Patent Description:
As disclosed in Patent Literature <NUM>, a screw compressor is known as a type of displacement compressor, and is used as a component of a refrigerant circuit built, for example, in a refrigerating machine or other machines. A known example of a screw compressor is a single-screw compressor including a casing in which one screw rotor having a spiral tooth groove and two gate rotors each having a plurality of gate rotor tooth portions configured to fit into the tooth groove of the screw rotor are housed. The single-screw compressor has a plurality of compression chambers formed by the tooth groove of the screw rotor and the gate rotor tooth portions of the gate rotors meshing and engaging with each other. One end of the screw rotor in a direction parallel to the axis of rotation serves as a suction side through which refrigerant is suctioned, and the other end of the screw rotor in a direction parallel to the axis of rotation serves as a discharge side through which refrigerant is discharged. The casing has its interior partitioned into a low-pressure space provided at a suction side of the compression chambers and a high-pressure space provided at a discharge side of the compression chambers.

The screw rotor is fixed to a screw shaft configured to be rotated by a drive unit provided in the casing. One axial end portion of the screw shaft is supported by a bearing housing having a bearing inside so that the screw shaft can rotate, and the other axial end portion of the screw shaft is coupled to the drive unit. The screw compressor is configured such that when the screw rotor is driven to rotate by the screw shaft being rotated by the drive unit, refrigerant in the low-pressure space is suctioned into the compression chambers, compressed in the compression chambers, and discharged into the high-pressure space.

Incidentally, there is a type of screw compressor including a pair of slide valves disposed in a slide groove formed in an inner cylindrical surface of a casing and provided so that the pair of slide valves can slide in a direction parallel to the axis of rotation of a screw rotor. The slide valves slide in a direction parallel to the axis of rotation of the screw rotor, and is provided to effect a change in internal volume ratio by varying discharge opening timing by changing the start position of discharge of high-pressure gas refrigerant compressed in a compression chamber. Each of these slide valves includes a valve body portion facing the screw rotor and a guide portion forming a sliding surface facing an outer circumferential surface of a bearing housing.

The screw compressor has a risk that a thermal expansion of the screw rotor by a rise in temperature of the refrigerant gas compressed in the compression chamber may cause reduced spacings between an outer circumferential surface of the screw rotor and the inner cylindrical surface of the casing and between the outer circumferential surface of the screw rotor and the slide valve. Further, the screw compressor has a risk that the screw rotor may rotate backward due to a differential pressure in the casing after stoppage of operation. The inverse rotation of the screw rotor undesirably causes the valve body portion of the slide valve to fall toward the screw rotor or rotate in a circumferential direction due to the influence of, for example, a variation in internal pressure of the compression chamber. As a result, the valve body portion of the slide valve may partially protrude from an inner circumferential surface of a casing bore to make contact with the screw rotor, which may invite a seizure or other trouble.

To address this problem, Patent Literature <NUM> discloses a structure in which contact between a slide valve and the screw rotor is avoided by providing a guide portion of the slide valve with a protruding portion relatively protruding more in a circumferential direction than a valve body portion of the slide valve and bringing the protruding portion into contact with a bearing holder when the slide valve rotates in a circumferential direction.

Patent Literature <NUM>, which forms the basis for the preamble of claim <NUM>, discloses a screw compressor, wherein in a partition part partitioning a discharge passage and an oil reservoir part, there are provided a first oil supply path for supplying oil staying in the oil reservoir part to a compression chamber and a second oil supply path for supplying oil staying in the discharge passage to the compression chamber. A changeover mechanism changes over among a first state that the oil can be supplied only from the first oil supply path to each slide part, a second state that the oil can be supplied only from the second oil supply path to each slide part, and a third state that the oil can be supplied from both the first oil supply path and the second oil supply path to each slide part.

Further exemplary screw compressors are known from Patent Literature <NUM> and Patent Literature <NUM>.

