US3735745A

US3735745A - Decompression device for internal combustion engines

Info

Publication number: US3735745A
Application number: US00128942A
Authority: US
Inventors: E Hatz
Original assignee: Motorenfabrik Hatz GmbH and Co KG
Current assignee: Motorenfabrik Hatz GmbH and Co KG
Priority date: 1970-04-23
Filing date: 1971-03-29
Publication date: 1973-05-29
Anticipated expiration: 1990-05-29
Also published as: DE2019755C3; BR7102084D0; ES195349U; DE2019755B2; ES195349Y; DE2019755A1; GB1319003A

Abstract

A decompression device for an internal combustion engine in which the control parts which open and close the exhaust valves of the combustion chambers include a rocking lever acting on the valve. The decompression device includes an eccentric bearing on which the rocking lever is freely mounted, rotation of the eccentric bearing thus moving the axis of the rocking lever to prevent full closing of the exhaust valve, that is, provide decompression of the chamber. The eccentric bearing may be turned to reference position at which it permits full closing of the exhaust valve by either manual or automatic means.

Description

United States Patent 1191 Hatz [ DECOMPRESSION DEVICE FOR INTERNAL COMBUSTION ENGINES [75] Inventor: Ernst Hatz, Ruhstorf, Germany [73] Assignee: Motorenfabrik Hartz KG., Germany 22] Filed: Mar.29, 1971 211 App]. 196.; 128,942

[30] Foreign Application Priority Data 3,146,772 9/1964 Hatzm, ..l23/l82 1451 May 29, 1973 Primary Examiner-Laurence M. Goodridge Assistant Examiner-Ronald B. Cox Attorney-Larson, Taylor & Hinds [5 7 ABSTRACT A decompression device for an internal combustion engine in which the control parts which open and close the exhaust valves of the combustion chambers include a rocking lever acting on the valve. The decompression device includes an eccentric bearing on which the rocking lever is freely mounted, rotation of the eccentric bearing thus moving the axis of the rocking lever to prevent full closing of the exhaust valve, that is, provide decompression of the chamber. The eccentric bearing may be turned to reference position at which it permits full closing of the exhaust valve by either manual or automatic means.

5 Claims, 5 Drawing Figures BACKGROUND OF THE INVENTION This invention relates to internal combustion engines, and in particular it relates to a decompression device for an internal combustion engine.

In internal combustion engine of the type having exhaust valves for the combustion chambers controlled by rocking levers and push rods, a means is often provided to prevent full closing of the exhaust valve to permit decompression or at least prevent a high level of compression which would impede the starting of the engine. The exhaust valves are normally controlled by a system of control parts which transmit engine motion to valve movement. In conventional decompression devices, a decompression cam is arranged to act on one of the control parts. It is often turnable either by hand or by an automatic means to terminate decompression.

In known decompression devices of this kind, the control part usually carries an adjustable screw which bears on the decompression cam sothat the amount of decompression travel of the exhaustvalve can be adjusted at will by varying the setting of the adjusting screw. By inappropriate use through unfamiliarity with operating conditions, it is therefore possible for the decompression travel to be set to exceed the maximum permissible amount with resulting serious drive failures or damage to the control parts.

Moreover, previously known decompression devices 'have had the further disadvantage that, at certain times during decompression movement the engagement within the system of control parts is momentarily interrupted. For example, in internal combustion engines 7 with a hydraulic valve clearance adjusting device in the push rod, the clearance which exists during interruption of the control engagement between the rocking lever and the push rod causes the push rod to extend so that the decompression cannot be terminated.

Thus, there exists a need for a new and improved decompression device which will overcome these disadvantages of the prior art.

SUMMARY OF THE INVENTION It is a purpose of the present invention to provide a new and improved decompression device for an internal combustion engine, which device overcomes disadvantages of the prior art.

This purpose of the present invention is achieved by providing an arrangement in which the maximum opening of the exhaust valve during decompression can be limited and controlled, and in which engagement between the control parts of the control system is permanently insured, especially the power connection between the push rod and the rocking lever.

These problems are solved in accordance with the present invention by providing an arrangement in which the decompression cam is in the form of an eccentric bearing forming a mounting about which the rocking lever rocks, thus varying the position of the rocking lever axis which in turn sets a-maximum decompression opening of the subject valve, such that the position of the-eccentric bearing determines the magnitude of the decompression opening. The maximum decompression opening is defined as that opening which willbe maintained even when the system of control parts normally would permit the valve to close all i the way were it not for the decompression device.

In a simple embodiment of a decompression device in accordance with the present invention, a means may be provided for controlling the eccentric bearing by hand, thus shutting off the decompression device at a convenient time such as when the engine has heated up sufficiently.

