Method for activating a parking brake in a motor vehicle, and motor vehicle with an electromechanical brake device

Abstract

The present invention relates to a method for activating a parking brake in a motor vehicle (10), comprising a plurality of wheels (11, 12) which can be driven by a vehicle drive, and at least one electromechanical brake device (1) which interacts with at least one wheel (11, 12) and can be moved selectively into a service brake position or a parking brake position. In order to enable reliable activation of the parking brake with a relatively small load and adjustment force, the invention proposes the following steps: a. adjusting the brake device (1) into a service brake position in order to generate a service brake torque for holding the vehicle (10) at a standstill, b. detecting a downhill torque exerted on the wheel (11) by a downhill force (H), c. applying a compensation torque, opposed to the downhill torque, by the vehicle drive, and reducing the service brake torque by the magnitude of the compensation torque, d. adjusting the brake device (1) into a parking brake position, e. cancelling the compensation torque.

Description

[0001] Method for activating a parking brake in a motor vehicle and motor vehicle with an electromechanical braking device

[0002] State of the art

[0003] The invention relates to a method for activating a parking brake in a motor vehicle, comprising a plurality of wheels drivable by a vehicle drive and at least one electromechanical braking device interacting with at least one wheel, which can be selectively brought into a service braking position or a parking braking position. The invention further comprises a motor vehicle with a braking device for implementing the method.

[0004] The method relates to the operation of a braking device of a motor vehicle designed as a friction brake, in which a braking part supported on the chassis and stationary relative to the rotation of a wheel to be braked can be brought into braking engagement by means of an adjusting device with a counter-braking part which rotates with the wheel. During braking engagement, frictional contact is generated between the braking part and the counter-braking part, whereby the braking torque generated by friction is greater the higher the adjusting force exerted by the adjusting device in the adjustment direction. In the known design as a disc brake, the braking part comprises a brake pad, and the counter-braking part comprises a brake disc rotating with the wheel.

[0005] The drivable wheels are each driven in rotation by the vehicle drive by coupling a wheel drive torque, whereby the drive torque of a drive motor can be distributed to several driven wheels of one or more axles, or - especially in modern electric drives - an individual wheel drive can be provided for each wheel.

[0006] To implement the generic method, a braking device is assigned to each drivable wheel, preferably the two wheels of one or more vehicle axles, which is used as a service brake during ferry operation. In the electromechanical braking device used in the generic method, an electromotive service brake actuator is controlled by manual and / or automated actuation to adjust the braking device to a service braking position in which the braking part is brought into braking contact with the counter-braking part and a service braking torque is applied to the wheel.

[0007] During dynamic braking in ferry operation, the service brake position is designed to be self-releasing. This means that after a braking operation, if no active brake application occurs, the brake is released and the friction contact is released again, separating the braking part from the opposing braking part and separating them by an air gap of a defined width.

[0008] To secure the parked vehicle, the braking system has a parking brake position in which it operates as a static parking brake, continuously exerting a parking braking torque. This serves as a holding torque, which is always greater than any downhill torque acting on the wheel from the outside. This is caused by the downhill component of the force of gravity acting on the vehicle when the vehicle is parked on a surface inclined in or against the direction of travel, i.e., on a slope.

[0009] To park a vehicle, it is common practice to brake it to a stop using the service brake and, if the vehicle is on a slope, to hold it against the slope's downward force. While the service brake remains applied, a permanent parking brake can be activated. The parking brake torque generates a parking brake force that counteracts the slope's downward force. The service brake can then be released.

[0010] DE 10 2027 123 266 A1 discloses an electromechanical braking device comprising a service brake actuator with a ball-ramp arrangement. This actuator has an operating adjustment range within which a service brake position can be set during normal ferry operation by applying the brake, and which is designed to be self-releasing. Furthermore, the service brake actuator can be moved into a self-holding or self-locking parking brake position by further adjustment beyond the aforementioned operating adjustment range. To ensure that this position is stably defined, a force threshold must be overcome during adjustment, whereby the service brake actuator securely engages in the parking brake position.

[0011] The aforementioned integration of the parking brake position into the service brake actuator enables an advantageously compact and reliable design. It must be ensured that a sufficiently high braking force is already exerted in the service brake position before the force threshold is reached. This means that an even higher adjustment force must be applied to overcome the force threshold, which leads to a high load on the service brake actuator and requires a correspondingly powerful drive. A lower load and a lower required drive power could theoretically be achieved by reducing the braking force or flattening the force threshold. However, this could impair the braking force and operating characteristics, which is therefore impractical.

[0012] In view of the problems explained above, it is an object of the present invention to enable a safe activation of the parking brake with relatively lower load and adjusting force.

[0013] Description of the invention

[0014] This object is achieved according to the invention by the braking device having the features of claim 1. Advantageous further developments emerge from the subclaims.

