Hybrid-electric vehicles hit the streets

May 18, 2000
New hybrid-electric vehicles perform as well as some conventionally powered models

The Honda Insight boasts 61 mpg for city driving and 70 mpg highway.

Honda's integrated motor assist (IMA) system combines a 1.0-liter, three-cylinder gasoline engine with an electric motor to improve efficiency.

Toyota Prius switches between a 58-hp gas engine and a 40-hp electric motor, or uses both.

The aerodynamic Precept boasts a low 0.163 Cd.

A low-storage requirement hybrid-electric powertrain on the Ford Prodigy concept includes a Diata engine.

A senior editor at a big-name car magazine relates what happened a few years ago when editors there road tested one of the first electric vehicles available to the public. The plan was not to baby the car. It would undergo the same braking and acceleration tests that ordinary vehicles went through during an evaluation.

The road test lasted less than a mile before the batteries were toast. The automaker came out and took back its creation in a huff, accompanied by a lot of hooting on the part of the automotive journalists involved.

It looks as though automakers need no longer fear similar embarrassments. The new crop of alternative-power vehicles now reaching showrooms can hold their own against more traditional designs. These hybrid-electrics combine a small diesel or gas engine with generators/motors to meet goals defined by the Partnership for a New Generation of Vehicles (PNGV). Honda beat the bunch to the market by offering the Insight, a two-seater vehicle that gets up to 70 mpg and garnered an award from the tree-hugging Sierra Club. Toyota is following suit this summer by introducing its Prius to the U.S., currently a big seller in Japan. Ford and GM are developing hybrids for production by 2004. DaimlerChrysler is bringing up the rear and will introduce a concept hybrid later this year, but claims it will also have one in production by 2004 as well.

But will hybrids weave smoothly into the current automotive fabric? According to Brendan Prebo, technical public affairs manager, Ford thinks so. It is developing a hybrid-electric model to be produced in volume by 2003. "We see hybrids as part of the transportation mix. The technology has matured and consumers are becoming knowledgeable about environmentally friendly vehicles. As this public knowledge grows, so will the demand for these vehicles."

Honda Insight
The first hybrid-electric vehicle to hit U.S. shores, the two-seater, five-speed manual Honda Insight uses an integrated motor assist (IMA) system. The system combines a 1.0-liter, three-cylinder gasoline engine with a small electric motor. The electric motor is powered by a 144-V nickel metal-hydride battery pack located under the rear hatch. Regenerative braking charges the batteries. When coasting or braking, the IMA captures energy normally lost through brake or engine heat.

In the 73-hp engine, the cylinders are offset from the crankshaft. When the spark plugs fire, the connecting rods are straight up, reducing force on the side cylinder walls. This cuts down on friction, squeezes more power out of the engine, and improves fuel economy.

A hemi-head engine design has four valves per cylinder with a spark plug in the center and runs at a 10.5:1 compression ratio. The valve train opens only one intake and exhaust valve at low speeds to reduce fuel consumption and, at higher speeds, opens all four. Each iridium-tipped spark plug uses direct injection to burn fuel more efficiently.

The cylinder head and manifold are cast together which helps the catalytic converter more quickly hit its operating temperature and cuts emissions as well. The adsorptive catalytic converter controls NOx emissions, capturing these molecules when the engine runs lean. As the engine runs a richer mixture, the NOx molecules mix with the exhaust to form carbon dioxide, nitrogen, and water vapor. The catalyst helps reduce hydrocarbon emissions by 84% and NOx emissions by 50%, meeting ultralow emission vehicle (Ulev) standards.

Aluminum plays a big role in the Insight. The 1.0-liter engine has an aluminum block, an aluminum head and exhaust manifold, and weighs in at a light 124 lb. The aluminum body and chassis cut overall vehicle weight and are joined together by diecast pieces for strength.

The chassis uses aluminum pipes with internal ribs for strength at the front and rear. For safety's sake, these extrusions fold up in an accident like a paper fan, absorbing the impact and pushing the energy upward as the frame bends. Aluminum beams protect against side impacts. The Insight has a 0.25 Cd, thanks to a tapered body, rounded noise, rear-wheel skirts, low height, and a flat underbody. And while it's environmentally friendly, performance figures state 110 mph and 0 to 60 in 12 sec.

