Motor vehicle brake, in particular electromechanically operated motor vehicle brake, and vehicle braking system with such a motor vehicle brake

Abstract

An electromechanically actuated motor vehicle brake (10) comprising a housing (12), a brake pad (20) displaceable relative to the housing (12), a motor drive (32), a displacement mechanism (30) arranged between the motor drive (32) and the displaceable brake pad (20), and a clamping arrangement (50) associated with the displacement mechanism (30), wherein the displacement mechanism (30) has a ball screw drive (36) with a rotatable spindle (38) and a nut (40) linearly displaceable in the housing (12), wherein the nut (40) is displaceable within the housing (12) for the displacement of the brake pad (20) by rotatably driving the spindle (38), characterized in that the clamping arrangement (50) is preloaded and can be further clamped beyond its preload when a predetermined clamping force is exceeded.

Description

The present invention relates to an electromechanically actuatable motor vehicle brake comprising a housing, a brake lining that can be displaced relative to the housing, a motor drive, a displacement mechanism arranged between the motor drive and the displaceable brake lining, and a prestressed clamping arrangement assigned to the displacement mechanism.Various types of motor vehicle brakes are known from the prior art. For example, there are conventional motor vehicle brakes in which brake pads are displaced via a hydraulic system, so that they engage a brake disc rotating with a wheel and achieve a more or less strong braking effect as a function of the applied hydraulic pressure. In addition to such hydraulically actuatable motor vehicle brakes, purely electromechanically actuatable motor vehicle brakes exist in the prior art, in which the brake pads can be displaced by an electromechanical drive, in particular using an electric motor. Brakes of this type have the advantage that no complicated hydraulic system is required for their actuation, but that instead the on-board electronics of the vehicle can be used to actuate the brake system.The prior art according to DE 101 26 556 A1 shows such an electromechanically actuatable vehicle brake in which a brake pad, which is arranged in a floating caliper arrangement in a conventional manner, can be displaced via a ball-ramp mechanism in order thus to achieve a braking effect.Furthermore, the prior art according to DE 195 11 287 A1 shows an electromechanically actuatable disc brake of the floating caliper type, in which the brake lining that is displaceable relative to the housing is displaceable by means of a spindle-nut arrangement. Threaded rollers are arranged between the spindle and the nut, which act as rolling bodies and form a roller screw drive together with the spindle and the nut.Further motor vehicle brakes with an electric motor are known from DE 197 11 382 A1, DE 198 35 550 A1 and WO 99 / 452 92 A1The object of the invention is to provide a motor vehicle brake and a vehicle brake system designed with a motor vehicle brake of this type, wherein the motor vehicle brake ensures reliable operating mode during service braking and high reliability in the case of parking brakes with a compact design.This object is achieved by a motor vehicle brake of the type described at the beginning, wherein the displacement mechanism has a ball screw drive with a spindle which can be driven in rotation and a nut which can be displaced linearly in the housing, wherein the nut can be displaced within the housing by driving the spindle in rotation in order to displace the brake lining, and wherein the clamping arrangement can be clamped beyond its prestress when a predetermined clamping force is exceeded.According to the invention, it is accordingly provided that a ball screw is provided for displacing the brake lining, wherein the clamping arrangement is activated only in the case of a parking brake, in which higher application forces generally have to be achieved than is required in the case of a service brake. Otherwise, the clamping arrangement remains substantially inactive. This can ensure that, by additionally tensioning the clamping arrangement beyond its prestressing force, a "force reserve" can be built up via the clamping arrangement when a parking brake state is brought about, which is available during the parking brake state. As soon as setting processes occur on the brake linings in the parking brake state, which can be attributed, for example, to cooling of the brake linings, as a result of which the application force would drop sharply per se, according to the invention a compensation of such an application force drop can be achieved in that the prestressed clamping arrangement relaxes, with compensation of these setting processes. This ensures that despite this relaxation, a relatively high application force can still be maintained, which ensures a safe parking brake state.According to a preferred embodiment of the invention, it is provided that the motorized drive has an electric motor which can be