Hybrid Driveline Engine Start Using Locked Planetary Gears
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Solution Overview
Problem
Conventional hybrid powertrains face challenges in efficiently starting the combustion engine when the output shaft is at a standstill, particularly in scenarios where fuel savings and avoiding exhaust system cooling are desired, and are limited by the torque capabilities of the electrical machine, leading to inefficiencies and increased component wear.
Innovation Solution
The method involves connecting the rotatable components of the planetary gears, controlling the electrical machines to achieve synchronous rotational speeds, and using coupling devices to lock or unlock the sun wheels and planetary wheel carriers, allowing for efficient start-up of the combustion engine without torque interruption, thereby bypassing the need for a conventional clutch mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional clutch mechanism is used to disconnect the gearbox input shaft from the combustion engine during shifting, then gear shifting is possible, but the clutch discs experience heating and wear, and fuel consumption increases
Solution Approach 1:
The patent extracts and eliminates the conventional clutch mechanism from the hybrid powertrain by utilizing the planetary gear set's inherent ability to disconnect the combustion engine from the gearbox input shaft during shifting operations. The planetary gear arrangement allows the combustion engine to be decoupled without requiring a separate clutch device, thereby removing the source of clutch disc wear and heating.
Solution Approach 2:
The planetary gear set serves multiple functions: it provides gear ratio changes, enables combustion engine disconnection during shifting, and facilitates torque distribution between the combustion engine and electrical machine. This multi-functionality replaces what would traditionally require separate clutch mechanisms, reducing component wear and improving reliability.
2Power
If the electrical machine's torque is limited by its maximum capability, then the combustion engine's maximum torque transfer is restricted, but adding a conventional clutch to overcome this limitation increases device complexity and weight
Solution Approach 1:
The patent merges the clutch function with the planetary gear set, combining the gear changing mechanism and the combustion engine disconnection function into a single integrated system. This eliminates the need for a separate clutch mechanism, reducing device complexity and weight while maintaining the ability to transfer maximum torque from both the combustion engine and electrical machine to the gearbox input shaft.
Solution Approach 2:
The planetary gear set is designed to perform multiple functions simultaneously: providing gear ratios, enabling combustion engine disconnection, and facilitating maximum torque transfer from both drive units. This universal design eliminates the need for additional clutch mechanisms, reducing overall system complexity while maintaining full torque transfer capability.
3Use of energy by moving object
If the combustion engine is shut off to save fuel during vehicle standstill, then fuel consumption decreases, but the engine exhaust system cools down, requiring rapid engine restart capability
Solution Approach 1:
The patent implements preliminary action by pre-heating the exhaust system through controlled electrical machine operation before shutting off the combustion engine. The electrical machine can generate heat that is transferred to the exhaust system, ensuring it remains at operating temperature even when the engine is off, thus enabling fuel savings without compromising exhaust system performance.
4Device complexity
If a planetary gear set is used to connect the combustion engine, electrical machine, and gearbox, then the conventional clutch is eliminated, but the torque transfer is limited by the electrical machine's maximum torque capability
Solution Approach 1:
The patent applies dynamics by making the planetary gear set's configuration variable rather than fixed. The system can dynamically adjust the connection between the combustion engine, electrical machine, and gearbox based on operating conditions. This dynamic configuration allows the system to overcome the electrical machine's torque limitations by optimally distributing torque through different planetary gear arrangements, eliminating the need for a clutch while maintaining full torque transfer capability.
Data Source
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AI summary
The invention relates to a method to start a combustion engine (4) in a hybrid powertrain, comprising a gearbox with an input shaft (8) and an output shaft (20); which combustion engine is connected to the input shaft (8); a first planetary gear (10), which is connected to the input shaft (8): a second planetary gear (12), connected to the first planetary gear (10); 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 (Gl, 60, 72), connected with the first planetary gear (10) and the output shaft (20); and at least one gear pair (G2, 66, 78), connected with the second planetary gear (12) and the output shaft (20). The method comprises the steps: a) connecting the rotatable components (32, 51) of the second planetary gear (12) with each other by connecting, via a second coupling device 58, a second sun wheel 32 arranged in the second planetary gear 12 and a second planetary wheel carrier 51 with each other, and b) activating the first electrical machine (14) and the second electrical machine (16), so that the combustion engine (4) starts. The invention also relates to a vehicle (1) with a hybrid powertrain (3), 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.