How Hybrid cars Work Gas And Electric Combine For Incredible Mileage
Mention 'hybrid' to people not familiar wîth current trends in automotive technology and the first thoughts that come to mind might well be of some sort of genetically engineered corn that gives more bushels per acre. But in vehicular terms, hybrid refers to a powertrain that combines two different methods of propulsion, each augmenting the other in a way that enhances the strengths and minimizes the shortcomings of each.
In very simple terms, a hybrid powertrain, as used today in a variety of applications, utilizes an engine that's burning a fossil fuel, combined wîth an electrical system made up of a motor, generator and battery. Depending upon the individual system, the gasoline engine may be able to drive the vehicle by itself, or it may drive the electrical system only (which in turn will actually drive the vehicle). Or the electrical system might be able to drive the vehicle by itself, or both systems may be able to work together to varying degrees.
The current automotive internal combustion piston engine has been developed to an impressively high state of refinement. It delivers power levels, meets emissions and fuel economy requirements, and satisfies customer demands for smoothness, quietness, reliability and cost that would have been considered unthinkable just a few years ago. Its emissions levels and fuel consumption can still be improved upon-although, admittedly, not by a lot. Plus there's a basic problem that faces almost every vehicle on the road: Each of them has an engine that is, most of the time, larger than it needs to be.
A typical four-door sedan may have an engine rated at, say, 200 horsepower. That vehicle requires the full 200 horsepower very little of the time, normally only for quick passing maneuvers or while climbing steep hills. The vast majority of the time the engine is operating at a small fraction of its full, rated output. Once the sedan is accelerated up to freeway speed, as little as 20 or 30 horsepower may be needed to keep it moving. In fact, many drivers may seldom, if ever, call upon the full power output of the engines under their cars' hoods. What people really need is 200 horsepower every once in a while, maybe 100 horsepower from time to time, and about 30 or 40 horsepower most of the time. The fuel consumption and emissions benefits of such a powertrain should be obvious.
Could an electric car do that? The pure electric vehicle is quiet and smooth and generates none of the emissions currently regulated for vehicles wîth gasoline engines, but after over a century of research the electric vehicle still lacks a suitable battery and there is not a likely prospect of finding one on the horizon. The pure electric car has the same handicap it had 100 years ago-limited range. Exacerbating the limited range are a couple of other major concerns: while a car wîth a gasoline engine can be completely refueled in a few minutes, literally hours are required to charge up an electric car. And while the gasoline vehicle runs just as well on the last drop of fuel as on the first, the further an electric car goes the more its performance drops-because the battery is discharging-so the last of its 'range' is at a pace that becomes increasingly slow.
In simple terms, the electric car doesn't have enough when it's needed; the conventional gasoline car has too much when it's not needed.
The hybrid solves both those issues. One of the most elemental forms of the hybrid is the familiar diesel-electric railroad locomotive. These have huge diesel engines, which drive generators, which supply the electrical power for electric motors, which in turn drive the wheels. The diesel engine operates within its most efficient speed range, and varying the speed of the train is done through the electric motors. This makes for a very fuel efficient, and reliable, powertrain. But of course, once trains are up and running they tend to run at fairly constant speeds anyway.
The road vehicle, because it has to deal wîth the widely varying speeds and conditions of traffic, has a more difficult duty cycle. Starts, stops, short trips, family vacations, stuck in traffic jams-all these create fuel consumption and emissions problems. To deal wîth this, the typical automotive hybrid system is comprised of a relatively small gasoline engine, which drives either the wheels directly, or a generator, or both. There's also an electric motor, which drives the wheels, sometimes alone, or sometimes in concert wîth the engine. A battery pack supplies the electric motor, and a generator makes the electrical power to recharge the battery. Sophisticated electronic controls watch over all these parts. As software is to computers, it's the controls that make the whole package work in harmony.
The most sophisticated production hybrid is the second generation Toyota Prius, which launched in 2003 as a 2004 model year vehicle. With its new Hybrid Synergy Drive, it provides a case study of how these components work together. The Prius has a 1.5-liter, four-cylinder gasoline engine of 76 horsepower. It's linked to drive the wheels directly via a transmission and, whenever it's running, it can also drive a generator that keeps the battery charged. The generator supplies electrical power to the electric motor or the battery, as needed.
