Hybrids And Electric Vehicles
Hybrid Electric Vehicles (HEVs), Plug-in Hybrid Electric Vehicles (PHEVs) and all Electric Vehicles (EVs) have made significant progress in the past decade. These vehicles contain many systems including the drive train system, safety system, air conditioning system, heating system, navigation and other systems of a modern car. In this section we will discuss only the electrical drive system of the cars. For more detailed information on all aspects of hybrid cars visit www.hybridcenter.org. All hybrids and electric cars have some form of regenerative braking. So lets take a look at what regenerative braking is.
Regenerative braking, or "regen", for short is a process of recapturing some of the energy of a moving car while braking. When you brake, the moving (kinetic) energy has to go somewhere because of the conservation of energy law of physics. Regen recaptures some of the energy instead of wasting it as heat as is normally the case with mechanical friction brakes. In hybrid cars this energy is used to recharge the main battery and in some designs negates the need to charge the battery every night. The energy is thus recaptured by the battery and later reused (or regenerated) to again power the car forward. The moving energy of a car in motion is proportional to the square of its speed. If you double the speed of a moving car the kinetic energy is quadrupled. When you just take your foot off the accelerator, some of the energy is lost due to air friction and some due to tire/road friction and the car begins to slow down.
Hybrids are normally front wheel drive cars powered by both the electric motor/generator and the internal combustion engine (ICE) depending on the speed situation. In a hybrid when you depress the brake pedal, the computer control electronics immediately reverses the direction of the electric motor and converts it into an electrical generator reversing the flow of energy from the front wheels back to the battery. This reverse action slows down the vehicle and stores most of the energy. Normally about 80% of the energy from a battery makes it to the front wheels, 20% is lost along the way. The same is true in reverse, about 80% of the energy is returned to the battery. The round trip efficiency is 80% times 80%, i.e. 64% of the original energy is returned to the battery. As the brake pedal is further depressed the control computer kicks in the friction brakes to both the front and the rear tires. This is a safety feature so the car can be stopped quickly in an emergency.
When an electric motor/gnerator is supplied with electricity it generates mechanical power; when it’s supplied with mechanical power in reverse, it generates electricity. But how does generating electricity slow the vehicle? Magnetic friction. The armature of the motor/generator is slowed by the force of inducing current in the windings as it passes over the opposing poles of the magnets of the motor's stator. It is this magnetic friction that zaps the vehicle’s kinetic energy and reduces its speed.
Regen can bring the car to a complete stop. But as a practical matter, the kinetic energy of a slowly moving car is so low that very little energy is returned to the battery. In fact, the last little bit of slowing the vehicle does not cover the losses in the motor and control circuitry. So friction brakes are utilized exclusively by the control computer as the car approaches zero. Another case of by-passing regenerative braking is when the battery is fully charged. Because additional charge from regenerative braking would cause the voltage of a full battery to rise above the safety level, the control computer inhibits regeneration. Top
Mild Hybrid Electric Vehicles
Hybrids are classified as either "mild" or "full". A mild hybrid can not run on battery power alone, they need an internal combustion engine (ICE) full time. Whereas a full hybrid can run on a battery full time until the battery is exhausted. The Honda Civic to the left (number two world wide in sales) is an example of a mild hybrid.
A mild hybrid has three innovations that separate it from a regular ICE vehicle. They are: 1) idle-off capability 2) regenerative braking and 3) power assist. Idle-off allows a vehicle to turn off its gasoline engine when stopped, saving fuel. The gasoline engine will turn back on and be ready to go in less time than it takes for you to move your foot from the brake to the gas pedal. Regenerative braking is explained above.
The basic definition of a hybrid vehicle is a car that uses two methods of providing power to the wheels. A vehicle meets this criteria only if it has a large enough battery pack such that the electric motor can actually supplement the engine to help accelerate the vehicle while driving.
Power assist ability reduces the demands on the gasoline engine, allowing for the use of a smaller, more efficient gasoline engine while maintaining the same performance as a vehicle with a larger engine. The Honda Civic includes all three of these features and gets about 42 miles per gallon. Customers like these features which is reflected in the Civic's number two hybrid world ranking. For more information on hybrid details visit How Hybrids Work. Top
Full Hybrid Electric Vehicles
The Toyota Prius (shown at the left), which first came out in Japan in 1997, is considered a full hybrid vehicle as it can run from a battery only, which it does when starting up. The car can go about one mile at a slow speed without using the gasoline engine. The Prius incorporates all three innovations described above in the "mild" hybrid. The battery never has to be charged from a plug and the car has a range of about 500 miles. The Prius battery has an eight-year/100,000 mile warranty.
