Modeling and Simulation of Dynamic Behavior of Pneumatic Brake

Downloaded from SAE International by Mithun Selvaraj, Tuesday, September 09, 2014

Modeling and Simulation of Dynamic Behavior of Pneumatic Brake System at Vehicle Level

2014-01-2494 Published 09/28/2014

Mithun Selvaraj Wabco India, Ltd.

Suresh Gaikwad

Wabco Vehicle Control Systems

Anand Kumar Suresh Wabco India, Ltd.

CITATION: Selvaraj, M., Gaikwad, S., and Suresh, A., "Modeling and Simulation of Dynamic Behavior of Pneumatic Brake System at Vehicle Level," SAE Technical Paper 2014-01-2494, 2014, doi:10.4271/2014-01-2494. Copyright © 2014 SAE International

Abstract The highest goal for a good brake system design must be that the vehicle when braking obtains a shorter stopping distance does not leave the track and remains steerable. From the perspective of road traffic, safety and for avoidance of accidents the time and location of a vehicle coming to halt after braking are crucial. In heavy commercial vehicle having longer wheel base, pneumatic brake system is being used.The pneumatic brake system configuration has to be designed in such a way that the response time should meet the safety regulation standards and thereby achieve shorter stopping distance and vehicle stability. Validating the effectiveness of pneumatic brake system layout experimentally on stopping distance and vehicle stability is expensive. This paper deals with the modeling of a typical heavy commercial vehicle along with the entire pneumatic brake system layout with actuating valves, control valves and foundation brakes to predict the dynamic behavior and stopping distance. The modeling and simulation was carried out using AMESim, commercially available multi-domain physical modeling software employing bond graph technique and lumped system. The model is simulated for actual conditions and is compared with the experimental results.

method involves more lead time and cost till the layout is finalized. Hence the modeling and analysis of the system layout and vehicle using AMESim was carried out. Past papers [2],[3] describes the detailed modelling and simulation of pneumatic brake system products and layout. This paper deals with the modelling of brake system layout and the vehicle modeling considering all the parameters contributing for braking dynamics and simulation of the stopping distance.

Pneumatic Brake System A typical Air brake system layout is shown in Fig.1, which mainly consist of Compressor (Energy source) Foot/Hand brake valves (Actuating unit) Relay valves (Control unit) and Actuators.

Introduction The heavy commercial vehicle brake system layout is designed keeping various vehicle parameters like GVW, wheel base, C.G of the vehicle, number of axles etc. The system layout design is extremely complex since it involves number of valves which have to function in a logical sequence during different stages of braking (Normal, emergency, and One circuit failed condition).Conventionally, the system layout design is arrived after many iterations based on field trials and experience. This

Figure 1. Typical Air brake System layout

The compressor provides the compressed air, which is the energy source of air brake system. The Air dryer in the layout absorbs the moisture in the pressurized air and also maintains the system pressure. The moisture free compressed air will be stored in the reservoirs through the system protection valve.


During normal brake application, when the driver presses the pedal, the dual brake valve having two deliveries get actuated [2]. The primary delivery gives signal to the relay valve which actuates the spring brake actuator actuator where the pressure is converted into braking force. The braking force is transmitted to the foundation brakes through the slack adjuster where it is converted into braking torque and applies brake on the rear wheels. The secondary delivery of the valve actuates the brake chamber thereby applies the brake in the front wheels.In case of emergency situations; the driver actuates the hand valve which applies the brake through the spring brake actuator.

Relay Valve Relay valve is used to speed up the application and release of brakes in case of longer wheel base vehicles. It operates on receipt of signal from the brake valve. The relay valve will graduate, hold, release air pressure from the brake chambers to which it is connected. It is normally mounted on the rear of the vehicle to balance the brake application time between front and rear. The relay valve cross section and the equivalent AMESim model were shown in the figure 3.

Modelling of Pneumatic Braking System Components As explained above the pneumatic brake system consists of various valves and actuators. Each and every components of the brake system were modelled using appropriate elements available in the AMESim libraries [5].The detailed modelling of the internal components of individual valves were discussed in [3].The brief function and the AMESim model of the brake system valves and actuators were described below.

Foot Brake Valve Foot brake valve provides graduated air pressure for applying and releasing of brakes on application of driver's effort on the brake pedal. The dual brake valve have two independent deliveries, which controls the primary(for rear brakes) and secondary (for front brakes) circuit of the brake system[2].The design of dual brake valve is such that it ensures uninterrupted supply of air pressure to secondary circuit even in case of primary circuit failure and vice versa.

Figure 3. Relay valve and its AMEsim Model

Brake Chamber The brake chambers were the one which generates the braking force in air brake system. It converts the air pressure into mechanical push rod force which engages the brake shoes of the foundation brake system through slack adjuster. The Brake chamber model was as shown in figure 4.

