RU2544046C2 - Mechanical low-amplitude vibration damper with rotating friction pairs - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention relates to machine building. A ring shaped spring is pivotally fastened on a damper base. A steel ring is installed inside the base. Coating with specified tribological characteristics is applied onto the internal surface of the ring. Inside the ring there mounted is a shaft-eccentric inside which a cylindrical through hole with the eccentricity in respect to the external cylindrical surfaces of the shaft is made. The shaft-eccentric is clamped in symmetrically mounted split elements by screws. The shaft-eccentric together with the split elements form a solid lever with its ends being rigidly connected to the outer shanks of the ring shaped spring ends by means of fastening units. A shaft with conical mounting seats is set inside the shaft-eccentric. A forked tie rod is attached to the shaft and serves for the transfer of reciprocating motion from a vibration source through two cylindrical holes equidistanced from the symmetry axis. Two rings with conical inner surfaces are mounted on the shaft to adjust the force of pressing the said surfaces to the conical surfaces of the shaft. Coating with specified tribological characteristics is applied onto the external cylindrical surfaces of the rings.

EFFECT: efficient damping with simultaneous increase of vibration system rigidity.

8 dwg

Description

The invention relates to the field of mechanical engineering and can be used to damp vibrations of various mechanical structures, provided that it is not possible to install a damping device at the most optimal points for attaching the damper, where its movements are greatest and the loads on the damper are minimal. However, the design features of the damped unit (for example, the engine on the pylon of an airplane wing) often do not allow this, the only possible points for attaching the damper are the points where the oscillation amplitudes of the structure are small (for example, near the supports of the engine pylon to the wing) and the loads on the damper are large . The use in these conditions of already known devices, in particular hydraulic dampers, is usually ineffective.

The aim of the work is to create friction dampers based on the work of rotational friction pairs. Fundamental in solving their design is the conversion of small translational movements due to vibration of the damped structure into significant angular displacements of the core in a friction pair.

Basically, dampers are used to damp vibrations of mechanical structures that are affected by loads that create vibrations in wide frequency ranges under conditions of small displacements of the point of attachment of the damper to the vibrating structure.

There are numerous designs of mechanical dampers (with the movement of bulk solids and spring), hydraulic, hydromechanical. Their designs are protected by a group of patents:

- patent RU No. 2464462 C1 dated 10.20.2012. HYDROMECHANICAL DAMPER, IPC F16F 9/14 F16F 5/00,

- patent RU No. 2461752 C1 dated 09/20/2012. ADAPTIVE HYDROMECHANICAL DAMPER, IPC F16F 9/14 F16F 5/00,

- patent RU No. 2427742 C1 dated 08/27/2011. HYDRAULIC DAMPER, IPC F16F 9/14 F16F 5/00,

- patent RU No. 2427741 C1 dated 08/27/2011. HYDRAULIC DAMPER OF OSCILLATIONS, IPC F16F 9/14 F16F 5/00,

- patent RU No. .. 2427740 C1 from 08.27.2011. HYDRAULIC DAMPER, IPC F16F 9/14 F16F 5/00,

- patent RU No. 2324090 C1 dated 05/10/2008. DAMPER, IPC F16F 9/14 F16F 5/00,

- patent RU No. 2324089 C1 dated 05/10/2008. HYDRAULIC DAMPER, IPC F16F 9/14 F16F 5/00,

- patent RU No. 2135856 C1 from 08.27.1999. HYDRODEMPHER, IPC F16F 9/14 F16F 5/00.

All of the above dampers can be used only in conditions where it is possible to install the damping device at the most optimal points for fastening the damper, where its movements are greatest and the loads on the damper are minimal.

We accept the HYDROMECHANICAL DAMPER for the prototype, the device is protected by patent RU No. 2258848 C2 dated 12.20.2004, IPC F16F 9/14, F16F 11/00, B64C 25/58.

The hydromechanical damper comprises a housing, inside of which are placed pistons rigidly interconnected and held in a neutral position by a spring, caps with fittings for connecting the piston cavities with hydraulic lines, an additional cup closed by said cover is placed in the housing, in which a constant choke and a variable choke are installed in series, the passage area of which is dependent on the pressure drop in it, forming a throttling device between the piston cavity and the hydraulic line, and the spring holding the pistons in the neutral position, are elastic elements that have the ability to change both shape and volume.

