Energy and the Natural Environment
Hybrid Cars- Some FAQs and Answers

by David A. Dobson, Ph.D.

This article is the third in a series, to appear in issues of the Warbler, dealing with energy sources, uses and technologies from various perspectives.

Q1: What is a hybrid car, and why is it called a hybrid?
A1: A hybrid of anything is a cross between two familiar, pre-existing forms. In this case it's a car that combines the technologies used in a gasolene-powered internal combustion (IC) engine with a battery-powered electric motor to gain the advantages of both propulsion systems.

Q2: What are the strengths and the shortcomings of conventional cars?
A2: Conventional cars are a versatile, convenient, reliable form of personal transportation, but they suffer from a couple of serious problems that are growing in importance. All hydrocarbon-powered IC engines emit toxic pollutants, a serious problem in dense urban environments. IC engines also are not very efficient converters of the energy stored in fuel to mechanical energy, especially under congested, stop-and-go driving conditions. The use of computer-controlled fuel injection, exhaust gas recirculation, alcohol-blended fuels, and catalytic converters have helped to mitigate these problems, but new solutions are needed as hydrocarbon fuels become scarcer and more expensive. IC engines are most efficient (about 20%) and least polluting when they are operated under fairly heavy load (wide-open throttle and 3000-4000 RPM). They will produce more power, but they lose efficiency, at high RPM. The car's efficiency goes all the way to zero, of course, when it's sitting in a traffic jam with the engine idling but still using fuel. Both of these problems are especially acute in so-called performance cars, with engines much larger than required for cruising at highway speeds.

Q3: What are the strengths and the shortcomings of electric cars?
A3: Electric cars, first proposed to solve the smog problem, are powered by large-capacity on-board rechargeable batteries and have no toxic emissions. The efficiency of properly engineered electric motors is very high under nearly all driving conditions. The Achilles' heel of electric cars is their limited range on one battery charge. The size and weight of the batteries, needed to propel a car as far as one tank of gas would take you, is much greater than the size and weight of a full tank of gas. Furthermore recharging the batteries takes far longer than filling the gas tank. Swapping out the batteries for a set of freshly recharged ones every 100 miles or so would be a real hassle and impractical for a number of reasons. Electric cars are quiet, pollution free and very efficient for trips up to 50 miles or so, where you can plug in to recharge, when you get home. They do especially well in congested urban traffic, but are quite unsuitable for very long commutes or highway trips of several hundred miles or more. (Hybrid cars combine IC engine and electric motor technologies to exploit the strengths of both systems.)

Q4: What is meant by the term regenerative braking, a standard feature of hybrid cars?
A4: Accelerating to higher speed requires energy, which gets stored in the moving car as kinetic energy. Each time you stop the car this kinetic energy must be removed; it is converted into heat energy by friction forces in the brakes, dissipated to the air, and wasted. A similar process occurs in hilly country. Going up hill, the engine must work to raise the potential energy of the car. This energy is wasted as heat in the brakes when you apply them to control your speed while going back down the hill. This energy is wasted in the sense that is cannot be recovered for any motive purpose, such as to get moving again or climb the next hill. Saving the brakes by shifting down and using engine braking still wastes the same amount of energy, this time as extra heat going out the exhaust pipe. In an electric car or hybrid car, stepping on the brake pedal at speeds above about 20 MPH temporarily changes the motor into an alternator, which recharges the batteries. Kinetic or potential energy is thus converted into stored chemical energy in the battery. In practice about 75% of this energy is recovered in the battery and then reused by the motor to accelerate the car or climb the next hill. This is regenerative braking, and it can greatly improve the car's overall energy efficiency, under some driving conditions.

Q5: Are all hybrid cars basically the same?
A5: No. There are two quite different strategies employed to combine the IC engine and electric motor/alternator systems in the hybrid cars that are available today. Each of these strategies will be addressed in the paragraphs below.

