Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to an apparatus for measurin~
the parallel alignment o F the front and rear wheel systems
of automotive vehicles, the ~setback~> angles between the wheels
of the front-wheel system, the side-slip angle of the vehicle,
as well as other angular parameters which are useful for
inspection and testing of a vehicle.
~ ifferent apparatus ~or checking the toe-in and
toe-out angles of the front and rear wheels of a vehicle are
already known. In a typical appliance, projectors placed in
front of the vehicle serve to direct light beams transversely
with respect to the vehicle in front of the front wheels as
well as longitudinal beams which are parallel to the front wheels
of the vehicle and are reflected from mirrors placed at the
level of the rear wheels.
Appliances of this type fail to achieve the
requisite degree of accuracy in the measurement of angles
and may prove difficult to read in some instances, especially
if they are e~posed to direct sunlight. Furthermore, in order
to carry out these known methods, it is first necessary to
align the front wheels with the rear wheels by turning the
steering-wheel of the vehicle until the two lines bisecting
the angles delimited by the front and rear wheels are caused
to coincide by means of a suitable lighting system.
It has also been proposed to employ laser emitters
instead of the conventional light-beam emitters, the laser
beams obtained being received on targets constituted by
arrays of diodes. This method has proved particularly
advantageous but results in relatively high cost of the cor-
responding e~uipment.
The aim of the invention is to provide an apparatus
which is not subject to the disadvantages of known apparatus
and therefore make it possible at moderate cost to perform
both fast and accurate measurement of a series of angular
measurements relating to the front and rear wheel systems as
`Ih` 2 - ~
well as other parameters of a vehicle~
According to the invention, the apparatus for
measuring the alignment of the front and rear wheel systems
of automotive vehicles as ~ function of the axis of thrust
of the vehicle, as well as the dynamic asetback angle
between the wheels of the front system, comprises an arm
attached laterally to each front wheel and means on each arm
for defining a straight line which connects two fixed points
located one on each arms, and an emitter on each arm. The
light beam produced by each emitter is parallel to the
plane of the corresponding front wheel and directed towards
the rear wheel which is located on the same side of the
vehicle. ~ mirror carried by the said rear wheel reflects
the corresponding light beam onto a photosensitive cell mounted
on the corresponding arm which is carried by the front wheel.
The means for defining a reference straight line comprises
angular displacement pickups mo~nted on the front ends of the
arms and connected to each other by a tensioning wire.
For each rear wheel, a photosensitive cell is mounted above
the mirror at a distance from the mid~plane of each wheel which
is equal in the case of both rear wheels, whereby the light
beams impinge alternately on the photosensitive cells when the
front wheels are turned in either direction.
In use, the steering system of the vehicle is
centered with respect to the center point of the vehicle as
indicated by the manufacturer. The angle between the afore-
said reference straight line and the line which is perpendi-
cular to the arm associated with the wheel and which is drawn
from the corresponding fixed point is measured successively
in the case of each front wheel in a first position of the
front wheel system such that the left-hand front light
beam impinges on the left-hand front cell whilst the right-
hand front li~ht beam is reflected beyond the corresponding
cell as a result of a suitable angular displacement of the
r.ight-hand front wheel in order to measure the wheel
alignment angle in the cas~ respectively of the right~hand
front wheel and the left-hand front wheel, then in a second
position of the front wheel system which is reverse to the
preceding and in which the right-hand front light beam is
reflected from the corresponding cell whilst the left-hand
front light beam impinges on a point located beyond the cell
of the left-hand front wheel after a suitable pivotal dis-
placement of this latter in orde:r to measure the wheel
alignment in the case respectively of the right-hand front
wheel and the left-hand front wheelO The following values
are determlned geometrically Erom the
/
. ~
four angles thus measured and computed successlvely ~
~10 = right-hand front wheel alignment angle as
a function of the thrust axis when the steering system i~
at its mechanical center-point.
~20 = left-hand front wheel alignment angle as
a function of the thru~t axis when the steering system is
at its mechanical center-point.
~13 = right-hand front wheel alignment angle
when the front wheel alignment i5 equally distributed with
respect to the thrust axis, that is, the dynamic alignment
angle of the right-hand front wheel with respect to the
thrust axis.
