GB2157613A - Moulding synthetic plastics wheels - Google Patents

Abstract

The synthetic plastics wheel consists of a rim (1), several spokes (2) and a hub (not shown) and is produced in one piece by injection-moulding from the hub. Between each two adjacent spokes (2) the rim possesses a wall part (6) extending in the rim circumferential direction which extends from the attachment point (5) of each spoke to the rim to the centre (IV-IV) of the rim section between the two spokes. The wall part (6) is of greater cross section than the outer rim walls (3,4) so that the plastics material flows more rapidly from the two spoke attachment points (5) to the middle of wall part (6) than do the two circumferential currents of synthetic plastics material advancing in the remaining rim walls (3,4). The material in wall part (6) then flows radially into rim walls (3,4) which prevents the two circumferential currents in the rim walls (3,4) meeting in the rim section centre with formation of a cold flow seam which would considerably reduce the strength of the rim at the rim section centre. <IMAGE>

Description

SPECIFICATION Synthetic plastics wheel for cycles and the like or for automobiles The invention relates to a synthetic plastics wheel as tyred road wheel for cycles and the like or as jacketed steering wheel for automobiles, consisting of a rim with approximately U-shaped cross-section and of spokes formed integrally on the rim by injection from the wheel hub.

In general a wheel of synthetic plastics material, in its production by injection in a moulding tool, by reason of its geometrical configuration and in order to achieve optimum substance properties, must be injected centrally at the wheel hub, from which the synthetic plastics material flows in the moulding tool to the wheel rim. In the similar production of a wheel, consisting of rim, spokes and hub, as a solid synthetic plastics wheel however, after the flow of the synthetic plastics material in the moulding tool through the spokes, disadvantages arise on the rim caused by the flow-seam formation approximately at the middle of the rim section between each two adjacent spokes.This flow seam formation, especially when glass-fibrereinforced synthetic plastics material is used, leads to a considerable reduction of the strength and impact toughness and also of the appearance of the rim at the above-mentioned centres of the rim sections. Attempts have been made to avoid these disadvantageous flow seam formations in the rim profile of a spoked wheel of synthetic plastics material by a multiple injection of the wheel at the rim. However the wheels produced according to this method display a strong tendency to distortion by reason of different pressure and shrinkage conditions in the moulding tool. In addition the flow seam formation occurs in the hub region of the wheel, whereby the problems of cold flow seams on the synthetic plastics hub, which takes up the wheel bearing and is subjected to heavy stresses, lead to an especially critical reduction of strength.

Now the invention has found that in the production of a synthetic plastics wheel, consisting of rim, spokes and wheel hub, by injection from the wheel hub the above-described flow problems and disadvantageous flow seam formations in the rim profile can be avoided in that between each two adjacent spokes the rim comprises a wall part extending in each case in the rim circumferential direction from the point of attachment of each spoke to the rim, to the middle of the rim section between the two spokes, which wall part is formed rheologically as preliminary flow cross-section in such a way that in this wall part the synthetic plastics material flows more quickly from the spoke attachment point to the centre of the rim section than in the other rim walls. Thus the following is achieved.

