GB2045700A - Improvements in or relating to vehicle wheels and to methods and apparatus for their construction - Google Patents

Abstract

Fiber-reinforced composite vehicle wheels and methods and apparatus for their construction are described in which the wheel comprises a disc portion having reinforcing fibers in substantially random orientation disposed predominantly in planes perpendicular to the wheel axis, and a rim portion having directional first reinforcing fibers substantially parallel to each other and oriented circumferentially of or substantially parallel to the wheel axis, or both, and second reinforcing fibers which are substantially randomly oriented circumferentially of the wheel axis. The methods include formation of separate rim and disc charges from sheet molding plastics resin compound and compression molding of the charges to form an integral composite rim and disc structure of essentially homogeneous resin reinforced by the fibers. Apparatus for molding the wheels features radially movable rim mold sections and axially reciprocable disc mold sections all having mold surface contours for forming a molded composite wheel of desired configuration. <IMAGE>

Description

SPECIFICATION Improvements in or relating to vehicle wheels and to methods and apparatus for their construction The present invention relates to vehicle wheels and to methods and apparatus for their construction.

According to one feature of the present invention a composite wheel of fiber-reinforced resin comprises a disc portion in which reinforcing fibers comprise random fibers, and a rim portion in which reinforcing fibers include first fibers oriented substantially randomly of the wheel axis and second fibers oriented in preselected directions with respect to the wheel axis.

According to another feature of the present invention a method of compression molding a fiber reinforced composite rim for a vehicle wheel comprises the steps of providing a mold having radially reciprocable first mold sections and axially reciprocable second mold sections with all of said mold sections co-operating to form a cavity for compression molding of a wheel rim including bead retaining flanges, forming a rim mold charge comprising a hoop of fiberreinforced resin sheet molding compound, and, with all said mold sections open, placing said rim charge hoop within said mold and then closing said mold sections under heat and pressure, opening said mold sections, and removing said rim.

According to a further feature of the present invention a method of constructing a vehicle wheel consisting of integral rim and disc portions comprises the steps of coiling a first sheet section of fiber reinforced plastics resin construction to form a rim charge hoop consisting of at least one coil ply, placing said rim charge hoop in a mold, placing a separate disc charge into said mold within said rim charge hoop, said disc charge comprising at least one second sheet section of fiber-reinforced plastics resin construction, compression molding said rim and disc charges to form an integral fiber-reinforced composite wheel, and removing said wheel from said mold.

According to yet another feature of the present invention a compression mold for forming a resin vehicle wheel comprises rim mold sections radially reciprocable with respect to a mold axis and disc mold sections for forming a mold cavity, in which said disc mold sections are both adapted to reciprocate axially and substantially simultaneously between closed positions for forming said cavity and open positions spaced from said cavity.

As used in this description and in the claims appended thereto the terms "composite wheel" and "fiber-reinforced composite wheel" are to be understood as referring to a wheel construction of fiber-reinforced plastics resin.

By utilizing the present invention it is possible to provide a vehicle wheel which has the strength and durability of conventional steel wheels but which is lighter in weight and yet economical to manufacture.

The present invention can provide a method of molding fiber-reinforced composite wheels which can minimize flow and knit line formation during the molding process, particularly in the rim flange area and around wheel disc discontinuities such as bolt and hand holes.

The invention will be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of a process for providing one type of raw fiber-reinforced plastics resin sheet molding compound utilized in carrying out various embodiments of the present invention, Figures 2 to 4 collectively illustrate presently preferred method steps for providing a fiberreinforced composite wheel in accordance with the invention Figure 5 is a fragmentary front elevational views of one wheel embodiment as molded in accordance with the steps of Figs. 2 to 4, Figures 6 and 7 are fragmentary side section and rear views of the wheel of Fig. 5 taken along the respective section lines 6-6 in Fig. 5 and 7-7 of Fig. 6, Figure 8 is a fragmentary front elevational view of a finished wheel in accordance with one embodiment of the invention, Figures 9 and 10 are fragmentary side section and rear views of the wheel of Fig. 8 taken along the respective lines 9-9 of Fig. 8 and 10-10 of Fig. 9 Figures 11 to 1 7 are schematic drawings illustrating various constructions of the rim charge for molding fiber-reinforced composite wheels in accordance with the invention, Figure 18 is a schematic illustration similar to that of Fig. 1 illustrating another process for providing sheet molding compound for use in carrying out various embodiments of the invention, Figure 19 is a fragmentary sectional view similar to a portion of Fig. 7 and illustrating a modification to the wheel of Figs. 5 to 10, and Figures 20 to 23 illustrate another embodiment of a wheel in accordance with the invention and respectively substantially correspond to Figs. 5, 6, 8 and 9 previously described.

In general, the present invention contemplates a fiber-reinforced molded resin wheel and method of construction wherein the wheel rim and disc portions are formed from respective separate mold charges of sheet molding compound. The separately formed charges are molded into an integral composite rim and disc structure of essentially homogeneous resin reinforced by the fibers. The disc charge preferably comprises a stack of precut sheet sections. The reinforcing fibers in the disc charge and in the final disc wheel portion are in substantially random orientation essentially in planes perpendicular to the wheel axis with each such plane corresponding to a layer of reinforcing fibers in the starting sections of sheet molding compound.

The rim charge preferably comprises one or more lengths of precut sheet molding compound coiled to form a spiral or hoop having at least one layer.The sheet layers in the rim charge loop are referred to herein as spiral plies. Preferably, the reinforcing fibers in the rim charge hoop and in the final rim wheel portion include at least first fibers oriented substantially randomly of the rim circumference and second directional fibers in one or more selected orientations with respect to the wheel axis and circumference. In various specific embodiments to be described, the directional fibers are oriented in parallel axially or circumferentially of the wheel axis. In other embodiments, the directional fibers are in a double helical array forming an X-like pattern transverse to the wheel rim.

By way of background, a process line for providing one type of raw fiber-reinforced plastics resin sheet molding compound or stock utilized in carrying out the invention is illustrated in Fig.

