current position:Home>[lecture hall] what makes AMG have the courage to give up the big V8? Axial flux motor!

[lecture hall] what makes AMG have the courage to give up the big V8? Axial flux motor!

2021-08-27 05:33:08 Wechat automobile

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The next generation C63 Will cancel the big V8 The engine , Change it to 2.0T Hybrid power system with four cylinder engine and electric motor , This is no longer news ,AMG The hybrid system will also be used in the top vehicle lines of , Deserve to go up 73e The tail standard .

What keeps the engine with large displacement , Violent output , It can be called the German muscle car AMG Embarked on the road of electrification ?

discharge ? Part of the , But not all . After all AMG The share of is quite small compared with Mercedes Benz as a whole , Energy conservation and emission reduction work will not let the performance of the brand play a role AMG Having to make the decision to cut the cylinder and break the arm , Then the answer is clear , It's performance , Give Way AMG Actively embrace electrification .

Look again. 7 month 22 Mercedes of the day • The latest electrification schedule released by Mercedes Benz group , from “ Electric first ” towards “ Fully electric ” The transformation of . Except from 2025 From the year onwards , All newly launched vehicle platform architectures will be pure electric architectures , Every model produced by the company will have a pure electric alternative , To 2030 Complete electrification by the end of the year, in addition to these group strategies , There is also an additional mention of an acquisition :

Through vertical integration and acquisition of ultra-high performance axial flux motor experts YASA, Improve the efficiency of electric drive system .

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this home YASA Who is holy , Why mention the axial flux motor again , What magic does it have , Give Way AMG With enough confidence to embrace electrification ?

—— Ferrari's first plug-in hybrid flagship sports car SF90 The reason of the hybrid system supplier is not sufficient ?

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Axial flux is relative to radial flux , At present, most of the motors used in electric vehicles are radial flux motors , The magnetic flux direction generated by the motor winding is perpendicular to the motor axis , It's radial . Axial flux refers to the flux direction generated by the stator winding is parallel to the motor axis . How to understand , Let's briefly review the knowledge of physics in high school .

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Basic structure of motor


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We know , The core structure of the motor includes the stator 、 A coil wound around a stator to produce a magnetic field 、 rotor 、 Bearings and shafts . The shape is generally cylindrical , Its internal section structure can be seen in the figure .

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Generally, the stator of vehicle motor is at the outermost side , Long like this , It's a big iron ring , There are teeth and grooves on it , The energized coil is wound around these teeth :

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See more clearly :

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According to our high school physics knowledge , The direction of the magnetic field generated by the energized coil is judged by the right-hand spiral rule :

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The winding mode of this coil winding will lead to from the center of the circle to the outside of the circle , Radial magnetic field .

The position of the teeth on the stator of the axial flux motor and the winding mode of the coil are perpendicular to the radial flux motor , Its stator looks like this :

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After winding the coil, it looks like this :

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The direction of the magnetic field generated by such a coil is parallel to the axis of the cylinder of the motor , Therefore, it is called axial flux motor . Because compared with radial flux motor , Axial flux motor shorter , Looks like a plate , Because it is also called disc motor .

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Advantages and disadvantages of axial flux motor

Let's take a look at the stator and rotor pole diagram of radial flux motor and axial flux motor , On the left is the radial flux motor , On the right is the axial flux motor .

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Obviously , Under the condition of the same external dimensions , The core advantage of axial flux motor is the larger diameter of rotor , It rotates along the stator , Instead of rotating inside the stator . Torque equals force times radius , Axial flux motor can obtain greater torque under the same force . This means that for using the same amount of permanent magnet and copper winding material , Axial flux motor can output more torque .

Compared with the traditional radial motor, axial flux motor can provide 30% Torque density advantage .

and ,YASA The motor topology also removes the stator yoke , This is also YASA The origin of the name ‘Yokeless And Segmented Armature’, This reduces up to 80% Stator iron mass . This innovation provides more than 30% Power density advantages and 5% Mileage advantage .

As opposed to high performance , It is the high cost and high manufacturing difficulty of axial flux motor , This restricts the application of axial flux motor . Even as early as 1821 The first motor invented by Faraday in was the axial flux motor , The radial flux motor, which was born later, has also been fully developed .

