GB2301418A

GB2301418A - Planetary Transmission Unit

Info

Publication number: GB2301418A
Application number: GB9605847A
Authority: GB
Inventors: Lothar Strach
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-04-25
Filing date: 1996-03-20
Publication date: 1996-12-04
Anticipated expiration: 2016-03-20
Also published as: DE19601103A1; GB2301418B; GB9605847D0

Abstract

A planetary transmission unit comprises an internal gear guided by means of three eccentric crank shafts 2,3 and meshing with an output spur gear 4 having a smaller number of teeth, wherein the internal and spur gear teeth have straight flanks 5,6. One of the eccentric shafts is a drive shaft 2 and the other two are idler cranks 3.

Description

Toothed gearing with two gears and teeth with flat surfaces.

The present invention relates to mechanical reduction gears and in particular to planetary gears. Mange of uses of reduction gears are torque converting and speed regulation with rotary or rectilinear movement. Intentions at all known reduction gears are the reducing of bulk and weight, to get a minimum of gear elements and production costs and a high efficiency, further the est force and load transmission.

Disadvantages at spur and helical gears are the gear tooth geometry.

The tooth profiles are a pair generation with "higher elements9', working on a line and the load capacity has a limitation with the max. permissible roll pressure, calculated with the empiric formulas from Hertz, PalmgrenjMiner or Stribeck.

It is known that this line is bound to have finite if very small width, so that at all times a finite area is available to transmit the driving force from one tooth to another.

The greater the difference in curvature between two surfaces, the greater will be the distortinal stresses in the material to provide the finite area; thus, two flat surfaces would not need to distort at all, two large cylinders slightly, and two small cylinders would have to distort greatly.

Teeth with flat surfaces would have the maximum degree of conformity of surface and would have the highest efficiency during the transmit of driving force from one tooth to another if the relative speed between the both surfaces would be zero or near z In use are fflearings with involute gear (since ,eonhard Euler 1765) and poccloid gear since de la ire 16?4) with modifications in consecuence of the two-fold generation of crcloids: epicycloid and peric-cloid.

The third tooth profile, named Circular Arc, was original proposed by ltlildhaber, USA in 1926, revived by Novikov, UdSSR in 1955 and is claimed to be particularly suitable for the transmission of very high tooth loads, 2 + 3-fold higher compared with involute gears. This tooth system is without of engaging surface, the backs lash is rising with the module from 0,2 up to 0,4 mm, an optimal flat surface pressure with relative speed near zero is not given.

The cooper-tion of gears (with involute, hypocycloid or Circular Arc - tooth profile) with two spur gears or with one spur and one internal gear result within a tangential convergence of two pitch circles with a following divergence.

Every pitch circle has a degree of freedom 1, only rotating round the rotation axis of a circular disc, called gear.

This is the cause for using the above tooth profiles, because the rotating round the own axis prevent the active use of an additional degree of freedom for to get teeth with flat surfaces.

The Invention A plane blank of me tall with irregular outer surface is provided with three uniform holes. The positions of this holes are on the edges of an acute-angled triangle. The distances of the three holes can be slightly different, the triangle scalene.

In every hole is pivoted an eccentric shaft with exact the same eccentricity and the shafts are pivoted in a support body with exact the same distances on the edges of an acute-angled triangle.

At a rnechanicrl action ith a torcue of one eccentric shaft the plane blank get into small orbits, in the kinematics named circular sliding motion. This system is a Darallel-crank-gear. The both other passiv rotating eccentric shafts are named blind crank. Their rotating follow a positive movement.

In this plane blank is bored a greater hole and the position of this hole can be inside the triangle on every point, also on every point outside of the triangle. This greater hole is provided with an exact quantity of teeth like an internal gear. In the kinematics his internal gear is marked with the sign Z2.

Inside of this internal gear is pivoted in the support body a spur gear with less teeth, marked with the sign Z1. The minimum difference of teeth is one and can be more.

At the rotation of the input eccentric shaft and guided by the both blind cranks the internal gear is following a gyration with the small orbits of the eccentric shafts, not rotating round the geometrically axis of the internal gear.

With this is given a reduction gear with the formula Z1 i = .

Z1-Z2 This reduction gear belong to the group of planetary gear units and is a planetary gear unit with two gears.

At one rotation of the internal gear, guided on ;he eccenters, every tooth comes in contact for a very brief period with every tooth of the spur gear. The peripheral speed is like the eccentric rotation speed with very little eccentricity, less compared to ear rotatings round the own axis. The angular velocity of the output ear is like the angular velocity of the input eccentric shaft divided with the number of reduction.

