Frame for automated two-wheel vehicles, and method for its manufacture

A pipe frame for a two or three-wheeled vehicle is formed by joining lugs having pipe receptors to other frame components such as seat rails and back stays. The parts are dimensioned so as to provide a slight clearance into which thermosetting resin is inserted. After assembly and finishing of the frame, the resin is set simultaneously with the baking on of the finish.

SUMMARY OF THE INVENTION 
The invention relates to frames for two-or-three-wheeled vehicles, and in 
particular to pipe frames, formed by joining lugs having pipe receptors 
for receiving other frame components with a predetermined clearance 
therebetween for the insertion of thermosetting resin. After assembly and 
painting, the resin is set simultaneously with the baking on of the 
finish. 
BACKGROUND OF THE INVENTION 
Frames used in automated two- or three-wheeled vehicles can be broadly 
classified as (a) those which use pipe as their primary material, i.e., 
pipe frames, and (b) those which use pressed steel plates, which are 
welded together to form a steel plate frame. 
The latter type of construction permits automatic welding, which results in 
high productivity, but for reasons of strength, it is applicable only to 
light-weight vehicles. By contrast, pipe frame construction provides 
adequate strength, and this type of construction is widely used for a 
variety of leisure, sport, competition and touring vehicles. 
In the past, cast or forged lugs have been used to connect the various 
types of pipe material. More recently, in order to produce lighter 
vehicles and to reduce costs, lugs have been eliminated in many cases in 
favor of arc welding or, in certain cases, by use of gussets made of steel 
plate and welding. 
However, welded connections create several problems: 
(1) If the welders are not highly trained, the welds will contain 
undercuts, overlaps or other deformities. When this kind of welding defect 
is present, because of the accumulation of stress upon the welded area, 
fatigue strength declines, so that further processing is required, such as 
polishing the weld area flat, shot blasting or shot peening, or heat 
treatment of the weld area. Obviously, this results in increased 
production costs. 
(2) In order to reduce frame weight, high tensile strength steels have been 
used. When such steels have been subjected to tempering or annealing, the 
large input of heat caused by welding produces soft areas which cause the 
yield point of the frame to decrease. This phenomenon is not confined to 
high tensile strength steels; the input of heat also causes such defects 
in normal steels. When this occurs, the entire vehicle frame must be 
subjected to further processing directly after welding, at which time 
close attention is required to prevent frame deformation. Such processing 
requires large scale facilities and increases production steps and hence 
costs. 
(3) Making the connecting lugs for the various pipes used in the frame from 
a light weight alloy is effective in reducing the proportion of lug weight 
in the total frame weight. However, because the lug and pipe are made of 
different materials, welding is impossible. 
(4) Even in cases where brazing (a type of welding) is employed, the 
problems mentioned in item (2) are encountered, since the brazing 
temperature exceeds the annealing temperature. 
(5) Whether or not lugs are used, the heating caused by welding can cause 
the frame to warp, so that, after welding, such warp must be corrected. 
OBJECT OF THE INVENTION 
It is an object of the present invention to overcome the aforementioned 
defects and disadvantages, and to provide a high quality permanent vehicle 
frame which is not subject to decrease in strength as a result of welding 
and the like. 
It is a further object of the invention to provide a vehicle frame in which 
the lugs, which normally account for a high proportion of the frame 
weight, are made of a light weight alloy, so that the manufacture of a 
light weight frame is possible. 
A further object of the invention is to simplify assembly, thereby 
decreasing the costs of construction.

