Patent ID: 12196308

DETAILED DESCRIPTION

In the following detailed description of embodiments, for the sake of clarity, the same reference signs designate substantially identical parts in or on these embodiments. However, for better clarification, the embodiments illustrated in the figures are not always drawn to scale.

For reasons of clarity, only those elements of the wheel brake100which are relevant for the embodiment of the approach are illustrated here.

FIG.1shows a view of a transmission assembly1as part of an electromechanical wheel brake100in a longitudinal section with some essential elements, although there is no claim to completeness.

The transmission assembly1is designed with at least a first and a second reduction ratio and comprises a planetary transmission10having a sun wheel11, which is connected for conjoint rotation to a drive shaft12, a number of planet wheels20, which are rotatably mounted on a planet carrier30, and an annulus40surrounding the planet wheels20. The planet carrier30is connected for conjoint rotation to an output shaft32, wherein the planet wheels20are supported by means of the planet carrier30in such a way that they can roll both on the sun wheel11and on the annulus40. During operation, the annulus40can rotate freely in a first position and is held fixed against rotation in a second position. A clutch50is provided between the drive shaft12and the planet carrier30.

In the present case, the example shown is a schematic view of a segment of an electromechanical disk brake, although the transmission assembly1can also be used for or together with an electromechanical drum brake.

The assembly shown in the exemplary embodiment provides for a brake application force to be produced by means of an electric motor or an electronic drive unit (not illustrated). For this purpose, the torque produced by the electric motor is first of all transmitted to the drive shaft12of the planetary transmission10. The sun wheel11is connected for conjoint rotation to the drive shaft12. The drive shaft12and the sun wheel11can, for example, be manufactured in one piece or can be assembled from individual components and connected to one another in an appropriate manner for conjoint rotation.

The planetary transmission10furthermore comprises a number of planet wheels20, of which two are depicted in the exemplary embodiment and which are mounted rotatably on a planet carrier30, also referred to as a spider. Finally, the planet wheels20are surrounded in a known manner by an annulus40. The sun wheel11, planet carrier20and annulus40can roll on one another. In the exemplary embodiment, they are in effective connection with one another via toothing.

The planet carrier30is in turn connected for conjoint rotation to the output shaft32.

In this case, the planet carrier30and the output shaft32can, for example, be manufactured in one piece or can be assembled from individual components and connected to one another in an appropriate manner for conjoint rotation.

The output shaft32is in engagement with a ball screw drive70. Instead of a ball screw drive, it is also possible to use a spindle or a rack. If a spindle is used, it may also be possible to enable a parking brake function with self locking. By means of a spindle nut71, a braking element80can be moved in translation in the axial direction during operation. The braking element80can be part of an electromechanically actuated floating caliper brake and can, for example, comprise a pressure piston or brake piston. The braking element80is designed with a rotation prevention means81, which can engage in a corresponding undercut82.

During the operation of the electromechanical wheel brake100, a brake application force is applied, which acts on the braking element80in the direction denoted by “Z”. In operation, a corresponding braking torque can thereby be produced at the wheel under consideration. Before the braking element80comes into contact with the brake disk during operation, the release clearance first of all has to be traversed in the axial direction.

After the release clearance has been traversed or upon contact of the braking element80with the brake disk, an axial force in the opposite direction is produced, indicated by “A” in the figure, and this may then rise when the brake lining comes into contact with the brake disk.

This axial force is used to shift the transmission assembly from the at least first into the second reduction ratio. The assembly shown inFIG.1exhibits a state of the transmission with a position of the annulus40in accordance with the second reduction ratio, in which the annulus40is accordingly braked or held fixed against rotation.

Here, the first reduction ratio forms a rapid motion ratio in order to traverse the release clearance when braking or at the beginning of a braking process during operation. The torque which must be applied during this process is lower than the torque which must be applied during active braking. In an embodiment, the magnitude of this torque can be, for example, 20% or less, e.g. 10% or 5%, of the torque which is required during an active braking process.

In the first torque range, as it were during the advance of the wheel brake, the torque is transmitted via the clutch50from the drive shaft12to the planet carrier30and thus to the output shaft32connected for conjoint rotation. For this purpose, the annulus40and the planet carrier30can rotate freely in the surrounding housing90in the first position and are thus as it were functionless. The output of the planetary transmission10is driven directly by the drive with the aid of the clutch50.

In other words, the braking element80is moved in the brake application direction Z. A further advance then leads to the counterforce on the output shaft32in the direction A, which leads to an axial movement of the output shaft in direction A. The annulus40is thereby moved in the axial direction as far as the second position, which is depicted inFIG.1. For this purpose, the annulus40and the output shaft32have an axial mobility and can move from a first into a second position depending on the acting axial force.

In order to ensure this, the teeth by means of which the sun wheel11, the planet wheels20and the annulus12are in effective connection are designed in such a way as to be aligned parallel to the rotational axis13. In this way, axial movement without radial misalignment is possible without problems, even when the teeth are intermeshing. Corresponding rolling of the components on one another is also conceivable and possible instead of the teeth if the axis of rotation is parallel to the rotational axis13of the transmission assembly1.

In the second position, the annulus40is accordingly prevented from performing a rotary motion during the operation of the wheel brake. Braking or holding the annulus40fixed against rotation thus brings the second reduction ratio of the planetary transmission10into use.

Thus, an electromechanical wheel brake100or a transmission assembly1allows the release clearance to be traversed quickly and thus allows an improved response.

