Motors: expansible chamber type – Relatively movable working members with one having motive... – Position of one working member controls motive fluid for...
Reexamination Certificate
2000-09-15
2001-05-01
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Relatively movable working members with one having motive...
Position of one working member controls motive fluid for...
C091S509000, C091S512000
Reexamination Certificate
active
06223646
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an hydraulic operating mechanism for a poppet valve of an internal combustion engine providing compression braking. The invention is particularly related to such a mechanism useful with altered exhaust valve timing and lift for braking. The invention further relates to such a mechanism wherein a fluid actuated unitary piston and valve is movably mounted within another piston and has a separate actuator motion providing a differential reaction surface to increase valve actuation force.
BACKGROUND OF THE INVENTION
In the normal or power providing operation of reciprocating internal combustion engines, exhaust occurs near the end of the power stroke where the combustion gas pressure is relatively low after expansion of the combustion gases. For compression braking, however, fuel is not provided and exhaust of compressed air occurs near the end of the compression stroke; and, in order to dissipate as much of the energy of compression as possible, the cylinder pressure at exhaust valve opening is much higher than in normal operation. As a result and for a poppet exhaust valve utilizing a spring to close the valve, the force for valve opening during compression braking operation is, typically, 3 to 8 times that for normal operation.
For engines having poppet valves providing these operations, hydraulically motivated and electronically controlled actuation of the valves is desirable to provide flexibility in timing for optimized response, power, noise control, efficiency, and pollution control. Many arrangements dispensing with cams and providing such actuation are possible and a number are well-known. Since these arrangements are not a part of the present invention, it will only be mentioned that such arrangements to which the described embodiment of the present invention is applicable utilize a source of low hydraulic pressure and a source of high hydraulic pressure selectively connected to an actuator for closing and opening each poppet valve at varying and optimal times in relation to the position of the engine crankshaft. The hydraulic source selection is, typically, performed by electrically motivated valves and is electronically determined by a control system sensing variables such as crankshaft rotational speed and position, air inlet pressure, desired power in normal operation, and desired amount of compression braking. The control system provides, in relation to crankshaft position, the different exhaust poppet valve opening timing for normal operation and compression braking.
However, typical hydraulically motivated poppet valve actuators lack the force capability to open the exhaust valve during compression braking due to the above mentioned large required force. While actuators could be constructed to provide the necessary force, this would result in wasted energy for valve actuation in normal operation. It would, of course, be possible to construct such actuators providing the appropriate required different forces for normal operation and braking as selected by a control system of the nature described above. However, both the actuator and control system would still not be directly receptive to an actual need for greater force and would thus be somewhat inefficient. In any event, such an actuator and control system would necessarily be more complex, and the actuator could not directly replace existing camless hydraulic actuators lacking the force capability to open an exhaust valve during a compression braking cycle.
SUMMARY OF THE INVENTION
The present invention is particularly directed to a hydraulic actuator for a poppet exhaust valve where the actuator is electronically controlled to provide for variable valve timing during normal engine operation and for compression release during compression braking. An actuator of the present invention provides poppet valve opening force which is high for compression braking and low for energy conservation during normal engine operation. Motion or lack of motion of a low force providing element during the initial phase of exhaust poppet valve lift determines, respectively, that the actuator will provide relatively low or relatively high force to complete the lift.
An exhaust poppet valve actuator of the invention includes an inner piston which extends centrally through an annular outer piston of relatively larger area. The inner piston extends from one side of the annular piston and terminates in an end of relatively smaller area. To open the exhaust poppet valve, high pressure hydraulic fluid is provided to this inner piston end from which a passage communicates with the outer piston side disposed toward the inner piston end. In normal operation, the force provided by the inner piston is sufficient to open the poppet valve, and this piston moves so as to open the poppet valve and block the passage communicating with the outer piston. During compression braking, however, the required force is greater so that the inner piston does not move initially and the high pressure fluid passes through the inner piston passage and acts on the outer piston which has a large enough surface area to provide enough force to open the poppet valve.
More specifically, the described actuator embodiment is for opening a poppet exhaust valve, which is closed by a spring and opens in normal operation against a relatively low pressure and which opens for braking against a relatively high pressure. The actuator is characterized by being motivated by the same hydraulic pressure in both modes of operation. The inner piston, with its fluid passage, is of unitary construction and is coaxial with the stem of the exhaust valve. The inner piston also extends from the outer piston at the side thereof opposite the inner piston end subjected to such pressure, and this opposite end bears a collar or annular projection for engagement with the corresponding side of the outer piston. The outer piston is slidably fitted internally to the inner piston and slidably fitted externally within a bore of a actuator body receiving the outer piston. In normal operation, the inner piston moves from its unactuated position and opens the exhaust valve. For braking, the force developed by the inner piston cannot move it and the exhaust valve, but the hydraulic pressure admitted through the inner piston passages to the outer piston moves it from its unactuated position to engage the inner piston collar with sufficient force to move the inner piston and open the exhaust valve.
In either mode of operation and when the hydraulic pressure is subsequently and sufficiently reduced, the exhaust valve spring closes the exhaust valve; and the stem thereof urges the inner piston toward its unactuated position with the collar engaging the outer piston and carrying the outer piston to its unactuated position if it has moved therefrom for compression braking operation.
In relation to normal operation, a lesser exhaust poppet valve movement may be used for braking operation as sufficient to release the compressed air and as necessary to limit the opening of the exhaust valve so that it does not contact an associated piston. Accordingly and to reduce valve operating energy, the actuator body may be constructed so as to engage the outer piston and stop the movement thereof from its unactuated position after such lesser movement, while the inner piston remains free to move the full poppet valve opening distance corresponding to normal engine operation.
REFERENCES:
patent: 5277222 (1994-01-01), Clarke
Carroll Thomas S.
Meister Steven F.
Miller Charles R.
Bram Eric M.
Caterpillar Inc.
Hampsch Robert J.
Lazo Thomas E.
Look Edward K.
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