Introduction of ESP sensor of the hottest automobi

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Introduction of automobile ESP sensor and analysis of its interface technology

I. Introduction

esp (Electronic Stability Program) is a landmark invention of automobile 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 control system (VSC), vehicle stability assist system (VSA) or vehicle electronic stability control system (ESC); BMW calls it dynamic stability control (DSC). Although the names are different, they all add a lateral stability controller on the basis of traditional vehicle dynamics control systems, such as ABS and TCS. By controlling the distribution and amplitude of lateral and longitudinal forces, it can control the dynamic operation of the vehicle under any road conditions to avoid rusting, so as to improve the dynamic performance of the vehicle under various working conditions, such as braking, sliding, driving, etc. ESP has been mass produced abroad and is still in the research stage in China. There is still a lot of work to be done to achieve the degree of industrialization

Figure 1 shows the composition diagram of automobile esp. its electronic components mainly include electronic control unit (ECU), steering wheel sensor, longitudinal acceleration sensor, lateral acceleration sensor, yaw rate sensor, wheel speed sensor, etc. ESP is an important electronic control system to ensure driving safety. The normal operation of its sensors is the basis for effective control. This paper introduces the characteristics of common ESP sensors, designs the sensor hardware interface and software interface, and has been verified in the real vehicle test

II. Introduction to common ESP sensors

as shown in Figure 1 and Figure 2, common ESP sensors are as follows

1. steering wheel angle sensor

esp identifies the driver's operation intention by calculating the size and change rate of steering wheel angle. The steering wheel angle sensor converts the steering wheel angle into a signal that can represent the driving direction expected by the driver. The steering wheel angle is generally determined according to the photoelectric code. The coding wheel installed on the steering column contains the encoded rotation direction, angle and other information. The information on the encoding disk is scanned by the proximity optocoupler. After the ignition switch is turned on and the steering wheel angle sensor turns a certain angle, the processor can determine the current absolute steering wheel angle through the pulse sequence. The communication between steering wheel angle sensor and ECU is generally completed through CAN bus

2. yaw rate sensor

the yaw rate sensor detects the deflection of the vehicle along the vertical axis, and the deflection represents the stability of the vehicle. If the deflection angle speed reaches a threshold value, it indicates that the vehicle has a dangerous working condition of sliding or tail flicking, the ESP control will be triggered. When the vehicle deflects around the vertical axis, the vibration plane of the micro tuning fork in the sensor changes, and the yaw rate is calculated through the change of the output signal

3. longitudinal/transverse acceleration sensor

the acceleration sensor in ESP includes the longitudinal acceleration sensor along the forward direction of the vehicle and the transverse acceleration sensor perpendicular to the forward direction. The basic principle is the same, but it is installed at an included angle of 90. Generally, micro mechanical acceleration sensor is used for esp. inside the sensor, a small piece of dense material is connected to a movable cantilever, which can reflect the longitudinal/transverse acceleration of the vehicle. Its output is about 2.5V in static state, and can accurately measure the physical performance data of various materials under the above experimental States. Positive acceleration corresponds to positive voltage change, and negative acceleration corresponds to negative voltage change, Every 1.0 ~ 1.4V corresponds to 1g acceleration change. Specific parameters vary with different sensors

4. wheel speed sensor

when detecting the wheel speed signal on the vehicle, the most commonly used sensor is the electromagnetic induction sensor. The general practice is to install the sensor on the non rotating part of the wheel assembly (such as the steering knuckle or shaft head), opposite to the gear ring made of magnetic conducting material rotating with the wheel. When the gear ring rotates relative to the sensor, due to the change of magnetoresistance, an alternating voltage signal is excited on the sensor. The frequency of this alternating voltage is directly proportional to the wheel speed. ECU uses a special signal processing circuit to convert the sensor signal into a square wave of the same frequency, and then calculates the wheel speed by measuring the frequency or period of the square wave

in the original ESP system, the longitudinal/transverse acceleration sensor and yaw rate sensor were realized separately. Now, the sensor cluster mode is basically used. The three sensors are designed as a whole and communicate with ECU through CAN bus. Figure 3 shows the sensor assembly produced by Simens VDO and Bei

in order to add new ESP functions and better control the stability system of the whole vehicle, such as hill hold control (HHC) and control by wire (SBW), Bosch has proposed modular HW and SW concepts and developed the third generation of highly flexible and low-cost chronic sensor assembly DRS mm3 x。

