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In the just-concluded 2020 "China Heart" Top Ten Engine Selection, Geely's 1.5 MHz three-cylinder engine, as the only three-cylinder engine that won the top ten in China in 2020, once again impressed everyone with Geely's engine technology.

This 1.5 MHz light hybrid engine combines a high-performance three-cylinder supercharged engine with 48V light hybrid technology, which perfectly overcomes the disadvantages of three-cylinder engine in vibration while achieving higher performance and lower fuel consumption. Today, we will introduce this engine from two aspects: engine technology and light hybrid technology.

I. R&D background

Geely's 1.5T three-cylinder engine is actually related to Volvo Drive E series T3 three-cylinder 1.5T engine, which can be said to be a product developed by Geely on the basis of Volvo 1.5T engine. Geely has been digesting and absorbing Volvo's engine technology since it acquired Volvo in 2010. At present, Geely has developed four versions of traditional engine, 48V MHEV light hybrid, HEV strong hybrid and PHEV plug-in hybrid on the basis of 1.5T engine.

This time, the MHEV 48V version was selected as one of the top ten engines of China Heart 2020. This powertrain was first installed on the MHEV version of Geely Bo Yue GE, and later extended to many models of Geely and Lectra, which became an important strategic product for the development of Geely's traditional internal combustion engine towards hybrid.

Second, the main technical characteristics of Geely 1.5TD three-cylinder engine

1, all-aluminum design

Geely 1.5TD engine adopts all-aluminum design. The cylinder block, cylinder head, camshaft cover and oil pan of the engine are all made of cast aluminum to reduce the weight, and the intake pipe is also made of plastic to further reduce the weight.

2. Direct injection system of central injector

Geely's 1.5TD adopts an advanced direct injection fuel system with a central injector of 200bar. Compared with the side injector design, the middle injector can reduce the possibility of gasoline injection on the cylinder wall and piston top, which can greatly reduce the emission of particulate matter and avoid the increase of engine oil level caused by engine oil dilution.

3. The cylinder head integrates an exhaust pipe and a low inertia supercharger.

Geely 1.5TD engine integrates the exhaust pipe into the cylinder head of the engine, which is a very popular design scheme for the newly designed engine at present. The cylinder head integrated exhaust pipe can use the exhaust temperature to heat the coolant during the warm-up process, so that the water temperature rises rapidly, which is beneficial to emissions and fuel consumption. At the same time, under the condition of heavy load, the cylinder head water jacket can be used to cool the exhaust gas, which greatly reduces the exhaust temperature, reduces the thermal load of the turbocharger turbine and reduces the enrichment of the temperature protection of the supercharger. Conducive to emissions and fuel consumption under heavy load.

Geely also adopted a low inertia supercharger on this engine, which helps to reduce the turbo lag effect and improve the dynamic response of the engine.

4. Double VVT and belt drive

Geely 1.5TD engine adopts dual VVT of intake and exhaust, which can flexibly adjust the intake and exhaust timing according to different engine working conditions to obtain the best efficiency. In terms of timing drive, the Geely 1.5TD engine uses a low-noise and long-life dry belt to drive the timing system, which is also the common design of Geely and Volvo's new Drive E platform, and the 2.0T engine also uses the timing belt to drive. Compared with chain, long-life timing belt has obvious advantages in noise and low friction.

5. Two-stage variable displacement oil pump

Geely 1.5T adopts two-stage variable displacement oil pump design, and the oil pump has two displacements, which reduces the oil pressure to reduce friction loss at low load, and switches to large displacement to increase the oil pressure at high load to ensure lubrication. The oil pump is installed in the oil pan and driven by the gear installed on the crankshaft. This gear not only drives the oil pump, but also drives the balance shaft installed on the cylinder block. This design is very compact.

5, balance shaft design

In order to balance the vibration of the 1.5T three-cylinder engine, Geely specially developed a set of balancing shaft system, and specially optimized the gear noise. The balance shaft is lightweight and hollow.

Third, the advantages brought by the 48V MHEV light hybrid system

Another very important technology of Geely's 1.5TD three-cylinder engine is the addition of 48V light hybrid technology. The 48V motor is arranged in P0 mode, that is, at the position of the traditional generator at the front end of the engine, instead of the traditional generator, it is driven by a belt. In the figure below, you can see the 48V light hybrid motor with a bidirectional belt tensioner.

The 48V light mixing system can realize the functions of no idle speed, start-stop function, acceleration and energy recovery, improve performance and reduce fuel consumption, so it is a very cost-effective mixing system. At the same time, the combination of 48V light hybrid system and this three-cylinder engine will bring great improvement in noise and vibration, which can completely eliminate the disadvantages of the three-cylinder engine in this respect, which is also the basis of Geely's excellent noise and vibration performance of this 1.5TD engine:

1, the complete elimination of idle vibration

The idling jitter of the three-cylinder engine is complained most, because the firing interval of the three-cylinder engine is 240, and the power stroke of the engine is only 180. This means that there is a 60 crank angle interval between the two cylinders. Especially when the idle speed is very low, this kind of jitter is the most obvious. Because the 48V light hybrid has the start-stop function, the engine stops directly when parking, and there is no idle speed, so the idle vibration of the three-cylinder engine can be completely eliminated.

2. Smooth engine starting process

Because the 48V light hybrid needs to start the engine frequently, how to improve the jitter of the three-cylinder engine when starting is a key point in the development of the 48V light hybrid system. The power of 48V motor is much larger than that of ordinary starter. It can directly pull the engine to more than 500 rpm, then the engine directly ignites to output torque, and the car directly starts and leaves. The engine can be very smooth from start to output power. This is much smoother than the traditional starter starting the engine first, and then the engine outputs torque, especially for the three-cylinder engine. This is another obvious advantage of the 48V MHEV light hybrid system.

3, improve the jitter when downtime.

When the three-cylinder machine stops, the jitter will be bigger than that of the four-cylinder machine. 48V light hybrid motor can use the torque output of the motor to control the speed, reduce the speed fluctuation, and make the engine stop very smooth.

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