Appartus and method for adjusting vehicle toe alignment angles

Toe of a pair of wheels on the same axle is adjusted by first measuring the toe of a first wheel of the axle. A specification value for the toe of the first wheel is then subtracted from the measured value of toe for that wheel, and the difference is stored as a first toe comparison value. The toe of a second wheel on that axle is adjusted until the total toe of the wheels on that axle minus a specification value for total toe for the wheels on that axle equals the first toe comparison value. The toe of the first wheel is subsequently adjusted until the total toe of the wheels on the axle is substantially equal to the specification value for the total toe for the wheels on that axle. Apparatus which performs the method is also disclosed.

BACKGROUND OF THE INVENTION 
This invention relates to vehicle wheel alignment systems, and in 
particular to method and apparatus for adjusting toe. 
Proper alignment of wheels in a vehicle is important for proper handling of 
the vehicle and proper tire wear. The alignment of a vehicle's wheels is 
performed primarily by adjusting camber, caster, steering axis inclination 
(SAI) and toe. Of paramount importance to the driver of the vehicle is 
that the vehicle drive straight down the mad when the steering wheel is 
held in its straight or rest position. This condition is a function of toe 
of the vehicle, and in particular is affected by the relative toe of one 
wheel on the steering axle with respect to the other. 
Heretofore, the method of adjusting toe on a vehicle was relatively 
complicated. The toe of each wheel on the steering axle is conventionally 
compared to a toe specification value for that wheel and vehicle, and the 
total toe is also compared with a total toe specification value for the 
vehicle. This procedure frequently required repeated attempts to get the 
individual toe values and the total toe to fall within specification. The 
prior art method also required locking the steering wheel in the straight 
ahead position, since any change in the steering wheel position would 
adversely affect the measurement of the individual toe values. 
Even with all this work on the part of the technician/user, correcting the 
toe of the wheels to specification did not always result in the vehicle 
driving straight ahead when the steering wheel was held in the straight 
ahead position. The tolerances on these specifications are such that 
adjusting each wheel to within the tolerance of the specification can 
result in substantial unbalanced side forces being applied by the wheels. 
SUMMARY OF THE INVENTION 
Among the various objects and features of the present invention may be 
noted the provision of an improved apparatus and method for adjusting 
vehicle toe. 
A second object is to provide such a method and apparatus which simplifies 
the adjustment of total toe and individual toe. 
A third object is the provision of such a method and apparatus which 
eliminates the need to repetitively adjust the individual toes of wheels 
on a single axle. 
A fourth object is the provision of such a method and apparatus which 
ensures that the toe is adjusted such that when the steering wheel is 
pointed in the straight ahead direction, the vehicle tracks straight 
ahead. 
A fifth object is the provision of such a method and apparatus which 
obviates the need to lock the steering wheel in position during the 
adjustment of toe. 
A sixth object is the provision of such a method and apparatus which guides 
the technician/user through the toe adjustment process. 
A seventh object is the provision of such a method and apparatus which 
includes a visual display of direction and magnitude of required toe 
adjustments. 
An eighth object is the provision of a novel method of adjusting toe and an 
apparatus for guiding the user through the novel method. 
Other objects and features will be in part apparent and in part pointed 
hereinafter. 
Briefly, in a first aspect of the present invention a method of adjusting 
toe of a pair of wheels on the same axle includes the steps of measuring 
the toe of a first wheel on a first axle of a vehicle, subtracting a 
specification value for the toe of the first wheel from the measured value 
of toe for the first wheel, and storing the result as a first toe 
comparison value. The toe of a second wheel on the axle of the vehicle is 
adjusted until the total toe of the first and second wheels on the axle 
minus a specification value for total toe for the wheels on the axle 
equals the first toe comparison value. The total toe minus the total toe 
specification value is adjusted total toe. The toe of the first wheel is 
subsequently adjusted until the adjusted total toe is substantially zero. 
