Machine element or mechanism – Gearing – Directly cooperating gears
Patent
1985-01-15
1986-10-07
Staab, Lawrence J.
Machine element or mechanism
Gearing
Directly cooperating gears
74425, 74410, 74421A, 74665A, 74665F, 744245, 310 83, F16H 116, F16H 120, F16H 3706, F16H 5700
Patent
active
046152300
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a gear transmission having a particularly high efficiency, said transmission being suitable, inter alia, for constituting a speed reducer suitable for driving automobile vehicle accessories, for example.
There has already been proposed, in French Pat. No. 2 372 998, a gear transmission comprising a driving shaft and a driven shaft, with different angular speeds, the two shafts having axes fixed relative to one another, one of the shafts carrying two worms having algebraically different pitches and being connected to the other shaft by two different gear kinematic channels each comprising one of the aforementioned two worms; at least one of the two kinematic channels comprises at least one intermediate worm-wheel having an axis which is fixed, neglecting tolerances, relative to the axes of the two shafts of the transmission. In a preferred embodiment of this gear transmission, it is proposed that the driving shaft of the transmission carry two worms with opposite directions, each of the two kinematic channels comprising a helical tooth intermediate worm-wheel meshing with one of the two worms, the two intermediate worm-wheels having their axes on opposite sides of the shaft carrying the two worms and each being fast with a coaxial intermediate gear-wheel, these two intermediate gear-wheels meshing with a common output gear-wheel fast with the driven shaft; the axes of the driving and driven shafts are perpendicular and axes of the intermediate worm-wheels are parallel to the axis of the driven shaft.
A device of this kind gives total satisfaction, in particular when it is used as a speed reducer for driving windshield wipers of an automobile vehicle by means of an electric motor. The two kinematic channels of a transmission in accordance with the hereinabove defined embodiment transmit in equal proportions the power fed into the driven shaft; each worm on the driven shaft is subjected to reaction forces and, if the pitches of the worms are equal and opposite, these reactions are symmetrical relative to the central point of the double worm: in a plane passing through the axis of the double worm and perpendicular to the axes of the two intermediate worm-wheels, the reaction components are equal, opposite and colinear and consequently cancel one another out; on the other hand, in a plane perpendicular to the preceding plane of projection and passing through the axis of the double worm, or perpendicular to this axis, the components of the reactions on the two worms do not cancel out and there results a bending moment in the worm and thus reaction forces in the bearings supporting the shaft carrying the double worm. The existence of this reaction force of the shaft on the bearings which carry it explains why the efficiency of a transmission of this kind is approximately 70%, which could be regarded as highly satisfactory as compared with prior art transmissions. Moreover, the magnitude of the reactions on the driving shaft bearings is directly proportional to the inclination of the helical threads of the double worm; thus in practice it has been necessary to limit the inclination of the threads of the double worm to a value in the vicinity of 15.degree.; it is known, however, that the efficiency of transmission between a worm and a tangential gear-wheel is optimum for values of the thread inclination two to three times higher. This practical limitation on the inclination of the worm threads thus also constitutes a limitation on the efficiency of a transmission of this kind.
The objective of the present invention is to define a gear transmission of the type mentioned hereinabove, said transmission having significantly improved efficiency. This improvement in efficiency is achieved by reducing or completely eliminating the torque produced by the reaction forces exerted on the two worms of the transmission, whence there results a considerable reduction or even elimination of the reaction forces exerted by the shaft carrying the worms on its bearings. For the same power transmission ca
REFERENCES:
patent: 1551474 (1925-08-01), Fasset
patent: 4287767 (1981-08-01), Guichard
patent: 4369387 (1983-01-01), Haar et al.
patent: 4444071 (1984-04-01), Guichard
Bednarek Michael D.
Staab Lawrence J.
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