MX-5 Hybrid conversion

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PLB-389
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MX-5 Hybrid conversion

Post by PLB-389 » Thu, 09 Aug 2018, 15:33

Hi All,
Long time no post. I'm putting together a hybrid electric MX5 based on an NA6 chassis. Parts are already bought as is the car. 10kW AC induction motor from HPEVs will be mounted on the transmission output shaft. 96V 1.4kWh battery pack made of 30x40150 LiFePo4's stuck in the boot along with a curtis controller. The controller will be taking instructions from a dSpace MicroAutoBox, which co-ordinates between the engine and the electric motor.
The project deadline is rapidly approaching but I've been having trouble getting workshops to understand, let alone do the fabrication work. The one I've been dealing with so far has had the car for months and seems quite afraid of quoting, I think because they've never done any EV work before (their workshop is filled with japanese mega-HP drag machines). Does anyone have any recommendations on who might be able to get the work done in quick time? I'd be willing to transport the car and electrical componentry anywhere along the east coast if I can get it done by the end of the year.
Cheers
Peter
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jonescg
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Re: MX-5 Hybrid conversion

Post by jonescg » Thu, 09 Aug 2018, 15:46

Geoff O'Toole in Sydney might be able to help - because he needs more things to work on :P
Sounds like a neat project - the motor will effectively be the transmission?
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PLB-389
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Re: MX-5 Hybrid conversion

Post by PLB-389 » Fri, 10 Aug 2018, 00:58

No we'll still have the standard 5 speed manual in place, the motor goes between the transmission and the diff. In that position it acts as a load regulator for the IC engine, can do pure EV operation (as far as the 1.4KWh battery will allow), and regen. It's a parallel arrangement but not one that has been done often before, and certainly not in any commercially available HEV we've seen. Because the motor is downstream of both the IC engine and the transmission it lets us do some nifty things with the gearshift process (seamless single-clutch shifting and potentially flat-shifting without crunching synchros), and we may try to do away with the gearstick altogether in stage 2 of the project, which is theoretically possible and makes gearshift control somewhat easier (no more predictive algorithms for target torque).
Cpt. Pete (Barge Pilot)

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Re: MX-5 Hybrid conversion

Post by antiscab » Fri, 10 Aug 2018, 06:52

Sounds like quite the project. I was originally going to suggest grabbing a Honda IMA unit, as that's around 10kw, already integrated, does Regen and has a 144v system voltage. Although that puts the motor on the motor side of the transmission

How are you planning on shifting clutchless even with the motor in place? Or are you talking more about not having to stop accelerating just to change gear, as the 10kw motor would still be supplying power?
Matt
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Re: MX-5 Hybrid conversion

Post by T1 Terry » Fri, 10 Aug 2018, 11:29

Is the idea to uncouple the electric motor from the gearbox output shaft for pure EV driving? Simply selecting neutral in the gearbox without the ICE running will result in a seized up gearbox fairly quickly because the lubrication requires splash feed created by the ICE spinning the input shaft.

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Re: MX-5 Hybrid conversion

Post by brendon_m » Fri, 10 Aug 2018, 11:54

In a manual box it shouldn't be an issue. You can flat tow a manual with out any traumas. There should still be enough oil splashing around to keep things lubed and with a small battery pack it's not like it'll be 100's of kilometres as ev only.

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Re: MX-5 Hybrid conversion

Post by T1 Terry » Fri, 10 Aug 2018, 14:26

brendon_m wrote:
Fri, 10 Aug 2018, 11:54
In a manual box it shouldn't be an issue. You can flat tow a manual with out any traumas. There should still be enough oil splashing around to keep things lubed and with a small battery pack it's not like it'll be 100's of kilometres as ev only.
In neutral none of the gears are actually turning when the output shaft turns but the input shaft is held stationary because all the drive gears are not engaged/locked to the output shaft. All the needle roller bearing are spinning inside the drive gears and around the output shaft bearing area with no oil to lubricate them, they don't last very long. After lots of gearbox failures in vehicles being flat towed behind motorhomes it was determined that only vehicles with a transfer box that could have neutral engages so the main box was not driven or dropping the tail shaft were the only safe methods for flat towing a vehicle, other than that they had to go on a trailer.
I really wish this was not the case because I'd love to flat tow my Kombi behind our motorhome but that will have to wait till we do the electric conversion, then we can tow it in 4th gear so all the oil required gets splashed around inside the box

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Re: MX-5 Hybrid conversion

Post by PLB-389 » Fri, 10 Aug 2018, 15:23

antiscab wrote:
Fri, 10 Aug 2018, 06:52
How are you planning on shifting clutchless even with the motor in place? Or are you talking more about not having to stop accelerating just to change gear, as the 10kw motor would still be supplying power?
Initially we're not going to try clutchless shifting but in theory our supervisory controller (the dSpace unit) can be used to torque match as it's controlling both the throttle angle and the e-motor torque. We can use it to target zero torque applied across the gearbox at which point you can disengage the gear clutchless. Then its a matter of speed matching engine and output shaft target speeds, and engagement should go back in clutchless. It's really just a neat party trick - our main aim is to do manual gearshifts without loss of acceleration for the time being.
T1 Terry wrote:
Fri, 10 Aug 2018, 11:29
Is the idea to uncouple the electric motor from the gearbox output shaft for pure EV driving?
The emotor is permanently coupled to the transmission - the clutch will be controlled disengaged for EV driving (which is only permissible at low speeds in gear 1, such as crawling in traffic). Remember its a 1.4KWh battery, and a hybrid, so EV mode will be very limited.
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Re: MX-5 Hybrid conversion

Post by brendon_m » Fri, 10 Aug 2018, 18:15

In neutral none of the gears are actually turning when the output shaft turns but the input shaft is held stationary because all the drive gears are not engaged/locked to the output shaft. All the needle roller bearing are spinning inside the drive gears and around the output shaft bearing area with no oil to lubricate them, they don't last very long. After lots of gearbox failures in vehicles being flat towed behind motorhomes it was determined that only vehicles with a transfer box that could have neutral engages so the main box was not driven or dropping the tail shaft were the only safe methods for flat towing a vehicle, other than that they had to go on a trailer.

Most owners handbooks will say it's safe to flat tow for a certain number of kilometres. Its normally about 80 to 100km . There will be some manual cars that can't be towed but they are the exception not the rule. Towing behind a motorhome for 500km without stopping is a bit different to driving/coasting for 10km down a hill or in ev mode. On top of that there is plenty of anecdotal evidence online from the USA where people tow their miata's behind their "RV's" without hassle and without modifications.

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