Flow Solenoid Control Conundrum

[bmsluite]

Hey guys,

I am trying to control a solenoid that controls the flow of power steering to my steering rack on this race car I have.
Currently the car controls the flow based on speed, engine rpm, and steering angle. As you can imagine this is not ideal on a race track. Having it change all the time is disconcerting.

I have attached a few pictures:
The first picture is the voltage and amperage range the car uses to control the flow. I need to match these.
The other two pictures are of an LM317 board I picked up showing the minimum voltage range and the highest voltage range I wish to use.

Will this work?
I have a bit of a stupid question: When I hook up my meter to the output of the LM317 I always get 5A. No matter where I put the voltage it is always 5A. When I hook this unit to the actual solenoid will the amperage vary along with the voltage because of Ohm's Law?

I know the position of the solenoid is what is important. Wattage to solenoid is the most important. Do I need a rheostat along with the LM317 to control the amperage output as well? The graph shows very low amperage output. I attempted to hook up a 20 OHM rheostat in a way that controls the current, however, that only gave me a range of between 4-5A unless I was wayyyy on the bottom end. There I could barely control it between like 2-4A but it was jumping all around all over the place. I imagine that will be very bad for the solenoid.

Should I be using something completely different? Am I approaching this all wrong?

I will read and appreciate all comments, opinions, and roasts of my lack of electrical prowess.
Thanks!

 

[rjenkinsgb]

I initially though you were trying to control an actual steering position valve, which would have been a big no-no!


However, having cross-referenced the graph, the solenoid appears to be a bypass control on an otherwise conventional hydraulic power steering system that uses a mechanical proportional hydraulic valve in the column.. Nissan, probably??

As long as that is correct, then your adjustable power supply board idea will work.

The output current will be (output voltage / load resistance).

The solenoid will likely have a very low resistance, so you need to add a fixed resistor in series with it.
(A normal potentiometer can only take milliamps; they are not suitable for high currents).


If the total resistance of the solenoid plus the fixed resistor was six ohms, that would give, over the voltage range you show, a current range of
1.2 / 6 = 0.2A up to 6.5 / 6 = 1.08A, near enough the 1.1A maximum in the graph.

The fixed resistor needs to be a high power one such as a 10W or larger metal cased type.
I'd try 5.6 Ohms and measure the current with that.


Note that if your circuit fails, you will lose all power steering!

A safer option is temporarily use that setup to find out the ideal current, then replace it with eg. a 50W fixed resistor feeding directly from switched battery power, with the resistance value selected to gives that same current to the solenoid.

The actual power dissipated in the resistor would be somewhere from 6 - 15W or so, depending on the current you chose, but using one rated well above that ensures it's not running at high temperatures that could cause failure.


Another safer option is to use a fixed resistor that gives eg. just under the 0.4A direct from switched battery power, around 33 or 39 Ohms, then use a couple of switches to connect one or two more similar resistors in parallel with that, so with both switches on, solenoid gets the full 1.1A current via all three resistors in parallel.

No electronics and you can select the "range" at any time.

The actual resistance values depend on the internal resistance of the solenoid itself.

(Note: Only ever use screw terminals, crimp terminals set with a good compound action crimp tool, or twisted, properly soldered then sleeved connections.

Neither the common plier style crimp tools or the "heatshrink-containing-solder" type wire connections produce 100% reliable joints and should never be used in any safety related application).

Any modifications you do do depend on the quality of the parts and installation and are done totally at your own risk!