In the screw compressor of Patent Literature <NUM>, in a case where there has occurred a torsional deformation between the valve body portion and the guide portion of the slide valve, the spacing between the valve body portion and the screw rotor is reduced more than necessary even when the protruding portion provided on the guide portion comes into contact with the bearing holder, with the result that the slide valve and the screw rotor may make contact with each other.

The present invention has been made to solve such a problem, and has as an object to provide a highly-reliable screw compressor capable of reducing contact between a slide valve and a screw rotor.

A screw compressor according to claim <NUM> includes a casing forming an outer shell, a screw shaft disposed in the casing and configured to be driven to rotate, a screw rotor, fixed to the screw shaft, that has a spiral tooth groove in an outer circumferential surface thereof, a gate rotor having a plurality of gate rotor tooth portions configured to fit into the tooth groove of the screw rotor and forming, together with the casing and the screw rotor, a compression chamber in which to compress refrigerant, a slide valve provided in a slide groove formed in an inner cylindrical surface of the casing and configured to slide in a direction parallel to an axis of rotation of the screw rotor, a bearing housing having a bearing inside and having an outer peripheral surface on which the slide valve slides, the bearing being configured to support one end of the screw shaft so that the screw shaft is able to rotate, an oil separator configured to separate oil mixed into refrigerant compressed in the compression chamber, and a heating mechanism connected to the oil separator and configured to, by utilizing oil separated by the oil separator, thermally expand the bearing housing in a radial direction during operation.

In the screw compressor according to the embodiment of the present invention, before the valve body portion of the slide valve falls toward the screw rotor or rotates in a circumferential direction, the bearing housing, which has thermally expanded, comes into contact with the slide valve to support the slide valve. This makes it possible to reduce contact between the slide valve and the screw rotor and achieve a highly-reliable screw compressor.

The following describes embodiments with reference to the drawings. Identical or equivalent components are given identical signs throughout the drawings, and a description of such components is omitted or simplified as appropriate. Further, the shapes, sizes, and locations, or other attributes of components shown in the drawings are subject to change as appropriate.

<FIG> is a cross-sectional view illustrating an internal structure of a screw compressor according to Embodiment <NUM>. <FIG> illustrates the internal structure of the screw compressor according to Embodiment <NUM> and illustrates a portion different from that shown in <FIG>. <FIG> is an enlarged cross-sectional view of main components as taken along line A-A in <FIG>. <FIG> is an enlarged cross-sectional view of main components as taken along line B-B in <FIG>. <FIG> is a perspective view illustrating a structure of a bearing housing of the screw compressor according to Embodiment <NUM>.

The screw compressor <NUM> according to Embodiment <NUM> is described by taking a single-stage single-screw compressor as an example. As shown in <FIG>, the screw compressor <NUM> includes a cylindrical casing forming an outer shell, a compression unit <NUM> provided in the casing <NUM>, a drive unit <NUM> provided in the casing <NUM>, and an oil separator <NUM> provided at one end of the exterior of the casing <NUM>. The casing <NUM> has its interior partitioned into a low-pressure space <NUM> and a high-pressure space <NUM>.

As shown in <FIG>, the compression unit <NUM> includes a screw shaft <NUM>, a screw rotor <NUM> fixed to the screw shaft <NUM>, a pair of gate rotors <NUM>, a gate rotor support (not illustrated), a pair of slide valves <NUM>, and a bearing housing <NUM> having a bearing <NUM> inside and having an outer circumferential surface on which the slide valves <NUM> slide. The bearing <NUM> supports an end portion of the screw shaft <NUM> so that the screw shaft <NUM> can rotate. Further, as shown in <FIG>, the compression unit <NUM> includes a heating mechanism <NUM> connected to the oil separator <NUM> and configured to, by utilizing oil separated by the oil separator <NUM>, thermally expand the bearing housing <NUM> in a radial direction during operation as shown in <FIG>.

