Lost Motion Rocker Arm Compression-Release Brake System
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Solution Overview
Problem
Conventional rocker arm brake systems experience reduced braking performance due to extended valve overlap, which allows exhaust gas to flow back into the engine intake system, causing unbalanced valve opening and potential engine damage, and result in decreased retarding performance.
Innovation Solution
A compression-release brake system incorporating a lost motion exhaust rocker assembly with an actuation piston and reset device that operates to open the exhaust valve late in the expansion stroke, reducing valve overlap and enhancing braking performance by using a hydraulic system to reset the exhaust valve and maintain balanced operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional rocker arm brake systems are used, then the system structure is simple, but valve overlap is extended causing exhaust gas to flow back into the intake system and reducing braking performance
Solution Approach 1:
The exhaust valve control is segmented into two independent systems: a hydraulic actuation system for precise timing control and a mechanical rocker arm system for valve operation. This segmentation allows the exhaust valve to be opened independently at the optimal time for braking while maintaining simple mechanical structures for other components.
Solution Approach 2:
A hydraulic actuator is introduced as an intermediary device between the control system and the exhaust valve. This intermediary enables precise control of valve opening timing without requiring complex mechanical linkages, thereby improving braking performance while keeping the overall system structure manageable.
2Productivity
If exhaust valve is opened near TDC to release compressed air, then braking performance is improved, but valve overlap is extended causing unbalanced valve opening and potential engine damage
Solution Approach 1:
The hydraulic actuator is pre-filled with hydraulic fluid and pre-positioned to open the exhaust valve at the precise moment near TDC. This preliminary preparation ensures that the valve opens exactly when needed for maximum braking effect without extending overlap into the intake stroke, preventing exhaust gas from flowing back into the intake system and maintaining engine safety.
Solution Approach 2:
The system incorporates feedback mechanisms through the hydraulic actuator's pressure sensing and control systems, which monitor cylinder pressure and valve position in real-time. This feedback ensures the exhaust valve opens at the optimal time for braking while preventing premature opening that would cause extended overlap and potential engine damage.
3Productivity
If lost motion concept is used to open exhaust valve near TDC, then compression release braking is achieved, but extended valve overlap allows exhaust manifold air mass flow into intake manifold
Solution Approach 1:
The system transitions from static mechanical valve timing to dynamic hydraulic control, allowing the exhaust valve opening timing to be precisely adjusted based on engine operating conditions. This dynamic control enables the valve to open exactly when needed for maximum braking effect while preventing extended overlap that would cause exhaust gas to flow back into the intake manifold, thereby reducing energy loss.
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 system achieves high retarding power over a wide engine speed range, reduces mechanical and thermal overload, operates quietly, and maintains engine performance by minimizing exhaust manifold air mass flow back into the intake manifold.
Implementation Method 1
an actuation piston including an actuation piston body slidably received by a first pocket of the rocker arm to define a piston cavity in the rocker arm and movable between a piston retracted position and a piston extended position
Implementation Method 2
The actuation piston body contains an actuation piston communication port and an actuation piston check valve configured to move between a first closed position and a first open position to provide a first hydraulic fluid flow pathway through the actuation piston communication port to the piston cavity
Implementation Method 3
the reset device is received by a second pocket of the rocker arm, operatively associated with the actuation piston through at least one connecting conduit, and includes a reset check valve configured to move between a second closed position and a second open position to provide a second hydraulic fluid flow pathway through the at least one connecting conduit to the piston cavity
Implementation Method 4
a reset pressure control spring for applying a biasing force to the reset check valve to urge the reset check valve toward a second open position
Data Source
AI summary
A compression-release brake system is provided that includes a lost motion exhaust rocker assembly, an actuation piston, and a reset device. The actuation piston includes an actuation piston body that is slidably received by the rocker arm to define a piston cavity in the rocker arm and is movable between piston retracted and extended positions. The actuation piston is configured to be operatively associated with the exhaust valve to permit unseating of the exhaust valve from the seated state. An actuation piston check valve is configured to move between closed and open positions to permit hydraulic fluid flow through an actuation piston communication port to the piston cavity. The reset device includes a reset check valve and a reset pressure control spring for applying a biasing force to the reset check valve to urge the reset check valve toward an open position.