Investigations on the Effect of Synchronizer Strut Detent Groove Profile on Static and Dynamic Gear Shift Quality of a Manual Transmission 2020-28-0319

Automotive manufacturers are constantly working towards enhancing the driving experience of the customers. In this context, improving the static and dynamic gear shift quality plays a major role in ensuring a pleasant and comfortable driving experience. Moreover, the gear shift quality of any manual transmission is mainly defined by the design of the synchronizer system. The synchronizer sleeve strut detent groove profile plays a vital role in defining the performance of the synchronizer system by generating the minimum required pre-synchronization force. This force is important to move the outer synchronizer ring (blocker ring) to the required index position and to wipe-out the oil from the conical friction surfaces to build rapid high cone torque. Both these functional requirements are extremely critical to have a smooth and quick synchronization of the rotating parts under dynamic shift conditions. However, the same pre-synchronization force could be perceived as a mild-obstruction in static shift conditions that could affect the perceived shift-quality of the vehicle. Hence, a detailed evaluation was conducted with two different strut groove profiles including 45° and 30°. The evaluations included a detailed mathematical calculation, vehicle level assessment using Gear-Shift Quality Assessment (GSQA) equipment and rig level measurements of cone torque generation.

The investigation results revealed that the 30° variant could offer a better shift quality in static conditions with a 23% reduction in the peak strut force. However, under dynamic conditions, the reduced pre-synchronization force of the 30° variant is observed to be harming the oil wiping pressure. The reduced oil wiping pressure leads to a reduction in the friction coefficient of the conical surfaces leading to a slight reduction in the cone torque by 5.4%. The 30° strut detent is better for showroom shift quality and 45° strut detent is better for dynamic impulse reduction. The authors explain the reasons behind the observed results supported by calculations and experimental measurements at the vehicle and rig level.