Integrated design of three-in-one electric drive system

The electric drive three-in-one is the standard configuration for entry-level passenger cars. Without the three-in-one, it is difficult to knock on the door of the passenger car factory. Next, let's take a look at the living environment of our industry.

In April 2020, the production and sales of new energy vehicles reached 80,000 and 72,000 respectively, up 31.6% and 9.7% month-on-month, and down 22.1% and 26.5% year-on-year. The year-on-year decline narrowed by 34.8 percentage points and 26.7 percentage points respectively from the previous month.

From January to April, the production and sales of new energy vehicles were both 205,000 units, and the cumulative sales of new energy passenger cars reached 155,000 units, accounting for 75.6% of the new energy vehicle sales market share.

It can be seen that the industry's cold winter is fading, and as market confidence recovers, we will eventually bathe in the warm sunshine of midsummer. So, let's focus on our work and see how to make a three-in-one electric drive assembly.

Advantages of three-in-one electric drive integration

①Adaptability:

The three-in-one electric drive requires top-level design and planning from the vehicle platform, which can significantly shorten the development cycle and meet the diverse needs of different customers at a lower cost.

② Low cost:

Reduce the number of high-voltage wires, connectors and other components inside the powertrain, lower the mass of the assembly, and save on connector and wiring harness costs.

③ Save space:

The motor, inverter, reducer and power transmission module are integrated in a relatively small housing, freeing up space and facilitating the overall vehicle layout.

④High energy efficiency:

Reducing or shortening the connection wiring between the inverter and the motor reduces power loss at the connection point and improves the efficiency of the drive system.

⑤Easy to maintain:

Reduce the number of suppliers; simplify the assembly of the main engine factory and improve the product qualification rate. Although the product is complex, difficult to disassemble and assemble, and inconvenient to repair, the efficiency is higher without the buck-passing of multiple suppliers, so it is easier to maintain.

⑥High reliability:

The common housing and coaxial design greatly improve the NVH performance of the whole machine, thereby improving the reliability of the assembly.

Disadvantages of three-in-one electric drive integration

①NVH challenges brought by high speed;

②Cooling concept and bearing life;

③EMC complexity increases;

④ The difficulty of cross-departmental component development collaboration increases.

The main three-in-one configurations are commonly seen as shown above, among which the first and fifth types are more popular in China.

Platform design

To do three-in-one, we must have a top-level design concept and plan from the vehicle platform, so as to extend the product life cycle and reduce the cost of vehicle development.

Modular design

According to the power requirements of the vehicle model planning, the Audi e-tron electric drive system adopts a modular development strategy. The arrangement and combination of various modules have resulted in a rich product line. This not only speeds up the R&D progress but also saves development costs, providing a perfect interpretation of modular development.

The above is the system-level module design, and the following is the vehicle-level module design, which is the electric drive axle module from ZF.

Example of three-in-one housing integrated design route

BMW's fifth-generation electric drive system has achieved a design in which the motor, electronic control, and reducer share a common housing, and is one of the most popular solutions at present. Let's take a look at the evolution of various technical solutions.

From solution ⑧, we can see that if the product strength of the components is not fully verified, hasty integration will lose all the economic benefits brought by integration due to the high system failure rate. As the saying goes, too much is as bad as too little, so stop when you are satisfied. Therefore, integration depends on whether the technology and equipment you can control can meet the design needs. The most suitable one is the best. The company where I first worked made AMTs for three types of vehicles, but they all failed in the durability test.

Summarize the three-in-one design techniques or solutions

Let’s take a look at how BYD does it:

The motor and electric control terminals are directly connected, eliminating the three-phase line and reducing costs.

The motor and electric control waterway are directly connected, eliminating water pipes and reducing costs.

The motor rotor shaft and the reducer input shaft share the same shaft, which improves coaxiality and reduces noise.

The motor housing and reducer housing are shared, which reduces costs, improves coaxiality, and increases assembly accuracy.

Assembly effect diagram

Example of Founder Motor Three-in-One Structure Design

The motor, reducer and controller are three-in-one, with a highly integrated design;

Modular combination design, the motor, reducer and two-in-one module are on the same platform;

Simplify high-voltage cables, connectors and other components between motors and controllers;

The motor shaft and the reducer input shaft are integrated into one, reducing the bearing support;

The reducer housing and the motor housing are integrated into one.

The motor end cover and the controller housing are integrated into one;

The powertrain adopts a parallel structure;

Adopt bevel gear structure differential;

Mechanical odometer output (optional);

Electronic parking mechanism (optional);

Integrated vehicle control unit (optional);

Integrated electronic parking brake system (optional).

The products of the above two companies have been put into mass production and have gained a good reputation in the market, proving that the structural solution is feasible and worth learning and promoting.

Next, let’s take a look at the electric drive product design of the international giant Audi e-tron:

APA250

AKA320

APA250 rotor shaft waterway

Audi e-tron 3-in-1 summary

1. The parallel axis three-in-one system of Audi e-tron uses a common housing solution for the motor and reducer. The motor controller is a separate module that shares a connection port with the motor housing and is directly connected to the copper busbar.

2. The motor controller can be used as a universal module in four different product models;

3. The rotor uses hollow shaft technology, which can be fully cooled while being lightweight;

4. The biggest highlight is undoubtedly the ubiquitous and sufficient cooling of the AC asynchronous motor. The water passes through the motor controller, bearing seat plate, rotor shaft, stator housing, and the opposite bearing seat plate before flowing out to the radiator;

5. Extensive use of planetary gear reducers and external-external meshing double-star planetary gear differentials, with compact and regular structure;

6. Audi uses an electronic differential instead of a mechanical differential in its rear axle dual-motor solution, which improves transmission efficiency and reduces hardware costs.

GKN three-in-one electric drive explosion diagram

Mercedes-Benz EQ3 electric drive explosion diagram

The solutions of these two are highly consistent with the three-in-one solution popular in China. Juyi, SAIC, Jingjin and others all have similar electric drive assembly products.

At present, most powertrains are equipped with single-speed ratio reducers. In some working conditions, the motor cannot work in the economic zone, resulting in high system energy consumption and low driving range. A gearbox with more than 2 gears can solve this problem well and provide more impressive power performance.

Technical route of EV two-speed solution

Summarize the possible trends of future integration

Integration of multiple thermal management systems;

Large-scale set topology circuit integration;

Multifunctional composite structure design and process integration;

Reduce physical connections and reduce costs;

As cars become more intelligent, some mechanical parts are eliminated, such as mechanical differentials.

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