Full hydraulic and hydraulic assisted steering

[Dave W]

A growing number of challenge vehicles, especially in the UK seem to be moving towards full hydraulic steering or hydra assist steering. I can understand some of the benefits but I'm trying to figure out what the limitations are in the way they behave. So, if you have first hand experience of either full or hydro assist could you answer a few questions regarding their use... preferably with some indication of the supplier so I can compare prices.

1) Does the steering self centre at all if you're travelling at, say 20MPH on a firm surface ?

2) If the engine stops running for any reason, how much control do you have of the steering and for how long ?

3) Do the systems have a failsafe - if, for example, a hydraulic pipe to the ram was damaged would the steering simply remain where it was, force the steering to full lock or centre the steering ?

4) What pressures do the systems actually run at ? (Some of the pumps I've been looking at give a maximum pressure but not really an indication of the actual pressure they run at normally).

[elbekko]

1) Does the steering self centre at all if you're travelling at, say 20MPH on a firm surface ?

That depends on the type of steering valve (often, possibly wrongly, referred to as the "orbital") used, load-reactive or not. Usually a fair amount of caster is added too to make self-centering more pronounced.

2) If the engine stops running for any reason, how much control do you have of the steering and for how long ?

You can still steer with the engine off, but it's very hard work, even on flat tarmac.

3) Do the systems have a failsafe - if, for example, a hydraulic pipe to the ram was damaged would the steering simply remain where it was, force the steering to full lock or centre the steering ?

I don't think there's any such failsafe for the last bit of hose, being from the overpressure valve to the ram. If one of those hoses is damaged, you'll have no control.

Then again, you also don't have much control when the balljoint on the drag link breaks...

4) What pressures do the systems actually run at ? (Some of the pumps I've been looking at give a maximum pressure but not really an indication of the actual pressure they run at normally).

Pretty high pressures, when you're steering against a solid block or something you're probably looking at the maximum pump pressure, or whatever you set the overpressure valve to.

Have a look through the hydro steer bible if you haven't yet, very informative:

http://www.pirate4x4.com/tech/billavista/PR-Hydro_Steering/index.html

[simonr]

1) Does the steering self centre at all if you're travelling at, say 20MPH on a firm surface ?

2) If the engine stops running for any reason, how much control do you have of the steering and for how long ?

3) Do the systems have a failsafe - if, for example, a hydraulic pipe to the ram was damaged would the steering simply remain where it was, force the steering to full lock or centre the steering ?

4) What pressures do the systems actually run at ? (Some of the pumps I've been looking at give a maximum pressure but not really an indication of the actual pressure they run at normally).

1) If the system is specified correctly then yes. When people have just sourced a random steering valve from eBay with a random ram that looks about the right size - generally no! If the valve is not load sensing (quite a few are not) then it will not return to centre and the steering wheel will be way too light.

2) With a load sensing valve, properly matched to the task, it should be the same as loosing power steering on a regular steering box. Hard work - but possible.

3) No - but nor does your normal steering!

4) Generally about 1500 PSI though some more, some less - so about the same as normal power steering.

The first time I tried it was with a valve & ram I had lying around. The steering was very light and could turn lock to lock in half a turn of the wheel! Made it quite exciting to drive!

I've been through various power assist schemes to full hydro and now back to a regular steering box! Why?

Hydro gives an 'advantage' in terms of the strength of the system and how much force you can deliver to the wheels to force them to steer. However, unless you are careful, this extra force can snap ball joints & steering arms a little too easily!

After a few too many of these, I had a look at why I was breaking boxes in the first place. The answer was the scrub radius of the wheels. It meant that more force was being transmitted back to the box. I changed the offset of my wheels back to almost zero and now even without the power assist, the wheels are easy to steer and the broken bits are a thing of the past. Hydro was just covering up the actual problem and moving the failure point!

Si

[zim]

I can only agree with all that's been posted above.

Mine doesn't self centre so the first time you try and drive fast going round a corner you **** yourself ! My truck isn't made for speed and it isn't nice going fast.

Likewise, when in mud, many a time my co driver will have to tell me that my wheels are pointing one way or the other and i'm just ploughing through.

BUT it was a very impressive upgrade for challenging I run M20 rosejoints in double sheer.

G

[tacr2man]

THis is intended for off road use only I take it ? , as not possible on road without mech back up.

Hydro assist no probs , as used on quite a few trucks years back , You could also by universal hydro assist kits , even for series landys .

[dirtydiesel]

A growing number of challenge vehicles, especially in the UK seem to be moving towards full hydraulic steering or hydra assist steering. I can understand some of the benefits but I'm trying to figure out what the limitations are in the way they behave. So, if you have first hand experience of either full or hydro assist could you answer a few questions regarding their use... preferably with some indication of the supplier so I can compare prices.1) Does the steering self centre at all if you're travelling at, say 20MPH on a firm surface ?2) If the engine stops running for any reason, how much control do you have of the steering and for how long ?3) Do the systems have a failsafe - if, for example, a hydraulic pipe to the ram was damaged would the steering simply remain where it was, force the steering to full lock or centre the steering ?4) What pressures do the systems actually run at ? (Some of the pumps I've been looking at give a maximum pressure but not really an indication of the actual pressure they run at normally).

