Eccentric gear

An eccentric gear comprises two differently large gear rings (6, 7), of which an outer ring (6) has a certain number of inwardly directed teeth and an inner ring (7) has a smaller number of outwardly directed teeth, of which only a few engage with the outer gear ring, in that the inner gear ring is eccentrically mounted in bearings. The inner gear ring (7) is integrated with a casing part (8) whose geometrical axis of rotation (A) is oblique relative to an axis of symmetry (B) through the center of the outer gear ring (6). During the generation of the inner gear ring, the casing part is submitted to a nutating motion, during which the axis of rotation (A) of the casing part moves as a generatrice along an imaginary cone, around a cone apex (C) that is axially distanced from the gear rings (6, 7). In a region that is equally distanced from the gear rings as the cone apex (C), the casing part is associated with a gear ring (12) that is ready to be led into engagement with a complementary second gear ring on the driven element of an application object in order to, jointly with the latter, form a force transmitting unit situated substantially in a plane (D--D) extending perpendicularly to said axis of symmetry, in which plane the cone apex (C) is located.

TECHNICAL FIELD OF THE INVENTION 
This invention relates to an eccentric gear for transmitting a torque or 
force from an input or driving, rotatable element to a driven element 
comprising two cooperating gear rings with differing pitch diameters, of 
which a first, outer gear ring with the largest diameter has a certain 
number of inwardly directed teeth and a second, inner gear ring has a 
smaller number of outwardly directed teeth of which only a minor number, 
e.g. one, is in engagement with the outer gear ring, in that the inner 
gear ring is mounted in bearings eccentrically relative to the outer one, 
the gear change between said driving and driven elements being dependent 
upon the total number of teeth in each gear ring. 
PRIOR ART 
Eccentric gears of the sort generally related to above are previously known 
in different embodiments. Thus, in SE 9203101-2 an eccentric gear is 
disclosed that is specially, although not exclusively, suitable for being 
used in industrial or other robots. In this case, the gear is delivered as 
an independent unit, which may be inserted between a driving source, for 
instance an electric motor, and a driven, rotating element of the robot or 
the application object in order to gear down a high rotation speed of an 
output shaft from the driving source to a lower speed of an input shaft 
that forms the driven element of the application object. An essential 
advantage of eccentric gears is that they in one single step make possible 
large gear change relations. Thus, in practice they manage gear changes in 
the range of 50:1 to 200:1. In comparison with other types of gears, in 
particular multiple gears, eccentric gears have a constructional 
simplicity that has been considered to offer an inexpensive solution to 
the generally occurring problem in mechanical engineering to attain large 
gear changes. However, such previously known eccentric gears that have 
been series-produced as independent or separate units for later 
application with the purchaser/user have had in common that they have 
always included both an input shaft or shaft part centrically mounted in 
bearings, and an output shaft or shaft part, likewise centrically mounted 
in bearings. The inner gear ring has then been provided on a ring- or 
disk-shaped body of a small axial extension, from which the down-geared 
rotary motion has been transferred to the output shaft via carrier 
mechanisms of a more or less complicated and thereby expensive nature. 
Each of the two shafts of the gear require not only a bearing, but also 
the installation space thereof; often in opposed ends of a more or less 
voluminous housing in which the tooth-carrying, eccentrically movable ring 
or disk body is built-in. Further, costly and space-demanding connections 
or couplings are required not only between the driving source and the 
input shaft of the gear but also between the output shaft of the gear and 
the driven rotary element comprised by the application object of the 
purchaser/user. 
As a further example of an eccentric gear of the sort initially related to, 
the gear disclosed in U.S. Pat. No. 5,030,184 (Rennerfelt) may also be 
mentioned. 
OBJECTS AND FEATURES OF THE INVENTION 
The present invention aims at removing the above-mentioned shortcomings of 
previously known eccentric gears of the sort related to and providing a 
constructionally extremely simple gear. Thus, a primary object of the 
invention is to provide an eccentric gear that not necessarily requires 
any output shaft and the bearings belonging thereto and which therefore 
does not require expensive couplings between the gear and the application 
object for its connection to the application object in question. Further, 
it is an object of the invention to provide an eccentric gear that may be 
connected to an arbitrary application object in a simple way. Still 
another object of the invention is to accomplish an eccentric gear which 
for its function requires very few components and which therefore can be 
produced to a very low cost with the ultimate purpose of making the use of 
the gear possible in application areas where high costs are unacceptable. 