As shown in <FIG>, the screw shaft <NUM> is disposed in the casing <NUM> and driven to rotate by the drive unit <NUM>. The screw shaft <NUM> extends in a direction parallel to the tube axis of the casing <NUM>. One axial end portion of the screw shaft <NUM> is supported by the bearing <NUM>, which is placed opposite a discharge side of the screw rotor <NUM>, so that the screw shaft <NUM> can rotate, and the other axial end portion of the screw shaft <NUM> is coupled to the driver unit <NUM>.

As shown in <FIG> and <FIG>, the screw rotor <NUM> has a plurality of spiral tooth grooves 5a in an outer circumferential surface of a cylinder. The screw rotor <NUM> is fixed to the screw shaft <NUM>, and rotates together with the screw shaft <NUM> as the screw shaft <NUM> is rotated by the drive unit <NUM>. A side of the screw rotor <NUM> facing the low-pressure space <NUM> in a direction parallel to the axis of rotation serves as a suction side through which refrigerant is suctioned, and an end of the screw rotor <NUM> facing the high-pressure space <NUM> serves as a discharge side through which refrigerant is discharged. Further, a predetermined spacing S is formed between the screw rotor <NUM> and the slide valves <NUM>. This is intended to prevent a seizure or other trouble from occurring, for example, due to contact during assembly of the screw compressor <NUM> or contact between the slide valves <NUM> and the screw rotor <NUM> during operation of the screw compressor <NUM>.

The gate rotors <NUM> have outer circumferential portions each provided with a plurality of gate rotor tooth portions 6a configured to fit into the tooth grooves 5a of the screw rotor <NUM> and, as shown in <FIG>, are disposed so that the screw rotor <NUM> is interposed between the gate rotors <NUM> in a radial direction. The compression unit <NUM> has a compression chamber <NUM> formed by the tooth grooves 5a of the screw rotor <NUM> and the gate rotor tooth portions 6a of the gate rotors <NUM> meshing and engaging with each other. The screw compressor <NUM> is configured such that two gate rotors <NUM> kept <NUM> degrees apart face one screw rotor <NUM>. Therefore, the compression chamber <NUM> includes two compression chambers <NUM> one of which is formed above the screw shaft <NUM> and the other of which is formed below the screw shaft <NUM>. The gate rotor support (not illustrated) has a plurality of gate rotor support tooth portions placed opposite the plurality of gate rotor tooth portions 6a, and serve to support the gate rotors <NUM>.

As shown in <FIG> and <FIG>, the slide valves <NUM> are provided in a slide groove <NUM> formed in an inner cylindrical surface of the casing <NUM>, and are configured to slide in a direction parallel to the axis of rotation of the screw rotor <NUM>. The slide valves <NUM> are for example internal volume ratio adjusting valves. Each of the slide valves <NUM> includes a valve body portion <NUM> facing the screw rotor <NUM> and a guide portion <NUM> having a sliding surface facing an outer circumferential surface of the bearing housing <NUM>. The valve body portion <NUM> and the guide portion <NUM> are coupled by a coupling portion <NUM>. Between the valve body portion <NUM> and the guide portion <NUM>, a discharge port 7a is provided through which refrigerant compressed in the compression chamber <NUM> is discharged. The refrigerant discharged from the discharge port 7a is discharged into the high-pressure space <NUM> through a discharge gas passage.

The slide valve <NUM> is connected to a slide valve drive device <NUM> via a rod <NUM> fixed to an end face of the guide portion <NUM>. That is, the slide valve <NUM> moves parallel to the screw shaft <NUM> as the rod <NUM> is driven by the slide valve drive device <NUM> to move in an axial direction. The slide valve drive device <NUM> is for example configured to drive with gas pressure, configured to drive with hydraulic pressure, or configured to drive with a motor.

