Devices For Controlling The Valves Of Internal Combustion Engines

Abstract

A device for controlling the valves of an internal combustion engine having overhead valves comprises a control cam, and two oscillating rockers for each valve. The free end of each rocker is disposed between the cam and the end of the valve stem. The free end of the rocker in contact with the cam has a roller which is in rolling contact with the cam. The lower planar surface of this rocker is in contact with the spherical head portion at the free end of the other rocker. This spherical free end is in in turn in contact with the end or tappet of the valve stem. The rocker in contact with the end of the valve stem oscillates in a plane perpendicular to the axis of the valve. The rocker in contact with the cam oscillates about an axis parallel to the axis of the camshaft. The mid-point of the path of contact between the spherical head portion and the end of the valve stem is disposed substantially along the axis of the valve.

Description

The present invention concerns a control device for valves for internal combustion engines, in particular for so-called radial valve type engines.

These types of engines whose combustion chambers are in the form of hemispherical heads and whose valve axes are disposed along radii of the hemispherical head, permit by this arrangement a maximum valve surface which enables high performances, the interest for these engines being in competition.

Nonetheless, these engines have only had until now a limited success in competition. In fact, the radial orientation of the valves therefore in different directions does not satisfactorily enable their control by a camshaft as the axis of the valve is not located in the plane of the cam. The control forces of the valves are not transmitted axially which results in the rapid wear and the jamming or seizing which give these motors a reputation of being fragile and lacking endurance.

Known devices for transmitting forces by a support finger in an annular member or by desmodromic pivoting control levers do not yield a satisfactory solution to this problem. The large amount of friction produced causes rapid heating and wear to the detriment of the precision of the timing of the valves and the endurance of the motor.

An object of the present invention is a device for controlling valves which provides a solution to this problem. This device essentially comprises the interposition, between the control cam and the end portion of the stem of the valve, the free ends of two rockers oscillating about a pivot at their other end, the free end of said first rocker being in contact with the cam, oscillating in a plane perpendicular to the axis of this cam and being in contact with a spherical head portion of the second rocker which is in contact with the end of the stem of the valve and oscillates in the plane of the axis of the valve, the mid-point of bearing contact of the spherical head portion on the end portion of this valve stem being disposed substantially along the axis of the valve.

The rocker or lever in contact with the cam is provided with a roller rolling along this cam, and the plane of the lower surface supported on the spherical head of the second rocker passes through the axis of oscillation of said lever, this axis being parallel to the axis of the camshaft.

The rocker or lever in contact with the spherical head portion oscillates about an axis situated in a plane perpendicular to the axis of the valve corresponding to the mid-point of the plane of the valve head.

The plane passing through the axis of symmetry of the cam perpendicular to the camshaft cuts the axis of the valve at a point corresponding substantially to the center of the spherical head portion of the support rocker on the valve.

The end of the valve stem is provided with a connecting end portion of a known type formed of a wear-resistant alloy whose thickness is adjusted to assure the clearance and thereby the correct timing of the valve.

The group of pivots of the rockers of each cylinder are mounted on a common connecting member independently centered on the cylinder head for example on the bore or socket for receiving the spark plug.

Such a device provides the advantage of the transmission of the movement from the cams to the valves with a minimum of friction, inherent looseness, and non-axial forces. The cam surfaces rest on followers in perfect rolling contact. The spherical head portion of the second rocker axially transmits the thrust of the cam. Its oscillating movement effects a combined rolling and sliding movement of the spherical head portion. This movement produces a superficial glossing of the contact surfaces which remain quite small in the order of several square millimeters. This results in practically no wear, a great precision of the transmission movements, a high mechanical efficiency and a great endurance.

Another advantage of the device is its simplicity of construction in the form of a separate sub-assembly which can be easily and quickly mounted and dismounted for adjusting and checking, this advantage being very important in competition. It also easily and inexpensively enables the provision of this type of valve gear to engines not originally provided therewith.

A preferred embodiment of a device according to the invention is set forth in the description hereinbelow and in the accompanying drawings. It corresponds to valve gear including four valves and a pair of camshafts for a hemispherical combustion chamber with a central spark plug. One camshaft controls two inlet valves arranged side by side, the other camshaft controls two exhaust valves also arranged side by side but opposite the inlet valves.

In the drawings:

FIG. 1 shows a view partially in section of the device taken along the line I--I of FIG. 2 which includes the axis of the spark plug and two diametrically opposed valves;

FIG. 2 shows a top plan view of the device without the camshafts;

FIG. 3 shows an elevation view showing a camshaft, the rockers and the valves in their relative positions;

FIG. 4 shows a side view showing the mounting of the camshafts, the rockers and the valve heads;

FIG. 5 shows perspective view in phantom lines of a cylinder head and its combustion chamber equipped according to the embodiment described according to the invention.

In FIG. 1 the cams 3 and 4 of the camshafts 1 and 2 partially shown bear against the rollers 5 and 6 mounted on the free ends of the rockers 7 and 8 whose other ends are pivotally mounted about the pins 9 and 10 fixed to a central connecting member 11.

The lower surfaces 12 and 13 of the rockers 7 and 8 come to bear against the spherical heads portions 14 and 15 of the rockers 16 and 17 which are also pivotally mounted about the pins 18 and 19 fixed to the member 11. Weight-reducing holes 20 and 21 can be provided in the spherical head portions 14 and 15 in order to diminish the inertia of the combination and to facilitate the mounting for machining.