In the embodiment shown inFIG.1, the planet carrier30has an axially projecting neck31, which surrounds the drive shaft12. The clutch50is arranged between the inner surface of the neck31and the outer lateral surface of the drive shaft12.

For this purpose, the inner surface of the neck31or the drive shaft12can also have a recess or cutouts (not illustrated) in order to hold or receive the clutch50in a fixed manner in the axial direction.

The clutch50serves for direct transfer of the drive torque to the planet carrier30in the first torque range up to a predetermined torque. In this way, a reduction ratio of about 1:1 can be achieved in the direct drive mode of the transmission assembly1.

According to an embodiment, the clutch50is designed as an “overload clutch”. This makes it possible to ensure that as far as possible no driving energy is lost due to the clutch50in the second torque range, in which active braking takes place.

According to another embodiment the clutch50can also comprise a friction clutch, as indicated inFIG.1. For this purpose, the clutch50is of annular design and surrounds the drive shaft in the exemplary embodiment. The friction clutch can apply a predetermined static friction to the drive shaft12when it is firmly connected to the planet carrier30or to the planet carrier30when it is firmly connected to the drive shaft12.

A magnetic clutch, which can be based on a magnetic reluctance torque and which shifts or changes over above a defined torque, is also possible and contemplated.

As shown inFIG.1, an axial bearing60, via which the axial force can be applied by the output shaft32to the annulus40, is furthermore provided. When the annulus40is braked or held fixed against rotation, the axial bearing60ensures that the output shaft can continue to rotate.

In the exemplary embodiment, the output shaft32has a radial projection33for this purpose, said projection running parallel to the side wall41of the annulus40. When an axial force is applied, the annulus40can then be supported against the projection33in the axial direction, as shown inFIG.1.

In the exemplary embodiment, the axial bearing60is shown as a cylindrical roller bearing, that is to say as a rolling bearing, but it can also be designed as a ball bearing, for example.

According to one embodiment, which is shown only indicatively inFIG.1, provision is made for braking or holding the annulus40fixed against rotation in the second position by the fact that the face side42of the annulus40is in effective interaction with a fixed stop91of the housing90.

For this purpose, the stop91and/or the face side42can, for example, be provided with corresponding friction linings, which bring about a high static friction when pressed onto one another and in this way inhibit or brake rotation of the annulus40.

Alternatively or in addition, it is possible to provide elements which can bring about positive engagement in the region of the contact surface. For this purpose, the face side42of the annulus40and/or the contact region of the housing90or the stop91can have extensions or pins which can engage in sockets of precisely mating design in the second position.

Toothing is also possible. This can also be implemented, for example, by means of teeth arranged in the axial direction on the outer circumferential surface of the annulus, which can engage in mating teeth on the inner wall of the housing.

Accordingly, the annulus can be connected frictionally and/or positively to the housing in the second position. Care should be taken here to ensure that this connection can be released again easily without force when the axial force decreases. This enables the annulus to return to its initial or first position again when the braking process is ended.

In order to assist even further the return process of the annulus from the second to the first position, a spring or a spring element (not illustrated) is provided according to a development. This is intended to move the annulus back into the first position if the axial force diminishes, e.g. owing to a reduction in the braking demand. The spring can be designed, for example, as a tension spring, which is tensioned as a function of an acting torque. The use of a compression spring or, for example, a torsion spring, which is arranged between the annulus40and the housing90, is likewise also possible. By means of a torsion spring, it is possible, for example, to limit the maximum free angle of rotation of the annulus40.

By using a spring, it is also possible to limit the forward stroke, i.e. the axial movement of the annulus40when subject to a torque, e.g. to the nominal release clearance distance. This can be useful for the accuracy with which the position of the brake piston is determined.

FIG.2shows, by means of a diagram, the characteristic of the axial force F as a function of time during a braking process of a transmission assembly in comparison with a transmission assembly from the prior art. It is clearly apparent that the axial force201rises significantly earlier in a transmission assembly1than the axial force202in a transmission assembly from the prior art. In the exemplary embodiment shown, the axial force in the transmission assembly1rises continuously from about 0.04 s to a certain point and then ceases to rise. From this time, in the example at about 0.21 s, the annulus is held fixed against rotation, and the transmission assembly1acts with the second reduction ratio.

FIG.3shows, in a diagram, the characteristic of the brake piston speed as a function of time during a braking process of a transmission assembly in comparison with a transmission assembly from the prior art. The characteristic of the brake piston speed in a transmission assembly1is plotted with the reference sign301, and the characteristic of the brake piston speed in an assembly from the prior art is plotted with the reference sign302.

FIG.4shows, in a diagram, the change in the position of a braking element in the axial direction as a function of time during a braking process of a transmission assembly according to the invention in comparison with a transmission assembly from the prior art. The position in a transmission assembly1is plotted with the reference sign401, and the position in an assembly from the prior art is plotted with the reference sign402. Here too, it is found that, in the transmission assembly1, the position of the braking element from which active braking takes place is reached after only about 0.21 s, whereas this position is reached only after about 0.25 s following the initiation of the braking process in a transmission assembly from the prior art.

The embodiments may include an electromechanical wheel brake100, in for example for a motor vehicle, comprising a transmission assembly1as described above. The electromechanical wheel brake100can be used as a service brake. Use as a parking brake is also possible.

Yet another further aspect also includes a method for operating an electromechanical wheel brake100of a motor vehicle.