Who is more advanced, plug-in hybrid or range extender?
From a technical point of view, whoever is more efficient is more advanced.
Although there are debates in the market from time to time, the industry has long been conclusive: plug-in mixing efficiency is higher than range extension.
This conclusion applies at this stage. With the evolution of technology, it is very likely that the plug-in hybrid pole will subtract the direct drive, and eventually return to the range extension - however, it needs to be understood that the range extension is not this range extension, and the range extension technology used by brands such as Ideal and Wenjie that we see now is still one level lower than that of plug-in hybrid.
There is an extra "direct drive" in the plug-in mix
Now the concept of plug-in mixing is a bit confusing, in fact, the range extender is also a kind of plug-in mixing.
What is Range Extender?
Range extension is to increase the range of electric vehicles. If the electric car can't run far, then add a set of engine and generator, which can generate electricity to continue the life of the car when the power is almost unbearable. This type of engine is also known as a "range extender".
The simplest range extender is the one used on the BMW i3 back then. The BMW i3 has a range-extended version of the electric car, which is equipped with a 650cc twin-cylinder engine for motorcycles, which starts generating electricity when the battery is exhausted.
▲BMW i3 has been launched in an extended-range version of the REx (with a fuel filler port on the right front fender)
This kind of range extender belongs to "weak range extender", the engine and generator power are small, and once the car enters the range extender mode, the performance will be significantly reduced. The function of weak range extension is to avoid the electric vehicle from losing power and support the car to drive to the charging point.
The engine has a generator to generate electricity, and then supplies the motor to drive the car, isn't this a "series hybrid"?
That's right, the engine→ generator → electric motor, this series of operations is "series hybrid".
▲Diagram of a series hybrid (photo by Nissan Motor)
If you use "big engine + big generator", the power generation is large enough (usually the power generation power exceeds half of the power of the drive motor), and the performance in the extended range mode is not weak, which is the "strong extended range" used on the ideal and Wenjie models.
If the engine can not only generate electricity, but also directly drive the car when necessary, there are two more modes: "engine direct drive mode" and "engine drive + motor drive" parallel mode, this hybrid is also called "series-parallel hybrid".
▲Schematic diagram of series and parallel hybrid
In a nutshell:
Range Extension = Electric + Series Hybrid;
Plug-in hybrid = extended range + parallel + engine direct drive.
How much more efficient is plug-in mixing than range extender?
Compared with the range extender (series), the plug-in hybrid (series-parallel) engine not only needs to generate electricity, but also directly participates in the drive.
Let's start with two authoritative reviews.
Ouyang Minggao, an academician of the Chinese Academy of Sciences, made the following speech on this issue at last year's "China Electric Vehicle 100 Forum":
"The series-parallel plug-in hybrid includes the function of a range extender, which is more versatile and has lower fuel consumption than the range extender."
▲Ouyang Minggao, an academician of the Chinese Academy of Sciences, believes that plug-in mixing is technically superior to range extension
The team of Professor Xu Xiangyang of Beijing University of Aeronautics and Astronautics has done special research on various hybrid technologies, and one of the conclusions is:
"The fuel economy of the series-parallel hybrid system is significantly better than that of the series-parallel hybrid system."
In other words, the fuel consumption of the plug-in hybrid is significantly lower than that of the extended range.
How much lower fuel consumption? It's about 7 percent.
Specifically, the larger the model and the higher the speed, the greater the advantage of plug-in hybrid. The plug-in hybrid advantage is the most obvious under high-speed working conditions, and the fuel consumption is about 10% lower.
▲Xu Xiangyang's team of Beihang University believes that series-parallel connection has obvious advantages over series-parallel hybrids
Regardless of the difference in fuel consumption of 7% or 10%, from the perspective of automobile technology, it is a considerable gap, or in other words, there is an obvious technical generation gap. It can be seen that the plug-mix ratio extends the range of multiple direct drives, which is not an extra move.
Why is "strong range extension" fuel-efficient?
"Strong range extension" is a very amazing technology, which not only has the sharp acceleration of electric vehicles, but also saves fuel compared to fuel vehicles. If compared with fuel vehicles with the same performance, it is not a problem to save one-third of fuel.
Many people can't figure out a question: the engine with a generator to generate electricity, and then supply the motor to drive the car, obviously a bend in the middle, why is it more fuel-efficient than directly driving the car?
This starts with understanding what engine thermal efficiency is.
The so-called engine thermal efficiency refers to how much of the heat energy generated by gasoline combustion is converted into power. The maximum thermal efficiency of a gasoline engine is usually more than 30 percent, which means that at most more than 30% of the thermal energy is turned into power.
Note that this is the "highest thermal efficiency". The thermal efficiency of the engine is related to the speed and load, and the average thermal efficiency of the fuel vehicle is about 25% when it is actually running.
▲Under different speeds and torque outputs, the thermal efficiency of the engine varies greatly (the figure comes from the Internet)
The engine of fuel vehicles is very hard, and it has to cope with various working conditions such as starting, acceleration, low speed, high speed, light load, heavy load, etc., and a lot of time is working in the low thermal efficiency zone.
The "strong extended range" engine only generates electricity, and there is no mechanical connection with the drive wheels, and the system can freely control the operation of the engine. This kind of engine does not need to cope with complex working conditions, first, the thermal efficiency can be designed higher, the maximum thermal efficiency can easily reach more than 40%; second, most of the time can work in the high thermal efficiency range; third, the working intensity is low, and there is a lot of rest time after power generation (there is a battery as a storage tank).
At the same time, the efficiency of the generator and motor is also very high, and the efficiency is above 90% most of the time.
▲The motor efficiency can be easily maintained at more than 90%.
