US3362390A - Automatic compression release - Google Patents

Description

/NvL-wroe Fie/was 5 [5f-Y ll 7//////,\"/// l Jan. 9, 1968 F. B. EsTY AUTOMATIC COMPRESSION RELEASE Filed Feb. 9. 1966 United States Patent O 3,362,390 AUTOMATIC COMPRESSION RELEASE Francis B. Esty, Brookfield, Wis., assignor to Wisconsin Motor Corporation, Milwaukee, Wis., a corporation of Wisconsin Filed Feb. 9, 1966, Ser. No. 526,275 11 Claims. (Cl. 123--182) ABSTRACT OF THE DISCLOSURE This disclosure relates to an automatic compression release for an internal combustion engine having an exhaust valve with a valve lifter and cam mechanism for actuating the valve lifter. The compression release includes a latch rotor pin having a bearing seat in the cam shaft and on which the pin may turn on its longitudinal axis, and a latch rotor pin turning mechanism responsive to engine speed to selectively rotate the pin and an eccentric part on the end of the pin above and below the cam. The eccentric part is above the cam so as to engage the valve lifter when the rotor pin is one position at low engine speeds and is below the cam so as not to engage the valve lifter at high engine speeds.

This invention relates to an improved automatic compression release for an internal combustion engine.

It is well known in the art to provide mechanism to hold the exhaust valve in the cylinder head of an internal combustion engine slightly open during the compression stroke thereof, thus to partially relieve the compression in the cylinder during starting so that starting torque requirements of the engine are greatly reduced. When the engine starts and comes up to running speed, the compression release mechanism is rendered ineffective to permit the exhaust valve to close, thus to achieve full power of the engine at running speeds. Such a mechanism also eliminates the need for a spark retarding mechanism, as the compression release prevents kickback during starting.

An early example of such an automatic compression release mechanism which automatically responds to engine speed changes under the control of a centrifugally responsive ilyweight is shown in British Patent 28,286 of A.D. 1912. The improvement of the present invention also relates to a centrifugally controlled automatic compression release mechanism. The structure of the present invention `is greatly simplified over that shown in the British patent aforesaid and is'adapted to readily be added to conventional internal combustion engines without substantial modification in the engine structure. The mechanism of the present invention is accordingly simple, lbut will achieve all of the advantages of an automatic compression release without materially adding to the cost of the engine.

In internal combustion engines provided with the automatic compression release of the present invention, the pressure in the cylinder head during starting is reduced to about one-half its value during running. A typical reduction is from about 110 p.s.i. to about 60 p.s.i. The mechanism is typically effective to partially relieve compression at engine seeds below about 650 r.p.m. At speeds in excess of 650 r.p.m., the compression release mechanism is automatically rendered inoperativeso that the exhaust valve closes under control of its timing cam on the cam shaft, thus to achieve full power at running speeds of the engine.

Other objects, features, and advantages of the invention will appear from the following disclosure in which:

FIG. `1 is a fragmentary'cross section taken through an automatic compression release mechanism embodying the invention, shown in operative relationship with the internal combusion engine exhaust valve and associated parts at the point in the cycle when the exhaust valve should normally :be closed, but in which it is held slightly open by the compression release mechanism.

FIG. 2 is a fragmentary end View taken along the line 2 2 of FIG. 1, showing the position of 'the parts at standstill or low starting speed of the engine.

FIG. 3 is a view similar to that shown in FIG. 2, but showing the position of the parts during high running speeds of the engine.

FIG, 4 is a perspective view of the flyweight and latch pin, shown in spaced apart relationship.

FIG. 5 is a cross section taken along the line 5-5 of FIG. l, when the engine is at standstill or turning slowly, as also shown in FIG. 2,

FIG. 6 is a cross section similar to FIG. 5, but showing the position of the parts when the engine is at running speeds, as is also shown in FIG. 3.

Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structure. The scope of the invention is defined in the claims appended hereto.

Cylinder head 10 of a four-stroke internal combustion engine is typically provided with a combustion chamber 11 in which there is an exhaust valve 12 which controls flow of gases through the duct 13 to the exhaust manifold 14. Valve 12 has a stem 15 which is actuated by a valve lifter including a tapper or pad 16. Tapper 16 normally follows the contour of cam 17 on cam shaft 18 under the influence of spring 22. As is conventional, cam shaft 18 is driven in the direction of arrow 45 by the engine crankshaft having pinion 19 which meshes with gear 33 on cam shaft 18. Accordingly, the operation of valve 12 is timed by the cam 17,

Cam 17 has a low profile lobe or base circle section 21 Which ordinarily permits the valve 12 to be closed during the compression stroke of the piston in the cylinder. The valve will close under pressure of the spring 22 which bears on the stern collar 23. During the exhaust stroke of the piston in the cylinder, the high lobe 24 of the cam 17 opens the valve 12 widely, to exhaust spent gases.

