ACTUATION DEVICE FOR A BRAKE SYSTEM

An actuation device for a brake system. The actuation device includes an electric machine, a rotor of the electric machine is arranged on a rotatably mounted drive shaft in a rotationally fixed manner; a displaceably mounted pressure element; a transmission device by means of which the drive shaft is operatively connected to the pressure element such that the pressure element can be moved by a rotation of the drive shaft, the transmission device having a displaceable threaded spindle; and an anti-rotation device which acts between the threaded spindle and a housing of the actuation device and which includes a circumferential backlash. The actuation device includes a spring element which applies a preload force to the threaded spindle in order to close the circumferential backlash.

FIELD

The present invention relates to an actuation device for a brake system, comprising an electric machine, wherein a rotor of the electric machine is arranged on a rotatably mounted drive shaft in a rotationally fixed manner, a displaceably mounted pressure element, a transmission device, by means of which the drive shaft is operatively connected to the pressure element such that the pressure element can be moved by a rotation of the drive shaft, said transmission device having a displaceable threaded spindle, and an anti-rotation device which acts between the threaded spindle and a housing of the actuation device and which has a circumferential backlash.

BACKGROUND INFORMATION

A hydraulic brake system of a motor vehicle typically comprises a plurality of friction brake devices. The friction brake devices are operatively connected to an actuation device of the brake system such that the friction brake devices can be actuated by the actuation device. With the increasing electrification of motor vehicles, actuation devices of brake systems are also becoming increasingly electrified. In this respect, a conventional method is to equip an actuation device for a brake system with an electric machine, wherein a rotor of the electric machine is arranged in a rotationally fixed manner on a rotatably mounted drive shaft. To make possible an actuation of the friction brake devices by the actuation device, the actuation device also includes a displaceably mounted pressure element. The drive shaft is operatively connected to the pressure element by a transmission device such that the pressure element is displaceable by rotating the drive shaft. The transmission device is therefore designed to convert a rotation of the drive shaft into a translational movement of the pressure element. For this purpose, the transmission device often has a displaceable threaded spindle. In order to limit the rotation of the threaded spindle when the actuation device is in operation, there is usually an anti-rotation device that acts between the threaded spindle and a housing of the actuation device. In order to achieve low-friction displacement of the threaded spindle, the anti-rotation device typically has a circumferential backlash. However, this comes with the problem that clicking noises or banging noises can occur when the actuation device is in operation.

SUMMARY

An actuation device according to the present invention may have an advantage of being relatively quiet when in operation. To this end, an example embodiment of the present invention provides that the actuation device comprises a spring element which applies a preload force to the threaded spindle in order to close the circumferential backlash. Because the anti-rotation device has a circumferential backlash, the threaded spindle can rotate at least slightly relative to the housing. The threaded spindle can generally be rotated in a first direction of rotation, which closes the circumferential backlash, and in a second direction of rotation, which opens the circumferential backlash. If the circumferential backlash is closed, a sufficiently strong force acting on the threaded spindle in the first direction of rotation causes the threaded spindle to be displaced in the direction of the pressure element. If the friction brake devices are to be actuated by the actuation device, the electric machine is therefore controlled such that it provides a force acting on the threaded spindle in the first direction of rotation. If the circumferential backlash is open before the electric machine is actuated, the threaded spindle is initially turned in the first direction of rotation by the force provided. Only when the circumferential backlash is closed is the threaded spindle then moved in the direction of the pressure element. However, closing the circumferential backlash is accompanied by the aforementioned clicking noises or banging noises. These noises can be avoided by the spring element according to the present invention. According to the present invention, the preload force provided by the spring element acts on the threaded spindle in order to close the circumferential backlash, i.e., in the first direction of rotation. Preferably, the spring element is designed such that the circumferential backlash is closed by the preload force. Because the circumferential backlash is already closed by the preload force, there is no need to first close the circumferential backlash when the friction brake devices are actuated by the electric machine. This avoids clicking noises or banging noises. According to a preferred embodiment, the transmission device has a spindle gear, wherein the spindle gear has the threaded spindle. According to an alternative embodiment of the present invention, the transmission device preferably has a ball screw drive, wherein the ball screw drive has the threaded spindle.