selectively rotationally driven in mutually opposite directions. This electric motor can be used to quickly and selectively apply or release the brake in the event of a service brake. Preferably, the housing is designed and mounted in the style of a conventional floating caliper arrangement, wherein a second brake pad fixed to the housing is displaceable with the housing in accordance with the relative displacement of the first brake pad relative to the housing. Furthermore, with regard to the implementation of the displacement mechanism, it can be provided that it has a planetary gear which is preferably arranged on or close to the output shaft of the electric motor.By means of the planetary gearing, a desired transmission ratio can be realized as required, which makes it possible to use a low-power and therefore small-dimensioned motor. Furthermore, it can be provided that the displacement mechanism has a gear arrangement, in particular a gear drive, friction wheel gear or a belt gear, which is arranged between the electric motor and the ball screw drive. By means of this gear arrangement of the displacement mechanism, a transmission ratio can also be achieved as required, which allows a low-performance design of the motor.Furthermore, it can be provided according to the invention that the displacement mechanism has a blocking device, by means of which the displacement mechanism can be locked in a specific state, for example when a specific clamping force is reached. Such a blocking device is required in particular for implementing the parking brake function. If the application force desired for the parking brake state is reached or exceeded to a sufficient extent for prestressing the prestressing device, the displacement mechanism must be blocked accordingly. This can be achieved, for example, by the blocking device having an electromagnetically actuatable actuating lever. In this context, it is thus possible for the actuating lever to be displaceable as required by actuating a lifting magnet.According to a preferred embodiment of the invention, it can be provided that the blocking device has a loop spring coupling. Such a loop spring coupling has the advantage that it responds relatively quickly, is easily detachable using the actuating lever and is subject to low wear during operation. Moreover, such a loop spring coupling is available in large numbers at low cost and requires only small installation space.With regard to the use of a loop spring coupling as part of the blocking device, a preferred embodiment of the invention provides that the loop spring coupling, in a release position of the actuating lever, permits a torque transmission from the motorized drive to the ball screw in both rotational directions of the motorized drive and, in a blocking position of the actuating lever, permits a torque transmission from the motorized drive to the ball screw only in the application direction of the motor vehicle brake, but blocks the motor vehicle brake in the release direction. In other words, by moving the actuating lever into its release position, the loop spring coupling is prevented from becoming effective. It is "switched off" so to speak and then permits rotation of the motor drive in its two rotational directions without it having a blocking effect. As a result, the motor vehicle brake can be applied and released unimpeded. In the blocking position of the actuating lever, on the other hand, the looper spring clutch permits a rotation of the motor drive in only a specific rotational direction, i.e., in the application direction. As soon as the components of the displacement mechanism move in the release direction of the motor vehicle brake, the looper spring clutch becomes directly active, i.e. after a short response distance, blocks any further movement in the release direction until it is released again by active actuation of the actuating lever and displacement of the same from the blocking position into the release position. In this way, the motor vehicle brake can be held securely and permanently in a parking brake state. In summary, it can be stated that the blocking device, which is embodied with a looper spring clutch, functions as a switchable freewheel, which can either be completely released, so that it permits rotations in both rotational directions, or becomes active depending on the rotational direction, and thereby blocks a release of the brake.With regard to the control of the actuating lever, there are various possibilities according to the invention. Thus, one embodiment variant of the invention provides that the actuating lever can be switched into the release position upon each actuation of the motorized drive. This ensures that in the event of service braking the blocking effect of the blocking device is prevented in a guaranteed manner. In the parking brake situation in which the motor drive is not actuated, deactivation of the blocking device thus also remains impossible.As an alternative to this activation possibility of the actuating lever, it can also be provided that the actuating lever