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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.

The objective of this work is to demonstrate the influence of line length concerning noise source generation using a coupled pump-motor-line model predicting superimposed pulsations of a hydrostatic transmission. This transmission model predicts superimposed flow pulsations throughout the connecting lines as well as oscillating forces dependant on system pressure variances; such oscillations are the primary sources of noise in hydrostatic transmissions which are known as FBN and SBN (Fluid Borne Noise and Structure Borne Noise), respectively. This study is a part of novel research where the prediction of superimposed noise sources considering interrelating dynamics of the pump/motor and connecting lines is accomplished and can potentially be used to develop noise source reduction strategies. An investigation considering the influence of line length demonstrates the potential to further reduce noise source generation in hydrostatic transmissions.

Mobile Earth Moving Machinery like Skid-steer loaders have tight turning radius in limited spaces due to a short wheelbase which prevents the use of suspensions in these vehicles. The absence of a suspension system exposes the vehicle to ground vibrations of high magnitude and low frequency. Vibrations reduce operator comfort, productivity and life of components. Along with vibrations, the machine productivity is also hampered by material spillage which is caused by the tilting of the bucket due to the extension of the boom. The first part of the paper focuses on vibration damping. The chassis’ vibrations are reduced by the use of an active suspension element which is the hydraulic boom cylinder which is equivalent to a spring-damper. With this objective, a linear model for the skid steer loader is developed and a state feedback control law is implemented.

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.

The aim of the presented study was to analyze the potentials of two different drive line concepts. The comparison is made for a simple Power Split Drive and a Hydrostatic Two-motor Transmission with a disconnectable hydromotor. The main focus is put on the achievable overall efficiency of both alternatives. The system complexity of the two compared transmissions is very different. The analysis therefore also looks towards this matter and further makes an assessment of the different control requirements.

The paper presents a new computer based design method for valve plate design using the simulation program CASPAR and the extension tool AVAS. CASPAR is based on a non-isothermal gap flow model considering time dependent gap heights and surface deformations due to high pressure loads for all connected gaps of swash plate axial piston machines. Among others the program allows the prediction of oscillating forces exerted on machine parts and the calculation of effective flow pulsation on both ports as a function of design and operating parameters. Together with the calculated instantaneous cylinder pressure the flow pulsation and oscillating forces can be taken as criterion to evaluate the effectiveness of design measures for noise reduction during the design phase, i.e. before prototype production. The models used in the program have been verified by different measurements on pumps and motors.

A new control concept was developed to minimize the power losses of a hydrostatic drive line for off-road vehicles. The drive line control concept is based on two separate closed loop controls, one for the hydrostatic transmission and another for the combustion engine. The command values for both control loops are calculated under consideration of the characteristic curves of the combustion engine and the losses within the hydrostatic transmission, using an on-line optimization procedure. This paper discusses the benefits of this control concept based on a comparison of typical realistic driving manoeuvres. Objective of the investigations for different output powers is the potential of fuel savings under different operating conditions. A hardware-in-the-loop test rig for the investigated hydrostatic propel drive is used for the experimental validation.

This paper deals with the use of a displacement controlled linear actuator for active oscillation damping of off-road machine structure. Aim is the development of system solutions and control concepts for the simultaneous use of displacement controlled (valveless) hydraulic actuators basing on single rod cylinder for the active oscillation damping of off-road machine structure and for the control of the working hydraulics movement. Thereby, the productivity of the machine and the operator comfort will be improved.

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.

Noise generation in axial piston machines can be attributed to two main sources; fluid borne and structure borne. Any attempt towards noise reduction in axial piston machines should focus on simultaneous reduction of these two sources. A multi-parameter multi-objective optimization approach to design valve plates to reduce both sources of noise for pumps which operate in a wide range of operating conditions has been detailed in a previous work (Seeniraj and Ivantysynova, 2008). The focus of this paper is to explain the background and to demonstrate the functionality and usefulness of the methodology for pump design.