How does Hill Descent mode work?

[DougM]

What's it using to slow the vehicle? A speed sensor and a way to apply the brakes? A device in the tranny for engine braking, like a hydraulic Jake Brake?

Thanks.

[Old Scout]

:confused: :confused: A Jake Brake is an Exhaust brake.

[DougM]

Yeah, I know what a Jake brake is. Was speculating that the LR system may use a similar non-brake system to slow the vehicle as the Jake brake does, but is doing it hydraulically in the auto tranny with some type of valve that shuts to cause enormous internal tranny braking. Total flyer. I have no clue what is actually used, but that was a random thought I had to impress you with my fathomless engineering savvy.

So, what is the Hill Descent braking force generated from?

[Cutter]

brakes...if you're really interested, I'll go out and read the owners manual in my Disco IISo, what is the Hill Descent braking force generated from?

[DougM]

Sure, that would be great if it goes into that detail. I'm interested enough in knowing about it if you're interested enough in grabbing the manual!

[evilfij]

Answer to your question:

poorly :)

Basically it works like ABS and limits your speed to whatever mph (dependent on what gear you are in)

LR installed it in part because they eliminated the CDL and thus the rear end tend to try to beat the front down the hill.

Ron

[DougM]

Holy Crap! I must be using Outer Mongolian language conversions here. Let me try this again:

Hill descent mode slows the vehicle. HOW does it do it? Brakes? Some internal engine braking via the torque converter/tranny? Elves? A 15lb Danforth anchor? JATO units? Fred Flinstone method? HOW is what I'm looking for - please explain that aspect of the system to me if someone knows, eh? Thanks.

[Strange Rover]

Heres what I think.

An exhaust break just blocks the exhaust off the slow the motor. This has nothing to do with hill decent

A Jake break actually alters the valve timing in the diesel motor and actually tries to run the motor backwards. Diesel engines that we get in OZ now have about 600hp driving power and the 600hp retarding power (via the Jake break) Also by pulling in the horten fan you get about anouther 50hp retarding. This also has nothing to do with hill decent.

Like Ron said hill decent works poorly. Ive had first hand experience at this. In some situations it is just plain dangerous.

The braking sys on the disco has a hydraulic pump and computer controlled solenoid valves. When the computer sences wheel speed greater than 7kph (4mph) (I think) then it brakes the wheels individually to slow the rig down (while retaining steering control). It uses the same components as the ABS system. The hill decent does work well in its element (works well for someone that has no off road driving ability) as it makes the vehicle much simpler to drive in that it does everything for you. Same goes for the traction control instead of the centre diff lock. To engauge the centre diff requires judgment and the traction control is totally automatic. The traction control also uses the same components.

So the answer the question how does it slow the vehicle, it just applies the brakes via solenoid valves and a hydraulic pump in a selectable and controlable manner. :D


Sam

[antiredneck]

To "split hairs" the Jake doesn't shut off the exhaust to increase back pressure. On the compression stroke, even without fuel introduced to cause burning/expansion, the piston just compresses air then bounces off of it, with no net energy being absorbed (other than friction). When the Jake brake is activated, It lets the piston compress the air in the cylinder, but denies it from using the pressure to be pushed back down by instead opening the exhaust valve and the pressure leaves through the exhaust, (and makes a blat sound. ) Read about this on the "howstuffworks.com" site.

[Strange Rover]

Originally posted by antiredneck
To "split hairs" the Jake doesn't shut off the exhaust to increase back pressure. On the compression stroke, even without fuel introduced to cause burning/expansion, the piston just compresses air then bounces off of it, with no net energy being absorbed (other than friction). When the Jake brake is activated, It lets the piston compress the air in the cylinder, but denies it from using the pressure to be pushed back down by instead opening the exhaust valve and the pressure leaves through the exhaust, (and makes a blat sound. ) Read about this on the "howstuffworks.com" site.

I knew it had something to do with the valve timing. Thanks for the explanation:beer:

Sam

[merv]

Of course, a real cliff decsent conrol involves a rear mounted winch :cool: :cool: :cool:

Merv.