~ 23 = lef,t-hand front wheel alignment angle
when the front wheel alignment is egually distributed with
respect to the thrust axis, that is, the dynamic alignment
angle of the left-hand front wheel with respect to the
thrust axis.
b = dynamic setback angle.
~ = alignment angle of the rear wheel system.
The thrllst axis of a vehicle being defined as
the line bisecting the angle formed by the vertical mid-
planes of the rear vehicle wheels, the "dynamic setback
angle" designates the angle whose vertex is the center of
each front wheel and whose sides are constituted on the
one hand by the line which joins the centers of the front
wheels and on the other hand by the line at right angles
to the thrust axis of the ~ehlcle.
It w~ll be postulated throughout the following
description that this angle is positive when the right-
hand front wheel leads with xespect to the left-hand front
wheel or conversely.
Similarly, it will be considered by convention
hereinafter that the rlght-hand front wheel alignment
angle as a function of the vehicle thrust axis is positive
if toe-in takes place with respect to the thrust axis. The
left-hand front wheel alignment angle as a function of the
vehicle thrust axis will also be considered as positive if
toe-in takes place with respect to the thrust axis. In
one embodiment of the method according to the invention~
the aforementioned angular values are determined in an
electronic computer by means of the following relations
which are established geometrically :
2 ~ = al2 ~ a21
~13 = _11 + _12 + b
~ _ 21 22 _ b (~13 = ~23)
b = 21 11 a22 ~ al2
~21~11 + ~22 ~12
~10 ~10 4
~21all + ~22 al2
~20 a20 4
and the compu~er i~ cau~ed to determine contlnuously
the values of the indivldual alignment ~1~ ~ the r~ght-
hand front wheel and of the ~ndiv~dual alignment ~2n of the
left-hand front wheel at the time instants "n~ according
5to the relations
a2~ + a2 ;2 ~ ~12
ln ~ ln 4
a21 all a22
~2n a2n 4
these values being displayed in order to be read by the
operator who then adjusts the alignment of the front wheels
to the desired values.
It is therefore apparent that the
invention permits accurate mearusement
of the aforementioned series of parameters or in oth r
- words the alignment angles of the front wheelsi of the
rear wheels as a function of the thrust axis, especially
~hen the front wheel alignment is centerea with respect
to the center~point of the steering system and also when
it is equally distributed wlth respect to the thrust axis,
and the dynamic setback angle. All these measurements
are made possible solely by carrying out the initial
measurement of the angles between the reference straight
line and the line at right angles ~o each associated arm
and by application of the aforesaid relations which are
demonstrated geometrically.
All these results can be displayed on a screen
~;~
~nd varied individually by the operator so that the
parameters involved may accordingly be adjusted to the
desired values with a high clegree of accuracy.
In accordance with the invention,
photosensitive cells are placed above mirrors
carried by the rear wheels i.n such a ma~n~r
as to ensure that the distances between said cells and the
mid-planes of the correspondlng wheels are equal and that .
the light beams impinge on the respective cells when the
front wheel system is turned from left to right or con-
verse~y from right to left, the followîng parameters being
defined
B = ~ide-slip angle of the vehicle or in other
words the angle whose sides are constituted on the one
hand hy the thrust axis and on the other hand by the axis
of symmetry of the ~ehicle,
Bl = right-hand front wheel alignment angle as
a function of the axis of symmetry,
~ 2 ~ left-hand front wheel alignment angle as a
function of the axis of symmetry,
~ 10= right-hand front wheel alignment angle with
respect to the axis of symmetry when the steering system
is centered~
' ~20= left hand front wheel alignment angle with
respect to the axis of symmetry when the steering system
is centered,
--8--
B13 = dynamic alignment angle of the right-hand
front wheel wlth respec to the axis of symmetry~
~3 = dynamic alignment angle of the left-hand
front wheel with respect to the axis of symmetry,
~1 = r~ght-hand rear whPel alignment angle as a
function of the axis of symmetry,
Y2 = left-han~ rear wheel alignment angle as a
function of the axis of symmetry,
the angular values of the aforementioned parameters are
~0 established yeometrically and determined in the electronic
computer. After visual display of these values by the
computer, an adjustment of ~1 and ~ to the desired values
is then performed whilst the interm~dia e values at the
As aforesaid, the ap~aratus according to the-
invention comprises an arm attached laterally to each
front wheel and means provided on each arm for defining
a reference straight line which connects two fixed points
~0 located on the arms, an emitter for a light beam which is
parallel to the plane of ~he corresponding front wheel
and directed towards the rear wheel located on the same
side, and a mirror carried by said rear wheel for reflect-
ing the light beam onto a photosensitive cell mounted on
the corresponding arm.
