DCCD info and FAQs

DCCD - DRIVER CONTROLLED CENTER DIFFERENTIAL

THE PLANETARY CENTER DIFFERENTIAL IN THE WRX STI SPLITS ENGINE TORQUE IN VARIABLE RATIOS BETWEEN THE FRONT AND REAR WHEELS. IT ALSO GIVES THE DRIVER A CHOICE – LEAVE RATIO CHOICE TO COMPUTERS OR SET IT YOURSELF.

All-wheel drive performance cars are rare enough. But the WRX STi is even more unique because the driver can choose the value of the torque split between the front and rear wheels! Whether the driver makes adjustments to torque distribution in the manual mode via the console-mounted control wheel or entrusts distribution decisions to the DCCD control module through the automatic mode, the ratio of front/rear torque distribution can vary from 35 percent front/65 percent rear to 50 percent front/50 percent rear.
In automatic mode, DCCD varies torque according to input indicating acceleration, deceleration, cornering force and wheel slippage. In manual mode, the driver selects from six stages of center-differential lock-up. The more lock-up, the greater the torque directed to the front wheels – up to the 50 percent front/50 percent rear ratio. Mechanical limited-slip front and rear differentials enhance the system’s effectiveness.
The intent of the adjustable torque split is to improve handling and give the driver an increased sense of performance driving. DCCD accomplishes this through the integrated functions of numerous components.
THE PARTS

Along with the mechanical components in the center differential, DCCD utilizes control units, sensors and switches from around the STi. Among them are the mode switch and control wheel on the console, throttle position sensor, parking brake switch, wheel speed sensors, ABS control unit, lateral G sensor with yaw rate sensor, rear differential oil temperature switch, brake light switch and instrument panel lights.
At the heart of it all, electronic control of a multi-plate transfer clutch in a center differential planetary gear set determines the torque split between the front and rear drive wheels. The split ranges from completely “free” (35/65 ratio) to “locked” (50/50 ratio). Clutch control is by an electromagnet. To lock the differentials, the clutch plates function to restrict torque to the rear axle, distributing more torque to the front. Lowering the torque restrictions frees up the ratio for more torque to the rear.
Fail-safe contingencies are built into the system. Should the electric coils that operate the clutch within the differential fail, power to operate the clutch turns off and the driver is alerted by a warning light. Sensor failure anywhere within the system fixes the last reading of that sensor as a default, and the driver is alerted that a fault has occurred.
THE WHOLE

AUTOMATIC MODE. Unless the STi is used for all-out off-road rallying and/or the driver is competition-competent, automatic mode is probably the best choice. The system utilizes sensor inputs that indicate driving style and changing road conditions. In automatic mode, DCCD reacts quicker with changes in front-to-rear torque ratio than most drivers are capable.
Grid Map: DCCD Automatic Mode

Under braking as the vehicle approaches a turn, the DCCD system reduces the restrictive force of the center differential toward a free state. Through a turn, between the turn-in point and the clipping point , the system receives input from the throttle as it opens and from the lateral G sensor. The center differential’s restriction torque gradually increases to improve cornering ability. Between the clipping point and the exit from the corner , input from the lateral G sensor decreases. The system increases the restricting force of the center differential toward the locked state to help maintain traction.
MANUAL MODE. Drivers who want or need to do things for themselves have six stages from which to select via the control wheel after hitting the DCCD manual switch. Both controls are on the console.

With the control wheel moved all the way forward, lock-up is 100 percent with torque distribution at 50 percent front/50 percent rear. The percentage of lock-up from the top “LOCK” stage to the bottom is:

• 100 percent (50% front/50% rear)
• 85 percent
• 65 percent
• 35 percent
• 15 percent
• 0 percent (35% front/65% rear)

PERSONALIZED PERFORMANCE

Automatic or manual mode, DCCD adds up to one of the most significant and enjoyable technologies in the auto industry. It enhances traction and control, which is much appreciated in a 300-horsepower performance car. Bring on the snow!
To see DCCD working in the hands of a professional race driver, go to www.drivesubaru.com. In the Online Exclusives box, select: “Training for Performance – Sales Consultants Learn More about the WRX STi.”
WRX STi COMPONENTS USED BY DCCD

