An impact buffering device based on coupling of pressure-torsion metamaterial and magneto-rheological fluid

Abstract

The application provides an impact buffering device based on coupling of pressure-torsion metamaterial and magneto-rheological fluid, and relates to the technical field of damping and buffering. The application provides an impact buffering device based on coupling of pressure-torsion metamaterial and magneto-rheological fluid, and relates to the technical field of damping and buffering. The application provides an impact buffering device based on coupling of pressure-torsion metamaterial and magneto-rheological fluid, and relates to the technical field of damping and buffering. The application provides an impact buffering device based on coupling of pressure-torsion metamaterial and magneto-rheological fluid, and relates to the technical field of damping and buffering. The application provides an impact buffering device based on coupling of pressure-torsion metamaterial and magneto-rheological fluid, and relates to the technical field of damping and buffering. The application provides an impact buffering device based on coupling of pressure-torsion metamaterial and magneto-rheological fluid, and relates to the technical field of damping and buffering.

Description

Technical Field

[0001] This invention relates to the field of vibration damping and buffering technology, and in particular to an impact buffering device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid. Background Technology

[0002] Automated equipment (such as robots and drones) often endures periodic impact loads during operation. When the impact frequency is high and the load is continuous, the system's control accuracy and platform stability are significantly affected. For example, in typical high-frequency impact operations, a single impact load can reach the 10,000 N range. Compared to traditional equipment that relies on manual adjustments by operators, these automated platforms lack flexible buffering and proactive adaptability, making the impact loads more significant on their attitude stability and operational accuracy.

[0003] Existing shock absorption solutions mostly employ spring-type dampers, which absorb impact energy through the compression deformation of elastic elements, effectively reducing the peak load transmitted to the platform. However, this type of damper has two inherent drawbacks under high-frequency continuous impact conditions: First, if the natural frequency of the spring-mass system is close to the operating excitation frequency, resonance will occur, drastically deteriorating the damping effect; second, after compression, the spring needs to undergo a reset process before it can withstand the next impact. When the impact interval (approximately 0.1s) is less than the spring reset time, the damper has not yet recovered before bearing the next load, leading to cumulative displacement and a decrease in damping performance. These problems make it difficult for traditional spring vibration dampers to guarantee operational accuracy under high-frequency impact conditions of 10–15Hz.

[0004] Compression-torsion metamaterials can couple linear and torsional deformation during axial compression, exhibiting large deformation energy dissipation characteristics and showing potential applications in impact protection. However, existing compression-torsion metamaterials mostly employ fixed geometric configurations, and their mechanical response characteristics cannot be adjusted after molding, making them difficult to adapt to the complex working conditions of frequency-controlled impacts on automated platforms. Magnetorheological fluids, as smart materials, can continuously adjust their shear yield stress and viscosity within milliseconds under the action of a magnetic field, providing a feasible approach for real-time control of damping forces.

[0005] This invention combines the large deformation energy dissipation mechanism of compression-torsion metamaterials with the damping magnetic field control characteristics of magnetorheological fluids. It utilizes the composite flow mode generated by the compression and torsion of metamaterials to improve the energy dissipation efficiency of magnetorheological fluids. At the same time, it adjusts the damping force in real time through the magnetic field to adapt to different impact conditions. It is expected to solve the dual problems of insufficient energy absorption and poor adaptability of existing solutions. Summary of the Invention

[0006] To address the technical problems of insufficient energy absorption and poor adaptability in existing technologies, this invention provides an impact buffer device based on the coupling of a pressure-torsion metamaterial and a magnetorheological fluid.

