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Old 04-19-2019, 11:44 PM   #1
Armorican
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Default 2002-2007 Vue EPS (electric power steering) question

Hello Vue enthousiasts!
I have owned many S series vehicles over the years, but I know next to nothing about the Vue model.
I have a project to add power steering to an old car for someone who has joint issues and doesn’t want to give up on driving their beloved car.
I have gathered conflicting information from my online research:
- The EPS motor has a fuse of 40 amps yet could need up to 65 amps during very short time periods under heavy load
The EPS fuse in the cab seems to be rated 10 amps, so my presumption is that it protects the electronics only, which I am not planning on using.

Using that non OEM controller, I am trying to figure out if I could use the Vue’s Electrical Power Steering system (the mechanical parts only) to help steer during very low speed maneuvers. I know of people who use such a setup with great success on different vehicles.
The vehicle that requires modification weights just below 1100 lbs, has narrow 6" wide tires, and has an alternator rated at 30 amps (engine is rated a whopping 29hp/22kw). The EPS from the Vue physically fits with some ingenuity, but may draw way more current than the car’s alternator/regulator can safely produce, even under light load.

Basically, I am hoping someone knows about the current draw for that EPS motor under light load and can share those numbers, or give a definitive answer on the feasibility of the project (and hopefully the rationale behind their answer ).

Last edited by Armorican; 04-19-2019 at 11:46 PM.. Reason: Clarity

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Old 04-20-2019, 12:15 AM   #2
fdryer
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2003 L-Series 3.0L Sedan
Default Re: 2002-2007 Vue EPS (electric power steering) question

Here's a reprint for '05 Vues using electric power steering. Rated for 65 amps. I don't know how eliminating part of the electronics will allow using it as its an all inclusive unit requiring sensors, circuitry to convert sensor signals for commands to the steering amplifier to raise current needed to power the steering motor. Unless you have specific info from other sites that details how to adapt and modify eps to another vehicle and how to bypass circuits, there's more electronics than most are willing to invest time and effort to modify it for custom steering in another vehicle. It may be better to find older manual steering systems that are geared before power steering became a standard.

2005 Saturn VUE - FWD

Power Steering System Description and Operation
The electric power steering (EPS) system reduces the amount of effort needed to steer the vehicle. The system uses the body control module (BCM), power steering control module (PSCM), torque sensor, discrete battery voltage supply circuit, EPS motor, serial data bus, and the instrument panel cluster (IPC) message center to perform the system functions. The PSCM, torque sensor, nor the EPS motor are serviced separately from each other or from the steering column. Ant EPS components diagnosed to be malfunctioning requires replacement of the steering column assembly, also known as the EPS assembly.

Torque Sensor
The PSCM uses a torque sensor as it's main input for determining the amount of steering assists. The steering column has an input shaft, from the steering wheel to the torque sensor, and an output shaft, from the torque sensor to the steering shaft coupler. The input and output shafts are separated by a torsion bar, where the torque sensor is located. The sensor consists of a compensation coil, detecting coil, and 3 detecting rings. These detecting rings have toothed edges that face each other. Detecting ring 1 is fixed to the output shaft, detecting rings 2 and 3 are fixed to the input shaft. The detecting coil is positioned around the toothed edges of detecting rings 1 and 2. As torque is applied to the steering column shaft the alignment of the teeth between detecting rings 1 and 2 changes, which causes the detecting coil signal voltage to change. The PSCM recognizes this change in signal voltage as steering column shaft torque. The compensation coil is used to compensate for changes in electrical circuit impedance due to circuit temperature changes from electrical current and voltage levels as well as ambient temperatures for accurate torque detection.

EPS Motor
The EPS motor is a 12 volt brushed DC reversible motor with a 65 amp rating. The motor assists steering through a worm shaft and reduction gear located in the steering column housing.

Power Steering Control Module (PSCM)
The PSCM uses a combination of torque sensor inputs, vehicle speed, calculated system temperature and the steering calibration to determine the amount of steering assist. When the steering wheel is turned, the PSCM uses signal voltage from the torque sensor to detect the amount of torque being applied to the steering column shaft and the amount of current to command to the EPS motor. The PSCM receives serial data from the engine control module (ECM) to determine vehicle speed. At low speeds more assist is provided for easy turning during parking maneuvers. At high speeds, less assist is provided for improved road feel and directional stability. The PSCM nor the EPS motor are designed to handle 65 amps continuously. The PSCM will go into overload protection mode to avoid system thermal damage. In this mode the PSCM will limit the amount of current commanded to the EPS motor which reduces steering assist levels. The PSCM also chooses which steering calibration to use when the ignition is turned ON, based on the VIN. The PSCM contains all 8 of the steering calibrations which are different in relation to the vehicles RPO's. The PSCM has the the ability to detect malfunctions within the EPS system. Any malfunction detected will cause the IPC message center to display the PWR STR (or Power Steering) warning message.

