CA1092983A - Wind rotor automatic air brake - Google Patents
Wind rotor automatic air brakeInfo
- Publication number
- CA1092983A CA1092983A CA297,956A CA297956A CA1092983A CA 1092983 A CA1092983 A CA 1092983A CA 297956 A CA297956 A CA 297956A CA 1092983 A CA1092983 A CA 1092983A
- Authority
- CA
- Canada
- Prior art keywords
- brake
- plate
- aerodynamic
- rotor
- blade
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 230000009467 reduction Effects 0.000 claims description 2
- 230000004044 response Effects 0.000 claims description 2
- 230000009471 action Effects 0.000 description 10
- 238000013461 design Methods 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 3
- 239000012530 fluid Substances 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- BCCGKQFZUUQSEX-WBPXWQEISA-N (2r,3r)-2,3-dihydroxybutanedioic acid;3,4-dimethyl-2-phenylmorpholine Chemical compound OC(=O)[C@H](O)[C@@H](O)C(O)=O.OC(=O)[C@H](O)[C@@H](O)C(O)=O.O1CCN(C)C(C)C1C1=CC=CC=C1 BCCGKQFZUUQSEX-WBPXWQEISA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03D—WIND MOTORS
- F03D7/00—Controlling wind motors
- F03D7/02—Controlling wind motors the wind motors having rotation axis substantially parallel to the air flow entering the rotor
- F03D7/0244—Controlling wind motors the wind motors having rotation axis substantially parallel to the air flow entering the rotor for braking
- F03D7/0252—Controlling wind motors the wind motors having rotation axis substantially parallel to the air flow entering the rotor for braking with aerodynamic drag devices on the blades
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
- F05B2240/00—Components
- F05B2240/20—Rotors
- F05B2240/30—Characteristics of rotor blades, i.e. of any element transforming dynamic fluid energy to or from rotational energy and being attached to a rotor
- F05B2240/307—Blade tip, e.g. winglets
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
- F05B2260/00—Function
- F05B2260/90—Braking
- F05B2260/901—Braking using aerodynamic forces, i.e. lift or drag
- F05B2260/9011—Braking using aerodynamic forces, i.e. lift or drag of the tips of rotor blades
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/72—Wind turbines with rotation axis in wind direction
Abstract
ABSTRACT OF THE DISCLOSURE
A spring-loaded pivoting end plate that is hinged such that it is deployed by centrifugal force into the airstream to thereby act as an aero-dynamic brake for wind turbines in overspeed conditions. The brake has a stationary portion fixed on the tip of the turbine rotor and a pivoting por-tion hinged for movement with respect to the fixed portion. The longitudinal centerline of the brake coincides with the chord line of the turbine blade and the pivoting movement is about a hinge axis that is normal to the rota-tional plane of the turbine. The planform of the brake has a low aspect ratio shape with the ratio of the fore and aft chordwise length to the width being one or greater. The edges of the brake in the normal running condition ex-tend beyond the contour of the turbine blade to serve as an end plate such that the aerodynamic efficiency of the blade is improved thereby.
A spring-loaded pivoting end plate that is hinged such that it is deployed by centrifugal force into the airstream to thereby act as an aero-dynamic brake for wind turbines in overspeed conditions. The brake has a stationary portion fixed on the tip of the turbine rotor and a pivoting por-tion hinged for movement with respect to the fixed portion. The longitudinal centerline of the brake coincides with the chord line of the turbine blade and the pivoting movement is about a hinge axis that is normal to the rota-tional plane of the turbine. The planform of the brake has a low aspect ratio shape with the ratio of the fore and aft chordwise length to the width being one or greater. The edges of the brake in the normal running condition ex-tend beyond the contour of the turbine blade to serve as an end plate such that the aerodynamic efficiency of the blade is improved thereby.
Description
~0929~3 BACKGROUND OF THE INVENTION
Field of the Invention . :-The present invention relates to wind motors such as wind turbines and the like, and, more particularly, to an automatic aerodynamic brake for :~
preventing overspeeding in such wind motors, SU~A~Y OF THE INVEWTION
I , This invention lies in the art of rotational speed limiters for wind ~:
¦motors. A conventional windmill rotor with no load on it will rotate at a speed : -lapproximately proportional to the free wind speed~ Because a rotor in high winds ¦can turn at rotational speeds that are great enough to result in structural dam-¦age and possible failure due to centrifugal forces, means generally are provided ¦ to prevent ove:speeding of the rotor. These means can take various forms sucl~ al, ~ ~ . '~
:, . , . :
., . . ': `
,, . '. ~
:~ ' ' ' .
' . -~` ' ,.:
9i~3 for example, the human operator in old-time Dutch-type - windmills whose duty it was to furl the sails, or to turn the whole rotor out of the wind when storm conditions occurred.
The more modern windmills, especially the larger ones, secure protection in high winds usually by means which vary the pitch of the blades so as to reduce the rotor rotational speed to a safe range. Such systems require a complex rotor hub design which is usually associated with ~ ~;
an outside power source to perform the pitch changing action.
Systems of the type generally are expensive, and although the cost penalty may be justified in a large machine, it is not suitable for the more popular small windmills. Over-speed preventers for wind motors have also taken the form - of mechanical arrangements for braking the rotor shaft, but such arrangements imply increased maintenance and re-liability problems. In addition, the implementation of mechanical braking systems designed for fully automatic operation introduces an undesirable level of complexity into the system.
Inasmuch as windmills derive their motive power from the action of air flowing over their rotor surfaces, it would appear that aerodynamic means for preventing turbine overspeed would be the most direct and effective approach to the problem. As will be discussed subsequently in some detail, aerodynamic means for regulating the speed of wind rotors have been suggested in the prior art.
