Motor vehicles – Including one or more ski-like or runner members – With at least one surface-engaging propulsion element
Patent
1993-10-12
1996-01-09
Hurley, Kevin T.
Motor vehicles
Including one or more ski-like or runner members
With at least one surface-engaging propulsion element
91380, B62D 508
Patent
active
054821312
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a hydraulic assistance device, which can especially be used as power-assisted steering for a motor vehicle, and suitable for converting an input rotational movement into an output rotational movement, this device comprising at least: main axis; translationally fixed along this direction, and rotationally driven about this main axis by the input rotational movement; substantially perpendicular to that of the latter; rotation of the input shaft so as to give rise to a pressure difference between first and second chambers, defined in the said cylinder; partially under the effect of the said pressure difference, this piston being substantially coaxial with the input shaft, at least partially surrounding the latter, and having, on the one hand, a sealing section separating the two chambers in a sealed fashion and, on the other hand, a transmission section endowed with a rack meshing with a toothed sector rotationally linked to the output shaft, and; to convert a rotational movement of the first into a translational movement of the second.
A device of this type is well known in the prior art and is described for example in U.S. Pat. No. 4,128,046.
Despite its overall very satisfactory operation, such a device has a relatively high weight and bulk.
Moreover, it requires adjustment of the meshing clearance of the toothed sector with the rack, which increases the complexity of manufacture and the cost thereof.
In this context, the object of the present invention is to provide a device of the aforementioned type having functional performance features which are greater than those of the known device, and especially a reduced size and weight for the same power assistance.
This object is achieved, according to the invention, by virtue of a device essentially characterized in that the transmission section of the piston has, seen in the direction of the said main axis, a profile with two branches in the shape of a U whose branches both form racks and mesh, at respective geometric sites, which are substantially coplanar with one another and with the said main axis, with respective toothed sectors which are integral with one another and with the output shaft.
Thus, in contrast with the device known and described in the aforementioned patent, the device of the invention makes it possible to avoid the reaction of the output torque on the transmission section of the piston causing the appearance on the latter, in addition to an axial force, of a parasitic torque which, due to the eccentric meshing of the toothed sector on the rack, tends to cause the piston to rotate about an axis perpendicular to its translational direction and gives rise to frictional forces which reduce the overall efficiency of the device.
According to another aspect of the invention, the movement converter preferably comprises, on the one hand, an essentially cylindrical sleeve, housed with clearance inside the U-shaped profile formed by the piston, and having, on its internal surface, a helical track for balls, and, on the other hand, means for fixing the sleeve to the piston, suitable for preventing practically any relative rotation of the piston and of the sleeve about the said main axis, and any relative translation other than relative translations along directions perpendicular to the said main axis.
Such an arrangement renders a certain offset of the piston possible, and especially of its transmission section, with respect to the input shaft, and therefore makes it possible to absorb the manufacturing tolerances of the various components without causing the appearance of strains or necessitating adjustments.
For example, the fastening means comprise: the sleeve; two studs are respectively inserted and can slide along their common direction without freedom of rotation about the said main axis; angular reference frame centered on this ring, with respect to each housing partially formed by this ring; and ring being intended to be received in one of these grooves and being housed therein so as to slide along its radial
REFERENCES:
patent: 3180233 (1965-04-01), Jablonsky
patent: 3832933 (1974-09-01), Jablonsky
patent: 4417501 (1983-11-01), Elser
Bacardit Juan S.
Cortes Guasch Esteve
Bendix Espana S.A.
Hurley Kevin T.
McCormick Jr. Leo H.
Palguta Larry J.
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