GB2063393A

GB2063393A - Freewheel unit for bicycles

Info

Publication number: GB2063393A
Application number: GB8036627A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-11-19
Filing date: 1980-11-14
Publication date: 1981-06-03
Also published as: ES254470U; IT7923170V0; FR2470289B3; ES254470Y; JPS5699130U; BE886165A; DE8030654U1; FR2470289A3

Abstract

A freewheel unit for a bicycle has an internal gear 1 with an even number of teeth 2 and two sprung pawls 5, 6 mounted diametrically opposed onto the freewheel inner body for simultaneous engagement with a pair of diametrically opposed teeth 2 of the gear 1. <IMAGE>

Description

SPECIFICATION Freewheel unit for bicycles The present invention relates to improvements in the freewheel units for bicycles.

As known, a bicycle freewheel unit is formed by two coaxial bodies, the inner body being mounted fixed to the hub of the bicycle rear wheel, for rotation therewith, and the outer body carrying a plurality of gearwheels for the bicycle transmission chain, as well as by ratchet gear means connecting said coaxial bodies for rotation only in the direction of rotation corresponding to the bicycle running direction. As also known, said ratchet gear means generally comprise an internal gear fixed to the outer body and a pair of spring pawls carried by the inner body and apt to engage with the teeth of the internal gearfor only one direction of relative rotation between the bodies and to freely slide thereon in the opposite direction.

In the freewheel units constructed up to date, the two pawls are mounted in diametrally opposed positions onto the inner body, and the internal gear is provided with an odd number of teeth, so that the engagement between the two coaxial bodies of the unit in the running direction is obtained only with one pawl at a time acting onto a tooth of the internal gear. The main purpose for this arrangement is to reduce the idle stroke having to be performed by the transmission (and thus by the pedal controlled by the cyclist) when passing from the position of disengagement to the running position.

In the freewheels of normal type, adopting steel crown gears, the aforedescribed arrangement provides no drawbacks from the point of view of the efficiency and of the life, though it gives rise to a certainly not properly balanced coupling between the two bodies forming the freewheels themselves.

Serious problems may instead arise, from the point of view of life and safety, in the event of adopting -- as recommended by the ever increasing requirements in the improvement of the product designed for cycling competitions -- light materials for the construction of the internal gear of the freewheel. In fact, these materials are less strong than steel and the stress produced onto the internal gear, only on one point thereof, by one of the transmission pawls - as in known technique -- may be exceedingly high and cause failures, which are evidently to be avoided with utmost care.

The problem of being able to adopt without any inconveniences, freewheels equipped with lighter crown gears -- without renouncing to safety and life - is now solved by the present invention, according to which the internal gear of a freewheel unit is a crown gear having an even number of teeth, and the two pawls are mounted diametrally opposed, so as to simultaneously both engage diametrally opposed teeth of the crown gear itself.

With this arrangement, the two pawls evidently work simultaneously and stress the crown gear of the freewheel in a far more balanced way than in known technique -- in two points, with a distribution of the stresses which may easily be absorbed, in fully safe conditions, even by materials having less satisfactory mechanical characteristics than steel, such as the light materials used in cycle constructions.

The invention will now be described in further detail hereinafter, with reference to the accompanying drawing which shows, by way of example, a cross section view of a preferred embodiment of the freewheel unit according to the invention itself.

The drawing shows a crown gear 1 with internal toothing 2 and a plurality of gearwheels 3 for the bicycle transmission chain (not shown) of the outer body of the freewheel unit according to the invention, as well as a portion of the inner body 4 of the same unit, equipped with pawls 5 and 6 apt to engage the teeth 2 of the crown gear 1 under the action of springs 7 and 8.

As can easily be seen on closely examining the drawing, the crown gear 1 has an even number of teeth 2, while the pawls 5 and 6 are mounted in diametrally opposed positions onto the body 4.

It can also be seen that, in these conditions, the pawls 5 and 6 are pressed by springs 7 and 8 into simultaneous engagement with two diametrally opposed teeth of the crown gear 1, the stresses on this latter thereby resulting very well balanced and distributed and hence well absorbed by the illustrated construction. In practice, the unitary stresses in correspondence of the engagement between the pawls and the crown gear are reduced to about half of the stresses normally existing in common freewheels, wherein a single pawl at a time is in engagement with the toothing of the crown gear, and it can therefore easily be understood why the material of the engaging parts may be chosen among those comprising the desired interesting properties -- as the lightness -- even if these have less strength than those normally used for such parts.

It should further be noted that the arrangement according to the invention allows to obtain a better distribution of the slacks between the balls interposed between the inner body and the outer body of the freewheel and a better distribution of the loads weighing thereon.

Moreover, by making the inside diameter of the crown gear 1 - and thus the circle of its toothing 2 - of reduced size compared to normal, one limits the increase of the idle stroke of the transmission (which the arrangement according to the invention is inclined to produce) at the moment in which it starts to work; from this point of view, therefore, no practical inconvenience arises in passing from the construction with single pawl of known technique, to the construction providing for two pawls into simultaneous engagement with the crown gear, according to the present invention.

Claims

1. Freewheel unit for bicycles, of the type formed by two coaxial bodies, the inner body being mounted fixed to the hub of the bicycle rear wheel, for rotation therewith, and the outer body carrying a plurality of gearwheels for the bicycle transmission chain, as well as by ratchet gear means connecting said coaxial bodies for rotation only in the direction of rotation corresponding to the bicycle running direction, characterized in that, said ratchet gear means comprise an internal gear fixed to the freewheel outer body having an even number of teeth and a pair of spring pawls mounted diametrally opposed onto the freewheel inner body for simultaneous engagement with two teeth, also diametrally opposed, of the said internal gear.

2. A freewheel unit for a bicycle, substantially as hereinbefore described with reference to the accompanying drawing.