Energy Savings in Hydraulic Hybrid Transmissions through Digital Hydraulics Technology

Abstract

Hydraulic hybrid drivetrains, which are fluid power technologies implemented in automobiles, present a popular alternative to conventional drivetrain architectures due to their high energy savings, flexibility in power transmission, and ease of operation. Hydraulic hybrid drivetrains offer multiple environmental benefits compared to other power transmission technologies. They provide heavy-duty vehicles, e.g., commercial transportation, construction equipment, wagon handling, drilling machines, and military trucks, with the potential to achieve better fuel economy and lower carbon emissions. Despite the preponderance of hydraulic hybrid transmissions, state-of-the-art hydraulic hybrid drivetrains have relatively low efficiencies, around 64% to 81%. This low efficiency is due to the utilization of conventional variable displacement pumps and motors that experience high power losses throughout the drive cycle and thus fail to maintain high operating efficiency at lower volumetric displacements. This work proposes and validates a new methodology to improve the overall efficiency of hydraulic hybrid drivetrains by replacing conventional pump/motor units with their digital counterparts. Compared to conventional pump/motors, the digital pump/motor can achieve higher overall efficiencies at a wide range of operating conditions. A proof-of-concept digital pump/motor prototype was built and tested. The experimental data were integrated into a multi-domain physics-based simulation model of a series hydraulic hybrid transmission. The proposed methodology permits enhancing the overall efficiency of a series hydraulic hybrid transmission and thus allows for energy savings. Simulating the system at moderate load-speed conditions allowed achieving a total efficiency of around 89%. Compared to the average efficiency of the series hydraulic hybrid drivetrains, our simulation results reveal that the utilization of the state-of-the-art digital pump enables improving the total efficiency of the series hydraulic hybrid drivetrain by up to 25%.

Influence of Hydraulic Drivetrain Configuration on Kinematic Discrepancy and Energy Consumption during Obstacle Overcoming in a 6 × 6 All-Wheel Hydraulic Drive Vehicle

“…The developed model allowed us to obtain different traction coefficient values depending on slip; see Figure 7. The dependency of the traction coefficient on the slip value of the wheel model is similar to the characteristics found in the literature [15,17,[28][29][30]. The slip factor is defined as the ratio between the theoretical wheel velocity (resulting from its angular velocity and dynamic radius) and the actual velocity.…”

“…Eckert et al [17], in their work, focused on examining the possibility of using multidomain optimization design and power management control in hydraulic hybrid vehicles in various configurations of the structure of the drive system. As a result of the research, they managed to increase the range of the vehicle, but the study was limited only to driving on a paved road.…”

“…The research showed the possibility of a reduction in fuel consumption by approximately 30%, only by changing the operating parameters. However, as in [17], they were limited to the load characteristics of the motor vehicle on firm ground. Azzam et al [19] demonstrated a beneficial effect on energy consumption of applications in a hybrid hydrostatic drive system instead of the conventional variable displacement pump or multi-piston digital pump.…”

“…Papers [17][18][19] concerned mainly motor vehicles. The developed models focused on the issues of modeling the drive systems themselves and their structures and did not consider the interaction between the wheel and the ground.…”

Digitalization of Radial Piston Pumps through Internal Mechanically Actuated Designs

“…They also offer various configuration options, allowing for standardized and cost-efficient equipment designs. Given all these advantages, fluid power has been occupying a well-defined research area and scholarly activities, serving prevalent industries like agriculture, transportation, construction, aerospace, manufacturing, and many other industrial applications requiring high actuation power and fast energy capture [4].…”