The compression release mechanism of the invention is mounted on the gear 33, which functions as a mounting plate for various parts of the release mechanism. A bearing opening 32 is provided in gear or plate 33 for a latch rotor in the form of a latching pin 25. The main body of rotor or pin 25 is cylindrical and ts into an elongated bearing seat or saddle 26 formed in the periphery of shaft 18, at one side of the cam 17. Saddle 26 is elongated on an axis parallel to the axis of shaft 18. At its end 27 which is adjacent cam 17, and beneath the valve lifter pad 16, pin 25 has a flat or relieved portion 28. This makes the outer periphery of part 27 eccentric to the axis of pin rotation. The pin 25 is rotatable on its longitudinal axis, between one position in which its end portion 27 lies below the profile of cam lobe 21, as shown in FIG. y6, and another position in which it extends above the profile of cam lobe 21, as shown in FIG. 5. The rotor or pin 25 is rocked in its seat 26 by applying pressure to a crank arm or lug 31, with which the other end of the pin is provided.

Mounting plate 33 has its outer peripheryV provided with the gear teeth 35 by which the cam shaft 18 is rotated by pinion 19. Accordingly, the mounting plate 33, pin 25, and cam 17 all rotate in unison with the cam shaft 18. All these parts maintain their same relative positions in all positions of the cam shaft, except that the pin 25 may be rocked or rotated in its seat 26 in accordance with the position of a flyweight 36, which is centrifugally responsive to engine speed.

Flyweight 36 is mounted on plate 33 by a pintle 37 extending through a bearing opening 38 near one end of the yweight. Near its other end, the flyweight is prvided with a slot i1 about a stop pin 42 which is fast to the plate 33. Pin 42 limits movement of the weight 36 about the pintle 37.

Weight 36 is also provided with a socket 43 into which the lug or tooth 31 of the pin 25 is received, as shown in FIGS. 2 and 3. Socket 43 is larger than the tooth 31 of pin 25 and is bounded by lingers 50, SI1 which bear on opposite sides of tooth 31. Accordingly, pivotal movement of the flyweight 36 about its pintle 37 will be transmitted to the crank arm or tooth 31 on the pin 215, thus to rotate the pin on its longitudinal axis and hence change the position o2 the flat 28 at end 27 of the pin, as shown in FIGS. 5 and 6. The ilyweight is biased radially inwardly toward its FIG. 2 position under pressure of a clock spring 44.

The relationship between the tooth 31 to the lingers 50, 51 bounding cavity 43 is such that relatively slight pivotal movement of the weight 36 will produce considerably greater pivotal movement of the pin 25. In a practical embodiment of the invention, for a pivotal movement of the weight of about 30, pin 25 will roll 65. This is because the distance between the axis of pintle 37 and the points of contact of ngers 50, 51 with the sides of tooth 31 is greater than the distance between said points and the axis of pin 295 and because lingers 50, 51 may slide along the sides of tooth 31 as the weight 36 swings on its pintle 37. Accordingly, the parts 43, S0, 51 and 311 constitute a motion multiplying drive coupling between the yweight 36 and pin 25.

At standstill and during initial starting cranking of the engine, the parts will be in -their positions shown in FIGS. 1, 2 and 5. The end 27 of latch pin rotor 25 will extend above the cam lobe 231 on cam 17, thus to intervene between the valve lifter `tapper 16 and the cam and hold the exhaust valve 12 slightly open. Accordingly, the engine will turn over easily because a substantial part of the compression in the head will be relieved through the partially open valve 12. In a practical embodiment of the invention, the pressure in chamber 111 is thus reduced from 110 p.s.i. to 60 p.s.i.

After the rst tiring stroke of the engine, the engine will rapidly build up speed. After the engine speed exceeds a certain predetermined value, for example, about 650 r.p.m., the centrifugal forces applied to the flyweight 36 are such that the flyweight will swing radially out- Wardly about its pintle 3-7 to impose turning torque on the lug 31 of pin 215. This will roll the pin to its position shown in FIG. 6 where its end 27 beneath the flat 218 is below the level of the cam lobe 2i1. In this position normal cam-valve action is restored. Thereafter, the cam 17 controls the position of the valve 12 and full engine power is restored.

As is clear from FIGS. 2 and 3, the respective axes of shaft 18, pin 25, and pintle 37 are radially aligned. Moreover, the ilyweight 36 is asymmetrically disposed on the mounting plate 33. The major portion of the flyweight 36 is ahead of the pintle with respect to its direction 0f rotation, as indicated by arrow 45. Thus inertia of the rotating iiyweight aids centrifugal force in swinging it ont against the bia-s of spring 44.