[0007] The technical solutions provided by the embodiments of the present invention are as follows: An impact buffer device based on the coupling of a pressure-torsion metamaterial and a magnetorheological fluid is provided in this embodiment of the invention, comprising: a cylinder, an impact end cap, a base assembly, a pressure-torsion metamaterial structure, and an excitation assembly; The interior of the cylinder is filled with magnetorheological fluid; The impact end cap is disposed at the upper end of the cylinder; an annular groove is formed on the outer peripheral surface of the impact end cap; The base assembly is disposed at the lower end of the cylinder and includes an outer base ring and an inner base ring. The outer base ring is fixedly connected to the cylinder, and the inner base ring is disposed inside the outer base ring and can rotate relative to the outer base ring. The pressure-torsion metamaterial structure is disposed inside the cylinder and includes an outer helical rod system and an inner helical rod system arranged coaxially; the outer helical rod system is connected between the impact end cap and the outer base ring, and the inner helical rod system is connected between the impact end cap and the inner base ring; The excitation assembly includes an excitation coil, which is embedded in the annular groove of the impact end cover; A first annular damping gap is formed between the outer peripheral surface of the impact end cap and the inner wall of the cylinder, and the annular groove and the excitation coil are located radially inside the first annular damping gap; a second annular damping gap is formed between the outer peripheral surface of the inner base ring and the inner peripheral surface of the outer base ring. The excitation coil generates a magnetic circuit passing through the first annular damping gap and the second annular damping gap, which is used to adjust the yield stress of the magnetorheological fluid within the gap.

[0008] In one possible implementation, the outer helical system has the opposite helical direction to the inner helical system.

[0009] In one possible implementation, when the impact end cap is subjected to axial impact and axial compression, the inner helical rod system, under the cooperation and bearing of the outer helical rod system, converts the axial compression displacement into circumferential torsional displacement, and synchronously drives the impact end cap to rotate circumferentially relative to the cylinder and the inner base ring relative to the outer base ring. The axial movement and circumferential rotation of the impact end cap force the magnetorheological fluid to simultaneously generate axial pressure differential flow and circumferential shear flow within the first annular damping gap, while the circumferential rotation of the inner base ring forces the magnetorheological fluid to generate circumferential shear flow within the second annular damping gap.

[0010] In one possible implementation, the outer helical rod system, the inner helical rod system, the impact end cap, the inner base ring, and the outer base ring are three-dimensional printed structures integrally formed by additive manufacturing processes.

[0011] In one possible implementation, the widths of both the first annular damping gap and the second annular damping gap are 0.25~2.5mm.

[0012] In one possible implementation, the diameters of both the outer and inner helical rod systems are 2-4 mm, and the overall height of the compression-torsion metamaterial structure is 50-60 mm, with an outer diameter of 35-45 mm.

[0013] In one possible implementation, the magnetorheological fluid is a mixture of silicone oil-based fluid and carbonyl iron powder, wherein the mass percentage of carbonyl iron powder is 60-80 wt%.

[0014] In one possible implementation, the excitation coil has 30 to 210 turns, and the excitation current is adjustable from 0.5 to 2.5 A.

[0015] In one possible implementation, the cylinder is sealed with a sealing ring to prevent leakage of the magnetorheological fluid.

[0016] In one possible implementation, the impact buffer device based on the coupling of the compression-torsion metamaterial and the magnetorheological fluid further includes a tie rod, a flange, a linear bearing, an upper end cover, a lower end cover, and a gasket; the tie rod passes through the interior of the compression-torsion metamaterial structure and is threadedly connected to the flange; the linear bearing is embedded in the inner wall of the lower end of the cylinder to guide the axial movement of the tie rod; the gasket is disposed between the base assembly and the lower end cover, serving a sealing and buffering function.

[0017] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following: (1) In this embodiment of the invention, the axial linear motion during impact is converted into torsional motion by the pressure-torsion metamaterial. The design of the inner and outer spirals with opposite directions ensures that the torsional torque generated by the inner and outer rods is in the same direction and superimposed when under pressure, avoiding the cancellation of internal torque that may occur in the same direction spirals, and improving the conversion efficiency from compression to torsion. With the double damping gaps at the upper and lower ends, the magnetorheological fluid is forced to undergo both axial pressure differential flow and circumferential shear flow at the same time, improving the deformation mode and energy dissipation path of the magnetorheological fluid, and solving the problem of insufficient energy absorption density.