(1) self centering is almost entirely down to caster angle, the quality of the steering valve can have an effect. Mine would self center perfectly.

(2) I set my system for around 4 turns lock to lock, with then engine off the steering was a little heavy stationary but as soon as the wheels are turning its light as.

(3)steering stays were it is.

(4)I used a stock 300tdi pump with a drilled output, then a PSC super pump, steering was insanely light with the PSC pump

I could park up tight against a wall with the wheel and push the car entire sideways with no effort.

[Dave W]

Thanks for all the responses, the link to pirate4x4 was really useful, can't believe I've not found that before, it cleared up a LOT of the misconceptions I had picked up.

I hadn't understood before how the steering could work without the pump but the inclusion of a "manual" pump in the steering valve makes a lot of sense.

THis is intended for off road use only I take it ? , as not possible on road without mech back up.

Is there actually a specific regulation for that ? I've not been able to find any mention of it. The only relevant regulations I have been able to find regarding C&U, MOT and IVA are the requirement for the steering to self centre and the requirement for the steering to function without assistance (the engine turned off). The more I read about it it seems that providing the steering valve is of the correct type it will meet both of those requirements. I have not been able to find any requirement for a mechanical linkage as such.

Any pointers to the appropriate legislation to the contrary would be a great help as that would have a major effect on the decision.

[dirtydiesel]

There is a regulation concerning speed limits and hydraulic steering,

On agri machines hydraulic steering is only really fitted to stuff with a 40kph limit, faster stuff nearly always has a steering box.

My biggest problem was overpowering at speeds over walking pace, I could have done with an e-mag clutch on the pump to turn it off assistance on the road.

I drove mine on the road once, for about 4.5 miles up to about 60mph, utmost concentration required and a sit down afterwards.

Jez drove a few thousand miles on his full PSC steering setup with no such issues.

PSC's valves and systems have a really good reputation for great "feel" look around the ultra4 racers in the USA they almost exclusively use PSC stuff.

[Hybrid_From_Hell]

Very interesting thread

What about Glyn Lewis Hydro assist ?

Llama 4x4s Similar kit,

how are they both on the Qs above ?

Nige

[Dave W]

There is a regulation concerning speed limits and hydraulic steering, On agri machines hydraulic steering is only really fitted to stuff with a 40kph limit, faster stuff nearly always has a steering box.

I've seen this quoted before but try as I might I've been unable to find any such piece of legislation that would apply to a hydro steer system that can still steer without hydraulic assistance. Do you have a reference for this regulation/legislation ?

[Daan]

4) Generally about 1500 PSI though some more, some less - so about the same as normal power steering.

Do we have a figure for the flow and pressure of a standard landrover pump vs a typical hydro steer pump?

[Hybrid_From_Hell]

Alfred Murray used a PAS pump for the Mile marker, I think that was limited to 1400 PSI ?

[elbekko]

I've seen this quoted before but try as I might I've been unable to find any such piece of legislation that would apply to a hydro steer system that can still steer without hydraulic assistance. Do you have a reference for this regulation/legislation ?

Define steering without hydraulic assistance. With the engine off, you're still using the hydraulic system to steer, and the steering valve is a hydraulic pump of sorts.

While some may argue that a hydraulic linkage is a mechanical linkage because it can't compress, I'm not sure the law sees it that way.

I know of at least one vehicle that had a plate and MOT with full hydro steering, not sure how that was obtained though

[dirtydiesel]

I think my PSC one was rated at 1600psi and 6.8gpm flow, I'm sure this info used to be on here website but I cannot find it now?

[Daan]

youre still ok on mot I believe. But I also believe this thread is meant to be purely technical, not legal....

Daan

[dirtydiesel]

youre still ok on mot I believe. But I also believe this thread is meant to be purely technical, not legal....Daan

It's in the wrong section then!!

[muddy]

The 40 and 50kph tractors at work do not have any kind of steering box neither to the new direct drives 55kph afaik and fendts such are up to 65kph do not have a steering box either, however the mog trantor and fastrac all agricural high speed vehicles designed as such from the outset have steering boxs.

Early mb tracs have two double acting rams and a track rod however I'm not sure about later ones.

Will.

[iomlt]

Gwyns hydro assist with the question

1) Does the steering self centre at all if you're travelling at, say 20MPH on a firm surface ?
2) If the engine stops running for any reason, how much control do you have of the steering and for how long ?
3) Do the systems have a failsafe - if, for example, a hydraulic pipe to the ram was damaged would the steering simply remain where it was, force the steering to full lock or centre the steering ?
4) What pressures do the systems actually run at ? (Some of the pumps I've been looking at give a maximum pressure but not really an indication of the actual pressure they run at normally).

