Hybrid Engine Cranking System Torque Management
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Solution Overview
Problem
Internal combustion engines face challenges in maintaining sufficient starting torque across all engine crankshaft speeds during the cranking cycle, leading to potential stalling, noise, and vibration issues due to the limitations of existing starter motor and starter/generator systems.
Innovation Solution
A cranking system that employs a combination of a starter motor and a starter/generator unit, controlled by a controller to manage the cranking cycle, where the starter motor engages the pinion gear with the ring gear and the starter/generator unit provides additional torque during peak compression strokes, ensuring consistent engine cranking from a stopped state to a top dead center position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a starter motor with high ring to pinion gear ratio is used to achieve high crankshaft torque at low speed, then starting torque is improved, but torque declines steeply as speed increases
Solution Approach 1:
The patent combines a starter motor and a starter/generator unit into a hybrid starting system. The starter motor provides high torque at low speeds through gear engagement, while the starter/generator unit supplements torque at higher speeds through belt drive, merging the strengths of both systems to maintain adequate torque across the entire cranking speed range.
2Force
If a starter/generator unit with low belt drive ratio is used to provide higher torque at higher engine speeds, then high-speed torque is improved, but low-speed torque is reduced
Solution Approach 1:
The system merges the starter motor and starter/generator unit so that the starter motor handles low-speed high-torque requirements through gear reduction, while the starter/generator unit handles high-speed torque needs through belt drive, with both units operating simultaneously during cranking to provide complementary torque across the speed spectrum.
3Device complexity
If a single starting system is used, then system complexity is reduced, but adequate torque across all crankshaft speeds cannot be maintained
Solution Approach 1:
The starter/generator unit serves multiple functions: it acts as a starter motor during engine cranking, a generator during engine operation, and provides supplemental torque during compression strokes. This multi-functionality justifies the added complexity by eliminating the need for separate starting systems while maintaining adequate torque across all operating conditions.
4Reliability
If cranking torque is insufficient during compression strokes, then engine can start, but stalling and speed deviations occur leading to NVH issues
Solution Approach 1:
The controller activates the starter/generator unit in advance during compression strokes before the piston reaches top dead center, providing supplemental torque to ensure the engine maintains sufficient cranking speed through the high-resistance compression phase. This preliminary action prevents speed deviations and subsequent NVH issues during engine startup.
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 solution provides adequate starting torque at all engine crankshaft speeds, reducing the likelihood of stalling and improving noise, vibration, and harshness (NVH) performance by optimizing the use of both electric machines during the cranking cycle.
Implementation Method 1
the electric motor being controllably energizable to cause rotation of the pinion gear
Implementation Method 2
a pinion gear of the first electric machine meshing with a ring gear coupled to a flywheel coupled to the crankshaft
Implementation Method 3
a belt drive arrangement including a first pulley coupled to the second electric machine, a second pulley coupled to the crankshaft, and a belt coupled between the first pulley and the second pulley
Implementation Method 4
Large displacement engines and higher compression engines require large spinning forces during engine start
Data Source
AI summary
Internal combustion engine cranking is carried out including with a limited overlapping of cranking with a starter motor and a starter/generator during at least the initial compression stroke during a cranking cycle.