US1957181A - Automatic valve timing device - Google Patents

Description

May 1, 1934- E. w. MITCHEL. 1,957,181

AUTOMATIC VALVE IIMING DEVICE Filed Feb. 27, 1932 ATTORNEYS` Patented May l, 1934 UNITED STATES PATENT FFECE AUToMATIo VALVE TIMrNc DEVICE Edward W. Mitchel, Detroit, Mich. Application February 27, 1932, serial 10,595,532

4 Claims.

This invention relates to internal combustion engine construction, and more particularly to such engines having cam-operated intake and exhaust valves. The invention has for one of its 5 objects provision of means for automatically changing the timing of the opening and closing of the intake and exhaust valves of such an engine in accordance with variations in the speed at which it is running.

As is well known, when a gasoline engine is running at high speed, the valves require more lead than when the engine is running at low speed, and in fact it is common to open the eX- haust valves of a high speed engine twenty or thirty degrees before the pistons reach the bottom of their power strokes. It is not possible in commercially practical constructions as now made, however, to provide as little lead as is required fer maximum einciency at low speed, else at higher speeds the back pressure would be so great as to cause undue vibration, knocking and stalling. I have found such back pressure caused by insuicient valve lead to be one of the most common causes of engine vibration. On the other hand, if adequate lead for high speed operation is provided, the premature opening of the valves at low speeds causes such loss of power as to very deleteriously affect the engines performance. It is the usual practice, in order to minimize these difliculties, to compromise as to valve settings, and to so arrange their timing that the lead is proper at some intermediate speed; so that even though it is therefore necessarily too little at higher speeds and too great at lesser speeds, the engines performance will be affected as little as possible. The ineiiciency thus introduced does, however, detract from the engines performance, and that to an extent so serious that marked improvement in iiexibility, smoothness and power is obtainable by remedying these undesirable conditions, and providing proper valve timing at all speeds. This my invention is aimed to and does accomplish as its most important object.

By means of my improved automatic valve timing construction I am enabled to maintain the proper valve lead at all times, and thus to greatly improve the performance of -a gasoline engine with which it is associated, at both low and high 50 speeds, reducing vibration at all speeds and adding considerably to the maximum speed of the engine, since back pressure, due to insuicient valve lead is not permitted to build up.

It is a further object of this invention to provide 55 such an automatic valve timing device which is so (Cl. (i4-90.5)

simple, rugged, and inexpensive in construction as to be practical for installation as standard equipment upon gasoline motors produced in quantities, and, barring material iiaws, invariably capable of lasting the full life of the engine without requiring attention or adjustment.

Other objects and advantages will be apparent from the following description, wherein reference is made to the accompanying drawing illustrating a preferred embodiment of my invention, and wherein similar reference numerals designate similar parts throughout the several views.

In the drawing:

Figure l is an elevational view showing in plan the arrangement of parts employed in one form of my invention.

Figure 2 is a vertical sectional view taken substantially on the line 2 2 of Figure 1 and looking in the direction of the arrows there shown.

Figure 3 is an elevational view taken looking at the opposite side of the assembly from Figure 1 with the closure plate partly broken away and showing in dotted lines the fly weights in their innermost positioning.

Figure 4 is a similar elevational view, with the closure plate removed, showing in dotted lines the fly weights in their outermost positioning, resulting from suiciently rapid rotation of the unit.

Figure 5 is a vertical sectional view taken substantially on the line 5-5 of Figure 1 and looking in the direction of the arrows there shown.

Figure 6 is a sectional elevational view taken 90 substantially on the line 6 6 of Figure 2 and looking in the direction ofthe arrows, bringing out the construction and arrangement of the inner faces of the fly weights and parts carried thereby, and showing the weights in their outwardly moved positioning, and f Figures '7 and 8 are detailed perspective views of the cam-actuating stud members I employ for rotating the hub relatively to the gear.

