GB1592114A

GB1592114A - Rotors preferably for wind power stations

Info

Publication number: GB1592114A
Application number: GB5631/78A
Authority: GB
Original assignee: PRAKTISK TEKNIK AB
Current assignee: PRAKTISK TEKNIK AB
Priority date: 1976-08-26
Filing date: 1978-02-13
Publication date: 1981-07-01
Also published as: SE401241B; NL7801830A; DE2806874A1; SE7609457L

Description

(54) ROTORS, PREFERABLY FOR WIND POWER STATIONS (71) We, PRAKTISK TEKNIK AB., a Swedish joint-stock company, of 1 Skoldmyrvagen, S-72 231 Vasteras, Sweden, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a rotor mounted on a horizontal shaft, preferably intended for wind power stations, comprising a hub and at least two blades supported on the hub, each blade having a main strut extending in the longitudinal direction of the blade.

Since alternative forms of energy have become of interest, it has been an ever increasing desire to be able to construct wind power stations of larger dimensions. The wind power stations existing today are not of such a size as to render them competitive with conventional power stations.

One of the difficulties of constructing larger wind power stations is to act on larger wind surfaces of the magnitude 1000 to 10,000 square meters. One way of acting upon surfaces of this size is to construct larger rotors with horizontal shafts and with diameters of 30 to 150 m, possibly even larger. It is extremely difficult, however, to design and manufacture wind motor blades of this size with free struts, capable to resist the great wind forces and the dynamic forces arising from the rotation. The mounting moments on the rotor hub and the bending moments in the blades are of such a magnitude that it is nearly impossible to design the structure with reasonable weight at a reasonable price without staying the structure.

It is also desirable, and possibly necessary, to design the blades turnable so as to render feathering of the rotor possible. This increases additionally the difficulties of attaching the blades to the hub with great mounting moments.

According to the present invention there is provided a rotor with a horizontal shaft, preferably for wind power stations, comprising a hub and at least two blades supported at the hub, each blade comprising a main strut extending in the longitudinal direction of the blade, means for pivotally attaching each said main strut to the hub, a main stay and a secondary stay attached to said main strut and to said hub at diametrically and axially spaced points on said hub for staying said blade relative to said hub and means extending between said hub and a rearward portion of each blade so that the blade and the main strut will not pivot in the plane containing the front and rear edge of the blade.

According to a preferred embodiment of the invention, the blades can be turned about the centre line of their main struts, so that the blades at strong wind automatically adjust whereby the stresses decrease and the speed can be controlled.

According to a further preferred embodiment of the invention, the turning moment of the blades takes place automatically at increasing wind pressure, by means of a counter-holding hydraulic piston of suitable design or some other mechanical device, for example a spring mechanism or weights.

This wind pressure control, however, requires that the rotation friction of the mounting blade on the hub must not be too high, and the turning centre for the blade is offset to its forward edge.

In the following, an embodiment of the invention is described with reference to the accompanying drawings, in which Fig. 1 is a schematic side view of a wind power station with a rotor according to the invention, Fig. 2 is a side view of the rotor according to Fig. I on a larger scale, Fig. 3 is a front view of the rotor, Fig. 4 is a perspective view of a blade mounting at the hub, Fig. 5 shows in detail how the rotor is supported at the hub, Fig. 6 shows in a schematic manner how the wind force acts upon the blade, Fig. 7 is a cross-sectional view of an embodiment of a blade, Fig. 8 is a cross-sectional view of an alternative embodiment of a blade.

The wind power station 1 shown in Fig. 1 comprises a rotor 2 mounted on a horizontal shaft and having two stayed blades 3 and 3'.

In this embodiment the stayed blades have one staying point 4 and, respectively, 4' which is located at a distance of about two thirds of the blade length from the rotor hub 5, which is a sheet metal cylinder.

As is more clearly apparent from Figs. 2 and 3, main and secondary stays 6 and 7 and, respectively, 6' and 7' extend from the staying points 4 and, respectively, 4'. Said stays 6 and 7 and, respectively, 6' and 7' are attached to the hub 5 with their end portions remote from the staying points 4 and, respectively, 4'.

