1. AC traction motor
This is a brushless, 4 pole, 3 phase, water cooled AC Induction motor. Weight is 200 lbs.
This is wound for 700 Volt operation for maximum performance which will take full advantage of the 200kW power inverter and high current battery cells.
May 14, 2008, The motor has arrived:
Size is 9.6 inches square by 17 inches long, not counting the shaft, which will be cut down to 1 inch in length.
Here is a direct comparison before and after. Funny that the smaller electric motor, with 1 moving part, has twice the performance of the big, complicated, and wear prone engine.
Since motor compartment space is needed for the battery pack, I need to shorten the output shaft length to mate with the transmission more compactly. A custom adaptor plate will be mounted to this shaft stub that the flywheel/clutch assembly will bolt to.
This shaft adaptor plate will bond with a precise interference fit on the short 1 inch stub.
The pilot bearing (blue seal visible), will be mounted in the new shaft adaptor to make it fit with the transmission input shaft just like this original crankshaft mounted plate did:
Motor mounting Tasks:
- Determine if 90 degree rotation of motor (clockwise) will clear steering assembly Done May 19, 2008. The updated modeling has proven that the motor rotation will work well. The electrical box is stepped at the corner giving the needed clearance to the steering rack power steering assembly. I may need to mill off a small piece of the casting which is inconsequential.
The lower right corner of the white box clears the steering assembly and gives more room for battery pack clearance above the motor. This is how I will mount the motor which is the next step. - Take measurements of motor plate and bell housing to create drawing for adaptor
- Remove transmission and digitize (accurately measure) the transmission bell housing for CAD input
- Design/CNC mill the adaptor plate that will mount the motor to the transmission precisely
- Construct motor mount bracket to the new motor position
A side by side look at the gas vs. electric drive system:
This is the view from the back
Here is the view from the front
With the full enclosure modeled, here is how it will look in the motor compartment:
And with the "inner" hood open:
This pack can be removed as a single unit (with an engine hoist) or as individual modules if so desired. There are 30 modules, differing in depth, depending on location.
June 7, 2008 update:
Mounting the motor to the transmission involves two primary tasks:
1. Adaptor plate design/construction - motor face to transmission bell housing face
2. Shaft adaptor design/construction/installation - mounts flywheel to motor shaft
Here I have placed them shaft-to-shaft, level, and in their proper orientation to look for any conflicts on the bolt placement around the bell housing relative to the electric motor.
The primary thing to look for is places where a bolt from each side of the adaptor plate share the same location or overlap slightly, interfering with each other.
I am happy to report that there are no bolt location conflicts in the planned orientation. If there were a conflict, the motor could be rotated slightly one direction or the other to allow clearance, as long as the shafts remain in concentric orientation.
I will be shortening the Siemens motor shaft by 3.25 inches that will leave exactly 0.75 inch between the two faces, the thickness of the aluminum adaptor plate I will be using. This will make the package much more compact and allow the use of the space for more cells.
Task #1 is relatively simple but needs precision with the alignment between the two shafts which is critical. I have a method planned for for this alignment task that I will show next update.
Task #2 is not so simple and must have a specialist involved to properly size the shaft adaptor to create the interference fit/mount that will handle a lifetime of torque delivery. This design uses undersized adaptor dimensions that are expanded with temperature shift to momentarily allow the adaptor to slide onto the shortened shaft. The temperature quickly equalizes and bonds them permanently (short of grinding it off and starting again). This is why the need for the specialist...
The other part of this design detail is that I will be imbedding a pilot bearing in the adaptor, just as the original motor had see photo above to allow the use of the clutch.
I have located a potential specialist in California and will be sending CAD files to get this started with him.
June 23, 2008 update:
The inverter finally arrives, and here is the first test fit:
It fits perfectly. The front face of this box will be nearly up against the back wall of the battery pack. All the water cooling plumbing and wires appear to have clear paths.
Below, with the interior air inlet cowling removed, you can see the fittings where the fluid heater connects and passes through the firewall (behind right rear corner of box) for interior heat as well as the air conditioning fittings (behind left rear corner of box).
There is 3 inches between the back wall of the box and the tip of the fittings. Perfect.
The three yellow cables are the 3 phase drive wires into the motor. The black cable passes the motor's rotor position data back to the inverter to maintain synchronous control.
Because the length of the inverter/motor wires, I decided to spin it 180 degrees to give a bit more clearance from the steering assembly. This does not affect the transmission mount because of the symmetry of the motor face. Got lucky again.
