Landing gear sled pull rod device and design method thereof

Abstract

The invention provides an undercarriage sled pull rod device, which belongs to the technical field of helicopter undercarriage design, and comprises an outer cylinder, a piston rod, a spring and a limiting joint, the outer cylinder is arranged on an undercarriage buffer, the piston rod is arranged on an undercarriage sled, and one end of the piston rod extends into an inner hole of the outer cylinder; the limiting connector is arranged at the joint of the outer cylinder and the piston rod, the limiting connector, the inner wall of the outer cylinder and the outer wall of the piston rod jointly form a closed space, and the spring is connected to the outer side of a piston rod body in a sleeving mode and located in the closed space. The purpose of keeping the posture of the helicopter sled can be achieved; meanwhile, due to the design of the pull rod device, the sleigh can be always kept in an upwarp posture, so that the sleigh cannot be inserted into accumulated snow when the helicopter wears snow or slides, and the helicopter can smoothly slide to the position above the accumulated snow.

Description

Technical Field

[0001] The invention belongs to the technical field of helicopter landing gear design, and in particular relates to a landing gear sled pull rod device and a design method thereof. Background Art

[0002] In extremely cold environments, most landing and take-off sites are covered with ice and snow. Helicopters taking off and landing on snowy ground can easily suffer from excessive wheel pressure, which can cause the landing gear to sink, making it impossible to take off and land safely. At the same time, when a helicopter is parked on a snowy road, its wheels sink and it cannot move normally.

[0003] Therefore, it is necessary to design a helicopter landing gear sled device to solve the problem that the traditional helicopter landing gear cannot take off or land on ice, snow, mud and other low-carrying grounds, and at the same time enable the helicopter to move on the snowy road surface to improve the helicopter's adaptability in different complex environments. For the design of the sled device, a spring rope is usually used to pull the sled at the front and back ends to ensure the horizontal position of the sled. This method has the disadvantages of easy aging of the spring rope, insufficient safety and poor reliability. Summary of the invention

[0004] In order to solve the technical problems of the sled device in the prior art that the spring rope is easy to age, the safety is insufficient and the reliability is poor, the present invention provides a pull rod device and a design method that can effectively limit the sled, so as to achieve the purpose of maintaining the posture of the helicopter sled; at the same time, the design of the pull rod device can keep the sled in an upward posture, which is beneficial for the helicopter to not be inserted into the snow when the helicopter lands on the snow or slides, and the helicopter can slide smoothly above the snow. The technical solution is as follows:

[0005] In a first aspect, a landing gear sled pull rod device is provided, comprising: an outer tube, a piston rod, a spring, and a limit joint;

[0006] The outer tube is arranged on the landing gear buffer, the piston rod is arranged on the landing gear sled, and one end of the piston rod extends into the inner hole of the outer tube; the limit joint is arranged at the connection between the outer tube and the piston rod, the limit joint, the inner wall of the outer tube, and the outer wall of the piston rod jointly form a closed space, and the spring is sleeved on the outside of the piston rod body and is located in the closed space.

[0007] Furthermore, the device also includes: an upper mounting shaft, a lower mounting bolt, a lower threaded joint, and a spherical bearing.

[0008] The lower threaded joint is arranged on the landing gear sled, and the end of the piston rod away from the outer tube 1 is provided with a threaded section threadedly connected to the lower threaded joint;

[0009] The spherical bearing is installed in the ear piece of the lower threaded joint, and the lower mounting bolt is installed in the inner hole of the spherical bearing;

[0010] The upper mounting shaft is connected to the steel cable and is installed in two ears at one end of the outer tube away from the piston rod through a nut. A support sleeve is arranged between the upper mounting shaft and the ear. The length of the support sleeve is greater than h, h=(LM) / 2, where L is the outer diameter of the outer tube and M is the span of the two ears. This can prevent the upper mounting shaft from moving up and down along the axial direction and prevent the steel cable from colliding with the outer tube.

[0011] Furthermore, the device also includes: a limiting bolt, which passes through the outer tube and the limiting joint in sequence.

[0012] Optionally, there are three limiting bolts 4, which are evenly distributed around the outer cylinder; an arc-shaped washer is provided between the limiting bolt and the outer cylinder, and the limiting bolt is kept in contact with the outer cylindrical surface of the outer cylinder by the arc-shaped washer.

