Method and apparatus for adjusting variable valve lift

Abstract

An apparatus for adjusting individual valve lift comprising a control arm assembly disposed between the cam lobes and the valve rockers for a multi-valve train. The control arm at each valve includes a driven gear. An actuator shaft includes a mating drive gear at each driven gear for rotating each control arm to vary the overall lift of the valves. In the prior art, the mating drive gears are fixed to the actuator shaft at identical fixed orientations. In accordance with the present invention, each mating drive gear is rotatably adjustable on the actuator shaft to permit changing of the orientation of each gear with respect to the actuator shaft, thereby changing the contact point of the control arm with its respective cam lobe. The lifts of the individual valves may be individually adjusted to provide equal air flow through all the valves in a multi-valve train.

Description

TECHNICAL FIELD

The present invention relates to variable valve actuation for internal combustion engines; more particularly, to a Continuously Variable Valve Lift (CVVL) apparatus incorporating a rotatable control rod to vary the contact point of a cam follower with an engine cam lobe; and most particularly, to a method and apparatus for adjusting the lift of individual valves in a multi-valve train.

BACKGROUND OF THE INVENTION

Methods and apparatus for varying the lift of combustion valves in internal combustion engines are well known. In a typical application of such apparatus, an entire multi-valve train, for example, all the intake valves on an inline engine, undergoes simultaneous and identical actuation. Such coordinated actuation is typically accomplished by providing a variable lift mechanism for each valve, and ganging these mechanisms together via a single rotatable actuator shaft controllably driven by a motor and controller. Rotation of the actuator shaft serves to vary, for each individual variable lift mechanism, the contact point of a control arm with its corresponding cam lobe, thus varying the maximum lift achievable by each valve during a full rotation of the camshaft.

A typical CVVL mechanism can vary an intake valve from a full lift position, e.g., about 10 mm, to a predetermined low lift position, e.g., about 1 mm or even completely closed (no lift).

An engine equipped with a CVVL mechanism idles typically in the low lift position, especially an engine employing valve lift as a throttling strategy, wherein it is important to have very low variation in air flow among the various cylinders. Such low variation in air flow requires very low variation in valve lift. Because of stack-ups of manufacturing tolerances among the various CVVL components and sub-assemblies, the net variation in valve lift and resulting air flow among the cylinders can be substantial in prior art engines. Such variation in lift typically is a trivial percentage at full lift but becomes highly significant at low lift.

What is needed in the art is a method and apparatus for fine-tuning the actual valve lift of each CVVL assembly at the valve actuator itself.

It is a principal object of the present invention to equalize the flow of air through all the valves in a multi-valve train.

SUMMARY OF THE INVENTION

Briefly described, an apparatus for adjusting individual valve lift in accordance with the present invention comprises a control arm assembly disposed between the cam lobes and the valve rockers for a multi-valve train. The control arm at each valve includes a driven gear. An actuator shaft driven by a motor as in the prior art includes a mating drive gear at each driven gear for rotating each control arm in a predetermined fashion to vary the overall lift of the valves. In the prior art, the mating drive gears are fixed to the actuator shaft at identical orientations. In accordance with the present invention, each mating drive gear is rotatably adjustable on the actuator shaft to permit changing of the rotational orientation of the gear with respect to the actuator shaft axis, thereby changing the contact point of the control arm assembly with its respective cam lobe. Thus, the lifts of the individual valves may be individually adjusted to provide equal air flow through all the valves in a multi-valve train.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is an elevational view of a prior art CVVL mechanism for an individual valve, equipped with an adjustable drive gear assembly in accordance with the present invention;

FIG. 2 is an elevational view like that shown in FIG. 1 but including the entire valve train, showing the valve in full lift position with the control arm on the full-lift nose of the cam lobe;

FIG. 3 is an elevational view like that shown in FIG. 2 but showing the drive gear assembly rotated such that the full-lift nose of the cam lobe produces zero lift;

FIG. 4 is an isometric view of a multi-valve train equipped with a CVVL system and adjustable drive gear assemblies in accordance with the present invention; and

FIG. 5 is an elevational cross-sectional view of an adjustable drive gear assembly mounted on the control shaft.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a method and apparatus for adjusting cylinder-to-cylinder air flow of a CVVL system during engine assembly and calibration to produce smooth idle quality by compensating for normal build tolerances.

Referring to FIG. 1, a prior art CVVL mechanism 10 for an individual valve 12 is equipped with an adjustable drive gear assembly 100 in accordance with the present invention, as described in detail below.

Prior art CVVL mechanism 10 comprises a control arm 14 pivotably mounted on a control arm shaft 16; a cam follower 18 rotatably mounted on a follower shaft 20 on control arm 14, and having a roller 22 for following the surface of a cam lobe 24 disposed on a camshaft 26, and having a contoured shoe 28 for actuating a roller rocker 30 pivotable on a hydraulic lash adjuster 32 to open and close valve 12. The curved shoe 28 has a cam profile which has an extended base circle portion and a sloped portion up to full valve lift. An actuator shaft 134 is disposed parallel to camshaft 26. A driven gear 36 is formed on control arm 14 and is engaged by a drive gear segment 102 of adjustable drive gear assembly 100.

