Realistic Evolution: Analysis of the Technological Innovation of the Three-Generation Prius Hybrid

Since 1997, Toyota Prius has become the most competitive hybrid model on the market, and the new generation of Toyota Prius is ready to meet the challenge of a new stage - returning to the Chinese market. As a mass-produced hybrid model sold in more than 70 countries in the world, the cumulative sales of more than 2 million units also prove its market recognition. Although the previous generation of Prius was also sold in small batches in China, the sales volume is indeed not worth mentioning. Now the Chinese market's desire for energy-saving, efficient and technologically mature hybrid models has driven the third-generation Prius, which is more suitable for China's national conditions, to return to China. So for such a model that is both familiar and unfamiliar to us consumers, what technical innovations does the new generation of Prius have? We will take a long-term view.

As an island country that needs to import 100% of its petroleum energy, Japan's developed automobile industry is always out of proportion to the shortage of energy supply. As a transitional product between traditional energy and new energy, hybrid models can maximize the input-output ratio, so they are also one of the most respected forms by Japanese car companies. Toyota, Japan's largest automobile company, launched its first hybrid product in 1997 - the first generation Prius codenamed XW10. Since the first generation Prius was in the stage of technical commercialization verification, it was only supplied to the Japanese domestic market at first. At that time, the model was equipped with a 1.5L 1NZ-FXE four-cylinder engine with an ultra-high compression ratio of 13.5:1, but the maximum power was only 58 horsepower and the peak torque was 102 Nm; the traditional power was matched with a 288V nickel-metal hydride battery, and the battery capacity was only 600W/kg at the primary level. The electric motor has a power of 40 horsepower and a torque of 305 Nm, and uses a planetary gear set mechanism as a transmission.

First generation Prius (XW10)

First generation Prius (XW10)

In 2000, after the verification was basically completed, the first generation Prius underwent a minor technical upgrade and was fully launched in the international market dominated by Europe and the United States. In order to adapt to the characteristics of the United States with a large area, sparse population and high speed, the power was focused on. The same model of engine added VVT-i variable valve timing, and the compression ratio was appropriately reduced to 13.0:1, so that its maximum power increased to 70 horsepower and torque increased to 110 Nm; the hybrid part was also adjusted, the battery voltage was reduced to 273.6V, but the specific capacity increased to 900W/kg, and the electric motor power reached 44 horsepower and the torque increased to 350 Nm. With a fuel consumption level of 5.7L/100km, it has obtained the North American ultra-low fuel consumption model rating.

Although the birth of Prius did not immediately bring a new competitive landscape to the world automobile market, it was enough to show the world the mass-produced, mature and reliable civilian hybrid technology. Therefore, the first generation of Prius also won the 1997-98 Japan Car of the Year award in the year of its birth. I think if Prius could be launched into the international market at the same time, it might have won the honor earlier.

If the first generation of Prius is a pioneering work, then the second generation of Prius can be said to be a work that completely occupied the market and established its position, and it is also a work of technological innovation.

Second generation Prius (XW20)

The second generation Prius, codenamed XW20, was launched in 2003. The Japanese, having tasted success, realized the core position of the US market, so the second generation Prius was first launched in the US and Japanese markets. This generation of Prius was also the beginning of the domestic Prius. Although the high price was subsidized by the government, it was still out of reach for ordinary consumers, so it was a bit untimely.

Second generation Prius (XW20)

The second generation Prius has achieved a technical upgrade of the hybrid system. The gasoline engine is still the 1.5L 1NZ-FXE VVT-i engine on the first generation Prius, and the power continues to increase slightly to 76 horsepower, and the torque rises to 115 Nm. The maximum power of the hybrid part is 67 horsepower and the peak torque is 400 Nm. Although it does not use the expensive lithium-ion battery at the time, it is still a nickel-hydrogen battery, but through the miniaturization and lightweight of the battery, the system energy consumption is successfully reduced, and a better energy-saving effect is achieved, and the comprehensive fuel consumption is reduced to 5.2L/100km.

This achievement is due to its ultra-low drag coefficient of 0.26 and the fact that electrical devices such as electronic power steering have replaced traditional mechanical power take-off devices to reduce engine power consumption. As a result, the second-generation Prius has won more than a dozen annual car awards around the world due to its wider sales.