1. Wheel speed sensor
2. Rear differential oil temperature switch
3. Wheel speed sensor
4. Manual mode switch
5. Manual control dial
6. DCCD electronic control unit
7. Parking brake switch
8. DCCD indicator lights
9. Battery
10. ABS control unit
11. Wheel speed sensor
12. Brake light switch
13. Throttle position sensor
14. Accelerator pedal
15. Wheel speed sensor
16. Lateral G sensor (with yaw rate sensor for 2005)
17. Main gear input from the engine
18. Front output
19. Rear output
20. Transmission assembly
21. Center differential
22. ABS monitor signal

here is another link regarding the DCCD, VDC and SI drive for the GR STi: http://www.driveperformance.subaru.com/version5_1/blueprint.asp

GR owners read this:
For the MY08 owners push in the VDC (traction control) button once to turn off the VDC. Push in the button for more than 2 seconds to activate "traction" mode.
For the MY09-11 push the button in once to activate "traction" mode. Push and hold for more than 2 seconds to turn the VDC off.
What "traction" mode does is allows the tires to spin a limited amount for more spirited driving.

The Driver Controlled Center Differential (DCCD) is a commonly misunderstood part of the STi. The DCCD can vary the torque split from 35f/65r on the 04-05 STi and 41f/59r on the 06-11 STi, but that is not where the DCCD stops. While these numbers are good to know they are only correct during normal driving conditions. This would be a situation such as straight line highway cruising. The DCCD is still a limited slip differential, therefore it will constantly vary the amount of torque front:rear when there is slippage. In reality, the the torque split can vary from 100:0 to 0:100 in extreme conditions. Hopefully this guide can shed some light on your understanding of the DCCD.
For explanations on how the DCCD works refer to the next 2 posts, this is info straight from the FSM regarding the DCCD for the 04-05 and 06-07.

When the DCCD is set to manual and the selector wheel is all the way to the rear(open) the initial torque split is 35f/65r(04-05) or 41f/59r(06+). In this configuration there will be no slip correction or torque transfer through the center diff for the 04-05MY STi. In this configuration on the 06+ MY STi there will be no slip correction or torque transfer other than what is provided by the mechanical LSD in the center diff. Unfortunately trying to calculate the torque transferred by a LSD is beyond my scope of expertise. When the DCCD is in manual mode with the dial all the way forward(lock) the torque split will vary depending on the driving surface. When the dial is in the "lock" position the torque split is not fixed, but is able to fully lock the differential to compensate for loss of tractrion at the front or rear wheels (however, the initial torque split remains 35/65{04-05}&41/59{06-11}). The DCCD only changes the percent of lockup allowed by the center diff. Subaru tries to tell us that by selecting different settings within the manual mode we are changing the torque split, this info is incorrect. When adjusting the manual settings you are adjusting the amount of center differential lock-up.

When the DCCD is in the lock setting and the front tries are on a slick surface(ice, grass, dirt, gravel, etc.) and the rear tires are on a high traction surface(tarmac, pavement, hardball, etc.) the amount of torque required to spin the front wheels wil be much less than the amount of torque required to spin the rear wheels. When the front tires start to spin the DCCD will sense the loss of traction and send all torque(minus what is needed in the front tires) to the rear tires to maintain positive traction. Once the car starts to move forward and the front tires move onto the tarmac and the rear tires move onto ice the DCCD will compensate again by transferring the torque to the front wheels.

When the DCCD is set to lock the front and rear wheels will rotate at the same speed, meaning that even though the rear wheels have more traction than the fronts and the rear wheels will get the majority of the torque the front wheels wil rotate at the same speed as the rears. Because of this function of the DCCD you may sometimes experience loud noises coming from the diff. For example, if the DCCD is set to lock and you are on tarmac making a sharp turn without a loss of traction you will experience clunking. Since the front wheels will be traveling a longer distance than the rears and the center diff makes the wheels rotate the same amount you will experience the clunking and popping of the center diff.

Also as a side note you should remember that the DCCD only controls the front to rear torque transfer. Our cars are also equipped with front and rear center differentials that also transfer torque from left to right when slipage occurs. That should be saved for another thread ut itis good to know that ach individual tire can have varied torque.

