RU2260149C2 - Compound hollow shaft of gas-turbine engine - Google Patents

Abstract

FIELD: gas-turbine engines.

SUBSTANCE: compound hollow shaft of gas-turbine engine has three parts connected rigidly all together. Medium part is made of titanium; its length is chosen within 0,5-0,7 length of total compound shaft and its diameter belongs to 1,15-1,25 diameters of end parts of shaft's body.

EFFECT: increased critical frequency of rotation; reduced weight of shaft.

1 dwg

Description

The invention relates to composite shafts with detachable joints.

Known shaft connecting the compressor and the turbine, which is a hollow cylinder located on 2 bearings [1].

Fully fulfilling its mission, it is very difficult to manufacture, because it is difficult to center the inner hole so that the walls of the hollow shaft have the same thickness. Different wall thicknesses cause shaft imbalance, which is undesirable.

The closest in technical solution is a composite hollow shaft of a gas turbine engine containing three sections rigidly connected to each other [2].

This design simplifies the manufacture of the shaft, but with a large length of the shaft its own shaft speed will be insufficient for operation. The natural frequency of the system is a constructive characteristic of this system, if it is possible to increase it, then the system wins. In this case, the natural frequency is slightly higher than the working frequency, increasing the natural frequency to a margin of 25%, we contribute to the smooth operation of the gas turbine engine. Otherwise, this will lead to an increase in the level of vibration, which is not damped, because This critical speed causes the shaft to bend and has a slight displacement in the bearings where the dampers are located.

The objective of the invention is to increase the critical shaft speed by 5% -10%, which in some cases is sufficient to obtain the necessary reserves for the critical shaft speed, in addition to this task, the shaft weight is also reduced, which is also useful for aviation.

This problem is solved in that the composite hollow shaft of a gas turbine engine containing three sections rigidly connected to each other, the middle section being made of titanium, its length being selected within 0.5-0.7 of the length of the entire composite shaft, and its diameter in the limits of 1.15-1.25 of the diameters of the extreme sections of the shaft body.

New is that the middle section is made of titanium, and its length is selected in the range of 0.5-0.7 of the length of the entire composite shaft, and its diameter is in the range of 1.15-1.25 of the diameters of the extreme sections of the shaft body.

The shaft, consisting of three parts, is double-supported. Two parts are made, for example, of steel, and the middle - of titanium. Two parts of steel suggest the location of bearings on them and should be of smaller diameter and greater thickness. The middle part is made of a larger diameter, the inner race of one of the bearings or the bearing shaft is fixed to the rotor shaft and it determines the possible dimensions of the diameter of the middle part while maintaining the possibility of transmitting torque.

The increased diameter of the middle part and the use of a lighter metal, for example titanium, leads to the fact that the middle part becomes lighter and has the same stiffness as the two extreme parts, as a result of which the critical (or natural) frequency increases. An increase in the natural frequency of the shaft is not more than 10%, but this is sufficient in some cases, in addition, due to the use of titanium, the shaft becomes lighter, which is also beneficial for gas turbine engines.

We give an example of calculating a three-part shaft for transmitting torque from a low-pressure compressor to a low-pressure turbine used for an aircraft gas turbine engine of a military standard.

Initial data

shaft length l = 1214.7 mm

left diameter

extreme part D ₁ / d ₁ = 55 / 47.5 (mm)

diameter right

extreme part D ₁ / d ₁ = 55 / 37.5 (mm)

diameter

middle part D ₃ / d ₃ = 64/60 (mm)

the length of the left side l ₁ = 273 mm

the length of the right side l ₂ = 279.3 mm

the length of the middle part l ₃ = 662.4 mm

The calculation performed by the method of initial parameters, if the entire shaft is made of steel:

n _cr = 1114.3 rpm m = 23.899 kg,

if the middle part is made of titanium

n _cr = 1223.3 rpm m = 20.398 kg,

the gain in mass is 3.5 kg, and the difference in critical speed is ≈9%.

The drawing shows a shaft of three sections, where the left end part 1, the right end part 2, the middle of the increased diameter of titanium 3, bearings 4, 5, cone 6.

The work is carried out as follows: when the engine is running, the shaft starts to accelerate and reaches its maximum speed at maximum speed (if the margin at the critical time frequency is insufficient, the shaft deflection increases and the critical requirement is the size of the margin in the normative documentation). If the shaft bend is large above normal, the load on the bearings 4, 5 increases, which can cause them to break. An increase in critical frequency margins increases the performance of bearings 4, 5.

The description shows that for the implementation of the devices used elements used in industry, which allows us to conclude that the industrial applicability of the invention.

Sources of information

1. Nikitin Yu.M. The design of elements, parts and components of aircraft engines (under the editorship of Dr. Sc. Prof. G.S. Skubachevsky), Moscow: Mashinostroenie, 1968, pp. 312-313, Fig. 9.6.

2. Ibid., P. 107, fig. 4.11.

Claims (1)

A composite hollow shaft of a gas turbine engine containing three sections rigidly interconnected, characterized in that the middle section is made of titanium, and its length is selected within 0.5-0.7 of the length of the entire composite shaft, and its diameter is within 1, 15-1.25 from the diameters of the extreme sections of the shaft body.