TABLE OF CONTENTS
INTRODUCTION.............................................................................................................................................................1
CHAPTER 1. SUSPENSION SYSTEMS ON THE ARMY VEHICLES. ........................................................................3
1.1 Suspension system of URAL-432067 vehicle...........................................................................................................3
1.2 Suspension system of UAZ-3160 vehicle..................................................................................................................6
1.3 Suspension system of GAZ-66 vehicle......................................................................................................................9
1.4 Conclusion of chapter 1............................................................................................................................................12
CHAPTER 2. CONSTRUCTION OF MILITARY VEHICLE SUSPENSION SYSTEM URAL-432067...........................13
2.1 Functions of suspension system...............................................................................................................................13
2.2 Classification and requirements of suspension system............................................................................................14
2.2.1 Classification..........................................................................................................................................................14
2.2.2 Requirements .......................................................................................................................................................14
2.3 Structural analysis of suspension system.................................................................................................................15
2.3.1 Front suspension structure....................................................................................................................................16
2.3.2 Rear suspension structure.....................................................................................................................................17
2.3.3 The linkages..........................................................................................................................................................19
2.3.4 Spring....................................................................................................................................................................21
2.3.5 Shock Absorber.....................................................................................................................................................25
2.4 Conclusion of chapter 2............................................................................................................................................29
CHAPTER 3. VIBRATION INVESTIGATION OF MILITARY VEHICLE SUSPENSION SYSTEM URAL-432067.......30
3.1 Criteria to evaluate the vibration of vehicle...............................................................................................................30
3.1.1 Criteria of smoothness of movement.....................................................................................................................30
3.1.2 Criteria to evaluate movement safety....................................................................................................................32
3.2 Dynamic equations of motion...................................................................................................................................33
3.2.1 Assumptions .........................................................................................................................................................33
3.2.2 Calculation of basic parameters of the suspension...............................................................................................35
3.2.3 Differential equation system of motion...................................................................................................................36
3.2.4 Mathematical description of the road surface........................................................................................................38
3.3 State space model....................................................................................................................................................39
3.4 Frequency response of dynamics.............................................................................................................................46
3.4.1 Frequency response of dynamics with half-car model ..........................................................................................46
3.4.2 Frequency response of dynamics with quarter-car model ....................................................................................52
3.5 Time response of dynamics......................................................................................................................................69
3.5.1 Differential equation system of order 1..................................................................................................................69
3.5.2 Define initial conditions .........................................................................................................................................70
3.6 Conclusion of chapter 3............................................................................................................................................77
CHAPTER 4. INSTRUCTIONS FOR SERVICE OF SUSPENSION SYSTEM...............................................................78
4.1 Notes in using the suspension system of URAL-432067 vehicle.............................................................................78
4.2 Types of suspension maintenance............................................................................................................................80
4.2.1 Regular maintenance.............................................................................................................................................81
4.2.2 Periodic maintenance.............................................................................................................................................82
4.3 Damages in the suspension system.........................................................................................................................86
4.4 Repair the suspension system..................................................................................................................................90
4.5 Conclusion of chapter 4............................................................................................................................................92
CONCLUSION................................................................................................................................................................93
REFERENCE..................................................................................................................................................................94
APPENDIX......................................................................................................................................................................95
INTRODUCTION
The smoothness and safety of vehicle motion, both in general and particularly in military vehicles, are economically significant technical indicators in the design and operation of various vehicle types. Research on automobile vibrations aims to enhance the smoothness of motion, towing quality, steering capability, motion stability, durability, and reliability. This is a highly important and necessary endeavor, especially given the rapid advancement of science and technology today. Worldwide automobile manufacturing corporations continually introduce modern vehicles to fulfill an increasing number of tasks for humanity, along with higher technical requirements.
In recent times, our country's economy is in a phase of development, with the automotive industry steadily growing in terms of both scale and production quality, including manufacturing and assembly. Automobile factories are gradually emerging in various locations, which will result in many types of vehicles being manufactured and assembled in Vietnam with high specifications and efficient features suitable for local operating conditions, terrains, and weather.
