6 months ago

MDA Technologies 2/2015

MDA Technologies 2/2015

Holistic powertrain

Holistic powertrain optimization Dennis Möller The hydraulic-mechanical powersplit transmission from Dana Rexroth Transmission Systems offers a modular hardware platform and modular transmission control software in addition to decoupling of engine and vehicle speed. This opens up new options with regard to increased efficiency and performance optimization of the vehicle and its powertrain including working hydraulics. Dipl.-Ing. Dennis Möller, Team Leader System Application and Simulation, Dana Rexroth Transmission Systems Srl, Arco, Italy Stricter requirements regarding emission limits and increasing fuel prices lead to higher requirements for vehicle efficiency in the Off-Highway market. While improving driving and working comfort with increased functionality, the fuel consumption shall be reduced without restricting the vehicle dynamics or productivity. Transferring this requirements to the powertrain of a mobile working machine, results the necessity to design all compo- nents in the powertrain to gain a high efficiency and to have an optimal coordination amongst them. This is applicable for both the hardware and the controller software. The transmission, as central interface between engine, vehicle drive axle and working hydraulics, plays here a crucial role. For this reason modern and advanced transmission concepts need to contribute towards improving the efficiency of the powertrain and vehicle holistically; bringing a high efficiency, an improved transmission controller and a high level of integration. HVT and its advantages The joint venture Dana Rexroth Transmission Systems (DRTS) was established between Dana Holding Corporation and Bosch Rexroth AG in 2011 with the objective of deve- 32 MDA Technologies 2/2015

DRIVE TECHNOLOGIES loping efficient powersplit transmissions for mobile working machines. The resulting hydrostatic-mechanical powersplit transmission HVT offers by its transmission concept the best premises for a holistic optimization of the complete powertrain, including working hydraulics and operation strategy for the internal combustion engine. Thus, it is the central element to react to the above mentioned requirements for a modern mobile working machine and to achieve best possible results regarding efficiency and handling performance. The HVT combines the comfort, a simpler positioning control at low driving speeds and the good efficiency of a purely hydrostatic first drive range with the high efficiency of a hydrostatic-mechanical powersplit transmission in second and third drive ranges at higher vehicle speeds (Image 1). The change of drive ranges is performed without noticeable interruption in traction; with synchronous shift point between first and second drive range and through an asynchronous powershift between the second and third drive range. The latter allows to move the shifting point within a specific transmission ratio range in favour of efficiency and vehicle dynamics. A decoupling of vehicle speed and diesel engine speed and thus a reduction of diesel engine speed in driving mode is possible through the continuous variable transmission ratio. The main operating range of the internal combustion engine can be moved closer to the optimal operating point from specific fuel consumption point of view and additional fuel savings can be achieved with an optimized control. The purely hydraulic first drive range provides the advantage of an almost wear-free, steady and very dynamic reversing without the required clutch shifting close to zero speed. This results in high efficiency and a good fine positioning capability. As even the braking in all drive ranges can be done hydrostatically through the transmission supported by the drag torque of the internal combustion engine, the wear of brakes can be reduced and even avoided in many cases, depending on the vehicle weight and load. The operating and maintenance costs for the vehicle owner are hereby reduced through almost wear-free braking and reversing. Overall the HVT makes it possible to achieve fuel savings of up to 35% depending on the application and possible downsizing of the internal combustion engine. Of course with equal or even an increased handling and driving performance. Modular approach The HVT-R2, which is currently undergoing a final testing in field tests and whereby its start of serial production is planned for the first half of 2015, can be customized to a series of different applications with a transmission input power between 135 kW and 01 Drive ranges and efficiency characteristic of the hydrostatic-mechanical powersplit transmission HVT-R2 195 kW due to its modular design. This includes wheel loaders, graders, skidders, reach stackers, empty container handlers, heavy forklift trucks and RoRo tractors. Simultaneously the HVT-R3 is being tested in first prototype vehicles. It is developed in DRTS for applications with a higher input power ranging from 200 kW to 260 kW and offers a similar hydrostatic-mechanical powersplit transmission concept and thus the same high potential for a holistic powertrain optimization. The modularity of the HVT is based on both transmission hardware and transmission control software. The HVT-R2 has for example up to three power-take-off interfaces for connecting working hydraulics and steering pumps. These interfaces offer a by approx. 20% to 35% increased operating speed of the working hydraulics compared with engine speed and thus enable using the same working hydraulics as in a standard transmission but with a simultaneous reduction of diesel engine speed and without restricting the maximum volume flow. Furthermore, the HVT is available with four different final gear ratio options in the transmission without changing the installation space, which corresponds to the space occupied by a standard torque converter. This allows a flexible adjustment of maximum output torque and output respectively driving speed to the requirements of different applications. In addition, it also offers the option of using a hybrid module with energy storage connected to a powertake-off on the transmission input side. This can feed back the recovered braking energy Optimized connection of powertrain and working hydraulics through powersplit transmission possible into the drivetrain or working hydraulics for reducing the load of the internal combustion engine and thus opens up an option for further fuel savings or further down-sizing of the internal combustion engine and hence a reduction of emissions. The transmission control software ensures the modularity mainly by providing a structure that reflects the physical components of the real transmission. It consists of three main components namely transmission control, vehicle control and electrical control unit. Each one of these components is again built in layers: Application Layer (AL), Communication Layer (Com) and Sensor/Actuator Layer (SAAL). The Physical Abstraction Layer (PAL) represents in the transmission controller each individual transmission hardware component in its own software module. By this design it is foreseen to replace only the respective software module when customizing or replacing individual physical components and their characteristic properties, without having to change the complete control software. This helps in achieving a high portability and simpler customization for different powertrain configurations. Additionally, the transmission control software becomes the central point for processing and controlling signals from the engine, transmission, working hydraulics, vehicle and brake/inch pedal and any hybrid modules. The HVT is completely integrated in the powertrain and the vehicle control by its modularity in hardware and software. Due to a high level of networking, the information from the accelerator pedal, brake/inch pedal and MDA Technologies 2/2015 33


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