Jim Holder’s recent blog outlining Jaguar’s switch to electrically assisted power steering for next year’s F-type will inspire among keen drivers the same fears they felt when Porsche went down the same route.
It’s thought that an electrically assisted system can’t offer the same level of steering feel as one with hydraulic assistance, as it smothers those important frequencies and sensations that are communicated from the tyres to the palms of the driver’s hands. A good system should allow us to sense what our tyres are up to on the road surface.
By coincidence, I’ve been driving a Jaguar F-Type and a Porsche Cayman. Now, the F-type has pretty good steering. To me, the rest of the car might be a little dubious, but you can’t deny the response and accuracy of the Jag’s meaty hydraulic set-up.
However, the Cayman’s (admittedly a GTS, but let’s not quibble) is better, despite its electric assistance, being more responsive and more accurate. It also requires less effort, thanks to its intelligent weighting and clever damping.
Purists will argue, though, that the Porsche lacks the level of feedback of earlier hydraulic Porsches, and that what you feel is artificially dialled in. That may be so, but is not the feedback to the driver through an hydraulically assisted rack corrupted too? How many meshing teeth and rubber joints and turns do the tyres’ messages have to go through, and how diluted are they by friction and damping before they reach the driver?
So if it’s a criticism made of electrically assisted units that there’s very little communication, does it actually matter? On most roads, in most cars and in most circumstances, probably not; after all, you rely on all sorts of senses when driving a car. And when every effort in a modern car is made to isolate the cabin from the road, why would you want the steering to have the kickback of a vintage racer?
Keen drivers like a bit of weight, though, presuming it to be sporty. Matched with a fire-breathing sports car, fast and low and heavy in its controls, I can see some of it might be desirable. What is really wanted is what we call well weighted steering, which is another vague term, but seeks to identify a level of weight that is neither too much nor too little, and a consistent amount of it.
This weight can be and already is quite easily tuned in to an electric power-assisted steering system, and to many potential degrees, so keen drivers needn’t worry. They could perhaps concentrate instead on the other, more tangible qualities that make for good steering, such as the alacrity of its responses, maybe, or its precision.
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Disappointing article and...
Steering feel is an essential quality which must be boasted by modern sports cars, equal in my opinion to chassis stiffness and balance, not to mention suspension settings and a good set of tires which together conspire to provide a precise and INVOLVING experience.
For Mr Pearson to suggest that steering feel is no longer important, may be acceptable if we are speaking of super-minis, saloons and SUVs that are not sporting in character, but to raise this argument referencing the likes of Porsche and Jaguar is preposterous.
The only reasons I can think of, for Mr Pearson to suggest this discussion in the way he has, are:
1) Autocar is a motoring magazine intent on promoting the latest industry products, be it cars, or their components. As such, with the current TREND moving towards EPAS, it has no option but to promote this system considered inferior by many enthusiasts; and/or
2) Mr Pearson doesn't care because presumably, he is not a sports car enthusiast, or has yet to drive a car which has excellent steering feel.
Which ever way you look at this, its a shame but I would simply take this sort of nonsense with a pinch of salt. After all, those who know, know.
Here is the real interview from the prodrive bloke on epas...
from an interview with a Prodrive engineer...
"Prodrive's Matthew Taylor does know what he's talking about, though, and it was he who made the analogy about helping your arm to push an object or pulling the object away from you. EPAS does sense movement rather than force, typically using a magnetic Hall-effect sensor which measures angular displacement of the column against the pinion shaft as the torsion bar between them flexes. The more movement, the greater the torque applied to the motor within the constraints of the ECU's programming. You turn the steering wheel, the motor's efforts follow. Obviously more movement comes from more force at the steering wheel, but the movement is what the system responds to and calculates from.
In a hydraulic system, which uses a similar torsion-bar arrangement between the column and the pinion shaft, the angular displacement between the two caused by the turning torque progressively opens a valve, which lets through the oil pressurised by the hydraulic pump into the hydraulic ram that helps move the rack. The end result is the same, but the hydraulic system gives an immediate connection (less so if it's powered by an electric pump less able to provide truly instant pressure) so you can say it responds directly to force. It's a subtle distinction, I admit. Perhaps I'll have another chat with Matthew.
The erudite Dr Ulrich Eichhorn, in his days at VW R&D, told me that his team had developed a steer-by-wire system with, he said, amazing feel and feedback. This was achieved, if I remember correctly, by using transducers on fractionally flexible joints in the trackrods which sent a signal back to the steering wheel's own transducer as forces acted on the trackrods. The signal applied a reactive torque to the steering wheel as the forces acting on the trackrods changed. As the steering wheel had no mechanical connection to the steering motor, there were no problems of rotational inertia. I hope we'll try something like this one day, but it will be a while before legislation allows steer-by-wire in production cars.
John S"
this is why so many of us take the tone we do with you