Mitsubishi S-AWC
Encyclopedia
Four-wheel drive
Four-wheel drive, 4WD, or 4×4 is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine simultaneously...
system developed by Mitsubishi Motors
Mitsubishi Motors
is a multinational automaker headquartered in Minato, Tokyo. In 2009 it was the fifth-largest Japan-based automaker and the 17th-largest in the world measured by production...
. The technology, specifically developed for the new 2007 Lancer Evolution
Mitsubishi Lancer Evolution
The Mitsubishi Lancer Evolution, colloquially known as the Lancer Evo or Evo, is a high-performance sedan manufactured by Mitsubishi Motors. There have been ten official versions to date, and the designation of each model is most commonly a roman numeral...
, is an advanced version of Mitsubishi's AWC
Mitsubishi AWC
All Wheel Control is the brand name of a four-wheel drive system developed by Mitsubishi Motors. The system was first incorporated in the 2001 Lancer Evolution VII. Subsequent developments have led to S-AWC , developed specifically for the new 2007 Lancer Evolution...
system. Mitsubishi first exhibited S-AWC integration control technology in the Concept-X model at the 39th Tokyo Motor Show
Tokyo Motor Show
The is a biennial auto show held in October-November at the Makuhari Messe, Chiba City, Japan for cars, motorcycles and commercial vehicles. Hosted by the Japan Automobile Manufacturers Association , it is a recognized international show by the Organisation Internationale des Constructeurs...
in 2005. According to Mitsubishi, "the ultimate embodiment of the company's AWC philosophy is the S-AWC system, a 4WD-based integrated vehicle dynamics control system".
It integrates management of its Active Center Differential (ACD), Active Yaw Control
Active yaw control
Active Yaw Control is an automobile feature that uses an active differential to transfer torque to the wheels that have the best grip on the road. Unlike traditional mechanical limited slip differentials, an AYC is electronically controlled....
(AYC), Active Stability Control (ASC), and Sports ABS
Anti-lock braking system
An anti-lock braking system is a safety system that allows the wheels on a motor vehicle to continue interacting tractively with the road surface as directed by driver steering inputs while braking, preventing the wheels from locking up and therefore avoiding skidding.An ABS generally offers...
components, while adding braking force control to Mitsubishi Motors' own AYC system, allowing regulation of torque and braking force at each wheel
Wheel
A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...
. S-AWC employs yaw rate feedback control, a direct yaw moment control technology that affects left-right torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
vectoring (this technology forms the core of S-AWC system) and controls cornering maneuvers as desired during acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
, steady state
Steady state
A system in a steady state has numerous properties that are unchanging in time. This implies that for any property p of the system, the partial derivative with respect to time is zero:...
driving, and deceleration. Mitsubishi claims the result is elevated drive power, cornering performance, and vehicle stability
Directional stability
Directional stability is stability of a moving body or vehicle about an axis which is perpendicular to its direction of motion. Stability of a vehicle concerns itself with the tendency of a vehicle to return to its original direction in relation to the oncoming medium when disturbed away from...
regardless of driving conditions.
Active Center Differential (ACD)
Active Center Differential incorporates an electronicElectronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
ally-controlled hydraulic multi-plate clutch. The system optimizes clutch cover clamp load for different driving conditions, regulating the differential limiting action between free and locked states to optimize front/rear wheel torque split and thereby producing the best balance between traction
Traction (engineering)
Traction refers to the maximum frictional force that can be produced between surfaces without slipping.The units of traction are those of force, or if expressed as a coefficient of traction a ratio.-Traction:...
and steering
Steering
Steering is the term applied to the collection of components, linkages, etc. which will allow a vessel or vehicle to follow the desired course...
response.
Active Yaw Control (AYC)
Active Yaw Control uses a torque transfer mechanism in the rear differential to control rear wheel torque differential for different driving conditions and so limit the yaw moment that acts on the vehicle body and enhance cornering performance. AYC also acts like a limited slip differentialLimited slip differential
A limited slip differential is a type of differential gear arrangement that allows for some difference in angular velocity of the output shafts, but imposes a mechanical bound on the disparity...
by suppressing rear wheel slip to improve traction. In its latest form, AYC now features yaw rate feedback control using a yaw rate sensor and also gains braking force control. Accurately determining the cornering dynamics on a realtime basis, the system operates to control vehicle behavior through corners and realize vehicle behavior that more closely mirrors driver intent.
