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Reduction gearbox concept

IP.com Disclosure Number: IPCOM000244460D
Publication Date: 2015-Dec-14

Publishing Venue

The IP.com Prior Art Database


Reduction gearbox concept

This text was extracted from a Microsoft PowerPoint presentation.
This is the abbreviated version, containing approximately 54% of the total text.

Slide 1 of 20

Reduction gearbox concept

The intermediate reduction between the motor and the clutch in the present technology is approximately 13:1.

A standard gear train reduction is bulky and noisy if straight cut spur gears are used.

An epicyclic gearbox is more compact and quieter, but can only step down to about 12:1.

It has been stated that a faster motor would be a more efficient solution, but would require a greater reduction ratio gearbox.

Slide 2 of 20

103 teeth

100 teeth

90 teeth

87 teeth

Fixed outer ring teeth (gearbox casing)

This example results in reduction ratio of -15.263:1

Ring gear rotates on a bearing around the eccentric

Input shaft

Output gear

Eccentric on input shaft, which drives the ring gear in a circular motion around the inside of the outer ring teeth

Output shaft

Slide 3 of 20

Kinematic representation

The following 13 slides, when clicked through in quick succession, show the precession effect of the gear train driving the output gear

The dots represent a fixed point on each element, e.g. a gear tooth.

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Apart from the input and output shafts, there is only one internal moving part (excluding bearings), which is the gear ring

The tooth size can be large as the gears themselves are large

Very high reduction ratios can be achieved within the same envelope by adjusting the number of teeth (e.g. 50:1)

The teeth can be helical cut for improved wear and quietness

The thrust from the helical teeth is easily countered

The offset thrust from each gear can be balanced by the opposing thrust

Compact arrangement

Coupled with a smaller/faster motor will improve weight and occupied volume

Slide 17 of 20

Note that some of the bearings are high speed (e.g. on input shaft), and some are low speed (e.g. relative rotation between input and output shafts)

Thrust due to helical teeth (red on green)

Mass balance to counter eccentricity

Mitigated by thrust due to opposite cut helical teeth (blue on orange)

Slide 18 of 20

The outer gear (with internal teeth A) is earthed to the gearbox casing.

The input shaft does not directly drive a gear, but instead has an eccentric whose centre is offset from the input shaft centreline by a specific value (to be explained below).

A ring gear with external teeth B and internal teeth C is mounted on the eccentric via a bearing. The external teeth B engage with the internal teeth A of the outer gear.

The difference in the number of teeth (A to B) is reflected in the pitch diameter of each tooth set. The offset value of the eccentric is half the pitch diameter difference.

As the input shaft rotates, it drives the eccentric around, which drives the ring gear B around the inside of the outer gear A. This causes the ring gear to precess around its own axis in the opposite direction to the input shaft, and at a much slower r...