The means for defining the reference straight
line can be constituted by angular d~splacement pickups
plaeed on ~he front ends of the arms and forming the fixed
points, said pickups being connected by a tension~ng wire
and constituted, for example, by potentiometers which
serve to measure the alignment angles of the front wheel
system.
It is also possible, however, to define said
reference straight line hy means of two projeckors which
are each placed at the front end of the arm and emit a
10 light beam which strikes a target placed on ~he end of the
other arm.
It is apparent that, starting from only two .
angular measurements.and by making use of relatively
inexpensive equipment, the apparatus according to the
invention makes it ~ossible to determine a complete
series of angular values of practical interest for the
vehicle and to carry out inspection and testing of the
vehicle as a function of the tolerance ranges established
for each vehicle by visually displaying the results
obtained by the computer.
These and other features of the invention will
be more apparent to those skilled in the art upon con-
sideration of the following description and accompanying
drawings, wherein :
. - Fig~ 1 is a simplified view in perspective
showing the front and rear wheel systems of a vehicle to
~10--
C?~S
which are attached the constltuent elements of a f~rst
embodiment of the apparatus accordin~ to the
invention ;
Fig~ 2 ls a geometrical dlagram showing a top
view of the vertical mid-planes representing the four
wheels of the vehicle, the front wheel system being
turned in such a manner as to ensure that the left-hand
light beam impinges on the l~eft-hand front cell after ,
reflection from the left-hand rear m~rror and that the
front light beam impinges on a point located beyond the
right--hand fron~ cell after reflection Xrom the right-
hand rear mirror ;
- Fig. 3 is a ~eometrical diagram which is
similar to Fig. 2 but reversed, the front wheel system
being turned in such a manner as to ensure that the right-
hand front light beam impinges on the right-hand front
cell after reflection from the:corresponding rear mirror
whilst the left-hand front light beam impinges on a point
located beyond the left-hand front cell ;
- Fig. 4 is a geometrical diagram showing the
front wheel system which i8 positioned in such a manner
as to ensure that the front wheel alignment is equally
distributed with respect to the axis of thrust of the
vehicle, the right hand and left-hand light beams being
~S therefore reflected at equal angles ;
- Fig. 5 is a diagram which is similar to the
S
preced~ng ~ut shows the paths ~f the l~ght beams and the
wheel al~gnment ang~es when the vehicle i8 placed at the
mechanical cent~r-polnt of the steering system ;
- Fig. 6 ~llustrates the second embodiment
of the apparatus accordinq to the invention,
wherein photosensit~ eells are positioned at
the rear above mirrors mo~ted on the r~ar wheels, the
front wheel system being turned in such a manner as to
ensure that the left-hand front light beam impinges on
10 the left-hand rear cell and that the right-hand front
light beam impinges on a point located beyond the risht-
hand rear cell ;
- Fig. 7 is a view which is similar to Fig. 6
but in which the right-hand front light beam impinges on
the right-hand rear cell whilst the left-hand front light
beam impinges on a point located beyond the left-hand
rear cell ;
Fig. 8 is a simplified view in perspective
which is similar to Fig. 1 and shows the second embodiment
of apparatus accordin~ to t~e invention illustrated in
Figs. 6 and 7.
Referring to Fig. 1, there is shown an
apparatus according to the invention for measurinq the
alignment of the front and rear wheel systems of auto-
motive vehicles as a function of the axis of thrust of thevehicle, as ~lell as the
... . _ _
-12-
dynamic "~e~back~ angle between the wheel~ o~ the front
systemO
It 1~ known that the thru~t axis of a vehicle
is the line bisect~ng the angle formed by the rear wheel~
5 of the vehlcle . The dynamic setback angle ~ s the angle
whose vertex is the center of one of th~ f ront wheels and
whose sides are constituted on the one hand by the straight
line joining the centers of the front wheels and on the
other hand by the line at right angles to the thrust axis
of the vehicley as will in any case become apparent fxom
the dxawings to which fur~her reference will be made
hereinafter.