The code name of the third-generation Prius is probably what you can guess, that’s right, XW30. The very successful low drag coefficient design of the previous model gave the third-generation Prius more opportunities to learn from it, so the unprecedented 0.25 drag coefficient was born. At the same time, the successful foundation of the first two generations of products also gave the third-generation Prius a strong market demand. Therefore, in the two years from 2009 to 2011, the sales of the third-generation Prius exceeded 1 million, becoming the best-selling hybrid model in one fell swoop.

Akihiko Otsuka, the chief engineer responsible for the development of the Prius, said that the THS (Toyota Hybrid System) installed in the third-generation Prius has been working on several aspects in pursuit of energy efficiency. The first is the efficiency of energy management.

Since the hybrid system is an integration of multiple systems such as traditional internal combustion engines, electric motors and battery modules, energy management will be one of the main factors affecting efficiency. The progress of energy management in the third-generation Prius is mainly due to the accumulation of experience, the development of a more effective management mechanism, and the improvement of management efficiency through more complex calculations based on the improvement of computer computing performance.

As for the power system itself, the most important difference between the third-generation Prius and the previous generation is the replacement of the 1.8L gasoline engine. In terms of the operating principle of the hybrid system, the electric motor and the gasoline engine each have their own responsibilities and play different roles in different driving stages. Generally speaking, the electric motor is mainly responsible for the starting or low-speed stage, because this stage is usually the stage where the gasoline engine has the worst energy efficiency and the most serious pollution emissions. But at the high-speed driving stage, the gasoline engine is the main engine because of its high operating efficiency and low pollution emissions.

The most important difference between the third-generation Prius and the previous generation is that it is equipped with a 1.8L gasoline engine.

The THS system used in the first two generations of Prius only uses a 1.5L gasoline engine. When cruising at high speed, the low-displacement engine needs to run at a higher speed, which makes high-speed driving a weakness of the first two generations of Prius. In response to this, the 1.8L Atkinson cycle engine equipped in the third-generation Prius has increased its maximum power from 76 horsepower in the previous generation to 99 horsepower in the third-generation model by increasing the displacement. With the increase in displacement, horsepower and torque, the most direct benefit is that the power performance is greatly improved in high-speed cruising sections where gasoline engine power is mainly responsible. With the CVT transmission system, the engine speed of the third-generation Prius drops by 10% when cruising at high speed, which also brings more economical fuel usage performance.

In addition to the direct increase in horsepower brought about by the increase in displacement, engineers have also made modifications to many engine details to continue to improve engine efficiency. This includes Toyota's first use of an electric water pump design, which is directly powered by a battery and abandons the belt drive design, reducing the loss of engine output power and allowing for more precise control of the amount of cooling water. In terms of valve structure, the roller rocker arm design can also reduce internal friction and further improve fuel efficiency. In addition, systems such as EGR exhaust gas recirculation and exhaust gas heat recirculation are all efforts to improve the efficiency of internal combustion engines. The third-generation Prius integrates the reduction gear into the electric motor, which increases torque output while reducing volume and weight, and increases the power output of the electric motor to 80 horsepower.

The third generation Prius integrates the reduction gear into the electric motor

The third-generation Prius has more battery options, thanks to a richer vehicle design. The regular version of the Prius is still equipped with an improved nickel-metal hydride battery pack with a voltage of 650V and a capacity increased to 1.4kWh. The plug-in version of the Prius is suitable for frequent high-voltage charging and discharging, so it is equipped with a lithium-ion battery pack with an available capacity of 4.4kWh.

Prius plug-in hybrid

In terms of power control system, the output voltage of the converter of the new generation Prius has been increased from 500 volts in the previous generation to 650 volts in the new generation. The manufacturer has also improved the nickel-metal hydride battery module to increase power output while reducing the volume. At the same time, the surrounding cooling system and components have been properly arranged to provide a wider passenger and storage space in the cabin.

Battery pack is further lightweight

The third-generation Prius's THS hybrid system has achieved a new level of overall power efficiency by increasing the displacement of the gasoline engine and technological advances in the electric transmission system. The maximum power output has increased to 136 horsepower, which is basically equivalent to the level of an ordinary 2.0L naturally aspirated engine, but the fuel consumption is only at the level of a 1.0L engine, with a comprehensive fuel consumption as low as 4.7L/100km.

The third generation Prius also spawned Prius V/C and other products

Overall, Prius is a story of evolution in interpretation. It not only shows the measures people take in the face of the oil crisis, but also demonstrates the substantial efforts they make for a better tomorrow for the earth.