The present invention resides in a wind driven motor having a rotor supported for rotation about an axis and an aerodynamic brake mounted on the tip of each blade of the rotor. Each brake includes a brake plate pivotally attached to the tip of the blade for relative pivotal . cbr/~
1~9~83 deployment therewith and having means responsive to centrifugal forces resulting from overspeed conditions of the rotor for pivotally deploying the plate between a stowed position in which the planform surfaces thereoE are substantially parallel to the circumference generated by the blade tip to various deployed positions which extend greater surface areas of the plate into the relative air-stream to create levels of drag proportional to the cen~ri-fugal forces so that the rotational speed of the rotor is affected thereby such that the rotor overspeed condition is remedied. The means responsive to centrifugal forces in-cludes a brake plate weight distribution in which the greater mass is forward of the pivot hinge line of the plate and in the direction of rotation of the rotor blade.
Means is provided for restoring the plate from the deployed positions to the stowed position in response to reductions in the centrifugal forces.
In a specific embodiment of the invention, the aerodynamic brake comprises a simple spring-loaded plate which is hinged on the tip of the rotor blade such as to rotate outwardly under the influence of the level of centri-fugal force resulting from overspeed conditions. In the range of rotational speeds of normal operation, the plate is retained by its spring in the stowed position with the edge of the plate presented to the direction of rotation.
~' In this stowed position, the brake serves as a tip end-plate and significantly increases the efficiency of the rotor.
When the rotor exceeds a predetermined rpm, centrifugal force on the brake plate overcomes the tension of the brake spring and the plate pivots to some deployed position that provides a drag on the rotor that is approximately proportional to the rotational overspeed.
: `:
; -3-~ cbr~
~9298~3 Objects of the Invention It is an important object oE the invention, therefore, to provide means for preventing overspeeding in windmills, which means utilize aerodynamic principles of operation.
It is another object of the invention to provide a windmill aerodynamic brake which is automatically actuated and does not require an outside power input for its operation.
It is a further object of the invention to provide a windmill overspeed preventer in which the means used to stop overrun serve to improve the aerodynamic efficiency of the windmill rotor in its normal operating condition.
It is yet another object of the invention to provide a windmill overspeed fluid brake which can be fitted readily on substantially any fluid-driven rotor.
A further object of the invention to provide a windmill overspeed preventer which has a minimum number of moving parts and which is operated by natural forces.
Another object of the invention is to provide a windmill overspeed preventer which is uncomplicated in construction such that its cost, installation, and maintenance are minimized.
Other and further objects of the invention will become apparent from the detailed description of the invention given in the accompanying specification and drawings.
Description of the Prior Art The use of aerodynamic means which are actuated automatically by centrifugal force to regulate or prevent overspeed in windmills is known in the prior art as evidenced by J. R. Albers et al., L. Blumschein, F. C. Plucker, and J. C. McColly (U. .S. Patent Nos.
RE 22, 726; 1,537,401; 2,058,500; and 2,126,202, respectively).
P. Deria~ (U. S. 2,751,190) shows that a similar arrangement is known in hydrau:Lic turbines. Neither Albers nor Deriaz are believed mb/~d 4 1~92983 to be particularly pertinent with respect to the instant invention, however, because their braking means are located at the hub of the rotor and are not mounted on the blades thereof. McColly is also not similar to the instant invention in that he teaches an air brake that is not mounted on the rotor blade, but which must be provided with a separate structure for its operation. Further, in ~IcColly and Plucker, the air brake is actuated by a translational movement of its mechanism rather than by a pivotal travel of the air brake itself about an axis transverse to the rotor blade chord.
Blumschein, it is seen, does provide a vane-type air brake that is deployed by centrifugal force about an axis transverse to the blade chord; however, Blumschein uses a vane on only one surface of the rotor blade and remotely from the blade tip. Thus, his brake does not produce drag at the maximum rotor radius for maximum torque effect nor does it, at its maximum actuated position, substantially destroy the air flow over the portion of the rotor blade that is normally very effective. In addition, unlike the air brake of the instant invention, the air brake of Blumschein in its stowed position does not act to restrict the spillage of airflow around the tip of the typical rotor. It is seen, therefore, that there is no teaching in the prior art of a centrifugally operated aerodynamic windmill overspeed preventer which is located at the blade tip with its hinge axis transverse to the rotor blade chord such that the device has maximum effectiveness when deployed for braking and which, in its stowed position, acts to improve the aerodynamics ;;
of the rotor blade itself.
Description of the Drawings For the purpose of illustrating the invention, there is .
shown in the drawings the forms which are presently preferred, it should be understood, however, that the invention is not necessarily -~
limited to the precise arrangements and instrumentalities here shown.
Fig. 1 is a front elevation view of a wind motor embodying an air brake in accordance with the invention;
mb~o - 5 --'': ''`, '~ ' :
9!33 Fig. 2 is a top plane view of the rotor blade of a wind motor embodying an air brake of the invention;
Fig. 3 is a side elevation of the air brake embodied in Fig. 2 illustrating the brake in its stowed position;
Fig. 4 is a side elevation of the air brake em-bodied in Fig. 2 illustrating the brake in a deployed position;
Fig. 5 is a perspective view partially in section of a further embodiment of an air brake of the invention;
and Fig. 6 is a plot of brake pivot hinge moments as a function of brake deflection of an air brake of the invention.
Description of the Preferred Embodiments Referring now to the drawings, Fig. 1 illustrates ; an embodiment of the air brake 10 of the invention mounted on the tips 12 of blades 14 of the rotor 16 of a windmill 18. As is well known, the rotor of the windmill is mounted on an output shaft 20 which is journaled in suitable bearings for rotation in the nose of a nacelle 22. Nacelle 22 is mounted on a column or tower 24 by means of the usual pivot arrangement 26 which allows the windmill to weathercock freely into the wind. A suitable power train (not shown) converts the energy output of the rotor in any known appro-priate manner into a form suitable for utilization. The hub of the rotor can be provided with a fairing 28 which may house pitch changing means for the rotor if such means are provided. It will be appreciated that the air brake 10 of this invention can be utilized as the sole braking means for a windmill to prevent overspeed conditions; or one or even two other braking or speed governing means can be provided ~ ' B cbrl,~l-~0929~3 and the brake of this invention can be used as a backup system in the event of malfunctioning or failure of the ~ther systems.
