Abstract Recently, for the aspects of ecology and economy, fuel efficiency improvement demand has been increased globally. And, various types of hybrid systems have been suggested. In response to this market demand, AISIN SEIKI has been developing Synchronizer-less hybrid automated manual transmission (HV-AMT) system aiming excellent transmission efficiency, excellent agility, and shift change quality like a step automatic transmission (AT). This hybrid system is constructed based upon a parallel 2-axis manual transmission (MT) which originally has high transmission efficiency. The synchronizer system of a MT is replaced by a Dog clutch system which does not spoil the transmission efficiency and never makes failure in synchronization. This Dog clutch system includes a modified detent function, a shift actuator of linear motor , advanced function controls for a clutch and a shift actuator. The system does have a motor, the traction motor, perhaps say that it does not need an additional motor for synchronization. This hybrid system also realizes smooth acceleration feel of the vehicle like a step AT and excellent drive feel of a MT for agility and drivability, eliminating torque interruption at power-on-down shift or power-on-up shift by coordinate control of a hybrid motor generator (MG), a clutch and an engine. In this paper, AISIN SEIKI describes the “Synchronizer-less system” for the HV-AMT system. 1. Introduction In the automotive industry, various hybrid systems have been proposed in response to the recent rise of demand for fuel efficiency improvement. Aisin has been developing a HV-AMT system to improve the fuel efficiency.The Gear train schematic of the HV-AMT system is shown in Figure 1. And the section view of the HV-AMT system is shown in Figure 2. The shift change operation table of the HV-AMT system is shown in Table 1 . The MG can be selected to connect to either input shaft or output shaft. The MG is connected to the input shaft by engaging ‘4-Dog’ for engine starting. On the other hand, it is connected to the output shaft by engaging ‘A-Dog’ for vehicle running. Figure 1. Gear train schematic of the HV-AMTDevelopment of the Synchronizer-Less System for HV-AMT 2016-01-1172 Published 04/05/2016 Takashi Iwata, Kyosuke Mori, Taketoki Maruyama, Shinobu Nakamura, Yusuke Yoshida, and Toshihiko Yamanaka Aisin Seiki Co., Ltd. CITATION: Iwata, T., Mori, K., Maruyama, T., Nakamura, S. et al., "Development of the Synchronizer-Less System for HV-AMT," SAE Technical Paper 2016-01-1172, 2016, doi:10.4271/2016-01-1172. Copyright © 2016 SAE InternationalDownloaded from SAE International by University of Minnesota, Tuesday, July 31, 2018Figure 2. Section view of the HV-AMT Table 1. Shift change operation table To reduce the transmission loss, the following three measures are adopted in the developed HV-AMT. • two parallel axes to reduce the bearing loss • allocating the counter axis at upper position • lowering the oil level by using an oil pump AISIN has developed the Synchronizer-less system in order to make further improvement of transmission efficiency. This paper describes design philosophy of the Dog gear teeth shape, design philosophy of the shift actuator, control strategies of gear shift change, and testing results for the vehicle performances in the Synchronizer-less system. 2. Motivation for Developing a Synchronizer- Less System The synchromesh system works as an apparatus for revolution speed synchronization in MT shifting and consists of “Synchronizer ring”, “Synchronizer key & Key spring” and “Synchronizer cone”. Those parts are equipped on the main shaft combined with a sleeve and a hub. (Figure 3) Upon shifting, the sleeve is moved toward the synchronizer cone, which is intended to be used, and then, the synchronizer ring generates a frictional force with the synchronizer cone integrated with the gear to enable changing the gear revolution to a desired synchronous main shaft r