This damper is used to damp the vibrations of the front landing gear of the aircraft, mounted on the front support, connected by hydraulic lines to the cavities of the actuating cylinder, that is, it can only be used in close proximity to vibration sources, when the damping device is located at the most optimal points for mounting the damper, where its movements are the largest, and the loads on the damper are minimal.

The objective and technical result of the invention is the creation of a mechanical damper of low-amplitude vibrations with rotational friction pairs for working in conditions where the only possible points for attaching the damper are the points where the vibration amplitudes of the structure are small (for example, near the supports of the engine pylon to the wing) and the load on the damper are large, that is, when it is impossible to access the “technically optimal” attachment points of the damper, in addition, this mechanical damper provides effective damping while increasing the rigidity of the vibrational system.

The solution of this problem and the technical result are achieved by the fact that a mechanical damper of low-amplitude vibrations with rotational friction pairs, containing a base (body) and a spring, a shaped ring spring is pivotally mounted on the base, a steel ring is installed inside the base, the inner surface of which is coated with specified tribological characteristics, an eccentric shaft is located inside the ring, inside of which a cylindrical through hole with an eccentricity with respect to to the outer cylindrical surfaces of the shaft, inside the eccentric shaft, there is a shaft with tapered seats, the shaft is clamped by screws in symmetrically arranged split elements and together with the split elements forms a single lever, the ends of which are rigidly connected to the outer shanks of the end of the annular shaped spring by a forked rod is attached to the shaft, through which a reciprocating movement from the oscillation source is transmitted to the damper through two cylinders equidistant from the axis of symmetry ical holes, in addition, two rings with conical inner surfaces are installed on the shaft to control the force of pressing these surfaces against the conical surfaces of the shaft, and the outer cylindrical surfaces of the rings are coated with predetermined tribological characteristics.

The work of the damper under consideration with rotational friction pairs is based on the property of the lever and is reduced to the transformation of relatively small linear displacements of the application points of the balancing static and dynamic forces into large angular displacements of the friction pairs with adjustable force of the rotational pairs, to which the forces are applied. Due to the adjustable friction force in pairs of rotation, the effective operation of the damper is achieved at very small intrinsic displacements in comparison with the displacements of the damped system.

The figure 1 shows the mechanical damper of low-amplitude vibrations with rotational friction pairs.

Figure 2 shows a damper with a section plane along the axes of rotation (forked rod not shown).

The figure 3 shows a cross section of the damper along the plane of the axes of rotation.

Figure 4 shows an example of the use of a damper with rotational friction pairs to damp free vibrations of a conditionally weightless beam (the mass of the beam is negligible compared to the mass of the load) with three concentrated masses.

The figure 5 presents a graph of free vibrations of the middle of the beam.

The figure 6 presents a graph of free oscillations of the points of attachment of the models of dampers to the beam.

The figure 7 shows the dependence of the efforts of the damper on the displacements of its attachment point 2 to the beam, a graph of free vibrations of the attachment points of the dampers.

The figure 8 shows the dependence of the efforts of the damper on the displacements of its attachment point 3 to the beam, a graph of free vibrations of the attachment points of the dampers' layouts is presented.

