Turbocharger with an annular rotary bypass valve

1. A turbocharger comprising:

a compressor including a compressor housing;

a turbine housing defining at least part of a generally annular chamber extending circumferentially about a longitudinal axis of the turbine housing, the turbine housing defining a bore extending along the longitudinal axis;

a turbine wheel disposed in the turbine housing;

a nozzle passage leading from the chamber radially inwardly into the turbine wheel;

the turbine housing defining an annular bypass volute surrounding the bore and arranged to allow exhaust gas to bypass the turbine wheel;

an annular bypass valve disposed in the bypass volute, the bypass valve comprising a fixed annular valve seat and a rotary annular valve member, the valve member being disposed against the valve seat and being rotatable about the longitudinal axis for selectively varying a degree of alignment between respective orifices defined through each of the valve seat and valve member, ranging from no alignment defining a closed condition of the bypass valve, to at least partial alignment defining an open condition of the bypass valve;

a rotary drive member penetrating through the turbine housing along a drive axis that is generally parallel to and transversely offset from the longitudinal axis about which the valve member rotates, wherein the rotary drive member includes a lengthwise section comprising a bellows having a substantially greater bending flexibility than that of a remainder of the rotary drive member, and a drive arm attached to a distal end of the rotary drive member, a distal end of the drive arm engaging the valve member such that rotation of the rotary drive member about the drive axis causes the drive arm to rotate the valve member about the longitudinal axis; and

a rotary actuator coupled to the rotary drive member and operable to rotatably drive the rotary drive member about the drive axis for rotating the valve member.

2. The turbocharger of claim 1 , wherein the lengthwise section has the substantially greater bending flexibility about a plurality of axes that are not parallel to the drive axis.

3. The turbocharger of claim 1 , wherein the rotary drive member has an integral first hollow cylindrical portion at a first end of the bellows and an integral second hollow cylindrical portion at an opposite second end of the bellows, and further comprising a first drive shaft rigidly affixed to the first hollow cylindrical portion and a second drive shaft rigidly affixed to the second hollow cylindrical portion, wherein the first drive shaft is connected to the drive arm and the second drive shaft is connected to the rotary actuator.

4. The turbocharger of claim 3 , wherein the bellows acts like a compression spring along the drive axis, and the bellows is axially compressed so as to create an axial compressive pre-load in the bellows.

5. The turbocharger of claim 3 , wherein the first drive shaft and the drive arm together constitute a single integral monolithic structure.

6. The turbocharger of claim 3 , wherein the second drive shaft is an output shaft of the rotary actuator.

7. The turbocharger of claim 3 , further comprising a bushing mounted in the turbine housing, the bushing defining a passage through which the first drive shaft passes, an inner surface of the passage constituting a bearing surface allowing the first drive shaft to rotate about the drive axis.

8. The turbocharger of claim 7 , wherein the bushing defines a first mechanical stop for the drive arm to limit rotation of the drive arm in a first direction.

9. The turbocharger of claim 8 , wherein the bushing further defines a second mechanical stop for the drive arm to limit rotation of the drive arm in a second direction.

10. The turbocharger of claim 1 , the valve member defining a plurality of first orifices therethrough, the valve seat defining a plurality of second orifices therethrough, and each first orifice having a corresponding second orifice.

11. The turbocharger of claim 10 , the first orifices having a first circumferential spacing therebetween and the second orifices having a second circumferential spacing therebetween, wherein the first circumferential spacing is different from the second circumferential spacing, and wherein at least partial alignment between one of the first orifices and a corresponding one of the second orifices creates a flow passage for flow of exhaust gas therethrough,

rotation of the valve member about the axis causing variation in a degree of alignment between the first orifices defined through the valve member and the second orifices defined through the valve seat, ranging from no alignment defining a closed condition of the bypass valve, to at least partial alignment defining an open condition of the bypass valve.

12. The turbocharger of claim 11 , wherein the first and second orifices are configured and arranged such that one subset of all flow passages begins to open before any of the other flow passages begin to open.

13. The turbocharger of claim 12 , wherein the first and second orifices are configured and arranged such that one flow passage opens at a time, until finally all flow passages are open.

14. The turbocharger of claim 1 ,

wherein the bypass volute has a non-uniform cross-sectional flow area around a circumference of the bypass volute.

15. The turbocharger of claim 14 , wherein the cross-sectional flow area of the bypass volute has a maximum value where the passage leads from the exhaust gas inlet into the bypass volute, and decreases from that maximum value with increasing circumferential distance away from the passage.