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The mobile power car is a vehicle-mounted mobile power station specially designed to fill the gap of power supply and supply power for various disasters. It is characterized by mobility and flexibility. In addition to providing mobile power, it can also carry certain construction personnel and construction tools with the vehicle to the construction site to perform various tasks for various users.
1.1 Customer groups with special requirements for noise reduction
This type of customer chooses a mobile power car and focuses on the selection of a vehicle-mounted silent mobile power car series, which has special requirements for the mobility and noise reduction of the entire vehicle. Mainly to provide mobile power or as an emergency power source for operations in urban areas or in densely populated areas, and to accompany the vehicle with certain construction personnel and construction tools to complete relevant operations at the construction site.
At present, this type of customer group mainly includes telecommunication departments such as China Telecom and China Mobile; troops, large shopping malls, movie studios, power companies, and municipal construction users.
1.2 Customer groups with no special requirements for noise reduction
This kind of customer chooses the mobile power car to focus on the selection of trailer-type mobile power station series, mainly to provide mobile power in suburban and field operations. During operation, a tractor can put multiple power trailers on multiple construction sites to complete the task of multi-point, long-cycle construction operations, which is both efficient and cost-reducing.
At present, this type of customer group mainly includes: Troops: It is used to provide mobile power for military equipment (the noise reduction requirements are generally required for the upper part).
Petroleum Exploration Department: Provides mobile power for field operations.
Various types of municipal construction and construction outside the construction department: to provide mobile power for various types of municipal construction, such as water companies, gas companies in the field for pipeline installation and maintenance operations.
1.3 Comprehensive customers:
Such customers may choose between two kinds of mobile power cars, usually as emergency power supply and on-site construction for their own use, and they can be used for rental purposes.
At present, such customer groups mainly include: power supply units and private construction units that often use mobile power stations.
In order to meet the different needs of various types of customers for mobile power vehicles, a series of mobile power car products with different structural characteristics have been formed from the chassis series to the top two, which are categorized as follows:
2.1 standard vehicle-mounted mobile power car
Power-generating equipment () is installed on mobile power cars on various standard truck chassis. This series of vehicles can directly use trucks such as Yuejin, Iveco and Dongfeng as the mobile power station vehicles.
This type of mobile power car has strong mobility, and it generally has a relatively high market demand for lowering the number of mobile power car products. 2 The noise requirements of typical mobile power cars on the market today. These types of mobile power cars are mainly used in urban areas to reduce High noise requirements (1).
2.2 Trailer-type mobile power station
The power generation equipment is installed on various types of trailers. The mobile power car is mainly used in the field for a long period of time, and the top is generally not subjected to special noise reduction. According to the structural characteristics of the chassis, the trailer-type mobile power station is divided into the following four. class:
1. Single-axle, two-wheel light trailer-type mobile power station (2) 2. Two-axis four-wheel-slide steering type light trailer-type mobile power station (multi-axis on the base) 3. Two-axis four-wheel rotary steering power station (3 )4.Double-axle four-wheel steering tractor mobile power station (4)
3.1 Single-Axis Dual-Wheel and Dual-Axis Four-Wheel Sliding Steering Trailer-Type Mobile Power Station
3.1.1 Single-axle, two-wheel light trailer-type mobile power station
The production cost is relatively low, mainly for relatively light weight generator sets.
According to the braking mode, it can be divided into inertia braking and ordinary braking.
3.1.2 Two-axis four-wheel-slip steering type mobile power station
The production cost is slightly higher than that of the single axis and is mainly used for relatively light weight generator sets.
Its characteristic is that the stability is better than the two-wheeled single-axis mobile station, but its steering performance is slightly worse.
According to the braking mode, it can be divided into two types: inertial braking and ordinary braking. In structure, it is only one axis more than the single-axle, two-wheel light trailer-type mobile power station.
3.2 Two-axis four-wheel rotary steering power station
The production cost is moderate and can be used for heavy generator () groups.
It is characterized by better steering performance and load-bearing performance than the previous two. The disadvantage is that the center of gravity is high, and the swept area of ​​the steering wheel is large, and the steering wheel will appear as a dislodgement on an uneven road surface.
3.3 Dual-Axis Four Wheel Steering Trailer Mobile Station
High grade, high production cost, suitable for users with special requirements such as troops.
Its characteristics are light, flexible, low center of gravity, high-yielding performance, and an air brake brake system that can be used in heavy and light mobile power stations.
