Research on integrated intelligent control technology of automobile power transmission system

With the development of science and technology, people's requirements for automobiles are getting higher and higher. In order to pursue the economy, power, safety and comfort of automobiles, countries around the world continue to use advanced technology and develop advanced devices to make unprecedented improvements in some performance of automobiles. In the mid-1980s, the timely application of traditional control greatly improved the performance of automobile system machine assemblies, but also exposed some shortcomings. The emergence and development of artificial intelligence has promoted the development of traditional control to intelligent control. Since the early 1990s, many experts and scholars have begun to pay attention to the application of intelligent control technology in the automotive field. At present, the most widely used intelligent control mainly includes fuzzy control and neural network control.

1 Concept of Integrated Intelligent Control of Automobile Powertrain System

1.1 Integrated control concept

The integrated control of automobile power transmission system refers to the application of electronic technology and automatic transmission theory, with the electronic control unit (ECU) as the core, controlling the separation and engagement of the clutch, the gear selection and shifting operation through the hydraulic actuator, and controlling the fuel supply of the engine through the electronic device to realize the automatic operation of starting and shifting. Its basic control idea is: according to the driver's intention (accelerator pedal, brake pedal, joystick, etc.) and the state of the vehicle (engine speed, input shaft speed, vehicle speed, gear position), according to the appropriate control law (gear shift law, clutch engagement law, etc.), with the help of the corresponding actuator (clutch actuator, gear selection and shifting actuator) and electronic device (engine fuel supply control electronic device) to jointly operate the vehicle's power transmission system (engine, clutch, transmission). As shown in Figure 1.

1.2 Integrated control method

The integrated control methods of power transmission system are generally divided into three categories:

(1) Use two or more machines to communicate. Realize information sharing between the engine ECU and the transmission ECU. This control method makes full use of mature engine and transmission control technologies, with few changes to the original system, easy to implement, and low development cost. However, due to the large amount of wiring, the integration is not high.

(2) Use a single ECU to achieve overall control of the engine and transmission. Its advantages are high integration, reduced peripheral wiring, and improved reliability, but it has high requirements for the ECU and high development costs. The power control system, four-speed automatic transmission A341 E with intelligent control system and engine on the Toyota Lexus Ls400 sedan use the same ECU. The ECU equipped with a microcomputer controls the shifting and locking time of the automatic transmission, the oil pressure of the actuator (clutch, brake) in the planetary gear system, and the engine torque during shifting, so as to achieve the best shifting quality.

(3) Use CAN bus structure for overall control. CAN bus is currently widely used in automobiles. The structure of connecting the engine and transmission control subsystems through CAN bus is shown in Figure 2. Through CAN bus, the two systems can not only transmit commands, requests and some basic states of the car (such as engine speed, vehicle speed, cooling water temperature, etc.), but also set higher priority for some data with strong real-time requirements such as fuel level and speed signal.

2 Basic components of the integrated control system of the automobile power transmission system

The function of the control system is to automatically adjust the transmission ratio and working state of the basic transmission components according to the driver's intention and the changes in the vehicle's driving environment to achieve the best transmission efficiency and the best overall vehicle performance. Generally speaking, the vehicle control system is mainly composed of three parts: the vehicle data acquisition system (sensor part), the electronic control unit and the actuator.

(1) Composition of the vehicle data acquisition system (sensor part).

In the entire control system, the sensor is partly used as the driver's visual, auditory and tactile system in the case of manually operated gear shifting vehicles, collecting and transmitting the parameter signals required for various gear shifting to the electronic control unit.

The vehicle drives and works according to the driver's intention, and the vehicle control system must be able to correctly identify and implement the driver's operation. The recognition of the driver's intention is obtained by testing the changes in the vehicle control mechanism (such as the accelerator pedal, brake pedal, steering wheel angle, etc.) through sensors and analyzing them.

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The sensors used in automobiles are mainly the following: magnetoelectric sensors, magnetoresistive sensors, photoelectric sensors, Hall sensors, thermal sensors, variable resistance sensors, piezoelectric crystal sensors, etc. The sensors used in the transmission part of the powertrain system are mainly: engine speed sensor, vehicle speed sensor, throttle opening sensor, clutch displacement sensor, etc. Among them, the engine speed sensor and vehicle speed sensor use magnetoelectric sensors and Hall sensors and other sensors that use the principle of magnetoelectric signals, while the throttle opening sensor and clutch displacement sensor both use variable resistance sensors.

In addition to sensors, other signals are transmitted through switches and controllers or other means. Commonly used switches include multi-function switches, forced low-speed switches, etc. Switches are also very important means of signal input.

(2) Electronic control unit.

The electronic control unit (ECU) is the core of the entire control system. Its function is to perform gear shifting or working state changes based on the driver's intention and the vehicle's motion state parameter detection and provided signals. The main functions of the electronic control unit include: signal acquisition and preprocessing, driver's manipulation intention recognition, vehicle state recognition, gear shift decision (gear shifting rules), gear shift quality control, fault diagnosis function, output and display, etc. A typical electronic control unit is shown in Figure 3.

