Patent Application
20050089414
The present invention relates to a rotor and a positive displacement compressor, and more particularly to a compressor which includes two rotors.
Positive displacement compressors including helical screw compressors as well as roots compressors are well known in the art. A helical compressor employs one male rotor axially aligned with and in combination with one female rotor. Usually the male rotor is the drive rotor driving the female rotor. In a compressor, one male rotor is commonly combined with one female rotor. Such a compressor is usually referred to as a twin helical screw rotor compressor.
An example of a known twin helical screw rotor compressor or screw compressor is shown in
A compressor 100 includes two mutually engaging screw rotors, of which a first rotor 101 is a male rotor and a second rotor 102 is a female rotor. The rotors 101, 102 are rotatably mounted in a working chamber that is delimited by a first end wall 103, a second end wall 104 and a barrel wall 105 that extends between the end walls 103, 104. As can be seen from
The male rotor 101 has a rotor body 22 that includes a plurality of lobes 106 and intermediate grooves 111 which extend in a helical line along the rotor 22. Similarly, the female rotor 102 has a rotor body 23 that includes a plurality of lobes 107 and intermediate grooves 112 that extend in a helical line along the rotor 23. The major part of each lobe 107 on the male rotor 101 is located outwardly of the circle of contact with the female rotor 102, whereas the major part of each lobe 107 on the female rotor 102 is located inwardly of said circle of contact. The female rotor 102 will normally have more lobes than the male rotor 101. A typical combination is one in which the male rotor 101 has four lobes and the female rotor 102 six lobes, as shown in
The gas to be compressed, normally air, is delivered to the working space of the compressor through an inlet port 108 and is then compressed in V-shaped working chambers defined between the rotors and the chamber walls. Each chamber moves to the right in
The male rotor 101 in
Such a compressor is coupled to an electrical motor or combustion engine in order to rotate the male rotor 101 and is for example used to enhance the performance of an engine in a vehicle such as an automobile or to enhance the performance of a fuel cell due a higher inlet pressure of air or oxygen. As a consequence thereof, the engine or fuel cell can be produced having a lower volume and mass. Also, there is a need for reducing the volume and weight of such a compressor for supercharging the engine or fuel cell.
It is an object of the invention to provide a small compressor.
According to the present invention, a new rotor for a positive displacement compressor is provided which includes a non-rotating rotor shaft; a rotatable rotor body having end surfaces and surrounding the rotor shaft; and means for rotating the rotor body around the non-rotating rotor shaft.
In a preferred arrangement, the means for rotating the rotor body around the non-rotating rotor shaft comprises rotor magnets on the rotor body, wherein the magnets are arranged in a circle centered on an axis of the rotor body and facing the shaft; and an electrical stator provided on the shaft in registration with the rotor magnets. When the stator is electrically energized, the rotor body is caused to rotate about the non-rotating rotor shaft.
In
The male rotor 1 comprises a rotor body 3 having the shape of a cylindrical shell. The outer surface of the rotor body 3 has helically extending lobes 6 separated by intermediate grooves 7. As is apparent from
Two bearings 8, 9 are disposed in a spaced relationship between the shaft 2 and the inner surface 10 of the male rotor body 3. Between the bearings 8, 9 on the inner surface 10 of the male rotor body 3, permanent magnets 11 in the form of rods or bars are placed in parallel such that they form a cylindrical shell ring. The magnets 11 are secured to the rotor body 3. The magnets 11 may be arranged in an insert to be placed inside the rotor body 3 and fixed (i.e., bonded) to the inner surface 10 of the rotor body 3 or may be bonded separately to this surface 10 as is known in the art.
The male rotor shaft 2 is provided with an axially extending blind bore 13 opening in one of the planar ends thereof. Further, a bore 13A in the cylindrical surface of the shaft 2 is connected to (in communication with) the axial bore 13.
Electrical windings 12 are wound on the shaft 2 of the rotor 1 between the bearings 8, 9 in registration with the cylindrical shell of magnets 11. These windings 12 function as stator leads. End parts 14 of the windings 12 are passed through the bore 13A from the cylindrical surface of the shaft 2 and through the axial bore 13 to the outside of the shaft 2 and are connected to an electrical power source 80. The stator leads 13 when energized will cooperate with the ring shaped shell of permanent magnets 11 in the same way as in an electrical motor. In this case, contrary to a conventional electrical motor, the outer part will rotate while the central part acts as a stator.
