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BYD debuts DM-i PHEV technology and 1.5L Xiaoyun Engine; 43% BTE

BYD launched its DM-i hybrid technology alongside the official announcement of the high efficiency version of the 1.5L Xiaoyun engine, which is dedicated for plug-in hybrid vehicles (PHEVs).

After defining new performance standards for PHEVs with its DM-p technology, BYD is prioritizing ultra-efficient fuel consumption with the DM-i technology.

The new 1.5L plug-in hybrid engine is specifically built for the DM-i hybrid technology. With a Brake Thermal Efficiency (BTE) of 43%, it stands as the highest thermally efficient gasoline engine in production. The engine’s fuel efficiency easily meets China’s newest national emissions standards, while also providing a distinctly smooth and quiet driving experience.

The Xiaoyun engine features a high compression ratio (CR) of 15.5, an increased B/S ratio, an Atkinson cycle for improved combustion efficiency, an Exhaust Gas Recirculation (EGR) system, a series of friction-reducing measures and an engine control system that is uniquely optimized for high thermal efficiency targets.

In addition, the Xiaoyun engine takes full advantage of the electrification of plug-in hybrid models, electrifying accessories and removing the traditional front-engine accessory drive system, further reducing wear and tear and improving efficiency.

BYD has, for the first time, implemented split cooling technology for an engine. Through on-demand cylinder head and cylinder block temperature measurements, this enables precise and accurate cooling for the Xiaoyun engine to reach optimal running temperatures. By mitigating heating losses, this shortens the length of warming up the engine after a cold start by 15-20%, reducing fuel consumption and carbon emissions during the process.

To improve noise, vibration, and harshness (NVH) performance significantly, the engine has specially-optimized designs for the crankshaft, bearings, cylinder block, intake manifold, oil pan, timing cover, cylinder head cover and other components of the plug-in hybrid system.

In the Chinese government’s recent New Energy Vehicle Industry Development Plan (2021-2035), NEVs are expected to account for 20% of the total sales of new vehicles in China by 2025. Among these, the path for PHEVs shows immense potential.

By leveraging its Dual Platform strategy, BYD’s dual-mode (DM) hybrid technologies—the DM-p and the DM-i—further enhance the competitiveness of PHEVs against traditional fuel vehicles.

The DM-p platform, with a focus on exceptional performance, provides a power output that surpasses large conventional cars. This has drawn the interest of consumer groups that strongly care about environmental protection and sustainable lifestyles, while also holding high expectations for driving experiences.

New models with the DM-i hybrid technology will see a wide array of improvements, including further reductions in fuel consumption, faster acceleration, smoother and quieter rides, and more environmentally-friendly electric power.

In addition, the prices of models with the DM-i hybrid technology are similar to the cost (tax and fee included) of fuel vehicles of the same type from outside of China. This is positioned to be a significant shift in the competition between PHEVs and fuel vehicles, impacting consumer and market perceptions of NEVs.



Sounds very impressive, 43% BTE is excellent for gasoline engines - beware western ICE companies ....


doesn't say explicitly, I assume this is a series hybrid

Roger Pham

I don't understand why a special effort was given to design a brand new 1.5-liter engine just for a PHEV, that would use its engine for only 20% of its total mileage. Why not just use a very compact and light-weight 1-liter 3-cylinder turbocharged engine capable of 125-150 hp that is already developed? Since filling up the fuel tank with gasoline is very fast, engine efficiency is not too important. Much more important is a very compact and light-weight engine to minimize dead-space and dead-weight during daily commuting, yet it must have enough power for adequate driving at high speeds to compete with BEV's performance.


Has anyone seen any comprehensive information on this engine? The article does not say anything.

Another information that came out recently was about a Chinese diesel engine with 50% efficiency. While the relative difference between these engines is about what we could expect for diesel and otto engines in general, the article about the diesel engines does not say anything either. Is this just a coincidence?


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