[0015] In the method for activating a parking brake in a motor vehicle, comprising a plurality of wheels drivable by a vehicle drive and at least one electromechanical braking device which interacts with at least one wheel and which can be brought selectively into a service braking position or a parking braking position, the following steps are provided according to the invention: a. adjusting the braking device to a service braking position to generate a service braking torque for holding the vehicle at a standstill, b. detecting a downhill torque exerted on the wheel by a downhill force, c. applying a compensating torque by the vehicle drive which is opposite to the downhill torque and reducing the service braking torque by the amount of the compensating torque, d. adjusting the braking device to a parking braking position, e. canceling the compensating torque.

[0016] In step a, braking during ferry operation occurs by actuating the service brake actuator of one, preferably several, wheels, so that a service braking torque is applied until the vehicle comes to a standstill in a parking position. This service braking position is designed to be self-releasing and is initially maintained even when stationary through continued – manual or automated – actuation, so that the service braking torque continues to be applied. This keeps the vehicle in the parking position even on an inclined surface on a slope.

[0017] The service braking torque generates a service braking force directed in the direction of travel.

[0018] In the subsequent step b, it is determined whether the vehicle is parked on a slope that slopes in or against the direction of travel. In such a slope, the force component of gravity, directed parallel to the ground, acts on the vehicle as a downhill force in the direction of the gradient. This exerts a downhill torque on each wheel, which increases the steeper the gradient.

[0019] In the next step c, the applied downhill torque, which in step a is initially compensated solely by the service braking torque, is compensated by additionally applying a compensation torque provided by the vehicle's drive for the respective wheel. In parallel with the continuous increase in the compensation torque, the service braking torque is reduced accordingly, so that the sum of the compensation torque and the service braking torque corresponds to and is opposite to the amount of the downhill torque.

[0020] In step c, the service brake actuator, preferably of a single wheel, is continuously released, thereby reducing the service braking torque accordingly. Concurrently, the compensation torque exerted by the vehicle's drive system as drive torque is increased to compensate for the decrease in the service braking torque.

[0021] The compensation torque is preferably controlled as a function of the service braking torque in such a way that the slope torque determined in step b is optimally compensated and the vehicle is held at a standstill essentially without noticeable movement.

[0022] The compensation torque for balancing the slope torque acting on a wheel when the service brake actuator is released can essentially be provided by the vehicle drive for that wheel. Additionally or alternatively, it is possible for compensation to compensate for the reduction in the service braking torque of one wheel to increase the braking torque of one or more other wheels, and additionally or alternatively, the drive torque of one or more other wheels to be reduced. In any case, it is essential that the slope torque is compensated as completely as possible when the service braking torque of at least one wheel is reduced.

[0023] In step d, the braking device is adjusted to a parking brake position. As described above, the service brake actuator can preferably be engaged in a stable parking brake position by adjusting it beyond the range of the service brake position. One advantage of the invention is that by reducing the service braking torque, the adjusting force required to overcome the force threshold for engaging the stable parking brake position can be reduced to such an extent that, on the one hand, there is no excessive load on the service brake actuator, and, on the other hand, a relatively low drive power is required to adjust the parking brake position, i.e., the parking brake for parking. This enables a lightweight and compact design, wear is reduced, and operating characteristics are improved.

[0024] Once the parking brake position is set and locked, the slope torque is compensated by the parking brake torque, and in step e the compensation torque can be canceled.

[0025] By applying the compensation torque according to the invention, the conflict of objectives described at the beginning can be resolved without compromising on braking effect, safety and driving comfort.

[0026] Preferably, the method provides for steps b) to e) to be performed sequentially for individual drivable wheels or groups of drivable wheels. The wheels are transferred individually or in subgroups sequentially from the service brake position to the parking brake position. The advantage of this is that only a portion of the downhill force needs to be compensated for at a time, so that unwanted movements when activating the parking brake can be virtually completely eliminated with relatively little effort, thereby increasing driving comfort.

[0027] It is further advantageous that the adjustment of the braking device is carried out by means of an electromotive actuating device, by which a braking part can be brought into braking engagement with a counter-braking part. At least one actuating device is assigned to each wheel to be braked. In the aforementioned embodiment, it can be provided that, before the braking device is adjusted to the parking brake position, a release position is set by means of the actuating device, in which release position an air gap is created between the braking part and the counter-braking part. The air gap, which is also synonymously referred to as the braking gap, completely separates the braking part and the counter-braking part from one another, so that the braking effect of the braking device is completely canceled out, and the wheel is held in place solely by compensation torque before step d is carried out.Because the brake part and the counter-brake part are no longer fixed relative to each other during braking engagement, they can be positioned relative to each other essentially force-free, allowing easy adjustment of the braking device to activate the parking brake position, for example, to switch to a self-locking or self-retaining, preferably positive-locking support of the brake part and the counter-brake part. The air gap can preferably be specified such that the force threshold for engaging the stable parking brake position can be overcome with a relatively low adjustment force. This advantageously enables low loading and can be implemented with a small-sized actuator.

