The present invention relates generally to a process and an apparatus for setting the toe-in/out of vehicle wheels and, in particular, to a process and apparatus for inspecting the toe-in/out on a vehicle front axle assembly during manufacture.
Toe-in and toe-out are defined as the distance between the front edges of the front wheels of a vehicle being shorter and longer respectively than the distance between the rear edges of those wheels. Vehicle front wheels are typically adjusted to a toe-in position and herein the term toe-in may be utilized to refer to both an actual toe-in position and any position from maximum toe-in to maximum toe-out. In the past, vehicle front wheel toe-in settings have been performed by a variety of methods. Initially, mechanical devices were attached to the spindles, wheel rims or brake backing plates for the measurement of the toe-in or toe-out. For example, an elongated paddle extending in a horizontal direction was attached to each of the axle spindles. Separate length measurements were taken at the front ends of the paddles and at the rear ends of the paddles using a tape measure and the difference between these two measurements was the toe-in or toe-out setting.
Another prior art method involved engaging the spindle or rim of each front wheel and measuring the angular deviation from a line parallel to the longitudinal axis of the vehicle with a mechanical linkage and pointer. In one such device, the pointer was replaced by a potentiometer for generating an electrical signal representing the measured angle.
Alternatively, the wheel rim or spindle was engaged by a level or inclination detector utilizing liquid or air to support an indicator of toe-in or toe-out of the wheels. In one form, electrodes were immersed in the liquid to generate electrical signals indicating the angle with respect to the wheel. Other prior art devices engaged the wheels with mechanical linkages coupled to mirrors for sighting reference lines or reflecting light beams.
Since the front wheel toe-in influences the steering stability and riding qualities of a vehicle and has a direct effect on tire wear, it is important to properly set the toe-in on an axle assembly line before the axle is installed in the vehicle. However, most of the devices and methods described above lack the necessary close tolerance required for current axle assembly procedures and may require two operators. Furthermore, since pointers, level detectors and line of sight techniques are utilized in those devices, the operator's judgement as to when correct alignment has been achieved is relied upon. One attempt to solve the above-identified problems in an axle assembly line involved an apparatus which referenced from the brake backing plate mounting surfaces of a front axle assembly for sensing and indicating whether the assembly, including an I-beam type front axle and a tie rod, initially has too much or too little toe-in, with provisions for sensing and indicating any change thereto resulting from manual manipulation of the tie rod. Such an apparatus was lowered by an operator onto the spindles of a front axle assembly, slid inwardly along the spindles and clamped against the oppositely disposed brake backing plate mounting surfaces. Air sensing means sensed the actual toe-in relationship between the two mounting surfaces, and visual indicators displayed such toe-in relationship to the operator. As the operator rotated the tie rod, the changes in the angular positions of the backing plates were conveyed to the operator through the display.
One disadvantage of the last described device is that after it is lowered into position over the spindles, clamping mechanisms must be slid into place and clamped on the brake backing plates before measurements can be made. This process is reversed after the measurements are made in order to remove the measured axle and replace it with a new axle. Such operation tends to slow down the axle assembly production process. In addition, the measurements of toe-in are made from the brake backing surfaces. Although these surfaces are machined perpendicular to the longitudinal axis of the associated spindle, the wheel will be mounted on the outside surface of the spindle and a more accurate measurement could be made from such surface.