Vehicle braking system and methods for operating such a vehicle braking system

Abstract

The invention relates to a vehicle braking system for a two-track vehicle, which has a vehicle brake (1, 3) on each of the two vehicle axles for each vehicle wheel. Two of the vehicle wheel brakes (3) each have a parking-capable actuator (21) that can be controlled by a brake control unit (6). This actuator applies a contact pressure to the vehicle wheel brake (3) in both braking and parking modes to exert a holding torque. During a change of operation between parking and braking modes, the parking-capable actuator (21) passes through a zero position (0) in which it exerts no contact pressure on the vehicle wheel brake (3). According to the invention, during the change of operation, the actuators (2), particularly those not capable of parking, of the other two vehicle wheel brakes (1) remain in braking mode at least until sufficient contact pressure for the holding torque is again established by the respective parking-capable actuator (21).

Description

[0001] The invention relates to a vehicle braking system according to the preamble of claim 1 and to a method for operating such a vehicle braking system according to claim 10.

[0002] A vehicle braking system of this type for a two-track vehicle is equipped with a brake for each wheel on both axles. Two of the wheel brakes each have a parking-capable actuator, controlled by a brake control unit, which can apply pressure to the wheel brake for both braking and parking operations.

[0003] Due to its design, the parking actuator passes through a zero position during a change of operation between parking and braking modes, in which it exerts no pressure on the vehicle's wheel brakes. If the vehicle is to be parked on a slope, a safety gap may arise during such a change of operation.

[0004] A device for preventing a vehicle from rolling away is known from DE 44 46 823 C1. A combined service and parking brake system is known from WO 97 / 29 292 A2.

[0005] The object of the invention is to provide a vehicle braking system or a method that provides increased functional reliability in a simple manner compared to the prior art.

[0006] The problem is solved by the features of claim 1 or 10. Preferred embodiments of the invention are disclosed in the dependent claims.

[0007] The invention relates to a vehicle braking system for a two-track vehicle, which is equipped with a vehicle brake for each wheel on both axles. Of the four vehicle brakes, two wheel brakes each have a parking actuator controllable by a brake control unit, which applies contact pressure to the wheel brake in both braking and parking modes. Due to its design, the parking actuator passes through a neutral position during a change of operation between parking and braking modes, in which it exerts no contact pressure on the wheel brake.According to the characterizing part of claim 1, the following measures are taken to prevent a safety gap when passing through the zero position: During the changeover, the non-parking actuators of the two other vehicle wheel brakes remain in braking mode at least until the respective parking actuator has passed through the zero position and has again built up sufficient contact pressure for the holding torque. The use of the non-parking vehicle wheel brakes temporarily compensates for the lack of braking pressure of the parking actuator during the zero position transition. Therefore, no safety gap occurs when passing through the zero position.

[0008] In one specific embodiment, the brake control unit can have an automatic function with a coordinating module. If an impending change in operating mode is detected, the coordinating module activates the non-parking actuators of the two other vehicle wheel brakes with a brake signal until sufficient contact pressure for a holding torque is generated by the respective parking actuator. As soon as sufficient contact pressure for the holding torque is generated by the two parking actuators to safely hold the vehicle, the brake control unit can deactivate the non-parking actuators. Alternatively, the driver can release the brake pedal, which deactivates the non-parking actuators.

[0009] In a technical implementation, the coordination module can control the two parking-capable actuators with a time delay. This means that during the transition control, one parking-capable actuator switches to its operating mode first. After the operating mode change of one actuator is complete, the other parking-capable actuator then switches to its operating mode. The braking operation of the two non-parking-capable actuators remains active during these staggered operating mode changes. This ensures that three vehicle wheels are always engaged with the brakes during the transition control, thus providing reliable parking protection.

[0010] In one specific embodiment, the two wheel brakes of the vehicle's rear axle are equipped with the parking-capable actuators, while the two wheel brakes of the vehicle's front axle are equipped with the non-parking-capable actuators.

[0011] In one technical implementation, the parking actuator can comprise a pair of discs consisting of a stationary disc and a coaxially rotating disc, as well as at least one intermediate ball-ramp unit. The vehicle wheel brake associated with the parking actuator can be designed as a multi-disc brake. With the aid of the parking actuator, the multi-disc brake can be subjected to contact pressure when the braking or parking mode is engaged. Conversely, the multi-disc brake can be pressure-relieved when the braking or parking mode is disengaged. The ball rolls between the opposing, inclined ball tracks of the two discs. To engage the braking mode, the rotating disc rotates from a neutral position in a braking direction, causing the ball to roll between the opposing ball tracks of the disc pair while the pair is axially spread.To engage the parking mode, the rotating disc turns from its neutral position in a parking direction opposite to the braking direction. This brings the facing sliding surfaces of the disc pair into contact, with axial spreading of the disc pair to apply pressure to the multi-disc brake. Simultaneously, the ball loses contact with the ball tracks of the disc pair.

