DESIGN AND ANALYSIS OF PASSIVE AUTOMOTIVE SUSPENSIONS
10.1 INTRODUCTION TO AUTOMOTIVE SUSPENSIONS
10.1.1 Full, half and quarter car suspension models
An automotive suspension supports the vehicle body on the axles. A “full car” model of a suspension with 7 rigid body degrees of freedom is shown in Figure 10-1. The vehicle body is represented by the “sprung mass” m while the mass due to the axles and tires are represented by the “unsprung” masses mu1 , mu2 , mu3 and mu4 . The springs and dampers between the sprung and unsprung mass represent the vehicle suspension. The vertical stiffness of each of the 4 tires are represented by the springs kt1 , kt2 , kt3 and kt4 .
The seven degrees of freedom of the full car model are the heave z , pitch T and roll I of the vehicle body and the vertical motions of each of the four unsprung masses. The variables r1 z , r 2 z , r3 z and r 4 z are the road profile inputs that excite the system.
A “half car” model with four degrees of freedom is shown in Figure 10-2. In the half car model, the pitch and heave motions of the vehicle body (T and z ) and the vertical translation of the front and rear axles ( u1 z and u2 z ) are represented.
A two-degree-of-freedom “quarter-car” automotive suspension system is shown in Figure 10-3. It represents the automotive system at each wheel i.e. the motion of the axle and of the vehicle body at any one of the four wheels of the vehicle. The suspension itself is shown to consist of a spring s k , a damper bs and an active force actuator Fa . The active force Fa can be set to zero in a passive suspension. The sprung mass ms represents the quartercar equivalent of the vehicle body mass. The unsprung mass mu represents the equivalent mass due to the axle and tire. The vertical stiffness of the tire is represented by the spring t k . The variables s z , uz and rz represent the vertical displacements from static equilibrium of the sprung mass, unsprung mass and the road respectively.
10.1.2 Suspension functions
The automotive suspension on a vehicle typically has the following basic tasks (D. Bastow, 1987): 1) To isolate a car body from road disturbances in order to provide good ride quality Ride quality in general can be quantified by the vertical acceleration of the passenger locations. The presence of a well-designed suspension provides isolation by reducing the vibratory forces transmitted from the axle to the vehicle body. This in turn reduces vehicle body acceleration. In the case of the quarter car suspension, sprung mass acceleration s z can be used to quantify ride quality.
- To keep good road holding The road holding performance of a vehicle can be characterized in terms of its cornering, braking and traction abilities. Improved cornering, braking and traction are obtained if the variations in normal tire loads are minimized. This is because the lateral and longitudinal forces generated by a tire depend directly on the normal tire load. Since a tire roughly behaves like a spring in response to vertical forces, variations in normal tire load can be directly related to vertical tire deflection ( u r z _x0010_ z ) . The road holding performance of a suspension can therefore be quantified in terms of the tire deflection performance.
- To provide good handling The roll and pitch accelerations of a vehicle during cornering, braking and traction are measures of good handling. Half-car and full-car models can be used to study the pitch and roll performance of a vehicle. A good suspension system should ensure that roll and pitch motion are minimized.
- To support the vehicle static weight This task is performed well if the rattle space requirements in the vehicle are kept small. In the case of the quarter car model, it can be quantified in terms of the maximum suspension deflection (Zs-Zu ) undergone by the suspension.
The outline of the rest of this chapter is as follows. In section 10.2 of the chapter, we will review standard results on modal decoupling. In sections 10.3-10.7, the use of modal decoupling and its approximation for the design and analysis of quarter car suspension systems will be studied. Section 10.8 verifies the results of the decoupled approximation using the accurate complete model. Section 10.9 of the chapter will study the decoupling of half car models and the extension of the result to full car models.
10.1.3 Dependent and independent suspensions
In the case of dependent suspensions, the vertical motions of one wheel of an axle are directly linked to that of the other wheel of that axle. Some cars are still designed and built with dependent rear suspension systems. Figure 10-4 shows a solid-axle leaf-spring dependent rear suspension system. The advantages of such a suspension are that it is simple and inexpensive. The drive axle is clamped to the leaf springs. The shock absorbers are also attached to the clamps. The ends of the leaf springs are attached directly to the chassis (vehicle body), as are the shock absorbers. Since the axle couples both the rear wheels, the vertical motion of one is transferred to the other.
In the case of dependent suspensions, the axle cannot be represented by 2 independent unsprung masses.
In all of the suspension system models considered in section 10.1.1 (full, half and quarter-car models), both the front and rear wheels were assumed to have independent suspensions.
