Hybrid vehicle

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File:Honda-Insight-'03.jpg
Honda Insight, a hybrid gas-electric vehicle
2004 Toyota Prius, a hybrid gas-electric vehicle

A hybrid vehicle uses multiple energy sources or propulsion systems to provide motive power. This most commonly refers to gasoline-electric hybrid vehicles, which use gasoline (petrol) and electric batteries for the energy used to power internal-combustion engines (ICEs) and electric motors. These powerplants are usually relatively small and would be considered "underpowered" by themselves, but they can provide a normal driving experience when used in combination during acceleration and other maneuvers that require greater power.

Modern mass-produced hybrids can recharge their batteries while underway. When cruising or idling, some of the output of the combustion engine is fed to a generator (sometimes merely the main electric motor running backwards) which generates electricity to charge the batteries. This contrasts with all-electric cars which use batteries charged by an external source. Most hybrids still require gasoline as fuel— though diesel and other fuels such as ethanol or plant based oils have also seen occasional use.

Hybrids are more environmentally-friendly than traditional internal combustion engine vehicles because they generally provide greater fuel economy. For greater discussion of specific operating modes used in different hybrid designs, see the Types section below.

The U.S. Energy Policy Act of 2005 provides a tax credit of up to $3,400 for owners of hybrid vehicles.

File:Graph median3.png
Median mpg (US) with boxplot from GreenHybrid.com Real Hybrid Mileage Database


(The term hybrid when used in relation with cars also has other uses. Prior to its modern meaning of hybrid propulsion, the word hybrid was used in the United States to mean a vehicle of mixed national origin; generally, a European car fitted with American mechanical components. This meaning has fallen out of use. Some have also referred to flexible-fuel vehicles as hybrids because they can use a mixture of different fuels - typically gasoline and ethanol alcohol fuel. For greater discussion of this meaning, see the Hybrid fuel section below.)


Hybrids currently available

Ford:

Honda:

General Motors:

Mazda:

Renault:

Toyota and Lexus:

History

The first successful hybrid-electric car was engineered by Ferdinand Porsche in 1899. Since then, hobbyists have continued to build hybrids but none was put into mass production by a major manufacturer until the waning years of the twentieth century. In the intervening period, the widest use of hybrid technology was actually in diesel-electric submarines, which operate in essentially the same manner as hybrid electric cars. However, in this case the goal was to allow operation underwater without consuming large amounts of oxygen, rather than economizing on fuel. Since then, many submarines have moved to nuclear power, which can operate underwater indefinitely, though a number of nations continue to rely on diesel-electric fleets.

Automotive hybrid technology became successful in the 1990s when the Honda Insight and Toyota Prius became available. These vehicles have a direct linkage from the internal combustion engine to the driven wheels, so the engine can provide acceleration power. The 2000s saw development of plug-in hybrid electric vehicles (PHEVs), which can be recharged from the electrical power grid and don't require conventional fuel for short trips. The Renault Kangoo was the first production model of this design, released in France in 2003.

The Prius has been in high demand since its introduction. Newer designs have more conventional appearance and are less expensive, often appearing and performing identically to their non-hybrid counterparts while delivering 50% better fuel efficiency. The Honda Civic Hybrid appears identical to the non-hybrid version, for instance, but delivers about 50 US mpg (4.7 L/100km). The redesigned 2004 Toyota Prius improved passenger room, cargo area, and power output, while increasing energy efficiency and reducing emissions. The Honda Insight is still on sale and has a devoted base of owners.

2004 saw the first hybrid SUV released, Ford Motor Company's Ford Escape Hybrid. Toyota announced model year 2005 hybrid versions of the Toyota Highlander and Lexus RX 400h, and has plans to add hybrid drivetrains to every model it sells in the coming decade. Honda has also announced the release of a hybrid version of the Accord. Also, Nissan announced the release of the Altima hybrid (technology supplied by Toyota) around 2006.

