A design method for the camshaft tube of a rear-mounted compression garbage truck

Abstract

A design method for a camshaft tube of a rear-mounted compression garbage truck, characterized in that it includes the following steps: establishing a 3D model of a real vehicle, measuring the positions of relevant components and stress points of the shaft tube on the 3D model; determining the maximum stress posture of the camshaft tube and establishing a mechanical model according to the motion posture of the flip mechanism in the 3D model when two garbage bins are hung and one garbage bin is hung for loading, and determining the most dangerous working condition according to the stress condition, and determining the theoretical cross-sectional size of the camshaft tube with its allowable stiffness and allowable deflection as constraints; rounding the obtained cross-sectional size to the nearest integer, expanding the cross-sectional size within a range of 5% after rounding, selecting a reasonable manufacturing size within the range according to relevant national standards, and ensuring that the camshaft tube has a certain safety margin; finally, performing strength verification on the shaft tube to confirm whether it is qualified. The present invention is easy to operate, has a short test cycle, and can effectively reduce the operating cost and manufacturing cost of an enterprise.

Description

Technical Field

[0001] The invention relates to the field of compression type garbage truck production, and in particular to a design method for a camshaft tube of a rear-mounted compression type garbage truck. Background Art

[0002] With the continuous advancement of science and technology, rear-loading compression garbage trucks have become the only choice for urban garbage transportation. According to the feedback of existing products in the market, when the flip mechanism is loading, the garbage can will generate bending moment and torque on the camshaft tube of the flip mechanism. The camshaft tube of the garbage truck often undergoes large deformation during the warranty period, resulting in plastic failure. If the camshaft tube is frequently replaced during the warranty period, it will affect the reputation of the company and affect the company's economic benefits. The fundamental reason for the deformation of the camshaft tube is the influence of the bending moment and torque generated by the garbage can on the camshaft tube of the flip mechanism during the lifting and unloading process. Only by ensuring that the service life of the camshaft tube of the flip mechanism meets the use requirements can the working efficiency of the flip mechanism unloading be guaranteed for a long time. In addition, the cross-sectional size of the camshaft tube is an important factor affecting its stiffness. How to choose a reasonable cross-sectional size has always been a difficult problem in the industry. Enterprises can only preliminarily select the cross-sectional size through engineering practice experience, and then trial-produce samples for multiple tests to finally determine the cross-sectional size of the camshaft tube. This method is time-consuming and labor-intensive and cannot bring economic benefits. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a design method for a camshaft tube of a rear-mounted compression garbage truck which is easy to operate, has a short test cycle, and can effectively reduce the operating cost and manufacturing cost of the enterprise.

[0004] To achieve the above objectives, the technical solution of the present invention is: a design method for a camshaft tube of a rear-mounted compression garbage truck, characterized in that it includes the following steps:

[0005] S1 Establish a 3D model of the real vehicle based on the garbage truck prototype, and measure the positions of the relevant components and the stress points of the axle tube on the 3D model;

[0006] S2 According to the motion posture of the flip mechanism in the 3D model when two trash cans are fully loaded, the maximum force posture of the camshaft tube is determined and a mechanical model is established;

[0007] S3 In the mechanical model established in step S2, for the working condition where the turning frame is fully loaded with two trash cans, the allowable stiffness and allowable deflection of the shaft are determined by looking up the table according to the stress condition of the shaft and the transmission mode of the shaft, and the theoretical cross-sectional size of the camshaft tube is determined with the allowable stiffness and allowable deflection as constraint conditions;

[0008] S4 According to the motion posture of the flip mechanism in the 3D model when only one garbage can is hung for loading, the maximum force posture of the camshaft tube is determined and a mechanical model is established, and it is compared with the force of the working condition in step S2 to determine the most dangerous working condition when the garbage truck is loading, and the calculated cross-sectional size is used as the final result;

[0009] S5: rounding the cross-sectional dimensions obtained in step S4 to the nearest integer, and then enlarging the cross-sectional dimensions within a range of 2 to 10% after rounding, selecting a reasonable manufacturing dimension within the range according to relevant national standards, and ensuring that a certain safety margin is left for the camshaft tube;

[0010] S6 Calculate the torque on the camshaft tube, perform strength check on the camshaft tube in the combined bending and torsion state according to the third strength theory, evaluate whether the strength of the tube meets the requirements, and then perform static strength check on the tube to evaluate whether the camshaft tube's resistance to plastic deformation is qualified.

