Electromechanical spreading device for drum brake

Abstract

The invention relates to an electromechanical spreading device (2) for a drum brake of a vehicle, comprising: an electric motor (4) having an output (6); a cam disc (12) which is connected to the output (6) in a torque-transmitting manner and which is arranged between two actuating elements (8, 10) for simultaneously actuating the two actuating elements (8, 10) in a braking action, a first actuating element (8) of the two actuating elements having a spring element (18) which is arranged between an actuating tappet (14) and a support (16), and a second actuating element (16) of the two actuating elements having a spring element (18) which is arranged between the actuating tappet (14) and the support (16), wherein the cam disc (12) is connected in a torque-transmitting manner to an actuating disc (20) of a step gear (22) and the step gear (22) is connected in a force-transmitting manner to a second actuating element (10) of the two actuating elements, in such a way that the second actuating element (10) can be adjusted in the direction of a brake shoe movable thereby by means of a rotation of the cam disc (12) in an engagement angle range of rotation in a first direction of rotation, and can be adjusted by means of the cam disc (12) The stepping gear (22) has an engagement angle range in which rotation in a second direction of rotation, which extends opposite the first direction of rotation, is adjusted away from the brake shoe in the opposite direction, in which engagement angle range the operating disc (20) is in torque-transmitting engagement with the rest of the stepping gear (22).

Description

Field of the Invention

[0001] The present invention relates to an electromechanical actuating device for a drum brake of the type described in the preamble of claim 1. Background Art

[0002] Such electromechanical actuating devices for drum brakes are already known from the prior art in a large number of implementation variants and have: an electric motor that can be controlled by a vehicle control device and includes an output end; a cam disk that is torque-transmittingly connected to the output end and is arranged between two oppositely arranged actuating elements that are each force-transmittingly connected to one of the brake shoes, the cam disk being used to simultaneously actuate the two actuating elements during the braking action of the actuating device, wherein a first actuating element of the two actuating elements has a spring element arranged between an actuating tappet that is in force-transmitting contact with the cam disk and a support of the first actuating element. Summary of the Invention

[0003] In view of this, the present invention is made.

[0004] The object of the present invention is to improve an electromechanical actuating device for a drum brake.

[0005] This object is solved by an electromechanical actuating device for a drum brake having the features of claim 1, characterized in that the cam disk is torque-transmittingly connected to an actuating disk of a step drive, and the step drive is force-transmittingly connected to a second actuating element of the two actuating elements, such that the second actuating element can be adjusted in the direction of the brake shoe that can be moved thereby by rotation of the cam disk in a first rotation direction within an engagement rotation angle range and can be adjusted away from the brake shoe in the opposite direction by rotation of the cam disk in a second rotation direction that extends opposite to the first rotation direction within the engagement rotation angle range, within the engagement rotation angle range, the actuating disk is in torque-transmitting engagement with the remainder of the step drive. The concept "spring element" should be understood broadly here and has all conceivable and suitable implementation forms of a spring element, where multiple springs of the spring element are also conceivable. Merely by way of example, only a spring group or the like is pointed out here. This also applies to the concept "cam disk", which can have every conceivable and suitable form of a cam for actuating an actuating tappet. The dependent claims relate to advantageous further configurations of the present invention.

[0006] A significant advantage of the present invention lies in particular in improving the electromechanical spreading device for drum brakes. The inventive configuration based on the electromechanical spreading device gives an electric spreading mechanism which combines the inherent advantages of a cam drive and a ball screw and thus creates an electromechanical spreading element which can effect the system brake (i.e. perform the braking action) and readjustment (i.e. perform the readjustment action for compensating for component tolerances and wear on the drum brake, in particular the brake shoes) by means of only one electric drive device. The central component here is the cam disk, which is divided into different working areas, namely a braking area for the system braking function and a readjustment area for the readjustment function. Since the cam disk always repeats, a step drive coupled to the cam disk is used in order to be able to effect a lead screw offset during spreading. The step drive enables the rotational movement of the cam disk to be divided into a locking section and a switching section. Based on the repetitive nature of the cam disk, each rotation of the cam disk can be easily found by means of the repetitive profiling. This allows a defined clearance to be reliably set when starting the spreading device according to the invention. The readjustment function is effected by means of the step drive. There is thus provided an electromechanical spreading device for drum brakes based on a cam drive, in which the functionality is achieved by superposition with a step drive, in which functionality the functions of operating the brake (i.e. performing the braking action) and brake lining compensation (i.e. performing the readjustment action) can be effected by means of a single drive device. In addition, by means of the present invention, the lead (i.e. the cam travel) of the cam disk is also achieved to be almost halved compared to, for example, a ball screw at the same load. Correspondingly, an electromechanical spreading device can be achieved in which a smaller torque and load can be achieved while the functionality is the same or improved, so that the spreading device according to the invention can be designed and manufactured, for example, in a smaller size.

