Electromechanical brake device for a motor vehicle

Abstract

The invention relates to an electromechanical brake device (1) for a motor vehicle, comprising an electrodynamic adjustment device (5) and a brake element (32) which is connected to the adjustment device (5) and which can be adjusted by the adjustment device (5) and which is in braking engagement with a counter brake element (2), in which: the adjustment device (5) has at least one adjustment drive (6, 7); the adjusting drive (6) has a ball ramp arrangement (6) comprising two cam discs (61, 62); the cam discs (61, 62) can be driven by an electric actuating mechanism (41, 42) in such a way that the cam discs (61, 62) rotate relative to one another about an axis (A) and the cam discs (61, 62) have raceways (64) axially opposite one another at an angle to the axis (A), between which raceways a ball (63) is arranged in such a way that the ball (63) can roll; the raceway (64) has an at least partially rounded cross-sectional profile with a raceway radius (rg). And the ball (63) has a ball diameter (Db). In order to achieve an improved function with optimized recovery characteristics, according to the invention the ratio (C) between the raceway radius (rg) and the ball diameter (Db) is greater than 0.5.

Description

Background Art

[0001] The invention relates to an electromechanical braking device for a motor vehicle, the electromechanical actuating device comprising an electromechanical actuating device and a braking part, which is connected to the electromechanical actuating device and can be adjusted by the actuating device and is in braking engagement with the counter-braking part, wherein the actuating device has at least one actuating drive, wherein the actuating drive has a ball ramp arrangement structure comprising two cam plates, wherein the cam plates can be driven by an electric actuating motor so as to be rotatable relative to each other about an axis, and the cam plates have raceways which are positioned axially relative to each other inclined to the axis, between which corresponding balls are arranged in a rollable manner, wherein the raceways have an at least partially rounded cross-sectional profile with a raceway radius and the balls have a ball diameter.

[0002] Such a braking device for a motor vehicle is designed as a friction brake, wherein a braking part, which is supported on the chassis and stationary relative to the rotation of the wheel to be braked, can be brought into braking engagement with a counter-braking part, which rotates with the wheel, by means of an actuating device. During braking engagement, frictional contact is produced between the braking part and the counter-braking part, wherein the greater the braking torque generated by friction, the greater the adjustment force applied by the actuating device in the adjustment direction. In designs known per se, such as disc brakes, the braking part comprises a brake pad, and the counter-braking part comprises a brake disc that rotates with the wheel.

[0003] The actuating device of the universal brake device has at least one electromechanical actuating drive. This actuating drive is designed to convert a torque applied by an electric motor about an axis into an axial adjustment or reciprocating movement, by means of which the brake part can be brought into or out of braking engagement.

[0004] In the general prior art, DE 10 2017 123 266 A1, for example, discloses an actuating drive configured as a ball ramp arrangement, also known as a ramp bearing. This actuating drive serves as a service brake to produce or release brake engagement in driving mode, either manually or automatically.

[0005] The ball ramp arrangement has two cam plates, one of which is connected to a drive wheel. The cam plates have raceways or ramps that are inclined relative to an axis, and balls are arranged circumferentially between the raceways or ramps for rollable movement. Relative rotation of the cam plates about the axis by an electric actuating motor is converted into relative axial displacement of the cam plates by the balls subsequently rolling in the raceways. This axial displacement causes adjustment of a brake portion connected to the cam plates.

[0006] To achieve a high force transfer between the drive torque introduced by the actuator motor and the adjustment of the cam plates, allowing the brake to engage with the highest possible braking force, a relatively flat slope (also known as a gradient) of the raceway is necessary. This results in high Hertzian stresses, i.e., high surface pressures, due to which the nearly point-like contact surfaces of the respective balls are pressed against the raceway. The higher this pressure, the flatter the slope. At the same time, when the brake is released, the actuator must quickly and safely return to its initial position before the braking process. To allow this return, a non-self-restraining design of the actuator is required, in which the two cam plates can be moved axially toward each other again by a slight axial return force applied from the outside. Here, the balls roll against the rotation applied by the actuator motor for braking, while the cam plates rotate relative to each other and return to their initial positions. To achieve this, the balls must be able to roll as easily as possible in the raceway with low rolling friction. While this non-self-restraining feature can, in principle, be facilitated by a steeper slope of the raceway, the force transfer would, however, be unacceptably reduced. Furthermore, it must be ensured that the raceways are not damaged by the high surface pressures over the entire service life of the brake, even after numerous braking processes.

[0007] Therefore, in the prior art, there is a conflict of objectives between achieving a high force transfer and a non-self-inhibiting resetting.

[0008] In view of the problems outlined above, it is an object of the present invention to achieve improved functionality with optimized resetting characteristics. Summary of the Invention

[0009] According to the invention, this object is achieved by a braking device having the features of claim 1. Advantageous developments are described in the dependent claims.

