Die cast compressor housing for centrifugal compressors with a true volute shape

A die cast compressor housing includes an outer shell having a partial outer circumferencial volute wall portion and a projection surrounding the circumference of an aperture in the shell that mates with an insert having a first portion with a substantially cylindrical outer wall that is received in the aperture in the outer shell and includes an air inlet. The insert has a second portion extending radially outwardly and including a mating projection for engagement with the outer shell projection to form an inner circumferencial volute wall portion. A backplate has a third projection adjacent its outer circumference that is received in a relief in the outer shell and completes the outer circumferncial volute wall portion. The outer shell projection has a first land engaging a second land on the mating projection, the first and second lands spirally descending relative to a datum and the relief has a third land in spaced relation to a fourth land on the third projection, the third and fourth lands spirally descending respectively relative to the datum.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates generally to cast compressor housings for
 centrifugal compressors. More particularly, the invention provides a die
 casting and method for providing a housing having a true volute shape for
 the compressor outlet.
 2. Description of the Related Art
 Housings for radial compressors are typically cast aluminum parts which are
 manufactured using a sand cast or p-mold technique due to the volute shape
 required in the compressor outlet duct for aerodynamic performance.
 Previously, the use of die casting was not employed because a true volute
 shape for the outlet duct could not be achieved, which penalized
 aerodynamic performance.
 Die casting is a very desirable process for volume production due to the
 inherent dimensional stability and reproducibility for cast parts as well
 as the material properties achieved by die cast aluminum. Finer tolerances
 and net shape requirements are more easily obtained with die casting as
 opposed to alternate techniques. Die casting additionally provides much
 higher production volume capability compared to the other casting
 processes. It is, therefore, desirable to provide a die cast compressor
 housing having a true volute shape in the outlet duct
 SUMMARY OF THE INVENTION
 The present invention provides a die cast compressor housing that includes
 an outer shell having a partial outer circumferencial volute wall portion
 and a projection surrounding the circumference of an aperture in the
 shell. An insert having a first portion with a substantially cylindrical
 outer wall is received in the aperture in the outer shell and includes an
 air inlet. The insert has a second portion extending radially outwardly
 and including a mating projection for engagement with the outer shell
 projection to form an inner circumferencial volute wall portion. A
 backplate has a third projection adjacent its outer circumference that is
 received in a relief in the outer shell and completes the outer
 circumferncial volute wall portion. The outer shell projection has a first
 land engaging a second land on the mating projection, the first and second
 lands spirally descending relative to a datum and the relief has a third
 land in spaced relation to a fourth land on the third projection, the
 third and fourth lands spirally descending relative to the datum.

DETAILED DESCRIPTION OF THE INVENTION
 Referring to the drawings, FIG. 1 shows a radial compressor housing
 incorporating the present invention. The compressor includes a housing
 outer shell 10, inlet and diffuser wall insert 12 and the backplate 14.
 The outlet connection 16 from the compressor housing is attached to the
 engine intake manifold or other device receiving the compressed air. Air
 for compression enters through an inlet 18, best seen in FIG. 2.
 In addition to the air inlet, the insert 12 includes a first portion
 providing an inducer wall 20 adjacent the compressor impeller (not shown)
 which rotates around an axis A. A second portion of the insert provides a
 radially extending surface substantially perpendicular to the axis of
 rotation of the impeller to form a diffuser outer wall 24. The second
 portion also forms a volute inner wall portion 26 and extends in a first
 mating projection 28 for a portion of the inner circumferencial wall of
 the volute. The first portion of the insert, which has a substantially
 cylindrical shape with a stepped outer surface is received in a central
 aperture 30 in the housing outer shell with an interference fit, in the
 embodiment shown, to retain the insert position relative to the backplate,
 which will be described in greater detail subsequently. The aperture is
 concentric with the axis of rotation for alignment of the housing.