Toyota Prius
The Prius, arriving this summer in the U.S., attempts to meet the upcoming California super-ultralow-emission vehicle (Sulev) standard. Sulev is approximately 85% cleaner than Ulev, the strictest existing gasoline vehicle standard.

The Prius runs on either electricity or gasoline, or a combination of the two. The key to the hybrid system is a power-split device which sends engine power directly to the wheels or to an electric generator that controls the electric motor and battery charge. This device uses a planetary gear to vary the amount of power supplied from the engine to either the wheels or the generator. This gearset controls engine speed independent of road speed to wring maximum fuel efficiency out of the powerplant. An electronically controlled transmission adjusts the rates of revolution of the gasoline engine, electric generator, and electric motor for acceleration and deceleration.

The primary power source for the Prius is a 1.5-liter gasoline engine. Specs for the Japanese model state the powerplant provides 58 hp at 4,000 rpm with peak torque of 75 lb-ft at 4,000 rpm. The U.S. models are expected to have an increase in horsepower and torque. Limiting engine revs to 4,000 rpm lets internal parts be built lighter. Also, the crankshaft has a smaller diameter, piston rings have lower tension, and the valve spring load is less compared to high-revving engines. The permanent-magnet electric motor generates 30 kW, or 40 hp from 940 to 2,000 rpm.

A regenerative braking system turns the motor into a generator when brakes are applied or the vehicle is coasting. This captures energy normally lost as heat or kinetic energy and transforms it into electricity to recharge the batteries. A computer sends a signal to the regenerative system to slow the vehicle when the driver presses the brake. Pushing the pedal harder makes hydraulic brakes kick in. The Prius has front discs with rear drums, and standard ABS.

The Prius carries a hydrocarbon adsorption catalyst and a vapor-reducing gas tank to meet Sulev specs. The catalyst uses what is said to be the thinnest-walled ceramic substrate with a high cell density. This increases catalytic surface area, raising efficiency. A hydrocarbon adsorbing unit catches and stores HCs on its surface until the catalyst warms to operating temperature.

The vapor-reducing gas tank has a plastic bladder inside. As fuel burns, the bladder collapses, decreasing vapor that normally escapes from the tank as well as cutting emissions. Thirty-eight nickel-metal hydride batteries weigh less than those in the Japanese model and allow for more cargo room in the trunk.

The five-passenger Prius has a 5.8-in.-wide display under its instrument panel which shows the condition and energy flow of the hybrid-drive system. For the U.S. model, a new front air dam and rear spoiler lowers the Cd from 0.30 to 0.29. Standard equipment will include ABS, automatic air conditioning, power windows, door locks, and mirrors, and a security system. Optional side air bags and cruise control will be offered.

Ford Prodigy Concept
The Prodigy hybrid-electric five-passenger sedan is Ford's latest contribution to the PNGV program. This vehicle joins the P2000 LSR concept and is part of a platform that will produce a variety of environmentally friendly vehicles. The Prodigy's low-storage requirement (LSR) hybrid-electric powertrain includes a direct-injection, aluminum throughbolt assembly (Diata) engine, starter/alternator, automatically shifted manual transmission, and a 288-V nickel-metal hydride battery pack.

An advanced powertrain combines two separate propulsion systems —a small diesel engine and a three-phase, alternating-current electric drive system linked to an automatically shifted manual transmission. The five-speed automated manual tranny shifts via computer controls that determine the optimum shifting time for maximum fuel efficiency. In short, it has the operating ease of an automatic married to the efficiency of a manual.

The four-cylinder 1.2-liter direct-injection powerplant provides 74 hp at 4,100 rpm. The aluminum engine features a variable geometry turbocharger, an intercooler, and four valves per cylinder.

The starter/alternator is a three-phase electric motor which sits between the transmission and engine and delivers up to 47 hp, with 207 lb-ft of torque. The starter/ alternator and electronics module stop at idle to conserve fuel. The electric motor powers the car in city driving and assists the Diata engine during hard acceleration. The Diata engine restarts 0.2 sec after touching the accelerator pedal.