[0018] (2) In this embodiment of the invention, the built-in coil can adjust the yield stress of the magnetorheological fluid in milliseconds, so that the damping force can be matched in real time according to the firing frequency and the magnitude of the recoil. Compared with traditional spring dampers, this structure can continuously consume energy without relying on the physical reset process of mechanical springs. Under high-frequency continuous impact conditions, it can effectively suppress the peak vibration response (simulation and theoretical analysis show that it can be reduced by about 20%), and each typical working point is located within the effective control area, which can continuously provide stable and adjustable damping support, and improve the attitude stability and working accuracy of the automated platform under continuous high-frequency impact operations.

[0019] (3) In the embodiments of the present invention, the flow and shear hysteresis energy dissipation mechanism of the magnetorheological fluid does not depend on the physical reset time of the mechanical spring. Its damping force responds automatically with the impact load, without resonance and rebound hysteresis problems, fundamentally solving the defects of resonance and untimely rebound of the spring damper under continuous impact. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of an impact buffer device based on the coupling of a pressure-torsion metamaterial and a magnetorheological fluid, provided for an embodiment of the present invention.

[0022] Figure 2 This is a cross-sectional view of an impact buffer device based on the coupling of a pressure-torsion metamaterial and a magnetorheological fluid, provided as an embodiment of the present invention.

[0023] Figure 3 The image shows the appearance of an impact buffer device based on the coupling of a pressure-torsion metamaterial and a magnetorheological fluid, as provided in an embodiment of the present invention.

[0024] Figure 4 The energy absorption simulation curve of an impact buffer device based on the coupling of a compression-torsion metamaterial and a magnetorheological fluid is provided for an embodiment of the present invention.

[0025] Figure 5 This is a diagram showing the influence of magnetic field strength on total energy absorption in a fluid-structure interaction simulation provided by an embodiment of the present invention.

[0026] Figure 6 This is a diagram illustrating the influence of the flow gap size on the total energy absorption in a fluid-structure interaction simulation provided by an embodiment of the present invention.

[0027] Reference numerals in the attached drawings: 1-Cylinder body; 2-Impact end cap; 3-Outer base ring; 4-Inner base ring; 5-Outer helical rod system; 6-Inner helical rod system; 7-Magnetorheological fluid; 8-Excitation coil; 9-Annular groove; 10-First annular damping gap; 11-Second annular damping gap; 12-Upper end cap; 13-Linear bearing; 14-Flange; 15-Lower end cap; 16-Gasket; 17-Sealing ring; 18-Tie rod.

[0028] As shown in the figure, specific structures and devices are marked in the figure to clearly illustrate the structure of the embodiments of the present invention. However, this is only for illustrative purposes and is not intended to limit the present invention to this specific structure, device and environment. Those skilled in the art can adjust or modify these devices and environments according to specific needs. Detailed Implementation

[0029] The technical solutions of the present invention will now be described with reference to the accompanying drawings. It should also be noted that, to make the embodiments more detailed, the following embodiments are the best and preferred embodiments. Those skilled in the art can also use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figures 1 to 3 As shown, an embodiment of the present invention provides an impact buffer device based on the coupling of a pressure-torsion metamaterial and a magnetorheological fluid, comprising: a cylinder 1, an impact end cap 2, a base assembly, a pressure-torsion metamaterial structure, and an excitation assembly; The interior of the cylinder 1 is filled with magnetorheological fluid; the lower end of the cylinder 1 may be provided with 4 threaded holes for fixed installation with an automated work platform.

