Research paperParametric design and regenerative braking control of a parallel hydraulic hybrid vehicle
Introduction
Improving vehicle fuel economy has become a promising way to solve the environmental degradation and energy shortage problems. Electric driving system and hybrid electric driving system have been widely used in passenger vehicles and light duty vehicles [1], [2], [3], [4]. For these medium duty and heavy duty vehicles, high power is demanded during accelerating and braking [5]. To satisfy the power demand, the size of electric motor and battery should be very big, which dramatically increases the cost and vehicle mass.
With high power density and low cost, hydraulic hybrid driving system has attracted a lot of attention in past decades [6], [7], [8], [9]. Hydraulic driving systems have been applied on delivery vehicles [10], refuse collection vehicles [11], military vehicles [12] and buses [13,14]. Among various driving systems, parallel hydraulic hybrid driving system can be refitted from conventional engine driving vehicle by adding a dual function hydraulic pump/motor (HPM) on driveshaft, which helps to reduce the design cost and simplify the system configuration [15]. In parallel hydraulic hybrid vehicles (PHHV), braking energy is recovered by HPM and stored in the high pressure accumulator. The energy is used for vehicle launching and driving the vehicle at low speed, by which the engine low efficiency operating regions are avoided and vehicle fuel economy is improved.
A balanced regenerative braking control strategy has essential influence on PHHV fuel economy. In braking control strategy design, the braking safety and regenerative braking efficiency should both be considered [16]. The braking control strategy should be designed to maximize the recovery rate of braking energy within safety regulations. The regenerative braking control strategy for electric vehicle (EV) and hybrid electric vehicle (HEV) have been deeply researched [17], [18], [19]. However, for PHHV, there are some specific characteristics should be considered. The PHHV are normally rear wheel driving while most of the HEV and EV are front wheel driving. Consequently more braking force should be allocated to rear wheels in PHHV to maximize recovered braking energy. However, to maintain vehicle stability during braking, the rear wheels should be locked after the front wheels. The braking force distribution between the front wheels and the rear wheels have to be well designed based on the requirements of braking energy recovery and safety restrictions [20].
Some research has made significant contribution to the hydraulic hybrid vehicle (HHV) braking control strategies. In [21], economic commission of Europe regulation is considered when designing the regenerative braking control strategy. Some typical city and urban driving cycles are adopted to validate the control strategy. Reference [22] takes the vehicle load into consideration when designing the regenerative braking control strategy. The braking force distribution lines are different for full load and no load. This control strategy is able to improve the fuel economy and braking performance, but the vehicle load identification during braking is a challenge.
In terms of practical design, the HPM output torque is proportional to its working pressure. A certain minimum high pressure accumulator pressure needs to be maintained to provide hydraulic braking torque required by braking control strategy. Suitable hydraulic driving system parameters should be selected, especially the high pressure accumulator capacity and minimum working pressure. In most research, these parameters are selected intuitively [1,11,23]. A rear driving HHV is researched in [23]. The braking force is more distributed to rear wheel to recover more braking energy. The proportional relationship of HPM output torque and its working pressure is also considered in this research, presented as minimum high pressure accumulator working pressure. Optimization is required to analyze the influence of high pressure accumulator parameters on regenerative braking efficiency and find suitable high pressure accumulator parameters for HHV.
In this paper, based on the power analysis of a medium duty PHHV and the braking control strategy, hydraulic driving system parameters are designed. The effectiveness and the energy benefits of the regenerative braking control strategy is validated by simulation. The main contribution of this paper is that the research results provide a practical parametric design methodology of the hydraulic driving system for PHHV, which is normally done empirically at the moment. The safety requirements and the energy benefit are compromised during the regenerative braking control strategy design. More importance is put to the braking safety here. The vehicle parameter sensitivity analysis verifies the effectiveness of the hydraulic driving system under different vehicle loading condition, which validates the practicality of the hydraulic driving system and promotes its commercial use.
The rest of this paper is organized as follows. In Section 2, the structure and working principle of the PHHV are proposed. The modeling of hydraulic driving system is conducted in Section 3 followed by the power analysis in Section 4. Energy management strategy is designed in Section 5, mainly focusing on the regenerative braking control strategy. Based on the braking torque requirement, high pressure accumulator parameters are optimized in Section 6. Parameter Sensitivity of vehicle load and load distribution are analyzed in Section 7. Section 8 gives a conclusion of the paper.
Section snippets
PHHV structure and working principle
The structure of the PHHV is shown in Fig. 1 [11,24]. Based on a conventional engine driving vehicle, the hydraulic driving system is installed at the driveshaft. In the engine driveline, engine power is transferred to the rear wheels via the engine clutch, AMT, driveshaft, differential and half shafts. In the hydraulic driving system, the high pressure accumulator is used to store high pressure oil and the low pressure accumulator is used to store low pressure oil. HPM could provide driving
Modeling of PHHV
The powertrain system is modelled in the Simulink environment of Matlab as rigid body, linear system. The system is solved using ODE4 with at fixed sample time of 0.1 s. As the focus of this paper is on system control and regenerative braking for energy recovery purposed, a number of assumptions have been made to reduce modeling complexity. By assuming the system is a rigid body, the degrees of freedom of the system are reduced, eliminating vibration response of the system and increasing
Power analysis of a medium duty truck
With high power density, the hydraulic driving system gets more energy benefits in city used medium and heavy duty vehicles with frequent starting and braking, such as delivery vehicles and refuse collection vehicles [27,28]. This paper selects a widely used medium duty truck as target vehicle. This truck is frequently refitted into refuse collection vehicle. The vehicle parameters are shown in Table 1.
In this section, half load is used as the vehicle mass to analyze the vehicle power demand.