Therefore, it is crucial to earnestly concentrate on theoretical research as it forms the foundation for vehicle improvements. This holds immense importance in the nation's construction and modernization efforts, allowing us to possess a production line in the automotive industry. This can have a substantial impact on both the domestic and international economies, promoting industrialization and modernization.
Therefore, the study of theoretical problems needs to be seriously focused, it is the basis for conducting vehicle improvement. This is extremely important in the construction and renovation of the country, which will help us to have the right to own a production line of the automobile industry, strongly affecting the domestic and foreign economy, promoting industrialization and modernization.
The objective of my graduation thesis is “Vibration investigation of suspension system using in the army ”. The primary method employed in my thesis is the state-space modeling in Matlab, a software widely applied in contemporary automotive research due to its high applicability and numerous useful calculation tools. This represents a new direction in modern automotive research, supplanting outdated traditional research methods.
However, this subject does not fall within my major's study program, so it required a considerable amount of time and effort to complete. Despite our utmost efforts, this project is bound to have limitations in terms of knowledge and time constraints. I hope that instructors and readers can provide suggestions for improving my thesis.
Hanoi, date ... month ... year 20..
Students perform
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CHAPTER 1
SUSPENSION SYSTEMS ON THE ARMY VEHICLES
Military vehicles are widely used in the military today due to their compact size, versatility, and various other features. Models such as URAL-432067, UAZ-3160, GAZ-66, and others are worth mentioning. Basic information about these models will be discussed in this chapter.
1.1 Suspension system of URAL-432067 vehicle
a. The front suspension system.
- The URAL- 432067 vehicle uses a front suspension system that is dependent.
-The front suspension system structure of the URAL- 432067 vehicle includes:
+ The elastic element is a semi-elliptic leaf spring.
+ The primary directional element is the leaf spring.
+ The damping element is a two-way hydraulic shock absorber.
+ Hydraulic shock absorber.
b. The rear suspension system
The rear suspension is dependent, using semi-elliptic leaf springs with auxiliary springs, working in conjunction with a two-way hydraulic shock absorber. The unique feature of this suspension system is the additional auxiliary springs in the rear suspension, allowing the stiffness of the leaf spring to be adjusted, accommodating a wide range of load variations, ensuring a smooth ride across different terrains. At lighter loads, the main leaf spring bears the load. As the load increases, the ends of the auxiliary springs engage with the notches on the vertical frame members.
- The structure of the rear suspension system of the URAL-432067 vehicles.
The vehicle is designed to operate on various terrains, leading to fluctuating loads on the leaf springs over a wide range. Therefore, the stiffness of the leaf springs needs to be adjustable to ensure a smooth ride when operating in diverse terrains. To meet this requirement, an additional set of auxiliary springs is installed in the rear suspension system, mounted on top of the main leaf springs.
1.2 Suspension system of UAZ-3160 vehicle
a. The front suspension system.
The front suspension system is an independent suspension system, composed of two coil springs, a horizontal stabilizer bar, a bidirectional hydraulic shock absorber, and a steering mechanism consisting of two vertical links and one horizontal link.
On figure 1.4, the overall structure and general layout of the suspension system are depicted.
The spring perch 18 of the suspension system is placed between two spring brackets 2 and the spring bracket (17). The spring's purpose is to bear vertical loads, allowing the wheel to move relative to the frame in a smooth oscillating manner, minimizing undesired wheel movements such as lateral and vertical swaying to the lowest extent. Spring bracket 2 is rigidly welded to the frame, and the spring bracket (17) is welded to the axle.
b. The rear suspension system.
The rear suspension system of the UAZ-3160 consists of the following main components.
Shock absorber mount 1, 10, leaf spring 2, shock absorber 3, frame 4, leaf spring cushion 5, 2 U-bolts 6, mobile pillow block bracket 8, spring pin 12, travel-stop bolt 14, mobile pillow block assembly, axle beam.
The rear suspension system of the UAZ-3160 is a dependent suspension system, with a half-elliptic leaf spring as the elastic element, and it features a two-way hydraulic shock absorber. This suspension system does not include a stabilizer element. The leaf spring (2) is composed of three individual leaves, with spring pads positioned between them and secured together through spring pins. One end of the leaf spring is fixed to the frame (4), while the other end is attached to a mobile pillow block. The mobile pillow block is fastened to the frame (4) through a bracket (8).