[0032] The impact end cap 2 is disposed at the upper end of the cylinder 1; the outer circumferential surface of the impact end cap 2 is provided with an annular groove 9; The base assembly is located at the lower end of the cylinder 1, including an outer base ring 3 and an inner base ring 4. The outer base ring 3 is fixedly connected to the cylinder 1, and the inner base ring 4 is located inside the outer base ring 3 and can rotate relative to the outer base ring 3. The compression-torsion metamaterial structure is set inside the cylinder 1, including an outer helical rod system 5 and an inner helical rod system 6 arranged coaxially; the outer helical rod system 5 is connected between the impact end cap 2 and the outer base ring 3, and is responsible for axial bearing and reset; the inner helical rod system 6 is connected between the impact end cap 2 and the inner base ring 4, and is responsible for efficiently converting axial displacement into circumferential torsion. The outer helical rod system 5 and the inner helical rod system 6 have opposite helical directions. This reverse helical direction setting ensures that the inner and outer torques are superimposed in the same direction.

[0033] The excitation assembly includes an excitation coil 8, which is embedded in the annular groove 9 of the impact end cover 2; A first annular damping gap 10 is formed between the outer peripheral surface of the impact end cap 2 and the inner wall of the cylinder 1. The annular groove 9 and the excitation coil 8 are located on the radial inner side of the first annular damping gap 10. A second annular damping gap 11 is formed between the outer peripheral surface of the inner base ring 4 and the inner peripheral surface of the outer base ring 3. The excitation coil 8 generates a magnetic circuit passing through the first annular damping gap 10 and the second annular damping gap 11, which is used to adjust the yield stress of the magnetorheological fluid within the gap. Specifically, after the excitation coil 8 is energized, the magnetic field lines pass radially through the first annular damping gap 10 into the wall of the cylinder 1, then axially downward along the cylinder, passing through the outer base ring 3, the second annular damping gap 11, and the inner base ring 4. They then return to the impact end cap 2 via the inner spiral rod system 6 made of magnetically conductive material, forming a closed magnetic circuit. The control system adjusts the excitation current in real time based on the impact feedback to change the shear yield stress of the magnetorheological fluid 7, thereby achieving continuous adjustment of the damping force.

[0034] When the impact end cap 2 is subjected to axial impact and axial compression, the inner spiral rod system 6, under the cooperation and bearing of the outer spiral rod system 5, converts the axial compression displacement into circumferential torsional displacement, and synchronously drives the impact end cap 2 to rotate circumferentially relative to the cylinder 1 and the inner base ring 4 to rotate circumferentially relative to the outer base ring 3. The axial movement and circumferential rotation of the impact end cap 2 force the magnetorheological fluid to generate axial pressure differential flow and circumferential shear flow simultaneously in the first annular damping gap 10. The circumferential rotation of the inner base ring 4 forces the magnetorheological fluid to generate circumferential shear flow in the second annular damping gap 11, forming a dual-gap composite damping energy dissipation.

[0035] Furthermore, the outer helical rod system 5, the inner helical rod system 6, the impact end cap 2, the inner base ring 4, and the outer base ring 3 are three-dimensional printed structures integrally formed through additive manufacturing processes.

[0036] Furthermore, the widths of the first annular damping gap 10 and the second annular damping gap 11 are both 0.25~2.5mm.

[0037] Furthermore, the diameters of the outer helical rod system 5 and the inner helical rod system 6 are both 2-4 mm, and the overall height of the compression-torsion metamaterial structure is 50-60 mm and the outer diameter is 35-45 mm.

[0038] Furthermore, the magnetorheological fluid is composed of a silicone oil-based fluid and carbonyl iron powder, with the carbonyl iron powder accounting for 60-80 wt% of the total mass.

[0039] Furthermore, the number of turns of the excitation coil 8 is 30 to 210, and the adjustment range of the excitation current is 0.5 to 2.5A.

[0040] Furthermore, the cylinder 1 is sealed by a sealing ring 17 to prevent leakage of the magnetorheological fluid.

