Vehicle braking system

Abstract

The invention relates to a vehicle braking system with a multi-disc brake or clutch (3) comprising an actuator (21) with a pair of discs consisting of a stationary disc (25) and a rotatable disc (27) coaxially thereto, as well as at least one intermediate ball-ramp unit (23), wherein, to engage a braking function, the rotatable disc (27) rotates from a zero-position position (0) in a braking direction (D). B ) rotates, causing the ball (29) to roll between opposing ball tracks (35) of the disc pair, with axial spreading of the disc pair to apply pressure to the multi-plate brake or clutch (3), and wherein, to engage the parking function, the rotatable disc (27) rotates from the zero-rotation position (0) in a direction relative to the braking direction (D). B ) opposite parking rotation direction (D P) rotates, whereby the opposing sliding ramps (38) of the disc pair can be brought into a sliding position, with axial spreading of the disc pair in order to apply contact pressure to the multi-plate brake or clutch (3). According to the invention, the ball-ramp unit (23) has a positioning aid (42) with which the ball (29), which is out of force transmission with the disc pair when the parking function is engaged, remains backlash-free in a predefined ball position.

Description

[0001] The invention relates to a vehicle braking system according to the preamble of claim 1.

[0002] A vehicle braking system of this type features, instead of conventional disc or drum brakes, at least one multi-disc brake acting on the vehicle axle. This brake allows for the activation or deactivation of a braking function for vehicle braking while driving or a parking function when the vehicle is parked. For this purpose, the multi-disc brake has two independently operating actuators: a brake actuator and a parking actuator. These are controlled by a control unit using electrical or hydraulic signals. For safety reasons, the brake actuator can be designed to be normally open (non-self-locking), while the parking actuator can be normally closed (self-locking). Integrating these two actuators into the multi-disc brake requires installation space and involves additional design effort.

[0003] From DE 102 52 974 A1, an engagement mechanism with a two-stage ramp angle is known. The engagement mechanism has a first ball ramp disk that interacts with the housing on one side. The first ball ramp disk has first ramps on the side interacting with the housing. The first ball ramp disk includes second ramps with a predetermined angle, which are provided on the side facing away from the housing. The engagement mechanism further comprises a rotatably driven ball ramp disk next to the first ball ramp disk on the side facing away from the housing. The engagement mechanism also has a spring element arranged between the first ball ramp disk and the second ball ramp disk.

[0004] From EP 2 093 450 A1, a ball ramp brake is known which has a disc arrangement within a housing and an annular, rotatable actuating element for actuating a brake by compressing the disc arrangement. The rotatable actuating element comprises a plurality of recesses which become progressively shallower in a first circumferential direction.

[0005] From DE 10 2010 039 448 A1, a device for the rotationally fixed connection of two components via switching element halves is known. Depending on the switching state, the bearing changes between toothing, clearance fit, or conical centering. This reduces drag torques and improves guidance. Figures show various switching elements, combinations with friction elements, and ball-ramp actuators.

[0006] A wet multi-plate clutch with regulated oil supply is known from US patent 2018 / 0216672A1. An adjustable cover element controls the oil flow depending on the engagement state. This reduces drag losses when the clutch is open and ensures cooling when it is slipping. Figures show the clutch, the cover element, and its integration into the transmission.

[0007] The object of the invention is to provide a vehicle braking system that, compared to the prior art, provides increased functional reliability in a simple manner.

[0008] The problem is solved by the features of claim 1. Preferred embodiments of the invention are disclosed in the dependent claims.

[0009] The invention relates to a vehicle braking system with at least one multi-disc brake or clutch acting on a vehicle axle, by means of which a braking function for vehicle braking during driving and a parking function when the vehicle is parked can be engaged / disengaged. Exactly one electrically controlled actuator is associated with the multi-disc brake or clutch. The actuator can be used to engage / disengage both the braking function and, alternatively, the parking function. For safety reasons, the electrically controlled actuator is normally open (i.e., not self-locking) when the braking function is engaged, while it is normally closed (i.e., self-locking) when the parking function is engaged. In this way, a simplified braking concept is achieved – compared to the prior art – with regard to cost, installation space, and component weight.