1.3 Suspension system of GAZ-66 vehicle
The GAZ-66 is a Soviet and later Russian 4x4 all-road (off-road) military truck produced by GAZ. It was one of the main cargo vehicles for motorized infantry of the Soviet Army and is still employed in former Soviet Union countries.
The front and rear suspension systems of the GAZ-66 are dependent suspension systems with a simple structure, and the elements of the front and rear suspensions have similar design and operating principles. Below is the structure of the front suspension system of the GAZ-66 vehicle.
* Advantages:
- Simple structure, cost-effective, while still meeting essential requirements, especially for vehicles with low speeds.
- Easy to disassemble and repair.
* Drawbacks.:
- The non-suspended mass is significant, especially on the driving axle. When the vehicle travels on uneven roads, the dynamic load generated can lead to a strong impact between the non-suspended and suspended parts (the vehicle body), reducing the smoothness of the car's motion. Additionally, the strong impact of the wheels on the road surface can negatively affect the contact between the wheels and the road.
- The space underneath the vehicle must be ample to allow for the axle to change position, which means either having a high center of gravity or reducing the cargo volume of the vehicle.
1.4 Conclusion of chapter 1
This chapter introduces several typical 4x4 military vehicles that are currently widely used in the military and are under research and improvement to serve various new military purposes. The next chapter will further select and analyze a specific type of vehicle. Due to the need for technological innovation to keep pace with current technological advancements, my thesis focuses on the analysis of vehicle vibrations.
CHAPTER 2
CONSTRUCTION OF MILITARY VEHICLE SUSPENSION SYSTEM URAL-432067
2.1 Functions of suspension system
The suspension system plays a pivotal role within an automobile. It establishes a vital connection between the wheels and the chassis or body of the vehicle, facilitating relative motion between the wheel and the chassis or frame. Its primary objectives encompass ensuring a smooth ride, enhancing the safety of the vehicle's movement, and mitigating undesirable wheel movements in both horizontal and vertical directions. Furthermore, it optimizes the friction between the car's tires and the road surface.
In conclusion, the components of this system perform six basic functions:
- Maintaining correct vehicle ride height
- Reducing the effect of shock forces
- Maintaining correct wheel alignment
2.2 Classification and requirements of suspension system
2.2.1 Classification
Suspension systems can differ based on the type of vehicle body and, in some instances, even by the manufacturer's brand. Below are the most prevalent methods of categorizing a car's suspension system:
a. According to the linkages:
Dependent and independent suspension systems represent two primary classifications. In a dependent suspension system, the wheels on one axle are interconnected by a rigid beam, so when one wheel moves, it induces movement in the other.
b. According to the springs:
- Metal: leaf springs, coil springs, torsion bars;
- Pneumatic: rubber-coated type, membrane type, tube type;
- Hydro-gas: tube type;
2.2.2 Requirements
The main requirements for the suspension system are as follows:
- This type of suspension is well-suited for various usage conditions, including those that require specific technical attributes, such as traveling on well-maintained roads or navigating diverse types of terrain. Its design is tailored to provide a smooth ride and ensure the comfort of both passengers and transported goods within the vehicle;
- It does not cause impact at frame or shell joints;
- It is capable of absorbing high dynamic loads;
2.3 Structural analysis of suspension system
The suspension system on the URAL-432067 is of the dependent type. The front axle is equipped with elliptical leaf springs, in conjunction with two-way hydraulic shock absorbers. Similarly, the rear axle also utilizes a dependent suspension, featuring semi-elliptic and auxiliary leaf springs, accompanied by two-way hydraulic shock absorbers.
2.3.1 Front suspension structure
To enhance durability, all the leaves are heat-treated on the top surface. Clamps are affixed to one of the leaves and secured with bolts. Leaf springs of varying lengths are grouped into sets and attached to the bridge girder using a central clamp (designated as 18) and a buffer (referred to as 20).
