Suspension Systems

Suspension Systems

Introduction

The vehicle suspension system is responsible for driving comfort and safety as the suspension caries the vehicle body and transmits all forces between the body and the road. - In order to positively influence these properties, semi-active and/or active components are introduced. These enable the suspension system to adapt to various driving conditions. - By adding a variable damper and/or spring, driving comfort and safety are considerably improved compared to suspension setups with fixed properties.
This strategy requires that the control behavior of these components is known and that laws on how to adapt the free parameters depending on the driving excitations are known. - This also requires the identification and fault detection of the involved components resulting in a mechatronic design.
• Vehicle Suspension System - The vehicle suspension system consists of wishbones, the spring, and the shock absorber to transmit and also filter all forces between the body and road. - The spring carries the body mass and isolates the body from road disturbances and thus contributes to drive comfort.
The damper contributes to both driving safety and comfort. Its task is the damping of body and wheel oscillations, where the avoidance of wheel oscillations directly refers to drive safety, as a non-bouncing wheel is the condition for transferring road-contact forces.
Driving Safety • Driving safety is the result of a harmonious suspension design in terms of wheel suspension, springing, steering, and braking, and is reflected in an optimal dynamic behavior of the vehicle. Tire load variation is an indicator for the road contact and can be used for determining a quantitative value for safety.
- Driving Comfort • Driving comfort results from keeping the physiological stress that the vehicle occupants are subjected to by vibrations, noise, and climatic conditions down to as low a level as possible. The acceleration of the body is an obvious quantity for the motion and vibration of the car body and can be used for determining a quantitative value for driving comfort.

In order to improve the ride quality, it is necessary to isolate the body, also called the sprung mass, from the road disturbances and to decrease the resonance peak of the sprung mass near 1 Hz, which is known to be a sensitive frequency to the human body.
- In order to improve the ride stability, it is important to keep the tire in contact with the road surface and therefore to decrease the resonance peak near 10 Hz, which is the resonance frequency of the wheel, also called the unsprung mass.
- For a given suspension spring, the better isolation of the sprung mass from road disturbances can be achieved with a soft damping by allowing a larger suspension deflection.
- However, better road contact can be achieved with a hard damping preventing unnecessary suspension deflections.
- Therefore, the ride quality and the drive stability are two conflicting criteria, as shown below.

As can be seen from the diagram, the fixed setting of a passive suspension system is always a compromise between comfort and safety for any given input set of road conditions and a specific stress.
- Semi-active / active suspension systems try to solve or at least reduce this conflict.
- The mechanism of semi-active suspension systems is the adaptation of the damping and/or stiffness of the spring to the actual demands.
- Active suspension systems in contrast provide an extra force input in addition to possible existing passive systems and therefore need much more energy The figure also clarifies the dependency of a vehicle suspension setup on parameter changes as a result of temperature, deflection, and wear and tear. These changes must be taken into account when designing a controller for an active or semi-active suspension to avoid unnecessary performance loss.
- In order to prevent this, a robust or an adaptive controller has to be implemented. The adaptive controller results in a parameter-adaptive suspension system that refers to a control system which adapts its behavior to the changing settings of the system to be controlled and its signals.
- Suspension systems are classified as passive, semi-active, active and various in-between systems.
- Typical features are the required energy and the characteristic frequency of the actuator.
This diagram points out the conflict that automotive manufacturers face in their endeavor to improve drive safety and comfort as high-performing suspension systems can only be achieved by high-energy demand and mostly expansive and complex actuation systems.

