Tuesday, March 3, 2015

Back to Work

It seems like forever since there's been any progress to report. Life happens and you deal with it as it comes, but now things are starting to free up and I'm very excited to see the project move forward.

Robert Juarez has been working on the accessory mounts: planning, positioning, and fabricating. It is truly a three dimensional jigsaw puzzle in the motor compartment and we don't have everything figured out yet, but we're making great strides.

First off, Robert made cardboard mock-ups of the Siemens motor, DMOC inverter, and battery blocks of four modules each. 

One dependency that has finally been nailed down is the method of mating the motor to the driveshaft. I had originally planned a conventional approach using a flywheel, clutch, and pressure plate, but delays in getting the adapter plate and coupler built led me to look around for an alternative. I found a very persuasive argument for going with a clutchless coupler on the Porsche 944 build blog of a fellow from Alberta, Canada and rather than repeat it here, follow this link and check it out for yourself.

Given that the primary goal of this project is to replace my Nissan Leaf, the numbers look good. The Leaf uses a single speed reduction gear with a final drive ratio of around 7.94:1. In second gear, the Porsche 924S has a final drive ratio of 8.26:1, just a bit shorter than the Leaf. The Porsche should be quicker than the Leaf from a standing start with the slightly lower gear ratio, lighter weight, and higher motor power (134 hp for the Siemens vs. 107 for the Leaf). Driving will be much like an automatic: start in second gear and just leave it there.

The other benefit of going clutchless is that the coupler is a good four inches shorter than would be possible with a full clutch setup, and that four inches makes a big difference under the hood. 

The thing that makes this possible is a sweat fit coupler blank for the Siemens motor developed by EV West. The coupler is heated up and positioned on the splined motor shaft and as it cools, it shrinks to a very tight fit. The center hub of a Porsche clutch disk with the friction surfaces removed provides the spline fit for the transaxle shaft, and a spacer in between accommodates the pilot shaft. Drill and tap the coupler and this sandwich will connect the motor shaft to the transaxle shaft.

In order to keep the power steering, we're using a Toyota MR2 electric power steering pump. It is a very popular item for drag racers and hot rods as well as electric conversions. As a result, they are getting a little hard to find, but wrecking yards do still have used ones. It has an integrated fluid reservoir, so makes a tidy installation. Robert found a perfect place for it on the passenger side of the motor bay and fabricated a custom mount. 

Directly behind the power steering pump, the niche that formerly held the starter battery now contains the main contactors and precharge resistor directly from the Better Place  battery pack along with the power brake vacuum pump. The vacuum pump is a Ford unit designed for the Transit Connect electric delivery vehicle. The Ford Transit Connect is also the source for the Siemens motor and Azure Dynamics DMOC 645 inverter, so the vacuum pump is in familiar territory.

On the other side of the motor bay, Robert has mounted the Benling Air Conditioning compressor. We've kept all of the other A/C components in place, so we should be able to tolerate Texas summer heat. Like the power steering pump, I'll need to have custom hoses built to match the fittings on these non-Porsche parts.

Moving around to the rear of the car, the battery structure is nearly complete. This will hold two full banks of sixteen battery modules and a small four module set along with the charger, mid-pack fuse, and maintenance disconnect. The outer skin for the battery box will be fabricated from sheet aluminum and fully caulked to seal out moisture, then finished off with black truck bed liner. Also to mount in the back is the 12 volt auxiliary battery and DC/DC converter. Those items will fit in the side storage areas beside the battery box. 

So things are starting to take shape. We are still trying to figure out where to put the remaining batteries and the cooling system components, but once the motor and inverter are mounted, those things should fall into place.

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