Without the wall part according to the invention the synthetic plastics material flowing into the rim through a spoke is distributed at the spoke attachment point over the rim cross-section and it flows in the rim walls with a front progressing relatively uniformly in the rim circumferential direction, and with simultaneous cooling to the middle of the rim section between two adjacent spokes, where the synthetic plastics material meets with the circumferential flow arriving in the same manner from an adjacent spoke through the rim walls, forming a flow seam between the two circumferential flows with reduced strength and impact toughness.With the wallpart formed and acting according to the invention rheologically as preliminary flow cross-section on the other hand in this wall part, by reason of its greater volume compared with the remainder of the rim walls and by reason of the consequently more slowly occurring cooling and solidification of the synthetic plastics material therein from the exterior inwards a more intensive and more rapid preliminary flow of the synthetic material occurs in the rim circumferential direction, which precedes the circumferential flow in the other rim walls and reaches the middle of the rim section between two adjacent spokes earlier.At the rim section middle the preliminary flow meets the preliminary flow arriving in the same way from the adjacent spoke with simultaneous pressure build-up in the preliminary flow cross- sections, so that the two preliminary flows, before the circumferential flows in the other rim walls can meet at the rim section middle, in distribution over the entire circumference of the rim section begin the inflow into the other rim walls extending partly in axial and partly in radial direction of the wheel. In this way the shaping of the rim section over its circumferential length is regularised in place and time and the disadvantageous cold flow seam formation at the middle of the rim section is avoided.Tests have shown that a synthetic plastics wheel which has been formed and produced with the rim wall parts in accordance with the invention displays a considerably higher strength of the rim than does a wheel which had been formed and produced without these rim wall parts.

The rim wall part formed and acting in accordance with the invention as preliminary flow crosssection can consist for example of a cross- sectional thickening of bead or rib form protruding from the base of the profile of the U-shaped rim on the inner side of the rim, which thickening extends in the rim circumferential direction over the rimexternal attachment points of the spokes to the remaining rim walls.In the case of this form of configuration the wall part itself, according to a further feature of the invention, can at the same time be formed so that two annular grooves for the reception of the flanks of a tyre are formed between it and the profile sides of the rim, and the distance between the sides of the wall part from the two profile sides and the radial height of the wall part are so dimensioned that the tyre flanks are applied by the wall part against the profile sides in contacting manner in every case in insertion into the annular grooves, that is even in the case where offsetting of centres occurs between rim and tyre.

This formation of the rim in accordance with the invention has the further great advantage that the wheel is especially suitable even for the use of a tubeless tyre, because after fitting the tyre is brought into such good and adequately airtight abutment with the profile sides of the rim that it can easily be pumped up even with a hand pump, as for example with an ordinary cycle pump, and does not after fitting first have to be expanded and presses outwards by rapid introduction of large quantities of air in such a way that it begins to apply itself in sealing manner to the profile sides of the rim.

The invention will be explained in greater detail hereinafter by reference to the drawing, in which various examples of embodiment are illustrated and wherein; Figure 1 shows a part of the synthetic plastics wheel in axial lateral view; Figures 2 to 4 show an example of embodiment in different radial cross-sections along the lines Il-Il to IV-IV in Figure 1; Figure 5 shows another example of embodiment in a radial cross- section; Figure 6 shows a further example of embodiment in radial cross- section, in special development for a tubeless tyre.

