Extension coupling for interconnecting trailer and tow hitch

1. An extension coupling for interconnecting a trailer to a tow hitch carried by a tow vehicle, said extension coupling comprising:

a pin box assembly including a first section, a second section and a pivot connecting said first section and said second section together;

a shock absorber connected between said first section and said second section;

an air spring connected between said first section and said second section;

a king pin carried on said second section, the pivot is positioned forward of the king pin when the king pin is engaged with the tow hitch; and

a locking wedge carried on said second section.

2. The extension coupling of claim 1 , including a pivot shaft carried on said first section.

3. The extension coupling of claim 2 , including a trailer mount wherein said trailer mount is fixed to the trailer and said pin box assembly is connected to said trailer mount by said pivot shaft.

4. The extension coupling of claim 3 , wherein said trailer mount includes a mounting plate having a reinforcing rib and at least two projecting mounting flanges.

5. The extension coupling of claim 4 , wherein said mounting plate includes a hub that receives said pivot shaft and said reinforcing rib is arc shaped and extends concentrically around said hub.

6. The extension coupling of claim 3 , wherein said shock absorber is provided between said air spring and said mount.

7. The extension coupling of claim 6 , wherein said air spring is provided between said shock absorber and said pivot.

8. The extension coupling of claim 7 , wherein said pivot is provided at a front end of said pin box assembly.

9. The extension coupling of claim 8 , wherein said air spring and said shock absorber are provided between said pivot shaft and said king pin.

10. The extension coupling of claim 9 , wherein said shock absorber and said air spring are both offset from said king pin and said pivot shaft.

11. The extension coupling of claim 10 , wherein said air spring is a rubber air bladder.

12. The extension coupling of claim 3 , wherein said trailer mount includes a v-shaped base and a hub that receives said pivot shaft.

13. The extension coupling of claim 12 , wherein said trailer mount includes at least two mounting flanges projecting from said base.

14. The extension coupling of claim 1 , further including a fastener securing said locking wedge to said second section.

15. The extension coupling of claim 1 , wherein said second section includes a skid plate.

16. The extension coupling of claim 15 , further including two fasteners securing said locking wedge to said skid plate.

17. The extension coupling of claim 16 , wherein said locking wedge includes two elongated slots and said two fasteners are received in said two elongated slots.

18. The extension coupling of claim 17 , wherein said king pin is received in and projects through said skid plate adjacent said locking wedge.

19. An extension coupling for connecting a trailer to a tow hitch carried by a tow vehicle, the extension coupling comprising:

a pin box assembly including a first section, a second section and a pivot connecting the first section to the second section;

a trailer mount pivotally connected to the pin box assembly;

a king pin pivotally connected to the second section, the king pin being selectively restrained from pivoting about the second section; and

wherein the extension coupling has an installation position in which the trailer mount is connected to the trailer and the king pin is engaged with the tow hitch, the pivot is forward of the king pin, and the king pin is restrained from movement.

20. The extension coupling of claim 19 , further comprising an air system mounted between the first section and the second section of the pin box assembly, the first section and the second section configured to cover the air system.

21. The extension coupling of claim 20 , wherein the air system includes an air spring and a shock absorber, the air spring is mounted on the second section and the shock absorber is mounted between the first section and the second section.

22. The extension coupling of claim 19 , further comprising a wedge positioned on the second section, the wedge configured to contact the king pin and to restrain the king pin from rotation.

23. The extension coupling of claim 22 , further comprising a fastener; and

wherein the wedge defines at least one slot, the fastener securing the wedge to the second section through the slot, the slot configured to allow the wedge to be selectively positioned on the second section.

24. An extension coupling for connecting a trailer to a tow hitch carried by a tow vehicle, the extension coupling comprising:

a pin box assembly including a first section, a second section and a pivot connecting the first section to the second section;

a trailer mount pivotally connected to the pin box assembly, the trailer mount configured to attach to the trailer;

a king pin pivotally connected with the second section, the pivot is positioned forward of the king pin when the king pin is engaged with the tow hitch;

means for dampening shock on the tow vehicle; and

means for regulating a compression rate and an expansion rate of the pin box assembly.

25. The extension coupling of claim 24 , wherein the means for dampening shock includes a shock absorber, the shock absorber is mounted between the first section and the second section.

26. The extension coupling of claim 24 , wherein the means for regulating includes an air bag mounted to the second section.

27. The extension coupling of claim 24 , wherein the first section and the second section define an enclosure, and the means for dampening shock and the means for regulating are positioned in the enclosure.