[0010] The actuator comprises a pair of discs, consisting of a stationary disc and a coaxially rotating disc, as well as at least one intermediate ball ramp unit. This assembly allows the multi-disc brake to be subjected to contact pressure when the braking or parking function is engaged. Conversely, the multi-disc brake can be relieved of pressure when the braking or parking function is disengaged. The ball rolls between opposing, inclined ball tracks on the two discs. To engage the braking function, the rotating disc turns from a neutral position in a braking direction, causing the ball to roll between the opposing ball tracks of the disc pair while axially spreading the pair. To engage the parking function, the rotating disc turns from a neutral position in a parking direction opposite to the braking direction.This causes the facing sliding surfaces of the disc pair to engage in a sliding position, with axial spreading of the disc pair in order to apply contact pressure to the multi-disc brake. Simultaneously, the ball loses contact with the ball tracks of the disc pair.

[0011] When the braking function is engaged, there is rolling resistance between the ball and the ball tracks of the disc pair. The low rolling resistance compared to a sliding system means that the ball-ramp unit is not self-locking; that is, it remains open when de-energized. Therefore, in the event of a power failure, the actuator's braking effect automatically cancels out, thus fulfilling safety requirements.

[0012] Conversely, the actuator is designed so that when the parking function is engaged, it is self-locking, meaning it remains closed when de-energized. Therefore, in the event of a power failure, the parking function – unlike the braking function – is permanently maintained, thus ensuring that the parking function also meets safety requirements.

[0013] According to the characterizing part of claim 1, the ball ramp unit has a positioning aid with which the ball, which is out of rolling contact with the ball tracks of the disc pair when the parking function is engaged, remains in a predefined ball position without play, in which it is clearly identifiable by an electronic control unit that controls the actuator. The invention solves the problem that, without such a positioning aid, the ball can move with play between the ball tracks when the parking function is engaged. In this case, the ball can assume an inaccurate ball position relative to the disc pair, which is no longer clearly identifiable by the electronic control unit of the actuator.

[0014] In a technical implementation, the positioning aid can have at least one ball movement stop against which the ball tracks terminate. The positioning aid also includes a spring element that biases the ball towards the ball movement stop with a spring force. When the parking function is engaged, the ball is therefore pressed by the spring force into the predefined ball position against the ball movement stop without any play.

[0015] With the ball track geometry described above, the ball can assume the predefined ball position as soon as the rotatable disc, which rotates from a brake setting range in the parking direction, reaches the zero rotation position, at which the disc pair exerts no pressure on the lamellar brake.

[0016] The ball tracks of the disc pair are therefore only in rolling contact with the ball when the braking function is engaged. In contrast, when the parking function is engaged, the ball is out of rolling contact with the ball tracks. This means that immediately upon the discs starting to rotate from the neutral position to the parking position, the sliding ramps engage and, simultaneously, the ball is released from rolling contact. For example, the spring element can be supported between a ball cage, in which the ball is guided, and the rotationally fixed disc of the disc pair.

[0017] The actuator features an electric motor, controlled by the electronic control unit, which is connected to the rotating disc. The electronic control unit also includes an evaluation module that performs a calibration step before the vehicle starts operating. During the calibration step, the electronic control unit rotates the disc in different directions, thereby activating and deactivating the braking function and, alternately, the parking function. The evaluation module of the electronic control unit records the current draw of the electric motor during the calibration step. Based on the current draw of the electric motor across the rotation of the disc, the evaluation module can identify the zero position, i.e., a corresponding angle of rotation of the disc, and store this information in a database.

[0018] To ensure unambiguous identification of the zero rotation position, the geometry of the sliding ramps is designed as follows: The sliding ramps can have steep calibration contours. When the rotating disc is turned in the park direction, the calibration contours of the sliding ramps come into sliding contact with each other, creating a pressure point. This pressure point can be overcome by applying increased force, which in turn results in a correspondingly increased current draw from the electric motor. The calibration contours of the sliding ramps are positioned so that the pressure point is established as soon as the rotating disc reaches its zero rotation position. The evaluation module thus identifies the zero rotation position of the rotating disc as soon as the pressure point is detected.

[0019] A comparative example not covered by the invention and an embodiment of the invention are described below with reference to the accompanying figures.

[0020] They show: Fig. 1 an electrified vehicle axle; Fig. 2 to 3c different views of a multi-disc brake with actuator installed in the vehicle axle; Fig. 4a to 8b the actuator according to the comparative example in different operating states; and Fig. 9a to 12b the actuator according to the invention in different operating states.

