Title:
DOVETAIL STRUCTURE OF FAN
Kind Code:
A1


Abstract:
The invention provides a dovetail structure of a fan which attaches the fan 20 having an inlet hub diameter smaller than an outlet hub diameter to a portion around a discoid disc 10 rotationally driven by a turbine. The disc 10 has a plurality of main dovetail grooves 12 extending in parallel to an axis 1 of a rotation axis from a leading edge to a trailing edge thereof. The fan 20 has a main dovetail portion 22 fitted to the main dovetail groove 12, and a sub engagement portion 24 for supporting a front centrifugal force. Further, the dovetail structure is provided with a spin cone 30 engaging with the sub engagement portion 24 so as to be capable of transmitting the front centrifugal force to the disc 10.



Inventors:
Fujimura, Tetsuji (Tokyo, JP)
Oka, Takashi (Tokyo, JP)
Application Number:
11/680010
Publication Date:
09/20/2007
Filing Date:
02/28/2007
Assignee:
ISHIKAWAJIMA-HARIMA HEAVY INDUSTRIES CO., LTD. (Tokyo, JP)
Primary Class:
International Classes:
F01D5/30
View Patent Images:



Primary Examiner:
WIEHE, NATHANIEL EDWARD
Attorney, Agent or Firm:
GRIFFIN & SZIPL, PC (SUITE PH-1, 2300 NINTH STREET, SOUTH, ARLINGTON, VA, 22204, US)
Claims:
1. A dovetail structure of a fan which attaches the fan having an inlet hub diameter smaller than an outlet hub diameter to a portion around a discoid disc rotationally driven by a turbine, wherein the disc has a plurality of main dovetail grooves extending in parallel to an axis of a rotation axis from a leading edge to a trailing edge thereof, and spaced at a fixed angle in a peripheral direction, wherein the fan has a main dovetail portion fitted to the main dovetail groove so as to be capable of transmitting a rear centrifugal force applied to a portion from an intermediate portion to a trailing edge, and a sub engagement portion for supporting a front centrifugal force applied to a portion from a leading edge to the intermediate portion, and wherein the dovetail structure is provided with a spin cone engaging with the sub engagement portion so as to be capable of transmitting the front centrifugal force to the disc.

2. The dovetail structure of the fan as claimed in claim 1, wherein the fan is constituted by a zero hub ratio fan which is capable of sucking an air close to a center of rotation, and in which a substantial inlet hub diameter is zero or close to zero, and a hub/tip ratio is between 0 and 0.35.

3. The dovetail structure of the fan as claimed in claim 1, wherein the sub engagement portion is constituted by a projection portion which is provided in an inner end portion of a forward end of the fan, and has an outer peripheral surface spaced at a fixed distance R from the axis of the rotating shaft, and the spin cone has a concave groove having an inner peripheral surface fitted to an outer peripheral surface of the projection portion, and a faucet portion fitted to a cylindrical inner surface provided in the disc.

4. The dovetail structure of the fan as claimed in claim 1, wherein the sub engagement portion is constituted by a plurality of slope dovetail portions extending at a fixed angle with respect to the axis of the rotating shaft from the leading edge of the fan to the intermediate portion, and spaced at a fixed angle in a peripheral direction, and the spin cone has a plurality of slope dovetail grooves fitted to the slope dovetail portions, and a faucet portion fitted to the cylindrical inner surface provided in the disc.

5. The dovetail structure of the fan as claimed in claim 1, wherein the sub engagement portion has a plurality of parallel dovetail portions extending in parallel to the axis of the rotating shaft from the leading edge of the fan to the intermediate portion, and spaced at a fixed angle in a peripheral direction, and the spin cone has a plurality of parallel dovetail grooves fitted to the parallel dovetail portions, and a faucet portion fitted to the cylindrical inner surface provided in the disc.

