24-07-2012, 09:52 AM
INTELLIGENT CONTROL OF COMMERCIAL VEHICLES BRAKING SYSTEM FUNCTION
INTELLIGENT CONTROL OF COMMERCIAL VEHICLES BRAKING SYSTEM FUNCTION.pdf (Size: 217.07 KB / Downloads: 91)
ABSTRACT
Ever-increasing demands in term of responsiveness and control are being made on system for brake and chassis management in commercial vehicles. Electronic Braking System (EBS) introduced in commercial vehicles providing rapid brake response and release for every single wheel of commercial vehicles according to the driver’s demands. EBS ability for electronically monitoring and controlling of the index pressures between the proportional relay valve (front axle), axle modulator (rear axle) and trailer control valve has been used in this paper for introducing a new adaptive control strategy for the braking forces distribution of commercial vehicles. Implementation, here proposed, intelligent control strategy has be done by artificial intelligence technology based on neural network control. The main benefit of the proposed intelligent control strategy is that future decisions related to the control of braking systems are based on the developed neural model of braking system operation of commercial vehicle.
INTRODUCTION
Braking systems of commercial vehicles were always given the highest importance concerning safety issues and in particular active safety. Due to different design and load characteristics of these vehicles, different performance of their braking system especially related to different wheel brakes and their tribological behaviour are the main reasons why the operation of their braking systems should be constantly monitored and controlled depending on the driver’s demands and the adhesion characteristics between tyres and road (1,2). Inappropriate braking of these vehicles may cause heavy accidents due to relatively longer stopping distances and higher energy output of brakes particularly in the case of vehicle combinations.
Ever-increasing demands in term of responsiveness and control are being made on system for brake and chassis management in commercial vehicles (3). The traditional medium used for brake system (compressed air) can be now controlled with the speed and precision offered by modern electronic abilities. Electronic Braking System (EBS) introduced in commercial vehicles providing rapid brake response and release for every single wheel according to the driver’s demands.
The extremely rapid response time provided by the electronic control can be used for crucially shortening the braking distance by introducing advanced control of braking system operation. The control of commercial vehicle’s braking system operation is related not only to vehicle speed but also to lateral acceleration together with the yaw moment control and significantly reducing the possibilities of the vehicle rolling over. Obviously, such a complex task imposed to the control of braking system can not be based on the driver abilities and need to be done independently of the driver. That is why a control program in EBS operation should be permanently improved.
EBS offers possibilities for further innovative solutions for controlling of braking systems performance of commercial vehicles. A need to improve braking performance of commercial vehicles simultaneously with resolving the problem of the vehicle combination braking compatibility leads to better control of the most relevant disturbing factors. An improved EBS braking forces management would certainly enable to reach the given task. The advanced strategy for the braking force management, proposed here, is based on intelligent controlling of the braking forces distribution between the front and rear axle of power-driven vehicle and/or between towing/trailer combination and/or between tractor/semi-trailer combination. Intelligent control of braking system operation can be considered as a critical point for further improving of commercial vehicles braking systems operation and active safety in general.
IMPROVING OF EBS CONTROL FUNCTIONS
From figure 1 (tractor for semi-trailer) it can be seen the principles of the EBS operation. The brake signal transmitter is used to generate electrical and pneumatic signals according to driver demands. The brake pedal’s travel measured is interpreted as the index retardation and converted by the central module into the index pressures for the front and rear axle. The index deceleration increases progressively with the amount of pedal travel. The axle modulator reads and controls the brake pressures of the wheel brakes on both sides of the rear axle. The signal received form the brake signal transmitter determines the vehicle intended retardation. Together with the wheel speed measured by the wheel speed sensors, the intended retardation is the input signal for EBS control, which uses these readings to establish the index pressure values for the front and rear axel, and the trailer control valve (4,5,6).
Figure 1. EBS of commercial vehicle- an example
Therefore, the proportional relay valve is controlled by ECU for application of the front brakes providing the braking rate line of front circuit (figure 2, service braking). Similarly, the rear brakes application is controlled by rear axle modulator providing braking rate line of rear circuit (figure 2, service braking). It can be seen from figure 2 that braking rates realized by front and rear circuits determining the total service braking rate line of the vehicle. The control of service braking rates line of the tractors’ can be considered as the most important factor in the braking system operation particularly from the adhesion utilization curves and compatibility requirements point of view (figure 2). That is why, a special attention should be
paid to the strategy for controlling of the front/rear braking rate lines of the tractor and their synchronization with the braking rate line of semi-trailer in this case, see figure 2. The same strategy could be used in the case of the towing vehicle -trailer combination.
Obviously, because the braking pressures are computed individually for both the tractor/semi-trailer or towing/trailer combination not only power-driven vehicles but also at the same time semi-trailer’s (trailer) braking system operation can be controlled. The EBS trailer module is designed to control the brake cylinders pressures for each side and communicates with tractor or towing vehicle via special trailer interface. If the deceleration of the trailer lies in the middle of the band prescribed by ECE R13 Annex 10 no coupling force occurs. If the trailer deviates from the middle band position, the motor vehicle ECU will perceive this by means of retardation control portion of the program and will adjust the trailer’s actuating pressure accordingly.
Figure 2. Requirements imposed to the braking system of power-driven vehicle-laden condition
Braking systems of road vehicles depends on a hierarchy, as shown in figure 3: subsystems (two independent service braking systems, emergency braking system, parking braking system), assemblies (control, transmission, wheel brakes, for example), subassemblies (calliper including brake piston), and components (brake rotor which may be drum or disc depending on the brake kind and type, friction material which may be brake pad or brake lining, and brake control device, which may be wheel cylinder, etc.).
Regarding aforementioned complexity of braking system’s structure, according to figure 3, the overall performance of braking system interrelates with performance of its subsystems and parts. The problem related to the control of braking system operation is primarily determined by the fact that the braking system performance are significantly affected by brakes operation i.e. friction pairs (drum/rotor-friction material) characteristics. That is why, the real braking system performance of commercial vehicles can be significantly changed by different friction
material characteristics, for example, than those illustrated on figure 2, due to a number mutually opposed requirements imposed to friction material (figure 3).
Figure 3. Interrelation of performance of braking system, its subsystem, and parts
Therefore, only improvement of the transmission part of the braking system operation by introducing EBS, the problem of braking system controlling cannot be successfully solved. That is why, EBS controlling function abilities could be better used for improving the braking performance of power-driven vehicle or tractor/semi-trailer combination or towing vehicle in combination with the trailer. This improvement is related to introduction of the new intelligent EBS function for advanced braking force distribution based on monitoring, identification, and adaptive controlling of braking system performance of commercial vehicles.