Car Suspension Systems

Car Suspension Systems
When people think of automobile performance, they normally think of horsepower, torque, and 0-60 acceleration. But all of the power generated by a piston engine is useless if the driver can't control the car. That's why automobile engineers turned their attention to the suspension system almost as soon as they had mastered the four-stroke internal combustion engine.The job of a car suspension is:
- to maximize the friction between the tires and the road surface - to provide steering stability with good handling - to ensure the comfort of the passengers • If a road were perfectly flat, with no irregularities, suspensions wouldn't be necessary. But roads are far from flat. Even freshly-paved highways have subtle imperfections that can interact with the wheels of a car. It's these imperfections that apply forces to the wheels that result in wheel acceleration.
Without an intervening structure, all of wheel's vertical energy is transferred to the frame, which moves in the same direction. In such a situation, the wheels can lose contact with the road completely. Then, under the downward force of gravity, the wheels can slam back into the road surface.
• What you need is a system that will absorb the energy of the vertically-accelerated wheel, allowing the frame and body to ride undisturbed while the wheels follow bumps in the road
The study of the forces at work on a moving car is called vehicle dynamics. Most automobile engineers consider the dynamics of a moving car from two perspectives:
- Ride - a car's ability to smooth out a bumpy road - Handling - a car's ability to safely accelerate, brake, and corner
• These two characteristics can be further described in three important principles: - road isolation - road holding - cornering

Car Suspension Parts

Car Suspension Parts
- A car's suspension, with its various components, provides all of the solutions described. - The suspension of a car is actually part of the chassis, which comprises all of the important systems located beneath the car's body.

Frame - structural, load-carrying component that supports the car's engine and body, which are in turn supported by the suspension - Suspension System - setup that supports weight, absorbs and dampens shock, and helps maintain tire contact - Steering System - mechanism that enables the driver to guide and direct the vehicle - Tires and Wheels - components that make vehicle motion possible by way of grip and/or friction with the road
• So the suspension is just one of the major systems in any vehicle.
• Springs
- Today's springing systems are based on one of four basic designs.
• Coil springs - This is the most common type of spring and is, in essence, a heavy-duty torsion bar coiled around an axis. Coil springs compress and expand to absorb the motion of the wheels.

• Leaf Springs - This type of spring consists of several layers of metal (called "leaves") bound together to act as a single unit. Leaf springs were first used on horse-drawn carriages and were found on most American automobiles until 1985. They are still used today on most trucks and heavy-duty vehicles.

Torsion Bars - Torsion bars use the twisting properties of a steel bar to provide coil-spring-like performance. One end of a bar is anchored to the vehicle frame. The other end is attached to a wishbone, which acts like a lever that moves perpendicular to the torsion bar. When the wheel hits a bump, vertical motion is transferred to the wishbone and then, through the levering action, to the torsion bar. The torsion bar then twists along its axis to provide the spring force.

Air Springs - Air springs, which consist of a cylindrical chamber of air positioned between the wheel and the car's body, use the compressive qualities of air to absorb wheel vibrations. The concept is actually more than a century old and could be found on horse-drawn buggies. Air springs from this era were made from air-filled, leather diaphragms, much like a bellows; they were replaced with molded-rubber air springs in the 1930s

Springs: Sprung and Un-sprung Mass - The sprung mass is the mass of the vehicle supported on the springs, while the un-sprung mass is loosely defined as the mass between the road and the suspension springs. The stiffness of the springs affects how the sprung mass responds while the car is being driven.
- Loosely-sprung cars, such as luxury cars, can swallow bumps and provide a super-smooth ride; however, such a car is prone to dive and squat during braking and acceleration and tends to experience body sway or roll during cornering.
- Tightly- sprung cars, such as sports cars, are less forgiving on bumpy roads, but they minimize body motion well, which means they can be driven aggressively, even around corners.
- So, while springs by themselves seem like simple devices, designing and implementing them on a car to balance passenger comfort with handling is a complex task.
- And to make matters more complex, springs alone can't provide a perfectly smooth ride. Why? Because springs are great at absorbing energy, but not so good at dissipating it. Other structures, known as dampers, are required to do this.

