Disc brake

1. A disc brake comprising:

a piston for applying an actuating force to a brake pad, the piston including an inner piston that is rotatable about an axis and an outer piston that receives the inner piston, wherein rotation of the inner piston causes the outer piston to extend; and

a wear adjustment mechanism for adjusting extension of the outer piston to account for wear of the brake pad, the wear adjustment mechanism including a friction clutch having an input plate and an output plate arranged in a face-contacting relationship, wherein the output plate is located within the inner piston and directly drivingly engages the inner piston, wherein the inner piston has a radially inner surface that faces toward the axis and an axial groove that is formed in the radially inner surface and wherein components in rotatable contact with the inner piston are only rotatable about the axis.

2. The disc brake of claim 1 wherein the output plate has a lug, that engages and is received in the axial groove.

3. The disc brake of claim 1 further comprising a clutch spring arranged to apply a predetermined force to axially compress the friction clutch.

4. The disc brake of claim 3 wherein the friction clutch further comprises a pressure plate to transmit force from the clutch spring to the friction clutch.

5. The disc brake of claim 1 wherein the wear adjustment mechanism further comprises a one-way clutch in driving communication with the friction clutch, the one-way clutch being configured to transfer an adjustment input to the input plate of the friction clutch, wherein the one-way clutch comprises a driving portion and a driven portion, and the driven portion mounts the input plate.

6. The disc brake of claim 5 wherein the driven portion of the one-way clutch comprises an axially extending projecting portion, and the driving portion is rotatably mounted on the axially extending projecting portion.

7. The disc brake of claim 5 wherein the driving portion of the one-way clutch comprises an axially extending projecting portion, and the driven portion is rotatably mounted on the axially extending projecting portion.

8. The disc brake of claim 5 wherein:

the driving portion of the one-way clutch is a drive drum; and

the driven portion of the one-way clutch is a driven drum in communication with the drive drum via a wrap spring arranged to overlie and bridge the drive drum and the driven drum.

9. The disc brake of claim 5 further comprising:

a driving link member, which is driven by an operating shaft; and

a driven link member, which is driven by the driving link member and drives the driving portion of the one-way clutch,

wherein a transmission path from the operating shaft comprises a predetermined amount of backlash between the operating shaft and the friction clutch, such that the input plate of the friction clutch is not driven until a predetermined running clearance is exceeded, wherein at least a proportion of the backlash is located between the operating shaft and the driving link member.

10. The disc brake of claim 9 wherein at least a proportion of the backlash is located between the driving link member and the driven link member.

11. The disc brake of claim 9 wherein at least a proportion of the backlash is located between the driven link member and the friction clutch.

12. The disc brake of claim 5 further comprising:

a driving link member, which is driven by an operating shaft; and

a driven link member, which is driven by the driving link member and drives the driving portion of the one-way clutch,

wherein a transmission path from the operating shaft comprises a predetermined amount of backlash between the operating shaft and the friction clutch, such that the input plate of the friction clutch is not driven until a predetermined running clearance is exceeded, wherein at least a proportion of the backlash is located between the driving link member and the driven link member.

13. The disc brake of claim 12 wherein at least a proportion of the backlash is located between the driven link member and the friction clutch.

14. The disc brake of claim 5 further comprising:

a driving link member, which is driven by an operating shaft; and

a driven link member, which is driven by the driving link member and drives the driving portion of the one-way clutch,

wherein a transmission path from the operating shaft comprises a predetermined amount of backlash between the operating shaft and the friction clutch, such that the input plate of the friction clutch is not driven until a predetermined running clearance is exceeded, wherein at least a proportion of the backlash is located between the driven link member and the friction clutch.

15. The disc brake of claim 5 further comprising:

a driving link member, which is driven by an operating shaft; and

a driven link member, which is driven by the driving link member and drives the driving portion of the one-way clutch,

wherein a transmission path from the operating shaft comprises a predetermined amount of backlash between the operating shaft and the friction clutch, such that the input plate of the friction clutch is not driven until a predetermined running clearance is exceeded, wherein at least a proportion of the backlash is located between (1) the operating shaft and the driving link member and (2) between the driving link member and the driven link member and (3) between the driven link member and the friction clutch.

16. The disc brake of claim 1 wherein the wear adjustment mechanism comprises an axially extending bore, and the disc brake further comprises a manual adjuster shaft assembly extending through the bore and being configured to drivingly engage an inner surface of the piston to permit manual de-adjustment the disc brake.

17. The disc brake of claim 1 wherein the outer piston is restrained from rotating and is in threaded engagement with the inner piston along an entire axial length of the inner piston such that rotation of the inner piston causes the outer piston to move axially relative to the inner piston so as to extend the outer piston.

18. A disc brake comprising:

a piston for applying an actuating force to a brake pad, the piston including an inner piston that is rotatable about an axis and an outer piston that receives the inner piston, wherein rotation of the inner piston causes the outer piston to extend; and

a wear adjustment mechanism for adjusting extension of the outer piston to account for wear of the brake pad, the wear adjustment mechanism being at least partially received inside the inner piston and including a friction clutch having an input plate and an output plate arranged in a face-contacting relationship, wherein the output plate is located within the inner piston and directly drivingly engages the inner piston; and

a manual adjuster shaft that is at least partially received inside the inner piston and is rotatable about the axis to manually adjust the wear adjuster mechanism.

19. A disc brake comprising:

a piston for applying an actuating force to a brake pad, the piston including an inner piston that is rotatable about an axis and an outer piston that receives the inner piston, wherein rotation of the inner piston causes the outer piston to extend; and

a wear adjustment mechanism for adjusting extension of the outer piston to account for wear of the brake pad, the wear adjustment mechanism including a friction clutch having an input plate and an output plate arranged in a face-contacting relationship, wherein the output plate is located within the inner piston and directly drivingly engages the inner piston, wherein the outer piston is the only component that is completely disposed outside of the inner piston that rotatably engages the inner piston.

20. The disc brake of claim 19 wherein the inner piston is completely received inside the outer piston before the wear adjuster mechanism is extended.