Pedal box as an alternative to brake vacuum pump.

Technical discussion on converting internal combustion to electric
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TooQik
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Pedal box as an alternative to brake vacuum pump.

Post by TooQik » Thu, 13 Jun 2013, 03:10

I've been looking at pedal boxes from here for my conversion rather than going down the vacuum pump path. (I am actually looking at the three pedal units but thought I'd link the boxes the company markets for EV use).

The positives I see for taking this path are as follows:
  • Saves weight
  • No noise from vacuum pump
  • New pedal assembly (purely asthetical)
  • Brake bias control
  • Saves room in engine bay
  • Less draw on ELV battery
The brake bias control would be a big plus for configuring the motor regen function and ensuring the brake balance is maintained for the vehicle given that it's rear wheel drive.

The only negative I can currently see is this is more expensive (potentially double) option. Has anyone either done this or is aware of any reason why is would not be a good idea or allowed? I've gone through NCOP 14 and the ADRs but nothing stands out to me as a red flag to this approach.

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Richo
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Pedal box as an alternative to brake vacuum pump.

Post by Richo » Thu, 13 Jun 2013, 04:40

I don't think NCOP14 goes into specifics for braking however you may still be asked show that it still works.

Do think that this will still give the same braking performance and be reliable?

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Pedal box as an alternative to brake vacuum pump.

Post by TooQik » Thu, 13 Jun 2013, 06:31

Richo wrote:Do think that this will still give the same braking performance and be reliable?
This kind of setup will give better braking performance than a standard setup as it increases the leverage action of the pedal for maximum braking effect. The brake bias bar is also adjustable to tune the front/rear balance.

I would also say that it would be more reliable in that there is no longer any vacuum parts and there is a seperate master cylinder and reservoir per brake circuit, so brake booster or vacuum line issues become a thing of the past.

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Johny
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Pedal box as an alternative to brake vacuum pump.

Post by Johny » Thu, 13 Jun 2013, 12:53

I think it will be more difficult to document and prove it works correctly than just adding a vacuum pump and reservoir.

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Pedal box as an alternative to brake vacuum pump.

Post by Tritium_James » Thu, 13 Jun 2013, 15:39

You'll have to meet NCOP5 (or whichever one it is) that deals with brake system modifications.

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Pedal box as an alternative to brake vacuum pump.

Post by TooQik » Thu, 13 Jun 2013, 19:36

Johny wrote:I think it will be more difficult to document and prove it works correctly than just adding a vacuum pump and reservoir.
Tritium_James wrote: You'll have to meet NCOP5 (or whichever one it is) that deals with brake system modifications.
NCOP14 states that regenarative braking isn't covered under the standard so any vehicle that utilizes regen must meet NCOP5 (thanks James) and the appropriate ADRs to ensure that brake balance is retained. Given that I'll need to have the vehicle tested for the regen functionality it doesn't seem like a lot of extra work/effort to run a pedal box.

I guess the bigger question is: for those people running regen, how was the vehicle brake balance checked and signed-off for registration?

NCOP5 does state what's tested, but I'd like to find out how they perform the test if anyone has any first hand knowledge of the process.

Lastly, from my readings I'm under the impression that my vehicle doesn't have to comply with ADR 31 as it was built prior to 1/1/1977. If that's the case then as long as the pedal box setup complies with the Australian Vehicle Standards Rules there shouldn't be any issues.

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Pedal box as an alternative to brake vacuum pump.

Post by Johny » Thu, 13 Jun 2013, 21:51

There is a lot of latitude for vehicles manufactured prior to 1969.
1969 to 1988 is covered by ADRs though - Second edition.
The first mention of braking systems appears to be in the Third edition - for vehicles manufactured from 1989. So all you have to do is use common sense - and convince your engineer.

Just a note here. I noticed when driving the 2011 Nissan LEAF that the regen system cuts out during a panic brake. They swap to totally hydraulic. It could be that ABS does it or that ABS gets too complex when regen is involved.

I'm always on the lookout for an approach that would let me run more regen on my EV without comprimising safety on wet corners (with me not the driver).

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Pedal box as an alternative to brake vacuum pump.

Post by woody » Thu, 13 Jun 2013, 22:51

Has anyone done any regen tests to see if lockup is possible?
e.g.
1. adjust regen to maximum torque
2. drive down wet road
3. apply maximum regen under a Jacaranda tree

Probably applicable to Johny and other old^H^H^H^H classic car drivers, I recently replaced my turn of the century tyres with new ones (Pirelli 3000 Energy?), and the Cortina no longer hangs the tail out on every second wet corner.

I suspect some kind of maximum deceleration setting may help, but you'd have to be careful that you didn't end up fighting the real brake.
Also you could work out via a sensor if the steering was straight ahead and/or work out the load on the rear wheels - an electronic version of the brake proportioning valve fitted to modern cars.
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Pedal box as an alternative to brake vacuum pump.

Post by Johny » Fri, 14 Jun 2013, 15:40

woody wrote:I suspect some kind of maximum deceleration setting may help, but you'd have to be careful that you didn't end up fighting the real brake.
I have my accel/de-accel ramps set to 0. I really dislike the idea that any speed ramp is involved for the reasons you said. The Vogue still drives almost exactly like an ICE with CVT except that torque is constant (it's as smooth a silk).

You are right through woody, some tests would be useful. Regen is active down to 1km/h but gets to less than 1 Amp battery current around 3km/h - so the rear wheels would never stop turning but would not get back to road speed once traction had been broken unless something intervenes.