6. The dovetail structure of the fan as claimed in claim 1, wherein the sub engagement portion is constituted by a plurality of expanded portions extending from the leading edge of the fan to the intermediate portion and spaced at a fixed angle in a peripheral direction, and the spin cone has a plurality of fitting grooves fitted to a front lower edge of the fan in an upper portion than the expanded portions, and a faucet portion fitted to the cylindrical inner surface provided in the disc.

Description:

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a turbofan engine which has a high bypass ratio and can achieve a good mileage and a low noise, and more particularly to a dovetail structure of a fan in which an inlet hub diameter is smaller than an outlet hub diameter.

2. Description of the Related Art

FIG. 1 is a schematic view of an aircraft engine 51 (a turbojet engine). As shown in this drawing, the turbojet engine is provided with a fan 52 taking in an air, a compressor 53 compressing the intake air, a burning device 54 burning a fuel by the compressed air, a turbine 55 driving the fan 52 and the compressor 53 on the basis of a combustion gas of the burning device 54, an afterburner 56 afterburning for increasing a thrust, and the like.

The afterburner 56 is constituted by a flame holder 57 having a triangular cross section or the like and forming a circulating region in a downstream side so as to achieve a flame holding, a fuel nozzle 58 for jetting out a fuel, a spark plug 59 and the like, jets out from an exhaust nozzle 62 through an inner side of a liner 61 in an inner side of an after duct 60, and increases a thrust.

In the turbojet engine mentioned above, a structure in which the fan 52 taking in the air is enlarged in size, and a bypass ratio is enlarged is called “turbofan engine”. The bypass ratio corresponds to a flow ratio (bypass flow/core flow) of a bypass flow bypassing a core engine (the compressor 53, the burning device 54 and the turbine 55 mentioned above) with respect an air flow (a core flow) flowing into the core engine. The larger the bypass ratio is, the more the flow rate of the exhaust jet is reduced, so that there is obtained an effect of lowering a noise and a specific fuel consumption.

However, in the turbo engine mentioned above, if the bypass ratio is enlarged, a fan first stage rotor blade (a fan blade in the front row) and an inner diameter of a casing surrounding it become enlarged, and there is a problem that a weight of the engine is increased.

In other words, since a fan first stage rotor blade 52a having a structure embedded in a spinner 63 of the turbofan engine has an embedded structure, a certain degree of hub/tip ratio (inlet hub diameter/tip diameter shown in FIG. 2: normally about 0.3) is necessary, and a fan inlet area becomes narrower at an area corresponding to the inlet hub diameter.

Accordingly, if it is intended to increase the bypass ratio in order to achieve the good mileage and the low noise, the fan diameter and the inlet hub diameter become further larger, and the weight of the engine is increased.

Then, in order to solve the problem, the same applicant as that of the present invention has already proposed “turbofan engine” in patent document 1.

The turbofan engine is provided with a fan first stage rotor blade 65 for taking in an air, and a spinner 64 rotationally driving the fan first stage rotor blade, as shown in FIG. 3, and the spinner has a spiral blade 66 extending spirally to an outer side in a radial direction from an axis thereof and sucking the air from a front surface of the spinner so as to supply to the fan first stage rotor blade.

In this case, reference numerals 67 and 67′ denote a casing inner diameter, and reference numeral 68 denotes an inflow air flow.

In accordance with the structure of the patent document 1, since the spinner 64 has the spiral blade 66 extending spirally to the outer side in the radial direction from the axis thereof and sucking the air from the front surface of the spinner so as to supply to the fan first stage rotor blade 65, it is possible to suck the air from the front surface of the spinner corresponding to the inlet hub diameter so as to compress the air and supply to the fan first stage rotor blade 65.

Therefore, since an entire area in the front side of the engine becomes the air inflow area of the fan first stage rotor blade 65, it is possible to make the fan diameter small, and it is possible to reduce the engine weight.

Further, since the fan first stage rotor blade 65 and the spiral blade 66 of the turbofan engine mentioned above are integrally coupled, it is possible to connect the respective blade surfaces smoothly, and it is possible to suck and compress the air efficiently. Hereinafter, the fan in which the fan first stage rotor blade 65 and the spiral blade 66 are integrally formed, the air can be sucked from the front surface of the spinner, and the substantial hub/tip ratio can be set to 0 is called as “zero hub tip ratio fan”.

