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This work aims to design a hydraulic hybrid vehicle model with a series transmission architecture. The hydraulic hybrid transmission uses hydro-pneumatic accumulators to store energy instead of batteries or capacitors and, although less well known, can offer several advantages compared to hybrid-electric systems. In the implemented model, a pump is connected to an engine and supplies hydraulic power to a hydraulic motor, linked to the vehicle wheels axle. Regenerative braking is enabled with the hydraulic motor, working as a pump, and returning fluid power to the accumulator. Optimization tools were used to select the dimensions of the components and to determine the values of the control variables for activating the pump/accumulator. The model implemented had its consumption reduced by about 50 \(\%\) in relation to the reference values, and the accumulator volume was reduced about 11 \(\%\) concerning the calculated analytical values.

The power on gear shift control of a parallel hydraulic hybrid vehicle (PHHV) is researched in this paper. A multibody dynamic model is built to capture the main vibration characteristics of PHHV powertrain, based on which the power on gear shift control strategy is designed and verified. To avoid the vehicle driving torque interruption during gear shift, power on gear shift control strategy is designed. In the control strategy, hydraulic pump/motor (HPM) compensates the engine torque when the engine clutch is disengaged for gear shift. The engine clutch engagement process is carefully controlled by LQR control strategy to mitigate the vehicle powertrain vibration and improve the vehicle driving comfort. Extended Kalman filter (EKF) is adopted to estimate the PHHV parameters required by LQR control. The available HPM torque depends on its working pressure which varies a lot with different accumulator state of charge. So the HPM torque compensation capability is investigated by analysing the traction force requirement during gear shift. To obtain the gear shift traction force demand, a gear shift schedule considering both vehicle fuel economy and dynamic performance is designed. The simulation results show that the HPM could satisfy most of the torque compensation requirements during gear shifts with the designed gear shift schedule in typical driving cycles.

This work proposes to model a small series hydraulic hybrid vehicle (SHHV) for the power demand of a real driving cycle. The real driving cycle was measured with a low-cost Bluetooth Scanner connec...

Parallel hydraulic hybrid vehicles have the benefit of reduced fuel consumption and emissions. However, the hydraulic driving system changes the vibration characteristics of the vehicle powertrain. To study the influence that the hydraulic driving system has on the vehicle powertrain, a multibody dynamic model is built by the lumped mass method in this chapter. The model considers the dual functional swashplate hydraulic pump/motor inertia and its clutch stiffness. Through the eigenvalue method, the natural frequencies and mode shapes of the vehicle powertrain are attained and compared with the conventional vehicle. The results show that the hydraulic driving system mainly changes the lower-order natural frequencies and mode shapes, whilst the higher-order natural frequencies and mode shapes are not affected. A new natural frequency and its corresponding mode shape are generated by the hydraulic driving system, to which further attention should be paid because the hydraulic motor/pump is the node with the biggest vibration in this mode shape.

Energy management strategy is very important for hydraulic hybrid vehicles to improve fuel economy. The rule-based energy management strategies are widely used in engineering practice due to their simplicity and practicality. However, their performances differ a lot from different parameters and control actions. A rule-based energy management strategy is designed in this paper to realize real-time control of a novel hydraulic hybrid vehicle, and a control parameter selection method based on dynamic programming is proposed to optimize its performance. Firstly, the simulation model of the hydraulic hybrid vehicle is built and validated by the data tested from prototype experimental platform. Based on the simulation model, the optimization method of dynamic programming is used to find the global optimal solution of the engine control for the UDDS drive cycle. Then, the engine control parameters of the rule-based energy management strategy are selected according to the engine control trajectory of the global optimal solution. The simulation results show that the 100 km fuel consumption of the proposed rule-based energy management strategy is 12.7L, which is very close to the global optimal value of 12.4L and is suboptimal.

