WO1999043539A1

WO1999043539A1 - Variable ratio drive system

Info

Publication number: WO1999043539A1
Application number: PCT/CA1999/000170
Authority: WO
Inventors: John Allard
Original assignee: John Allard
Priority date: 1998-02-25
Filing date: 1999-02-25
Publication date: 1999-09-02
Also published as: CA2230426A1; AU3242199A

Abstract

A variable ratio drive system (10) including a variable diameter sprocket (12) and a sprocket diameter changing mechanism (14) is described herein. The variable diameter sprocket (12) includes sprocket portions (26) so mounted in radial channels (28) of a circular support as to be radially movable therein. The sprocket portions (26) include a pin (46) that may be inserted in apertures (44) of the channels (28). The diameter changing mechanism (14) includes first (72) and second (74) angled abutting portions configured and sized to first move the sprocket portions (26) laterally, then move them radially before allowing them to be reinserted in a new position to cause the diameter modification.

Description

TITLE OF THE INVENTION

VARIABLE RATIO DRIVE SYSTEM

FIELD OF THE INVENTION

The present invention relates to drive systems. More particularly, the present invention relates to a drive system including a variable diameter sprocket.

BACKGROUND OF THE INVENTION

Variable diameter sprockets are well known in the art.

For example, each of United States patents numbers 4,030,373; 4,832,660; 5,041,061 ; 5,013,284; 5,094,653; and 5,104,357, all naming Hamlin Leonard as an inventor, describes variable speed drive systems for bicycles provided with variable diameter pulleys. By modifying the diameter of the variable diameter pulley, the ratio of the front to rear pulleys is modified.

The systems described by Leonard do not use a conventional bicycle chain but instead use a flexible driving means under the form of a V-belt. The different mechanisms described by Leonard have the same common drawback that the diameter changing mechanisms provided to modify the diameter of the pulley are generally complex. The use of a V-belt is also a drawback since it must be tensioned to prevent it from slipping. It is also to be noted that adverse temperature conditions, such as rain, may nevertheless cause the V-belt to slip in the pulleys.

OBJECTS OF THE INVENTION

An object of the present invention is therefore to provide an improved variable ratio drive system.

It is also an object of the present invention to provide a variable ratio drive system provided with an improved sprocket diameter changing mechanism.

SUMMARY OF THE INVENTION

More specifically according to an embodiment of the present invention, there is provided a variable diameter drive system including: a variable diameter sprocket including: a support provided with at least three radial channels each provided with at least two apertures; at least three sprocket portions, each being so mounted to a respective radial channel of the support as to be radially movable therein; each of the three sprocket portions including a projection configured and sized to enter one of the two apertures; and a biasing assembly biasing the projection towards the two apertures; and a sprocket diameter changing mechanism including: a fixed portion; and a movable portion so mounted to the fixed portion as to be linearly movable; the movable portion including first and second angled abutting element configured, positioned and sized to sequentially, for each of the three sprocket portions, a) pull the projection from one of the apertures, b) reposition the sprocket portion so that the projection is generally positioned over another of the two apertures and c) replace the projection in another of the two apertures.