The central portion of the leaf springs is secured to the axle housing using clamps. The upward movement of the axle is restricted by the presence of spring buffer 2, which is installed alongside buffers 20 and 13. Case 13 is attached to bracket 6 and firmly connected to the vehicle's chassis.
2.3.3 The linkages
a. Function
Linkages in the suspension system are the sturdy connections that utilize mechanical fasteners to join the vehicle's mainframe with the wheel knuckles. These linkages play a crucial role in transmitting horizontal and vertical forces, as well as moments, from the road surface to the chassis.
b. Requirements
The linkages have the following basic requirements:
- Keeping the kinematics of the wheels when the car is moving. When the wheels move vertically, the wheel angles, widths, and wheelbases must remain the same.
- Shifting the wheel horizontally (changing of the track width) will make the tire wear faster and increase the vehicle's resistance to movement on soft soils.
- Simple structure, it should be easy to use and maintain.
- The linkages must ensure that the suspension arrangement on the car is convenient and does not prevent the installation of the engine at the front. This can optimize the space in the chassis. The linkages can also increase the smoothness of the movement if the sprung parts are rearranged properly.
c. Structure
URAL-432067 uses a dependent suspension with a semi-elliptic leaf springs. In order to ensure the transmission of force between the chassis and the axle, the springs are mounted to the axle with clamps and attached to the chassis by joints. Those joints ensure the change in length of the leaf springs when they deform.
Some advantages and disadvantages of this suspension:
- Advantages: Simple structure, easy maintenance.
- Disadvantages: When a wheel is raised, the bridge will also be lifted because the wheels are connected by a bridge girder, then the change in the track will generate lateral forces, reducing the car’s ability to grip the road and causing the car to slide sideways.
2.3.4 Spring
a. Function
Springs in the suspension system serve the crucial function of supporting the vehicle's frame, body, and the loads it carries. They enable the wheels to effectively absorb the shocks caused by uneven road surfaces and establish a flexible connection between the wheels and the vehicle's body.
b. Structure
The URAL-432067 features a dependent suspension system with semi-elliptic leaf springs on both axles, as depicted in figures 2.1 and 2.2. The front axle suspension system, as shown in figures 3-5, comprises multiple leaf springs constructed from steel strips or leaves of varying lengths, joined together using a central bolt. At each end of the largest or master leaf, there is a rolled eye that serves as an attachment point for connecting the spring to the spring hanger and spring shackle.
Front leaf springs:
- Quantity: 11 leaves;
- Working length: 1420 mm;
- Leaf width: 65 mm;
Rear leaf springs:
+ Main springs:
- Quantity: 12 leaves;
- Working length: 1500 mm;
- Leaf width: 75 mm;
* Disadvantages:
- The largest weight in springs. Therefore, different length leaf springs will be manufactured to meet the suspension requirements, reducing unnecessary weight.
- Short working time: The leaf springs are subjected to various stresses, including initial stresses, complex stress states, repeated dynamic forces, and fatigue. Their fatigue strength is up to four times lower than that of torsion bars. When a vehicle operates on well-maintained roads, the service life of leaf springs typically ranges from 100,000 to 150,000 kilometers. However, when subjected to rough or poor road conditions, this service life can decrease significantly, sometimes by as much as 10 to 50 times.
2.4 Conclusion of chapter 2
This chapter provides an introduction to the function and classification of suspension systems and subsequently conducts an in-depth analysis of the suspension structure of the URAL-432067 vehicle. The analysis focuses on specific components, including leaf springs, linkages, and dampers. Additionally, it offers detailed insights into the advantages, disadvantages, and working principles of each of these components.
CHAPTER 3
VIBRATION INVESTIGATION OF MILITARY VEHICLE SUSPENSION SYSTEM URAL-432067
3.1 Criteria to evaluate the vibration of vehicle
There are many different criteria to evaluate automobile vibration, some of the most important ones are: the criteria of smoothness of movement, the criteria of motion safety and load acting on the road surface, and the criteria of the working space of the suspension system.
