Controlled Area Progression Vaned Diffuser

Abstract

A controlled area progression vaned diffuser (CAPVD) for a compressor may be defined by a bearing diffuser wall of a bearing housing and a compressor diffuser wall of a compressor housing that are spaced apart in the axial direction, with a plurality of vanes extending between the diffuser walls and circumferentially spaced about a rotational axis of a compressor wheel. Airflow from the compressor wheel enters the CAPVD through a diffuser inlet, flows between the diffuser walls and past the vanes, and flows out of a diffuser outlet to a volute. The diffuser walls may be shaped so that a width of pinch point between the diffuser inlet and the vanes is less than a width at the vanes, and a width of the diffuser outlet is less than the width at the vanes.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional patent application claiming priority under 35 U.S.C. § 119 (e) to U.S. Provisional Patent No. 63/649,796 filed on May 20, 2024.

TECHNICAL FIELD

The present disclosure relates generally to turbocharger systems for internal combustion engines and, more particularly, to compressors having controlled area progression vaned diffusers configured for efficient operation.

BACKGROUND

Turbochargers are used in numerous applications such as automotive, marine, and aerospace applications. Turbochargers operate by forcing more intake air into a combustion chamber of an internal combustion engine to improve the efficiency and power output of the engine. A turbocharger may generally include a compressor connected to a turbine by an interconnecting shaft. The turbine may extract energy from the flow of exhaust gases to drive the compressor via the interconnecting shaft, while the compressor may increase the pressure of intake air for delivery to the combustion chamber. The compressor may include a radial impeller that accelerates the intake air and expels the air in a radial direction, and a diffuser that slows down the expelled air to cause a pressure rise.

The design of turbocharger compressors is a highly refined art. The shape, curvature, and surface finish of the compressor rotor, compressor housing, and diffuser are designed to produce maximum pressure boost across the desired range of operating conditions. When very high pressure ratios are required, as in the case of large commercial diesel engines, vaned diffusers may be preferred over vaneless diffusers because they provide a higher maximum pressure ratio and increased efficiency, albeit frequently at the cost of a reduced map width, as depicted on a compressor map well known in the art as showing the relationship between pressure ratio and volume or mass flow rate. The vanes of a vaned diffuser define channels into which high velocity gas from the compressor is received, and through which the gas is decelerated in order to convert its kinetic energy into a static pressure. Circumferentially spaced guide vanes provide passages that expand radially in area to diffuse the flow.

While effective, the operating range of turbocharger compressors may be limited to certain mass flow rates and pressure ratios outside of which the compressor may exhibit undesirable choke or surge behavior. In particular, the operating range of a compressor may be characterized by the compressor map of operable mass flow rates and pressure ratios, with right and left boundaries respectively defining the choke and surge lines of the compressor. The choke line defines the maximum mass flow rate of the compressor, and the surge line defines the minimum mass flow rate of the compressor. Compressor surge occurs when the direction of flow through the compressor reverses to relieve pressure at the compressor outlet under low mass flow rate and high pressure ratio conditions. That is, at certain low mass flow rates and high pressure ratios, the flow can no longer adhere to the suction side of the blades, interrupting the discharge process and resulting in a pressure build up at the compressor outlet. The direction of air flow through the compressor may be reversed until a stable pressure ratio is reached, at which point the air flow proceeds in the forward direction again. This flow instability continues within the surge range of the compressor map and produces a noise known as “surging”. Operating the turbocharger in surge for extended periods is undesirable, and may negatively impact the performance of the turbocharger.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a controlled area progression vaned diffuser for a compressor is disclosed. The compressor may include a bearing housing in which a shaft is supported by a bearing to rotate about a rotational axis, a compressor wheel disposed on the shaft and having a compressor radius, and a compressor housing connected to the bearing housing, defining a chamber within which the compressor wheel rotates and a volute for receiving airflow generated by the compressor wheel. The controlled area progression vaned diffuser may include a bearing diffuser wall of the bearing housing having an annular shape and extending from the chamber to the volute, a compressor diffuser wall of the compressor housing having an annular shape and extending from the chamber to the volute, wherein the bearing diffuser wall and the compressor diffuser wall are spaced apart in an axial direction. The controlled area progression vaned diffuser may further include a plurality of vanes extending from the bearing diffuser wall and the compressor diffuser wall and circumferentially spaced about the rotational axis, each vane have a vane leading edge and a vane trailing edge, a diffuser inlet proximate the chamber, and a diffuser outlet proximate the volute, wherein the airflow from the compressor wheel enters the controlled area progression vaned diffuser through the diffuser inlet, between the bearing diffuser wall and the compressor diffuser wall and past the plurality of vanes, and flows out of the diffuser outlet to the volute. The bearing diffuser wall and the compressor diffuser wall may be spaced apart by a vane leading edge width at the vane leading edge, the bearing diffuser wall and the compressor diffuser wall may define a pinch point between the diffuser inlet and the vane leading edge, wherein pinch point has a pinch point width that is less than the vane leading edge width, and diffuser outlet may have a diffuser outlet width that is less than the vane leading edge width.