Patent Document 1: Japanese Unexamined Patent Publication No. 2004-27854, “TURBOFAN ENGINE”

Patent Document 2: U.S. Pat. No. 6,764,282, “BLADE FOR TURBINE ENGINE”

It is necessary to attach the fan blade of the turbofan engine to a portion around a discoid disc (or spinner) rotationally driven by a turbine. Accordingly, in conventional, there has been generally employed a dovetail structure in which a dovetail portion extending in a longitudinal direction is provided in a root portion of the fan blade, and the dovetail portion is fitted to a dovetail groove formed around the disc.

In the conventional dovetail structure mentioned above, the dovetail portion and the dovetail groove are provided in parallel to a rotation axis Z-Z of the disc, thereby preventing a centrifugal force applied to the fan blade from generating a component force in an axial direction. Hereinafter, this structure is called as “parallel dovetail structure”.

However, in the case that a diameter change in an inner side of a donut-shaped flow path to which the fan blade is attached is large, if the parallel dovetail structure is employed, it is necessary to make a diameter of the dovetail portion and the dovetail groove equal to or smaller than a minimum diameter of the flow path, and there is a risk that a stress generated in the dovetail portion and the dovetail groove becomes too large.

Accordingly, there has been proposed a dovetail structure in which the dovetail portion and the dovetail groove shown in FIG. 4 are sloped with respect to the rotation axis (for example, patent document 2). In this drawing, reference numeral 71 denotes a disc, reference numeral 73 denotes a blade, reference numeral 77 denotes a dovetail, and reference numeral 79 denotes a tab.

Hereinafter, this structure is called as “slope dovetail structure”.

However, in the case of the zero hub tip ratio fan mentioned above, since the hub/tip ratio is between 0 and 0.35, and the diameter of the inner side of the donut-shaped flow path to which the zero hub tip ratio fan is attached is zero or close to zero, there is a problem that the parallel dovetail structure can not be essentially applied.

Further, even in the case that the slope dovetail structure is applied, it is impossible to support the centrifugal force of the front side portion (the portion corresponding to the spiral blade mentioned above) of the zero hub tip ratio fan by the disc (or the spinner).

Further, in the case that the slope dovetail structure is applied to the zero hub tip ratio fan, since the component force in the axial direction of the centrifugal force applied to the fan blade is large, there is a risk that the generated stress becomes too large in the structure having a small shear area such as the tab disclosed in the patent document 2.

SUMMARY OF THE INVENTION

The present invention is made for the purpose of solving the problems mentioned above. In other words, an object of the present invention is to provide a dovetail structure of a fan which can securely attach a fan having an inlet hub diameter smaller than an outer hub diameter to a portion around a disc rotationally driven by a turbine, and can securely support component forces in a radial direction and an axial direction of a centrifugal force applied to the fan having the inlet hub diameter smaller than the outlet hub diameter by a low stress.

In accordance with the present invention, there is provided a dovetail structure of a fan which attaches a fan having an inlet hub diameter smaller than an outlet hub diameter to a portion around a discoid disc rotationally driven by a turbine,

wherein the disc has a plurality of main dovetail grooves extending in parallel to an axis of a rotation axis from a leading edge to a trailing edge thereof, and spaced at a fixed angle in a peripheral direction,

wherein the fan has a main dovetail portion fitted to the main dovetail groove so as to be capable of transmitting a rear centrifugal force applied to a portion from an intermediate portion to a trailing edge, and a sub engagement portion for supporting a front centrifugal force applied to a portion from a leading edge to the intermediate portion, and

wherein the dovetail structure is provided with a spin cone engaging with the sub engagement portion so as to be capable of transmitting the front centrifugal force to the disc.

