How to make the strongest blending system in China？ In-depth analysis of SAIC DMH super hybrid system

Nowadays, new energy vehicles have become the absolute mainstream of the industry. Among the three mainstream new energy vehicle forms, pure electric, HEV and PHEV (extended program can be classified as PHEV category), PHEV (plug-in hybrid, hereinafter referred to as plug-in hybrid) is not the ultimate solution, but it is the relatively best energy form of new energy vehicles at this stage.

So how to "mix" this mixture becomes very important. Not long ago, at the launch conference of Roewe’s new car D7, SAIC announced the DMH super hybrid system and called it the strongest hybrid system in China. In the subsequent media interview, SAIC further stated that the DMH super hybrid system will be widely spread in various brands and models of SAIC system in the future.

So, what is the structure of the hybrid system? How to "mix"? Why can DMH super hybrid system be called the strongest hybrid system in China? In the following long article, we will give you an in-depth analysis.

Structure, main configurations and advantages of PHEV

PHEV plug-in hybrid system is actually a fuel engine and motor "tied together" through a coupling system. In terms of decomposition structure, the PHEV system consists of a hybrid engine, a hybrid gearbox, a drive motor, the coupling structure mentioned above, and an electronic control system for controlling two power modules, ICE and EV.

At present, there are three common configurations of PHEV technology in the market: P1+P3, P2 and E-CVT. Among them, P1+P3 and P2 are similar in structure, but the crucial coupling work is all taken care of by an independent motor.

The difference between P1+P3 and P2 is in this motor. The core component of the whole hybrid system is actually a hybrid gearbox. As the name implies, this is a gearbox, but it is completely different from the gearbox on the fuel vehicle that we understand. There are three shafts in this thing: the first shaft is the input shaft, which is connected to the engine crankshaft. The No.3 shaft is the output shaft, which is connected with the transmission parts outside the gearbox, and there is also a No.2 shaft for follow-up in the middle of the input and output shafts. Just three gears, the structure is very simple.

The "P" mentioned above is actually a motor (Power). In the plug-in configuration, you can see which number is followed by P, which represents which axis the motor is installed on. Therefore, P1+P3 means that two motors are installed on the input and output shafts respectively, and P2 is a motor installed on the follow-up shaft, which is also easy to understand.

The main advantage of P1+P3 configuration is that it uses two motors to solve the mechanical coupling vibration of the hybrid system, and by the way, it adds torque to the engine, and it can also take into account the pure electric output. Moreover, the two motors are "independent", which is not only convenient for tuning, but also beneficial for future maintenance. Therefore, compared with a single P2 structure with a bunch of clutches bound in one motor, P1+P3 is the mainstream choice for most car companies at present.

The structure of traditional P1+P3 configuration is insufficient.

But P1+P3 actually has some shortcomings, the most obvious one is the P1 motor. P1 motor not only needs to pass the torque of the oil filter (the torque of the oil filter is inherently unstable), but also needs to increase the torque of the oil filter, and even needs to indirectly participate in driving the vehicle under some working conditions. Therefore, P1 motor has more things to do, and its size is naturally not small. Therefore, the traditional P1 motor is actually connected with the input gear of the gearbox in the form of "plug-in" through a short shaft and a transmission gear.

This is the off-axis P1 motor, which is the mainstream structure of most hybrid systems at present. The off-axis P1 motor will bring several problems: because there is an extra transmission shaft connecting the motor and the No.1 shaft and an extra gear, the mechanical transmission efficiency will be affected. At the same time, it also means that there is a torque coupling time difference between the torque output of the oil engine and the P1 motor, which will produce vibration, and this vibration will lead to two phenomena: firstly, the passengers can feel the vibration at the moment when the engine is involved, and secondly, this vibration, which is essentially an unsteady mechanical impact, will affect the whole set of insertion.

Structural improvement of P1 end by DMH system

How to solve this problem has always been a big problem. The DMH super hybrid system of SAIC gives a temporary solution as well as a permanent solution.

The DMH super hybrid system mounted on Roewe D7 DMH was first launched, and the above-mentioned off-axis P1 motor was replaced by coaxial P1 motor design. What is a coaxial P1 motor? The coaxial P1 motor of DMH super hybrid system is no longer a traditional cylindrical motor, but a structure similar to direct driver on drum washing machine, which is directly installed on the periphery of P1 gear end.

The power output by the crankshaft of P1 engine is directly connected to the clutch of the coaxial motor. When P1 motor is required to work, the clutch is engaged, and the torque of the engine directly enters the rotor of the coaxial motor after a heavy torque filter through the clutch, and then is reflected on the input shaft gear after being directly filtered and twisted by the motor.

In this way, the coaxial motor not only directly solves the NVH problem of the off-axis motor, eliminates the perceptible vibration of the occupants in the car, and enhances the structural and mechanical stability of the whole P1 shaft under long-term operation, but also solves the defect that the traditional P1 motor is difficult to arrange and requires extremely high engine compartment space.

