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Questions for 4Drive, how it works, modes, etc.

12K views 4 replies 2 participants last post by  Anonymous 
#1 ·
Sorry for spamming the forum with questions but yeah, can't do anything else while waiting :D

I'm wondering how exactly 4Drive works and its dependency on the selected mode. Here some random questions:

- Suppose I am in standard drive or sport mode. If I take off with a lot of throttle, say after a traffic light, will it help in acceleration preventing front wheels slip by transferring torque to the rear wheels at instant? On my Leon it seems 180HP is a bit too much for a front-wheel drive and it's very rare that I can use the full power for acceleration and that kind of beats its purpose...
- How about if the road is wet?
- Do I have to be in offroad then?
- What's the difference between offroad and snow?
- Is the middle diff locked when in offroad/snow?
- Is the distribution between front axle and rear axle dependent on the mode?
- Is the detection reaction for transferring to the rear axle or another wheel dependent on the mode?
- I have a steep twisted and dusty gradient when exiting my underground parking spot and with the manual, FWD and powerful Leon it's a real pain in the ass, needs very precise throttle and clutch touch. I hope situations like this can be solved by the 4Drive system but wondering if this is really true? If it is very slow to switch to the rear axle and will wait for a lot of slippage to happen in the front, then it won't be of any real use. Or maybe I should be in offroad when exiting my parking?
 
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#2 ·
Many questions. :D

4Drive (which is a SEAT marketing name) is actually a Haldex multi-plate clutch system (currently generation 5 Haldex). It uses several sensors (speed, accelerator pedal position, steering wheel angle, acceleration (G-force) on different axis etc. etc.) to constantly alter the torque distribution between front and rear wheels. It can go from (almost) 100 % front wheel drive to 50-50 distribution. There is no center differential in this system, only the multi-plate clutch. And there are no locks on the front or rear differential either, they are normal "open" diffs. There's also so called "electronic differential lock" on both axles, which uses the normal hydraulic brakes to brake the slipping wheel, in order to transfer some torque to the other side wheel.

All this magic is fully automatic, there's basically nothing you can adjust about it. I have not had a change to test Ateca's 4wd properly (still waiting for the winter ;) ) but I think there's not much difference in it's functions between different driving modes.

Here's some reading about Haldex AWD. Remember, Ateca has Gen. 5 haldex.
http://www.awdwiki.com/en/haldex/
 
#3 ·
I think you get Hill Descent Control Enabled in offroad. Snow typically limits the power put to the wheels in other cars and the Ateca too I assume.

Because under more spirited driving the 4drive can push a fair amount of traction to the rear wheels it makes it a little more fun to drive (not quite as fun as the RWD biased Macan) but some of the way there.
 
#4 ·
Thank you for the answers. I've read some description of the Haldex 5 and it is clear to me now how the system works. What remains is whether the software that controls it changes with the modes but I guess we'll need to see that for ourselves. I found a great reply under a YouTube video which explains in an excellent way how the Haldex 5 works:

Simply put, yes that is what it does, +James Bradley. But you ask if "that's all?" - and I think there's a bit more to it, so I'll try and explain. :)

The "point" or rather, "what makes it special", is that it's a further evolution on a different type of all wheel drive, than "just" applying three differentials - one on each axle, and one center differential, and then possibly making each of them lockable.

The Haldex system is very light and compact, so it is applied to a much larger variety of vehicles, that can then benefit from all whell drive in - for example - snowy conditions, while they normally are just regular family cars, that aren't intended to i.e. go rock crawling or river crossing, but on the other hand would benefit from extra traction in winter.

It's also different in terms of the way power is distributed between the axles. When you apply a differential, you distribute power, but you also allow the power to choose the path it wants. And the power will use the path of least resistance. So if one wheel is on ice, and the other three on tarmac, then a three-differential system with no locks will in theory be left standing, with all the power going to the one spinning wheel being on ice. That's where the locking ability comes in, but you can only lock it in a specific ratio, say 50/50 front/rear, and obviously 50/50 on each axle. That means, that if for instance you are driving up hill, and the rear axle looses traction, then the front axle has to pull the total weight of the car, but with only 50% of the power, since the other 50% are sent to the spinning rear wheels.

A Haldex system is clutch based, so it can transfer power with no steps. It can run solely on the front axle, which is what it will do almost all the time. If the front looses traction, it's able to send a varying amount of power to the rear axle, typically upwards of 95-100% of the engines power. That makes it much more efficient in smaller vehicles, since you don't rely on a massive overcapacity in the engine to pull the car ahead. This change of power distribution happens very quickly, usually within less than an eight turn of a spinning wheel.

Usually, Haldex systems does not incorporate lockable differentials on the axles themselves either. Instead, the cars disc brakes are used to form what's called "EDL" or "Electronic Differential Lock" (which is a marketing term for "differential lock equivelant, achieved electronically" and not to be confused with electrical actuation (command) of an actual differential lock). This uses the brakes individually on spinning wheels, and means that in theory 100% of the engine power can be sent to one wheel. This also implies that a car with three wheels on ice should be able to crawl forward - however, the management software of the system might not always detect these situations accurately, so even though the system has this capability, putting it to use might not be so easy. The reason for this is, that as the brake is applied to a spinning wheel to make it stationary, obviously it's also no longer possible to detect spin (as the wheel is not moving). Thus, to find out when the wheel has power again, it must be unbraked and allowed to either spin or grip at intervals, in order for the management software to find out, if there is traction or not. That means that these systems are often "cradling" the car along, and that they often require quite an aggresive throttle to actually operate, if you compare it to e.g. a Land Rover Discovery with differential locks and anti-stall, that you can basically take through anything without touching the throttle.

What's new about this specific construction is the centrifugal pump, which allows a quicker reaction time of the actuator that drives the clutch pack. That means, that the power distribution can now happen much quicker and thus much closer to the actual demand based on e.g. spinning wheels or driver input. That should allow the system to come even closer to recognizing and acting on difficult situations correctly.

Basically, as a headline, you can think of these Haldex systems as being a full offroad setup with front, center and rear differential that all are lockable, only achieved through various electronic gadgetry in order to get the "same" potential out of a much smaller platform (i.e. a Volkswagen Golf rather than a Jeep Grand Cherokee) and a much smaller engine (i.e. 150 HP TDI rather than 300 BHP V6/V8). When you're done picturing that, of course you then realize that all this gadgetry of course has it's own limitations, and then understand why "same" potential was in quotes. :) But it gets a long way, considering the vehicle types and engines it can be applied to. Especially considering that a full Haldex system might weigh something like 70 kg.
 
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