Additional aspects are defined by the claims of this patent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an engine airflow system including a turbocharger for an internal combustion engine in which a controlled are progression vaned diffuser in accordance with the present disclosure may be implemented;

FIG. 2 is a partial cross-sectional view of a prior art compressor of the turbocharger of the engine airflow system of FIG. 1;

FIG. 3 is a graph of diffuser annulus area versus diffuser radius for diffusers of the compressor of FIG. 2;

FIG. 4 is the partial cross-sectional view of FIG. 2 of the compressor with an embodiment of a controlled area progression vaned diffuser in accordance with the present disclosure; and

FIG. 5 is a compressor map of compressor pressure ratio versus compressor mass flow comparing the vaned diffuser of the compressor of FIG. 2 and the controlled area progression vaned diffuser of the compressor of FIG. 4.

DETAILED DESCRIPTION

The following description of various embodiments is merely illustrative in nature and is in no way intended to limit the scope of the invention, its application or its uses.

As shown in FIG. 1, an engine airflow system 12 may include an internal combustion engine 14 that may have a number of cylinders for the controlled combustion of fuel to produce power. Exhaust gas generated during combustion may exit the engine 14 at an exhaust manifold 16 that may be connected to an exhaust passage 18. The exhaust passage 18 may lead to a turbine 20 of a turbocharger. The exhaust gas may be expanded in the turbine 20 and release energy to rotate a turbine wheel 22. The exhaust gas may continue from the turbine 20 through an exhaust passage 24, an exhaust after treatment device 54 and an exhaust throttle valve 56 to an exhaust discharge 26.

The turbine wheel 22 may be connected to a compressor wheel 28 directly or indirectly by a shaft 30. The compressor wheel 28 may be disposed in a compressor 32. Through the action of routing exhaust gases to rotate the turbine wheel 22, the compressor wheel 28 may be correspondingly rotated by the shaft 30. The rotating compressor wheel 28 may draw air in through an intake passage 34 and compress the air. Compression of the intake air may charge an intake system 36 of the engine 14 through a passage 38, a charge air cooler 40, a passage 42 and intake manifold 44. An intake throttle valve 45 may be provided to selectively throttle the passage 42 when desired, though the intake throttle valve 45 may be omitted in embodiments of the engine airflow system 12.

While controlled area progression vaned diffusers (CAPVDs) according to the present disclosure are illustrated and described herein as being implemented in a turbocharger for an internal combustion engine, those skilled in the art will understand that the CAPVDs may be implemented in any centrifugal compressors used to boost the performance of a power source. For example, the CAPVDs may be implemented in electrically driven boosters that are driven by an electric motor as opposed to a turbine drive by combustion exhaust. Alternatively, CAPVDs may be implemented in fuel cell air supplies for electric vehicles that may or may not include a turbine. Further alternative implementations of CAPVDs according to the present disclosure in centrifugal compressors are contemplated by the inventors. Moreover, while the compressor 32 is described herein as drawing in, compressing and discharging air, compressors in accordance with the present disclosure may be implemented to compress any gas that flows through the process such as, for example, exhaust gas.

