Patent Application
20050274341
The present invention relates to systems and methods for actuating valves in internal combustion engines. In particular, the present invention relates to systems and methods for actuating valves using a one or more rocker arms.
Internal combustion engines typically use either a mechanical, electrical, or hydro-mechanical valve actuation system to actuate the engine valves. These systems may include a combination of camshafts, rocker arms, and push rods that are driven by the engine's crankshaft rotation. When a camshaft is used to actuate the engine valves, the timing of the valve actuation may be fixed by the size and location of the lobes on the camshaft.
For each 360 degree rotation of the camshaft, the engine completes a full cycle made up of four strokes (i.e., expansion, exhaust, intake, and compression). Both the intake and exhaust valves may be closed, and remain closed, during most of the expansion stroke wherein the piston is traveling away from the cylinder head (i.e., the volume between the cylinder head and the piston head is increasing). During positive power operation, fuel is burned during the expansion stroke and positive power is delivered by the engine. The expansion stroke ends at the bottom dead center point, at which time the piston reverses direction and the exhaust valve may be opened for a main exhaust event. A lobe on the camshaft may be synchronized to open the exhaust valve for the main exhaust event as the piston travels upward and forces combustion gases out of the cylinder. Near the end of the exhaust stroke, another lobe on the camshaft may open the intake valve for the main intake event at which time the piston travels away from the cylinder head. The intake valve closes and the intake stroke ends when the piston is near bottom dead center. Both the intake and exhaust valves are closed as the piston again travels upward for the compression stroke.
The above-referenced main intake and main exhaust valve events are required for positive power operation of an internal combustion engine. Additional auxiliary valve events, while not required, may be desirable. For example, it may be desirable to actuate the intake and/or exhaust valves during positive power or other engine operation modes for compression-release engine braking, bleeder engine braking, exhaust gas recirculation (EGR), or brake gas recirculation (BGR).
With respect to auxiliary valve events, flow control of exhaust gas through an internal combustion engine has been used in order to provide vehicle engine braking. Generally, engine braking systems may control the flow of exhaust gas to incorporate the principles of compression-release type braking, exhaust gas recirculation, exhaust pressure regulation, and/or bleeder type braking.
During compression-release type engine braking, the exhaust valves may be selectively opened to convert, at least temporarily, a power producing internal combustion engine into a power absorbing air compressor. As a piston travels upward during its compression stroke, the gases that are trapped in the cylinder may be compressed. The compressed gases may oppose the upward motion of the piston. As the piston approaches the top dead center (TDC) position, at least one exhaust valve may be opened to release the compressed gases in the cylinder to the exhaust manifold, preventing the energy stored in the compressed gases from being returned to the engine on the subsequent expansion down-stroke. In doing so, the engine may develop retarding power to help slow the vehicle down. An example of a prior art compression release engine brake is provided by the disclosure of the Cummins, U.S. Pat. No. 3,220,392 (November 1965), which is hereby incorporated by reference.
During bleeder type engine braking, in addition to, and/or in place of, the main exhaust valve event, which occurs during the exhaust stroke of the piston, the exhaust valve(s) may be held slightly open during remaining three engine cycles (full-cycle bleeder brake) or during a portion of the remaining three engine cycles (partial-cycle bleeder brake). The bleeding of cylinder gases in and out of the cylinder may act to retard the engine. Usually, the initial opening of the braking valve(s) in a bleeder braking operation is in advance of the compression TDC (i.e., early valve actuation) and then lift is held constant for a period of time. As such, a bleeder type engine brake may require lower force to actuate the valve(s) due to early valve actuation, and generate less noise due to continuous bleeding instead of the rapid blow-down of a compression-release type brake.
Exhaust gas recirculation (EGR) systems may allow a portion of the exhaust gases to flow back into the engine cylinder during positive power operation. EGR may be used to reduce the amount of NOx created by the engine during positive power operations. An EGR system can also be used to control the pressure and temperature in the exhaust manifold and engine cylinder during engine braking cycles. Generally, there are two types of EGR systems, internal and external. External EGR systems recirculate exhaust gases back into the engine cylinder through an intake valve(s). Internal EGR systems recirculate exhaust gases back into the engine cylinder through an exhaust valve(s). Embodiments of the present invention primarily concern internal EGR systems.
