fail-proofing full hydro steering

[mudguppy]

... And someone just posted this over on the pirate forum. ...

wow - looks like a servo-driven worm rod. crazy, but i see no reason that it couldn't/wouldn't/shouldn't work. servo capability and reliability is increasing about as fast as memory chips.

talk about true 'drive-by-wire'...

 

[mudguppy]

... And his 'basic' setups are just about the best out there, so this could get interesting...

sounds exciting - let us (or me at least) know what develops.

i'll be keeping my PSC system when i do the repower in a couple weeks. but since i'm introducing hydro-boost to the circuit i'll be upgrading to a larger capacity gear-driven pump that will put out more flow at all rpms and higher pressures. should work well.

 

[jesusgatos]

sounds exciting - let us (or me at least) know what develops.

i'll be keeping my PSC system when i do the repower in a couple weeks. but since i'm introducing hydro-boost to the circuit i'll be upgrading to a larger capacity gear-driven pump that will put out more flow at all rpms and higher pressures. should work well.

Oh, right on. Are you using hydro-boost or hydro-max stuff? I'm going to switch over to hydro-max brakes at the same time.

 

[mudguppy]

hydro-boost: F550 master cylinder, brake booster, and calipers all the way around. 15.365" front rotors and 14" rears. Steve at Differential Engineering.

already have the MC/BB, should have the caliper/rotor kits next week.

 

[mudguppy]

btw - i can't believe i haven't posted in this thread earlier?

to those naysayers that can only speculate:
my truck drives great at highway speeds.

 

[jollyroger]

www.aviationtoday.com/av/issue/.../Power-By-Wire_12671.html

en.wikipedia.org/wiki/Electro-hydrostatic_actuator

They are now called EHA's or Electro-Hydrostatic Actuators.

This is all part of the "Power by wire" systems being developed and now implemented into aircraft.

www.mpcproducts.com/electroHydrostaticActuators.asp

This is a company that makes them and what they look like.

A lot more stuff comes up on Google.

Reactor was a conceptual term for what these have become. I apologize for using old terminology that does not compute nowdays.

 

[jesusgatos]

Thanks for the info, but none of those links are working for me?

 

[jollyroger]

The mpc Products one worked for me. The other two did not. I am sorry. You may have to go old school and type those in manually in Google. I know. I know. I should not put you through so much stress.

The Aviation Mag article popped right up when I googled it last night. The Wiki article is general in nature but get's you in the realm. Wiki "Power by wire" and "Electro-Hydrostatic Actuators". Then Google "EHU's" or Electro-Hydrostatic Actuators. That's the best I can do on short notice.

 

[SoldierwithaM109A3]

Just pray to god it does not lock up going straight on a curve off a cliff .Beeing friends dads a lawer he states you can design this but anyone gets hurt or dies you are fully held accountable and the courts will tear you up . And make a full example of you .
Good luck though .

 

[jesusgatos]

Lock-up? Lock up how exactly? Thanks for the warning I guess, but is that really all you have to add to this discussion?

 

[Fredo Corleone]

I have been watching this thread with interest. Why not install a power steering box and adapt the rest why does it have to be full hydro steering?

 

[jesusgatos]

I have been watching this thread with interest. Why not install a power steering box and adapt the rest why does it have to be full hydro steering?

Please see my reply to someone else that asked the same question earlier in this thread.

Got Mah Deuce pretty well stripped down. Took the old cab off today, and I'm getting ready to pull the engine. Removed the pitman arm so I can take the steering box out, and took a few measurements. I would have to take the leafsprings apart and cycle the suspension and steering to do this accurately, but I just wanted to get some rough numbers to support my position - that the stock drag-link is a major limitation when it comes to modifying the front suspension for better off-road performance.

The tierod-end at the knuckle is really the limiting factor, so that's what I focused on. First I made sure that the front wheels were pointed straight ahead. Then I removed the pitman arm from the steering box, and let the drag-link drop. Making sure that the drag-link was still aligned with the steering box when viewed from above, I made a note of the distance from the bottom of the framerail to the center of the tie-rod end (the one that's connected to the pitman arm). Then I lifted the drag-link up until the tierod-end at the knuckle made me stop, and making sure that the drag link was still aligned with the steering box, I made another measurement. The distance between those two measurements was only 9.5".

What this means is that in a best case scenario, the stock drag-link might allow for up to 9.5" of vertical suspension travel. But the tierod-end at the knuckle isn't anywhere close to binding when the suspension is at full compression, probably because it has to allow for articulation and steering. Depending on how much the front bumpstops actually compress, it looks like that eats up about 2.5" right there. And we can't actually let that tie-rod end bind when the suspension reaches full extension, because that could obviously cause that tierod-end to fail. So that leaves us with less than 7" of suspension travel. I'm talking about vertical wheel travel. Straight up and down. Not enough. Not for me.

