j9fd3s

iTrader: (3)

i have noticed that just about every new car turns off at a stop light, and restarts with the starter when it turns green. for an improvement in gas mileage

after a bit of poking around the only hardware difference is that they get a larger starter, battery and cables.

in the Rx7 world we have the Rx8 starters. we also regularly do the cables, and the battery is easy enough.

has anyone tried it?

peejay

I'd want to do it the BMW way, with a flywheel starter. They also do regenerative braking to make sure teh battery is fully charged. The key is being able to crank the engine at 800-1000rpm.

When stop/start is active, the engine will start as soon as you take your foot off the brake and will be running before you have time to touch the accelerator. Only stop/start I've experienced that was worth a damn.

lastphaseofthis

iTrader: (8)

im in a 2016 altima that does not have start stop...

the mazda way doesn't use the starter, but stops the engine at TDC under compression, and holds cylinder pressure, until its time to start, then throws fuel and then spark.

peejay

Start/stop is IIRC mandatory in Europe so you mainly see it in European cars. Or cars designed for the European market and start/stop was left in for North America because why not?

Aaron Cake

iTrader: (1)

Many cars time the engine stop so that at least one cylinder is under compression. The starters are also designed for this type of duty (saw them at the Denso booth at the NAIAS). They spin faster, have better bearings, better brushes. But that's for OEM reliability. If we are experimenting, that probably doesn't matter. Works a LOT better with an automatic transmission I'd assume because a standard driver could probably toss it into gear and let off the clutch before the engine is started. Unless one uses a large motor like Honda's IMA.

Actually for years I've been thinking of how one would implement this on an RX-7 with say, an MS3-Pro. Since the Megasquirt is open source, we can change the software.

Need inputs from:
-clutch switch
-transmission neutral safety switch

Outputs to:
-starter

Have to modify the main loop in the software to check for the following sequence:
-clutch pressed
-transmission moved to neutral
-clutch released

Fairly simple at that point. Actually without code modifications the MS3-Pro could do that.

Now the custom code would come into play. The closed loop PWM idle engages shortly after the engine has reached idle RPM. Check that status for 2 - 3 seconds and if continuous, cut injectors.

Engine stops, ECU stops running fuel pump.

Code keeps looping and checks for the clutch switch to be pressed. Once press is detected, make sure the car is in neutral then engage starter output. As soon as engine is no longer cranking (ECU status) open the idle valve a bit and continue normal operation.

Obviously we'd need some automatic defeat for creep situations. Honda's IMA does this. If the start/stop cycle repeats a few times, the engine will not be autostopped until the ECU has decided the car has actually been driven and isn't creeping. Or the timeout period was reached.

Clearly this was just the basics. But aside from adding the clutch, neutral and starter connections, experimenting is just software.

In the same sense, an external box could do the job as well run by something like an Arduino. It would receive a signal from the ECU (set up in "programmable outputs") saying the engine is running. Then a signal one idle PWM is entered. Box triggers a relay which kills power to injectors. Engine stops. When clutch input is seen, starter activated.

peejay

They also monitor things like battery state of charge (not sure if they do this by actual direct measurement or by extrapolation) and A/C position. If the battery is discharged or at a low state of health it won't enable stop/start, likewise if you have the A/C on the engine will remain running.

Not sure what they do if you have the heat on. Then again, with electric water pumps, does it really matter?

BLUE TII

iTrader: (9)

To me the prime rotary "reliability" weakness is starting.

I would skip the systems that try to start the engine and then get you under way with engine power and go straight to a "hybrid" drivetrain system of a starter/battery strong enough to move the car away from a stop while starting the engine.

Bonus- say goodby to low compression hot start problems.

It would be awesome if it was direct coupled/full rpm so it could be used as the alternator, to regen charge the batteries on braking/engine braking as well and an electric supercharger for a little squirt of torque/response when you put the pedal down.

Basically, it would be all the work of an EV conversion with lower costs from needing less power and range.



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Hmmn, I guess it doesn't even need to be coupled to the motor... You could do a wheel coupled system- this makes more sense on a FWD chassis. Front engine RWD is a little cramped up front to try to squeeze in halfshafts to pancake motors.

FWD torsion beam or such could just slap a golfkart motor/axle back there.

I was thinking of trying a very simple EV conversion for my 1,300lb leaf spring straight axle rear suspension Honda N600 like this the other day, but even hopped up golfkarts are still pretty slow it turns out (~45mph).

But it woulda been so EASY...

Wait, I just found 10KW EV axle systems from China...

Honda N600 rear


EV conversion


Wheelie time!

j9fd3s

iTrader: (3)

the Rx8 would be easy to do this, the front hubs probably come in some variation that uses a FWD axle.

there are a TON of cars that use a hub design like the Rx8. worst case you'd make a bearing carrier