Simulation of Leaf Spring Balanced Suspension Based on Virtual Test-Rig

Abstract

In ADAMS/Car, the simulation platform—six-post test-rig which can identify dual-tire model was developed specialty for testing leaf spring balanced suspension of heavy truck. Based on this, the virtual prototype model of the drive form of 6 × 4 heavy truck was built, and simulation containing four excitation modes were conducted by assembling the virtual prototype model of heavy truck with leaf spring balance suspension to the special six-post test-rig. Design bugs of the leaf spring balance suspension were fund out and approach improving on these problems was proposed by analyzing computed results.

F2012-E03-002

1 Introduction

The leaf spring balanced suspension is commonly used in modern heavy-duty truck. It can improve the transportation efficiency and ensure the ride comfort and handling stability at the same time. As an indispensable part of the balanced suspension, the guide mechanism plays an important role in transmitting force and torque between the frame (or body) and the wheels. Therefore, scientific method and reasonable layout in guide mechanism design is essential to improving the performance of balanced suspension and even the vehicle [1–3].

The integrated application of computer 3D modeling technology, virtual prototyping technology, CAD and CAE is the modern vehicle design and analysis direction. It is significant for improving vehicle design and analysis level [4–6].

In this paper, the multi-body system dynamic simulation software of ADAMS is used for detailed kinematics/dynamics simulation analysis to the leaf spring balanced suspension of the heavy truck. The goal is to find the deficiency of existing guide mechanism and propose improvement scheme. For this purpose, the simulation platform—six-post test-rig which can identify dual-tire model was developed in ADAMS/Car, especially for testing leaf spring balanced suspension of heavy truck. Simulation to virtual prototype is carried out with this test platform. The results show that both ends of the thrust rod bear the most serious force in warp condition, which has a great impact on rubber bush’s life. On the other hand, there is interference between the leaf spring and lateral guide plate, which is a direct reason to lateral guide plate’s serious attrition.

2 Development of Six-Post Test-Rig

Analysis to guide mechanism of tri-axial truck’s leaf spring balanced suspension is carried out with virtual test-rig. The test-rig is simply defined by four parts representing the tire pads that support the vehicle. These tire pads are constrained to move in only the vertical direction and a displacement actuator (motion controller) controls their vertical motion. The only constraint between the pads and the vehicle’s tires is the friction of the tire itself. Because the Delft tire model supports zero velocity tire friction, this is all that is required to constrain the vehicle during the dynamic portion of the simulation. So the guide mechanism’s motion and force situation can be calculated [7].

2.1 Creating a Test-Rig Template in ADAMS/Car

A test-rig in ADAMS/Car is almost completely comparable to a template in ADAMS/Car. Test-rigs differ from templates mainly because test-rigs contain actuator elements, such as motions and forces, to excite the assembly.

The procedure for creating a test-rig template in ADAMS/Car is just like the procedure of creating a normal template, with a few differences. The steps for creating a test-rig template are: Creating a test-rig template; saving the test-rig template; modifying the test-rig template.

ADAMS/Car works with test-rigs as templates. However, in order to incorporate a test-rig for use on an assembly, the test-rig must be converted to a test-rig model file (.cmd) and a private ADAMS/Car binary created. We can, of course, create a new test-rig template from the ADAMS/Car interface very easily, but it is often best to work with existing templates in order to better understand the capabilities of MSC.ADAMS.

We start by modifying an existing test-rig model file (.cmd) in the template builder. Start by locating the file acme_4PostRig.cmd. This is a test-rig model file (.cmd) that contains a test-rig currently equipped with four active posts. As simulation to three-axis vehicle needs six-posts, two more posts need to be added to the original four-post test-rig. For specific information about building six-post test-rig templates and communicators see [7, 8]. The six-post test-rig templates created is shown in Fig. 1. Communicators are shown in Table 1.

Fig. 1

Six-post test-rig templates

Table 1 Communicators between test-rig and wheels

2.2 Creating a Private Binary

To use the six-post test-rig for vehicle simulation, We can now add both new test-rig model file acme_6PostRig.cmd (This is a six-post test-rig model file) and the new macro files to build a custom private ADAMS/Car binary which can implement this new test-rig. These new macro commands include acar_build.cmd, mac_ana_ful_six_sub.cmd, macros_ana.cmd and acme_6PostRig.cmd.

acar_build.cmd is the file upon which MSC.ADAMS will call when building a private binary. In general, this file contains any commands to: modify the MSC.ADAMS car interface; import the test-rig model files; add libraries (which show up in the command navigator); add macros; as well as some standard commands which should be in any acar_build.cmd file.

acme_6PostRig.cmd file contains the test-rig model file (.cmd) that we just created. This test-rig model will be imported into our private binary and now be available to any future assemblies.

macros_ana.cmd file serves as a pointer to mac_ana_ful_six_sub.cmd. It contains a hard-coded file location. It is good practice to use pointers like this rather than to import the simulation macros themselves. This allows for easy modification. Edit this file to make sure the commands are appropriate to our computer.

mac_ana_ful_six_sub.cmd is a macro that instructs ADAMS/Car on how to simulate the model. It contains parameters input window for simulation and four excitation modes (heave, roll, pitch and warp). This file is discussed in depth in Adding custom analysis procedures to ADAMS/Car, on [8].