In the screw compressor <NUM>, the timing of discharge of refrigerant suctioned into the compression chamber <NUM> is adjusted by the valve body portion <NUM> of the slide valve <NUM> moving parallel to the screw shaft <NUM>. Specifically, the slide valve <NUM> can advance the timing of discharge by being located at the suction side to advance the opening of the discharge port 7a, and can delay the timing of discharge by being moved to the discharge side to delay the opening of the discharge port 7a. That is, the screw compressor <NUM> operates at a low internal volume ratio when the timing of discharge is advanced, and operates at a high internal volume ratio when the timing of discharge is delayed.

As shown in <FIG>, the bearing housing <NUM> is provided in proximity to an end portion of the screw rotor <NUM> situated at the discharge side. The bearing housing <NUM> is formed so that the outside diameter of the bearing housing <NUM> is larger than the outside diameter of the screw rotor <NUM>. Meanwhile, since the bearing housing <NUM> needs to be inserted in a place in the casing <NUM> in which the screw rotor <NUM> is housed, the bearing housing <NUM> is formed to have an outside diameter smaller than the inside diameter of the casing <NUM> in the place. In some cases, the outside diameter of the bearing housing <NUM> may be smaller than the outside diameter of the screw rotor <NUM>.

As shown in <FIG>, the oil separator <NUM> serves to separate oil <NUM> mixed into gas refrigerant compressed in the compression chamber <NUM>. The oil <NUM> separated by the oil separator <NUM> circulates through the interior of the casing <NUM>, for example, to lubricate the bearing <NUM>, which supports one end of the screw shaft <NUM> or to seal the gap between an inner wall surface of the casing <NUM> and the screw rotor <NUM>.

The drive unit <NUM> is formed by an electric motor <NUM>. The electric motor <NUM> is formed by a stator <NUM>, fixed in internal contact with the interior of the casing <NUM>, that has a gap in a radial direction and a motor rotor <NUM> disposed inside the stator <NUM> so that the motor rotor <NUM> can rotate. The motor rotor <NUM> is connected to an axial end portion of the screw shaft <NUM>, and is disposed on the same axis as the screw rotor <NUM>. In the screw compressor <NUM>, the screw rotor <NUM> is rotated by the electric motor <NUM> driving the screw shaft <NUM> to rotate. In a case where the electric motor <NUM> is of an inverter type, the electric motor <NUM> is driven at a variable speed of rotation by an inverter (not illustrated) and operated with an increase or decrease in the speed of rotation of the screw shaft <NUM>.

Next, an operation of the screw compressor <NUM> according to Embodiment <NUM> is described with reference to <FIG>. <FIG> is an explanatory diagram illustrating a suction step of the operation of the screw compressor according to Embodiment <NUM>. <FIG> is an explanatory diagram illustrating a compression step of the operation of the screw compressor according to Embodiment <NUM>. <FIG> is an explanatory diagram illustrating a discharge step of the operation of the screw compressor according to Embodiment <NUM>. It should be noted that <FIG> describe the respective steps with attention focused on a compression chamber <NUM> indicated by dot hatching.

In the screw compressor <NUM>, as shown in <FIG>, the screw rotor <NUM> is caused by the electric motor <NUM> to rotate via the screw shaft <NUM>, whereby the gate rotor tooth portions 6a of the gate rotors <NUM> relatively move within the tooth grooves 5a forming the compression chamber <NUM>. This causes a cycle of the suction step (<FIG>), the compression step (<FIG>), and the discharge step (<FIG>) to be repeated in the compression chamber <NUM>.

<FIG> shows a state of the compression chamber <NUM> during the suction step. The screw rotor <NUM> is driven by the electric motor <NUM> to rotate in the direction of a solid arrow. This causes a reduction in volume of the compression chamber <NUM> as shown in <FIG>.

When the screw rotor <NUM> keeps on rotating, the compression chamber <NUM> comes to communicate with the discharge port 7a as shown in <FIG>. This causes high-pressure refrigerant gas compressed in the compression chamber <NUM> to be discharged outward through the discharge port 7a. Then, similar compression is performed at the back of the screw rotor <NUM> again.