The apparatus according to the invention
comprises an arm 3, 4 attached laterally to each respective
front wheel 1, 2. Means are provided on each arm 3, 4 for
defining a reference straight line 9 which joins two fixed
points 20, 21 located on the arms 3, 4 respectively. The
equipment unit further comprises an emitter 22S 5 placed
on each arm 3, 4. Said emitters produce respec~ively a
light beam 7a, 18a which is parallel to the plane of the
corresponding front wheel 1, 2 and directed towards the
rear wheel 13, 15 which is located on the same side.
Said rear wheel is adapted to carry a mirror 8,
12 for reflecting the light beam 7a, 18a constituted by a
line parallel to the mid-plane of ~he corresponding front
wheel, said beam being reflected onto a photosensitive
-13-
cell 14, 24 which is mounted on the respective horizontal
arm 3 t 4-
The front wheels 1, 2 of the vehicle are movedonto turntables 16, 17 and the arms 3, 4 are carried by
the rim of the associated wheel 1, 2 by means of an attach-
ment device 6 which i5 known per se and will therefore not
be described here.
In the example of construction illustrated in
Fig. l; the means for defining the reference straight line
9 are constituted by the combination of a tensioning wire
9, the ends of which are attached to the fron~ end
portions of the horizontal arms 3, 4 and by two angular
displacement pickups 20, 21 which are carried respectively
by the arms 3, 4~ By way of examplet said pickups can
consist of potentiometers which are connected to each
other by means of the tensioning wire 90
Each mirror 8, 12 is placed at right angles to
the plane of the corresponding rear wheel 13, 15~ the
reflected light beam being returned to the photosensitive
cell 14, 24.
Referring now to Figs. 2 to 5, the different
angles which can be measured by means of said equipment
unit will now be defined.
Let al and a2 be the angles delivered respect-
ively by the right-hand front piclcup 21 and the left-hand
front pickup 20 : all is the angle between the reference
straight llne 9 and the line 25 drawn at right angles to
the arms 4 from the corresponding fixed point 21, u21 being
the angle between the straight line g and the line 26
drawn at right angles to the arms 3 from the corresponding
fixed point 20.
The angles all and a21shown in Fig. 2 are
measured respeckively by the pickups 21 and 20 and are
considered by convention as positive when the arm 4, 3 and
the tensioning wire 9 ~orm an obtuse angle as is the case
in Fig. 2 ~it will readily be apparent that a contrary
convention could be adopted).
The second index "1" assiyned to the afore-
mentioned angles all and a21 is the time-interval index,
Fig. 2 being considered as the situation at the instant
"1". At the instant "2", the indices will therefore
become "2", and so on~
Thus in Fig. 2, the front wheel system i~ in a
first position such that the left-hand front light beam
7a, 7b impinges on the left-hand front cell whilst the
right-hand front light beam 18a, 18b is reflected beyond
the corresponding cell 24 as a result of a suitable
angular displacement of the front wheel system.
In a second angular position of the front wheel
system which is illustrated in Fig~ 3 and reverse to the
preceding, the right~hand front light beam 18a, 18b is
reflected from the corresponding cell 24 whilst the le~t-
-15-
hand front light beam 7a, 7b impinge~ on a point located
beyond the cell 14 of the left-hand front wheel 1 after a
suitable pivotal displacement of this latter.
In Fig. 3I the above-mentioned angles become
respectively al2 and a22, the angle al2 being negative and
the angle a22 being positive.
The axis of thrust of the vehicle is designated
~y the xeference 27 whilst the straight lines 28 and 2;9
are parallel to the axis of thrust 27 and dra~m from the
points of impact of the light rays 7a, 18a on the corre-
sponding mirrors 8, 12.
~ 1 is the angle of alignment of the right-hand
front wheel as a function of the thrust axis 27 (the angle
being positive if it corresponds to toe in and negative if
it corxesponds to toe-out of the wheel). It is apparent
from Figs. 2 and 3 that this angle ~ 11 in Fig- 2 and
~12 in Fig. 3) is the angle between the straight line 25
which is perpendicular to the vertical plane containing
the light beam l~a and drawn from the fixed point 21, and
the line which is perpendicular to the axis 27 and also
drawn from the point 21.