It is also a feature of the present invention to provide a device for automatically terminating decompression. In such a device for automatically terminating decompression, a toothed disc may be provided for rotational movement with the eccentric bearing. A suitable means which undergoes oscillatory movement upon normal operation of the engine may then be operatively connected to the toothed disc to turn the same during each oscillation thereof. For example, this suitable means may be a rocking lever controlling the inlet to the combustion chamber. The suitable means may be connected to he toothed disc by a driving member comprising a spring-tongue which engages the toothed disc and is biased radially inwardly relative thereto but which can be sprung outwardly to permit stepwise turning of the toothed disc, and hence stepwise turning of the eccentric bearing, the latter thus returning to its original position at which decompression is terminated. In an advantageous arrangement, the disc is mounted on the same shaft as the eccentric bearing and the rock ing lever of the valve being controlled.

Thus, it is an object of this invention to provide a new and improved decompression device for an internal combustion engine, which device overcomes the disadvantages of the prior art.

It is another object of this invention to provide a new and improved internal combustion engine decompression device in which maximum decompression can be controlled while eliminating the danger of maintaining unacceptably high decompression.

It is another object of this invention to provide for an internal combustion engine a decompression device in which the control parts which operate the decompression device are not interrupted during the operation of the decompression device.

Other objects and the intended advantages of the present invention will become apparent from the detailed description to follow, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS There follows a detailed'description of preferred embodiments of the invention to be read together with the accompanying drawings.

FIG. 1 is a sectional view of a portion of an internal combustion engine showing the decompression device constructed in accordance with the present invention.

FIG. 2 is a plan view of FIG. 1.

FIG. 3 is an enlarged sectional view taken along line III-III of FIG. 2.

FIG. 4 is a sectional view similar to FIG. 3 but showing the device in a different operative position.

FIG. 5 is a plan view of a simple construction of the decompression device which can be operated manually.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, like numerals represent like elements throughout the several views.

An exhaust valve 2 is provided in a valve housing 1 of afour stroke internal combustion engine of known form and is biassed upwardly against a valve seat 4 under the influence of a closing spring 3. A push rod 5, which is moved up and down by a non-illustrated control drive, engages a double-armed rocking lever 6 for moving the exhaust valve 2 downwardly in the open direction. The valve 2 is opened by upward movement of the push rod 5, while it is closed under the action of its spring 3 during upward movement of the same.

A mounting shaft 7 is mounted in the valve housing 1' and carries an eccentric bearing 7a, on which a boss 6a of the rocking lever 6 is mounted for free turning movement. Accordingly, during operation of the valve, the rocking lever 6 performs a to and fro turning movement on the eccentric bearing 7a.

Fitted to a projecting end 7b of the mounting shaft 7 is a hand grip 8 by which the mounting shaft can be turned about its longitudinal axis to adjust the position of its-eccentric bearing about the axis of the mounting shaft. Thus, the eccentric bearing 7a can be moved from its normal drive position shown in FIGS. 1 and 3, into the position of FIG. 4, in which decompression of the combustion chamber is effected. That is, when the eccentric bearing 7a is positioned as shown in FIG. 4, the axis of rotation of the rocking lever 6 has been lowered while the rest position of the push rod 5 has remained the same, as a result of which the valve 2 cannot fully close against its seat 4. Rather, in the uppermost position of the valve 2 it will remain separated from its seat 4 by the distance H as shown in FIG. 1 which corresponds to the distance E of movement of the axis of the rocking lever 6 which resulted from movement of the eccentric bearing 7a from the FIG. 3 position to the FIG. 4 position. As a result, the combustion chamber with which the valve 2 is associated does not fully close. Thus, in accordance with the purpose of a decompression device, full compression does not occur within the chamber, which full compression would impede the starting of the engine. Specifically, this movement of the eccentric bearing 7a results from turning the hand grip 8 from the position of FIGS. 1 and 3 into the position of FIG. 4. The end 6b of the rocking lever 6 is supported by abutment with the push rod 5 so that the other end 6c swings downwardly through an angular amount, the maximum extent of which is determined by the eccentricity E of the eccentric bearing 7a. A decompression travel smaller than H can of course be set if the eccentric bearing 7a, when set to decompression, is adjusted, not through 180 as shown in FIG. 4, but through a smaller angular amount.

In the embodiment according to FIGS. 1 to 4, the device is also provided for automatically terminating the decompression. This comprises a drive disc 9 which is fitted to the mounting shaft 7, the boss 9a of the drive disc 9 being, for example, fitted to the mounting shaft 7 by a tapered pin 10. The drive disc 9 is provided around its periphery with inclined teeth 9b. The drive disc 9 is completely toothed around its periphery, except for a gap 90.