Referring now to the drawing: Reference character 20 designates the cam shaft gear of an in-` ternal combustion engine, generally designated 50, This gear, in ordinary engine constructions, is rigidly secured to the cam shaft and positively driven, usually at fractional crank shaft speed, by a driving gear on the crank shaft. In such a construction it is possible to Vary the timing of all the valves simultaneously only by turning one of these gears a few teeth relatively to the other, or one of the shafts relatively to the gears In my improved construction I provide a hub 21 for the gear 20, which is loose relatively thereto, so that the hub and the toothed portion of the gear may turn relatively to each other. The gear is of ring form, and interiorly provided with a flange 22, as shown in Figures 2 and 5. Secured to the ilange. as by screws 23, are the annular plates 24-25, the aligned axial apertures 26-27 of which rotatably carry the hub 2l. The hub 2l is keyed or otherwise ilxed to the cam shaft, and integrally carries the fla-nge plate 28, which radially projects and is slidable between the plates 24-25. The hub 21 and flange 28 are thus free to turn relatively to the gear and plates 24-25.

Cam slots 29-30 are formed in the flange 28, their substantial contour being best shown in Figures 3 and 4, and slidable therein are stud-like followers 3l and 32, which extend through guide slots 33 in the plate 25. The slots 29, 30, and 33 are so contoured as to enable circumferential movement of the hub relatively to the gear when the studs 3l and 32 are simultaneously moved outwardly or inwardly in the slots 33. When the studs are moved outwardly, they move the hub 21 and thus the cam shaft in the proper direction to advance-the lead, by turning the plate 28, and thus the hub, relatively to the positively driven ring gear portion 20, due to the inclination of the cam slots.

In order to provide for gradual automatic outward movement of the cam studs concurrently with increasing engine speed, and for similar inward movement thereof ccncomitantly with decrease of engine speed, I provide the governing ily weights 34-35, which are mutually outwardly movable under increasing centrifugal force caused by mounting engine speeds but normally indrawn by tensile springs, as 36-37-56--5'7-58. All of these with the exception of the spring 58 act in tension, their ends being secured directly to the fly weights, in apertures in which they are also partially housed, as clearly shown in the drawing. Companion spring 58 is trapped upon the overlapping portions of the hooked supporting stops rigidly carried byl and projecting inwardly from the ily weights in such manner that the spring 58 acts to supplement the resistance of the remaining springs to outward movement of the weights when the latter approach the outer limit of their travel, while the hooked supports additionally provide, in combination with the spring 58, a positive stop limiting outward movement of the weights. The ily weights may be directly connected to the studs, as by extending the threaded end portions 38-39 of the studs for that purpose, and forming suitable apertures 40 in the ily weights to receive them. Securing nuts 4l are screwed upon the threaded end portions 38 and 39 of the studs, and set flush if desired in counterbored portions 42 of the stud apertures 40. To insure smooth sliding movement of the fly weights relatively to each other, I preferably secure to each an extended slotted slide bar (43- 44). Slots 45 and 46 in the bars serve as slideways in which the flattened central portions 32 of the studs 32 slidably lit, as shown in Figures 1, 5 and 6. The bars 43-44 additionally control the sliding movements of the weights by engaging in slots or kerfs 47-48, one formed in each ily weight opposed to that carrying the slide bar which engages therein, to enable their engagement in the slideways -46. The central portions 32 of the studs 32 are made longer than the similar portions 3l of the studs 31, so that in the case of the studs 32, these portions project a suitable distance from the plate 25 for engagement in the slots, as shown in Figures 5, 7 and 8.

The resistance of the springs 36-37 is of course so proportioned to the weights 34-35, and to the cam slots, as well as to the extent of the relative movement desired to be imparted to the hub 2l, that upon any increase of engine speed, the extent of outward movement of the ly weights will be so proportioned relatively to such increase as to advance the hub relatively to the driven portion of the gear, and thus the lead of the valves, to an extent adapted to maintain such lead in proper relation to the engine speed. It will be seen that speed variations will result in whatever outward or inward movement of the weights is necessary to balance the centrifugal and centripetal forces acting upon them. These movements are translated, by the described mechanism, into relative turning movement 0f the cam-shaft with respect to its driving gear, in the proper direction and to the proper extent to maintain the valve lead at its most elcient setting.

The actual quantity and design values of such factors as weights, spring resistances, cam slot development, etc. are of course dependent upon the characteristics of the engine with which the device is to be used, and those skilled in the art will be readily capable of calculating these factors for any given case, now that I have disclosed a mechanical method by means of which the desired result may be effected.

