For ride control, machine vision helps a bit, but it’s limited due to the need to determine high fidelity road z-measurements which requires very high resolution and clarity at speed, and no visual occlusion. It helps with simple problems like bump vs hill (which is not trivial to predict just with accelerometers), but we’ve figured out how to get most of the benefit of machine vision with just accelerometers and fast actuators. GM was able to use vision to improve pothole performance, but it’s still a semi-active system that only provides fast adjustable stiffness (damping).

For pre-crash, the system uses cameras to detect a collision-path vehicle and determine an optimized impact zone for that vehicle. For example, the frame or bumper has more structural rigidity which may be desirable in certain crash scenarios.

And those electric motors and control hardware would not have been cheap. But nobody knows how to estimate it - just that it would be prohibitively expensive.

Their build quality is fine, at least contemporarily to the rest of the market; of course today, we would find its steel pitiful. It's not without reason that people who maintain Citroëns of that era tend to replace the panels with fibreglass ones.

Additionally, as Citroën pulled out, the maintenance network in North America began to falter, as the suspension system required significant know-how. There are still a dedicated group of Citroën fans in North America (albeit small), and I met a lot of them when I drove from coast to coast (and back again) back in 2017 in a 1998 Citroën Xantia. A car that may not seem particularly interesting to Europeans (although it was the Activa V6 model), but it was extremely rare in North America.

p.s. long time ago i bought a 15y old hydraulic Citroen, drove it for 10 years.. the hydraulics was less breaking than the engine :/ . Now i have another (recent) Citroen but that "road-surface-ignorant" feeling of the hydraulics is completely gone.

For a simple example, let's say you are simply driving in a circle. The car wants to lean toward the outside. The linear motors can provide a countering force, lifting the outside, lowering the inside, so the car stays level. Variable damping can only control the rate that it rolls. It will still roll in sub-second timescales, unless it completely locks down the suspension, which is terrible for both handling and comfort.

For another simple example: going over a speed bump. Linear motors can lift the front wheels over the bump, and then the rear wheels, so the body stays level the whole time. An active damper can go full-soft the moment the wheel hits the bump, but the compressed spring will still start lifting the front of the car. An active damper can do a better job managing the rebound on the far side so it doesn't oscillate, but it can't entirely prevent the bump from pitching the body up and down in the first place.

That's not to say it's worthless. Very fast active dampers can improve both handling and comfort. It's just nowhere near the level which is possible with linear motors.

Consider it in the context of camera based self-driving cars, it's tangential to this discussion but it's an easy to visualize metaphor:

- A car traveling 60mph is traveling at 88 feet per second

- Assuming a 60hz camera, there would be a 16.67 ms gap between each frame

- The car is traveling 1.5 feet between each frame interval

- A certain amount of exposure time is necessary for the camera to generate even 1 frame or it will be blurry

- High framerate cameras often work around this by staggering/interlacing multiple sensors, but doing this implicitly increases the latency of each frame

- A 120hz camera might deliver double the frames per second, but each frame could be arriving 4 frames late in exchange

- 4 frames would be imperceptible to humans, it would be 3 feet for the car

- You haven't even processed any of these frames yet.

- Your off the shelf library introduces a random 1 second delay for some reason and costs you 88 miles in processing time

- The car can drive as fast as 120mph

All digital sensors implicitly have a sampling frequency, and the fundamental disconnect is always high sampling frequency =/= low latency. People constantly make this mistake over and over, and by the time you notice you are already too deep into development to make a change.

Decreasing latency is expensive, and requires specialized knowledge. Often you get expert software engineers who end up bottlenecked by the hardware limitations they can't even comprehend or the reverse, hardware guys bottlenecked by the software they can't introspect. The latency is only truly understood when you get to integration testing.

Nearly every step of the way you discover you need specialized hardware, software, operating systems, sensors. Every part of the chain each costing you more latency. It's like it's own ecosystem where almost everyone writes everything from scratch and doesn't share anything. It's gotten better in recent years though.

Full disclosure: I work in medtech and don't actually deal with cars, but it's a very similar problem space. We often use the same hardware/software cars use for this reason.

That'd what it's called when you put the FEA in the circular file because the part is an inconsequential revision of something that's been in production forever and works fine.

Both this and the Bose linear actuator one lift just the wheel that needs lifting, just enough to clear the obstacle, keeping everything perfectly steady, it's incredible.

The fact that it can also do silly jumps for marketing reasons is a different topic.

Surely the system takes cornering into account. Having a suspension that can use predictive motions to compensate for a pothole would ideally produce better handling by minimizing the disruption of a pothole imparting a massive disturbance to the vehicle.

