GB2078880A

GB2078880A - Drive unit for a chain drive mechanism

Info

Publication number: GB2078880A
Application number: GB8117147A
Authority: GB
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1980-06-28
Filing date: 1981-06-04
Publication date: 1982-01-13
Also published as: IT8167889A0; DE8017422U1; FR2485672A1; IT8153394V0; JPS5743045A

Abstract

In a first embodiment (Figure 1) a chain retaining disk 44 is provided with fixing elements engaging fixing apertures of a drive sprocket 36c. In a second embodiment (Figure 5) the chain retaining disk 144 is dot-welded at 150 to the drive sprocket. The drive sprocket is mounted on a bicycle and damage to spokes 42 is prevented by the disk 44, 144. <IMAGE>

Description

SPECIFICATION Drive unit for a chain drive mechanism This invention relates to a drive unit for a chain drive mechanism, particularly for bicycles. A new kind of connection is provided between a drive sprocket and a chain retaining disk associated to said drive sprocket for preventing the respective chain to lose engagement with the drive sprocket and to block the drive unit and damage the spokes as a result thereof.

This new kind of connection is both economic and reliable.

According to German Patent 2535943 the drive sprocket and the chain retaining disk are manufactured from one integral piece of sheet metal by a punching and pressing operation. This method has been found to be rather difficult in practice particularly because working of the drive sprocket after the punching and pressing step is difficult. From German Offenlegungsschrift 29 15 181 it is known to fix the chain retaining disk to a spoke flange of the respective wheel of the bicycle. It has been found that also this method is not fully satisfactory because a replacement of spokes becomes difficult and also because the chain retaining disk is not fixed as rigidly as desired.

This invention relates to a drive unit for a chain drive mechanism, particularly for bicycles comprising at least one drive sprocket having a sprocket body with an axis, with a ring of chain teeth at the outer diameter thereof and with a first and second substantially axially directed side face and further comprising an annular chain retaining disk, said annular chain retaining disk having an outer diameter larger than the outer diameter of said drive sprocket and being maintained in co-axial position with respect to said drive sprocket, so as to have a predetermined axial distance from said first side face of said drive sprocket along a circle having a diameter equal to the outer diameter of said drive sprocket.

The drive unit of this invention can for example be used as a part of a free-wheel unit of a rear wheel of a bicycle or as a part of a food-pedal unit of a bicycle.

The chain retaining disk is to prevent the respective chain form losing engagement with the teeth of the sprocket or to prevent the chain from coming into collision with the spokes of a respective rear wheel when the chain has once come out of engagement with the teeth of the sprocket. It is to be noted that a loss of the engagement between the chain and the sprocket could result in blocking the rear wheel of the bicycle or in damage to the spokes of the rear wheel.

The need for a chain retaining disk exists particularly in connection with a multi-stage chain drive mechanism in which the chain is to be transfered for various speeds between a plurality of drive sprockets. In this case there is a considerable risk that the chain on such a change of speed is axially moved beyond a terminal one of a plurality of drive sprockets. Therefore the chain retaining ring is particularly associated to a terminal drive sprocket in cases in which a plurality of co-axial drive sprockets is provided.

It is an object of this invention to provide an improved connection between the drive sprocket and the annular chain retaining disk such that both the stability of mechanical connection is improved on the one hand and the drive sprocket can be worked separately from the chain retaining disk on the other hand.

These objects are attained in accordance with this invention in that said annular chain retaining disk is made as a member separate from said chain sprocket and is fixed to the body of said chain sprocket.

In view of facilitating the mounting of the chain retaining disk onto the drive sprocket on the one hand and obtaining a desired distance between the chain retaining disk and the drive sprocket at the outer diameter of said drive sprocket on the other hand, it is proposed that said chain retaining disk comprises a radially inner portion fixed to said drive sprocket and a radially outer portion having said desired axial distance from said first side face of said drive sprocket.

According to one embodiment of the invention the annular chain retaining disk is welded, preferably dot-welded, to the body of the drive sprocket.

According to a preferred embodiment, the annular chain retaining disk is provided with fixing elements integral therewith, said fixing elements being engaged with fixing apertures of said drive sprocket distributed on said drive sprocket along a circle having a diameter smaller than said outer diameter of said drive sprocket. In this embodiment the fixing elements may be engaged with said fixing apertures by a snapping action so as to achieve a most economic way of mounting.

The fixing elements may be defined by radially inwardly directed tongues punched out from said securing disk, the radially inner ends of said tongues being shaped for engagement with said fixing apertures.

A most rigid mounting is obtainable when the radially inner ends of said tongues are shaped as hooks, said hooks having a substantially axially directed portion for engagement with a radially outer edge of the respective fixing aperture and a substantially radially outwardly directed terminal portion engaging said second side face of said drive sprocket.