Preferably, according to an example embodiment of the present invention, the anti-rotation device has at least one first stop connected to the threaded spindle in a rotationally fixed manner and at least one second stop arranged fixed to the housing, wherein the spring element presses the first stop against the second stop in order to close the circumferential backlash. If the first stop is in contact with the second stop, the circumferential backlash is closed. If the first stop is at a distance from the second stop, the circumferential backlash is at least partially open. The first stop is preferably aligned in the first direction of rotation. The second stop is then correspondingly aligned against the first direction of rotation, i.e., in the second direction of rotation. The stops ensure mechanically robust guidance of the threaded spindle in the housing when the circumferential backlash is closed.

Preferably, according to an example embodiment of the present invention, the spring element is a coil spring. This design of the spring element keeps manufacturing costs low. In addition, a spring element designed as a coil spring can be integrated into the actuation device to save space.

According to a preferred embodiment of the present invention, it is provided that the preload force is a torsional force. The spring element is therefore twisted such that it provides the preload force as a torsional force. In this embodiment, the spring element is preferably arranged such that the longitudinal center axis of the spring element is aligned parallel to the longitudinal center axis of the threaded spindle. According to an alternative embodiment, it is preferable that the preload force is a compressive force. The spring element is therefore compressed such that it provides the preload force as a compressive force. According to an alternative embodiment, it is preferably provided that the preload force is a tensile force. The spring element is therefore stretched such that it provides the preload force as a tensile force. In the two aforementioned embodiments, the spring element is preferably arranged such that the longitudinal center axis of the spring element is aligned perpendicular to the longitudinal center axis of the threaded spindle.

According to a preferred embodiment of the present invention, it is provided that the spring element is designed such that, in addition to the preload force, it applies a restoring force directed away from the pressure element to the threaded spindle. The function of the spring element is therefore extended such that the spring element resets the threaded spindle following actuation of the friction brake devices. In this embodiment, the spring element is preferably designed such that the preload force is a torsional force. The spring element is then twisted such that it provides the preload force as a torsional force, and compressed or stretched such that it provides the restoring force as a compressive force or as a tensile force.

Preferably, according to an example embodiment of the present invention, the threaded spindle and the spring element are arranged coaxially to each other. This achieves a space-saving integration of the spring element into the actuation device. In addition, a coaxial arrangement of the threaded spindle and the spring element prevents the aforementioned restoring force from causing the threaded spindle to tip or tilt. Preferably, the spring element surrounds the threaded spindle radially in relation to the longitudinal center axis of the threaded spindle.

According to a preferred embodiment of the present invention, it is provided that a first end of the spring element is arranged on the threaded spindle or on an element that is connected to the threaded spindle in a rotationally fixed manner. This ensures reliable transmission of the preload force to the threaded spindle.

According to a preferred embodiment of the present invention, it is provided that the threaded spindle has a first end section facing away from the pressure element with an axial stop, and the first end of the spring element is arranged on the axial stop. The first end section facing away from the pressure element is technically easily accessible, which is why the arrangement of the spring element on the axial stop of the first end section is preferred.

Preferably, according to an example embodiment of the present invention, a second end of the spring element is arranged on the housing or on an element fixed to the housing. This provides a mechanically robust support for the spring element so that the preload force is reliably transmitted to the threaded spindle.

Preferably, according to an example embodiment of the present invention, the second end of the spring element is arranged on a bearing ring of a rotary bearing of the actuation device that is fixed to the housing. This allows a mechanically robust arrangement of the second end of the spring element to be achieved. As mentioned above, the transmission device preferably comprises a spindle gear, wherein the spindle gear comprises the threaded spindle. Particularly preferably, a spindle nut of the spindle gear is rotatably mounted by means of the rotary bearing. The rotary bearing thus serves both to support the spindle nut and to support the spring element.

Preferably, according to an example embodiment of the present invention, the threaded spindle interacts directly with the housing to form the anti-rotation device. This provides a mechanically particularly robust anti-rotation device. Because the threaded spindle interacts directly with the housing to form the anti-rotation device, the tolerance chain with regard to the anti-rotation device is also minimized.