Contrary to what one might think, electric motors are more powerful during start up than gasoline engines. However, gasoline engines are more efficient during freeway driving at 60 miles per hour or more. Hence the optimum hybrid performance is obtained as follows: from 0 to about 20 mph the electric engine only is used assuming a steady speed increase (not flooring it); from 20 mph to 60, both the electric and gasoline engines are used; over 60 mph only the gasoline engine is used. The control computer evaluates items like the depression amount on the accelerator, the current speed, internal losses, etc. and then elects to use either the electric motor, the gasoline motor or both. The computer controls in a hybrid are very, very sophisticated.
In addition to the gasoline saved at low speeds when the engine is off, a smaller overall engine is used as a large one is not needed for initial acceleration. The engine in a typical Prius is four cylinders with only 1.6 liters in displacement and is about 75 horsepower. Together with the electric engine the total horsepower is only about 135. The real secret to the 50 miles per gallon efficiency achieved by the car is its small engine, which weighs less and consumes less gasoline.
In most cars large engines are necessary only for quick acceleration from a stop. Driving on a freeway at 60 mph requires only about 20 horse power to overcome internal losses and the air and tire friction. Large engines are only needed to "floor it". While driving a full hybrid may not win any "drag races," the acceleration is very acceptable and resembles any normal gasoline car.
Another very interesting part of a Prius is the "Power Split Device" which is the drive train technology that allows the Prius to use either the electric motor, the gasoline motor, or both. This device is a major drive train innovation. For a detailed description see The Power Split Device.
The chart to the left shows the top selling hybrids in the US during 2013. The total Prius family had a 50% market share of all hybrids sold in the US. The Prius family is the number one selling hybrid in the world. The total number of Prius cars that have been sold woldwide is over 3 million units as of December, 2013 and the total number of Toyota hybrids of all kinds is over 6 million. Top
Plug-In Hybrid Electric Vehicles (PHEVs)
Prius PHEV - Toyota introduced a fourth generation plug-in version of the Prius in 2012. The battery pack can be charged with either a standard 110v outlet or a 220v outlet. Using a 110v outlet, it takes 3 hours to charge the battery from scratch. Using a 220v outlet it takes 1.5 hours. The battery is lithium-ion instead of the nickel-metal hydrate battery used in other Prius models. Lithium-ion batteries are lighter weight and more compact. Even so, the battery pack is larger than the standard Prius models and 300 pounds heavier. The payoff is that the range for an all electric trip will be about 14 miles.
The average gas mileage will jump to over 100 miles per gallon if there are no long trips included. The gasoline engine does not kick in until about 60 miles per hour (mph) unless the pedal is floored. That does not seem necessary as the acceleration is quite good. The car is very quiet up to about 40 mph where the wind noise begins to be heard.
The Prius PHEV costs $32,760 in the US. As of December 2013, Toyota has sold 48,600 units worldwide and about 24,800 in the US. With a plug-in vehicle like the Prius PHEV, it is estimated that 25% of the miles driven in the US could be powered by electricity say the researchers at Argonne National Laboratory.
Chevy Volt - The Chevy Volt (introduced in 2011) with a full charge operates completly as an electric car for the first 25 to 50 miles (depending on driving conditions). It burns no gasoline during those miles, drawing current from a 400 pound lithium ion battery pack. Current from the battery pack powers a 150 hp electric motor that drives the Volt’s front wheels. The Volt also has a 1.4 liter gasoline engine. However, the gasoline engine doesn’t drive the wheels, it drives a generator that keeps the battery charged long enough to give the car a total range of 300 miles. The gasoline engine does not kick in until the battery is run down. This configuration is called a “series” hybrid. It is very different from a “parallel” hybrid (like the Prius) in which the car’s electronic control unit constantly switches back and forth between the gasoline engine and a battery pack.
The Volt has impressive specs - the electric equivalent of 150 horsepower, zero-to-60 in about 9 seconds, and a top speed of 100 mph. When GM says the Volt is a “real car”, they are not only referring to the Volt’s range of 300 miles or its acceleration, but the same philosophy is evident in its outward appearance that is decisively un-hybrid and un-EV in looks and feel. The silent whooshy feeling is fully supported by a solid but not too tight steering and handling system.
The Volt retails for about $41,000 before a $7,500 federal tax credit in the US. GM has sold approximately 46,500 Volts to US retail customers and about 70,000 units wordwide as of December, 2013. The Volt is viewed as a rich man's car as the average income of a Volt buyer is a whopping $175,000 a year. The people buying Volts are early adopters who are comfortable taking risks. Top
All Electric Vehicle - Nissan Leaf
Nissan Leaf - Nissan is calling the Leaf, shown at the left, the "world's first affordable, zero-emission car." And with a post US Government incentive price of $21,400 plus state incentives that could reduce it even further ($2,500 in California), Nissan has set an aggressive price for the competition to meet. In December 2010, the Nissan LEAF became available in five early US rollout markets of California, Washington, Oregon, Arizona and Tennessee. By mid 2012 the LEAF was available for purchase in all 50 states.
