Study On The Calibrating Method And Apparatus Of Four-wheel Aligners

With the development of the automobile industry, automobile has becomenecessary traffic equipment in people's everyday work and life. It brings humannot only benefit but also traffic accidents and environment pollution at the sametime.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 fuelconsumption and worse security,which have great influences to economy andefficiency of automobile, even will be a threat to safety. So the former automobileperformances should be kept by all means. To check the automobile performancesregularly is one of them. But if the test equipment was imprecise, we could not getthe exact situations of automobile. It is a pity that the problems exist widely in ourcountry, which brings more dangerous factors and hidden troubles. We trace themeasures to the national standards regularly to make sure the right status of the testequipments so that we can trust the test results. So it makes great sense to calibratethe automobile test equipments regularly according to correlative calibratingstandards.Wheel alignment failure is the commonest one of troubles. It brings on tyresabrasion, front-wheels sway and sideslip, which will influence controlling stabilityand driving safety of the automobile. So wheel alignment detection is the mostimportant test item of automobile safety tests.Four-wheel aligner is the special equipment to test the wheel alignmentparameters. Now four-wheel aligners have been widely used in automobilemanufacture and service. 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.First, because the four-wheel aligner adopts geometry model and approximateformula, the formulas being widely used now have academic errors. We shouldknow how to appraise the errors from the approximation exactly.Second, there are various four-wheel aligners. They have different structuresand metrical methods. Their performances and the reliability of test results are vitalto the stability and security of automobile. But how to evaluate the technicalperformance of four-wheel aligners is not solved.Several aspects of these problems referred above are studied in this paperaccording to the references read.1. The four-wheel aligner test theory and precision analysisFirst, the importance of correct wheel alignment parameters is introduced, aswell as the structure, test method and test process of the four-wheel aligners widelyused now.3 geometry models are built and analyzed to get the formula of testing camber.In the process of deduce, we know that the result of camber and toe-in is testeddirectly, which do not have theory error. Because of the dimensional position of themaster pin, there is no benchmark in the test of caster and SAI. To get indirectresults we should deduce the errors of the formulas by turning the front wheels. tochange the angle between the light beam and sensor .By this way the caster andSAI measured can be obtained. Then caster and SAI can be got based on theseveral models,.For the precision of the sensors used to test caster and SAI is less than 0.01°after being calibrated, errors of the four-wheel aligner apparatus come from thetheoretical error of different survey models and the inter-affects between SAI andthe angle measured.From 3 models we can see that the angle measured by lightbeam and angle sensor is the function of the caster and SAI,which can not be gotby corresponding relations separation method of caster,SAI and angle mesuredfrom formulas. Therefore,the measurement of caster influncesor the measurementof SAI, vice versa. For the functions deduced from different models are different,under which the test results will be different,too.At the same time, the differencebetweenlinear approximate model deduced from small angle of the measurementand the not approximate one causes errors.So precision of 3 models and the linearmodel need to be considered,which should be guaranteed by calibratingthefour-wheel aligner apparatus.2 Study on structure of four-wheel aligner calibrating apparatusThis part introduce the request of four-wheel aligner industry standard abouttest parameters, range, precision, analyze the function of other four-wheel alignercalibrating apparatus, point out the problem of calibrating caster and SAI by them.According to the movement track of wheel, sensors, master pin in test process,it supplies a 5 crossed axes model, which can be used to calibrate toe-in, camber,caster, SAI and thrust angle.The innovation of the structure design of four-wheel aligner calibratingapparatus lies in:Aiming at the character that all kinds of four-wheel aligner have the sameclamp fashion, we design the mechanical interface. By use of the quality thatcamber and SAI are measured in the same plane, we calibrate camber and SAI byone rotarytables. The calibrating apparatus can adjust caster and SAI independentlyby two mutual vertical oriented arms. This structure avoids the mutual influence ofcaster and SAI. It also uses the universal gearing to realize the aim transforminghorizontal angle displacement to angle displacement rotating master pin.Considering the difference between front wheel and rear wheel and lower cost,the calibrating apparatus get the camber by vernier. The calibrating apparatus of thethrust angle are got by adopting fission structure of two tables and transformingmovement between two tables by worm.The important calibrating apparatus of turntable are designed.3 Research on precision of four-wheel aligner calibrating apparatusThe main errors source of four-wheel aligner calibrating apparatus is analyzedqualitatively, which are the manufacture installation error, the gap error and thedistorted error under the gravity force. According to the profession standard of thechecking device request, the precision examination will sum up to the angleexamination and the geometry installment relation examination. In view of theprecision request, the calibrating measures are proposed and traced to the nationalstandards. How to carry on examinations using the multi-surface prism and thecollimator for the rotary table angle is introduced and confirmed by experiments.How to examine the position of the apparatus installment is introduced as well. Theexamination result accuracy of four-wheel aligner calibrating apparatus is proved.4 Experimental confirmations and result analysisThe standard curves of the calibrating apparatus obtained and the theoreticalerrors of simplified linear model are analyzed to know the influence to the casterand SAI mesurement based on different models. Carried on the arrangement toseveral kind of models accordding to their examination precision.The experimentalplan of calibrating the four-wheel aligner apparatus is introduced.One four-wheelaligner apparatus based on the linear simplified model and A,C four-wheel alignerapparatuses based on sensors are tesed,in which the toe-in,camber,caster and CAIare calibrated in main.The experiments indicated that the error of the toe-in andcamber is mainly zero error,which shows when one of the casters or SAIs isbig,the other one's error will be bigger.The true reason for the error of caster andSAI is explained,then the caster correlation formula is obtained under differentcasters.