US3915591A

US3915591A - Flexible blade fan

Info

Publication number: US3915591A
Application number: US319860A
Authority: US
Inventors: Shigeo Aiki; Takanobu Hori; Masaharu Hayashi
Original assignee: Aisin Seiki Co Ltd
Current assignee: Aisin Corp
Priority date: 1971-12-09
Filing date: 1972-12-29
Publication date: 1975-10-28
Anticipated expiration: 1992-10-28
Also published as: JPS4872707A; DE2263310B2; DE2263310A1; JPS512647B2

Abstract

A screw type multiblade molded fan of plastic material comprising a central hub and a plurality of blades radially extending from said hub in an imaginary plane normal to the axis of rotation of the fan, each blade being integral with said hub and curved forwardly away from said plane characterized in that each blade decreases thickness thereof at the middle portion in cross sectional shape. A flexible trailing portion is provided in each blade by such formation of each blade to thereby decrease an inclination angle of each blade as the rotational speed of the fan is increased. The reduction of the angle is then decreases the air flow which thereby decreases the horsepower requirement and the fan noise as the rotational speed of the fan is increased.

Description

United States Patent 1 Aiki et al.

[ Oct. 28, 1975 FLEXIBLE BLADE FAN [73] Assignee: Aisin Seiki Kabushiki Kaisha,

Kariya, Japan [22] Filed: Dec. 29, 1972 [21] Appl. No.: 319,860

[30] Foreign Application Priority Data Dec. 29, 1971 Japan 47-2956 [52] US. Cl 416/132; 416/240 [51] Int. Cl? F04D 29/38 [58] Field of Search 416/132, 240, 241 A [56] References Cited UNITED STATES PATENTS 1,798,299 3/1931 Antoni 416/240 3,054,355 9/1962 Neely 416/240 X 3,584,969 6/1971 Aiki et al. 416/132 FOREIGN PATENTS OR APPLICATIONS 2,013,481 10/1970 Germany 416/132 Primary Examiner Everette A. Powell, Jr. Attorney, Agent, or FirmWaters, Schwartz & Nissen [5 7] ABSTRACT A screw type multiblade molded fan of plastic material comprising a central hub and a plurality of blades radially extending from said hub in an imaginary plane normal to the axis of rotation of the fan, each blade being integral with said hub and curved forwardly away from said plane characterized in that each blade decreases thickness thereof .at the middle portion in cross sectional shape. A flexible trailing portion is provided in each blade by such formation of each blade to thereby decrease an inclination angle of each blade as the rotational speed of the fan is increased. The reduction of the angle is then decreases the air flow which thereby decreases the horsepower requirement and the fan noise as the rotational speed of the fan is increased.

3 Claims, 6 Drawing Figures US. Patent 'Oct.28,'1975 Sheet1of2 3,915,591

US. Patent Oct. 28, 1975 SheetZ of? 3,915,591

FIG.

FLOW OF AIR PRODUCED FLEXIBLE BLADE FAN BACKGROUND OF THE INVENTION This invention relates to multiblade molded plastic fans, and particularly to a fan of the flexible multiblade molded screw type.

The screw type multiblade fans which are employed on automotive vehicle engines are driven at a greater speed as the speed of the travelling vehicle is increased. This increases the horsepower requirement due to the increase in air velocity.

While various means have been previously employed for a fan of the flexible multiblade molded screw type to decrease the horsepower requirement and the noise which would be increased if the flow of air were increased, none have proven to be entirely sufficient.

SUMMARY OF THE INVENTION A principal object of the invention is to provide an improved fan of the flexible multiblade molded plastic type to decrease the horsepower requirement and the noise as the rotational speed of the fan increases.

The foregoing object and others are attained according to at least one aspect of the present invention through the provision of a plurality of flexible molded plastic blades extending from a hub and integral with the hub wherein thickness of each blade decreases in successive steps at the middle portion in cross sectional shape to form a series of partial blades different from each other in thickness. Each of said blades may be further provided with at its foot portion a recess so as to separate a trailing portion from the hub.

