Strategy to manage Toyota MR2 SW20 Power Steering Module

[Aqmar]

My plan is to have the Link Fury G4x to manage the MR2 SW20 Power Steering (PS). Let me explain some overview of the MR2 power steering module.

The OEM setup of this PS is a separate systems. It has it own ECU to manage the PS motor. The module consist of

1) PS ECU

2) PS hydraulic motor 80ampere

3) PS relay (uses a solid state relay)

4) Steering angle sensor

On OEM setup, The PS will operate once the PS ECU receive input from the steering angel sensor (activate after 33 degree angle) and speed sensor.

The PS motor will run with 9-11v current with the combination of this condition

1. PS angle sensor reads more than 33 degree; and
2. speed = 0km/h

The PS motor will run with 3-5v current with the combination of this conditions:

1. PS angel sensor read more than 33 degree; and
2. Speed = 65km/h

To my understanding, this PS module is a electrical run hydraulic systems. The steering angle sensor will determine how much PS oil need to pump according to angle (correct me if i am wrong) when the PS motor runs.

My question is, how can I get Link G4x Fury to run the PS motor according to this table:

Vehicle speed (km/h)	0	10	20	30	40	50
PS Motor Speed (%)	100	60	50	40	25	0

 

2. Which Link g4x AUX can manage the OEM relay? Or should I just get other type of relay?

3. Anyone experience running the MR2 PS motor with LINK ECU? Care to share some wiring diagram of your setup? Anything that I should know as a heads up before I embark on this project?

[ellisd1984]

I've got a MK3 MR2 power steering pump and wiring loom I'm hoping to use with the Link g4X pnp to replace the mechanical power steering on my celica GTfour. I'm a while awy from fitting it though but would be interested in how you got this system running so I've got something to compare to.

[Adamw]

As far as my understanding goes, to vary the PS assist you need to vary the pressure, changing the motor speed will not vary pressure, only flow rate.  They probably vary the motor speed when high flow rate is not needed to save power, but I expect there must also be some other type of pressure control signal to vary the assist level based on speed etc.

 

[Aqmar]

@ellisd1984

I am not overall clear on the electric-hydro PS that MR2 is running. But I am interested to have it manage by Link ECU as I feel maybe we could have it to manage it better. Therefore I am hoping could have a good advice on how could I go about on this plan.

From the manual of MR2 I couldn't find any pressure control but based on logic, the operation should be as what @Adamw explained 

Therefore I try my best to lay out the overall mechanism on my 1st post here. Hope someone here has had the experience setting up the PS module of Toyota MR2 SW20 so we could make a good reference out of it.

 @Adamw, will increasing the flow rate decrease the pressure in a constant area? Means to say here, by increasing the speed of the motor, won't it decrease the pressure within the PS  systems? (Bernouli's Principle)

 

[Adamw]

20 hours ago, Solace said:

From the manual of MR2 I couldn't find any pressure control but based on logic, the operation should be as what @Adamw explained 

Maybe the assist effort control is in the rack?  Or maybe there is no effort control and it just runs constant effort at all speeds.

 

20 hours ago, Solace said:

 @Adamw, will increasing the flow rate decrease the pressure in a constant area? Means to say here, by increasing the speed of the motor, won't it decrease the pressure within the PS  systems? (Bernouli's Principle)

If you think of a car that has an old belt driven pump, when you rev the engine (increase pump speed/flow), the steering doesnt suddenly get lighter.  There is a releif valve so pressure stays constant even at near minimum speed.  Later cars usually have some sort of assist control to give more feel at higher speeds, which could be done either at the pump end or the rack end.

[ellisd1984]

From memory I think the pump operation is quite basic.  It runs at 100% up until a certain road speed then switches to a lower setting (maybe through a resistor i'm not 100%)  I know that's how they controlled there fuel pumps at the time.  I'd assuming there's some sort of valve in the rack that lightens the steering if the pump speed gets above a curtain point

https://www.dropbox.com/s/ul1bl1ggha9axaj/Screenshot 2020-11-28 at 05.58.56.png?dl=0

https://www.dropbox.com/s/c4e93qpoimu72pk/Screenshot 2020-11-28 at 06.02.41.png?dl=0