The instrument panel has an energy flow display showing the status of the operating systems. For example, because the engine shuts off when the vehicle stops at a traffic light or brakes, the display assures the driver that power will be available when needed.

The Prodigy's exterior takes aerodynamics seriously. Side-mounted cameras replace traditional sideview mirrors. Variable ride height, and grille shutters and shields under the car add to the aerodynamics. A louvered front grille lets air in and out only when necessary. These factors contribute to the vehicle's low 0.199 Cd.

GM Precept Concept
The five-passenger Precept uses a dual-axle regenerative parallel hybrid propulsion system with a 35-kW three-phase electric motor driving the front wheels. An Isuzu 54-hp compression-ignition direct-injection (Cidi) engine drives the rear wheels.

The combustion engine kicks in for acceleration and hill climbing. It directly injects fuel and air into each cylinder, where pistons compress it under high pressure and ignite the mixture, eliminating spark plugs. The engine controls the correct mixture of fuel and air and the ignition timing, maximizing power and reducing pollutants.

The electric motor handles city driving and helps the combustion engine during acceleration. It can be reversed, eliminating a reverse transmission gear. The motor will be powered by either a lithium-polymer battery pack or a nickel-metal hydride system, both providing a 350-V, 3-kW capacity.

The brain behind the hybrid propulsion system is a Power PC processor-based controller. This 32-bit 266-MHz device talks to the accelerator, brakes, transmission, energy management system, electric traction, multipurpose unit (MPU), engine controller, transaxle controller, thermal system controller, and brake controller. It also decides which or both of the motors should operate. Forty-seven distributed computer modules provide smart control throughout the Precept.

A smaller, electric motor in the rear of the vehicle is coupled to the combustion engine. It starts the engine in less than a second, eliminating a starter. The motor powers the air conditioning when the engine isn't running and gives the vehicle an extra power jolt if needed.

The electric motors bear the burden of stopping the Precept. They slow it by acting as generators and gathering the energy of the spinning front and rear wheels. This energy is converted to electricity to recharge the battery pack under the front seat. A four-wheel disc brake-by-wire system uses a small electrically powered hydraulic pump near each brake caliper. These friction brakes give extra stopping power if needed.

An automatically shifted five-speed manual transmission is modified from an Opel Astra. It has no fifth and reverse gears and uses an automatic, computer-controlled operation instead of clutch shifting. The Cidi engine starts in any gear, and changes gears in under a second.

The aerodynamic exterior of the Precept boasts a 0.163 Cd. Placing the engine in the rear with an exhaust grille eliminates an air-catching front grille, cutting air turbulence. Like the Ford Prodigy, tiny cameras replace the sideview mirrors. A third, rear-facing camera sits inside the rear window, giving a panoramic rear view on an instrument panel LCD.

The LCD operates as a driver-vehicle interface. The operator enters a five-digit security code on a keypad to start the car. This keypad also pops open the doors, eliminating door handles that catch air and add drag. A "smart switch" in the control panel works like a mouse for the laptop computer docked at the top of the instrument panel. It scrolls through a menu on the laptop. The screen sits forward and under the base of the windshield, easing the transition from looking at the road to checking instruments.

Powder-coated steel and aluminum frame the front seats, with minimal foam padding and trim for the bolsters. Mesh material fills out the seat bottom, back, and center insert. Lightweight, rubber textured flooring replaces conventional carpeting.

A torque transducer is sandwiched into the drivetrain of a Toyota Prius to gather data while the engine is fully integrated with the control system.

Engineers at Argonne National Labs constructed an engine map from the four-cylinder engine of the Toyota Prius. Normally, the engine is removed and connected to a dynamometer which measures its torque. However, the Prius engine is integrated with the drivetrain and computer-control system, making it nearly impossible for it to work outside the vehicle.

A new torque transducer, from HBM Technologies of Germany, was put in a housing the size of a small snare drum and squeezed into the crowded engine compartment of the Prius. Argonne engineers collected 16 streams of data on all aspects of the powertrain operation simultaneously. The resulting engine map pegs engine efficiency at about 36%, which is high for an ICE. Efficiency of an average vehicle under normal conditions is 25%.

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