~ 2 is the angle of alignmen~ of the left-hand
front wheel as a function of the thrust axis 27 (said
angle being positive if it corresponds to toe-in and
negative if it corresponds to toe-out).
It: is apparent from Figs. 2 and 3 that said
-16-
"3~
angle ~ 1 in Fig. 2 and ~22 in Fig. 3) is the angle
between the straight line 26 which is perpendicular to the
vextical plane containing the light beam 7a and which is
drawn from the fixed point 20, and the line which is per-
pendicular to the axis 27 and drawn from the point 20.
The second indices assigned to the different
angles represent the successive instants corresponding to
Figs. 5, 2 and 3 which therefore show the respective
angles a10 (negati~e), ~20 (positive), ~10 (positive),
~20 (positive), ~11 (positive),a21 ~positive), ~11
(positive~, ~21 (negative) ; al~ (negative), ~22 (positive3,
~12 (negative) and ~22 (positive)0
It can al~o be seen in these figures that the
vertex of the angle b of dynamic setback of the vehicle
corresponds to the center of each front wheel 1, 2 and that
the sides of said angle are constituted on the one hand by
the straight line 60 (shown in Fig. 2) which joins the
centers of the front wheels 1, 2 and on the other hand by
the line 61, 62 which is perpendicular to the axis of
thrust 27 and drawn from the center of the front wheel 2, 1.
Said angle is positive when the right-hand front
wheel 2 leads with respect to the left-hand front wheel 1
as is the case in Figs. 2 to 5.
~ is the half-angle of rear wheel alignment as a
function of the thrust axis 27 or in other words the angle
made in the case of each wheel 13, 15 by the line 64
-17-
perpendicular ~o the axis 27 and the line 63, ~5 per-
pend~cular to the mid-plane of the corresponding wheel
13, 15, these perpendicular lines being materialized by
the planes of the mirrors 8, 12.
This angle is negative in the figures slnce the
rear wheels are set in a "toe-out" position.
By reason of the ~small movement o~ rotation to
be performed by the wheels in order to pass through the
~uccessive stages of Figs. 2, 3 and ~, it may be con-
sidered that the dynamic se~back angle b remains
practically constant.
In operation, one measures by
means of angular displacement pickups 21, 20 the ~ngles ~1
15 and ~;~ successively in the situation of Fig. 2 and ~n the
situation of Fig. 3 in order to obtain all and 21 in the
first position, then al2 and ~22 in the second position.
By means of the four angles thus measured, it is then
possible to determine geometxically and to compute
successively in an electronic computer forming par~ of the
equipment unit accordiny to the invention (but not shown
in the drawings~ the following values :
13' 23'
However, before placing the wheels in the posi-
tions illustrated in Figs. 2 and 3, the operator centersthe steering system of the vehicle with respect to the
]8
. . .~ ~.
center-point of this latter as indicated by th~ manu-
facturer tposition of the wheels of Fig. 5), with the
result that-the values a10 and a20 can be measured by the
pickups 21, 20 and stoxed in the computer, consequently
at the instant 0.
As mentioned earlier, the operator then turns
the vehicle wheels successively from left to right and
conversely in order to establish ~he conditions of
Figs. 2 and 3. It is apparent from FigO 2 that the light
ray 7b impinges on the left-hand front cell 14. We
therefore have the following equations :
~21 a21 - b =
~11 = ~11; ~ b
From Fig. 3, it is apparent that the light ray
18b impinges on the right-hand front cell 24 and that we
therefore have the equations :
~12 al2 ~ b =
~22 = a22 ~ b
From this it is possible to deduce the total
rear wheel alignment :
2~ = al2 + a21
. In Fig. 4, the front wheel alignment is dis-
tributed as a function of the thrust axis 27, with the
result that we have the relation :
~:L3 = ~23 = ~13 + b = a23 ~ b
The relationship between Figs. 2, 3 and 4 is as
--19--
~ollows :
~13 = 11 2- 12
~21 ~ ~22
23 2
- Thus, without passing physically thxough Fig. 4
13~ ~23 and b are obtained by computation as
foll~ws :
_ all +~12 + b
~23 = 2 ~ 13 = ~23)
b ~21 ~ 22 ~12
--
The relation 313 = ~23 represents physically
the individual dynamic alignment angle of each front wheel 2,1,
that is, when the front wheel alignment i5 distributed with
respect to the thrust axis 27, which corresponds to the
real wheel alignment on the road when the driver releases
the steering~wheel.