[0013] Furthermore, the inner wall of the outer cylinder is coated with grease to enable the spring to slide smoothly in the closed space and avoid jamming and severe wear.

[0014] In a second aspect, a design method for a landing gear sled pull rod device according to any one of the first aspects is provided.

[0015] The design process of the spring is as follows:

[0016] Determine the maximum spring deformation f1 = H0-H1, and the minimum spring deformation f2 = H0-H2, where H1 is the minimum spring length, H2 is the maximum spring length, and H0 is the free length of the spring;

[0017] Determine the outer diameter D1 of the spring according to the cross-sectional dimensions of the outer tube and determine the spring diameter d, and obtain the center diameter D2 of the spring;

[0018] According to the spring diameter d, the spring pitch t is determined by the relationship t>d;

[0019] Determine the effective working number of the spring n = (H0-2d) / t;

[0020] Determine the total number of spring turns n0=n+2 according to the effective working number of turns n;

[0021] Determine the maximum working load of the spring P1 = (f1*G*d 4 ) / (8n0*D2 3 ), and the minimum working load of the spring P2 = (f2*G*d 4 ) / (8n0*D2 3 ), where G is the shear modulus of the spring material;

[0022] Determine the spring stiffness K = (P1-P2) / (f1-f2);

[0023] Determine the spring pitch ratio C = D2 / d; and the curvature coefficient M = (4*C - 1) / (4*C - 4) + 0.615 / C; and thus obtain the allowable load of the spring P = (3.14*d 3 *G) / (8*D2*M);

[0024] Determine the single - loop deformation amount f3 of the spring under the maximum working load, f3 = f1 / n0, and the single - loop deformation amount f4 of the spring under the minimum working load, f4 = f2 / n0;

[0025] The design process of the outer cylinder, piston rod and limit joint is as follows:

[0026] According to the flight state of the helicopter landing gear, determine the maximum length value S1 of the distance between the outer cylinder installation point and the piston rod installation point; according to the parking state of the helicopter landing gear, determine the minimum length value S2 of the distance between the outer cylinder installation point and the piston rod joint installation point; S1, S2, the structural length S3 of the outer cylinder, and the structural length S4 of the piston rod satisfy the constraint conditions: S3 < S2; S4 < S2; S1 < S3 + S4;

[0027] According to the strength calculation results, determine that the outer diameter O3 of the piston rod body and the inner diameter O4 of the limit joint satisfy the relationship: O3 + 0.02 < O4 < O3 + 0.05; the outer diameter O5 of the limit joint satisfies the relationship: O1 - 0.05 < O5 < O1 - 0.02, where O1 is the inner diameter of the inner cavity of the outer cylinder.

[0028] Such a design can ensure the fitting relationship between the outer cylinder 1, the limit joint 12 and the piston rod 2.

[0029] Furthermore, the method further includes:

[0030] Verify the design parameters of the spring. If P2 < P1 < P; f4 < f3 < t - d; n0 < (H1 / d), then it passes the verification.

[0031] Optionally, the minimum spring length H1, the maximum spring length H2, and the spring free - state length H0 are determined according to the change amount of the buffer length of the helicopter landing gear after landing and taking off.

[0032] The beneficial effects of the present invention are at least as follows:

[0033] 1. The pull - rod device elongates and reversely compresses the spring, so that the landing gear sled always has a clockwise moment acting on it, preventing the sled from inserting into the snow track surface when the helicopter lands on the snow and slides;

[0034] 2. There is a limit bolt perpendicular to the outer cylinder cylindrical surface at the joint of the outer cylinder and the piston rod, and the limit bolt is installed on the outer cylinder cylindrical surface through an arc washer, so that the outer cylinder and the limit joint form a closed cavity, and the end of the piston rod can move in the formed closed cavity without coming out;

[0035] 3. The spring design method can reasonably determine the spring parameters so that the spring has a designable spring force corresponding to different length positions of the pull rod;

[0036] 4. The installation position of the lower threaded joint can be fine-tuned by screwing the thread length of the lower threaded joint and the piston rod body, which is convenient for assembly;

[0037] 5. The spring pull rod has the function of shock absorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram of a landing gear sled pull rod device provided by an embodiment of the present invention;

[0039] Figure 2 A cross-sectional view of a landing gear sled pull rod device provided by an embodiment of the present invention;

[0040] Figure 3 This is a cross-sectional view of the device taken along line AA provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below through specific implementation modes and drawings.

