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Planetary gear trains (PGT) are widely used in automatic transmissions (AT), hybrid electric powertrains (HEP) and plug-in hybrid electrical powertrains (PHEP) for automotive vehicles. Many PGTs have been developed by the industry including 6, 7, 8, 9 or 10 speeds automatic transmissions for internal combustion engine (ICE) powertrain systems; PGTs with two electrical machines (EM) and an ICE for single mode or multi-mode HEP systems; PGTs with single EM and an ICE for PHEP systems. Facing the new competitive challenges in motor vehicle electrification, synthesizing the simpler or if possible simplest PGTs for PHEP becomes an important task. The work reported in this article is such an effort which results in much simpler, if not the simplest, PGT designs for PHEP as well as for automatic transmissions.

While the basic working principle and the mechanical construction of automatic transmissions has not changed significantly, increased requirements for performance, fuel economy, and drivability, as well as the increasing number of gears has made it more challenging to design the systems that control modern automatic transmissions. New types of transmissions—continuously variable transmissions (CVT), dual clutch transmissions (DCT), and hybrid powertrains—have presented added challenges. Gear shifting in today’s automatic transmissions is a dynamic process that involves synchronized torque transfer from one clutch to another, smooth engine speed change, engine torque management, and minimization of output torque disturbance. Dynamic analysis helps to understand gear shifting mechanics and supports creation of the best design for gear shift control systems in passenger cars, trucks, buses, and commercial vehicles.

This paper presents a newly developed integrated powertrain control system. The system coordinates the controls between engine and transmission to optimize powertrain operation for drive quality and fuel economy. This new control system uses the desired engine power as the common load variable for both engine and transmission control instead of throttle as is used in conventional powertrain controls. The main advantages to this control system are improved fuel economy and drive quality. Other advantages and a brief description of the control system will be described in more detail in the following discussion.

The ratio changing mechanics of the continuously variable transmissions are developed. The lever analogy of gear sets, comparison to step gear transmission mechanics, differential calculus analysis, and the step gear ratio changing equations are used. Power on up-shifts, power on downshifts, power off up-shifts, and power off downshifts are analyzed. Approaches to minimize the disturbances are considered.

The non-freewheeler shift control technology (clutch-to-clutch shift) is the key enabler for a compact, low mass and low cost automatic transmission design, especially when the transmission has an extended number of speeds. For the past two decades, a variety of non-freewheeler shift control technologies have been developed. The Allison Transmission LCT, the Saturn MP7 and the Chrysler 42LE can be considered as representatives of those technologies. All of those technologies (traditional) use two independent pressure control valves to control the oncoming and the off-going clutches. The synchronization of these two clutches is accomplished by means of electronic controls. Due to the variation of the system parameters and the difficulty of detecting the oncoming clutch fill, the consistency and robustness have always been the issues, even after years of development.