Press the Brake Pedal - Get More Regen

[azemon]

I noticed something surprising while driving in D mode. If I take my foot off the gas, the needle moves about half way into the regen portion of the gauge. When I lightly touch the brake pedal, the needle moves all the way to the bottom of the gauge indicating full regenerative braking. Very cool. Does anyone know if the mechanical brakes are even engaged at that point? Or if the additional braking force is only from the regen?

-- Art Z.

 

[PV1]

The first inch or so of travel has next to no friction brakes (enough to hold you stopped on level ground in neutral, but just barely).

I coasted in neutral to get a feel for the friction brakes. (not recommending you to do this, just explaining what I did). If you manage to find a decent downgrade with a full charge, you may experience what a difference low regen makes.

 

[Don]

Mitsubishi says the regenerative braking is added to the friction braking when you touch the brake pedal - Some here say it's not, but they don't reference anything written on the subject

The next time I get over to Harbor Freight I'm gonna pick up a laser thermometer and do some tests to see if you can actually get that 'extra' regen without heating up the brakes

I drive 100% of the time in 'B' mode, so it buries the needle all the way to the left anytime I lift completely off the go pedal . . . . I seldom ever touch the brakes until I'm under 15 mph or so

Don

 

[siai47]

It's kind of a mechcanical and electronic mix. If you look under the dash, right up near the top of the brake pedal, you will see a round switch which is the brake light switch. You will also see, to the left, another switch (potentiometer) connected by a linkage to the brake pedal. This is the regen control. Think of it a a accelerator pedal in reverse. The more you push the brake, the farther the linkage rotates the switch applying more regen. Kind of a simple way to provide regen control. A lot of vehicles use brake fluid pressure sensors to provide control of the regen, however this system could (if properly adjusted) provide regen with no brake pressure. So, the amount of regen in the I-MiEV is directly related to pedal movement not brake pressure. At a certain point (after the free pedal in the hydraulic brake system) both the regen and hydraulic brakes will come into play. If you want to see what regen is doing during braking--at a safe location--slip the car into netural during braking. The regen will stop and only the hydraulic breaks will be stopping the vehicle.

 

[aarond12]

I also run in "B" mode all the time. I've noticed if I press the brake pedal a little bit, the regen goes even higher than the normal deceleration of "B" mode. I have to press it farther to notice friction brakes being engaged. Most of the time I take advantage of this extra regen while braking, unless some Honda Odyssey pulls out in front of me and other traffic, even with horn sounding, and stops. Not that it would ever happen yesterday.

 

[RobbW]

While on the subject of brakes, has anyone else noticed this? Often, when traffic slows down/stops faster than I would prefer, I start pressing the brake pedal and at some point there is a momentary lapse of braking. It only lasts for a split second, but it freaks me the heck out. I assume this must be the point where the regen completely stops and the mechanical brakes fully engage. Like I said, this usually only happens when I have to stop quickly. And that's the reason it really freaks me out when this happens because I'm trying to stop faster. And when this happens I get a momentary flash of panic thinking my brakes are failing and I'm going to rear-end the car in front of me.

 

[justind]

I've noticed that as well. For me it's happening after hitting a bump while braking. I have thought that is was a function of the ABS and somehow a bump translates to wheel slippage to the sensors and that turns off the regen. I have noticed the same thing with my Honda Fit, on that car the ABS will pump the brakes if I drive over a good sized bump while braking.

 

[PV1]

The quick lapse in a panic brake is the time it takes the controller (most likely limited in firmware) to switch from power to regen. The same happens when you go from power (2/3 to full power) to no pedal input in B mode. For example, mash the pedal for full acceleration, then let off when you get up to speed. you'll feel a moment with no power or regen, then regen kicks in. It's masked by the slower power meter moving so you think the power ramps down and immediately goes to regen.

Any braking you feel in this short moment is all friction. Just goes to show how the car can hit 40 kW regen (I've seen this when almost driving past my exit). Bumps definitely kick out the "regen+" and takes about 3 seconds to re-engage.

 

[azemon]

Fascinating. Thanks for all the good info!

-- Art Z.

P.S. I'm excited. My car should be at the dealership in a few hours. If everything goes well, I can pick it up tonight.