MY06 technical data for DCCD

MY04 specific DCCD info


A: FEATURES
-The driver-controllable center differential system consists of a planetary gear set and electromagnetically engaged variably controlled multi plate clutches, distributing the drive torque to the front and rear wheels at a ratio of 35:65. The driver can optionally change the locking rate of the center differential.
-The system optimally controls the restricting action of the center differential using a computer and works together with the ABS control.
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(1) Wheel speed sensor (RR)
(2) Rear differential oil temperature switch
(3) Wheel speed sensor (RL)
(4) Manual mode switch
(5) Control dial
(6) Driver-controllable center differential unit
(7) Parking brake switch
(8) Driver-controllable center differential indicator light
(9) Battery
(10) ABSCU & H/U
(11) Wheel speed sensor (FL)
(12) Brake light switch
(13) Throttle position sensor
(14) Accelerator pedal
(15) Wheel speed sensor (FR)
(16) Lateral G sensor
(17) Input from main reduction gear
(18) Front output
(19) Rear output
(20) Transmission assembly
(21) Center differential
(22) ABS monitor signal

Hand brake control
When the hand brake is operated, the current to the coil is lowered to forcibly free the center differential.
Brake control
Controls the center differential restriction torque toward the Free State in response to brake switch input.
Center differential control
Based on throttle respondent torque control and slip control as basic controls, the differential restriction torque of the center differential is controlled between the free state and locked state through PWM control. Also, information received from other various switches and sensors are used in correcting the instruction torque for center differential control.
Fail-safe control
If a failure such as breakage of the coil drive element is detected, the coil driving power is turned off and warning indication is given on the meter cluster at a 1 Hz cycle to call attention of the driver. If a failure occurs in any of the sensors, a fixed value is substituted for the value from the failed sensor to maintain control as usual, while activating a warning indication on the meter at a 1 Hz cycle to call attention of the driver.
ABS control
When the ABS operates, the ABSCU & H/U outputs an activating signal to the center differential control unit to decrease the differential restriction torque of the driver-controllable center differential.
Throttle respondent torque control
Controls the restriction torque of the center differential in response to the throttle opening. The restriction torque of the center differential calculated for each mode is corrected using particular values, however, basically toward the locked state when the throttle is wide open or toward the free state when the throttle is fully closed.
Slip control
Controls the restriction torque of the center differential based on the amount of slip derived from the speed of four wheels.
Tight cornering control
A correction value is calculated from the left and right wheel speed ratio and applied to the restriction torque of center differential, which is derived from the throttle respondent, slip control, etc.
Volume control
By operating the control dial, the driver can optionally control the restriction torque of the center differential.
Cornering control
The restriction torque of center differential is controlled based on a value derived from the throttle opening, lateral G sensor, four wheel speeds, etc.
Rear differential oil control
When the rear differential oil temperature rises and the oil temperature switch activates, the center differential restriction torque is controlled toward the free state.
B: INPUT AND OUTPUT SIGNALS

C: DRIVER-CONTROLLABLE CENTER DIFFERENTIAL
-The driver-controllable center differential consists of a differential case, planetary carrier, planetary gears, electro-magnetic coils, armature, main clutch (multi-plate clutch), pilot clutch, and ball bearings.
-The engine torque enters the differential case from the transmission?s driven shaft. The torque from the differential case is divided into front and rear directions at the planetary carrier; the torque to the front is transferred from the planetary carrier through the planetary gears to the sun gear, while the torque to the rear is transferred from the transfer drive gear (integrated with the planetary carrier) through the driven gear to the propeller shaft.
-If either of the front or rear wheels spins, the driver-controllable center differential controls the differential action between the front and rear wheels.

-When current flows through the electromagnetic coils, magnetism is generated at components in the following sequence: electromagnet, differential case, armature (A). The armature is moved to the right (B) by this magnetism causing the pilot clutch to engage, and a magnetic field is formed in the area from the electromagnet, differential case, armature, and to the pilot clutch. The pilot clutch locks the differential case side and cam 1 side together, thus the rotational speed of the cam 1 and differential case are synchronized. The engagement of the pilot clutch is controlled by adjusting the current flowing through the electromagnetic coils.