An R.L. Polk survey of 2003 model year cars showed that hybrid car registrations in the United States rose to 43,435 cars, a 25.8 % increase from 2002 numbers. California, the nation's largest state with 1/8th of the country's population, had the most hybrid cars registered with 11,425. The proportionally high number may be partially due to the state's higher gasoline prices and stricter emissions rules, which hybrids generally have little trouble passing.

Honda, which offers Insight, Civic and Accord hybrids, sold 26,773 hybrids in the first 11 months of last year alone. Toyota has sold a cumulative 306,862 hybrids between 1997 and Nov. 2004 and Honda has sold a total of 81,867 hybrids between 1999 and November 2004.[1]

Hybrid light trucks were introduced 2004 by Mercedes (Hybrid Sprinter) and Micro-Vett SPA (Daily Bimodale).

Benefits

Benefits of the hybrid design include the following:

  • In comparison with purely electric vehicles of comparable size and power, hybrids are usually lighter and roomier because fewer batteries are needed. Batteries store less energy per unit mass and per unit volume than does gasoline.
  • The internal-combustion engine in a hybrid vehicle is much smaller, lighter, and more efficient than the one in a conventional vehicle, because the engine can be sized for average power demand rather than peak power demand. The power curve of electric motors is better suited to variable speeds and can provide substantially greater torque at low speeds compared with internal-combustion engines.
  • Like many electric cars, but in contrast to conventional vehicles, braking in a hybrid is controlled in part by the electric motor which can recapture part of the kinetic energy of the car to partially recharge the batteries. This is called regenerative braking and one of the reasons for the high efficiency of hybrid cars. In a conventional vehicle, braking is done by mechanical brakes, and the kinetic energy of the car is wasted as heat.

Government agencies in the US and elsewhere offer various incentives to encourage the purchase of certain qualifying hybrid or electrical vehicles.

  • The purchase of hybrid cars qualifies for a $2000 tax deduction on the IRS 1040 form for the year of 2003. The deduction reduces by $500 each year until it reaches zero. HR 1308 Sec. 319 proposed the phasing out of the deduction to put on hold for the year 2004 and 2005 (i.e., hybrid car buyers can enjoy the $2000 deduction before the phasing out resumes at $500 in 2006).
  • The Federal tax deduction will turn into a tax credit starting Jan 1, 2006. However only 60,000 new cars sold by each car manufacturer would qualify for such tax credit.
  • Many states give tax credits to hybrid car buyers.
  • Certain states (e.g., California, Virginia and Florida) allow singly-occupied hybrid vehicles to enter the HOV lanes on the highway, although the Federal Highway Administration has ruled that is a violation of the federal statute. [2]
  • Some states, e.g. California, exempt hybrid cars from the biennial smog inspection, which costs over $50 (as of 2004).
  • Hybrid cars can go on certain toll roads for free.
  • City of San Jose, CA issues a free parking tag for hybrid cars that were purchased at a San Jose dealership. The qualified owners do not have to pay for parking in any city garage or road side parking meters.
  • City of Los Angeles, CA offers free parking to all hybrid vehicles starting on October 1, 2004. The experiment is an extension to an existing offer of free parking for all pure electrical vehicle.
  • Annual vehicle registration fees in the District of Columbia are half ($36) that paid for conventionally vehicles ($72).
  • Drivers of hybrid vehicles in the United Kingdom benefit from the lowest band of Vehicle Excise Duty (car tax) which is based on CO2 emissions. In London, these vehicles are also exempt from the £5 ($9) daily congestion charge in Central London.

Trade-offs

While some manufacturers are using power generated from the hybrid systems to give vehicles added performance, these hybrid vehicles still offer equal or better fuel efficiency over their conventionally-powered counterparts. The trade-off between added performance and improved fuel efficiency is mainly something controlled by the software within the hybrid system. In the future, manufacturers may provide hybrid-owners with the ability to set this balance (fuel efficiency vs. added performance) as they wish, through a user-controlled setting.