As is well known in the prior art, rotation of control arm 14 about shaft 16 changes both the contact point 33 of roller 22 on cam lobe 24 and the distance of follower shaft 20 from camshaft 26, thus affecting the portion of the curved shoe 28 acting on the roller rocker 30. As the control arm 14 moves in relation to the camshaft 26, the portion of the curved shoe 28 contacting the roller rocker 30 changes and varies the amount valve 12 opens.

Referring to FIG. 2, when adjustable drive gear assembly 100 is mounted on actuator shaft 134 at a first orientation 35, as described below, control arm 14 is positioned such that rotation of cam lobe 24 and camshaft 26 causes nose portion 25 of the cam lobe to come in contact with roller 22 and causes valve 12 to be fully opened from seat 40. When control arm 14 and assembly 100 are rotated as shown in FIG. 3, when nose portion 25 of cam lobe 24 comes in contact with roller 22, valve 12 remains closed (no lift) on seat 40.

Referring to FIGS. 4 and 5, a multi-valve train 200 assembly is shown, equipped with a CVVL system and adjustable drive gears in accordance with the present invention. A CVVL actuator shaft assembly 202 provides individual adjustment of valve lift. At each engine cylinder, drive gear segment 102 is mounted on actuator shaft 134 that mates with a control arm 14 having driven gear 36. By adjusting the orientation of each of the actuator shaft gear segments 102 about the axis 103 of actuator shaft 134, the matching control arm can be rotated about the axis of control arm shaft 16 to set valve opening to a valve lift specification, which is necessary to balance airflow across all cylinders for smooth idle.

The actual adjustment may be accomplished by the following procedure. First and second adjustment set screws 104 are provided, threaded into adjustment block 106 which is fastened to actuator shaft 134 as by a bolt 108 or other attachment means at a rotational location nominal for the CVVL mechanism. Because only a segment of gear 102 is required for CVVL operation, two flats 110 are provided on gear segment 102 for adjustment set screws 104 to act against. Gear segment 102 is allowed to rotate about actuator shaft 134 until the required valve lift specification is met. Gear segment 102 then is locked onto actuator shaft 134 by tightening a locker such as clamping bolt 112 that is threaded into gear segment 102 via an oversize bore 114 through actuator shaft 134. Preferably, bolt 112 is tightened on shaft 134 via a bolt shoe 116 matching the curvature of shaft 134. This procedure is repeated on each of the remaining valves so all valves have equal lift.

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.

Claims

1. An assembly for adjustably varying the actuation of a continuously variable valve lift mechanism in an internal combustion engine, comprising:

a) an actuator shaft; and

b) at least a segment of a gear disposed on said actuator shaft for variably engaging said continuously variable valve lift mechanism, wherein said gear segment is rotationally adjustable upon said actuator shaft.

2. An assembly in accordance with claim 1 further comprising:

a) an adjustment block mounted on said actuator shaft;

b) at least one adjustment screw engagingly disposed in said adjustment block and bearing upon said gear segment; and

c) a locker disposed in said adjustment block and received in said gear segment.

3. An assembly in accordance with claim 2 wherein said locker is a locking screw.

4. An assembly for adjustably varying the actuation of a continuously variable valve lift system in an internal combustion engine, comprising:

a) a plurality of continuously variable valve lift mechanisms for actuating a plurality of engine combustion valves, defining said system;

b) an actuator shaft disposed along said plurality of variable valve lift mechanisms; and

c) a plurality of gear segments disposed on said actuator shaft and positioned at each of said plurality of continuously variable valve lift mechanisms, wherein at least one of said gear segments is rotationally adjustable upon said actuator shaft.

5. A method for varying the orientation of a segment of a gear disposed and rotationally adjustable upon on an actuator shaft for variably engaging a continuously variable valve lift mechanism, comprising the steps of:

a) providing an adjustment block mounted on said actuator shaft;

b) providing an adjustment screw engagingly disposed in said adjustment block and bearing upon said gear segment; and

c) adjusting said adjustment screw to cause said gear segment to rotate about said actuator shaft to a desired orientation.

6. A method in accordance with claim 5 comprising the further steps of:

a) providing a locker received in said gear segment; and

b) tightening said locker after said adjusting step.

7. A method for equalizing the lifts of a plurality of combustion valves in a multi-valve train, comprising the steps of:

a) providing a plurality of continuously variable valve lift mechanisms for actuating said plurality of engine combustion valves,

b) providing an actuator shaft disposed along said plurality of continuously variable valve lift mechanisms, and

c) providing a plurality of gear segments disposed and rotationally adjustable upon said actuator shaft and positioned at each of said plurality of continuously variable valve lift mechanisms;

d) providing an adjustment block mounted on said actuator shaft adjacent each of said continuously variable valve lift mechanisms;

e) providing an adjustment screw engagingly disposed in each of said adjustment blocks and bearing upon said gear segment; and

h) adjusting each of said adjustment screws to cause each of said gear segments to rotate about said actuator shaft to a desired orientation.

8. A method in accordance with claim 7 comprising the further steps of:

a) providing a locker received in said gear segment; and

b) tightening said locker after said adjusting step.