How does the automobile DSC control system? Analysis of the principle of automobile DSC control system

How does the car DSC control system

ESP electronic stability system is no longer a high-end active safety device, and more and more models have included it as standard configuration. The effect of ESP electronic stability system is obvious. It uses sensors to monitor the vehicle's driving status, driver's driving status and behavior in real time, and controls the speed of the four wheels separately after analysis and processing, thus stabilizing the vehicle. However, it is precisely because of the automatic intervention of ESP electronic stability program that the driving posture is not in line with the rules, which affects the driving pleasure.

Anyone who has driven a car with ESP will feel that it lacks passion in the corners. In fact, it is the silent and precise braking control of the wheels by ESP that eliminates the driving feeling that people expect. BMW, which sells its sportiness, will naturally not be constrained by ESP. The DSC active stability control system developed by BMW can be said to have added a lot of vitality to the somewhat dull ESP electronic stability system.

In normal mode, the BMW DSC active stability control system is the same as most ESP electronic stability systems, but when the owner activates the DTC mode through the DTC button on the center console, the vehicle's performance will be very different. The function of DTC is an auxiliary system that increases or decreases the speed of the rear wheels. Since BMW models are all rear-wheel drive, after activating DTC, the response limit of the DSC active stability control system will be extended, and the rear-wheel driving force of the vehicle will also increase. When snaking around corners, it is easy to have a dynamic performance of tailspinning. Therefore, with the help of DTC, the owner can enjoy a sporty driving experience under the safety protection of DSC.

DSC has many auxiliary functions

Activating DTC does not mean letting your horse run wild. BMW DSC dynamic stability control system also has a special function: CBC cornering brake control system. It can perform slight braking in a corner and eliminate the oversteering tendency of rear-wheel drive vehicles through asymmetric braking force control. Therefore, when driving a BMW to drift, you will find it very handy. In fact, this is not because of the driving skills, but the advanced DSC dynamic stability control system secretly helps.

In addition, the BMW DSC active stability control system also integrates several other auxiliary functions. For example, the dual-stage brake shoe friction pad wear indicator can automatically calculate the remaining mileage of the brake friction pad and accurately determine the time when the brake friction pad needs to be replaced; the brake drying function, which uses the rain sensor to determine the rainfall, so that the brake friction pad and the brake disc automatically come into slight contact during driving, and uses the heat generated during braking to evaporate the water film adsorbed on the brake disc; the hill start assist function, which is somewhat similar to the AutoHold function in the ESP electronic stability program, which can remain in place when the brake is released on the slope, and will not slide backward to ensure a comfortable and smooth start. With this function provided by DSC, even manual transmission models can easily start on a hill without using the handbrake.

DSC Dynamic Stability Control

The performance is similar to the ESP (electronic stability system) of Bosch in Germany. It can provide good controllability when the car is moving at high speed, prevent the vehicle from skidding or drifting, and thus obtain precise controllability. It is a kind of electronic active safety protection system. Since the name of ESP has been registered by Bosch in Germany, the electronic stability system developed by other companies can only use other names, such as DSC.

How ESP works

Analysis of the causes of automobile instability

Since the driving conditions of a car are very complex, such as changes in the friction coefficient of the road, the braking drive of the car, and the interference of the car by the side wind, all of these may cause the car to become unstable.

The steering movement of a car is caused by the front wheels generating a slip angle and lateral force after applying a steering angle to the steering wheel, which causes the car to yaw. The yaw movement of the car causes the rear wheels to also generate a slip angle, which in turn generates a lateral force. The lateral force of the front and rear wheels provides the centripetal force for the car to turn. When the car is driving stably, for example, when the lateral acceleration of the steering is small on a high-adhesion road surface, the tire slip angle is small, and is approximately linearly related to the tire lateral force, and the tire characteristics are in the linear region. In this case, the car's center of mass slip angle is also very small, close to zero, and it drives along the expected trajectory. When the car becomes unstable, such as when making an emergency turn, the centrifugal force becomes larger, the tire is in the nonlinear region, the slip angle and the lateral force generated by the tire are no longer linearly related, the lateral force gradually saturates, the road surface cannot provide enough lateral force, and it no longer drives along the expected trajectory, and loses control. When the lateral force on the front axle is saturated, the car exhibits understeering characteristics, the front axle skids, the vehicle drifts, the actual turning radius of the vehicle is larger than the driver expected, and the car deviates from the expected trajectory; when the lateral force on the rear axle is saturated, the car exhibits oversteering characteristics, the rear axle skids, resulting in dangerous conditions such as sudden turns, rollovers, slow reactions, and tailspin.

