Disc brake actuator for a vehicle

1. A disc brake actuator for a vehicle with an electrical drive and a transmission unit driven by the electrical drive, the transmission unit comprising a ramp transmission system and a threaded transmission system,

wherein the ramp transmission system and the threaded transmission system are arranged in series in the force flow of the transmission unit,

wherein the ramp transmission system comprises

a) a rotating driving element having a fixed axial position and being driven by the electrical drive,

b) a driven element which is both movable in an axial direction as well as rotatable and

c) a rolling element which is clamped between the driving element and the driven element and rolls along contact surfaces of the driving element and the driven element,

d) wherein the contact surface of the driving element as well as the contact surface of the driven element each form a ramp, at least one of the ramps having portions of different inclinations in different circumferential portions, the different inclinations located in different parts of a brake stroke, and wherein the inclination of the at least ramp continuously decreases in the circumferential direction over the brake stroke.

2. The disc brake actuator of claim 1 wherein the threaded transmission system is arranged downstream from the ramp transmission system.

3. The disc brake actuator of claim 1 wherein

a) a brake stroke of the disc brake actuator for applying a brake an actuation of the electrical drive

first operates the threaded transmission system and

then operates the ramp transmission system and/or

b) in a return brake stroke of the disc brake actuator for releasing the brake a return actuation of the electrical drive

first operates the ramp transmission system and

then operates the threaded transmission system.

4. The disc brake actuator of claim 3 wherein the ramp transmission system is biased by a spring which does not bias the threaded transmission system.

5. The disc brake actuator of claim 3 wherein a switching from the operation of the threaded transmission system to the operation of the ramp transmission system and/or vice versa is automatically triggered by

a friction in the threaded transmission system,

a rolling resistance due to the inclinations of the ramps in the ramp transmission system and/or

a spring biasing the ramp transmission system towards a starting point of the ramps.

6. The disc brake actuator of claim 1 wherein the driving element is a gearwheel and the contact surface forming one of the ramps is a front surface of the gearwheel, the gearwheel comprising a radial outer surface with teeth.

7. The disc brake actuator of claim 1 wherein the rolling element is a double-roller which is in particular accommodated in a cage element.

8. The disc brake actuator of claim 7 wherein the roller is disc-shaped and comprises

a) a bevelled transition surface,

b) a curved front surface and/or

c) a rolling surface having a curved contour.

9. The disc brake actuator of claim 1 wherein the driven element of the ramp transmission system is fixedly connected to a threaded driving element of the threaded transmission system.

10. The disc brake actuator of claim 9 wherein the driven element of the ramp transmission system and the threaded driving element of the threaded transmission system are integrally formed by a sleeve wherein the contact surface of the driven element of the ramp transmission system is formed by a ring-shaped radial shoulder of the sleeve and a thread of the threaded driving element is formed by an outer or inner surface of the sleeve.

11. The disc brake actuator of claim 1 wherein an axial supporting force of the ramp transmission system in axial direction is sensed by an axial force sensor.

12. The disc brake actuator of claim 1 wherein an axial supporting force of the ramp transmission system in axial direction is sensed by an axial force sensor.

13. The disc brake actuator of claim 1 wherein the threaded transmission system comprises

a) a rotatable threaded driving element and

b) a threaded driven element, which is fixed against rotation, wherein

c) the threaded driving element and the threaded driven element are threaded with each other and

d) the threading angle between the threaded driving element and the threaded driven element changes with a rotation of the threaded driving element.

14. The disc brake actuator of claim 13 wherein the threaded driving element of the threaded transmission system is biased by a torsional spring.

15. The disc brake actuator of claim 14 wherein the application of a torque of the torsional spring is controlled by a sliding clutch mechanism, a uni-directional clutch mechanism, a one-way needle roller or a one-way wrap spring.

16. The disc brake actuator of claim 1 wherein the transmission unit is driven by the electrical drive via a further transmission unit.

17. The disc brake actuator of claim 16 wherein the further transmission unit comprises a planetary gear set, a cycloidal drive or a worm transmission unit.

18. The disc brake actuator of claim 17 wherein

a) a planet carrier of the planetary gear set is fixed against relative rotation to a gearwheel meshing with the gearwheel of the transmission unit and

b) a sun gear of the planetary gear set is driven by the electrical drive.

19. The disc brake actuator of claim 1 wherein a fixing unit is provided for fixing an operational state of the disc brake actuator independent on the energization of the electrical drive.

20. The disc brake actuator of claim 1 wherein a sensor is integrated into the disc brake actuator and the sensor senses an operational state of the threaded transmission system.

21. The disc brake actuator of claim 8 wherein a sensor is integrated into the disc brake actuator and the sensor senses an operational state of the threaded transmission system.

22. The disc brake actuator of claim 17 wherein a sensor is integrated into the disc brake actuator and the sensor senses an operational state of the threaded transmission system.

23. The disc brake actuator of claim 18 wherein a sensor is integrated into the disc brake actuator and the sensor senses an operational state of the threaded transmission system.

24. A disc brake actuator for a vehicle with an electrical drive and a transmission unit driven by the electrical drive, the transmission unit comprising a ramp transmission system and a threaded transmission system,

wherein the ramp transmission system and the threaded transmission system are arranged in series in the force flow of the transmission unit,

wherein the ramp transmission system comprises

a) a rotating driving element having a fixed axial position and being driven by the electrical drive,

b) a driven element which is both movable in an axial direction as well as rotatable and

c) a rolling element which is clamped between the driving element and the driven element and rolls along contact surfaces of the driving element and the driven element,

d) wherein the contact surface of the driving element as well as the contact surface of the driven element each form a ramp, at least one of the ramps having portions of different inclinations in different circumferential portions, the different inclinations located in different parts of a brake stroke, and wherein the portions of the at least one ramp with smaller inclinations are arranged in a circumferential direction at positions used in operating states of the brake disc where a more sensitive control of the brake force is desired.

25. A disc brake actuator for a vehicle with an electrical drive and a transmission unit driven by the electrical drive, the transmission unit comprising a ramp transmission system and a threaded transmission system,

wherein the ramp transmission system and the threaded transmission system are arranged in series in the force flow of the transmission unit,

wherein the ramp transmission system comprises

a) a rotating driving element having a fixed axial position and being driven by the electrical drive,

b) a driven element which is both movable in an axial direction as well as rotatable and

c) a rolling element which is clamped between the driving element and the driven element and rolls along contact surfaces of the driving element and the driven element,

d) wherein the contact surface of the driving element as well as the contact surface of the driven element each form a ramp, at least one of the ramps having portions of different inclinations in different circumferential portions, the different inclinations located in different parts of a brake stroke, and wherein the at least one ramp in a first portion starts with a constant large inclination, then in a second portion the inclination continuously decreases to a smaller inclination and then the ramps comprise a constant small inclination in the third portion.