Mitsubishi 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 system was first incorporated in the 2001 Lancer Evolution VII
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...
. Subsequent developments have led to S-AWC
Mitsubishi S-AWC
S-AWC is the brand name of an advanced full-time four-wheel drive system developed by Mitsubishi Motors. The technology, specifically developed for the new 2007 Lancer Evolution, is an advanced version of Mitsubishi's AWC system. Mitsubishi first exhibited S-AWC integration control technology in...
(Super All Wheel Control), developed specifically for the new 2007 Lancer Evolution. The system is referred by the company as its unique 4-wheel drive technology umbrella
Umbrella term
An umbrella term is a word that provides a superset or grouping of concepts that all fall under a single common category. Umbrella term is also called a hypernym. For example, cryptology is an umbrella term that encompasses cryptography and cryptanalysis, among other fields...
, cultivated through its motor sports activities and long history in rally racing spanning almost half a century.
According to Mitsubishi, "the AWC is a four-wheel dynamic control philosophy for maximally exploiting the capability of all four tires of a vehicle in a balanced manner to realize predictable handling and high marginal performance." The core of the AWC philosophy is the integration of Mitsubishi's various proprietary
Property
Property is any physical or intangible entity that is owned by a person or jointly by a group of people or a legal entity like a corporation...
technologies, such as 4WD drivetrains
Powertrain
In a motor vehicle, the term powertrain or powerplant refers to the group of components that generate power and deliver it to the road surface, water, or air. This includes the engine, transmission, drive shafts, differentials, and the final drive...
, suspension technologies, braking systems, stability/traction control systems and various differentials. Although initially developed for high performance Lancer Evolution full-time four-wheel drive models, the system is now incorporated in Mitsubishi's other 4WD vehicles, each having its own distinct configuration.
AWC philosophy
According to Mitsubishi, AWC philosophy is put into practice by means of three forms of control:- The first form of control is control over the four tires’ vertical loadingStructural loadStructural loads or actions are forces, deformations or accelerations applied to a structure or its components.Loads cause stresses, deformations and displacements in structures. Assessment of their effects is carried out by the methods of structural analysis...
, by means of which each tire is kept in firm contact with the road surface for consistently maximum grip. The vehicle’s basic specifications and its body and 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...
technologies are exploited for this purpose. - The second form of control is control over the four tires’ slip ratioSlip ratioSlip ratio is a means of calculating and expressing the locking status of a wheel and is vital to the effectiveness of any anti-lock braking system....
s and slip angleSlip angleIn vehicle dynamics, slip angle or sideslip angle is the angle between a rolling wheel's actual direction of travel and the direction towards which it is pointing...
s (control that is effected over the respective slip ratios and slip angles of the four tires such that the longitudinal and lateral forces produced by each of the four tires are maximized in a balanced manner). An anti-lock braking systemAnti-lock braking systemAn 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...
(ABS), a traction controlTraction control systemA traction control system , also known as anti-slip regulation , is typically a secondary function of the anti-lock braking system on production motor vehicles, designed to prevent loss of traction of driven road wheels...
(TCL) system, and steeringSteeringSteering is the term applied to the collection of components, linkages, etc. which will allow a vessel or vehicle to follow the desired course...
-system control technologies are exploited for this purpose. - The third form of control is control over the four tires’ force assignment (control that is effected over the distribution of longitudinal forces and lateral forces among the four tires such that the tires are uniformly loaded for well-balanced utilization). PowertrainPowertrainIn a motor vehicle, the term powertrain or powerplant refers to the group of components that generate power and deliver it to the road surface, water, or air. This includes the engine, transmission, drive shafts, differentials, and the final drive...
and braking-system control technologies are exploited for this purpose.