According to another aspect of the present invention, there is provided a a transmission system to be mounted between a driving shaft and a driven shaft; the transmission system comprising: a support bracket; first variable diameter sprocket to be mounted to the driving shaft and including: a first support provided with at least three radial channels each provided with at least two apertures; at least three sprocket portions, each being so mounted to a respective radial channel of the support as to be radially movable therein; each of the three sprocket portions including a projection configured and sized to enter one of the two apertures; and a biasing assembly biasing the projection towards the two apertures; first sprocket diameter changing mechanism including: a first fixed portion mounted to the support bracket; and a first movable portion so mounted to the first fixed portion as to be linearly movable; the first movable portion including first and second angled abutting element configured, positioned and sized to sequentially, for each of the three sprocket portions, a) pull the projection from one of the apertures, b) reposition the sprocket portion so that the projection is generally positioned over another of the two apertures and c) replace the projection in another of the two apertures; second variable diameter sprocket to be mounted to the driven shaft and including: a second support provided with at least three radial channels each provided with at least two apertures; at least three sprocket portions, each being so mounted to a respective radial channel of the support as to be radially movable therein; each of the three sprocket portions including a projection configured and sized to enter one of the two apertures; and a second biasing assembly biasing the projection towards the two apertures; second sprocket diameter changing mechanism including: a second fixed portion mounted to the support bracket; and a second movable portion so mounted to the second fixed portion as to be linearly movable; the second movable portion including first and second angled abutting element configured, positioned and sized to sequentially, for each of the three sprocket portions, a) pull the projection from one of the apertures, b) reposition the sprocket portion so that the projection is generally positioned over another of the two apertures and c) replace the projection in another of the two apertures; an interconnecting mechanism configured and sized to interconnect the first and second movable portions of the first and second sprocket diameter changing mechanisms; wherein the first and second movable portions of the first and second sprocket diameter changing mechanisms are so positioned that a) their simultaneous movement in a first predetermined direction cause the diameter of the first variable diameter sprocket to increase while causing the diameter of the second variable diameter sprocket to decrease and b) their simultaneous movement in a second predetermined direction, opposite the first predetermined direction, cause the diameter of the second variable diameter sprocket to increase while causing the diameter of the first variable diameter sprocket to decrease.

Other objects, advantages and features of the present invention will become more apparent upon reading of the following non restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings: Figure 1 is a front elevational view of a variable ratio drive system according to an embodiment of the present invention;

Figure 2 is a rear elevational view of the variable diameter sprocket of the variable ratio drive system of Figure 1 ;

Figure 3 is a sectional view taken along line 3-3 of Figure 1;

Figure 4 is a schematic view illustrating the operation of the sprocket diameter changing mechanism;

Figure 5 is a sectional side elevational view of a variable ratio drive system according to a second embodiment of the present invention where the variable diameter sprockets rotate in a clockwise direction; and

Figure 6 is a sectional side elevational view of the variable ratio drive system of Figure 5 where the variable diameter sprockets rotate in a counterclockwise direction.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to Figures 1-3 of the appended drawings, a variable ration drive system 10 according to an embodiment of the present invention will be described. The system 10 generally includes a variable diameter sprocket 12, to which a conventional bicycle chain 13 (shown in dashed lines in Figure 1), is engaged, and a sprocket diameter changing mechanism 14.

The variable diameter sprocket 12, better seen from Figure 2, is configured and sized to be mounted to a conventional shaft 15 of a bicycle via a mounting sleeve 17. The variable diameter sprocket 12 is provided with a support 16 including a central portion 18, a peripheral portion 20 and six (6) radial branches 22a-22f extending from the central portion to the peripheral portion in a symmetrical manner. The branches 22a-22f are defined by identical cutouts 24a-24f. The variable drive sprocket 12 also includes six (6) identical sprocket portions 26a-26f each mounted to a respective branch 22a-22f of the support 16.

For concision purposes and since the variable diameter sprocket 12 is symmetrical, only branch 22a and its respective sprocket portion 26a will be described in greater details hereinbelow.

Branch 22a includes a radial channel 28a and five (5) radially aligned circular apertures 30, 32, 34, 36 and 38 provided in the radial channel 28a.

The sprocket portion 26a includes a dented portion 40 configured and sized to engage the conventional bicycle chain 13, a channel engaging portion 42, better seen in Figure 3, integrally formed with the dented portion 40 and provided with an internally threaded aperture 44. An externally threaded pin 46, provided with a pan head 47 is mounted in the aperture 44. The distal end of the pin 46 defines a projection that is configured and sized to enter any of the apertures 30- 38. Finally, the sprocket portion 26a includes a biasing element, under the form of a spring 48, having a proximate end fixedly mounted to the shaft 15 and a distal end slidably mounted to an aperture 50 in the pin 46. The spring 48 biasing the pin 46 towards the apertures 30-38.