A rocking lever 11 for the inlet valve of the combustion chamber is mounted for free turning on the central part of the mounting shaft 7, being operated in similar fashion to rocking lever 6 from the control drive. Fitted to the rocking lever 11, e.g. by screws, is a spring tongue 72 which extends in the axial direction of the shaft 7. The end of this tongue operates as a driver 12a for the teeth 9b on the drive disc 9. Thus, during engine operation, the driver 12a and rocking lever 11 perform an oscillating to and fro turning motion through a predetermined, fixed angular amount A.

When the engine is either completely off or running normally, the decompression device is in the position of FIG. 3. Upon movement of the rocking lever 11 in the clockwise direction, the driver 12a cannot engage the toothing 9b because of the gap 9c, because the gap 9c lies within angle A. Both valves operate normally, i.e., opening and closing completely. If, on the other hand, a stationary engine is to be started up with the aid of the decompression device, the mounting shaft 7 is moved in the clockwise direction by the hand grip 8 to turn the eccentric bearing 7a. If maximum decompression travel is required at this time, this setting movement is through so that the components are moved from the position of FIG. 3 to the position of FIG. 4. The uppermost position of the end 60 of the rocking lever 6 is therefore moved down and the exhaust valve 2, in its uppermost position remains open by an amount H, as it moves from its closed position 0 to its decompression position D. When the engine is turned over and the push rod 5 moved upwards, the exhaust valve is accordingly opened further from the decompression position D until it reaches position V (completely open). When closing, however, the exhaust valve 2 does not, on the other hand, return completely to the closed position 0, but only to the decompression position D. (The positions D and V indicated schematically in FIG. 1 are not in corresponding proportions; in practice, the decompression travel II will be approximately 1 mm. and the opening travel approximately 10 mm.).

During the portion of each oscillation when the parts move in direction X, the rocking lever 11 moves the drive disc 9 through an angular amount A by means of its driver 12a, so that the drive disc 9 and the shaft 7 coupled thereto, together with the eccentric 7a are also moved in this direction. During the return movement of rocking lever 11 and driver 12a in direction Y, the drive disc 9 remains stationary and the driver 12a slides back in spring action over the adjacent tooth and occupies a new drive position in front of the next tooth 9b. This sequence is repeated until the driver 12a has engaged all he teeth 9b stepwise and it engages gap 9c. The mounting shaft 7b together with the drive disc 9 again occupy the positions of FIG. 3. The decompression movement is decreased in steps from the maximum amount H in FIG. 4 until it again becomes zero in the position of FIG. 3, i.e., the exhaust valve 2 opens and closes as normal.

It is up to the discretion of the operator to set the duration of the decompression and also the point at which the decompression is terminated. With the setting according to FIG. 4 the maximum decompression and therefore the longest time is set. If, on the other hand, the drive disc is moved in the clockwise direction from the position of FIG. 3, for example, through 270, for about half the decompression travel H, the driver 12a cooperates step by step with less teeth 9b and so that termination occurs more quickly.

The rest position of the shaft 7, at the top dead center 1 position of the eccentric bearing 7a as shown in FIGS.

1 and 3, is stable because the re-setting forces acting on the rocking lever 6 tend to hold the parts in this position. If necessary, the mounting shaft 7 could be held in the position of FIGS. 1 and 3 by a stop. Equally, a safety device, e.g. a ratchet device, could be provided to allow setting movement of the drive disc 9 in one direction only, (in the clockwise direction according to the drawing because of the tooth form). Moreover, an indicator is preferably associated with the hand grip 8, which gives, on a fixed scale, both the setting direction and the set amount ofdecompression travel. Finally, it is possible to provide, around the periphery of the drive disc 9, an additional, larger gap in which the driver 12a does not drive. In this region permanent decompression exists (decompression for a period of selected duration) should the-operator turn the eccentric 7a so far that the driver 12a engages in this additional gap. The permanent decompression is preferably used to ventilate or turn the engine freely in extreme cold.

Obviously, a construction can be provided in which the termination of decompression can be effected by hand only as shown in the embodiment of FIG. 5. Here, the

drive elements

9 and 12 are omitted, while the mounting of the rocking lever 6 on the eccentric bearing 7a of the mounting shaft 7 is retained in similar fashion. The other rocking lever (11) is separately mounted and no longer influences the first rocking lever 6 so that the operator must, in this embodiment, move the elements of the decompression device by hand by means of grip 8, from the normal position of FIG. 1 into the decompression position, and, after the starting procedure has been carried out, must return them by hand from the decompression position, to the normal position of FIG. 1. (In this case, a release, per haps a reset spring associated with the hand grip 8, is sufficient).

Although the invention has been described in considerable detail with respect to the preferred embodiments thereof, it will be apparent that numerous modifications and variations apparent to those skilled in the art are possible within the spirit and scope of the invention.

