Energy absorber for motor vehicle steering column

An energy absorber for a motor vehicle steering column including a yoke pivotable about a lateral centerline of a body of the motor vehicle and an energy absorbing structure responsive to linear translation of a mast jacket of the steering column relative to the yoke in the direction of a longitudinal centerline of the mast jacket. The mast jacket extends through a bore in the yoke and is prevented by the bore from tipping relative to the yoke. The energy absorbing structure includes a convex anvil on the mast jacket and a J-shaped flat metal strap seated on the convex anvil with a short leg rigidly attached to the yoke and a long leg juxtaposed a wall of the mast jacket. An impact on the steering column initiates linear translation of the mast jacket in the direction of its longitudinal centerline relative to the yoke during which the convex anvil translates linearly relative to the stationary metal strap so that the metal strap is pulled over the convex anvil and plastically deformed to convert into work a fraction of the kinetic energy of the impact.

FIELD OF THE INVENTION 
This invention relates to energy-absorbing steering columns for motor 
vehicles. 
BACKGROUND OF THE INVENTION 
A known energy absorber of simple construction for a motor vehicle steering 
column consists of an anvil on the steering column near the upper end 
thereof and a metal strap bent around the anvil and attached at one end to 
a body structure of the motor vehicle. During impact initiated linear 
translation of the steering column through an energy-absorbing collapse 
stroke, the metal strap is plastically deformed as the anvil is pulled 
along the length of the strap. Plastic deformation of the strap converts 
into work a fraction of the kinetic energy of the impact. The placement of 
the energy absorber near the upper end of the steering column, however, 
consumes space in an already congested environment. Further, optimum 
energy-absorbing performance requires that the metal strap be parallel to 
the direction of linear translation of the steering column before and 
during the collapse stroke. It is difficult to maintain such parallelism 
where the steering column is "raked" or "rake adjustable", i.e., pivotable 
up and down about a centerline at the bottom of the steering column for 
adjustment of the vertical position of a steering wheel. It is, likewise, 
difficult to maintain such parallelism during the collapse stroke. 
SUMMARY OF THE INVENTION 
This invention is a new and improved energy absorber for a motor vehicle 
steering column including a yoke pivotable about a lateral centerline of a 
body of the motor vehicle and an energy absorbing means responsive to 
linear translation of a mast jacket of the steering column relative to the 
yoke in the direction of a longitudinal centerline of the mast jacket. The 
mast jacket extends through a bore in the yoke and is prevented by the 
bore from tipping relative to the yoke before and during linear 
translation relative to the yoke. The energy absorbing means includes a 
convex anvil on the mast jacket and a J-shaped flat metal strap seated on 
the convex anvil with a short leg rigidly attached to the yoke and a long 
leg juxtaposed a wall of the mast jacket and confined in a guide means 
which maintains the long leg of the metal strap parallel to the 
longitudinal centerline of the mast jacket. An impact on the steering 
column initiates linear translation of the mast jacket in the direction of 
its longitudinal centerline relative to the yoke during which linear 
translation the convex anvil translates linearly with the mast jacket 
relative to the stationary metal strap. Relative to the mast jacket, the 
metal strap is concurrently pulled over the convex anvil to plastically 
deform the metal strap and convert into work a fraction of the kinetic 
energy of the impact.

DESCRIPTION OF A PREFERRED EMBODIMENT 
A motor vehicle steering column 10 includes a tubular mast jacket 12 having 
an upper end 14, FIG. 1, and a lower end 16, FIGS. 2-4. A longitudinal 
centerline 18 of the mast jacket 12 coincides with the longitudinal 
centerline of the steering column. A plastic ring 20 is rigidly fitted 
inside the mast jacket adjacent the lower end 16 thereof and includes a 
pair of diametrically opposite slots 22A, 22B parallel to the longitudinal 
centerline 18 of the mast jacket 12 and a cylindrical inner wall 24, FIG. 
5, which terminates at an internal annular shoulder 26 facing the lower 
end of the mast jacket. 
