CA1075042A

CA1075042A - Friction drive transmission

Info

Publication number: CA1075042A
Application number: CA281,129A
Authority: CA
Inventors: Yves J. Kemper
Original assignee: VADETEC
Current assignee: VADETEC
Priority date: 1976-07-12
Filing date: 1977-06-22
Publication date: 1980-04-08
Also published as: BR7704556A; AR216472A1; SE7706904L; ES460498A2; IT1116624B; NL7706848A; AU2696277A

Abstract

VARIABLE SPEED TRANSMISSION DEVICE
Abstract of the Disclosure A variable speed transmission device of the type in which a first rotatable element is in rolling friction engage-ment with a second nutatable element having an axis movable in a biconical path about the axis of the first element in a manner such that two points of contact are established and which are equally spaced on opposite sides of a point at which the two axes intersect. A pair of rolling surfaces provided on each of the first and second elements are defined by curved generatrices which may be concave on one of the elements, preferably the first element, and convex on the other of the elements, pre-ferably the second. The generatrices defining the rolling surfaces of revolution on the first and second elements are similar lengths and long relative to the average radial distance of the surfaces from their axes of revolution. A mechanical linkage connects the second element with the supporting frame of the transmission, such mechanical linkage preferably being in the form of a diaphragm-like structure having flexibility in a radial direction but being relatively rigid in a circumferen-tial direction.

Description

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This invention relates to variable speed mechanical torque transmissions and more particularly, it concerns improve-ments in transmissions by which a variable speed ratio is achieved by varying the radii of one set of rolling surfaces relative to another set of rolling surfaces in frictional engagement with the one set and in which one set of rolling surfaces is moved orbitally relative to the other.
Canadian Patent Application No. 258,210, filed July 20, 1976 and commonly owned with the present invention, discloses several embodiments of a variable speed transmission having a first element defining a pair of rolling surfaces of revolution about a first axis, a second element having a pair of rolling surfaces about a second axis intersecting the first at a point of axes intersection, a frame in which the first and second elements are supported to fix the angular orientation of the two axes, and a mechanical system for urging the respective rolling surfaces into frictional engagement with each other at two points of contact on opposite sides of the point of axes intersection. The rolling surfaaes on one of the members are cone-like in shape whereas the rolling surfaces on the other element are ring-like and movable axially in opposite directions with respect to the point of axes intersection. The relative ratio of rolling surface radii at the points of contact may be made to vary to provide an infinitely variable speed ratio.
In one embodiment, the first element is provided with the cone-like rolling surfaces and is rotatable about the first axis at a velocity ~. The second element carries the ring-like rolling surfaces and is journalled in a crank-like support such that the second axis may travel in a biconical path about the first axis at a velocity ~. The second element may or may not undergo rotation about the second axis at a velocity ~. Also, ' ,, ~b ~075042 the disclosure incorporates a mechanical linking system by which any two of the components rotating at velocities a, and ~ may be interconnected or in which all three of such velocity components may be connected by means of an epicycloidal train. -In the operation of one embodiment, the first element on which the cone-like rolling surfaces are provided is connected directly with an output shaft and thus rotatable -at a velocity ~. The second element is driven in nutational movement in which the second axis travels in a biconical path about the first axis at a velocity a. The second element is prevented from rotating on the second axis t~ = 0) by a -mechanical linkage in the form of conical gears having an apex coincident with the point of axes intersection, one of which gears is fixed to the frame while the other is carried by the second element. Thus, the output shaft velocity w O
will be related to input velocity a as a result of the ratio of radii at the two points of rolling friction contact between the rolling surfaces on the first and second elements. -- -Although the aforementioned embodiment disclosed in Canadian Application Serial No. 258,210 provides a highly ,~ effective variable speed transmission, the rolling surfaces of the first element are defined by two truncated cones with --opposing bases, and having an apical half-angle equal to or slightly less than the angle of inclination of the second axis with respect to the first axis. The rolling surfaces of the second element are formed by two annular rings.
Because of their respective geometrical forms, at least one ---.' .
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of the two couples of rolling surfaces of the transmissions described must be moved with respect to each other over a relatively long distance by means of a maneuvering component in order to produce a pronounced variation of transmission ratio. This diminishes rapidity of maneuver and increases consumption of power. Additionally, there is room for improvement in the mechanical linkage by which the second element is linked with the frame. The conical gear linkage is relatively noisy and represents a source of friction losses which diminish the efficiency of the overall transmission.
Also because the gears are located midway along the length of the second element, they increase the overall transverse size of the transmission in some measure.
In accordance with the present invention, a trans-mission is provided which is similar in operation to the mentioned embodiment of Canadian Patent Application Serial No. 258,210 and as such, includes a frame, a first element on a first axis fixed in the frame and having rolling surfaces of revolution about said first axis, one such rolling surface on each side of a first plane perpendicular to said first axis at a point of axes intersection, a second element on a second axis intersecting the first axis at the point of axes intersection and having concentric journal and rolling surfaces of revolution about the second axis, the rolling surfaces of the second element being disposed one on each side of a second plane passing through the point of axes intersection ~ and perpendicular to the second axis, support means rotatable ; on the first axis and journalled with the journal surfaces . .

