Freescale ABS解决方案
Anti-Lock Braking Systems (ABS) are designed to maintain driver control and stability of the car during emergency braking. Locked wheels will slow a car down but will not provide steering ability. ABS allows maximum braking to be applied while retaining the ability to steer out of trouble. The operation of ABS can slightly reduce stopping distance in some cases like on wet road surfaces, but it can increase the stopping distance in others, as may be the case in deep snow or gravel. An ABS system monitors four wheel speed sensors to evaluate wheel slippage. Slip can be determined by calculating the ratio of wheel speed to vehicle speed, which is continuously calculated from the four individual wheel speeds. During a braking event, the function of the control system is to maintain maximum possible wheel grip on the road - without the wheel locking - by adjusting the hydraulic fluid pressure to each brake by way of electronically controlled solenoid valves. For passenger car applications, the majority of ABS components are often housed together in a single, under-hood mounted module. ABS system components include the following: Wheel speed sensors on each vehicle wheel Electrically controlled hydraulic valves Electric motor powered hydraulic pump Electronic control unit (ECU The following example solution uses the 16-bit 68HC912D60 microcontroller for main application processing, with a 68HC08AZ32 processor functioning as an asymmetrical watchdog processor. Both controllers incorporate controller area network (CAN) communications modules to allow the ABS ECU to communicate with other vehicle systems. Standard devices such as the MC33293AT and MC33186 are designed to enable control of the higher power loads in the system. CAN physical layer devices and power supply regulation components are also available. Freescale also has extensive experience in the development of specialized components for high-volume ABS applications. Freescales SMARTMOS technology allows a large number of the analog and power electronics functions of the system to be integrated into a single device. Novel microcontroller architectures with comprehensive self-testing features have also been developed. Block Diagram  |
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