] When located at the straight section at the end of the leaf spring, = end thickness.

[0038] Preferably, in step S32, the calculation formula of the deflection ω is:

[0039] ω= (VI)

[0040] in, is the leaf spring angle.

[0041] Preferably, in step S33, the stiffness The calculation formula is:

[0042] (VII)

[0043] in, is the load and ω is the deflection.

[0044] Preferably, during the actual calculation of steps S31-S33, a calculation program may be written using Visual Studio C++ according to design calculation requirements, and the leaf spring parabola coefficient k and leaf shape parameters may be accurately and quickly calculated through iteration.

[0045] Preferably, in step S4, the leaf spring design stress The calculation formula is:

[0046] (VIII)

[0047] Where M is the bending moment of the corresponding section of the leaf spring, I is the moment of inertia of a certain section of the leaf spring, is the leaf spring thickness.

[0048] Preferably, in step S5, the leaf spring impact stress The calculation formula is:

[0049] (IX)

[0050] Among them, M is the bending moment of the corresponding section of the leaf spring when it is impacted, I is the moment of inertia of a section of the leaf spring, is the leaf spring thickness.

[0051] Preferably, in step S7, the leaf spring bias frequency The calculation formula is:

[0052] = (Ⅹ)

[0053] in, is the load, For stiffness.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] 1. The present invention adopts three unequal length leaf springs to form a stepped structure, and is equipped with a three-stage stepped leaf spring bracket, so that as the load increases, the secondary leaf spring and the tertiary leaf spring work in sequence, ensuring that the inherent frequency deviation of the leaf spring is always within a reasonable range from no-load to full-load. The no-load frequency deviation can reach 2.5-3.0Hz, and the full-load frequency deviation is 2.3-2.8Hz, thereby ensuring the same comfort of the vehicle when it is empty and fully loaded;

[0056] 2. The three leaf springs adopt different parabolic designs. According to the loads they bear and the load changes when the vehicle bounces, the design stress of each level of leaf springs is reasonably distributed to ensure the equal strength and life of each level of leaf springs;

[0057] 3. Except for the middle part, the leaf springs of each level do not contact each other, eliminating the friction between the leaves and reducing the dynamic stiffness. The dynamic stiffness can be reduced to 1.2-1.3 times of the static stiffness, thereby improving the vibration reduction effect of the leaf spring. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a schematic diagram of the structure of the present invention;

[0059] Figure 2 It is the load, eccentric frequency and deflection curve coordinate diagram of the present invention;

[0060] Figure 3 It is a coordinate diagram of the existing single-stage stiffness leaf spring load, frequency deviation and deflection curve.

[0061] In the figure: 1. primary leaf spring; 2. secondary leaf spring; 3. tertiary leaf spring; 4. three-stage stepped leaf spring bracket. DETAILED DESCRIPTION

[0062] The present invention is further described below in conjunction with specific embodiments.

[0063] Example 1

[0064] like Figure 1 As shown, the stepped structure three-stage stiffness non-equal length automobile suspension steel leaf spring described in this embodiment is a stepped structure, including a primary leaf spring 1, a secondary leaf spring 2 and a tertiary leaf spring 3, the primary leaf spring 1, the secondary leaf spring 2 and the tertiary leaf spring 3 are arranged from top to bottom and the effective lengths decrease in sequence; it also includes a matching three-stage stepped leaf spring bracket 4, the three-stage stepped leaf spring bracket 4 supports the primary leaf spring 1, the secondary leaf spring 2 and the tertiary leaf spring 3 according to the load conditions; when unloaded, the three-stage stepped leaf spring bracket 4 only supports the primary leaf spring 1, and as the load increases, the three-stage stepped leaf spring bracket 4 supports the secondary leaf spring 2 and the tertiary leaf spring 3 in sequence according to different fulcrums; the contact surface between the three-stage stepped leaf spring bracket 4 and the leaf springs at each level is an arc surface;

[0065] The primary leaf spring 1, the secondary leaf spring 2 and the tertiary leaf spring 3 are designed with different parabolas, and the thickness of the middle parts of the primary leaf spring 1, the secondary leaf spring 2 and the tertiary leaf spring 3 are equal; the lower part of the middle part of the primary leaf spring 1 contacts the middle part of the secondary leaf spring 2, and the lower part of the middle part of the secondary leaf spring 2 contacts the middle part of the tertiary leaf spring 3, and the remaining parts of the leaf springs of each level do not contact each other, so as to eliminate the friction between the leaf spring leaves, reduce the dynamic stiffness, and further reduce the inherent frequency deviation.