According to the structural characteristics and classification of the typical mobile power car, the difficulties and focuses of the design and development of the mobile power car series products should be placed on the expansion of the series of trailer chassis and on the noise reduction system of the top mounted generator cabin.
4.1 Chassis Design and Development
The standard car chassis can be directly purchased. This article focuses on the design and development of the trailer chassis.
4.1.1 Single-Axis Two-Wheel and Two-Axis Four-Wheel Sliding Steering Trailer Type Mobile Power Station
The inertia brake system is a key direction for the development of the above two chassis designs. The structural principles are as shown.
Inertia braking and traction function realization: When the tractor brake stops, the trailer moves forward with respect to the inertia of the tractor, causing an impact at the towing ring joint, forcing the brake arm to produce a "turning angle" while allowing the brake to turn The arm also generates corresponding “turning angle†and “brake stroke†to drive the brake cable mechanism to brake the brake, and the trailer brake stops to realize the braking function; when the tractor moves forward, the impact point is dragged to the front of the collision. In the position, the brakes are naturally relieved.
The realization of reversing function: When it is necessary to reverse the car, the braking wall is locked in the inserting locking hole to realize the reversing function. On the other hand, removing the "reverse parking lock" and "reverse parking lock" trailers are in an inertial braking state.
4.1.2 Dual-Axis 4-Wheel Rotary Steering Chassis (6)
The structure of the chassis is relatively simple. The front axle frame and the rear chassis assembly are connected through a turntable. The two can rotate relative to the center of the turntable. When the tractor is turning, the front axle frame is driven by the trailing ring to rotate relative to the rear chassis assembly. Realized synchronized steering with the preceding vehicle.
4.1.3 Dual-Axis Four Wheel Steering Trailer Chassis (7)
The structure of such chassis is relatively complex, and the wheeled steering mechanism is the focus of development and design.
The front wheel steering of the trailer is achieved by the tractor driving the double isosceles trapezoidal mechanism to drive the left and right front wheels to turn. Among them, the two front wheels are respectively connected with left and right two rocker isosceles trapezoidal mechanisms.
When the car is driving along a straight line (turn radius R = ∞), the two left and right axes line up with the rack.
Take the tractor turning right, for example, it requires two rounds to turn through different angles B and C (B is greater than C). Theoretically, it is hoped that the intersection point P of the front axle two-axis extension line can always fall on the extension line of the rear axle. In this way, the entire body can be rotated around the O point, so that all four wheels can form a pure rolling with the ground to reduce the wear of the tires. The left and right wheel rotation angles meet Ackerman's law and can achieve pure rolling of the four wheels and the ground.
According to Ackerman's law (as shown in the figure when the car is turning right), the tractor drives the tow bar to turn the angle A, the right wheel turns the angle B, and the left wheel turns the angle C, so the functional relationship between B and C is :ctgB-ctgC=JL steering angle difference D=B-C Derivation of turning radius R=(1/SinDmax)+Rs 4 Design and development of mobile power car series
J is the distance between the left and right wheel spindle pin R is the turning radius O point is the turning center Rs is the spindle pin offset distance Under the premise of determining the wheelbase and the wheelbase, a reasonable design of the isosceles trapezoidal mechanism parameters can meet the above formula. Kerman's functional relationship realizes pure steering of the trailer steering system with four wheels.
The main function of the mobile power car is to provide mobile power, work cabin part, and can be designed as a generator cabin and a tool cabin as required. The power of on-board generators varies from 20KW-400KW, and the operation of the generator usually produces 90-110DB noise. Reasonable use of the limited space of the vehicle body, according to the characteristics of noise sources, the application of a variety of noise reduction technology can achieve a larger amount of noise reduction, to meet the national standard noise reduction standards. The noise reduction system of the generator set is the focus of the design and development of the top part of the mobile power car.
5.1 National Standard for Noise Reduction of Mobile Power Cars
The noise reduction processing of mobile power car motor units must comply with the corresponding national standards. The requirements for environmental noise of national standards GB12348-90 and GB12349-90 are: Category II standards (applicable to residential, commercial, industrial mixed areas and commercial center areas) Between the daytime 60db (a), night 50db (a); three types of standards (applicable to industrial areas) 65db (a), 55db (a) at night.
Low noise engineering is usually designed to meet the 60db(a) standard.
5.2 Typical structure of noise reduction on mobile power generators
8 is a mute type mobile power layout schematic.
5.3 Noise Analysis
In order to effectively control noise, it is first necessary to analyze the generation and distribution of noise from the generating units in order to use targeted noise control techniques. According to the working principle of the gas turbine generator set, its noise generation is very complicated.
