1 idle stop start system works
The car idle stop start system stops the car when the shift lever is in neutral, and automatically shuts down the engine. When the driver takes his foot off the brake pedal, the engine restarts and the car starts smoothly. When the engine is restarted, an auxiliary battery system is used to supply power. When the car is parked, if there is a traffic jam or a red light, the ISS saves fuel by automatically shutting down the engine. When the car brakes, ISS performs brake energy recovery.
Electric power is supplied to vehicle electrical equipment and CVT (Continuously Variable Transmission) oil pumps and electric water pumps for heaters. The CVT oil pump allows the vehicle to maintain stable CVT oil pressure during idle stop, enabling good smooth response and maneuverability when the engine is started from a standstill. When the engine electronic control unit (ECU: Electronic Control Unit) determines that the vehicle is in braking or decelerating state, the energy recovery is realized by the braking energy recovery system. At this time, the motor generates electricity and the system recovery braking energy is stored in the energy storage device. When the engine ECU determines that the vehicle meets the start condition, the engine starts quickly.
2ISS measurement and control plan design
In order to test the running characteristics of the vehicle under the idle stop start condition, the measurement and control test system is shown in Fig. 1. It includes the vehicle ISS control module, brake energy recovery control module, inertia module, road resistance simulation module, brake pedal control module, and motor. Torque control module, measurement and control system module, etc.
Vehicles ISS Control Modules Control Signals Test Signals Mechanical Drives Measurement and Control System Modules Road Simulation Modules Inertial Module Motor Torque Control Module Brake Pedal Control Module Brake Energy Recovery Control Module Signal Bus Brake Pedal Position Sensor Vehicle Speed ​​Sensor Gear Position Sensor Accelerator Pedal Position Sensor Engine
The purpose of the measurement and control system test is to simulate the driving conditions and the running process of the car. The hardware-in-loop simulation of the proposed idling stop start method and control strategy is performed to improve the system control method and control strategy to achieve the optimal control system. Therefore, the test system should have functions such as vehicle driving conditions, idle stop and start performance simulation, road resistance simulation, and regenerative braking energy recovery.
The system uses a motor to simulate the engine's speed, torque, and power while the vehicle is on the road. During the braking process, the motor torque control module is used to control the reverse current flow to cause the load motor to output a reversed torque that simulates the road load and completes the road simulation link, thereby realizing the simulation of different road conditions of the vehicle. The inertia of the vehicle's actual road is modeled by the inertia module.
The measurement and control system module can determine the driving status of the vehicle at any time by collecting signals such as the vehicle speed, accelerator pedal position, brake pedal position and gear position. When the engine ECU determines that the vehicle is braking or decelerating, it cuts off the fuel supply and passes the signal to the vehicle ISS control module for processing. The vehicle ISS-ECU then transmits the command via the signal bus to the brake energy recovery control module to achieve braking energy recovery.
The brake pedal control signal of the measurement and control system consists of two parts, one part is from the brake pedal position sensor; the other part is the brake pedal control module, which simulates the driver according to the brake pedal model and brake force correlation and brake ride comfort requirements. Perform braking actions and braking intent.
3ISS mathematical model
3.1 Drive Motor Model
The use of a motor instead of an engine drive has strong controllability and is conducive to different operating conditions. The torque output and rotational speed drive system output by the motor is consistent with the vehicle speed, acceleration, and inertia of the vehicle when the vehicle is running in a specific road condition.
The torque provided by the drive motor simulation engine is: wb R wb ef eb wfe R v RFR av J i R a JT + = 2 4 (1) where: T e-drive motor torque, Nm; a - vehicle acceleration, m/ s 2;v-vehicle speed,km/h;i eb―total drive ratio of drive motor power and electromagnetic clutch;i ef-total drive ratio of drive motor power and flywheel;R w-simulated wheel radius,m;FR- The total resistance of the vehicle on a straight road, N; R b-brake action radius, m; J b-brake and motor total moment of inertia, kgm 2; J f-flywheel inertia, kgm2.
3.2 Road Resistance Model
The road resistance is simulated by an electromagnetic brake. The electromagnetic brake can control the brake torque by controlling the current of the electromagnetic brake. There are: T eb = K et I eb 2ω (2) where: K et - the electromagnetic brake torque constant; I eb - Electromagnetic brake supply current, A; ω - Speed ​​at a specific speed, r/min; Teb - Braking torque, Nm.
Combined with the driving equations of the automobile, the electromagnetic torque brake simulates the driving conditions of the vehicle output torque: m-vehicle weight, kg; g-gravity acceleration, 9.8 m/s 2; f-rolling resistance coefficient of the vehicle tire; A-winding area of ​​the vehicle ,m 2;z―Brake strength of automobile; CD—windward drag coefficient of vehicle; α—Hydraulic brake share rate.
3.3 brake pedal model
The equivalent structure of the system brake pedal is as follows: (2) s (sk) (sd) (s F cp F 2 Equivalent physical model of the brake pedal Mathematical physical equation of the kinematics of the first-order nonlinear time-delay system: k(s) ―Elasticity coefficient varying with pedal displacement; d(s)―Damping coefficient varying with pedal displacement; F c(s)―Coulomb friction force, N;s―Pedal displacement, m; F p―Brake pedal Force, N.
4ISS test analysis
In order to verify the effectiveness of the designed measurement and control scheme, a simulation test of the measurement and control system was performed using a hardware-in-the-loop simulation test platform.
4 is a hardware-in-the-loop simulation test for a test vehicle with a vehicle speed of 80 km/h. (a) The change of the motor braking torque for the system drive motor module. (b) and (c) are the changes of the front and rear electromagnetic brake torque of the system road resistance module. (d) and (e) are the accumulator charge currents and SOC changes for the system's brake energy recovery module. From the test results, it can be concluded that the designed ISS measurement and control system has strong controllability in the hardware-in-the-loop simulation test and can meet the measurement and control requirements.
5 ends
The vehicle idle start detection and control system integrates the drive motor module, road resistance simulation, brake energy recovery, brake pedal and other modules. The analysis of the measurement and control process of the vehicle stop start system was performed.
Based on the hardware-in-the-loop simulation test system, a preliminary verification was carried out to provide a good test platform for the verification and continuous optimization of the vehicle energy-saving theory and control method using the ISS measurement and control system.
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