If BYD is the first brother of domestic new energy vehicles at this stage, then DM-i technology has made great contributions. The plug-in hybrid that can be oiled and electric has instantly become a technical form that the majority of ordinary consumers like to see. At present, BYD's new products, such as Qin L, Seal 06, Song PLUS DM-i, etc., are expected to adopt the new DM-i technology after iteration. Interestingly, the whole network is going viral, and the new DM-i technology will change from the current series-parallel structure to a power-split structure similar to Toyota's THS hybrid. So, with the declaration information recently exposed by the new BYD Song PLUS DM-i. Let's disassemble the quality of the new BYD DM-i technology.
Save fuel with clutch and power with planetary gears
First of all, the all-new BYD DM-i technology is indeed very likely to adopt a planetary gear structure. But there is a planetary gear structure, which is not necessarily equal to the Toyota THS scheme. After all, planetary gears are widely used in automotive powertrains, such as traditional AT gearboxes, which need to rely on a series of planetary structures to perform gear shifting actions. Returning to BYD's DM-i technology, dual motors and engines can be pure electric drive, fuel direct drive, and oil-electric parallel drive, which is the most basic perception of users. But no technical solution can be perfect.
The current BYD DM-i technology cannot liberate the P1 motor from the power generation function in the first place. Although this part of the motor is not very powerful, in terms of utilization, it can also push the maximum performance of the vehicle and reduce the calibration pressure of the hybrid system. The difficulty of calibration is a major problem for traditional DM-i technology, of course, this is still in the case of its single-speed direct drive, and if multi-gear is used, it is even more difficult. The texture of power connection directly affects the driving quality and performance of the vehicle. However, it is precisely because the traditional DM-i does not have multiple gears that the engine is difficult to suppress after intervening in the direct drive, resulting in fuel consumption not being suppressed in the lower range.
In the patent drawing that is suspected to be the new DM-i technology, in fact, in addition to the more topical planetary gears, the dual-clutch structure at the rear end of the engine is, in a sense, the core of the new solution. Because of this dual-clutch transmission, not only can the engine continue to be decoupled from the power flow. It is also possible to detach from the engine and incorporate the P1 motor into the power flow. Even the P1 motor can directly perform the driving task, but its own horsepower is limited. In the case of pure electric drive, the P1 and P3 motors can work together, which not only brings stronger performance. It can also further reduce the intervention range of the engine direct drive to avoid the difficulty of limited efficiency of the single-speed direct drive in the case of engine drive. Even the drive support of the two electric motors can effectively reduce the speed of the engine intervention direct drive. Generally speaking, it is an operation that reduces fuel consumption while improving performance.
This is very clear through the declaration information of the new Song PLUS DM-i. With almost no change in weight, fuel consumption has been reduced to 4.95L/100km and 4.98L/100km. Fuel consumption has been reduced by up to 0.42 liters/100 km for the current model. In addition, the maximum output of the P3 motor has been increased to 160 kW (145 kW for the current model). Coupled with the new DM-i technology, it is likely that the drive function of the P1 motor will be liberated. The two are superimposed, and the performance of the new Song PLUS DM-i in 000 acceleration is likely to enter 8 seconds (8.2-8.5 seconds for the current model).
However, the Song PLUS DM-i, which may use more electricity in function and has been objectively strengthened in performance, will it lead to the sacrifice of pure electric range? This brings us back to the original topic, why planetary gears. In the patent drawing, which is suspected to be the new DM-i technology, BYD uses two sets of planetary gears for the two motors to intervene in the spindle. This is the most essential difference compared to Toyota, because Toyota THS is a planetary gear structure, coupling the engine and two motors, that is, power splitting. Splitting the suspected new BYD DM-i technology can clearly find that the new technology is still a series-parallel structure. The planetary gear only plays the role of a reducer for the motor, and it can also be regarded as providing the motor with the function of gear switching. In addition to increasing efficiency and flexibility, planetary gears intervene in the spindle to achieve better coupling smoothness.
So theoretically, this system will also reduce the power consumption performance of the vehicle. According to the information on the new Song PLUS DM-i, the power battery capacity of the new car remains basically unchanged, at about 18.3 kWh and about 26.6 kWh. However, the corresponding WLTC all-electric range has been increased to 91 km and 128 km. This is an increase of 6 km and 12 km, respectively.
The power of the internal combustion engine is reduced, more like a range extender?
As mentioned earlier, this technical solution is suspected to be the new DM-i, through a set of dual clutches and two sets of planetary gear structure, so that the engine and two motors have a higher degree of freedom, thereby unleashing the performance potential and strengthening the energy economy. But new technologies don't always mean moving forward, and there may be "regressions", such as the internal combustion engine of the new Song PLUS DM-i, which has a maximum power of only 74 kW. Traditionally, a 1.5-liter naturally aspirated engine is a bit too small, 7 kW less than the current 81 kW. However, if we look at it from the perspective of a range extender, the reduction of the ultimate power just means that the efficiency of the internal combustion engine has been improved.
The balance between efficiency and performance is the core contradiction that needs to be overcome in the development of traditional engines. But if it's just to do more work with less oil, then the problem is simpler. To sum up, it is nothing more than a narrow and long cylinder block, reducing air intake, and reducing losses. The traditional 1.5L engine of BYD DM-i technology already has a bore-diameter stroke ratio of 1.28, and the compression ratio has also reached 15.5, and the narrow and long cylinder block design can be said to be very well executed. Reducing losses, water-cooled EGR, split cooling of cylinder heads and blocks, and various technical applications to reduce friction have been comprehensively applied in the price range of models for technical applications. The only way to improve engine efficiency without a significant increase in costs is to further reduce the amount of air intake.
In fact, from the previous disassembly, we can also find that BYD's new DM-i technology is likely to occupy more costs in terms of structure. As a result, there is no spare energy to add weight to the engine in terms of variable valves on the exhaust side, high-pressure direct injection of fuel, or even direct turbocharging. Another circumstantial evidence is that in the declaration information of the new Song PLUS DM-i, its engine model is BYD472QC, which is very similar to the current BYD472QA, and it also shows that there is a high probability that there is no iterative relationship between the two.
Returning to the technology itself, as a naturally aspirated engine, the so-called reduction of air intake is the use of the Atkinson cycle. That is, after the intake valve enters the gas mixture, it is pushed back into the intake tract by the piston, which reduces the fuel-gas mixture in the cylinder, and uses the inertia of combustion to make the piston go through more work strokes. BYD's new DM-i technology is likely to increase the capacity of the gas mixture pushed back into the air intake tract in engine tuning. In this way, you can achieve lower fuel consumption and generate more electricity. As for the performance of direct drive, the intervention of dual motors has reduced the working condition range of the direct drive of the engine, so it is not bad for the extreme performance of 7kW. It is only with the manifold injection retained that the combustible gas is pushed back into the intake tract with mixed fuel. Even without the high temperature tempering pressure due to the extreme performance requirements, the increase in the amount of gas mixture increases the difficulty of calibrating the amount of manifold injection that mixes with the air.