Patent Application
20090205595
The present invention relates to variable valve lift systems for internal combustion engines; more particularly, to a system for continuously variable lift of dual intake valves; and most particularly, to such a system wherein the valvetrain of one of the dual intake valves is further equipped with means for lost motion valve deactivation.
Continuously variable valve lift systems are known in the engine arts. See, for example, the system disclosed in US Patent Application Publication No. 2007/0125329, published Jun. 7, 2007 and incorporated herein by reference. Such a system incorporates a crank mechanism for selective continuous variation of the contact point of a special rocker subassembly (RS) with the engine camshaft to vary the angular rotational motion of the RS. The RS is positioned between the engine camshaft and the valvetrain's roller finger follower (RFF). The RS includes a secondary cam surface followed by the RFF. Varying the contact point of the RS on the camshaft has the effect of varying the lift and the opening and closing timing of the associated engine combustion valve. For a cylinder having dual intake or dual exhaust valves, the RS comprises a wide secondary cam surface that is followed identically by the RFF for each valve.
Variable valve activation/deactivation (WA) systems are also known in the engine arts. See, for example, U.S. Pat. No. 6,321,704 that discloses a deactivating hydraulic lash adjuster (DHLA), and U.S. Pat. No. 7,093,572 that discloses a deactivating roller finger follower (DRRF), both of which are incorporated herein by reference. Each of these prevents the rotary motion of the camshaft lobe from being translated into reciprocal motion of the associated valve stem by absorbing the equivalent motion within itself (“lost motion”). Thus the valve is “deactivated” and prevented from opening on schedule.
For gasoline engines, compromises inherent with fixed valve lift and event timing of a conventional valve train have prompted engine designers to consider Continuously Variable Valve Lift (CVVL) systems for more flexible air flow control optimized for each engine load and speed condition. In recent years, some relatively basic forms of CVVL have been introduced into production engines. Greater performance and drivability expectations of customers, more stringent emission regulations set by government legislators, and the mutual desire for higher fuel economy are increasingly at odds. As a solution, some vehicle manufacturing companies are considering large-scale application of higher function CVVL mechanisms in their next generation vehicles, mainly to improve fuel economy, by reducing pumping loss, and cold start combustion stability, with increased cylinder air flow tumble motion. However, the CVVL engine has two critical engineering challenges for turbulence (swirl or tumble) enhancement and cylinder by cylinder valve lift variation, which requires combustion chamber masking for tumble enhancement and costly select fit of output rocker cam or roller finger followers for CVVL.
When applying a prior art CVVL system, current engine combustion strategies allow the intake valve to open from zero to full lift, as described above. However, the use of variable lift mechanisms has been limited on dual intake valves to the same lift on both valves of each cylinder, which cannot provide any in-cylinder air flow turbulence enhancement.
What is needed in the art is a CVVL system wherein in-cylinder turbulence is enhanced during variable-lift operation of an internal combustion engine, and especially under low lift flow conditions.
It is a principal object of the present invention to provide increased in-cylinder turbulence during variable-lift operation of an internal combustion engine.
Briefly described, in a dual intake valve system for an internal combustion engine, a CVVL system is provided for both intake valves for one or more engine cylinders. In each cylinder, one of the intake valvetrains includes a valve deactivation device such as a DHLA or a DRFF, and the other intake valvetrain includes a non-deactivating HLA and RFF. To improve in-cylinder air flow turbulence (mainly swirl) under low valve lift, one of the intake valves is deactivated by an external actuator system, resulting in intake air or air/fuel mixture through only one valve, which generates strong swirl by unbalanced flow because the open valve is off-axis of the cylinder.
In a presently preferred embodiment, a CVVL engine including a valve deactivation device provides the same amount air flow for the same engine load as a non-CVVL engine by providing higher valve lift (approximately 2 times the lift of a prior art CVVL-only maximum valve lift). The higher valve lift also reduces the impact of valve lift variation by component tolerance stack-up on engine performance to provide an expanded CVVL operating zone, and especially to extend the low lift limit zone.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
a and 4b respectively are schematic lift curves for the corresponding valves shown in
a and 6b respectively are schematic lift curves for the corresponding valves shown in
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate currently preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
The present invention includes a CVVL system combined with a valve deactivation device. In each cylinder, one of the intake valvetrains is installed with a valve deactivation device whereas the other intake valvetrain is installed with a non-deactivating regular HLA and roller finger follower. To improve in-cylinder air flow turbulence (mainly swirl) under low valve lift conditions, one of the intake valves is deactivated by an external actuator system to provide air or fuel/air mixture entirely through the other valve, which generates strong swirl by unbalanced air flow. The CVVL engine combined with a valve deactivation device provides the same amount of air flow with higher valve lift for the same engine load. For conventional CVVL operation, the valve deactivation device is not operative and thus transmits the full lift generated by the output rocker cam to its associated valvetrain. For swirl enhancement purposes under low lift conditions, the valvetrain with the valve deactivation device is deactivated to keep the valve closed through lost motion within the valve deactivation device.
Referring to
CVVL system 10 may take the form of a prior art system for variable valvetrain actuation, substantially as disclosed in US Patent Application Publication No. 2007/0125329 A1. Alternatively, a CVVL system 10 may take the form shown in
A rocker subassembly (RS) 12 is disposed between camshaft 300 and first and second rocker arms, shown herein as roller finger followers (RFFs) 14a,14b of valvetrains 100a,100b. RS 12 is pivotable on or about RS shaft 16 and includes a roller 17 for engaging a lobe 302 of camshaft 300 and further includes first and second cam plates 18a,18b having output cam profiles that themselves engage the respective rollers 20a,20b of RFFs 14a,14b.
A RS-positioning crank subassembly (CS) 22 includes a crankshaft 24 supportive of first and second crank arms 26a,26b rotatably disposed on non-rotatable circular throws 28a,28b eccentrically mounted on crankshaft 24. Each of arms 26a,26b includes a nose 30 (only nose 30b visible in
As camshaft 300 rotates counter-clockwise, the opening flank of cam lobe 302 pushes rocker roller 18 away, causing RS 12 to rotate in a counter-clockwise direction. As RS 12 rotates, it turns about the axis of shaft 16. Continued counter-clockwise rotation of RS 12 advances the output cam profiles ground into cam plates 18a,18b. The further that RS 12 is rotated counter-clockwise about shaft 16, the greater the lift imparted through RFFs 14a,14b to valvetrains 100a,100b. However, the total lift is governed by the action of CS 22 as described above.
Each RFF pivots on the ball shaped tip of a hydraulic valve lash adjuster (HLA) 34a,34b conventionally disposed in engine 200. HLA 34a is a conventional non-deactivating HLA. However, in accordance with the present invention, HLA 34b is a deactivating HLA in accordance with the prior art, permitting complete activation or deactivation of valvetrain 100b as may be desired.
Referring to
a) both HLA 34a and 34b′ are conventional non-deactivating HLAs; and
b) RFF 14b′ is a deactivating roller finger follower (DRFF) in accordance with the prior art.
It will be seen that the deactivation of valvetrain 100b can be carried out to equal effect by either embodiment 10 or embodiment 10′, or any other method of valve deactivation such as, by way of example, a deactivating hydraulic lash adjuster.
Referring to
Referring to
Because the activation or deactivation of second valvetrain 100b is independently controlled from the action of CS 22 (
In this manner, air flow turbulence such as swirl can be introduced into the cylinder for improved combustion. For example, at a time when it is desirous to introduce a swirl to the mixture charge entering the combustion chamber, only one of the two intake valves may be opened, as shown in
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