With re~erence to Fig. 5, the computer can then
c~lculate the individual alignment values ~10 and ~20 f
- the front wheels as a function of the thrust axis 27 when
the steering system is at its mechanical center-point :
~10 = ~1 ~ 21 _ 11 22 12
a - a + a ~ a
Thus/ in order to achieve this result when start-
-20-
ing from the situation of Fig. 5, the operator passes
successiveLy through the situations of Figs. 2 and ~ from
which the value b is obtained, thus permitting the final
computatiorl of the values ~10 and ~20.
It is apparent tha~, at the end sf this second
stage~ the equipment unit can indicate ~he following
results ~
~10' ~20
~ ~13' ~23~ b
- 2~
Should the operator desire to carry out an
adjustment of the front wheel alignment after a vehicle
inspection and testing operation, it is apparent that the
computer i5 capable of continuously providing the operator
with the individual alignment values ~1 and ~2 of the
front wheels since the angular displacement pickups 21 and
20 perform continuous measurement of a and ~ :
ln 2n
~ln = al + 21~ a22 - al2
a21 ~ 22 ~12
~2n a2n 4
Thus the values ~1 and ~2 can be adjusted as
the checkin'g operation proceeds by virtue of the visual
display of these angles on a screen and the operator can
accordingly adjust the wheel alignment to the desired
values.
-21-
A number of alternatlves may be contemplated
for the USe of the apparatus described in
the foregoing. By way o example, it is ~hus possible to
~ 10 ~2t)) representing the diference
between the alignment angles of the front wheels 2, 1 with
respect to the thrust axis ;27 when the steering system ~s
centered as well as the value 10 2 ~20 representing the
angle between the line bisecting the front wheels 1, 2-and
the thrust axis 27 when the steering system is centered.
10This technique can also be used for providing the
operator with an indication of the direction of turning
of the vehicle wheels in order to obtain ~he configuration
corresponding to dynamic wheel alignment of the vehicle or
in other words the state corresponding to Fig. 4. This
enables the operator.to determine the position of the
steering-wheel and of the center-point of the steering
system when he releases the steering-wheel on a roadway.
With this objective, the equipment unit provides the
operator with an indication of the direction of turning vf
the wheels, then of the exact position which satisfies the
following relations :
all + ~12
al3 = ~ 2
a21 + a22
23 2
This position of the steering-wheel accordingly
corresponds to the situation of Fig. 4
-22-
Referring to Figs. 6 to 8, there will now be
described a second embodiment of the apparatus
according to the invention.
The apparatus illustrated in ~ig. 8 com-
5 pri~es a photosensitl ve ce;!l 30, 31 associated with each
rear wheel 13, 15 and respectively mounted above the corre
sponding mirror 8~ 12 at a distance from the mid-plane of
each wheel 13, 15 which is equal in the case of both ;
whee 1 s .
At the time of turning of the front wheels 1, 2
from l~ft to right and conversely, the light rays which
are parallel to the mid-planes of the front wheels 7a~ 18a
thus impinge alternately on the cells 30 and 31.
Thus in the situation of Fig. 6, the light ray
7a impinges on the left-hand rear cell 30 whilst the light
; ray 18a impinges on a point located beyond the right-hand
rear cell 31, this situation being reversed in Fig. 7.
; Furthermore, in the case of the vehicle shown diagrammatic-
ally in these figures, the front-wheel track width 2e îs
larger than the rear-wheel track width 2h and the front
axle 1, 2 i~ displaced to the right with respect to the
rear axle 13, 15.
The angles and references appearing in these
figures are deflned as follows :
The straight line 32 is the axis of symmetry o~
the vehic]e or in other words the line which joins the
-~3-
;
centers of the two axle^~.
The ~traight lines 33 and 34 are par~llel to the
axis of symmetry 32 and pass respectlvely through the
points of impact of the lic~t rays 7a and 18a.