[0011] In the step S1, the positions of the force points of the 7-shaped arm, the pulling arm, the turning frame and the axle tube are measured on the 3D model.

[0012] The maximum force posture in steps S2 and S4 is the posture when the flipping mechanism lifts the trash can counterclockwise to the maximum height.

[0013] In the step S5, the cross-sectional size is enlarged within a range of 5% after rounding, and a reasonable manufacturing size is selected within the range according to the national standard for seamless steel pipes GB / T 17395-2008.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The design method of the present invention is rigorous and meticulous, and is easy to operate. By establishing a mechanical model of the camshaft tube, there is no need for field testing in a working environment. The cross-sectional size of the camshaft tube of the flip mechanism can be quickly determined through calculation and reasoning, avoiding the time loss and material loss problems in traditional design methods, and reducing the company's operating costs and production costs.

[0016] 2. The present invention can design a reasonable cross-sectional size of the camshaft tube according to different vehicle models, effectively guaranteeing the anti-plastic deformation capability of the camshaft tube within the warranty period, thereby improving the economic benefits for the enterprise. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the design method of the present invention.

[0018] Figure 2 Schematic diagram of various stress points on the camshaft tube.

[0019] Figure 3 Schematic diagram of the mechanical model of the camshaft tube when the flipping mechanism is fully loaded with two trash cans.

[0020] Figure 4 Bending moment diagram and shear force diagram of the camshaft tube when the tipping mechanism is fully loaded with two trash cans.

[0021] Figure 5 Schematic diagram of a cantilever beam model with a concentrated load acting on the free end.

[0022] Figure 6 Schematic diagram of the mechanical model of the camshaft tube when only one trash can is hung on the flipping mechanism for loading.

[0023] Figure 7 Top and side views of the camshaft tube when loading the tipping mechanism with two full trash cans. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0025] A design method for a camshaft tube for a rear-mounted compression garbage truck, the flow chart of which can be found in Figure 1 , including the following steps:

[0026] S1 Establish a 3D model of the real vehicle based on the garbage truck prototype, and measure the positions of the force points of the 7-shaped arm, the pulling arm, the turning frame and the axle tube on the 3D model;

[0027] S2 According to the motion posture of the flip mechanism in the 3D model when two trash cans are fully loaded, the maximum force posture of the camshaft tube is determined and a mechanical model is established;

[0028] S3 In the mechanical model established in step S2, for the working condition where the turning frame is fully loaded with two trash cans, the allowable stiffness and allowable deflection of the shaft are determined by looking up the table according to the stress condition of the shaft and the transmission mode of the shaft, and the theoretical cross-sectional size of the camshaft tube is determined with the allowable stiffness and allowable deflection as constraint conditions;

[0029] S4 According to the motion posture of the flip mechanism in the 3D model when only one garbage can is hung for loading, the maximum force posture of the camshaft tube is determined and a mechanical model is established, and it is compared with the force of the working condition in step S2 to determine the most dangerous working condition when the garbage truck is loading, and the calculated cross-sectional size is used as the final result;

[0030] S5 rounding the cross-sectional dimensions obtained in step S4 to the nearest integer, and then enlarging the cross-sectional dimensions within a range of 5% after rounding, selecting a reasonable manufacturing dimension within the range according to the national standard for seamless steel pipes GB / T 17395-2008, and ensuring that a certain safety margin is left for the camshaft tube;

[0031] S6 Calculate the torque on the camshaft tube, perform strength check on the camshaft tube in the combined bending and torsion state according to the third strength theory, evaluate whether the strength of the tube meets the requirements, and then perform static strength check on the tube to evaluate whether the camshaft tube's resistance to plastic deformation is qualified.

