Tesla SDU oil pump modification for reverse operation

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FJ3422
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Tesla SDU oil pump modification for reverse operation

Post by FJ3422 »

Some of you might already have seen the info below on my Instagram, but would like to document it for all of you here.
Started with the dismantling. Encoderwheel is pressed onto the shaft; had to make a (impact-)puller and pulled it off preheated. Motorshaft was really tight in the bearing and I did not want to apply too much heat to the bearing, so made a tool to push it out.
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When running the Tesla SDU in reverse, there are two (potential) issues.
1. Oil pump (does not work in reverse)
2. Bearings (possibly not designed for maximum torque in reversal). Did read some yells on the internet that you would destroy all

Oil pump:
It indeed does not work in reverse operation. You could simply swap the tubes, then it will pump again, but the internal pressure regulation valve does not work anymore. This could lead to extremely high oil pressures popping hoses or destroy the plastic drivegear (due to the higher drive torque at high pressures).
Solution 1: Mount an additional oilpump. Have seen something like that on this forum
Solution 2: Modify the original oilpump. I went this way and made a quick test setup.
-> Pressure regulation valve seems to regulate the pressure at around 1 bar. First video in the Insta post below (could not upload movies here)
-> When running the original pump just in reverse direction, there is no pressure regulation, second video
-> After have modified the pump, regulation is stable at 1 bar when running in reversal, last video


How did I modify the pump ?
-> Original pressure regulation valve is located between both hose connections. Behind the cover cap is a spring and a piston.
-> There are three ports. 1. Piston actuation (the regulated pressure), 2. pressure relief (back to the suction side of the pump) and 3. venting of the piston rear side.
-> What has been modified:
1. Closed the original piston actuation port with a turned piece (left on the picture). Inside has M6 thread, but that was just to be able to pull it out when it wouldn't work as expected. Piece is made of stainless steel (what I had around) and presses into the preheated pumphousing. This piece pushes the initial position of the piston 4mm forward. So the original 'relief' port now actuates the piston.
2. Made a new pressure relief port. This is de large oval port at the side of the pump. Just milled by hand (dremel). You can see the groove in the piston, that's not the piston top. The relief now unloads directly to the bottom of the transmission. Only drawback of this could be the generation of air bubbles in the oil which could be picked up by the pump if the bubbles don't disappear quick enough, but I don't expect any issues when that happens since we are just pumping some oil around mainly for cooling, not lubricating shell bearing or other air-bubble-sensitive things.
3. Closed the original 3mm venting hole (inside in the pump, not on picture) by threading and closing it with a M4 setscrew. Drilled a new 3mm venting hole on the side of the pump.
4. Compensated the cover cap for the 4mm moved piston travel to get the same spring force.
5. Original oil pickup filterhousing (mesh thingy) did not fit anymore. Tried to find a universal one (in the industrial hydraulic world), but it was difficult to find something that fits, so made one myself. Turned something from an aluminium bar that takes the original mesh filter and slides over the pump connection. Kept into place by the original plastic mount (grinded some unneccesary plastic away with the dremel).



Some pictures:
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Amount of attachments seems to be limited, so see next post :)
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Re: Tesla SDU modification for reverse operation

Post by FJ3422 »

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Re: Tesla SDU modification for reverse operation

Post by FJ3422 »

Regarding the bearings:

Diff: Two standard SKF 6309 deep-groove single row ball bearing. Diff axially shimmed into place

Intermediate-shaft: One standard SKF 6307 deep-groove single row ball bearing. Shaft axially tightened with a nut, bearing locked into place with a plate and five M6 screws. On the other side one SKF RNU2206 roller bearing.

Motor-shaft: One standard SKF 6208 deep-groove single row ball bearing on the encoderside. Shaft and bearing axially locked into place with circlips. Motorside not yet known, but I suspect a roller bearing, or a standard single-row ball bearing between some disc springs to allow the shaft for some thermal expansion.