Dynamic Four, Dynamic ECS, Active TCL
In line with this development philosophy, Mitsubishi developed its first high performance four-wheel driveFour-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...
vehicle in 1987, when it equipped the Galant VR-4 with "Dynamic Four", which featured a center differential-type full-time four-wheel drive system (this system incorporated a viscous coupling unit
Viscous coupling unit
A viscous coupling is a mechanical device which transfers torque and rotation by the medium of a viscous fluid. It is made of a number of circular plates with tabs or perforations, fitted very close to each other in a sealed drum. Alternate plates are connected to a driving shaft at one end of the...
), a four wheel steering system, four-wheel independent suspension
Independent suspension
Independent suspension is a broad term for any automobile suspension system that allows each wheel on the same axle to move vertically independently of each other. This is contrasted with a beam axle, live axle or deDion axle system in which the wheels are linked – movement on one side affects...
, and a four-wheel ABS (the first total integration of these systems in the world that were highly advanced at the time), thereby dramatically improving dynamic performance. The 1987 Galant also featured "Dynamic ECS", a world’s first production semi-active electronically controlled suspension
Active suspension
Active or adaptive suspension is an automotive technology that controls the vertical movement of the wheels with an onboard system rather than the movement being determined entirely by the road surface...
system (a means of actively controlling a vehicle’s cornering attitude and dynamic performance) that Mitsubishi developed. Mitsubishi's active ECS enhanced ride comfort and kept body inclination to a minimum under all driving conditions by controlling the grip between the tires and the road surface. The Galant won the 1987–1988 Japan Car of the Year, the country's most prestigious automotive award. The Dynamic-Four system was honored by the Japan Society for the Promotion of Machine Industry (JSPMI).
In 1990, Mitsubishi released the Diamante
Mitsubishi Diamante
The Mitsubishi Diamante is a car manufactured by Mitsubishi Motors between 1990 and 2005. It was first introduced to the public at the Tokyo Motor Show in 1989, and went on sale in Japan in May 1990. The name was derived from the Spanish, Portuguese, and Italian words for diamond. It became the...
(Sigma) in Japan. It featured a new electronically controlled active trace & traction control system (the first integration of these two systems in the world) that Mitsubishi developed. Simply named TCL in 1990, the system has now evolved into Mitsubishi's modern Active Skid and Traction Control (ASTC) system. Developed to help the driver maintain the intended line through a corner; an onboard computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
monitored several vehicle operating parameters through various sensors. When too much throttle
Throttle
A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which...
has been used when taking a curve, engine output and braking are automatically regulated to ensure the proper line through a curve and to provide the proper amount of traction under various road surface conditions. While conventional traction control systems at the time featured only a slip control function, Mitsubishi's newly developed TCL system had a preventive (active) safety function which improved the course tracing performance by automatically adjusting the traction force (called "trace control") thereby restraining the development of excessive lateral acceleration while turning. Although not a ‘proper’ modern stability control system, trace control monitors steering angle, throttle position and individual wheel speeds although there is no yaw input. The TCL system's standard wheel slip control function enables better traction on slippery surfaces or during cornering. In addition to the TCL system's individual effect, it also works together with Diamante's electronic controlled suspension and four-wheel steering that Mitsubishi had equipped to improve total handling and performance. The Diamante won the Car of the Year Japan
Car of the Year Japan
The annual Car of the Year Japan award, also known as Japan Car of the Year , is given to newly released or redesigned vehicles released to the Japanese car buying market from November 1 of the previous year to October 31 of the current, and each award spans two calendar years. The award has been...
award in 1990–1991.
Birth of the AWC system
In 1996, Mitsubishi equipped the Lancer Evolution IV with the world's first Active Yaw ControlActive 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) system. The AYC transfers drive 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....
between the left and right drive wheels as required. This was achieved by utilising a torque transfer rear differential which is controlled by various sensors and an electronic control unit
Electronic 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....
