Why is it so fragrant? Analysis of BYD DM-I hybrid system
March 9th, 2022

BYD’s rise this time, many people put the origin on the blade battery. The new battery packaging technology enables BYD’s deep ploughed lithium iron phosphate to compete with ternary lithium. At least under the current market state, its energy density is enough to meet the demand. Then it also achieved the demand of BYD’s high-end, bringing 200000 class products with a monthly sales of more than 10000 yuan.

However, for the brand, the real trump card belongs to the hybrid system dm-i. the popularity of Han still has limitations. This limitation does not come from the product itself, but from the industry restrictions of BEV market. 2021 is the best year for China’s pure electricity market, but by contrast, the penetration rate is only 15%, and DM-I has helped BYD completely open the door of the market. At present, the gap between hybrid models and fuel vehicles has been gradually smoothed out, and BYD stands in front of a huge market for the first time.

DM-I system structure

In detail, BYD’s hybrid system has undergone three generations of upgrading, and there are great differences in structural layout. Today’s DM-I has an obvious “Atavism” phenomenon in structural characteristics and power transmission ideas. It has many similarities with F3DM born in 2008, although it is different in the advanced degree of technical details.

Skipping the “dm-p” technology with “542” strategy and performance orientation, we can directly look at dm-i. its EHS electromechanical coupling unit is indeed similar to F3DM in power layout. The engine is directly connected with the generator through speed change mechanism to generate power, and the motor is directly driven by gears. The engine can directly drive the vehicle through the clutch. It can be regarded as P1 + P3 series parallel scheme. In the system, when the clutch is separated, it belongs to the series form of engine power generation + motor drive, and when the clutch is combined, it belongs to the parallel form of engine and motor directly driving wheels at the same time.

Friends familiar with the hybrid system can see that in fact, this transmission path is very similar to Honda i-mmd, which belongs to series parallel structure. The biggest difference between the two lies in the layout form of motor and generator. BYD EHS adopts the form of motor / generator off-axis layout, and Honda’s latest third-generation i-mmd adopts the form of motor / generator coaxial layout.

The arrangement of this off-axis motor is also more in line with the proportion of electricity in BYD DM-I system. Compared with i-mmd, BYD selects plug-in hybrid and larger battery pack. The motor unit can independently support the vehicle for long-time and long-distance operation. Even if the engine does not participate in the work, it can drive as a “complete” vehicle. Therefore, BYD also puts forward higher requirements for motor power, which is naturally larger in volume. The different axis layout is just to accommodate the arrangement of this power unit.

The EHS system is divided into three versions according to the power of the driving motor, namely ehs132, ehs145 and ehs160. The peak power of the corresponding generator / driving motor is 75 / 132kw, 75 / 145kw and 90 / 160kW respectively. There are also two kinds of engines suitable for these three EHS systems. Ehs132 and ehs145 adopt 1.5L Xiaoyun engine, and ehs160 adopts 1.5ti Xiaoyun engine.

EHS technical details

It can be seen that DM-I hybrid system has no special advantages in structure and does not adopt complex structure, but the final effect is quite amazing. This is because there are corresponding technical breakthroughs in many details of the whole system, especially in core control systems such as engine control system, motor control system and battery management system.

First, let’s look at some internal characteristics of EHS system. Different from the first generation DM hybrid system, DM-I places two high-speed motors with 16000 revolutions in parallel, which reduces the volume of the whole hybrid special transmission by about 30% and the weight by about 30%.

In terms of motor, BYD adopts the self-developed flat wire motor. From the official data, the flat wire forming winding technology can make the maximum efficiency of the motor reach 97.5%, the rated power increase by 32%, the high efficiency range (the range with efficiency greater than 90%) accounts for 90.3%, and the mass power density reaches 5.8kw/kg.

At the same time, there is the self-developed fourth generation IGBT system. According to the official data, its comprehensive efficiency is as high as 98.5%, and the proportion of electronic control high efficiency area (i.e. the area with efficiency more than 90%) is as high as 93%, which greatly reduces the electronic control loss and improves the efficiency.

Xiaoyun engine

At present, there are two main types of Xiaoyun series engines, namely, the 1.5L plug-in hybrid engine focusing on economy and the 1.5ti plug-in hybrid engine taking into account high performance. 1.5ti engine has a compression ratio of 12.5. The technical highlight is that its turbocharger adopts the design of variable cross-section, so that the supercharger can boost within a wider speed range, which can ensure the boost effect under low speed conditions and does not affect the exhaust pressure under high speed conditions.

The 1.5L engine is more inclined to extreme fuel economy. The technical details inconsistent with the traditional engine are adopted in the overall structure and technical means, and finally the thermal efficiency is 43.04%.

The first is the application of the basic variable valve timing technology. By delaying the closing time of the inlet valve, the energy consumption of the compression stroke is reduced and remains unchanged in the expansion stroke, so that the mixed gas can do more work, improve the utilization of the mixed gas energy and reduce the exhaust loss.

Secondly, this engine has an ultra-high compression ratio of 15.5. Through simple data comparison, it will be found that few models in the market adopt such a high compression ratio. In addition, the exhaust gas recirculation system has been re optimized to increase the EGR rate to 25%, reduce the intake loss of the engine under medium and low load conditions, and reduce the emission of nitrogen oxides.

Some improvements have also been made in the structure, such as canceling the traditional gear train, adopting the split cooling technology, electronizing all the mechanical compressors, mechanical vacuum pumps, mechanical power steering pumps and mechanical water pumps on the engine, and combining the electric water pump with the electronic double thermostat to realize the split cooling of the cylinder block and cylinder head.

Subscribe to Thomas
Receive the latest updates directly to your inbox.
Verification
This entry has been permanently stored onchain and signed by its creator.
More from Thomas

Skeleton

Skeleton

Skeleton