[0066] Example 2

[0067] The design method of the stepped structure three-level stiffness non-equal length automobile suspension leaf spring described in this embodiment comprises the following steps:

[0068] S1. Determine the target frequency deviation of the leaf spring from no-load to full-load according to the smoothness requirements ;

[0069] S2, according to the leaf spring load is no-load load , 1-1.1T, when only the primary leaf spring 1 works, calculate the target stiffness of the primary leaf spring 1 ; According to the leaf spring load , When the primary leaf spring 1 and the secondary leaf spring 2 work at the same time, calculate the target stiffness of the secondary leaf spring 2 ; Based on the leaf spring load as full load , When the primary leaf spring 1, the secondary leaf spring 2 and the tertiary leaf spring 3 work at the same time, calculate the target stiffness of the tertiary leaf spring 3. ;

[0070] S3, according to the leaf spring action length L, leaf spring width B installation dimension requirements and the corresponding relationship between the leaf spring parabolic coefficient k and the leaf spring stiffness, respectively calculate the parabolic coefficient k and leaf type parameters of the primary leaf spring 1, the secondary leaf spring 2, and the tertiary leaf spring 3, specifically including the following steps:

[0071] S31, preliminarily setting the parabolic coefficient k and leaf type parameters of each level of leaf springs, and calculating the rotation angle θ of each level of leaf springs;

[0072] S32, calculating the deflection ω of the leaf springs at each level according to the calculated rotation angle θ of the leaf springs at each level;

[0073] S33, according to the calculated leaf spring deflection ω of each level, calculate the stiffness of each level of leaf spring respectively ;

[0074] S34, the calculated stiffness Respectively with the target stiffness , , Compare and observe whether the deviation between the two is less than the specified value. If not, readjust the parabola k and the sheet type parameters and repeat steps S31-S34 until the stiffness is meet the requirements;

[0075] S4. Calculate the leaf spring design stress based on the adjusted leaf spring parabola coefficient k and leaf shape parameters. ;

[0076] S5. Calculate the impact stress of leaf springs using the energy conversion principle ;

[0077] S6. Calculate the design stress and impact stress , check with the leaf spring design specification value. If it does not meet the requirements, readjust the leaf spring raw material thickness, end thickness and other parameters, repeat steps S31-S6, re-iterate and calculate the parabola coefficient k and leaf shape parameters, and recalculate the design stress and impact stress , until the design requirements are met;

[0078] S7. Calculate the leaf spring frequency deviation , see if it meets the requirements, if not, adjust the leaf spring raw material thickness, end thickness and other parameters, repeat steps S31-S8, and iterate the calculation repeatedly until the design requirements are met;

[0079] S8. According to customer requirements or leaf spring standard requirements, determine the installation dimensions such as center bolt, middle gasket, end width, etc., and draw the leaf spring assembly drawing.

[0080] In step S2, the target stiffness of the primary leaf spring 1 is The calculation formula is:

[0081] = (I)

[0082] Secondary leaf spring 2 target stiffness The calculation formula is:

[0083] = (II)

[0084] Three-stage leaf spring 3 target stiffness The calculation formula is:

[0085] = (III)

[0086] in, is the target frequency deviation of the leaf spring, is the no-load load, is the load when the primary leaf spring 1 and the secondary leaf spring 2 act at the same time, For full load, is the acceleration due to gravity.

[0087] In step S31, the calculation formula of the leaf spring rotation angle θ is:

[0088] θ = (IV)

[0089] Among them, M is the bending moment of the corresponding section of the leaf spring, E is the elastic modulus of the material, I is the moment of inertia of the corresponding section of the leaf spring, and L is the effective length of the leaf spring. is the distance between the corresponding section and the center of the leaf spring, is the number of leaf springs, B is the width of the leaf spring, is the arc coefficient of the corresponding section, is the leaf spring thickness, is the load;

[0090] When it is located in the middle straight section of the leaf spring, =Raw material thickness;

[0091] When it is in the transition section of the leaf spring, = Raw material thickness - ( - middle straight length) × (raw material thickness - parabola starting point thickness) / transition section length;

[0092] When located on the parabola segment of the leaf spring,

[0093] =k ; (V)

[0094] Where, k is the parabola coefficient of the leaf spring;

[0095] When located at the straight section at the end of the leaf spring, = end thickness.

[0096] In step S32, the calculation formula of the deflection ω is:

[0097] ω= (VI)

[0098] in, is the leaf spring angle.

