Method for forming an energy absorbing coupling for a steering wheel

A method for forming an energy absorbing coupling for connecting a steering wheel to a steering shaft is provided. The energy absorbing coupling is formed from a deformable member, a junction to the steering wheel and a junction to the steering shaft, each of which are formed as separate members. The deformable member includes a deformable part which functions to absorb energy from the force of an impact on the steering wheel. The deformable member is formed by bending without drawing. Work hardening effects of drawing are therefore avoided. The energy absorbing coupling formed has stable energy absorbing characteristics.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for forming a coupling which 
connects an auto steering wheel with an auto steering shaft. Specifically, 
the present invention relates to a method for forming an energy absorbing 
coupling which can absorb the impact energy of a force applied to the 
steering wheel of an automobile. 
2. Description of the Prior Art 
In recent years, a contractable shock-absorbing steering shaft which can 
absorb the impact energy from a force applied to a steering wheel and a 
steering wheel equipped with a self-aligning mechanism which can change 
the support direction of the steering wheel and can thereby absorb energy 
from an applied force have come to be widely employed in auto steering 
systems. 
The energy absorbing mechanism including the self-aligning mechanism is 
constructed as illustrated, for example, in FIGS. 8 and 9 (U.S. Pat. No. 
4,390,193). In this self-aligning mechanism, steering wheel 21 and 
steering shaft 22 are connected by an energy absorbing coupling 23 which 
by deforming itself can absorb the energy of an applied force. 
In this type of energy absorbing coupling 23, the flange 23a which is a 
junction to the steering wheel, the deformable member 23b for energy 
absorption and the boss 23c which is a junction to the steering shaft are 
integrated. The transitional part from the deformable member 23b to the 
boss 23c especially is formed from an integral piece by press-drawing. 
Generally speaking, when a piece is drawn, a work-hardening of the piece to 
a certain extent occurs. Thus, when press-drawn, the deformability of the 
deformable member 23b which absorbs the energy deteriorates through the 
work-hardening and it is liable to fail in exhibiting the desired stable 
energy absorbing characteristics. To avoid this trouble due to 
work-hardening, the use of an annealing process would be necessary. 
However, annealing would lower productivity and lead to an increased cost 
in production. 
SUMMARY OF THE INVENTION 
An object of the present inventon is to provide a new method for forming an 
energy absorbing coupling to be used in a self-aligning mechanism, thereby 
stabilizing the energy absorbing characteristics of the coupling and at 
the same time decreasing the production cost while increasing 
productivity. 
To accomplish the above object, an energy absorbing coupling is provided 
which connects the steering wheel and the steering shaft and which absorbs 
the impact energy of a force applied to the steering wheel by deforming 
itself. 
The energy absorbing coupling is formed from three separate members, i.e., 
a deformable member including a part which deforms to absorb energy, a 
junction which is connected to the steering wheel and a junction which is 
connected to the steering shaft. The deformable part is molded by being 
bent without being drawn. The deformable member, the junction to the 
steering wheel and the junction to the steering shaft, each of which are 
separately formed, are then joined together to form a complete energy 
absorbing coupling with a specified configuration. 
According to this method, the deformable member including an energy 
absorbing part which is formed separately from the junction to the 
steering wheel and the junction to the steering shaft can easily and 
individually be bent. 
In the deformable part which is formed by bending alone without being 
drawn, no work-hardening occurs and accordingly the desired stable energy 
absorbing characteristics can be obtained. Thus, there is no need for an 
additional annealing step to correct the work-hardening. The coupling can 
be produced by a simple process in which the conventional drawing process 
is replaced with a bending technique, thereby elevating the productivity 
and reducing the production cost.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 to 5 illustrate one embodiment of the invention of a self-aligning 
mechanism including an energy absorbing coupling. A steering wheel 1 is 
composed of a steering wheel ring 3, a steering wheel spoke 4 and a 
steering wheel pad 5. The steering shaft 2 is coupled to the front wheels 
of the auto through a suitable transmission mechanism. 
An energy absorbing coupling 6 connects the steering wheel 1 to the 
steering shaft 2. 