The steering column 10 further includes a steering shaft 28 having an upper 
end 30 projecting beyond the upper end 14 of the mast jacket 12 and a 
lower end, not shown, projecting beyond the lower end 16 of the mast 
jacket. A ball bearing 32 is interference fitted in the cylindrical inner 
wall 24 of the plastic ring 20 against the annular shoulder 26 and 
cooperates with additional bearings, not shown, in supporting the steering 
shaft 28 on the mast jacket 12 for rotation about the longitudinal 
centerline 18. Thrust bearings, not shown, transfer thrust in the 
direction of the longitudinal centerline 18 from the steering shaft to the 
mast jacket so that forces attributable to an impact on a steering wheel, 
not shown, on the upper end 30 of the steering shaft are transferred from 
the steering shaft to the mast jacket. 
A fragmentarily illustrated body structure 34, FIG. 1, of the motor vehicle 
includes a vertical panel 36 at the forward extremity of a passenger 
compartment of the motor vehicle and a bracket 38 bolted to the vertical 
panel. The bracket 38 includes a horizontal panel 40 and a pair of 
integral supports 42A, 42B. The horizontal panel 40 is flanked on opposite 
sides by a pair of depending vertical sides 44A, 44B of the bracket 38 
integral with the horizontal panel and with the supports 42A, 42B, 
respectively. 
An energy absorber 46 according to this invention includes a yoke 48 having 
a first side 50 facing the upper end of the mast jacket, an opposite 
second side 52, a bore 54 between the first and second sides, a 
counterbore 56 in the second side 52 around the bore 54, and a pair of 
diametrically opposite slots 58A, 58B facing the bore 50 and extending the 
length thereof. A pair of bolts 60A, 60B threaded into holes in opposite 
ends of the yoke through a corresponding pair of apertures in the vertical 
sides 44A, 44B, respectively, of the bracket 38 define a pair of trunnions 
supporting the yoke 48 on the body structure 34 for pivotal movement about 
a lateral centerline 62 of the body structure. 
An outer cylindrical wall 64 of the mast jacket 12 is closely received in 
the bore 54 in the yoke with the longitudinal centerline 18 of the mast 
jacket intersecting the lateral centerline 62. The slots 22A, 22B in the 
plastic ring 20 are disposed in the plane defined by the intersecting 
centerlines 18, 62. The slots 58A, 58B in the yoke 48 are similarly 
disposed in the plane defined by the intersecting centerlines 18, 62 
radially outboard of the slots 22A, 22B. An annular collar 66 is rigidly 
attached to the mast jacket 12 over the lower end 16 thereof and is 
interference fitted in the counterbore 56. 
The bore 54 and the counterbore 56 cooperate with the outer cylindrical 
wall 64 and the collar 66 in uniting the yoke 48 and the mast jacket 12 
for rake adjustment of the steering column 10, i.e., up and down pivotal 
movement about the lateral centerline 62 at the bottom of the steering 
column, between upper and lower limit positions represented by positions 
18' and 18" of the centerline 18 of the steering column, FIG. 1. The bore 
54 also defines a slide bearing for linear translation of the mast jacket 
relative to the yoke in the direction of the longitudinal centerline 18 
and prevents tipping of the mast jacket 12 relative to the yoke 48 before 
and during relative linear translation so that the slots 22A, 22B and 58A, 
58B remain in the plane of the intersecting centerlines 18, 62 regardless 
of the angular position of the steering column 10 relative to the vehicle 
body structure. 
A generic clamp 68, FIGS. 1-2, is disposed between the bracket 38 and the 
mast jacket 12 and includes a box-shaped bracket 70 having a pair of 
vertical sides 72A, 72B on opposite sides of the mast jacket and a pair of 
horizontal flanges 74A, 74B extending outward from the vertical sides 72A, 
72B, respectively. Each of the flanges 74A, 74B has a notch 76, FIG. 4, 
open toward the upper end 14 of the mast jacket in which is received a 
capsule 78. The capsules are retained in the notches 76 by plastic shear 
pins, not shown, and have openings through which a pair of hanger bolts 80 
extend. A nut, not shown, on each hanger bolt 80 clamps the corresponding 
capsule 78 to the horizontal panel 40 of the bracket 38. 