I claim:

1. A device for decompressing a combustion chamber of an internal combustion engine of the type in which the chamber has an exhaust valve, a rocking lever mounted on a mounting shaft for movement thereabout to operatively engage the exhaust valve to open the same, and a closing means for closing the valve in the absence of an opening force applied by the rocking lever, said device comprising: a decompression cam in the form of an eccentric bearing mounted on said mounting shaft eccentrically relative to the axis of the-mounting shaft and for rotation with the mounting shaft, said rocking lever being freely mounted on the eccentric hearing such that rotation of the eccentric bearing varies the position of the axis of rotation of the rocking lever, said eccentric bearing being positioned and shaped such that in at least one position the exhaust valve is permitted to close all the way, an in a plurality of other positions the rocking lever prevents the closing member from closing the exhaust valve all the way, thus providing a decompression opening of the chamber, a setting member mounted to actuate the mounting shaft to rotate said eccentric bearing to any one of a plurality of angular positions to set the rocking lever to any one of said plurality of other positions including a maximum decompression valve opening position or any one of a plurality of valve opening positions between the maximum opening and the valve closed position, the magnitude of this decompression opening being variable at will and dependent on the angular position of said setting member and thus on the angular position of the eccentric bearing, and a return means for automatically turning the eccentric bearing from the said other positions to said one position in response to operation of the internal combustion engine, said return means comprising a toothed disc mounted for rotational movement with the mounting shaft, and a member mounted for oscillating movement upon normal operation of the engine, said member being operatively engaged with the teeth of the disc to turn the disc in steps by engaging and turning one tooth during each of said oscillations.

2. A device according to claim 1, said setting member including a handle grip fixedly connected relative to said eccentric bearing to turn the eccentric bearing and the mounting shaft about the axis of the latter at will to one of said plurality of angular positions.

3. A device according to claim 1, wherein said member is an oscillating lever mounted to rotate freely about the said mounting shaft and controllable to operate an inlet valve of the said chamber, and a spring tongue element connected to the oscillating lever and engaging the teeth of the discs, such that in one direction of movement of the oscillating lever, the tongue turns the disc and the mounting shaft, and in the opposite direction it is sprung out of contact with the disc.

4. A device according to claim 3, wherein the said disc is fixed to the mounting shaft immediately adjacent the said rocking lever.

5. A device according to claim 1, wherein said memher is an oscillating lever, and including a spring tongue element connected to the oscillating lever and engaging the teeth of the discs, said tongue being biassed radially inwardly relative to the disc and sufficiently resilient to pass over the teeth, such that in one direction of movement of the oscillating lever the tongue turns the disc and mounting shaft and in the opposite direction it is sprung out of contact with the disc.

Claims

1. A device for decompressing a combustion chamber of an internal combustion engine of the type in which the chamber has an exhaust valve, a rocking lever mounted on a mounting shaft for movement thereabout to operatively engage the exhaust valve to open the same, and a closing means for closing the valve in the absence of an opening force applied by the rocking lever, said device comprising: a decompression cam in the form of an eccentric bearing mounted on said mounting shaft eccentrically relative to the axis of the mounting shaft and for rotation with the mounting shaft, said rocking lever being freely mounted on the eccentric bearing such that rotation of the eccentric bearing varies the position of the axis of rotation of the rocking lever, said eccentric bearing being positioned and shaped such that in at least one position the exhaust valve is permitted to close all the way, and in a plurality of other positions the rocking lever prevents the closing member from closing the exhaust valve all the way, thus providing a decompression opening of the chamber, a setting member mounted to actuate the mounting shaft to rotate said eccentric bearing to any one of a plurality of angular positions to set the rocking lever to any one of said plurality of other positions including a maximum decompression valve opening position or any one of a plurality of valve opening positions between the maximum opening and the valve closed position, the magnitude of this decompression opening being variable at will and dependent on the angular position of said setting member and thus on the angular position of the eccentric bearing, and a return means for automatically turning the eccentric bearing from the said other positions to said one position in response to operation of the internal combustion engine, said return means comprising a toothed disc mounted for rotational movement with the mounting shaft, and a member mounted for oscillating movement upon normal operation of the engine, said member being operatively engaged with the teeth of the disc to turn the disc in steps by engaging and turning one tooth during each of said oscillations.

4. A device according to claim 3, wherein the said disc is fixed to the mounting shaft immediately adjacent the said rocking lever. 5. A device according to claim 1, wherein said member is an oscillating lever, and including a spring tongue element connected to the oscillating lever and engaging the teeth of the discs, said tongue being biassed radially inwardly relative to the disc and sufficiently resilient to pass over the teeth, such that in one direction of movement of the oscillating lever the tongue turns the disc and mounting shaft and in the opposite direction it is sprung out of contact with the disc.