Hybrid Drivetrain Separation Clutch Control for Speed Differential Management
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Solution Overview
Problem
In hybrid drive trains, purely electric driving modes can lead to high differential speeds at the separation clutch, potentially causing mechanical damage and rotor over-speeding, especially during downhill driving when the electric machine cannot absorb enough power, and this is not effectively managed by existing methods.
Innovation Solution
Engaging the separation clutch when high differential speeds are anticipated, connecting the combustion engine to the drive train to apply drag torque and reduce rotational speed differences, thereby protecting the clutch and rotor, and ensuring transmission functionality by counteracting mass inertia torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the separation clutch remains disengaged during purely electric driving mode, then the electric machine can operate independently without combustion engine interference, but the differential speed at the clutch can reach supercritical values causing mechanical damage
Solution Approach 1:
The control method applies preliminary anti-action by engaging the separation clutch before the differential speed reaches the supercritical limit. The control unit monitors the differential speed between input and output shafts and proactively engages the clutch when approaching critical values, preventing the harmful high-speed differential condition from occurring in the first place
Solution Approach 2:
The separation clutch acts as an intermediary element that can be strategically engaged to limit the differential speed between the input and output shafts. By positioning the clutch between these shafts and controlling its engagement state, the system mediates the speed difference without requiring direct modification of the electric machine or transmission components
2Reliability
If the separation clutch is engaged to limit differential speed, then mechanical damage is prevented, but the combustion engine is connected to the drive train reducing purely electric operation efficiency
Solution Approach 1:
The system dynamically adjusts the separation clutch engagement state based on real-time operating conditions. The clutch is engaged only when and where needed to prevent supercritical differential speeds, and disengaged during normal purely electric operation. This dynamic control allows the system to maintain high electric driving efficiency while providing protective engagement when safety requires
Solution Approach 2:
The control method monitors and responds to changes in operational parameters such as differential speed, vehicle deceleration rate, and electric machine load. By detecting when parameters approach critical thresholds (e.g., differential speed approaching supercritical values), the system changes the clutch engagement parameter to prevent damage, then returns to disengaged state when parameters normalize
3Power
If the electric machine operates at high speeds during strong acceleration, then power delivery is improved, but the rotor may exceed maximum permissible peripheral speed causing permanent magnet detachment
Solution Approach 1:
The control unit implements feedback control by continuously monitoring the rotational speed of the electric machine and the differential speed across the separation clutch. When the rotor speed approaches the maximum permissible peripheral speed threshold, the system receives feedback and responds by engaging the separation clutch, which limits further speed increase and protects the rotor from structural failure
4Reliability
If the separation clutch is designed with high speed capacity, then rotor over-speeding is prevented, but the clutch size and complexity increase
Solution Approach 1:
The speed protection function is segmented between two components: the separation clutch handles speed limitation by being engaged when differential speed becomes excessive, while the one-way clutch handles rotor over-speed protection by allowing free wheeling when rotor speed exceeds the maximum permissible value. This segmentation allows each clutch to be designed for its specific function rather than requiring one complex clutch to handle all speed protection scenarios
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 method effectively reduces rotational speed differences at the separation clutch, preventing mechanical damage and rotor over-speeding, while maintaining transmission functionality, especially during downhill driving and strong acceleration scenarios, and allows for controlled deceleration based on defined conditions.
Implementation Method 1
The separation clutch is designed as a friction clutch. By engaging the separation clutch, the combustion engine is connected with the drive train so that the drag torque of the combustion engine decelerates the drive train.
Implementation Method 2
By engaging the separation clutch, the combustion engine is connected to the drive train, so that the drag torque of the combustion engine decelerates the drive train. This deceleration can prevent the rotor from rotating at impermissibly high rotational speeds.
Implementation Method 3
If the calculated rotational speed difference is larger than a limit value, the combustion engine is started. By starting the combustion engine, the rotational speed at the input side of the separation clutch is increased so that the created rotational speed difference is reduced when the gear is engaged.
Data Source
AI summary
A method for operating a hybrid drive train of a motor vehicle (X) which has a combustion engine (VM), a transmission (G), an electric machine (EM), as well as a separation clutch (KO) positioned between the combustion engine (VM) and the electric machine (EM). During a purely electric drive operation in which the separation clutch (KO) is disengaged and, when a gear is selected in the transmission (G), and during expectation, reaching, or exceeding a rotational speed difference of the separation clutch (KO) is larger or equal to a limit value, and/or in an expectation, reaching, or exceeding a rotational speed limit of the electric machine (EM), the separation clutch (KO) is engaged. Further, an electronic control unit (ECU) executes the method and a motor vehicle (X) having such an electronic control unit (ECU).