[0007] In principle, the spreading device for drum brakes according to the invention can be freely selected within a wide range of suitable types, modes of operation, materials and dimensions.

[0008] A further advantageous configuration of the spreading device according to the invention provides that the spreading device is configured such that the cam disk is supported in a floating manner between two actuating elements, preferably the cam disk is supported on a second actuating element which is connected in a force-transmitting manner to the step drive. In this way, the simultaneous actuation of the two actuating elements and thus of the two brake shoes of the drum brake can be achieved in a particularly simple manner in terms of structure and manufacturing technology. This applies in particular to the preferred embodiment of this further configuration. However, in principle, other embodiments of the invention with different floating supports are also conceivable. For example, another embodiment of the invention provides that the electromechanical spreading device as a whole is supported in a floating manner, for example by means of the housing of the electromechanical spreading device, on the remaining part of the drum brake of the vehicle.

[0009] According to another advantageous further configuration of the spreading device according to the invention, the cam disk is torque-transmittingly connected to the output by means of the control disk. Preferably, the output has an output face gear and the control disk has a face tooth section that meshes with the output face gear. Thereby, the structure and manufacture of the spreading device according to the invention are further simplified. This is particularly applicable to the preferred embodiment of this further configuration. In addition, torque transmission by means of the face tooth section is a proven, robust, and durable technique for torque transmission.

[0010] According to another advantageous further configuration of the spreading device according to the invention, the step drive is configured as a Maltese cross drive, preferably including a five-spoke star wheel that is in engagement with the control disk within the engagement rotation angle range of the cam disk. In this way, the step drive is realized by means of a simple and proven technique in many applications. For example, the Maltese cross drive has a five-spoke star wheel. Alternatively, a Maltese cross drive with more or fewer steps, i.e., a star wheel with n spokes, where n is a natural number other than zero and five, can also be envisaged. In addition, alternative step drives, such as a star wheel drive including a plurality of locking seats, are also possible. Although this step drive is more demanding in terms of structure, it also allows for better design of the two shafts of the step drive. In addition, a cam step drive is mentioned purely by way of example as an additional variant of the step drive.

[0011] According to another advantageous further configuration of the spreading device according to the invention, the step drive is force-transmittingly connected to a corresponding second control element by means of a worm gear drive of the spreading device that is torque-transmittingly connected to the step drive and a lead screw drive of the spreading device that is torque-transmittingly connected to the worm gear drive. Thereby, a force-transmitting connection according to the invention between the step drive on one side and the second control element on the other side can be realized in a particularly simple and very space-saving manner in terms of structure and manufacturing technology. Here, for example, a simple trapezoidal lead screw without ball bearings is sufficient for the lead screw embodiment. If the readjustment action (with respect to the cam disk) of the step drive is in a different stage from the running braking function (i.e., the braking action), and there are no requirements for good efficiency in terms of the transmission function, then the lower efficiency caused by dispensing with ball bearings is acceptable here. Additionally, the lead screw drive uses a worm gear reduction, so that, for example, even when a high spring preload is applied by means of a spring element, readjustment, i.e., the readjustment action, can be performed with a small force. By virtue of the reduction of the lead screw drive using the worm gear, even when a high spring preload is applied by means of a spring element, readjustment can be performed with only a small force.

[0012] According to another advantageous further configuration of the spreading device according to the invention, the actuating tappet has an actuating wheel which is in force-transmitting contact with the cam disk and is rotatably supported on the rest of the actuating tappet. In this way, the friction between the cam disk on the one hand and the actuating tappet on the other hand is significantly reduced. For the actuating wheel, due to its problematic Hertzian pressure design, variants of the actuating tappet including more than one actuating wheel or including concave actuating wheels which are thus more favorable in the sense of Hertzian pressure are also conceivable. Correspondingly, the concept "actuating wheel" should be understood broadly here, so that rolling elements adapted to the above-mentioned variants are also included.