The damper with rotational pairs contains a base (housing) 1 (Fig. 1, 2), on which the shaped ring spring 2 is hinged. The hinge 3 is made using a spherical bearing of the ШС series, the shaft of which is attached with pins to the inner end of the shaped ring spring 2. Inside base 1 is installed a steel ring 4 (see figure 3). The inner cylindrical surface of the ring is coated with a special coating with predetermined tribological characteristics. The ring 4 is fixedly fixed in the base 1 by tightening with a screw 5 of the cut of the base from the side closest to the hinge 3. An eccentric shaft 6 is installed inside the ring 4. The shaft fit, sliding or running, is controlled by the gap width. A through hole is made inside the shaft. Its cylindrical surface of the smallest diameter is a landing surface, the cylindrical surface is made with eccentricity with respect to the outer cylindrical surfaces of the shaft. In the mounting position, the axes of the inner and outer landing cylinders of the shaft lie in the same plane as the axis of the shaft of the hinge 3. This plane is called the plane of the axes of rotation. The cross section of the damper along the plane of the axis of rotation is shown in figure 3. The axes are indicated by the indices A, B and C. The position of the axes A, B and C on the same plane in the mounting unloaded condition is fixed using two split elements 7 equidistant from the axis of symmetry of the damper (Fig. 12). The shaft 6 is clamped in the elements 7 by compressing their cuts with the screws 8. When the shaft 6 rotates around the C axis, it forms a single lever together with the elements 7. The ends of this lever are rigidly connected by means of nodes 9 to the outer shanks of the end of the annular shaped spring 2. The nodes 9 consist of pins with threads on the free end, a shaped clamping washer and nut. When a moment is applied to the lever from elements 6 and 7 relative to the C axis, the lever will rotate around it by a certain angle, determined mainly by the magnitude of the applied moment, the stiffness of the annular shaped spring 2 and the friction moment along the seating surfaces of the shaft 6 and ring 4. Application of the moment is carried out by applying at the point of intersection of the axis of symmetry and axis B to the shaft 10 (Fig. 1, 2) a force normal to the plane of the axes of rotation. This force is applied to the forked rod 14 (Fig. 1), which is attached to the shaft 10 through two cylindrical holes equidistant from the axis of symmetry. The shaft 10 has a thread and two conical surfaces for mounting rings. On the shaft 10 there are two rings 11 (figure 2). Their inner surfaces are conical, and the outer cylindrical with a special coating with predetermined tribological characteristics. The outer diameter of the rings 11 is changed to some extent by their extension by adjusting the force of pressing the inner conical surfaces to the conical surfaces of the shaft by the loads applied to the ends of the rings. These loads are applied with sleeves 12, pressed against the ends of the rings by nuts 13 (two pairs of nuts - a nut and a lock nut, see figure 2). When a vertical load is applied to the shaft 10 through the rod 14, it does not rotate around its axis B and therefore rubs the outer surfaces of the rings 11 along the surfaces of the hole in the shaft - eccentric 6.

The work of the mechanical damper of low-amplitude vibrations with rotational friction pairs is considered by the example of damping of free vibrations of a beam with three concentrated masses (Fig. 3), the mass of the beam is negligible compared to the mass of the load. A beam of length L ₁ = 8.4m is pivotally fixed at the ends. In the middle of the beam is a mass m ₁ = 97.5 kg (point 1). Two equal masses m ₂ = 440 kg are located at points 2 and 3 at distances L ₂ = 0.2 m from the hinges. The fastening of dampers (mock-demonstrators) to the masses m _{2 is} made in the positions of the static equilibria of the beam and dampers (without initial effort). The stiffness of the beam is equal to the stiffness of the box of two channels No. 14 GOST 82539-56 (moment of inertia J = 2 · 291 cm ⁴ ).

The calculated frequencies of free vibrations of concentrated masses without damping are: ω ₁ = 6.4 Hz, ω ₂ = 47.9 Hz, ω ₃ = 57.5 Hz. In this case, the frequencies of the first and third tones coincide with the frequencies of the first and third tones of free vibrations of a heavy beam in the form of a named box of two channels No. 14 with a linear mass m _p = 2 · 12.3 kg / m. Its first three natural frequencies are equal: ω ₁ = 6.4 Hz, ω ₂ = 25.5 Hz, ω ₃ = 57.5 Hz.

The purpose of the calculation is to determine the logarithmic decrement of free vibrations of the first tone of the beam when the dampers are located next to the supports and there are conditions for the occurrence of other vibration tones.

Calculations are performed in the basic units of the SI system (m, N, s) using the Mathcad-13 mathematical package. The dependences presented on the graphs were obtained at zero initial speeds of motion and the following initial coordinates of the concentrated masses:

y ₁ (0) = - 1.2 · y _1s is the initial coordinate of point 1,

y ₂ (0) = - y _2s , y ₃ (0) = - y _3s - the initial coordinates of points 2 and 3,

Where

y _1s = -9.60 · 10 ^-3 m - coordinate of the static position of point 1,

y _2s = y _3s = -7.63 · 10 ^-4 m - the coordinates of the static positions of points 2 and 3.