~' .:
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As perhaps best shown in Fig. 2, each of the air brakes lO
is mounted on the tip 12 of rotor blade 16 by suitable mea~s such as bolts or screws 30 which Easten a fi~ed mounting portion 32 of the brake to the rotor. Hinged to the fixed portion of the brake for rotation about pivot 34 is a pivoting brake plate 36 which has a range of angular travel from its stowed position illustrated in ~-Fig. 3 to some fully deployed positioll as shown in Fig. 4 in which the surface 38 of the brake plate 36 :is generally perpendicular to the direction of travel of the blade tip. To insure the proper action of the brake plate 36, the hinge line 40 of pivot 34 should be approximately perpendicular to the direction of rotor blade travel and to the plane of rotation of the rotor.
Means such as a tension spring 42 can be provided to resist deploying movements on the plate and to assist in returning - the plate to its stowed position when it has been displaced therefrom.
To avoid the deployment of the brake plate until some predetermined minimum rotor speed is reached, it may be preferable to have spring 42 under some initial tension. Any suitable mounting arrangement can be used for the spring and can comprise brackets 44,46 fastened -to the rotor blade 14 and surface 38 of the brake plate, respectively, to which the ends 48950 of the spring are secured for operation.
- It is preferable if the brake plate is balanced so that it tends to pivot toward its deployed braking position as a result of the action of the centifugal force developed as a function of rotor speed. If the weight distribution of the plate does not favour this action, means such as a weight 52 can be employed to insure that the plate has a proper weight distribution. ~;~
Although the weight distribution of the plate should be such that the brake deploys as a result of centrifugal force, it is preferable if the plate planform and the selection of the hinge point are such that the brake plate is essentially aerodynamically balanced at all brake deflections between the stowed and fully ~;
mb/ ~ 7 ~
- , - ~ . ~ ~ . .
deployed positions. In actual practice it is difficult to secure perfect aerodynamic balance, but satisfactory operation is obtainable if the design produces a small moment, particularly those tending to stow the brake plate In operation, when a predetermined rotor rotational speed i5 exceeded, centrifugal force on the hinged plate acts to pivot it about its hinge point into some deployed position. This action is opposed by the tension of spring 42 and, to a degree determined by its design, the aerodynamic moments of the plate.
The plate will pivot into some deployed braking position which depends on the degree the rotor has exceeded its normal design speed to thereby provide an aerodynamic drag force which produces a braking action on the rotor roughly proportional to rotor overspeed.
When the overspeed condition is corrected, aerodynamic moments and/or the tension of spring 42 will rotate the brake plate back into its stowed, normal running position.
~ The braking action of the air brake of my invention is `~ extremely effective, principally for two reasons: Firstly, because the brake is located at the rotor blade tip, it will be seen that ~'``
; 20 the drag produced by the brake is at the greatest possible rotor ~` radius such that a maximum torque effect is achieved. Secondly, because when the brake plate is deployed (see Fig. 4), the trailing edge aft of the hinge line is rotated inwardly such that it is interposed over the tip area of the rotor blade. The brake, ;
therefore, not only produces a drag at the maximum possible moment ; arm but, at the same time, it destroys efficient air flow over a portion of the blade that is normally very effective in driving the rotor.
On the other hand, in the stowed, normal-running position, the brake acts as a tip or end plate to restrict the airElow spillage that generally occurs at the tip of the normal rotor blade.
~ .
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lO9Z9~33 This action serves to increase the efficiency of the rotor significantly because the rotor tip sections provide tlle greatest power and losses in that region are critical.
As stated previously, it is preferable if the plate planform (as well as the hinge point) are such that the brake plate is essentially aerodynamically balanced through the entire range of its deflection. The desired aerodynamic characteristics are attainable with a wide variety of plate planforms, such as that shown in Fig. 2. That planform can be described as having a low aspect ratio shape with a ratio of fore and aft length to width of 1 or greater. To provide for a fence or end plate effect on the airflow over the rotor blade, the edges of the plate should e~tend as shol~n beyond the contour of the rotor blade itself. In this invention, the air brake will deflect to provide a braking action proportionally to the overspeed rpm of the rotor. For -maximum efficiency in operation, the end plate weight distribution, planform, and the hinge point must be selected so that its deflection is a function of centrifugal force and not of the relative airspeed at the tip of the rotor blade. The planform considerations are satisfied by selecting a plate configuration that provides zero, or a very small variation of moment about the pivot regardless of airspeed. This air moment consideration is important in assuring that the brake deflection is proportional to rotor overspeed. I
have found that a triangular or delta planform, such as illustrated in Fig. 2, produces a stable pitching moment with deflection that satisfies the requirements.
It will be recognized the air brake of this invention is an aerodynamic clevice that is amenable to aerodynamic palliatives in its design. Thus, known techniques such as leading edge vents, spoilers, or trailing edge trim tabs and the like, can be used to produce the desired moments and such techniques thus fall within the scope of th~s invention. For example, air brake lOb installed mb/J~ - ~ 9 ~
~La~z9~3 on a rotor turning in a direction indicated by directional arrow 66 can be provided ~ith a leading edge spoiler 68, vent holes 70 pierced through the brake plate 36 parallel to the leading edge thereof, and the trailing edges 72 of the plate along line 7~ can be bent 15 relative to the plane of the plate and in the direction of the hub of the rotor to thereby act as a "trim tab". Air brake lOb has the usual fixed portion 32, hinge 34, tension spring 42 (mounted in a spring tube arrangement 76), and the like and can be provided with a tip gusset 78 if such is required. As indicated in the plot of Fig. 6 which gives the hinge moment as a function of brake deflection, an air brake of a design similar to brake lOb -demonstrated a very slight closing moment at low brake deflèctions, along with a stable break at about 45 deflection of the brake that was followed by a stable increase in moment at higher deflections.
