The interpretation of BYD DM-i technology is really not the traditional PHEV.

In the technical roadmap of energy-saving and new energy vehicles 2.0 released by China Automotive Engineering Society, it is clearly stated that the future 15 should fully "mix" traditional vehicles. That is, by 2035, in the non-new energy pure electric vehicles that still occupy half of the market, hybrid power will become the leading force; Or it can be understood that by 2035, all existing fuel vehicles will be withdrawn from the market, and their original market share will be completely filled by HEV light hybrid PHEV plug-in hybrid vehicles.

But the goal is ambitious, but the reality is very skinny. Because the comprehensive threshold of hybrid power is actually not low, this directly leads to the unsatisfactory speed of most car companies in promoting new technologies; Especially for PHEV hybrid technology, when most PHEV models are used in scenes without charging conditions, the fuel consumption of the feed is even higher than that of the traditional fuel version; Even HEV, which is famous for its absolute fuel economy, has basically entered the bottleneck period of technical development-the index of 4.0L/100 km has become an insurmountable barrier. For example, the latest "lemon hybrid DHT" technology released by Great Wall Motor in June 5438+February1February 5, the comprehensive fuel consumption of its A-class SUV equipped with HEV is 4.6L/ 100km. In this regard, it has surpassed the performance of many joint venture models.

Of course, when there is general consistency, there must be special cases, and BYD is one of the most representative car companies.

According to the new vehicle data released and declared by the Ministry of Industry and Information Technology, BYD will launch a batch of plug-in hybrid vehicles with brand-new DM-i technology on 202 1, in which the car will achieve an amazing low fuel consumption of 3.8L/ 100km without charging, while even the Song PRO of an A-class SUV will only consume 4.4L without charging, even lower than the latest HEV hybrid of the Great Wall above.

So, how complicated will BYD, a new technology that looks powerful in terms of indicators, be?

The answer may be beyond your expectation. The principle of DM-i technology is really simple, and the main innovation is "logic and concept"-because what BYD is doing now has never been thought of by other manufacturers.

Technical architecture: The principle is extremely simple.

At present, HEV hybrid power systems, such as TOYOTA THS and Honda i-MMD, are recognized as excellent in fuel economy, especially Honda i-MMD. Its unique working logic makes the whole hybrid power system maintain the high efficiency of the whole system regardless of low-speed congestion or high-speed: because the internal combustion engine avoids the low-efficiency working range from the beginning and is driven by the high-efficiency motor, it is directly driven by the internal combustion engine after it is transferred to the high-efficiency section of the internal combustion engine.

Undoubtedly, decoupling engine operation from driving and reasonably distributing the working range of internal combustion engine and motor are the core of hybrid energy saving. If we want to continue to achieve the breakthrough hybrid energy-saving index, we must develop on this road.

According to this picture of BYD DM-i, BYD has indeed achieved this: by integrating the transverse ECVT gearbox of the generator motor and the driving motor, the power is merged and coordinated.

However, because DM-i's new car has not yet been listed, it is impossible to predict the actual motor power of the production car at present, and it is impossible to know the specific working condition calibration. However, we already know that, unlike THS and i-MMD mentioned above, BYD's DM-i is positioned in PHEV plug-in hybrid power, which can meet at least 50 kilometers of full working conditions in pure electric mode, so the power standard of its driving motor should be not low, and dozens of cars should be guaranteed.

In addition, we can also find the coupled working logic of BSG and engine of this system on the specific structural schematic diagram, which is an absolute bright spot compared with other hybrid power systems! Although DM-i is still an engine +BSG+ hybrid gearbox, its working principle is completely different from our current common MHEV light hybrid, because the low-power BSG of MHEV light hybrid vehicle can only assist in outputting power at the initial acceleration stage to drive the engine to idle, thus achieving the purpose of reducing the operating load (fuel saving) of the internal combustion engine.