1. A thermosetting resin paste 10 is metered as by a doctor blade or dam 1 2 onto a continuous sheet 14 of polyethylene film as the latter is drawn onto an endless belt conveyor 1 6. Paste 10 may include an unsaturated polyester, vinyl ester or epoxy resin, a thickener such as a Group II oxide or hydroxide, catalysts such as organic peroxides or hardeners, inert fillers such as CaCO3 or clay, and a mold release agent such as zinc stearate. At a first stage 18, continuous fiber filaments or strands 20 are pulled over a roller 22 and chopped by a multiple knife roll arbor 23 to form fibers 24 which fall by gravity onto the paste layer 25 in a substantially random pattern essentially in the plane of the resin layer surface.The random fiber orientation accomplished at process stage 1 8 is illustrated in plan view schematically at 26. Preferably, the strands 20 are drawn from the inside of a fiber ball or roll (not shown) to promote random twisting of the fibers 24 in the resin layer. Reinforcing fibers 24 may be glass, aramid, carbon or graphite. Glass fibers, specifically E and S type glass fibers, are preferred.

At a second process stage 28, continuous fiber filaments 30 are laid upon resin layer 25 in a parallel equally spaced unidirectional pattern over the random chopped fibers 24 in a direction parallel to the direction of travel of conveyor 1 6. The fiber pattern at stage 28 is illustrated in plan view at 32. To prevent twisting of continuous fibers 30 in the sheet molding compound, the fiber strands are drawn from the outside of the roll 34. A second layer 35 of paste 36 identical to paste 10 is metered by a doctor blade dam 38 onto a second polyethylene film 40 and directed by rollers 42 onto the traveling film layer 25 to form a sandwich in which the continuous fiber strands 30 and the chopped fibers 27 are disposed essentially in the middle between layers 25, 35 of plastic resin sheet material.At a third process stage 44, radially protruding blades 46 carried by an arbor 48 pierce upper film layer 35 and cut the continuous strands 30 to form the discontinuous parallel and substantially unidirectional fiber pattern illustrated in plan at 50. The blades 46 are disposed around the surface of arbor 48 so as to pierce the individual strands 30 at selected intervals, and thereby form a staggered array of discontinuous parallel and substantially unidirectional fiber strands 52 of a desired preselected length. The sandwiched sheet is then compacted as by rollers 54 and rolled into a roll 56 of continuous sandwich sheet material molding stock. The resin stock should be allowed to thicken by maturation to a molding viscosity in the range of 5,000 to 60,000 Pa-sec.It will be appreciated that the directional fibers are illustrated at 30, 52 in Fig. 1 as being thicker than the random fibers 24 for purposes of contrast only, the fibers normally being of identical thickness and of the same type in actual practice.

As an alternative and presently preferred process mode, the step of piercing film layer 35 and cutting strands 30 can be performed after formation of the roll 56 of continuous sandwich sheet material. In this case, arbor 48 is not present in the process apparatus as shown in Fig. 1, but rather is disposed in a separate machine (not shown). The molding stock is fed beneath the arbor to pierce film 40 and cut strands 30 after the molding stock has been allowed to thicken or maturate, i.e., after sufficient time has elapsed for the polyester resin and Group II oxide or hydroxide to enter into a hydroxyl-carboxyl ionic reaction and for the reaction to progress until the paste layer 35 reaches the aforementioned viscosity of 5,000 to 60,000 Pa-sec. Piercing and cutting of strands 30 with the sandwich sheet material molding stock in this higher viscosity condition ensures a minimum of resin squeeze-out or displacement through film 40.

It will be evident that the process illustrated schematically in Fig. 1 is adaptable for making sheet molding stock with only random fiber orientation or with only continuous fiber orientation, for example, rather than the multi-laminar directional-random orientation illustrated at 50. For example, process stages 28 and 44 may be deactivated such that the rolled sheet stock will contain only random chopped fibers 24 in the configuration illustrated at 26. Similarly, process stages 1 8 and 44 may be deactivated such that the ultimate rolled stock will include only continuous parallel strands 30 in the configuration illustrated at 32. It has been found to be advantageous in some instances to cover compacting rollers 54 with an endless belt or the like to help prevent reorientation or twisting of the fiber strands by serrations on the roller surfaces.

For the fabrication of wheels, the random fiber configuration illustrated at 26 and the randomdirectional configuration illustrated at 50 possess particular advantages. The random-continuous fiber configuration illustrated at 32 also has been utilized in wheel fabrication in accordance with the present invention, although it is not presently preferred.

For a discussion of manufacture of sheet molding compound of the type hereinafter described, reference may be had to United States Patent Specification No. 4,167,130; "SMC and RIM: Calling up Reinforcements", Automotive Engineering, Vol 86, No. 3, March 1978, pages 27 to 33; "Structural SMC: Material, Process and Performance Review", Owens-Corning Fiberglas Corp., Pub. 5-TM-8364, 1 978. Glass fiber reinforcements, including E-glass and S-glass herein preferred, are discussed in "Evaluating Glass-Fiber-Reinforcements", Plastics Compounding, July/August 1978, pages 1 4 to 25.The thickening or maturation process is discussed more fully in Deis et al, "Magnesium Oxide and Hydroxide for SMC", Modern Plastics, November 1974, pages 94 to 98; and Lawonn et al, "Fast Maturing of Unsaturated Polyester Resin Prepregs", German Plastics, translated from Kunstatoffe, Vol 65, October 1975, pages 678 to 680.

A process for molding fiber-reinforced composite wheels in accordance with the invention is illustrated in Figs. 2 to 4. Referring first to Fig. 2, a continuous strip of fiber-reinforced plastic resin molding stock is first coiled to form a rim mold charge hoop 60 of multiple spiral plies or layers. The molding sheet stock may be cut from roll 56 (Fig. 1) and coiled (with polyethylene films 14, 20 removed). Alternatively, the sheet stock may be cut from the roll 206 of Fig. 1 8 manufactured in a manner to be described in connection therewtih.

