1 Working principle of idle stop start system

 

The car idling stop start system stops the car and automatically turns off the engine when the shift lever is in neutral; and when the driver takes his foot off the brake pedal, the engine restarts to make the car start smoothly. When the engine restarts, the auxiliary battery system is used to supply power. When the car is parked, such as a traffic jam or a red light, ISS saves fuel by automatically turning off the engine. When the car is braking, the ISS performs braking energy recovery.

 

It supplies electric power to automotive electrical equipment and CVT (Continuously Variable Transmission) oil pumps and electric water pumps for heaters. The CVT oil pump can maintain a stable CVT oil pressure when the vehicle is idling and stopped, so that the engine has good smooth response and driving maneuverability when the engine is started from a stopped state. When the engine electronic control unit (ECU: Electronic Control Unit) judges that the vehicle is braking or decelerating, the braking energy recovery system realizes energy recovery. At this time, the electric motor generates power, and the system recovers the braking energy and stores it in the energy storage. When the engine ECU judges that the vehicle meets the starting conditions, the engine starts quickly.

 

2ISS measurement and control scheme design

 

In order to test the operating characteristics of the vehicle under the idling stop start condition, the measurement and control test system is shown in 1, including vehicle ISS control module, brake energy recovery control module, inertia module, road resistance simulation module, brake pedal control module, motor Torque control module, measurement and control system module, etc.

 

Vehicle ISS control module control signal test signal mechanical transmission measurement and control system module road simulation module inertia 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 various driving conditions and operating processes of the car, and to perform hardware-in-the-loop simulation of the proposed idle stop start method and control strategy in order to improve the system control method and control strategy to achieve the best control system. Therefore, the test system must have functions such as vehicle driving conditions, idling stop and starting performance simulation, road resistance simulation, and regenerative braking energy recovery.

 

The system uses the motor to simulate the engine's speed, torque and power when the vehicle is driving on the actual road. In the braking process, the motor torque control module is used to control the current reverse energization to make the load motor output a reverse torque that simulates the road load to complete the road simulation link, thereby realizing the simulation of different road conditions of the vehicle. The inertia of the actual road driving of the car is simulated by the inertia module.

 

The measurement and control system module collects signals such as vehicle speed, accelerator pedal position, brake pedal position, gear position, etc., to determine the driving state of the vehicle at all times. When the engine ECU judges that the vehicle is braking or decelerating, it cuts off the fuel supply and transmits the signal to the vehicle ISS control module for processing. The vehicle ISS-ECU then transmits the command to the braking energy recovery control module through the signal bus to achieve braking energy recovery.

 

The brake pedal control signal of the measurement and control system consists of two parts, one part comes from the brake pedal position sensor; the other part is the brake pedal control module, which simulates the driver according to the relationship between the brake pedal model and the braking force and braking comfort requirements Perform braking behavior and braking intention.

 

3ISS mathematical model

 

3.1 Drive motor model

 

The use of electric motors instead of engine drives has strong controllability and is conducive to realizing different working conditions. Make the torque and rotational speed output by the motor drive system consistent with the vehicle speed, acceleration and vehicle inertia when the vehicle is running on the actual road under specific conditions.

 

The torque provided by the drive motor to simulate the 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 drive motor power and the total transmission ratio of the electromagnetic clutch; i ef-drive motor power and the total transmission ratio of the flywheel; R w-simulated wheel radius, m; FR-vehicle in level Total resistance on straight roads, N; R b-brake radius, m; J b-total moment of inertia of brake and motor, kgm 2; J f-moment of inertia of flywheel, kgm2.

 

3.2 Road resistance model

 

The road resistance is simulated by electromagnetic brakes. The electromagnetic brakes can control the braking torque by controlling the current of the electromagnetic brake. There are: T eb = K et I eb 2ω (2) where: K et-electromagnetic brake torque constant; I eb-electromagnetic brake power supply current, A; ω-rotation speed at a specific vehicle speed, r/min; T eb-braking torque, Nm.

 

Combined with the vehicle driving equation, the torque formula output by the electromagnetic brake in the simulated vehicle driving conditions is obtained: m vehicle weight, kg; g gravity acceleration, 9.8 m/s 2; f vehicle tire rolling resistance coefficient; A vehicle windward area, m 2; z Automobile braking strength; CD vehicle wind resistance coefficient; α hydraulic brake sharing rate.

 

3.3 Brake pedal model

 

The equivalent structure of the brake pedal of the system, such as 2: s) (sk) (sd) (s F cp F 2) The equivalent physical model of the brake pedal. In the mathematical and physical equation of the motion characteristics of the first-order nonlinear time-delay system: k(s) The elastic coefficient that varies with the pedal displacement; d (s) the damping coefficient that varies with the pedal displacement; F c (s) Coulomb friction, 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 hardware-in-the-loop simulation test platform is used to simulate the measurement and control system.

 

4 is the hardware-in-the-loop simulation test of the test vehicle at a speed of 80km/h. (A) is the change of the electric mechanism torque of the system drive motor module, (b) and (c) are the change of the electromagnetic braking torque before and after the system road resistance module. (D) and (e) are the energy storage charging current and SOC changes of the braking energy recovery module of the system. It can be concluded from the test results 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 end

 

The automobile idle stop start measurement and control system integrates the drive motor module, road resistance simulation, braking energy recovery, brake pedal and other modules. The measurement and control process of the vehicle stop and start system are analyzed respectively.

 

Preliminary verification based on the hardware-in-the-loop simulation test system provides a good test platform for the verification and continuous optimization of automobile energy-saving theory and control methods using the ISS measurement and control system.