Optimal Energy Use in a Light Weight Hydraulic Hybrid Passenger Vehicle

Abstract

In this study we present a procedure for the design and implementation of a control strategy to optimize energy use within a light weight hydraulic hybrid passenger vehicle. The hydraulic hybrid utilizes a high pressure accumulator for energy storage which has superior power density than conventional battery technology. This makes fluid power attractive for urban driving applications in which there are frequent starts and stops and large startup power demands. A dynamic model of a series hydraulic hybrid powertrain is presented along with the design of a model predictive control based energy management strategy. Model predictive control was chosen for this study because it uses no future information about the drive cycle in its design. This increases the flexibility of the controller allowing it to be directly applied to a variety of drive cycles. Using the model predictive framework, a holistic view of the powertrain was taken in the design of the control strategy, and the impact of each actuator’s efficiency on overall efficiency was evaluated. A hardware-in-the-loop experiment using an electro-hydraulic powertrain testbed was then used to validate the dynamic model and control performance. Through a simulation study in which each actuator’s efficiency was given varying levels of priority in the objective function, it was found that overall system efficiency could be improved by allowing for small sacrifices in individual component performance. In fact, the conventional wisdom of using the additional degrees of freedom within a hybrid powertrain to optimize engine efficiency was found to yield the lowest overall powertrain efficiency. In this work we present a rigorous framework for the design of an energy management strategy. The design method improves the powertrain’s operational efficiency by finding the best balance between optimizing individual component efficiencies. Furthermore, since the design of the control strategy is built upon an analysis of individual components, it can be readily extended to other architectures employing different actuators.

Energy Efficiency Comparison between Hydraulic Hybrid and Hybrid Electric Vehicles

“…Operating variables such as pressure difference and volumetric flow rate, hydraulic motor-pump parameters (volumetric displacement), and fluid parameters (fluid viscosity coefficient, density, and bulk modulus) typically influence efficiency. The efficiency of the hydraulic pump and motor varies according to the operating conditions such as pressure and volumetric flow rate [17]. The majority of the pump efficiency map, at a fixed flow rate, is populated with efficiency above 80%.…”

A Model Predictive Control Approach for Fuel Economy Improvement of a Series Hydraulic Hybrid Vehicle

“…The controller estimates a future control trajectory that minimizes the quadratic cost function, which reflects the optimization goals, and is subject to the dynamic constraints of the system over a finite prediction horizon. Recently, MPC has been applied to solve the optimal control problem in power-split HEVs [9][10][11], and in HHVs [12,13].…”

“…Deppen et al developed MPC-based energy management for a parallel HHV [12] and a lightweight passenger SHHV [13]. Engine throttle, pump displacement, and valve opening are the input variables.…”

Structural-parametric synthesis of hydro-mechanical drive of hoisting and lowering mechanism of package-forming machines

“…The obtained results of papers [5] do not cover research in loading of the drive at various stages of the technological cycle. The most extensive description of the mathematical model of the process of cargo formation with the use of a hydromechanical drive is given in article [6]. The experimental studies, described in this source, make it possible to estimate power consumption of a drive, but only with one kind of loading on the operating sector.…”

“…Taking into account actual properties of gas essentially complicates computations [5,6]. We also selected the range of values of working pressure (5-10 MPa) and temperature (5-30 ºC), at which a hoisting and lowering mechanism functions.…”