[0042] An embodiment of the present invention provides a landing gear sled pull rod device, see Figure 1 , including: an outer tube 1, a piston rod 2, a spring 9, and a limit joint 12;

[0043] The outer tube 1 is arranged on the landing gear buffer, the piston rod 2 is arranged on the landing gear sled, and one end of the piston rod 2 extends into the inner hole of the outer tube 1; the limit joint 12 is arranged at the connection between the outer tube 1 and the piston rod 2, and the limit joint 12, the inner wall of the outer tube 1, and the outer wall of the piston rod 2 jointly form a closed space, and the spring 9 is sleeved on the outside of the rod body of the piston rod 2 and is located in the closed space.

[0044] In another embodiment, see Figure 2 The device also includes: an upper mounting shaft 5, a lower mounting bolt 8, a lower threaded joint 3, and a spherical bearing 10.

[0045] The lower threaded joint 3 is arranged on the landing gear sled, and the end of the piston rod 2 away from the outer tube 1 is provided with a threaded section threadedly connected to the lower threaded joint 3;

[0046] The spherical bearing 10 is installed in the ear piece of the lower threaded joint 3, and the lower mounting bolt 8 is installed in the inner hole of the spherical bearing 10;

[0047] The upper mounting shaft 5 is installed in the two ears at one end of the outer cylinder 1 away from the piston rod 2 through a nut 7; the upper mounting shaft 5 is connected to the steel cable, and a support sleeve 6 is arranged between the upper mounting shaft 5 and the ear. The length of the support sleeve 6 is greater than h, h = (LM) / 2, L is the outer diameter of the outer cylinder 1, and M is the span of the two ears. This can prevent the upper mounting shaft 5 from moving up and down along the axial direction and prevent the steel cable from colliding with the outer cylinder 1.

[0048] In another embodiment, see Figure 2 The inner wall of the outer cylinder 1 can be coated with grease to enable the spring 9 to slide smoothly in the closed space to avoid jamming and severe wear.

[0049] See also Figure 3 The device further comprises: a limiting bolt 4, which passes through the outer tube 1 and the limiting joint 12 in sequence.

[0050] In one embodiment, see Figure 3 There are three limit bolts 4, which are evenly distributed around the outer tube 1; an arc-shaped washer 11 is provided between the limit bolt 4 and the outer tube 1, and the arc-shaped washer 11 is used to keep the limit bolt 4 in contact with the outer cylindrical surface of the outer tube 1.

[0051] An embodiment of the present invention provides a method for designing a landing gear sled pull rod device, comprising the following steps:

[0052] (1) The change in the length of the helicopter landing gear's buffer after landing and takeoff causes the change in the length of the sled pull rod. The different pull rod lengths cause the change in the spring length, so there is a minimum spring length H1, a maximum spring length H2, and a spring free state length H0. The maximum spring deformation f1 = H0-H1 and the minimum spring deformation f2 = H0-H2 are obtained.

[0053] (2) The outer diameter D1 of the spring can be determined according to the cross-sectional dimensions of the outer tube; the spring diameter d can be determined according to the strength load estimation, and the spring center diameter D2 = D1-d can be obtained;

[0054] (3) t is the spring pitch, i.e., the axial distance between the corresponding points of two adjacent coils of the spring on the median diameter. Its size should satisfy the requirement of being greater than twice the radius of the two adjacent coils of the spring, i.e., the relationship t>d, so as to preliminarily determine the value of t;

[0055] (4) According to the geometry of the spring structure, the total number of spring coils n0 = (H0-2d) / t;

[0056] (5) According to the number of support turns of a general compression spring, take 1 / 4, 1 / 2 or a full turn. Here, take 1 turn at each end of the spring as a support turn, and the number of support turns is 2. Therefore, the effective working turns n = n0-2;

