A Free Trial That Lets You Build Big!
Start building with 50+ products and up to 12 months usage for Elastic Compute Service
The vehicle anti-lock braking system, also known as ABS, is a safety brake control system with the advantages of anti-skid and anti-lock. ABS Not Installed
In the case of an emergency, the system's vehicle cannot be slowed down step by step, and only one foot can be trampled to death. At this time, the wheel is easy to lock, and the vehicle sprints inertia, dangerous situations such as slide, deviation, and uncontrolled direction may occur.
ABS cars, when the wheel is about to reach the next lock point, the brakes can work 60 to 120 in one second
It is equivalent to stopping and relaxing, that is, similar to the mechanical "Point brake ". Therefore, it is possible to avoid out-of-control and wheel slide during emergency braking, so that the wheel is not locked during braking, and the tires are not on the ground at one point.
Friction increases the friction and increases the brake efficiency by more than 90% .
The key control component of the ABS system is the ABS electronic controller (ECU. This article analyzes the ABS
Based on the braking principle and controller structure, a dsPIC30F5011 single-chip microcomputer with powerful data processing function is selected for a vehicle model. Combined with the ABS system chip, the ABS_ECU is completed.
The hardware is designed and the control program is developed. The simulation experiment of the self-developed hardware on the loop Simulator is carried out, which achieves good results.
1 ABS braking principle
In the Automobile Braking Process
In, the external force that causes the vehicle to brake and slow down is the ground braking force on the tire surface on the road surface, but the ground braking force depends on the friction of the two friction pairs: first, the friction of the brake device on the wheel, brake
The other is the friction between the tire and the road surface, that is, the ground adhesion. Sufficient ground braking force can be obtained only when the vehicle has enough brake force and ground adhesion . During Automobile Braking
There is a slide phenomenon, that is, there is a relative slide between the speed and the wheel speed, the degree of this slide is represented by the Slide Rate:
The relationship between the adhesion coefficient and the tire slip rate is shown in curve 1 during Automobile Braking. In the figure, "Phi" indicates the adhesion coefficient.
As shown in figure 1, when the slide rate is between 15% and 20%, the adhesion coefficient between the horizontal and vertical directions is relatively large, and a large number of research experiments also show that the braking effect of the car is the best at this time.
In the automobile braking process, when the wheel tends to lock, the pressure of the braking system is quickly reduced, and the wheel Slide Rate is restored to the ideal stable zone. The pressure of the braking system is adjusted automatically and frequently, slide wheels
To make full use of the Longitudinal Peak adhesion coefficient and high transverse adhesion coefficient between the wheel and the road surface, to prevent wheel lock and obtain the best braking efficiency .
2 ECU hardware design
2.1 ECU structure composition
The ABS system consists of three parts: wheel speed sensor, electronic controller (ECU), and solenoid valve. The core part of the system is ECU, which consists of two parts: system power management, wheel speed signal processing, processor (Single Chip Microcomputer), solenoid valve driver and ABS Fault Detection.
The speed signal processing module changes the input analog wheel speed signal to obtain a regular digital Wheel Speed Input to the processor. The processor calculates and determines whether each wheel tends to be locked; solenoid Valve Drive monitoring module amplified
The solenoid valve control signal of the Self-processor enables it to drive the implementing mechanism (brake pressure regulator) to adjust the brake pressure so that the wheel speed is in the continuously circulating pressurization-pressure maintaining-decompression status, at the same time, the current solenoid valve control signal is reversed
Feed the processor to monitor the control logic.
2.2 processor Selection and Design
The most important part of ECU is the processor. Currently, most 16-bit single-chip microcomputer is used as the ECU.
On the one hand, it collects wheel speed signals into ABS
Algorithm processing: On the other hand, the solenoid valve control command is sent to the implementing agency to handle the pressure-maintaining pressure-decompression of the wheel. At the same time, it also expands the fault detection and solenoid valve monitoring to ensure the ECU
Normal operation. Both wheel speed acquisition and algorithm processing and wheel brake pressure control have high requirements on core processors: strong real-time performance, good stability, and high data processing accuracy. Microchip
Company dspic30f5011 as high performance 1
Bit digital signal controller, not only has the single-chip microcomputer control function, but also integrates with the DSP
Digital signal processing capability. The chip contains a complete DSP engine: contains a high-speed 16 × 16 integer multiplier, a 40-bit ALU, and two 40
Bit saturation accumulators and a 40-bit bidirectional device can significantly improve the chip computing capability. Command systems are divided into two categories: single-chip microcomputer and DSP
Class. The single-level command prefetch mechanism makes most of the commands in a single cycle. On-chip integration with 66 K flash, 1 k eeprom, 4 k ram, 8-channel input capture, an 8
The pulse width modulation module (PWM) of the channel ). Combined with icd2 (in-chip debugger) in the maplab IDE development environment, program editing, compilation, and online
Debug and download.
The distribution of functional interfaces is shown in figure 3. Input capture port using dspic30f5011 (IC1... 4) Collection 4
The Set wheel speed signal can accurately detect the Wheel Speed Signal status according to the set collection method. After the ABS algorithm, the solenoid valve control signal is output through eight I/O Ports, at the same time, the solenoid valve status from 8
The I/O port is fed back to the processor to form a closed loop to monitor the control logic of the algorithm. At the same time, a PWM
Output the alarm light signal and determine the fault type by setting the flashing frequency of the alarm light. The braking signal from the brake pad is isolated by optical coupling and enters the microcontroller. The effective braking signal is to enter ABS
An entry condition of the algorithm.
