Growing awareness of climate change, and an increase in fuel prices, has sparked a renewed interest in hybrid vehicle technologies. While electric hybrids have thus far received most of the attention, hydraulic hybrids have shown significant benefits especially for larger vehicles. Currently a number of architectures exist for hydraulic hybrid transmissions, each with their own benefits and deficiencies. One of the most popular architectures known as a series hybrid suffers from periods of low efficiency due to continual operation at high minimum system pressures, poor torque response when the required pressure is higher than the current system pressure, and the requirement for more expensive over-center units.

The authors have previously presented a novel blended hybrid system architecture which addresses the aforementioned deficiencies. This novel architecture blends components of a hydrostatic transmission and a parallel hybrid thereby increasing system efficiency and response to levels greater than either transmission could provide individually. The hydrostatic path improves efficiency over series hybrids by permitting the system to operate at the lowest required pressure for a given load. Additionally the hydrostatic path improves response and user feel to that of a mechanical transmission. Further a series of check valves removes the need for over-center units while braking. Finally a second set of check valves allow engine and accumulator power to be combined together while still maintaining a stiff and responsive system.

Power split transmissions (PST) represent the next generation of hydraulic hybrid architectures. They combine the flexibility and energy recovering potential of series hybrids with the efficiency of a pure mechanical transmission. In this paper the authors will incorporate the previously introduced blended hybrid into the hydraulic path of a power split transmission. A baseline automatic transmission, a traditional hydraulic hybrid PST, and the novel blended hybrid PST will be modeled and simulated in a class II truck.

Previous research has demonstrated the major influence controller design has on fuel economy. In fact a poor system architecture with good control can outperform a superior system architecture utilizing a substandard controller. To ensure a fair system comparison dynamic programming will be used to optimally control all three transmissions, thereby removing the effect of controller design on fuel consumption. The authors will conclude the paper with a detailed analysis and comparison of the three system architectures

Aktuelle Herausforderungen für ventilgesteuerte hydrostatische Verbraucher ist die Minimierung der energetischen Verluste entlang des Steuerstrangs, die Erhöhung der Positioniergenauigkeit und der Stellzeiten im Kontrast zum Streben nach kostengünstigen und robusten Systemen. Die Freiheitsgrade dieses Optimierungsproblems sind sowohl komponenten- als auch regelungstechnischer Art. Ventile mit aufgelösten Steuerkanten zur getrennten Regelung von Vor- und Rücklauf und die daraus hervorgehende Einführung digitaler Ventiltechnik sind die technischen Träger des Fortschritts. Neue regelungstechnische Methoden, wie beispielhaft die Nutzung der Eigendynamik eines Ventils durch die Ansteuerung mit einem Signalimpuls, werden dem großen Komponentenspielfeld überlagert. Für den Planer hydraulischer Anlagen ergeben sich so unüberschaubare Arbeitsfelder, eine objektive Systemauslegung unter Berücksichtigung aller Möglichkeiten ist nicht realisierbar. Dem Ingenieur kann hier kein Vorwurf gemacht werden, da kein geeignetes Werkzeug zur Verfügung steht, um die Topologie eines Systems in Frage zu stellen, sondern lediglich Parameteroptimierungen automatisiert durchgeführt werden können.

Am Institut für Fluidsystemtechnik wird eine innovative Methodik zur Systemauslegung entwickelt: Technical Operational Research (TOR) sieht im Kern folgendes Vorgehen zur Auflösung der nicht-trivialen Problematik vor: Der erste Schritt der Systemauslegung ist immer die Klärung der grundlegenden Funktion des Systems. Anschließend folgt die Frage nach dem Ziel der Planung. Dieses Ziel ist immer subjektiv und erfordert vom Planer eine Positionierung des Projekts im Zwiespalt von Energieeffizienz, Robustheit, Genauigkeit und Kosten. Der zur Erfüllung von Ziel und Funktion vorhandene Komponentenbaukasten wird im nächsten Schritt beschrieben. Dazu werden die Gleichungen zur Beschreibung einer Komponente formuliert. An dieser Stelle sind alle Entscheidungen zur Auslegung des Systems getroffen, aber dessen Struktur noch unbekannt. In einem weiteren Abstraktionsschritt entsteht ein gemischt-ganzzahliges lineares Programm (MILP) zur Topologievariation. Durch die Nutzung von stückweise linearer Optimierung kann die globale Optimalität des Systems hinsichtlich der definierten Funktion und Ziele garantiert werden, ohne dass Kompromisse hinsichtlich der Genauigkeit gemacht werden müssen. Dieser Schritt stellt den bisherigen „missing link“ zwischen Planung und Validierung bisheriger Auslegungsprinzipien dar. Die innerhalb des Optimierungsmodells optimalen Lösungen werden physikalisch durch 0-dimensionale Modelle, z.B. mittels des Sprachstandards Modelica überprüft. Zur Validierung dienen konventionelle dreidimensionale Simulationen oder Versuche, bevor das System realisiert wird.