In accordance with a preferable aspect of the present invention, the fan is constituted by a zero hub ratio fan which is capable of sucking an air close to a center of rotation, and in which a substantial inlet hub diameter is zero or close to zero, and a hub/tip ratio is between 0 and 0.35.

Further, the sub engagement portion is constituted by a projection portion which is provided in an inner end portion of a forward end of the fan, and has an outer peripheral surface spaced at a fixed distance R from the axis of the rotating shaft, and

the spin cone has a concave groove having an inner peripheral surface fitted to an outer peripheral surface of the projection portion, and a faucet portion fitted to a cylindrical inner surface provided in the disc.

Further, in accordance with the other preferable embodiment, the sub engagement portion is constituted by a plurality of slope dovetail portions extending at a fixed angle with respect to the axis of the rotating shaft from the leading edge of the fan to the intermediate portion, and spaced at a fixed angle in a peripheral direction, and

the spin cone has a plurality of slope dovetail grooves fitted to the slope dovetail portions, and a faucet portion fitted to the cylindrical inner surface provided in the disc.

Further, in accordance with the other preferable embodiment, the sub engagement portion has a plurality of parallel dovetail portions extending in parallel to the axis of the rotating shaft from the leading edge of the fan to the intermediate portion, and spaced at a fixed angle in a peripheral direction, and

the spin cone has a plurality of parallel dovetail grooves fitted to the parallel dovetail portions, and a faucet portion fitted to the cylindrical inner surface provided in the disc.

Further, in accordance with the other preferable embodiment, the sub engagement portion is constituted by a plurality of expanded portions extending from the leading edge of the fan to the intermediate portion and spaced at a fixed angle in a peripheral direction, and

the spin cone has a plurality of fitting grooves fitted to a front lower edge of the fan in an upper portion than the expanded portions, and a faucet portion fitted to the cylindrical inner surface provided in the disc.

In accordance with the structure of the present invention mentioned above, since the disc has the main dovetail groove extending in parallel to the axis of the rotation axis from the leading edge to the trailing edge, and the fan having the inlet hub diameter smaller than the outlet hub diameter has the main dovetail portion extending at the same angle as the angle of the dovetail groove and capable of being fitted to the dovetail groove, it is possible to securely attach the fan to the portion around the disc, and it is possible to securely transmit the rear centrifugal force applied to the fan to the disc via the main dovetail portion and the main dovetail groove.

Further, since the main dovetail portion and the main dovetail groove extend in parallel to the axis of the rotation axis, it is possible to set a sufficient long main dovetail groove capable of transmitting the rear centrifugal force applied to the portion from the intermediate portion to the trailing edge, even in the case of attaching the fan having the inlet hub diameter smaller than the outlet hub diameter, and it is possible to sufficiently suppress the stress generated in the main dovetail portion and the main dovetail groove.

Further, since the fan has the sub engagement portion for supporting the front centrifugal force applied to the portion from the leading edge to the intermediate portion, and is provided with the spin cone engaging with the sub engagement portion so as to be capable of transmitting the front centrifugal force to the disc, it is possible to securely support the front centrifugal force applied to the portion having the small hub diameter of the fan in which the inlet hub diameter is smaller than the outlet hub diameter, via the spin cone so as to be capable of securely transmitting to the disc.

Further, since the rear centrifugal force applied to the portion from the intermediate portion to the trailing edge is transmitted to the disc by the main dovetail groove and the main dovetail portion extending in parallel to the axis of the rotating shaft, it is possible to make the component force along the main dovetail groove of the centrifugal force applied to the fan in which the inlet hub diameter is smaller than the outlet hub diameter small, and it is possible to securely support the component force by the low stress on the basis of the retainer structure having the same structure as the conventional one.