The particular rim charge embodiment illustrated at 60 in Fig. 2 comprises three spiral plies coiled from a continuous length of strip stock and having lapped ends 61. In actual practice it has been found that sheet molding compound is not always presently commercially available in lengths sufficient to form hoop 60 from a continuous length of strip stock. In such instances it is necessary to "dovetail" the ends of shorter sheet lengths. It is anticipated that sheet strips of desired length will be made available for high volume production of wheels. It should also be noted that some embodiments to be discussed include different types of sheet molding compound, i.e. having differing fiber orientations, necessitating multiple lengths of strip stock.

In every case, the number of spiral plies required depends upon the number of different types of sheet molding compound needed and the thickness of each sheet. Hoop 60 in Fig. 2 is for illustrative purposes only.

Hoop 60 may be formed by coiling about a rotatable mandrel (not shown) to a diameter approximating the ultimate desired median diameter of the wheel rim. Where the wheel rim is of a type which includes bead retaining flanges at one or both of the opposite rim edges, it has been found to be advantageous to flare outwardly the axial hoop edges prior to placing the hoop in a wheel mold. Accordingly, the hoop 60 is preferably placed on a rotatable die 62 having an outer surface 64 which cooperates with a rotatable roll follower 66 to give a slight outward flare to the hoop edges 68 to thus provide a first preform 69. The flared rim charge hoop preform 69 is then placed between two radially outwardly opened rim mold half sections 72 and 74 such that the lower flared end 68 rests upon the upper face of a lower disc mold section 84.Mold sections 72, 74 are connected by push rods 73, 75 to hydraulic cylinders 77, 79 (Fig. 3) and are slidable inwardly on guideways 76, 78. Cylinders 77, 79 are operatively coupled to a suitable hydraulic control 85. The radially inner or forming surfaces 81 and 83 of mold sections 72 and 74 respectively are preferably contoured to form a rim well, bead retaining flanges and suitable tire bead seats on the outer rim surface. After flared charge hoop preform 69 is placed on disc mold section 84 between rim mold sections 72, 74, the rim mold sections are closed and the preform 69 is captured therein in slight radial compression. In a continuous production process, mold sections 72, 74 are maintained at an elevated temperature in the range of about 270"F (132"C) to about 320"F (160"C).

Referring next to Fig. 3, a plurality of flat sheet sections 80 of fiber-reinforced (plastic) sheet molding compound, suitably cut from a roll of stock similar to roll stock 56 after stripping films 14 and 40 therefrom, are then stacked one upon another to form a disc mold charge. The roll of stock preferred for use in making these disc charge sections 80 is made in the manner described in connection with Fig. 1, except that continuous fibers 30 are omitted, as is the step of piercing and cutting thereof by arbor 48. This disc charge stack is then placed in the mold on the forming surface 82 of a lower disc mold section 84 coaxially within the rim mold charge 69.

As shown in Fig. 3, disc charge stack 80 is supported in the mold by the horns 90 extending upwardly therefrom to co-operate with corresponding cavities 100 in the upper disc mold section 94 to form pockets for the disc hand holes, as will be described hereinafter. Preferably, the disc charge sections 80 are each substantially square and are stacked with section corners circumferentially staggered in a rosette pattern so as to obtain maximum coverage of the disc mold face 82. This particular configuration has been found to result in minimized material flow and resulting knit lines in the final disc.Mold parts 84, 94 and 91, (in addition to mold parts 72, 74) are continuously maintained at an elevated temperature in the aforementioned range of about 270"F (132"C) to about 320"F (160"C) during and between the molding sequence or cycle of operation.

Where the eventual wheel is of a type which is to include a hub extending axially from the main portion of the disc, a number of smaller square hub charge sheet sections 86 are disposed between the disc stack 80 and mold face 82 over the cavity 88 formed in the mold face. Cavity 86 cooperates with a horn 98 mounted on the opposing surface 99 of upper disc mold section 94 to form a hub pocket in the wheel disc. Sections 86 help displace air that may otherwise become entrapped in cavity 88 upon closure of.the disc mold sections. The outwardly directed radial surface 101 and 103 of disc mold sections 84 and 94 respectively cooperate with surfaces 81, 83 to define in a mold cavity contour the rim well, flange and bead seat rim portions of generally uniform thickness.It should be noted that the number of plies in disc charges 80, 86 and rim charge 69 in Fig. 3 depends upon the desired wheel thickness and upon sheet stock density. As indicated above, it is desirable to lay disc charge sections 80 in a pattern which substantially covers the mold face and thereby approximates the eventual disc geometry to reduce material flow during the ensuing compression molding operation. Given any particular density of sheet molding compound and the desired wheel size, the number of plies, etc. may readily be determined by persons skilled in the art to fill the mold volume with minimal overflow. It is also envisaged that disc mold charges other than the presently preferred rosette stack-up may be used to form discs of other configurations, such as a square charge to form a four-spoke disc.

As a next step in the compression molding operation bridging Figs. 3 and 4, lower disc mold section 84 is displaced upwardly from its rest position on lower stops 92, and upper mold disc section 94 is simultaneously displaced downwardly by hydraulic control 85 until the disc mold sections are in axially opposed initial forming positions within the closed rim mold 72, 74, which are very close to the fully closed and final compression molding positions illustrated in Fig. 4. Preferably, motion of mold sections 84, 94 is controlled such that the mold sections move together and reach their final positions (Fig. 4) substantially simultaneously. Since upper mold section 94 must be initially positioned away from mold sections 72, 74 and 84 to permit placement of the mold charges, this necessitates a greater controlled rate of travel for the upper mold section.Mold section 84 is guided by a surrounding sleeve 1 20 having an axial stop shoulder 93 thereon to co-operate with a lip 95 on mold section 84 to limit upward motion of the disc section, and is connected by a rod 97 to a suitable hydraulic cylinder (not shown). A sleeve skirt 96 axially projecting from the radially outer edge of upper mold 94 captures rim mold sections 72, 74 as mold 94 is lowered whereby to clamp the rim mold sections and simultaneously guide disc mold section 94 into position.

