Concentric camshaft with varying wall geometry and method of assembly

1. A camshaft comprising:

a first shaft formed as a one-piece tubular member and including an annular wall defining a first bore, the wall including a first portion having a first radial outermost surface and a second portion having a second radial outermost surface that is radially offset relative to the first radial outermost surface;

a first lobe member defining a second bore having the first portion of the first shaft located therein and frictionally engaged with the first shaft for rotation with the first shaft; and

a second lobe member defining a third bore having the second portion of the first shaft located therein, the second lobe member being rotatably disposed on the second portion of the first shaft.

2. The camshaft of claim 1 , wherein the first portion of the first shaft has a wall thickness that is greater than a wall thickness of the second portion of the first shaft.

3. The camshaft of claim 1 , wherein the second portion of the first shaft has a wall thickness that is greater than a wall thickness of the first portion of the first shaft.

4. The camshaft of claim 1 , wherein the first radial outer surface of the first portion is offset radially outwardly relative to the second radial outer surface of the second portion.

5. The camshaft of claim 1 , wherein a first radial inner surface of the first portion is offset radially inwardly relative to a second radial inner surface of the second portion.

6. The camshaft of claim 1 , wherein a first radial inner surface of the first portion is offset radially outwardly relative to a second radial inner surface of the second portion.

7. The camshaft of claim 1 , further comprising a second shaft that is rotatably disposed within the first bore, the second lobe member being fixed for rotation with the second shaft.

8. The camshaft of claim 7 , further comprising a third lobe member located on and fixed for rotation with the first shaft, the second lobe member being located axially between the first and third lobe members.

9. An engine assembly comprising:

an engine structure;

a first valve lift mechanism supported on the engine structure;

a second valve lift mechanism supported on the engine structure; and

a camshaft including:

a first shaft formed as a one-piece tubular member and including an annular wall defining a first bore, the wall including a first portion having a first radial outermost surface and a second portion having a second radial outermost surface that is radially offset relative to the first radial outermost surface;

a first lobe member engaged with the first valve lift mechanism, the first lobe member defining a second bore having the first portion of the first shaft located therein and frictionally engaged with the first shaft for rotation with the first shaft; and

a second lobe member engaged with the second valve lift mechanism, the second lobe member defining a third bore having the second portion of the first shaft located therein, the second lobe member being rotatably disposed on the second portion of the first shaft.

10. The engine assembly of claim 9 , wherein the first portion of the first shaft has a wall thickness that is greater than a wall thickness of the second portion of the first shaft.

11. The engine assembly of claim 9 , wherein the second portion of the first shaft has a wall thickness that is greater than a wall thickness of the first portion of the first shaft.

12. The engine assembly of claim 9 , wherein the first radial outer surface of the first portion is offset radially outwardly relative to the second radial outer surface of the second portion.

13. The engine assembly of claim 9 , wherein a first radial inner surface of the first portion is offset radially inwardly relative to a second radial inner surface of the second portion.

14. The engine assembly of claim 9 , wherein a first radial inner surface of the first portion is offset radially outwardly relative to a second radial inner surface of the second portion.

15. The engine assembly of claim 9 , further comprising a second shaft that is rotatably disposed within the first bore, the second lobe member being fixed for rotation with the second shaft.

16. The engine assembly of claim 15 , further comprising a third lobe member located on and fixed for rotation with the first shaft, the second lobe member being located axially between the first and third lobe members.

17. An engine assembly comprising:

an engine structure;

a first valve lift mechanism supported on the engine structure;

a second valve lift mechanism supported on the engine structure; and

a camshaft including:

a first shaft formed as a one-piece tubular member and including an annular wall defining a first bore, the wall including a first portion defining a first wall thickness and having a first radial outermost surface and a second portion defining a second wall thickness different than the first wall thickness and having a second radial outermost surface;

a first lobe member engaged with the first valve lift mechanism, the first lobe member defining a second bore having the first portion of the first shaft defining the first wall thickness located therein and frictionally engaged with the first shaft for rotation with the first shaft; and

a second lobe member engaged with the second valve lift mechanism, the second lobe member defining a third bore having the second portion of the first shaft defining the second wall thickness located therein, the second lobe member being rotatably disposed on the second portion of the first shaft.

18. The engine assembly of claim 17 , wherein the first wall thickness is greater than the second wall thickness.

19. The engine assembly of claim 17 , wherein the first wall thickness is less than the second wall thickness.

20. The engine assembly of claim 17 , further comprising a second shaft that is rotatably disposed within the first bore, the second lobe member being fixed for rotation with the second shaft.