Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
2000-02-09
2001-12-04
Butler, Douglas C. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S162000
Reexamination Certificate
active
06325180
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to an electric actuator, comprising a screw mechanism and an electric motor which is driveably connected to the screw mechanism which provides a linear movement in response to a rotational movement of the electric motor, said screw mechanism comprising a screw and a nut one of which is supported rotatably with respect to the housing by means of an angular contact ball bearing, said angular contact ball bearing comprising two pairs of contact points the working lines of which intersect each other.
2. Description of Related Art
Such actuator is known from WO-A-9603301. The screw member thereof protrudes from a housing, in which housing said screw member is slidably guided by means of a pair of supports. In most applications, said known actuator behaves satisfactorily for providing a rectilinear movement. However, its proper behaviour can only be guaranteed in case said movement and also the loadings are strictly in line with the axis of the screw member. For applications in which the screw member is loaded transversely, and/or is displaced transversely due to external influences exerted by an external actuatable component, the actuator will be blocked and eventually destroyed.
SUMMARY OF THE INVENTION
The object of the invention is to provide an actuator of this kind which provides a better support of the nut, and thereby of the screw member, in relation to the transverse loadings and/or displacements. This object is achieved by one pair of contact points having a working line the contact angle of which with respect to the axis of the bearing is smaller than the corresponding contact angle of the other working line.
In the actuator according to the invention, the nut is supported particularly well with respect to axial loadings in one direction, i.e. in the direction of forces which exert a load on the pair of contact points having a working line with a smaller contact angle with respect to the axis. In the other direction, a limited loading is also possible. The stability of the bearing with respect to bending moments is maintained to a large degree, and also with respect to combinations of such moments with respect to axial and radial loadings.
The outer ring or the inner ring of the angular contact ball bearing is a split outer ring respectively a split inner ring comprising two axial halves, which are pressed against one another under axial forces for providing the desired bearing clearance (positive or negative).
Furthermore, the axial ring halves may have facing radial abutment faces.
The axial ring halves may be connected to each other, and may be preloaded in axial direction, by means of a clamping means.
According to a first possibility, the nut is rotatably supported and driveably connected to the electric motor, and the screw mechanism may comprise a hollow screw having a central bore opening out at one end of the screw and accommodating an actuating member, which actuating member protrudes from the open end and is connected to the screw at a distance from said open end.
The actuating member of the actuator according to this embodiment may be connected to an external component, which means that any transverse forces exerted on and/or displacements of such external component will have no direct influence on the screw member. Thus, said screw member will be exposed mainly to axial loadings, which safeguards its proper functioning.
Preferably, the actuating member is accommodated with a radial play within the hollow screw. This radial play may be tuned with respect to the expected transverse displacements.
The actuator can be connected to the hollow screw in several ways. For instance, the end of the actuator could be connected to the internal end wall of a bottom which closes the internal hollow space of the screw. In particular, the actuating member can be connected to the screw by means of a sleeve which fits between said member and screw, which sleeve is at a distance from the open end and which is shorter than said member and the bore.
According to a second possibility, the screw may be rotatably supported and driveably connected to the electric motor, and the nut is connected to a brake pad support.
In particular, the screw may be connected to a concentric mounting sleeve, which mounting sleeve at least partly surrounds the screw and which is connected to the inner ring of the angular contact ball bearing, the nut being accommodated at least partly between mounting sleeve and screw.
The screw mechanism may comprise a roller spindle or a ball spindle. A particular favourable embodiment, which requires little space, is obtained in case the nut of the spindle forms an integral part of the inner bearing ring of an axial thrust bearing.
The angular contact ball being may be either a single row four-point contact ball bearing, or a double row angular contact ball bearing.
The actuator according to the invention can be applied in various fields. In particular however, said actuator is fit for a brake calliper, comprising a claw piece with two opposite brake pads and an electric actuator according to any of the preceding claims, said actuator comprising an electric motor and a screw mechanism which is driveably connected to the electric motor for providing a linear movement in response to a rotational movement of the electric motor, said screw mechanism comprising a screw and a nut which is supported rotatably with respect to the housing by means of full complement four-point contact ball bearing, said four-point contact ball bearing comprising two pairs of contact points the working lines of which intersect each other. Such brake calliper is also known from WO-A-9603301.
In a brake calliper, the actuator is mainly loaded in one and the same direction, i.e. in the direction of pressing the brake pads onto the brake disc. According to the invention, advantageous use is made of the actuator described before, in that one pair contact points has a working line the angle of which with respect to the axis of the bearing is smaller than the corresponding angle of the other working line.
In particular, the pair of contact points with a working line having an angle with respect to the axis of the bearing less than the corresponding angle of the other working line, is loaded by the brake force exerted on the brake pads.
Preferably, the outer ring of the four-point contact ball bearing comprises two axial halves, which are pressed against one another under axial forces for providing the desired bearing clearance.
The working line of the pair of contact points which is loaded by the brake force exerted on the brake pads, may have a contact angle with respect to the axis of the bearing less than 45°.
In a preferred embodiment, the screw mechanism may comprise a hollow screw having a central bore opening out at one end of the screw and accommodating an actuating member, which actuating member protrudes from the open end and is connected to the screw within the bore at a distance from said open end, wherein the actuating member cooperates with one of the brake pads and the screw mechanism cooperates with the opposite brake pad.
As is usual in disc brakes, the pads thereof have some transverse play within the claw piece, which play manifests itself as soon as said pads are pressed onto the rotating disc to be braked. The actuating member of the actuator according to this embodiment is perfectly fit for taking such play, thus preventing the screw mechanism from getting blocked.
The stator of the electric motor may be connected to the claw piece, and the rotatable part of said motor may be connected to the screw mechanism. Furthermore, the electric motor can be accommodated on a support piece which is rotatably supported in the claw piece, and which is in cooperation with the nut of a roller spindle or a ball spindle.
Preferably, the screw mechanism of the brake calliper is a roller spindle or a ball spindle; the nut of the spindle may form an integral part of the inner bearing ring of an axial thrust bearing.
De Vries Alexander Jan Carel
Druet Clair
Haas Roland
Kapaan Hendrikus Jan
Olschewski Armin Herbert Emil August
Butler Douglas C.
Oliff & Berridg,e PLC
SKF Engineerings and Research Centre B.V.
Torres Melanie
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