Circuits related to sensor and interface technology in ESP

ESP (Electronic Stability Program) is an iconic invention of automotive electronic control. Different R&D institutions have different names for this system. For example, Bosch (BOSCH) called it Vehicle Dynamics Control (VDC) in the early days, and now Bosch and Mercedes-Benz call it ESP; Toyota calls it Vehicle Stability Control (VDC). Stability Control (VSC), Vehicle Stability Assist (VSA) or Electronic Stability Control (ESC); BMW calls it Dynamic Stability Control (DSC). Although the names are different, they all add a lateral stability controller based on traditional vehicle dynamics control systems, such as ABS and TCS, to control the distribution and amplitude of lateral and longitudinal forces in order to control the vehicle's stability under any road conditions. Dynamic sport mode, which can improve the car's dynamic performance under various working conditions.

This article introduces the circuit analysis of sensors and interface technology in ESP:

Circuit principle

Steering wheel angle sensor interface

The output of the steering wheel angle sensor is a quadrature encoded pulse. Quadrature-encoded pulses consist of two pulse trains with varying frequency and a fixed phase offset of one-quarter period (90°), as shown in Figure 1. By detecting the phase relationship between the two signals, it can be judged as clockwise and counterclockwise, and the signals can be counted up/down accordingly to obtain the current cumulative count value, that is, the absolute turning angle of the steering wheel, and the rate of change of the turning angle. That is, the angular velocity can be measured through the signal frequency. In addition, the steering wheel angle sensor has a zero output signal. When the steering wheel is in the middle position, the signal outputs 0V, otherwise it outputs 5V. Through this signal, the absolute turning angle can be calibrated online.

Figure 1 Steering wheel angle sensor pulse sequence waveform

The interface circuit between C164CI and steering wheel angle sensor is shown in Figure 2. There is a built-in incremental coding orthogonal decoder on the chip. The decoder uses the two pins of timer 3 (T3IN, T3EUD) as the input of orthogonal pulses. After the relevant registers are correctly set, the data register of timer 3 The value is proportional to the steering wheel angle, so the steering angle can be easily calculated. The steering wheel angle sensor used in this article corresponds to 44 pulses per revolution. If the data register of timer 3 is set to T3, the absolute rotation angle is.

Figure 2 Steering wheel angle sensor interface circuit

By performing a differential operation, the rotation angle change rate can be obtained. The microcontroller sends the calculated parameters to the ECU through CAN.