[0013] Furthermore, according to a particularly advantageous further configuration of the spreading device according to the invention, the cam disk has a groove on the contact surface with the peripheral side of the actuating tappet, the groove being used to receive the actuating tappet during the parking brake action of the spreading device. Preferably, the groove is arranged between a section of the contact surface which is configured as a brake area for performing the brake action and a section of the contact surface which is configured as a readjustment area for performing the readjustment action of the spreading device and which corresponds to the engagement rotation angle range, wherein during the readjustment action the second actuating element is adjusted in the direction of the brake shoe which can be adjusted thereby by means of the step drive. Thereby, the functionality of the spreading device according to the invention is additionally improved because, in addition to the brake action and the readjustment action, a parking brake action can also be achieved. The groove ensures that the actuating tappet also remains in the position set relative to the cam disk in the currentless state of the electric motor during the parking brake action. That is to say, the parking brake function is reliably fulfilled also in this currentless state of the electric motor. During the period when the actuating tappet is in the brake area (i.e., the system brake) and the parking brake area (i.e., the parking brake function) of the cam disk, the step drive remains in the latched state, i.e., - different from the switching state of the step drive - it does not move. Spring elements are used for the parking brake function as usual.

[0014] According to an advantageous further configuration of the above-mentioned configuration of the spreading device according to the invention, the spreading device is configured such that the readjustment action is only carried out when the actuating tappet is in contact with the readjustment area. In this way, a strict separation of the individual functions of the spreading device according to the invention according to this further configuration is achieved, so that a defined structural and manufacturing-technical design of the individual functions of the cam disk and the individual drives and thus the corresponding areas can be realized.

[0015] According to another advantageous further configuration of the spreading device according to the invention, the cam travel of the cam disk for actuating the actuating tappet is only configured to overcome a predefined clearance and elasticity of the drum brake. Since the configuration according to the invention of the electromechanical spreading device eliminates the temporarily provided wear travel, for example twice 6 mm, the cam travel of the cam disk can be kept very small compared to the prior art. This relatively small cam travel results in a smaller torque on the electric motor, the face gear stage, and the cam disk and thus allows a significant reduction of the spreading device according to the invention in accordance with this further configuration, and thus also requires a smaller strength of the individual components of the spreading device according to the invention.

[0016] According to another advantageous further configuration of the spreading device according to the invention, the spreading device is configured such that during the execution of the readjustment action, the readjustment travel of the second actuating element is at least 5 times smaller, preferably more than 10 times smaller, than the cam travel of the cam disk for actuating the actuating tappet during the execution of the braking action, with respect to one full rotation of the cam disk. The readjustment function is implemented, for example, via a step drive onto the above-mentioned lead screw drive. Each passed step, i.e., the readjustment travel for each full rotation of the cam disk, is significantly smaller, i.e., at least 5 times smaller in multiples, than the cam travel of the cam disk during the braking function, i.e., during the execution of the braking action. Thus, the cam travel ensures that the complete clearance and complete elasticity of the drum brake can be implemented with a single cam travel in each case. The readjustment travel only results in a small offset during the spreading of the two brake shoes by means of the two actuating elements of the spreading device according to the invention.

[0017] Furthermore, according to another advantageous further configuration of the spreading device according to the invention, the spring element is configured such that the spring preload of the spring element can compensate for at least 1 mm of thermal expansion of the spreading device during the execution of the parking braking action and is greater than the predefined maximum braking force during the execution of the braking action and the parking braking action. Preferably, the maximum braking force during the execution of the parking braking action is greater than or equal to 5 kN. Thereby, the spring preload is selected such that the spring element can compensate for at least 1 mm of thermal length compensation in the spreading element, while the spreading force does not drop below a minimum level, i.e., the parking braking function has sufficient braking force in each case even if the spreading element cools and contracts. Since the spring preload is selected so high here that the spring preload is higher than the spring preload required for the operating braking function (i.e., the braking action), it is ensured that the small cam travel of the cam disk is sufficient to apply the maximum braking force. Description of the Drawings

