Rocker Arm for Valve Actuation in Internal Combustion Engines (U.S. Pat. 7,171,930)
Abstract
A rocker arm is disclosed for valve actuation in an internal combustion engine. The rocker arm includes at least two rotational axes which can be selected as desired to modify a relation between a force arm and a load arm. Control times and valve lift can be influenced in a targed manner.
Inventor: Alberto Keel, Switzerland
Foreigen Application Priority Data: Aug. 20, 2002 (CH)
Related U.S. Application Data: May 14, 2003
Filed: Feb. 22, 2005
Prior Publication Data: Aug. 4, 2005
Status: Expired
How It Works (Basics of U.S. Patent 7,171,930)
Two Pivots
The main element of the invention is an eccentric integrated into the rocker arm body. Each eccentric has two pivots. The first pivot is formed by the outer circumference of the eccentric (marked in red).
The second pivot is formed by the bore of the eccentric (marked in yellow).
Low-lift Mode
In low lift mode, the rocker arm body rotates around the outer diameter of the eccentric, while the eccentric does not move (supported by a stop plate... see animation on the right).
High-lift Mode
In high lift mode, the rocker arm body rotates together with the eccentric around the eccentric bore. The eccentric is connected to the rocker arm body by a mode pin to form a single unit (see animation on the right).
Switchover Process
Switching between the two operating modes is performed by a hydraulically actuated mode pin.
When oil is pressed into the rocker arm from the main shaft, the mode pin is pushed outwards. The connection between the rocker arm body and the eccentric is released. The rocker arm operates in low lift mode.
When the oil pressure is released, a spring (not visible in the animation) pushes the mode pin against the eccentric and connects it to the rocker arm body. The rocker arm now operates in high lift mode.
The Relationships Between Rocker Arm Ratio, Valve Clearance, Valve Timing, Valve Overlap and Valve Speed
The following principles apply:
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The smaller the rocker arm ratio, the flatter the valve lift curve.
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The flatter the valve lift curve, the more camshaft or crankshaft rotation degrees are required to compensate a specified valve clearance.
The resulting effects are shown in the following diagrams.
Valve Opening Ramp
This diagram shows the different positions (crankshaft degrees) at which the valve begins to open, depending on the rocker arm ratio and three different valve clearance settings.
Valve Duration
This diagram shows the effective valve opening times in crankshaft degrees, depending on the rocker arm ratio and valve clearance.
Valve Overlap
This diagram shows the effective valve overlap in crankshaft degrees, depending on the rocker arm ratio and valve clearance.
Valvetrain Noise
This diagram shows the speeds at which the valve is struck by the rocker arm, also depending on the rocker arm ratio and valve clearance.
The angles shown are directly related to the impact speed and, accordingly, to the noise generated by the valve train.
Different Valve Lash Adjustment for Low-Lift Mode and High-Lift Mode
One of the most interesting features of the Vari-Lift rocker system is that different valve clearances can be assigned for the two operating modes (low-lift mode and high-lift mode).
This allows the engine to operate in low-lift mode with increased valve clearance (additional shortened valve timing), while the duration for the high-lift mode remains unaffected. Compared to the high-lift mode, the increased valve clearance in low-lift mode does not cause additional noise. This is because the valve lift curves (ramps) are flatter in low-lift mode, which in turn reduces noise... show also...
Explanation of the function:
During the switching process, the mode pin slides tangentially along the circumference of the stop pin. Because the milled surface on the mode pin has a slight angle, the mode pin pushes the stop pin away during the engagement process. This causes a slight clockwise rotation of the eccentric.
The slight rotation of the eccentric results in a reduction in valve clearance for the high lift mode. When the mode pin slides back and the eccentric disengages, the eccentric rotates back counter-clockwise, and the valve clearance increases for the low-lift mode.
The two different valve clearances are adjusted via the basic setting of the stop plates and the adjustment screws on the rocker arms. The Vari-Lift rocker system allows for an additional valve clearance of up to 0.05" in low-lift mode. This shortens the valve opening duration in low-lift mode by an additional 6° to 8° (depending on the camshaft).