Incidentally, the screw compressor <NUM> has a risk that a thermal expansion of the screw rotor <NUM> by a rise in temperature of the refrigerant gas compressed in the compression chamber <NUM> may cause reduced spacings S between an outer circumferential surface of the screw rotor <NUM> and the inner cylindrical surface of the casing <NUM> and between the outer circumferential surface of the screw rotor <NUM> and the slide valve <NUM>. Further, the screw compressor <NUM> has a risk that the screw rotor <NUM> may rotate backward due to a differential pressure in the casing <NUM> after stoppage of operation, and the inverse rotation of the screw rotor <NUM> undesirably causes the valve body portion <NUM> of the slide valve <NUM> to fall toward the screw rotor <NUM> or rotate in a circumferential direction due to the influence of, for example, a variation in internal pressure of the compression chamber <NUM>. As a result, the valve body portion <NUM> of the slide valve <NUM> may partially make contact with the screw rotor <NUM>, which may invite a seizure or other trouble.

To address this problem, as shown in <FIG>, and <FIG>, the screw compressor <NUM> according to Embodiment <NUM> includes a heating mechanism <NUM> connected to the oil separator <NUM> and configured to, by utilizing oil separated by the oil separator <NUM>, thermally expand the bearing housing <NUM> in a radial direction during operation. The heating mechanism <NUM> includes an oil passage <NUM> formed in a wall of the casing <NUM> facing the bearing housing <NUM> and connected to the oil separator <NUM> and a groove portion <NUM> formed in the bearing housing <NUM> and configured to communicate with the oil passage <NUM>. That is, the heating mechanism <NUM> is configured to circulate high-temperature and high-pressure oil separated by the oil separator <NUM> to the groove portion <NUM> through the oil passage <NUM> to thermally expand the bearing housing <NUM> in a radial direction during operation.

The groove portion <NUM> is formed along a circumferential direction of the bearing housing <NUM>. In Embodiment <NUM>, as shown in <FIG>, the groove portion <NUM> is formed by two groove portions, namely a first groove portion 91a and a second groove portion 91b, laid side-by-side at a spacing in a direction parallel to the tube axis of the bearing housing <NUM>. One end of the first groove portion 91a serves as a suction port 91c connected to the oil passage <NUM>, and the other end of the first groove portion 91a is connected to the second groove portion 91b. One end of the second groove portion 91b is connected to the first groove portion 91a, and the other end of the second groove portion 91b serves as a discharge port 91d leading to the compression chamber <NUM>. As shown in <FIG>, the discharge port 91d and the compression chamber <NUM> are connected by an oil connecting passage 90a formed in the wall of the casing <NUM>. High-temperature and high-pressure oil having flowed into the groove portion <NUM> of the bearing housing <NUM> circulates under a differential pressure within the casing <NUM>, and is fed to the tooth grooves 5a of the screw rotor <NUM>, the bearing <NUM>, or other components.

In the screw compressor <NUM> according to Embodiment <NUM>, as shown in <FIG>, before the valve body portion <NUM> of the slide valve <NUM> falls toward the screw rotor <NUM> or rotates in a circumferential direction, the bearing housing <NUM>, which has thermally expanded, comes into contact with the guide portion <NUM> of the slide valve <NUM> to support the guide portion <NUM>. This makes it possible to reduce contact between the slide valve <NUM> and the screw rotor <NUM> and achieve a highly-reliable screw compressor.

It is difficult to machine the groove portion <NUM> only in a portion of the outer circumferential surface of the bearing housing <NUM> with a lathe machine. This problem is addressed by using a casting mold in advance to mold the bearing housing <NUM> with the groove portion <NUM> formed in an outer circumferential portion of the bearing housing <NUM> and performing surface treatment with a lathe machine. Since the surface of the groove portion <NUM> does not affect the function of the screw compressor <NUM>, there is no problem even if the surface of the groove portion <NUM> remains a casting surface <NUM>. Therefore, the surface of the groove portion <NUM> remains a casting surface <NUM> formed by a casting mold. That is, making the groove portion <NUM> of the screw compressor <NUM> according to Embodiment <NUM> remain the casting surface <NUM> eliminates the need for additional processing of the groove portion <NUM> and makes it possible to reduce manufacturing cost and enhance productivity.