The other problem with the stock steering arrangement is the relationship of the drag-link to the leafsprings. Specifically, I'm talking about the length of the drag-link, compared to the length of the front half of the front leafsprings, when looking at the vehicle from the driver's-side. Ideally, they should be close to the same length, and close to parallel. But the stock drag-link is only about 16.5" long, while the front half of the leafsprings is something like 24" long. This creates, and exaggerates, bump-steer.

So it's a matter of quantity AND quality. I could make some adjustments to the steering linkage, like tweaking the tie-rod to allow for more droop-travel. I'm sure I could get somewhere close to 8-8.5" by modifying the stock setup, but I think that's about the limit when it comes to what a person can do with the stock steering linkage. And I could push the steering box forward in order to lengthen the drag-link, which would help to reduce bump-steer. But we would quickly run into clearance issues, and the pitman arm and drag-link would be a lot more vulnerable. I'm guessing that's why the steering geometry is the way it is.

I'm sure that the engineers that designed these vehicles knew all about the compromises they were making, and I think they did a **** fine job. But I'm looking to go beyond their original intent, and improve on things a bit. Switching over to a fully hydraulic steering system means that the steering will never restrict the suspension in any way, and it will also virtually eliminate bump-steer, AND make Mah Deuce easier and more enjoyable to drive on/off-road. I hope this helps to clarify things for those of you that are questioning my intentions (and maybe my sanity).

 

[BIG_RED]

If it were my project - I'd go full hydro. But if I were gonna go that far, I'd go independant suspension, or 4-link - instead of solid front axle on leafs. That's just me though, no disrespect to your ideas. I would also not do it to a motorhome, but you've been ragged on enough for that and it's none of my business.

The GM hydroboost for brakes on the M1009's has an accumulator on the break booster so that you can stop once after you lose engine power. It is essentially a tiny hydraulic ram on the feed from the pump (pressure side) that pushes a bada$$ spring(don't take a hydroboost apart without learning what's in them.. that spring could kill people). When the engine is running, the working pressure is enough to compress the spring. When the engine shuts off, any hydraulic braking is done by the spring pushing on the ram, moving fluid through the brake booster. It's not as strong as the engine, but every little bit helps when it's life on the line.

Hydraulic lines checked often are pretty safe. I would used dividers and combiners to run 4 lines from the frame to the diff so that if one blew, stuff would still work. Or use two rams and separate 4 hoses.

My main concern would be loss of engine power. In my experience with hydro steering, it was impossible to steer without the engine (but this was not a highway vehicle, it was heavy machinery that only went like 10 MPH)

What I would do to solve this, is get an big old scuba tank and mount it upside down (under the hood, far from people). Get a steel one from the 70's, the're good for like 4000 PSI. Get someone who works in refrigeration to vacuum the air out and fill it with argon/co2 at room pressure from a welding set up while it is connected to the pressure side output of the pump. While the pump is running, it will almost fill the bottle with hydraulic fluid, trapping the co2/argon at the top of the tank at 1500 PSI. (this compressible gas would act as a spring in the GM accumulator)(use argon or co2 so that no oxygen corrodes the steel). When the pump fails, the high pressure gas will keep pressure on the system for the first 2 quarts (depending on the size of scuba tank) of fluid that passes through the rams. This should be enough hydraulic power let you steer straight if you were turning. Or steer for the ditch. (depending on what bore rams you're using. Might need real big/multiple accumulator tanks)

I can draw you a picture (but it will look like a ten year old drew it) of how this would work if you like. I have used similar systems with old propane tanks (at a lower pressure, since they're only good for 300 psi) with great success.

I love hydro steering. I want to go full hydro steering, hydro suspension (would take a while to explain... basically, can raise/lower at will and adjust how "springy" for when under heavy loads) and even hydro breaks. Important thing is keeping things separate enough that one failure won't kill to much. If you can't steer, you'll want breaks, and vice versa. Safety first! happy you're thinking that way. Good thread, good luck with project!

 

[mudguppy]

... My main concern would be loss of engine power. In my experience with hydro steering, it was impossible to steer without the engine (but this was not a highway vehicle, it was heavy machinery that only went like 10 MPH) ...

again, this is a manual transmission equipped vehicle - a loss of engine power does not mean you have a loss of pumping power unless you take it out of gear. the only way you would have catastrophic pumping loss is:

1. hydraulic pump belt loss (not an issue with gear-driven units)
2. complete failure of hi-pressure pump-to-valve hose
3. complete catastrophic failure of hydraulic pump

and modern brake booster accumulators utilize a high-pressure nitrogen charge rather than the spring you mentioned. the accumulator is usually designed for at least one full-stroke, full-pressure actuation after pressure loss.

 

[BIG_RED]

"a loss of engine power does not mean you have a loss of pumping power unless you take it out of gear" - good point. I was thinking about things that don't move fast enough for that to matter. You're right. FYI, I was being supportive of the full hydro idea, not putting it down.

