Geometrical instruments – Gauge – Wheel
Reexamination Certificate
2001-11-26
2003-10-21
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Gauge
Wheel
C033S288000, C033S203120, C033S203180
Reexamination Certificate
active
06634109
ABSTRACT:
FIELD OF THE DISCLOSURE
The present disclosure relates to a method and system for characterizing the steering system of a vehicle and determining symmetry and Ackermann geometry status thereof, and more particularly, to a fault tolerant method and system for determining symmetry and Ackermann geometry of the steering system of a vehicle.
BACKGROUND OF THE DISCLOSURE
The magnitude of total toe during turns affects both tire wear and vehicle handling. An asymmetrical steering system with different amounts of total toe when steering left or right may indicate faulty components in the vehicle, which can degrade the vehicle handling and cause problems, such as the darting to one side as the vehicle goes over an undulation. Therefore, it is important to know whether the steering system of a vehicle is symmetrical.
For determining proper steering geometry and symmetry of steering systems, automobile manufacturers provide a specification for Toe Out On Turns (TOOT). TOOT is generally measured by requiring technicians to turn the inner wheel in a first direction, say, left, at 20 degrees and measures the toe angle of the outer wheel. The measurement is then compared with a specification value. The same procedure and measurement are repeated for the other direction (in this example, right). As an alternative, total toe is measured and compared with the specification. Asymmetry in the steering system, as indicated by dissimilar TOOT values, is a fairly reliable indicator of damaged or improper steering components, or even chassis damage, including improper repairs after an accident.
Symmetry checks using TOOT measurements have drawbacks. First, TOOT is not always checked during an alignment process. Second, TOOT specification requires taking measurement at 20 degrees, technicians have to precisely position the wheels at the specific angle before toe angle measurements can be taken. Positioning a wheel at a specific angle requires high maneuver precision.
Furthermore, while TOOT measurements are taken at 20 degrees of turn, measurements for various alignment parameters, such as caster and steering axis inclination (SAI, are taken at ten degrees of toe. As a consequence, technicians have to turn the steerable wheels from the straight ahead position through precisely ten degrees to determine caster and steering axis inclination, and then turn another ten degrees to determine TOOT.
Besides, TOOT specifications require taking measurement at 20 degrees of turn. Many aligners do not have the angular range to measure twenty degrees of turn by purely electro-optical means. Although other equipment, such as electronic turnplates, can be used in place of the aligner's measurement instrument, additional installation is needed, which adds expenses.
Another important characteristic of the steering system of a vehicle is Ackermann geometry. One hundred percent Ackermann geometry is created by using a trapezoidal shaped steering linkage. Ackermann geometry causes all of the vehicle wheels to describe arcs about a common point. Thus, theoretically, eliminating any wheel scrub at low speeds and minimizing tire wear from cornering. Even though most vehicles are designed to have less than one hundred percent Ackermann geometry, significant deviation from one hundred percent Ackermann geometry may be an indication of damaged, non-compliant, or mis-adjusted parts in a vehicle's steering system, which can cause problems similar to an asymmetric steering system.
FIG. 1
shows a vehicle having true Ackermann geometry. A pair of fixed-direction wheels
10
a
and
10
b
are mounted for rotation upon a rear axle
12
, and a pair or steerable wheels
14
a
and
14
b
are rotatably mounted upon a front axle
16
, both pair of wheels being conventionally positioned about the longitudinal axis of the vehicle chassis.
As the wheels are turned, the outer wheel must turn at a lesser angle than the inner wheel to prevent scuffing of the wheels as the vehicle makes a turn. The center lines of the rear and front axles are represented by the axle lines
18
and
20
, respectively. The lines
22
and
24
represent the axes of the respective steerable wheels
14
a
and
14
b
. A steering system having perfect Ackermann geometry will have an optimum rolling action relative to point O. For purpose of reference, the steerable wheel that is closer to point O during turning is referred to as the inner wheel, while the steerable wheel that is farther than the other steerable wheel relative to point O is referred to as the outer wheel.
Practical limitations of design and requirements for optimizing handling at higher speeds require steering systems designed at other than perfect Ackermann geometry. It has been known that, due to the design of steering systems, perfect Ackermann geometry can be achieved only at one specific turning angle for each turning direction (i.e., left and right). However, significant deviation from Ackermann geometry may indicate defects in the steering system.
Even though pure Ackermann geometry is not practical and generally not desired, the relationship of steering characteristics to theoretically pure Ackermann is an extremely useful tool for the developers of steering systems. Applications for a steering analysis system include vehicle development engineers, racing car development and tuning, collision repair analysis, and heavy truck fleets.
Automobile manufacturers, however, do not publish Ackermann specifications. Without an Ackermann geometry specification, garages have no way to detect and correct errors related to Ackermann geometry.
Therefore, there is a need for effective determination of symmetry of a vehicle's steering system. There is another need to determine symmetry of a vehicle's steering system at any toe angle. Still another need exists for determining Ackermann geometry without an Ackermann geometry specification. These and other needs are addressed by the present disclosure.
SUMMARY OF THE DISCLOSURE
The disclosure provides a method and system for determining symmetry and Ackermann geometry of a steering system of a vehicle. An advantage of methods and systems according to the disclosure is that, during determining symmetry measurement of a steering system, the steerable wheels can be positioned at any toe angle. Methods and systems according to disclosure are also advantageous in that it allows determination of Ackermann geometry based on a TOOT specification, even without an Ackermann specification. A further advantage of systems and methods according to the disclosure arises from providing an improved alignment procedure that incorporates determination of symmetry of the steering system into other alignment procedures. The present disclosure provides a novel procedure to determine Ackermann geometry of a steering system based on theoretical Ackermann angles. Additionally, a system and method according to the disclosure determines symmetry in a steering system of a vehicle without the need to turn steering wheels through a huge angular range.
A method according to the present disclosure determines symmetry of the steering system of a vehicle of a type having first and second steerable wheels normal to a common axis when the wheels are aligned to a longitudinal axis of the vehicle. The method detects a first measured toe angle of the first steerable wheel when the second steerable wheel is positioned in a first direction at a reference toe angle, such as 10 degrees, and a second measured toe angle of the second steerable wheel when the first steerable wheel is positioned in a second direction at the reference toe angle. The second direction is opposite to the first direction relative to the longitudinal axis of the vehicle. The method determines symmetry of the steering system based on the first measured toe angle and the second measured toe angle.
In one aspect, the method compares determines symmetry of steering system based on the first measured toe angle, the second measured toe angle, and a threshold value. An angle difference between the first measured toe an
Dale, Jr. James L.
Jackson David A.
Cohen Amy R
Gutierrez Diego
McDermott & Will & Emery
Snap-on Technologies, Inc.
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