Thursday, October 13, 2016
MOST ADVANCE ACTIVE SUSPENSION SYSTEM IN VEHICLES
MOST ADVANCE ACTIVE SUSPENSION SYSTEM IN VEHICLES
INTRODUCTION
Traditionally automotive suspension designs have been compromise between the three conflicting criteria’s namely road handling, load carrying, and passenger comfort. The suspension system must support the vehicle, provide directional control using handling maneuvers and provide effective isolation of passengers and load disturbance. Good ride comfort requires a soft suspension, where as insensitivity to apply loads require stiff suspension. Good handling requires a suspension setting somewhere between it. Due to these conflicting demands, suspension design has to be something that can compromise of these two problems.
Active suspension system has the ability to response to the vertical changes in the road input. The damper or spring is interceding by the force actuator. This force actuator has it own task which is to add or dissipate energy from the system. The force actuator is control by various types of controller determine by the designer. The correct control strategy will give better compromise between comfort and vehicle stability. Therefore active suspension system offer better riding comfort and vehicle handling to the passengers. Figure 1.3 shows simple block diagram to explain how the active suspension can achieve better performance. Figure
describe basic component of active suspension. In this type of suspension the controller can modify the system dynamics by activating the actuators.
All these three types of suspension systems have it own advantages and disadvantages. However researchers are focus on the active car suspension and it is because the performance obtained is better than the other two types of suspension systems as mentioned before. For example the passive suspension system the design is fix depend on the goal of the suspension. The passive suspension is an open loop control system. It doesn’t have any feedback signal to correct the error. It means that the suspension system will not give optimal ride comfort. In other side which is active suspension, it has that ability to give ride comfort. This is happen by having force actuator control by the controller. The active suspension system is a close loop control system. It will correct the error and gave the output to the desired level. In this project observation will be made at the vertical acceleration of the vehicle body called sprung mass and tire deflection. By using the right control strategy the ride quality and handling performance can be optimize. Therefore, in this project there
will be modeling for active and passive suspension only.
· Active Suspension
ØCOMPONENTS
1. A Computer or an electronic control unit (ECU)
Short for Electronic Control Unit, the ECU is a name given to a device that controls one or more electrical systems in a vehicle. It operates much like the BIOS does in a computer. The ECU provides instructions for various electrical systems, instructing them on what to do and how to operate. Below are two pictures of what an ECU might look like, depending on the vehicle.
There are a number of different types of ECUs, including an Engine Control Module (ECM), Powertrain Control Module (PCM), Brake Control Module (BCM), General Electric Module (GEM) and others. Newer vehicles can have as many as 80 ECUs and due to their increasing complexity, the programming involved in developing the ECUs is becoming more challenging to maintain.
2. SENSORS
Linear acceleration sensors, also called G-force sensors, are devices that measure Acceleration caused by movement, vibration, collision, etc. All acceleration sensors operate based on a simple principle in which Newtons second law of motion is applied to a spring-mass system. A mass is connected to the base of the acceleration sensor through an equivalent spring. Since the force between the mass and base is proportional to the acceleration of the mass and the relative distance between them has a linear relationship with the force due to the spring, the acceleration can be calculated from a measurement of the relative position of the mass or force on the spring as it varies with time. Generally, the most common types of acceleration sensors include: piezoelectric, piezoresistive, variable capacitance and variable reluctance.
Automotive Applications of Acceleration Sensors:
- Collision detection and airbag deployment: To measure intensity of collision and signal to initiate airbag deployment.
- Electronics stability programs and control: Measures acceleration along various axes, (e.g. forward, braking and cornering accelerations, to compute relative movements and regulate them).
- Antilock braking systems.
- Active suspension systems: Measures longitudinal and lateral accelerations as well as vehicle roll characteristics to change damper characteristics accordingly.
- Hill descent/hold control: Measures vehicle inclination and speed to regulate system.
- Monitoring Noise,Vibration and Harshness.
- Vehicle navigation systems to determining vehicle location, speed, etc.
3. ACTUATOR OR SERVO
A servomechanism, sometimes shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the performance of a mechanism and is defined by its function. It usually includes a built-in encoder. A servomechanism is sometimes called a heterostat since it controls a systems behavior by means of heterostasis. The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position, speed or other parameters. For example, an automotive power window control is not a servomechanism, as there is no automatic feedback that controls position—the operator does this by observation. By contrast a cars cruise control uses closed loop feedback, which classifies it as a servomechanism.
Uses
Position control
A common type of servo provides position control. Servos are commonly electrical or partially electronic in nature, using an electric motor as the primary means of creating mechanical force. Other types of servos use hydraulics, pneumatics, or magnetic principles. Servos operate on the principle of negative feedback, where the control input is compared to the actual position of the mechanical system as measured by some sort oftransducer at the output. Any difference between the actual and wanted values (an "error signal") is amplified (and converted) and used to drive the system in the direction necessary to reduce or eliminate the error. This procedure is one widely used application of control theory.
Speed control
Speed control via a governor is another type of servomechanism. The steam engine uses mechanical governors; another early application was to govern the speed of water wheels. Prior to World War II the constant speed propeller was developed to control engine speed for maneuvering aircraft. Fuel controls for gas turbine engines employ either hydromechanical or electronic governing.
Other
Positioning servomechanisms were first used in military fire-control and marine navigation equipment. Today servomechanisms are used in automatic machine tools, satellite-tracking antennas, remote control airplanes, automatic navigation systems on boats and planes, and antiaircraft-gun control systems. Other examples are fly-by-wire systems inaircraft which use servos to actuate the aircrafts control surfaces, and radio-controlled models which use RC servos for the same purpose. Many autofocus cameras also use a servomechanism to accurately move the lens, and thus adjust the focus. A modern hard disk drive has a magnetic servo system with sub-micrometre positioning accuracy. In industrial machines, servos are used to perform complex motion, in many applications.
4. ADJUSTABLE SHOCKS AND SPRINGS
A shock absorber (in reality, a shock "damper") is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energyof the shock into another form of energy (typically heat) which is then dissipated. A shock absorber is a type of dashpot.
Description
Pneumatic and hydraulic shock absorbers are used in conjunction with cushions and springs. An automobile shock absorber contains spring-loaded check valves and orifices to control the flow of oil through an internal piston (see below).[1]
One design consideration, when designing or choosing a shock absorber, is where that energy will go. In most shock absorbers, energy is converted to heat inside the viscous fluid. In hydraulic cylinders, the hydraulic fluid heats up, while in air cylinders, the hot air is usually exhausted to the atmosphere. In other types of shock absorbers, such as electromagnetic types, the dissipated energy can be stored and used later. In general terms, shock absorbers help cushion vehicles on uneven roads.
Vehicle suspension