Put the above macro command file into the acar_private folder. Then enter command “acar—cr_privatebin” in Adams command window and file acar.bin can be generated in the acar_private folder. Restart the Adams command window and input commands “acar—ru_private—i”, the ADAMS/Car can be started. Now _acme.6PostRig option can be seen in the drop-down menu of Vehicle Test-Rig. The option “acme” will also be added into the simulation command navigator, as is shown in Fig. 2.

Fig. 2

Simulation command navigators

3 Creation of Vehicle Virtual Prototype Model

All the models used in this paper are established in ADAMS/Car, and the following are some key points when building models.

• 1. The model is created by importing 3D balanced suspension (as is shown in Fig. 3) established in UG into the ADAMS/Car Template Builder interface. In this process, each assembly of the balanced suspension needs to be accordingly classified (middle and rear suspension, leaf spring and frame etc.). At the same time, the relative coordinates position relationship between different assemblies must be keep unchanged.

  Fig. 3

  

  3D balanced suspension model

• 2. Each assembly’s geometric parameters, physical parameters and mechanical parameters need to be write into each template after each assembly template is imported and established.

• 3. When changing the templates into subsystems, the Minor Role needs to be noticed as it concerns subsystems’ effectiveness in assembling.

• 4. Reasonable match between various subsystems needs to be established when assembling. The assembly relationship between subsystems is transferred by communicators. So it is necessary to establish correct communicators in modeling.

It needs to be emphasized that establishing correct connection relationship and communicators in modeling is significant. These data cannot be changed in subsystem and assembly, although general parts’ position and parameters can be changed in the following process. The balanced suspension model assembly model is shown in Fig. 4.

Fig. 4

Balanced suspension model in ADAMS/Car

Each of the above assembly needs to be compiled into the corresponding subsystem (save as sub file) in the Standard Interface. Then the vehicle assembly can be created with the subsystems and the six-post test-rig (_acme.6PostRig). The final vehicle model is shown in Fig. 5.

Fig. 5

Vehicle assembly model

4 Analysis of Balanced Suspension’s Guide Mechanism

The six-post test-rig can be used for analyzing the balanced suspension’s actual situation when the vehicle assembly is completed. There are four excitation modes, Heave: all tire pads move vertically in phase; Pitch: the front tire pads move 180° out of phase with the rear tire pads; Roll: the left tire pads move 180° out of phase with the right tire pads and Warp: the left-front and right-rear tire pads move 180° out of phase with the right-front and left-rear pads.

For heave motion simulation, the frequency is 0.5 Hz and the tire pads’ maximum displacement is 120 mm, so as to analog the suspension’s quasi-static maximum vertical load situation. The simulation results are summarized in Table 2.

Table 2 The upper and lower thrust rod’s maximum load

For the roll motion simulation (as is shown in Fig. 6), the frequency is 0.5 Hz and the pads’ maximum displacement is 100 mm so as to analog the maximum roll angle situation. The simulation results are summarized in Table 2.

Fig. 6

Roll motion simulation

For the pitch motion simulation (as is shown in Fig. 7), the front and rear posts move up and down relatively. The tires tract the middle posts move. The frequency is 0.5 Hz and the maximum displacement is 100 mm so as to analog the situation that braking force and driving force works together. The simulation results are summarized in Table 2.

Fig. 7

Pitch motion simulation

For the warp motion simulation (as is shown in Fig. 8), the frequency is 0.5 Hz and the maximum displacement is 90 mm so as to analog the suspension’s force situation in rough road. The upper and lower thrust rod’s maximum load (force and moment) in the above four situation simulation results are in Table 2.

Fig. 8

Warp motion simulations

Data in Table 2 clearly shows the following rules.

• 1. The vehicle gravity generates maximum axial force (resultant force) in the upper thrust rod in pitch and heave conditions. The maximum value is 18576.69 and 7498.85 N respectively.

• 2. Generally the axial force of the lower thrust rod is larger than upper thrust rod except the heave motion. The vehicle gravity generates maximum lateral force (Y axis) and axial force (resultant force) in warp and pitch conditions. The maximum values are 6255.48, 6192.63 and 20129.33, 20127.3 N respectively.

• 3. In warp condition, the upper and lower thrust rod gets the maximum moment. The upper thrust rod’s maximum moment is R _z (48280.6 N mm) around Z axis, which is shown in Fig. 9. The lower thrust rod’s maximum moment is R _x (64943.7 N mm) around X axis. These torqueses have little effect on thrust rod’s strength but have a greater impact on rubber bushings’ life.

  Fig. 9

  

  The upper thrust rod’s tensional deflection in warp condition

Figure 10 show the interference of leaf spring and lateral guide plate in warp condition, which the main reason is leading to the leaf spring and lateral guide plate’s abrasion.

Fig. 10

The interference of leaf spring and lateral guide plate

5 Conclusions

• 1. A six-post test-rig which supports dual tires simulation is established by macro command development tools on basis of the existed four-post test-rig in ADAMS/Car. These extend the software function;

• 2. A vehicle simulation model is assembled by six-post test-rig. Simulation for a tri-axial vehicle with balanced suspension is carried out in four excitation modes. The results show that the upper and lower thrust rod gets the maximum moment in warp motion, which have a greater impact on rubber bushings’ life. On the other hand, the interference of leaf spring and lateral guide plate in warp is the main reason leading to the leaf spring and lateral guide plate’s abrasion.

The research method and conclusions of this paper have some reference value to the modeling of multi-axis heavy truck and the design of guide mechanism in balanced suspension.