[0021] In the Fig. Figure 1 shows an electrified vehicle axle with an electric motor EM and a gearbox. The electric motor EM is connected to a high-voltage battery (not shown). Conventional wheel disc or drum brakes are omitted from the vehicle axle. Instead of such conventional wheel brakes, the vehicle axle features multi-disc brakes 3, which enable vehicle braking.

[0022] The electric machine EM is connected via its rotor shaft 5 and an intermediate reduction stage 7 to the input side of an axle differential 9. The output sides of the differential are driven by output shafts 11 and connected to the vehicle wheels. In the Fig. 1 The electric motor EM is installed transversely in the vehicle axle. Accordingly, the rotor shaft 5 and the output shafts 11 are parallel to each other. Likewise, the multi-disc brakes 3 installed in the vehicle axle are aligned parallel to each other in the transverse direction y of the vehicle.

[0023] Viewed in the transverse direction y of the vehicle, the axle has one of the multi-disc brakes 3 on each side of the vehicle. These can be controlled by an electronic control unit (not shown) to perform uniform or uneven braking at both vehicle wheels.

[0024] The reduction gear stage 7 is driven by an input-side axle differential gear 13. The axle differential gear 13 is rotationally fixed to a rotating differential housing 15. According to the Fig. 1 drives the axle differential 9 with the multi-plate brakes 3 open in the transverse direction y of the vehicle in a 50 / 50 distribution on both sides to the two output shafts 11 leading to the vehicle wheels.

[0025] In the Fig. 1. The two multi-disc brakes 3 act directly on the output shafts 11. This means that the inner disc carrier 18 of the multi-disc brake 3 is connected to the respective output shaft 11, while the outer disc carrier 17 is fixed to a gearbox housing wall 19. The disc assembly located between the outer disc carrier 17 and the inner disc carrier 18 can be subjected to contact pressure via an actuator 21. The actuator 21 can be controlled by the control unit by means of electrical signals.

[0026] Actuator 21 consists of a [missing information] in the Fig. 2 indicated spindle drive 16 with electric motor 22, which is in drive connection with a toothed section 31 of a rotatable disc 27. The rotatable disc 27, together with a non-rotating disc 25, forms part of a clamping mechanism. The non-rotating disc 25 can be supported circumferentially by an indicated torque support 14. In addition, the non-rotating disc 25 is supported axially on a counter support 12. The clamping mechanism has a total of four circumferentially distributed ball-ramp units 23, as can be seen from the Fig. 3a to 3b. Each ball-ramp unit 23 has a ball 29 that rolls between the two disks 25, 27.

[0027] The lamellar assembly located between the outer lamella carrier 39 and the inner lamella carrier can be subjected to contact pressure by means of the actuator 21. Depending on the control of the actuator 21, a braking function for vehicle braking while driving, or alternatively a parking function when the vehicle is parked, can be engaged or disengaged. A key aspect of the invention is that both the braking function and the parking function can be engaged / disengaged by means of the actuator 21. For safety reasons, the electrically controlled actuator 21 is normally open (i.e., not self-locking) when the braking function is engaged. In contrast, the electrically controlled actuator 21 is normally closed (i.e., self-locking) when the parking function is engaged.

[0028] As from the Fig. As can be seen from Figures 3a to 3c, each of the ball-ramp units 23 has ball ramps 34 and spaced-apart sliding ramps 38 that act between the disks 25, 27. The balls 29 of the four ball-ramp units 23 are, according to the Fig. 3b led in a cage 30.

[0029] For the sake of a simpler understanding of the invention, the following will first be explained using the following: Fig. Sections 4a to 8b describe a comparative example not encompassed by the invention. Accordingly, in the Fig. 4a and Fig. 4b shows one of the ball-ramp units 23 in unfolded form. Fig. Figure 4a shows two corresponding sliding ramps 38 of the disk pair, while Fig. Figure 4b shows two corresponding ball ramps 34 of the disc pair with an intermediate ball 29. Each of the ball ramps 34 consists of a braking ball track 35 and a parking ball track 37, which merge into each other at a ramp depression 39. In the Fig. In section 4b, the ball 29 is located in the ramp recess 39. The ramp recess 39 defines a zero rotation position 0, in which the pair of discs exerts no contact pressure on the lamellar assembly. The braking ball tracks 35 of the two discs 25, 27 are point-symmetrical with respect to the ball 29 (which is in the zero rotation position 0). Furthermore, the parking ball track 37 and the braking ball track 35 of each ball ramp 34 are symmetrical with respect to an axis of symmetry passing through the ramp recess 39, with equal angles of inclination.