Types

There are many types of hybrids, differentiated by how the electric and fueled halves of the powertrain connect, and at what times each portion is in operation. Two major categories are series hybrids and parallel hybrids, though parallel designs are most common today. Some hybrid vehicles don't even use electricity for auxiliary energy storage.

Most hybrids, no matter the specific type, use regenerative braking to recover energy when slowing down the vehicle. This simply involves running the motor backwards as a generator. Many designs also shut off the internal combustion engine when it is not needed in order to save energy. That concept is not unique to hybrids—the Volkswagen Lupo 3L is one example of a conventional vehicle that shuts off its engine when at a stop.

Series

In a series design, the internal combustion engine is not connected to the drivetrain at all, but powers an electrical generator instead. Electricity from the generator is fed to the motor or motors that actually move the car, and excess energy can be used to charge batteries. When large amounts of power are required, electricity comes from both the battery pack and the engine-generator section. Because electrical motors can operate quite efficiently over a wide range of speeds, this design removes or reduces the need for a complex transmission. The engine can also be finely tuned to operate at its most efficient speed whenever it is running. However, series hybrids require separate motor and generator portions, which can be combined in some parallel hybrid designs. It is likely that some hydrogen cars running on fuel cells will use a series-style setup, with fuel cells replacing the engine-generator section.

This is similar to the operation of diesel-electric train locomotives, but they are not hybrids because they do not store auxiliary power in batteries for later use.

Parallel

Parallel systems, which are most common at present, connect both the electrical and fueled halves to the mechanical transmission. They can be subcategorized depending upon how balanced the different portions are at providing motive power. In many cases, the internal combustion engine is the dominant portion and is used for primary power, with the motor turning on only when a boost is needed. Others can run with just the electric or combustion half operating alone. Many designs combine an electrical generator and a motor into one unit, and this device can also replace the starter motor used to get the engine to turn over.

In the second generation, the internal combustion engine drives the wheels directly with the electric motor serving as a power assist when extra power is needed, and to recapture the kinetic energy usually lost during braking.

Full hybrid

A full hybrid, sometimes also called a strong hybrid, is a vehicle that can run on just the engine, just the batteries, or a combination of both. The Prius and Escape Hybrids are examples of this, as both cars can be moved forward on battery power alone. A large, high-capacity battery pack is usually needed for battery-only operation. These vehicles have a split power path that allows more flexibility in the drivetrain by interconverting mechanical and electrical power, at some cost in complexity. To balance the forces from each portion, the vehicles use a differential-style linkage between the engine and motor connected to the head end of the transmission.

The Toyota brand name for this technology is Hybrid Synergy Drive, which is being used in the Prius and the Highlander sport-utility vehicle (SUV). A computer oversees operation of the entire system, determining which half should be running, or if both should be in use. The computer also optimizes the fuel usage by shutting off the internal combustion engine when the electric motor is sufficient to provide the power. The hybrid drivetrain of the Prius, in combination with aerodynamics to reduce drag, results in 80%–100% gains in fuel economy compared to four-door conventional cars of similar weight and size.

Assist hybrid

Assist hybrids use the engine for primary power, with a torque-boosting electric motor also connected to a largely conventional powertrain. The electric motor is essentially a very large starter motor, which operates not only when the engine needs to be turned over, but also when the driver "steps on the gas" and requires extra power. Honda's hybrids including the Insight use this design; their system is dubbed Integrated Motor Assist (IMA). Assist hybrids differ fundamentally from full hybrids in that they cannot run on electric power alone. However, since the amount of electrical power needed is much smaller, the size of the battery systems is reduced.

A variation on this type is Mazda's e-4WD system, offered on the Mazda Demio sold in Japan. This front wheel drive vehicle has an electric motor which can drive the rear wheels when extra traction is needed. The system is entirely disengaged in all other driving conditions, so it does not enhance performance or economy.

