Method and system for conducting wheel alignment

Details Method and system for conducting wheel alignment Method and system for conducting wheel alignment

2001-06-26

2003-05-13

Gutierrez, Diego (Department: 2859)

Geometrical instruments

Gauge

Wheel

C033S203180, C033S288000

Reexamination Certificate

active

06560883

ABSTRACT:

FIELD OF INVENTION
The present invention relates to a wheel alignment system, and more particularly, to a method and system providing an improved technique for adjusting camber during wheel alignment.
BACKGROUND OF THE INVENTION
Proper wheel alignment of an automotive vehicle is important for handling of the vehicle and for tire wear. In addition, proper wheel alignment increases fuel efficiency and safety.
The wheels of a motor vehicle may be aligned in a number of ways. For example, an operator or an alignment technician can use a vision imaging system such as a computer-aided, three-dimensional (3D) machine vision that employs optical sensing devices, such as cameras, to determine the positions of various objects. Examples of such apparatus and methods are disclosed in U.S. Pat. No. 5,724,743, entitled “Method and Apparatus for Determining the Alignment of Motor Vehicle Wheels,” issued to Jackson, et al. on Mar. 10, 1998 and in U.S. Pat. No. 5,535,522, entitled “Method and Apparatus for Determining the Alignment of Motor Vehicle Wheels,” issued to Jackson, et al. on Jul. 16, 1996, each incorporated herein by reference.
During an alignment process, a number of parameters are measured and adjusted to achieve proper wheel alignment. These parameters include camber, caster, steering axis inclination (SAI) and toe.
A camber angle is the inclination of the wheel plane from side view with respect to the vertical plane. A camber angle is defined positive when the wheel leans outward at the top, and negative when it leans inward.
A caster angle is the measurement between the tire's vertical centerline of the steering axis through the upper and lower ball joints. Caster angle is the angle between the tire's vertical centerline of the steering axis through the upper and lower ball joints. A caster angle is considered positive when the top of steering axis is inclined rearward and negative when the top of the steering axis is inclined forward. Positive caster settings provide a greater degree of steering efforts, self-centering and stability to the vehicle. Therefore, nearly every car has a positive caster setting. A large positive caster provides greater stability in high-speed, straight-ahead driving, but at low speeds, steering is heavy. A smaller positive caster setting makes for easier low-speed steering, but at high speeds, the vehicle will tend to wander.
Steering axis inclination (SAI) is the angle in the front elevation between the steering axis and vertical.
A toe angle of a wheel, at a specified wheel, is the angle between a longitudinal axis of the vehicle and the line of intersection of the wheel plane and the road surface. The wheel is toe-in if the forward portion of the wheel is turned toward a central longitudinal axis of the vehicle, and toe-out if turned away.
Camber, caster, and SAI are typically measured using inclinometers attached to the wheel. With camber, the inclinometer measures the angle that the plane of the wheel makes with the vertical. To measure caster, the wheel is turned through an arc, and the difference in the camber readings is used to derive the caster value. This procedure is called a caster swing.
SAI is measured in a manner similar to caster, except that the inclinometer used for the SAI reading measures the change in pitch angle of a line in the plane of the wheel as the wheel is turned through an arc. The SAI measuring inclinometer is aligned at 90° to the inclinometer used for reading camber and caster.
A camber angle indicates the amount of inclination of a steerable wheel. The value of camber is affected by several different factors and changes with the directions of steerable wheels. In other words, the degree of wheel inclination of a steerable wheel changes during the rotation of the steerable wheel. The factors affecting the value of camber include the steering angle, caster and SAI. The values of caster and SAI will cause a unique relationship to exist between steering angle (toe), camber and SAI. Changes of camber are proportional to the values of caster, the steering angle and the SAI. Since caster and SAI are fixed, then a relationship of camber relative to toes exits. This may be measured empirically, or may be calculated, based upon camber, caster and SAI settings.
FIGS. 1
a
and
1
b
illustrate camber angles of a steerable wheel at different toe angles. The steerable wheel depicted in
FIGS. 1
a
and
1
b
is the left front wheel of an automotive vehicle. In
FIG. 1
a
, the steerable wheel is at zero toe. The steerable wheel has a negative camber of &phgr;1 degree. In
FIG. 1
b
, the steerable wheel is at &thgr; degree toe-out and has a positive camber of &phgr;2 degree. As a result, if an adjustment of camber is to be made at &thgr; degree toe-out to achieve a specification camber angle, for example, zero degree camber, a &phgr;2 degree adjustment must be made to achieve zero degree camber. However, the &phgr;2 degree adjustment in camber will result in a camber at (&phgr;1+&phgr;2) degree at zero toe. Therefore, an adjustment of camber carried out at non-zero toe is usually inaccurate.
For purpose of wheel alignment, manufacturers specify an acceptable camber value at zero toe. However, some technicians may make camber adjustment when toe is not zero because by doing so, the technicians do not have to turn the wheel to zero toe every time before making an adjustment to the camber.
Adjusting camber at non-zero toe is sometimes acceptable for vehicles with small caster and SAI. If the caster and SAI are small, the difference of camber at different steerable angle is also very small. Thus, the amount of camber adjustment at different steering angles is similar and the differences can be ignored.
However, for vehicles with large caster and SAI, such as Mercedes-Benz, this approach will cause inaccurate adjustment of camber. For example, the camber at zero toe may be two degree, but the camber for the same vehicle might be 15 degrees at ten degrees toe. If a technician makes a 15 degrees camber adjustment at ten degrees toe, the camber will become minus 13 degrees at zero toe.
Accordingly, vehicle manufacturers, especially those vehicles with large caster, strictly require camber adjustment to be made at zero toe.
This requirement causes problems to technicians. For instance, if a technician wants to adjust the camber of the left front wheel, the technician would have to turn the steering wheel to turn the left front wheel to zero toe first and then adjust the camber and relate it to the manufacturer's specification. Then the technician would have to take the steering wheel again, turn the right front wheel to zero toe and then adjust camber for the right front wheel. Consequently, the problem is that the procedure is time consuming because the technician is constantly adjusting the steering wheel to position the steerable wheels to zero toe positions. In addition, this procedure could introduce errors because any small deviation of toe from zero during the adjustment will affect camber.
SUMMARY OF THE INVENTION
Accordingly, there exists a need for increasing alignment efficiency. There is also a need to simplify alignment procedures. There is also a need for accurately adjusting camber. Still another need exists for providing an alignment procedure that does not require precise positioning of steerable wheels at zero toe position.
These and other needs are addressed by the present invention. The present invention provides a method and system for providing an improved camber adjustment technique. This invention increases technicians' efficiency by simplifying alignment procedures and at the same time provides accurate camber adjustment.
One aspect of the present invention relates to a method for measuring the amount of camber adjustment for a steerable wheel. The method comprises the steps of: turning the steerable wheel to a first position in which the steerable wheel is either toe-in or toe-out; turning the steerable wheel to a second position in which the steerable wheel is toe-out if the steerable whe

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