Did read some messages on the internet "the thing will fail immediately, explode, fall apart into pieces" when generating max torque in reversal (because it is 'just designed for regenerative torque in reversal'. I really don't know why that would be a problem !

If anyone has some additions or corrections (I'm just a hobbyist as well), please let us know !

Some pictures:
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Re: Tesla SDU oil pump modification for reverse operation

Post by EV_Builder »

Long time ago, any news?

The only difference between forward and backwards I can come up with is the different direction of bending / bearing play / tooth play increasement. Si instead of bearing play closing tooth distance unther load, now tooth play will increase unther load.

How much difference it will make for the wear no clue. Allot will depend on how you drive and the vehicle weight.

If I recall correctly, the Mercedes Tesla motor drive had the tooth shape the other way , since it runs the other way round in operation.
Converting an Porsche Panamera
see http://www.wdrautomatisering.nl for bespoke BMS modules.
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Re: Tesla SDU oil pump modification for reverse operation

Post by catphish »

FJ3422 wrote: Wed Jun 23, 2021 6:43 pm Some of you might already have seen the info below on my Instagram, but would like to document it for all of you here.
Thank you for your extremely detailed post! I have (I hope) replicated this on my own SDU today. I did the following:
1) Tap the original piston actuation port and insert M10 grub screw. Allow 5mm protrusion so that the piston doesn't return to the bottom. This allows the original outlet to become the new inlet as per the above design.
2) Tap the original pressure relief port and insert a grub screw (M4).
4) Drill new outlet and pressure relief holes. I have drilled the outlet hole rather conservatively to begin with.

I have not modified the spring or end plug yet. Hopefully in the next few days I will be able to get the pump hooked up to a pressure gauge. At that point I can test the pressure (I expect it to be excessively high initially), and then enlarge the outlet port and/or bring the spring back, until the pressure is steady at 1 bar.

Photos attached. I don't think they add much that you haven't already covered.

One major problem I experienced was that tapping the pressure relief port, and drilling the new outlet created significant burring inside the shaft. I had to very carefully file these to allow the piston to move freely. I'm still not entirely happy with this, as it has the potential to snag the piston in the future.
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Re: Tesla SDU oil pump modification for reverse operation

Post by FJ3422 »

catphish wrote: Wed Mar 23, 2022 7:36 pm ....One major problem I experienced was that tapping the pressure relief port, and drilling the new outlet created significant burring inside the shaft. I had to very carefully file these to allow the piston to move freely....
If you enlarge the hole with a small (3mm) carbide mill, use a spiral type. That 'pulls' the material towards you and leaves no burr at the front.
Small_stiftfrees.jpg
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Re: Tesla SDU oil pump modification for reverse operation

Post by catphish »

FJ3422 wrote: Sun Mar 27, 2022 7:45 pm If you enlarge the hole with a small (3mm) carbide mill, use a spiral type. That 'pulls' the material towards you and leaves no burr at the front.
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Thanks for the suggestion! I actually did enlarge the hole a little (arbitrarily, hopefully not too much), and after lots of very careful filing and cleaning, I'm happy with it.
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I'm now waiting for a pressure gauge so I can test and adjust the spring if needed (I haven't drilled out the end cap that retains the spring yet and will do so if needed to reduce the pressure).

I've done most of the construction of the oil pickup too. I machined an open tube, and a plug for each end (one for a pipe, one closed), which will be glued in place once I've milled the opening to pick up the oil.
PXL_20220324_175238460.jpg
Thanks again! I am quite apprehensive about testing, so fingers crossed I've done it correctly.
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Re: Tesla SDU oil pump modification for reverse operation

Post by catphish »

I've now tested my pump modification. The pressure is steady, generally around 1 bar, and can rise to about 1.5 bar depending on how much resistance I apply to the output pipe. Here's an example of the pump running with a moderate kink in the output pipe at 1.2 bar: https://photos.app.goo.gl/NvLVjM9acev4BazC9