It is most clearly apparent from Fig. 4 that the end points of the stays 6 and 7 are attached to the hub 5 in diametrically opposed places. This, of course, applies equally to the stays 6' and 7'.

Fig. 5 shows in detail the support of the rotoi 2 on the hub 5. It further can be seen in Fig. 5 that the blades 3 and 3' are attached to the hub 5 partly by ball-pivoted bearings 8 and 8', respectively, and partly by spherical joint bearings 9 and 9', respectively. The ball-pivoted bearings 8 and 8' are connected to the blades 3 and 3', respectively, via main struts 10 and 10', which are arranged in the centre of rotation of the blades 3 and 3', respectively. The spherical joint bearings 9 and 9', respectively, are arranged at the rear edges of the blades 3 and, respectively, 3' and connected to rotary yokes 11 and, respectively, 11', which in their turn are supported at the hub 5 with the same centre of rotation as the blades 3 and 3'.The yokes 11 and 11' prevent each blade and main strut from pivotting in the plane containing the front and rear edges of the blade. Due to the fact that both the ball-pivoted bearings and the spherical joint bearings can be pivoted spherically, the blades 3 and 3' are pivotal transverse to the blade sections and cannot receive any bending moments in these directions. By means of the yokes 11 and 11' the blades 3 and, respectively, 3' can be turned through about 40 . For controlling the turning of the blades 3 and 3', hydraulic pistons 12 and, respectively, 12' are provided between the yokes 11 and, respectively, 11' and the hub 5. The function of these hydraulic pistons is described below. In Fig. 6 is shown in principle how a blade is acted upon by the wind force, in this case the normal wind force in operation.The wind force, of course, is a spread load, but for reasons of better illustration it is here shown only as a point load. The wind direction shown by arrow A (Fig. 6) always is in parallel with the mounting shaft of the hub 5, because the wind power station always assumes such a position relative to the wind direction. The forces thereby acting on the blade are an axial force B and a tangential force C relative to the mounting shaft of the hub (see Fig. 6). The resultant for these two forces is shown by a dashed vector in Fig. 6. In the direction of this resultant the main stay 6 and 6', respectively, is positioned.

Due to this directioning of the main stay, the whole wind force is transferred in axial direction. By choosing a suitable inclination of the stay to the hub in relation to the hub diameter, also the whole rotation moment is transferred to the hub, because the two main stays 6 and 6' form a couple acting on the shell surface of the cylinder.

The blades 3 and 3' according to the present invention are stayed in four directions. Two of these directions consist of the bending resistance of the blade section on edge with two mountings 8 and 9 and, respectively, 8' and 9' of the blade, and the two remaining staying directions consist of the main and secondary stays 6 and 7 and, respectively, 6' and 7'.

Owing to the aforedescribed directioning of the main stays 6 and 6' the remaining three staying directions substantially will not be subjected to any forces arising from the wind force. Said three staying directions, instead, receive forces arising from dead weight moment, accelerations, retardations, wind direction errors and other undefined magnitudes.

In Fig. 2 is shown how wind force and centrifugal force act on the lower blade 3'. As in Fig. 6 also here it is a question of spread loads. As appears from Fig. 2, the main stay 6' has such a direction relative to the main strut 10' (see Fig. 5) that the centrifugal force in the blade to a substantial part relieves the pressure force in the main strut 10' inside of the stay 6'. Due to the inclination of the blade in the direction of the wind, the centrifugal force gives rise to a moment about the mounting 8' of the blade 3', which moment counteracts the wind pressure.

It is, thus, possible (see Fig. 2) by a combination of the stay angle and the blade inclination in a suitable way to reduce the forces in the main strut 10' inside of the stay point 4' to substantially zero at normal load of the wind pressure at maximum energy output. The secondary stay 7' together with the bending resistance of the blade 3' on edge take up forces transverse to the direction of the main stay and forces from behind.