Lagrange multiplier approach is a computationally efficient method for computing optimal energy management strategy for a hydraulic hybrid vehicle under the assumption that the accumulator dynamics can be ignored and only the net use of storage energy is considered. Although it provides a close estimate to the fuel economy compared to that obtained using dynamic programming, the resulting control strategy does not respect the physical limits of the storage capacity of the hydraulic accumulator. Thus, the synthesized control strategy is not feasible for actual driving. This article investigates the basic Lagrange multiplier approach for real-time control and proposes modifications so that the storage capacity is respected. It is shown that the Lagrange multiplier can be interpreted as an equivalent loss factor which turns out to be the marginal loss associated with the discharge of stored energy. The two proposed modifications are as follows: (1) a moving horizon approach and (2) making the Lagrange multiplier a function of the current state of charge. Both methods are successful in maintaining the accumulator state of charge within limits with modest effect on fuel economy (3%–5% lower).

High Stopping frequency of heavy vehicles such as refuse trucks produces a large amount of energy which is generated by driving engine during vehicle acceleration. Most of this energy is wasted in form of heat to the environment when the vehicle brakes. This wasted energy normally lost during braking is significant especially in repeated stopping vehicles. This research presents a concept for the hydraulic hybrid system design using automation studio software to build the suggested hydraulic circuit. The classical mechanical traction in traditional vehicle can be replaced by this system without lowering vehicle performance and other satisfaction criteria in addition to achieving the main target from hybridization; regenerate energy which is always lost during vehicle braking and reuse to accelerate it again. It also includes the hydro- mechanical system architecture (which is called SHHS) and its component specification after changes in traditional vehicle structure. The switching matrix for control unit also illustrated. In this paper, the dynamics model for the SHHS (Series hydraulic hybrid vehicle) is constructed by MATLAB/SIMULINK package. The vehicle performance is investigated during various modes of operation at different condition.

Energy management strategy is a critical technology for improving the fuel economy of wheel-drive hydraulic hybrid vehicles. For driving, a power-following control strategy is proposed in this study by adding several working points of the engine in the optimal fuel economy power curve. For braking, the “I” curve distribution strategy based on critical braking strength zmin was adopted. A test bench was constructed according to the quarter of the prototype vehicle. Taking the typical working conditions of Federal Urban Driving Schedule (FUDS) and the selfset extra-urban driving schedule (EUDC-1) cycle condition into consideration, the energy management strategy was studied. The torque and speed of the simulated engine and pressure of the accumulator were obtained. The test fuel consumption in this research was compared with the original fuel consumption of the prototype vehicle. It was found that the proposed energy management strategy could effectively improve the fuel economy by more than 24 % under the requirement of satisfying the dynamic performance of the whole vehicle.

Hydraulic hybrid technologies improve the fuel economy of city-use medium duty vehicles by recovering braking energy and reusing it for driving, most notably vehicle launching. In this paper, a parametric design of hydraulic driving system for a medium duty truck is conducted based on its power demand in typical urban driving cycles. The braking control strategy is designed considering both the safety regulations and braking energy recovery rate. The proportional relationship of hydraulic pump/motor output torque and its working pressure is considered when designing the braking control strategy. The influence of the high pressure accumulator minimum working pressure and the corresponding gas volume at the minimum pressure on the braking energy recovery rate is analyzed. The simulation results show that the proposed hydraulic driving system and braking control strategy helps greatly increase the braking energy recovery rate. Besides, different vehicle mass and load distributions are investigated to analyze the regenerative braking effect on various loading conditions.

Hydraulic electric hybrid vehicle (HEHV) is designed, and its energy management control strategy is discussed in this paper. Matlab/Simulink is used to establish a battery electric vehicle (BEV) and HEHV models, and backward simulation is adopted for the simulation to get the variation of torque and battery state of charge (SOC) through New York City cycle of the US Environmental Protection Agency (NYCC). In this paper, the rule-based control strategy and the genetic algorithm are applied for the energy distribution management strategy. The simulation results show that the electricity economic performance of the designed hydraulic hybrid vehicle is improved by 43.65% than that of battery electric vehicle.

