Bose Suspension

[Tommy Cookers]

My feeling is that bandwidth will be limited by the mechanical inertia of the system, not the electrics. As Dave pointed out, they are already very fast.

Dave's work ie the F1 active system had servo-valved hydraulic actuators
no electric actuator can be as fast as these
the controller will always be much faster than any actuators, its got the easy job
(true, digital control will be slower than analogue, as shown in the X-31 project)

[Tommy Cookers]

... the dominant issue for high bandwidth (race) active ride suspension is the control intelligence, or insufficiency thereof which makes academic the bandwidth inherent in the systems configuration and components?

Fully digital control systems have been available for active suspension since 1983, to my knowledge. These were capable of controlling four hydraulic actuators with a transport delay of <150 microsecs, control the hydraulic power supply and generate their own data stream with an overall iteration rate of 1 millisecond. By 1987, they also ran monitoring algorithms and could survive a single transducer failure. The most complex vehicle system we built controlled active suspension, active rear steer, active front steer, active steering wheel "feel", active throttle & brakes: 10 EHSV's in all controlled by a single computer iterating at 1 millisecond.
Today, there should be no issues with controlling a fully active suspension, though incorporating it into the existing MES might be a stretch, I suppose.
p.s. I like the idea of an electrically driven suspension. Two issues to be addressed are actuator life & failure mode.

I must apologise, particularly to DaveW, for the above result of my bad habit of posting first, then (re)draughting

what I meant to say was that active ride performance would in principle benefit from real (and synthetic) predictive input
without this the performance of even F1 active was impeded ??
and such predictive input could also allow the use of lower bandwidth types of actuator eg electro-mechanical instead of hydraulic
imagine an off-roader scanning the upcoming terrain, or a supercar curb-hopping like an F1 car (or cancelling speed-humps)

with mechanical suspension, for most purposes the required stiffness can only be achieved with high natural frequencies
with active suspension this limitation does not apply, so how much bandwidth do we really need eg in F1?
F1 tyres appear to be even more compliant than when active suspension was F1 legal ??
they must filter out more of the higher frequencies than ever

[Tommy Cookers]

I like the idea of an electrically driven suspension. Two issues to be addressed are actuator life & failure mode.

Right. It is curious to watch the mind of electronic engineers and the like as they consider the safety implications of Electric Power Assisted Steering Systems on passenger cars. eg
http://www.linkedin.com/groupAnswers?vi ... _140208214
The downside of failure of an electric suspension on a race car is probably less than in a production car,admittedly.

where can I get a manual steering car (not necessarily a Hindustan Ambassador) ?
my Peugeot shopping-only car gave a lot of trouble with intermittent loss of its electro-hydraulic power steering
relays allowed the car to be started with a low line voltage due to high PAS pump power consumption and little charging time
typically on drive back from shop the PAS was lost

the replacement car has protection from this problem, it can't be started if the line voltage is even slightly under 12 V
although I always park it with wheels dead ahead

[Greg Locock]

"where can I get a manual steering car (not necessarily a Hindustan Ambassador) ?"

Stuffed if I know. I do know that every study or clinic we have ever done says that low parking efforts score better than high efforts, although there does seem to be some sort of lower limit to how low we need to go. Small turning circles and limited lock to lock travel also score highly. As such EPAS has taken over the world of production cars.

[DaveW]

... As such EPAS has taken over the world of production cars.

I guess the legal departments would argue that it is power assist, rather than power steering. I recall (from a few years back) that one company was about to install a true power steering system in a bus. It would be interesting to hear how they solved the failure cases.

For suspensions, I agree that failures of road car systems is rather more significant than race car failures (though Massa, for one, might disagree).

The increasing use of "active damping" is interesting. Early systems tended to fail "hard" when not driven, which might arguably be considered "safe", although Ohlins - to their credit - has developed a complicated valve that fails "semi-hard" (The valve is also used by some other damper manufacturers). Latterly, systems like "magnaride", & I guess Bose, require to be driven to be damped (at all).

At least the above remain "sprung" after a failure. The same cannot be said for hydro-pneumatic systems. I recall that Citreon's response is to illuminate a "STOP" warning light in the event of a hydraulic failure. I think that a geared electrical system might have similar issues. The prototype system we built for Lotus had no back-up springs. One experience of a hydraulic system failure was sufficient to convince me that back-up springs are a very good idea...

[Tim.Wright]

These are all reasons why I like the Mercedes system, because it has a normal spring damper backup.

I see another advantage of using a normal spring/damper in the system. If you actually incorporate the spring/damper into the primary suspension use (i.e. not just as a backup) you can let it take care of the high frequency stuff, which leaves the actuator tasked only with the low-speed/high-force movements. In this case the actuator doesnt have to be so highly spec'd for velocity.