In an electric motor assisted hybrid car, such as the Honda Civic Hybrid or the Honda Insight, the electric motor/alternator (M/A) is connected directly to the crankshaft of the IC engine, so that both units always rotate at the same speed. This motor-engine combination is then coupled to the wheels through a transmission-differential power train, just as it is in a conventional car. The IC engine must always be running for the car to move, even when crawling along at very low speed. But whenever the car comes to a full stop, such as at a red light, the engine stops running automatically. Then when you step on the accelerator pedal the engine automatically starts, cranked by the M/A, and away you go! The whole process is computer controlled and smooth, not jerky as if you had stalled the engine. In ordinary driving the M/A automatically acts as an alternator whenever that's needed to maintain the batteries at nearly full charge. Whenever you need peak power for accelerating, passing or hill climbing, the M/A acts as a motor to boost the power of the IC engine. The M/A acts as an alternator when you apply the brakes to slow down, giving the car energy recovery through regenerative braking. Honda's strategy gives you improved milage by using a smaller IC engine, shutting it down under idle conditions, and using the M/A to maintain the performance of a car with a larger IC engine. For example, the regular Civic has a 1.8 liter IC engine, but the Civic Hybrid has a 1.3 liter IC engine assisted by a 20 HP M/A. The EPA city milage rating improves from 30 mpg to 50 mpg, and the EPA highway milage rating improves from 40 mpg to 50 mpg. (As always, the milage you can actually get in any vehicle depends on many factors including weather, altitude, tire inflation, speed, and how you drive.)

In a parallel system hybrid car, such as the Toyota Prius or Highlander Hybrid, or the Ford Escape Hybrid or Mercury Mariner Hybrid, the electric motor/alternator (M/A) and the IC engine are coupled to each other, and to the transmission, through a planetary gear unit (Hybrid Synergy Drive ©). This coupling allows the IC engine and the M/A to turn at different speeds while either or both of them are delivering power to the transmission. The IC engine can thus be completely stopped, and using no fuel whatsoever, while the car moves slowly under power from the M/A! The IC engine is always controlled by the computer system. When the computer senses that the battery needs charging or that the driver's foot on the accelerator is asking for more power than the M/A alone can efficiently supply, the computer will start the IC engine. Whenever the engine is not needed, the computer shuts it down to save fuel. To the driver, the hybrid car feels just like a regular automatic transmission car, and the driver may be completely unaware of when the IC engine starts or stops. On the highway, the power sharing capabilities of electric assist and parallel hybrid cars are very similar, and both types make efficient use of regenerative braking. The Prius and the Civic Hybrid are quite similar in size, weight, cost, and other characteristics, so it's useful to compare their milage performance. The difference between their EPA city ratings: 60 mpg (Prius) and 50 mpg (Civic Hybrid) nicely illustrates the competitive advantage of the parallel system in city driving. On the highway, their EPA ratings at essentially identical (51 mpg & 50 mpg respectively).

Q6: These hybrid cars' specifications say they use CVT transmissions. What is that?
A6: All of the hybrid cars mentioned above employ a new type of automatic transmission, the CVT or continuously variable transmission. Gears are replaced by contacting cones, which allow the transmission's in/out speed ratio to change continuously, rather than in discrete steps. It's an old concept, but has been engineered over the last decade into a practical, highly efficient way to smoothly match engine speed to the widely-varying wheel rotation speed. The CVT replaces the familiar 3-6 speed automatic transmission and its torque converter.

Q7: What about other Hybrid Models? Are there some you haven't yet discussed?
A7: The Ford/Mercury, Toyota Highlander and Lexus RX400 hybrids are SUVs. They are significantly more expensive, heavier and available in 4-wheel drive models. They have more ground clearance, larger engines and poorer gas milage than the sedans referred to earlier. These hybrid SUVs all use the Toyota Hybrid Synergy Drive parallel system, and they are all expected to get improved milage, compared to their non-hybrid counterparts. Other hybrid sedans planned for the 2006 or 2007 model years include a Honda Accord, Toyota Camry, Lexus and Nissan Altima. These sedans will trade optimal gas milage for a larger engine size, compared to the Prius and the Civic Hybrid. Apparently GM plans to tack the hybrid label on a couple of full-size pickup truck models, with only marginal improvement in their poor milage figures.