III. ESP common sensor interface design

the block diagram of the design in this paper is shown in Figure 4. In the figure, the steering wheel angle sensor signal is processed by the microcontroller and sent to the ECU through the CAN bus (B in Figure 4); The yaw rate sensor and longitudinal/transverse sensor are designed in the same module (a in Figure 4) because their signal characteristics and installation positions are similar; Since ESP requires high real-time performance of the wheel speed sensor signal, it is directly sent to ECU (C in Figure 4) after signal conditioning. In a and B of Figure 4, the microprocessor is required to process the signal and transmit data through CAN bus. Sak-c164ci of Infineon company is selected in this paper. The chip is specially designed for automotive applications, with built-in AD converter, input signal capture and quadrature decoder. It has fast operation speed and is very suitable for ESP sensor signal processing

1. steering wheel angle sensor interface

the output of steering wheel angle sensor is quadrature coded pulse. The orthogonal coded pulse consists of two pulse sequences with varying frequency and a fixed phase offset of one quarter period (90), as shown in Fig. 5. By detecting the phase relationship of the two signals, it can be judged as clockwise and counterclockwise, and the signals are counted up/down accordingly, so as to obtain the current cumulative count value, that is, the absolute rotation angle of the steering wheel, and the change rate of the rotation angle, that is, the angular velocity, can be measured through the signal frequency. In addition, the steering wheel angle sensor has a zero position output signal. When the steering wheel is in the middle position, the signal outputs 0V, otherwise it outputs 5V. Through this signal, the absolute angle can be calibrated

c164ci interface circuit with steering wheel angle sensor is shown in Figure 6. An on-chip quadrature decoder with incremental coding is built. The decoder uses two pins (t3in and t3eud) of timer 3 as the input of quadrature pulses. After the relevant registers are correctly set, the value of the data register of timer 3 is directly proportional to the steering wheel angle, so the steering wheel angle sensor used in this paper corresponds to 44 pulses per turn, and the data register of timer 3 is set to T3. Through calculation, The change rate of rotation angle can be obtained

the microcontroller sends the calculated parameters to ECU through can

2. wheel speed sensor interface

according to the signal characteristics of the wheel speed sensor introduced in the previous section, the interface circuit is designed as shown in Figure 7

the circuit adopts two-stage filtering and shaping to ensure that the wheel speed signal will not be lost at very low speed and avoid signal interference caused by suspension vibration. In the figure, resistance R2 is used to introduce the first stage hysteresis comparison, while 74hc14 is used to introduce the second stage hysteresis comparison

3. yaw rate and longitudinal/transverse acceleration sensors

the installation positions of yaw rate and longitudinal/transverse acceleration sensors are basically the same, and the outputs are 0v-5v analog quantities. Since the signal fluctuation characteristics caused by vehicle bumps are consistent, they are packaged in the same module. Its hardware interface is shown in Figure 8, which realizes hardware analog pre filtering to suppress the high-frequency noise components in the analog signal from the sensor and prevent aliasing in the sampling process. The op amp uses the lmx324 with full swing output

adjust the parameters of each resistance capacitance element in Figure 8 to set the filter cut-off frequency and delay. When the vehicle is running on a good road, due to the good signal, the delay should be as small as possible. When driving on a bumpy road, it is hoped that the filtering effect will be better. However, once the frequency characteristics of the hardware filter are designed, it is impossible to 11 Power supply: 220V real-time modification, so it is necessary to design digital filter in the software. The commonly used digital filters include Wiener filter, Kalman filter, linear predictor, adaptive filter, etc. Here, the first-order low-pass filter with small amount of calculation and good real-time performance is selected

The selection of

k depends on the current road condition, which is identified by the original signal before digital filtering. The microcontroller packs the filtered signal, original signal, K value and road recognition result and sends them to ECU through CAN bus. Figures 9a and 9b respectively show a group of comparison curves of longitudinal acceleration sensors collected in the real vehicle test on bumpy road

IV. conclusion

this paper discusses that the future development trend of common medical packaging in ESP system is to accelerate the product upgrading of packaging system. The structural characteristics and signal characteristics of sensors are discussed, and the signal processing interfaces of each sensor are designed, including hardware interface circuit and software processing scheme. The integrated module including yaw rate and longitudinal/transverse acceleration sensor is designed. The data is transmitted with ECU through CAN bus, which has good anti-interference and reliability. The design of this paper has been verified in the real vehicle test

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