Steering shaft assembly for automotive vehicles

A steering shaft assembly for automotive vehicles comprises an upper shaft mounted thereon with a steering wheel, a lower shaft rotatably supported in place within a column tube and telescopically connected to the upper shaft in such a manner to permit axial adjustment of the upper shaft, and a lock mechanism for releasably fastening the upper shaft to the lower shaft in its adjusted position, a pair of stopper elements respectively integral with the upper and lower shafts to be abutted against each other when the upper shaft is moved downward over a predetermined stroke, an annular tapered projection integral with one of the shafts, and a single shock absorber element of elastic material in the form of a short sleeve member coupled with the other shaft and located between the stopper elements. The shock absorber element is formed at one end thereof with an annular tapered portion to be resiliently coupled over the annular tapered projection by abutment with the stopper elements.

BACKGROUND OF THE INVENTION 
The present invention relates to a steering shaft assembly for automotive 
vehicles, and more particularly to a steering shaft assembly of the 
telescopic type adjustable in its axial direction. 
A conventional steering shaft assembly of the telescopic type as described 
above comprises an upper shaft mounted thereon with a steering wheel, a 
lower shaft telescopically connected to the upper shaft, a lock mechanism 
for releasably fastening the upper shaft to the lower shaft at its 
adjusted position, and stopper means for restricting downward movement of 
the upper shaft over a predetermined stroke during adjustment of the shaft 
assembly. Such stopper means includes, in general, a pair of stopper 
elements which are arranged respectively integral with the upper and lower 
shafts to be abutted at a predetermined position. In adjustment of the 
steering shaft assembly, it has been experienced that when the upper shaft 
is moved to its downward stroke end, the steering wheel is applied with an 
impact caused by abutment of the stopper elements. Even if in the shaft 
assembly a single shock absorber element of elastic material was 
interposed between the stopper elements to absorb the impact acting on the 
steering wheel, sufficient effect would not be expected because the 
magnitude of such impact changes in dependence upon the downward movement 
speed of the upper shaft. For example, if such a shock absorber element 
was made of soft elastic material, it would be effective to absorb a 
relatively small impact but ineffective to absorb a large impact. 
Alternatively, if such a shock absorber element was made of hard elastic 
material, it would be effective to absorb a large impact but ineffective 
to absorb a relatively small impact. 
SUMMARY OF THE INVENTION 
It is, therefore, the primary object of the present invention to provide an 
improved steering shaft assembly of the telescopic type in which a single 
shock absorber element is arranged to cooperate with the stopper elements 
so as to effect sufficient absorption of various impacts acting on the 
steering wheel during adjustment of the shaft assembly. 
According to the present invention there is provided a steering shaft 
assembly for automotive vehicles which comprises an upper shaft mounted 
thereon with a steering wheel, a lower shaft rotatably supported in place 
within a column tube and telescopically connected to the upper shaft in 
such a manner as to permit axial adjustment of the upper shaft, and a lock 
mechanism for releasably fastening the upper shaft to the lower shaft in 
its adjusted position, a pair of stopper elements respectively integral 
with the upper and lower shafts to be abutted against each other when the 
upper shaft is moved downward over a predetermined stroke, an annular 
tapered projection integral with one of the shafts, and a single shock 
absorber element of elastic material in the form of a sleeve member 
coupled with the other shaft and located between the stopper elements, in 
which the shock absorber element is formed at one end thereof with an 
annular tapered portion to be coupled over the annular tapered projection 
by abutment with the stopper elements. 