Further, as shown in <FIG>, the casing <NUM> has an inner wall surface provided with a spacer <NUM> in a place facing the bearing housing <NUM> across the screw rotor <NUM>. Moreover, the heating mechanism <NUM> has a branch passage 90b, connected to the spacer <NUM>, that branches off from the oil passage <NUM> and extends in a direction parallel to the tube axis of the casing <NUM>. That is, the heating mechanism <NUM> can circulate the high-temperature and high-pressure oil separated by the oil separator <NUM> to the branch passage 90b through the oil passage <NUM> to increase a heat-transfer area to thermally expand the inner wall surface of the casing <NUM>. Therefore, the screw compressor <NUM> according to Embodiment <NUM> can effectively reduce contact between the casing <NUM> and the screw rotor <NUM>.

The screw compressor <NUM> according to Embodiment <NUM> does not necessarily need to provide the spacer <NUM> or connect the branch passage 90b branching off from the oil passage <NUM>, and may be configured to omit the spacer <NUM> and the branch passage.

As mentioned above, a screw compressor <NUM> according to Embodiment <NUM> includes a casing <NUM> forming an outer shell, a screw shaft <NUM> disposed in the casing <NUM> and configured to be driven to rotate, a screw rotor <NUM>, fixed to the screw shaft <NUM>, that has a spiral tooth groove 5a in an outer circumferential surface thereof, a gate rotor <NUM> having a plurality of gate rotor tooth portions 6a configured to fit into the tooth groove 5a of the screw rotor <NUM> and forming, together with the casing <NUM> and the screw rotor <NUM>, a compression chamber <NUM> in which to compress refrigerant, a slide valve <NUM> provided in a slide groove <NUM> formed in an inner cylindrical surface of the casing <NUM> and configured to slide in a direction parallel to an axis of rotation of the screw rotor <NUM>, a bearing housing <NUM> having a bearing <NUM> inside and having an outer peripheral surface on which the slide valve <NUM> slides, the bearing <NUM> being configured to support one end of the screw shaft <NUM> so that the screw shaft <NUM> is able to rotate, an oil separator <NUM> configured to separate oil mixed into refrigerant compressed in the compression chamber <NUM>, and a heating mechanism <NUM> connected to the oil separator <NUM> and configured to, by utilizing oil separated by the oil separator <NUM>, thermally expand the bearing housing <NUM> in a radial direction during operation.

The heating mechanism <NUM> includes an oil passage <NUM> formed in a wall of the casing <NUM> facing the bearing housing <NUM> and connected to the oil separator <NUM> and a groove portion <NUM> formed in the bearing housing <NUM> and configured to communicate with the oil passage <NUM>. The heating mechanism <NUM> is configured to circulate high-temperature and high-pressure oil separated by the oil separator <NUM> to the groove portion <NUM> through the oil passage <NUM> to thermally expand the bearing housing <NUM> in a radial direction during operation.

Therefore, in the screw compressor <NUM> according to Embodiment <NUM>, before the valve body portion <NUM> of the slide valve <NUM> falls toward the screw rotor <NUM> or rotates in a circumferential direction, the bearing housing <NUM>, which has thermally expanded, comes into contact with the guide portion <NUM> of the slide valve <NUM> to support the guide portion <NUM>. This makes it possible to reduce contact between the slide valve <NUM> and the screw rotor <NUM> and achieve a highly-reliable screw compressor.

