Introduction to the core functions of vehicle VCU

火辣西米秀

Introduction to the core functions of vehicle VCU [Copy link]

Figure 1 High and low voltage components coordinated controlled by VCU

The electrified powertrain of new energy vehicles has added many high and low voltage electrical components (as shown in Figure 1). VCU is the "brain" of the new energy vehicle drive system control. Mature system software plays an important role in improving operating efficiency, reducing energy consumption and emissions, and improving the robustness of post-fault processing . It is one of the core capabilities for the real implementation of electrified powertrain system solutions.

As the core controller of the vehicle drive coordination control system, VCU is responsible for the most basic and important functions such as vehicle status coordination and driver driving demand realization. Therefore, the perfection of VCU software directly affects the stability and driving safety of vehicle operation . With the promotion of the concept of "domain integration", more and more new functions are gradually integrated into the VCU controller, such as: AC/DC vehicle-side charging master control function related to charging, and electric four-wheel drive control function related to chassis.

From the perspective of system function division, the functions of VCU can be divided into: vehicle system, transmission system, power system, thermal management system, as well as OBD diagnosis, communication, safety monitoring and other system functions . The main functions of VCU are shown in Figure 2.

Figure 2 VCU system function classification and overview

VCU software core functions introduction

Based on multiple mass-produced customer projects, after years of system knowledge building and functional software development and verification, UAES's VCU software now has complete VCU system solutions in the three core areas of "torque", "electricity" and "heat", which can be flexibly configured according to customer needs. This article will mainly introduce some core functions in VCU software around vehicle drive related to "torque". There will be other articles in the future to introduce the core functions related to "electricity" and "heat".

Supports multi-mode vehicle operation mode management function (hybrid power)

The operation mode decision and switching process control of hybrid vehicles can realize three operation mode decisions and switching: pure electric operation, series extended range, and parallel drive (Figure 3).

Figure 3 Hybrid operation mode and energy flow

The vehicle operation mode decision function is based on the ECMS (equivalent fuel consumption minimum) algorithm (Figure 4), which determines the operation mode with the lowest energy consumption under various working conditions (Figure 5) and realizes the optimal energy distribution ratio of the motor/engine to achieve better power and economy: at low and medium speeds, the range extender generates electricity, so that the engine always works in the high-efficiency zone and provides power for the power system; at high speeds, the engine and motor drive the vehicle together to meet the power and economy requirements. Compared with the widely used rule-based energy management strategy in the industry, ECMS can achieve better fuel-saving effects. Compared with the global optimization strategy and the energy management strategy based on working condition adaptation, ECMS can be better applied to actual engineering projects.

Figure 4 Hybrid mode management functional architecture

Figure 5. Distribution of modes in the WLTC cycle

When the vehicle operating conditions change and the vehicle operating mode needs to be switched, the mode switching process control function can ensure that the VCU achieves a fast and smooth mode switching control process by coordinating the speed and torque between the engine, range extender, drive motor and clutch without affecting the realization of the driver's driving torque requirements (Figure 6).

Figure 6: Test results of mode switching process

Torque management based on component physical level

Torque management needs to coordinate the driving and braking torque requirements from the driver and driving assistance functions, and can coordinate the various drive components (engine, generator, front drive motor, rear drive motor) to accurately respond to torque requirements from various sources based on the output of the vehicle's operating mode function and mode switching function.

The developed and applied torque management function realizes a flexibly configurable and expandable torque structure (Figure 7), which can support the flexible configuration of pure electric, hybrid projects, and four-wheel drive/two-wheel drive projects . The torque structure based on the physical level of actual components is also easier to expand and apply to hybrid/pure electric vehicles with other topological structures.

Figure 7 Schematic diagram of torque management

Four-wheel drive control function with multiple distribution methods

The four-wheel drive control function distributes the driver's required torque to the front and rear axles according to the current four-wheel drive control requirements, and finally outputs it to the front and rear drive motors . The four-wheel drive control function can fully consider the influence of different factors when distributing the front and rear axle torque, taking into account the economy, power and handling stability of the vehicle. It can also identify the movement trend of the vehicle, actively intervene in the vehicle's movement control, and realize stepless full-range distribution ratio adjustment (Figure 8).

Figure 8 Four-wheel drive control functional architecture

The four-wheel drive economy distribution function can make the front and rear axle drive motors operate at the optimal point of the overall system efficiency under current demand during smooth driving, achieving the optimal efficiency distribution of dual-motor, triple-motor and quad-motor, reducing energy consumption and increasing cruising range.

The load distribution function in the four-wheel drive power distribution can identify the current road slope and vehicle acceleration and deceleration conditions, establish the front and rear axle load model to calculate the optimal distribution ratio of the front and rear axle torque, and fully utilize the maximum ground adhesion through intelligent distribution of the front and rear axle torque during load transfer, thereby reducing wheel slip and improving vehicle acceleration capability (Figure 9).

Figure 9 Accelerated load transfer four-wheel drive distribution test results

The anti-skid function in the four-wheel drive power distribution can actively adjust the front and rear axle torque distribution to the non-slip axle when the vehicle's single axle is in a slipping state, reducing power loss. When the front and rear axles are identified to be slipping alternately, the front and rear axle torque distribution is dynamically controlled to make full use of the road adhesion coefficient, improve the vehicle's ability to get out of trouble at low speeds, reduce the feeling of powerlessness, and improve driving comfort. (Figure 10)

Figure 10 Driving anti-skid function test results

The four-wheel drive handling stability distribution enables the car to follow the driver's steering intention and improves steering agility, mainly including steering state monitoring and steering torque control. The vehicle's motion posture can be adjusted in real time through the front and rear axle torque distribution before ESP intervention, and the instability of understeer (US) and oversteer (OS) can be suppressed in time. The frequency of ESP intervention is reduced in acceleration steering conditions, reducing braking shock and yaw, and improving the driver's driving experience (Figure 11).

Figure 11 Stability control under OS and US conditions

The four-wheel drive control function is highly scalable and versatile, and can be used on both EV and PHEV vehicles. This solution integrates some related control functions in the power domain and chassis domain, improving the cross-domain integration capabilities related to vehicle movement.

paodekuai123

Very well written, thanks for sharing, I am learning about new energy vehicle design. I come to the forum every day.