[0028] An advantageous further development can provide that the electromotive actuating device has two serially coupled actuators, wherein the first actuator is designed as a service brake actuator and the second actuator is designed as a feed drive for adjusting the air gap of the braking device, wherein the release position is generated by actuating the service brake actuator while the compensation torque is applied, wherein an air gap is generated between the braking part and the counter-braking part, the air gap is then enlarged by means of the feed drive, and the service brake actuator is then moved from a service brake position to a parking brake position. The feed drive preferably operates independently of the service brake actuator, whereby the air gap can be adjusted by means of the feed drive in any adjustment state of the service brake actuator. The feed drive is preferably designed to be self-locking.This ensures that the set width of the air gap remains unchanged regardless of the external forces acting. In the release position of the service brake actuator, an air gap is already formed at the end of step c. To further facilitate the subsequent execution of step d, the air gap can be further increased using the feed drive before the service brake actuator is adjusted to the parking brake position outside the range of the possible service brake position. In the parking brake position, the service brake actuator rigidly supports the braking part and the counter-braking part against each other, preferably self-locking or self-holding, for example in a form-fitting manner against the adjustment direction, so that the braking force applied by the actuating device is maintained without active actuation of the braking device.

[0029] It can be provided that the feed drive is adjusted to reduce the air gap in the parking brake position. This allows any increase in the air gap previously made to facilitate engagement of the parking brake position to be reversed. This allows the parking brake torque to be increased.

[0030] An actuator can be designed to convert a torque exerted by an electric motor about an axis into an axial adjustment or lifting movement by which the braking part can be brought into or out of braking engagement.

[0031] To implement the method, it is advantageous for the first actuator to have a ball ramp arrangement comprising two cam discs, wherein the cam discs are driven by a first electric actuator motor to rotate relative to one another about an axis and have axially opposite raceways arranged at an angle to the axis, between each of which a ball is arranged for rolling movement. The first actuator forms the service brake actuator.

[0032] The ball ramp assembly comprises two cam discs, one of which is connected to a drive wheel. The cam discs have tracks or ramps inclined relative to the axis, between which balls are arranged to roll in the circumferential direction. A relative rotation of the cam discs by the electric servomotor about an axis is converted into a relative axial displacement of the cam discs by the balls rolling in the tracks, which causes an adjustment of the associated braking component.

[0033] It can be provided that the raceways have a linear or non-linear inclination. A substantially linear inclination allows for uniform force transmission over the entire adjustment path of the ball ramp arrangement. A non-linear inclination, which can be designed, for example, in an arc or S-shape over the circumferential extent of a raceway, allows for a non-linear force transmission to be achieved depending on the respective angular position of the cam disks. For example, a steeper inclination at the beginning or in the middle section of the raceway can achieve faster adjustment at a constant speed of the motor drive, and a flatter inclination in the end section, shortly before the braking element enters frictional braking engagement, can achieve a higher adjustment force, which ensures an increased braking effect.

[0034] An advantageous embodiment for carrying out the method according to the invention is that the raceway has a flattened area in at least one end section, in which the ball is held in a self-locking manner in the parking brake position. The raceway extends in the circumferential direction over a defined length which limits the rolling or rolling path of the ball between its circumferential ends. Between the ends, the raceway has a defined inclination, which can also be referred to as a pitch. An end section is formed by a section at the end of the possible rolling path which, measured in the circumferential direction, preferably corresponds to at least one sphere radius. In the region of the flattened area, the inclination of the raceway relative to the axis is reduced relative to a rolling section adjoining the end section. For example, an inclination of zero can be formed, with the raceway running perpendicular to the axis.This allows the ball to be self-locking in the flat area against axial restoring forces acting on the actuator from the outside. This allows the function of a parking brake to be realized. This parking brake position is simply adjusted by rotating the cam discs relative to each other until the ball reaches the flat area.

[0035] An advantageous further development of the aforementioned embodiment can be realized in that the raceway has a trough-shaped depression in at least one end section, in which the ball engages in the parking brake position. The depression is arranged in an end region, also referred to as the end section, of the raceway in which the braking engagement is generated. In the region of the depression, the inclination is partially opposite to the inclination between the end sections. The depression can preferably be arc-shaped. Preferably, it can be spaced from the end of the raceway by at least one sphere radius, measured in the circumferential direction. When the braking engagement is reached, the ball can roll into the depression and assume a circumferentially stable locking position. In the locking position, the ball is held independently of the axial restoring force acting on the cam disks.This allows a defined, self-locking parking brake position of the ball ramp assembly to be achieved. Because the trough-shaped depression is formed deeper into the track, a force threshold is formed in front of the depression, which the ball must overcome to set the parking brake position. The method according to the invention allows the operating braking torque to be reduced in step c, preferably by adjusting an air gap, which is advantageously set to a relatively low value for engaging the ball in the parking brake position.

