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With the continuous development of the economy, people's demand for automobiles is increasing. Correspondingly, the consumer groups of automobiles have become more and more mature, mainly because consumers pay more and more attention to cars in addition to the appearance of cars. The intrinsic quality, in which the safety features of the car gradually become the primary purchase condition for users to consider. As a result, the anti-lock braking system (ABS), one of the main safety systems, is attracting more and more attention. The following table (Table 1) is the prediction of China's ABS market by the world-famous consulting firm Strategy Analytics. We can clearly see this growing trend and estimate the compound annual growth rate of China's ABS market during 2006-2015. Will reach 9.0%.
This growing demand has also prompted many companies and research institutes to increase investment in the development and production of ABS, which has led to the birth of many new ABS system manufacturers. This phenomenon is particularly evident in China, South Korea and India. But these companies have a long history of producing ABS products, so a mature and reliable solution is especially important to them. The general structure and characteristics of the ABS system will be briefly described below.
Introduction to ABS
ABS mainly judges the road condition and the upcoming motion state of the car by monitoring the speed change of each wheel when the car brakes, and makes the wheel adjust the action according to a preset algorithm to avoid being locked.
As shown in Figure 1, usually a brake system with ABS function consists of the following components: brake master cylinder, proportional distribution valve, brake pressure regulator, brake wheel cylinder, wheel speed sensor, ABS master unit, ABS Alarm lights and brake lights.
In this system, the components associated with ABS are: wheel speed sensor, ABS master unit, brake pressure regulator and ABS warning light. The wheel speed sensor is mainly used to measure the rotation speed of the wheel, and the signal is input into the ABS main control unit after preliminary processing. In the main control unit, there are generally one or two microcontrollers. When the ABS acts, they receive the information from the sensor, analyze the wheel speed, and calculate the parameters such as the wheel acceleration, the reference vehicle speed and the slip ratio. According to the set algorithm, the corresponding action that the car should take is deduced, and then the corresponding instruction is issued to the executing device also located on the main control unit. The brake pressure regulating device receives the command issued by the actuator to adjust the brake pressure on each wheel so that the wheel is in the maximum adhesion coefficient state and prevents the wheel from being locked and the pure sliding friction occurs. In this process, the wheel speed sensor is a signal input device, and the main control portion is completed by the ABS master unit. Therefore, the ABS master unit must meet the following requirements:
(1) Ability to process sensor signals at high speed
Since some of the lower-end sensors have only signal transmission capability and do not have computing power themselves, the signal processing of the sensor is often performed by the main control unit. At higher vehicle speeds, the speed of the input signal from the sensor side is also increased, and a typical system needs to process at least four wheel speed signals simultaneously. In order to process these signal information in time, the main control unit must have strong signal processing capability.
(2) The ability of high speed computing
The master unit of the ABS shoulders the ability to execute a predetermined algorithm. It needs to calculate various state information of the car according to the speed information of the wheel, such as vehicle speed, vehicle acceleration, slip rate, etc., and according to the information, the matching state in the algorithm is searched, and then the algorithm preset according to the state. Calculate the various actions and parameters that should be taken. All of this needs to be completed in a very short time, so the main control unit is required to have a strong computing power. At least one 16-bit microcontroller is typically used on this unit.
(3) Ability to execute quickly and effectively
ABS must also play a corresponding role in the high-speed state of the vehicle, that is, to continuously complete the process of pressurization, holding pressure, and decompression to control the running state of the vehicle, so the actuator must also be fast and effective.
(4) Ability to handle large currents
Since the ABS has to control the movement of up to eight valves, the peak current of the whole system will reach a higher value, so the main control unit must have the ability to handle large currents, such as the device to be able to pass larger capacity, devices and The system must have a strong heat dissipation capability.
(5) Ability to communicate with other systems
ABS wheel speed information is often used by other systems, so there is often a need to exchange information between ABS and other systems. In addition, when the ABS is expanded into a traction control system (TCS) or an electronic stability system (with the ESC/ESP/VSC/DSC and other names, the name ESC will be used hereinafter), the engine needs to be controlled, so Communication between engine management systems (EMS). Therefore, the ABS master unit should include a CAN or LIN interface.