[0032] In step S1, the positions of various stress points on the camshaft tube are measured, such as Figure 2 shown.

[0033] in,

[0034] Points A and A' represent the stress points of the 7-shaped arms at both ends and the camshaft tube;

[0035] Points B and B' represent the stress points of the trailing arms at both ends and the camshaft tube;

[0036] Points C and C' represent the stress points of the two ends of the flip frame and the camshaft tube;

[0037] Points D and D' represent the stress points between the trash can and the camshaft tube;

[0038] Point E is the midpoint of the camshaft tube;

[0039] Specifically, in step S2, when the turnover mechanism lifts the trash can counterclockwise to the maximum height, the camshaft tube is in the maximum force position under this condition. Assuming that the gravity on one side of the turnover frame is G1, and the gravity of a single trash can when fully loaded is G2; then the force on points C and C' is G1, and the force on points D and D' is G2. The mechanical model is as follows: Figure 3 As shown, the circular force on point A (A') is F , can be decomposed into the horizontal direction (x) and the vertical direction (y):

[0040] (1)

[0041] Specifically, in step S3, if Figure 4 As shown in the figure, the bending moment diagram and shear force diagram of the camshaft tube in the horizontal direction (x) and vertical direction (y) are made when the flip rack is hung with two trash cans. From the bending moment diagram in the vertical direction (y), it can be seen that the maximum bending moment and the maximum shear stress are:

[0042] (2)

[0043] From the horizontal (x) bending moment diagram, we can know that the maximum bending moment is:

[0044] (3)

[0045] Since the force component in the vertical direction (y) is much larger than the force component in the horizontal direction (x), only the bending moment in the vertical direction is considered.

[0046] In the maximum force position, the camshaft tube is mainly subjected to bending moment, the BB' segment can be equivalent to a simply supported beam, and the B'A' segment and the BA segment are equivalent to cantilever beams. It is known that there is the following relationship between the curvature of the deflection curve within the elastic range at a point and the bending moment and bending stiffness on the cross section at this point:

[0047] (4)

[0048] Where k is the curvature, EI is the bending stiffness of the cross section, ρ and M are functions of the cross section position x, which can be expressed as ρ=ρ(x) and M=M(x).

[0049] It is known that the curvature formula of an arc at a certain point is:

[0050] (5)

[0051] Combining (4) and (5) we get:

[0052] (6)

[0053] In the case of small deformation, , the above formula will become:

[0054] (7)

[0055] This equation is called the small deflection differential equation, where the sign is related to the coordinate orientation. If the coordinate system is such that w is downward and x is to the right, the sign is negative.

[0056] For a beam of uniform cross-section, the bending moment equation M(x) is obtained and substituted into equation (7). Two indefinite integrals are performed on x to obtain the rotation angle and deflection equations of the beam:

[0057] (8)

[0058] (9)

[0059] Where θ is the rotation angle, w is the deflection, and C and D are integration constants.