The spherical head portions 14 and 15 also bear on the connecting end portions 22 and 23 covering the heads of the valves 24 and 25. The valves slide in the guide bushings 26 and 27 and are seated against their seats 28 and 29 according to a known arrangement by the play or free motion between two springs 30 and 31 and the annular members 32 and 33.

The connecting member 11 for pivoting the rockers 8, 9 and 16, 17 is adjusted on the cylinder head 34 of the motor by centering circular shoulders 35 at the opening of the bore or socket for receiving the spark plug 36. This bore as well as the screw-threaded hole 37 for mounting the spark plug are aligned along the axis of the cylinder. The threaded hole 37 for the spark plug opens into the center of the hemispherical head 39 delimiting the combustion chamber 40 with the surface of the piston head (FIG. 5).

FIG. 2 shows the star-arrangement of the four rockers 16, 16', 17, 17' which correspond to the four valves about the spark plug bore or socket 36, their pivot axes 18, 18', 19, 19' on the member 11 and the rockers 7-8' and 7'-8 disposed two by two in opposed relationship.

FIG. 3 shows the mounting of the bearings 42 for the camshaft 1 on the cylinder head 34 by means of bolts 43. The camshaft 1 is driven by a chain-driven gear wheel 44 at its end. A casing 41 covers the entire device.

In operation the rotation of the cams 3, 3', 4, 4' rolling along the followers 5, 5', 6, 6' causes the oscillation of the rockers 7, 7', 8, 8', situated in the same plane as the cams, about pivots perpendicular to this plane. The planes of the lower surface 12, 12', 13, 13' of the rockers extend along the axes of oscillation 9, 9', 10, 10' and come into sliding and rolling support against the spherical head portions 14, 14', 15, 15' of the rockers 16, 16', 17, 17' which in turn oscillate about axes 18, 18', 19, 19'. The spherical head portions rest in rolling and sliding contact on the connecting end portions of tappets 22, 22', 23, 23' which cover the ends of the stems of the valves 24, 24', 25, 25', the mid-point of the path of bearing contact corresponding to the axis of the valve.

The combination of the rolling and sliding movement of the spherical head portion brings about a rapid glossing or glazing action along the contact surfaces and a very great resistance to the wear of these surfaces. These surfaces are linear on the surfaces 12, 12', 13, 13', of the rockers and circular owing to the rotations of the valves on the end portions and are of the order of several square millimeters.

The pivots for the rockers are mounted on the common connecting member 11 in the form of a pre-mounted and -adjusted sub-assembly. The member 11 is not subject to any particular stress or strain and can be economically formed as a cast iron body. The device is economical which accrues from its ease of assembly and adjustment.

Claims

I claim:

1. A device for controlling the valves of an internal combustion engine of the type having overhead camshafts, comprising:

a first and second rocker for each valve,

each of said rockers being disposed between a control cam on a camshaft and the end portion of the stem of the valve;

the free end of said first rocker being in contact with the control cam; oscillating in a plane perpendicular of the axis of this cam and being in contact with a spherical head portion on the second of said rockers,

said second rocker being in contact with the end portion of the valve stem and oscillating in a plane containing the axis of the valve, the mid-point of the bearing contact of the spherical head portion on the end portion of the valve stem being disposed substantially along the axis of the valve;

and a connecting member for supporting pivots for said rockers is centered on the cylinder head by an opening therein which is substantially coaxial with the spark plug bore of the cylinder.

2. A device according to claim 1, wherein said first and second rockers are fitted on oscillation pins in a common connecting member which is connected to the cylinder head of the engine.

3. A device for controlling the valves of an internal combustion engine of the type having overhead camshafts, comprising:

a first and second rocker arm for each valve,

each rocker mounted for oscillation on a pin at one of its ends, the free ends of said rockers being disposed between a control cam on a camshaft and the end portion of the stem of a valve,

the free end of said first rocker having a roller in contact with the control cam, said first rocker being oriented for oscillation in a plane perpendicular of the axis of the control cam,

said second rocker comprising a spherical head portion which is in contact with the end portion of the valve stem, and oriented for oscillation in a plane containing the axis of the valve, the bearing contact surface of the spherical head portion with the end of the valve stem being centered on the axis of the valve, and

a connecting member for supporting pivots for said rockers, said connecting member being centered on the cylinder head by an opening therein which is substantially coaxial with the spark plug bore of the cylinder.

4. A device for controlling the valves of an internal combustion engine of the type having overhead camshafts, comprising:

a first and second rocker arm for each valve,

each rocker mounted for oscillation on a pin at one of its ends, the free ends of said rockers being disposed between a control cam on a camshaft and the end portion of the stem of a valve,

the free end of said first rocker having a roller in contact with the control cam and a bearing surface for contacting the second rocker, said bearing surface comprising a plane surface disposed beneath said roller and extending along the axis of the oscillation pin of said first rocker, said first rocker being oriented for oscillation in a plane perpendicular to the axis of the control cam,

and said second rocker is oriented for oscillation in a plane containing the axis of the valve, and comprises an integral spherical head portion which is in contact with the end portion of the valve stem and centered on the axis of the valve, and is also in contact with the bearing surface of said first rocker, and control cam, and first rocker being in a plane which substantially passes through the center of said spherical head portion of the second rocker.