Vehicle braking system

Abstract

The invention relates to a vehicle braking system having at least one multi-disc brake or clutch (3) which acts on a vehicle axle of a vehicle and by means of which a brake function for a vehicle braking process during a driving operation and a parking function when the vehicle is parked can be engaged / disengaged. According to the invention, an electrically controllable actuator (21) is provided which is associated with the multi-disc brake or clutch (3) and by means of which the braking function as well as the parking function can be engaged / disengaged.

Description

[0001] Vehicle braking system

[0002] DESCRIPTION:

[0003] The invention relates to a vehicle braking system according to the preamble of claim 1.

[0004] A generic vehicle braking system has, instead of conventional disc or drum brakes, at least one multi-disk brake acting on the vehicle axle, by means of which a braking function for vehicle braking during ferry operation or a parking function when the vehicle is parked can be engaged or disengaged. For this purpose, the multi-disk brake has two separately operating actuators, namely a brake actuator and a parking actuator, which can be controlled by a control unit using electrical or hydraulic signals. For safety reasons, the brake actuator can be designed to be normally open or non-self-locking, while the parking actuator can be normally closed or self-locking. Installing these two actuators on the multi-disk brake requires additional space and involves additional design effort.

[0005] The object of the invention is to provide a vehicle braking system which can be implemented with reduced installation space and reduced design effort compared to the prior art.

[0006] The object is solved by the features of claim 1. Preferred developments of the invention are disclosed in the subclaims.

[0007] The invention is based on a vehicle braking system with at least one multi-disk brake or clutch acting on a vehicle axle of a vehicle, by means of which a braking function for vehicle braking during ferry operation and a parking function when the vehicle is parked can be engaged / disengaged. According to the characterizing part of claim 1, the multi-disk brake or clutch is assigned precisely one electrically controllable actuator. Both the braking function and, alternatively, the parking function can be engaged / disengaged with the actuator. For safety reasons, the electrically controllable actuator is normally open when the braking function is engaged, i.e., not self-locking, while it is normally closed when the parking function is engaged, i.e., self-locking. This results in a braking concept that is simplified in terms of cost, installation space, and component weight compared to the prior art.

[0008] In one technical implementation, the actuator can have at least one ball-ramp unit. This allows the multi-disk brake or clutch to be subjected to contact pressure when the brake function or the parking function is engaged. Conversely, the multi-disk brake or clutch can be pressure-relieved when the brake or parking function is disengaged. The ball-ramp unit consists of a pair of discs, one stationary and one coaxially rotatable. The ball can roll between the discs' facing, inclined brake ball tracks.

[0009] In this case, the braking function can be engaged as follows: An electric rotary drive (i.e., a spindle drive) of the actuator moves the rotating disc from a zero rotation position in a braking direction by a braking angle into a braking setting range. This causes the ball to roll along the braking ball tracks, axially expanding the pair of discs over an axial expansion path. This applies a contact pressure to the multi-disk brake / clutch. This pressure varies depending on the magnitude of the braking angle.

[0010] When the brake function is engaged, rolling resistance occurs between the ball and the brake ball tracks of the disc pair. This low rolling resistance, compared to a sliding system, means that the ball-ramp unit is not self-locking, meaning it remains open when de-energized. In the event of a power failure, the actuator's braking effect is automatically canceled, thus meeting safety requirements.

[0011] Conversely, the pressure mechanism according to the invention is designed so that when the parking function is engaged, the actuator is self-locking, meaning it remains closed without power. In the event of a power failure, the parking function – unlike the braking function – remains permanently active, ensuring that the parking function also meets safety requirements.

[0012] The braking and parking functions can be implemented as follows: The ball-ramp unit can have corresponding, inclined sliding slopes. These are formed on both discs and can be brought into sliding contact with one another. To engage the parking function, the electric rotary drive (i.e., the spindle drive) of the actuator moves the rotating disc from the zero rotation position in a parking direction opposite to the braking direction, through a parking angle, into a parking setting range. In the parking setting range, the sliding slopes of the two discs come into sliding contact, with the disc pair axially spreading by the axial spreading distance, exerting contact pressure on the multi-disk brake / Z-clutch.