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of the second element for movement of the second element in - a biconical path circumferentially of the first axis, the apex of such biconical path being coincident with said point of axes intersection, the respective rolling surfaces on the first and second elements being in rolling frictional engage-ment at two points of contact in a third plane containing the first and second axes and located one on each side of the first plane, the rolling surfaces of at least one of the first and second elements being defined by generatrices 10 inclined oppositely with respect to the axis of revolution thereof and symmetrically with respect to the point of axes - intersection, thereby to provide in the respective rolling surfaces of said first and second elements a variable ratio . of rolling surface radii at points of contact for variation in the spacing of the points of contact from the point of axes intersection, and means for forcing said respective .~ rolling surfaces on said first and second elements into rolling friction engagement with each other at the two points of contact. In the present invention, however, the 20 rolling surfaces on one of the first and second elements is characterized as being defined by a curved generatrix to be convex in longitudinal section and the rolling surfaces of the other of the elements is characterized as being also defined by a curved generatrix bent to be concave in longitu-; dinal section.
Described in detail below, as non-limiting examples, are a particular method of construction in accordance with .
. the invention, referring to the appended drawings.

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~ ` 107S042 Figure 1 shows a longitudinal section of a trans-mission designed in the above-mentioned manner made by a plane passing through the first and second axes.
Figures 2, 3 and 4 shown respectively, in perspec-tive and on a larger scale, three of the components of the transmission of Figure 1 which have ~een shown in a cutaway perspective view in Figures 2 and 4 in order to make the drawing clearer.
The transmission shown includes a fixed frame having two ends of flanks Al and A2 at each end which are joined by a crank case A3 of a generally cylindrical form.
On this frame A, a first element 2 and a second element 3 ~- -are mounted so as to be rotatable by means of bearings.
The first element 2 is rotatable around a first axis 7 which is the longitudinal axis of the transmission and which is fixed with respect to the frame A. The first element

2 includes two semi-sections 4 and 5 containing two rolling surfaces 8 and 9 approximately of the shape of truncated cones and which will be more specifically described below. These two semi-sections 4 and 5 are mounted on a shaft 11 (output shaft) that is coaxial with the first axis 7 and are movable axially with respect to each other in the longitudinal direction of the first axis 7. Keys 22a and 22b fasten the semi-sections 4 and S to the shaft 11 so that they may rotate together.
Two annular chambers 14a and 14b are constructed between the interior wall of the two semi-sections 4 and 5 and the exterior surface of shaft 11. These annular chambers communicate with the outside by means of conduits 17a, 17b and 15 which are constructed .. ~
for this purpose in the body of shaft 11. A cylindrical groove 18, which surrounds shaft 11, permits introducing a fluid into chambers 14a and 14b when shaft 11 rotates on itc own axis 7.
Sealing joints 21a, 21b, 21c, 21d, 21e and 21f assure tightness of the system of annular chambers and of the fluid supply conduits for these annular chambers. The effect of introducing a fluid into the annular chambers 14a and 14b is to simultaneously dis-place the two semi-sections 4 and 5 and the rolling surfaces 8 and 9 axially, thus separating them. The hydraulic apparatus consists of the maneuvering component intended to modify the relative positions of contact points Pl and P2 and consequently, the txansmission ratio.
The rolling surfaces 8 and 9 rotate around the first axis 7. They are symmetrically arranged on opposite sides of a plane that is perpendicular to the first axis 7 at a point S of -this axis. The two major bases of the semi-sections 4 and 5 face each other.
The shaft 11 is supported by frame A, at each of its extremities, by a system of bearings including a first series of roller bearings la and lb which are coaxial with the first --axis 7.
A support 13 is rotatable around the first axis 7 by means of bearings 25a and 25b inserted between frame A and a ` support 13. The abovementioned bearing lb is itself mounted inside of support 13, approximately within the transversal plane of bearing 25b at one extremity of the transmission so that the first element 2 may turn with respect to support 13 which may itself turn with respect to frame A.
Support 13, which is essentially symmetrical, is in-; clined with respect to the longitudinal axis 7 of the transmission.
It is intended to support the second element 3 by means of roller bearings 26a and 26b.
- The second element 3 is a solid of revolution, cylind-rical in form, and it is rotatable with respect to support 13 :;