(ECU) to enable a difference in torque to go to each of the rear wheels. The result is a dramatic improvement in cornering performance and improved safety. The eighth generation Galant/Legnum VR-4 model was released for the Japanese market in 1996 that also featured the AYC system, in addition integrated to now fully evolved active stability control (ASC) system. The ASC generates turning force by employing braking force differentials in left and right wheels. The AYC and ASC integrated system maximizes the adhesion
Adhesion
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....
limits of the vehicle's tires. Controlling each wheel interdependently, AYC and ASC achieved dramatic improvements in safety and performance. The eighth generation Galant won the Car of the Year Japan
Car of the Year Japan
The annual Car of the Year Japan award, also known as Japan Car of the Year , is given to newly released or redesigned vehicles released to the Japanese car buying market from November 1 of the previous year to October 31 of the current, and each award spans two calendar years. The award has been...
award in 1996–1997.
In 2001, Mitsubishi equipped the Lancer Evolution VII with the AYC system, Mitsubishi's own Sports ABS and a newly developed Active Center Differential (ACD), which used an electronically controlled variable multi-plate clutch. The ACD has a differential limiting capacity three times greater than that of the viscous coupling-type differential used to date. Also, the ACD's ability to tailor slippage for different driving conditions enabled the levels of steering response and traction control not possible with a viscous coupling differential. In addition, a three-way manual override
Manual override
A manual override is a mechanism wherein control is taken from an automated system and given to the user. For example, a manual override in photography refers to the ability for the human photographer to turn off the automatic aperture sizing, automatic focusing, or any other automated system on...
switch enables the driver to select tarmac
Tarmac
Tarmac is a type of road surface. Tarmac refers to a material patented by Edgar Purnell Hooley in 1901...
, gravel
Gravel
Gravel 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...
or snow
Snow
Snow 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...
modes to suit his preferences or driving conditions. The ACD also frees the differential on operation of the hand brake
Hand brake
In cars, the hand brake is a latching brake usually used to keep the car stationary, and in manual transmission vehicles, as an aid to starting the vehicle from stopped when going up an incline - with one foot on the clutch , the other on the accelerator In cars, the hand brake (emergency brake,...
, allowing the driver to make more effective use of side brake turns in rallies
Rallying
Rallying, also known as rally racing, is a form of auto racing that takes place on public or private roads with modified production or specially built road-legal cars...
and gymkhana
Gymkhana
Gymkhana is a typical Anglo-Indian expression, which is derived from the Hindi-Urdu word for "racket court," is an Indian term which originally referred to a place where sporting events take place. The meaning then altered to denote a place where skill-based contests were held...
s. On the Evolution VII, control of the ACD and AYC systems is integrated for the very first time (integrated management of these systems is the core of Mitsubishi's AWC philosophy). In the integrated system, ACD feedback and feedforward information is transmitted to the AYC control system using parameters in such a way that the larger the ACD differential limiting force is, the larger the yaw moment generated by the AYC system. This integrated control operates so that, for example when accelerating out of a corner, the ACD enhances traction and the AYC enhances steering response and cornering performance. Because of its seamless nature, the driver is unaware of the integrated system as it operates to improve acceleration and handling more than the ACD and AYC systems would if they were operating independently. By doing so, the Lancer Evolution VII heralded the birth of Mitsubishi’s AWC technology.
Outlander
Mitsubishi’s AWC philosophy for the second generation OutlanderMitsubishi Outlander
The Airtrek was first introduced to the Japanese market on June 20, 2001, priced from ¥1.7–2.3 million. It offered a choice of either a 4G63 2.0 L or a 4G64 2.4 L GDI, mated to a standard INVECS-II 4-speed semi-automatic transmission. Both front- and four-wheel drive were available...
introduced in 2005 combines an electronically controlled four-wheel drive with an Active Skid and Traction Control (ASTC) system. Mitsubishi used an aluminum roof to lower the center of gravity for better handling response. The Outlander is also available with standard front-wheel drive
Front-wheel drive
Front-wheel drive is a form of engine/transmission layout used in motor vehicles, where the engine drives the front wheels only. Most modern front-wheel drive vehicles feature a transverse engine, rather than the conventional longitudinal engine arrangement generally found in rear-wheel drive and...
layout that also included the ASTC system. The previous Outlander employed a 50:50 full-time four-wheel drive system using a viscous coupling center differential. Mitsubishi decided to use the AWC system on the new Outlander that offers three vehicle drive modes and proactively reduces the likelihood of wheel slippage.