In a second asset of the present invention a vehicle wheel alignment 
apparatus is provided for guiding the adjustment of toe of a pair of 
wheels on the same axle of a vehicle. The apparatus includes first sensor 
apparatus for measuring the toe of a first wheel on a first axle of a 
vehicle, second sensor apparatus for measuring the toe of a second wheel 
on the axle, and a circuit element for storing a specification value for 
the toe of the first wheel. A controller is responsive to the sensor 
apparatus and to the storing element for subtracting the specification 
value from the measured value of toe for the first wheel and for storing 
the result in the storing element as a first toe comparison value. The 
storing element has stored therein a specification value for total toe for 
the axle, the total toe being the sum of the toe for the first and second 
wheels. The controller is responsive to the sensor apparatus for the first 
wheel and to the sensor apparatus for the second wheel to compute total 
toe and to update the computation of total toe as additional measurements 
of the toe of the first wheel and the second wheel are made by the sensor 
apparatus. The controller is further responsive to the stored 
specification of total toe to compute the difference between measured 
total toe and the total toe specification, the difference being updated by 
the determining means as additional toe measurements are made by the 
sensor apparatus. A display is provided which is responsive to the 
controller for visually guiding the adjustment of the toe of the second 
wheel to a point where the total toe of the first and second wheels minus 
the total toe specification value equals the first toe comparison value. 
The total toe minus the total toe specification value is adjusted total 
toe. The controller is responsive to the adjusted total toe falling within 
a predetermined tolerance of the first toe comparison value for 
controlling the display to visually guide the adjustment of the toe of the 
first wheel until the adjusted total toe is substantially zero.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning to FIG. 1, a wheel alignment system 1 of the present invention 
includes a main console having a microprocessor 3, left and right front 
head units 5L and 5R, and left and right rear head units 7L and 7R. Head 
units 5L and 5R mid 7L and 7R each include their own microprocessors 2 
(see FIG. 3) which are connected to microprocessor 3 by cables 8 or any 
other suitable communication channel such as radio or infrared. The head 
units are substantially similar to the head units described in U.S. Pat. 
No. 4,319,838 to Grossman et al., which is incorporated herein by 
reference. Although the head units are preferably connected to an external 
microprocessor 3 or a digital signal processor (DSP), microprocessors 2 
(or equivalently DSPs) may be organized in a network without an external 
microprocessor. 
The head units are mounted to the left front wheel LFW, the right front 
wheel RFW, the left rear wheel LRW, and the right rear wheel RRW of a 
vehicle to measure the vehicle's alignment parameters. The head units are 
supported on the wheels by suitable adapters 9. A front head unit is shown 
in more detail in FIG. 2. Each front head unit includes a housing 11, a 
sleeve 13 and an arm 15. (The rear head units are substantially similar to 
the front head units. The only significant difference is that the rear 
head units lack the arms 15.) Sleeve 13 mounts over a spindle of the 
corresponding support adapter 9 to support the head unit. The head unit 
can swing freely about the spindle. The head unit can be positionally 
fixed by tightening a knob 17. A level mounted on arm 15 indicates when 
the unit is horizontally level. Once the head unit is leveled, knob 17 is 
tightened to hold the head unit in its level position. 
The front head units each include two sensor units 19 and 21 (see FIG. 1), 
sensor units 19 being used for the measurement of too. Each rear head unit 
includes one sensor unit 23. Each sensor unit includes a signal emitter 25 
and a receiver 27 (see FIG. 3), each receiver being operatively connected 
through its sensor unit microprocessor 2 to microprocessor 3 via lines 8. 
The sensor units operate in pairs, as set forth fully in the above noted 
U.S. Pat. No. 4,319,838 to determine the alignment angles for the vehicle 
tested. In particular, the pair of sensor units 19 operate to determine 
the too angles of their respective wheels, and microprocessor 3 from those 
toe angles calculates total too. 
Also shown in FIG. 3 is a display 31 (preferably a CRT type display 
conventionally used with microprocessors) for displaying information to 
the user, and in particular for guiding the technician/user through the 
too adjustment process. A memory 33 is also provided for storing 
specification information (such as individual toe specification values and 
tolerances, as well as total too specification values and tolerances. 
Although shown as a separate component, memory 33 may be incorporated into 
console processor 3. Alternatively, the memory may be associated with the 
individual wheel processors 2, depending upon the overall computer system 
design. 