An embodiment of a compressor 32 of a turbocharger is illustrated in FIG. 2. The description of the compressor 32 may include references to axial or axially, which is indicated by reference numeral 61 and means a direction along or parallel to a rotational axis A of the shaft 30. The description may further include references to radial or radially, which is indicated by the reference numeral 63 and means a direction toward or away from the rotational axis A of the shaft 30 in any of the 360 degrees around the shaft 30. The shaft 30 may be supported by bearings (not shown) in a bearing housing 60 that may be disposed between the compressor 32 and the turbine 20. The compressor wheel 28 may be disposed in a chamber 62 that may be defined by the bearing housing 60 and a compressor housing 64. The compressor wheel 28 may include a central hub 66 having an annular outer edge 68 and connected to the shaft 30, and a plurality of circumferentially spaced blades 70 having blade tips 72 at their radial ends. A compressor inlet 74 to the chamber 62 may be defined by the compressor housing 64 through which air may be drawn by the compressor wheel 28. Air may be delivered from the compressor wheel 28 through a diffuser 80 and may be collected in a volute 82 for communication to the passage 38 via a compressor outlet (not shown). The diffuser 80 may be defined between the bearing housing 60 at a bearing diffuser wall 84, and the compressor housing 64 at a compressor diffuser wall 86. A plurality of circumferentially spaced vanes 88 as known in the art may extend between the diffuser walls 84, 86 to define channels through which high velocity gas flows and is decelerated. The diffuser 80 may form an annular passage extending radially outward from the chamber 62 proximate the blade tips 70 to the volute 82. Air drawn in through the compressor inlet 74 may be acted upon in the chamber 62 by the blades 68 of the compressor wheel 28 and delivered through the diffuser 80 to the volute 82.

The flow of air leaving the compressor wheel tip 72 enters the adjacent segment of the diffuser 80 which may be referred to as a diffuser inlet 90, and exits the diffuser 80 to the volute 82 at a diffuser outlet 92. The diffuser inlet 90 is a segment of the diffuser 80 closest to the compressor wheel 28, which also has the highest gas flow velocity since the annulus area A_D of the diffuser 80 is smaller radially inward, and becomes greater moving radially outward. The annulus area A_D of the diffuser 80 at a given radial distance r_D from the axis A of the compressor wheel 28 may be determined by the following equation:

$\begin{array}{cc}{A}_D=2\pi r_D*w_D& \left(1\right)\end{array}$

where w_D is a width of the diffuser 80 at a given radial distance r_D. In the compressor 32 of FIG. 2, the diffuser 80 has a conventional design wherein the diffuser walls 84, 86 are parallel and the diffuser width wp is constant as the diffuser 80 extends radially from the diffuser inlet 90 to the outlet to the volute 82. Each of the vanes 88 may start at a vane leading edge (VLE) 94 proximate the diffuser inlet 90 and extend through the diffuser 80 to a vane trailing edge (VTE) 96 proximate the diffuser outlet 92 and the volute 82.

FIG. 3 presents a graph 100 representing the diffuser annulus area A_D versus the diffuser radius r_D of vaned diffusers. A line 102 represents an area progression of the vaned diffuser 80 of the conventional compressor 32 as the diffuser radius r_D increases. Initially, the diffuser width w_D and the corresponding diffuser annulus area A_D may decrease from the outer edge 68 of the compressor wheel hub 66 as the compressor housing 64 converges toward the compressor blade tips 72 and the bearing housing 60 until reaching the diffuser inlet 90. After the diffuser inlet 90, the diffuser width w_D remains constant and the diffuser walls 84, 86 remain parallel as the diffuser radius r_D increases and the diffuser annulus area A_D increases linearly until the diffuser 80 intersects with the volute 82 at the diffuser outlet 92. While the compressor 32 is illustrated and described as having the diffuser inlet 90 radially outward from the outer edge 68 of the hub 66 and proximate the blade tips 72, the diffuser inlet 90 may be defined at any position proximate the compressor wheel 28 that is relevant to a particular implementation of the diffuser 80. Regardless of the defined location of the diffuser inlet 90, the diffuser walls 84, 86 are parallel with a fixed diffuser width w_D from the diffuser inlet 90 to the diffuser outlet 92 in conventional compressors 32.

In the present embodiments, the area progression is controlled by varying the diffuser width w_D as the diffuser extends from the diffuser inlet 90 to the volute 82. FIG. 4 illustrates an embodiment of the compressor 32 wherein a CAPVD 110 has a varying diffuser width created by a compressor diffuser wall 112 that is contoured relative to the bearing diffuser wall 84. The outer edge 68 of the compressor hub 66 defines a compressor radius r_C from the rotational axis A, and a diffuser inlet 116 may be defined at a diffuser inlet radius r_DI that is approximately equal to a radial distance to the blade tips 70. The diffuser inlet 116 may have a diffuser inlet width w_DI between the corresponding portions of the diffuser walls 84, 112. As the CAPVD 110 extends radially outward from the diffuser inlet 116, a first compressor diffuser wall portion 118 may be angled toward the bearing diffuser wall 84 so that the width of the CAPVD 110 decreases until the compressor diffuser wall 112 reaches a first transition or pinch point 120 at a pinch point radius r_PP and a pinch point width w_PP. Radially beyond the pinch point 120, a second compressor diffuser wall portion 122 is angled away from the bearing diffuser wall 84 so that the width of the CAPVD 110 increases until the compressor diffuser wall 112 reaches a second transition point 124 at a second transition point radius r_2TP with the diffuser width w_D. The VLEs 94 of the vanes 88 may be located at a VLE radius r_VLE that may be equal to the second transition point radius r_2TP as shown, or may be greater than the second transition point radius r_2TP in alternative implementations.