[0057] (6) According to the selected spring material, the shear modulus G of the spring material is a constant value. Calculate the maximum working load of the spring P1 = (f1 * G * d 4 ) / (8n0 * D2 3 ), and the minimum working load of the spring P2 = (f2 * G * d4) / (8n0 * D2 3 );

[0058] (7) The spring stiffness is the ratio of the load change value to the spring length change value. Therefore, the spring stiffness K = (P1 - P2) / (f1 - f2) can be calculated;

[0059] (8) Calculate the spring pitch ratio C = D2 / d; calculate the curvature coefficient M = (4 * C - 1) / (4 * C - 4) + 0.615 / C; thus, the allowable load of the spring P = (3.14 * d 3 * G) / (8 * D2 * M);

[0060] (9) Calculate the single - turn deformation of the spring under the maximum working load f3 = f1 / n0, and calculate the single - turn deformation of the spring under the minimum working load f4 = f2 / n0.

[0061] When designing the outer cylinder 1, piston rod 2, and limit joint 12 of the sled pull rod device,

[0062] Define the inner - hole cavity diameter of the outer cylinder 1 as O1, the outer - diameter of the wall thickness at the mating part of the outer cylinder 1 and the limit joint 12 as O2, the outer - diameter of the piston - rod 2 as O3, the inner - hole diameter of the limit joint 12 as O4, and the outer - diameter of the limit joint 12 as O5;

[0063] Determine the outer - diameter of the piston - rod 2 as O3 according to the strength calculation results. Then, design the inner - hole diameter dimension O4 of the limit joint 12 to satisfy the relationship: O3 + 0.02 < O4 < O3 + 0.05; in this way, it is ensured that the outer - diameter of the piston - rod 2 can be closely fitted with the inner - hole of the limit joint 12, and the piston - rod 2 can be smoothly inserted into the inner - hole of the limit joint 12 without excessive clearance between the piston - rod 2 and the inner - hole of the limit joint 12.

[0064] Similarly, design the outer - diameter O5 of the limit joint 12 to satisfy the relationship O1 - 0.05 < O5 < O1 - 0.02; in this way, it is ensured that the inner - hole O1 of the outer cylinder 1 can be closely fitted with the outer - diameter of the wall thickness O5 at the mating part of the limit joint 12, and the limit joint 12 can be smoothly inserted into the inner - hole of the outer cylinder 1 without excessive clearance between the outer - wall of the limit joint 12 and the inner - hole of the outer cylinder 1.

[0065] Furthermore, the design parameters of the spring can be checked:

[0066] The design results should satisfy the relational inequalities P2 < P1 < P; f4 < f3 < t - d; n0 < (H1 / d).

[0067] P2 is the minimum working load, P1 is the maximum working load, and P is the allowable load of the spring. Therefore, it is necessary to satisfy P2 < P1 < P;

[0068] f3 is the single - coil deformation of the spring under the maximum working load, and f4 is the single - coil deformation of the spring under the minimum working load. Therefore, naturally f4 < f3. And t refers to the axial distance between corresponding points of two adjacent coils of the spring on the mean diameter. Since the spring is a compression spring, from the inevitable geometric relationship, f3 needs to be less than the value of t minus twice the value of 1 / 2 spring diameter d. Therefore, the relational expression f4 < f3 < t - d is obtained. Similarly, from the geometric relationship, the total number of turns n0 of the spring should be smaller than the spring minimum length H1 divided by the spring diameter d. Otherwise, interference will occur between adjacent coils of the spring, which does not conform to the actual situation. Therefore, there is a relational expression n0 < (H1 / d).

[0069] The above only expresses the implementation modes of the present invention, and its description is relatively specific and detailed. However, it should not be construed as a limitation on the scope of the patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. In addition, the parts not elaborated in the present invention are all conventional techniques.

Claims

1. A landing gear sled pull rod device, characterized in that: Comprising: An outer cylinder, a piston rod, a spring, and a limit joint; The outer cylinder is arranged on the landing gear buffer, the piston rod is arranged on the landing gear sled, and one end of the piston rod extends into the inner hole of the outer cylinder; the limit joint is arranged at the connection between the outer cylinder and the piston rod, and the limit joint, the inner wall of the outer cylinder, and the outer wall of the piston rod jointly form a closed space, and the spring is sleeved outside the piston rod body and is located in the closed space.