The other objects and advantageous features of the present invention will be apparent from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a conventional turbofan engine;

FIG. 2 is an explanatory view of a hub/tip ratio;

FIG. 3 is a schematic view of “turbofan engine” in patent document 1;

FIG. 4 is a schematic view of “slope dovetail structure” in patent document 2;

FIG. 5 is a transverse cross sectional view of a fan provided with a dovetail structure in accordance with a first embodiment of the present invention;

FIGS. 6A, 6B, 6C and 6D are partly cross sectional views of FIG. 5;

FIG. 7 is a view of a second embodiment of the dovetail structure in accordance with the present invention;

FIGS. 8A, 8B and 8C are partly perspective views and a partly cross sectional view of FIG. 7;

FIG. 9 is a view of a third embodiment of the dovetail structure in accordance with the present invention;

FIG. 10 is a partly perspective view of FIG. 9;

FIG. 11 is a view of a fourth embodiment of the dovetail structure in accordance with the present invention; and

FIGS. 12A and 12B are partly perspective views of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given below of a preferable embodiment in accordance with the present invention with reference to the accompanying drawings. In this case, in each of the drawings, the same reference numerals are attached to a common portion, and an overlapping description will be omitted.

FIG. 5 is a transverse cross sectional view of a fan provided with a dovetail structure in accordance with a first embodiment of the present invention, and shows only an upper side of an axis 1 of a rotating shaft.

Further, FIGS. 6A, 6B, 6C and 6D are partly cross sectional views of FIG. 5, and are respectively cross sectional views along a line A-A, a line B-B, a line C-C and a line D-D.

A dovetail structure in accordance with the present invention is structured such that a fan in which an inlet hub diameter is smaller than an outlet hub diameter is attached to a portion around a discoid disc 10 rotationally driven by a turbine (not shown).

Further, in this embodiment, the fan is constituted by a zero hub tip ratio fan which can suck an area close to a center of rotation, and in which a substantial inlet hub diameter is zero or close to zero, and a hub/tip ratio is between 0 and 0.35.

In this case, in FIG. 5, reference numeral 1 denotes an axis of a rotating shaft of a disc 10 and the zero hub tip ratio fan 20, reference numeral 2 denotes an air flow path, reference numeral 3 denotes an inner peripheral surface of the air flow path, reference numeral 4 denotes a bearing rotatably supporting the disc 10, and reference numeral 5 denotes a flow of an inflow air.

The zero hub tip ratio fan 20 is formed such that a fan first stage rotor blade 20a for taking in the air and a spiral blade 20b sucking the air from the portion close to the center of rotation so as to compress and supply to the fan first stage rotor blade are integrally coupled, and respective blade surfaces are smoothly connected. In this case, the substantial hub/tip ratio of the zero hub tip ratio fan 20 is not 0, but can be set to 0.

In FIGS. 5, 6A, 6B, 6C and 6D, the disc 10 has a plurality of (for example, eighteen in this embodiment) main dovetail grooves 12 spaced at a fixed angle (for example, 20 degree in this embodiment) in a peripheral direction. Further, the main dovetail grooves 12 extend in parallel to the axis 1 of the rotating shaft from a leading edge 10a to a trailing edge 10b of the disc 10.

The zero hub tip ratio fan 20 has a main dovetail portion 22 in an inner end thereof. The main dovetail portion 22 extends in parallel to the axis 1 of the rotating shaft in the same manner as the main dovetail groove 12 of the disc 10, and is structured such as to be capable of being fitted to the main dovetail groove 12.

It is preferable that the main dovetail portion 22 is provided at a position corresponding to a fan first stage rotor blade 20a, and is structured such as to be capable of transmitting a rear centrifugal force applied to a portion from an intermediate portion to a trailing edge of the fan to the disc 10.

The zero hub tip ratio fan 20 further has a sub engagement portion 24 for supporting a front centrifugal force applied to a portion from a leading edge to the intermediate portion of the fan. The sub engagement portion 24 is preferably provided at a position corresponding to a spiral blade 20b. In this case, reference numeral 26 in this drawing denotes a platform portion constituting the inner peripheral surface 3 of the air flow path 2 of the zero hub tip ratio fan 20.