Dampers: Shock Absorbers
- Unless a dampening structure is present, a car spring will extend and release the energy it absorbs from a bump at an uncontrolled rate. The spring will continue to bounce at its natural frequency until all of the energy originally put into it is used up. A suspension built on springs alone would make for an extremely bouncy ride and, depending on the terrain, an uncontrollable car.
- Enter the shock absorber, or snubber, a device that controls unwanted spring motion through a process known as dampening. Shock absorbers slow down and reduce the magnitude of vibratory motions by turning the kinetic energy of suspension movement into heat energy that can be dissipated through hydraulic fluid.

A shock absorber is basically an oil pump placed between the frame of the car and the wheels. The upper mount of the shock connects to the frame (i.e., the sprung weight), while the lower mount connects to the axle, near the wheel (i.e., the un-sprung weight). In a twin-tube design, one of the most common types of shock absorbers, the upper mount is connected to a piston rod, which in turn is connected to a piston, which in turn sits in a tube filled with hydraulic fluid. The inner tube is known as the pressure tube, and the outer tube is known as the reserve tube. The reserve tube stores excess hydraulic fluid.
- When the car wheel encounters a bump in the road and causes the spring to coil and uncoil, the energy of the spring is transferred to the shock absorber through the upper mount, down through the piston rod and into the piston. Orifices perforate the piston and allow fluid to leak through as the piston moves up and down in the pressure tube. Because the orifices are relatively tiny, only a small amount of fluid, under great pressure, passes through. This slows down the piston, which in turn slows down the spring.
- Shock absorbers work in two cycles -- the compression cycle and the extension cycle.
• The compression cycle occurs as the piston moves downward, compressing the hydraulic fluid in the chamber below the piston.
• The extension cycle occurs as the piston moves toward the top of the pressure tube, compressing the fluid in the chamber above the piston. A typical car or light truck will have more resistance during its extension cycle than its compression cycle. With that in mind, the compression cycle controls the motion of the vehicle's un-sprung weight, while extension controls the heavier, sprung weight.
- All modern shock absorbers are velocity-sensitive --the faster the suspension moves, the more resistance the shock absorber provides. This enables shocks to adjust to road conditions and to control all of the unwanted motions that can occur in a moving vehicle, including bounce, sway, brake dive, and acceleration squat.

Electromagnetic Linear Actuators in Suspension Systems

Electromagnetic Linear Actuators in Suspension Systems

The use of electromagnetic linear actuators in automobile suspensions is under development. - The reliability of electrical drives and the unconstrained integration with electronic control systems are factors that justify their use.
-> Rotational electromagnetic actuators have been proposed, however, their use requires a gearbox to convert the rotational movement into linear movement and to increase the force value. Linear actuators do not require a gearbox

The main objective of ground vehicle suspension systems is to isolate the vehicle body from road irregularities in order to maximize passenger ride comfort and to produce continuous road-wheel contact, improving the vehicle handling quality.
- Today, three types of vehicle suspensions are used:
passive, semi-active, and active. All systems implemented in automobiles today are based on hydraulic or pneumatic operation. However, these solutions do not satisfactorily solve the The main objective of ground vehicle suspension systems is to isolate the vehicle body from road irregularities in order to maximize passenger ride comfort and to produce continuous road-wheel contact, improving the vehicle handling quality.
- Today, three types of vehicle suspensions are used:
passive, semi-active, and active. All systems implemented in automobiles today are based on hydraulic or pneumatic operation. However, these solutions do not satisfactorily

Suspension Types

Suspension Types: Rear
Dependent Rear Suspensions• Leaf spring - If a solid axle connects the rear wheels of a car, then the suspension is usuallyquite simple -- based either on a leaf spring or a coil spring.
• In the former design, the leaf springs clamp directly to the drive axle. The ends of the leaf springs attach directly to the frame, and the shock absorber is attached at the clamp that holds the spring to the axle. For many years, American car manufacturers preferred this design because of its simplicity.
• The same basic design can be achieved with coil springs replacing the leaves. In this case, thespring and shock absorber can be mounted as a single unit or as separate components. Whenthey're separate, the springs can be much smaller, which reduces the amount of space thesuspension takes up.
Independent Rear Suspensions• If both the front and back suspensions are independent, then all of the wheels are mountedand sprung individually, resulting in what car advertisements tout as "four-wheel independentsuspension."
• Any suspension that can be used on the front of the car can be used on the rear, and versions ofthe front independent systems previously described can be found on the rear axles.
• Of course, in the rear of the car, the steering rack -- the assembly that includes the pinion gear wheel and enables the wheels to turn from side to side --is absent. This means that rear independent suspensions can be simplified versions of front ones, although the basic principles remain the same