[0018] The invention is further explained below with the aid of the attached roughly schematic drawings. Here:

[0019] Figure 1 Perspective view showing an embodiment of an electromechanical spreading device according to the present invention;

[0020] Figure 2 Top view showing the embodiment;

[0021] Figure 3 Top view of a first part of the embodiment for better visibility of the step drive;

[0022] Figure 4 Top view of a second part of the embodiment for better visibility of the support of the cam disk;

[0023] Figure 5 View showing a cam disk divided into a braking area, a groove for a parking brake function, and a readjustment area;

[0024] Figure 6 View showing the superposition of the offset of the lead screw drive and the radius of the cam disk;

[0025] Figure 7 View showing the braking force varying according to the rotational position of the cam disk; and

[0026] Figure 8 View showing the torque of the cam disk varying according to the rotational position of the cam disk. DETAILED DESCRIPTION

[0027] In Figures 1 to 8 a pure exemplary manner, an embodiment of an electromechanical spreading device for a drum brake of a vehicle according to the present invention is shown, the spreading device being adapted to spread two brake shoes of the drum brake away from each other as needed. The drum brake including the two brake shoes and the vehicle are not shown here.

[0028] The electromechanical spreading device 2 has: an electric motor 4 including an output end 6 that can be controlled by a control device (not shown) of the vehicle; a cam disk 12 that is torque-transmittingly connected to the output end 6 and is disposed between two oppositely disposed operating elements 8, 10 that are respectively force-transmittingly connected to one of the brake shoes, the cam disk being adapted to simultaneously operate the two operating elements 8, 10 during the braking action of the spreading device 2, wherein a first operating element 8 of the two operating elements has a spring element 18 disposed between an operating tappet 14 that force-transmittingly contacts the cam disk 12 and a support 16 of the first operating element 8.

[0029] According to the present invention, the cam disk 12 is torque-transmittingly connected to the control disk 20 of the step drive 22, wherein the step drive 22 is force-transmittingly connected to the second control element 10 of the two control elements, such that the second control element 10 can be adjusted in the direction of the brake shoe movable thereby by rotation of the cam disk 12 in the engagement rotation angle range in a first rotation direction and can be adjusted away from the brake shoe in the opposite direction by rotation of the cam disk 12 in a second rotation direction extending opposite to the first rotation direction in the engagement rotation angle range, in which engagement rotation angle range, the control disk 20 is in torque-transmitting engagement with the remainder of the step drive 22.

[0030] Furthermore, the spreading device 2 is configured such that the cam disk 12 is floatingly supported between the two control elements 8, 10, wherein the cam disk 12 is supported on the second control element 10 which is force-transmittingly connected to the step drive 22. For this, reference is made in particular to Figure 2 and 4 , from which in combination with the subsequent embodiments it can be further seen the support of the cam disk 12 on the second control element 10. However, in principle, other embodiments of the present invention with different floating support parts are also conceivable. For example, another embodiment of the present invention not shown provides that the electro-mechanical spreading device as a whole is floatingly supported, for example, on the remainder of the drum brake of the vehicle by means of the housing of the electro-mechanical spreading device.

[0031] The cam disk 12 is torque-transmittingly connected to the output end 6 by means of the control disk 20 in the present embodiment, wherein the output end 6 has an output end face gear 24 and the control disk 20 has an end face tooth part 26 meshing with the output end face gear 24.

[0032] As can be seen from Figures 1 to 4 , the step drive 22 is configured here as a Maltese cross drive, wherein the control disk 20 is in engagement with the five-spoke star wheel 28 of the step drive 22 in the engagement rotation angle range of the cam disk 12.

[0033] Furthermore, the step drive 22 is force-transmittingly connected to the corresponding second actuating element 10 by means of a worm gear drive 30 of the spreading device 2 that is torque-transmittingly connected to the step drive 22 and a lead screw drive 32 of the spreading device 2 that is torque-transmittingly connected to the worm gear drive 30. The cam disk 12 is floatingly supported on the second actuating element 10 by means of a bearing bolt 13 that is rotatably supported on the cam disk 12, wherein the bearing bolt 13 projects through a hollow face gear 31 of the worm gear drive 30 and extends into a pocket hole (not shown) of the lead screw drive 32 and is indirectly supported on the second actuating element 10 by means of the lead screw drive 32. However, alternatively, it is also conceivable that the bearing bolt projects through the hollow face gear of the worm gear drive and the hollow lead screw drive and is directly supported on a support of the second actuating element 10, such as the support 11. In the first-mentioned case, the support 11 is not required.