[0036] If the actuating device has at least two serially coupled actuators, these can be arranged axially in series with respect to their adjustment paths. The actuators can preferably be arranged coaxially. Each actuator can have a drive wheel that can be driven to rotate about the axis and that can be geared to a servomotor. In the embodiment according to the invention, a drive wheel, for example a gear, can be connected in a rotationally fixed manner to a drive-side cam disk.

[0037] In the aforementioned embodiment, it can be advantageous for the first actuator to have a ball ramp arrangement, and for the second actuator to have an adjustment device operating according to a different principle, for example as a spindle drive that can be driven by a second electric servomotor. The second spindle drive forms the feed drive. In this case, the drive element can have a spindle nut that can be driven in rotation, and the output element can have a threaded spindle engaging therein and axially displaceable relative thereto, or vice versa. Other types of actuators can also be used, which can, for example, comprise cam or cam disks, tilt pin arrangements or the like, and preferably likewise convert a motor-driven rotation of a drive element into a linear adjustment of the output element.

[0038] In an advantageous embodiment, at least one of the cam discs can be designed as a sintered component or as a cold-formed part. Sintered components are made from powdered materials, with the material being bonded into a solid body through pressure and heating. This allows complex contours to be produced efficiently and with high dimensional accuracy. Furthermore, advantageous material properties can be realized, such as high hardness and thus high wear resistance.

[0039] In the method according to the invention, the aforementioned torques acting on or exerted on the wheel(s), namely the operating and parking braking torque, the downhill force, and the compensation torque, are correlated with corresponding forces acting between the vehicle and the ground, i.e., the roadway, namely the operating and parking braking force, the downhill force, and the compensation force exerted as the vehicle's driving force. Therefore, the forces can be clearly assigned to the torques.

[0040] The invention further relates to a method for deactivating a parking brake in a motor vehicle, comprising a plurality of wheels drivable by a vehicle drive and at least one electromechanical braking device which interacts with at least one wheel and which can be brought selectively into a service braking position or a parking braking position, comprising the steps of: f. detecting a downhill torque exerted on the wheel by a downhill force when the vehicle is stationary, g. applying a compensating torque of equal magnitude to the downhill torque by the vehicle drive, h. adjusting the braking device to a service braking position, i. canceling the compensating torque.

[0041] By detecting and compensating the downhill force and the resulting downhill torque, the advantages described above when activating the parking brake can in principle be realized when the parking brake is released.

[0042] Furthermore, the invention comprises a motor vehicle comprising a plurality of wheels drivable by a vehicle drive and at least one electromechanical braking device cooperating with at least one wheel, which can be selectively brought into a service braking position or a parking braking position, and having a control unit for controlling the vehicle drive and the braking device, in which it is provided according to the invention that a sensor for detecting a slope torque acting on the wheel when the vehicle is stationary is connected to the control unit.

[0043] It is preferably provided that the control unit is designed to carry out the method according to the invention described above. All features disclosed above in connection with the implementation of the method according to the invention can be implemented in the vehicle.

[0044] It is particularly advantageous that the vehicle drive is designed as an electric motor. This allows for the control and regulation of the compensation torque generated by the electric motor to be implemented in the electronic control unit with minimal effort. The electric drive and the electric braking devices can be integrated particularly effectively.

[0045] Description of the drawings

[0046] Advantageous embodiments of the invention are explained in more detail below with reference to the drawings. In detail:

[0047] Figure 1 shows a braking device according to the invention in a schematic perspective view,

[0048] Figure 2 is a side view of the braking device according to Figure 1,

[0049] Figure 3 shows the adjusting device according to the invention of the braking device according to Figure 1 in a schematic perspective view,

[0050] Figure 4 shows a section QQ through the braking device according to Figure 1,

[0051] Figure 5 shows the first actuator of the braking device according to Figure 1 in a schematic perspective view,

[0052] Figure 6 is an enlarged detailed view of the adjusting device from Figure 4,

[0053] Figure 7 shows a longitudinal section through an actuator according to the invention according to Figure 5,

[0054] Figure 8 shows an enlarged section of Figure 7,

[0055] Figure 9 is a schematic axially exploded view of the actuator according to Figures 7 to 8,

[0056] Figure 10 isolated perspective views of the cam discs of the actuator according to Figures 7 to 9,

[0057] Figure 11 is an enlarged view of section BB from Figure 10, Figure 12a-e is a schematic view of the steps of the method according to the invention,

[0058] Figure 13 is a diagram showing the forces and moments occurring in the method according to the invention shown in Figure 12.

