The ultimate differential thread

This one of the most valid reason sto look into the E-Diff software further. Not by deleting it but to adjust the model...

I'm just having fun with you Some people get so uptight about the subject of modifications. I am not one of them.

Its true though that I would never delete the E-Diff just so I could run 20" rims. Not only will the extra size likely make the rims heavier than what you replaced them with and thus made the car handle worse anyway. I remember trying 20" rims over 2 decades ago now on the F131 platform and it really made the car dreadful to drive vs the stock much lighter tire+rim OEM package. Braking distances where extended and the car felt much less nimble in the corners. It was such a retrograde step from a performance perspective but they did sure get a lot more attention. If your only driving in straight lines to cars and coffee ain't nothing wrong with your choices, if that's what you bought your Ferrari for not hating on you for that. Everyone enjoys their cars in different ways. Again, that's your personal choice and I don't really care. I just would like people to understand what they are getting themselves into or not if they go a certain path with their modifications.

The only thing as you've discovered is the E-Diff calibration will require adjustment in the model.

Yes its possible and its a far more sensible approach than deleting in entirely. Lets look into the technical details for those still following this...

Electronic Differential (E-Diff) Algorithm:
The E-Diff algorithm aims to improve traction, handling, and stability by dynamically adjusting the torque distribution between the wheels. This can be achieved through various approaches, depending on the specific E-Diff system and its intended application.

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Here's a general outline of a common E-Diff algorithm:

Inputs:

• Rear Wheel speeds (WrearL, WrearR)
• Vehicle speed (V)
• Yaw rate (Psip)
• Lateral acceleration (AY)
• Steering angle/speed (dvol)
• Driver input (Pacc)

State Estimation:

• Estimate tire slip angles (α_rearL, α_rearR) based on wheel speeds and vehicle speed.
• Estimate tire forces based on tire model and estimated slip angles.

Control Law:

1. Calculate the desired torque difference (ΔT) between the wheels:
   • Based on a pre-defined control strategy, considering:
     • Difference in tire slip angles between the wheels.
     • Vehicle yaw rate and desired yaw rate.
     • Lateral acceleration and desired lateral acceleration.
     • Driver input and desired vehicle behavior.
     • Tire-road friction coefficient.
2. Limit the torque difference (ΔT):
   • To prevent excessive torque transfer and potential damage to the differential.
   • The limit might depend on various factors like vehicle speed, road conditions, and driver input.
3. Adjust individual wheel torques:
   • By adding or subtracting ΔT to the engine torque (ENG torque) applied to each rear wheel.

Control Strategies:

Several control strategies can be implemented within the E-Diff algorithm, including:

• Open Differential Simulation: Mimics the behavior of an open differential by allowing some slip between the wheels.
• Limited Slip Differential (LSD): Limits the difference in wheel speeds to improve traction and stability.
• Active Torque Vectoring (ATV): Actively distributes torque between the wheels to enhance handling and cornering performance.
• Predictive Control: Uses real-time data and future estimations to anticipate potential situations and adjust torque distribution pre-emptively.

Additional Features:

• Adaptive Control: Adjusts the control strategy and parameters based on driving conditions, road surface, and driver behavior.
• Fault Detection and Diagnosis: Monitors system health and identifies potential issues for maintenance purposes.

Challenges:

• Computational complexity and requirement for fast processing power.
• Tuning and calibration of the control algorithm for optimal performance.
• Integration with other vehicle dynamics systems for coordinated control.

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General Algorithm for Slip Angle Calculations

1. The algorithm receives three arguments:
   
   • WrearL: Rear left wheel speed in rpm.
   • WrearR: Rear right wheel speed in rpm.
   • V: Vehicle speed in km/h.
2. It calculates the wheel angular velocities by dividing the wheel speeds by the tire rolling radius.
3. It converts the vehicle speed from km/h to m/s for further calculations.
4. It calculates the longitudinal tire slip for each wheel using the formula slip_long = (v_vehicle - omega * R_tire) / v_vehicle.
5. It estimates the tire slip angles using the atan function based on the longitudinal slip.
6. Finally, it returns the estimated slip angles for both rear wheels.

estimate_tire_slip_angles(WrearL, WrearR, V):
{
// Calculate wheel angular velocities
omega_rearL = WrearL / R_tire // R_tire is the tire rolling radius that needs adjusting
omega_rearR = WrearR / R_tire

// Calculate vehicle speed in m/s
v_vehicle = V * 1000/3600 # Convert km/h to m/s

# Estimate longitudinal tire slip for each wheel
slip_long_L = (v_vehicle - omega_rearL * R_tire) / v_vehicle
slip_long_R = (v_vehicle - omega_rearR * R_tire) / v_vehicle

# Estimate tire slip angles using a simple tire model
alpha_rearL = atan(slip_long_L)
alpha_rearR = atan(slip_long_R)

return alpha_rearL, alpha_rearR
}

# Example usage

... cut ...

