Rotary positive displacement compressor with capacity control

(54) Name: Rotary displacement compressor with capacity control

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The present invention relates to a rotary displacement compressor which comprises a driven, cylindrical rotor with helical or groove extending groove, and at least one gear whose teeth are sealingly engaged with the rotor grooves and whose rotational axis intersects the rotor axis of rotation of the rotor. suitable housing and part of the gear or gears extending through the wall of the housing, and the gas to be compressed; is sucked in through the open ends of the rotor grooves at one end of the rotor and an outlet port connected to a pressure line is placed in the wall of the housing adjacent the other end of the rotor in front of the gear or any gear seen in the direction of rotation of the rotor.

A compressor of this kind in the form of an air compressor is described in US Patent No. 3 133,695.

The object of the present invention is to provide a compressor of this kind with a capacity regulation in principle without loss of capacity, which compressor is particularly useful in plants for cooling or freezing. Without capacity control and at a constant speed of the rotor, the compressor would suck out substantially the same gas volume, regardless of the cooling requirements required by the plant. To prevent a decrease in suction pressure, when loaded

If the evaporator of the system is reduced, the compressor should be regulated so that a smaller volume is sucked out.

However, even with compressors for air and other media, capacity regulation in principle without capacity loss is of great importance.

The ratio of suction volume to pressure volume and consequently also the pressure ratio of a particular gas is always determined for each type of compressor as a result of the design.

The ratio between the suction volume and the pressure volume and thus also the compressor pressure ratio is suitably chosen to such an extent that the pressure ratio corresponds to the ratio of gas pressure in front of and behind the compressor, the latter pressure being determined by the process in which the compressor is included.

The object of the present invention is to adapt the compressor capacity to the desired need, whereby the ratio of suction volume to pressure volume, which relates to the maximum capacity, remains substantially constant during the reduction of capacity, so that a control without losses is obtained.

It is a further object of the invention to vary the ratio of suction volume to pressure volume with maximum compressor capacity within set limits to adapt the compressor to different processes with different pressure ratios.

According to the invention, both objects can be achieved independently of one another and in combination with each other.

The above-mentioned intentions are achieved by means of a compressor of the configuration which is further defined in the appended claims.

An embodiment of the invention will now be described in detail with reference to the accompanying schematic drawings, in which Fig. 1 is a top view of a compressor according to the invention, comprising two gears and a capacity control; Fig. 2 is a section along the line AA in Fig. 1 at full load; Fig. 3 shows a distribution of half of the rotor of the compressor according to fig.

at full load; FIG. 4 is a section along line AA of FIG.

in part load and Fig. 5 is a distribution of half of the rotor at part load.

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Fig. 1 shows a rotor 1 and two gears Sr denoted by 2 and 3. The rotor is driven by a shaft 4.

The rotor is enclosed by a cylindrical housing 5 and the gears 2 and 3 extend through openings in the wall of the housing 5 (see Figures 2 and 4).

In a cooling compressor, the housing 5 is closed at both ends. A suction chamber 6 is formed between one end of the rotor 1 and a end surface of the housing

5th An inlet line 7 is connected to the suction chamber 6.

As the rotor 1 rotates, the gas to be sucked in is therefore introduced into the groove of the rotor through the open ends. At a definite moment, each open end is closed by a tooth of the gears 2 and 3 and the compression is initiated as each groove at the opposite end is to the end of the house's 5 wall.

At a definite moment, the other end of each groove reaches an outlet port 8 in the wall of the housing 5. A pressure line 9 is connected to this outlet port.

The compressor described so far is a known, rotary displacement compressor without capacity control.

However, it is desirable to have an effective control of the compressor's capacity in such a way that the ratio between the suction volume and the pressure volume, ie the volume ratio, remains substantially constant over a control range, the range being as large as possible.

According to the present invention, this intention is achieved by the use of a closed control ring. This ring is fitted in a groove in the housing 5 or, if desired, in a recess of the rotor 1.

Means not shown can act on the regulating ring 10, so that it is rotatable at a certain angle with respect to the housing 5.

For each half of the rotor, the regulating ring 10 is provided with a side projection 11, which forms the actual control element. The side projection 11 has at one end a straight regulating edge 12, which edge together with a fixed, regulating edge 13 in the housing limits an opening 14 in the wall of the housing 5.

This opening 14, the so-called return port, is connected to a return line 15 which communicates with the suction chamber 6.

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In the position shown in Fig. 1, the return port 14 is open. When the regulating ring 10 is rotated to such an extent that the regulating edges 12 and 13 abut each other, the return port 14 is closed.

This is the position at full load (see Figures 2 and 3).

In Figs. 1, 3 and 5, it can be seen that the aforementioned outlet port 8 is in fact composed of two parts, ie a fixed outlet port 8a and an adjustable outlet port 8b, which can be enlarged or reduced by an inclined regulating edge 16 of the side projection 11. When the While the regulating ring is in the position of the smallest partial load, the adjustable outlet port 8b is reduced, while the fixed outlet port 8a maintains its size. The purpose of this is to obtain a limited starting torque of the drive motor during the start-up process. A small pressure or no pressure at all is now built up during the start. The disadvantage of the fixed outlet port 8a, however, is that during operation at partial load the built-in volume ratio is low and does not correspond to the actual pressure ratio. Consequently, the consumed power increases.

A fixed outlet port is therefore not necessary or desirable under all conditions.

At minimum partial load, the return port 14 must be as large as possible. Obviously, the size of this port is determined by the axial width of the side projection 11 and by the possible pivoting angle of the regulating ring 10. However, the pivot angle becomes smaller as the lateral projection '11 is enlarged in the axial direction. Therefore, a maximum must be determined somewhere for the width of the side projections 11 of the control ring 10.

By shifting the regulating ring 10 from the position shown in Figures 2 and 3 to the position shown in Figures 4 and 5, the return port 14 is increased, which allows gas to flow back to the suction chamber 6. The The theoretical amount of suction gas is thereby equal to the capacity of the track at that moment, when the track has just passed the gate 14.

During rotation of the regulating ring 10 from full load to minimum partial load, the adjustable outlet port 8b gradually becomes smaller. Therefore, the process of expelling gas begins at a gradually later moment.

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By providing the compressor with side projections 11 of various shapes and / or dimensions, which of course also the groove in the housing 5 must be adapted, the compressor obtains a different, built-in volume ratio.

For technical manufacturing reasons, it is desirable that the straight regulating edge 12 of each side projection 11 does not cooperate with a straight regulating edge 13 of the housing 5, but that this regulating edge 13 is applied to a separate filling ring 17. By providing the compressor with lateral protrusion 11 or with fill rings 17, both with different dimensions, the compressor obtains a different built-in volume ratio.

Of course, the built-in volume ratio can only be changed within certain limits by a different shape and / or other dimensions of the side projections 11 and if required by the fill rings 17. The capacity control according to the invention has the following advantages:

The control is continuous and is performed using a single moving element. The control range is considerable, ie from full load to a minimum partial load of approximately 25%. No further viscous friction is introduced. The capacity loss is very small.

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