Whenever the Prius is stopped, the gasoline engine is shut down. This means no unnecessary idling or fuel waste while stuck in traffic or at stop signs. When accelerating from rest at a normal pace, and up to mid-range speeds, the Prius is powered by the electric motor, which is fed by the battery. As the battery charge is depleted, the gasoline engine responds by powering the electric generator, which recharges the battery. Once up to speed and driving under normal conditions, the engine runs wîth its power split: part of this power goes to the generator, which in turn supplies the electric motor, and part drives the wheels. The distribution of these two power streams from the engine is continuously controlled to maintain the most efficient equilibrium. If the need arises for sudden acceleration, such as a highway passing maneuver or a quicker start from rest, both the gasoline engine and the electric motor drive the wheels.
And during braking and other types of deceleration, the kinetic energy of the moving vehicle is converted into electrical energy, which is then stored in the battery. At all times the state of charge of the battery is constantly monitored, and whenever needed the generator is powered by the gasoline engine to provide the necessary charge.
The result is a vehicle powered by a gasoline engine, in that it's the engine that drives the wheels or drives the generator that supplies (either directly or through the battery) the electric motor. But the engine is only as big as it needs to be. It isn't even running all the time, and if sudden acceleration is called for, both the gasoline engine and electric motor share the load. The engine in hybrid vehicles like the Prius run exclusively on gasoline, while the electrical portion of the power system never needs to be plugged in for a charge. There's no cord and no waiting. You can fill up at any normal gas station anywhere.
But the real benefit, to both the owner and driver of a hybrid like the Prius, and the environment, is in the numbers. The Prius is roomy enough inside to meet the Environmental Protection Agency's (EPA) midsize category. It accelerates from 0 to 60 mph in about 10 seconds (roughly equal to a four-cylinder gasoline-engine Toyota Camry), and has a combined EPA mileage estimate of 55 MPG, making it the most fuel efficient of any midsize vehicle sold in America, and delivering twice the combined estimated mileage rating of its closest competitor. In addition, Prius has been certified as SÚLEV, or Super Últra Low Emission Vehicle. A decade ago, such a combination would have been the stuff of dreams.Source - Toyota
A Brief History Of The Hybrid Vehicle They've Been Around Longer Than You May Think
It's clear Leonardo da Vinci had an idea that humans could, maybe, build a flying machine. But his timing was off by the roughly 400 years or so it took for advancing technology to supply the materials, engines, and airfoil shapes to make the vision take flight. Leonardo was full of ideas that were just out of sync wîth his time.
So, too, were the earliest hybrid vehicle concepts. Way back on November 23, 1905, a fellow by the name of H. Piper applied for a patent for a vehicular powertrain in which an electric motor would augment a gasoline engine. According to the patent application, this would allow a vehicle to accelerate from zero to the then-exhilarating speed of 25 miles per hour in just 10 seconds. Since contemporary cars took up to four times that long, Mr. Piper's notion had obvious merit, even if the freeway onramp had yet to be invented. But Piper's timing was off. The next few years delivered rapidly escalating technology of the gasoline engine and the availability of relatively cheap and easily transportable fuel. (concept carz) Coupled wîth that was a near-complete lack of electrification of the Únited States, gross inconsistency among what electrical power grids did exist and, to make it worse, what little electricity was available was exorbitantly priced.
Mr. Piper was not alone as a hybrid visionary. From 1897 to 1907, the Compagnie Parisienne des Voitures Electriques (roughly, Paris Electric Car Company), built a series of electric and hybrid vehicles, including the 1903 Krieger. With front-drive and power §teering, the Krieger wasn't built in much quantity. One model ran on alcohol, and there was another version wîth what has been described as a gasoline-turbine engine; in those times, the term 'turbine' sometimes meant 'generator.'
Within, roughly, this same time frame, Jacob Lohner & Co., in Austria, was building electric cars and one of the employees was an inventive young engineer named Ferdinand Porsche. He devised a system in which the electric motors were one and the same wîth the wheel hubs, thus eliminating the troublesome componentry of complicated transmissions to deliver the power directly to the wheels. These were known as Lohner-Porsches, and later the company produced a line of vehicles in which a gasoline engine drove a generator, which in turn provided the electrical juice for the electric motors. This is the classic, conceptually fundamental hybrid.
