Abstract
The characteristics of electro-hydraulic braking systems have a direct influence on the fuel consumption, emissions, brake safety, and ride comfort of hybrid electric vehicles. In order to realize efficient energy recovery for ensuring braking safety and considering that the existing electro-hydraulic braking pressure control systems have control complexity disadvantages and functional limitations, this study considers the front and rear dual-motor-driven hybrid electric vehicle as the prototype and based on antilock brake system (ABS) hardware, proposes a new braking pressure coordinated control system with electro-hydraulic braking function and developed a corresponding control strategy in order to realize efficient energy recovery and ensure braking safety, while considering the disadvantages of control complexity and functional limitations of existing electro-hydraulic system. The system satisfies the pressure coordinated control requirements of conventional braking, regenerative braking, and ABS braking. The vehicle dynamics model based on braking control strategy and pressure coordinated control system is established, and thereafter, the performance simulation of the vehicle-based pressure coordinated control system under typical braking conditions is carried out to validate the performance of the proposed system and control strategy. The simulation results show that the braking energy recovery rates under three different conditions—variable braking intensity, constant braking intensity and integrated braking model—are 66%, 55% and 47%. The battery state of charge (SOC) recovery rates are 0.37%, 0.31% and 0.36%. This proves that the motor can recover the reduced energy of the vehicle during braking and provide an appropriate braking force. It realizes the ABS control function and has good dynamic response and braking pressure control accuracy. The simulation results illustrate the effectiveness and feasibility of the program which lays the foundation for further design and optimization of the new regenerative braking system.
Highlights
Hybrid electric vehicles (HEVs) meet can satisfy the comprehensive requirements of low emissions and low fuel consumption, and as one of the most important fuel-saving technologies of HEVs, regenerative braking can save vehicle energy and reduce emissions significantly [1,2,3].The electro-hydraulic braking system of hybrid electric vehicles consists of the regenerative braking system, vehicle hydraulic braking system, and engine braking system [4]
Toyota designed a system that regulates wheel-cylinder pressure by adjusting a linear solenoid valve current based on the Electronic Hydraulic Brake (EHB) system; the system can simulate the feel of a braking pedal and satisfy the pressure requirement during electro-hydraulic braking [8]
When thefor emergency braking is applied, the vehicle speed toothe low, or the provided by the master cylinder, and the front and rear axle hydraulic braking forces are distributed suitable for charging, the system works in conventional braking mode; the braking force is only in accordance with the traditional β -line
Summary
Hybrid electric vehicles (HEVs) meet can satisfy the comprehensive requirements of low emissions and low fuel consumption, and as one of the most important fuel-saving technologies of HEVs, regenerative braking can save vehicle energy and reduce emissions significantly [1,2,3]. For the control strategy of electro-hydraulic composite braking system, Ko et al considered the braking force between the tire and road, and increased the friction braking force of the rear wheel according to the friction coefficient They designed a control algorithm for the regenerative braking of the front wheel [9]. The design of an efficient electro-hydraulic composite braking system, a new braking force distribution strategy and pressure coordination control method can greatly improve the contribution of regenerative braking to the improvement of overall vehicle fuel economy. In this study, taking a plug-in hybrid electric vehicle driven by front and rear axle double motors as the research object, based on the functional requirements of the brake system and based on the ABS hardware, a new braking force control strategy is proposed to ensure braking safety and maximize the braking energy recovery, and subsequently, a braking pressure coordinated control system is designed. The simulation verified the validity of the braking force control strategy and pressure coordinated control system
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