[0099] In step S33, the stiffness The calculation formula is:

[0100] (VII)

[0101] in, is the load and ω is the deflection.

[0102] During the actual calculation of steps S31-S33, a calculation program may be written in Visual Studio C++ according to the design calculation requirements, and the leaf spring parabola coefficient k and leaf shape parameters may be calculated accurately and quickly through iteration.

[0103] In step S4, the leaf spring design stress The calculation formula is:

[0104] (VIII)

[0105] Where M is the bending moment of the corresponding section of the leaf spring, I is the moment of inertia of a certain section of the leaf spring, is the leaf spring thickness.

[0106] In step S5, the leaf spring impact stress The calculation formula is:

[0107] (IX)

[0108] Among them, M is the bending moment of the corresponding section of the leaf spring when it is impacted, I is the moment of inertia of a section of the leaf spring, is the leaf spring thickness.

[0109] In step S7, the leaf spring frequency The calculation formula is:

[0110] = (Ⅹ)

[0111] in, is the load, For stiffness.

[0112] Example 3

[0113] like Figure 2 As shown, the step structure three-level stiffness non-equal length automobile suspension leaf spring designed by the design method of Example 2 has a stiffness that increases with the increase of load, and a frequency deviation that increases with the load. The difference is small, the vehicle is comfortable, and the cargo is less impacted and not easily damaged;

[0114] like Figure 3 As shown, the stiffness of the existing single-stage stiffness leaf spring remains unchanged, the frequency deviation varies greatly with different loads, the friction between the leaf spring leaves causes the leaf spring damping to be large, the vehicle comfort is poor, the cargo is subjected to a large impact and is easily damaged.

[0115] The parameter comparison of the stepped structure three-stage stiffness non-equal length automobile suspension leaf spring and the existing single-stage stiffness leaf spring is shown in Table 1:

[0116] Table 1

[0117]

[0118] Of course, the above contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of the embodiments of the present invention. The present invention is not limited to the above examples, and equal changes and improvements made by ordinary technicians in the technical field within the essential scope of the present invention should all fall within the scope of the patent coverage of the present invention.