The driver can use a drive-mode dial on the center console
Center console (automobile)
The center console in an automobile refers to the control-bearing surfaces in the center of the front of the vehicle interior...
to select “FWD” for best fuel economy; with “4WD Auto” mode selected, the system uses a rear-mounted electronically controlled transfer clutch to automatically and seamlessly route more power to the rear wheels, depending on driving and road surface conditions. The driver can freely change the drive mode at any time. When “4WD Auto” mode is selected, the Outlander's 4WD system always sends some power to the rear wheels, automatically increasing the amount under full throttle acceleration. The coupling transfers up to forty percent of available torque to the rear wheels under full-throttle acceleration, and this is reduced to twenty five percent over 40 miles per hour. At steady cruising speeds, up to fifteen percent of available torque is sent to the rear wheels. At low speeds through tight corners, coupling torque is reduced, providing a smoother feel through the corner.
For driving in particularly challenging conditions, such as snow, the driver can select “4WD Lock” mode. In Lock mode, the system still apportions front and rear torque automatically, but enables greater power transfer to the rear wheels. In dry conditions, 4WD Lock mode places priority on performance. More torque is directed to the rear wheels than in 4WD Auto mode to provide greater power off the line, better control when accelerating on snowy or loose surfaces, and enhanced stability at high speeds. Rear wheel torque transfer is increased by 50 percent over the amounts in 4WD Auto mode – meaning up to 50 percent of available torque is sent to the rear wheels under full-throttle acceleration on dry pavement. When in 4WD Lock mode, torque at the rear wheels is reduced by a smaller degree through corners than with 4WD Auto mode.
The new Outlander features standard ASTC system on all models, unlike the previous-generation. ASTC helps to prevent side slipping (spin and side drift) as a result of sudden steering wheel operation or on slippery roads. Overall vehicle stability is enhanced in all driving conditions. In front-wheel drive Outlander models – and under all driving modes in four-wheel drive models – ASTC helps keep the vehicle traveling in the driver’s intended direction. The ASTC system takes data input from a number of sensors, including steering angle, individual wheel speed and yaw, as well as from the powertrain electronic control unit (ECU). When it detects side-slipping or wheel spin, ASTC provides integrated control of brakes, engine torque (via the electronic throttle control), transmission and electronically controlled four-wheel drive to improve vehicle stability.
Delica
The 2007 Delica D:5Mitsubishi Delica
The Mitsubishi Delica is a range of trucks and multi-purpose vehicles built by Mitsubishi Motors since 1968. It was originally based on a small pickup truck introduced the previous year, also called the Delica, its name a contraction of the English language phrase Delivery car...
uses the same electronically controlled four-wheel drive system that is used on the new Outlander, which tailors front and rear wheel torque split to the driving conditions. Delica also features the same selector dial next to the shift selector that allows the driver to switch between three drive modes: 2WD, 4WD AUTO and 4WD LOCK. Mitsubishi's skid-preventing Active Stability Control (ASC) system is also present. Mitsubishi has refined the Delica's four-wheel drive management software from the Outlander by increasing the proportion of torque directed to the rear wheels during uphill driving and reducing it during smaller steering maneuvers in 4WD mode because of the vehicle's difference in wheelbase
Wheelbase
In both road and rail vehicles, the wheelbase is the distance between the centers of the front and rear wheels.- Road :In automobiles, the wheelbase is the horizontal distance between the center of the front wheel and the center of the rear wheel...
and weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...
compared to the Outlander. The results are better hill-climbing performance and cornering stability. Also, in LOCK mode the system senses when wheels on the diagonally opposite corners are in danger of spinning without traction during vehicle operation at low speeds. By activating the brake traction control function at lower speeds than the system in the Outlander, Mitsubishi improved the vehicle's all-terrain performance at low speeds.