The synthetic plastics wheel consists of a rim 1 of approximately U-shaped cross-section, several spokes 2 integrally formed on the rim and a wheel hub (not shown further), from which the synthetic plastics wheel is injected in the production in a moulding tool. The rim profile comprises, as ordinary relatively thin-walled rim walls, two profile sides 3 and a profile base 4 to which the spokes 2 are attached at attachment points 5.On each rim section between two adjacent spokes the rim 1 has a wall part which, starting from the attachment point 5 of each spoke 2, extends in the rim circumferential direction as far as the middle of the rim section between two spokes and is formed rheologically as preliminary flow cross-section of larger volume compared with the flow cross-section of the remaining rim walls 3 and 4, in such a way that the synthetic plastics material which flows out of the spokes 2 into the rim profile at the spoke attachment points 5 flows more rapidly in this wall part from the spoke attachment point to the middle of the rim section than in the remaining rim walls 3 and 4.This wall part is formed in a preferred and rheologically favourable manner on the profile base 4 of the rim profile and in the example of embodiment as illustrated in Figures 1 to 4 consists of a rim flange 6 projecting on the outside of the rim and attached with its ends to the spokes. The flange 6, which can have a radial cross-sectional height desired for an additional rim stiffening, is made so large in cross-sectional dimensions, preferably with a greater cross-sectional width than the remaining rim walls 3 and 4, that the flange 6 forms a through- flow passage of large volume for the synthetic plastics material, in which therefore a slower cooling and solidification of the synthetic plastics material takes place from the moulding tool wall to the core of the cross-section than in the remaining rim walls 3 and 4.Thus in the flange 6, starting from the attachment points of two adjacent spokes 2, a rheological preliminary flow current of synthetic plastics material is established to the middle of the rim section, which in forward flow and'or after reaching the middle of the rim section, commences on the entire circumferential length of the rim section with inflow into the rim profile base 4 and with radial inflow into the rim profile sides 3, before the two circumferential currents of synthetic plastics material, advancing from the spoke attachment points 5 in the rim walls 3 and 4, reach the middle of the rim section between two adjacent spokes 2. This prevents cold flow seam formation of the synthetic plastics material at the middle of the rim section.In order to promote the forward flow of synthetic plastics material in the flange 6 towards the middle of the rim section, the flange can preferable be formed so that at its circumferential edge merging into the remaining rim walls 3 and 4 it possesses a cross-sectional width 7 reducing from the rim section middle to the spokes or spoke attachment points 6, as shown by Figures 2 to 4 of the example of embodiment dS illustrated. Thus in the vicinity of the spokes the emergence of synthetic plastics material from the flange 6 into the remaining rim wails 3 and 4 is constricted and braked and a still more dinstinct rheological forward flow is effected in the flange 6 towards the middle of the rim section.

In addition to or in place of the rim flange 6 on the exterior of the rim, the rim can also be formed, according to the example of ernbodiment in Figure 5, with a cross-sectional thickening 8 projecting in bead or rib form from the profile base 4 on the interior of the rim as rheological preliminary flow cross-section. The cross-sectionai thickening 8 of large volume extends in the circumferential direction of the rim in annular form over all the spoke attachment points 5 and merges laterally into the profile base 4 with cross-sections 9 having a constricting effect.The synthetic plastics material entering the rim profile at a spoke attachment point 5 is divided into a circumferential flow in the rim walls 3 and 4 and a preliminary flow current in the cross-sectional thickening E, from which synthetic plastics material, in part distributed over the wheel circumference, flows through the cross-sections 9 axially and radially into the rim walls 3 and 4, but predominantly synthetic plastics material flows forward from two adjacent spokes to the rim section middle and after meeting at the rim section middle flows in the rim walls 3 and 4 contrarily of the circumferential currents in order thus to prevent the occurrence of a cold flow seam between the two circumferential currents at the middle of the rim section.

In the example of embodiment according to Figure 6 a wall part 10 projecting from the profile base 4 is provided on the interior of the rim and can be formed with such an effective throughflow cross-section for a material throughflow in the rim circumferential direction that analogously with the cross-sectional thickening 8 in the example of embodiment according to Figure 5 it acts as a rheological preliminary flow passage of large volume, or can equally consist of a material-saving rib arrangement which supplements the rheological preliminary flow effect of a rim flange 6 arranged on the exterior of the rim, after the style of the example of embodiment in Figures 1 to 4.The wall part 10 of the example of embodiment of Figure 6 is so formed, as speciality, that two annular grooves for the reception of the flanks 11 of a tyre are formed between it and the two profile sides 3 of the rim.