Q8: What about the cost of hybrid models? Do they make obvious economic sense?
A8: In general the MSRP and dealer invoice prices of hybrid models seem to be about $3,000 to $5,000 more than their non-hybrid counterparts. (There is no such thing as a non-hybrid Prius or Insight.) With $3/gal. gasolene and an EPA city milage comparison of 50 mpg vs 30 mpg , you get $6,000 (hybrid) vs $10,000 (non-hybrid) for the total cost of gas to drive 100,000 miles. The incremental purchase cost is up front, while the gas savings is spread over at least several years of driving. So the decision to buy the hybrid is not obviously justified by fuel savings alone, unless the cost of gas rises well above the $3 level in the lifetime of the car. It's well known that ordinary cars seldom deliver EPA-rated milage performance. This is often attributable to poor driving habits and tire under-inflation, which would have a large detrimental effect on hybrid milage also. Driving green, as if you had a thorn sticking into the bottom of your right foot, may be the best way to save on gas expense.

Q9: Are there other reasons to buy a hybrid rather than a comparable non-hybrid model?
A9: If the CAFE (corporate average fuel efficiency) standard for all personal-use vehicles were 40 mpg, and that standard were being met today, the USA would not need to import any oil from the Middle East region. Driving a hybrid may be viewed as a patriotic act, one that's in the National interest. That said, it may be justified for the Government to offer us tax incentives.

Q10: Are there tax incentives for buying hybrid cars?
A10: Yes. Currently there is a $2,000. adjustment (above-the-line deduction) available on hybrid cars delivered to the purchaser before the end of 2005. This incentive expires very soon, but it's being replaced by a much better one, a tax credit that could be as much as $3,000. or even a bit more, depending on the vehicle being purchased. For a taxpayer in the 25% bracket, the 2005 adjustment would reduce the year's total tax by $500., but the 2006 credit will come right off the bottom line. The American Council for an Energy Efficient Economy has produced a table of preliminary estimates of the size of the tax credit for most hybrid models under the new tax law, which will depend on the hybrid's fuel economy improvement, compared with a comparable car.

Their table is reproduced below:

$3,150. Prius

$2,600. Insight, Escape(2wd), Highlander(2wd)

$2,200. Highlander(4wd), Lexus RS400

$2,100. Civic(CVT)

$1,950. Escape(4wd), Mariner

$1,700. Civic(Manual)

$1,300. Camry, Lexus GS450, Altima

$ 650. Accord

$ 250. Chevrolet/GMC trucks

(The last three lines represent planned models that are not yet in production.)

There is an important Catch-22 in this tax credit law. For a given manufacturer of hybrid cars (not just a given model), the tax credit available will quickly phase out after that manufacturer has sold 60,000 hybrid vehicles. Please note that Toyota and Honda have already surpassed that mark, so for them (and their customers) the credit will evaporate completely by about the end of 2006. This credit is then a reward to the car companies, who were late (or not very successful) in entering the hybrid market. For them, the credits will continue until the end of 2009.

A bill has been introduced (Assembly Bill 745 and Senate Bill 252) in the Wisconsin legislature, sponsored by assemblyman Joe Parisi and senator Fred Risser, to create a $1,000. sales tax exemption on the purchase of a hybrid car that gets at least 40 mpg combined city/highway EPA milage. Let your representatives know your thoughts on this proposed legislation.

Q11: Should you buy a hybrid car, if you need a new car?
A11: This is a complex question, with many factors for the car buyer to consider. What kind/size of vehicle do you need, and is a hybrid alternative available? Do you do mostly city or mostly highway driving? What importance do you give to fuel economy, road performance, etc.? What is your best assessment of each vehicle's safety, reliability, maintenance cost, etc.? What kind of a statement will you make, or want to make, with the car you choose to drive? If you want a current Toyota or Honda hybrid model, there seems to be a very short window of opportunity for obtaining the 2006 tax credit.