SE455012B - DEVICE FOR PREPARING A LEAF SPRING - Google Patents

Description

LS fx) 455 012 is wound on the frame, means for resin impregnation of the strand between the supply and the frame, the spirits of the frame holding the fiberglass strand under tensile stress, a press comprising a pair of mated parts, which form a cavity for forming the leaf spring, the frame being larger than the press parts, and wherein said parts of the press are separable for receiving the strands in the cavity while these are wound on the frame.

The invention is further defined in the appended claims.

The invention will in the following be described in more detail in exemplary form with reference to the accompanying drawing.

Pig. 1 shows a horizontal view of a spring assembly according to the invention. Pig. 2 shows a side view of the spring unit in mounted condition between sprung and non-sprung bodies. Pig. 3 shows a section taken along line 3-3 of Pig. 2. Pig. 4 shows a section similar to Figs. 3 except that the spring is shown in its unassembled condition. Pig. 5 shows a section taken along line S-5 in Figs. 2. Pig. 6 shows a modified embodiment of a spirit bracket. Pig. 7 schematically shows the apparatus used for manufacturing the spring according to the invention. Pig. 8 shows a section through the forming apparatus used in the manufacture of the spring. Pig. 9 shows a horizontal view of the lower part of it in Pig. 8 showed the shape. Pig. 10 shows a part of it in Pig. 9 illustrated the construction. Pig. 11 shows a horizontal view of another embodiment of a spring assembly.

Pig. 12 shows a partially sectioned side view of that of Figs. ll illustrated the spring assembly. Pig. 13 shows a section taken along line 13-13 of Figs. 12. Pig. 14 shows a section taken along line 14-14 of FIG. 12. Pig. 15 schematically shows the arrangement of filament strips in the manufacture of the spring assembly according to Figs. ll and 12. Pig. 16 shows a view of a mold in its fibrous state just before casting. Pig. 17 shows a view of the shape, taken along line 17-17 of Pig. 15. Pig. 18 shows a view of a part of a strip of fiberglass strands used for forming the spring according to Figs. ll and 12.

Referring to the drawing, Pig shows. 1 shows a first embodiment of a spring assembly 10, which comprises an elongate leaf spring element 12 having end fittings 14 for connecting the spring assembly 10 to a resilient structure 16 and a central mounting assembly 18, by means of which the spring element 12 can be extended. 455 455 012 is connected to a non-sprung element 20 such as a vehicle axle.

The spring body 12 comprises a plurality of continuous strands of fibers such as glass fibers, which are arranged in parallel close relation to each other in a matrix of polymerized resin, such as epoxy. As shown in Pig. 2, the configuration of the spring body 12 is such that it is thickest or has its greatest vertical height at a point substantially midway between its opposing spirits and is thinnest at its opposing spirits. The spring body 12 has a uniform cross-sectional area along its entire length. Due to the varying thickness of the spring body 12, it is therefore required that the central part of the spring is narrowest and that the opposite ends are wide as shown in Fig. 1 and of a comparison of the section of the spring body 12 in Figs. 4 and 5. By maintaining such uniform cross-sectional area along the length of the spring body 12, it is possible to use continuous strands with the same number of strands in all cross-sections and to at the same time achieve a uniform distribution of the strands. In practice, it has been found desirable that when using glass fiber to keep the ratio between the area of the strands and the resin area at least equal to each other, the area of the strands not exceeding about 63 percent or less than 50 percent of the total cross-sectional area.

