It's easy to forget that beyond all the talk of batteries, regenerative braking and range, the 2009 Mini E is an otherwise normal car--and a pretty damn good one, at that. The last Mini Cooper we had in our long-term fleet pre-dated the suspension walkaround series, but the underpinnings of the Mini E are more or less identical.
Let's have a look ...
At first glance, the Mini Cooper's rear suspension looks like semi-trailing arm suspension, a type of rear suspension found in a lot of older BMWs. The "semi" prefix refers to the diagonal pivot axis, a feature that makes the arm serve dual duty as a trailing and lateral locating device. But as such, rear semi-trailing arm suspension isn't particularly good at controlling camber and toe-in as the suspension moves towards the extremes of its arc.
But this isn't semi-trailing arm suspension because we're not seeing one massive arm spanning across the pivot axis. Instead we see at least two links: a trailing link (black) and a diagonal semi-trailing/semi-lateral link (green).
Here we see the final missing piece of the puzzle: there are two semi-trailing/semi-lateral links, not one. And because there are two, the camber and toe-in can be accurately controlled as the suspension moves up and down. Dual links are possible in the Mini Cooper because it's front-wheel drive; a drive axle wouldn't have a clear shot to the hub past two moving diagonal links.
Find the most massive link and you'll find the one that carries the most load. In the Mini E/Mini Cooper, that's the trailing arm (white), a complex-looking piece of cast aluminum.
It's tasked with primary fore-aft wheel location, it resists all of the brake-torque loads and it's the attachment point for the spring and damper (yellow). In a gasoline-powered Mini, it would also be the attachment for the rear stabilizer bar. But the rear stabilizer bar has been removed from the Mini E and the mounting hole (green) sits unused.
The Mini E's rear brakes consist of single-piston sliding calipers and solid rear discs. Here you can see the rear electronic pad wear sensor (green) and the linkage (white) that allows the parking brake cable to mechanically clamp the caliper.
In front, the Mini Cooper uses a front-wheel drive staple: A MacPherson strut (yellow) with a single lower control arm (green).
From behind, we can see how the direct-acting stabilizer bar connects to the strut housing via a slender link (yellow).
The fuzzy inner fender liner material seen here helps reduce noise transmission from the fender wells to the cabin.
Here I've removed the fuzzy fender liners for a better look. The Mini E's L-shaped lower control arm (white) is nothing special, but the inner pivot (green) is a ball joint instead of a rubber bushing, a choice that contributes to the Mini's steering precision.
The rear lower control arm bushing housing bolts to both the subframe and the unibody. And just out of sight, this bracket also carries the pivot bushings for the stabilizer bar (yellow).
The Mini E's Delphi-made front shocks are from a Cooper S. The springs probably are, too, though I'm less certain of that.
Use of the stiffer "S" suspension makes sense in light of the heavier weight of the electric drivetrain, particularly the batteries. In the rear, where most of the battery weight resides, I wouldn't be surprised if something firmer than "S" specification was necessary.
If wondering if the strut housing is dented, it's not. Well, it IS, but it's an intentional flattening to provide tire clearance. This is only possible because this is a twin-tube damper; the unseen inner tube is the precision tube in which the piston rides up and down, while the outer tube--the one you can see--is more or less an oil reservoir.
The Mini E's single-pistion sliding calipers and ventilated rotors don't get much of a workout because of the aggressive regenerative braking we've talked about earlier, so these pads and rotors ought to last a good long time--doubly so because the electronic leash and city-only suitability of the Mini E makes it unlikely that anyone could put more than 10,000 miles per year on this car.
The Mini E has no spare tire, so Continental 195/55R16 run-flat rubber is used. There's room for a spare underneath the rear floor and the mini-winch from the donor base Cooper is still in place, but a stowed spare represents extra weight the already-porky Mini E doesn't need in it's quest for 100 miles of range. In addition, the intake slot for battery cooling air sits near this area, and a stowed tire could obstruct airflow.
We'll get into this and other details of the electrical components of the Mini E in an upcoming blog post.
Dan Edmunds, Director of Vehicle Testing
bodyblue says:
11:07 PM, 12/20/09
I really like the walk-arounds, Dan. How do you like your new jack so far?
tomm250 says:
07:33 AM, 12/21/09
Nice job Dan, but the comment: "doubly so because the electronic leash and city-only suitability of the Mini E makes it unlikely that anyone could put more than 10,000 miles per year on this car." Is ridiculous.
I have had my MINI-E since June and I have 17,800 miles on it in 6 months, most of which are highway miles! I'm going to have over 34,000 miles on it when my year with the car is up.
I also know at least 10 others in the program that have over 10,000 miles already and they also have another six months to go. I suspect that there will be more than 100 people in the one year trial that will have more than 10,000 miles once it's over and probably about 50 of them will have more than 20k.
Still, the rest of the post was nicely done and informative.
Tom M
MINI-E #250 @ 17,800 miles
http://minie250.blogspot.com/
prndlol says:
01:51 PM, 12/21/09
Say, where are the regenerative braking bits anyway? I assumed they were close to the hub...
chunky_azian says:
05:12 PM, 12/21/09
prndlol, regenerative braking bits are right under the hood.
Electric motors create a voltage that opposes the sourced voltage, which comes from the battery in the case of the Mini. It is called back EMF, which rises with the speed of the motor. When the sourced voltage is higher than back EMF, you have an electric motor. If not, you have a generator, doing regenerative braking.
Back to the Mini's suspension, I wonder why it uses 2 lateral links in the rear instead of one. The mounting points of those links on the chassis seem so close it looks as the hub is attached to a triangle that swings on one pivot on the body.