can be switched into the release position depending on the direction of rotation of the motorized drive. This control is possible because the looper spring clutch only becomes effective in a certain rotational direction of the motor drive. If an active actuation of the motor takes place in this direction of rotation, a corresponding displacement (release) of the brake is in fact desired, so that the blocking device must be deactivated in order not to impede this desired displacement of the brake.Alternatively, it is also possible that the actuating lever can be selectively switched into the release position depending on a predetermined operating situation, in particular for releasing a parking brake position. This mode of operation also ensures that the blocking device only becomes active in a parking brake situation. The activation can be achieved by means of a rectifier.A further development of the invention provides that the clamping arrangement has a captive spring arrangement. In this case, it can be provided that the spring arrangement is encapsulated for protection against external influences. According to a preferred embodiment of the invention, it can be provided that the spring arrangement comprises a helical spring which is coupled at one end in a rotationally fixed manner to an output gearwheel of the transmission arrangement and at the other end in a rotationally fixed manner to the threaded spindle of the ball screw, wherein a torque transmission from the transmission arrangement to the ball screw takes place by means of the helical spring. In this case, it can be provided that the relative rotation between the threaded spindle and the driven gearwheel is limited by means of a stop arrangement. In order to implement this constructionally, a further development of the invention provides that the stop arrangement has a stop disk, which is coupled to the threaded spindle in a rotationally fixed manner and has at least one stop formation, and that the output gearwheel has a counterstop formation which can be brought into engagement with the stop formation, wherein the stop formation is movable relative to the counterstop formation within a predetermined play. The play is determined by the available passable distance between the stop formation and the counterstop formation.By means of these measures, a reliably acting clamping arrangement can be realized in a simple and compact manner with a spring arrangement which is sufficiently prestressed (constrained) in the initial state and can be further clamped only to a certain extent. The maximum tension is achieved by suitable dimensioning of the predetermined play. As soon as this play has passed through, no further application of the clamping arrangement is possible, so that any further application of the brake is transmitted directly to the spindle and from there to the displaceable brake lining. This makes it possible to avoid the spiral spring from being over-tensioned.In this context, it may further be provided that the prestressing force of the spring arrangement is selected such that during a service braking process, the application force of the motor vehicle brake does not exceed the prestressing force and that, when a parking braking process is carried out, the application force of the motor vehicle brake exceeds the prestressing of the spring arrangement. Thus, according to the invention, it is possible, for example, for the prestressing force of the spring arrangement to be in a range between 15 and 18 kN, preferably approximately 16.5 kN.The invention further relates to a motor vehicle brake system having a motor vehicle brake of the type described above.The invention is explained in the following by way of example with reference to the attached figures. They represent: FIG. 1 is a sectional view through a vehicle brake according to the invention; FIG. 2 is a sectional view along the section line II-II from FIG. 1 ; FIG. 3 is a sectional view along the section line III-III from FIG. 1 ; FIG. 4 shows a perspective detailed view of a combination of drive device and blocking device of the vehicle brake; FIG. 5 is an explanatory sectional view taken along the line V--V of FIG. 4 of the locking mechanism; FIG. 6 is a sectional view taken along the line VI-VI of FIG. 5 to further explain the locking mechanism; FIG. 7 shows a detailed view of the spindle together with the helical spring; FIG. 8 is a sectional view illustrating the coil spring taken along section line VIII-VIII of FIG. 7 ; FIG. 9 is a front view of the spindle in detail, as is also already evident from the sectional view according to FIG. 2 ; FIG. 10 is a graph in which the clamping force is plotted over the clamping path with respect to the prior art and the invention; FIG. 11 is a longitudinal sectional perspective view of a ball screw according to the present invention; FIG. 12 is a longitudinal sectional view of the ball screw in detail; FIG. 13 is a side view of the ball screw according to the invention; FIG. 14 is a front view of the ball screw according to the present invention; FIG. 