RU2597042C1 - Method for vibration isolation of helicopter pilot and seat suspension for realising said method - Google Patents

Abstract

FIELD: aviation.

SUBSTANCE: invention relates to methods and devices for vibration isolation of workstations of aircraft pilots. Method for vibration isolation of a helicopter pilot consists in that suspension includes an additional elastic element with controlled stiffness element in parallel to action of first elastic element. Method includes minimising total stiffness of both flexible elements at specified interval of amplitudes of relative displacements of system, defined by conditions of its safe operation. Method includes generating and activating an addition signal for controlling parameters of elastic element at frequency which is less than main frequency of natural vibrations of system. Seat suspension comprises guide mechanism, elastic element and device for control of parameters of elastic element. Suspension is equipped with additional elastic element with adjustable alternating rigidity, installed parallel to action of first elastic element. Control device comprises two channels, one of which has possibility of activation at frequency which is less than main frequency of vibrational motion system.

EFFECT: wider range of frequencies of vibration isolation at preset amplitude limitations of relative displacements.

3 cl, 13 dwg

Description

The invention relates to methods of vibration isolation and can be used in equipping workplaces for pilots, other crew members, as well as passengers of helicopters for various purposes.

It is known that in flight the helicopter fuselage vibrates in a wide range of low frequencies, 1 ÷ 100 Hz, especially intensively in the range of infra-low frequencies, 1 ÷ 10 Hz, the most harmful for the safe and efficient operation of the crew, as well as passenger comfort. Doses of harmful effects of vibration to a person in the range of infra-low frequencies become critical with increasing flight duration. It is also known that vibration isolation in the range of infra-low frequencies is the most difficult technical task for this type of aircraft.

Known methods (P. Konstanzer et al., Recent advances in Euro copter's passive and active vibration control: Proceedings of the 64 ^th Annual Forum of the American Helicopter Society, Montreal, Canada, 2008, pp. 75-93) helicopter pilots, consisting in the introduction of elastic elements in the vibration-isolating system of the pilot seats. However, these methods provide a certain effect in the frequency range of 20 ÷ 40 Hz and above and, accordingly, are ineffective in the range of infra-low frequencies.

There is also known a method (RG Camilo, MT Jonathan. A device for reducing vibration of a helicopter pilot's seat. / RF Patent 2504487, publ. 01.20.2014, bull. No. 2) vibration isolation of helicopter pilots, the closest to the claimed method for the technical result, which consists in introducing into the vibration-insulating system the pilot's seat of the suspension, equipped with an elastic element and a guiding mechanism, the structural elements of which form a kinematic chain of movable joints to ensure vibrational movement of the system in a given direction and reduce the intensity of the action of pulsed loads, in the formation and activation of the control signal for the parameters of the elastic element. The method gives a certain effect, starting from 7 ÷ 8 Hz and above, and high-quality vibration isolation - from 12 ÷ 16 Hz. Therefore, this method is ineffective in most of the frequency range, the most harmful and dangerous to the health and functional activity of helicopter pilots, as well as passenger comfort. The main causes of inefficiency: (a) high rigidity of the elastic element in the vertical (main) direction of the vibrational movement of the system; (b) limiting the amplitudes of relative displacements and, accordingly, the dimensions of the working space of the system to ensure its safe operation; (c) low mechanical quality factor of the system due to the structural redundancy of the kinematic chain.

Known seat suspension (O. Krejcir, Pneumaticka Vibroizolace, Doctorska disertacna prace. Liberec, Czech Republic, 1986), containing a guide mechanism, an elastic element in the form of a rodless pneumatic spring and a device for controlling the parameters of the elastic element. Drawbacks of the suspension: a) the section of relative displacements during which the suspension can be effective in case of vibrations in the range of infra-low frequencies is significantly less than the suspension travel; b) the effect is unstable and depends on the design features of the suspension; c) an increase in the length of this section leads to a significant increase in the dimensions of the suspension, incompatible with the requirements for compactness and safety of the vibration-isolating system of the pilot.