3.1.1 Criteria of smoothness of movement
a. Criteria of acceleration
There are many criteria to evaluate the smoothness of motion. In which acceleration as well as amplitude and frequency of oscillation have a direct influence on driver, passengers and cargo.
b. Criteria of frequency
Criteria of frequency is based on people's walking habits. When people walk, they are actually making an oscillation. For each person, depending on different habits and physique, the steps taken are different, but in general, they can take about 60-90 steps per minute, that is, the corresponding frequency is 1-1.5 Hz. In other words, people from childhood are familiar with the frequency of vibrations in this range.
3.1.2 Criteria to evaluate movement safety
There are many criteria to evaluate movement safety. However, the vertical dynamic load acting between the wheel and the road surface is the main cause of unsafe movement (loss of control). When the car moves on a road with a random profile, the vertical load of wheel is also random.
3.2 Dynamic equations of motion
3.2.1 Assumptions
The oscillation of a rigid body in space has six degrees of freedom: three degrees of freedom that translate along the axes: X, Y, and Z, and three degrees of freedom of rotation about those axes.
- The analytical model is a planar model, meaning that it assumes the car is symmetrical about its longitudinal axis, and it considers the road surface roughness to be uniform for both wheels on a single axle.
- The chassis and frame are absolutely solid objects.
- Cars are created by inertial masses moving with the car's mass center.
- The car's mass center is located in the car’s longitudinal plane of symmetry.
- Rolling wheels do not slip on absolute hard ground, always in contact with the road surface.
- The connection of the system is the ideal connection.
Based on the above assumptions, a bicycle vibrating model of a vehicle as shown in Figure 3.2 is used to study the vibration dynamics.
3.2.2 Calculation of basic parameters of the suspension
The fundamental parameters of the suspension system include the natural frequency of the sprung mass, the natural frequency of the unsprung mass, the damping coefficient of the vehicle's body, and the static and dynamic displacements of the wheels.
3.2.3 Differential equation system of motion
Setting up the system of differential equations to describe wheel oscillation involves using mathematical methods to analyze vibrations. The primary parameters of automobiles utilized in vibration analysis include:
- The stiffness of the suspension springs;
- The stiffness of tire;
- The sprung mass;
- The unsprung mass;
3.2.4 Mathematical description of the road surface
When studying vibrations, the fundamental parameters of the road profile's geometric dimensions play a crucial role, assuming the road profile to be completely rigid. In practical vehicle applications, particularly with military vehicles, road conditions can vary significantly. To examine the system's frequency response, we assume that the road excitation can be represented as a harmonic function.
3.3 State space model
A state space model represents a system by a series of first order differential state equations and algebraic output equations. State space models are efficient to solve complex systems, allow for more geometric understanding of dynamic systems, and form the basis for much of modern control theory.
In the above equation, the A matrix describes how the internal states are connected to each other and the B matrix describes how the inputs enter into the system, which states are they affecting.
The first state changes as a function of states and inputs, the same for the rest functions. We finally have a system of linear equations that we can package into matrix form, which will be represented in detail below.
3.4 Frequency response of dynamics
3.4.1 Frequency response of dynamics with half-car model
This project delves deeply into the study of vibrations in the URAL-432067 vehicle. Consequently, the parameters of this vehicle will be utilized for the analysis. The attributes of the bicycle model of the car are presented in the table below.
3.4.2 Frequency response of dynamics with quarter-car model
When a car moves on an uneven road surface, under the influence of road profile deformation (dynamic excitation), the car undergoes forced oscillations. The characteristics of these oscillations are determined by the structural properties of the system and the laws governing external excitation forces.
In this section, it is necessary to determine the frequency response of oscillations with varying input amplitudes:
+ At what car velocity within the operating speed range and for what wavelength of the road surface wave will the phenomenon of resonance occur.
+ Is the damping coefficient of the oscillation suitable or not.
In the process of calculating the car's oscillation, we make use of the following assumptions:
- The oscillations of the front and rear suspension masses are independent of each other.
- The oscillations of the car occur only in the vertical plane of the vehicle.
- The oscillations of the car are stable oscillations.