The new generation of controllers has comprehensive functions and excellent control performance. They use high-performance 16-bit or 32-bit microprocessors, and some even use customized microprocessors, which include most of the functions required for control, simplify the control circuit, and enhance the function and reliability of the circuit. For example, the products of Japan's JATC Q company all use NEC and Motorola 16-bit and 32-bit microprocessors; Germany's ZF company uses Motorola's 32-bit POWERPC microprocessor to develop a 5-speed automatic transmission-SHP19 shift controller. Due to the replacement of the controller's microprocessor, the shift control is more complicated, and due to the expansion of the processor's peripheral circuit, the input and output functions are more powerful. In order to further improve the control performance, these controllers use not only control programs but also embedded real-time operating systems.

(3) Executive body:

After sampling the input signal, the control system sends it to the controller for data processing. After the data processing is completed, the control signal of the electronic control unit will change the working state of the power transmission system through the actuator to ensure the control of vehicle performance. At the same time, the actuator ensures the control of the shift quality. The actuator for gear switching generally uses a solenoid valve.

3 Intelligent control technology and its application in power transmission system

3.1 Intelligent control technology

The emergence of intelligent control comes from the high complexity and uncertainty of the controlled system and people's increasingly higher requirements for control performance. This controlled system is difficult to describe with an accurate mathematical model (differential equations and difference equations). Fuzzy control, as one of the intelligent control methods, has three advantages over traditional control: it can simulate people's fuzzy reasoning and decision-making process in terms of behavior; it can achieve better control without building a mathematical model; it can achieve nonlinear control tasks, while conventional controllers usually have difficulty in achieving control requirements for nonlinear characteristics.

As the forefront of automatic control technology, intelligent control technology is based on intelligent control theory, computer technology, artificial intelligence, and operations research. It is suitable for situations where the controlled object and environment have unknown or uncertain factors, mathematical models are difficult to establish, and the operating environment and working conditions undergo unpredictable changes. A good intelligent control system should be able to meet the requirements of multiple objectives and multiple performance indicators, use knowledge for reasoning and learning, adapt to changes in object characteristics and operating conditions, and have good robustness, adaptability, fault tolerance, real-time and diversity.

3.2 Application of Intelligent Control Technology in Automobile Power Transmission System

A car is a complex multi-degree-of-freedom system. Under the influence of external uncertainties, its dynamic characteristics will change greatly or even become unstable. Many experts are looking for an effective way to control the dynamic characteristics of the car to meet the requirements. Since the performance of intelligent control is better than that of traditional control, it is widely used in the automotive field.

At present, intelligent control technology has penetrated into all aspects of automobiles, such as automobile motion control, driver model, tire model, and control of braking system, suspension system, steering system, transmission system and engine.

3.2.1 Engine Control

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Engine technology determines and influences the development of basic vehicle technology. Due to fierce market competition and the formulation and implementation of new fuel emission standards, engine technology has shifted from simply pursuing power and reliability to pursuing good fuel economy and reducing exhaust emissions. Engine control includes: fuel injection control, ignition timing control, knock control, idle speed control, exhaust gas recirculation control and air-fuel ratio closed-loop control.

In the early 1990s, Fiat successfully implemented fuzzy control of engine idle speed. Later, Mitsubishi was not far behind and proposed related plans. In the mid-1990s, Martinez and Jamshidi applied fuzzy control to the engine to control the engine idle speed and air-fuel ratio. The structural principle is shown in Figure 4.

The fuzzy controller inputs the error of speed and acceleration, and obtains a suitable throttle opening value u through fuzzy calculation. Soon, Majors and others successfully used neural network theory to realize the control of engine fuel-air ratio.

3.2.2 Transmission system control

In the early 1990s, Ford and Honda had conducted many studies on the application of neural networks and fuzzy logic systems in the dynamic characteristics and control of automobiles. Nissan was the first to use fuzzy controllers to control the speed change law of automobile transmission systems and the pressure modulator of anti-lock braking systems. In the mid-1990s, Sakai et al. studied and developed a speed change law fuzzy controller considering the uphill and downhill driving conditions of automobiles. Its principle is shown in Figure 5. The fuzzy controller takes the vehicle speed, acceleration, throttle opening, road resistance, braking time and current speed change as inputs, and obtains the appropriate shift value after fuzzy calculation.

4 Conclusion

The integrated control system of automobile power transmission is the product of integrated control of power transmission system by high-performance microcontroller. With the development of automobile electronic technology and the improvement of living standards, people's requirements for automobile performance are getting higher and higher. Relying on microcontroller to control the overall automobile power transmission system has become a technology that is being developed at home and abroad. At the same time, intelligent control technology is increasingly widely used in the field of automobile control, making intelligent control technology one of the important development directions of automobile overall control.