Closest to the claimed is the suspension (RG Camilo, MT Jonathan. Device for reducing vibration of the helicopter pilot's seat. / RF Patent 2504487, publ. 01.20.2014, bull. No. 2) for implementing the known method, installed under the pilot's seat and containing a steering mechanism, an elastic element in the form of a rodless pneumatic spring and a device for controlling the parameters of the elastic element. This suspension is ineffective in most of the range of infra-low frequencies, the most harmful and dangerous for pilots, as well as the comfort of helicopter passengers. The main causes of inefficiency: a) high rigidity of the elastic element in the vertical (main) direction of the vibrational movement of the system; b) low mechanical quality factor of the suspension due to the structural redundancy of its kinematic chain.

The objective of the invention (technical result): improving the quality and expanding the frequency range of vibration isolation with given restrictions on the amplitudes of the relative movements of the vibration isolating system.

The problem is solved using the method according to which a suspension is introduced into the vibration-isolating system of the pilot's seat, equipped with an elastic element and a guiding mechanism, the structural elements of which form a kinematic chain of movable joints to provide vibrational movement of the system in a given direction, form and activate a control signal for the parameters of the elastic element, an additional elastic element with adjustable stiffness is also introduced, which is attached to the system without increasing its working pressure space in a given direction parallel to the action of the elastic element, then minimize the total stiffness of both elastic elements in a given range of amplitudes of relative displacements of the system, determined by the conditions of its safe operation, then increase the mechanical quality factor of the kinematic chain by generating and activating an additional control signal at a frequency lower than the main frequency vibrational motion of the system. In addition, an additional elastic element is assembled in the form of modules from interchangeable springs of alternating stiffness and attached to the suspension, at least without increasing the structural redundancy of the chain, for example, by force closure.

The technical result is also achieved by the fact that the known suspension of the pilot seat, comprising a steering mechanism, an elastic element and a device for controlling the parameters of the elastic element, is provided with an additional elastic element with adjustable alternating stiffness set parallel to the action of the elastic element without increasing the working space of the suspension, and the control device contains at least two control channels, one of which has the ability to activate at a frequency lower than the main vibration frequency ion motion system.

The invention is illustrated using examples of the method, for which the following illustrations are presented:

FIG. 1. The general structural diagram of the vibration isolating system.

FIG. 2. General view of the suspension guide mechanism with an additional elastic element (option for flight tests).

FIG. 3. Elastic and strength characteristics of an additional elastic element with adjustable alternating stiffness.

FIG. 4. The effect of reducing the mechanical quality factor of the kinematic chain during the vibrational movement of the system at infralow frequencies.

FIG. 5. Additional activation of the system at a frequency lower than the main frequency of the vibrational movement of the system.

FIG. 6. Suspension characteristics before and after the introduction of additional activation of the system (results of static bench tests).

FIG. 7. Step-by-step improvement of the quality and expansion of the vibration isolation frequency range (results of dynamic bench tests).

FIG. 8. Reducing impulse loads on the system with air damping and an elastic element.

FIG. 9. Reducing the impulse loads on the system with air damping and both elastic elements.

FIG. 10. General view of the vibration-isolating seat for the pilot (option for flight tests on a Mi-8 helicopter).

FIG. 11. Scheme of facilities and means for comparative flight tests.

FIG. 12. The quality of the vibration isolation of the system according to the method in the range of infralow frequencies at one of the transitional flight modes at a speed of 70 km / h (flight test results).

FIG. 13. The quality of the vibration isolation of the system according to the method in the range of infralow frequencies in the steady flight mode with a cruising speed of 200 ± 3 km / h (flight test results).

