【Hybrid Encyclopedia】Technical analysis of the first generation of SAIC EDU hybrid system

Recently, with the productization of a number of independent brand DHT hybrid systems, I have to recall an oem that started very early, but has not been replaced for a long time, that is, SAIC, today I will make up for this hybrid system that should have been talked about for a long time, but has not been talked about - "SAIC EDU Hybrid System".

Structural features: double motor + double clutch + two gears of transmission

SAIC Motor belongs to the earliest batch of self-developed hybrid system OEMs in China, as early as 2008 to 2009 began to approve the project, in 2013 SAIC released the first generation of hybrid system "SAIC EDU Hybrid System" (or "EDU electric drive system") and applied for a patent for it.

Structural explosion diagram of the first generation of SAIC EDU hybrid system

The first generation of the SAIC EDU Hybrid System belongs to the "series parallel architecture" we introduced earlier, which consists of an "engine" and two "motors", one of which is a "P1 motor" (ISG motor) mainly used to generate power and adjust the speed of the "engine", while the other is a "P2 motor" (TM motor) mainly used for driving.

Schematic diagram of the structure of the first generation saic motor EDU hybrid system (for reference only)

The three power components are connected by two sets of "clutches", a set of "synchronizers" and several variable speed gears. The first group of "clutch C1" controls the "engine" to connect to the entire system, while the "clutch C2" is closed for a long time (more on this later), mainly responsible for integrating the power of the "P2 motor" into the system.

Schematic diagram of the structure of the first generation SAIC EDU hybrid system (for reference only)

The reason why this system has won many awards issued by the state in the following years is that a 2-speed transmission mechanism (2AMT) has been added to the system, and its original design is to allow the "engine" and "motor" to maintain a relatively efficient operating range. Looking at it today, it seems that there is nothing remarkable, but in that era when even the single-stop hybrid system was not understood, it was a huge challenge.

How it works: All-encompassing, slightly more complex

Working principle of the first generation of SAIC EDU hybrid system (for reference only)

The structure of the first generation of "SAIC EDU Hybrid System" determines that this system can realize almost all hybrid modes such as pure electric mode, series mode, parallel mode and kinetic energy recovery mode. In the previous chapters, we have listed the basic logic of the 6 official working modes given by the official (see table above). Due to the existence of the 2-speed transmission mechanism, I continue to refine it to deduce the possibilities of at least 14 working modes, so let's see what exactly are there.

Pure Electric Mode: When the "battery" is fully charged or the vehicle's torque demand is moderate, the "battery" is powered by the "P2 motor" and the "P2 motor" directly outputs power, and finally reaches the wheel end. From the above figure, we can already see that the so-called 2-gear shift is to change the speed through the gear on the left or the gear on the right, and the timing of the power coupling is to make a decision through the "motor controller", physically adjust through the "synchronizer", and the subsequent shift logic is basically the same, so after that, it will not be repeated, and everyone can understand it through the GIF;

Series mode: When the power of the "battery" is low or the vehicle demand for torque is low, the "engine" drives the "P1 motor" as the "range extender" to generate electricity, and in most cases, the power emitted by the "P1 motor" is used as the "battery" to replenish the energy, at this time, the "P2 motor" is still the only driving source;

Parallel mode: When a large torque is required, then all the units that can be driven must be fully involved, the "clutch C1" is closed, the "engine" is directly connected to the drive, the "P1 motor" continues to generate electricity under the belt of the "engine", and if necessary, the "P2 motor" is directly powered, and the "P2 motor" is connected to the drive;

Driving charging: During the driving process, when the "battery" power is lower than the specified value, the role of the "engine" is amplified at this time, although in most cases, the system still maintains the working state of "parallel mode" at this time, but the control logic of the "P2 motor" will be adjusted. If the power of the "battery" is too low, and the system determines that the power supplied by the "P1 motor" is also not suitable for dragging the "P2 motor" to drive, then the system will briefly enter the "engine direct drive" mode. Therefore, I also added this working condition diagram of "engine direct drive" in the above figure;

Parking charging (idle charging): When the vehicle is in a static state and the "battery" power is lower than the specified value, the "engine" idle drives the "P1 motor" to charge and recharge the "battery";

Kinetic energy recovery mode: When sliding or depressing the brake pedal, the system will recover from the wheel end and inside the system, if the vehicle is in "parallel mode", then the two "motors" work at the same time; and when the vehicle is in "pure electric mode", the "P2 motor" for kinetic energy recovery.