The variable diameter sprocket 12 therefore includes a biasing assembly comprising six individual springs 48. Of course, this biasing assembly could be replaced by any other assembly used to bias the pins 46 towards the apertures 30-38. It is also to be noted that the proximate end of the springs 48 could be mounted to the mounting sleeve 17.

The width of the channel engaging portion 42 is slightly smaller than the width of the channel 28a allowing the sprocket portion 26a to be radially and laterally moved therein. As will be easily understood by one skilled in the art, when a sufficient lateral movement of the sprocket portion 26a is obtained, the pin 46 will egress the aperture in which it is inserted (aperture 32 in Figures 1-3) and radial movement of the sprocket portion 26a in the channel 28a will be possible.

The force applied by the spring 48 (see arrow 52 in Figure 3) maintains the pin 46 in one of the apertures 30-38 unless an opposite external force is applied to the sprocket portion 26a, as will be described hereinafter.

Turning now more specifically to Figure 3 of the appended drawings, the sprocket diameter changing mechanism 14 will be described. This mechanism 14 includes a fixed assembly 54 mounted to the bicycle and a movable assembly 56 so mounted to the fixed assembly 54 as to be longitudinally movable (see double-arrow 58).

The fixed assembly 54 includes a generally L-shaped bracket 60, a plate 62 and a fastener 64, both used to mount the bracket

60 to the bicycle. The L-shaped bracket 60 includes a longitudinal slot 66 to which the movable assembly 56 may be mounted as described hereinbelow.

The movable assembly 56 includes a support 68 slidably mounted to the slot 66 via a fastener 69. A sleeve 70, two friction reducing elements 71a, 71b and a washer 71c are used to secure the support 68 to the bracket 60 while allowing longitudinal displacement of the support 68.

The movable assembly 56 also includes a first angled abutting element 72 and a second angled abutting element 74, both fixedly mounted to the support 68 via fasteners (not shown). As will be described hereinafter in greater details, the first angled abutting element 72 has the function of selectively reducing the diameter of the variable diameter sprocket 12 while the second angled abutting element 74 has the function of selectively increasing the diameter of the variable diameter sprocket 12.

The first and second angled abutting elements 72 and

74 respectively include bevels 76, 78 having angles similar to the angle of the pan head 47 of the pin 46. The pin passage 73, defined by the shortest distance between the first and second angled abutting elements 72 and 74, is slightly larger than the width of the pin 46, therefore allowing 10

the pin to thread in the pin passage 73 when the pin 46 is correctly positioned for the desired diameter of the variable diameter sprocket 12.

Of course, as will be easily understood by one skilled in the art upon reading the following description of the operation of the sprocket diameter changing mechanism 14, the sprocket diameter changing mechanism 14 also includes means (not shown), fixedly mounted to the fixed assembly 54 or to the bicycle to move the movable assembly 56 (see double arrow 58) upon user's control, as will be described hereinbelow.

Turning now to Figure 4 of the appended drawings, the operation of the variable diameter sprocket 12 will now be described.

It is to be noted that, in Figure 4, branch 22a is illustrated twice in different positions as the support 16 is rotated (see arrow 80). More specifically, Figure 4 illustrates the sprocket portion 26a as it is moved from the second aperture 32 of the channel 28a to the third aperture 34 of the same channel, causing an increase of the diameter of the variable diameter sprocket 12.

To cause the radial and lateral movements of the sprocket portion 26a, the assembly 56 of the sprocket diameter changing mechanism 14 is moved outwardly (see arrow 82) to place the pin passage 73 above the desired aperture of the support 16, in the example of Figure 4, the aperture 34.

This movement of the movable assembly 56 places the second angled abutting element 74 in the path of the pin 46 of the 11

sprocket portion 26a since the pin 46 is inserted in the second aperture 32 of the arm 22a.

Therefore, since the pin 46 rotates with the support 16, the head 47 will contact the bevel 78 of the second angled abutting element 74 since it is now in its path.

