Project Justification - Why not just swap in the E-Axle motor from an EV car hybrid or Battery EV? - Torque comparison with diesel powertrain.
Explaining what the concept is and is not.
Since the beginning of this project i have been troubled by the issue of how the concept is similar to but crucially different from doing an EV conversion. When i say 'troubled' i mean by way of finding suitable technical knowledge for my project, because my project requirements are not the same as doing an EV conversion.
The most important distinction being the need for a high reduction gear combined with the disconnect.
Firstly, is to mention doing a hybrid i.e. retaining the ICE while adding an electric motor and transmission where there was before none (only freewheeling hubs) - this is already a really big challenge for a DIY home project. To be honest, it is too much difficulty, expense and perhaps impossible to have such design safe or legal for road use.
Hence, my approach all along is to have a design which is only for off-highway use. It is on-demand and only for low speeds, and should not be dependent upon high voltage EV hardware. As such, it will strike some people to be pretty stupid not to 'go all-in' with the EV side, where from that basis could become a step towards a full BEV conversion. However, i believe for this vehicle type, a 3.5ton+ heavy cargo van with FWD ICE, there is a strong and rational argument for adding a so called 'Split-Axle' / 'P4' electric assistance.
I think for many owners of these vehicles who use them for more adventurous campervan touring, will understand the value in such a concept, especially when combined with the upgrade of onboard battery system becoming available with LiFePo4 technology, while also avoiding a complete upgrade of the vehicle to an unnecessarily expensive full 4x4 or one of the AWD 'equivalents'.
An important distinction to make - is that from an oem point of view, now especially with the EV revolution ramping up, these 'white cargo delivery' vans are an extremely important vehicle to become fully electrified to reduce carbon emissions in cities with the increasing volume of online shopping and parcel deliveries. However, the distinction is this - that with the former ICE vans they provided a convenient spin-off of being a great, cost effective leisure vehicle with huge space for fitting out as a camper-van while also affording long range and a high performance (sustained 70mph cruising) in respect of highway driving and towing. Those attributes of low cost (especially in the used market), long range, highway cruising and towing capacity, none of those are yet or are likely to be soon provided by a Battery Electric Van. Yes, really - contrary to the abundant marketing spin in the present media frenzy with EV industry start-ups. And we have not yet added the goal of improved traction which would demand a further expensive and heavier 4x4 BEV.
For full BEV campervans, this vehicle category will become provided by the smaller, low roofed, lighter category of vans, such as the e-NV200, gross eight 2250kg is actually lighter than many SUV BEVs. Where reducing energy consumption and restricted performance are the compromises compared with former Ducato and Sprinter sized van camper conversions.
Okay, so - i can try to explain the primary goals of the project are to provide a sufficiently high torque to be useful for a low speed recovery, but within the constraints of a low voltage, low cost retro-fittable kit. With these features in mind, i have spent/wasted many hours thinking over and analysing the torque and the traction requirements of my electric assistance drive.
Much of the time spent agonising over how explain it in a meaningful way, I did begin, like an engineer does, by examining the fundamental traction requirements. This provides many valuable charts explaining the traction limits, resistance curves and grade-ability targets of a vehicle. It was from this basis that i arrived first to my target of circa 3000Nm axle torque and by some luck i found that my limited choice of 48v motor, the one salvaged from the Twizy car, and the reduction gear combined with the added rear diff axle could meet the target.
More intuitively, and easier for most people to understand, is to present a comparison between the amount of axle torque being provided by the electric assistance compared with the native diesel powertrain. This explanation starts from what most people recognise, which is the manufactUre quotes motor or engine shaft torque, (which is really rather misleading when quoted in absence from the rest of the powertrain!), not helpful i must say!) - and i try to build the charts showing how the powertrain proper(gearbox ratios and final drive/diff ratio) lead to what really matters = the torque at the road wheels. There are two parts i have uploaded in this post and a next post, a first part focuses on the common diesel powertrain* and the envelope of my electric assistance design, and the second part adds for comparison some the electric motors available as eAxles and from other BEV equipped Ducato/Promaster vans including the latest official E-Ducato. My hope with presenting this information, is to avoid unfair criticism and comparison between what i am doing and what is appearing elsewhere within the EV community and from oem BEV vans.
(*The Promaster van also uses a V6 gasoline engine with an auto 6-speed gearbox using a torque converter. This powertrain i have also charted, i will post it another time.)
There is another further presentation i will post where i have researched some of the other concepts which have been done in the past. Just to give something away, the ALKO-Hybrid-power chassis (https://www.alko-tech.com/en/hybrid-power-chassis) vehicle is certainly the most interesting in my view, but that company (i think now owned by Dana) have yet to bring that vehicle to market, i think since last year(2020) they are very close. It is though (the ALKO-Hybrid power chassis) a high voltage, full time, non-retrofit system and will surely have a high price tag. I leave you now to become overwhelmed by too many charts with rather too many different colored line and notes. But - the information is all in there to explain itself.
https://drive.google.com/file/d/1_3YJ3RkBCmzEZ4l-8KZHttf5p74pK2LN/view?usp=sharing
How are you synchronizing the FWD and RWD mechanisms? They seem totally independent. Regen ability while braking or going down a hill would be great too.
ReplyDeleteyes, the synchronizing of the electric rwd with the diesel fwd is a most interesting aspect. My intention is to calibrate the foot throttle pedal position combined with diesel enginine fueling(*) first as a request to bring a proportional torque from the electric drive with speed limit on rear wheels to avoid them spinning faster than the front wheels. The main challenge i expect is to depend upon how instanteous and accurate can be the diesel fuel signal as representing Torque at the Front Wheels. The Important complication to bear in mind here, is Q. How to know the actual torque being applied at the front wheels, given that it controlled by the foot clutching of the diesel transmission. Hence teh ide to hope that instantaneous fueling can be used as a measure of that actual torque at fwd.
DeleteFrom that model, the strategy is for the Electric motor to provide a complimentary proportional amount of torque adding to the fwd. And to achieve that with minimal wheelspin (might look cool but is ineffective traction.) Difficulty may arise if there is excessive fwd wheelspin, but since this should be accompanied by a drop in applied torque(i.e. reduced engine fuel) this signal will feed the control of the rear electric motor.
Regarding Regenerative braking, Yes for sure this is a desireable feature. But in this first prototype build i am not thinking about it, it adds too much complication. The benefits of regen would be greater if the system could remain engaged for some higher road speeds, then it could be useful for those long hill descends rather than using friction brakes. But for the so far intended off road track use at 20mph, there is small benefit from regen.
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