-When a speed difference occurs, a force (B) pushing the cam 2 to the left is generated at the steel balls sandwiched between cam 1 and cam 2, pushing the planetary carrier to the left.

-When the planetary carrier moves to the left (A) , the main clutch is engaged. The main gear locks the planetary gears and the sun gear together to generate a differential action restriction torque.

D: LATERAL G SENSOR
A lateral G sensor is installed to the body at inside the console. The lateral G sensor detects the acceleration of the vehicle in the lateral direction and controls the differential action restriction torque.

E: MANUAL MODE SWITCH
The manual mode switch enables the driver to select the mode (auto mode or manual mode) by pressing the switch each time.

F: CONTROL DIAL
A rotary type switch is provided on the center console enabling the driver to optionally set the front rear differential action restricting torque in the range between locking rate 0% (free) to 100% (locked). Also, detents are provided between free and locked positions.

G: DRIVER-CONTROLLABLE CENTER DIFFERENTIAL INDICATOR LIGHT
Driver-controllable indicator lights which indicate the locking rate of the center differential are provided in the meter cluster. When the driver-controllable center differential is in the auto mode the ?AUTO? at the upper part of the meter cluster illuminates, and when in manual mode and the differential restriction torque is varied
manually the driver-controllable center differential indicator lights illuminate. If the control unit detects a fault in a component or unit during self diagnosis, the driver-controllable center differential indicator lights flash until the ignition switch is turned OFF. Faulty components or units can be identified by reading diagnostic trouble codes (DTC), and faults which occurred in the past can be retrieved from the memory.

H: DRIVER-CONTROLLABLE CENTER DIFFERENTIAL CONTROL UNIT
The control unit is located behind the glove box at the front passenger?s side. If the control unit detects a fault in a component or unit during self diagnosis, the driver-controllable center differential indicator light (FREE light at the bottom) flashes until the ignition switch is turned OFF. Faulty components or units can be identified by reading diagnostic trouble codes (DTC), and faults which occurred in the past can be retrieved from the memory. The differential restriction torque of the driver-controllable center differential is controlled based on signals from various sensors and switches, ABS monitor signals and ABS wheel speed signals (from four wheels) from the ABSCU & H/U, and by taking into account the conditions of the road surface and the vehicle.

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I: OPERATION
-When the vehicle is braked (A) while running:
To enhance safety of the vehicle during braking the restriction force of the center differential is controlled toward the free state.
-When the vehicle is in between the turn-in point (B) and clipping point (C):
When the vehicle is running from the turn-in point toward the clipping point, the throttle opening increases (vehicle accelerates) and a signal from the lateral G sensor is input. Accordingly the center differential restriction torque is gradually increased to improve the cornering ability.
-When the vehicle is in between the clipping point (C) and exit point (D):
When the vehicle is running past the clipping point toward the exit point the input from the lateral G sensor decreases. Accordingly the control interprets this as the vehicle is tracking out from the corner and increases the restricting force of the center differential toward the locked state to maintain traction.

Oh man this is awesome! I cant wait to read it all. (delete my post if needed)

Nice write up, thanks!

I am still researching the subject. I am trying to find as many tech articles by subaru as I can. This is a very technical topic and can't be half assed. if anyone has any good tech articles or write-ups please feel free to post them up here.

Thanks for that. I have been looking for some of those pics. I will rip them off of here to put in my 4th post. Later.....

thanks Paul for a great thread about DCCD.

I always wanted to know how it works, and I want to know the real reason why my car judders during slow maneuvering to parking and my car feels very nervous cllimbing uphill slowly with some twists and turns, it feels like someone is stepping the brakes on those situations. I really hate the feeling when it does that.

I'm hoping that an aftermarket DCCD controller can somehow fix that problem.

The juddering is usually a result of the dccd setting. If you have your DCCD set to lock and try to make slow sharp turns, like parking, the car will react like this. The reason is that the front and rear wheels will have to travel different distances in order to make the turn. Since the DCCD is in lock it forces all 4 wheels to travel the same distance. This causes binding and the jerky feeling. Check your settings and see if that helps.

