Rotary kinetic fluid motors or pumps – Plural runners supported for relative motion or on separate... – With means for selective runner operation or drive shaft...
Reexamination Certificate
2003-03-17
2004-11-16
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Plural runners supported for relative motion or on separate...
With means for selective runner operation or drive shaft...
C416S120000, C416S19800R
Reexamination Certificate
active
06817831
ABSTRACT:
BACKGROUND
A typical automotive engine-cooling fan assembly consists of one or more fans, each powered by an electric motor, and housed in a shroud which guides air through one or more heat exchangers. Each motor is typically supported by arms, or stators, which are supported by the shroud. Such a fan assembly can be placed upstream or downstream of the heat exchangers, which typically include both a radiator which cools the engine and an air conditioning condenser.
A fan assembly is required to efficiently provide the required amount of engine cooling while satisfying various noise criteria. These noise criteria usually concern both broadband noise and tones. At a given fan power, broadband noise is often found to be minimized by maximizing fan diameter, although fan noise, and particularly the tonal content of fan noise, increases if the fan overlaps an edge of the heat exchanger.
Fan efficiency is also often improved by maximizing fan diameter. One reason for this is that power expended in accelerating air through the fan is generally not recovered. This power is minimized by maximizing the fan area. Another reason is that a larger fan area provides better coverage of the heat exchangers. Due to the typically shallow depth of the fan assembly, the velocity of air through the heat exchanger cores outside the fan projected area is generally less than that inside the fan projected area. This flow non-uniformity increases the mean pressure drop, and decreases the effectiveness of the heat exchangers.
When the heat exchanger core area is approximately square, flow non-uniformity can be made reasonably small by using a single fan, the diameter of which is approximately equal to the length of a side of the square. When one dimension (typically the width) of the core is larger than the other dimension (typically the height), noise considerations generally limit the fan diameter to the smaller dimension. As a result, flow non-uniformity for a non-square core is generally larger than in the case of a square core, unless the aspect ratio of the core (the ratio of the longest side to the shortest side) is large enough to make practical the fitting of two fans side by side. Although the ideal core aspect ratio for a dual-fan assembly is two, such an assembly can offer a significant advantage in flow non-uniformity at smaller aspect ratios.
A measure of the extent to which a given fan arrangement provides good coverage of a heat exchanger core is the area ratio A
f
/A
c
. This is the ratio of the total fan disk area A
f
to the area of the heat exchanger core A
c
. For a single fan on a square core, the largest area ratio achievable without overlapping the edge of the core is □/4, or 0.79. This is also the largest value achievable with a side-by-side dual-fan arrangement on a core of aspect ratio 2.
In practice, many automotive heat exchangers have an aspect ratio approximately midway between one, corresponding to a square and ideal for a single fan, and two, ideal for a dual fan. This presents a problem for the fan designer in that neither a single-fan configuration nor a conventional dual-fan arrangement has a favorable flow distribution through the cores. An aspect ratio of approximately 1.35 represents perhaps the worst case, where the ratio of fan area to core area is equally small for single-fan and dual-fan assemblies. Schematics of these two arrangements are shown in
FIGS. 1
a
and
1
b
. For both single-fan and dual-fan assemblies, the area ratio is approximately 0.58. In fact, a 3-fan assembly, as shown in
FIG. 1
c
, also has an area ratio of 0.58. Because the total fan area of the configurations shown in
FIGS. 1
a
,
1
b
, and
1
c
are approximately equal, the efficiency and noise of these configurations will be approximately equal, as well.
In addition to the problem of maximizing fan area, another problem sometimes faced is maximizing fan power. This sometimes favors the use of multiple fans. In particular, in those cases where the largest motor available is too small to deliver the required cooling in a single-fan system, a multiple-fan assembly can be required, even at the expense of optimum system efficiency. This situation can be encountered when designing electric cooling systems to replace engine-driven fans for the cooling of light trucks. It also is likely to be encountered in the cooling of the new generation of fuel cell vehicles.
SUMMARY OF THE INVENTION
The present invention is an automotive engine-cooling fan assembly using two or more fans, where at least two fans overlap each other when viewed from the upstream or downstream direction. The set of arms which supports the motor driving one fan of an overlapping pair of fans is upstream of that fan, and the set of arms which supports the motor driving the other fan of the pair is downstream of that other fan. Overlap of a pair of fans can be demonstrated by projecting those fans onto a plane perpendicular to the axis of one or both of the fans. A first circular disk centered on the projection of the axis of one fan (the diameter of the first disk being equal to the diameter of that fan) overlaps a second circular disk centered on the projection of the axis of the other fan (the diameter of the second disk being equal to the diameter of that other fan).
In a preferred embodiment, the axial position of the set of arms which supports the motor driving each fan of an overlapping pair is substantially the same as the axial position of the other fan of that pair. The set of support arms for each fan of the pair excludes any members which would interfere with the placement of the other fan of the pair at the same axial location as that set of arms. This allows the module to be quite compact in the axial direction.
Preferably, a small clearance gap is maintained between said shroud and each of the fans along the portion of the fan's circumference outside the overlap region. Preferably, a projection of the shroud opening, in a plane perpendicular to one or both of the fan axes is two generally circular elements that overlap in the region of fan overlap.
In a preferred embodiment, the two motors are approximately the same distance from the heat exchanger core. In this embodiment the distance between the core and the farthest point on one of the motors is between 0.8 and 1.25 times the distance between the core and the farthest point on the other motor. The length of the motors is often a limiting factor in making a fan assembly which is axially compact.
When a fan assembly according to a most preferred embodiment is viewed axially from upstream or downstream, the projected area of the set of arms supporting the motor driving one fan of the overlapping pair falls outside the projected disk area of the other fan of the pair.
In one embodiment the fan assembly is a dual-fan assembly. This arrangement provides good flow uniformity through a heat exchanger core in those cases where single-fan assemblies or conventional side-by-side dual-fan assemblies cannot, namely in those cases where the shroud covers a rectangular area of the heat exchanger core, and where the aspect ratio of that rectangular area is approximately midway between 1 and 2. In a preferred embodiment the assembly is a dual-fan system and is sized to move air through a core area with an aspect ratio of approximately 1.25 to 1.8. In a most preferred embodiment the assembly is a dual-fan system and the fan diameters are equal, or, if unequal, the fan diameter of the smaller fan is greater than 85 percent of the diameter of the larger fan, and the diameter of the larger fan is greater than 75 percent of the smaller dimension of the core area.
In other embodiments the fan assembly comprises more than two fans.
In preferred embodiments the extent of overlap, when measured in a plane which contains the rotation axis of at least one fan of an overlapping pair of fans and at least one point on the axis of the other fan, is greater than 10 percent of the diameter of the smaller of the two fans, and less than the blade span of the smaller fan. The diamete
Coté F. Raymond
Stevens William M.
Fish & Richardson P.C.
Look Edward K.
McAleenan James M.
Robert Bosch Corporation
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