APPARATUS FOR CHANGING SPEED BETWEEN TWO PARALLEL SHAFTS

TECHNICAL FIELD

The present invention relates to an apparatus for changing speed between two parallel shafts. Though the invention was designed specifically for bicycle application, the teachings of the present invention apply to any device that involves changing speed between parallel shafts. BACKGROUND ART

As is known, most marketed bicycles shift gears by shifting the chain between a number of coaxial pinions of different diameters.

Often, however, this means not all the links in the chain are in the same plane, thus impairing operation.

Moreover, in currently marketed bicycles, shifting the chain from one pinion to another is a delicate operation, in which normal load is not advised.

DISCLOSURE OF INVENTION In the apparatus according to the invention, motion is transmitted by a flexible member, which may be a chain or belt.

Gear shifting is achieved by directly altering the circumference of one or both of the pinions engaged by the flexible member.

The transmission described herein enables the chain (or belt) to operate in the best possible conditions, i.e. with all the links in the same plane. Moreover,

gear shifting is smoother and more continuous, with the chain fully engaging the pinions at all times, and no change in normal load is required.

Among other improvements , the apparatus according to the present invention also makes unseating of the moving chain highly unlikely.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a first configuration of bicycle application of an apparatus for changing speed between two parallel shafts in accordance with the present invention; Figure 2 shows a second configuration of the Figure 1 apparatus;

Figures 3A and 3B show two configurations of parts of a speed-change device forming part of the Figure 1 and 2 apparatus; Figure 4A shows a first configuration of parts of the Figure 3A and 3B speed-change device;

Figure 4B shows a second configuration of the Figure 3A parts;

Figure 5 shows a view in perspective of a cog, in accordance with the invention, which meshes with a drive chain;

Figures 6 and 7 show further parts of the speed- change device forming part of the Figure 1 and 2

apparatus .

BEST MODE FOR CARRYING OUT THE INVENTION As shown in Figures 1 and 2, an apparatus 1000 comprises a speed-change device 100*, such as a rear- wheel pinion, and a front device 100**, such as a pedal pinion, with a chain tensioner in between.

The speed-change device 100 will now be described in detail with reference to Figures 3A, 3B, 4A, 4B, 5, 6, 7. Devices 100* and 100** are identical to device 100.

Device 100 comprises a substantially circular first plate 10 fixed to a hub (MZ) (Figures 3A, 3B) with an axis of rotation (X) ; and hub (MZ) in turn has a shaft 251 fixed to the bicycle frame. As shown in Figures 3A, 3B, a first group of guide slots HA, HB, lie and a second group of guide slots 12A, 12B, 12C are formed in plate 10.

Guide slots 11A, HB, HC have complex profiles. Guide slots HA and HB are roughly arc-shaped and located on one side of axis of rotation (X) , while guide slot HC is roughly in the form of a line segment and located on the opposite side of axis of rotation (X) .

Likewise, guide slots 12A, 12B, 12C have complex profiles. Guide slots 12A and 12B are roughly arc-shaped and located on one side of axis of rotation (X) , while guide slot 12C is roughly in the form of a line segment and located on the opposite side of axis of rotation

(X) -

The first group is associated with an arc-shaped first flexible strap (BNLl) fitted with a number of cogs 13, one of which is shown in detail in Figure 5.

Likewise, the second group is associated with an arc-shaped second flexible strap (BNL2) fixed with a number of cogs 14 (Figure 3A) .

Cogs 14 are identical to cogs 13. In the embodiment shown in the drawings, flexible strap (BNLl) is longer than flexible strap (BNL2); the two arc-shaped flexible straps (BNLl) , (BNL2) together define a complete circle (as shown, for example, in Figure 3B) ; and cogs 13 are located outwards of cogs 14, and slide on cogs 14 when changing velocity ratio.

The arc described by flexible strap (BNLl) is always centred about a point along axis of rotation (X) ; whereas strap (BNL2), which, as stated, is also arc- shaped, is centred about a variable point, but still close to axis of rotation (X) .

As shown in Figures 3A and 3B, flexible strap (BNLl) fitted with cogs 13 is fitted with three pins 15A, 15B, 15C, each of which slides in a respective guide slot HA, HB, HC.

More specifically, pins 15A and 15B are fixed to the two ends of flexible strap (BNLl) , while pin 15C is fixed to a point roughly halfway along strap (BNLl) .

