Pumps – Condition responsive control of pump drive motor – Plural pumps having separate drive motors – supply sources,...
Reexamination Certificate
2002-02-20
2004-06-29
Yu, Justine R. (Department: 3746)
Pumps
Condition responsive control of pump drive motor
Plural pumps having separate drive motors, supply sources,...
C417S244000, C417S286000
Reexamination Certificate
active
06755620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-stage variable speed compressor provided with a plurality of compressors.
2. Description of the Related Art
Recently, a multi-stage variable speed compressor has been known, of which an object is to obtain a desired pressure by serially connecting a plurality of compressors to increase pressure step by step, when the desired pressure cannot be obtained using one compressor. A method for controlling such a multi-stage variable speed compressor has already known from Japanese Laid-open Patent Publication No. Hei 10-82391. This technique is to obtain said target discharge pressure by setting a suction flow rate and a target discharge pressure in a multi-stage variable speed compressor provided with a two-stage compressor.
The control of this multi-stage variable speed compressor is intended to obtain the desired discharge pressure, in such a manner that values to be taken for each part of the multi-stage variable speed compressor, which are corresponding to said setting (for example, a mid-pressure between the two compressor stages, a rotation ratio of the two compressors, the rotational speed and etc.), are previously stored in a control device as operation data, and the control device of the multi-stage variable speed compressor determines operation data corresponding to said setting and controls the multi-stage compressor, so that each part of the multi-stage variable speed compressor is laid to these operation data values.
However, because a multi-stage variable speed compressor is subject to a secular change (for example, loss of gas-tightness, abrasion of bearing parts or the like) while being used and thus its specifications are changed, it may be impossible to obtain a desired pressure even if each part of the multi-stage variable speed compressor is controlled using operation data previously stored as explained in the above.
In addition, it is frequent that a compressor (including a multi-stage) is usually intended to obtain a desired discharge pressure. Accordingly, if a flow rate of working fluid is changed during the operation, the rotational speed of the compressor or the like should be changed in response to the change of flow rate so as to obtain said desired discharge pressure.
For that reason, if the control of a multi-stage variable speed compressor is performed using operation data as in the prior art, it is necessary to prepare operation data corresponding to a flow rate-changing width of working fluid for each of discharge pressures that the multi-stage variable speed compressor can output.
In particular, if it is possible for the multi-stage variable speed compressor to be controlled up to 75% of a flow rate-changing width with a 1% pitch of changing width for one discharge pressure, it is necessary to prepare 75 kinds of operation data. In addition, if it is possible to operate said multi-stage variable speed compressor at a discharge pressure in the range of 2 to 10 kg/cm
2
with a 0.1 kg/cm
2
pitch of pressure, it is necessary to prepare 80 kinds of operation data. Then, it is required to prepare 6000 (75×80=6000) kinds of operation data for the multi-stage variable speed compressor and is necessary to prepare a large amount of operation data.
Furthermore, if the multi-stage variable speed compressor is subject to a secular change as explained in the above said large amount of operation data cannot be used. Therefore, it is difficult to say that the prior art can endure a practical use.
SUMMARY OF THE INVENTION
Therefore, the present invention is conceived considering the above situation. It is an object of the present invention to provide a multi-stage variable speed compressor, wherein the compressors from the first stage to the final stage are controlled to obtain the desired target pressure.
In order to achieve the above object, the present invention provides a multi-stage variable speed compressor comprising:
a plurality of compressors of which the rotational speeds are variable and which are serially connected each other so that working fluid is compressed step by step;
a pressure detector for detecting a discharge pressure of the compressor of the final stage among said plurality of compressors; and
a control device for controlling the rotational speeds of said plurality of compressors so that the discharge pressure of the compressor of said final stage among said plurality of compressors is laid to a desired target pressure,
wherein said control device inputs a pressure signal detected by said pressure detector, calculates a deviation between said target pressure and said pressure signal, and controls the rotational speeds of said plurality of compressors using said deviation.
As constructed in this manner, the discharge pressure is always controlled to be the desired target pressure. Accordingly, it becomes possible to operate the multi-stage variable speed compressor with a discharge pressure of a good precision. In addition, it becomes possible to perform the control without needing operation data as used in the prior art at all.
The multi-stage variable speed compressor according to the present invention, further comprises a pressure detector provided for each of compressors on and after the second stage among said plurality of compressors and detecting a discharge pressure of a compressor of a stage preceding the corresponding compressor or a suction pressure of the corresponding compressor, wherein said control device can be constructed to control the rotational speed of the compressor of the first stage among said plurality of compressors using said deviation, to input a pressure signal from said pressure detector provided for each of compressors on and after the second stage among said plurality of compressors and detecting a discharge pressure of a compressor of a stage preceding the corresponding compressor or a suction pressure of the corresponding compressor, and to control the rotational speed of each compressor on and after the second stage among said plurality of compressors based on the discharge pressure of the compressor of a stage preceding the corresponding compressor or the suction pressure of the corresponding compressor.
Herein, it is preferred that said control device calculates the rotational speed of the compressor of the first stage among said plurality of compressors by PID (Proportional Integral Derivative) operation rather than the deviation of the discharge pressure of the compressor of the final stage from the target pressure. It is also preferred that said control device calculates the rotational speed of each of compressors on and after the second stage from a discharge pressure of a compressor of a stage preceding the corresponding compressor or a suction pressure of the corresponding compressor by PID operation.
In addition, said discharge pressure of a compressor of a stage preceding the corresponding compressor and the suction pressure of the corresponding compressor are substantially equal if a structure such as a throttle valve or the like which causes a change of pressure is not interposed between the preceding compressor and the corresponding compressor.
According to said construction, the control for allowing the discharge pressure of the final stage to be laid to the desired target pressure is performed with a good precision.
Also, the multi-stage variable speed compressor according to the present invention further comprises a pressure detector for detecting a discharge pressure of the corresponding compressor with regard to compressors except the final stage compressor among said plurality of compressors, wherein said control device can be constructed in such a manner as to feed-back control the rotational speed of a compressor of each stage based on a pressure deviation between a target discharge pressure given to a compressor of each stage and a pressure from the pressure detector for detecting said discharge pressure of each stage, for all of said plurality of compressors. Herein, it is prefe
Nakamura Hajime
Totsuka Junichiro
Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel Ltd).
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Solak Timothy P.
Yu Justine R.
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