15 is a perspective view of the ball screw according to the invention, with the nut cut away; and FIGS. 16, 17 to 18 show representations for explaining the control of the blocking device.Referring now to FIG. 1, a vehicle brake according to the present invention is shown in cross-section and is generally designated 10. This includes a housing 12 in which a first brake lining carrier 14 with a brake lining 16 is mounted in a fixed position. Furthermore, a second brake lining carrier 18 with a brake lining 20 is provided in the housing 12. This second brake lining carrier 18 is displaceable in the housing 12. Between the brake pads 16 and 20 a brake disc 22 is arranged which is connected to a motor vehicle wheel in a rotationally fixed manner.For displacing the brake lining 20, a piston 24 is accommodated displaceably in the housing 12. This piston 24 has at its left end a piston closure 26 which serves for displacing the brake lining carrier 18 with the brake lining 20. The piston 24 is sealed against external influences, such as moisture and dirt, by a crank arrangement 28.For displacing the brake lining 18 via the piston 24, an electromechanical drive arrangement 30 is provided. This comprises a motor 32 (see FIG. 3 ) which drives a ball screw 36 via a gear drive 34 described in more detail below. The ball screw 36 has a spindle 38 rotationally driven by the motor. Further, the ball screw 36 includes a nut 40 disposed around the spindle 38. In the nut 40, running grooves 41 for a rolling element arrangement 42 are provided. The spindle 38 further comprises at the end a threaded bushing 44 which is connected to the spindle 38 in a rotationally fixed manner and in turn comprises radially outer running grooves 45 for the rolling body arrangement 42. The spindle 38 is provided with a central bore 47 from its left-hand end in FIG. 1. A tension spring 46 is received in this central bore 47, which is held in the spindle 38 in a rotationally fixed manner at its right-hand end in FIG. 1. With its left-hand end in FIG. 1, the tension spring 46 engages a pressure piece 48 which, for its part, is in contact with the rolling body arrangement 42 and prestresses the latter into its starting position shown in FIG. 1. In the following, the ball screw 36 will also be discussed in detail with reference to FIGS. 11, 12, 13, 14 to 15.Furthermore, FIG. 1 shows a spiral spring 50, which is accommodated under prestress in the space between a transmission element 51 of stepped design and a receiving bush 52. The transmission element 51 has an internal toothing 53 with which it is connected pressure-tightly to the spindle 38 via a corresponding complementary toothing. The receiving bushing 52, on the other hand, is rotatable relative to the spindle 38 and to the transmission element 51. The receiving bush 52 is provided on its outer periphery with an external toothing 54 which is in engagement with an intermediate gearwheel ( 74, see FIG. 2 ) for rotationally driving the receiving bush 52. The receiving bushing 52 is closed on its right-hand side in FIG. 1 by a closure cover 56. The closure cover 56 is connected in a rotationally fixed manner to the spindle 38 and the transmission element 51 via a clamping screw 58.Finally, FIG. 1 also shows an axial bearing 60 which serves to support axial forces.FIGS. 2, 3 and 4 provide information about the design of the drive of the spindle 38. the motor 32 is provided with an output shaft 61 on which a gearwheel 62 is arranged in a rotationally fixed manner. The gear 62 acts as a sun gear with which planet gears 64 mesh. The planet gears 64 are rotatably mounted on a planet carrier 66. They mesh with a ring gear 68 formed in the housing 12, as is customary in a planetary transmission. The planet carrier 66 also has a smaller diameter externally toothed shaft portion 70 which rotates at a certain speed when the motor 32 rotates in accordance with the transmission ratio of the planetary gear. It should be noted that although the shaft portion 70 is disposed and supported on the motor output shaft 61, it is rotatable relative thereto.The housing 12 also supports a bearing journal 72, on which a transmission gear 74 is rotatably arranged. As already indicated above, this drives the receiving bushing 52 provided with the external toothing 54. It can be seen in FIG. 2 that the receiving bushing 52 has recesses 80 along its inner periphery, which extend in the circumferential direction over a specific distance a or a corresponding angle α. On the closure cover 56, corresponding radial projections 82 are provided, which extend into the recesses 80. The radial projections 82 have a smaller extension b (or angular extension β) in the circumferential direction than the dimension a (α) of the recesses 80, so that the cover disk 56 can be rotated about the axis A relative to the receiving bushing 52. More specifically, relative rotational movement about axis A between components 52 and 56 is possible over distance d=a-b and over angle δ=a-β, respectively.This is also apparent in detail from the detailed illustration