In FIG. 5, the dovetail structure in accordance with the present invention is further provided with a spin cone 30 capable of being fixed to the disc 10 by a coupling bracket 15 in a forward side (a left side in the drawing) of the zero hub tip ratio fan 20. The spin cone 30 engages with the sub engagement portion 24 of the zero hub tip ratio fan 20 and has a function of transmitting a front centrifugal force applied to the portion from the leading edge to the intermediate portion of the fan to the disc 10.

In the first embodiment in FIG. 5, the sub engagement portion 24 is constituted by a projection portion 25 which is provided in an inner end portion of a forward end of the zero hub tip ratio fan 20, and has an outer peripheral surface 25a spaced at a fixed distance R from the axis 1 of the rotating shaft.

Further, in this embodiment, the spin cone 30 has a concave groove 31 having an inner peripheral surface fitted to the outer peripheral surface 25a of the projection portion 25, and a faucet portion 37 fitted to a cylindrical inner surface 10c provided in the disc 10.

In this embodiment, the spin cone 30 has a cone head 36 attached to a leading end thereof by a coupling bracket 35.

In the case of the zero hub tip ratio fan 20 in which a substantial inlet hub diameter is zero or close to zero, a flow path diameter of the inner peripheral surface 3 of the air flow path 2 is largely changed from zero or a small diameter close to zero to a large diameter reaching three times or more (about three times in this embodiment) thereof. Accordingly, a diameter of outer peripheral surface 25a of the projection portion 25 becomes equal to or less than one third of the maximum diameter of the mounting portion of the main dovetail portion 22.

Further, the front centrifugal force applied to the portion from the leading edge to the intermediate portion of the fan corresponds to a centrifugal force applied to the spiral blade 20b positioned in an outer side thereof, and is smaller in comparison with a rear centrifugal force applied to the portion from the intermediate portion to the trailing edge of the fan.

Accordingly, it is possible to support the front centrifugal force on the basis of the engagement between the projection portion 25 provided in the inner end portion of the forward end and the concave groove 31 of the spin cone 30.

In accordance with the structure mentioned above, since the disc 10 has the main dovetail groove 12 extending in parallel to the axis 1 of the rotating shaft from the leading edge 10a to the trailing edge 10b, and the zero hub tip ratio fan 20 has the main dovetail portion 22 which is fitted to the main dovetail groove and can transmit the rear centrifugal force applied to the portion from the intermediate portion to the trailing edge, it is possible to securely attach the zero hub tip ratio fan 20 to the portion around the disc 10, and it is possible to securely transmit the rear centrifugal force applied to the zero hub tip ratio fan 20 to the disc 10 via the main dovetail portion 22 and the main dovetail groove 12.

Further, since the main dovetail portion 22 and the main dovetail groove 12 extend in parallel to the axis 1 of the rotating shaft, it is possible to set the sufficiently long main dovetail groove which can transmit the rear centrifugal force applied to the portion from the intermediate portion to the trailing edge, even in the case of attaching the zero hub tip ratio fan in which the substantial inlet hub diameter is zero or close to zero, and it is possible to suppress the stress generated in the main dovetail portion 22 and the main dovetail groove 12 sufficiently small.

Further, since the zero hub tip ratio fan 20 has the sub engagement portion 24 (the projection portion 25 in this embodiment) for supporting the front centrifugal force applied to the portion from the leading edge to the intermediate portion, further has the concave groove 31 and the faucet portion 37 in this embodiment, and is provided with the spin cone 30 engaging with the sub engagement portion 24 so as to be capable of transmitting the front centrifugal force to the disc 10, it is possible to securely support the front centrifugal force applied to the portion in which the hub diameter of the zero hub tip ratio fan is zero or close to zero via the concave groove 31 and the faucet portion 37 of the spin cone 30 so as to securely transmit to the disc 10.

Further, since the rear centrifugal force applied to the portion from the intermediate portion to the trailing edge is transmitted to the disc 10 by the main dovetail groove 12 and the main dovetail portion 22 extending in parallel to the axis of the rotating shaft, it is possible to make the component force along the main dovetail groove of the centrifugal force applied to the zero hub tip ratio fan 20 small, and it is possible to securely support the component force by the low stress on the basis of the retainer structure having the same structure as the conventional one.