Horn 98 on upper mold surface 99 initially forms the hub charge 86 into opposing cavity 88 in lower mold section 84. At the same time, horns 90 initially form the disc charge 80 into corresponding recesses 100 in the upper mold surface so as to mold initially a circular array of pockets 102 (Figs. 4 to 7) offset from the wheel disc but integrally connected thereto by a narrow circumferentially continuous bridging section around each pocket. The closed mold is then subjected to high pressure of the order of 1 500 psi (10.3 megapascals) at an elevated temperature of 132"C to 160"C of the order of 5 minutes to form by compression molding an integral rim and disc structure of essentially homogeneous resin reinforced by the dispersed fibers.The mold sections are then opened in an order reverse to that previously described and the molded wheel 11 6 (Figs. 5 to 7) is removed for finishing.

It may be noted at this time that a particular advantage of the molding process thus far described is thought to lie in the provision of a movable lower disc mold section, particularly in combination with the step of flaring the ends of the rim charge to form the open flanges 68 as previously described. As will be appreciated from Figs. 2 to 4, the slightly retracted position of lower disc mold section 84 at the time when flanged rim charge 69 is placed in the mold permits the lower flanged portion of the rim charge which will ultimately become the outboard rim flange 1 22 (Fig. 6) to be located closely adjacent the flange-forming surfaces of rim mold sections 72, 74 when the latter are closed. This, in turn, means that the mold material will not be "pushed" into the flange area as the disc mold sections are closed. This feature results in a more uniform distribution of reinforcing fibers in the flange than would be the case if mold section 84 were fixed. This is particularly important when directional fibers transverse to the wheel rim are utilized, as in Figs. 1 3 to 1 7 to be discussed. In molds for production wheels, rim molds possessing more than two mold sections may be utilized without departing from the invention.

The wheel 11 6 as molded includes a rim section 1 20 with integral bead retaining flanges 122, 1 23 and a center drop well 1 24 (Fig. 6) coupled to flanges 122, 1 23 by the bead seats 126, 1 27. As best seen in Fig. 6, drop well 124 is offset or asymmetric with respect to the rim centerline, which is to say that drop well 1 24 is located nearer outer flange 1 22 than inner flange 1 23 ("outer" and "inner" being taken with reference to the preferred orientation of the finished wheel mounted on a vehicle).The disc portion of wheel 116, which is generally indicated at 130, is coupled to rim portion 1 20 at the lower outer edge of drop well 124. The outboard face of disc 130, best seen in Figs. 5 and 6, includes a symmetrical array of five circumferentially spaced radial ribs 1 32 alternating with pockets 102 previously described. Each rib 1 32 extends wideningly from adjacent drop well 1 24 to flare into a central outwardly cupped hub shell 1 34. Ribs 1 32 not only strengthen the wheel, but also lend an ornamental spoked configuration thereto. The outer surface of shell 1 34 includes an axially extending channel 1 38 in radial alignment with the center of each pocket 102.

Ribs 1 32 are hollow, which is to say that a pocket 1 36 extends into each rib 1 32 at the inboard face of the wheel disc, as best seen in Fig. 7. Each rib pocket 1 36 is straddled by a pair of strengthening ribs 140 (Fig. 7) which flare into the base of drop well 1 24. Similarly, each hand hole 110 is surrounded by a continuous strengthening ledge or bead 141 best seen in Fig. 7. The radially outer portion of each ledge 141 is separated from rim well 124 by the pockets 1 44 (Figs. 6 and 7). Between ribs 1 32 and openings 110, disc portion 1 30 tapers narrowingly from a thickened region 146 (Fig. 6) adjacent shell 1 34.

During the finishing operation, flash is removed from the edges of bead retaining flanges 122, 1 23. The bottom and side edges of each pocket 102 are removed flush with ledge 141 along the phantom line 108 in Fig. 6 so as to form a circular array of openings or hand holes 110 (Figs. 8 to 10) in the wheel disc to co-operate with ribs 1 32 in lending a spoken configuration to the wheel as a whole. A hub center hole 11 4 is bored in the base of shell 1 34.

A circular array of mounting holes 11 2 is drilled or otherwise formed in the thicker portion 146 of wheel disc 1 30 coaxially with wheel pilot surface 11 3 (Figs. 6 and 9), one bolt hole 11 2 in outwardly spaced radial alignment with each channel 1 38 in the hub shell outer surface. An opening 1 50 is drilled in rim 1 20 for an inflation valve.It has been found that molding of an imperforate disc as previously described; although requiring finishing operations on the molded wheel for removal of the pockets 102 and drilling of the bolt holes 112, etc., reduces knit line formation in the molded product and thus enhances strength and reliability of the finished wheel 11 4 during operation. The wheel as molded and as finished is illustrated at 11 6 (Figs. 5 to 7) and 11 7 (Figs. 8 to 10) respectively.

In construction of wheels in accordance with the invention to the extent thus far described and utilizing sheet molding compound as described with reference to Fig. 1, glass fiber-to-resin weight ratios from about 45% up to about 75% have been tested, with a fiber/resin weight ratio of 50/50 being preferred. Fiber/resin ratios below 30% are considered to contain too little fiber reinforcement for manufacture of automobile road wheels, while ratios above 75% exceed the "wetting limit" of the glass fiber and thereby possess both reduced moldability and poor resin-glass adhesion. The paste is of about 50% resin and about 50% filler with small amounts of catalysts, etc. as previously described.In the construction of wheels in accordance with one embodiment of the invention, the random fiber pattern 25 (Fig. 1) and the directional/random pattern 50 are particularly advantageous in the disc charge and in the rim charge respectively.

Preferably, although not necessary, the rim charge is coiled such that the directional fibers lie radially inward of the random fiber layer in each charge ply. Random fibers 24 may be from 1.25 cm to 10 cm in length, all fibers having the same length, preferably 5 cm. Directional fibers 52 may be between 5 cm and 30 cm in length, with a 20 cm length being preferred. The usable range of fiber lengths, as fiber/weight ratios, is determined by strength and moldability.

Using a 50% glass fiber weight ratio as is preferred, directional/random fiber weight ratios in the range of 5/45 to 45/5 are envisioned, with a range of 20/30 to 30/20 being preferred.