Further, the casing <NUM> has an inner wall surface provided with a spacer <NUM> in a place facing the bearing housing <NUM> across the screw rotor <NUM>. The heating mechanism <NUM> has a branch passage 90b, connected to the spacer <NUM>, that branches off from the oil passage <NUM> and extends in a direction parallel to a tube axis of the casing <NUM>. That is, the heating mechanism <NUM> can circulate the high-temperature and high-pressure oil separated by the oil separator <NUM> to the branch passage 90b through the oil passage <NUM> to increase a heat-transfer area to thermally expand the inner wall surface of the casing <NUM>. Therefore, the screw compressor <NUM> according to Embodiment <NUM> can effectively reduce contact between the casing <NUM> and the screw rotor <NUM>.

Further, the groove portion <NUM> is a casting surface <NUM> formed by a casting mold. That is, making the surface of the groove portion <NUM>, which does not affect the function of the screw compressor <NUM> according to Embodiment <NUM>, remain the casting surface <NUM> eliminates the need for additional processing of the groove portion <NUM> and makes it possible to reduce manufacturing cost and enhance productivity.

Next, a screw compressor <NUM> according to Embodiment <NUM> is described with reference to <FIG> is a cross-sectional view illustrating an internal structure of the screw compressor according to Embodiment <NUM>. <FIG> is a perspective view illustrating a structure of a bearing housing of the screw compressor according to Embodiment <NUM>. Components identical to those of the screw compressor <NUM> described in Embodiment <NUM> are given identical reference signs, and a description of such components is omitted as appropriate.

In the screw compressor <NUM> according to Embodiment <NUM>, as shown in <FIG>, the heating mechanism <NUM> has its groove portion <NUM> formed up to a place facing a guide portion <NUM> of the slide valve <NUM>. That is, the heating mechanism <NUM> is configured to circulate high-temperature and high-pressure oil separated by the oil separator <NUM> to the groove portion <NUM> through the oil passage <NUM> to thermally expand the bearing housing <NUM> in a radial direction during operation and thermally expand the guide portion <NUM> of the slide valve <NUM> in a radial direction. In the screw compressor <NUM> according to Embodiment <NUM>, a branch passage 90c branching off from the oil passage <NUM> is connected to the compression chamber <NUM>. High-temperature and high-pressure oil having flowed into the oil passage <NUM> circulates under a differential pressure within the casing <NUM>, and is fed to the tooth grooves 5a of the screw rotor <NUM>, the bearing <NUM>, or other components.

Therefore, in the screw compressor <NUM> according to Embodiment <NUM>, before the valve body portion <NUM> of the slide valve <NUM> falls toward the screw rotor <NUM> or rotates in a circumferential direction, the bearing housing <NUM>, which has thermally expanded, and the guide portion <NUM> of the slide valve <NUM>, which has thermally expanded, come into contact with each other. This makes it possible to reduce contact between the slide valve <NUM> and the screw rotor <NUM> and achieve a highly-reliable screw compressor.

Although not illustrated, the screw compressor <NUM> according to Embodiment <NUM> may be configured such that a spacer <NUM> is provided on an inner wall surface of the casing <NUM> located between the compression unit <NUM> and the drive unit <NUM> and a branch passage 90b branching off from the oil passage <NUM> is connected to the spacer <NUM>.

Next, a screw compressor <NUM> according to Embodiment <NUM> is described with reference to <FIG> is a cross-sectional view illustrating an internal structure of the screw compressor according to Embodiment <NUM>. Components identical to those of the screw compressor <NUM> described in Embodiment <NUM> are given identical reference signs, and a description of such components is omitted as appropriate.

As shown in <FIG>, the screw compressor <NUM> according to Embodiment <NUM> is configured such that the groove portion <NUM> is formed along a direction parallel to a tube axis of the bearing housing <NUM>. That is, the heating mechanism <NUM> is configured to circulate high-temperature and high-pressure oil from the oil separator <NUM> to the groove portion <NUM> through the oil passage <NUM> to thermally expand the whole surface of the bearing housing <NUM> in a radial direction during operation. As shown in <FIG>, the groove portion <NUM> formed along a direction parallel to the tube axis may be formed by a plurality of the groove portions <NUM> formed in parallel as shown in <FIG> or may be formed by one groove portion <NUM>.