Active Stability Control (ASC)
Active Stability Control stabilizes vehicle attitude while maintaining optimum traction by regulating engine power and the braking force at each wheel. Taking a step beyond the previous generation Lancer Evolution, the fitting of a brake pressure sensor at each wheel allows more precise and positive control of braking force. ASC improves traction under acceleration by preventing the driving wheels from spinning on slippery surfaces. It also elevates vehicle stability by suppressing skidSkid
Skid may refer to:* Skid, a pallet, a metal, wood or plastic platform for holding machinery or equipment* Skid , an outward side-slip in an aircraft turn* Skid steering, a method of steering in which wheels or tracks are skidded sideways...
ding in an emergency
Emergency
An emergency is a situation that poses an immediate risk to health, life, property or environment. Most emergencies require urgent intervention to prevent a worsening of the situation, although in some situations, mitigation may not be possible and agencies may only be able to offer palliative...
evasive maneuver or the result of other sudden steering inputs.
Sport ABS
The Sports ABSAnti-lock braking system
An anti-lock braking system is a safety system that allows the wheels on a motor vehicle to continue interacting tractively with the road surface as directed by driver steering inputs while braking, preventing the wheels from locking up and therefore avoiding skidding.An ABS generally offers...
system supports braking when entering into a corner by controlling power to all tires depending on handling characteristics. Braking can be controlled to obtain optimal damping at each tire based on information from four wheel-speed sensors and steering wheel angle sensor. The addition of yaw rate sensors and brake pressure sensors to the Sport ABS system has improved braking performance through corners compared to the Lancer Evolution IX.
Concept components
The prototype system also featured two additional components controlling suspensionSuspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
s and steering
Steering
Steering is the term applied to the collection of components, linkages, etc. which will allow a vessel or vehicle to follow the desired course...
, which failed to make the production version of S-AWC system:
Active Steering System
Active Steering System realizes handling with more linear response by adaptively controlling front wheel turn angle according to steering input and vehicle speed. At slower vehicle speeds the system improves response by shifting to a quicker steering gear ratioGear ratio
The gear ratio of a gear train is the ratio of the angular velocity of the input gear to the angular velocity of the output gear, also known as the speed ratio of the gear train. The gear ratio can be computed directly from the numbers of teeth of the various gears that engage to form the gear...
, while at higher speeds it substantially improves stability by moving to a slower gear ratio. For rapid steering inputs, S-AWC momentarily increases front wheel turn angle and Super AYC control to realize sharper response. In countersteer situations, S-AWC increases responsiveness further to assist the driver with steering precision.
Roll Control Suspension (RCS)
RCS effectively reduces body rollBody roll
On wheeled or tracked vehicles, body roll is a reference to the load transfer of a vehicle towards the outside of a turn. When a vehicle is fitted with a suspension package, it works to keep the wheels or tracks in contact with the road, providing grip for the driver of vehicle to control its...
and pitching by hydraulically connecting all the shock absorber
Shock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...
s together and regulating their damping
Damping
In physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...
pressures as necessary. Able to control both roll and pitching stiffness separately, RCS can operate in a variety of ways. It can, for example, reduce roll only when required during turn in or in other situations while being set up on the soft side to prioritize tire contact and ride comfort. Since the system controls roll stiffness hydraulically, it eliminates the need for stabilizer bars
Sway bar
A sway bar or anti-roll bar or stabilizer bar is a part of an automobile suspension that helps reduce the roll of a vehicle that is induced by cornering or road irregularities. It connects opposite wheels together through short lever arms linked by a torsion spring...
. In the integrated control of its component systems, S-AWC employs information from RCS's hydraulic system to estimate the tire load at each wheel.
Control system
The use of engine torque and brake pressure information in the regulation of the ACD and AYC components allows the S-AWC system to determine more quickly whether the vehicle is accelerating or decelerating. S-AWC also employs yaw rate feedbackFeedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...
for the first time. The system helps the driver follow his chosen line more closely by comparing how the car is running, as determined from data from the yaw rate sensors, and how the driver wants it to behave, as determined from steering inputs, and operates accordingly to correct any divergence. The addition of braking force regulation to AYC's main role of transferring torque between the right and left wheels allows S-AWC to exert more control over vehicle behavior in on-the-limit driving situations. Increasing braking force on the inside wheel during understeer and on the outer wheel during oversteer situations, AYC's new braking force control feature works in conjunction with torque transfer regulation to realize higher levels of cornering performance and vehicle stability.
