Approaches to Achieving AWD Torque Accuracy 2008-01-0303
In an actively managed AWD driveline system, a vehicle-level controller communicates a torque request to a torque-transfer device which couples the front and rear drive axles, in order to achieve a desired vehicle behavior. The accuracy with which the coupling device responds to the torque request has a significant impact on both the vehicle performance and the durability of the driveline. Inaccurate torque response may affect vehicle performance by degrading vehicle traction, handling, and stability, or by producing undesirable NVH behavior. Driveline durability may be at risk in modern vehicles where lighter, lower-cost driveline components require that driveline torque be limited, in order to prevent mechanical failure.
The degree to which the AWD system is successful in accurately transferring torque is dependant upon several factors, including unit-to-unit production variation inherent in the manufacturing process, mechanical and electrical component variation over the range of operating conditions, and changes in the characteristics of the coupling over the expected life of the system.
This paper discusses several methods which may be employed to reduce or compensate for these sources of inaccuracy, including factory break-in, controls calibration, and controls compensation for thermal operating conditions. Data is presented which indicates that these methods complement each other in producing a more accurate torque response.