An important relationship of the parts is that the cam shaft 18 provides a solid abutment to support the latch pin rotor 2S in its FIG. 5 position, in which it holds the valve 12 Iin slightly open position. There is direct support bearing contact between the valve tapper 16, pin 25, and the shaft 18, thus to oppose the bias of spring 22.

.The prole of the cam iiat 2S can be varied for timing the compression release period with respect to the overall cycle of the engine. This may be calculated for each specific engine for optimum results.

I claim:

1. `In an internal combustion engine having an exhaust valve, an exhaust valve lifter, a cam shaft and cam to engage the valve lifter and open the valve, and latching mechanism to engage the valve lifter to hold the valve open when the cam would otherwise allow it to close, the improvement in said latching mechanism comprising:

a latch rotor adjacent said cam and valve lifter,

latch rotor turning mechanism responsive to engine speed,

said latch rotor comprising a pin lfor which the cam shaft has a bearing seat in which the pin may turn on its longitudinal axis, said pin having a part eccentric to its axis of rotation to extend above the cam to engage said valve lifter when the rotor pin is turned to one position in response to low engine speed and which is below the cam so as not to engage the valve lifter when the rotor pin is turned to another position in response to high engine speed.

2. yIn an internal combustion engine having an exhaust valve, an exhaust valve litter, a cam shaft and cam to engage the valve lifter and open the valve, and latching mechanism to engage the valve lifter to hold the valve open when the cam would otherwise allow it to close, the improvement in said latching mechanism comprising a latch rotor adjacent said cam and valve lifter, latch ro'tor turning mechanism responsive to engine speed, said latch rotor having a part eccentric to its axis of rotation to extend above the cam to engage said valve lifter when the rotor is turned to one position in response to low engine speed and which is below the cam so as not to engage the valve lifter when the rotor is turned to another position in response to high engine speed, said latch rotor comprising a pin, said cam shaft having a bearing seat for the pin in which the pin may turn on its longitudinal axis, one end of Ithe pin being disposed adjacent the cam and valve lifter and having said part thereon, the other end of the pin having a crank arm by which turning movement is imparted to the pin.

3. The improvement of claim 2 in which said latch rotor turning mechanism comprises a centrifugal weight driven by the engine and a connection between said weight and crank arm by which the pin will be turned by the weight in response to engine speed.

4. The improvement of claim 3 in which said cam shaft has a mounting plate thereon, said plate having a pintle on which the weight is mounted.

`5. lThe improvement of claim 4 in combination with a spring biasing said Weight radially inwardly to oppose centrifugal force.

6. '[he improvement of claim 3 in which the respective axes of the cam shaft, pin, and pintle are radially aligned.

7. An automatic compression release mechanism for an internal combustion engine which has a cylinder head, an exhaust Valve in the cylinder head, a valve lifter with a spring biasing the valve toward closed position, a cam shaft and cam to engage the valve lifter and open the valve, said automatic compression release mechanism comprising an elongated latch pin for which said cam shaft has a bearing seat parallel to its longitudinal axis, said pin being rotatable in said seat and having one end thereof adjacent the cam, said end having a portion eccentric to its axis of rotation and which will extend above the cam to engage the valve lifter when the latch pin is turned to one position in response to low engine speed and which will be below the cam so as not to engage the valve lifter when the rotor is turned to another position in response to high engine speed, said bearing seat in the cam shaft providing a positive abutment for the pin to hold the valve open against the bias of the valve lifter closing spring when the pin is turned to said one position, and latch pin turning mechanism responsive to engine speed.

8. The automatic compression release mechanism of claim 7 in which said latch pin turning mechanism comprises a centrifugal weight, a mounting plate for the weight, said plate being connected to the cam shaft, a pintle between the weight and mounting plate whereby rotation of the cam shaft and the mounting plate will transmit centrifugal force to the weight to turn it about its pintle, sa-id latch pin having a crank arm in motion transmitting connection with said weight whereby the Weight will turn the pin in its bearing seat in response to speed changes in the cam shaft.

9. The automatic compression release mechanism of claim 8 in which the respective axes of the cam shaft, latch pin, and pintle are radially aligned. 4

10. The automatic compression release mechanism of 10 claim 8 in which the Weight has a spring -olpposing centrifugal force and biasing the Weight radially inwardly, said 5 nection comprises a motion multiplying drive coupling.

References Cited UNITED STATES PATENTS 3,314,408 4/1967 Fenton 12B-182 RALPH D. BLAKESLEE, Primary Examiner.

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