Suspension Types: Front
The four wheels of a car work together in two independent systems -- the two wheels connected by the front axle and the two wheels connected by the rear axle. That means that a car can and usually does have a different type of suspension on the front and back. Much is determined by whether a rigid axle binds the wheels or if the wheels are permitted to move independently.
The former arrangement is known as a dependent system, while the latter arrangement is known as an independent system.
Dependent Front Suspensions
• Dependent front suspensions have a rigid front axle that connects the front wheels. Basically, this looks like a solid bar under the front of the car, kept in place by leaf springs and shock absorbers. Common on trucks, dependent front suspensions haven't been used in mainstream cars for years.
Independent Front Suspensions
• In this setup, the front wheels are allowed to move independently. The MacPherson strut, developed by Earle S. MacPherson of General Motors in 1947, is the most widely used front-suspension system.
• The MacPherson strut combines a shock absorber and a coil spring into a single unit. This provides a more compact and lighter suspension system that can be used for front-wheel drive vehicles.

Specialized Suspensions: Formula One Racers

Specialized Suspensions: Formula One Racers Specialized Suspensions: Formula One Racers
The Formula One racing car represents the pinnacle of automobile innovation and evolution. Lightweight, composite bodies, powerful V10 engines, and advanced aerodynamics have led to faster, safer, and more reliable cars.
To elevate driver skill as the key differentiating factor in a race, stringent rules and requirements govern Formula One racecar design. For example, the rules regulating suspension design say that all Formula One racers must be conventionally sprung, but they don't allow computer-controlled, active suspensions. To accommodate this, the cars feature multi-link suspensions, which use a multi-rod mechanism equivalent to a double-wishbone system.
Recall that a double wishbone design uses two wishbone shaped control arms to guide each wheel's up and down motion. Each arm has three mounting positions two at the frame and one at the wheel hub and each joint is hinged to guide the wheel's motion.
In all cars, the primary benefit of a double wishbone suspension is control. The geometry of the arms and the elasticity of the joints give engineers ultimate control over the angle of the wheel and other vehicle dynamics, such as lift, squat, and dive.
Unlike road cars, however, the shock absorbers and coil springs of a Formula One racecar don't mount directly to the control arms. Instead, they are oriented along the length of the car and are controlled remotely through a series of pushrods and bell cranks. In such an arrangement, the pushrods and bell cranks translate the up and down motions of the wheel to the back and forth movement of the spring and damper apparatus.

The Bose Suspension System

The Bose Suspension System
While there have been enhancements and improvements to both springs and shock absorbers, the basic design of car suspensions has not undergone a significant evolution over the years. But all of that's about to change with the introduction of a brand new suspension design conceived by Bose the same Bose known for its innovations in acoustic technologies. Some experts are going so far as to say that the Bose suspension is the biggest advance in automobile suspensions since the introduction of an allindependent design.

The Bose system uses a linear electromagnetic motor (LEM) at each wheel in lieu of a conventional shock-and-spring setup. Amplifiers provide electricity to the motors in such a way that their power is regenerated with each compression of the system.
The main benefit of the motors is that they are not limited by the inertia inherent in conventional fluid-based dampers. As a result, an LEM can extend and compress at a much greater speed, virtually eliminating all vibrations in the passenger cabin. The wheel's motion can be so finely controlled that the body of the car remains level regardless of what's happening at the wheel. The LEM can also counteract the body motion of the car while accelerating, braking, and cornering, giving the driver a greater sense of control.