In FIG. 5, the main dovetail portion 22 of the zero hub tip ratio fan 20 has a vertical rear surface 23 which is orthogonal to the main dovetail groove 12, in a rearward end thereof.

Further, the dovetail structure in accordance with the present invention has a rear retainer 16 fixed to a rear end surface (a rear edge 10b) of the disc 10 by a coupling bracket (for example, a bolt and a nut) (not shown).

The rear retainer 16 is structured such that a front surface thereof is closely attached to the vertical rear surface 23 so as to prevent the main dovetail portion 22 from moving backward.

In accordance with this structure, it is possible to make a surface pressure of a contact surface of the rear retainer substantially constant, and it is possible to reduce the internal stress generated in the rear retainer.

In this case, the fixing means in the axial direction of the zero hub tip ratio fan 20 is not limited to the vertical rear surface 23 and the rear retainer 16 mentioned above, but may employ the other well-known means singly or together.

FIG. 7 is a view showing a second embodiment of the dovetail structure in accordance with the present invention. Further, FIG. 8A is a partly perspective view of a fan front portion, FIG. 8B is a perspective view along a line B-B in FIG. 7, and FIG. 8C is a partly cross sectional view along a line C-C in FIG. 7.

In this embodiment, the sub engagement portion 24 is constituted by a plurality of slope dovetail portions 27. The slope dovetail portions 27 extend at a fixed angle Θ with respect to the axis 1 of the rotating shaft from the leading edge to the intermediate portion of the zero hub tip ratio fan 20, and are spaced at a fixed angle (for example, 20 degree in this embodiment) in a peripheral direction.

The fixed angle Θ corresponds to an angle in which a forward side is close to the axis 1 and a rearward side is away from the axis 1, and preferably corresponds to an angle along the inner peripheral surface 3 of the air flow path 2. In this case, the angle Θ is about 40 degree in this embodiment.

Further, in this embodiment, the spin cone 30 has a plurality of slope dovetail grooves 32 fitted to the slope dovetail portions 27, a faucet portion 37 fitted to a cylindrical inner surface 10c provided in the disc 10, and a faucet portion 38 fitted to a cylindrical inner surface 10d provided in an outer side of the disc 10.

The other structures are the same as those of the first embodiment.

In accordance with the structure mentioned above, since the zero hub tip ratio fan 20 has the sub engagement portion 24 (the slope dovetail portion 27 in this embodiment) for supporting the front centrifugal force applied to the portion from the leading edge to the intermediate portion, further has the slope dovetail groove 32 and the faucet portions 37 and 38 in this embodiment, and is provided with the spin cone 30 engaging with the sub engagement portion 24 so as to be capable of transmitting the front centrifugal force to the disc 10, it is possible to securely support the front centrifugal force applied to the portion in which the hub diameter of the zero hub tip ratio fan is zero or close to zero via the slope dovetail groove 32 and the faucet portions 37 and 38 of the spine cone 30 so as to be capable of securely transmitting to the disc 10.

The other operations and effects are the same as those of the first embodiment.

FIG. 9 is a view of a third embodiment of the dovetail structure in accordance with the present invention. Further, FIG. 10 is a partly perspective view of a fan front portion of FIG. 9.

In this embodiment, the sub engagement portion 24 is constituted by a plurality of parallel dovetail portions 28. The parallel dovetail portions 28 extend in parallel to the axis 1 of the rotating shaft from the leading edge to the intermediate portion of the zero hub tip ratio fan 20, and are spaced at a fixed angle (for example, 20 degree in this embodiment) in the peripheral direction.

A centrifugal force (a front centrifugal force) applied to the parallel dovetail portion 28 corresponds to a centrifugal force applied to the spiral blade 20b positioned in an outer thereof, and is smaller in comparison with a centrifugal force of the fan first stage rotor blade 20a applied to the main dovetail portion 22.

