Brakes – Operators – Electric and mechanical
Reexamination Certificate
2000-04-26
2001-11-20
Schwartz, Christopher P. (Department: 3613)
Brakes
Operators
Electric and mechanical
C188S1960BA, C188S162000, C188S202000, C192S084600
Reexamination Certificate
active
06318516
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a bearing arrangement comprising a central threaded spindle which is arranged in a stationary housing, and an inner ring which, together with rolling elements, concentrically surrounds the threaded spindle, said ring being arranged for rotation in the housing through a thrust rolling bearing that is constituted by a planet drive which comprises a plurality of rolling elements forming planets that are arranged between the inner ring and a bore wall of the housing coaxial to the inner ring.
BACKGROUND OF THE INVENTION
In a bearing arrangement of the pre-cited type known from EP-A-0 249 674, the inner ring and the threaded spindle can rotate in a stationary housing. A rotary drive independent from the rolling elements is not provided for the inner ring and neither can it be accommodated because the spaces of the housing adjacent to the inner ring are occupied by roller carrier rings and are closed.
A bearing arrangement disclosed in EP-OS-0 743 470 uses a planetary transmission for converting the rotary motion of a rotor of a motor into a sliding motion of a spindle that actuates a brake. This planetary transmission permits the transmission of a large force to the brake disc by a small forward movement of the spindle due to the fact that the spindle has a fine thread with a very small thread pitch while the inner ring, which is configured as a spindle nut, has a coarse thread. The rolling elements are configured as roller bodies and are situated in the annular space between the spindle and the spindle nut. They circle round the spindle as planets during the rotation of the spindle nut and mesh with the threads of the spindle and the spindle nut and therefore require two different threads, a fine thread for meshing with the spindle and a coarse thread for meshing with the spindle nut. This arrangement therefore has the drawback of being very complicated and expensive.
The prior art inner ring configured as a spindle nut is surrounded by a pot-shaped brake piston attached to the threaded spindle. During the axial motion of the threaded spindle, the cylindrical wall of the brake piston slides with its inner surface along the inner ring and with its outer surface along the inner wall of the bore of the stationary housing in which these components are arranged. This results in a considerable loss of energy due to friction.
The mounting of the inner ring in the housing is effected with the help of the coupled rotor of the electromotor, said rotor comprising two ball bearings configured as radial bearings and one roller bearing configured as a thrust bearing.
SUMMARY OF THE INVENTION
The object of the invention is to create a bearing arrangement for the actuating device of the vehicle brake which permits a reduction of friction losses and thus improves the overall efficiency.
This object is achieved according to the invention by the fact that, in the bearing arrangement, the threaded spindle is secured against rotation and is arranged for axial displacement toward and away from a brake disc of a vehicle brake, said inner ring is coupled at one end to the rotatable rotor of an electromotor and is additionally retained for rotation with this rotor in the housing through a radial rolling bearing which is constituted by two needle roller bearings whose needle roller bushings bear against the bore wall and are arranged adjacent to ends of an outer ring of the thrust bearing.
The use of two needle roller bearings for the radial mounting of the inner ring has the advantage that the buckling resistance of the inner ring is enhanced. A further advantage of a thrust bearing of this type in which the thrust force is transmitted by a plurality of planets is that the moment of friction of the bearing, especially in the case of very high thrust loads, is substantially smaller than in comparable conventional thrust bearings. The reason for this is that the contact pressure occurring in a conventional thrust bearing is very much higher.
The planets of the thrust bearings can be balls for which the inner ring and the bore wall comprise raceways made as grooves that are circular in peripheral direction and arc-shaped in longitudinal section.
But the planets of the thrust rolling bearing may also be rollers having circular grooves extending in peripheral direction and meshing with corresponding circular grooves of the inner ring and of the outer ring that is fixed on the bore wall of the housing.
The rolling elements that are arranged within the inner ring immediately surrounding the threaded spindle can be rollers having circular grooves extending in peripheral direction and meshing both with a thread of the inner ring and with the thread of the threaded spindle. However, it is also possible to use balls as rolling elements which would then mesh with a spiral ball raceway of the inner ring and with a corresponding raceway of the threaded spindle.
The embodiment of the invention comprising a threaded spindle and grooved planetary rollers for the axial mounting of its drive ring can also be designated as a “spindle-based thrust bearing”.
Tests have shown that the moments of friction in the region of high thrust loads in the spindle-based thrust bearing lie clearly below the values of an angular contact thrust ball bearing. This is due to the fact that the thrust force in a spindle-based thrust bearing is distributed over many points of contact.
This results in smaller pressure ellipses than in angular contact thrust ball bearings. Additionally, due to the osculation between the raceways and the rolling elements in angular contact ball bearings, the magnitude of the pressure ellipses in angular contact ball bearings increases more strongly upon an increase of load than in the spindle-based thrust bearing whose planet flanks may have a crowned configuration.
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Hartmann Jurgen
Lang Johannes
Zernickel Alexander
Bierman, Muserlian and Lucas
Ina Walzlager Schaeffler OHG
Nguyen Xuan Lan
Schwartz Christopher P.
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