Claims

1. A design method for a stepped structure three-level stiffness non-equal length automobile suspension leaf spring, characterized in that: The invention comprises a stepped structure three-level stiffness non-equal length automobile suspension steel leaf spring, which is a stepped structure and comprises a primary leaf spring (1), a secondary leaf spring (2) and a tertiary leaf spring (3), wherein the primary leaf spring (1), the secondary leaf spring (2) and the tertiary leaf spring (3) are arranged from top to bottom and their effective lengths decrease in sequence; the invention also comprises a matching three-level stepped leaf spring bracket (4), wherein the three-level stepped leaf spring bracket (4) supports the primary leaf spring (1), the secondary leaf spring (2) and the tertiary leaf spring (3) according to load conditions; when unloaded, the three-level stepped leaf spring bracket (4) only supports the primary leaf spring (1), and as the load increases, the three-level stepped leaf spring bracket (4) supports the secondary leaf spring (2) and the tertiary leaf spring (3) in sequence at different fulcrums; The first-stage leaf spring (1), the second-stage leaf spring (2) and the third-stage leaf spring (3) are designed in different parabolic shapes. The thickness of the middle parts of the first-stage leaf spring (1), the second-stage leaf spring (2) and the third-stage leaf spring (3) is equal. The lower part of the middle part of the first-stage leaf spring (1) contacts the middle part of the second-stage leaf spring (2), and the lower part of the middle part of the second-stage leaf spring (2) contacts the middle part of the third-stage leaf spring (3). The remaining parts of the leaf springs of each stage do not contact each other. The design method includes the following steps: S1. Determine the target frequency deviation of the leaf spring from no-load to full-load according to the smoothness requirements ; S2, according to the leaf spring load is no-load load , when only the primary leaf spring (1) is in effect, calculate the target stiffness of the primary leaf spring (1) ; According to the leaf spring load When the primary leaf spring (1) and the secondary leaf spring (2) act simultaneously, calculate the target stiffness of the secondary leaf spring (2) ; Based on the leaf spring load as full load When the primary leaf spring (1), the secondary leaf spring (2) and the tertiary leaf spring (3) act simultaneously, the target stiffness of the tertiary leaf spring (3) is calculated. ; S3. According to the leaf spring action length L, the leaf spring width B installation dimension requirements and the corresponding relationship between the leaf spring parabolic coefficient k and the leaf spring stiffness, the parabolic coefficient k and the leaf shape parameters of the primary leaf spring (1), the secondary leaf spring (2) and the tertiary leaf spring (3) are calculated respectively, which specifically includes the following steps: S31, preliminarily setting the parabolic coefficient k and leaf type parameters of each level of leaf springs, and calculating the rotation angle θ of each level of leaf springs; S32, calculating the deflection ω of the leaf springs at each level according to the calculated rotation angle θ of the leaf springs at each level; S33, according to the calculated deflection ω of the leaf springs at each level, calculate the stiffness of the leaf springs at each level respectively ; S34, the calculated stiffness Respectively with the target stiffness , , Compare and observe whether the deviation between the two is less than the specified value. If not, readjust the parabola k and the sheet type parameters and repeat steps S31-S34 until the stiffness is meet the requirements; S4. Calculate the leaf spring design stress based on the adjusted leaf spring parabola coefficient k and leaf shape parameters. ; S5. Calculate the impact stress of leaf springs using the energy conversion principle ; S6. Calculate the design stress and impact stress , check with the leaf spring design specification value, if it does not meet the requirements, readjust the leaf spring raw material thickness, end thickness parameters, repeat steps S31-S6, re-iterate and calculate the parabola coefficient k and leaf type parameters, and recalculate the design stress and impact stress , until the design requirements are met; S7. Calculate the leaf spring frequency deviation , see if it meets the requirements, if not, adjust the thickness of the leaf spring raw material and the end thickness parameters, repeat steps S31-S8, and iterate the calculation repeatedly until the design requirements are met; S8. Determine the installation dimensions of the center bolt, middle gasket, and end width according to customer requirements or leaf spring standard requirements, and draw the leaf spring assembly drawing; In step S31, the calculation formula of the leaf spring rotation angle θ is: θ= (IV) Among them, M is the bending moment of the corresponding section of the leaf spring, E is the elastic modulus of the material, I is the moment of inertia of the corresponding section of the leaf spring, and L is the effective length of the leaf spring. is the distance between the corresponding section and the center of the leaf spring, is the number of leaf springs, B is the width of the leaf spring, is the arc coefficient of the corresponding section, is the leaf spring thickness, is the load; When it is located in the middle straight section of the leaf spring, = thickness of raw material; When it is in the transition section of the leaf spring, = Raw material thickness - ( - middle straight length) × (raw material thickness - parabola starting point thickness) / transition section length; When located on the parabola segment of the leaf spring, =k ；（Ⅴ） Where, k is the parabola coefficient of the leaf spring; When located at the straight section at the end of the leaf spring, = end thickness.

2. The design method of a stepped structure three-level stiffness non-equal length automobile suspension leaf spring according to claim 1 is characterized in that: In step S2, the target stiffness of the primary leaf spring (1) is The calculation formula is: = （Ⅰ） Secondary leaf spring (2) target stiffness The calculation formula is: = （Ⅱ） Target stiffness of three-stage leaf spring (3) The calculation formula is: = （Ⅲ） in, is the target frequency deviation of the leaf spring, is the no-load load, is the load when the primary leaf spring (1) and the secondary leaf spring (2) act simultaneously, For full load, is the acceleration due to gravity.

3. The design method of a stepped structure three-level stiffness non-equal length automobile suspension leaf spring according to claim 1, characterized in that: In step S32, the calculation formula of the deflection ω is: ω= (VI) in, is the leaf spring angle.

4. The design method of a stepped structure three-level stiffness non-equal length automobile suspension leaf spring according to claim 1, characterized in that: In step S33, the stiffness The calculation formula is: （Ⅶ） in, is the load and ω is the deflection.

5. The design method of a stepped structure three-level stiffness non-equal length automobile suspension leaf spring according to claim 1, characterized in that: In step S4, the leaf spring design stress The calculation formula is: （Ⅷ） Where M is the bending moment of the corresponding section of the leaf spring, I is the moment of inertia of a certain section of the leaf spring, is the leaf spring thickness.

6. The design method of a stepped structure three-level stiffness non-equal length automobile suspension leaf spring according to claim 1, characterized in that: In step S5, the leaf spring impact stress The calculation formula is: （Ⅸ） Among them, M is the bending moment of the corresponding section of the leaf spring when it is impacted, I is the moment of inertia of a section of the leaf spring, is the leaf spring thickness.

7. The design method of a stepped structure three-level stiffness non-equal length automobile suspension leaf spring according to claim 1, characterized in that: In step S7, the leaf spring frequency The calculation formula is: = （Ⅹ） in, is the load, For stiffness.

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