Low power linear drives (P < 5 kW) are used in a wide field of applications, ranging from process automation via wind power plants, automotive applications to plastic machinery. Conventional valve controlled hydraulic drives are increasingly displaced by electromechanical drives due to several advantages (good energy-efficiency, less required space, low maintenance effort, easy plug and play connectivity). In recent years, new energy-efficient electrohydraulic compact drives came up, which improve user-friendliness of hydraulic drives significantly. Configured as speed-controlled Turn-Key-Assembly these compact drives combine the advantages of both electromechanical drives and hydraulic drives (reliability, robustness, large forces, good overload protection) and accordingly improve the competitiveness of hydraulic drives.

In the recent past, investigations on electrohydraulic compact drives were carried out at Dresden Institute of Fluid Power augmentively. After investigating systematically circuit variants as well as static, dynamic and efficiency performance of preferred variants, the next important step is to investigate the thermoenergetic behaviour. In order to guarantuee a temperature stable process of electrohydraulic compact drives the knowledge of the thermo energetic properties is essential. Owing to the complexity of thermal processes a lumped parameter simulation model is appropriate, in order to simulate, analyze and optimize the thermo energetic behaviour of electrohydraulic compact drives with reasonably effort.

Due to the good energy-efficiency of the compact drive a cooling aggregate is not installed. As a consequence, the thermal behaviour is governerd by the interaction between heat input (via dissipated energy) and the passive heat output (via free convevtion and radiation). Moreover, in comparison with conventional hydraulic systems electrohydaulic compact drives are only equipped with a small oil volume. This leads to a high sensitivity to incoming heat flows. Approaches known from literature, which describe the thermo energetic behaviour of conventional hydraulic systems with lumped parameters, can not be transferred on electrohydraulic compact drives. Main reasons for this are the complex 3-dimensional interferences between the highly integrated components and the passive heat transfer. An appropriate way to simulate the thermo energetic behaviour of electrohydraulic compact drives with lumped parameters is not known yet.

The proposed paper highlights the thermoenergetic behaviour of an electrohydraulic compact drive, which was built up as a demonstrator in the laboratory. Based on measurements of energy-efficiency an analysis of heat sources, heat flows and heat sinks is done. Derived from the analytic description of the components thermal behaviour a thermo-hydraulic simulation model with lumped parameters was built up and validated by measurements on the demonstrator. Besides thermo elements a thermographic camera was used to detect the specific temperatures in different regions of the compact drive in detail.

The results of the measurements show the thermoenergetic behaviour of the compact drive in different operating cycles. However, in comparison with simulation results some divergences appear. It can be shown, which differences occur between model and experiment and which accuracy can be achieved with the present knowledge and methods. New approaches for the investigation and simulation of the thermoenergetic behaviour of electrohydraulic compact drives are proposed.

The construction machinery is widely used in all kinds of earthwork construction, but due to the low efficiency of hydraulic systems, some energy regeneration should be put forward. The paper will introduce a novel potential energy regeneration system that based on electric-hybrid system. Potential energy regeneration system which shares an electrical storage component with power system, can effectively improve the energy utilization without additional expense. However the traditional potential energy regeneration system results in poor dynamic characteristic. A novel potential energy regeneration system which combine throttle-governing and regeneration devices, can guarantee the dynamic characteristic of system, and realize the maximum efficiency of energy recovery. For its simple layout, it can be applied to different actuator, the paper will analyze the novel potential energy regeneration system in theory in comparison to throttle-governing system and traditional potential energy regeneration system, finally some simulations will be presented,the simulation results show the effectiveness and dynamic characteristics of novel potential energy regeneration.