~24 = alignment angle of the left hand front
wheel 1 with respect to the thrust axis 27 when the light
ray 7a impinges on the left-hand rear cell 30 (Fig~ 6) ;
a24 = value of the angle ~2 of the left-hand
front wheel~ ~hen--the light ray 7a i~pin~es on the le~t~
1~ hand rear cell 30 (Fig. 6) ;
~14 = alignment angle of the r~ght-hand front
-- wheel 2 with respect t~ the thrust axis 27 when the
situation corresponds to Fig. 6 ,
al4 = value of the angle al of the right-hand
~ 15 front wheel 2-when the situation corresponds to Fig. 6 ;
~ 15 ~ alignment angle of the right-hand front
wheel 2 with respect to the thrust axis 27 when the light
~ ray l~a impinges on the right-hand rear cell 31 (Fig. 7) ; ~
al5 = value of the angle ~1 in the case of the
right-hand front wheel 2 when the light ray 18a impinges
on the right-hand rear cell 31 ;
~25 = alignment angle of the left-hand front
wheel 1 with respect to the thrust axis 27 in the situa-
tion corre~ponding to Fig. 7 ;
~25 = value of the angle a2 in the case of the
left-hand :front wheel 1 when the situation corresponds to
-24-
.
~ig. 7 :
~ = side-slip angle of the vehicle in which the
sides of the angle are constituted on the one hand by the
thrust axis 27 and on the other hand by the axis of
symmetry 32 of the vehicle ;
~ 1 = angle of right--hand front wheel alignment
as a function of the axis of symmetry 32 ;
~ 2 = angle of left-hand front wheel-alignment as
a function of the axis of sy~metry 32 ;
~10 = angle of right-hand front wheel alignment
with respect to the axis of symmetry 32 when the steering
system is at its mechanical center-point ,
~ 20 = angle of left-hand fxont wheel alignment
with respect to the axis of symmetry 32 when the steering
system is at its mechanical center-point ;
~13 = angle of dynamic alignment of the right-
hand front wheel with respec~ to the axis of symmetry 32 ;
~23 = angle of dynamic alignment of the left-hand
front wheel with respect to the axis of symme~ry 32 ;
Yl = angle of alignment of the right-hand rear
wheel as a function of the axis of symmetry 32 (Fig. 6);
Y2 = angle of alignment of the left-hand rear
wheel as a function of the axis of symmetry 32.
By virtue of simple geometrical considerations
and with reference to Figs. 6 and 7, it is apparent that
the side-slip angle ~ is given by the formula :
-25-
~ ~15 ~24
: As a function of the measurement~ performed
successively by the pickups 21 and 20, thls relation
becomes :
~ = 15 2 24 + 21 11 22 12
It ls further apparent from Figs. 6 and 7 that
the angles of front and rear wheel alignment as a function
of the axis o~ symmetry 32 ]have the following values :
~14 ~14 ~ al~
~24 24 ~ 24 2
~15 = ~15 ~ ~ = al5 _ 15 2 24
~25 ~25 ~ ~25
The results thereby achieved are as follows O
al2 + a21 ~lS ~24 a21 ~ all + a22 a
rl = ~ 2-- ~ 2 ~ 4 ~~~-
Y = ~ + ~ = 12 _ 21 + 15 24 + 21 all a22 a12
g s ~14' ~24' ~5' ~25 do not provide the
operator with advantageous results in a physical sense.
On the other hand, the application of these angles to the
sltuations of Figs. 4 and 5 and ~heir general extension to
the adjustment stage produce the following results :
-26-
- angle of ali.gnment of the right-hand front
wheel with respect to the axis of symmetry 32 wnen the
steering system is centered (Fig. 5) :
glO = ~10 - 15 ~24
- angle of alignment of the left-hand front
wheel with respect to the axis of symmetry 3~ when the
steering system is centered :
~20 = a20 + 15 24
- angle of dynamic alignment of the right-hand
front wheel with respect to the axis of symmetry 32 :
~ 12 ~15 - ~24
- angle of dynamic alignment of the left-hand
front wheel with respect to the axis of symmetry 32 :
~ 23 = 21 a2~ + al5 ~ a24
- ~ - - angle of alignment of the right-hand front
wheel with respect to the axis of symmetry 32 in the
adjustment stage :
~ln aln
- angle of alignment of the left-hand front
wheel with respect to the axis of symmetry 32 in the
adjustment stage :
~211 = a2 + 15 24
Fig. 6 lndicates the following additional
elements :
The straight line 35a is the line which is per-
pendicular to the axis of symmetry 32 and drawn from the
ront end of the right-hand front arm 4, that is, from the
fixed point 21.