Brake gas recirculation (BGR) systems may allow a portion of the exhaust gases to flow back into the engine cylinder during engine braking operation. Recirculation of exhaust gases back into the engine cylinder during the intake stroke, for example, may increase the mass of gases in the cylinder that are available for compression-release braking. As a result, BGR may increase the braking effect realized from the braking event.
A valve actuation system may be adapted to provide one or more of the auxiliary valve events described above, in addition to providing main valve events. Moreover, the motion imparted by a valve train element to produce a main valve event may be used to provide an auxiliary valve event. For example, a main intake event lobe on a camshaft may be used to additionally actuate one or more valves for an EGR event. In valve actuation systems providing both main and auxiliary valve events, packaging, cost, reliability, and/or performance are design factors that may be considered.
Responsive to the foregoing challenges, Applicant has developed an innovative system for actuating an engine valve. In one embodiment of the present invention, the system comprises: a rocker arm shaft; a means for imparting primary valve actuation motion; a primary rocker arm disposed on the rocker arm shaft, the primary rocker arm being adapted to actuate an engine valve and receive motion from the means for imparting primary valve actuation motion; a means for imparting auxiliary valve actuation motion selected from the group consisting of: engine braking motion, exhaust gas recirculation motion, and brake gas recirculation motion; an auxiliary rocker arm disposed on the rocker arm shaft adjacent to the primary rocker arm, the auxiliary rocker arm being adapted to receive motion from the means for imparting auxiliary valve actuation motion; and a rocker arm coupling assembly disposed between the auxiliary rocker arm and the primary rocker arm, the coupling assembly being adapted to selectively transfer one or more auxiliary valve actuation motions from the auxiliary rocker arm to the primary rocker arm.
Applicant has further developed a system for actuating an engine valve comprising: a rocker arm shaft; means for imparting primary valve actuation motion; a primary rocker arm disposed on the rocker arm shaft, the primary rocker arm being adapted to actuate an engine valve and receive motion from the means for imparting primary valve actuation motion; means for imparting auxiliary valve actuation motion; an auxiliary rocker arm disposed on the rocker arm shaft adjacent to the primary rocker arm, the auxiliary rocker arm being adapted to receive motion from the means for imparting auxiliary valve actuation motion; and a coupling assembly, comprising: an actuator piston disposed in a bore formed in the primary rocker arm; and a slot formed in the auxiliary rocker arm for selectively receiving the actuator piston, wherein the actuator piston includes a curved surface to facilitate engagement with the slot.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.
In order to assist the understanding of this invention, reference will now be made to the appended drawings, in which like reference characters refer to like elements.
Reference will now be made in detail to an embodiment of the present invention, an example of which is illustrated in the accompanying drawings. With reference to
The valve actuating system includes at least two rocker arms disposed on a rocker shaft (500, as shown in
The engine valves 400 comprise poppet-type valves that are used to control communication between the combustion chambers (e.g., cylinders) in an engine and aspirating (e.g., intake and exhaust) manifolds. The system may further include a rocker arm coupling assembly 300 disposed between the primary rocker arm 100 and the auxiliary rocker arm 200 so as to selectively transfer one or more valve actuation motions from the auxiliary rocker arm 200 to the primary rocker arm 100.
In one embodiment of the present invention, the primary rocker arm 100 may comprise an exhaust rocker arm and the auxiliary rocker arm 200 comprises an intake rocker arm. The exhaust rocker arm 100 may be adapted to actuate one or more exhaust valves to produce a main exhaust event, and an auxiliary valve event, such as, an engine braking event, an exhaust gas recirculation (EGR) event, and/or a brake gas recirculation event (BGR). The intake rocker arm 200 is adapted to actuate one or more intake valves to produce an engine valve event, such as, for example, a main intake event. In one embodiment of the present invention, the exhaust valve actuated by the exhaust rocker arm 100 and the intake valve actuated by the intake rocker arm 200 are in the same engine cylinder. It is contemplated, however, that the engine valves may be in different engine cylinders.
In an alternative embodiment, as shown in
In one embodiment of the present invention, the primary rocker arm 100 may actuate one or more engine valves 400 to produce an engine braking event.
The system may include a lash piston 120 disposed in a bore formed in the primary rocker 100 and in selective contact with the cam 150. A spring 126 biases the lash piston 120 away from the cam 150. The system may include a plunger 122 extending into the lash piston bore, and a locking nut 124. The locking nut 124 may be adjusted to extend the plunger 122 a desired distance within the bore, and, correspondingly, adjust the position of the lash piston 120 relative to the cam 150. The lash piston 120 may include a surface 128 suitable for contacting and following the motion of the cam 150.