;ith the moving of he internal gear as a parallel-crank-gear, guided on three eccenters, is exclusive given the possibility for pplications of teeth with flat surfaces.

The reason is a new active degree of freedom, compared with the con- and divergence 0 pitch circles.

The 'itte :iRmeler 0? the circular liding motion slnsists of changing parts for moving radial directed to the output gear and tangential directed to the output gear in steady repeating.

The radial directed motion is the lead-in of an internal gear tooth into a tooth space of the output spur gear.

This locomotion is named in the kinematics " nidged epicycloid ".

The tangential directed motion is he brief neriod of contact and load transmission with a minimum motion parts of radial motion.

The relative speed between the both flat surfaces is zero during every narrow contact between internal gear and output spur gear, moving around the periphery of the output gear. Afterwards the tangential directed motion goes over in the radial negative directed motion and with this in a lead-out of an internal gear tooth off the tooth space of the output spur gear.

At the lead-in the both flat surfaces are forming a wedge-shaped space with a different speed to each other before contacting and with this an automatic h-droarnamic tooth-lubrication with the oil on the surface on all parts inside of a ;ear box with oil slash lubrication.

Depth and width of tooth face depend on the load transmission.

The total angle of tooth crest and space depend on tooth depth, quantity of teeth and gear ratio for to prevent an overlap at lead-in Rnd lead-out ith neighbouring teeth.

Computer- nalysis are made and find an optimal angle of tooth crest -nd -pace nearly 700.

The theoretical deviation from the straight line along this contact plin is zero t the internal gear tooth, 0,006599 mm at the top of the spur gar, and 0,00012 mm at the base of he tooth of he spur gear,'nsgnificant compared with she lubricatIng film thickness of approx. 0,020 mm.

Figure 1 shows the toothed gearing ith two gears and teeth with flat surfaces. A plane blank with irregular outer surface (1) with three uniform holes for one pivoted eccentric drive shaft (2) and two pivoted eccentric blind cranks (3) is provided with a greater hole and an exact quantity of teeth like an internal gear and this teeth are formed with straight flanked surfaces (5).

Inside of the internal gear is pivoted the output gear with less quantity of teeth and this teeth (6) are also formed with straight flanked surfaces.

Claims

1 A planetary transmission unit to transmit the driving force with flat surface pressure comprising a parallel-crank-gear with one eccentric drive shaft and two eccentric blind cranks, an inter: nal gear guided by the three eccentric shafts, one output spur gear with less teeth compared with the internal gear, with absolutely straight flanked surfaces of the teeth at the internal and at the spur gear.

2 A planetary transmission unit as claimed in Claim 1 wherein tooth and opposite tooth space have the same trapezium.

9 4 planetary transmission unit as claimed in Claim 1 wherein the tooth is an acute angled triangle and the angle of pressure plain at a trapezoid o r triangle is the same or different.

4 A planetary transmissiDn unit as claimed in Claim 1 wherein the teeth are axially parallel or a helical gearing.

5 A planetary transmission unit as claimed in Claim 1 or Claim 2 wherein at rotation the flat surfaces together form a wedge- shaped potion with different speed and with this a hydrodanamic lubrication.

6 A planetary transmission unit as claimed in Claim 1 or Claim 2 or Claim 5 wherein the loaded teeth are working without Hertzor tribeck - roll pressure.

6 : =ne tRrE tnnsmission unit as claimed in Claim 1 or Claim 2 or Claim 5 nerein the loaded teeth are working without Hertz- or Stribeck - roll pressure.

Amendments to the claims have been filed as follows 1 A planetary transmission unit to transmit the driving force with flat surface pressure comprising a parallel-crank-gear with one eccentric drive shaft and two eccentric blind cranks, an inter: nal gear guided by the three eccentric shafts, one output spur gear with less teeth compared with the internal gear, with absolutely straight flanked surfaces of the teeth at the internal and at the spur gear.

2 A planetary transission unit as claimed in Claim 1 wherein -ot tooth and opposite tooth space havesthe same trapezium.

3 A planetary Qr~~nsmission unit as claimed in Claim 1 wherein the tooth is an acute angled triangle and the angle of pressure plain at a trapezoid or a triangle is the same or different.

4 A planetary transmission unit as claimed in Claim 1 wherein the teeth are axially parallel or a helical gearing.

5 A planetary transmission unit as claimed in Claim 1 or Claim 2 wherein at rotation the flat surfaces together form a wedge- shaped motion with different speed and with this a hydrodvnamic lubrication.