Study On The Detection Method Of Heavy Vehicles Wheel Alignment

With the development of the automobile industry and transportation, more and more motor trucks are used in common life. Motor truck plays an increasingly important role. It brings human not only benefit but also traffic accidents and environment pollution at the same time.The automobile performance problems come from many aspects. First, automobile is a complex mechanical-electronic system, as the mileage increasing, some technical status will change, such as lower dynamic performance, more fuel consumption and worse security,which have great influences to economy and efficiency of automobile, even will be a threat to safety. So the former automobile performances should be kept by all means. To check the automobile performances regularly is one of them. But if the test equipment was imprecise, we could not get the exact situations of automobile. To research the measurement of vehicle safety test equipments and to make sure the right status of the test equipments are very important. And then we can get reliable test results. So it makes great sense to calibrate the automobile test equipments regularly according to correlative calibrating standards.Wheel alignment failure is the commonest one of troubles. It brings on tyres abrasion, front-wheels sway and sideslip, which will influence controlling stability and driving safety of the automobile. At the same time the influence wheel alignment failure on heavy vehicles. So wheel alignment detection is the most important test item of automobile safety tests, especially heavy vehicles'.Four-wheel aligner is the special equipment to test the wheel alignment parameters. It can test the position parameters such as camber, toe-in, caster, SAI, thrust angle and so on based on the analysis of the geometry model. Nowadays, four-wheel aligners for car and miniature vehicle have rapidly developed. But the research of the test equipment which is specialized for the detection of heavy vehicle wheel alignment parameters has not been profound. At present, the test results of the wheel alignment equipments are unreliable because of the imprecise test model. All of these are directly related to the stability and safety of the vehicle operation.Several aspects of these problems referred above are studied in this paper according to the references read.1. Theoretical analysis of the effects of wheel alignment and it's influence on vehicles.First, reference datum of the wheel alignment detection and the wheel alignment method are analyzed. This paper selects the geometric center line position as the heavy vehicles wheel alignment method. Second, the main function of some parameters of the wheel alignment is analyzed theoretically in this paper. Based on these, the paper researches the influence of the wheel alignment parameters on vehicle performance, such as straight driving stability, controlling stability and sideslip. From the analysis, we can see that wheel alignment parameters have important influence on vehicle performance. Finally, the relationship between vehicle failure and wheel alignment is studied. These mentioned above provides a theoretical basis for the detection theory and method of the heavy vehicle wheel alignment parameters.2. Research of the measuring principle of heavy vehicle wheel alignment parameters.Camber angle can be directly measured with angle sensor. The measurement of toe is as follows: first, select geometric center line as the measuring datum, and then establish the measurement model. At last, toe can be derived from this model. Toe and camber angle are directed measured during these process. So there are no theoretical errors. Kingpin is an imaginary axis. And the kingpin angle measurement is lack of measurement datum. Therefore wheels should turn a certain angle, and the kingpin measured angle is derived from the certain angle of the angle sensor. In this paper, the measurement theory of the Pre-show angle at 20°is expounded.3. Research of the measuring method of heavy vehicle wheel alignment parameters.In this part, the measurement methods of main parameters of wheel positioning, such as camber angle, kingpin inclination angle, caster angle, toe-in are researched. First, the toe-in measurement model is established. During the process the influences of the scale position deviation and frame deflection on the model accuracy are considered. In this paper, all of those influences are modified. At last a modified formula for the model is shown in this paper. Second, the measurement method of camber angle is analyzed considering the measurement theory and characters of camber angle. And angle sensor is selected is this part. Third, kingpin angle measurement model is studied. Calculation formulas of kingpin caster angle and inclination angle are derived. At the same time, the influence of the symmetry degree of steering angles on the measurement model accuracy. From the analysis results, we can see that when the steering angles are symmetry the measurement model is precise. The relationship between kingpin caster angle and inclination angle is analyzed. The result is kingpin caster angle measurement model is insensitive to the change of inclination angle and vice versa. And this paper has also carried on the analysis to the influence of the steering angle accuracy on the model. The steering angle measurement equipment must meet the strict accuracy requirement.4. Carry on the error compensation and simulation experiment to the measuring method.In this paper, the errors caused by the bracket installation error and tire rim deviation are analyzed. And the compensated mode is derived from the analysis. The compensated mode of wheel camber angle and toe-in measure error is also researched in this paper. The method mentioned above can eliminate the errors caused by the bracket installation error, tire rim deviation and so on. And moreover, this paper carries on simulation experiment using SolidWorks platform and MatLab to establish the geometric middle line which is important for toe-in measurement. The experimental result shows that the toe-in survey model can establish the geometry middle line effectively, enhance the toe-in survey the accuracy.