The development of fuel-efficient vehicles has increased along with the needs of consumers and the rise of environmental issues. Hybrid vehicles have become a popular alternative to conventional powertrains in the passenger vehicle market. Hydraulic hybrid vehicles have been applied to certain applications with clear benefits, such as high power density. To increase the base of academic knowledge, the energy characteristics of hydraulic hybrids were experimentally and theoretically studied for thermal management. First, measurement data for a series hydraulic hybrid system were collected by hardware in the loop test rig for different temperature conditions. The experimental results were compared for different thermal management conditions, thus showing the power consumption behaviors at different system temperatures. Also, a theoretical approach with thermodynamic properties was introduced for analyzing the energy characteristics of hydraulic hybrid systems. The theoretical results revealed possible explanations for the relationship between energy saving and thermal management for hydraulic hybrid systems. This study was worthy not only in that the experimental data itself worth as reference data for energy characteristics of hydraulic hybrid systems for thermal management, but also in that a novel theoretical approach for energy characteristics analysis was introduced, using energy and exergy analysis for the first time.

Hybridization of hydraulic drivetrains offers the potential of efficiency improvement for on- and off-road applications. To realize the advantages, a carefully designed system and corresponding control strategy are required, which are commonly obtained through a sequential design process.Addressing component selection and control parameterization simultaneously through simulation-based optimization allows for exploration of a large design space as well as design relations and trade-offs, and their evaluation in dynamic conditions which exist in real driving scenarios. In this paper, the optimization framework for a hydraulic hybrid vehicle is introduced, including the simulation model for a series hybrid architecture and component scaling considerations impacting the system’s performance.Anumber of optimization experiments for an on-road light-duty vehicle, focused on standard-drivecycle- performance, illustrate the impact of the problem formulation on the final design and thus the complexity of the design problem. The designs found demonstrate both the potential of energy storage in series hybrids, via an energy balance diagram, as well as some challenges. The framework presented here provides a base for systematic evaluation of design alternatives and problem formulation aspects.

Simulation-based optimization is a useful tool in the design of complex engineering products. Simulation models are used to capture numerous aspects of the design problem for the objective function. Optimization results obtained can be assessed from various perspectives. In this study, component and control optimization of a series hydraulic hybrid vehicle is used as an application, and different robustness and performance aspects are evaluated. Owing to relatively high computational loads, efficient optimization algorithms are important to provide sufficient quality of results at reasonable computational costs. To estimate problem complexity and evaluate optimization algorithm performance, the definitions for information entropy and the related performance index are extended. The insights gained from various simulation-based optimization experiments and their subsequent analysis help characterize the efficiency of the optimization problem formulation and parameterization, as well as optimization algorithm selection with respect to parallel computation capabilities for further development of the model and optimization framework.

© 2019 SAE International. All Rights Reserved. In this paper, hydraulic driving system parameters of a parallel hydraulic hybrid vehicle are designed based on the regenerative braking requirement. Torque, speed and power demands during typical driving cycles are analyzed. The braking control strategy is designed considering both the braking safety and braking energy recovery efficiency. The hydraulic braking torque is determined by the braking control strategy. The proportional relationship of hydraulic pump/ motor output torque and its working pressure is considered. Through simulation with typical city driving cycles, most braking energy can be recovered by the proposed hydraulic driving system and braking control strategy.

Hydraulic hybrid technology offers superior power density, when compared to competing vehicle hybrid technologies. This allows the hydraulic hybrid vehicle (HHV) to absorb most of the kinetic energy during braking. This paper estimates the fuel economy of a parallel HHV, based on Perodua Myvi passenger vehicle, controlled by a rule-based control strategy. The study simulates the HHV on city and highway drive cycles that are based on Malaysian roads. The simulation results show the parallel HHV offers 39% fuel economy improvement when operates on the city drive cycle and 31% fuel economy improvement on highway drive cycle.