[0010] In an electromechanical braking device for a motor vehicle, the electromechanical braking device comprises an electromechanical actuating device and a braking part, which is connected to the electromechanical actuating device and can be adjusted by the actuating device and brakingly engaged with the counter-braking part, wherein the actuating device has at least one actuating drive, wherein the actuating drive has a ball ramp arrangement mechanism comprising two cam plates, wherein the cam plates can be driven by an electric actuating motor so as to rotate relative to each other about an axis, and the cam plates have raceways that are axially positioned relative to each other inclined to the axis, wherein corresponding balls are arranged in a rollable manner between the raceways, wherein the raceways have an at least partially rounded cross-sectional profile with a raceway radius, and the balls have a ball diameter, and according to the invention, it is provided that the ratio between the raceway radius rg and the ball diameter is greater than 0.5.

[0011] For a given raceway radius rg and ball diameter Db, the ratio C: C=rg / Db>0.5.

[0012] According to the present invention, an optimized ratio between raceway radius and ball diameter is proposed, which allows resolving the initially described conflict between the highest possible force transmission for the motorized drive of the actuator and non-self-restraining resetting. This is achieved by taking into account the structural and functional features of the ball ramp arrangement. These relate in particular to the fact that a small number of raceways are provided on each cam plate, with precisely one ball being arranged between two raceways positioned axially opposite each other in pairs. Due to the relatively small number of balls, which transmit the entire applied adjustment force to the raceways via their contact surfaces, correspondingly high Hertzian stresses arise. However, in a ball ramp arrangement, for functional reasons, it is not possible to increase the number of balls between the two raceways to reduce the corresponding surface pressure, as is the case with conventional rolling bearings. Increasing the number of raceways for the same purpose, for example, in the axial adjustment range, would also not be feasible without compromising functionality.

[0013] In order to optimize the ball ramp arrangement taking into account the above-mentioned characteristics, it has surprisingly been found that a ratio greater than 0.5 – which defines a lower limit for the relative raceway radii – allows acceptably low Hertzian stresses while having sufficiently low rolling friction. Thus, the advantages of high load carrying capacity and adjustment force can be achieved while having a sufficient non-self-inhibiting return.

[0014] Preferably, this ratio can be set to be less than or equal to 0.75. The ratio C between the raceway radius rg and the ball diameter Db is set to be less than or equal to 0.75, such that: 0.75 ≥ C = rg / Db > 0.5. This defines an upper limit. While the Hertzian stress is indeed higher than 0.5, the reduced rolling friction is beneficial.

[0015] According to the invention, within a ratio range between 0.5 and 0.75, a qualitative improvement of the specific functional properties of the ball ramp arrangement can be achieved.

[0016] Particularly preferably, it can be provided that the ratio is 0.55. It has been found that in this design, this allows for a particular optimization of relatively mild Hertzian stresses and relatively low rolling resistance. This embodiment offers particular advantages in a triple ball ramp arrangement with three balls and three raceways per cam plate.

[0017] It is particularly advantageous if the cam plate has precisely three raceways and is provided with precisely three balls. This creates a so-called triple ball ramp arrangement. The raceways and balls are preferably identically designed and evenly distributed around the circumference. The three raceways and three balls clearly define a plane perpendicular to the axis, creating a well-defined three-point bearing. This is particularly advantageous for adjusting the brake element and, therefore, for the safety function. The present invention, particularly in this embodiment, allows for optimized functionality.

[0018] In an advantageous embodiment, the raceway has a cross-sectional profile with a continuous circular curve. The cross-sectional profile is formed by a single, continuous arcuate section, with the ball axially contacting the raceway at a single, approximately point-shaped contact surface. The ratio according to the invention allows for optimally reduced surface pressure with low rolling resistance. Furthermore, the maximum material stress can advantageously be limited, enabling known ball bearing steels to be used for the cam plate, thus ensuring sufficient durability and operational reliability.

[0019] Alternatively, the raceway can have a Gothic cross-sectional profile. By definition, a Gothic profile has two mirror-symmetrical arcuate segments that meet at a point and form opposing sides of the raceway. Each of the arcuate segments can have a raceway radius according to the present invention. The balls contact each of the two arcuate segments at corresponding axially offset contact surfaces. In other words, the balls contact both raceways at a total of four contact surfaces. This reduces Hertzian stresses and rolling friction.

[0020] The raceway can have a linear or nonlinear ramp path. A substantially linear path allows for uniform force transmission over the entire adjustment stroke. A nonlinear path, which can be formed, for example, as an arcuate or S-shaped path in the circumferential direction over the extent of the raceway, can achieve a nonlinear force transmission path, depending on the respective angular position of the cam plate. For example, at a constant rotational speed of the motorized drive, a steeper ramp at the beginning or in the middle region of the raceway allows for faster adjustment, while a flatter ramp in the end region shortly before the brake element enters frictional braking engagement allows for a higher adjustment force, thereby ensuring an increased braking effect.

[0021] In an advantageous embodiment, the raceway has a flattened portion in at least one end portion. The raceway extends over a defined length in the circumferential direction, which limits the rolling or bearing travel of the balls between their circumferential ends. Between the ends, the raceway has a defined slope, which can also be referred to as a gradient. The end portion is formed by a portion located at the end of the possible rolling travel, which portion, measured in the circumferential direction, preferably corresponds to at least one ball radius. In the region of the flattened portion, the slope of the raceway relative to the axis is reduced compared to the rolling portion adjacent to the end portion. For example, a zero slope can be formed, in which the raceway extends perpendicular to the axis. The balls can thus be fixed by self-restraining against a reset force acting axially from the outside on the actuating drive. This makes it possible to implement a holding or parking brake function.

