Fluid reaction surfaces (i.e. – impellers) – Rotor having flow confining or deflecting web – shroud or... – Axially extending shroud ring or casing
Reexamination Certificate
1998-12-30
2001-06-05
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Rotor having flow confining or deflecting web, shroud or...
Axially extending shroud ring or casing
C416S22300B, C416SDIG002, C416SDIG005
Reexamination Certificate
active
06241474
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an axial flow fan, and more specifically but not exclusively to such a fan for use as a generator of air flow through a heat exchanger.
DISCUSSION OF PRIOR ART
Axial flow fans are widely used to move air, especially in such applications as cooling systems, and in particular for cooling systems for motor vehicles.
In motor vehicle cooling applications, such fans are commonly powered by electric motors, although belt drive and other drive systems are also used. In identifying components which detract from low power consumption, it has been noted that state of the art fans tend to be wasteful of energy, thus necessitating relatively powerful drive motors. Waste of energy normally manifests itself as high noise, and in view of the many successful measures taken to reduce the general level of noise both within and outside of the vehicle, state of the art fans have been identified as a substantial source of noise. To provide adequate performance, state of the art fans may be over-dimensioned and thus heavier than required.
It is thus an object of the present invention to provide an axial flow fan which at least partly mitigates the problems of the prior art.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided an axial flow fan having a hub portion, a plurality of blades and a blade tip support portion, each blade extending from the hub portion to the blade tip support portion, wherein each blade has a pitch which decreases over a first inner part of the radial extent of the blade and increases over a second outer part of the radial extent of the blade.
Preferably each blade has a root portion and a tip portion, and said first inner part extends to between 40% and 60% of the blade extent, and the second part extends from said first part to the blade tip portion.
Advantageously said first part extends to substantially 50% of the blade extent.
Conveniently each blade has a leading edge, whereby a radial line passing through the root of said blade at said leading edge also passes through the tip of said blade at the leading edge.
Advantageously for each blade, the trailing edge at the blade tip and the median point of the blade root are situated on a common radial line.
Conveniently the fan has a root portion and a tip portion, said root portion having a root chord and said tip portion having a tip chord, wherein a median point of said tip chord is disposed angularly ahead with respect to the direction of rotation of a median point of said root chord.
Preferably each blade has a camber defined by the maximum deviation of a medial line through a blade cross-section from the corresponding chord, said camber being no more than 8% of the length of said corresponding chord.
Conveniently the ratio of maximum blade thickness to the chord length of each blade is less than or equal to 1:10.
According to a second aspect of the invention there is provided an axial flow fan having a hub portion, a plurality of blades, each blade having a root, a tip, a leading edge and a trailing edge, the root being secured to said hub portion, wherein for each blade, the trailing edge at the blade tip and the median point of the blade root are situated on a common radial line.
According to a third aspect of the invention there is provided an axial flow fan having a hub portion, a plurality of blades, each blade comprising a root portion having a root chord, a tip portion having a tip chord, a leading edge and a trailing edge, the root being secured to said hub portion, wherein a median point of said tip chord is disposed angularly ahead with respect to the direction of rotation of a median point of said root chord.
Advantageously the angle subtended at the centre of rotation by said tip chord median point and said root chord median is less than or equal to 360°/(4n+k), where n is the number of blades and k is a correction value which depends on the number of blades.
Advantageously the angle subtended at the centre of rotation by said tip chord median point and said root chord median is greater than or equal to 360°/(16n+k) where n is the number of blades and k is a correction value which depends on the number of blades.
Conveniently each blade has a camber defined by the maximum deviation of a medial line through a blade cross-section from the corresponding chord, said camber being no more than 8% of the length of said corresponding chord.
Advantageously the ratio of the maximum blade thickness to the chord length of each blade is less than or equal to 1:10.
According to a fourth aspect of the invention there is provided an axial flow fan having a hub portion and a plurality of blades, each blade comprising a root portion having a root chord and each blade having a leading edge extending from the root portion to a blade tip, wherein a median point of each blade root chord is disposed angularly behind with respect to the direction of rotation of said tip of the leading edge of the blade.
Advantageously the angle subtended at the centre of rotation of said fan by said median point and said tip of said leading edge is less than or equal to 360°/(2n+k) where n is the number of blades and k in a value which depends on the number of blades.
Advantageously the angle subtended at the centre of rotation of said fan by said median point and said blade tip is greater than or equal to 360°/(8n+k), where n is the number of blades and k is a value which depends on the number of blades.
Conveniently each blade has a camber defined by the maximum deviation of a medial line through a blade cross section from the corresponding chord, said camber being no more than 8% of the length of said corresponding chord.
According to a fifth aspect of the invention there is provided an axial flow fan having a plurality of blades, each blade having a camber defined by the maximum deviation of a medial line through a blade cross-section from the corresponding chord, said camber being no more than 8% of the length of said corresponding chord.
Preferably the ratio of the camber to the chord length of each blade increases along the radially inner half of the blade and decreases along the radially outer half of the blade.
According to a sixth aspect of the invention there is provided an axial flow fan having a plurality of blades wherein the ratio of the maximum blade thickness to the chord length of each blade is less than or equal to 1:10.
Preferably the ratio of the maximum blade thickness to the chord length of each blade substantially decreases along the substantially first half of the radial extent and substantially increases along the substantially second half of the radial extent.
REFERENCES:
patent: 4684324 (1987-08-01), Perosino
patent: 5273400 (1993-12-01), Amr
patent: 5326225 (1994-07-01), Gallivan et al.
patent: 5624234 (1997-04-01), Neely et al.
patent: 5769607 (1998-06-01), Neely et al.
patent: 5961289 (1999-10-01), Lohmann
patent: 177047 (1922-03-01), None
Alizadeh Ahmad
Belhabib Mustapha
Look Edward K.
McAleenan James M
Morgan & Finnegan , LLP
Valeo Thermique Moteur
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