according to FIGS. 7, 8 to 9, wherein the radially inner end 84 of the spiral spring 56 is held in the transmission element 51 in a rotationally fixed manner. The radially outer end 88 of the spiral spring 50, on the other hand, is held in a rotationally fixed manner in a corresponding radial bore 90 which is formed in the receiving bushing 52. The spiral spring 56 is prestressed. Since-as already described above-the receiving bush 52 is rotatable relative to the transmission element 51 by the distance d, which in turn is coupled to the spindle 38 in a rotationally fixed manner via the toothing 53, as a result of a rotational drive of the receiving bush 52 in the clockwise direction according to arrow P (FIG. 9 ), the rotational movement is transmitted via the helical spring 50 to the transmission element 51 while increasing the prestress of the spring and from there is then tensioned to the spindle 38. The relative movement between the receiving bushing 52 and the transmission element 51 which is connected to the spindle 38 in a rotationally fixed manner and is likewise connected to the closure cover 56 in a rotationally fixed manner is limited to the distance d or the angle δ by the radial projections 82 and the recess 80.As soon as the radial projections 82 abut the opposite radial flank of the recesses 80 starting from the position shown in FIG. 9 after passing through the distance d, no further relative movement takes place any longer and the rotational movement is transmitted directly from the receiving bush 52 to the transmission element 51 and from there to the spindle 38. The spiral spring 50 is then prestressed to the maximum extent.Due to the relative movement by the distance d, it is possible to achieve a tension state with a "tension force reserve" on the spindle 38 via the spiral spring 50, which tension state serves to compensate setting processes on the brake pads 16 and 20 as a result of cooling or the like after the brake 10 is applied in the parking brake mode. In this regard, a detailed discussion will be given with reference to FIG. 10.Turning once again to the overview illustration according to FIG. 3 and the individual part illustrations according to FIGS. 4, 5 to 6, it can be seen that a blocking device 100 is also provided on the motor output shaft 61. The blocking device 100 serves to block the electromechanical drive arrangement 30 in the case of a parking brake operation, in which the brake pads 16 and 20 must be locked after a certain clamping force has been reached on the brake disc 22.The blocking device 100 is also shown in detail in FIGS. 4, 5 to 6. It comprises a loop spring 102 which is wound around a sleeve-like projection 104 of the shaft section 70 of the planet carrier 66 with little play. At its one end 106, the loop spring 102 is held in a rotationally fixed manner in a cover cap 108. Starting from this end 106, a plurality of adjoining turns extend wound onto the section 104 as far as the second end 110. This second end 110 of the loop spring 102 is opposite a pushing side of a lever 112 of the blocking device 100. The lever 112 is displaceable along the arrow R. A lifting magnet arrangement 116 which can be fixed to the housing 12 by means of fastening elements 114 is used for this purpose. This comprises a magnet coil 118 that can be energized as required and a permanent magnet 120 that assumes the position shown in FIGS. 5 and 6 when the coil 118 is not energized and that ensures that the lever 112 is displaced to the right in FIGS. 5 and 6 when the coil 118 is energized. The lever 112 is additionally guided linearly in the direction R in the housing 12 of the lifting magnet 116 via a guide pin 122.The blocking device 100 acts like a freewheel, which enables a rotation in one direction of rotation, but blocks it in the other direction of rotation, and which can be switched as required by electromagnetic control in such a way that it permits rotations in both directions of rotation. If the motor 32 is rotationally driven in such a way that the gearwheel 70 rotates counterclockwise according to arrow Q (see FIGS. 4 and 5 ), the loop spring 102 remains ineffective. In other words, the bushing-shaped part 104 slips through relative to the loop spring 102 without exhibiting a blocking effect. Such a rotary drive takes place, for example, for applying the brake during a service braking process or during a parking braking process.If, however, the gear wheel 70 now moves in the opposite direction, as is shown by the arrow S in FIG. 5, the free end of the loop spring 110 is carried along. As a result, the loop spring 102 contracts and already after a short rotational stroke of the part 104 blocks any further rotation thereof due to the friction and wrap occurring. This locks the gear wheel 70. This blocking effect can be used to block the brake 10 for a parking brake operation after application to a specific clamping force.In order to be able to release the brake, the coil 118 is energized, so that the lever 112 is displaced to the right in each case in accordance with arrow R