Figure 4. Brake chamber cross section & its Model

Spring Brake Actuator The spring Brake actuator performs the same as the brake chamber. But it consists of two chambers namely service chamber and spring chamber. The construction and working of the service chamber is same as that of the brake chamber. The spring chamber which is connected to the hand control valve consists of a heavy coil spring. During brake released condition the heavy coil spring will be in compressed position by the air pressure acting on the ram. When the driver actuates the hand valve in case of emergency, the air inside the spring chamber get exhausted and the spring force will actuates the brakes. The cross section and the equivalent AMESim model of the spring brake actuator is shown in figure 5. Figure 2. Foot Brake valve and its AMEsim Model

Based on its geometry and construction the product will be modeled using appropriate mechanical and pneumatic components like piston, spring, and mass available in the library. Figure 5. Spring Brake actuator cross section & its Model


Drum Brakes A drum brake is a brake that uses friction caused by a set of shoes or pads that press against a rotating drum-shaped part called a brake drum.

(1)

Figure 7. 15 degree of freedom chassis model

Road Tire Interface The road tire interface includes the tire model, road model along with the adherence

Tire Model

Figure 6. Drum Brake Model

The drum brake is modelled using the governing equation (1) using the signal library as shown in figure 6.

AMESim libraries has predefined model for modelling the tires. It includes tire kinematics model, a stiffness element and a belt slip model. The tire kinematic model computes the kinematics of tire and tire ground contact. The geometric properties of tire like free rolling radius, effective rolling radius and rim offset need to be given as input. The effective rolling radius of the tire can be defined either by Pacejka 92 definition in which it is fixed, else using Delft 97 definition in which the effective rolling radius is a variable as below

Vehicle Dynamics Modelling In order to predict the dynamic behavior of vehicle under braking the entire vehicle along with the contributing parameters for braking need to be modelled. AMESim had predefined library for modelling the entire vehicle.

Modelling of Chassis The chassis model is the central module for vehicle dynamics modeling to which all vehicle sub modules like suspension, spring, damper, end stop, antiroll bar aerodynamic module, tire, road, sensors, engine, brakes, steering system, powertrain module, external load etc. can be connected. The major components in contributing for the chassis modelling are vehicle body, steering rack, spindle and wheel. For a twin axle trucks two models are available in AMESim. A semi axle system having 7 Degrees of Freedom and a 15 degree of freedom model. The 15 Degree of freedom model as shown in Fig 7 is considered for our simulation.

(2)

Rfree - Free radius of the tire D- Peak value of effective rolling radius of the tire B- Stifness of the tire under low load F- Stiffness of the tire under high load Fz0 - Nominal Wheel load ρFzo -Nominal tire deflection ρ - Tire deflection Ktire- Tire stiffness In our case the effective rolling radius of the tire is maintained as constant.


The tire belt model allows the computation of characteristic inputs of tire model. It allows the transfer of absolute velocity of the wheel center expressed in the reference frame and the absolute position of center of wheel to the road model. The stiffness and the damping characteristics of the tire is included by using the spring damper as shown in figure 8.

Figure 10. Vehicle suspension model

Case Study A typical 16 tonne vehicle which is already proven and having experimental results was taken up for validating the model. Figure 8. Tire model

Road Model The road model includes the road model which defines the profile of the road and adherence model which defines the road grip. The road model has the flexibility to model flat roads, sinusoidal road, gradient, uneven road etc. It also got the capability to include the measured 3D road profile data. For predicting the stopping distance flat road is considered.

Figure 11. A typical 16 tonne vehicle Table 1. Vehicle details

Figure 9. Road tire interface model

The adherence model is used to define the road grip. The adherence can be input independently at each wheel. This allows the possibility of several road grip modelling as constant or variable adherence, Split mu conditions. For simulation of stopping distance as per the specification [1] the road grip to be considered is 0.8.

Suspension Modelling The suspension of the vehicle is modelled using a spring damper element shown in Figure. The spring stiffness and the damping charecteriscts were given as input. The suspension model can be directly connected to the chassis model as shown in the figure.

The specification of the vehicle is as shown in table 1.

Brake System Layout The individual components of pneumatic brake system were modelled and now need to be connected. Since the individual brake system product models are assembly of various components and elements, connecting together as is will appear complex. For easy representation of these models, the individual product models were shrink and wrap together into a single icon namely super component and assembled together as shown in figure 12.


Stopping Distance Calculation The stopping distance is the distance covered by the vehicle from the moment when the driver begins to actuate the control of the braking system until the moment when the vehicle stops. Figure 14 shows the simulated stopping distance. The stopping distance of the vehicle travelling at 60kmph on braking is 33meters.

