Power Steering Project

Now that the pump is mounted, it needs to be put into operation. The goal is to have power steering when you need it, but be able to turn it off when you don't. Also the goal is to have reasonable steering control if or when the pump fails. I call it "Fail Safe", part time power steering.

To accomplish this, there will be a shunt between the high pressure delivery line and the low pressure return line when the pump is off. Of course there can't be such a hydraulic connection when the pump is on. So the plan is to have a control valve in the shunt line. After considering several alternatives involving a solenoid valve, a check vale was settled on, for the shunt line. This passive device will close in response to the high pressure produced when the pump comes on. When the pump is off, any attempt to steer will relieve pressure in the high pressure delivery line and produce pressure in the low pressure return line causing the check valve to open.

As the driver turns the wheel, the piston is advanced in the cylinder attached to the rack. This relieves pressure behind the piston in the high pressure delivery line. At the sane time as the piston advances, it produces pressure in front of the piston in the low pressure return line. This combination of forcess opens the check valve and permits a reasonable level of unassisted steering control.

Update: This part failed in first few minutes of operation. Seee below.

This animation ignores the proportional nature of the system and focuses on the direction of flow between the compoonents.

It is intended to show how the flow between the pump and the gear box is always in the same direction, while the flow in the hydraulic cylinder reverses, as you turn from right to left and back again.

As the piston advances in the hydraulic cylinder, regardless of direction, and regardless of whether there is any asssist from the pump, fluid is forced out the return line to rhe reservoir in the pump. It is a function of the gear box to reverse the connection of the hydraulic cylinder lines to the pump when the piston changes direction.

The purpose of the shunt is to allow fluid to flow, more easily, when the pump is off. When the pump is on the check valve in the shunt is closed. When the pump is off the low pressure in front of the advancing pistion opens the check valve. The check valve cracking pressure is 5 psi.

What is important is that flow through the system is the same whether the pump is on or off. The gear box functions in the same manner. The advancing pistion always moves the fluid in front of it up the low pressure return line to the pump reservoir and, if the pump is off, draws fluid down the high pressure line through the check valve. When the pump is on and the check valve is closed, high presssure from the pump assists the advancing piston and the makes steering easier for the driver.

You can click on the animation to see a largerview of the action.

The low current wire from the dash sitch is yet to be installed.

Mr Brown returned with all the necessary parts to make the connection to the pump. He said they only had one fitting with that thread. As luck would have, that was all we needed.

We tried the pump and no luck. It turned out my ground cable from the Anderson connector was loose. Ed put a new lug on the wire and sanded the paint off the chassis behind the screw holding it and we were in business. After adding some merciron we started to get some assist. I paid Ed $302 for his days work and was on my way with the power steering working. When I arrived home, I couldn't hear the pump. After some diagnosic analysis I figured out the solenoid had failed. I discussed it with Dave Park and we decided I needed a continuous duty solenoid rather than the starter solenooid I had chosen.

I purchased an iluminated blue switch at AutoZone for $4.99 today. I will install this on the dash horazontally above the A/C switch shich is vertical. I also need to run the wire to the pump solenoid and replace the failed solenoid when the new Prestolite 15-139 Grounded 3 terminal, 12 volt, Continuous duty operation solenoid, at 100 amps arrives ($33.75 including shipping).

Intermittent duty 600 amps make, 
200 amps break. 
Features universal mounting, 
metal case construction & 
Hi-temp phenolic insulaton on all terminals.

February 11, 2009: The replacement solenoid arrived. I installed it in a few minutes and took it for a test drive. Drove six miles with power steering on the whole time. added fluid to reservoir.

Experience

On May 25th as I backed out of the driveway I noticed I had no power assist. After some pain and anguish I realized it could be just the fuse. I checked and sure enought the 40 amp fuse had blown. This pump draws 5-10amps when running and you don't turn the steering wheel at all, and when you turn the steering wheel draws 40-50amps. I was using a 40 amp fuse because it is the largest ATO/ATC fuse you can get. I have replaced the 40 amp fuse for now, but have ordered a Maxi Fuse holder so I can use a 50 amp fuse.

From February 11th to May 25th, I had no problems. So I hope, just a little larger fuse will do the job.

I have found that I was getting some shudder during turning. I followed the bleeding proceedure, jacking the front end and turning from lock to lock. I found over time that leaving the pump on full time eliminated this problem. Turning the pump on and off during driving seems to introduce air into the system.

The check valve allows manual un-assisted steering with no damage to the pump. When the fuse blew, I was able to drive with no problem. Once I replaced the fuse the shudder was back.

I had imagined turning the pump on and off while driving to conserve poower. This results in shudder during hard steering. I find the pump and other accessories cause the DC -DC converter to draw only 2.5 amps from the traction pack. This does not have a significant effect on range.

So, in conclusion, I would say this is not part time, fail safe power steering, but rather full time, failsafe power steering.

It may be that the check valve is unnecessary. But it does bypass the pump when the pump is off whether it is necessary or not.