The physical relationship between the configuration of the second angled abutting element 74 and the head 47 of the pin 46 is such that this contact will gradually laterally move the pin 46, therefore the sprocket portion 26a, so that the pin 46 egress the aperture 32. The angle of the abutting element 74 will then radially move the sprocket portion 26a inside its channel 28a.

When the position of the variable diameter sprocket 12 is such that the head 47 no longer contacts the abutting element 74, i.e. when the pin 46 is aligned with and exits the pin passage 73, the sprocket portion 26a is then moved back laterally by the spring 48, causing the pin 46 to enter the aperture 34, completing the displacement of the sprocket portion 26a.

Of course, as will be easily understood by one skilled in the art, upon a full rotation of the variable diameter sprocket 12, the six sprocket portions 26a-26f will be moved from the aperture 32 to the aperture 34 of their respective channels 28a-28f.

It is to be noted that the sprocket portions are moved laterally and radially while they are not engaged with the chain 13. 12

It is also to be noted that if the sprocket portions 26a-26f were to be moved so as to reduce the diameter of the variable diameter sprocket 12, for example from the aperture 34 to the aperture 32, the first angled abutting element 72 would be the element contacting the head 47 of the sprocket portions in a similar fashion to lift, move and finally release the sprocket portions.

As will be easily understood by one skilled in the art, the controls (not shown) to be manipulated by the user should be provided with a mechanism (not shown) that ensure that the position of the pin passage 73 is such that it always corresponds to the position of one of the apertures 30-38.

It is believed within the skills of one skilled in the art to design a similar variable diameter sprocket where the sprocket portions would be only movable radially in their respective channel and where the pin 46 would not be fixedly mounted to the sprocket portions but would be slidably inserted therein to provide the lateral movement.

It is to be noted that even though the variable diameter sprocket 12 has been illustrated and described as having six (6) sprocket portions, this number has been given as an example and should not be used to limit the scope of the present invention. Similarly, the number of apertures in each channel could be other than five (5).

It is to be noted that while the variable ratio drive system 10 is illustrated and described in Figures 1-3 herein as replacing the front sprocket of a bicycle drive system, it would be within the reach of one skilled in the art to use the general principles of the present invention to 13

design a rear sprocket cluster replacement for bicycle. Similarly, virtually any sprocket clusters could be designed according to the general principles of the present invention.

Turning to Figures 5 and 6 of the present invention, a transmission system 100, including two variable diameter sprockets 102 and 104 interconnected by a conventional bicycle chain 106 (shown in dashed lines), two sprocket diameter changing mechanisms 108 and 110 and an interconnecting mechanism 117 interconnecting both mechanism 108 and 110, will be briefly described.

The transmission 100 includes an enclosure 113 and a support bracket 115 mounted to the enclosure 113.

It is to be noted that, since the variable diameter sprockets 102 and 104 are identical to the sprocket 12 described hereinabove with respect to Figures 1-4, these sprockets 102 and 104 will not be described in details herein. However, it is to be noted that the shaft 114, to which the sprocket 102 is mounted, is a driving shaft, i.e. that power is transferred to the transmission 100 from an external power source via the shaft 114. Conversely, the shaft 116 to which the sprocket 104 is mounted is a driven shaft, i.e. that power is transferred from the transmission 100 to an external system via the shaft 116.

The sprocket diameter changing mechanism 108 is identical to the mechanism 14 described hereinabove. On the other hand, the angled abutting elements of the sprocket diameter changing mechanism 110 are inverted since the sprocket portions must be radially moved during their downward movement. 14

The fixed portions of both mechanisms 108 and 110 are mounted to the support bracket 115.

The movable portions 109 and 111, respectively of the mechanisms 108 and 110, are interconnected via a rigid bar 112, of the interconnecting mechanism 117, that is so mounted to the support bracket 115 via a guiding tube 118 as to longitudinally slide therein.

The interconnecting mechanism 117 also includes a bar moving mechanism 120 mounted to the support bracket 115 and connected to the bar 112 to longitudinally move the bar 112.