 

[fjpod]

I've never felt this lapse in braking with my i. But my Prius has this phenomenon and it is well documented by many drivers. They say it is caused by the anti-lock brake system kicking in when the car rumbles over uneven or wet surfaces...wet bumps, gravel, etc. It is not thought to be the relationship between friction and regenerative braking. What it seems to me is that the anti-lock system engages too easily with minor wheel slippage.

I don't know if this exactly applies to the i....

on a slightly different note...did someone say that MM said that friction braking engages first, before regen? I would highly doubt this as the ampmeter indicates otherwise. I suppose its possible, but why would MM build an inefficient system like this?

 

[PV1]

I don't know about anything Mitsubishi has said about this, but my 2 cents for the split second it takes for regen to kick in during a panic brake, friction beats the regen, but regen quickly comes on after (which led to another member saying they thought their brakes were failing during a panic brake).


Regen always beats friction in normal driving.

1. If you panic brake with the regen already on (someone pulls right out in front of you while traveling downhill), you'll immediately get full regen and whatever friction by pushing on the brake.

2. If you hit a bump while your foot is on the brake, you can lose the extra regen from pushing on the brake (ASC cutout), but you'll still have "no-pedal" regen. It goes back to normal after a few seconds and a pump of the brake pedal.

note: One thing that caught me off guard, if you push the brake quickly enough, you'll engage emergency brake assist where you'll get extra assistance and the pedal will sink very easily. I almost stood my car on its nose the one day.

Congrats on getting the i-MiEV. Let us know when you get it.

 

[JoeS]

We actually have ventured into three separate topics:

1. Variable regeneration with brake pedal application.
2. Transition between regen and friction brakes.
3. Vehicle response when ASC/ABS kicks in.

1. Regeneration is activated when first slightly depressing the brake pedal and continues all the way through to the activation of friction brakes (and indeed continues, complementing friction braking). The amount of regeneration is a function of vehicle speed, and I'm under the impression that the amount of regeneration is also a function of brake pedal travel (need to pay attention to this the next time my wife lets me drive 'her' iMiEV). There is a transducer attached to the brake pedal that I *think* performs this variable-regen function. As I've mentioned many times before, I would sure love to have a paddle by the steering wheel to be able to control the amount of regen with my fingertip - I have such a setup on my Gen1 Insight.

2. The transition between regenerative and friction braking on the iMiEV is (almost?) imperceptible IMO, and a tribute to Mitsu's engineers for having fine-tuned such a smooth transition. I wouldn't mind having a dashboard indicator turn on when friction braking actually engages (so I can stay away from it). Perhaps a tap into the hydraulic brake line and a simple switch would suffice, or maybe it already exists and Canion could pick it up?

3. A separate topic is the strange rough-surface response of the ABS and ASC. This is IMO way too sensitive and the disabling of regen (and very slow re-enabling) is especially bothersome on California's neglected roads. For example, on a high-speed sweeping downhill curves as regen is nicely holding the car back and pumping amps back into our battery, when the car then hits a rough spot on the road the regen instantly turns off and ASC/ABS starts selectively loudly chattering away hitting various wheels' brakes and (presumably) keeping the car's attitude in check. It does take quite a few seconds for the system to recover and regen to start working again. I am very happy Mitsu included the ASC disable switch as in my case it enhances spirited mountain driving of what I consider a well-balanced and easily-controllable little car.

 

[Don]

While on the subject of brakes, has anyone else noticed this? Often, when traffic slows down/stops faster than I would prefer, I start pressing the brake pedal and at some point there is a momentary lapse of braking. It only lasts for a split second, but it freaks me the heck out. I assume this must be the point where the regen completely stops and the mechanical brakes fully engage.

In 18 months and more than 13,000 miles, I've never noticed this even once . . . . but it's sure interesting to read what others theorize is causing it!

Don

 

[fjpod]

We actually have ventured into three separate topics:

1. Variable regeneration with brake pedal application.
2. Transition between regen and friction brakes.
3. Vehicle response when ASC/ABS kicks in.