Lancer Evolution
The Lancer Evolution IX introduced in 2005 features an electronically controlled full-time four wheel drive system, which incorporates Super AYC, ACD and Sport ABS. The Super AYC is an improved version of the AYC system first introduced on the Lancer Evolution IV. Compared to the previous system it now uses a planetary gear differentialEpicyclic gearing
Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...
that can transfer almost twice the torque between the rear wheels. Lancer Evolution IX also uses a revised AWC system that is even more pro-active than in previous generations. On the Evo VIII, the AWC system gave priority to the Sport ABS system in order to stabilise the car under heavy braking. The ACD and Super AYC modules were effectively disengaged. The AWC system has been revised so that the driving force is still controlled actively, even when the Sports ABS is operational. Through a series of high-speed bends, for example, the system will continue to control the yaw moment of the car, even if the driver is applying braking force. The car’s agility and stability are both improved, and the car responds more accurately to steering input on the entry to a corner.
According to Mitsubishi, the Lancer Evolution uses its four-wheel drive system to improve the handling, rather than simply to increase traction. Super AYC acts like a limited slip differential to optimise the Lancer’s handling during hard driving. It improves cornering performance by transferring torque between the rear wheels. It also works harmoniously with the ACD, which was introduced on the Evolution VII. Mitsubishi's Sports ABS system is used to enhance the steering control during hard driving. The Sport ABS ECU uses inputs from steering angle, lateral G and vehicle speed sensors to individually apportion braking pressure to each of the four wheels.
Pajero
The fourth generation Pajero launched in 2006 employs a Super Select 4WD IISuper Select
Super Select is the brand name of a four-wheel drive system produced by Mitsubishi Motors, used worldwide except for North America, where it was initially known as Active-Trac...
four-wheel driveline from the previous model which offers four drive modes (2H, 4H, 4HLc, 4LLc) and delivers optimum traction to increase stability and handling characteristics over all surfaces. Pajero also features an upgraded version of Mitsubishi's Active Stability & Traction Control (ASTC) system that can accommodate the installation of a new rear differential lock. Pajero is also equipped with Mitsubishi's Engine Brake Assist Control (EBAC), Multi-Mode Anti-lock Braking System (ABS), Electronic Brakeforce Distribution (EBD), Hill Hold Assist and with Mitsubishi Body Optimised Suspension (MBOS).
SS4-II allows the driver to lock the center differential for maximum drive torque over poor surfaces. The driver can also allow the viscous coupling type center differential to automatically tailor its basic 33:67 F-R torque split to suit different surfaces and conditions.
In 2H mode, the road friction losses are minimized to allow maximum fuel economy and is also the ideal mode for urban driving in fine weather. The standard operating mode for SS4 II is the 4H mode which caters to a wide range of conditions: driving around town, on expressways
Limited-access road
A limited-access road known by various terms worldwide, including limited-access highway, dual-carriageway and expressway, is a highway or arterial road for high-speed traffic which has many or most characteristics of a controlled-access highway , including limited or no access to adjacent...
or country roads; and driving over packed snow, icy surfaces, flat dirt and other off-road conditions. Selecting 4HLc mode locks the center differential so that drive is transmitted through all four wheels to enable driving in soft snow, sand, dirt or other high-resistance conditions. The 4LLc mode locks the center differential and by keeping the transmission in a low gear it enables driving on rocky terrains or swampy conditions where extra drive is required.
Available on all models as a factory-fitted option is a rear differential lock that eliminates the differential between the rear wheels. Working hand-in-hand with the front/rear center differential lockup this new feature helps the driver extract his vehicle when bogged down in soft surfaces. Refining improvements have been made to Mitsubishi's ASTC system that regulates brake force and drive torque on an individual wheel basis to deliver better handling and vehicle stability on all surfaces. The ASTC system is now capable of detecting the operating status of the rear differential lock. This allows both systems to be installed at the same time and thereby extending Pajero's off-road capabilities even further.