Accordingly, it is preferable that a size of the parallel dovetail portion 28 is made sufficiently smaller than a size of the main dovetail portion 22.

Further, in this embodiment, the spin cone 30 has a plurality of parallel dovetail grooves 33 fitted to the parallel dovetail portion 28, and a faucet portion 37 fitted to a cylindrical inner surface 10c provided in the disc 10.

The other structures are the same as those of the first embodiment.

In accordance with the structure mentioned above, since the zero hub tip ratio fan 20 has the sub engagement portion 24 (the parallel dovetail portion 28 in this embodiment) for supporting the front centrifugal force applied to the portion from the leading edge to the intermediate portion, further has the parallel dovetail groove 33 and the faucet portion 37 in this embodiment, and is provided with the spin cone 30 engaging with the sub engagement portion 24 so as to be capable of transmitting the front centrifugal force to the disc 10, it is possible to securely support the front centrifugal force applied to the portion in which the hub diameter of the zero hub tip ratio fan is zero or close to zero via the parallel dovetail groove 33 and the faucet portion 37 of the spin cone 30 so as to be capable of securely transmitting to the disc 10.

The other operations and effects are the same as those of the first embodiment.

FIG. 11 is a view of a fourth embodiment of the dovetail structure in accordance with the present invention, FIG. 12A is a partly perspective view of the fan front portion, and FIG. 12B is a partly perspective view of the spin cone.

In this embodiment, the sub engagement portion 24 is constituted by a plurality of expanded portions 29. The expanded portions 29 extend to the intermediate portion from the leading edge of the zero hub tip ratio fan 20, and are spaced at a fixed angle (for example, 20 degree in this embodiment) in the peripheral direction. A width in the peripheral direction of the expanded portion 29 is preferably formed thicker than a front lower edge of the fan.

In this case, “structure in which the width in the peripheral direction of the expanded portion 29 is formed thicker than the front lower edge of the fan” is not essential in the case that the front centrifugal force applied to the intermediate portion from the leading edge of the zero hub tip ratio fan 20 is sufficiently low. In other words, it is not essential to employ a structure in which a thickness is increased and a load is transmitted.

Further, in this embodiment, the spin cone 30 has a plurality of fitting grooves 34 fitted to the front lower edge of the fan in the upper portion than the expanded portion 29, a faucet portion 37 fitted to the cylindrical inner surface 10c provided in the disc 10, and a faucet portion 38 fitted to the cylindrical inner surface 10d provided in an outer side of the disc 10.

The other structures are the same as those of the first embodiment.

In accordance with the structure mentioned above, since the zero hub tip ratio fan 20 has the sub engagement portion 24 (the expanded portion 29 in this embodiment) for supporting the front centrifugal force applied to the portion from the leading edge to the intermediate portion, further has the fitting groove 34 and the faucet portions 37 and 38 in this embodiment, and is provided with the spin cone 30 engaging with the sub engagement portion 24 so as to be capable of transmitting the front centrifugal force to the disc 10, it is possible to securely support the front centrifugal force applied to the portion in which the hub diameter of the zero hub tip ratio fan is zero or close to zero via the fitting groove 34 and the faucet portions 37 and 38 of the spin cone 30 so as to be capable of securely transmitting to the disc 10.

The other operations and effects are the same as those of the first embodiment.

In the fourth embodiment mentioned above, (1) it is possible to transmit the front centrifugal force applied to the portion in which the hub diameter of the zero hub tip ratio fan is zero or close to zero, and the hub/tip ratio is between 0 and 0.35, to the disc 10 on the basis of the fitting between the main dovetail portion 22 and the main dovetail groove 12, and (2) it is possible to make the size of the expanded portion 29 small or substantially omit the expanded portion 29, as far as the front lower edge of the fan in the upper portion than the expanded portion 29 and the fitting groove 34 are fitted so as to suppress the vibration of the fan.

In this case, it goes without saying that the present invention is not limited to the embodiments mentioned above, but can be variously modified in a range within the scope of the present invention.





 
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