FIELD

The present invention relates to a scroll shape of a compressor in a supercharger in which a rotary shaft connects a turbine and the compressor, and a supercharger to which the scroll shape of the compressor is applied.

BACKGROUND

A flue gas turbine supercharger is configured by integrally connecting a compressor and a turbine by a rotary shaft and accommodating the compressor and the turbine in a housing in a rotatable manner. Flue gas is supplied into the housing to rotate the turbine, so that the rotary shaft is driven and rotated to rotationally drive the compressor. The compressor introduces the air from the outside, pressurizes the air by an impeller to provide compressed air, and supplies the compressed air to an internal combustion engine and the like.

In the above-mentioned flue gas turbine supercharger, the compressor as a centrifugal compressor is configured by fixing a plurality of blades to an outer circumferential portion of the compressor impeller and is accommodated in a compressor housing. The compressor housing has a diffuser, a scroll portion, and a discharge port provided on the outer circumferential side of the compressor. The diffuser has a substantially donut shape and decreases the velocity of fluid discharged from the compressor, thereby recovering static pressure. The scroll portion is formed on the outer circumferential side of the diffuser such that a passage cross-sectional area thereof is increased in a spiral manner in the circumferential direction and collects the fluid over the entire circumference. When the compressor rotates, the blades compress the fluid introduced through an air intake. Then, the compressed air is discharged to the diffuser from the outer circumferential side of the compressor, passes through the scroll portion, and is sent to the outside through the discharge port.

A conventional scroll portion has the passage cross-sectional area that is gradually increased from a tongue portion position at about 60° in the clockwise direction to a position at 360° when a scroll winding end position is 0° as a reference. An increase rate of the scroll passage cross-sectional area is designed such that a flow velocity is substantially constant in the circumferential direction at a design flow rate. When the scroll portion operates at a flow rate lower than the designed flow rate, the flow velocity in the vicinity of the tongue portion is increased with an effect of flow recirculating toward the tongue portion side from the scroll winding end side. As a result, the flow velocity is relatively decreased toward the downstream side. For example, the following Patent Literature 1 discloses the above-mentioned compressor.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent No. 5439423

SUMMARY

Technical Problem

FIG. 15is a graph indicating a volumetric flow rate and a flow velocity for a scroll angle in a scroll shape of a conventional compressor.

As illustrated inFIG. 15, in the conventional compressor, the passage cross-sectional area of a scroll portion is gradually increased from a tongue portion position at about 60° to a position at 360° (dashed-dotted curve illustrated inFIG. 15). When the scroll portion operates at a flow rate lower than a designed flow rate, the flow velocity (solid line illustrated inFIG. 15) is gradually decreased with the above-mentioned recirculating effect. It has been, however, found by CFD analysis that actually, the flow velocity is increased, and then, is drastically decreased in a range of the scroll portion from a position beyond the tongue portion position at about 60° to around a position at 180° (alternate long and two short dashes curve illustrated inFIG. 15). This increase and decrease occurs because an effective flow path area of the scroll is decreased due to separation that has occurred in the scroll with the drastic decrease in the flow velocity and the flow velocity is locally increased.

As a result, lowering of efficiency and decrease in a surge margin can possibly occur. That is to say, separation of the fluid in the scroll portion is estimated to occur because as a result of extreme increase in the flow velocity at a winding start portion with a small passage cross-sectional area with generation of the recirculating flow, the velocity of the fluid is drastically decreased toward the downstream side in the circumferential direction from the scroll winding start portion.

With the above-mentioned scroll shape of the compressor disclosed in Patent Literature 1, in a range from the scroll winding start portion to the scroll winding end position, separation can occur with drastic decrease in the velocity and efficiency can be lowered due to mixture of the range with the decreased velocity and the range with the increased velocity.

The present invention has been made in order to solve such problems, and an object thereof is to provide a scroll shape of a compressor and a supercharger that improve efficiency while preventing occurrence of separation of fluid in a scroll portion.

Solution to Problem

To achieve the object described above, a scroll shape according to the present invention is a scroll shape of a compressor that forms into a spiral shape a flow path of fluid discharged from a diffuser provided on a downstream side of the compressor in a fluid flow direction. An increase degree of a ratio A/R is set to be increased in a range from a winding start position to a winding end position of a scroll portion where A is a passage cross-sectional area of the scroll portion and R is a radius from a center of the compressor to a center of a passage cross section of the scroll portion.

The scroll portion is designed such that the passage cross-sectional area is gradually increased from the winding start position to the winding end position and a flow velocity is substantially constant in the circumferential direction at a design flow rate. When the scroll portion operates at a flow rate lower than the designed flow rate, flow recirculating from the winding end position side to the winding start position side of the scroll portion is generated, and the flow velocity is increased on the upstream side and is decreased on the downstream side with increase in the passage cross-sectional area. Then, the flow velocity is drastically decreased on the downstream side relative to the winding start position of the scroll portion, and separation tends to occur in the scroll portion. To cope with this situation, the increase degree of the ratio A/R of the radius R relative to the passage cross-sectional area A is set to be increased in a range from the winding start position to the winding end position of the scroll portion. With this setting, the passage cross-sectional area is decreased to increase the flow velocity on the downstream side relative to the winding start position of the scroll portion. Difference in the flow velocity between the downstream side and the winding start position is therefore decreased, and a decrease rate of the flow velocity is moderated. As a result, the flow velocity is prevented from being drastically decreased on the downstream side relative to the winding start position of the scroll portion. Consequently, separation of the fluid from a wall surface of the scroll portion is prevented, and in particular, efficiency at a small flow-rate operation point can be improved.

