Patent Application
20220178377
The present disclosure relates to a centrifugal compressor and a turbocharger.
In recent years, for widening the operating range and improving efficiency at the operating point on the low flow rate side (near the surge point) of a centrifugal compressor, it has been proposed to install a throttle mechanism (inlet variable mechanism) at the inlet pipe portion of the centrifugal compressor, as described in Patent Document 1, for example.
At the low flow rate operating point of the centrifugal compressor, backflow tends to occur on the tip side of the impeller blades. The throttle mechanism described in Patent Document 1 has an annular portion disposed in the intake passage to suppress the backflow, and reduces the flow passage area of the intake passage by blocking an outer peripheral portion of the intake passage corresponding to the tip side of the impeller blades. When the flow passage area of the intake passage is reduced, although the peak efficiency is reduced due to the reduced area, it is possible to reduce the surge flow rate and improve the efficiency near the surge point. In other words, by performing a variable control to increase the flow passage area of the intake passage during operation on the high flow rate side and to reduce the flow passage area of the intake passage during operation on the low flow rate side, it is possible to achieve wide range and improved efficiency at the operating point on the low flow rate side. This indicates that the impeller blade height is lowered (trimmed) to be adapted to the low flow rate operating point artificially, which is called variable inlet compressor (VIC) or variable trim compressor (VTC).
Patent Document 1: U.S. Pat. No. 9,777,640B
When a throttle mechanism is installed at the inlet pipe portion of a centrifugal compressor, the efficiency improvement amount at the low flow rate operating point depends on specific conditions such as the throttle position of the intake passage and the flow passage area at the throttle position. However, Patent Document 1 does not disclose any knowledge on how to set the specific conditions to improve efficiency at the low flow rate operating point.
In view of the above, an object of at least one embodiment of the present invention is to provide a centrifugal compressor that can improve the efficiency at the low flow rate operating point, and a turbocharger including the same.
(1) A centrifugal compressor according to at least one embodiment of the present invention comprises: an impeller; an inlet pipe portion forming an intake passage to introduce air to the impeller; and a throttle mechanism capable of reducing a flow passage area of the intake passage upstream of the impeller. When PA is a throttle position where the throttle mechanism minimizes the flow passage area of the intake passage, PB is a tip position of a leading edge of a blade of the impeller, L is a distance between the throttle position PA and the tip position PB of the leading edge in an axial direction of the impeller, and D is a diameter of the impeller at the tip position PB of the leading edge, the distance L and the diameter D satisfy L/D≤0.2.
According to the inventor's knowledge, the smaller the ratio L/D in the above (1), the more it is possible to suppress the development of backflow at the tip side of the blade of the impeller at the low flow rate operating point, and the higher efficiency can be achieved at the low flow rate operating point. In particular, when L/D≤0.2 is satisfied, the efficiency at the low flow rate operating point can be significantly improved.
(2) In some embodiments, in the centrifugal compressor described in the above (1), the distance L and the diameter D satisfy L/D≤0.1.
With the above configuration (2), it is possible to achieve a higher efficiency at the low flow rate operating point.
(3) In some embodiments, in the centrifugal compressor described in the above (1) or (2), when A1 is an area of a circle having the diameter D, and A2 is a minimum flow passage area of the intake passage at the throttle position PA, the area A1 and the area A2 satisfy 0.55<A2/A1<0.65.
When the flow passage area of the intake passage is constricted by the throttle mechanism, the efficiency at the low flow rate operating point can be improved, but the efficiency at the high flow rate operating point tends to decrease. Accordingly, if the flow passage area of the intake passage is excessively constricted by the throttle mechanism, the performance characteristics are likely to rapidly change and become difficult to control. Thus, there is an appropriate range in the constriction amount of the flow passage area by the throttle mechanism.
According to the inventor's knowledge, A2/A1 such that the efficiency at the low flow rate operating point is maximum exists in the range satisfying 0.55<A2/A1<0.65, and the peak efficiency drops steeply in the region where A2/A1 is smaller than 0.55. Therefore, by setting A2/A1 to satisfy 0.55<A2/A1<0.65 as described in the above (3), it is possible to achieve a high efficiency at the low flow rate operating point and suppress the decrease in peak efficiency.
(4) A centrifugal compressor according to at least one embodiment of the present invention comprises: an impeller; an inlet pipe portion forming an intake passage to introduce air to the impeller; and a throttle mechanism capable of reducing a flow passage area of the intake passage. When D is a diameter of the impeller at a tip position of a leading edge of a blade of the impeller, A1 is an area of a circle having the diameter D, PA is a throttle position where the throttle mechanism minimizes the flow passage area of the intake passage, and A2 is a minimum flow passage area of the intake passage at the throttle position PA, the area A1 and the area A2 satisfy 0.55<A2/A1<0.65.