[0059] Embodiments of the invention

[0060] In the various figures, identical parts are always provided with the same reference symbols and are therefore usually named or mentioned only once.

[0061] Fig. 1 shows a braking device according to the invention as a whole, designed as a disc brake. This comprises a brake disc 2, which forms a counter-braking part according to the invention and is connected to a vehicle wheel (not shown here) rotatable about a wheel axis R. A brake caliper 3 engages the two axial end faces of the brake disc 2.

[0062] Brake disc 2 is designed as a non-ventilated brake disc made of solid material. Alternatively, it can also be designed as an internally ventilated brake disc.

[0063] An electric brake actuator 4 according to the invention is attached to the brake caliper 3, which is shown in Figure 3 in a separate, isolated schematic perspective view and is explained in detail in Figures 4 to 7.

[0064] The brake actuator 4 comprises an adjusting device 5 which extends axially in the direction of an axis A which is parallel to the wheel axis R and indicates the adjustment direction V of the adjusting device 5.

[0065] As can be seen in the sectional view of Figure 4 along axis A, the brake disc 2 is arranged axially between two brake pads 31 and 32. One brake pad 31 is firmly supported on the brake caliper 3 on the side facing away from the brake actuator 4. The other brake pad 32, which forms a braking part within the meaning of the invention, is attached to the adjusting device 5 and can be adjusted by it in the axial adjustment direction V defined by the axis A to generate the braking engagement on the brake disc 2, as indicated by the arrow in Figure 4. In the unactuated state of the braking device 1, there is an axial air gap L between the brake disc 2 and the adjustable brake pad 32, which is shown schematically as exaggerated in width in Figure 4.

[0066] The structure of the adjusting device 5 is shown in Figure 4 and in the enlarged section thereof in Figure 6.

[0067] The actuating device 5 comprises a first actuating drive 6, which has a ball ramp arrangement, also referred to as a ramp bearing, and a second actuating drive 7, which is axially (with respect to the axis A) serially coupled thereto and has a spindle drive.

[0068] The first actuator 6, which in the example shown is designed as a ball ramp arrangement or ramp bearing, comprises a drive-side cam disk 61 and an output-side cam disk 62, which are axially and rotationally fixedly supported on the brake actuator 4. Balls 63 are arranged between the cam disks 61 and 62. As can be seen in the schematically isolated view in Figure 5, the cam disks 61 and 62 have axially opposite, ramp-like raceways 64 arranged obliquely to the axis A, between which balls 63 can roll. A rotation of the output-side cam disk 62, at the top in Figure 5, relative to the stationary drive-side cam disk 61 - as schematically indicated by the curved arrows - leads to a linear adjustment of the output-side cam disk 62 in the adjustment direction V parallel to the axis A.As a result, the brake pad 32 can be brought into braking engagement by actuating the first actuator 6, as shown in Figure 4.

[0069] The first actuator 6 forms a service brake actuator in the sense of the method according to the invention.

[0070] The cam disc 62 is connected to a coaxial gear 65, which is designed as a spur gear and forms a drive wheel in the sense of the invention.

[0071] The gear 65 is in gear engagement with a first electric actuator 41. This enables the rotating drive of the cam disc 62 and thus the actuation of the first actuator 6.

[0072] The second actuator 7, which in the example shown is designed as a spindle drive, has a threaded spindle 71 on the output side, which engages the internal thread of a drive-side spindle nut 72. This internal thread is formed in the output-side cam disc 62 of the first actuator 6, so that the functions of the output-side cam disc 62 and the drive-side spindle nut 72 are combined in one component.

[0073] The second actuator 7 forms a feed drive in the sense of the method according to the invention.

[0074] The threaded spindle 71 is connected via a hub part 74 to a coaxial gear 75, which is axially fixed and rotatably mounted in the brake actuator 4. The threaded spindle is coupled to the gear 75 in a torque-locking but axially displaceable manner via drivers 73, which may, for example, have radially projecting projections or teeth that engage axially displaceably in axial slots of the hub part 74.

[0075] Like gear 65, gear 75 can be designed as a spur gear and is arranged coaxially adjacent to it. This gear 75 is in gear engagement with a second electric actuator 42. This enables the rotating drive of the threaded spindle 71 and thus the actuation of the second actuator 7.

[0076] The threaded spindle 71 is axially connected via a thrust bearing 43, for example, an axial roller bearing as shown, to a thrust piece 44, to which the movable brake pad 32 is attached, as can be seen in Figure 4. The thrust piece 44 can also be referred to as a piston.

[0077] The clutch device according to the invention comprises a friction element 8, which is designed as a coaxial, conical extension extending from the cam disc 62 toward the second actuator 7. The conical extension has a conical friction surface 81 arranged externally on an outer cone. The friction element 81 can preferably be formed integrally with the cam disc 62 / spindle nut 72.