[0013] When the parking function is engaged, a sliding resistance acts between the corresponding sliding slopes of the discs. This resistance is significantly greater than the rolling resistance between the ball and the brake ball tracks of the disc pair. Therefore, when the parking function is engaged, the ball-ramp unit is designed to be self-locking (unlike the braking function), meaning it remains closed without power. When the parking function is engaged, the braking effect can be maintained despite a power failure.

[0014] To ensure reliable engagement of the parking function, the following measure is preferred: The parking setting range can be divided into a first sub-range and a second sub-range following in the parking direction of rotation. In the first sub-range, the ball can roll between facing parking ball tracks of the disc pair. In contrast, in the second sub-range, the ball is no longer in rolling contact with the disc pair. To engage the parking function, the rotatable disc is adjusted from the zero rotation position in the parking direction by a parking rotation angle into the first sub-range until a transfer point is reached. When adjusted in the first sub-range, the ball rolls on the parking ball tracks of the disc pair. This occurs with axial expansion of the disc pair over an axial expansion path. In this way, any clearance in the multi-disk brake / clutch is eliminated.When the transfer point is exceeded, the rotating disc is adjusted with a further increasing parking angle in the second sub-range until the parking function is engaged.

[0015] During the adjustment process in the first partial range, the sliding slopes of the two discs remain out of contact. Only when the transfer point is exceeded do the two sliding slopes come into sliding contact with each other, while at the same time the ball is no longer in rolling contact with the pair of discs.

[0016] The pitch angle of the two sliding slopes is preferably larger than the pitch angle of the parking ball tracks. This ensures that when the transfer point is exceeded, the ball safely lifts off the parking ball tracks of the pair of discs, meaning that the ball is no longer rolling contact with the parking ball tracks. When the parking function is engaged, this ensures that only the sliding resistance of the corresponding sliding slopes acts between the discs.

[0017] The parking ball tracks and the brake ball tracks can merge into one another in the disc's circumferential direction at a ramp recess. This defines the zero rotation position. The parking ball tracks can be mirror-symmetrical to the brake ball tracks with reference to a symmetry running through the ramp recess. Starting from the zero rotation position, as the braking or parking angle increases, the clearance of the multi-disk brake / clutch is initially eliminated. A kiss point is then reached at which the multi-disk brake / clutch transmits a measurable or predefined torque. To ensure reliable engagement of the parking function, it is preferable if the transfer point is exceeded in the parking setting range shortly before the kiss point is reached.

[0018] Operational reliability is further increased when the parking function is engaged, ensuring that the ball remains in a predefined free-running position (after lifting off the two parking ball tracks). In the free-running position, the ball can roll between the parking ball tracks of the pair of discs with some play, i.e., without rolling contact.

[0019] The predefined ball freewheel position can be achieved, for example, as follows: Each of the parking ball tracks of the two discs, viewed in the parking direction of rotation, can end at a ball track runout, which forms a ball movement stop. When the parking function is engaged, the two ball track runouts can be spaced apart from each other by a ball freewheel, viewed in the disc's circumferential direction, which defines the ball freewheel position. When the parking function is disengaged, the rotating disc is adjusted counter to the parking direction of rotation until it reaches the zero rotation position.

[0020] By providing the ball freewheel position, it is ensured that the ball comes into rolling contact with the parking ball tracks at least approximately at the transfer point and that the ball is in the ramp recess when the rotational zero position is reached.

[0021] An embodiment of the invention is described below with reference to the attached figures.

[0022] They show:

[0023] Figs. 1 to 8b show different views describing the structure and operation of the vehicle braking system according to the invention. Figure 1 shows an electrified vehicle axle with an electric motor EM and a transmission. The electric motor EM is connected to a high-voltage battery (not shown). Conventional vehicle wheel disc or drum brakes are omitted from the vehicle axle. Instead of such conventional vehicle wheel brakes, the vehicle axle has multi-disk brakes 3, by means of which vehicle braking can be performed.