I changed the design for the oil pickup. It's now a lot more like FJ3422's, though I used a pipe to reach into the sump (more like the OEM pickup) rather than a slot. The final pickup pipe was shortened a little, to increase flow.
PXL_20220329_160055312.jpg
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Re: Tesla SDU oil pump modification for reverse operation

Post by FJ3422 »

Nice work !
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Re: Tesla SDU oil pump modification for reverse operation

Post by kellis91789 »

This looks like a lot of effort. Can I ask why you needed to run the motor in reverse ? I suppose to get the motor in front of the drive axles, but doesn't the small drive unit stand almost upright rather than flat anyway ? Or are you using a rear sdu and it sits flat like the ldu ?

I am trying to decide if I can use a front sdu in a rwd car, but there is no space behind the axles for the motor and inverter case in my donor -- the back of old rear diff bolts to a large rear suspension subframe.

So it is great that you have confirmed a mod that would fit my car, but I am wondering if a front sdu couldn't simply be tilted forward so the motor and inverter were above or slightly forward of the sdu axles. In the donor car I am considering, there is plenty of space forward and above the axles because that is where the gas tank and drive shaft pass under the rear seats.

Will the oil sump and pump not work correctly unless the sdu is tilted backward ? Would rerouting the oil pickup tube to what would then be the low point with the motor rotated 90 degrees from usual mounting work ? How much rotation could the motor stand without the oil vent location becoming a problem ? Not horizontal with motor ahead of axles, I assume, or people would not even need to consider running in reverse.
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Re: Tesla SDU oil pump modification for reverse operation

Post by kellis91789 »

I found a tear-down video showing the internals of the front sdu with the oil pump and pickup screen clearly labelled.

https://www.bing.com/videos/search?q=te ... %26ghpl%3D

At 26:17 un the video he is holding the case in the normal upright position that places the drive axles ahead of the motor/inverter. Tilting it 90 degrees forward looks like the oil pickup screen would still be submerged, but the crescent shaped opening that allows oil to return from the housing where oil is sprayed onto the rotor bearings and stator for cooling/lube might be too high to flow back down to the sump area.
https://openinverter.org/forum/download ... c1e400fc79

Besides that, depending on whether the oil is actually "spraying" onto the bearings and gears vs. more gravity fed "dripping" onto them, it looks like a more or less vertical mounting with the diff housing slightly behind the motor/inverter housing should work. That could be a solution for some people who have no space behind the old diff location, but means now you need about 12" space above the axle line. Drain location would be wrong, but it looks like the fill location would still be high enough without adding an extension.
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Re: Tesla SDU oil pump modification for reverse operation

Post by Proton »

I just modified mine but I used the original filter case. I cut it from the plastic cover and moved it lower.
The only mistake was to cut the intake shorter. I cannot move the original intake lower because of the cover support. Pretty much the back of the oil pump sits in the same position, but lower and it is connected to the original exit.
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Re: Tesla SDU oil pump modification for reverse operation

Post by Proton »

For anybody that wants to run the motor upside down, I would no do it. The oil is pushed by the Oil pump all the way back in the TOP of the motor.

oil loop.jpg
The oil comes back at the bottom. if you run the motor upside Down the motor would swim in oil. probably would need 2 gallons of oil to come out of the opening if it is upside down.
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Re: Tesla SDU oil pump modification for reverse operation

Post by nubster »

Would it be possible to fit a separate/inline pressure regulator and leave the stock pump and pickup as-is? My unit will be mounted right side up, just in reverse. Thanks.
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Re: Tesla SDU oil pump modification for reverse operation

Post by Proton »

nubster wrote: Wed Sep 06, 2023 8:27 pm Would it be possible to fit a separate/inline pressure regulator and leave the stock pump and pickup as-is? My unit will be mounted right side up, just in reverse. Thanks.
The oil returns in the bottom opening, where the 3 phase cable go to the motor. If it is upside down the whole chamber of the motor will be filed by oil that cannot drain.
Best is to get the motor and open it to get a better idea of what is going on.
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Re: Tesla SDU oil pump modification for reverse operation