"and modern brake booster accumulators utilize a high-pressure nitrogen charge rather than the spring you mentioned. the accumulator is usually designed for at least one full-stroke, full-pressure actuation after pressure loss" - I didn't know that. I am usually working on old stuff. Thanks for the info.

 

[mudguppy]

... FYI, I was being supportive of the full hydro idea, not putting it down. ...

i understand. not trying to be hard about it, but these same statements come up a lot, and i wanted to be sure that the correct info is in this thread.

this is a very specific application and it is imperitive that you (not 'you' specifically, Big Red, 'you' in general) fully understand how the system would work in different applications.

the recent 'engine power loss' concern is hardly a concern in a manual vehicle, but is it a concern in an auto trans truck? well, yes and no. if you lost engine power at highway speed, there will be a decent amount of time that the torque converter will stay locked and will continue to turn the engine, thus creating pumping pressure. however, as you slow down, eventually the converter will unlock - then will you have enough torque converter speed to turn the engine over and keep the pump pumping?

what about if you're driving around town and at a relatively low speed and you lost the engine?

what if your auto trans doesn't have a locking torque converter?

what if you're at highway speed but your auto trans' locking converter is electronically controlled by the ECM of your electronically controlled engine and you lose the ECM?

what if it's a deuce w/ a manual trans and a rod goes through the block like they seem to do so often lately?

point: there are a tremendous amount of variables in each situation. it is important to know exactly how each system will be set up in order to do a proper failure mode analysis.

that's what this thread is aimed at - a specific set up that would give a high rate of reliability among various failure modes.

 

[59apache]

ok, i want to tell you my personal, real life experience with full hydro. i had case 4240 agri tractor with full hydro. the hydro pump fails, means lose power/pressure. this doesn't matter at high rpm, will say i didn't realise it. it fails without warning.

i was driving down the road and turn into a gas station.....and go (logically) from the throttle. the rpm drops and in this moment i haven't any assist. the hydro has an orbitrol but with the huge tires and the speed it was pure luck, that i didn't hit the pump....

it was a well maintened tractor.
a factory installed system
the vehicle was slow (25 mph)

and it is pure luck that i can tell you this story.

full hydro is in germany only for vehicles limited to 30 mph. for a good reason.
and as long as possible i drive only vehicles with a manual connection between steering wheel and steering box.
no steer by wire, no shift by wire, no full hydro.

 

[mudguppy]

... the hydro pump fails, means lose power/pressure. ...

yep. please see pt. 3 in post 94 above.

as already stated, it is a potiential failure point. in my opinion it is extremely unlikely to go out completely and without warning - but that's my opinion, but it actually happened to you, so i'm not arguing.

 

[59apache]

travis, the problem is:
pumps dies at high rpm, in this case they have close to no pressure at idle and low (but enough) pressure at high rpm.
while youre driving, you didn't realise the problem. steering effort is low, required pressure also.
if youre slowing down you have suddenly no steering. with 6 tons and a narrow street its hard not to panic. and i wasn't that cool to press the clutch and hit the gas to have high pressure.
the problem for me was in this second:
what to **** is happen???
if you don't know happen, you don't know what to do......
from one second to the other my vehicle changed from normal driving to out of control.

possible problems are also:

unusual high oil temperature
clogged filter
low oil (or break / leak on the suction side)
air in the system (leak)

if someone planning to build a full hydro i would suggest:
temperature and pressure gages
warning light / buzzer for low pressure



just my 2 cents

 

[mudguppy]

travis, the problem is:
pumps dies at high rpm, in this case they have close to no pressure at idle and low (but enough) pressure at high rpm. ...

i hear you - i wondered if that is possibly what happened.

... if someone planning to build a full hydro i would suggest:
temperature and pressure gages
warning light / buzzer for low pressure ...

this was a concern of mine also, since my hydraulic system is going through my hydro-boost unit. i put a large oil cooler with thermostatically controlled fan in the system, and a 1 gal resevoir. this should keep good temperature control on the system.

the problem with a low pressure buzzer is that it will always be going off: the system doesn't see high pressure until the demand (i.e. resistance/force) is there. driving straight or sitting still, you'll have minimal pressure at the pump because the steering valve flows freely in 'neutral' position, much like a power beyond valve. pressure is only seen once the steering valve directs fluid into the cylinder and the cylinder meets resistance. you won't know the pump isn't making pressure until you need it to and it doesn't.

a guage could work, but you'll have to look at it while turning the wheel to understand that there is no pressure. this will just tell you there is a problem somewhere in the system, but since you're cranking the wheel expecting power steering and not receiving it, chances are you already realize that there is a problem somewhere in the system.


don't get me wrong, i'm not trying to fool anyone into thinking that full-hydro is the right choice for everyone, or even anyone. in my application, it is a good choice given the truck mods. and as long as i fully understand the potential failure points and perform due diligence in PM and pre-drive inspections, then i am mitigating the risk as best as possible.

mitigating the risk, not eliminating the risk.