Patent Application
20070151815
The invention relates to a self-boosting electromechanical friction brake having the characteristics of the preamble to claim 1.
One such friction brake is known from International Patent Disclosure WO 03/056204 A1. The known friction brake is embodied as a disk brake. It has a friction brake lining, which for braking can be pressed by an electromechanical actuation device against a brake body to be braked; in the case of a disk brake, the brake body is a brake disk. The electromechanical actuation device of the known friction brake has an electric motor, a step-down gear, and a screw drive as a rotation/translation conversion gear. With the actuation device, the friction brake lining can be moved transversely or at an angle obliquely to the brake disk and thus pressed against it. The construction of the electromechanical actuation device can differ from the construction described here.
To attain self-boosting, the known friction brake has a ramp mechanism, with a ramp extending at an angle to the brake disk, on which ramp the friction brake lining is braced upon being pressed against the brake disk. If in braking the friction brake lining is pressed against the rotating brake disk, then the brake disk exerts a frictional force on the friction brake lining, which urges the friction brake lining in the direction of an increasingly narrow wedge-shaped gap between the ramp that supports the friction brake lining and the brake disk. The bracing of the friction brake lining on the ramp, extending obliquely to the brake disk, of the ramp mechanism exerts a force on the friction brake lining that has a force component transverse to the brake disk. This force component transverse to the brake disk is a contact pressure, which presses the friction brake lining against the brake disk. The contact pressure exerted by the ramp mechanism increases a contact pressure exerted by the electromechanical actuation device and thus increases a braking force of the friction brake. This increasing of the contact pressure and braking force is called self boosting.
An angle at which the ramp of the ramp mechanism extends relative to the brake disk can change over the course of the ramp. A special case or limit case of a ramp mechanism is a wedge mechanism in which the angle at which the ramp extends to the brake disk is constant over the course of the ramp. In this case, the ramp is called a wedge. A plurality of ramp mechanisms may be provided, which are distributed over a back side of the friction brake lining facing away from the brake disk and that brace the friction brake lining jointly.
In the known friction brake, balls or rollers are provided as roller bodies, by way of which the friction brake lining is braced on the ramp and which reduce friction upon displacement of the friction brake lining along the ramp. The roller bodies in the known friction brake roll on raceways that are provided on a back side, facing away from the brake disk, of the friction brake lining and on an abutment plate facing toward the friction brake lining. The raceways extend in the displacement direction of the friction brake lining and are at their lowest point at the center of their length; their depth decreases from the center of the length in both directions. As a result, the raceways form the ramp or ramps of the ramp mechanism. The raceways are mounted in sunken fashion in the back side of the friction brake lining and in the abutment plate; they guide the roller bodies, and via the roller bodies the friction brake lining, transversely to the displacement direction.
The self-boosting electromechanical friction brake has been described above in terms of a disk brake, because it can be explained clearly in terms of a disk brake since known friction brakes of this kind are predominantly embodied as disk brakes, and because even the friction brake named as prior art is a disk brake. This does not preclude the implementation of the invention in other types of brake.
If the friction brake lining of the known friction brake is pushed back and forth for braking and for releasing the brake, the roller bodies ideally roll along the raceways, and they are in their original position when the friction brake lining is also in its original position again. This is true, in the strict sense, only if brake lining wear is ignored, or in a friction brake with readjustment for wear. However, it cannot be precluded that the roller bodies will not merely roll but will also slide on their raceways when the friction brake lining is pushed back and forth. In that case, the roller bodies no longer return to their original position. When the friction brake lining has been pushed back and forth many times, the roller bodies can “wander away” farther and farther from their outset position.
The friction brake of the invention having the characteristics of claim 1 has a positive controller for the roller bodies, which prevents sliding of the roller bodies on the raceways, or at least limits it such that the roller bodies do not leave their raceways. The invention prevents the roller bodies from being able to move arbitrarily far away from their outset position and preferably causes the roller bodies to return to their outset position when the friction brake lining is thrust back into its outset position. A gradual “wandering” of the roller bodies toward the ends of their raceways or out of the raceways when the friction brake is actuated many times is avoided.
The dependent claims have advantageous features and refinements of the invention defined by claim 1 as their subject.
