Electric over hydraulic power steering

[Russell_E]

I am currently in development of a specialized off road low speed hunting vehicle that I hope to put in to low volume production.

This is an electric vehicle so there is no typical power steering pump available for the steering. It is also drive by wire with a joystick controlling the traction motors and steering. The vehicle is approximately 5,000# empty weight and has a max speed of 30 mph.

For steering I am currently using a fairly standard SPX Stone double acting pump and manifold, mated to a variable speed 1/2 hp motor which is controlled by a Roboteq motor controller. The pump drives a typical double rodded steering cylinder from PSC motorsports.

In the current setup the joystick commands the pump to turn the desired direction and how fast to turn. Although this system does work, I am not happy with the the performance.

I have decided I need to add a sensor and feedback loop so that when the joystick is deflected a certain amount, the steering the angle of the wheels will move to that position. This is all doable with the pump/motor/controller that I have but it will take a good deal more programming since the program has to tell the solenoids when to open and close in addition to telling the motor to run and how fast.

Since I hope to put this vehicle into production, I need to keep my parts count as low as possible. My question is this:

Could I easily mate a reversible hydraulic motor to my variable speed electric motor and use it as the pump for my double rodded hydraulic cylinder? If so, this would simplify my system.

My issues with going this route are that I have no experience with a closed loop system like this. How do you include an oil tank in the system for fluid loss due to leaks, etc? When the motor stops to hold a position, will I have drift? If so, can I install pilot operated check valves on both sides of the hydraulic motor to prevent drift?

In my research on the internet I have found similar hydraulic power 7nits for marine autopilots that do this exact thing. Unfortunately they are just a little low on pressure and volume to meet my specs. I really need about 2 GPM at around 800-1000 psi to meet my design goals.

If anyone has any ideas they would be greatly appreciated. Additionally, if anyone knows of a product out there that already does this I would love to hear obit it also.

 

[hydtools]

http://ph.parker.com/us/en/compact-hydraulic-power-unit-165-series

Ted

 

[Russell_E]

Thanks for the reply Ted but that power unit is basically what I am using right now except that I put the manifold and pump together with a variable speed motor that peaks at 1750 rpm. The motor that comes with that and other power units like it turn constant speed at typically 3000-5000 rpm which makes them fairly loud. Low noise is very important to me since this is an electric vehicle used for hunting. The electric motor on those units only turn one direction and it uses the solenoids to change the direction of flow.

I am trying to find a simpler solution that would use a relatively inexpensive gear motor and just reverses the electric motor to change the direction of flow. This is how most of the boat steering units work but all that I have seen off the shelf don’t produce enough flow for my application.

 

[Russell_E]

One other thing I failed to mention is that I need a variable speed motor so that the rate of turn can vary inversely with the speed of the vehicle. I don’t want it to turn as fast at higher vehicle speeds since that could create a dangerous situation. This is fairly easily done with the motor controller I have.

Here is a link to the gear motor I think might work as a pump:

https://www.surpluscenter.com/Hydra...ker-MGG20016-BB1A3-Hydraulic-Motor-9-8500.axd