The bar moving mechanism 120 includes a pulling element 122 going through a guiding tube 124 before being connected to a lateral projection 126 of the bar 112. A compression spring 128 is provided between the tube 124 and the element 126, therefore biasing the bar 112 in the direction of arrow 130. A flexible non-stretchable wire 132 is connected to the pulling element 122 and exits the enclosure 113 via an aperture 134. The unseen end of the wire 132 is connected to an actuator (not shown) used to selectively move the bar 112 to change the gear ratio of the transmission 100.

As will be easily understood by one skilled in the art, the controls (not shown) to be manipulated by the user should be provided with a mechanism (not shown) that ensure that the position of the pin passages of the movable portions 109 and 111 are such that they always corresponds to the position of one of the apertures of the sprockets 102 and 104. 15

As will be easily understood by one of ordinary skills in the art, since the sprockets 102 and 104 are identical and since their respective diameter changing mechanisms 108 and 110 are so connected that when the diameter of one of the sprockets increases the diameter of the other sprocket decreases, a conventional chain 106 having a predetermined length may be used.

However, the configuration of the transmission 100 is such that when the diameters of the sprockets is changed via the mechanisms 108 and 110, the sprocket that increases in diameter does so before the decrease in diameter of the other sprocket allows an adequate slack of the chain. A longer chain is therefore used and a chain tensioning mechanism 136 is mounted to the support bracket 115.

The chain tensioning mechanism 136 includes a biased telescopic assembly 138 having first and second ends respectively provided with sprockets 140 and 142. The sprockets 140 and 142 are engaged to the chain 106 and the biased telescopic assembly 138, via its compression spring 144, ensures that the chain 106 is properly tensioned. The assembly 138 is slidably mounted to the support bracket 115 via a guide tube 146.

When the rotation direction of the sprockets 102 and 104 is reversed, as illustrated in Figure 6, the chain tensioning mechanism 136 automatically slides in the guide tube 146 to thereby ensure proper chain tension.

The operation of the transmission 100 is quite similar to the operation of the single variable diameter sprocket described 16

hereinabove with respect to Figures 1 to 4. The main difference is that the two variable diameter sprockets 102 and 104 will move simultaneously to provide an increase gear ratio range.

As will be easily understood by one skilled in the art, the diameter of the variable diameter sprockets 102 and 104 may only be changed when the sprockets rotate clockwise as shown in Figure 5. However, it is believed within the reach of one skilled in the art to modify the first and second angled abutting elements so that they are symmetrical with respect to an imaginary axis (not shown) going through the center of the bar 112 to thereby allow the diameter of the sprockets to be changed notwithstanding the rotation direction of the sprockets.

Of course, as will be apparent to one skilled in the art, the transmission 100 described hereinabove is schematic and could be modified according to the particular application for which it is designed.

Transmissions according to the present invention could be used, as non-limitating examples, on bicycles, electric vehicles, motorcycles and conveyors.

Although the present invention has been described hereinabove by way of preferred embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.

Claims

17WHAT IS CLAIMED IS:

1. A variable diameter drive system including: a variable diameter sprocket including: a support provided with at least three radial channels each provided with at least two apertures; at least three sprocket portions, each being so mounted to a respective radial channel of said support as to be radially movable therein; each of said at least three sprocket portions including a projection configured and sized to enter one of said at least two apertures; and a biasing assembly biasing said projection towards said at least two apertures; and a sprocket diameter changing mechanism including: a fixed portion; and a movable portion so mounted to said fixed portion as to be linearly movable; said movable portion including first and second angled abutting element configured, positioned and sized to sequentially, for each of said at least three sprocket portions, a) pull said projection from one of said apertures, b) reposition said sprocket portion so that said projection is generally positioned over another of said at least two apertures and c) replace said projection in another of said at least two apertures.

2. A variable diameter drive system as recited in claim 1, wherein said projection of each said at least three sprocket portions is defined by a pin mounted in an aperture of said sprocket portion. 18

3. A variable diameter drive system as recited in claim 2, wherein said pin in externally threaded and wherein said aperture of said sprocket portion includes corresponding internal threads; whereby, when said projection is pulled from on of said aperture of said radial channel, said sprocket portion is pulled.