In accordance with a particular aspect, the invention aims at providing a 
gear that is capable of setting the driven element of the application 
object not only in rotary motion but, also in a simultaneous reciprocate, 
axial motion. In accordance with a further aspect, the invention also aims 
at providing a gear that, despite a simple construction, manages to 
transform a rotary motion from the gear into an exclusively reciprocate 
motion of the driven element of the application object. 
According to the invention, at least the primary object is attained by 
means of providing an eccentric gear comprising two cooperating gear rings 
with differently sized pitched diameters. A first outer gear ring having a 
large diameter has a certain number of inwardly directly teeth and a 
second inner gear ring has a small number of outwardly directed teeth of 
which only a minor proportion are in engagement with the outer gear ring. 
The inner gear ring is mounted in bearings eccentrically relative to the 
outer gear ring. The gear change between the driving and driven elements 
are dependent upon the total number of teeth in each gear ring, the 
eccentric inner gear ring being in the form of separate unit being 
connectible to an arbitrary application object in which the driving 
element is included. The inner gear ring is connected with a rotatable, 
enlongated body whose geometrical axis of rotation is oblique relative to 
an imaginary geometrical axis of symmetry through the center of the outer 
gear ring in which during the generating motion of the inner gear ring 
against the outer gear ring is submitted to a rotating motion, during 
which the axis of rotation of the body moves as a generatrice along the 
surface of an imaginary cone apex. The body is positioned within a region 
substantially equally distanced from the gear ring and the cone apex, and 
is associated with a first engaging means which is adapted for engagement 
with a complimentary second engaging means appurtenant to the driven 
element of the application object, in order to jointly with this second 
means from a force transmitting unit substantially situated in a plane 
that is perpendicular relative to the axis of symmetry of the plane of the 
cone apex. 
According to a particularly preferred embodiment, the elongated body on 
which the inner eccentrically movable gear rind is formed, has the shape 
of a casing or a casing-like part according to a further embodiment this 
casing part can be used for carrying a third gear ring intended to be 
brought into engagement with an analogous gear ring that constitutes a 
part of the driven element of the application object, said driven element 
forming a stationary part in the space that determines the position of the 
cone apex around which the casing part moves during its nutating motion. 
FURTHER ELUCIDATION OF PRIOR ART 
An eccentric gear mechanism with a tooth-carrying casing part exerting a 
nutating motion during use is previously known per se from WO 93/06999. 
However, in that case the gear mechanism in included as an integrated, 
internal component into a cylindrical roll, wherefore a separate arbitrary 
application object cannot be connected to the gear mechanism at all, and 
even less so in the simple way that characterizes the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
In FIG. 1 to 3, reference numeral 1 generally designates an eccentric gear 
made according to the invention, which gear at its input side is connected 
to a driving source in the form of a motor 2, for instance an electric 
motor. At its output side, the gear 1 is connected to an application 
object which is schematically shown at reference numeral 3. In the example 
this object is assumed to be in the form of a valve housing comprising a 
valve spindle 4 that is turn- or rotatable for the regulation of the 
appurtenant valve. In the case where the valve spindle 4 comprises a 
thread, it is also axially movable. 
One component in the gear 1 consists of an outer frame-forming ring 5 which 
on its inside has a first gear ring 6 arranged to cooperate in a known 
manner with a second gear ring 7 on a rotatable body designated 8. The 
first outer gear ring 6 has a larger pitch diameter than the gear ring 7 
and has a certain number of inwardly directed teeth, while the inner gear 
ring 7 has a smaller number of outwardly directed teeth of which only a 
minor number, for instance one, is in engagement with the outer gear ring 
6, in that the inner gear ring is eccentrically mounted in bearings 
relative to the outer one. More precisely, the body 8 that carries the 
inner gear ring 7 at its one end is carried by a bearing 9, e.g. a ball 
bearing, that is arranged outside an eccentric body 10 which in turn is 
co-rotatively connected with a shaft 11 pertaining to the motor 2 and 
which is centrically mounted in the same in bearings. The eccentric body 
10 forms the driving, rotatable input element of the eccentric gear, to 
which the shaft 11 is connectable. The gear change of the gear is 
dependent upon the total number of teeth in the two gear rings 6, 7. 
