Rotary kinetic fluid motors or pumps – Bearing – seal – or liner between runner portion and static part – Between blade edge and static part
Reexamination Certificate
2001-06-18
2003-07-22
Verdier, Christopher (Department: 3745)
Rotary kinetic fluid motors or pumps
Bearing, seal, or liner between runner portion and static part
Between blade edge and static part
C415S208100, C415S211100, C415S222000, C416S189000, C416S22300B, C416S228000, C416S238000, C416SDIG002, C416SDIG005, C123S041740
Reexamination Certificate
active
06595744
ABSTRACT:
BACKGROUND
The engine in an automotive vehicle is typically cooled by liquid coolant which is pumped through a liquid-to-air heat exchanger, or radiator. Due to the difference in density between coolant and air, the radiator is typically relatively narrow in width, but has a large face area through which the cooling air passes. Other vehicular heat exchangers, such as a condenser for the air-conditioning system, have similar configuration and are often cooled in series with the radiator.
The location of these heat exchangers is typically the front of the vehicle, behind openings in the vehicle body, so high pressure due to forward motion of the vehicle can cause air to move through them. However, in order to assure that sufficient air moves through the heat exchangers when the cooling requirements are severe, or when the vehicle is not moving, a fan assembly is fitted either upstream or downstream of the heat exchangers.
The fan assembly typically includes a fan and a shroud which surrounds the fan and guides air between the heat exchanger and the fan. The fan is typically driven by an electric motor supported by a bracket which is attached to, or integral with, the shroud. Due to under-hood space constraints, the shroud must in general be of minimum depth while at the same time covering a large area of heat exchanger surface. Because of this, much of the cooling air approaches the fan from essentially the (negative) radial direction, and must turn almost 90 degrees if it is to flow through the tip region of the fan.
If it fails to turn sufficiently, it will separate from the shroud surface, and compromise the efficiency and acoustic performance of the fan.
Another constraint on the fan design is that its noise be acceptable to the customer. Fan noise includes both broadband noise and tones, the latter being generated by the fan's interacting with a non-axisymmetric inflow. One way of minimizing these tones is to incorporate skew in the blade design. Skewed blades can, however, have structural problems which radial blades do not encounter.
There are many other constraints on the design of the fan assembly. One requirement is that the fan and shroud be inexpensive to manufacture. For this reason it is typically a plastic injection-molded part. Clearances between the fan and shroud must accommodate manufacturing tolerances as well as deflections of the parts in service. These deflections include long-term creep, and depend on time, temperature, and humidity. Fan deflections arise from centrifugal and aerodynamic forces and include components in both the radial and the axial directions. The fan assembly must be designed in such a way that the fan does not contact the shroud at any time, and yet have a sufficiently small clearance gap that leakage between the fan and the shroud does not overly compromise efficiency or noise. Two types of fans have been used for this application, differing in the nature of the clearance gap through which leakage occurs.
One type of fan is a free-tipped fan, where the clearance gap is between the shroud and the ends of the rotating blades. This type of fan typically has blades which are almost radial in configuration, with only a small amount of skew. Typically the blades have a constant-radius tip shape, so that only a radial deflection, which is minimized by their almost-radial configuration, can cause contact with the shroud.
FIG. 1
a
shows a typical free-tipped engine-cooling fan.
The second type of fan is a banded fan, the blade tips of which are attached to a rotating band. The clearance gap through which recirculation takes place is between the rotating band and the shroud. One advantage of this configuration is that the leakage flow can be minimized by use of various leakage control devices (U.S. Pat. No. 5,489,186). Another advantage is that the band can provide structural support for skewed blades (U.S. Pat. Nos. 4,569,631, 4,569,632), minimizing their deflection.
Both of these fan types have disadvantages.
The efficiency of free-tipped fans depends strongly on the tip gap. Air moves around the blade tip from the pressure side to the suction side, thereby reducing the pressure difference across the blade in the tip region and generating a concentrated tip vortex. This vortex is a loss mechanism, and can be a source of noise. A configuration such as that shown in
FIG. 1
b
minimizes the tip gap, but at the expense of flow separation due to the small inlet radius on the shroud barrel.
FIG. 1
c
shows a more typical free-tip fan assembly, where separation is minimized by allowing the forward portion of the blade tip to extend into the fan plenum and employing a more generous inlet radius. This configuration, however, has higher tip leakage losses, since small tip gaps are maintained only at the rearward portion of the blade tips. Free-tipped fans tend to be noisier than banded fans, particularly at more resistive operating points. Stall tends to be more extreme and more sudden for these fans.
Although banded fans have reduced tip clearance losses relative to free-tipped fans, they have the additional viscous losses of the rotating band. These losses are particularly severe at lightly-loaded operating points, where the fan speed is relatively high for the pressure and flow developed. Such operating points are common in automotive applications, since they allow the use of inexpensive low-torque motors. Another source of parasitic loss for a banded fan is flow separation at the band. Due to molding requirements, the inner surface of the band must be essentially cylindrical over the axial extent of the blades, as shown in
FIG. 1
d.
A lip is usually added to the front of the band, but it is of necessity of limited extent, due to the tight space requirements. Flow separation is often the result. The rotating band also leads to some noise and vibration problems. Any axial run-out of the band causes a large couple imbalance which can lead to vibration problems in the vehicle. Also, the large moment of inertia of a banded fan prolongs the time during which the fan coasts down when the fan is de-powered. The coast-down process can lead to objectionable noise in the vehicle. In addition to these performance issues, banded fans can be more expensive to manufacture than free-tipped fans. The mass of the band at a large radius makes a banded fan more likely to require a separate balancing operation than a free-tipped fan. A banded fan requires the use of more material than would be required for a free-tipped fan, and the presence of knit lines in the band requires the use of more expensive material than might otherwise be used.
OBJECTS OF THE INVENTION
One object of the invention is to maximize the efficiency of an automotive engine-cooling fan assembly by minimizing leakage between the fan and the shroud.
Another object is to maximize the efficiency of the fan assembly by minimizing flow separation.
Another object is to minimize the noise generated by the fan.
Another object of the invention is to provide a low-cost assembly by minimizing the amount and cost of the plastic material used in its manufacture.
Another object is to minimize the static and couple imbalance of the fan, and thereby reduce the cost of balancing the fan and the amount of vibration in the vehicle.
Another object is to minimize the moment of inertial of the fan in order to shorten the coast-down process when the fan is de-powered.
SUMMARY
The present invention is an un-banded automotive engine-cooling fan and shroud assembly. The shroud has a barrel with a flared inlet and at least a portion of each blade tip conforms to the shape of this inlet. The radius of the blade tip is larger at the upstream end of the conforming portion than at the downstream end of this portion.
In a preferred embodiment, the entire blade tip conforms to the shape of the shroud inlet. Also in a preferred embodiment, the clearance gap between the blade tip and the shroud is approximately constant. Because the tip gap is maintained at its minimum value over substantially the entire blade tip, tip c
Fish & Richardson P.C.
Robert Bosch Corporation
Verdier Christopher
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