[0024] The electric motor EM is connected via its rotor shaft 5, with a transmission stage 7 interposed, 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. In Figure 1, the electric motor EM is installed transversely in the vehicle axle. Accordingly, the rotor shaft 5 and the output shafts 11 are axially parallel to each other. Likewise, the multi-disk brakes 3 installed in the vehicle axle are axially parallel to each other in the vehicle's transverse direction y.

[0025] The vehicle axle has one of the multi-disk brakes 3 on each side of the vehicle, viewed in the vehicle transverse direction y. These can be controlled by an electronic control unit (not shown) in order to perform uniform or uneven vehicle braking on both vehicle wheels.

[0026] The intermediate gear stage 7 is in driving connection with an input-side axle differential gear 13. The axle differential gear 13 is connected in a rotationally fixed manner to a rotating differential housing 15. According to Figure 1, when the multi-disk brakes 3 are open, the axle differential 9 drives in the vehicle's transverse direction y in a 50 / 50 distribution on both sides to the two output shafts 11 leading to the vehicle wheels.

[0027] In Figure 1, the two multi-disk brakes 3 each act directly on the output shafts 11. This means that the multi-disk brake 3 is connected to the respective output shaft 11 with its inner disc carrier 18, while the outer disc carrier 17 is fixed to a transmission 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 an actuator 21. The actuator 21 can be controlled by the control unit using electrical signals.

[0028] The actuator 21 consists of a spindle drive (not shown) with an electric motor, which is in driving connection with a toothing 31 of a rotatable disc 27. The rotatable disc 27, together with a non-rotatable disc 25, is part of a pressure mechanism with a total of four circumferentially distributed ball-ramp units 23, as shown in Figures 3a to 3b. Each ball-ramp unit 23 has a ball 29 that rolls between the two discs 25, 27.

[0029] The plate pack located between the outer plate carrier 39 and the inner plate 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 during ferry operation, or alternatively a parking function when the vehicle is parked, can be engaged or disengaged. A core 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 controllable actuator 21 is de-energized when the braking function is engaged, i.e., not self-locking. In contrast, the electrically controllable actuator 21 is de-energized when the parking function is engaged, i.e., self-locking.

[0030] As can be seen from Figures 3a to 3c, each of the ball-ramp units 23 has ball ramps 34 and spaced-apart sliding bevels 38 that act between the disks 25, 27. The balls 29 of the four ball-ramp units 23 are guided in a cage 30 as shown in Figure 3b. Figures 4a and 4b each show a developed view of one of the ball-ramp units 23. Figure 4a shows two corresponding sliding bevels 38 of the disk pair, while Figure 4b shows two corresponding ball ramps 34 of the disk 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 one another at a ramp recess 39. In Figure 4a, the ball 29 is located in the ramp recess 39. The ramp recess 39 defines a rotational zero position 0, in which the disc pair exerts no contact pressure on the disc pack.The ball ramps 34 of the two discs 25, 27 are point-symmetrical to each other with respect to the ball 29. Furthermore, the parking ball track 37 and the braking ball track 35 of each ball ramp 34 are symmetrical to each other with the same pitch angles with respect to an axis of symmetry passing through the ramp recess 39.

[0031] A core of the invention is that, depending on the direction of rotation DB, DP of the rotatable disc 27, either a braking function for vehicle braking during ferry operation or, alternatively, a parking function when the vehicle is stationary can be engaged / disengaged. An important aspect of the invention is that the pair of discs of the actuator 21 is normally open when the braking function is engaged, i.e., is not self-locking. In contrast, the pair of discs of the actuator 21 is normally closed when the parking function is engaged, i.e., is self-locking.

[0032] In Figures 4a and 4b, the pair of discs is shown in its zero rotational position 0. In the zero rotational position 0 (unlike shown in Figure 4a), the two sliding bevels 38 are out of contact. According to Figure 4b, the ball 29 is located in the ramp recesses 39 of the ball ramps 34 of the two discs 25, 27.