In one wheel constructed in accordance with the invention, a disc charge consisted of multiple plies of 50% random fibers by weight, with the random fibers 24 being about 2.5 cm in length and being oriented essentially in planes perpendicular to the mold axis. The rim charge consisted of a hoop of directional/random sheet molding compound, again 50% fibers by weight. The rim charge hoop was coiled with the directional fibers 52 disposed radially inwardly of the random fibers 24 in each ply and oriented in the circumferential direction. The random fibers 24 were thus disposed essentially in a spiral pattern of revolution about the mold axis.

Directional fibers 52 were 20 cm in length and random fibers 24 were 5 cm in length at a directional/random weight ratio of 30/20.

In the following material specification for both the disc and rim charge of the aforementioned example of a wheel in accordance with the invention (see construction B3 in Table Ill for test results), "SMC" is a trade designation for sheet molding compound. The particular compounds utilized were manufactured by Owens-Corning Fiberglas. D refers to directional fibers of the type illustrated at 52 in Fig. 1, and R refers to random fibers 24. Thus, SMC-R50 means sheet molding compound containing 50% random fibers by weight. (See the above-referenced Automotive Engineering publication).

TABLE I SMC-Sheet Molding Compound For Disc Charge Type SMC-R50 Product Width 46 cm (69 cm, 92 cm or 11 5 cm optional) Product Weight 4.6 kg/m2 Product Density 1.9 g/cm3 Package 32 kg minimum-180 kg maximum/roll Glass % 50% + 1 Glass Type OCF 433/AB/47 (47 is yield in m/kg) Glass Source Owens/Corning Fiberglas Glass Length 2.54 cm Paste Formulation: Parts by Weight Source Resin DERAKANE 790 100 Dow Chemical Co.

Catalyst t-butyl perbenzoate 1% BOR U.S. Peroxygen Co.

Filler Camel Wite (CaCO3) 100 H. T. Campbell 8 Sons Mold release Synpron ABG (Zinc Stearate) 3% BOR" Synthetic Products Thickener 40% MAGLITE D/60% DERAKANE 470-45 + 4.7% BOR* MERCK Co/Dow Chemical Paste Viscosity: HBT Brookfield Viscometer, T-F spindle &commat; 29"C 5 days 50,000 Pa-sec t Magnesium oxide slurry BOR Based on resin Material Specification Resin Trade name DERAKANE 790 Source Dow Chemical Co.

Chemical Name Vinyl ester Non-volatiles 45% Monomer Styrene Acid Number 25 Viscosity 1.1 Pa-sec Density (gm/ml &commat; 25"C) 1.03 SPI Gel time &commat; 82"C 30 minutes Time to peak 32 minutes Peak exotherm 188"C SMC-Sheet Molding Compound For Rim Charge Type SMC-D/R Product Width 38 cm (87 cm or 11 5 cm optional) Product Weight 2.88-3.16 kg/m2 Package 32 kg-135 kg/roll Glass Length D-20 cm; R-5 cm Glass % D-30%; R-20% Glass Type OCF 433/AB/47 (47 yield in m/kg) Source Owens/Corning Fiberglas Color CM-1003 Black (variable) Plasticolors, Inc.

Added to Paste Formulation Paste formulation and paste viscosity (same as for SMC-R50) A number of different wheel constructions have been constructed and tested to the following 1 978 original equipment fatigue test specifications for intermediate size car body styled wheels: TABLE II Dynamic Cornering Fatigue Disc Fatigue B,,-30,000 cycles No failure below 20,000 cycles.

Bending Moment 2263 N-m SAE J 328a requires 18,000 cycles.

Dynamic Radial Fatigue Rim Fatigue B,o-1,000,000 cycles No failure below 800,000 cycles.

Radial Load 12,910 N Test Tire Pressure 448 kPa SAE J 328a requires 400,000 cycles.

All of the tested wheels (with the exception of one construction D wheel) embodied SMC-R50 material in the disc charge pattern as previously described, and all of the wheels as finished were identical to that shown to scale at 117 in Figs. 8 to 1 0. The various rim (belt) constructions are illustrated schematically in Figs. 11 to 1 7 and the following table compares belt construction to test results: TABLE Ill GLASS DISC FATIGUE RIM FATIGUE BELT DWG. LENGTH (cm) (cycles) (cycles) CONSTRUCTION FIG.D/R &commat; 2263 N m &commat; 12,910 N None* - None/2.5 428,000** 169,000 A (R-50) 11 None/2.5 1,090,000 5,382,390 Bi (D-30/R-20) 12 20/2.5 376,592" 289,830 B2 (D-20/R-30) 12 20/5 - 159,390 B3 (D-30/R-20) 12 20/5 1,100,000 3,599,000 B4 (D-10/R-40) 12 20/2.5 - 288,400 C (D-30/R-20) 13 20/5 - up to 8.7M**** D (R-65, X/DR 16 (None/2.5) 865,000*** up to 21 M 63 to 65) (DR = 2.5) E (D-30/R-20, 14 20/2.5 - avg. 2M to 4M R-50) None/2.5 F (R-65, 17 None/2.5 - from 4.6M X/DR 63 to 65) (DR = 2.5) G (R-50, 15 None/2.5 - up to 6.5M D-30/R-20) 20/2.5 * Disc and rim compression molded from one mold charge consisting of a rosette stack-up of SMC-R50 arranged in a manner to sections of Fig. 3.

**Wheel construction an early version of Figs. 5 to 10 with radial ribs 142 spanning cavities 144 as shown in Fig. 19.

***Only wheel tested had disc constructed of SMC-R65.

M M = mega or million cycles.

Figs. 11 to 1 7 schematically illustrate lay-ups of sheet molding compounds in various belt constructions in accordance with the invention. In each of Figs. 11 to 17, the stock is viewed from the tire-side or radially outer side of the rim charge. The bead-to-bead direction is vertical as shown in Fig. 11, the horizontal dimension being broken to facilitate illustration. Fig. 11 illustrates construction A in Table lil wherein the belt is comprised of three spiral plies of sheet molding compound with 50% by weight random glass rovings (i.e. SMC-R50) manufactured in accordance with the previous discussion relative to Fig. 1. Although the test results for construction A are good. it was found that this selection of belt material gave less than desired uniformity wheel-to-wheel.

