“ESP (Electronic Stability Program) is a landmark invention of automotive electronic control. Different R&D institutions have different names for this system. For example, Bosch (BOSCH) was called Vehicle Dynamics Control (VDC) in the early days, and now Bosch and Mercedes-Benz are called ESP; Toyota is called Vehicle Stability. Vehicle Stability Control (VSC), Vehicle Stability Assist (VSA) or Vehicle Electronic Stability Control (ESC); BMW calls it Dynamic Stability Control (DSC).
ESP (Electronic Stability Program) is a landmark invention of automotive electronic control. Different R&D institutions have different names for this system. For example, Bosch (BOSCH) was called Vehicle Dynamics Control (VDC) in the early days, and now Bosch and Mercedes-Benz are called ESP; Toyota is called Vehicle Stability. Vehicle Stability Control (VSC), Vehicle Stability Assist (VSA) or Vehicle Electronic Stability Control (ESC); BMW calls it Dynamic Stability Control (DSC). Although the names are different, they all add a lateral stability controller to the traditional vehicle dynamics control system, such as ABS and TCS, by controlling the distribution and magnitude of lateral and longitudinal forces, so as to control the vehicle’s stability under any road conditions. Dynamic sports mode, which can improve the dynamic performance of the car under various working conditions.
This article introduces the circuit analysis of sensors and interface technology in ESP:
Steering wheel angle sensor interface
The output of the steering wheel angle sensor is a quadrature coded pulse. A quadrature coded pulse consists of two pulse trains with varying frequency and a fixed phase offset of a quarter cycle (90°), as shown in Figure 1. By detecting the phase relationship of the two signals, the clockwise and counterclockwise directions can be judged, and the signals are counted up/down accordingly, so as to obtain the current accumulated count value, that is, the steering wheel angle, and the rate of change of the angle is The angular velocity can be measured by 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 rotation angle can be calibrated online.
Fig.1 Pulse train waveform of steering wheel angle sensor
The interface circuit between C164CI and steering wheel angle sensor is shown in Figure 2. The built-in incremental encoding quadrature decoder uses the two pins of timer 3 (T3IN, T3EUD) as the input of the quadrature pulse. After setting the relevant registers correctly, the data register of the timer 3 The value is proportional to the steering wheel angle, so the rotation angle can be easily calculated. The steering wheel angle sensor used in this paper corresponds to 44 pulses per turn. If the data register of timer 3 is T3, the rotation angle is .
Figure 2 Steering wheel angle sensor interface circuit
The difference operation is performed to obtain the rate of change of the corner. The microcontroller sends the calculated parameters to the ECU through CAN.
Wheel speed sensor interface
According to the characteristics of the wheel speed sensor signal introduced in the previous part, the interface circuit is designed as shown in Figure 3.
Figure 3 Wheel speed sensor interface circuit
The circuit adopts two-stage filtering and shaping to ensure that the wheel speed signal will not be lost at extremely low speed, and at the same time avoid signal interference caused by suspension vibration. In the figure, the first-stage hysteresis comparison is introduced by the resistor R2, and the second-stage hysteresis comparison is introduced by using 74HC14.
Yaw rate, longitudinal/lateral acceleration sensors
The installation positions of the yaw rate and longitudinal/lateral acceleration sensors are basically the same, and the outputs are all analog quantities of 0V-5V. Since the signal fluctuation characteristics caused by the bumping of the car are the same, they are packaged in the same module. Its hardware interface is shown in Figure 4, which implements hardware analog pre-filtering to suppress high-frequency noise components in the analog signal from the sensor and prevent aliasing during the sampling process.
By adjusting the parameters of each RC element in Figure 4, the filter cutoff frequency and delay size can be set. During the operation of the car, when driving on a better road, the delay should be as small as possible due to the better signal, and when driving on a bumpy road, it is hoped that the filtering effect will be better. However, once the frequency characteristics of hardware filtering are designed, they cannot be modified in real time, so it is necessary to design digital filtering links in software. Digital filtering commonly used Wiener filter, Kalman filter, linear predictor, adaptive filter and so on. Here, the first-order low-pass filter with small computational cost and good real-time performance is selected.
Figure 4 Yaw angular velocity, longitudinal/lateral acceleration sensor interface circuit
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