The main gearbox of the helicopter
Rotational speed of modern gas turbine HPT ranges from 6000 17000 to rev / min (low power engines and higher). For best efficiency in the current HB helicopter flight mode HB speed must be considerably lower than the frequency of rotation of the gas turbine is achieved by GH.
The gearbox can be source of a shaft torsional oscillation, as in the wheels are always errors in Step teeth, as well as deformation of the teeth under load, causing changes angular velocities of shafts. Reduce the excitation of these oscillations can increase the coefficient of overlapping meshes, increasing manufacturing precision gears and special tooth profile correction.
The size of the gears, bearings and shafts GR determined mainly by depending on the transmission gear torque. Therefore, the mass is calculated according to the formula GH
The coefficient k c can be considered comparable to the size of gears, and similar schemes with close gear ratios. From the analysis it follows that with a reduction gear transmission of torque to the increased weight. This is because the wall thickness of the main parts in small gears are relatively more as a result of the technological difficulties in producing parts with very small wall thicknesses, and for reasons of ensuring the necessary rigidity and static stability of the walls. Because of this, many details of small gear turns relatively higher. In order to somehow reduce this effect, it is advisable to make such gearboxes by a simpler scheme, in particular with the transmission output torque by a smaller number of points of engagement.
In the kinematic scheme of the mechanism gear can be divided into three groups: simple peredachami- gear, planetary gears, which have single and double satellites; Mixed gears, mechanisms that are simple and planetary gears. To prevent large voltage in the teeth of a simple transfer, you must install several
bust, placing them evenly over the circumference. It is necessary to have an exhaustive search each clutch or elastic member, which allows to collect send a guaranteed clearance and ensure uniform loading of all bust.
In the case of combined gear rationally use the planetary gear in a second stage, which reduces the speed of the leash and centrifugal forces, which load bearing satellites.
In 4.3.1 shows kinematics GR Mi-26. Creating GR for transmission to the HB power from two theater equal 22000 hp, due to the solution of a number of difficult technical and technological problems. This problem was solved GP Smirnov, engineer Moscow Helicopter Plant (MVZ) them. ML Mile.
Design feature of GH BP-26 is a large reduction ratio in the last stage of reduction. First time in the world helicopter as the last stage of the reduction has been applied conventional involute gear with a large gear ratio (i = 8,76). The gearbox has a modular design. Some of its modules: ball bearing motors, plate expansion joints, freewheel, front and rear bevel gears, drive RVs, top gear (the last two stages of the reduction of the basic kinematic chain), and sump oil system blocks are designed as independent units in their own buildings. They are interconnected flanges and splined shafts. In principle, each module can be manufactured, tested, structurally modified and applied in other constructions. Modular design with respect to the gear unit of this size simplifies manufacturing and finishing, reduce weight.
The top gear consists of a case in which two bearing supports the shaft mounted HB. Directly on this shaft by means of two fixed hubs, two driven bevel gears, each of which are in engagement with eight driving wheels. The gears of the upper and lower row have opposite directions of inclination of the teeth. Each drive wheel is mounted on two roller bearings having no thrust on the inner rings turners. Axial forces occurring on the drive wheels of the last stage, have the opposite direction and are perceived tubular ties.
The result is a kind of herringbone gearing, in which each half of the drive wheel is mounted in its bearings. The possibility of free axial movement of the groups of gears consisting of two drive wheels of the last stage and the second stage of the driven wheel, allows a uniform power division between upper and lower drive wheels of the last stage. HB shaft in its lower part is made thin-walled barrel-shaped, which allows to give it the required strength and stiffness with minimum weight.
Housing top gear takes all the loads coming from the NV, including torque, and transmits them to the fuselage of the helicopter through eight podreduktornuyu pivotal frame. In the middle part of the body has a belt attachment with six flanges, which are attached to the flanges of the frame.
Modular design makes it easy to create the required rigidity of the problem cases. All gear wheels are simple and technological forms. In order to simplify the manufacture of wheels, introduced the traditional flange connectors.
One of the main features of the main gearbox VR-26 is to ensure uniform distribution of power flows due to spline shafts (spring) with low torsional stiffness. Dividing the power in the last stage of reduction achieved by opposite the direction of inclination of the teeth in the upper and lower ranks of the gears. Dividing the power in the first and second stage reduction is carried out by low torsional stiffness of the springs are mainly springs last stage of reduction. The design of the equality of torsional stiffness in parallel streams.
The required uniformity of load distribution based backlash in gears and splines, backlashes in bearings provided in the process of assembling the gear through the use of a number of structural and technological methods.
Torsional rigidity of the basic kinematic chain and drive RV, backlash in the teeth and splines its drive selected accordingly. As a result, when using one engine at maximum takeoff power of the RV through the drive goes to the opposite side of the bevel gearboxes, bevel gearboxes unloading on the side of the engine running.
Gears BP-26 made of steel 12H2N4A-III undergo carburizing and hardening. As used finishing grinding.
Body parts of the upper gear diameter 2000 mm, made by stamping of high strength aluminum alloy AKCH-1 followed by treatment in the milling machines. Body parts other nodes are made of cast alloy MJI-5. Hubs top gear driven gears are made of a titanium alloy forging VPP-1. Shafts and springs are made of steel 40H2N2MA nitride.
Many threading, modularity similar layout GR create certain advantages over planetary gears.
As a result of these structural and kinematic solutions specific gravity BP GR-26 unit takeoff torque is significantly smaller than the GH Mi-6, performed by a four kinematic scheme.
The loads are transferred from the body of the GR in the corresponding power elements of the fuselage usually with a rod system.
In 4.3.2 given one option frame fixing KSS GR.
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