[0034] The actuating tappet 14 has, here for reducing friction, an actuating wheel 34 that is force-transmittingly in contact with the cam disk 12 and is rotatably supported on the remainder of the actuating tappet 14.

[0035] The cam disk 12 has a groove 36 on the contact surface with the peripheral side of the actuating tappet 14, which groove is for receiving the actuating wheel 34 of the actuating tappet 14 during the parking brake action of the spreading device 2, that is, such that the groove 36 is provided between a section of the contact surface that is configured as a braking region 38 for performing the braking action and a section of the contact surface that is configured as a readjustment region 40 for performing the readjustment action of the spreading device 2 and that corresponds to the engagement rotation angle range, wherein during the readjustment action the second actuating element 10 is adjusted in the direction of the brake shoe that can be moved thereby by means of the step drive 22. The above-mentioned regions 38, 40 and especially the groove 36 can be Figure 5 seen clearly. As can be seen from Figure 5 it, the braking region extends from 0° to approximately 233°, the groove 36 extends from approximately 233° to approximately 252°, and the readjustment region extends from approximately 252° to 0°.

[0036] Furthermore, the spreading device 2 is configured such that the readjustment action is only carried out when the actuating tappet 14 is in contact with the readjustment region 40.

[0037] Furthermore, the cam disk 12 is configured such that the cam stroke of the cam disk 12 for actuating the actuating tappet 14 is only configured to overcome a predetermined clearance and elasticity of the drum brake. The clearance is to be understood as the dead travel of the spreading device 2, during which no braking action yet exists because the brake shoes have not yet abutted against the drum of the drum brake.

[0038] Here too, the expansion device 2 is designed such that the readjustment path of the second actuating element 10 during the readjustment action is 12 times smaller than the cam path of the cam disk 12 for actuating the actuating tappet 14 during the braking action, relative to one complete rotation of the cam disk 12 .

[0039] Finally, the spring element 18 is designed in the present embodiment so that the spring preload of the spring element 18 can compensate for the thermal expansion of the expansion device 2 of at least 1 mm when performing the parking brake action and is greater than the maximum braking force previously determined when performing the braking action and the parking brake action, wherein the maximum braking force when performing the parking brake action is greater than or equal to 5 kN.

[0040] Then with the help of Figures 1 to 8 The mode of operation of the electromechanical spreading device according to the invention according to the present exemplary embodiment is explained in more detail.

[0041] Starting from the electric motor 4, the torque is transmitted through the face gear stage, that is, the output end 6 and the operating disk 20. From there, the torque is transmitted to the cam disk 12 which is connected to the operating disk 20 in a torque-transmitting manner. Figure 5 It can be seen that the cam disc 12 is divided into the functions of braking, parking and readjustment. Figure 5 In FIG. 1 , the peripheral contour of the cam disk 12 is shown in bold lines in an angularly resolved manner. The braking region 38 for the braking effect is shown in bold solid lines, the recess 36 for the parking brake function is shown in bold dashed lines, and the readjustment region 40 for the readjustment function is shown in bold dashed lines. Figure 5 The radially arranged numbers 2, 4, 6, 8 and 10 in the figure represent 2, 4, 6, 8 and 10π and reflect the number of revolutions, wherein one revolution corresponds to 2π. If the cam disk 12 moves in the braking region 38, i.e. the actuating tappet 14 abuts against the cam disk 12 in the braking region 38, then the positive radius change of the cam disk 12 acts directly via the actuating wheel 34 and the preloaded spring element 18 on the expansion of the drum brake. The preload force of the spring element 18 is selected such that the maximum expansion force for the drum brake is lower than the preload force. As a result, the spring element 18 is not compressed during braking during the braking action by the expansion force used. The use of the preloaded spring element 18 is a conventional prior art in the construction of the parking brake and serves to compensate for the expansion, mainly thermal expansion, of the tensioned parking brake. This also applies in the present exemplary embodiment to the parking brake function during the parking brake action, i.e. when the actuating tappet 14 is in the recess 36. In this case, the tensioning force exceeds the preload force of the spring element 18 and the spring element 18 is compressed for expansion compensation.