[0030] Depending on a direction of rotation D B , D PThe rotating disc 27 can be configured to either engage or disengage a braking function for vehicle braking while driving, or alternatively, a parking function when the vehicle is parked. When the braking function is engaged, the disc pair of actuator 21 is normally open (i.e., not self-locking). In contrast, when the parking function is engaged, the disc pair of actuator 21 is normally closed (i.e., self-locking).

[0031] In the Fig. 4a and Fig. Figure 4b shows the pair of discs in their zero rotation position 0. In the zero rotation position 0 (unlike in the Fig. (as shown in 4a) the two sliding ramps 38 are out of contact. The ball 29 is located according to the Fig. 4b in the ramp recesses 39 of the ball ramps 34 of the two discs 25, 27.

[0032] The following will be based on the Fig. Sections 5a to 6b initially describe how to engage the brake function. Starting from the point described in the Fig. 4a and Fig. In the zero position shown in 4b, the rotatable disc 27 is turned in a braking direction D. B via a brake rotation angle to the left into a brake adjustment range S B The ball 29 rolls on the two brake ball tracks 35 of the disc pair, with the disc pair being axially spread over an axial spreading path s. In this way, the lamellar pack of the multi-disc brake 3 is subjected to contact pressure. The contact pressure varies depending on the size of the brake rotation angle. Immediately after leaving the zero rotation position 0, the rotatable disc 27 is adjusted by an axial spreading path s, thereby eliminating any play in the lamellar pack. Further rotational adjustment of the rotatable disc 27 within the brake adjustment range S... B A Kisspoint KP ( Fig. 5b) is achieved, in which the lamellar brake 3 transmits a measurable, predefined torque. In the Kisspoint KP, the rotatable disc 27 (starting from the rotational zero position 0) is rotated by a first axial spreading path Δs1. In the Fig. 6a and Fig. 6b the rotatable disk 27 is adjusted to an end position in which the rotatable disk 27 is adjusted by a second axial spreading path Δs2.

[0033] When the braking function is engaged, a comparatively low rolling resistance acts between the ball 29 and the brake ball tracks 35 of the disc pair. This low rolling resistance means that the ball-ramp units 23 are not self-locking, i.e., they are open when de-energized. Accordingly, in the event of a power failure, the braking effect of the actuated actuator 21 would decrease, thus fulfilling safety requirements.

[0034] To implement the brake function, the rotatable disc 27 (starting from its end position ( Fig. 6a and Fig. 6b) opposite to the direction of braking rotation D B back to the zero rotation position 0 ( Fig. 4a and Fig. 4b) adjusted.

[0035] During the adjustment movement in the brake adjustment range S B The corresponding, inclined sliding ramps 38 remain out of contact with each other, so that smooth rotation of the rotatable disc 27 is ensured.

[0036] Based on the Fig. Sections 7a to 8b below describe how to engage the parking function. Starting from the position shown in the Fig. 4a and Fig. In the zero position shown in 4b, the rotatable disc 27 is used to engage the parking function in a direction of rotation D relative to the brake direction. B opposite parking direction D P via a parking swivel angle into a parking space S P twisted to the right.

[0037] According to the Fig. 7b is parking area S Psubdivided into a first sub-area S P1 and into a second sub-area S P2 In the first sub-area S P1 The ball 29 rolls between the facing parking ball tracks 37 of the pair of discs, while the corresponding sliding ramps 38 are still out of contact. In contrast, in the second sub-area S P2 The sliding surfaces 38 are in sliding contact with each other, while the ball 29 is out of rolling contact with the pair of discs. To engage the parking function, the rotatable disc 27 is rotated from the zero position 0 in the parking direction D. P to a parking rotation angle in the first sub-area S P1 until reaching a transfer point U, as described in the Fig. 7a and Fig. 7b is indicated. According to the Fig. 7a and Fig. 7b generates a third axial spreading path Δs3 at the transfer point U of the disk pair.

[0038] During the adjustment movement in the first sub-area S P1 The ball 29 rolls along the parking ball tracks 37 of the disc pair, with axial spreading of the disc pair, thus eliminating any play in the lamellar brake 3. Upon passing the transfer point U, the rotatable disc 27, with a further increasing parking rotation angle, moves into the second sub-area S. P2 twisted until the parking function is engaged.

