Coil spring for spring suspension of freight car body

Abstract

FIELD: mechanical engineering.SUBSTANCE: coil spring of the spring suspension of a freight car bogie is made from a rod, the cross-section of which contains two smoothly connected sections without bending. The envelope of the first section is made in the form of a part of a circle, and the envelope of the second section is made in the form of a part of an oval. Both sections of the rod cross-section are located symmetrically relative to the longitudinal axis of the rod cross-section, passing through the most distant points of the rod cross-section. The radius of the oval's vertex, which is the section with the greatest curvature, is less than the radius of the first section. The area of the second section does not exceed the area of the first section of the rod cross-section. The spring coils are made with the first section of the rod located outside the spring and the second section inside the spring.EFFECT: increased reliability of the coil spring.4 cl, 8 dwg, 6 tbl

Description

[0001] The invention relates to springs for the spring suspension of a railway freight car bogie.

[0002] Public Patent No. CN 206299721 discloses a coil compression spring with a variable cross-section. The outer diameter of the spring is variable. At the ends of the spring, the outer diameter of the coils is smaller than the outer diameter of the coils in the center section.

[0003] The disadvantage of the spring known from patent No. CN 206299721 is its insufficient reliability when operating under loads due to the fact that the stresses arising from the loads are distributed unevenly across the cross-section of the rod.

[0004] From U.S. Patent No. 11821485 for the invention, a known coil spring is made from a wire rod with first and second ends. The wire rod includes a circular portion including a first circular cross-section perpendicular to the longitudinal direction of the wire rod, a rectangular portion including a second rectangular cross-section perpendicular to the longitudinal direction, and a portion with a variable cross-section formed between the circular portion and the rectangular portion of the wire rod. The cross-section of the portion with a variable cross-section changes from circular to rectangular from the circular portion to the rectangular portion. The end portion of the coil spring includes a rectangular portion. The width and thickness of the second cross-section are less than the diameter of the first cross-section. The area of ​​the second cross-section is less than the area of ​​a square inscribed in a circle with a diameter of the first cross-section.

[0005] The disadvantage of the spring known from US Patent No. 11821485 is its insufficient reliability when operating under loads due to the fact that the stresses arising from the loads are distributed unevenly across the cross-section of the rod.

[0006] The spring known from US Patent No. 11821485 is chosen as a prototype.

[0007] The technical problem solved by the proposed invention is to eliminate the shortcomings of analogues.

[0008] The technical result achieved by the invention consists in increasing the reliability of the coil spring.

[0009] The technical result is achieved due to the fact that in the coil spring of the spring suspension of the bogie of a freight car, made from a rod, the cross-section of which contains two smoothly without bending conjugated sections, the envelope of the first section is made in the form of a part of a circle, and the envelope of the second section is made in the form of a part of an oval, both sections of the cross-section of the rod are located symmetrically relative to the longitudinal axis of the cross-section of the rod, passing through the most distant from each other points of the cross-section of the rod, the radius of the top of the oval, which is the section with the greatest curvature, is less than the radius of the first section, the area of ​​the second section does not exceed the area of ​​the first section of the cross-section of the rod, the turns of the spring are made with the first section of the rod located outside the spring, and the second section inside the spring.

[0010] The envelope of the second section can be a part of an ellipse.

[0011] The radius of the oval top of the second section can be 0.65 - 0.85 of the radius of the first section.

[0012] The distance between the most distant points of the second section relative to the longitudinal axis at the junction with the first section of the rod cross-section can be 1.00 - 0.9 of the diameter of the first section.

[0013] The claimed invention is explained by figures.

[0014] Fig. 1 shows a circular cross-section of a spring rod and the stress distribution under loads on the spring.

[0015] Fig. 2 shows comparative cross-sectional shapes of a round rod and a rod of the claimed spring.

[0016] Fig. 3 shows a coil spring - an analogue with a round cross-section of the rod.

[0017] Fig. 4 shows a cross-section of a round rod of a spring - analogue.

[0018] Fig. 5 shows the claimed coil spring.

[0019] Fig. 6 shows a cross-section of the rod of the claimed spring.