. . .
The spring force variation of tension spring 42 should be matched ` ~
to these aerodynamic characteristics of the brake to obtain a I ~ -~stable variation of brake deployment throughout its range of travel.
i~ It will also be appreciated that aerodynamic palliatives ~;
can be incorporated in the rotor blade itself to achieve the desired pivot moments of the brake. Such means can take a variety of forms such as, for example, a splitter plate 80 fixed on the rotor blade as at the leading edge thereof.
Although shown and described in what is believed to be the most practical and preferred embodiments, it is apparent that departures from the specific method and apparatus described will suggest themselves to those skilled in the art and may be made without departiDg from the spirit and scope of the invention. I, therefore, do not wish to restrict myself to the particular methods illustrated and described, but desire to avail myself of all modifications that may fall within the scope of the appended claims.
mb/J~ - 10 -~()92~83 increase in moment at higher deflections. The spring force variation of tension spring 42 should be matched to these aerodynamic characteristics of the brake to obtain a stable variation of brake deployment throughout its range of travel.
It will also be appreciated that aerodynamic palliatives can be incorporated in the rotor blade itself to achieve the desired pivot moments o~ the brake. Such means can take a variety of forms such as5 for example, a splitter plate 80 fixed on the rotor blade as at the leading edge thereof.
- Although shown and described in what is believed to be the most practical and preEer~ed embodiments, it is apparent that`departures from the specific method and apparatus described uill suggest themselves to those skilled in the art and may be made without departing from the spirit and scope ; of the invention. I, therefore, do not wish to restrict myself to the par-ticular methods lllustrated and described, but desire to avail myself of all modifications that may fall within the scope of the appended claims.
:
.
Field of the Invention . :-The present invention relates to wind motors such as wind turbines and the like, and, more particularly, to an automatic aerodynamic brake for :~
preventing overspeeding in such wind motors, SU~A~Y OF THE INVEWTION
I , This invention lies in the art of rotational speed limiters for wind ~:
¦motors. A conventional windmill rotor with no load on it will rotate at a speed : -lapproximately proportional to the free wind speed~ Because a rotor in high winds ¦can turn at rotational speeds that are great enough to result in structural dam-¦age and possible failure due to centrifugal forces, means generally are provided ¦ to prevent ove:speeding of the rotor. These means can take various forms sucl~ al, ~ ~ . '~
:, . , . :
., . . ': `
,, . '. ~
:~ ' ' ' .
' . -~` ' ,.:
9i~3 for example, the human operator in old-time Dutch-type - windmills whose duty it was to furl the sails, or to turn the whole rotor out of the wind when storm conditions occurred.
The more modern windmills, especially the larger ones, secure protection in high winds usually by means which vary the pitch of the blades so as to reduce the rotor rotational speed to a safe range. Such systems require a complex rotor hub design which is usually associated with ~ ~;
an outside power source to perform the pitch changing action.
Systems of the type generally are expensive, and although the cost penalty may be justified in a large machine, it is not suitable for the more popular small windmills. Over-speed preventers for wind motors have also taken the form - of mechanical arrangements for braking the rotor shaft, but such arrangements imply increased maintenance and re-liability problems. In addition, the implementation of mechanical braking systems designed for fully automatic operation introduces an undesirable level of complexity into the system.
Inasmuch as windmills derive their motive power from the action of air flowing over their rotor surfaces, it would appear that aerodynamic means for preventing turbine overspeed would be the most direct and effective approach to the problem. As will be discussed subsequently in some detail, aerodynamic means for regulating the speed of wind rotors have been suggested in the prior art.
The present invention resides in a wind driven motor having a rotor supported for rotation about an axis and an aerodynamic brake mounted on the tip of each blade of the rotor. Each brake includes a brake plate pivotally attached to the tip of the blade for relative pivotal . cbr/~
1~9~83 deployment therewith and having means responsive to centrifugal forces resulting from overspeed conditions of the rotor for pivotally deploying the plate between a stowed position in which the planform surfaces thereoE are substantially parallel to the circumference generated by the blade tip to various deployed positions which extend greater surface areas of the plate into the relative air-stream to create levels of drag proportional to the cen~ri-fugal forces so that the rotational speed of the rotor is affected thereby such that the rotor overspeed condition is remedied. The means responsive to centrifugal forces in-cludes a brake plate weight distribution in which the greater mass is forward of the pivot hinge line of the plate and in the direction of rotation of the rotor blade.
Means is provided for restoring the plate from the deployed positions to the stowed position in response to reductions in the centrifugal forces.
In a specific embodiment of the invention, the aerodynamic brake comprises a simple spring-loaded plate which is hinged on the tip of the rotor blade such as to rotate outwardly under the influence of the level of centri-fugal force resulting from overspeed conditions. In the range of rotational speeds of normal operation, the plate is retained by its spring in the stowed position with the edge of the plate presented to the direction of rotation.
~' In this stowed position, the brake serves as a tip end-plate and significantly increases the efficiency of the rotor.
When the rotor exceeds a predetermined rpm, centrifugal force on the brake plate overcomes the tension of the brake spring and the plate pivots to some deployed position that provides a drag on the rotor that is approximately proportional to the rotational overspeed.
: `:
; -3-~ cbr~
~9298~3 Objects of the Invention It is an important object oE the invention, therefore, to provide means for preventing overspeeding in windmills, which means utilize aerodynamic principles of operation.
It is another object of the invention to provide a windmill aerodynamic brake which is automatically actuated and does not require an outside power input for its operation.
It is a further object of the invention to provide a windmill overspeed preventer in which the means used to stop overrun serve to improve the aerodynamic efficiency of the windmill rotor in its normal operating condition.
It is yet another object of the invention to provide a windmill overspeed fluid brake which can be fitted readily on substantially any fluid-driven rotor.
A further object of the invention to provide a windmill overspeed preventer which has a minimum number of moving parts and which is operated by natural forces.