According to an alternative embodiment of the present invention, it is preferably provided that an anti-rotation element is connected to the threaded spindle in a rotationally fixed manner and that the anti-rotation element interacts directly with the housing to form the anti-rotation device. This can reduce the weight and/or the manufacturing costs for the actuation device. For this purpose, the anti-rotation element is preferably made of plastic. The threaded spindle, on the other hand, is preferably made of a metal material. The anti-rotation element is particularly preferably arranged on a second end section of the threaded spindle facing the pressure element.

According to a preferred embodiment of the present invention, it is provided that the housing has at least one radial recess in which a radial projection of the threaded spindle or a radial projection of the anti-rotation element engages radially to form the anti-rotation device. This results in a mechanically robust anti-rotation device. Preferably, the radial recess is designed as a groove that extends through the housing in the direction of displacement of the threaded spindle. Preferably, the threaded spindle or the anti-rotation element comprise a plurality of radial projections, wherein each of the radial projections engages radially in a different radial recess of the housing. Two radial projections that are diametrically opposite one another in relation to the longitudinal center axis of the threaded spindle are particularly preferred.

The present invention is explained in more detail below with reference to the figures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG.1shows a longitudinal section through an actuation device1for a brake system2, not shown in detail, of a motor vehicle. The actuation device1has a displaceably mounted pressure element3, which, in the case at hand, is designed as a pressure rod3. The pressure element3is displaceable along its longitudinal center axis4in a first direction5and in a second direction6opposite to the first direction5. The pressure element3is arranged at least partially in a housing7of the actuation device1. The housing7has a casing wall8that is closed in the peripheral direction and is therefore cylindrical in shape. The casing wall8forms or encloses the inside of the housing7.

On the housing7, a master brake cylinder9of the actuation device1is arranged fixed to the housing. In the case at hand, the master brake cylinder11is arranged on a first end face10of the casing wall8. A first hydraulic piston11and a second hydraulic piston12are displaceably mounted in the master brake cylinder9, namely in the first direction5and in the second direction6. The master brake cylinder9comprises a plurality of hydraulic connections13,14. If the actuation device1is installed as intended in the brake system2, the hydraulic connections13,14are fluidically connected to slave cylinders of friction brake devices of the brake system2. The friction brake devices can then be actuated by moving the hydraulic pistons11and12in the first direction5. The pressure element3is coupled to the hydraulic pistons11and12such that the hydraulic pistons11and12are displaceable in the first direction5by the pressure element3. The friction brake devices can therefore be actuated by moving the pressure element3. A housing plate15is fixed to the housing7. In the present case, the housing plate15is arranged on a second end face16of the casing wall8facing away from the first end face10. The housing plate15at least partially closes the interior of the housing7.

The actuation device1also comprises a drive unit17. The drive unit17comprises a motor housing18in which an electric machine19is arranged. An annular rotor20of the electric machine19is arranged on a drive shaft21in a rotationally fixed manner, wherein the drive shaft21is mounted so that it can rotate about an axis of rotation49. The motor housing18is attached to the housing7.

The drive shaft21is coupled to the pressure element3by a transmission device22such that the pressure element3is displaceable by a rotation of the drive shaft21. The transmission device22is therefore designed to convert a rotation of the drive shaft21into a translational displacement of the pressure element3. For this purpose, the transmission device22comprises a displaceable threaded spindle23. The threaded spindle23is displaceable in the first direction5and in the second direction6. In the case at hand, the threaded spindle23is part of a spindle gear24of the transmission device22. In addition to the threaded spindle23, the spindle gear24has a spindle nut25. The spindle nut25is rotatably mounted by means of a rotary bearing26. A drive gearing27of the threaded spindle23meshes with an output gearing28of the spindle nut25. The spindle nut25can be rotated by rotating the drive shaft21. In the case at hand, the spindle nut25is operatively connected to the drive shaft21by a worm gear not shown in the figures.