[olefud]

A system that would reasonable attain the Bose suspension –and perhaps what they’re doing- is one in which the vehicle weight is supported, or tared- by a low rate mechanical spring to a null point at the vehicle rest ride height and null position. The voice coil would function as a push/pull servo system utilizing a null sensor to drive the system back to the null point upon a variation therefrom. The servo PLD, properly selected, would allow for compliance to upset inputs and the slew rate would determine ride stiffness. The spring would do the heavy lifting while the voice coil servo would control dynamic response.

[DaveW]

These are all reasons why I like the Mercedes system, because it has a normal spring damper backup ... In this case the actuator doesnt have to be so highly spec'd for velocity.

I can't disagree. But, if you were to delete the pancake actuators and replace the dampers with hydraulic actuators (leaving the coil-over springs) think what you could achieve.... with a little more flow, perhaps (but not that much more, because the springs carry the dead weight). This was the basis of the Lotus active system. It was first active F1 car and, ultimately, the first active car to win a Grand Prix. It also, I think, made a fairly capable road car system, lacking the refinement of a "boulevard cruiser", perhaps, but great fun - and with perfectly acceptable failure modes.

[DaveW]

A system that would reasonable attain the Bose suspension –and perhaps what they’re doing- is one in which the vehicle weight is supported ...

I think you are correct, but perhaps it might not work on an F1 vehicle.

[olefud]

A system that would reasonable attain the Bose suspension –and perhaps what they’re doing- is one in which the vehicle weight is supported ...

I think you are correct, but perhaps it might not work on an F1 vehicle.

Agreed. The simplistic outline addresses the energy/heat concern. Since three tires define a plane, the null sensors would have to talk among themselves to agree on appropriate null positions; and maybe a few other details would need to be addressed.

[Pierce89]

I like the idea of an electrically driven suspension. Two issues to be addressed are actuator life & failure mode.

Right. It is curious to watch the mind of electronic engineers and the like as they consider the safety implications of Electric Power Assisted Steering Systems on passenger cars. eg
http://www.linkedin.com/groupAnswers?vi ... _140208214
The downside of failure of an electric suspension on a race car is probably less than in a production car,admittedly.

where can I get a manual steering car (not necessarily a Hindustan Ambassador) ?
my Peugeot shopping-only car gave a lot of trouble with intermittent loss of its electro-hydraulic power steering
relays allowed the car to be started with a low line voltage due to high PAS pump power consumption and little charging time
typically on drive back from shop the PAS was lost

the replacement car has protection from this problem, it can't be started if the line voltage is even slightly under 12 V
although I always park it with wheels dead ahead

I know that in the mid noughties a Honda Civic could be purchased without power steering(at least in the US). A former girlfriend had one without power steering. She hated it, but I loved the amount of road feeling it had.

[thisisatest]

where can I get a manual steering car (not necessarily a Hindustan Ambassador) ?

after searching around, looks like the lotus elise is one. on the poorer end, kia rio may still be available w/o.

[Richard]

Caterham and Ginetta abhor power assist anything!

[Tommy Cookers]

FWIW I now think that emergency manual reversion on EPAS would only involve disconnecting the power cabling
this would reduce the backdriving force required for any EPAS electrical fault state
although the starter might still be disabled if the system thinks the line voltage is too low to work the EPAS

so EPAS is better than EHPAS

IIRC the earlier Boeing 747s and all DC10s have manual reversion (of the primary flight controls)
but it has been designed out of modern airliners

[Tommy Cookers]

PAS demands steering and suspension geometries that are disadvantageous for the enthusiast ......
but car manufacturers like strut suspension/transverse powerpacks that naturally have offset/scrub radius suitable for PAS
and there is no value in closing the stable door, they tell me

back on the suspension thread ??
the vehicle weight can only be tared by springing that is in parallel with the actuator
the Mercedes system mentioned is a series arrangement ie untared ??
this is consistent with the inclusion of an hydraulic element, it will take the vehicle weight without consuming energy
no electrical system can do this (and would have to be slow-acting to minimise energy consumption, however implemented)

the electric or electromechanical actuator must have springing in parallel for it to control the dynamic response
so it will need to be rather capable in both force capacity and bandwidth
and can beyond its nominal bandwidth be allowed some managed 'free' backdriving ie on severe/high frequency bumps

in any parallel system there will be force differences ie some conflict (in this case between the actuator and the springs)
this happens in conventional suspension (that's what dampers do), and in the F1 Active
that's what design is about
there's no easy way out, strut compliance must be manageable by the millisecond, this demands both power and bandwidth
a low-power electromechanical system will give mostly uncontrolled Newtonian damping

such an 'electro-mechanical strut' is judgeable in its potential to do the same job as the hydraulic actuation in F1 Active
it's cheaper and more energy-efficient (recycling much of its damping energy)
my semi-guess is the electromechanical system bandwidth could be 10 Hz, is there reason to think this is not enough ??