Clutch to clutch shift control technology, which is the key enabler for a compact and low cost transmission design, is important for both automatic and hybrid transmissions. To ensure a smooth clutch to clutch shift, precise synchronization between the on-coming and off-going clutches is critical. This further requires the on-coming clutch to be filled and ready for engagement at the predetermined time. Due to the compact design, currently there is no pressure sensor inside the clutch chamber, and therefore the clutch fill can only be controlled in an open loop fashion. The traditional clutch fill approach, by which the clutch fill input pressure command is manually calibrated, has a couple of limitations. First, the pressure profile is not optimized to reduce the peak flow demand during clutch fill. Moreover, it is not systematically designed to account for uncertainties in the system, such as variations of solenoid valve delay and parameters of the clutch assembly. In this paper, we present a systematic approach to evaluate the clutch fill dynamics and synthesize the optimal pressure profile. First, a clutch fill dynamic model, which captures the key dynamics in the clutch fill process, is constructed and analyzed. Second, the applicability of the conventional numerical dynamic programming (DP) method to the clutch fill control problem, which has a stiff dynamic model, is explored and shown to be ineffective. Thus, we proposed a customized DP method to obtain the optimal and robust pressure profile subject to specified constraints. The customized DP method not only reduces the computational burden significantly, but also improves the accuracy of the result by eliminating the interpolation errors. To validate the proposed method, a transmission clutch fixture has been designed and built in the laboratory. Both simulation and experimental results demonstrate that the proposed customized DP approach is effective, efficient and robust for solving the clutch fill optimal control problem.

Clutch fill control is critical for automotive transmission performance and fuel economy, including both automatic and hybrid transmissions. The traditional approach, by which the clutch fill pressure command is manually calibrated, has a couple of limitations. First, the pressure profile is not optimized to reduce the peak clutch fill flow demand. Moreover, it is not systematically designed to account for uncertainties in the system, such as variations of solenoid valve time delay and parameters of the clutch assembly. In this paper, we present a systematic approach to evaluate the clutch fill dynamics and synthesize the optimal pressure profile. First, a clutch fill dynamic model is constructed and analyzed. Second, the applicability of the conventional numerical Dynamic Programming (DP) algorithm to the clutch fill control problem is explored and shown to be ineffective. Thus we developed a new customized DP method to obtain the optimal and robust pressure profile subject to specified constraints. After a series of simulations and case studies, the new customized DP approach is demonstrated to be effective, efficient, and robust for solving the clutch fill optimal control problem.

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The perturbation method of renormalization is used to study the effect of nonlinearity on a hard-walled rectangular waveguide. The excitation would induce only the fundamental nonplanar symmetric mode if the system were linear. The analysis develops a solution that satisfies a nonlinear wave equation for the velocity potential, as well as all boundary conditions. The response consists of a pair of oblique planar waves that interact through second-order excitation of the true planar mode. The investigation discloses that in the highfrequency limit the signal has a quasiplanar behavior. In contrast, for very low frequencies exceeding the cutoff value, the oblique waves are essentially independent. The distortion is then a result of self-refraction, in which the particle motion shifts the wave fronts and rays. The transition between the low-and high-frequency limits is marked by the appearance of nonlinear frequency dispersion, which produces asymmetrical distortion of the waveform. PACS numbers: 43.25.Cb, 43.20.Mv

Hydraulic assist power system (HAPS) is a low-cost system that converts vehicle kinetic energy during vehicle deceleration or braking into hydraulic energy and then uses it to assist vehicle propulsion. Unlike conventional hybrid electrical vehicles (HEV) or hydraulic hybrid vehicles (HHV), where a separate motor/generator or motor/pump set is required, the present concept uses the existing hydraulic pump of the transmission unit as the motor/pump set directly. This leads to reduced size, lower weight and less cost. Typical applications of HAPS include energy recovery, engine restart, and hill-holding, etc.