Ford/Mazda "Control Blade" rear suspension: the blade has to flex...?

[d00df00d]

Been reading up on the Control Blade rear suspension in a lot of Fords and Mazdas pre-2014 or so (e.g. our family's own 2012 Mazda5). One thing I've seen mentioned in multiple places – though not everywhere – is that the blade itself is meant to flex so that other joints in the suspension can move as intended. E.g.: https://www.edmunds.com/car-reviews/track-tests/2010-mazdaspeed3-suspension-walkaround.html

The control blade (blue) is a trailing arm that locates the wheel in the fore-aft direction. The trick here is its very thin cross-section that allows it to flex a little so it won't interfere with the smooth operation three lateral locating links.

Fair enough. Makes sense of the fact that it's a blade rather than, say, a boxed design like a lot of front LCAs.

But the forward bushing also has a bunch of compliance, right? Given that, how relevant is the compliance of the Control Blade? Like, if something needs to give in that part of the suspension, won't it be the forward bushing rather than the blade itself? What's the blade's own compliance really adding?

Been thinking about this because I came across some presentation slides from when Ford eventually replaced Control Blade with a design based on an integral link. They cited the flex as a weakness of the design because it generates its own vibrations:

Ignoring practicality for a moment, if one were to make the Control Blade a bunch more rigid while keeping the stock forward bushing, how much (and what) would be lost? Would it just toe in less under compression, or might things start binding up?

Curious to hear any thoughts on this!

 

[Rogueman2016s]

this is an interesting design I am wondering if my 2006 Mazda 3 had this rear suspension. the vehicle handled really well and as I recall did not have much road noise.

 

[d00df00d]

this is an interesting design I am wondering if my 2006 Mazda 3 had this rear suspension. the vehicle handled really well and as I recall did not have much road noise.

It does.

We love how our Mazda5 handles with this suspension design, too.

Apparently it generates less road noise than previous designs, but more than newer ones. We notice a fair bit of road noise in our Mazda5, especially with tires that are more performance-oriented than most people use (Michelin Pilot Sport All Season 4). It's all relative, though. Could be much, much worse...

 

[Number_35]

We have a 2009 Mazda 5 in the family. The one weakness with this type of suspension is that the rubber bushings can deteriorate, and then the weight of the vehicle causes the rear tires to deflect inwards (i.e. exhibit excessive positive camber).

I changed the bushings out 3 or years ago. Not a bad job at all.

I think the designers nailed it - that particular suspension design offers both a pleasant ride and good handling.

I suspect the bushings were designed for the Focus/Mazda 3 platform, and are a bit overstressed with the extra weight of the 5.

 

[vavavroom]

It's sort of a combination of trailing arm and wishbone and it's a bit fancier than a trailing arm torsion beam rear suspension.

 

[d00df00d]

I get the general principles of the design. What I’m wondering is how important it is for the blade itself to flex, especially given the compliance in the forward bushing.

 

[Rogueman2016s]

Gives similar ride and handling characteristics of a multi-link without the complexity and cost.

 

[d00df00d]

Alright. I give up.

 

[d00df00d]

FWIW, I found some answers elsewhere.

My understanding: Yes, the blade's flex is intentional and important. It basically makes sure the blade doesn't interfere with how the rest of the suspension controls toe angles. The amount of flex is calibrated accordingly and designed into the blade itself. The forward bushing couldn't do the same job because it doesn't have enough compliance in the right axis. So, if one were to make the blade rigid, that would likely require other parts of the suspension to be redesigned – at least the forward bushing, and maybe other parts as well.

"Control Blade" rear suspension: the blade has to flex...?

"Control Blade" rear suspension: the blade has to flex...?

grassrootsmotorsports.com

https://www.eng-tips.com/viewthread.cfm?qid=506545

https://www.eng-tips.com/viewthread.cfm?qid=108706 <–––– some info from someone who apparently helped develop this suspension design