WRC cars, locked center diff, handbrake turns ? 1

[Ibrahim M]

Hello,

I know for a fact that actual WRC cars is no center diff, it is locked between front and rear axle.

What happens when they use the E brake for a tight turn ?

Is the driveline elasticity enough to lock the rear wheels and not the front at the same time, just long enough to break rear traction ?

Or do they use some kind of freewheel system maybe ?

Is front braking force transmited to the rear as well ???

Thank you

 

[GregLocock]

As statements go "actual WRC cars is no center diff" seems at odds with google.

https://www.youtube.com/watch?v=FiqdNDjSS_o

Cheers

Greg Locock


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[Ibrahim M]

Well maybe not actual ones then , i meant the ones about 2014/2018 about. They had no center diff at this time.

 

[GregLocock]

That would be rather hard to work around, with no control over brake balance front to rear.

Cheers

Greg Locock


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[TugboatEng]

At least on the production models I think they had no center differential but a viscous coupling instead.

 

[BrianPetersen]

Lots of AWD systems have no center diff but have a clutch of some sort to engage the rear drive, with the front drive always connected. It's real simple to have handbrake status as an input to the logic for controlling that clutch.

 

[LionelHutz]

I believe they run a rear drive disconnect box of inline with the driveshaft to the back of the car, and it is either engaged or disengaged. The hand brake lever disengages it obviously, other things might too but I have no idea what would or wouldn't. You are correct that there is no diff that gives an adjustable amount of drive between the front and rear.

 

[MC6]

Keep in mind that different teams and drivers have different settings, for different stages/conditions.

I will remind you that the car is driven mostly with weight transfer to facilitate rotation of the chassis. Rather than active steering input. How or why a rear disconnect is implemented is then one of many aspects of vehicle dynamics tuning.

Some stages where you have dry rocky thick gravel, this is will have a different slide/scrub behavior than soft moist dirt stages, snow stages, partial asphalt stages. So under engine braking it may significantly slow the car to have the rear wheels driven or locked to the driveline, other situations that may allow enough vehicle control on slippery or fast sections. Same thing applies with speed of the turn.

We don't have the telemetry of these WRC vehicles, but in many cases the driver "uses" the hand brake, to mostly disconnect rear drive for a F/R power differential, facilitating the rotation of the vehicle. It would be very easy to make the handbrake have multiple stages for this purpose. Again, all comes back to the vehicle setup, driver preferences, and stage requirements.