As a simple possibility for a positive controller, claim 2 provides an end stop for the roller bodies, which restricts a travel of the roller bodies. This feature of the invention is especially suitable for friction brakes with self-boosting in only one direction of rotation of the brake body. The end stop, or two end stops, can be mounted on the end of the raceway or raceways, respectively, so that the roller body is moved in compulsory fashion back into its outset position when the friction brake lining is thrust back into its outset position. The roller body as a result necessarily occupies its outset position at the onset of each brake actuation. It is an advantage that the friction brake is released when a roller body is moved back into its outset position from the end stop. That is, no contact pressures, or at most only slight contact pressures make sliding of the roller body on the raceways for restoration to the outset position difficult are operative. However, an end stop may also be located at some other point, such as a different end of the raceway of the roller body. It is understood that braking is also possible for the opposite direction of rotation of the brake body, although then without self boosting or even with self-attenuation. The end stop need not come directly into contact with the roller body; for instance, it may cooperate with a roller body cage instead.
Claim 4 contemplates a forced motion of the roller bodies with the displacement of the friction brake lining upon actuation of the friction brake. The roller bodies are accordingly moved for instance at half the speed and for half the distance as the friction brake lining, compared to a purely rolling motion without sliding. In this feature of the invention, the applicable position of the roller bodies is determined in compulsory and unambiguous fashion by the position of the friction brake lining.
One possibility for such a positive controller is as in claim 5 to provide a gear wheel on the roller body, which meshes with a rack on the friction brake lining and/or on the ramp.
Claim 7 provides a roller body cage, which keeps all or some of the roller bodies of the friction brake at their spacing from one another. The roller body cage, which has the same function as a ball cage of a ball bearing, moves the roller bodies with one another in compulsory fashion and prevents a displacement of one roller body or individual roller bodies relative to the other roller bodies. In this case, one positive controller of a roller body suffices for all the roller bodies connected to the roller body cage.
The positive controller may engage one or more roller bodies directly. Claim 8 is directed to the possibility that the positive controller engages the roller body cage and by way of it indirectly moves the roller bodies in compulsory fashion. For instance, the gear wheel that meshes with the rack is mounted on the roller body cage.
Claim 9 provides that at least one roller body guides the friction brake lining transversely to its displacement direction in a statically determined way. The phrase “transversely to the displacement direction” means guidance of the friction brake lining in a plane parallel to a brake disk, or radially to an axis of rotation of the brake disk. This feature avoids play of the friction brake lining transversely to its displacement direction, in a plane parallel to the brake disk. A static overdeterminedness of the bearing and guidance of the friction brake lining transversely to its displacement direction, which because of manufacturing tolerances can cause mechanical stresses and increased wear, is also avoided. This feature of the invention has the advantage of making only slight demands in terms of manufacturing tolerances.
A refinement according to claim 10 provides that two roller bodies guide the friction brake lining transversely to its displacement direction in a statically determined way. As a result, in addition to the play-free guidance of the friction brake lining transversely to its displacement direction, a rotation of the friction brake lining about an imaginary axis that penetrates the friction brake lining at a right angle is avoided. A third roller body and optionally further roller bodies have no guidance function for the friction brake lining transversely to its displacement direction, in order to avoid a static overdeterminedness of the transverse guidance of the friction brake lining, or in other words radially to a brake disk.
If the roller bodies that guide the roller body transversely to its displacement direction in a statically determined way are balls, claim 10 provides for a four-point bearing of the friction brake lining by the balls. This means that the balls, in each spherical channel in which they rest, rest on the spherical channel at two points, one on each side of an imaginary longitudinal center line of the spherical channel. That is, the balls rest in the two spherical channels at a total of four points. The desired two-point contact in each spherical channel can be attained by means of a rounding, of other than circular shape, of the spherical channel, or for instance by means of a prismatic shape of the spherical channels.
If cylindrical or conical rollers are used as roller bodies, then in accordance with claim 12 they are disposed with an inclination transversely to the displacement direction of the friction brake lining, in order to accomplish the desired statically determined guidance of the friction brake lining transversely to its displacement direction.
The features of the invention defined by claims 9 through 12 can be realized in a friction brake of the invention jointly with or independently of the positive controller of the roller bodies recited in claims 1 through 8.
The invention is described below in terms of exemplary embodiments shown in the drawing. Shown are:
The drawings should be understood as schematic, simplified illustrations.