As can be seen from the structure diagram , Unlike radial flux motors , The stator and rotor of axial flux motor will attract each other , Generate axial force . We all know that metals are not resistant to compression , Axial force is what the motor fears most , Light increases friction , Increase vibration , If it is serious, the bearing will be dislocated and fall off , The shaft breaking machine is destroyed . therefore , Axial flux motor generally adopts double stators on both sides , Design of intermediate single rotor , There are also single stator and double rotors , Multi disc and other schemes to counteract the axial force .

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secondly , The gap between stator and rotor is called air gap , It is an essential part of the motor magnetic circuit . The axial flux rotor is laid flat on the stator , The air gap area is significantly larger . Check the flatness of its surface , The gap uniformity is very high .

This means manufacturing accuracy 、 The requirement of assembly accuracy is very high , It brings very high manufacturing cost , With very low production flexibility .

High manufacturing difficulty also leads to insufficient large-scale production of axial flux motor , Small market capacity , Matching parts can't keep up . Not only the axial flux motor itself , After connecting the drive shaft , The axial movement caused by the rear end load will also seriously affect the magnetic balance between the rotor and stator of the axial flux motor , Once you break through the tipping point , The rotor is adsorbed to the stator , It would be a disaster .

These disadvantages in turn lead to difficulties in the application of axial flux motor , As a result, there are few practitioners in this field , Low product maturity , Lack of R & D verification system and other problems . Under the cycle , It is difficult to compete with ordinary radial flux motor .

therefore , At present, very few applications of axial flux motor are motor racing 、 High performance sports car, which requires high volume and weight but is not sensitive to cost .

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Why does Mercedes Benz value axial flux motor

As a high-performance brand of Mercedes Benz , Always with large displacement , The image of German muscle car shows people AMG It is impossible to abandon the internal combustion engine for a long time , Its route to embrace electrification is hybrid . So what kind of hybrid structure is suitable for AMG Well ?

Toyota's power split scheme ? no way , This structure focuses more on the adjustment of motor to engine working conditions , That is, economy , The output of the engine and the two motors are involved with each other , Power cannot be fully utilized . The engine 100kW, The motor 100kW, The total output may be only 150kW. This feature is completely unsuitable for AMG.

Empathy , Honda i-MMD, BYD DM-i Such a clutch switching hybrid scheme is rejected for the same reason : Emphasis on economy , Not powerful enough .

P4 programme ,AMG No emphasis on 4WD capability , On the contrary, the latter drive is the main , veto .

Then put aside those who are not suitable for forced mixing P0、P1 programme , That's all P2 and P3 Plan . and P3 The scheme is not suitable for vertical layout , Sum up ,P2 yes AMG The most suitable hybrid scheme , The engine and motor are output in parallel , Powerful .

Review the P2 programme , It means that the motor is installed between the engine and the gearbox , After flywheel , Connect to the transmission housing .

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I can't find the picture of Mercedes Benz , Audi's come and make do , Here, praise Audi , In the official map, the solution of this structure is quite comprehensive , You can see , Because the vertical layout , The size of the engine and the gearbox itself is long , Therefore, the size of the motor inserted in the middle is extremely limited . The thin characteristic of axial flux motor is particularly suitable .

and , because P2 The structure motor is in the front section of the gearbox , You can enjoy the effect of reducing the speed and increasing the torque of the transmission , This also makes up for the high moment of inertia caused by the large rotor diameter of axial flux motor , The disadvantage of low maximum speed .

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Because of structural differences , Compared with the radial flux motor, the axial flux motor has smaller output size , Larger torque in the same size . In particular, its axial size is small , thin . Mercedes Benz pays attention to this feature of axial flux motor . As an early application object of axial flux motor ,AMG It also meets the requirements of weight and volume , And not sensitive to cost .

In the era of the unification of radial flux motors , Why axial flux motor can emerge suddenly , have a look DOE( The U.S. Department of energy )2017 Electric drive system of automobile published in 2025 The description in the annual R & D plan may find the answer :

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You can see , In the planning , Electric drive system , Including motor and motor controller , stay 2020 Year to 2025 The most important index for the development of component technology in the year is the volume specific power density . in other words , The motor needs to be small , Even higher power . This is exactly the specialty of axial flux motor .

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Mercedes Benz acquired YASA Nor will it just be AMG Special supplies for . With AMG Bear the market development and development cost of axial motor in the early stage , Through the most difficult moments of the early days , With the increase of scale , Establishment of upstream and downstream supply chain , Axial flux motor will also gradually reduce the cost .

When the , Its high efficiency , High power density , And the outstanding characteristics of high volume specific power density will provide great help on the road of Mercedes Benz electrification .


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