From the point of view of the causes and parts, the noise of the gas turbine generator set can include the following parts: (1) engine exhaust smoke noise; (2) mechanical noise; (3) combustion noise; (4) cooling fan and exhaust air Noise; (5) Inlet noise; (6) Generator noise.
According to its propagation path, it can be classified into the following types of noise: (1) The exhaust noise of an internal combustion engine is the exhaust passage noise of an internal combustion engine, and the exhaust noise is a high-temperature, high-speed pulsating airflow noise. The part, which is much higher than the intake noise and mechanical noise emitted by the body, is the main component of the total noise of the unit and is also the focus of noise control. Its fundamental frequency is the ignition frequency of the internal combustion engine. (2) The intake noise is the noise at the inlet of the box. Inlet noise is mainly organic mechanical noise, generator noise, and airflow noise. Since the intake air is passive air intake and is located away from the main noise source, the noise level is relatively low compared to other locations and the required noise reduction is small. (3) Exhaust noise refers to the noise at the outlet of the box. The main components of the exhaust noise are exhaust noise, airflow noise, fan noise, mechanical noise, and combustion noise of the internal combustion engine. There are many noise sources in this area and the noise level is high. Because the unit uses strong exhaust air to cool down and increase the outward propagation of noise, noise control here is relatively difficult.
5.4 mobile power car cabin design
For the functional requirements of the mobile power car cabin, the cabin is designed as a front generator silent cabin and a rear tool cabin. The noise reduction processing system of the generator cabin is the focus of design and development. In order to effectively control various noises, sound control, sound absorption, and noise elimination are used to process the noise in different parts. The specific design is as follows:
5.4.1 Control of Engine Exhaust Noise
Since the exhaust pipe is the largest noise diffusion source of diesel generator sets, it is the focus of noise reduction processing. Therefore, the simplest and most effective way to suppress engine exhaust noise is to install a muffler on the exhaust pipe. The muffler used should minimize the pressure loss of various parts of the channel, so it is necessary to adhere to the following principles: 1 Minimize the airflow velocity of each component in the exhaust channel; 2 Minimize the number of right angle elbows in the exhaust channel, and expand the row Tracheal section.
Therefore, the above principles should be followed when designing noise reduction processing. According to the unit noise level, a combination of a resistive muffler, a resistance muffler, or a combination of the two can be used to achieve the goal of noise reduction.
Resistive muffler (namely what we usually call industrial muffler): It uses porous sound-absorbing material and is arranged in a certain way in the pipeline. When the airflow passes through the resistive muffler, the sound waves cause air and fine fibers in the pores of the sound-absorbing material. The shock. Due to friction and viscous resistance, acoustic energy becomes heat energy and absorbs, thus playing a role in noise elimination.
Resistive muffler (which we usually refer to as a residential muffler) is a combination of pipes and resonant cavities of different shapes, reflecting and interfering with acoustic impedance mismatch caused by changes in pipe section and shape. To achieve the purpose of attenuating noise. The noise reduction effect is related to the shape, size and structure of the pipeline, and generally has a strong selectivity, which is suitable for narrowband noise and reduction of low and medium frequency noise.
According to the above analysis, the noise reduction treatment of the exhaust system of the unit can adopt the following combination of measures: a combination of a ripple damping section, an industrial-type muffler, and a residential-type muffler is generally used to effectively block exhaust vibration and exhaust noise. Spread. At the same time, the thermal insulation and soundproofing of the exhaust pipe can improve the unit's operating environment and the noise caused by the exhaust pipe; the exhaust outlet of the mobile power car has two methods: exhaust on the roof and exhaust under the car. select. The actual measurement shows that the exhaust noise (at the exhaust pipe outlet lm) is reduced by 30dB.
5.4.2 Sound insulation, sound absorption calculation and design of quiet cabin in mobile power car cabin
The soundproof box is a closed space designed to effectively reduce the impact of noise on the outside of the unit and effectively block the noise propagation path. When the unit is placed inside the box, due to sound insulation technology, sound absorption and other technologies to effectively prevent the noise from spreading out, the noise of the noise source is controlled inside the box, thereby reducing its impact on the outside world. The sound insulation technology uses a sound insulator to change the direction of the sound wave (reflection, refraction) so that the energy of the sound wave penetrating the object is weakened, thereby reducing the noise on the other side of the sound insulator. The sound insulation amount TL of the object is related to the areal density of the component and the excitation frequency of the acoustic wave. The formula for calculating the sound insulation of the single layer board is: TL = 181gm + 121gf - 25 (1) Therefore, the greater the surface density, the greater the inertial resistance, and the more difficult it is to excite the vibration. The more difficult it is to transmit sound waves, the greater the amount of sound insulation. Therefore, when designing, try to choose a material with a large surface density as the panel wall.