De i Fíg. 1 and 2, by means of which the spring body 12 can be supported relative to the resilient structure 16, is generally U-shaped and has spaced parallel legs 24 which are arranged to be located at opposite top and bottom sides of the spring body 12. The end fittings 14 are held in position relative to the spring element 12 by means of bolts 25. The legs 24 are connected by means of a loop part 26, which is arranged to receive a transverse mounting bolt 28. The front end of the spring body or in Fig. 2 may be pivotally supported by means of a bolt 28 extending through a fixed fitting 29, and the rear or right end of the spring body 12 may be pivotally connected by means of a bolt 28 to a link structure 32 to accommodate changes in the distance between the pair of bolts 28 connected to each of the springs, when the spring element 12 is bent out. In the present case, the end fittings 14 and in particular the ends 34 of the legs 24 are substantially wider than the loops 26, the width of the ends 34 being equal to the relatively wide end of the spring element 12. The duct fittings 14 are held in place by means of the bolts 25 which extend through the legs 24 and through the ends of the spring body 12 to hold the end fittings 14 firmly in place. The wider part of the legs 24 serves to more evenly distribute the loads applied via the end fittings 14, along the entire width of the spring element 12 without any local stress concentrations.

Another type of end fitting that can be used with the spring element 12 is shown in Fig. 6 and is generally indicated by 36. The end fitting 36 comprises a base part 38 which is arranged to be placed on the upper surface of the end of the spring element 12. The base part 38 is provided with a folded-down flange 40 which abuts against the end of the spring element 12. A loop 42 is provided opposite the flange 40 to receive mounting bolts and bushings such as the shackle bolts 28 shown in Figs. 2. The end fittings 36 are secured to the spring element 12 by means of bolts 25 in a manner corresponding to the attachment of the end fittings 14 according to Figs. 1 and 2. The mounting assembly 18, which is arranged at a central part of the spring element 12 and serves to connect the spring element 12 to a non-resilient construction such as a shaft 20, comprises a pair of channel elements 44 which are arranged at opposite upper and lower parts of the spring element 12, with the cavities of the channel elements facing each other. The bottoms 45 of the channel elements are each provided with a rubber cushion 46. The rubber cushions 46 are bonded or mechanically locked to their respective channel elements 44 and to the spring element 12. One or both channel elements 44 may be provided with a guide lug 48 which is fixedly connected to the associated channel element 44. The lugs 48 are intended to be received in complementary openings arranged in a clamping element S0 or in a shaft seat S1 which is arranged on the shaft 20.

The shaft 20 is secured to the spring member 12 by means of U-bolts 52, the ends of which extend through the clamping member 50 at the top of the spring member 12. In the unassembled state of the spring element 12, the channel elements 44 are slightly separated and the rubber cushions 46 are in their unloaded condition as shown in Figs. 4. In the mounted condition, however, the mounting assembly 18 has the appearance shown in Fig. 3. In this condition, the U-bolts S2 are engaged to bring the channel elements 44 into contact with each other. By bringing the channel elements 44 into contact with each other, the elements 44 serve to limit the size of the load that can be applied to the rubber cushions 46. In a tested embodiment of the invention, it was found to be desirable subjecting the rubber pads 46 to a load that would reduce its unloaded thickness to about half. Under these conditions, it was found that the load was of the order of 175 kg per cm 2. By bonding or gluing the rubber pads 46 to the spring member 12 and to the channel members 44 and subjecting the rubber pads 46 to the compressive force, it is possible to subject the assembly to forces which tend to displace the mounting assemblies relative to the spring member 12; The rubber cushions 46 have an essential function in that they prevent local stress concentrations between the mounting assemblies 18 and the spring element 12.

In practice, it has been found that the rubber cushions 46 can be bonded to the spring elements 12 and the channel elements 44 by using a suitable adhesive, such as an epoxy glue, or by vulcanizing the cushions 46 both against the spring element 12 and the channel elements 44. the elements 44 make it possible to locate the mounting assembly 18 and in particular the clamping elements 50 and the shaft seat 51 in a substantially fixed relation relative to the spring element 12 without the need for hole drilling which is common in connection with steel leaf springs. By avoiding the production of holes in the non-metallic spring element 12 according to the invention, undesired packing stress concentrations can be avoided.

