Friction gear transmission systems or components – Friction gear includes idler engaging facing concave surfaces – Toroidal
Patent
1998-05-19
2000-05-23
Bucci, David A.
Friction gear transmission systems or components
Friction gear includes idler engaging facing concave surfaces
Toroidal
476 42, 74388PS, B62D 500, F16H 1538
Patent
active
060660678
DESCRIPTION:
BRIEF SUMMARY
This invention relates to position servo systems, in which the detection of an error between the desired relative positions of actuating (i.e. driving) and driven members causes power to be applied to tend to reduce that error. The invention applies particularly but not exclusively to power-assisted steering systems, of the known general kind in which a steering mechanism--for instance of rack or worm type--is driven by a gear or pinion, typically carried at one end of a shaft, the other end of which tarries a steering wheel or other control member. Means are provided to sense torsional deflection in the shaft. When that deflection exceeds a predetermined value, indicating that a substantial steering effort is being applied, an auxiliary source of power is activated and applied to the worm or gear to augment the steering wheel torque, and so reduce the deflection in the shaft.
BACKGROUND OF THE INVENTION
It has been proposed in Japanese Patent Publication 63291770A to incorporate a continuously-variable-ratio transmission ("CVT") of the "variable-ratio-epicyclic" type in a power-assisted steering system. The customary components of such a CVT are an epicyclic gear set and a speed-varying component or "variator", the latter comprising an input member, and intermediate reaction member and an output member. By the "variable-ratio-epicyclic" type of CVT we mean the type in which the axes of rotation of all three of the elements of the variator are concentric, so that the total configuration of the variator bears some resemblance to a conventional geared epicyclic or planetary gear set. The present invention is to be distinguished from the embodiment of JP-A-63291770 principally in that in the system described in that prior publication, the CVT does not generate and transmit any power to assist the steering effort provided by the operator. Instead, the function of the CVT appears to be to vary the manual steering ratio, between the steering wheel and the steering rack to which it is connected, so that quite separate means to generate power assistance receive relatively strong signals at low vehicle speeds and weak ones at high speeds.
The present invention is also of course to be distinguished from the many prior automotive CVT's of concentric arrangement (of which U.S. Pat. No. 4,922,788 shows an example), by the fact that in those CVT's the sole source of motive input has been the prime mover of the automobile. In the position servo systems to which the present invention relates there must be two separate sources of such inputs. For example, in a power steering system a first and manual input is applied via the steering wheel and the CVT must be driven by a second source of motive power in order to contribute the power-assistance that is required.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described by way of example with reference to the accompanying figures of simplified and partly-schematic drawings in which:
FIG. 1 is a schematic view of a power assisted steering system;
FIG. 2 includes a sectional view taken in a plane including the shaft 3;
FIG. 3 illustrates linkages and movements associated with one of the rollers of the variator, and
FIG. 4 shows an alternative to the arrangement shown in FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows that the output of a constant speed electric motor 10 is connected both to the "input" member 7 of a variator of the variable-ratio epicyclic type and also (at 11) to one component of a typical three-part epicyclic gear set 6. The other two components of the gear set 6 are connected to the "output" member 9 of the variator and to a torque-limiting device 21 respectively. The third and intermediate member 8 of the variator produces an output 13 which constitutes one input to a pinion 2 driving a steering rack 4, the other input being from a steering wheel 1 by way of a shaft 3. The parts which make up the CVT are shown within the broken line 5 and comprise the gear set 6 and variator (7, 8 and 9), and those parts are mounted to ro
REFERENCES:
patent: 4751976 (1988-06-01), Higuchi et al.
patent: 4922788 (1990-05-01), Greenwood
Japanese Abstract, vol. 013, No. 89, dated Mar. 1989, JP-A-6321770.
Bucci David A.
Joyce William C
Torotrak Limited
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