August 2008 update:
I have sent the motor and flywheel to a specialist that will install the flywheel mount on the cut motor shaft.
I supplied this CAD drawing for the adaptor where Leo will calculate the ID to create the needed interference using math and physics. This is a very tricky process and must be done right the first time. The part is heated to a specific temperature and then slid on the shaft stub, which will then equalize in temp. The resulting interference forces are stronger than a weld.
September 08 update:
The motor has been returned with the custom adaptor mounted. This critical detail was handled by a power coupling specialist in California. Thank you Leo, excellent job.
Here is the first check of the resulting fit:
With exact alignment, the transmission shaft slides into the pilot bearing and bottoms out leaving 5/8 inch between motor face and bell housing. This means that when the 3/4 inch plate is installed between the two, it will leave 1/8 inch gap between the ends of the shafts. Perfect.
All the torque is transferred through this interference fit on the short 1 inch length stub.
(For reference, the original shaft can be seen at the top photo on this page)
The pilot bearing is visible here, pressed into the adaptor
This flywheel from the original BMW engine mounts directly to this adaptor. The fit is precise, as needed to prevent vibration when spinning up to 10,000 RPM.
The clutch assembly mounts on the face of the flywheel. I will be machining an aluminum equivalent to reduce the weight, i.e. side load on the motor which has a spec limit of 10kg (22 lbs) of side loading for the sake of bearing life. After all, the bearings are the only wear items in this motor.
This flywheel has built-in vibration reduction that will certainly not be needed when driven from a smooth electric motor. The flywheel's only function now is to hold the clutch for the occasional shifting at highway speeds. Since the clutch will not be used when accelerating from a stop, there is no wear issue using plain 6061 Aluminum for the flywheel face.
To ensure the motor and transmission shafts are in precise concentric alignment, I will be inserting alignment pins in the corners of this motor face, just like the bell housing is aligned to the block on the original gas engine. These will be the hollow type alignment pins that the mounting bolts pass through. These 4 mounting holes happen to be the exact size of the mounting holes with alignment pins/bolts on the transmission so the same ones will be used.
October 2008 update:
The adaptor plate prepared for attachment to the transmission. The four larger holes are the pinned bolt holes that mount the plate to the electric motor. They drop in next.
The two bolts standing up are in locations that the electric motor overlaps, so I had to mill out a pockets for their heads and insert them before attaching plate to the electric motor.
The new power package:
Going in with ease. I installed the motor/transmission by myself in about a half hour with no problem. I lowered it down onto the floor jack that allowed me to pull it back from below, engaging the alignment pin in the driveline and spinning in the transmission mount bolts with my fingers. The easiest motor/trans install ever.
Sitting on a block up front initially, the fit looks good.
Now with the peripheral components bolted in:
Next up: fabrication of the front mount. This will be a stainless steel structure that will put the weight onto the original rubber isolated motor mounts, visible on each side. There will be enough margin around the motor to allow torque induced movement without contact.
December 29 2008 update:
The motor is now attached to the factory motor mounts.
There still remains the corner gussets to be welded in and a pair of side arm stiffener plates for long term reliability. I would have already done this but a shipment of materials has been held up for weeks due to heavy snow that prevents UPS from making deliveries up our road. The road is finally beginning to clear now so it should be just a few days to take delivery. But even without the added strength, the mount appears rigid.
After blocking the motor in it's exact location (plus 1/8 inch for settling on rubber mounts), I fabricated the mount structure. By tacking the , I made an adjuguess on how much settling, or movement down would occur, due to the weight of the motor/trans on the rubber mounts. It turns out, 1/8 inch was a good guess. The net result is the clearance is exactly as planned between the motor and steering rack.
As luck would have it, the ideal location for the motor resulted in exact concentric alignment between motor output shaft and transmission input shaft (i.e. motor is level).
January 02 2009 update:
Mechanical drive train complete
This stainless steel box structure has to be able to withstand the significant torque the motor puts out (or takes in with regen) to/from the driveshaft. This low profile design allows for best clearance with the battery pack and water cooling lines.
The 0.25 Inch thick plate all welded into a rigid, 20 pound structure. Yep, some of that weight could be removed.. maybe later.
Here is the mounted end result firmly "floating" in place
The only remaining detail in the mechanical drive train is the installation of the lightweight ALU flywheel to reduce the side loading on the electric motor shaft for long life. It is functional for now.
BTW speaking of long life, this motor will not change it's power delivery over time as there is simply no wear mechanism other than the bearings, which can be replaced every decade or so.