[0020] Fig. 7 shows the control points of the spring - an analogue made of a rod with a round cross-section;

[0021] Fig. 8 shows the control points of the claimed spring.

[0022] Positions on figures:

[0023] 1 - the first section of the rod cross-section;

[0024] 2 - the second section of the rod cross-section;

[0025] 2.1 - the apex of the oval (the section with the greatest curvature);

[0026] 3 - longitudinal axis of the rod cross-section.

[0027] The claimed coil spring for the spring suspension of a freight car bogie is made of a rod, the cross-section of which contains two smoothly connected sections 1 and 2 without bending. The envelope of the first section 1 is made in the form of a part of a circle, and the envelope of the second section 2 is made in the form of a part of an oval. Both sections 1, 2 of the cross-section of the rod are located symmetrically with respect to the longitudinal axis 3 of the cross-section of the rod, passing through the most distant points of the cross-section of the rod. The radius R2 of the vertex of the oval 2.1, which is the section with the greatest curvature, is less than the radius R1 of the first section 1. The area of ​​the second section 2 does not exceed the area of ​​the first section 1 of the cross-section of the rod. The turns of the spring are made with the first section 1 of the rod located outside the spring, and the second section 2 inside the spring.

[0028] The envelope of the second section 2 may be a part of an ellipse.

[0029] The radius R2 of the vertex 2.1 of the oval of the second section can be 0.65 - 0.85 of the radius R1 of the first section 1.

[0030] The distance between the most distant points A and B relative to the longitudinal axis 3 (Fig. 2) of the second section 2 at the junction with the first section 1 of the rod cross-section can be 1.00 - 0.9 of the diameter of the first section 1.

[0031] Increasing the reliability and durability of freight car bogie spring suspensions is a pressing issue in the face of increasing loads and intensive operation. During operation, freight car bogie spring suspension springs are subject to both vertical loads (from the weight of the car and cargo) and horizontal (bending) loads (when negotiating curves and turns).

[0032] Within the torsion theory, a spring rod is considered a rod subjected to torsion. A key feature of spring calculations is the need to account for complex stress states.

[0033] Springs with a round rod cross-section are characterized by uneven stress distribution across the rod cross-section. Maximum stresses occur on the inner surface of the rod (point A, Fig. 1), where the summation of the shear stresses from the torque (τ) occurs. кр ) and shear force (τ ср ). The diagrams of the distribution of shear stresses for a circular cross-section of a helical spring are shown in Fig. 1.

[0034] The maximum stress on the inner fiber of a round rod is determined by the formula:

[0035]

[0036] where F1 is the spring force at maximum deformation, N;

[0037] D0 - average diameter of spring coil, mm;

[0038] d K - spring rod diameter, mm;

[0039] k is a coefficient that takes into account the curvature of the spring coil, which

[0040] is determined by the formula:

[0041]

[0042] where i is the spring index, equal to:

[0043]

[0044] Spring force at maximum deformation F1, N, is calculated using the formula:

[0045]

[0046] where F рд - spring force at working deformation (corresponds to the greatest forced displacement of the movable link in the mechanism), N;

[0047] δ - relative inertial gap of the spring.

[0048] From the shear stress diagrams shown in Fig. 1, it follows that the internal fibers of the spring experience higher stresses due to the fact that their length is shorter than the length of the external fibers, therefore, when the rod is torsion, the shear deformation of the internal fibers is greater than the deformation of the external fibers, and this difference will increase with a decrease in the spring index.

[0049] The following notations are used in Fig. 1:

[0050] - D ВН - inner diameter of the spring;

[0051] - D0- average spring diameter;

[0052] - d K - diameter of a rod with a round cross-section;

[0053] - τ кр - shear stresses due to torsion;

[0054] - τ ср - shear stresses caused by shear;

[0055] - τ сум - total shear stresses.

[0056] Analysis of coil springs revealed significant unevenness in the stress distribution within the material of coil springs (e.g., steel) made from round rod (Fig. 1). This unevenness is a consequence of the structural curvature of the coils, which leads to stress concentration on the inner surface of the spring, as well as the predominance of torsional shear stresses.