Another object of the invention is to provide a windmill overspeed preventer which is uncomplicated in construction such that its cost, installation, and maintenance are minimized.
Other and further objects of the invention will become apparent from the detailed description of the invention given in the accompanying specification and drawings.
Description of the Prior Art The use of aerodynamic means which are actuated automatically by centrifugal force to regulate or prevent overspeed in windmills is known in the prior art as evidenced by J. R. Albers et al., L. Blumschein, F. C. Plucker, and J. C. McColly (U. .S. Patent Nos.
RE 22, 726; 1,537,401; 2,058,500; and 2,126,202, respectively).
P. Deria~ (U. S. 2,751,190) shows that a similar arrangement is known in hydrau:Lic turbines. Neither Albers nor Deriaz are believed mb/~d 4 1~92983 to be particularly pertinent with respect to the instant invention, however, because their braking means are located at the hub of the rotor and are not mounted on the blades thereof. McColly is also not similar to the instant invention in that he teaches an air brake that is not mounted on the rotor blade, but which must be provided with a separate structure for its operation. Further, in ~IcColly and Plucker, the air brake is actuated by a translational movement of its mechanism rather than by a pivotal travel of the air brake itself about an axis transverse to the rotor blade chord.
Blumschein, it is seen, does provide a vane-type air brake that is deployed by centrifugal force about an axis transverse to the blade chord; however, Blumschein uses a vane on only one surface of the rotor blade and remotely from the blade tip. Thus, his brake does not produce drag at the maximum rotor radius for maximum torque effect nor does it, at its maximum actuated position, substantially destroy the air flow over the portion of the rotor blade that is normally very effective. In addition, unlike the air brake of the instant invention, the air brake of Blumschein in its stowed position does not act to restrict the spillage of airflow around the tip of the typical rotor. It is seen, therefore, that there is no teaching in the prior art of a centrifugally operated aerodynamic windmill overspeed preventer which is located at the blade tip with its hinge axis transverse to the rotor blade chord such that the device has maximum effectiveness when deployed for braking and which, in its stowed position, acts to improve the aerodynamics ;;
of the rotor blade itself.
Description of the Drawings For the purpose of illustrating the invention, there is .
shown in the drawings the forms which are presently preferred, it should be understood, however, that the invention is not necessarily -~
limited to the precise arrangements and instrumentalities here shown.
Fig. 1 is a front elevation view of a wind motor embodying an air brake in accordance with the invention;
mb~o - 5 --'': ''`, '~ ' :
9!33 Fig. 2 is a top plane view of the rotor blade of a wind motor embodying an air brake of the invention;
Fig. 3 is a side elevation of the air brake embodied in Fig. 2 illustrating the brake in its stowed position;
Fig. 4 is a side elevation of the air brake em-bodied in Fig. 2 illustrating the brake in a deployed position;
Fig. 5 is a perspective view partially in section of a further embodiment of an air brake of the invention;
and Fig. 6 is a plot of brake pivot hinge moments as a function of brake deflection of an air brake of the invention.
Description of the Preferred Embodiments Referring now to the drawings, Fig. 1 illustrates ; an embodiment of the air brake 10 of the invention mounted on the tips 12 of blades 14 of the rotor 16 of a windmill 18. As is well known, the rotor of the windmill is mounted on an output shaft 20 which is journaled in suitable bearings for rotation in the nose of a nacelle 22. Nacelle 22 is mounted on a column or tower 24 by means of the usual pivot arrangement 26 which allows the windmill to weathercock freely into the wind. A suitable power train (not shown) converts the energy output of the rotor in any known appro-priate manner into a form suitable for utilization. The hub of the rotor can be provided with a fairing 28 which may house pitch changing means for the rotor if such means are provided. It will be appreciated that the air brake 10 of this invention can be utilized as the sole braking means for a windmill to prevent overspeed conditions; or one or even two other braking or speed governing means can be provided ~ ' B cbrl,~l-~0929~3 and the brake of this invention can be used as a backup system in the event of malfunctioning or failure of the ~ther systems.
~' .:
,~:
;'.,.
-6a- :~.
,"
cbr/~
As perhaps best shown in Fig. 2, each of the air brakes lO
is mounted on the tip 12 of rotor blade 16 by suitable mea~s such as bolts or screws 30 which Easten a fi~ed mounting portion 32 of the brake to the rotor. Hinged to the fixed portion of the brake for rotation about pivot 34 is a pivoting brake plate 36 which has a range of angular travel from its stowed position illustrated in ~-Fig. 3 to some fully deployed positioll as shown in Fig. 4 in which the surface 38 of the brake plate 36 :is generally perpendicular to the direction of travel of the blade tip. To insure the proper action of the brake plate 36, the hinge line 40 of pivot 34 should be approximately perpendicular to the direction of rotor blade travel and to the plane of rotation of the rotor.
Means such as a tension spring 42 can be provided to resist deploying movements on the plate and to assist in returning - the plate to its stowed position when it has been displaced therefrom.
To avoid the deployment of the brake plate until some predetermined minimum rotor speed is reached, it may be preferable to have spring 42 under some initial tension. Any suitable mounting arrangement can be used for the spring and can comprise brackets 44,46 fastened -to the rotor blade 14 and surface 38 of the brake plate, respectively, to which the ends 48950 of the spring are secured for operation.
- It is preferable if the brake plate is balanced so that it tends to pivot toward its deployed braking position as a result of the action of the centifugal force developed as a function of rotor speed. If the weight distribution of the plate does not favour this action, means such as a weight 52 can be employed to insure that the plate has a proper weight distribution. ~;~
Although the weight distribution of the plate should be such that the brake deploys as a result of centrifugal force, it is preferable if the plate planform and the selection of the hinge point are such that the brake plate is essentially aerodynamically balanced at all brake deflections between the stowed and fully ~;
mb/ ~ 7 ~
- , - ~ . ~ ~ . .
deployed positions. In actual practice it is difficult to secure perfect aerodynamic balance, but satisfactory operation is obtainable if the design produces a small moment, particularly those tending to stow the brake plate In operation, when a predetermined rotor rotational speed i5 exceeded, centrifugal force on the hinged plate acts to pivot it about its hinge point into some deployed position. This action is opposed by the tension of spring 42 and, to a degree determined by its design, the aerodynamic moments of the plate.
