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Discussion Starter · #1 ·
Can someone please explain to me the functions of Active Yaw Control (AYC) and Active Center Differential (ACD) or at least point me to a thread or website that explains this? I keep hearing about the new EVO8 not offering these. I did a search and could not find anything. Thanks
 

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From Automotive Engineering magazine:
The mechanical component of the AYC system is the torque-transfer differential located at the rear between the wheels incorporated with the final drive/differential unit, and is driven by the propeller shaft from the front-mounted transverse power plant. The torque-transfer differential comprises a planetary gear mechanism that generates two differing rotational speeds which are "fast (13%)" or "slow (13%)"–either relative to the differential case rotational speed; clutch units for left and right turns that transfer torque to either the left or the right wheel.

Five input sources to "read" the driver's intention are steering wheel angle, accelerator stroke, wheel (all four) speeds, longitudinal acceleration, and lateral acceleration. The ECU judges road surface frictional coefficient, actual vehicle behavior, the driver's intention, determines optimum transfer of driving torque between the rear wheels, and signals the hydraulic actuating unit.

Mitsubishi's system differs from Honda's in that it employs an electrically driven hydraulic pump and a magnetic hydraulic valve. Honda adopts a mechanically driven pump from the drive shaft. A senior engineer says that this system is much quicker, works from very low vehicle speeds, and its on-demand characteristics are energy efficient. The system functions in a circle as small as 14 m to, according to the Mitsubishi engineer's estimate, Honda's 30 m.

The AYC's benefits are, again, superior corner tractability, greatly improved cornering behavior, relief from a "held-back" feel during cornering, and traction control capability on split-µm surfaces. Applied to an all-wheel-drive car, the AYC improved accelerative performance on packed-snow, 30-m radius by as much as 30% over a front-wheel-drive model, claims Mitsubishi.


Re: ACD, from Myevo.com
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.

Under hard acceleration, the ACD reduces slippage and approaches a locked state, thereby transmitting more torque to the road surface for better traction and acceleration. When the driver makes rapid steering inputs, meanwhile, the ACD operates virtually as an open differential to improve steering response and feel through corners while retaining outstanding 4WD stability. The ACD also enables the driver to manually select one of three modes - Tarmac, Gravel, Snow Last but not least the ACD operates in a virtually open state when the parking brake is used, thereby enabling rapid and effective side brake turns.


More on AYC from myevo.com
Active Yaw Control
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.


Finally, re: Mitsu's integration of the two, again from Myevo.com
Integrated ACD & AYC system control

...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)


Hope this helps!
 

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Discussion Starter · #3 ·
AutoXJunkie


I was hoping for a little more detail! haha :) Thanks! That's exactly what I was looking for.
 

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No prob!! ;)
 
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