[0057] As a technical solution to this problem, a coil spring with a variable rod cross-section is proposed. The rod cross-section comprises two smoothly connected sections, 1 and 2, without any bending. The envelope of the first section 1 is formed as a partial circle, while the envelope of the second section 2 is formed as a partial oval.

[0058] It is known that an ellipse is a "regular" oval (source 1: Handbook of Higher Mathematics / M. Ya. Vygotsky. - Moscow: AST Publishing House, 2019 - 703 p., p. 42). From the same source 1 on p. 42, it is known that the proportions of an ellipse are strictly regulated, therefore figures based on an ellipse are easier to calculate.

[0059] From the theory of torsion of a beam with an oval (elliptical) cross-section, it is known that maximum stresses occur at points described by the ellipse's largest radius of curvature, while minimum stresses occur at points described by the smallest radius of curvature. Consequently, maximum stresses in a spring rod cross-section can be reduced by describing the surface of the rod forming the spring's inner diameter with a small radius, and the surface of the rod forming the spring's outer diameter with a large radius.

[0060] The curvature of a spring coil can have a significant impact on the stress distribution within the spring's cross-section. Fig. 2 shows a diagram of the relationship between radii R1 and R2 within the spring's cross-section, which helps reduce stress on the spring's internal fibers.

[0061] To compare the research results and evaluate the level of stress reduction, a cylindrical coil spring made of a round rod was selected for the bogie suspension (Fig. 3, Fig. 4). The spring's geometric parameters are listed in Table 1.

[0062] Table 1

[0063] Parameter Rod diameter, dK, mm Average spring diameter, D0, mm Working number of turns, np Total number of turns, n Height in free state, HCB, mm Meaning 23 119 6,6 8,1 265

[0064] Fig. 5, Fig. 6 show a general view and a sketch of the claimed spring with a variable cross-section of the rod, which is a combination of a part of a circle and a part of an oval.

[0065] The geometric parameters of the declared spring are given in Table 2.

[0066] Table 2

[0067] Parameter Radius of the first section of the rod, R1, mm Radius of the oval top of the second section of the rod, R2, mm Average spring diameter, D0, mm Working number of turns, np Total number of turns, n Height in free state, HCB, mm Meaning 20,7 8,3 119 6,6 8,1 265

[0068] The average diameter D0 of the claimed spring was determined along the axis passing along the line through the junction points of the first and second sections of the cross-section of the spring rod (Fig. 6).

[0069] Considering that the maximum stresses on the inner fiber of a spring coil made from a round rod are inversely proportional to the diameter of this coil, a comparison can be made using the equality of the cross-sectional areas of these springs.

[0070] The strength and stiffness of coil springs for both design variants were calculated. The calculations yielded the vertical and horizontal stiffness values ​​presented in Table 3, as well as the stresses in the spring control zones under design conditions according to GOST 33211-2014, presented in Table 4.

[0071] The stress control zones of the spring made of a round rod are shown in Fig. 7, and of the claimed spring - in Fig. 8.

[0072] Table 3

[0073] Name Horizontal stiffness, N / m Vertical stiffness, N / m Round bar spring 217620 253185 The declared spring 203780 252546

[0074] Table 4

[0075] Control zone number Stresses in control zones, MPa, according to design modes Allowable stresses, MPa Ia Iv Round bar spring 1 367 378 955,5 2 544 550 3 659 712 4 474 539 5 533 600 6 627 774 The declared spring 1 360 363 955,5 2 537 554 3 635 651 4 465 501 5 524 598 6 623 766

[0076] An assessment of the strength of the claimed spring showed that, in comparison with a spring made from a round rod, the stresses are reduced in all control zones, while on the inner side of the coil (the inner side of the rod), the stresses are reduced by 4% under the action of a vertical load (mode Ia) and by 9% under the combined action of a vertical and lateral load (mode Ib).

[0077] The spring safety factor was assessed using the fatigue safety factor in accordance with the requirements of GOST 32208-2013. Since GOST 32208-2013 does not provide methods for assessing shear stresses in spring coils with rod cross-sections other than circular, the safety factor was assessed using the fatigue safety factor using the finite element method.

[0078] The values ​​of shear stress are given in Table 5.