in FIGS. 5 and 6. As a result, the free end 110 of the loop spring 102 is displaced relative to the bushing-like part 104 in such a way that a clearance again results between the loop spring 102 and the bushing-like part 104. The tight wrap around the part 104 and the static friction caused thereby are canceled out, so that the gearwheel 70 can be released for a rotational movement.In other words, the blocking device 100 allows the blocking of rotation of the gear 70 in the one direction and the release in the other direction by using a loop spring 102. It should be noted that in a service braking situation, the release of the brake is of course not hindered by the blocking device 100. In such a service braking situation, the lever 112 is adjusted by energizing the coil 118 such that a blocking effect of the loop spring 102 is permanently absent.The structure of the ball screw 36 will be described in detail below with reference to FIGS. 11, 12, 13, 14 to 15. It can be seen in these figures that the spindle 38 is provided in its left-hand region with a central bore 47 and in its right-hand region with a central bore 130. The central bore 130 serves to receive the fastening screw 58, as already described above. The tension spring 46 is received in the central bore 47, the right end 132 of which is received in a radial bore 134 in a substantially rotationally fixed manner and against undesired axial displacement. The tension spring 46 has an elongated fastening bracket 136 which comprises a fastening hook 138 at its end section. With the fastening hook 138, the spring element 46 is accommodated in one of a plurality of receiving openings 140, which are formed in the pressure piece 48, already mentioned at the beginning, around a central opening. Starting from this central opening of the pressure piece 48, a cup-shaped guide section 142 extends into the bore 47, with which the pressure piece is guided in the opening 47 so as to be axially displaceable. The cup-shaped guide section 142 also has positioning lugs 144 at its end axially located in the bore 47 for positioning the spring section 136.Furthermore, it can be seen in FIG. 11, but in particular in the perspective illustration according to FIG. 15, that the rolling body arrangement 42 is formed by a helically running rolling body chain which has a helical cage 146, in which spherical rolling bodies 148 are accommodated. As already stated, the rolling element arrangement 42 is guided in corresponding running grooves in the nut 40 and in the threaded bushing 44. The threaded bushing 44 comprises two stop pins 150 and 152 which limit the relative movement between the rolling element arrangement 42 and the threaded bushing 44 firmly connected to the spindle 38. The pressure piece 48 is prestressed via the spring element 46 into the starting position shown in FIGS. 11 and 12, in which the rolling body arrangement 42 bears against the stop pin 152. This prestress ensures that the rolling element arrangement 42 returns repeatedly to its starting position shown in the figures when it is free of load. In other words, this means that, for example when releasing a parking brake state, when the clamping force is reduced, the spring element 46 finally automatically returns the rolling body arrangement 42 into the initial position shown.Finally, FIGS. 11 and 12 also show a star-shaped attachment 154, which is mounted on the nut 40 in a rotationally fixed manner and is guided in the housing 12 in a linearly movable manner. With this attachment guided in the housing in a linearly movable manner, the nut 40 engages the piston closure 26 for displacing the brake lining 20. Furthermore, a radial bearing 156 is also visible, with which the spindle is mounted in the housing 12.The ball screw 36 according to the invention has the advantage that, unlike conventional ball screws, it does not require any complicated and space-requiring rolling element return. As a result, it can be dimensioned relatively small in the axial direction as well as in the radial direction. Due to the respective return of the rolling body arrangement 42 by means of the spring element 46 into its starting position, the same maximum application travel is always available after each actuation and subsequent return. Wear compensation is effected solely by follow-up displacement of the nut 40. This also ensures that the ball screw 36 according to the invention only has to perform a relatively small stroke of 2 mm, for example, for the actual clamping function.The vehicle brake according to the invention functions as follows:During a service braking process, as already described above, the motor 32 is energized, so that the gearwheel 70 rotates counterclockwise in FIG. 4 (clockwise in FIG. 5 ). The gear 74 is then driven accordingly and ultimately drives the receiving bushing 52. The rotational movement is transmitted to the spindle 38 via the helical spring 50, wherein the helical spring 50 is already prestressed to such an extent that, in the case of the comparatively low clamping forces which usually occur during a