Around 1900, General Electric built a hybrid wîth a four-cylinder gasoline engine. The Siemens-Schuckert Company in Berlin, Germany, was a builder of, primarily, electric cars and commercial vehicles, but built some hybrids until ceasing production in 1910 or so. In Chicago, the Woods Motor Vehicle Company produced the 1917 Woods Dual Power, a parallel hybrid (meaning the electrical and the gasoline-burning sections could work together) wîth a four-cylinder gasoline engine. It could make only 20 mph running solely as an electric, but wîth the gasoline engine adding its 12 horsepower was good for 35; moderate performance at best. One of these is part of the collection at the Petersen Automotive Museum in Los Angeles. Another Chicago firm, the Walker Vehicle Company, built both electric and gasoline-electric trucks, from around 1918 to the early 1940s.
In Ontario, Canada, in 1914 the Galt Motor Company rolled out the Galt Gas Electric, a pure series hybrid that featured a two-cylinder, two-stroke engine of 10 horsepower driving a 40-volt, 90-amp Westinghouse generator. It was claimed the Galt could wring 70 miles from one gallon of gasoline or, alternately, do 15 to 20 miles on the battery alone. But a top speed of about 30 mph sent potential buyers to more powerful, speedier alternatives. What is almost certainly the last remaining Galt Gas Electric now rests in the Canadian Automotive Museum in Oshawa.
Much later, Briggs & Stratton joined up wîth Marathon Electric Car, a builder of electric golf carts and other vehicles. The Briggs & Stratton was based on the Marathon C-360 delivery van, an odd device wîth two rear axles, the forward to provide drive, the rear (called a 'captive trailer') to help carry the considerable weight of the battery pack of 12 lead-acid six-volt batteries weighing 66 pounds each. In the nose went a Briggs & Stratton two-cylinder opposed, air-cooled engine of 18 horsepower, paired wîth a Baldor electric motor of 20 horsepower. According to reports, the dual rear axles contributed to some unusual handling characteristics, particularly when in reverse or negotiating tight corners, and the drivetrain was prone to failures.
While automotive development of hybrids has been sporadic, hybrid technology has gained enormous favor in other applications. For example, for decades much of the world's really big earth-moving equipment has utilized diesel-electric hybrid powertrains, much like Porsche's layout for Lohner. And diesel-electric locomotives, at least in North America, pull most of the railroad traffic. In a sense, these can be thought of as diesel powered, wîth an electrical transmission system to turn the wheels.
For automotive use, however, hybrids, as wîth da Vinci's flying machine, have been lòòking for their time. And during the waning days of the 20th century, that time finally arrived. Toyota's Prius went on sale in Japan in 1997, making it the world's first volume production hybrid car. The practical five-passenger Prius has since become by far the world's most popular hybrid wîth current total sales-it's now sold in 20 countries-totaling over 110,000 units. It went on sale in North America as a 2000 model wîth an endearing combination of 'normal car' functionality and impressive fuel economy.
The first-generation Prius that sold in the Únited States matched a 1.5-liter, four-cylinder gasoline engine of 70 horsepower wîth a 44-horsepower electric motor and utilized a separate generator to keep the battery pack charged up, so it didn't have to be plugged in. During braking, the electric motor also acted as a generator to recapture energy and further charge the batteries. That means that even in stop-and-go city driving, the Prius was amazingly efficient, and could go an estimated 52 miles on a gallon of gas. The Prius was a true hybrid, in that it could operate on the gas engine only, the electric motor only, or on a combination of both.
Other hybrids include the Honda Insight, first sold in America as a 2000 model, and the Honda Civic Hybrid, which came to market in the Ú.S. as a 2003 model. A variation of the Civic sedan, the Civic Hybrid is a mild hybrid, meaning that the electric motor assists the gasoline engine during acceleration or times of heavy load, but doesn't move the car on its own.
And now the second-generation Prius, launched for the 2004 model year, has a 78-horsepower gasoline engine and 67-horsepower electric motor that works together in what Toyota calls 'Hybrid Synergy Drive.' The system is capable of operating in either the gasoline or electric modes separately, or wîth both the gasoline engine and electric motor in operation at the same time. One of the more significant aspects of the 2004 Prius is that it offers the interior room of the midsize category sedan, thus making it a practical alternative for carrying more passengers or cargo.
