Road Parameters Acquirement And Its Application In Shift Control

Nowadays the automatic transmission techniques are already widely used in different kinds of vehicles. As using this technique, the vehicle's speed can be changed easily and drivers also don't need to press the pedal frequently. So automotive transmission techniques have lightened the burden of driving and improved the safety and comfortableness of driving, and it becomes an aim which people have pursued for a long time. Along with the rapid development of automotive techniques,electronic control techniques and computer techniques, the automatic transmission techniques also have a prodigious improvement.In order to enhance vehicle's dynamic performance and economical efficiency, the vehicles must always run under the best gear. So selection and determination a shift schedule become one of the most important techniques in the research and development of automatic transmission techniques. The shift schedules can be divided into three kinds by the parameters it used, e.g. single parameter shift schedule,two parameters shift schedule and three parameters shift schedule. But the existing shift schedules only consider the vehicle's status parameters, such as throttle,velocity and acceleration, yet not consider the road's characteristic parameters sufficiently. Using this kind of shift schedules will cause unnecessary shift operations under some road environments, the gear and the shift timing also conflict with the road environment and driver's intension. So it is necessary to introduce road parameters into automatic transmission control system. Thus it is possible to make the vehicle's shift operations coordinate with the road environment, improve the shift quality, as well as the comfortableness and safety of driving, and enhance vehicle's dynamic performance and economical efficiency.At present, GPS techniques have been matured and are widely used in precisely position for moving target carrier. Using GPS can make us get the precise position coordinate and moving direction for the target carrier. High-accuracy electronic maps with plentiful information already service for vehicle navigation,personal movement position and different kinds of monitor and service systems. The map matching algorithm which is used to match the GPS position data and the electronic maps is also widely used in navigation system; the accuracy and real-time capability of this algorithm are improved greatly along with the development of its application in different fields. Combining the foregoing techniques, based on the precise position data acquired from GPS and the plentiful road spatial and attributes information in electronic maps, it is now possible to precisely locate the vehicle on the road and acquire the road parameters at the vehicle's current position. Due to the fact that the automatic transmission control system lacks of road environment parameters in the process of executing gear shift, based on GPS position data and the plentiful road information in electronic map, we have researched how to acquire the road parameters at vehicle's position and use road gradient information in shift control, and this paper is mainly carried out on the following three parts.Part 1: Map matching algorithm. In order to locate the vehicle on the road, the GPS position data must be matched with electronic maps. As GPS and electronic maps are not very accurate due to different reasons, if the position data acquired from GPS receiver are directly displayed on electronic maps, the position data will stray away from the actual road and this matching result can cause position deviation, so map matching becomes a useful method to solve this problem.In the map matching algorithm used in this system, the topological connection relation of road network is sufficiently used to search candidate road sections. When the GPS position data or the saved history information are invalidation, the map grids are used to decrease the search range of candidate road sections, and the candidate road sections are searched in the map grid into which the vehicle is falling. In order to select the optimal matching road section from the candidate road section set, D-S evidence reasoning is used. The orthogonal projection point which is from GPS position point to the optimal matching road section is used as the vehicle's position on the road, namely the matching point of the vehicle's position.Part 2: Acquiring the road parameters in real time .When the vehicle's position on the road is known, based on the topological connection relation of road network and vehicle's moving direction, the road on which it will run can be forecasted, the road parameters information of these roads can be pre-read out from electronic maps and stored into cache, this process is done by a pre-read algorithm. When the automatic transmission control system needs road parameters, it can fetch the parameters from cache instead of electronic maps, in this way the real-time characteristics are improved. After acquiring the road's gradient characteristic parameters, according to the practical situation of slope road, curve fitting method is used to calculate the gradient value for every position on the slope.Part 3: Using road parameters in shift control. When the vehicle is running in some complex road environments, for example upslope, downslope or curved road, as the automatic transmission control system don't know the current road environment situation, it may execute some unnecessary shift operations.In this system, only how road's gradient information affects the shift operation is considered. When the vehicle is running on upslope or downslope, the entry parameter (velocity) of shift schedule is adjusted according to the gradient, so that the shift operations can fit in with current road environment.Finally,a simulation experiment environment is built to verify the road parameters acquirement method and the road parameter's application effect in shift control, thought the experiments we can watch and analyze the affection of road gradient on gear shift. In the simulation experiments, map matching algorithm is used to get the vehicle's matching point on the road, and the road gradient parameters at current position are acquired in real time based on the matching point and electronic map, then the entry parameters of shift schedule is adjusted according to this parameters. From the experiments results we can know that, when the vehicle is running in slope environment, after acquiring the road gradient parameters and adjusting the shift schedule'entry parameter, the recursive shift operations on upslope or frequent shift operations in slope environment can be avoided effectually. The experiment result makes it clear that it is necessary,viable and effectual to introduce road parameters into shift control .When realizing the system's software, the map matching model and shift control model are implemented in C language, so they can be easily transplanted into embedded system. In order to watch the map matching result and the road parameters as well as vehicle status parameters in experiments, in VC6.0 development environment MFC is used to load MapObjects and display the electronic maps. When the vehicle is running, the vehicle's position is displayed on the electronic map in real time, road parameters and vehicle status parameters are also shown in a parameters information dialog.According to the theory research and simulation experiments, together with the experiment results analysis, we can draw a conclusion that it is viable to locate the vehicle on the road and acquire the road parameters at the vehicle's position based on GPS position data and road information in electronic maps. On the base of current road environment, the automatic transmission performs reasonable shift operations; this enhances the adaptive capacity of shift operations to road environment, improves the comfortableness and safety of driving, enhances the dynamic performance and economical efficiency, and provides a more comfortable driving environment for drivers. All the research makes a base for continuative works.