Display 31 is controlled by console processor 3 to display to the 
technician/user an initial toe adjustment screen such as is shown in FIG. 
4. This screen display includes a set of instructions 35 for the 
technician/user to begin the too adjustment process of the present 
invention. The first instruction displayed is "Level and lock the steering 
wheel." Although this step is not required when using the present process, 
it does simplify the procedure and reassures the technician/user who is 
accustomed to locking the steering wheel during toe adjustment procedures. 
The second instruction is to "Level and lock the sensors." This step is 
conventional. The screen display also includes a pair of visual indicia in 
the form of diagrams 37 and 39 which indicate to the user the desired 
action and the particular wheels which are the subject of the 
instructions. When the user has performed these actions, he presses the 
"Ready" key, and the display advances. 
The next visual display, the screen shown in FIG. 5, begins the actual toe 
adjustment process. This screen includes new instructions 35, which state: 
"Adjust right toe. Adjust the value toward zero." 
The desired action diagram 37 points to the right wheel in this screen, 
while the from wheels are still highlighted in diagram 39. A new visual 
indicia, graphical representation 41, on this screen provides to the 
technician user a visual indication of the direction and magnitude of the 
required adjustment to toe of the right front wheel. Specifically, this 
graph includes a set of bars 43 which represent out of tolerance values, a 
target area 45 indicating within tolerance values, and an arrow 47 
representing the present value. Also shown below these graphical elements 
is a numeric indication 49 of the magnitude of the desired adjustment. 
Target area 45 includes a pair of stepped bars 51 separated by a line 53. 
The shoulder in stepped bars 51 represents the point at which the 
measurement changes from being within the tolerance to being within 50% of 
the tolerance. Line 53 represents the desired value (zero point) for the 
adjustment. 
One aspect that makes this display unique is that the displayed information 
indicated by arrow 47 and numeric display 49 is not right toe measurement 
minus right toe specification. Instead, the present invention operates 
using an entirely different approach. Processor 3 is responsive to the 
initial toe measurements for the left front wheel LFW from the toe sensors 
to determine left front toe at the start of the toe adjusting procedure 
and to subtract the specification value for left front toe from the 
initial measured left front toe value. The result is stored in memory 33 
as a first toe comparison value. 
After recording this initial value of left from toe, the processor 
thereafter deals solely with total toe minus total toe specification. The 
aim of this step of the method (which is represented by the target line 53 
in display 41) is to adjust the toe of the right wheel until the total toe 
equals the first comparison value, which may be represented in equation 
form as follows: 
EQU TT-TT(spec.)=LFT-LFT(spec.), 
where TT equals measured total toe, TT(spec.) equals the specification 
value for total toe, LFT is the initially measured value of left front 
toe, and LFT(spec.) is the left front toe specification value. As the 
measured total toe (minus total toe specification) approaches the first 
comparison value, arrow 47 is controlled to approach target line 53. If 
rite target line is passed, the arrow appears at the appropriate position 
on the other side of target line 53. In addition, as the target line 53 is 
approached, the numeric indicia 49 are controlled to represent 
correspondingly smaller numbers. The situation where the toe of the right 
front wheel is adjusted until the total toe minus specification equals the 
first comparison value is illustrated in FIG. 6. When the user has 
performed these actions, he again presses the "Ready" key, and the display 
again advances. At this point, all adjustment of the right toe is 
complete, and adjustment to the toe of the left front wheel is begun. 
Adjustment of the left front wheel toe is illustrated in FIGS. 7 and 8. At 
this point in the process, the processor causes the instruction display to 
read 
"Adjust left toe. Adjust the value toward zero." 
The desired action diagram 37 now has indicia pointing to the left wheel, 
while diagram 39 continues to indicate that the action is to be performed 
on the front wheels of the vehicle. The bar graph display 41 is controlled 
during this step to display to guide the technician/user to adjust the toe 
of the left wheel so that the difference between total toe and the total 
toe specification becomes zero. The processor 2 uses the bar graph 41, and 
particularly the placement of the arrow 47 with respect to the rest of the 
bar graph to indicate to the user the desired magnitude and direction of 
the adjustment. The processor in determining this magnitude and direction 
does not at this point in the process compare measured left toe with left 
toe specification, but rather compares total toe with total toe 
specification. Since the right toe, has already been adjusted using a 
similar scheme, adjustment of total toe (minus specification) at this 
point in the procedure results in left toe being adjusted to the desired 
value. 