As the blade has no moment-loaded attachment to the hub 5, except for the yoke 11 and, respectively, 11', which takes up secondary forces, the rotary friction of the blade will be small. The main strut 10 and, respectively, 10', see Fig. 4, is located in the forward edge of the blade 3 and, respectively, 3'. This is possible thereby that the main strut 10 and, respectively, 10' must not be designed so stout, because it is not appreciably momentloaded. Due to this arrangement, the wind tends to turn the blade aside. The counterforce against this force consists of the afore mentioned hydraulic piston 12 and, respectively, 12' or the like, which acts on the yoke 11 and, respectively, 11'. Said yoke transfers the force to the rear edge of the blade which is connected to the main strut 10 and, respectively, 10' via a crosspiece 13 and, respectively, 13'.The counter-force is so dimensioned as to give way for an insignificant increase in the normal wind pressure.

The blade in this way being balanced against the wind, it will adjust aside at wind forces exceeding the normal force, thereby preventing overload on the structure.

As appears from Fig. 5, the yokes 11, 11' are connected to a synchronization device 14 causing the blades to turn in synchronism.

The stayed structure is loaded favourably also with respect to fatigue stresses as regards the pressure-exposed main strut and stay wires. The structure also has a good safety margin to breaking stresses, because the staying easily can be dimensioned with ample safety margin.

The rotor 2 described above has one staying point 4 and, respectively, 4' at each blade 3 and, respectively, 3'. The number of staying points, however, is optional and can be selected according to the desired break length of the main strut 10 and, respectively, 10'.

The rotor 2 shown in Fig. 2 comprises two blades, it may, however, also be designed with three or four blades.

The invention is not restricted, either, to a rotor with featherable blades, but the staying principle may be applied also to a rotor with non-featherable blades.

As appears from Figs 4 and 5, the main strut 10 and, respectively, 10' of the blade 3 and, respectively, 3' is completed with a rear strut 15 and, respectively, 15'. Between these two struts crosspieces 13 and, respectively, 13' are provided. An alternative to this design is shown in Fig. 7, where the main strut is a shell structure receiving the entire blade section or parts thereof. A great number of details can be changed, of course, besides the ones mentioned above, without thereby abandoning the original inventive idea. The invention, thus, can be varied freely within the scope of the attached

Claims

claims. WHAT WE CLAIM IS:

1. A rotor with a horizontal shaft, preferably for wind power stations, comprising a hub and at least two blades supported at the hub, each blade comprising a main strut extending in the longitudinal direction of the blades, means for pivotally attaching each said main strut to the hub, a main stay and a secondary stay attached to said main strut and to said hub at diametrically and axially spaced points on said hub for staying said blade relative to said hub and means extending between said hub and a rearward portion of each blade so that the blade and the main strut will not pivot in the plane containing the front and rear edge of the blade.

2. A rotor according to claim 1 wherein, the main stay of each blade is located in the direction of the resultant acting on the blade from the normal wind force.

3. A rotor according to claim 1 or 2, wherein the main stay of each blade is given such an inclination to the hub in relation to the hub diameter, that the entire torque of the blade is transferred to the hub.

4. A rotor according to one or several of the preceding claims, wherein the main stay of each blade and the blade proper are given such inclinations relative to the shaft direction of the hub, that the centrifugal force acting at rotation on the blade substantially balances the thrust in the main strut inside of the staying point.

5. A rotor according to one or several of the preceding claims wherein the blades of the rotor are turnable about the centre line of their main struts.

6. A rotor according to claim 4, wherein a yoke supported in the hub with the same centre of rotation as the blade is connected to the main strut, and that by control of said rotary yoke the turning of the blade can be controlled.

7. A rotor according to claim 6, wherein the control of the yoke, is effected by means of a hydraulic piston.

8. A rotor according to claim 6 or 7, wherein the control of the yoke is designed so that the blade automatically turns aside at increased wind pressure load and also automatically turns back at decreased wind pressure load.

9. A rotor with a horizontal shaft, substantially as herein described with reference to the accompanying drawings.