The Nissan LEAF is powered by compact lithium-ion batteries that drive its electric motor to deliver 107 horsepower. This enables the LEAF to drive at speeds of up to 90 mph and deliver a 0 to 60 time of about 8 seconds.
As opposed to a combustion engine (which doesn't reach its maximum horsepower and torque until it achieves a high rpm) the LEAF's motor has 100% of its torque available from a standing start. As a result, the LEAF has much better low speed performance than even some high performance gas powered cars and can hold its own from 0 to 60 mph. The LEAF has no transmission and does not need to shift gears as it accelerates, resulting in a very smooth ride. The heaviest object of the car is the battery pack, shown at the left, which is in the center of gravity to make the car one of the most stable vehicles on the road. Since most people drive less than 40 miles a day and their vehicles spend a whopping 80% of the time parked in their garages, the vast majority of charging will be done in their garage during the evening (picture at left below).
While charging on a Level 2 station at home, a LEAF can add approximately 14 additional miles of range per hour. Charging from empty to 100% full at home is estimated to take approximately eight hours using a Level 2 station. The LEAF's battery can also be charged at locations that install industrial level DC Fast Chargers - which can add about 80 miles of range to an electric car in under 30 minutes (80% of a LEAF's battery capacity). To take advantage of the DC Fast Charging stations, a $700 option has to be added at the time of purchase.
The LEAF's total traveling mileage can vary from a high of 140 miles to a low of 45 miles depending on local conditions and driving habits. Nissan says the LEAF will nominally travel 84 miles - meaning things such as temperature, terrain, extra weight, high speeds and aggressive driving could reduce the actual travel range dramatically.
The Leaf has a base price of $28,900 before the federal tax credit of $7,500 which yields a net price of $21,400. In addition, a charger needs to be installed in the garage which will cost about $1,300 including installation. By the end of December, 2013, worldwide sales of the Leaf were approximately 100,000 cars. This section excerpted from www.plugincars.com Nissan LEAF. Top
Electric Vehicle Charging Stations
One of the biggest challenges facing wide acceptance of electric vehicles (EVs) is not their cost or range, but the availability of charging stations. Electric cars take hours to charge, so stations are needed where cars are parked, i.e. in their garages, etc. In the U.S. there are 250 million cars, but only 50 million garages. Most driving is local over short distances which reduces the need for charging mid-trip. In the US, 78% of commutes are less than 40 miles round-trip.
Leading edge providers are putting parking meter like chargers in parking garages and at employee workplaces. 240 Volt AC charging is known as Level 2 charging. 500 Volt DC high current charging is known as DC Fast Charge. Owners normally install a Level 2 charging station at home. Businesses and local governments provide Level 2 and/or DC Fast Charge public stations that supply electricity for a fee. A relatively inexpensive Level 2 charging station providing 3.3 kilowatts of power (240 volts at 14amps) will take about 8 hours to fully recharge an electric vehicle. However, most users will charge every day at home, so they will very rarely need to fully recharge their battery. Level 2 charging is more than enough for charging at home, but not for "refueling" in the middle of a trip.
NRG, a Fortune 500 Company, is one of the country’s largest power generation and retail electricity businesses. NRG power plants provide about 47,000 megawatts of generation capacity. Also NRG retail and thermal subsidiaries serve more than 2 million customers in 16 states. NRG eVgo (pronounced ee-vee-go) created the nation’s first privately funded, comprehensive electric vehicle ecosystem.
In November, 2010, NRG's EV Services started offering a range of integrated products and services that enable both home and public charging of EVs in the Houston area, the start of a rollout across the rest of Texas. Under the brand name eVgo Freedom Stations, NRG provides EV owners throughout the greater Houston and Dallas Fort Worth areas with convenient and affordable fueling packages.
NRG was the first company to equip an entire major market with the privately funded infrastructure needed for successful EV adoption and integration. As part of the NRG endeavor, drugstore chain Walgreens linked up with NRG to install NRG charging stations at 18 Walgreens locations in Houston. See the photo at the left. NRG also installed a similar system in the Dallas/Fort Worth area. At the end of 2012, NRG had 32 fast charging stations in Texas. NRG is also planning to install 200 fast charging systems in California.
For $49 a month, a customer gets a home charging station. For $79 a month, the customer also gets access to NRG's network of public stations. For $89 a month, the customer gets all the electricity he can use in his vehicle, at home and on the road. The idea of having a charging station at home that you don’t have to pay for upfront, in addition to ready access to chargers when you're out and about sounds very appealing; because even the most expensive package is about half the estimated gas bill the average American driver pays per month.Top