1. Yes just alittle slower in return

2. Yes normal operation as factory set up just alittle heavier

3.if you bend snap the ramp i guess it will keep running but nnot very well as its just the steering box.

4. factory lr pump.

since fitting mine, far more steady on the road. steering much more positive and in the heavy stuff assists the steering nicely. great bit of kit.

[CwazyWabbit]

Interesting discussion about the legality of it here http://forums.lr4x4.com/index.php?showtopic=45927

Seems from that thread an SVA inspector had said doen't need mechanical link as such but must be able to steer in the event of hydraulic failure such as a hose bursting. Not sure how you achieve that without a mechanical link. Also how does rear steering work? Is it a case that rear steering self centres in failure mode so is fine?

[Dave W]

youre still ok on mot I believe. But I also believe this thread is meant to be purely technical, not legal....

The legal aspect is important to me too. My initial understanding was that hydro steer was not road legal BUT the only evidence of this amounts to "hearsay" on forums with no reference to the actual legislation or documentation that would back it up. I've spent some time looking at it and have not been able to find any legislation at all that would make such a system illegal for use on UK roads.

The legislation and guidelines that I have found so far primarily cover the condition and operation of the steering components that are fitted. I have not found any legislation or even guidelines that would prevent hydro steer being fitted to a road legal vehicle providing the ability to self centre and control the vehicle when the engine is stopped is met.

I'd prefer not to get into further swapping of "hearsay" but if anyone has references to specific regulations/legislation or even guidelines that would make such a system road legal or not, it would be very useful in the decision making process.

[RedLineMike]

I had a good read through the sva/iva manual & couldn't find any reference to requiring a mech link, the only thing I did find was that in the case of full hydro steer that its up to the person presenting the vehicle for test to prove to the tester that its adequate, when I get home ill list the paragraphs etc as I've just got in the door from Koh

[CwazyWabbit]

http://www.dft.gov.uk/vosa/repository/M1%20IVA%20Inspection%20Manual.pdf Passenger car
http://www.dft.gov.uk/vosa/repository/N1%20IVA%20Inspection%20Manual.pdf Light goods vehicle

Either could apply to your vehicle I assume.

Both contain the following in section 5 Steering effort.

Vehicles fitted with complex drive by wire or hydraulic steering systems
cannot be assessed by inspection, therefore documentary evidence must
be provided.

3. The steering system must operate smoothly from lock to lock
and without undue stiffness with and without power assistance
(if fitted).

5. If the vehicle is fitted with power assisted steering, the steering
must still operate with the assistance disabled.

8. When the vehicle is driven at speeds above 10mph, there must
be a degree of steering “self centring” evident.

Nissan are also releasing an electronically steered vehicle but with a backup clutch to reconnect a mechanical element in the event of failure http://www.bbc.co.uk/news/technology-19979380

The construction and use regulations that I could find just said steering should be maintained, nothing about it's design.

So like you I have been unable to find any documentary evidence that says full hydro is illegal. It's hard to prove a negative.

EDIT: hadn't read RedLineMikes post above, guess I should refresh the page before posting!

[RedLineMike]

In all fairness you have posted what I was gonna post anyways

[nicks90]

if having no mechanical link between the steering wheel and road wheels was against the law, or C&U - then how did citroen get a licence to sell the Citroen SM back in the 70s? that uses a purely hydraulic system with return to centre being controlled by a speed sensitive seperate hydro tank 'fighting' the steering hydraulics.

[Tom A]

Wikipedia seems to have the answer for the Citroen SM (it did retain a mechanical link) and I think I have the answer to the wider legal question. There's nothing in C&U about the need for a mechanical link but there used to be a requirement in UN Reg 79 (and the equivalent EC regulation) which governs all passenger and goods vehicles in the EU. However, with the progress in electric steering systems and driver aids, this has been relaxed. The intro to Reg 79 has a pretty good explanation:

"The intention of the Regulation is to establish uniform provisions for the layout and performance of steering systems fitted to vehicles used on the road. Traditionally the major requirement has been that the main steering system contains a positive mechanical link between the steering control, normally the steering wheel, and the road wheels in order to determine the path of the vehicle. The mechanical link, if amply dimensioned, has been regarded as not being liable to failure.

Advancing technology, coupled with the wish to improve occupant safety by elimination of the mechanical steering column, and the production advantages associated with easier transfer of the steering control between left and right hand drive vehicles, has led to a review of the traditional approach and the Regulation is now amended to take account of the new technologies. Accordingly it will now be possible to have steering systems in which there is not any positive mechanical connection between the steering control and the road wheels."

Link to reg 79 if you want full details - http://www.unece.org/trans/main/wp29/wp29regs61-80.html

I'm not sure if IVA / your local MOT tester is fully up to date with this yet!