- The source of oscillation excitation is the road surface wave, with the wave equation given by:
z = z0 [1-cos( .t)] (3.28)
3.4.2.1. Determination of the natural frequency and damping coefficient of the oscillation system
a. The survey diagram
The symbols and specific data used in the calculation process include:
C: The stiffness of a suspension;
Cf: The stiffness of the front suspension: Cf = 130000 [N/m];
Cr: The stiffness of the rear suspension.: Cr = 260000 [N/m];
Ct: The stiffness of a car tire;
CFT: The stiffness of the front tires: CFT = 400000 [N/m];
CRT: The stiffness of the rear tires: CRT = 400000 [N/m];
M: The mass sprung;
M1: Front spung mass: M1 = 3350 [kg]; Ct
M2: Rear spung mass: M2 = 6125 [kg];
b. Some fundamental parameters include:
* The natural frequency of the non-suspended part when the suspended part is fixed, as per [1]:
The natural frequency of the non-suspended mass when the suspended part is fixed and C1 = 0
* The natural frequency of the non-suspended mass when the suspended part is fixed and when Ct = 0.
* The damping coefficient of the non-suspended mass when the suspended part is fixed:
The low-frequency oscillation frequency of the system, denoted as: Ω
The high-frequency oscillation frequency of the system, denoted as: Ωk
The damping coefficient corresponding to the low-frequency oscillation of the system: h
The damping coefficient corresponding to the high-frequency oscillation of the system: hk
3.4.2.2. Determining the amplitude of oscillation of the suspended mass and the amplitude of oscillation of the non-suspended mass
* The formula for calculating the oscillation frequency of the suspended and non-suspended masses when resonance occurs at low-frequency (When = U).
3.4.2.3. Determining the acceleration of oscillation of the suspended mass
* The acceleration of oscillation of the suspended mass when resonance occurs at low frequency (when = V is determined by the following formula.
* The acceleration of oscillation of the suspended mass when resonance occurs at high frequency (when = V) is determined by the following formula.
3.4.2.4. Constructing the frequency-amplitude characteristic of oscillation
The frequency-amplitude characteristic is a graph representing the relationship between the amplitude of car oscillations and the amplitude of oscillation of the suspended mass, non-suspended mass, and the acceleration of the suspended mass with the excitation frequency of the road surface wave.
- According to the formulas in section 3.4.2.1, we can determine the specific values as shown in Table 3.2
During vehicle movement, the excitation frequency changes depending on the length of the pavement wave and the speed of the vehicle. Based on the frequency response diagram, it is possible to evaluate the motion smoothness corresponding to different frequencies. The vertical axis of the graph represents the ratio values between the displacement of sprung mass , the displacement of unsprung mass , the acceleration of the vehicle body and the bumpy height of the pavement profile is . The horizontal axis represents the excitation frequency ω.
As shown in Figure 3.18, the amplitude frequency characteristic consists of 5 regions: pre-resonant region, low-frequency resonant region, low-frequency and high-frequency mid-resonant region, high-frequency resonant region, and high-frequency post-resonant region.
The second zone (low-frequency resonant region) is characterized by the increased displacement of the vehicle body relative to the bumpy height of the road profile. The suspension amplifies body oscillations, so its displacement and acceleration increase. At the same time, the oscillation of the vehicle body increases the amplitude of the wheel's oscillation.
3.6 Conclusion of chapter 3
This chapter introduced the criteria for assessing the safety of movement, built a model to analyse the vibration of the car, and explained the basic concepts of the State Space model. On that basis, Chapter 3 has built the car's vibration analyzed graphs, with the input parameters of URAl-432067 vehicle.
CHAPTER 4
INSTRUCTIONS FOR SERVICE OF SUSPENSION SYSTEM
4.1 Notes in using the suspension system of URAL-432067 vehicle
The suspension system is one of the crucial systems in vehicles. A well-functioning suspension system, in compliance with the manufacturer's specifications, not only ensures safety during driving but also provides comfort for both the driver and passengers. Because of its structural and functional characteristics, the suspension system is situated in a hard-to-reach area, making maintenance and care challenging. It operates under high stress in rugged environments, frequently subjected to elevated temperatures and significant dirt exposure.
- Avoid overloading the vehicle. Prolonged operation with excessive loads can result in decreased performance of the suspension system, as well as negative effects on the engine and tires. The elastic components of the suspension will experience accelerated wear and a reduction in stiffness. Furthermore, overloading the vehicle can lead to increased fuel consumption and decreased maneuverability. Therefore, drivers should adhere strictly to the specified vehicle load limits.