From the user’s actual driving experience, you can notice the vibration generated at the moment when the engine is involved in the traditional P1+P3 hybrid system. Besides the engine itself, this vibration is actually caused by the above-mentioned off-axis P1 motor.

However, the feeling of driving Roewe D7 DMH is completely different. Even when the engine intervenes at a low speed, it can’t perceive its vibration and torque changes (sound is another topic). This kind of power intervention is very close to being completely insensitive, and the root cause is the structural advantage of coaxial P1 motor in eliminating the coupling torque time difference.

P3 motor with the same structure but optimized in many places

In fact, in the DMH super hybrid system, the structural improvement of P1 motor is the most important, and it is also the main factor that reflects the advantages of the DMH super hybrid system in terms of transmission efficiency compared with other mainstream P1+P3 configurations. But the P1 motor that we have been talking about for so long, and the P3 motor of DMH super hybrid system also have to be mentioned.

In fact, the P3 motor of DMH super hybrid system has not been optimized too much. As a driving motor, it is the same as other mainstream hybrid systems, and it is also a traditional cylindrical off-axis design. Because P3 motor is a driving motor, the demand for power and torque is more stringent than P1 motor.

However, although it adopts the same P3 motor layout and structure as other mainstream hybrid systems, SAIC has also made many technical improvements for the P3 motor itself of DMH super hybrid system. Among them, the more important ones are the multi-piece strong magnetic rotor and the stator with greater magnetic flux.

These improvements are reflected in the driving experience. Whenever the Roewe D7 goes down with a big switch, you won’t feel too much noise from the motor (or motor howling), which gives the user the feeling that the motor sound is much weaker and the car is much quieter. For some people who are extremely sensitive to motor howling, riding Roewe D7 DMH is less prone to carsickness.

A learned PIPU integrated electronic control

Among several main technical points of DMH super hybrid system, highly integrated and miniaturized PICU integrated electronic control is also a very big technical highlight. Compared with the previous motor part, electronic control is an invisible and intangible thing, which is difficult to show directly, but the electronic control system directly determines all the technical indexes of a set of hybrid system.

The hardware ontology of the electronic control system is a single-chip microcomputer system, and the integration of the traditional PICU system is not high, because many core functions need an independent subsystem, such as BMS battery management system, and a very large subsystem is needed to be responsible for it. In addition, there are the coupling control, air conditioning and so on that we mentioned earlier.

So many subsystems will bring a lot of problems: they are all integrated on one motherboard, and the components on the whole motherboard are very densely arranged. There are more wiring underneath, more components and more complicated wiring, and the higher the power consumption of the motherboard, the greater the heat generation. If it is a digital device like a computer working in a normal temperature environment, this may not have much impact, but everyone should know that the installation location of PICU is in the engine compartment, next to the internal combustion engine.

Everyone knows how bad the temperature and environment in the engine compartment are, so the probability of failure of a large PICU with low integration and multiple components is high. What DMH super hybrid system does on PICU system is to greatly reduce the size of the whole PICU motherboard and realize as many functions as possible in as few chips as possible. Even SAIC integrated the control module of air conditioning system on a single chip.

To do this, it depends on real hard power. Without knowing all the sub-modules of the whole hybrid system and practical chip-level development ability, there is no way to realize so many independent subsystems on a few chips. Therefore, the appearance of DMH super hybrid system, a highly integrated PICU electronic control system, actually proves in a sense that SAIC has the core chip-level development capability of the hybrid system.

The strongest mixed, well-deserved.

The characteristics of DMH super hybrid system can be summed up in one sentence: simple things are often complicated, and willing to work hard in seemingly simple places will generally achieve unexpected good results. As the strongest plug-in hybrid system in China, DMH super hybrid system has low energy consumption, long battery life and quiet, which has lower energy consumption and longer battery life than traditional plug-in hybrid vehicles, and also restores the quiet experience like a tram.

The appearance of DMH super hybrid system shows us the technical strength of SAIC, the earliest pioneer in China. Based on this system, we also see that Roewe D7 DMH has achieved amazing results, such as official fuel consumption of 4.3L per 100 kilometers, comprehensive battery life of 1,400 kilometers, measured fuel consumption of 3.4L per 100 kilometers and comprehensive battery life of 1,704 kilometers.

On the basis of all this, the price of Roewe D7 is very shocking. A car with the space and comfort of a B-class car, a seat with a length of nearly 4.9 meters and full comfort, and even a double-decker sound insulation glass, the comfort of the whole car is stronger than that of some 200,000-class old B-class cars. The limited-time equity price of such a car is only 109,800.

It can be said that Roewe D7 is one of the biggest "king bombs" of SAIC in 2023, and the DMH super hybrid system in D7 DMH, which will be widely used in various models of SAIC in the future, really deserves the name of the strongest hybrid in China.