[0022] An advantageous improvement can provide that the raceway has a groove-shaped recess in at least one end section. The recess is arranged in an end region of the raceway, also referred to as an end section, in which the braking engagement occurs. In the region of the recess, a ramp extends between the end sections in a section opposite the ramp. The recess can preferably be rounded in an arcuate manner. Preferably, the recess can be spaced apart from the end of the raceway by at least one ball radius, measured in the circumferential direction. When the braking engagement is achieved, the balls can roll into the recess and assume a latched position that is stable in the circumferential direction. In the latched position, the balls are retained regardless of the axial reset force acting on the cam plate. Thus, a defined, self-retaining parking brake position of the ball ramp arrangement can be achieved.

[0023] An advantageous development can provide that the raceway has a shoulder in at least one end portion. When the balls abut against the shoulder of the end portion, the brake is in the released position, i.e., there is no braking engagement. The shoulder delimits the raceway in the circumferential direction.

[0024] Preferably, the raceway has a first end portion having a recess formed therein and a second end portion having a shoulder formed therein. In another advantageous refinement, the shoulder of the first raceway and the recess of the second raceway each form a side surface of a protrusion. The protrusion forms a boundary between one raceway and another, for example, between the first raceway and the second raceway, in the circumferential direction and is arranged circumferentially between the raceways.

[0025] It can be preferably provided that the actuating device has at least two actuators connected in series. The first and second actuators are arranged axially in a straight line relative to their adjustment travels. The second adjustment drive, which is preferably arranged coaxially with the first adjustment drive, is preferably also configured to convert a rotation of the drive element into an axial adjustment of the brake portion. The service brake can be implemented by the first actuator, which can be configured according to the present invention. For example, a second actuator connected in series to the first actuator can be provided to adjust the air gap between the brake element and the counter-brake element.

[0026] Advantageously, the serially coupled actuators are coaxially arranged. Each actuator can include a drive wheel that can be driven to rotate about an axis and engage with an actuator motor gear. With the design according to the present invention, the drive wheel, such as a large gear, can be rotationally fixedly connected to the drive-side cam plate.

[0027] In the above-described embodiment, it can be advantageous for one of the actuating drives to include a ball ramp arrangement, and for the other actuating drive to include an adjustment device operating according to another principle of action. For example, the second actuating drive can include a spindle drive, wherein the input element comprises a rotatably driven spindle nut, and the output element comprises a threaded spindle engaged therein and axially displaceable relative thereto, or vice versa. Other actuating drive designs can also be used, which may, for example, include cam plates or curved plates, tilting pin arrangements, or the like, and preferably also convert a motorized rotation of the input element into a linear adjustment of the output element.

[0028] In an advantageous refinement, at least one of the cam plates can be formed as a sintered component or a cold extruded part. Sintered components are made from a powdered material that is solidified by pressure and heat. This allows complex contours to be produced efficiently and with high dimensional accuracy. Furthermore, advantageous material properties, such as high hardness and, therefore, high wear resistance, can be achieved.

[0029] An advantageous embodiment can provide that the braking device comprises an actuating device and a braking part, which is connected to the actuating device and can be adjusted along the axis by the actuating device and is in braking engagement with the counter-braking part, wherein the actuating device has a first actuating drive and a second actuating drive connected in series to the first actuating drive, wherein the first actuating drive has a first rotatably driven drive wheel and the second actuating drive has a second rotatably driven drive wheel coaxial with the first drive wheel, wherein a coupling device is arranged between the first drive wheel and the second drive wheel.

[0030] The actuating device can be driven by at least one electric actuating motor. This is preferably geared to at least one drive wheel. Preferably, an actuating motor can be provided for each of the first and second drive wheels. According to the present invention, one or more actuating motors can be controlled by a wheel brake control unit assigned to the braking device.

[0031] It can be provided that the coupling device is designed as a friction clutch having a friction element which, when the coupling is engaged, can be connected to a counter-friction element by means of a friction fit.

[0032] The first drive wheel and the second drive wheel are also collectively referred to as two drive wheels or simply drive wheels below.

[0033] The drive wheels can each be designed as a gearwheel, for example as a spur gearwheel, or be formed by a pulley or toothed belt pulley or a worm gear, so that a gearwheel is usually provided via which the drive torque from the electric actuating motor can be coupled into the actuating drive.

[0034] A friction clutch is implemented between the drive wheels. This friction clutch comprises a friction element connected to one of the drive wheels via a torque-locked connection, and a corresponding counter-friction element connected to the corresponding other drive wheel via a torque-locked connection. The friction element can engage with the counter-friction element in a friction-locked connection at any arbitrary relative angular position. This achieves a purely force-locked connection, compared to a positive-locking latching connection. In this way, the relative position of the drive wheels relative to each other can be continuously predefined, compared to the discrete latching steps of a latching connection. This therefore allows for uniform, continuous adjustment of the second actuator relative to the first actuator, and for continuous adjustment of the air gap. This is particularly advantageous for uniformly adapting the optimal operating point of the braking device to the continuous wear of the brake parts during use, i.e., the continuous wear of the brake pads. Compared to a merely stepped adjustment device, this allows for a continuously improved response behavior of the braking device, thereby increasing operational reliability and greater operating comfort.

