2008-32-0040 (SAE) / 20084740 (JSAE) New Generation Hydraulic-Mechanical Transmission with Lock-up Mechanisms and Automatic Start Clutch Yoshihiro Yoshida, Nobuyuki Yakigaya, Kazuhiko Nakamura, Kazuhiro Takeuchi, Kenichi Nakano and Yasutaka Usukura Honda R&D Co., Ltd. Copyright © 2008 SAE International and Copyright © 2008 SAE Japan ABSTRACT New Generation Advanced Hydraulic-Mechanical Transmission (A-HMT) with the Lock-Up mechanism and the automatic start clutch mechanism was developed. In the lock-up mechanism, an electronic control in conjunction with transmission control was adopted using oil temperature, throttle opening, and input / output rotation ratio as parameter to reduce a rotational energy change of input and output axis caused by the volumetric efficiency of A-HMT. In the automatic start clutch, the load sensing function, damper function, and cooling function by replacing the simple hydraulic mechanism are equipped. By these solutions, the transmission efficiency has enhanced approximately 10% compared with former A-HMT, and excellent starting performance and smooth transmission performance have achieved. INTRODUCTION In these years, even with straddle-type motorcycles, simplification of driving operations by automatic transmission has been required. In applying a V belt-type continuously variable transmission that is popular in scooter-type motorcycle, however, it is necessary to change the location on the engine or the power transmission structure to the driving wheel. The Advanced Hydraulic Mechanical Transmission (A-HMT) adopted for All Terrain Vehicle (ATV) in 2000 has a merit of easy accommodation inside the engine of straddle-type motorcycle by its unique uniaxial structure and can be defined as continuously variable transmission (CVT) suited for straddle-type motorcycle with its excellent transmission performance. Details of the structure and the performance have been reported in the past (1) (2). The A-HMT is composed of a pair of fixed displacement axial piston pump and variable displacement axial piston motor and features a uniaxial structure with the cylinders of hydraulic pump and hydraulic motor connected together and integrated with the output axis. This characteristic is noticeable in power transmission as shown in Figure 1 and Table 1. General parallel axial-type hydro-static transmission (HST) allows the input mechanical power to be converted to fluid power by means of the hydraulic pump and then output after being converted to mechanical power again by means of the hydraulic motor. Theoretical formulae in HST are shown below. ( 1 ) in pumpmotor out ( 2 ) T in: Input torque Tout: Output torque Nin: Input rotational speed Nout: Output rotational speed Dpump: Pump displacement Dmotor: Motor displacement The A-HMT is a kind of power split drive. The output power from hydraulic motor is similar to that of HST. The output power from hydraulic pump depends on the hydraulic reaction force generated in it. They are synthesized and output finally. Theo retical formulae in A-HMT are shown here. ( 3 ) ( 4 ) Output power delivery is executed by the hydraulic motor. The hydraulic pump has a swash plate of a fixed angle TDT/g32D pumpmotor outin DD NN/g32 in pumpmotor in out T T T/g14 /g32DD pumpmotor outin D N/g321D N/g14 SAE Int. J. Engines | Volume 1 | Issue 1 1381 and transmits the torque equal with the input torque. The transmission torque and the output rotational speed of hydraulic motor are changed by the variable control of the swash plate. Especially, when the motor swash plate is in the position perpendicular to the rotation axis, conversion to mechanical power is not carried out but driving power transmission is carried out by the hydraulic pump. In this case, the hydraulic motor is only to get leakage loss and mechanical loss caused by the high-pres