Post by nubster »

Proton wrote: Fri Sep 08, 2023 8:41 pm The oil returns in the bottom opening, where the 3 phase cable go to the motor. If it is upside down the whole chamber of the motor will be filed by oil that cannot drain.
Best is to get the motor and open it to get a better idea of what is going on.
Thanks for the reply. To be clear, my motor is NOT mounted upside down. It is right side up but rotated 180 degrees (i.e., reverse operation).

My understanding is that if I swap the hoses around, the pump will work in reverse but create high pressure at higher RPMs due to the regulator not functioning. Many inline oil pressure regulators are available, so I'm wondering if I could install one inline on the pump output instead of machining the stock oil pump, fabbing a new pickup, etc.

I understand the connection from the pump to the regulator would see high pressure, but in theory, everything downstream would be none the wiser, right? That is, if I can find a regulator that fits without interfering with the gears. It was just a thought, and I am curious what I might be overlooking.
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Re: Tesla SDU oil pump modification for reverse operation

Post by nubster »

I see now that the front SDU oil pump is different than the rear SDU oil pump. The front pump has the intake and output ports on opposite sides, whereas the rear pump has them on the same side. Even if I could modify my pump to work in reverse, I'm not sure there is enough room to route both hoses past the differential gear (which would be required to swap the hoses around). Maybe if I made some rigid steel lines it would work, but I dunno. Seems like an external pump might be the way to go when reverse mounting a front SDU. Any other thoughts or suggestions?
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Re: Tesla SDU oil pump modification for reverse operation

Post by Lood »

Hi nubster,
I did it like this: viewtopic.php?p=56088#p56088
Not yet driving so i dont know if it will last.
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Re: Tesla SDU oil pump modification for reverse operation

Post by nubster »

Lood wrote: Sat Sep 30, 2023 5:50 pm Hi nubster,
I did it like this: viewtopic.php?p=56088#p56088
Not yet driving so i dont know if it will last.
Oh wow, that's a cool way to do it. So you modded the valve, rotated the pump 180, tapped a new mounting hole, and are only using two of the three bolts now? I see why you'd be skeptical about the longevity, but it seems like it could work. Rotating it makes it so you don't have to route both hoses past the diff gear. Thanks for sharing, I like it!
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Re: Tesla SDU oil pump modification for reverse operation

Post by Lood »

Yes only 2 bolts now. For the new bolt I used a rivet nut.
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Re: Tesla SDU oil pump modification for reverse operation

Post by nubster »

How did you manage to get the hose barb nozzle out? Is it just pressed in?
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Re: Tesla SDU oil pump modification for reverse operation

Post by Lood »

Yes just add some heat to the housing and pull/twist it out.
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Re: Tesla SDU oil pump modification for reverse operation

Post by nubster »

So, I finally completed the oil pump reverse mod for my Front SDU. I followed @catphish's method with the grub screws for the regulator part and @Lood's approach for mounting the pump 180 degrees backward (with a slight difference). Thanks again for the help, guys!

The main difference is I decided to try to make an adapter/bracket to mount the pump in reverse. While not pretty, it feels solid and uses all three mounting points instead of just two, so we'll see how it goes. I made the POC from steel just to test if it works well. If so, I'll make the CAD file available and maybe try to get some nicer ones made from aluminum. I did have to Dremel the case a little bit to make room for the adapter.

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Re: Tesla SDU oil pump modification for reverse operation

Post by nubster »

The bracket seems to work well, so I had it CNC'd from aluminum.

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If anyone is interested, I'll make the CAD file available and probably make a small batch to sell. DM me for info.
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Re: Tesla SDU oil pump modification for reverse operation

Post by EVS2K »

I read through this thread and managed to follow the instructions, with some modifications.

I produced a video on my YouTube channel.



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