No, the Citroen Activa active suspension was in production from 1996.

I drive a Smart Fortwo, which goes in the opposite direction - there's not much suspension to speak of, and the short wheelbase means you rock around a lot more on uneven street surfaces, so you're very much connected to the outside world. One of the things I've noticed when switching back and forth between that and a normal sedan is that, if I'm not consciously thinking about it, I'll drive slightly more aggressively in the sedan than in the Smart. And I think it's precisely because of that difference in connection with the outside world.

The same happened when I rented a pickup truck a while back to move some furniture; I don't remember the model, but I think it was a fairly recent/common one. It was very clear that movements that would have felt pretty aggressive to me if I were walking or biking around felt less so from the driver's seat. And I bet the same is true of these luxury cars.

This is of particular interest to me because my day-to-day method of getting around is not driving but rather walking and biking, and it's worrying to me if drivers are subconsciously acting more aggressively just because they feel more disconnected from the world around them.

Which is pretty neat considering it has a 6.7 liter bi-turbo under the hood.

For example see the "rodeo test" where the car moves each corner up and down to test the system. ABC involves active feedback control of the body and rapidly adjusts force/displacement of individual struts, just like what the Bose system does with electric actuators.

https://youtu.be/391IPl3LJOs

That’s the point. They’re not supposed to damage the car. They’re supposed to be a little uncomfortable if you’re going too fast.

It’s more reminder than a physical stopper.

> In fact the faster you hit them or the more load you're carrying the better the suspension handles it because you open up the high speed compression valves.

This is a case of knowing just enough about a topic to be dangerous.

Entering the higher shaft velocity part of the damper curve doesn’t mean the suspension is handling it “better”. The high speed behavior of the valving simply means the damping forces aren’t increasing linearly with shaft velocity. They trade extra travel for reduced peak forces.

Make no mistake, though. The faster you go, the higher the forces. The high speed valving (if the OEM dampers are even digressive) isn’t changing that.

If the speed bump is tall enough and the bump stops get completely compressed you could bottom out the damper, which is not good for it.

> I'll often hit them at 30mph+ with no issue.

Just because nothing immediately breaks doesn’t mean you’re reducing the life of the OEM dampers. Repeated high speed impacts and will shorten the life. Getting the wheels bumped up into the range where you’re compressed bump stops transfers a lot of energy into the bushings and other components.

> Rolling over them at a slower speed where your shocks stay uncompressed forces your whole car to go up and then down again, instead of absorbing the energy in the shocks.

That’s the ideal way to do it. This is better than the sudden sharp impact of high speed crossing. You’re not doing your car any favors by driving quickly over speed bumps. Fortunately for you, OEM replacement dampers aren’t too expensive but replacing prematurely worn bushings is kind of a pain.

They only work because the average consumer doesn't know this.

Well, you can take money out of an ATM machine to pay for that. Just try to remember your PIN number.

Smallblock Chevys have a timing chain at the front but it's basically never a failure point. I agree with your other points, however; the trend is to optimise for short-term efficiency and cost, resulting in complex and relatively fragile designs.

As a result, I hated them until years later, when I encountered one that was done correctly. After that, I completely flipped my opinion. Done right, they can completely beat a traffic light for wait time and throughput.

They were rare in the US before, I want to say, 15 or 20 years ago but I see them all the time now and new ones are always being installed. Good traffic devices, with the above tradeoffs in mind.

For America specifically: they're not a great fit for places where everything is spread out and the road system is sensibly designed. I can drive from one side of Tulsa to the other (on streets, not freeways) in a fraction of the time I could drive across a similarly-sized European city. That's because the city itself is designed for cars. It has straight major streets with 40-45 mph speed limits that form a grid. Neighborhoods sit inside the grid and the streets in them curve with the landscape. In most of the city you have maybe 3-5 traffic lights per mile on the major streets, so unless it's rush hour you get minimal slowdowns. Sometimes I can drive several miles without hitting a red light.

The ideal situation is to have a straight road with no traffic directly between you and where you want to go. Obviously, that's not possible. So you have to compromise. Roundabouts suck, but they're better than almost any other option in places that have twisty narrow streets and lots of pedestrians. Many (most?) American cities aren't like that (at least to the extent European cities are), so roundabouts don't make as much sense here.

They are in the Northeast. But they don't always keep bad drivers away.

They're getting more popular in the Puget Sound area. We have been re-engineering streets to include roundabouts all over the place. I think they're a great thing, but too many people still stop at the wrong time.