The clamp 68 further includes a cross bolt 82 on the mast jacket 12 
projecting through a pair of arc-shaped slots 84A, 84B in the vertical 
sides 72A, 72B centered about the lateral centerline 62 and a lever 86 
which rotates the cross bolt. When the cross bolt 82 is loose between the 
vertical sides 72A, 72B, the mast jacket 12 is rake adjustable. When the 
cross bolt 82 is tight between the vertical sides 72A, 72B, the mast 
jacket 12 is rigidly clamped to the box-shaped bracket 70. 
An energy absorbing means 88 of the energy absorber 46 includes a pair of 
convex anvils 90A, 90B on the collar 66 molded integrally therewith of 
hard plastic. The convex anvils 90A, 90B are diametrically opposite each 
other in the plane defined by the intersecting centerlines 18, 62 and are, 
therefore, aligned with the slots 22A, 22B in the plastic ring 20 and the 
slots 58A, 58B in the yoke 48. The convex surface of each of the convex 
anvils radially overlaps the wall of the mast jacket 12. 
The energy absorbing means 88 further includes a pair of flat metal straps 
92A, 92B each plastically deformed into generally the shape of a "J". Each 
flat metal strap includes a concave web 94 seated against a corresponding 
one of the convex anvils 90A, 90B, a short leg 96 parallel to the 
longitudinal centerline 18 in a corresponding one of the slots 58A, 58B, 
the yoke 48, and a long leg 98 inside of the mast jacket in a 
corresponding one of the slots 22A, 22B in the plastic ring 20 outboard of 
the bearing 32 and parallel to the longitudinal centerline 18. An end of 
the short leg 96 of each flat metal strap 92A, 92B is bent back against 
the first side 50 of the yoke and rigidly attached to the yoke by a 
fastener 100. The slots 22A, 22B, the outside diameter of the bearing 32, 
and the steering shaft 28 define guide means which maintain substantial 
parallelism between the long leg 98 of each metal strap 92A, 92B and the 
longitudinal centerline 18. 
An energy-absorbing collapse stroke of the steering column 10 commences 
with an impact toward the vertical panel 36 on the steering wheel on the 
upper end 30 of the steering shaft 28. Force attributable to the impact is 
transferred from the steering shaft 28 to the mast jacket 12 through the 
aforesaid thrust bearings and fractures the shear pins between the flanges 
74A, 74B and the capsules 78 and releases the annular collar 66 from the 
counterbore 56. With the short legs 96 of the metal straps restrained by 
the fasteners 100, linear translation of the mast jacket 12 in the 
direction of its longitudinal centerline 18 relative to the yoke 48 causes 
relative sliding of the straps 92A, 92B across the convex anvils 90A, 90B 
with corresponding plastic deformation of the straps as each is bent 
through about 180.degree.. 
Plastic deformation of the straps 92A, 92B converts into work a fraction of 
the kinetic energy of the impact on the steering wheel. Importantly, 
because the bore 54 and the outside cylindrical wall 64 of the mast jacket 
12 cooperate to maintain the angular relationship between the yoke 48 and 
the mast jacket 12 throughout the energy-absorbing collapse stroke, the 
metal straps 92A, 92B remain parallel to the longitudinal centerline 18 
throughout the collapse stroke regardless of the angular position of the 
mast jacket 12 relative to the body structure of the motor vehicle for 
optimum energy absorbing performance. In addition, because the long legs 
98 are concealed within the mast jacket 12 until the occurrence of an 
energy-absorbing collapse stroke of the steering column, they are shielded 
against accidental damage during transport and installation of the 
steering column 10. 