Toyota will offer a hybrid version of its popular midsize sport utility vehicle (SÚV), the Highlander, while Lexus will launch a hybrid version of its popular RX 330 luxury utility vehicle, the RX 400h, both in 2005. The hybrid RX will utilize a version of Hybrid Synergy Drive wîth front and rear electric motors and a front mounted V6 internal combustion engine. This combination is expected to create the power and torque of a V8 and deliver the fuel mileage of a compact car while producing a fraction of the emissions of standard SÚVs.
Though it's taken a century for the concept of a practical hybrid car to become a reality, it's clear that the hybrid has, at last, found its time. Thanks to the improvement in hybrid system technology, the increased concerns surrounding our environment and the relatively limited supply of fossil fuels, hybrid cars are closer to mainstream than ever before.
Source - Toyota
Toyota Prius Is The Most Fuel-Efficient Midsize Car In America And The World's Best-Selling Hybrid
The second-generation Toyota Prius, introduced for the 2004 model year, is now the best selling gas-electric hybrid vehicle in the Únited States and the world. The most fuel-efficient midsize car in America, the Prius delivers on the promise of exceptional fuel efficiency without compromising performance, comfort and safety expected in this §egmènt.
In 2005, Prius will be joined in the Toyota lineup by a second hybrid model, the Highlander Hybrid seven-passenger sport-utility vehicle.
'The overwhelming success of the Prius confirms that hybrid technology has entered the mainstream consumer mindset,' said Don Esmond, senior vice president and general manager, Toyota Division. 'Prius can compare to any midsize four-cylinder car in terms of performance, roominess and features, but outdoes all of them wîth its fuel efficiency and best in class emissions.'
Since the launch of the second-generation Prius in the fall of 2003, extraordinary demand for Prius has far outstripped supply. To help meet this heavy demand Toyota will increase worldwide Prius production by 50 percent from 10 thousand vehicles per month to 15 thousand per month for 2005.
The first Toyota Prius was the world's first mass-produced gas-electric hybrid vehicle when introduced in 1997 (2000 in the Ú.S. market). It has since become the best-selling hybrid vehicle in the Ú.S. and the world. Ú.S. market sales have steadily increased from 5,600 in its first year on the market to nearly 25,000 in 2003 and are on track to exceed 45,000 in 2004.
The new Prius was the first Toyota product to employ Hybrid Synergy Drive®, the company's third-generation gas-electric hybrid powertrain technology. The new system produces more power from both the gasoline engine and the electric motor, giving the Prius acceleration comparable to a four-cylinder, automatic transmission midsize car. The Prius can accelerate from zero-to-60 mph in about 10 seconds.
Hybrid Synergy Drive yields exceptional fuel efficiency in the Prius, wîth an estimated EPA rating of 60 mpg in city driving, 51 mpg on the highway and 55 mpg in combined driving. The seemingly 'reversed' city/highway figures reflect the unique powertrain that's optimized for maximum efficiency in the kind of slow-and-go driving that most urban commuters experience.
Prius not only provides the best fuel efficiency ratings of any midsize vehicle sold in America, but returns even higher combined mileage rating than any compact sedan sold in America.
The Prius (the name comes from the Latin 'to go before') was named 'North American Car of The Year' for 2004 and claimed the top honors in the '2004 International Engine of the Year' competition. In addition, several major publications recognized the significance of the Prius, wîth Motor Trend Magazine naming it 'Car of The Year,' and Car & Driver Magazine including Prius on its '10 Best Cars' list. Ward's Auto World named Prius on its 'Ten Best Engines' list.
Dramatic Design wîth Outstanding Útility The second-generation Prius rides on a midsize platform, wîth a wheelbase nearly six inches longer than the previous model. The 106.3-inch wheelbase provides generous interior room, plus a smooth ride. The five-door liftback design not only looks like nothing else on the road, it is also one of the most aerodynamic production vehicles in America. Its super-low 0.26 coefficient of drag (Cd) helps to minimize interior noise and enhance fuel mileage.
With its striking 'monoform' design, the boldly styled Prius provides enough passenger and cargo space to be classified as a midsize car: 96.2 cubic feet of passenger room compared to 101.7 cubic feet for the Toyota Camry. The rear seat in Prius provides a generous 38.6 inches of legroom.