[0012] When the brake 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.

[0013] Conversely, the actuator is designed so that when park mode 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.

[0014] The ball tracks of the disc pair can only be in rolling contact with the ball when the brake is engaged. In contrast, when the parking mode is engaged, the ball can be out of rolling contact with the ball tracks. This means that immediately upon the disc's rotation 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.

[0015] The parking actuator has an electric motor that can be controlled by the electronic brake control unit and is in drive connection with the rotating disc.

[0016] For example, a vehicle transition from braking to parking mode can be performed as follows: The driver activates parking mode and simultaneously depresses the brake pedal, thus activating the non-parking actuators of the vehicle's brakes. The parking actuators switch to their respective operating modes while the non-parking actuators remain active. The driver then switches off the vehicle's ignition, whereupon the vehicle is held securely in its parking position by the two normally closed (NC) parking actuators. With the ignition switched off, the two normally open (NO) parking actuators lose their braking effect.

[0017] For example, a vehicle transition from parking mode to operating mode can be performed as follows: The driver switches on the vehicle ignition, activating operating mode while simultaneously depressing the brake pedal. As a result of the brake pedal being depressed, the non-parking actuators of the vehicle's brakes are engaged. With the ignition switched on, the control unit enables power to be supplied to the parking actuators, allowing them to switch from parking mode to braking mode while the non-parking actuators remain active. After the driver releases the brake pedal, driving can commence.

[0018] An embodiment of the invention is described below with reference to the accompanying figures.

[0019] They show: Fig. Figures 1a to 8b show different views illustrating the structure and function of the vehicle braking system.

[0020] In the Fig. Figure 1a shows a rough schematic representation of a vehicle braking system of a two-track vehicle, insofar as it is necessary for understanding the invention. The vehicle braking system has wheel brakes 1 on the front axle of the vehicle for each wheel, which are designed as conventional disc brakes. The rear axle of the vehicle is equipped with a drive / brake module 4, the transmission structure of which is shown in the Fig. Figure 1b shows that the rear wheel brakes, designed as multi-disc brakes 3, are integrated into the drive / brake module 4 and can be actuated by means of parking actuators 21. Both the actuators 21 of the rear wheel brakes 3 and the actuators 2 of the front wheel brakes 1 can be controlled via signal lines 10 by means of an electronic control unit 6, in which a later based on the Fig. The automatic function 8 described in section 2 is integrated.

[0021] In the transmission structure of the drive / brake module 4 installed in the rear vehicle axle, an electric motor 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 connected to the vehicle wheels via output shafts 11. Fig. In diagram 1b, 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.

[0022] 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. 1b 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.

[0023] In the Fig. 1b The two multi-disc brakes 3 each act directly on the output shafts 11. This means that the multi-disc brake 3 with its inner disc carrier 18 is connected to the respective output shaft 11, while the outer disc carrier 17 is fixedly connected to a gearbox housing wall 19. The disc pack located between the outer disc carrier 17 and the inner disc carrier 18 can be subjected to contact pressure via the parkable actuator 21.

[0024] In the Fig. 2 Each of the two parkable actuators 21 consists of an implicit spindle drive 16 with an electric motor, which is driven by 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 implicit 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.

[0025] The lamellar assembly located between the outer lamella carrier 17 and the inner lamella carrier 18 can be subjected to contact pressure by means of the actuator 21. Depending on the control signal of the actuator 21, a braking mode for vehicle braking or, alternatively, a parking mode when the vehicle is parked can be engaged or disengaged. A key aspect of the invention is that both the braking mode and the parking mode can be engaged or disengaged by means of the actuator 21. For safety reasons, the electrically controlled actuator 21 is not self-locking when the braking mode is engaged. In contrast, the electrically controlled actuator 21 is self-locking when the parking mode is engaged.

[0026] 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.

[0027] The following is based on the Fig. Sections 4a to 8b describe the functionality of the respective parking-capable actuator 21. 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.

[0028] Depending on a direction of rotation D B , D PThe rotating disc 27 can be used either for braking the vehicle while driving, or alternatively for 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).