The Lenze VFD can actually provide me with a differentiated speed signal internally so I could look at rate-of-change of motor under regen and stop torque if it exceeds a given value. Kind of like ABS.

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Pedal box as an alternative to brake vacuum pump.

Post by carnut1100 » Tue, 16 Jul 2013, 16:02

Is there a way to ramp up the amount of regen based on hydraulic brake system pressure?
The higher the brake system pressure the more you are obviously desiring to stop, and as most brake systems are 70% front biased the more you press the brakes the less imbalance will be seen on a RWD vehicle with higher regen rates, a FWD vehicle would see no regen imbalance at all.
Also high hydro prssures imply that you want a reasonably quick stop and are already in "stop mode" and are therefore mentally prepared better for the effects of higher regen rates.......
Barking up the wrong tree, or would it work?

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Pedal box as an alternative to brake vacuum pump.

Post by Johny » Tue, 16 Jul 2013, 16:50

carnut1100 wrote: Is there a way to ramp up the amount of regen based on hydraulic brake system pressure?
That's most likely possible but I would not want to do it. Using hydraulic pressure means that the hydraulic brakes are engaging to some extent. When you drive a car with regen you find yourself using every possible moment on regen. and staying off hydraulic brakes unless absolutely required. If I knew the mechanical brakes were "stealing" power from me I'd be annoyed.

The way iMiev and Leaf appear to do it is to use the first 20mm or so of brake pedal for regen. then engage hydraulic brakes further down the pedal. (The Honda Insight Hybrid also does this.) The Leaf also completely cuts regen on a panic stop (tried that!).

In my conversion I just use the top 12% of the accelerator pedal for regen which is completely un-noticable when taking off and lots of fun to drive the rest of the time. Most times I can get to work and back without touching the brake pedal at all (other than to hold on a hill) unless some $&#%wit cuts in front when stopping.

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Pedal box as an alternative to brake vacuum pump.

Post by jonescg » Tue, 16 Jul 2013, 17:14

Just make sure the regen isn't so strong that the car behind you doesn't plough into you because your brake lights didn't come on. I found this when driving the iMiEV around; even throttling off (but not touching the brake pedal) was enough to slow the vehicle down as much as say, dabbing the brakes on a regular car. I had a few cars get right on my tail this way.
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Pedal box as an alternative to brake vacuum pump.

Post by Johny » Tue, 16 Jul 2013, 17:38

jonescg wrote: Just make sure the regen isn't so strong that the car behind you doesn't plough into you because your brake lights didn't come on.
Good point. My brake lights are turned on by my motor controller when I exceed a certain amount of regen. (about 7kW generally). I think it must look like I'm riding my brakes all the way down some hills.

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Pedal box as an alternative to brake vacuum pump.

Post by carnut1100 » Tue, 16 Jul 2013, 18:00

What I meant was to have a small amount of regen on lifting off the throttle, to simulate a petrol engine on overrun, but to get around the problem of excessive regen causing stability issues by overbraking the drive wheels only is it possible to have say 5 kW regen on lift off but as you squeeze the brakes harder and harder the regen ramps up as the car is already settled into a slowing mode, weight transfer has already taken place, and the driver is expecting harsher slowing of the vehicle. Also as the wheels are all being slowed by the hydraulic brakes, if RWD the front brakes are doing a lot of slowing so the rear regen effect is a lower percentage of overall slowing, on a FWD car it merely adds to the front brakes which are already doing most of the stopping.....
Feasible, or crazy?

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Post by Johny » Tue, 16 Jul 2013, 18:10

It's all technically feasible - you could even adjust brake balance permanently to allow for regen. I can't see you getting any changes other than "resembling engine braking" past an engineer though. I think there is a topic "Soapbox on regen braking" or similar where all this has been thrashed out before. Regen comes up a lot!

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Post by carnut1100 » Tue, 16 Jul 2013, 19:53

Don't tell the engineer...... Image
Seriously, it wouldn't replace the need for a proper brake system, but it could significantly reduce brake wear....even if it was dumped to a resistor.

I just finished reading the soapbox thread this morning...it goes off on a few tangents!
As for regen or not, that's a big argument that will keep on coming and going...just thinking if the argument has come down on the yes side, how best to weave that into the braking system as a whole....
Personally, if ya can, why wouldn't ya?

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Pedal box as an alternative to brake vacuum pump.

Post by TooQik » Tue, 16 Jul 2013, 20:19

jonescg wrote:Just make sure the regen isn't so strong that the car behind you doesn't plough into you because your brake lights didn't come on.
I found this a while back and posted it on the DIY Electric car forums. You may have seen it but thought I'd post it here also...

http://www.freescale.com/files/microcon ... AN3380.pdf

This sort of setup would allow control of brake lights based on deceleration rather than the regen function and would avoid the scenario you mention.

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Pedal box as an alternative to brake vacuum pump.

Post by Johny » Tue, 16 Jul 2013, 20:27

carnut1100 wrote:As for regen or not, that's a big argument that will keep on coming and going...
There no argument about whether or not regen is wanted. Even the series DC guys would like it. It's really how to control it and in a conversion it seems there are lots of ideas. Mine is allready too light in the rear end for heavy regen. and other people driving it so, other than a spring loaded "extra regen" control for freeway slow downs, I've got about as much as I dare.

You definitely do not need a dump resistor. I used to have function blocks to re-enable regen after an overvoltage event (by selecting neutral) but I removed them since it never happened. I will require the driver to stop and re-start the car if they want to re-enable regen should an overvoltage event (or BMS alarm during de-acceleration) ever happen. Both those events now cancel regen until next power up - it never happens - and I've tried to cause it!

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