Fig. 1 2 illustrates the construction previously described in detail and for which test results for different glass compositions and lengths are shown in exemplary constructions B1, B2, B3 and B4 in Table Ill. In the various types of sheet molding compound constructed in accordance with Fig. 1, the random and directional fibers are deposited at separate stages as previously described in essentially separate layers. Fig. 1 2 illustrates the preferred orientation wherein the random fibers in each ply are disposed radially outwardly of the directional fibers in the same ply with reference to the rim charge axis. Three to six plies are required depending upon material thickness and density. The directional fibers are oriented circumferentially of the wheel rim.As will be appreciated from Table Ill, construction B3 gave good test results.

Fig. 1 3 illustrates belt construction C consisting of a continuous spirally wound sheet with circumferential directional fibers as previously described and with a second spiral pattern of individual charge pieces located between the continuous spiral plies and having axially oriented directional fibers, i.e. transversely of the final wheel rim. This charge was constructed by cutting the individual pieces from a first continuous strip of sheet molding compound and then laying the pieces side-to-side on a second strip before the latter was spirally wound. The directional fibers in the continuous spiral ply were oriented lengthwise of the strip and therefore essentially circumferentially of the charge axis.The directional fibers in the individual pieces or segmented charge ply, however, were oriented axially of the charge-i.e. at an angle of 90 with respect to those in the continuous ply-so that the directional fibers in the composite lay-up formed an essentially grid pattern directed circumferentially and axially of the rim and wheel. Wheels molded from a rim charge so constructed and tested under load conditions ran for up to 8.7M (million) cycles prior to rim failure (construction C in Table III). It should be noted at this point that all wheels actually tested and exemplified in constructions A and B2-G in Table Ill were that previously discussed in connection with Figs. 5 to 10 and included (with the exception of one construction D wheel) discs molded from SMC-R50 rosette stack-ups (Fig. 3).It was therefore believed that disc performance would be consistent throughout with the performance of constructions A and B3 and was not tested (with the exception of one construction D wheel).

It is also contemplated that continuous directional fibers may be used in the rim charge.

However, directional discontinuous fibers are preferred over continuous fibers circumferentially of the rim charge for reasons of superior moldability in the disclosed process, i.e. to allow separation of the reinforcing fibers circumferentially of the hoop blank 60 during the molding operation. Such separation must occur since in the preferred process the rim charge is made smaller than the ultimate rim diameter and must be capable of circumferential stretching, with attendant increased fiber separation, as the hoop blank is expanded in mold 62 to 66 and in mold 74.

As another modification, it is contemplated that the spiral three-layer wrap for rim charge hoop 60 (Fig. 2) may be replaced by three separate concentric hoops with circumferentially staggered lap joints. Alternatively, the rim charge may comprise one coil of thick (sheet) molding compound (TMC) of the type described in "Best of SMC and BMC-And Then Some", Plastics World, July 1 977. See also United States Patent Specification No. 3,932,980. Similarly, rosette disc charge pattern 80 (Fig. 3) may be replaced by one sheet section of TMC which is a trademark of United States Steel. Such a modification has the potential advantage when using TMC-R of providing random (R) fibers oriented in all directions, i.e. not just primarily in planes perpendicular to the wheel axis.Thus, although SMC is preferred for molding the wheel of the instant invention in the embodiments thus far described, TMC may be utilized and is contemplated in accordance with the invention in its broadest aspects.

Figs. 14 and 15 respectively illustrate complementary belt constructions E and G (Table Ill).

In construction E (Fig. 14) three inner layers of SMC-D/R with directional fibers oriented transversely of the wheel rim are surrounded by a ply of SMC-R50. In construction G (Fig. 15) the SMC-R50 is the inner ply. In each belt construction E and G, three plies of D30/R20 compound weighing 2.0 kilograms (kg.) and one ply of R50 compound weighing 1.3 kg. gave a total weight of 3.3 kg. Fiber content was 50%, 31.8% random (R) and 18.2 directional (D).

The preferred range for both random and directional fibers is 18% to 32% with the total of both being about 50%, all by weight. Test results are shown in Table Ill.

Fig. 1 6 illustrates a belt construction D comprising one ply of SMC-R65 and two plies of sheet molding compound marketed by PPG Industries, Inc. of Pittsburgh, PA under the trademark XMC. This sheet molding compound is constructed in accordance with the process schematically illustrated in Fig. 1 8 by drawing a plurality of continuous fibers 200 from corresponding individual creels (not shown) through a resin bath 202 and a number of eyelets 204 onto a rotating mandrel 206. Eyelets 204 are mounted on a carriage 208 which oscillates in a direction parallel to the axis of mandrel 206, such that the fibers 200 are deposited in multiple helical layers in either direction to form essentially a double-helical pattern.

A chopper/gun 210 is mounted on carriage 208 and receives one or more fiber threads 212.

These fibers are chopped to preselected lengths and blown onto the wrap or lay-up 214 on mandrel 206. Because of the motion of carriage 208 and chopper/gun 210 with respect to the mandrel axis, the chopped fibers redeposited in a "random" pattern essentially or substantially in a direction parallel to the mandrel axis. These fibers are referenced herein as "directional- random" fibers, or DR in Table III. The rate of oscillation of carriage 208 with respect to the angular velocity of mandrel 206 may be varied to control the helix angle of fibers 200.