[0060] The above derived calculation formula for the angular deflection is based on two calculation assumptions: 1) linear elasticity assumption, 2) small deformation assumption. Because the AB section and the A'B' section of the shaft tube are completely symmetrical, the bending deformation of the shaft tube can be divided into the AB section and the BB' section for analysis. For the stress condition of the AB section, it can be equivalent to Figure 5 Cantilever beam model. From the table, we can know the rotation angle and deflection calculation formula of this model:

[0061] (10)

[0062] For the force of the BB' segment, due to the linear elastic assumption, the symmetric case shows that the deflection and rotation of the beam under the action of two loads (G1, G2) are equal to the sum of the deflection and rotation of the two loads. When G1 and G2 act separately, it can also be equivalent to Figure 5 Cantilever beam model. When G1 acts:

[0063] (11)

[0064] G2 works when:

[0065] (12)

[0066] Combination Figure 4 From the analysis of equations (10), (11) and (12), it can be seen that the rotation angle and deflection of the camshaft tube caused by the AB segment are much smaller than those of the BB' segment, so the bending deformation caused by the AB segment can be ignored. In the BB' segment, the bending deformation of the camshaft tube is mainly caused by G2, and the bending deformation caused by G1 can also be ignored.

[0067] The section moment of inertia of the hollow shaft is:

[0068] (13)

[0069] In engineering practice, the camshaft tube of the flip mechanism generally takes the wall thickness , Combining equations (12) and (13) we can get:

[0070] (14)

[0071] (15)

[0072] Where:

[0073] F —Circumferential force generated by the cylinder;

[0074] E —Elastic modulus of the steel used;

[0075] θ —Circumferential force F Angle with vertical direction;

[0076] ψ, ω—permissible rotation angle and permissible deflection of the camshaft tube;

[0077] When the rotation angle and deflection of the camshaft tube meet the requirements at the same time, the final result should take the maximum value in equations (14) and (15).

[0078] Specifically, in step S4, when the turnover mechanism lifts the trash can counterclockwise to the maximum height, the camshaft tube is in the maximum force position under this condition. Assume that the gravity on one side of the turnover frame is G1, and the gravity on a single trash can when fully loaded is G2; then the force on point C, C' is G, and the force on point D or D' is G2, such as Figure 6 shown.

[0079] Figure 6 (a) shows the stress condition of the trash can hung on one side of the flip frame (taking the left side as an example). Since the camshaft tube is a symmetrical structure, the stress condition of the trash can hung on the right side can be obtained in the same way, and the direction, magnitude and stress point of each force are consistent with those on the left side.

[0080] From the knowledge of structural mechanics, we know that in a symmetrical structure, forces in the same position and direction can be superimposed. Figure 6 The mechanical model of (a) can be obtained by Figure 6 (b) and (c) are superimposed. Figure 6 (b) and Figure 3 From the force model of (mechanical model of two trash cans hanging), we can know that Figure 6 (b) The forces at points C, C'D, and D' are Figure 3 and the direction of the force is the same. Figure 6 (c) The force direction at point D' is Figure 6 (b) Point D' is opposite, so Figure 6 (c) The total vertical downward pressure on the camshaft tube is less than Figure 6 (c). Figure 6 The bending deformation of the camshaft tube caused by the mechanical model in (c) is less than Figure 6 (b). In summary, the most dangerous working condition is when the tipping rack is hung with two fully loaded trash cans.

[0081] Specifically, in step S5, the calculated dimensions in step S4 are rounded, and after rounding, the cross-sectional dimensions are enlarged within a range of 5% according to the national standard for seamless steel pipes GB / T 17395-2008, and a reasonable manufacturing dimension within the range is selected to ensure that a certain safety margin is left for the camshaft tube.

[0082] Specifically, in step S6, when the force is at its maximum, the gravity G2 of the trash can will also generate torque on the camshaft tube, such as Figure 7 As shown, the torque is:

[0083] (16)

[0084] The deformation coordination equation when the circular shaft is torsion is known to be:

[0085] (17)

[0086] In the formula, is the relative torsion angle per unit length, ρ is the distance from any point of the circular shaft section to the axis, and γ(ρ) is the shear strain.

[0087] It is known that within the elastic range, Hooke's law for isotropic shear materials is:

[0088] (18)

[0089] Where G is the shear modulus.

