MINI E regenerative brakes will turn on brake lights without hitting the pedal
Click the MINI E for a high res gallery
An interesting question came up the other day regarding my quick drive review of the new battery powered MINI E. I noted that the MINI uses much more regen than other electrically-driven vehicles that I've tried, with deceleration on the order of about 0.4 g. That's actually pretty heavy braking. The deceleration from most braking by drivers in typical operation is less than 0.2-0.25g. With conventional friction brakes, as soon as the brake pedal is applied, a switch on the pedal arm turns on the brake lights, warning following drivers that you are slowing down. Since most cars with regenerative braking usually don't give that much decel without applying the brakes, it's not a problem. We checked MINI spokesperson Nathalie Bauters who told us the brake lights come on when the deceleration tops about 0.15-0.2 g, or just a bit more than you might get from engine braking. So with the MINI E you need to adjust your driving to modulate light braking by adjusting pressure on the accelerator instead of the brake pedal.
Gallery: Quick Drive: MINI E
[Source: MINI]
Photos Copyright ©2008 Sam Abuelsamid / Weblogs, Inc.
Reader Comments (Page 1 of 1)
Yanquetino 3:00PM (11/26/2008)
I would expect this, since AC Propulsion is providing the drivetrain. Over two years ago the first review of their eBox (http://www.stefanoparis.com/piaev/acpropulsion/eBox/ebox.html) stated this:
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In case you are wondering about aggressive regen and notifying drivers behind you of your deceleration via brake lights, don't worry because AC Propulsion has already figured this out. Their motor control samples motor speed at something like 10Hz, and since the motor drives through a fixed ratio, motor speed is an unambiguous indicator of vehicle speed. So, by continually sampling speed one knows when the car is slowing down, and the brake lights are turned on automatically if the deceleration exceeds a low threshold. It works in reverse too. The brake lights also come on with actuation of the brake pedal as in a normal car. Interestingly, you can be using quite strong regen holding speed steady on a downhill and the brake light will not come on.
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That's a pretty clever bit of engineering. It's nice to know that if you are heading downhill, with your foot competely off the accelerator, and thus regenerating juice, the brake lights do not come on. It is only a significant drop in motor speed (or actually pushing the brake pedal) that triggers those lights --which drivers behind you would appreciate!
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gorr 3:16PM (11/26/2008)
I won't buy it if renegerative breaking is not ajustable by the driver.
This is the perfect thing to crash when the road is slippery, especially when there is snow or heavy rain. You left off the gas pedal then you car break without you modulate it and this is annoying and can be dangerous sometime is close traffic. This recharge the battery but compromise hypermilling done and modulate by the driver. In canada where there is snow and ice on road, most often we just let off the gas pedal and gently apply the breaks to slow down smootly without losing control. This thing can block the wheels on less then perfect road condition.
Maybe this is the reason a tesla had an accident one week ago, the driver had the breaks turn on automaticaly on wet road conditions and the back wheels jam and he destroy his car.
These cars are badly though from the start by peoples that don't know how to drive and desigh a car. Even Gm is better then that.
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Bill 5:32PM (11/26/2008)
Tesla's traction control works on regen braking as well as acceleration (as it should). See their blog on the subject:
http://www.teslamotors.com/blog4/?p=65
The e-vehicle drivetrain offers *much* more control over wheel skidding than an ICE vehicle. Rapid throttle lift off in a turn and/or in slippery conditions is never a good option in a car with a manual transmission, especially in low gears. The 1st gear deceleration in my '89 BMW has got to be ~0.4g or more and there is no drivers' aid to help as there can be in an e-vehicle.
-Bill
Chris M 11:37PM (11/26/2008)
The regen is controllable by the driver. There is a lever that allows full adjustment of the degree of regen to suit your driving, you can reduce the degree of regen or even turn it off if you prefer.
ed 3:32PM (11/26/2008)
It does seem a pointless thing to have such aggressive regen, its always going to be more efficient to let a vehicle coast under its kinetic energy rather than converting it back to electricity then back to motion & so on, a driver adjustable option would be essential i would say.
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PeterG 3:49PM (11/26/2008)
I agree and disagree with some of the replies so far. I do think having different regen settings might be a good idea for those not used to driving such a car (mostly those coming from automatics, used to coasting).
But personally I think this strong regen controled by the go pedal is ideal. The behavior should be second nature to those who drive manual and use a lot of engine braking already like I do. Of course it will take some getting used to.
This will give you excellent control of acceleration/deceleration to balance the car perfectly. make the brakes a redundant emergency only system.
It does not mean you can't coast. You just have to find the right spot on the accelerator to essentially coast.
This does not make the car spin out if you take your foot off the pedal by mistake, the ABS sensor will certainly be hooked up to regen to keep the wheels from locking.
This is really the way to go IMO. Maybe I will enjoy an electric after all.
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Geoff de Ruiter 6:47PM (11/26/2008)
I completely agree. you just back off the pedal just enough that the vehicle doesn't accelerate, thus coasts, and the then electricity stops flowing. Such a minor learned behavior that is already so similar to what we do. Then if you know you'll be stopping or wanting to slow down you take your foot fully off and regen kicks in. This is similar to when one tops out in an electric car and then goes faster by going down hill that bit more, the engine turns off because otherwise it would wreck the motor/drive train. This is actually a very intelligent system and hyper-milling wont be compromised. More aggressive regen is what we will want, but only with the option for coasting by half letting off the accelerator. This is the way it should be.
rob 9:46PM (11/26/2008)
What might be nice is if you could configure the size of the "dead spot" in the accelerator travel where you're neither applying drive power, nor regenerating. Or maybe get some tactile feedback when you're in the "coast" position. Just a little detente in the travel or something.
And a hill-holder would be nice. If you're stopped and the car detects it is on a slope, when your foot comes off the brake the motor should hold the car from rolling back. This could be incorporated hydro-mechanically in the rear brakes (Subaru's system) or via software in the drive system.
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paulwesterberg 9:13AM (11/27/2008)
The prius already does engages regen when you take your foot off of the accelerator. It is probably less than the mini since you cant adjust it, Im not sure if the brake lights come on.
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Matthijs 4:28PM (11/27/2008)
Here is a test drive of the E-Box in 2007 and 1:00 into the video everything about the breaking is explained. The system must be identical to that of the mini, also AC-Propulsion.
http://www.youtube.com/watch?v=6UvD6dQvsB8
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