Similarly, as also shown in
Two bearings 28, 29 are disposed in a spaced relationship between the female rotor shaft 22 and the inner surface 30 of the female rotor body 23. Between the bearings 28, 29 on the inner surface 30 of the female rotor body 23 permanent magnets 31 in the form of rods or bars are placed in parallel such that they form a cylindrical shell ring. The magnets 31 are secured to the female rotor body 23. The magnets 31 may be arranged in an insert to be placed inside the female rotor body 23 and be fixed (i.e., bonded) to the inner surface 30 of the female rotor body 23 or may be bonded separately to this surface 30 as is known in the art.
The female rotor shaft 22 is provided with an axially extending blind bore 33 opening in one of the planar ends thereof. Further, a bore 33A in the cylindrical surface of the shaft 22 connects to (communicates with) the axial bore 33.
Electrical windings 32 are wound on the shaft 22 of the female rotor 21 between the bearings 28, 29 in registration with the cylindrical shell of magnets 31. The windings 32 function as stator leads. End parts 34 of the windings 32 are passed through the bore 33A from the cylindrical surface of the female rotor shaft 22 and through the axial bore 33 to the outside of the female rotor shaft 22 and are connected to an electrical power source 80. The stator leads 33 when energized will cooperate with the ring shaped shell of permanent magnets 31 in the same way as in an electrical motor. In this case, contrary to a conventional electrical motor, the outer part will rotate while the central part acts as a stator.
Reverting to
As seen from the foregoing, according to the present invention, a rotor for a positive displacement compressor comprises a non-rotating shaft around which a rotatable rotor body is mounted. The rotatable rotor body has a central bore in which the shaft is inserted. The rotor body has a shape which essentially corresponds to an elongated shell having planar parallel end walls. An outer surface of the rotor body comprises lobes and intermediate grooves helically extending between the end walls. There are typically at least 2 but less than 10 lobes and intermediate grooves. The lobes and grooves extend helically from the outer surface of the rotor body. The helical twist is preferably in a range of 5-90° for a roots compressor and 150-330° for a helical screw compressor. End parts of the rotor shaft extend beyond the rotor body and serve as trunnions. Two bearings are arranged in a space between the rotor shaft and the rotor body in a spaced relationship. The bearings allow the rotor body to be rotated relative to the shaft.
Further, on an inner part of the rotor body facing the shaft, magnets are arranged in a circle around the shaft. Metal wires are wound on the shaft as electrical windings which are arranged such that, when fed with electrical power, the windings cooperate with the magnets in the rotor body. This cooperation results in rotation of the rotor body around the rotor shaft.
The positive displacement compressor according to the invention thus comprises a housing including a first and a second end wall, a barrel wall having an inner shape substantially corresponding to two intersecting cylinders between the end walls, an inlet port and an outlet port for fluid. Two cooperating rotors are mounted in parallel in the two intersecting cylinders. One of the rotors is a male rotor and the other one is a female rotor. The two end portions of the non-rotating shafts of the respective rotors are mounted in the end walls of the rotor housing.
Each of the rotors comprises a rotor body which has a central bore and is arranged rotatably around the non-rotating shaft, and bearings mounted on the shaft. The bearings are arranged in a spaced relationship near each end of the respective rotor body. Each rotor body is provided with magnets, preferably permanent magnets, arranged in a circle and facing the shaft. On the periphery of the shaft there are windings for cooperation with the magnets on the rotor body. Both the windings and the magnets are arranged between the bearings. The windings have leads which are connectable to a power source. When the windings are energized, the respective rotors are caused to rotate, like a motor.
Each rotor body is provided with lobes and intermediate grooves on the outer surface. The lobes and grooves are preferably arranged as a helix. The male rotor body has usually two or more lobes. The number of lobes of the female rotor body is usually but not necessarily greater than the number of lobes of the male rotor body. Such a difference in the number of lobes requires that the two rotors rotate with different revolution units of time.
Additional advantages and modifications will occur to those readily skilled in the art. For example, although according to the present invention each of the rotors 1, 21 is driven by its own source of energy, in known compressors a motor drives one rotor while the other rotor is driven indirectly by the driven rotor or by means of synchronizing gears. Additionally, the bearings in the present compressor may be conventional bearings, such as roller bearings, or radial induction bearings. Preferably, at least one of the bearings 8, 9 and 28, 29, respectively, is a radial induction bearing. Various additional modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