[0029] 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.

[0030] The following will be based on the Fig. Sections 5a to 6b initially describe how to engage the brakes. 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 multi-disc brake 3 transmits a measurable, predefined torque. In the Kisspoint KP, the rotatable disc 27 (starting from the zero rotation 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.

[0031] When the brake 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 remain 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.

[0032] To set up the brake operation, 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.

[0033] 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.

[0034] Based on the Fig. Sections 7a to 8b below describe how to engage the parking mode. Starting from the point described in the Fig. 4a and Fig. In the zero position shown in 4b, the rotatable disc 27 is turned to engage the parking mode in a direction of rotation D relative to the braking direction. B opposite parking direction D P via a parking swivel angle into a parking space S P twisted to the right.

[0035] 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 mode, 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.

[0036] 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.

[0037] With regard to ensuring the safe operation of the parking system, the parking space S is located in parking area S. PThe transfer point U is positioned between the rotation zero position 0 and the kiss point KP. When parking mode 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.

[0038] 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 outlets 41 of the park ball tracks 37. When the park mode is engaged, the ball track outlets 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 park 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, which are in sliding contact.

[0039] To engage the parking mode, the rotating disc 27 is turned in the opposite direction to the parking rotation D. P rotated back to the zero position (0).

[0040] To bring the vehicle to a stop, the driver presses the brake pedal, which engages all vehicle brakes 1, 3. If the vehicle is to be safely parked after coming to a standstill, the driver activates a parking mode, for example by pressing the P button while still pressing the brake pedal. The brake control unit 6 then activates the parking actuators 21 of the two rear vehicle brakes 3 to engage parking mode. Each actuator 21 switches from braking mode to parking mode. Due to its design, each parking actuator 21 passes through its zero position (0) during the changeover from braking mode to parking mode (or vice versa), in which it exerts no pressure on the multi-disc brake assembly 3.

[0041] Since both front axle brakes 1 are engaged at the time of the change of operation as a result of the brake pedal being actuated, a safety gap is avoided.

[0042] In an autonomously or automatically operated vehicle, the following measures are taken according to the invention to avoid such a security gap: The brake control unit 6 has an automatic function 8, the program modules of which are shown in the block diagram of the Fig. 2 are indicated. Accordingly, the automatic function 8 consists of a determination module 42 and a coordination module 43. The determination module 42 is in the Fig.2 exemplified by a signal connection with a rotary angle sensor 45, which detects the current rotation angle of the rotatable disc 27 of the respective parking-capable actuator 21. Furthermore, other relevant driving operation parameters are present at the signal input of the detection module 42. Based on this, the detection module 42 determines whether the actuator 21 will pass through the zero rotation position 0 during further operation, i.e., whether a change of operation is imminent. If such an imminent change of operation is present, the coordination module 43 controls the two front, non-parking-capable actuators 2 with a brake signal y for a period of time. B until the two rear actuators 21 capable of parking have built up sufficient contact pressure to provide a holding torque.

[0043] A key aspect of the invention is that the coordination module 43 controls the two parking-capable actuators 21 with a time delay. This ensures that during the transition control, the operating mode of one parking-capable actuator 21 changes first, followed by the operating mode of the other parking-capable actuator 21. The braking operation of the two non-parking-capable actuators 2 remains active during these two staggered operating mode changes. This guarantees that three vehicle wheels are always engaged during the transition control.

[0044] For example, the driver can bring a parked vehicle, still in park mode, into operating mode as follows. The driver performs the following steps: First, the driver switches on the vehicle ignition and activates operating mode (i.e., by pressing a D button for forward travel or an R button for reverse travel) while simultaneously depressing the brake pedal. Due to the depressed brake pedal, the non-parking actuators 2 of the vehicle brakes 1 are in braking mode. With the ignition switched on, the brake control unit 9 supplies power to the parking actuators 21. This allows the parking actuators 21 to switch from park mode to braking mode while the brake pedal is still depressed. After releasing the brake pedal, the driver can begin driving.