When the flow passage area of the intake passage is constricted by the throttle mechanism, the efficiency at the low flow rate operating point can be improved, but the efficiency at the high flow rate operating point tends to decrease. Accordingly, if the flow passage area of the intake passage is excessively constricted by the throttle mechanism, the performance characteristics are likely to rapidly change and become difficult to control. Thus, there is an appropriate range in the constriction amount of the flow passage area by the throttle mechanism.
According to the inventor's knowledge, A2/A1 such that the efficiency at the low flow rate operating point is maximum exists in the range satisfying 0.55<A2/A1<0.65, and the peak efficiency drops steeply in the region where A2/A1 is smaller than 0.55. Therefore, by setting A2/A1 to satisfy 0.55<A2/A1<0.65 as described in the above (4), it is possible to achieve a high efficiency at the low flow rate operating point and suppress the decrease in peak efficiency.
(5) In some embodiments, in the centrifugal compressor described in the above (3) or (4), the area A1 and the area A2 satisfy 0.58<A2/A1<0.62.
With the above configuration (5), it is possible to achieve a higher efficiency at the low flow rate operating point and suppress the decrease in peak efficiency.
(6) In some embodiments, in the centrifugal compressor described in any one of the above (1) to (5), the throttle mechanism includes an annular portion disposed in the intake passage. The annular portion is configured to move between a first position and a second position upstream of the first position in the axial direction of the impeller.
With the centrifugal compressor described in the above (6), the constriction amount of the flow passage area of the intake passage can be adjusted by moving the annular portion along the axial direction.
(7) In some embodiments, in the centrifugal compressor described in the above (6), in a cross-section along a rotational axis of the impeller, a straight line connecting a leading edge and a trailing edge of the annular portion is inclined inward in a radial direction of the impeller as going downstream in the axial direction.
In order to increase the effect of efficiency improvement at the low flow rate operating point by the throttle mechanism, it is desirable to secure a certain constriction amount of the flow passage area of the intake passage. If the constriction amount by the throttle mechanism is increased by simply increasing the thickness of the annular portion (thickness in the direction perpendicular to the straight line connecting the leading edge and the trailing edge of the annular portion), the pressure loss when air passes through the annular portion increases as the thickness of the annular portion increases.
On the other hand, as shown in the above (7), when the straight line connecting the leading edge and the trailing edge of the annular portion is inclined inward in the radial direction as it goes downstream in the axial direction, the constriction amount by the throttle mechanism can be increased while suppressing the increase in thickness of the annular portion. Accordingly, it is possible to efficiently increase the efficiency at the low flow rate operating point while suppressing the increase in pressure loss due to the thickness of the annular portion.
(8) In some embodiments, in the centrifugal compressor described in the above (7), an inner peripheral surface of the inlet pipe portion includes an inclined surface that is inclined such that an inner diameter of the inlet pipe portion increases downstream in the axial direction. In a cross-section along the rotational axis of the impeller, an angle between the straight line and the axial direction is smaller than an angle between the inclined surface and the axial direction.
When the annular portion is in the second position, since the annular portion is separated from the inclined surface of the inlet pipe portion inward in the radial direction, the angle between the streamline near the annular portion and the axial direction is smaller than the angle between the inclined surface and the axial direction. Therefore, when the angle between the straight line connecting the leading edge and the trailing edge of the annular portion and the axial direction is smaller than the angle between the inclined surface and the axial direction as described above, the air can smoothly flow along the annular portion, and the pressure loss due to the annular portion can be effectively reduced.
(9) A turbocharger according to at least one embodiment of the present invention comprises a centrifugal compressor described in any one of the above (1) to (8).
With the centrifugal compressor described in the above (9), since the centrifugal compressor described in any one of the above (1) to (8) is included, it is possible to achieve a high efficiency at the low flow rate operating point.
At least one embodiment of the present invention provides a centrifugal compressor that can improve the efficiency at the low flow rate operating point, and a turbocharger including the same.
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions, and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.
For instance, an expression of relative or absolute arrangement such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “centered”, “concentric” and “coaxial” shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function.
For instance, an expression of an equal state such as “same” “equal” and “uniform” shall not be construed as indicating only the state in which the feature is strictly equal, but also includes a state in which there is a tolerance or a difference that can still achieve the same function.
Further, for instance, an expression of a shape such as a rectangular shape or a cylindrical shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved.
On the other hand, an expression such as “comprise”, “include”, “have”, “contain” and “constitute” are not intended to be exclusive of other components.
As shown in
Hereinafter, the axial direction of the impeller 8 is referred to as merely “axial direction”, and the radial direction of the impeller 8 is referred to as merely “radial direction”, and the circumferential direction of the impeller 8 is referred to as merely “circumferential direction”.
