I think there's an agreement on the goal.

I believe the poster is asking why do we need another sensor to achieve that goal? We already have a speedometer based on wheel motion. A trivial computation gives acceleration.

Because tires can block, not all tire turn at the same speed all the time, because redundancy is a good thing... There a lot of reasons. And if the number of sensors in your car bother you, well, the early 80s, with carbs and without ABS, are last model years you can buy.

Many late 80s/very early 90s fuel injection vehicles have shockingly low numbers of electronic sensors also. MAP, O2, TPS, CPS is all you really need. Some of them are even analog.

No need to get snarky :)

Redundancy is a good thing. Do we feel manufacturers are cross-checking accelerometer with the speedometer? If not, there is no redundancy gained.

On the other hand, if your speedometer is faulty, or not working, you'll know pretty fast. If your dedicated accelerometer is faulty, you might have no idea what your brake lights are doing in the back.

Dunno; it just feels "we need to know acceleration, let's add an accelerometer" is a non-imaginative, add-cost, add-complexity idea. Again, if we think ABS and speedometer and the new accelerometer are being cross-checked and sanity-checked, awesome, but I'm just a bit cynical of that, compared to adding the 3rd thing to do the same thing.

> add-complexity idea

You're on a forum where a lot of people think Kubernetes is a good idea.

;-)

No idea what Kubernetes are, and I am serious here, since I am no software dev. On the hardware side of things, there is redundancy and complexity. Those two might look similar on the surface, they are totally different beasts so.

To simplify it as much as possible, Kubernetes is a system that deploys and manages containers. Containers allow multiple programs to run under the same system while being completely isolated.

However, Kubernetes is actually incredibly complex. It's powerful, but holy hell does it add complexity. And yet it's basically a buzzword and people are using it in very basic scenarios that don't call for the complexity that Kubernetes adds.

So that's where my joke comes from. There are people that behave as if adding unnecessary complexity is a feature.

Thank you a lot for the explanation!

An accelerometer will show braking when going at constant speed down a hill. Change in wheel speed is better.

I’d say you are braking somehow if you are going at a constant speed downhill, are you not?

What do you save by not having that sensor? Nothing. What do you lose by not having that sensor? The ability for the system to perform its requirements.

I'm assuming you read the context of loss of traction being a requirement.

Relatedly, having a dedicated accelerometer sensor is a baseline dependency of many of other modern features like cross-comparing compass headings and GPS for map heading information (much less any of the Level 2+ "self-driving" mechanics). Most cars likely want one, anyway, even in base models. It's one of the cheapest sensors in a suite of increasingly standard sensors (in almost any form factor of device, not just cars, but phones/watches/toasters/etc).

> What do you save by not having that sensor?

A $9000 repair bill in 6 years when your mechanic tells you “Sorry your car is immobilized and won’t start, the deceleration brake light sensor went and we need to remove the motor and 3/4 of the wiring harness to replace it”. And for anyone who thinks I’m being sarcastic, try owning a BMW or an Audi and you’ll know it’s the truth.

The problem there is owning an Audi or BMW, not the sensor itself.

A MEMS accelerometer is pennies. If it is critical then add redundancy and don't accept single fault tolerance. If it is optional or the signal can be estimated from other sources with acceptable error then fail gracefully. This is honestly simple stuff. Accepting less from manufacturers is a bad deal.

>>A MEMS accelerometer is pennies.

That's an dishonest argument (perhaps not intentionally). NOTHING is "pennies" to a consumer when it comes to repairing a vehicle. More frequently, you pay $1,500 in labour and parts to replace something that costs "pennies" in some bulk manufacturer wholesale catalogue.

Modern cars are getting more and more awesome, in terms of safety and convenience; but the sticker shock when going to dealership for repair is also becoming bigger and bigger, and it absolutely is intertwined with the significant effort to make 3rd party or even self-repair difficult to impossible.

So again, IFF this is an easily replaceable part that is thought-through and cross-checked intelligently with other existing sensors, brilliant. But can you at any level understand my skepticism that any of these are true? :)

I'm not talking about the price of maintenance but the cost of manufacture. Please give generous interpretations rather than ones that fit an argumentative narrative. Assuming the topic is cost of repair rather than manufacture makes no sense when we're talking about system engineering to accomplish functional requirements.

I have owned a troublesome 2010 BMW for 8 years now. No individual repair has been over $2,700.00. Most are closer to $1,500. I was quoted (by a dealer) $15,000.00 for engine repair once but it turned out to be a spark plug. $9,000.00 sounds like a dealer quote. Find a good independent shop.