system design

hi guys,
i am working on a project in which i need to control motion of two
cylinders simultaneously and also need to keep their motion free during
valve ports blocked. the pump i am using is of low capacity and i also
need to add an accumulator to the circuit. can anyone give me advice on
how to synchronize the cylinder motions by using low-cost DCVs and Pr.
Regulating valves. i also need advice on sizing of accumulator and
reservoir needed.
Reply to
gophane.harsh
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Dear gophane.harsh:
Position feedback, proportional control valve (or a servo valve, which requires high pressure and very good filtration).
3-way valve on each cylinder port.
Why? To "store" capacity for a while?
For accumulator and reservoir sizing, go to a hydraulics professional. It isn't rocket science, but you haven't given *us* enough information to help you.
What do you mean by "DCV"? I have used "temposonics" in balancing 4 ton tanks of various fluids between just two cylinders (think hammock).
You will get no sort of positioning control with a pressure regulating valve, unless you have a spring in the cylinder. If you have a spring in the cylinder, it won't be "keep their motion free".
David A. Smith
Reply to
N:dlzc D:aol T:com (dlzc)
hi david, i am working on roll control system development for a Sport Utility Vehicle. i am supposed to use the power steering pump in the initial stages. the system works in parallel with anti roll bar to additionally stiffen the suspension and thus achieving the roll angle reduction. During a straight drive this roll control system is supposed to be inactive (i.e. free floating) As the pump used is power steering pump, to fulfill the flow needs of the actuators i need to install accumulators in the circuit. also for concept proving we are trying to use solenoid operated direction control valves (DCV) i hope you might give me some advice on this situation.
harsh gophane
Reply to
gophane.harsh
Dear gophane.harsh:
Is this a school project?
Better to compress the inside shock(s) / extend the outside shock(s), making the vehicle roll into the turn.
Note that as the power steering pump is also largely inactive in straight line driving, you really will be taxing its capacities.
OK. The reservoir of the power steering pump needs to be increased to hold the volume of oil held by the total of the accumulators. Now for the bad news. The power steering pump runs at very low pressure in straight line driving. Your accumulators won't charge. You need a dedicated pump, in my opinion.
Thanks. It is always a good idea to define acronyms before you use them. It is a Good Idea (IIAGI).
Stiffening the suspension only serves to remove any hint the vehicle is in trouble. The driver can oversteer and have no ability to recover because he can't read the roll angle of the vehicle.
Better still, automatically apply the brakes if an SUV even requires "automatic" turning assitance. Anyone that drives one fast through a turn is trying to die. Off road ability and high speed do mix, unless you are a jet.
Just my opinion.
David A. Smith
Reply to
N:dlzc D:aol T:com (dlzc)
Using the power steering pump could overload it, or over heat it's oil. It's desined for "intermitant use" when the steering is central it's just idling as the rack alows the oil to bypass, any attempt to intercept this low pressure flow would mess up the control system of the rack. ( it works by blocking the flow partly diverting it to the left or right side and relies on a constant volume flow ).
Is the method of roll reduction going to require a large actuator effort, or will the oil pressure simply be giving a control type signal ( tipping the roll bar mounts with a jacking cylinder, or driving a pin valve to shut a restrictor in a shock absorber )
Another possible hazard.. could pressure pulses genetated by a road wheel hiting a bump feed back to the power steering and kick the steering ?
How would your system work in a skid situation if a driver applied negative steering lock ? would it be trying to flip the car ???
Regards Jonathan.
Reply to
Jonathan Barnes
snipped-for-privacy@gmail.com wrote in news:1141212144.679670.159160 @v46g2000cwv.googlegroups.com:
In addition to what the other two posters have said, DCV valves would be a bad choice, as they are either on or off, and the change is very sudden in either direction. Also, most are not rated for rapid, continuous use as I imagine could be the case in this situation. You would be better off with an electronic proportional valve, which are fast reacting and made for continuous variable use. Vickers, Bosch, Parker, and Moog are some suppliers.
Reply to
Anthony
the OP specified " low cost DCV valves ", The last time I looked the proportional valves where expensive, especialy in the size required to drive cylinders of suficent power to affect the roll of a car. Having said that, I think you are correct in saying that proportional valves are probably needed. Sometimes there is just no cheap way to get a job done... especialy when human safety is involved.
Reply to
Jonathan Barnes
Dear Jonathan Barnes:
You can actually get proportional performance from smaller, cheaper valves. But then your electrical requirements go up, since you are running them with PWM power supplies.
David A. Smith
Reply to
N:dlzc D:aol T:com (dlzc)
hi to all, as you pointed out i am not going to burden the powesteering pump. to simplify the things our suggestion was to disconnect the powersteering circuit and simply use the whole pump flow for this roll control system. now as this project is running on low budget and we have to prove this concept first so as to allocate more funds, we have no option but to use solenoid operated direction control valves. as far as roll system is concerned we are trying to use linear hydraulic actuators inbetween the chassis and lower wishbone to provide additional resisting force for the rolling action. the actual displacement needed for these actuators is only 40mm. but we have to use actuators of strokelength @ 140 mm to accomodate the complete travel of the suspension in reboun and bump. also the forces encountered were of the magnitude 3000 N and pressures encoutered in the system are 45-46 bar max.
Reply to
gophane.harsh
"Jonathan Barnes" wrote in news:du6dqm$ph1$ snipped-for-privacy@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com:
Expensive is a relative term though :)
Reply to
Anthony
snipped-for-privacy@gmail.com wrote in news:1141362682.432671.193070 @t39g2000cwt.googlegroups.com:
While fully realizing the low-budget deal, I have a feeling you are going to introduce some unexpected problems by using DCV valves, from what I understand from above, you are are basically going to use this as a shock absorber. You are possibly either dumping flow from the cylinder into a dead-head state, or possibly through a flow control valve or system.
Reply to
Anthony
Dear gophane.harsh:
Better still, add a second pump. Have you ever tried to steer a vehicle set up for power steeering, but with the pump not working?
On a "bump" it will be higher.
I'd recommend you consider air shocks, an air compressor, and a receiver tank. No "water hammer" effects to account for, pretty responsive, and already in a key place to allow them to do what you seek. The compressor can simply keep the receiver tank filled, and be powered elecrically. You will need position indication... as well as some sort of tilt sensor. Schaevitz made one that was really cool.
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David A. Smith
David
Reply to
N:dlzc D:aol T:com (dlzc)
hi all, i am not vehicle dyanmics expert so i may be making mistakes in judgement. can anyone suggest me about the references to be studied before plunging into this suspension related project work. i also came across some papers on the active roll control system from Cambridge Vehicle Dynamics Consortium (CVDC) but those are mostly related with heavy commercial vehicles. can anyone knows about research papers related to Active Roll Control in SUVs? hope to see you all soon
Reply to
gophane.harsh
Dear gophane.harsh:
You can write it when you are done.
A typical SUV will have similar suspension to a "heavy commercial" vehicle. The time constants will be smaller/shorter. The necessary instrumentation and controls will be similar, with an increased response time. Less total forces will be required.
You need to stop "looking outwards". This is your task. You have not accepted the advice you have been given. You either want to do it yourself, or you are looking for someone to hand it all to you free.
If you are ever looking for a small 12vdc electrically powered hydraulic power unit with integral reservoir, Oildyne (which has also been agglomerated by Parker) is a good choice for a research unit.
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David A. Smith
Reply to
N:dlzc D:aol T:com (dlzc)

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