Mild Hybrid Powertrain Gear Reduction for 48V Engine Starting
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Solution Overview
Problem
Mild Hybrid Electric Vehicles (MHEVs) face challenges in providing sufficient torque for starting engines in medium and heavy-duty vehicles, as 48V electric machines are not designed to handle the required torque, and upgrading to higher voltage systems like 160V is costly and requires stringent compliance with new standards.
Innovation Solution
A powertrain design featuring a gear reduction mechanism with two interdependent but non-fixed torque ratios, allowing the electric machine to operate as a motor for starting and as a generator for other modes, using a 48V electric machine without the need for additional starters or generators, and enabling efficient operation of auxiliaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a 48V electric machine is used in medium and heavy-duty vehicles, then the vehicle can benefit from mild hybrid technology, but the electric machine cannot provide sufficient torque for starting the engine
Solution Approach 1:
A gear reduction mechanism is introduced as an intermediary between the 48V electric machine and the engine crankshaft. This mechanism multiplies the torque output of the electric machine, enabling it to provide sufficient starting torque for medium and heavy-duty engines while maintaining the benefits of the 48V system.
Solution Approach 2:
The gear reduction mechanism changes the torque parameter by providing a reduction ratio greater than 1:1. This allows the electric machine to operate at lower torque while the gear mechanism transforms this into high torque at the crankshaft, resolving the contradiction between electric machine power limitations and starting torque requirements.
2Adaptability or versatility
If the electric machine is mechanically disconnected from the engine, then the electric machine can operate independently, but the electric machine cannot provide sufficient torque for starting
Solution Approach 1:
The system dynamically engages and disengages the gear reduction mechanism based on operational requirements. During starting, the gear mechanism is engaged to multiply torque; during normal operation, it can be disengaged to allow independent electric machine operation, thus providing both mechanical disconnection benefits and sufficient starting torque when needed.
3Force
If a higher voltage system like 160V is used, then sufficient torque for starting can be achieved, but the system becomes more expensive and requires stringent compliance with new standards
Solution Approach 1:
Instead of upgrading to a higher voltage system, a gear reduction mechanism is used as an intermediary to multiply the torque output of the existing 48V electric machine. This approach achieves the required starting torque while maintaining the simpler and more cost-effective 48V system architecture.
4Force
If a larger electric machine is used to provide higher torque, then sufficient starting torque can be achieved, but a larger and more expensive battery is required
Solution Approach 1:
The gear reduction mechanism changes the torque parameter by providing mechanical multiplication. This allows a smaller, less expensive battery to power a compact electric machine that, when combined with the gear reduction ratio, delivers sufficient starting torque without requiring a larger and more expensive battery system.
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
Enables the use of 48V electric machines in medium and heavy-duty vehicles by providing high torque for engine starting and efficient operation in various modes, reducing component stress and eliminating the need for additional power sources, while allowing for compact and efficient powertrain design.
Implementation Method 1
a gear reduction mechanism having a free wheel and at least three separate and rotatable junction elements, the rotational speeds of the junction elements being interdependent but not having a fixed ratio relative to one another
Data Source
AI summary
A powertrain includes an engine; a driveline including a gearbox having an input shaft connected to the engine, an output shaft to be connected to driving wheels of the vehicle and a countershaft for transmitting a rotation of the input shaft to the output shaft which can be coupled to the input shaft; an electric machine; a gear reduction mechanism having a free wheel and at least three separate and rotatable junction elements, the rotational speeds of the junction elements being interdependent but not having a fixed ratio relative to one another: a first junction element that is connected to the electric machine; a second junction element that is connectable to the free wheel; a third junction element that is connected to the countershaft. The torque ratio between the third junction element and the first junction element can be selected from at least two different ratios.