Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DESCRIPTIO~
~ his invention relates to a skeleton
structure for steering wheels for motor vehicles, con-
sisting of a steering wheel hub, a tubular steering wheel
rim, and steering wheel s~okes, which connect said hub and
rim.
Owing to the-relativel~ high active
drivi~g safety and the ride comfort of modern motor
vehi¢les, they afford 3uch an ov~rall comfort that even
very slight disturbances of the vibration level will be
regarded as an inconvenien¢e by the driver of the motor
vehicle. A significant inconveniencs i8 constituted by the
wheelfight, which describes a vibrational state Or the
eDtire axle system of the motor vehicle, particularlg of
~the spring suspension of the front axle inclusive of the
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~: steering system. ~hat vibration will be noticed by the
driver of the motor vehicle as a rotational vibration
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(wo~ g) a~d a vertical vibratio~ (shaking, tremDl-
i~g) of the steering INheel during a travel at a speed
in the ra~ge from about 80 to 130 km/h. A jumping of
the wheels resu~ti~lg from static un~alance a.~d the
wo~oling motion whic~ is due to dynamic unDalance as
well as the rotatio~al vi~ration of the steering ~heel
which is caused by fluttering due to a-p~rameter-
excited vibr~tion owing to variable spring a~d da~ping
characteristics of the tires in the transverse direction
may ~e oppo~ed by the use of a steerirlg wheel w~ich has
a large moment of inertia or flywheel mass.
The unDalance of the wheels on the
rear axle gives rise to a horizontal vibration of the
body of the ve~icle and, as a result, to a vertical vi-
~ratio~ of the steering wheel. A steering wheel having a
small ma~s is desiraole for eliminating the resulting
shaki~g of tke steering Nheel.
An overshooting of the steering ~heel
will ofte~ occur ~hen a motor vehi~le having a front
wheel or all-wheel drive has tqken a corner a~d the
steering wheel is then allo~ed to return while the ve-
h~icle is accelerated with the largest possiDle driving
force. ~he vibration of the vehicle which then occurs
around tne roll axis and the vertical axis (roll and
yaw) ca~ ~e influenced lrl a sense to stabilize the
vehicle by the use o~ a steering wheel having a small
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moment of il~ertia, i.e., ~ small fl~heel mass. The
parameter in~luences affecting the overshooting of the
steering wheel caD be evaluated in depende.ice o~ the
frequency a~d the decay rate as a fu~ction of the
moment of inertia of the steering wheel. A decre~se of
the mome~t of i~ertia of the steering wheel will strong-
ly staDilize the vehicle. The requireme~ts whi~h snould
~e met ~y the steering ~heel for an optimum ride com-
fort and handling of a motor vehicle ca~ be summarized
as callillg for a steering wheel having the followi~g
features:
- Light weight, and a concentration of the mass as
close as possiDle to the axis of rotation ~shaking,
tremblin6);
- A moment of inertia or flywheel mass which co~stitutes
a compromise ~etween the req~rements to miuimize the
rotational vivration of the steering wheel and to
preve~t a~ overshooting, which compromise should
specificall~ oe selected for vehi~les of each type.
The calculatio~ of the moment of inertia
will lndicate that for a steering wheel having giveu
dimensions and ~ given diameter the moment of inertia
can be influenced only by a decrease of the mass which
can be associated with the radius of the steering wheel.
For instauce, EP-A-0 29Z 0~8 describes for steering
wheels of motor vehi~les a skeleton structure i~ which
the hu~ a~d spo~es of the steering wheel and the portions
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of the spokes in wni~h the rim of 'he steerlng -~heel
is embedded are constituted vy an integral die casting
of alumi~lum a~d i~ dependence on the ~esired moment of
inertia the rim of the steerlng wheel is solid or tubu-
l~r alld is made of steel or aluminum or an alumi~um
alloy. DE-A-3 625 372 discloses a steering wheel i~
whi~h the huD and spokes are made of synthetic thermo-
plastics a~d said huu and spokes as well ~s the rim of
the steering wheel are covered by a layer of a deform-
able plastic. In dependence on the desired mass moment
of inertia the rim of the steering wheel may be made of
steel, light metal or wound endless filaments embedded
in plastic. In a steering wheel having given dimensions~
a variation of the moment o~ inertia ln conjunctio~
with a minimum mass of the steering wheel ca~ be selected
for vehicles of a given type b~J a selection of the de-
sign of the rim of the steering wheel in con~unction with
a give~ hub geometry a~d witn a spoke geometry selected
for a~ optimum weight.
In a steering wheel having a
n ~ predetermined style, e.g., in 3 single-spoke steering
whéel or in a steering wheel having two spokes 3rranged
,
ke an arrowhead in the lower portion of the steering
wheel, the above measures will be restricted by the
strength limits of the overall s~ste~ because a steering
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wheel must have a~l adequate strength under the action
of restraining forces iu the direction of travel of the
vehi~le. A force of 380 N acting in the direction of
st;raight-ahead travel o~ the larger arc must slot ef-
fect a permanent deformatio~ of tne steering wheel oy
more than 105 mm.
It is a,. ooject of the i~vention to
i~rease in the design of a steering wheel having given
dime~lsio~s the limits wnich are imposed by the strength
requirements and tG urther reduce the mass mome~t of
inertia of such steering wheel whereas the relia~ility
and safety of the steering wheel should not adversely
be affected.
That object is accomplis~ed in that
the tubular rim of the steeri~g wheel is filled iu part
by a fluid medium.
The quantity of the fluid medium
will vary iu depe~dence ou the de~lsity of the fluid me-
dium contained in the rim of the steering wheel a~d pre-
feraDlg amou~ts to 0~5 to 2,5 %, particularly 1.0 to 2.0 %,
of tne weight of the steering wheel.
Suitable fluid media may particularly
consist of oil-water emulsions and glycol-water emulsion~.
The accelerating forces acting on the
rim of the steerin~ wheel during a return swing of the
steering wheel are directly proportional to the mass of
the fluid medium aDd the rim of the steeriug ~heel as well
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as the fluid medium will be subjected to the same i!li-
tial accelerations. For this reason the product of
forces will be a linear function of mass so that the
return swing of the steering wheel will be damped and
there wil; be no overshooti~g. An additional ~raking
action is due to the friction between the fluid medium
and the inside surf~ce of the rim of the steering wheel.
The measures described hereinbefore
will oppose the overshooting of the steering wheel
~ecause there will always be two opposing components of
force and the fluid medium will lag Dehind the motion
of the rim of the steering wheel. As a result, t~e mass
moment of inertia a~d the flywheel mass mag ~e reduced
3~ more tha~ l~h without a need to change the material
or the dimension~ which change would adversely affect the
stre~gth which will determine the stiffnes_ of the stee-
ring wheel.
The invention will now De descriDed
more in detail and by wa~ of example.
Figure l is a top plan view showing
a steering wheel 1 comprising a skeleton .~h~h is covered
oy a sheath 2 of poIyurethane foam. The skeleton com-
prises spokes 5, which are arranged on the smaller arc
n a configuration like an arrowhead and are connected
to the huv 3 and the rim 4 of the steering wheel and
clude a~l acute angle of 30. The steerin~ wheel 1 i9
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shown in Figure 2 iLI a transverse sectio~al view take..
O~l line I~ igure 1 al~d ~veighs 1970.2 g and is 450 mm
i~l diameter. The rim 4 of the steering wheel was ~illed
with 27.5 g of a~ glycol-water mixture 6.
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