[0045] The above process sequence can be carried out in an autonomous or automated vehicle, largely independently of the driver, using the automatic function 8 of the brake control unit 6. REFERENCE MARK LIST: 1. Front vehicle wheel brake 2 non-parking actuators 3-disc brake or rear vehicle brake 4 Drive / brake module 5 Rotor shaft 6 Brake control unit 7th reduction stage 8 Automatic function 9 axle differential 10 Signal line 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 parking actuator 23 Ball Ramp Unit 25 fixed disc 27 rotating disc 29 balls 30 cage 31 Gearing 34 Ball Ramp 35 Brake ball track 37 Park Ball Track 38 sliding ramps 39 Ramp recess 41 Marble Run Run 42 Investigation module 43 Coordination module 45° rotary angle sensor 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, p P2 Sub-areas D B Brake rotation direction D P Parking direction f ball freewheel y B Brake signal

Claims

[1] Vehicle braking system for a two-track vehicle, which has a vehicle brake (1, 3) on each of the two vehicle axles for each vehicle wheel, of which two vehicle wheel brakes (3) each have a parking actuator (21) controllable by a brake control unit (6), which builds up a contact pressure acting on the vehicle wheel brake (3) in both braking and parking modes in order to exert a holding torque, wherein during a change of operation between parking mode and braking mode the parking actuator (21) passes through a zero position (0) in which the parking actuator (21) does not exert any contact pressure on the vehicle wheel brake (3), characterized by , that during the change of operation the non-parking actuators (2) of the two other vehicle wheel brakes (1) remain in braking operation at least until sufficient contact pressure for the holding torque is built up again by the respective parking actuator (21). [2] Vehicle braking system according to claim 1, characterized by , that the brake control unit (6) has an automatic function (8) with a coordination module (43) which, when the operation of the parking actuators (21) changes, activates the braking operation of the non-parking actuators (2). [3] Vehicle braking system according to claim 1 or 2, characterized by , that the two parking-capable actuators (21) can be controlled with a time delay, so that first one parking-capable actuator (21) performs the change of operation, and subsequently the other parking-capable actuator (21) performs the change of operation, so that The vehicle is securely held by three wheels during the change of operation. [4] Vehicle braking system according to claim 3, wherein the rear axle brakes (3) are equipped with the parking actuators (21), while the front axle brakes (1) are equipped with the non-parking actuators (2). [5] Vehicle braking system according to any one of the preceding claims, characterized by , that as soon as sufficient contact pressure for the holding torque has been built up again by the two parking actuators (21) to hold the vehicle securely, the non-parking actuators (2) are deactivated. [6] Vehicle braking system according to any one of the preceding claims, characterized by , that the parkable actuator (21) is designed with a pair of disks consisting of a stationary disk (25) and a rotatable disk (27) coaxially thereto, as well as at least one intermediate ball-ramp unit (23), such that To engage the brake operation, the rotatable disc (27) is rotated from the zero position (0) in a braking direction (D). B) rotates, causing a ball (29) to roll between opposing ball tracks (35) of the pair of discs, with axial spreading of the pair of discs in order to apply pressure to the vehicle wheel brake designed as a lamellar brake (3); and that To engage park mode, rotate the disc (27) from the zero position (0) in a direction of rotation relative to the braking direction (D). B ) opposite parking rotation direction (D P ) rotates, whereby mutually facing sliding ramps (38) of the disc pair can be brought into a self-locking sliding position, with axial spreading of the disc pair in order to apply pressure to the vehicle wheel brake designed as a lamellar brake. [7] Vehicle braking system according to any one of the preceding claims, characterized by , that the parking actuator (21) has an electric motor that can be controlled by the brake control unit (6), and in particular the electric motor is in drive connection with the rotatable disc (27). [8] Vehicle braking system according to claim 7, characterized by , that for a transition of the vehicle from the braking function to a parking mode, the non-parking actuators (2) can be activated in braking mode, so that The changeover of the operating mode of the parking-capable actuators (21) takes place while the non-parking-capable actuators (2) are activated; and that subsequently, the driver switches off the vehicle ignition, whereupon the vehicle is held securely in its parked position by means of the two parking-capable, normally closed actuators (21), while the two non-parking-capable, normally open actuators (2) lose their braking effect. [9] Vehicle braking system according to claim 7 or 8, characterized by , that for a transition of the vehicle from a parking function to an operating mode, in particular the driver switches on the vehicle ignition, activates the operating mode and simultaneously depresses the brake pedal or activates the non-parking actuators (2), whereby the non-parking actuators (2) of the vehicle brakes (1) are in braking mode, that With the ignition switched on, the brake control unit (6) releases a vehicle power supply to the parking actuators (21) in order to transfer the parking actuators (21) from parking mode to braking mode, while the non-parking actuators (2) are still activated, and that Driving begins after the brake pedal is released. [10] Method for operating a vehicle braking system according to any of the preceding claims.

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