The seat suspension for implementing the method (see Fig. 1) contains a guiding mechanism including a base 1, two pairs of levers 2 and 3 placed in parallel planes, symmetrically to the longitudinal axis of the suspension, and forming a kinematic chain of movable joints between themselves and the output structural element 4 using bearings 5 and 6, while the element 4 is equipped with a platform for attaching the seat 7 of the seat with the possibility of its movement and fixing using mechanism 8 during the setup process, as well as an elastic element made, for example , in the form of a rodless pneumatic spring 9. In addition, the suspension is equipped with an additional elastic element made, for example, in the form of two removable modules compactly placed in parallel planes on the outer surfaces of the base 1, each module containing springs 10, a central sleeve 11 and the housing 12, as well as the device for presetting the spring 10 (not shown), and the spring 10 is made in the form of interchangeable sets of plates of spring steel, one ends of which are placed in the grooves made with angular pitch on the central sleeve 11 mounted in the bearing support 5 on the base 1, and the other ends in grooves made with the same angular pitch on the housing 12, with the possibility of supercritical elastic deformation during assembly and adjustment, and the bushings 11 are provided, for example , slots 13 for power closure with levers 3, and the housings 12 are rigidly connected to the base 1. In addition, the suspension is equipped with a device for controlling the parameters of the elastic element containing block 14 for air selection from the pneumatic network of the helicopter, block 15 preparation air and at least two control channels, one of which (conditionally, control channel No. 1) contains an air distributor 16 with an electromagnetic actuator, and the other (conditionally, control channel No. 2) contains an air distributor 17 with an electromagnetic actuator, the device is equipped with a sensor 18 of angular movements of the levers 2 relative to the base 1, an air pressure sensor 19 at the entrance to the spring 9 and a controller 20, consisting of a programmable microprocessor equipped with a power source and working on a given set of algorithms.

Several suspension options have been developed. A small series of pendants was made for their bench static and dynamic (vibration) tests; one of the options (see Fig. 2) is for comparative flight tests consisting of seats for pilots of Mi-8 helicopters of various modifications, as well as seats for operators controlling the process of ground work conducted using Mi-26 helicopters. A methodology for online design design and optimization of the parameters of an additional elastic element in the form of a module with a spring 10 has been developed and tested, the alternating stiffness ± k ₂ (φ) of which is adjustable within specified limits. The module is designed for use in systems with a certain static load. A variant of the module in FIG. 2 is designed for a load of up to 0.75 kN and has dimensions: height 120 mm, width 155 mm, depth 25 mm (excluding the length of the slots and the thickness of the cover of the protective casing). A set of two modules occupies less than 5–7% of the total suspension volume.

) в соответствии с критерием вида $${\tilde{\sigma }}_{\max }=\sigma /{\sigma }_e<1$$

, σ_e - предел упругости. В результате обеспечивается работоспособность пружин 10 и виброизолирующей системы в целом в течение заданного числа циклов нагружения.An example of the elastic characteristic (torque T) of the springs 10 obtained from the design results is shown in FIG. 3. Here, in sections P ₁ O ₁ and O ₂ P ₂ - spring stiffness 10 is variable "positive", in section O ₁ O ₂ - variable "negative", at points O ₁ and O ₂ - zero. At the same time, in the process of designing and optimizing the design, the strength of the springs 10 is monitored (see dimensionless bending stresses $$\tilde{\sigma }$$

) in accordance with the criterion of the form $${\tilde{\sigma }}_{\max }=\sigma /{\sigma }_e<\mathrm{one}$$

, σ _e is the elastic limit. The result is the operability of the springs 10 and the vibration isolation system as a whole for a given number of loading cycles.

The method is carried out using a seat suspension as follows. Each module with springs 10 is assembled, pre-configured and coupled to the suspension in such a way that their total stiffness ± 2k ₂ (φ) ensures that one of the following conditions is met:

where k ₁ (z) is the stiffness of the elastic element 9; Ф - transfer function, determined by the parameters of geometric characteristics (working length of pairs of levers 2 and 3) and the requirements of compact suspension; φ is the parametric degree of freedom (in this case, the angle of the rotational motion of the sleeve 11 in the process of elastic deformation of the spring 10).

The springs 10 are set parallel to the action of the elastic element 9, so as not to increase the magnitudes of the relative displacements of the vibration-insulating system, determined by the conditions of its safe operation, and, accordingly, the size of the working space of the system in the vertical (main) direction z of its vibrational movement.

In order to fulfill conditions (1a) and (1b), the total stiffness of both elastic elements within section 1 is minimized (see the elastic characteristic of springs 10 in Fig. 3) throughout the entire suspension travel z ₀ , the value of which is determined by the conditions of safe operation of the vibration-isolating system pilot (see below). As a result, the stiffness of the suspension is reduced to a value necessary to obtain a certain quality of vibration isolation in the range of infra-low frequencies. For example, as shown by bench tests, suspension stiffness can be reduced in the direction z with k ₁ ≤4200 ÷ 5500 N / m (using a rodless air spring as a resilient member 9) to k≤420 ÷ 450 N / m by using additional elastic element with springs 10.