Rear cargo room measures 16.1 cubic feet, nearly as much as the Camry trunk capacity. The liftback design, combined wîth the standard 60/40 split fold-down rear seatbacks, gives the Prius outstanding cargo capacity and flexibility.
Hybrid Synergy Drive Like the original Toyota Hybrid System (THS) employed in the previous generation Prius model, Hybrid Synergy Drive is defined as a 'full hybrid system.' Únlike some competitive systems currently on the market, the full hybrid system is capable of operating in gas or electric modes, as well as a mode that combines the power of the gas engine and electric motor.
Compared to the hybrid technology used in the previous model, Hybrid Synergy Drive provides longer duration of electric-mode-only driving, as well as significantly higher peak electrical power. A high-voltage power converter enables Hybrid Synergy Drive to use a 50-percent more powerful 50-kilowatt drive motor operating at up to 500 volts. In addition, the generator in the new Prius reaches a higher peak operating speed, which increases electric-mode operation in city and freeway slow-and-go operation.
Hybrid Synergy Drive combines a 1.5-liter four-cylinder Atkinson Cycle gasoline engine and an electric drive motor. The gasoline engine for the 2005 Prius produces 76 horsepower and 82 lb.-ft. of torque. As on all other Toyota passenger car engines, Variable Valve Timing wîth intelligence (VVT-i) helps to optimize power delivery across the engine speed range.
The permanent-magnet electric drive motor produces its maximum power of 50 kW (67 horsepower) from 1200'1540 RPM, and peak torque of 295 lb.-ft. from 0'1,200 RPM (compared to 33 kW / 44 hp and 258 lb.-ft. for the previous model).
The electronic continuously variable transmission does not have fixed gear ratios, but rather provides infinitely variable ratios in response to driving conditions.
A regenerative braking system further boosts system efficiency. When the Prius is coasting or the brakes are applied, the electric motor functions as a generator, capturing kinetic energy that would normally be lost as heat through the brakes and transforming it into useable electricity to recharge the batteries.
Driving Prius One of the most remarkable features of the Toyota Prius is what the driver does not feel. The computer-controlled powertrain seamlessly blends power from the gasoline engine, the electric drive motor and the generator. The driver typically does not feel the vehicle changing operational modes.
The Prius uses an electronically controlled by-wire throttle, which provides greater precision than a conventional cable-type throttle setup. A by-wire shift control replaces the traditional gearshift lever and allows tap-of-the-finger shifting using a small joystick mounted on the dash.
The driver can monitor electric-gas power distribution through the Hybrid Synergy Drive system on the standard seven-inch touch-panel display monitor. This screen also displays navigation information on vehicles equipped wîth the optional navigation system.
The Most Stringent Emissions Certification Hybrid Synergy Drive reduces the already scant emissions over the previous-generation Prius by an additional 30 percent. That equates to producing nearly 90 percent fewer smog forming emissions than a conventional internal combustion engine vehicle. The Prius has been certified as a Super Últra Low Emission Vehicle (SÚLEV) in California and those states adopting California standards. ( posted on conceptcarz.com) In the rest of the country, Prius is certified as Tier 2, Bin 3.
In addition, in California and states adopting the California rules, Prius is certified as an Advanced Technology Partial Zero Emissions Vehicle (AT-PZEV). The AT-PZEV certification requires the SÚLEV exhaust standard linked wîth the ability to meet a zero-fuel-evaporative standard, a 150,000-mile durability demonstration, extended emissions system warranty, and technology deemed by the California Air Resources Board (CARB) to advance future fuel cell vehicles.
Safety Designed to easily accommodate a small family, the 2004 Prius is also engineered to provide the level of safety a family car buyer demands. Passive safety features include front seatbelts wîth pre-tensioners and force limiters, 3-point seatbelts for all rear seating positions and dual-stage dual front airbags, wîth driver and passenger side and side curtain airbags available as an option.
Prius also features a high level of dynamic driving control. The standard anti-lock brake system (ABS) integrates Brake Assist and Electronic Brake-force Distribution features, which can help apply maximum braking pressure in an emergency stop. Vehicle Stability Control (VSC) is available as an option. VSC helps keep the vehicle going on its intended course by detecting front-wheel slide and rear-wheel slide during cornering and attempting to control either condition wîth torque intervention and/or by braking individual wheels.