[0078] In clutch engagement, the friction element 8 is frictionally coupled to a counter friction element 9. The conical projection axially engages a corresponding conical opening of the counter friction element 9, which has a conical friction surface 91 arranged in an inner cone. In clutch engagement, the friction surface 81 and the counter friction surface 91 are in frictional contact with each other, as can be clearly seen in Figure 6.

[0079] The counter friction element 9 is coupled to the gear 75 in a torque-locking but axially displaceable manner via drivers 92, which engage axially displaceably in corresponding slots 76 in the hub part 74 or the gear 75. A spring element 93 is arranged between the gear 75 or the hub part 74 connected thereto and the counter friction element 9. Due to its axially effective spring force, the counter friction element 9 is elastically braced against the friction element 8. This generates a defined clutch torque of the friction clutch according to the invention formed by the friction element 8 and the counter friction element 9.

[0080] Figure 7 shows a longitudinal section along the axis A through the actuator 6 according to the invention according to Figures 5 and 6. Figure 8 shows an enlarged section of Figure 7 in the area of ​​the tracks 64.

[0081] The ball 63 has a ball diameter Db.

[0082] In the example shown, the raceways 64 have a continuously circularly curved cross-sectional profile which has a raceway radius rg.

[0083] According to the invention, the ratio C = rg / Db : C > 0.5, and preferably: 0.75 > C = rg / Db > 0.5.

[0084] In Figure 10, the two cam discs 61 and 62 are shown separately in perspective, each in a view of the raceways 64. In Figure 10, the curved arrows indicate the inclination of the raceways 64, which increase in the direction of the arrow relative to the axis A in the circumferential direction.

[0085] Exactly three raceways 64 are arranged evenly distributed around the circumference. The three balls 63 rolling in them are also evenly distributed around the circumference and are held in a ball cage 66, allowing free rotation in their relative positions.

[0086] Figure 11 shows an enlarged sectional view BB from Figure 10 through the end regions of the raceway 64 (in the circumferential direction), which projects axially furthest from the cam disk 61 or 62. One end region belongs to one raceway 64 and the other end region to the adjacent raceway 64. The inclination of the raceway 64 is schematically indicated in a greatly exaggerated manner by the oblique arrow. In the first end region, a trough-shaped depression 67 is formed in the raceway 64, which is schematically indicated in the drawing by a downward-pointing arrow. In the second end region, a shoulder 68 is provided which is designed to limit the running of the balls 63, wherein the shoulder 68 and the depression 67 each form the flanks 67F, 68F of the elevation 69.The ball 63 can engage in this recess 67 when, during adjustment, it reaches the end position in which the cam disks 61 and 62 are moved almost as far apart axially, thereby achieving a stroke h. This adjustment position corresponds to the braking engagement. The cam disks 61 and 62 are moved as far apart axially when the balls 63 are just about to move into the recess 67. This position is marked H. The seat in the recess 67 releasably fixes the ball 63 in order to realize a holding or parking brake position in which the braking force is held stable against the axial restoring force exerted by the brake disk 2 on the brake pad 32. Thanks to this recess 67, it is possible to operate the servo motor 41 with a very low current or even without current in the holding brake position, so that this parking position can be held without time restrictions.In contrast, the adjusting drive 6 is not self-locking if the ball 63 is located outside the recess 67 and the shoulder 68 along the track 64. Then, after a braking operation has ended, the cam discs 61 and 62 can be moved axially toward each other again by a relatively low restoring force in order to release the braking engagement. If the balls 63 are located outside the recess 67 along the track 64 and not in contact with the shoulder 68, the brake is in the service braking position. If the balls 63 are in contact with the shoulder, the brake is in the release position, meaning no braking engagement takes place.

[0087] In Figure 12 a) to e), the method according to the invention is shown by way of example using individual phases of a parking process in which a motor vehicle 10 is parked on an inclined roadway 100 which represents a subsurface.

[0088] In the illustration shown, the direction of travel of the vehicle is from right to left, and accordingly, left is by definition front.

[0089] In the example, lane 100 is inclined from top left to bottom right. Accordingly, the slope slopes downwards.

[0090] The motor vehicle 10 has a front axle with a wheel 11 facing the viewer, namely the left front wheel, and a rear axle with a wheel 12, namely the left rear wheel. A drive torque can be exerted on the wheels 11 and 12 by a vehicle drive (not shown here) in a separately controlled manner, generating a drive force directed in the direction of travel. For example, an electric motor-driven individual wheel drive, each with its own electric motor, can be provided for each of the wheels 11, 12. Alternatively, a single-axle drive is also possible. A downhill force H, which depends on the gradient and mass, acts on the motor vehicle 10 and is directed downwards in the direction of the slope—to the right in Figure 12. As a result, a corresponding downhill torque is exerted on the wheels 11 and 12, which is not shown separately here due to the above-mentioned relationship between forces and torques.

