Popular science： What is BYD DM-i hybrid and why does it save fuel？ Technical Analysis of Motor／Battery／Engine

BYD’s DM-i hybrid technology is now a household name. Why can it stand out among the hybrid technologies of a large number of automobile brands? As we all know, BYD’s hybrid cars have a history of more than ten years, and as early as 2008, a plug-in version of F3 was introduced. So why does today’s DM-i make BYD’s sales increase greatly, and what is the difference from the early hybrid technology? Let’s analyze it in detail from three aspects: motor, internal combustion engine and hybrid mode.

16,000 rpm motor and blade battery

DM-i is the abbreviation of Dual Mode-Intelligente dual-mode intelligence. Compared with the previous hybrid technology, it pays more attention to the use of motor, which is a hybrid technology of "electricity-oriented", with high-power motor drive, large-capacity battery power supply and internal combustion engine as the supplement, subverting the traditional hybrid "oil-oriented" design, which is a concept that really makes the fuel vehicle transition to new energy. In the past, the plug-in hybrid model was a fuel vehicle because the battery life was too short, and most people rarely charged when driving.

While BYD’s DM-i pays more attention to electrification. The maximum speed of the motor it carries is 16,000 rpm, with the highest efficiency of 97.5%, and the high-efficiency interval with efficiency exceeding 90% reaches 90.3%. Compared with the thermal efficiency of the fuel vehicle of about 40%, the energy utilization rate of the motor is higher. Because the instantaneous torque of BYD’s single permanent magnet synchronous motor exceeds 310Nm, it can completely replace the internal combustion engine, such as Song PLUS DM-i, which accelerates 100 kilometers.

The motor is equipped with a blade motor that has been safely verified in BYD’s pure tram. Combining the thermal stability advantage of lithium iron phosphate battery core, the blade structure makes up for the shortcoming of low energy density in Ferrous lithium phosphate, which achieves ternary lithium energy density and is safer. At present, the blade battery of DM-i has two capacities, of which the 8.3-degree version brings a cruising range of 51 kilometers; The 18.3-degree version brings 110 kilometers of battery life, of which 110 kilometers of battery life is close to Hongguang MINI EV, and commuters in urban areas can drive in pure electric mode.

1.5L hybrid engine with 43% thermal efficiency

After electrification, BYD developed Xiaoyun plug-in hybrid engine specially for hybrid vehicles. Taking the 1.5L self-priming version as an example, the braking thermal efficiency (BTE) is as high as 43%, which is the key to fuel economy. In order to achieve a record thermal efficiency, the engine has several core technologies.

First of all, compared with turbocharging, naturally aspirated air has a lower intake temperature, which can increase the compression ratio of the engine. By using pistons and connecting rods with higher strength, the compression ratio of Xiaoyun engine is as high as 15.5:1, which exceeds Mazda’s famous 14:1 (European version) Chuangchi Blue Sky engine. In the process of supercharging and compression ratio, in order to prevent knocking, the intake valve is opened in advance in the compression process through the variable timing mechanism of intake and exhaust valves, so as to solve the problem of cylinder pressure, make the expansion ratio greater than the compression ratio, and the larger expansion ratio converts more energy from heat to useful mechanical energy, thereby increasing the thermal efficiency.

This fuel-saving method brings the problem of low power density. The torque at low speed is very low. The torque of a turbine engine with the same displacement can reach 300Nm, while the peak torque of this engine is only 135Nm, and it needs to reach 4,500 rpm to explode. It is obviously not enough to drive the whole vehicle alone, but when it is used in a hybrid vehicle, the low speed is completely driven by a motor, so there is no problem of low starting torque.

Another advantage of blending is that the engine parts are electrified, and the traditional front engine parts drive system, such as air conditioning compressor, mechanical vacuum pump and mechanical water pump, is cancelled, which further reduces wear and improves efficiency. Cooperate with variable displacement oil pump to reduce oil resistance during cold start.

Xiaoyun hybrid is the first time BYD has installed split cooling for the engine. By measuring the temperature of cylinder head and cylinder block on demand, accurate cooling effect can be provided to achieve the optimal operating temperature of the engine, especially in winter, which can reduce heat loss, shorten the engine preheating time after cold start by 20% and reduce the fuel consumption of hot cars.

Four completely different driving modes

DM-i is mainly powered by electricity. When the power is sufficient, it is driven by pure electricity in urban areas, especially in traffic jams. The starting torque of the motor is large and it is easy to change lanes and overtake.

In the second case, the power is insufficient, the driving computer automatically switches the HEV series mode, Xiaoyun internal combustion engine enters the power generation mode, and the motor is still responsible for driving.

In the third case, if you are driving on a mountain road or want to experience the abundant hybrid power, you will enter the HEV parallel motion mode at medium and high speed (above 60km/h), and the motor and internal combustion engine will drive the car at the same time.

The fourth is high-speed cruise driving, which is directly driven by a 1.5L internal combustion engine. This is the stage with the highest engine efficiency, just like the 90km/h high-end and low-speed of an ordinary fuel vehicle. Although driving at high speed, the fuel consumption is low.

Car detective’s point of viewByd changed the early hybrid internal combustion engine, and then added the "chicken ribs" of the motor. DM-i started from three aspects: hybrid internal combustion engine, blade battery and high-efficiency motor, and developed a hybrid car from zero, forming a pure electric drive form, without endurance anxiety. Even if the power is fed, the fuel consumption per 100 kilometers is only 4-5L, which really reduces the car cost. What do you think of BYD DM-I technology? Praise, comment and attention are our greatest encouragement, thank you!