Two-Mode Valve Actuator for Diesel Engine Compression
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Solution Overview
Problem
Diesel engines face a compromise between compression ratio for cold starting and optimal performance, economy, and emissions, where high compression ratios for cold starting hinder fuel economy and emissions, and low ratios for economy reduce cold startability.
Innovation Solution
A two-mode valve actuator system that partially disables the valve lifter during cold starting and warm-up conditions, allowing earlier valve closure and reduced lift, thereby adjusting the effective compression ratio without altering the combustion chamber design, and incorporates damping to mitigate noise and vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high compression ratio is used for cold starting, then cold startability is improved, but fuel economy and emissions performance worsen
Solution Approach 1:
The valve lifter is designed to operate in two dynamic modes: a first mode during cold starting conditions that provides extended valve closure to increase effective compression ratio, and a second mode during normal operation that provides reduced valve closure for optimized fuel economy and emissions. The system automatically transitions between modes based on engine temperature sensors, allowing the compression ratio to be dynamically adjusted without permanent engine redesign.
Solution Approach 2:
The invention changes the valve timing parameters by adjusting the valve closure crank angle. During cold starting, the valve is closed earlier (e.g., 10-20 degrees before top dead center) to increase effective compression ratio. During normal operation, the valve closes later to optimize the air-fuel mixture and reduce emissions. This parameter adjustment is achieved through the two-mode lifter mechanism without altering the physical combustion chamber geometry.
2Loss of energy
If low compression ratio is used for fuel economy, then fuel economy and emissions are improved, but cold startability worsens
Solution Approach 1:
The valve lifter system dynamically adjusts its operation based on engine conditions. During cold starting, it operates in a first mode that extends valve closure to increase effective compression ratio for improved cold startability. During normal warm operation, it transitions to a second mode that reduces valve closure for optimized fuel economy and emissions, effectively allowing the engine to operate at lower compression ratio without sacrificing cold start performance.
Solution Approach 2:
The system performs preliminary valve timing adjustment during the cold starting phase before normal operation begins. By closing the valve earlier during cold start, the effective compression ratio is temporarily increased to ensure reliable starting. Once the engine reaches operating temperature, the valve timing returns to normal, allowing the engine to benefit from lower effective compression ratio for improved fuel economy throughout the remainder of the operating cycle.
3Reliability
If valve closure is extended for higher compression ratio, then cold startability is improved, but noise and vibration increase
Solution Approach 1:
The damping mechanism is applied locally at the valve train components that generate noise and vibration during the valve closure event. A damper is integrated into the valve lifter or pushrod assembly to specifically target and reduce the harmful vibrations and noise generated during early valve closure, while leaving the rest of the valve timing characteristics unchanged. This localized damping allows extended valve closure for improved cold startability without proportionally increasing overall noise and vibration.
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
Improves cold startability, fuel economy, and reduces emissions by optimizing the effective compression ratio and retaining unburned exhaust gases, while minimizing noise and vibration, and allows for increased power boost without significant engine redesign.
Implementation Method 1
a lost motion spring which is functionally attached to the spring tower
Implementation Method 2
means for damping mitigates any objectionable noise and vibration resulting from the TVA
Data Source
AI summary
A two mode valve lifter for Diesel engines which varies the compression ratio between higher for cold starting and other selected operating conditions, and lower for warmed-up running. This is accomplished during engine starting and selected other conditions by causing the intake valve to close early (near bottom center), providing for example, up to three ratios additional compression. The invention incorporates a conventional valve lifter packaged within a sleeve, the sleeve being moved by the engine cam. In its conventional operating mode, the sleeve is rigidly attached to the lifter and the cam moves the assembly to lift the valve in the ordinary manner. When the sleeve is not attached, partial lost motion occurs, causing the valve to open later and close earlier. In the modified mode and as needed, optional damping can be introduced to allow the valve to open and close gradually and quietly. Similarly, a two mode valve lifter which retains additional exhaust gas in the cylinder to assist cold starting and warm-up by closing the exhaust valve earlier can be incorporated either alone or in combination with the intake two mode lifter.