Rotary expansible chamber devices – Interengaging rotating members – Helical or herringbone
Reexamination Certificate
2000-07-25
2001-08-21
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Interengaging rotating members
Helical or herringbone
Reexamination Certificate
active
06276911
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a screw compressor comprising a housing with a rotor chamber, two screw rotors arranged in the rotor chamber, the screw rotors being mounted in the housing for rotation about their respective axes of rotation and being intermeshingly drivable in order to convey a medium to be compressed from a suction gas inlet of the housing to a pressure gas outlet of the housing and thereby compress the medium to be compressed, a slide movable in the direction of the rotor axes and adjoining the rotor chamber for controlling the capacity via the effective length of the screw rotors, an adjusting device comprising a cylinder to which pressure is applied by a medium and which is formed by a cylinder chamber and a piston coupled with the slide, and a control device associated with the cylinder for controlling in an continuous control mode an inflow and a return flow of the medium provided for actuating the piston.
Such screw compressors are known from the prior art. Herein, in an continuous control mode for controlling the adjusting device a supply line is provided for the pressure cylinder, via which the piston is movable into all conceivable positions either by inflow of the medium actuating the piston or by return flow of the medium actuating the piston.
In order that the control device of such a screw compressor will operate reliably, it is, however, necessary to be able to recognize the position of the piston of the control device so as to be able to reliably operate the screw compressor in the mixed control ranges.
For this reason, in a screw compressor known from the prior art a position recognition is required for the piston and/or the slide, which involves expenditure.
SUMMARY OF THE INVENTION
The object underlying the invention is, therefore, to so improve a screw compressor of the generic kind that the control device will operate reliably with a design which is structurally as simple as possible.
This object is accomplished in a screw compressor of the kind described at the outset, in accordance with the invention, in that the cylinder chamber comprises a return flow opening defining a minimum position, the piston being returnable to the minimum position from any position between the maximum position and the minimum position upon activation of the return flow opening, in that the cylinder chamber comprises an intermediate return flow opening defining at least one intermediate position, the piston being displaceable as far as this intermediate position upon activation of the intermediate return flow opening, in that the control device activates the return flow opening in the control mode for the continuous control of the piston position in a partial control range between the intermediate position and the minimum position, and in that the control device activates the corresponding intermediate return flow opening for the continuous control of piston positions outside of the partial control range between the intermediate position and the minimum position.
The advantage of the inventive solution is thus to be seen in the fact that it is possible, by defining the return flow of the medium actuating the piston via the intermediate return flow opening, to operate the piston only in a desired partial control range, and, therefore, to also provide the control device with reliable information to the effect that undesired partial control ranges, for example, the partial control range between the intermediate position and the minimum position can be excluded for the continuous control of the piston.
It is, therefore, possible for a positional monitoring of the piston and/or the slide to be eliminated, but, nevertheless, the control device operates with the necessary reliability, with the control states being recognizable either directly by the kind of control or by detecting the kind of control.
In principle, the inventive solution is fully functional with a single intermediate return flow opening.
It is, however, particularly expedient for several intermediate return flow openings, each defining different partial control ranges, to be associated with the cylinder chamber, and for the control device to define the minimum permissible position of the piston in the respective partial control range by the respectively activated intermediate return flow opening.
This means that with this solution it is possible to define several partial control ranges each with a minimum permissible position of the piston by activating different intermediate return flow openings.
A particularly advantageous control mode provides for the control device to operate the piston exclusively in partial control ranges lying outside of the partial control range between the intermediate position and the minimum position by the control device activating only the corresponding intermediate return flow opening and not, in addition, the return flow opening for the control so that by virtue of the construction it is already possible to exclude the undesired partial control range, for example, the partial control range lying between the intermediate position and the minimum position.
In order to be able to carry out an exact continuous control, it is necessary for the control device to recognize the position of the piston. For this reason, it is preferably provided for the control device to determine the position of the piston starting from the intermediate position corresponding to the activated intermediate return flow opening as reference position, and to thus be capable, starting from this reference position, for example, by integration of the inflow times and return flow times, of determining the position of the piston at least approximately, with an exact new detection of the piston always being possible when the latter is driven back again to the respective intermediate position, from which, as starting point, the position of the piston can then be determined again.
In order to be able to activate the return flow opening and the intermediate return flow openings by the control device, complex valves would, for example, be conceivable. A simple possibility provides for a valve controllable by the control device to be associated with each of the return flow openings and intermediate return flow openings.
The valves could, for example, be designed such that control of the amount is also possible with these. However, in order to design the control device particularly simply, it is preferably provided for each valve to be a valve which is switchable only between a through-flow position and a shut-off position and to thus have only two switching states.
For the structural design of the adjusting device, in particular, to order to attain the minimum position, very different variants are conceivable. It would, for example, be conceivable to act upon the piston on two sides with a medium, with the one medium generating the force for moving the piston from the minimum position to the maximum position, and the other medium generating the returning force for returning the piston in the direction of the minimum position upon activation of the return flow openings or intermediate return flow openings.
Structurally it is, however, particularly simple for the piston to be acted upon in the direction of its minimum position by an elastic energy storing device, for example, a spring, which constantly ensures that the piston moves in the direction of the minimum position upon activation of at least one return flow opening or intermediate return flow opening, insofar as this return flow opening or intermediate return flow opening still opens into the cylinder volume enclosed between piston and cylinder chamber.
For the coupling between the piston and the slide, it would, for example, be conceivable to provide a mechanical transmission or a flexible coupling. However, it is particularly simple for the slide to be connected to the piston via an actuation rod.
Preferably, the slide is rigidly connected to the piston.
However, the inventive solution relates not only to operation of the inventive
Hossner Klaus
Krusche Karl-Joachim
Sandkoetter Wolfgang
Bitzer Kuehlmaschinenbau GmbH
Denion Thomas
Lipsitz Barry R.
Trieu Theresa
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