The other friction brake lining 14 is movable in a direction of rotation and transversely to the brake disk 16. The phrase “in the direction of rotation of the brake disk 16” means that the movable friction brake lining 14 is rotatable about an imaginary axis, which coincides at least approximately with an axis of rotation of the brake disk 16. In principle, a displaceability of the movable friction brake lining 14 in a tangent or secant direction to the brake disk 16 is also possible. The motion of the friction brake lining 14 for actuating the friction brake 10 is effected with an electromechanical actuation device, which is not shown, for the sake of clarity in the drawing. Such actuation devices are familiar from the prior art, in various constructions, to one skilled in the art, and since they do not form the actual subject of the invention, they will not be described in detail here.
The friction brake lining 14 is connected as usual fixedly and nondetachably to a brake lining holder plate 20, which on their back side facing away from the brake disk 16 have ramps 22, which extend in the direction of rotation of the brake disk 16, or in other words in the displacement direction of the friction brake lining 14. On a front side of an abutment plate 24, oriented toward the brake disk 16, there are ramps 26, complementary to the ramps 22 of the brake lining holder plate 20, on which the ramps 22 of the friction brake lining 14 are braced via roller bodies 28. The roller bodies 28 are located between the ramps 22 of the friction brake lining 14 and the ramps 26 of the abutment plate 24; the roller bodies 28 roll on the ramps 22, 26. The roller bodies serve to reduce friction. In
The abutment plate 24 is approximately coincident with the brake lining holder plate 20, on the back side of that plate facing away from the brake disk 16. In
For actuating the friction brake 10, the movable friction brake lining 14 is displaced in the direction of rotation of the brake disk 16. The direction of rotation of the brake disk 16 is represented in
The ramps 22, 26 extend at what is typically an acute ramp angle to the brake disk 16. The ramp angle may vary over the course of the ramps 22, 26, or in other words in their longitudinal direction. If the ramp angle is constant over the length of the ramps 22, 26, the ramps also called wedges. The ramps 22, 26 form a ramp mechanism, which brings about the self boosting of the friction brake 10.
In the exemplary embodiment shown, three ramps 22 are disposed on the brake lining holder plate 20, and three complementary ramps 26 are disposed on the abutment plate 24. This produces a statically determined bracing of the friction brake lining 14. A statically overdetermined bracing with more than three pairs of ramps 22, 26 is conceivable. Fewer than three pairs of ramps 22, 26 are also possible, for instance if two pairs of ramps extend over a width of the brake lining holder plate 20 or if one pair of ramps extends or a large proportion of the surface area of the friction brake lining holder plate 20 (not shown).
In the exemplary embodiment shown in
Only in the theoretical ideal case do the roller bodies 28 execute solely a rolling motion on the ramps 22, 26. In practice, it must be expected that the roller bodies 28, on the motion of the friction brake lining 14 back and forth for actuating and releasing the friction brake 10, will not solely roll on the ramps 22, 26 but will also slide on them. Over time, this can lead to “wandering” of the roller bodies 28; that is, after many motions of the friction brake lining 14 back and forth, the roller bodies 28 are no longer located in their original outset position at the beginning of the ramps 22, 26. The invention therefore provides a positive controller for the roller bodies 28, for which exemplary embodiments are shown in
Another exemplary embodiment of a positive controller of the invention is shown in
According to the invention, each roller body 28 may be provided with its own positive controller.
In
To guide the friction brake lining 14 transversely to its displacement direction, it is known in the prior art to use balls as roller bodies 28, which are mounted in groovelike ball races in the brake lining holder plate 20 and in the abutment plate 24. By means of a greater depth of the ball races at the middle and ball races that become shallower toward their ends, the ramp effect is achieved. With cylindrical or conical rollers as well, the desired guidance of the friction brake lining 14 transversely to its displacement direction can be achieved, if ramplike raceways have raised edges, which guide the rollers on the face ends of the rollers. Both possibilities are disclosed in WO 03/056204 discussed at the outset. When three or more roller bodies 28 are used, they have the disadvantage of a static overdeterminedness of the guidance of the movable friction brake lining 14 transversely to its displacement direction, or in other words radially to an axis of rotation of the brake disk 16. This necessitates high-precision manufacture, in order to achieve low tolerances, and leads to increased wear.
For guiding the movable friction brake lining 14 transversely to its displacement direction, one exemplary embodiment of the invention has the ball guide, shown in
Another exemplary embodiment of a statically determined guidance transversely to the displacement direction of the movable friction brake lining 14 is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 103 61 264.5 | Dec 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP04/52994 | 11/17/2004 | WO | 6/23/2006 |