(6) System diagnostic monitoring and failure protection performance
ABS is one of the most important safety systems for automobiles, and its performance is often related to the safety of the occupants in the car. Therefore, it must be able to diagnose and monitor itself, even in the event of failure, to provide emergency replacement and protection measures to ensure that the vehicle will not lose control.
As mentioned above, ABS is the basic form of intelligent vehicle braking system. If you add some additional equipment and functions based on this, it can be expanded into other systems. Here is a brief introduction to automotive electronic stability system (ESC). ). Unlike ABS, which only works when braking, ESC can monitor the driving state of the vehicle in real time and correct the driving state in time by adjusting the braking force on the corresponding wheel and the traction of the engine before the vehicle is out of control, so as to prevent the situation beforehand. . Therefore, the ESC system requires more sensors, and in addition to the wheel speed sensor, it usually includes a yaw angle sensor, a lateral acceleration sensor, and a steering wheel angle sensor. In addition, ESC also needs to add 4 valves to control the flow of hydraulic fluid in the same circuit. Because the ESC system handles complex traffic conditions in real time, its software system is also larger and more complex, which requires faster signal processing and computing power, as well as faster response times.
In response to these requirements of ABS/ESC, as a chip supplier that provides a complete product chain, Infineon has combined its successful experience with decades of major ABS/ESC suppliers around the world to launch its own reference solution. . In the following sections, we will describe this in detail.
Next: Infineon ABS/ESC solution
Infineon ABS/ESC solution
Infineon has continuously accumulated experience in the cooperation with the world's major ABS/ESC suppliers, and combined with its comprehensive product line, developed a unique ABS/ESC reference solution for customers to develop their own solutions. . The current version of this program has been improved over time and accumulated as shown below (Figure 2). This plan includes both ABS and ESC. The entire diagram depicts an ESC system. If the steering wheel angle sensor, the yaw angle sensor and the accelerometer group are removed, and the lower right corner is used to control the four additional solenoid coils, the remaining components are an ABS system.
In this solution, Infineon uses the most advanced XC2000 series as the main microcontroller. The XC2000 is a family of 16-bit microcontrollers manufactured by Infineon based on 130nm technology and has the ability to execute certain 32-bit instructions. It uses Infineon's proven C166S-V2 architecture and is improved with a maximum clock frequency of 80MHz. The architecture uses multiple data buses, and most of the instructions can be completed in one clock cycle, as well as DSP technology. It has 16 levels of interrupts and 8 peripheral channels with extremely short response times. The XC2000 Series uses Multiple Flash Modules to read program code and data in parallel. It also has a wide power supply range of 3.0V to 5.5V and enables single voltage supply. The XC2000 series supports 1-6 CAN bus interfaces and communicates with the FlexRay bus via an external or built-in FlexRay bus interface. It has 64/100/144/176 pin counts and is pin compatible, in a green (lead-free) small outline quad flat (LQFP) package, and thanks to enhanced energy-saving technology in standby mode The current is only about 30Î¼A, which is the industry's leading in terms of size and power consumption. To enhance data security and computational reliability, the XC2000 Series employs multiple data processing techniques such as hardware ECC (Error Correction Code, including ECC Flash and SRAM ECC technology), Built in self test (BIST), and self repair ( BISR) technology and so on. In addition, the XC2000 series uses 64-bit encryption to prevent data leakage. The XC2000 series is divided into three word series, of which the XC2300 series is specially developed for safety applications with great reliability and stability. The XC2364 microcontroller used in this solution has a clock frequency of up to 80MHz, 576kB of flash memory and 50kB of random access memory (RAM), and also has 16 AD conversion ports, 2 CAN interfaces and 2 serial interfaces. These features ensure that it can handle the heavier signal processing and computational tasks to ensure the normal function of the ABS/ESC system.
In addition to this main microcontroller, this solution also uses an Infineon 8-bit microcontroller XC866 as a backup microcontroller. This is a microcontroller with 8051 core. In addition to assisting in some signal processing and state detection, its main function is to provide the most suitable controller for the host when the main microcontroller fails. Basic system functions to prevent the vehicle from entering an uncontrolled state and causing danger.