Radially beyond the second transition point 124, a third compressor diffuser wall portion 126 may be parallel to the bearing diffuser wall 84 to maintain the diffuser width w_D for at least the radial length of the vanes 88 to a VTE radius r_VTE. In some embodiments, the compressor diffuser wall 112 may continue to extend beyond the VTEs 96 parallel to the bearing diffuser wall 84 to the diffuser outlet 92. In the illustrated embodiment, however, radially beyond a third transition point 128 at a third transition point radius r_3TP, a fourth compressor diffuser wall portion 130 may be angled toward the bearing diffuser wall 84 so that the width of the CAPVD 110 decreases until the compressor diffuser wall 112 reaches a diffuser outlet 132 at a diffuser outlet radius r_DO with a diffuser outlet width w_DO. The third transition point radius r_3TP may be equal to the VTE radius r_VTE as shown, or greater than the VTE radius r_VTE such that the third transition point 128 is radially outward of the VTEs 96.

Referring back to FIG. 3, a line 140 represents the annulus area progression of the diffuser 110. As with the line 140 for the conventional vaned diffuser 80, the annulus area A_D may decrease from the outer edge 68 of the compressor wheel hub 66 as the compressor housing 64 converges toward the compressor blade tips 72 and the bearing housing 60 until reaching the diffuser inlet 116. From the diffuser inlet 116 to the pinch point 120, the annulus area A_D increases at a low rate as the first compressor diffusor portion 118 extends radially as the decreasing diffuser width offsets the increasing radial dimension in Equation (1). After the pinch point 120, the annulus area A_D increases at a greater rate as both the radius and the diffuser width increase until the second transition point 124 proximate the VLE 94. From the second transition point 124 to the third transition point 128, the annulus area A_D increases at a lower rate that may be approximately a linear rate as the radius increases and the diffuser width is constant. After the third transition point 128, the annulus area A_D may decrease as shown when the decrease in the diffuser width offsets the increase in the radius as the diffuser 110 extends to the diffuser outlet 132.

Those skilled in the art will understand that the shape of the line 140 may change for particular designs of the diffuser 110 as the radial positions of the diffuser inlet 116, VLE 94, VTE 96, points 120, 124, 128 and diffuser outlet 132 and the various widths are tuned to achieve desired performance characteristics for the design and for the turbochargers or other devices in which compressors 32 with the diffuser 110 in accordance with the present disclosure are implemented. Table 1 below provides a summary of the parameters discussed above that are relevant to the design of the diffuser 110:

TABLE 1
		Example Scaled
Parameter	Value Range	Value
compressor radius (rC)	N/A	1.0	rC
diffuser inlet width (wDI)	0.08-0.14 * rC	0.11	rC
diffuser width (wD)	0.7-1.2 * wDI	1.16	wDI
diffuser outlet radius (rDO)	1.65-2.00 * rC	1.94	rC
diffuser outlet width (wDO)	0.7-1.2 * wDI	0.84	wDI
pinch point radius (rPP)	1.05-1.3 * rC	1.125	rC
pinch point width (wPP)	0.6-1.0 * wDI	0.86	wDI
VLE radius (rVLE)	1.1-1.4 * rC	1.29	rC
VLE width (wVLE)	1.0 * wD	1.0	wD
VTE radius (rVTE)	1.3-1.7 * rC	1.56	rC
VTE width (wVTE)	1.0 * wD	1.0	wD

The first column of Table 1 lists the parameters illustrated in FIG. 3 and discussed in the accompanying text, and the second column provides approximate value ranges for each parameter that may provide guidance in designing the diffuser 110 for a particular application. The value ranges for the parameters may be derived from the compressor 32 in which the diffuser 110 is implemented. For example, the value of the diffuser inlet width w_DI may be derived from the compressor radius r_C of the compressor wheel 28 and be within a range of 0.08-0.14 times the compressor radius r_C. Other values may then be derived from the compressor radius r_C or the diffuser inlet width w_DI. An exemplary design of the diffuser 110 may have the scaled values shown in the third column that indicate that the parameter values in the exemplary design fall within the values ranges of the respective parameters.