In this paper, an optimization algorithm of energy recovery efficiency is proposed for parallel hydraulic hybrid systems (PHHS) using dynamic programming (DP). Global optimal solution of pump displacement and transmission ratio under the known urban drive cycles is obtained by using the DP approach, where the total amount of energy recovery is defined as the cost function, and the pump displacement and the transmission ratio of the torque coupler are defined as the deciding variables. Two major steps are involved in verifying the proposed approach. Firstly, a PHHS Simulink model is accurately obtained by repeated comparison with the bench test. Subsequently, we derive a parallel hydraulic hybrid vehicle (PHHV) from adding a hydraulic hybrid system to an electric vehicle in ADVISOR (advanced vehicle simulator). This vehicle is used to validate the effectiveness of the proposed method in energy recovery efficiency.

Hydraulic hybrid vehicle is an alternative clean automobile technology. A novel hydraulic hybrid vehicle with wheel motors is proposed in this paper to improve vehicle fuel economy. A vehicle power system controller is designed and a rule-based control strategy is applied by the controller. A forward simulation model of the vehicle is built and system parameters are matched. The JC08 cycle is simulated by the model. Simulation results indicate that fuel consumption is decreased from 15L to 10.61L per 100 kilometers compared with the conventional vehicle. Vehicle fuel economy is improved about 29.27%. The designed controller makes engine work in best performance area.

Hybrid transmissions are characterized by their utilization of more than one form of energy storage. They have the potential to help reduce overall fuel consumption and vehicle emissions by providing the possibility of brake energy recuperation and prime mover operation management. Electric hybrids and electric vehicle drives are nowadays ubiquitous, and mechanical energy storage in flywheel has been investigated in the past. The use of fluid power technology with a combustion engine has also been investigated since the late 1970s, and is frequently revisited. Hydraulic hybridization is especially attractive for heavy vehicles with frequent braking and acceleration which benefit most from fluid power components’ high power density, typically busses, delivery or refuse vehicles, and vehicles with existing hydraulic circuits and transmissions, such as forest and construction machinery, but have been considered for smaller vehicles as well. Due to the characteristic discharge profile of hydraulic energy storage, special attention needs to be paid to control aspects in the design process to guarantee drivability of the vehicle. In this respect, simulation models can be of use in early design process stages for cheaper and faster evaluation of concepts and designs than physical experiments and prototyping, and to generate better understanding of the system studied. Engineering optimization aids in the systematic exploration of a given design space, to determine limits and potentials, evaluate trade-offs and potentially find unexpected solutions. In the optimization of a hydraulic hybrid transmission, the integration of component and controller design is of importance, and different strategies (sequential, iterative, bi-level and simultaneous approaches) are conceivable, with varying consequences for the implementation. This thesis establishes a simulation-based optimization framework for a hydraulic hybrid transmission with series architecture. Component and control parameter optimization are addressed simultaneously, using a rule-based supervisory control strategy. The forward-facing dynamic simulation model at the centre of the framework is built in Hopsan, a multi-disciplinary open-source tool developed at Linköping University. The optimization is set up and conducted for an example application of an on-road light-duty truck over standard drive cycles. Both results from these experiments as well as the framework itself are studied and evaluated. Relevant design aspects, such as explicit design relations to be considered and performance requirements for more robust design, are identified and addressed, and the optimization problem is analysed with regard to algorithm performance and problem formulation. The final result is an optimization framework that can be adjusted for further in-depth studies, for example through the inclusion of additional components or optimization objectives, and extendable for comparative analysis of different topologies, applications and problem formulations.

Hybridization is recently a tendency of the vehicle development since it can relieve the stress of energy problem. Therefore, a hybrid powertrain, which is called thermal-electric-hydraulic (i.e.tri-energy) hybrid powertrain, is studied in this paper for the mutual complement between hydraulic hybrid vehicle and hybrid electric vehicle. The three types of power sources coupled in this configuration are regulated by the 2-DOF planetary gear sets for the accurate shifting between several driving conditions. The fuzzy logic control strategy with the benefit of good adaptability, robustness and real-time, is adopted in the paper in order to improve the fuel economy effectively. The fuzzy torque distribution controller with a two-layer structure is designed based on the selection of membership functions and the determination of a set of fuzzy rules. The simulation under the Chinese Urban Bus Cycle (CUBC) is built on the Matlab/Simulink/Driveline platform, whose following speed error is less than 1km/h. The results, which are analyzed under urban condition, suburb condition and high-speed condition, show an overall improvement of composite fuel consumption compared to deterministic rule based method, which indicates that the proposed fuzzy control strategy is quite suitable to be applied on the tri-energy bus.