In the screw compressor <NUM> according to Embodiment <NUM>, a branch passage 90d branching off from the oil passage <NUM> is connected to the compression chamber <NUM>. High-temperature and high-pressure oil having flowed into the oil passage <NUM> circulates under a differential pressure within the casing <NUM>, and is fed to the tooth grooves 5a of the screw rotor <NUM>, the bearing <NUM>, or other components.

Therefore, in the screw compressor <NUM> according to Embodiment <NUM>, before the valve body portion <NUM> of the slide valve <NUM> falls toward the screw rotor <NUM> or rotates in a circumferential direction, the bearing housing <NUM>, which has thermally expanded, comes into contact with the slide valve <NUM> to support the slide valve <NUM>. This makes it possible to reduce contact between the slide valve <NUM> and the screw rotor <NUM> and achieve a highly-reliable screw compressor.

While the screw compressor <NUM> has been described above with reference to an embodiment, the screw compressor <NUM> is not limited to the configuration of the aforementioned embodiment. For example, the internal configuration of the screw compressor <NUM> is not limited to the aforementioned content but may include other components. Further, while the screw compressor <NUM> has been described by taking a single-stage single-screw compressor as an example, the screw compressor <NUM> may for example be a two-stage screw compressor. Further, the slide valve <NUM> is not limited to an internal volume ratio adjusting valve but may be configured, for example, to adjust compression capacity. Further, the gate rotor <NUM> is not limited to being formed by the two gate rotors <NUM> illustrated, but may be formed by one gate rotor <NUM>. In other words, the screw compressor <NUM> encompasses a range of design changes and variations in application that persons skilled in the art normally make so that the screw compressor still would fall in the scope of the claims.

Claim 1:
A screw compressor (<NUM>, <NUM>, <NUM>) comprising:
a casing (<NUM>) forming an outer shell;
a screw shaft (<NUM>) disposed in the casing (<NUM>) and configured to be driven to rotate;
a screw rotor (<NUM>), fixed to the screw shaft (<NUM>), that has a spiral tooth groove (5a) in an outer circumferential surface thereof;
a gate rotor (<NUM>) having a plurality of gate rotor tooth portions (6a) configured to fit into the tooth groove (5a) of the screw rotor (<NUM>) and forming, together with the casing (<NUM>) and the screw rotor (<NUM>), a compression chamber (<NUM>) in which to compress refrigerant;
a slide valve (<NUM>) configured to slide in a direction parallel to an axis of rotation of the screw rotor (<NUM>);
a bearing housing (<NUM>) having a bearing (<NUM>) inside and having an outer peripheral surface, the bearing (<NUM>) being configured to support one end of the screw shaft (<NUM>) so that the screw shaft (<NUM>) is able to rotate; and
an oil separator (<NUM>) configured to separate oil mixed into refrigerant compressed in the compression chamber (<NUM>);
characterized in that:
the slide valve (<NUM>) is provided in a slide groove (<NUM>) formed in an inner cylindrical surface of the casing (<NUM>),
the slide valve (<NUM>) slides on the outer peripheral surface of the bearing housing (<NUM>), and
the screw compressor (<NUM>, <NUM>, <NUM>) further comprises a heating mechanism (<NUM>) connected to the oil separator (<NUM>) and configured to, by utilizing oil separated by the oil separator (<NUM>), thermally expand the bearing housing (<NUM>) in a radial direction during operation, wherein
the heating mechanism (<NUM>) includes
an oil passage (<NUM>) formed in a wall of the casing (<NUM>) facing the bearing housing (<NUM>) and connected to the oil separator (<NUM>), and
a groove portion (<NUM>) formed in the bearing housing (<NUM>) and configured to communicate with the oil passage (<NUM>), and
the heating mechanism (<NUM>) is configured to circulate oil separated by the oil separator (<NUM>) to the groove portion (<NUM>) through the oil passage (<NUM>) to thermally expand the bearing housing (<NUM>) in a radial direction during operation.