Hollow Rotor Shaft Cooling With Jet Supply to Reduce Leakage
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Solution Overview
Problem
Electrical machines with internal rotor cooling face issues of asymmetrical oil distribution and leakage due to the introduction of cooling fluid from one axial side, leading to increased drag torque and leakage losses, especially at higher speeds.
Innovation Solution
A jet apparatus is fixed to the housing to supply cooling fluid to the hollow rotor shaft, utilizing a combination of driving and suction flows through outer and inner nozzles to enhance flow symmetry and reduce leakage, with the fluid being directed into the rotor laminated core through radially inclined outlet openings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a cooling fluid is supplied axially to the hollow rotor shaft from one axial side, then the cooling fluid can be introduced into the rotor, but asymmetrical oil distribution occurs at the hollow rotor shaft outlets
Solution Approach 1:
The single axial supply is segmented into multiple supply points: one axial supply at the inlet end and additional radial supplies at intermediate locations. This segmentation allows symmetric distribution of cooling fluid to outlets located at opposite ends of the hollow rotor shaft, eliminating the asymmetry caused by single-sided axial supply.
2Speed
If a gap is provided between the hollow rotor shaft and the supply line to allow rotation, then rotation is enabled, but leakage increases with increasing rotational speed
Solution Approach 1:
A centrifugal pump is introduced as an intermediary device within the hollow rotor shaft. This pump actively transports cooling fluid from the inlet toward the outlets, counteracting the leakage through the gap between the shaft and supply line. The pump maintains positive pressure and flow direction, preventing leakage losses that would otherwise increase with rotational speed.
3Speed
If a gap is provided between the hollow rotor shaft and the supply line, then rotation is enabled, but shear flows in the gap generate detrimental drag torque
Solution Approach 1:
The centrifugal pump acts as an intermediary that establishes controlled flow paths and pressure gradients, minimizing uncontrolled shear flows in the gap between the hollow rotor shaft and supply line. By maintaining positive pressure and directing flow through defined paths, the pump reduces the magnitude of shear flows that generate drag torque, thereby reducing the detrimental effect on rotational speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration increases cooling fluid flow by a factor of two to three, reduces leakage, and ensures symmetrical distribution within the hollow rotor shaft, minimizing drag torque and enhancing cooling efficiency.
Implementation Method 1
DE 10 2018 101 641 B3 discloses a method for cooling the hollow rotor shaft of an electric motor, wherein a cooling liquid transport is effected by acting centrifugal forces
Implementation Method 2
a cooling fluid supplied to the tube can be guided into the interior space of the hollow rotor shaft
Data Source
Figure 1
Figure 2
AI summary
To provide an electric machine with a hollow rotor shaft that allows for increased flow of a cooling fluid and reduces leakage losses, an electric machine (100) comprising a housing (10), a stator (11), and a rotor (12) is proposed, wherein the rotor (12) comprises a hollow rotor shaft (13) with an interior space (15), wherein a tube (16) is arranged in the interior space (15) and is fixed to rotation with the hollow rotor shaft (13), wherein the hollow rotor shaft (13) has an inlet (17) through which a cooling fluid can be supplied to the tube (16), wherein the tube (16) has at least one outlet opening (18, 18a, 18b) through which a cooling fluid supplied to the tube (16) can be directed into the interior space (15) of the hollow rotor shaft (13), and wherein a supply device (19) is provided with which a cooling fluid is supplied to the inlet (17) of the The rotor hollow shaft (13) can be supplied, wherein it is provided thatthat the feed device (19) is a fixedly arranged jet apparatus (20).