Automotive Engineer

To replace the Mondeo's hydraulic power steering system with EPAS what would your main challenges be in making its performance as good or better?

If you replace an outgoing model then it has to be better than, and not just as good. The challenge there is that the Mondeo is quite a heavy vehicle and it’s in the upper range of where we think EPAS makes sense. A few years ago we would have excluded Mondeo-sized vehicles from EPAS application but the technology has been moving on. But, EPAS is limited in its power output.

Why is system power a limiting factor?

Big motors mean lots of inertia. You’d be surprised how often you make small fast steering corrections, and a big, heavy motor gets in the way of this. With a car as big as the Mondeo, that’s what you struggle with. So you need a big motor that can be controlled in away that makes it feel nimble.

Control gets better and better, especially the low-level control just taking care of the motor position, and the suppliers get cleverer all thetime. So now we think we can do it with the Mondeo. But bear in mind that Mondeo isn’t alone; there is also S-Max and Galaxy running off the same platform and they are even heavier, so it’s not straightforward.

What about the other system components?

A big motor means high torque so the reduction gears also get bigger, meaning more friction. You don’t want that friction – it’s one of the biggest enemies of steering feel in EPAS systems and can completely ruin it. On the other hand, if you have too little friction everything is loose and you can get rattling noises. In Asia and North America especially, consumers are a lot more sensitive to rattling noises.

Much of that is driven by the road conditions. European roads are rather smooth compared to North American and Chinese roads. But the worst case is usually Brazil: consumers there are always the first to come back when it comes to noises and that has always been the case, even with hydraulics. We have to keep that in mind and not just look at the very demanding European consumers who have this preference for good steering feel; everything is global now.

How does friction affect steering feel and feedback?

Especially during cornering you pick up every disturbance from the road and that constantly changes your steering angle. When you want to go around a corner at speed and the road surface isn't perfect, you really don't want to have those undulations mess up your line by wriggling the steering wheel around. So you need a little bit of friction but that's really a luxury problem confined to hydraulics. With EPAS you never have too little friction – the fight is to get friction down. With hydraulics you can even fall off the other end of the scale – the old Mondeo's steering had, at the beginning, too little friction.