On BYD's coupling system, BSG can directly pull the hybrid special engine to a higher economic speed before ignition, completely avoiding the inefficient range of internal combustion engine operation. By amplifying the power of BSG motor and introducing ECVT gearbox with integrated drive motor, BYD's DM-i achieved absolute innovation.

The second innovation in concept and logic is to improve the comprehensive thermal efficiency of the whole system. Because we know that the power loss of internal combustion engine is not only the loss of intake, exhaust and cooling, but also the compressor and various "pumps" connected to the engine crankshaft are actually losing the torque of the crankshaft. The existence of the pump system will inevitably reduce the comprehensive thermal efficiency of the vehicle and increase the fuel consumption during normal driving.

However, the internal combustion engines of ECVT's ordinary fuel vehicles and HEV hybrid vehicles still have these shortcomings, including Toyota Honda and so on. However, on the new car of BYD DM-i system, we saw that Xiaoyun 1.5L naturally aspirated engine directly canceled the pump system. Because it is a PHEV plug-in hybrid vehicle, it has enough power and voltage to support the operation of various accessories. No matter the compressor or the water pump, DM-i is driven by electricity, which can effectively reduce fuel consumption.

Innovative ideas bring new technical highlights.

To support a series of innovative logic and ideas of DM-i, related technological innovation is definitely needed. In DM-i system, the only fuel-consuming 1.5L Xiaoyun hybrid engine is the epitome of new technology.

In terms of data, the thermal efficiency of this Xiaoyun 1.5L hybrid engine of DM-i is as high as 43%, which is one of the highest thermal efficiency engines among the mass-produced Atkinson-Miller cycle engines. In addition, the ideal output power range of the engine is in the range of 2000/3000rpm. When it is used as an auxiliary power device, this range can not only meet the power generation of BSG motor, but also have good high-speed cruise power output performance.

Of course, in order to achieve a thermal efficiency of 43%, in addition to the "cancellation of the pump system" mentioned above, the compression ratio of this machine has also been increased to 15.5: 1, which is almost on the same level as the well-known Mazda compression ignition technology in the industry.

In addition, this engine also has EGR exhaust gas recirculation system; Its working principle is that a small part of exhaust gas produced by combustion is re-sent to the intake manifold, and then mixed with mixed oil and gas for the second time and then burned again. EGR can heat the mixed oil and gas in advance, assist the compression stroke, and use a large amount of nitrogen and CO2 in the tail gas to reduce the heat loss during combustion, thus achieving more efficient combustion of the whole machine.

And in order to realize the efficient utilization of waste heat energy exceeding 43% thermal efficiency, BYD also mentioned the "double thermostat" system in the previous announcement, that is, the traditional paraffin thermostat was kept in the cylinder block and an electronic thermostat was added in the cylinder head.

Because we know that the highest thermal efficiency of internal combustion engine is no matter how high, it can't reach the theoretical value in the cold start stage anyway; Because heat energy will be conducted from a high-temperature object to a low-temperature object, this is the second law of thermodynamics. Therefore, when the engine is cold-started, the combustion heat energy will be absorbed by the engine body and antifreeze coolant, resulting in a large torque loss at this time, and ECU has to increase fuel injection to compensate for power, which is also one of the reasons for high fuel consumption.

However, it is much better to divide the control system into three parts by using double thermostats: when the cooling system does not run during cold start, the heating efficiency of the machine body will be high; When the cylinder head starts cooling alone at low temperature, the heat loss will still be very low; When the temperature is high, the cylinder head and the gas will cool at the same time. This three-in-one cooling control system is also unique in the internal combustion engine-and it can also achieve a small amount of low-temperature air intake during cold start and a small amount of high-temperature air intake during hot start to achieve the lowest heat loss.

Write it at the end

Although DM-i performs well in fuel saving, the cost of new technology is still unknown. As a green brand, its fuel consumption is lower than that of HEV. If it can maintain good price competitiveness after listing next year, it is estimated that the new BYD cars DM-i will completely rewrite the pattern of PHEV market.

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.