WrearL = 2000 // Wheel speed in rpm
WrearR = 1800
V = 50 // Vehicle speed in km/h

alpha_L, alpha_R = estimate_tire_slip_angles(WrearL, WrearR, V)

print("Estimated tire slip angles:", alpha_L, alpha_R)

.. cut ...

Note: This is a simplified example, and Bosch do in fact use more advanced tire models are used for more accurate slip angle estimation, especially at higher speeds and slip values but this at least helps people to understand what's going on and why the radius of the wheel is so important to be in the model.

 

I have decided to bypass my e-diff, what is the general consensus out there about this ?

 

The F430 came out in 2005 as a pure rwd so yes there where clear limits on what they could do with the generation of the ABS and technology available to them for both budget and time reasons. It gets a lot easier to accomplish on EV's when you have full 4-wheel electric drive motors

I recall there where also some patents around which limited what you could and couldn't do with active rear wheel steering for example to improve turn in and stability/agility (e.g. HICAS on Nissan R34 GT-R V-spec, anyone remember that?).

Again if your interested in understanding this subject there is an SAE paper here;
https://saemobilus.sae.org/content/891978/

The logical description outline of a basic algorithm I gave was of a 'representative of modern E-Diff algorithms' just so people can get their heads around the logical operation of how an E-Diff works from an engineering perspective - its not entirely accurate of exactly how Bosch and Ferrari built their E-Diff in the F430 I am sorry if people felt I was describing exactly the F430 use-case - for that you'd need to fully reverse engineer the entire code base and all its components, which while possible is beyond the scope of this discussion.

I really wanted people to understand that the modelling elements so they can appreciate that the E-Diff only as good as the 'assumption's hardcoded into the software. In this case one of the key ones is rolling radius - which is obviously altered with bigger rims. If interested and from an engineering inclined mindset I was hopeful it would now be possible to visualize this with the descriptions I gave. You can obviously add or delete from this to get either cheaper or more expensive (e.g. higher computational horsepower to allow you to do more advanced predictive modelling to allow you to do better prediction). Taking it to its ultimate conclusion it gets significantly more complex than these older implementations from nearly 20 years ago, to the latest systems from today and you end up with full "fighter jet" style 4-wheel torque vectoring in full x/y/z space dimensions with hybrid electric "instant" torque assist allowing rapid changes in real-time.

As for the questions which where asked previously about why a mechanical LSD is fitted in 430 Challenge racing and then E-Diff on the road car. The thinking being it therefore must be somehow 'better', well it depends on what your trying to accomplish in your project. Typically the decision comes down to multiple reasons, either budget related (to pay Bosch millions of $ to re-calibrate the E-diff system for a small group of challenge cars and all its configuration of tires, suspension geo setup, ride height, anti-roll bars, etc. which can all be tweaked and therefore differ between races). Then you need special software to allow the technicians to input all those changes into the model so the E-Diff can adapt - and then training and so forth. It gets a lot more complicated to setup the car because you need both mechanics and software engineers or advanced software to allow the technicians to adjust the parameters correctly.

Furthermore in racing the "technical regulations" can often prevent new technologies from being adopted (look at the McLaren road cars vs their racing application GT3 cars for more on this). Particularly if you get out of one make racing and into more serious fields like GT3. Even F1 cars do not have active suspension due to basically regulations, not technical and not for weight savings - as far as I am aware active suspension control has been banned per technical regulations indefinitely, as have other computer assisted vehicle dynamics models.

 

Use of 4-electric drive motors which can provide "instant torque" in either forward or reverse direction instantly to do real time torque vectoring is vastly superior (much faster acting) than using using purely clutch driven differentials and ability to brake individual wheels. It can even be used to pivot a stationary vehicle on the spot around its origin which makes for a great show, although not particularly useful due to crazy tire wear! lol

 

The 10th dentist.

 

Apologies if answered but why during manual conversions is the e diff an issue to stay integrated??

 

It’s not an issue at all, it’s just easier to delete it. By easier, I don’t mean better. It’s easier to remove and block off lines than it is to have to rewire some electronics and bleed the Ediff to maintain it.

Personally I think it is absolutely worth the effort to maintain the Ediff during conversion, and will be doing just that over the next few months.