Reference may be had to United States Patent Specification No. 4,167,429 for a general discussion for the process hereinabove described in connection with Fig. 18. When wrap 214 is completed, it may be cut axially and removed from mandrel 206. For construction of wheel rim charges in accordance with the invention, the sheet is further cut in the direction of the mandrel axis as at 21 6 to preselected widths generally corresponding to rim width. The result is a plurality of lengths of strip stock, preferably eight inches wide, of which one is partially illustrated in Fig. 18. Each strip includes directional fibers 222 in essentially an X-pattern at acute angles transversely of the strip and with the directional-random 220 fibers oriented essentially lengthwise of the strip.Following is a material specification of XMC sheet molding compound utilized in constructing wheels in accordance with the invention and to be discussed: TABLE IV Type Designation XMC Weight 5.5 kg/m2 (18 oz./sq. ft.) Glass Content: Total: Range 55% to 80% Preferred 60% to 65% Directional-Random: Range 15% to 20% of total Preferred 20% of total Directional Remainder Glass length (directional-random): Range 1.25 cm to 5.0 cm (0.5 in. to 2.0 in.) Preferred 2.5 cm (1.0 in.) Glass type: Directional PPG K1 5 E glass Directional-Random PPG K37 E glass Helix angle: Range 79 to 82 (with reference to the mandrel axis) Preferred 80. 16 (with reference to the mandrel axis) Paste Formulation (sources same as in Table I):: Resin DERAKANE 790 80% Filler Calcium Carbonate 20% Mold Release Zinc Stearate 3% BOR Catalyst T.Butyl Perbenzoate 1% BOR Thickener Magnesium Oxide 2% BOR Formulation for SMC-R65 same as above except containing 65% random 2.5 cm (1 in.) fibers.

Above 80% total glass content, the sheet molding compound is thick and difficult to handle.

Below 55% glass, the resulting wheel rims are weak. Below a helix angle of 79 , the fiber ends in the rim flanges are too spread to yield desired strength. Above 82", the wheel rim exhibits diminished circumferential strength. The angle of 80. 16 is one available in this range without modification in the existing wrap-winding machine at PPG Industries, Inc. and is presently preferred for this reason. The degree of criticality of the helix angle within the range of 79' to 82 is unknown. The number of layers of directional fibers, i.e. the number of passes of carriage 208 (Fig. 18) across mandrel 206, must be sufficient to "fill" all diamond-shaped openings between the directional strands.

Fig. 1 6 illustrates a belt construction D comprising an inner layer of SMC-R65 and two outer layers of X-pattern/directional-random sheet material (X/DR in Table Lit). Total weight of each belt was 3.2 kg., consisting of 2.48 kg. XMC compound (total for two plies) and 0.72 kg. R65 compound. Total glass was of the order of 65% by weight, comprising 14.7% random (R), 10% directional-random (DR) and 40.3% directional or Fibers.

As will be appreciated from Table Ill, belt construction D gave surprisingly excellent results, particularly when it is recalled that steel wheels are normally expected to run only 800,000 cycles without a rim fatigue failure. It is believed that the improved test results of construction D are due at least in part to the orientation of directional fibers transversely of the wheel rim, i.e.

axially of the wheel. Due to the improved molding process previously described, these transverse directional fibers extend into the rim flange and thereby strengthen the flange-bead seat radius where fatigue failures often occur in steel wheels. Indeed, it was found that the most common mode of eventual failure of construction D wheels consisted of small cracks at the front rim well radius. Since this failure mode results in a slow air leak, it would be a preferred mode of failure during actual highway use.

Fig. 1 7 illustrates a belt construction F comprising an X/DR ply sandwiched between plies of SMC-R65. In wheels possessing belt construction F constructed and tested, total belt weight was 3.2 kg., comprising 1.92 kg. R65 compound (total for two plies) and 1.28 kg. XMC compound. As with construction D, total glass content was 65% by weight. In construction F, this total was divided as 39% random (R), 20.8% directional and 5.2% directional random (DR). Presently preferred ranges for belts of construction as in D and F are about 15% to 39% random, about 4% to 11 % directional random and about 19% to 40% directional, all by weight. Total glass content is preferably in the range of about 60% to 65%, with 65% being particularly preferred.

As will be appreciated from construction F in Table III, test results for this belt configuration were not as good as those for construction D (Fig. 16). This- is believed to be due to a loss of lateral strength resulting from replacement of the outer-most X/DR ply in Fig. 1 6 with an allrandom (R) ply in Fig. 1 7. Construction D of Fig. 1 6 is presently preferred. In production, it is contemplated that the separate X/DR plies will be replaced by one continuous length of strip stock (of a length not commercially available at this time ). It is anticipated that wheel rims so constructed will be stronger than those heretofore tested due to elimination of potential weak spots where the separate plies are now joined end-to-end.Disc constructions of stacked SMC-R50 (test results at A and B3 in Table lll are presently preferred.

Figs. 20 and 21 illustrate an alternative embodiment of a wheel constructed in accordance with the invention as molded, and Figs. 22 and 23 illustrate the same wheel as finished. The wheel of Figs. 20 to 23 is specifically designed for front-wheel drive vehicles and is characterized by a substantially increased disc offset as compared with the wheel of Figs. 5 to 10. Elements in Figs. 20 to 23 similar to elements in Figs. 5 to 10 previously described in detail are indicated by corresponding reference numerals followed by the suffix "a". Pocketconnection bridging sections 106a in Fig. 21 are substantially thinner than are those at 106 in Fig. 6 which will permit pockets 102 to be broken off from the wheel disc without requiring a separate finishing operation.

In accordance with another important feature of the invention, a method of providing a quality control for inspecting directional fiber patterns in molded wheels is envisaged. This feature is accomplished by winding into the raw sheet stock and molding into the wheel directional fibers of X-ray opaque material such as barium-glass or leaded glass. Thus, in the embodiments of Figs. 1 6 and 17, the quality control feature of the invention may be carried out by utilizing Xray opaque fibers as one or more of the fibers 200 in Fig. 1 8. Similar modifications may be readily incorporated in the SMC process of Fig. 1. Wheels as molded and/or finished may then be sampled and examined by X-ray for inspection of the directional fiber layout.

In the following claims, the term "directional fibers" refers to fibers of controlled orientation in the raw sheet molding stock and, thus, essentially of controllable orientation in the molded wheel. Fibers 30 and 52 (Fig. 1) and 222 (Fig. 18) are examples of directional fibers as previously discussed in detail. The term "random fibers" refers to fibers oriented substantially randomly in at least one plane, for example as at 24 in Fig. 1. "Directional-random fibers" refers to random fibers controlled during the process of fabricating the sheet molding compound so as to be oriented substantially in a given direction, for example as at 220 in Fig. 18. All directional terms are with reference to the axis of a finished wheel unless otherwise indicated.