The parameter value ranges of the example design in Table 1 are also exemplary for the CAPVD 110 in accordance with the present disclosure. For example, the value ranges and scaled values of Table 1 show the VLE width w_VLE and the VTE width w_VTE being equal to the diffuser width wD and, consequently, equal to each other such that the diffuser walls 84, 112 are parallel from the VLE 94 to the VTE 96. In alternative embodiments, the VLE width w_VLE may be greater than or less than the VTE width w_VTE such that the portion of the CAPVD 110 from the VLE 94 to the VTE 96 is tapered. Further alternative geometries for CAPVDs 110 in accordance with the present disclosure are contemplated.

INDUSTRIAL APPLICABILITY

The CAPVD 110 may provide improved efficiencies over conventional vaned diffusers such as the diffuser 80. FIG. 5 presents a compressor map 140 of a compressor pressure ratio (outlet pressure over inlet pressure) versus compressor mass flow. The compressor map 140 represents a comparison of simulation data for the operation of the compressor 32 with the baseline vaned diffuser 80 of FIG. 2 and the controlled area progression vaned diffuser 110 of FIG. 4 having the exemplary parameter values set forth in Table 1. In the compressor map 140, a choke line 142 defines a maximum compressor mass flow rate of the compressor 32 with the diffuser 80 above which the high flow rate and low compressor pressure ratio may cause the compressor 32 to choke. A surge line 144 for the diffuser 80 may define the minimum compressor mass flow rate below which the discharge process may be interrupted. Lines 146 may represent combinations of compressor pressure ratios and corresponding compressor mass flows for various rotational speeds of the compressor wheel 28.

The data for the diffuser 110 includes a choke line 152 to the left of the choke line 142 in this comparison, a surge line 154 and constant compressor rotational speed lines 156. As shown by the data, the surge line 154 for the diffuser 110 is shifted to the left from the surge line 144 of the diffuser 80 indicating that diffuser 110 will allow the compressor 32 to operate at lower compressor mass flow rates without encountering surging. The area between the surge lines 144, 154 represents operating conditions where the geometry of the diffuser 110 is having a meaningful effect to suppress the surge mechanism.

The data further shows that improvements in efficiencies can be achieved by controlled area progression vaned diffusers in accordance with the present disclosure. As shown in the compressor map 140, improvements in efficiency may be achieved with the diffuser 110 in both choke and surge. The greatest efficiency gains may be realized proximate the choke lines 142, 152 and the surge lines 144, 154 of the compressor map 140.

Controlled area progression vaned diffusers in accordance with the present disclosure may allow compressors of turbochargers to operate more efficiently at low compressor mass flows, and reduce the occurrences of surging during low mass flow conditions. By shaping the compressor diffuser wall 112 to vary the diffuser width wp and control the annulus area progression of the diffuser 110, separation of air from the diffuser walls 84, 112 at low mass flows can be suppressed and the amount of separation may be reduced to reduce drag within the diffuser 110 and maintain efficiency of the compressor 32 under such conditions. Controlled area progression allows controlled pressure in the diffuser 110 that leads to suppression of separation and instability in the diffuser 110, which can improve efficiency.

Previously known diffusers 80 provided two variables for controlling their performance within the compressor 32: the diffuser width w_D and the radial length of the diffuser 80. Controlled area progression vaned diffusers 110 in accordance with the present disclosure provide greater flexibility in tuning the diffuser to improved the efficiency of compressors 32 by contouring the shape of the compressor diffuser wall 112. Contouring of the compressor diffuser wall 112 facilitates reducing annulus area A_D in zones where the diffuser flow is unstable and tends to separate. Conversely, the annulus area A_D may be increased where the diffuser flow is stabilized by the vanes to reduce flow speeds and friction losses. More stable flow through the diffuser 110 can result in greater efficiency, and the increased efficiency may be achieved while maintaining or expanding the width of the compressor map 140.