, необходимая для преодоления сопротивления и начала движения в заданном направлении, уменьшена примерно в 1,2 раза, соответственно, увеличена механическая добротность подвески. Здесь с помощью индексов 1↑ и 1↓ и 2↑ и 2↓ показаны, соответственно, безразмерные нагрузочные и разгрузочные ветви упругой характеристики подвески (суммарной характеристики обоих упругих элементов) при определенном значении номинальной статической нагрузки F_ном на сиденье, до и после введения дополнительной активации. В результате, амплитуда относительных перемещений подвески восстановлена до необходимых значений, например, до 2z₂ (см. фиг. 4); стало возможным дополнительно минимизировать суммарную жесткость обоих упругих элементов, причем без потери несущей способности системы. Например, в ходе стендовых испытаний показано, что суммарную жесткость возможно снизить до величины k≤180÷185 Н/м.To improve the quality of the pilots' vibration isolation in the infrared frequency band of 1 ÷ 4 Hz and less, regulation and minimization of stiffness only within section 1 (see Fig. 3) may be insufficient. With vibrational motion at these frequencies, a softer suspension may be required. Then it is necessary to go from section 1 of the elastic characteristic of the springs 10 for movement relative to some initial position N ₁ to segment 2 and to ensure movement relative to some new initial position N ₂ . The transition from the base section 1 of the elastic characteristic to the extended section 1 + 2 of regulation of the "negative" stiffness of the additional elastic element is carried out by, for example, changing the initial angular position of the sleeve 11 relative to the levers 3 (see Fig. 1), choosing the appropriate sequence of slots 13 in the process assembly and suspension settings. However, to ensure the operation of the system on segment 2, it is necessary to increase the mechanical quality factor of the suspension. Low mechanical quality factor due to friction in the movable joints of the guide mechanism results, as illustrated in FIG. 4, to partial blocking and, as a consequence, to a decrease in the amplitude of relative displacements, for example, to a value of 2z ₁ . In this case, increase the mechanical quality factor by additional activation of the elastic element 9. Let us show one of the practical examples. To overcome the resistance, especially with an input vibration signal with small amplitudes, the suspension vibrations are activated at a frequency lower than the main frequency of the system’s vibrational movement. In FIG. 5 it is shown that in a system vibrating with a fundamental frequency f ₀ = (0.5 ÷ 0.6) Hz, additional oscillations are excited with a frequency f≈0.4 ± 0.02 Hz and an amplitude of the order of 4.5 mm. From FIG. 6 it follows that dimensionless force $$\tilde{F}$$

necessary to overcome the resistance and the beginning of movement in a given direction, reduced by about 1.2 times, respectively, increased the mechanical quality factor of the suspension. Here, using indices 1 ↑ and 1 ↓ and 2 ↑ and 2 ↓, respectively, the dimensionless loading and unloading branches of the elastic characteristic of the suspension (the total characteristic of both elastic elements) are shown for a certain value of the nominal static load F _nom on the seat, before and after the introduction of additional activation. As a result, the amplitude of the relative movements of the suspension is restored to the required values, for example, to 2z ₂ (see Fig. 4); it became possible to further minimize the total stiffness of both elastic elements, and without loss of the bearing capacity of the system. For example, during bench tests it was shown that the total stiffness can be reduced to a value of k≤180 ÷ 185 N / m.

Figure 7 illustrates a phased increase in the quality of vibration isolation (in terms of "transmission coefficient") and the expansion of the range of infra-low frequencies due to the combined action of an additional elastic element and additional activation. During comparative bench tests, for a given level of external vibrational impact (see the graph “input vibration signal”), it was found that the prototype system containing an elastic element 9 and a standard hydraulic damper provides vibration isolation, starting from 7 ÷ 8 Hz. That is, the prototype system is ineffective in most of the infrared frequency range, moreover, it amplifies the input vibration signal in the frequency band 3 ÷ 7 Hz (see graph 1). However, the system according to the method provides vibration isolation in the frequency range starting from 1.5 ÷ 2 Hz, due to the joint work of the elastic element 9 and the springs 10 of the additional elastic element (see graph 2). And the introduction of additional activation of the system at a frequency lower than the main frequency of the vibrational movement allows you to expand the frequency range of high-quality vibration isolation. The graph in figure 3 shows that vibration isolation can be carried out starting from 0.1 Hz, while the efficiency of the system can increase up to 30 times or more in comparison with the prototype system, and in the entire range of infra-low frequencies, 1 ÷ 10 Hz, the most harmful and dangerous for the pilots, as well as passenger comfort.