[0033] The following describes the engagement of the braking function using Figures 5a to 6b. Starting from the zero rotation position 0 shown in Figures 4a and 4b, the rotating disc 27 is adjusted in a braking direction of rotation DB over a braking angle to the left into a braking adjustment range SB. This causes the ball 29 to roll on the two braking ball tracks 35 of the disc pair, specifically with the disc pair axially spreading over an axial spreading distance s. In this way, the disk pack of the multi-disk brake 3 is subjected to contact pressure. The contact pressure varies depending on the size of the braking angle. Immediately after leaving the zero rotation position 0, the rotating disc 27 is adjusted by an axial spreading distance s, by means of which any clearance in the disk pack is eliminated.Upon further rotational adjustment of the rotating disc 27 within the brake adjustment range SB, a kiss point KP (Figure 5b) is reached, at which the multi-disk brake 3 transmits a measurable, predefined torque. At the kiss point KP, the rotating disc 27 is rotated (starting from the zero rotation position 0) by a first axial spreading distance Asi. In Figures 6a and 6b, the rotating disc 27 is adjusted to an end position, in which the rotating disc 27 is adjusted by a second axial spreading distance AS2.

[0034] 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 remain open without power. Accordingly, in the event of a power failure, the braking effect of the actuated actuator 21 would decrease, thus fulfilling safety requirements.

[0035] To disable the braking function, the rotating disc 27 is moved back to the zero rotation position 0 (Figures 4a and 4b) from its end position (Figures 6a and 6b) against the braking direction of rotation DB.

[0036] During the adjustment movement in the brake adjustment range SB, the mutually corresponding, inclined sliding bevels 38 remain out of contact with each other, so that a smooth rotational adjustment of the rotatable disc 27 is ensured.

[0037] The engagement of the parking function is described below with reference to Figures 7a to 8b. Starting from the zero rotation position 0 shown in Figures 4a and 4b, to engage the parking function, the rotatable disc 27 is rotated to the right in a parking rotation direction Dp opposite to the braking rotation direction DB through a parking rotation angle into a parking setting range SP. According to Figure 7b, the parking setting range SP is divided into a first partial area SPI and a second partial area SP2. In the first partial area SPI, the ball 29 rolls between the mutually facing parking ball tracks 37 of the disc pair, while the corresponding sliding bevels 38 are still out of sliding contact. In contrast, in the second partial area SP2, the sliding bevels 38 are in sliding contact with one another, while the ball 29 is out of rolling contact with the disc pair.To engage the parking function, the rotatable disc 27 is adjusted, starting from the zero rotation position 0, in the parking rotation direction Dp by a parking rotation angle into the first partial range SPI until a transfer point U is reached, as indicated in Figures 7a and 7b. According to Figures 7a and 7b, the disc pair generates a third axial spreading path Ass at the transfer point U.

[0038] During the adjustment movement in the first partial range SPI, the ball 29 rolls on the parking ball tracks 37 of the disc pair, with the disc pair axially expanding, so that any clearance in the multi-disk brake 3 is eliminated. Upon exceeding the transfer point U, the rotatable disc 27 is rotated into the second partial range SP2 with a further increasing parking angle of rotation until the parking function is engaged.

[0039] To ensure reliable engagement of the parking function, the transfer point U located in the parking setting range SP is positioned between the zero rotation position 0 and the kiss point KP. When the parking function is engaged, the transfer point U is therefore exceeded shortly before reaching the kiss point K. Upon reaching the kiss point KP, the two corresponding sliding slopes 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 Figures 8a and 8b, the rotatable disc 27 is rotated to its parking end position, in which the parking function is fully engaged. When the parking function is engaged, the ball 29 is in a predefined ball freewheel position P (Figure 8b). The ball freewheel position P is defined in Figure 8b by means of ball track run-outs 41 of the parking ball tracks 37. When the parking function is engaged, the ball track run-ins 41 are spaced from one another in the disc circumferential direction 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 built up exclusively by means of the sliding bevels 38 in sliding contact.

[0041] To disengage the parking function, the rotating disc 27 is turned back against the parking direction Dp to the zero position 0. The

[0042] Remaining of the ball 29 in the ball freewheel position P ensures that the ball 29 comes into rolling contact with the parking ball track 37 at least approximately at the transfer point U and is again in the ramp recess 39 when the rotational zero position 0 is reached.