Claims (25)

1. A composite wheel of fiber-reinforced resin comprising a disc portion in which reinforcing fibers comprise random fibers, and a rim portion in which reinforcing fibers include first fibers oriented substantially randomly of the wheel axis and second fibers oriented in preselected directions with respect to the wheel axis.

2. A wheel as claimed in claim 1, in which said second fibers include directional fibers oriented substantially parallel to the wheel axis.

3. A wheel as claimed in claim 2, in which said rim portion includes bead retaining flanges and said directional fibers extend across said rim portion and into said flanges.

4. A wheel as claimed in claim 1 or 2, in which said second fibers further include directional fibers oriented substantially circumferentially of the wheel axis.

5. A wheel as claimed in claim 2, 3 or 4, in which said directional reinforcing fibers are intermittently discontinuous.

6. A wheel as claimed in claim 3, in which said directional reinforcing fibers are disposed in symmetrical crossed paterns at an acute angle with respect to the wheel axis.

7. A wheel as claimed in claim 6, in which said rim portion further includes directionalrandom reinforcing fibers oriented substantially circumferentially of the wheel axis.

8. A wheel as claimed in any preceding claim, in which said reinforcing fibers in said disc portion are disposed predominantly in planes perpendicular to the rim axis.

9. A wheel as claimed in any preceding claim, in which said reinforcing fibers are of a construction selected from the group consisting of glass, aramid, graphite and carbon.

10. A wheel as claimed in any preceding claim, consisting essentially of fiber-reinforced plastics resin and comprising a rim portion and an imperforate disc portion integral with said rim portion, and having a plurality of pockeks homogeneously integral with the remainder of said disc portion and adapted to be removed from said disc portion so as to leave openings in said disc portion which lend a spoked appearance to said disc portion and to said wheel as a whole.

11. A method of compression molding a fiber reinforced composite rim for a vehicle wheel as claimed in any preceding claim, comprising the steps of providing a mold having radially reciprocable first mold sections and axially reciprocable second mold sections with all of said mold sections co-operating to form a cavity for compression molding of a wheel rim including bead retaining flanges, forming a rim mold charge comprising a hoop of fiber-reinforced resin sheet molding compound, with all said mold sections open, placing said rim charge hoop within said mold and then closing said mold sections under heat and pressure, opening said mold sections, and removing said rim.

1 2. A method of constructing a vehicle wheel consisting of integral rim and disc portions as claimed in any of claims 1 to 10, comprising the steps of coiling a first sheet section of fiber reinforced plastics resin construction to form a rim charge hoop consisting of at least one coil ply placing said rim charge hoop in a mold, placing a separate disc charge into said mold within said rim charge hoop, said disc charge comprising at least one second sheet section of fiberreinforced plastics resin construction, compression molding said rim and disc charges to form an integral fiber-reinforced composite wheel, and removing said wheel from said mold.

1 3. A method as claimed in claim 11 or 12, including the additional step of flaring axial ends of said hoop prior to placing said charge hoop within said mold.

1 4. A method as claimed in claim 11 or 13, in which said step of placing said rim charge within said mold comprises the steps of placing said rim charge hoop within said mold and then closing said first mold sections so as to capture said rim charge hoop within said mold with axial ends of said rim charge mold extending into portions of said mold cavity for forming said bead retaining flanges, and then closing said second mold sections such that material for forming said beam retaining flanges is captured within said portions of said mold cavity rather than forced under pressure to flow into said portions of said cavity by closure of said second mold sections.

1 5. A method as claimed in claim 14, in which said rim charge hoop is formed of sheet molding compound containing directional fibers such that said directional fibers extend generally axially of said hoop.

16. A method as claimed in claim 14, in which second mold sections are closed by displacing said second mold sections so as to reach their respective closed positions substantially simultaneously.

1 7. A method as claimed in any of claims 11 to 16, for constructing a wheel which includes a circular array of openings around the disc portion to lend a spoked appearance to the wheel as a whole, in which at each opening location a pocket is molded integral with but offset from said disc portion, and including the further step of removing said pockets from the wheel as molded to form said pockets from the wheel as molded to form said openings.

18. A method as claimed in claim 17, in which said disc portion is imperforate in the wheel as molded, and in which said method further comprises the step of opening a circular array of mounting holes in said disc portion or mounting said wheel on a vehicle.

1 9. A compression mold for forming a resin vehicle wheel as claimed in any of claims 1 to 10, comprising rim mold sections radially reciprocable with respect to a mold axis and disc mold sections for forming a mold cavity, in which said disc mold sections are both adapted to reciprocate axially and substantially simultaneously between closed positions for forming said cavity and open positions spaced from said cavity.

20. A composite wheel of fiber-reinforced resin, constructed and arranged substantially as hereinbefore particularly described with reference to and as illustrated in Figs. 5 to 10 or Fig.

1 9 or Figs. 20 to 23 of the accompanying drawings.

21. A wheel as claimed in claim 20, including fibre reinforcement constructed and arranged substantially as herein before particularly described with reference to and as illustrated in Figs. 1 to 4, and/or Fig. 11, or Fig. 12, or Fig. 13, or Fig. 14, or Fig. 15, or Fig. 16, or Fig. 17, or Fig. 18 of the accompanying drawings.

22. A method of compression molding a fiber-reinforced composite rim of a vehicle wheel substantially as hereinbefore particularly described with reference to and as illustrated in Figs. 2, 3 and 4.

23. A method as claimed in claim 22, including arranging the fibre-reinforcement substan tialiy as hereinbefore particularly described with reference to and as illustrated in Fig. 1 or Fig.

11, or Fig. 12, or Fig. 13, or Fig. 14, or Fig. 15, or Fig. 16, or Fig. 17, or Fig. 18 of the accompanying drawings.

24. A method as constructing a vehicle wheel, substantially as-hereinbefore particularly described with reference to and as illustrated in Figs. 2 to 4, or in Figs. 1 to 4, or in Figs. 2 to 4 and Fig. 11, or Fig. 12, or Fig. 13, or Fig. 14, or Fig. 15, or Fig. 16, or Fig. 17, or Fig. 18 of the accompanying drawings.

25. A compression mold for forming a resin vehicle wheel, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Figs. 2, 3 and 4 of the accompanying drawings.