[0039] With regard to ensuring reliable engagement of the parking function, the parking space S PThe transfer point U is positioned between the rotation zero position 0 and the kiss point KP. When the parking function is engaged, the transfer point U is therefore passed shortly before reaching the kiss point KP. Upon reaching the kiss point KP, the two corresponding sliding ramps 38 are already in sliding contact with each other, while the ball 29 is out of rolling contact with the two parking ball tracks 37.

[0040] In the Fig. 8a and Fig. 8b the rotatable disc 27 is rotated to its park end position, in which the park function is fully engaged. In the engaged park function, the ball 29 is in a predefined ball freewheel position P ( Fig. 8b). The ball freewheel position P is in the Fig. 8b is defined by means of ball track exits 41 of the parking ball tracks 37. When the parking function is engaged, the ball track exits 41 are spaced apart from each other in the circumferential direction of the discs by a ball freewheel f, in which the ball 29 rolls with play, i.e., without rolling contact, between the parking ball tracks 37 of the disc pair. The contact pressure of the disc pair is therefore generated exclusively by means of the sliding ramps 38 in sliding contact.

[0041] To engage the parking function, the rotating disc 27 is turned in the opposite direction of rotation D to the parking function. P rotated back to the zero position (0).

[0042] In the comparative example of the Fig. 4a to 8b defines the ball freewheel f ( Fig. 7b and Fig. 8b) a ball resting area in which the ball 29 can move with play. Due to this play in the ball's movement, when the parking function is engaged, i.e., when the rotatable disc 27 rotates back towards its zero position 0, the ball 29's position relative to the ball tracks 37 is imprecise, meaning it can no longer be unambiguously identified by an electronic control unit 41 of the electric motor 22. Therefore, in the comparative example, the problem arises that the ball 29 may not be in the ramp recess 39 as soon as the rotatable disc 27 reaches its zero position 0, which could impair operational reliability.

[0043] The following measures are described to keep the ball 29 in a defined ball position when the parking function is engaged, which is uniquely identifiable by the electronic control unit 41 of the electric motor 22.

[0044] This refers to the Fig. Reference is made to Figures 9a to 12b, which describe the inventive design of the actuator 21. The basic structure of the actuator according to the invention is identical to that of the actuator 21 described in Figures 9a to 12b. Fig. 4a to 8b are described, so reference is made to the preliminary description. In contrast to the comparative example, the actuator 21 according to the invention has a positioning aid 42 for the ball 29. With the aid of the positioning aid 42, the ball 29 remains in position when the parking function is engaged ( Fig. 11a, Fig. 11b) except for rolling contact with the ball tracks 35 of the disc pair, is free of play in a predefined ball position. With the parking function engaged ( Fig. 11a, Fig. 11b) the ball 29 is out of force flow with the pair of disks, that is, the ball 29 lifts off from a boundary contour 28 of the rotatable disk 27.

[0045] As from the Fig. As shown in Figures 9a to 12b, the parking ball tracks 37 are omitted according to the invention. Instead, the braking ball tracks 35 terminate at the ramp recess 39 with a ball movement stop 43, which is part of the positioning aid 42. Furthermore, the positioning aid 42 has a spring element 45, which is supported between the rotationally fixed disc 25 and the ball cage 30 and biases the ball 29 with a spring force towards the ball movement stop 43.

[0046] In the Fig. 9a to 12b is the ball ramp unit 23 of the actuator 21 - analogous to the preceding Fig. 4a to 8b - each shown in its unfinished state. Fig. Figure 9a shows two corresponding sliding ramps 38 of the disk pair, while the Fig. Figure 9b shows two corresponding ball ramps 34 of the disc pair with an intermediate ball 29. The brake ball track 35 of the stationary disc 25 terminates at the ramp recess 39 with the ball movement stop 43. The ramp recess 39 defines – as in the comparative example – the zero rotation position 0, in which the disc pair exerts no contact pressure on the lamellar pack of the lamellar brake 3. The braking function is engaged by means of the ball-ramp unit 23 according to the invention analogously to the comparative example, with the difference that the rotatable disc 27 rotates in the braking direction D. B The position is adjusted in the opposite direction to the spring force exerted by the spring element 45. Otherwise, the engagement of the brake function is identical to the comparison example.

