Experts reveal: Toyota Prius gasoline/electric hybrid

Given the Toyota Prius gasoline/electric hybrid's sports car looks, aviation-like dashboard display and smooth, noiseless start, it's no surprise that the Toyota Prius is the fastest-selling vehicle in its class. (Figure 1) However, in addition, the car has one identifiable important feature: fuel economy. The U.S. Environmental Protection Agency (EPS) gives fuel ratings of 61 miles per gallon (mpg) on ​​the street and 50 mpg on the highway (ideal testing conditions). Realistically, drivers can expect 45 to 50 mpg combined street/highway performance. Hybrids feature a gasoline engine that starts the vehicle and then converts it to battery power for acceleration. However, the Prius takes a different approach, running on battery power and then switching to a gasoline engine when the speed exceeds 20mph. Although the Prius is a big breakthrough, drivers don't have to press the accelerator from full braking to maximize fuel economy. With gas prices among the highest the U.S. and the rest of the world have ever faced, the Prius' gas mileage is a welcome sign in a market that otherwise doesn't have the luxury to consume gasoline.

The Prius design is based on hybrid system technology that Toyota calls Hybrid Synergy. The concept goal is to synergize electric motor power and gasoline engine power and make it possible to maximize vehicle power and environmental performance. Recent models of the Prius are based on Toyota's Total Hybrid System II (THS-II) technology. Each successive generation of the THS-II system has improved fuel efficiency and reduced heat dissipation, including a coaxial 4-cylinder 1.5-liter engine, a high-voltage nickel metal hydride battery (NiMH), and an intelligent hybrid drive with a planetary gear system. bridge and a complex engine control component (Figure 2).

A MIXTURE OF TWO APPROACHES Basically, two forms of automotive powertrains exist: series and parallel. Each has its own set of positive and negative characteristics. Unlike other hybrid gasoline-electric vehicles, the Prius combines the two, maximizing each's strengths and complementing their weaknesses. In a series hybrid system, the gasoline engine starts the generator, and the current generated causes the electric motor to drive the wheels (Figure 3). When the car is running, the low-output engine used here keeps the car running at a stable speed within the most economical range and allows it to effectively recharge the battery.

In a parallel hybrid system, both the gasoline engine and the electric motor directly drive the wheels. In addition to supplementing the original power of the engine, the electric motor can also be used as a generator to recharge the battery while the car is running. The Prius uses two permanent magnet 500-V AC motor generators: MG1 and MG2. Both motors are driven by a transformer bank that converts the DC voltage from the battery into AC high voltage. A hybrid transaxle and planetary gear system connect the two engines and two generators. (Figure 4)

Since the MG1 and MG2 produce an output of 67hp from 1040rpm to 5600rpm, the MG1 and MG2 have enough torque to launch the car without the help of a gasoline engine. The maximum speed of the Prius engine is only 5000rpm, providing an output of 75hp. First, the high-voltage battery supplies power to MG2 to drive the wheels. When the engine wheel is driven by the engine through the planetary gear, MG1 is rotated by the engine and supplies generated current to MG2. Then, the engine rotates MG1 through the planetary gear to charge the high-voltage battery. When the car decelerates, the kinetic energy of the wheels is recovered and converted into electrical energy, which can be used to charge the high-voltage battery through MG2 (Figure 5). This is known as "regenerative braking".

The core of the Prius is the power take-off device, the planetary gearbox, which links the electric engine, generator and electric motor together (Figure 6). For example, in a parallel hybrid system, this allows the car to operate with the electric motor providing power independently, the gasoline engine providing power independently, or both at the same time.

This split power plant allows the vehicle to operate as a series hybrid system. The gasoline engine can thus operate independently of the vehicle's speed to charge the high-voltage battery or power the wheels if necessary. The equipment also assumes the function of continuously variable speed transmission, eliminating the need for manual transmission or automatic transmission. Because the split power device starts the gasoline engine through the generator, the car does not require a starter.

The electronic motor is connected to the ring gear of the gear set and also to the differential that drives the wheels. Therefore, the rotation rate of the electronic motor and the ring gear determine the speed of the car. The generator is connected to the sun gear of the gear train, and the engine is connected to the planet carrier. The speed of the ring gear is determined by three components that must work simultaneously to control the output speed. All 32-bit microprocessor units are used in the engine control module (ECM), high voltage electrical control unit (ECU), battery ECU and brake control ECU. This indicates an upgrade from an earlier 16-bit design. Interactive communication occurs via the controller area network bus. Advanced battery design NiMH battery consists of 168 1.2V DC cells, interconnected with 28 battery modules to produce a nominal DC voltage of 201.6V, and is placed in an impact-resistant container and placed behind the car. Now, the continuous improvement of batteries has reached the third generation. (The batteries used in Toyota's Lexus RH400h and Highlander sport utility vehicles are fourth-generation designs.) Under the hood, there's the engine, transmission group and hybrid transaxle. (Figure 7)

Toyota said it has been asked about battery life and replacement prices. To be clear, the battery pack and all hybrid components are considered part of the “lifetime of the vehicle.” No matter which part, they guarantee it for 8 years or 100,000 miles. In the United States, the warranty period is longer (10 years and 150,000 miles) according to California-type emission standards. (California, Connecticut, Massachusetts, Maine, New Jersey, New York, Rhode Island, Vermont, Washington, and soon to join Oregon all adopt this standard). Moreover, since the Prius was launched in the United States five years ago, there have been no instances of battery failure requiring replacement. A Toyota spokesperson declared, "Our batteries have been tested for 180,000 miles without failure. In the first-generation Prius used as a taxi in northwest Atlantic City, the original battery has exceeded 200,000 miles." Still, if it's under warranty, If the battery fails outside the period, you still need to consider replacing it. Without a history of battery failure, there is no stated cost of battery replacement, and energy storage experts estimate the price at $3,000 to $4,000. According to expert opinion, "The key issue in battery life is good energy consumption monitoring. Proper use of the battery increases battery life (such as not completely charging and discharging, keeping it running at a reasonable temperature, etc.)." He uses the Prius with high voltage Battery co-design is seen as a milestone, but it is certainly not the final and most economical solution for energy storage. He foresees even newer technologies within sight that will make cars run more efficiently and greener. Ultracapacitors are one such technology. They are not batteries. Rather, they are ion energy storage devices that last eight to 10 years longer than batteries. Moreover, they only take up about 20% of the energy reserve capacity. But he believes the Prius design sparked a revolution in autonomous energy storage and low-pollution technology. Of course, the gasoline-electric hybrid vehicle movement is just getting started and will indeed expand considerably. By 2008, other car manufacturers are expected to enter this market. Recently, Toyota issued a voluntary recall of 75,000 Prius units sold in the United States (160,000 worldwide) due to a potential software glitch that could cause the car's engine to stall or shut down. According to Toyota, no accidents or injuries occurred. He also said that the problem was minor and the company had successfully resolved it.