Injection unit for an injection molding machine

1. An injection unit for an injection molding machine, comprising:

a) a barrel for receiving a plasticizing screw, the barrel extending horizontally along an injection axis between a barrel front end and a barrel back end;

b) a housing having a housing interior and an outer front face directed toward the barrel back end;

b) a cylindrical body rotatably supported in the housing interior for rotational coupling with the plasticizing screw, the cylindrical body coaxial with the injection axis and fixed to rotate with the plasticizing screw;

c) a gear train supported in the housing, the gear train including a central gear mounted about the cylindrical body coaxial with the injection axis and fixed to rotate with the cylindrical body, the central gear having an uppermost extent vertically above the injection axis and opposed first and second lateral extents on horizontally opposed sides of the injection axis;

d) a rotary drive mounted to the housing for powering rotation of the plasticizing screw via the gear train, the rotary drive including a first motor having a first motor shaft rotatable about a first motor axis, the first motor axis parallel to the injection axis, the first motor axis at a first elevation below the uppermost extent of the central gear, and laterally outboard of the first lateral extent of the central gear on the first side of the injection axis.

2. The injection unit of claim 1 , wherein the first motor is mounted to the outer front face of the housing with the first motor shaft protruding rearward of the first motor into the housing interior.

3. The injection unit of claim 2 , wherein the rotary drive further includes a second motor having a second motor shaft rotatable about a second motor axis, the second motor axis parallel to the injection axis, the second motor axis at a second elevation below the uppermost extent of the central gear, and laterally outboard the second lateral extent of the central gear on the second side of the injection axis, opposite the first side.

4. The injection unit of claim 3 , wherein the second motor is mounted to the outer front face of the housing with the first motor shaft protruding rearward of the first motor into the housing interior.

5. The injection unit of claim 4 , wherein the first elevation and of the first motor shaft is generally equal to the second elevation of the second motor shaft.

6. The injection unit of claim 5 , further comprising a gear oil chamber internal the housing for containing gear oil to lubricate the gear train.

7. The injection unit of claim 1 , further comprising at least one front bearing mounted to the housing for rotationally supporting a body front end of the cylindrical body, and a rear bearing spaced axially apart from the front bearing for rotationally supporting a body back end of the cylindrical body, wherein the central gear is axially intermediate the front and rear bearings.

8. The injection unit of claim 1 , wherein the cylindrical body comprises a fluid cylinder internal the cylindrical body, the fluid cylinder slidably receiving a piston for urging translation of the plasticizing screw, the piston fixed to rotate with the cylindrical body and translatable along the injection axis relative to the cylindrical body for urging translation of the piston along the injection axis between advanced and retracted positions.

9. The injection unit of claim 8 , further comprising a pressure chamber in the fluid cylinder axially rearward of the piston for urging the piston toward the advanced position when pressurized.

10. An injection unit for an injection molding machine, comprising:

a) a barrel for receiving a plasticizing screw, the barrel extending horizontally along an axis between a barrel front end and a barrel back end;

b) a housing adjacent the barrel back end;

c) a first cylinder within a cylindrical body rotatably supported in the housing for rotation about the axis;

d) a shaft coaxial with the axis and axially fixed relative to the housing, the shaft having a shaft back end proximate a housing back end of the housing and a shaft front end spaced axially forward of the shaft back end;

e) a piston slidably received in a first annular space radially intermediate a first inner surface of the first cylinder and an outer surface of the shaft, the piston including a second cylinder coaxial with the axis and having a second cylinder front end for connection to the plasticizing screw and a second cylinder back end spaced axially rearward of the second cylinder front end, the piston further including a first piston head received in sealed sliding fit in the first annular space and affixed to the second cylinder back end, and the piston fixed to rotate with the first cylinder and translatable relative to the first cylinder along the axis between advanced and retracted positions;

f) a first pressure chamber in the first annular space axially rearward of the first piston head for urging the piston toward the advanced position when pressurized;

g) a second piston head received in sealed sliding fit in an interior of the second cylinder and affixed to the shaft front end; and

h) a second pressure chamber axially forward of the first piston head and in a second annular space radially intermediate the shaft and the second cylinder, the second pressure chamber bounded axially by the first and second piston heads for urging the piston toward the retracted position when pressurized.

11. The injection unit of claim 10 , wherein the second cylinder has a second cylinder inner surface directed toward and spaced radially apart from the shaft outer surface to form the second annular space therebetween, and wherein the second piston head is in sealed sliding engagement with the second cylinder inner surface.

12. The injection unit of claim 10 , wherein when the piston is in the advanced position, the first piston head is axially proximate the second piston head, and when the piston is in the retracted position, the first piston head is spaced away from the second piston head toward the shaft back end.

13. The injection unit of claim 10 , wherein the shaft has an internal first fluid conduit extending between the first pressure chamber and a first fluid port for conducting pressurized fluid to and from the first pressure chamber, and an internal second fluid conduit extending between the second pressure chamber and a second fluid port for conducting pressurized fluid to and from the second pressure chamber.

14. The injection unit of claim 10 , further comprising a gear train supported in the housing for transmitting power from a rotary drive to rotation of the first cylinder about the axis, and a gear oil chamber internal the housing for containing gear oil to lubricate the gear train, and wherein the piston is fixed to rotate with the first cylinder through a spline coupling therebetween, the spline coupling in fluid communication with the gear oil chamber for lubrication thereof.

15. The injection unit of claim 10 , further comprising a cylinder cap mounted to a first cylinder back end of the first cylinder and fixed to rotate with the first cylinder, the first pressure chamber bounded axially by the first piston head and the cylinder cap.

16. An injection unit for an injection molding machine, comprising:

a) a barrel for receiving a plasticizing screw, the barrel extending horizontally along an axis between a barrel front end and a barrel back end;

b) a housing adjacent the barrel back end;

c) a first cylinder within a cylindrical body rotatably supported in the housing for rotation about the axis;

d) a piston slidably received in the first cylinder, the piston including a second cylinder having a second cylinder front end for connection to the plasticizing screw and a second cylinder back end spaced axially rearward of the second cylinder front end, the piston further including a first piston head in the first cylinder and affixed to the second cylinder back end, and the piston fixed to rotate with the first cylinder and translatable relative to the first cylinder along the axis between advanced and retracted positions;

e) a first pressure chamber in the first cylinder axially rearward of the first piston head for urging the piston toward the advanced position when pressurized; and

f) a second pressure chamber in the second cylinder axially forward of the first piston head for urging the piston toward the retracted position when pressurized.

17. The injection unit of claim 16 , further comprising a second piston head in the second cylinder and axially fixed relative to the housing, the second pressure chamber bounded axially by the first and second piston heads.

18. The injection unit of claim 17 , further comprising a shaft coaxial with the axis and axially fixed relative to the housing, the shaft extending through the first pressure chamber and a through-hole in the first piston head between a shaft back end axially rearward of the first piston head and a shaft front end axially forward of the first piston head and in the second cylinder, the second piston head affixed to the shaft front end.

19. The injection unit of claim 18 , wherein the piston is slidably received in a first annular space radially intermediate the first cylinder and the shaft, and the first pressure chamber is in the first annular space.

20. The injection unit of claim 18 , wherein the second pressure chamber is in a second annular space radially intermediate the shaft and the second cylinder.