DESCRIPTION OF PREFERRED EMBODIMENT 
FIG. 1 shows a unitized lug 1 having a head pipe 2 and pipe receptor arms 3 
and 4 with reinforcing ribs 1a. While the lug may be constructed of steel, 
as in the prior art, the present invention permits it to be constructed of 
light weight alloy, resulting in a lighter vehicle frame. 
In assembling the frame, main pipe 20 and down tubes 21 are inserted into 
arms 3 and 4, respectively, and joined thereto by adhesive. It will be 
understood that the cross sections of the respective elements to be 
assembled are similar, e.g., circular or rectangular. 
In FIG. 2, pipe receptors 6, 7 and 8 of unitized lug 5 are shown joining 
seat rail 22, back stay 23 and cross member 24. Reinforcing ribs 5a and 5b 
are provided. 
FIG. 3 shows the dimensional relationships upon insertion of seat rail 22 
into pipe receptor 6, by way of example. Similar relationships will of 
course apply to the joining of other elements. 
It will be noted that the depth of insertion Q of seat rail 22 is at least 
twice as great as the wall thickness of the thinner of the two elements 22 
and 6, i.e., the thinner of thicknesses t and t'. The clearance m between 
the two elements should be no greater than 1 mm. The reason for this 
dimensional relationship is that the adhesive A inserted in clearance 
space m provides the required connection shear strength, strength to 
withstand the moment of bending, and rigidity. 
After insertion of each pipe into the multiple pipe receptors on each lug, 
a thermosetting resin such as epoxy or acrylic resin, which hardens 
between about 120.degree. and 140.degree. C., is injected into the 
clearance space m. 
It is also possible to coat the outside circumference of the pipe with the 
adhesive prior to inserting it into the pipe receptor or the lug, or to 
coat the inside circumference of the pipe receptor area prior to insertion 
of the pipe. Moreover, as illustrated in FIGS. 15 to 18, the joining 
members may be secured temporarily by means of bolts 25, pins, rivets 26, 
caulking 27 or spot welding while the operation is performed. This enables 
preassembly of the frame to provide good operational efficiency and ease 
of transport to the next operation station, e.g., to the painting line. It 
can also be used as an auxiliary means to increase the strength of the 
joint. 
After painting, the adhesive can be hardened in the paint baking process, 
which may include the following steps: 
(1) Surface processing line: after degreasing the vehicle frame, a primer 
coat of a synthetic skin of zinc phosphate is applied. 
(2) Finish painting: after cleaning the frame surface, using an air blower, 
for example, an amino alkyd resin (solid color) or an amino alkyd resin 
(metallic color) paint is applied with an electrostatic painting device. 
Since the resin is of the thermosetting type, it is baked in a furnace 
heated to between 120.degree. and 140.degree. C. for about 30 minutes. 
As a result of this baking process, the adhesive is hardened 
simultaneously, thereby completing the assembly of the vehicle frame. 
FIGS. 4 and 5 show a frame for a two-wheeled scooter type vehicle which 
employs a swing type power unit. Lug 9 having pipe receptors 10 and 11 
connects down tube 25 and rear frame 26. Reinforcing ribs 9a are provided. 
In order to increase the strength of the adhesive joints, dimples and 
projections, channels or roughened surfaces can be effectively used in the 
junction areas, i.e., the internal circumferential surfaces of the pipe 
receptors and the external circumferential surfaces of the pipe ends. For 
example, FIG. 6 shows a channel G on the outside circumferential surface 
of seat rail 22a, and this channel G increases the adhesive force of 
adhesive A in the direction of removal (arrow) of the seat rail. Moreover, 
toward the end of pipe receptor 6a, there is an increasing taper which 
augments the effect of adhesive A. FIGS. 7 to 14 illustrate others of the 
above-mentioned means for strengthening the attachment. 
As will be clear from the foregoing description, lugs are used for the 
assembly of the frame, and a thermosetting resin is used to fill the joint 
areas between the lugs and pipes. Then, after the frames have been 
painted, the adhesive is hardened during the paint baking process. This 
has the following advantages: 
(1) As opposed to welded joints, diverse materials for lugs and pipes may 
be joined together, so that a high tensile strength steel with thin walls 
may be used for the pipe material, while a light weight aluminum alloy may 
be used for the lugs, thereby greatly lightening the vehicle frame. 
(2) The joining operations using an adhesive are much simpler than welding 
and do not require as much training or skill, so that productivity is 
improved. 
(3) Paint baking temperatures are between about 120.degree. and 140.degree. 
C., so that there are no adverse effects on the processed steel pipe 
resulting from heating to temperatures above annealing temperature. Also, 
because of the adhesive joints, there are no weld deformities to cause 
stress accumulation. As a result, it is possible to utilize effectively 
high tensile strength steel pipe to achieve high strength and longevity. 
Because post-junction processing is obviated, facilities can be decreased 
and a number of processing steps eliminated. 
(4) By using the paint baking process after painting, the adhesive is 
hardened, thereby eliminating a separate adhesive hardening process, 
reducing overhead and speeding up processing.