[0090] Substituting (17) into (18), we obtain:

[0091] (19)

[0092] The static equation for calculating the moment of cross section is:

[0093] (20)

[0094] Substitute (19) into (20) and integrate to obtain:

[0095] (twenty one)

[0096] For a circular shaft subjected to torque at both ends, the relative torsion angle ψ of the cross sections at both ends is:

[0097] (twenty two)

[0098] I p is the polar moment of inertia of the circular section about its center. For a hollow circular shaft with inner and outer diameters d and D, .

[0099] After the bending moment and torque of the shaft are known, the combined bending and torsion strength verification calculation can be performed for certain dangerous sections. According to the third strength theory, the calculated stress is:

[0100] (twenty three)

[0101] Usually, the bending stress σ generated by the bending moment is a symmetrical cyclic variable stress, and the torsional shear stress τ generated by the torque is often not a symmetrical cyclic variable stress. In order to consider the different cyclic characteristics of the two, the conversion coefficient α is introduced, and the calculated stress is:

[0102] (twenty four)

[0103] In the formula, when the torsional shear stress τ is a static stress, α=0.3; when the torsional shear stress τ is a pulsating cyclically variable stress, α=0.6; if the torsional shear stress τ is a symmetrical cyclically variable stress, α=1.

[0104] Bending stress calculation formula The calculation formula of torsional shear stress is: For a hollow circular shaft with inner and outer diameters d and D, ;in Substituting into equation (24), the combined bending and torsion strength condition is:

[0105] (25)

[0106] In the formula, σ ca —Calculated stress of the shaft, MPa;

[0107] M —bending moment on the shaft, N·mm;

[0108] T —Torque on the shaft, N·mm;

[0109] W —Bending section coefficient of the shaft, mm 3 ;

[0110] [ σ -1 ]—Permissible bending stress of the shaft during symmetrical cyclic variable stress, MPa;

[0111] The purpose of static strength check is to evaluate the shaft's resistance to plastic deformation. The conditions for static strength check are:

[0112] (26)

[0113] In the formula, S Sca —Calculation safety factor of static strength of dangerous sections;

[0114] S Sσ —Safety factor when only bending moment and axial force are considered;

[0115] S Sτ —Safety factor when only torque is considered;

[0116] S S —Design safety factor based on yield strength. S S =1.2~1.4, used for high plasticity materials

[0117] σ s / σ b ≤0.6 steel shaft; S S =1.2~1.4(σ s / σ b =0.6~0.8) for steel shafts made of medium plastic materials; SS =1.8~2, used for steel shafts made of low plastic materials.

[0118] in,

[0119] (27)

[0120] (28)

[0121] In the formula, σ s , τ s —Bending and torsional yield limits of materials, MPa; where τ s =(0.55~0.62)σ s

[0122] M max、 T max —The maximum bending moment and maximum torque on the dangerous section of the shaft, N·mm;

[0123] F max —The maximum axial force on the dangerous section of the shaft, N;

[0124] A—area of ​​dangerous section of shaft, mm 2 .

[0125] Taking a 25-cubic-meter garbage truck as an example, according to the density of garbage ρ=488.85kg / m 3 And the volume of the trash can is L=240L, so the mass of the trash in each operation is 235kg, and the acceleration of gravity is g=10m / s 2 . And it was measured that l1=130mm, l2=162mm, l3=572mm, l4=740mm, l5=572mm, l6=162mm, l7=130mm, G1=450N, G2=2350N, θ=36°, L=50mm.

[0126] In addition, the material used for the camshaft tube is 20 steel, whose elastic modulus E=206GPa, shear modulus G=77.5GPa, bending limit σ s =240MPa, torsional yield limit τ s =144MPa.

[0127] The torque tester measures the circumferential force when the cylinder piston rod is fully extended. F =2268N. Substituting into (1) we get F Ay =1837N.

[0128] According to the relevant design manual, the allowable rotation angle of the shaft that mainly bears radial force is [ψ] / rad=0.005. For the shaft that only bears static load and is not used for transmission, [ω] / m=0.003 l , l is the span between the two supporting points of the axis. Then [ω]=0.0066m.