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around a second axis 12 passing through point S of the first axis 7 and inclined at a constant angle a with respect to the latter.
The second element 3 carries two rolling surfaces 19 and 20 concentric with a second axis 12 and which are arranged in s~mmetrical fashion to the second axis at point S. These rolling surfaces are formed on two annular rings 27 and 28 which are movable axially with respect to each other in the longitud-inal direction of the second axis 12, inside the body of the second element 3, and which are coupled for rotation with the second element 3.
A mechanical system drives the two rolling surfaces 19 and 20 of the second element 3 axially in such a manner as to apply them with force at two constant points Pl and P2, against the rolling surfaces 8 and 9 of the first element 2.
Several methods of designing this mechanical system are des-cribed in the aforementioned Canadian Application Serial No.
258,210 and these methods are applicable in the case of the present improvements. By way of illustration, another method is indicated in Figures 1 to 3 which are herewith appended. Accord-ing to this method, each ring 27 and 28 (Figures 1 and 3) poss-esses exterior helicoidal ramps, opposite in direction, which make contact with interior helicoidal ramps 121a and 121b borne by rings 122 and 123 which are housed within the second element

3 and are fastened to it. It is clear that the reaction between the helicoidal ramps 120a and 120b, on the one hand, and 121a and 121b, on the other hand, has a tendency to separate the semi-sections 4 and 5 from each other and to apply the bearing tracks 8 and 9 against bearing tracks 19 and 20 with a normal force sufficient to transmit the input torque without slipping.
Apparatus which shall be described below prevents the second element 3 from turning around the first axis 7 with respect . ~P `

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to frame A. Finally, an input shaft 33 is mounted so as to rotate in support 13. This shaft 33 is coaxial with axis 7.
The transmission which has been described up to this point with reference to Figure 1 is practically identical to the one for which several designs have been described in the aforementioned co-pending patent application. It would be use-ful to review its method of operation here.
The rolling surfaces 8 and 9 of the first element 2 are in rolling frictional contact at Pl and P2 against surfaces 19 and 20 of the second element 3. The specific contact pressure is created by ramps 120a and 120b, 121a and 121b. Due to the action of an input torque couple applied to shaft 33, surfaces 19 and 20 are caused to rotate, on the one hand, at velocity ~* around their own axis ~the second axis 12) and, on the other hand, in a conical motion of the apex S, around the first axis 7, at velocity a.
The aforementioned rotational velocities ~*, a and the rotational velocity ~ of the first element 2 around axis 7 are related to each other by a kinematic equation depending on the geometry of the rolling surfaces. In the present case where O O
the velocities ~ and ~ are maintained at a constant ratio (equal -to 1), there is therefore only one output velocity at which the transmission output shaft 11 will be driven for a given relative position of points Pl and P2. -It should be pointed out that the rolling surfaces 8 - and 9 of the first element 2 and the surfaces 19 and 20 of the second element 3 automatically center themselves symmetrically with respect to point S. In fact, decentering of one of these surfaces of the first element would have the effect of correla-tively decentering the corresponding surface of the second , .

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i . . , ' ~ ' , -' element. Consequently, the pressure at contact points Pl and P2 would be different since one of the surfa¢es would receive less thrust from the helicoidal ramps 120a and 120b than the other one. This would result in a difference of fluid pressure contained in annular chambers 14a and 14b, which is impossible since these chambers are connected. Therefore, dissymmetry between the surface, it does occur, disappears automatically.
The present improvements concern the mechanical link-age introduced in the case of the special design employed between frame A and the second element 3 in order to prevent the latter from turning around the first axis 7 with respect to frame A. ~Consequently, ~* = ~ = 0).
In accordance with these improvements, this linking system is arranged to drive the second element 3 by one of the longitudinal extremities, that is, the left extremity in accord-ance with Figure 1. Although this system could be designed to use an Oldham or similar joint, it is preferable to design it using a transverse component connecting frame A to the second element 3 and offering, on the one hand, sufficient flexibi-lity in the transverse direction to permit conical movement of the second element 3 around point S and, on the other hand, offering practically zero flexibility in the circumferential direct~on.
In accordance with the preferred design method which is depicted in Figures 1 and 4, the abovementioned transverse component is an annular diaphragm 124 with concentric corruga-tions whose exterior edge is attached to frame A by means o~ a first rigid ring 125 and whose interior edge is attached to the second element 3 on one of the extreme transversal faces of the latter by means of a second rigid ring 126. Ring 125 may be axially blocked by flank Al against the exterior cage of bearing 25a by interposing an annular brace 127 and prevented --~ -- ~3 .
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from rotating by means of keys 128 inserted in exterior slots 129 ~Figure 4) of ring 125. As for ring 126, it can be attached to the second element 3 by means of screw 130 which also serves to attach annular ring 122. The operation of diaphragm 124 (or equivalent component) does not need any supplementary explana-tion. It is obvious that, with respect to the conical gears of the aforementioned patent application, it facilitates the con-struction of the transmission by freeing the central portion of the latter and by permitting the entire essentially cylindri-cal portion of support 13 to be constructed in one place.
In accordance with another aspect, the present improve-ments concern the shape of the rolling surfaces 8 and 9 of the first element 2 and rolling surfaces,l9 and 20 of the second element 3 and aim to provide surfaces of a nature such that a relatively small axial displacement performed by the hydraulic type maneuvering component will result in a relativel~ large axial displacement of contact points Pl and P2.
For this purpose, the two couples of these rolling surfaces have curved generatrices whose radii of curvature are comparable and are long with respect to the average distance of each surface from its axis of revolution 7 or 12. The ratio between these radii of curvature and this average distance is preferably between 10 and 100.
According to the method of construction shown in Figure 1, the generatrices of the two rolling surfaces 8 and 9 of one of the couples, that is, those of the first element 2, are concave in form whereas the generatrices of the two sur-faces 19 and 20 are convex in form~ In Figure 1, rl indicates the radius of curvature of one of the two generatrices of the surface 8 which are located within the plane of the fig-ure and r2 indicates the radius of curvature of one of the two generatrices of the surfa~e 19 which also is located within Il _ ~ _ ,;

