Variable-Compression Connecting Rod With Stable Hydraulic Switching
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Solution Overview
Problem
Internal combustion engines with fixed compression ratios face inefficiencies during part-load operations due to limited adjustable compression ratios, leading to potential knocking and instability, which can be improved by variable compression systems but require effective hydraulic management to prevent pressure drops and maintain stability.
Innovation Solution
A connecting rod with an eccentric adjusting device featuring hydraulic chambers and a changeover valve that controls fluid flow, utilizing check valves and throttles to manage pressure drops and ensure hydraulic preload, allowing for adjustable compression ratios while preventing oil drainage and maintaining system stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If hydraulic fluid is routed directly from the first hydraulic chamber to the second hydraulic chamber without pressure drop control, then the adjustment speed of the connecting rod is increased, but the hydraulic pressure in the second chamber becomes excessive causing instability
Solution Approach 1:
A throttle is introduced as an intermediary element in the hydraulic connection between the first and second hydraulic chambers. This throttle creates a defined pressure drop that mediates the direct fluid transfer, allowing controlled adjustment speed while preventing excessive pressure buildup in the second chamber, thus resolving the contradiction between speed and stability.
2Device complexity
If the second hydraulic chamber has the same volume as the first hydraulic chamber, then the hydraulic system is simpler to design, but the ability to hydraulically pretension the chamber and control oil flow is reduced
Solution Approach 1:
The second hydraulic chamber is designed with a smaller volume than the first chamber, creating a local differentiation in chamber characteristics. This volume difference enables the second chamber to be hydraulically pretensioned more effectively and allows for better control of oil flow during compression ratio adjustment, sacrificing some design simplicity for enhanced functional adaptability.
3Device complexity
If check valves are not used in the hydraulic chambers, then the hydraulic system has fewer components and is simpler, but hydraulic fluid cannot be prevented from draining out of the chambers
Solution Approach 1:
Check valves are installed in the hydraulic chambers to enable the system to self-regulate fluid flow. These valves automatically prevent hydraulic fluid from draining out of the chambers while allowing fluid to be fed into them, providing passive, reliable fluid retention without requiring active control mechanisms, thus improving reliability with minimal added complexity.
4Device complexity
If the compression ratio is kept fixed to avoid knocking during full-load operation, then the engine is simpler to control, but the efficiency in the part-load range is reduced
Solution Approach 1:
The compression ratio system is transformed from a fixed configuration to a dynamic, adjustable system. By implementing variable connecting rod lengths through the hydraulic adjustment mechanism, the compression ratio can now be changed based on operating conditions, allowing the engine to optimize efficiency in the part-load range while maintaining control during full-load operation to prevent knocking.
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
The solution enables stable switching behavior and efficient adjustment of compression ratios, preventing pressure drops and maintaining hydraulic preload, thus enhancing the operating performance and reducing dynamic forces during compression changes.
Implementation Method 1
hydraulic fluid can be routed from a larger hydraulic chamber on a gas force side (GKS hydraulic chamber) of the adjustable connecting rod directly into a smaller hydraulic chamber on a mass force side (MKS hydraulic chamber)
Implementation Method 2
hydraulic fluid can be routed from the first hydraulic chamber into the second hydraulic chamber directly and via means for defined pressure drop
Implementation Method 3
A check valve is assigned to each of the hydraulic chambers, which enables hydraulic fluid to be fed into the hydraulic chambers and prevents hydraulic fluid from being discharged from the hydraulic chambers
Data Source
Figure 1~2
Figure 3
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AI summary
The invention relates to a connecting rod (1) for a variable-compression internal combustion engine with an adjusting device (2) for adjusting the effective connecting rod length, wherein the adjusting device (2) has at least a first hydraulic chamber (14) and a second hydraulic chamber (15). Each hydraulic chamber (14, 15) has an inlet (16, 17) for supplying hydraulic fluid to it from a supply source (P) and each has an outlet (20, 21) for draining hydraulic fluid from it. A switching valve (5) for controlling the flow of hydraulic fluid has a piston movable in a housing, which can be selectively moved into a first switching position (S1) or a second switching position (S2).In the first switching position (S1), the outlet (21) of the second hydraulic chamber (15) and in the second switching position (S2), the outlet (20) of the first hydraulic chamber (14) are connected to the supply source (P). Each hydraulic chamber (14, 15) is assigned a check valve (18, 19), which allows hydraulic fluid to flow into the hydraulic chambers (14, 15) and prevents hydraulic fluid from flowing out of them. The hydraulic chambers (14, 15) are connected such that in the second switching position (S2), hydraulic fluid can flow directly from the first hydraulic chamber (14) to the second hydraulic chamber (15) with a defined pressure drop.