Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Reexamination Certificate
2001-11-09
2003-11-18
Solis, Erick (Department: 3747)
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
C123S322000, C123S090120, C123S090150
Reexamination Certificate
active
06647954
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and system for improving engine braking. In particular, the present invention relates to methods and systems using variable valve operation to improve engine braking performance.
BACKGROUND OF THE INVENTION
Valve actuation in an internal combustion engine is required in order for the engine to produce positive power. During positive power operation of an engine, one or more intake valves may be opened to allow air and fuel into a cylinder for combustion. This intake event is routinely carried out while the piston in the cylinder travels from a near top dead center (TDC) position to a near bottom dead center (BDC) position. After the intake stroke, the intake valve(s) are closed and the air/fuel charge in the cylinder is compressed as the piston travels back from the BDC position to a TDC position during a compression stroke. The compressed mixture is combusted around TDC, which drives the piston back toward a BDC position during what is known as an expansion stroke. Following the expansion stroke, one or more exhaust valves that communicate with the cylinder may be opened to allow the combustion gas to escape therefrom. The foregoing intake and exhaust valve events are commonly referred to as the main intake and main exhaust events, respectively.
During 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 are compressed. The compressed gases oppose the upward motion of the piston. During engine braking operation, as the piston nears TDC, at least one exhaust valve is opened to release the compressed gases to atmosphere, 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 develops retarding power to help slow the vehicle down.
The operation of a compression-release type engine brake, as described in the preceding paragraph, has long been known. One of the earliest descriptions of a system used for compression-release braking is provided in Cummins, U.S. Pat. No. 3,220,392. The system described in the Cummins '392 patent derives the motion to open a pair of exhaust valves for a compression-release event from an existing intake, exhaust, or injector pushrod or rocker arm. The compression-release motion is conveyed from a pushrod or rocker arm to a bridge joining two exhaust valves by a selectively expandable hydraulic linkage. This hydraulic linkage is expanded to convey the compression-release motion during engine braking operation, and contracted to absorb such motion during positive power operation. The contraction of the hydraulic linkage during positive power operation causes the compression-release motion to be “lost” during positive power, and accordingly, such systems are commonly referred to as “lost motion” valve actuation systems.
As shown in the Cummins '392 patent, many contemporary engines are multi-valve engines that employ, for example, four valves per cylinder, i.e., two intake valves and two exhaust valves, in order to improve overall performance. The conventional multi-valve actuation system typically opens both intake or both exhaust valves for a particular cylinder simultaneously. For example, in various embodiments described in the Cummins '392 patent, both of the exhaust valves for a given cylinder are actuated (opened and closed) simultaneously for a compression-release event. Because the two exhaust valves are actuated in response to motion imparted by a single source, both exhaust valves are provided with substantially the same lift and duration, in addition to being provided with substantially identical timing.
Over the years there have been various improvements to the systems and methods described in the Cummins '392 patent. One such improvement is described in Jakuba et al., U.S. Pat. No. 4,473,047. Like the system described in the Cummins patent, the Jakuba patent describes the use of a lost motion system in conjunction with an engine having two exhaust valves per cylinder. However, unlike the system described in the Cummins patent, the system described in the Jakuba patent conveys the compression-release motion to only one of the two exhaust valves associated with each engine cylinder. The inventors of the Jakuba system stated that they, “discovered that by opening only one of the exhaust valves during engine braking a surprising increase in retarding horsepower can be achieved. The increase in retarding horsepower is accompanied by a decrease in the observed operating pressure in the hydraulic system and is related to a decrease in the overall load in parts of the braking system.”
For a system designed for two-valve braking with one rocker arm, the braking load is basically cut into half by opening only one valve if the same peak cylinder pressure is maintained before compression-release blow-down. Therefore, the system should be able to sustain much higher cylinder pressure by a later opening of one valve to achieve higher retarding power and lower overall braking load at the same time. As described in more detail below, the Applicant has determined that if two individual rocker arms are used to open the two valves independently, then opening two valves is better than opening one due to faster compression-release blow-down from the same high peak cylinder pressure since braking load is not an issue for two valve braking with two rocker arms.
Other improvements over the system described in the Cummins patent have involved hardware, which falls into two broad categories: lost motion systems, and common rail systems. Several advancements in lost motion systems have been made to accommodate the modern prevalence of overhead cam engines. For example, recent lost motion system advancements have involved the placement of the hydraulic linkage in expandable tappets between a cam and a rocker arm or the engine valve itself, such as shown in Vorih et al., U.S. Pat. No. 5,829,397, which is hereby incorporated by reference. Lost motion components have also been integrated into rocker arms, such as is shown in Cartledge, U.S. Pat. No. 3,809,033, and Hu, U.S. Pat. No. 5,680,841, which are hereby incorporated by reference. Still other lost motion advancements, such as those shown in Vorih, U.S. Pat. No. 6,085,705 and which is hereby incorporated by reference, have been made to enable variable valve actuation (WA), which provides for the modification of individual valve actuation events on an engine cycle-by-cycle basis.
In the lost motion systems described above, the engine valves are typically driven by fixed profile cams, more specifically, by one or more fixed lobes on each of the cams. The use of fixed profile cams makes it difficult to adjust the timing and/or magnitude of the engine valve lift needed to optimize engine performance for various engine operating conditions, such as different engine speeds during engine braking. Rapid adjustment of valve timing in a system utilizing fixed profile cams is only now becoming viable using WA systems such as the one described in the Vorih '705 patent.
In common rail valve actuation systems, a source of high pressure hydraulic fluid is selectively applied to a piston to actuate the one or more exhaust valves for the compression-release events. Examples of such systems are shown in Meistrick et al., U.S. Pat. Nos. 5,787,859, 5,809,964, and 6,082,328, which are hereby incorporated by reference.
Common rail systems may provide virtually limitless adjustment to valve timing because the source of high pressure hydraulic fluid is constantly available for valve actuation. Accordingly, given sophisticated and high speed control over the application of this hydraulic pressure, a common rail system should be able to deliver valve actuation on demand, as well as provide some control over lift and duration. To date, h
Egan, III James F.
Yang Zhou
Collier Shannon Scott PLLC
Diesel Engine Retarders, Inc.
Rygiel Mark W.
Solis Erick
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