Abstract
Estimation of road slope is important for transmission control unit (TCU), because different shift patterns should be applied at different slopes to prevent busy shift caused by a lack of traction at high speed gear. In case trailer is mounted on the vehicle, however, estimating road slope is not enough to prevent busy shift, because even more traction is needed by the extra weight and drag of trailer. It is normal to have a trailer switch around cabin on vehicles for towing trailer, and TCU can using different pattern accordingly. However, it is also possible to renovate vehicles which are not for towing trailer to drag trailers, and, in this case, TCU cannot get any input for trailer existence. The absence of trailer existence notification is very likely to lead to busy shift by lack of traction if vehicle moves uphill with trailer mounted. Thus, it is necessary to determine if the trailer is mounted without any additional sensor. Slope can be estimated based on engine torque and resistance force of vehicle. This algorithm provides the value of slope which takes overall load on the vehicle into account, not an actual slope of the road. On the other hand, slope estimation algorithm based on G-sensor value detects actual slope of road, not the load of the vehicle. However, it has benefits compared with the engine torque based algorithm in terms of accuracy and availability. To overcome this limitation when using G-sensor based slope estimation, algorithm of detecting extra weight of vehicle is proposed based on simple vehicle dynamics. A simulation with real vehicle data was performed to check if the algorithm is effective, and the result was positive. Algorithm is implemented in embedded controller and trailer weight estimation is validated with real vehicle. Modified slope value is introduced based on actual slope and estimated trailer weight, and this newly proposed slope can be used for shift pattern selection. Accuracy of slope estimation is critical for the vehicle weight estimation. However, since the availability of slope estimation is also important, compromise between accuracy and availability should be made, and some experiencebased conditions are applied to enable weight estimation without reducing the availability of slope estimation. Road slope estimation based on G-sensor value has many benefits compared with engine torque based estimation, but it has a limitation that additional load due to vehicle weight is not considered. With this trailer detection algorithm, trailer load can be not only detected but also calculated for slope compensation. Trailer detection becomes available by calculating estimated trailer weight. With this estimated weight, it is also possible to apply different shift pattern by applying modified slope value considering extra weight on the vehicle. Furthermore, trailer detection availability can prevent uncomfortable situation by busy shifting with no additional cost for the trailer mode option.