[0041] Furthermore, the impact buffer device based on the coupling of the pressure-torsion metamaterial and the magnetorheological fluid also includes a tie rod 18, a flange 14, a linear bearing 13, an upper end cover 12, a lower end cover 15, and a gasket 16; the tie rod 18 passes through the interior of the pressure-torsion metamaterial structure and is threadedly connected to the flange 14; the linear bearing 13 is embedded in the inner wall of the lower end of the cylinder 1 to provide guidance for the axial movement of the tie rod 18; the gasket 16 is disposed between the base assembly and the lower end cover 15, serving a sealing and buffering function.

[0042] The working process of the impact buffer device based on the coupling of compressive-torsional metamaterials and magnetorheological fluid of the present invention is described below: When automated special equipment is subjected to high-frequency continuous impact, the impact force is transmitted to the upper surface of the impact end cap 2 through the tie rod 18. When the impact end cap 2 is pressed down, the outer spiral rod system 5 undergoes elastic compression deformation, providing axial stiffness and storing reset potential energy; the inner spiral rod system 6, due to its opposite spiral direction configuration to the outer layer, converts the axial compression into strong circumferential torsion. The torsional deformation synchronously drives the top impact end cap 2 to rotate, and the bottom inner base ring 4 to rotate. During this process, the magnetorheological fluid 7 is forced to undergo compound flow in two gaps: in the first annular damping gap 10, axial pressure differential flow is generated by the downward pressure of the impact end cap 2, and circumferential shear flow is generated by the rotation of the impact end cap 2; in the second annular damping gap 11, circumferential shear flow is generated by the rotation of the inner base ring 4. The superposition of flows in the two gaps increases the hysteresis energy dissipation of the magnetorheological fluid 7. The control system outputs current to the built-in excitation coil 8 to adjust the damping force of the magnetorheological fluid 7, achieving precise adjustment of the damping force. After the impact, the outer helical rod system 5 drives the impact end cap 2 to reset, and the inner helical rod system 6 drives the inner base ring 4 to reset, preparing for the next buffering. To verify the energy dissipation performance of the device under different working conditions, static energy absorption simulation and fluid-structure interaction simulation were performed on the structure. The simulation results are as follows.

[0043] (1) Static energy absorption simulation: such as Figure 4As shown, the compression-torsion metamaterial structure is made of Corrax die steel with an elastic modulus of 170 GPa, a yield strength of 1600 MPa, and a Poisson's ratio of 0.3. Under quasi-static compression test conditions, the compression-torsion metamaterial structure absorbs approximately 42.8 J of energy during a single compression; under a 3000 N (10 Hz) impact test condition, the compression-torsion metamaterial structure absorbs approximately 8.3 J of energy during a single compression.

[0044] (2) Fluid-structure interaction simulation analysis: Under the condition of 3000N impact load, the influence of magnetic field strength and flow gap size on damping energy consumption is studied by establishing a magnetic field and fluid dynamics coupling model.

[0045] First, the influence of magnetic field strength: such as Figure 5 As shown, with the increase of magnetic field strength, the proportion of liquid energy absorption to total energy absorption increases significantly, reaching a maximum (approximately 10.2 J) at a magnetic field strength of about 200 mT. When the magnetic field strength continues to increase to 350 mT, the relative flow decreases due to the increased stiffness of the liquid chain structure, resulting in a slight decrease in energy absorption. Therefore, it is preferable to control the working magnetic field range at around 200 mT.

[0046] Secondly, the size of the flow gap has an impact: such as Figure 6 As shown, the energy absorption was investigated under a magnetic field of 200 mT for flow gap sizes of 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, and 3.0 mm. Simulation results show that the total energy absorption reaches its peak (10.4398 J) when the gap size is 2.0 mm. Too small a gap leads to excessive flow resistance and liquid stagnation; too large a gap leads to reduced flow velocity and insufficient shear energy dissipation.