Ford has dubbed Honda's hybrids "mild" in their advertising for the Escape Hybrid, arguing that the Escape's full hybrid design is more efficient. However, assist hybrids should not be confused with actual mild hybrids like the Chevrolet Silverado Hybrid.

Mild hybrid

Mild hybrids are essentially conventional vehicles with oversized starter motors, allowing the engine to be turned off whenever the car is coasting, braking, or stopped, yet restart quickly and cleanly. Accessories can continue to run on electrical power while the engine is off, and as in other hybrid designs, the motor is used for regenerative braking to recapture energy. The larger motor is used to spin up the engine to operating rpm speeds before injecting any fuel.

Many don't consider these to be hybrids at all, and these vehicles do not achieve the fuel economy of "true" hybrid models. A major example is the 2005 Chevrolet Silverado Hybrid, a fullsize pickup truck. Chevrolet was able to get a 10% improvement on the Silverado's fuel efficiency by shutting down and restarting the engine on demand. Mild hybrids often use 48 volt systems to supply the power needed for the startup motor, as well as to compensate for the increasing number of electronic accessories on modern vehicles.

Plug-in hybrid

Main article: Plug-in hybrid electric vehicle

A plug-in hybrid electric vehicle (PHEV) is a full hybrid, able to run in electric-only mode, with larger batteries and the ability to recharge from the electric power grid. They are also called gas-optional, or griddable hybrids. Their main benefit is that they can be gasoline-independent for daily commuting, but also have the extended range of a hybrid for long trips. They can also be multi-fuel, with the electric power supplemented by diesel, biodiesel, or hydrogen. The Electric Power Research Institute's research indicates a lower total cost of ownership for PHEVs due to reduced service costs and gradually improving batteries. The "well-to-wheel" efficiency and emissions of PHEVs compared to gasoline hybrids depends on the energy sources of the grid (the US grid is 50% coal; California's grid is primarily natural gas, hydroelectric power, and wind power). Particular interest in PHEVs is in California where a "million solar homes" initiative is under way, and global warming legislation has been enacted.

Prototypes of plug-in hybrid cars, with larger battery packs that can be recharged from the power grid, have been built in the U.S., notably at Prof. Andy Frank's Hybrid Center at UC Davis and one production PHEV, the Renault Kangoo, went on sale in France in 2003. DaimlerChrysler is currently building PHEVs based on the Mercedes-Benz Sprinter van. Light Trucks are also offered by Micro-Vett SPA the so called Daily Bimodale.

The California Cars Initiative has converted the '04 and newer Toyota Prius to become a prototype of what it calls the PRIUS+.

See also: vehicle to grid

Hydraulic hybrid

A hydraulic hybrid vehicle uses hydraulic and mechanical components instead of electrical ones. A variable displacement pump replaces the motor/generator, and a hydraulic accumulator replaces the batteries. The hydraulic accumulator, which is essentially a pressure tank, is potentially cheaper and more durable than batteries. Hydraulic hybrid technology was originally developed by Volvo Flygmotor and was used experimentally in buses from the early 1980s and is still an active area.

Initial concept involved a giant flywheel for storage connected to a hydrostatic transmission, but it was later changed to a simpler system using a hydraulic accumulator connected to a hydraulic pump/motor. It is also being actively developed by Eaton and several other companies, primarily in heavy vehicles like buses, trucks and military vehicles. An example is the Ford F-350 Mighty Tonka concept truck shown in 2002. It features an Eaton system that can accelerate the truck up to highway speeds.

Engines and fuel sources

Gasoline

Gasoline engines are used in most hybrid designs, and will likely remain dominant for the foreseeable future. While petroleum-derived gasoline is the primary fuel, it is possible to mix in varying levels of ethanol created from renewable energy sources. Like most modern ICE-powered vehicles, hybrids can typically use up to about 15% ethanol. Manufacturers may move to flexible-fuel engines, which would increase allowable ratios, but no plans are in place at present.

