GB2025542A - Gear wheel assemblies - Google Patents

Abstract

A free wheel, such as a sprocket gear wheel assembly for a chain driven bicycle, comprises two surface recessed annular parts 14, 15 disposed so that the recesses define tracks 17 which are opposed to each other to form a race with a sprocket gear wheel 18 located between the annular parts. The sprocket gear wheel has a recessed inner wall 19 in the recesses 20 of which are located rolling elements such as balls 21. The balls also locate in the race formed by the tracks 17. The recesses 20 in the inner wall 19 have radially deeper and shallower parts into which the balls 21 can enter so as to disengage or engage the gear wheel 18 with annular parts 14, 15 via the balls 21 depending respectively on whether the gear wheel 18 is driven in one direction or the other. <IMAGE>

Description

SPECIFICATION Gear wheel assembies This invention relates to gear wheel assemblies.

Known gear wheel assemblies, having a free-wheel mode, for use with pedal cycles have two pawls cooperating with a ratchet wheel, and, during free-wheeling, the pawls ratchet over the teeth of the ratchet wheel, causing considerable noise. Also, in such constructions, the two pawls are one half tooth out of pitch with each other so that only one pawl at a time is drivingly associated with the ratchet. This arrangement reduces the amount of relative movement between the pawls and the ratchet wheel when changing from freewheel to drive, and vice-versa, as compared with an arrangement in which there is a single pawl cooperable with the ratchet wheel to obtain drive.

The present invention is concerned with the matter of providing a free-wheel operating with less noise whilst having multiple points of driving contact.

According to this invention a gear wheel assembly comprises opposed first and second members between which is located a gear wheel having an aperture therethrough defining an inner wall, a plurality of recesses in the inner wall, rolling members respectively engaged in the recesses and engaging opposed tracks on the first and second members which together form a race each recess having a radially deeper part and a radially shallower part and each rolling member being movable between the deeper and shallower parts of the respective recess, the arrangement being such that, on rotation of the gear wheel in one sense the rolling members are at the deeper parts of the recesses and the gear wheel is free of the first and second members and on rotation of the gear wheel in the opposite sense the rolling members are at the shallows parts of the recesses and are engaged between the opposed tracks and a drive connection is formed between the gear wheel and the first and second members.

According to a preferred embodiment a gear wheel assembly comprises an externally threaded annular mount member, a gear wheel having a central aperture defining an inner wall and through which aperture the mount member extends, a plurality of angularly spaced similarly shaped recesses in said wall, first and second parts engaged on the mount member and on opposite sides of the gear wheel, the first and second parts providing opposed annular surfaces which are partcircular in cross-section, a plurality of ball bearings respectively located in the recesses and engageable by the part-circular surfaces, each recess having a radially deeper part and a radially shallower part, each ball being movable between the deeper and shallower parts of the respective recess, the arrangement being such that on rotation of the gear wheel in one sense relative to the mount member the balls are at the deeper parts of the recesses and the gear wheel is free of the mount member and the first and second parts, and on rotation of the gearwheel in the opposite sense the balls are at the shallower parts of the recesses and are engaged between the part-circular surfaces to form a drive connection between the gear wheel and the mount member.

The mount member may have a threaded bore.

Preferably the radial depth of each recess increases steadily between the narrower and deeper parts.

The invention may be performed in various ways and one specific embodiment will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is an exploded perspective view of a gear wheel assembly according to the invention; and Figure 2 is a diametral section through a modified gear wheel assembly generally similar to that of Fig. 1.

Referring to Fig. 1 a gear wheel assembly 10 comprises a central tubular mount member 11 which is screw-threaded in its inner surface 1 2 and also on its outer surface 1 3.

Two generally similarly shaped annular parts 14, 1 5 have screw-threaded bores 1 6 and are engaged on the outer surface 1 3 of the mount member. The parts provide opposed annular surfaces or tracks 1 7 which are approximately semi-circular in cross-section and together form a race.