The plate will pivot into some deployed braking position which depends on the degree the rotor has exceeded its normal design speed to thereby provide an aerodynamic drag force which produces a braking action on the rotor roughly proportional to rotor overspeed.
When the overspeed condition is corrected, aerodynamic moments and/or the tension of spring 42 will rotate the brake plate back into its stowed, normal running position.
~ The braking action of the air brake of my invention is `~ extremely effective, principally for two reasons: Firstly, because the brake is located at the rotor blade tip, it will be seen that ~'``
; 20 the drag produced by the brake is at the greatest possible rotor ~` radius such that a maximum torque effect is achieved. Secondly, because when the brake plate is deployed (see Fig. 4), the trailing edge aft of the hinge line is rotated inwardly such that it is interposed over the tip area of the rotor blade. The brake, ;
therefore, not only produces a drag at the maximum possible moment ; arm but, at the same time, it destroys efficient air flow over a portion of the blade that is normally very effective in driving the rotor.
On the other hand, in the stowed, normal-running position, the brake acts as a tip or end plate to restrict the airElow spillage that generally occurs at the tip of the normal rotor blade.
~ .
mb/~o - 8 ~
~ `.
lO9Z9~33 This action serves to increase the efficiency of the rotor significantly because the rotor tip sections provide tlle greatest power and losses in that region are critical.
As stated previously, it is preferable if the plate planform (as well as the hinge point) are such that the brake plate is essentially aerodynamically balanced through the entire range of its deflection. The desired aerodynamic characteristics are attainable with a wide variety of plate planforms, such as that shown in Fig. 2. That planform can be described as having a low aspect ratio shape with a ratio of fore and aft length to width of 1 or greater. To provide for a fence or end plate effect on the airflow over the rotor blade, the edges of the plate should e~tend as shol~n beyond the contour of the rotor blade itself. In this invention, the air brake will deflect to provide a braking action proportionally to the overspeed rpm of the rotor. For -maximum efficiency in operation, the end plate weight distribution, planform, and the hinge point must be selected so that its deflection is a function of centrifugal force and not of the relative airspeed at the tip of the rotor blade. The planform considerations are satisfied by selecting a plate configuration that provides zero, or a very small variation of moment about the pivot regardless of airspeed. This air moment consideration is important in assuring that the brake deflection is proportional to rotor overspeed. I
have found that a triangular or delta planform, such as illustrated in Fig. 2, produces a stable pitching moment with deflection that satisfies the requirements.
It will be recognized the air brake of this invention is an aerodynamic clevice that is amenable to aerodynamic palliatives in its design. Thus, known techniques such as leading edge vents, spoilers, or trailing edge trim tabs and the like, can be used to produce the desired moments and such techniques thus fall within the scope of th~s invention. For example, air brake lOb installed mb/J~ - ~ 9 ~
~La~z9~3 on a rotor turning in a direction indicated by directional arrow 66 can be provided ~ith a leading edge spoiler 68, vent holes 70 pierced through the brake plate 36 parallel to the leading edge thereof, and the trailing edges 72 of the plate along line 7~ can be bent 15 relative to the plane of the plate and in the direction of the hub of the rotor to thereby act as a "trim tab". Air brake lOb has the usual fixed portion 32, hinge 34, tension spring 42 (mounted in a spring tube arrangement 76), and the like and can be provided with a tip gusset 78 if such is required. As indicated in the plot of Fig. 6 which gives the hinge moment as a function of brake deflection, an air brake of a design similar to brake lOb -demonstrated a very slight closing moment at low brake deflèctions, along with a stable break at about 45 deflection of the brake that was followed by a stable increase in moment at higher deflections.
. . .
The spring force variation of tension spring 42 should be matched ` ~
to these aerodynamic characteristics of the brake to obtain a I ~ -~stable variation of brake deployment throughout its range of travel.
i~ It will also be appreciated that aerodynamic palliatives ~;
can be incorporated in the rotor blade itself to achieve the desired pivot moments of the brake. Such means can take a variety of forms such as, for example, a splitter plate 80 fixed on the rotor blade as at the leading edge thereof.
Although shown and described in what is believed to be the most practical and preferred embodiments, it is apparent that departures from the specific method and apparatus described will suggest themselves to those skilled in the art and may be made without departiDg from the spirit and scope of the invention. I, therefore, do not wish to restrict myself to the particular methods illustrated and described, but desire to avail myself of all modifications that may fall within the scope of the appended claims.
mb/J~ - 10 -~()92~83 increase in moment at higher deflections. The spring force variation of tension spring 42 should be matched to these aerodynamic characteristics of the brake to obtain a stable variation of brake deployment throughout its range of travel.
It will also be appreciated that aerodynamic palliatives can be incorporated in the rotor blade itself to achieve the desired pivot moments o~ the brake. Such means can take a variety of forms such as5 for example, a splitter plate 80 fixed on the rotor blade as at the leading edge thereof.
- Although shown and described in what is believed to be the most practical and preEer~ed embodiments, it is apparent that`departures from the specific method and apparatus described uill suggest themselves to those skilled in the art and may be made without departing from the spirit and scope ; of the invention. I, therefore, do not wish to restrict myself to the par-ticular methods lllustrated and described, but desire to avail myself of all modifications that may fall within the scope of the appended claims.
:
.
Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a wind-driven motor having a rotor including a plurality of blades and being supported for rotation about an axis, an aerodynamic brake mounted on the tip of each blade of said rotor, each of said brakes comprising:
a brake plate pivotally attached to the tip of said blade for relative pivotal deployment therewith;
means responsive to centrifugal forces resulting from overspeed conditions of said rotor for pivotally de-ploying said plate between a stowed position in which the planform surfaces thereof are substantially parallel to the circumference generated by said blade tip to various deployed positions which extend greater surface areas of said plate into the relative airstream to create levels of drag proportional to said centrifugal forces whereby the rotational speed of said rotor is affected thereby such that the rotor overspeed condition is remedied, said means responsive to centrifugal forces comprising a brake plate weight distribution in which the greater mass is forward of the pivot hinge line of said plate and in the direction of rotation of said rotor blade; and means for restoring said plate from said deployed positions to said stowed position in response to reductions in said centrifugal forces.
a brake plate pivotally attached to the tip of said blade for relative pivotal deployment therewith;
means responsive to centrifugal forces resulting from overspeed conditions of said rotor for pivotally de-ploying said plate between a stowed position in which the planform surfaces thereof are substantially parallel to the circumference generated by said blade tip to various deployed positions which extend greater surface areas of said plate into the relative airstream to create levels of drag proportional to said centrifugal forces whereby the rotational speed of said rotor is affected thereby such that the rotor overspeed condition is remedied, said means responsive to centrifugal forces comprising a brake plate weight distribution in which the greater mass is forward of the pivot hinge line of said plate and in the direction of rotation of said rotor blade; and means for restoring said plate from said deployed positions to said stowed position in response to reductions in said centrifugal forces.
2. The aerodynamic brake as defined in claim 1 wherein the pivotal axis of the brake plate is perpendicular to the plane of rotation of the rotor blade.
3. The aerodynamic brake as defined in claim 1 wherein the means for restoring said plate to said stowed position is a spring.
4. The aerodynamic brake as defined in claim 4 wherein the restoring means is a tension spring in biasing association between the rotor blade and the brake plate.
5. The aerodynamic brake as defined in claim 1 wherein the restoring means is a brake plate planform in which the aerodynamic pitching moments on said plate in its deployed positions are in a direction tending to pivot said plate into its stowed position.
6. The aerodynamic brake as defined in claim 1 wherein the planform of the brake plate extends beyond the contours of the rotor blade section whereby said plate in its stowed position serves as a tip plate to restrict airflow spillage around the end of said rotor blade such that the aerodynamic efficiency of said blade is improved thereby.
7. The aerodynamic brake as defined in claim 1 wherein the hinge line of the brake plate is located intermediate the leading and trailing ends thereof such that the leading end portions of said plate in its deployed positions project outside the tip path of the rotor.
8. The aerodynamic brake as defined in claim 8 wherein the trailing end of said plate is cut away along the plate longitudinal axis, the cut-away portion being sized to accommodate the rotor blade such that in the deployed positions of the brake, portions of its trailing end are pivoted over the surfaces of said rotor blade whereby the airflow thereover is influenced.
9. The aerodynamic brake as defined in claim 6 wherein the brake plate has a delta planform with the base of the delta comprising the leading edge of said plate.
10. The aerodynamic brake as defined in claim 9 wherein the plate planform has a low-aspect ration with the ratio of fore and aft length to width of at least 1.
11. The aerodynamic brake as defined in claim 6 wherein the leading edge of the plate is provided with a spoiler such that the airflow over the plate is influenced thereby.
12. The aerodynamic brake as defined in claim 12 wherein the spoiler is a rigid strip extending perpendicular to the planform surface of the plate at least on one side thereof.
13. The aerodynamic brake as defined in claim 6 wherein the leading edge portion of the plate is provided with at least one vent intermediate the width thereof.
14 The aerodynamic brake as defined in claim 1 wherein aerodynamic means are fixed on the tip of the rotor blade radially inward of said brake such that the airflow at said blade tip during the deployment of the brake plate is influenced thereby.
15. The aerodynamic brake as defined in claim 14 wherein the aerodynamic means is a plate whose planform surfaces are substantially parallel to the circumference generated by the rotor blade tip.
16. The aerodynamic brake as defined in claim 15 wherein the planform of the aerodynamic means extends beyond the contours of the rotor blade at least in the leading edge portions thereof.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/773,538 US4180372A (en) | 1977-03-02 | 1977-03-02 | Wind rotor automatic air brake |
| US773,538 | 1977-03-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1092983A true CA1092983A (en) | 1981-01-06 |
Family
ID=25098598
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA297,956A Expired CA1092983A (en) | 1977-03-02 | 1978-03-01 | Wind rotor automatic air brake |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4180372A (en) |
| CA (1) | CA1092983A (en) |
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| US4297076A (en) * | 1979-06-08 | 1981-10-27 | Lockheed Corporation | Wind turbine |