Thus, in the disclosed embodiments, there are comprised a central hub and a plurality of blades radially extending from said hub in an imaginary plane disposed normal to the axis of rotation of the fan, each said blade being integral with said hub and curved forwardly away from said plane characterized in that each said blade decreases thickness thereof at the middle portion in cross sectional shape so as to form a series of two or more partial blades different from each other in thickness, whereby a flexible trailing portion is provided to be deflected in each said blade by centrifugal force and that of the contact of the air as the rotational speed of the fan is increased. For assistance of such deflection of the trailing portion, the fan may be beneficially provided with a recess at the foot portion of each blade so as to have the trailing portion separated from the hub and render the remaining part of said blade a leading portion.

. BRIEF DESCRIPTION OF THE DRAWINGS Additional objects and the novel features of this invention will become apparent from the description which follows, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a front view of a preferred embodiment of the invention, wherein however only a fan blade has been specifically represented and the remaining blades have been shown only in their whole or partial general configuration;

FIG. 2 is a cross section of a fan blade, in the section being taken along the line II-II in FIG. 1 and in the direction of the arrow;

FIG. 3 is a cross sectional view of the embodiment of FIG. 2 in which shown common function by additional symbols for convenience of understanding;

FIG. 4 shows a graph showing flow of air relative to the rotational speed of the fan as compared with the flow of air of the conventional fan; and

FIGS. 5(a) and 5(b) are cross sections of other embodiments according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring in detail to the drawings, particularly to the form of the invention shown in the FIGS. 1 to 5, the same comprises a hub 1 and a plurality of properly pitched blades 2 integral therewith and extended radially therefrom. The said hub and blades are formed of a suitable molded flexible plastic material which is capable of production, especially, by the existing methods of injection molding.

The hub l is formed with a central opening 3 to provide means for mounting on a shaft (not shown) driven by the known engine driving shaft through a band (not shown) in the known manner. About the opening 3, are provided a suitable number of spaced holes 4 to provide means to rotate the hub 1 together with the driven shaft. Each of the blades is reduced at its bottom portion as at 5 so that a trailing portion 6 is formed separately from the hub and the remaining part of the blade is rendered a leading portion 8. The trailing portion 6 is deflected by centrifugal force: and that of the contacting air as the rotational speed of the fan is increased. Thus, by selecting the proper :shape and curvature of the blade 2 and its resistance, namely cross sectional shape, to deflection, the air flow may be maintained substantially constant, thereby reducing the horsepower requirement as the speed of rotation in the direction of arrow A of the fans is increased.

A fan of this type will have special applications on an automotive engine as a substantial flow of air is required when the engine is idling or driving the vehicle at low speed, which requirement progressively reduces as the speed of the vehicle increases. If the same amount of air is propelled by the blades of the fan at high speed a substantial amount of horsepower is required, resulting in inefficient operation of the vehicle. With the flexible blade type of fan as herein illustrated and described, the increased speed will progressively flatten the blades 2 namely an inclination angel a in FIG. 2 is reduced to increasing degree of rotational speed of the fan. Thus when a substantial amount of air is required at low speed, the blades will maintain the initial form and produce a maximum flow of air. As the speed increases requiring a less amount of air, the blades will flatten and produce a decrease in air flow which thereby decreases such horsepower requirement and the noise which would be increased if the flow of air were increased.

What has been thus far described is a flexible fan of previously provided structure, as commonly used in automotive vehicles. The fan of the present invention is further characterized in that, means to flatten the blade is better provided by combining two or more types of blade different in thickness so that a cross section of the resultant complexed blade varies in successive steps to alternation of types of blade. The fan may beneficially and additionally be provided in practical use with a recess at the bottom of each blade as shown in FIGS. 1 and 2. If the leading portion 8 shown in FIG. 2 is combined with another imaginary trailing portion 6' indicated in dot and dash line in FIG. 2, a full section of a single type of blade is obtained in the absence of the proposal of the invention, while resulting another full cross section of another single type of blade from combining the trailing portion 6 with another imaginary leading portion 8' indicated by the broken line in the view.