In the actual practice of the present invention, it is preferable that one 
of the stopper elements is integrally provided on the upper end of the 
lower shaft, while the other stopper element is integrally provided on an 
intermediate portion of the upper shaft, and wherein the annular tapered 
projection is formed at the upper end of the lower shaft, and the shock 
absorber element is coupled with the upper shaft between the stopper 
elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, FIG. 1 illustrates a steering shaft assembly 
of the telescopic type 10 in accordance with the present invention which 
includes lower and upper shafts 11 and 12. The lower shaft 11 includes a 
main shaft portion 11a, a cylindrical member 11b secured to the upper end 
of main shaft portion 11a, and a yoke portion 11c formed at the lower end 
of main shaft portion 11a. The cylindrical member 11b of lower shaft 11 is 
rotatably supported by a ball bearing 22 which is fixedly mounted within a 
stationary column tube member 13 fixed at an angle to a portion of a 
vehicle body structure, and the yoke portion 11c of lower shaft 11 is 
connected in a usual manner to a steering gear box (not shown). The upper 
shaft 12 is axially telescopically connected at its lower end with the 
cylindrical member 11b of lower shaft 11. A fastener ring 21 is fixed to 
the upper end portion of cylindrical member 11b and engaged with the upper 
shaft 12 to restrict relative rotation between lower and upper shafts 11 
and 12. The fastener ring 21 is further in engagement with the ball 
bearings 22 to position the lower shaft 11 in its axial direction through 
the ball bearing 22, which ring 21 acts as a stopper element to restrict 
downward movement of the upper shaft 12 by abutment therewith. 
A steering wheel 14 is coupled at its boss portion 14a with the upper end 
of shaft 12 and fastened in place by a nut 15b threaded over the upper end 
of shaft 12 through a washer 15a. An annular retainer member 24 is 
rotatably mounted on an intermediate portion of upper shaft 12 to receive 
one end of a compression coil spring 23. As can be well seen in FIG. 2, 
the annular retainer member 24 is supported by a pair of annular bushes 
25a and 25b which are made of hard synthetic resin and positioned in place 
by means of a pair of fastener rings 26a and 26b fixed to the shaft 12. In 
this arrangement, the lower bush 25a and ring 26a act as another stopper 
element to restrict downward movement of the upper shaft 12 by abutment 
with the fastener ring 21 through a single shock absorber element 40 of 
elastic material such as rubber. An annular retainer member 27 is fixed to 
the upper end of stationary column tube 13 by screws and opposite to the 
annular retainer member 24 to receive the other end of compression coil 
spring 23. The compression coil spring 23 is located eccentrically with 
respect to the axis of upper shaft 12 in a predetermined distance to 
resiliently support thereon the upper shaft 12. A guide rod 28 in parallel 
with the upper shaft 12 is fixed at its one end to the annular retainer 24 
and is slidably engaged at its other end with an axial groove 13a in the 
upper end of column tube 13 through a portion of annular retainer member 
27 to restrict relative rotation of the annular retainer member 24 to the 
column tube 13. The upper shaft 12 is further provided at its outer 
periphery with an axial flat recess of a predetermined length the lower 
end of which is formed as a stepped stopper 12a to be abutted against an 
inner end of the fastener ring 21 in upward movement of the upper shaft 12 
over the predetermined stroke. 
A lock mechanism 30 is provided to releasably fasten the upper shaft 12 to 
the lower shaft 11 in its adjusted position, which mechanism 30 comprises 
an operation rod 31 disposed in an axial bore 12b of upper shaft 12, three 
metallic balls 32 contained within an oblique bore 12c extending outwardly 
from the lower end of axial bore 12b, and a manual lever 33 fixed to the 
upper end of rod 31. The operation rod 31 is axially slidable in the axial 
bore 12b and is retractably threaded at its upper end into the axial bore 
12b of shaft 12. The oblique bore 12c in shaft 12 opens toward a portion 
of an axial groove 11d which is formed in the inner peripheral wall of the 
cylindrical member 11b of lower shaft 11. Thus, the outside ball 32 is 
arranged to engage the axial groove 11d of cylindrical member 11b upon 
operation of the manual lever 33. The manual lever 33 is connected at its 
one end with the upper end of shaft 12 and fastened in place by a nut 34. 
