1509

Item 1509

DESIGN: UniCopter - Power Train - Alternative Idea - Ball-Worm & Gear Reducer

Overview:

A combining of the worm & gear drive train proposed for the Flettner Fl 339 and the current development of ball worm drives:

FORGET ~ There are approximately a dozen patents for ball worm and gear reduction, however, I have only been able to find one product that utilizes it. It appears, to me at least, that there exists a problem with ball scuffing and speed limitation. Consider a 3-gear hypoid or 6-gear spiral bevel gearbox instead. ~ June 9, 2006.

Objective:

A power transmission unit that is much simpler than existing conventional ones are.

A power transmission unit for laterally disposed twin main-rotor configurations, and specifically for the Intermeshing configuration.

The primary feature of this device is the use of a single 3-gear unit to provide the large reduction between high-speed turbine engines or future high-speed electric motors, and the much lower speed rotors.

In addition, this single gear-set can accommodate the three different axis angles of the two rotors and the engine.

Drive train for the Proposed Intermeshing Flettner Fl 339:

Drawing:

Sketch of a conventional worm & gear reducer; except that it includes balls between the 'gear's teeth'.

Input shaft from motor.

Single output shaft.

Balls located in spiral worm track.

Dammed if I know. Probably a ball retainer.

Proposed arrangement for Intermeshing Configuration.

Description:

Low friction: The worm gear and gear can provide large speed reductions with the use of only two gears. However, the teeth of the worm and the gear slide against each other and this will result in level of friction far above what is acceptable for a rotorcraft. The inclusion of balls between the 'teeth' of the two gears will significantly reduce this friction because it changes the friction from sliding to rolling. See Related Patents below.

Only 3 gears: The worm gear and gear arraignment should allow for one worm to drive two gears. In addition, the axes of the two gears do not have to be parallel. This allows for the use of rotor masts, which are at an angle to each other. Two examples of this are the Intermeshing and the Interleaving configurations.

Autorotation: Conventional worm & gear reducers (w/ sliding friction) can back drive (from gear to worm) at ratios below 10:1. This transmission has 'ball bearings' (w/ rolling friction) therefore it will be able to back-drive at much higher ratios. This means that the gears can drive the worm and thereby assure that the rotors will turn in a synchronized manner during autorotation.

Related Patents:

Patent. No.	Title
7,051,610	Ball worm transmission	Have hard copy.
5,816,103	Ball worm and worm gear device	Have hard copy.
5,655,410	Worm type reduction gear mechanism
5,373,753	Power transmission device	Have hard copy.
5,090,266	Ball circulation path in rotation transmitter using balls	Have hard copy.
4,782,716	Roller bearing gear system
4,023,433	Power transfer	Have hard copy.
4,006,646	Anti-friction worm and wheel drive
3,672,239	WORM GEAR DRIVE
3,581,592	WORM GEAR
3489026	WORM GEAR MECHANISM
	There are many more

Other Related Patents:

	Patent. No.	Title
	6,148,683	A worm/worm gear transmission, particularly for use in a helicopter

Concerns:

Re the above patents: Conventional radial and axial ball bearings have a force that is transferred from the centerline of one race's groove through the balls to the centerline of the other race's groove. These patents are transferring the force from the edge of one race's groove through the balls to the edge of the other race's groove. IMO, this is something like applying an axial load to a radial bearing. REVIEW THIS CONCERN

It seems that the path of the balls in the worm is not in alignment with the path in the gear. This will cause the balls to want to depart from one or both paths and the forced return will result in sliding friction and wear on the balls and raceway; particularly since the balls have a point contact.

Related to the above, it looks like the speed of the balls (rotation and linear velocity) will vary. Assuming that more than one ball in a track is carrying the load, this may result in sliding friction and wear on the balls and raceway also.

Can the mechanism be designed for the use of rollers (perhaps tapered or barrel) instead of balls?

Can the device operate at the high input RPMs of turbine engines and electric motors?

Will the device be reliable, considering that the balls and ball track are critical parts of the operation. This is particularly important since this device;

Must be on the rotor side of any overrunning clutch.
Is responsible for maintaining the rotational positioning between the two intermeshing rotors.

Note that reliability will not be such a great concern for UAV craft.

Note that the simplicity and low weight of the transmission allows for it to be designed with a significantly higher safety factor than existing transmissions.

Caged ball bearings are better for high speeds then are full compliment bearings;

Possible Improvements:

Unconsidered idea for improving the assurance that the rotational position of the two intermeshing rotors will be maintained.

Consider a secondary much smaller (non-ball) worm and gear located above or below the primary ball worm and gears. The secondary unit will have a ratio significantly smaller than the primary, say 10:1. In fact, the ration would be approximately 5:1, which allows its gears to back drive the worm. The two worms would be interconnected by a 10:1 ratio spur gear set. Should their be a loss of power, the secondary unit will maintain synchronization during autorotation, while at the same time the worm of the secondary unit will drive the primary worm so that it also maintains synchronized autorotation.