[0047] Through the above structural optimization and simulation verification, the device of the present invention can effectively couple the mechanical deformation of the compression-torsion metamaterial with the rheological properties of the magnetorheological fluid, providing continuous and stable damping adjustable support capability under high-frequency continuous impact of 10-15Hz.

[0048] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the preferred embodiments, while those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0049] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid, characterized in that, include: Cylinder, impact end cap, base assembly, compression-torsion metamaterial structure, and excitation assembly; The interior of the cylinder is filled with magnetorheological fluid; The impact end cap is disposed at the upper end of the cylinder; an annular groove is formed on the outer peripheral surface of the impact end cap; The base assembly is disposed at the lower end of the cylinder and includes an outer base ring and an inner base ring. The outer base ring is fixedly connected to the cylinder, and the inner base ring is disposed inside the outer base ring and can rotate relative to the outer base ring. The pressure-torsion metamaterial structure is disposed inside the cylinder and includes an outer helical rod system and an inner helical rod system arranged coaxially; the outer helical rod system is connected between the impact end cap and the outer base ring, and the inner helical rod system is connected between the impact end cap and the inner base ring; The excitation assembly includes an excitation coil, which is embedded in the annular groove of the impact end cover; A first annular damping gap is formed between the outer peripheral surface of the impact end cap and the inner wall of the cylinder, and the annular groove and the excitation coil are located radially inside the first annular damping gap; a second annular damping gap is formed between the outer peripheral surface of the inner base ring and the inner peripheral surface of the outer base ring. The excitation coil generates a magnetic circuit passing through the first annular damping gap and the second annular damping gap, which is used to adjust the yield stress of the magnetorheological fluid within the gap.

2. The impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid according to claim 1, characterized in that, The outer helical system has the opposite helical direction to the inner helical system.

3. The impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid according to claim 1, characterized in that, When the impact end cap is subjected to axial impact and axial compression, the inner helical rod system, under the cooperation and bearing of the outer helical rod system, converts the axial compression displacement into circumferential torsional displacement, and synchronously drives the impact end cap to rotate circumferentially relative to the cylinder and the inner base ring relative to the outer base ring. The axial movement and circumferential rotation of the impact end cap force the magnetorheological fluid to simultaneously generate axial pressure differential flow and circumferential shear flow within the first annular damping gap, while the circumferential rotation of the inner base ring forces the magnetorheological fluid to generate circumferential shear flow within the second annular damping gap.

4. The impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid according to claim 1, characterized in that, The outer helical rod system, the inner helical rod system, the impact end cap, the inner base ring, and the outer base ring are three-dimensional printed structures integrally formed by additive manufacturing process.

5. The impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid according to claim 1, characterized in that, The widths of both the first and second annular damping gaps are 0.25~2.5mm.

6. The impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid according to claim 1, characterized in that, The diameter of both the outer and inner helical rod systems is 2-4 mm, and the overall height of the compression-torsion metamaterial structure is 50-60 mm, with an outer diameter of 35-45 mm.

7. The impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid according to claim 1, characterized in that, The magnetorheological fluid is composed of a silicone oil-based fluid and carbonyl iron powder, wherein the mass percentage of the carbonyl iron powder is 60-80 wt%.

8. The impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid according to claim 1, characterized in that, The excitation coil has 30 to 210 turns, and the excitation current can be adjusted from 0.5 to 2.5A.

9. The impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid according to claim 1, characterized in that, The cylinder is sealed by a sealing ring.

10. The impact buffer device based on the coupling of a compressive-torsional metamaterial and a magnetorheological fluid according to claim 1, characterized in that, It also includes a tie rod, a flange, a linear bearing, an upper end cover, a lower end cover, and a gasket; the tie rod passes through the interior of the compression-torsion metamaterial structure and is threadedly connected to the flange; the linear bearing is embedded in the inner wall of the lower end of the cylinder to guide the axial movement of the tie rod; the gasket is disposed between the base assembly and the lower end cover.

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