In previously known vaned diffusers, such as the vaned diffuser 80, the VLE 94 is typically located at approximately 1.1-1.2*r_C due to the belief that positioning the vanes 88 proximate the compressor wheel 28 achieves optimum efficiency. In contrast, the VLE 94 in the present design of the vaned diffuser 110 can be positioned in the range from 1.3-1.4 r_C due to the pinch point 120 stabilizing the fluid flow proximate the diffuser inlet 90. With the vanes 88 positioned further from the compressor wheel 28, efficiency may be maintained while potentially reducing vibration and high cycle fatigue (HCF) on the compressor blades 70.

While the preceding text sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of protection is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the scope of protection.

It should also be understood that, unless a term was expressly defined herein, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to herein in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term be limited, by implication or otherwise, to that single meaning.

Claims

1. A controlled area progression vaned diffuser (CAPVD) for a compressor, wherein the compressor includes a bearing housing in which a shaft is supported by a bearing to rotate about a rotational axis, a compressor wheel disposed on the shaft and having a compressor radius, and a compressor housing connected to the bearing housing, defining a chamber within which the compressor wheel rotates and a volute for receiving airflow generated by the compressor wheel, the CAPVD comprising:

a bearing diffuser wall of the bearing housing having an annular shape and extending from the chamber to the volute;

a compressor diffuser wall of the compressor housing having an annular shape and extending from the chamber to the volute, wherein the bearing diffuser wall and the compressor diffuser wall are spaced apart in an axial direction;

a plurality of vanes extending from the bearing diffuser wall and the compressor diffuser wall and circumferentially spaced about the rotational axis, each vane have a vane leading edge and a vane trailing edge;

a diffuser inlet proximate the chamber; and

a diffuser outlet proximate the volute, wherein the airflow from the compressor wheel enters the CAPVD through the diffuser inlet, between the bearing diffuser wall and the compressor diffuser wall and past the plurality of vanes, and flows out of the diffuser outlet to the volute,

wherein the bearing diffuser wall and the compressor diffuser wall are spaced apart by a vane leading edge width at the vane leading edge,

wherein the bearing diffuser wall and the compressor diffuser wall define a pinch point between the diffuser inlet and the vane leading edge, wherein pinch point has a pinch point width that is less than the vane leading edge width, and

wherein the diffuser outlet has a diffuser outlet width that is less than the vane leading edge width.

2. The CAPVD of claim 1, wherein a diffuser inlet width at the diffuser inlet is greater than the pinch point width.

3. The CAPVD of claim 2, wherein the diffuser inlet width is with a range from 0.04 to 0.07 times the compressor radius.

4. The CAPVD of claim 2, wherein the diffuser inlet width is less than the vane leading edge width.

5. The CAPVD of claim 2, wherein the vane leading edge width is within a range from 0.7 to 1.2 times the diffuser inlet width.

6. The CAPVD of claim 2, wherein the diffuser outlet width is within a range from 0.7 to 1.2 times the diffuser inlet width.

7. The CAPVD of claim 2, wherein the pinch point width is within a range from 0.6 to 1.0 times the diffuser inlet width.

8. The CAPVD of claim 1, wherein a diffuser outlet radius from the rotational axis to the diffuser outlet is within a range from 1.45 to 2.0 times the compressor radius.

9. The CAPVD of claim 1, wherein a pinch point radius from the rotational axis to the pinch point is within a range from 1.05 to 1.3 times the compressor radius.

10. The CAPVD of claim 1, wherein a vane leading edge radius from the rotational axis to the vane leading edge is within a range from 1.1 to 1.4 times the compressor radius.

11. The CAPVD of claim 1, wherein the vane leading edge radius is within a range from 1.3 to 1.4 times the compressor radius.

12. The CAPVD of claim 1, wherein a vane trailing edge radius from the rotational axis to the vane trailing edge is within a range from 1.3 to 1.7 times the compressor radius.

13. The CAPVD of claim 1, wherein the bearing diffuser wall and the compressor diffuser wall are spaced apart by a vane trailing edge width at the vane trailing edge, and wherein the vane trailing edge width is equal to the vane leading edge width.

14. The CAPVD of claim 1, wherein an axial distance between the bearing diffuser wall and the compressor diffuser wall decreases at a constant rate from the diffuser inlet to the pinch point.

15. The CAPVD of claim 1, wherein an axial distance between the bearing diffuser wall and the compressor diffuser wall increases at a constant rate from the pinch point to the vane leading edge.

16. The CAPVD of claim 1, wherein an axial distance between the bearing diffuser wall and the compressor diffuser wall decreases at a constant rate from the vane trailing edge to the diffuser outlet.