Figure 19 Underneath view of the rear compartment in Electrovair II showing the commutating and filter capacitors, the oil cooler and the power resistors.

are electrically isolated and shock mounted. All electrical connectors face inward for accessibility.

A bank of commutating capacitors and an iron core inductor are mounted on the right side of the drive motor and cooling package. Filter capacitors and the oil pump assembly are located on the left side. These components are mounted to two horizontal plates. The capacitors are insulated and project beneath the mounting plates to be cooled by road draft as seen in Figure 19.

The mounting plates define the floor of the rear compartment enclosure between the side rails which provides splash protection. In addition, a front panel, sheet metal side panels and the induction motor shroud complete the enclosure. Rubber boots isolate the driveline and oil cooling package from the sheet metal.

Figure 19 also shows two pairs of power resistors which are used in the commutation circuit of the modulating inverter. They are mounted under the fenderwell floor panels beneath the logic and inverter trigger controls and are cooled by road draft and protected by perforated shrouds and splash baffles.

BRAKE AND SUSPENSION MODIFICATIONS

Electrovair II is about 800 pounds heavier than the production Corvair. Thus brake and suspension modifications were required. Heavy duty brakes were fabricated with microfinished steel drums and sintered metal linings. Larger front wheel cylinders were also installed. A heavier stabilizer bar was fabricated for the front suspension. Higher load coil springs were mounted at the front and

SAFETY AND DRIVER CONTROLS

The high voltage of the battery pack presents a severe shock hazard to personnel. Several precautions were taken to isolate the high voltage circuit from the vehicle chassis. We reasoned that with the high voltage ungrounded, two shorts would be necessary to complete a current path. Thus, anyone inadvertently grounding the pack with part of his body would still be safe. Wet roads or rainy weather presented additional possibilities for electrical short circuits, and adequate sealing provisions have not yet been developed for Electrovair II.

Several control system interlocks are provided to protect both the driver and the electrical components. These include protection if the driver turns the key on with the throttle depressed, shifts from forward to reverse at high speed, or tries to back up with full throttle. Over-speed protection is also provided in the event of a driveshaft failure.

The car is started by simply a turn of the ignition key. A green light indicates that the system is ready for power and the drive selector can then be put in forward or reverse and the accelerator depressed. A switch on the accelerator turns the system off each time the accelerator is released. For shutdown the procedure is reversed. The high voltage capacitors in the system are automatically bled down, to minimize the shock hazard.

INSTRUMENTATION AND CHECKOUT

The installation of the control system in the car was a major wiring job. Of course, the wiring had to be checked out, but in addition the operation of the complete system had to be retested because the physical relationship of the components influences their behavior. Magnetic and electrostatic coupling between cables and components can cause electrical noise. In extreme cases this can result in SCR misfiring, blown fuses or destruction of the SCR. Shielding and dressing the control cables was one of our major development problems in the car.

Many hours of running on a chassis dynamometer were required to find subtle electrical problems and correct them. A feedback torsional vibration, which was described previously, was the most difficult. Our other problems were typical electronic difficulties such as loose wires, component failures, voltage stability, temperature drift, or electrical noise. Intermittent failures were the most difficult to find and fix.

Figure 20 shows that Electrovair II has the same full power acceleration performance as a high performance 1966 Corvair with an automatic transmission. Initially, the production Corvair accelerates faster than Electrovair II, because our present control system limits the starting torque of the motor. At 20 mph, Electrovair II starts to catch up and actually accelerates faster than the production Corvair from this point on. In spite of the head start which the production car achieved, the 0-60 mph times are almost the same, about 16 seconds. The response of the control system as the accel

MILES

RANGE

erator is depressed is very good. At any given speed, full torque can be obtained in 0.2 seconds. Torque control is smooth throughout the speed range except for a small step in torque as the accelerator is first depressed.

The performance of Electrovair II is satisfactory. However, the range is a different story; the production Corvair far exceeds the electric car. A plot of the Electrovair Il range in miles versus car speed in miles per hour is shown on Figure 21. The maximum range was 40 to 70 miles, while a production Corvair will travel 250-300 miles on a tank of gasoline. In addition, the production car can be refueled in a few minutes and be on its way again. The range of Electrovair II is far too short to compete with normal cars. A major improvement in battery or fuel cell technology will be necessary to change this situation.