2. The device according to claim 1, characterized in that The device further comprises: an upper mounting shaft, a lower mounting bolt, a lower threaded joint, and a spherical plain bearing, The lower threaded joint is arranged on the landing gear sled, and a threaded section for threaded connection with the lower threaded joint is provided at one end of the piston rod far from the outer cylinder 1; The spherical plain bearing is installed in the lug of the lower threaded joint, and the lower mounting bolt is installed in the inner hole of the spherical plain bearing; The upper mounting shaft is connected with a cable, the upper mounting shaft is installed in the two lugs at one end of the outer cylinder far from the piston rod through nuts, and a support sleeve is arranged between the upper mounting shaft and the lugs, and the length of the support sleeve is greater than h, where h = (L - M) / 2, L is the outer diameter of the outer cylinder, and M is the span of the two lugs.

3. The device according to claim 1, characterized in that The device further comprises: a limit bolt, and the limit bolt sequentially passes through the outer cylinder and the limit joint.

4. The device according to claim 3, characterized in that There are 3 limit bolts, and they are evenly distributed in the circumferential direction of the outer cylinder; an arc washer is arranged between the limit bolt and the outer cylinder, and the limit bolt is kept in contact with the outer circular surface of the outer cylinder through the arc washer.

5. The device according to claim 1, characterized in that The inner wall of the outer cylinder is coated with grease.

6. A design method for the landing gear sled pull rod device according to any one of claims 1 to 5, characterized in that The design process of the spring is as follows: Determine the maximum deformation amount f1 = H0 - H1 of the spring, and the minimum deformation amount f2 = H0 - H2, where H1 is the minimum value of the spring length, H2 is the maximum value of the spring length, and H0 is the free state length of the spring; Determine the outer diameter D1 of the spring according to the cross-sectional dimension of the outer cylinder and determine the spring diameter d to obtain the mean diameter D2 of the spring; Determine the spring pitch t according to the spring diameter d from the relationship t > d; Determine the effective number of working turns n of the spring = (H0 - 2d) / t; Determine the total number of turns n0 of the spring = n + 2 according to the effective number of working turns n; Determine the maximum working load of the spring P1 = (f1*G*d 4 ) / (8n0*D2 3 ), and the minimum working load of the spring P2 = (f2*G*d 4 ) / (8n0*D2 3 ), where G is the shear modulus of the spring material; Determine the spring stiffness K = (P1 - P2) / (f1 - f2); Determine the spring winding ratio C = D2 / d; and the curvature coefficient M = (4*C-1) / (4*C-4)+0.615 / C; and thus obtain the spring allowable load P = (3.14*d 3 *G) / (8*D2*M); Determine the single-turn deformation amount f3 of the spring under the maximum working load = f1 / n0, and the single-turn deformation amount f4 of the spring under the minimum working load = f2 / n0; The design process of the outer cylinder, the piston rod, and the limit joint is as follows: According to the flight state of the helicopter landing gear, determine the maximum value S1 of the length between the outer cylinder installation point and the piston rod installation point; according to the parking state of the helicopter landing gear, determine the minimum value S2 of the length between the outer cylinder installation point and the piston rod joint installation point; S1, S2, the structural length S3 of the outer cylinder, and the structural length S4 of the piston rod satisfy the constraint conditions: S3 < S2; S4 < S2; S1 < S3 + S4; Determine the outer diameter O3 of the piston rod body according to the strength calculation result, and the inner hole diameter O4 of the limit joint satisfies the relationship: O3 + 0.02 < O4 < O3 + 0.05; the outer diameter O5 of the limit joint satisfies the relationship: O1 - 0.05 < O5 < O1 - 0.02, where O1 is the inner hole cavity diameter of the outer cylinder.

7. The method according to claim 6, characterized in that The method further comprises: Verify the design parameters of the spring. If P2 < P1 < P; f4 < f3 < t - d; n0 < (H1 / d) are satisfied, then the verification is passed.

8. The method according to claim 6, characterized in that The minimum spring length H1, the maximum spring length H2, and the spring free state length H0 are determined according to the change in the buffer length of the helicopter landing gear after landing and taking off.

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