Presume that the number of teeth in the outer gear ring 6 amounts to 90 
while the number of teeth in the inner gear ring 7 amounts to 89. When the 
shaft 11 and the eccentric body 10 rotate, then the inner gear ring 7 will 
generate on the outer gear ring 6 like a planet wheel and thereby turn 
around its axis of symmetry in the opposite direction of rotation relative 
to shaft 11, more specifically by 1 tooth pitch since the difference in 
numbers of teeth is 1. In order to make the inner gear ring 7 and, 
thereby, the body 11 rotate a whole revolution, the shaft 11 has to rotate 
89 revolutions. In other terms, a gear change or a reduction in the number 
of revolutions of 89:1 is obtained. 
The eccentric gear shown in FIG. 1 to 3 as described so far is 
substantially previously known. 
According to the invention, the body 8 carrying the inner gear ring 7 is 
elongated and has in the example according to FIG. 1 to 3 the shape of a 
casing or casing-like part, which, at its end being distanced from the 
gear ring 7, has a first means that is ready to be connected or be brought 
into engagement with a complementary second means on the valve spindle 4, 
which constitutes the element driven by the gear. According to the shown 
example, said first engagement means consists of an internal third gear 
ring 12 that is connected or integrated with the free end portion of the 
casing part. The complementary engagement means on the valve spindle 4 
consists of a cooperating fourth gear ring 13 with outwardly directed 
teeth, said ring being provided upon a disk-shaped body 14 which is 
corotatively connected with the valve spindle 4. 
The casing part 8 has a geometrical axis of symmetry designated A (see FIG. 
2) which is oblique relative to an imaginary geometrical axis of symmetry 
B through the centre of the outer gear ring 6. During the gear generation 
of the inner gear ring 7 against the outer gear ring 6, the casing part is 
submitted to a nutating or tilting motion during which its axis of 
symmetry A moves like a generatrice along an imaginary conical surface, 
more specifically around a cone apex designated C that is axially 
distanced by a considerable stretch from the gear rings 6, 7. In the 
example, each one of the gear rings 6, 7 has a conical basic shape with 
small ends and large ends. More specifically, the conicity is such that 
the small ends of the gear rings point into the same direction. 
Specifically in the shown example, they point in a direction towards the 
motor 2. It should be observed that the previously mentioned cone apex C 
is located in a plane designated D--D which extends substantially 
perpendicularly to the axis of symmetry B. The distance between this cross 
plane D--D and the cross plane designated E--E that extends 
perpendicularly to the axis of symmetry B and in which the gear rings 6, 7 
are located, is substantially as large as the distance of the gear ring 12 
to the plane E--E. In other words, the gear ring 12 is substantially 
located in the cross plane D--D. 
Within the casing part 8 a shoulder 15 is arranged which according to the 
example has the form of an intermediate wall. Against this wall is placed 
the one end of a pressure spring 16, for instance a helical pressure 
spring, whose opposite end is placed against the tooth-carrying disk-body 
14 being carried by the spindle shaft 4. The spring 16 has the purpose of 
always keeping the casing part 8 spring-tensioned in a direction towards 
the motor 2, more specifically for keeping the tooth/teeth of the inner 
gear ring 7 being engaged with analogous teeth on the outer gear ring 6 in 
a gap-free engagement with the latter. In this way, a distinct and silent 
force transmission is secured between the gear rings. 