[0047] Based on the Fig. 10a and Fig. Section 10b describes a calibration step that can be performed before the vehicle starts operating. In the calibration step, the electronic control unit 41 identifies, based on a reading from an ammeter 51 ( Fig. 1) The current consumption I of the electric motor 22 of the actuator 21 during a rotation of the rotatable disk 27 is recorded, the zero position 0 and the corresponding rotation angle of the rotatable disk 27 are stored in a database of the electronic control unit 41.

[0048] For unambiguous identification of the rotational zero position 0, the two sliding ramps 38, in addition to the shallow flat sections 46, have steep calibration contours 47. During a disk rotation starting from the position shown in the Fig. 9a and Fig. 9b shows the zero position of rotation 0 via a travel path w1 in the parking direction of rotation D. PThe opposing calibration contours 47 come into sliding contact and define a pressure point. The pressure point can be overcome by increasing the force applied or by correspondingly increasing the current draw I of the electric motor 22. As soon as an evaluation module 49 ( Fig. 1) When the pressure point is detected by the electronic control unit 41 with the ammeter 51, the corresponding rotation angle of the rotatable disc 27 is stored as the rotation zero position 0 in the control unit 41.

[0049] In the calibration step, the pressure point is overcome by rotating the rotatable disk 27. After overcoming the pressure point, the flat sections 46 of the two sliding ramps 38 come into sliding contact with each other, so that the current consumption I is abruptly reduced. For example, the transition from the pressure point to the flat sections 46 of the sliding ramps 38 can be defined as the point in time at which the rotatable disk 27 reaches its zero rotation position 0.

[0050] The following will be based on the Fig. Sections 9a to 12b describe the engagement of the parking function according to the invention. Starting from the Fig. 9a and Fig. 9b (where the rotatable disc 27 is in its zero rotation position 0) the rotatable disc 27 is moved into the parking rotation direction D P adjusted. Immediately after leaving the zero rotation position 0, the rotatable disc 27 is moved by an axial spreading distance s ( Fig. 11a) adjusted, by means of which any play is eliminated and the kiss point KP is reached. Immediately after leaving the zero rotation position 0, the ball 29 is no longer in contact with the pair of discs, i.e., it is no longer in rolling contact with the ball tracks 35. By means of the spring element 45, the ball 29 is held in the Fig. 11b pressed to the right against the ball movement stop 43. This ensures that the ball position remains clearly defined even after the parking function is engaged. By further rotating the rotatable disc 27 ( Fig. 12a and Fig. 12b) the pair of discs spreads further by a further axial path s to a maximum position, while the ball 29 remains in contact with the ball movement stop 43.

[0051] For example, from the Fig. As further shown in Figure 11b, the spring 45 is supported against the cage 30 at a slight angle. The cage 30, together with the ball 29, is therefore subjected to a spring force component in the direction of the rotatable disk 27 (i.e., in the axial direction). In this case, the limiting contour 28 of the rotatable disk 27 acts as an axial stop, limiting the axial movement of the ball 29 and the cage 30.

[0052] To engage the parking function, the rotating disc 27 is turned in the opposite direction of rotation D to the parking function. PThe ball 29 is rotated back to its zero rotation position 0. The ball 29 remaining in the predefined ball position ensures that, upon reaching the zero rotation position 0, it is again in the ramp recess 39 and there comes back into rolling contact with the ball tracks 35. REFERENCE MARK LIST: 3-disc brake 5 Rotor shaft 7 reduction gears 9 axle differential 11 Output shaft 12 Counterholds 13 Axle differential gear 14 Torque support 15 Differential housings 16 Spindle drive 17 outer slat carriers 18 internal slat carriers 19 Gearbox housings 21 Actuator 23 Ball Ramp Unit 25 fixed disc 27 rotating disc 28 Boundary contour of the rotating disc 27 29 balls 30 cage 31 Gearing 34 Ball Ramp 35 Brake ball track 37 Park Ball Track 38 sliding ramps 39 Ramp recess 41 electronic control unit 42 Positioning aid 43 Ball movement stop 45 spring element 46 Flat section of the sliding slope 38 47 steep calibration contour of the sliding slope 38 49 Evaluation module 51 Current meter 0 Rotation zero position U handover point KP Kisspoint P Ball freewheel position s axial spreading path S B Brake adjustment range S P Parking area SP1, SP2 sub-areas D B Brake rotation direction D P Parking direction I Current consumption f ball freewheel w1, w2, w3 Positioning paths of the rotating disc 27 in the parking / positioning area S P

