It has to withstand a 50G shock - insight into eLION development

Deep dive into drive technology

The development of electric drive systems for mobile work machines presents designers with particular challenges. In the podcast "Industry rethought", Dr. Thomas Finken from Bosch Rexroth explains the background.

In addition to the traditional requirements for performance and efficiency, resistance to extreme environmental conditions such as vibration and shock also plays a key role. A critical point is the mechanical design of the drives, which have to withstand much tougher conditions in mobile machines than in stationary applications. Typical factory motors rarely have to withstand extreme loads such as immersion in water or strong vibrations. However, this is the norm for mobile machines, such as those used in quarries or on construction sites. "This presented us with challenges at the beginning, but we were able to solve them quickly," explains Finken.

The use of digital twins, i.e. the simulation of the machine before it is physically built, enables weak points to be identified and eliminated in advance. According to Finken, resonances caused by vibrations and shock loads in particular can place a great deal of strain on the system. "Precise simulations enable these problems to be identified and eliminated at an early stage," explains the engineer.

One of the eLION team's greatest innovations in development is the ability to design motors to provide high torque at low speeds while remaining efficient at high speeds. This flexibility is crucial for the various applications of mobile machines. However, the electromagnetic design of such drives leads to a fundamental conflict of objectives for the engineers. To achieve high torque, either the magnetic flux in the rotor or the current in the stator must be increased. The magnetic flux can be increased by using more permanent magnets in the rotor. However, a stronger magnetic flux at high speeds also leads to higher mutual induction voltages in the system. This means that the voltage threshold of the overall system is reached more quickly, which in turn limits the speed. To get around this problem, the engineers rely on what is known as field weakening. This involves feeding a current into the stator, which creates a magnetic field that counteracts the rotor field. This allows the voltage to be kept within the permissible limits while the speed continues to increase.

In order to meet the different requirements in the mobile working world, Bosch Rexroth follows a modular approach in the development of its drive systems. This allows drives to be adapted depending on the application. For example, special heavy-duty housings can be used for particularly stress-intensive applications such as quarries, while a lighter standard version is sufficient for less demanding applications.

Modular concepts are also used inside the motors, allowing the electromagnetic components to be adapted depending on the required power and torque. This modular approach ensures that customers receive an optimized solution for every application.

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