 The outer shell provides an outer wall 32 for the volute and incorporates a
 second mating projection 34 adjacent and surrounding the aperture that
 receives the insert, the second mating projection engaging the first
 mating projection to form the remainder of the inner circumferencial wall
 portion of the volute.
 The backplate includes a diffuser inner wall 36 and incorporates a third
 mating projection 38 that constitutes a portion of the outer
 circumferencial wall portion of the volute. The third mating projection is
 received in a relief 40 in the outer shell. For the embodiment shown in
 the drawings, the peripheral portion 42 of the outer shell engages the
 peripheral portion 44 of the backplate at a plane defined by numeral 45
 and is secured by bolts (not shown) or other attachment means (i.e.,
 v-band clamp, adhesives, etc.) received in mating apertures 46 and 48 of
 flange tangs 50 and 52 as best seen in FIG. 1 or 3. Returning to FIG. 2,
 the mating surfaces of the peripheral portions of the outer shell and
 backplate are machined. The peripheral portion 42 of the outer shell
 includes a chamfer 54 adjacent a groove 56 in the backplate that engage an
 o-ring or metallic seal 58. An aperture 60 accommodates a shaft attaching
 the compressor impeller (not shown) to its motoring device such as a
 turbocharger turbine or mechanical/electrical drive. For the embodiment
 shown in the drawings, the backplate includes a sealing land 64 and bolt
 attachment tangs 66, as best seen in FIG. 1, for attachment of the
 compressor housing to a turbocharger center housing.
 The complete volute is formed by the integrated assembly of the outer
 shell, insert and backplate. Viewing as exemplary the lower portion of
 FIG. 2, beginning at the left and moving clockwise, the third projection
 on the backplate and the outer shell adjacent the relief form the
 circumferencial outer portion of the volute wall, the outer shell itself
 forms the outer portion of the wall, the first projection on the outer
 shell and the mating projection on the insert form the inner
 circumferencial portion of the wall and, finally, the continuation of the
 second portion of the insert forms the inner portion of the wall.
 Referring again to FIG. 2, the first and second projections terminate in
 mating lands 70 and 72 which are spirally ascending relative to a datum,
 which for the embodiment shown is the plane of engagement 45 between the
 outer shell and backplate. Similarly, the third projection and relief in
 the outer shell terminate in lands 74 and 76 that are spirally descending
 relative to the datum. The dimensions of lands 70, 72, 74, and 76 for the
 first projection 28, second projection 34 and third projections 38 and the
 relief are as defined by dimensions M, N and R in FIG. 2 which are
 delineated for the embodiment shown in Table 1. The sector locations for
 the dimensional references of Table 1 are in 15.degree. increments from a
 0.degree. datum shown in FIG. 3. Table 1 also shows the radial dimension
 of the projections from the axis A with D1 and D2 corresponding to the
 first projection 28 and second projection 34 while B1 and B2 correspond to
 the third projection 38. Dimensions C1 and C2 correspond to the radial
 dimension of the inner circumference of land 76 and the relief 40 in the
 outer shell. The values in Table 1 have been non-dimensionalized using the
 diameter of the diffuser identified in FIG. 2 as .PHI. as the divisor.
 Each of the three elements of the compressor housing employing the present
 invention provides a clear draw for the respective casting die. The spiral
 ascent and descent of the mating lands on the elements allows a true
 volute shape to be maintained for maximum aerodynamic performance of the
 compressor housing. Each element is cast at near net shape and dimension
 with final machining required only as necessary for sealing on the mating
 lands 70 and 72, the insert receiving aperture in the outer shell and the
 mating surfaces of the peripheral portions of the outer shell and
 backplate. Dimensional relief is provided in the mating lands 74 and 76
 which maintain a relational spacing with sufficient tolerance to allow
 substantially sealing contact of lands 70 and 72. Any leakage from the
 interface of lands 74 and 76 is contained by seal 58 and the mating
 surfaces of the peripheral portions of the outer shell and backplate.
