(archive clone from deleted jstaubel.com page - modified by brucedp)

EV Pusher Trailer

(version 1)

Recent Trips:
Palo Alto, CA to Woodburn, OR and back (1250 mi in two days)

Performance Specs:

Top Speed: ~70 mph (flat ground, 4th gear, no electric assist)
Top Speed: 90 mph with electric assist. (limited by IC engine rpm)
Cruise Speed: 50-65 mph (depending on ambient temperature...IC is air cooled)
Displacement: 1600 cc Volkswagen Bug stock engine (1971)
Transmission: '71 bug stock manual 4 speed
Efficiency: 25 mpg (EV with trailer net at 55+ mph) Range: 300 miles (12 gallon capacity)

On the road in Oregon (400 miles from home in the same morning)

On the road in Oregon (400 miles from home in the same morning)


As anyone involved with EV's knows range is the one central problem (combined with slow re-charge times.) EV's will have ranges between 25-110 miles (home-built to optimized production.) Recharge times can be as low as 1-3 hours with high capacity chargers. These range/charge times still do not allow long-distance freeway travel on the occasions when it is needed.

The idea of the pusher trailer, and generator trailer, is to give the normal EV long-range capability with fast fuel stops without permanently installing an IC hybrid system in the vehicle. This saves the weight, and mess, of having the IC engine with you (in the EV) for the %80+ of driving that is done within the EV's normal range. For long-range operation, the IC engine will take over all of the load and battery drain will cease or slowly reverse.

Generator vs. Pusher (Series vs. Parallel hybrid)

The "normal" approach to hybrid trailers is to have an IC engine driving a generator that sends electricity forward to the EV to supply the energy needed for highway cruising.

Generator benefits:

* Energy can be stored in the batteries when IC output is more than needed.
* The IC load is very level as the generator output can be nearly constant.
* No transmission is needed
* Standard trailer dynamics apply

However, this approach suffers from the inherent problem that the energy is transformed from mechanical (at the IC shaft) into electrical, and then back to mechanical (at the EV motor.) The energy will in the best case go through the generator, EV motor controller, and EV motor. In the worst case it will also cycle in and out of the batteries. All of these conversions deal a serious blow to the best efficiency possible. For a typical EV system you will need between 1/2 and 2/3 of the IC horsepower to simply push the car as you will to generate enough electricity to drive it.

Pusher Benefits:

* Fewer energy conversions Chemical--->Thermal--->Mechanical
* Less IC horsepower needed
* Potentially lighter than a gen trailer (no generator, less fuel, less hp)
* EV system does not need to be sized for continuous use
* Cheaper (no generator, more standard system)

But, the pusher trailer is not at all suited for city use. It ONLY makes sense for long distance freeway travel. Since the IC output can't be used unless the car is being pushed, efficiency will fall at slower speeds. However, the whole premise behind the hybrid trailer is that it is only needed for long-range trips (where most of the time is spent on the freeway!)

More Pictures

(image taken by brucedp at JB's home)

(image taken by brucedp at JB's home)

Crowds at Woodburn, (world's quickest electric dragster background above the hood)

Control: One difficult problem with the pusher trailer is how to control the throttle and transmission remotely. I have chosen to keep all control electrical so that there is only a simple electrical connector to the EV. This prototype does not yet have any transmission control. The lights are linked to the EV's (brake, running, turn.) The throttle is controlled by a small DC motor that drives a lead screw to pull it in or let it out. There is also a switch in series with the IC ignition system inside the EV.

Operation: The current version of this trailer is fairly difficult to use. Since there is no transmission control, you need to stop and get out to change gears. Luckily, this doesn't happen to often. For all flat freeway travel (with small hills) 4th gear is fine. So, just before getting on the highway you pull over, put it in 4th and then accelerate. As the EV accelerates it is cranking the IC engine up, at some reasonable rpm you flip the ignition switch and the engine begins firing. You then crank up the throttle, let the IC finish accelerating and hold you at the highway cruise speed as you take the EV off-line. Now your range is 300 miles. To stop simply kill the ignition and drive with the EV to a convenient place to stop and put the engine back into neutral. Dragging the motor around in gear when it is not pushing is an obvious waste, not to mention the "chugging" at very low <10mph speeds. For driving in the mountains, leaving the motor in 3rd gear works fine, but the top speed is 60-65 mph.

Things to Improve!

* Automatic transmission
* IC engine cruise control (built in throttle actuator)
* Water-cooled IC engine (VW overheats under heavy load)
* More modern engine (cat converter, sealed fuel tanks, fuel injected...cleaner/more efficient)
* Slightly more powerful IC engine
* Auxiliary high-voltage alternator on the IC (1000-2000 watts) to keep batteries charged
* "nice" fiberglass cover (less drag, less crazy looking)

So, if I had to do it again I would use a different vehicle. This made an excellent test bed... and it can work! This was also a very cheap test ($300 for the bug, ~$100 in parts for trailer/tank/control.) But it is a loud, dirty, crazy contraption that makes it *impossible* to go anywhere without answering questions and being on display. This is all tolerable for limited use and as a simple substitute to towing your EV to and from various events. But, unless you really want to have the EV where you are going...it needs some work.

With all of these improvements, it should be perfectly possible to get by without a dedicated IC car at all. This could allow the normal EV to meet 100% of your driving needs without sacrificing zero-emission city driving and grid recharge-ability (as all production hybrids today do)

Last Updated On May/04/2000

(archive clone from deleted jstaubel.com page - modified by brucedp)
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