Machine element or mechanism – Gearing – Directly cooperating gears
Patent
1996-10-08
1998-12-15
Lorence, Richard M.
Machine element or mechanism
Gearing
Directly cooperating gears
74 8915, 192 34, 192 6991, 254102, B60S 908, F16H 2520
Patent
active
058485546
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention pertains to a multistep spindle drive for converting a rotary movement into a linear movement with different speeds of withdrawal and extension, including at least two threaded spindles with different pitches which telescopically mesh with one another and are in threaded connection with one another, wherein one spindle is connected to a drive element and another spindle is connected to an output element via a nut and wherein the threaded spindles and the speeds of withdrawal and extension can be changed over by frictional force.
BACKGROUND OF THE INVENTION
Such a spindle drive has been known from EP-A-0 552 129. The purpose of this arrangement is to perform the height adjustment of the support wheel more rapidly, when this wheel is not loaded, than in the loaded state. The spindle drive comprises two threaded spindles, which mesh with each other, are in a threaded connection with one another, and have different pitches and diameters. The smaller inner spindle with the lower pitch is rotated by means of a crank, and is screwed into the larger outer or hollow spindle. A nut, to which a support wheel is fastened via a pipe, is seated on the hollow spindle having the higher pitch. Due to the different pitches, the spindle drive has a fast motion and a load motion, which are changed over depending on the load by different frictional forces in the threads. During fast motion and load-free spindle drive, the inner spindle is said to carry the hollow spindle due to the higher friction and rotate it in relation to the nut. As soon as a supported load appears and the better transmitted, slower load motion is needed, the friction between the hollow spindle and the nut is said to become higher due to the load than the friction between the inner spindle and the hollow spindle, so that the inner spindle rotates in relation to the stationary hollow spindle during load motion. The differences in friction in the spindles which are needed for the fast motion are said to be achieved by the differences in pitch and diameter alone, which cannot always be achieved reliably and maintained for the long term in practice. It is also problematic that the thread between the hollow spindle and the nut is intentionally designed without self-locking. The consequence of this is, on the one hand, that the spindle drive may automatically withdraw under load in an undesired manner, and the position of the crank must therefore be compulsorily secured. However, the operator may forget about this. On the other hand, the spindle drive operates only when the supported load acts eccentrically from the spindle axis and it exerts an overturning movement reinforcing the frictional force on the hollow spindle
ut pair.
Another spindle drive with fast motion and load motion for actuating a support wheel for vehicle trailers has been known from DE-A 38 29 131. It likewise has an inner spindle and an outer spindle with different pitches and diameters, which are guided concentrically one inside the other, but are not screwed to one another. The housing of this support wheel comprises two parts, which are connected to one another via a thread and form the outer or hollow spindle. The lower part is flanged stationarily to the vehicle trailer. The upper part is adjustable in height by means of this thread and guides the inner spindle, which is connected to the support wheel via a nut and a pipe section. A pretensioned friction clutch, by means of which the upper part of the outer spindle can be carried during the rotation of the crank, is located on the crankshaft. The carrying takes place in fast motion, with both spindles rotating and their strokes adding up. During load motion, the moment of friction is greater in the parts of the outer spindle than in the friction clutch, so that only the inner spindle rotates.
SUMMARY AND OBJECTS OF THE INVENTION
The basic object of the present invention is to provide a multistep spindle drive, which makes possible easy handling and is able to function for a long time
REFERENCES:
patent: 1974687 (1934-09-01), Morrison
patent: 3157258 (1964-11-01), Cronholm
patent: 3986409 (1976-10-01), Tripp et al.
patent: 4609179 (1986-09-01), Chern et al.
patent: 5002172 (1991-03-01), Stringer
patent: 5201084 (1993-04-01), Johnson
patent: 5337627 (1994-08-01), Nakamura
Kober Kurt
Rampp Armin
Al-Ko Kober AG
Fenstermacher David
Lorence Richard M.
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