[0043] LIST OF REFERENCE SYMBOLS:

[0044] 3-disk brake

[0045] 5 Rotor shaft

[0046] 7 countershafts

[0047] 9 axle differential

[0048] 11 Output shaft

[0049] 13 Axle differential gear

[0050] 15 Differential housing

[0051] 17 outer disc carrier

[0052] 18 inner disc carriers

[0053] 19 Gearbox housing

[0054] 21 Actuator

[0055] 23 Ball ramp unit

[0056] 25 fixed disc

[0057] 27 rotating disc

[0058] 29 ball

[0059] 30 cage

[0060] 31 Gearing

[0061] 34 ball ramp

[0062] 35 brake ball track

[0063] 37 Park Marble Run

[0064] 38 sliding bevels

[0065] 39 Ramp recess

[0066] 0 Rotary zero position

[0067] U Transfer point

[0068] KP Kisspoint

[0069] P Ball freewheel position s Axial expansion path

[0070] SB brake adjustment range

[0071] SP parking area

[0072] SRI, SP2 sub-areas

[0073] DB brake rotation direction

[0074] Dp Park rotation direction ball freewheel

Claims

PATENT CLAIMS:

1. Vehicle braking system with at least one multi-disk brake or clutch (3) acting on a vehicle axle of a vehicle, by means of which a braking function for vehicle braking during ferry operation and a parking function when the vehicle is parked can be engaged / disengaged, characterized in that the multi-disk brake or clutch (3) is assigned an electrically controllable actuator (21) with which both the braking function and the parking function can be engaged / disengaged, and in that in particular the electrically controllable actuator (21) is open when de-energized when the braking function is engaged, that is to say is not self-locking, and is closed when de-energized, that is to say is self-locking, when the parking function is engaged.

2. Vehicle according to claim 1, characterized in that the actuator (21) has a pressure mechanism with at least one ball-ramp unit (23), with which the multi-disk brake or clutch (3) can be subjected to pressure when the braking function or parking function is engaged and can be relieved of pressure when the braking or parking function is disengaged, and in particular that the pressure mechanism consists of a pair of discs consisting of a fixed disc (25) and a disc (27) which is coaxially rotatable thereto, and in that the ball-ramp unit (23) has a ball (29) which rolls between mutually facing, inclined ball tracks (35, 37) of the pair of discs, and in that in particular for engaging the braking function an electric rotary drive of the actuator (21) rotates the rotatable disc (27) starting from a rotational zero position (0) in a braking rotational direction (DB) over a braking rotational angle adjusted to a brake setting range (SB),whereby the ball (29) rolls on brake ball tracks (35), with axial spreading of the pair of discs over an axial spreading path (s), in order to, The multi-disk brake Z-clutch (3) is to be subjected to contact pressure which varies depending on the size of the brake rotation angle.

3. Vehicle according to claim 2, characterized in that when the braking function is engaged, a rolling resistance acts between the ball (29) and the brake ball tracks (35) of the pair of discs, and that in particular the rolling resistance leads to the ball-ramp unit (23) not being self-locking, that is to say it is open when de-energized, so that in particular in the event of a power failure the braking effect of the actuator (21) is canceled out.

4. Vehicle according to claim 3, characterized in that the ball-ramp unit (23) has mutually corresponding, inclined sliding bevels (38) which are formed on both discs (25, 27) and can be brought into sliding contact with one another, and in that, in order to engage the parking function, the electric rotary drive of the actuator (21) moves the rotatable disc (27) starting from the rotational zero position (0) in a parking rotational direction (Dp) opposite to the braking rotational direction (DB) via a parking rotation angle into a parking setting range (SP), in which the sliding bevels (38) of the two discs (25, 27) come into sliding contact, specifically with axial spreading of the pair of discs by the axial spreading path (s), in order to apply contact pressure to the multi-disk brake / clutch (3).

