Pumps – Condition responsive control of pump drive motor – By stopping pump in response to leakage into or from system
Utility Patent
1999-08-11
2001-01-02
Thorpe, Timothy S. (Department: 3746)
Pumps
Condition responsive control of pump drive motor
By stopping pump in response to leakage into or from system
C417S274000, C418S002000, C418S083000
Utility Patent
active
06168385
ABSTRACT:
The present invention relates to a rotary device.
FIELD OF THE INVENTION
In WO-A-91/06747, there is disclosed a rotary device having interacting rotors which have a helical form in their axial direction.
BACKGROUND OF THE INVENTION
In an internal combustion engine using such a rotary device, there are separate rotary compression and expansion sections.
In a fluid compressor using such a rotary device, the rotor pairs serve to compress and deliver compressible fluids into receivers in which the receiver pressure is substantially greater than that of the fluid source. Power is supplied by an external prime mover in order to drive the rotor pair and thus to compress the fluid, raising its pressure from that of the supply source to that of the receiver.
The rotary device of this prior art provides for compression and expansion of gases by means of the interaction between a first recessed rotor and a second lobed rotor. The number of lobes and recesses on the rotors determines the required speed ratio between the rotors. Counter-rotation of the rotors is effected at the required speed ratio by meshing gear wheels which are integral with the rotor shafts and which maintain a fixed angular relationship between the rotors.
The interaction of the rotors takes place between a pair of close-fitting side walls. One of the side walls contains a port for delivery of the fluid charge either to or from the rotors depending on whether they are effecting compression or expansion of the charge. Provision is made for mechanical or liquid seals between rotor/rotor and rotor/stator elements to reduce or virtually eliminate gas leakage during the operation of these machines. However, it is difficult to ensure that such seals remain in position and are capable of effective operation over a useful life because of the nature of the interaction between the rotors. There are, in any event, considerable disadvantages in the use of such seals due to the mechanical friction to which they give rise. On the other hand, there are substantial gains of efficiency when the leakage is contained to very low levels in the absence of seals, by providing for extremely small clearances between rotor/rotor and rotor/stator interfaces. The restricted gas leakage across the small clearances takes place in response to the pressure differential across the leak path only during the very brief periods of the cycle when such pressure differentials exist.
Intermeshing rotor components can be manufactured to within sufficiently restricted design tolerances such that leakage rates are within acceptable limits, provided that the clearances can be maintained during operation of the machine. However, components are subject to change of size and shape during operation due to the effects of heat and pressure. Clearances which are apparent when the machine is at rest and all components are uniformly at ambient temperature may change significantly during normal operation due to temperature differentials within and between components. These differentials are caused by local concentration of heat and the extent to which heated and cooled surfaces are separated, which give rise to the formation of temperature gradients.
If temperature changes and associated temperature gradients in one component are matched by equivalent changes of temperature and gradient occurring simultaneously in all components and all components have similar coefficients of thermal expansion, then no significant changes in clearance between the rotors will occur. However, in practice, it is most likely that differentials in temperature between components will occur, at least temporarily, thus causing changes in the clearance between the rotors. If the clearances are enlarged as a result, then the level of leakage may become unacceptably high. Conversely, if the clearances become too small, there is danger that the rotors may contact each other, which could result in structural failure.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a rotary device, the device comprising: a first rotor rotatable about a first axis; a second rotor counter-rotatable to said first rotor about a second axis; the first and second rotors being coupled for rotation and being intermeshed such that, for a portion of the rotation of the rotors, there is defined between the first and second rotors a transient chamber of volume which progressively decreases on rotation of the rotors; and, monitoring means for monitoring the clearance between the rotors.
Thus, the present invention allows the clearance between the rotors to be monitored. In a preferred embodiment, as described below, the clearance can then be controlled so that the clearance is maintained within preset limits.
In a preferred embodiment, the monitoring means comprises capacitance monitoring means for monitoring the variation in capacitance between the rotors as the rotors rotate and as the clearance between the rotors varies.
Whilst monitoring the capacitance is the preferred manner of monitoring the clearance, other physical properties, and especially other electrical properties such as inductance, may alternatively be monitored to provide a measure of the clearance.
Means are preferably provided for adjusting the distance between the rotors if the clearance between the rotors falls outside a pre-set limit.
The rotors may be supportedly mounted in walls of a housing in which the rotors are contained, and the adjusting means may comprise heating means and cooling means for selectively heating and cooling at least a portion of the housing walls between said rotors to cause said portion to expand or contract thereby to adjust the distance between the rotors. The heating means may comprise an electrical heating element. The cooling means may comprise a passage in at least one of said walls for carrying a cooling fluid.
The rotors may be contained in a housing having walls which support the rotors, the rotors being supported by bearings which are mounted in the housing walls, the bearings being translatable to adjust the distance between the rotors.
The bearings can conveniently be eccentrically rotatably mounted in the housing walls, the bearings being eccentrically rotatable thereby to adjust the distance between the rotors.
It will be understood that both the heating and cooling means and the translatable bearings may be provided in the rotary device. Adjustment of the distance between the rotors can be achieved by operation of the heating and/or cooling means or by means of the translatable bearings or by using both systems.
According to a second aspect of the present invention, there is provided a rotary device, the device comprising: a first rotor rotatable about a first axis; a second rotor counter-rotatable to said first rotor about a second axis; the first and second rotors being coupled for rotation and being intermeshed such that, for a portion of the rotation of the rotors, there is defined between the first and second rotors a transient chamber of volume which progressively decreases on rotation of the rotors; and, adjusting means for adjusting the distance between the rotors.
Thus, the clearance between the rotors of this aspect can be adjusted to an optimum value or to be within certain preset limits for example.
The rotors may be supportedly mounted in walls of a housing in which the rotors are contained, and the adjusting means may comprise heating means and cooling means for selectively heating and cooling at least a portion of the housing walls between said rotors to cause said portion to expand or contract thereby to adjust the distance between the rotors.
The heating means may comprise an electrical heating element.
The cooling means may comprise a passage in at least one of said walls for carrying a cooling fluid.
The rotors may be contained in a housing having walls which support the rotors, the rotors being supported by bearings which are mounted in the housing walls, the bearings being translatable to adjust the distance between the rotors.
The bearings may be e
Pillsbury Madison & Sutro LLP
Rotary Power Couple Engines Limited
Thorpe Timothy S.
Tyler Cheryl J.
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