The straight line 36a is the line which is per-
pendicular to the axis of symmetry 32 and drawn from the
front end 20 of the left-hand front arm 3.
- k is the s~atic setback angle or the vehicle
or in other words the angle whose vertex is the center l~
2 of each front wheel 1, 2 and whose sides are constit-
uted on the one hand by the straight line l' 2 which
joins the centers l and 2 and on the other hand by the
respective line 36, 35 perpendicular to the axis 32.
It should be noted.that the static setback k of
the vehicle is given by the formula -
k = b - ~
a ~ a
k = ~ 2
It is apparent by way of conclusion that, if the
rear cells 30 and 31 are added in an improved embodiment
of the equipment unit according to the invention, the
device is accordi.ngly capable of displaying the following
results at the end of the second checking stage :
-28-
Anqular values as a unction of the axis of
thrust 27
10' ~20
~ ~13' ~23~ b
- 2~
Anqular values as a function of the axis of
symmetry 32 :
~10' ~20
~13' ~23
- Yl ~ .Y2
- ~, k
While the adjustment stage is in progress, the
following results can also be displayed continuously :
~ln' ~2n' ~ln' ~2n
The invention is not limited to the sequences
of operation described in the foregoing. It is possible,
in fact, not only to display the values ~ 20) and
~ -) mentioned earlier but also to display the
value (~10 ~ ~20) representing,the difference between the
angles of alignment of the front wheels 1, 2 with respect
to the axis of symmetry 32 when the steering system is
centered. It is also possible to display the value
( 10 2 - ) representing the angle between the bisector-
line of the front wheels 1, 2 and the axis of symmetry
32 when the steering system i5 centered.
-29-
In more general terms, the invention permits
determinat~on of all the results obtained by means of the
linear combinat~on o
~1 alO ~ ~2 ' ~20 ~ C3 ~ ~11 + ~4 ' a21 +
~12 C~ ~ a22 ~ C~ al~ + Cg ~24 +
g al5 Cl~ a25, where Ci with i from 1
to lO are real ~nbers,
- on the one hand, determination of the values
al, ~2 is possible~ which values are read continuously by
the angular displacement pickups 21 and 20,
- and on the other, determination hand of the valu2s ~10~20
~11' a21' al2' ~22' al4~ ~24~ als~ a2s is D~ssible, ~hich
; val~l~s ~re ~tor~ at~~he ou~set of t~e m.easurinq ~rccess and at the t
of reception of the pulses delivered by the photosensitive
cells 14, 24, 30 and 31.
Among the different possible alternative modes
of execution, the following desexve partlcular mention.
The means ~or defining the reference straight line 9 can
consist of two projectors each placed at the front end of
the arm 3 and 4 and adapted to emit a light beam which
impinges on a target placed on the end of the other arm.
It is ~hus possible to make provision on each arm either
for a fixed beam directed at right angles to the emitter
support arm toward a linear diode array placed on the
opposite arm and thus to determine the values al and a2 or
for a movable beam which carries out a continuous scan and
-30-
is associated with a fixed receiver. In fact, it proves
unnecessary to provide a physlcal connectlon between the
arms 3~ 4 as constltuted by the tension~ng wire 9
The cells 14, 24 are preerably but not
necessarily positioned in ~he vertical plane of the
respective ~eam 7a, 18a~ Should the cells not be placed
in the vertical planes, however, then a correction would
have to be made.
- The ~istances a ~etween the ~ells 30-and 31 and
the mid-planes of the rear wheels are not necessarily
equal between the front wheel system and the rear wheel
system (as shown in Fig~ 6).
The apparatus according to the
invention therefore makes it possible by means of initial
measurement of two basic angular values al and a2, and in
the di.fferent wheel configurations described in the fore~
going, to determine by means of a computer an entire
series of angular parameters of the vehicle and to adjust
these latter continuously by displaying the results
obtained from the computer. These values are computed
with a very high degree of accuracy and it should be
emphasized that the system of application of this method
is relatively inexpensive in compaxison with certain known
systems, especially those which employ laser emitters and
diode arrays~
. -31-