Figure 12. A typical 16 tonne vehicle

Vehicle Model The equivalent vehicle model for the 16 tonn vehicle is shown in the figure 13. The engine was not considered in the simulation. The initial velocity of the vehicle was directly given as input. Figure 14. Stopping distance of the vehicle

Mean Fully Developed Deceleration The mean fully developed deceleration dm was calculated as the deceleration averaged with respect to distance over the interval Vb to Ve according to the following formula

(3)

V - Initial velocity of the vehicle in kmph Vb - Vehicle speed at 0.8 V in kmph Ve - Vehicle speed at 0.1 V in kmph Figure 13. A typical 16 tonne vehicle

Sb - Distance travelled in between V1 and Vb in m

Simulation of Stopping Distance and MFDD Calculation

Se - Distance travelled in between V1 and Ve in m

The brake system layout was first simulated and the pressure response at the actuators of the layout was studied by applying pedal travel of the foot brake valve model as input. The transient torque generated at the end of foundation brake model was mapped to the vehicle model as shown in figure 13.

Simulation Conditions The initial velocity of the vehicle is set as 60kmph equivalent to the test conditions. The steering of the vehicle is fixed. The response of the pneumatic brake system was mapped to the vehicle. On mapping the braking torque obtained form the brake system layout the velocity of the vehicle were studied to compute the stopping distance and the Mean Fully Developed Deceleration.

Figure 15. Velocity plot and the absolute position of the vehicle

From the above figure the distance travelled and the velocities were found out which is shown in table-1.The calculated MFDD is 5.154 m/s2.

Downloaded from SAE International by Mithun Selvaraj, Tuesday, September 09, 2014 Table 1. Simulation results

Table 3. Comparison

Parametric Study Validation of the Model

With the validated model the behavior of the vehicle at condition and on different road conditions were studied.

To validate the simulated model the vehicle considered in our simulation was tested in the test track as per the standard.

Experimental Setup and Testing The experimental setup of the vehicle considered in the simulation is shown in figure.16. Figure 17. stability of vehicle under ideal and brake failed condition

Figure 17 shows the behavior of the vehicle under ideal and one circuit failed condition. It is seen that under one circuit failed conditions the vehicle leaves the track.

Figure 16. Vehicle testing in the Test track

The test setup includes 5th wheel speed sensor to measure the vehicle speed, Pressure transducer for measuring brake chamber pressure while braking and deceleration sensor for measuring the vehicle deceleration. The performance test requirement is as shown in table-2. Table 2. Performance test as per IS11852 PART3 / ECE R13

The stopping distance and MFDD was experimentally found out.

Comparison of the Results The simulated results were compared with the experimentally obtained stopping distance and the MFDD, which correlate well with the experimental results as shown in table.3.This validates our brake system and the vehicle model.

Figure 18. Behavior of vehicle under different road condition

Figure 18 shows the behavior of vehicle under different road conditions. [6]

Design & Optimization of Brake System Layouts The effective braking of heavy commercial vehicles having varying wheel base and GVW depends mainly on the brake system layout having various transmission and control valves. Apart form that the connecting pipes, positioning of the valves plays a major role on brake system response and thereby the stopping distance of the vehicle. Hence every heavy commercial vehicle needs unique layout with different brake system components and piping layout. Having validated model for brake system components /layout and vehicle model, aids the design of brake system layouts for new vehicles in simulation itself. Using this we can propose brake system with optimized number of valves and piping layout.


Summary/Conclusions The Brake system model and the vehicle model considering all the design parameters were done using the available libraries in AMESim. A typical 4X2 heavy commercial vehicle having validated test data was taken up for simulation. The brake system parameters and the vehicle parameters were fed into the simulation model and simulated for the dynamic behavior of the vehicle. The simulated stopping distance and the MFFD matches with the experimental results. The brake system, vehicle model was flexible enough to study the role of individual valves and design parameters on the dynamic behavior of the vehicle. Apart from this the model can be further expanded for design and optimization of brake system layout for other heavy commercial vehicle having multi axles. This approach will significantly reduce the overall system design lead time when compared to the conventional method

References 1. IS 11852_4 “Automotive Vehicles - Brakes and Braking system”, Indian Standard, 2001. 2. Sridhar, S., Narayanan, S., and Kumaravel, B., “Dynamic Simulation of a Brake Valve in Air Brake System,” SAE Technical Paper 2009-28-0030, 2009, doi:10.4271/200928-0030.

4. Wu, J., Zhang, H., Zhang, Y., and Chen, L., “Robust Design of a Pneumatic Brake System in Commercial Vehicles,” SAE Int. J. Commer. Veh. 2(1):17-28, 2009, doi:10.4271/2009-01-0408. 5. AMESim Handbook, LMS Imagine S.A. 1995-2012. 6. Wong J.Y.., Theory of Ground Vehicles, JOHN WILEY & SONS, INC, 2001.

Contact Information Mr. S. Mithun Simulation Engineer WABCO India Ltd [email protected] [email protected] Contact Number: 9962422714

Acknowledgments Authors would like to express their gratitude to Ms WABCO India Ltd for the encouragement and permission to report this article.

Definitions/Abbreviations MFDD - Mean Fully Developed Deceleration

3. Mithun, S., Mariappa, S., Gayakwad Suresh., “Modeling and simulation of pneumatic brake system used in heavy commercial vehicle” IOSR, Journal of Mechanical and civil Engineering doi:10.9790/1684-11120109.

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