Generally, a steering column is structured to envelope a steering shaft, which transmits driver's steering wheel rotations to a rack and pinion mechanism. Thus, the steering column supports rotations of the steering shaft as it secures the position of the steering shaft through a bracket mounted to a vehicle body portion.
Such a steering column is presently equipped with a collision energy absorbable mechanism that provides an extra function of collapsing at both the steering column and steering shaft in response to an accidental vehicle collision in order to prevent the driver from receiving a severe injury from striking the steering wheel. This is based on the fact that in a vehicle collision during operation the driver's upper body hits the steering wheel of the vehicle interior following the law of inertia. As the driver impacts the steering wheel, the underside steering column and steering shaft yield and collapse to help reduce the impact onto the driver. However, depending on the conditions of the driver and vehicle the impact of the driver must act differently on the steering wheel. For example, the impact may be high or low proportional to the corresponding vehicle speed. In addition, whether the driver has bucked up with the safety belt and air bags deployed or not will affect the impact onto the steering wheel. In order to handle this situation better, a steering system equipped with a tearing plate has been developed.
FIG. 1 is a brief side elevational view of a conventional collision energy absorbable steering column 100. As illustrated, conventional column 100 comprises a steering shaft 102 having an upper end connected to a steering wheel (not shown) and a lower end connected to a rack and pinion mechanism (not shown), an inner tube 110 enveloping steering shaft 102, an outer tube 120 over inner tube 110, an upper bracket 130 for supporting outer tube 120 at its periphery surface while being secured to a vehicle body 104 through a capsule 140, and a tearing plate 170 having one end fixed to capsule 140 by a fastening means 150 and the opposite end fixed to upper bracket 130 by a fastening means 160.
With this type of steering column 100, in case of a frontal vehicle collision the driver's upper body may impact the steering wheel to collapse it in the same direction as the impacting course, whereby upper bracket 130 is adapted to shift from capsule 140 on vehicle body 104 along with outer tube 120 in that collapsing direction. Specifically, upon receiving the collision effect upper bracket 130 is detached from capsule 140 breaking easy off the vehicle body 104. Thereby, moving in the impacting and thus collapsing direction the steering column 100 telescopically collapses.
In addition, when steering column 100 contracts to shift upper bracket 130 downwardly relative to the fixed capsule 140 the tearing plate 170 will be subjected to opposing forces of capsule 140 and upper bracket 130.
Thus, a tearing groove formed on tearing plate 170 breaks along the upper bracket 130 shift to absorb the impact. I.e., fastening means 160 installed on upper bracket 130 deforms the tearing plate 170 in order to absorb the collision energy.
However, this method of absorbing the collision load by the capsule on the upper bracket or the tearing plate is susceptible to difficulty in absorbing the collision energy due to the convenience tilting option generally exercised resulting in the collision absorption correspondingly angled with respective to the collapsing direction. Furthermore, a high number of components added to the increase of assembling processes and the cost for manufacturing the conventional steering columns. Also, there have been customary problems of interferences between adjacent components and thus an unbalanced collision load to handle therefrom.