Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
2001-06-11
2003-08-05
Fenstermacher, David (Department: 3682)
Machine element or mechanism
Gearing
Directly cooperating gears
C074S413000
Reexamination Certificate
active
06601467
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a multistage spur-type gearing for small and miniature electric motors, comprising a gearing housing including an input shaft opening through which a motor shaft can be inserted into the interior of the housing for operating the spur-type gearing with the small or miniature electric motor, at least two gear shafts that are held in the gearing housing and extend in parallel with a center axis of the gearing, and spur gears of different diameters which are arranged on the gear shafts, at least one of the gear shafts being fixedly held as a gear axle in the gearing housing, and at least two spur gears being fixedly connected to one another and combined to form at least one dual gear set which is rotatably supported on a gear shaft or axle.
BACKGROUND OF THE INVENTION
Small and miniature electric motors are electric motors, most of the time d.c. motors, with small to very small dimensions, normally a diameter below 50 mm and a length below 150 mm, and a high motor output per weight. Small and miniature electric motors often rotate at a very fast speed and are normally used at speeds around 10,000 r.p.m. and more. To reduce the high speeds of said motors, use is made of spur-type gearings of a corresponding size which most of the time are directly flanged onto the motor housing. The transmission or gear ratios of the gearings or transmissions, which are respectively adapted to a specific motor, are often preset by the works for the customer. Motor and gearing can be ordered together and are also supplied jointly, being already pre-assembled as a unit. That is why the conventional spur-type gearings are most of the time provided with a cylindrical housing whose outer diameter corresponds to that of the associated motor. The front sides of the gearing are formed by flanges with which the gearing can be fastened to the motor or to another device.
In conventional spur-type gearings, the gear shafts are rotatably supported in the front flanges of the gearing housing. Each gear shaft has fixedly mounted thereon a spur gear which is in meshing engagement with a spur gear of a different diameter that is arranged on another gear shaft. In the conventional spur-type gearings, each of the spur gears is thus integrally rotating with the associated shaft. In conventional multistage spur-type gearings two spur gears of different diameters, a toothed gear and a pinion gear are thus arranged on a gear shaft at the most. The distance of the gear shafts of one reduction stage is defined by the gear ratio of the respective reduction stage.
In practice, the typical high speeds of small and miniature electric motors require a high reduction, i.e. a high ratio of input speed to output speed of the gearing. Such reduction ratios cannot be realized in a single gear stage on account of the predetermined small constructional dimensions. Therefore, in conventional spur-type gearings, the total gear ratio is distributed over several gear or transmission stages, so that at least two gear shafts are provided for.
A considerable drawback of the conventional structure of spur-type gearings is that the available space cannot be used in an optimum manner per reduction stage. Every additional reduction stage requires the installation of an additional gear shaft, which is bound to enlarge the gearing.
A further drawback of the gearings or transmissions normally used for small and miniature electric motors is the relatively large space required by said gearing at high reduction ratios, which is due to the fact that each gear shaft only carries one pair of toothed gears fixedly connected to said gear shaft. Therefore, a separate shaft has to be provided for each pair of toothed gears, which in the end leads to a relatively large number of parts in said conventional spur-type gearings. This creates relatively high costs during production and assembly.
To avoid said problems, the prior art discloses spur-type gearings in which at least two spur gears are rigidly connected to one another and combined to form at least one dual gear set. The dual gear set is rotatably supported on a gear shaft or axle. Since the dual gear set is supported in a rotatable manner, the gear axle or shaft can accommodate more than one transmission stage. As a result, a separate gear shaft need no longer be provided for every reduction stage.
For instance, DE 43 42 185 A1 describes a gearing having a number of meshing dual gear sets. A respective dual gear set is seated on a gear axle integrally formed by the gearing housing. However, the gearing according to DE 43 42 185 A1 has the drawback that the offset between motor and output shaft of the gearing is relatively large.
This problem is solved in the transmission of EP 371 690 A1 which is of a smaller constructional size than the transmission of DE 43 42 185 A1. However, this transmission is still relatively large, occupying more space than the motor itself. Because of their constructional size, the transmissions of EP 371 690 A2 and DE 43 42 185 A1 are not suited for today's small and miniature electric motors which should combine a minimum volume with maximum performance.
This drawback has been eliminated in the transmission of FR 1,448,923. In a cut transverse to the motor shaft, the transmission described therein has about the same cross-sectional area as the electric motor. Since the motor shaft in the transmission of FR 1,448,923 itself forms a transmission shaft with spur gears, it is very troublesome to separate the motor from the transmission shown therein. Use of such a transmission on an industrial scale (where many different transmissions with different reduction stages are mounted on the motor in accordance with the customers' desires just before delivery) is thereby made unprofitable. Furthermore, the transmission of U.S. Pat. No. 1,521,882 can also not be detached from the motor.
By contrast, U.S. Pat No. 2,831,364 shows a mechanical transmission which in the illustrated embodiment would not be useful because of the usual sizes of small and miniature electric motors and the high speeds thereof.
Finally, U.S. Pat. No. 2,908,180 forms the generic prior art for the subject matter of claim 1. This document shows a spur-type gearing which is screwed onto an induction motor. This gear mechanism has the drawback of a relatively large constructional volume in the radial direction. In this instance, too, the gear mechanism is larger than the associated electric motor.
It has been found in the case of all of the above-mentioned transmissions that there is a high wear at the high speeds as are arising during operation of today's small and miniature electric motors together with the power density achieved today.
SUMMARY OF THE INVENTION
It is there fore the object of the present invention to improve the above spur-type gearings by simple constructional measures in such a manner that even at high speeds they are hardly subject to any wear and can have the same constructional size as the corresponding electric motors.
According to the invention this object is achieved for a multistage spur-type gearing of the above-mentioned type in that the gear shaft or axle is made from a hard material and that the input shaft opening is arranged to be essentially coaxial to the center axis of the gearing housing.
Gear shafts which are stationary relative to the gearing housing and do not transmit any torques are designated as gear axles. Dual gear set primarily means the connection of two spur gears at the front sides thereof and at a distance that is as small as possible.
This solution is simple and permits the construction of small gearings or transmissions even at extremely high reductions and at high input speeds.
According to the invention the problem of premature wear is solved in that at least one gear axle is made from a hard material; hard materials within the meaning of the technical teaching of this invention permit the substantially dry support of the typically rapidly rotating spur gears on the gear shaft or axle without a
Fenstermacher David
Marshall Gerstein & Borun
Maxon Motor GmbH
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