Full Hydraulic Steering

 

   
 
 

Full Hydraulic Steering - Page 2

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The ram is coupled to the tie rod with this bracket, made from a 1" thick piece of steel.   I added a gusset to the end and made it as long as possible. 

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Steering stops are critical on a full hydro system and should be on the cylinder itself.  Do not rely on the steering stops on your knuckles to hold up to 2-4000 lbs. of force.  My system is setup so when the ram is fully extended, I am turned as far as the knuckles will allow.  So the ram bottoms out on itself internally.  My steering only requires roughly 4" of stroke to fully turn the wheels lock to lock, so I made a small collar which I slipped over the cylinders shaft.  I used a pair of shaft collars to keep this collar from sliding around on the shaft.  The inner shaft collar has a healthy chamfer on the inside diameter to ensure it bottoms out on the cylinder body and not the seal that protrudes slightly from the body.  When driving this setup off road I will often turn till I can't turn anymore and then back off slightly.  The cylinder has enough force that you can hold tires at any angle without needing to provide a lot of steering input.  This is much different than when I had a steering box.  The usual routine back then was to turn the wheels as far as I could and then continue applying force in that direction on the steering wheel to try and keep the tires from getting pushed the other way by the obstacle.

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Pressure is supplied to the orbital valve via a power steering pump.  The more flow the better, usually measured in gallons per minute (gpm).  I purchased (from Spidertrax) an AGR TC style pump which is modified to put out roughly 1500psi of pressure and 4-5 gpm.  They also supplied a bracket and pulley designed for use with my 1.6, 16v motor. This pump has a reservoir attached to it which caused me a lot of problems.  You need a pump with an external reservoir and the reservoir needs to be tall, the bigger the better.   When I started driving with the system, everything was fine until the engine rpms got above 2k.  At that point the reservoir would be sucked completely dry causing a ton of noise due to pump cavitation.  You could add more fluid but as soon as you shut the motor down it would slowly fill the reservoir to the top and then overflow.  Also, since the cylinder displaced more fluid in one direction than the other, that extra fluid had to be taken into account as well.  Bottom line is a small reservoir will not work.  I ended up making an adapter which was pressed into the pumps input port (like some YJ's).  I tapped the other side of the adapter for a 3/8 npt fitting.  I am using 5/8" hose to feed the pump.

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The original reservoir had a smaller fitting on it and I believe may have been partially responsible for the fluid starvation.  Here's a picture of the orifice size of the original fitting on the left and the new fitting that screws into my adapter on the right.

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I had a stainless steel tank made that holds a gallon of fluid.  The tank should be mounted so it is the highest point in your fluid circuit to help in bleeding all the air out of the system.  I am experimenting with running the system sealed.  Based on some calculations a co-worker did, we estimated that the tank will build up a max of 20psi due to a 100 deg rise in temperature of the fluid.  I put a small pressure relief valve (seen on the far left in the picture above) on the tank to relieve any pressure built up above this.  We'll see if this setup works.  I would like it sealed to avoid any leaks if I roll the vehicle.

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Back to the adapter I made.  It's basic shape resembles the orifice on the reservoir that attaches to the pump (2nd picture above).  I also machined a groove in the adapter for an o-ring for a secondary seal in case the press fit wasn't enough.