In the scroll shape of the compressor according to the present invention, the increase degree of the ratio A/R is a change rate of the ratio A/R, and the change rate of the ratio A/R is set to be increased from the winding start position toward the winding end position of the scroll portion.

In this scroll shape, the change rate of the ratio A/R is set to be increased from the winding start position toward the winding end position of the scroll portion. With this setting, the passage cross-sectional area is decreased to increase the flow velocity on the downstream side relative to the winding start position of the scroll portion. The difference in the flow velocity between the downstream side and the winding start position is therefore decreased, and the decrease rate of the flow velocity is moderated. As a result, the flow velocity is prevented from being drastically decreased on the downstream side relative to the winding start position of the scroll portion, and separation of the fluid from the wall surface of the scroll portion can be prevented.

In the scroll shape of the compressor according to the present invention, in a graph in which a horizontal axis indicates range shift from the winding start position to the winding end position of the scroll portion and a vertical axis indicates the ratio A/R, a line shape of the ratio A/R has a downward convex shape projecting toward a zero side.

With this scroll shape, the flow velocity is prevented from being drastically decreased, and separation of the fluid from the wall surface of the scroll portion can be prevented.

In the scroll shape of the compressor according to the present invention, when an angle at the winding end position of the scroll portion is 0°, the line shape of the ratio A/R has the downward convex shape projecting toward the zero side in at least a range of about 60° to 240° shifted toward a winding start side of the scroll portion.

With this scroll shape, the flow velocity is prevented from being drastically decreased in at least a range on the winding start side of the scroll portion, and separation of the fluid from the wall surface of the scroll portion can be prevented.

In the scroll shape of the compressor according to the present invention, a range with a large increase degree of the ratio A/R and a range with a constant increase degree of the ratio A/R are set in the range from the winding start position to the winding end position of the scroll portion.

With this scroll shape, in the range with the large increase degree of the ratio A/R, the flow velocity is prevented from being drastically decreased and separation of the fluid from the wall surface of the scroll portion can be prevented. On the other hand, in the range with the constant increase degree of the ratio A/R, decrease in the flow velocity is prompted and increase in pressure loss with increase in the flow velocity can be decreased.

In the scroll shape of the compressor according to the present invention, there is no range with a small increase degree of the ratio A/R in the range from the winding start position to the winding end position of the scroll portion.

With this scroll shape, separation of the fluid from the wall surface of the scroll portion due to drastic fluctuation in the flow velocity can be prevented.

In the scroll shape of the compressor according to the present invention, the ratio A/R at the winding start position of the scroll portion is set to be equal to or higher than 20% of the ratio A/R at the winding end position of the scroll portion.

With this scroll shape, the flow velocity is prevented from being drastically decreased by increasing the passage cross-sectional area at the winding start position of the scroll portion, and separation of the fluid from the wall surface of the scroll portion can be prevented.

A scroll shape of a compressor according to the present invention is a scroll shape of a compressor that forms into a spiral shape a flow path of fluid discharged from a diffuser provided on a downstream side of the compressor in a fluid flow direction. A ratio A/R at a winding start position of a scroll portion is set to be equal to or higher than 20% of a ratio A/R at a winding end position of the scroll portion, and a ratio A/R is set to be increased from the winding start position toward the winding end position of the scroll portion where A is a passage cross-sectional area of the scroll portion and R is a radius from a center of the compressor to a center of a passage cross section of the scroll portion.

In this scroll shape, the ratio A/R of the radius R relative to the passage cross-sectional area A at the winding start position of the scroll portion is set to be equal to or higher than 20% of the ratio A/R at the winding end position. With this setting, the passage cross-sectional area at the winding start position of the scroll portion is increased. Difference in the flow velocity between the winding start position and the downstream side relative to the winding start position is therefore decreased, and the decrease rate of the flow velocity is moderated. As a result, the flow velocity is prevented from being drastically decreased on the downstream side relative to the winding start position of the scroll portion. Consequently, separation of the fluid from a wall surface of the scroll portion is prevented, and in particular, efficiency at a small flow-rate operation point can be improved.

In the scroll shape of the compressor according to the present invention, an increase degree of the ratio A/R is set to be constant in the range from the winding start position to the winding end position of the scroll portion.

With this scroll shape, decrease in the flow velocity is prompted, and increase in the pressure loss with increase in the flow velocity can be decreased.

A supercharger according to the present invention includes a housing that has a hollow shape; a rotary shaft that is rotatably supported on the housing; a turbine that is provided on one end portion of the rotary shaft in an axial direction, and a compressor that is provided on another end portion of the rotary shaft in the axial direction. A scroll portion of the compressor in the housing has the scroll shape of the compressor described above.

In the scroll portion of the compressor, the flow velocity is prevented from being drastically decreased on the downstream side relative to the winding start position of the scroll portion, separation of the fluid from the wall surface of the scroll portion is prevented, and in particular, efficiency at a small flow-rate operation point can be improved.

Advantageous Effects of Invention

A scroll shape and a supercharger of the present invention can improve efficiency while preventing occurrence of separation of fluid in a scroll portion.