In recent years, increasing concerns regarding environmental pollution and requirements for lower fossil fuel consumption have increased interest in alternative hybrid powertrains. As a result, this paper presents a novel hydraulic/electric synergy powertrain with multiple working modes. The three energy sources (i.e., engine, battery, and hydraulic accumulator) in this configuration are regulated by a dual planetary gear set to achieve optimal performances. This paper selects the component sizes of a hybrid electric vehicle (HEV), a hydraulic hybrid vehicle (HHV), and a hydraulic/electric synergy vehicle (HESV), based on the dynamic performance of a target vehicle (TV). In addition, this paper develops the forward simulation models of the four aforementioned vehicles in the MATLAB/Simulink/Driveline platform, in which the fuel economy simulations are carried out in relation to the Chinese urban bus cycle. The simulation results show that the fuel consumption of the three hybrid vehicles is similar, but much better than, that of the TV. Finally, based on the operating cost calculations over a five-year working period, the lowest cost ranges of the three hybrid vehicles are determined, which provides a method for choosing the optimal hybrid scheme.

This paper presents a fuzzy-based control strategy for a 3.5- ton series hydraulic hybrid truck in term of improving fuel economy. In this work, the vehicle speed demand is considered as the input of the fuzzy logic controller. The output of the controller is the reference value of the accumulator pressure. A PID controller will be used to regulate the accumulator pressure by adjusting the power of the engine. With the flexibility characteristic of the fuzzy logic controllers, its membership function can be further modified to achieve smoother control surface. The effectiveness of the proposed controller is evaluated under different driving condition. The performance of the system is acceptable in comparison with other rule-based control strategies.

Targeting the application of medium and heavy vehicles, a hydraulic electric hybrid vehicle (HEHV) was designed, and its energy management control strategy is discussed in this paper. Matlab/Simulink was applied to establish the pure electric vehicle and HEHV models, and backward simulation was adopted for the simulation, to get the variation of torque and battery state of charge (SOC) through New York City Cycle of the US Environmental Protection Agency (EPA NYCC). Based on the simulation, the energy management strategy was designed. In this research, the rule-based control strategy was implemented as the energy distribution management strategy first, and then the genetic algorithm was utilized to conduct global optimization strategy analysis. The results from the genetic algorithm were employed to modify the rule-based control strategy to improve the electricity economic performance of the vehicle. The simulation results show that the electricity economic performance of the designed hydraulic hybrid vehicle was improved by 36.51% compared to that of a pure electric vehicle. The performance of energy consumption after genetic algorithm optimization was improved by 43.65%.

With strong demands of energy-saving and environment-friendly vehicles, hydraulic hybrid powertrain is a suitable solution for urban transportation. This article proposes a novel hydraulic hybrid vehicle with wheel motors to improve vehicle power performance and fuel economy. A forward-looking simulation model of the vehicle is built. System parameters are determined according to the power performance demands. A smaller engine is chosen, the peak power of which is reduced by 11.96%. The simulation model is calibrated and verified by experimental tests on the designed test bench. Parameterized simulation results indicate that the acceleration time 0–100 km/h of the designed vehicle is decreased by 36.3% from 19.63 to 12.5 s compared with the conventional vehicle. The maximum vehicle speed is 140 km/h, and the maximum gradeability is 29%. When the engine works in economy mode, fuel consumption is decreased by 35.59% from 15 to 9.66 L per 100 km on the Urban Dynamometer Driving Schedule cycle compared with the conventional vehicle.

Fossil fuel depletion risk forecasting and growing environmental concerns are strong impetus for developing higher efficient transportation system nowadays. Hybridization is considered as one of the most efficient short and mid-term solutions. In particular, series hydraulic hybrid vehicle (SHHV) provides a further advantage when it provides more degree of freedom of engine control. By meaning of cruising control, the problem is not only to track the vehicle speed but also the engine torque, engine speed, and accumulator pressure to their references. The aim of this paper is to develop a multi-input-multi-output model-based controller for a 3.5 ton truck class SHHV. The effectiveness of the proposed controller is comparing with conventional PID controller with different power management strategies under certain driving curriculums.