Necessary lubricating grease for the gear rings 6, 7 is enclosed by means 
of a radial seal 17, preferably a standard seal, which according to the 
example in FIG. 1 to 3 has the shape of a cross-sectionally V-shaped, 
elastic ring, e.g. of plastic or rubber. Similarly to the gear ring 12, 
the sealing ring 17 is located in the cross section D--D, 
The frame ring 5 has lugs 18, 19, a flange or similar means for fastening 
the gear 1 to, on one hand, the motor 2 and, on the other hand, the 
application object 3. More specifically, the lugs 18 allow a 
screw-fastening of the gear to a flange 20 on the motor 2, while the lugs 
19 may be screwed to suitable connecting taps or means 21 which in turn 
are stiffly fastened to the application object 3. In its screw-fastened 
state as shown in FIG. 1, the frame ring is immovable in the space 
relative to both the motor 2 and the application object 3. 
It should also be pointed out that a cup spring 22 operates between the 
bearing 9 and an internal shoulder in the casing part 8, with the purpose 
of keeping the bearing in place and lightly stressing the same axially in 
order to avoid any looseness. 
The Function of the Eccentric Gear According to the Invention 
As previously mentioned, the comparatively elongated casing part 8 will 
perform a nutating or tilting motion when the inner gear ring 7 makes a 
generating motion against the outer gear ring 6 in a way similar to a 
planet wheel. The size of the angle .alpha. that the axis of symmetry A 
forms with the axis of symmetry B is determined by on one hand the size of 
the eccentricity of the gear rings 6, 7 and on the other hand the distance 
between the cross planes E--E and D--D. At a small distance between these 
cross planes, a comparatively large angle .alpha. is required for a 
certain eccentricity. With increasing distance between the cross planes, 
the angle .alpha. may be reduced. In practice, the angle .alpha. may lie 
within the range of 0,1 to 3.degree., suitably 0,2 to 2.degree. or 
preferably 0,3 to 1.degree.. The axial length of the casing part 8 should 
amount to at least 50% of the diameter of the gear ring 7 and suitably 
more in order not to necessitate too large angles .alpha.. 
Of course, during the nutating motion of the casing part 8 the inner gear 
ring 12 will obtain a slewing or tilting movement at its right, free end. 
However, since the gear ring in question is located in the cross plane 
D--D which is common to the cone apex C, said ring will not obtain any 
eccentrically or radially directed motion and the deflection of the axial 
movement component will be very limited. Therefore, it does not present 
any practical difficulties to absorb these motions in the tooth connection 
between on one hand the gear ring 12 and on the other hand the gear ring 
13 associated with the valve spindle 4, for instance by making the teeth 
with a certain adapted play. It is also feasible to make the teeth with a 
certain curvature instead of making them completely straight. If the 
casing part 8 at the end that comprises the gear ring 12 is wholly or 
partly made of plastic or another plastic material, also a play-free 
elastic pre-stress may be obtained in the tooth engagement with the gear 
ring 13. 
In FIG. 1 it should particularly be noted that the inner gear ring 12 on 
the free end portion of the casing part 8 has a width that is smaller than 
the width of the outer gear ring 13 on the disk body 14. Moreover, it 
should be noted that the inner edge of the gear ring 12 is located at a 
certain distance from a shoulder surface 23 in the casing part, whereby a 
gap 24 is created between the shoulder and the gear ring. By this shaping, 
the disk body 14 and the appurtenant gear ring 13 are free to move axially 
in both directions without the gear rings 13, 14 losing their meshing with 
each other and without the apex C of the cone changing its spatial 
position in relation to the fixed frame ring 5 and the valve housing 3, 
respectively. Thus, a valve spindle 4 with threads may also be connected 
with the gear without losing the axial mobility that is necessary for 
adjusting the valve in question into different regulating positions. It 
should be obvious that the gear attends to a gear reduction of the 
relatively high rotation speed and low torque to a reduced rotation speed 
or deflection of angle of rotation, these being dependent as a function of 
the factual gear change, and an increased torque of the valve spindle 4. 