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Old 04-20-2019, 02:41 AM   #3
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Default Re: 2002-2007 Vue EPS (electric power steering) question

Thanks fdryer,

I do have info and parts to make the EPS work successfully based on a variable amount of power steering assist. some require the ECU to provide assist, some don't and require a knob to manually set the amount of assist.


What I am hoping to learn is if the current draw of such an EPS under very light work load could be under my 30 amps constraint, without having to purchase the EPS and test the build to discover it won't work.

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Old 04-20-2019, 01:26 PM   #4
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Default Re: 2002-2007 Vue EPS (electric power steering) question

Obviously, you're beta testing and require advanced knowledge of electronics and mechanical engineering or just plain intuition based on a healthy background of self education. Good luck and if possible, feedback if you find a solution? I'm always interested in how anyone can adapt things to suit. The most wonderful adaptation are those utilizing their knowledge of 3D printing, mechanical engineering, and human physiology to make prosthetics for little ones for little to no cost.

Are there any other smaller eps units that draw less power? I recall a tv episode of the first eps system from Honda in the NSX and S2000(?).

Last edited by fdryer; 04-20-2019 at 01:32 PM..

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Old 04-20-2019, 03:42 PM   #5
KCW
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2004 VUE 2.2L
Default Re: 2002-2007 Vue EPS (electric power steering) question

why do you have a 30A current limit / restraint?

if you have an alternator you must also have a battery that it is charging, right?

even a small car 12V battery can supply a hundred amps for short periods of time (which is more than the Vue steering motor will need). The voltage across the battery will drop from 12.6 to maybe 12.0V, the alternator will jump up and kick in its 30A limit

and then when the 65A peak has ended the alternator will charge the battery back up, to make up for that brief high current surge.

on a car the alternator output is a function of the motor RPMs. With some cars if you are sitting stopped with all the lights on, the blower and rear window defogger, the wipers going, you are pulling more power from the battery than the alternator can supply and keep up with. This is why some cars go dead when they are stuck in grid lock traffic. Back when cars had AMP gauges on the dash board, you could see if you were pulling more power from the battery than the alternator could keep up with.

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Old 04-21-2019, 03:36 AM   #6
Armorican
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Default Re: 2002-2007 Vue EPS (electric power steering) question

Thanks KCW,
I appreciate your help.

I totally agree with you regarding the battery taking up the slack for a very brief period of time, and because of that, the peak amperage is not my main concern.
On the other hand, an alternator working hard to keep up with the average demand will burn out rapidly (in hours, not months) due to overheat.

This is why I came to the forum hoping to find out is if the low/regular/average/ draw for the unit is below 30 amps.

If I had access to the vehicle right now, it would be easy enough to record an ammeter's readings on a laptop under different driving conditions after doing the install.

If no one has the information I need, this is totally fine, it was worth asking.

It may be more work, but I can also see if an ATV PS motor could be mated to the Vue's PS 'gearbox'.

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Old 04-21-2019, 10:26 AM   #7
KCW
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Default Re: 2002-2007 Vue EPS (electric power steering) question

I dont know what this 1000 lb vehicle you are building looks like, or how much load its going to put on the power steering, being driven around relatively slowly with 6" wide tires.

the power steering on the vue will draw its max current if you sit and turn the steering while the car is not moving, like you are trying to K turn or get out of a tight parallel parking space.

I had a base model SL with no power steering. When you did that dead-stop steering described above it was very hard to turn the steering wheel. If you creep the car forward or back even just 1mph, the steering load dropped by 90%.

If you are doing this by trial and error that is the place to start, assemble it, do some dead stop steering turns on the wheels, then repeat with it moving forward at 1 or 2 mph, with a quality RMS current meter (like a FLUKE 87 and a proper sized current shunt to measure 100A). If you use a cheap meter it will read average current, and if the control module is PWMing the current you will get a very false reading - you need to know the RMS current (equal to a DC load).

I dont know if you can get an accurate DC reading with a clamp on current probe around the wire. I know those work well with AC power, but I have no experience with DC clamp on ammeters.

I think the worry about overloading the alternator is a urban myth. The alternator is designed to put out 30A, then it will run at 30A continuous without overheating or damage. The regulator in the alternator will not allow it to burn itself out from an overload. The indicator that your vehicle is drawing more power than the alternator can supply is that you will be drawing more power from the battery than the alternator can source, and your battery voltage will continue to drop and will go dead.

Sounds like a fun project.

BTW, if dead-head steering take a lot of power, put more air in the tires :^)

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