A modified energy absorber 102 according to this invention is illustrated 
in FIGS. 6-8. Features of the modified energy absorber 102 corresponding 
to features of the energy absorber 46 are identified by primed reference 
characters. The modified energy absorber 102 includes a yoke 48' supported 
on a motor vehicle body structure, not shown, for pivotal movement about a 
lateral centerline 62'. The yoke has a first side 50', an opposite second 
side 52', and a lateral slot 104 in the first side across the yoke. A 
cylindrical bore 54' in the yoke 48' intersects the lateral slot 104 and 
an elongated cavity 106 in the second side 52' of the yoke. 
An outer cylindrical wall 64' of the mast jacket 12' is closely received in 
the bore 54' in the yoke with a longitudinal centerline 18' of the mast 
jacket intersecting the lateral centerline 62'. The bore 54' cooperates 
with the outer cylindrical wall 64' in uniting the yoke 48' and the mast 
jacket 12' for rake adjustment of the steering column, i.e., up and down 
pivotal movement about the lateral centerline 62' at the bottom of the 
steering column. The bore 54' also defines a slide bearing for linear 
translation of the mast jacket relative to the yoke in the direction of 
its longitudinal centerline 18' and prevents tipping of the mast jacket 
relative to the yoke before and during relative linear translation of the 
mast jacket. 
A plastic ring 20' is rigidly fitted inside the mast jacket 12' adjacent a 
lower end 16' thereof and includes a cylindrical inner wall 24' which 
terminates at an internal annular shoulder 26' facing the lower end of the 
mast jacket. A ball bearing 32' is interference fitted in the inner 
cylindrical wall 24' of the plastic ring 20' against the annular shoulder 
26' and cooperates with additional bearings, not shown, in supporting a 
steering shaft 28' on the mast jacket 12' for rotation about the 
longitudinal centerline 18'. Thrust bearings, not shown, transfer thrust 
in the direction of the longitudinal centerline 18' from the steering 
shaft 28' to the mast jacket 12' so that forces attributable to an impact 
on a steering wheel on the steering shaft are transferred to the mast 
jacket 12'. 
A collar 108 shaped to nest in the cavity 106 in the yoke is rigidly 
attached to the lower end 16' of the mast jacket 12'. A pair of 
diametrically opposite passages 110A, 110B in the collar 108 closely 
adjacent the outer cylindrical wall 64' of the mast jacket 12' are 
disposed in the plane defined by the intersecting centerlines 18', 62'. A 
pair of convex anvils 112A, 112B are formed on the collar 108 radially 
outboard of the passages 110A, 110B and in the plane defined by the 
intersecting centerlines 18', 62'. Spaces between the ends of the collar 
108 and the cavity 106 define a pair of passages 114A, 114B, FIG. 7, in 
the yoke parallel to the longitudinal centerline 18' radially outboard of 
the convex anvils 112A, 112B and also in the plane defined by the 
intersecting centerlines 18', 62'. 
The modified energy absorber 102 further includes a pair of flat metal 
straps 92A', 92B' each plastically deformed into generally the shape of a 
"J". Each flat metal strap includes a concave web 94' seated against a 
corresponding one of the convex anvils 112A, 112B, a short leg 96' 
parallel to the longitudinal centerline 18' in a corresponding one of the 
passages 114A, 114B in the yoke, and a long leg 98' juxtaposed the outside 
cylindrical wail 64' of the mast jacket parallel to the longitudinal 
centerline 18' in a corresponding one of the passages 110A, 110B in the 
collar 108. An end of the short leg 96' of each flat metal strap 92A', 
92B' is bent back against and rigidly attached to the yoke 48' by a 
fastener 100'. The passages 110A, 110B and the outside cylindrical wall 
64' of the mast jacket define guide means which maintain substantial 
parallelism between the long leg 98' of each metal strap 92A', 92B' and 
the longitudinal centerline 18'. 
Linear translation of the mast jacket 12' in the direction of the 
longitudinal centerline 18' relative to the yoke 48' causes relative 
sliding of the straps 92A', 92B' across the convex anvils 112A, 112B with 
corresponding plastic deformation of the straps as each is bent through 
about 180.degree.. Concurrently, the aforesaid guide means maintain 
parallelism between the long legs 98' and the longitudinal centerline 18' 
of the steering column for optimum energy absorbing performance.