The advantages of the invention are evident. By the fact that the freely 
exposed gear ring 12 is available on the casing part 8, the gear may 
easily and quickly be connected to the valve spindle without the necessity 
of any special couplings of the kind that has been previously required 
between an output shaft mounted in bearings of the gear and the rotation 
element in question of the application object. Further, the described gear 
assumes a very simple construction, comprising extremely few components, 
namely substantially only the frame ring 5, the casing part 8, the bearing 
9 and the eccentric body 10, and where appropriate, the spring 16 and the 
sealing 17. In other terms, the gear can be produced at a very low cost in 
comparison with previously known eccentric gears. 
In FIG. 4 a modified embodiment is shown, according to which the V-shaped 
sealing ring 17 has been replaced by a simple O-ring 25. Also this sealing 
ring is located in the cross plane D--D in which the cone apex C of the 
casing part 8' is located. In FIG. 3 it is indicated how the gear ring 12 
exerts slewing motions with restricted motion deflections under the 
nutating motion of the casing part. Thus, a major part of the upper 
portion of the O-ring is shown situated somewhat to the right of the cross 
plane D--D, while the major part of the lower portion is shown to the left 
of the same plane. The O-ring 25, which is relatively stiff in radial 
direction, simplifies the assemblage of the gear relative to the spindle. 
The cone apex C should be located on the axis of symmetry B in order to 
obtain the best possible contact between the gear rings 6 and 7. 
Although the gear ring 12 related with the casing part is shown as an inner 
ring intended to be connected with an outer gear ring on the driven 
element of the application object, also the reversed relation is possible, 
i.e., an outer gear ring on the casing part and an inner gear ring on the 
driven element. 
Reference is now made to FIG. 5 and 6 that illustrate an alternative 
embodiment according to which an element 4' driven by the gear 1 is 
indicated in the form of a shaft comprised by an arbitrary application 
object (not shown). The gear comprises a casing part 8", which is mounted 
in bearings not only by means of a first eccentrically placed bearing 9, 
but also by means of a centrically placed second bearing 26 at the free 
end of the casing part. This bearing is kept in place by means of a holder 
which is designated 27 in its entirety and which comprises an angle-shaped 
arm 28 being stiffly connected with a frame ring 5', and a support ring 29 
being carried by said arm. The eccentric body 10', which in this case has 
a counter-weight 30, has an extension 31 whose free end is mounted in 
bearings in the support ring 29. 
According to the embodiment of this example, the casing part 8", has an 
external fifth gear ring 32 which forms the first engaging or 
force-transmitting means of the gear. As may be seen in FIG. 5, the gear 
ring 32 engages with a gear belt 33 which in turn engages with a gear belt 
disk 34 on the driven shaft 4'. 
Similar to the third gear ring 12 of the embodiment according to FIG. 1 to 
3, the gear ring 32 is located in one and the same cross plane as the cone 
apex around which the casing part 8" exerts its nutating motion. Also in 
this case the gear ring 32 makes a slewing or tilting motion which, 
however, has a limited deflection, wherefore the resilient or flexible 
gear belt 33 manages to absorb the motions in question without any 
problems. 
In FIG. 7 an embodiment is shown according to which the stationary holder 
27' for the bearing 26' has the shape of a cover in which there is an 
opening 35 for a gear wheel 34' whose teeth are brought into direct 
engagement with the gear ring 32'. Thus, in the present case the other 
engaging means associated with the driven element 4' consists of the gear 
wheel 34' in lieu of the gear belt 33 as according to the embodiment of 
FIG. 5 and 6. 
In FIG. 8 an embodiment is shown according to which the gear in question is 
formed for direct connection with a cable or chain transmission. In this 
case an outer, carrying frame ring 5" is fixedly attached to a carrier 36 
of a suitable type. At its free outer end the frame 5" carries a bearing 
26" on which a chain wheel or sprocket 37 is rotatably mounted, which in 
turn is co-rotatively connected with a shaft 38 that constitutes an 
extension of a casing part designated 8'". On its disk-shaped portion 39, 
this casing part carries an inner gear ring 7 which in a previously 
described manner cooperates with an outer gear ring 6 on the inside of a 
part-ring 5'" that is detachably connected with the frame ring 5". A motor 
2 is connected with the gear. The wheel 37 has a toothing 40 for engaging 
with the chain in question. This toothing constitutes the first engaging 
means of the gear. 