The front wheelrsquo;s suspension systems are always designed to be independent (except for the presence of an antiroll bar). In an independent suspension, the vertical motions of the two wheels are not directly linked to each other. This was the implicit assumption in the full, half and quarter-car models introduced in section 10.1.1. Figure 10-5 shows a double-A arm type of independent suspension. The wheel
全文共20897字，剩余内容已隐藏，支付完成后下载完整资料
DESIGN AND ANALYSIS OF PASSIVE AUTOMOTIVE SUSPENSIONS
10.1 INTRODUCTION TO AUTOMOTIVE SUSPENSIONS
10.1.1 Full, half and quarter car suspension models
An automotive suspension supports the vehicle body on the axles. A “full car” model of a suspension with 7 rigid body degrees of freedom is shown in Figure 10-1. The vehicle body is represented by the “sprung mass” m while the mass due to the axles and tires are represented by the “unsprung” masses mu1 , mu2 , mu3 and mu4 . The springs and dampers between the sprung and unsprung mass represent the vehicle suspension. The vertical stiffness of each of the 4 tires are represented by the springs kt1 , kt2 , kt3 and kt4 .
The seven degrees of freedom of the full car model are the heave z , pitch T and roll I of the vehicle body and the vertical motions of each of the four unsprung masses. The variables r1 z , r 2 z , r3 z and r 4 z are the road profile inputs that excite the system.
A “half car” model with four degrees of freedom is shown in Figure 10-2. In the half car model, the pitch and heave motions of the vehicle body (T and z ) and the vertical translation of the front and rear axles ( u1 z and u2 z ) are represented.
A two-degree-of-freedom “quarter-car” automotive suspension system is shown in Figure 10-3. It represents the automotive system at each wheel i.e. the motion of the axle and of the vehicle body at any one of the four wheels of the vehicle. The suspension itself is shown to consist of a spring s k , a damper bs and an active force actuator Fa . The active force Fa can be set to zero in a passive suspension. The sprung mass ms represents the quartercar equivalent of the vehicle body mass. The unsprung mass mu represents the equivalent mass due to the axle and tire. The vertical stiffness of the tire is represented by the spring t k . The variables s z , uz and rz represent the vertical displacements from static equilibrium of the sprung mass, unsprung mass and the road respectively.
10.1.2 Suspension functions
The automotive suspension on a vehicle typically has the following basic tasks (D. Bastow, 1987): 1) To isolate a car body from road disturbances in order to provide good ride quality Ride quality in general can be quantified by the vertical acceleration of the passenger locations. The presence of a well-designed suspension provides isolation by reducing the vibratory forces transmitted from the axle to the vehicle body. This in turn reduces vehicle body acceleration. In the case of the quarter car suspension, sprung mass acceleration s z can be used to quantify ride quality.
- To keep good road holding The road holding performance of a vehicle can be characterized in terms of its cornering, braking and traction abilities. Improved cornering, braking and traction are obtained if the variations in normal tire loads are minimized. This is because the lateral and longitudinal forces generated by a tire depend directly on the normal tire load. Since a tire roughly behaves like a spring in response to vertical forces, variations in normal tire load can be directly related to vertical tire deflection ( u r z _x0010_ z ) . The road holding performance of a suspension can therefore be quantified in terms of the tire deflection performance.
- To provide good handling The roll and pitch accelerations of a vehicle during cornering, braking and traction are measures of good handling. Half-car and full-car models can be used to study the pitch and roll performance of a vehicle. A good suspension system should ensure that roll and pitch motion are minimized.
- To support the vehicle static weight This task is performed well if the rattle space requirements in the vehicle are kept small. In the case of the quarter car model, it can be quantified in terms of the maximum suspension deflection (Zs-Zu ) undergone by the suspension.
The outline of the rest of this chapter is as follows. In section 10.2 of the chapter, we will review standard results on modal decoupling. In sections 10.3-10.7, the use of modal decoupling and its approximation for the design and analysis of quarter car suspension systems will be studied. Section 10.8 verifies the results of the decoupled approximation using the accurate complete model. Section 10.9 of the chapter will study the decoupling of half car models and the extension of the result to full car models.
10.1.3 Dependent and independent suspensions
In the case of dependent suspensions, the vertical motions of one wheel of an axle are directly linked to that of the other wheel of that axle. Some cars are still designed and built with dependent rear suspension systems. Figure 10-4 shows a solid-axle leaf-spring dependent rear suspension system. The advantages of such a suspension are that it is simple and inexpensive. The drive axle is clamped to the leaf springs. The shock absorbers are also attached to the clamps. The ends of the leaf springs are attached directly to the chassis (vehicle body), as are the shock absorbers. Since the axle couples both the rear wheels, the vertical motion of one is transferred to the other.
In the case of dependent suspensions, the axle cannot be represented by 2 independent unsprung masses.
In all of the suspension system models considered in section 10.1.1 (full, half and quarter-car models), both the front and rear wheels were assumed to have independent suspensions.
The front wheelrsquo;s suspension systems are always designed to be independent (except for the presence of an antiroll bar). In an independent suspension, the vertical motions of the two wheels are not directly linked to each other. This was the implicit assumption in the full, half and quarter-car models introduced in section 10.1.1. Figure 10-5 shows a double-A arm type of independent suspension. The wheel
全文共26750字，剩余内容已隐藏，支付完成后下载完整资料
资料编号：[11804]，资料为PDF文档或Word文档，PDF文档可免费转换为Word
以上是毕业论文外文翻译，课题毕业论文、任务书、文献综述、开题报告、程序设计、图纸设计等资料可联系客服协助查找。