service braking operation, there is no relative rotation between the receiving bush 52 and the transmission element 51. In other words, during application in a service braking situation, the spiral spring 50 acts like an uncompliantly stiff element, so that decelerations caused by the spiral spring 50 during application in a service braking process do not occur.The brake pads 16 and 20 are applied depending on the actuation of a brake pedal and / or according to driving assistance systems, such as an anti-lock brake system, a spacing system, a control for regenerative braking, etc. To release the brake during a service braking, the gearwheel 70 is correspondingly rotationally driven in another direction. As already described above with regard to the blocking device 110, it can be kept inactive during service braking by the lever 112 engaging the free end of the loop spring 102 and displacing it relative to the gearwheel 70. With reference to FIGS. 16, 17 to 18, however, other possibilities for controlling the blocking device 110 are described.In the case of parking braking, on the other hand, it is desirable to reach a certain clamping force level when the brake is applied and to substantially maintain this level permanently even despite setting processes on the brake linings 16 and 20 which are caused by cooling. For this purpose, the brake 10 is operated in the same manner as described above with reference to the service braking, but with higher clamping forces. A clamping force level of, for example, 22 kN is initially achieved via the motor drive. This can be seen, for example, in the graph according to FIG. 10, the helical spring 50 is prestressed in such a way that a relative rotation between the spindle 38 and the receiving bush 52 does not occur until approximately 16.5 kN.With a further increasing tension force, the spiral spring 50 is tensioned more strongly beyond the degree of its prestress until the play d is finally completely passed through. This is followed by a rise again with a steeper gradient. This explains the bends K1 and K2 in the solid line according to FIG. 10. In other words, the curve section between both bending points K 1 and K 2 just reflects the clamping of the spiral spring 50 during a traversing of the play d. After the point K2 has been reached, the brake is applied with a once again steeper characteristic curve up to an application force of approximately 21.5 kN, which corresponds to an application travel of a total of approximately 1.5 mm.As is generally known, after cooling of the brake linings in the parking brake state, a setting process usually occurs, i.e. the brake linings contract slightly. As a result, the brake application force applied to the brake disk falls. However, it must be ensured that despite this setting process, a sufficiently large clamping force of approximately 16.5 kN is still maintained in order to ensure a reliable parking brake state. This setting process can be compensated for within certain limits by the helical spring 50. In other words, the spindle 38, driven by the tension force of the spiral spring 50, is "pushed" or "turned" upon a thermally induced shrinkage of the brake pads 16 and 20, wherein the tension force can still be kept above the desired level of 16.5 kN.It should also be noted, as already explained above, that initially no blocking of the mechanical drive arrangement 30 takes place during the establishment of the parking brake state. Only when the clamping force of approximately 21.5 kN is reached and the motor 32 is switched off does the blocking device 110 become active and prevents a rotation of the gearwheel 70 in the direction of the release position. The blocking device 110 acts in such a way that the restoring torque resulting from the brake applied can be supported thereon in the style of a blocking freewheel.To release the parking brake, the coil 118 is then energized and the lever 112 is pushed onto the end 110 of the loop spring 102, so that the wrap effect of the loop spring 102 is canceled and the latter releases the gearwheel 70 again for rotation into the relaxed position of the brake.As already indicated above, the blocking device 110 can be operated in various ways. The loop spring 102 can be switched to a state releasing the part 104 according to various modes. Thus, it is possible to energize the coil 118 at each motor connection in order to displace the lever 112. This is achieved by a circuit as shown in Fig. 16.Alternatively, it is possible to perform only current-direction-dependent energization of the coil 118 and thus to perform current-supply as a function of the direction of rotation of the motor. In other words, the blocking device 110 becomes current only when the motor 32 rotates in the application direction. This is achieved by using two diodes, as shown in Fig. 17.Alternatively, as shown in FIG. 18, it is also possible to use a circuit for a lifting magnet with a permanent magnet armature, a rectifier being connected between the motor circuit and the circuit serving for controlling the blocking device 100.

