[t vago]

Originally Posted by Ardent

Thanks for tolerating my questions and for the detailed responses.

No problemo. It's good to share information.

Originally Posted by Ardent

I'm guessing you meant pressure instead of speed there.

I would agree, except there is nothing I can find within either the MR2 service manual or on the intertubes that points to a "pressure sensor," as such.

There are a couple of error codes that the service manual mentions, that point to excessive current draw, and it also mentions that the motor has a speed sensor on it. I know that the combination of current draw and pump speed will directly tell what the loading is, and indirectly what the pump pressure is, so I assume that controlling pump speed is how steering system pressure is controlled.

I did find at one point a picture of a MR2 pump module with the electronics cover off, showing a nice large shiny coil of copper, but I cannot currently find this picture. I'm willing to bet that this coil is key to measuring current.

Originally Posted by Ardent

It sounds like after going through a "prime" routine, it enters a feedback loop that simply attempts to maintain system psi.

That's my guess, too.

Originally Posted by Ardent

Any thoughts on the feasibility of converting an existing pump from being belt driven from the crankshaft to either direct or belt driven from an electric motor?

Sounds like a workable idea. You could probably get away with a 3/4 HP motor, as that is effectively the rating of the Toyota EHPS pump motor. Belt-driven is probably more feasable than direct mounting, especially in a tight engine bay. You'd probably want to convert to some EHPS compatible power steering fluid, to minimize unnecessary pump loading, but you'd also want to make sure this fluid would still be compatible with your existing rack seals. I'm using AMSOIL synthetic universal power steering fluid, which claims to be compatible with both Toyota Type EH power steering fluid and Chrysler MS-9602 (ATF +4) power steering fluid.

Originally Posted by Ardent

It seems like it'd be relatively easy. Find a spot to tap in a pressure sensor and then add an Arduino with input from that sensor and the VSS with a PWM output from a PID routine to a motor speed controller. Hmmm.

I was thinking along similar lines about creating a motor controller for the older 1st generation MR2 pump. That system had a separate computer, motor driver, and pump/motor unit, and the computer and motor driver each were pricy. That system also required the usage of a steering wheel rate sensor, which I'm sure is not necessary. Only thing I'd do differently would be to measure current draw and pump speed, instead of using a pressure sensor.