The epitome of racing feeling in everyday traffic starts a new round. 35 years after the debut of the first BMW M3, BMW M GmbH presents the latest generation of its high-performance automobiles in the premium mid-size segment. Time to introduce the two new vehicles. In the #M3M4explained series, the developers have the floor.
Mastering curves! Dominik keeps an eye on aspects such as track, stability, or axle kinematics in his considerations. The BMW M developer is responsible for the engineering and integration of the rear axle. In the video, Dominik introduces the rear axle transmission and explains important details.
BMW M ENTHUSIASTS ASK, BMW M EXPERTS ANSWER.
What is the weight of the differential?
Dominik: The differential weighs 43.5 kg.
Why does the differential need an electric motor?
The electric motor controls the pressure on the friction plates. In contrast to passive systems, we can actively influence the locking torque.
When there is permanent variation of the characteristic of the differential (road, driver, weather etc.): is the behaviour of the car still foreseeable for the driver?
Yes, the vehicle's behaviour is designed to be always foreseeable for the driver. With the same circumstances, the car will behave in exactly the same way again.
Is there wear? How long is the lifetime of the differential?
Careful break-in period, initial oil service and further oil changes depending on actual use ensure the differential will last the car's entire life span.
How do you compute an efficiency of 98 %?
It was measured on a test rig by comparing the torque difference between input and output.
Where is the heat coming mainly from: from the differential or from the transmission itself?
The heat loss is mainly a result of the friction within the transmission itself. The diff lock only contributes a small amount.
Is there still a need of a 5.000 km run in like in the past?
The recommended break-in period lasts 2.000 km followed by a service where the rear differential oil is changed. Afterwards, it is recommended to increase speed levels continuously.
How long does the oil in the rear axle transmission last?
At 2.000 km, after breaking in the car, a first oil change is required. Further oil changes depend on the actual use case. Please, refer to your dealer with regards to maintenance programs.
Why does it need an adapter plate?
The adapter plate provides NVH (noise, vibration, harshness) decoupling of the differential towards the rear axle subframe which is rigidly mounted to the car body.
Why are there output shafts with different diameters? I don’t understand the point – how does it work?
The two rear output shafts are designed with different stiffness resulting in an optimized harmonic behaviour of both rear wheels and thereby increasing traction.
How old are you?
I am 33 years old.
What did you study?
I majored in mechanical engineering (TU Munich).
What is your favorite classic BMW?
This would be the legendary BMW M1 for me.
What is your favorite engine?
I always admired the S70 engine - the McLaren F1's V12 engine.
What car do you drive?
I currently own a BMW M140i F20 with manual transmission.