- Ensure that all tires are correctly inflated. When one tire or one side of the vehicle has low tire pressure, it can result in vehicle tilting. This leads to uneven load distribution on the suspension, causing the car to lean to one side. If this issue persists, the elastomers may develop uneven stiffness between the wheels. Consequently, even when tire pressure is corrected, the vehicle may still tilt and exhibit instability during straight-line movement, as it tends to veer to one side.
4.2 Types of suspension maintenance
Suspension maintenance encompasses several essential tasks, primarily centered on inspecting the condition, cleaning, securing, changing lubricating grease, diagnosing technical conditions, and making necessary adjustments. Periodically examine the state of the multi-leaf spring and shock absorbers, inspect and tighten the connections, and repair any identified damage.
The shock absorber should not be adjusted during normal use. It should only be removed in the following cases:
- Occurrence of irreparable oil leakage.
- Loss of force at compression and extension cycle
- Need to change the working fluid.
4.2.1 Regular maintenance
a. For multi-leaf spring
- Observe whether the leaf spring are displaced within the same bundle of leaves or between the left and right sides; whether the rear of the vehicle is tilted when standing still, if it is, the springs will have uneven stiffness;
- Observe whether the leaves are cracked or broken;
- Check the tightening of rebound clips with leaves bundle.
b. For shock absorber
- Check the occurrence of oil leakage or cracks of the dampers; whether it’s housing is wet or dusty;
- Check the fastening of the dampers to the chassis and axle;
- Check whether the shock absorber is working or not: after using the car, it is possible to check if the damping temperature has increased. If not, there is a high chance that the shock absorber has lost its working effect.
4.2.2 Periodic maintenance
Periodic maintenance is the responsibility of mechanics or workers in the service station, and it is performed after a set cycle of vehicle operation, determined by the distance traveled or the operating time. This type of maintenance typically involves the use of specialized equipment to inspect valves, adjust thermal clearances, change bearings, replace brake pads and clutch discs, along with performing minor repairs and part replacements as needed, depending on the level of periodic maintenance required.
Vehicle maintenance must strictly adhere to the prescribed procedures for each maintenance level, following the specific requirements and technical standards outlined for each vehicle type. Mixing or altering assemblies and parts on the vehicle is prohibited; they must remain fastened in their correct positions. The addition of necessary parts is permitted as long as it falls within the permissible limits of the technical standards.
a. Maintenance level I:
Mainly includes checking, doing all the work of daily maintenance and the following additional things:
- Clean the leaf springs, lubricate the working surface of them by lead grease;
- Check the deflection of the leaves, the tightness of the rebound clips bolts;
- Supply the damping oil if necessary;
b. Maintenance level II:
Includes all the work of level I and the following additional tasks:
- For the leaf spring:
+ Adjust them if they are displaced;
+ Removed and replaced them if they are cracked or broken (use the spring of the same type);
- For the shock absorbers:
+ Supply the working oil if lacking;
+ Replace it with a new one if it is cracked or broken;
4.3 Damages in the suspension system
The common malfunctions in the suspension system:
a. For the leaf springs:
+ A reduction in stiffness leads to a lowering of the vehicle's body height, which in turn increases the likelihood of a harsh collision between the frame and the axle during braking, acceleration, or when navigating rough terrain. This can result in increased noise levels and intensify the car's vibrations.
+ The phenomenon of leaf spring jamming occurs when there is a lack of lubricating grease, leading to an increase in stiffness. A jammed leaf spring causes the vehicle to experience pronounced vibrations when driving on rough roads, resulting in a loss of smoothness in its movement. This increased stiffness also elevates the forces acting on the vehicle's body, diminishes its road grip, and shortens the lifespan of the shock absorber.
b. For the damper:
The shock absorber must operate with appropriate resistance to rapidly dampen the vehicle's body vibrations. Damper damage can result in a change in this resistance, leading to reduced capacity to dampen the vehicle's vibrations, decreased smoothness, and, most importantly, a significant reduction in the car's road grip. Common issues with shock absorbers include:
+ Wear of cylinders and pistons: The piston-cylinder assembly serves as a guide and, along with the rings and seals, is responsible for sealing the oil chambers. During the operation of the shock absorber, the piston and cylinder move relative to each other, leading to significant wear on the piston. This wear impairs its guiding and sealing capabilities. Consequently, the change in the oil chamber's volume (in addition to the oil flowing through the orifice, some oil also flows through the gap between the piston and the cylinder) reduces resistance during both compression and extension strokes, gradually diminishing its ability to dampen vibrations effectively.
