Braking device for a hydraulic motor vehicle braking system having a ball screw drive

1. A braking device for a hydraulic motor vehicle braking system, comprising:

an electromechanical booster stage, which is driven by an electric-motor drive unit and has a booster housing, in which a ball screw drive having a rotatable ball screw nut and a spindle that can be moved in a linear manner is arranged for converting a rotary driving force of the drive unit into a translational boosting force,

a brake master cylinder having a cylinder piston which can be moved in a linear manner therein and acted upon both with an unboosted actuating force by the driver and with the boosting force by the booster stage, wherein the actuating force from a piston rod is introduced into the spindle, and wherein the piston rod can be moved axially to a limited extent relative to the spindle and a spring element is inserted in the flow of force of the actuating force between the piston rod and the spindle, which spring is compressed axially when the actuating force is introduced, the spring element being housed in a spring element housing formed separately from and coupled to the spindle, the spring element housing being directly joined to the spindle by a joint which transmits force, at least in the axial direction.

2. The braking device as claimed in claim 1 , wherein the ball screw drive has an outer pot with external toothing, to which rotation is imparted by the drive unit via the external toothing, and the ball screw drive is secured against rotation and guided in a manner which allows linear movement in the outer pot by virtue of the fact that the ball screw nut has a noncircular outer contour which cooperates with an inner contour of the outer pot, said inner contour corresponding thereto at least in some region or regions.

3. The braking device as claimed in claim 1 , wherein the spring element housing is mounted in a manner which allows linear movement in the booster housing.

4. The braking device as claimed in claim 3 , wherein the piston rod is mounted in a manner which allows axial movement relative to the spring element housing.

5. The braking device as claimed in claim 1 , wherein the booster housing is made of plastic.

6. The braking device as claimed in claim 1 , wherein the spring element has at least one diaphragm spring.

7. The braking device as claimed in claim 1 , wherein the spring element comprises elastomeric material.

8. The braking device as claimed in claim 1 , wherein a bearing housing made of metal is arranged in the booster housing in order to hold bearing elements for the rotatable mounting of the outer pot.

9. The braking device as claimed in claim 1 , wherein a sensor device having a fixed sensing part and a transmitter part that can be moved in a linear manner for detecting the position and/or the movement of the piston rod is provided, wherein the transmitter part is coupled to the piston rod.

10. The braking device as claimed in claim 8 wherein a return spring for returning the spindle to the unbraked initial position thereof is clamped between the bearing housing and the spring element housing, wherein the return spring is axially preloaded both by the action of the actuating force and that of the boosting force.

11. The braking device as claimed in claim 1 , wherein a sensor device having a fixed sensing part and a transmitter part that can be moved in a linear manner for detecting the position and/or the movement of the piston rod is provided, wherein the transmitter part is coupled to the piston rod via a connecting element which extends through an aperture in the spring element housing.