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this plane, these two generatricec being tangent at point Pl.
Radius rl is slightly larger than radius r2 but is of the same order of magnitude.
It is easy to calculate (generally with the help of a computer) the radius of curvature rl and r2 as a function of the angle of inclination a so as to obtain the desired result.
The latter is a compromise between acceptable efficiency (related to the area of contact points or zones) and a large displace-ment of points Pl and P2 for a relatively small displacement of semi-sections 4 and 5 and, consequently, of rings 27 and 28.
Because of this, a variation of transmission ratio is obtained which is not only economical but practically without inertia.
Having explained the invention and its importance as justified by detailed examples, the applicant reserves exclu-sive rights to it for the duration of the patent without any limitations other than the terms of the following claims.

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Claims

1. A transmission device having a frame, a first ele-ment on a first axis fixed in the frame and having rolling sur-faces of revolution about said first axis, one such rolling sur-face on each side of a first plane perpendicular to said first axis at a point of axes intersection, a second element on a second axis intersecting the first axis at the point of axes inter-section and having concentric journal and rolling surfaces of revolution about the second axis, the rolling surfaces of the second element being disposed one on each side of a second plane passing through the point of axes intersection and perpendicular to the second axis, support means rotatable on the first axis and journalled with the journal surfaces of the second element for movement of the second element in a biconical path circum-ferentially of the first axis, the apex of such biconical path being coincident with said point of axes intersection, the re-spective rolling surfaces on the first and second elements being in rolling frictional engagement at two points of contact in a third plane containing the first and second axes and located one on each side of the first plane, the rolling surfaces of at least one of the first and second elements being defined by generatrices inclined oppositely with re-spect to the axis of revolution thereof and symmetrically with respect to the point of axes intersection, thereby to provide in the respective rolling surfaces of said first and second ele-ments a variable ratio of rolling surface radii at points of contact for variation in the spacing of the points of contact from the point of axes intersection, and means for forcing said respective rolling surfaces on said first and second elements into rolling friction engagement with each other at the two points of contact, characterized in that the rolling surfaces on one of the first and second elements being defined by a curved generatrix to be convex in longitudinal section and the rolling surfaces of the other of the elements being also defined by a curved generatrix to be concave in longitudinal section.

2. A transmission as defined by claim l characterized in that the respective convex and concave generatrices are arcs established by radii slightly different in length from each other and long relative to the average distance of each rolling sur-face from its axis of revolution.

3. A transmission as defined by claim 2 characterized in that the radius in lengths of said generatrices is approx-imately twenty times the length of said average distance.

4. A transmission as defined by any of claims 1-3 wherein said concave generatrix defines the rolling surfaces of said first element and wherein said convex generatrix defines the rolling surfaces of said second element.

5. A transmisison as defined by claim 1 characterized in that the second element is connected to the frame by a mechanical linkage preventing relative rotation of the second element and the frame but having flexibility in a radial direction to permit the mentioned conical motion of the second element about the first axis.

6. A transmission as defined by claim 5 characterized in that said mechanical linkage is an annular diaphragm having concentric corrugations.

7. A transmission as defined by claim 6 characterized in that the inner edge of said annular diaphragm is connected directly to the second element and the outer peripheral edge thereof being connected to the frame.