| US4456429A (en) * | 1982-03-15 | 1984-06-26 | Kelland Robert E | Wind turbine |
| US4500257A (en) * | 1983-02-24 | 1985-02-19 | The United States Of America As Represented By The United States Department Of Energy | Wind turbine spoiler |
| GB2140508B (en) * | 1983-05-25 | 1987-01-07 | Howden James & Co Ltd | Wind turbines |
| WO1985004930A1 (en) * | 1984-04-26 | 1985-11-07 | Sir Henry Lawson-Tancred, Sons & Co Ltd | Wind turbine blades |
| EP0200823B1 (en) * | 1985-04-26 | 1988-12-28 | JAMES HOWDEN & COMPANY LIMITED | Wind turbine |
| US4715782A (en) * | 1985-12-24 | 1987-12-29 | Fayette Manufacturing Corp. | Hydraulic control device for wind turbine |
| DE4434764A1 (en) * | 1993-09-30 | 1995-04-06 | Egon Gelhard Engineering | Wind power installation (wind power system) having a Darrieus-H rotor |
| ES2156475B1 (en) * | 1998-02-13 | 2002-01-16 | Perez Adolfo Gonzalez | UNIVERSAL WIND AND HYDRAULIC TURBINE AND APPLICATIONS. |
| US6265785B1 (en) | 1998-11-30 | 2001-07-24 | Zond Systems, Inc. | Non-volatile over speed control system for wind turbines |
| CN2420228Y (en) * | 2000-02-29 | 2001-02-21 | 韩玮 | High performance propeller |
| DE10016912C1 (en) * | 2000-04-05 | 2001-12-13 | Aerodyn Eng Gmbh | Operation of offshore wind turbines dependent on the natural frequency of the tower |
| US6726439B2 (en) | 2001-08-22 | 2004-04-27 | Clipper Windpower Technology, Inc. | Retractable rotor blades for power generating wind and ocean current turbines and means for operating below set rotor torque limits |
| US6923622B1 (en) | 2002-03-07 | 2005-08-02 | Clipper Windpower Technology, Inc. | Mechanism for extendable rotor blades for power generating wind and ocean current turbines and means for counter-balancing the extendable rotor blade |
| US7581926B1 (en) * | 2004-03-22 | 2009-09-01 | Clipper Windpower Technology, Inc. | Servo-controlled extender mechanism for extendable rotor blades for power generating wind and ocean current turbines |
| US7582977B1 (en) | 2005-02-25 | 2009-09-01 | Clipper Windpower Technology, Inc. | Extendable rotor blades for power generating wind and ocean current turbines within a module mounted atop a main blade |
| NO20054704D0 (en) * | 2005-10-13 | 2005-10-13 | Sway As | Method and method for wind turbines and propulsion systems with magnetically stable main bearing and load control system |
| US8165221B2 (en) | 2006-04-28 | 2012-04-24 | Netapp, Inc. | System and method for sampling based elimination of duplicate data |
| US7989973B2 (en) * | 2006-12-22 | 2011-08-02 | Birkestrand Orville J | Fluid-responsive oscillation power generation method and apparatus |
| US7828523B2 (en) * | 2007-03-27 | 2010-11-09 | General Electric Company | Rotor blade for a wind turbine having a variable dimension |
| JP2009008041A (en) * | 2007-06-29 | 2009-01-15 | Mecaro:Kk | Magnus type wind power generator |
| PL2085610T3 (en) * | 2008-01-29 | 2011-04-29 | Claus Colling | Vertical axis wind turbine with control system and method of aerodynamic braking |
| CA2761811C (en) * | 2009-05-20 | 2018-06-05 | Deka Products Limited Partnership | Centrifugally driven aerodynamic rotor blade brake assembly |
| US20100135806A1 (en) * | 2009-06-22 | 2010-06-03 | General Electric Company | Hinged wind turbine blade tips |
| US20110187114A1 (en) * | 2010-02-04 | 2011-08-04 | Bert Socolove | Wind driven turbine |
| DK177278B1 (en) * | 2011-05-19 | 2012-09-17 | Envision Energy Denmark Aps | A wind turbine and associated control method |
| TWI431194B (en) * | 2011-09-22 | 2014-03-21 | Hi Vawt Technology Corp | Device for controlling blade speed of a vertical axis windmill by using the rotating centrifugal force of blades and the method thereof |
| US8491262B2 (en) | 2011-10-27 | 2013-07-23 | General Electric Company | Method for shut down of a wind turbine having rotor blades with fail-safe air brakes |
| US20120134814A1 (en) * | 2011-10-27 | 2012-05-31 | General Electric Company | Wind turbine rotor blade with fail-safe air brake flaps |
| FR2996592B1 (en) * | 2012-10-10 | 2014-12-19 | Snecma | PROPELLER COMPRISING A DYNAMIC MOBILE ECOPE |
| US10100809B2 (en) * | 2013-05-29 | 2018-10-16 | Magnelan Technologies Inc. | Wind turbine for facilitating laminar flow |
| TWI522529B (en) * | 2013-06-28 | 2016-02-21 | 國立臺灣海洋大學 | Vertical axis wind turbine |
| US9267491B2 (en) | 2013-07-02 | 2016-02-23 | General Electric Company | Wind turbine rotor blade having a spoiler |
| US9273666B2 (en) * | 2013-09-01 | 2016-03-01 | Hamid Reza Kheirandish | Magnus type wind power generator |
| EP3293392B1 (en) * | 2016-09-08 | 2020-08-12 | Vestas Wind Systems A/S | Wind turbine blade comprising an edgewise stabilizer |
| JP6426869B1 (en) * | 2018-06-08 | 2018-11-21 | 株式会社グローバルエナジー | Horizontal axis rotor |
| US11204016B1 (en) | 2018-10-24 | 2021-12-21 | Magnelan Energy LLC | Light weight mast for supporting a wind turbine |
| DE202021003573U1 (en) | 2021-11-16 | 2023-02-17 | Andreas Mark Dreseler | Decentralized Vertical Wind Turbine |
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| US932521A (en) * | 1909-01-23 | 1909-08-31 | Hugh M Wallace | Wind-wheel for windmills. |
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| US2037528A (en) * | 1934-07-30 | 1936-04-14 | Charles E Miller | Wind motor |
| US2076520A (en) * | 1936-01-21 | 1937-04-06 | L H Cutler | Automatic air motor governor |
| US2148921A (en) * | 1938-04-12 | 1939-02-28 | Walter J Allen | Governor mechanism |
| GB800890A (en) * | 1956-06-26 | 1958-09-03 | Gyrodyne Company Of America In | Directional control system for rotary wing aircraft |
| US3038543A (en) * | 1960-10-03 | 1962-06-12 | Hudson Engineering Corp | Air brake for wind driven propellers |
| US3448811A (en) * | 1968-01-09 | 1969-06-10 | Bolkow Gmbh | Device for stabilizing the rotor blades of a rotary wing aircraft |
| US3874816A (en) * | 1973-10-23 | 1975-04-01 | Thomas E Sweeney | Windmill blade |
-
1977
- 1977-03-02 US US05/773,538 patent/US4180372A/en not_active Expired - Lifetime
-
1978
- 1978-03-01 CA CA297,956A patent/CA1092983A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4180372A (en) | 1979-12-25 |
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