The distance of the sides of the wall part 10 from the two profile sides 3, that is to say the axial clear internal width of the two annulur grooves, is so dimensioned that the two tyre flanks 11, after insertion into the annular grooves, are applied by the wall part 10 in contacting manner against the two profile sides 3. Furthermore the radial height of the wall part 10 is dimensioned so that the two tyre flanks 11 engage in the annular grooves and are brought to abut with the profile sides 3 by the wall part 10 even if the tyre is fitted with an offsetting of centres between rim and tyre, which can occur due to the difference, usual for example in cycle tyres, between the internal diameter of the tyre flanks 10 and the diameter of the rim profile base 4.Thus the example of embodiment according to Figure 6 renders it possible to use on the wheel rim even a tubeless tyre which is already pressed in fitting by the wall part 10 against the profile sides 3 of the rim in such a way that the escape of pumped-in air does not occur or at least is limited so much that the tyre can be pumped up and filled with a normal hand pump.The formation of a rim with a wall part 10 after the style of the example of embodiment according to Figure 6 as described above is suitable for the use of tubed tyres without tube or special tubeless tyres with equal advantage and also for other wheels the rime of which are for example not connected by spokes with the wheel hur or rims of which are not produced integrally with the spokes from synthetic plastics material and are attached airtightly in suitable manner at the spoke attachment points.

The invention is not limited to a synthetic plastics wheel for use as tyred road wheel for example for cycles, but is suitable and usable with the described advantageous effect equally for synthetic plastics wheels for other purposes, where the described problem of strength reduction due to cold flow seam formation in the rim must be mastered, as for example equally in synthetic plastics spoked wheels for use as steering wheel for automobiles, where the synthetic plastics wheel replaces the metal steering wheel core of spoked wheel type usual hitherto as steering wheel skeleton and is enveloped at least at the rim ring with an ordinary steering wheel jacket of tyre type, the steering wheel ring, similarly to the example of embodiment of the invention as illustrated, expediantly having a radially outwardly open U-shaped crosssection in order that the steering wheel ring may be formed and produced in a thin-walled and synthetic plastics material-saving manner and nonetheless with high static stability.

Claims (6)

1. Synthetic plastics wheel as tyred road wheel for cycles and the like or jacketed steering wheel for automobiles, consisting of a rim with approximately U-shaped cross-section and with spokes integrally formed on the rim by injection-moulding from the wheel hub, characterised in that the rim (1) comprises between each two adjacent spokes (2) a wall part (6, 8, 10) extending in the rim circumferential direction from the attachment point (5) of each spoke to the rim as far as the middle of the rim section between the two spokes, which wall part is formed rheologically as preliminary flow cross-section in such a way that the synthetic plastics material in this wall part flows more rapidly from the spoke attachment point to the middle of the rim section than in the other rim walls (3, 4).

2. Synthetic plastics wheel according to Claim 1, characterised in that the wall part consists of a rim flange (6) protruding at the exterior of the rim and attached with its ends to the spokes (2), and the rim flange preferably possesses at its circumferential edge merging into the remaining rim walls a cross-sectional width (7) diminishing from the middle of the rim section to the spokes.

3. Synthetic plastics wheel according to Claim 1, characterised in that the wall part consists of a cross-sectional thickening (8) of bead or rib form projecting on the interior of the rim from the profile base (4) of the U-shaped rim, which thickening extends in the rim circumferential direction over the attachment points (5), on tfle exterior of the rim, of the spokes to the remaining rim walls (3, 4).

4. Synthetic plastics wheel according to one of Claims 1 to 3, characterised in that the wall part, formed rheologically as preliminary flow cross-section, or a rim wall part extending additionally thereto in the rim circumferential direction, protrudes on the rim interior from the profile base (4) of the U-shaped rim in such a way that two annular grooves for the reception of the flanks (11) of a tyre are formed between the wall part (10) and the two profile sides (3) of the rim, and further in that the distance between the sides of the wall part (10) and the two profile sides (3) and the radial height of the wall part are of such dimensions that the tyre flanks (11) are applied in contacting manner by the wall part (10) against the profile sides (3) in insertion into the annular grooves, with or without offsetting of centres between rim and tyre.

5. A synthetic plastics wheel substantially as hereinbefore described with reference to, and as shown in, Figs 1 to 4, Fig 5 or Fig 6 of the accompanying drawings.

6. A method of injection-moulding a spoked wheel of plastics material including the step of designing the rim section rheologically and in accordance with the description hereinabove.