In practical engineering applications, the sound insulation amount of the wallboard is often calculated by the average sound insulation amount. The calculation formula is: TLsoo=181gm+8 (2) According to the actual sound insulation requirement, the thickness of the wallboard is calculated by the formula (2). While performing sound insulation processing, a large amount of sound waves are reflected back inside the box and form a reverberation sound with the original sound waves, which will increase the internal noise level and noise energy, thereby reducing the sound insulation effect of the wall panels.
Therefore, in the sound insulation treatment, sound absorption materials are attached to the inner side of the wall panel to absorb sound inside. The noise energy in the box is reduced while the noise is radiated outward, thereby effectively reducing the overall noise level. Absorption is the process of sound absorption. When a sound wave encounters various types of materials, some acoustic energy propagates to the interior of the material, resulting in energy transfer, conversion, or interference superposition. As a result, the energy of the sound wave is weakened, which is intuitively reflected in the reduction of sound level. The noise value drops. Different materials have different sound absorption coefficients, and their sound absorption effects are also different. The amount of sound absorption can be calculated by the following formula: ΔLp=lOlg(a2/a1) (3) where a1, a2 are the average sound absorption coefficients before and after the surface treatment, a=Σaisi/S, ai is “absorption on the surface of the room†Coefficient", si is the area where ai is located in the plane, and S is the sum of the surface area in the room.
According to the sound insulation and sound absorption theory and calculation formula above, the enclosure of the enclosure is made of 2mm steel plate with 80-120mm sound-absorbing material (rockwool) attached, and then fixed with a 1.0mm perforated plate. These parts are assembled together as a compartment. Acoustic wallboard can effectively block noise more than 25dB. The siding structure is as shown. Doors and observation windows set for the convenience of maintenance and observation data become weak links in the sound insulation wall panels. Therefore, the doors are thickened and sealed in multiple layers. After the electrical windows are used in observation windows, the noise is effectively resolved from the doors and windows. And the problems that came out of the gap.
5.4.3 noise reduction design and calculation of noise inlet and exhaust ports
Because the box adopts natural air intake and forced air discharge, holes are formed in the air intake and exhaust vents, resulting in leakage sound, ie, an intake noise area and an exhaust noise area are formed. In order to prevent the noise from being transmitted from the inlet and outlet air ducts, the inlet and outlet air outlets must be installed into the exhaust muffler (structures). According to the amount of exhaust gas and the amount of gas, the intake and exhaust muffler channel is designed to ensure that all the required noise reduction effects are achieved under the premise of smooth intake and exhaust (wind speed is generally about 5m/s). In the specific design, a multi-channel folded-plate resistive muffler is used, the thickness of the noise reduction sheet is 80-100mm, the width of the channel is 120-150mm, and the material is used.
The cross-sectional area of ​​the passage of the muffler passage is not less than 1.5 times the cross-sectional area of ​​the air exhaust of the unit. The inlet and outlet air duct muffler can be designed as a labyrinth S-shaped combined structure to increase the noise reduction effect, and blinds are added at the inlet and outlet of the muffler. Avoid the entry of rainwater and effectively protect it.
5.4.4 Noise reduction of mechanical vibration noise of generator set In order to achieve the noise reduction goal, the generator set must be vibration-isolated on the vehicle and vehicle body in an on-board environment. It needs to be carried out in the following two aspects: 1) Generator set and body Connection: The generator set and the main beam of the car body are reliably connected through a special shock absorber set with a low natural frequency and a special fixed channel set. The shock absorber group can achieve the purpose of vibration isolation.
2) Vehicle body connection support device: The four mechanical or hydraulic support legs are reliably connected with the main girder of the car. After the car arrives at the work site, the support leg is lowered, and the vehicle body and the ground are reliably supported to eliminate the vibration caused by the vehicle body suspension system. .
5.4.5 Other functions of mobile power car The device can be equipped with generator set operation, data display device, insulation monitoring alarm device, power output device, and grounding protection safety device according to different customer requirements.
The development of mobile power car trailer chassis series and the design and development of work cabins are two important directions for the mobile power car market to meet the all-round and multi-level demand for mobile power car products. This article through the two aspects of the design and development of the discussion, for the company to develop a suitable mobile power car series products to provide the basis for market requirements.
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