[0035] Another advantage over latching couplings is that, to activate and release the coupling device, essentially no axial relative movement between the coupled coupling elements, such as the drive wheel or the latching element, is required. These latching elements must be movable relative to one another in order to establish and release the latchable, form-fitting connection. In contrast, the purely force-fitting connection between the friction element and the counter-friction element according to the present invention can be predefined simply by the applied axial actuation force, without the friction element and the counter-friction element having to move axially relative to one another. This allows for a simpler and more reliable design of the coupling device.

[0036] It can preferably be provided that the friction clutch has a clearly predefinable coupling torque. The coupling torque is the maximum differential torque that can be transmitted by the friction fit in the coupling engagement, by the force fit between the friction element and the counter-friction element. When the coupling torque is exceeded, the coupling device slips out, causing the two drive wheels to twist relative to each other. This has the advantage that the friction clutch according to the present invention slips out continuously, thus allowing for improved and uniform readjustment of the air gap. Furthermore, there is no need to structurally account for and compensate for axial deviations of the latching element, such as are required with known latching couplings.

[0037] Advantageously, the friction element and the counter-friction element are arranged coaxially. This coaxial arrangement corresponds to the coaxial arrangement of the drive wheel. The friction element and the counter-friction element can be arranged in the region of the drive wheel's axially oriented end faces, resulting in a simple and compact design. Because the coupling is established purely through a force fit, as described above, no moving parts are required.

[0038] In an advantageous embodiment, the friction element and the counter-friction element can be conically shaped. The friction element can include a conical portion that tapers at least partially in the axial adjustment direction and has a conical friction surface that can be configured as an outer or inner cone. This conical portion mates with a corresponding conical portion on the counter-friction element, which is designed inversely to the inner or outer cone and has a conical counter-friction surface. To form the coupling engagement, the outer cone is inserted into the inner cone, with the conical friction surface and the counter-friction surface being loaded against each other by the axial clutch engagement force through a friction fit. The advantage of this is that, due to the cone, the axially acting clutch engagement force can be forcibly transferred into a normal force acting between the conical friction surfaces in frictional contact. Consequently, due to the flatter gradient, a relatively small axial engagement force is converted into a larger normal force in the frictional contact, thereby achieving a high coupling torque even with a relatively low axial clutch engagement force.

[0039] As an alternative or in addition to the above-described design, it is possible to provide that the friction element and the counter-friction element are designed to be planar. In this case, the mutually corresponding friction surfaces are at least partially formed as planar axial surfaces, similar to a plate clutch. This allows for a compact arrangement, particularly when only relatively low coupling torques are to be achieved.

[0040] It can be preferably provided that the friction element and the counter-friction element are pre-tensioned against each other. Preferably, the friction element and the counter-friction element are pre-tensioned against each other elastically or in a spring-like manner. Here, the friction surfaces and the counter-friction surfaces are pressed against each other in the friction fit with a predefined axial pre-tensioning force. To generate the pre-tensioning force, an elastic pre-tensioning element, such as a spring element or the like, can preferably be provided. The coupling torque of the friction clutch is determined by the activation force acting perpendicularly to the friction contact, i.e., the force applied axially between the friction element and the counter-friction element. The pre-tensioning force increases with increasing coupling torque. This provides the advantageous possibility of pre-defining the coupling torque simply by means of the pre-tensioning force applied by the pre-tensioning element. For example, in the case of a spring element with axial compressive elasticity, such as a compression spring, the applied pre-tensioning force can be easily pre-defined and adjusted by means of the spring contact and spring compression.

[0041] The above embodiment can advantageously be implemented in the following manner: the friction element and / or the counter-friction element is axially displaceable and supported against the first or second drive wheel via an axially acting spring element. The friction element or counter-friction element is here axially displaceably connected to one of the drive wheels via a torque fit, for example, via a radially protruding carrier that creates a form fit acting in the circumferential direction. A spring element, preferably configured as an axially acting compression spring and clamped between the friction element or counter-friction element and one of the drive wheels, ensures that the friction element or counter-friction element is axially prestressed against the corresponding counter-friction element or friction element, which is axially supported on the other drive wheel, i.e., is axially pressed against the other drive wheel in friction contact. The corresponding counter-friction element or friction element is connected to the respective other drive wheel via a rotational fit. Alternatively or additionally, the counter-friction element can also be supported on one of the drive wheels via the spring element. The advantage of this arrangement is that the friction clutch can be structurally easily and compactly integrated between the drive wheels.

