Hybrid Driveline Engine Start Using Dual Planetary Gear Torque Split
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Solution Overview
Problem
Hybrid powertrains face challenges in efficiently starting a combustion engine while minimizing fuel consumption and avoiding torque interruptions, particularly due to limitations in torque transfer from electrical machines to the transmission, leading to increased weight, complexity, and reduced reliability.
Innovation Solution
The method involves using a gearbox with interconnected planetary gears and electrical machines to achieve desired torque in the output shaft, allowing for efficient combustion engine start-up by balancing torque between the electrical machines and disconnecting components to avoid torque interruptions, utilizing a locking mechanism and coupling devices for compact and reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional clutch mechanism is used to disconnect the combustion engine during shifting, then torque interruption is avoided, but the device complexity and weight increase
Solution Approach 1:
The patent removes the conventional clutch mechanism from the hybrid powertrain by utilizing the planetary gear set's inherent torque transfer characteristics. The electrical machine and combustion engine are directly coupled through the planetary gears, eliminating the need for a separate clutch device while maintaining smooth torque transfer during shifting operations.
Solution Approach 2:
The planetary gear set serves multiple functions: it acts as both the transmission mechanism and the coupling device between the combustion engine and electrical machine. This multi-functional design replaces the conventional clutch's torque interruption function while integrating seamlessly with the hybrid powertrain's existing components.
2Power
If the electrical machine's torque is increased to match the combustion engine's maximum torque, then the highest torque transfer capability is improved, but the electrical machine's size and weight increase
Solution Approach 1:
The patent utilizes the planetary gear set's variable gear ratios to transform the electrical machine's torque output. By changing the gear ratio parameters, the system can achieve high torque multiplication at the output shaft without requiring the electrical machine itself to be oversized, thus maintaining a compact and lightweight design.
Solution Approach 2:
The planetary gear set acts as a torque amplifier that counterbalances the limitation of the electrical machine's maximum torque. The gear mechanism provides mechanical advantage, allowing a smaller, lighter electrical machine to deliver the same effective torque as a larger one would provide directly.
3Ease of operation
If separate devices are added to eliminate torque interruption during gear shifts, then the perception of stepless gear shifts is improved, but the device complexity and manufacturing costs increase
Solution Approach 1:
The patent combines the gear shifting function with the existing planetary gear set structure. The electrical machine's rotor is directly connected to the planetary gear's sun wheel or ring gear, allowing seamless torque transfer during shifts without requiring separate interruption-prevention devices. This integration maintains stepless shifting perception while simplifying the overall transmission system.
4Loss of time
If the combustion engine is started quickly with high torque, then the engine start-up time is reduced, but the fuel consumption and mechanical stress increase
Solution Approach 1:
The system prepares for engine start-up by pre-positioning the planetary gear set and electrical machine in the optimal configuration. The electrical machine can be pre-charged or pre-positioned to assist the combustion engine during start-up, reducing the peak torque requirement and allowing for a faster, more fuel-efficient start-up sequence.
Solution Approach 2:
The planetary gear set acts as an intermediary mechanism that mediates between the electrical machine and combustion engine during start-up. It allows for smooth torque transfer and can distribute the start-up load, reducing the peak fuel consumption and mechanical stress while maintaining quick start-up response.
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 approach enables efficient and reliable start-up of the combustion engine, reduces weight and manufacturing costs, and enhances the reliability of the powertrain by eliminating the need for conventional clutches and allowing for compact design, while maintaining high torque transfer capabilities.
Implementation Method 1
The planetary gearbox usually comprises three components, which are rotatably arranged in relation to each other, namely a sun wheel, a planetary wheel carrier and an internal ring gear. With knowledge about the number of cogs in the sun wheel and the internal ring gear, the mutual speeds of the three components may be determined during operation.
Implementation Method 2
When the vehicle is braked, the electrical machine generates electric power, which is stored in the energy storage device. This is usually referred to as regenerative braking, which entails that the vehicle is decelerated with the help of the electrical machine and the combustion engine.
Implementation Method 3
The electrical machine is equipped with at least one energy storage device, such as an electro-chemical energy storage device, for storage of electric power
Data Source
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AI summary
The invention relates to a method to start a combustion engine (4) in a hybrid powertrain (3), comprising a gearbox (2) with an input shaft (8) and an output shaft (20); a first planetary gear (10), connected to the input shaft (8) and a first main shaft (34); a second planetary gear (12), connected to the first planetary gear (10) and a second main shaft (36); a first electrical machine (14), connected to the first planetary gear (10); a second electrical machine (16), connected to the second planetary gear (12); at least one gear pair (G1, 60, 72), connected with the first main shaft (34), and therefore with the first planetary gear (10) and the output shaft (20); and at least one gear pair (G2, 66, 78), connected with the second main shaft (36), and therefore with the second planetary gear (12) and the output shaft (20), wherein the combustion engine (4), via the input shaft (8), is connected with a first planetary wheel carrier (50), arranged in the first planetary gear (10), and wherein the second main shaft (36) is connected with a planetary wheel carrier (51) arranged in the second planetary gear (12). The method comprises the steps: a) determining a desired torque (ΤDrv) in the output shaft (20); b) determining a torque (TFlywheel) in an output shaft (97) of the combustion engine (4), required to start the combustion engine (4) and c) controlling the first electrical machine (14) and the second electrical ma- chine (16), in such a way that the desired torque (TDrv) in the output shaft (20) and the torque (TFlywheel) required in the output shaft (97) of the combustion engine (4) is achieved. The invention also relates to a computer program (P) to start a combustion engine (4) and a computer program product comprising program code for an electronic control device (48) or another computer (53) to implement the method according to the invention.