4. A variable diameter drive system as recited in claim 2, wherein said pin includes a pan head having a predetermined angle and wherein each said first and second angled abutting elements includes a bevel generally corresponding to said angle of said pan head; whereby, a) when said pan head contacts one of said first and second angled abutting element, said pin is pulled away from said apertures of said channel and b) when said pin is pulled, it follows said angle of said one of said angled abutting element to thereby be radially moved.

5. A variable diameter drive system as recited in claim 4, wherein a distance between said first and second angled abutting elements defines a pin passage, whereby when said pin is pulled and follows said angle of said one of said angled abutting element, it is replaced in another of said at least two apertures when said pin exits said pin passage.

6. A variable diameter drive system as recited in claim 1 , wherein said biasing assembly includes at least three springs each mounted between said support and a respective sprocket portion.

7. A variable diameter drive system as recited in claim 1 , wherein said support generally defines a wheel provided with a central portion, a peripheral portion and at least three radial branches extending 19

from said central portion to said peripheral portion in a symmetrical manner.

8. A variable diameter drive system as recited in claim 1 , wherein: said at least three radial channels include six radial channels; said at least three sprocket portions include six sprocket portions; and said at least two apertures of each said six radial channels include five apertures.

9. A transmission system to be mounted between a driving shaft and a driven shaft; said transmission system comprising: a support bracket; first variable diameter sprocket to be mounted to the driving shaft and including: a first support provided with at least three radial channels each provided with at least two apertures; at least three sprocket portions, each being so mounted to a respective radial channel of said support as to be radially movable therein; each of said at least three sprocket portions including a projection configured and sized to enter one of said at least two apertures; and a biasing assembly biasing said projection towards said at least two apertures; first sprocket diameter changing mechanism including: a first fixed portion mounted to said support bracket; and 20

a first movable portion so mounted to said first fixed portion as to be linearly movable; said first movable portion including first and second angled abutting element configured, positioned and sized to sequentially, for each of said at least three sprocket portions, a) pull said projection from one of said apertures, b) reposition said sprocket portion so that said projection is generally positioned over another of said at least two apertures and c) replace said projection in another of said at least two apertures; second variable diameter sprocket to be mounted to the driven shaft and including: a second support provided with at least three radial channels each provided with at least two apertures; at least three sprocket portions, each being so mounted to a respective radial channel of said support as to be radially movable therein; each of said at least three sprocket portions including a projection configured and sized to enter one of said at least two apertures; and a second biasing assembly biasing said projection towards said at least two apertures; second sprocket diameter changing mechanism including: a second fixed portion mounted to said support bracket; and a second movable portion so mounted to said second fixed portion as to be linearly movable; said second movable portion including first and second angled abutting element configured, positioned and sized to sequentially, for each of said at least three sprocket 21

portions, a) pull said projection from one of said apertures, b) reposition said sprocket portion so that said projection is generally positioned over another of said at least two apertures and c) replace said projection in another of said at least two apertures; an interconnecting mechanism configured and sized to interconnect said first and second movable portions of said first and second sprocket diameter changing mechanisms; wherein said first and second movable portions of said first and second sprocket diameter changing mechanisms are so positioned that a) their simultaneous movement in a first predetermined direction cause the diameter of said first variable diameter sprocket to increase while causing the diameter of said second variable diameter sprocket to decrease and b) their simultaneous movement in a second predetermined direction, opposite said first predetermined direction, cause the diameter of said second variable diameter sprocket to increase while causing the diameter of said first variable diameter sprocket to decrease.

10. A transmission system as recited in claim 10, wherein said interconnecting mechanism includes a rigid bar interconnecting said first and second movable portions of said first and second sprocket diameter changing mechanisms, and a bar moving mechanism mounted between said support bracket and said rigid bar to selectively move said rigid bar.