ABSTRACT Driveline torque distribution has long been a research topic, and in the last several decades research has been directed towards enhancing on-road vehicle stability and agility through application of controllable driveline systems. This paper discusses the impact of Direct Yaw Control AWD systems (DYC AWD Systems) on the combined acceleration and turning performance as it pertains to maneuverability and stability on all road surfaces. To achieve higher levels of both safety and performance, the application of a controllable DYC AWD system capable of applying direct yaw moment to the vehicle chassis serves as a key goal to achieve the optimal result. A classification of existing driveline systems is discussed and compared to these optimal requirements. Representative on-vehicle scenarios are discussed to illustrate the impact of AWD control on the vehicle stability and maneuverability and to highlight the effects to the vehicle operator. Finally, the integration of the AWD feed-forward control with feedback control demands from a yaw stability control algorithm are discussed. INTRODUCTION Driveline system design is affected by a variety of factors such as cost, weight, packaging, etc. Of the various designs and constructions, each has its own fundamental character and function. Some designs are oriented towards off-road traction, others towards part-time function, and some towards on-road performance (1,2). Invariably, the design constraints and vehicle level targets often lead to specific choices that determine the final tradeoff between various performance traits. Some customers use their vehicles in severe off-road conditions such as steep slopes and in deep mud; and, hence some driveline systems are specifically oriented towards this area. However, generally, customers use their vehicles for on-road driving on a regular basis. Because of this, a vehicle’s on-road performance is an important aspect to the overall safety and performance of the vehicle. On-road conditions vary from day to day according to weather; and, various geographic regions have their own characteristics. Accordingly, an AWD system’s operation should provide similar characteristics in order to provide driving confidence and security to the driver. One such characteristic that is important for driving confidence and hence dynamic safety is the ability of the AWD system to produce accelerating and turning results that are reasonably consistent across a wide range of driving conditions. LINE TRACE DYNAMICS DURING COMBINED ACCELERATION AND TURNING AWD systems have the inherent capability to distribute torque to the various wheels of the vehicle under driving (and sometimes engine coasting) situations. The overall effect of the distributed driveline torque generally contributes to understeer or oversteer depending on the surface condition of the road, the vehicle speed and the lateral acceleration level. As pointed out by Williams (1,2), many of the modern AWD systems are constructed from either a FWD or RWD basis and may be part time, full time, on-demand, etc.. The basis from which the AWD system is constructed has an impact on the fundamental behavior of the line trace dynamics. Hence the fundamentals of the line trace dynamics can be discussed at a basic level in the comparison between the behaviors of a FWD vehicle versus a RWD vehicle. LINE TRACE DYNAMICS OF FWD VEHICLES In the case of a FWD vehicle, addition of driveline torque to the front axle under turning conditions generally contributes to increased understeer. Since the front wheels are responsible for both cornering and driving force loads, increase of the driving torque requirement reduces the ability to achieve the same cornering result compared to when there is no driving load. As a standard metric to quantify the accelerating and turning line trace dynamics, a simple test can be prescribed termed the R/R O test. In the R/R O test, the vehicle is acceler