The apparatus by which the spring element 12 is manufactured will now be described in more detail. Referring first to Fig. 7, a continuous strand 60 of fiberglass is drawn from a roll 62 and through a tray 64 containing liquid resin 66 and to a winding frame 68. The winding frame 68 is generally rectangular as shown in Fig. 9. The frame 68 has side members 70 which are connected to each other by means of a transverse end member 72. The sides 70 telescopic in two tubular sides 74, which are joined by a transverse end member 72. The two tubular members 74 contain a pair of springs 78 which acts against the spirits of the smaller tubes 78 and tends to tension the spirit elements 72, 76 away from each other. Clamping elements in the form of adjusting screws 80 are mounted on each of the rudder sides 74 to contact the sides 70. To initiate the winding operation, the end members 72 and 76 are brought against each other against the force of the springs 78 and the clamping elements 80 are held to hold the spirit elements in a temporary fixed relationship relative to each other.

The frame 68 is also provided with a shaft member 82 which is axially aligned with the opposite sides of the frame 68 and is removably mounted therein in Figs. 7 shows the supporting structure 84.

During the bonding operation, the frame 68 is rotated about the axis 82 of the support frame 84 so that strands 60 impregnated with liquid resin 66 are wound around the opposite ends 72 and 76 of the frame.

During this winding, the frame 68 can be rotated in any well known manner, either manually or by means of drive means not shown.

The frame 68 is rotated a predetermined number of turns to obtain the desired ratio of fiber strands to resin in the manufactured product. A large number of sweeps are required and in a spring design more than two hundred sweeps are required, each comprising two fiber strand lengths, which were used in a spring having a cross-sectional area of less than 19.4 cm. The winding of the strands is performed to distribute the fibrous material uniformly over a width of the frame 68 corresponding to the maximum width of the spring element 12. After winding is completed, the clamping elements or screws 80 are released so that the springs 78 apply a tensile stress to the strands so that the strands are kept under a certain tensile stress and in parallel relation to each other.

After completion of the winding, the frame 68 is removed from its supporting frame 84 and placed in place relative to a mold 90. The press 90 comprises an upper mold 92 and a lower mold 94, which meet to form a cavity 96 having a configuration corresponding to the The upper 92 and the lower mold 94 have outer dimensions that fit inside the frame 68. The forming operation is performed by placing the frame 68 around the lower mold 94 with the filaments wound thereon placed in the lower cavity 96. The lower mold 94 ends are provided at the opposite ends of the cavity 96 with ponds or throttles 98 and extend across the cavity 96. With the frame 68 in place around the lower mold 94, the strands extend out through the ends of the cavity 96. When the upper mold 92 is brought into place, the fiber strands and the liquid resin 66 will be pressed into the cavity 96. The strands extend through opposite ends of the closed mold and over the ponds 98 which serve to contain and prevent release of resin from the cavity. 96. The mold parts 92 and 94 are heated to a temperature of approximately 455 012 10 ° C at which the resin begins to cure. After the resin has hardened sufficiently to allow handling, the spring member 12 is removed from the press 90, after which the ends are cut to the desired shape to remove excess resin and excess fibrous material at the ends of the spring member 12. Å When the upper and lower mold halves 92, 94 are moved towards each other. the ends of the strands are displaced downwards, whereby the frame 68 tends to be shortened so that the strands 60 are subjected to additional tensile stress. Due to the design of the spring element 12 and the cavity 96, it can be seen that the strands cannot remain completely parallel to each other, but the application of tensile stress to the filaments tends to distribute them uniformly along all cross-sections which, as previously mentioned, have equal area.

With reference to Pig. 11 shows a modified form of a spring assembly 110 comprising a spring element 112, which, like the spring element 12 in the previously described embodiment, consists of glass fiber in a matrix of polymerized resin. In this particular embodiment, however, the spring member 112 is of uniform width, the thickness varying from a maximum in an area between the opposite ends of the member to a minimum width at its ends. The spring element 112 is illustrated provided with end fittings 36 of the type shown in Figs. 6.