Schematic diagram of the working mode of the first generation SAIC EDU hybrid system (GIF, for reference only)

Here we will recycle the question left over when talking about structure, "Why is "clutch C2" normally closed?" From the above figure, we can see that the first generation of "SAIC EDU hybrid system" is a hybrid system that tends to be electric drive, in other words, there are a large number of working conditions that require the participation of "P2 motor", so the "clutch" that controls the access to the "P2 motor" is closed in most working conditions.

Advantages are disadvantages: it is difficult to improve, and change is a foregone conclusion

The advantage of the first generation of "SAIC EDU Hybrid System", which can also be said to be its biggest design feature, is the addition of a 2-speed transmission mechanism, which can better realize the adjustment of the working point of "motor" and "engine".

Schematic diagram of the layout of the two-stop gear and synchronizer (image from the network)

For example, by changing gears to amplify the torque of the "P2 motor", so that the start of pure electricity can be more energetic, in addition, an additional gear can also allow the "engine" to intervene in the entire power system earlier, while ensuring fuel consumption, expanding the economic working area of the "engine".

2014 Roewe 550 Plug-in Flagship Edition (Image from the Internet)

The representative model of the first generation of "SAIC EDU Hybrid System" is Roewe 550 Plug-in, taking the 2013 "Roewe 550 Plug-in" (2014 flagship version) as an example, which is equipped with a 1.5L "engine" (not a 1.0T three-cylinder engine Oh ~), its maximum power is 80kW, "P1 motor" and "P2 motor" The maximum power is 27kW and 50kW, from the parameter point of view, the power performance is better than BYD's first generation "DM hybrid system" It is much stronger, but the rated continuous output power and torque still retain the taste of that era, and it is estimated that it is also considered to be fuel economy.

2014 Roewe 550 Plug-in Flagship Specifications (for reference only)

However, the first generation of "SAIC EDU Hybrid System" has many disadvantages, first of all, the 2-speed transmission mechanism is a "double-edged sword", and the logical control of the gear shift is very difficult, because each shift needs to go 3 steps:

1. First of all, the "synchronizer" should be disconnected, which means that a power interruption is required;

2. Then synchronize the speed of the next gear with the torque of the "motor";

3. Finally , a "cluck" is made for docking, which means that there is a possibility of setbacks.

Schematic diagram of clutch failure case

Therefore, from the experience of many car owners (especially chauffeurs) at that time, the system's setbacks in shifting gears could not be avoided. In addition, in our maintenance cases, more is the failure of "clutch C2" encountered, because the general owner of this car is more violent (weaker power, so the foot will be fierce), normally closed "clutch C2" failure will be more.

Engine compartment stuffed by the first-generation SAIC EDU hybrid system (image from the Internet)

The first generation of "SAIC EDU Hybrid System" also has a headache structural shortcoming - the horizontal occupation space is too large! Although the whole system is not a simple "oil to electricity" design idea, it has to be admitted that the volume of its "hybrid transmission" can still not be compared with the volume optimization of the "Honda i-MMD hybrid system" at that time.

3-axis vs 2-axle + 2-speed transmission, the logic is different

Since the "Honda i-MMD Hybrid System" uses three parallel axes, the dual motors can be placed up and down, taking advantage of the longitudinal space. The first generation of the "SAIC EDU Hybrid System" is two shafts, and the two "motors" cannot be placed up and down, so the lateral space is difficult to optimize. This also laid the groundwork for the birth of the second generation of "SAIC EDU Hybrid System".