Modification.

It may not be necessary that the worm axis be normal to the gear axis. I.e. the motor and propeller might be able to have an incline without requiring a CVJ or double universal.

Increased load handling by the worm & gear bearings.

It may be possible to use Radial Crossed Roller Bearing method between the worm and the gears.

Or perhaps basic roller bearings, since the overrunning clutches assure that the torque can only flow in one direction; from engine to rotors.

Micro balls:

Could a slurry of micro-ball be used in a conventional worm & gear gearbox where there is clearances between the gear teeth.

Ball return track in gear:

Could the ball recirculate within the gears?

Hypoid ~ alternative:

GAM Dyna Series with Hypoid Gearing http://www.gamweb.com/dyna_series.asp

Note that the hypoid 10:1 shows a > 96% efficiency. http://www.gamweb.com/view_doc.asp?file=dyna_series.pdf

Consider hypoid between motor and one mast and then spur gears between masts. Can a hypoid be back-drive for autorotation?

From looking at the GAM Dyna series it looks like the hypoid input shaft is offset from the output shaft by approximately 15% of the gearbox's width. This should mean that a gearbox can be built where one hypoid gear can drive two crown gears. One crown gear would be above the hypoid gear and the other crown gear would be below it, plus the axe of the two would have a 25º angle or less between them.

The friction would be double the conventional 6- gear unit, however, the gearbox would be smaller and lighter. Would the decrease in weight offset the loss in output horsepower?

Miscellaneous Stuff:

Search phrases;

"ball worm gear" ~ 8 hits on Goggle
"ball worm" AND wheel ~ 102 hits on Google

"An especially suitable configuration of a recirculating-ball worm gear is available for example from the company Amsler & Co AG in CH-8245 Feuerthalen with the type designation "Star" and the name `Kugelgewindetrieb` (ball screw). With this model an especially compact, precise converter configuration with high efficiency can be attained."

There is the option to locate a second electric motor on a second shaft, which is on the other side of the worm gear from the existing shaft.

Consider the possibility of combining this idea with the Variable Speed Rotors and Prop idea.

For additional Information see:

Raw Information Pulled from the Internet

This article appears to be related to patent 7,051,610

Less Wriggle Room

Calling his invention a ball worm, a mechanical engineering professor at Baltimore's Johns Hopkins University has coupled a low-friction ball screw to a speed-reducing worm gear. The result is a precision, high-ratio gearbox so low in friction that in many cases it can be back-driven-an impossible feat for everyday worm drives.

The impetus for the project came from needle-sticking robots that accompany patients in CT scanners. Such robots can deliver precisely guided shots into the heart of a tumor by working from the coordinates of a reconstructed 3-D scan. Needle-sticking robots can deliver drugs with precision that is unmatched by human touch. They also spare doctors radiation exposure.

Balls serve the same function in this worm that they do in screws: negate friction and slop. Modern tools make it possible to build an old concept.

The professor, Dan Stoianovici, and co-inventor Louis Ka- voussi needed the precision of linear ball screws for rotary motion in the needle-handling robot arms. Each arm uses two ball worms, Stoianovici said. He expects other applications to surface for the new device.

A computer numerical control machine, for example, typically uses linear ball screws for three axes while relying on an ordinary worm gear to drive a fourth-axis rotary table. Stoianovici thinks that a ball worm could turn the rotary table with better precision and lower backlash.

Backlash in a worm gear is reduced by adjusting the distance between axes-not by too much, though, or friction rises enormously. Backlash in the new ball worm can be lessened without causing a big jump in friction. The new device also wears better than conventional worm drives, because elements roll rather than slide by each other.

In leafing through patents that date from as far back as the early 1900s, Stoianovici found about 30 that made similar claims to that of his invention. "None had been built and none were commercially available," he said. He attributed this only to the recent catching-up of design and manufacturing technologies that can handle the calculations and machining needed for the device's complicated geometry.

To make the balls rolls correctly, for instance, a manufacturer has to machine a tooth profile that widens as it moves from the center of the gear face to the outer edges. Someone also has to create the thread from two distinct circular profiles, he said.

http://urology.jhu.edu/urobotics/pub/2001-stoianovici-cas.pdf

Initially displayed: May 23, 2006 ~ Posted on PPRuNe; May 24, 2006 ~ Posted on Rotary Wing; June 4, 2006 ~ Latest revision; May 2, 2008

The above utility invention is openly and publicly disclosed on the Internet to negate an entity from patenting it, to the exclusion of all others whom may wish to use them. ~ Reference patent law 35 U.S.C. 102 A person shall be entitled to a patent unless - (a) the invention was known ... by others in this country, ..., before the invention thereof by the applicant for patent.