Hydropnuematic brakes instant lock

JohnCKL · Post by **JohnCKL** » 15 Sep 2004, 08:20

I've come across this statement from the website below (under tibdbits).
'Hydropneumatic cars need high pressure to brake. They are the only road cars capable to instantly lock the 4 wheels at any speed.'
http://encyclopedia.thefreedictionary.c ... opneumatic
Have searched the net for more info on above statement but can't find any. Does anybody know where are there any info to explain that difference with other normal brakes?

PeterMann · Post by **PeterMann** » 15 Sep 2004, 12:19

I have read that the C5 has computer-detection of rapid brake application, and in that circumstance overrides the driver by very rapidly taking braking pressure to the point of ABS activation. It was claimed that a substantial reduction in braking distance was achieved, and this is a feature that could not be implemented on a car with passive brakes (ie your leg creates and controls the pressure)

Homer · Post by **Homer** » 15 Sep 2004, 13:56

Anyone who has driven a GS will know execty what it means. The BX could also easily lock all 4 wheels, especially in the wet.
The difference is that with the Cit hydropneumatic system there is no real connection between the force you apply to the brake pedal and the force applied to the brakes. It's more like opening a tap with only a very small movement between closed and fully open.
As for the C5, that doesn't have Hydropneumatic brakes, they are a conventional system.
I'm not sure the statement applies these days though, modern conventional braking systems have improved a lot, I am sure there are many cas these days capable of locking all 4 wheels but it would be much easier to control than the GS/BX.

tomsheppard · Post by **tomsheppard** » 15 Sep 2004, 14:15

I would disagree; (Well I would, wouldn't I?)
Any car with good brakes and poor tyres will lock the brakes on all four wheels if provoked.
Citroens have fierce brakes until you get used to the idea of pressure rather than travel. They are also very powerful. That suits me!. They will not instantly lock all four wheels at any speed because the rotational force on the wheel needs to be overcome by pad friction. They will give rapid deceleration though!
If you are worried about getting caught out on an emergency stop and you don't cadence brake by reflex, you can buy an ABS equipped car and let that do it for you.

Panjandrum · Post by **Panjandrum** » 15 Sep 2004, 14:22

What a curious statement: it seems to imply that being able to "instantly lock the 4 wheels at any speed" is a good thing.

JohnCKL · Post by **JohnCKL** » 15 Sep 2004, 21:41

I interpret that statement as a compliment to the hydropneumatic system instead of a disadvantage. I think what it meant was it will apply braking force at a very fast speed to lock on all 4 brakes simultaneously. I don't think they are saying it will lock up the brakes which will cause the car to slide but to lock on the brakes. Since it is ambiguous, I thought of searching for more answers to verify that statement. Was wondering how different it is to other brakes as it said the hydropneumatic is the only road car that can do that. That's something special, isn't it.

AWG · Post by **AWG** » 16 Sep 2004, 13:13

It might be a reference to the twin characteristics of the braking/suspension system of reducing front end dive and increasing the rear braking applied under load thus permitting more braking force to be applied at all four wheels when braking hard rather than overwhelmingly at the front. This is a GOOD THING.

alexx · Post by **alexx** » 20 Sep 2004, 18:06

Conventional brakes react differently than hydraulic ones, because air needs several fractions of a second to enter backside of a servo unit through a small valve, to build maximum braking force. This is a problem especially with big 10" units. So they invented BAS, to shorten this delay.
Hydraulic brakes react almost instantly. So drivers of other cars always had problems with Citroen 'sharp brakes'.
So far, I didn't drive a car with better feel on the pedal than my ex. BX.

JohnCKL · Post by **JohnCKL** » 20 Sep 2004, 18:27

Ah, at last someone who understands the difference and gives a clear explanation. This would certainly explain that statement. Thanks alexx, now we know the advantage of our hydraulic brakes over the conventional ones.

NiSk · Post by **NiSk** » 20 Sep 2004, 18:34

Many new car models have an "emergency braking" function that applies maximum retardation if the system detects that the force/reaction time on the brake pedal exceeds a certain criteria. Mercedes started it (as far as I know) and now everyone seems to be climbing on the bandwagon, Peugeot included and it doesn't need a hydropnuematic system to work either, any vehicle fitted with ABS brakes has a brake force amplifier (EXCEPT hydropneumatic citreöns, of course, because they don't need one!)
//NiSk

JohnCKL · Post by **JohnCKL** » 24 Sep 2004, 08:36

Brings to mind the spring under the brake pedal to retard the 'instant' braking which is too strong for conventional drivers, I guess.

DoubleChevron · Post by **DoubleChevron** » 24 Sep 2004, 10:21

Which of course begs the question.
Why the hell did the complete idiots at Citroen put a spring between the brake pedal and brake valve on the Xantia. It's brakes are the hardest to regulate of any car I've ever driven. Seriously a Traction with 4 wheel non assisted drums is easier to regulate.
Yes I know I can remove this stupid spring, I just haven't found the time to do it [:(]
seeya,
Shane L.

xantiaBFY · Post by **xantiaBFY** » 24 Sep 2004, 10:24

Cit hydraulic car owners are a different breed of drivers.[}:)][8D][:D][:D]