The centrifugal compressor 4 includes a throttle mechanism 28 (inlet variable mechanism) capable of reducing the flow passage area of the intake passage 24 upstream of the impeller 8 in the axial direction. The throttle mechanism 28 includes an annular portion 30 (movable portion) disposed in the intake passage 24 concentrically with the impeller 8.
In the illustrated exemplary embodiment, the annular portion 30 is configured to be movable along the axial direction between a first position P1 (see
An inner peripheral surface 40 of the inlet pipe portion 26 includes an inclined surface 42 that is inclined such that the inner diameter of the inlet pipe portion 26 increases upstream in the axial direction in order to suppress the increase in pressure loss due to the annular portion 30. In the illustrated exemplary embodiment, the inclined surface 42 is linearly shaped in a cross-section along the rotational axis of the impeller 8.
An outer peripheral surface 44 of the annular portion 30 is disposed so as to face the inclined surface 42. When the annular portion 30 is in the second position P2, the outer peripheral surface 44 of the annular portion 30 is separated from the inclined surface 42. As the annular portion 30 moves downstream in the axial direction from the second position P2, the distance between the outer peripheral surface 44 of the annular portion 30 and the inclined surface 42 decreases. The annular portion 30 is configured to come into contact with the inclined surface 42 when it is in the first position P1 to block an outer peripheral portion 38 of the intake passage 24 corresponding to a tip portion 36 of a blade 32 of the impeller 8 (a radially outer end portion of the blade 32). The annular portion 30 faces a leading edge 34 of the tip portion 36 of the blade 32 of the impeller 8 in the axial direction when it is in the first position P1. In other words, in an axial view, the annular portion 30 and the tip portion 36 at least partially overlap.
Thus, the annular portion 30 reduces the flow passage area of the intake passage 24 of the impeller 8 by blocking the outer peripheral portion 38 of the intake passage 24 corresponding to the tip portion 36 of the blade 32 of the impeller 8. As a result, although the peak efficiency is reduced due to the reduced flow passage area, it is possible to reduce the surge flow rate and improve the efficiency near the surge point. In other words, by adjusting the throttle mechanism 28 so that the annular portion 30 is in the first position P1 at the low flow rate operating point (operating point near the surge point) and the annular portion 30 is in the second position P2 at the high flow rate operating point (for example, during rated operation) where the flow rate is higher than the low flow rate operating point, the efficiency of the low flow rate operating point can be improved, and the operating range of the centrifugal compressor 4 can be expanded.
Here, as shown in
When A1 is an area of a circle having the diameter D (=D2*π/4), and A2 is a minimum flow passage area of the intake passage 24 constricted by the throttle mechanism 28 at the throttle position PA, the area A1 and the area A2 satisfy 0.55<A2/A1<0.65. More preferably, the area A1 and the area A2 satisfy 0.58<A2/A1<0.62.
In the throttle mechanism 28, the outer peripheral portion 38 of the intake passage 24 is blocked in order to suppress the development of backflow that occurs at the tip side of the blade 32 during operation at the low flow side operating point. Accordingly, as shown in
Meanwhile, when the flow passage area of the intake passage 24 is constricted by the throttle mechanism 28, the efficiency at the low flow rate operating point can be improved, but the efficiency at the high flow rate operating point tends to decrease. Accordingly, if the flow passage area of the intake passage 24 is excessively constricted by the throttle mechanism 28, the performance characteristics are likely to rapidly change and become difficult to control. Thus, there is an appropriate range in the constriction amount of the flow passage area by the throttle mechanism 28.
The inventor's analysis revealed that, as shown in
In some embodiments, for example as shown in
In order to increase the effect of efficiency improvement at the low flow rate operating point by the throttle mechanism 28, it is desirable to secure a certain constriction amount of the flow passage area of the intake passage 24. Here, as shown in
On the other hand, in the embodiment shown in
Further, as shown in
When the annular portion 30 is in the second position P2, since the annular portion 30 is separated from the inclined surface 42 inward in the radial direction, the angle between the streamline near the annular portion 30 and the axial direction is smaller than the angle θ1 between the inclined surface 42 and the axial direction. Therefore, when the angle θ2 is smaller than the angle θ1 as described above, the air can smoothly flow along the annular portion 30, and the pressure loss due to the annular portion 30 can be effectively reduced.
The present invention is not limited to the embodiments described above, but includes modifications to the embodiments described above, and embodiments composed of combinations of those embodiments.
For example, in the above-described embodiments, the throttle mechanism 28 reduces the flow passage area of the intake passage 24 upstream of the impeller 8 by moving the annular portion 30 along the axial direction from the second position P2 to the first position P1.
However, the configuration of the throttle mechanism 28 is not limited to the above-described embodiments. For example as shown in
Alternatively, for example as shown in
As described above, the configuration of the throttle mechanism 28 is not limited, and any method other than those described above can be adapted. In any case, as in the embodiment shown in
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/011532 | 3/19/2019 | WO | 00 |