[0091] Figure 12 a) illustrates step a of the method according to the invention. By actuating the brake actuators 4 of the wheels 11, 12, a service braking torque is exerted, resulting in a service braking force B1 for wheel 11 and a braking force B2 for wheel 12. The service braking forces B1 and B2 are shown in dashed lines, with their sum corresponding to and opposite to the magnitude of the slope force H. Accordingly, the vehicle is at a standstill.

[0092] In Figure 12 b), the downhill torque acting on the wheel 11 due to the downhill force is determined according to step b of the method.

[0093] According to step c of the method, depending on this, a compensation torque is exerted on the wheel 11 by the vehicle drive, which generates a compensation force K, which is indicated by the solid arrow and which is opposite to the component of the slope force H acting on the wheel 11. Together with the increase in the compensation force K, the service braking force B1 is reduced by releasing the brake actuator 4 until the braking device 1 assigned to the wheel 11 is completely released and no more braking torque is exerted, and accordingly no service braking force B1 acts, as shown in Figure 12 c).

[0094] In principle, it is possible to increase the compensation force K to the amount of the braking torque so that the service braking force B1 is completely compensated at wheel 11. Alternatively, it can also be provided that the amount of the compensation force K remains lower than the service braking force B1 of wheel 11. In this case, the service braking force B2 of the other wheel 12 can be increased such that the sum of the compensation force K and the service braking force B2 completely compensates for the slope force H. This case is illustrated as an example in Figure 12c.

[0095] In any case, the motor vehicle 10 is held stationary against the downhill force H.

[0096] The brake actuator 4 of the brake device 1 assigned to the wheel 11 can then be released by the first actuator 6 of the actuator 5 to such an extent that a defined air gap L is formed.

[0097] Subsequently, while the compensation torque K is still applied, the braking device 1 of the wheel 11 is adjusted to the parking brake position according to step d of the method according to the invention, as shown in Figure 12 d). In this case, the first actuator 6, which forms a service brake actuator according to the method according to the invention, is adjusted to the parking brake position, as described in detail above with reference to Figures 9, 10, and 11.

[0098] Engaging into the parking brake position is facilitated by the fact that the service brake actuator 6, which has a ball ramp arrangement, is completely released until an air gap L is formed. As a result, the force threshold formed by the elevation 69 can be overcome with less adjustment force in order to engage the ball 63 in the recess 67 to produce the parking brake position.

[0099] In the parking brake position, the braking device 1, preferably through the service brake actuator 6, exerts a parking brake torque on the wheel 11, generating a parking brake force P, which is shown in Figure 12 d) as a dash-dotted arrow. As the parking brake force P increases, the compensation force K decreases. In parallel, the service brake force B2 of the other wheel 12 can be reduced back to the original value from step a.

[0100] As soon as the parking brake force P at least substantially matches the direction and magnitude of the service brake force B1 applied in step a, the compensation torque K is canceled, as shown in Figure 12 e). In this state, the service brake force B1 according to step a is completely replaced by the parking brake force P.

[0101] The procedure described for wheel 11 can subsequently be carried out successively for wheel 12 and the other wheels of motor vehicle 10.

[0102] In Figure 13, the service braking force B1 of wheel 11, the compensation force K, the parking braking force P, and the service braking force B1 of wheel 11 are plotted over time t during steps a) to e), which add up to the total force F acting on motor vehicle 10. Through the inventive use of the compensation force K, a low-stress and gentle switching of the service brake actuator 6 from the service braking position to the parking braking position can occur. A further advantage is that the downhill force H is completely and uninterruptedly compensated during the entire process of activating the parking brake, so that no undesirable movements or vibrations of the motor vehicle occur.

[0103] List of reference symbols

[0104] 1 braking device

[0105] 10 motor vehicle

[0106] 100 Roadway (subsurface)

[0107] 11, 12 wheels

[0108] 2 brake discs

[0109] 3 brake caliper

[0110] 31, 32 brake pad

[0111] 4 Brake actuator

[0112] 41, 42 Actuator

[0113] 43 thrust bearings

[0114] 44 Pressure piece

[0115] 5 Adjusting device

[0116] 6 first actuator (service brake actuator)

[0117] 61 cam disc

[0118] 62 cam disc (integrated with spindle nut 72)

[0119] 63 ball

[0120] 64 Career

[0121] 65 gear

[0122] 66 ball cage

[0123] 67 Deepening

[0124] 69 Survey

[0125] 7 second actuator (feed drive)

[0126] 71 threaded spindle

[0127] 72 spindle nut (integrated with cam disc 62)