[0042] In an advantageous refinement, the friction element and / or counter-friction element can be arranged in the first or second drive wheel. Thus, for example, one drive wheel can be designed to be approximately drum-shaped, so that the friction element or counter-friction element can be arranged in the interior space enclosed by the circulating gearwheel or crown wheel. This allows for a compact design that is protected from external influences. Thus, for example, the drive wheel of the first actuating drive can have a conical friction element that axially engages in a counter-friction element, which is designed as an inner cone and is arranged at least partially inside the second drive wheel.

[0043] A particularly compact design can be achieved—particularly in the latter embodiment—if the drive wheel is arranged in the axial region of the actuating drive, ie the drive wheel is not mounted so as to protrude axially on one side.

[0044] The friction element and / or the counter-friction element preferably have a friction coating. The friction element and the counter-friction element preferably have a metal base body, for example made of steel. To avoid metal-to-metal contact, a coating or covering, for example made of sintered metal and / or ceramic friction material, a composite material, or the like, can be applied to create a friction pair with defined friction forces. This ensures a defined and reproducible coupling torque.

[0045] It can be provided that the actuating drive comprises a spindle drive. In this case, a threaded spindle engages in a spindle nut in a known manner, and the relatively rotating drive is connected to the threaded spindle or the spindle nut via a drive wheel. The spindle nut can form the input-side drive element of the actuating drive, and the threaded spindle forms the output-side output element linearly adjustable relative thereto, or vice versa.

[0046] The actuating drive can comprise a ball ramp arrangement, a wedge disk arrangement or a tilting pin arrangement. In the case of a ball ramp arrangement, also referred to as a ramp bearing, the input element and the output element preferably comprise cam plates with raceways or ramps which are inclined relative to the axis and between which balls which can roll in the circumferential direction are arranged. Due to the rolling of the balls on the ramps, the relative rotation results in an axial displacement of the output element relative to the input element. In a tilting pin arrangement (known per se), a tilting pin is arranged between the input element and the output element and is each supported in the circumferential direction, so that during relative rotation, depending on the direction of rotation, the tilting pin is tilted to a greater or lesser extent relative to the axis, whereby the distance between the input element and the output element is also adjustable.

[0047] In an actuating device, two identically acting actuating drives can be combined as a first actuating drive and a second actuating drive, for example, two spindle drives. It is also possible to combine two different designs, for example, a ball ramp arrangement as a first actuating drive and a spindle drive as a second actuating drive for adjusting the air gap. This allows for optimal utilization of the respective characteristic features of each design. For example, with a ball ramp arrangement, nonlinear control characteristics and / or at least partial self-restraint characteristics can be cost-effectively implemented, as well as defined dead points or tension positions, which allow for a defined adjustment range. To achieve these positive characteristics, a precise pre-determination of the air gap may be necessary, at least in part, which can be readily achieved with the friction clutch according to the present invention.

[0048] The braking device according to the invention can comprise an actuating device and a braking portion, which is connected to the actuating device and can be adjusted by the actuating device along an axis and is in braking engagement with the counter-braking portion, wherein the actuating device has a first actuating drive and a second actuating drive coupled in series to the first actuating drive, wherein the first actuating drive has a first rotatably driven drive wheel, and the second actuating drive has a second rotatably driven drive wheel coaxial with the first drive wheel, wherein a coupling device is arranged between the first drive wheel and the second drive wheel.

[0049] The actuating device can be driven by at least one electric actuating motor. This is preferably geared to at least one drive wheel. Preferably, an actuating motor can be provided for each of the first and second drive wheels. According to the present invention, one or more actuating motors can be actuated by a wheel brake control unit assigned to the braking device.

[0050] In the latter embodiment of the braking device, it can preferably be provided that the coupling device is designed as a friction clutch having a friction element which can be connected to a counter-friction element by means of a friction fit in the coupling engagement.

[0051] In this way, the advantages outlined above in conjunction with the brake system can be achieved.

[0052] In order to implement the method according to the present invention, it can be provided that the braking device has an actuating device, which can be coupled to the actuating motor and includes a first actuating drive and a second actuating drive coupled in series to the first actuating drive, and the actuating device acts on a braking portion, which can be brought into braking engagement with a counter-braking portion in an axial direction; wherein the first actuating drive has a first drive wheel, which is rotatably driven, and in order to activate, a first driving torque can be applied to the first drive wheel, and the second actuating drive has a second drive wheel, which is rotatably driven and coaxial with the first drive wheel, and in order to activate, A second drive torque is applied to the second drive wheel; wherein a coupling device is arranged between the first drive wheel and the second drive wheel; wherein, according to the present invention, it is configured that the coupling device is configured as a friction clutch and has a predefinable coupling torque, exceeding which causes the first drive wheel to slip relative to the second drive wheel; wherein, to enable the first actuating drive, the first drive wheel and the second drive wheel are driven synchronously, so that the second actuating drive remains inactivated, and to enable the second actuating drive, the second drive wheel is driven and the first drive wheel is stationary relative to the second drive wheel, so that the friction clutch slips and the first actuating drive remains inactivated.

[0053] The features listed above in conjunction with the braking device according to the invention can be used individually or in combination in order to implement the method according to the invention.

[0054] To adjust the first actuating drive, an actuating torque can be coupled into the first drive wheel by means of the first electric actuating motor, and correspondingly the second actuating drive can be driven by the second electric actuating motor.