Energy management control strategy
Due to low energy density of the accumulator, the hydraulic driving system is mainly used to recover the braking energy and launch the vehicle. The engine is still the primary power source for driving. During the vehicle launching, the hydraulic driving system is first used if hydraulic torque is available. The engine takes over the HPM to drive the vehicle when the hydraulic energy is used up or a minimum desired driving speed is achieved.
During braking, the braking force is composed of
High pressure accumulator parameters design
The HPM efficiency is influenced by working pressure, displacement and speed. As shown in Fig. 5, the HPM generally has relatively higher efficiency under higher pressure and higher displacement. The HPM has better working efficiency with the working pressure from 15 MPa to 30 MPa. The high pressure accumulator pressure during working is determined by its minimum working pressure and the initial gas volume at the minimum pressure. Increasing the accumulator minimum working pressure is favorable
Parameter sensitivity analysis
The hydraulic system parameters are selected based on the vehicle mass with half load which is 7000 kg. The vehicle mass is variable between 3300 kg and 10,700 kg with different load conditions. It is necessary to analyze the regenerative braking benefit under different vehicle loads, including both load distribution and total load. Fig. 13 shows the braking energy recovery rate across the range of vehicle mass.
From Fig. 13, the hydraulic system gets good energy benefit within the no load to
Conclusions
In this paper, HHV hydraulic driving system parameters are designed based on vehicle power analysis and energy management control strategy, especially the regenerative braking control strategy. Braking safety is considered as the most important factor when designing the braking control strategy. The distinctive characteristics of the HPM such as its output torque is proportional to its working pressure are taken into consideration in the parametric design process. By analyzing different
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This project was supported by the Australian Research Council under Discovery Early Career Researcher Award (DE0170100134).
References (30)
- et al.
A comparative study energy consumption and costs of battery electric vehicle transmissions
Appl. Energy
(2016) - et al.
Implementation of an optimal control strategy for a hydraulic hybrid vehicle using CMAC and RBF networks
Scientia Iranica
(2012) - et al.
Hydraulic/electric synergy system (HESS) design for heavy hybrid vehicles
Energy
(2010) - et al.
An investigation on the fuel savings potential of hybrid hydraulic refuse collection vehicles
Waste Manag.
(2014) - et al.
Torque control strategy for a parallel hydraulic hybrid vehicle
J. Terramech.
(2009) - et al.
A novel control strategy of regenerative braking system for electric vehicles under safety critical driving situations
Energy
(2018) - et al.
Hierarchical control strategy with battery aging consideration for hybrid electric vehicle regenerative braking control
Energy
(2018) - et al.
Nonlinear pressure control of self-supplied variable displacement axial piston pumps
Control Eng. Pract.
(2010) - et al.
The dynamic performance and economic benefit of a blended braking system in a multi-speed battery electric vehicle
Appl. Energy
(2016) - et al.
Analysis of downshift’s improvement to energy efficiency of an electric vehicle during regenerative braking
Appl. Energy
(2016)
A model predictive control approach for fuel economy improvement of a series hydraulic hybrid vehicle
Energies
Hydraulic Hybrid Heavy Duty Vehicles-Challenges and Opportunities
Hierarchical control of dry clutch for engine-start process in a parallel hybrid electric vehicle
IEEE Trans. Transport. Electrif.
Hydraulic hybrid propulsion for heavy vehicles: combining the simulation and engine-in-the-loop techniques to maximize the fuel economy and emission benefits
Oil & Gas Science and Technology – Revue de l’Institut Français Du Pétrole
Simulation study on the operating characteristics of a hybrid hydraulic passenger car with a power split transmission
Veh. Syst. Dyn.
Cited by (36)
Path-following and tire loss investigation of a front in-wheel-drive electric vehicle with off-centre CG
2023, Mechanism and Machine TheoryDesign and implementation of a series hydraulic hybrid propulsion system to increase regenerative braking energy saving range
2023, Energy Conversion and ManagementEnergy management strategy of a novel mechanical–electro–hydraulic power coupling electric vehicle under smooth switching conditions
2022, Energy ReportsCitation Excerpt :The above studies have improved the economy and power of the vehicle. Still, how to improve the stability and reliability of the vehicle power and hydraulic load work simultaneously, there are few types of research at present (Zhou et al., 2020; Zhao et al., 2019). In the existing construction machinery, heavy vehicles, and other models, the method of realizing the mutual conversion of mechanical–hydraulic–electric power is to take power from the energy end through the power take-off.
An overview of regenerative braking systems
2022, Journal of Energy StorageExperimental investigation of supercapacitor based regenerative energy storage for a fuel cell vehicle equipped with an alternator
2022, International Journal of Hydrogen EnergyCitation Excerpt :Pei et al. [14] proposed a coordinated control strategy based on a genetic algorithm to parallelly control hydraulic brake and regenerative brake (RB) according to the wheel speed and the severity of braking. Zhou et al. [15] designed a hydraulic driving system for commercial vehicles with power analysis and proposed a parallel regenerative braking control strategy by considering braking safety and regenerative braking efficiency. A serial control method in which the initial part is for regenerative braking and the last portion is for parallel braking was proposed and tested for electric vehicles [16] and for a fuel cell hybrid electric bus [17] based on direct torque control by using a single brake pedal.
Research on driving control strategy and Fuzzy logic optimization of a novel mechatronics-electro-hydraulic power coupling electric vehicle
2021, EnergyCitation Excerpt :Therefore, electric power's peak power can be reduced significantly with the synergy of hydraulic power. The working modes and energy flow direction of the MEH-PCEV are demonstrated in Fig. 3 [36,37]. To reduce the electric peak torque when the vehicle is started, the MEH-PCEV enters hydrodynamic drive mode (HD mode).