The energy absorbing coupling 6 is designed so as to be able to absorb the 
energy of a shock applied to the steering wheel 1 by deforming itself and 
this energy absorbing coupling 6 constitutes a self-aligning mechanism of 
the steering wheel. The energy absorbing coupling 6 is composed of a boss 
plate 7 which is the connection to the steering wheel 1, a boss 8 which is 
the connection to the steering shaft 2, and a deformable member 9 
including a deformable part 9a which connects the boss plate 7 to the boss 
8 and which absorbs impact energy by deforming itself. These members 7, 8 
and 9 are separately formed and then joined together to form the complete 
energy absorbing coupling 6. 
In this embodiment of the invention, the deformable member 9 consists of 
deformable part 9a, the connection 9b to the boss plate 7 and the 
connection 9c to the boss 8. The deformable part 9a in the deformable 
member 9 extends radially from the boss 8 to the boss plate 7. Connections 
9b and 9c are located at the ends of the deformable member 9 and they are 
welded to the boss plate 7 and boss 8, respectively. The deformable part 
9a is bent into a "U" shape between the connections 9b and 9c. The boss 
plate 7 and the boss 8 are designed to be rigid enough so that they will 
not deform under a small external force, but the deformable part 9a is 
designed so as to be deformable by a small load. 
The energy absorbing coupling 6 thus constituted is manufactured as 
illustrated in FIG. 6. 
To form the energy absorbing coupling, the boss 8, the deformable member 9 
and the boss plate 7 are formed as separate members. As illustrated in 
FIG. 6, the boss 8 is machined from, for example, a round bar 10 such as a 
block (for instance S25C). However, depending on the end shape desired, 
the boss 8 may be blanked from a plate and then bent to the final shape. 
The boss plate 7 is molded by blanking a broad ring out of, for example, 
plate 11 (first instance, SPHC, 2.6 mm thick), flange-bending it and 
finally punching it. 
The deformable member 9 is molded by radially blanking, for example, a 
plate (for instance SPHC, 3.2 mm thick), bending the blanked piece to a 
"U" shape in two stages and finally punching it. The boss 8 and the 
deformable member 9 thus molded to a required shape are then 
circumferentially welded. Thereafter, the deformable member 9 and the boss 
plate 7 are joined by welding to complete the energy absorbing coupling 6. 
In the process for forming the deformable member 9, the "U" shaped 
deformable part 9a which absorbs the energy is formed by bending alone 
without use of a conventional drawing technique. Consequently, the stable 
energy absorbing characteristics desired can be obtained because, being 
free from work-hardening which originates from the conventional drawing 
technique, the plate 12 or its "U" shaped configuration ensures the 
stability of the elastic deformability characteristics. 
Thus, as seen from FIG. 7, when an impact force F is applied to the 
steering wheel 1, the deformable part 9a of the energy absorbing coupling 
6 will deform in such a manner that it mitigates the impact force F in the 
direction of the application of the force. The shock energy of the force 
applied to the steering wheel 1 is absorbed by the deformable part 9a 
because of the maintenance of the deformability characteristics of the 
deformable part 9a. 
FIGS. 2 and 7 illustrate a state of deformation and a state of recovery 
from deformation when an impact force F is applied. The impact force F 
acting on the steering wheel ring 3 is transmitted from the steering wheel 
spoke 4 via the boss plate 7 to the deformable part 9a of the deformable 
member 9. The deformable part 9a functions as an energy absorbing plate 
and it is elastically deformed as shown in FIG. 7. After the removal of 
the force F, the deformable part recovers from the deformation as 
illustrated in FIG. 2, thus performing a self-aligning function. It should 
be noted that the steering wheel spoke 4, which can be deformed by a load 
larger than the load that deforms the deformable part 9a, also performs a 
shock-abating function. 
Thus, the function of the deformable part 9a in bending to absorb the 
energy from an impact force can be improved by separately molding the 
different members in the energy absorbing coupling 6. Stable energy 
absorbing characteristics of the deformable part 9a can be achieved by 
molding the deformable part 9a by bending alone without resorting to 
drawing. Since an annealing process to stabilize the energy absorbing 
characteristic is needless and the desired energy absorbing 
characteristics can be obtained simply by bending, the molding method is 
simplified and the productivity is enhanced and the production cost is 
reduced. 
Although only preferred embodiments of the present invention have been 
described in detail, it will be appreciated by those skilled in the art 
that various modifications and alterations can be made to the particular 
embodiments shown without materially departing from the novel teachings 
and advantages of the invention. Accordingly, it is to be understood that 
all such modifications and alterations as defined by the following claims 
are included within the scope of the invention.