Additional rigidity in connection between the chain retaining disk and the drive sprocket may be obtained by providing a radially inner supporting portion on said chain retaining disk, said supporting portion extending radially inward of said fixing apertures and engaging with said first side face of said drive sprocket. In view of maximum rigidity of the connection between said chain retaining disk and said drive sprocket, said supporting portion may be applied with axial pressure against said first side face of said drive sprocket, said axial pressure being maintained by said fixing elements.

A particular advantage of this invention lies in the fact that chain sprockets are usually provided with apertures in view of weight reduction. These usual apertures may fulfil the function of said fixing apertures. So the drive unit may have a conventional design and it is only necessary to provide the chain retaining disk with said fixing elements for engagement with the usual apertures provided in the drive sprocket. As a result thereof it is also possible to provide the chain retaining disk after the drive unit has already been in use.

In view of preventing the respective chain to lose engagement with the teeth of the drive sprocket the above mentioned predetermined axial distance is preferably smaller than the axial width of the respective chain. This is however not a necessary feature. The chain retaining disk may fulfil a certain protective function even if the above mentioned axial distance is larger than the axial width ofthe respective chain. In this latter case the chain, though it may come out of engagement with the teeth of the respective drive sprocket, is prevented from blocking the bicycle wheel and from destroying the spokes of the bicycle wheel.

If the chain retaining disk is to be mounted to the drive sprocket by a welding operation, particularly by dot-welding, the chain retaining disk is preferably made of a weldable sheet metal.

In cases in which the chain retaining disk is attached to the drive sprocket by mechanical fixing elements, the chain retaining disk may be made both of sheet metal and of plastic material. In cases in which the chain retaining disk is mounted by a snapping action, plastic made chain retaining disks are prefered due to their higher elastic deformabiiity.

For a better understanding of the invention reference may be made of the following detailed description of exemplary embodiments, in which: Figure 1 shows a free-wheel unit of a rear wheel of a bicycle with a first embodiment of a drive unit according to this invention; Figure 2 shows an elevational view of a part of the chain retaining disk of the drive unit of Figure 1; Figure 3 shows a sectional view of the chain retaining disk according to line Ill-Ill of Figure 2; Figure 4 shows an elevational view of the largest sprocket ofthe drive unit of Figure 1 and Figure 5 shows a free-wheel unit of a rearwheel of a bicycle with a second embodiment of the drive unit of this invention.

In Figure 1 the rearwheel of a bicycle is generally designated by 10. This rear wheel comprises a free-wheel unit 12. The free-wheel unit 12 comprises a hub axis 14 and a hub sleeve 16. The hub sleeve 16 is provided with terminal bearing members 18 and 20. The bearing members 18 and 20 are rotatably mounted on the hub axis by bearing balls 22 and 24.

On the bearing member 20 there is rotatably mounted a drive unit 26 by balls 28 and 30. The drive unit 26 comprises a driving sleeve 32. A rachet mechanism 34 is provided between the bearing member 20 and the driving sleeve 32. On the driving sleeve 32 there is fixed a plurality of drive sprockets 36a to 36e. The drive sprockets 36a to 36e are mounted onto the driving sleeve 32 for common rotation therewith.

The bearing member 18 is shaped with a spoke flange 18a which is connected to spokes 38. The bearing member 20 carries a spoke flange 40 which is connected to spokes 42. A chain retaining disk 44 is attached to the drive sprocket 36e.

As can be seen from Figure 3 and 4 the drive sprocket 36e is provided with a ring of chain teeth 36e1. A usual bicycle chain 46 is in engagement with the teeth 36e1. The drive sprocket 36e further comprises a first axially directed side face 36e2 and a second axially directed side face 36e3. The drive sprocket 36e is provided with a plurality of apertureses 36e4.

The chain retaining disk 44 is shown more detailed in Figure 3. This chain retaining disk comprises a radial outer portion 44a and a radial inner portion 44b. The radially inner portion 44b is attached to the drive sprocket 36e. The radial outer portion 44a has an axial distance A from the side face 36e2 of the drive sprocket 36e. The axial distance A is smaller than the axial width B of the drive chain 46. So the drive chain 46 can't enter into the gap between the radially outer portion 44a and the drive sprocket 36e.

As can be seen from Figure 2 and 3 there are provided radially inward directed tongues 44c in the radial inner portion 44b of the chain retaining disk 44. These tongues 44c are made by punching or molding. At their radial inner ends the tongues 44c are provided with an axially directed portion 44d and with a radially outward directed portion 44e. The axially directed portion 44d is in engagement with a radially outward edge 36e5 of an aperture 36e4. The terminal portion 44e is in engagement with the side face 36e3 of the drive sprocket 36e. The terminal portion 44e of the tongue 44c is provided with a chamfered face 44f. The radial inner portion 44b is further provided with radially inwardly directed segments 449 which are in contact with the side face 36e2 under axial pressure, said axial pressure being maintained by the tongues 44c.

