Hydraulic Variable Valve Actuator with Retarded Default Timing
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Solution Overview
Problem
Existing variable cam timing systems in engines face challenges in selecting default valve timing positions, particularly during low hydraulic pressure conditions, which can lead to conflicting requirements for engine operation such as cold starting, warmed-up idle, and shutdown, affecting fuel economy, emissions, and noise vibration harshness (NVH).
Innovation Solution
A hydraulic variable valve actuator system with dual retard strategy, where intake and exhaust valve timings are set to retarded positions by default when hydraulic pressure is insufficient, allowing for improved engine operation in hybrid propulsion systems by optimizing valve timing based on operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the default valve timing is set to advanced timing, then cold starting performance is improved, but fuel economy and emissions deteriorate during warmed-up idle conditions
Solution Approach 1:
The patent implements dynamic valve timing adjustment where the default timing changes based on operating conditions. During cold starting, the default timing is advanced to improve combustion stability and starting reliability. During warmed-up idle conditions, the default timing switches to retarded position to improve fuel economy and reduce emissions. This dynamic switching resolves the contradiction by adapting the timing strategy to the specific operating phase.
Solution Approach 2:
The patent changes the valve timing parameter based on engine operating conditions. The controller monitors engine temperature, load, and speed to determine whether to use advanced or retarded default timing. This parameter change allows the system to optimize for cold starting (advanced timing) versus fuel economy (retarded timing) at different operational stages.
2Loss of energy
If the default valve timing is set to retarded timing, then fuel economy and emissions are improved, but cold starting performance deteriorates
Solution Approach 1:
The system dynamically switches the default valve timing between advanced and retarded positions based on operating conditions. During cold starting, advanced timing is used to ensure reliable combustion. During warmed-up idle and low-speed conditions, the system transitions to retarded timing to optimize fuel economy and emissions, thus resolving the contradiction through conditional adaptation.
Solution Approach 2:
The controller adjusts the valve timing parameter based on engine temperature and operating phase. When the engine is cold, advanced timing is applied. When the engine is warmed up, the timing parameter changes to retarded position, allowing the system to achieve both cold starting reliability and fuel economy under appropriate conditions.
3Ease of operation
If hydraulic pressure is insufficient, then the actuator cannot adjust valve timing, but using a fixed default position creates conflicting requirements for different operating conditions
Solution Approach 1:
The patent segments the valve timing control into two independent parts: a fixed mechanical default position (retarded timing) that provides a baseline safe operating mode under low hydraulic pressure, and a controllable variable timing component that adjusts timing when hydraulic pressure is sufficient. This segmentation allows the system to maintain reliable operation in all pressure conditions while adapting timing when possible.
Solution Approach 2:
The controller acts as an intermediary that monitors hydraulic pressure conditions and selectively engages the variable timing actuator. When pressure is insufficient, the system relies on the retarded default position. When pressure is sufficient, the controller activates the actuator to adjust timing to optimal positions, thus mediating between the fixed mechanical constraint and the need for adaptive timing control.
4Power
If earlier valve timing is used during low-speed operation, then engine performance is improved, but hydraulic pressure may be insufficient to move the actuator
Solution Approach 1:
The patent establishes a retarded default timing position that is mechanically set and does not require hydraulic pressure to maintain. This preliminary positioning ensures that under low-speed, low-pressure conditions, the engine operates in a safe, fuel-efficient mode. When hydraulic pressure becomes sufficient, the system then applies the preliminary action of advancing timing to improve performance, thus sequencing the timing adjustment to match pressure availability.
Solution Approach 2:
The mechanical actuator design includes an internal spring mechanism that automatically maintains the retarded default position without requiring external hydraulic pressure. The system serves itself by using the spring force to hold timing when pressure is low, and only engages hydraulic pressure when sufficient pressure is available to overcome the spring force and advance timing for improved performance.
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 enhances fuel economy, reduces emissions, and improves engine starting and shutdown performance by controlling valve timing to minimize oxygen flow to the catalyst and reduce torque pulsations, thereby enhancing vehicle drive feel and reducing NVH.
Implementation Method 1
One type of variable cam timing system utilizes hydraulic oil pressure to adjust an actuator between the camshaft and crankshaft
Implementation Method 2
when oil pressure is not available, a biasing spring and locking pin hold the actuator, and thus cam timing, in a default position
Data Source
AI summary
A system for adjusting valve timing of an engine is disclosed. In one embodiment, valve timing is adjusted during an engine start before the engine is started. The system may reduce engine emissions during engine starting.