Diesel

One particularly interesting hybrid vehicle combination uses a diesel engine for power. Diesels are excellent at delivering constant power for long periods of time, suffering less wear while operating at higher efficiency. However, the engines also suffer from poor acceleration due to having a limited rpm range. This poor acceleration can be addressed with the hybrid technique, and such designs may offer performance in a car of over 100 mpg US (2.35 L per 100 km).

Diesel vehicles, and therefore diesel hybrids, have the advantage they can use 100% pure biofuels (biodiesel), so they don't need petroleum at all. Diesels are not widely used for passenger cars in the United States, where only Volkswagen and Mercedes Benz offer them as of 2005. However, they are popular in Europe—Mercedes Benz claims 56% (as of February 2005) of all the cars they sell in Europe are diesels, and almost half of all the vehicles sold there have a diesel engine.

Part of the reason for limited popularity in the US is lack of acceptable fuel. Diesel in the US has long been considered very "dirty", with relatively high levels of sulfur and other contaminants in comparison to the Eurodiesel fuel in Europe, where greater restrictions have been in place for many years. Despite the dirtier fuel, the US has tough restrictions on exhaust, and it has been difficult for car manufacturers to meet emissions levels given what is put into the engine. However, ultra-low sulfur diesel is set to be mandated in the United States in June 2006.

The use of hybrid diesels remains limited. VW made a prototype diesel-electric hybrid car that achieved 118 mpg US fuel economy (2 liters per 100 km), but has yet to sell a hybrid vehicle. So far, hybrid diesels have primarily appeared in mass transit buses, primarily made by General Motors' New Flyer division.

Fuel cells

Some fuel cell-powered vehicles currently in development use some hybrid-like technology to store auxiliary energy. Like diesels above and steam power outlined below, fuel cells are best at delivering a fairly constant flow of electricity, so having a secondary system is helpful. In some cases, batteries have been replaced with ultracapacitors, which can store and retrieve energy quickly, but are inappropriate for long-term electrical storage.

Steam and turbines

At present, no current or planned mass-market car is driven by a steam engine, but hybrid technology could bring back the steam-powered car. In the early 20th century, steam-powered cars made by the Stanley Steamer Company did compete successfully with the internal combustion engine. Steam engines can be much more efficient (and generate less pollution) than internal combustion engines, which is why most of the world's electric power comes from steam turbines heated by fossil fuels or a nuclear heat source. However, steam engines have not been able to compete with internal combustion for vehicles for several reasons:

  • Lower power-to-weight ratio
  • Smaller range of operating speeds
  • Much longer warm-up time
  • More complex controls

The driver of a Stanley Steamer had to keep a close eye on several pressure and temperature gauges while driving. With modern computers, much of this could be handled automatically. Similarly, the availability of relatively lightweight turbines increases the power-to-weight ratio and reduces thermal inertia.

Similarly, turbine engines directly burning fuel could also be used. From the 1950s to the 1970s Chrysler created several turbine-powered vehicles, though only small numbers were produced. They had complex drivetrains and achieved relatively slow starting speeds, with effects reminiscent of "turbo lag," but demonstrated that turbines could be used for automobiles (see Chrysler Turbine engines).

Hybrid fuel

In addition to vehicles that use two or more different devices for creating motive power, some also consider vehicles that use distinct energy input types (fuels) to be hybrids:

Hybrids vs. electric vehicles

All-electric cars are more popular in Europe than in the U.S. The official argument of the major U.S. automobile manufacturers is lack of customer demand for pure electric cars. However, this will change as battery technology advances and gas prices continue to increase.

For now, car manufacturers are focusing on fuel cell-based cars and hybrids. Toyota intends that all of its vehicles be hybrid electric by 2012.

See also

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