Note that the tolerance bars 51 shown in FIG. 6 are larger than those shown 
in FIG. 5. Processor 3 controls file size of the bars such that as the 
tolerance is approached, the bars become larger. This provides a larger 
target 45 for the technician/user and improves the precision of the 
adjustment. In this connection note that in FIG. 8 (as in FIG. 6), the 
tolerance bars 51 are larger still. In addition, processor 3 causes the 
display of different sized tolerance bars for difference tolerances--the 
tolerance bars for a larger tolerance being larger than those for a 
smaller tolerance. 
Processor 3 controls the display of screens such as those described above 
to prevent the technician/user from going on to the next step in the 
procedure until the previous step is satisfactorily completed. That is, 
the processor will not continue to subsequent screens until the adjustment 
of the current screen is performed to within the tolerance indicated by 
the tolerance bars 51. If the adjustment is not made to within tolerance, 
the next screen showing the magnitude and direction of the required change 
to toe of the other wheel is not displayed. 
Although it is preferred that the technician/user make the adjustment of 
toe to the exact specification, this does not always occur. In those cases 
where the adjustment results in the toe being within tolerance, but not to 
the exact specification value, a problem can arise. This is because the 
present invention is concerned with total toe, not individual toe, in 
general. Any deviation or error in the adjustment of the right wheel toe 
from specification, therefore, effects file total toe used to guide the 
adjustment of the left wheel toe. Using this total toe value can result in 
the toe of the left wheel also varying from specification by a similar 
amount. When this occurs the two wheels point in the same direction, but 
that direction is not straight ahead when the steering wheel is pointed 
straight ahead. Such a condition is unacceptable. Consequently, 
microprocessor 3 records any residual error in the adjustment of the right 
front toe and biases the display used to adjust left toe 41 and 49 such 
that, if left toe were adjusted exactly "to specification" per the display 
41 and 49, it would have the same residual error as right toe. This 
results in "symmetric toe", such that the two wheels have the same toe 
angles when the steering wheel is level. Even though right toe is not 
adjusted perfectly, the adjustment of left toe is not compromised, and the 
steering wheel is level when the vehicle tracks in a straight line. 
Note that the legend at the bottom of the display of FIG. 8 reads "When 
Everything is Ready, Press `Ready`". When this command is followed, a 
screen such as that of FIG. 9 is displayed, which shows the toe within 
specifications and instructs the user to perform the next step, in this 
case "Measure Caster." It should be appreciated that the particular next 
step is not a part of the present invention. 
Although the present invention has been described using bar graph type 
indicia to guide the technician/user in making the toe adjustments, 
numeric indicia may be used as well. See FIGS. 10-12. In these displays, 
the numbers shown are "measurements minus specifications." In FIG. 10, the 
user begins the procedure by steering the steering wheel until it is 
level, then observing and remembering the numeric display for "left toe," 
which is a display of the measurement minus the specification for left 
front toe. In the second step, which is shown in FIG. 11, the user adjusts 
the right toe by observing the "total toe" display until this display 
equals the amount remembered from the previous step. After the right toe 
is adjusted, the user moves on to the third step, which is shown in FIG. 
12, and adjusts left toe by observing the "total toe" display until it 
reads zero. Even if the wheels are steered and the steering wheel moves 
during the procedure, the adjustments are correct, because only total toe 
is being observed, and total toe is not sensitive to the steering of the 
wheel during the procedure. 
In either embodiment, processor 3 continuously updates the total toe 
measurements and subtracts the specification for total toe to update the 
displays. In this context, continuously means sufficiently often that the 
technician/user does not unnecessarily adjust the toe past the desired 
target before the display is updated. 
In view of the above, it will be seen that the various objects and features 
of the present invention are achieved, and other advantageous results 
obtained. The examples of the present invention described herein are 
illustrative only and are not to be construed in a limiting sense.