While the operation of the device is doubtless clear from the foregoing description, it might brieily be summarized as follows: When the motor is turning over slowly, centrifugal force is insufficient to throw the weights 34-35 outwardly to an appreciable extent against the tension of the springs 36-37-56-57-58, and their centripetal pull maintains the weights in indrawn position, and thus holds the cam-actuating studs 3l and 32 at the inner ends of the slots 33. The inclination of the cam slots 29 and 30 is such that the stud heads, upon moving outwardly therein, rotate the flange 28 and thus the hub 21 in the proper direction, and to the proper extent, in accordance with and dependent upon the instant speed of the engine, to compensatingly advance the valve lead to maintain the same at the point of maximum efficiency, while likewise upon slowing of the engine the stud heads, drawn inwardly by the springs 36-37-56-57-58, retard the hub 21 and thus the cam shaft relatively to the gear in like manner to decrease the valve lead. The directions of rotation and of movement of the parts upon acceleration of the motor are indicated in this particular case by arrows 50, 51, and 52 in Figure 1.

It will be seen that the movement imparted by the studs is irreversible, however, and that no matter what changing resistance to rotation the cam shaft may offer, no thrust thus imparted can vary the spacing of the ily weights which is for all practical purposes entirely controlled by centrifugal force and the opposing spring tension.

The preferred embodiment of my invention herein disclosed and illustrated has been chosen as illustrative of the most effective and compact organizations of basically similar or equivalent parts for the accomplishment of the purposes herein stated, but I desire it to be understood that within the fair field and spirit of the language of the subjoined claims structural variations from what is herein illustrated may be indulged` in without departure from the intended eld of this disclosure.

What I claim is:

1. Means for controlling the cam shaft of a poppet valve engine, comprising a gear and hub rotatable relatively to one another and having overlapping portions with intersecting cooperating cam slots therein, said slots having portions angularly disposed relatively to each other, a pin extending through and slidable in both slots and adapted when moved therein to turn the hub relatively to the gear, the relative angularity of the slots being small, so that the pin can not be moved in the slots by torque applied to either the hub or gear member, and a fly Weight connected to the pin to move the same and so change the relative positioning of gear and hub in response to speed variations.

2. Means for automatically controlling in response to engine speed the valve timing of an internal combustion engine incorporating intake and exhaust valves and a valve actuating shaft, comprising a hub adapted to be affixed to such a shaft, an annular gear carried by the hub and rotatable relatively thereto, means for positively driving the hub by the gear at any of various relative angular positions, comprising a limitedly radially movable fly-weight ca ried by the gear, and combined driving and shifting means connecting the weight and hub for both continuously turning the hub and for shifting the hub relatively to the gear upon radial movement of the ily-weight caused by variation of its speed of revolution, including a plurality of cam portions arranged at small angles relatively to each other, and common actuating means therefor connected to the ily-weight, said Weight being thereby not radially shiftable by torque transmitted through the hub.

3. Means operatively connectible with the valve actuating shaft of an internal combustion engine whereby timing of the opening and closing of the valves may be automatically regulated, comprising a pair of overlapping and relatively movable driving and driven members having a plurality of pairs of partly registering cam slots therein with relatively angular portions, a driving pin extending through each pair of slots and movable therein to turn the driving and driven members relatively to each other, the slots of said pairs being arranged at small angles relatively to the paths of pin movement, whereby neither the driving nor driven member can be moved relatively to the other by force transmitted through the pins, and means including a fly-weight responsive to speed variances for actuating said driving pins responsively to engine speed variances, and means resiliently in-drawing the last mentioned means.

4. Means for controlling the valve-timing of an internal combustion engine incorporating intake and exhaust valves and a valve-actuating shaft, comprising a driving member adapted to be carried by such a shaft in lost motion connection therewith, a driven member adapted to be rigidly aixed to the shaft, said driving and driven members having partly registering relatively angular oam slots therein, a driving pin extending through said slots and movable theree in to change the relative angularity of the driving and driven members, and means including a fly-weight for moving the pin in response to speed changes, the slots being arranged at a small angle relatively to the paths of pin movement, whereby the pin is movable by the ilyweight but not by torque applied through a slotted member.

EDWARD W. MITCHEL.

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