Claims

Electromechanically actuatable motor vehicle brake (10), comprising a housing (12), a brake pad (20) which can be displaced relative to the housing (12), a motor drive (32), a displacement mechanism (30) which is arranged between the motor drive (32) and the displaceable brake pad (20), and a clamping arrangement (50) which is assigned to the displacement mechanism (30), wherein the displacement mechanism (30) has a ball screw drive (36) having a spindle (38) which can be driven in rotation and a nut (40) which can be displaced linearly in the housing (12), wherein the nut (40) can be displaced within the housing (12) by driving the spindle (38) in rotation in order to displace the brake pad (20), characterized in that the clamping arrangement (50) is prestressed and can be further tensioned beyond its prestress if a predetermined clamping force is exceeded.Motor vehicle brake (10) according to Claim 1, characterized in that the motor drive has an electric motor (32) which can be selectively rotationally driven in mutually opposite directions.Motor vehicle brake (10) according to Claim 2, characterized in that the displacement mechanism (30) has a planetary gearing which is arranged on or close to the output shaft (61) of the electric motor (32).Motor vehicle brake (10) according to Claim 2 or 3, characterized in that the displacement mechanism (30) has a gear arrangement (34) which is arranged between the electric motor (32) and the ball screw drive (36).Motor vehicle brake (10) according to one of the preceding claims, characterized in that the displacement mechanism (30) has a blocking device (100), by means of which the displacement mechanism (30) can be locked when a specific clamping force is reached.Motor vehicle brake (10) according to Claim 5, characterized in that the blocking device (100) has an electromagnetically actuatable actuating lever (112).Motor vehicle brake (10) according to Claim 6, characterized in that the actuating lever (112) can be displaced by actuating a lifting magnet (118).Motor vehicle brake (10) according to one of Claims 5 to 7, characterized in that the blocking device (100) has a loop spring clutch (102).Motor vehicle brake (10) according to Claim 8, characterized in that, in a release position of the actuating lever (112), the loop spring clutch (102) permits a torque transmission from the motor drive (32) to the ball screw drive (36) in both rotational directions of the motor drive (32), and, in a blocking position of the actuating lever (112), permits a torque transmission from the motor drive (32) to the ball screw drive (36) only in the application direction of the motor vehicle brake (10), but blocks the motor vehicle brake (10) in the release direction.Motor vehicle brake (10) according to Claim 9, characterized in that the actuating lever (112) can be switched into the release position upon each actuation of the motorized drive (32).Motor vehicle brake (10) according to Claim 9, characterized in that the actuating lever (112) can be switched into the release position as a function of the direction of rotation of the motor drive (32).Motor vehicle brake (10) according to Claim 9, characterized in that the actuating lever (112) can be switched into the release position selectively as a function of a predetermined operating situation, for releasing a parking brake position.Motor vehicle brake (10) according to one of the preceding claims, characterized in that the clamping arrangement has a captive spring arrangement (50).Motor vehicle brake (10) according to Claim 13, characterized in that the spring arrangement (50) is encapsulated.Motor vehicle brake (10) according to Claim 13 or 14, characterized in that the spring arrangement comprises a helical spring (50) which is coupled at one end in a rotationally fixed manner to an output gearwheel (52) of the transmission arrangement and is coupled at the other end in a rotationally fixed manner to the threaded spindle (38) of the ball screw drive (36), wherein a torque transmission from the transmission arrangement to the ball screw drive (36) takes place by means of the helical spring (50).Motor vehicle brake (10) according to Claim 15, characterized in that the relative rotation between the threaded spindle (38) and the driven gearwheel (52) is limited by means of a stop arrangement (82).Motor vehicle brake (10) according to Claim 16, characterized in that the stop arrangement has a stop disc (56), which is coupled to the threaded spindle in a rotationally fixed manner and has at least one stop formation (82), and in that the output gearwheel (52) has a counterstop formation which can be brought into engagement with the stop formation, the stop formation being movable relative to the counterstop formation within a predetermined play d.Motor vehicle brake (10) according to one of Claims 13 to 17, characterized in that the prestressing force of the spring arrangement (50) is selected such that, during a service braking process, the application force of the motor vehicle brake (10) does not exceed the prestressing force, and in that, when a parking braking process is carried out, the application force of the motor vehicle brake (10) exceeds the prestressing of the spring arrangement (50).Motor vehicle brake (10) according to Claim 18, characterized in that the prestressing force of the spring arrangement (50) is in a range between 15 and 18 kN.Motor vehicle brake system having a motor vehicle brake (10) according to one of the preceding claims.

Images