The dampers located at the supports perceive the displacement of the beam during free vibrations of the middle of the beam. Figure 4 shows a graph of free vibrations of the middle of the beam (displacement of point 1 minus the coordinates of its static position) and the dependence N ₁ (t) = - 21 · e ^{-3.0 · t} , enveloping the local minimums of displacements. The natural frequency of the first tone became equal to ω ₁ = 7.6 Hz instead of ω ₁ = 6.4 Hz, characteristic of the case of free oscillations without dampers. When a vertical load is applied to the shaft 10 (reciprocating movement of the beam attached to the rod 14), the shaft 10 does not rotate around its axis and rubs the outer surfaces of the rings 11 along the surfaces of the bore in the eccentric shaft 6. These oscillations through the fork rod 14 (Fig. 1 , 2) they are transferred to an annular spring 2, which is connected at one end to a fixed base 1, and the second end to a shaft - an eccentric 6. Applying a vertical load to the shaft causes the eccentric 6 to rotate about the axis C of the ring 4 inside the base 1 and rotate his mouth at an angle α _k . When this occurs, the deformation of the annular spring, rigidly connected to the eccentric and pivotally connected to the base. Due to the friction force and the stiffness of the spring, the oscillations die out after a short period of time. The figure 5 shows the movement of the attachment points of the dampers to the beam (the movement of points 2 and 3 minus the coordinates of their static positions).

The figure 6 shows the dependence of the efforts of the damper on the movements of its attachment point 2 to the beam. From the moment the movement started from point 0 of the graph, point 2 or 3 of the beam sequentially moved along the coordinates at points 1, 2, 3, 4, 5, 6, closing at the same time at point 6 a flat figure in the form of a “butterfly”. At the moment the point 2 of the beam hits the position with coordinates 6, the first period of the natural vibrations of the beam in the first tone has ended. This point turns into point 0 for the second period of oscillation, which ends at the next closure of the “butterfly” of a smaller scale. The process ends with stopping the movement at the origin of the graph (zero point). The figure 7 shows the dependence of the efforts of the damper on the movements of its attachment point 3 to the beam. The process of damping oscillations for point 3 also ends with a stop of movement at the origin of the graph coordinates (zero point). The total damping time of the vibration of the points of attachment of the dampers to the beam (points 2 and 3) is 1.5 ÷ 2 seconds.

Effective damping while increasing the rigidity of the oscillatory system is one of the advantages of using the studied dampers in comparison with the use of hydromechanical and hydraulic (linear) dampers, which reduce the natural frequency of oscillations of the system. The logarithmic decrement of the oscillation of the first tone, determined in accordance with the found values of the frequency and exponent of the exponent of the function N ₁ (t), is equal to the value: 0.39.

A comparison of the graphs in figures 4 and 5 shows that the relatively small movements of the dampers provide effective damping of the vibrations of the entire beam.

The ability to work effectively with very small intrinsic displacements compared with the displacements of the damped system is the main advantage of mechanical dampers based on rotational friction pairs.

Claims (1)

A mechanical damper of low-amplitude vibrations with rotational friction pairs, containing a base and a spring, characterized in that an annular shaped spring is pivotally fixed to the base, a steel ring is installed inside the base, the inner surface of which is coated with predetermined tribological characteristics, an eccentric shaft is located inside the ring, inside of which a cylindrical through hole with an eccentricity with respect to the outer cylindrical surfaces of the shaft is made, the shaft is clamped by a screw and in symmetrically located split elements and together with split elements forms a single lever, the ends of which are rigidly connected with attachment points to the outer shanks of the end of the shaped spring, inside the cam shaft there is a shaft with tapered seats, a fork link is attached to the shaft, through which reciprocating movement from the oscillation source through two cylindrical holes equally spaced from the axis of symmetry is transmitted to the damper; in addition, two rings are mounted on the shaft with conical inner surfaces for controlling the contact pressure of these surfaces to the tapered surfaces of the shaft and the outer cylindrical surface of the rings is coated with desired tribological characteristics.

Images