Electric Power Steering - experience?

[eurocat]

I'm working on a three-wheeled vehicle and am concerned about the force required for steering. I'd like to use an electric power steering system, such as e-steer by Delphi. This is current used on Fiat Punto.

Does anyone have experience with this system or a similar one? I'd like to know how much force is generated and any specific engineering knowledge of it use. Anyone?

Regards,
Glenn

 

[GregLocock]

I have had a technical presentation on it by Delphi, but I can't remember anything ground breaking. Max current draw is around 50A. It isn't powerful enough for large cars. There are still some issues with feel.

Is your vehicle single front wheel or twin? What is the weight per wheel? What size are the tyres?

Cheers

Greg Locock

 

[eurocat]

Hi Greg,
The arrangement is two wheels up front. It is a city car in a motorcycle weight class, initially 125cc. I'm using vespa suspension for the front wheels, 3.5 x 10. It is a tilting vehicle where the lean provides the turning, like a BMW skateboard. Because the weight distribution changes the steering force needed, and the loads are high at the rim of the steering wheel, I think an electric power system would help. Since it is a two-place side-by-side arrangement it really needs self centering as well. Any ideas?

 

[Gerry45]

Its a few years ago now but I had a lot of involvment with some of the NSK systems. Unfortunately I cant remember any typical rack forces because this wasnt a figure we talked about much. Initial system selection for a new application was generally based on 'front axle weight' since this was a main contributor to tyre friction. After this it was all down to 'suck-it-and-see engineering' and tuning. As the previous message said, small cars (FAL~700Kg) would typically use 40~55 amp motors. This is the continous motor power so an elec motor speciallist may be able to estimate what torque this is approximately equal to. The internal worm and wheel gear box usually had a ratio of around 17~19:1 Typical rack ratios are generally as for manual steering cars.

But yours sounds an unusual application where the normal 'rules' may not apply. The necessary motor torque or rack force can be achieved by changing gearing ratios and king pin lever lengths etc. The question is what % of time are you going to operate at a given torque level. Most elec steering systems output performance is limited by internal heating. When worked hard the ecu will detect the temp rise and cut back the power automatically to self protect. So using a system that is too "small" in normal automotive terms can be tuned to work reasonably well in 'normal' driving, but will start to let you down in a 'carpark test'. After a minute or two of abusive steering wheel twirling you will start to notice a gradual increasing steering effort is required.

Gerry

 

[kerriet]

I have a GM unit as fitted to the Corsa C. It's rather heavy and the ECU is heavily integrated into the car, requiring signals from the engine, Immobiliser and ABS ECU's before it works. It can't be back engineered either (I realise that can't is a relative word, but in this case it's a major hassle). The only way to use it is another ECU suppling the correct signals to the first. These are retailing at 400 GPB. Does anyone know if the e-steer is a stand alone device?

 

[Gerry45]

Kerriet,
All automotive electric systems will be integrated into the car. Its the only way to control its integrity, performance and safety.

To use the steering system out of a car you'd have to either feed the original ecu with dummy inputs or drive the column directly from a much simpler box of electronics.

 

[gluedog]

for stand alone electric power steering checkout wiringlooms.com