5. Vehicle according to claim 4, characterized in that when the parking function is engaged, a sliding resistance acts between the corresponding sliding slopes (38), which is substantially greater than the rolling resistance between the ball (29) and the brake ball tracks (35) of the pair of discs, so that when the parking function is engaged, the ball-ramp unit (23) is self-locking, that is to say is closed without current, whereby in particular when the parking function is engaged, despite a In the event of a power failure, the braking effect is permanently maintained, in particular in contrast to the engaged braking function, in which the braking effect of the actuator (21) is cancelled out in the event of a power failure, and in particular that the parking setting range (SP) is divided into a first partial range (SRI), in which the ball (29) rolls between mutually facing parking ball tracks (37) of the pair of discs, and a second partial range (SP2), in which the sliding bevels (38) of the pair of discs are in sliding contact with one another, while the ball (29) is out of rolling contact with the pair of discs.

6. Vehicle according to claim 5, characterized in that to engage the parking function the rotatable disc (27) is adjusted starting from the rotational zero position (0) in the parking direction of rotation (Dp) by a parking angle of rotation into the first partial range (SP1) until a transfer point (U) is reached, during which time the ball (29) rolls on the parking ball tracks (37) of the pair of discs, specifically with axial spreading of the pair of discs over an axial spreading path (s), in particular in order to eliminate a clearance in the multi-disk brake (3), and that in particular when the transfer point (U) is exceeded the rotatable disc (27) is adjusted with a further increasing parking angle of rotation into the second partial range (SP2) until the parking function is engaged.

7. Vehicle according to claim 6, characterized in that the angle of inclination of the sliding slopes (38) is dimensioned to be greater than the angle of inclination of the parking ball tracks (37), so that after exceeding the transfer point (U) the ball (29) lifts off from the parking ball tracks (37) of the pair of discs, that is to say the ball (29) comes out of rolling contact with the parking ball tracks (37), so that in particular when the parking function is engaged it is ensured that between the discs (25, 27) only the sliding resistance of the corresponding sliding bevels (38) acts.

8. Vehicle according to claim 6 or 7, characterized in that the parking ball track (37) and the brake ball track (35) of the respective disc (25, 27) merge into one another in the circumferential direction at a ramp recess (39) which defines the zero rotational position (0), and in particular that the parking ball track (37), in particular up to the transfer point (U), is mirror-symmetrical to the brake ball track (35) with respect to an axis of symmetry passing through the ramp recess (39), and in particular that starting from the zero rotational position (0) with increasing braking angle or parking angle of rotation, first the air play of the multi-disk brake (3) is eliminated, and then a kiss point (KP) is reached at which the multi-disk brake (3) transmits a measurable or predefined torque.

9. Vehicle according to one of claims 6 to 8, characterized in that when the parking function is engaged, the ball (29) remains in a predefined ball freewheel position (P), in which the ball (29) rolls with play, i.e., without rolling contact, between the parking ball tracks (37) of the pair of discs, and in particular that each of the parking ball tracks (37) of the two discs (25, 27), at least viewed in the parking direction of rotation (Dp), ends at a ball track outlet (41) which forms a ball movement stop, and in that when the parking function is engaged, the two ball track outlets (41) are spaced apart from one another in the disc circumferential direction by a ball freewheel (f), which defines the ball freewheel position (P), and in that the ball freewheel (f) is dimensioned such that, on the one hand, there is no rolling contact between the ball (29) and the parking ball tracks (37) is present, and on the other hand the ball (29) cannot escape from the ball freewheel (f).

10. Vehicle according to claim 9, characterized in that when the parking function is disengaged, the rotatable disc (27) is adjusted in a return movement counter to the parking direction of rotation (Dp) into the rotational zero position (0), in particular when the contact pressure acting on the pair of discs decreases and when the ball freewheel (f) increases in the circumferential direction, and in that the ball (29) can move freely in the circumferential direction in the ball freewheel (f) due to the decreasing contact pressure, thereby ensuring that the ball (29) returns into the ramp recesses (39) of the ball ramps (34) of the pair of discs as soon as the rotatable disc (27) reaches the rotational zero position (0) in the return movement.

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