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Continuously variable transmissions (CVT) have been gaining popularity because they decouple the engine of a vehicle from the vehicle wheels, providing seamless shifting in vehicle operation and allowing the engine to operate in a speed range where fuel consumption and emissions are minimized. In particular, the power-split CVT, or power split drive (PSD), combines the variability of a CVT with the high efficiency of a mechanical transmission, providing potential benefits for both on road and off road vehicles. Hybrid PSDs allow further fuel savings by transferring the vehicle's kinetic energy to an energy storage device such as a battery, flywheel, hydraulic accumulator or other means during braking and utilizing the stored energy during the next propulsion cycle. While many power split configurations exist in literature (Miller 2005), this paper focuses on a dual stage input coupled PSD with a flywheel energy storage device.

With the need for improvement in the fuel economy along with reduction in emissions due to stringent regulations, powertrain hybridization has become the focal point of research for the automotive sector. Hydraulic hybrids have progressively gained acceptance due to their high power density and low component costs relative to their electric counterpart and many different architectures have been proposed and implemented on both on and off-highway applications. The most commonly used architecture is the series hybrid which offers great flexibility for implementation of power management strategies. But the direct connection of the high pressure accumulator to the system often results in operation of the hydraulic units in high pressure and low displacement mode. However, in this operating mode the hydraulic units are highly inefficient. Also, the accumulator renders the system highly compliant and makes the response of the transmission sluggish.

Continuously variable transmissions (CVT) provide seamless shifting in vehicle operation, allowing the engine to operate at a nominal speed range resulting in lower fuel consumption and emissions. However, typical CVTs suffer from either low shaft-to-shaft efficiency or low torque handling capabilities. The power split CVT combines the variability of the CVT with the efficiency of a mechanical transmission, providing potential benefits for both on road and off road vehicles. By modifying the architecture and layout of a power split transmission, the characteristics and maximum speed of the vehicle drive cycle can be altered. This paper will present a comparison between the different architectures of power split transmissions utilizing hydraulic units as the variators, with a focus on efficiency, control effort, and system complexity. Applications based on the characteristics of the specific transmission architectures will be suggested.

This paper compares two different rule-based power management (PM) strategies, in terms of their resultant fuel consumptions, through a simulation study as applied to a hybrid hydraulic multi-actuator displacement controlled (DC) system. Specifically, the system analyzed is a mini-excavator, wherein the digging functions are powered using four variable displacement pump/motors - these units are also shared by the auxiliary functions. In addition, the on-board hydraulic energy storage device, or accumulator, is charged or discharged using an additional pump/motor, called the storage unit. A parallel architecture is used for the hybrid system wherein the additional pump/motor is on the engine shaft, running at the same speed as the engine (and the other four pumps). An aggressive and fast, digging cycle was used to size the storage unit and accumulator, as well as to compare the performance of the two different strategies.

Modern on-road vehicles have been making steady strides when it comes to employing technological advances featuring active safety systems. However, off-highway machines are lagging in this area and are in dire need for modernization. One chassis system that has been receiving much attention in the automotive field is the steering system, where several electric and electrohydraulic steering architectures have been implemented and steer-by-wire technologies are under current research and development activities. On the other hand, off-highway articulated steering vehicles have not adequately evolved to meet the needs of Original Equipment Manufacturers (OEM) as well as their end customers. Present-day hydrostatic steering systems are plagued with poor energy efficiency due to valve throttling losses and are considered passive systems relative to safety, adjustability, and comfort.

A novel Blended Hydraulic Hybrid transmission architecture is presented in this paper with benefits over conventional designs. This novel configuration combines elements of a hydrostatic transmission, a parallel hybrid, and a selectively connectable high pressure accumulator using passive and actively controlled logic elements. Losses are reduced compared to existing series hybrid transmissions by enabling the units to operate efficiently at pressures below the current high pressure accumulator's pressure. A selective connection to the high pressure accumulator also allows for higher system precharge which increases regenerative braking torque and energy capture with little determent to system efficiency. Finally operating as a hydrostatic transmission increases transmission stiffness (i.e. driver response) and may improve driver feel in certain situations when compared to a conventional series hybrid transmission.

Original equipment manufacturers and their customers are demanding more efficient, lighter, smaller, safer, and smarter systems across the entire product line. In the realm of automotive, agricultural, construction, and earth-moving equipment industries, an additional highly desired feature that has been steadily trending is the capability to offer remote and autonomous operation. With the previous requirements in mind, the authors have proposed and validated a new electrohydraulic steering technology that offers energy efficiency improvement, increased productivity, enhanced safety, and adaptability to operating conditions. In this paper, the authors investigate the new steering technology's capacity to support remote operation and demonstrate it on a compact wheel loader, which can be remotely controlled without an operator present behind the steering wheel. This result establishes the new steer-by-wire technology's capability to enable full autonomous operation as well.