Hybrid Power Split Device Torque Control for Engine Start
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Solution Overview
Problem
Hybrid vehicles face difficulties in starting the internal combustion engine due to the direct coupling of the electric motor with the crankshaft, leading to increased energy consumption and decreased driveability, and the use of planetary gear speed reducers results in inefficient engine operation at low speeds.
Innovation Solution
A power transmission apparatus with a power split device comprising three rotors that split power among an electric rotating machine, an internal combustion engine, and a driven wheel, featuring a torque transmission control mechanism, a connecting mechanism, and a speed variator, allowing for controlled torque transmission and speed adjustment to minimize mechanical vibrations and optimize engine efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric motor is directly coupled to the crankshaft to start the internal combustion engine, then the engine can be started, but torque load is exerted on the electric motor when the engine is not fired, increasing energy consumption
Solution Approach 1:
A clutch mechanism is introduced as an intermediary between the electric motor and the crankshaft. This clutch selectively engages or disengages the mechanical connection, allowing the motor to start the engine without bearing continuous torque load. The clutch acts as a mediator that permits torque transmission only when needed for engine starting, thereby resolving the contradiction between ensuring startability and reducing energy consumption.
2Reliability
If the electric motor is directly coupled to the crankshaft, then the engine can be started, but torque pulsation occurs during engine start-up, decreasing driveability
Solution Approach 1:
The clutch mechanism serves as an intermediary that smooths the torque transmission during engine start-up. By controlling the engagement and disengagement timing, the clutch mitigates torque pulsations that would otherwise be directly transmitted to the motor and vehicle drivetrain, thereby maintaining driveability while ensuring reliable engine starting.
3Reliability
If a planetary gear speed reducer is used to split power, then the engine can be started by the carrier rotation, but the engine runs at low speed after start-up, reducing engine efficiency
Solution Approach 1:
The system dynamically switches between different power transmission paths. Initially, the planetary gear speed reducer is engaged to start the engine by rotating the carrier. After engine start-up, the system transitions to a direct power transmission path that allows the engine to operate at higher speeds within its efficient operating range, thereby resolving the contradiction between startability and operational efficiency.
Solution Approach 2:
The power transmission system is segmented into multiple paths: one through the planetary gear speed reducer for engine starting, and another direct path for post-start operation. This segmentation allows the system to optimize for different operational phases, using the appropriate transmission path for each phase to maintain both startability and engine efficiency.
Data Source
AI summary
A power transmission apparatus for a vehicle which includes a first, a second, and a third rotor which split power among a motor-generator, an internal combustion engine, and a driven wheel of the vehicle. The apparatus also includes a torque transmission control mechanism which selectively transmits torque between the first rotor and the engine. When the torque transmission control mechanism establishes the transmission of torque between the first rotor and the engine, powers, as produced by the second and third rotors, are opposite in sign to each other. This enables the speed of the first rotor to be set to zero (0) or a very low speed. Therefore, when an initial torque is applied to the engine through the first rotor to start the engine, the mechanical vibration which usually arises from the application of initial torque and is to be exerted on the power transmission apparatus is minimized.