Emergency Steering Reservoir Size

[paulgerber240]

Hi All,

We currently have a emergency steering system in our vehicle that is connected to the driveline to enable power steering should the engine cut out.
The reservoir currently fitted needs to be optimize for space and I was hoping you guys could give me a hand on what the typical size is and how to improve it.

Information:
Pump: 27cc
RPM: up to 3000 rpm
Fluid: Mobile 220 ATF
Reservoir Size: 19 l fluid volume
Working Pressure: 110 bar
Maximum flow for working pressure: 30 l/min (the rest will be dumped with a flow control valve)

The system as is has been tested an we did not encounter any heating problems.
Note: The pump will always move fluid when the vehicle is moving but will only generate pressure when needed (this is about 1% of the time)

Thanks for the help!

 

[GregLocock]

I think you need to define what usage profile you are protecting against. For example you might define it s full maneuvaribilty at speeds above 30 kph for 30s. Or something like that. I'm guessing you are talking about military or mining.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[MintJulep]

By reservoir I guess that you really mean accumulator? I.E. A bladder or diaphragm type?

You have a back-up pump driven from the vehicle drive shaft? "In case the engine should cut out".

In case the engine cuts out I guess the vehicle will stop within some time.

So do you need steering for any longer than that time?

And if the back up pump is powered by vehicle motion than you really only need storage when the speed drops below the pump capacity to keep up.

 

[BrianPetersen]

"The pump will always move fluid when the vehicle is moving but will only generate pressure when needed (this is about 1% of the time)"

... which means the valving that controls the power assistance is probably the usual open-center design (it just passes flow through, unless the driver is applying force in one direction, in which case the valve moves off center and causes back-pressure which is what applies the actual power steering assistance.

... which means that a pressure reservoir in the pump output circuit won't accomplish anything because it will simply empty itself out when the steering is centered (not applying force).

Or maybe I'm wrong. Schematic, please.

 

[BrianPetersen]

Old thread that may have discussion of interest to the original poster.

https://www.eng-tips.com/viewthread.cfm?qid=415380

 

[paulgerber240]

Hi Greg Locock

The usage profile:
120km/h for 90s - Engine cut out at high speed
50km/h for 5min - High speed towing wih engine off
30km/h for 2 hours - Low speed towing with engine off

The system is a emergency steering system, I am not concerned that it will overheat under pressure as this will only be for a limited time. My concern is with the circulation of the high volume of oil through the hoses. Steering gear used ZF THP 92, it has a supply for normal steering operation (this system is cooled and not a issue) and a separate supply for emergency steering that is only active should the normal supply be interrupted.

By reservoir I mean hydraulic tank.

Thanks for the feedback and help thus far.

 

[MintJulep]

What is the maximum volume of the devices being powered? That is the driver for the reservoir size.

 

[BrianPetersen]

Ask ZF.