2.3 wheel speed Collection and Processing
The magnetic wave rotation speed sensor converts the rotation speed directly to the sine signal of the rotation speed. Generally, the rotation speed signal frequency is lower than 1 kHz, and the amplitude is relatively low, and the interference volume is large, so it must be converted to TTL.
Level of the square wave signal, so the signal conversion circuit needs to input the transformed wheel speed signal into the processor. This design uses four channels of Wheel Speed collection, by LM324A
The rotation speed signal is amplified, and the interference amount is reduced using the low-pass filter and the filtering part in the algorithm. The digital rotation speed signal after 74HC14 shaping is a square wave, which can be input to the processor.
2.4 solenoid valve control signal output and Processing
After the ABS algorithm, the processor generates 8-way solenoid valve control signals, and uses two-way solenoid valve control signals as a group to control a wheel. The combined control policy is: 00 pressure holding; 01
Decompression. The control signal of the solenoid valve output by the processor is only dozens of milliliters, and the current required for the execution part is 1 ~ 2A, so the solenoid valve needs to control the signal amplification. This design uses Infineon
The company's ABS system drive chip TLE6216, each chip can drive four-way solenoid valve control signal, while the current solenoid valve Status feedback to the processor, monitoring control effect.
2.5 power supply and Fault Detection
The power supply in the car is a battery or generator. The battery of heavy vehicles is 24 V, the working voltage of the generator is 28 V, and the working voltage of the single chip microcomputer is 5 V. Therefore, in addition to the power supply, the voltage conversion is also required. Design
With the Infineon ABS system power chip TLE6210, it can
The voltage is converted to 5 V for single-chip microcomputer, and integrated with functions such as alarm lights and engine drivers. In addition, TLE6210
The voltage monitoring logic module is integrated internally. When the input/output voltage is detected to be too high or too low, pin RES1/RES2
A reset pulse is generated to reset the entire system. Because the system power supply has the analog part and the digital part, it is necessary to add the isolating inductance between the two parts of the power supply to prevent mutual interference between the analog circuit and the digital circuit in the system.
ABS faults include system power supply faults, wheel speed sensor faults, ABS system operation faults, Solenoid Valve Faults, etc, the operator can determine the fault source and type by the flashing frequency of the fault lawn lamp, and store the corresponding fault code in the EEPROM for the host computer to identify and handle the fault.
3. Software Design
Currently, the ABS system mainly adopts the Bosch control logic by referring to the threshold value control method. This is a widely used logic today. In this way, the combination of wheel angle reduction speed, angle acceleration and slide ratio is used as the control parameter 
This article uses the angle acceleration and angle reduction speed of the wheel as the main threshold, and the slide rate as the auxiliary Threshold Control Policy. The specific implementation flow chart is shown in Figure 4.
When an effective brake signal is detected, the processor collects the wheel speed pulse signal through the wheel speed sensor and calculates the speed and acceleration. When the speed is high, the logic threshold algorithm of the slip rate is called, the solenoid valve is used to output pressure,
Decompression and pressurization signals, that is, pressure increase during initial braking. When the acceleration threshold is reached, and the slide rate remains in a stable area, the pressure is maintained. After a period of time, the sliding rate reaches the stable critical value of decompression. So reciprocating, making the speed show
The current wave is reduced. If the speed is low, the solenoid valve directly outputs the pressure or pressure holding signal. At this time, the wheel speed is decreasing, and no recovery continues until it is reduced to zero.
4 hardware in-loop simulation test
Using the hardware in-loop simulation system (5) developed in the early stage of the national "863" project "embedded system development platform for Automotive Electronic Control and Its Applications" (2004aa1z2380 ), the braking process of the ABS controller is simulated. simulation result 6 and Figure 7 are shown.
6. Figure 7
It is the braking process of a pneumatic brake heavy truck in the case of low adhesion coefficient road surface and initial speed of 33 (m/s. Observe the status changes of the solenoid valve corresponding to the wheel speed curve: Pressurization-pressure maintaining-decompression; when the wheel speed rises
Stage, the status change of the solenoid valve is: decompression-packing-pressurization. It can be seen that when the vehicle is in the ABS ECU
The control well prevents lock of wheels, wheel speed fluctuation is relatively stable, and the braking time is short, so this controller has good braking effect.
Company dspic30f5011 as ABS
The processor of the system enables fast collection, identification, and calculation of parameters such as the rotation rate, ensuring real-time and stable control. Combined with Infineon ABS
The system chip makes the system power management and solenoid valve drive more optimized. through multiple simulation tests, we can see that the ABS controller has good braking effect.
The author's Innovation: Using DCS
Signal Controller) dsPIC30F5011, as a processor, solves the rapid and massive data transmission and computation, and uses ABS compiled in C Language
The operation cycle of the logical threshold algorithm can be kept within 5 ms. the ABS is optimized by using a dedicated ABS chip.
The power management and solenoid valve drive of the controller can shorten the development time and ensure the system integrity and stability. It provides experimental data and design reference for the productization of ABS controllers.
Start building with 50+ products and up to 12 months usage for Elastic Compute Service