Claims

[1] Vehicle braking system with a multi-disc brake or clutch (3) comprising an actuator (21) with a pair of discs consisting of a stationary disc (25) and a rotatable disc (27) coaxially thereto, and at least one intermediate ball-ramp unit (23), wherein, to engage a braking function, the rotatable disc (27) rotates from a zero-position position (0) in a braking direction (D) B ) rotates, causing the ball (29) to roll between opposing ball tracks (35) of the disc pair, with axial spreading of the disc pair to apply pressure to the multi-plate brake or clutch (3), and wherein, to engage the parking function, the rotatable disc (27) rotates from the zero-rotation position (0) in a direction relative to the braking direction (D). B ) opposite parking rotation direction (D P) rotates, whereby the opposing sliding ramps (38) of the disc pair can be brought into a sliding position, with axial spreading of the disc pair in order to apply contact pressure to the multi-plate brake or clutch (3), whereby, when the parking function is engaged, a sliding resistance acts between the corresponding sliding ramps (46) which is significantly greater than the rolling resistance between the ball (29) and the ball tracks (35) of the disc pair, so that when the parking function is engaged the ball-ramp unit (23) is self-locking, i.e., closed when de-energized, characterized by , that the ball ramp unit (23) has a positioning aid (42) with which the ball (29), which is out of force flow with the disc pair when the parking function is engaged, remains free of play in a predefined ball position. [2] Vehicle braking system according to claim 1, characterized by, that the positioning aid (42) has at least one ball movement stop (43) at which the ball tracks (35) terminate, and that the positioning aid (42) has a spring element (45) which biases the ball (29) with a spring force towards the ball movement stop (43), and that when the parking function is engaged, the ball (29) is pressed by the spring force into the predefined ball position against the ball movement stop (43) without play, and that the positioning aid (42) also has a limiting contour (28) formed on the rotatable disc (27) which, when the parking function is engaged, forms an axial stop for the ball (29) which is no longer in the force flow. [3] Vehicle braking system according to claim 2, characterized by , that the spring element (45) is supported between a ball cage (30) in which the ball (29) is guided and the non-rotating disc (25). [4] Vehicle braking system according to any one of the preceding claims, characterized by, that the ball (29) assumes the predefined ball position as soon as it leaves a braking adjustment range (S B ) coming and in the direction of rotation in the parking direction (D P ) rotating rotatable disc (27) reaches the rotation zero position (0). [5] Vehicle braking system according to one of the preceding claims characterized by , that immediately with the start of the disc rotation from the rotation zero position (0) into the park position (S P ), that is, when the parking function is engaged, the sliding ramps (38) come into sliding contact and at the same time the ball (29) is no longer in rolling contact or force flow with the disc pair, and / or that immediately with the start of the disc rotation from the rotation zero position (0) into the brake adjustment range (S B), that is, when the brake function is engaged, the sliding ramps (38) come out of the sliding position and at the same time the ball (29) comes into rolling contact or force flow with the disc pair from its predefined ball position. [6] Vehicle braking system according to one of the preceding claims characterized by , that the actuator (21) has an electric motor (22) which can be controlled by an electronic control unit (41) and which is in drive connection with the rotatable disk (27), and that the electronic control unit (41) has an evaluation module (49) with which a calibration step can be carried out in which the evaluation module (49) identifies the zero rotation position (0) of the rotatable disk (27) on the basis of the current consumption (I) of the electric motor (22) during a rotation of the rotatable disk (27). [7] Vehicle braking system according to claim 6, characterized by, that the sliding ramps (38) have steep calibration contours (47) which define a pressure point upon sliding contact, which can be overcome with increased force or a correspondingly increased current consumption (I) of the electric motor (22), and that on the basis of a pressure point detection the evaluation module (49) identifies the rotation zero position (0). [8] Vehicle braking system according to any one of the preceding claims, characterized by , that when the braking function is engaged, a rolling resistance acts between the ball (29) and the ball tracks (35) of the disc pair, and that the rolling resistance causes the ball-ramp unit (23) to not be self-locking, i.e., to be open when de-energized, so that in the event of a power failure the braking effect of the actuator (21) is canceled out.

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