[0079] Table 5

[0080] Control zone number Shear stresses, MPa Round bar spring The declared spring 1 109 100 2 9 6 3 502 397 4 270 250 5 61 55 6 33 30

[0081] The results of calculating the safety factor for fatigue resistance of springs according to GOST 32208-2013 are given in Table 6

[0082] Table 6

[0083] Spring Fatigue resistance safety factor Round coil spring 1,135 The declared spring 1,245

[0084] The analysis of the spring strength by the fatigue safety factor showed that the minimum fatigue safety factor for a spring with a variable coil cross-section is 1.245, which exceeds the required standard value according to GOST 32208-2013.

[0085] Considering that the service life of structures according to the “Standards for the calculation and design of wagons, railways of the Ministry of Railways of 1520 mm gauge (non-self-propelled)”, M., GosNIIV-VNIIZhT, 1996, 319 p., as a rule, is inversely proportional to the fatigue safety factor to the power m (m is the fatigue curve index) and taking m = 4 (according to the specified source), it is possible to predict an increase in the service life of a spring with a variable coil cross-section in comparison with a spring with a round coil cross-section by 44%.

[0086] The conducted studies also showed that the resource characteristics of the claimed spring will be higher (comparative parameters are given in Tables 4 - 6) than those of a spring made from a rod with a round cross-section with the same outer and average diameters of the compared springs, as well as with the same number of working turns, with the following parameters (illustrated in Fig. 2):

[0087] - R1= 0.89 - 0.95 R К ;

[0088] - R2= 0.65 - 0.85 R1;

[0089] where:

[0090] R К - radius of the round rod of the spring - analogue.

[0091] When R1< 0.89 R К there will be a risk of reducing the vertical rigidity of the declared spring;

[0092] When R1> 0.95 R К - it is difficult to maintain the ratio of diameters when manufacturing a spring with a variable coil cross-section.

[0093] When R2 < 0.65 R1, the manufacturing complexity of the spring increases, as the connection between the first and second cross-sectional sections of the rod from which the spring is made must be smooth, without kinks, with the outer and middle diameters specified in the design documentation. A lack of smoothness and the presence of kinks will lead to stress concentration points and a reduction in the spring's strength characteristics.

[0094] At R2> 0.85 R1-, the spring's safety margin will be slightly increased compared to a similar spring made from a round rod. Their strength characteristics will be similar.

[0095] The distance L between the most distant points of the second section 2 relative to the longitudinal axis 3 at the junction with the first section 1 of the rod cross-section, equal to 1.00 - 0.9 of the diameter of the first section 1, is selected to ensure a smooth, kinked junction of the rod cross-sectional sections, as well as to ensure the average diameter of the spring, its index, based on the requirements of the design documentation. It is obvious that the line passing through the junction points of the first and second sections of the spring rod cross-section will not pass along the diameter of the first section of the coil; the length of this line within the rod cross-section will be less than the diameter of the first section of the rod cross-section from which the claimed spring is made.

[0096] Thus, the claimed invention ensures a reduction in stress on the inner surface of the coil and, due to this, an increase in the resource of the coil spring of the spring suspension of the freight car bogie, and, consequently, an increase in the reliability of the spring is ensured.

Claims

1. A coil spring for suspension of a freight car bogie, made from a rod, the cross-section of which contains two smoothly connected sections without bending, the envelope of the first section is made in the form of a part of a circle, and the envelope of the second section is made in the form of a part of an oval, both sections of the cross-section of the rod are located symmetrically relative to the longitudinal axis of the cross-section of the rod, passing through the most distant from each other points of the cross-section of the rod, the radius of the top of the oval, which is the section with the greatest curvature, is less than the radius of the first section, the area of ​​the second section does not exceed the area of ​​the first section of the cross-section of the rod, the turns of the spring are made with the first section of the rod located outside the spring, and the second section inside the spring.

2. A spring according to claim 1, characterized in that the envelope of the second section is part of an ellipse.

3. A spring according to paragraph 1, characterized in that the radius of the top of the oval of the second section is 0.65-0.85 of the radius of the circle of the first section.

4. A spring according to claim 1, characterized in that the distance between the most distant points of the second section relative to the longitudinal axis at the junction with the first section of the cross-section of the rod is 1.00-0.9 of the diameter of the first section.

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