[0042] If the cam disk 12 moves in the readjustment region 40, i.e., the actuating tappet 14 is in the readjustment region 40, the step drive 22 is input-coupled by means of the drive member 21 of the actuating disk 20. The worm gear drive 30 now moves together with the rotation of the cam disk 12 and drives the lead screw drive 32. The lead screw drive 32 is input-coupled such that a readjustment stroke of the lead screw drive 32 is produced as the radius of the cam disk increases. The readjustment stroke here is significantly smaller than the cam stroke of the cam disk 12. Thereby, for each rotation of the cam disk 12, a small offset of the lead screw drive 32 is produced. This offset is used to provide compensation for the wear of the brake lining which is force-transmittingly connected to the actuating elements 8, 10. The superposition of the offset of the lead screw drive 32 and the cam disk radius is shown in Figure 6 As can be seen by viewing together Figure 5 and Figure 6 it is clearly known that the readjustment stroke of each full rotation of the cam disk 12 by means of the lead screw drive 32, which is shown by means of a thick solid line in Figure 6 is significantly smaller than the cam stroke of the cam disk 12 which is shown in Figure 5 .

[0043] The stepwise readjustment by means of the step drive 22 allows the spreader device 2 to be guided countably. By means of this counting, the readjustment can result in there always being a minimum clearance of the spreader device, i.e., a minimum dead stroke. Correspondingly, this dead stroke can be kept as short as possible, so that the response time during braking in the case of a braking action or a parking braking action is also short. In addition, the counting allows the brake to be reliably opened without the clearance, i.e., the dead stroke, being opened too wide - which is generally problematic for braking. For this, see Figure 7 , in which the braking force in N is given as a function of the rotational position of the cam disk. It is shown there that ideal readjustment takes place in the range from 8π to 10π, i.e., during 4 to 5 rotations. It can be seen in the range from 0π to 6π that no braking force is formed or only a weak braking force is formed. In the range greater than 10π it can be seen that the braking force does not decrease at all. I.e., the brake shoe will always abut against the drum in an undesirable manner in the last-mentioned case, i.e., it will grind. If readjustment is carried out to compensate for component tolerances and brake shoe wear, i.e., the cam disk 12 rotates, for example, four to five times completely in the first rotational direction such that the actuating element 10 has been adjusted in the direction of the assigned brake shoe, the braking action starts in the braking region 38 at, for example, 8π. Between 8π and 10π, each rotational position of the cam disk 12 can be approached purposefully in order to carry out a braking action or a parking braking action. If the cam disk 12 rotates further in this first rotational direction, the braking action of the brake shoe is strengthened, as shown by Figure 7It is visible. The groove 36 starts at the very end of the braking region 38. By means of the groove 36, the parking brake function with the parking brake action can be carried out. If the actuating tappet 14 is in the groove 36, the braking force only changes in the uppermost region, in which both the cam disk 12 and the spring element 18 act to generate force. If the cam disk 12 now rotates further in the aforementioned first rotational direction, then if necessary, the readjustment region 40 starts to carry out a further readjustment action again. When carrying out the readjustment action, the braking force decreases again until the step drive 22 is no longer input-coupled by means of the drive element 21 and the readjustment action ends. When the cam disk 12 rotates further in the aforementioned first rotational direction, then thereafter the braking region 38 starts again.

