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Upgrades (non TDI Engine related) The place of handling, lighting and other upgrades that do not relate to the performance or economy of the TDI engine. In other words upgrades to your TDI that don't fit into TDI Fuel Economy & TDI Engine Enhancements.Please note the Performance Disclaimer

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Old January 12th, 2018, 05:27   #1
efeballi
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Default Crazy project: Hybrid retrofit

Hello all,
My country passed a law, allowing a hybrid to pay less taxes. I've always been intrigued by the idea of having a hybrid car, so I thought maybe it'll be doable.
So the idea originally is,
-9 kWh underboot battery
-Two 60 kW in-wheel motors
-Necessary electronics (inverters etc.) on other available spaces of the car
I summed up the costs to be in the $7-8000 region with some margin for unexpected stuff. With the reduced taxes I'll (hopefully) recoup this. Not to mention the savings in fuel (which is crazy expensive here).
However, I have some reservations in this config, those being:
-inwheel motors are circa 20 kg in (unsprung) weight, this will adversely affect handling
-inwheel motors generally don't leave enough space for brakes, for those cases they are offering a 2002 Opel/Vauxhall Astra rear drum brake integrated to the assembly, adding 6 kg (integration of this brake to the car?)
-how will ESP play with powered rear wheels?
-engine-off driving would be very nice and is actually one of my goals, how could I power the car systems (brake vacuum, power steering, cooling etc.)? I've been googling for electric powered substitutes but so far found nothing
In case the in-wheel motors are a no go, another option that I thought of is to fit a Golf 4Motion/Altea Freetrack rear axle (w/o propshaft) and power the wheels using a single electric motor, better if clutched. This would have the obvious benefits of having less unsprung weight and the ability to use normal brakes, not to mention simpler electronics to power one electric motor instead of two.
So I've been mentioning potential drawbacks, here are the potential benefits:
-5.6 sec 0-60 time (stock 9.8), limited by the power cap of the battery
-up to 15 miles electric range
-30% less fuel used in a 100 mile trip
Obviously the economy gains are reduced the longer the trip gets.
The battery pack will be charged at home every night and also through regenerative braking.
This all sounds lunatic, I know, feel free to shoot down my ideas.
Thanks
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Old January 12th, 2018, 12:04   #2
SilverGhost
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We had the Jetta Hybrid her is USA. I have often thought about taking a donor car and maybe swapping the 1.4 TSI for a TDI. Car already has all the electronics worked out and can get mid 40's MPG (5.2 l/100?).

Did VW sell hybrid Mk6 Jetta over there? Maybe a smaller Audi hybrid? Easiest way to build is probably going to be start with a donor hybrid. Maybe a car that was totaled by side or rear impact?

Jason
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Old January 12th, 2018, 12:13   #3
efeballi
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No VAG hybrids were ever sold in Turkey as far as I know. My only candidate was a Golf GTE, I google'd it, no luck.
Also the Jetta you mention is a series hybrid, no? It would be a lot of headache to have the engine and electric motor to play together, I would think...
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Old January 12th, 2018, 14:55   #4
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"In wheel" motors - particularly of the power and size that you are talking about - are not practical. Put the thought out of your mind.

The 4motion rear drive assembly with a motor operating it instead of a propshaft is a much more viable way to do this.

The main problem you are going to run into, and unless you are either an electronics wizard or are happy with driveability problems that would drive the average person nuts, is integrating your new homegrown power unit with the vehicle's native systems. How do you interface with the accelerator and brake without causing problems with the vehicle's own powertrain?
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and before that ... 1996 Passat TDI, Silk Blue
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Old January 12th, 2018, 15:36   #5
efeballi
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Quote:
Originally Posted by GoFaster View Post
"In wheel" motors - particularly of the power and size that you are talking about - are not practical. Put the thought out of your mind.

-snip-
Um...
https://in-wheel.com/product-category/motors/

Have a look. I calculated the 0-60 time and sized the battery for the M700 motors.

You're right about the drivability issues which will need to be painstakingly sorted, but that's part of the challenge for me.
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Old January 12th, 2018, 18:22   #6
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There are reasons why all production electric vehicles from mainstream manufacturers do not use anything of the sort. Don't think for a moment that the engineers don't know about that option and have not explored it!
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and before that ... 1996 Passat TDI, Silk Blue
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Old January 13th, 2018, 12:14   #7
efeballi
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I'm not a mainstream manufacturer so I have different constraints.