As shown in the fully distended configuration of flexible straps (BNLl), (BNL2) in Figure 3B, flexible strap (BNL2) is also fitted with three pins 16A, 16B,

16C .

Pins 16A and 16B are fixed to the two ends of flexible strap (BNL2) , while pin 16C is fixed to a point roughly halfway along strap (BNL2) . As shown in the Figure 3B configuration, two cogs 13 and 14 are only superimposed close to pins 15A, 16A on one side, and close to pins 15B, 16B on the other.

The velocity ratio is changed by simply switching from one diameter (Dl) (radius (Rl)) of a first circle (CRl) containing the tips of cogs 13, 14 (Figure 3A), to a diameter (D2) (radius (R2)) of a second circle (CR2) containing the tips of cogs 13 , 14 in another configuration (Figure 3B) .

An important aspect of the present invention lies in having designed innovative cam means by which to convert user pulling action on a Bowden cable (see below) to translation of pins 15A, 15B, 15C and 16A,

15B, 16C as required to achieve the diameter (D) of circle (CR) and the velocity ratio desired by the user. By virtue of the cam means employed in the present invention, pins 15A, 15B, 15C and 16A, 15B, 16C all diverge or converge simultaneously from or towards axis of rotation (X) when changing gear.

Divergence or convergence of the pins is permitted by rotation of a first member 20 and a second member 30, as shown in Figures 4A and 4B.

At each gear change, members 20 and 30 rotate by the same angle and at the same speed, but in opposite

directions .

First member 20 has three guide slots 21A, 21B, 21C engaged, in use, by respective pins 15A, 15C, 16B (Figures 4A, 4B) . Likewise, second member 30 has three guide slots 31A, 31B, 31C, in which respective pins 16A, 16C, 15B slide in use.

Guide slots 21A, 21B, 21C and 31A, 31B, 31C intersect with guide slots HA, HB, HC and 12A, 12B, 12C in plate 10, and the six pins 15A, 15B, 15C and 16A, 16B, 16C are located at the points of intersection.

As they rotate, members 20 and 30 move the points of intersection between the twelve guide slots HA, HB, HC, 12A, 12B, 12C, 21A, 21B, 21C, 31A, 31B, 31C, thus moving the six pins 15A, 15B, 15C, 16A, 16B, 16C.

Moreover, members 20, 30 and plate 10 are designed so that the two flexible straps (BNLl), (BNL2) together assume a circular shape for each velocity ratio.

Members 20 and 30 are also rotated by a third member 40 shown in Figure 6.

Translation of third member 40 translates pins 41 and 42 shown in Figures 4A, 4B and 6 and connected rigidly to the third member.

Pin 41 is connected to a guide slot of first member 20, and pin 42 is connected to a guide slot of second member 30.

Translation of third member 40 is permitted by pins 43A, 43B, 43C, connected rigidly to the third member,

sliding along respective guide slots 51A, 51B, 51C formed in a fourth member 50 shown in Figure 7.

Fourth member 50 is connected rigidly to hub (MZ) and by four spacers 52A, 52B, 52C, 52D to plate 10 (Figure 7) .

The system formed by plate 10 and members 20, 30, 40 and 50 convert linear displacement in a two-way direction (Fl) (Figure 7) into a variation of circle (CR) defined by the tips of cogs 13, 14. The conversion of linear displacement of third member 40 (in two-way direction (Fl) ) into a variation of diameter (D) of circle (CR) may therefore be said to be an important characteristic of the present invention.

The forces required to move member 40 are provided by a metal wire 60 for pull, and by a spring 61 (wound about a rod 61A) for the opposite effect (Figure 7) .

Apparatus 1000 may also comprise the chain tensioner shown in Figures 1 and 2.

The advantages of the apparatus according to the present invention are as follows:

- because the flexible transmission member operates in one plane only, motion can also be transmitted by a belt;

- by eliminating passage of a chain from one pinion to another, the chain can be subjected to normal loads at all times; the velocity ratio is changed by directly altering the circumference of one or both of the pinions

engaged by the flexible member (chain or belt) ;

- the transmission described enables the chain (or belt) to operate in the best possible conditions, i.e. with all the links in the same plane; moreover, gear shifting is smoother and more continuous (as compared with ordinary transmissions), with the chain fully engaging the pinions at all times; and

- the apparatus according to the present invention also makes unseating of the moving . chain highly unlikely.