The middle part of the spring element 112 is provided with a mounting unit 18 corresponding to that which is used in connection with the spring element 12.

In this embodiment, the spring member 112 has the largest cross-sectional area at a center point, with the cross-sectional areas of the spring member 112 decreasing toward the ends of the spring member.

However, in each of the different cross-sectional areas, the distribution of fibers or strands has substantially the same proportion to resin as in the previous embodiment with uniform cross-sectional areas. In other words, a distribution of at least S0 percent and up to 63 percent fiber strands is arranged in each cross section.

In this case, however, the central part of the spring element 112 contains a larger number of strands than the smaller end sections.

The spring element 112 is made of layers of fiber tape 114 which have a uniform width which is substantially equal to the width of the spring element 112. The tape 114 comprises fiber strands 116 extending in the longitudinal direction of the tape and transverse strands 118. The layers of tape or tape 114 are cut lengthwise and arranged in layers. As best seen in Pig. 15, the top and bottom layers of fiber tape are the longest, their length being at least equal to the length of the spring member 112, with successive layers of tape 114 being shorter toward the interior of the spring.

The spring element 112 of the spring assembly 110 is manufactured in a shape similar to that shown in Figs. 8 and 9 except that an upper mold 122 and a lower mold 124 form a cavity 126 having the configuration of the spring member 112. With the mold halves 122 and 124 in their open position, as shown in Figs. 16, the layers of fiber tape 114 are saturated in liquid resin and laid in the mold cavity 126 with the long foam at the bottom, the successive layers being progressively shorter. At the center of the spring, a mass of chopped fibers, indicated at 128 in Fig. 13 and moistened with liquid resin, can be added to the mold cavity if desired. Thereafter, a short layer of tape 114 may be placed in the mold cavity, each of the adjacent layers becoming progressively longer until the top layer is reached which should or should have a length which is at least equal to the desired length of the spring. .

Thereafter, the mold parts 122 and 124 are brought into mating relationship, so that the resin is pressed against the dams 98 at the ends of the mold, and the resin is allowed to harden. After the resin has hardened at least to such an extent that the cast product can be handled, the spring member 112 is removed from the press, after which its ends are considered to provide the desired length of the spring member 112.

In the manner described, a non-metallic leaf spring is provided in which a unitary element is formed by strands of fiber such as glass fiber, distributed in a matrix of polymerized resin such as epoxy. End fittings and a central mounting assembly are provided, by means of which stress concentrations are avoided between the metallic elements and the non-metallic spring element in the leaf spring assembly. The apparatus by which the spring is manufactured ensures that the fiber strands are arranged extending along the spring element and with a substantially uniform density, the molds in which the springs are made being provided with resin ponds which ensure that the mold cavity is completely filled with fiber strands and resin.

Claims (3)

9 455 012 PATENT REQUIREMENTS Apparatus for producing a leaf spring, characterized by an elongate rectangular frame (68), means for tensioning the opposite end portions (72,76) of the frame away from each other, means (8234) for supporting the frame for rotation about a shaft between said ends (7Z, 76), a supply (62) of a continuous glass fiber strand (60), which strand is wound on the frame (68), means for resin impregnating the strand between the supply (62) and the frame (68), the frame ends hold the glass fiber strand under tensile stress, a press (90) comprising a pair of mating members (92,94) which form a cavity for forming the leaf spring, the frame being larger than the press members, and said parts of the press being separable to in the cavity receive the strings while these are wound on the frame. Apparatus according to claim 1, characterized by means (80) for releasably holding said ends (72,76) of the frame in fixed relation to each other during winding of the strings on the frame. Apparatus according to claim 1 or 2, characterized in that the mating parts (92, 94) of the press (90) have dams (98) at opposite ends of the cavity for contact with the strands and for holding uncured resin in the cavity under pressure until the resin hardens. L