Between the parts 14, 1 5 is located a sprocket wheel 1 8 having a central bore providing an inner wall 1 9. Formed in the wall 1 9 are a plurality of equi-spaced similarly shaped recesses 20. Each recess 20 has a radially deeper part 20a and a radially shallower part 20b connected by a straight portion 20c. A plurality of spherical ball bearings 21, corresponding in number to the number of the recesses 20, are engaged between the tracks 1 7 and extend into the respective recesses 20.

One end of the mount member 11 is formed with opposed slots 22 for engagement by a holding tool. The outer faces of the parts 14, 1 5 are formed with angularly spaced peripheral recesses 23 providing angularly spaced radial shoulders for engagement by a holding or turning tool to assist in assembling the parts.

In use, for example in a pedal bicycle or tricycle, the threads 1 2 of the mount member are received on a threaded shaft coaxial with a wheel and a drive chain extends round the sprocket 1 8 and around a further sprocket mounted for rotation with the pedals.

When the pedals are turned in a direction to rotate the sprocket 1 8 in clockwise direction in relation to the parts 11, 14, 1 5 (as indicated by the arrow) the sprocket 1 8 drives the parts 14, 15 because the balls 21 are located adjacent the shallower ends of the recesses and are thereby forced against the tracks 17.

When the pedals are operated to turn the sprockets 1 8 in an anti-clockwise direction the balls 21 move to the deeper ends of the respective recesses and the increased depth of the recesses causes the balls to disconnect the drive. The assembly thus operates as a free wheel.

Clearly the free-wheel assembly could be used other than in a pedal cycle.

The number of recesses 20 and balls 21 need not be six, as shown, but could be another number.

In Fig. 2 the tracks 1 7 have an approximately -41-circular section which is contacted by the balls 21 and an section 40 which is not contacted by the balls.

It will be appreciated that with the described arrangements no pawls and ratchets are involved so that, during free-wheeling, there is no noise caused by pawls ratchetting over ratchet teeth. In the freewheel assembly described, a plurality of driving elements, constituted by the ball bearings, are located in their respective recesses at all times. When changing from free-wheel to drive or viceversa, there is only a small relative angular movement between the sprocket and the parts 14, 1 5. Drives takes place at six points represented by the six balls.

Claims (4)

1. A gear wheel assembly comprising opposed first and second members 14, 1 5 between which is located a gear wheel 18, having an aperture therethrough defining an inner wall 19, a plurality of recesses 20, in the inner wall, rolling members 21 respectively engaged in the recesses and engaging opposed tracks 1 7 on the first and second members which together form a race, each recess 20, having a radially deeper part 20a and a radially shallower part 206 each rolling member being movable between the deeper and shallower parts of the respective recess; the arrangement being such that, on rotation of the gear wheel in one sense the rolling members are at the deeper parts of the recesses and the gear wheel is free of the first and second members; and on rotation of the gear wheel in the opposite sense the rolling members are at the shallower parts of the recesses and are engaged between the opposed tracks and a drive connection is formed between the gear wheel and the first and second member.

2. A gear wheel assembly comprising an externally threaded annular mount member 11, a gear wheel 1 8 having a central aperture defining an inner wall 1 9 and through which aperture the mount member extends, a plurality of angularly spaced similarly shaped recesses 20 in said wall, first and second parts 14, 1 5 engaged on the mount member and on opposite sides of the gear wheel, the first and second parts providing opposed annular surfaces 1 7 which are part-circular in crosssection, a plurality of ball bearings 21 respectively located in the recesses 20 and engagable by the part-circular surfaces, each recess having a radially deeper part 20cand a radially shallower part 20b and each ball being movable between the deeper and shallower parts of the respective recess; the arrangement being such that on rotation of the gear wheel in one sense relative to the mount member the balls are at the deeper parts of the recesses and the gear wheel is free of the mount member and the first and second parts, and on rotation of the gearwheel in the opposite sense the balls are at the shallower parts of the recesses and are engaged between the part-circular surfaces to form a drive connection between the gear wheel and the mount member.

3. A gear wheel assembly as claimed in claim 1 or 2 in which the gear wheel is a sprocket.

4. A gear wheel assembly substantially as hereinbefore described with reference to the Fig. 1 of the accompanying drawing or as modified by Fig. 2.