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Lancer Evolution VII

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NEW! Active Center Differential (ACD)

This revolutionary 4WD system regulates differential limiting force. The ACD replaces the viscous coupling-type differential used in the past with a hydraulically actuated multi-plate clutch. Developed with rally use in mind, the ACD uses a center differential to distribute drive torque equally between front and rear wheels and thereby improve steering response at the same time as enhancing traction. 

The multi-plate clutch employs the same kind of steel plates as mechanical limited-slip differentials, Using sensors, the system electronically optimizes the cover clamp load to match driver input and vehicle operating status. Thus able to regulate center differential limiting action from free to locked, as conditions require. ACD's multi-plate clutch delivers up to three times the differential limiting force of a viscous couple.

Mitsubishi's Active Yaw Control traction enhancement system uses a computer to optimally regulate torque transfer in the rear differential on 4WD models and thereby tailor rear wheel differentials to match driver operation and vehicle operating status. In this way, MMC's proprietary system both equalizes the load on the four tires by adaptively regulating the yaw moment that acts on the body and improves cornering performance without inducing any sense of deceleration.

When accelerating through a corner, AYC reduces understeer by transferring torque to the outer wheel; when decelerating in a corner, AYC enhances stability by transferring torque to the inner wheel. AYC also improves traction on surfaces with low or split friction coefficients and has fully proven its worth since it was first introduced in Evolution IV.

For Evolution VII, all parts of the torque transfer mechanism of rear differential have been uprated to match the increase in engine torque, while breather and clutch operating durability have been improved. The system shares the same computer, hydraulic actuator unit and sensors as the ACD, thus reducing weight and improving reliability.

Integrated ACD & AYC system control

On Evolution VII, control of the ACD and AYC systems is integrated by computer. ACD control is based on: (1) A feedback control strategy to improve vehicle stability by keeping actual body attitude as close as possible to pre-determined attitudes as derived from steering angle and vehicle speed and, (2) A feedforward control strategy that responds rapidly to driver acceleration and deceleration actions. By combining these strategies in an optimal manner, ACD achieves the outstanding stability of a full-time 4WD vehicle and enhances steering response while realizing the superior traction of locked up 4-wheel drive. 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 precise and 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. And 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.

ACD+AYC control schematic Reduces slippage in proportion to deceleration to improve stability.

Increases slippage in proportion to steering angle and steering input speed to improve steering through corner Reduces slippage in proportion to throttle opening to boost traction Transfers torque to outer wheel to match steering angle and steering input speed, to improve steering through corner.

Transfers torque to outer wheel in proportion to throttle opening to reduce understeer and improve cornering performance (In cornering under deceleration, reduces oversteer by transferring torque to inside wheel)

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Evolution VII uses the W5M51-type five-speed manual gearbox that has built up a winning track record in successive generations of Evolution models. To cope with the higher torque generated by the Evolution VII's engine, higher-strength steel is used in some of the transmission gears to increase high-loaddurability and reliability, while first gear uses a lower ratio (GSR:RS 2.785 2.928) for better standing start acceleration. And reflecting the increased engine torque, fifth gear uses a higher ratio (GSR:RS 0.761 0.720) for increased comfort and fuel economy at high cruising speeds.

Clutch

To handle Evolution VII's higher engine torque, the clutch uses a higher cover clamp load as well as larger disc and flywheel diameters, while optimization of the clutch cover and other component shapes has reduced the overall rotational moment of inertia. As a result, the clutch combines superbly responsive drive torque transmission qualities with outstanding durability.

Transfer

For improved durability and reliability, Evolution VII's transfer uses up-rated hypoid gear and drive pinion teeth, and taper bearings. Reinforcing ribs have been added to the front differential case for better durability and reliability.

Propeller and drive shafts

To handle the increased engine torque, Evolution VII uses up-rated propeller shaft sleeves and yokes, Cardan universals and cross groove universal joints. The front drive shafts use up-rated constant velocity joints, while the output shafts use a higher strength steel. These components have the strength and durability required for use in the motor sports arena.

Transmission specifications

Cornering performance - from initial response right up to the limit - has been improved in a well-balanced manner by widening the track, optimizing the roll center height and increasing the bump stroke by 15mm. The steering gear box has been lowered to realize greater linearity in toe changes, and to increase vehicle stability when turning. The adoption of a flatter-section cross member and a structure that uses two reinforcing bars to link the front of the lower control arm anchorages has increased stiffness.

The result is better steering feel, and also less roll in high G cornering. The rear wheels are located and controlled by Mitsubishi's well-proven multi-link suspension that centers around a double-wishbone setup. As at the front, the rear suspension uses a wider track, roll center height has been optimized and bump stroke increased by 10mm. In addition, Evolution VII gets more powerful rear dampers, while damping, spring constants and bush characteristics have all been optimized. 

Suspension specification (Unless otherwise noted, unit = mm)

GSR  (RS)

Front 

Type MacPherson strut

Wheel stroke (bump/rebound) 175 (90/85)

Stabilizer diameter 24

Initial alignment Toe-in 0

Camber -1°00´ 

Caster 3°55

King pin inclination 13°45´

Track 1515  ( 1500 )

Rear 

Type Multi-link

Wheel stroke (bump/rebound) 185 

Stabilizer diameter 22

Initial alignment Toe-in 3

Camber -1°00´ 

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