The present invention relates to electric solenoids as used in mechanical linear actuators; more particularly, to such solenoids intended for continuous, controlled linear travel between two extremes; and most particularly, to such solenoids as may be required to operate without regard to orientation.
Electric solenoids are well known in electrical engineering and are widely used as actuating components in electromechanical actuators. A typical electric solenoid consists of a plurality of windings of an electric conductor about north and south polepieces. When current is passed through the windings, a characteristic toroidal magnetic field is produced having field lines at the axis which are parallel to the axis. A ferromagnetic armature is slidably disposed in an axial bore in the polepieces. An axial force is exerted by the magnetic field on the armature which tends to displace the armature axially. The strength of such force can be varied by varying the current flowing through the windings. Thus, by attaching the armature to a shaft, a solenoid may be adapted readily to provide linear mechanical actuation of a device to which it is attached. Solenoids are probably the commonest type of such actuators in use today.
The maximum force which may be exerted on the armature is in part a function of the axial size and stability of the cylindrical air gap between the armature and the polepieces. Ideally, the thickness of the air gap is zero, but conversely, the armature must not touch the polepieces. Further, the armature is not spontaneously centered in the bore, and non-axial magnetic vectors within the bore destabilize centering of the armature, resulting in unpredictable variances in the size and shape of the air gap and in the corresponding response of the armature.
It is known in the art to provide a lubricious, non-magnetic, cylindrical sleeve in the air gap to keep the armature centered in the polepieces and to function as a journal bearing to facilitate low-friction motion of the armature. Such a sleeve can reduce the centering problem but in itself still contributes to the thickness of the non-magnetic gap between the armature and the polepieces, thus limiting the maximum actuating force of the solenoid.
Further, because of necessary tolerances between the sleeve and the armature and between the sleeve and the polepieces, the armature may still be unacceptably decentered by gravity if the actuator is used in orientations wherein the actuator axis is inclined more than about 30° from vertical. Thus, prior art solenoid actuators can impose serious engineering design restrictions in their use.
What is needed is an improved solenoid which may be used in any orientation without loss in effectiveness, wherein the thickness of the gap between the armature and the polepieces is minimized and controlled to be substantially cylindrical without resort to a guiding sleeve therein.
The present invention is directed to an improved solenoid for providing linear actuation. The outer polepiece of the solenoid is provided with an axial, self-lubricated, non-magnetic journal bearing for supporting an actuating shaft extending coaxially from the solenoid armature. Preferably, the radial tolerance between the diameters of the bearing inner bore and the shaft is as small as in practically possible without inducing significant drag of the shaft in the bearing. This permits reduction of the air gap between the armature and the polepieces to a minimal thickness. Preferably, the armature is axially tapered slightly to avoid contact with the polepieces as a result of residual tolerances between the bearing and shaft. A significant increase in actuating force is realized in comparison with a prior art solenoid actuator.
The foregoing and other objects, features, and advantages of the invention, as well as presently preferred embodiments thereof, will become more apparent from a reading of the following description in connection with the accompanying drawings, in which:
The benefits afforded by the present invention will become more readily apparent by first considering a prior art solenoid actuator. Referring to
Referring to
Preferably, the axial length of bearing 40 is at least 1.5 times the diameter of shaft 22′ to minimize wobble of the shaft in the bearing and resulting cocking of the armature in the polepieces. To accommodate the small tolerances necessary between the shaft and bearing, preferably the armature is tapered slightly to be frusto-conical having a cone angle substantially equal and opposite to the cone angle describable by the excursion limit of the shaft in the bearing, to provide the absolute minimum thickness of air gap while positively precluding the armature from striking the polepieces. Thus, air gap 36 is slightly thinner at the lower end 42 of armature 20′ and slightly thicker at the upper end 44. Because the air gap is substantially fixed in size and shape and the armature cannot strike the polepieces, solenoid actuators in accordance with the invention may be used freely without regard to spatial orientation. This feature can be extremely useful, for example, in fitting an EGR valve into the engine compartment of a vehicle.
Referring to
Referring to
The foregoing description of the preferred embodiment of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above teachings. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, the foregoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the following claims.
Number | Name | Date | Kind |
---|---|---|---|
3921111 | Kowalski | Nov 1975 | A |
4153890 | Coors | May 1979 | A |
4527590 | Kolze | Jul 1985 | A |
4729252 | Huber et al. | Mar 1988 | A |
4855702 | Swanson | Aug 1989 | A |
4873959 | Law et al. | Oct 1989 | A |
5144272 | Nishimura | Sep 1992 | A |
5362209 | Day | Nov 1994 | A |
5460146 | Frankenberg | Oct 1995 | A |
5699995 | Robertson, III | Dec 1997 | A |
5779220 | Nehl et al. | Jul 1998 | A |
5782267 | Yoo | Jul 1998 | A |
5804962 | Kather et al. | Sep 1998 | A |
5947092 | Hussey et al. | Sep 1999 | A |
5984261 | Akita | Nov 1999 | A |
6053472 | DeLand | Apr 2000 | A |
6230673 | Sugimoto et al. | May 2001 | B1 |
6260522 | Stolk et al. | Jul 2001 | B1 |
6313726 | Golovatai-Schmidt et al. | Nov 2001 | B1 |
6315268 | Cornea et al. | Nov 2001 | B1 |
Number | Date | Country |
---|---|---|
2433775 | May 1975 | DE |
9107436.3 | Feb 1991 | DE |
2184604 | Jun 1987 | GB |
Number | Date | Country | |
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20020104977 A1 | Aug 2002 | US |