 FIG. 4 shows an alternative embodiment of the invention which incorporates
 the compressor inlet 78 as a portion of the outer shell and the diffuser
 wall insert neck 80 is received within the inlet portion of the outer
 shell.
 Having now described the invention in detail as required by the patent
 statutes, those skilled in the art will recognize modifications and
 substitutions to the specific embodiments disclosed herein. Such
 modifications and substitutions are within the scope and intent of the
 present invention as defined in the following claims.
 TABLE 1
 Section # 1 2 3 4 5 6 7
 Angle -- 15 30 45 60 75 90
 B1 -- 5.9035745 5.8783902 5.8508936 5.8325209 5.8160229 5.7922134
 B2 -- 6.0281839 6.0033120 5.9760654 5.9575053 5.9408198 5.9173853
 C1 -- 5.9029496 5.8775153 5.8501437 5.8319585 5.8155230 5.7914635
 C2 -- 6.0888638 6.0637420 6.0361829 6.0177477 6.0013123 5.9775028
 D1 -- 2.9744406 3.0058742 3.0382452 3.0780527 3.1205474 3.1606049
 D2 -- 3.1621047 3.1934758 3.2260342 3.2655293 3.3080239 3.3483939
 M -- 2.0341832 2.0258092 1.9885014 1.9400699 1.8935758 1.8511436
 N -- 2.3058367 2.2487189 2.1971003 2.1489188 2.1019247 2.0561804
 R -- 1.9716285 1.9635045 1.9262592 1.8775153 1.8310211 1.7885889
 Section # 8 9 10 11 12 13
 Angle 105 120 135 150 165 180
 B1 5.7646544 5.7385951 5.7164104 5.6971003 5.6752280 5.6481689
 B2 5.8895763 5.8634545 5.8413948 5.8220847 5.8001499 5.7732158
 C1 5.7636545 5.7374078 5.7152855 5.6960379 5.6741032 5.6467941
 C2 5.9500062 5.9238845 5.9016997 5.8823897 5.8605799 5.8334583
 D1 3.2020997 3.2491563 3.3033370 3.3638295 3.4261342 3.4893138
 D2 3.3898262 3.4369453 3.4913135 3.5517435 3.6140482 3.4896887
 M 1.8088363 1.7620922 1.7108486 1.6571678 1.6037370 1.5513060
 N 2.0122484 1.9701912 1.9282589 1.8844519 1.8373953 1.7874015
 R 1.7462192 1.6994750 1.6482939 1.5946131 1.5411823 1.4887514
 Section # 14 15 16 17 18 19
 Angle 195 210 225 240 255 270
 B1 5.613798 5.575678 5.538807 5.503812 5.459192 5.396075
 B2 5.738845 5.700662 5.663792 5.628421 5.584301 5.521184
 C1 5.612173 5.573865 5.536932 5.501937 5.457442 5.394263
 C2 5.799150 5.761092 5.724159 5.689163 5.644606 5.394075
 D1 3.552555 3.616860 3.684976 3.755093 3.826584 3.895325
 D2 3.740532 3.805399 3.872953 3.943069 4.014560 4.083239
 M 1.499250 1.445694 1.388326 1.325771 1.258342 1.188038
 N 1.735908 1.683789 1.630921 1.575178 1.513685 1.442944
 R 1.436695 1.383139 1.325771 1.263154 1.195663 1.125359
 Section # 20 21 22 23 24 25
 Angle 285 300 315 330 345 360
 B1 5.319147 5.239470 -- -- -- --
 B2 5.444256 5.364829 -- -- -- --
 C1 5.317147 5.224534 -- -- -- --
 C2 5.504749 5.425071 -- -- -- --
 D1 3.963567 4.042494 5.381139 3.342394 3.028308 2.945944
 D2 4.152480 4.231283 4.320147 3.554243 3.408386 3.133483
 M 1.115735 1.038057 -- -- -- --
 N 1.361579 1.271528 1.178415 2.492125 2.427821 2.366891
 R 1.052993 0.975253 -- -- -- --