The current vehicle stability control system usually selects these two parameters as control objects. One is the main control variable and the other is the auxiliary variable. For example, BOSCH's ESP system uses yaw rate as the main control target, and TOYOTA's VSC uses the center of mass side slip angle as the main control target.

Control system structure

Each sensor estimates the slip rate, vertical load, friction coefficient, center of mass sideslip angle and longitudinal speed of each wheel, and calculates the nominal value of the vehicle through signal processing. The ECU controller analyzes the difference, calculates the yaw moment increment that needs to be applied, and determines the controlled wheel. The secondary circuit brakes the specified wheel or adjusts the engine output torque through the anti-lock braking (ABS) subsystem, anti-drive slip (ASR) subsystem and anti-backward torque control (MSR) subsystem to control the braking force and driving force to meet the control of the main circuit and achieve vehicle stability.

Analysis of the comprehensive control principle of ESP system

Analysis of the Comprehensive Control Principle of ESP System

1. Avoid understeer or oversteer

The steering stability of a car can be measured by understeering, oversteering and neutral steering. When the car is driving at a low speed, it will not understeer or oversteer regardless of the lateral wind force or the rapid steering. However, when driving at a high speed, a slight steering wheel turn or a small external lateral force can cause the car to understeer or oversteer, that is, the steering trajectory of the car at this time is no longer in line with the driver's wishes, and it is difficult for ordinary drivers to correct this dangerous tendency. The center of gravity of the car will also move forward with the change of passengers or cargo on the car, resulting in understeer, or move backward, resulting in oversteer.

During the car's steering process, ESP monitors the steering wheel angle and yaw rate, obtains the vehicle speed signal, and calculates the floating angle generated during the car's steering process, such as the angle β (the angle at which the car's driving direction deviates from the car's longitudinal axis) shown in Figure 3.2. If this floating angle causes the car to oversteer, the outer wheels of the car are braked to make the car rotate clockwise around an axis perpendicular to the ground, thereby reducing the floating angle and making the car tend to neutral steering. Similarly, when the car understeers, the inner wheels of the car are braked to make the car rotate counterclockwise around an axis perpendicular to the ground, similarly reducing the floating angle and making the car tend to neutral steering.

2. Prevent the car from exceeding the turning limit

The driving performance of a car when accelerating on a curve can be obtained by a circle driving test. By comparing the vehicles without and with the ESP system, it is concluded that the ESP system can effectively prevent the car from exceeding the turning limit. The conditions of this test are: on a solid hard road surface with an adhesion coefficient of 1, the speed of the car is slowly increased to the physical limit speed of a circle radius of 100m and maintained. The experimental results are as follows:

(1) Cars not equipped with ESP system

In the driving test of the circle driving, the car reaches its physical limit speed when the speed exceeds about 95 km/h. The required steering becomes very difficult, and the floating angle increases rapidly, but the driver can still keep the car in the circular lane. At a speed of about 98 km/h, the car without the ESP system becomes unstable, the rear of the car is thrown out, and the driver must reverse and drive out of the circular lane. This experiment can verify that there is a limit speed during the steering process of the car, and this limit speed changes with the change of the adhesion coefficient and the turning radius. In the above experiment, the limit speed of the car is 95 km/h. At 98 km/h, the car becomes unstable and cannot be overcome by driving skills without slowing down.