The energy of the range extender seems to have taken a detour, the mechanical energy is converted to electrical energy and then back to mechanical energy, but the engine can work in the high-efficiency range for a long time, and the conversion efficiency between mechanical energy and electrical energy is very high. The fuel car is very sad, the engine deviates from the high-efficiency range at every turn, and the gearbox loses part of the power.
What is the use of adding a direct drive?
The fuel-saving know-how of hybrid technology is hidden in a picture.
When you understand this engine thermal efficiency diagram, everything suddenly becomes clear.
Again: the thermal efficiency of an engine is not only related to the speed, but also to the load. All hybrid technologies are nothing more than trying to control the engine speed and load, and try to keep the engine working in the efficient range.
Generally speaking, the engine is most efficient at 2000 to 3000 rpm and when the load is also high.
▲Hybrid technology controls engine speed and torque to keep the engine running in the high-efficiency zone as much as possible
The extended-range (series hybrid) engine only generates electricity, and there is no mechanical connection between it and the wheels, and the speed and load can be flexibly controlled within a certain range.
If the power demand of the car is large, and the engine can only meet the motor drive with high speed and large load power generation, the battery will be discharged to replenish and press the speed and load;
If the power demand of the car is small, and the power generation at low speed and small load can be satisfied, the speed and load will be raised, and the power generated will be stored in the battery if it is not used up.
With the help of batteries to "peak shaving and valley filling", the engine can maintain working in the high-efficiency range.
But there are some special cases.
For example, when the car is cruising at medium and high speeds, if the engine is allowed to drive the wheels directly (through the appropriate gear ratio), it can also fall right in the high-efficiency range. At this time, if you go through the process of power generation, electric drive, and battery charging and discharging, there will be several more energy conversion processes, and considering the electrical loss in the middle, it is not as efficient as direct drive.
▲Schematic diagram of the series mode of engine power generation and motor drive (photo according to Honda Motor)
▲Schematic diagram of the series mode of engine power generation and motor drive (photo according to Honda Motor)
▲Engine direct drive mode (according to Honda)
On the basis of range extension, plug-in hybrid adds a direct drive mode, which takes care of more comprehensive working conditions, more detailed accounting, and higher system efficiency.
When will the direct drive disappear?
The engine of fuel vehicles is tired of coping with various working conditions, and needs to provide power at various speeds and loads, and the stay time in the high thermal efficiency area is small, which naturally consumes fuel.
All hybrid technologies, regardless of their genre, strive for the same direction: to reduce the range of engine speed and load to the high-efficiency zone as much as possible. The smaller this range, the more efficient it is.
The worst is the "surface condition", that is, when the engine is running, the combination of speed and load is relatively arbitrary, like a submachine gun sweeping a large area with a shuttle, and it is inevitable to waste bullets.
▲Under low speed and low load conditions, the engine of the fuel vehicle seriously deviates from the high fuel efficiency zone (according to Nissan Motor)
At the medium level, the "line condition", when the engine is running, the combination of speed and load can be controlled in a line in the high-efficiency zone, which is like a burst shot, and the hit rate is significantly improved.
▲Hybrid technology can control the engine operating point in the high-fuel economy zone (Photo courtesy of Nissan Motor)
The ideal is the "point condition", where the engine speed and load are controlled at the point with the highest fuel efficiency, which is like a sniper, one shot to solve the problem.
▲The ideal state of hybrid technology is to let the engine "run at a fixed point" (Photo courtesy of Nissan Motor)
With the progress of technology, the "line working condition" is reduced, reduced, and then reduced, and the "fixed-point operation" of the engine is about to come out.
The "fixed-point operation" of the engine is the highest level of hybrid, and when it really reaches this realm, it is time for direct drive to withdraw from the rivers and lakes. The reason is very simple, when driving directly, the engine and the wheel are mechanically connected and rotate synchronously, and there is no way to "run at a fixed point".
What is the current level of range extension?
Driven by brands such as Ideal and Wenjie, range extension has become a popular hybrid technology in recent years.
▲Ideal car with fire range extension technology
The reason why the "new forces" prefer range extension technology is as Ouyang Minggao said:
"If you want to say that the technical threshold, it must be that plug-in hybrid (higher than range extension) is higher, so generally new car manufacturers will not choose plug-in hybrid."
The advantage of the range extender is that the structure and control are relatively simple, and the cost is also low. The disadvantage is that the efficiency is worse under working conditions such as medium and high speed cruise, and the motor is easy to overheat under ultra-high speed, climbing and other working conditions. Some people think that low efficiency and high fuel consumption are nothing, but for the evolution of automobile technology, this difference in fuel consumption by a few percent means a significant generation difference in technology.
▲ New brands such as Wenjie also prefer range extension technology
It's like the thermal efficiency of an engine, every 1% increase is extremely difficult, but who's to say that 1% improvement doesn't matter?
Will the plug-in hybrid evolve into a range extension (of course, not a range extension in the current sense)?
The thermal efficiency and performance of the engine are contradictory to some extent, pushing up the thermal efficiency, which affects the power. The engine of a hybrid vehicle is gradually freed from the burden of driving, or even completely does not participate in the drive, and can give up some performance in pursuit of higher thermal efficiency. When the thermal efficiency is pushed to a certain level (such as 50%), the engine is only suitable for "fixed-point operation", and it is not enough to think about direct drive.
High thermal efficiency engine + fixed-point operation, the future range extension technology is worth looking forward to. According to the research of Xu Xiangyang's team at Beihang University, the thermal efficiency of the engine is increased by 5%, and the energy consumption of the hybrid system is reduced by 11% - the ultimate version of the range extender technology, the fuel consumption performance must be amazing.