Attaching an additional elastic element to the suspension is performed by force closure using a spline connection 13. This allows at least not to increase the structural redundancy (static indeterminacy) of the kinematic chain of the suspension guide mechanism. This, in turn, contributes to an additional increase in the mechanical quality factor of the system and, accordingly, the quality of vibration isolation in an extended range of infra-low frequencies with small vibration amplitudes. To predict this possibility, the authors developed and tested a formula for quantifying the rational values of structural redundancy, convenient for practical engineering calculations (all structural characteristics are integers):

where m is the number of degrees of freedom of the system; n _KC is the total number of kinematic chains; H _i - the number of degrees of freedom of one mobile connection with i-th mobility; S is the total number of degrees of freedom in all compounds; q _RC is the value of structural redundancy.

Using formula (2), it is possible to show that in the prototype system, for example, with one degree of freedom, m = 1, the kinematic chain has structural redundancy q _RC = 21, i.e. 21 times statically indefinable. However, in the system according to the method, also with one degree of freedom, m = 1, the chain has structural redundancy an order of magnitude lower: q _RC = 3, even after attaching an additional elastic element (in the form of a set of two modules with springs 10) to suspension by power short circuit. In this case, four movable joints 5, ΣH ₁ = 4, with one degree of freedom each (radial bearings) and four movable joints 6, ΣH ₃ = 12, with three degrees of freedom each (spherical bearings) can be used to assemble the circuit. Such a short circuit does not at least increase the structural redundancy of the circuit. Using formula (2), by enumerating the types of bearings for joints 5 and 6, a statically determinable kinematic chain is obtained, i.e. q _RC = 0.

Consider the features of active control of the parameters of the elastic element 9. In FIG. 7 it can be seen that the system according to the method became, in contrast to the prototype system, resonantless in the entire investigated frequency range. Moreover, this is achieved without an external damping mechanism (without a hydraulic damper), which is a necessary structural element of the prototype system. That is, an external damper to the “soft” system is not required. In a steady motion, active control of the “soft” system is also not required. In this case, both control channels are closed if the trajectory of the system is in the vicinity of point N ₁ or N ₂ (see Fig. 3). Active control (for example, channel No. 1 continuously operates with distributor 16) is used to prevent the drift of the initial position towards the point O ₂ . From the solution of the continuity equation, a dimensionless criterion is obtained (the ratio of the cross-sectional area of the distributor 16 and the working chamber of the elastic element 9, made in the form of a rodless pneumatic spring):

When designing a real system, the values of criterion (3) are clarified by optimizing the relationship between the operating parameters of the valves used in practice and the intensity of the input impact on the system at certain values of the relative speeds (system response) and transient times.

Some damping of the “soft” resonance-free system is required only when the static load changes abruptly, for example: (a) when the pilot suddenly leaves his seat and / or places another pilot on it, the weight of which differs sharply from the weight of the previous pilot; (b) in emergency situations (emergency landing, etc. emergency flight situations). An effective solution to this particular problem is possible, for example, by using the variable structure of the air damping system. In FIG. 8 for a variant in which the elastic element 9 is made in the form of a rodless pneumatic spring, it is shown that at certain values of the speeds of the relative motion of the system, the amplitude of the relative displacements increases. This can lead to the system reaching the travel limiter and impulse action on it. In this case, the operation of the elastic element 9 only when controlled by channel No. 1 (through the distributor 16) is not able to prevent the system from reaching the travel limiter. At the same time, control over the channel No. 2 (through the distributor 17) allows you to position the system containing both elastic elements, almost instantly (see Fig. 9). In the examples of FIG. 8 and FIG. 9 bench tests were performed with external vibration exposure with a displacement amplitude of up to 100 mm, which is several times higher than the suspension travel. The ratio between the size of the bore of the distributor 17 and the working chamber of the air spring (dimensionless criterion of effective air damping) was:

In FIG. 12 and FIG. 13 shows the results of an instrumental study of the effectiveness of a vibration isolating system in flight. A vibrodevice with two accelerometers was used, one of which was fixed on the cockpit floor, and the second, alternately, was mounted on technological plates placed on the elastic cushions of the seats of the first and second pilots. The tests were carried out on helicopters that left the scheduled overhaul. An example of the layout of a variant of the system according to the method for equipping the workplace of the second pilot of the Mi-8 helicopter is shown in FIG. 10. The main tasks of flight tests: (a) comparison of the quality of the analog system (the workplace of the first pilot) and the system according to the method (workplace of the second pilot); (b) analysis of the quality of both systems for compliance with standards in accordance with the international standard ISO 2631. The layout of the equipment is presented in FIG. 11. It is shown here that the largest suspension dimension for implementing the method does not exceed 250 mm. The suspension travel in the vertical direction did not exceed 50 mm. This is important because, as was established during bench tests and confirmed by the results of flight tests, the stroke cannot exceed 50 ± 5 mm, because otherwise, the safety of the pilot is reduced, and helicopter control is impaired. In particular, according to the reports of test pilots, they “lose their horizon” in certain flight modes if the amplitude of the relative displacements of the system exceeds 25 mm. Obviously, under such restrictions on the relative displacements, the analog system or the prototype system cannot be effective, especially in the range of infra-low frequencies. Therefore, in the transition mode of flight, the vibration isolation system of the first pilot amplifies the input vibration signal at frequencies of 1, 4, and 10 Hz. At the same time, the vibration isolation system of the second pilot shows high efficiency in this frequency range. In the steady state, the vibration isolation system of the first pilot is ineffective in the frequency range of 1, 8, and 10 Hz and, therefore, does not meet the requirements of the ISO 2631 standard. Moreover, the vibration isolation system of the second pilot shows high efficiency in the studied frequency range. The vibration isolation system of the second pilot reduces the input vibration signal at least 3 ÷ 30 times more efficiently than the system of the first pilot and ensures the quality that meets the standards of vibration safety and functional comfort of crew members and passengers of helicopters, including in the range of the most harmful and dangerous infra-low frequencies.

Thus, the inventive method with the help of the suspension allows you to solve the problem of improving the quality and expanding the frequency range of vibration isolation of pilots, as well as passengers of helicopters with given restrictions on the amplitudes of the relative movements of the system. The inventive method and suspension for its implementation can be effective in improving existing systems and in creating promising developments.

Claims (3)

1. The method of vibration isolation of a helicopter pilot, according to which a suspension is introduced into the vibration-isolating system of the seat, equipped with an elastic element and a guiding mechanism, the structural elements of which form a kinematic chain of movable joints to provide vibrational movement of the system in a given direction, and also form and activate a control signal for the parameters of the elastic element characterized in that they also introduce an additional elastic element with adjustable stiffness, which is attached to the system without increased By means of its working space in a given direction parallel to the action of an elastic element, the total stiffness of both elastic elements is minimized over a given range of amplitudes of relative displacements of the system determined by the conditions of its safe operation, then the mechanical quality factor of the kinematic chain is increased by generating and activating an additional control signal at a frequency lower fundamental frequency of the vibrational movement of the system. 2. The method according to p. 1, characterized in that the additional elastic element is assembled in the form of modules from interchangeable springs of alternating stiffness and attached to the suspension, at least without increasing the structural redundancy of the circuit, for example, by means of a power circuit. 3. The seat suspension for implementing the method according to claim 1 or 2, comprising a guiding mechanism, an elastic element and a device for controlling the parameters of the elastic element, characterized in that it is equipped with an additional elastic element with adjustable alternating stiffness, set in parallel with the action of the elastic element, without increasing the working suspension space, and the control device contains at least two channels, one of which has the ability to activate at a frequency less than the main frequency of the vibrational movement system.

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