This invention concerns axial fluid flow inducing devices such as fans, which use a set of rotating blades reacting with the fluid to cause axial fluid flow.
In the above-referenced copending application there is described a unique direct magnetic drive in which impeller blades are permanently magnetized to establish a magnetic pole at each blade tip, which interacts with pulsed magnetic fields set up by one or more electromagnets located around the perimeter of the impeller or rotor in such a way that magnetic repulsion and attraction forces acting on the blades cause the impeller to rotate.
In the past, in order to increase the static pressure generated by an axial flow impeller, it has been the practice to provide fixed stator blades providing fluid reaction surfaces increasing the static pressure generated downstream of the impeller. The presence of the stator blades creates flow resistance, reducing flow. To avoid this disadvantage, it is known that counter-rotating impellers increase the static pressure without increasing flow losses in the system. However, complex mechanical drives are necessary in order to drive two or more closely positioned coaxial impellers in opposite directions.
It is one object of the present invention to provide a drive for multi counter rotating impellers not requiring a complex mechanical drive means.
Another known flow device has multiple impellers connected together and rotating in the same direction in order to provide a multiple stage pumping action. However, in order to enable proper multistage operation of synchronously rotating impellers, reduced blade areas must be established that increased the cost. In this application blade area remains the same while rotation speed is changed.
It is thus another object of the present invention to provide a multistage impeller in which the material and labor costs are reduced.
The above objects as well as others that will become apparent upon reading of the following specification and claims are achieved by an arrangement of a plurality of impellers that are coaxially mounted in a shroud and independently rotated with respect to each other. In a first application of the invention, the impellers are driven by forces created by intermittently generated magnetic fields acting on magnetized portions of each of the impellers so as to rotate the impellers. By causing rotation of two impellers in opposite directions a much-simplified means is provided for obtaining increased static pressure of the fluid flow induced by rotation of the impeller blades. Preferably, the magnetic field is generated by a pulsed generating means including one or more driver coils each having an U-shaped core with opposite core legs extending generally radially and with their ends located adjacent the outer perimeter of the associated impeller.
Preferably, a pair of electromagnetic driver coils is provided which are arranged at an angle to each other and spaced apart so that when one pair of core legs straddles one blade, the other pair has sequential blades aligned with each leg. A pair of sensors, such as Hall effect sensors, are arranged to detect the passage of the leading edge of each successive impeller blade and to control the energization and magnetic polarity of the driver coils such as to induce rotation in opposite directions of each impeller by magnetic interaction between the field of the respective coils and the magnetic field of the permanently magnetized portions of the impeller blades.
For the embodiment of the invention having two counter rotating impellers, each electromagnetic coil is preferably skewed such that respective legs of the coil core are located at the outer perimeter of a respective impeller so that both impellers are energized and driven by the same pair of electromagnetic coils making synchronization of the rotation of the two impellers much simpler. However, using more than one pair of electromagnetic coils is also possible, each disposed around the perimeter of a respective impeller.
Driving the impellers by a single driver coil is also possible. In this case, a simple electromagnet may be utilized in order to locate each impeller in a proper start up position with respect to the driving electromagnetic coil in which the spaced core legs straddle a blade tip.
The impellers preferably have blades of a type of plastic material that is permanently magnetizable and the magnetized tips comprise the outer portions of the impeller blades that are magnetized to interact with the pulsed magnetic fields.
The impellers may be constructed in two sections, each having an alternate set of impeller blades with the tips magnetized with the same polarity, and each impeller section having its tips magnetized with opposite poles to the other section. The impeller sections are interfit at assembly to produce an impeller in which successive blades are magnetized with opposite polarities.
Alternatively, instead of a stationary shroud, the fluid flow passage can be formed by an outer ring that concludes, which is formed by a series of arcuate segments attached to the tip of each rotor blade, each segment interfit to the next adjacent segment on either side. Again, a two-section impeller construction may be advantageously employed.
An intermediate ring fixed to one impeller may also be employed with a labyrinth seal formed between the ring and adjacent end of the corresponding impeller.
The impeller ring segments adjacent the housing end wall may be provided with projecting portions that are received within the housing to form a labyrinth seal, such that while each ring rotates independently of the other, a sealed confinement of the fluid flow is assured.
In another version, the outer ring can be attached to the tips of blades and magnetized by segments with opposite polarities.
The impellers may also have magnetized outer portions which are driven by pairs of driver coils in such a manner as to be driven in the same direction at controllably different rates of rotation such as to produce a multistage pumping action which does not require differing impeller blade areas. A set of stator blades is required to be placed between impellers.
In another version, connected impellers can be disposed on either side of a set of stator blades.