Crankshaft Synchronization for Variable Displacement Engine NVH Reduction
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Solution Overview
Problem
Existing engine arrangements that connect coaxial crankshafts for varying the number of active cylinders in internal combustion engines often experience noise, vibration, and harshness (NVH) issues due to unsynchronized relative angular positions of the crankshafts.
Innovation Solution
The method involves partially coupling and decoupling crankshafts using a controllable friction clutch, with synchronization achieved by determining the relative angular position between the crankshafts and camshafts through sensor signals processed by an engine control unit (ECU), and connecting them at a predetermined relative angle of 720° for optimal firing order, using mechanical connecting means like ratchets to secure the alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a friction clutch is used to connect crankshafts for changing the number of active cylinders, then the engine can operate with variable displacement, but noise, vibration and harshness (NVH) problems occur due to unsynchronized relative angular positions of the crankshafts
Solution Approach 1:
The system performs preliminary synchronization of the crankshafts' angular positions before engaging the friction clutch to connect the engines. The ECU calculates the required ignition timing adjustments in advance and pre-synchronizes the crankshaft positions using sensor feedback, ensuring that when the clutch engages, the crankshafts are already aligned at the correct relative angle (e.g., 720 degrees apart), thereby preventing NVH issues from the outset
Solution Approach 2:
The system uses position sensors on both crankshafts to continuously monitor their relative angular positions and feeds this information back to the ECU. The ECU processes this feedback to dynamically adjust ignition timing and control clutch engagement timing, ensuring that the crankshafts maintain synchronized positions during variable displacement operation, thus eliminating NVH problems while maintaining adaptability
2Ease of operation
If the crankshafts are connected without considering relative angular position, then the clutch engagement is simple, but the subsequent engine operation experiences noise, vibration and harshness problems
Solution Approach 1:
The system replaces complex mechanical synchronization mechanisms with an electronic control system. The ECU uses position sensor feedback to calculate and control the angular positions of the crankshafts electronically, adjusting ignition timing and clutch engagement commands to achieve precise synchronization without requiring additional mechanical linkages or synchronization gears, thereby maintaining ease of operation while eliminating NVH issues
Solution Approach 2:
The system dynamically changes the ignition timing parameter based on the relative angular positions of the crankshafts. By adjusting the ignition advance angle according to the measured crankshaft positions and the desired relative alignment (e.g., 720 degrees), the system ensures proper synchronization during clutch engagement and operation, preventing NVH problems while keeping the mechanical engagement simple
3Productivity
If the second engine is started by actuating a clutch driven by the first engine, then the second engine can be started without external power, but the clutch must be maintained in positive engagement causing torque loss
Solution Approach 1:
The system dynamically controls the friction clutch engagement based on real-time operating conditions. During second engine starting, the clutch is temporarily engaged to transfer torque from the first engine. Once the second engine is running and synchronized, the clutch is disengaged or maintained in a slip state, allowing the engines to operate independently without continuous torque transfer, thereby enabling self-starting capability while minimizing ongoing torque loss
Solution Approach 2:
The clutch engagement occurs periodically only when needed for engine starting or load sharing transitions, rather than being continuously engaged. The ECU monitors engine operating conditions and activates the clutch only during specific transitions, allowing the engines to operate independently during normal operation, thus achieving starting capability while minimizing energy loss from continuous engagement
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 ensures smooth operation by synchronizing the engines, minimizing NVH issues and allowing the second engine to start without a sudden jerk, reducing torque loss and enabling efficient operation with optimized ignition timing and torque output.
Implementation Method 1
a controllable friction clutch arranged between the crankshafts
Data Source
AI summary
A method for operating an engine arrangement with a first internal combustion engine and a second internal combustion engine in a vehicle is provided. The method may include partially coupling a first crankshaft of the first internal combustion engine in the vehicle with a second crankshaft of the second internal combustion engine in the vehicle to start the second internal combustion engine, where the first crankshaft and second crankshaft are partially coupled with a clutch. The method may further include decoupling the first and second crankshaft when the second engine is operating under its own power. The method may further include coupling the first crankshaft and the second crankshaft, where the first and second crankshafts are coupled with the clutch when a speed difference between the first and second crankshafts is below a predetermined value and a relative angular position between the first and second crankshafts is less than 360°.