In operation, when the fan rotates in the direction indicated by the arrow A in FIG. 1 and as the speed of rotation of the fan increases, the action of the centrifugal force and the pressure of the air on the flexible blades will cause the blades to flatten particularly against the foot portions to an increasing degree with an increase in speed. A centrifugal force on the center of gravity M of the trailing portion 6 is exerted as at CF. in FIG. 1, and let the arrow C.F. denote the amount of the force, and arrow P in FIG. 2 the pressure of the air on the trailing portion 6. The centrifugal force and the pressure together serve to reduce the inclination angle a as the rotational speed of the fan increases so that the blades are flattened as hereinbelow described in detail. The reduction of the angle a, namely flattening of the blades substantially reduces the air flow produced thereby and reduces the horsepower requirement. This reduction in air flow maintains the fan noise at a minimum. The centrifugal force CF. is divided into a horizontal component II.C. and vertical component V.C. as indicated in FIG. 1. The horizontal component BC. is further divided into peripheral component RC. and normal component N.C. as shown in FIG. 3. The normal component N.C. seves substantially to rotate or swing the blade 2 about the axis X of the leading portion 8. The torque about the axis X is derived from the foregoing as l X N.C., while 1 being an arm defined by the axis X and center of gravity M as will be seen in FIG. 3. The pressure P of the air shown in FIG. 2 may be divided into a surface component SC. and normal component N.C'. The normal component N.C'. also serves to swing the blade about the axis X.

The above two normal components NC. and N.C'. together serve in cooperation to swing the blade 2 or the trailing portion 6 about the axis X in the direction indicated by the arrow B in FIG. 2 when the fan is rotated in the direction indicated by the arrow A in FIG. 1 and as increases the rotational speed.

It has been found beneficial in decreasing the horsepower requirement as the rotational speed is increased ously presented fan. In FIG. 4, the higher reduction rate of the airflow of the present invention may be noted as compared with the previous fan as the speed of the fan increases.

In FIGS. 5(a) and 5(b), there are shown two other different embodiments in which two different type blades are combined together to form a complexed cross section of blade in a manner such that any one of the component blades is unsymmetrical relative to the axis of the other component blade.

It should be noted that the surface of the resultant blade must be smoothly continued from one type blade to the other type blade for maintaining the irregular eddy current of air at a minimum in operation.

What is claimed is: y

1. A screw type multiblade molded fan of plastic material comprising a central hub and a plurality of blades radially extending from said hub in an imaginary plane disposed normal to the axis of rotation of the fan, each blade being integral with said hub and curved forwardly away from said plane, each blade decreasing in thickness at the middle portion of said blade and then increasing in thickness rearwardly of said middle portion, at least one side of said blade being shaped to reduce said thickness at the middle portion, sections of the blade with different thicknesses being interconnected by smooth continuous surface contours, each blade having at the foot portion thereof a recess so that a trailing portion of each blade is separated from said hub to thereby decrease the horsepower requirement and the fan noise as the rotational speed of the fan increases.

2. A screw type multiblade molded fan of plastic material of claim 1 wherein said decrease of the thickness is on any one of said faces of said blade.

3. A screw type multiblade molded fan of plastic material comprising a central hub and a plurality of blades radially extending from said hub in an imaginary plane disposed normal to the axis of rotation of the fan, each blade being integral with said hub and curved forwardly away from said plane, each blade decreasing in thickness at the middle portion of said blade, at least one side of said blade being shaped to reduce said thickness at the middle portion, sections of the blade with different thicknesses being interconnected by smooth continuous surface contours, each blade having at the foot portion thereof a recess so that a trailing portion of each blade is separated from said hub to thereby decrease the horsepower requirement and the fan noise as the rotational speed of the fan increases, said decrease of the thickness of said blade being on both faces of the blade.