The rocker arm shaft 500 may include one or more internal passages for the delivery of hydraulic fluid, such as engine oil, to the rocker arms mounted thereon. Hydraulic fluid may be selectively supplied to the primary rocker arm 100 by a fluid supply valve (not shown), such as a solenoid valve, to initiate engine braking operation.
A control valve 110 may be disposed in a bore 112 formed in the primary rocker arm 100. The control valve 110 controls fluid communication between the passage in the rocker shaft 500 and the lash piston 120 through a hydraulic passage 105 formed in the primary rocker arm 100. A spring 114 biases the control valve 110 into a first position, as shown in
When engine braking is desired, a supply valve, such as, for example, a solenoid valve (not shown), is activated and hydraulic fluid is supplied through the rocker shaft 500 to the control valve bore 112. The hydraulic pressure created by the fluid causes the control valve 110 to actuate from the first position, as shown in
The intake rocker arm 200 may include a cam roller 210 for following the motion of an intake cam 250 (not shown). The motion from the intake cam 250 may be used to actuate an intake valve to provide a main intake event. The motion from the intake cam 250 also may be transferred to the primary rocker arm 100 through the coupling assembly 300 such that the primary rocker arm 100 actuates the exhaust valve 400 to provide an auxiliary valve event, such as an EGR valve event.
In one embodiment of the present invention, with reference to
Hydraulic fluid may be selectively supplied from a passage in the rocker arm shaft 500 (not shown) to the bore 320 through a hydraulic passage 360 formed in the primary rocker arm 100. The hydraulic fluid may be selectively supplied by a fluid supply valve (not shown), such as, for example, a solenoid valve. The hydraulic pressure created by the fluid in the bore 320 causes the piston 310 to translate against the bias of the spring 340 and extend into the slot 330. A mechanical stop 350 limits the travel of the piston 310 within the bore 320.
A partial detailed view of the coupling assembly 300 according to an embodiment of the present invention is shown in
Operation of an embodiment of the valve actuation system of the present invention will now be described. During positive power operation, when engine braking is not desired, hydraulic fluid is not supplied to the control valve bore 112 through the rocker shaft 500. The control valve 110 remains seated in the rocker shaft detent 505, in an “engine brake off” position, substantially preventing hydraulic fluid communication to the lash piston 120. Without sufficient hydraulic pressure acting on it, the lash piston 120 remains in a retracted position, as shown in
During engine braking operation, hydraulic fluid is supplied to the control valve bore 112 through the rocker shaft 500. The hydraulic pressure causes the control valve 110 to translate in the bore 112 against the bias of the spring 114, as shown in
When auxiliary exhaust valve actuation is desired for EGR and/or BGR, for example, a solenoid supply valve (not shown) may be activated so as to provide hydraulic fluid through the rocker shaft 500 through the hydraulic passage 360 to the actuator piston bore 320. The hydraulic fluid pressure created in the bore 320 causes the piston 310 to translate against the bias of the spring 340 and extend into the slot 330. As auxiliary valve motion is applied to the auxiliary rocker arm 200, the auxiliary rocker arm 200 begins to rotate. Because the piston 310 is engaged in the slot 330, the rotation of the auxiliary rocker arm 200, in turn, causes the primary rocker arm 100 to rotate and actuate the exhaust valve 400. The timing of the auxiliary valve motion may be appropriate to provide an auxiliary valve event, such as an EGR or BGR event.
With reference to
It will be apparent to those skilled in the art that various modifications and variations can be made in the construction, configuration, and/or operation of the present invention without departing from the scope or spirit of the invention. For example, it is appreciated that the primary rocker arm 100 could be implemented as an intake rocker arm, or an auxiliary rocker arm, without departing from the intended scope of the invention. Further, where engine braking functionality is not required, it is contemplated that embodiments of the valve actuation system may be provided without the control valve 110 and/or the lash piston 120. In addition, the rocker shaft 500 may further include a hydraulic passage adapted to provide lubrication fluid to the one or more rocker arms. These and other modifications to the above-described embodiments of the invention may be made without departing from the intended scope of the invention.
This application relates to and claims priority on U.S. Provisional Application No. 60/570,814, filed May 14, 2004 and entitled “Rocker Arm System for Engine Valve Actuation,” a copy of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60570814 | May 2004 | US |
