Slightly OT: what is the last best analog sports car with hydraulic power steering Options

[Tdskip]

Just as a thought exercise – if you had to pick a new – modern sports car that had proper hydraulic, rather than electric, power steering what would it be?

Just walked past about a 7 year old Audi R8, hence the question.

I’m sure the last generation Cayman would have be on the short list...

[Tdskip]

Addresses the feel issue

Jason on Electric Power Steering

[Superhawk996]

Addresses the feel issue

Jason on Electric Power Steering

@Tdskip

Not so much. Other than he agrees with you. (IMG:style_emoticons/default/biggrin.gif)

Althouh it is a good video primer on EPAS there is no technical discussion in there that explains why EPAS would have less feedback.

Let's not forget that hydraulic power assist is not magic. For years everyone complained that all power assist was (IMG:style_emoticons/default/stromberg.gif) . The video author talked about damping but the fact is the damping of an EPAS rack is far more adjustable than the damping of a hydraulic system which is also damped by the fluid dynamics of steering fluid flows though tiny orrifices and power steering hydraulic hose expansion/contraction.

EPAS most definately can be made to have communicative feedback.

As was posted earlier there are a technical reasons EPAS isn't as communicative as a manual rack. The primary reasons:


1) The nature of mechanical leverage is working against any assisted steering (EPAS or hydraulic) with respect to up stream feedback from the road. The purpose of the system is to make steering efforts lighter. This is done with mechanical leverage. In the example of a gear, if we have a 4:1 gear, you get 4 times the output for 1 unit of input. Same principle pertains wheter the leverage comes from gearing, hydraulics, or electric motor assit.

In the case of steering, the unit of input torque is at the steering wheel and the 4 units of output is at the road wheels. Now work that backwards from the road. 1 unit of input of road force (or feedback / communication with the road) is now only 1/4 of what you feel at the steering wheel.

2) Customer demand for "light" steering efforts. Though this may not be you (or me), take a quick informal "survey" on your next drive. How many people do you see driving with one hand? Wrist flopped over the steering wheel at 12:00? One or two fingers? Driving with knee while eating a burger or sipping Starbuck? How about driving with hands a 10 & 2? All these these jacked up steering positions give the driver less mechanical advantage on the steering wheel than 9 & 3 and then translates to the need to "boost" the steering assist further just to make them happy.

The demand for more assist to lighten steering efforts works directly agaist communicative feedback . . . basically goes back to point #1 above.

I'm actually torn on whether this is #1 or #2 thing that degrades road feel & communication feedback. The customer data is clear, most drivers want LESS effort and LESS road feedback. As sports car guys, we are the oddballs.

The more any brand like BMW or Porsche caters to non-drivers that are simply buying their cars as a lifestyle statement, and want nice light steering efforts so they don't have to expend as much effort to drive, the worse your steering feel will get. Likewise the older your buying demographic gets, the worse your steering feel will get.

3) One of the downsides of EPAS is a controls / motor issue that can occur if too much damping is taken out of the system and the controls are made to be too responsive. The assist motor will go into an instability which is just a small amplitude uncontrolled oscillation (i.e. steering shudder). I'm not talking about massive steering wheel movement, but only a perceptible vibration in the steering wheel that shouldn't be there. It is a byproduct of the system compliances & tuning. Damping is added in the controls algorithm to address this. Damping is variable as a tunable parameter at the discretion of the engineer tuning it. Hydraulic steering can have the same shudder problem but to a lesser degree because the system is less "stiff". In the case of hydraulic's the damping is added by tuning hose, diameter, lengths, and expansion characteristics or via orrifice sizes within the control valve. There is actually more compliance in a hydrauic system due to hoses, brackets, etc. that make the hydraulic system less prone to instability (i.e. steering shudder) but belive me when I say I've spent a lot of time dealing with hydraulic power steering moan, shudder, and assymetric efforts.

4) The location of the EPAS motor location matters. Column mounted EPAS systems typically feel worse, more numb, and communicate less road feedback. Rack mounted EPAS tends to be more communicative in my experience. Regarless, either are highly dependent on how they were tuned and what the rest of the system steering system dynamics are (low/high scrub radius, high friction ball joints, high friction struts, etc.) that can seriously degrade road feel too.

OK, I'm tired of typing. If anyone really cares, we can deep dive further (IMG:style_emoticons/default/sad.gif)