The basic idea requires that the drive motor become a generator with all of the associated design problems, i.e. the motor voltage must exceed the battery open circuit voltage, and the battery must be able to accept the braking energy at the rate it is being delivered. Detailed studies on regeneration indicate that the amount of energy returned to the battery on a typical city schedule is probably not worth the added circuit complexity. There are also substantial losses in the regeneration cycle because of the numerous energy transformations. The only real advantage regenerative braking appears to offer is that it retains the traditional drag which is felt when the throttle is closed on a conventional engine. However, this does not appear to be a significant problem in Electrovair II.

INTRODUCTION

This paper describes the integration of a hydrogenoxygen fuel cell system and an experimental electric motor drive to power a small van-type vehicle. Development of the fuel cells, the fuel cell system, and the motor and controls is described in companion papers. 1, 2, 3, 4 This work is part of an overall evaluation of the problems and potential of electric powered vehicles.

Over three years ago General Motors Engineering Staff began a program with the objective of building several electric powered vehicles. These vehicles were to employ the most advanced technology which could be reduced to practice during the program. The purpose of these vehicles was to establish more clearly the development goals for research work on the basic electric drive components: the motor, its controls, and the electric power source. The Electrovan vehicle, described in this paper, was built to explore the potential and problems of one possible power source, the

fuel cell.

Fuel cells were chosen for this evaluation for two reasons. First, they offer relief from the traditional disadvantage of electric cars, limited range, A fuel cell will continue to produce electricity as long as it is supplied with fuel and an oxidant, just as a conventional engine will continue to run as long as it is supplied with gasoline and air. The second reason for evaluating fuel cells is that they offer the potential of much better fuel economy. Fuel cells are not restricted in their maximum efficiency by the same thermodynamic principles as are combustion engines.

The fuel cell obtains these advantages over a battery power source at the sacrifice of simplicity. By its very nature, the fuel cell requires an auxiliary system to supply the fuel and oxidant in the proper manner and to maintain the mass and heat transfer conditions necessary to keep the cell operating. These functions are performed in different ways in the various fuel cell concepts now being developed. The functions, however, are common to all systems and the Electrovan was built to determine how well these functions could be performed in an automotive vehicle.

are size, weight, cost, and lifetime. These problems must be solved by continuing research and development on fundamental fuel cell processes and the basic materials used in their construction. A portion of the development work which made possible the fuel cell modules used in this project is described in Reference 1.

GOALS

Electrovan was built to determine the state-of-theart of fuel cells as they might be applied to vehicle propulsion. Hydrogen-oxygen fuel cells were chosen since these were the only ones available which would give the vehicle normal automotive performance and would fit within the available space. We recognize that it is not practical to carry hydrogen and oxygen except in an experimental vehicle. However, by using cryogenic containers it is possible to store enough of these liquids to obtain reasonable vehicle range and evaluate the characteristics of the fuel cells. We wanted to determine the vehicle problems inherent in the fuel cell system regardless of the type of fuel and oxidant used.

The motor and control system used in Electrovan is very similar to the one developed for Electrovair II. The major unknowns were related to the performance of a large fuel cell system in a vehicle and the interactions between the fuel cells, the motor and its controls, and the vehicle. Electrovan has explored these problems.

ELECTROVAN DESCRIPTION

A 1966 GMC Handivan was selected for the test vehicle. The basic body and chassis are lightweight, yet can tolerate a heavy load, and have ample space for the bulky fuel cell powerplant. Although some minor changes were made in the appearance, it can be seen in Figure 1 that the fuel cell and electric drive systems are accommodated within the standard body. The greatest portion of the fuel cell system is installed under the floor.

The sports wagon (or small bus) configuration was chosen to provide additional volume above the floor for auxiliary systems. Thus, two bench seats are installed back to back with a sheet metal enclosure between and under them forming a large hidden