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

EV Pusher Trailer
Version 2!

Recent Trips:
Palo Alto, CA to Sacramento, CA and back (300 miles in one day)

Performance Specs:

Top Speed: ~80 mph (flat ground, gasoline only)
Top Speed: >100 mph with electric and gasoline use
Cruise Speed: 65-70 mph
Engine: 1800 cc Volkswagen Rabbit stock, water-cooled, fuel-injected, gasoline engine (1981)
Transmission: '81 Rabbit stock automatic
Efficiency: 30 mpg (EV with trailer net at 65+ mph)
Range: >300 miles (13 gallon capacity)
Emissions: Catalytic converter, and fuel vapor recovery system


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/or 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 (if there is one) is to have an IC engine driving a generator that sends electricity forward to the EV to supply the energy needed for highway cruising.
Click to See ---> AC Propulsion's hybrid generator trailer
Generator benefits:

* Energy can be stored in the batteries when IC output is greater 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 (smaller generator, less fuel, less IC hp)
* EV system does not need to be sized for continuous use
* Cheaper (no generator, more standard automotive parts)

The hybrid trailer in general only makes sense for long distance freeway travel (roughly greater than 50 miles.) The trailer efficiency will fall at slower speeds since the IC output must be cycled through the batteries or throttled back in the case of the pusher. In addition, urban driving raises the obvious problem of parking with the trailer in congested areas.

More Pictures:

Trailer connection to the EV, two simple plugs and a standard ball

Fuel tank and trailer structure

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 (see photo.) With the second generation trailer, the automatic transmission takes care of shifting. The lights are linked to the EV's (brake, running, turn.) The throttle is controlled by a large hobby RC-type servo motor. There is a micro-controller on the trailer that takes an input signal from a 5k potentiometer in the EV and then sends the proper command to the throttle servo (see servo picture.)

Operation: This second generation hybrid trailer is very easy to "drive." All of the controls have been integrated into the dashboard of the EV so there are no dangling wires, etc. Since the trailer has an automatic transmission, it is left in the "drive" position always. The interlock that normally prevents starting the engine in drive has been removed. When towing the trailer without the engine on, the automatic transmission (AT) clutch is disengaged and the IC engine does not spin. So the wheels turn freely (with only a slight extra drag from the AT.) Towing the trailer for long distances with the engine off is "not advised" since the AT does not have proper lubrication. But long distances are defined as 10-30 miles in the service manual (in between engine starts.) And, since the EV probably can't even tow the trailer 30 miles in between charges...this isn't a large concern. It just isn't possible (and doesn't make sense) to tow the trailer "long distances" without turning it on.

In the EV there is an ignition on/off switch and an engine start button (see picture below.) There is also a small, 5k potentiometer that controls the throttle on the engine. This could be wired directly into the 5k pot that is on the gas pedal running to the EV controller, but I opted for totally separate controls during initial testing.

Driving the EV/trailer combination is a piece of cake. The AT shifts as needed and you simply control the desired throttle level. It's also fun to simply turn the engine off when the traffic slows down or stops in rush hour and creep along silently with the electric drive.


Dynamics: Despite the facts that I shortened the trailer of the Gen-2 pusher by two feet and added more IC horsepower and much more pushing force with the ability of the AT to downshift...I have still found it basically impossible to get into a condition of over-steer. (This is where the car would want to turn into the direction of the turn if you take your hand off the wheel, normally if you release the wheel a vehicle will straighten itself out of a turn) Even in relatively tight turns with the trailer at nearly full power, the car wants to straighten itself out. The shortened trailer also drafts behind the EV much better further improving the mpg.

Things to add...

* IC engine cruise control (built in throttle actuator)
* Auxiliary high-voltage alternator on the IC (1000-2000 watts) to keep batteries charged
(And to allow for greater electric use during hill climbing and hard acceleration)

The hybrid trailer makes it completely possible to get by without a dedicated IC car at all. This allows 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.)

Site Last Updated On: Oct/26/2000

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