In this scheme as a power chip is a low dropout fixed voltage output regulator TLE4271-2G. This is an improved version of the TLE4271 with over-temperature, over-voltage, reverse-connection, short-circuit and other protections. It can withstand up to 65V for 400ms and has a watchdog to monitor the microcontroller connected to it. The chip is stable and can be used for both 12V and 24V voltages. The output voltage is accurate to Â±2% under normal operating conditions and is available in an environmentally friendly green package.
In order to meet the growing demand for active sensors in ABS, this solution uses the voltage follower TLE4250-2G as the power source for the sensor. It has a low cost and can effectively prevent the short circuit of the sensor from impacting the microcontroller. The chip is available in a small SMD package. It has a wide input voltage range, can output a maximum current of 50mA, and protects against over temperature, reverse connection, short circuit, etc.
On the load side, this solution uses the BTS6143D as the master switch for all load coils and protects the system as a high-side switch. This is a fully protected integrated chip with a nominal current rating of 10A and current monitoring for all resistive, inductive and capacitive loads and for 12V and 24V. As the low side switch is the TLE6216GP. It is a four-channel solenoid valve coil driver chip designed for ABS/ESC systems with comprehensive diagnostics and independent safety diagnostics for each channel. As a control switch for the solenoid valve coil, the TLE6212GP has a fast response and its response time is microsecond, which improves the performance of the system.
In order to meet the needs of inter-system communication, the CAN transceiver TLE6250 (or TLE6251) and the LIN transceiver TLE6258-2G are used in this scheme. Among them, in addition to its general function as a CAN transceiver, the TLE6250 has industry-leading electrostatic protection and immunity to electromagnetic interference. The TLE6251 also features comprehensive failure analysis detection and extremely low sleep power. The TLE6258-2G is compatible with the 1.2, 1.3 and 2.0 LIN specifications and also has very low sleep power.
From the perspective of the entire system, the chips used in this solution are designed for automotive applications, with an application temperature range of at least âˆ’40 Â° C ~ 125 Â° C, and have strong electrostatic protection and electromagnetic interference resistance. In addition, most of these chips are made of lead-free materials and are environmentally friendly green chips.
At present, ABS/ESC systems are experiencing rapid development. For example, wheel speed sensors are being converted from passive sensors to active sensors, using more powerful microcontrollers, adding backup microcontrollers to the system, and so on. In terms of performance, the above solution fully satisfies the requirements of the ABS/ESC for the main control unit. However, with the rapid development of the automotive industry, the requirements for reliability and light weight of automobiles are constantly increasing. In addition, almost all manufacturers are under pressure to cut costs. Because the above scheme adopts a fully discrete device design, the number of devices is large, and the cost is high from the whole system and the main control unit has the possibility of failure. In addition, the volume of the entire main control unit may be large.
Next: Infineon ABS/ESC solution based on integrated L-Chip
Infineon ABS/ESC solution based on integrated L-Chip
An effective means of enhancing the reliability of the main control unit, reducing its size and reducing the cost is to reduce the number of chips used, so the use of a more integrated chip becomes an inevitable choice. Infineon's ABS/ESC-specific high-integration chip has been developed and put on the market. The chip is named TLE6212, and the figure below (Figure 3) is a functional diagram of Infineon's new ABS/ESC reference solution based on this chip. Due to the shape of the chip in such a functional diagram, such a highly integrated chip is called L-Chip.
As shown, the TLE6212 integrates power supplies, Watchdog and safety monitoring logic, driving MOSFETs for oil pumps, driving MOSFETs as high-side switches, active and passive wheel speed sensor interfaces, K-line transceivers and two small Current low side switch. It is packaged in a 64-pin PGLQFP64-4 package that provides a compact form factor for thermal dissipation. As a result, the number of devices used for the entire ABS/ESC main control unit is greatly reduced, and the size of the PCB board is also reduced. From a cost perspective, the price of this integrated chip will also be lower than the sum of the discrete devices it replaces.
As an important application of automotive safety systems, ABS/ESC is being installed on more and more cars. A reliable and competitive solution is not only about the safety of car users, but also to promote the rapid growth of the market. The ABS/ESC technology solution based on Infineon products described in this paper has the advantages of comprehensive functions and high reliability. It can help automotive system suppliers shorten the R&D process, reduce R&D costs, and launch products into the market at a faster rate.
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