Paul.c said:

The juddering is usually a result of the dccd setting. If you have your DCCD set to lock and try to make slow sharp turns, like parking, the car will react like this. The reason is that the front and rear wheels will have to travel different distances in order to make the turn. Since the DCCD is in lock it forces all 4 wheels to travel the same distance. This causes binding and the jerky feeling. Check your settings and see if that helps.

Click to expand...

I always drive my car with DCCD at full open, I want it to behave like a RWD as much as possible but even at full open it still judder when climbing steep, twisty parking areas going to mall parkings.

berdugo said:

I always drive my car with DCCD at full open, I want it to behave like a RWD as much as possible but even at full open it still judder when climbing steep, twisty parking areas going to mall parkings.

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That makes me wonder if Maybe your dccd is malfunctioning. It honestly sounds like it may be stuck in the lock position. Is there anywhere you could take it to have it checked out? Maybe I am way off. I know that the manual says not to worry about it but it shouldn't do that in open I don't believe.

Paul.c said:

That makes me wonder if Maybe your dccd is malfunctioning. It honestly sounds like it may be stuck in the lock position. Is there anywhere you could take it to have it checked out? Maybe I am way off. I know that the manual says not to worry about it but it shouldn't do that in open I don't believe.

Click to expand...

I had it checked when it was still in warranty (we have one year warranty for STIs here), they said "it could" have been the tranny and rear diff oil, I decided to put Amsoil SG 75W-140. The judder during maneuver at parking lot on flat surface is almost gone now but climbing twisty uphill going to mall parking lots still have judder. My friend here with exact the same car as mine told me his car did that too when it was relatively new, but now judder is gone on his car. He use his car a lot more than I do.

Paul if you don't mind me asking, can you include info about front, center and rear diffs too?

I think I found an answer why my car hates uphill twisty ramps but I don't fully understand it. Theres too many info and conflicting info, it's all very confusing to me.

http://forums.nasioc.com/forums/showthread.php?t=423584

http://forums.nasioc.com/forums/showpost.php?p=4622415&postcount=2

http://forums.nasioc.com/forums/showthread.php?t=1987180

Fuji, here is the part about vdc from my owners manual.



From what I understand. The colors were the same, the only difference is the button pushes were reversed. Subaru did this to make it so that in order to turn the vdc off it would require a more deliberate action.

I would like to see an 09+ manual if anyone has one, so I can verify.

berdugo said:

Paul if you don't mind me asking, can you include info about front, center and rear diffs too?

I think I found an answer why my car hates uphill twisty ramps but I don't fully understand it. Theres too many info and conflicting info, it's all very confusing to me.

http://forums.nasioc.com/forums/showthread.php?t=423584

http://forums.nasioc.com/forums/showpost.php?p=4622415&postcount=2

http://forums.nasioc.com/forums/showthread.php?t=1987180

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I'll see what I can get together. I think that topic calls for a new thread.

This is a great write up thanks for sharing!!

For 08+ I'd like some info about Auto (+) and Auto (-). Is it + is more lock and - is less lock? (just uses different algorithms with a preference to more or less lock) Maybe I'm way off base but i think i remember seeing somewhere like in snow you want auto+ and on a tarmac track you want auto-. Also, when I was talking to a driver at STPR (RallyAmerica) he said that they had multiple maps they could use depending on the type of gravel surface, ice, snow, pavement etc and could switch them on the fly. This leads me to believe either our stock DCCD computer is programmable or he had an aftermarket unit, is this possible?

Paul.c said:

here is another link regarding the DCCD, VDC and SI drive for the GR STi: http://www.driveperformance.subaru.com/version5_1/blueprint.asp

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Link is dead.

EDIT:
Also all those wrx.grapon.com images that rek posted.

rek888v2 said:

Since this question has been rehashed so many times and almost always gets answered incorrectly (as above), I am ending the thread here. For more information on this topic, check:
http://wallace.as.arizona.edu/~cgrop.../DCCD_FAQ.html

Click to expand...

That link also doesnt work. It looks like its just improperly formatted with the "..." in the middle of a link.