[0128] 73 drivers

[0129] 74 Hub part

[0130] 75 gear

[0131] 76 slot

[0132] 8 Friction element

[0133] 81 Friction surface

[0134] 9 Counter friction element

[0135] 91 Counter friction surface

[0136] 92 drivers

[0137] 93 spring element

[0138] A Axle R Wheel axle

[0139] V Adjustment direction

[0140] L Air gap

[0141] Db ball diameter rg raceway radius

[0142] H slope force

[0143] B1,B2 Service braking force

[0144] K Compensation force

[0145] P Parking brake force

Claims

PATENT CLAIMS 1. A method for activating a parking brake in a motor vehicle (10), comprising a plurality of wheels (11, 12) drivable by a vehicle drive and at least one electromechanical braking device (1) which interacts with at least one wheel (11, 12) and which can be selectively brought into a service braking position or a parking braking position, comprising the steps of: a. adjusting the braking device (1) to a service braking position to generate a service braking torque for holding the vehicle (10) at a standstill, b. detecting a downhill torque exerted on the wheel (11) by a downhill force (H), c. applying a compensating torque by the vehicle drive that is opposite to the downhill torque and reducing the service braking torque by the amount of the compensating torque, d. adjusting the braking device (1) to a parking braking position, e. canceling the compensating torque.

2. Method according to claim 1, characterized in that steps b) to e) are carried out successively for individual drivable wheels (11, 12) or groups of drivable wheels.

3. Method according to one of the preceding claims, characterized in that the adjustment of the braking device (1) is carried out by means of an electromotive actuating device (5), of which a braking part (32) can be brought into braking engagement with a counter-braking part (2).

4. Method according to claim 3, characterized in that before adjusting the braking device (1) into the parking brake position by means of the adjusting device (5), a release position is set in which an air gap (L) is created between the braking part (32) and the counter-braking part (2).

5. Method according to claim 4, characterized in that the electromotive actuating device (5) has two serially coupled actuating drives (6, 7), wherein the first actuating drive (6) is designed as a service brake actuating drive and the second actuating drive (7) is designed as a feed drive for adjusting the air gap (L) of the braking device (1), wherein the release position is generated by actuating the service brake actuator (6) while the compensation torque is applied, wherein an air gap (L) is generated between the brake part (32) and the counter-brake part (2), the air gap is then enlarged by means of the feed drive (7), and the service brake actuator (6) is then brought from a service brake position into a parking brake position.

6. Method according to claim 5, characterized in that in the parking brake position the feed drive (7) is adjusted to reduce the air gap (L).

7. Method according to one of the preceding claims 5 to 6, characterized in that the first actuator (6) has a ball ramp arrangement (6) comprising two cam discs (61, 62), wherein the cam discs (61, 62) can be driven by a first electric actuator motor (41) to rotate relative to one another about an axis (A), and have axially opposite raceways (64) lying obliquely to the axis (A), between each of which a ball (63) is arranged so as to roll.

8. Method according to one of the preceding claims 5 to 7, characterized in that the tracks (64) have a linear or non-linear inclination.

9. Method according to one of the preceding claims 5 to 8, characterized in that the track (64) has a flattening in at least one end section in which the ball (62) is held in a self-locking manner in the parking brake position.

10. Method according to one of the preceding claims 5 to 9, characterized in that the track (64) has a trough-shaped depression (67) in at least one end section, in which the ball (62) engages in the parking brake position.

11. Method according to one of the preceding claims 5 to 10, characterized in that the second actuator (7) is designed as a spindle drive which can be driven by a second electric actuator motor (42).

12. Method for deactivating a parking brake in a motor vehicle (10), comprising a plurality of wheels (11, 12) drivable by a vehicle drive and at least one electromechanical brake cooperating with at least one wheel (11, 12). see braking device which can be brought selectively into a service braking position or a parking braking position, comprising the steps: f. detecting a downhill torque exerted on the wheel (11) by a downhill force (H) when the vehicle (10) is stationary, g. applying a compensation torque of equal magnitude to the downhill torque by the vehicle drive, h. adjusting the braking device (1) into a service braking position, i. cancelling the compensation torque.

13. Motor vehicle (10), comprising a plurality of wheels (11, 12) drivable by a vehicle drive and at least one electromechanical braking device (1) which interacts with at least one wheel (11) and which can be brought selectively into a service braking position or a parking braking position, and with a control unit for controlling the vehicle drive and the braking device (1), characterized in that a sensor for detecting a slope torque acting on the wheel (11, 12) when the vehicle (10) is stationary is connected to the control unit.

14. Motor vehicle according to claim 13, characterized in that the control unit is designed to carry out a method according to claims 1 to 12.

15. Motor vehicle according to claim 13 or 14, characterized in that the vehicle drive is designed as an electric motor.

Images