EV1 Electric:  Series Hybrid

General Motors used aerospace technology to design the Series Hybrid-a hybrid electric vehicle that's highly efficient, low in emissions, and provides excellent all-around vehicle performance. The vehicle's series architecture allows it to be operated either as an "infinite"-range hybrid or as a zero-emissions, electric-only vehicle.

HYBRID HIGHLIGHTS
In daily "hybrid-mode" use of the Series Hybrid, the auxiliary power unit (APU) automatically starts and produces power whenever the battery's state-of-charge drops below 40 percent. Assuming the driver has just unplugged the car from its wall charger, this would normally be after about 25 miles of zero-emission mode driving. After the APU starts, it normally delivers just enough electrical power to run the propulsion motor and to slowly return the batteries to a 50 percent state-of-charge.

The series architecture of this hybrid vehicle allows the vehicle to be operated as either an "infinite" range hybrid or as an emission-free electric-only vehicle. The driver simply flips a switch that disables the APU so this experimental car can be driven in the zero-emissions mode for up to 40 miles. The 6.5-gallon fuel capacity provides more than 350 miles of continuous highway range, better than most cars on the road today. Acceleration is equivalent to today's two-passenger EV1.

Except for the 19-inch stretch necessary to provide rear-seat space for two extra passengers, the EV1 body and chassis systems are essentially unmodified in this series hybrid electric vehicle. The electric drive and accessories are standard EV1. An I-shaped pack of 44 NiMH batteries replaces the T-shaped assembly of 26 lead-acid cells. The major additions are a turbine-powered auxiliary power unit (APU) located in the front part of the trunk compartment.

The APU, the smallest, lightest and most efficient device of its kind ever made, is the product of a three-year joint effort between GM and Williams International, an aerospace turbine engine maker in Walled Lake, Michigan. Combining a single-stage, single-shaft, recuperated gas turbine engine with a high-speed permanent-magnet AC generator, the 220 lb. APU is shaped like a cylinder, measuring 20 inches in diameter by 22 inches long. Running between 100,000 and 140,000 rpm, this smooth, quiet device delivers up to 40 kW of electrical energy -- enough to power the car's electric drive system and accessories and/or charge its batteries underway at speeds up to 80 mph.

TECHNOLOGICAL ASPECTS
One means of improving a vehicle's operating efficiencies and emissions is to leverage technology developed for aerospace use to create an advanced series hybrid vehicle. A series hybrid uses one device to drive the wheels, as opposed to a parallel hybrid, which uses two. GM's series hybrid integrates a turbine engine-powered electric generator and Nickel Metal Hydride (NiMH) batteries into a four-passenger version of the EV1. This results in a highly fuel-efficient, low-emission, highway range measured in the hundreds of miles, as well as excellent all-around vehicle performance. Since the GM EV1 is the foundation for the Series Hybrid, the lessons learned from the EV1 platform may someday make this concept vehicle a common vehicle.

The braking system automatically blends three different braking technologies to provide smooth, stable deceleration while reclaiming some of the energy of the moving vehicle. The propulsion motor is used as a brake in conjunction with front disk and rear drum brakes. Using the motor in this way generates electricity from the "motion energy" of the vehicle, which is returned to the battery pack. In a conventional braking system the motion energy is lost as heat at the brake pads.

CHARGING
The Series Hybrid Electric EV1 can be charged safely in all weather conditions using a system known as "inductive charging". Charging requires less than 2 hours using the 220 volt standard charger.

The GM Ovonic battery pack consists of 44 Nickel Metal Hydride battery modules that are electrically connected in series. These modules have been specifically designed for operation in hybrid vehicles.

The Series Hybrid Electric EV1 is powered by a GM ATV Drive Unit consisting of a 137 horsepower, 3-phase, AC induction motor and uses a single-speed, dual reduction gear-set with a ratio of 10.946:1.

GAS TURBINE
The Williams Gas Turbine Power Unit uses a single-shaft, recuperated gas turbine coupled directly to a high-speed permanent-magnet AC generator. This turbine operates between 100,000 and 140,000 rpm, delivering up to 40 kW of electrical power.

DRIVING RANGE
The Series Hybrid Electric EV1 is capable of more than 350 miles.

Contributed by GM-Electric Vehicles