Thursday, October 15, 2009

How I Used an Automatic Transmission in an EV

I have been lots of questions on how exactly I used the automatic transmission in my EV. So this insanely long post is a summary of how I did the whole transmission setup.


The first thing I did was design a motor coupling and plates that mimicked the old ICE. I kept the torque converter and flywheel setup, and since it mimics the original engine, the adapter plates and motor coupling can be used with the automatic or a manual transmission. I used the transmission's Flex Plate to design the motor coupler, which is a taper locking coupling. The aluminum plates were created using a second transmission I bought off Craiglist because at the time the car was still driving and I wanted to have as little down time as possible, so I bought the second transmission (which was skipping gears) as a EV sacrifice so I could use it as a template for the coupling and for the bolt hole pattern on the plates.Next, I left the Automatic transmission installed with the existing radiator/transmission cooler. I also left the PCM and ECU installed as they are needed to operate the transmission and the dash board. I also used the old engine mount to hold up the rear side of the 9" ADC FB1-4001A series wound motor. The motor has a rear shaft that will connect to the Power Steering pump and A/C compressor.
After all the mechanical is done, comes "fooling" the PCM. I Do not idle the motor at all. It does take about 6 seconds to build up pressure for the clutches to operate, but that only happens when the EV is first started before a trip. During driving the pressure stays up while at stop lights and such, and getting going again is no slower than with using a manual with a clutch.

Now comes the big question: How did I change the shift points on the transmission? Did I reprogram the PCM? Modify the transmission soleniods? I did nothing of the sort! The key to using to changing the shift points: replace the TPS with a 5 k potentiometer!

In and ICE he TPS tells the transmission when to shift, depending on how hard the pedal is pressed, when accelerating or cruising or coasting. By replacing the TPS with a 5K potentiometer I now can manually tell the PCM when to shift. The higher I set it, the longer it stays in each gear. After 1,000 miles of driving like this, I have had no problems and I have found a few settings that work well depending on which terrain I drive on. Higher RPMS mean better efficiency while lower RPMS allow for better acceleration.

I usually leave it at about 1/4 turn, however it needs to be set to 0 every time I start up the EV because if the TPS (5k pot) is higher than 0, the transmission thinks you are stepping on the gas and will lock the Shifter into place so you cant move it from Park. Annoying, but effective safety measure. And I will not be bypassing that protocol, but if I do the transmission can easily be shifted into Neutral with the EV off, and that is a safety issue that is checked during the yearly Inspection.

11 comments:

Zain said...

I visit your blog daily and it is fun every time.

Nice machine.

Justin said...

I've read the entire blog chronicling your efforts...I've got a '96 LX much like yours, but has a 5 speed manual. Hoping to build basically what you've got, right down to the aux output shaft on the motor to drive the a/c and power steering. Thanks for sharing your story. Looking forward to reading more about it as the project evolves!

Steve Peichel said...

Thanks for answering my question in the EV discussion. It led me to your blog which is very interesting.

I'm converting an automatic chevy venture van to electric, and I was nervous about controlling the shift points. Therefore, I bought my way out nervousness and got an expensive TCU from PCS. Here's the link if you're curious:

http://www.powertraincontrolsolutions.com/transcontrol.php

The component uses a software program shift points (much of it can be done automatically by entering the transmission and vehicle information). Shifting occurs automatically without doing anything... but one may want to adjust the shift points from the factory settings based on personal preferences. I haven't used it yet so I can't comment on how well it works. Currently, I'm waiting for the Zilla to arrive to replace the Logisystem control which I've had to remove because there has recently been reported problems with this controller. In short, I've had my share of problems and frustrations to this point too, and I feel your conversion pains in your blog!

I like the idea of manual shifting each gear. Have you determined each shift points and do you have an RPM gauge? How did you take data and decided when to shift?

I'm happy to hear that the TC maintains pressure, and that you don't have to wait 6 seconds each stop light.

Thank you for sharing your experience.

goingreen said...

Was wondering what kind of 5k potentiometer. you used. and where to get one. Love what you did. Dave.

David Harrington said...

I used a standard 5K potentiometer from Radio Shack. It has been working great for over 5,000 miles.

David Loveland said...

David,
To eliminate your annoying need to zero the pot before starting, you could run the Park and Neutral switches (the ones that tell the dash which gear your in) in parallel to the TPS pot circuit. That way, whenever the vehicle is in either Park or Neutral, the circuit would be closed with zero resistance, just as if you have turned the pot down.

I have not yet made a conversion, but have been interested for some time. I will eventually get there. This blog gave me some knowledge that I need and I enjoyed it. If I were to adapt this to a similar conversion, I would eventually like to know the resistance values of the preferred pot setting and possibly replace it with a fixed selector switch/resister block set up.
Dave

tim riggins said...

I've read the entire blog chronicling your efforts...I've got a '96 LX much like yours, but has a 5 speed manual. Hoping to build basically what you've got, right down to the aux output shaft on the motor to drive the a/c and power steering. Thanks for sharing your story. Looking forward to reading more about it as the project evolves! transmission maintenance calgary

Jae Gunderson said...

You do have an extraordinary talent, my friend! Thanks for sharing this blog post! This will indeed help a lot who wants to have a mechanic experience of their own. Does it work with any type of EV? I've always wanted to upgrade my transmission gear. Hoping to hear from you soon! By the way, my EV car is a Fiat.
Jae Gunderson

jake ostler said...

This is a really great idea. I would love to use my transmission in Lethbridge for something like this.

shirlsw12 said...

I've never seen anybody try this before. I think it's a really interesting concept. I could definitely see myself trying this out. I think it would be interesting to see how this would work with other things. I love modifying my cars, and when I find new things I just can't wait to try them out.
http://atransmissionrepair.com

shirlsw12 said...

I've never seen anybody try this before. I think it's a really interesting concept. I could definitely see myself trying this out. I think it would be interesting to see how this would work with other things. I love modifying my cars, and when I find new things I just can't wait to try them out.
http://atransmissionrepair.com