[0055] During normal braking operation, the first and second drive wheels rotate synchronously. This can be achieved by first and second actuating motors with synchronous drive torques. Secondly, while driving the first drive wheel, the second drive wheel can be synchronously supported by the coupling device, as long as the transmitted drive torque remains below the coupling torque. In this operating mode, the second actuating drive remains inactive and rotates integrally with the brake element during idling.

[0056] In this method, when the coupling torque is exceeded, the coupling device can be continuously and evenly extended in a sliding manner to adjust the air gap. This can be achieved, for example, by immobilizing the drive wheel of the first actuating drive, for example by braking or correspondingly controlling the first drive motor, while the second drive motor simultaneously applies a second drive torque to the second drive wheel that is greater than the coupling torque. In this way, the second drive wheel is twisted relative to the first drive wheel, and by activating the second actuating drive, the air gap can be continuously and finely adjusted, thereby optimally compensating for the progressive wear of the brake element or brake pad.

[0057] The first and second drive wheels can be coupled by a friction clutch through torque locking to produce synchronous drive. This eliminates the need for synchronous drive of the two drive wheels via an actuating motor. Any torque differences can be compensated within predefined tolerances.

[0058] Advantageously, a higher coupling torque can be predefined when the first actuating drive is activated than when the second actuating drive is activated. The first actuating drive is activated by the synchronous driving of the first and second drive wheels. The friction element and the counter-friction element are prestressed against each other by the spring force of the spring element, and the adjustment force of the first actuating drive acts in opposition to the spring force. This achieves a relatively high coupling torque. However, if only the second drive wheel is rotated to adjust the air gap, only the spring force is effective, thus setting a lower coupling torque. This facilitates adjustment of the air gap. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Advantageous embodiments of the present invention are described in more detail below with reference to the accompanying drawings, in which:

[0060] Figure 1 A schematic perspective view shows a braking device according to the present invention.

[0061] Figure 2 Shown from Figure 1 A side view of the braking device,

[0062] Figure 3 The schematic perspective view shows the Figure 1 an actuating device of a brake device according to the present invention,

[0063] Figure 4 Shown through the Figure 1 The cross section of the brake device is QQ,

[0064] Figure 5 The schematic perspective view shows the Figure 1 a first actuating drive of the braking device,

[0065] Figure 6 Shown from Figure 4 An enlarged detail of the actuator,

[0066] Figure 7 Shown from Figure 5 a longitudinal section through the actuating drive according to the invention,

[0067] Figure 8 Shown from Figure 7 A magnified excerpt of

[0068] Figure 9 Shown from Figures 7 and 8 Schematic axial exploded view of the actuating drive,

[0069] Figure 10 Shown from Figures 7 to 9 A separate perspective illustration of the cam plate of the actuating drive,

[0070] Figure 11 Shown from Figure 10 An enlarged view of section BB. DETAILED DESCRIPTION

[0071] In the various figures, identical components are always provided with the same reference symbols and are therefore generally only referenced or mentioned once in each case.

[0072] Figure 1 The braking device according to the invention is generally shown and is designed as a disc brake. It comprises a brake disc 2, which forms a counter-braking portion within the meaning of the invention and is connected to a vehicle wheel (not shown here) that is rotatable about a wheel axis R. A brake caliper 3 encloses the two axial end faces of the brake disc 2.

[0073] The brake disc 2 is formed here as a non-ventilated brake disc made of solid material. Alternatively, the brake disc 2 can also be configured as an internally ventilated brake disc.

[0074] The electric brake actuator 4 according to the present invention is mounted on the brake caliper 3 and Figure 3 In the separate perspective view shown separately and schematically in Figures 4 to 7 Explained in detail in .

[0075] The brake actuator 4 comprises an actuating device 5 extending axially in the direction of an axis A, which is situated parallel to the wheel axis R and constitutes an adjustment direction V of the actuating device 5 .

[0076] As in Figure 4 As is apparent from the cross-sectional view along the axis A, the brake disc 2 is arranged axially between two brake pads 31 and 32. One brake pad 31 is fixedly supported on the brake caliper 3 on the side facing away from the brake actuator 4. The other brake pad 32, which forms the braking part in the sense of the invention, is mounted on the actuating device 5 and can thus be adjusted in the axial adjustment direction V given by the axis A toward the brake disc 2 in order to produce a braking engagement, as in Figure 4 Indicated by the arrow.

[0077] In the inactive state of the brake device 1 , there is an axial air gap L between the brake disc 2 and the adjustable brake pad 32 . The air gap L is Figure 4 Schematically shown as being disproportionately wide.

[0078] The structure of the actuator 5 is Figure 4 The picture is shown in Figure 6 An enlarged excerpt is shown in the figure.

[0079] The actuating device 5 has a first actuating drive 6 comprising a ball ramp arrangement also known as a ramp bearing, and a second actuating drive 7 coupled axially (relative to the axis A) in series to the first actuating drive 6 and comprising a spindle drive.