1. Regeneration is activated when first slightly depressing the brake pedal and continues all the way through to the activation of friction brakes (and indeed continues, complementing friction braking). The amount of regeneration is a function of vehicle speed, and I'm under the impression that the amount of regeneration is also a function of brake pedal travel (need to pay attention to this the next time my wife lets me drive 'her' iMiEV). There is a transducer attached to the brake pedal that I *think* performs this variable-regen function. As I've mentioned many times before, I would sure love to have a paddle by the steering wheel to be able to control the amount of regen with my fingertip - I have such a setup on my Gen1 Insight.

2. The transition between regenerative and friction braking on the iMiEV is (almost?) imperceptible IMO, and a tribute to Mitsu's engineers for having fine-tuned such a smooth transition. I wouldn't mind having a dashboard indicator turn on when friction braking actually engages (so I can stay away from it). Perhaps a tap into the hydraulic brake line and a simple switch would suffice, or maybe it already exists and Canion could pick it up?

3. A separate topic is the strange rough-surface response of the ABS and ASC. This is IMO way too sensitive and the disabling of regen (and very slow re-enabling) is especially bothersome on California's neglected roads. For example, on a high-speed sweeping downhill curves as regen is nicely holding the car back and pumping amps back into our battery, when the car then hits a rough spot on the road the regen instantly turns off and ASC/ABS starts selectively loudly chattering away hitting various wheels' brakes and (presumably) keeping the car's attitude in check. It does take quite a few seconds for the system to recover and regen to start working again. I am very happy Mitsu included the ASC disable switch as in my case it enhances spirited mountain driving of what I consider a well-balanced and easily-controllable little car.

+1

 

[JoeS]

One of the features of ASC is a brake pedal application rate detector: in a panic braking situation, the iMiEV detects the brake pedal being jabbed and applies SERIOUS braking - saved a deer's bacon more than once and I'm amazed at how well the car stops despite the skinny tires. Like Don, I've never noticed the "momentary lapse in braking" that RobbW describes.

 

[PV1]

While on the subject of brakes, has anyone else noticed this? Often, when traffic slows down/stops faster than I would prefer, I start pressing the brake pedal and at some point there is a momentary lapse of braking. It only lasts for a split second, but it freaks me the heck out.

Robb, what speed does this occur? After re-reading your post, I think I might have an idea what you're talking about (originally thought you were talking about panic braking).

 

[jray3]

In 18 months and more than 13,000 miles, I've never noticed this even once . . . . but it's sure interesting to read what others theorize is causing it!
Don

Though I'd wager that Don's car hasn't been more than 20 feet above sea level since he bought it, unless it's climbed the parking garage at MS Coast Coliseum!

I've felt the slip on many wet and steep slopes here around Seattle.

 

[Don]

Though I'd wager that Don's car hasn't been more than 20 feet above sea level since he bought it, unless it's climbed the parking garage at MS Coast Coliseum!

Close . . . . but the elevation of my house is . . . . 47 feet! :lol:

You forgot the bridges - I-10 over back bay is about 80 feet above the water and the new 330 million dollar Biloxi - Ocean Springs bridge is right at 100 feet

But . . . . I think it's safe to say that my car has never been driven above about 200 feet elevation since I bought it new

Don

 

[RobbW]

Robb, what speed does this occur? After re-reading your post, I think I might have an idea what you're talking about (originally thought you were talking about panic braking).

I'll try to pay more attention to the exact speed the next time it happens. With that said, it seems to all depend on what my original speed is and how quickly I am braking. No, this is not happening during a panic brake. Luckily, I have not had one of those yet since getting the Meepster. It most often happens as I am slowing to a stop and the car in front of me starts slowing faster than I anticipated. It's not a panic brake but definitely have to apply more pressure than I had been. Sometimes the "slip" seems to happen around 20-25 mph when I'm braking from an original speed of 45-50 mph. Other times it has happened at a slower speed, say around 15 mph when I'm slowing from 35 mph or so.

 

[PV1]

I noticed that regen will sort of drop out between 10 and 15 mph. Nowadays, I have a tendency to ride regen out, then get on the brakes right as I come up on the person. However, if there is no one around, I'll regen down until it cuts out, put it in neutral (for zero creep), and ease up to the light, just in time for it to turn green as soon as I stop. :roll: