Rotary expansible chamber devices – Interengaging rotating members – Helical or herringbone
Reexamination Certificate
2000-04-07
2001-12-11
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
Interengaging rotating members
Helical or herringbone
Reexamination Certificate
active
06328546
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a screw compressor with adjustable full-load capacity of which the capacity adjustment of the screw compressor that compresses working fluids by engaging a male rotor and a female rotor within a casing is enabled in a wide range.
PRIOR ART
Conventionally, a non-step capacity adjustment by a slide valve system is used to adjust the capacity of a screw compressor. The slide valve system is a method of which a part of the gas sucked into the rotor is returned to the suction room via a slide valve during the compression process. Since this method is integrated to the compressor as part of the system, although the method is useful in respect to being equipped with a system which enables a change in the capacity after the compressor is produced, there is a problem of which the efficiency of compression (isothermal efficiency/insulation efficiency) lowers as the air flow is adjusted to decrease.
Consequently, in order to achieve high compression efficiency while keeping the cost low, when performing an actual compression, a compressor in proportion to the necessary capacity is selected out of limited types of compressors. Therefore, rather than being based on safety, a compressor type of which the full-load capacity is slightly larger than the necessary capacity is selected.
However, in this case, since it is impossible to infinitely manufacture different types of compressors, a compressor type on the large side is inevitably selected. Thus a compressor is forced to operate in an intermittent manner, making the actual operation inefficient.
A capacity control depending on a slide system is also inefficient because the airflow is controlled by returning partway compressed gas to the intake side via a highly resistant bypass, necessitating an uneconomical recompression. Also, another factor that makes a capacity control depending on a slide system inefficient is that there is no practical change in the mechanical-loss even when the airflow decreases.
Meanwhile, as in the former case where many compressor types are prepared according to the necessary capacity, as an example, in order to prevent the airflow from increasing, it is necessary to shorten the length of the rotor. However, if the length of the rotor is shortened without changing the helix angle of the rotor, it is difficult to maintain a smooth rotation. Therefore, it was necessary to change the helix angle every time the rotor was shortened, causing problems in the cost of manufacture, as well as technological problems. As an attempt to take a measure against the above described problem, a proposal is disclosed in published Unexamined Japanese Patent Application No. Showa 56-12092.
The aforementioned proposal is shown in
FIG. 7
(A), in which a notch
51
is provided so as to connect through space
52
with the teeth of the intake side end of the female rotor
50
. Another embodiment of the proposal is shown in
FIG. 7
(B), in which notch
56
is provided on alternate teeth of the male rotor
55
, so as to connect through space
57
with the teeth of the intake side end, so as to obtain any capacity between 80~100%.
In the above described case, by delaying the starting position of compression of the male rotor (with 4 teeth) which starts at an angle of rotation of &agr;°=0° to a maximum of &agr;°=90°, the capacity may be adjusted to a minimum of 80%. The degree of capacity between 80% and 100% is set by adjusting the passage resistance by changing the size of notch
51
or
56
.
This method may be applied only to rotors which consist of an even number of teeth, and further, it is necessary to provide a notch on alternate teeth. Moreover, there exists a problem whereas the aforementioned capacity adjustment between 80% and 100% must be performed by a complicated adjusting means. That is, the capacity is adjusted by a passage resistance of the bypass which is controlled by the shape, size, etc. of the notch.
SUMMARY OF THE INVENTION
The present invention is made to resolve such ever existing problems, and its object is to offer a screw compressor with adjustable full-load capacity which enables an optional change of the capacity without changing the shape, number of components, basic dimensions, and basic specifications of the compressor.
The screw compressor according to the present invention utilizes a method of capacity adjustment of which was conventionally regarded as impossible, the method being enabled by suitably shortening the length of the rotors. Also, contrary to the conventional idea, the adjustment of capacity is performed without changing the helix angle.
That is, the degree of capacity is adjusted without changing the rotor diameter, the rotor length, the casing dimension, and the basic specifications of a drive power necessary for a full-load output of 100%, and by a slight after-process, it is made to be in proportion to the necessary capacity by a slight after-process.
Also, the originally set, preferable action ratio of the rotors is not changed by the after-process, and does not cause any inconvenience to the rotation.
Further, it is necessary to control the amount of sucked in airflow in order to control the capacity; however, it is also necessary for the sucked in airflow not to affect the process of compression after the capacity is adjusted.
Furthermore, it is necessary to provide a large bypass for returning working fluids to the intake side, so that the above described capacity control is not affected by a passage resistance.
Accordingly, the screw compressor with adjustable full-load capacity of the present invention is:
a screw compressor for compressing working fluids by engaging a male rotor and a female rotor within a casing,
wherein an airflow rate reducing section is provided by eliminating a part of the rotor engagement of the screw rotor from the intake side end towards the direction of the shaft, and a bypass is provided for returning reduced airflow to the intake side, and the airflow rate reducing section and bypass is constructed so as to reduce the length of action of the screw rotors to correspond with the reduced capacity amount.
According to the above construction, by referring to the capacity percentage corresponding to the angle of rotation of the rotor, the angle of rotation in proportion to the reduced capacity percentage is set in advance. Then, the addendum of the rotor is eliminated from the intake side end of the rotor, until the corresponding angle of rotation is obtained, and the length of action of the rotors are reduced, while the bypass for returning reduced air to the intake side end is provided. Therefore, since the compression operation initiates only after the angle of rotation of the rotors pass the prescribed angle of rotation, theoretically, at the time of initiating compression, the tooth-space volume is smaller. Accordingly, compression power needed for a conventional capacity control method using a slide valve is unnecessary, and a capacity adjusted in proportion to the prescribed percentage of reduced airflow enables an efficient compression.
The airflow rate reducing section is formed stepwise on the outer circumferential section excluding the bottomland of the rotor, so as to serve as both an air flow rate reducing section and the bypass.
According to the above described construction, the airflow rate reducing section eliminates the outer circumferential section of teeth above the bottomland of the rotor in a stepwise manner, and since the center shaft portion including the pitch circle is left remaining, a smooth rotation is maintained, and a change of the helix angle is unnecessary.
Further, in an oil injecting type compressor, by eliminating a part of the tooth of the rotor, a loss due to oil agitation is decreased, reducing mechanical-loss. Furthermore, a large bypass towards the intake port is formed between the rotor shaft including the pitch circle nearby the bottomland and the inner surface of the casing, by providing an airflow rate reducing section formed by eliminating the tee
Kishi Takayuki
Nishio Toshio
Crowell & Moring LLP
Mayekawa Mfg., Ltd.
Vrablik John J.
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