[0080] The first actuating drive 6, which is designed as a ball ramp arrangement or ramp bearing in the example shown, comprises an input-side cam plate 61 and an output-side cam plate 62, which are mounted axially and rotationally fixed on the brake actuator 4. Balls 63 are arranged between the cam plates 61 and 62. Figure 5As shown in the schematic open view of FIG, the cam plates 61 and 62 have raceways 64 positioned axially relative to each other in the form of ramps inclined to the axis A, and the balls 63 can roll between the raceways 64. The output side cam plate 62 (at Figure 5 The rotation of the input-side cam plate 61 relative to the stationary input-side cam plate 61, as schematically indicated by the curved arrow, results in a linear adjustment of the output-side cam plate 62 in an adjustment direction V parallel to the axis A. Figure 4 As shown in FIG, the brake pad 32 can be braked engaged by activating the first actuating drive 6.

[0081] The cam plate 62 is connected to a coaxial gearwheel 65 which is configured as a spur gear and forms a drive wheel in the sense of the invention.

[0082] The large gear wheel 65 is in gear engagement with the first electric actuating motor 41 . This allows the cam plate 62 to be driven in rotation and thus the first actuating drive 6 to be activated.

[0083] The second actuating drive 7, which is designed as a spindle drive in the example shown, has a threaded spindle 71 on the output side, which engages in an internal thread of an input-side spindle nut 72. This internal thread is formed in the output-side cam plate 62 of the first actuating drive 6, so that the functions of the output-side cam plate 62 and the input-side spindle nut 72 are combined in one structural element.

[0084] The threaded spindle 71 is connected via a hub portion 74 to a coaxial gearwheel 75 which is rotatably and axially fixedly mounted in the brake actuator 4. The threaded spindle is coupled to the gearwheel 75 in a torque-fitting but axially displaceable manner via a carrier 73 which can, for example, have radially projecting projections or teeth which engage in an axially displaceable manner in an axial groove of the hub portion 74.

[0085] The gearwheel 75 can be configured as a spur gear like the gearwheel 65 and is arranged coaxially adjacent to the gearwheel 65. The gearwheel 75 is in gear engagement with the second electric actuating motor 42. This allows the threaded spindle 71 to be driven in rotation and thus the second actuating drive 7 to be activated.

[0086] The threaded spindle 71 is axially connected via a thrust bearing 43, for example an axial rolling bearing as shown, to a pressure piece 44 to which the displaceable brake pad 32 is attached, as shown. Figure 4 The pressure piece 44 can also be referred to as a piston.

[0087] The coupling device according to the invention has a friction element 8, which is oriented toward the second actuating drive 7 as a coaxial conical lug of the cam plate 62. The conical lug has a conical friction surface 81 arranged on the outside on an outer cone. The friction element 81 can preferably be configured integrally with the cam plate 62 / spindle nut 72.

[0088] In the coupling engagement, the friction element 8 is coupled to the counter-friction element 9 by friction fit. Here, the conical lugs are axially inserted into corresponding conical openings of the counter-friction element 9, which has a conical friction surface 91 arranged in an inner cone. In the coupling engagement, the friction surface 81 and the counter-friction surface 91 abut against each other by friction fit, as shown in FIG. Figure 6 Clearly visible.

[0089] The counter-friction element 9 is coupled to the gearwheel 75 by a torque fit but in an axially displaceable manner via a carrier 92 which engages in an axially displaceable manner on a corresponding groove 76 in the hub portion 74 or the gearwheel 75 .

[0090] A spring element 93 is arranged between the gearwheel 75 or the hub portion 74 connected to the gearwheel 75 and the counter-friction element 9. Due to the axially acting spring force of the spring element 93, the counter-friction element 9 is elastically tensioned against the friction element 8. This results in a defined coupling torque of the friction clutch according to the invention formed by the friction element 8 and the counter-friction element 9.

[0091] Figure 7 A longitudinal section along the axis A through the actuating drive 6 according to the invention is shown, as Figure 5 and Figure 6 As shown in . Figure 8 Shown from Figure 7 An enlarged excerpt in the region of the raceway 64 .

[0092] The ball 63 has a ball diameter Db.

[0093] In the example shown, the raceway 64 has a cross-sectional profile having a continuously circular curve with a raceway radius rg.

[0094] According to the invention, the ratio C=rg / Db: C>0.5, and preferably: 0.75≧C=rg / Db>0.5.

[0095] Figure 10 In each case, the two cam plates 61 and 62 are shown in a perspective view on the raceway 64. Figure 10 In FIG. 6 , the curved arrows indicate the slope of the raceways 64 , wherein these raceways 64 rise in the circumferential direction relative to the axis A in the direction of the arrows.

[0096] In each case, there are precisely three raceways 64 arranged evenly distributed on the circumference. The three balls 63 that can roll in the raceways 64 are also evenly distributed on the circumference and are held in their relative positions in a freely rotatable manner in the ball cage 66.