It is easily to be understood that the chain retaining disk 44 can be easily mounted onto the drive sprocket 36e. It is only necessary to bring the chamfered faces 44e in contact with the radially outer edges 36e5 of the apertures 36e4 and to apply axial pressure onto the radially outer portion 44a of the chain retaining disk 44. The tongues 44c are then deflected in clockwise direction as seen in Figure 3 so thatthetermilial portion 44fcan pass through the aperture 36e4.

In the embodiment as shown in Figure 5 a chain retaining disk 144 is fixed to the drive sprocket 136e by dot-welding as indicated at 150.

The outer diameter of the chain retaining disk exceeds the outer diameter of the drive sprocket 36e by at least 20 mm.

Although the invention has been described as - illustrated herein by reference to specific embody ments thereof, it will be understood that many modifications and variations of such embodiments may be made without departing from the inventive concepts disclosed.

It isto be noted that the reference numerals in the claims are only used for better understanding and are not to be understood as being restrictive.

Claims

1. In a drive unit for a chain drive mechanism, particularly for bicycles, comprising at least one drive sprocket (36e) having a sprocket body with an axis, with a ring of chain teeth (36e,) at the outer diameter thereof and with a first and a second substantially axially directed side face (36e2, 36e3) and an annular chain retaining disk (44), said annular chain retaining disk (44) having an outer diameter larger than the outer diameter of said drive sprocket (36e) and being maintained in co-axial position with respect to said drive sprocket (36e), so as to have a predetermined axial distance (A) from said first side face (36e2) of said drive sprocket (36e) along a circle having a diameter equal to the outer diameter of said drive sprocket (36e), the improvement comprising that said annular chain retaining disk (44) is made as a member separate from said drive sprocket (36e) and is fixed to the body of said drive sprocket (36e).

2. A drive unit as set forth in claim 1, wherein said chain retaining disk (44) comprises a radially inner portion (44b) fixed to said drive sprocket (36e) and a radially outer portion (44a) having said predetermined axial distance (A) from said first side face (36e2) of said drive sprocket (36e).

3. A drive unit as set forth in claim 1, wherein said annular chain retaining disk (144) is dot-welded to the body of said drive sprocket (136e).

4. A drive unit as set forth in claim 1, wherein said annular chain retaining disk (44) is provided with fixing elements (44c, 44d, 44e) integral therewith, said fixing elements being engaged with fixing apertures (36e4) of said drive sprocket (36e) distributed on said drive sprocket (36e) along a circle having a diameter smaller than said outer diameter of said drive sprocket (36e).

5. A drive unit as set forth in claim 4, wherein said fixing elements (44c, 44d, 44e) are engaged with said fixing apertures (36e4) by a snapping action.

6. A drive unit as set forth in claim 4, wherein said fixing elements are defined by radially inwardly directed tongues (44c) the radial inner ends (44d, 44e) of said tongues (44c) being shaped for engagement with said fixing apertures (36e4).

7. A drive unit as set forth in claim 6, wherein the radially inner ends of said tongues are shaped as hooks (44d, 44e), said hooks having a substantially axially directed portion (44d) for engagement with a radially outer edge (36e5) of the respective fixing aperture (36e4) and a substantially radially outwardly directed terminal portion (44e) engaging said second side face (36e3) of said drive sprocket (36e).

8. A drive unit as set forth in claim 6, wherein said annular chain retaining disk (44) has a radially inner supporting portion (449) extending radially inward of said fixing apertures (36e4) and engaging with said first side face (36e2) of said drive sprocket (36e).

9. A drive unit as set forth in claim 8, wherein said radially inner supporting portion is applied with axial pressure against said first side face (36e2) of said drive sprocket (36e), said axial pressure being maintained by said fixing elements (44c, 44d, 44e).

10. A drive unit as set forth in claim 4, wherein said fixing apertures (36e4) of said drive sprocket (36e) are established by usual apertures provided for weight reduction of said drive sprocket (36e).

11. A drive unit as set forth in claim 1, wherein said predetermined axial distance (A) is smaller than the axial width (B) of the respective chain (46).

12. A drive unit as set forth in claim 1, wherein said chain retaining disk (44) is made of sheet metal.

13. A drive unit as set forth in claim 4, wherein said annular chain retaining disk (44) is made of plastic material.

14. A drive unit for a chain drive mechanism, substantially as described herein with reference to the accompanying drawings.