I find this line of thinking the same as anti-tuning people who say manufacturers would also sell tuned cars straight from the factory if tuning was as easy as a software flash.

There are reasons why people flash their ECU's and there are reasons why manufacturers use conservative tunes for their cars. This does not make either side stupid.
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Old January 13th, 2018, 14:31   #8
GoFaster
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OK, obviously you need to be pointed directly to some of the issues.

Think "unsprung weight" for a moment. The proponents of wheel motors love to gloss over its bad side effects.

Read this: http://www.eng-tips.com/viewthread.cfm?qid=343389

The other thing you're going to have to be careful about, is the design of the cables carrying the current to the motors. They are generally made of copper, and given the amount of power involved, they have to be reasonably heavy cables - these are not ABS wheel-speed-sensor cables. Copper does not have an infinite fatigue life. If you bend it, it eventually breaks. By mounting the motors on the wheels, those cables have to flex with all suspension movement. They will eventually fail. How many cycles until failure? Depends on your design. When the motor is fixed to the chassis or subframe, you don't have this issue. Sure, there is still a bit of relative movement, because chassis and subframes are mounted in bushings to absorb vibration, and bushings flex. But it's peanuts in comparison to suspension movement. The fatigue life of the cables should not be taken for granted.

Electric motors generally like spinning fast. Spinning fast (and using a gear-reducer to obtain the required torque) makes better use of the magnetic fields and makes better use of the copper and iron in the motor. Easy to do when the motor is mounted separately and drives through reduction gearing. Not so much when you are stuck with the same rotation speed as the drive wheels.

What about sealing? Normal wheel bearings are sealed (to a practical extent) against ingress of water (and salt-water solution, for those of us in areas that have winter). The short term consequence of a little bit of water intrusion into a bearing is not catastrophic. Obviously in the long term it leads to corrosion and worn-out wheel bearings. Salt water intrusion + high voltage electrical components ... you tell me.

Obviously the vendor that you have found has an interest in promoting their product. All I'm saying is "buyer beware". I work for automotive parts manufacturers and I've seen some of the testing that the OEMs are doing. The OEM engineers are fully aware that you can put electric motors within wheel hub assemblies. And yet, they don't do it that way. Ask yourself why. Ask tough questions. Don't accept sugar-coated answers.
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Old January 13th, 2018, 14:43   #9
efeballi
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Thank you for the detailed explanation. This was what I've been seeking all this time. I think I know better than to buy sugar coated marketing bullcr@p.

I'd mentioned the unsprung weight issue in the OP, thank you for raising the other issues like water ingress and cable flex with suspension movement.

And sorry for not accepting "forget about it, they are $hite" as an answer

Well I guess the in-wheel solution is out the window. Now to find an electric motor to drive the rear diff. Any idea of the torque rating of the Golf 4M rear diff?
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Old January 13th, 2018, 15:38   #10
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I don't think you need to worry about the input torque rating of the 4motion rear diff, you're not going to exceed it with what you are trying to do!

It appears that your vehicle is on the VW PQ35 platform, same as Mk5 Golf, and if that's the case, it should already have independent rear suspension which is mounted on a subframe. The entire 4motion rear subframe assembly is completely interchangeable with what you have. Brakes, hubs, and all that will swap over with the subframe and will work with what's already in your vehicle. Unbolt the non-driven subframe, bolt in the complete 4motion subframe, sort out the alignment, done! There may be some fuel tank and exhaust system modifications needed but I'm pretty sure a fuel tank from a 4motion vehicle will fit (and it will be designed to clear the drive shaft). Then it's basically a matter of finding a motor and gear reducer that will work and fit in the chassis, and modify a drive shaft so that the motor will drive it.