[0097] Figure 11 Shown from Figure 10 An enlarged cross-section BB (in the circumferential direction) through the end regions of raceway 64, which protrude axially furthest from cam plate 61 or 62. Here, one end region belongs to one raceway 64, and the other end region belongs to the adjacent raceway 64. The slope of raceway 64 is schematically and greatly exaggerated by oblique arrows. In the first end region, a corresponding groove-like recess 67 is formed in raceway 64; recess 67 is schematically indicated by a downward-pointing arrow in the figure. In the second end region, a shoulder 68 is provided, which is configured to limit the travel of ball 63. Shoulder 68 and recess 67 form side faces 67F and 68F of projection 69, respectively. When ball 63 reaches an end position during adjustment, it can latch into recess 67. In this position, cam plates 61 and 62 are axially displaced almost to their maximum separation, thus completing travel h. This adjustment position corresponds to brake engagement. Just as the ball 63 is about to move into the recess 67, the cam plates 61 and 62 move axially apart to their maximum possible separation. This position is designated H. By being seated in the recess 67, the ball 63 is releasably secured to achieve the holding or parking brake position, in which the braking force remains stable against the axial restoring force exerted by the brake disc 2 on the brake pad 32. Due to the recess 67, in the parking brake position, the actuator motor 41 can be operated with very little current, or even without current, allowing the parking position to be maintained without time constraints. In contrast, when the ball 63 lies outside the recess 67 and shoulder 68 in the path of the raceway 64, the adjustment drive 6 is not self-inhibiting. After the braking process is complete, the cam plates 61 and 62 can be moved axially toward each other again using a relatively low restoring force to release the braking engagement. When the ball 63 lies outside the recess 67 in the path of the raceway 64 and does not contact the shoulder 68, the brake is in the service brake position. When the ball 63 abuts the shoulder, the brake is in a released position, or no brake engagement has occurred.

[0098] Reference Signs List

[0099] 1 Braking device

[0100] 2 brake discs

[0101] 3 brake calipers

[0102] 31, 32 brake pads

[0103] 4 brake actuators

[0104] 41, 42 actuating motor

[0105] 43 thrust bearing

[0106] 44 pressure piece

[0107] 5 Actuator

[0108] 6. First Actuator

[0109] 61 Cam plate

[0110] 62 cam plate (combined with spindle nut 72)

[0111] 63 Ball

[0112] 64 Rollerway

[0113] 65 large gear

[0114] 66 Ball Cage

[0115] 67 recess

[0116] 7 Second actuator

[0117] 71 threaded spindle

[0118] 72 spindle nut (combined with cam plate 62)

[0119] 73 bearing parts

[0120] 74 hub part

[0121] 75 large gear

[0122] 76 slots

[0123] 8 Friction element

[0124] 81 friction surface

[0125] 9 Reverse friction element

[0126] 91 Opposing friction surface

[0127] 92 bearing parts

[0128] 93 Spring element

[0129] A axis

[0130] R wheel axis

[0131] V adjustment direction

[0132] L Air gap

[0133] Db ball diameter

[0134] rg raceway radius

Claims

1. An electromechanical brake device (1) for a motor vehicle, the brake device (1) comprising an electromechanical actuating device (5) and a braking portion (32), the braking portion (32) being connected to the actuating device (5) and adjustable by the actuating device (5) and being in braking engagement with a counter-braking portion (2), in, The actuating device (5) has at least one actuating drive (6, 7), wherein the actuating drive (6) has a ball ramp arrangement (6) comprising two cam plates (61, 62), wherein the cam plates (61, 62) are drivable by electric actuating motors (41, 42) so as to rotate relative to each other about an axis (A), and The cam plates (61, 62) have raceways (64) positioned axially opposite to each other at an angle to the axis (A), and corresponding balls (63) are rollably arranged between the raceways (64). wherein the raceway (64) has an at least partially rounded cross-sectional profile with a raceway radius (rg), and the balls (63) have a ball diameter (Db), It is characterized by: The ratio (C) between the raceway radius (rg) and the ball diameter (Db) is greater than 0.

5.

2. The braking device according to claim 1, characterized in that The ratio (C) is less than or equal to 0.

75.

3. Braking device according to any one of the preceding claims, characterized in that The ratio (C) was 0.

55.

4. Braking device according to any one of the preceding claims, characterized in that The raceway (64) has a cross-sectional profile with a continuous circular curve.

5. Braking device according to any one of the preceding claims, characterized in that The raceway (64) has a Gothic cross-sectional profile.

6. Braking device according to any one of the preceding claims, characterized in that The raceway (64) has a linear or non-linear ramp course.

7. Braking device according to any one of the preceding claims, characterized in that The cam plates (61, 62) have precisely three raceways (64) and are provided with precisely three balls (63).

8. Braking device according to any one of the preceding claims, characterized in that The raceway (64) has a flat portion in at least one end portion.

9. Braking device according to any one of the preceding claims, characterized in that The raceway (64) has a groove-shaped recess (67) in at least one end portion.

10. Braking device according to any one of the preceding claims, characterized in that The actuating device has at least two actuating drives (6, 7) connected in series.

11. The braking device according to claim 10, characterized in that: One of the actuating drives (6) comprises a ball ramp arrangement, and the other actuating drive (7) comprises an adjusting device operating according to another principle of action.

12. Braking device according to any one of the preceding claims, characterized in that At least one of the cam plates (61, 62) is formed as a sintered component or a cold extruded part.

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