Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Utility Patent
1999-04-01
2001-01-02
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090310
Utility Patent
active
06167854
ABSTRACT:
FIELD OF INVENTION
This invention relates to valve trains of an internal combustion engine and, more particularly, concerns a mechanism for varying the timing of the opening and closing of the intake and exhaust valves with respect to the phase of the piston stroke.
BACKGROUND OF THE INVENTION
During the operation of an internal combustion engine, especially a diesel engine, it is important to have the intake valves close as soon as possible after bottom-dead-center and to retard the opening of the exhaust valve at low speeds to provide a better air cycle. Many types of mechanisms have heretofore been proposed for accomplishing this result and a few examples of such mechanisms can be seen in my U.S. Pat. No. 5,673,659 entitled “Lead Screw Driven Shaft Phase Control Mechanism”, issued on Oct. 7, 1997 and assigned to the assignee of this invention.
In general, each of the mechanisms disclosed in the above-mentioned patent provide a selective timing or phase adjusting system between a drive gear and a driven camshaft with the drive gear being coaxially mounted and axially affixed with respect to the driven camshaft for rotation together. An intermediate connecting member is coaxially mounted with respect to the drive gear and the camshaft and is capable of axial movement and angular movement with respect to either the camshaft or the drive gear when experiencing its relative axial movement. The intermediate connection and a coupling member are connected to a geared device that is selectively activated by an electric motor which produces axial movement of both the intermediate connection and the coupling member with respect to the camshaft and the drive gear to any desired axial position between predetermined first and second positions. The gearing device provides a unidirectional drive system which allows the electric control motor to drive the mechanism to provide the optimum shaft phasing and is operably connected to a sleeve that is axially affixed to the intermediate connecting member. When in operation, the gearing device moves the sleeve axially, which in turn, moves the intermediate member axially with respect to both the drive gear and the camshaft. The intermediate connection member is an axially shifting member that has helical splines that rotationally affix it to the camshaft to allow relative rotation of the camshaft with respect to the drive gear. In one embodiment, the gearing device drives the sleeve while in another embodiment the gearing device is a threaded lead screw engaging complementary threads formed on the sleeve. In a third embodiment disclosed in the patent, the gearing device is a part of a gear sprocket that has an internally threaded hub that engages complementary external threads on the sleeve.
SUMMARY OF THE INVENTION
The present invention is functionally similar to the mechanisms described above and seen in my patent but differs in one respect therefrom in that a new form of power transmission is substituted for the threaded jackscrew system which executes the axial motion of the shifting sleeve. Inasmuch as the lowest possible friction level is desired in variable valve timing mechanisms to minimize wear and to allow use of a small electric motor for varying the position of the camshaft, it is important to have a transmission arrangement with less friction than an ACME screw. In this regard, the optimum replacement would be the ball-nut recirculating screw device which enjoys very low friction in operation. However, irrespective of the many advantages provided by such a device, using it for a variable valve timing mechanism according to this invention is not possible from a practical standpoint because the required ball-return duct would interfere with the drive gear. Accordingly, in this instance, I have incorporated into the variable valve timing mechanism made according to the present invention one of the ball-nut transmissions disclosed in my co-pending patent application Daimler-Chrysler File No. 98-1422, entitled “BALL-NUT TRANSMISSION”, filed on Mar. 17, 1999, and assigned to the assignee of this invention. Other changes are also part of the present invention and will become more apparent from the detailed description of the new and improved variable valve timing mechanism contained in the specification.
One object of the present invention is to provide a new and improved variable valve timing mechanism that is provided with two major parts one of which is located at the front end of an internal combustion engine and the other is located at the rear end of the engine and in which the control section of the mechanism incorporates a ball-nut transmission for providing linear movement of a quill shaft interacting with straight splines and helical splines for changing the phase of a camshaft.
Another object of the present invention is to provide a new and improved variable valve timing mechanism which has an axially movable quill shaft extending through a hollow camshaft and has one end of the quill shaft directly connected to the camshaft through straight splines and is indirectly connected to helical splines so that axial movement of the quill shaft provided by a ball nut transmission located at the other end of the quill shaft serves to rotate the camshaft a predetermined distance upon actuation of an electric stepper motor.
A further object of the present invention is to provide a new and improved variable valve timing mechanism incorporating a non-recirculating ball-nut transmission for linearly moving a quill shaft and in which balls are incapsulated in hemispherical cavities formed in an axially movable sleeve surrounded by a nut member having a helical groove which cooperates with the balls for providing axial movement of the quill shaft.
The above objects and others are realized in accordance with the invention by a variable valve timing mechanism for an internal combustion engine that in its broadest form comprises a drive timing assembly located at the front end of the engine and a control assembly section located at the rear end of the engine. The timing drive assembly includes a drive gear adapted to be driven by the crankshaft of the engine and a hollow camshaft that extends between the timing drive assembly and the control assembly. A quill shaft is co-axially mounted within the camshaft and has a first portion located at the front end of the engine and is connected to the hollow camshaft by a plurality of straight splines. A hub member is fixed with the drive gear while the first portion of the quill shaft is connected to the hub member by a plurality of helical splines. An axially movable sleeve member is connected to and surrounds a second portion of the quill shaft at the rear end of the engine. In addition, a nut member surrounds the sleeve member and is drivingly connected to the sleeve member through a plurality of circumferentially spaced non-recirculating balls encapsulated between a hemispherical cavity and a helical groove formed in the other of the members so that, upon rotation of the nut member, the sleeve member and the quill shaft move axially relative to the camshaft and, as a result of the helical splines, simultaneously cause the camshaft to rotate relative to the drive gear a predetermined angle so as to provide a change in the opening and closing of the valves of the engine.
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DaimlerChrysler Corporation
Lo Weilun
MacLean Kenneth H.
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