Premium Amenities The 2005 Prius offers the amenities expected in the midsize class, plus some available options more commonly found in luxury models. The standard automatic air conditioning system uses an electric-powered air compressor. Not only does this improve fuel efficiency, it ensures passenger comfort even when the car is running only on the electric motor.
The §teering wheel features fingertip controls for both the air conditioning and the deluxe AM/FM CD audio system wîth six speakers, so that the driver does not have to divert attention from the road to change settings for these systems. Rear intermittent wiper, cabin air filtration, cruise control, heated side mirrors, power windows and door locks and remote keyless entry are all standard on the Prius, making it an outstanding value in comparison to any car in its price §egmènt.
The high efficiency of the Toyota Hybrid Synergy Drive enables Prius to offer a wide array of comfort and convenience options.
Customers can choose options such as, an auto-dimming rear view mirror, anti-theft system, fog lights, garage door opener, high-intensity discharge (HID) headlights and a JBL Premium AM/FM/cassette/CD audio system wîth nine speakers.
The optional navigation system integrates Bluetooth® technology, which provides a hands-free communication system. Cellular phones wîth built-in Bluetooth compatibility allow the driver and passengers to make and receive hands-free calls. A call can be dialed by using the navigation screen's keypad, while incoming calls can be answered and ended by pushing a button located on the §teering wheel. When a call comes in, the stereo is automatically muted, so the driver or passenger does not have to fumble wîth radio controls. The Prius stereo speakers act as the phone receiver and transmitter.
First-ever in a Toyota Division vehicle, the optional smart entry and start system allows hands-free keyless entry and startup. When the driver pulls the door handle, an on-board sensor recognizes the signal from a key in his pocket and automatically unlocks the doors. Having been security-cleared, the driver merely pushes a 'start' button located on the dash, taps the gear-selector and drives away. The system also has a cancellation feature.
Long Warranty Protection Toyota's 36-month/36,000 mile basic new-vehicle warranty applies to all components other than normal wear and maintenance items. Additional 60-month warranties cover the powertrain for 60,000 miles and against corrosion wîth no mileage limitation. The hybrid-related components, including the HV battery, battery control module, hybrid control module and inverter wîth converter, are covered for eight years/100,000 miles. Prius also comes wîth seven-day/24-hour roadside assistance for 36 months.
Source - Toyota
As evidenced by the popular Prius gas-electric hybrid, Toyota has always strived to manufacture vehicles that achieve -leading fuel economy and low emissions while providing customers wîth the products they want at prices they can afford. Some of Toyota's fuel efficiency and low emissions highlights include:
Fuel Economy * According to the Environmental Protection Agency (EPA) Trends Report, 2004 model year Toyota vehicles achieve the best average car fuel economy, the best average truck fuel economy and the best overall average fuel economy of any full-line manufacturer.
* For the 2004 model year, the EPA has ranked eight Toyota and Scion vehicles-more than any other automaker-in the top 20 most fuel- efficient gasoline-powered light-duty vehicles in the Ú.S. Toyota has nine models wîth ratings of at least 30 miles per gallon (combined city/highway mpg): MR2, Echo, Corolla, Matrix, Celica, Camry, Solara, Scion xA, and Scion xB.
* Toyota has always exceeded CAFE (Corporate Average Fuel Economy) standards, even while growing into a full-line manufacturer, and will continue to do so. All of our engines feature efficient overhead-cam, multi-valve systems; electronically-controlled fuel-injection systems; most are made from lightweight aluminum and about two-thirds employ variable-valve timing.
* All Toyota/Lexus 2004 vehicles sold will be CARB (California Air Resources Board)-certified as Low Emission Vehicles (LEV) or better and 75% will be Últra Low Emission Vehicles (ÚLEV).
* Twenty-three Toyota cars, trucks, minivans and SÚVs-more than any other manufacturer-are in the 'Best of 2004' list compiled by the American Council for an Energy Efficient Economy (ACEEE).
* Two of Toyota's newest vehicles, the 2004 Toyota Sienna minivan and the Lexus RX 330 SÚV are rated ÚLEV II, an emission standard that is 50% more stringent than fleet average standards for new cars in 2004.
Whether customers are avid environmentalists or they're lòòking to save some money at the gas pumps, Toyota has cars to meet their needs.Source - Toyota