[0129] Substituting the above data into equations (14) and (15), we can obtain:

[0130] D max =58.97mm, d max =38.97mm

[0131] After rounding, take D=59mm, d=39mm. Check the national standard for seamless steel pipes GB / T 17395-2008 and choose the manufacturing dimensions of D=60mm, d=40mm.

[0132] For the calculation of the torque of the shaft tube, substituting the data into formula (16), we can get T D =117.5 N m. For the combined bending and torsion strength check of the shaft tube, Figure 4 From the bending moment diagram and shear force diagram, it can be seen that the maximum bending moment and maximum shear stress both appear in the BB' segment. From (2), the maximum bending moment M D =M3=2092.6 N m, maximum shear stress F Smax =F S3 =2800N. The bending stress calculation formula is σ=M / w, and the torsional shear stress calculation formula is τ=T / W T We calculated σ = 9.87 MPa, τ = 0.35 MPa, and substituted the conversion coefficient α = 0.3 into (24) to obtain σ ca =9.87MPa. From the calculation results, it can be seen that the torsional shear stress can be ignored.

[0133] Take the safety factor S S =1.5, allowable bending stress , obviously ca <[σ -1 ], so the combined bending and torsion strength check of the shaft tube meets the requirements.

[0134] For the static strength check of the shaft tube, S can be calculated from equations (27) and (28): Sσ =20.6, substituting into (26) to obtain S Sca =20.6. According to the relevant design manual, the tensile strength of 20 steel is b =410MPa, yield strength σ s =240410MPa, so , that is, S S=1.2~1.4. Obviously S Sca =20.6>S S =1.2~1.4, so the static strength check of the shaft tube meets the requirements, that is, the ability to resist plastic deformation meets the standards.

Claims

1. A design method for a camshaft tube of a rear-mounted compression garbage truck, characterized in that: The following steps are involved: S1 Establish a 3D model of the real vehicle based on the garbage truck prototype, and measure the positions of the force points of the 7-shaped arm, the pulling arm, the turning frame and the axle tube on the 3D model; S2 According to the motion posture of the flip mechanism in the 3D model when two trash cans are fully loaded, the maximum force posture of the camshaft tube is determined and a mechanical model is established; S3 In the mechanical model established in step S2, for the working condition where the turning frame is fully loaded with two trash cans, the allowable stiffness and allowable deflection of the shaft are determined by looking up the table according to the stress condition of the shaft and the transmission mode of the shaft, and the theoretical cross-sectional size of the camshaft tube is determined with the allowable stiffness and allowable deflection as constraint conditions; S4 According to the motion posture of the flip mechanism in the 3D model when only one garbage can is hung for loading, the maximum force posture of the camshaft tube is determined and a mechanical model is established, and it is compared with the force of the working condition in step S2 to determine the most dangerous working condition when the garbage truck is loading, and the calculated cross-sectional size is used as the final result; S5 rounding the cross-sectional dimensions obtained in step S4 to the nearest integer, enlarging the cross-sectional dimensions within a range of 2 to 10% after rounding, and then selecting a reasonable manufacturing dimension within the range according to the national standard for seamless steel pipes GB / T 17395-2008 to ensure that a certain safety margin is left for the camshaft tube; S6 Calculate the torque on the camshaft tube, perform strength check on the camshaft tube in the combined bending and torsion state according to the third strength theory, evaluate whether the strength of the tube meets the requirements, and then perform static strength check on the tube to evaluate whether the camshaft tube's resistance to plastic deformation is qualified.

2. The method for designing a camshaft tube for a rear-mounted compression garbage truck according to claim 1, characterized in that: The maximum force posture in steps S2 and S4 is the posture when the flipping mechanism lifts the trash can counterclockwise to the maximum height.

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