The outer end of manual lever 12 extends outwardly through a portion of a 
cover 14b fixed to the steering wheel 14. When the manual lever 33 is 
turned clockwisely, the operation rod 31 moves downward to press the balls 
32 against the axial groove 11d of cylindrical member 11b and to retain 
them in their pressed positions. As a result, the upper shaft 12 is 
fastened to the lower shaft 11 in its adjusted position by frictional 
engagement of the outside ball 32 with the axial groove 11d. When the 
manual lever 33 is released counterclockwisely, the operation rod 31 
retracts upward to release the balls 32 from the axial groove 11d of 
cylindrical member 11d. As a result, the frictional engagement of the 
ouside ball 32 with the axial groove 11d is released to permit axial 
adjustment of the upper shaft 12 relative to the lower shaft 11. Thus, the 
steering wheel 14 can be adjusted to a desired position in the axial 
direction of the shaft assembly. In such adjustment of the steering wheel 
14, the compression coil spring 23 acts to prevent an excessive load 
acting on a portion between the shafts 11 and 12 to ensure smooth 
adjustment of the steering wheel 14. 
As can be well seen in FIG. 2, the single shock absorber element 40 is 
coupled with an intermediate portion of upper shaft 12, which is in the 
form of a short sleeve member arranged between the fastener ring 21 and 
the bush 25a. The sleeve-like shock absorber element 40 is formed with an 
axial bore 41 which is provided at the opposite ends thereof with a pair 
of tapered portions 42a and 42b. Meanwhile, the cylindrical member 11b of 
lower shaft 11 is formed at its upper end with an annular tapered shoulder 
11e which confronts with the tapered portion 42a of shock absorber element 
40. In this case, the length of tapered shoulder 11e is determined to be 
longer than that of the tapered portion 42a of element 40, and also the 
maximum diameter of tapered shoulder 11e is determined to be larger than 
that of tapered portion 42a of shock absorber element 40. 
With the above arrangement of the shock absorber element 40, when the 
steering wheel 14 is pushed downward against compression coil spring 23 in 
adjustment of the steering shaft assembly, the bush 25a and retainer ring 
26a abut against the shock absorber element 40 to subsequently abut it 
against the tapered shoulder 11e of cylindrical member 11b so as to 
restrict the downward movement of upper shaft 12 over the predetermined 
stroke. If in such operation, an impact force acting on the upper shaft 12 
is relatively small, as shown in FIG. 3, the lower tapered portion 42a of 
element 40 will be coupled slightly over the tapered shoulder 11e of 
cylindrical member 11b and expanded radially to absorb the impact by its 
tensile strain. If an impact force acting on the upper shaft 12 is large, 
as shown in FIG. 4, the shock absorber element 40 will be axially pressed 
by abutment against the bush 25a and retainer ring 26a and expanded 
radially by the annular tapered shoulder 11e of cylindrical member 11b to 
absorb the impact by its pressed strain. From the above description, it 
will be understood that the shock absorber element 40 is deformed in 
accordance with the magnitude of impact acting thereon to ensure 
sufficient absorption of the impact. 
In FIG. 5 there is illustrated a modification of the steering shaft 
assembly in which the lower fastener ring 26a is replaced with a tapered 
fastener ring 26a', while the tapered portion 42a of element 40 and the 
tapered shoulder 11e of cylindrical member 11b are eliminated. In the 
actual practice of the present invention, the stopper elements 21, 11e and 
25a, 26a may be replaced with other stopper elements in an appropriate 
manner, and the cylindrical member 11b of lower shaft 11 may be formed in 
a piece with the main shaft portion 11a of shaft 11. 
Having now fully set forth both structure and operation of certain 
preferred embodiments of the concept underlying the present invention, 
various other embodiments as well as certain variations and modifications 
of the embodiments herein shown and described will obviously occur to 
those skilled in the art upon becoming familiar with said underlying 
concept. It is to be understood, therefore, that within the scope of the 
appended claims, the invention may be practiced otherwise than as 
specifically set forth herein.