Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1989-05-08
1991-05-14
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
74 8914, 74425, 318618, H02K 2400, F16H 116
Patent
active
050158988
DESCRIPTION:
BRIEF SUMMARY
A continuously variable drive according to the definition of the species of claim 1 is known from the DE-OS 24 15 859. With this known drive, a motor drives a cage with radially oriented bevel wheels, via an angular reduction gear. The bevel wheels engage two ring gears. One ring gear is connected to a power takeoff shaft. A servo motor drives the other ring gear via a worm reduction gear. The worm gear is designed so that it is just barely self-locking. When the drive motor has a constant rotational speed, the rotational speed of the power takeoff shaft can be controlled with relatively little effort by varying the rotational speed of the servo motor. However, the power expended by the servo motor depends strongly on the rotational speed, and the rotational speed can be controlled down to stoppage or even to a reversal of the sense of rotation only with a strong stepdown in the angular gear. The maximum rotational speed of the power takeoff shaft is thus much less than the rotational speed of the drive motor.
On the other hand, there are other proposals, with a similar basis, that provide for less reduction between the drive motor and the power takeoff shaft. However, with these proposals the rotational speed of the power takeoff shaft can be varied only over a narrow range about the rated speed.
It is an object of the invention to further develop a drive of the type mentioned in the introduction in such a fashion that the rotational speed of the driveshaft can be varied over a broad range with little power on the part of the element that controls the rotational speed. This object is achieved by the characteristic features of claim 1.
With standard worm gears, the ratio of the worm diameter to the worm wheel diameter is significantly below 0.4, because otherwise efficiency is too poor. However, in the inventive application the choice of a large worm yields significant advantages: (a) The step-down ratio of the worm gear becomes less and thus a broader range of rotational speed for the power takeoff shaft can be achieved while the range of rotational speed of the member controlling the rotational speed remains the same; (b) Surprisingly it has appeared that, with a constant torque of the worm wheel, the torque of the worm with a large worm diameter depends much less on the rotational speed than with a small worm diameter. In this way, a large takeoff power can be regulated with a very small power on the part of the element which controls the rotational speed.
The pitch angle of the thread of the worm gear is chosen so that the worm gear is just barely not self-locking when it is running. The element which controls rotational speed therefore acts mainly as a brake. Here the worm gear is used "upside down" compared to standard worm gears, because the worm gear is seated on the drive side, while the worm is seated on the output side. In this "upside down" arrangement, the worm gear has very poor efficiency, so that the controlled braking power of the element which controls the rotational speed amounts to only a few percent of the drive power of the drive motor.
An embodiment of the invention is explained below by way of the drawing. Here FIG. 1 schematically shows a first embodiment and FIG. 2 a second embodiment.
The drive according to FIG. 1 comprises: a drive motor 1, a differential gear 2 with two input shafts 3, 4 and one output shaft 5, a worm gear 6 with a worm 7 and a worm wheel 8 connected to a shaft 4, and a servo motor 10 controlled by a control 9. The differential gear 2 is a planetary gear and has a sun wheel 15 seated on the shaft 3, a coaxial sprocket wheel 16 connected to the shaft 4, and planetary gears 17 distributed over its circumference, only one of which is shown, and which engage the sun wheel 15 and the sprocket wheel 16. The planetary wheels 17 are rotatably mounted on a planetary support 18. The planetary support 18 is rigidly connected to the shaft 5.
The worm 7 is seated on the output shaft 19 of the servo motor 10. The gear of the worm 7 has a pitch between 5.degree. and about 9.d
REFERENCES:
patent: 4208930 (1980-06-01), Hermann
patent: 4268343 (1981-05-01), Schulze
patent: 4619151 (1986-10-01), Trachman et al.
Hall, "Worm Gears", Schaum's Outline Series, Machine Design (prior to 1980) pp. 249-251.
Kaplan Blum
Rebsch D. L.
Stephan Steven L.
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