+ The seal is compromised, leading to oil leakage from the damper. This issue is commonly observed in tube-type shock absorbers, especially mon-tube ones. Over time, wear is inevitable due to limited lubrication of the seal and piston. This wear can result in the leakage of the working oil, causing a loss of damping effectiveness. In twin-tube dampers, the oil shortage can lead to the formation of air bubbles, which reduces stability during operation. When the seal is compromised, it not only expels oil rapidly, causing a sharp drop in pressure, but also allows external contaminants to enter, accelerating the wear of friction components.
+ Overloading can lead to the bending of the damper's piston rod, causing the damper to become completely jammed.
+ A broken rubber cushion at the connection between the shock absorber and the chassis can be detected by inspecting the joints. In such cases, when the vehicle travels on rough roads, it may experience strong impacts and produce noise in the suspension system.
4.4 Repair the suspension system
Based on the typical issues observed in the suspension system, the following repair and corrective actions can be implemented. To maintain the suspension system's optimal performance and ensure safety, it's crucial to conduct regular monitoring, promptly identify issues, adhere to the specified load limits for the vehicle, and follow the manufacturer's instructions.
4.5 Conclusion of chapter 4
This chapter has provided an overview of how to maintain and repair the vehicle's suspension system to meet technical standards, ensuring the long-term optimal performance of the vehicle.
CONCLUSION
After a period of extensive research and referencing documents, under the dedicated guidance of Doctor : Mr……………… I have successfully completed the project as per the specified requirements. Upon the completion of my graduation thesis, I have achieved the following objectives:
1. A comprehensive study and comprehension of military vehicle suspension systems.
2. Analyzing the suspension system's structure with a particular focus on the URAL-432067 vehicle's suspension system.
3. Utilizing the vehicle's parameters and standards to analyze the suspension system for prolonged operational conditions.
4. Investigating the technical diagnosis procedures and maintenance and repair techniques for the suspension system.
5. Gaining fundamental knowledge of Matlab software for the analysis of automotive vibrations.
6. Proficiently constructing the state space model for the bicycle car model to analyze vibrations, serving as a basis for future in-depth research.
This project has allowed me to solidify my existing specialized knowledge while also enabling me to acquire and familiarize myself with new knowledge, tools, and research methods in the automotive field.
After diligently working on my thesis with the valuable guidance and support from : Mr……………… and other instructors from the Military Automobile Department, I have successfully completed my graduation thesis. Looking ahead, there are plans to make substantial improvements to this project for its ongoing development and completion.I’m thankful to all of my lecturers for providing guidance regarding this thesis.
REFERENCE
[1]. Nguyễn Phúc Hiểu, Lý thuyết ô tô quân sự, Pencle's Army Publishing House - Hanoi 2002.
[2]. Vũ Đức Lập, Cấu tạo ô tô quân sự tập 1-2. Military Technical Academy - Hanoi 2000.
[3]. Vũ Đức Lập, Sổ tay tra cứu tính năng kỹ thuật ô tô, Military Technical Academy - Hanoi 2004.
[4]. Tô Văn Ban, Giáo trình giải tích II, Vietnam Education Publishing House – Hanoi 2015
[5]. Bernard Friedland - Control System Design: An Introduction to State-Space Methods - Dover Publications.
[6]. B.E. L.K. & Bona Timothy, State Space Analysis: An Introduction.
7[1]. Hunt H.E.M, Stochastic modeling of vehicles for calculation of ground vibration, 11th IAVSD – Symposium The Dynamics of Vehicles on Roads and Tracks, 1990
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