You are on your own for the electronics. I know nothing of it. You are going to have to mess with the Haldex clutch in the rear differential. No idea how it works but it defaults to "open" (no drive transmitted).
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formerly ... 2006 Jetta TDI 5-sp, Spice Red, Unitronics stage 1, 0.681 5th gear.
and before that ... 1996 Passat TDI, Silk Blue

Last edited by GoFaster; January 13th, 2018 at 15:43.
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Old January 13th, 2018, 16:22   #11
efeballi
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Yes, it's the Mk5 Golf platform.
My reasoning for the rear diff torque is as follows:
Engine with most torque in Mk5 4Motions: BMN 2.0 TDI, 350 Nm
Assume equal torque F/R, diff ratio 1:1
1st gear final drive ratio 14.26 for my trans (DQ250, 6sp DSG) -->
Diff torque limit 2500 Nm
No way I'm getting near that!

To my understanding, the 4Motion clutch uses a single output channel which is normally fed from the ESP to vary between open and closed states. I would trick that signal to engage the clutch by default and disengaged when there is brake pressure at the rear wheels (either ESP command or brake application)

I have two options regarding electronics, one is to find a simple brushed DC motor and greatly simplify electronics or find an AC induction motor and see how deep the rabbit hole goes. I used to work for a company that did developmental work on electric vehicles, but last time I checked they were building mild hybrids that were much like the Mk6 Jetta Hybrid like you have over in the States. And they were buying their motors and inverters from Europe at great cost.

The Renault Fluence Z.E., Renault's saloon version of Nissan Leaf Mk1, was once sold here and I used to own one, until the car learned to swim. Luckily it was empty. Insurance totaled it. There are some other Z.E.'s popping up used with flood damage, I hope some are parted as there are many common parts with the dinosaur burning Renaults. I could buy a motor and necessary electronics of the Z.E. if I come across a parted one.

The potential EMI of the electronics with the rest of the car is another unknown.

The plot thickens...
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Old January 15th, 2018, 11:29   #12
SilverGhost
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Quote:
Originally Posted by efeballi View Post
No VAG hybrids were ever sold in Turkey as far as I know. My only candidate was a Golf GTE, I google'd it, no luck.
Also the Jetta you mention is a series hybrid, no? It would be a lot of headache to have the engine and electric motor to play together, I would think...
Some of the more recent ECMs I have seen have coding options that imply they can work with Hybrid motor and/or start stop functions.

And as far as electronics and getting them to "play together" i would take entire electronics system out of donor car.

But sounds like you already have a very good idea with the 4motion rear axle and motor setup. Maybe have a CAN buss interface to pull throttle and brake input. Then build a simple motor controller to run the electric motor and Haledex clutch based on those inputs. Only draw back with this setup is the extra drag from the rear axle components.

Sounds very doable. Good luck and keep us updated on your progress.

Jason
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Old January 15th, 2018, 13:03   #13
efeballi
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Hey,
For now it seems easier to have a 2nd throttle lever to operate the electric motor. In the grand scheme of things, it's really a tiny detail to operate both engines with one throttle pedal/lever.

Right now, my biggest problem is to somehow increase the reduction ratio between the diff input shaft and wheels. As it stands with the Haldex rear diff, it's 1.6 . I need at least 4 to be able to use electric motors and converters widespread in EV propulsion.

Options are:
-find another diff and somehow affix that to the subframe
-add a 3:1 reduction gear between motor and diff input.

EV forums are full of suggestions of electric motor and controllers but they all use the car's existing tranny to transmit power to the wheels. The one similar example I've seen to my idea is a Subaru Justy conversion, which has a suitable 4.1:1 diff reduction ratio. I need to change something somewhere so that I can make use of the EV knowledge/parts pool.

Last edited by efeballi; January 15th, 2018 at 13:08.
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Old January 15th, 2018, 14:11   #14
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The VAG hybrid puts the e-motor in the bellhousing and replaces the traditional clutch, so it has access to the full range of the transmission's ratios. Both transverse (Jetta) and longitudinal (Touareg) use similar layouts for the e-motor pack. Finding a wrecked example as a donor might be your best bet with the least re-engineering necessary.
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Old Yesterday, 05:35   #15
efeballi
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I have no intention of touching the front half of the car. I'm not really interested in a series hybrid because of the modifications involved and an EV conversion is out of the picture as I need the range. These, and the 4WD capability in acceleration and loose surfaces is why I'm taking the route of powering a rear diff with an electric motor.
Thus, the Jetta and Touareg hybrids would help only with substitute ancillaries for engine off driving.
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