As according to the previous embodiments, said first engaging means 40 is 
located in the cross plane D--D in which the cone apex C as well as the 
bearing 26" are located. In this case the distance between the cross plane 
D--D and the cross plane for the gear rings 6, 7 is comparatively large 
(larger than the diameter of the gear ring 7), implying that the obliquity 
angle .alpha..degree. between the previously mentioned shafts A and B may 
be comparatively small. Thus, in the embodiment according to FIG. 8, it is 
feasible that this angle amounts to merely about 0,20-0,309.degree.. 
In FIG. 9 an eccentric gear is schematically illustrated, which has the 
purpose of transforming a rotary motion of an output shaft of a motor 2 
into an axial, reciprocating motion of a driven element, e.g. in the form 
of a swivelling arm 4" to an application object 3' in the form of a 
stationary holder. In this case, a screw or screw-shaped tap 41 is 
co-rotatively connected with the casing part 8'", the external thread of 
said screw or screw-shaped tap being in engagement with an internal thread 
in a through-hole through the holder 3'. When the screw 41 is brought to 
rotate by means of the eccentric gear, with a speed of rotation that is 
reduced in comparison with the speed of rotation of the motor 2, then the 
screw 41 will--thanks to the thread engagement--be submitted to an axial 
motion which is directed either to the left or to the right on the 
drawing, depending on the direction of rotation of the casing part. In 
turn, this axial motion of the screw is transformed into a slowing motion 
of the arm 4" that is pivotable relative to the holder 3' via a joint 
designated 42. The screw tap 41 may either be fixedly connected with the 
casing part 8'" or be provided with splines. Then the casing part, and 
thereby the cone apex C, will be moved axially relative to the object 3'. 
This motion is usually small and can be accepted. Alternatively, the 
threaded tap 41 may constitute the application object and be provided with 
splines which engage into corresponding splines in the casing part 8"" 
(cf. FIG. 1). 
Eventually, in FIG. 10 an embodiment is shown according to which a gear 1 
according to the invention has the purpose of transmitting a torque from a 
motor 2. e.g. a hydraulic motor, to a wheel 43 with a tire, which wheel 
comprises a rubber tyre 43' and a rim part 43". In conformity with the 
sprocket 37 according to FIG. 8, the wheel 43 is mounted in a bearing 44 
which is located in the same cross plane as the cone apex of a nutating 
casing part 8'", in a previously described manner. By the lateral 
resilience of the tire, the tilting motions in question can be accepted. 
According to the example in FIG. 10, the rim part 43" forms the driven 
element of the application object, which element may be easily connected 
via a screw joint 46 with a ring flange 45 that is co-rotatively connected 
with the casing part 8'". 
Feasible Modifications of the Invention 
It is evident that the invention is not restricted merely to the 
embodiments as described and shown in the drawings. Thus, it is for 
instance feasible to make the first and second outer and inner gear rings, 
respectively, of the gear in another way than in the form of gear rings 
which both have a conical basic shape. Hence, the outer gear ring may, 
e.g., be cylindrical at the same time as the inner gear ring is conical. 
For simple gears with small requirements of accuracy, it is even feasible 
to make both gear rings substantially cylinder-shaped. Furthermore, it is 
feasible to make the teeth of at least one gear ring with a slight 
curvature, and it is also feasible to construct the teeth so that the 
contact points between the same extend helically and are distributed along 
several consecutive teeth or pairs of teeth. Although a casing-shaped part 
is preferred as an elongated, gear ring-carrying body, the body in 
question may also be formed in another way. Thus, as indicated in FIG. 8, 
the elongated body could also consist of a disk-shaped, tooth-carrying 
part and a central axial tap, being directly connected or integrated with 
the former. It should also be mentioned that according to the embodiment 
of FIG. 8, the wheel 37 may be modified in different ways in order to make 
possible the connection of the gear with other objects than just a chain. 
The wheel may for instance be formed for being connected with a 
transmission belt, e.g., a belt encompassed by a patient-lift, it being 
possible to effect the force transmission by a friction engagement between 
the wheel and the belt.