Using integrated management of the ASC and ABS systems allows S-AWC to effectively and seamlessly control vehicle dynamics when accelerating, decelerating or cornering under all driving conditions. S-AWC offers three operating modes:
- TarmacTarmacTarmac is a type of road surface. Tarmac refers to a material patented by Edgar Purnell Hooley in 1901...
for dry, paved surfaces; - GravelGravelGravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
for wet or unmade surfaces; - SnowSnowSnow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
for snow covered surfaces.
When the driver selects the mode best suited to current road surface conditions S-AWC operates to control vehicle behavior accordingly and allow the driver to extract the maximum dynamic performance from his vehicle.
ECU integration
Two electronic control unitElectronic control unit
In automotive electronics, electronic control unit is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle....
s (ECU) regulate vehicle motion. One is an ECU developed by Mitsubishi Electric
Mitsubishi Electric
is a multinational electronics and information technology company headquartered in Tokyo, Japan. It is one of the core companies of the Mitsubishi Group....
to control ACD and AYC. The other is an ECU developed by Continental Automotive Systems
Continental Automotive Systems
Continental Automotive Systems , founded in 1906 by Alfred Teves, a division of Continental AG, is a leading brake and electronics supplier to the automotive industry, delivering systems, components, electronics, lithium-ion batteries and engineering services for vehicle safety, comfort and...
of Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
that controls ASC and ABS. The two ECUs can communicate with other ECUs through a CAN
Controller Area Network
Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....
, an in-vehicle LAN
Län
Län and lääni refer to the administrative divisions used in Sweden and previously in Finland. The provinces of Finland were abolished on January 1, 2010....
interface
Interface (computer science)
In the field of computer science, an interface is a tool and concept that refers to a point of interaction between components, and is applicable at the level of both hardware and software...
standard. In addition, the two ECUs are communicating with each other through a dedicated CAN, enabling vehicle motion to be controlled more quickly. The cable
Cable
A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...
and communication
Communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
standard for the dedicated CAN are the same as those for other CANs.
A longitudinal acceleration sensor, lateral acceleration sensor and yaw rate sensor are installed as one module near the gravity center
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
of a vehicle, which is located between the driver's and passenger's seats. Other sensors, such as a wheel-speed sensor and steering-angle sensor, are installed in different places. However, no vertical
Vertical direction
In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force at that point...
acceleration sensor is used.
Also, when the vehicle is equipped with Mitsubishi's Twin Clutch SST
Twin Clutch SST
Twin Clutch SST is the brand name of a six-speed dual clutch transmission developed by Getrag for Mitsubishi Motors...
transmission, S-AWC analyzes the behavior of the turning vehicle and if it judges that it is safer not to shift gears, it sends a signal to tell Twin Clutch SST that the gear must not be changed. However, S-AWC does not control vehicle motion by using control information from Twin Clutch SST. The co-operation is a one-way communication.
The control algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
s of vehicle motion were developed by Mitsubishi in-house, with MATLAB
MATLAB
MATLAB is a numerical computing environment and fourth-generation programming language. Developed by MathWorks, MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs written in other languages,...
and Simulink
Simulink
Simulink, developed by MathWorks, is a commercial tool for modeling, simulating and analyzing multidomain dynamic systems. Its primary interface is a graphical block diagramming tool and a customizable set of block libraries. It offers tight integration with the rest of the MATLAB environment and...
, a control system modeling tools. Mitsubishi adopted model-based method, which combines an algorithm and physical model of a vehicle to run a simulation
Simulation
Simulation is the imitation of some real thing available, state of affairs, or process. The act of simulating something generally entails representing certain key characteristics or behaviours of a selected physical or abstract system....
. The physical model of a vehicle was constructed with CarSim
Carsim
CarSim is a commercial software package that predicts the performance of vehicles in response to driver controls in a given environment...
, a simulation-package software developed by Mechanical Simulation Corporation of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. The algorithms were developed for each function such as ACD and AYC, not for each vehicle type. Therefore, the algorithms can be employed by various types of vehicles.
External links
S-AWC schematics- "S-AWC Super All Wheel Control - S-AWC Management", .pdf file, Mitsubishi Motors North America press release
- "S-AWC Super All Wheel Control - S-AWC Systematic", .pdf file, Mitsubishi Motors North America press release
- "S-AWC Super All Wheel Control - ACD (Active Center Differential)", .pdf file, Mitsubishi Motors North America press release
- "S-AWC Super All Wheel Control - AYC (Active Yaw Control)", .pdf file, Mitsubishi Motors North America press release