In order to prevent the threaded spindle23from rotating with the spindle nut25when the spindle nut25rotates, an anti-rotation device29is assigned to the threaded spindle23. The anti-rotation device29acts between the threaded spindle23and the housing7and limits the rotation of these two elements relative to each other.FIG.2shows a cross-section through the actuation device1in the area of the anti-rotation device29. In the case at hand, the actuation device1has an anti-rotation element30that is connected to the threaded spindle23in a rotationally fixed manner. The anti-rotation element30interacts with the housing7to form the anti-rotation device29. According to a further embodiment example, the anti-rotation element30is dispensed with, wherein the threaded spindle23interacts directly with the housing7to form the anti-rotation device29. In the present case, the anti-rotation element30has two radial projections31, each of which engages radially in a different radial recess32of the housing7to form the anti-rotation device29. In the present case, the radial projections31are diametrically opposite each other in relation to the longitudinal center axis of the threaded spindle23. The radial recesses32are formed as grooves32, which extend through the housing7in the axial direction.

As can be seen fromFIG.2, a width33of the radial recesses32is greater than a width34of the radial projections31. Accordingly, the anti-rotation device29comprises a circumferential backlash35, so that at least a slight rotation of the threaded spindle23relative to the housing7is possible. The threaded spindle23can generally be rotated in a first direction of rotation36, which closes the circumferential backlash35, and in a second direction of rotation37, which opens the circumferential backlash35. If the circumferential backlash35is closed, a sufficiently strong force acting on the threaded spindle23in the first direction of rotation36causes the threaded spindle23to be displaced in the direction of the pressure element3, i.e., in the first direction5. If the friction brake devices are to be actuated by the actuation device1, the electric machine19is therefore controlled such that it provides a force acting on the threaded spindle23in the first direction of rotation36. If the circumferential backlash35is open before the electric machine19is actuated, the threaded spindle23is initially turned in the first direction of rotation36by the force provided. The threaded spindle23is only moved in the first direction5when the circumferential backlash35is closed. However, the closing of the circumferential backlash35is accompanied by the generation of a clicking noise or banging noise. In the actuation device1shown inFIG.2, the circumferential backlash35is closed. As can be seen fromFIG.2, a first stop38of the radial projections31is in contact with a second stop39of the radial recesses32when the circumferential backlash35is closed.

FIG.3shows a further longitudinal section of the actuation device1in the area of the threaded spindle23. As can be seen fromFIG.3, the actuation device comprises a spring element40. The spring element40applies a preload force to the threaded spindle23in order to close the circumferential backlash35. The preload force thus acts on the threaded spindle23in the first direction of rotation36. The preload force ensures that the circumferential backlash35is always closed, in particular independently of any actuation of the electric machine19. Because the circumferential backlash35is closed by the preload force, there is no need for the electrical machine19to overcome or close the circumferential backlash35when the friction brake devices are actuated. This means that the aforementioned clicking noise or banging noise does not occur.

According to the embodiment example shown in the figures, the spring element40is designed as a coil spring40. The spring element40is arranged coaxially to the threaded spindle23and encloses the threaded spindle23radially with respect to the longitudinal center axis of the threaded spindle23.

The threaded spindle23comprises a first end section41facing away from the pressure element3having an axial stop42. The axial stop42faces the pressure element3. A first end43of the spring element40is arranged at the axial stop42. The spring element40also comprises a second end44. The second end44is arranged on a bearing ring45of the rotary bearing26which is fixed to the housing. However, other arrangements of the spring element40are also possible. For example, according to a further embodiment example, the first end43is not arranged on the threaded spindle23, but on the anti-rotation element30. According to a further embodiment example, the second end44is not arranged on the bearing ring45, but for example directly on the housing7.

According to the embodiment example shown in the figures, the spring element40is twisted such that it provides the preload force as a torsional force. In addition, the spring element40is compressed such that it applies, in addition to the preload force, a restoring force directed away from the pressure element3to the threaded spindle23. However, other embodiments of the spring element40are also possible. According to a further embodiment example, the spring element40is arranged in one of the radial recesses32and is compressed such that it provides a compressive force acting on the radial projection31in the first direction of rotation36. Even in such an embodiment, closing of the circumferential backlash35can be achieved by the spring element40.

The actuation device1also comprises an actuating element50which is displaceably mounted in an axial aperture51of the threaded spindle23. A first end52of the actuating element50can be/is coupled to a brake pedal of the brake system2by an input rod53, so that the actuating element50can then be displaceably actuated by an actuation of the brake pedal. A second end54of the actuating element50is coupled to the pressure element3such that the pressure element3is displaceable by the actuating element50. The friction brake devices can therefore also be actuated by pressing the brake pedal.