In a hybrid hydraulic vehicle, the hydraulic accumulator is used as the secondary power source in addition to the engine to propel the vehicle. Because of the low energy density characteristic, the accumulator can only afford the required power in a short period. After that the engine mush be involved. Published works provide evidences that the hydraulic hybrid vehicle is suitable for vehicles working under start-stop-and-go driving patterns. This paper present three rule-based control schemes for a 3.5- ton series hydraulic hybrid truck. The simulation results indicate that by applying suitable control scheme, the proposed series hydraulic hybrid system might offer better fuel economy improvements for both urban and highway driving condition.

A hydraulic hybrid vehicle equipped with the hydraulic transformer is proposed. The hybrid system features in rotary swash plate type hydraulic transformer and pressure cross-feedback control. The full numerical model has been built. Extensive simulated and tested results are given. The contributions of the hydraulic transformer dynamics to the hydraulic hybrid vehicle performance are investigated. The proposed hydraulic hybrid vehicle can achieve the ideal vehicle dynamic performance by adjusting the hydraulic transformer controlled angle. The switching between the driving and the regenerative breaking of the hydraulic hybrid vehicle is realized by the pressure cross-feedback control. The propulsion mode of the hydraulic hybrid vehicle can be changed automatically. The larger hydraulic transformer controlled angle realises a higher driving pressure while the smaller one achieves a higher driving flow. Due to the small inertia of the hydraulic transformer, the hybrid system is able to satisfy the speed requirement of the driver.

Along with the shortage of energy and the increasingly serious pollution of environment in cities, automobile industries all over the world are exploring and developing energy saving and clean automobile. Hydraulic hybrid vehicle has better potential in medium-size and large-size passenger vehicles than its electric counterparts. The key components' sizes have remarkable influence on the vehicle performance and fuel economy, and an optimization process is needed to find the best design parameters for maximum fuel economy while satisfying the vehicle performance constraints. Multi-Objective optimization method based on adaptive simulated annealing genetic algorithm (ASAGA) is proposed to optimize the key components in HHV. In the objective function of the optimization, all the weighting factors can be set with different values according to different requirements. The optimal results show that the proposed method effectively distinguishes the key components' optimal parameters' position of HHV, enhances the performance and fuel consumption.

This paper presents the development and implementation of a PID-based control system for a series hydraulic hybrid propulsion system. At first, a configuration of the system is discussed and modeled in MATLAB/Simulink environment. Then, based on the established model, a two-level control system is developed. Monitoring demands from driver and current states of the system, the top-level controller sends out appropriate demands for the component-level controllers to meet the driver requests under any condition. Performance of the control system is evaluated in different situation of driver demand. The established model provides an efficient tool for control system development. The robustness of the proposed control system allows developing and evaluating the benefit of different power management strategies for the series hydraulic hybrid propulsion system.

A supervisory controller strategy for a hybrid vehicle coordinates the operation of the two power sources onboard of a vehicle to maximize objectives like fuel economy. In the past, various control strategies have been developed using heuristics as well as optimal control theory. The Stochastic Dynamic Programming (SDP) has been previously applied to determine implementable optimal control policies for discrete time dynamic systems whose states evolve according to given transition probabilities. However, the approach is constrained by the curse of dimensionality, i.e. an exponential increase in computational effort with increase in system state space, faced by dynamic programming based algorithms. This paper proposes a novel approach capable of overcoming the curse of dimensionality and solving policy optimization for a system with very large design state space. We propose developing a supervisory controller for hybrid vehicles based on the principles of reinforcement learning and neuro-dynamic programming, whereby the costto-go function is approximated using a neural network. The controller learns and improves its performance over time. The simulation results obtained for a series hydraulic hybrid vehicle over a driving schedule demonstrate the effectiveness of the proposed technique.