Study On Passenger Cars Handling Objective Benchmark Targets Setting

During the developing process of new car products, it is the tasks on guaranteeing and improving chassis dynamics that participate the most significant roles while among the programming flow of chassis dynamics, it is the design on handling that occupies the core status, which is also regarded as an essential in conjunction with the level of safe driving.The advanced chassis programming flow of modern vehicles is shown in Fig. 1. From this figure, it is illustrated that the flow generally constitutes of three phases namely"real world field test","computer aided design on vehicle dynamics"and"subjective evaluation and adjustment". Among the first phase, the taches of"benchmarking target setting"and"design target determining"have provided guide lines for the rest phases. Therefore, study on vehicle handling objective benchmark targets setting should be firstly campaigned and conducted for an auto corporation when deciding to initiate new car products developing.On the other hand, due to the reasons of technique gaps between China and the aboard as well as the inavailability to getting access to the design methodology of those key parameters, the auto corporations in China have to attach to the power from overseas in the field of"benchmarking"and"target setting", which is not only a waste of money but also a handicap of technique evolution. Thus, study on passenger cars handling objective benchmark targets setting should be paid much attention to at this time, which, I'd like to say a very time of witness the rejuvenation and prosperity of China's auto industry.The passenger cars handling objective benchmark targets include mainly two fundamental aspects: the objective targets of handling and the test conditions on benchmarking. Here, the objective targets of handling indicate a series of open-loop indexes which are used to establish guide lines for the taches of"concept design"and"performance cascade"(see Fig.1) while the test conditions on benchmarking refers to the certain procedure for obtaining these targets, especially the regulated test speeds and lateral accelerations.For the selection of the above mentioned handling objective targets, this paper has concentrated its horizon on those open-loop indexes and characteristic values revealed by ISO and GB test methods concerning vehicle handling performance. With the help of a pre-research on the taxonomy of chassis dynamics, a concept named"sub-performance"is introduced and the relations between these certain sub-performances and those potential objective targets are proposed. On this basis, the dynamic mechanisms of all the open-loop indexes and characteristic values are seriously studied and corresponding affiliations toward certain sub-performances are established. Finally, by canceling those indexes and values which may redundantly describing the same aspect of chassis dynamic behaviors, a set of handling objective targets is established.For the matching of the benchmarking test conditions, a concept named"longitudinal speed– lateral acceleration"characteristic field is proposed, which demonstrates a 2-D longitudinal speed– lateral acceleration cross-plane laid out with three sub-areas i.e. the linear region, the nonlinear region and the on-center region. From the viewpoint of chassis dynamics objective evaluation, it can be found that most of the ISO and GB test methods are virtually initiated to examine the vehicle performance at certain positions in this plane. Therefore, in order to give an elaborate description of passenger car handling dynamics, test conditions should be chosen to cover the area of the"longitudinal speed– lateral acceleration"characteristic field as much as possible. On this basis, the work of test conditions benchmarking is conducted and fulfilled and the passenger cars handling objective benchmark targets are primarily established. Fig. 2 indicates the distribution of each sub-performance in the"longitudinal speed– lateral acceleration"characteristic field.After accomplishing the handling objective benchmark targets setting, the author has calculated and extracted all the concerned indexes according to the real world test data from a three-box import-car. During this course, problems of frequency response fluctuation caused by the GB 6323.2—94 (steering wheel pulse input test method) recommended data processing approach have been discovered, which may lead to a relatively low accuracy for indexes displaying. In order to settling these problems, systematic analysis both on the characteristics of the input/output signals and the principle of the data processing method itself has been conducted. As a result, a fire-new approach based-on ARMAX model is advanced. By comparing with the traditional data processing method, higher accuracy and better consistency of the ARMAX approach have been proved. On this basis, the author has transplanted this method into the steering wheel step input test method and anticipant effects of this transplantation have been achieved. Therefore, it is possible now to use only the steering wheel step input test method to both obtain the time-domain and frequency-domain properties of vehicle lateral dynamics and the benchmarking test conditions could be correspondingly simplified.