[0044] In Figure 8 shows the torque variation curve of the cam disk 12 for the braking, readjustment and parking functions. In this figure, the torque of the cam disk 12 in Nm as a function of the cam disk rotational position change is shown. It is shown here that by advantageously using the cam disk 12 to reduce the lead of the cam stroke, the torque reduction as described above can be achieved, and for this model shown, it is calculated that the torque is reduced to approximately 2 Nm. This results in a reduction in the input transmission ratio transmitted to the cam disk 12 and thus a significant improvement in the dynamic characteristics of the spreader device 2 compared to the prior art. For the parking function, a maximum spreader force greater than 5 kN and a compensation for thermal expansion of approximately 1 mm are required, so that there is always sufficient braking force during the parking brake action. In addition, by means of the groove 36 of the cam disk 12, it is possible to provide the parking brake function even when the electric motor 4 is de-energized. The actuating tappet 14 also remains reliably in the groove 36 when the electric motor 4 is de-energized, which will be explained in more detail later. Although in Figure 8 there are also torque peaks that briefly exceed 2 Nm respectively. However, this is only short-term in the case where the cam disk 12 continues to rotate starting from the parking brake action, i.e., from the groove 36, in order to reach the readjustment region 40, for example, to carry out the readjustment action. Here, the actuating tappet 14 must move out of the groove 36, which briefly results in a higher torque. However, this load only has a short duration and does not exist at all during normal operation, i.e., during the braking action.

[0045] For the parking function, i.e. the parking brake function, there is a groove 36 on the cam disk 12, in which the operating wheel 34 of the operating tappet 14 can also rest when the electric motor 4 is de-energized. In order to generate the tensioning force for the parking function, the cam disk 12 is rotated several times, so that a plurality of readjustment strokes are performed by the joint action of the stepper drive 22 and the coupled spindle drive 32, which tension the pre-tensioned spring element 18 by approximately 1 mm in order to achieve the required expansion compensation. By counting the steps of the stepper drive 22, the expansion compensation can be reliably measured in the tensioned spring element 18, because the readjustment stroke per step and the number of steps of the stepper drive 22 are known. If the operating tappet 14 is in the groove 36, the cam disk 12 is in this rotational position when de-energized. The rotational position of the groove 36 is visible in the torque curve by means of a torque peak, i.e. a current peak in the motor current of the electric motor 4. As an alternative to the Maltese cross transmission with five steps shown here, alternatives with more or fewer steps can also be envisioned in other embodiments of the present invention. In addition, alternative step transmissions, such as a star wheel transmission including multiple locking seats, are also possible. Although the star wheel transmission has higher structural requirements, it also allows a better design of the shaft of the step transmission. In addition, a curved step transmission can also be envisioned as another variant of the step transmission. The above-mentioned step transmission implementation is pointed out purely by way of example. In order to design the operating tappet, especially the operating wheel, due to its problematic Hertz suppression, it is also conceivable to include more than one operating wheel or a concave and thereby more advantageous operating wheel in the sense of Hertz suppression. Correspondingly, as already explained in the introduction to the specification, the concept "operating wheel" should be understood very broadly.

[0046] The invention is not limited to the present exemplary embodiment. For this purpose, reference is made, for example, to the relevant embodiments in the introduction to the description and to the comments made when explaining the exemplary embodiment.

[0047] Reference numerals list

[0048] 2Electromechanical opening device

[0049] 4 Electric motors

[0050] 6 Output

[0051] 8 First operating element

[0052] 10 Second operating element

[0053] 11 Support for the operating element 10

[0054] 12 Cam disc

[0055] 13 Bearing bolt for cam disc 12

[0056] The actuating tappet of the actuating element 8

[0057] The support of the actuating element 8

[0058] The spring element of the actuating element 8

[0059] The actuating disk of the step drive 22

[0060] The driving part of the actuating disk 20

[0061] The step drive

[0062] The output face gear of the output end 6

[0063] The face tooth part of the actuating disk 20

[0064] The star wheel of the step drive 22

[0065] The worm gear drive

[0066] The face gear of the worm gear drive 30

[0067] The lead screw drive

[0068] The actuating wheel of the actuating tappet 14

[0069] The groove of the cam disk 12

[0070] The braking area of the cam disk 12

[0071] The readjustment area of the cam disk 12

Claims

1. An electromechanical spreading device (2) for a drum brake of a vehicle, for spreading two brake shoes of the drum brake away from each other as required, having: an electric motor (4) that can be controlled by a control device of the vehicle and includes an output end (6); a cam disk (12) that is torque-transmittingly connected to the output end (6) and is arranged between two oppositely arranged operating elements (8, 10) that are respectively torque-transmittingly connected to one of the brake shoes, the cam disk being used to simultaneously operate the two operating elements (8, 10) during the braking action of the spreading device (2), wherein a first operating element (8) of the two operating elements has a spring element (18) arranged between an operating tappet (14) that is in force-transmitting contact with the cam disk (12) of the first operating element (8) and a support (16) of the first operating element (8). It is characterized in that the cam disk (12) is torque-transmittingly connected to an operating disk (20) of a step drive (22), and the step drive (22) is torque-transmittingly connected to a second operating element (10) of the two operating elements, such that the second operating element (10) can be adjusted in the direction of the brake shoe that can be moved thereby by the rotation of the cam disk (12) in a first rotation direction within an engagement rotation angle range and can be adjusted away from the brake shoe in the opposite direction by the rotation of the cam disk (12) in a second rotation direction that extends opposite to the first rotation direction within the engagement rotation angle range. Within the engagement rotation angle range, the operating disk (20) is in torque-transmitting engagement with the rest of the step drive (22).

2. The electromechanical spreading device (2) according to claim 1, It is characterized in that the spreading device (2) is configured such that the cam disk (12) is floatingly supported between the two operating elements (8, 10). Preferably, the cam disk (12) is supported on the second operating element (10) that is torque-transmittingly connected to the step drive (22).

3. The electromechanical spreading device (2) according to claim 1 or 2, It is characterized in that the cam disk (12) is torque-transmittingly connected to the output end (6) by means of the operating disk (20). Preferably, the output end (6) has an output face gear (24) and the operating disk (20) has a face tooth portion (26) that meshes with the output face gear (24).

4. The electromechanical spreading device (2) according to any one of claims 1 to 3, It is characterized in that the step drive (22) is configured as a Maltese cross drive, preferably including a five-spoke star wheel (28) that is in engagement with the operating disk (20) within the engagement rotation angle range of the cam disk (12).

5. The electromechanical spreading device (2) according to any one of claims 1 to 4, It is characterized in that The step drive (22) is force-transmittingly connected to the corresponding second actuating element (10) by means of a worm gear drive (30) of the spreading device (2) that is torque-transmittingly connected to the step drive (22) and a lead screw drive (32) of the spreading device (2) that is torque-transmittingly connected to the worm gear drive (30).

6. The electromechanical spreading device (2) according to one of claims 1 to 5, characterized in that the actuating tappet (14) has an actuating wheel (34) that contacts the cam disk (12) in a force-transmitting manner and is rotatably supported on the rest of the actuating tappet (14).

7. The electromechanical spreading device (2) according to one of claims 1 to 6, characterized in that the cam disk (12) has a groove (36) on the contact surface on the peripheral side of the actuating tappet (14), and the groove is used to receive the actuating tappet (14) during the parking brake action of the spreading device (2). Preferably, the groove (36) is provided between a section of the contact surface configured as a brake area (38) for performing the braking action and a section of the contact surface configured as a readjustment area (40) for performing the readjustment action of the spreading device (2) and corresponding to the engagement rotation angle range. During the readjustment action, the second actuating element (10) is adjusted in the direction of the brake shoe that can be adjusted thereby by means of the step drive (22).

8. The electromechanical spreading device (2) according to claim 7, characterized in that the spreading device (2) is configured such that the readjustment action is only carried out when the actuating tappet (14) is in contact with the readjustment area (40).

9. The electromechanical spreading device (2) according to one of claims 1 to 8, characterized in that the cam disk (12) is configured such that the cam stroke of the cam disk (12) for actuating the actuating tappet (14) is only configured to overcome a predetermined clearance and elasticity of the drum brake.

10. The electromechanical spreading device (2) according to one of claims 1 to 9, characterized in that the spreading device (2) is configured such that during the execution of the readjustment action, the readjustment stroke of the second actuating element (10) is at least 5 times smaller, preferably more than 10 times smaller, than the cam stroke of the cam disk (12) for actuating the actuating tappet (14) during the execution of the braking action, with respect to one full rotation of the cam disk (12).

11. The electromechanical spreading device (2) according to one of claims 1 to 10, characterized in that the spring element (18) is configured such that the spring preload of the spring element (18) can compensate for at least 1 mm of thermal expansion of the spreading device (2) during the execution of the parking brake action and is greater than the predetermined maximum braking force during the execution of the braking action and the parking brake action. Preferably, the maximum braking force during the execution of the parking brake action is greater than or equal to 5 kN.

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